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Sample records for femtosecond pump-probe photoionization

  1. Femtosecond pump-probe photoionization-photofragmentation spectroscopy: Photoionization-induced twisting and coherent vibrational motion of azobenzene cation

    NASA Astrophysics Data System (ADS)

    Ho-Wei, Jr.; Chen, Wei-Kan; Cheng, Po-Yuan

    2009-10-01

    We report studies of ultrafast dynamics of azobenzene cation using femtosecond photoionization-photofragmentation spectroscopy. In our experiments, a femtosecond pump pulse first produces an ensemble of azobenzene cations via photoionization of the neutrals. A delayed probe pulse then brings the evolving ionic system to excited states that ultimately undergo ion fragmentation. The dynamics is followed by monitoring either the parent-ion depletion or fragment-ion formation as a function of the pump-probe delay time. The observed transients for azobenzene cation are characterized by a constant ion depletion modulated by a rapidly damped oscillatory signal with a period of about 1 ps. Theoretical calculations suggest that the oscillation arises from a vibration motion along the twisting inversion coordinate involving displacements in CNNC and phenyl-ring torsions. The oscillation is damped rapidly with a time constant of about 1.2 ps, suggesting that energy dissipation from the active mode to bath modes takes place in this time scale.

  2. Towards XUV pump-probe experiments in the femtosecond to sub-femtosecond regime: New measurement of the helium two-photon ionization cross-section

    NASA Astrophysics Data System (ADS)

    Barillot, T. R.; Matia-Hernando, P.; Greening, D.; Walke, D. J.; Witting, T.; Frasinski, L. J.; Marangos, J. P.; Tisch, J. W. G.

    2017-09-01

    Non-linear photoionization of molecules in the 10-50 eV range is a prerequisite for pump-probe measurements with sub-femtosecond resolution, but hitherto has been limited to femtosecond resolution, low repetition rate and high photon flux laser systems. We demonstrate two-photon single ionization of helium atoms using 100 pJ, 1.34 fs pulses (main peak FWHM = 680 as) at 1 kHz repetition rate with a central photon energy of 19.6 eV. We obtained an exponent of 2.27 ± 0.21 for the intensity dependence of the signal and a two-photon ionization cross-section of 5.0 ± 0.5 × 10 -50 cm4 s. Our work opens the possibility of attosecond pump-probe measurements of ultrafast molecular processes.

  3. Nonlinear femtosecond pump-probe spectroscopy using a power-encoded soliton delay line.

    PubMed

    Saint-Jalm, Sarah; Andresen, Esben Ravn; Bendahmane, Abdelkrim; Kudlinski, Alexandre; Rigneault, Hervé

    2016-01-01

    We show femtosecond time-resolved nonlinear pump-probe spectroscopy using a fiber soliton as the probe pulse. Furthermore, we exploit soliton dynamics to record an entire transient trace with a power-encoded delay sweep. The power-encoded delay line takes advantage of the dependency of the soliton trajectory in the (λ,z) space upon input power; the difference in accumulated group delay between trajectories converts a fast power sweep into a fast delay sweep. We demonstrate the concept by performing transient absorption spectroscopy in a test sample and validate it against a conventional pump-probe setup.

  4. Femtosecond pump-probe microscopy generates virtual cross-sections in historic artwork.

    PubMed

    Villafana, Tana Elizabeth; Brown, William P; Delaney, John K; Palmer, Michael; Warren, Warren S; Fischer, Martin C

    2014-02-04

    The layering structure of a painting contains a wealth of information about the artist's choice of materials and working methods, but currently, no 3D noninvasive method exists to replace the taking of small paint samples in the study of the stratigraphy. Here, we adapt femtosecond pump-probe imaging, previously shown in tissue, to the case of the color palette in paintings, where chromophores have much greater variety. We show that combining the contrasts of multispectral and multidelay pump-probe spectroscopy permits nondestructive 3D imaging of paintings with molecular and structural contrast, even for pigments with linear absorption spectra that are broad and relatively featureless. We show virtual cross-sectioning capabilities in mockup paintings, with pigment separation and nondestructive imaging on an intact 14th century painting (The crucifixion by Puccio Capanna). Our approach makes it possible to extract microscopic information for a broad range of applications to cultural heritage.

  5. Femtosecond pump-probe microscopy generates virtual cross-sections in historic artwork

    PubMed Central

    Villafana, Tana Elizabeth; Brown, William P.; Delaney, John K.; Palmer, Michael; Warren, Warren S.; Fischer, Martin C.

    2014-01-01

    The layering structure of a painting contains a wealth of information about the artist's choice of materials and working methods, but currently, no 3D noninvasive method exists to replace the taking of small paint samples in the study of the stratigraphy. Here, we adapt femtosecond pump-probe imaging, previously shown in tissue, to the case of the color palette in paintings, where chromophores have much greater variety. We show that combining the contrasts of multispectral and multidelay pump-probe spectroscopy permits nondestructive 3D imaging of paintings with molecular and structural contrast, even for pigments with linear absorption spectra that are broad and relatively featureless. We show virtual cross-sectioning capabilities in mockup paintings, with pigment separation and nondestructive imaging on an intact 14th century painting (The Crucifixion by Puccio Capanna). Our approach makes it possible to extract microscopic information for a broad range of applications to cultural heritage. PMID:24449855

  6. SwissFEL instrument ESB femtosecond pump-probe diffraction and scattering

    SciTech Connect

    Ingold, G. Rittmann, J. Beaud, P.; Divall, M.; Erny, C.; Flechsig, U.; Follath, R.; Hauri, C. P.; Hunziker, S.; Juranic, P.; Mozzanica, A.; Pedrini, B.; Sala, L.; Patthey, L.; Patterson, B. D.; Abela, R.

    2016-07-27

    The ESB instrument at the SwissFEL ARAMIS hard X-ray free electron laser is designed to perform pump-probe experiments in condensed matter and material science employing photon-in and photon-out techniques. It includes a femtosecond optical laser system to generate a variety of pump beams, a X-ray optical scheme to tailor the X-ray probe beam, shot-to-shot diagnostics to monitor the X-ray intensity and arrival time, and two endstations operated at a single focus position that include multi-purpose sample environments and 2D pixel detectors for data collection.

  7. Coherence and Relaxation in Potassium-Doped Helium Droplets Studied by Femtosecond Pump-Probe Spectroscopy

    NASA Astrophysics Data System (ADS)

    Stienkemeier, F.; Meier, F.; Hägele, A.; Lutz, H. O.; Schreiber, E.; Schulz, C. P.; Hertel, I. V.

    1999-09-01

    Superfluid helium droplets are doped with potassium atoms to form complexes in which the metal atom is weakly bound to the cluster surface. The dynamics of these systems upon electronic excitation of the metal atom is probed by means of femtosecond pump-probe spectroscopy. Alignment of the excited potassium p orbital parallel to the cluster surface leads to quantum interferences, the decay of which gives information on the ultrafast perturbation of the induced atomic coherence by the superfluid environment; exciting the p state aligned perpendicularly, the strong repulsive interaction with the helium surface comes into play and the response of the helium environment is followed in time.

  8. Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics

    NASA Astrophysics Data System (ADS)

    Picón, A.; Lehmann, C. S.; Bostedt, C.; Rudenko, A.; Marinelli, A.; Osipov, T.; Rolles, D.; Berrah, N.; Bomme, C.; Bucher, M.; Doumy, G.; Erk, B.; Ferguson, K. R.; Gorkhover, T.; Ho, P. J.; Kanter, E. P.; Krässig, B.; Krzywinski, J.; Lutman, A. A.; March, A. M.; Moonshiram, D.; Ray, D.; Young, L.; Pratt, S. T.; Southworth, S. H.

    2016-05-01

    New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Particularly, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. Here we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site.

  9. Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics

    DOE PAGES

    Picón, A.; Lehmann, C. S.; Bostedt, C.; ...

    2016-05-23

    New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Specifically, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. In this paper, we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ionsmore » during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site.« less

  10. Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics.

    PubMed

    Picón, A; Lehmann, C S; Bostedt, C; Rudenko, A; Marinelli, A; Osipov, T; Rolles, D; Berrah, N; Bomme, C; Bucher, M; Doumy, G; Erk, B; Ferguson, K R; Gorkhover, T; Ho, P J; Kanter, E P; Krässig, B; Krzywinski, J; Lutman, A A; March, A M; Moonshiram, D; Ray, D; Young, L; Pratt, S T; Southworth, S H

    2016-05-23

    New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Particularly, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. Here we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site.

  11. Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics

    PubMed Central

    Picón, A.; Lehmann, C. S.; Bostedt, C.; Rudenko, A.; Marinelli, A.; Osipov, T.; Rolles, D.; Berrah, N.; Bomme, C.; Bucher, M.; Doumy, G.; Erk, B.; Ferguson, K. R.; Gorkhover, T.; Ho, P. J.; Kanter, E. P.; Krässig, B.; Krzywinski, J.; Lutman, A. A.; March, A. M.; Moonshiram, D.; Ray, D.; Young, L.; Pratt, S. T.; Southworth, S. H.

    2016-01-01

    New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Particularly, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. Here we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site. PMID:27212390

  12. Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics

    SciTech Connect

    Picón, A.; Lehmann, C. S.; Bostedt, C.; Rudenko, A.; Marinelli, A.; Osipov, T.; Rolles, D.; Berrah, N.; Bomme, C.; Bucher, M.; Doumy, G.; Erk, B.; Ferguson, K. R.; Gorkhover, T.; Ho, P. J.; Kanter, E. P.; Krässig, B.; Krzywinski, J.; Lutman, A. A.; March, A. M.; Moonshiram, D.; Ray, D.; Young, L.; Pratt, S. T.; Southworth, S. H.

    2016-05-23

    New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Specifically, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. In this paper, we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site.

  13. Investigation of electronically excited indole relaxation dynamics via photoionization and fragmentation pump-probe spectroscopy

    SciTech Connect

    Godfrey, T. J.; Yu, Hui; Ullrich, Susanne

    2014-07-28

    The studies herein investigate the involvement of the low-lying {sup 1}L{sub a} and {sup 1}L{sub b} states with {sup 1}ππ{sup *} character and the {sup 1}πσ{sup *} state in the deactivation process of indole following photoexcitation at 201 nm. Three gas-phase, pump-probe spectroscopic techniques are employed: (1) Time-resolved photoelectron spectroscopy (TR-PES), (2) hydrogen atom (H-atom) time-resolved kinetic energy release (TR-KER), and (3) time-resolved ion yield (TR-IY). Each technique provides complementary information specific to the photophysical processes in the indole molecule. In conjunction, a thorough examination of the electronically excited states in the relaxation process, with particular focus on the involvement of the {sup 1}πσ{sup *} state, is afforded. Through an extensive analysis of the TR-PES data presented here, it is deduced that the initial excitation of the {sup 1}B{sub b} state decays to the {sup 1}L{sub a} state on a timescale beyond the resolution of the current experimental setup. Relaxation proceeds on the {sup 1}L{sub a} state with an ultrafast decay constant (<100 femtoseconds (fs)) to the lower-lying {sup 1}L{sub b} state, which is found to possess a relatively long lifetime of 23 ± 5 picoseconds (ps) before regressing to the ground state. These studies also manifest an additional component with a relaxation time of 405 ± 76 fs, which is correlated with activity along the {sup 1}πσ{sup *} state. TR-KER and TR-IY experiments, both specifically probing {sup 1}πσ{sup *} dynamics, exhibit similar decay constants, further validating these observations.

  14. Femtosecond pump probe studies of chlorine dioxide photochemistry in water and acetonitrile

    NASA Astrophysics Data System (ADS)

    Philpott, Matthew J.; Hayes, Sophia C.; Reid, Philip J.

    1998-09-01

    The reaction dynamics of chlorine dioxide (OClO) dissolved in water and acetonitrile are investigated using femtosecond pump-probe spectroscopy. The change in optical density following photoexcitation of OClO at 400 nm is monitored at 12 wavelengths ranging from 267 to 900 nm. The dynamics observed at 267 and 400 nm demonstrate that the geminate recombination quantum yield of the primary ClO and O photofragments to reform ground-state OClO is reduced by a factor of six in acetonitrile relative to water. Calculations are presented that model the contribution of vibrationally excited OClO formed by geminate recombination to the pump-probe dynamics. Comparison of the experimental and computational results demonstrates that a portion of the dynamics can be attributed to vibrationally excited OClO. However, the optical-density changes observed between 700 and 900 nm are similar in magnitude for both solvents, suggesting that another species not produced by geminate recombination is responsible for these dynamics. The appearance and relaxation kinetics in acetonitrile are significantly slower than in water demonstrating the solvent dependence of photoproduct formation and ground-state vibrational relaxation. Reasons for this dependence including Coulombic solvent-solute interactions and intermolecular hydrogen bonding are discussed.

  15. Influence of self-diffraction effect on femtosecond pump-probe optical Kerr measurements.

    PubMed

    Yan, Lihe; Yue, Juanjuan; Si, Jinhai; Hou, Xun

    2008-08-04

    We investigated influence of the self-diffraction effect on optical Kerr signals of Bi2O3-B2O3-SiO2 glass (BI glass) and CS2 in femtosecond non-collinear pump-probe optical Kerr experiments. By measuring the dependence of the Kerr signals on the pump power and on the polarization angle between pump and probe beams, we found that the optical Kerr signals of CS2 consisted of two components: a fast response and a slow response,which were attributed to the self-diffraction effect and the photoinduced birefringence effect, respectively. The contribution of the self-diffraction effect to the Kerr signals increased with increase of the pump power. For the BI glass, no evident influence of self-diffraction on the Kerr signals was observed.

  16. Approximate calculation of femtosecond pump-probe spectra monitoring nonadiabatic excited-state dynamics

    NASA Astrophysics Data System (ADS)

    Dilthey, Stefan; Hahn, Susanne; Stock, Gerhard

    2000-03-01

    An approximate theory of femtosecond spectroscopy of nonadiabatically coupled electronic states is developed. Neglecting the commutators of vibrational Hamiltonians pertaining to different diabatic electronic states, the formulation represents a generalization of the semiclassical Franck-Condon approximation to the case of nonadiabatic dynamics. Explicit expressions for various time- and frequency-resolved spectra are derived which allow for a simple interpretation of femtosecond spectroscopy of vibronically coupled molecular systems. Employing multidimensional model problems describing (i) the nonadiabatic cis-trans isomerization of an electronic two-state system, and (ii) the S2→S1 internal conversion of pyrazine, exact reference data are compared to approximate calculations of transient absorbance and emission as well as time-resolved photoelectron spectra. In all cases considered, the approximation is shown to be appropriate for probe-pulse durations that are shorter than the period of the fastest relevant vibrational mode of the molecular system. Reducing the numerical costs of pump-probe simulations to the costs of a standard time-dependent wave-packet propagation, the approximate theory leads to substantial computational savings.

  17. Unusual enhancement of triplet carotenoid formation in pigmentprotein complexes as revealed by femtosecond pump-probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Maruta, S.; Kosumi, D.; Horibe, T.; Fujii, R.; Sugisaki, M.; Cogdell, R. J.; Hashimoto, H.

    Ultrafast excited state dynamics of carotenoids in solution and bound to pigment-protein complexes have been investigated by means of femtosecond pump-probe spectroscopic measurements. Ultrafast triplet formation of carotenoids bound to pigmentprotein complexes was observed upon excitation of both carotenoids and bacteriochlorophyll. The anomalous reaction of triplet formation of carotenoids bound to pigment-protein complexes is discussed in terms of ultrafast triplet-triplet excitation energy transfer between carotenoid and bacteriochlorophyll.

  18. Femtosecond pump-probe studies of actinic-wavelength dependence in aqueous chlorine dioxide photochemistry

    SciTech Connect

    Bixby, Teresa J.; Bolinger, Joshua C.; Patterson, Joshua D.; Reid, Philip J.

    2009-04-21

    The actinic or photolysis-wavelength dependence of aqueous chlorine dioxide (OClO) photochemistry is investigated using femtosecond pump-probe spectroscopy. Following photoexcitation at 310, 335, and 410 nm the photoinduced evolution in optical density is measured from the UV to the near IR. Analysis of the optical-density evolution illustrates that the quantum yield for atomic chlorine production ({Phi}{sub Cl}) increases with actinic energy, with {Phi}{sub Cl}=0.16{+-}0.02 for 410 nm excitation and increasing to 0.25{+-}0.01 and 0.54{+-}0.10 for 335 and 310 nm excitations, respectively. Consistent with previous studies, the production of Cl occurs through two channels, with one channel corresponding to prompt (<5 ps) Cl formation and the other corresponding to the thermal decomposition of ClOO formed by OClO photoisomerization. The partitioning between Cl production channels is dependent on actinic energy, with prompt Cl production enhanced with an increase in actinic energy. Limited evidence is found for enhanced ClO production with an increase in actinic energy. Stimulated emission and excited-state absorption features associated with OClO populating the optically prepared {sup 2}A{sub 2} surface decrease with an increase in actinic energy suggesting that the excited-state decay dynamics are also actinic energy dependent. The studies presented here provide detailed information on the actinic-wavelength dependence of OClO photochemistry in aqueous solution.

  19. Femtosecond pump-probe studies of actinic-wavelength dependence in aqueous chlorine dioxide photochemistry

    NASA Astrophysics Data System (ADS)

    Bixby, Teresa J.; Bolinger, Joshua C.; Patterson, Joshua D.; Reid, Philip J.

    2009-04-01

    The actinic or photolysis-wavelength dependence of aqueous chlorine dioxide (OClO) photochemistry is investigated using femtosecond pump-probe spectroscopy. Following photoexcitation at 310, 335, and 410 nm the photoinduced evolution in optical density is measured from the UV to the near IR. Analysis of the optical-density evolution illustrates that the quantum yield for atomic chlorine production (ΦCl) increases with actinic energy, with ΦCl=0.16±0.02 for 410 nm excitation and increasing to 0.25±0.01 and 0.54±0.10 for 335 and 310 nm excitations, respectively. Consistent with previous studies, the production of Cl occurs through two channels, with one channel corresponding to prompt (<5 ps) Cl formation and the other corresponding to the thermal decomposition of ClOO formed by OClO photoisomerization. The partitioning between Cl production channels is dependent on actinic energy, with prompt Cl production enhanced with an increase in actinic energy. Limited evidence is found for enhanced ClO production with an increase in actinic energy. Stimulated emission and excited-state absorption features associated with OClO populating the optically prepared A22 surface decrease with an increase in actinic energy suggesting that the excited-state decay dynamics are also actinic energy dependent. The studies presented here provide detailed information on the actinic-wavelength dependence of OClO photochemistry in aqueous solution.

  20. Pump-probe imaging of the fs-ps-ns dynamics during femtosecond laser Bessel beam drilling in PMMA.

    PubMed

    Yu, Yanwu; Jiang, Lan; Cao, Qiang; Xia, Bo; Wang, Qingsong; Lu, Yongfeng

    2015-12-14

    A pump-probe shadowgraph imaging technique was used to reveal the femtosecond-picosecond-nanosecond multitimescale fundamentals of high-quality, high-aspect-ratio (up to 287:1) microhole drilling in poly-methyl-meth-acrylate (PMMA) by a single-shot femtosecond laser Bessel beam. The propagation of Bessel beam in PMMA (at 1.98 × 10⁸ m/s) and it induced cylindrical pressure wave expansion (at 3000-3950 m/s in radius) were observed during drilling processes. Also, it was unexpectedly found that the expansion of the cylindrical pressure wave in PMMA showed a linear relation with time and was insensitive to the laser energy fluctuation, quite different from the case in air. It was assumed that the energy insensitivity was due to the anisotropy of wave expansion in PMMA and the ambient air.

  1. Femtosecond time-resolved EUV photoion imaging studies of pure helium nanodroplets

    NASA Astrophysics Data System (ADS)

    Buenermann, Oliver; Kornilov, Oleg; Gessner, Oliver; Leone, Stephen R.; Neumark, Daniel M.

    2010-03-01

    Helium nanodroplets provide a cryogenic, weakly interacting matrix for the isolation and spectroscopy of molecules and clusters. The relaxation dynamics of electronically excited helium nanodroplets are investigated by femtosecond time resolved photoion imaging studies. The droplets are excited into a broad absorption band centered at 23.8 eV. The electronic and nuclear dynamics following this excitation are monitored by photoionization with a 785nm probe pulse. A Wiley-McLaren time of flight spectrometer equipped with a time- and position sensitive delay line detector facilitates the measurement of mass selective ion kinetic energy distributions. First measurements reveal differences in the kinetic energy release of the Helium monomer, dimer and trimer ions. Furthermore, the pump-probe time-delay dependent ion spectra exhibit several features evolving on various timescales. The combination of these results with previously recorded photoelectron imaging measurements allows for a new level of insight into the electronic and nuclear dynamics of electronically excited helium nanodroplets.

  2. Focal overlap gating in velocity map imaging to achieve high signal-to-noise ratio in photo-ion pump-probe experiments

    DOE PAGES

    Shivaram, Niranjan; Champenois, Elio G.; Cryan, James P.; ...

    2016-12-19

    We demonstrate a technique in velocity map imaging (VMI) that allows spatial gating of the laser focal overlap region in time resolved pump-probe experiments. This significantly enhances signal-to-noise ratio by eliminating background signal arising outside the region of spatial overlap of pump and probe beams. This enhancement is achieved by tilting the laser beams with respect to the surface of the VMI electrodes which creates a gradient in flight time for particles born at different points along the beam. By suitably pulsing our microchannel plate detector, we can select particles born only where the laser beams overlap. Furthermore, this spatialmore » gating in velocity map imaging can benefit nearly all photo-ion pump-probe VMI experiments especially when extreme-ultraviolet light or X-rays are involved which produce large background signals on their own.« less

  3. Focal overlap gating in velocity map imaging to achieve high signal-to-noise ratio in photo-ion pump-probe experiments

    NASA Astrophysics Data System (ADS)

    Shivaram, Niranjan; Champenois, Elio G.; Cryan, James P.; Wright, Travis; Wingard, Taylor; Belkacem, Ali

    2016-12-01

    We demonstrate a technique in velocity map imaging (VMI) that allows spatial gating of the laser focal overlap region in time resolved pump-probe experiments. This significantly enhances signal-to-noise ratio by eliminating background signal arising outside the region of spatial overlap of pump and probe beams. This enhancement is achieved by tilting the laser beams with respect to the surface of the VMI electrodes which creates a gradient in flight time for particles born at different points along the beam. By suitably pulsing our microchannel plate detector, we can select particles born only where the laser beams overlap. This spatial gating in velocity map imaging can benefit nearly all photo-ion pump-probe VMI experiments especially when extreme-ultraviolet light or X-rays are involved which produce large background signals on their own.

  4. Focal overlap gating in velocity map imaging to achieve high signal-to-noise ratio in photo-ion pump-probe experiments

    SciTech Connect

    Shivaram, Niranjan; Champenois, Elio G.; Cryan, James P.; Wright, Travis; Wingard, Taylor; Belkacem, Ali

    2016-12-19

    We demonstrate a technique in velocity map imaging (VMI) that allows spatial gating of the laser focal overlap region in time resolved pump-probe experiments. This significantly enhances signal-to-noise ratio by eliminating background signal arising outside the region of spatial overlap of pump and probe beams. This enhancement is achieved by tilting the laser beams with respect to the surface of the VMI electrodes which creates a gradient in flight time for particles born at different points along the beam. By suitably pulsing our microchannel plate detector, we can select particles born only where the laser beams overlap. Furthermore, this spatial gating in velocity map imaging can benefit nearly all photo-ion pump-probe VMI experiments especially when extreme-ultraviolet light or X-rays are involved which produce large background signals on their own.

  5. Visualization of surface transformations during laser ablation of solids by femtosecond pump-probe time-resolved microscopy

    NASA Astrophysics Data System (ADS)

    Carrasco-García, Irene; Vadillo, José M.; Javier Laserna, J.

    2015-11-01

    A femtosecond time-resolved microscope (fs-TRM) based on pump-probe excitation has been used to follow the dynamic of the processes occurring during laser-matter interaction, from initial surface alterations to final solidification through transient melting. The time-resolved microscope described in the manuscript has been designed to allow a precise control of the excitation beam to cover ranges below and above the plasma formation energy, and a large temporal variation in the pump-probe delay to include the different timescales of the different processes occurring up to the plasma formation. The microscope has been demonstrated to be robust and allows the subpicosecond monitoring of laser ablation single-shot events, of importance in the analysis of ultra thin layers, or biological tissues. The fs-TRM excites (pump) the sample with 35-fs laser pulses at 800 nm and follows the processes by a second (probe) beam at 400 nm. The relative delay between both beams allows the acquisition of pictures with a temporal resolution of 200 fs up to 3 ns after the reaching of the pump pulse. In the ablative regime near the ablation threshold, transient surface reflectivity patterns (dynamic Newton fringes) are observed from a ps to ns time-scale. The timescale and number of such rings are affected by the fluence value. Significant differences between metals (Al, Cu and Sn), semiconductors (Si) and polymers (polytetrafluoroethylene and polyurethane) have been also observed in the transformation patterns.

  6. Pump-probe reflectometric and ellipsometric investigation of femtosecond laser pulse induced ablation in molybdenum

    NASA Astrophysics Data System (ADS)

    Rapp, S.; Winter, J.; Huber, H. P.; Schmidt, M.

    2017-02-01

    Ultrashort pulsed laser sources offer new possibilities in precise and efficient material processing. Deep understanding of the fundamental laser-material interaction aspects is of great importance. We report on pump-probe reflectometric investigations of the ablation process on molybdenum over the complete temporal process range from the pulse impact to the final steady state. The ablation process can roughly be separated in three sections. In the first tens of picoseconds mainly the optical material properties are changed without significant material motion. Between 50 ps and a few ns the irradiated material is bulging in a spallation or phase explosion process. The actual ablation by material ejection is observed at delay times greater than 20 ns. The transient reflectivity during and in the first tens of ps after the laser irradiation in conjunction with the transient absorption influences decisively the laser-matter interaction for example when working with longer pulse durations or double pulse sequences. Direct measurements of the absorption properties by ultrafast time-resolved ellipsometry at fluences close to the ablation threshold fluence are missing to date. In this paper, pump-probe ellipsometric measurements on molybdenum - complementing the pump-probe reflectometric measurements - are presented showing ultrafast changes of the complex refractive index N = n - ik including additional information on the absorption. The imaginary part k is reduced already after 10 ps by 50% representing an increase of the optical penetration depth by a reduction of the material density. These extensive investigations pave the road towards a better understanding of pulse duration dependent laser ablation efficiency, double or burst mode laser ablation and lattice modifications in the first ps after the laser pulse impact.

  7. Observation of femtosecond X-ray interactions with matter using an X-ray-X-ray pump-probe scheme.

    PubMed

    Inoue, Ichiro; Inubushi, Yuichi; Sato, Takahiro; Tono, Kensuke; Katayama, Tetsuo; Kameshima, Takashi; Ogawa, Kanade; Togashi, Tadashi; Owada, Shigeki; Amemiya, Yoshiyuki; Tanaka, Takashi; Hara, Toru; Yabashi, Makina

    2016-02-09

    Resolution in the X-ray structure determination of noncrystalline samples has been limited to several tens of nanometers, because deep X-ray irradiation required for enhanced resolution causes radiation damage to samples. However, theoretical studies predict that the femtosecond (fs) durations of X-ray free-electron laser (XFEL) pulses make it possible to record scattering signals before the initiation of X-ray damage processes; thus, an ultraintense X-ray beam can be used beyond the conventional limit of radiation dose. Here, we verify this scenario by directly observing femtosecond X-ray damage processes in diamond irradiated with extraordinarily intense (∼10(19) W/cm(2)) XFEL pulses. An X-ray pump-probe diffraction scheme was developed in this study; tightly focused double-5-fs XFEL pulses with time separations ranging from sub-fs to 80 fs were used to excite (i.e., pump) the diamond and characterize (i.e., probe) the temporal changes of the crystalline structures through Bragg reflection. It was found that the pump and probe diffraction intensities remain almost constant for shorter time separations of the double pulse, whereas the probe diffraction intensities decreased after 20 fs following pump pulse irradiation due to the X-ray-induced atomic displacement. This result indicates that sub-10-fs XFEL pulses enable conductions of damageless structural determinations and supports the validity of the theoretical predictions of ultraintense X-ray-matter interactions. The X-ray pump-probe scheme demonstrated here would be effective for understanding ultraintense X-ray-matter interactions, which will greatly stimulate advanced XFEL applications, such as atomic structure determination of a single molecule and generation of exotic matters with high energy densities.

  8. Time-dependent photoionization of azulene: Optically induced anistropy on the femtosecond scale

    NASA Astrophysics Data System (ADS)

    Raffael, Kevin; Blanchet, Valérie; Chatel, Béatrice; Turri, Giorgio; Girard, Bertrand; Garcia, Ivan Anton; Wilkinson, Iain; Whitaker, Benjamin J.

    2008-07-01

    We measure the photoionization cross-section of vibrationally excited levels in the S 2 state of azulene by femtosecond pump-probe spectroscopy. At the wavelengths studied (349-265 nm in the pump) the transient signals exhibit two distinct and well-defined behaviours: (i) short-term (on the order of a picosecond) polarization dependent transients and (ii) longer (10 ps-1 ns) timescale decays. This Letter focuses on the short-time transient. In contrast to an earlier study by Diau et al. [E.G. Diau, S. De Feyter, A.H. Zewail, J. Chem. Phys. 110 (1999) 9785.] we unambiguously assign the fast initial decay signal to rotational dephasing of the initial alignment created by the pump transition.

  9. Wave packet theory of dynamic stimulated Raman spectra in femtosecond pump-probe spectroscopy.

    PubMed

    Sun, Zhigang; Jin, Zhongqi; Lu, J; Zhang, Dong H; Lee, Soo-Y

    2007-05-07

    The quantum theory for stimulated Raman spectroscopy from a moving wave packet using the third-order density matrix and polarization is derived. The theory applies, in particular, to the new technique of femtosecond broadband stimulated Raman spectroscopy (FSRS). In the general case, a femtosecond actinic pump pulse first prepares a moving wave packet on an excited state surface which is then interrogated with a coupled pair of picosecond Raman pump pulse and a femtosecond Raman probe pulse and the Raman gain in the direction of the probe pulse is measured. It is shown that the third-order polarization in the time domain, whose Fourier transform governs the Raman gain, is given simply by the overlap of a first-order wave packet created by the Raman pump on the upper electronic state with a second-order wave packet on the initial electronic state that is created by the coupling of the Raman pump and probe fields acting on the molecule. Calculations are performed on model potentials to illustrate and interpret the FSRS spectra.

  10. Photodissociation of (SO2)m(H2O)n clusters employing femtosecond pump-probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Knappenberger, K. L.; Castleman, A. W.

    2005-04-01

    A femtosecond pump-probe technique was employed to study the photodissociation dynamics of (SO2)m(H2O)n clusters in real time for clusters, where m =1, 2 and n as large as 11. The pump (excitation) step occurs through a multiphoton process which populates the dissociative E state as well as a lower-lying bound state of the sulfur dioxide (SO2) chromosphore. Dissociation of the SO2 monomer occurs through the E state and the decay is fit to a lifetime of 230 fs. The present study is in agreement with our previous investigations of homogeneous (SO2)m clusters that have shown that cluster formation inhibits the dissociation process owing to a steric effect induced by the cluster environment [K. L. Knappenberger, Jr. and A. W. Castleman, Jr., J. Chem. Phys. 121, 3540 (2004)]. The E state lifetime increases sequentially as a function of cluster size to as much as 668 fs when 11 water molecules solvate the chromophore. We have employed a method to compare the ratio of amplitude coefficients, which reflect a respective component of the mathematical fit, to determine the nature of the wave packet evolution in binary clusters. An increase of this ratio by as much as 440% was observed for large cluster sizes. A preferential ion state charge transfer, rather than dissociation, was observed in binary clusters. The significance of cluster size on evaporation processes has been investigated.

  11. Water Hydrogen-Bonding Network Structure and Dynamics at Phospholipid Multibilayer Surface: Femtosecond Mid-IR Pump-Probe Spectroscopy.

    PubMed

    Kundu, Achintya; Błasiak, Bartosz; Lim, Joon-Hyung; Kwak, Kyungwon; Cho, Minhaeng

    2016-03-03

    The water hydrogen-bonding network at a lipid bilayer surface is crucial to understanding membrane structures and its functional activities. With a phospholipid multibilayer mimicking a biological membrane, we study the temperature dependence of water hydrogen-bonding structure, distribution, and dynamics at a lipid multibilayer surface using femtosecond mid-IR pump-probe spectroscopy. We observe two distinguished vibrational lifetime components. The fast component (0.6 ps) is associated with water interacting with a phosphate part, whereas the slow component (1.9 ps) is with bulk-like choline-associated water. With increasing temperature, the vibrational lifetime of phosphate-associated water remains constant though its relative fraction dramatically increases. The OD stretch vibrational lifetime of choline-bound water slows down in a sigmoidal fashion with respect to temperature, indicating a noticeable change of the water environment upon the phase transition. The water structure and dynamics are thus shown to be in quantitative correlation with the structural change of liquid multibilayer upon the gel-to-liquid crystal phase transition.

  12. A split-beam probe-pump-probe scheme for femtosecond time resolved protein X-ray crystallography

    SciTech Connect

    van Thor, Jasper J.; Madsen, Anders

    2015-01-01

    In order to exploit the femtosecond pulse duration of X-ray Free-Electron Lasers (XFEL) operating in the hard X-ray regime for ultrafast time-resolved protein crystallography experiments, critical parameters that determine the crystallographic signal-to-noise (I/σI) must be addressed. For single-crystal studies under low absorbed dose conditions, it has been shown that the intrinsic pulse intensity stability as well as mode structure and jitter of this structure, significantly affect the crystallographic signal-to-noise. Here, geometrical parameters are theoretically explored for a three-beam scheme: X-ray probe, optical pump, X-ray probe (or “probe-pump-probe”) which will allow experimental determination of the photo-induced structure factor amplitude differences, ΔF, in a ratiometric manner, thereby internally referencing the intensity noise of the XFEL source. In addition to a non-collinear split-beam geometry which separates un-pumped and pumped diffraction patterns on an area detector, applying an additional convergence angle to both beams by focusing leads to integration over mosaic blocks in the case of well-ordered stationary protein crystals. Ray-tracing X-ray diffraction simulations are performed for an example using photoactive yellow protein crystals in order to explore the geometrical design parameters which would be needed. The specifications for an X-ray split and delay instrument that implements both an offset angle and focused beams are discussed, for implementation of a probe-pump-probe scheme at the European XFEL. We discuss possible extension of single crystal studies to serial femtosecond crystallography, particularly in view of the expected X-ray damage and ablation due to the first probe pulse.

  13. A split-beam probe-pump-probe scheme for femtosecond time resolved protein X-ray crystallography

    DOE PAGES

    van Thor, Jasper J.; Madsen, Anders

    2015-01-01

    In order to exploit the femtosecond pulse duration of X-ray Free-Electron Lasers (XFEL) operating in the hard X-ray regime for ultrafast time-resolved protein crystallography experiments, critical parameters that determine the crystallographic signal-to-noise (I/σI) must be addressed. For single-crystal studies under low absorbed dose conditions, it has been shown that the intrinsic pulse intensity stability as well as mode structure and jitter of this structure, significantly affect the crystallographic signal-to-noise. Here, geometrical parameters are theoretically explored for a three-beam scheme: X-ray probe, optical pump, X-ray probe (or “probe-pump-probe”) which will allow experimental determination of the photo-induced structure factor amplitude differences, ΔF,more » in a ratiometric manner, thereby internally referencing the intensity noise of the XFEL source. In addition to a non-collinear split-beam geometry which separates un-pumped and pumped diffraction patterns on an area detector, applying an additional convergence angle to both beams by focusing leads to integration over mosaic blocks in the case of well-ordered stationary protein crystals. Ray-tracing X-ray diffraction simulations are performed for an example using photoactive yellow protein crystals in order to explore the geometrical design parameters which would be needed. The specifications for an X-ray split and delay instrument that implements both an offset angle and focused beams are discussed, for implementation of a probe-pump-probe scheme at the European XFEL. We discuss possible extension of single crystal studies to serial femtosecond crystallography, particularly in view of the expected X-ray damage and ablation due to the first probe pulse.« less

  14. A split-beam probe-pump-probe scheme for femtosecond time resolved protein X-ray crystallography

    PubMed Central

    van Thor, Jasper J.; Madsen, Anders

    2015-01-01

    In order to exploit the femtosecond pulse duration of X-ray Free-Electron Lasers (XFEL) operating in the hard X-ray regime for ultrafast time-resolved protein crystallography experiments, critical parameters that determine the crystallographic signal-to-noise (I/σI) must be addressed. For single-crystal studies under low absorbed dose conditions, it has been shown that the intrinsic pulse intensity stability as well as mode structure and jitter of this structure, significantly affect the crystallographic signal-to-noise. Here, geometrical parameters are theoretically explored for a three-beam scheme: X-ray probe, optical pump, X-ray probe (or “probe-pump-probe”) which will allow experimental determination of the photo-induced structure factor amplitude differences, ΔF, in a ratiometric manner, thereby internally referencing the intensity noise of the XFEL source. In addition to a non-collinear split-beam geometry which separates un-pumped and pumped diffraction patterns on an area detector, applying an additional convergence angle to both beams by focusing leads to integration over mosaic blocks in the case of well-ordered stationary protein crystals. Ray-tracing X-ray diffraction simulations are performed for an example using photoactive yellow protein crystals in order to explore the geometrical design parameters which would be needed. The specifications for an X-ray split and delay instrument that implements both an offset angle and focused beams are discussed, for implementation of a probe-pump-probe scheme at the European XFEL. We discuss possible extension of single crystal studies to serial femtosecond crystallography, particularly in view of the expected X-ray damage and ablation due to the first probe pulse. PMID:26798786

  15. Nanosecond pump-probe device for time-resolved serial femtosecond crystallography developed at SACLA.

    PubMed

    Kubo, Minoru; Nango, Eriko; Tono, Kensuke; Kimura, Tetsunari; Owada, Shigeki; Song, Changyong; Mafuné, Fumitaka; Miyajima, Ken; Takeda, Yoshihiro; Kohno, Jun Ya; Miyauchi, Naoya; Nakane, Takanori; Tanaka, Tomoyuki; Nomura, Takashi; Davidsson, Jan; Tanaka, Rie; Murata, Michio; Kameshima, Takashi; Hatsui, Takaki; Joti, Yasumasa; Neutze, Richard; Yabashi, Makina; Iwata, So

    2017-09-01

    X-ray free-electron lasers (XFELs) have opened new opportunities for time-resolved X-ray crystallography. Here a nanosecond optical-pump XFEL-probe device developed for time-resolved serial femtosecond crystallography (TR-SFX) studies of photo-induced reactions in proteins at the SPring-8 Angstrom Compact free-electron LAser (SACLA) is reported. The optical-fiber-based system is a good choice for a quick setup in a limited beam time and allows pump illumination from two directions to achieve high excitation efficiency of protein microcrystals. Two types of injectors are used: one for extruding highly viscous samples such as lipidic cubic phase (LCP) and the other for pulsed liquid droplets. Under standard sample flow conditions from the viscous-sample injector, delay times from nanoseconds to tens of milliseconds are accessible, typical time scales required to study large protein conformational changes. A first demonstration of a TR-SFX experiment on bacteriorhodopsin in bicelle using a setup with a droplet-type injector is also presented.

  16. Two-color FEL amplifier for femtosecond-resolution pump-probe experiments with GW-scale X-ray and optical pulses

    NASA Astrophysics Data System (ADS)

    Feldhaus, J.; Körfer, M.; Möller, T.; Pflüger, J.; Saldin, E. L.; Schneidmiller, E. A.; Schreiber, S.; Yurkov, M. V.

    2004-08-01

    The paper describes a scheme for pump-probe experiments that could be performed at the soft X-ray SASE FEL at the TESLA Test Facility (TTF) at DESY and determines what additional hardware developments will be required to bring these experiments to fruition. Pump-probe experiments combining pulses from a XFEL and optical femtosecond laser are very attractive for sub-picosecond time-resolved studies. Since the synchronization between the two light sources to an accuracy of 100 fs is not yet solved, it is proposed to derive both femtosecond radiation pulses from the same electron bunch but from two insertion devices. This eliminates the need for synchronization and developing tunable, high power femtosecond quantum laser. In the proposed scheme for pump-probe experiments, GW-level soft X-ray pulse is naturally synchronized with his GW-level optical pulse and cancel jitter. The concept is based on generation of the optical radiation in the master oscillator-power FEL amplifier configuration. An attractive feature of the FEL amplifier scheme is the absence of limitation which would prevent operation in the femtosecond regime in a wide (200- 900 nm) wavelength range. The problem of tunable quantum seed laser can be solved with commercially available long pulse dye laser. An important feature of the proposed scheme is that optical radiator uses the spent electron beam. As a result, saturation mode of operation of the optical FEL does not interfere with the main mode of the soft X-ray SASE FEL operation.

  17. Tracing few-femtosecond photodissociation dynamics on molecular oxygen with a single-color pump-probe scheme in the VUV

    NASA Astrophysics Data System (ADS)

    Schepp, Oliver; Baumann, Arne; Rompotis, Dimitrios; Gebert, Thomas; Azima, Armin; Wieland, Marek; Drescher, Markus

    2016-09-01

    Molecular wave-packet dynamics in oxygen are studied in the time domain, using a single-color VUV-pump-VUV-probe scheme. 17-fs VUV pulses, centered at 161 nm are generated via high-order harmonic generation driven by an intense 800-nm pulse leading to VUV pulse energies that reach 1.1 μ J per pulse. An all-reflective interferometric pump-probe scheme is used for studying the delay dependence of the molecular oxygen ion signal with simultaneous nonresonant photoionization of krypton as a precise timing-reference. Access to the excited dissociative state lifetime is provided by the resulting delay-dependent O2 + signal, ultimately limited by the molecular ionization window. The ability to use a two-photon VUV probe provides the delay-dependent detection of O+ as an additional observable, extending the dissociation observation window.

  18. Femtosecond laser pulse induced phase transition of Cr-doped Sb2Te1 films studied with a pump-probe system

    NASA Astrophysics Data System (ADS)

    Jiang, Minghui; Wang, Qing; Lei, Kai; Wang, Yang; Liu, Bo; Song, Zhitang

    2016-10-01

    The Femtosecond laser pulse induced phase transition dynamics of Cr-doped Sb2Te1 films was studied by real-time reflectivity measurements with a pump-probe system. It was found that crystallization of the as-deposited CrxSb2Te1 phase-change thin films exhibits a multi-stage process lasting for about 40ns.The time required for the multi-stage process seems to be not related to the contents of Cr element. The durations of the crystallization and amorphization processes are approximately the same. Doping Cr into Sb2Te1 thin film can improve its photo-thermal stability without obvious change in the crystallization rate. Optical images and image intensity cross sections are used to visualize the transformed regions. This work may provide further insight into the phase-change mechanism of CrxSb2Te1 under extra-non-equilibrium conditions and aid to develop new ultrafast phase-change memory materials.

  19. The influences of surface plasmons and thermal effects on femtosecond laser-induced subwavelength periodic ripples on Au film by pump-probe imaging

    NASA Astrophysics Data System (ADS)

    Zhou, Kan; Jia, Xin; Jia, Tianqing; Cheng, Ke; Cao, Kaiqiang; Zhang, Shian; Feng, Donghai; Sun, Zhenrong

    2017-03-01

    In this paper, the influences of surface plasmons and thermal effects on the formation of subwavelength periodic ripples on Au films irradiated by 800 nm femtosecond laser pulses were studied by collinear pump-probe imaging. The spatial and temporal resolutions of the experiment were 300 nm and 1 ps, respectively. No periodic ripples were observed on the Au film during ablation by the first pump pulse, but during ablation by the second pump pulse the appearance of transient ripples was evident from a delay time of hundreds of picoseconds to several nanoseconds. These ripples, however, were not retained after solidification. When the sample was immersed in water during ablation, however, the ripples were retained. It is proposed that, during the second laser pulse irradiation, the surface defects produced by the first pulse induced surface plasmon polaritons on the Au film, which caused a modulated energy deposition and the formation of transient ripples. The weak electron-phonon coupling and significant residual heat erase these ripples after the molten surface was solidified.

  20. In-Situ Probing Plasmonic Energy Transfer in Cu(In, Ga)Se2 Solar Cells by Ultrabroadband Femtosecond Pump-Probe Spectroscopy

    NASA Astrophysics Data System (ADS)

    Chen, Shih-Chen; Wu, Kaung-Hsiung; Li, Jia-Xing; Yabushita, Atsushi; Tang, Shih-Han; Luo, Chih Wei; Juang, Jenh-Yih; Kuo, Hao-Chung; Chueh, Yu-Lun

    2015-12-01

    In this work, we demonstrated a viable experimental scheme for in-situ probing the effects of Au nanoparticles (NPs) incorporation on plasmonic energy transfer in Cu(In, Ga)Se2 (CIGS) solar cells by elaborately analyzing the lifetimes and zero moment for hot carrier relaxation with ultrabroadband femtosecond pump-probe spectroscopy. The signals of enhanced photobleach (PB) and waned photoinduced absorption (PIA) attributable to surface plasmon resonance (SPR) of Au NPs were in-situ probed in transient differential absorption spectra. The results suggested that substantial carriers can be excited from ground state to lower excitation energy levels, which can reach thermalization much faster with the existence of SPR. Thus, direct electron transfer (DET) could be implemented to enhance the photocurrent of CIGS solar cells. Furthermore, based on the extracted hot carrier lifetimes, it was confirmed that the improved electrical transport might have been resulted primarily from the reduction in the surface recombination of photoinduced carriers through enhanced local electromagnetic field (LEMF). Finally, theoretical calculation for resonant energy transfer (RET)-induced enhancement in the probability of exciting electron-hole pairs was conducted and the results agreed well with the enhanced PB peak of transient differential absorption in plasmonic CIGS film. These results indicate that plasmonic energy transfer is a viable approach to boost high-efficiency CIGS solar cells.

  1. In-Situ Probing Plasmonic Energy Transfer in Cu(In, Ga)Se2 Solar Cells by Ultrabroadband Femtosecond Pump-Probe Spectroscopy

    PubMed Central

    Chen, Shih-Chen; Wu, Kaung-Hsiung; Li, Jia-Xing; Yabushita, Atsushi; Tang, Shih-Han; Luo, Chih Wei; Juang, Jenh-Yih; Kuo, Hao-Chung; Chueh, Yu-Lun

    2015-01-01

    In this work, we demonstrated a viable experimental scheme for in-situ probing the effects of Au nanoparticles (NPs) incorporation on plasmonic energy transfer in Cu(In, Ga)Se2 (CIGS) solar cells by elaborately analyzing the lifetimes and zero moment for hot carrier relaxation with ultrabroadband femtosecond pump-probe spectroscopy. The signals of enhanced photobleach (PB) and waned photoinduced absorption (PIA) attributable to surface plasmon resonance (SPR) of Au NPs were in-situ probed in transient differential absorption spectra. The results suggested that substantial carriers can be excited from ground state to lower excitation energy levels, which can reach thermalization much faster with the existence of SPR. Thus, direct electron transfer (DET) could be implemented to enhance the photocurrent of CIGS solar cells. Furthermore, based on the extracted hot carrier lifetimes, it was confirmed that the improved electrical transport might have been resulted primarily from the reduction in the surface recombination of photoinduced carriers through enhanced local electromagnetic field (LEMF). Finally, theoretical calculation for resonant energy transfer (RET)-induced enhancement in the probability of exciting electron-hole pairs was conducted and the results agreed well with the enhanced PB peak of transient differential absorption in plasmonic CIGS film. These results indicate that plasmonic energy transfer is a viable approach to boost high-efficiency CIGS solar cells. PMID:26679958

  2. In-Situ Probing Plasmonic Energy Transfer in Cu(In, Ga)Se2 Solar Cells by Ultrabroadband Femtosecond Pump-Probe Spectroscopy.

    PubMed

    Chen, Shih-Chen; Wu, Kaung-Hsiung; Li, Jia-Xing; Yabushita, Atsushi; Tang, Shih-Han; Luo, Chih Wei; Juang, Jenh-Yih; Kuo, Hao-Chung; Chueh, Yu-Lun

    2015-12-18

    In this work, we demonstrated a viable experimental scheme for in-situ probing the effects of Au nanoparticles (NPs) incorporation on plasmonic energy transfer in Cu(In, Ga)Se2 (CIGS) solar cells by elaborately analyzing the lifetimes and zero moment for hot carrier relaxation with ultrabroadband femtosecond pump-probe spectroscopy. The signals of enhanced photobleach (PB) and waned photoinduced absorption (PIA) attributable to surface plasmon resonance (SPR) of Au NPs were in-situ probed in transient differential absorption spectra. The results suggested that substantial carriers can be excited from ground state to lower excitation energy levels, which can reach thermalization much faster with the existence of SPR. Thus, direct electron transfer (DET) could be implemented to enhance the photocurrent of CIGS solar cells. Furthermore, based on the extracted hot carrier lifetimes, it was confirmed that the improved electrical transport might have been resulted primarily from the reduction in the surface recombination of photoinduced carriers through enhanced local electromagnetic field (LEMF). Finally, theoretical calculation for resonant energy transfer (RET)-induced enhancement in the probability of exciting electron-hole pairs was conducted and the results agreed well with the enhanced PB peak of transient differential absorption in plasmonic CIGS film. These results indicate that plasmonic energy transfer is a viable approach to boost high-efficiency CIGS solar cells.

  3. Time-resolved multi-mass ion imaging: Femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera

    NASA Astrophysics Data System (ADS)

    Forbes, Ruaridh; Makhija, Varun; Veyrinas, Kévin; Stolow, Albert; Lee, Jason W. L.; Burt, Michael; Brouard, Mark; Vallance, Claire; Wilkinson, Iain; Lausten, Rune; Hockett, Paul

    2017-07-01

    The Pixel-Imaging Mass Spectrometry (PImMS) camera allows for 3D charged particle imaging measurements, in which the particle time-of-flight is recorded along with (x, y) position. Coupling the PImMS camera to an ultrafast pump-probe velocity-map imaging spectroscopy apparatus therefore provides a route to time-resolved multi-mass ion imaging, with both high count rates and large dynamic range, thus allowing for rapid measurements of complex photofragmentation dynamics. Furthermore, the use of vacuum ultraviolet wavelengths for the probe pulse allows for an enhanced observation window for the study of excited state molecular dynamics in small polyatomic molecules having relatively high ionization potentials. Herein, preliminary time-resolved multi-mass imaging results from C2F3I photolysis are presented. The experiments utilized femtosecond VUV and UV (160.8 nm and 267 nm) pump and probe laser pulses in order to demonstrate and explore this new time-resolved experimental ion imaging configuration. The data indicate the depth and power of this measurement modality, with a range of photofragments readily observed, and many indications of complex underlying wavepacket dynamics on the excited state(s) prepared.

  4. The relaxation dynamics of the excited electronic states of retinal in bacteriorhodopsin by two-pump-probe femtosecond studies

    PubMed Central

    Logunov, S. L.; Volkov, V. V.; Braun, M.; El-Sayed, M. A.

    2001-01-01

    We present the results of two-pump and probe femtosecond experiments designed to follow the relaxation dynamics of the lowest excited state (S1) populated by different modes. In the first mode, a direct (S0 → S1) radiative excitation of the ground state is used. In the second mode, an indirect excitation is used where the S1 state is populated by the use of two femtosecond laser pulses with different colors and delay times between them. The first pulse excites the S0 → S1 transition whereas the second pulse excites the S1 → Sn transition. The nonradiative relaxation from the Sn state populates the lowest excited state. Our results suggest that the S1 state relaxes faster when populated nonradiatively from the Sn state than when pumped directly by the S0 → S1 excitation. Additionally, the Sn → S1 nonradiative relaxation time is found to change by varying the delay time between the two pump pulses. The observed dependence of the lowest excited state population as well as its dependence on the delay between the two pump pulses are found to fit a kinetic model in which the Sn state populates a different surface (called S′1) than the one being directly excited (S1). The possible involvement of the Ag type states, the J intermediate, and the conical intersection leading to the S0 or to the isomerization product (K intermediate) are discussed in the framework of the proposed model. PMID:11447258

  5. A Dual-Colour Architecture for Pump-Probe Spectroscopy of Ultrafast Magnetization Dynamics in the Sub-10-femtosecond Range

    PubMed Central

    Gonçalves, C. S.; Silva, A. S.; Navas, D.; Miranda, M.; Silva, F.; Crespo, H.; Schmool, D. S.

    2016-01-01

    Current time-resolution-limited dynamic measurements clearly show the need for improved techniques to access processes on the sub-10-femtosecond timescale. To access this regime, we have designed and constructed a state-of-the-art time-resolved magneto-optic Kerr effect apparatus, based on a new dual-color scheme, for the measurement of ultrafast demagnetization and precessional dynamics in magnetic materials. This system can operate well below the current temporal ranges reported in the literature, which typically lie in the region of around 50 fs and above. We have used a dual-colour scheme, based on ultra broadband hollow-core fibre and chirped mirror pulse compression techniques, to obtain unprecedented sub-8-fs pump and probe pulse durations at the sample plane. To demonstrate the capabilities of this system for ultrafast demagnetization and precessional dynamics studies, we have performed measurements in a ferrimagnetic GdFeCo thin film. Our study has shown that the magnetization shows a sudden drop within the first picosecond after the pump pulse, a fast recovery (remagnetization) within a few picoseconds, followed by a clear oscillation or precession during a slower magnetization recovery. Moreover, we have experimentally confirmed for the first time that a sub-10-fs pulse is able to efficiently excite a magnetic system such as GdFeCo. PMID:26976721

  6. Low frequency dynamics of the nitrogenase MoFe protein via femtosecond pump probe spectroscopy - Observation of a candidate promoting vibration.

    PubMed

    Maiuri, Margherita; Delfino, Ines; Cerullo, Giulio; Manzoni, Cristian; Pelmenschikov, Vladimir; Guo, Yisong; Wang, Hongxin; Gee, Leland B; Dapper, Christie H; Newton, William E; Cramer, Stephen P

    2015-12-01

    We have used femtosecond pump-probe spectroscopy (FPPS) to study the FeMo-cofactor within the nitrogenase (N2ase) MoFe protein from Azotobacter vinelandii. A sub-20-fs visible laser pulse was used to pump the sample to an excited electronic state, and a second sub-10-fs pulse was used to probe changes in transmission as a function of probe wavelength and delay time. The excited protein relaxes to the ground state with a ~1.2ps time constant. With the short laser pulse we coherently excited the vibrational modes associated with the FeMo-cofactor active site, which are then observed in the time domain. Superimposed on the relaxation dynamics, we distinguished a variety of oscillation frequencies with the strongest band peaks at ~84, 116, 189, and 226cm(-1). Comparison with data from nuclear resonance vibrational spectroscopy (NRVS) shows that the latter pair of signals comes predominantly from the FeMo-cofactor. The frequencies obtained from the FPPS experiment were interpreted with normal mode calculations using both an empirical force field (EFF) and density functional theory (DFT). The FPPS data were also compared with the first reported resonance Raman (RR) spectrum of the N2ase MoFe protein. This approach allows us to outline and assign vibrational modes having relevance to the catalytic activity of N2ase. In particular, the 226cm(-1) band is assigned as a potential 'promoting vibration' in the H-atom transfer (or proton-coupled electron transfer) processes that are an essential feature of N2ase catalysis. The results demonstrate that high-quality room-temperature solution data can be obtained on the MoFe protein by the FPPS technique and that these data provide added insight to the motions and possible operation of this protein and its catalytic prosthetic group. Copyright © 2015 Elsevier Inc. All rights reserved.

  7. Communication: State-to-state photodissociation study by the two-color VUV-VUV laser pump-probe time-slice velocity-map-imaging-photoion method

    NASA Astrophysics Data System (ADS)

    Gao, Hong; Song, Yu; Jackson, William M.; Ng, C. Y.

    2013-05-01

    We demonstrate that combining two independently tunable vacuum ultraviolet (VUV) lasers and the time-slice velocity-map-imaging-photoion (VMI-PI) method allows the rovibronically state-selected photodissociation study of CO in the VUV region along with the state-selective detection of product C(3P0,1,2) using the VUV-UV (1+1') resonance-enhanced photoionization and the VUV Rydberg autoionization methods. Both tunable VUV lasers are generated based on the two-photon resonance-enhanced four-wave mixing scheme using a pulsed rare gas jet as the nonlinear medium. The observed fine-structure distributions of product C(3PJ), J = 0, 1, and 2, are found to depend on the CO rovibronic state populated by VUV photoexcitation. The branching ratios for C(3P0) + O(3PJ): C(3P0) + O(1D2), C(3P1) + O(3PJ): C(3P1) + O(1D2), and C(3P2) + O(3PJ): C(3P2) + O(1D2), which were determined based on the time-slice VMI-PI measurements of C+ ions formed by J-state selective photoionization sampling of C(3P0,1,2), also reveal strong dependences on the spin-orbit state of C(3P0,1,2). By combining the measured branching ratios and fine-structure distributions of C(3P0,1,2), we have determined the correlated distributions of C(3P0,1,2) accompanying the formation of O(1D2) and O(3PJ) produced in the VUV photodissociation of CO. The success of this demonstration experiment shows that the VUV photodissociation pump-VUV photoionization probe method is promising for state-to-state photodissociation studies of many small molecules, which are relevant to planetary atmospheres as well as fundamental understanding of photodissociation dynamics.

  8. Communication: State-to-state photodissociation study by the two-color VUV-VUV laser pump-probe time-slice velocity-map-imaging-photoion method.

    PubMed

    Gao, Hong; Song, Yu; Jackson, William M; Ng, C Y

    2013-05-21

    We demonstrate that combining two independently tunable vacuum ultraviolet (VUV) lasers and the time-slice velocity-map-imaging-photoion (VMI-PI) method allows the rovibronically state-selected photodissociation study of CO in the VUV region along with the state-selective detection of product C((3)P(0,1,2)) using the VUV-UV (1+1') resonance-enhanced photoionization and the VUV Rydberg autoionization methods. Both tunable VUV lasers are generated based on the two-photon resonance-enhanced four-wave mixing scheme using a pulsed rare gas jet as the nonlinear medium. The observed fine-structure distributions of product C((3)P(J)), J = 0, 1, and 2, are found to depend on the CO rovibronic state populated by VUV photoexcitation. The branching ratios for C((3)P0) + O((3)P(J)): C((3)P0) + O((1)D2), C((3)P1) + O((3)P(J)): C((3)P1) + O((1)D2), and C((3)P2) + O((3)PJ): C((3)P2) + O((1)D2), which were determined based on the time-slice VMI-PI measurements of C(+) ions formed by J-state selective photoionization sampling of C((3)P(0,1,2)), also reveal strong dependences on the spin-orbit state of C((3)P(0,1,2)). By combining the measured branching ratios and fine-structure distributions of C((3)P(0,1,2)), we have determined the correlated distributions of C((3)P(0,1,2)) accompanying the formation of O((1)D2) and O((3)P(J)) produced in the VUV photodissociation of CO. The success of this demonstration experiment shows that the VUV photodissociation pump-VUV photoionization probe method is promising for state-to-state photodissociation studies of many small molecules, which are relevant to planetary atmospheres as well as fundamental understanding of photodissociation dynamics.

  9. Analysis of a measurement scheme for ultrafast hole dynamics by few femtosecond resolution X-ray pump-probe Auger spectroscopy.

    PubMed

    Cooper, Bridgette; Kolorenč, Přemysl; Frasinski, Leszek J; Averbukh, Vitali; Marangos, Jon P

    2014-01-01

    Ultrafast hole dynamics created in molecular systems as a result of sudden ionisation is the focus of much attention in the field of attosecond science. Using the molecule glycine we show through ab initio simulations that the dynamics of a hole, arising from ionisation in the inner valence region, evolves with a timescale appropriate to be measured using X-ray pulses from the current generation of SASE free electron lasers. The examined pump-probe scheme uses X-rays with photon energy below the K edge of carbon (275-280 eV) that will ionise from the inner valence region. A second probe X-ray at the same energy can excite an electron from the core to fill the vacancy in the inner-valence region. The dynamics of the inner valence hole can be tracked by measuring the Auger electrons produced by the subsequent refilling of the core hole as a function of pump-probe delay. We consider the feasibility of the experiment and include numerical simulation to support this analysis. We discuss the potential for all X-ray pump-X-ray probe Auger spectroscopy measurements for tracking hole migration.

  10. Relaxation dynamics of the LH2 complex from a photosynthetic purple bacterium Thiorhodospira sibirica studied by the near-IR femtosecond pump-probe method

    SciTech Connect

    Razjivin, A P; Pishchal'nikov, R Yu; Kozlovskii, V S; Kompanets, V O; Chekalin, Sergei V; Moskalenko, A A; Makhneva, Z K

    2005-01-31

    Photoinduced changes in the absorption spectrum of the LH2 (B800-830-850) complex from a Thiorhodospira sibirica (Trs. sibirica) bacterium are studied by the pump-probe method. The complex has the anomalous absorption spectrum exhibiting three bands in the near-IR region at 793, 826.5, and 846.5 nm. At room temperature, the excitation energy transfer from the B800, B830, and B859 bands was detected with the time constants {tau}{sub 1{approx}}0.5 ps, {tau}{sub 2{approx}}2.5 ps, and {tau}{sub 3} of the order of a few hundreds of picoseconds, respectively. A rapid energy transfer from the B830 band compared to energy transfer from the B850 band ({tau}{sub 2}||{tau}{sub 3}) suggests that all the three bands belong to the same complex (i.e., that the LH2 complex from Trs. sibirica is homogeneous). A slower energy transfer (by three - five times) from the B830 band of the LH2 complex from Trs. sibirica compared to energy transfer from the B800 band of the LH2 complexes (B800-850 and especially B800-820) from other purple bacteria suggests that the electronic structures of ensembles of bacteriochlorophyll molecules in these complexes are substantially different. (laser applications and other topics in quantum electronics)

  11. Angular resolved photoionization of C60 by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Li, Hui; Wang, Zhenhua; Suessmann, Frederik; Zherebtsov, Sergey; Skruszewicz, Slawomir; Tiggesbaeumker, Josef; Fennel, Thomas; Meiwes-Broer, Karl-Heinz; Cocke, C.; Kling, Matthias; JRM laboratory, Kansas State University Team; University of Rostock Collaboration; Max-Planck InstitutQuantumoptik Collaboration

    2013-03-01

    Neutral C60 molecules are ionized by intense femtosecond laser pulses around the wavelength of 800 nm with pulse durations 4 fs and 30 fs. We measure photoelectrons utilizing velocity-map imaging (VMI) and analyze the photoelectron angular distributions. For particular photoelectron energies, these distributions might reflect the excitation and ionization of superatomic molecular orbitals (SAMOs) which have been theoretically predicted and only recently experimentally observed. SAMOs arise from the hollow core spherical structures of the C60 molecules and differ from Rydberg states of C60 by their potential to exhibit electron density within the C60 cage. We have recorded the carrier envelope phase (CEP) dependence of the electron emission for 4 fs pulses using single shot CEP-tagging. The CEP-dependent asymmetry in the electron emission is observed to strongly depend on the laser polarization. Furthermore, the amplitudes and phases of the CEP-dependent electron emission are analyzed and show that thermal electron emission can be avoided enabling a more direct comparison to theory.

  12. Dissociative photoionization of 1,2-dichloroethane in intense near-infrared femtosecond laser field

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Yang, Yan; Li, Zhipeng; Zhang, Shian; Sun, Zhenrong

    2017-01-01

    We experimentally demonstrate the dissociative photoionization of 1,2-C2H4Cl2 molecules in femtosecond laser field by time-of-flight mass spectrum and dc-slice imaging technology. Our results show the low kinetic energy components are from the dissociative ionization process of singly charged molecular ions, and the positive charge assignment are greatly influenced by the appearance energy of the fragment ions. The high kinetic energy components result from Coulomb explosion of multi-charged molecular ions, and the different angular distribution of these fragments along Csbnd C and Csbnd Cl bond dissociation can be explained by the potential energy surfaces of the molecular ions.

  13. Ultrafast x-ray-induced nuclear dynamics in diatomic molecules using femtosecond x-ray / x-ray pump-probe spectroscopy

    SciTech Connect

    Lehmann, C. S.; Picon, A.; Bostedy, C.; Rudenko, A; Marinelli, A.; Moonshiram, D.; Osipov, T; Rolles, D; Berrah, N; Bomme, C; Bucher, M.; Doumy, G.; Ho, P. J.; Kanter, E.P.; Krassig, B.; March, A. M.; Young, L.; Pratt, S. T.; Southworth, S.H.

    2016-07-26

    The availability at x-ray free electron lasers of generating two intense, femtosecond x-ray pulses with controlled time delay opens the possibility of performing time-resolved experiments for x-ray induced phenomena. We have applied this capability to molecular dynamics. In diatomic molecules composed of low-Z elements, K-shell ionization creates a core-hole state in which the main decay is an Auger process involving two electrons in the valence shell. After Auger decay, the nuclear wavepackets of the transient two-valence-hole states continue evolving on the femtosecond timescale, leading either to separated atomic ions or long-lived quasi-bound states. By using an x-ray pump and an x-ray probe pulse tuned above the K-shell ionization threshold of the nitrogen molecule, we are able to observe ion dissociation in progress by measuring the time-dependent kinetic energy releases of different breakup channels. We simulated the measurements on N2 with a molecular dynamics model that accounts for K-shell ionization, Auger decay, and time evolution of the nuclear wavepackets. In addition to explaining the time-dependent feature in the measured kinetic energy release distributions from the dissociative states, the simulation also reveals the contributions of quasi-bound states.

  14. Plasma switch as a temporal overlap tool for pump-probe experiments at FEL facilities

    NASA Astrophysics Data System (ADS)

    Harmand, M.; Murphy, C. D.; Brown, C. R. D.; Cammarata, M.; Döppner, T.; Düsterer, S.; Fritz, D.; Förster, E.; Galtier, E.; Gaudin, J.; Glenzer, S. H.; Göde, S.; Gregori, G.; Hilbert, V.; Hochhaus, D.; Laarmann, T.; Lee, H. J.; Lemke, H.; Meiwes-Broer, K.-H.; Moinard, A.; Neumayer, P.; Przystawik, A.; Redlin, H.; Schulz, M.; Skruszewicz, S.; Tavella, F.; Tschentscher, T.; White, T.; Zastrau, U.; Toleikis, S.

    2012-08-01

    We have developed an easy-to-use and reliable timing tool to determine the arrival time of an optical laser and a free electron laser (FEL) pulses within the jitter limitation. This timing tool can be used from XUV to X-rays and exploits high FELs intensities. It uses a shadowgraph technique where we optically (at 800 nm) image a plasma created by an intense XUV or X-ray FEL pulse on a transparent sample (glass slide) directly placed at the pump - probe sample position. It is based on the physical principle that the optical properties of the material are drastically changed when its free electron density reaches the critical density. At this point the excited glass sample becomes opaque to the optical laser pulse. The ultra-short and intense XUV or X-ray FEL pulse ensures that a critical electron density can be reached via photoionization and subsequent collisional ionization within the XUV or X-ray FEL pulse duration or even faster. This technique allows to determine the relative arrival time between the optical laser and the FEL pulses in only few single shots with an accuracy mainly limited by the optical laser pulse duration and the jitter between the FEL and the optical laser. Considering the major interest in pump-probe experiments at FEL facilities in general, such a femtosecond resolution timing tool is of utmost importance.

  15. Photoelectron and photoion spectroscopy of atoms, nanoparticles, and nanoplasmas irradiated with strong femtosecond laser fields

    NASA Astrophysics Data System (ADS)

    Hickstein, Daniel D.

    Modern femtosecond lasers can produce pulses of light that are shorter than the vibrational periods in molecules and have electric fields stronger than the Coulomb field that binds electrons in atoms. These short pulse lasers enable the observation of chemical reactions, the production of attosecond bursts of high-energy photons, and the precision-machining of solid materials with minimal heat transport to the material. In this thesis, I describe three experiments that provide new insight into strong-field (1014 Watts/cm2) femtosecond laser-matter interactions in three important regimes. First, I discuss the strong-field ionization of gas-phase atoms, identify a new structure in the photoelectron angular distribution of xenon gas, and explain this structure as a result of field-driven electrons colliding with the Coulomb potential of the ion. Second, I describe a new method to perform photoelectron and photoion spectroscopy on single, isolated nanoparticles and demonstrate this technique by observing the directional ion ejection that takes place in the laser ablation of nanostructures. Finally, I present the first experimental observations of shock wave propagation in nanoscale plasmas. These findings will guide future efforts to probe the structure of atoms and molecules on the femtosecond timescale, design nanomaterials that enhance light on the subwavelength scale, and produce high-energy ions from plasmas.

  16. Tabletop Femtosecond VUV Photoionization and PEPICO Detection of Microreactor Pyrolysis Products

    DOE PAGES

    Couch, David E.; Buckingham, Grant T.; Baraban, Joshua H.; ...

