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Sample records for resonance-enhanced two-photon ionization

  1. Resonance-enhanced two-photon ionization of ions by Lyman alpha radiation in gaseous nebulae.

    PubMed

    Johansson, S; Letokhov, V

    2001-01-26

    One of the mysteries of nebulae in the vicinity of bright stars is the appearance of bright emission spectral lines of ions, which imply fairly high excitation temperatures. We suggest that an ion formation mechanism, based on resonance-enhanced two-photon ionization (RETPI) by intense H Lyman alpha radiation (wavelength of 1215 angstroms) trapped inside optically thick nebulae, can produce these spectral lines. The rate of such an ionization process is high enough for rarefied gaseous media where the recombination rate of the ions formed can be 10(-6) to 10(-8) per second for an electron density of 10(3) to 10(5) per cubic centimeter in the nebula. Under such conditions, the photo-ions formed may subsequently undergo further RETPI, catalyzed by intense He i and He ii radiation, which also gets enhanced in optically thick nebulae that contain enough helium.

  2. Non-Liouvillean ion injection via resonantly enhanced two-photon ionization

    NASA Astrophysics Data System (ADS)

    Knyazev, B. A.

    2004-03-01

    The charge-exchange method is now one of the main techniques for ion injection into accelerators and storage rings. The disadvantages of conventional methods, based on the atom or ion stripping in a material target, are emittance growth, energy straggling, and production of ions in many charge states. Recently suggested stripping methods based on direct photoionization require employment of hard-UV lasers, which still do not exist and must obviously be very bulky and expensive. An alternative method, suggested for injection of proton beams, employs excitation of the atom to 3p intermediate state with subsequent Lorentz ionization in a magnetic field gradient. This technique applies rigid requirements to laser characteristic and is not free of growing of the beam divergence. In this paper a variant of the stripping technique based on the resonantly enhanced two-photon ionization (RETPI) is considered. The technique allows ionization of singly charged ions of the elements from helium to bismuth. A variant of the technique can be used for proton injection. RETPI can be applied for both ion injection and stacking, as well as for diagnostics of ion beam characteristics on the orbit. Stripping efficiency can be about 100% for the singly charged ions having the singlet ground state and decreases for the other ions. Special methods for “cleaning” unwanted atomic states in such ions, that can provide high stripping efficiency, are discussed. Excimer lasers with very moderate parameters can be employed for implementation of this technique for almost all elements. Numerical examples show that for most of the singly charged ions and for hydrogen atom necessary laser-beam energy density is merely 0.5 8 J/cm2 for a 1m interaction region, and is 10times higher for several light ions.

  3. Investigation of some Rydberg states of ketene by two-photon resonance-enhanced multiphoton ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Shiliang; Shi, Yujun; Dénommée, Stéphane; Simard, Benoit; Lee, Yuan-Pern

    2003-10-01

    Rydberg states of CH2CO and CD2CO in the 54 000-72 000 cm-1 spectral range have been reinvestigated using two-photon resonance-enhanced multiphoton-ionization spectroscopy. Improved resolution and sensitivity has allowed for identifications of more Rydberg states than in previous work. Based on an analysis of rotational structures and quantum defects and a comparison with the results of theoretical calculations, transitions to the 3pz, 4py, 4pz, and 5py, three components of 4d, and two components of 4f Rydberg states with a ground-state ionic core (X˜ 2B1) are identified. Several transitions have been reassigned. Vibrational wave numbers indicate that the geometry of the [X˜ 2B1]3py(1A2) state is almost identical to that of the corresponding cation in its ground electronic state, with C2v symmetry, whereas that of the [X˜ 2B1]3px(1A1) state differs significantly from those of the neutral molecule and the cation in their ground states, consistent with previous quantum chemical calculations that indicated that the [X˜ 2B1]3px(1A1) state has Cs symmetry. The energy ordering of the three components of the 3p Rydberg states is found to be 3px<3py<3pz, in agreement with a previous theoretical prediction using the equation-of-motion coupled-cluster singles and doubles polarized basis set methods and a first-principles vibronic model simulation. Excitations of the vibrational modes of b1 (e.g., C=C=O out-of-plane bending, CH2 or CD2 wagging) and b2 symmetries (e.g., C=C=O in-plane bending) are observed in several Rydberg states of CH2CO and CD2CO.

  4. Probing Competitive Noncovalent Interactions: Resonance Enhanced Two-Photon Ionization (R2PI) Spectroscopy of Haloaromatic Clusters

    NASA Astrophysics Data System (ADS)

    Nyambo, Silver; Muzangwa, Lloyd; Uhler, Brandon; Reid, Scott A.

    2013-06-01

    Non-covalent interactions in bromobenzene have been studied here using resonance two-photon ionization (R2PI) spectroscopy combined with a linear TOF-mass spectrometer. Bromobenzene clusters were created in a supersonic expansion with helium as a carrier gas. The molecules were excited and ionized from the ground state in a two stage process. The general trend observed in the R2PI spectra of all the clusters is the broadness and a red-shift relative to the monomer absorption. Optimized dimer and trimer structures were calculated at the M06-2x/aug-cc-pVDZ level, which show that π-stacked and C-H/π interactions are most important in these clusters. TD-DFT calculations of the different cluster conformers have been carried out to assess the geometry changes active upon electronic excitation. The theoretical studies are helpful in explaining trends observed in the R2PI spectra.

  5. Slow-electron velocity-map imaging study of aniline via resonance-enhanced two-photon ionization method

    NASA Astrophysics Data System (ADS)

    Qu, Zehua; Qin, Zhengbo; Zheng, Xianfeng; Wang, Hui; Yao, Guanxin; Zhang, Xianyi; Cui, Zhifeng

    2017-02-01

    Slow electron velocity-map imaging (SEVI) of aniline has been investigated via two-color resonant-enhanced two-photo (1 + 1‧) ionization (2C-R2PI) method. A number of vibrational frequencies in the first excited state of neutral (S1) and 2B1 ground electronic state of cation (D0) have been accurately determined. In addition, photoelectron angular distributions (PADs) in the two-step transitions are presented and reveal a near threshold shape resonance in the ionization of aniline. The SEVI spectra taken via various S1 intermediate states provide the detailed vibrational structures of D0 state and directly deduce the accurate adiabatic ionization potential (IP) of 62,271 ± 6 cm- 1. Ab initio calculations excellently reproduce the experimental IP value (Theo. 62,242 cm- 1). For most vibrational modes, good agreement between theoretical and experimental frequencies in the S0 and D0 states of aniline is obtained to aid us to clearly assign vibrational modes. Especially, the vibrational frequencies calculated at the CASSCF level are much better consistent with experimental data than that obtained using the TDDFT and CIS methods.

  6. Slow-electron velocity-map imaging study of aniline via resonance-enhanced two-photon ionization method.

    PubMed

    Qu, Zehua; Qin, Zhengbo; Zheng, Xianfeng; Wang, Hui; Yao, Guanxin; Zhang, Xianyi; Cui, Zhifeng

    2017-02-15

    Slow electron velocity-map imaging (SEVI) of aniline has been investigated via two-color resonant-enhanced two-photo (1+1') ionization (2C-R2PI) method. A number of vibrational frequencies in the first excited state of neutral (S1) and (2)B1 ground electronic state of cation (D0) have been accurately determined. In addition, photoelectron angular distributions (PADs) in the two-step transitions are presented and reveal a near threshold shape resonance in the ionization of aniline. The SEVI spectra taken via various S1 intermediate states provide the detailed vibrational structures of D0 state and directly deduce the accurate adiabatic ionization potential (IP) of 62,271±6cm(-1). Ab initio calculations excellently reproduce the experimental IP value (Theo. 62,242cm(-1)). For most vibrational modes, good agreement between theoretical and experimental frequencies in the S0 and D0 states of aniline is obtained to aid us to clearly assign vibrational modes. Especially, the vibrational frequencies calculated at the CASSCF level are much better consistent with experimental data than that obtained using the TDDFT and CIS methods.

  7. Resonance-enhanced two-photon ionization mass spectroscopy of ephedrine: Indication for a state-selective fragmentation in a flexible molecule

    NASA Astrophysics Data System (ADS)

    Karaminkov, R.; Chervenkov, S.; Härter, P.; Neusser, H. J.

    2007-07-01

    The vibronic structure of the S 1 ← S 0 spectrum of ephedrine was measured by resonance-enhanced two-photon ionization spectroscopy with mass resolution under cold molecular beam conditions. The spectra recorded at four different mass channels, m/ z = 165 (parent), 58, and the hitherto unknown 71, 85 fragment ions show dissimilar vibronic fine structure and the observed mass pattern strongly depends on the selected intermediate vibrational state. This points to an intermediate state-selected process resulting in a different fragmentation mass pattern. Ab initio calculations at the MP2/6-311++G ∗∗ level demonstrate that the AG (a) conformer is more stable by 238 cm -1 than the next stable GG (a) conformer.

  8. High resolution UV resonance enhanced two-photon ionization spectroscopy with mass selection of biologically relevant molecules in the gas phase

    NASA Astrophysics Data System (ADS)

    Chervenkov, S.; Wang, P. Q.; Karaminkov, R.; Chakraborty, T.; Braun, Juergen E.; Neusser, Hans J.

    2005-04-01

    The high resolution Doppler-free resonance-enhanced two-photon ionization (R2PI) spectroscopy with mass selection of jet-cooled (2-12 K) molecular species is a powerful experimental method providing comprehensive information on both isolated molecules and molecular clusters. We have demonstrated for the first time that this technique can be applied to large molecules and provides detailed information on their conformational structure. It allows rotationally resolved (FWHM = 70 MHz) spectra of the vibronic bands of the S1<--S0 electronic transition of the studied molecular systems to be measured. A specially designed computer-assisted fitting routine based on genetic algorithms is used to determine their rotational constants in the ground and excited electronic states, respectively, and the transition moment ratio. To interpret the experimental information and to discriminate and unambiguously assign the observed approach to the study of the neurotransmitter molecule, ephedrine. The results elucidate the role of the intramolecular hydrogen bonds stabilizing the respective conformations and affecting their intrinsic properties.

  9. Resonance-enhanced two-photon ionization of helium using an Ar{sup +} mode-locked laser synchronized with VUV synchrotron radiation pulses

    SciTech Connect

    Lacoursiere, Jean; Meyer, Michael; Nahon, Laurent; Morin, Paul; Larzilliere, Michel

    1995-04-01

    We report a new experimental set-up consisting in the synchronization of 74.9094 MHz pulses from a mode-locked Ar{sup +} laser with 8.32 MHz pulses of vacuum ultraviolet (VUV) synchrotron radiation from the Super-ACO storage ring of the Laboratorie pour l'Utilisation du Rayonnement Electromagnetique (LURE). The capabilities of the set-up are demonstrated in a time-resolved pump-probe (VUV+visible) experiment in which free helium atoms are resonantly ionized via the short-lived 1s3p ({sup 1}P) state. This experiment allowed us to show the relevance of this technique for the investigation of nanosecond dynamics on gas phase species.

  10. State-selective preparation of A r2 + and K r2 + by resonantly enhanced two-photon double ionization via intermediate Rydberg states using high-order harmonics

    NASA Astrophysics Data System (ADS)

    Yamada, Kana; Iwasaki, Atsushi; Sato, Takahiro; Midorikawa, Katsumi; Yamanouchi, Kaoru

    2016-11-01

    Simultaneous two-electron emission processes of Ar induced by high-order harmonics of near-infrared femtosecond laser pulses were investigated by coincidence photoelectron spectroscopy. Two-photon double ionization processes via the 3 s 3 p6n p (n ˜25 ) intermediate resonances of Ar were observed, which selectively created the 3 s 3 p51P state of A r2 + . The similar double ionization processes were also observed in Kr. The selective creation indicates that the core electron configuration of the doubly ionized state tends to be the same as that of the intermediate state and that the emitted two electrons tend to form the singlet state.

  11. Suppression of two-photon resonantly enhanced nonlinear processes in extended media

    SciTech Connect

    Garrett, W.R.; Moore, M.A.; Payne, M.G.; Wunderlich, R.K.

    1988-11-01

    On the basis of combined experimental and theoretical studies of nonlinear processes associated with two-photon excitations near 3d and 4d states in Na, we show how resonantly enhanced stimulated hyper-Raman emission, parametric four-wave mixing processes and total resonant two-photon absorption can become severely suppressed through the actions of internally generated fields on the total atomic response in extended media. 7 refs., 3 figs.

  12. Intracluster reactions in phenylacetylene ammonia clusters initiated through resonant enhanced ionization

    SciTech Connect

    Breen, J.J.; Tzeng, W.; Kilgore, K.; Keesee, R.G.; Castleman A.W. Jr.

    1989-01-01

    Protonated ammonia clusters of specific size are observed to form following the resonant enhanced ionization of phenylacetylene--ammonia clusters PAx(NH/sub 3/)/sub n/ in the 0/sup 0//sub 0/ region of the S/sub 1/--S/sub 0/ transition of the (unclustered) PA. The resonance enhanced absorption of two photons, approx. =8.8 eV total energy, are found to cause intracluster reactions for ngreater than or equal to5. The findings imply that the adiabatic ionization potential of (NH/sub 3/)/sub 4/ is greater than 8.8 eV, while that of (NH/sub 3/)/sub 5/ is (slightly) less.

  13. Photoelectron angular distributions from two-photon ionizations of atoms

    NASA Astrophysics Data System (ADS)

    Haber, Louis Hamilton

    Photoelectron angular distributions provide detailed information about interferences between different quantum pathways of photoionization. Measurements of photoelectron energies and angular distributions from two-color two-photon ionizations of atoms using ultrashort pulses of extreme ultraviolet and optical light are performed using a novel, homebuilt experimental instrument. The setup is composed of an amplified femtosecond laser system, a high-order harmonic generation source, and an interaction region with photoelectron velocity map imaging The experimental temporal resolution is determined to be approximately 100 fs. Two different types of two-photon ionizations are investigated. Photoelectron angular distributions from resonant two-photon ionizations of helium are measured using the 15th high-order harmonic to excite from the ground state to either the 1s3p 1P1 state at 23.1 eV or to the 1s4p 1 P1 state at 23.7 eV and either 800, 400, or 267 nm to ionize. The anisotropy parameters allow for the determination of the energy-dependent ratios of radial dipole matrix elements and the phase shift differences between the S and D partial waves. Using available total cross section measurements, the absolute partial cross sections of the 1s3p1P 1 state are obtained, providing the complete information on photoionization. The experimental results are in excellent agreement with theoretical predictions using the one-electron model. Additional experiments are aimed at studying atomic free-free transitions. Two-color two-photon above threshold ionizations of helium and argon are investigated using selected high-order harmonics and perturbative infrared dressing fields. The measured anisotropy parameters and cross section ratios of the positive and negative above threshold ionization sidebands are compared to theoretical predictions using second-order perturbation theory and the soft-photon approximation. In general, deviations between the experimental results and the

  14. Resonance Enhanced Multiphoton Ionization (rempi) Spectroscopy of Weakly Bound Complexes

    NASA Astrophysics Data System (ADS)

    Muzangwa, Lloyd; Nyambo, Silver; Uhler, Brandon; Reid, Scott A.

    2012-06-01

    We have recently implemented Resonance Enhanced Multiphoton Ionization (REMPI) spectroscopy in our laboratory as a spectroscopic probe of transient species. We will report on initial gas-phase studies of the spectra of weakly bound van der Waals and halogen bonded complexes involving aromatic organic donors. The complexes are formed in the rarified environment of a supersonic molecular beam, which is skimmed prior to passing into the differentially pumped flight tube of a linear time-of-flight mass spectrometer. Ionization is initiated both by 1+1 and 1+1' REMPI schemes; the latter is used to minimize fragmentation. Our initial studies have examined van der Waals and halogen bonded complexes involving the phenol and toluene chromophores. Progress in the coupling of a discharge source into this apparatus will also be discussed.

  15. Plasma induced by resonance enhanced multiphoton ionization in inert gas

    SciTech Connect

    Shneider, Mikhail N.; Zhang Zhili; Miles, Richard B.

    2007-12-15

    We present a detailed model for the evolution of resonance enhanced multiphoton ionization (REMPI) produced plasma during and after the ionizing laser pulse in inert gas (argon, as an example) at arbitrary pressures. Our theory includes the complete process of the REMPI plasma generation and losses, together with the changing gas thermodynamic parameters. The model shows that the plasma expansion follows a classical ambipolar diffusion and that gas heating results in a weak shock or acoustic wave. The gas becomes involved in the motion not only from the pressure gradient due to the heating, but also from the momentum transfer from the charged particles to gas atoms. The time dependence of the total number of electrons computed in theory matches closely with the results of coherent microwave scattering experiments.

  16. Simultaneous resonant enhanced multiphoton ionization and electron avalanche ionization in gas mixtures

    SciTech Connect

    Shneider, Mikhail N.; Zhang Zhili; Miles, Richard B.

    2008-07-15

    Resonant enhanced multiphoton ionization (REMPI) and electron avalanche ionization (EAI) are measured simultaneously in Ar:Xe mixtures at different partial pressures of mixture components. A simple theory for combined REMPI+EAI in gas mixture is developed. It is shown that the REMPI electrons seed the avalanche process, and thus the avalanche process amplifies the REMPI signal. Possible applications are discussed.

  17. Flame temperature measurements by radar resonance-enhanced multiphoton ionization of molecular oxygen.

    PubMed

    Wu, Yue; Sawyer, Jordan; Zhang, Zhili; Adams, Steven F

    2012-10-01

    Here we report nonintrusive local rotational temperature measurements of molecular oxygen, based on coherent microwave scattering (radar) from resonance-enhanced multiphoton ionization (REMPI) in room air and hydrogen/air flames. Analyses of the rotational line strengths of the two-photon molecular oxygen C(3)Π(v=2)←X(3)Σ(v'=0) transition have been used to determine the hyperfine rotational state distribution of the ground X(3)Σ(v'=0) state. Rotationally resolved 2+1 REMPI spectra of the molecular oxygen C(3)Π(v=2)←X(3)Σ(v'=0) transition at different temperatures were obtained experimentally by radar REMPI. Rotational temperatures have been determined from the resulting Boltzmann plots. The measurements in general had an accuracy of ~±60 K in the hydrogen/air flames at various equivalence ratios. Discussions about the decreased accuracy for the temperature measurement at elevated temperatures have been presented.

  18. Resonant enhanced multiphoton ionization studies of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Dixit, S. N.; Levin, D.; Mckoy, V.

    1987-01-01

    In resonant enhanced multiphoton ionization (REMPI), an atom absorbs several photons making a transition to a resonant intermediate state and subsequently ionizing out of it. With currently available tunable narrow-band lasers, the extreme sensitivity of REMPI to the specific arrangement of levels can be used to selectively probe minute amounts of a single species (atom) in a host of background material. Determination of the number density of atoms from the observed REMPI signal requires a knowledge of the multiphoton ionization cross sections. The REMPI of atomic oxygen was investigated through various excitation schemes that are feasible with available light sources. Using quantum defect theory (QDT) to estimate the various atomic parameters, the REMPI dynamics in atomic oxygen were studied incorporating the effects of saturation and a.c. Stark shifts. Results are presented for REMPI probabilities for excitation through various 2p(3) (4S sup o) np(3)P and 2p(3) (4S sup o) nf(3)F levels.

  19. Two-photon ionization and three-photon above-threshold ionization of argon

    SciTech Connect

    Bouhal, A.; Hamoniaux, G.; Mysyrowicz, A.; Antonetti, A.; Breger, P.; Agostini, P.; Constantinescu, R.C.; Muller, H.G.; DiMauro, L.F.

    1998-03-01

    Studies of nonlinear laser-matter interaction have been so far limited to wavelengths from the near ultraviolet to infrared, because of the low brightness of currently available sources outside this range. However nonlinear processes in the VUV/Soft X-ray domain would initiate multiphoton innershell spectroscopy, XUV nonlinear optics and applications of such processes to metrology. The probability of multiphoton transitions decreases rapidly with the number of photons involved. A typical two-photon bound-free transition has a rate of the order of .1 ps{sup {minus}1} at 10{sup 12} W.cm{sup {minus}2} and scales as the square of the intensity. Such an intensity is therefore required to saturate a two-photon transition with a 100 fs pulse. This is difficult to achieve with the present state-of-the-art techniques for producing intense XUV pulses. To the authors knowledge, only two cases of such transitions have been reported so far. The first one is a two-photon ionization of argon by the third harmonic of a KrF laser. Since the photon energy (15 eV) is just below the ionization energy (15.75 eV) for argon, the transition is quasi-resonant. The second case is a two-photon ionization of helium by the 9th harmonic of a Ti:S laser. In the latter case an autocorrelation measurement of the harmonic pulse has been reported. In the present work, the authors report on two-photon ionization of argon at 133 nm (9.3 eV) from the third harmonic of a frequency doubled Ti:S laser, and a three-photon above-threshold ionization involving two 9.3 eV photons and one 3.1 eV photon.

  20. Competition between two-photon-resonant three-photon ionization and four-wave mixing in Xe

    SciTech Connect

    Nagai, Hidekazu; Nakanaga, Taisuke

    2011-12-15

    Competitive inhibition of a resonance enhanced multiphoton ionization process by a resonant four-wave mixing has been observed in Xe atoms. When an intense IR (1064 nm) laser was applied to a sample of Xe which was also being irradiated by a UV laser tuned to the two-photon absorption line of Xe, the two-photon-resonant three-photon ionization signals decreased with increasing IR laser power. This phenomenon is dependent on the resonant states of Xe and the polarization of the two laser beams. Three 6s excited states [5/2]{sub 2}, [3/2]{sub 2}, and [1/2]{sub 0} were examined. At the [1/2]{sub 0} resonant state, the ion signals were not decreased but slightly increased with the increase of the IR laser power. No suppression of the ion signal was observed at the [5/2]{sub 2} resonant state, when the polarization directions of the lasers were perpendicular to each other. The result of the polarization dependence reflects the selection rules of four-wave mixing. A simple rate equation analysis including the contribution of two-photon ionization from the [1/2]{sub 0} state by the IR laser well represents the IR laser-power dependence of the ion signal.

  1. Photofragmentation, state interaction, and energetics of Rydberg and ion-pair states: Resonance enhanced multiphoton ionization of HI

    SciTech Connect

    Hróðmarsson, Helgi Rafn; Wang, Huasheng; Kvaran, Ágúst

    2014-06-28

    Mass resolved resonance enhanced multiphoton ionization data for hydrogen iodide (HI), for two-photon resonance excitation to Rydberg and ion-pair states in the 69 600–72 400 cm{sup −1} region were recorded and analyzed. Spectral perturbations due to homogeneous and heterogeneous interactions between Rydberg and ion-pair states, showing as deformations in line-positions, line-intensities, and line-widths, were focused on. Parameters relevant to photodissociation processes, state interaction strengths and spectroscopic parameters for deperturbed states were derived. Overall interaction and dynamical schemes to describe the observations are proposed.

  2. Particle modeling of microplasma generated by resonance enhanced multiphoton ionization

    NASA Astrophysics Data System (ADS)

    Tholeti, Siva Sashank

    Resonance-enhanced multiphoton ionization (REMPI) is a technique applied to the spectroscopy of atoms. The REMPI technique typically involves a resonant single or multiple photon absorption to an electronically excited intermediate state followed by another photon which ionizes the atom. Rayleigh scattering of REMPI plasma has given rise to a non-intrusive, time accurate measurement of electron formation and loss, which lead to many applications viz. trace species detection and micro-plasma diagnostics. It is very important to quantify the expansion process and the evolution of energy of electrons and ions. The operation scale of this process is in microns and non continuum nature of the process lead to the use of PIC/MCC scheme to compu- tationally model REMPI technique. This work attempts to understand and analyze the processes taking place during the expansion of REMPI plasma computationally using the PIC/MCC scheme. One dimensional and two dimensional approximations are considered to analyze the REMPI plasma expansion in Argon gas generated by a laser with a focal shape of a prolate ellipsoid. The expansion of the plasma is found to be very sensitive to the initial velocity distribution of the electrons. REMPI plasma expansion is shown to be ambipolar in nature, with the radial expansion more predominant than axial expansion, hence requiring the 2D model. Electron energy distribution functions(EEDFs) are found at various radial locations along with the corresponding mean energies. The deviation of the EEDFs from that of equilibrium Maxwell-Boltzmann energy distribution is presented both qualitatively and quanti- tatively, indicating the predominant processes at various instances in time.

  3. Two-photon ionization of atomic hydrogen with elliptically polarized light

    NASA Technical Reports Server (NTRS)

    Kassaee, A.; Rustgi, M. L.; Long, S. A. T.

    1988-01-01

    The theory of two-photon ionization of a hydrogenic state in the nonrelativistic dipole approximation is generalized for elliptically polarized light. An application to the metastable 2S state of atomic hydrogen is made. Significant differences in the angular distribution of the outgoing electrons are found depending upon the polarization of the photons. It is claimed that two-photon ionization employing elliptically polarized photons from lasers may provide an additional test for the theories of multiphoton ionization.

  4. Modulation of attosecond beating in resonant two-photon ionization.

    PubMed

    Jiménez-Galán, Álvaro; Argenti, Luca; Martín, Fernando

    2014-12-31

    We present a theoretical study of the photoelectron attosecond beating due to interference of two-photon transitions in the presence of autoionizing states. We show that, as a harmonic traverses a resonance, both the phase shift and frequency of the sideband beating significantly vary with photon energy. Furthermore, the beating between two resonant paths persists even when the pump and the probe pulses do not overlap, thus providing a nonholographic interferometric means to reconstruct coherent metastable wave packets. We characterize these phenomena by means of a general analytical model that accounts for the effect of both intermediate and final resonances on two-photon processes. The model predictions are in excellent agreement with those of accurate ab initio calculations for the helium atom in the region of the N=2 doubly excited states.

  5. Modulation of Attosecond Beating in Resonant Two-Photon Ionization

    NASA Astrophysics Data System (ADS)

    Jiménez-Galán, Álvaro; Argenti, Luca; Martín, Fernando

    2014-12-01

    We present a theoretical study of the photoelectron attosecond beating due to interference of two-photon transitions in the presence of autoionizing states. We show that, as a harmonic traverses a resonance, both the phase shift and frequency of the sideband beating significantly vary with photon energy. Furthermore, the beating between two resonant paths persists even when the pump and the probe pulses do not overlap, thus providing a nonholographic interferometric means to reconstruct coherent metastable wave packets. We characterize these phenomena by means of a general analytical model that accounts for the effect of both intermediate and final resonances on two-photon processes. The model predictions are in excellent agreement with those of accurate ab initio calculations for the helium atom in the region of the N =2 doubly excited states.

  6. Resonance enhanced multiphoton ionization spectroscopy of carbonyl sulphide

    NASA Astrophysics Data System (ADS)

    Morgan, Ross A.; Orr-Ewing, Andrew J.; Ascenzi, Daniela; Ashfold, Michael N. R.; Buma, Wybren Jan; Scheper, Connie R.; de Lange, Cornelis A.

    1996-08-01

    Rydberg excited states of the OCS molecule in the energy range 70500-86000 cm-1 have been investigated via the two and three photon resonance enhancements they provide in the mass resolved multiphoton ionization (MPI) spectrum of a jet-cooled sample of the parent molecule. Spectral interpretation has been assisted by companion measurements of the kinetic energies of the photoelectrons that accompany the various MPI resonances. The present study supports the earlier conclusions of Weinkauf and Boesl [J. Chem. Phys. 98, 4459 (1993)] regarding five Rydberg origins in the 70500-73000 cm-1 energy range, attributable to, respectively, states of 3Π, 1Π, 3Δ, 1Δ and 1Σ+ symmetry arising from the 4pλ←3π orbital promotion. We also identify a further 21 Rydberg origins at higher energies. These partition into clumps with quantum defects ca. 3.5 and 4.5, which we associate with the orbital promotions npλ←3π (n=5,6), and others with near integer quantum defect which are interpretable in terms of excitation to s,d and (possibly) f Rydberg orbitals. We also identify MPI resonances attributable to CO(X 1Σ+) fragments and to S atoms in both their ground (3P) and excited (1D) electronic states. Analysis of the former resonances confirms that the CO(X) fragments resulting from one photon dissociation of OCS at excitation wavelengths ca. 230 nm are formed with a highly inverted, bimodal rotational state population distribution, whilst the latter are consistent with previous reports of the wavelength dependence for forming ground and excited state S atoms in the near uv photolysis of OCS.

  7. Photoelectron distribution of nonresonant two-photon ionization of neutral atoms

    NASA Astrophysics Data System (ADS)

    Hofbrucker, J.; Volotka, A. V.; Fritzsche, S.

    2017-07-01

    Photoelectron angular distributions following the nonresonant two-photon K -shell ionization of neutral atoms are studied theoretically. Using the independent particle approximation and relativistic second-order perturbation theory, the contributions of screening and relativistic effects to the photoelectron angular distribution are evaluated. A simple nonrelativistic expression is presented for the angle-differential cross section in dipole approximation for two-photon ionization by elliptically polarized photons, and its limitations are analyzed numerically. Moreover, we show that screening effects of the inactive electrons can significantly affect the photoelectron distributions and can also lead to a strong elliptical dichroism. Numerical results are presented for the case of two-photon K -shell ionization of neutral Ne, Ge, Xe, and U atoms.

  8. Relativistic calculations of the nonresonant two-photon ionization of neutral atoms

    NASA Astrophysics Data System (ADS)

    Hofbrucker, J.; Volotka, A. V.; Fritzsche, S.

    2016-12-01

    The nonresonant, two-photon, one-electron ionization of neutral atoms is studied theoretically in the framework of relativistic second-order perturbation theory and independent particle approximation. In particular, the importance of relativistic and screening effects in the total two-photon ionization cross section is investigated. Detailed computations have been carried out for the K -shell ionization of neutral Ne, Ge, Xe, and U atoms. The relativistic effects significantly decrease the total cross section; for the case of U, for example, they reduce the total cross section by a factor of two. Moreover, we have found that the account for the screening effects of the remaining electrons leads to occurrence of an unexpected minimum in the total cross section at the total photon energies equal to the ionization threshold; for the case of Ne, for example, the cross section drops there by a factor of three.

  9. Spectroscopic Study of ThCl+ by Two-Photon Ionization

    NASA Astrophysics Data System (ADS)

    Bartlett, Joshua; VanGundy, Robert A.; Heaven, Michael; Peterson, Kirk

    2016-06-01

    Despite the irreplaceable role experimental data plays for evaluating the performance of computational predictions, diatomic actinide species have not received much spectroscopic attention. As an early actinide element, thorium-containing species are ideal candidates for these types of studies. The electronic structure is expected to be relatively simple compared to later actinides, and therefore allows straightforward assessment of calculations. Here, we have studied ThCl+ for the first time via resonant two-photon ionization of jet-cooled ThCl produced by laser ablation of the metal reacted with dilute Cl2. Laser-induced Fluorescence (LIF) spectra have been recorded for the neutral molecule from 16000 - 23500 cm-1 in search of a suitable intermediate state for subsequent two-photon ionization experiments. Monochromator dispersion of the fluorescence has recovered the ground state vibration and anharmonic constants of ThCl. Resonant Two-Photon Ionization (R2PI) within a time-of-flight mass spectrometer was used to confirm ThCl production, and Pulsed Field Ionization Zero Kinetic Energy photoelectron spectroscopy (PFI-ZEKE) has been performed to identify the ionization energy as well as several of the low-lying states of the ThCl+ molecule. These constants have been predicted at the CASPT2 and CCSD(T) levels of theory, and a discussion of the calculations' performance will be presented alongside the recorded spectra.

  10. Resonance enhanced multiphoton ionization spectra of molecules and molecular fragments. Technical report, January 1990--December 1990

    SciTech Connect

    1997-07-01

    The objective of our effort is to carry out theoretical studies of resonance enhanced multiphoton ionization processes in molecules and molecular fragments. These studies are designed to provide a quantitatively robust analysis and prediction of key spectral features of interest in several ongoing experimental studies and applications of this technique.

  11. Two-photon double ionization of the helium atom by ultrashort pulses

    SciTech Connect

    Palacios, Alicia; Horner, Daniel A; Rescigno, Thomas N; McCurdy, C William

    2010-05-14

    Two-photon double ionization of the helium atom was the subject of early experiments at FLASH and will be the subject of future benchmark measurements of the associated electron angular and energy distributions. As the photon energy of a single femtosecond pulse is raised from the threshold for two-photon double ionization at 39.5 eV to beyond the sequential ionization threshold at 54.4 eV, the electron ejection dynamics change from the highly correlated motion associated with nonsequential absorption to the much less correlated sequential ionization process. The signatures of both processes have been predicted in accurate \\textit{ab initio} calculations of the joint angular and energy distributions of the electrons, and those predictions contain some surprises. The dominant terms that contribute to sequential ionization make their presence apparent several eV below that threshold. In two-color pump probe experiments with short pulses whose central frequencies require that the sequential ionization process necessarily dominates, a two-electron interference pattern emerges that depends on the pulse delay and the spin state of the atom.

  12. Angular distributions in two-colour two-photon ionization of He

    NASA Astrophysics Data System (ADS)

    Rey, H. F.; van der Hart, H. W.

    2014-11-01

    We present R-Matrix with time dependence (RMT) calculations for the photoionization of helium irradiated by an EUV laser pulse and an overlapping IR pulse with an emphasis on the anisotropy parameters of the sidebands generated by the dressing laser field. We investigate how these parameters depend on the amount of atomic structure included in the theoretical model for two-photon ionization. To verify the accuracy of the RMT approach, our theoretical results are compared with the experiment.

  13. Electronic spectroscopy of large van der waals molecules by resonant two-photon ionization

    NASA Astrophysics Data System (ADS)

    Leutwyler, Samuel; Even, Uzi; Jortner, Joshua

    1982-03-01

    Tunable laser two-photon ionization of large van der Waals molecules, combined with time-of-flight mass spectroscopy. was applied to the identification of the electronic origin and of some low vibrational excitations of the S 0 — S 1 electronic transition of fluorene·Ar 1, fluorene·Ar 2 and fluorene·Kr 1 produced in supersonic expansions.

  14. Perturbative calculation of two-photon double electron ionization of helium

    NASA Astrophysics Data System (ADS)

    Ivanov, I. A.; Kheifets, A. S.

    2008-05-01

    We report the total integrated cross-section (TICS) of two-photon double ionization of helium in the photon energy range from 40 to 54 eV. We compute the TICS in the lowest order perturbation theory (LOPT) using the length and Kramers-Henneberger gauges of the electromagnetic interaction. Our findings indicate that the LOPT gives results for the TICS in agreement with our earlier non-perturbative calculations.

  15. Two-photon double ionization of neon using an intense attosecond pulse train

    NASA Astrophysics Data System (ADS)

    Manschwetus, B.; Rading, L.; Campi, F.; Maclot, S.; Coudert-Alteirac, H.; Lahl, J.; Wikmark, H.; Rudawski, P.; Heyl, C. M.; Farkas, B.; Mohamed, T.; L'Huillier, A.; Johnsson, P.

    2016-06-01

    We present a demonstration of two-photon double ionization of neon using an intense extreme ultraviolet (XUV) attosecond pulse train (APT) in a photon energy regime where both direct and sequential mechanisms are allowed. For an APT generated through high-order harmonic generation (HHG) in argon we achieve a total pulse energy close to 1 μ J , a central energy of 35 eV, and a total bandwidth of ˜30 eV. The APT is focused by broadband optics in a neon gas target to an intensity of 3 ×1012W cm-2 . By tuning the photon energy across the threshold for the sequential process the double ionization signal can be turned on and off, indicating that the two-photon double ionization predominantly occurs through a sequential process. The demonstrated performance opens up possibilities for future XUV-XUV pump-probe experiments with attosecond temporal resolution in a photon energy range where it is possible to unravel the dynamics behind direct versus sequential double ionization and the associated electron correlation effects.

  16. Photo-ionization probability of 3+1 resonance enhanced multi-photon process

    NASA Astrophysics Data System (ADS)

    Zhang, Guiyin; Li, Mengjun; Jin, Yidong

    2012-11-01

    Analytic expression of the ionization probability about 3+1 resonance enhanced multi-photon ionization (REMPI) process is deduced with the theory of rate equation, which implies the interaction of photon and material. Based on the expressions, the influence of laser intensity, laser pulse duration and spontaneous radiation lifetime on the ionization probability is analyzed theoretically. It is found that the ionization probability increases with laser intensity and laser pulse duration until gets to saturation. After that, the ionization probability will oscillate around the saturation value if laser intensity increases further. The amplitude of oscillation increases with laser intensity at first, and then it will decrease even get to zero after a maximum peak comes out. We attribute the appearance of the oscillation to the phenomena of quantum coherence caused by the splitting of energy level in strong laser field. As to the fact that the ionization probability becomes to zero with the increase of laser intensity, it indicates that laser intensity is strong enough so as to make the neutral particles getting to the region of ionization suppression. It is also found that the variation of ionization probability with spontaneous radiation lifetime is far smaller than the one with ionization rate. So the influence of the spontaneous radiation lifetime on ionization probability could be ignored.

  17. Electron correlation in two-photon double ionization of helium from attosecond to FEL pulses

    SciTech Connect

    Collins, Lee

    2009-01-01

    We investigate the role of electron correlation in the two-photon double ionization of helium for ultrashort pulses in the extreme ultraviolet (XUV) regime with durations ranging from a hundred attoseconds to a few femtoseconds. We perform time-dependent ab initio calculations for pulses with mean frequencies in the so-called 'sequential' regime ({Dirac_h}{omega} > 54.4 eV). Electron correlation induced by the time correlation between emission events manifests itself in the angular distribution of the ejected electrons, which strongly depends on the energy sharing between them. We show that for ultrashort pulses two-photon double ionization probabilities scale non-uniformly with pulse duration depending on the energy sharing between the electrons. Most interestingly we find evidence for an interference between direct ('nonsequential') and indirect ('sequential') double photoionization with intermediate shake-up states, the strength of which is controlled by the pulse duration. This observation may provide a route towards measuring the pulse duration of x-ray free-electron laser (XFEL) pulses.

  18. Interference effects in one- and two-photon ionization by femtosecond VUV pulses

    NASA Astrophysics Data System (ADS)

    Gryzlova, Elena V.; Staroselskaya, Ekaterina I.; Grum-Grzhimailo, Alexei N.; Venzke, Joel; Bartschat, Klaus

    2015-05-01

    Investigations of coherent control of atomic and molecular processes have rapidly developed since the advent of coherent light sources such as X-ray free electron lasers (XFELs) and achievements in high harmonic generation. In practice, radiation from XFELs contains a small fraction of the second harmonic, which is difficult to filter out but can strongly influence experimental data on the two-photon ionization process, such as the angular distribution. Specifically, the direct first-order second-harmonic ionization process may interfere with, and possibly even dominate a second-order two-photon process caused by the fundamental. While this interference has been investigated in the optical regime with many-cycle pulses, possible effects due to short pulses, as well as a physical intermediate resonance state that may serve as a stepping stone for the second-order process, need a careful study for particular experimental conditions. Here we consider the photoionization of atomic hydrogen for photon energies near the excitation energy of the 2p state (0.375 a.u. or 121.6 nm). We compare results obtained from a direct numerical solution of the time-dependent Schrödinger equation and second-order perturbation theory. This work is supported by the United States National Science Foundation under grant No. PHY-1430245 and the XSEDE allocation PHY-090031, and by the Russian Foundation for Basic Research under Grant No. 12-02-01123.

  19. O{sub 2} rotational temperature measurements in an atmospheric air microdischarge by radar resonance-enhanced multiphoton ionization

    SciTech Connect

    Sawyer, Jordan; Wu, Yue; Zhang, Zhili; Adams, Steven F.

    2013-06-21

    Nonintrusive spatially resolved rotational temperature measurements in an atmospheric air microdischarge are presented. The measurements were based on coherent microwave Rayleigh scattering (Radar) from resonance-enhanced multiphoton ionization of molecular oxygen. The open air DC microdischarge source operated in a stable 'normal-glow' mode and pin-to-pin electrodes spaced 1.3 mm apart. The second harmonic of a tunable dye laser beam was focused between the two electrodes and scanned between 286 and 288 nm. Coherent microwave Rayleigh scattering was used to collect the two-photon rotational spectra of O{sub 2} at C{sup 3}{Pi}(v = 2) Leftwards-Arrow X{sup 3}{Sigma}(v Prime = 0) transitions. The Boltzmann plots from analyses of the O{sub 2} rotational lines determined local rotational temperatures at various axial locations between the electrodes. The molecular oxygen rotational temperature varied from {approx}1150 K to {approx}1350 K within the discharge area. The measurements had an accuracy of {approx}{+-}50 K.

  20. Resonance-Enhanced Multiphoton Ionization Mass Spectrometry (REMPI-MS): Applications for Process Analysis

    NASA Astrophysics Data System (ADS)

    Streibel, Thorsten; Zimmermann, Ralf

    2014-06-01

    Process analysis is an emerging discipline in analytical sciences that poses special requirements on analytical techniques, especially when conducted in an online manner. Mass spectrometric methods seem exceedingly suitable for this task, particularly if a soft ionization method is applied. Resonance-enhanced multiphoton ionization (REMPI) in combination with time-of-flight mass spectrometry (TOFMS) provides a selective and sensitive means for monitoring (poly)aromatic compounds in process flows. The properties of REMPI and various variations of the ionization process are presented. The potential of REMPI for process analysis is highlighted with several examples, and drawbacks of the method are also noted. Applications of REMPI-TOFMS for the detection and monitoring of aromatic species in a large variety of combustion processes comprising flames, vehicle exhaust, and incinerators are discussed. New trends in technical development and combination with other analytical methods are brought forward.

  1. Resonance-enhanced multiphoton ionization mass spectrometry (REMPI-MS): applications for process analysis.

    PubMed

    Streibel, Thorsten; Zimmermann, Ralf

    2014-01-01

    Process analysis is an emerging discipline in analytical sciences that poses special requirements on analytical techniques, especially when conducted in an online manner. Mass spectrometric methods seem exceedingly suitable for this task, particularly if a soft ionization method is applied. Resonance-enhanced multiphoton ionization (REMPI) in combination with time-of-flight mass spectrometry (TOFMS) provides a selective and sensitive means for monitoring (poly)aromatic compounds in process flows. The properties of REMPI and various variations of the ionization process are presented. The potential of REMPI for process analysis is highlighted with several examples, and drawbacks of the method are also noted. Applications of REMPI-TOFMS for the detection and monitoring of aromatic species in a large variety of combustion processes comprising flames, vehicle exhaust, and incinerators are discussed. New trends in technical development and combination with other analytical methods are brought forward.

  2. Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of p-chlorofluorobenzene

    NASA Astrophysics Data System (ADS)

    Tuttle, William D.; Gardner, Adrian M.; Wright, Timothy G.

    2017-09-01

    The S1 ← S0 (A˜1 B2 ← X˜1 A1) electronic transition of para-chlorofluorobenzene has been investigated using resonance-enhanced multiphoton ionization (REMPI) spectroscopy. Assignment of the vibrational structure has been achieved by comparison with corresponding spectra of related molecules, via quantum chemical calculations, and via shifts in bands between the spectra of the 35Cl and 37Cl isotopologues. In addition, we have also partially reassigned a previously-published spectrum of para-dichlorobenzene.

  3. Direct Analysis of Xanthine Stimulants in Archaeological Vessels by Laser Desorption Resonance Enhanced Multiphoton Ionization.

    PubMed

    Owens, Shawn C; Berenbeim, Jacob A; Ligare, Marshall R; Gulian, Lisa E; Siouri, Faady M; Boldissar, Samuel; Tyson-Smith, Stuart; Wilson, Gregory; Ford, Anabel; de Vries, Mattanjah S

    2017-03-07

    Resonance enhanced multiphoton ionization spectroscopy (REMPI) generates simultaneous vibronic spectroscopy and fragment free mass spectrometry to identify molecules within a complex matrix. We combined laser desorption with REMPI spectroscopy to study organic residues within pottery sherds from Maya vessels (600-900 CE) and Mississippian vessels (1100-1200 CE), successfully detecting three molecular markers, caffeine, theobromine, and theophylline, associated with the use of cacao. This analytical approach provides a high molecular specificity, based on both wavelength and mass identification. At the same time, the high detection limit allows for direct laser desorption from sherd scrapings, avoiding the need for extracting organic constituents from the sherd matrix.

  4. Resonant two-photon ionization spectroscopy of Al atoms and dimers solvated in helium nanodroplets

    SciTech Connect

    Krasnokutski, Serge A.; Huisken, Friedrich

    2015-02-28

    Resonant two-photon ionization (R2PI) spectroscopy has been applied to investigate the solvation of Al atoms in helium droplets. The R2PI spectra reveal vibrational progressions that can be attributed to Al–He{sub n} vibrations. It is found that small helium droplets have very little chance to pick up an aluminum atom after collision. However, the pick-up probability increases with the size of the helium droplets. The absorption band that is measured by monitoring the ions on the mass of the Al dimer is found to be very little shifted with respect to the Al monomer band (∼400 cm{sup −1}). However, using the same laser wavelength, we were unable to detect any Al{sub n} photoion with n larger than two.

  5. Resonant two-photon ionization spectroscopy of Al atoms and dimers solvated in helium nanodroplets.

    PubMed

    Krasnokutski, Serge A; Huisken, Friedrich

    2015-02-28

    Resonant two-photon ionization (R2PI) spectroscopy has been applied to investigate the solvation of Al atoms in helium droplets. The R2PI spectra reveal vibrational progressions that can be attributed to Al-He(n) vibrations. It is found that small helium droplets have very little chance to pick up an aluminum atom after collision. However, the pick-up probability increases with the size of the helium droplets. The absorption band that is measured by monitoring the ions on the mass of the Al dimer is found to be very little shifted with respect to the Al monomer band (∼400 cm(-1)). However, using the same laser wavelength, we were unable to detect any Al(n) photoion with n larger than two.

  6. Cross sections for non-sequential two-photon double ionization of helium

    NASA Astrophysics Data System (ADS)

    Feist, Johannes; Nagele, Stefan; Pazourek, Renate; Persson, Emil; Burgdörfer, Joachim; Schneider, Barry; Collins, Lee

    2008-05-01

    The generalized cross sections for non-sequential two-photon double ionization of helium at photon energies from 39.5,V to 54.4,V have been the subject of several recent theoretical studies. Quantitative agreement between the different approaches has not yet been reached. In this contribution, we present converged results for the total integrated and triply differential cross sections for the above process, which are based on the direct integration of the time-dependent Schr"odinger equation. We compare our data with calculations from other authors and investigate to what extent electronic correlation in the representation of the double continuum affects the cross sections. We also study the influence of the pulse shape on the value of the cross sections extracted from time-dependent approaches.

  7. Resonant two-photon mass-analyzed threshold ionization spectroscopy of 1-fluoronaphthalene and 2-fluoronaphthalene

    NASA Astrophysics Data System (ADS)

    Tzeng, Sheng Yuan; Wu, Jui Yang; Zhang, Shudong; Tzeng, Wen Bih

    2012-11-01

    We applied the resonant two-photon mass-analyzed threshold ionization (MATI) technique to record the cation spectra of 1-fluoronaphthalene (1FN) and 2-fluoronaphthalene (2FN) by ionizing via several intermediate vibronic states. The adiabatic ionization energies of 1FN and 2FN are found to be 66 194 and 66 771 ± 5 cm-1, respectively. Distinct MATI bands resulting from in-plane ring deformation are found at 437, 517, 703, and 779 cm-1 for 1FN; and 286, 455, 494, 764, and 1031 cm-1 for 2FN. Frequencies of these modes are slightly greater than the corresponding ones in the vibronic spectra. This indicates that the molecular geometry in the cationic D0 state is slightly more rigid than that in the neutral S1 state. Comparing the present experimental data with those of naphthalene suggests that the frequency difference of each mode depends on the vibrational pattern, location of the F atom, and degree of the F atom involved in the overall vibration.

  8. Resonantly enhanced multiphoton ionization under XUV FEL radiation: a case study of the role of harmonics

    NASA Astrophysics Data System (ADS)

    Nikolopoulos, G. M.; Lambropoulos, P.

    2015-12-01

    We provide a detailed quantitative study of the possible role of a small admixture of harmonics on resonant two-photon ionization. The motivation comes from the occasional presence of 2nd and 3rd harmonics in FEL radiation. We obtain the dependence of ionic yields on the intensity of the fundamental, the percentage of 2nd harmonic and the detuning of the fundamental from resonance. Having examined the cases of one and two intermediate resonances, we arrive at results of general validity and global behaviour, showing that even a small amount of harmonic may seem deceptively innocuous.

  9. Chirp control of multi-photon resonance ionization and charge-resonance enhanced ionization on molecular harmonic generation

    NASA Astrophysics Data System (ADS)

    Liu, Hang; Li, Wenliang; Feng, Liqiang

    2017-05-01

    The effects of the multi-photon resonance ionization (MPRI) and the charge-resonance enhanced ionization (CREI) on the molecular high-order harmonic generation (MHHG) from H2+ have been investigated by using the chirped pulses. It is found that the MHHG only comes from the MPRI in the shorter pulse duration. As the pulse duration increases, both the MPRI and the CREI contribute to the MHHG. But the MPRI plays the main role in the generations of the above-threshold harmonics and the CREI mainly contributes to the below-threshold harmonics. With the introductions of the up-chirped and the down-chirped pulses, the contributions of the MHHG from the CREI and the MPRI can be enhanced, respectively. Finally, the isotopic investigation (e.g. T2+) shows that due to the slower nuclear motion of the heavy nuclei, the contributions of MHHG from the CERI can be suppressed in the heavy nuclei.

  10. Acoustic detection of resonance-enhanced multiphoton ionization for spatially resolved temperature measurement.

    PubMed

    Wu, Yue; Gragston, Mark; Zhang, Zhili

    2017-09-01

    In this Letter, acoustic detection of resonance-enhanced multiphoton ionization (A-REMPI) is characterized and used to measure spatially resolved O2 rotational temperature in air. The acoustic signal is generated using O2 REMPI in air and is detected by a single microphone operating within the audible range. Compared to electron number measurements by coherent microwave scattering, nonlinear light absorption and subsequent local pressure perturbation are captured by the microphone. A typical acoustic cycle of compression and rarefication of the acoustic wave is observed in the A-REMPI. Since the pressure perturbation can be regarded as close to thermodynamic equilibrium, the rotational temperature measured by A-REMPI is lower and closer to the realistic condition.

  11. Identification of four rotamers of m-methoxystyrene by resonant two-photon ionization and mass analyzed threshold ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Yanqi; Tzeng, Sheng Yuan; Shivatare, Vidya; Takahashi, Kaito; Zhang, Bing; Tzeng, Wen Bih

    2015-03-01

    We report the vibronic and cation spectra of four rotamers of m-methoxystyrene, recorded by using the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques. The excitation energies of the S1← S0 electronic transition are found to be 32 767, 32 907, 33 222, and 33 281 cm-1, and the corresponding adiabatic ionization energies are 65 391, 64 977, 65 114, and 64 525 cm-1 for these isomeric species. Most of the observed active vibrations in the electronically excited S1 and cationic ground D0 states involve in-plane ring deformation and substituent-sensitive bending motions. It is found that the relative orientation of the methoxyl with respect to the vinyl group does not influence the vibrational frequencies of the ring-substituent bending modes. The two dimensional potential energy surface calculations support our experimental finding that the isomerization is restricted in the S1 and D0 states.

  12. Identification of four rotamers of m-methoxystyrene by resonant two-photon ionization and mass analyzed threshold ionization spectroscopy

    SciTech Connect

    Xu, Yanqi; Tzeng, Sheng Yuan; Takahashi, Kaito; Shivatare, Vidya; Zhang, Bing; Tzeng, Wen Bih

    2015-03-28

    We report the vibronic and cation spectra of four rotamers of m-methoxystyrene, recorded by using the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques. The excitation energies of the S{sub 1}← S{sub 0} electronic transition are found to be 32 767, 32 907, 33 222, and 33 281 cm{sup −1}, and the corresponding adiabatic ionization energies are 65 391, 64 977, 65 114, and 64 525 cm{sup −1} for these isomeric species. Most of the observed active vibrations in the electronically excited S{sub 1} and cationic ground D{sub 0} states involve in-plane ring deformation and substituent-sensitive bending motions. It is found that the relative orientation of the methoxyl with respect to the vinyl group does not influence the vibrational frequencies of the ring-substituent bending modes. The two dimensional potential energy surface calculations support our experimental finding that the isomerization is restricted in the S{sub 1} and D{sub 0} states.