    2017-06-29

    Here, we report the combination of tabletop vacuum ultraviolet photoionization with photoion--photoelectron coincidence spectroscopy for sensitive, isomer-specific detection of nascent products from a pyrolysis microreactor. Results on several molecules demonstrate two essential capabilities that are very straightforward to implement: the ability to differentiate isomers, and to distinguish thermal products from dissociative ionization. We derive vacuum ultraviolet light is from a commercial tabletop femtosecond laser system, allowing data to be collected at 10 kHz; this high repetition rate is critical for coincidence techniques. The photoion—photoelectron coincidence spectrometer uses the momentum of the ion to identify dissociative ionization events, and coincidence techniquesmore » to provide a photoelectron spectrum specific to each mass, which is used to distinguish different isomers. We also have used this spectrometer to detect the pyrolysis products that result from the thermal cracking of acetaldehyde, cyclohexene, and 2-butanol. The photoion—photoelectron spectrometer can detect and identify organic radicals and reactive intermediates that result from pyrolysis. Direct comparison of laboratory and synchrotron data illustrate the advantages and potential of this approach.« less

  17. Ultrafast pump-probe microscopy with high temporal dynamic range.

    PubMed

    Domke, Matthias; Rapp, Stephan; Schmidt, Michael; Huber, Heinz P

    2012-04-23

    Ultrafast pump-probe microscopy is a common method for time and space resolved imaging of short and ultra-short pulse laser ablation. The temporal delay between the ablating pump pulse and the illuminating probe pulse is tuned either by an optical delay, resulting in several hundred femtoseconds temporal resolution for delay times up to a few ns, or by an electronic delay, resulting in several nanoseconds resolution for longer delay times. In this work we combine both delay types for temporally high resolved observations of complete ablation processes ranging from femtoseconds to microseconds, while ablation is initiated by an ultrafast 660 fs laser pump pulse. For this purpose, we also demonstrate the calibration of the delay time zero point, the synchronization of both probe sources, as well as a method for image quality enhancing. In addition, we present for the first time to our knowledge pump-probe microscopy investigations of the complete substrate side selective ablation process of molybdenum films on glass. The initiation of mechanical film deformation is observed at about 400 ps, continues until approximately 15 ns, whereupon a Mo disk is sheared off free from thermal effects due to a directly induced laser lift-off ablation process. © 2012 Optical Society of America

  18. Electron localization following attosecond molecular photoionization.

    PubMed

    Sansone, G; Kelkensberg, F; Pérez-Torres, J F; Morales, F; Kling, M F; Siu, W; Ghafur, O; Johnsson, P; Swoboda, M; Benedetti, E; Ferrari, F; Lépine, F; Sanz-Vicario, J L; Zherebtsov, S; Znakovskaya, I; L'huillier, A; Ivanov, M Yu; Nisoli, M; Martín, F; Vrakking, M J J

    2010-06-10

    For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10(-15)-s) timescale. However, studying the inner workings of atoms and molecules on the electronic timescale has become possible only with the recent development of isolated attosecond (10(-18)-s) laser pulses. Such pulses have been used to investigate atomic photoexcitation and photoionization and electron dynamics in solids, and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H(2) and D(2) was monitored on femtosecond timescales and controlled using few-cycle near-infrared laser pulses. Here we report a molecular attosecond pump-probe experiment based on that work: H(2) and D(2) are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends-with attosecond time resolution-on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump-probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born-Oppenheimer approximation.

  19. Excited-state decay of hydrocarbon radicals, investigated by femtosecond time-resolved photoionization: Ethyl, propargyl, and benzyl

    NASA Astrophysics Data System (ADS)

    Zierhut, Matthias; Noller, Bastian; Schultz, Thomas; Fischer, Ingo

    2005-03-01

    The excited state decay of the hydrocarbon radicals ethyl, C2H5; propargyl, C3H3; and benzyl, C7H7 was investigated by femtosecond time-resolved photoionization. Radicals were generated by flash pyrolysis of n-propyl nitrite, propargyl bromide, and toluene, respectively. It is shown that the 2A'2(3s) Rydberg state of ethyl excited at 250nm decays with a time constant of 20fs. No residual signal was observed at longer delay times. For the 3B12 state of propargyl excited at 255nm a slower decay with a time constant 50±10fs was determined. The 4B22 state of benzyl excited at 255nm decays within 150±30fs.

  20. Time-resolved pump-probe experiments beyond the jitter limitations at FLASH

    SciTech Connect

    Azima, A.; Duesterer, S.; Radcliffe, P.; Redlin, H.; Stojanovic, N.; Li, W.; Schlarb, H.; Feldhaus, J.; Cubaynes, D.; Meyer, M.

    2009-04-06

    Using a noninvasive, electro-optically based electron bunch arrival time measurement at FLASH (free electron laser in Hamburg) the temporal resolution of two-color pump-probe experiments has been significantly improved. The system determines the relative arrival time of the extended ultraviolet pulse of FLASH and an amplified Ti:sapphire femtosecond-laser pulse at the interaction region better than 90 fs rms. In a benchmarking pump-probe experiment using two-color above threshold ionization of noble gases, an enhancement in the timing resolution by a factor of 4 compared to the uncorrected data is obtained.

  1. Ultrafast Molecular Photodissociation Dynamics Studied by Femtosecond Photoelectron-Photoion Coincidence Spectroscopy

    NASA Astrophysics Data System (ADS)

    Thaler, Bernhard; Heim, Pascal; Ernst, Wolfgang E.; Koch, Markus

    2017-06-01

    To completely characterize photodissociation mechanisms with time-resolved spectroscopy, it is essential to obtain unequivocal experimental information about the fragmentation dynamics induced by the laser pulse. We apply time-resolved photoelectron-photoion coincidence (PEPICO) detection in combination with different excitation schemes to obtain a mechanistic picture of the fragmentation process. For gas phase acetone molecules excited to high lying Rydberg states we are able to disentangle different ionization channels and investigate the fragmentation behavior of each channel separately. In particular, the high differentiability of PEPICO allows to distinguish channels where fragmentation proceeds after ionization from channels with fragmentation in the neutral. We show that excited Rydberg state population undergoes internal conversion due to coupling to valence states, which takes place within (150 ± 30) fs. The corresponding non-adiabatic, ultrafast relaxation dynamics to lower lying states causes conversion of electronic to vibrational energy and is found to play a crucial role in the fragmentation process (see figure 1). By studying the influence of photon energy, pulse duration, chirp and intensity of the laser pulses, we are able to determine the energy-threshold that is required for fragmentation, as well as corresponding fragmentation ratios. Surprisingly, for excitation with pulses possessing a strong negative chirp we observe significantly reduced fragmentation, indicating different internal conversion pathways and the associated intramolecular vibrational redistribution.

  2. Improving Phase Measurement Procedures for Pump-Probe Experiments

    SciTech Connect

    Perkins, Cara P.; /Merrimack Coll. /SLAC

    2011-06-22

    Pump-probe experiments use a visible laser to excite an atom or molecule, while an X-ray pulse measures its shape. The phases and pulse times of each beam are used to calculate the object's positing at a given time - a moving picture of the chemical reaction. Currently, the fastest X-ray pulses can travel a time-length of five femtoseconds. However, present-day phase measurements can only be done as quickly as 50 femtoseconds. The purpose of this research is to explore ways in which phase-timing measurements can be improved. Three experiments are undergone to find the key factors in phase-timing. Different frequency mixers, the radio frequency (RF) components used for phase measurement, are tested for the highest sensitivity. These same mixers are then tested using two different power splitters for the lowest noise-to-sensitivity ratio. Lastly, the temperature dependency of phase is explored by testing each component at a range of temperatures to see how the phase is affected. This research demonstrated that certain mixers were more sensitive than others; on average, one mixer performed the best with a sensitivity of 0.0230 V/ps. The results also showed that same mixer combined with one splitter gave the best noise-to-sensitivity ratio overall with an average of 6.95E-04 fs/{radical}(Hz). All the components tested exhibited a temperature-dependent phase change (ranging from 1.69 to 81.6 fs/{sup o}C); the same mixer that performed at the highest sensitivity with the least noise had a significantly greater phase change than the other two. In conclusion, the experiments showed that a temperature-controlled environment is most appropriate for phase measurement. They also demonstrated that mixers are not significantly noisy and that certain types of mixers may perform better than others, which could be accounted for in their construction. The results of this research encourage further investigation into the study of different mixers and other RF components used in pump-probe

  3. Invited Review Article: Pump-probe microscopy

    NASA Astrophysics Data System (ADS)

    Fischer, Martin C.; Wilson, Jesse W.; Robles, Francisco E.; Warren, Warren S.

    2016-03-01

    Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications.

  4. Invited Review Article: Pump-probe microscopy.

    PubMed

    Fischer, Martin C; Wilson, Jesse W; Robles, Francisco E; Warren, Warren S

    2016-03-01

    Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications.

  5. Invited Review Article: Pump-probe microscopy

    PubMed Central

    Wilson, Jesse W.; Robles, Francisco E.; Warren, Warren S.

    2016-01-01

    Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications. PMID:27036751

  6. Invited Review Article: Pump-probe microscopy

    SciTech Connect

    Fischer, Martin C. Wilson, Jesse W.; Robles, Francisco E.; Warren, Warren S.

    2016-03-15

    Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications.

  7. Effect of nuclear motion on molecular high order harmonic pump probe spectroscopy.

    PubMed

    Bredtmann, Timm; Chelkowski, Szczepan; Bandrauk, André D

    2012-11-26

    We study pump-probe schemes for the real time observation of electronic motion on attosecond time scale in the molecular ion H(2)(+) and its heavier isotope T(2)(+) while these molecules dissociate on femtosecond time scale by solving numerically the non-Born-Oppenheimer time-dependent Schrödinger equation. The UV pump laser pulse prepares a coherent superposition of the three lowest lying quantum states and the time-delayed mid-infrared, intense few-femtosecond probe pulse subsequently generates molecular high-order harmonics (MHOHG) from this coherent electron-nuclear wavepacket (CENWP). Varying the pump-probe time delay by a few hundreds of attoseconds, the MHOHG signal intensity is shown to vary by orders of magnitude. Due to nuclear movement, the coherence of these two upper states and the ground state is lost after a few femtoseconds and the MHOHG intensity variations as function of pump-probe delay time are shown to be equal to the period of electron oscillation in the coherent superposition of the two upper dissociative quantum states. Although this electron oscillation period and hence the periodicity of the harmonic spectra are quite constant over a wide range of internuclear distances, a strong signature of nuclear motion is seen in the actual shapes and ways in which these spectra change as a function of pump-probe delay time, which is illustrated by comparison of the MHOHG spectra generated by the two isotopes H(2)(+) and T(2)(+). Two different regimes corresponding roughly to internuclear distances R < 4a(0) and R > 4a(0) are identified: For R < 4a(0), the intensity of a whole range of frequencies in the plateau region is decreased by orders of magnitude when the delay time is changed by a few hundred attoseconds whereas in the cutoff region the peaks in the MHOHG spectra are red-shifted with increasing pump-probe time delay. For R > 4a(0), on the other hand, the peaks both in the cutoff and plateau region are red-shifted with increasing delay times

  8. Ultrafast and Nanoscale Plasmonic Phenomena in Exfoliated Graphene Revealed by Infrared Pump-Probe Nanoscopy

    NASA Astrophysics Data System (ADS)

    Wagner, Martin; Fei, Zhe; McLeod, Alexander S.; Rodin, Aleksandr S.; Bao, Wenzhong; Iwinski, Eric G.; Zhao, Zeng; Goldflam, Michael; Liu, Mengkun; Dominguez, Gerardo; Thiemens, Mark; Fogler, Michael M.; Castro Neto, Antonio H.; Lau, Chun Ning; Amarie, Sergiu; Keilmann, Fritz; Basov, D. N.

    2014-02-01

    Pump-probe spectroscopy is central for exploring ultrafast dynamics of fundamental excitations, collective modes and energy transfer processes. Typically carried out using conventional diffraction-limited optics, pump-probe experiments inherently average over local chemical, compositional, and electronic inhomogeneities. Here we circumvent this deficiency and introduce pump-probe infrared spectroscopy with ~20 nm spatial resolution, far below the diffraction limit, which is accomplished using a scattering scanning near-field optical microscope (s-SNOM). This technique allows us to investigate exfoliated graphene single-layers on SiO2 at technologically significant mid-infrared (MIR) frequencies where the local optical conductivity becomes experimentally accessible through the excitation of surface plasmons via the s-SNOM tip. Optical pumping at near-infrared (NIR) frequencies prompts distinct changes in the plasmonic behavior on 200 femtosecond (fs) time scales. The origin of the pump-induced, enhanced plasmonic response is identified as an increase in the effective electron temperature up to several thousand Kelvin, as deduced directly from the Drude weight associated with the plasmonic resonances.

  9. Pump-probe laser development for the European X-ray Free-Electron Laser facility

    NASA Astrophysics Data System (ADS)

    Lederer, Max J.; Pergament, Mikhail; Kellert, Martin; Mendez, Cruz

    2012-10-01

    The successful implementation of superconducting LINAC technology at the European XFEL will boost the time averaged X-RAY power density substantially above current values. In fact, the XFEL will operate at repetition rates of up to 4.5MHz. However, this high pulse rate occurs only during 600μs long bursts of 10Hz repetition rate, rendering up to 27000 pulses per second. Matching this peculiar burst mode operation is a requirement also for the pump-probe femtosecond laser used in experiments. There is currently no commercially available femtosecond laser technology offering this kind of output at close to mJ-level energies per pulse and sub-20fs pulse width. We will outline the scheme of the pump-probe laser currently under development at the European XFEL. The laser design is based on a noncollinear optical parametric amplifier (NOPA) which will be pumped by sub-picosecond pulses from a high power, frequency-doubled Yb:YAG slab amplifier, delivering up to 20kW of fundamental average power during a burst. The design aims at highest possible flexibility regarding intra-burst rep-rates and pulse energies. Also, the use of uncompressed as well as compressed NOPA pump pulses at fundamental wavelength will enhance the flexibility in experiments.

  10. Pump-probe experiments at the TEMPO beamline using the low-α operation mode of Synchrotron SOLEIL.

    PubMed

    Silly, Mathieu G; Ferté, Tom; Tordeux, Marie Agnes; Pierucci, Debora; Beaulieu, Nathan; Chauvet, Christian; Pressacco, Federico; Sirotti, Fausto; Popescu, Horia; Lopez-Flores, Victor; Tortarolo, Marina; Sacchi, Maurizio; Jaouen, Nicolas; Hollander, Philippe; Ricaud, Jean Paul; Bergeard, Nicolas; Boeglin, Christine; Tudu, Bharati; Delaunay, Renaud; Luning, Jan; Malinowski, Gregory; Hehn, Michel; Baumier, Cédric; Fortuna, Franck; Krizmancic, Damjan; Stebel, Luigi; Sergo, Rudi; Cautero, Giuseppe

    2017-07-01

    The SOLEIL synchrotron radiation source is regularly operated in special filling modes dedicated to pump-probe experiments. Among others, the low-α mode operation is characterized by shorter pulse duration and represents the natural bridge between 50 ps synchrotron pulses and femtosecond experiments. Here, the capabilities in low-α mode of the experimental set-ups developed at the TEMPO beamline to perform pump-probe experiments with soft X-rays based on photoelectron or photon detection are presented. A 282 kHz repetition-rate femtosecond laser is synchronized with the synchrotron radiation time structure to induce fast electronic and/or magnetic excitations. Detection is performed using a two-dimensional space resolution plus time resolution detector based on microchannel plates equipped with a delay line. Results of time-resolved photoelectron spectroscopy, circular dichroism and magnetic scattering experiments are reported, and their respective advantages and limitations in the framework of high-time-resolution pump-probe experiments compared and discussed.

  11. Jitter-correction for IR/UV-XUV pump-probe experiments at the FLASH free-electron laser

    DOE PAGES

    Savelyev, Evgeny; Boll, Rebecca; Bomme, Cedric; ...

    2017-04-10

    In pump-probe experiments employing a free-electron laser (FEL) in combination with a synchronized optical femtosecond laser, the arrival-time jitter between the FEL pulse and the optical laser pulse often severely limits the temporal resolution that can be achieved. Here, we present a pump-probe experiment on the UV-induced dissociation of 2,6-difluoroiodobenzene C6H3F2I) molecules performed at the FLASH FEL that takes advantage of recent upgrades of the FLASH timing and synchronization system to obtain high-quality data that are not limited by the FEL arrival-time jitter. Here, we discuss in detail the necessary data analysis steps and describe the origin of the time-dependentmore » effects in the yields and kinetic energies of the fragment ions that we observe in the experiment.« less

  12. Ultrafast spatiotemporal relaxation dynamics of excited electrons in a metal nanostructure detected by femtosecond-SNOM.

    PubMed

    Li, Zhi; Yue, Song; Chen, Jianjun; Gong, Qihuang

    2010-06-21

    Ultrahigh spatiotemporal resolved pump-probe signal near a gold nano-slit is detected by femtosecond-SNOM. By employing two-color pump-probe configuration and probing at the interband transition wavelength of the gold, signal contributed by surface plasmon polariton is avoided and spatiotemporal evolvement of excited electrons is successfully observed. From the contrast decaying of the periodical distribution of the pump-probe signal, ultrafast diffusion of excited electrons with a time scale of a few hundred femtoseconds is clearly identified. For comparison, such phenomenon cannot be observed by the one-color pump-probe configuration.

  13. Femtosecond multiphoton ionization of ammonia clusters

    SciTech Connect

    Wei, S.; Purnell, J.; Buzza, S.A.; Stanley, R.J.; Castleman, A.W. Jr. )

    1992-12-15

    Herein, we report on femtosecond time-resolved experiments in ammonia clusters. The mechanisms of their ionization and the subsequent formation of the protonated ammonia cluster ions are studied using a femtosecond pump-probe technique at 620 nm. It is found that an intermediate corresponding to [ital C][prime] states of the monomer is responsible for the ionization of ammonia clusters. Femtosecond pump--probe studies show that the lifetime of the intermediate to the formation of the protonated cluster ions (NH[sub 3])[sub [ital n

  14. Effective temporal resolution in pump-probe spectroscopy with strongly chirped pulses

    SciTech Connect

    Polli, D.; Lanzani, G.; Brida, D.; Cerullo, G.; Mukamel, S.

    2010-11-15

    This paper introduces a general theoretical description of femtosecond pump-probe spectroscopy with chirped pulses whose joint spectral and temporal profile is expressed by Wigner spectrograms. We demonstrate that the actual experimental time resolution intimately depends on the pulse-sample interaction and that the commonly used instrumental response function needs to be replaced by a sample-dependent effective response function. We also show that, using the proper configurations in excitation and/or detection, it is possible to overcome the temporal smearing of the measured dynamics due to chirp-induced pulse broadening and recover the temporal resolution that would be afforded by the transform-limited pulses. We verify these predictions with experiments using broadband chirped pump and probe pulses. Our results allow optimization of the temporal resolution in the common case when the chirp of the pump and/or probe pulse is not corrected and may be extended to a broad range of time-resolved experiments.

  15. Femtosecond single-electron diffraction

    PubMed Central

    Lahme, S.; Kealhofer, C.; Krausz, F.; Baum, P.

    2014-01-01

    Ultrafast electron diffraction allows the tracking of atomic motion in real time, but space charge effects within dense electron packets are a problem for temporal resolution. Here, we report on time-resolved pump-probe diffraction using femtosecond single-electron pulses that are free from intra-pulse Coulomb interactions over the entire trajectory from the source to the detector. Sufficient average electron current is achieved at repetition rates of hundreds of kHz. Thermal load on the sample is avoided by minimizing the pump-probe area and by maximizing heat diffusion. Time-resolved diffraction from fibrous graphite polycrystals reveals coherent acoustic phonons in a nanometer-thick grain ensemble with a signal-to-noise level comparable to conventional multi-electron experiments. These results demonstrate the feasibility of pump-probe diffraction in the single-electron regime, where simulations indicate compressibility of the pulses down to few-femtosecond and attosecond duration. PMID:26798778

  16. Ultrafast pump-probe study of the excited-state charge-transfer dynamics in blue copper rusticyanin.

    PubMed

    Bizzarri, Anna Rita; Brida, Daniele; Santini, Simona; Cerullo, Giulio; Cannistraro, Salvatore

    2012-04-12

    We have used femtosecond pump-probe spectroscopy to investigate the excited-state dynamics of the anticancer blue copper protein rusticyanin, by exciting its ligand to metal charge-transfer band with 25 fs pump pulses centered at 585 nm. The charge-transfer excited state decays exponentially to the ground state with a time constant of about 230 fs, and its recovery is modulated by coherent oscillations. The Fourier transform of the oscillatory component of the signal provides most of the vibrational modes obtained by means of conventional resonance Raman studies, in addition to the low frequency modes below 80 cm(-1) believed to reflect collective motions of biological relevance.

  17. Pump-Probe Fragmentation Action Spectroscopy: A Powerful Tool to Unravel Light-Induced Processes in Molecular Photocatalysts.

    PubMed

    Imanbaew, Dimitri; Lang, Johannes; Gelin, Maxim F; Kaufhold, Simon; Pfeffer, Michael G; Rau, Sven; Riehn, Christoph

    2017-05-08

    We present a proof of concept that ultrafast dynamics combined with photochemical stability information of molecular photocatalysts can be acquired by electrospray ionization mass spectrometry combined with time-resolved femtosecond laser spectroscopy in an ion trap. This pump-probe "fragmentation action spectroscopy" gives straightforward access to information that usually requires high purity compounds and great experimental efforts. Results of gas-phase studies on the electronic dynamics of two supramolecular photocatalysts compare well to previous findings in solution and give further evidence for a directed electron transfer, a key process for photocatalytic hydrogen generation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. High-Precision Time Delay Control with Continuous Phase Shifter for Pump-Probe Experiments Using Synchrotron Radiation Pulses

    SciTech Connect

    Tanaka, Yoshihito; Ohshima, Takashi; Moritomo, Yutaka; Tanaka, Hitoshi; Takata, Masaki

    2010-06-23

    Brilliant pulsed x-ray synchrotron radiation (SR) is useful for pump-probe experiment such as time-resolved x-ray diffraction, x-ray absorption fine structure, and x-ray spectroscopy. For laser pump-SR x-ray probe experiments, short pulsed lasers are generally synchronized to the SR master oscillator controlling the voltage for acceleration of electron bunches in an accelerator, and the interval between the laser and the SR pulses is changed around the time scale of target phenomenon. Ideal delay control produces any time delay as keeping the time-precision and pointing-stability of optical pulses at a sample position. We constructed the time delay control module using a continuous phase shifter of radio frequency signal and a frequency divider, which can produce the delayed trigger pulses to the laser without degradation of the time precision and the pointing stability. A picoseconds time-resolved x-ray diffraction experiment was demonstrated at SPring-8 storage ring for fast lattice response by femtosecond pulsed laser irradiation, and suggested the possibility of accurate sound velocity measurement. A delay control unit operating with subpicosecond precision has also been designed for femtosecond pump-probe experiments using a free electron laser at SPring-8 campus.

  19. Phasor analysis for nonlinear pump-probe microscopy

    PubMed Central

    Robles, Francisco E.; Wilson, Jesse W.; Fischer, Martin C.; Warren, Warren S.

    2012-01-01

    Pump-probe microscopy provides molecular information by probing transient, excited state dynamic properties of pigmented samples. Analysis of the transient response is typically conducted using principal component analysis or multi-exponential fitting, however these methods are not always practical or feasible. Here, we show an adaptation of phasor analysis to provide an intuitive, robust, and efficient method for analyzing and displaying pump-probe images, thereby alleviating some of the challenges associated with differentiating multiple pigments. A theoretical treatment is given to understand how the complex transient signals map onto the phasor plot. Analyses of cutaneous and ocular pigmented tissue samples, as well as historical pigments in art demonstrate the utility of this approach.

  20. Coherence specific signal detection via chiral pump-probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Holdaway, David I. H.; Collini, Elisabetta; Olaya-Castro, Alexandra

    2016-05-01

    We examine transient circular dichroism (TRCD) spectroscopy as a technique to investigate signatures of exciton coherence dynamics under the influence of structured vibrational environments. We consider a pump-probe configuration with a linearly polarized pump and a circularly polarized probe, with a variable angle θ between the two directions of propagation. In our theoretical formalism the signal is decomposed in chiral and achiral doorway and window functions. Using this formalism, we show that the chiral doorway component, which beats during the population time, can be isolated by comparing signals with different values of θ. As in the majority of time-resolved pump-probe spectroscopy, the overall TRCD response shows signatures of both excited and ground state dynamics. However, we demonstrate that the chiral doorway function has only a weak ground state contribution, which can generally be neglected if an impulsive pump pulse is used. These findings suggest that the pump-probe configuration of optical TRCD in the impulsive limit has the potential to unambiguously probe quantum coherence beating in the excited state. We present numerical results for theoretical signals in an example dimer system.

  1. Time resolved EUV pump-probe microscopy of fs-LASER induced nanostructure formation

    NASA Astrophysics Data System (ADS)

    Freiberger, R.; Hauck, J.; Reininghaus, M.; Wortmann, D.; Juschkin, L.

    2011-05-01

    We report on our efforts in design and construction of a compact Extreme Ultraviolet (EUV)-pump-probe microscope. The goal is the observation of formation of nanostructures, induced by a femtosecond (fs)-laser pulse. The unique interaction processes of fs-laser radiation with matter open up new markets in laser material processing and, therefore, are actively investigated in the last decade. The resulting "sub 100 nm"-structures offer vast potential benefits in photonics, biotechnology, tribological surface design, plasmonic applications and production of nanoparticles. Focused fs-laser radiation causes a local modification resulting in nanostructures of high precision and reproducibility. However the formation dynamics is not well understood. Research in this field requires high temporal and spatial resolution. A combination of fs-laser and EUV-microscope provides a tool for "in situ"-observation of the formation dynamics. As exemplary structures to be investigated, we use nanojets on thin gold films and periodic surface structures (ripples) on dielectrics. In the future, the EUV-pump-probe microscope can become a versatile tool to observe physical or biological processes. Microscopy using EUV-light is capable of detecting structures on a scale down to several tens of nanometers. For detailed investigations a compact EUV-microscope has been realized utilizing OVI Balmer-alpha radiation at 17.3 nm coming from a discharge produced oxygen plasma. As optical elements a grazing incidence elliptical collector and a zone plate with a width of outermost zone of 50 nm and a spectral filter to avoid chromatic aberrations are used. The detector is a fast gated microchannel plate with a pore size of 2 microns contacted by a low impedance transmission line. The expected spatial resolution of the setup is better than 100 nm and the time resolution is better than 1 ns. The newly developed EUV-microscope is a powerful tool for a wide field of investigations that need high time

  2. Ultra-Broadband Two-Dimensional Electronic Spectroscopy and Pump-Probe Microscopy of Molecular Systems

    NASA Astrophysics Data System (ADS)

    Spokoyny, Boris M.

    Ultrafast spectroscopy offers an unprecedented view on the dynamic nature of chemical reactions. From charge transfer in semiconductors to folding and isomerization of proteins, these all important processes can now be monitored and in some instances even controlled on real, physical timescales. One of the biggest challenges of ultrafast science is the incredible energetic complexity of most systems. It is not uncommon to encounter macromolecules or materials with absorption spectra spanning significant portions of the visible spectrum. Monitoring a multitude of electronic and vibrational transitions, all dynamically interacting with each other on femtosecond timescales poses a truly daunting experimental task. The first part of this thesis deals with the development of a novel Two-Dimensional Electronic Spectroscopy (2DES) and its associated, advanced detection methodologies. Owing to its ultra-broadband implementation, this technique enables us to monitor femtosecond chemical dynamics that span the energetic landscape of the entire visible spectrum. In order to demonstrate the utility of our method, we apply it to two laser dye molecules, IR-144 and Cresyl Violet. Variation of photophysical properties on a microscopic scale in either man-made or naturally occurring systems can have profound implications on how we understand their macroscopic properties. Recently, inorganic hybrid perovskites have been tapped as the next generation solar energy harvesting materials. Their remarkable properties include low exciton binding energy, low exciton recombination rates and long carrier diffusion lengths. Nevertheless, considerable variability in device properties made with nearly identical preparation methods has puzzled the community. In the second part of this thesis we use non-linear pump probe microscopy to study the heterogeneous nature of femtosecond carrier dynamics in thin film perovskites. We show that the local morphology of the perovskite thin films has a

  3. Pump-probe study of atoms and small molecules with laser driven high order harmonics

    NASA Astrophysics Data System (ADS)

    Cao, Wei

    A commercially available modern laser can emit over 1015 photons within a time window of a few tens of femtoseconds (10-15second), which can be focused into a spot size of about 10 mum, resulting in a peak intensity above 1014W/cm2. This paves the way for table-top strong field physics studies such as above threshold ionization (ATI), non-sequential double ionization (NSDI), high order harmonic generation (HHG), etc.. Among these strong laser-matter interactions, high order harmonic generation, which combines many photons of the fundamental laser field into a single photon, offers a unique way to generate light sources in the vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) region. High order harmonic photons are emitted within a short time window from a few tens of femtoseconds down to a few hundreds of attoseconds (10 -18second). This highly coherent nature of HHG allows it to be synchronized with an infrared (IR) laser pulse, and the pump-probe technique can be adopted to study ultrafast dynamic processes in a quantum system. The major work of this thesis is to develop a table-top VUV(EUV) light source based on HHG, and use it to study dynamic processes in atoms and small molecules with the VUV(EUV)-pump IR-probe method. A Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) apparatus is used for momentum imaging of the interaction products. Two types of high harmonic pump pulses are generated and applied for pump-probe studies. The first one consists of several harmonics forming a short attosecond pulse train (APT) in the EUV regime (around 40 eV). We demonstrate that, (1) the auto-ionization process triggered by the EUV in cation carbon-monoxide and oxygen molecules can be modified by scanning the EUV-IR delay, (2) the phase information of quantum trajectories in bifurcated high harmonics can be extracted by performing an EUV-IR cross-correlation experiment, thus disclosing the macroscopic quantum control in HHG. The second type of high harmonic source

  4. Photoacoustic imaging of fluorophores using pump-probe excitation

    PubMed Central

    Märk, Julia; Schmitt, Franz-Josef; Theiss, Christoph; Dortay, Hakan; Friedrich, Thomas; Laufer, Jan

    2015-01-01

    A pump-probe technique for the detection of fluorophores in tomographic PA images is introduced. It is based on inducing stimulated emission in fluorescent molecules, which in turn modulates the amount of thermalized energy, and hence the PA signal amplitude. A theoretical model of the PA signal generation in fluorophores is presented and experimentally validated on cuvette measurements made in solutions of Rhodamine 6G, a fluorophore of known optical and molecular properties. The application of this technique to deep tissue tomographic PA imaging is demonstrated by determining the spatial distribution of a near-infrared fluorophore in a tissue phantom. PMID:26203378

  5. Pump probe spectroscopy of quasiparticle dynamics in cuprate superconductors

    SciTech Connect

    Segre, Gino P.

    2001-01-01

    Pump probe spectroscopy is used to examine the picosecond response of a BSCCO thin film, and two YBCO crystals in the near infrared. The role of pump fluence and temperature have been closely examined in an effort to clarify the mechanism by which the quasiparticles rejoin the condensate. BSCCO results suggest that the recombination behavior is consistent with the d-wave density of states in that quasiparticles appear to relax to the nodes immediately before they rejoin the condensate. The first substantial investigation of polarized pump probe response in detwinned YBCO crystals is also reported. Dramatic doping dependent anisotropies along the a and b axes are observed in time and temperature resolved studies. Among many results, we highlight the discovery of an anomalous temperature and time dependence of a- axis response in optimally doped YBCO. We also report on the first observation of the photoinduced response in a magnetic field. We find the amplitude of the response, and in some cases, the dynamics considerably changed with the application of a 6T field. Finally, we speculate on two of the many theoretical directions stimulated by our results. We find that the two-fluid model suggests a mechanism to explain how changes at very low energies are visible to a high-energy probe. Also discussed are basic recombination processes which may play a role in the observed decay.

  6. Pump-probe spectroscopy in organic semiconductors: monitoring fundamental processes of relevance in optoelectronics.

    PubMed

    Cabanillas-Gonzalez, Juan; Grancini, Giulia; Lanzani, Guglielmo

    2011-12-08

    In this review we highlight the contribution of pump-probe spectroscopy to understand elementary processes taking place in organic based optoelectronic devices. The techniques described in this article span from conventional pump-probe spectroscopy to electromodulated pump-probe and the state-of-the-art confocal pump-probe microscopy. The article is structured according to three fundamental processes (optical gain, charge photogeneration and charge transport) and the contribution of these techniques on them. The combination of these tools opens up new perspectives for assessing the role of short-lived excited states on processes lying underneath organic device operation.

  7. Synchronized pulses generated at 20 eV and 90 eV for attosecond pump-probe experiments

    NASA Astrophysics Data System (ADS)

    Fabris, D.; Witting, T.; Okell, W. A.; Walke, D. J.; Matia-Hernando, P.; Henkel, J.; Barillot, T. R.; Lein, M.; Marangos, J. P.; Tisch, J. W. G.

    2015-06-01

    The development of attosecond pulses across different photon energies is an essential precursor to performing pump-probe attosecond experiments in complex systems, where the potential of attosecond science can be further developed. We report the generation and characterization of synchronized extreme ultraviolet (90 eV) and vacuum ultraviolet (20 eV) pulses, generated simultaneously via high-harmonic generation. The vacuum ultraviolet pulses are well suited for pump-probe experiments that exploit the high photo-ionization cross-sections of many molecules in this spectral region as well as the higher photon flux due to the higher conversion efficiency of the high harmonic generation process at these energies. We temporally characterized all pulses using the attosecond streaking technique and the FROG-CRAB retrieval method. We report 576 ± 16 as pulses at 20 eV and 257 ± 21 as pulses at 90 eV. Our demonstration of synchronized attosecond pulses at different photon energies, which are inherently jitter-free due to the common-path geometry implemented, offers unprecedented possibilities for pump-probe studies.

  8. Mapping CTTS dynamics of Na- in tetrahydrofurane with ultrafast multichannel pump-probe spectroscopy.

    PubMed

    Shoshana, O; Pérez Lustres, J L; Ernsting, N P; Ruhman, S

    2006-06-14

    Using multichannel femtosecond spectroscopy we have followed Na- charge transfer to solvent (CTTS) dynamics in THF solution. Absorption of the primary photoproducts in the visible, resolved here for the first time, consists of an asymmetric triplet centered at 595 nm, which we assign to a metastable incompletely solvated neutral atomic sodium species. Decay of this feature within approximately 1 ps to a broad and structureless solvated neutral is accompanied by broadening and loss of spectral detail. Kinetic analysis shows that both the spectral structure and the decay of this band are independent of the excitation photon frequency in the range 400-800 nm. With different pump-probe polarizations the anisotropy in transient transmission has been charted and its variation with excitation wavelength surveyed. The anisotropies are assigned to the reactant bleach, indicating that due to solvent-induced symmetry breaking, the CTTS absorption band of Na- is made up of discreet orthogonally polarized sub bands. None of the anisotropy in transient absorption could be associated with the photoproduct triplet band even at the earliest measurable time delays. Along with the documented differences in the spatial distribution of ejected electrons across the tested excitation wavelength range, these results lead us to conclude that photoejection is extremely rapid, and that loss of correlations between the departing electron and its neutral core is faster than our time resolution of approximately 60 fs.

  9. Ultrafast dynamics of MnSi1.7 film studied by pump-probe technique

    NASA Astrophysics Data System (ADS)

    Han, Yaping; Fu, Qiang; Hou, Qingrun; Wu, Wenzhi

    2016-08-01

    Manganese silicide (MnSi1.7) semiconductor thin films with a thickness of 80 nm are prepared by magnetron sputtering deposition technology. The reflectivity change of thin film samples is studied by femtosecond (fs) pump-probe technique under different pump pulse energies and the laser pulse width is 120 fs. The results show that the transient reflectivity increases within a time-scale of about 100 fs. Then, a fast decay of reflectivity occurs in 0.6 picosecond (ps), and it is mainly due to the carrier-carrier scattering. Next, a slower decay of the reflectivity on a time-scale of dozens of ps is detected, and the Auger recombination and diffusion are the main processes. The effective mass of electron and hole in MnSi1.7 film are calculated by using the pseudo-potential plane wave method on first-principles methods. The effective mass of electron is 0.25m0 (m0 is the electron mass), while 0.13m0 for hole. Experimental results are explained with the results of theoretical simulation.

  10. Quantum Dynamics Simulations for Modeling Experimental Pump-Probe Measurements

    NASA Astrophysics Data System (ADS)

    Pearson, Brett; Nayyar, Sahil; Liss, Kyle; Weinacht, Thomas

    2016-05-01

    Time-resolved studies of quantum dynamics have benefited greatly from developments in ultrafast table-top and free electron lasers. Advances in computer software and hardware have lowered the barrier for performing calculations such that relatively simple simulations allow for direct comparison with experimental results. We describe here a set of quantum dynamics calculations in low-dimensional molecular systems. The calculations incorporate coupled electronic-nuclear dynamics, including two interactions with an applied field and nuclear wave packet propagation. The simulations were written and carried out by undergraduates as part of a senior research project, with the specific goal of allowing for detailed interpretation of experimental pump-probe data (in additional to the pedagogical value).

  11. Pump-probe and other timing experiments in synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Rehn, Victor; Rosenberg, Richard A.; Williams, R. Stanley

    1990-05-01

    There are many transient, kinetic, intermediate-state and other time-dependent scientific phenomena that remain poorly understood. Intense undulator radiation (UR) from insertion devices in third-generation synchrotron radiation sources creates new possibilities for high energy pump-probe-timing research. We propose a VUV/SXR dual beam, two-color facility for (1) pump-probe-type experiments with continuously variable pump-pulse-to-probe-pulse interval, (2) harmonic phase-shift experiments that should achieve a time resolution of better than 1 ps [1], and (3) Michelson-type interferometric experiments, such as Fourier-transform stimulated-emission spectroscopy [2] for wavelengths shorter than 1000 Å. As conceived for the Advanced Light Source (ALS). Lawrence Berkeley Laboratory, the proposed beamline utilizes a pump beam of high-intensity UR from a 61-period undulator with 8-cm periods, and a probe beam of monochromatized synchrotron radiation (SR) from the following bending magnet. A unique optical variable delay unit (which also greatly reduces the higher-order content of the SR) is used to delay the arrival of the SR pulse at the crossing point of the two beams. The SR pulse may be delayed to arrive between 0.1 and 2.5 ns after the UR pulse. Because the UR pulse from the next electron bucket of the ALS is emitted 2.0 ns later, delay of the SR pulse by 2.0 ns allows superposition of two pulses, and utilization of the coherence properties of UR.

  12. One- and two-photon pump-probe optical spectroscopic measurements reveal the S 1 and intramolecular charge transfer states are distinct in fucoxanthin

    NASA Astrophysics Data System (ADS)

    Kosumi, Daisuke; Kusumoto, Toshiyuki; Fujii, Ritsuko; Sugisaki, Mitsuru; Iinuma, Yoshiro; Oka, Naohiro; Takaesu, Yuki; Taira, Tomonori; Iha, Masahiko; Frank, Harry A.; Hashimoto, Hideki

    2009-11-01

    The ultrafast relaxation kinetics of fucoxanthin in polar and non-polar solvents have been studied by femtosecond dispersed one- and two-photon pump-probe spectroscopies. Transient absorption kinetics of the lowest singlet S 1 (2 1Ag-) state and/or intramolecular charge transfer (ICT) state after excitation to the optically allowed S 2(11Bu+) state depend strongly on solvent polarity. Transient absorption spectra and the kinetics of absorbance changes after direct two-photon excitation to S 1/ICT depend strongly on excitation energy in non-polar solvent. The results suggest that the ICT state is a distinct state from S 1 in polar solvent.

  13. Probing calculated O2+ potential-energy curves with an XUV-IR pump-probe experiment

    NASA Astrophysics Data System (ADS)

    Cörlin, Philipp; Fischer, Andreas; Schönwald, Michael; Sperl, Alexander; Mizuno, Tomoya; Thumm, Uwe; Pfeifer, Thomas; Moshammer, Robert

    2015-04-01

    We study dissociative photoionization of molecular oxygen in a kinematically complete XUV-IR pump-probe experiment. Detecting charged fragments and photoelectrons in coincidence using a reaction microscope, we observe a pump-probe delay-dependent yield of very low energetic O+ ions which oscillates with a period of 40 fs . This feature is caused by a time-dependent vibrational wave packet in the potential of the binding O2+(a Π4u) state, which is probed by resonant absorption of a single infrared photon to the weakly repulsive O2+(f Π4g) state. By quantitative comparison of the experimental kinetic-energy-release (KER) and quantum-beat (QB) spectra with the results of a coupled-channel simulation, we are able to discriminate between the calculated adiabatic O2+ potential-energy curves (PECs) of Marian et al. [Marian, Marian, Peyerimhoff, Hess, Buenker, and Seger, Mol. Phys. 46, 779 (1982), 10.1080/00268978200101591] and Magrakvelidze et al. [Magrakvelidze, Aikens, and Thumm, Phys. Rev. A 86, 023402 (2012), 10.1103/PhysRevA.86.023402]. In general, we find a good agreement between experimental and simulated KER and QB spectra. However, we could not reproduce all features of the experimental data with these PECs. In contrast, adjusting a Morse potential to the experimental data, most features of the experimental spectra are well reproduced by our simulation. By comparing this Morse potential to theoretically predicted PECs, we demonstrate the sensitivity of our experimental method to small changes in the shape of the binding potential.

  14. Time-resolved pump-probe experiments at the LCLS

    SciTech Connect

    Glownia, James; Cryan, J.; Andreasson, J.; Belkacem, A.; Berrah, N.; Blaga, C.L.; Bostedt, C.; Bozek, J.; DiMauro, L.F.; Fang, L.; Frisch, J.; Gessner, O.; Guhr, M.; Hajdu, J.; Hertlein, M.P.; Hoener, M.; Huang, G.; Kornilov, O.; Marangos, J.P.; March, A.M.; McFarland, B.K.; /SLAC /Stanford U., Phys. Dept. /SLAC /IRAMIS, Saclay /Stanford U., Phys. Dept. /Georgia Tech /Argonne /Kansas State U. /SLAC /Stanford U., Phys. Dept. /SLAC /Stanford U., Appl. Phys. Dept. /Stanford U., Appl. Phys. Dept. /SLAC /LBNL /Argonne /SLAC /SLAC /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept.

    2011-08-12

    The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize an ultrafast optical laser to the linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-ray-induced fragmentation spectra. These alignment features were used to find the temporal overlap of the pump and probe pulses. The strong-field dissociation of x-ray generated quasi-bound molecular dications was used to establish the residual timing jitter. This analysis shows that the relative arrival time of the Ti:Sapphire laser and the x-ray pulses had a distribution with a standard deviation of approximately 120 fs. The largest contribution to the jitter noise spectrum was the locking of the laser oscillator to the reference RF of the accelerator, which suggests that simple technical improvements could reduce the jitter to better than 50 fs.

  15. Time-resolved pump-probe experiments at the LCLS.

    PubMed

    Glownia, James M; Cryan, J; Andreasson, J; Belkacem, A; Berrah, N; Blaga, C I; Bostedt, C; Bozek, J; DiMauro, L F; Fang, L; Frisch, J; Gessner, O; Gühr, M; Hajdu, J; Hertlein, M P; Hoener, M; Huang, G; Kornilov, O; Marangos, J P; March, A M; McFarland, B K; Merdji, H; Petrovic, V S; Raman, C; Ray, D; Reis, D A; Trigo, M; White, J L; White, W; Wilcox, R; Young, L; Coffee, R N; Bucksbaum, P H

    2010-08-16

    The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize an ultrafast optical laser to the linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-ray-induced fragmentation spectra. These alignment features were used to find the temporal overlap of the pump and probe pulses. The strong-field dissociation of x-ray generated quasi-bound molecular dications was used to establish the residual timing jitter. This analysis shows that the relative arrival time of the Ti:Sapphire laser and the x-ray pulses had a distribution with a standard deviation of approximately 120 fs. The largest contribution to the jitter noise spectrum was the locking of the laser oscillator to the reference RF of the accelerator, which suggests that simple technical improvements could reduce the jitter to better than 50 fs.

  16. Pump-probe Kelvin-probe force microscopy: Principle of operation and resolution limits

    SciTech Connect

    Murawski, J.; Graupner, T.; Milde, P. Raupach, R.; Zerweck-Trogisch, U.; Eng, L. M.

    2015-10-21

    Knowledge on surface potential dynamics is crucial for understanding the performance of modern-type nanoscale devices. We describe an electrical pump-probe approach in Kelvin-probe force microscopy that enables a quantitative measurement of dynamic surface potentials at nanosecond-time and nanometer-length scales. Also, we investigate the performance of pump-probe Kelvin-probe force microscopy with respect to the relevant experimental parameters. We exemplify a measurement on an organic field effect transistor that verifies the undisturbed functionality of our pump-probe approach in terms of simultaneous and quantitative mapping of topographic and electronic information at a high lateral and temporal resolution.

  17. Chemical-contrast imaging with pulse-shaping based pump-probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Flynn, Daniel C.; Bhagwat, Amar R.; Ogilvie, Jennifer P.

    2013-02-01

    Ultrafast pump-probe spectroscopy and pulse-shaping techniques are providing new modes of contrast for the field of multiphoton microscopy. Endogenous species such as heme proteins show rich nonlinear spectroscopic signatures of excited state absorption, stimulated emission and ground-state bleaching. Commercially available octave-spanning Ti:sapphire oscillators offer new opportunities for imaging based on pump-probe contrast. Spatial light modulators take advantage of this large bandwidth, shaping pulses of light to selectively excite molecular structures with similar spectral properties. We present two-color pump-probe imaging of heme proteins solutions and red blood cells.

  18. Ultrafast pump-probe dynamics of iron oxide based earth pigments for applications to ancient pottery manufacture

    NASA Astrophysics Data System (ADS)

    Villafana, Tana E.; Brown, William; Warren, Warren S.; Fischer, Martin

    2015-06-01

    We demonstrate that ultrafast pump-probe microscopy provides unique dynamics for natural iron oxide and iron hydroxide earth pigments, despite their chemical similarity. First, we conducted a pump-probe spectroscopy study on heat-treated hematite (the pure red iron oxide mineral) and found the pump-probe dynamics to be temperature dependent. Second, we investigated pottery fired under known conditions and observed firing dependent pump-probe dynamics. Finally, we imaged a New World potshard from the North Carolina Museum of Art. Our results indicate that pump-probe microscopy could be a useful tool in elucidating pottery manufacture.

  19. Suppression of perturbed free-induction decay and noise in experimental ultrafast pump-probe data.

    PubMed

    Nuernberger, Patrick; Lee, Kevin F; Bonvalet, Adeline; Polack, Thomas; Vos, Marten H; Alexandrou, Antigoni; Joffre, Manuel

    2009-10-15

    We apply a Fourier filtering technique for the global removal of coherent contributions, like perturbed free-induction decay, and noise, to experimental pump-probe spectra. A further filtering scheme gains access to spectra otherwise only recordable by scanning the probe's center frequency with adjustable spectral resolution. These methods cleanse pump-probe data and allow improved visualization and simpler analysis of the contained dynamics. We demonstrate these filters using visible pump/mid-infrared probe spectroscopy of ligand dissociation in carboxyhemoglobin.

  20. Imaging microscopic pigment chemistry in conjunctival melanocytic lesions using pump-probe laser microscopy.

    PubMed

    Wilson, Jesse W; Vajzovic, Lejla; Robles, Francisco E; Cummings, Thomas J; Mruthyunjaya, Prithvi; Warren, Warren S

    2013-10-21

    To report the application of a novel imaging technique, pump-probe microscopy, to analyze patterns of pigment chemistry of conjunctival melanocytic lesion biopsies. Histopathologic specimens of eight previously excised conjunctival melanocytic lesions were analyzed with pump-probe microscopy. The technique uses a laser scanning microscope with a two-color pulsed laser source to distinguish hemoglobin, eumelanin, and pheomelanin pigment based on differences in transient excited state and ground state photodynamics. The pump-probe signatures of conjunctival melanins were compared with cutaneous melanins. The distributions of hemoglobin, eumelanin, and pheomelanin were analyzed, and pump-probe images were correlated with adjacent hematoxylin and eosin (H&E)-stained sections. The pump-probe signatures of conjunctival melanins are similar, but not identical to cutaneous melanins. In addition, there are qualitative and quantitative differences in the structure and pigment chemistry of conjunctival benign nevi, primary acquired melanosis of the conjunctiva (PAM), and conjunctival melanomas. The pump-probe images correlated well with histopathologic features observed in the adjacent H&E-stained sections, and provided a label-free means of discerning conjunctival anatomic features and pathologic benign or malignant tissue. Pump-probe laser microscopy shows promise as an adjuvant diagnostic tool in evaluation of ocular melanocytic lesions based on morphologic correlation with the histopathology results and pigment chemistry. This initial study suggests systematic differences in pigmentation patterns among conjunctival benign nevi, primary acquired melanosis, and melanomas. In addition, pump-probe microscopy has the potential for use as a noninvasive "in vivo" optical biopsy technique to aid clinical and surgical management of conjunctival melanocytic lesions.

  1. Femtosecond dissociation dynamics of methyl iodide clusters

    NASA Astrophysics Data System (ADS)

    Poth, L.; Zhong, Q.; Ford, J. V.; Castleman, A. W.

    1998-09-01

    The photodissociation dynamics of methyl iodide clusters using λ=270 nm as pump and λ=405 nm as probe are studied using a femtosecond two color pump-probe laser arrangement combined with a reflectron time-of-flight (RTOF) mass spectrometer. This enables the à state and 10s Rydberg state of methyl iodide to be accessed with the pump beam. Of particular interest is a comparison of the femtosecond dynamics of the methyl iodide monomer with the clustered species. Clocking of the monomer dissociation shows a transient which is indicative of a fast C-I bond breakage as is to be expected upon excitation of methyl iodide into the fast dissociating à state, or into the predissociative 10s Rydberg state. Clusters, however, show a very different pump-probe transient composed of a fast decay and a subsequent dip in ion signal followed by a rise for pump-probe delay times greater than 2 ps. The cluster ion signal shows an enhancement for pump probe delay times up to 70 ps. The results are interpreted in terms of the electronic state diagram of the methyl iodide monomer and effects resulting from clustering of these species, shifts of electronic energy levels and caging of excited species in the cluster.

  2. A versatile apparatus for time-resolved photoemission spectroscopy via femtosecond pump-probe experiments.

    PubMed

    Carpene, E; Mancini, E; Dallera, C; Ghiringhelli, G; Manzoni, C; Cerullo, G; De Silvestri, S

    2009-05-01

    A laser-based system for time-resolved photoemission spectroscopy using up to 6.2 eV photons is presented. The versatility of the laser source permits several combinations of pump and probe photon energies with pulse durations of 50-100 fs. The ultrahigh vacuum system, equipped with evaporators, a low energy electron diffraction system and an Auger spectrometer, grants the possibility to grow and characterize thin films in situ. The electron energy analyzer is a time-of-flight spectrometer with a multianode detector allowing high count rates. The performance of the whole experimental setup is investigated on Cu(100), Cu(111), and Ag(111) single crystals.

  3. Femtosecond IR pump-probe spectroscopy of nonlinear energy localization in protein models and model proteins.

    PubMed

    Hamm, Peter

    2009-02-01

    This paper reviews our experimental and theoretical efforts toward understanding vibrational self-trapping of the amide I and N-H mode of crystalline acetanilide (ACN), other similar hydrogen-bonded crystals, as well as of model peptides. In contrast to previous works, we used nonlinear IR spectroscopy as the experimental tool, which is specifically sensitive to the anharmonic contributions of the intramolecular interactions (as the nonlinear IR response of set of harmonic oscillators vanishes exactly). Our work reconfirms the previous assignment of the two bands of the amide I mode of ACN as being a self-trapped and a free exciton state, but in addition also establishes the lifetimes of these states and identifies the relevant phonons. Furthermore, we provide evidence for vibrationally self-trapped states also in model alpha-helices. However, given the short lifetime, any biological relevance in the sense of Davydov's initial proposal can probably be ruled out.

  4. Intervalley energy of GaN conduction band measured by femtosecond pump-probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Marcinkevičius, Saulius; Uždavinys, Tomas K.; Foronda, Humberto M.; Cohen, Daniel A.; Weisbuch, Claude; Speck, James S.

    2016-12-01

    Time-resolved transmission and reflection measurements were performed for bulk GaN at room temperature to evaluate the energy of the first conduction band satellite valley. The measurements showed clear threshold-like spectra for transmission decay and reflection rise times. The thresholds were associated with the onset of the intervalley electron scattering. Transmission measurements with pump and probe pulses in the near infrared produced an intervalley energy of 0.97 ±0.02 eV. Ultraviolet pump and infrared probe reflection provided a similar value. Comparison of the threshold energies obtained in these experiments allowed estimating the hole effective mass in the upper valence band to be 1.4 m0 . Modeling of the reflection transients with rate equations has allowed estimating electron-LO (longitudinal optical) phonon scattering rates and the satellite valley effective mass.

  5. Probing calculated O 2 + potential curves with an XUV-IR pump-probe experiment

    NASA Astrophysics Data System (ADS)

    Coerlin, Philipp; Fischer, Andreas; Schoenwald, Michael; Sperl, Alexander; Mizuno, Tomoya; Pfeifer, Thomas; Moshammer, Robert; Thumm, Uwe

    2015-05-01

    We study dissociative photo-ionization of O2 in a kinematically complete XUV-IR pump-probe experiment, preparing a vibrational wave packet in the potential of the binding O2+(a4Πu)state by ionization with a single XUV photon. After a variable time-delay the wave packet is promoted to the repulsive O2+(f4Πg)state by a weak IR probe pulse. Comparing the results of a coupled-channel simulation with the experimental kinetic-energy-release and quantum-beat spectra, we are able to discriminate between the adiabatic O2+potential-energy curves (PECs) calculated by. The overall agreement between simulated and experimental results is good; however, not all features of the experimental spectra could be reproduced using these PECs. Using a Morse potential adjusted to the experimental data instead, most features of the experimental spectra are well reproduced by our simulation. This optimized Morse potential is remarkably similar to the theoretically predicted PECs, demonstrating the sensitivity of our experimental method to small changes in the shape of the binding potential. Supported by the DoE, NSF, and Alexander von Humboldt foundation.

  6. Femtosecond response of a single metal nanoparticle.

    PubMed

    Muskens, Otto L; Del Fatti, Natalia; Vallée, Fabrice

    2006-03-01

    The ultrafast nonlinear optical response of a single metal nanoparticle is investigated by combining a high-sensitivity femtosecond pump-probe setup with a spatial modulation microscope. Experiments are performed on 20 and 30 nm silver nanospheres, in situ characterized via their optical linear extinction spectrum. The measured transient response permits investigation of the electron-phonon energy transfer time in a single nanoparticle. Its dependence on the electronic temperature is quantitatively interpreted using the two-temperature model.

  7. In vivo pump-probe microscopy of melanoma and pigmented lesions

    NASA Astrophysics Data System (ADS)

    Wilson, Jesse W.; Degan, Simone; Mitropoulos, Tanya; Selim, M. Angelica; Zhang, Jennifer Y.; Warren, Warren S.

    2012-03-01

    A growing number of dermatologists and pathologists are concerned that the rapidly rising incidence of melanoma reflects not a true 'epidemic' but an increasing tendency to overdiagnose pigmented lesions. Addressing this problem requires both a better understanding of early-stage melanoma and new diagnostic criteria based on more than just cellular morphology and architecture. Here we present a method for in-vivo optical microscopy that utilizes pump-probe spectroscopy to image the distribution of the two forms of melanin in skin: eumelanin and pheomelanin. Images are acquired in a scanning microscope with a sensitive modulation transfer technique by analyzing back-scattered probe light with a lock-in amplifier. Early-stage melanoma is studied in a human skin xenografted mouse model. Individual melanocytes have been observed, in addition to pigmented keratinocytes. Combining the pump-probe images simultaneously with other noninvasive laser microscopy methods (confocal reflectance, multiphoton autofluorescence, and second harmonic generation) allows visualization of the skin architecture, framing the functional pump-probe image in the context of the surrounding tissue morphology. It is found that pump-probe images of melanin can be acquired with low peak intensities, enabling wide field-of-view pigmentation surveys. Finally, we investigate the diagnostic potential of the additional chemical information available from pump-probe microscopy.

  8. Dual-wavelength pump-probe microscopy analysis of melanin composition

    NASA Astrophysics Data System (ADS)

    Thompson, Andrew; Robles, Francisco E.; Wilson, Jesse W.; Deb, Sanghamitra; Calderbank, Robert; Warren, Warren S.

    2016-11-01

    Pump-probe microscopy is an emerging technique that provides detailed chemical information of absorbers with sub-micrometer spatial resolution. Recent work has shown that the pump-probe signals from melanin in human skin cancers correlate well with clinical concern, but it has been difficult to infer the molecular origins of these differences. Here we develop a mathematical framework to describe the pump-probe dynamics of melanin in human pigmented tissue samples, which treats the ensemble of individual chromophores that make up melanin as Gaussian absorbers with bandwidth related via Frenkel excitons. Thus, observed signals result from an interplay between the spectral bandwidths of the individual underlying chromophores and spectral proximity of the pump and probe wavelengths. The model is tested using a dual-wavelength pump-probe approach and a novel signal processing method based on gnomonic projections. Results show signals can be described by a single linear transition path with different rates of progress for different individual pump-probe wavelength pairs. Moreover, the combined dual-wavelength data shows a nonlinear transition that supports our mathematical framework and the excitonic model to describe the optical properties of melanin. The novel gnomonic projection analysis can also be an attractive generic tool for analyzing mixing paths in biomolecular and analytical chemistry.

  9. Dual-wavelength pump-probe microscopy analysis of melanin composition

    PubMed Central

    Thompson, Andrew; Robles, Francisco E.; Wilson, Jesse W.; Deb, Sanghamitra; Calderbank, Robert; Warren, Warren S.

    2016-01-01

    Pump-probe microscopy is an emerging technique that provides detailed chemical information of absorbers with sub-micrometer spatial resolution. Recent work has shown that the pump-probe signals from melanin in human skin cancers correlate well with clinical concern, but it has been difficult to infer the molecular origins of these differences. Here we develop a mathematical framework to describe the pump-probe dynamics of melanin in human pigmented tissue samples, which treats the ensemble of individual chromophores that make up melanin as Gaussian absorbers with bandwidth related via Frenkel excitons. Thus, observed signals result from an interplay between the spectral bandwidths of the individual underlying chromophores and spectral proximity of the pump and probe wavelengths. The model is tested using a dual-wavelength pump-probe approach and a novel signal processing method based on gnomonic projections. Results show signals can be described by a single linear transition path with different rates of progress for different individual pump-probe wavelength pairs. Moreover, the combined dual-wavelength data shows a nonlinear transition that supports our mathematical framework and the excitonic model to describe the optical properties of melanin. The novel gnomonic projection analysis can also be an attractive generic tool for analyzing mixing paths in biomolecular and analytical chemistry. PMID:27833147

  10. Dual-wavelength pump-probe microscopy analysis of melanin composition.

    PubMed

    Thompson, Andrew; Robles, Francisco E; Wilson, Jesse W; Deb, Sanghamitra; Calderbank, Robert; Warren, Warren S

    2016-11-11

    Pump-probe microscopy is an emerging technique that provides detailed chemical information of absorbers with sub-micrometer spatial resolution. Recent work has shown that the pump-probe signals from melanin in human skin cancers correlate well with clinical concern, but it has been difficult to infer the molecular origins of these differences. Here we develop a mathematical framework to describe the pump-probe dynamics of melanin in human pigmented tissue samples, which treats the ensemble of individual chromophores that make up melanin as Gaussian absorbers with bandwidth related via Frenkel excitons. Thus, observed signals result from an interplay between the spectral bandwidths of the individual underlying chromophores and spectral proximity of the pump and probe wavelengths. The model is tested using a dual-wavelength pump-probe approach and a novel signal processing method based on gnomonic projections. Results show signals can be described by a single linear transition path with different rates of progress for different individual pump-probe wavelength pairs. Moreover, the combined dual-wavelength data shows a nonlinear transition that supports our mathematical framework and the excitonic model to describe the optical properties of melanin. The novel gnomonic projection analysis can also be an attractive generic tool for analyzing mixing paths in biomolecular and analytical chemistry.

  11. A photoelectron-photoion coincidence imaging apparatus for femtosecond time-resolved molecular dynamics with electron time-of-flight resolution of {sigma}=18 ps and energy resolution {delta}E/E=3.5%

    SciTech Connect

    Vredenborg, Arno; Roeterdink, Wim G.; Janssen, Maurice H. M.

    2008-06-15

    We report on the construction and performance of a novel photoelectron-photoion coincidence machine in our laboratory in Amsterdam to measure the full three-dimensional momentum distribution of correlated electrons and ions in femtosecond time-resolved molecular beam experiments. We implemented sets of open electron and ion lenses to time stretch and velocity map the charged particles. Time switched voltages are operated on the particle lenses to enable optimal electric field strengths for velocity map focusing conditions of electrons and ions separately. The position and time sensitive detectors employ microchannel plates (MCPs) in front of delay line detectors. A special effort was made to obtain the time-of-flight (TOF) of the electrons at high temporal resolution using small pore (5 {mu}m) MCPs and implementing fast timing electronics. We measured the TOF distribution of the electrons under our typical coincidence field strengths with a temporal resolution down to {sigma}=18 ps. We observed that our electron coincidence detector has a timing resolution better than {sigma}=16 ps, which is mainly determined by the residual transit time spread of the MCPs. The typical electron energy resolution appears to be nearly laser bandwidth limited with a relative resolution of {delta}E{sub FWHM}/E=3.5% for electrons with kinetic energy near 2 eV. The mass resolution of the ion detector for ions measured in coincidence with electrons is about {delta}m{sub FWHM}/m=1/4150. The velocity map focusing of our extended source volume of particles, due to the overlap of the molecular beam with the laser beams, results in a parent ion spot on our detector focused down to {sigma}=115 {mu}m.

  12. Gadolinium photoionization process

    DOEpatents

    Paisner, Jeffrey A.; Comaskey, Brian J.; Haynam, Christopher A.; Eggert, Jon H.

    1993-01-01

    A method is provided for selective photoionization of the odd-numbered atomic mass gadolinium isotopes 155 and 157. The selective photoionization is accomplished by circular or linear parallel polarized laser beam energy effecting a three-step photoionization pathway.

  13. Gadolinium photoionization process

    DOEpatents

    Paisner, J.A.; Comaskey, B.J.; Haynam, C.A.; Eggert, J.H.

    1993-04-13

    A method is provided for selective photoionization of the odd-numbered atomic mass gadolinium isotopes 155 and 157. The selective photoionization is accomplished by circular or linear parallel polarized laser beam energy effecting a three-step photoionization pathway.

  14. Mapping and controlling ultrafast dynamics of highly excited H2 molecules by VUV-IR pump-probe schemes

    DOE PAGES

    Sturm, F. P.; Tong, X. M.; Palacios, A.; ...

    2017-01-09

    Here, we used ultrashort femtosecond vacuum ultraviolet (VUV) and infrared (IR) pulses in a pump-probe scheme to map the dynamics and nonequilibrium dissociation channels of excited neutral H2 molecules. A nuclear wave packet is created in the B1Σmore » $$+\\atop{u}$$ state of the neutral H2 molecule by absorption of the ninth harmonic of the driving infrared laser field. Due to the large stretching amplitude of the molecule excited in the B1Σ$$+\\atop{u}$$ electronic state, the effective H2+ ionization potential changes significantly as the nuclear wave packet vibrates in the bound, highly electronically and vibrationally excited B potential-energy curve. We probed such dynamics by ionizing the excited neutral molecule using time-delayed VUV-or-IR radiation. We identified the nonequilibrium dissociation channels by utilizing three-dimensional momentum imaging of the ion fragments. We also found that different dissociation channels can be controlled, to some extent, by changing the IR laser intensity and by choosing the wavelength of the probe laser light. Furthermore, we concluded that even in a benchmark molecular system such as H2*, the interpretation of the nonequilibrium multiphoton and multicolor ionization processes is still a challenging task, requiring intricate theoretical analysis.« less

  15. Mapping and controlling ultrafast dynamics of highly excited H2 molecules by VUV-IR pump-probe schemes

    NASA Astrophysics Data System (ADS)

    Sturm, F. P.; Tong, X. M.; Palacios, A.; Wright, T. W.; Zalyubovskaya, I.; Ray, D.; Shivaram, N.; Martín, F.; Belkacem, A.; Ranitovic, P.; Weber, Th.

    2017-01-01

    We used ultrashort femtosecond vacuum ultraviolet (VUV) and infrared (IR) pulses in a pump-probe scheme to map the dynamics and nonequilibrium dissociation channels of excited neutral H2 molecules. A nuclear wave packet is created in the B Σ+1u state of the neutral H2 molecule by absorption of the ninth harmonic of the driving infrared laser field. Due to the large stretching amplitude of the molecule excited in the B Σ+1u electronic state, the effective H2+ ionization potential changes significantly as the nuclear wave packet vibrates in the bound, highly electronically and vibrationally excited B potential-energy curve. We probed such dynamics by ionizing the excited neutral molecule using time-delayed VUV-or-IR radiation. We identified the nonequilibrium dissociation channels by utilizing three-dimensional momentum imaging of the ion fragments. We found that different dissociation channels can be controlled, to some extent, by changing the IR laser intensity and by choosing the wavelength of the probe laser light. Furthermore, we concluded that even in a benchmark molecular system such as H2*, the interpretation of the nonequilibrium multiphoton and multicolor ionization processes is still a challenging task, requiring intricate theoretical analysis.

  16. Comparison of pump-probe and hyperspectral imaging in unstained histology sections of pigmented lesions

    PubMed Central

    Wilson, Jesse W.; Robles, Francisco E.; Deb, Sanghamitra; Warren, Warren S.; Fischer, Martin C.

    2017-01-01

    Microscopic variations in melanin composition can be mapped through linear and nonlinear optical responses. Though instrumentation to measure linear attenuation is simple and inexpensive, the nonlinear response provides more degrees of freedom with which to spectroscopically resolve pigments. The objective of this study is to assess differences in imaging melanin contrast by comparing hyperspectral (linear) versus pump-probe (nonlinear) microscopy of unstained histology sections of pigmented lesions. The images and analysis we have presented here show that pump-probe uncovers a greater variation in pigment composition, compared with hyperspectral microscopy, and that the two methods yield complimentary biochemical information. PMID:28856057

  17. In vivo and ex vivo epi-mode pump-probe imaging of melanin and microvasculature

    PubMed Central

    Matthews, Thomas E.; Wilson, Jesse W.; Degan, Simone; Simpson, Mary Jane; Jin, Jane Y.; Zhang, Jennifer Y.; Warren, Warren S.

    2011-01-01

    We performed epi-mode pump-probe imaging of melanin in excised human pigmented lesions and both hemoglobin and melanin in live xenograft mouse melanoma models to depths greater than 100 µm. Eumelanin and pheomelanin images, which have been previously demonstrated to differentiate melanoma from benign lesions, were acquired at the dermal-epidermal junction with cellular resolution and modest optical powers (down to 15 mW). We imaged dermal microvasculature with the same wavelengths, allowing simultaneous acquisition of melanin, hemoglobin and multiphoton autofluorescence images. Molecular pump-probe imaging of melanocytes, skin structure and microvessels allows comprehensive, non-invasive characterization of pigmented lesions. PMID:21698020

  18. Imaging pigment chemistry in melanocytic conjunctival lesions with pump-probe microscopy

    NASA Astrophysics Data System (ADS)

    Wilson, Jesse W.; Vajzovic, Lejla; Robles, Francisco E.; Cummings, Thomas J.; Mruthyunjaya, Prithvi; Warren, Warren S.

    2013-03-01

    We extend nonlinear pump-probe microscopy, recently demonstrated to image the microscopic distribution of eumelanin and pheomelanin in unstained skin biopsy sections, to the case of melanocytic conjunctival lesions. The microscopic distribution of pigmentation chemistry serves as a functional indicator of melanocyte activity. In these conjunctival specimens (benign nevi, primary acquired melanoses, and conjunctival melanoma), we have observed pump-probe spectroscopic signatures of eumelanin, pheomelanin, hemoglobin, and surgical ink, in addition to important structural features that differentiate benign from malignant lesions. We will also discuss prospects for an in vivo `optical biopsy' to provide additional information before having to perform invasive procedures.

  19. Analysis of multicrystal pump-probe data sets. I. Expressions for the RATIO model.

    PubMed

    Fournier, Bertrand; Coppens, Philip

    2014-09-01

    The RATIO method in time-resolved crystallography [Coppens et al. (2009). J. Synchrotron Rad. 16, 226-230] was developed for use with Laue pump-probe diffraction data to avoid complex corrections due to wavelength dependence of the intensities. The application of the RATIO method in processing/analysis prior to structure refinement requires an appropriate ratio model for modeling the light response. The assessment of the accuracy of pump-probe time-resolved structure refinements based on the observed ratios was discussed in a previous paper. In the current paper, a detailed ratio model is discussed, taking into account both geometric and thermal light-induced changes.

  20. Ultra-Fast Pump-Probe Detection Using Plasmas

    SciTech Connect

    Tatchyn, R.; /SLAC

    2006-02-17

    The temporal resolution of pump-flash interactions in the femtosecond-attosecond (fs-as) regime is limited by the characteristic time constants of the excited states in the detector material. If the relaxation time constant is appreciably longer that the time interval between the pump and probe signals the response of the detector material to the probe represents a temporal convolution with the pump and probe responses, setting a lower limit on the resolution to which the interval between the two pulses can be measured. In most of the solid state ultrafast detection schemes that are being considered for the ultrashort pulse x-ray sources under current development at SLAC and elsewhere the characteristic time constants are related to the bound states of the atoms comprising the material or to the relaxation times of phase transitions or charge carrier populations of the lattice, setting a probable lower limit on the attainable resolution on the order of {approx}0.1 ps. In this paper we consider a novel detection principle based on the excitation of specially prepared unbound states in an ionized plasma with high pump and probe fields, and estimate its potential for extending the lower limit of resolution into the attosecond (as) regime.