  13. 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.

  14. A simple resonance enhanced laser ionization scheme for CO via the A1Π state

    NASA Astrophysics Data System (ADS)

    Sun, Z. F.; von Zastrow, A. D.; Parker, D. H.

    2017-07-01

    We investigate the laser ionization process taking place when the CO molecule is exposed to vacuum ultraviolet (VUV) radiation resonant with the CO A1Π (v = 0) ← X1Σ+ (v = 0) transition around 154 nm, along with the ultraviolet (UV) and visible (Red) radiation used to generate VUV by four-wave difference-frequency mixing. By measuring the CO+ ion recoil and a room temperature gas spectrum, it is possible to assign the ionization process as 1 + 1' + 1'' REMPI where the one-photon steps refer to the VUV, UV, and Red radiation, respectively. Resonance enhanced ionization of rotational states around J = 12 arise due to the overlap of the fixed wavelength UV (˜250 nm) with the R band-head of a transition assigned to CO E1Π (v = 6) ← A1Π (v = 0) with a term value of 104 787.5 cm-1. The REMPI process is efficient and polarization sensitive and should be useful in a wide range of studies involving nascent CO.

  15. Nuclear Recoil Cross Sections from Time-dependent Studies of Two-Photon Double Ionization of Helium

    SciTech Connect

    Horner, Daniel A.; Rescigno, Thomas N.; McCurdy, C. William

    2009-12-21

    We examine the sensitivity of nuclear recoil cross sections produced by two-photon double ionization of helium to the underlying triple differential cross sections (TDCS) used in their computation. We show that this sensitivity is greatest in the energy region just below the threshold for sequential double ionization. Accurate TDCS, extracted from non-perturbative solutions of the time-dependent Schroedinger equation, are used here in new computations of the nuclear recoil cross section.

  16. Two-Photon Complete Fragmentation of Helium

    NASA Astrophysics Data System (ADS)

    Colgan, James; Pindzola, M. S.

    2002-05-01

    A time-dependent close-coupling method is used to calculate, for the first time, fully differential cross sections for the complete fragmentation of helium by two photons. Surprising differences are found in comparisons with previous calculations. These differences are found to be due to a core-excited resonance enhancement of the two-photon proces for both single and double ionization. These calculations provide theoretical support for ground-breaking measurements expected to be obtained from free-electron X-ray laser experiments to be made at Hamburg.

  17. Measurements of trap dynamics of cold OH molecules using resonance-enhanced multiphoton ionization

    NASA Astrophysics Data System (ADS)

    Gray, John M.; Bossert, Jason A.; Shyur, Yomay; Lewandowski, H. J.

    2017-08-01

    Trapping cold, chemically important molecules with electromagnetic fields is a useful technique to study small molecules and their interactions. Traps provide long interaction times, which are needed to precisely examine these low-density molecular samples. However, the trapping fields lead to nonuniform molecular density distributions in these systems. Therefore, it is important to be able to experimentally characterize the spatial density distribution in the trap. Ionizing molecules at different locations in the trap using resonance-enhanced multiphoton ionization (REMPI) and detecting the resulting ions can be used to probe the density distribution even at the low density present in these experiments because of the extremely high efficiency of detection. Until recently, one of the most chemically important molecules, OH, did not have a convenient REMPI scheme identified. Here, we use a newly developed 1 +1' REMPI scheme to detect trapped cold OH molecules. We use this capability to measure the trap dynamics of the central density of the cloud and the density distribution. These types of measurements can be used to optimize loading of molecules into traps, as well as to help characterize the energy distribution, which is critical knowledge for interpreting molecular collision experiments.

  18. Verification Results of Jet Resonance-enhanced Multiphoton Ionization as a Real-time PCDD/F Emission Monitor

    EPA Science Inventory

    The Jet REMPI (Resonance Enhanced Multiphoton Ionization) monitor was tested on a hazardous waste firing boiler for its ability to determine concentrations of polychlorinated dibenzodioxins and dibenzofurans (PCDDs/Fs). Jet REMPI is a real time instrument capable of highly selec...

  19. Verification Results of Jet Resonance-enhanced Multiphoton Ionization as a Real-time PCDD/F Emission Monitor

    EPA Science Inventory

    The Jet REMPI (Resonance Enhanced Multiphoton Ionization) monitor was tested on a hazardous waste firing boiler for its ability to determine concentrations of polychlorinated dibenzodioxins and dibenzofurans (PCDDs/Fs). Jet REMPI is a real time instrument capable of highly selec...

  20. One-color two-photon mass-analyzed threshold ionization spectroscopy of ethyl bromide through a dissociative intermediate state

    NASA Astrophysics Data System (ADS)

    Tang, Bifeng; Zhang, Song; Wang, Yanmei; Tang, Ying; Zhang, Bing

    2005-10-01

    Mass-analyzed threshold ionization (MATI) spectra of ethyl bromide were obtained using one-color two-photon ionization through a dissociative intermediate state. Accurate values for the adiabatic ionization energy have been obtained, 83099±5 and 85454±5cm-1 for the X˜1E2 and X˜2E2 states of the ethyl bromide cation, respectively, giving a splitting of 2355±10cm-1. Compared with conventional photoelectron data, the two-photon MATI spectrum exhibited a more extensive vibrational structure with a higher resolution, mainly containing the modes involving the dissociation coordinate. The observed modes were analyzed and discussed in terms of wave packet evolving on the potential-energy surface of the dissociative state.

  1. Resonant two-photon ionization of fluorene rare-gas van der Waals complexes

    NASA Astrophysics Data System (ADS)

    Leutwyler, Samuel; Even, Uzi; Jortner, Joshua

    1983-12-01

    Resonant two-photon ionization combined with time-of-flight mass spectrometry was applied for the interrogation of the S0 → S1 electronic-vibrational excitations of van der Waals complexes of fluorene (FL) with rare-gas atoms and N2 in supersonic jets. Energy-resolved and mass-resolved spectra of FL ṡ Ne, FL ṡ Arn (n=1-3), FL ṡ Kr, FL ṡ Xe, and FL ṡ N2 were recorded over the energy range 0-800 cm-1 above the electronic origin of S1. The red microscopic spectral shifts of the electronic origins of FL ṡ R (R=Ar, Kr, and Xe) complexes are dominated by dispersive interactions, being proportional to the polarizability of R. The vibrational level structure of FL ṡ Rn (R=Ar, Kr, and Xe) complexes exhibits intramolecular vibrational excitations of FL, as well as intermolecular vibrations, which involve the relative motion of FL and R in the complex. The spectra of FL ṡ Ne and FL ṡ N2 reveal a rich vibrational structure in the vicinity of the electronic origin, indicating a substantial change of the nuclear configuration upon electronic excitation. Upper and lower bounds on the dissociation energies of FL ṡ R (R=Ne, Kr, and Xe) and FL ṡ Ar2 were inferred from the vibrational level structure in the mass-resolved spectra, where the disappearance of the signal of the parent van der Waals ion and the appearance of the ion signal of the fragments mark the onset of the vibrational predissociation process.

  2. Spatially resolved measurement of singlet delta oxygen by radar resonance-enhanced multiphoton ionization.

    PubMed

    Wu, Yue; Zhang, Zhili; Ombrello, Timothy M

    2013-07-01

    Coherent microwave Rayleigh scattering (Radar) from resonance-enhanced multiphoton ionization (REMPI) was demonstrated to directly and nonintrusively measure singlet delta oxygen, O(2)(a(1)Δ(g)), with high spatial resolution. Two different approaches, photodissociation of ozone and microwave discharge plasma in an argon and oxygen flow, were utilized for O(2)(a(1)Δ(g)) generation. The d(1)Π(g)←a(1)Δ(g) (3-0) and d(1)Π(g)←a(1)Δ(g) (1-0) bands of O(2)(a(1)Δ(g)) were detected by Radar REMPI for two different flow conditions. Quantitative absorption measurements using sensitive off-axis integrated cavity output spectroscopy (ICOS) was used simultaneously to evaluate the accuracy and sensitivity of the Radar REMPI technique. The detection limit of Radar REMPI was found to be comparable to the ICOS technique with a detection threshold of approximately 10(14) molecules/cm(3) but with a spatial resolution that was 8 orders of magnitude smaller than the ICOS technique.

  3. Investigating two-photon double ionization of D{sub 2} by XUV-pump-XUV-probe experiments

    SciTech Connect

    Jiang, Y. H.; Kurka, M.; Kuehnel, K. U.; Toppin, M.; Schroeter, C. D.; Moshammer, R.; Rudenko, A.; Foucar, L.; Perez-Torres, J. F.; Plesiat, E.; Morales, F.; Martin, F.; Herrwerth, O.; Lezius, M.; Kling, M. F.; Jahnke, T.; Doerner, R.; Sanz-Vicario, J. L.; Tilborg, J. van; Belkacem, A.

    2010-05-15

    We used a split-mirror setup attached to a reaction microscope at the free-electron laser in Hamburg (FLASH) to perform an XUV-pump-XUV-probe experiment by tracing the ultrafast nuclear wave-packet motion in the D{sub 2}{sup +}(1s{sigma}{sub g}) with <10 fs time resolution. Comparison with time-dependent calculations shows excellent agreement with the measured vibrational period of 22{+-}4 fs in D{sub 2}{sup +}, points to the importance of accurately knowing the internuclear distance-dependent ionization probability, and paves the way to control sequential and nonsequential two-photon double-ionization contributions.

  4. Electron capture of dopants in two-photonic ionization in a poly(methyl methacrylate) solid

    SciTech Connect

    Tsuchida, Akira; Sakai, Wataru; Nakano, Mitsuru; Yamamoto, Masahide

    1992-10-29

    Behavior of the electron produced by two-photonic excitation of an aromatic donor in a poly(methyl methacrylate) solid was studied by the addition of the electron scavengers to the system. According to the Perrin type analysis for the two-photonically ejected electron, the capture radii (R{sub c}) of the scavengers examined were estimated to be from 8 to 40 {Angstrom}. For the two-photonically ejected electrons, R{sub c} is a capture radius for thermalized electrons. In this case the parent electron donor is not necessarily within this radius. On the other hand, for the fluorescence quenching, the distance between the donor and acceptor is within the static quenching radius (R{sub q}) of the donor. 13 refs., 4 figs., 2 tabs.

  5. Application of resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) for on-line trace analysis of combustion and pyrolysis products in technical processes

    NASA Astrophysics Data System (ADS)

    Zimmermann, Ralf; Heger, H. J.; Dorfner, R.; Kettrup, A. A.; Boesl, Ulrich

    1997-05-01

    We present first applications of resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) for on-line monitoring of technical water incinerator flue gases and coffee roasting process off- gases. The results were obtained with a newly developed, mobile REMPI-TOFMS device. The combination of laser induced resonance-enhanced multiphoton ionization and time-of-flight mass spectrometry represents a highly selective as well as sensitive analytical technique, well suited for species selective real-time on-line monitoring of trace-products in of-gases from thermal processes or technical incinerators. The achievable sensitivities are in the ppb-range or better for aromatic compounds. The high selectivity is due to the combination of mass- and optical selectivity, the high sensitivity is caused by the high cross sections of resonance-enhanced two photon ionization with lasers. On- line monitoring of trace chemicals, formed during combustion- or pyrolysis-processes, is useful e.g. for feed back steering of combustion processes in order to minimize the formation of hazardous byproducts or for optimization of the economic efficiency of thermal production processes.

  6. Grid-based methods for diatomic quantum scattering problems II: Time-dependent treatment of single- and two-photon ionization of H2+

    SciTech Connect

    Rescigno, Thomas N.; Tao, L.; McCurdy, C.W.

    2009-04-20

    The time-dependent Schr\\"odinger equation for H2+ in a time-varying electromagnetic field is solved in the fixed-nuclei approximation using a previously developed finite-element/ discrete variable representation in prolate spheroidal coordinates. Amplitudes for single- and two-photon ionization are obtained using the method of exterior complex scaling to effectively propagate the field-free solutions from the end of the radiation pulse to infinite times. Cross sections are presented for one-and two-photon ionization for both parallel and perpendicular polarization of the photon field, as well as photoelectron angular distributions for two-photon ionization.

  7. The influence of molecular pre-orientation on the resonance-enhanced multi-photon ionization dynamics

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Miao; Li, Jing-Lun; Yu, Jie; Cong, Shu-Lin

    2017-03-01

    We investigate theoretically the influence of molecular pre-orientation on the resonance-enhanced multi-photon ionization (REMPI) dynamics, taking the LiH molecule for example. The LiH molecule is first pre-oriented by a single-cycle pulse (SCP) in terahertz (THz) region, and then excited by the femtosecond pump pulse, and finally ionized by the femtosecond probe pulse. We focus on the impact of the pre-orientation on the ionization probability, energy- and angle-resolved photoelectron spectra and photoelectron angular distribution (PAD). It is found that the ionization probability and peak intensity of energy-resolved photoelectron spectra are significantly affected by molecular orientation. The angle-resolved photoelectron spectra are related to the molecular orientation. The PAD can be changed by varying the delay time between the THz SCP and pump pulse. We also investigate the effect of temperature on excitation and ionization dynamics.

  8. Electronic dynamics of charge resonance enhanced ionization probed by laser-induced alignment in C2H2

    NASA Astrophysics Data System (ADS)

    Cornaggia, C.

    2016-10-01

    Although charge resonance enhanced ionization (CREI) be an ubiquitous effect in molecules in strong laser fields, the associated electron emission remains difficult to deal with. The main reason relies on the fact that CREI is part of an overall multielectron ionization, where the initial steps of single and dissociative ionization of neutral species dominate the electron spectrum. Using the rescattered electrons, we show that it is possible to address the electron signal from CREI without any contribution from other electron signals. The electrons from CREI are preferentially emitted when the molecular axis is parallel to the laser electric field as expected from its electronic dynamics. Acetylene is chosen for demonstration purpose because single ionization, which is not related to CREI, is more pronounced when the C2H2 molecular axis is perpendicular to the laser electric field.

  9. Polarization effects in two-photon nonresonant ionization of argon with extreme-ultraviolet and infrared femtosecond pulses

    SciTech Connect

    O'Keeffe, P.; Lopez-Martens, R.; Mauritsson, J.; Johansson, A.; L'Huillier, A.; Veniard, V.; Taieeb, R.; Maquet, A.; Meyer, M.

    2004-05-01

    We report the results of experimental and theoretical investigations of the two-color, two-photon ionization of Ar atoms, using femtosecond pulses of infrared laser radiation in combination with its extreme-ultraviolet harmonics. It is shown that the intensities of the photoelectron lines resulting from the absorption of photons from both fields strongly depend both on the respective phases of the fields and on atomic quantities such as the asymmetry parameter. These phases, which are notoriously difficult to measure, can be estimated by changing the polarization state of the laser radiation.

  10. Investigating two-photon double ionization of D2 by XUV-Pump -- XUV-Probe experiments at FLASH

    SciTech Connect

    FLASH Collaboration; Jiang, Y.; Rudenko, A.; Perez-Torres, J.; Foucar, L.; Kurka, M.; Kuhnel, K.; Toppin, M.; Plesiat, E.; Morales, F.; Martin, F.; Herrwerth, O.; Lezius, M.; Kling, M.; Jahnke, T.; Dorner, R.; Sanz-Vicario, J.; van Tilborg, J.; Belkacem, A.; Schulz, M.; Ueda, K.; Zouros, T.; Dusterer, S.; Treusch, R.; Schroter, C.; Moshammer, R.; Ullrich, J.

    2010-08-02

    Using a novel split-mirror set-up attached to a Reaction Microscope at the Free electron LASer in Hamburg (FLASH) we demonstrate an XUV-pump -- XUV-probe ((hbar omega = 38 eV) experiment by tracing the ultra-fast nuclear wave-packet motion in the D2+ (1s sigma g-state) with<10 fs time resolution. Comparison with time-dependent calculations yields excellent agreement with the measured vibrational period of 22+-4 fs in D2+, points to the importance of the inter-nuclear distance dependent ionization probability and paves the way to control sequential and non-sequential two-photon double ionization contributions.

  11. Generation of highly vibrationally excited H2 and detection by 2+1 resonantly enhanced multiphoton ionization

    NASA Astrophysics Data System (ADS)

    Robie, Daniel C.; Jusinski, Leonard E.; Bischel, William K.

    1990-02-01

    We report the first detection by optical means of highly vibrationally excited H2 X1Σ+g(vx=6-11). Vibrationally excited H2 was generated using a recently discovered hot-wire effect in H2 gas, and was detected in 40 bands with 2+1 resonantly enhanced multiphoton ionization via the EF state (vEF=0-14). Rotational temperatures are in the range 200-650 K, well below that required for thermal excitation of the observed vibrational levels.

  12. (2 + 1) resonant enhanced multiphoton ionization of H2 via the E,F 1Sigma(+)g state

    NASA Technical Reports Server (NTRS)

    Rudolph, H.; Lynch, D. L.; Dixit, S. N.; Mckoy, V.; Huo, Winifred M.

    1987-01-01

    In this paper, the results of ab initio calculations of photoelectron angular distributions and vibrational branching ratios for the (2 + 1) resonant enhanced multiphoton ionization (REMPI) of H2 via the E,F 1Sigma(+)g state are reported, and these are compared with the experimental data of Anderson et al. (1984). These results show that the observed non-Franck-Condon behavior is predominantly due to the R dependence of the transition matrix elements, and to a lesser degree to the energy dependence. This work presents the first molecular REMPI study employing a correlated wave function to describe the Rydberg-valence mixing in the resonant intermediate state.

  13. Control of resonance enhanced multi-photon ionization photoelectron spectroscopy by phase-shaped femtosecond laser pulse

    SciTech Connect

    Zhang Shian; Lu Chenhui; Jia Tianqing; Sun Zhenrong; Qiu Jianrong

    2012-11-07

    In this paper, we theoretically demonstrate that the (2+1+1) resonance enhanced multi-photon ionization photoelectron spectroscopy in sodium atom can be effectively controlled by shaping femtosecond laser pulse with a {pi} phase step modulation in weak laser field, involving its total photoelectron energy, maximal photoelectron intensity, and spectroscopic bandwidth. Our results show that the total photoelectron energy can be suppressed but not enhanced, the maximal photoelectron intensity can be enhanced and also suppressed, and the photoelectron spectroscopy can be tremendously narrowed. These theoretical results can provide a feasible scheme to achieve the high-resolution photoelectron spectroscopy and study the excited state structure in atomic and molecular systems.

  14. One- and two-photon ionization of DNA single and double helices studied by laser flash photolysis at 266 nm.

    PubMed

    Marguet, Sylvie; Markovitsi, Dimitra; Talbot, Francis

    2006-06-15

    The ionization of the DNA single and double helices (dA)20, (dT)20, (dAdT)10(dAdT)10 and (dA)20(dT)20, induced by nanosecond pulses at 266 nm, is studied by time-resolved absorption spectroscopy. The variation of the hydrated electron concentration with the absorbed laser intensity shows that, in addition to two-photon ionization, one-photon ionization takes place for (dAdT)10(dAdT)10, (dA)20(dT)20 and (dA)20 but not for (dT)20. The spectra of all adenine-containing oligomers at the microsecond time-scale correspond to the adenine deprotonated radical formed in concentrations comparable to that of the hydrated electron. The quantum yield for one-photon ionization of the oligomers (ca. 10(-3)) is higher by at least 1 order of magnitude than that of dAMP, showing clearly that organization of the bases in single and double helices leads to an important lowering of the ionization potential. The propensity of (dAdT)10(dAdT)10, containing alternating adenine-thymine sequences, to undergo one-photon ionization is lower than that of (dA)20(dT)20 and (dA)20, containing adenine runs. Pairing of the (dA)20 with the complementary strand leads to a decrease of quantum yield for one photon ionization by about a factor of 2.

  15. Identification of Two Allylbenzene Conformers by One- and Two-Photon Resonant Multiphoton Ionization Spectroscopy in a Supersonic Jet

    NASA Astrophysics Data System (ADS)

    Philis, John G.; Kosmidis, Constantine

    1997-02-01

    Two allylbenzene conformers have been identified using resonance-enhanced multiphoton ionization spectroscopy (REMPI) in a supersonic jet expansion. Their existence has been confirmed by the vibrational analysis of theS1← S0ππ* transition, recorded under (1 + 1) and (2 + 2) REMPI schemes and by the intensity variation of their spectra under various expansion conditions. The conformer with higher excitation energy shows strong dependence on the terminal beam temperature, which is consistent with a shallow potential energy well as predicted by theory. The relative abundance of the two conformers and the frequency values of several vibrational modes in their lower excited singlet electronic stateS1have been determined.

  16. Two-photon ionization of H{sub 2}{sup +} by short laser pulses

    SciTech Connect

    Palacios, A.; Martin, F.; Barmaki, S.; Bachau, H.

    2005-06-15

    We present a theoretical study of dissociative multiphoton ionization of the H{sub 2}{sup +} molecular ion in perturbative and nonperturbative regimes including both electronic and nuclear degrees of freedom. Differential (in proton and electron energy) ionization cross sections have been evaluated for various photon energies, laser intensities, and pulse lengths. We have found that the proton energy distribution is modulated by vertical Franck-Condon transitions but also by vibrational resonances associated with intermediate electronic states. We have also found that, as expected, nonperturbative results tend to the time-independent perturbative ones when both the pulse length increases and the laser intensity decreases. No divergence near intermediate-state resonances is found in the perturbative results when the nuclear motion is properly taken into account in the calculations.

  17. Two-photon double ionization of helium in the region of photon energies 42-50eV

    NASA Astrophysics Data System (ADS)

    Ivanov, I. A.; Kheifets, A. S.

    2007-03-01

    We report the total integrated cross section (TICS) of two-photon double ionization of helium in the photon energy range from 42to50eV . Our computational procedure relies on a numerical solution of the time-dependent Schrödinger equation on a square-integrable basis and subsequent projection of this solution on a set of final field-free states describing correlation in the two-electron continuum. Our results suggest that the TICS grows monotonically as a function of photon energy in the region of 42-50eV , possibly reaching a maximum in the vicinity of 50eV . We also present fully resolved triple-differential cross sections for selected photon energies.

  18. Two-photon double ionization of helium in the region of photon energies 42-50 eV

    SciTech Connect

    Ivanov, I. A.; Kheifets, A. S.

    2007-03-15

    We report the total integrated cross section (TICS) of two-photon double ionization of helium in the photon energy range from 42 to 50 eV. Our computational procedure relies on a numerical solution of the time-dependent Schroedinger equation on a square-integrable basis and subsequent projection of this solution on a set of final field-free states describing correlation in the two-electron continuum. Our results suggest that the TICS grows monotonically as a function of photon energy in the region of 42-50 eV, possibly reaching a maximum in the vicinity of 50 eV. We also present fully resolved triple-differential cross sections for selected photon energies.

  19. Rotamers of m-chloroanisole studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Huang, Hsin Chang; Shiung, Kui Shiu; Jin, Bih Yaw; Tzeng, Wen Bih

    2013-11-01

    We apply the resonant two-photon ionization (R2PI) and mass-analyzed threshold ionization (MATI) techniques to record the vibronic and cation spectra of m-chloroanisole. The vibronic features appear in two series, built on 35,822 ± 2 and 35,868 ± 2 cm-1, corresponding to the origins of the S1 ← S0 electronic transition (E1's) of the two rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 67,645 ± 5 and 68,008 ± 5 cm-1 for these two isomeric species. Comparing these data with those of anisole, we find that the chlorine substitution at the meta position leads to a red shift in the E1 and a blue shift in the IE. The observed R2PI and MATI bands mainly result from the in-plane ring deformation and substituent-sensitive bending vibrations of these species in the electronically excited S1 and cationic ground D0 states.

  20. Benchmark for two-photon ionization of atoms with generalized Sturmian functions

    NASA Astrophysics Data System (ADS)

    Gómez, Antonio I.; Gasaneo, Gustavo; Mitnik, Darío M.; Ambrosio, Marcelo J.; Ancarani, Lorenzo U.

    2016-10-01

    The description with traditional methods of the single or multiple ionization of atoms and molecules by two or more successive photons requires some special treatment. Difficulties occur when a spatially non-decaying driven term appears in the Schrödinger-like non-homogeneous equation for the scattering wave function. We propose using the intrinsic physical and mathematical properties of generalized Sturmian functions to efficiently deal with the Dalgarno-Lewis second order equation. In contrast to other approaches, our methodology provides a practical way to extract the transition amplitude from the asymptotic behavior of the scattering wave function, and this without requiring any further projection onto some final approximate state. As an illustration, the hydrogen case is studied in details, for both pulsed and monochrome laser radiation fields. The successful comparison with analytical and time-dependent solutions provides a benchmark, and allows us to master the numerical aspects of the methodology. Appropriately chosen generalized Sturmian functions manage to easily reproduce the beat-type asymptotic behavior observed in the photoelectron wave function after absorption by the atom of two successive photons.

  1. Alignment effects in two-photon double ionization of H{sub 2} in femtosecond xuv laser pulses

    SciTech Connect

    Guan Xiaoxu; Bartschat, Klaus; Schneider, Barry I.

    2011-09-15

    Triple-differential cross sections for two-photon double ionization of the aligned hydrogen molecule at the equilibrium distance are presented for a central photon energy of 30 eV. The temporal response of the laser-driven molecule is investigated by solving the time-dependent Schroedinger equation in full dimensionality using two-center elliptical coordinates and a finite-element discrete-variable-representation approach. The molecular orientation is found to have a strong effect on the emission modes of the two correlated photoelectrons. This molecular effect is most noticeable when the molecular axis and the laser polarization vector are oriented parallel to each other. For intermediate cases between the parallel and perpendicular geometries, the dominant emission modes for two-electron ejection oscillate between those for the two extreme cases. The contributions from different ionization channels are also analyzed in detail. Depending on the emission direction of the reference electron, the interference contributions from the various channels can be constructive or destructive at small alignment angles, while they always contribute constructively to the triple-differential cross sections near the perpendicular geometry.

  2. Double-arm three-dimensional ion imaging apparatus for the study of ion pair channels in resonance enhanced multiphoton ionization

    NASA Astrophysics Data System (ADS)

    Poretskiy, M. S.; Chichinin, A. I.; Maul, C.; Gericke, K.-H.

    2016-02-01

    We present a novel experimental configuration for the full quantitative characterization of the multichannel resonance enhanced multiphoton ionization (REMPI) of small molecules in cases when the ion-pair dissociation channel is important. For this purpose, a double-arm time-of-flight mass spectrometer with three-dimensional (3D) ion imaging detectors at both arms is constructed. The REMPI of HCl molecules is used to examine the constructed setup. The apparatus allows us to perform simultaneous measurements of the 3D velocity vector distributions of positive (H+, HCl+, and Cl+) and negative (Cl-) photoions. The characterization consists of the determination of "two-photon absorption cross sections" for the process HCl(X)+2hν → HCl∗, one-photon absorption cross sections for subsequent processes HCl∗ + hν → HCl∗∗, and the probability of the subsequent non-adiabatic transition HCl∗∗ → HCl(B) → H+ + Cl-, which leads to ionic pairs. All these data should be obtained from the analysis of the dependencies of the number of ions on the laser energy. The full characterization of the laser beam and the knowledge of the ion detection probability are necessary parts of the analysis. Detailed knowledge of losses of produced ions in the mass spectrometer before detection requires understanding and characterization of such processes like electron emission from metallic grids under ion bombardment or charge transfer between positive ions and the metal surface of the grids, like Cl+ + (grid) → Cl-. These important phenomena from surface science are rarely discussed in the imaging literature, and here, we try to compensate for this shortcoming.

  3. The design of double electrostatic-lens optics for resonance enhanced multiphoton ionization and photoelectron imaging experiments

    SciTech Connect

    Qu, Zehua; Li, Chunsheng; Qin, Zhengbo E-mail: xfzheng@mail.ahnu.edu.cn; Zheng, Xianfeng E-mail: xfzheng@mail.ahnu.edu.cn; Yao, Guanxin; Zhang, Xianyi; Cui, Zhifeng

    2015-06-15

    Compared to single ion/electron-optics for velocity-map imaging, a double-focusing lens assembly designed not only allows for mapping velocity imaging of photoelectrons but also allows for investigating the vibrational structure of the intermediate states of neutral species in resonance enhanced multiphoton ionization (REMPI) spectra. In this presentation, in order to record REMPI and photoelectron spectra separately, we have constructed a compact photoelectron velocity-map imaging (VMI) apparatus combined with an opposite linear Wiley-Mclaren time-of-flight mass spectrometer (TOFMS). A mass resolution (m/Δm) of ∼1300 for TOFMS and electron energy resolution (ΔE/E) of 2.4% for VMI have been achieved upon three-photon ionization of Xe atom at 258.00 nm laser wavelength. As a benchmark, in combination of one-color (1 + 1) REMPI and photoelectron imaging of benzene via 6{sup 1} and 6{sup 1}1{sup 1} vibronic levels in the S{sub 1} state, the vibrational structures of the cation and photoelectron angular anisotropy are unraveled. In addition, two-color (1 + 1′) REMPI and photoelectron imaging of aniline was used to complete the accurate measurement of ionization potential (62 271 ± 3 cm{sup −1}). The results suggest that the apparatus is a powerful tool for studying photoionization dynamics in the photoelectron imaging using vibrational-state selected excitation to the intermediate states of neutrals based on REMPI technique.

  4. The design of double electrostatic-lens optics for resonance enhanced multiphoton ionization and photoelectron imaging experiments

    NASA Astrophysics Data System (ADS)

    Qu, Zehua; Li, Chunsheng; Qin, Zhengbo; Zheng, Xianfeng; Yao, Guanxin; Zhang, Xianyi; Cui, Zhifeng

    2015-06-01

    Compared to single ion/electron-optics for velocity-map imaging, a double-focusing lens assembly designed not only allows for mapping velocity imaging of photoelectrons but also allows for investigating the vibrational structure of the intermediate states of neutral species in resonance enhanced multiphoton ionization (REMPI) spectra. In this presentation, in order to record REMPI and photoelectron spectra separately, we have constructed a compact photoelectron velocity-map imaging (VMI) apparatus combined with an opposite linear Wiley-Mclaren time-of-flight mass spectrometer (TOFMS). A mass resolution (m/Δm) of ˜1300 for TOFMS and electron energy resolution (ΔE/E) of 2.4% for VMI have been achieved upon three-photon ionization of Xe atom at 258.00 nm laser wavelength. As a benchmark, in combination of one-color (1 + 1) REMPI and photoelectron imaging of benzene via 61 and 6111 vibronic levels in the S1 state, the vibrational structures of the cation and photoelectron angular anisotropy are unraveled. In addition, two-color (1 + 1') REMPI and photoelectron imaging of aniline was used to complete the accurate measurement of ionization potential (62 271 ± 3 cm-1). The results suggest that the apparatus is a powerful tool for studying photoionization dynamics in the photoelectron imaging using vibrational-state selected excitation to the intermediate states of neutrals based on REMPI technique.

  5. Two-color resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of 4-chlorostyrene

    NASA Astrophysics Data System (ADS)

    Wu, Pei Ying; Huang, Hsin Hsuan; Lin, King Chuen; Tzeng, Wen Bih

    2017-08-01

    The first electronic excitation and adiabatic ionization energies of 35Cl and 37Cl 4-chlorostyrene were similar, with values of 33,977 ± 2 and 67,972 ± 5 cm-1, respectively. The general features in the obtained vibronic and cation spectra of the two isotopologues were similar. A frequency shift of 1-5 cm-1 was observed on many active vibrations of the 35Cl and 37Cl isotopologues of 4-chlorostyrene in the S1 and D0 states. This frequency difference at each mode may reflect the degree of Cl atom involvement in the overall vibration.

  6. Detection of NO and NO(2) by (2 + 2) resonance-enhanced multiphoton ionization and photoacoustic spectroscopy near 454 nm.

    PubMed

    Pastel, R L; Sausa, R C

    1996-07-20

    Trace concentrations of NO and NO(2) are detected with a dye laser operating near 454 nm. NO is detected by a (2 + 2) resonance-enhanced multiphoton ionization process by means of NO A(2)Σ+-X(2)Π(0, 0) transitions with miniature electrodes, and NO(2) is detected by a one-photon absorption photoacoustic process by means of NO(2)A¯' (2)B(1)(0, 8, 0)- X¯ (2)A(1)(0, 0, 0) transitions with a miniature microphone. Rotationally resolved excitation spectra show that the spectral resolution is sufficiently high to identify these species at 1 atm. The technique's analytical merits are evaluated as functions of concentration, pressure, and laser intensities. Low laser intensities favor NO(2) photoacoustic detection whereas high laser intensities favor NO ionization. Limits of detection (signal-to-noise ratio 3) of 160 parts in 10(9) for NO and 400 parts in 10(9) for NO(2) are determined at 1 atm for a 10-s integration time. Signal response and noise analyses show that three decades of NO/NO(2) mixtures can be measured with a computational relative error in concentration that is three times the relative error in measuring the NO and NO(2) signals.

  7. Kinetic modeling of evolution of 3 + 1:Resonance enhanced multiphoton ionization plasma in argon at low pressures

    SciTech Connect

    Tholeti, Siva Sashank; Alexeenko, Alina A.; Shneider, Mikhail N.

    2014-06-15

    We present numerical kinetic modeling of generation and evolution of the plasma produced as a result of resonance enhanced multiphoton ionization (REMPI) in Argon gas. The particle-in-cell/Monte Carlo collision (PIC/MCC) simulations capture non-equilibrium effects in REMPI plasma expansion by considering the major collisional processes at the microscopic level: elastic scattering, electron impact ionization, ion charge exchange, and recombination and quenching for metastable excited atoms. The conditions in one-dimensional (1D) and two-dimensional (2D) formulations correspond to known experiments in Argon at a pressure of 5 Torr. The 1D PIC/MCC calculations are compared with the published results of local drift-diffusion model, obtained for the same conditions. It is shown that the PIC/MCC and diffusion-drift models are in qualitative and in reasonable quantitative agreement during the ambipolar expansion stage, whereas significant non-equilibrium exists during the first few 10 s of nanoseconds. 2D effects are important in the REMPI plasma expansion. The 2D PIC/MCC calculations produce significantly lower peak electron densities as compared to 1D and show a better agreement with experimentally measured microwave radiation scattering.

  8. Intermediate state dependence of the photoelectron circular dichroism of fenchone observed via femtosecond resonance-enhanced multi-photon ionization

    NASA Astrophysics Data System (ADS)

    Kastner, Alexander; Ring, Tom; Krüger, Bastian C.; Park, G. Barratt; Schäfer, Tim; Senftleben, Arne; Baumert, Thomas

    2017-07-01

    The intermediate state dependence of photoelectron circular dichroism (PECD) in resonance-enhanced multi-photon ionization of fenchone in the gas phase is experimentally studied. By scanning the excitation wavelength from 359 to 431 nm, we simultaneously excite up to three electronically distinct resonances. In the PECD experiment performed with a broadband femtosecond laser, their respective contributions to the photoelectron spectrum can be resolved. High-resolution spectroscopy allows us to identify two of the resonances as belonging to the B- and C-bands, which involve excitation to states with 3s and 3p Rydberg character, respectively. We observe a sign change in the PECD signal, depending on which electronic state is used as an intermediate, and are able to identify two differently behaving contributions within the C-band. Scanning the laser wavelength reveals a decrease of PECD magnitude with increasing photoelectron energy for the 3s state. Combining the results of high-resolution spectroscopy and femtosecond experiment, the adiabatic ionization potential of fenchone is determined to be I PaF e n =(8.49 ±0.06 ) eV.

  9. REAL TIME, ON-LINE CHARACTERIZATION OF DIESEL GENERATOR AIR TOXIC EMISSIONS BY RESONANCE ENHANCED MULTI-PHOTON IONIZATION TIME OF FLIGHT MASS SPECTROMETRY

    EPA Science Inventory

    The laser based resonance, enhanced multi-photon ionization time-of-flight mass spectrometry (REMPI-TOFMS) technique has been applied to the exhaust gas stream of a diesel generator to measure, in real time, concentration levels of aromatic air toxics. Volatile organic compounds ...

  10. REAL TIME, ON-LINE CHARACTERIZATION OF DIESEL GENERATOR AIR TOXIC EMISSIONS BY RESONANCE ENHANCED MULTI-PHOTON IONIZATION TIME OF FLIGHT MASS SPECTROMETRY

    EPA Science Inventory

    The laser based resonance, enhanced multi-photon ionization time-of-flight mass spectrometry (REMPI-TOFMS) technique has been applied to the exhaust gas stream of a diesel generator to measure, in real time, concentration levels of aromatic air toxics. Volatile organic compounds ...

  11. Resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of the selected rotamers of m-methoxyaniline and o-methoxyaniline

    NASA Astrophysics Data System (ADS)

    Lin, Jung Lee; Huang, Chen-Jso; Lin, Cheng-Huang; Tzeng, Wen Bih

    2007-07-01

    We report the resonant two-photon ionization and mass-analyzed threshold ionization (MATI) spectra of m-methoxyaniline and o-methoxyaniline. The vibronic features of m-methoxyaniline are built on 34308 ± 2 and 34495 ± 2 cm -1 corresponding to the origins of the S 1 ← S 0 electronic transition ( E1's) of the cis and trans rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 59983 ± 5 and 60879 ± 5 cm -1 for these two species. o-Methoxyaniline is found to have only one stable structure whose E1 and IE are 33875 ± 2 and 58678 ± 5 cm -1, respectively. Most of the active vibrations of m- and o-methoxyaniline in the electronically excited S 1 and cationic ground D 0 states result from the in-plane ring vibrations. Comparing these data with those of p-methoxyaniline allows us to learn about the vicinal substitution effects resulting from the relative locations of the NH 2 and OCH 3 substituents.

  12. Resonantly Enhanced Betatron Hard X-rays from Ionization Injected Electrons in a Laser Plasma Accelerator

    NASA Astrophysics Data System (ADS)

    Huang, K.; Li, Y. F.; Li, D. Z.; Chen, L. M.; Tao, M. Z.; Ma, Y.; Zhao, J. R.; Li, M. H.; Chen, M.; Mirzaie, M.; Hafz, N.; Sokollik, T.; Sheng, Z. M.; Zhang, J.

    2016-06-01

    Ultrafast betatron x-ray emission from electron oscillations in laser wakefield acceleration (LWFA) has been widely investigated as a promising source. Betatron x-rays are usually produced via self-injected electron beams, which are not controllable and are not optimized for x-ray yields. Here, we present a new method for bright hard x-ray emission via ionization injection from the K-shell electrons of nitrogen into the accelerating bucket. A total photon yield of 8 × 108/shot and 108 photons with energy greater than 110 keV is obtained. The yield is 10 times higher than that achieved with self-injection mode in helium under similar laser parameters. The simulation suggests that ionization-injected electrons are quickly accelerated to the driving laser region and are subsequently driven into betatron resonance. The present scheme enables the single-stage betatron radiation from LWFA to be extended to bright γ-ray radiation, which is beyond the capability of 3rd generation synchrotrons.

  13. Resonantly Enhanced Betatron Hard X-rays from Ionization Injected Electrons in a Laser Plasma Accelerator

    PubMed Central

    Huang, K.; Li, Y. F.; Li, D. Z.; Chen, L. M.; Tao, M. Z.; Ma, Y.; Zhao, J. R.; Li, M. H.; Chen, M.; Mirzaie, M.; Hafz, N.; Sokollik, T.; Sheng, Z. M.; Zhang, J.

    2016-01-01

    Ultrafast betatron x-ray emission from electron oscillations in laser wakefield acceleration (LWFA) has been widely investigated as a promising source. Betatron x-rays are usually produced via self-injected electron beams, which are not controllable and are not optimized for x-ray yields. Here, we present a new method for bright hard x-ray emission via ionization injection from the K-shell electrons of nitrogen into the accelerating bucket. A total photon yield of 8 × 108/shot and 108 photons with energy greater than 110 keV is obtained. The yield is 10 times higher than that achieved with self-injection mode in helium under similar laser parameters. The simulation suggests that ionization-injected electrons are quickly accelerated to the driving laser region and are subsequently driven into betatron resonance. The present scheme enables the single-stage betatron radiation from LWFA to be extended to bright γ-ray radiation, which is beyond the capability of 3rd generation synchrotrons. PMID:27273170

  14. Resonantly Enhanced Betatron Hard X-rays from Ionization Injected Electrons in a Laser Plasma Accelerator.

    PubMed

    Huang, K; Li, Y F; Li, D Z; Chen, L M; Tao, M Z; Ma, Y; Zhao, J R; Li, M H; Chen, M; Mirzaie, M; Hafz, N; Sokollik, T; Sheng, Z M; Zhang, J

    2016-06-08

    Ultrafast betatron x-ray emission from electron oscillations in laser wakefield acceleration (LWFA) has been widely investigated as a promising source. Betatron x-rays are usually produced via self-injected electron beams, which are not controllable and are not optimized for x-ray yields. Here, we present a new method for bright hard x-ray emission via ionization injection from the K-shell electrons of nitrogen into the accelerating bucket. A total photon yield of 8 × 10(8)/shot and 10(8 )photons with energy greater than 110 keV is obtained. The yield is 10 times higher than that achieved with self-injection mode in helium under similar laser parameters. The simulation suggests that ionization-injected electrons are quickly accelerated to the driving laser region and are subsequently driven into betatron resonance. The present scheme enables the single-stage betatron radiation from LWFA to be extended to bright γ-ray radiation, which is beyond the capability of 3(rd) generation synchrotrons.

  15. Tracing direct and sequential two-photon double ionization of D{sub 2} in femtosecond extreme-ultraviolet laser pulses

    SciTech Connect

    Jiang, Y. H.; Kurka, M.; Kuehnel, K. U.; Ergler, Th.; Schroeter, C. D.; Moshammer, R.; Rudenko, A.; Foucar, L.; Plesiat, E.; Perez-Torres, J. F.; Martin, F.; Herrwerth, O.; Lezius, M.; Kling, M. F.; Titze, J.; Jahnke, T.; Doerner, R.; Sanz-Vicario, J. L.; Schoeffler, M.; Tilborg, J. van

    2010-02-15

    Two-photon double ionization (TPDI) of D{sub 2} is studied for 38-eV photons at the Free Electron Laser in Hamburg (FLASH). Based on model calculations, instantaneous and sequential absorption pathways are identified as separated peaks in the measured D{sup +}+D{sup +} fragment kinetic energy release (KER) spectra. The instantaneous process appears at high KER, corresponding to ionization at the molecule's equilibrium distance, in contrast to sequential ionization mainly leading to low-KER contributions. Measured fragment angular distributions are in good agreement with theory.

  16. Resonance enhanced multiphoton ionization/secondary neutral mass spectrometry and cesium attachment secondary ion mass spectrometry of bronze : a comparison.

    SciTech Connect

    McCann, M. P.; Calaway, W. F.; Pellin, M. J.; Veryovkin, I. V.; Constantinides, I.; Adriaens, A.; Adams, F.; Materials Science Division; Sam Houston State Univ.; Univ. of Antwerp

    2002-05-01

    Archaeologists have considerable interests in ancient bronzes. They want to know how these alloys were produced and how they corroded with time. Modern bronzes, with compositions very close to that of some ancient bronzes, have been produced and two methods were examined to characterize one of these modern bronzes. Analysis of this modern bronze using resonance enhanced multiphoton ionization/secondary neutral mass spectrometry (REMPI/SNMS) is examined in detail and compared to cesium attachment secondary ion mass spectrometry (CsAMS) results. Both REMPI/SNMS and CsAMS were used to quantify the composition of Fe, Ni and Mn in a modern quaternary bronze designed to serve as a certified reference material for an ancient bronze. Both methods exhibit reduced matrix effects when compared to secondary ion mass spectrometry (SIMS) and thus quantification should be simplified. It was found that when relative sensitivity factors obtained from a standard bronze material are used to calibrate the instruments, the REMPI/SNMS measurements yield results that were more sensitive and more accurate.

  17. Resonance Enhanced Multi-Photon Ionization (rempi) and Double Resonance Uv-Uv and Ir-Uv Spectroscopic Investigation Isocytosine

    NASA Astrophysics Data System (ADS)

    Lee, Seung Jun; Min, Ahreum; Ahn, Ahreum; Moon, Cheol Joo; Choi, Myong Yong; Ishiuchi, Shun-Ichi; Miyazaki, Mitsuhiko; Fujii, Masaaki

    2013-06-01

    Isocytosine(iC), 2-aminouracil, is a non-natural nucleobase and its functional group's positions resemble those of guanine; therefore, its spectroscopic investigation is worthy of attention especially for the natural/unnatural base pairs with guanine and isoguanine. In this study, resonance enhanced multi-photon ionization (REMPI) and UV/IR-UV double resonance spectra of iC in the gas phase are presented. The collaboration work between Tokyo Institute of Technology, Japan and Gyeongsang National University, Korea using laser ablation and thermal evaporation, respectively, for producing jet-cooled iC is presented and discussed. The REMPI spectrum of iC monomers is recorded in the spectral range of 35000 to 36400cm-1, showing very congested π-π* vibronic bands. UV-UV hole burning spectroscopy is further conducted to investigate the conformational landscapes of iC monomers. Moreover, the presence of free OH band from IR-UV double resonance spectroscopy in combination with quantum chemical calculations convinces that the iC monomer in free-jet expansion experiment is an enol tautomer. However, a possible presence of a keto tautomer of iC may be provided by employing a pico-second experiment on iC.

  18. Zero kinetic energy photoelectron spectroscopy of jet cooled benzo[a]pyrene from resonantly enhanced multiphoton ionization

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Harthcock, Colin; Han, Fangyuan; Kong, Wei

    2011-12-01

    We report zero kinetic energy (ZEKE) photoelectron spectroscopy of benzo[a]pyrene (BaP) via resonantly enhanced multiphoton ionization (REMPI). Our analysis concentrates on the vibrational modes of the first excited state (S1) and those of the ground cationic state (D0). Similar to pyrene, another peri-condensed polycyclic aromatic hydrocarbon we have investigated, the first two electronically excited states of BaP exhibit extensive configuration interactions. However, the two electronic states are of the same symmetry, hence vibronic coupling does not introduce any out-of-plane modes in the REMPI spectrum, and Franck-Condon analysis is qualitatively satisfactory. The ZEKE spectra from the in-plane modes observed in the REMPI spectrum demonstrate strong propensity in preserving the vibrational excitation of the intermediate state. Although several additional bands in combination with the vibrational mode of the intermediate state are identifiable, they are much lower in intensity. This observation implies that the molecular structure of BaP has a tremendous capability to accommodate changes in charge density. All observed bands of the cation are IR active, establishing the role of ZEKE spectroscopy in mapping out far infrared bands for astrophysical applications.

  19. Rotationally resolved photoelectron spectra in resonance enhanced multiphoton ionization of HCl via the F 1Δ2 Rydberg state

    NASA Astrophysics Data System (ADS)

    Wang, Kwanghsi; McKoy, V.

    1991-12-01

    Results of studies of rotational ion distributions in the X 2Π3/2 and X 2Π1/2 spin-orbit states of HCl+ resulting from (2+1') resonance enhanced multiphoton ionization (REMPI) via the S(0) branch of the F 1Δ2 Rydberg state are reported and compared with measured threshold-field-ionization zero-kinetic-energy spectra reported recently [K. S. Haber, Y. Jiang, G. Bryant, H. Lefebvre-Brion, and E. R. Grant, Phys. Rev. A (in press)]. These results show comparable intensities for J+=3/2 of the X 2Π3/2 ion and J+=1/2 of the X 2Π1/2 ion. Both transitions require an angular momentum change of ΔN=-1 upon photoionization. To provide further insight into the near-threshold dynamics of this process, we also show rotationally resolved photoelectron angular distributions, alignment of the ion rotational levels, and rotational distributions for the parity components of the ion rotational levels. About 18% population is predicted to occur in the (+) parity component, which would arise from odd partial-wave contributions to the photoelectron matrix element. This behavior is similar to that in (2+1) REMPI via the S(2) branch of the F 1Δ2 state of HBr and was shown to arise from significant l mixing in the electronic continuum due to the nonspherical molecular ion potential. Rotational ion distributions resulting from (2+1) REMPI via the S(10) branch of the F 1Δ2 state are also shown.

  20. 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.

  1. Comparison of the resonance-enhanced multiphoton ionization spectra of pyrrole and 2,5-dimethylpyrrole: Building toward an understanding of the electronic structure and photochemistry of porphyrins

    NASA Astrophysics Data System (ADS)

    Beames, Joseph M.; Nix, Michael G. D.; Hudson, Andrew J.

    2009-11-01

    The photophysical properties of porphyrins have relevance for their use as light-activated drugs in cancer treatment and sensitizers in solid-state solar cells. However, the appearance of their UV-visible spectra is usually explained inadequately by qualitative molecular-orbital theories. We intend to gain a better insight into the intense absorption bands, and excited-state dynamics, that make porphyrins appropriate for both of these applications by gradually building toward an understanding of the macrocyclic structure, starting with studies of smaller pyrrolic subunits. We have recorded the (1+1) and (2+1) resonance-enhanced multiphoton ionization (REMPI) spectra of pyrrole and 2,5-dimethylpyrrole between 25 600 cm-1 (390 nm) and 48 500 cm-1 (206 nm). We did not observe a (1+1) REMPI signal through the optically bright B12 (ππ ∗) and A11 (ππ ∗) states in pyrrole due to ultrafast deactivation via conical intersections with the dissociative A12 (πσ ∗) and B11 (πσ ∗) states. However, we did observe (2+1) REMPI through Rydberg states with a dominant feature at 27 432 cm-1 (two-photon energy, 54 864 cm-1) assigned to a 3d←π transition. In contrast, 2,5-dimethylpyrrole has a broad and structured (1+1) REMPI spectrum between 36 000 and 42 500 cm-1 as a result of vibronic transitions to the B12 (ππ ∗) state, and it does not show the 3d←π Rydberg transition via (2+1) REMPI. We have complemented the experimental studies by a theoretical treatment of the excited states of both molecules using time-dependent density functional theory (TD-DFT) and accounted for the contrasting features in the spectra. TD-DFT modeled the photochemical activity of both the optically dark π1σ∗ states (dissociative) and optically bright π1π∗ states well, predicting the barrierless deactivation of the B12 (ππ ∗) state of pyrrole and the bound minimum of the B12 (ππ ∗) state in 2,5-dimethylpyrrole. However, the quantitative agreement between vibronic

  2. Comparison of the resonance-enhanced multiphoton ionization spectra of pyrrole and 2,5-dimethylpyrrole: Building toward an understanding of the electronic structure and photochemistry of porphyrins.

    PubMed

    Beames, Joseph M; Nix, Michael G D; Hudson, Andrew J

    2009-11-07

    The photophysical properties of porphyrins have relevance for their use as light-activated drugs in cancer treatment and sensitizers in solid-state solar cells. However, the appearance of their UV-visible spectra is usually explained inadequately by qualitative molecular-orbital theories. We intend to gain a better insight into the intense absorption bands, and excited-state dynamics, that make porphyrins appropriate for both of these applications by gradually building toward an understanding of the macrocyclic structure, starting with studies of smaller pyrrolic subunits. We have recorded the (1+1) and (2+1) resonance-enhanced multiphoton ionization (REMPI) spectra of pyrrole and 2,5-dimethylpyrrole between 25 600 cm(-1) (390 nm) and 48 500 cm(-1) (206 nm). We did not observe a (1+1) REMPI signal through the optically bright (1)B(2) (pipi( *)) and (1)A(1) (pipi( *)) states in pyrrole due to ultrafast deactivation via conical intersections with the dissociative (1)A(2) (pisigma( *)) and (1)B(1) (pisigma( *)) states. However, we did observe (2+1) REMPI through Rydberg states with a dominant feature at 27 432 cm(-1) (two-photon energy, 54 864 cm(-1)) assigned to a 3d<--pi transition. In contrast, 2,5-dimethylpyrrole has a broad and structured (1+1) REMPI spectrum between 36 000 and 42 500 cm(-1) as a result of vibronic transitions to the (1)B(2) (pipi( *)) state, and it does not show the 3d<--pi Rydberg transition via (2+1) REMPI. We have complemented the experimental studies by a theoretical treatment of the excited states of both molecules using time-dependent density functional theory (TD-DFT) and accounted for the contrasting features in the spectra. TD-DFT modeled the photochemical activity of both the optically dark (1)pisigma( *) states (dissociative) and optically bright (1)pipi( *) states well, predicting the barrierless deactivation of the (1)B(2) (pipi( *)) state of pyrrole and the bound minimum of the (1)B(2) (pipi( *)) state in 2,5-dimethylpyrrole

  3. Time-dependent configuration-interaction-singles calculation of the 5 p -subshell two-photon ionization cross section in xenon

    NASA Astrophysics Data System (ADS)

    Karamatskou, Antonia; Santra, Robin

    2017-01-01

    The 5 p two-photon ionization cross section of xenon in the photon-energy range below the one-photon ionization threshold is calculated within the time-dependent configuration-interaction-singles (TDCIS) method. The TDCIS calculations are compared to random-phase-approximation calculations [Wendin et al., J. Opt. Soc. Am. B 4, 833 (1987), 10.1364/JOSAB.4.000833] and are found to reproduce the energy positions of the intermediate Rydberg states reasonably well. The effect of interchannel coupling is also investigated and found to change the cross section of the 5 p shell only slightly compared to the intrachannel case.