  1. Optical pump-probe microscopy for biomedicine and art conservation

    NASA Astrophysics Data System (ADS)

    Fischer, Martin

    2013-03-01

    Nonlinear optical microscopy can provide contrast in highly heterogeneous media and a wide range of applications has emerged, primarily in biology, medicine, and materials science. Compared to linear microscopy methods, the localized nature of nonlinear interactions leads to high spatial resolution, optical sectioning, and larger possible imaging depth in scattering media. However, nonlinear contrast (other than fluorescence, harmonic generation or CARS) is generally difficult to measure because it is overwhelmed by the large background of detected illumination light. This background can be suppressed by using femtosecond pulse or pulse train shaping to encode nonlinear interactions in background-free regions of the frequency spectrum. We have developed this shaping technology to study novel intrinsic structural and molecular contrast in biological tissue, generally using less power than a laser pointer. For example we have recently been able to sensitively measure detailed transient absorption dynamics of melanin sub-types in a variety of skin lesions, showing clinically relevant differences of melanin type and distribution between cancerous and benign tissue.[1] Recently we have also applied this technology to paint samples and to historic artwork in order to provide detailed, depth-resolved pigment identification. Initial studies in different inorganic and organic pigments have shown a rich and pigment-specific nonlinear absorption signature.[2] Some pigments, for example lapis lazuli (natural ultramarine), even show marked differences in signal depending on its geographic origin and on age, demonstrating the potential of this technique to determine authenticity, provenance, technology of manufacture, or state of preservation of historic works of art.

  2. The initial pump-probe polarization anisotropy of colloidal PbS quantum dots

    SciTech Connect

    Park, Samuel; Baranov, Dmitry; Ryu, Jisu; Jonas, David

    2016-07-20

    Pump-probe polarization anisotropy measurements with 15 fs pulses are employed to investigate the electronic structure of PbS quantum dots. Here, the initial anisotropy at the bandgap is anomalously low (<0.1) and suggests large electronic couplings.

  3. Pump-probe surface photovoltage spectroscopy measurements on semiconductor epitaxial layers

    SciTech Connect

    Jana, Dipankar Porwal, S.; Sharma, T. K. Oak, S. M.; Kumar, Shailendra

    2014-04-15

    Pump-probe Surface Photovoltage Spectroscopy (SPS) measurements are performed on semiconductor epitaxial layers. Here, an additional sub-bandgap cw pump laser beam is used in a conventional chopped light geometry SPS setup under the pump-probe configuration. The main role of pump laser beam is to saturate the sub-bandgap localized states whose contribution otherwise swamp the information related to the bandgap of material. It also affects the magnitude of Dember voltage in case of semi-insulating (SI) semiconductor substrates. Pump-probe SPS technique enables an accurate determination of the bandgap of semiconductor epitaxial layers even under the strong influence of localized sub-bandgap states. The pump beam is found to be very effective in suppressing the effect of surface/interface and bulk trap states. The overall magnitude of SPV signal is decided by the dependence of charge separation mechanisms on the intensity of the pump beam. On the contrary, an above bandgap cw pump laser can be used to distinguish the signatures of sub-bandgap states by suppressing the band edge related feature. Usefulness of the pump-probe SPS technique is established by unambiguously determining the bandgap of p-GaAs epitaxial layers grown on SI-GaAs substrates, SI-InP wafers, and p-GaN epilayers grown on Sapphire substrates.

  4. The initial pump-probe polarization anisotropy of colloidal PbS quantum dots

    DOE PAGES

    Park, Samuel; Baranov, Dmitry; Ryu, Jisu; ...

    2016-07-20

    Pump-probe polarization anisotropy measurements with 15 fs pulses are employed to investigate the electronic structure of PbS quantum dots. Here, the initial anisotropy at the bandgap is anomalously low (<0.1) and suggests large electronic couplings.

  5. Frequency domain approach for time-resolved pump-probe microscopy using intensity modulated laser diodes

    NASA Astrophysics Data System (ADS)

    Miyazaki, J.; Kawasumi, K.; Kobayashi, T.

    2014-09-01

    We present a scheme for time-resolved pump-probe microscopy using intensity modulated laser diodes. The modulation frequencies of the pump and probe beams are varied up to 500 MHz with fixed frequency detuning typically set at 15 kHz. The frequency response of the pump-probe signal is detected using a lock-in amplifier referenced at the beat frequency. This frequency domain method is capable of characterizing the nanosecond to picosecond relaxation dynamics of sample species without the use of a high speed detector or a high frequency lock-in amplifier. Furthermore, as the pump-probe signal is based on the nonlinear interaction between the two laser beams and the sample, our scheme provides better spatial resolution than the conventional diffraction-limited optical microscopes. Time-resolved pump-probe imaging of fluorescence beads and aggregates of quantum dots demonstrates that this method is useful for the microscopic analysis of optoelectronic devices. The system is implemented using compact and low-cost laser diodes, and thus has a broad range of applications in the fields of photochemistry, optical physics, and biological imaging.

  6. Femtosecond imaging of nonlinear acoustics in gold.

    PubMed

    Pezeril, Thomas; Klieber, Christoph; Shalagatskyi, Viktor; Vaudel, Gwenaelle; Temnov, Vasily; Schmidt, Oliver G; Makarov, Denys

    2014-02-24

    We have developed a high-sensitivity, low-noise femtosecond imaging technique based on pump-probe time-resolved measurements with a standard CCD camera. The approach used in the experiment is based on lock-in acquisitions of images generated by a femtosecond laser probe synchronized to modulation of a femtosecond laser pump at the same rate. This technique allows time-resolved imaging of laser-excited phenomena with femtosecond time resolution. We illustrate the technique by time-resolved imaging of the nonlinear reshaping of a laser-excited picosecond acoustic pulse after propagation through a thin gold layer. Image analysis reveals the direct 2D visualization of the nonlinear acoustic propagation of the picosecond acoustic pulse. Many ultrafast pump-probe investigations can profit from this technique because of the wealth of information it provides over a typical single diode and lock-in amplifier setup, for example it can be used to image ultrasonic echoes in biological samples.

  7. The rotating-crystal method in femtosecond X-ray diffraction.

    PubMed

    Freyer, B; Stingl, J; Zamponi, F; Woerner, M; Elsaesser, T

    2011-08-01

    We report the first implementation of the rotating-crystal method in femtosecond X-ray diffraction. Applying a pump-probe scheme with 100 fs hard X-ray probe pulses from a laser-driven plasma source, the novel technique is demonstrated by mapping structural dynamics of a photoexcited bismuth crystal via changes of the diffracted intensity on a multitude of Bragg reflections. The method is compared to femtosecond powder diffraction and to Bragg diffraction from a crystal with stationary orientation.

  8. Theory of pump-probe experiments of metallic metamaterials coupled to the gain medium

    SciTech Connect

    Huang, Zhixiang; Koschny, Thomas; Soukoulis, Costas

    2012-05-04

    We establish a new approach for pump-probe simulations of metallic metamaterials coupled to the gain materials. It is of vital importance to understand the mechanism of the coupling of metamaterials with the gain medium. Using a four-level gain system, we have studied light amplification of arrays of metallic split-ring resonators with a gain layer underneath. We find that the differential transmittance ΔT/T can be negative for split-ring resonators on the top of the gain substrate, which is not expected, and ΔT/T is positive for the gain substrate alone. These simulations agree with pump-probe experiments and can help to design new experiments to compensate for the losses of metamaterials.

  9. Alignment, vibronic level splitting, and coherent coupling effects on the pump-probe polarization anisotropy.

    PubMed

    Smith, Eric R; Jonas, David M

    2011-04-28

    The pump-probe polarization anisotropy is computed for molecules with a nondegenerate ground state, two degenerate or nearly degenerate excited states with perpendicular transition dipoles, and no resonant excited-state absorption. Including finite pulse effects, the initial polarization anisotropy at zero pump-probe delay is predicted to be r(0) = 3/10 with coherent excitation. During pulse overlap, it is shown that the four-wave mixing classification of signal pathways as ground or excited state is not useful for pump-probe signals. Therefore, a reclassification useful for pump-probe experiments is proposed, and the coherent anisotropy is discussed in terms of a more general transition dipole and molecular axis alignment instead of experiment-dependent ground- versus excited-state pathways. Although coherent excitation enhances alignment of the transition dipole, the molecular axes are less aligned than for a single dipole transition, lowering the initial anisotropy. As the splitting between excited states increases beyond the laser bandwidth and absorption line width, the initial anisotropy increases from 3/10 to 4/10. Asymmetric vibrational coordinates that lift the degeneracy control the electronic energy gap and off-diagonal coupling between electronic states. These vibrations dephase coherence and equilibrate the populations of the (nearly) degenerate states, causing the anisotropy to decay (possibly with oscillations) to 1/10. Small amounts of asymmetric inhomogeneity (2 cm(-1)) cause rapid (130 fs) suppression of both vibrational and electronic anisotropy beats on the excited state, but not vibrational beats on the ground electronic state. Recent measurements of conical intersection dynamics in a silicon napthalocyanine revealed anisotropic quantum beats that had to be assigned to asymmetric vibrations on the ground electronic state only [Farrow, D. A.; J. Chem. Phys. 2008, 128, 144510]. Small environmental asymmetries likely explain the observed absence

  10. Pump-Probe Spectroscopy of Two-Body Correlations in Ultracold Gases

    SciTech Connect

    Koch, Christiane P.; Kosloff, Ronnie

    2009-12-31

    We suggest pump-probe spectroscopy to study pair correlations that determine the many-body dynamics in weakly interacting, dilute ultracold gases. A suitably chosen, short laser pulse depletes the pair density locally, creating a 'hole' in the electronic ground state. The dynamics of this nonstationary pair density is monitored by a time-delayed probe pulse. The resulting transient signal allows us to spectrally decompose the hole and to map out the pair correlation function.

  11. Pump-probe quantum state tomography in a semiconductor optical amplifier.

    PubMed

    Grosse, N B; Owschimikow, N; Aust, R; Lingnau, B; Koltchanov, A; Kolarczik, M; Lüdge, K; Woggon, U

    2014-12-29

    Pump-probe quantum state tomography was applied to the transmission of a coherent state through an In(Ga)As based quantum dot optical amplifier during the interaction with an optical pump pulse. The Wigner function and the statistical moments of the field were extracted and used to determine the degree of population inversion and the signal-to-noise ratio in a sub-picosecond time window.

  12. Optimizing pump-probe switching ruled by free-carrier dispersion.

    PubMed

    Malaguti, S; Bellanca, G; Trillo, S

    2013-07-01

    We address theoretically and numerically pump-probe switching in a nonlinear semiconductor nanocavity where tuning is achieved via a dominant mechanism of free-carrier plasma dispersion. By using coupled-mode approach we give a set of guidelines to optimize the switching performances both in terms of avoiding self-pulsation and keeping switching power to the minimum, ending up by showing that such devices can achieve high-performances with relatively low-power consumption.

  13. Pump-probe photoelectron spectroscopy by a high-power 90 nm vacuum-ultraviolet laser

    NASA Astrophysics Data System (ADS)

    Sato, Motoki; Suzuki, Yoshi-ichi; Suzuki, Toshinori; Adachi, Shunsuke

    2016-02-01

    We present pump-probe photoelectron spectroscopy of Kr and NO using a high-power vacuum-ultraviolet (VUV) laser at a wavelength of 90 nm. Clear quantum beats are observed in the photoelectron angular distributions as well as in the photoelectron yields, resulting from the coherent excitation of two Kr Rydberg states by the VUV pump. The entire Franck-Condon envelope of the NO A(2Σ+) excited state is also successfully captured by the VUV probe.

  14. Ultrafast internal conversion dynamics of highly excited pyrrole studied with VUV/UV pump probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Horton, Spencer L.; Liu, Yusong; Chakraborty, Pratip; Matsika, Spiridoula; Weinacht, Thomas

    2017-02-01

    We study the relaxation dynamics of pyrrole after excitation with an 8 eV pump pulse to a state just 0.2 eV below the ionization potential using vacuum ultraviolet/ultraviolet pump probe spectroscopy. Our measurements in conjunction with electronic structure calculations indicate that pyrrole undergoes rapid internal conversion to the ground state in less than 300 fs. We find that internal conversion to the ground state dominates over dissociation.

  15. Polarized pump--probe spectroscopy of electronic excitation transport in photosynthetic antennas

    SciTech Connect

    Struve, W.S. )

    1990-08-01

    Polarized pump--probe spectroscopy was performed with 1.5--2 psec resolution on the bacteriochlorophyll a protein antenna complex from the green sulfur bacterium Prosthecochloris aestuarii and on native and enriched photosystem I particles from spinach. The resulting photobleaching profiles reflect the details of singlet electronic-excitation transport in these photosynthetic antennas, in which the pigments are complexed by proteins into clusters of five or more chromophores.

  16. Photoacoustic pump-probe tomography of fluorophores in vivo using interleaved image acquisition for motion suppression

    NASA Astrophysics Data System (ADS)

    Märk, Julia; Wagener, Asja; Zhang, Edward; Laufer, Jan

    2017-01-01

    In fluorophores, the excited state lifetime can be modulated using pump-probe excitation. By generating photoacoustic (PA) signals using simultaneous and time-delayed pump and probe excitation pulses at fluences below the maximum permissible exposure, a modulation of the signal amplitude is observed in fluorophores but not in endogenous chromophores. This provides a highly specific contrast mechanism that can be used to recover the location of the fluorophore using difference imaging. The practical challenges in applying this method to in vivo PA tomography include the typically low concentrations of fluorescent contrast agents, and tissue motion. The former results in smaller PA signal amplitudes compared to those measured in blood, while the latter gives rise to difference image artefacts that compromise the unambiguous and potentially noise-limited detection of fluorescent contrast agents. To address this limitation, a method based on interleaved pump-probe image acquisition was developed. It relies on fast switching between simultaneous and time-delayed pump-probe excitation to acquire PA difference signals in quick succession, and to minimise the effects of tissue motion. The feasibility of this method is demonstrated in tissue phantoms and in initial experiments in vivo.

  17. Photoacoustic pump-probe tomography of fluorophores in vivo using interleaved image acquisition for motion suppression

    PubMed Central

    Märk, Julia; Wagener, Asja; Zhang, Edward; Laufer, Jan

    2017-01-01

    In fluorophores, the excited state lifetime can be modulated using pump-probe excitation. By generating photoacoustic (PA) signals using simultaneous and time-delayed pump and probe excitation pulses at fluences below the maximum permissible exposure, a modulation of the signal amplitude is observed in fluorophores but not in endogenous chromophores. This provides a highly specific contrast mechanism that can be used to recover the location of the fluorophore using difference imaging. The practical challenges in applying this method to in vivo PA tomography include the typically low concentrations of fluorescent contrast agents, and tissue motion. The former results in smaller PA signal amplitudes compared to those measured in blood, while the latter gives rise to difference image artefacts that compromise the unambiguous and potentially noise-limited detection of fluorescent contrast agents. To address this limitation, a method based on interleaved pump-probe image acquisition was developed. It relies on fast switching between simultaneous and time-delayed pump-probe excitation to acquire PA difference signals in quick succession, and to minimise the effects of tissue motion. The feasibility of this method is demonstrated in tissue phantoms and in initial experiments in vivo. PMID:28091571

  18. Comparing in vivo pump-probe and multiphoton fluorescence microscopy of melanoma and pigmented lesions

    NASA Astrophysics Data System (ADS)

    Wilson, Jesse W.; Degan, Simone; Gainey, Christina S.; Mitropoulos, Tanya; Simpson, Mary Jane; Zhang, Jennifer Y.; Warren, Warren S.

    2015-05-01

    We demonstrate a multimodal approach that combines a pump-probe with confocal reflectance and multiphoton autofluorescence microscopy. Pump-probe microscopy has been proven to be of great value in analyzing thin tissue sections of pigmented lesions, as it produces molecular contrast which is inaccessible by other means. However, the higher optical intensity required to overcome scattering in thick tissue leads to higher-order nonlinearities in the optical response of melanin (e.g., two-photon pump and one-photon probe) that present additional challenges for interpreting the data. We show that analysis of pigment composition in vivo must carefully account for signal terms that are nonlinear with respect to the pump and probe intensities. We find that pump-probe imaging gives useful contrast for pigmented structures over a large range of spatial scales (100 μm to 1 cm), making it a potentially useful tool for tracking the progression of pigmented lesions without the need to introduce exogenous contrast agents.

  19. Effect of optical pumping in V and λ type pump probe systems

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Shrabana; Ray, Biswajit; Ghosh, Pradip N.

    2008-05-01

    We have investigated the effect of a strong pump laser copropagating with a probe laser for both λ and V type level schemes of the pump and probe fields inside a room temperature Rb vapour cell. With the λ type scheme certain absorption enhanced peaks are observed across the Doppler broadened probe absorption profile. In addition to these peaks an Electromagnetically Induced Transparency dip is also observed at the centre of one of these peaks. For V type scheme pump probe spectroscopy with co and counter propagating pump probe beams are studied. In both cases we observe velocity selective resonances (VSR) which are strongly modified by optical pumping effects to another hyperfine component of the ground state. A repumping laser, from the dark ground level is used to transfer atoms from the dark state to the pump probe cycle to reduce the optical pumping effect. The effect of a control laser on the Lamb dip spectrum of the probe laser has also been investigated.

  20. Ultrafast and nanoscale plasmonic phenomena in exfoliated graphene revealed by infrared pump-probe nanoscopy.

    PubMed

    Wagner, Martin; Fei, Zhe; McLeod, Alexander S; Rodin, Aleksandr S; Bao, Wenzhong; Iwinski, Eric G; Zhao, Zeng; Goldflam, Michael; Liu, Mengkun; Dominguez, Gerardo; Thiemens, Mark; Fogler, Michael M; Castro Neto, Antonio H; Lau, Chun Ning; Amarie, Sergiu; Keilmann, Fritz; Basov, D N

    2014-02-12

    Pump-probe spectroscopy is central for exploring ultrafast dynamics of fundamental excitations, collective modes, and energy transfer processes. Typically carried out using conventional diffraction-limited optics, pump-probe experiments inherently average over local chemical, compositional, and electronic inhomogeneities. Here, we circumvent this deficiency and introduce pump-probe infrared spectroscopy with ∼ 20 nm spatial resolution, far below the diffraction limit, which is accomplished using a scattering scanning near-field optical microscope (s-SNOM). This technique allows us to investigate exfoliated graphene single-layers on SiO2 at technologically significant mid-infrared (MIR) frequencies where the local optical conductivity becomes experimentally accessible through the excitation of surface plasmons via the s-SNOM tip. Optical pumping at near-infrared (NIR) frequencies prompts distinct changes in the plasmonic behavior on 200 fs time scales. The origin of the pump-induced, enhanced plasmonic response is identified as an increase in the effective electron temperature up to several thousand Kelvin, as deduced directly from the Drude weight associated with the plasmonic resonances.

  1. Pump-probe spectroscopy and circular dichroism of nanocrystalline benzophenone--towards absolute kinetic measurements in solid state photochemical reactions.

    PubMed

    Chin, Khin K; Natarajan, Arunkumar; Gard, Matthew N; Campos, Luis M; Shepherd, Heather; Johansson, Erik; Garcia-Garibay, Miguel A

    2007-11-07

    Nanocrystals suspended in water can be used to record steady state and pump-probe absorption spectra, which should be useful for the study of excited states and reactive intermediates in the solid state.

  2. Theory of attosecond delays in molecular photoionization

    NASA Astrophysics Data System (ADS)

    Baykusheva, Denitsa; Wörner, Hans Jakob

    2017-03-01

    We present a theoretical formalism for the calculation of attosecond delays in molecular photoionization. It is shown how delays relevant to one-photon-ionization, also known as Eisenbud-Wigner-Smith delays, can be obtained from the complex dipole matrix elements provided by molecular quantum scattering theory. These results are used to derive formulae for the delays measured by two-photon attosecond interferometry based on an attosecond pulse train and a dressing femtosecond infrared pulse. These effective delays are first expressed in the molecular frame where maximal information about the molecular photoionization dynamics is available. The effects of averaging over the emission direction of the electron and the molecular orientation are introduced analytically. We illustrate this general formalism for the case of two polyatomic molecules. N2O serves as an example of a polar linear molecule characterized by complex photoionization dynamics resulting from the presence of molecular shape resonances. H2O illustrates the case of a non-linear molecule with comparably simple photoionization dynamics resulting from a flat continuum. Our theory establishes the foundation for interpreting measurements of the photoionization dynamics of all molecules by attosecond metrology.

  3. Chasing charge localization and chemical reactivity following photoionization in liquid water

    NASA Astrophysics Data System (ADS)

    Marsalek, Ondrej; Elles, Christopher G.; Pieniazek, Piotr A.; Pluhařová, Eva; VandeVondele, Joost; Bradforth, Stephen E.; Jungwirth, Pavel

    2011-12-01

    The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within ˜30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as H2O+ + H2O → OH + H3O+. The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM/MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with ˜40 fs time resolution and broadband spectral probing across

  4. Chasing charge localization and chemical reactivity following photoionization in liquid water.

    PubMed

    Marsalek, Ondrej; Elles, Christopher G; Pieniazek, Piotr A; Pluhařová, Eva; VandeVondele, Joost; Bradforth, Stephen E; Jungwirth, Pavel

    2011-12-14

    The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within ~30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as H(2)O(+) + H(2)O → OH + H(3)O(+). The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM∕MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with ~40 fs time resolution and broadband spectral probing

  5. Chasing charge localization and chemical reactivity following photoionization in liquid water

    SciTech Connect

    Marsalek, Ondrej; Pluharova, Eva; Jungwirth, Pavel; Elles, Christopher G.; Pieniazek, Piotr A.; Bradforth, Stephen E.; VandeVondele, Joost

    2011-12-14

    The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within {approx}30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as H{sub 2}O{sup +}+ H{sub 2}O {yields} OH + H{sub 3}O{sup +}. The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM/MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with {approx}40 fs time

  6. Maximizing hole coherence in ultrafast photoionization of argon with an optimization by sequential parametrization update

    NASA Astrophysics Data System (ADS)

    Goetz, R. Esteban; Merkel, Maximilian; Karamatskou, Antonia; Santra, Robin; Koch, Christiane P.

    2016-08-01

    Photoionization with attosecond pulses populates hole states in the photoion. Superpositions of hole states represent ideal candidates for time-dependent spectroscopy, for example via pump-probe studies. The challenge consists in identifying pulses that create coherent superpositions of hole states while satisfying practical constraints. Here, we employ quantum optimal control to maximize the degree of coherence between these hole states. To this end, we introduce a derivative-free optimization method with sequential parametrization update (SPA optimization). We demonstrate the versatility and computational efficiency of SPA optimization for photoionization in argon by maximizing the coherence between the 3 s and 3 p0 hole states using shaped attosecond pulses. We show that it is possible to maximize the hole coherence while simultaneously prescribing the ratio of the final hole state populations.

  7. Femtosecond Synchronization of Laser Systems for the LCLS

    SciTech Connect

    Byrd, John; Doolittle, Lawrence; Huang, Gang; Staples, John; Wilcox, Russell; Arthur, John; Frisch, Josef; White, William; /SLAC

    2012-08-24

    The scientific potential of femtosecond x-ray pulses at linac-driven free-electron lasers such as the Linac Coherent Light Source is tremendous. Time-resolved pump-probe experiments require a measure of the relative arrival time of each x-ray pulse with respect to the experimental pump laser. An optical timing system based on stabilized fiber links has been developed for the LCLS to provide this synchronization. Preliminary results show synchronization of the installed stabilized links at the sub-20-femtosecond level. We present details of the implementation at LCLS and potential for future development.

  8. Diagnosis and staging of female genital tract melanocytic lesions using pump-probe microscopy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Robles, Francisco E.; Selim, Maria A.; Warren, Warren S.

    2016-02-01

    Melanoma of the vulva is the second most common type of malignancy afflicting that organ. This disease caries poor prognosis, and shows tendencies to recur locally and develop distant metastases through hematogenous dissemination. Further, there exists significant clinical overlap between early-stage melanomas and melanotic macules, benign lesions that are believed to develop in about 10% of the general female population. In this work we apply a novel nonlinear optical method, pump-probe microscopy, to quantitatively analyze female genitalia tract melanocytic lesions. Pump-probe microscopy provides chemical information of endogenous pigments by probing their electronic excited state dynamics, with subcellular resolution. Using unstained biopsy sections from 31 patients, we find significant differences between melanin type and structure in tissue regions with invasive melanoma, melanoma in-situ and non-malignant melanocytic proliferations (e.g., nevi, melanocytic macules). The molecular images of non-malignant lesion have a well-organized structure, with relatively homogenous pigment chemistry, most often consistent with that of eumelanin with large aggregate size or void of metals, such as iron. On the other hand, pigment type and structure observed in melanomas in-situ and invasive melanomas is typically much more heterogeneous, with larger contributions from pheomelanin, melanins with larger metal content, and/or melanins with smaller aggregate size. Of most significance, clear differences can be observed between melanocytic macules and vulvar melanoma in-situ, which, as discussed above, can be difficult to clinically distinguish. This initial study demonstrates pump-probe microscopy's potential as an adjuvant diagnostic tool by revealing systematic chemical and morphological differences in melanin pigmentation among invasive melanoma, melanoma in-situ and non-malignant melanocytic lesions.

  9. Time-resolved pump-probe spectroscopy of intraband absorption by a semiconductor nanorod

    NASA Astrophysics Data System (ADS)

    Leonov, Mikhail Y.; Rukhlenko, Ivan D.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2013-09-01

    We develop a theory of time-resolved pump-probe optical spectroscopy of intraband absorption of a probe pulse inside an anisotropic semiconductor nanorod. The absorption is preceded by the absorption of the pump pulse resonant to an interband transition. It is assumed that the resonantly exited states of the nanorod are interrelated via the relaxation induced by their interaction with a bath. We reveal the conditions for which the absorption of the probe's pulse is governed by a simple formula regardless of the pulse's shape. This formula is useful for the analysis of the experimental data containing information on the relaxation parameters of the nanorod's electronic subsystem.

  10. Ultrafast infrared pump-probe spectroscopy of water: A theoretical description

    NASA Astrophysics Data System (ADS)

    Bratos, S.; Leicknam, J.-Cl.

    1994-09-01

    A theory is developed to describe a recent infrared pump-probe experiment in water. This theory is a statistical theory, similar to those elaborated earlier to interpret ultraviolet and visible spectra. Nonlinear optical processes involved are analyzed in terms of four-time correlation functions of the electric dipole moment of the system and of the incident electric fields, respectively. An analytical expression for the transient infrared signal is presented. The observed spectral characteristics are attributed to a gradual thermalization of the initial, pump-prepared state. The substructure of the observed bands is interpreted. This experiment probes the kinetics of conversion of H-bonds of different lengths into each other.

  11. Ultrafast pump-probe spectroscopy in gallium arsenide at 25 T.

    PubMed

    Curtis, Jeremy A; Tokumoto, Takahisa; Nolan, Nicholas K; McClintock, Luke M; Cherian, Judy G; McGill, Stephen A; Hilton, David J

    2014-10-01

    We have performed high-fluence, nondegenerate pump-probe spectroscopy in the Split Florida-Helix magnet at 25 T and 15 K. The electronic component of our ultrafast differential reflectivity can be described with a simplified four-level approximation to determine the scattering and recombination rates. Ultrafast oscillations are well described by a coherent acoustic phonon model. Our free-space ultrafast spectroscopic technique will permit future experimental investigations to study novel photoinduced phase transitions and complex interactions in correlated electron systems, which will require the high pulse energies of our free-space alternative.

  12. Simulating Energy Relaxation in Pump-Probe Vibrational Spectroscopy of Hydrogen-Bonded Liquids.

    PubMed

    Dettori, Riccardo; Ceriotti, Michele; Hunger, Johannes; Melis, Claudio; Colombo, Luciano; Donadio, Davide

    2017-03-14

    We introduce a nonequilibrium molecular dynamics simulation approach, based on the generalized Langevin equation, to study vibrational energy relaxation in pump-probe spectroscopy. A colored noise thermostat is used to selectively excite a set of vibrational modes, leaving the other modes nearly unperturbed, to mimic the effect of a monochromatic laser pump. Energy relaxation is probed by analyzing the evolution of the system after excitation in the microcanonical ensemble, thus providing direct information about the energy redistribution paths at the molecular level and their time scale. The method is applied to hydrogen-bonded molecular liquids, specifically deuterated methanol and water, providing a robust picture of energy relaxation at the molecular scale.

  13. Theoretical description of pump/probe experiments in electron-mediated charge-density-wave insulators

    NASA Astrophysics Data System (ADS)

    Freericks, J. K.; Matveev, O. P.; Shen, Wen; Shvaika, A. M.; Devereaux, T. P.

    2017-03-01

    In this review, we develop the formalism employed to describe charge-density-wave insulators in pump/probe experiments that use ultrashort driving pulses of light. The theory emphasizes exact results in the simplest model for a charge-density-wave insulator (given by a noninteracting system with two bands and a gap) and employs nonequilibrium dynamical mean-field theory to solve the Falicov-Kimball model in its ordered phase. We show how to develop the formalism and how the solutions behave. Care is taken to describe the details behind these calculations and to show how to verify their accuracy via sum-rule constraints.

  14. Quantum well intersubband lifetimes measured by mid-IR pump-probe experiments

    SciTech Connect

    Woods, G.L.; Sung, B.; Proctor, M.

    1995-12-31

    Semiconductor quantum wells exhibit quantum-confined electronic energy levels, or subbands, that are similar to one-dimensional {open_quotes}particle in a box{close_quotes} wavefunctions. The light effective mass of electrons allows large spatial extents of the wavefunctions and concomitantly large dipole overlaps between states. These large dipoles have been exploited in a variety of experiments including nonlinear frequency conversion, infrared photodetection, and lasing. A key parameter for many devices is the upper state lifetime. The decay of carriers in the upper state is believed to be dominated by optical phonon scattering and lifetimes on-the order of 1ps are expected. While Raman and saturation measurements have shown good agreement with theory, direct pump-probe measurements have reported longer lifetimes, partially due to carrier heating. In this paper, we discuss our mid-IR (5{mu}m) pump-probe measurements of intersubband lifetimes, performed at the Stanford Picosecond Free Electron Laser Center. At low excitation densities we observe lifetimes of about 1.5 ps, in good agreement with phonon theory. At high excitation densities the lifetime increases to 3.5 ps, demonstrating the transition from the low- to high-excitation agree.

  15. Pump-probe optical coherence tomography using indocyanine green as a contrast agent

    NASA Astrophysics Data System (ADS)

    Yaqoob, Zahid; McDowell, Emily; Wu, Jigang; Yang, Changhuei

    2006-02-01

    Use of indocyanine green (ICG), an FDA-approved dye, in a pump-probe scheme for optical coherence tomography (OCT) is reported. Aqueous solutions of ICG are not stable, i.e., the dye degrades over time especially in the presence of light. Addition of protein such as bovine serum albumin (BSA) stabilizes the ICG; however, when exposed to high intensity illumination, the dye still degrades. Moreover, the photodegradation is permanent and occurs swiftly if the illumination band corresponds to the ICG absorption peak. The permanence of the photobleached state illustrates that ICG photobleaching phenomenon has great potential to achieve contrast in OCT. ICG solutions with 50 micromolar concentration were prepared in water, 1% BSA, and 0.8% agarose to study the dynamics of the dye for different illumination intensity levels. In addition, different molar concentrations of ICG in water were studied for fixed illumination intensity. In each case, probability of photobleaching, defined as the ratio of the total photobleached ICG molecules to the total photons absorbed by the ground-state molecules, is evaluated to characterize the photobleaching phenomenon in ICG. We also demonstrate ICG-based pump-probe MCOCT imaging by mapping the distribution of ICG in a stage 54 Xenopus laevis.

  16. Towards pump-probe experiments of defect dynamics with short ion beam pulses

    NASA Astrophysics Data System (ADS)

    Schenkel, T.; Lidia, S. M.; Weis, C. D.; Waldron, W. L.; Schwartz, J.; Minor, A. M.; Hosemann, P.; Kwan, J. W.

    2013-11-01

    A novel, induction type linear accelerator, the Neutralized Drift Compression eXperiment (NDCX-II), is currently being commissioned at Berkeley Lab. This accelerator is designed to deliver intense (up to 3 × 1011 ions/pulse), 0.6 to ∼600 ns duration pulses of 0.05-1.2 MeV lithium ions at a rate of about 2 pulses per minute onto 1-10 mm scale target areas. When focused to mm-diameter spots, the beam is predicted to volumetrically heat micrometer thick foils to temperatures of ∼30,000 °K. At lower beam power densities, the short excitation pulse with tunable intensity and time profile enables pump-probe type studies of defect dynamics in a broad range of materials. We briefly describe the accelerator concept and design, present results from beam pulse shaping experiments and discuss examples of pump-probe type studies of defect dynamics following irradiation of materials with intense, short ion beam pulses from NDCX-II.

  17. Towards pump probe experiments of defect dynamics with short ion beam pulses

    SciTech Connect

    Schenkel, T.; Lidia, S.; Weis, C. D.; Waldron, W. L.; Schwartz, J.; Minor, Andrew; Hosemann, P; Kwan, J. W.

    2013-01-01

    A novel, induction type linear accelerator, the Neutralized Drift Compression eXperiment (NDCX-II), is currently being commissioned at Berkeley Lab. This accelerator is designed to deliver intense (up to 3 1011 ions/pulse), 0.6 to 600 ns duration pulses of 0.05 1.2 MeV lithium ions at a rate of about 2 pulses per minute onto 1 10 mm scale target areas. When focused to mm-diameter spots, the beam is predicted to volumetrically heat micrometer thick foils to temperatures of 30,000 K. At lower beam power densities, the short excitation pulse with tunable intensity and time profile enables pump probe type studies of defect dynamics in a broad range of materials. We briefly describe the accelerator concept and design, present results from beam pulse shaping experiments and discuss examples of pump probe type studies of defect dynamics following irradiation of materials with intense, short ion beam pulses from NDCX-II.

  18. Pump-probe X-ray Diffraction Technique for Irreversible Phase Change Materials

    SciTech Connect

    Fukuyama, Yoshimitsu; Yasuda, Nobuhiro; Kimura, Shigeru; Osawa, Hitoshi; Kim, Jungeun; Tanaka, Yoshihito; Takata, Masaki; Murayama, Haruno; Moritomo, Yutaka; Toriumi, Koshiro; Tanaka, Hitoshi

    2010-06-23

    We have developed a pump-probe X-ray diffraction measurement system for a sample with irreversible reaction at BL40XU in the SPring-8. The system mainly consists of a time-resolved measurement system, a sample disk rotation system, and an X-ray microbeam system. The time-resolved measurement system gives time resolution of 50 ps in laser-pump and X-ray probe method. A sample disk rotation system for repetitive measurements was made to give a virgin sample for every measurement. The number of repetitions for one sample disk was increased by using the X-ray microbeam technique. To keep the overlap of the X-ray microbeam and the laser beam on the sample surface during the disk rotation, the sample disk rotation system was constructed by a low-eccentric spindle motor. By using this system, the pump-probe X-ray diffraction measurement was demonstrated for a crystallization process of a DVD material.

  19. Retrieval of spectral and dynamic properties from two-dimensional infrared pump-probe experiments.

    PubMed

    Chelli, Riccardo; Volkov, Victor V; Righini, Roberto

    2008-07-15

    We have developed a fitting algorithm able to extract spectral and dynamic properties of a three level oscillator from a two-dimensional infrared spectrum (2D-IR) detected in time resolved nonlinear experiments. Such properties go from the frequencies of the ground-to-first and first-to-second vibrational transitions (and hence anharmonicity) to the frequency-fluctuation correlation function. This last is represented through a general expression that allows one to approach the various strategies of modeling proposed in the literature. The model is based on the Kubo picture of stochastic fluctuations of the transition frequency as a result of perturbations by a fluctuating surrounding. To account for the line-shape broadening due to pump pulse spectral width in double-resonance measurements, we supply the fitting algorithm with the option to perform the convolution of the spectral signal with a Lorentzian function in the pump-frequency dimension. The algorithm is tested here on 2D-IR pump-probe spectra of a Gly-Ala dipeptide recorded at various pump-probe delay times. Speedup benchmarks have been performed on a small Beowulf cluster. The program is written in FORTRAN language for both serial and parallel architectures and is available free of charge to the interested reader.

  20. Excitons in Cuprous Oxide: Photoionization and Other Multiphoton Processes

    NASA Astrophysics Data System (ADS)

    Frazer, Nicholas Laszlo

    In cuprous oxide (Cu2O), momentum from the absorption of two infrared photons to make an orthoexciton is conserved and detected through the photon component of a resulting mixed exciton/photon (quadrupole exciton polariton) state. I demonstrated that this process, which actually makes the photon momentum more precisely defined, is disrupted by photoionization of excitons. Some processes are known to affect exciton propagation in both the pump and exciton stages, such as phonon emission, exciton-exciton (Auger) scattering, and third harmonic generation. These processes alone were not able to explain all observed losses of excitons or all detected scattering products, which lead me to design an optical pump-probe experiment to measure the exciton photoionization cross section, which is (3.9+/-0.2) x 10-22 m2. This dissertation describes the synthesis of cuprous oxide crystals using oxidation of copper, crystallization from melt with the optical floating zone method, and annealing. The cuprous oxide crystals were characterized using time and space resolved luminescence, leading to the discovery of new defect properties. Selection rules and overall efficiency of third harmonic generation in these crystals were characterized. Exciton photoionization was demonstrated through the depletion of polariton luminescence by an optical probe, the production of phonon linked luminescence as a scattering product, temporal delay of the probe, and time resolved luminescence. The results are integrated with the traditional dynamical model of exciton densities. An additional investigation of copper/cuprous oxide/gold photovoltaic devices is appended.

  1. Origin of the thermal expansion anomaly in layered Bi2X3 topological insulators: Ultrafast time-resolved pump-probe experiments and theory

    NASA Astrophysics Data System (ADS)

    Prakash, Gyan; Pal, Koushik; Jain, Manish; Waghmare, U. V.; Sood, A. K.

    2017-08-01

    Recent experiments on the thermal expansion of Sb2Te3 , a prototypical example of strong three-dimensional topological insulators, have shown an intriguing anomaly in the thermal expansion coefficient along the hexagonal axis (α ∥), which drops sharply to almost zero in a narrow range of temperature around ˜225 K. With no accompanying signatures in other properties, the origin of this anomaly is not understood. We present here femtosecond pump-probe differential reflectivity measurements on single crystals of Sb2Te3 as a function of temperature from 3 to 300 K to determine the temperature dependence of coherent optical and acoustic phonons along with the dynamics of the photoexcited carriers. We find clearly anomalous temperature dependence of the parameters associated with vibrational and electronic relaxation in the narrow temperature range of 200-250 K. Within first-principles density functional theoretical analysis, we show that the observed anomalies can be explained with a mechanism of formation of stacking faults stabilized by vibrational entropy above 200 K. As a similar anomaly in the thermal expansion is also observed in other chalcogenides in the same family, the proposed mechanism may also be applicable to these layered strong topological insulators.

  2. Direct Imaging of Ultrafast Charge Carrier Dynamics in Semiconducting Nanowires Using Two-Photon Excitation and Spatially-Separated Pump-Probe Microscopy

    NASA Astrophysics Data System (ADS)

    Kirschbrown, Justin Robert

    The increasing use of nanoscale materials in scientific research and device design places a greater emphasis on characterizing the heterogeneity of nanostructures. When designing electronic components around the use of individual nanoparticles, it is important to understand variability between seemingly identical particles produced in the same synthesis. To do this, we have developed an ultrafast optical microscope capable of studying single nanostructures with spatial resolution of hundreds of nanometers. Emission images of zinc oxide needle-like nanowires show a modulated pattern along the long axis of the wire that are attributed to the coupling of the optical field into structurally dependent resonance modes. Simulations suggest that these are size dependent hybrid modes, containing character of both whispering gallery and Fabry-Perot modes. By incorporating transient absorption pump-probe techniques into the microscope design, we can observe the recombination dynamics of excited carriers on femtosecond timescales following excitation. Due to the high resolution of the instrument, it is possible to observe the dynamics at different locations within a single nanostructure. This technique is used to study the correlation between the decay kinetics of silicon nanowires and doping density for a variety of surface treatments. The motion of excited carriers in silicon nanowires was directly imaged by holding the pump beam in a particular location and scanning the probe beam over the entire structure. The resulting images show free carriers spreading out from the area of excitation, leaving the immobile trapped carriers behind.

  3. Photoionization of molecular clusters

    NASA Astrophysics Data System (ADS)

    Andres, R. P.; Calo, J. M.

    1981-12-01

    An experimental apparatus consisting of a novel multiple expansion cluster source coupled with a molecular beam system and photoionization mass spectrometer has been designed and constructed. This apparatus has been thoroughly tested and preliminary measurements of the growth kinetics of water clusters and the photoionization cross section of the water dimer have been carried out.

  4. Reversible Strain-Induced Electron-Hole Recombination in Silicon Nanowires Observed with Femtosecond Pump-Probe Microscopy

    DTIC Science & Technology

    2014-01-01

    Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 Ultrafast imaging, strained nanomaterials, spectroscopy REPORT...devices with indirect-bandgap materials such as silicon. KEYWORDS: Ultrafast imaging, strained nanomaterials, spectroscopy Lattice strain produced by...where ks, kr, kSRH, and kA represent the rates associated with surface, radiative, Shockley−Read−Hall (SRH), and Auger recombination, respectively

  5. Broadband pump-probe imaging spectroscopy applicable to ultrafast single-shot events

    NASA Astrophysics Data System (ADS)

    Minami, Yasuo; Yamaki, Hiromoto; Katayama, Ikufumi; Takeda, Jun

    2014-02-01

    We propose a scheme for frequency-resolved single-shot spectroscopy with an echelon mirror. The echelon mirror is employed to generate spatially encoded time delays for the white-light continuum probe beam; it produces a temporal step of 66 fs and an overall time delay of 33 ps. We demonstrate broadband pump-probe imaging spectroscopy and present time-frequency two-dimensional images of the transient absorption of β-carotene between 420 and 630 nm with single-shot detection. The results show that this technique is a powerful tool for observing the ultrafast, broadband transient dynamics of materials that exhibit irreversible reactions or deterioration by laser pulse irradiation.

  6. Analysis of the Thermo-Reflectivity Coefficient Influence Using Photothermal Pump-Probe Techniques.

    PubMed

    Zanuto, Vitor S; Capeloto, Otávio A; Sandrini, Marcelo; Malacarne, Luis C; Astrath, Nelson G C; Bialkowski, Stephen E

    2016-11-18

    Recent improvements in the modeling of photo-induced thermo-optical-mechanical effects have broadened the application of photothermal techniques to a large class of solids and fluids. During laser excitation, changes in optical reflectivity due to temperature variation may affect the photothermal signal. In this study, the influence of the reflectivity change due to heating is analyzed for two pump-probe photothermal techniques, thermal lens and thermal mirror. A linear equation for the temperature dependence of the reflectivity is derived, and the solution is tested using optical properties of semi-transparent and opaque materials. For semi-transparent materials, the influence of the reflectivity change in photothermal signals is less than 0.01%, while for opaque materials it is lower than 3%.

  7. Picosecond pump-probe using an FEL and a synchrotron source

    SciTech Connect

    Denbeaux, G.; Straub, K.D.; Madey, J.M.J.

    1995-12-31

    Two color pump-probe experiments using both the Duke Storage Ring as a synchrotron light source for visible light the Mark III FEL as a tunable, high peak power IR source are possible. The visible synchrotron source can be used as a probe of vibrational excitation from the FEL in an experiment using vibrationally-assisted fluorescence as an indicator of overlap of the IR and the visible pulses. An optical delay line in the FEL beam will allow adjustment of the arrival time of the IR pulse relative to the visible probe. The storage ring RF booster and the Mark III FEL RF sources will be both driven by the same master oscillator with a timing jitter between sources of less than 20 psec. Exploration of coupling between electronic excitation and lifetimes of vibrational excitation of fluorescent compounds in solution can be carried out with this configuration.

  8. Resolution enhancement of pump-probe microscopy with an inverse-annular spatial filter

    NASA Astrophysics Data System (ADS)

    Kobayashi, T.; Kawasumi, K.; Miyazaki, J.; Nakata, K.

    2016-12-01

    We have introduced a pupil filter, an inverse-annular pupil filter in a pump-probe photothermal microscope, which provides resolution enhancement in three dimensions. The resolution is probed to be improved in lateral and axial resolution by imaging experiment using 20 nm gold nanoparticles. The improvement in X (perpendicular to the common pump and probe polarization direction), Y (parallel to the polarization direction), and Z (axial direction) are by 15±6, 8±8, and 21±2 % from the resolution without a pupil filter. The resolution enhancement is even better than the calculation using vector field, which predicts the corresponding enhancement of 11, 8, and 6 %. The discussion is made to explain the unexpected results. We also demonstrate the photothermal imaging of thick biological samples (cells from rabbit intestine and kidney) stained with hematoxylin and eosin dye with the inverse-annular filter.

  9. Coherent pump-probe spectroscopy in sodium vapor: From electromagnetically induced transparency to parametric amplification

    SciTech Connect

    Takahashi, Ken-ichi; Hayashi, Nobuhito; Kido, Hiroaki; Sugimura, Shota; Hombo, Naoya; Mitsunaga, Masaharu

    2011-06-15

    We have theoretically and experimentally investigated coherent pump-probe spectra for the 3S{sub 1/2}-3P{sub 1/2} D1 transition of sodium atomic vapor. Probe transmission spectra in the presence of a coupling beam exhibit dramatic changes depending on experimental conditions. In the weak-excitation, low-atomic-density limit, the spectra are mainly characterized by electromagnetically induced transparency (EIT) and saturated absorption, but for the strong-excitation, high-density case, parametric amplification (PA) is dominant, featuring high probe gain and Stokes-wave generation. We have developed a theory that can explain these two seemingly totally different phenomena (EIT and PA) within the same theoretical framework by manipulating a few experimentally controllable parameters, and have successfully reproduced the observed spectra. Other than the main spectral features, many other interesting physical processes have been predicted and observed.

  10. Dissipative dynamics of a system passing through a conical intersection: Ultrafast pump-probe observables

    NASA Astrophysics Data System (ADS)

    Gelman, David; Katz, Gil; Kosloff, Ronnie; Ratner, Mark A.

    2005-10-01

    The dynamics of a system incorporating a conical intersection, in the presence of a dissipative environment, is studied with the purpose of identifying observable ultrafast spectroscopic signatures. A model system consisting of two vibronically coupled electronic states with two nuclear degrees of freedom is constructed. Dissipation is treated by two different methods, Lindblad semigroup formalism and the surrogate Hamiltonian approach. Pump-probe experimental expectation values such as transient emission and transient absorption are calculated and compared to the adiabatic and diabatic population transfer. The ultrafast population transfer reflecting the conical intersection is not mirrored in transient absorption measurements such as the recovery of the bleach. Emission from the excited state can be suppressed on the ultrafast time scale, but the existence of a conical intersection is only one of the possible mechanisms that can provide ultrafast damping of emission.

  11. Measuring excited state lifetime of Rb atoms with pump-probe technique

    SciTech Connect

    Zeng, X.; Boiko, D. L.

    2015-08-31

    A technique for measuring the excited state lifetime τ{sub ex} of optical transitions in alkali atoms is presented. It is a form of pump-probe technique based on time-resolved optical transmission through the atomic vapor cell. This technique can serve as an alternative to the traditionally used time-resolved photofluorescence methods when measuring alkali vapor cells with heavily quenched fluorescence, where the τ{sub ex} is expected to be on the order of a few nanoseconds, and the highly sensitive fluorescence detectors with sub-nanosecond temporal resolution that are required may not be available. We use this technique to measure the τ{sub ex} of Rb atoms in vapor cells with different buffer gas pressures.

  12. Deducing fast electron density changes in randomly orientated uncrystallized biomolecules in a pump-probe experiment.

    PubMed

    Pande, K; Schwander, P; Schmidt, M; Saldin, D K

    2014-07-17

    We propose a method for deducing time-resolved structural changes in uncrystallized biomolecules in solution. The method relies on measuring the angular correlations of the intensities, when averaged over a large number of diffraction patterns from randomly oriented biomolecules in solution in a liquid solvent. The experiment is somewhat like a pump-probe version of an experiment on small angle X-ray scattering, except that the data expected by the algorithm are not just the radial variation of the averaged intensities. The differences of these correlation functions as measured from a photoexcited and dark structure enable the direct calculation of the difference electron density with a knowledge of only the dark structure. We exploit a linear relation we derive between the difference in these correlation functions and the difference electron density, applicable for small structural changes.

  13. Localized thin film damage sourced and monitored via pump-probe modulated thermoreflectance

    NASA Astrophysics Data System (ADS)

    Donovan, Brian F.; Tomko, John A.; Giri, Ashutosh; Olson, David H.; Braun, Jeffrey L.; Gaskins, John T.; Hopkins, Patrick E.

    2017-05-01

    Damage in the form of dewetting and delamination of thin films is a major concern in applications requiring micro- or nano-fabrication. In non-contact nanoscale characterization, optical interrogation must be kept to energies below damage thresholds in order to conduct measurements such as pump-probe spectroscopy. In this study, we show that the thermoreflectance of thin films can indicate the degree of film damage induced by a modulated optical heating source. By adjusting the absorbed power of the pump heating event, we identify the characteristics of the change in the thermoreflectance signal when leading up to and exceeding the damage threshold of gold films of varying thicknesses on glass substrates.

  14. Observation of stimulated Brillouin scattering in polymer optical fiber with pump-probe technique.

    PubMed

    Mizuno, Yosuke; Kishi, Masato; Hotate, Kazuo; Ishigure, Takaaki; Nakamura, Kentaro

    2011-06-15

    Stimulated Brillouin scattering (SBS) in a perfluorinated graded-index polymer optical fiber (POF) with 120 μm core diameter was experimentally observed for the first time, to the best of our knowledge, at 1.55 μm wavelength with the pump-probe technique. Compared to spontaneous Brillouin scattering previously reported, the Brillouin gain spectrum (BGS) was detected with an extremely high signal-to-noise ratio, even with a short POF (1 m) and scrambled polarization state. We also investigated the BGS dependences on probe power and temperature, which indicate that SBS in a POF measured with this technique can be utilized to develop high-accuracy temperature sensing systems.

  15. Probing dynamics in colloidal crystals with pump-probe experiments at LCLS: Methodology and analysis

    DOE PAGES

    Mukharamova, Nastasia; Lazarev, Sergey; Meijer, Janne -Mieke; ...

    2017-05-19

    We present results of the studies of dynamics in colloidal crystals performed by pump-probe experiments using an X-ray free-electron laser (XFEL). Colloidal crystals were pumped with an infrared laser at a wavelength of 800 nm with varying power and probed by XFEL pulses at an energy of 8 keV with a time delay up to 1000 ps. The positions of the Bragg peaks, and their radial and azimuthal widths were analyzed as a function of the time delay. The spectral analysis of the data did not reveal significant enhancement of frequencies expected in this experiment. As a result, this allowedmore » us to conclude that the amplitude of vibrational modes excited in colloidal crystals was less than the systematic error caused by the noise level.« less

  16. Direct Detection of Pure ac Spin Current by X-Ray Pump-Probe Measurements

    NASA Astrophysics Data System (ADS)

    Li, J.; Shelford, L. R.; Shafer, P.; Tan, A.; Deng, J. X.; Keatley, P. S.; Hwang, C.; Arenholz, E.; van der Laan, G.; Hicken, R. J.; Qiu, Z. Q.

    2016-08-01

    Despite recent progress in spin-current research, the detection of spin current has mostly remained indirect. By synchronizing a microwave waveform with synchrotron x-ray pulses, we use the ferromagnetic resonance of the Py (Ni81Fe19 ) layer in a Py /Cu /Cu75Mn25/Cu /Co multilayer to pump a pure ac spin current into the Cu75Mn25 and Co layers, and then directly probe the spin current within the Cu75Mn25 layer and the spin dynamics of the Co layer by x-ray magnetic circular dichroism. This element-resolved pump-probe measurement unambiguously identifies the ac spin current in the Cu75Mn25 layer.

  17. Comparison of chlorine dioxide photochemistry in acetonitrile and water using subpicosecond pump probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Philpott, Matthew J.; Charalambous, Sophia; Reid, Philip J.

    1997-12-01

    The photochemical reaction dynamics of chlorine dioxide (OClO) dissolved in water and acetonitrile are investigated using subpicosecond pump-probe spectroscopy. The spectral dynamics observed at 267 and 400 nm demonstrate that the quantum yield for geminate recombination of ClO and O to form OClO is reduced in acetonitrile relative to water. However, the dynamics at 800 nm are similar for both solvents consistent with ClOO rather than OClO being responsible for the evolution at this wavelength. The kinetics for ground-state ClOO production and decomposition are significantly slower in acetonitrile relative to water suggesting that solvent-solute hydrogen bonding is important in defining the ground state reactivity of this photoproduct.

  18. High P-T Thermal Conductivity of Periclase using an Ultrafast Pump-Probe Method

    NASA Astrophysics Data System (ADS)

    Dalton, D. A.; Goncharov, A. F.; Hsieh, W.; Cahill, D.

    2011-12-01

    Measurements of thermal conductivity were carried out on MgO at elevated pressures via a diamond anvil cell (DAC) at ambient and high temperatures. The time domain thermoreflectance (TDTR) technique is an optical pump-probe method for heating and probing the dynamics of thermal diffusion. Samples of MgO (~10 μm) coated with aluminum (~70 nm) are loaded into a diamond cell with argon as the pressure medium. Ambient temperature results are presented up to 60 GPa, while high P-T measurements were performed in a resistively heated cell up to 45 GPa and ~600 K, where ruby and SrB4O7:Sm2+ were used as P-T calibrants. The extrapolation of these results to conditions that are relevant to the mantle will be discussed.

  19. Pulse accumulation, radial heat conduction, and anisotropic thermal conductivity in pump-probe transient thermoreflectance.

    PubMed

    Schmidt, Aaron J; Chen, Xiaoyuan; Chen, Gang

    2008-11-01

    The relationship between pulse accumulation and radial heat conduction in pump-probe transient thermoreflectance (TTR) is explored. The results illustrate how pulse accumulation allows TTR to probe two thermal length scales simultaneously. In addition, the conditions under which radial transport effects are important are described. An analytical solution for anisotropic heat flow in layered structures is given, and a method for measuring both cross-plane and in-plane thermal conductivities of thermally anisotropic thin films is described. As verification, the technique is used to extract the cross-plane and in-plane thermal conductivities of highly ordered pyrolytic graphite. Results are found to be in good agreement with literature values.

  20. Theoretical description of pump/probe experiments in nesting induced charge density wave insulators

    NASA Astrophysics Data System (ADS)

    Freericks, J. K.; Matveev, O. P.; Shvaika, A. M.; Devereaux, T. P.

    2016-05-01

    We present a theoretical description of time-resolved photoemission in charge-density-wave insulators that derive their ordering from electron nesting effects. In these pump/probe experiments, a large amplitude (but short duration) pump pulse excites the system into nonequilibrium and then a higher frequency low amplitude probe pulse photoexcites electrons, which are measured at the detector. We describe effects of electron correlations on the photoelectron spectroscopy and provide details for the theoretical techniques used to solve these problems. We also show how the gap fills in as the system is excited, even though the order parameter does not go to zero. The theory is developed for the Falicov-Kimball model, which can be solved exactly with nonequilibrium dynamical mean-field theory.

  1. A two-parameter nondiffusive heat conduction model for data analysis in pump-probe experiments

    NASA Astrophysics Data System (ADS)

    Ma, Yanbao

    2014-12-01

    Nondiffusive heat transfer has attracted intensive research interests in last 50 years because of its importance in fundamental physics and engineering applications. It has unique features that cannot be described by the Fourier law. However, current studies of nondiffusive heat transfer still focus on studying the effective thermal conductivity within the framework of the Fourier law due to a lack of a well-accepted replacement. Here, we show that nondiffusive heat conduction can be characterized by two inherent material properties: a diffusive thermal conductivity and a ballistic transport length. We also present a two-parameter heat conduction model and demonstrate its validity in different pump-probe experiments. This model not only offers new insights of nondiffusive heat conduction but also opens up new avenues for the studies of nondiffusive heat transfer outside the framework of the Fourier law.

  2. Photoionization studies of oxygen and hydrogen

    NASA Astrophysics Data System (ADS)

    Padmanabhan, Arathi

    A toroidal spectrometer designed to perform (gamma, 2e) studies, was for the first time employed for Threshold Photoelectron Photoion Coincidence (TPEPICO) study. The angular distributions of O+(4S) ions produced from dissociative photoionization (DPI) of O2 + c4Sigma-u(nu =0,1) using the TPEPICO technique, i.e. by measuring the coincidence yield between threshold photoelectrons and photoions have been investigated. The results for lifetimes, taunu, corresponding to the vibrational levels nu = 0,1, along with the value obtained for inherent anisotropic photoion angular distribution betaO+, are presented. Recently, Fernandez and Martin (New J Phys 11 34 (2009)), have performed an extensive ab initio study of DPI in H2, in which large oscillatory behaviour in the electron angular distribution, as a function of electron energy, has been predicted. The result of their ab anitio calculations reveal that the electron angular, theta, distributions oscillate between a cos2theta pattern and isotropic with less than a 1 eV.change in electron energy. Due to the very low cross section and the requirement for high energy resolution in the electron detection system, these measurements require sensitive instrumentation that is now available at the Canadian Light Source. For this particular H 2 study, the electron angular distributions as a function of electron energy are the signature of quantum mechanical interference between, essentially, two specific doubly excited states (namely, 1Q11Sigma u+ and 1Q21piu) decaying at different internuclear distances. While interference between 'direct' photoionization and autoionization is well-known, the first unambiguous observation of interference between two autoionization processes, occurring on the femtosecond timescale is presented. A simple semi-classical model captures the essence of both our experimental observations and the results of full ab initio calculations. It does this through explicitly linking the electron angular

  3. Tracking ultrafast relaxation dynamics of furan by femtosecond photoelectron imaging

    NASA Astrophysics Data System (ADS)

    Liu, Yuzhu; Knopp, Gregor; Qin, Chaochao; Gerber, Thomas

    2015-01-01

    Ultrafast internal conversion dynamics of furan has been studied by femtosecond photoelectron imaging (PEI) coupled with photofragmentation (PF) spectroscopy. Photoelectron imaging of single-color multi-photon ionization and two-color pump-probe ionization are obtained and analyzed. Photoelectron bands are assigned to the related states. The time evolution of the photoelectron signal by pump-probe ionization can be well described by a biexponential decay: two rapid relaxation pathways with time constants of ∼15 fs and 85 (±11) fs. The rapid relaxation is ascribed to the ultrafast internal conversion (IC) from the S2 state to the vibrationally hot S1 state. The second relaxation process is attributed to the redistributions and depopulation of secondarily populated high vibronic S1 state and the formation of α-carbene and β-carbene by H immigration. Additionally, the transient characteristics of the fragment ions are also measured and discussed as a complementary understanding.

  4. Signal-to-noise in femtosecond electron diffraction.

    PubMed

    Kealhofer, Catherine; Lahme, Stefan; Urban, Theresa; Baum, Peter

    2015-12-01

    Pump-probe electron diffraction can directly record atomic-scale motion within molecules or materials. However, the available current in femtosecond experiments is limited, making it challenging to reach the sensitivity required for detecting the fastest structural dynamics, which are encoded in time-dependent diffraction intensities. Here we present a unified analysis of signal-to-noise for an ultrafast electron diffraction apparatus. We characterize the noise of realistic ultrafast electron sources and detectors, test the performance on crystalline and polycrystalline samples and discuss practical approaches for improving measurement sensitivity. The analysis is found sufficient to predict the achievable signal-to-noise ratio in pump-probe electron diffraction before actually starting an investigation.

  5. Molecular imaging of endogenous and exogenous chromophores using ground state recovery pump-probe optical coherence tomography.

    PubMed

    Applegate, Brian E; Izatt, Joseph A

    2006-10-02

    We present a novel molecular imaging technique which combines the 3-D tomographic imaging capability of optical coherence tomography with the molecular sensitivity of pump-probe spectroscopy. This technique, based on transient absorption, is sensitive to any molecular chromophore. It is particularly promising for the many important biomarkers, such as hemoglobin, which are poor fluorophores and therefore difficult to image with current optical techniques without chemical labeling. Previous implementations of pump-probe optical coherence tomography have suffered from inefficient pump-probe schemes which hurt the sensitivity and applicability of the technique. Here we optimize the efficiency of the pump-probe approach by avoiding the steady-state kinetics and spontaneous processes exploited in the past in favor of measuring the transient absorption of fully allowed electronic transitions on very short time scales before a steady-state is achieved. In this article, we detail the optimization and characterization of the prototype system, comparing experimental results for the system sensitivity to theoretical predictions. We demonstrate in situ imaging of tissue samples with two different chromophores; the transfectable protein dsRed and the protein hemoglobin. We also demonstrate, with a simple sample vessel and a mixture of human whole blood and rhodamine 6G, the potential to use ground state recovery time to separate the contributions of multiple chromophores to the ground state recovery signal.

  6. Molecular imaging of endogenous and exogenous chromophores using ground state recovery pump-probe optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Applegate, Brian E.; Izatt, Joseph A.

    2006-10-01

    We present a novel molecular imaging technique which combines the 3-D tomographic imaging capability of optical coherence tomography with the molecular sensitivity of pump-probe spectroscopy. This technique, based on transient absorption, is sensitive to any molecular chromophore. It is particularly promising for the many important biomarkers, such as hemoglobin, which are poor fluorophores and therefore difficult to image with current optical techniques without chemical labeling. Previous implementations of pump-probe optical coherence tomography have suffered from inefficient pump-probe schemes which hurt the sensitivity and applicability of the technique. Here we optimize the efficiency of the pump-probe approach by avoiding the steady-state kinetics and spontaneous processes exploited in the past in favor of measuring the transient absorption of fully allowed electronic transitions on very short time scales before a steady-state is achieved. In this article, we detail the optimization and characterization of the prototype system, comparing experimental results for the system sensitivity to theoretical predictions. We demonstrate in situ imaging of tissue samples with two different chromophores; the transfectable protein dsRed and the protein hemoglobin. We also demonstrate, with a simple sample vessel and a mixture of human whole blood and rhodamine 6G, the potential to use ground state recovery time to separate the contributions of multiple chromophores to the ground state recovery signal.

  7. High efficiency photoionization detector

    DOEpatents

    Anderson, D.F.

    1984-01-31

    A high efficiency photoionization detector is described using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36 [+-] 0.02 eV, and a vapor pressure of 0.35 torr at 20 C. 6 figs.

  8. High efficiency photoionization detector

    DOEpatents

    Anderson, David F.

    1984-01-01

    A high efficiency photoionization detector using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36.+-.0.02 eV, and a vapor pressure of 0.35 torr at 20.degree. C.

  9. Photoionization of Ar VIII

    NASA Astrophysics Data System (ADS)

    Liang, Liang; Jiang, Wen-xian; Zhou, Chao

    2017-01-01

    The photoionization cross section, energy levels and widths of 22 Rydberg series (in the autoionization region) for Na-like Ar VIII were investigated by using of R-matrix method. The relativistic distorted-wave method is used to calculate the radial functions, and QB method of Quigly-Berrington [Quigley et al. 1998] is employed to calculate the resonance levels and widths. We have identified the formant in the figure of the photoionization cross section.

  10. Femtosecond Raman induced polarization spectroscopy studies of coherent rotational dynamics in molecular fluids

    SciTech Connect

    Morgen, Michael Mark

    1997-05-01

    We develop a polarization-sensitive femtosecond pump probe technique, Raman induced polarization spectroscopy (RIPS), to study coherent rotation in molecular fluids. By observing the collisional dephasing of the coherently prepared rotational states, we are able to extract information concerning the effects of molecular interactions on the rotational motion. The technique is quite sensitive because of the zero background detection method, and is also versatile due to its nonresonant nature.

  11. Control of femtosecond laser driven retro-Diels-Alder-like reaction of dicyclopentadiene

    NASA Astrophysics Data System (ADS)

    Das, Dipak Kumar; Goswami, Tapas; Goswami, Debabrata

    2010-12-01

    Using femtosecond time resolved degenerate pump-probe mass spectrometry coupled with simple linearly chirped frequency modulated pulse, we elucidate that the dynamics of retro-Diels-Alder reaction of diclopentadiene (DCPD) to cyclopentadiene (CPD) in supersonic molecular beam occurs in ultrafast time scale. Negatively chirped pulse enhances the ion yield of CPD, as compared to positively chirped pulse. This indicates that by changing the frequency (chirp) of the laser pulse we can control the ion yield of a chemical reaction.

  12. Dynamics of nanoscopic water: vibrational echo and infrared pump-probe studies of reverse micelles.

    PubMed

    Piletic, Ivan R; Tan, Howe-Siang; Fayer, M D

    2005-11-17

    The dynamics of water in nanoscopic pools 1.7-4.0 nm in diameter in AOT reverse micelles were studied with ultrafast infrared spectrally resolved stimulated vibrational echo and pump-probe spectroscopies. The experiments were conducted on the OD hydroxyl stretch of low-concentration HOD in the H2O, providing a direct examination of the hydrogen-bond network dynamics. Pump-probe experiments show that the vibrational lifetime of the OD stretch mode increases as the size of the reverse micelle decreases. These experiments are also sensitive to hydrogen-bond dissociation and reformation dynamics, which are observed to change with reverse micelle size. Spectrally resolved vibrational echo data were obtained at several frequencies. The vibrational echo data are compared to data taken on bulk water and on a 6 M NaCl solution, which is used to examine the role of ionic strength on the water dynamics in reverse micelles. Two types of vibrational echo measurements are presented: the vibrational echo decays and the vibrational echo peak shifts. As the water nanopool size decreases, the vibrational echo decays become slower. Even the largest nanopool (4 nm, approximately 1000 water molecules) has dynamics that are substantially slower than bulk water. It is demonstrated that the slow dynamics in the reverse micelle water nanopools are a result of confinement rather than ionic strength. The data are fit using time-dependent diagrammatic perturbation theory to obtain the frequency-frequency correlation function (FFCF) for each reverse micelle. The results are compared to the FFCF of water and show that the largest differences are in the slowest time scale dynamics. In bulk water, the slowest time scale dynamics are caused by hydrogen-bond network equilibration, i.e., the making and breaking of hydrogen bonds. For the smallest nanopools, the longest time scale component of the water dynamics is approximately 10 times longer than the dynamics in bulk water. The vibrational echo

  13. Control of wave packets in lithium dimers with a state-selected pump-probe scheme

    NASA Astrophysics Data System (ADS)

    Dai, Xingcan

    A state-selected pump-probe scheme is used to control wave packet dynamics in Li2. In this scheme, a cw laser selects one electronic transition from the thermally populated ground state to the launch state A1Sigmau+ of Li2, from which an ultrashort pump pulse creates a superstition state on the electronic states of Li2 followed by another ultrashort pulse to excite the wave packet to the ground state of Li2+. Usually, an unperturbed level at the A1Sigmau+ state of Li2 is selected by the cw laser pulses. However, if the level of A1Sigmau+ is perturbed by b3piu, and then the wave packets that consist of the triplet states as well as the singlet states of Li2 are detected from the mixed levels. Since one of the triplet states is predissociative, the fast decay of the amplitudes of the wave packets that have the components of this predissociative state is observed. In order to study coherent multiphoton processes, Raman wave packets are created and manipulated with a pulse shaping system. The phase difference between the amplitude coefficients induced by resonant and off-resonant Raman transitions is shown directly by comparing the phases of the Raman wave packets excited by the resonant and off-resonant Raman transitions. The ionization processes employed in the probe step of the state-selective pump-probe scheme is fully explored in the second pulse shaping system in the path of the probe beam. It shows that the direct transitions from the electronic states involved in the wave packets are unlikely; while the autoionization and collision induced ionization from highly-excited Rydberg states are the main sources of the final ion signals. Some degree of the control of the wave packet dynamics is realized by shaping the probe pulses. The decoherence rates of quantum beats at the shelf region of the E1Sigma g+ state are measured to test theoretical results about pure dephasing rate in Li2. Finally, some schemes and preliminary results on physical realization of quantum

  14. Ultrafast pump-probe spectroscopy of the photoreceptor stentorins from the ciliate stentor coeruleus

    SciTech Connect

    Savikhin, S.; Struve, W.S. ); Tao, N.; Song, P.S. )

    1993-11-25

    Polarized absorption difference profiles have been obtained with 3-6-ps resolution between 565 and 630 nm for the chromoproteins stentorin I and stentorin II, isolated from the protozoan ciliate Stentor coeruleus. Control experiments were performed on hypericin and on the stentorin chromophore in methanol. The isotropic decays of stentorin I and the stentorin chromophore are dominated by components with lifetimes conservatively longer than 1 ns. Stentorin I, the stentorin chromophore, and hypericin all develop, within <5 ps, an intense excited-state absorption band that is blue-shifted from and polarized essentially perpendicular to the main long-wavelength absorption band. The presence of this excited-state absorption band is signaled by the appearance of strongly wavelength-dependent initial anisotropies r(0), which assume large positive as well as negative values (>0.4 and <[minus]0.2). To our knowledge, such anisotropies have not been reported in polarized pump-probe studies of rotational diffusion in solution or of energy-transfer kinetics in photosynthetic antennae. Hypericin itself exhibits 0.4-6-ps excited-state absorption decay kinetics, which are likely associated with intramolecular excited-state proton transfer. 19 refs., 8 figs., 5 tabs.