  4. New perspectives in laser analytics: Resonance-enhanced multiphoton ionization in a Paul ion trap combined with a time-of-flight mass spectrometer

    NASA Astrophysics Data System (ADS)

    Bisling, Peter; Heger, Hans Jörg; Michaelis, Walfried; Weitkamp, Claus; Zobel, Harald

    1995-04-01

    A new laser analytical device has been developed that is based on resonance-enhanced multiphoton ionization in the very center of a radio-frequency quadrupole ion trap. Applications in speciation anlaysis of biological and enviromental samples and in materials science will all benefit from laser-optical selectivity in the resonance excitation process, combined with mass-spectropic sensivity which is further enhanced by the ion accumulation and storage capability.

  5. Investigation of the photoionization properties of pharmaceutically relevant substances by resonance-enhanced multiphoton ionization spectroscopy and single-photon ionization spectroscopy using synchrotron radiation.

    PubMed

    Kleeblatt, Juliane; Ehlert, Sven; Hölzer, Jasper; Sklorz, Martin; Rittgen, Jan; Baumgärtel, Peter; Schubert, Jochen K; Zimmermann, Ralf

    2013-08-01

    The photoionization properties of the pharmaceutically relevant substances amantadine, diazepam, dimethyltryptamine, etomidate, ketamine, mescaline, methadone, and propofol were determined. At beamline U125/2-10m-NIM of the BESSY II synchrotron facility (Berlin, Germany) vacuum ultraviolet (VUV) photoionization spectra were recorded in the energy range 7.1 to 11.9 eV (174.6 to 104.2 nm), showing the hitherto unknown ionization energies and fragmentation appearance energies of the compounds under investigation. Furthermore, (1+1)-resonance-enhanced multiphoton ionization (REMPI) spectra of selected compounds (amantadine, diazepam, etomidate, ketamine, and propofol) were recorded by a continuous scan in the energy range between 3.6 and 5.7 eV (345 to 218 nm) using a tunable optical parametric oscillator (spectral resolution: 0.1 nm) laser system. The resulting REMPI wavelength spectra of these compounds are discussed and put into context with already known UV absorption data. Time-of-flight mass spectrometry was used for ion detection in both experiments. Finally, the implications of the obtained physical-chemical results for potential analytical applications are discussed. In this context, fast detection approaches for the considered compounds from breath gas using photoionization mass spectrometry and a rapid pre-concentration step (e.g., needle trap device) are of interest.

  6. Laser induced avalanche ionization in gases or gas mixtures with resonantly enhanced multiphoton ionization or femtosecond laser pulse pre-ionization

    SciTech Connect

    Shneider, Mikhail N.; Miles, Richard B.

    2012-08-15

    The paper discusses the requirements for avalanche ionization in gas or gas mixtures initiated by REMPI or femtosecond-laser pre-ionization. Numerical examples of dependencies on partial composition for Ar:Xe gas mixture with REMPI of argon and subsequent classic avalanche ionization of Xe are presented.

  7. Fraunhofer-like diffracted lateral photoelectron momentum distributions of H2+ in charge-resonance-enhanced ionization in strong laser fields

    NASA Astrophysics Data System (ADS)

    Xin, Lin; Qin, Han-Cheng; Wu, Wan-Yang; He, Feng

    2015-12-01

    For H2+ at the critical internuclear distance where the charge-resonance-enhanced ionization is most prominent, the lateral photoelectron momentum distribution presents the Fraunhofer-like diffraction pattern: a central disk surrounded by one or more rings. We study this phenomenon by simulating the time-dependent Schrödinger equation and unveil the mechanism: the stretched molecule constructs an interatomic Coulomb potential, which works as a circular aperture and diffracts the electron when it travels between two nuclei. This distinct lateral photoelectron momentum distribution offers another perspective to look into molecular structures.

  8. Application of two-photon absorption in PWO scintillator for fast timing of interaction with ionizing radiation

    NASA Astrophysics Data System (ADS)

    Auffray, E.; Buganov, O.; Korjik, M.; Fedorov, A.; Nargelas, S.; Tamulaitis, G.; Tikhomirov, S.; Vaitkevičius, A.

    2015-12-01

    This work was aimed at searching for fast phenomena in scintillators in sub-10-ps range, a benchmark timing for the time response of radiation detectors in particle colliders. The pump-and-probe optical absorption technique with a tunable-wavelength parametric oscillator as the pump and a continuous-spectrum source as the probe beam was used to study lead tungstate PbWO4 (PWO) single crystals. It is shown that the rise time of the probe pulse absorption induced by the pump pulse is shorter than the pump pulse width of 200 fs. The approximately linear dependence of the probe absorption on the pump pulse energy density evidences that the induced absorption is caused by two-photon absorption involving one probe and one pump photon. We demonstrate that the intensity of the induced absorption at certain wavelengths is influenced by gamma irradiation, provided that an appropriate light polarization is selected. The application of the irradiation-sensitive nonlinearity for fast timing in radiation detectors is discussed.

  9. Resonance Enhanced Multi-Photon Ionization and Uv-Uv Hole-Burning Spectroscopic Studies of Jet-Cooled Acetanilide Derivatives

    NASA Astrophysics Data System (ADS)

    Moon, Ceol Joo; Min, Ahreum; Ahn, Ahreum; Lee, Seung Jun; Choi, Myong Yong; Kim, Seong Keun

    2013-06-01

    Conformational investigations and photochemistry of jet-cooled methacetine (MA) and phenacetine (PA) using one color resonant two-photon ionization (REMPI), UV-UV hole-burning and IR-dip spectroscopy are presented. MA and PA are derivatives of acetanilide, substituted by methoxyl, ethoxyl group in the para position of acetanilide, respectively. Moreover, we have investigated conformational information of the acetanilide derivatives (AAP, MA and PA)-water. In this work, we will present and discuss the solvent effects of the hydroxyl group of acetanilide derivatives in the excited state.

  10. Photofragmentations, state interactions, and energetics of Rydberg and ion-pair states: two-dimensional resonance enhanced multiphoton ionization of HBr via singlet-, triplet-, Ω = 0 and 2 states.

    PubMed

    Long, Jingming; Hróðmarsson, Helgi Rafn; Wang, Huasheng; Kvaran, Ágúst

    2012-06-07

    Mass spectra were recorded for one-colour resonance enhanced multiphoton ionization (REMPI) of H(i)Br (i = 79, 81) for the two-photon resonance excitation region 79,040-80,300 cm(-1) to obtain two-dimensional REMPI data. The data were analysed in terms of rotational line positions, intensities, and line-widths. Quantitative analysis of the data relevant to near-resonance interactions between the F(1)Δ(2)(v' = 1) and V(1)Σ(+)(v' = m + 7) states gives interaction strengths, fractional state mixing, and parameters relevant to dissociation of the F state. Qualitative analysis further reveals the nature of state interactions between ion-pair states and the E(1)Σ(+) (v' = 1) and H(1)Σ(+)(v' = 0) Rydberg states in terms of relative strengths and J' dependences. Large variety in line-widths, depending on electronic states and J' quantum numbers, is indicative of number of different predissociation channels. The relationship between line-widths, line-shifts, and signal intensities reveals dissociation mechanisms involving ion-pair to Rydberg state interactions prior to direct or indirect predissociations of Rydberg states. Quantum interference effects are found to be important. Moreover, observed bromine atom (2 + 1) REMPI signals support the importance of Rydberg state predissociation channels. A band system, not previously observed in REMPI, was observed and assigned to the k(3)Π(0)(v' = 0) ←← X transition with band origin 80,038 cm(-1) and rotational parameter B(v('))=7.238 cm(-1).

  11. Angular and internal state distributions of H2+ generated by (2 + 1) resonance enhanced multiphoton ionization of H2 using time-of-flight mass spectrometry

    NASA Astrophysics Data System (ADS)

    Perreault, William E.; Mukherjee, Nandini; Zare, Richard N.

    2016-06-01

    We report direct measurement of the anisotropy parameter β for the angular distribution of the photoelectron and photoion in (2 + 1) resonance enhanced multiphoton ionization process of H2 X 1 Σg + (v = 0, J = 0) molecules through the intermediate H2 E,F 1 Σg + (v' = 0, J' = 0) level (λ = 201.684 nm) using a time-of-flight mass spectrometer. The time-of-flight spectra were recorded as the direction of polarization of the ionizing laser was varied with respect to the flight axis of the H2 molecular beam and were fitted to an angular distribution in an appropriately rotated coordinate system with the z-axis oriented along the time-of-flight axis. The anisotropy parameter β was found to be 1.72 ± 0.13 by fitting the time-of-flight spectra and agreed with previous measurements. Using secondary ionization with a delayed laser pulse of different wavelength, we also determined the vibrational energy distribution of the ions, showing that 98% ± 4% of the ions are generated in their ground vibrational state, in agreement with the calculated Franck-Condon factors between the H2 E,F 1 Σg + (v' = 0) and H 2+ X 1 Σg + (v″) vibrational levels.

  12. Angular and internal state distributions of H2 (+) generated by (2 + 1) resonance enhanced multiphoton ionization of H2 using time-of-flight mass spectrometry.

    PubMed

    Perreault, William E; Mukherjee, Nandini; Zare, Richard N

    2016-06-07

    We report direct measurement of the anisotropy parameter β for the angular distribution of the photoelectron and photoion in (2 + 1) resonance enhanced multiphoton ionization process of H2 X (1)Σg (+) (v = 0, J = 0) molecules through the intermediate H2 E,F (1)Σg (+) (v' = 0, J' = 0) level (λ = 201.684 nm) using a time-of-flight mass spectrometer. The time-of-flight spectra were recorded as the direction of polarization of the ionizing laser was varied with respect to the flight axis of the H2 molecular beam and were fitted to an angular distribution in an appropriately rotated coordinate system with the z-axis oriented along the time-of-flight axis. The anisotropy parameter β was found to be 1.72 ± 0.13 by fitting the time-of-flight spectra and agreed with previous measurements. Using secondary ionization with a delayed laser pulse of different wavelength, we also determined the vibrational energy distribution of the ions, showing that 98% ± 4% of the ions are generated in their ground vibrational state, in agreement with the calculated Franck-Condon factors between the H2 E,F (1)Σg (+) (v' = 0) and H2 (+) X (1)Σg (+) (v″) vibrational levels.

  13. Isotopically-selective two-photon ionization of 12C- and 13C-benzene and hexadeuterobenzene in a time-of-flight mass spectrometer

    NASA Astrophysics Data System (ADS)

    de La Cruz, A.; Ortiz, M.; Cabrera, J. A.; Campos, J.

    1994-04-01

    In this work the 610 band spectra for 12C6H6, 12C6D6, 13C12C5H6 and 13C12C5D6 isotopically-substituted benzenes are reported. Spectra of deuterated species are given for the first time. These molecular spectra can be employed to test the technical performances of REMPI-TOFMS systems. The experimental method was laser-induced two-photon ionization of molecules cooled in a He supersonic beam followed by time-of-flight mass spectrometry. A splitting of the 610 band appears when a 13C atom is present in the benzene-ring, favoring the isotope selectivity. In the present experiment a complete mass discrimination has been accomplished by using appropriate electronic circuits. A proportional counter has been used to obtain the corresponding spectra of the molecules at 300 K. The device is very useful to tune the laser wavelength to resonance in this kind of mass spectrometry experiment.

  14. A spectroscopic study of nicotine analogue 2-phenylpyrrolidine (PPD) using resonant two-photon ionization (R2PI), microwave, and 2D NMR techniques.

    PubMed

    Martin, Danielle E; Robertson, Evan G; MacLellan, Jonathan G; Godfrey, Peter D; Thompson, Christopher D; Morrison, Richard J S

    2009-02-25

    Conformational preferences of the nicotine analogue 2-phenylpyrrolidine (PPD) have been studied in both gaseous and solution phases. Theoretical calculations at the MP2 and B3LYP levels point to 5-6 stable conformers which differ in three degrees of conformational freedom; torsion between the two rings, inversion at the pyrrolidine (PY) amine, and PY ring puckering, characterized using the Cremer-Pople definition for pseudorotation. Only one conformer has a trans arrangement between the amino hydrogen and the phenyl substituent. It is 6-8 kJ mol(-1) more stable than the cis conformers, has a perpendicular ring arrangement, and puckers at the nitrogen atom--similar to structures reported for nicotine. Resonant two-photon ionization (R2PI) data, including hole burn spectra, indicate only one conformer is present in the free jet expansion, and band contour analysis suggests assignment to the trans conformer. Confirmation was provided by microwave spectroscopy. Fifty-seven lines measured in the 48-72 GHz region were assigned to 206 b-type transitions and fitted to yield rotational constants within 2 MHz of MP2 values predicted for the trans conformer. The solution-phase conformers of PPD were studied using 1D and 2D (1)H NMR spectroscopy and solvent-based theoretical calculations. In marked contrast to the gas phase, NMR data reveals only cis conformers present in solution. Calculations confirm increased stability for these conformers when placed in simulated chloroform or water environments. Solvent molecules are believed to disrupt a crucial N...H(ortho) stabilizing interaction present within the trans conformer.

  15. Photofragmentations, state interactions, and energetics of Rydberg and ion-pair states: resonance enhanced multiphoton ionization via E and V (B) states of HCl and HBr.

    PubMed

    Long, Jingming; Wang, Huasheng; Kvaran, Ágúst

    2013-01-28

    (2 + n) resonance enhanced multiphoton ionization mass spectra for resonance excitations to diabatic E(1)Σ(+) (v') Rydberg and V (1)Σ(+) (v') ion-pair states (adiabatic B(1)Σ(+)(v') states) of H(i)Cl (i = 35,37) and H(i)Br (i = 79,81) were recorded as a function of excitation wavenumber (two-dimensional REMPI). Simulation analyses of ion signal intensities, deperturbation analysis of line shifts and interpretations of line-widths are used to derive qualitative and quantitative information concerning the energetics of the states, off-resonance interactions between the E states and V states, closest in energy as well as on predissociation channels. Spectroscopic parameters for the E(1)Σ(+) (v')(v' = 1) for H(35)Cl and v' = 0 for H(79)Br states, interaction strengths for E - V state interactions and parameters relevant to dissociation of the E states are derived. An overall interaction and dynamical scheme, to describe the observations for HBr, is proposed.

  16. Rotational branching ratios and photoelectron angular distributions in resonance enhanced multiphoton ionization of HBr via the F sup 1. Delta. sub 2 Rydberg state

    SciTech Connect

    Wang, K.; McKoy, V. )

    1991-12-01

    Results of theoretical studies of rotational ion distributions in the {ital X} {sup 2}{Pi}{sub 1/2} ground state of HBr{sup +} resulting from (2+1) resonance enhanced multiphoton ionization (REMPI) via the {ital S}(2) branch of the {ital F} {sup 1}{Delta}{sub 2} Rydberg state are reported. These results show a strongly parity-favored ion distribution with about 80% population in the ({minus}) component of the {Lambda} doublet of {ital J}{sup +} rotational levels. The 20% population in the other parity component of the {Lambda} doublet can be seen to be due to odd partial wave contributions to the photoelectron matrix elements which arise primarily from non-atomic-like behavior of the electronic continuum. This, in turn, is due to angular momentum coupling in the photoelectron orbital brought about by the torques of the nonspherical molecular ion potential. We demonstrate that the effect of alignment on these ion distributions, although not large, is important. Photoelectron angular distributions and alignment of the {ital J} levels of the HBr{sup +} ions are also presented. Rotational branching ratios and photoelectron angular distributions resulting from (2+1{prime}) REMPI of HBr via several {ital S} branches of the {ital F} {sup 1}{Delta}{sub 2} state are also shown for near-threshold photoelectron energies.

  17. On-line derivatization for resonance-enhanced multiphoton ionization time-of-flight mass spectrometry: detection of aliphatic aldehydes and amines via reactive coupling of aromatic photo ionization labels.

    PubMed

    Fernandes-Whaley, Maria; Mühlberger, Fabian; Whaley, Alexander; Adam, Thomas; Zimmermann, Ralf; Rohwer, Egmont; Walte, Andreas

    2005-01-01

    Resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) is a powerful technique for the on-line analysis of aromatic compounds with unique features regarding selectivity and sensitivity. Aliphatic compounds, however, are difficult to address by REMPI due to their unfavorable photo ionization properties. This paper describes the proof of concept for an on-line derivatization approach for converting nonaromatic target analytes into specific, photoionizable aromatic derivatives that are readily detectable by REMPI-TOFMS. A multichannel silicone trap or poly(dimethylsiloxane) (PDMS) open tubular capillary was used as a reaction medium for the derivatization of volatile alkyl aldehydes and alkylamines with aromatic "photoionization labels"and to concentrate the resulting aromatic derivatives. The aldehydes formaldehyde, acetaldehyde, acrolein, and crotonal, which when underivatized are poorly detectable by REMPI, were converted into their easily photoionizable phenylhydrazone derivatives by the on-line reaction with phenylhydrazine as reagent. Similarly, the methyl-, ethyl-, propyl-, and butylamines were converted into their REMPI-ionizable benzaldehyde alkylimine derivatives by the on-line reaction with benzaldehyde as reagent. The derivatives were thermally desorbed from the PDMS matrix and transferred into the REMPI-TOFMS for detection. The REMPI-TOFMS detection limits obtained for acetaldehyde; acrolein; crotonal; and methyl-, ethyl-, propyl-, and butylamine using this photo ionization labeling method were in the sub-parts-per-million range and, thus, readily below the permissible exposure limits set by OSHA.

  18. Vibronic spectra of jet-cooled 2-aminopurine·H2O clusters studied by UV resonant two-photon ionization spectroscopy and quantum chemical calculations.

    PubMed

    Sinha, Rajeev K; Lobsiger, Simon; Trachsel, Maria; Leutwyler, Samuel

    2011-06-16

    For understanding the major- and minor-groove hydration patterns of DNAs and RNAs, it is important to understand the local solvation of individual nucleobases at the molecular level. We have investigated the 2-aminopurine·H(2)O monohydrate by two-color resonant two-photon ionization and UV/UV hole-burning spectroscopies, which reveal two isomers, denoted A and B. The electronic spectral shift δν of the S(1) ← S(0) transition relative to bare 9H-2-aminopurine (9H-2AP) is small for isomer A (-70 cm(-1)), while that of isomer B is much larger (δν = -889 cm(-1)). B3LYP geometry optimizations with the TZVP basis set predict four cluster isomers, of which three are doubly H-bonded, with H(2)O acting as an acceptor to a N-H or -NH2 group and as a donor to either of the pyrimidine N sites. The "sugar-edge" isomer A is calculated to be the most stable form with binding energy D(e) = 56.4 kJ/mol. Isomers B and C are H-bonded between the -NH2 group and pyrimidine moieties and are 2.5 and 6.9 kJ/mol less stable, respectively. Time-dependent (TD) B3LYP/TZVP calculations predict the adiabatic energies of the lowest (1)ππ* states of A and B in excellent agreement with the observed 0(0)(0) bands; also, the relative intensities of the A and B origin bands agree well with the calculated S(0) state relative energies. This allows unequivocal identification of the isomers. The R2PI spectra of 9H-2AP and of isomer A exhibit intense low-frequency out-of-plane overtone and combination bands, which is interpreted as a coupling of the optically excited (1)ππ* state to the lower-lying (1)nπ* dark state. In contrast, these overtone and combination bands are much weaker for isomer B, implying that the (1)ππ* state of B is planar and decoupled from the (1)nπ* state. These observations agree with the calculations, which predict the (1)nπ* above the (1)ππ* state for isomer B but below the (1)ππ* for both 9H-2AP and isomer A.

  19. Two-photon photocurrent autocorrelation using intersubband transitions at nearly-resonant excitation.

    PubMed

    Schneider, Harald; Maier, Thomas; Liu, H C; Walther, Martin

    2008-02-04

    We investigate nonlinear mid-infrared detection via two-photon transitions involving two bound subbands and one continuum resonance in an n-type multiple quantum well. By varying the excitation energy, we have tuned the two-photon transition from resonant, yielding optimum resonant enhancement with a real intermediate state, to nearly-resonant, with a virtual but resonantly enhanced intermediate state. For autocorrelation purposes, the latter configuration improves time resolution whilst partially retaining a resonant enhancement of the two-photon transition strength.

  20. Opacity from two-photon processes

    NASA Astrophysics Data System (ADS)

    More, Richard M.; Hansen, Stephanie B.; Nagayama, Taisuke

    2017-09-01

    The recent iron opacity measurements performed at Sandia National Laboratory by Bailey and collaborators have raised questions about the completeness of the physical models normally used to understand partially ionized hot dense plasmas. We describe calculations of two-photon absorption, which is a candidate for the observed extra opacity. Our calculations do not yet match the experiments but show that the two-photon absorption process is strong enough to require careful consideration.

  1. Opacity from two-photon processes

    DOE PAGES

    More, Richard M.; Hansen, Stephanie B.; Nagayama, Taisuke

    2017-07-22

    Here, the recent iron opacity measurements performed at Sandia National Laboratory by Bailey and collaborators have raised questions about the completeness of the physical models normally used to understand partially ionized hot dense plasmas. We describe calculations of two-photon absorption, which is a candidate for the observed extra opacity. Our calculations do not yet match the experiments but show that the two-photon absorption process is strong enough to require careful consideration.

  2. Photodissociation dynamics of halogenated thiophenes at 235 nm: a resonance enhanced multiphoton ionization-time-of-flight (REMPI-TOF) study.

    PubMed

    Kawade, Monali; Saha, Ankur; Upadhyaya, Hari P; Kumar, Awadhesh; Naik, Prakash D; Bajaj, P N

    2012-11-08

    The photodissociation dynamics of halogen-substituted thiophenes, namely, 2-chlorothiophene and 2-bromo-5-chlorothiophene, has been studied in a supersonic molecular beam around 235 nm, using resonance enhanced multiphoton ionization (REMPI) time-of-flight (TOF) technique, by detecting the nascent state of the primary halogen atoms. A single laser has been used for excitation of halothiophenes, as well as for the REMPI detection of photoproducts, namely, chlorine and bromine atoms, in their spin-orbit states X((2)P(3/2)) and X*((2)P(1/2)). We have determined the translational energy distribution, the recoil anisotropy parameter, β, and the spin-orbit branching ratio, for chlorine and bromine atom elimination channels. State-specific TOF profiles are converted into kinetic energy distributions, using a least-squares fitting method, taking into account the fragment anisotropies, β(ι). The TOF profiles for Cl, Cl*, Br, and Br* are found to be independent of laser polarization; i.e., the β is well characterized by a value of ~0.0, within the experimental uncertainties. For 2-chlorothiophene, we have observed two components for the Cl and only one component for the Cl* atom elimination channel in the translational energy distributions. The average translational energies for the fast and the slow components of the Cl channel are 3.0 ± 1.0 and 1.0 ± 0.5 kcal/mol, respectively. For Cl*, the average translational energy is 3.5 ± 1.0 kcal/mol. For 2-bromo-5-chlorothiophene, we have observed only one component for Cl, Cl*, Br, and Br* in the translational energy distributions. The average translational energies for the Cl and Cl* channels are 3.5 ± 1.0 and 5.0 ± 1.0 kcal/mol, respectively, whereas the average translational energies for the Br and Br* channels are 2.0 ± 1.0 and 3.5 ± 1.0 kcal/mol, respectively. The energy partitioning into the translational modes is interpreted with the help of various models, such as impulsive and statistical models. The ΔH(f)(298

  3. Terahertz two-photon quantum well infrared photodetector.

    PubMed

    Schneider, H; Liu, H C; Winnerl, S; Song, C Y; Walther, M; Helm, M

    2009-07-20

    A two-photon detector based on intersubband transitions in GaAs/AlGaAs quantum wells operating in the Terahertz regime below the Reststrahlenband is reported. Resonantly enhanced optical nonlinearities enables sensitive quadratic detection at pJ pulse energies. We demonstrate its use in a quadratic autocorrelator for far-infrared picosecond pulses at around 7 THz.

  4. Resonance Enhanced Multi-photon Spectroscopy of DNA

    NASA Astrophysics Data System (ADS)

    Ligare, Marshall Robert

    For over 50 years DNA has been studied to better understand its connection to life and evolution. These past experiments have led to our understanding of its structure and function in the biological environment but the interaction of DNA with UV radiation at the molecular level is still not very well understood. Unique mechanisms in nucleobase chromaphores protect us from adverse chemical reactions after UV absorption. Studying these processes can help develop theories for prebiotic chemistry and the possibility of alternative forms of DNA. Using resonance enhanced multi-photon spectroscopic techniques in the gas phase allow for the structure and dynamics of individual nucleobases to be studied in detail. Experiments studying different levels of structure/complexity with relation to their biological function are presented. Resonant IR multiphoton dissociation spectroscopy in conjunction with molecular mechanics and DFT calculations are used to determine gas phase structures of anionic nucleotide clusters. A comparison of the identified structures with known biological function shows how the hydrogen bonding of the nucleotides and their clusters free of solvent create favorable structures for quick incorporation into enzymes such as DNA polymerase. Resonance enhanced multi-photon ionization (REMPI) spectroscopy techniques such as resonant two photon ionization (R2PI) and IR-UV double resonance are used to further elucidate the structure and excited state dynamics of the bare nucleobases thymine and uracil. Both exhibit long lived excited electronic states that have been implicated in DNA photolesions which can ultimately lead to melanoma and carcinoma. Our experimental data in comparison with many quantum chemical calculations suggest a new picture for the dynamics of thymine and uracil in the gas phase. A high probability of UV absorption from a vibrationally hot ground state to the excited electronic state shows that the stability of thymine and uracil comes from

  5. Two-photon cryomicroscope

    NASA Astrophysics Data System (ADS)

    Breunig, H. G.; Köhler, C.; König, K.