  15. Photoexcited State Molecular Structures in Solution Studied by Pump-Probe XAFS

    NASA Astrophysics Data System (ADS)

    Chen, Lin

    2002-03-01

    The photoexcitation causes displacement of electron densities within or among molecules, which consequently leads to nuclear movements. Such nuclear displacements often occur in transient states with short lifetimes. Knowing transient molecular structures during photochemical reactions is important for understanding fundamental aspects of solar energy conversion and storage. Fast x-ray techniques provide direct probes for these transient structures. Using x-ray pulses from the Advanced Photon Source at Argonne, a laser pulse pump, x-ray pulse probe XAFS technique has been developed to capture transient molecular structures in disordered media with nanosecond time resolution. We have carried out several pump-probe XAFS measurements on 1)identifying a transient molecular structure of the photodissociation product of nickel-tetraphenylporphyrin with piperidine axial ligands (NiTPP-L2); 2)determination of the MLCT state structure of Bis(2,9-dimethyl-1,10-phenanthroline) Copper(I) [Cu(I)(dmp)2]+, and 3) triplet state molecular structures of metalloporphyrins. These studies not only prove the feasibility of the technique, but also gain structural information that otherwise will not be available. Future studies include probing transient structures in electron donor-acceptor complexes and optical polarization selected XAFS (OPS-XAFS) using the same technique with a 100-ps time resolution. This work is supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, U. S. Department of Energy, under contract W-31-109-Eng-38.

  16. Nematicity in FeSe single crystals probed by pump-probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Luo, C. W.; Cheng, P. C.; Wu, K. H.; Juang, J. Y.; Wang, S.-H.; Chiang, J.-C.; Lin, J.-Y.; Chareev, D. A.; Volkova, O. S.; Vasiliev, A. N.

    The anisotropic quasiparticle dynamics in FeSe single crystals have been studied by polarized pump-probe spectroscopy. Two distinguishable relaxation components were unambiguously observed in transient reflectivity changes (ΔR / R) . The orientation-dependent fast component with the timescale of 0.1-1.5 ps associated with the electronic structure clearly shows two-fold symmetry, which further reveals the gap opening along ky below the temperature of structure phase transition (Ts) and the electronic nematicity can persist up to 200 K. For the slow component with the timescale of 8-25 ps, it is assigned to the energy relaxation through spin sub-system and also shows a two-fold symmetry below Ts. However, this two-fold symmetry is dramatically weakened above Ts and surprisingly persists up to at least 200 K. Consequently, the high-temperature nematic fluctuations in FeSe may be driven by the order parameters which associated with both charge (orbital) and spin sub-systems. This project is financially sponsored by the MOST, Taiwan, (Grants No. 103-2923-M-009-001-MY3) and the MOE-ATU plan at NCTU.

  17. Pump-probe optical coherence tomography using microencapsulated methylene blue as a contrast agent (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Kim, Wihan; Zebrowski, Erin; Lopez, Hazel C.; Applegate, Brian E.; Charoenphol, Phapanin; Jo, Javier A.

    2016-03-01

    Molecular contrast imaging can target specific molecules or receptors to provide detailed information on the local biochemistry and yield enhanced visualization of pathological and physiological processes. When paired with Optical Coherence Tomography (OCT) it can simultaneously supply the morphological context for the molecular information. We recently demonstrated in vivo molecular contrast imaging of methylene blue (MB) using a 663 nm diode laser as a pump in a Pump-Probe OCT (PPOCT) system. The simple addition of a dichroic mirror in the sample arm enabled PPOCT imaging with a typical 830-nm band spectral-domain OCT system. Here we report on the development of a microencapsulated MB contrast agent. The poly lactic-co-glycolic acid (PLGA) microspheres loaded with MB offer several advantages over bare MB. The microsphere encapsulation improves the PPOCT signal both by enhancing the scattering and preventing the reduction of MB to leucomethylene blue. The surface of the microsphere can readily be functionalized to enable active targeting of the contrast agent without modifying the excited state dynamics of MB that enable PPOCT imaging. Both MB and PLGA are used clinically. PLGA is FDA approved and used in drug delivery and tissue engineering applications. 2.5 μm diameter microspheres were synthesized with an inner core containing 0.01% (w/v) aqueous MB. As an initial demonstration the MB microspheres were imaged in a 100 μm diameter capillary tube submerged in a 1% intralipid emulsion.

  18. Velocity anisotropy effect in pump-probe spectra of cesium in a micrometric thickness optical cell

    NASA Astrophysics Data System (ADS)

    Ghosh, P. N.; Mitra, S.; Ray, B.; Krasteva, A.; Slavov, D.; Todorov, P.; Cartaleva, S.

    2015-01-01

    The pump-probe spectra in a cell of micrometric thickness containing cesium vapor are reported. The line shape and nonlinear features observed in the case of fluorescence in the direction parallel to the cell windows and the transmission spectra observed along the propagation direction of the probe beam show considerable differences in the spectral profiles. We observed Electromagnetically Induced Transparency (EIT) and enhanced Velocity Selective Optical Pumping (VSOP) signals. Atoms moving nearly parallel to the windows and perpendicular to the collinear pump and probe beams will see much lower Doppler shift of incident frequencies and hence will lead to considerable narrowing of the Doppler background in the fluorescence spectra. The coherence decay rate is also low for such atoms as they do not meet with the cell walls. A theoretical model based on five level optical Bloch equations is used to simulate the spectra. The Doppler convolution includes all possible orientation of atomic velocities with respect to the laser beam direction. The simulated curves reproduce the observed sharp EIT peaks and enhanced broad VSOP signals for the closed probe transition in the fluorescence and absorption spectra. The observed effect of the light intensity and temperature change on the non-linear features is reproduced by the simulation.

  19. Ultrafast Pump-Probe Study of Halide Dependence in Primary Reaction Dynamics of Halorhodopsin

    NASA Astrophysics Data System (ADS)

    Nakamura, Takumi; Takeuchi, Satoshi; Shibata, Mikihiro; Kandori, Hideki; Tahara, Tahei

    2007-03-01

    Halorhodopsin is a retinal protein in Haloarchaeal cell membrane. The light-induced all-trans to 13-cis isomerization of the retinal chromophore triggers unidirectional chloride-ion pump in millisecond timescale. Here, we present pump-probe study of the primary ultrafast dynamics of Natronobacterium pharaonis halorhodopsin that contains Cl^-, Br^- or I^-. All the temporal behaviors of the S1 absorption, ground-state bleaching, and stimulated emission consisted of three components, and their time constants showed halide-ion dependency. The ˜50-fs component corresponds to the spectral shift of the S1 absorption and stimulated emission bands, which is due to the wavepacket motion from the Franck-Condon region, forming the reactive and nonreactive S1 states. Referring to previous reports, the ˜2-ps component is assignable to the isomerization process from the reactive S1 state to the ground-state 13-cis form via the conical intersection, while the ˜5-ps component to the internal conversion of the nonreactive S1 state. Quantitative analysis indicated that the isomerization quantum yield increased in order of Cl^-, Br^- and I^-. On the basis of the halide-ion dependence observed, we discuss the relation between the initial halide-ion pump process and the isomerization mechanism.

  20. Indirect monitoring shot-to-shot shock waves strength reproducibility during pump-probe experiments

    NASA Astrophysics Data System (ADS)

    Pikuz, T. A.; Faenov, A. Ya.; Ozaki, N.; Hartley, N. J.; Albertazzi, B.; Matsuoka, T.; Takahashi, K.; Habara, H.; Tange, Y.; Matsuyama, S.; Yamauchi, K.; Ochante, R.; Sueda, K.; Sakata, O.; Sekine, T.; Sato, T.; Umeda, Y.; Inubushi, Y.; Yabuuchi, T.; Togashi, T.; Katayama, T.; Yabashi, M.; Harmand, M.; Morard, G.; Koenig, M.; Zhakhovsky, V.; Inogamov, N.; Safronova, A. S.; Stafford, A.; Skobelev, I. Yu.; Pikuz, S. A.; Okuchi, T.; Seto, Y.; Tanaka, K. A.; Ishikawa, T.; Kodama, R.

    2016-07-01

    We present an indirect method of estimating the strength of a shock wave, allowing on line monitoring of its reproducibility in each laser shot. This method is based on a shot-to-shot measurement of the X-ray emission from the ablated plasma by a high resolution, spatially resolved focusing spectrometer. An optical pump laser with energy of 1.0 J and pulse duration of ˜660 ps was used to irradiate solid targets or foils with various thicknesses containing Oxygen, Aluminum, Iron, and Tantalum. The high sensitivity and resolving power of the X-ray spectrometer allowed spectra to be obtained on each laser shot and to control fluctuations of the spectral intensity emitted by different plasmas with an accuracy of ˜2%, implying an accuracy in the derived electron plasma temperature of 5%-10% in pump-probe high energy density science experiments. At nano- and sub-nanosecond duration of laser pulse with relatively low laser intensities and ratio Z/A ˜ 0.5, the electron temperature follows Te ˜ Ilas2/3. Thus, measurements of the electron plasma temperature allow indirect estimation of the laser flux on the target and control its shot-to-shot fluctuation. Knowing the laser flux intensity and its fluctuation gives us the possibility of monitoring shot-to-shot reproducibility of shock wave strength generation with high accuracy.

  1. Probing ultrafast molecular dynamics in O2 using XUV/IR pump-probe studies

    NASA Astrophysics Data System (ADS)

    Ray, D.; Sturm, F. P.; Wright, T. W.; Ranitovic, P.; Shivaram, N. H.; Bocharova, I.; Belkacem, A.; Weber, Th.

    2015-05-01

    We investigate the molecular dynamics via different dissociative and autoionizing pathways in molecular oxygen using a pump-probe scheme with ultrashort extreme ultraviolet (XUV) laser pulses. Our primary focus is to study the molecular dynamics in the superexcited Rydberg states in a time-resolved manner. The O2 molecules are pumped by 20.2 eV and 23.1 eV XUV pulses (13th and 15th harmonics). Probing the relaxation dynamics with an infrared (IR) pulse at very long delays (100s of fs) enables us to measure the lifetimes of these Rydberg states. We also observe an enhancement and suppression of vibrational levels of the O2+ion due to the presence of IR. The high flux XUV pulses used for this experiment are generated in an Ar gas by IR pulses from our state-of-the-art 30 mJ, 50 Hz laser system. The pulses are overlapped with the supersonic jet in our Momentum Imaging for TimE Resolved Studies (MISTERS) setup. The cold target in our setup, combined with a very tight focussing geometry and a 3D momentum detection capability gives a high kinetic energy resolution. Molecular dynamics in other polyatomic molecules are also under investigation. Chemical Sciences Division, Lawrence Berkeley National Laboratory.

  2. A wide-range model for simulation of pump-probe experiments with metals

    NASA Astrophysics Data System (ADS)

    Povarnitsyn, Mikhail E.; Andreev, Nikolay E.; Apfelbaum, Eugeny M.; Itina, Tatiana E.; Khishchenko, Konstatntin V.; Kostenko, Oleg F.; Levashov, Pavel R.; Veysman, Mikhail E.

    2012-09-01

    High precision pump-probe experiments can provide a valuable information about material states out of equilibrium. A wide-range numerical model is used for the description of material response on ultrashort laser action. The model is developed on the basis of two-temperature hydrodynamics with heat transport, ionization, plasma expansion, electron-ion collisions and two-temperature equation of state for an irradiated substance. Comparison of experimental findings with the results of simulation is used both for the numerical model verification and for calculation of plasma thermodynamic parameters that cannot be measured directly in experiment. An aluminum target is heated by an intense 400 nm (2ω) pump laser pulse that is incident normal to the planar target. Weak S- and P-polarized probe pulses with wavelength 800 nm (1ω) are used for diagnostics of the plasma. Both probe pulses illuminate the target at a 45° angle. Calculation of the reflectivity and phase shift of probe pulses with both polarizations are in good agreement with experiment.

  3. Infrared-x-ray pump-probe spectroscopy of the NO molecule

    SciTech Connect

    Guimaraes, F.F.; Felicissimo, V.C.; Kimberg, V.; Gel'mukhanov, F.; Aagren, H.; Cesar, A.

    2005-07-15

    Two color infrared-x-ray pump-probe spectroscopy of the NO molecule is studied theoretically and numerically in order to obtain a deeper insight of the underlying physics and of the potential of this suggested technology. From the theoretical investigation a number of conclusions could be drawn: It is found that the phase of the infrared field strongly influences the trajectory of the nuclear wave packet, and hence, the x-ray spectrum. The trajectory experiences fast oscillations with the vibrational frequency with a modulation due to the anharmonicity of the potential. The dependences of the x-ray spectra on the delay time, the duration, and the shape of the pulses are studied in detail. It is shown that the x-ray spectrum keep memory about the infrared phase after the pump field left the system. This memory effect is sensitive to the time of switching-off the pump field and the Rabi frequency. The phase effect takes maximum value when the duration of the x-ray pulse is one-fourth of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The manifestation of the phase is different for oriented and disordered molecules and depends strongly on the intensity of the pump radiation.

  4. Plasmonic "pump-probe" method to study semi-transparent nanofluids.

    PubMed

    Hewakuruppu, Yasitha L; Dombrovsky, Leonid A; Chen, Chuyang; Timchenko, Victoria; Jiang, Xuchuan; Baek, Sung; Taylor, Robert A

    2013-08-20

    Nanofluids have been increasingly used in a wide range of thermal applications. Although these applications can benefit greatly from investigating the behavior of nanoparticles under different heating scenarios, there is a lack of experiments that can achieve this. To overcome this challenge, an optical "pump-probe"-type experiment is suggested in this paper. In experiments of this type, a set of "pumping" nanoparticles are specifically selected to absorb laser radiation. These particles represent a flexible tool for volumetric heating. A second set of "probing" nanoparticles can be tailored to scatter a separate optical probing signal. This work presents a selection procedure for nanoparticles of both types. The selection procedure is then demonstrated for a specific example where the pump and probe wavelengths are of 980 and 532 nm, respectively. Gold nanorods with diameters of 10 and a length of 58 nm are selected as the "most suitable" absorbing particles, while silver nanospheres with a diameter of 110 nm are selected as the "most suitable" scattering particles. These particles are synthesized and shown to experimentally match the desired optical properties. Overall, this paper proposes and demonstrates an approach by which it is possible to design and fabricate particles for a wide range of optical studies in semi-transparent nanofluids.

  5. Hyperfine Quantum Beat Spectroscopy of the Cs 8p level with Pulsed Pump-Probe Technique

    NASA Astrophysics Data System (ADS)

    Bayram, Burcin; Popov, Oleg; Kelly, Stephen; Boyle, Patrick; Salsman, Andrew

    2013-05-01

    Quantum beats arising from the hyperfine interaction were measured in a three-level excitation (lambda) scheme: pump for the 6s2S1 / 2 --> 8p2P3 / 2 and stimulated emission pump (probe) for the 8p2P3 / 2 --> 5d2D5 / 2 transitions of atomic cesium. In the technique, pump laser instantaneously excites the hot atomic vapor and creates anisotropy in the 8p2P3 / 2 level, and probe laser comes after some time delay. Delaying the probe time allows us to map out the motion of the polarized atoms like a stroboscope. According to the observed evolution of the hyperfine structure dependent parameters, e.g. alignment and atomic polarization, by delaying the arrival time of the stimulated emission pump laser (SEP), precise values of the magnetic dipole and electric quadrupole coefficients are obtained with an improved precision over previous results. The usefulness of the PUMP-SEP excitation scheme for the polarization hyperfine quantum beat measurements without complications from the Doppler effect will also be discussed. The financial support of the Research Corporation under the Grant number CC7133 and MiamiUniversity, College of the Arts and Sciences are acknowledged.

  6. Discriminating Bio-aerosols from Non-Bio-aerosols in Real-Time by Pump-Probe Spectroscopy

    PubMed Central

    Sousa, Gustavo; Gaulier, Geoffrey; Bonacina, Luigi; Wolf, Jean-Pierre

    2016-01-01

    The optical identification of bioaerosols in the atmosphere and its discrimination against combustion related particles is a major issue for real-time, field compatible instruments. In the present paper, we show that by embedding advanced pump-probe depletion spectroscopy schemes in a portable instrument, it is possible to discriminate amino acid containing airborne particles (bacteria, humic particles, etc.) from poly-cyclic aromatic hydrocarbon containing combustion particles (Diesel droplets, soot, vehicle exhausts) with high selectivity. Our real-time, multi-modal device provides, in addition to the pump-probe depletion information, fluorescence spectra (over 32 channels), fluorescence lifetime and Mie scattering patterns of each individually flowing particle in the probed air. PMID:27619546

  7. SOA gain recovery wavelength dependence: simulation and measurement using a single-color pump-probe technique.

    PubMed

    Mathlouthi, W; Vacondio, F; Lemieux, P; Rusch, Leslie A

    2008-12-08

    Measurements to date of the wavelength dependency of gain recovery time in semiconductor optical amplifiers (SOAs) have mostly used pump-probe techniques with a pump and probe operated on distinct wavelengths. Choice of pump wavelength, and its relative proximity to the probe wavelength, could influence measurements and impede unambiguous observation of wavelength dependence on recovery dynamics. We use a single-color pump-probe measurement technique to directly access the wavelength dependence of the gain recovery time in bulk InGaAsP SOAs. We used ultrashort pulses from a single mode locked laser to measure unambiguously the spectral dependency and temporal behavior of SOAs. Simulation results using a model that takes into account intra-band and inter-band contributions to SOA saturation, as well as experimental results for the SOA tested, show recovery rate dependency similar to gain spectrum.

  8. Discriminating Bio-aerosols from Non-Bio-aerosols in Real-Time by Pump-Probe Spectroscopy

    NASA Astrophysics Data System (ADS)

    Sousa, Gustavo; Gaulier, Geoffrey; Bonacina, Luigi; Wolf, Jean-Pierre

    2016-09-01

    The optical identification of bioaerosols in the atmosphere and its discrimination against combustion related particles is a major issue for real-time, field compatible instruments. In the present paper, we show that by embedding advanced pump-probe depletion spectroscopy schemes in a portable instrument, it is possible to discriminate amino acid containing airborne particles (bacteria, humic particles, etc.) from poly-cyclic aromatic hydrocarbon containing combustion particles (Diesel droplets, soot, vehicle exhausts) with high selectivity. Our real-time, multi-modal device provides, in addition to the pump-probe depletion information, fluorescence spectra (over 32 channels), fluorescence lifetime and Mie scattering patterns of each individually flowing particle in the probed air.

  9. Discriminating Bio-aerosols from Non-Bio-aerosols in Real-Time by Pump-Probe Spectroscopy.

    PubMed

    Sousa, Gustavo; Gaulier, Geoffrey; Bonacina, Luigi; Wolf, Jean-Pierre

    2016-09-13

    The optical identification of bioaerosols in the atmosphere and its discrimination against combustion related particles is a major issue for real-time, field compatible instruments. In the present paper, we show that by embedding advanced pump-probe depletion spectroscopy schemes in a portable instrument, it is possible to discriminate amino acid containing airborne particles (bacteria, humic particles, etc.) from poly-cyclic aromatic hydrocarbon containing combustion particles (Diesel droplets, soot, vehicle exhausts) with high selectivity. Our real-time, multi-modal device provides, in addition to the pump-probe depletion information, fluorescence spectra (over 32 channels), fluorescence lifetime and Mie scattering patterns of each individually flowing particle in the probed air.

  10. Surface phonon coupling within boron nitride resolved by a novel near-field infrared pump-probe imaging technique

    NASA Astrophysics Data System (ADS)

    Gilburd, Leonid; Xu, Xiaoji G.; de Beer, Sissi; Bando, Yoshio; Golberg, Dmitri; Walker, Gilbert C.

    2016-09-01

    The excitation of surface phonon-polariton (SPhP) modes in polar materials using scattering type near-field optical microscopy (s-SNOM) has recently become an area of interest because of its potential for application as naturally occurring meta-materials and in low-loss energy transfer. Within this area, hexagonal boron nitride (h-BN) and boron nitride nanotubes (BNNTs) are the primary structures under investigation. Here we present pump-probe continuous wave (CW) scattering-type scanning near-field optical microscopy (s-SNOM) - a novel two color pump-probe infrared technique which uses two continuous wave tunable light sources and is based on s-SNOM. The technique allows us to spatially resolve coupling of the longitudinal optical and surface phonon polariton modes in BNNTs. However, no similar coupling is observed in two-dimensional h-BN crystals.

  11. BOTDA sensing system employing a tunable low-cost Brillouin fiber ring laser pump-probe source

    NASA Astrophysics Data System (ADS)

    Iuliano, M.; Marini, D.; Bastianini, F.; Bolognini, G.

    2017-04-01

    In this paper we show a Brillouin optical time-domain analysis (BOTDA) sensing system experiment employing a tunable narrow-linewidth dual pump-probe source based on modified Brillouin ring laser technology. The developed cost-effective source generates a pump-locked and tunable probe light, with wavelength shift and a large tuning range ( 200 MHz), narrow linewidth (<2.5 MHz) and adequate power ( 0.5 mW). The developed source was hence employed in BOTDA system experiments providing distributed sensing over 10 km single mode optical fiber, and attaining strain and temperature resolutions of 10μɛ and 0.5 °C respectively, indicating the pump-probe source as an efficient and cost-effective solution for BOTDA avoiding high-frequency signal generators or complex locking techniques.

  12. In vivo pump-probe microscopy of melanoma: characterizing shifts in excited state photodynamics with respect to invasiveness

    NASA Astrophysics Data System (ADS)

    Wilson, Jesse W.; Degan, Simone; Gainey, Christina S.; Deb, Sanghamitra; Dall, Christopher P.; Tameze-Rivas, Yasmine; Zhang, Jennifer; Warren, Warren S.

    2015-03-01

    Pump-probe microscopy is a multiphoton technique that generates molecular contrast from absorptive pigments, such as melanin. It holds the potential to be used as a non-invasive screening tool to discern whether a given early-stage melanoma has acquired the capacity for metastasis. Here, we examined lesions in a Braf(V600E)-driven model of melanoma to assess whether loss of the tumor suppressor gene Pten in a is accompanied by a shift in pigment expression, as measured in vivo by pump-probe microscopy. The data were analyzed to determine differences in the excited-state lifetime of melanins expressed in Pten-competent and Pten-loss pigmented lesions. Loss of the tumor suppressor Pten was found to be accompanied by a statistically significant decrease in pixel-average excited state lifetime (p = 1.3e-4).

  13. Photoionization and Recombination

    NASA Technical Reports Server (NTRS)

    Nahar, Sultana N.

    2000-01-01

    Theoretically self-consistent calculations for photoionization and (e + ion) recombination are described. The same eigenfunction expansion for the ion is employed in coupled channel calculations for both processes, thus ensuring consistency between cross sections and rates. The theoretical treatment of (e + ion) recombination subsumes both the non-resonant recombination ("radiative recombination"), and the resonant recombination ("di-electronic recombination") processes in a unified scheme. In addition to the total, unified recombination rates, level-specific recombination rates and photoionization cross sections are obtained for a large number of atomic levels. Both relativistic Breit-Pauli, and non-relativistic LS coupling, calculations are carried out in the close coupling approximation using the R-matrix method. Although the calculations are computationally intensive, they yield nearly all photoionization and recombination parameters needed for astrophysical photoionization models with higher precision than hitherto possible, estimated at about 10-20% from comparison with experimentally available data (including experimentally derived DR rates). Results are electronically available for over 40 atoms and ions. Photoionization and recombination of He-, and Li-like C and Fe are described for X-ray modeling. The unified method yields total and complete (e+ion) recombination rate coefficients, that can not otherwise be obtained theoretically or experimentally.

  14. In-line femtosecond common-path interferometer in reflection mode.

    PubMed

    Chandezon, J; Rampnoux, J-M; Dilhaire, S; Audoin, B; Guillet, Y

    2015-10-19

    An innovative method to perform femtosecond time-resolved interferometry in reflection mode is proposed. The experiment consists in the combined use of a pump-probe setup and of a fully passive in-line femtosecond common-path interferometer. The originality of this interferometer relies on the use of a single birefringent crystal first to generate a pair of phase-locked pulses and second to recombine them to interfere. As predicted by analytical modeling, this interferometer measures the temporal derivative of the ultrafast changes of the complex optical reflection coefficient of the sample. Working conditions are illustrated through picosecond opto-acoustic experiments on a thin film.

  15. Pump-probe microscopy of respiratory chain pigments: towards non-fluorescent label-free metabolic imaging

    NASA Astrophysics Data System (ADS)

    Domingue, Scott R.; Chicco, Adam J.; Bartels, Randy A.; Wilson, Jesse W.

    2017-02-01

    Current label-free metabolic microscopy techniques are limited to obtaining contrast from fluorescent molecules NAD(P)H and FAD+, and are unable to determine redox state along the mitochondrial respiratory chain itself. The respiratory chain electron carriers do not fluoresce, but some are heme proteins that have redox-dependent absorption spectra. The most prominent of these, cytochrome c, has been extensively characterized by transient absorption spectroscopy, which suggests that pump-probe measurements in the vicinity of 450 - 600 nm can provide strong contrast between its redox states. Motivated by the success of pump-probe microscopy targeting another heme protein, hemoglobin, we seek to extend the technique to the cytochromes, with the ultimate goal of dissecting respiratory chain function of individual cells in live tissue. To that end, we have developed a new optical system producing ultrafast, visible, independently-tunable pulse pairs via sum-frequency generation of nonlinearly broadened pulses in periodically-poled lithium niobate. The system is pumped by a homebuilt fiber-based oscillator/amplifier emitting 1060 nm pulses at 1.3 W (63 MHz repetition rate), and produces tunable pulses in the vicinity of 488 and 532 nm. Pump-probe spectroscopy of cytochrome c with this source reveals differences in excited-state absorption relaxation times between redox states. Though redox contrast is weak with this setup, we argue that this can be improved with a resonant galvo-scanning microscope. Moreover, pump-probe images were acquired of brown adipose tissue (which contains dense mitochondria), demonstrating label-free contrast from excited-state absorption in respiratory chain hemes.

  16. Measurement of femtosecond atomic lifetimes using ion traps

    NASA Astrophysics Data System (ADS)

    Träbert, Elmar

    2014-01-01

    Two types of experiment are described that both employ an electron beam ion trap for the production of highly charged ion species with the aim of then measuring atomic level lifetimes in the femtosecond range. In one experiment (done by Beiersdorfer et al. some time ago), the lifetime measurement depends on the associated line broadening. In a recent string of experiments at Linac Coherent Light Source Stanford, the HI-LIGHT collaboration employed pump-probe excitation using the FEL as a short-pulse X-ray laser.

  17. Formation of protonated ammonia clusters probed by a femtosecond laser

    SciTech Connect

    Purnell, J.; Wei, S.; Buzza, S.A.; Castleman, A.W. Jr. )

    1993-12-02

    Femtosecond pump-probe techniques combined with a reflection time-of-flight mass spectrometer are employed to investigate the formation mechanisms of protonated ammonia clusters. Pump pulses are employed to excite the ammonia clusters to electronically excited states corresponding to selected A or C' states, while probe pulses with variable delay times are used to ionize the clusters. The results reveal that both the absorption-ionization-dissociation and absorption-dissociation-ionization mechanisms occur in the A state, while the absorption-ionization-dissociation mechanism is the sole one operative in the C' state. 23 refs., 7 figs.

  18. Single laser based pump-probe technique to study plasma shielding during nanosecond laser ablation of copper thin films

    NASA Astrophysics Data System (ADS)

    Nammi, Srinagalakshmi; Vasa, Nilesh J.; Gurusamy, Balaganesan; Mathur, Anil C.

    2017-09-01

    A plasma shielding phenomenon and its influence on micromachining is studied experimentally and theoretically for laser wavelengths of 355 nm, 532 nm and 1064 nm. A time resolved pump-probe technique is proposed and demonstrated by splitting a single nanosecond Nd3+:YAG laser into an ablation laser (pump laser) and a probe laser to understand the influence of plasma shielding on laser ablation of copper (Cu) clad on polyimide thin films. The proposed nanosecond pump-probe technique allows simultaneous measurement of the absorption characteristics of plasma produced during Cu film ablation by the pump laser. Experimental measurements of the probe intensity distinctly show that the absorption by the ablated plume increases with increase in the pump intensity, as a result of plasma shielding. Theoretical estimation of the intensity of the transmitted pump beam based on the thermo-temporal modeling is in qualitative agreement with the pump-probe based experimental measurements. The theoretical estimate of the depth attained for a single pulse with high pump intensity value on a Cu thin film is limited by the plasma shielding of the incident laser beam, similar to that observed experimentally. Further, the depth of micro-channels produced shows a similar trend for all three wavelengths, however, the channel depth achieved is lesser at the wavelength of 1064 nm.

  19. Label-Free Imaging of Female Genital Tract Melanocytic Lesions With Pump-Probe Microscopy: A Promising Diagnostic Tool

    PubMed Central

    Robles, Francisco E.; Deb, Sanghamitra; Fischer, Martin C.; Warren, Warren S.; Selim, Maria Angelica

    2017-01-01

    Objectives Melanomas of the female genital tract present a unique clinical challenge. Not only are these lesions in an anatomically sensitive area, but also they tend to be multifocal and have high recurrence rates. Furthermore, several benign melanocytic proliferations resemble early-stage melanoma clinically and/or histopathologically. Thus, there is a significant need for additional tools that can help correctly diagnose and stage these lesions. Here, we quantitatively and nondestructively analyze the chemical composition of melanin in excised pigmented lesions of the female genital tract using pump-probe microscopy, a high-resolution optical imaging technique that is sensitive to many biochemical properties of melanin. Materials and Methods Thirty-one thin (~5 μm) tissue sections previously excised from female genital tract melanocytic lesions were imaged with pump-probe microscopy and analyzed. Results We find significant quantitative differences in melanin type and structure between melanoma and nonmalignant melanocytic proliferations. Our analysis also suggests a link between the molecular signatures of melanins and lesion-specific genetic mutations. Finally, significant differences are found between metastatic and nonmetastatic melanomas. The limitations of this work include the fact that molecular information is restricted to melanin pigment and the sample size is relatively small. Conclusions Pump-probe microscopy provides unique information regarding the biochemical composition of genital tract melanocytic lesions, which can be used to improve the diagnosis and staging of vulvar melanomas. PMID:28157824

  20. The polarization anisotropy of vibrational quantum beats in resonant pump-probe experiments: Diagrammatic calculations for square symmetric molecules.

    PubMed

    Farrow, Darcie A; Smith, Eric R; Qian, Wei; Jonas, David M

    2008-11-07

    By analogy to the Raman depolarization ratio, vibrational quantum beats in pump-probe experiments depend on the relative pump and probe laser beam polarizations in a way that reflects vibrational symmetry. The polarization signatures differ from those in spontaneous Raman scattering because the order of field-matter interactions is different. Since pump-probe experiments are sensitive to vibrations on excited electronic states, the polarization anisotropy of vibrational quantum beats can also reflect electronic relaxation processes. Diagrammatic treatments, which expand use of the symmetry of the two-photon tensor to treat signal pathways with vibrational and vibronic coherences, are applied to find the polarization anisotropy of vibrational and vibronic quantum beats in pump-probe experiments for different stages of electronic relaxation in square symmetric molecules. Asymmetric vibrational quantum beats can be distinguished from asymmetric vibronic quantum beats by a pi phase jump near the center of the electronic spectrum and their disappearance in the impulsive limit. Beyond identification of vibrational symmetry, the vibrational quantum beat anisotropy can be used to determine if components of a doubly degenerate electronic state are unrelaxed, dephased, population exchanged, or completely equilibrated.

  1. Flash-photoionized nebulae

    NASA Technical Reports Server (NTRS)

    Katz, J. I.

    1989-01-01

    Under conditions of high radiation intensity and low gas density, recombination may be neglected in determining the ionization state of a photoionized gas. Calculations of the ionization structure of nebulae in this 'flash-photoionized' regime are reported. Very hard spectra of ionizing ultraviolet radiation may be produced by filtration of the ionizing flux through a neutral hydrogen layer which preferentially absorbs photons just above the hydrogen photoionization threshold. Fluxes with these hard spectra produce gas layer in which helium is largely doubly ionized while hydrogen is largely neutral. Such a layer leads to anomalously high ratios of He II to H I recombination line strengths. These results are applied to the problem of the spectrum of the arc in the cluster of galaxies A370. It is found that the spectrum may possibly be reconciled with the light echo model.

  2. Flash-photoionized nebulae

    SciTech Connect

    Katz, J.I.

    1989-05-01

    Under conditions of high radiation intensity and low gas density, recombination may be neglected in determining the ionization state of a photoionized gas. Calculations of the ionization structure of nebulae in this 'flash-photoionized' regime are reported. Very hard spectra of ionizing ultraviolet radiation may be produced by filtration of the ionizing flux through a neutral hydrogen layer which preferentially absorbs photons just above the hydrogen photoionization threshold. Fluxes with these hard spectra produce gas layer in which helium is largely doubly ionized while hydrogen is largely neutral. Such a layer leads to anomalously high ratios of He II to H I recombination line strengths. These results are applied to the problem of the spectrum of the arc in the cluster of galaxies A370. It is found that the spectrum may possibly be reconciled with the light echo model. 25 refs.

  3. Double Photoionization Near Threshold

    NASA Technical Reports Server (NTRS)

    Wehlitz, Ralf

    2007-01-01

    The threshold region of the double-photoionization cross section is of particular interest because both ejected electrons move slowly in the Coulomb field of the residual ion. Near threshold both electrons have time to interact with each other and with the residual ion. Also, different theoretical models compete to describe the double-photoionization cross section in the threshold region. We have investigated that cross section for lithium and beryllium and have analyzed our data with respect to the latest results in the Coulomb-dipole theory. We find that our data support the idea of a Coulomb-dipole interaction.

  4. A novel electro-optical pump-probe system for bioelectromagnetic investigations

    NASA Astrophysics Data System (ADS)

    De Angelis, Annalisa; Couderc, Vincent; Leproux, Philippe; Labruyère, Alexis; Tonello, Alessandro; El Amari, Saad; Arnaud-Cormos, Delia; Leveque, Philippe

    2012-10-01

    In the area of bioelectromagnetic studies there is a growing interest to understand the mechanisms leading to nanosecond electric fields induced electroporation. Real-time imaging techniques at molecular level could probably bring further advances on how electric fields interact with living cells. However the investigations are limited by the present-day lack of these kinds of advanced instrumentations. In this context, we present an innovative electro-optical pump-probe system. The aim of our project is to provide a performing and compact device for electrical stimulation and multiplex Coherent anti-Stokes Raman Scattering (M-CARS) imaging of biological cells at once. The system consists of a 1064 nm sub-nanosecond laser source providing both a monochromatic pump and a polychromatic Stokes optical beam used in a CARS process, as well as the trigger beam for the optoelectronic switching-based electrical pulse generator. The polychromatic Stokes beam (from 600 to 1700 nm) results from a supercontinuum generation in a photonic crystal fiber (PCF). A detailed spectro-temporal characterization of such a broadband spectrum shows the impact of the nonlinear propagation in the fiber on the Stokes wave. Despite the temporal distortions observable on Stokes pulse profiles, their spectral synchronization with the pump pulse remains possible and efficient in the interesting region between 1100 nm and 1700 nm. The electrical stimulation device consists of a customized generator combining microstrip-line technology and laser-triggered photoconductive semiconductor switches. Our experimental characterization highlights the capability for such a generator to control the main pulse parameters (profile, amplitude and duration) and to be easily synchronized with the imaging system. We finally test and calibrate the system by means of a KDP crystal. The preliminary results suggest that this electro-optical system provides a suitable tool for real-time investigation of

  5. Picosecond Pump-Probe Raman Spectroscopy of Excited States and Relaxation Phenomena in the Condensed Phase.

    NASA Astrophysics Data System (ADS)

    Lingle, Robert, Jr.

    This dissertation describes the development and application of pump-probe Raman spectroscopy using 8 ps laser pulses as a technique for the study of relaxation phenomena in the condensed phase. I show three examples of systems studied by this technique. First, the dissipation of the heat deposited in the cage of solvent molecules surrounding a photodissociated diatomic solute is directly measured in the solvent Raman spectrum. Second, we provide a full characterization of the excited A^ ' state of iodine which is formed in solution following photodissociation. This work discusses the solvent dependence of the iodine atom recombination process and points toward (iodine atom-solvent molecule) complexes as an intermediate species leading to recombination on the A^' state. We measure and rationalize the rates for both vibrational relaxation within and electronic relaxation out of the A^ ' state. Turning to a laser system, we measure the chromophore-to-protein vibrational relaxation time in deoxyhemoglobin. We learn that mechanical energy finds its way out of the heme and into the protein matrix with 2 to 5 ps exponential time constant. Both the study of iodine and deoxyhemoglobin emphasize that measuring the dynamics of the Stokes and anti-Stokes transient Raman signals provides a direct and powerful method to study vibrational population relaxation. Raman spectra are directly sensitive to vibrational level spacings and populations. As a result, Raman bands dynamics can be affected by electronic, vibrational, and conformational processes. Most previous Raman picosecond experiments have lacked the sensitivity necessary to probe the weak, transient anti-Stokes spectrum, which provides invaluable information on vibrational population dynamics. We also use a subtraction procedure to isolate the transient features in the spectrum, making our spectra taken at kiloHertz repetition rates very sensitive to small changes in the spectrum. This enables us to compare directly the

  6. Quantum chemistry based inversion of experimental pump-probe spectra: Model simulations for CpMn(CO) 3

    NASA Astrophysics Data System (ADS)

    Full, Jürgen; González, Leticia; Manz, Jörn

    2006-10-01

    Experimental pump-probe spectra may be used to refine a quantum chemistry based model Hamiltonian for quantum simulations of photodissociation and -ionization. The design of the model Hamiltonion involves several steps which are demonstrated, exemplarily for the organo-metallic model system, cyclo-pentadienyl-manganese-tricarbonyl CpMn(CO) 3 (cymanthrene). First, we consider the specific experimental scenario e.g. single photon transitions, zero electron kinetic energy (ZEKE) of the resulting free electron, and investigations of just the short time evolution (few 100 fs). This suggests to describe the molecular dynamics in reduced dimensionality of just the most important degree(s) of freedom, e.g. the bond distance between the metal atom Mn and the photodissociated ligand CO, assuming C s symmetry. Next, the relevant adiabatic potential energy surfaces (PES) are evaluated by means of ab initio quantum chemistry techniques, together with the transition dipole and kinetic couplings of the neutral or ionic states. Non-Condon transition dipole couplings between excited neutral and ionic states are approximated in terms of the coefficients for configuration interaction, depending on electron correlation. Exemplarily, we consider the effects of five plus three coupled adiabatic PES of the neutral and ionic systems, respectively. The resulting laser driven reaction dynamics is then simulated in terms of representative time-dependent wave packets moving on the coupled PES, together with corresponding pump-probe spectrum of the parent ion, CpMn(CO)3+. Few parameters of the quantum chemistry based model are then adjusted, within the accuracy of the quantum method, in order to achieve near quantitative agreement of the experimental and theoretical pump-probe spectra. In the present application, the relevant excitation energies, kinetic couplings, and the relative displacement of two potential wells in the electronic ground and excited states, are scaled and adjusted. The

  7. Femtosecond Carrier Dynamics in Aluminum Gallium Arsenide.

    NASA Astrophysics Data System (ADS)

    Ulman, Morrison

    The femtosecond dynamics of electrons and holes in AlGaAs are studied by combining femtosecond laser spectroscopy and ensemble Monte Carlo simulation. A femtosecond pulsed laser system is used to investigate ultrafast dynamics in the semiconductor via pump-probe spectroscopy. An ultrashort optical pulse focussed on the sample excites a transient carrier distribution. The evolution of this distribution is determined from transmission measurements of a probe pulse which is delayed for some time after the exciting ("pump") pulse. The delay between the pump and probe pulses is varied in sub-femtosecond steps so the measurement time resolution is limited only by the laser pulse duration which is 40 femtoseconds. The nonlinear optical response of the material is caused by the dynamics of electrons and holes. They are characterized by an energy distribution function. In thermal equilibrium the distribution function is the Fermi function multiplied by the density of states. After optical excitation, however, the distribution is non-thermal. In fact its shape reflects the spectrum of the exciting optical pulse and the allowed optical transitions in the system. The non-equilibrium distribution thermalizes in approximately 100 fs and cools to the lattice temperature in about 1000 fs. Pump-probe data are measurements of pump pulse induced changes in the transmission of the probe pulse through the sample. These data do not directly reveal the underlying carrier distributions, however. Accurate modelling is complicated by the need to take into account several optical transitions and many carrier relaxation mechanisms. In collaboration with theorists at the University of Florida we are able to establish correspondence between our experimental results and predicted carrier distributions through the use of ensemble Monte Carlo simulations. The theory fits the data well and and may be used to predict behavior in future experiments and possibly AlGaAs optoelectronic devices. (Copies

  8. Photoionization-photoelectron research

    SciTech Connect

    Berkowitz, J.; Ruscic, B.

    1993-12-01

    The photoionization research program is aimed at understanding the basic processes of interaction of vacuum ultraviolet (VUV) light with atoms and molecules. This research provides valuable information on both thermochemistry and dynamics. Recent studies include atoms, clusters, hydrides, sulfides and an important fluoride.

  9. Femtosecond photodissociation of molecules facilitated by noise

    SciTech Connect

    Singh, Kamal P.; Kenfack, Anatole; Rost, Jan M.

    2008-02-15

    We investigate the dynamics of diatomic molecules subjected to both a femtosecond midinfrared laser pulse and Gaussian white noise. The stochastic Schroedinger equation with a Morse potential is used to describe the molecular vibrations under noise and the laser pulse. For weak laser intensity, well below the dissociation threshold, it is shown that one can find an optimum amount of noise that leads to a dramatic enhancement of the dissociation probability. The enhancement landscape, which is shown as a function of both the noise and the laser strength, exhibits a global maximum. A frequency-resolved gain profile is recorded with a pump-probe setup which is experimentally realizable. With this profile we identify the linear and nonlinear multiphoton processes created by the interplay between laser and noise and assess their relative contribution to the dissociation enhancement.

  10. Theoretical Simulations and Ultrafast Pump-probe Spectroscopy Experiments in Pigment-protein Photosynthetic Complexes

    SciTech Connect

    Buck, D. R.

    2000-09-12

    Theoretical simulations and ultrafast pump-probe laser spectroscopy experiments were used to study photosynthetic pigment-protein complexes and antennae found in green sulfur bacteria such as Prosthecochloris aestuarii, Chloroflexus aurantiacus, and Chlorobium tepidum. The work focused on understanding structure-function relationships in energy transfer processes in these complexes through experiments and trying to model that data as we tested our theoretical assumptions with calculations. Theoretical exciton calculations on tubular pigment aggregates yield electronic absorption spectra that are superimpositions of linear J-aggregate spectra. The electronic spectroscopy of BChl c/d/e antennae in light harvesting chlorosomes from Chloroflexus aurantiacus differs considerably from J-aggregate spectra. Strong symmetry breaking is needed if we hope to simulate the absorption spectra of the BChl c antenna. The theory for simulating absorption difference spectra in strongly coupled photosynthetic antenna is described, first for a relatively simple heterodimer, then for the general N-pigment system. The theory is applied to the Fenna-Matthews-Olson (FMO) BChl a protein trimers from Prosthecochloris aestuarii and then compared with experimental low-temperature absorption difference spectra of FMO trimers from Chlorobium tepidum. Circular dichroism spectra of the FMO trimer are unusually sensitive to diagonal energy disorder. Substantial differences occur between CD spectra in exciton simulations performed with and without realistic inhomogeneous distribution functions for the input pigment diagonal energies. Anisotropic absorption difference spectroscopy measurements are less consistent with 21-pigment trimer simulations than 7-pigment monomer simulations which assume that the laser-prepared states are localized within a subunit of the trimer. Experimental anisotropies from real samples likely arise from statistical averaging over states with diagonal energies shifted by

  11. A wavelength dependent investigation of the indole photophysics via ionization and fragmentation pump-probe spectroscopies.

    PubMed

    Godfrey, T J; Yu, Hui; Biddle, Michael S; Ullrich, Susanne

    2015-10-14

    A wavelength dependent study investigating the low-lying (1)La and (1)Lb states, both possessing (1)ππ* character, and the (1)πσ* state in the deactivation process of indole is presented here. Relaxation dynamics following excitation at 241, 250, 260, 270, 273, and 282 nm are examined using three gas-phase, pump-probe spectroscopic techniques: (1) hydrogen atom (H-atom) time-resolved kinetic energy release (TR-KER), (2) time-resolved photoelectron spectroscopy (TR-PES), and (3) time-resolved ion yield (TR-IY). Applied in combination, a more complete picture of the indole relaxation dynamics may be gleaned. For instance, TR-PES experiments directly observe all relaxation pathways by probing the evolution of the excited states following photoexcitation; whereas, TR-KER measurements indirectly, yet specifically, probe for (1)πσ*-state activity through the detection of H-atoms eliminated along the indole nitrogen-hydrogen (N-H) stretch coordinate-a possible outcome of (1)πσ*-state relaxation in indole. In addition, mass information obtained via TR-IY monitors fragmentation dynamics that may occur within the neutral electronically excited and/or cationic states. The work herein assesses the onset and importance of the (1)πσ* state at various pump wavelengths by systematically tuning across the ultraviolet absorption spectrum of indole with a particular focus on those pump wavelengths longer than 263 nm, where the involvement of the (1)πσ* state is under current debate. As far as this experimental work is concerned, there does not appear to be any significant involvement by the (1)πσ* state in the indole relaxation processes following excitation at 270, 273, or 282 nm. This investigation also evaluates the primary orbital promotions contributing to the (1)La, (1)Lb, and (1)πσ* transitions based on ionization preferences observed in TR-PES spectra. Relaxation time constants associated with dynamics along these states are also reported for excitation at all

  12. Libration induced stretching mode excitation for pump-probe spectroscopy in pure liquid water.

    PubMed

    Amir, Wafa; Gallot, Guilhem; Hache, François

    2004-10-22

    We developed an experimental approach to study pure liquid water in the infrared and avoid thermal effects. This technique is based on libration induced stretching excitation of water molecules. A direct correspondence between frequencies within the libration and OH stretching bands is demonstrated. Energy diffusion is studied in pure liquid water by measuring wave packet dynamics of OH stretching vibrator with infrared femtosecond spectroscopy. Wave packet dynamics reveals ultrafast energy dynamics and reflects 130 fs intermolecular energy transfer between water vibrators. Energy diffusion is almost two orders of magnitude faster than self diffusion in water.

  13. Optical synchronization system for femtosecond X-ray sources

    DOEpatents

    Wilcox, Russell B [El Cerrito, CA; Holzwarth, Ronald [Munich, DE

    2011-12-13

    Femtosecond pump/probe experiments using short X-Ray and optical pulses require precise synchronization between 100 meter-10 km separated lasers in a various experiments. For stabilization in the hundred femtosecond range a CW laser is amplitude modulated at 1-10 GHz, the signal retroreflected from the far end, and the relative phase used to correct the transit time with various implementations. For the sub-10 fsec range the laser frequency itself is upshifted 55 MHz with an acousto-optical modulator, retroreflected, upshifted again and phase compared at the sending end to a 110 MHz reference. Initial experiments indicate less than 1 fsec timing jitter. To lock lasers in the sub-10 fs range two single-frequency lasers separated by several teraHertz will be lock to a master modelocked fiber laser, transmit the two frequencies over fiber, and lock two comb lines of a slave laser to these frequencies, thus synchronizing the two modelocked laser envelopes.

  14. Multi-metastable states induced by the optical pump-probe process in terahertz quantum cascade lasers

    SciTech Connect

    Wang, F.; Guo, X. G. Wang, C.; Cao, J. C.

    2014-07-14

    The optical pump-probe process in terahertz quantum cascade lasers is studied theoretically by using the open system simulation method. The emitter injection is considered and the charge neutrality in the active region is broken. We find that nonequilibrium oscillations may appear in the recovery processes. In particular, the formation of different equilibrium values of the population change after the periodic pulse pumping is observed clearly. Here, the phenomenon of multi-metastable states stems from the electron regulation by the emitter injection. Finally, we discuss the important impacts of the equilibrium stabilization time and obtain an in-depth understanding of the emitter injection.

  15. Generation of 8.5-fs pulses at 1.3 microm for ultrabroadband pump-probe spectroscopy.

    PubMed

    Brida, Daniele; Bonora, Stefano; Manzoni, Cristian; Marangoni, Marco; Villoresi, Paolo; De Silvestri, Sandro; Cerullo, Giulio

    2009-07-20

    We report on a near-infrared non-collinear optical parametric amplifier (NOPA) based on periodically poled stoichiometric lithium tantalate. The NOPA generates muJ-energy pulses with spectrum spanning the 1-1.7 microm wavelength range, which are compressed to nearly transformlimited 8.5 fs duration by a deformable mirror. By synchronizing this source with a sub-10-fs visible NOPA, we demonstrate an unprecedented combination of temporal resolution and spectral coverage in two-colour pump-probe spectroscopy.

  16. Excitons recombination investigation in CdSe/ZnS quantum dots solutions by pump-probe technique

    NASA Astrophysics Data System (ADS)

    Kulagina, A. S.; Danilov, V. V.; Shilov, V. B.; Grigorenko, K. M.; Vlasov, V. V.; Ermolaeva, G. M.

    2017-07-01

    It reports results of the pump-probe experiment on colloidal solutions of semiconductor CdSe/ZnS quantum dots with 5 nm diameter for intense pulsed resonant excitation at 560 nm wavelength. The dependence of intensity of a transmitted probe pulse on time delay relative to the pump pulse was used to determine relaxation time τexc of excited excitons in the QDs. The intensity of nonlinear reducing of QDs solution transmittance served the reason to set it for pump pulse. We found that the excited states in the QDs recombine within 300 ps after interaction with a 20-ps pump pulse.

  17. Bases for time-resolved probing of transient carrier dynamics by optical pump-probe scanning tunneling microscopy.

    PubMed

    Yokota, Munenori; Yoshida, Shoji; Mera, Yutaka; Takeuchi, Osamu; Oigawa, Haruhiro; Shigekawa, Hidemi

    2013-10-07

    The tangled mechanism that produces optical pump-probe scanning tunneling microscopy spectra from semiconductors was analyzed by comparing model simulation data with experimental data. The nonlinearities reflected in the spectra, namely, the excitations generated by paired laser pulses with a delay time, the logarithmic relationship between carrier density and surface photovoltage (SPV), and the effect of the change in tunneling barrier height depending on SPV, were examined along with the delay-time-dependent integration process used in measurement. The optimum conditions required to realize reliable measurement, as well as the validity of the microscopy technique, were demonstrated for the first time.

  18. Exciton spin coherence in InGaAs/GaAs quantum dots revisited by heterodyne pump-probe experiment

    NASA Astrophysics Data System (ADS)

    Eble, B.; Siarry, B.; Bernardot, F.; Grinberg, P.; Testelin, C.; Lemaître, A.

    2016-10-01

    We demonstrate here the phase control of the neutral exciton quantum beats in InGaAs/GaAs quantum dots. A longitudinal magnetic field is used as a tuning parameter to change the phase of the oscillations in a deterministic way. This effect arises from the competition between the Zeeman splitting and the electron/hole exchange interaction on the exciton dipole symmetry. To explore this mechanism, we have developed a pump-probe setup based on the optical heterodyne detection of the quantum dots reflectivity allowing one to measure the exciton dynamics from a small quantum dots ensemble (˜300).

  19. Vibrational spectroscopy of water in hydrated lipid multi-bilayers. I. Infrared spectra and ultrafast pump-probe observables.

    PubMed

    Gruenbaum, S M; Skinner, J L

    2011-08-21

    The vibrational spectroscopy of hydration water in dilauroylphosphatidylcholine lipid multi-bilayers is investigated using molecular dynamics simulations and a mixed quantum/classical model for the OD stretch spectroscopy of dilute HDO in H(2)O. FTIR absorption spectra, and isotropic and anisotropic pump-probe decay curves have been measured experimentally as a function of the hydration level of the lipid multi-bilayer, and our goal is to make connection with these experiments. To this end, we use third-order response functions, which allow us to include non-Gaussian frequency fluctuations, non-Condon effects, molecular rotations, and a fluctuating vibrational lifetime, all of which we believe are important for this system. We calculate the response functions using existing transition frequency and dipole maps. From the experiments it appears that there are two distinct vibrational lifetimes corresponding to HDO molecules in different molecular environments. In order to obtain these lifetimes, we consider a simple two-population model for hydration water hydrogen bonds. Assuming a different lifetime for each population, we then calculate the isotropic pump-probe decay, fitting to experiment to obtain the two lifetimes for each hydration level. With these lifetimes in hand, we then calculate FTIR spectra and pump-probe anisotropy decay as a function of hydration. This approach, therefore, permits a consistent calculation of all observables within a unified computational scheme. Our theoretical results are all in qualitative agreement with experiment. The vibrational lifetime of lipid-associated OD groups is found to be systematically shorter than that of the water-associated population, and the lifetimes of each population increase with decreasing hydration, in agreement with previous analysis. Our theoretical FTIR absorption spectra successfully reproduce the experimentally observed red-shift with decreasing lipid hydration, and we confirm a previous interpretation

  20. Pump-probe optical switching in prism-coupled Au :SiO2 nanocomposite waveguide film

    NASA Astrophysics Data System (ADS)

    Lee, Kyeong-Seok; Lee, Taek-Sung; Kim, Won-Mok; Cho, Sunghun; Lee, Soonil

    2007-10-01

    The resonance properties due to the surface plasmon excitation of metal nanoparticles make the nanocomposite films promising for various applications such as optical switching devices. In spite of the well-known ultrasensitive operation of optical switches based on a guided wave, the application of nanocomposite film has inherent limitation originating from the excessive optical loss related to the surface plasmon resonance. In this study, we address this problem and present the experimental and theoretical analyses on the pump-probe optical switching in prism-coupled Au(1vol%):SiO2 nanocomposite waveguide film.

  1. Laser-Induced Damage with Femtosecond Pulses

    NASA Astrophysics Data System (ADS)

    Kafka, Kyle R. P.

    The strong electric fields of focused femtosecond laser pulses lead to non-equilibrium dynamics in materials, which, beyond a threshold intensity, causes laser-induced damage (LID). Such a strongly non-linear and non-perturbative process renders important LID observables like fluence and intensity thresholds and damage morphology (crater) extremely difficult to predict quantitatively. However, femtosecond LID carries a high degree of precision, which has been exploited in various micro/nano-machining and surface engineering applications, such as human eye surgery and super-hydrophobic surfaces. This dissertation presents an array of experimental studies which have measured the damage behavior of various materials under femtosecond irradiation. Precision experiments were performed to produce extreme spatio-temporal confinement of the femtosecond laser-solid damage interaction on monocrystalline Cu, which made possible the first successful direct-benchmarking of LID simulation with realistic damage craters. A technique was developed to produce laser-induced periodic surface structures (LIPSS) in a single pulse (typically a multi-pulse phenomenon), and was used to perform a pump-probe study which revealed asynchronous LIPSS formation on copper. Combined with 1-D calculations, this new experimental result suggests more drastic electron heating than expected. Few-cycle pulses were used to study the LID performance and morphology of commercial ultra-broadband optics, which had not been systematically studied before. With extensive surface analysis, various morphologies were observed, including LIPSS, swelling (blisters), simple craters, and even ring-shaped structures, which varied depending on the coating design, number of pulses, and air/vacuum test environment. Mechanisms leading to these morphologies are discussed, many of which are ultrafast in nature. The applied damage behavior of multi-layer dielectric mirrors was measured and compared between long pulse (150 ps

  2. Technical brief: Pump-probe paradigm in an integrating cavity to study photodecomposition processes

    PubMed Central

    Betts-Obregon, Brandi; Tsin, Andrew T.; DeSa, Richard J.

    2016-01-01

    dark” period allowed actinic flashes to be placed between scans. Exposure of the all-trans retinol to 366 nm flashes resulted in marked reduction in absorbance and a blue shift of the λmax. A white LED, despite its higher photon output, did not support all-trans retinol photolysis. Singular value decomposition (SVD) analysis revealed three spectral intermediates with mechanism, I -> II -> III. HPLC analysis of the reactants at the beginning and the conclusion of the light exposure confirmed the retinol photodecomposition. Conclusions The highly reflecting cavity acts as a multipass cuvette that markedly increased the light path length and, thus, sensitivity. Triggering the LED during a dark period within the scan time allowed the actinic flashes to be interleafed between scans in a pump-probe paradigm. Furthermore, the entire sample was exposed to scan beam and actinic flashes, which is not possible in traditional spectrophotometers. Finally, the integrating cavity cuvette allowed use of turbid samples. SVD was useful for resolving spectral intermediates. Although the identity of the intermediates was not determined here, the ability to define molecular intermediates during photodecomposition reactions will allow future studies to isolate and identify the degradation products and determine the mechanism of light-induced retinoid degradation and that of retinoid-binding protein-mediated photoprotection. PMID:27559291

  3. Following the dynamics of matter with femtosecond precision using the X-ray streaking method

    SciTech Connect

    David, C.; Karvinen, P.; Sikorski, M.; Song, S.; Vartiainen, I.; Milne, C. J.; Mozzanica, A.; Kayser, Y.; Diaz, A.; Mohacsi, I.; Carini, G. A.; Herrmann, S.; Färm, E.; Ritala, M.; Fritz, D. M.; Robert, A.

    2015-01-06

    X-ray Free Electron Lasers (FELs) can produce extremely intense and very short pulses, down to below 10 femtoseconds (fs). Among the key applications are ultrafast time-resolved studies of dynamics of matter by observing responses to fast excitation pulses in a pump-probe manner. Detectors with sufficient time resolution for observing these processes are not available. Therefore, such experiments typically measure a sample's full dynamics by repeating multiple pump-probe cycles at different delay times. This conventional method assumes that the sample returns to an identical or very similar state after each cycle. Here we describe a novel approach that can provide a time trace of responses following a single excitation pulse, jitter-free, with fs timing precision. We demonstrate, in an X-ray diffraction experiment, how it can be applied to the investigation of ultrafast irreversible processes.

  4. Following the dynamics of matter with femtosecond precision using the X-ray streaking method

    DOE PAGES

    David, C.; Karvinen, P.; Sikorski, M.; ...

    2015-01-06

    X-ray Free Electron Lasers (FELs) can produce extremely intense and very short pulses, down to below 10 femtoseconds (fs). Among the key applications are ultrafast time-resolved studies of dynamics of matter by observing responses to fast excitation pulses in a pump-probe manner. Detectors with sufficient time resolution for observing these processes are not available. Therefore, such experiments typically measure a sample's full dynamics by repeating multiple pump-probe cycles at different delay times. This conventional method assumes that the sample returns to an identical or very similar state after each cycle. Here we describe a novel approach that can provide amore » time trace of responses following a single excitation pulse, jitter-free, with fs timing precision. We demonstrate, in an X-ray diffraction experiment, how it can be applied to the investigation of ultrafast irreversible processes.« less

  5. Photocarrier dynamics in anatase TiO{sub 2} investigated by pump-probe absorption spectroscopy

    SciTech Connect

    Matsuzaki, H. E-mail: okamotoh@k.u-tokyo.ac.jp; Matsui, Y.; Uchida, R.; Yada, H.; Terashige, T.; Li, B.-S.; Sawa, A.; Kawasaki, M.; Tokura, Y.; Okamoto, H. E-mail: okamotoh@k.u-tokyo.ac.jp

    2014-02-07

    The dynamics of photogenerated electrons and holes in undoped anatase TiO{sub 2} were studied by femtosecond absorption spectroscopy from the visible to mid-infrared region (0.1–2.0 eV). The transient absorption spectra exhibited clear metallic responses, which were well reproduced by a simple Drude model. No mid-gap absorptions originating from photocarrier localization were observed. The reduced optical mass of the photocarriers obtained from the Drude-model analysis is comparable to theoretically expected one. These results demonstrate that both photogenerated holes and electrons act as mobile carriers in anatase TiO{sub 2}. We also discuss scattering and recombination dynamics of photogenerated electrons and holes on the basis of the time dependence of absorption changes.

  6. Calculating time-resolved differential absorbance spectra for ultrafast pump-probe experiments with surface hopping trajectories.

    PubMed

    Petit, Andrew S; Subotnik, Joseph E

    2014-10-21

    We report a surface hopping approach for modeling the full time- and frequency-resolved differential absorbance spectra (beyond the inhomogenous limit) obtained in ultrafast pump-probe experiments. In our approach, we combine dynamical information obtained from ensembles of classical trajectories propagated on the ground and on the excited potential energy surfaces to directly calculate optical response functions and hence spectral lineshapes. We demonstrate that our method is exact for the model problem of two shifted harmonic potentials with identical harmonic frequencies in the absence of electronic relaxation. We then consider a model three state system with electronic relaxation and show that our method is able to capture the effects of nonadiabatic excited state dynamics on the time-dependent differential absorbance spectra. Furthermore, by comparing our spectra against those spectra calculated with either an (1) inhomogenous expression, (2) ground-state Kubo theory, or (3) excited-state Kubo theory, we show that including dynamical information from both the ground and excited potential energy surfaces significantly improves the reliability of the semiclassical approximations. As such, our surface hopping method should find immediate use in modeling the time-dependent differential abosrbance spectra of ultrafast pump-probe experiments.

  7. Pump-probe studies of radiation induced defects and formation of warm dense matter with pulsed ion beams

    NASA Astrophysics Data System (ADS)

    Schenkel, T.; Persaud, A.; Gua, H.; Seidl, P. A.; Waldron, W. L.; Gilson, E. P.; Kaganovich, I. D.; Davidson, R. C.; Friedman, A.; Barnard, J. J.; Minior, A. M.

    2014-10-01

    We report results from the 2nd generation Neutralized Drift Compression Experiment at Berkeley Lab. NDCX-II is a pulsed, linear induction accelerator designed to drive thin foils to warm dense matter (WDM) states with peak temperatures of ~ 1 eV using intense, short pulses of 1.2 MeV lithium ions. Tunability of the ion beam enables pump-probe studies of radiation effects in solids as a function of excitation density, from isolated collision cascades to the onset of phase-transitions and WDM. Ion channeling is an in situ diagnostic of damage evolution during ion pulses with a sensitivity of <0.1% displacements per atom. We will report results from damage evolution studies in thin silicon crystals with Li + and K + beams. Detection of channeled ions tracks lattice disorder evolution with a resolution of ~ 1 ns using fast current measurements. We will discuss pump-probe experiments with pulsed ion beams and the development of diagnostics for WDM and multi-scale (ms to fs) access to the materials physics of collision cascades e.g. in fusion reactor materials. Work performed under auspices of the US DOE under Contract No. DE-AC02-05CH11231.

  8. Molecular contrast optical coherence tomography: A pump-probe scheme using indocyanine green as a contrast agent.

    PubMed

    Yaqoob, Zahid; McDowell, Emily; Wu, Jigang; Heng, Xin; Fingler, Jeff; Yang, Changhuei

    2006-01-01

    The use of indocyanine green (ICG), a U.S. Food and Drug Administration approved dye, in a pump-probe scheme for molecular contrast optical coherence tomography (MCOCT) is proposed and demonstrated for the first time. In the proposed pump-probe scheme, an optical coherence tomography (OCT) scan of the sample containing ICG is first acquired. High fluence illumination (approximately 190 kJ/cm2) is then used to permanently photobleach the ICG molecules--resulting in a permanent alteration of the overall absorption of the ICG. A second OCT scan is next acquired. The difference of the two OCT scans is used to determine the depth resolved distribution of ICG within a sample. To characterize the extent of photobleaching in different ICG solutions, we determine the cumulative probability of photobleaching, phi(B,cum), defined as the ratio of the total photobleached ICG molecules to the total photons absorbed by the ground state molecules. An empirical study of ICG photobleaching dynamics shows that phi(B,cum) decreases with fluence as well as with increasing dye concentration. The quantity phi(B,cum) is useful for estimating the extent of photobleaching in an ICG sample (MCOCT contrast) for a given fluence of the pump illumination. The paper also demonstrates ICG-based MCOCT imaging in tissue phantoms as well as within stage 54 Xenopus laevis.

  9. Inner-shell photoionized x-ray lasers

    SciTech Connect

    Moon, Stephen J.

    1998-09-01

    repetition rate (Pavg = 1μW) makes this source of coherent x rays ideal for pump-probe experiments to study fast dynamical processes in chemistry and material science.

  10. State-to-State Spectroscopy and Dynamics of Ions and Neutrals by Photoionization and Photoelectron Methods

    NASA Astrophysics Data System (ADS)

    Ng, Cheuk-Yiu

    2014-04-01

    Recent advances in high-resolution photoionization, photoelectron, and photodissociation studies based on single-photon vacuum ultraviolet (VUV) and two-color infrared (IR)-VUV, visible (Vis)-ultraviolet (UV), and VUV-VUV laser excitations are illustrated with selected examples. VUV laser photoionization coupled with velocity-map-imaging threshold photoelectron (VMI-TPE) detection can achieve comparable energy resolution but has higher-detection sensitivities than those observed in VUV laser pulsed field ionization photoelectron (PFI-PE) measurements. For molecules with known intermediate states, IR-VUV and Vis-UV excitation schemes are highly sensitive for rovibronically selected and resolved PFI-PE studies. The successful applications of the VUV-PFI-PE, VUV-VMI-TPE, and Vis-UV-PFI-PE methods to state-resolved and state-to-state photoelectron studies of transient radicals and transitional metal-containing molecules are highlighted. The most recently established VUV-VUV pump-probe time-slice VMI photoion method is shown to be promising for state-to-state photodissociation studies of small molecules relevant to planetary atmospheres and for the fundamental understanding of photodissociation dynamics.

  11. State-To Spectroscopy and Dynamics of Ions and Neutrals by Photoionization and Photoelectron Methods

    NASA Astrophysics Data System (ADS)

    Ng, Cheuk-Yiu

    2014-06-01

    Recent advances in high-resolution photoionization, photoelectron, and photodissociation studies based on single-photon vacuum ultraviolet (VUV) and two-color infrared (IR)-VUV, visible (VIS)-ultraviolet (UV), and VUV-VUV laser excitations are illustrated with selected examples. We show that VUV laser photoionization coupled with velocity-map-imaging (VMI)-threshold photoelectron (VMI-TPE) detection can achieve comparable energy resolutions, but higher detection sensitivities than those observed in VUV laser pulsed field ionization-photoelectron (PFI-PE) measurements. For molecules with known intermediate states, IR-VUV and VIS-UV excitation schemes are highly sensitive for rovibronically selected and resolved PFI-PE studies. The successful applications of the VUV-PFI-PE, VUV-VMI-TPE and VIS-UV-PFI-PE methods to state-resolved and state-to-state photoelectron studies of transient radicals and transitional metal-containing molecules are highlighted. The most recently established VUV-VUV pump-probe time-slice VMI-photoion method is shown to be promising for state-to-state photodissociation studies of small molecules relevant to planetary atmospheres and for the fundamental understanding of photodissociation dynamics.

  12. State-to-state spectroscopy and dynamics of ions and neutrals by photoionization and photoelectron methods.

    PubMed

    Ng, Cheuk-Yiu

    2014-01-01

    Recent advances in high-resolution photoionization, photoelectron, and photodissociation studies based on single-photon vacuum ultraviolet (VUV) and two-color infrared (IR)-VUV, visible (Vis)-ultraviolet (UV), and VUV-VUV laser excitations are illustrated with selected examples. VUV laser photoionization coupled with velocity-map-imaging threshold photoelectron (VMI-TPE) detection can achieve comparable energy resolution but has higher-detection sensitivities than those observed in VUV laser pulsed field ionization photoelectron (PFI-PE) measurements. For molecules with known intermediate states, IR-VUV and Vis-UV excitation schemes are highly sensitive for rovibronically selected and resolved PFI-PE studies. The successful applications of the VUV-PFI-PE, VUV-VMI-TPE, and Vis-UV-PFI-PE methods to state-resolved and state-to-state photoelectron studies of transient radicals and transitional metal-containing molecules are highlighted. The most recently established VUV-VUV pump-probe time-slice VMI photoion method is shown to be promising for state-to-state photodissociation studies of small molecules relevant to planetary atmospheres and for the fundamental understanding of photodissociation dynamics.

  13. Photoionization of the Buckminsterfullerene Cation.

    PubMed

    Douix, Suzie; Duflot, Denis; Cubaynes, Denis; Bizau, Jean-Marc; Giuliani, Alexandre

    2017-01-05

    Photoionization of a buckminsterfullerene ion is investigated using an ion trap and a merged beam setup coupled to synchrotron radiation beamlines and compared to theoretical calculations. Absolute measurements derived from the ion trap experiment allow discrepancies concerning the photoionization cross section of C60(+) to be solved.

  14. Photoionization of FE3+ Ions

    SciTech Connect

    Ovchinnikov, O.; Schlachter, F.

    2003-01-01

    Photoionization of Fe3+ ions was studied for the first time using synchrotron radiation from the Advanced Light Source (ALS) and the merged-beams technique. Fe3+ ions were successfully produced using ferrocene in an electron cyclotron resonance ion source (ECR). The measured yield of Fe4+ photoions as a function of photon energy revealed the presence of resonances that correspond to excitation of autoionizing states. These resonances are superimposed upon the photoion yield produced by direct photoionization, which is a smooth, slowly decreasing function of energy. The spectra for the photoionization of Fe3+ will be analyzed and compared with theory. The data collected will also serve to test models for the propagation of light through ionized matter.

  15. Clean sub-8-fs pulses at 400 nm generated by a hollow fiber compressor for ultraviolet ultrafast pump-probe spectroscopy.