    2012-03-01

    We report on a new two-photon cryomicroscope which consist of a compact laser-scanning microscope combined with a motorized heating and freezing stage. Samples can be cooled down to -196 °C (77 K) and heated up to 600 °C (873 K) with adjustable heating/freezing rates between 0.01 K / min and 150 K / min. Two-photon imaging is realized by near infrared femtosecond-laser pulse excitation. The abilities of the two-photon cryomicroscope are illustrated in several measurements: imaging of fluorescent microspheres inside a piece of ice illustrates the feasibility of deep-microscopic imaging inside frozen sample. The temperature-dependent structural integrity of collagen is monitored by detection of second harmonic generation signals from porcine cornea. The measurements reveal also the dependence of the collagendenaturation temperature on hydration state of the cornea collagen. Furthermore, the potential of the two-photon cryomicroscope for optimization of freezing and thawing procedures as well as to evaluate the viability of frozen cells and tissue is discussed.

  6. a 1+1' Resonance-Enhanced Multiphoton Ionization Scheme for Rotationally State-Selective Detection of Formaldehyde via the ˜{A}^1A_2←˜{X}^1A_1 Transition

    NASA Astrophysics Data System (ADS)

    Park, Barratt; Krueger, Bastian C.; Meyer, Sven; Wodtke, Alec; Schaefer, Tim

    2017-06-01

    The formaldehyde molecule is an important model system for understanding dynamical processes in small polyatomic molecules. However, prior to this work, there have been no reports of a resonance-enhanced multiphoton ionization (REMPI) detection scheme for formaldehyde suitable for rovibrationally state-selective detection in molecular beam scattering experiments. Previously reported tunable REMPI schemes are either non-rotationally resolved, involve multiple resonant steps, or involve many-photon ionization steps. In the current work, we present a new 1+1' REMPI scheme for formaldehyde. The first photon is tunable and provides rotational resolution via the vibronically allowed ˜{A}^1A_2←˜{X}^1A_1 transition. Molecules are then directly ionized from the ˜{A} state by one photon of 157 nm. The results indicate that the ionization cross section from the 4^1 vibrational level of the ˜{A} state is independent of the rotational level used as intermediate, to within experimental uncertainty. The 1+1' REMPI intensities are therefore directly proportional to the ˜{A}←˜{X} absorption intensities and can be used for quantitative measurement of ˜{X}-state population distributions.

  7. Theoretical investigation of the origin of the multipeak structure of kinetic-energy-release spectra from charge-resonance-enhanced ionization of H{sub 2}{sup +} in intense laser fields

    SciTech Connect

    He Haixiang; Guo Yahui; Lu Ruifeng; Zhang Peiyu; Han Keli; He Guozhong

    2011-09-15

    The dynamics of hydrogen molecular ions in intense laser pulses (100 fs, I = 0.77 x 10{sup 14} W/cm{sup 2} to 2.5 x 10{sup 14} W/cm{sup 2}) has been studied, and the kinetic-energy-release spectra of Coulomb explosion channel have been calculated by numerically solving the time-dependent Schroedinger equation. In a recent experiment, a multipeak structure from charge-resonance-enhanced ionization is interpreted by a vibrational 'comb' at a critical nuclear distance. We found that the peaks could not be attributed to a single vibrational level but a collective contribution of some typical vibrational states in our calculated Coulomb explosion spectra, and the main peak shifts toward the low-energy region with increasing vibrational level, which is also different from the explanation in that experiment. We have also discussed the proton's kinetic-energy-release spectra for different durations with the same laser intensity.

  8. Resonantly-enhanced, four-photon ionization of krypton at laser intensities exceeding 10/sup 13/ W/cm/sup 2/

    SciTech Connect

    Perry, M.D.; Landen, O.L.; Campbell, E.M.

    1987-12-01

    The yield of singly- and multiply- charged ions of krypton and xenon is presented as a function of laser intensity and frequency. The measurements were performed using the second harmonic output of a well-characterized, tunable picosecond dye laser in the range 285 to 310 nm at laser intensities from 1 x 10/sup 12/ to 10/sup 14/ W/cm/sup 2/. Enhancement of the Kr/sup +/ yield by two orders of magnitude by three-photon resonant, four-photon ionization is observed in the vicinity of the 4d'(5/2)/sub 3/ and the 4d(3/2)/sub 1/ intermediate states. A model incorporating line shifts and widths scaling linearly with intensity is in good agreement with the experimental results.

  9. Effect of the coherent cancellation of the two-photon resonance on the generation of vacuum ultraviolet light by two-photon reasonantly enhanced four-wave mixing

    SciTech Connect

    Payne, M.G.; Garrett, W.R.; Judish, J.P.; Wunderlich, R.

    1988-11-01

    Many of the most impressive demonstrations of the efficient generation of vacuum ultraviolet (VUV) light have made use of two- photon resonantly enhanced four-wave mixing to generate light at ..omega../sub VUV/ = 2..omega../sub L1/ +- ..omega../sub L2/. The two-photon resonance state is coupled to the ground state both by two photons from the first laser, or by a photon from the second laser and one from the generated VUV beam. We show here that these two coherent pathways destructively interfere once the second laser is made sufficiently intense, thereby leading to an important limiting effect on the achievable conversion efficiency. 4 refs.

  10. Ab initio study of the one- and two-photon circular dichroism of R-(+)-3-methyl-cyclopentanone

    NASA Astrophysics Data System (ADS)

    Rizzo, Antonio; Lin, Na; Ruud, Kenneth

    2008-04-01

    One- and two-photon circular dichroism spectra of R-(+)-3-methyl-cyclopentanone, a system that has been the subject of recent experimental studies of (2+1) resonance-enhanced multiphoton ionization circular dichroism, have been calculated with an origin-invariant density functional theory approximation in the region of the lowest electronic excited states, both for the gas phase and for a selection of solvents. A polarizable continuum model is used in the calculations performed on the solvated system. Two low-lying conformers are analyzed, and a comparison of the intensities and characteristic features is made with the corresponding two-photon absorption for each species, also for the Boltzmann-averaged spectra. The effect of the choice of geometry, basis set, and exchange-correlation functional is carefully analyzed. It is found that a density functional theory approach using the Coulomb attenuating method variant of Becke's three-parameter exchange and the Lee-Yang-Parr correlation functionals with correlation-consistent basis sets of double-zeta quality can reproduce the experimental electronic circular dichroism spectra very well. The features appearing in experiment are characterized in terms of molecular excitations, and the differences in the response of each state in the one- and two-photon processes are highlighted.

  11. EUV two-photon-ionization cross sections of helium from the solution of the time-dependent Schrödinger equation, and comparison with measurements using free-electron lasers

    NASA Astrophysics Data System (ADS)

    Mercouris, Theodoros; Komninos, Yannis; Nicolaides, Cleanthes A.

    2016-12-01

    Two recent experimental papers reported the first measurements of absolute two-photon-ionization cross sections σ (2 ) of helium, for EUV wavelengths, using free-electron laser (FEL) pulses [Sato et al., J. Phys. B 44, 161001 (2011), 10.1088/0953-4075/44/16/161001; Fushitani et al., Phys. Rev. A 88, 063422 (2013), 10.1103/PhysRevA.88.063422]. The wavelengths correspond to transitions that are off resonance as well as on resonance with the 1 s 2 p and 1 s 3 p 1Po Rydberg states. Inspection of their results reveals considerable discrepancies, while their comparison with theoretical results obtained earlier from time-independent calculations, one perturbative and two nonperturbative ones, cannot lead to secure conclusions as to the true values of σ (2 ) . We examined this prototypical problem by implementing a time-dependent approach, which utilizes the nonperturbative solution of the time-dependent Schrödinger equation. This solution was obtained in terms of the state-specific expansion approach, in an upgraded version where the coupling matrix elements are computed using the full electric operator of the multipolar Hamiltonian. The σ (2 ) were obtained for pulses of 300 fs, as in the 2011 FEL experiment. Their computation was achieved by fitting the time-dependent ionization survival probability to e-Γ t, where Γ is the rate of ionization. The wavelengths and intensities are those of the FEL experiments, as well as others, such as the wavelengths 52.22 and 51.56 nm, for which the 1 s 4 p 1Po and 1 s 5 p 1Po levels are on resonance with the initial 1S state. Apart from the predictions for these wavelengths, the paper contains characteristic comparisons among all the results on these EUV σ (2 ) , experimental and theoretical. In general, the trends predicted by nonperturbative methods are confirmed by the FEL measurements. However, discrepancies exist among the absolute numbers. Furthermore, comparison among the results of the three nonperturbative approaches

  12. Two-photon quantum well infrared photodetectors below 6 THz

    NASA Astrophysics Data System (ADS)

    Franke, Carsten; Walther, Martin; Helm, Manfred; Schneider, Harald

    2015-05-01

    Two-photon quantum well infrared photodetectors (QWIPs) are nonlinear detectors for the mid-infrared and terahertz regimes optimized for resonant two-photon absorption. Here we present first results on two-photon QWIP samples based on the GaAs/AlGaAs material system with intersubband energies between 25 and 12 meV (6-3 THz) confirmed by photocurrent spectra. The dark current showed large discontinuities, presumably caused by impact ionization. We performed interferometric autocorrelation experiments at the free-electron laser FELBE and observed nonlinear interferograms for all samples.

  13. Two Photon Detection Techniques for Atomic Fluorine

    DTIC Science & Technology

    1988-06-30

    to the two-photon detection technique. ’.d. %.. %9I Flowing He/F Mixture CaF 2 (20% F) from Pellin- Broca ionization Microwave Discharge Prism 1~~T6th...Stokes (AS) orders are separated using a CaF2 Pellin- Broca prism. The sixth AS at 170 un is propagated through an evacuated beam path (10 .5 torr) and...CaF2 Pellin- Broca prism. The atoms Br (Ref. 5) and Cl (Ref. 6) with limited sensitiv- sixth AS wave at 170 nm is propagated through a series ity6

  14. Analysis of the (1)A' S1 ← (1)A' S0 and (2)A' D0 ← (1)A' S1 band systems in 1,2-dichloro-4-fluorobenzene by means of resonance-enhanced-multi-photon-ionization (REMPI) and mass-analyzed-threshold-ionization (MATI) spectroscopy.

    PubMed

    Krüger, Sascha; Grotemeyer, Jürgen

    2016-03-14

    Resonance enhanced multiphoton ionization (REMPI) and mass analyzed threshold ionization (MATI) spectroscopy have been applied in order to investigate the vibrational structure of 1,2-dichloro-4-fluorobenzene (1,2,4-DCFB) in its first excited state (S1) and the cationic ground state (D0). The selection of the state prior to ionization resulted in MATI spectra with different intensity distributions thus giving access to many vibrational levels. To support the experimental findings, geometry optimizations and frequency analyses at DFT (density functional) and TDDFT (time-dependent density functional) levels of theory have been applied. Additionally, a multidimensional Franck-Condon approach has been used to calculate the vibrational intensities from the DFT calculations. An excellent agreement between simulated and measured REMPI and MATI spectra allowed for a confident assignment of vibrational levels and mechanisms active during excitation and ionization. In order to avoid any ambiguity regarding the assignment of the vibrational bands to normal modes, Duschinsky normal mode analysis has been performed to correlate the ground state (S0) normal modes of 1,2,4-DCFB with the benzene derived Wilson nomenclature. From the REMPI spectra the electronic excitation energy (EE) of 1,2-dichloro-4-fluorobenzene could be determined to be 35 714 ± 2 cm(-1) while the MATI spectra yielded the adiabatic ionization energy (IE) of 1,2-dichloro-4-fluorobenzene which could be determined to be 73 332 ± 7 cm(-1).

  15. Two-photon resonance fluorescence

    SciTech Connect

    Alexanian, Moorad; Bose, Subir K.

    2006-12-15

    We present a theory of two-photon resonance fluorescence of an atom or molecule in which the excitation by an external electromagnetic field as well as fluorescence emission is mediated by two-photon processes. The treatment is based on first dressing the atom or molecule by the external field and then evaluating perturbatively the effect of the interaction with the vacuum or fluorescent field and so resonance fluorescence can be considered as spontaneous emission from the dressed atom. The introduction of the combined system of atom and external field via dressed states leads to simpler calculations and more transparent physics. The fluorescence spectrum derived by us has similarities as well as differences with that of one-photon resonance fluorescence and earlier theoretical predictions for the two-photon case.

  16. Two-photon geometric optics

    NASA Astrophysics Data System (ADS)

    Pittman, T. B.; Strekalov, D. V.; Klyshko, D. N.; Rubin, M. H.; Sergienko, A. V.; Shih, Y. H.

    1996-04-01

    We report two-photon correlation experiments using spontaneous parametric down-conversion under a severe manipulation of the input pump field. Considering the case of passing the laser beam through a focusing lens before the down-conversion crystal, theoretical calculations and a series of imaging experiments demonstrate two-photon geometric optics effects. In particular, the imaging in coincidence counts of an aperture placed in one of the down-conversion beams is found to be the analog of a simple spherical mirror system, which displays a ``vacuum dispersion'' effect in that the object and image distances are wavelength weighted.

  17. Two-photon geometrical phase

    NASA Astrophysics Data System (ADS)

    Strekalov, D. V.; Shih, Y. H.

    1997-10-01

    An advanced wave model is applied to a two-photon interference experiment to show that the observed interference effect is due to the geometrical phase of a two-photon state produced in spontaneous parametric down-conversion. The polarization state of the signal-idler pair is changed adiabatically so that the ``loop'' on the Poincaré sphere is opened in the signal channel and closed in the idler channel. Therefore, we observed an essentially nonlocal geometrical phase, shared by the entangled photon pair, or a biphoton.

  18. Two-Photon Absorption and Two-Photon Four-Wave Mixing for the Terbium Ion in Insulators.

    NASA Astrophysics Data System (ADS)

    Huang, Jin

    Resonant enhancement of over two orders of magnitude of direct two-photon absorption from the ground state ^7F_6 to the excited state ^5G_6 of the 4f^8 configuration of Tb^{3+} at 40,200 cm ^{-1} has been observed in time resolved experiments with two separate lasers. The results provide clear evidence for resonant enhancement of two-photon absorption in rare earth compounds and imply the same for Raman scattering. Two separate transition mechanisms have been observed. When a single laser frequency was used, the intermediate states making the largest contribution were from excited configurations of opposite parity which were far from resonance. Detailed two-frequency experiments showed, however, that near the single photon resonance, there was a much stronger contribution from the 4f ^8 configuration ^5D _4 intermediate state. The phase-matching-induced frequency selectivity in the single-photon-resonant four-wave mixing has been observed in further rare earth compounds. These observations provide additional evidence that the phase matching effects, resulting from anomalous dispersion associated with the single-photon resonance, play a major role in determining both the intensity and the line narrowing of the mixing signal, and that similar effects will be observable in any rare earth compound. An effect of two-photon-resonant four-wave mixing has been observed for a transition to the 4f^8 configuration ^5K _8 state of the Tb^{3+ } ion in LiYF_4. The strength of the resonance is comparable to that of single -photon resonances. This technique holds promise as a new spectroscopic tool, especially for studies of two-photon transitions in non-fluorescent materials.

  19. Two-Photon Flow Cytometry

    NASA Technical Reports Server (NTRS)

    Zhog, Cheng Frank; Ye, Jing Yong; Norris, Theodore B.; Myc, Andrzej; Cao, Zhengyl; Bielinska, Anna; Thomas, Thommey; Baker, James R., Jr.

    2004-01-01

    Flow cytometry is a powerful technique for obtaining quantitative information from fluorescence in cells. Quantitation is achieved by assuring a high degree of uniformity in the optical excitation and detection, generally by using a highly controlled flow such as is obtained via hydrodynamic focusing. In this work, we demonstrate a two-beam, two- channel detection and two-photon excitation flow cytometry (T(sup 3)FC) system that enables multi-dye analysis to be performed very simply, with greatly relaxed requirements on the fluid flow. Two-photon excitation using a femtosecond near-infrared (NIR) laser has the advantages that it enables simultaneous excitation of multiple dyes and achieves very high signal-to-noise ratio through simplified filtering and fluorescence background reduction. By matching the excitation volume to the size of a cell, single-cell detection is ensured. Labeling of cells by targeted nanoparticles with multiple fluorophores enables normalization of the fluorescence signal and thus ratiometric measurements under nonuniform excitation. Quantitative size measurements can also be done even under conditions of nonuniform flow via a two-beam layout. This innovative detection scheme not only considerably simplifies the fluid flow system and the excitation and collection optics, it opens the way to quantitative cytometry in simple and compact microfluidics systems, or in vivo. Real-time detection of fluorescent microbeads in the vasculature of mouse ear demonstrates the ability to do flow cytometry in vivo. The conditions required to perform quantitative in vivo cytometry on labeled cells will be presented.

  20. Two-Photon Flow Cytometry

    NASA Technical Reports Server (NTRS)

    Zhog, Cheng Frank; Ye, Jing Yong; Norris, Theodore B.; Myc, Andrzej; Cao, Zhengyl; Bielinska, Anna; Thomas, Thommey; Baker, James R., Jr.

    2004-01-01

    Flow cytometry is a powerful technique for obtaining quantitative information from fluorescence in cells. Quantitation is achieved by assuring a high degree of uniformity in the optical excitation and detection, generally by using a highly controlled flow such as is obtained via hydrodynamic focusing. In this work, we demonstrate a two-beam, two- channel detection and two-photon excitation flow cytometry (T(sup 3)FC) system that enables multi-dye analysis to be performed very simply, with greatly relaxed requirements on the fluid flow. Two-photon excitation using a femtosecond near-infrared (NIR) laser has the advantages that it enables simultaneous excitation of multiple dyes and achieves very high signal-to-noise ratio through simplified filtering and fluorescence background reduction. By matching the excitation volume to the size of a cell, single-cell detection is ensured. Labeling of cells by targeted nanoparticles with multiple fluorophores enables normalization of the fluorescence signal and thus ratiometric measurements under nonuniform excitation. Quantitative size measurements can also be done even under conditions of nonuniform flow via a two-beam layout. This innovative detection scheme not only considerably simplifies the fluid flow system and the excitation and collection optics, it opens the way to quantitative cytometry in simple and compact microfluidics systems, or in vivo. Real-time detection of fluorescent microbeads in the vasculature of mouse ear demonstrates the ability to do flow cytometry in vivo. The conditions required to perform quantitative in vivo cytometry on labeled cells will be presented.

  1. Two photon physics at RHIC

    SciTech Connect

    Klein, S.

    1995-05-01

    Because the two photon cross section is proportional to Z{sup 4}, heavy ion colliders offer an unmatched luminosity. However, because nuclei have finite sizes, the photon spectrum is gradually cut off by a nuclear form factor. For RHIC, this cutoff occurs at a few GeV; below this energy, RHIC will have the highest {gamma}{gamma} luminosity in the world when it turns on. In addition to the high rates, because Z{alpha} {approximately} 0.6, the nuclear environment provides a window to strong field QED and new phenomena like multiple pair production. To study {gamma}{gamma} physics, regions where the nuclei interact hadronically must be avoided; this leads to roughly a factor of two loss in usable luminosity. The rates expected by the Solenoidal Tracker at RHIC (STAR) collaboration will be given. Backgrounds will be discussed, along with several rejection techniques.

  2. A velocity map imaging study of the one and two photon dissociations of state-selected DCl+ cations

    NASA Astrophysics Data System (ADS)

    Webb, Alexander D.; Nahler, N. Hendrik; Dixon, Richard N.; Ashfold, Michael N. R.

    2006-11-01

    DCl+(XΠ3/22,v+'=0) cations have been prepared by 2+1 resonance enhanced multiphoton ionization, and their subsequent fragmentation following excitation at numerous wavelengths in the range of 240-350nm studied by velocity map imaging of the resulting Cl+ products. This range of excitation wavelengths allows selective population of AΣ+2 state levels with all vibrational (v+') quantum numbers in the range 0⩽v+'⩽15. Image analysis yields wavelength dependent branching ratios and recoil anisotropies of the various D +Cl+ (PJ3, D1, and S1) product channels. Levels with 10⩽v+'⩽15 have sufficient energy to predissociate, forming D +Cl+(PJ3) products with perpendicular recoil anisotropies—consistent with the AΣ+2←XΠ2 parent excitation and subsequent fragmentation on a time scale that is fast compared with the parent rotational period. Branching into the various spin-orbit states of the Cl+(PJ3) product is found to depend sensitively upon v+' and, in the case of the v+'=13 level, to vary with the precise choice of excitation wavelength within the AΣ+2←XΠ2(13,0) band. Such variations have been rationalized qualitatively in terms of the differing contributions made to the overall predissociation rate of DCl+(A,v+') molecules by coupling to repulsive states of Π4, Σ-4, and Σ-2 symmetries, all of which are calculated to cross the outer limb of the AΣ+2 state potential at energies close to that of the v+'=10 level. Cl+(PJ3) fragments are detected weakly following excitation to AΣ+2 state levels with v+'=0 or 1, Cl+(D1) fragments dominate the ion yield when exciting via 2⩽v+'⩽6 and via v+'=9, while Cl+(S1) fragments dominate the Cl+ images obtained when exciting via levels with v+'=7 and 8. Analysis of wavelength resolved action spectra for forming these Cl+ ions and of the resulting Cl+ ion images shows that (i) these ions all arise via two photon absorption processes, resonance enhanced at the one photon energy by the various A(v+'<10) levels, (ii

  3. Two-photon transitions in primordial hydrogen recombination

    NASA Astrophysics Data System (ADS)

    Hirata, Christopher M.

    2008-07-01

    The subject of cosmological hydrogen recombination has received much attention recently because of its importance to predictions for and cosmological constraints from cosmic microwave background observations. While the central role of the two-photon decay 2s→1s has been recognized for many decades, high-precision calculations require us to consider two-photon decays from the higher states ns, nd→1s (n≥3). Simple attempts to include these processes in recombination calculations with an effective two-photon decay coefficient analogous to the 2s decay coefficient Λ2s=8.22s-1 have suffered from physical problems associated with the existence of kinematically allowed sequences of one-photon decays, e.g. 3d→2p→1s, that technically also produce two photons. These correspond to resonances in the two-photon spectrum that are optically thick to two-photon absorption, necessitating a radiative transfer calculation. We derive the appropriate equations, develop a numerical code to solve them, and verify the results by finding agreement with analytic approximations to the radiative transfer equation. The related processes of Raman scattering and two-photon recombination are included using similar machinery. Our results show that early in recombination the two-photon decays act to speed up recombination, reducing the free electron abundance by 1.3% relative to the standard calculation at z=1300. However, we find that some photons between Lyα and Lyβ are produced, mainly by 3d→1s two-photon decay and 2s→1s Raman scattering. At later times, these photons redshift down to Lyα, excite hydrogen atoms, and act to slow recombination. Thus, the free electron abundance is increased by 1.3% relative to the standard calculation at z=900. Our calculation involves a very different physical argument than the recent studies of Wong and Scott and Chluba and Sunyaev, and produces a much larger effect on the ionization history. The implied correction to the cosmic microwave

  4. Single-Ion Two-Photon Source

    SciTech Connect

    Dubin, F.; Rotter, D.; Mukherjee, M.; Gerber, S.; Blatt, R.

    2007-11-02

    A single trapped ion is converted into a pseudo-two-photon source by splitting its resonance fluorescence, delaying part of it and by recombining both parts on a beam splitter. A destructive two-photon interference is observed with a contrast reaching 83(5)%. The spectral brightness of our two-photon source is quantified and shown to be comparable to parametric down-conversion devices.

  5. Two Photon Exchange for Exclusive Pion Electroproduction

    SciTech Connect

    Afanaciev, Andrei V.; Aleksejevs, Aleksandrs G.; Barkanova, Svetlana G.

    2013-09-01

    We perform detailed calculations of two-photon-exchange QED corrections to the cross section of pion electroproduction. The results are obtained with and without the soft-photon approximation; analytic expressions for the radiative corrections are derived. The relative importance of the two-photon correction is analyzed for the kinematics of several experiments at Jefferson Lab. A significant, over 20%, effect due to two-photon exchange is predicted for the backward angles of electron scattering at large transferred momenta.

  6. Resonance-Enhanced Nonlinear Optical Effects

    NASA Astrophysics Data System (ADS)

    Sun, Xuan

    Nonlinear optical processes, which manifest as many interesting phenomena such as nonlinear wave mixing, optical rectification, intensity-dependent refractive index change, harmonic generation, etc., have found very broad applications. Unfortunately, most optical media exhibit rather weak optical nonlinearities and a majority of nonlinear optical processes have to rely on substantial optical powers to support nonlinear wave interactions, which becomes a major challenge for nonlinear photonic application. This thesis is devoted to exploring enhanced nonlinear optical phenomena, by taking advantage of a certain type of resonance to enhance the nonlinear wave interactions. For this purpose, we employed both natural atomic resonances via electron transition and engineered optical resonances in micro/nanophotonic device structures, for different applications. These two types of resonances, although distinctive in their physical natures, both are able to significantly increase the strength and elongate the time of optical wave interactions, thus leading to dramatic enhancement of nonlinear optical effects. On one hand, we utilized unique energy-level structures in alkali vapor plasmas to dramatically enhance the electron tunneling ionization process and to produce significant resonance-enhanced four-wave mixing for efficient terahertz (THz) wave generation that is crucial for long-wave application. On the other hand, we utilized the enhancement offered by high-Q optical resonances inside microresonators to produce significant photothermal backaction to dramatically suppress the fundamental temperature fluctuations of microresonators, which is essential for sensing and metrology applications. With such cavity-resonance enhancement, we revealed a new regime of nonlinear optical oscillation dynamics in lithium niobate microresonators that results from unique competition between the thermo-optic nonlinear effect and the photorefractive effect, which is inaccessible to

  7. Two-photon excitation fluorescence microscopy.

    PubMed

    So, P T; Dong, C Y; Masters, B R; Berland, K M

    2000-01-01

    Two-photon fluorescence microscopy is one of the most important recent inventions in biological imaging. This technology enables noninvasive study of biological specimens in three dimensions with submicrometer resolution. Two-photon excitation of fluorophores results from the simultaneous absorption of two photons. This excitation process has a number of unique advantages, such as reduced specimen photodamage and enhanced penetration depth. It also produces higher-contrast images and is a novel method to trigger localized photochemical reactions. Two-photon microscopy continues to find an increasing number of applications in biology and medicine.

  8. Two-photon collisions and QCD

    SciTech Connect

    Gunion, J.F.

    1980-05-01

    A critical review of the applications of QCD to low- and high-p/sub T/ interactions of two photons is presented. The advantages of the two-photon high-p/sub T/ tests over corresponding hadronic beam and/or target tests of QCD are given particular emphasis.

  9. Fano interference in two-photon transport

    NASA Astrophysics Data System (ADS)

    Xu, Shanshan; Fan, Shanhui

    2016-10-01

    We present a general input-output formalism for the few-photon transport in multiple waveguide channels coupled to a local cavity. Using this formalism, we study the effect of Fano interference in two-photon quantum transport. We show that the physics of Fano interference can manifest as an asymmetric spectral line shape in the frequency dependence of the two-photon correlation function. The two-photon fluorescence spectrum, on the other hand, does not exhibit the physics of Fano interference.

  10. The 700-1500 cm{sup −1} region of the S{sub 1} (A{sup ~1}B{sub 2}) state of toluene studied with resonance-enhanced multiphoton ionization (REMPI), zero-kinetic-energy (ZEKE) spectroscopy, and time-resolved slow-electron velocity-map imaging (tr-SEVI) spectroscopy

    SciTech Connect

    Gardner, Adrian M.; Green, Alistair M.; Tamé-Reyes, Victor M.; Reid, Katharine L.; Davies, Julia A.; Parkes, Victoria H. K.; Wright, Timothy G.

    2014-03-21

    We report (nanosecond) resonance-enhanced multiphoton ionization (REMPI), (nanosecond) zero-kinetic-energy (ZEKE) and (picosecond) time-resolved slow-electron velocity map imaging (tr-SEVI) spectra of fully hydrogenated toluene (Tol-h{sub 8}) and the deuterated-methyl group isotopologue (α{sub 3}-Tol-d{sub 3}). Vibrational assignments are made making use of the activity observed in the ZEKE and tr-SEVI spectra, together with the results from quantum chemical and previous experimental results. Here, we examine the 700–1500 cm{sup −1} region of the REMPI spectrum, extending our previous work on the region ≤700 cm{sup −1}. We provide assignments for the majority of the S{sub 1} and cation bands observed, and in particular we gain insight regarding a number of regions where vibrations are coupled via Fermi resonance. We also gain insight into intramolecular vibrational redistribution in this molecule.

  11. Observation of Two-Photon Speckle Patterns

    NASA Astrophysics Data System (ADS)

    Peeters, W. H.; Moerman, J. J. D.; van Exter, M. P.

    2010-04-01

    We report the observation of speckle patterns in quantum correlations within light that is scattered by a disordered medium. The random medium is illuminated with spatially entangled photon pairs, and fourth-order speckle patterns are spatially resolved by two independently scanning detectors. Spatial entanglement gives two-photon speckle a much richer structure than ordinary one-photon speckle. Our experiments demonstrate that two-photon speckle from a surface scatterer and a volume scatterer look entirely different.

  12. Two-Photon Laser Scanning Microscopy

    NASA Astrophysics Data System (ADS)

    Nimmerjahn, A.; Theer, P.; Helmchen, F.

    Since its inception more than 15 years ago, two-photon laser scanning microscopy (2PLSM) has found widespread use in biological and medical research. Two-photon microscopy is based on simultaneous absorption of two photons by fluorophores and subsequent fluorescence emission, a process which under normal illumination conditions is highly improbable. Theoretically described around 1930 by Maria Göppert-Mayer [1], the first experimental demonstration of two-photon excitation had to await the invention of the laser, which produced sufficiently high light intensities to observe two-photon absorption events [2]. Only after the development of ultrafast lasers providing subpicosecond light pulses with high peak power intensities, however, two-photon-excited fluorescence became practical in a laser-scanning microscope [3]. Since then 2PLSM has developed into the method of choice for high-resolution imaging in living animals (reviewed in [4,5]). One of the main reasons is the low sensitivity of 2PLSM to light scattering, which enables imaging relatively deep inside biological tissue and direct observation of the dynamic behavior of cells in their native environment. In this chapter, we introduce the physical principles governing 2PLSM and briefly describe the key instrument components. We give an overview of fluorescence labeling techniques and how they are combined with 2PLSM for functional imaging and photomanipulation in living tissue. Finally, we discuss limitations and provide some future perspectives.

  13. Two-Photon Laser Scanning Microscopy

    NASA Astrophysics Data System (ADS)

    Nimmerjahn, A.; Theer, P.; Helmchen, F.

    Since its inception more than 15 years ago, two-photon laser scanning microscopy (2PLSM) has found widespread use in biological and medical research. Two-photon microscopy is based on simultaneous absorption of two photons by fluorophores and subsequent fluorescence emission, a process which under normal illumination conditions is highly improbable. Theoretically described around 1930 by Maria Göppert-Mayer [1], the first experimental demonstration of two-photon excitation had to await the invention of the laser, which produced sufficiently high light intensities to observe two-photon absorption events [2]. Only after the development of ultrafast lasers providing subpicosecond light pulses with high peak power intensities, however, two-photon-excited fluorescence became practical in a laser-scanning microscope [3]. Since then 2PLSM has developed into the method of choice for high-resolution imaging in living animals (reviewed in [4,5]). One of the main reasons is the low sensitivity of 2PLSM to light scattering, which enables imaging relatively deep inside biological tissue and direct observation of the dynamic behavior of cells in their native environment. In this chapter, we introduce the physical principles governing 2PLSM and briefly describe the key instrument components. We give an overview of fluorescence labeling techniques and how they are combined with 2PLSM for functional imaging and photomanipulation in living tissue. Finally, we discuss limitations and provide some future perspectives.

  14. Multiphoton inner-shell ionization of the carbon atom

    NASA Astrophysics Data System (ADS)

    Rey, H. F.; van der Hart, H. W.

    2015-07-01

    We apply time-dependent R -matrix theory to study inner-shell ionization of C atoms in ultrashort high-frequency light fields with a photon energy between 170 and 245 eV. At an intensity of 1017 W /cm2, ionization is dominated by single-photon emission of a 2 ℓ electron, with two-photon emission of a 1 s electron accounting for about 2-3% of all emission processes, and two-photon emission of 2 ℓ contributing about 0.5-1%. Three-photon emission of a 1 s electron is estimated to contribute about 0.01-0.03%. Around a photon energy of 225 eV, two-photon emission of a 1 s electron, leaving C+ in either 1 s 2 s 2 p3 or 1 s 2 p4 , is resonantly enhanced by intermediate 1 s 2 s22 p3 states. The results demonstrate the capability of time-dependent R -matrix theory to describe inner-shell ionization processes including rearrangement of the outer electrons.

  15. Polymer Microstructures through Two-Photon Crosslinking.

    PubMed

    Schwärzle, David; Hou, Xiaoqang; Prucker, Oswald; Rühe, Jürgen

    2017-08-18

    Two-photon crosslinking of polymers (2PC) is proposed as a novel method for the fabrication of freestanding microstructures via two-photon lithography. During this process in the confocal volume, two-photon absorption leads to (formal) C,H-insertion reactions, and consequently to a strictly localized crosslinking of the polymer. To achieve this, the polymer is coated as a solvent-free (glassy) film onto an appropriate substrate, and the desired microstructure is written by 2PC into this glass. In all regions outside of the focal volume where no two-photon process occurs, the polymer remains uncrosslinked and can be washed away during a developing process. Using a self-assembled monolayer containing the same photoreactive group allows covalent attachment of the forming freestanding structures to the substrate, and thus guarantees an improved stability of these structures against shear-induced detachment. As the two photon process is carried out in the glassy state, in a simple way, multilayer structures can be used to write structures having a varying chemical composition perpendicular to the surface. As an example, the 2PC process is used to build a structure from both protein-repellent and protein-adsorbing polymers so that the resulting 3D structure exhibits spatially controlled protein adsorption. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Vibrational and vibrational-torsional interactions in the 0-600 cm-1 region of the S1 ← S0 spectrum of p-xylene investigated with resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) spectroscopy

    NASA Astrophysics Data System (ADS)

    Tuttle, William D.; Gardner, Adrian M.; O'Regan, Kieran B.; Malewicz, William; Wright, Timothy G.

    2017-03-01

    We assign the 0-600 cm-1 region of the S1 ← S0 transition in p-xylene (p-dimethylbenzene) using resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) spectroscopy. In the 0-350 cm-1 range as well as the intense origin band, there are a number of torsional and vibration-torsion (vibtor) features. The latter are discussed in more detail in Paper I [A. M. Gardner et al., J. Chem. Phys. 146, 124308 (2017)]. Here we focus on the origin and the 300-600 cm-1 region, where vibrational bands and some vibtor activity are observed. From the origin ZEKE spectrum, we derive the ionization energy of p-xylene as 68200 ± 5 cm-1. The assignment of the REMPI spectrum is based on the activity observed in the ZEKE spectra coupled with knowledge of the vibrational wavenumbers obtained from quantum chemical calculations. We assign several isolated vibrations and a complex Fermi resonance that is found to comprise contributions from both vibrations and vibtor levels, and we examine this via a two-dimensional ZEKE spectrum. A number of the vibrational features in the REMPI and ZEKE spectra of p-xylene that have been reported previously are reassigned and now largely consist of totally symmetric contributions. We briefly discuss the appearance of non-Franck-Condon allowed transitions. Finally, we find remarkably similar spectral activity to that in the related disubstituted benzenes, para-difluorobenzene, and para-fluorotoluene.

  17. Vibrational and vibrational-torsional interactions in the 0-600 cm(-1) region of the S1← S0 spectrum of p-xylene investigated with resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) spectroscopy.

    PubMed

    Tuttle, William D; Gardner, Adrian M; O'Regan, Kieran B; Malewicz, William; Wright, Timothy G

    2017-03-28

    We assign the 0-600 cm(-1) region of the S1← S0 transition in p-xylene (p-dimethylbenzene) using resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) spectroscopy. In the 0-350 cm(-1) range as well as the intense origin band, there are a number of torsional and vibration-torsion (vibtor) features. The latter are discussed in more detail in Paper I [A. M. Gardner et al., J. Chem. Phys. 146, 124308 (2017)]. Here we focus on the origin and the 300-600 cm(-1) region, where vibrational bands and some vibtor activity are observed. From the origin ZEKE spectrum, we derive the ionization energy of p-xylene as 68200 ± 5 cm(-1). The assignment of the REMPI spectrum is based on the activity observed in the ZEKE spectra coupled with knowledge of the vibrational wavenumbers obtained from quantum chemical calculations. We assign several isolated vibrations and a complex Fermi resonance that is found to comprise contributions from both vibrations and vibtor levels, and we examine this via a two-dimensional ZEKE spectrum. A number of the vibrational features in the REMPI and ZEKE spectra of p-xylene that have been reported previously are reassigned and now largely consist of totally symmetric contributions. We briefly discuss the appearance of non-Franck-Condon allowed transitions. Finally, we find remarkably similar spectral activity to that in the related disubstituted benzenes, para-difluorobenzene, and para-fluorotoluene.

  18. Control of photoemission delay in resonant two-photon transitions

    NASA Astrophysics Data System (ADS)

    Argenti, L.; Jiménez-Galán, Á.; Caillat, J.; Taïeb, R.; Maquet, A.; Martín, F.

    2017-04-01

    The photoelectron emission time delay τ associated with one-photon absorption, which coincides with half the Wigner delay τW experienced by an electron scattered off the ionic potential, is a fundamental descriptor of the photoelectric effect. Although it is hard to access directly from experiment, it is possible to infer it from the time delay of two-photon transitions, τ(2 ), measured with attosecond pump-probe schemes, provided that the contribution of the probe stage can be factored out. In the absence of resonances, τ can be expressed as the energy derivative of the one-photon ionization amplitude phase, τ =∂EargDE g , and, to a good approximation, τ =τ(2 )-τcc , where τcc is associated with the dipole transition between Coulomb functions. Here we show that, in the presence of a resonance, the correspondence between τ and ∂EargDE g is lost. Furthermore, while τ(2 ) can still be written as the energy derivative of the two-photon ionization amplitude phase, ∂EargDEg (2 ) , it does not have any scattering counterpart. Indeed, τ(2 ) can be much larger than the lifetime of an intermediate resonance in the two-photon process or more negative than the lower bound imposed on scattering delays by causality. Finally, we show that τ(2 ) is controlled by the frequency of the probe pulse, ωIR , so that by varying ωIR , it is possible to radically alter the photoelectron group delay.

  19. Two-Photon Fluorescence Correlation Spectroscopy

    NASA Technical Reports Server (NTRS)

    Zimmerli, Gregory A.; Fischer, David G.

    2002-01-01

    We will describe a two-photon microscope currently under development at the NASA Glenn Research Center. It is composed of a Coherent Mira 900 tunable, pulsed Titanium:Sapphire laser system, an Olympus Fluoview 300 confocal scanning head, and a Leica DM IRE inverted microscope. It will be used in conjunction with a technique known as fluorescence correlation spectroscopy (FCS) to study intracellular protein dynamics. We will briefly explain the advantages of the two-photon system over a conventional confocal microscope, and provide some preliminary experimental results.

  20. Two-photon polymerization of polydiacetylene.

    PubMed

    Shusterman, Olga; Berman, Amir; Golan, Yuval; Horovitz, Baruch; Zeiri, Leila

    2009-02-05

    We show that visible light can polymerize diacetylene monomers into polydiacetylene (PDA) in a two-photon process. We monitor the process by measuring Raman intensities of PDA using a Raman laser at 633 nm with variable intensity I and show that the Raman cross section at short times increases as I3, corresponding to a two-photon process. The process generates a relatively stable blue phase PDA, in contrast with UV polymerization that leads to a fast blue to red phase transformation.

  1. Two-Photon Resonant Second Harmonic Generation in Atomic Xeon

    NASA Astrophysics Data System (ADS)

    Shi, Y. J.; Al-Basheer, W.; Thompson, R. I.

    2009-06-01

    Vacuum ultraviolet (VUV) radiation at 124.8 nm (9.93 eV) was produced from two-photon resonant second harmonic generation (SHG) in a Xeon gaseous medium and used to probe molecular samples of acetone, furan, thiophene, ammonia, and methane. The mass spectra recorded from the species with ionization energies below 9.93 eV were dominated by the parent ions. The parent ions were only observed when the incident UV radiation was tuned to resonate with the two-photon transition 5p^5(^2P_{3/2}^0)6p[1/2]_0 - 5p^6 ^1S_0 of Xe at 80119.474 cm^{-1}. The pressure dependence and the resonant nature of the parent ions observed support the mechanism for SHG as the ionization-initiated electric field induced SHG via the third-order nonlinear susceptibility, χ^{(3)}, which is enhanced by the coupling between the 5p^5(^2P_{3/2}^0)6p[1/2]_0 and the nearby 5p^5(^2P_{3/2}^0)5d[1/2]_1 states of Xe atoms.

  2. Two-photon resonant second harmonic generation in atomic xeon.

    PubMed

    Shi, Y J; Al-Basheer, W; Thompson, R I

    2009-03-07

    Vacuum ultraviolet (VUV) radiation at 124.8 nm (9.93 eV) was produced from two-photon resonant second harmonic generation (SHG) in a xeon gaseous medium and used to probe molecular samples of acetone, furan, thiophene, ammonia, and methane. The mass spectra recorded from the species with ionization energies below 9.93 eV were dominated by the parent ions. The parent ions were only observed when the incident UV radiation was tuned to resonate with the two-photon transition 5p(5)((2)P(3/2) (0))6p[1/2](0)<--5p(6) (1)S(0) of Xe at 80 119.474 cm(-1). The pressure dependence and the resonant nature of the parent ions observed support the mechanism for SHG as the ionization-initiated electric field induced SHG via the third-order nonlinear susceptibility chi((3)), which is enhanced by the coupling between the 5p(5)((2)P(3/2) (0))6p[1/2](0) and the nearby 5p(5)((2)P(3/2) (0))5d[1/2](1) states of Xe atoms.

  3. Two-photon resonant second harmonic generation in atomic xeon

    NASA Astrophysics Data System (ADS)

    Shi, Y. J.; Al-Basheer, W.; Thompson, R. I.

    2009-03-01

    Vacuum ultraviolet (VUV) radiation at 124.8 nm (9.93 eV) was produced from two-photon resonant second harmonic generation (SHG) in a xeon gaseous medium and used to probe molecular samples of acetone, furan, thiophene, ammonia, and methane. The mass spectra recorded from the species with ionization energies below 9.93 eV were dominated by the parent ions. The parent ions were only observed when the incident UV radiation was tuned to resonate with the two-photon transition 5p5(P23/20)6p[1/2]0←5p6S10 of Xe at 80 119.474 cm-1. The pressure dependence and the resonant nature of the parent ions observed support the mechanism for SHG as the ionization-initiated electric field induced SHG via the third-order nonlinear susceptibility χ(3), which is enhanced by the coupling between the 5p5(P23/20)6p[1/2]0 and the nearby 5p5(P23/20)5d[1/2]1 states of Xe atoms.

  4. Determination of Hexachlorocyclohexane by Gas Chromatography Combined with Femtosecond Laser Ionization Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Yang, Xixiang; Imasaka, Tomoko; Li, Adan; Imasaka, Totaro

    2016-12-01

    Structural isomers and enantiomers of hexachlorocyclohexane (HCH) were separated using a chiral column by gas chromatography and quantitatively determined by multiphoton ionization mass spectrometry using an ultraviolet femtosecond laser (200 and 267 nm) as the ionization source. The order of elution of the enantiomers (i.e., (+)-α-HCH and (-)-α-HCH) was predicted from stabilization energies calculated for the complexes using permethylated γ-cyclodextrin as the stationary phase of the column, and the results were compared with the experimental data. The molecular ions observed for HCH were weak, even though they can be ionized through a process of resonance enhanced two-photon ionization at 200 nm. This unfavorable result can be attributed to the dissociation of the molecular ion, as predicted from quantum chemical calculations.

  5. Two Photon Spectroscopy of Pyrazine and Triazine.

    DTIC Science & Technology

    1979-09-01

    Two photon absorption spectra, detected by fluorescence, phosphorescence, and photoacoustic methods are presented for pyrazine and triazine. Vibronic...assignments are made in both systems based on polarization and contour analysis. For pyrazine , origin intensity is observed which suggests the (B)(3U

  6. Scattering of entangled two-photon states.

    PubMed

    Schotland, John C; Cazé, A; Norris, Theodore B

    2016-02-01

    We consider the scattering of entangled two-photon states from collections of small particles. We also study the related Mie problem of scattering from a sphere. In both cases, we calculate the entropy of entanglement and investigate the influence of the entanglement of the incident field on the entanglement of the scattered field.

  7. Two-photon microscopy for chemical neuroscience.

    PubMed

    Ellis-Davies, Graham C R

    2011-04-20

    Microscopes using non-linear excitation of chromophores with pulsed near-IR light can generate highly localized foci of molecules in the electronic singlet state that are concentrated in volumes of less than one femtoliter. The three-dimensional confinement of excitation arises from the simultaneous absorption of two IR photons of approximately half the energy required for linear excitation. Two-photon microscopy is especially useful for two types of interrogation of neural processes. First, uncaging of signaling molecules such as glutamate, as stimulation is so refined it can be used to mimic normal unitary synaptic levels. In addition, uncaging allows complete control of the timing and position of stimulation, so the two-photon light beam provides the chemical neuroscientist with an "optical conductor's baton" which can command synaptic activity at will. A second powerful feature of two-photon microscopy is that when used for fluorescence imaging it enables the visualization of cellular structure and function in living animals at depths far beyond that possible with normal confocal microscopes. In this review I provide a survey of the many important applications of two-photon microscopy in these two fields of neuroscience, and suggest some areas for future technical development.

  8. Two photon photoemission of deposited silver clusters

    NASA Astrophysics Data System (ADS)

    Busolt, U.; Cottancin, E.; Röhr, H.; Socaciu, L.; Leisner, T.; Wöste, L.

    We use time resolved two photon photoemission to study the stability of size selected silver clusters deposited onto highly oriented pyrolytic graphite (HOPG) substrates. Size-selected Agn+ clusters (n=2-9) are deposited at low coverage onto HOPG surfaces at liquid nitrogen temperatures. After deposition, the samples are irradiated by a series of ultrashort laser pulse pairs. Photoelectrons created by two photon photoemission are collected in a magnetic bottle type time-of-flight photoelectron spectrometer. Their kinetic energy distribution is recorded as a function of the delay time between subsequent light pulses. With the exception of Ag3 the size dependence of the photoelectron spectra reveals a pronounced odd/even effect, which is well known for gas phase silver clusters. This indicates that the deposited clusters retain their size and identity on the sample. The lifetime of the photoexcitation rises with cluster size. This is attributed to an increasing electronic density of states for larger clusters.

  9. Third-order nonlinearities in molecular hydrogen - Two-photon resonance enhanced third-harmonic generation and Raman scattering

    NASA Technical Reports Server (NTRS)

    Pan, C.-L.; She, C.-Y.; Fairbank, W. M., Jr.; Billman, K. W.

    1977-01-01

    Effects of quantum mechanical interferences on third-order susceptibilities in molecules are studied. First principle calculations for molecular hydrogen are presented and shown to agree with results derived from experimental stimulated Raman gain and spontaneous Raman cross-section data. 10 percent third-harmonic conversion efficiency in H2 at 1 atm without phase matching should require a 150 MW per sq cm at 4.81 microns. As little as 5.9-MW power is sufficient when the beam is properly focused. Resonance Raman scattering (RRS) is proposed for experimentally investigating the interference effects, which tend to reduce the strength of third-order nonlinear susceptibilities.

  10. Magnetic two-photon scattering and two-photon emission - Cross sections and redistribution functions

    NASA Technical Reports Server (NTRS)

    Alexander, S. G.; Meszaros, P.

    1991-01-01

    The magnetic two-photon scattering cross section is discussed within the framework of QED, and the corresponding scattering redistribution function for this process and its inverse, as well as the scattering source function are calculated explicitly. In a similar way, the magnetic two-photon emission process which follows the radiative excitation of Landau levels above ground is calculated. The two-photon scattering and two-photon emission are of the same order as the single-photon magnetic scattering. All three of these processes, and in optically thick cases also their inverses, are included in radiative transport calculations modeling accreting pulsars and gamma-ray bursters. These processes play a prominent role in determining the relative strength of the first two cyclotron harmonics, and their effects extend also to the higher harmonics.

  11. Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of bromobenzene and its perdeuterated isotopologue: Assignment of the vibrations of the S{sub 0}, S{sub 1}, and D{sub 0}{sup +} states of bromobenzene and the S{sub 0} and D{sub 0}{sup +} states of iodobenzene

    SciTech Connect

    Andrejeva, Anna; Tuttle, William D.; Harris, Joe P.; Wright, Timothy G.

    2015-12-28

    We report vibrationally resolved spectra of the S{sub 1}←S{sub 0} transition of bromobenzene using resonance-enhanced multiphoton ionization spectroscopy. We study bromobenzene-h{sub 5} as well as its perdeuterated isotopologue, bromobenzene-d{sub 5}. The form of the vibrational modes between the isotopologues and also between the S{sub 0} and S{sub 1} electronic states is discussed for each species, allowing assignment of the bands to be achieved and the activity between states and isotopologues to be established. Vibrational bands are assigned utilizing quantum chemical calculations, previous experimental results, and isotopic shifts. Previous work and assignments of the S{sub 1} spectra are discussed. Additionally, the vibrations in the ground state cation, D{sub 0}{sup +}, are considered, since these have also been used by previous workers in assigning the excited neutral state spectra. We also examine the vibrations of iodobenzene in the S{sub 0} and D{sub 0}{sup +} states and comment on the previous assignments of these. In summary, we have been able to assign the corresponding vibrations across the whole monohalobenzene series of molecules, in the S{sub 0}, S{sub 1}, and D{sub 0}{sup +} states, gaining insight into vibrational activity and vibrational couplings.

  12. Determination of Nerve Agent Metabolites by Ultraviolet Femtosecond Laser Ionization Mass Spectrometry.

    PubMed

    Hamachi, Akifumi; Imasaka, Tomoko; Nakamura, Hiroshi; Li, Adan; Imasaka, Totaro

    2017-04-04

    Nerve agent metabolites, i.e., isopropyl methylphosphonic acid (IMPA) and pinacolyl methylphosphonic acid (PMPA), were derivatized by reacting them with 2,3,4,5,6-pentafluorobenzyl bromide (PFBBr) and were determined by mass spectrometry using an ultraviolet femtosecond laser emitting at 267 and 200 nm as the ionization source. The analytes of the derivatized compounds, i.e., IMPA-PFB and PMPA-PFB, contain a large side-chain, and molecular ions are very weak or absent in electron ionization mass spectrometry. The use of ultraviolet femtosecond laser ionization mass spectrometry, however, resulted in the formation of a molecular ion, even for compounds such as these that contain a highly-bulky functional group. The signal intensity was larger at 200 nm due to resonance-enhanced two-photon ionization. In contrast, fragmentation was suppressed at 267 nm (non-resonant two-photon ionization) especially for PMPA-PFB, thus resulting in a lower background signal. This favorable result can be explained by the small excess energy in ionization at 267 nm and by the low-frequency vibrational mode of a bulky trimethylpropyl group in PMPA.