    PubMed

    Liu, Jun; Okamura, Kotaro; Kida, Yuichiro; Teramoto, Takahiro; Kobayashi, Takayoshi

    2010-09-27

    Clean 7.5 fs pulses at 400 nm with less than 3% energy in tiny satellite pulses were obtained by spectral broadening in a hollow fiber and dispersive compensating using a prism pair together with a deformable mirror system. As an example, this stable and clean pulse was used to study the ultrafast pump-probe spectroscopy of photoactive yellow protein. Moreover, the self-diffraction signal shows a smoothed and broadened laser spectrum and is expected to have a further clean laser pulse, which makes it more useful in the ultrafast pump-probe spectroscopy in the future.

  16. Production of high power femtosecond terahertz radiation

    SciTech Connect

    Neil, George R.; Carr, G.L.; Gubeli III, Joseph F.; Jordan, K.; Martin, Michael C.; McKinney, Wayne R.; Shinn, Michelle; Tani, Masahiko; Williams, G.P.; Zhang, X.-C.

    2003-07-11

    The terahertz (THz) region of the electromagnetic spectrum is attracting interest for a broad range of applications ranging from diagnosing electron beams to biological imaging. Most sources of short pulse THz radiation utilize excitation of biased semiconductors or electro-optic crystals by high peak power lasers. For example, this was done by using an un-doped InAs wafer irradiated by a femtosecond free-electron laser (FEL) at the Thomas Jefferson National Accelerator Facility. Microwatt levels of THz radiation were detected when excited with FEL pulses at 1.06 mm wavelength and 10W average power. Recently substantially higher powers of femtosecond THz pulses produced by synchrotron emission were extracted from the electron beamline. Calculations and measurements confirm the production of coherent broadband THz radiation from relativistic electrons with an average power of nearly 20W, a world record in this wavelength range by a factor of 10,000. We describe the source, presenting theoretical calculations and their experimental verification. Potential applications of this exciting new source include driving new non-linear phenomena, performing pump-probe studies of dynamical properties of novel materials, and studying molecular vibrations and rotations, low frequency protein motions, phonons, superconductor band gaps, electronic scattering, collective electronic excitations (e.g., charge density waves), and spintronics.

  17. Dual echelon femtosecond single-shot spectroscopy

    SciTech Connect

    Shin, Taeho; Wolfson, Johanna W.; Teitelbaum, Samuel W.; Kandyla, Maria; Nelson, Keith A.

    2014-08-15

    We have developed a femtosecond single-shot spectroscopic technique to measure irreversible changes in condensed phase materials in real time. Crossed echelons generate a two-dimensional array of time-delayed pulses with one femtosecond probe pulse. This yields 9 ps of time-resolved data from a single laser shot, filling a gap in currently employed measurement methods. We can now monitor ultrafast irreversible dynamics in solid-state materials or other samples that cannot be flowed or replenished between laser shots, circumventing limitations of conventional pump-probe methods due to sample damage or product buildup. Despite the absence of signal-averaging in the single-shot measurement, an acceptable signal-to-noise level has been achieved via background and reference calibration procedures. Pump-induced changes in relative reflectivity as small as 0.2%−0.5% are demonstrated in semimetals, with both electronic and coherent phonon dynamics revealed by the data. The optical arrangement and the space-to-time conversion and calibration procedures necessary to achieve this level of operation are described. Sources of noise and approaches for dealing with them are discussed.

  18. Pump-probe scheme to study the autoionization decay of optically-forbidden H2 doubly excited states.

    PubMed

    Rivière, P; Silva, R E F; Martín, F

    2012-11-26

    A pump-probe scheme is proposed to investigate the autoionization dynamics of the optically forbidden Q(1)(1)Σ(g)(+) doubly excited states of the H(2) molecule. The scheme consists of a pump that contains an attosecond pulse train (APT) and an infrared (IR) pulse, which is phase-locked with the APT, and an IR probe identical to the former IR pulse. The dynamical information is obtained by analyzing the electron kinetic energy spectra (EKE) and proton kinetic energy spectra (PKE) as a function of the time delay between the pump and the probe. The essential requirement for an efficient population of the Q(1)(1)Σ(g)(+) states is that they are resonantly coupled to both the dipole-allowed Q(1)(1)Σ(u)(+) doubly excited states and the ground state of H(2) by the combined effect of the APT + IR fields.

  19. Time-integrated photoluminescence and pump-probe reflection spectroscopy of Si doped InN thin films

    SciTech Connect

    Mohanta, Antaryami; Jang, Der-Jun Wang, Ming-Sung; Tu, L. W.

    2014-01-28

    Temperature and excitation power dependent time-integrated photoluminescence of Si doped InN thin films are investigated. Photoluminescence (PL) spectra at low temperatures are described by single emission peak ensued due to “free-to-bound” recombination; whereas PL spectra at higher temperatures above 150 K are characterized by both “band-to-band” and “free-to-bound” transition. Carrier dynamics of Si doped InN thin films is studied using pump-probe reflection spectroscopy at room temperature. The hot electron cooling process is well described by electron-electron scattering. The dependence of the hot electron cooling rate on total electron density shows sublinear to linear behavior with increase of background electron density. The variation of the carrier recombination lifetime with total electron density implicates the dominance of the defect-related nonradiative recombination channel over other recombination processes.

  20. Study of all-optical switching properties of zinc phthalocyanine thin film by pump-probe technique

    NASA Astrophysics Data System (ADS)

    Kumar, Anil; Punia, Rajesh; Gupta, Arun K.; Mohan, Devendra; Kapoor, Kirti

    2017-10-01

    The nonlinear optical absorption, refraction and switching behavior of Zinc phthalocyanine (Zn(II)Pc) thin films are reported. Z-scan technique is employed to study the nonlinear absorption and nonlinear refraction behavior of the thin films with nanosecond pulses of Nd:YAG laser at ∼532 nm. Optical switching behavior of the dye is studied using pump-probe technique with ∼5 ns pulses of Nd:YAG at ∼532 nm as the pump beam and ∼632.8 nm cw He-Ne laser as the probe beam. The switching behavior of the dye is attributed to excited state absorption (ESA) of the probe beam by the dye molecules. Probe beam modulation with increasing pump intensity is also investigated.

  1. Probing nonlinear magnetization dynamics in Fe/MgO(001) film by all optical pump-probe technique

    SciTech Connect

    He, Wei; Hu, Bo; Zhang, Xiang-Qun; Cheng, Zhao-Hua; Zhan, Qing-Feng

    2014-04-07

    An all-optical pump-probe technique has been employed to investigate the nonlinear magnetization dynamics of a 10 nm Fe/MgO(001) thin film in time domain. The magnetization precession was excited by pump-laser pulses and modulated by laser fluence variations. With increasing the laser fluence up to 7.1 mJ/cm{sup 2}, in addition to the uniform precession mode, a second harmonic signal was detected. The time evolution of the second harmonic signal was obtained in time-frequency domain. Based on the Landau-Lifshitz-Gilbert equation, the numerical simulation was performed to reproduce the observed the frequency doubling behaviors in Fe/MgO(001) film.

  2. Optical spectroscopy and ultrafast pump-probe studies on the heavy-fermion compound CePt2In7

    DOE PAGES

    Chen, R. Y.; Zhang, S. J.; Bauer, E. D.; ...

    2016-07-29

    We report optical spectroscopy and ultrafast pump-probe measurements on the antiferromagnetic heavy-fermion compound CePt 2 In 7 , a member showing stronger two dimensionality than other compounds in the CeIn 3 -derived heavy-fermion family. Here, we identify clear and typical hybridization spectral structures at low temperature from the two different spectroscopy probes. But, the strength and related energy scale of the hybridization are much weaker and smaller than that in the superconducting compounds CeCoIn 5 and CeIrIn 5 . The features are more similar to observations on the antiferromagnetic compounds CeIn 3 and CeRhIn 5 in the same family. Ourmore » results clearly indicate that the Kondo interaction and hybridizations exist in the antiferromagnetic compounds but with weaker strength.« less

  3. Gauge invariance in the theoretical description of time-resolved angle-resolved pump/probe photoemission spectroscopy

    SciTech Connect

    Freericks, J. K.; Krishnamurthy, H. R.; Sentef, M. A.; Devereaux, T. P.

    2015-10-01

    Nonequilibrium calculations in the presence of an electric field are usually performed in a gauge, and need to be transformed to reveal the gauge-invariant observables. In this work, we discuss the issue of gauge invariance in the context of time-resolved angle-resolved pump/probe photoemission. If the probe is applied while the pump is still on, one must ensure that the calculations of the observed photocurrent are gauge invariant. We also discuss the requirement of the photoemission signal to be positive and the relationship of this constraint to gauge invariance. We end by discussing some technical details related to the perturbative derivation of the photoemission spectra, which involve processes where the pump pulse photoexcites electrons due to nonequilibrium effects.

  4. Fabry-perot modes enhanced pump-probe coupling in gold micro-disk patterned ruby thin film

    NASA Astrophysics Data System (ADS)

    Kumari, Satchi; Khare, Alika; Gupta, Reema; Tomar, Monika; Gupta, Vinay

    2017-10-01

    Enhanced pump-probe coupling has been experimentally observed in epitaxial Ruby thin film patterned with equidistant gold micro-disks (∼100 μm), as compared to pure Ruby film. This has been attributed to Fabry-Perot and surface plasmon modes in Ruby/gold film. In case of S polarized pump and probe beam, Fabry-Perot modes leads to a two-wave mixing gain of ∼1.35. Moreover gain was ∼1.62 in P-polarization case, it has been attributed to coupling of Fabry-Perot and surface plasmon modes. Enhanced coupling for P-polarization can lead to improved nonlinear response in the thin film geometry. It can find applications in thin film based compact photonic devices.

  5. Pump-Probe Spectroscopy of Thermal Cis-Trans Isomerization Process of Methyl Red in 1-Octanol

    NASA Astrophysics Data System (ADS)

    Joukai, Tatsuya; Kita, Kenji; Yano, Ryuzi

    Thermal cis-trans isomerization process of Methyl Red in 1-Octanol at room temperature was studied by pump-probe spectroscopy. The isomerization rate increased as the dye concentration was increased. However, at concentrations above ~ 3 × 10-5 mol/L, the isomerization rate became almost constant regardless of the dye concentration. We interpreted that the concentration dependence of the thermal isomerization rate was caused by the creation of hydrogen-bonded dimer molecules. When a dimer is formed, one of the dye molecules which form the dimer easily changes its form from the cis isomer to the trans isomer. As the dye concentration is increased, the ratio of dyes which form dimer molecules will increase. When the dye concentration is high enough, most dye molecules form dimer molecules. Thus the isomerization rate averaged over the dye molecules is constant.

  6. Study on the nonlinear polarization rotation law in a bulk semiconductor optical amplifier in a pump-probe scheme

    NASA Astrophysics Data System (ADS)

    Feng, Xianghua; Ji, Jiarong; Dou, Wenhua; Zhang, Guomin

    2012-10-01

    The physical mechanisms for the polarization rotation of the light in a bulk semiconductor optical amplifier (SOA) originate from the significant nonuniform distributions of carrier density across the active region. Due to this carrier density's nonuniformity, the effective refractive indexes experienced by transverse-electric (TE) and transverse-magnetic (TM) modes of the probe are different. This results in a phase shift between TE and TM modes of the light upon leaving the SOA. The bulk SOA polarization rotation's law can be analyzed theoretically and experimentally based on the method of measuring output power in a pump-probe scheme. The experiment employs polarizer driving by walking electromotor and power meter, the light power of every orientation is measured. The transformation law of output polarization is find for obvious polarization rotation in other perpendicular axes based on connection of ellipse in difference axes.

  7. Extended pump-probe Faraday rotation spectroscopy of the submicrosecond electron spin dynamics in n -type GaAs

    NASA Astrophysics Data System (ADS)

    Belykh, V. V.; Evers, E.; Yakovlev, D. R.; Fobbe, F.; Greilich, A.; Bayer, M.

    2016-12-01

    We develop an extended pump-probe Faraday rotation technique to study submicrosecond electron spin dynamics with picosecond time resolution in a wide range of magnetic fields. The electron spin dephasing time T2* and the longitudinal spin relaxation time T1, both approaching 250 ns in weak fields, are measured thereby in n -type bulk GaAs. By tailoring the pump pulse train through increasing the contained number of pulses, the buildup of resonant spin amplification is demonstrated for the electron spin polarization. The spin precession amplitude in high magnetic fields applied in the Voigt geometry shows a nonmonotonic dynamics deviating strongly from a monoexponential decay and revealing slow beatings. The beatings indicate a two spin component behavior with a g -factor difference of Δ g ˜4 ×10-4 , much smaller than the Δ g expected for free and donor-bound electrons. This g -factor variation indicates efficient, but incomplete spin exchange averaging.

  8. The limit of time resolution in frequency modulation atomic force microscopy by a pump-probe approach

    NASA Astrophysics Data System (ADS)

    Schumacher, Zeno; Spielhofer, Andreas; Miyahara, Yoichi; Grutter, Peter

    2017-01-01

    Atomic force microscopy (AFM) routinely achieves structural information in the sub-nm length scale. Measuring time resolved properties on this length scale to understand kinetics at the nm scale remains an elusive goal. We present a general analysis of the lower limit for time resolution in AFM. Our finding suggests that the time resolution in AFM is ultimately limited by the well-known thermal limit of AFM and not as often proposed by the mechanical response time of the force sensing cantilever. We demonstrate a general pump-probe approach using the cantilever as a detector responding to the averaged signal. This method can be applied to any excitation signal such as electrical, thermal, magnetic or optical. Experimental implementation of this method allows us to measure a photocarrier decay time of ˜1 ps in low temperature grown GaAs using a cantilever with a resonant frequency of 280 kHz.

  9. Enhanced nonlinear spectroscopy for monolayers and thin films in near-Brewster's angle reflection pump-probe geometry

    NASA Astrophysics Data System (ADS)

    Nishida, Jun; Yan, Chang; Fayer, Michael D.

    2017-03-01

    We experimentally demonstrate and theoretically explicate a method that greatly enhances the detection of third-order nonlinear signals from monolayers and thin films on dielectric substrates. Nonlinear infrared signals, including two dimensional infrared (2D IR) vibrational echo signals, were detected from a functionalized alkyl chain monolayer on a dielectric SiO2 surface in a near-Brewster's angle reflection pump-probe geometry. We observed a tremendous enhancement of the signal-to-noise (S/N) ratio in this geometry compared with a conventional transmission pump-probe geometry signal. The S/N enhancement is achieved by the greatly increased modulation of the local oscillator (LO) field that is induced by the nonlinear signal field. By reducing the LO field without loss of the signal field, the modulation amplitude acquired in this geometry was enhanced by more than a factor of 50. The incident angle dependence of the enhancement was measured and the result agreed remarkably well with theoretical calculations. We combined this geometry with a germanium acousto-optic modulator pulse shaping system to apply 2D IR spectroscopy to the monolayer. The enhanced and phase-stable 2D IR spectra gave detailed dynamical information for the functionalized alkyl chain monolayer. The application of the method to films with finite thickness was described theoretically. The range of film thicknesses over which the method is applicable is delineated, and we demonstrate that accurate dynamical information from thin films can be obtained in spite of dispersive contributions that increase with the film thickness. While we focus on infrared experiments in this article, the method and the theory are applicable to visible and ultraviolet experiments as well.

  10. Light Driven Energy Research at LCLS: Planned Pump-Probe X-ray Spectroscopy Studies on Photosynthetic Water Splitting

    NASA Astrophysics Data System (ADS)

    Bergmann, Uwe

    2010-02-01

    Arguably the most important chemical reaction on earth is the photosynthetic splitting of water to molecular oxygen by the Mn-containing oxygen-evolving complex (Mn-OEC) in the protein known as photosystem II (PSII). It is this reaction which has, over the course of some 3.8 billion years, gradually filled our atmosphere with O2 and consequently enabled and sustained the evolution of complex aerobic life. Coupled to the reduction of carbon dioxide, biological photosynthesis contributes foodstuffs for nutrition while recycling CO2 from the atmosphere and replacing it with O2. By utilizing sunlight to power these energy-requiring reactions, photosynthesis also serves as a model for addressing societal energy needs as we enter an era of diminishing fossil hydrocarbon resources. Understanding, at the molecular level, the dynamics and mechanism of how nature has solved this problem is of fundamental importance and could be critical to aid in the design of manufactured devices to accomplish the conversion of sunlight into useful electrochemical energy and transportable fuel in the foreseeable future. In order to understand the photosynthetic splitting of water by the Mn-OEC we need to be able to follow the reaction in real time at an atomic level. A powerful probe to study the electronic and molecular structure of the Mn-OEC is x-ray spectroscopy. Here, in particular x-ray emission spectroscopy (XES) has two crucial qualities for LCLS based time-dependent pump-probe studies of the Mn-OEC: a) it directly probes the Mn oxidation state and ligation, b) it can be performed with wavelength dispersive optics to avoid the necessity of scanning in pump probe experiments. Recent results and the planned time dependent experiments at LCLS will be discussed. )

  11. High-efficiency photoionization detector

    SciTech Connect

    Anderson, D.F.

    1981-05-12

    A high efficiency photoionization detector using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36 +- 0.02 eV, and a vapor pressure of 0.35 torr at 20/sup 0/C.

  12. Photoelectron photoion molecular beam spectroscopy

    SciTech Connect

    Trevor, D.J.

    1980-12-01

    The use of supersonic molecular beams in photoionization mass spectroscopy and photoelectron spectroscopy to assist in the understanding of photoexcitation in the vacuum ultraviolet is described. Rotational relaxation and condensation due to supersonic expansion were shown to offer new possibilities for molecular photoionization studies. Molecular beam photoionization mass spectroscopy has been extended above 21 eV photon energy by the use of Stanford Synchrotron Radiation Laboratory (SSRL) facilities. Design considerations are discussed that have advanced the state-of-the-art in high resolution vuv photoelectron spectroscopy. To extend gas-phase studies to 160 eV photon energy, a windowless vuv-xuv beam line design is proposed.

  13. Photoionization of sodium clusters

    SciTech Connect

    Peterson, K.I.; Dao, P.D.; Farley, R.W.; Castleman, A.W. Jr.

    1984-03-01

    Sodium clusters, Na/sub x/ (2< or =x< or =8), were produced in a supersonic jet by coexpansion with argon and subjected to analysis via photoionization coupled with mass spectrometry. The present measurements, made at somewhat higher resolution than earlier literature studies, yield ionization potentials in excellent agreement for x = 1 to 4 and x = 7, and reveal heretofore unreported structure in the post-threshold spectra. The present measurements enable a more definitive assignment of the ionization potentials, giving a lower value for x = 6 and pointing to lower ones for x = 5 and 8. The frequently discussed odd--even alternation in ionization potentials is no longer evident beyond the pentamer. Values for the binding energies of Na to Na/sup +//sub x/ (3< or =x< or =8) are deduced.

  14. Photoionization-photoelectron research.

    SciTech Connect

    Ruscic, B.

    1998-03-06

    In the broad sense of a general definition, the fundamental goal of this research program is to explore, understand, and utilize the basic processes of interaction of vacuum UV light with atoms and molecules. In practical terms, this program uses photoionization mass spectrometry and other related techniques to study chemically relevant transient and metastable species that are intimately connected to energy-producing processes, such as combustion, or play-prominent roles in the associated environmental issues. Some recent examples of species that have been studied are: CH{sub 3}, CH{sub 2}, CH{sub 3}O, CH{sub 2}OH, CH{sub 3}S, CH{sub 2}SH, HCS, HNCO, NCO, HNCS, NCS, the isomers of C{sub 2}H{sub 5}O, HOBr, CF{sub 3} and CF{sub 3}OH. The ephemeral species of interest are produced in situ using various suitable techniques, such as sublimation, pyrolysis, microwave discharge, chemical abstraction reactions with H or F atoms, laser photodissociation, on-line synthesis, and others. The desired information is obtained by applying a variety of suitable photoionization methods, which use both conventional and coherent light sources in the vacuum W region. The spiritus movens of our studies is the need to provide the chemical community with essential information on the species of interest, such as accurate and reliable thermochemical, spectroscopic and structural data, and thus contribute to the global comprehension of the underlying chemical processes. The scientific motivation is also fueled by the necessity to unveil useful generalities, such as bonding patterns within a class of related compounds, or systematic behavior in the ubiquitous autoionization processes. In addition, the nature of the results obtained in this program is such that it generates a significant impetus for further theoretical work. The experimental work of this program is coordinated with other related experimental and theoretical efforts of the Chemical Dynamics Group to provide a broad perspective

  15. Validity Using Pump-Probe Pulses to Determine the Optical Response of Niobate Crystals

    NASA Technical Reports Server (NTRS)

    Liu, Huimin; Jia, Weiyi

    1997-01-01

    A variety of niobate crystals have found their places in nonlinear optical applications as well as in laser devices. In recent years much attention has been paid to study the ultrafast optical response in a variety of photorefractive crystals such as KTa(1-x)Nb(x)O3 and KNbO3 crystals, glasses, semiconductors and polymers for applications in optical switching, information processing, optical computing, and all-optical device systems. Third-order optical nonlinearity is the most important property for realization of all-optical switching. Therefore experiments have been performed on the third order susceptibility using a variety of techniques such as the third-order harmonic generation, EFISH and degenerate four-wave mixing(DFWM). The latter has been conducted with a variety of pump wavelengths and with nanosecond, picosecond and femtosecond pulses. Niobate crystals, such as potassium niobate KNbO3, potassium tantalate niobate KTN family (KTa(1-x)Nb(x)O3), strontium barium niobate SBN (Sr(x)Ba(1-x)Nb2O6) and potassium-sodium niobate SBN (KNSBN) are attractive due to their photorefractive properties for application in optical storage and processing. The pulsed probe experiments performed on theses materials have suggested two types of time responses. These responses have been associated with an coherent response due to Chi(sup 3), and a long lived component due to excited state population. Recent study of DFWM on KNbO3 and KTN family reveals that the long lived component of those crystals depends on the crystal orientation. A slowly decaying signal is observable when the grating vector K(sub g) is not perpendicular to the C-axis of those photorefractive crystals', otherwise the optical response signal would be only a narrow coherent peak with FWHM equal to the cross-correlation width of the write beam pulses. Based on this understanding, we study the photodynamical process of a variety of niobate crystals using DFWM in a Kg perpindicular to C geometry with a ps

  16. Ultrafast optical response of the Au-BaO thin film stimulated by femtosecond pulse laser

    NASA Astrophysics Data System (ADS)

    Wu, J. L.; Wang, C. M.; Zhang, G. M.

    1998-06-01

    The pump-probe method was applied to study the dependence of the transient optical transmissivity upon time delay for the Au-BaO composite thin film stimulated by a femtosecond pulsed laser. It was observed that the light absorption of the thin film increased rapidly and then resumed its initial value in several picoseconds. Optical relaxation is a process in which nonequilibrium electrons, excited by laser pulses and originating from Au ultrafine particles, return to the equilibrium state. In this article, the value of the electron-phonon coupling constant g of gold ultrafine particles in the composite thin film was calculated theoretically.

  17. Controlling femtosecond-laser-driven shock-waves in hot, dense plasma

    NASA Astrophysics Data System (ADS)

    Adak, Amitava; Singh, Prashant Kumar; Blackman, David R.; Lad, Amit D.; Chatterjee, Gourab; Pasley, John; Robinson, A. P. L.; Ravindra Kumar, G.

    2017-07-01

    Ultrafast pump-probe reflectometry and Doppler spectrometry of a supercritical density plasma layer excited by 1017-1018 W/cm2 intensity, 30 fs, and 800 nm laser pulses reveal the interplay of laser intensity contrast and inward shock wave strength. The inward shock wave velocity increases with an increase in laser intensity contrast. This trend is supported by simulations as well as by a separate independent experiment employing an external prepulse to control the inward motion of the shock wave. This kind of cost-effective control of shock wave strength using femtosecond pulses could open up new applications in medicine, science, and engineering.

  18. A flexible experimental setup for femtosecond time-resolved broad-band ellipsometry and magneto-optics

    SciTech Connect

    Boschini, F.; Hedayat, H.; Piovera, C.; Dallera, C.; Gupta, A.; Carpene, E.

    2015-01-15

    A versatile experimental setup for femtosecond time-resolved ellipsometry and magneto-optical Kerr effect measurements in the visible light range is described. The apparatus is based on the pump-probe technique and combines a broad-band probing beam with an intense near-infrared pump. According to Fresnel scattering matrix formalism, the analysis of the reflected beam at different polarization states of the incident probe light allows one to determine the diagonal and the off-diagonal elements of the dielectric tensor in the investigated sample. Moreover, the pump-probe method permits to study the dynamics of the dielectric response after a short and intense optical excitation. The performance of the experimental apparatus is tested on CrO{sub 2} single crystals as a benchmark.

  19. Spectra of resonance surface photoionization

    SciTech Connect

    Antsiferov, V.V.; Smirnov, G.I.; Telegin, G.G.

    1995-09-01

    The theory of nonactivated electron transfer between atoms interacting reasonantly with coherent radiation and a metal surface is developed. The spectral resonances in photoabsorption and surface photoionization are found to be related to nonlinear interference effects in the interaction between discrete atomic levels and the continuum formed by the quasi-continuous electron spectrum of a normal metal. The asymmetry in the resonance surface photoionization spectrum is shown to have a shape typical of the Fano autoionization resonances. 18 refs.

  20. Theoretical studies on the femtosecond real-time measurement of ultrafast electronic decay in polyatomic molecules

    NASA Astrophysics Data System (ADS)

    Stock, G.; Schneider, R.; Domcke, W.

    1989-06-01

    We present a computer simulation of the real-time detection of ultrafast electronic decay dynamics in polyatomic molecules with femtosecond laser pulses. The intramolecular non-Born-Oppenheimer quantum dynamics is treated numerically exactly for a two-state three-mode vibronic coupling model representing the conically intersecting S1 and S2 excited states of pyrazine. The pump-probe signal is evaluated in lowest order perturbation theory with respect to the radiation-matter interaction by numerical integration over the pump and probe pulses. We discuss in some detail the dependence of the pump-probe signal on the properties of the laser pulses (frequencies and pulse durations). The calculations predict a dramatic (˜12 000 cm-1) and ultrafast (˜20 fs) red shift of the stimulated-emission signal as well as distinctive quantum beats in the pump-probe signal as a function of the delay time. Both effects are very pronounced and should therefore be relatively easily detectable experimentally. They are expected to be generic features of ultrafast internal-conversion processes in polyatomic molecules.

  1. Nodal Quasiparticle Meltdown in Ultra-High Resolution Pump-Probe Angle-Resolved Photoemission

    SciTech Connect

    Graf, Jeff; Jozwiak, Chris; Smallwood, Chris L.; Eisaki, H.; Kaindl, Robert A.; Lee, Dung-Hai; Lanzara, Alessandra

    2011-06-03

    , finding any strong dependencies of the nodal QPs will alter the conventional view and enrich our understanding of high temperature superconductivity. Time resolution through pump-and-probe techniques adds a new dimension to ARPES by directly measuring how the electronic structure of a material responds to perturbations on femtosecond time scales. Here we report a unique ultrafast time-resolved ARPES study of a high-T{sub c} cuprate superconductor. Compared to previous time-resolved studies, the primary advantage of this work is an unprecedented momentum (angular) resolution ({Delta} k~ 0.003 vs. 0.05 { Angstrom}{sup -1}), on par with that of state-of-the-art ARPES. This has allowed the time-resolved measurement of signi cantly sharper QP spectral peaks with strikingly larger peak-to-background ratios than previously reported.16 Additionally, a lower pump fluence is used (<40{micro} J/cm{sup 2} vs. 100 {micro}J/cm{sup 2}), which reduces pump-induced sample temperature increase and related thermal smearing of spectral features. This allows us to uncover a surprising meltdown of nodal QP spectral weight following pump laser excitation. This meltdown is only observed in the superconducting state and for QPs with binding energy less than the kink energy,19 revealing a link between nodal QPs and superconductivity.

  2. Probing Intrawire, Interwire, and Diameter-Dependent Variations in Silicon Nanowire Surface Trap Density with Pump-Probe Microscopy.

    PubMed

    Cating, Emma E M; Pinion, Christopher W; Christesen, Joseph D; Christie, Caleb A; Grumstrup, Erik M; Cahoon, James F; Papanikolas, John M

    2017-10-11

    Surface trap density in silicon nanowires (NWs) plays a key role in the performance of many semiconductor NW-based devices. We use pump-probe microscopy to characterize the surface recombination dynamics on a point-by-point basis in 301 silicon NWs grown using the vapor-liquid-solid (VLS) method. The surface recombination velocity (S), a metric of the surface quality that is directly proportional to trap density, is determined by the relationship S = d/4τ from measurements of the recombination lifetime (τ) and NW diameter (d) at distinct spatial locations in individual NWs. We find that S varies by as much as 2 orders of magnitude between NWs grown at the same time but varies only by a factor of 2 or three within an individual NW. Although we find that, as expected, smaller-diameter NWs exhibit shorter τ, we also find that smaller wires exhibit higher values of S; this indicates that τ is shorter both because of the geometrical effect of smaller d and because of a poorer quality surface. These results highlight the need to consider interwire heterogeneity as well as diameter-dependent surface effects when fabricating NW-based devices.

  3. Sample exchange by beam scanning with applications to noncollinear pump-probe spectroscopy at kilohertz repetition rates

    NASA Astrophysics Data System (ADS)

    Spencer, Austin P.; Hill, Robert J.; Peters, William K.; Baranov, Dmitry; Cho, Byungmoon; Huerta-Viga, Adriana; Carollo, Alexa R.; Curtis, Anna C.; Jonas, David M.

    2017-06-01

    In laser spectroscopy, high photon flux can perturb the sample away from thermal equilibrium, altering its spectroscopic properties. Here, we describe an optical beam scanning apparatus that minimizes repetitive sample excitation while providing shot-to-shot sample exchange for samples such as cryostats, films, and air-tight cuvettes. In this apparatus, the beam crossing point is moved within the focal plane inside the sample by scanning both tilt angles of a flat mirror. A space-filling spiral scan pattern was designed that efficiently utilizes the sample area and mirror scanning bandwidth. Scanning beams along a spiral path is shown to increase the average number of laser shots that can be sampled before a spot on the sample cell is resampled by the laser to ˜1700 (out of the maximum possible 2500 for the sample area and laser spot size) while ensuring minimal shot-to-shot spatial overlap. Both an all-refractive version and an all-reflective version of the apparatus are demonstrated. The beam scanning apparatus does not measurably alter the time delay (less than the 0.4 fs measurement uncertainty), the laser focal spot size (less than the 2 μ m measurement uncertainty), or the beam overlap (less than the 3.3% measurement uncertainty), leading to pump-probe and autocorrelation signal transients that accurately characterize the equilibrium sample.

  4. Ultrashort laser ablation of metals: pump probe experiments, the role of ballistic electrons and the two-temperature model

    NASA Astrophysics Data System (ADS)

    Schmidt, V.; Husinsky, W.; Betz, G.

    2002-09-01

    The dynamics of laser ablation from metallic surfaces (Ag, Al, Fe and Ni) induced by the combined effect of two 30 fs sub-threshold laser pulses has been examined. In a pump-probe setup the yield of the emitted secondary ions and neutrals has been determined as a function of the delay between the two laser pulses. The instantaneous generation of highly excited (ballistic) electrons by the laser pulse and the thermal properties of the metal, which have been modified to be valid into the regime of high electron temperatures have been found to be determining factors for the ablation process. Unexpectedly, two distinct maxima for particle emission have been observed as a function of the time separation of the pump and the probe pulse. The energy relaxation is discussed within the frame of the two-temperature model (TTM) and it is shown that the measured behavior (in the time domain) of ablated particles can only be explained by taking into account a general expression for the thermal conductivity, valid for a wide range of electron temperatures and in addition a substantial role of hot, ballistic electrons.

  5. Pump-probe and pump-deplete-probe spectroscopies on carotenoids with N =9-15 conjugated bonds

    NASA Astrophysics Data System (ADS)

    Buckup, Tiago; Savolainen, Janne; Wohlleben, Wendel; Herek, Jennifer L.; Hashimoto, Hideki; Correia, Ricardo R. B.; Motzkus, Marcus

    2006-11-01

    A series of all-trans-carotenoids with N =9, 13, and 15 conjugated bonds has been studied by pump-probe and pump-deplete-probe spectroscopies to obtain a systematic analysis of the energy flow between the different electronic states. The ultrafast dynamics in the carotenoids are initialized by excitation to the S2 state and subsequently manipulated by an additional depletion pulse in the near-IR spectral range. The changes in the dynamics after depletion of the excited state population allowed differentiation of the excited state absorption into two components, a major one corresponding to the well known S1 state and the small contribution on the red wing of the S0-S2 absorption band originating from the hot ground state. We found no evidence for an additional electronically excited state, usually called S*. Instead, a deactivation mechanism that includes the hot ground state supports the observed results nicely in the framework of a simple three state model (S2, S1, and S0).

  6. NDT of fiber-reinforced composites with a new fiber-optic pump-probe laser-ultrasound system.

    PubMed

    Pelivanov, Ivan; Buma, Takashi; Xia, Jinjun; Wei, Chen-Wei; O'Donnell, Matthew

    2014-06-01

    Laser-ultrasonics is an attractive and powerful tool for the non-destructive testing and evaluation (NDT&E) of composite materials. Current systems for non-contact detection of ultrasound have relatively low sensitivity compared to contact peizotransducers. They are also expensive, difficult to adjust, and strongly influenced by environmental noise. Moreover, laser-ultrasound (LU) systems typically launch only about 50 firings per second, much slower than the kHz level pulse repetition rate of conventional systems. As demonstrated here, most of these drawbacks can be eliminated by combining a new generation of compact, inexpensive, high repetition rate nanosecond fiber lasers with new developments in fiber telecommunication optics and an optimally designed balanced probe beam detector. In particular, a modified fiber-optic balanced Sagnac interferometer is presented as part of a LU pump-probe system for NDT&E of aircraft composites. The performance of the all-optical system is demonstrated for a number of composite samples with different types and locations of inclusions.

  7. Probing with randomly interleaved pulse train bridges the gap between ultrafast pump-probe and nanosecond flash photolysis.

    PubMed

    Nakagawa, Tatsuo; Okamoto, Kido; Hanada, Hiroaki; Katoh, Ryuzi

    2016-04-01

    Despite the long-standing importance of transient absorption (TA) spectroscopy, many researchers remain frustrated by the difficulty of measuring the nanosecond range in a wide spectral range. To address this shortcoming, we propose a TA spectrophotometer in which there is no synchronization between a pump pulse and a train of multiple probe pulses from a picosecond supercontinuum light source, termed the randomly-interleaved-pulse-train (RIPT) method. For each pump pulse, many monochromatized probe pulses impinge upon the sample, and the associated pump-probe time delays are determined passively shot by shot with subnanosecond accuracy. By repeatedly pumping with automatically varying time delays, a TA temporal profile that covers a wide dynamic range from subnanosecond to milliseconds is simultaneously obtained. By scanning wavelength, this single, simple apparatus acquires not only wide time range TA profiles, but also broadband TA spectra from the visible through the near-infrared regions. Furthermore, we present a typical result to demonstrate how the RIPT method may be used to correct for fluorescence, which often pollutes TA curves.

  8. Dynamics of photon-induced processes in adsorbate-surface systems studied by laser-synchrotron pump-probe techniques

    NASA Astrophysics Data System (ADS)

    Winter, Bernd J.; Gatzke, Johannes; Quast, T.; Will, Ingo; Wick, Manfred T.; Liero, A.; Pop, D.; Hertel, Ingolf V.

    1998-12-01

    We report on the MBI User Facility at BESSY II, presently under construction, which is dedicated to study the dynamics of photo-induced processes by combining laser and synchrotron pulses. In this paper we focus on the synchronization of a modelocked ultrafast Ti:sapphire laser to the Berlin electron storage ring for synchrotron radiation (BESSY). Two different techniques have been applied -- one based on a digital phase comparator and the other based on analog high-harmonic mixing. Both schemes may be easily adjusted to either single, multi- or hybrid-bunch operation of the synchrotron. Moreover, the temporal accuracy of the synchronization unit suitably matches the widths of the synchrotron pulses (some ten picoseconds) to be expected at BESSY II. Therefore, the currently performed test experiments at BESSY I provide the basis for time- resolved photon-induced experiments which combine laser and SR-undulator pulses in a pump-probe scheme at BESSY II. This facility will be available within the first half of 1999.

  9. Trapped electronic states in YAG crystal excited by femtosecond radiation

    NASA Astrophysics Data System (ADS)

    Zavedeev, E. V.; Kononenko, V. V.; Konov, V. I.

    2017-07-01

    The excitation of an electronic subsystem of an yttrium aluminum garnet by 800 nm femtosecond radiation was studied theoretically and experimentally. The spatio-temporal dynamics of the refractive index ( n) inside the beam waist was explored by means of the pump-probe interferometric technique with a submicron resolution. The observed increase in n indicated the formation of bound electronic states relaxed for {˜}150 ps. We showed that the experimental data agreed with the computational simulation based on the numerical solution of the nonlinear Schrödinger equation only if these transient states were considered to arise from a direct light-induced process but not from the decay of radiatively generated free-electron-hole pairs.

  10. Photodissociation of Small Molecules and Photoionization of Free Radicals Using the VUV Velocity-Map Imaging Photoion and Photoelectron Method

    NASA Astrophysics Data System (ADS)

    Gao, Hong

    (2012). (Chapter 2) 2. Hong Gao, Yu Song, Lei Yang, Xiaoyu Shi, Qing-Zhu Yin, C. Y. Ng and William M. Jackson. "Branching ratio measurements of the predissociation of 12C16O by time-slice velocity-map ion imaging in the energy region from 108,000 to 110,500 cm-1", the Journal of Chemical Physics, 137, 034305 (2012). (Chapter 3) 3. Hong Gao, Yu Song, Yih-Chung Chang, Xiaoyu Shi, Qing-Zhu Yin, Roger C. Wiens, William M. Jackson, C. Y. Ng, "Branching Ratio Measurements for Vacuum Ultraviolet Photodissociation of 12C16O", the Journal of Physical Chemistry A. (article online ASAP). (Chapter 4) 4. Hong Gao, Yu Song, C. Y. Ng, William M. Jackson, " Communication: State-to-state photodissociation study by the two-color VUV-VUV laser pump-probe time-slice velocity-map-imaging-photoion method", the Journal of Chemical Physics, 138, 191102(2013). (Chapter 5) 5. Hong Gao, Zhou Lu, Lei Yang, Jingang Zhou, C. Y. Ng, "Communication: A vibrational study of propargyl cation using the vacuum ultraviolet laser velocity-map imaging photoelectron method", the Journal of Chemical Physics, 137, 161101(2012). (Chapter 6)

  11. Temperature Dependence in Femtosecond Desorption at Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Misewich, James

    1998-03-01

    Femtosecond laser induced desorption at metal surfaces is distinguished by two salient observations: the high yield of the reaction and the short correlation time in pump-probe measurements. This has led to the proposal of a model for desorption induced by multiple electronic transitions (DIMET). (J.A. Misewich, T.F. Heinz, and D.M. Newns, Phys. Rev. Lett. v.68 (1992) 3737.) The effect of the adsorbate temperature in DIMET has been studied using stochastic trajectory calculations with initial adsorbate vibrational quantum state occupation. We find that initial vibrational excitation substantially increases the desorption yield. These findings are related to two experimental observations. The long time-scale wings found in femtosecond time-resolved correlation measurements are thought to reflect the residual vibrational excitation left in the undesorbed adlayer following the first laser pulse. (J.A. Misewich, A. Kalamarides, T.F. Heinz, U. Hoefer, and M.M.T. Loy, J. Chem. Phys. v.100 (1994) 736.) Also, the wavelength dependence of femtosecond desorption experiments (S. Deliwala, R.J. Finlay, J.R. Goldman, T.H. Her, W.D. Mieher, and E. Mazur, Chem. Phys. Lett. v.242 (1995) 617 and D.G. Busch and W. Ho, Phys. Rev. Lett. v.77 (1996) 1338.) suggests a role for nonthermalized electrons which is interpreted in terms of the vibrational excitation left in the adlayer from unsuccessful DIET (single excitation) events as a result of the wavelength dependent nonthermalized electron distribution.

  12. Photoionization Dynamics of Small Molecules

    SciTech Connect

    Dehmer, Joseph L.; Dill, Dan; Parr, Albert C.

    1985-01-01

    The last decade has witnessed remarkable progress in characterizing dynamical aspects of the molecular photoionization process. The general challenge is to gain physical insight into those processes occuring during photo excitation and eventual escape of the photoelectron through the anisotropic molecular field, in terms of various observables such as photoionization cross-sections and branching ratios, photoelectron angular distributions and even newer probes mentioned below. Much of the progress in this field has mirrored earlier work in atomic photoionization dynamics where many key ideas were developed (e.g., channel interaction, quantum defect analysis, potential barrier phenomena and experimental techniques). However, additional concepts and techniques were required to deal with the strictly molecular aspects of the problem, particularly the anisotropy of the multicenter molecular field and the interaction among rovibronic modes.

  13. Electron spin dynamics of Ce3 + ions in YAG crystals studied by pulse-EPR and pump-probe Faraday rotation

    NASA Astrophysics Data System (ADS)

    Azamat, D. V.; Belykh, V. V.; Yakovlev, D. R.; Fobbe, F.; Feng, D. H.; Evers, E.; Jastrabik, L.; Dejneka, A.; Bayer, M.

    2017-08-01

    The spin relaxation dynamics of Ce3 + ions in heavily cerium-doped YAG crystals is studied using pulse-electron paramagnetic resonance and time-resolved pump-probe Faraday rotation. Both techniques address the 4 f ground state, while pump-probe Faraday rotation also provides access to the excited 5 d state. We measure a millisecond spin-lattice relaxation time T1, a microsecond spin coherence time T2, and a ˜10 ns inhomogeneous spin dephasing time T2* for the Ce3 + ground state at low temperatures. The spin-lattice relaxation of Ce3 + ions is due to modified Raman processes involving the optical phonon mode at ˜125 cm-1 . The relaxation at higher temperature goes through a first excited level of the 5/2 2F term at about ℏ ω ≈228 cm-1 . Effects provided by the hyperfine interaction of the Ce3 + with the 27Al nuclei are observed.

  14. Two-wavelength pump-probe technique using single distributed feedback laser array to probe gain recovery of an erbium-doped fiber amplifier

    NASA Astrophysics Data System (ADS)

    Kuroda, Keiji; Yoshikuni, Yuzo

    2017-03-01

    We propose a two-wavelength pump-probe technique to probe the gain recovery characteristics of an erbium-doped fiber amplifier. The two-wavelength pulse pairs are generated through the direct modulation of a single distributed feedback laser array. The proposed technique allows us to measure the wavelength dependence of the recovery time after gain saturation is induced by a signal of the same wavelength.

  15. Initial Atomic Motion Immediately Following Femtosecond-Laser Excitation in Phase-Change Materials.

    PubMed

    Matsubara, E; Okada, S; Ichitsubo, T; Kawaguchi, T; Hirata, A; Guan, P F; Tokuda, K; Tanimura, K; Matsunaga, T; Chen, M W; Yamada, N

    2016-09-23

    Despite the fact that phase-change materials are widely used for data storage, no consensus exists on the unique mechanism of their ultrafast phase change and its accompanied large and rapid optical change. By using the pump-probe observation method combining a femtosecond optical laser and an x-ray free-electron laser, we substantiate experimentally that, in both GeTe and Ge_{2}Sb_{2}Te_{5} crystals, rattling motion of mainly Ge atoms takes place with keeping the off-center position just after femtosecond-optical-laser irradiation, which eventually leads to a higher symmetry or disordered state. This very initial rattling motion in the undistorted lattice can be related to instantaneous optical change due to the loss of resonant bonding that characterizes GeTe-based phase change materials. Based on the amorphous structure derived by first-principles molecular dynamics simulation, we infer a plausible ultrafast amorphization mechanism via nonmelting.

  16. Cylindrical shockwave-induced compression mechanism in femtosecond laser Bessel pulse micro-drilling of PMMA

    NASA Astrophysics Data System (ADS)

    Wang, Guoyan; Yu, Yanwu; Jiang, Lan; Li, Xiaowei; Xie, Qian; Lu, Yongfeng

    2017-04-01

    Femtosecond (fs) laser Bessel pulses can be employed for high-quality and high-speed fabrication of high-aspect-ratio uniform microhole arrays. This technique exhibits prominent potential in three-dimensional packaging, fluidic devices, fiber sensing, biomedical devices, and aeronautics. However, the fundamental mechanisms remain mysterious. Using the femtosecond time-resolved pump-probe shadowgraph technique, this study revealed that the generation of cylindrical shockwaves inside the bulk material and the corresponding compression mechanism play key roles in the formation of high-aspect-ratio microholes. The phenomena were observed in all experiments of Bessel beam drilling of polymethyl methacrylate. In the aforementioned cases, the compression mechanism was confirmed by measuring sample mass losses that were experimentally determined to be negligible. By contrast, neither cylindrical shockwave nor compression mechanism was observed when a fused silica or Gaussian laser beam was involved.

  17. Femtosecond few-fermion dynamics and deterministic single-photon gain in a quantum dot

    NASA Astrophysics Data System (ADS)

    Sotier, Florian; Thomay, Tim; Hanke, Tobias; Korger, Jan; Mahapatra, Suddhasatta; Frey, Alexander; Brunner, Karl; Bratschitsch, Rudolf; Leitenstorfer, Alfred

    2009-05-01

    The ability to coherently manipulate single electron and photon states is vital for quantum information processing. However, typical quantization and correlation energies restrict processing rates in real implementations owing to the time-energy uncertainty. Here we report optical initialization, manipulation and probing of a single CdSe/ZnSe semiconductor quantum dot on femtosecond timescales, the ultimate limit for clean quantum operations in such `artificial atoms'. Resonant pump-probe measurements on a donor-charged quantum dot reveal that the fundamental exciton absorption is switched off through instantaneous Coulomb renormalization. Optical gain builds up following ultrafast intraband relaxation, with a thermalization rate determined by the electron spin. Operating the system in a nonlinear regime, we demonstrate the ability to change the number of quanta in a femtosecond light pulse by exactly +/-1. This deterministic single-photon amplifier is characterized by a flat gain spectrum.

  18. Femtosecond powder diffraction with a laser-driven hard X-ray source.

    PubMed

    Zamponi, F; Ansari, Z; Woerner, M; Elsaesser, T

    2010-01-18

    X-ray powder diffraction with a femtosecond time resolution is introduced to map ultrafast structural dynamics of polycrystalline condensed matter. Our pump-probe approach is based on photoexcitation of a powder sample with a femtosecond optical pulse and probing changes of its structure by diffracting a hard X-ray pulse generated in a laser-driven plasma source. We discuss the key aspects of this scheme including an analysis of detection sensitivity and angular resolution. Applying this technique to the prototype molecular material ammonium sulfate, up to 20 powder diffraction rings are recorded simultaneously with a time resolution of 100 fs. We describe how to derive transient charge density maps of the material from the extensive set of diffraction data in a quantitative way.

  19. Investigating radiation induced damage processes with femtosecond x-ray pulses (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Song, Changyong

    2017-05-01

    Interest in high-resolution structure investigation has been zealous, especially with the advent of X-ray free electron lasers (XFELs). The intense and ultra-short X-ray laser pulses ( 10 GW) pave new routes to explore structures and dynamics of single macromolecules, functional nanomaterials and complex electronic materials. In the last several years, we have developed XFEL single-shot diffraction imaging by probing ultrafast phase changes directly. Pump-probe single-shot imaging was realized by synchronizing femtosecond (<10 fs in FWHM) X-ray laser (probe) with femtosecond (50 fs) IR laser (pump) at better than 1 ps resolution. Nanoparticles under intense fs-laser pulses were investigated with fs XFEL pulses to provide insight into the irreversible particle damage processes with nanoscale resolution. Research effort, introduced, aims to extend the current spatio-temporal resolution beyond the present limit. We expect this single-shot dynamic imaging to open new science opportunity with XFELs.

  20. Correlating quasiparticle excitations with quantum femtosecond magnetism in photoexcited nonequilibrium states of insulating antiferromagnetic manganites

    NASA Astrophysics Data System (ADS)

    Lingos, P. C.; Patz, A.; Li, T.; Barmparis, G. D.; Keliri, A.; Kapetanakis, M. D.; Li, L.; Yan, J.; Wang, J.; Perakis, I. E.

    2017-06-01

    We describe a mechanism for insulator-to-metal transition triggered by spin canting following femtosecond laser excitation of insulating antiferromagnetic (AFM) states of colossal magnetoresistive (CMR) manganites. We show that photoexcitation of composite fermion quasiparticles dressed by spin fluctuations results in the population of a broad metallic conduction band due to canting of the AFM background spins via strong electron-spin local correlation. By inducing spin canting, photoexcitation can increase the quasiparticle energy dispersion and quench the charge excitation energy gap. This increases the critical Jahn-Teller (JT) lattice displacement required to maintain an insulating state. We present femtosecond-resolved pump-probe measurements showing biexponential relaxation of the differential reflectivity below the AFM transition temperature. We observe a nonlinear dependence of the ratio of the femtosecond and picosecond relaxation component amplitudes at the same pump fluence threshold where we observe femtosecond magnetization photoexcitation. We attribute this correlation between nonlinear femtosecond spin and charge dynamics to spin/charge/lattice coupling and population inversion between the polaronic majority carriers and metallic quasielectron minority carriers as the lattice displacement becomes smaller than the critical value required to maintain an insulating state following laser-induced spin canting.

  1. Mass-Selective Laser Photoionization.

    ERIC Educational Resources Information Center

    Smalley, R. E.

    1982-01-01

    Discusses the nature and applications of mass-selective laser photoionization. The ionization can be done with a single intense laser pulse lasting a few billionths of a second with no molecular fragmentation. Applications focus on: (1) benzene clusters, excimers, and exciplexes; (2) metal clusters; and (3) triplet formation and decay. (Author/JN)

  2. Mass-Selective Laser Photoionization.

    ERIC Educational Resources Information Center

    Smalley, R. E.

    1982-01-01

    Discusses the nature and applications of mass-selective laser photoionization. The ionization can be done with a single intense laser pulse lasting a few billionths of a second with no molecular fragmentation. Applications focus on: (1) benzene clusters, excimers, and exciplexes; (2) metal clusters; and (3) triplet formation and decay. (Author/JN)

  3. PHOTOIONIZATION IN THE SOLAR WIND

    SciTech Connect

    Landi, E.; Lepri, S. T.

    2015-10-20

    In this work we investigate the effects of photoionization on the charge state composition of the solar wind. Using measured solar EUV and X-ray irradiance, the Michigan Ionization Code and a model for the fast and slow solar wind, we calculate the evolution of the charge state distribution of He, C, N, O, Ne, Mg, Si, S, and Fe with and without including photoionization for both types of wind. We find that the solar radiation has significant effects on the charge state distribution of C, N, and O, causing the ionization levels of these elements to be higher than without photoionization; differences are largest for oxygen. The ions commonly observed for elements heavier than O are much less affected, except in ICMEs where Fe ions more ionized than 16+ can also be affected by the solar radiation. We also show that the commonly used O{sup 7+}/O{sup 6+} density ratio is the most sensitive to photoionization; this sensitivity also causes the value of this ratio to depend on the phase of the solar cycle. We show that the O{sup 7+}/O{sup 6+} ratio needs to be used with caution for solar wind classification and coronal temperature estimates, and recommend the C{sup 6+}/C{sup 4+} ratio for these purposes.

  4. Femtosecond excitation transfer processes in biliprotein trimers

    NASA Astrophysics Data System (ADS)

    Sharkov, A. V.; Khoroshilov, E. V.; Kryukov, I. V.; Palsson, Lars-Olof; Kryukov, P. G.; Fischer, R.; Scheer, Hella-Christin; Gillbro, Tomas

    1993-06-01

    Femtosecond processes in allophycocyanin, C-phycocyanin and phycoerythrocyanin trimers and monomers have been examined by means of polarization pump-probe technique. No femtosecond kinetics were observed in monomeric preparations. The isotropic absorption recovery kinetics with (tau) equals 440 +/- 50 fs which is not accompanied by anisotropy decay kinetics was obtained in allophycocyanin trimers at 612 nm. The conclusion about energy transfer between neighboring (alpha) 84 and (beta) 84 chromophores with different absorption spectra was made. The proposed model takes into account a stabilizing role of the linker peptide. Spectral and kinetic measurements were made in the 635 - 690 nm spectral region where the proposed acceptor should absorb. The bleaching of the 650-nm band occurs with a delay relative to the bleaching at 615 nm. Only a rise term was observed at 658 nm in consistence with the proposed model. Anisotropy values calculated around 650 nm at 3 ps after excitation are in the range 0.1 - 0.25 corresponding to an angle of 30 degree(s) - 45 degree(s) between the donor and acceptor transition dipole moments. A 500-fs absorption recovery and anisotropy decay process was obtained for C-phycocyanin trimers and explained by Forster energy transfer over 20.8 angstroms between neighboring (alpha) 84 and (beta) 84 chromophores of different monomeric subunits having similar absorption spectra and with a 65 degree(s) angle between their orientations. Energy transfer between violobilin ((alpha) 84) and phycocyanobilin ((beta) 84) chromophores was examined in donor and acceptor spectral regions of phycoerythrocyanin trimers, and was found to take 400 fs.

  5. Photoionization dynamics of pure helium droplets: exciton formation vs autoionization

    NASA Astrophysics Data System (ADS)

    Kornilov, Oleg; Gessner, Oliver; Buennermann, Oliver; Wang, Chia; Leone, Steve; Neumark, Daniel

    2010-03-01

    ^4He droplets possess unique properties. In addition to fundamental quantum effects of superfluidity the droplets show ability to efficiently pick-up foreign atoms, molecules and complexes, which is used in a number of matrix isolation spectroscopies in energy domain. Complementary to these studies, novel time-domain experiments will be presented emphasizing dynamics of photoionization of pure helium droplets. The experiments follow up on a recent observation of ultraslow (E<1 meV) photoelectrons emitted from droplets upon ionization by synchrotron radiation. The dynamics of photoionization is studied by exciting droplets with a pulsed VUV radiation generated using the high-order harmonic generation technique. The droplets subsequently interact with an IR pulse, which probes transient electronic states before droplet autoionization. Femtosecond and picosecond relaxation dynamics and competition between droplet ionization and formation of a long-lived excited state are observed. Probe pulse leads to droplet ``re-excitation'' and production of even more ultraslow electrons. The results will be extended to doped droplets anticipating indirect dopant ionization dynamics.

  6. Photoionization of oxidized metal clusters

    SciTech Connect

    Dao, P.D.; Peterson, K.I.; Castleman, A.W. Jr.

    1984-01-01

    Oxidized metal clusters (Na/sub x/O and K/sub x/O for 2< or =x< or =4) were formed in a gas phase reaction between metal clusters and an oxidizing gas using a double expansion technique. Their appearance potentials were measured using a molecular beam-photoionization mass spectrometer system. These first photoionization data for oxidized clusters provide information on trends of ionization potentials as a function of the degree of aggregation. The ionization potentials do not differ greatly from the analogous metallic species, but in the case of the sodium tetramer the value does fall below that of the bare metal cluster. This finding is in accord with what has been observed as an influence of impurities on the work function of the bulk sodium. The results are also of interest concerning questions of octet rule violations and hypervalency.

  7. Flexible attosecond beamline for high harmonic spectroscopy and XUV/near-IR pump probe experiments requiring long acquisition times

    SciTech Connect

    Weber, S. J. Manschwetus, B.; Billon, M.; Bougeard, M.; Breger, P.; Géléoc, M.; Gruson, V.; Lin, N.; Ruchon, T.; Salières, P.; Carré, B.

    2015-03-15

    We describe the versatile features of the attosecond beamline recently installed at CEA-Saclay on the PLFA kHz laser. It combines a fine and very complete set of diagnostics enabling high harmonic spectroscopy (HHS) through the advanced characterization of the amplitude, phase, and polarization of the harmonic emission. It also allows a variety of photo-ionization experiments using magnetic bottle and COLTRIMS (COLd Target Recoil Ion Momentum Microscopy) electron spectrometers that may be used simultaneously, thanks to a two-foci configuration. Using both passive and active stabilization, special care was paid to the long term stability of the system to allow, using both experimental approaches, time resolved studies with attosecond precision, typically over several hours of acquisition times. As an illustration, applications to multi-orbital HHS and electron-ion coincidence time resolved spectroscopy are presented.

  8. Insights into the reaction dynamics of molecules and clusters using femtosecond spectroscopy

    NASA Astrophysics Data System (ADS)

    Hurley, Sean Michael

    In this dissertation, studies of the ultrafast dynamics of HBr, HBr-water clusters, HBr clusters, acetone-water clusters and SO2 clusters are reported. Interrogation of the state formed by the avoided crossing of the Rydberg E(1Sigma+) state and valence state V( 1Sigma+) of HBr and DBr revealed dynamic behavior that was different for the two isotopomers. Pump-probe experiments on HBr showed no change in the lifetime over the range of pump wavelengths of 256.7 to 254.7 nm. However, the lifetime of DBr decreased as the pump wavelength was tuned bluer. Tunneling is involved in the scheme. Dissolution of acids is one of the most fundamental of solvation processes, where experimentally there is still a paucity of information regarding the dynamics of the phenomenon and the nature of the hydration complex leading to ion-pair formation. Herein we address these issues using femtosecond pump-probe spectroscopy. Evidence is presented showing that five water molecules are necessary for complete dissolution of an HBr molecule to form the contact ion-pair H+·Br-(H2O) n in the electronic ground state. Studies have revealed that in small mixed clusters (n < 5), the ion-pair formation can be photoinduced by electronic excitation. The ultrafast dynamics of HBr-water clusters have been investigated using the pump-probe technique coupled with reflectron time-of-flight mass spectrometry. HBr clusters, mixed HBr-water clusters and protonated water clusters are observed in the mass spectra. Dynamic studies reveal that when an HBr chromophore of a cluster is excited electronically, solvent reorganization occurs to form the solvent separated ion-pair. The influence of excitation wavelength and clustering on the dynamics are discussed. In addition, further evidence is presented confirming that complete dissolution of HBr requires five solvent molecules in the isolated complex. The ultrafast dynamics of mixed clusters of acetone and water, H +(CH3COH3)n(H2O) m, have been investigated using

  9. Generation of isolated attosecond pulses with double optical gating and electronic dynamics in molecules studied via attosecond pump-probe experiment

    NASA Astrophysics Data System (ADS)

    Mashiko, Hiroki

    2010-03-01

    Single isolated attosecond pulses are useful tools for studying electron dynamics. Previously, such as pulses can be generated by few cycle 5 fs driving lasers. It is still a technical challenge to reproduce daily such pulses. In order to allow longer driving laser pulses, two optical gating methods of polarization gating and two-color gating are combined. This approach is dubbed double optical gating. Due to less depletion of the ground state population by the leading edge of the field, this technique can produce isolated 250 as pulses using up to ˜25 fs driving laser pulses. Also, the supercontinuous spectra (28-620 eV) can in principle support a 16 as pulse duration, obtained from 8 fs driving lasers. Because of the relaxation on the driving laser requirements, more laboratories can enter the isolated attosecond pulse science field. Pump-probe experiments with such isolated attosecond pulses and IR pulses can provide quantitative information on electronic dynamics. In recent work, the photoelectron spectra of sulfur hexafluoride (SF6) clearly indicates the precise shape of the IR driving pulse (1.5 eV), verifying that isolated ˜400 as pulses (93 eV) are achieved and these pulses produce an instantaneous inner valence ionization in the molecule. The pump-probe spectra of cation fragments resulting from double and triple ionization show 6-7 fs rise times (SF4^2+, SF3^2+, SF2^2+ and S^2+) or decay times (SF^+ and S^+) times governed by the overlap of the IR and XUV pulses. A suppression or enhancement of certain fragmentation channels is tentatively interpreted as resulting from the IR laser exciting the initial cations to higher states that exhibit different decay channels. This type of pump-probe experiment with isolated attosecond pulses is powerful for the study of electronic dynamics as well as resulting nuclear fragmentation measurements.

  10. Femtosecond spectral holography

    SciTech Connect

    Weiner, A.M.; Leaird, D.E.; Reitze, D.H.; Paek, E.G. )

    1992-10-01

    Storage, recall, and processing of shaped femtosecond waveforms are achieved by performing spectral holography within a femtosecond pulse shaping apparatus. Time reversal, as well as correlation and convolution, of femtosecond temporal signals is demonstrated. Applications of this technique to matched filtering, dispersion compensation, encryption and decoding, and femtosecond waveform synthesis are also discussed. The work extends the powerful principles of holographic signal processing, which have been used extensively for pattern recognition and filtering of two-dimensional spatial signals, to the femtosecond time domain. 44 refs.

  11. Femtosecond spectral holography

    NASA Astrophysics Data System (ADS)

    Weiner, Andrew M.; Leaird, Daniel E.; Reitze, David H.; Paek, Eung G.

    1992-10-01

    Storage, recall, and processing of shaped femtosecond waveforms are achieved by performing spectral holography within a femtosecond pulse shaping apparatus. Time reversal, as well as correlation and convolution, of femtosecond temporal signals is demonstrated. Applications of this technique to matched filtering, dispersion compensation, encryption and decoding, and femtosecond waveform synthesis are also discussed. The work extends the powerful principles of holographic signal processing, which have been used extensively for pattern recognition and filtering of two-dimensional spatial signals, to the femtosecond time domain.

  12. An infrared pump-probe measurement of the Sm3+6H7/2 lifetime in LiYF4

    NASA Astrophysics Data System (ADS)

    Horvath, Sebastian P.; Wells, Jon-Paul R.; van der Meer, Alexander F. G.; Reid, Michael F.

    2017-04-01

    We report a pump-probe measurement of the lifetime of the 6H7/2 multiplet of Sm3+:LiYF4. A lifetime of 3.1 ± 0.3 ps was inferred for the Y2 level of the 6H7/2 multiplet. This lifetime is two orders of magnitude faster than for a similar energy gap in Nd3+:LiYF4, and does not follow the prediction of a simple exponential energy-gap law for non-radiative relaxation in this material.

  13. Time-averaging approximation in the interaction picture: Anisotropy of vibrational pump-probe experiments for coupled chromophores with application to liquid water

    NASA Astrophysics Data System (ADS)

    Yang, Mino

    2012-10-01

    A time-averaging approximation method developed to efficiently calculate the short-time dynamics of coupled vibrational chromophores using mixed quantum/classical theories is extended in order to be applicable to the study of vibrational dynamics at longer time scales. A quantum mechanical time propagator for long times is decomposed into the product of short-time propagators, and a time-averaging approximation is then applied to each of the latter. Using the extended time-averaging approximation, we calculate the anisotropy decay of the data obtained from impulsive vibrational pump-probe experiments on the OH stretching modes of water, which is in excellent agreement with numerically exact results.

  14. Weak-field few-femtosecond VUV photodissociation dynamics of water isotopologues

    NASA Astrophysics Data System (ADS)

    Baumann, Arne; Bazzi, Sophia; Rompotis, Dimitrios; Schepp, Oliver; Azima, Armin; Wieland, Marek; Popova-Gorelova, Daria; Vendrell, Oriol; Santra, Robin; Drescher, Markus

    2017-07-01

    We present a joint experimental and theoretical study of the VUV-induced dynamics of H2O and its deuterated isotopologues in the first excited state (A ˜1B1 ) utilizing a VUV-pump VUV-probe scheme combined with a b initio classical trajectory calculations. 16-fs VUV pulses centered at 161 nm created by fifth-order harmonic generation are employed for single-shot pump-probe measurements. Combined with a precise determination of the VUV pulses' temporal profile, they provide the necessary temporal resolution to elucidate sub-10-fs dissociation dynamics in the 1+1 photon ionization time window. Ionization with a single VUV photon complements established strong-field ionization schemes by disclosing the molecular dynamics under perturbative conditions. Kinetic isotope effects derived from the pump-probe experiment are found to be in agreement with our by ab initio classical trajectory calculations, taking into account photoionization cross sections for the ground and first excited state of the water cation.

  15. Dynamics of femtosecond laser-induced periodic surface structures on silicon by high spatial and temporal resolution imaging

    SciTech Connect

    Jia, X.; Jia, T. Q. Peng, N. N.; Feng, D. H.; Zhang, S. A.; Sun, Z. R.

    2014-04-14

    The formation dynamics of periodic ripples induced by femtosecond laser pulses (pulse duration τ = 50 fs and central wavelength λ = 800 nm) are studied by a collinear pump-probe imaging technique with a temporal resolution of 1 ps and a spatial resolution of 440 nm. The ripples with periods close to the laser wavelength begin to appear upon irradiation of two pump pulses at surface defects produced by the prior one. The rudiments of periodic ripples emerge in the initial tens of picoseconds after fs laser irradiation, and the ripple positions keep unmoved until the formation processes complete mainly in a temporal span of 1500 ps. The results suggest that the periodic deposition of laser energy during the interaction between femtosecond laser pulses and sample surface plays a dominant role in the formation of periodic ripples.

  16. Characterisation of the UFXC32k hybrid pixel detector for time-resolved pump-probe diffraction experiments at Synchrotron SOLEIL

    NASA Astrophysics Data System (ADS)

    Dawiec, A.; Maj, P.; Ciavardini, A.; Gryboś, P.; Laulhé, C.; Menneglier, C.; Szczygieł, R.

    2017-03-01

    The experimental set-up for time-resolved studies of ultra-fast photo-induced structural dynamics at the Synchrotron SOLEIL is based on a general pump-probe scheme that has been developed and implemented on the CRISTAL hard X-ray diffraction beamline [1,2]. In a so-called pump-probe cycle, the sample is excited with an ultra-short laser pulse of ≈40 fs duration (the pump), and induced changes in its atomic structure are studied by measuring, with a precisely controlled delay, a diffraction pattern from a single pulse of synchrotron radiation (the probe) with a 2-D pixel detector. An improvement to the classical scheme is proposed, where the sample's response is probed at two different delays after each laser excitation. The first measurement at short delays allows studying the photo-induced dynamics. The second one is a reference measurement taken after sample's relaxation, which permits detection of drifts in the experimental conditions (e.g. beam misalignment, sample degradation). A hybrid pixel detector with a very fast readout time, a high dynamic range and extended linearity was tested to achieve the experiment objectives. In this paper, the first results obtained with the UFXC32k single photon counting detector are presented.

  17. The principles of infrared-x-ray pump-probe spectroscopy. Applications on proton transfer in core-ionized water dimers.

    PubMed

    Felicíssimo, V C; Guimarães, F F; Gel'mukhanov, F; Cesar, A; Agren, H

    2005-03-01

    In this paper we derive the basic physics underlying infrared-x-ray pump-probe spectroscopy (IR, infrared). Particular features of the spectroscopy are highlighted and discussed, such as dependence on phase of the infrared pulse, duration and delay time of the x-ray pulse, and molecular orientation. Numerical applications are carried out for the water dimer using wave packet techniques. It is shown that core ionization of the donor oxygen of the water dimer results in a drastic change of the potential with the global minimum placed in the proton transfer region. The results of the modeling indicate that IR-x-ray pump-probe spectroscopy can be used to study the dynamics of proton transfer in this core-ionized state, and that, contrary to conventional core level photoelectron spectroscopy, x-ray core-ionization driven by an IR field is a proper method to explore the proton transfer in a system like the water dimer. We observe that the trajectory of the nuclear wave packet in the ground state potential well is strongly affected by the absolute phase of the IR pulse.

  18. A Bloch equation approach to intensity dependent optical spectra of light harvesting complex II: excitation dependence of light harvesting complex II pump-probe spectra.

    PubMed

    Richter, Marten; Renger, Thomas; Knorr, Andreas

    2008-01-01

    On the basis of the recent progress in the resolution of the structure of the antenna light harvesting complex II (LHC II) of the photosystem II, we propose a microscopically motivated theory to predict excitation intensity-dependent spectra. We show that optical Bloch equations provide the means to include all 2( N ) excited states of an oligomer complex of N coupled two-level systems and analyze the effects of Pauli Blocking and exciton-exciton annihilation on pump-probe spectra. We use LHC Bloch equations for 14 Coulomb coupled two-level systems, which describe the S (0) and S (1) level of every chlorophyll molecule. All parameter introduced into the Hamiltonian are based on microscopic structure and a quantum chemical model. The derived Bloch equations describe not only linear absorption but also the intensity dependence of optical spectra in a regime where the interplay of Pauli Blocking effects as well as exciton-exciton annihilation effects are important. As an example, pump-probe spectra are discussed. The observed saturation of the spectra for high intensities can be viewed as a relaxation channel blockade on short time scales due to Pauli blocking. The theoretical investigation is useful for the interpretation of the experimental data, if the experimental conditions exceed the low intensity pump limit and effects like strong Pauli Blocking and exciton-exciton annihilation need to be considered. These effects become important when multiple excitations are generated by the pump pulse in the complex.

  19. The principles of infrared-x-ray pump-probe spectroscopy. Applications on proton transfer in core-ionized water dimers

    SciTech Connect

    Felicissimo, V.C.; Guimaraes, F.F.; Gel'mukhanov, F.; Cesar, A.; Aagren, H.

    2005-03-01

    In this paper we derive the basic physics underlying infrared-x-ray pump-probe spectroscopy (IR, infrared). Particular features of the spectroscopy are highlighted and discussed, such as dependence on phase of the infrared pulse, duration and delay time of the x-ray pulse, and molecular orientation. Numerical applications are carried out for the water dimer using wave packet techniques. It is shown that core ionization of the donor oxygen of the water dimer results in a drastic change of the potential with the global minimum placed in the proton transfer region. The results of the modeling indicate that IR-x-ray pump-probe spectroscopy can be used to study the dynamics of proton transfer in this core-ionized state, and that, contrary to conventional core level photoelectron spectroscopy, x-ray core-ionization driven by an IR field is a proper method to explore the proton transfer in a system like the water dimer. We observe that the trajectory of the nuclear wave packet in the ground state potential well is strongly affected by the absolute phase of the IR pulse.

  20. Non-degenerate fs pump-probe study on InGaN with multi-wavelength second-harmonic generation.

    PubMed

    Wang, Hsiang-Chen; Lu, Yen-Cheng; Chen, Cheng-Yen; Chi, Chun-Yung; Chin, Shu-Cheng; Yang, C C

    2005-07-11

    Non-degenerate fs pump-probe experiments in the UV-visible range for ultrafast carrier dynamics study of InGaN with adjustable pump and probe photon energies are implemented with simultaneously multiwavelength second-harmonic generation (SHG) of a 10 fs Ti:sapphire laser. The multi-wavelength SHG is realized with two beta-barium borate crystals of different cutting angles. The full-widths at half-maximum of the SHG pulses are around 150 fs, which are obtained from the cross-correlation measurement with a reverse-biased 280-nm light-emitting diode as the twophoton absorption photo-detector. Such pulses are used to perform nondegenerate pump-probe experiments on an InGaN thin film, in which indium-rich nano-clusters and compositional fluctuations have been identified. Relaxation of carriers from the pump level to the probe one through the scattering-induced local thermalization (<1 ps) and then the carrier-transport-dominating global thermalization (in several ps) processes is observed.

  1. IONIS: Approximate atomic photoionization intensities

    NASA Astrophysics Data System (ADS)

    Heinäsmäki, Sami

    2012-02-01

    A program to compute relative atomic photoionization cross sections is presented. The code applies the output of the multiconfiguration Dirac-Fock method for atoms in the single active electron scheme, by computing the overlap of the bound electron states in the initial and final states. The contribution from the single-particle ionization matrix elements is assumed to be the same for each final state. This method gives rather accurate relative ionization probabilities provided the single-electron ionization matrix elements do not depend strongly on energy in the region considered. The method is especially suited for open shell atoms where electronic correlation in the ionic states is large. Program summaryProgram title: IONIS Catalogue identifier: AEKK_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKK_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1149 No. of bytes in distributed program, including test data, etc.: 12 877 Distribution format: tar.gz Programming language: Fortran 95 Computer: Workstations Operating system: GNU/Linux, Unix Classification: 2.2, 2.5 Nature of problem: Photoionization intensities for atoms. Solution method: The code applies the output of the multiconfiguration Dirac-Fock codes Grasp92 [1] or Grasp2K [2], to compute approximate photoionization intensities. The intensity is computed within the one-electron transition approximation and by assuming that the sum of the single-particle ionization probabilities is the same for all final ionic states. Restrictions: The program gives nonzero intensities for those transitions where only one electron is removed from the initial configuration(s). Shake-type many-electron transitions are not computed. The ionized shell must be closed in the initial state. Running time: Few seconds for a

  2. Biomedical applications of laser photoionization

    NASA Astrophysics Data System (ADS)

    Xiong, Xiaoxiong; Moore, Larry J.; Fassett, John R.; O'Haver, Thomas C.

    1991-07-01

    Trace elements are important for many essential metabolic functions. Zinc is a structural/functional component in more than 200 enzymes active in the biochemistry of cell division and tissue growth, neurology and endocrine control. Calcium is involved in intracellular control mechanisms and in skeletal bone building and resorption processes related to osteoporosis. Sensitive and selective laser photoionization is being developed to understand mechanisms in smaller samples and biological units approaching the cellular domain. Zinc has an ionization potential of 9.4 eV, or 75766.8 cm-1. Several processes are being explored, including two-photon resonant, three- photon ionization utilizing sequential UV transitions, e.g., 4s2 1S0 yields 4s4p 3P1 and 4s4p 3P1 yields 4s5d 3D1. Preliminary zinc stable isotope ratio data obtained by thermal atomization and laser photoionization agree with accepted values within 2 to 5%, except for anomalous 67Zn. Photoionization of calcium is being studied for isotope enrichment and ratio measurement using narrow and medium bandwidth lasers. Several ionization pathways, e.g., 4s2 1S0 - 2hv1 yields 4s10s - hv2 yields Ca+ (4s2S), are being investigated for isotopically selective ionization. Auto-ionization pathways are explored for greater efficiency in isotopic analysis. All studies have utilized a Nd:YAG- pumped laser system with one or two frequency-doubled tunable dye lasers coupled either to a magnetic sector or time-of-flight mass spectrometer.

  3. Photoionization of methanol and formaldehyde

    NASA Technical Reports Server (NTRS)

    Warneck, P.

    1971-01-01

    Photoions produced in methanol and formaldehyde by radiation in the spectral region 450-1150 A were analyzed mass spectrometrically, and their relative yields were determined as a function of wavelength. First ionization potentials were determined, and the ion yield curves were interpreted in terms of ionization processes in conjunction with other data. Fragment ions were detected on mass numbers of 31, 30, 29, 15, and 14 for methanol, and 29, 2, and 1 for formaldehyde. The associated appearance potentials were determined and were used to calculate heats of formation of the ions CH2OH(+) and HCO(+), and the radicals CH3, CH2, and HCO.

  4. Photoionization Efficiencies of Five Polycyclic Aromatic Hydrocarbons.

    PubMed

    Johansson, K Olof; Campbell, Matthew F; Elvati, Paolo; Schrader, Paul E; Zádor, Judit; Richards-Henderson, Nicole K; Wilson, Kevin R; Violi, Angela; Michelsen, Hope A

    2017-06-15

    We have measured photoionization-efficiency curves for pyrene, fluoranthene, chrysene, perylene, and coronene in the photon energy range of 7.5-10.2 eV and derived their photoionization cross-section curves in this energy range. All measurements were performed using tunable vacuum ultraviolet (VUV) radiation generated at the Advanced Light Source synchrotron at Lawrence Berkeley National Laboratory. The VUV radiation was used for photoionization, and detection was performed using a time-of-flight mass spectrometer. We measured the photoionization efficiency of 2,5-dimethylfuran simultaneously with those of pyrene, fluoranthene, chrysene, perylene, and coronene to obtain references of the photon flux during each measurement from the known photoionization cross-section curve of 2,5-dimethylfuran.

  5. Photoionization Efficiencies of Five Polycyclic Aromatic Hydrocarbons

    DOE PAGES

    Johansson, K. Olof; Campbell, Matthew F.; Elvati, Paolo; ...

    2017-05-18

    We have measured photoionization-efficiency curves for pyrene, fluoranthene, chrysene, perylene, and coronene in the photon energy range of 7.5-10.2 eV and derived their photoionization cross-section curves in this energy range. All measurements were performed using tunable vacuum ultraviolet (VUV) radiation generated at the Advanced Light Source synchrotron at Lawrence Berkeley National Laboratory. The VUV radiation was used for photoionization, and detection was performed using a time-of-flight mass spectrometer. We measured the photoionization efficiency of 2,5-dimethylfuran simultaneously with those of pyrene, fluoranthene, chrysene, perylene, and coronene to obtain references of the photon flux during each measurement from the known photoionization cross-sectionmore » curve of 2,5- dimethylfuran.« less

  6. Photoionization of helium by attosecond pulses: Extraction of spectra from correlated wave functions

    NASA Astrophysics Data System (ADS)

    Argenti, Luca; Pazourek, Renate; Feist, Johannes; Nagele, Stefan; Liertzer, Matthias; Persson, Emil; Burgdörfer, Joachim; Lindroth, Eva

    2013-05-01

    We investigate the photoionization spectrum of helium by attosecond XUV pulses both in the spectral region of doubly excited resonances as well as above the double ionization threshold. In order to probe for convergence, we compare three techniques to extract photoelectron spectra from the wave packet resulting from the integration of the time-dependent Schrödinger equation in a finite-element discrete variable representation basis. These techniques are projection on products of hydrogenic bound and continuum states, projection onto multichannel scattering states computed in a B-spline close-coupling basis, and a technique based on exterior complex scaling implemented in the same basis used for the time propagation. These methods allow one to monitor the population of continuum states in wave packets created with ultrashort pulses in different regimes. Applications include photo cross sections and anisotropy parameters in the spectral region of doubly excited resonances, time-resolved photoexcitation of autoionizing resonances in an attosecond pump-probe setting, and the energy and angular distribution of correlated wave packets for two-photon double ionization.

  7. Femtosecond resonance-enhanced multiphoton-ionization photoelectron spectrum of ammonia

    NASA Astrophysics Data System (ADS)

    Liu, Hong Ping; Yin, Shu Hui; Zhang, Jian Yang; Wang, Li; Jiang, Bo; Lou, Nan Quan

    2006-11-01

    We have studied the multiphoton dissociation dynamics of the Ẽ'A1'1 Rydberg state of ammonia (NH3) on a homebuilt femtosecond pump-probe system by resonance-enhanced multiphoton ionization photoelectron (REMPI-PE) spectroscopy. The highly excited Rydberg state, Ẽ'1A1' , of ammonia was accessed by two 267nm pump photons and then ionized by a 401nm probe pulse delayed in time. The variation of the REMPI-PE spectra of ammonia with pump-probe delay time provides valuable information on the dynamics of the excited intermediate accessed by the pump pulse. We find that the Frank-Condon preferred transition during ionization does not occur for Δυ1=0 but for Δυ1=1 , which implies that the intermediate has a different geometry from the ionic ground state. Different dynamical behavior has been observed for each of the transitions Δυ1=0,1,2,3 , giving a full temporal description of the excited intermediate state by projection onto the eigenspace of the ionic ground state.

  8. Studies of Ultrafast Femtosecond-Laser-Generated Strain Fields with Coherent X-rays

    SciTech Connect

    Dufresne, Eric M.; Adams, Bernhard; Landahl, Eric C.; Khounsary, Ali M.; Reis, David; Fritz, David M.; Lee, SooHeyong

    2007-01-19

    In its 324 bunch-mode of operation, the Advanced Photon Source (APS) has opened new avenues of femtosecond-laser science and techniques. In this new mode, if one uses the tightly focused low-pulse energy (nJ), high repetition rate fs-laser Ti:sapphire oscillator (88 MHz) on beamline 7ID, every laser pulse and X-ray bunch can be overlapped and delayed with respect to each other, resulting in a high-repetition rate pump-probe experiment that uses all the APS X-ray bunches. This paper describes an example of how coherent X-ray experiments may be used to study laser-generated strain fields in semiconductors. With an oscillator beam focused to 6 {mu}m onto GaAs, we have observed coherent X-ray diffraction patterns with a high-resolution camera. We have developed two techniques to observe the strain field, a topographic technique and a coherent diffraction technique. The topographic technique is quite useful to achieve a coarse spatial overlap of the the laser and X-ray beams. The coherent X-ray technique allows one to push the alignment to a few microns. This paper focuses solely on the latter technique. This experiment may help to develop techniques that will be used at the future free electron laser sources, where coherent and pump-probe experiments can be done simultaneously.

  9. Evolution of energy deposition during glass cutting with pulsed femtosecond laser radiation

    NASA Astrophysics Data System (ADS)

    Kalupka, C.; Großmann, D.; Reininghaus, M.

    2017-05-01

    We report on investigations of the energy deposition in the volume of thin glass during an ablation cutting process with pulsed femtosecond laser radiation by time-resolved pump-probe shadowgraphy. For a single laser pulse, the temporal evolution of the transient electronic excitation of the glass volume is imaged up to 10 ps after initial excitation. For an increasing number of laser pulses, the spatial excitation of the glass volume significantly changes compared to single pulse irradiation. Sharp spikes are observed, which reduce the transmission of the illuminating probe pulse. This indicates local maxima of the absorption and, therefore, energy deposition of the pump pulse energy in the glass volume. Furthermore, for an increasing number of pulses, different shapes of the surface ablation crater are observed. To study the correlation between the shape of the surface ablation crater and the energy deposition in the glass volume, simulations of the spatial intensity distribution of the pump pulse are executed by means of linear beam propagation method. We show that the transient excitation spikes observed by pump-probe shadowgraphy can be explained by refraction and diffraction of the laser radiation at the surface ablation crater. Our results provide an experimental validation for the physical reason of an ablation stop for an ablation cutting process. Moreover, the simulations allow for the prediction of damage inside the glass volume.

  10. Investigating vibrational relaxation in cyanide-bridged transition metal mixed-valence complexes using two-dimensional infrared and infrared pump-probe spectroscopies

    PubMed Central

    Slenkamp, Karla M.; Lynch, Michael S.; Brookes, Jennifer F.; Bannan, Caitlin C.; Daifuku, Stephanie L.; Khalil, Munira

    2016-01-01

    Using polarization-selective two-dimensional infrared (2D IR) and infrared pump-probe spectroscopies, we study vibrational relaxation of the four cyanide stretching (νCN) vibrations found in [(NH3)5RuIIINCFeII(CN)5]− (FeRu) dissolved in D2O or formamide and [(NC)5FeIICNPtIV(NH3)4NCFeII(CN)5]4− (FePtFe) dissolved in D2O. These cyanide-bridged transition metal complexes serve as models for understanding the role high frequency vibrational modes play in metal-to-metal charge transfers over a bridging ligand. However, there is currently little information about vibrational relaxation and dephasing dynamics of the anharmonically coupled νCN modes in the electronic ground state of these complexes. IR pump-probe experiments reveal that the vibrational lifetimes of the νCN modes are ∼2 times faster when FeRu is dissolved in D2O versus formamide. They also reveal that the vibrational lifetimes of the νCN modes of FePtFe in D2O are almost four times as long as for FeRu in D2O. Combined with mode-specific relaxation dynamics measured from the 2D IR experiments, the IR pump-probe experiments also reveal that intramolecular vibrational relaxation is occurring in all three systems on ∼1 ps timescale. Center line slope dynamics, which have been shown to be a measure of the frequency-frequency correlation function, reveal that the radial, axial, and trans νCN modes exhibit a ∼3 ps timescale for frequency fluctuations. This timescale is attributed to the forming and breaking of hydrogen bonds between each mode and the solvent. The results presented here along with our previous work on FeRu and FePtFe reveal a picture of coupled anharmonic νCN modes where the spectral diffusion and vibrational relaxation dynamics depend on the spatial localization of the mode on the molecular complex and its specific interaction with the solvent. PMID:27158634

  11. Intercomparison of the comparative reactivity method (CRM) and pump-probe technique for measuring total OH reactivity in an urban environment

    NASA Astrophysics Data System (ADS)

    Hansen, R. F.; Blocquet, M.; Schoemaecker, C.; Léonardis, T.; Locoge, N.; Fittschen, C.; Hanoune, B.; Stevens, P. S.; Sinha, V.; Dusanter, S.

    2015-10-01

    The investigation of hydroxyl radical (OH) chemistry during intensive field campaigns has led to the development of several techniques dedicated to ambient measurements of total OH reactivity, which is the inverse of the OH lifetime. Three techniques are currently used during field campaigns, including the total OH loss rate method, the pump-probe method, and the comparative reactivity method. However, no formal intercomparison of these techniques has been published so far, and there is a need to ensure that measurements of total OH reactivity are consistent among the different techniques. An intercomparison of two OH reactivity instruments, one based on the comparative reactivity method (CRM) and the other based on the pump-probe method, was performed in October 2012 in a NOx-rich environment, which is known to be challenging for the CRM technique. This study presents an extensive description of the two instruments, the CRM instrument from Mines Douai (MD-CRM) and the pump-probe instrument from the University of Lille (UL-FAGE), and highlights instrumental issues associated with the two techniques. It was found that the CRM instrument used in this study underestimates ambient OH reactivity by approximately 20 % due to the photolysis of volatile organic compounds (VOCs) inside the sampling reactor; this value is dependent on the position of the lamp within the reactor. However, this issue can easily be fixed, and the photolysis of VOCs was successfully reduced to a negligible level after this intercomparison campaign. The UL-FAGE instrument may also underestimate ambient OH reactivity due to the difficulty to accurately measure the instrumental zero. It was found that the measurements are likely biased by approximately 2 s-1, due to impurities in humid zero air. Two weeks of ambient sampling indicate that the measurements performed by the two OH reactivity instruments are in agreement, within the measurement uncertainties for each instrument, for NOx mixing ratios

  12. Intercomparison of the comparative reactivity method (CRM) and pump-probe technique for measuring total OH reactivity in an urban environment

    NASA Astrophysics Data System (ADS)

    Hansen, R. F.; Blocquet, M.; Schoemaecker, C.; Léonardis, T.; Locoge, N.; Fittschen, C.; Hanoune, B.; Stevens, P. S.; Sinha, V.; Dusanter, S.

    2015-06-01

    The investigation of hydroxyl radical (OH) chemistry during intensive field campaigns has led to the development of several techniques dedicated to ambient measurements of total OH reactivity, which is the inverse of the OH lifetime. Three techniques are currently used during field campaigns, including the total OH loss rate method, the pump-probe method, and the comparative reactivity method. However, no formal intercomparison of these techniques has been published so far, and there is a need to ensure that measurements of total OH reactivity are consistent among the different techniques. An intercomparison of two OH reactivity instruments, one based on the Comparative Reactivity Method (CRM) and the other based on the pump-probe method, was performed in October 2012 in a NOx-rich environment, which is known to be challenging for the CRM technique. This study presents an extensive description of the two instruments, the CRM instrument from Mines Douai (MD-CRM) and the pump-probe instrument from the University of Lille (UL-FAGE), and highlights instrumental issues associated with the two techniques. It was found that the CRM instrument used in this study underestimates ambient OH reactivity by approximately 20 % due to the photolysis of Volatile Organic Compounds (VOCs) inside the sampling reactor; this value is dependent on the position of the lamp within the reactor. However, this issue can easily be fixed, and the photolysis of VOCs was successfully reduced to a negligible level after this intercomparison campaign. The UL-FAGE instrument may also underestimate ambient OH reactivity due to the difficulty to accurately measure the instrumental zero. It was found that the measurements are likely biased by approximately 2 s-1, due to impurities in humid zero air. Two weeks of ambient sampling indicate that the measurements performed by the two OH reactivity instruments are in agreement, within the measurement uncertainties for each instrument, for NOx mixing ratios

  13. Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon source based on laser high-order harmonic generation.

    PubMed

    Wernet, Philippe; Gaudin, Jérôme; Godehusen, Kai; Schwarzkopf, Olaf; Eberhardt, Wolfgang

    2011-06-01

    A laser-based tabletop approach to femtosecond time-resolved photoelectron spectroscopy with photons in the vacuum-ultraviolet (VUV) energy range is described. The femtosecond VUV pulses are produced by high-order harmonic generation (HHG) of an amplified femtosecond Ti:sapphire laser system. Two generations of the same setup and results from photoelectron spectroscopy in the gas phase are discussed. In both generations, a toroidal grating monochromator was used to select one harmonic in the photon energy range of 20-30 eV. The first generation of the setup was used to perform photoelectron spectroscopy in the gas phase to determine the bandwidth of the source. We find that our HHG source has a bandwidth of 140 ± 40 meV. The second and current generation is optimized for femtosecond pump-probe photoelectron spectroscopy with high flux and a small spot size at the sample of the femtosecond probe pulses. The VUV radiation is focused into the interaction region with a toroidal mirror to a spot smaller than 100 × 100 μm(2) and the flux amounts to 10(10) photons/s at the sample at a repetition rate of 1 kHz. The duration of the monochromatized VUV pulses is determined to be 120 fs resulting in an overall pump-probe time resolution of 135 ± 5 fs. We show how this setup can be used to map the transient valence electronic structure in molecular dissociation. © 2011 American Institute of Physics

  14. Dynamics of ultrafast internal conversion processes studied by femtosecond time-delayed photoelectron spectroscopy

    SciTech Connect

    Cyr, D.R.; Hayden, C.C.

    1995-08-01

    The authors have studied the dynamics of ultrafast internal conversion processes using femtosecond time-resolved photoionization and photoelectron spectroscopy. In hexatriene, following femtosecond pulse excitation at 250 nm, they use time-delayed photoionization to observe the formation and decay of an intermediate species on the subpicosecond time scale. With time-resolved photoelectron spectroscopy, the rapid evolution of vibrational excitation in this intermediate is observed, as electronic energy is converted to vibrational energy in the molecule. The photodynamics of cis and trans isomers of hexatriene are compared and found to be surprisingly different on the 2-3 psec time scale. These results are important for understanding the fundamental photochemical processes in linear polyenes, which have served as models for the active chromophores of many biological photosystems.

  15. Photoionization of rare gas clusters

    NASA Astrophysics Data System (ADS)

    Zhang, Huaizhen

    This thesis concentrates on the study of photoionization of van der Waals clusters with different cluster sizes. The goal of the experimental investigation is to understand the electronic structure of van der Waals clusters and the electronic dynamics. These studies are fundamental to understand the interaction between UV-X rays and clusters. The experiments were performed at the Advanced Light Source at Lawrence Berkeley National Laboratory. The experimental method employs angle-resolved time-of-flight photoelectron spectrometry, one of the most powerful methods for probing the electronic structure of atoms, molecules, clusters and solids. The van der Waals cluster photoionization studies are focused on probing the evolution of the photoelectron angular distribution parameter as a function of photon energy and cluster size. The angular distribution has been known to be a sensitive probe of the electronic structure in atoms and molecules. However, it has not been used in the case of van der Waals clusters. We carried out outer-valence levels, inner-valence levels and core-levels cluster photoionization experiments. Specifically, this work reports on the first quantitative measurements of the angular distribution parameters of rare gas clusters as a function of average cluster sizes. Our findings for xenon clusters is that the overall photon-energy-dependent behavior of the photoelectrons from the clusters is very similar to that of the corresponding free atoms. However, distinct differences in the angular distribution point at cluster-size-dependent effects were found. For krypton clusters, in the photon energy range where atomic photoelectrons have a high angular anisotropy, our measurements show considerably more isotropic angular distributions for the cluster photoelectrons, especially right above the 3d and 4p thresholds. For the valence electrons, a surprising difference between the two spin-orbit components was found. For argon clusters, we found that the

  16. Determination of electron-impact transfer rate coefficients between argon 1s2 and 1s3 states by laser pump-probe technique

    NASA Astrophysics Data System (ADS)

    Carbone, E. A. D.; Hübner, S.; van der Mullen, J. J. A. M.; Kroesen, G. M. W.; Sadeghi, N.

    2013-10-01

    In a microwave argon plasma, the electron-impact population transfers between the first four excited states of argon are studied by time-resolved laser pump-probe technique. Metastable atoms in the 1s5 state (in Paschen's notation) are selectively pumped up to the 2p3 state, with a nanosecond pulsed dye laser tuned to the 706 nm argon transition and the temporal response of the densities in the 1s3, 1s4 and 1s5 states are monitored by time-resolved laser diode absorption. The electron density and temperature are also measured by Thomson scattering along the plasma column for different pressures. The rate coefficient measured for the 1s3 to 1s2 state transfer, for which only rough estimations exist in the literature is found to be 9 × 10-13 m3 s-1, almost five times larger than the value commonly assumed.

  17. Time-resolved pump-probe photoelectron spectroscopy of helium using a mode-locked laser synchronized with synchrotron radiation pulses

    NASA Astrophysics Data System (ADS)

    Lacoursière, Jean; Meyer, Michael; Nahon, Laurent; Morin, Paul; Larzillière, Michel

    1994-12-01

    We report a new experimental setup consisting in the synchronization of 74.9094 MHz pulses from a mode-locked Ar + laser with 8.32 MHz pulses of vacuum ultraviolet (VUV) synchrotron radiation from the Super-ACO storage ring of the Laboratoire pour l'Utilisation du Rayonnement Electromagnétique (LURE). The capabilities of the setup are demonstrated in a time-resolved pump-probe (VUV + visible) experiment in which free helium atoms are resonantly ionized via the short-lived 1s3p ( 1P) state. This experiment allowed us to obtain the value of 1.12 ns for the temporal resolution (FWHM) of the experimental setup and to show the relevance of this technique for the investigation of nanosecond dynamics on gas phase species.

  18. Double photoionization of halogenated benzene

    SciTech Connect

    AlKhaldi, Mashaal Q.; Wehlitz, Ralf

    2016-01-28

    We have experimentally investigated the double-photoionization process in C{sub 6}BrF{sub 5} using monochromatized synchrotron radiation. We compare our results with previously published data for partially deuterated benzene (C{sub 6}H{sub 3}D{sub 3}) over a wide range of photon energies from threshold to 270 eV. A broad resonance in the ratio of doubly to singly charged parent ions at about 65 eV appears shifted in energy compared to benzene data. This shift is due to the difference in the bond lengths in two molecules. A simple model can explain the shape of this resonance. At higher photon energies, we observe another broad resonance that can be explained as a second harmonic of the first resonance.

  19. Nondipole effects in helium photoionization

    NASA Astrophysics Data System (ADS)

    Argenti, Luca; Moccia, Roberto

    2010-12-01

    An accurate calculation of the nondipole anisotropy parameter γ in the photoionization of helium below the N = 2 threshold is presented. The calculated results are in fairly good agreement with the experimental results of Krässig et al (2002 Phys. Rev. Lett. 88 203002), but not as good as the accuracy of the calculation should have warranted. A careful examination of the possible causes for the observed discrepancies between theory and experiment seems to rule out any role either of the multipolar terms higher than the electric quadrupole, or of the singlet-triplet spin-orbit mixing. It is argued that such discrepancies might have an instrumental origin, due to the difficulty of measuring vanishingly small total cross sections σtot with the required accuracy. In such eventuality, it might be more appropriate to use a parameter other than γ, such as for instance the drag current, to measure the nondipole anisotropy of the photoelectron angular distribution.

  20. Photoionization of ClII

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana; Hernández, E.; Antillón, A.; Morales, A.; González, O.; Macaluso, D.; Hanstorp, D.; Aguilar, A.; Juárez, A.; Hinojosa, G.

    2014-05-01

    The cross section and spectrum for the process of single photoionization of the chlorine cation was measured in the energy range of 19.5 to 28.0 eV with a photon energy resolution of 20 meV. Over a non resonant cross section, resonant structures originated from initinal Cl+ 3P(J=0,1,2) manifold converging mainly to 2P(J=3/2) and 2D(J=5/2) are identified. A theoretical calculation based on the close coupling R-matrix is under progress. CONACYT CB-2011 167631. US National Science Fundation, DGAPA IN106813, The ALS is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. DOE Cntrct. DE-AC02-05CH11231. Montana Space Grant Consortium, Swedish Research Council.

  1. Indirect double photoionization of water

    NASA Astrophysics Data System (ADS)

    Resccigno, T. N.; Sann, H.; Orel, A. E.; Dörner, R.

    2011-05-01

    The vertical double ionization thresholds of small molecules generally lie above the dissociation limits corresponding to formation of two singly charged fragments. This gives the possibility of populating singly charged molecular ions by photoionization in the Franck-Condon region at energies below the lowest dication state, but above the dissociation limit into two singly charged fragment ions. This process can produce a superexcited neutral fragment that autoionizes at large internuclear separation. We study this process in water, where absorption of a photon produces an inner-shell excited state of H2O+ that fragments to H++OH*. The angular distribution of secondary electrons produced by OH* when it autoionizes produces a characteristic asymmetric pattern that reveals the distance, and therefore the time, at which the decay takes place. LBNL, Berkeley, CA, J. W. Goethe Universität, Frankfurt, Germany. Work performed under auspices of US DOE and supported by OBES, Div. of Chemical Sciences.

  2. Ultrafast pump-probe and 2DIR anisotropy and temperature-dependent dynamics of liquid water within the E3B model.

    PubMed

    Ni, Yicun; Skinner, J L

    2014-07-14

    Recently, Tainter et al. [J. Chem. Phys. 134, 184501 (2011)] reparameterized a new rigid water model (E3B) that explicitly includes three-body interactions in its Hamiltonian. Compared to commonly used water models such as SPC/E and TIP4P, the new model shows better agreement with experiment for many physical properties including liquid density, melting temperature, virial coefficients, etc. However, the dynamics of the E3B model, especially as a function of temperature, has not been systematically evaluated. Experimental nonlinear vibrational spectroscopy is an ideal tool to study the dynamics of matter in condensed phases. In the present study, we calculate linear and nonlinear vibrational spectroscopy observables for liquid water using the E3B model at five temperatures: 10, 30, 50, 70 and 90 °C. Specifically, we calculate absorption and Raman spectra and pump-probe anisotropy for HOD in H2O at all temperatures, frequency-resolved pump-probe anisotropy for HOD in both H2O and D2O at 30 °C, and 2DIR anisotropy for HOD in D2O at 30 °C. In all cases, we find reasonable agreement with experiment, and for the ultrafast spectroscopy our results are a significant improvement over those of the SPC/E model. A likely reason for this improvement is that the three-body interaction terms in the E3B model are able to model cooperative hydrogen bonding. We also calculate rotational and frequency relaxation times at all temperatures, and fit the results to the Arrhenius equation. We find that the activation energy for hydrogen-bond switching in liquid water is 3.8 kcal/mol, which agrees well with the experimental value of 3.7 kcal/mol obtained from anisotropy decay experiments.

  3. 2006 Photoions, Photoionization & Photodetachment held on January 29-February 3, 2006

    SciTech Connect

    Robert Continetti Nancy Ryan Gray

    2006-09-06

    The 4th Gordon Conference on Photoions, Photoionization and Photodetachment will be held January 29-February 3, 2006 at the Santa Ynez Valley Marriott in Buellton, California. This meeting will continue to cover fundamentals and applications of photoionization and photodetachment, including valence and core-level phenomena and applications to reaction dynamics, ultrashort laser pulses and the study of exotic molecules and anions. Further information will be available soon at the Gordon Conference Website, and will be announced.

  4. Electronic decoherence following photoionization: Full quantum-dynamical treatment of the influence of nuclear motion

    NASA Astrophysics Data System (ADS)

    Arnold, Caroline; Vendrell, Oriol; Santra, Robin

    2017-03-01

    Photoionization using attosecond pulses can lead to the formation of coherent superpositions of the electronic states of the parent ion. However, ultrafast electron ejection triggers not only electronic but also nuclear dynamics—leading to electronic decoherence, which is typically neglected on time scales up to tens of femtoseconds. We propose a full quantum-dynamical treatment of nuclear motion in an adiabatic framework, where nuclear wave packets move on adiabatic potential energy surfaces expanded up to second order at the Franck-Condon point. We show that electronic decoherence is caused by the interplay of a large number of nuclear degrees of freedom and by the relative topology of the potential energy surfaces. Application to H2O , paraxylene, and phenylalanine shows that an initially coherent state evolves to an electronically mixed state within just a few femtoseconds. In these examples the fast vibrations involving hydrogen atoms do not affect electronic coherence at short times. Conversely, vibrational modes involving the whole molecular skeleton, which are slow in the ground electronic state, quickly destroy it upon photoionization.

  5. Separating pairing from quantum phase coherence dynamics above the superconducting transition by femtosecond spectroscopy.

    PubMed

    Madan, I; Kurosawa, T; Toda, Y; Oda, M; Mertelj, T; Kusar, P; Mihailovic, D

    2014-07-11

    In classical superconductors an energy gap and phase coherence appear simultaneously with pairing at the transition to the superconducting state. In high-temperature superconductors, the possibility that pairing and phase coherence are distinct and independent processes has led to intense experimental search of their separate manifestations. Using femtosecond spectroscopy methods we now show that it is possible to clearly separate fluctuation dynamics of the superconducting pairing amplitude from the phase relaxation above the critical transition temperature. Empirically establishing a close correspondence between the superfluid density measured by THz spectroscopy and superconducting optical pump-probe response over a wide region of temperature, we find that in differently doped Bi(2)Sr(2)CaCu(2)O(8+δ) crystals the pairing gap amplitude monotonically extends well beyond Tc, while the phase coherence shows a pronounced power-law divergence as T → T(c), thus showing that phase coherence and gap formation are distinct processes which occur on different timescales.

  6. Non-equilibrium phonon dynamics studied by grazing-incidence femtosecond X-ray crystallography.

    PubMed

    Johnson, S L; Beaud, P; Vorobeva, E; Milne, C J; Murray, E D; Fahy, S; Ingold, G

    2010-03-01

    The timescales for structural changes in a single crystal of bismuth after excitation with an intense near-infrared laser pulse are studied with femtosecond pump-probe X-ray diffraction. Changes in the intensity and reciprocal-lattice vector of several reflections give quantitative information on the structure factor and lattice strain as a function of time, with a resolution of 200 fs. The results indicate that the majority of excess carrier energy that remains near the surface is transferred to vibrational modes on a timescale of about 10 ps, and that the resultant increase in the variance of the atomic positions at these times is consistent with the overall magnitude of lattice strain that develops.

  7. Excitation of an electronic subsystem of YAG crystal with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Kononenko, V. V.; Zavedeev, E. V.; Okhrimchuk, A. G.; Konov, V. I.

    2017-06-01

    The temporal dynamics of refractive index change induced by intense femtosecond 800 nm laser radiation in a yttrium aluminum garnet (YAG) crystal was explored using pump-probe interferometry. Beyond the Kerr effect, only a positive laser-induced rise of permittivity was detected ( Δ n˜ +{{10}-3} ), whereas most of the material demonstrates a remarkable transient response opposite in sign to that assigned usually to free carrier generation. Observed dynamics of n indicates that (i) the possible formation of free electron-hole (e-h) pairs is totally masked and (ii) the formation of tightly bound electronic states (transient defects) takes time approximately equal to a pulse duration. We discuss whether the latter could be a direct light-induced process or still a result of the ultrafast decay of radiatively generated electron-hole pairs.

  8. Imaging molecular structure through femtosecond photoelectron diffraction on aligned and oriented gas-phase molecules.

    PubMed

    Boll, Rebecca; Rouzée, Arnaud; Adolph, Marcus; Anielski, Denis; Aquila, Andrew; Bari, Sadia; Bomme, Cédric; Bostedt, Christoph; Bozek, John D; Chapman, Henry N; Christensen, Lauge; Coffee, Ryan; Coppola, Niccola; De, Sankar; Decleva, Piero; Epp, Sascha W; Erk, Benjamin; Filsinger, Frank; Foucar, Lutz; Gorkhover, Tais; Gumprecht, Lars; Hömke, André; Holmegaard, Lotte; Johnsson, Per; Kienitz, Jens S; Kierspel, Thomas; Krasniqi, Faton; Kühnel, Kai-Uwe; Maurer, Jochen; Messerschmidt, Marc; Moshammer, Robert; Müller, Nele L M; Rudek, Benedikt; Savelyev, Evgeny; Schlichting, Ilme; Schmidt, Carlo; Scholz, Frank; Schorb, Sebastian; Schulz, Joachim; Seltmann, Jörn; Stener, Mauro; Stern, Stephan; Techert, Simone; Thøgersen, Jan; Trippel, Sebastian; Viefhaus, Jens; Vrakking, Marc; Stapelfeldt, Henrik; Küpper, Jochen; Ullrich, Joachim; Rudenko, Artem; Rolles, Daniel

    2014-01-01

    This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray free-electron laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C(8)H(5)F) and dissociating, laser-aligned 1,4-dibromobenzene (C(6)H(4)Br(2)) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments.

  9. Separating pairing from quantum phase coherence dynamics above the superconducting transition by femtosecond spectroscopy

    PubMed Central

    Madan, I.; Kurosawa, T.; Toda, Y.; Oda, M.; Mertelj, T.; Kusar, P.; Mihailovic, D.

    2014-01-01

    In classical superconductors an energy gap and phase coherence appear simultaneously with pairing at the transition to the superconducting state. In high-temperature superconductors, the possibility that pairing and phase coherence are distinct and independent processes has led to intense experimental search of their separate manifestations. Using femtosecond spectroscopy methods we now show that it is possible to clearly separate fluctuation dynamics of the superconducting pairing amplitude from the phase relaxation above the critical transition temperature. Empirically establishing a close correspondence between the superfluid density measured by THz spectroscopy and superconducting optical pump-probe response over a wide region of temperature, we find that in differently doped Bi2Sr2CaCu2O8+δ crystals the pairing gap amplitude monotonically extends well beyond Tc, while the phase coherence shows a pronounced power-law divergence as T → Tc, thus showing that phase coherence and gap formation are distinct processes which occur on different timescales. PMID:25014162

  10. Femtosecond laser-generated high-energy-density states studied by x-ray FELs

    NASA Astrophysics Data System (ADS)

    Nakatsutsumi, M.; Appel, K.; Baehtz, C.; Chen, B.; Cowan, T. E.; Göde, S.; Konopkova, Z.; Pelka, A.; Priebe, G.; Schmidt, A.; Sukharnikov, K.; Thorpe, I.; Tschentscher, Th; Zastrau, U.

    2017-01-01

    The combination of powerful optical lasers and an x-ray free-electron laser (XFEL) provides unique capabilities to study the transient behaviour of matter in extreme conditions. The high energy density science instrument (HED instrument) at the European XFEL will provide the experimental platform on which an unique x-ray source can be combined with various types of high-power optical lasers. In this paper, we highlight selected scientific examples together with the associated x-ray techniques, with particular emphasis on femtosecond (fs)-timescale pump-probe experiments. Subsequently, we present the current design status of the HED instrument, outlining how the experiments could be performed. First user experiments will start at the beginning of 2018, after which various optical lasers will be commissioned and made available to the international scientific community.

  11. Femtosecond Spectroscopy of Electron-Lattice Coupling in LuMnO3

    NASA Astrophysics Data System (ADS)

    Lou, Shitao

    2005-03-01

    Hexagonal manganite LuMnO3 is a ferroelectric (Tc 900 K) and strongly frustrated antiferromagnetic (TN 90 K) crystal. Strong coupling between lattice, electronic, and magnetic degrees of freedom make it a promissing electronic material. We have used femtosecond pump-probe spectroscopy to observe the interaction of electron excitation and lattice vibration in real time. Optical excitation at a sharp absorption peak at 800 nm corresponding to a Mn d(x^2-y^2),(xy)->d(3z^2-r^2)transition served as the primary excitation step. Reflectivity changes as a function of delay time reveal electronic relaxation and coherent oscillations of several optical phonon modes. Electron and phonon excitation and relaxation dynamics were studied using different polarization geometries and symmetry analysis. The interaction mechanisms of photons, electrons, and coherent phonons are discussed.

  12. Optical nonlinear dynamics in ZnS from femtosecond laser pulses

    SciTech Connect

    Wu, Yu-E; Ren, Mengxin Wang, Zhenhua; Li, Wenhua; Wu, Qiang; Zhang, Xinzheng Xu, Jingjun; Yi, Sanming

    2014-05-15

    A wavelength swapping nondegenerate pump-probe technique to measure the magnitudes of the nonlinear optical dynamics as well as the relaxation time of electrons in high energy levels is presented using a ZnS single crystal wafer as an example. By pumping the sample with 800 nm femtosecond pulses and probing at 400 nm, nondegenerate two-photon absorption (N-2PA) happens exclusively, and the measured curves only show instantaneous features without relaxation tails. The N-2PA coefficient was derived explicitly as 7.52 cm/GW. Additionally, when the wavelengths of the pump and probe beams are swapped, extra information about the relaxation time of the hot electrons excited in the conduction band is obtained. The combined results above are helpful for evaluating the characteristics of an optical switches based on ZnS or other materials with respect to its nonlinear optical dynamic aspect.

  13. Compton Scattering and Its Applications: The PLEIADES Femtosecond X-ray Source at LLNL

    SciTech Connect

    Hartemann, F V; Brown, W J; Anderson, S G; Barty, C P J; Betts, S M; Booth, R; Crane, J K; Cross, R R; Fittinghoff, D N; Gibson, D J; Kuba, J; Rupp, B; Tremaine, A M; Springer, P T

    2003-05-01

    Remarkable developments in critical technologies including terawatt-class lasers using chirped-pulse amplification, high brightness photoinjectors, high-gradient accelerators, and superconducting linacs make it possible to design and operate compact, tunable, subpicosecond Compton scattering x-ray sources with a wide variety of applications. In such novel radiation sources, the collision between a femtosecond laser pulse and a low emittance relativistic electron bunch in a small ({micro}m{sup 3}) interaction volume produces Doppler-upshifted scattered photons with unique characteristics: the energy is tunable in the 5-500 keV range, the angular divergence of the beam is small (mrad), and the pulses are ultrashort (10 fs - 10 ps). Two main paths are currently being followed in laboratories worldwide: high peak brightness, using ultrahigh intensity femtosecond lasers at modest repetition rates, and high average brightness, using superconducting linac and high average power laser technology at MHz repetition rates. Targeted applications range from x-ray protein crystallography and high contrast medical imaging to femtosecond pump-probe and diffraction experiments. More exotic uses of such sources include the {gamma}-{gamma} collider, NIF backlighting, nonlinear Compton scattering, and high-field QED. Theoretical considerations and experimental results will be discussed within this context.

  14. Femtosecond photoelectron diffraction: a new approach to image molecular structure during photochemical reactions

    NASA Astrophysics Data System (ADS)

    Rolles, Daniel; Boll, Rebecca; Tamrakar, Samyak R.; Anielski, Denis; Bomme, Cédric

    2014-09-01

    Continuing technical advances in the creation of (sub-) femtosecond VUV and X-ray pulses with Free-Electron Lasers and laser-based high-harmonic-generation sources have created new opportunities for studying ultrafast dynamics during chemical reactions. Here, we present an approach to image the geometric structure of gas-phase molecules with fewfemtosecond temporal and sub-Ångström spatial resolution using femtosecond photoelectron diffraction. This technique allows imaging the molecules "from within" by analyzing the diffraction of inner-shell photoelectrons that are created by femtosecond VUV and X-ray pulses. Using pump-probe schemes, ultrafast structural changes during photochemical reactions can thus be directly visualized with a temporal resolution that is only limited by the pulse durations of the pump and the probe pulse and the synchronization of the two light pulses. Here, we illustrate the principle of photoelectron diffraction using a simple, geometric scattering model and present results from photoelectron diffraction experiments on laser-aligned molecules using X-ray pulses from a Free-Electron Laser.

  15. Distinctive features of photoionized plasma from short x-ray-pulse interaction with gaseous medium

    SciTech Connect

    Bychenkov, V.Yu.; Romanov, D.V.; Rozmus, W.; Capjack, C.E.; Fedosejevs, R.

    2006-01-15

    The study of a photoionized plasma created through the interaction of a short linearly polarized x-ray pulse with a gaseous medium is presented in the context of the future design of experiments involving femtosecond free-electron laser pulses. The dispersion properties and instabilities of such x-ray-produced plasma are studied. It is shown that a two-stream type of instability can be obtained with a growth rate comparable to the plasma frequency. This is expected to have a dramatic effect on the evolution of an x-ray laser-produced plasma. A model for describing electromagnetic-field generation and emission resulting from the interaction of a short x-ray laser pulse with a gas jet is proposed. Issues addressed include the effect of the thermal electromotive force at the edge of a plasma driven by the anisotropic electron energy distribution that arises from the photoionization of a gas. Terahertz pulse emission from these photoionized plasma is also predicted.

  16. Alignment of photoions far from threshold

    NASA Astrophysics Data System (ADS)

    Das, Romith; Wu, Chuanyong; Mihill, A. G.; Poliakoff, E. D.; Wang, Kwanghsi; McKoy, V.

    1994-09-01

    We present results of measurements and calculations of the alignment for CO+(B 2Σ+) photoions over an extended energy range (0≤Ek≤210 eV). The polarization of CO+(B 2Σ+→X 2Σ+) fluorescence indicates that the photoions retain significant alignment even at high energies. Agreement between the measured and calculated polarization of the fluorescence is excellent.

  17. Monitoring the dynamics of the surface deformation prior to the onset of plasma emission during femtosecond laser ablation of noble metals by time-resolved reflectivity microscopy

    NASA Astrophysics Data System (ADS)

    Carrasco-García, I.; Vadillo, José M.; Javier Laserna, J.

    2017-05-01

    The generation of an expanding plasma during laser ablation is preceded at early times by the formation and evolution of a subsurface melted front. The monitoring of such transient event can't be studied by conventional spectroscopic techniques. Pump-probe femtosecond microscopy allows the following of the surface changes during femtosecond laser ablation taking advantage of the formation of a number of dynamic Newton rings that evolve with time. Measurements at different times allow the quantification of the radial expansion velocity of the molten material. For Au and Ag, expansions in the range of 7000-12,000 m/s for Au and 3000-21,000 m/s have been calculated depending on the pump energies. Such values correspond to hypersonic velocities with Mach number between 3 and 6.

  18. 2001 Gordon Research Conference on Photoions, Photoionization and Photodetachment. Final progress report [agenda and attendees list

    SciTech Connect

    Johnson, Mark

    2001-07-13

    The Gordon Research Conference on Photoions, Photoionization and Photodetachment was held at Williams College, Williamstown, Massachusetts, July 8-13, 2001. The 72 conference attendees represented the spectrum of endeavor in this field, coming from academia, industry, and government laboratories, and including US and foreign scientists, senior researchers, young investigators, and students. Emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate discussion about the key issues in the field today. Time for formal presentations was limited. Sessions included the following topics: Vibrational structure, Time resolved studies: nuclear wavepackets, Valence photoionization, Clusters and networks, Resonance structures and decay mechanisms, Ultrafast photoionization, Threshold photoionization, Molecule fixed properties, and Collisional phenomena.

  19. Double Photoionization of Atomic Beryllium

    NASA Astrophysics Data System (ADS)

    Yip, Frank L.; McCurdy, C. William; Rescigno, Thomas N.

    2010-03-01

    One-photon double ionization (DPI) of beryllium represents the next step in the evolution of DPI investigations that began with helium in order to sensitively probe electron correlation. Beryllium is the simplest atomic species of the alkaline earth elements which, in general, possess two electrons outside of a fully occupied inner shell that spherically screens the nucleus. This provides a natural basis for comparison to 1s^2 helium DPI. However, the valence state of beryllium has n=2, thus making the valence excited target 2s2p more accessible relative to the 2s^2 ground state as compared to ground-state and metastable helium. Also, the symmetry of photoionizing from either the ^1S or ^1P initial state will have consequences for the angular distributions for double ionization. Triply differential cross sections (TDCS) are presented for DPI from both ground state 2s^2 and excited state 2s2p beryllium calculated using exterior complex scaling (ECS) for the valence electrons.

  20. Femtosecond Spectroscopy of LuMnO3

    NASA Astrophysics Data System (ADS)

    Lou, Shitao; Zimmermann, Frank M.; Bartynski, Robert A.; Hur, Namjun; Cheong, Sang-Wook

    2006-03-01

    Hexagonal LuMnO3 manganite is a ferroelectric and strongly frustrated antiferromagnetic crystal. Strong coupling between lattice, electronic, and magnetic degrees of freedom makes it a promising electronic material. We have used femtosecond pump-probe spectroscopy to study the interaction of electron excitations with lattice vibrations in real time. Optical excitation of a Mn d(x^2-y^2),(xy)->d(3z^2-r^2)transition served as the primary excitation step. With both pump and probe beam polarization perpendicular to the c axis, the probe reflectivity shows a sharp drop due to saturation of the transition, recovering on a timescale of 1 ps. We also observed displacive excitation of a coherent optical phonon vibration at 3.6 THz, which is assigned to an A1 symmetry mode involving Lu ion motion along the c axis. This mode was excited in longitudinal (LO) and transverse mode (TO) geometries. While the LO-TO frequency splitting is small (<0.1 THz), a remarkable phase reversal of the reflectivity curve was observed. This is attributed to a large linear electro-optic effect (Pockels effect), induced by the THz electric field associated with the LO mode.

  1. Coherent nuclear wavepacket motions in ultrafast excited-state intramolecular proton transfer: sub-30-fs resolved pump-probe absorption spectroscopy of 10-hydroxybenzo[h]quinoline in solution.

    PubMed

    Takeuchi, Satoshi; Tahara, Tahei

    2005-11-17

    The dynamics of the excited-state intramolecular proton transfer of 10-hydroxybenzo[h]quinoline (10-HBQ) and the associated coherent nuclear motion were investigated in solution by femtosecond absorption spectroscopy. Sub-picosecond transient absorption measurements revealed spectral features of the stimulated emission and absorption of the keto excited state (the product of the reaction). The stimulated emission band appeared in the 600-800-nm region, corresponding to the wavelength region of the steady-state keto fluorescence. It showed successive temporal changes with time constants of 350 fs and 8.3 ps and then disappeared with the lifetime of the keto excited state (260 ps). The spectral feature of the stimulated emission changed in the 350-fs dynamics, which was likely assignable to the intramolecular vibrational energy redistribution in the keto excited state. The 8.3-ps change caused a spectral blue shift and was attributed to the vibrational cooling process. The excited-state absorption was observed in the 400-600-nm region, and it also showed temporal changes characterized by the 350-fs and 8.3-ps components. To examine the coherent nuclear dynamics (nuclear wavepacket motion) in excited-state 10-HBQ, we carried out pump-probe measurements of the stimulated emission and absorption signals with time resolution as good as 27 fs. The obtained data showed substantially modulated signals due to the excited-state vibrational coherence up to a delay time of several picoseconds after photoexcitation. This means that the vibrational coherence created by photoexcitation in the enol excited state is transferred to the product. Fourier transform analysis indicated that four frequency components in the 200-700-cm(-1) region contribute to the oscillatory signal, corresponding to the coherent nuclear motions in excited-state 10-HBQ. Especially, the lowest-frequency mode at 242 cm(-1) is dephased significantly faster than the other three modes. This observation was

  2. EUV optics in photoionization experiments

    NASA Astrophysics Data System (ADS)

    Bartnik, Andrzej; Wachulak, Przemysław; Fiedorowicz, Henryk; Fok, Tomasz; Jarocki, Roman; Kostecki, Jerzy; Szczurek, Anna; Szczurek, Mirosław; Pina, Ladislav; Sveda, Libor

    2013-05-01

    In this work photoionized plasmas were created by irradiation of He, Ne and Ar gases with a focused EUV beam from one of two laser-plasma sources employing Nd:YAG laser systems of different parameters. First of them was a 10-Hz laser-plasma EUV source, based on a double-stream gas-puff target, irradiated with the 3-ns/0.8J laser pulse. EUV radiation in this case was focused using a gold-plated grazing incidence ellipsoidal collector in the wavelength range λ = 9÷70 nm. The most intense emission was in the relatively narrow spectral region centred at λ = 11 +/- 1 nm. The second source was based on a 10 ns/10 J/10 Hz laser system. In this case EUV radiation was focused using a gold-plated grazing incidence multifoil collector or a Mo-coated ellipsoidal collector. The most intense emission in this case was in the 5 ÷ 15 nm spectral region. Radiation fluence ranged from 60 mJ/cm2 to 400 mJ/cm2. Different gases were injected into the interaction region, perpendicularly to an optical axis of the irradiation system, using an auxiliary gas puff valve. Irradiation of the gases resulted in ionization and excitation of atoms and ions. Spectra in EUV range were measured using a grazing incidence, flat-field spectrometer (McPherson Model 251), equipped with a 450 lines/mm toroidal grating. In all cases the most intense emission lines were assigned to singly charged ions. The other emission lines belong to atoms or doubly charged ions. The spectra were excited in low density gases of the order of 1 ÷ 10% atmospheric density.

  3. Ultrafast dynamics of a near-solid-density layer in an intense femtosecond laser-excited plasma

    SciTech Connect

    Adak, Amitava; Chatterjee, Gourab; Kumar Singh, Prashant; Lad, Amit D.; Brijesh, P.; Kumar, G. Ravindra; Blackman, David R.; Robinson, A. P. L.; Pasley, John

    2014-06-15

    We report on the picosecond dynamics of a near-solid-density plasma generated by an intense, infrared (λ = 800 nm) femtosecond laser using time-resolved pump-probe Doppler spectrometry. An initial red-shift is observed in the reflected third harmonic (λ = 266 nm) probe pulse, which gets blue-shifted at longer probe-delays. A combination of particle-in-cell and radiation-hydrodynamics modelling is performed to model the pump laser interaction with the solid target. The results are post-processed to predict the Doppler shift. An excellent agreement is found between the results of such modelling and the experiment. The modelling suggests that the initial inward motion of the critical surface observed in the experiment is due to the passage of a shock-wave-like disturbance, launched by the pump interaction, propagating into the target. Furthermore, in order to achieve the best possible fit to the experimental data, it was necessary to incorporate the effects of bulk ion-acceleration resulting from the electrostatic field set up by the expulsion of electrons from the laser envelope. We also present results of time-resolved pump-probe reflectometry, which are corroborated with the spectrometry results using a 1-D reflectivity model.

  4. Time-resolved investigations of the non-thermal ablation process of graphite induced by femtosecond laser pulses

    SciTech Connect

    Kalupka, C. Finger, J.; Reininghaus, M.

    2016-04-21

    We report on the in-situ analysis of the ablation dynamics of the, so-called, laser induced non-thermal ablation process of graphite. A highly oriented pyrolytic graphite is excited by femtosecond laser pulses with fluences below the classic thermal ablation threshold. The ablation dynamics are investigated by axial pump-probe reflection measurements, transversal pump-probe shadowgraphy, and time-resolved transversal emission photography. The combination of the applied analysis methods allows for a continuous and detailed time-resolved observation of the non-thermal ablation dynamics from several picoseconds up to 180 ns. Formation of large, μm-sized particles takes place within the first 3.5 ns after irradiation. The following propagation of ablation products and the shock wave front are tracked by transversal shadowgraphy up to 16 ns. The comparison of ablation dynamics of different fluences by emission photography reveals thermal ablation products even for non-thermal fluences.

  5. Photo-ionization rate coefficients for the rare gases

    NASA Astrophysics Data System (ADS)

    Pang, Xuexia

    2005-01-01

    By introducing the converting method from electron-impact ionization cross sections to rate coefficients through using a semi-experiential formula, we try to probe a semi-experiential formula for converting the photo-ionization cross sections into photo-ionization rate coefficient. It"s found that photo-ionization rate coefficient is direct proportion to photo-ionization cross sections, the rate S is related with light resource.

  6. Optical pump-probe processes in Nd 3+ doped KPb2Br5, RbPb2Br5, and KPb2CI5

    SciTech Connect

    Rademaker, K; Huber, G; Payne, S A; Osiac, E; Isaenko, L I

    2004-10-28

    Recently, laser activity has been achieved in the low phonon energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd{sup 3+}:KPb{sub 2}Br{sub 5}) and rubidium lead bromide (Nd{sup 3+}:RbPb{sub 2}Br{sub 5}). Laser activity at 1.07 {micro}m was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 {micro}m and 0.97 {micro}m resulting from the {sup 4}F{sub 5/2}+{sup 2}H{sub 9/2} {yields} {sup 4}I{sub J} transitions (J=13/2 and 11/2) in Nd:RPB was achieved for the first time in a solid state laser material. In this paper we present cw pump-probe spectra in order to discuss excited state absorption, reabsorption processes due to the long lived lower laser levels as well as possible depopulation mechanisms feasible for more efficient laser operation in these crystals. The bromides will be compared with potassium lead chloride (Nd{sup 3+}:KPb{sub 2}Cl{sub 5}).

  7. Development of a pump-probe facility combining a far-infrared source with laser-like characteristics and a VUV free electron laser

    NASA Astrophysics Data System (ADS)

    Faatz, B.; Fateev, A. A.; Feldhaus, J.; Krzywinski, J.; Pflueger, J.; Rossbach, J.; Saldin, E. L.; Schneidmiller, E. A.; Yurkov, M. V.

    2001-12-01

    The TESLA Test Facility (TTF) at DESY is a facility producing sub-picosecond electron pulses for the generation of VUV or soft X-ray radiation in a free electron laser (FEL). The same electron pulses would also allow the direct production of high-power coherent radiation by passing the electron beam through an undulator. Intense, coherent far-infrared (FIR) undulator radiation can be produced from electron bunches at wavelengths longer than or equal to the bunch length. The source described in this paper provides, in the wavelength range 50- 300 μm, a train of about 1- 10 ps long radiation pulses, with about 1 mJ of optical energy per pulse radiated into the central cone. The average output power can exceed 50 W. In this conceptual design, we intend to use a conventional electromagnetic undulator with a 60 cm period length and a maximum field of 1.5 T. The FIR source will use the spent electron beam coming from the VUV FEL which allows one to significantly extend the scientific potential of the TTF without interfering with the main option of the TTF FEL operation. The pulses of the coherent FIR radiation are naturally synchronized with the VUV pulses from the main TTF FEL, enabling pump-probe techniques using either the FEL pulse as a pump or the FIR pulse as a probe, or vice versa.

  8. Discrimination of the effects of saturation and optical pumping in velocity-dependent pump-probe spectroscopy of rubidium: A simple analytical study

    SciTech Connect

    Noh, Heung-Ryoul; Moon, Geol; Jhe, Wonho

    2010-12-15

    This paper presents a simple analytical theory for the velocity-dependent pump-probe laser spectroscopy of {sup 87}Rb and {sup 85}Rb atoms where the pump and the probe beams are circularly or linearly polarized. The analytical solutions of the line shapes of the velocity-selective optical pumping spectroscopy [G. Moon and H. R. Noh, Phys. Rev. A 78, 032506 (2008)] and saturated absorption spectroscopy [G. Moon and H. R. Noh, J. Opt. Soc. Am. B 25, 701 (2008); 27, 1741 (2010)] obtained in the previous reports, expressed as a sum of several Lorentzian functions, could be approximated as one (or in some cases, two) Lorentzian function(s). In particular, the contributions of the saturation and optical pumping effects could be discriminated explicitly in these simple analytical solutions, which is not possible in existing theories such as Nakayama's model. The simple analytical results for the saturation spectroscopy were compared with experimental results, and good agreement between them was observed.

  9. A 1 kHz A-scan rate pump-probe laser-ultrasound system for robust inspection of composites.

    PubMed

    Pelivanov, Ivan; Shtokolov, Alex; Wei, Chen-Wei; O'Donnell, Matthew

    2015-09-01

    We recently built a fiber-optic laser-ultrasound (LU) scanner for nondestructive evaluation (NDE) of aircraft composites and demonstrated its greatly improved sensitivity and stability compared with current noncontact systems. It is also very attractive in terms of cost, stability to environmental noise and surface roughness, simplicity in adjustment, footprint, and flexibility. A new type of a balanced fiber-optic Sagnac interferometer is a key component of this all-optical LU pump-probe system. Very high A-scan rates can be achieved because no reference arm or stabilization feedback are needed. Here, we demonstrate LU system performance at 1000 A-scans/s combined with a fast 2-D translator operating at a scanning speed of 100 mm/s with a peak acceleration of 10 m/s(2) in both lateral directions to produce parallel B-scans at high rates. The fast scanning strategy is described in detail. The sensitivity of this system, in terms of noise equivalent pressure, was further improved to be only 8.3 dB above the Nyquist thermal noise limit. To our knowledge, this is the best reported sensitivity for a noncontact ultrasonic detector of this dimension used to inspect aircraft composites.

  10. Study on vibrational relaxation dynamics of phenol-water complex by picosecond time-resolved IR-UV pump-probe spectroscopy in a supersonic molecular beam

    NASA Astrophysics Data System (ADS)

    Miyazaki, Yasunori; Inokuchi, Yoshiya; Ebata, Takayuki; Petković, Milena

    2013-06-01

    A comparative study of vibrational energy relaxation (VER) between the monohydrated complexes of phenol-d0 and phenol-d1 is investigated in a supersonic molecular beam. The direct time-resolved measurement of energy redistribution from the phenolic OH/OD stretching mode of the phenol-d0-H2O/phenol-d1-D2O is performed by picosecond IR-UV pump-probe spectroscopy. Two complexes follow the same relaxation process that begins with the intramolecular vibrational energy redistribution (IVR) and the intermolecular vibrational energy redistribution (IVR), which is followed by the vibrational predissociation (VP). The difference in the relaxation lifetimes between them is discussed by anharmonic force field and RRKM calculations. Anharmonic analysis implies that intra- (IVR) and intermolecular (IVR) relaxations occur in parallel in the complexes. The RRKM-predicted dissociation (VP) lifetimes show qualitative agreement with the observed results, suggesting that VP takes place after the statistical energy distribution in the complexes.

  11. Carbon Dioxide in a Supported Ionic Liquid Membrane: Structural and Rotational Dynamics Measured with 2D IR and Pump-Probe Experiments.

    PubMed

    Shin, Jae Yoon; Yamada, Steven A; Fayer, Michael D

    2017-08-16

    Supported ionic liquid membranes (SILMs) are porous membranes impregnated with ionic liquids (ILs) and used as advanced carbon capture materials. Here, two-dimensional infrared (2D IR) and IR polarization selective pump-probe (PSPP) spectroscopies were used to investigate CO2 reorientation and spectral diffusion dynamics in SILMs. The SILM contained 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonly)imide in the poly(ether sulfone) membrane with average pore size of ∼350 nm. Two ensembles of CO2 were observed in the SILM, one in the IL phase in the membrane pores and the other in the supporting membrane polymer. CO2 in the polymer displayed a red-shifted IR absorption spectrum and a shorter vibrational lifetime of the asymmetric stretch mode compared to the IL phase. Despite the relatively large pore sizes, the complete orientational randomization of CO2 and structural fluctuations of the IL (spectral diffusion) in the pores are slower than in the bulk IL by ∼2-fold. The implication is that the IL structural change induced by the polymer interface can propagate out from the interface more than a hundred nanometers, influencing the dynamics. The dynamics in the polymer are even slower. This study demonstrates that there are significant differences in the dynamics of ILs in SILMs on a molecular level compared to the bulk IL, and the study of dynamics in SILMs can provide important information for the design of SILMs for CO2 capture.

  12. Construction of a magnetic bottle spectrometer and its application to pulse duration measurement of X-ray laser using a pump-probe method

    SciTech Connect

    Namba, S.; Hasegawa, N.; Kishimoto, M.; Nishikino, M.; Ishino, M.; Kawachi, T.

    2015-11-15

    To characterize the temporal evolution of ultrashort X-ray pulses emitted by laser plasmas using a pump-probe method, a magnetic bottle time-of-flight electron spectrometer is constructed. The design is determined by numerical calculations of a mirror magnetic field and of the electron trajectory in a flight tube. The performance of the spectrometer is characterized by measuring the electron spectra of xenon atoms irradiated with a laser-driven plasma X-ray pulse. In addition, two-color above-threshold ionization (ATI) experiment is conducted for measurement of the X-ray laser pulse duration, in which xenon atoms are simultaneously irradiated with an X-ray laser pump and an IR laser probe. The correlation in the intensity of the sideband spectra of the 4d inner-shell photoelectrons and in the time delay of the two laser pulses yields an X-ray pulse width of 5.7 ps, in good agreement with the value obtained using an X-ray streak camera.

  13. Vacuum Ultraviolet Photoionization of Complex Chemical Systems.

    PubMed

    Kostko, Oleg; Bandyopadhyay, Biswajit; Ahmed, Musahid

    2016-05-27

    Tunable vacuum ultraviolet (VUV) radiation coupled to mass spectrometry is applied to the study of complex chemical systems. The identification of novel reactive intermediates and radicals is revealed in flame, pulsed photolysis, and pyrolysis reactors, leading to the elucidation of spectroscopy, reaction mechanisms, and kinetics. Mass-resolved threshold photoelectron photoion coincidence measurements provide unprecedented access to vibrationally resolved spectra of free radicals present in high-temperature reactors. Photoionization measurements in water clusters, nucleic acid base dimers, and their complexes with water provide signatures of proton transfer in hydrogen-bonded and π-stacked systems. Experimental and theoretical methods to track ion-molecule reactions and fragmentation pathways in intermolecular and intramolecular hydrogen-bonded systems in sugars and alcohols are described. Photoionization of laser-ablated molecules, clusters, and their reaction products inform thermodynamics and spectroscopy that are relevant to astrochemistry and catalysis. New directions in coupling VUV radiation to interrogate complex chemical systems are discussed.

  14. Vacuum Ultraviolet Photoionization of Complex Chemical Systems

    NASA Astrophysics Data System (ADS)

    Kostko, Oleg; Bandyopadhyay, Biswajit; Ahmed, Musahid

    2016-05-01

    Tunable vacuum ultraviolet (VUV) radiation coupled to mass spectrometry is applied to the study of complex chemical systems. The identification of novel reactive intermediates and radicals is revealed in flame, pulsed photolysis, and pyrolysis reactors, leading to the elucidation of spectroscopy, reaction mechanisms, and kinetics. Mass-resolved threshold photoelectron photoion coincidence measurements provide unprecedented access to vibrationally resolved spectra of free radicals present in high-temperature reactors. Photoionization measurements in water clusters, nucleic acid base dimers, and their complexes with water provide signatures of proton transfer in hydrogen-bonded and π-stacked systems. Experimental and theoretical methods to track ion-molecule reactions and fragmentation pathways in intermolecular and intramolecular hydrogen-bonded systems in sugars and alcohols are described. Photoionization of laser-ablated molecules, clusters, and their reaction products inform thermodynamics and spectroscopy that are relevant to astrochemistry and catalysis. New directions in coupling VUV radiation to interrogate complex chemical systems are discussed.

  15. Double photoionization of hydrocarbons and aromatic molecules

    NASA Astrophysics Data System (ADS)

    Wehlitz, R.

    2016-11-01

    This article reviews the recent progress in the field of double photoionization of hydrocarbons and aromatic molecules using synchrotron radiation. First I will describe the importance of carbon-based molecules, which are all around us and are literally part of our life. They exhibit intriguing properties some of which can be probed via double photoionization, i.e., the simultaneous emission of two electrons. Furthermore, I will discuss the different mechanisms that can lead to a doubly charged organic molecule and will highlight those findings by comparing them with the results for atoms and other (simple) molecules. Finally, I will give an outlook on future directions on this subject.

  16. Time resolved digital-holographic analysis of femtosecond laser-induced photodisruption

    NASA Astrophysics Data System (ADS)

    Saerchen, Emanuel; Wenzel, Johannes; Antonopoulos, Georgios; Krueger, Alexander; Lubatschowski, Holger; Ripken, Tammo

    2016-03-01

    Femtosecond laser oscillator systems with low pulse energy (< 1 μJ) and high repetition rate (MHz) are increasingly used for precise, fast and safe eye surgery. Therefore, the laser tissue interaction process is of great interest to optimize and improve established and future surgical protocols. Besides, using faster laser systems leads to unintended self-induced interaction effects, where a femtosecond laser pulse modifies the vicinity in the material in such a way that the focus of following laser pulses is changed. We used a femtosecond oscillator laser system with high repetition rate and 66 nJ pulse energy to produce photodisruption in water. Water was used as phantom material for ocular tissue, because tissue mainly consists of water. A custom made digital-holographic system was used to measure the temporal material modification from picoseconds until seconds after occurrence of the photodisruption. For illumination of the sample we used either a continuously light source or the femtosecond laser pulse itself in a pump-probe configuration. The holographic system provides quantitative data of phase difference Δφ for the full field of view of several tenth of micrometers. Phase difference is equivalent to the laser induced change in the material's refractive index which can alter focusing conditions of following laser pulses and might impair surgical outcome. We obtained the largest change in Δφ during the first picoseconds, followed by a slow relaxation of Δφ within some milliseconds. The results of time resolved measurements of the laser induced material modification will help to optimize scanning schemes in ocular surgery.

  17. Micromachining using femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Toenshoff, Hans K.; Ostendorf, Andreas; Nolte, Stefan; Korte, Frank; Bauer, Thorsten

    2000-11-01

    Femtosecond laser systems have been proved to be effective tools for high precision micro-machining. Almost all solid materials can be processed with high precision. The dependence on material properties like thermal conductivity, transparency, heat- or shock sensitivity is strongly reduced and no significant influence on the remaining bulk material is observed after ablation using femtosecond laser pulses. In contrast to conventional laser processing, where the achievable precision is reduced due to a formed liquid phase causing burr formation, the achievable precision using femtosecond pulses is only limited by the diffraction of the used optics. Potential applications of this technique, aincluding the structuring of biodegradable polymers for cardiovascular implants, so-called stents, as well as high precision machining of transparent materials are presented.

  18. Correlation between photoeletron and photoion in ultrafast multichannel photoionization of Ar

    SciTech Connect

    Itakura, R.; Fushitani, M.; Hishikawa, A.; Sako, T.

    2015-12-31

    We theoretically investigate coherent dynamics of ions created through ultrafast multichannel photoionization from a viewpoint of photoelectron-photoion correlation. The model calculation on single-photon ionization of Ar reveals that the coherent hole dynamics in Ar{sup +} associated with a superposition of the spin-orbit states {sup 2}PJ (J = 3/2 and 1/2) can be identified by monitoring only the photoion created by a Fourier-transform limited extreme ultraviolet (EUV) pulse with the fs pulse duration, while the coherence is lost by a chirped EUV pulse. It is demonstrated that by coincidence detection of the photoelectron and photoion the coherent hole dynamics can be extracted even in the case of ionization by a chirped EUV pulse with the sufficiently wide bandwidth.

  19. New transient absorption observed in the spectrum of colloidal CdSe nanoparticles pumped with high-power femtosecond pulses

    SciTech Connect

    Burda, C.; Link, S.; Green, T.C.; El-Sayed, M.A.

    1999-12-09

    The power dependence of the transient absorption spectrum of CdSe nanoparticle colloids with size distribution of 4.0 {+-} 0.4 nm diameter is studied with femtosecond pump-probe techniques. At the lowest pump laser power, the absorption bleaching (negative spectrum) characteristic of the exciton spectrum is observed with maxima at 560 and 480 nm. As the pump laser power increases, two new transient absorptions at 510 and 590 nm with unresolved fast rise (<100 fs) and long decay times ({much{underscore}gt}150 ps) are observed. The energy of each of the positive absorption is red shifted from that of the bleach bands by {approximately}120 MeV. The origin of this shift is discussed in terms of the effect of the internal electric field of the many electron-hole pairs formed within the quantum dot at the high pump intensity, absorption from a metastable excited state or the formation of biexcitons.

  20. Properties of optical breakdown in BK7 glass induced by an extended-cavity femtosecond laser oscillator.

    PubMed

    Do, Binh T; Phillips, Mark C; Miller, Paul A; Kimmel, Mark W; Britsch, Justin; Cho, Seong-Ho

    2009-02-16

    Using an extended-cavity femtosecond oscillator, we investigated optical breakdown in BK7 glass caused by the accumulated action of many laser pulses. By using a pump-probe experiment and collecting the transmitted pump along with the reflected pump and the broadband light generated by the optical breakdown, we measured the build-up time to optical breakdown as a function of the pulse energy, and we also observed the instability of the plasma due to the effect of defocusing and shielding created by the electron gas. The spectrum of the broadband light emitted by the optical breakdown and the origin of the material modification in BK7 glass was studied. We developed a simple model of electromagnetic wave propagation in plasma that is consistent with the observed behavior of the reflection, absorption, and transmission of the laser light.

  1. On the Resolution Limit of Femtosecond Stimulated Raman Spectroscopy: Modelling Fifth-Order Signals with Overlapping Pulses.

    PubMed

    Fumero, Giuseppe; Batignani, Giovanni; Dorfman, Konstantin E; Mukamel, Shaul; Scopigno, Tullio

    2015-11-16

    Femtosecond stimulated Raman scattering (FSRS) spectroscopy is a powerful pump-probe technique that can track electronic and vibrational dynamics with high spectral and temporal resolution. The investigation of extremely short-lived species, however, implies deciphering complex signals and is ultimately hampered by unwanted nonlinear effects once the time resolution limit is approached and the pulses overlap temporally. Using the loop diagrams formalism we calculate the fifth-order response of a model system and address the limiting case where the relevant dynamics timescale is comparable to the pump-pulse duration and, consequently, the pump and the probe overlap temporally. We find that in this regime, additional diagrams that do not contribute for temporally well separated pulses need to be taken into account, giving rise to new time-dependent features, even in the absence of photoinduced dynamics and for negative delays.

  2. Ultrafast pump-probe spectroscopy in the UV-blue range with an extremely broad probe spectrum for the carrier relaxation study in an InGaN thin film with indium-rich nano-clusters.

    PubMed

    Wang, Hsiang-Chen; Lu, Yen-Cheng; Chen, Cheng-Yen; Yang, C C

    2007-03-19

    We implement an extremely broad second-harmonic spectrum of about 90 nm in width based on a 7-fs mode-locked Ti:sapphire laser. This broadband second-harmonic signal is used as the probe in a non-degenerate pump-probe experiment to investigate the ultrafast carrier dynamics in wide band-gap semiconductors. To properly calibrate the pump-probe data, the time delays between the pump of a particular wavelength and the probes of various spectral portions are determined through the interferometry measurement and the dispersion calculation. To demonstrate the pump-probe experiment operation, we measure the carrier relaxation process from the excitation levels down to the free-carrier and the localized states in an InGaN thin-film sample, in which indium-rich nano-clusters exist to form the localized states. From the time-resolved differential transmission profiles at various spectral positions of an infinitesimal spectral width and the temporal evolution of probe spectrum, one can observe the following relaxation process: First, once carriers are excited, only a small portion of carriers relaxes into the free-carrier and localized states independently within 1 ps. Then, the major part of carriers starts to relax into the two groups of states not until several ps after excitation. Such a relaxation process does not seem to be cascading, i.e., relaxation into the localized states through the free-carrier states.

  3. Rotational distributions of molecular photoions following resonant excitation

    NASA Astrophysics Data System (ADS)

    Poliakoff, E. D.; Chan, Jeffrey C. K.; White, M. G.

    1986-11-01

    We demonstrate that the photoelectron energy mediates the rotational energy distribution of N+2 ions created by photoionization, and conversely, that rotational energy determinations probe resonant excitation in molecular photoionization. Experimentally, this is accomplished by monitoring the dispersed fluorescence from N+2 (B 2Σ+u) photoions to determine their rotational energy distribution. These results demonstrate that while dipole selection rules constrain the total angular momentum of the electron-ion complex, the partitioning of angular momentum between the photoelectron and photoion depends on the photoejection dynamics. Implications for photoionization and electron impact ionizatin studies are discussed.

  4. Femtosecond optical pulse amplification

    NASA Astrophysics Data System (ADS)

    Knox, Wayne H.

    1988-02-01

    A number of techniques have been developed for amplification of optical pulses of approximately 100-fs duration. These amplifiers span a wide range of operating parameters from kilowatt to gigawatt peak powers and from 10 Hz to megahertz repetition rates. Amplification of femtosecond pulses has also been demonstrated at several wavelengths including visible, near-infrared, and ultraviolet regions. Several problems arise when amplifying short optical pulses to very high intensities. The problems are discussed and the state of the art of femtosecond optical pulse amplification is reviewed.

  5. Absolute partial photoionization cross sections of ozone.

    SciTech Connect

    Berkowitz, J.; Chemistry

    2008-04-01

    Despite the current concerns about ozone, absolute partial photoionization cross sections for this molecule in the vacuum ultraviolet (valence) region have been unavailable. By eclectic re-evaluation of old/new data and plausible assumptions, such cross sections have been assembled to fill this void.

  6. Reactions induced in (CF{sub 3}I){sub n} clusters by femtosecond UV laser pulses

    SciTech Connect

    Apatin, V. M.; Kompanets, V. O.; Lokhman, V. N.; Ogurok, N.-D. D.; Poydashev, D. G.; Ryabov, E. A. Chekalin, S. V.

    2012-10-15

    The excitation and ionization of CF{sub 3}I molecules and their clusters by femtosecond UV laser pulses is studied. It is concluded that the types of excitation of free CF{sub 3}I molecules and their clusters by femtosecond UV laser pulses are different. The composition and kinetic energy of ion products observed upon the ionization of (CF{sub 3}I){sub n} clusters by femtosecond pulses are found to differ considerably from those obtained upon ionization by nanosecond pulses. It is shown that the molecular I{sub 2}{sup +} ion is produced in reactions induced in (CF{sub 3}I){sub n} clusters by UV radiation. Using the pump-probe method, we found the two channels of producing I{sub 2}{sup +} ions with characteristic times {tau}{sub 1} Almost-Equal-To 1 ps and {tau}{sub 2} Almost-Equal-To 7 ps. A model of the reactions under study proposed in the paper is consistent with our experimental results.

  7. Photoassociation and coherent transient dynamics in the interaction of ultracold rubidium atoms with shaped femtosecond pulses. I. Experiment

    SciTech Connect

    Mullins, Terry; Salzmann, Wenzel; Goetz, Simone; Albert, Magnus; Eng, Judith; Wester, Roland; Weidemueller, Matthias; Weise, Fabian; Merli, Andrea; Weber, Stefan M.; Sauer, Franziska; Woeste, Ludger; Lindinger, Albrecht

    2009-12-15

    We experimentally investigate various processes present in the photoassociative interaction of an ultracold atomic sample with shaped femtosecond laser pulses as an detailed extension of previous work [W. Salzmann et al., Phys. Rev. Lett. 100, 233003 (2008)]. We demonstrate the photoassociation of pairs of rubidium atoms into electronically excited, bound molecular states using spectrally cut femtosecond laser pulses tuned below the rubidium D{sub 1} or D{sub 2} asymptote. Time-resolved pump-probe spectra reveal oscillations of the molecular formation rate, which are due to coherent transient dynamics in the electronic excitation. The oscillation frequency corresponds to the detuning of the spectral cut position to the asymptotic transition frequency of the rubidium D{sub 1} or D{sub 2} lines, respectively. Measurements of the molecular photoassociation signal as a function of the pulse energy reveal a nonlinear dependence and indicate a nonperturbative excitation process. Chirping the association laser pulse allowed us to change the phase of the coherent transients. Furthermore, a signature for molecules in the electronic ground state is found, which is attributed to molecule formation by femtosecond photoassociation followed by spontaneous decay. In a subsequent article [A. Merli et al., Phys. Rev. A 80, 063417 (2009)] quantum mechanical calculations are presented, which compare well with the experimental data and reveal further details about the observed coherent transient dynamics.

  8. A versatile femtosecond stimulated Raman spectroscopy setup with tunable pulses in the visible to near infrared

    SciTech Connect

    Zhu, Liangdong; Liu, Weimin; Fang, Chong

    2014-07-28

    We demonstrate a versatile and efficient setup to perform femtosecond stimulated Raman spectroscopy (FSRS). Technical innovations are implemented to achieve the wavelength tunability for both the picosecond narrowband Raman pump pulse and femtosecond broadband Raman probe pulse. Using a simplified one-grating scheme in a home-built second harmonic bandwidth compressor followed by a two-stage noncollinear optical parametric amplifier, we tune the Raman pump pulse from ca. 480 to 750 nm. To generate the suitable Raman probe pulse in tandem, we rely on our recently demonstrated broadband up-converted multicolor array technique that readily provides tunable broadband laser sidebands across the visible to near-infrared range. This unique setup has unparalleled flexibility for conducting FSRS. We measure the ground-state Raman spectra of a cyclohexane standard using tunable pump-probe pairs at various wavelengths across the visible region. The best spectral resolution is ∼12 cm{sup −1}. By tuning the pump wavelength closer to the electronic absorption band of a photoacid pyranine in water, we observe the pre-resonantly enhanced Raman signal. The stimulated Raman gain of the 1627 cm{sup −1} mode is increased by over 15 times.

  9. Femtosecond spectroscopic study of photochromic reactions of bacteriorhodopsin and visual rhodopsin.

    PubMed

    Feldman, Tatiana B; Smitienko, Olga A; Shelaev, Ivan V; Gostev, Fedor E; Nekrasova, Oksana V; Dolgikh, Dmitriy A; Nadtochenko, Victor A; Kirpichnikov, Mikhail P; Ostrovsky, Mikhail A

    2016-11-01

    Photochromic ultrafast reactions of bacteriorhodopsin (H. salinarum) and bovine rhodopsin were conducted with a femtosecond two-pump probe pulse setup with the time resolution of 20-25fs. The dynamics of the forward and reverse photochemical reactions for both retinal-containing proteins was compared. It is demonstrated that when retinal-containing proteins are excited by femtosecond pulses, dynamics pattern of the vibrational coherent wave packets in the course of the reaction is different for bacteriorhodopsin and visual rhodopsin. As shown in these studies, the low-frequencies that form a wave packets experimentally observed in the dynamics of primary products formation as a result of retinal photoisomerization have different intensities and are clearer for bovine rhodopsin. Photo-reversible reactions for both retinal proteins were performed from the stage of the relatively stable photointermediates that appear within 3-5ps after the light pulse impact. It is demonstrated that the efficiency of the reverse phototransition K-form→bacteriorhodopsin is almost five-fold higher than that of the Batho-intermediate→visual rhodopsin phototransition. The results obtained indicate that in the course of evolution the intramolecular mechanism of the chromophore-protein interaction in visual rhodopsin becomes more perfect and specific. The decrease in the probability of the reverse chromophore photoisomerization (all-trans→11-cis retinal) in primary photo-induced rhodopsin products causes an increase in the efficiency of the photoreception process. Copyright © 2016 Elsevier B.V. All rights reserved.

  10. Goniometer-based femtosecond X-ray diffraction of mutant 30S ribosomal subunit crystals

    SciTech Connect

    Dao, E. Han; Sierra, Raymond G.; Laksmono, Hartawan; Lemke, Henrik T.; Alonso-Mori, Roberto; Coey, Aaron; Larsen, Kevin; Baxter, Elizabeth L.; Cohen, Aina E.; Soltis, S. Michael; DeMirci, Hasan

    2015-04-30

    In this work, we collected radiation-damage-free data from a set of cryo-cooled crystals for a novel 30S ribosomal subunit mutant using goniometer-based femtosecond crystallography. Crystal quality assessment for these samples was conducted at the X-ray Pump Probe end-station of the Linac Coherent Light Source (LCLS) using recently introduced goniometer-based instrumentation. These 30S subunit crystals were genetically engineered to omit a 26-residue protein, Thx, which is present in the wild-type Thermus thermophilus 30S ribosomal subunit. We are primarily interested in elucidating the contribution of this ribosomal protein to the overall 30S subunit structure. To assess the viability of this study, femtosecond X-ray diffraction patterns from these crystals were recorded at the LCLS during a protein crystal screening beam time. During our data collection, we successfully observed diffraction from these difficult-to-grow 30S ribosomal subunit crystals. Most of our crystals were found to diffract to low resolution, while one crystal diffracted to 3.2 Å resolution. These data suggest the feasibility of pursuing high-resolution data collection as well as the need to improve sample preparation and handling in order to collect a complete radiation-damage-free data set using an X-ray Free Electron Laser.

  11. Goniometer-based femtosecond X-ray diffraction of mutant 30S ribosomal subunit crystals.

    PubMed

    Dao, E Han; Sierra, Raymond G; Laksmono, Hartawan; Lemke, Henrik T; Alonso-Mori, Roberto; Coey, Aaron; Larsen, Kevin; Baxter, Elizabeth L; Cohen, Aina E; Soltis, S Michael; DeMirci, Hasan

    2015-07-01

    In this work, we collected radiation-damage-free data from a set of cryo-cooled crystals for a novel 30S ribosomal subunit mutant using goniometer-based femtosecond crystallography. Crystal quality assessment for these samples was conducted at the X-ray Pump Probe end-station of the Linac Coherent Light Source (LCLS) using recently introduced goniometer-based instrumentation. These 30S subunit crystals were genetically engineered to omit a 26-residue protein, Thx, which is present in the wild-type Thermus thermophilus 30S ribosomal subunit. We are primarily interested in elucidating the contribution of this ribosomal protein to the overall 30S subunit structure. To assess the viability of this study, femtosecond X-ray diffraction patterns from these crystals were recorded at the LCLS during a protein crystal screening beam time. During our data collection, we successfully observed diffraction from these difficult-to-grow 30S ribosomal subunit crystals. Most of our crystals were found to diffract to low resolution, while one crystal diffracted to 3.2 Å resolution. These data suggest the feasibility of pursuing high-resolution data collection as well as the need to improve sample preparation and handling in order to collect a complete radiation-damage-free data set using an X-ray Free Electron Laser.

  12. Serial Femtosecond Crystallography and Ultrafast Absorption Spectroscopy of the Photoswitchable Fluorescent Protein IrisFP.

    PubMed

    Colletier, Jacques-Philippe; Sliwa, Michel; Gallat, François-Xavier; Sugahara, Michihiro; Guillon, Virginia; Schirò, Giorgio; Coquelle, Nicolas; Woodhouse, Joyce; Roux, Laure; Gotthard, Guillaume; Royant, Antoine; Uriarte, Lucas Martinez; Ruckebusch, Cyril; Joti, Yasumasa; Byrdin, Martin; Mizohata, Eiichi; Nango, Eriko; Tanaka, Tomoyuki; Tono, Kensuke; Yabashi, Makina; Adam, Virgile; Cammarata, Marco; Schlichting, Ilme; Bourgeois, Dominique; Weik, Martin

    2016-03-03

    Reversibly photoswitchable fluorescent proteins find growing applications in cell biology, yet mechanistic details, in particular on the ultrafast photochemical time scale, remain unknown. We employed time-resolved pump-probe absorption spectroscopy on the reversibly photoswitchable fluorescent protein IrisFP in solution to study photoswitching from the nonfluorescent (off) to the fluorescent (on) state. Evidence is provided for the existence of several intermediate states on the pico- and microsecond time scales that are attributed to chromophore isomerization and proton transfer, respectively. Kinetic modeling favors a sequential mechanism with the existence of two excited state intermediates with lifetimes of 2 and 15 ps, the second of which controls the photoswitching quantum yield. In order to support that IrisFP is suited for time-resolved experiments aiming at a structural characterization of these ps intermediates, we used serial femtosecond crystallography at an X-ray free electron laser and solved the structure of IrisFP in its on state. Sample consumption was minimized by embedding crystals in mineral grease, in which they remain photoswitchable. Our spectroscopic and structural results pave the way for time-resolved serial femtosecond crystallography aiming at characterizing the structure of ultrafast intermediates in reversibly photoswitchable fluorescent proteins.

  13. Macrospin dynamics in antiferromagnets triggered by sub-20 femtosecond injection of nanomagnons.

    PubMed

    Bossini, D; Dal Conte, S; Hashimoto, Y; Secchi, A; Pisarev, R V; Rasing, Th; Cerullo, G; Kimel, A V

    2016-02-05

    The understanding of how the sub-nanoscale exchange interaction evolves in macroscale correlations and ordered phases of matter, such as magnetism and superconductivity, requires to bridging the quantum and classical worlds. This monumental challenge has so far only been achieved for systems close to their thermodynamical equilibrium. Here we follow in real time the ultrafast dynamics of the macroscale magnetic order parameter in the Heisenberg antiferromagnet KNiF3 triggered by the impulsive optical generation of spin excitations with the shortest possible nanometre wavelength and femtosecond period. Our magneto-optical pump-probe experiments also demonstrate the coherent manipulation of the phase and amplitude of these femtosecond nanomagnons, whose frequencies are defined by the exchange energy. These findings open up opportunities for fundamental research on the role of short-wavelength spin excitations in magnetism and strongly correlated materials; they also suggest that nanospintronics and nanomagnonics can employ coherently controllable spin waves with frequencies in the 20 THz domain.

  14. Tunable Broadband Nonlinear Optical Properties of Black Phosphorus Quantum Dots for Femtosecond Laser Pulses

    PubMed Central

    Jiang, Xiao-Fang; Zeng, Zhikai; Li, Shuang; Guo, Zhinan; Zhang, Han; Huang, Fei; Xu, Qing-Hua

    2017-01-01

    Broadband nonlinear optical properties from 500 to 1550 nm of ultrasmall black phosphorus quantum dots (BPQDs) have been extensively investigated by using the open-aperture Z-scan technique. Our results show that BPQDs exhibit significant nonlinear absorption in the visible range, but saturable absorption in the near-infrared range under femtosecond excitation. The calculated nonlinear absorption coefficients were found to be (7.49 ± 0.23) × 10−3, (1.68 ± 0.078) × 10−3 and (0.81 ± 0.03) × 10−3 cm/GW for 500, 700 and 900 nm, respectively. Femtosecond pump-probe measurements performed on BPQDs revealed that two-photon absorption is responsible for the observed nonlinear absorption. The saturable absorption behaviors observed at 1050, 1350 and 1550 nm are due to ground-state bleaching induced by photo-excitation. Our results suggest that BPQDs have great potential in applications as broadband optical limiters in the visible range or saturable absorbers in the near-infrared range for ultrafast laser pulses. These ultrasmall BPQDs are potentially useful as broadband optical elements in ultrafast photonics devices. PMID:28772566

  15. Femtosecond time-resolved energy transfer from CdSe nanoparticles to phthalocyanines

    NASA Astrophysics Data System (ADS)

    Dayal, S.; Królicki, R.; Lou, Y.; Qiu, X.; Berlin, J. C.; Kenney, M. E.; Burda, C.

    2006-07-01

    The first real-time observation of the early events during energy transfer from a photoexcited CdSe nanoparticle to an attached phthalocyanine molecule are presented in terms of a femtosecond spectroscopic pump-probe study of the energy transfer in conjugates of CdSe nanoparticles (NPs) and silicon phthalocyanines (Pcs) with 120 fs time resolution. Four different silicon phthalocyanines have been conjugated to CdSe NPs. All of these have proven potential for photodynamic therapy (PDT). In such NP-Pc conjugates efficient energy transfer (ET) from CdSe NPs to Pcs occurs upon selective photoexcitation of the NP moiety. Spectral analysis as well as time-resolved fluorescence up-conversion measurements revealed the structure and dynamics of the investigated conjugates. Femtosecond transient differential absorption (TDA) spectroscopy was used for the investigation of the non-radiative carrier and ET dynamics. The formation of excitons, trapped carriers states, as well as stimulated emission was monitored in the TDA spectra and the corresponding lifetimes of these states were recorded. The time component for energy transfer was found to be between 15 and 35 ps. The ET efficiencies are found to be 20-70% for the four Pc conjugates, according to fluorescence quenching experiments. Moreover, as a result of the conjugation between NP and the Pcs the photoluminescence efficiency of the Pc moieties in the conjugates do not strictly follow the quantum yields of the bare phthalocyanines.

  16. A multi-MHz single-shot data acquisition scheme with high dynamic range: pump-probe X-ray experiments at synchrotrons.

    PubMed

    Britz, Alexander; Assefa, Tadesse A; Galler, Andreas; Gawelda, Wojciech; Diez, Michael; Zalden, Peter; Khakhulin, Dmitry; Fernandes, Bruno; Gessler, Patrick; Sotoudi Namin, Hamed; Beckmann, Andreas; Harder, Manuel; Yavaş, Hasan; Bressler, Christian

    2016-11-01

    The technical implementation of a multi-MHz data acquisition scheme for laser-X-ray pump-probe experiments with pulse limited temporal resolution (100 ps) is presented. Such techniques are very attractive to benefit from the high-repetition rates of X-ray pulses delivered from advanced synchrotron radiation sources. Exploiting a synchronized 3.9 MHz laser excitation source, experiments in 60-bunch mode (7.8 MHz) at beamline P01 of the PETRA III storage ring are performed. Hereby molecular systems in liquid solutions are excited by the pulsed laser source and the total X-ray fluorescence yield (TFY) from the sample is recorded using silicon avalanche photodiode detectors (APDs). The subsequent digitizer card samples the APD signal traces in 0.5 ns steps with 12-bit resolution. These traces are then processed to deliver an integrated value for each recorded single X-ray pulse intensity and sorted into bins according to whether the laser excited the sample or not. For each subgroup the recorded single-shot values are averaged over ∼10(7) pulses to deliver a mean TFY value with its standard error for each data point, e.g. at a given X-ray probe energy. The sensitivity reaches down to the shot-noise limit, and signal-to-noise ratios approaching 1000 are achievable in only a few seconds collection time per data point. The dynamic range covers 100 photons pulse(-1) and is only technically limited by the utilized APD.

  17. Comparison of vibrational dynamics between non-ionic and ionic vibrational probes in water: Experimental study with two-dimensional infrared and infrared pump-probe spectroscopies

    NASA Astrophysics Data System (ADS)

    Okuda, Masaki; Ohta, Kaoru; Tominaga, Keisuke

    2016-09-01

    Dynamics of the hydration structure around small vibrational probes have been extensively studied over the past few decades. However, we need to gain insight into how vibrational dynamics is affected by the molecular nature of the probe molecules in water. In this study, 2-nitro-5-thiocyanate benzoic acid (NTBA), which has an SCN group attached to an aromatic ring, and thiocyanate ion (SCN-) were used to investigate the vibrational dynamics of two vibrational probes, including vibrational frequency fluctuations and rotational relaxation. By performing two-dimensional infrared spectroscopic measurements, the vibrational frequency fluctuations of the SCN anti-stretching modes of these solutes were compared. The frequency-frequency time correlation function (FFTCF) of these solutes can be modeled by a delta function plus an exponential function and a constant. The FFTCF of NTBA was characterized by a time constant of 1.1 ps, which is similar to that of SCN-. Moreover, no component was longer than this constant. Consequently, the loss of the correlation in frequency fluctuations of the SCN anti-stretching mode of NTBA may be controlled by a mechanism similar to that of the ionic probe, which involves the hydrogen bonding dynamics of water. Polarization-controlled IR pump-probe measurements were performed for these vibrational probes in water to study the vibrational energy relaxation (VER) and reorientational relaxation processes. The VER rate of NTBA is much smaller than that of SCN-, which indicates that the intramolecular relaxation process is significant for VER of NTBA. Based on the rotational relaxation time of NTBA being shorter than that of SCN-, the internal rotational motion of the SCN group around the Cphenyl-S bond axis, where Cphenyl denotes a carbon atom of the aromatic ring to which the SCN group is attached, may play an important role in the anisotropic decay of NTBA in H2O.

  18. Monitoring the formation and decay of transient photosensitized intermediates using pump-probe UV resonance Raman spectroscopy. I: Self-modeling curve resolution.

    PubMed

    Kleimeyer, James A; Harris, Joel M

    2003-04-01

    Resolution of transient excited-state Raman scattering from ground-state and solvent bands is a challenging spectroscopic measurement since excited-state spectral features are often of low intensity, overlapping the dominant ground-state and solvent bands. The Raman spectra of these intermediates can be resolved, however, by acquiring time-resolved data and using multidimensional data analysis methods. In the absence of a physical model describing the kinetic behavior of a reaction, resolution of the pure-component spectra from these data can be accomplished using self-modeling curve resolution, a factor analysis technique that relies on the correlation in the data along a changing composition dimension to resolve the component spectra. A two-laser UV pump-probe resonance-enhanced Raman instrument was utilized to monitor the kinetics of amine quenching of excited-triplet states of benzophenone. The formation and decay of transient intermediates were monitored over time, from 15 ns to 100 micros. Factor analysis of the time-resolved spectral data identified three significant components in the data. The time-resolved intensities at each Raman wavenumber shift were projected onto the three significant eigenvectors, and least-squares criteria were developed to find the common plane in the space of the eigenvectors that includes the observed data. Within that plane, the three pure-component spectra were resolved using geometric criteria of convex hull analysis. The resolved spectra were found to arise from benzophenone excited-triplet states, diphenylketyl radicals, and the solvent and ground-state benzophenone.

  19. Dynamics of a Room Temperature Ionic Liquid in Supported Ionic Liquid Membranes vs the Bulk Liquid: 2D IR and Polarized IR Pump-Probe Experiments.

    PubMed

    Shin, Jae Yoon; Yamada, Steven A; Fayer, Michael D

    2017-01-11

    Supported ionic liquid membranes (SILMs) are membranes that have ionic liquids impregnated in their pores. SILMs have been proposed for advanced carbon capture materials. Two-dimensional infrared (2D IR) and polarization selective IR pump-probe (PSPP) techniques were used to investigate the dynamics of reorientation and spectral diffusion of the linear triatomic anion, SeCN(-), in poly(ether sulfone) (PES) membranes and room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2). The dynamics in the bulk EmimNTf2 were compared to its dynamics in the SILM samples. Two PES membranes, PES200 and PES30, have pores with average sizes, ∼300 nm and ∼100 nm, respectively. Despite the relatively large pore sizes, the measurements reveal that the reorientation of SeCN(-) and the RTIL structural fluctuations are substantially slower in the SILMs than in the bulk liquid. The complete orientational randomization, slows from 136 ps in the bulk to 513 ps in the PES30. 2D IR measurements yield three time scales for structural spectral diffusion (SSD), that is, the time evolution of the liquid structure. The slowest decay constant increases from 140 ps in the bulk to 504 ps in the PES200 and increases further to 1660 ps in the PES30. The results suggest that changes at the interface propagate out and influence the RTIL structural dynamics even more than a hundred nanometers from the polymer surface. The differences between the IL dynamics in the bulk and in the membranes suggest that studies of bulk RTIL properties may be poor guides to their use in SILMs in carbon capture applications.

  20. Ultrafast vibrational spectroscopic studies on the photoionization of the α-tocopherol analogue trolox C.

    PubMed

    Parker, Anthony W; Bisby, Roger H; Greetham, Gregory M; Kukura, Philipp; Scherer, Kathrin M; Towrie, Michael

    2014-10-23

    The initial events after photoexcitation and photoionization of α-tocopherol (vitamin E) and the analogue Trolox C have been studied by femtosecond stimulated Raman spectroscopy, transient absorption spectroscopy and time-resolved infrared spectroscopy. Using these techniques it was possible to follow the formation and decay of the excited state, neutral and radical cation radicals and the hydrated electron that are produced under the various conditions examined. α-Tocopherol and Trolox C in methanol solution appear to undergo efficient homolytic dissociation of the phenolic -OH bond to directly produce the tocopheroxyl radical. In contrast, Trolox C photochemistry in neutral aqueous solutions involves intermediate formation of a radical cation and the hydrated electron which undergo geminate recombination within 100 ps in competition with deprotonation of the radical cation. The results are discussed in relation to recently proposed mechanisms for the reaction of α-tocopherol with peroxyl radicals, which represents the best understood biological activity of this vitamin.

  1. Intense-Field Photoionization of Molecules using Ultrashort Radiation Pulses: Carbon Disulfide and Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Beck, Joshua; Uiterwaal, Cornelis

    2016-05-01

    We experimentally investigate the photoionization and photofragmentation of molecules using intense fields from an 800 nm, femtosecond laser source and an experimental method that eliminates the focal volume effect without the need for data deconvolution. Targets include carbon disulfide and carbon dioxide. We show that ionization is insignificant for intensities that maximize alignment of carbon disulfide, which validates ultrafast electron diffraction experiments from aligned carbon disulfide. For comparison, we also investigate the analogous molecule carbon dioxide. In this molecule the molecular bonding orbitals include the n = 2 atomic orbitals of the oxygen atom, while in carbon disulfide the n = 3 orbitals of the sulfur atom contribute to the bonding. Recent work will be presented. This work supported by U.S. Dept. of Education GAANN Grants Nos. P200A090156 and P200A120188 and National Science Foundation EPSCoR RII Track-2 CA Award No. IIA-1430519 (Cooperative Nebraska-Kansas Grant).

  2. Photoionization-pumped x-ray lasers using ultrashort-pulse excitation.

    PubMed

    Kapteyn, H C

    1992-08-20

    Recent advances in the production of ultrashort x-ray pulses by using femtosecond laser-produced plasmas coupled with the development of terawatt ultrashort-pulse lasers may make possible ultrashortpulse photoexcited x-ray lasers. I examine the creation of a population inversion on the K-alpha transition of neon at 1.5 nm by using the photoionization scheme first suggested by Duguay and Rentzepis in 1967. It is shown that this laser can be produced by using a pump laser of ~ 10 J in 50 fs, provided that a sufficiently bright laser-produced plasma x-ray source can be created. Recent experimental and theoretical results are discussed that verify the potential feasibility of this scheme.

  3. Isomer-dependent fragmentation dynamics of inner-shell photoionized difluoroiodobenzene

    DOE PAGES

    Ablikim, Utuq; Bomme, Cédric; Savelyev, Evgeny; ...

    2017-05-11

    The fragmentation dynamics of 2,6- and 3,5-difluoroiodobenzene after iodine 4d inner-shell photoionization with soft X-rays are studied using coincident electron and ion momentum imaging. By analyzing the momentum correlation between iodine and fluorine cations in three-fold ion coincidence events, we can distinguish the two isomers experimentally. Classical Coulomb explosion simulations are in overall agreement with the experimentally determined fragment ion kinetic energies and momentum correlations and point toward different fragmentation mechanisms and time scales. Finally, while most three-body fragmentation channels show clear evidence for sequential fragmentation on a time scale larger than the rotational period of the fragments, the breakupmore » into iodine and fluorine cations and a third charged co-fragment appears to occur within several hundred femtoseconds.« less

  4. Ultrafast molecular processes mapped by femtosecond x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Elsaesser, Thomas

    2012-02-01

    X-ray diffraction with a femtosecond time resolution allows for mapping photoinduced structural dynamics on the length scale of a chemical bond and in the time domain of atomic and molecular motion. In a pump-probe approach, a femtosecond excitation pulse induces structural changes which are probed by diffracting a femtosecond hard x-ray pulse from the excited sample. The transient angular positions and intensities of diffraction peaks give insight into the momentary atomic or molecular positions and into the distribution of electronic charge density. The simultaneous measurement of changes on different diffraction peaks is essential for determining atom positions and charge density maps with high accuracy. Recent progress in the generation of ultrashort hard x-ray pulses (Cu Kα, wavelength λ=0.154 nm) in laser-driven plasma sources has led to the implementation of the powder diffraction and the rotating crystal method with a time resolution of 100 fs. In this contribution, we report new results from powder diffraction studies of molecular materials. A first series of experiments gives evidence of a so far unknown concerted transfer of electrons and protons in ammonium sulfate [(NH4)2SO4], a centrosymmetric structure. Charge transfer from the sulfate groups results in the sub-100 fs generation of a confined electron channel along the c-axis of the unit cell which is stabilized by transferring protons from the adjacent ammonium groups into the channel. Time-dependent charge density maps display a periodic modulation of the channel's charge density by low-frequency lattice motions with a concerted electron and proton motion between the channel and the initial proton binding site. A second study addresses atomic rearrangements and charge dislocations in the non-centrosymmetric potassium dihydrogen phosphate [KH2PO4, KDP]. Photoexcitation generates coherent low-frequency motions along the LO and TO phonon coordinates, leaving the average atomic positions unchanged

  5. Toward Femtosecond X-ray Spectroscopy at the Advanced Light Source

    SciTech Connect

    Chong, Henry Herng Wei

    2004-01-01

    The realization of tunable, ultrashort pulse x-ray sources promises to open new venues of science and to shed new light on long-standing problems in condensed matter physics and chemistry. Fundamentally new information can now be accessed. Used in a pump-probe spectroscopy, ultrashort x-ray pulses provide a means to monitor atomic rearrangement and changes in electronic structure in condensed-matter and chemical systems on the physically-limiting time-scales of atomic motion. This opens the way for the study of fast structural dynamics and the role they play in phase transitions, chemical reactions and the emergence of exotic properties in materials with strongly interacting degrees of freedom. The ultrashort pulse x-ray source developed at the Advanced Light Source at the Lawrence Berkeley Laboratory is based on electron slicing in storage rings, and generates ~100 femtosecond pulses of synchrotron radiation spanning wavelengths from the far-infrared to the hard x-ray region of the electromagnetic spectrum. The tunability of the source allows for the adaptation of a broad range of static x-ray spectroscopies to useful pump-probe measurements. Initial experiments are attempted on transition metal complexes that exhibit relatively large structural changes upon photo-excitation and which have excited-state evolution determined by strongly interacting structural, electronic and magnetic degrees of freedom. Specifically, iron(II) complexes undergo a spin-crossover transition upon optical irradiation. The dynamics of the transition involve a metal-to-ligand charge transfer, a ΔS=2 change in magnetic moment and 10% bond dilation in the first coordination shell of the iron. Studies of the electronic dynamics are studied with time-resolved optical absorption measurements. The current progress of time-resolved structural studies to complete the picture of the spin-crossover transition is presented.

  6. Toward femtosecond X-ray spectroscopy at the Advanced Light Source

    NASA Astrophysics Data System (ADS)

    Chong, Henry Herng Wei

    The realization of tunable, ultrashort pulse x-ray sources promises to open new venues of science and to shed new light on long-standing problems in condensed matter physics and chemistry. Fundamentally new information can now be accessed. Used in a pump-probe spectroscopy, ultrashort x-ray pulses provide a means to monitor atomic rearrangement and changes in electronic structure in condensed-matter and chemical systems on the physically-limiting time-scales of atomic motion. This opens the way for the study of fast structural dynamics and the role they play in phase transitions, chemical reactions and the emergence of exotic properties in materials with strongly interacting degrees of freedom. The ultrashort pulse x-ray source developed at the Advanced Light Source at the Lawrence Berkeley Laboratory is based on electron slicing in storage rings, and generates ˜100 femtosecond pulses of synchrotron radiation spanning wavelengths from the far-infrared to the hard x-ray region of the electromagnetic spectrum. The tunability of the source allows for the adaptation of a broad range of static x-ray spectroscopies to useful pump-probe measurements. Initial experiments are attempted on transition metal complexes that exhibit relatively large structural changes upon photo-excitation and which have excited-state evolution determined by strongly interacting structural, electronic and magnetic degrees of freedom. Specifically, iron(II) complexes undergo a spin-crossover transition upon optical irradiation. The dynamics of the transition involve a metal-to-ligand charge transfer, a DeltaS = 2 change in magnetic moment and 10% bond dilation in the first coordination shell of the iron. Studies of the electronic dynamics are studied with time-resolved optical absorption measurements. The current progress of time-resolved structural studies to complete the picture of the spin-crossover transition is presented.

  7. Photoionization and Dissociative Photoionization Study of Cholesterol by IR Laser Desorption/Tunable Synchrotron VUV Photoionization Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Pan, Yang; Zhang, Li-dong; Guo, Hui-jun; Yin, Hao; Qi, Fei

    2009-04-01

    Elementary cholesterol was analyzed with IR laser desorption/tunable synchrotron vacuum ultraviolet photoionization mass spectrometry. An exclusive molecular ion of cholesterol is observed by near threshold single-photon ionization with high efficiency. Fragments are yielded with the increase of photon energy. The structures of various fragments are determined with commercial electron ionization time-of-flight mass spectrometry. Dominant fragmentation pathways are discussed in detail with the aid of ab initio calculations.

  8. Low temperature plasmas created by photoionization of gases with intense radiation pulses from laser-produced plasma sources

    NASA Astrophysics Data System (ADS)

    Bartnik, A.; Pisarczyk, T.; Wachulak, P.; Chodukowski, T.; Fok, T.; Wegrzyński, Ł.; Kalinowska, Z.; Fiedorowicz, H.

    2016-12-01

    A comparative study of photoionized plasmas created by soft X-ray (SXR) and extreme ultraviolet (EUV) laser plasma sources was performed. The sources, employing high or low energy laser systems, utilized double-stream Xe/He gas-puff targets irradiated with laser pulses of different parameters. The SXR/EUV beams were used for irradiation of a gas stream, injected into a vacuum chamber synchronously with the radiation pulse. Photoionized plasmas produced this way in Ne gas emitted radiation in the SXR/EUV range. The corresponding spectra were dominated by emission lines originating from singly charged ions. Significant differences between spectra obtained in different experimental conditions concern specific transitions in Ne II ions. Creation of photoionized plasmas by SXR or EUV irradiation resulted in K-shell or L-shell emissions respectively. In case of the low energy system absorption spectra were measured additionally. In case of the high energy system, the electron density measurements were performed by laser interferometry, employing a femtosecond laser system. A maximum electron density reached the value of 2·1018cm-3. For the low energy system, a detection limit was too high for the interferometric measurements, thus only an upper estimation for electron density could be made.

  9. Precision measurements of spectral phases in femtosecond spectroscopy and application to doubly degenerate electronic dynamics in silicon naphthalocyanine

    NASA Astrophysics Data System (ADS)

    Ferro, Allison Albrecht

    Femtosecond lasers have been used to reveal the timescales for important physical processes including the primary steps of vision and photosynthesis. It is demonstrated here that spectral interferometry has the accuracy necessary to distinguish phase shifts from time delays for femtosecond pulses. This distinction opens up access to new levels of information and has consequences for experimental practice, coherent control, phase-locked pulse pair experiments, and the theory of femtosecond nonlinear spectroscopy. In particular, the distinction makes optical two-dimensional (2D) Fourier transform spectroscopy possible. A complete measurement of the femtosecond linear free induction decay in a dye solution is also demonstrated using spectral interferometry. For weak pulses, it is shown that Beer's law predicts the amplitude change and appropriate dispersion relations can be used to calculate the spectral phase change. The results indicate that the rotating wave approximation used in nonlinear spectroscopy can fail at the 6% level for molecular spectra with widths 15% of the center frequency. The doubly degenerate electronic dynamics of silicon 2,3- naphthalocyanine bis(trihexylsilyloxide) (C84H102N8O 2Si3) were investigated using transient grating signals, pump-probe polarization anisotropy measurements, and 2D electronic spectra. The signals displayed weak vibrational quantum beats and a resolvable sub 100 fs initial anisotropy decay. The pump-probe anisotropy disagreed with current theory and led to a reformulation of the theory which explicitly includes ground state depopulation, excited state emission, and excited state absorption. Jahn-Teller electronic reorientation is proposed as a likely mechanism for the anisotropy decay. A model for the electronic reorientation and vibrational motion in silicon naphthalocyanine was constructed. Calculations of the nonlinear signals using the model reproduced the quantum beats and the anisotropy decay outside the pulse

  10. Femtosecond optical engineering

    NASA Astrophysics Data System (ADS)

    Li, Peng

    The last a few decades have witnessed the rapid progress of ultrafast optics, which has been driving the technology revolutions in scientific research and engineering applications. For instance, several recent Nobel Prize winners have made their discoveries using femtosecond optics applications in physics, chemistry and biomedicine. This dissertation covers three important applications of ultrafast femtosecond lasers. First, we study the single particle scattering spectroscopy using supercontinuum white light tweezers. We have developed supercontinuum white light optical tweezers by using the ultrabroad band supercontinuum (SC) generated in highly nonlinear photonic crystal fibers pumped by ultrafast laser pulses and for the first time studied the scattering spectra in tightly focused supercontinuum. When the scatterer is of spherical shape, we describe modeling based on Mie's scattering theory and angular spectrum decomposition. For the non-spherical-shaped scatterers, when the size of the scatterer is small or the refractive index of the scatterer is close to the surrounding medium, another modeling based on Born approximation and Green's function is derived. The calculation results are provided as well. This work has built the foundation to understand optical scattering spectroscopy of single particles in the supercontinuum white light optical tweezers and further application to probe the single particle's physical and chemical properties via the linear and nonlinear optical scattering spectra, which can lead to many important applications particularly in nanoparticle characterization and sensing. The second part of this dissertation is dedicated to the study of the femtosecond pulse beam shaping. For femtosecond laser pulses, which cover bandwidths of tens of nanometers, the performance of beam-shaping a Gaussian beam into a flat-topped rectangular intensity profile is discussed for a practical realization. In the meantime, the convergence of the improved

  11. Time-dependent Cooling in Photoionized Plasma

    NASA Astrophysics Data System (ADS)

    Gnat, Orly

    2017-02-01

    I explore the thermal evolution and ionization states in gas cooling from an initially hot state in the presence of external photoionizing radiation. I compute the equilibrium and nonequilibrium cooling efficiencies, heating rates, and ion fractions for low-density gas cooling while exposed to the ionizing metagalactic background radiation at various redshifts (z = 0 ‑ 3), for a range of temperatures (108–104 K), densities (10‑7–103 cm‑3), and metallicities (10‑3–2 times solar). The results indicate the existence of a threshold ionization parameter, above which the cooling efficiencies are very close to those in photoionization equilibrium (so that departures from equilibrium may be neglected), and below which the cooling efficiencies resemble those in collisional time-dependent gas cooling with no external radiation (and are thus independent of density).

  12. Photoionization of P+: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Nahar, S. N.; Hernández, E. M.; Hernández, L.; Antillón, A.; Morales-Mori, A.; González, O.; Covington, A. M.; Chartkunchand, K. C.; Hanstorp, D.; Juárez, A. M.; Hinojosa, G.

    2017-01-01

    An experimental and theoretical study of the single photoionization cross section of the P+ cation of phosphorus is presented. Photoionization (PI) cross sections are instrumental for the determination of abundances in the interstellar medium. The experiment was performed by merging an ion beam with a photon beam. The photon beam was nearly monochromatic and had an energy resolution of 24 meV. Calculations were carried out using the Breit-Pauli R-matrix method. The combined study was developed in the photon energy interval from 18 eV (68.9 nm) to 50 eV (24.8 nm). Comparison between the measured and the calculated cross section shows good agreement in general and identifies features of the process and existence of states in the experimental beam. The present results should provide for more accurate modeling of P+.

  13. Photoionization of atomic hydrogen in electric field

    SciTech Connect

    Gorlov, Timofey V; Danilov, Viatcheslav V

    2010-01-01

    Laser assisted ionization of high energy hydrogen beams in magnetic fields opens wide application possibilities in accelerator physics and other fields. The key theoretical problem of the method is the calculation of the ionization probability of a hydrogen atom affected by laser and static electric fields in the particle rest frame. A method of solving this problem with the temporal Schr dinger equation including a continuum spectrum is presented in this paper in accurate form for the first time. This method allows finding the temporal evolution of the wave function of the hydrogen atom as a function of laser and static electric fields. Solving the problem of photoionization reveals quantum effects that cannot be described by the cross sectional approach. The effects play a key role in the problems of photoionization of H0 beams with the large angular or energy spread.

  14. Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra

    DOE PAGES

    Wolf, Thomas; Holzmeier, Fabian; Wagner, Isabella; ...

    2017-07-01

    Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine's neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependentmore » dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.« less

  15. Surgical applications of femtosecond lasers.

    PubMed

    Chung, Samuel H; Mazur, Eric

    2009-10-01

    Femtosecond laser ablation permits non-invasive surgeries in the bulk of a sample with submicrometer resolution. We briefly review the history of optical surgery techniques and the experimental background of femtosecond laser ablation. Next, we present several clinical applications, including dental surgery and eye surgery. We then summarize research applications, encompassing cell and tissue studies, research on C. elegans, and studies in zebrafish. We conclude by discussing future trends of femtosecond laser systems and some possible application directions.

  16. Neon photoionized plasma experiment at Z

    NASA Astrophysics Data System (ADS)

    Mayes, D. C.; Mancini, R. C.; Bailey, J. E.; Loisel, G. P.; Rochau, G. A.

    2016-10-01

    We discuss an experimental effort to study the atomic kinetics in neon photoionized plasmas via K-shell line absorption spectroscopy. The experiment employs the intense x-ray flux emitted at the collapse of a Z-pinch to heat and backlight a photoionized plasma contained within a cm-scale gas cell placed at various distances from the Z-pinch and filled with neon gas pressures in the range from 3.5 to 30 torr. The experimental platform affords an order of magnitude range in the ionization parameter characterizing the photoionized plasma from about 3 to 80 erg*cm/s. An x-ray crystal spectrometer capable of collecting both time-integrated and time-gated spectra is used to collect absorption spectra. A suite of IDL programs has been developed to process the experimental data to produce transmission spectra. The spectra show line absorption by several ionization stages of neon, including Be-, Li-, He-, and H-like ions. Analysis of these spectra yields ion areal-densities and charge state distributions, which can be compared with results from atomic kinetics codes. In addition, the electron temperature is extracted from level population ratios of nearby energy levels in Li- and Be-like ions, which can be used to test heating models of photoionized plasmas. This work was sponsored in part by the DOE National Nuclear Security Administration Grant DE-FG52-09NA29551, DOE Office of Science Grant DE-SC0014451, and the Z Facility Fundamental Science Program of SNL.

  17. Femtosecond laser materials processing

    NASA Astrophysics Data System (ADS)

    Banks, Paul S.; Stuart, Brent C.; Komashko, Aleksey M.; Feit, Michael D.; Rubenchik, Alexander M.; Perry, Michael D.

    2000-05-01

    The use of femtosecond lasers allows materials processing of practically any material with extremely high precision and minimal collateral damage. Advantages over conventional laser machining (using pulses longer than a few tens of picoseconds) are realized by depositing the laser energy into the electrons of the material on a time scale short compared to the transfer time of this energy to the bulk of the material, resulting in increased ablation efficiency and negligible shock or thermal stress. The improvement in the morphology by using femtosecond pulses rather than nanosecond pulses has been studied in numerous materials from biological materials to dielectrics to metals. During the drilling process, we have observed the onset of small channels which drill faster than the surrounding material.

  18. Femtosecond Laser Materials Processing

    SciTech Connect

    Banks, P.S.; Stuart, B.C.; Komashko, A.M.; Feit, M.D.; Rubenchik, A.M.; Perry, M.D.

    2000-03-06

    The use of femtosecond lasers allows materials processing of practically any material with extremely high precision and minimal collateral damage. Advantages over conventional laser machining (using pulses longer than a few tens of picoseconds) are realized by depositing the laser energy into the electrons of the material on a time scale short compared to the transfer time of this energy to the bulk of the material, resulting in increased ablation efficiency and negligible shock or thermal stress. The improvement in the morphology by using femtosecond pulses rather than nanosecond pulses has been studied in numerous materials from biologic materials to dielectrics to metals. During the drilling process, we have observed the onset of small channels which drill faster than the surrounding material.

  19. Excitation delocalization in the bacteriochlorophyll c antenna of the green bacterium Chloroflexus aurantiacus as revealed by ultrafast pump-probe spectroscopy.

    PubMed

    Savikhin, S; Buck, D R; Struve, W S; Blankenship, R E; Taisova, A S; Novoderezhkin, V I; Fetisova, Z G

    1998-07-03

    Room temperature absorption difference spectra were measured on the femtosecond through picosecond time scales for chlorosomes isolated from the green bacterium Chloroflexus aurantiacus. Anomalously high values of photoinduced absorption changes were revealed in the BChl c Qy transition band. Photoinduced absorption changes at the bleaching peak in the BChl c band were found to be 7-8 times greater than those at the bleaching peak in the BChl a band of the chlorosome. This appears to be the first direct experimental proof of excitation delocalization over many BChl c antenna molecules in the chlorosome.

  20. Photoionization of atoms and molecules. [of hydrogen, helium, and xenon

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.

    1976-01-01

    A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.

  1. Femtosecond laser materials processing

    SciTech Connect

    Stuart, B. C., LLNL

    1998-06-02

    Femtosecond lasers enable materials processing of most any material with extremely high precision and negligible shock or thermal loading to the surrounding area Applications ranging from drilling teeth to cutting explosives to making high-aspect ratio cuts in metals with no heat-affected zone are made possible by this technology For material removal at reasonable rates, we developed a fully computer-controlled 15-Watt average power, 100-fs laser machining system.

  2. Femtosecond laser materials processing

    SciTech Connect

    Stuart, B

    1998-08-05

    Femtosecond lasers enable materials processing of most any material with extremely high precision and negligible shock or thermal loading to the surrounding area. Applications ranging from drilling teeth to cutting explosives to precision cuts in composites are possible by using this technology. For material removal at reasonable rates, we have developed a fully computer-controlled 15-Watt average power, 100-fs laser machining system.

  3. Time-resolved study of femtosecond laser induced micro-modifications inside transparent brittle materials

    NASA Astrophysics Data System (ADS)

    Hendricks, F.; Matylitsky, V. V.; Domke, M.; Huber, Heinz P.

    2016-03-01

    Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones or tablets, cover glass needs to be cut precisely in various shapes. The unique advantage of material processing with femtosecond lasers is efficient, fast and localized energy deposition in nearly all types of solid materials. When an ultra-short laser pulse is focused inside glass, only the localized region in the neighborhood of the focal volume absorbs laser energy by nonlinear optical absorption. Therefore, the processing volume is strongly defined, while the rest of the target stays unaffected. Thus ultra-short pulse lasers allow cutting of the chemically strengthened glasses such as Corning Gorilla glass without cracking. Non-ablative cutting of transparent, brittle materials, using the newly developed femtosecond process ClearShapeTM from Spectra-Physics, is based on producing a micron-sized material modification track with well-defined geometry inside. The key point for development of the process is to understand the induced modification by a single femtosecond laser shot. In this paper, pump-probe microscopy techniques have been applied to study the defect formation inside of transparent materials, namely soda-lime glass samples, on a time scale between one nanosecond to several tens of microseconds. The observed effects include acoustic wave propagation as well as mechanical stress formation in the bulk of the glass. Besides better understanding of underlying physical mechanisms, our experimental observations have enabled us to find optimal process parameters for the glass cutting application and lead to better quality and speed for the ClearShapeTM process.

  4. Characterization of femtosecond electron bunches from a laser-wakefield accelerator using THz radiation

    NASA Astrophysics Data System (ADS)

    van Tilborg, Jeroen

    2005-10-01

    We report on the temporal characterization of laser-plasma-produced electron bunches, indicating ultra-short sub-50 fs charge structure. In the LOASIS laboratory at LBNL, the electron bunches are produced through the interaction of an intense (>10^19 Wcm-2) laser pulse with an underdense (˜10^19 cm-3) Helium plasma. The femtosecond multi-nanoCoulomb bunches have relativistic energies, with a 100% energy spread. As the bunch exits the plasma-vacuum interface, coherent transition radiation is emitted. Since the electron bunch is still dense and compact at the emission interface, the coherent spectrum of the intense radiation pulse covers the THz regime. Spectral and temporal measurements on the THz pulse are performed and correlated to the temporal properties of the electron bunch. Detection techniques such as Michelson interferometry, semiconductor switching, and electro-optic sampling are applied. The latter technique, where the THz electric field versus time is mapped out, provides detailed temporal structure of the radiation pulse, and by inference the electron bunch. The measurements indicate that THz radiation is emitted by a skewed bunch with a sub-50 fs rise time and a ˜600 fs tail (half-width-at-half-maximum), which is consistent with ballistic debunching of 100%-energy-spread beams during propagation. The electro-optic time resolution of the method was limited by the crystal properties. The Michelson interferometry and semiconductor switching experiments confirmed the femtosecond nature of the electron bunches. The electro-optic measurement also demonstrates shot-to-shot stability of the laser-wakefield accelerator (LWFA) as well as femtosecond synchronization between the electron bunch and the probe beam. This highlights the applicability of the LWFA in pump-probe experiments, where synchronized emission of x-rays, gamma rays, THz waves, NIR beams, and electron bunches is available. This work is supported by DoE under contract DE-AC02-05CH11231.

  5. Femtosecond Optical Tweezers

    NASA Astrophysics Data System (ADS)

    Peng, Jiahui; Wang, Lei; Sokolov, Alexei

    2004-10-01

    Optical tweezers has drawn much attention of people since recent years, which shows great advantages on biological applications due to quite straightforward ideas and simple configurations. Optical tweezers rely upon the extremely high gradient in the electric field produced near the beam waist of a tightly focused laser beam, which creates a force sufficient to trap micron-sized dielectric particles in three dimensions.(J.E. Molloy and M.J. Padgett, Light, Action: Optical Tweezers, Contemporary P)hysics, 43 241 (2002). We applied a femtosecond laser on optical tweezers as light source and got successfully ``optical trapping'' and ``optical tweezers.'' Further, due to the characters of short pulse width and extremely high intensity of laser, femtosecond optical tweezers may direct us to new optics field. Under such strong intensity many non-linear optical phenomena could be observable, such like optical Kerr effect, stimulated Raman effect and so on. Our work will shows that it may be applied into the recently proposed FAST CAR (Femtosecond Adaptive Spectroscopic Techniques for Coherent Anti-Stokes Raman Spectroscopy) by M. Scully et. al.(M. O. Scully, G. W. Kattawar, R. P. Lucht, T. Opatrny, H. Pilloff, A. Rebane, A. V. Sokolov, and M. S. Zubairy, ``FAST CARS: Engineering a Laser Spectroscopic Technique for Rapid Identification of Bacterial Spores,'' Proceedings of NASE (2002).)

  6. Femtosecond probing around the K-edge of a laser heated plasma using X-rays from betatron oscillations in a laser wakefield accelerator

    NASA Astrophysics Data System (ADS)

    Behm, Keegan; Zhao, Tony; Maksimchuk, Anatoly; Yanovsky, Victor; Nees, John; Mangles, Stuart; Krushelnick, Karl; Thomas, Alexander; CenterUltrafast Optical Science Team; Plasmas Group Team

    2015-11-01

    Presented here are data from a two-beam pump-probe experiment. We used synchrotron-like X-rays created by betatron oscillations to probe a thin metal foil that is pumped by the secondary laser beam. The Hercules Ti:Sapph laser facility was operated with a pulse duration of 34 fs and a power of 65 TW split to drive a laser wakefield accelerator and heat the secondary target. We observed opacity changes around the K-edge of thin foils as they were heated by an ultrafast pump laser. To understand how the opacity is changing with heating and expansion of the plasma, the delay between the two laser paths was adjusted on a fs and ps time scale. Experimental data for polyvinylidene chloride (PVDC) and aluminum show variations in opacity around the Cl and Al K-edges with changes in the probe delay. The transmitted synchrotron-like spectrum was measured using single photon counting on an X-ray CCD camera and was available on a shot-by-shot basis. The success of this work demonstrates a practical application for X-rays produced from betatron oscillations in a wakefield accelerator. The compact size of these ``table-top'' accelerators and the ultrashort nature of the generated X-ray pulses allows pump-probe experiments that can probe events that occur on the femtosecond time scale.

  7. Analysis of Femtosecond Timing Noise and Stability in Microwave Components

    SciTech Connect

    Whalen, Michael R.; /Stevens Tech. /SLAC

    2011-06-22

    To probe chemical dynamics, X-ray pump-probe experiments trigger a change in a sample with an optical laser pulse, followed by an X-ray probe. At the Linac Coherent Light Source, LCLS, timing differences between the optical pulse and x-ray probe have been observed with an accuracy as low as 50 femtoseconds. This sets a lower bound on the number of frames one can arrange over a time scale to recreate a 'movie' of the chemical reaction. The timing system is based on phase measurements from signals corresponding to the two laser pulses; these measurements are done by using a double-balanced mixer for detection. To increase the accuracy of the system, this paper studies parameters affecting phase detection systems based on mixers, such as signal input power, noise levels, temperature drift, and the effect these parameters have on components such as the mixers, splitters, amplifiers, and phase shifters. Noise data taken with a spectrum analyzer show that splitters based on ferrite cores perform with less noise than strip-line splitters. The data also shows that noise in specific mixers does not correspond with the changes in sensitivity per input power level. Temperature drift is seen to exist on a scale between 1 and 27 fs/{sup o}C for all of the components tested. Results show that any components using more metallic conductor tend to exhibit more noise as well as more temperature drift. The scale of these effects is large enough that specific care should be given when choosing components and designing the housing of high precision microwave mixing systems for use in detection systems such as the LCLS. With these improvements, the timing accuracy can be improved to lower than currently possible.

  8. Development of a hard X-ray delay line for X-ray photon correlation spectroscopy and jitter-free pump-probe experiments at X-ray free-electron laser sources.

    PubMed

    Roseker, Wojciech; Franz, Hermann; Schulte-Schrepping, Horst; Ehnes, Anita; Leupold, Olaf; Zontone, Federico; Lee, Sooheyong; Robert, Aymeric; Grübel, Gerhard

    2011-05-01

    A hard X-ray delay line capable of splitting and delaying single X-ray pulses has been developed with the aim of performing X-ray photon correlation spectroscopy (XPCS) and X-ray pump-probe experiments at hard X-ray free-electron laser sources. The performance of the device was tested with 8.39 keV synchrotron radiation. Time delays up to 2.95 ns have been demonstrated. The feasibility of the device for performing XPCS studies was tested by recording static speckle patterns. The achieved speckle contrast of 56% indicates the possibility of performing ultra-fast XPCS studies with the delay line.

  9. Advances in femtosecond laser technology

    PubMed Central

    Callou, Thais Pinheiro; Garcia, Renato; Mukai, Adriana; Giacomin, Natalia T; de Souza, Rodrigo Guimarães; Bechara, Samir J

    2016-01-01

    Femtosecond laser technology has become widely adopted by ophthalmic surgeons. The purpose of this study is to discuss applications and advantages of femtosecond lasers over traditional manual techniques, and related unique complications in cataract surgery and corneal refractive surgical procedures, including: LASIK flap creation, intracorneal ring segment implantation, presbyopic treatments, keratoplasty, astigmatic keratotomy, and intrastromal lenticule procedures. PMID:27143847

  10. 2008 Photoions, Photoionization & Photodetachment Gordon Research Conference January 27-February 1, 2008

    SciTech Connect

    Klaus Muller-Dethefs Nancy Ryan GRay

    2009-03-31

    This conference brings together scientists interested in a range of basic phenomena linked to the ejection and scattering of electrons from atoms, molecules, clusters, liquids and solids by absorption of light. Photoionization, a highly sensitive probe of both structure and dynamics, can range from perturbative single-photon processes to strong-field highly non-perturbative interactions. It is responsible for the formation and destruction of molecules in astrophysical and plasma environments and successfully used in advanced analytical techniques. Positive ions, which can be produced and studied most effectively using photoionization, are the major components of all plasmas, vital constituents of flames and important intermediates in many chemical reactions. Negative ions are significant as transient species and, when photodetached, the corresponding neutral species often undergoes remarkable, otherwise non-observable, dynamics. The scope of the meeting spans from novel observations in atomic and molecular physics, such as Coulomb Crystals, highly excited states and cold Rydberg plasmas, to novel energy resolved or ultrafast time-resolved experiments, photoionization in strong laser fields, theoretical method development for electron scattering, photoionization and photodetachment and more complex phenomena such as charge transfer and DNA and protein conductivity, important for biological and analytical applications.

  11. Temperature and magnetic field dependence of rare -earth ↔iron exchange resonance mode in a magnetic oxide studied with femtosecond magneto-optical Kerr effect

    NASA Astrophysics Data System (ADS)

    Deb, Marwan; Molho, Pierre; Barbara, Bernard; Bigot, Jean-Yves

    2016-08-01

    In magnetic materials, the exchange is the strongest quantum interaction due to the Pauli exclusion principle. For that reason it can induce high-frequency modes fexch of the magnetization precession. In this work we investigate these modes over a wide range of temperatures (50 -300 K ) and magnetic fields up to 10 T in a bismuth-doped garnet with perpendicular magnetic anisotropy by performing femtosecond magneto-optical pump-probe experiments. Near the compensation temperature TM the divergence of 1 /fexch(T ) allows identifying unambiguously fexch with the rare-earth ↔ iron exchange mode. In addition, at low temperature fexch is independent of the field as usually observed. In contrast, we find that near TM,fexch decreases linearly with an increasing magnetic field. This behavior is explained in the context of the ferromagnetic resonance theory by including the perturbation term linear in the external applied field Hext.

  12. Complete characterization of double photoionization processes

    NASA Astrophysics Data System (ADS)

    Ivanov, I. A.; Kheifets, A. S.

    2011-06-01

    We analyze correlated photoelectron spectra of single-photon two-electron ionization [double photoionization (DPI)] of helium to reconstruct the phase of the spectral amplitude of this process. The phase can be reconstructed reliably in a wide range of photoelectron momenta, thus allowing one to retrieve information about the wave function of the DPI process and its temporal evolution. Our simulation indicates that the proposed phase reconstruction technique can be applied in experiment to trace dynamics of the DPI process with attosecond precision.

  13. Spin effects in double photoionization of lithium

    NASA Astrophysics Data System (ADS)

    Kheifets, A. S.; Fursa, D. V.; Hines, C. W.; Bray, I.; Colgan, J.; Pindzola, M. S.

    2010-02-01

    We apply the nonperturbative convergent close-coupling (CCC) and time-dependent close coupling (TDCC) formalisms to calculate fully differential energy and angular resolved cross sections of double photoionization (DPI) of lithium. The equal energy sharing case is considered in which dynamics of the DPI process can be adequately described by two symmetrized singlet and triplet amplitudes. The angular width of these amplitudes serves as a measure of the strength of the angular correlation between the two ejected electrons. This width is interpreted in terms of the spin of the photoelectron pair.

  14. Spin effects in double photoionization of lithium

    SciTech Connect

    Kheifets, A. S.; Fursa, D. V.; Hines, C. W.; Bray, I.; Colgan, J.; Pindzola, M. S.

    2010-02-15

    We apply the nonperturbative convergent close-coupling (CCC) and time-dependent close coupling (TDCC) formalisms to calculate fully differential energy and angular resolved cross sections of double photoionization (DPI) of lithium. The equal energy sharing case is considered in which dynamics of the DPI process can be adequately described by two symmetrized singlet and triplet amplitudes. The angular width of these amplitudes serves as a measure of the strength of the angular correlation between the two ejected electrons. This width is interpreted in terms of the spin of the photoelectron pair.

  15. Complete characterization of double photoionization processes

    SciTech Connect

    Ivanov, I. A.; Kheifets, A. S.

    2011-06-15

    We analyze correlated photoelectron spectra of single-photon two-electron ionization [double photoionization (DPI)] of helium to reconstruct the phase of the spectral amplitude of this process. The phase can be reconstructed reliably in a wide range of photoelectron momenta, thus allowing one to retrieve information about the wave function of the DPI process and its temporal evolution. Our simulation indicates that the proposed phase reconstruction technique can be applied in experiment to trace dynamics of the DPI process with attosecond precision.

  16. Double Photoionization of Aligned Molecular Hydrogen

    SciTech Connect

    Vanroose, Wim; Horner, Daniel A.; Martin, Fernando; Rescigno,Thomas N.; McCurdy, C. William

    2006-07-21

    We present converged, completely ab initio calculations ofthe triple differential cross sections for double photoionization ofaligned H2 molecules for a photon energy of 75.0 eV. The method ofexterior complex scaling, implemented with both the discrete variablerepresentation and B-splines, is used to solve the Schroedinger equationfor a correlated continuum wave function corresponding to a single photonhaving been absorbed by a correlated initial state. Results for a fixedinternuclear distance are compared with recent experiments and show thatintegration over experimental angular and energy resolutions is necessaryto produce good qualitative agreement, but does not eliminate somediscrepancies. Limitations of current experimental resolution are shownto sometimes obscure interesting details of the crosssection.

  17. K-shell photoionization cross-sections.

    NASA Technical Reports Server (NTRS)

    Daltabuit, E.; Cox, D. P.

    1972-01-01

    Approximate values for the threshold energies, threshold cross sections, and energy dependence of the cross sections for K-shell photoionization are tabulated for H, He, C, N, O, Ne, Mg, Si, and S in all stages of ionization. The approximation of these data is based on the assumptions that the threshold energy is a simple function of the nuclear charge and the number of electrons present in the atom, and that the threshold values and energy dependence of the cross sections are determined only by the threshold energy.

  18. Photoionization of zinc by TDLDA calculations

    NASA Astrophysics Data System (ADS)

    Stener, M.; Decleva, P.

    1997-10-01

    Absolute photoionization cross section profiles of Zn have been calculated at TDLDA and LDA level, employing a very accurate B-spline basis set and the modified Sternheimer approach. The van Leeuwen - Baerends exchange correlation potential has been used, since its correct asymptotic behaviour is able to support virtual states and describe core-excited resonances. A comparison with available theoretical and experimental data has been performed when possible. The present method has been proven to be robust to analyse wide photon energy regions (from threshold up to 200 eV) and discuss the various shapes of one-electron resonances.

  19. Atomic photoionization experiment by harmonic-generation spectroscopy

    NASA Astrophysics Data System (ADS)

    Frolov, M. V.; Sarantseva, T. S.; Manakov, N. L.; Fulfer, K. D.; Wilson, B. P.; Troß, J.; Ren, X.; Poliakoff, E. D.; Silaev, A. A.; Vvedenskii, N. V.; Starace, Anthony F.; Trallero-Herrero, C. A.

    2016-03-01

    Measurements of the high-order-harmonic generation yield of the argon (Ar) atom driven by a strong elliptically polarized laser field are shown to completely determine the field-free differential photoionization cross section of Ar, i.e., the energy dependence of both the angle-integrated photoionization cross section and the angular distribution asymmetry parameter.

  20. Calculated photoionization cross sections using Quantemol-N

    NASA Astrophysics Data System (ADS)

    Brigg, Will J.; Harvey, Alex G.; Dzarasova, Anna; Mohr, Sebastian; Brambila, Danilo S.; Morales, Felipe; Smirnova, Olga; Tennyson, Jonathan

    2015-06-01

    Quantemol-N is an expert system designed to run the widely used UK Molecular R-matrix code (UKRMol). Originally designed to consider electron-molecule collision problems, here we present an extension to treat molecular photoionization. Sample results are given for the photoionization of molecular nitrogen and methane. Comparisons are made with experimental results showing good agreement.

  1. Core-level transient absorption spectroscopy as a probe of electron hole relaxation in photoionized H+(H2O)n.

    PubMed

    Li, Zheng; El-Amine Madjet, Mohamed; Vendrell, Oriol; Santra, Robin

    2014-01-01

    There is fundamental interest in understanding the coupled nuclear and electronic dynamics associated with charge transfer processes in complex molecules and materials, which are often mediated by electron, electron hole or proton motion. With dramatic improvements in the techniques to generate extreme ultraviolet (XUV) and X-ray femtosecond pulses, it now becomes possible to trigger and probe these kinds of processes in real time. Here we study the dynamics of an electron hole created by photoionization in the valence shell of protonated water clusters H(+)(H(2)O)(n). We demonstrate that the electron hole is strongly correlated with the protons forming the hydrogen bond network. We show that it is possible to probe key aspects of the valence electron hole dynamics and the coupled nuclear motion with femtosecond time resolution by resonantly exciting K-shell 1s electrons to fill the electron hole. This represents an opportunity for X-ray transient absorption spectroscopy.

  2. Determining the partial photoionization cross-sections of ethyl radicals.

    PubMed

    FitzPatrick, B L; Maienschein-Cline, M; Butler, L J; Lee, S-H; Lin, J J

    2007-12-13

    Using a crossed laser-molecular beam scattering apparatus, these experiments photodissociate ethyl chloride at 193 nm and detect the Cl and ethyl products, resolved by their center-of-mass recoil velocities, with vacuum ultraviolet photoionization. The data determine the relative partial cross-sections for the photoionization of ethyl radicals to form C2H5+, C2H4+, and C2H3+ at 12.1 and 13.8 eV. The data also determine the internal energy distribution of the ethyl radical prior to photoionization, so we can assess the internal energy dependence of the photoionization cross-sections. The results show that the C2H4++H and C2H3++H2 dissociative photoionization cross-sections strongly depend on the photoionization energy. Calibrating the ethyl radical partial photoionization cross-sections relative to the bandwidth-averaged photoionization cross-section of Cl atoms near 13.8 eV allows us to use these data in conjunction with literature estimates of the Cl atom photoionization cross-sections to put the present bandwidth-averaged cross-sections on an absolute scale. The resulting bandwidth-averaged cross-section for the photoionization of ethyl radicals to C2H5+ near 13.8 eV is 8+/-2 Mb. Comparison of our 12.1 eV data with high-resolution ethyl radical photoionization spectra allows us to roughly put the high-resolution spectrum on the same absolute scale. Thus, one obtains the photoionization cross-section of ethyl radicals to C2H5+ from threshold to 12.1 eV. The data show that the onset of the C2H4++H dissociative photoionization channel is above 12.1 eV; this result offers a simple way to determine whether the signal observed in photoionization experiments on complex mixtures is due to ethyl radicals. We discuss an application of the results for resolving the product branching in the O+allyl bimolecular reaction.

  3. Studies of x-ray emission properties of photoionized plasmas

    NASA Astrophysics Data System (ADS)

    Wang, Feilu; Han, Bo; Jin, Rui; Salzmann, David; Liang, Guiyun; Wei, Huigang; Zhong, Jiayong; Zhao, Gang; Li, Jia-ming

    2016-03-01

    In this paper three aspects of photoionized plasmas are discussed in both laboratory and astrophysical contexts. First, the importance of accurate atomic/ionic data for the analysis of photoionized plasmas is shown. Second, an overview of present computer codes for the analysis of photoionized plasmas is given. We introduce our computer model, radiative-collisional code based on the flexible atomic code (RCF), for calculations of the properties of such plasmas. RCF uses database generated by the flexible atomic code. Using RCF it is shown that incorporating the satellite lines from doubly excited Li-like ions into the He{}α triplet lines is necessary for reliable analysis of observational spectra from astrophysical objects. Finally, we introduce a proposal to generate photoionized plasmas by x-ray free electron laser, which may facilitate the simulation in lab of astrophysical plasmas in photoionization equilibrium.

  4. Double photoionization of helium with synchrotron x-rays: Proceedings

    SciTech Connect

    Not Available

    1994-01-01

    This report contains papers on the following topics: Overview and comparison of photoionization with charged particle impact; The ratio of double to single ionization of helium: the relationship of photon and bare charged particle impact ionization; Double photoionization of helium at high energies; Compton scattering of photons from electrons bound in light elements; Electron ionization and the Compton effect in double ionization of helium; Elimination of two atomic electrons by a single energy photon; Double photoionization of helium at intermediate energies; Double Photoionization: Gauge Dependence, Coulomb Explosion; Single and Double Ionization by high energy photon impact; The effect of Compton Scattering on the double to single ionization ratio in helium; and Double ionization of He by photoionization and Compton scattering. These papers have been cataloged separately for the database.

  5. Spectral dependence of photoemission in multiphoton ionization of NO2 by femtosecond pulses in the 375-430 nm range.

    PubMed

    Poullain, S Marggi; Cireasa, R; Cornaggia, C; Simon, M; Marin, T; Guillemin, R; Houver, J C; Lucchese, R R; Dowek, D

    2017-08-23

    We investigate the multiphoton ionization of NO2 using tunable (430-375 nm) femtosecond pulses and photoelectron-photoion coincidence momentum spectroscopy. In order to understand the complex electronic and nuclear photodynamics at play following absorption of three to five photons, we also report extended photoionization calculations using correlated targets and coupled channels. Exploring the multiphoton dissociative ionization (MPDI) and multiphoton ionization (MPI) processes over such a broad energy range enables us to lend further support to our work carried out around 400 nm of a femtosecond laser [S. Marggi Poullain et al., J. Phys. B: At., Mol. Opt. Phys., 2014, 47, 124024]. Two excitation energy regions are identified and discussed in terms of the proposed reaction pathways, highlighting the significant role of Rydberg states, such as the [R*(6a1)(-1), 3pσ] Rydberg state, in the NO2 multiphoton excitation and photoionization. These new results support our previous assumption that different bent and linear geometries of the NO2(+)(X(1)Σg) ionic state contribute to the MPDI and MPI, consistent with the reported calculations which reveal an important vibronic coupling characterizing the photoemission. Remarkably, the strong anisotropy of the recoil frame photoelectron angular distribution (RFPAD) previously observed at 400 nm appears as a fingerprint across the whole explored photon energy range.

  6. Spin-resolved photoelectron spectroscopy using femtosecond extreme ultraviolet light pulses from high-order harmonic generation

    NASA Astrophysics Data System (ADS)

    Plötzing, M.; Adam, R.; Weier, C.; Plucinski, L.; Eich, S.; Emmerich, S.; Rollinger, M.; Aeschlimann, M.; Mathias, S.; Schneider, C. M.

    2016-04-01

    The fundamental mechanism responsible for optically induced magnetization dynamics in ferromagnetic thin films has been under intense debate since almost two decades. Currently, numerous competing theoretical models are in strong need for a decisive experimental confirmation such as monitoring the triggered changes in the spin-dependent band structure on ultrashort time scales. Our approach explores the possibility of observing femtosecond band structure dynamics by giving access to extended parts of the Brillouin zone in a simultaneously time-, energy- and spin-resolved photoemission experiment. For this purpose, our setup uses a state-of-the-art, highly efficient spin detector and ultrashort, extreme ultraviolet light pulses created by laser-based high-order harmonic generation. In this paper, we present the setup and first spin-resolved spectra obtained with our experiment within an acquisition time short enough to allow pump-probe studies. Further, we characterize the influence of the excitation with femtosecond extreme ultraviolet pulses by comparing the results with data acquired using a continuous wave light source with similar photon energy. In addition, changes in the spectra induced by vacuum space-charge effects due to both the extreme ultraviolet probe- and near-infrared pump-pulses are studied by analyzing the resulting spectral distortions. The combination of energy resolution and electron count rate achieved in our setup confirms its suitability for spin-resolved studies of the band structure on ultrashort time scales.

  7. Spin-resolved photoelectron spectroscopy using femtosecond extreme ultraviolet light pulses from high-order harmonic generation

    SciTech Connect

    Plötzing, M.; Adam, R. Weier, C.; Plucinski, L.; Schneider, C. M.; Eich, S.; Emmerich, S.; Rollinger, M.; Aeschlimann, M.; Mathias, S.

    2016-04-15

    The fundamental mechanism responsible for optically induced magnetization dynamics in ferromagnetic thin films has been under intense debate since almost two decades. Currently, numerous competing theoretical models are in strong need for a decisive experimental confirmation such as monitoring the triggered changes in the spin-dependent band structure on ultrashort time scales. Our approach explores the possibility of observing femtosecond band structure dynamics by giving access to extended parts of the Brillouin zone in a simultaneously time-, energy- and spin-resolved photoemission experiment. For this purpose, our setup uses a state-of-the-art, highly efficient spin detector and ultrashort, extreme ultraviolet light pulses created by laser-based high-order harmonic generation. In this paper, we present the setup and first spin-resolved spectra obtained with our experiment within an acquisition time short enough to allow pump-probe studies. Further, we characterize the influence of the excitation with femtosecond extreme ultraviolet pulses by comparing the results with data acquired using a continuous wave light source with similar photon energy. In addition, changes in the spectra induced by vacuum space-charge effects due to both the extreme ultraviolet probe- and near-infrared pump-pulses are studied by analyzing the resulting spectral distortions. The combination of energy resolution and electron count rate achieved in our setup confirms its suitability for spin-resolved studies of the band structure on ultrashort time scales.

  8. State-Resolved and State-To Photodissociation Study of CO_2 by Two-Color Vuv-Vuv Laser Pump-Probe Method

    NASA Astrophysics Data System (ADS)

    Lu, Zhou; Chang, Yih-Chung; Jackson, William M.; Ng, Cheuk-Yiu

    2014-06-01

    CO_2 is known as a strong contributor to the greenhouse effect, and its concentration in the atmosphere increases annually. Photodissociation of CO_2 is considered an important photochemical sink of CO_2 molecules which could ultimately limit the increase of CO_2 concentration in the atmosphere. Since CO_2 molecules have negligibly small absorption from the visible region down to about 200 nm, photodissociation studies of CO_2 in the vacuum ultraviolet (VUV) region below 200 nm are of great importance in understanding the photochemical decomposition processes of CO_2 molecules. State-to-state photodissociation of CO_2 has been investigated by employing two independent VUV lasers and the time-slice velocity-map-imaging-photoion (VMI-PI) method. The spin-allowed photoproduct channels, CO(X1Σ+) + O(1D), CO(X1Σ+) + O(1S), CO(a3Π) + O(3PJ), and C(3PJ) + O2(X3Σg-), and the spin-forbidden photoproduct channel, CO(X1Σ+) + O(3PJ), were directly observed from the time-slice VMI-PI images. The angular anisotropic parameters were evaluated, allowing us to estimate the lifetimes for the formations of these dissociation channels. To the authors' knowledge, the current CO_2 photodissociation studies show for the first time that all of the energetically available photodissociation channels are formed in the CO_2 photoexcitation energy of interest.

  9. Gas-Phase Photoionization Of A Protein

    NASA Astrophysics Data System (ADS)

    Milosavljevic, A. R.; Giuliani, A.; Nicolas, C.; Gil, J.-F.; Lemaire, J.; Refregiers, M.; Nahon, L.

    2010-07-01

    We present preliminary results on gas phase photoionization of electrosprayproduced multiply protonated cytochrome c protein (104 amino acids; ˜12.4 kDa), which has been achieved with a newly developed experimental system for spectroscopy of electrosprayed ions in a linear quadrupole ion trap using a monochromatized vacuum ultraviolet (VUV) synchrotron radiation and tandem mass spectrometry method. The investigation of proteins in the gas phase, where they are free of the influence of counterions and solvent molecules, offer a possibility to understand their intrinsic molecular properties. However, due to limited both ion densities and available number of photons, the use of synchrotron radiation for the trapped ions spectroscopy is a rather challenging task. The feasibility of coupling a Fourier transform ion cyclotron resonance ion trap with soft x-ray synchrotron beamline and the first successful use of synchrotron radiation for spectroscopy of electrosprayed negative ions stored in a three-dimensional quadrupole ion trap have been demonstrated only recently (R. Thissen et al., 2008, Phys. Rev. Lett., 100, 223001; A. Giulliani et al., Proc. 57th ASMS Conf., Philadelphia, 2009). The present results are the first reported on photoionization of kDa species in the gas phase and are valuable regarding both a fundamental interest of accessing physical properties of large biological ions isolated in vacuo and potential development of a new technique for proteomics.

  10. Photoionization of aligned molecular excited states

    NASA Astrophysics Data System (ADS)

    Appling, J. R.; White, M. G.; Kessler, W. J.; Fernandez, R.; Poliakoff, E. D.

    1988-02-01

    Photoelectron angular distributions of several excited states of NO have been measured in an effort to better elucidate the role of alignment in resonant multiphoton excitation processes of molecules. In contrast to previous molecular REMPI measurements on NO, (2+1) angular distributions taken for low rotational levels of the E 2Σ+ (4sσ) Rydberg state of NO exhibit complex angular behavior which is characteristic of strong spatial alignment of the optically prepared levels. Photoelectron angular distributions were also found to be strongly branch and J dependent with the lowest rotational levels of the R21+S11 branch exhibiting the full anisotropy expected for an overall three-photon process. Fluorescence anisotropies extracted from complementary two-photon fluorescence angular distribution measurements reveal small, but nonzero alignment in all rotational levels with J>1/2, in contrast to the photoelectron results. Additional photoelectron angular distributions taken for (1+1) REMPI via the A 2Σ+ (3sσ), v=0 state exhibit near ``cos2θ'' distributions characteristic of photoionization of unaligned target states. The observed photoelectron data are qualitatively interpreted on the basis of the angular momentum constraints of the excitation-induced alignment and photoionization dynamics which determine the observable moments in the angular distribution.

  11. Double photoionization of doubly-excited lithium

    NASA Astrophysics Data System (ADS)

    Armstrong, G.; Pindzola, M. S.; Kheifets, A.; Schuricke, M.; Veeravalli, G.; Dornes, Ch.; Zhu, G.; Joachimsmeyer, K.; Treusch, R.; Dorn, A.; Colgan, J.

    2012-06-01

    We present triple differential cross sections and recoil ion momentum distributions for double photoionization of the 1s2s2p state of lithium. Double ionization of lithium may be treated as a two-active-electron process, where the ``active'' 2s and 2p electrons move in the field of the ``frozen-core'' Li^2+ 1s state.The time-dependent close-coupling (TDCC) method is used to solve the two-electron time-dependent Schr"odinger equation in full dimensionality. This work is motivated by recent FLASH experiments, which have obtained recoil-ion momentum distributions at a photon energy of 59 eV, where the 1s2s2p state is first reached via a 1s-2p photoexcitation from the initial ground state, and may then be doubly-ionized after the absorption of a second photon. The TDCC calculations in this work treat the subsequent photoionization of this doubly-excited state. The results are compared to those obtained by the convergent close-coupling method and to measurement, and provide a first comparison between theory and experiment in this fundamental few-photon few-body problem.

  12. Mode specific photoionization dynamics in polyatomic molecules

    NASA Astrophysics Data System (ADS)

    Rathbone, Gerald Jeffery

    2002-11-01

    The work presented in this dissertation presents new work on polyatomic photoionization. In these investigations, the broad range behavior of both allowed and forbidden vibrational modes in linear triatomic systems were studied to understand mode specific aspects of photoionization. The current study is made possible by the experimental strategy of exploiting high resolution photoelectron spectroscopy and the high brightness of third generation synchrotron radiation sources. The data is taken typically tens of eV's past the ionization potential. The strategy that I employ is to probe alternative vibrational modes which are frequently affected differently following resonant ionization. Such vibrationally resolved data can be used to understand how the correlation between vibration and electron energy reveals microscopic insights into the photoelectron scattering process. Moreover, the mode specific behavior contains a wealth of information not only regarding allowed transitions, but also contains information on how forbidden transitions gain surprising amounts of intensity. A previously overlooked mechanism for the appearance of forbidden nontotally symmetric vibrations was discovered---resonantly amplified vibronic symmetry breaking. The photoelectron the culprit for the symmetry breaking which induces the excitation of nominally forbidden vibrational excitations. In a more general sense, these results will demonstrate that some fundamental spectroscopic approximations are not always valid, and can lead to surprising consequences.

  13. Femtosecond photoelectron point projection microscope

    SciTech Connect

    Quinonez, Erik; Handali, Jonathan; Barwick, Brett

    2013-10-15

    By utilizing a nanometer ultrafast electron source in a point projection microscope we demonstrate that images of nanoparticles with spatial resolutions of the order of 100 nanometers can be obtained. The duration of the emission process of the photoemitted electrons used to make images is shown to be of the order of 100 fs using an autocorrelation technique. The compact geometry of this photoelectron point projection microscope does not preclude its use as a simple ultrafast electron microscope, and we use simple analytic models to estimate temporal resolutions that can be expected when using it as a pump-probe ultrafast electron microscope. These models show a significant increase in temporal resolution when comparing to ultrafast electron microscopes based on conventional designs. We also model the microscopes spectroscopic abilities to capture ultrafast phenomena such as the photon induced near field effect.

  14. Photoionization research on atomic beams. 2: The photoionization cross section of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Comes, F. J.; Speier, F.; Elzer, A.

    1982-01-01

    An experiment to determine the absolute value of the photo-ionization cross section of atomic oxygen is described. The atoms are produced in an electrical discharge in oxygen gas with 1% hydrogen added. In order to prevent recombination a crossed beam technique is employed. The ions formed are detected by a time-of-flight mass spectrometer. The concentration of oxygen atoms in the beam is 57%. The measured photoionization cross section of atomic oxygen is compared with theoretical data. The results show the participation of autoionization processes in ionization. The cross section at the autoionizing levels detected is considerably higher than the absorption due to the unperturbed continuum. Except for wavelengths where autoionization occurs, the measured ionization cross section is in fair agreement with theory. This holds up to 550 A whereas for shorter wavelengths the theoretical values are much higher.

  15. New resonances from the coherence of Auger and intercoulombic (ICD) processes in the photoionization of endohedral fullerenes

    NASA Astrophysics Data System (ADS)

    Chakraborty, Himadri; Wise, Jacob; de, Ruma; Javani, Mohammad; Manson, Steve; Madjet, Mohamed

    2014-05-01

    Considering the photoionization of Ar@C60 , we predict resonant femtosecond decays of both Ar and C60 vacancies through the continua of atom-fullerene hybrid final states. The resulting resonances emerge from the interference between simultaneous autoionizing and intercoulombic decay (ICD) processes. For Ar 3s --> np excitations, these resonances are far stronger than the Ar-to-C60 resonant ICDs, while for C60 excitations they are strikingly larger than the corresponding Auger features. The results indicate the power of hybridization to enhance decay rates, and modify lifetimes and line profiles. These decays are also likely to exist generally in the ionization of molecules, nano-dimers and -polymers, and fullerene onions that support hybridized electrons as well. A jellium based time-dependent local density approximation (TDLDA), with the Leeuwen and Baerends exchange-correlation functional to produce accurate asymptotic behavior, is employed to calculate the dynamical response of the system to the photon field.

  16. Femtosecond Stimulated Raman Spectroscopy.

    PubMed

    Dietze, Daniel R; Mathies, Richard A

    2016-05-04

    Femtosecond stimulated Raman spectroscopy (FSRS) is an ultrafast nonlinear optical technique that provides vibrational structural information with high temporal (sub-50 fs) precision and high spectral (10 cm(-1) ) resolution. Since the first full demonstration of its capabilities ≈15 years ago, FSRS has evolved into a mature technique, giving deep insights into chemical and biochemical reaction dynamics that would be inaccessible with any other technique. It is now being routinely applied to virtually all possible photochemical reactions and systems spanning from single molecules in solution to thin films, bulk crystals and macromolecular proteins. This review starts with an historic overview and discusses the theoretical and experimental concepts behind this technology. Emphasis is put on the current state-of-the-art experimental realization and several variations of FSRS that have been developed. The unique capabilities of FSRS are illustrated through a comprehensive presentation of experiments to date followed by prospects.

  17. Absorption spectroscopy of a laboratory photoionized plasma experiment at Z

    SciTech Connect

    Hall, I. M.; Durmaz, T.; Mancini, R. C.; Bailey, J. E.; Rochau, G. A.; Golovkin, I. E.; MacFarlane, J. J.

    2014-03-15

    The Z facility at the Sandia National Laboratories is the most energetic terrestrial source of X-rays and provides an opportunity to produce photoionized plasmas in a relatively well characterised radiation environment. We use detailed atomic-kinetic and spectral simulations to analyze the absorption spectra of a photoionized neon plasma driven by the x-ray flux from a z-pinch. The broadband x-ray flux both photoionizes and backlights the plasma. In particular, we focus on extracting the charge state distribution of the plasma and the characteristics of the radiation field driving the plasma in order to estimate the ionisation parameter.

  18. Dynamics of femtosecond laser absorption of fused silica in the ablation regime

    SciTech Connect

    Lebugle, M. Sanner, N.; Varkentina, N.; Sentis, M.; Utéza, O.

    2014-08-14

    We investigate the ultrafast absorption dynamics of fused silica irradiated by a single 500 fs laser pulse in the context of micromachining applications. A 60-fs-resolution pump-probe experiment that measures the reflectivity and transmissivity of the target under excitation is developed to reveal the evolution of plasma absorption. Above the ablation threshold, an overcritical plasma with highly non-equilibrium conditions is evidenced in a thin layer at the surface. The maximum electron density is reached at a delay of 0.5 ps after the peak of the pump pulse, which is a strong indication of the occurrence of electronic avalanche. The results are further analyzed to determine the actual feedback of the evolution of the optical properties of the material on the pump pulse. We introduce an important new quantity, namely, the duration of absorption of the laser by the created plasma, corresponding to the actual timespan of laser absorption by inverse Bremsstrahlung. Our results indicate an increasing contribution of plasma absorption to the total material absorption upon raising the excitation fluence above the ablation threshold. The role of transient optical properties during the energy deposition stage is characterized and our results emphasize the necessity to take it into account for better understanding and control of femtosecond laser-dielectrics interaction.

  19. Goniometer-based femtosecond X-ray diffraction of mutant 30S ribosomal subunit crystals

    DOE PAGES

    Dao, E. Han; Sierra, Raymond G.; Laksmono, Hartawan; ...

    2015-04-30

    In this work, we collected radiation-damage-free data from a set of cryo-cooled crystals for a novel 30S ribosomal subunit mutant using goniometer-based femtosecond crystallography. Crystal quality assessment for these samples was conducted at the X-ray Pump Probe end-station of the Linac Coherent Light Source (LCLS) using recently introduced goniometer-based instrumentation. These 30S subunit crystals were genetically engineered to omit a 26-residue protein, Thx, which is present in the wild-type Thermus thermophilus 30S ribosomal subunit. We are primarily interested in elucidating the contribution of this ribosomal protein to the overall 30S subunit structure. To assess the viability of this study, femtosecondmore » X-ray diffraction patterns from these crystals were recorded at the LCLS during a protein crystal screening beam time. During our data collection, we successfully observed diffraction from these difficult-to-grow 30S ribosomal subunit crystals. Most of our crystals were found to diffract to low resolution, while one crystal diffracted to 3.2 Å resolution. These data suggest the feasibility of pursuing high-resolution data collection as well as the need to improve sample preparation and handling in order to collect a complete radiation-damage-free data set using an X-ray Free Electron Laser.« less

  20. Filamentation and damage in fused silica induced by tightly focused femtosecond laser pulses

    SciTech Connect

    Couairon, A.; Sudrie, L.; Franco, M.; Prade, B.; Mysyrowicz, A.

    2005-03-15

    We investigate experimentally and numerically the damage tracks induced by tightly focused (NA=0.5) infrared femtosecond laser pulses in the bulk of a fused silica sample. Two types of irreversible damage are observed. The first damage corresponds to a permanent change of refractive index without structural modifications (type I). It appears for input pulse energies beyond 0.1 {mu}J. It takes the form of a narrow track extending over more than 100 {mu}m at higher input powers. It is attributed to a change of the polarizability of the medium, following a filamentary propagation which generates an electron-hole plasma through optical field ionization. A second type of damage occurs for input pulse energies beyond 0.3 {mu}J (type II). It takes the form of a pear-shaped structural damage associated with an electron-ion plasma triggered by avalanche. The temporal evolution of plasma absorption is studied by pump-probe experiments. For type I damage, a fast electron-hole recombination is observed. Type II damage is linked with a longer absorption.

  1. C S2 decay dynamics investigated by two-color femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Liu, Hongping; Zhang, Jianyang; Yin, Shuhui; Wang, Li; Lou, Nanquan

    2004-10-01

    The Rydberg-state decay dynamics of carbon disulfide (CS2) has been investigated by (2+1') resonance-enhanced multiphoton ionization with the pump-probe technique (pump wavelength 266nm and probe wavelength 400nm ) on our homebuilt femtosecond laser system. The CS2 is pumped into Rydberg state 6sσg by two 266-nm photons, corresponding to the excitation energy 9.4eV , and then ionized by temporally delayed 400-nm pulse. The CS2 ion yield dependence on the time delay determines the excited-state lifetime to be 409±6fs for C32S32S and 441±7fs for C32S34S , respectively, at 265nm pump and the isotopically averaged lifetime 1034±31fs at 267.5nm pump. The wavelength dependence of the lifetime may be due to the effect of electron spin on the potential energy surface—namely, separately subjected to two different mechanisms: internal conversion and intersystem crossing interaction.

  2. Ultrafast relaxation of fullerenes and fullerites by broadband femtosecond laser spectrometry

    NASA Astrophysics Data System (ADS)

    Boucher, Daniel; Chekalin, Sergey V.; Kovalenko, S. A.; Matveets, Juru A.; Masselin, P.; Novikov, M. G.; Ragulsky, V. V.; Stepanov, Andrei G.

    1997-09-01

    Relaxation of fullerenes in solids and solutions was investigated by femtosecond pump-probe technique at various experimental setups. Intensity of excitation pulse was varied at 1010 - 1012 W/cm2, energies of pump and probe quanta were changed from 1.57 to 3.14 eV, pulse duration -- from 60 to 350 fs. An increase of absorption was observed in solutions with a time scale of 1.2 ps for C60 and 0.15 ps for C70 after excitation of HOMO-LUMO transition. It was attributed to symmetry breaking of excited molecules. Observed for solid C60 dependence of relaxation rate on the density of excited molecules and on the wavelengths of the pump and probe pulses is explained by 'hot' singlet-singlet annihilation the rate of which is proportional to R-3. Comparison of photoinduced absorption and bleaching decays allowed to conclude that only a small fracture of excited molecules produce localized charge carriers, mainly by excitonic annihilation proces and these carriers are responsible for long-lived residual absorption observed in photoinduced absorption kinetics. Difference absorption spectra observed near zero delay time were similar to electroabsorption ones superimposed on excited state absorption of C60 film. This electroabsorption feature disappeared in phase with pumping pulse. This phenomenon is connected with Stark shift in strong electric field of the powerful pumping pulse.

  3. Initial reaction dynamics of proteorhodopsin observed by femtosecond infrared and visible spectroscopy.

    PubMed

    Neumann, Karsten; Verhoefen, Mirka-Kristin; Weber, Ingrid; Glaubitz, Clemens; Wachtveitl, Josef

    2008-06-01

    We present a comparative study using femtosecond pump/probe spectroscopy in the visible and infrared of the early photodynamics of solubilized proteorhodopsin (green absorbing variant) in D(2)O with deprotonated (pD 9.2) and protonated (pD 6.4) primary proton acceptor Asp-97. The vis-pump/vis-probe experiments show a kinetic isotope effect that is more pronounced for alkaline conditions, thus decreasing the previously reported pH-dependence of the primary reaction of proteorhodopsin in H(2)O. This points to a pH dependent H-bonding network in the binding pocket of proteorhodopsin, that directly influences the primary photo-induced dynamics. The vis-pump/IR-probe experiments were carried out in two different spectral regions and allowed to monitor the retinal C=C (1500 cm(-1)-1580 cm(-1)) and C=N stretching vibration as well as the amide I mode of the protein (1590 cm(-1)-1680 cm(-1)). Like the FTIR spectra of the K intermediate (PR(K)-PR difference spectra) in this spectral range, the kinetic parameters and also the quantum efficiency of photo-intermediate formation are found to be virtually independent of the pD value.

  4. Femtosecond stimulated Raman scattering for polyatomics with harmonic potentials: Application to rhodamine 6G

    NASA Astrophysics Data System (ADS)

    Niu, Kai; Cong, Shulin; Lee, Soo-Y.

    2009-08-01

    The perturbation theory of stimulated Raman scattering (SRS), with Raman pump on minus pump off and heterodyne detection along the probe direction, is reviewed. It has four third-order polarization terms, labeled as SRS or inverse Raman scattering (IRS): SRS(I), SRS(II), IRS(I), and IRS(II). These four polarizations have a wave packet interpretation. The polarizations, with homogenous and inhomogeneous broadening included, can be written as integrals over four-time correlation functions, and analytic formulas are derived for the latter for multidimensional harmonic potential surfaces with Franck-Condon displacements in the modes which facilitates the calculation of the SRS cross sections. The theory is applied to understand recent experimental results on the femtosecond SRS (FSRS) of a fluorescent dye, rhodamine 6G (R6G), where the Raman pump pulse is about 1 ps long, and the probe pulse is about 10 fs. The calculations compared very well with the R6G experimental results for off-resonance and resonance FSRS spectra spanning both Stokes and anti-Stokes bands, and for negative and positive pump-probe delay times on resonance.

  5. Two-temperature relaxation and melting after absorption of femtosecond laser pulse

    NASA Astrophysics Data System (ADS)

    Inogamov, N. A.; Zhakhovskii, V. V.; Ashitkov, S. I.; Khokhlov, V. A.; Petrov, Yu. V.; Komarov, P. S.; Agranat, M. B.; Anisimov, S. I.; Nishihara, K.

    2009-09-01

    The theory and experiments concerned with the electron-ion thermal relaxation and melting of overheated crystal lattice constitute the subject of this paper. The physical model includes two-temperature (2T) equation of state, many-body interatomic potential, the electron-ion energy exchange, electron thermal conductivity, and optical properties of solid, liquid, and two phase solid-liquid mixture. Two-temperature hydrodynamics and molecular dynamics codes are used. An experimental setup with pump-probe technique is used to follow evolution of an irradiated target with a short time step 100 fs between the probe femtosecond laser pulses. Accuracy of measurements of reflection coefficient and phase of reflected probe light are 1% and ˜1 nm, respectively. It is found that, firstly, the electron-electron collisions make a minor contribution to a light absorption in solid Al at moderate intensities; secondly, the phase shift of a reflected probe results from heating of ion subsystem and kinetics of melting of Al crystal during 0ps

  6. Femtosecond laser excitation of coherent optical phonons in ferroelectric LuMnO3

    NASA Astrophysics Data System (ADS)

    Lou, Shi-Tao; Zimmermann, Frank M.; Bartynski, Robert A.; Hur, Namjung; Cheong, Sang-Wook

    2009-06-01

    We have used femtosecond pump-probe spectroscopy to excite and probe coherent optical phonon vibrations in single crystals of hexagonal ferroelectric LuMnO3 . An optical phonon mode of A1 symmetry was coherently excited with 25 fs pump-laser pulses (λ≈800nm) . The phonon mode, involving Lu ion motion along the c axis, was identified as the soft mode driving the ferroelectric transition. The excitation mechanism was determined to be purely displacive in nature due to resonant excitation of a narrow intra-atomic dxy,x2-y2→d3z2-r2 transition in Mn. The lifetime of the Mndxy,x2-y2→d3z2-r2 excitation was measured to be 0.8 ps. A remarkable reversal of the sign of the oscillation amplitude ( π phase shift) of the reflectivity curve was observed upon comparing longitudinal-optical (LO) with transverse-optical (TO) mode geometries. The phase reversal is attributed to the macroscopic electric depolarization field accompanying infrared-active longitudinal phonon modes but absent in TO modes. In addition to the direct effect of the ion motion on the optical properties, which is the same in LO and TO modes, the longitudinal depolarization field of the LO mode gives rise to an additional modulation of the refractive index via the linear electro-optic effect which dominates the optical response.

  7. Long-lived nonthermal electron distribution in aluminum excited by femtosecond extreme ultraviolet radiation

    NASA Astrophysics Data System (ADS)

    Bisio, Francesco; Principi, Emiliano; Magnozzi, Michele; Simoncig, Alberto; Giangrisostomi, Erika; Mincigrucci, Riccardo; Pasquali, Luca; Masciovecchio, Claudio; Boscherini, Federico; Canepa, Maurizio

    2017-08-01

    We report a time-resolved study of the relaxation dynamics of Al films excited by ultrashort intense free-electron laser (FEL) extreme ultraviolet pulses. The system response was measured through a pump-probe detection scheme, in which an intense FEL pulse tuned around the Al L2 ,3 edge (72.5 eV) acted as the pump, while a time-delayed ultrafast pulse probed the near-infrared (NIR) reflectivity of the Al film. Remarkably, following the intense FEL excitation, the reflectivity of the film exhibited no detectable variation for hundreds of femtoseconds. Following this latency time, sizable reflectivity changes were observed. Exploiting recent theoretical calculations of the EUV-excited electron dynamics [N. Medvedev et al., Phys. Rev. Lett. 107, 165003 (2011), 10.1103/PhysRevLett.107.165003], the delayed NIR-reflectivity evolution is interpreted invoking the formation of very-long-living nonthermal hot electron distributions in Al after exposure to intense EUV pulses. Our data represent the first evidence in the time domain of such an intriguing behavior.

  8. Vacuum ultraviolet photoionization and photodissociation of polyatomic molecules and radicals

    SciTech Connect

    Ng, C.Y.

    1993-12-01

    In the past decade, tremendous progress has been made in understanding the photodissociation (PD) dynamics of triatomic molecules. However, the PD study of radicals, especially polyatomic radicals, has remained essentially an unexplored research area. Detailed state-to-state PD cross sections for radicals in the UV and VUV provide challenges not only for dynamical calculations, but also for ab initio quantum chemical studies. The authors have developed a laser based pump-probe apparatus for the measurement of absolute PD cross sections for CH{sub 3}S and HS is summarized.

  9. Photodetachment and photoionization rainbows and glories

    NASA Astrophysics Data System (ADS)

    Cohen, S.; Kalaitzis, P.; Danakas, S.; Lépine, F.; Bordas, C.

    2017-03-01

    Quantum scattering has many similarities with the physics of the atmospheric rainbow. Diffraction effects, including rainbows and glories, have long been introduced in the physics of scattering, and particularly in nuclear, atomic and molecular physics. In this paper we describe the striking similarity between the optics of the primary rainbow and supernumerary bows and photodetachment microscopy, with the latter term referring to the photodetachment of a structureless anion in the presence of a static electric field. Further, we extend the aforementioned analogy to the more complex and fertile case of photoionization microscopy. Despite the fact that in the latter situation the analogy is only approximate, we demonstrate the emergence of additional features that are also found in classical optics, like higher-order bows and glories. Finally, based on the conclusions drawn from the above analyses, we discuss the significant contribution of glories in threshold photoelectron spectroscopy.

  10. Nondipole Effects in Double Photoionization of He

    SciTech Connect

    Istomin, A. Y.; Starace, A. F.; Manakov, N. L.; Meremianin, A. V.

    2006-01-09

    Lowest-order nondipole effects are studied in double photoionization (DPI) of the He atom. Ab initio parametrizations of the quadrupole transition amplitude for DPI from the 1S0-state are presented in terms of the exact two-electron reduced matrix elements. Parametrizations for the dipole-quadrupole triply differential cross section (TDCS) and doubly differential cross section (DDCS) are presented in terms of polarization-independent amplitudes for the case of an elliptically polarized photon. Expressions for the DDCS in terms of the reduced two-electron matrix elements are also given. A general analysis of retardation-induced asymmetries of the TDCS including the circular dichroism effect at equal energy sharing is presented. Our numerical results exhibit a nondipole forward-backward asymmetry in the TDCS for DPI of He at an excess energy of 450 eV that is in qualitative agreement with existing experimental data.

  11. Double photoionization of tropone and cyclooctatetraene

    NASA Astrophysics Data System (ADS)

    Hartman, Tim; Wehlitz, Ralf

    2017-05-01

    We have studied the double-photoionization process of tropone (C7H6O) and cyclooctatetraene (C8H8) as a function of photon energy using monochromatized synchrotron radiation between 18 and 270 eV. We compare our results with previously published data for partially deuterated benzene (C6H3D3), which exhibits three distinct features in the ratio of doubly to singly charged parent ions, whereas pyrrole (C4H4N) exhibits only two of these features. The question that we address in this paper is how molecules with different molecular structures (pentagonal, hexagonal, heptagonal, and octagonal carbon rings) affect the photon-energy dependence of this ratio.

  12. Metallic and semiconductor nanoparticles: Synthesis, characterization and femtosecond laser spectroscopic studies

    NASA Astrophysics Data System (ADS)

    Mohamed, Mona Bakr

    The optical properties and the femtosecond relaxation dynamics of metallic and semiconductor nanoparticles and their dependence on the particle shapes were studied. Metallic and semiconductor nanoparticles were synthesized and characterized using optical absorption and emission spectroscopy as well as the Transmission Electron Microscopy (TEM). The ultrafast relaxation dynamics and the transient absorption spectra have been monitored using femtosecond pump-probe experiment. Regarding the shape dependent optical properties of metallic nanoparticles, gold nanospheres show surface plasmon absorption at 520 nm, however gold nanorods show two plasmon absorption bands due to the oscillation of the surface electrons along the transverse and the longitudinal modes. New absorption features appear, which are assigned to quadrupole resonance absorption along the short axis perpendicular to the triangular or hexagonal nanoplatelets. One of the most unique properties of gold nanorods is that they fluoresce with quantum yield enhancement one million times than the gold bulk due to the local field effect created by the longitudinal surface plasmon absorption (lightning nanorod effect). To study the effect of the surrounding matrix on the electron-phonon and phononphonon ultrafast relaxation dynamics of gold particles, the relaxation dynamics of the gold particles embedded in hydrogel and in organic gels have been compared. A large decrease in the phonon-phonon relaxation time was observed in the organic gel due to their lower thermal conductivity compared to water. The chemical interaction between the solvent molecules trapped inside the gel network and the gold particles surface enhances the rate of the heat transfer between the particles and the bath, giving rise a faster rate of relaxation. Shape dependent optical and ultrafast electron dynamics of semiconductor CdSe nanocrystals was studied. The femtosecond transient absorption spectra of CdSe nanorods show more spectral

  13. Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging.

    PubMed

    Cocker, Tyler L; Peller, Dominik; Yu, Ping; Repp, Jascha; Huber, Rupert

    2016-11-10

    Watching a single molecule move on its intrinsic timescale has been one of the central goals of modern nanoscience, and calls for measurements that combine ultrafast temporal resolution with atomic spatial resolution. Steady-state experiments access the requisite spatial scales, as illustrated by direct imaging of individual molecular orbitals using scanning tunnelling microscopy or the acquisition of tip-enhanced Raman and luminescence spectra with sub-molecular resolution. But tracking the intrinsic dynamics of a single molecule directly in the time domain faces the challenge that interactions with the molecule must be confined to a femtosecond time window. For individual nanoparticles, such ultrafast temporal confinement has been demonstrated by combining scanning tunnelling microscopy with so-called lightwave electronics, which uses the oscillating carrier wave of tailored light pulses to directly manipulate electronic motion on timescales faster even than a single cycle of light. Here we build on ultrafast terahertz scanning tunnelling microscopy to access a state-selective tunnelling regime, where the peak of a terahertz electric-field waveform transiently opens an otherwise forbidden tunnelling channel through a single molecular state. It thereby removes a single electron from an individual pentacene molecule's highest occupied molecular orbital within a time window shorter than one oscillation cycle of the terahertz wave. We exploit this effect to record approximately 100-femtosecond snapshot images of the orbital structure with sub-ångström spatial resolution, and to reveal, through pump/probe measurements, coherent molecular vibrations at terahertz frequencies directly in the time domain. We anticipate that the combination of lightwave electronics and the atomic resolution of our approach will open the door to visualizing ultrafast photochemistry and the operation of molecular electronics on the single-orbital scale.

  14. Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging

    NASA Astrophysics Data System (ADS)

    Cocker, Tyler L.; Peller, Dominik; Yu, Ping; Repp, Jascha; Huber, Rupert

    2016-11-01

    Watching a single molecule move on its intrinsic timescale has been one of the central goals of modern nanoscience, and calls for measurements that combine ultrafast temporal resolution with atomic spatial resolution. Steady-state experiments access the requisite spatial scales, as illustrated by direct imaging of individual molecular orbitals using scanning tunnelling microscopy or the acquisition of tip-enhanced Raman and luminescence spectra with sub-molecular resolution. But tracking the intrinsic dynamics of a single molecule directly in the time domain faces the challenge that interactions with the molecule must be confined to a femtosecond time window. For individual nanoparticles, such ultrafast temporal confinement has been demonstrated by combining scanning tunnelling microscopy with so-called lightwave electronics, which uses the oscillating carrier wave of tailored light pulses to directly manipulate electronic motion on timescales faster even than a single cycle of light. Here we build on ultrafast terahertz scanning tunnelling microscopy to access a state-selective tunnelling regime, where the peak of a terahertz electric-field waveform transiently opens an otherwise forbidden tunnelling channel through a single molecular state. It thereby removes a single electron from an individual pentacene molecule’s highest occupied molecular orbital within a time window shorter than one oscillation cycle of the terahertz wave. We exploit this effect to record approximately 100-femtosecond snapshot images of the orbital structure with sub-ångström spatial resolution, and to reveal, through pump/probe measurements, coherent molecular vibrations at terahertz frequencies directly in the time domain. We anticipate that the combination of lightwave electronics and the atomic resolution of our approach will open the door to visualizing ultrafast photochemistry and the operation of molecular electronics on the single-orbital scale.

  15. Signal to noise considerations for single crystal femtosecond time resolved crystallography of the Photoactive Yellow Protein.

    PubMed

    van Thor, Jasper J; Warren, Mark M; Lincoln, Craig N; Chollet, Matthieu; Lemke, Henrik Till; Fritz, David M; Schmidt, Marius; Tenboer, Jason; Ren, Zhong; Srajer, Vukica; Moffat, Keith; Graber, Tim

    2014-01-01

    Femtosecond time resolved pump-probe protein X-ray crystallography requires highly accurate measurements of the photoinduced structure factor amplitude differences. In the case of femtosecond photolysis of single P63 crystals of the Photoactive Yellow Protein, it is shown that photochemical dynamics place a considerable restraint on the achievable time resolution due to the requirement to stretch and add second order dispersion in order to generate threshold concentration levels in the interaction region. Here, we report on using a 'quasi-cw' approach to use the rotation method with monochromatic radiation and 2 eV bandwidth at 9.465 keV at the Linac Coherent Light Source operated in SASE mode. A source of significant Bragg reflection intensity noise is identified from the combination of mode structure and jitter with very small mosaic spread of the crystals and very low convergence of the XFEL source. The accuracy with which the three dimensional reflection is approximated by the 'quasi-cw' rotation method with the pulsed source is modelled from the experimentally collected X-ray pulse intensities together with the measured rocking curves. This model is extended to predict merging statistics for recently demonstrated self seeded mode generated pulse train with improved stability, in addition to extrapolating to single crystal experiments with increased mosaic spread. The results show that the noise level can be adequately modelled in this manner, indicating that the large intensity fluctuations dominate the merged signal-to-noise (I/σI) value. Furthermore, these results predict that using the self seeded mode together with more mosaic crystals, sufficient accuracy may be obtained in order to resolve typical photoinduced structure factor amplitude differences, as taken from representative synchrotron results.

  16. Ultrafast supercontinuum fiber-laser based pump-probe scanning magneto-optical Kerr effect microscope for the investigation of electron spin dynamics in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution

    SciTech Connect

    Henn, T.; Kiessling, T. Ossau, W.; Molenkamp, L. W.; Biermann, K.; Santos, P. V.

    2013-12-15

    We describe a two-color pump-probe scanning magneto-optical Kerr effect microscope which we have developed to investigate electron spin phenomena in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution. The key innovation of our microscope is the usage of an ultrafast “white light” supercontinuum fiber-laser source which provides access to the whole visible and near-infrared spectral range. Our Kerr microscope allows for the independent selection of the excitation and detection energy while avoiding the necessity to synchronize the pulse trains of two separate picosecond laser systems. The ability to independently tune the pump and probe wavelength enables the investigation of the influence of excitation energy on the optically induced electron spin dynamics in semiconductors. We demonstrate picosecond real-space imaging of the diffusive expansion of optically excited electron spin packets in a (110) GaAs quantum well sample to illustrate the capabilities of the instrument.

  17. Optical spectroscopy and ultrafast pump-probe studies on the heavy-fermion compound CePt2In7

    SciTech Connect

    Chen, R. Y.; Zhang, S. J.; Bauer, E. D.; Thompson, J. D.; Wang, N. L.

    2016-07-29

    We report optical spectroscopy and ultrafast pump-probe measurements on the antiferromagnetic heavy-fermion compound CePt 2 In 7 , a member showing stronger two dimensionality than other compounds in the CeIn 3 -derived heavy-fermion family. Here, we identify clear and typical hybridization spectral structures at low temperature from the two different spectroscopy probes. But, the strength and related energy scale of the hybridization are much weaker and smaller than that in the superconducting compounds CeCoIn 5 and CeIrIn 5 . The features are more similar to observations on the antiferromagnetic compounds CeIn 3 and CeRhIn 5 in the same family. Our results clearly indicate that the Kondo interaction and hybridizations exist in the antiferromagnetic compounds but with weaker strength.

  18. Terahertz radiation driven by two-color laser pulses at near-relativistic intensities: Competition between photoionization and wakefield effects

    PubMed Central

    González de Alaiza Martínez, P.; Davoine, X.; Debayle, A.; Gremillet, L.; Bergé, L.

    2016-01-01

    We numerically investigate terahertz (THz) pulse generation by linearly-polarized, two-color femtosecond laser pulses in highly-ionized argon. Major processes consist of tunneling photoionization and ponderomotive forces associated with transverse and longitudinal field excitations. By means of two-dimensional particle-in-cell (PIC) simulations, we reveal the importance of photocurrent mechanisms besides transverse and longitudinal plasma waves for laser intensities >1015 W/cm2. We demonstrate the following. (i) With two-color pulses, photoionization prevails in the generation of GV/m THz fields up to 1017 W/cm2 laser intensities and suddenly loses efficiency near the relativistic threshold, as the outermost electron shell of ionized Ar atoms has been fully depleted. (ii) PIC results can be explained by a one-dimensional Maxwell-fluid model and its semi-analytical solutions, offering the first unified description of the main THz sources created in plasmas. (iii) The THz power emitted outside the plasma channel mostly originates from the transverse currents. PMID:27255689

  19. Communication: Ultrafast time-resolved ion photofragmentation spectroscopy of photoionization-induced proton transfer in phenol-ammonia complex

    SciTech Connect

    Shen, Ching-Chi; Tsai, Tsung-Ting; Ho, Jr-Wei; Chen, Yi-Wei; Cheng, Po-Yuan

    2014-11-07

    Photoionization-induced proton transfer (PT) in phenol-ammonia (PhOH-NH{sub 3}) complex has been studied using ultrafast time-resolved ion photofragmentation spectroscopy. Neutral PhOH-NH{sub 3} complexes prepared in a free jet are photoionized by femtosecond [1+1] resonance-enhanced multiphoton ionization via the S{sub 1} state, and the subsequent dynamics occurring in the cations is probed by delayed pulses that result in ion fragmentation. The observed temporal evolutions of the photofragmentation spectra are consistent with an intracomplex PT reaction. The experiments revealed that PT in [PhOH-NH{sub 3}]{sup +} cation proceeds in two distinct steps: an initial impulsive wave-packet motion in ∼70 fs followed by a slower relaxation of about 1 ps that stabilizes the system into the final PT configuration. These results indicate that for a barrierless PT system, even though the initial PT motions are impulsive and ultrafast, the reaction may take a much longer time scale to complete.

  20. Terahertz radiation driven by two-color laser pulses at near-relativistic intensities: Competition between photoionization and wakefield effects

    NASA Astrophysics Data System (ADS)

    González de Alaiza Martínez, P.; Davoine, X.; Debayle, A.; Gremillet, L.; Bergé, L.

    2016-06-01

    We numerically investigate terahertz (THz) pulse generation by linearly-polarized, two-color femtosecond laser pulses in highly-ionized argon. Major processes consist of tunneling photoionization and ponderomotive forces associated with transverse and longitudinal field excitations. By means of two-dimensional particle-in-cell (PIC) simulations, we reveal the importance of photocurrent mechanisms besides transverse and longitudinal plasma waves for laser intensities >1015 W/cm2. We demonstrate the following. (i) With two-color pulses, photoionization prevails in the generation of GV/m THz fields up to 1017 W/cm2 laser intensities and suddenly loses efficiency near the relativistic threshold, as the outermost electron shell of ionized Ar atoms has been fully depleted. (ii) PIC results can be explained by a one-dimensional Maxwell-fluid model and its semi-analytical solutions, offering the first unified description of the main THz sources created in plasmas. (iii) The THz power emitted outside the plasma channel mostly originates from the transverse currents.

  1. A mixed quantum-classical molecular dynamics study of the hydroxyl stretch in methanol/carbon tetrachloride mixtures III: nonequilibrium hydrogen-bond dynamics and infrared pump-probe spectra.

    PubMed

    Kwac, Kijeong; Geva, Eitan

    2013-06-27

    We present a mixed quantum-classical molecular dynamics study of the nonequilibrium hydrogen-bond dynamics following vibrational energy relaxation of the hydroxyl stretch in a 10 mol % methanol/carbon tetrachloride mixture and pure methanol. The ground and first-excited energy levels and wave functions are identified with the eigenvalues and eigenfunctions of the hydroxyl's adiabatic Hamiltonian and as such depend parametrically on the configuration of the remaining, classically treated, degrees of freedom. The dynamics of the classical degrees of freedom are in turn governed by forces obtained by taking the expectation value of the force with respect to the ground or excited vibrational wave functions. Polarizable force fields and nonlinear mapping relations between the hydroxyl transition frequencies and dipole moments and the electric field along the hydroxyl bond are used, which were previously shown to quantitatively reproduce the experimental infrared steady-state absorption spectra and excited state lifetime [Kwac, K.; Geva, E. J. Phys. Chem. B 2011, 115, 9184; 2012, 116, 2856]. The relaxation from the first-excited state to the ground state is treated as a nonadiabatic transition. Within the mixed quantum-classical treatment, relaxation from the excited state to the ground state is accompanied by a momentum-jump in the classical degrees of freedom, which is in turn dictated by the nonadiabatic coupling vector. We find that the momentum jump leads to breaking of hydrogen bonds involving the relaxing hydroxyl, thereby blue-shifting the transition frequency by more than the Stokes shift between the steady-state emission and absorption spectra. The subsequent nonequilibrium relaxation toward equilibrium on the ground state potential energy surface is thereby accompanied by red shifting of the transition frequency. The signature of this nonequilibrium relaxation process on the pump-probe spectrum is analyzed in detail. The calculated pump-probe spectrum is found

  2. Photoionization of psoralen derivatives in micelles: Imperatorin and alloimperatorin

    NASA Astrophysics Data System (ADS)

    El-Gogary, Sameh R.

    2010-11-01

    The fluorescence properties of psoralen derivatives, 8-methoxypsoralen (8-MOP), imperatorin (IMP) and alloimperatorin (ALLOI), were investigated in various solvent and micellar solutions. The variation in intensity and maxima of the fluorescence in micellar solutions suggest that psoralens are located in the micelle-water interface region. Radical cations and hydrated electrons were generated by photoionization in micellar solution upon excitation at 266 nm. A nonlinear relationship between transient yield and photon fluency was obtained for each compound, indicating that a two-photon mechanism is predominant in the photoionization of the sensitizers. The photoionization efficiencies are significantly higher in anionic sodium dodecyl sulfate (SDS) than in cationic cetyltrimethylammonium bromide (CTAB) micelles, reflecting the influence of micelle charge on the efficiency of the separation of the photoproduced charge carriers. The photoionization efficiencies of IMP and ALLOI are similar.

  3. Photoionization of noble-gas atoms by ultrashort electromagnetic pulses

    SciTech Connect

    Astapenko, V. A. Svita, S. Yu.

    2014-11-15

    The photoionization of atoms of noble gases (Ar, Kr, and Xe) by ultrashort electromagnetic pulses of a corrected Gaussian shape is studied theoretically. Computations are performed in the context of perturbation theory using a simple expression for the total probability of photoionization of an atom by electromagnetic pulses. The features of this process are revealed and analyzed for various ranges of the parameters of the problem.

  4. An Atomic Photoionization Experiment by Harmonic Generation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Trallero, Carlos; Frolov, Mikhail; Sarantseva, Tatiana S.; Manakov, Nikolay; Fulfer, Kristen D.; Wilson, Benjamin; Troß, Jan; Ren, Xiaoming; Poliakoff, Erwin; Silaev, Alexander A.; Vvedenskii, Nikolay; Starace, Anthony

    2016-05-01

    Measurements of the high-order harmonic generation yield of the argon (Ar) atom driven by a strong elliptically polarized laser field are shown to completely determine the field-free differential photoionization cross section of Ar, i.e., the energy dependence of both the angle-integrated photoionization cross section and the angular distribution asymmetry parameter. NSF EPSCoR Track II Nebraska-Kansas Awards No. 1430519 and No. 1430493.

  5. Nonlinear femtosecond near infrared laser structuring in oxide glasses

    NASA Astrophysics Data System (ADS)

    Royon, Arnaud

    nonlinear third-order susceptibility properties have been measured. Moreover, the structuring of fused silica at the subwavelength scale into "nanogratings" is observed and the form of birefringence induced by these structures is discussed. In addition to the fused silica samples, several oxide glasses presenting very distinct chemical compositions have been studied. A sodium-borophosphate glass containing niobium oxide exhibits micro-cracks and nano-crystallites following irradiation. A silicate glass with or without a silver component reveals fluorescent rings or "nanograting" structures. A zinc phosphate glass containing silver also presents fluorescent ring structures, with a size of the order of 80 nm, well below the diffraction limit. Pump-probe microscope techniques have been performed on this glass to investigate the laser-glass interaction. The absorption mechanism is determined to be four-photon absorption. The generated free electron density is ˜ 1017 cm-3, which suggests the conclusion that an electron gas rather than a plasma is formed during the laser irradiation.

  6. Photoionization and photofragmentation of SF6 in helium nanodroplets.

    PubMed

    Peterka, Darcy S; Kim, Jeong Hyun; Wang, Chia C; Neumark, Daniel M

    2006-10-12

    The photoionization of He droplets doped with SF6 was investigated using tunable vacuum ultraviolet (VUV) synchrotron radiation from the Advanced Light Source (ALS). The resulting ionization and photofragmentation dynamics were characterized using time-of-flight mass spectrometry combined with photofragment and photoelectron imaging. Results are compared to those of gas-phase SF6 molecules. We find dissociative photoionization to SF5+ to be the dominant channel, in agreement with previous results. Key new findings are that (a) the photoelectron spectrum of the SF6 in the droplet is similar but not identical to that of the gas-phase species, (b) the SF5+ photofragment velocity distribution is considerably slower upon droplet photoionization, and (c) fragmentation to SF4+ and SF3+ is much less than in the photoionization of bare SF6. From these measurements we obtain new insights into the mechanism of SF6 photoionization within the droplet and the cooling of the hot photofragment ions produced by dissociative photoionization.

  7. Sub-cycle directional control of the dissociative ionization of H2 in tailored femtosecond laser fields

    NASA Astrophysics Data System (ADS)

    Li, H.; Gong, X.; Lin, K.; de Vivie-Riedle, R.; Tong, X. M.; Wu, J.; Kling, M. F.

    2017-09-01

    Being the simplest molecule on the planet, H2, as well as its isotopes, have been the prototype systems for strong-field molecular physics for decades. Photoionization and dissociation of H2 have been extensively investigated. After single ionization, the electron left in the molecular ion and its microscopic localization around the two dissociating nuclei can be effectively manipulated using intense femtosecond laser fields with broken symmetry. In this paper, we review the recent progress made on the sub-cycle directional control of the dissociative ionization of hydrogen molecules by tailoring the waveform of femtosecond laser fields, including few-cycle pulses and 2-color fields polarized along the same direction (one-dimension) or different directions (two-dimension).

  8. Femtosecond photography lessons

    NASA Astrophysics Data System (ADS)

    Fanchenko, S. D.

    1999-06-01

    Antic scientists, sailors, warriors, physician, etc. were perceiving the space by means of their eye vision system. Nowadays the same people use eyeglasses, telescopes, microscopes, image converters. All these devices fit the necessary magnification, intensification gain and image spectrum to the eyes. The human brain is processing the image data offered to him in a format pertaining to eyes. Hence, the cognition of images can be regarded as a direct measurement. As to the time scale converters, they turned out to be harder done as compared with the spatial scale converters. Hence, the development of the high-speed photography (HSP) continues for more than a hundred and fifty years. The recent pico- femtosecond HSP branch sprang up in 1949 at the Kurchatov Institute -- its cradle. All about the HSP had been advertised. Instead of reprinting what is already well known, it makes sense to emphasize some instructive lessons drawn from past experience. Also it is tempting to look a bit into the high-speed photography future.

  9. High-Resolution Photoelectron and Photoionization Spectroscopy

    NASA Astrophysics Data System (ADS)

    Merkt, F.

    2012-06-01

    Since its development in the late 1950s and early 1960s, photoelectron spectroscopy has established itself as an important method to study the electronic structure of molecules, their photoionization dynamics, and the structure and dynamics of molecular cations. In recent years, and particularly since the development of pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy, considerable progress has been made in the resolution that can be achieved by photoelectron spectroscopy. This progress relies on the systematic exploitation of the unusual physical properties of high Rydberg states and enables one today to resolve the rotational structure in the photoelectron spectra of even large molecules and the hyperfine structure in the photoelectron spectra of small molecules. This talk will begin with a brief historical review of photoelectron spectroscopy. Then, the relationship between photoelectron spectroscopy, photoionization spectroscopy and the spectroscopy of high Rydberg states will be discussed. It will be explained how this relationship is currently exploited to improve the resolution achievable by PFI-ZEKE photoelectron spectroscopy. Then, the physical principles that are at the heart of the latest methods related to high-resolution photoelectron spectroscopy will be described together with their fundamental limitations. Depending on the resolution and the spectral range needed to address a specific scientific problem, a choice can be made between several different methods with spectral resolutions ranging from 30 GHz to better than 1 MHz. The talk will summarize the current state of the art in gas-phase photoelectron spectroscopy and be illustrated by several examples, primarily taken from the research in my group, in which photoelectron spectroscopy has contributed to answer questions concerning the structure and dynamics of small-sized molecular cations. F. I. Vilesov, B. C. Kurbatov, and N. Terrenin, Soviet Phys. (Doklady) 6

  10. Dynamics of photoprocesses induced by femtosecond infrared radiation in free molecules and clusters of iron pentacarbonyl

    SciTech Connect

    Kompanets, V. O.; Lokhman, V. N.; Poydashev, D. G. Chekalin, S. V.; Ryabov, E. A.

    2016-04-15

    The dynamics of photoprocesses induced by femtosecond infrared radiation in free Fe(CO){sub 5} molecules and their clusters owing to the resonant excitation of vibrations of CO bonds in the 5-μm range has been studied. The technique of infrared excitation and photoionization probing (λ = 400 nm) by femtosecond pulses has been used in combination with time-of-flight mass spectrometry. It has been found that an infrared pulse selectively excites vibrations of CO bonds in free molecules, which results in a decrease in the yield of the Fe(CO){sub 5}{sup +} molecular ion. Subsequent relaxation processes have been analyzed and the results have been interpreted. The time of the energy transfer from excited vibrations to other vibrations of the molecule owing to intramolecular relaxation has been measured. The dynamics of dissociation of [Fe(CO){sub 5}]{sub n} clusters irradiated by femtosecond infrared radiation has been studied. The time dependence of the yield of free molecules has been measured under different infrared laser excitation conditions. We have proposed a model that well describes the results of the experiment and makes it possible, in particular, to calculate the profile of variation of the temperature of clusters within the “evaporation ensemble” concept. The intramolecular and intracluster vibrational relaxation rates in [Fe(CO){sub 5}]{sub n} clusters have been estimated.

  11. Model propagation of a femtosecond laser radiation in the vitreous of the human eye

    NASA Astrophysics Data System (ADS)

    Rogov, P. Y.; Bespalov, V. G.

    2016-04-01

    The paper presents a mathematical model of linear and nonlinear processes occurring due to propagation of femtosecond laser pulses in vitreous of the human eye. By methods of numerical simulation, we have solved a nonlinear spectral equation describing dynamics of two-dimensional TE-polarized radiation. The solution was performed in a homogeneous isotropic medium with instantaneous cubic nonlinearity without using slowly varying envelope approximation. For simulation we used medium with parameters close to the optical media of the eye. The model of femtosecond radiation takes into account the dynamics of the process of dispersion pulse broadening in time and occurrence of self-focusing of the retina when passing through vitreous body of the eye. The dependence between pulse duration on the retina and duration of the input pulse was found, as well as the values of power density at which self-focusing occurs. It was shown that the main mechanism of radiation damage caused while using Ti-sapphire laser is photoionization. The results coincide with the results obtained by other scientists. They can be used to create Russian laser safety standards for femtosecond laser systems.

  12. Femtosecond optomagnetism in dielectric antiferromagnets

    NASA Astrophysics Data System (ADS)

    Bossini, D.; Rasing, Th

    2017-02-01

    Optical femtosecond manipulation of magnetic order is attractive for the development of new concepts for ultrafast magnetic recording. Theoretical and experimental investigations in this research area aim at establishing a physical understanding of magnetic media in light-induced non-equilibrium states. Such a quest requires one to adjust the theory of magnetism, since the thermodynamical concepts of elementary excitations and spin alignment determined by the exchange interaction are not applicable on the femtosecond time-scale after the photo-excitation. Here we report some key milestones concerning the femtosecond optical control of spins in dielectric antiferromagnets, whose spin dynamics is by nature faster than that of ferromagnets and can be triggered even without any laser heating. The recent progress of the opto-magnetic effect in the sub-wavelength regime makes this exciting research area even more promising, in terms of both fundamental breakthroughs and technological perspectives.

  13. CdS and Cd-Free Buffer Layers on Solution Phase Grown Cu2ZnSn(SxSe1- x)4 :Band Alignments and Electronic Structure Determined with Femtosecond Ultraviolet Photoemission Spectroscopy

    SciTech Connect

    Haight, Richard; Barkhouse, Aaron; Wang, Wei; Yu, Luo; Shao, Xiaoyan; Mitzi, David; Hiroi, Homare; Sugimoto, Hiroki

    2013-12-02

    The heterojunctions formed between solution phase grown Cu2ZnSn(SxSe1- x)4(CZTS,Se) and a number of important buffer materials including CdS, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission spectroscopy (fs-UPS) and photovoltage spectroscopy. With this approach we extract the magnitude and direction of the CZTS,Se band bending, locate the Fermi level within the band gaps of absorber and buffer and measure the absorber/buffer band offsets under flatband conditions. We will also discuss two-color pump/probe experiments in which the band bending in the buffer layer can be independently determined. Finally, studies of the bare CZTS,Se surface will be discussed including our observation of mid-gap Fermi level pinning and its relation to Voc limitations and bulk defects.

  14. Vacuum ultraviolet photoionization of carbohydrates and nucleotides

    SciTech Connect

    Shin, Joong-Won; Bernstein, Elliot R.

    2014-01-28

    Carbohydrates (2-deoxyribose, ribose, and xylose) and nucleotides (adenosine-, cytidine-, guanosine-, and uridine-5{sup ′}-monophosphate) are generated in the gas phase, and ionized with vacuum ultraviolet photons (VUV, 118.2 nm). The observed time of flight mass spectra of the carbohydrate fragmentation are similar to those observed [J.-W. Shin, F. Dong, M. Grisham, J. J. Rocca, and E. R. Bernstein, Chem. Phys. Lett. 506, 161 (2011)] for 46.9 nm photon ionization, but with more intensity in higher mass fragment ions. The tendency of carbohydrate ions to fragment extensively following ionization seemingly suggests that nucleic acids might undergo radiation damage as a result of carbohydrate, rather than nucleobase fragmentation. VUV photoionization of nucleotides (monophosphate-carbohydrate-nucleobase), however, shows that the carbohydrate-nucleobase bond is the primary fragmentation site for these species. Density functional theory (DFT) calculations indicate that the removed carbohydrate electrons by the 118.2 nm photons are associated with endocyclic C–C and C–O ring centered orbitals: loss of electron density in the ring bonds of the nascent ion can thus account for the observed fragmentation patterns following carbohydrate ionization. DFT calculations also indicate that electrons removed from nucleotides under these same conditions are associated with orbitals involved with the nucleobase-saccharide linkage electron density. The calculations give a general mechanism and explanation of the experimental results.

  15. Extreme ultraviolet-induced photoionized plasmas

    NASA Astrophysics Data System (ADS)

    Bartnik, Andrzej; Wachulak, Przemyslaw; Fiedorowicz, Henryk; Fok, Tomasz; Jarocki, Roman; Szczurek, Miroslaw

    2014-05-01

    In this work photoionized plasmas were created by irradiation of He or Ne gases with a focused extreme ultraviolet (EUV) beam from one of two laser-plasma sources employing Nd:YAG laser systems. The first of them was a 10 Hz laser-plasma EUV source, based on a double-stream gas-puff target, irradiated with a 3 ns per 0.8 J laser pulse. EUV radiation in this case was focused using a gold-plated grazing incidence ellipsoidal collector. The second source was based on a 10 ns per 10 J per 10 Hz laser system. In this case EUV radiation was focused using a gold-plated grazing incidence multifoil collector. Gases were injected into the interaction region, perpendicularly to an optical axis of the irradiation system, using an auxiliary gas puff valve. Spectral measurements in the EUV range were performed. In all cases the most intense emission lines were assigned to singly charged ions. The other emission lines belong to atoms or doubly charged ions.

  16. Cooling and Heating Functions of Photoionized Gas

    NASA Astrophysics Data System (ADS)

    Gnedin, Nickolay Y.; Hollon, Nicholas

    2012-10-01

    Cooling and heating functions of cosmic gas are crucial ingredients for any study of gas dynamics and thermodynamics in the interstellar and intergalactic media. As such, they have been studied extensively in the past under the assumption of collisional ionization equilibrium. However, for a wide range of applications, the local radiation field introduces a non-negligible, often dominant, modification to the cooling and heating functions. In the most general case, these modifications cannot be described in simple terms and would require a detailed calculation with a large set of chemical species using a radiative transfer code (the well-known code Cloudy, for example). We show, however, that for a sufficiently general variation in the spectral shape and intensity of the incident radiation field, the cooling and heating functions can be approximated as depending only on several photoionization rates, which can be thought of as representative samples of the overall radiation field. This dependence is easy to tabulate and implement in cosmological or galactic-scale simulations, thus economically accounting for an important but rarely included factor in the evolution of cosmic gas. We also show a few examples where the radiation environment has a large effect, the most spectacular of which is a quasar that suppresses gas cooling in its host halo without any mechanical or non-radiative thermal feedback.

  17. Intergalactic magnetogenesis at Cosmic Dawn by photoionization

    NASA Astrophysics Data System (ADS)

    Durrive, J.-B.; Langer, M.

    2015-10-01

    We present a detailed analysis of an astrophysical mechanism that generates cosmological magnetic fields during the Epoch of Reionization. It is based on the photoionization of the intergalactic medium by the first sources formed in the Universe. First the induction equation is derived, then the characteristic length and time-scales of the mechanism are identified, and finally numerical applications are carried out for first stars, primordial galaxies and distant powerful quasars. In these simple examples, the strength of the generated magnetic fields varies between the order of 10-23 G on hundreds of kiloparsecs and 10-19 G on hundreds of parsecs in the neutral intergalactic medium between the Strömgren spheres of the sources. Thus, this mechanism contributes to the premagnetization of the whole Universe before large-scale structures are in place. It operates with any ionizing source, at any time during the Epoch of Reionization. Finally, the generated fields possess a characteristic spatial configuration which may help discriminate these seeds from those produced by different mechanisms.

  18. Vacuum ultraviolet photoionization of carbohydrates and nucleotides

    NASA Astrophysics Data System (ADS)

    Shin, Joong-Won; Bernstein, Elliot R.

    2014-01-01

    Carbohydrates (2-deoxyribose, ribose, and xylose) and nucleotides (adenosine-, cytidine-, guanosine-, and uridine-5'-monophosphate) are generated in the gas phase, and ionized with vacuum ultraviolet photons (VUV, 118.2 nm). The observed time of flight mass spectra of the carbohydrate fragmentation are similar to those observed [J.-W. Shin, F. Dong, M. Grisham, J. J. Rocca, and E. R. Bernstein, Chem. Phys. Lett. 506, 161 (2011)] for 46.9 nm photon ionization, but with more intensity in higher mass fragment ions. The tendency of carbohydrate ions to fragment extensively following ionization seemingly suggests that nucleic acids might undergo radiation damage as a result of carbohydrate, rather than nucleobase fragmentation. VUV photoionization of nucleotides (monophosphate-carbohydrate-nucleobase), however, shows that the carbohydrate-nucleobase bond is the primary fragmentation site for these species. Density functional theory (DFT) calculations indicate that the removed carbohydrate electrons by the 118.2 nm photons are associated with endocyclic C-C and C-O ring centered orbitals: loss of electron density in the ring bonds of the nascent ion can thus account for the observed fragmentation patterns following carbohydrate ionization. DFT calculations also indicate that electrons removed from nucleotides under these same conditions are associated with orbitals involved with the nucleobase-saccharide linkage electron density. The calculations give a general mechanism and explanation of the experimental results.

  19. Holographic vector-wave femtosecond laser processing

    NASA Astrophysics Data System (ADS)

    Hayasaki, Yoshio; Hasegawa, Satoshi

    2016-03-01

    Arbitrary and variable beam shaping of femtosecond pulses by a computer-generated hologram (CGH) displayed on a spatial light modulator (SLM) have been applied to femtosecond laser processing. The holographic femtosecond laser processing has been widely used in many applications such as two-photon polymerization, optical waveguide fabrication, fabrication of volume phase gratings in polymers, and surface nanostructuring. A vector wave that has a spatial distribution of polarization states control of femtosecond pulses gives good performances for the femtosecond laser processing. In this paper, an in- system optimization of a CGH for massively-parallel femtosecond laser processing, a dynamic control of spatial spectral dispersion to improve the focal spot shape, and the holographic vector-wave femtosecond laser processing are demonstrated.

  20. VUV photoionization and dissociative photoionization spectroscopy of the interstellar molecule aminoacetonitrile: Theory and experiment

    NASA Astrophysics Data System (ADS)

    Bellili, A.; Schwell, M.; Bénilan, Y.; Fray, N.; Gazeau, M.-C.; Mogren Al-Mogren, M.; Guillemin, J.-C.; Poisson, L.; Hochlaf, M.

    2015-09-01

    Aminoacetonitrile (AAN) is a key compound in astrochemistry and astrobiology. We present a combined theoretical and experimental investigation concerning the single photoionization of gas-phase AAN and the fragmentation pathways of the resulting cation. At present, we measured photoelectron photoion coincidence (PEPICO) spectra in the 9.8-13.6 eV energy regime using synchrotron radiation as exciting light source. In order to interpret the VUV experimental data obtained, we explored the ground potential energy surface (PES) of AAN and of its cation using standard and explicitly correlated quantum chemical methodologies. This allowed us to deduce accurate thermochemical data for this molecule. We also determined, for the first time, the adiabatic ionization energy of AAN to lie at AIE = (10.085 ± 0.03) eV. The unimolecular decomposition pathways of the resulting AAN+ parent cation are also investigated. The appearance energies of five fragments are determined for the first time, with 30 meV accuracy. Interestingly, our work shows the possibility of the formation of both HCN and HNC isomeric forms. The implications for the evolution of prebiotic molecules under VUV irradiation are briefly discussed.