  13. Denoising two-photon calcium imaging data.

    PubMed

    Malik, Wasim Q; Schummers, James; Sur, Mriganka; Brown, Emery N

    2011-01-01

    Two-photon calcium imaging is now an important tool for in vivo imaging of biological systems. By enabling neuronal population imaging with subcellular resolution, this modality offers an approach for gaining a fundamental understanding of brain anatomy and physiology. Proper analysis of calcium imaging data requires denoising, that is separating the signal from complex physiological noise. To analyze two-photon brain imaging data, we present a signal plus colored noise model in which the signal is represented as harmonic regression and the correlated noise is represented as an order autoregressive process. We provide an efficient cyclic descent algorithm to compute approximate maximum likelihood parameter estimates by combing a weighted least-squares procedure with the Burg algorithm. We use Akaike information criterion to guide selection of the harmonic regression and the autoregressive model orders. Our flexible yet parsimonious modeling approach reliably separates stimulus-evoked fluorescence response from background activity and noise, assesses goodness of fit, and estimates confidence intervals and signal-to-noise ratio. This refined separation leads to appreciably enhanced image contrast for individual cells including clear delineation of subcellular details and network activity. The application of our approach to in vivo imaging data recorded in the ferret primary visual cortex demonstrates that our method yields substantially denoised signal estimates. We also provide a general Volterra series framework for deriving this and other signal plus correlated noise models for imaging. This approach to analyzing two-photon calcium imaging data may be readily adapted to other computational biology problems which apply correlated noise models.

  14. Platinum Acetylide Two-Photon Chromophores (Postprint)

    DTIC Science & Technology

    2007-01-01

    L.; Pierce, B. M. Science 1994, 265, 632. (14) Prasad, P. N.; Reinhardt, B. A. Chem. Mater. 1990, 2, 660. (15) Larson, E . J.; Friesen , L. A.; Johnson...PROGRAM ELEMENT NUMBER 62102F 5d. PROJECT NUMBER 4348 5e. TASK NUMBER RG 6. AUTHOR(S) Joy E . Rogers (UES) Jonathan E . Slagle (AT&T Government...afford T1. Platinum Acetylide Two-Photon Chromophores Joy E . Rogers,†,‡ Jonathan E . Slagle,†,§ Douglas M. Krein,†,| Aaron R. Burke,†,| Benjamin C. Hall

  15. Erasing nonlocal like two photon interference

    NASA Astrophysics Data System (ADS)

    Olindo, C.; Sagioro, M. A.; Pádua, S.; Monken, C. H.

    2015-12-01

    Over the years, since the 1980s, various two photon interference experiments have been reported with photon pairs generated by parametric down conversion. Some of them have shown local interference features and non-local ones. An experiment is shown here which joins the two features at the same time in a Hong-Ou-Mandel interferometer. However, the non-local effects are lost if the photons' arrival time difference at the beam splitter is much larger than the pulse length of the pump beam that generates the photon pair.

  16. Two-Photon Excitation and Relaxation of the 3d-4d Resonance in Atomic Kr

    SciTech Connect

    Meyer, M.; Cubaynes, D.; Richardson, V.; Costello, J. T.; Radcliffe, P.; Li, W. B.; Duesterer, S.; Fritzsche, S.; Mihelic, A.; Papamihail, K. G.; Lambropoulos, P.

    2010-05-28

    Two-photon excitation of a single-photon forbidden Auger resonance has been observed and investigated using the intense extreme ultraviolet radiation from the free electron laser in Hamburg. At the wavelength 26.9 nm (46 eV) two photons promoted a 3d core electron to the outer 4d shell. The subsequent Auger decay, as well as several nonlinear above threshold ionization processes, were studied by electron spectroscopy. The experimental data are in excellent agreement with theoretical predictions and analysis of the underlying multiphoton processes.

  17. Encoded multisite two-photon microscopy.

    PubMed

    Ducros, Mathieu; Goulam Houssen, Yannick; Bradley, Jonathan; de Sars, Vincent; Charpak, Serge

    2013-08-06

    The advent of scanning two-photon microscopy (2PM) has created a fertile new avenue for noninvasive investigation of brain activity in depth. One principal weakness of this method, however, lies with the limit of scanning speed, which makes optical interrogation of action potential-like activity in a neuronal network problematic. Encoded multisite two-photon microscopy (eMS2PM), a scanless method that allows simultaneous imaging of multiple targets in depth with high temporal resolution, addresses this drawback. eMS2PM uses a liquid crystal spatial light modulator to split a high-power femto-laser beam into multiple subbeams. To distinguish them, a digital micromirror device encodes each subbeam with a specific binary amplitude modulation sequence. Fluorescence signals from all independently targeted sites are then collected simultaneously onto a single photodetector and site-specifically decoded. We demonstrate that eMS2PM can be used to image spike-like voltage transients in cultured cells and fluorescence transients (calcium signals in neurons and red blood cells in capillaries from the cortex) in depth in vivo. These results establish eMS2PM as a unique method for simultaneous acquisition of neuronal network activity.

  18. Encoded multisite two-photon microscopy

    PubMed Central

    Ducros, Mathieu; Houssen, Yannick Goulam; Bradley, Jonathan; de Sars, Vincent; Charpak, Serge

    2013-01-01

    The advent of scanning two-photon microscopy (2PM) has created a fertile new avenue for noninvasive investigation of brain activity in depth. One principal weakness of this method, however, lies with the limit of scanning speed, which makes optical interrogation of action potential-like activity in a neuronal network problematic. Encoded multisite two-photon microscopy (eMS2PM), a scanless method that allows simultaneous imaging of multiple targets in depth with high temporal resolution, addresses this drawback. eMS2PM uses a liquid crystal spatial light modulator to split a high-power femto-laser beam into multiple subbeams. To distinguish them, a digital micromirror device encodes each subbeam with a specific binary amplitude modulation sequence. Fluorescence signals from all independently targeted sites are then collected simultaneously onto a single photodetector and site-specifically decoded. We demonstrate that eMS2PM can be used to image spike-like voltage transients in cultured cells and fluorescence transients (calcium signals in neurons and red blood cells in capillaries from the cortex) in depth in vivo. These results establish eMS2PM as a unique method for simultaneous acquisition of neuronal network activity. PMID:23798397

  19. Resonance Enhanced Multiphoton Ionization of Molecules and Molecular Fragments

    DTIC Science & Technology

    1994-03-31

    Rudolph, R.L. Dubs, and V. McKoy J. Chem. Phys. 93, 7513 (1990) 28. Non-Franck-Condon Effects in Photoionization of the 3 31- Rydberg State of NH K... cisco , California, October 1994 IV The following graduate student was partially supported by this contract Matthew Braunstein (1990-91) The following

  20. LASERS IN MEDICINE: Two-photon excitation of aluminium phthalocyanines

    NASA Astrophysics Data System (ADS)

    Meshalkin, Yu P.; Alfimov, E. E.; Vasil'ev, N. E.; Denisov, A. N.; Makukha, V. K.; Ogirenko, A. P.

    1999-12-01

    A demonstration is given of the feasibility of two-photon excitation of aluminium phthalocyanine and of the pharmaceutical preparation 'Fotosens', used in photodynamic therapy. The excitation source was an Nd:YAG laser emitting at the 1064 nm wavelength. The spectra of the two-photon-excited luminescence were obtained and the two-photon absorption cross sections were determined.

  1. Resonant Enhancement of Turbulent Energy Dissipation

    SciTech Connect

    Cekli, Hakki Ergun; Tipton, Carl; Water, Willem van de

    2010-07-23

    We periodically modulate a turbulent wind-tunnel flow with an active grid. We find a resonant enhancement of the mean turbulent dissipation rate at a modulation frequency which equals the large-eddy turnover rate. Thus, we find the best frequency to inject energy into a turbulent flow. The resonant response is characterized by the emergence of vortical structures in the flow and depends on the spatial mode of the stirring grid.

  2. The CLAS Two Photon Exchange Experiment

    NASA Astrophysics Data System (ADS)

    Adikaram, Dasuni; Bennett, Robert; Weinstein, Larry; Rimal, Dipak; Khetarpal, Puneet; Raue, Brian

    2013-04-01

    There is a large discrepancy between the proton electron form factor (GE^p(Q^2)) measured using the Rosenbluth separation and polarization transfer methods. The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section. The TPE contribution can be extracted in a model-independent way from the measured ratio of the cross sections of positron-proton and electron-proton elastic scattering. This ratio was measured in Hall B at Jefferson Lab using a simultaneous mixed tertiary beam of electrons and positrons incident on a liquid hydrogen target in the center of the CLAS detector in 2010-2011. In this talk, the experimental techniques to produce e^+/e^- beam, the analysis techniques to identify the elastic scattering events, and some preliminary results will be presented.

  3. Two-photon fluorescence anisotropy imaging

    NASA Astrophysics Data System (ADS)

    Li, Wei; Wang, Yi; Shao, Hanrong; He, Yonghong; Ma, Hui

    2006-09-01

    We have developed a novel method for imaging the fluorescence intensity and anisotropy by two-photon fluorescence microscopy and tested its capability in biological application. This method is applied to model sample including FITC and FITC-CD44 antibody solution and also FITC-CD44 stained cells. The fluorescence anisotropy (FA) of FITC-CD44ab solution is higher than the FITC solution with the same concentration. The fluorescence in cell sample has even higher FA than in solution because the rotation diffusion is restrained in membrane. The method is employed to study the effect of berberine a kind of Chinese medicine, on tumor metastasis. The results indicated that tumor cell membrane fluidity is decreasing with increasing the concentration of berberine in culture medium.

  4. Two photon annihilation operators and squeezed vacuum

    NASA Technical Reports Server (NTRS)

    Roy, Anil K.; Mehta, C. L.; Saxena, G. M.

    1993-01-01

    Inverses of the harmonic oscillator creation and annihilation operators by their actions on the number states are introduced. Three of the two photon annihilation operators, viz., a(sup +/-1)a, aa(sup +/-1), and a(sup 2), have normalizable right eigenstates with nonvanishing eigenvalues. The eigenvalue equation of these operators are discussed and their normalized eigenstates are obtained. The Fock state representation in each case separates into two sets of states, one involving only the even number states while the other involving only the odd number states. It is shown that the even set of eigenstates of the operator a(sup +/-1)a is the customary squeezed vacuum S(sigma) O greater than.

  5. Two-photon imaging of stem cells

    NASA Astrophysics Data System (ADS)

    Uchugonova, A.; Gorjup, E.; Riemann, I.; Sauer, D.; König, K.

    2008-02-01

    A variety of human and animal stem cells (rat and human adult pancreatic stem cells, salivary gland stem cells, dental pulpa stem cells) have been investigated by femtosecond laser 5D two-photon microscopy. Autofluorescence and second harmonic generation have been imaged with submicron spatial resolution, 270 ps temporal resolution, and 10 nm spectral resolution. In particular, NADH and flavoprotein fluorescence was detected in stem cells. Major emission peaks at 460nm and 530nm with typical mean fluorescence lifetimes of 1.8 ns and 2.0 ns, respectively, were measured using time-correlated single photon counting and spectral imaging. Differentiated stem cells produced the extracellular matrix protein collagen which was detected by SHG signals at 435 nm.

  6. Two-photon standard technique for measuring the two-photon absorption cross section in complex organic molecules

    SciTech Connect

    Alfimov, E.E.; Groshev, D.E.; Makukha, V.K.; Meshalkin, Y.P.

    1995-03-01

    The two-photon standard technique for measuring the absolute cross sections for two-photon absorption of complex organic molecules is proposed, which is quite insensitive to the spatial and temporal fluctuations of the laser beam. n-Bismethylsterilbenzene (MSB) with a known value of the two-photon absorption cross section is used as a standard. 9 refs., 2 figs.

  7. Wavelength dependent photoelectron circular dichroism of limonene studied by femtosecond multiphoton laser ionization and electron-ion coincidence imaging

    NASA Astrophysics Data System (ADS)

    Rafiee Fanood, Mohammad M.; Janssen, Maurice H. M.; Powis, Ivan

    2016-09-01

    Enantiomers of the monoterpene limonene have been investigated by (2 + 1) resonance enhanced multiphoton ionization and photoelectron circular dichroism employing tuneable, circularly polarized femtosecond laser pulses. Electron imaging detection provides 3D momentum measurement while electron-ion coincidence detection can be used to mass-tag individual electrons. Additional filtering, by accepting only parent ion tagged electrons, can be then used to provide discrimination against higher energy dissociative ionization mechanisms where more than three photons are absorbed to better delineate the two photon resonant, one photon ionization pathway. The promotion of different vibrational levels and, tentatively, different electronic ion core configurations in the intermediate Rydberg states can be achieved with different laser excitation wavelengths (420 nm, 412 nm, and 392 nm), in turn producing different state distributions in the resulting cations. Strong chiral asymmetries in the lab frame photoelectron angular distributions are quantified, and a comparison made with a single photon (synchrotron radiation) measurement at an equivalent photon energy.

  8. Resonantly enhanced four-wave mixing

    DOEpatents

    Begley, Richard F.; Kurnit, Norman A.

    1978-01-01

    A method and apparatus for achieving large susceptibilities and long interaction lengths in the generation of new wavelengths in the infrared spectral region. A process of resonantly enhanced four-wave mixing is employed, utilizing existing laser sources, such as the CO.sub.2 laser, to irradiate a gaseous media. The gaseous media, comprising NH.sub.3, CH.sub.3 F, D.sub.2, HCl, HF, CO, and H.sub.2 or some combination thereof, are of particular interest since they are capable of providing high repetition rate operation at high flux densities where crystal damage problems become a limitation.

  9. Two-photon mapping of neocortical circuits

    NASA Astrophysics Data System (ADS)

    Nikolenko, Volodymyr

    The synaptic circuits of the cerebral cortex are still poorly understood, yet knowing their basic structure appears key for understanding their function (Lorente de No, 1949). While some argue that there is a basic modular circuit present in all cortical regions (Douglas et al., 1989; Hubel and Wiesel, 1977), others suggest that synaptic circuits could be randomly structured (Braitenberg and Schuz, 1998). To investigate the patterns of synaptic connections present in neocortex, I have developed a novel two-photon optical mapping method (Nikolenko et al., 2007) to systematically reveal cells that connect to four classes of neurons in slices of mouse primary sensory cortex. Inputs to these cells originated preferentially from specific cortical layers and often were laterally restricted, revealing functional columnar circuits with sharp boundaries. Moreover, many neurons extensively sampled particular territories, and, in some cases, virtually every cell from a particular layer was connected to the postsynaptic target. The results reveal circuits with dense columnar connectivity, approximating in some cases the complete sampling from every potential presynaptic cell in an input layer. I discuss the implications of these findings in the context of the computational strategies used by the cortex.

  10. Exclusive Two-Photon Processes in QCD

    SciTech Connect

    Brodsky, Stanley J.; /SLAC

    2005-12-02

    Hadron pair production from two-photon annihilation plays an important role in unraveling the perturbative and non-perturbative structure of QCD, first by testing the validity and empirical applicability of leading-twist factorization theorems, second by verifying the structure of the underlying perturbative QCD subprocesses, and third, through measurements of angular distributions and ratios which are sensitive to the shape of the distribution amplitudes. In effect, photon-photon collisions provide a microscope for testing fundamental scaling laws of PQCD and for measuring distribution amplitudes. The determination of the shape and normalization of the distribution amplitude is particularly important in view of their importance in the analysis of exclusive semi-leptonic and two-body hadronic B-decays. The data from the Belle and CLEO collaborations on single and double meson production are in excellent agreement with the QCD predictions. In contrast, the normalization of the nominal leading-order predictions of PQCD for proton pair production appears to be significantly below recent Belle measurements. I also review issues relating to renormalization scale setting.

  11. Calculation of One-Photon and Two-Photon Absorption Spectra of Porphyrins Using Time-Dependent Density Functional Theory.

    PubMed

    Day, Paul N; Nguyen, Kiet A; Pachter, Ruth

    2008-07-01

    Time-dependent density functional theory has been used to calculate the one-photon and two-photon absorption spectra of free-base porphyrin, a substituted zinc porphyrin, and a zinc porphyrin dimer, in order to assess the validity of the method to reproduce the large increase in the two-photon absorption (TPA) cross-section for the dimer. Three hybrid functionals with varying amounts of exact exchange were tested, and the calculated one-photon absorption spectra for each of the molecular systems were shown to be in qualitative agreement with the measured spectra. All three functionals predict a large enhancement in the TPA cross-section for the dimer relative to the monomer, in agreement with experimental results. However, because of the sensitivity of the resonance enhancement factor to small differences in the relevant state energies, quantitative prediction of the TPA cross-section by this method is still a challenge.

  12. Two-photon absorption properties of fluorescent proteins

    PubMed Central

    Drobizhev, Mikhail; Makarov, Nikolay S.; Tillo, Shane E.; Hughes, Thomas E.; Rebane, Aleksander

    2016-01-01

    Two-photon excitation of fluorescent proteins is an attractive approach for imaging living systems. Today researchers are eager to know which proteins are the brightest, and what the best excitation wavelengths are. Here we review the two-photon absorption properties of a wide variety of fluorescent proteins, including new far-red variants, to produce a comprehensive guide to choosing the right FP and excitation wavelength for two-photon applications. PMID:21527931

  13. Ordering of azobenzenes by two-photon isomerization

    SciTech Connect

    Ishitobi, Hidekazu; Sekkat, Zouheir; Kawata, Satoshi

    2006-10-28

    We report on light induced orientation by two-photon isomerization of azobenzenes in films of polymer. The dynamics of isomerization and orientation by one-photon absorption and two-photon absorption (TPA) are similar, and TPA creates a degree of molecular orientation which is comparable to that achieved by single-photon isomerization, in agreement with the theoretical predictions of two-photon isomeric orientation.

  14. Two-photon absorption by a quantum dot pair

    NASA Astrophysics Data System (ADS)

    Scheibner, Michael; Economou, Sophia E.; Ponomarev, Ilya V.; Jennings, Cameron; Bracker, Allan S.; Gammon, Daniel

    2015-08-01

    The biexciton absorption spectrum of a pair of InAs/GaAs quantum dots is being studied by photoluminescence excitation spectroscopy. An absorption resonance with the characteristics of an instantaneous two-photon process reveals a coherent interdot two-photon transition. Pauli-selective tunneling is being used to demonstrate the transduction of the two-photon coherence into a nonlocal spin singlet state. The two-photon transition can be tuned spectrally by electric field, enabling amplification of its transition strength.

  15. Resonance production in two-photon interactions

    SciTech Connect

    Roe, N.A.

    1989-02-01

    Resonance production in two-photon interactions is studied using data collected with the ASP detector at the PEP e/sup +/e/sup /minus// storage ring located at the Stanford Linear Accelerator Center. The ASP detector is a non-magnetic lead-glass calorimeter constructed from 632 lead-glass bars. It covers 94% of 4..pi.. in solid angle, extending to within 20/degree/ of the beamline. Lead-scintillator calorimeters extend the coverage to within 21 mr of the beamline on both sides. Energy resolution of ..sqrt..E/10%, where E is the energy is GeV, is achieved for electrons and photons in the lead-glass calorimeter, and particle trajectories are reconstructed with high efficiency. A total luminosity of 108 pb/sup /minus/1/ was collected with the ASP detector at a center-of-mass energy of 29 GeV. The observed process is e/sup +/e/sup /minus// ..-->.. e/sup +/e/sup /minus//..gamma..*..gamma..* ..-->.. e/sup +/e/sup /minus//X, is a pseudoscalar resonance (J/sup PC/ = 0/sup /minus/+/) and ..gamma..* is a virtual (mass /ne/ 0) photon. The outgoing electrons scatter down the beampipe and are not detected. The observed resonances are the /eta/ and /eta/' mesons, with masses of 549 and 958 MeV, respectively. They are detected in the ..gamma gamma.. decay mode; a total of 2380 +- 49 /eta/ ..-->.. ..gamma gamma.. and 568 +- 26 /eta/' ..-->.. ..gamma gamma.. events are observed. From the number of events, the detection efficiency, and the calculated production cross sections the radiative widths, GAMMA/sub ..gamma gamma../, of the /eta/ and /eta/' were measured and found to be: GAMMA/sub ..gamma gamma../(/eta/) = .481 +- .010 +- .047keV and GAMMA/sub ..gamma gamma../(/eta/') = 4.71 +- .22 +- .70keV. These results are in good agreement with the world average values. 67 refs., 42 figs., 20 tabs.

  16. Nanoparticle electrostriction acoustic resonance enhanced nonlinearity

    NASA Astrophysics Data System (ADS)

    Xiang, Dao; Gordon, Reuven

    2016-09-01

    Four-wave mixing can be used for all-optical wavelength conversion to manipulate communication channels in wavelength division multiplexing. Most wavelength conversion techniques rely on small intrinsic optical nonlinearities, leading to the low conversion efficiency and high energy usage while requiring a long light-matter interaction lengths. Here, we demonstrate a resonantly enhanced nonlinear process by introducing the vibrational excitation, where the electrostrictive force excites the acoustic modes of nanoparticles and induces a travelling periodic variation in refractive index of the sample. We show experimentally and theoretically strong nanoparticle resonances ranging from tens of GHz to THz, which can be utilized to achieve higher frequency conversion for fast all-optical data processing.

  17. Two-photon finite-pulse model for resonant transitions in attosecond experiments

    NASA Astrophysics Data System (ADS)

    Jiménez-Galán, Álvaro; Martín, Fernando; Argenti, Luca

    2016-02-01

    We present an analytical model capable of describing two-photon ionization of atoms with attosecond pulses in the presence of intermediate and final isolated autoionizing states. The model is based on the finite-pulse formulation of second-order time-dependent perturbation theory. It approximates the intermediate and final states with Fano's theory for resonant continua, and it depends on a small set of atomic parameters that can either be obtained from separate ab initio calculations or be extracted from a few selected experiments. We use the model to compute the two-photon resonant photoelectron spectrum of helium below the N =2 threshold for the RABITT (reconstruction of attosecond beating by interference of two-photon transitions) pump-probe scheme, in which an XUV attosecond pulse train is used in association with a weak IR probe, obtaining results in quantitative agreement with those from accurate ab initio simulations. In particular, we show that (i) the use of finite pulses results in a homogeneous redshift of the RABITT beating frequency, as well as a resonant modulation of the beating frequency in proximity to intermediate autoionizing states; (ii) the phase of resonant two-photon amplitudes generally experiences a continuous excursion as a function of the intermediate detuning, with either zero or 2 π overall variation.

  18. Two-photon absorption in arsenic sulfide glasses

    NASA Astrophysics Data System (ADS)

    Chunaev, D. S.; Snopatin, G. E.; Plotnichenko, V. G.; Karasik, A. Ya.

    2016-10-01

    The two-photon absorption coefficient of 1047-{\\text{nm}} light in {\\text{As}}35{\\text{S}}65 chalcogenide glass has been measured. CW probe radiation has been used to observe the linear absorption in glass induced by two-photon excitation. The induced absorption lifetime was found to be ∼ 2 {\\text{ms}}.

  19. TPZ, a bright centrosymmetric two-photon scaffold for bioimaging.

    PubMed

    Lei, Zuhai; Yue, Ping; Wang, Xueli; Li, Xinran; Li, Yi; He, Haihong; Luo, Xiao; Meng, Xiangming; Chen, Jinquan; Qian, Xuhong; Yang, Youjun

    2017-10-03

    The development of biocompatible two-photon fluorophores with a large absorption cross-section is challenging, despite the presence of theoretical guidelines. By rendering asymmetric PRODAN dye centrosymmetric, we designed and synthesized a novel class of two-photon fluorophores (TPZ). Their photophysical properties were investigated and their imaging potentials in cells, tissues and zebrafish were showcased.

  20. Two-photon fluorescence excitation spectroscopy of biological molecules

    NASA Astrophysics Data System (ADS)

    Meshalkin, Yuri P.; Alfimov, E. E.; Groshev, D. E.; Makukha, V. K.

    1996-06-01

    The UV fluorescence spectra of aromatic amino-acids and some proteins at two photon excitation by second harmonic of Nd:YAG laser are received. Two-photon absorption cross sections of tryptophan, tyrosine, phenylalanine and proteins: bovine serum albumin, lysozyme, trypsin, (alpha) - chymotrypsinogen and pepsin at wavelength 532 nm were measured by means of the two-quantum standard method.

  1. Two-photon excitation based photochemistry and neural imaging

    NASA Astrophysics Data System (ADS)

    Hatch, Kevin Andrew

    Two-photon microscopy is a fluorescence imaging technique which provides distinct advantages in three-dimensional cellular and molecular imaging. The benefits of this technology may extend beyond imaging capabilities through exploitation of the quantum processes responsible for fluorescent events. This study utilized a two-photon microscope to investigate a synthetic photoreactive collagen peptidomimetic, which may serve as a potential material for tissue engineering using the techniques of two-photon photolysis and two-photon polymerization. The combination of these techniques could potentially be used to produce a scaffold for the vascularization of engineered three-dimensional tissues in vitro to address the current limitations of tissue engineering. Additionally, two-photon microscopy was used to observe the effects of the application of the neurotransmitter dopamine to the mushroom body neural structures of Drosophila melanogaster to investigate dopamine's connection to cognitive degeneration.

  2. Two-photon imaging with diffractive optical elements.

    PubMed

    Watson, Brendon O; Nikolenko, Volodymyr; Yuste, Rafael

    2009-01-01

    Two-photon imaging has become a useful tool for optical monitoring of neural circuits, but it requires high laser power and serial scanning of each pixel in a sample. This results in slow imaging rates, limiting the measurements of fast signals such as neuronal activity. To improve the speed and signal-to-noise ratio of two-photon imaging, we introduce a simple modification of a two-photon microscope, using a diffractive optical element (DOE) which splits the laser beam into several beamlets that can simultaneously scan the sample. We demonstrate the advantages of DOE scanning by enhancing the speed and sensitivity of two-photon calcium imaging of action potentials in neurons from neocortical brain slices. DOE scanning can easily improve the detection of time-varying signals in two-photon and other non-linear microscopic techniques.

  3. Two-Photon Imaging with Diffractive Optical Elements

    PubMed Central

    Watson, Brendon O.; Nikolenko, Volodymyr; Yuste, Rafael

    2009-01-01

    Two-photon imaging has become a useful tool for optical monitoring of neural circuits, but it requires high laser power and serial scanning of each pixel in a sample. This results in slow imaging rates, limiting the measurements of fast signals such as neuronal activity. To improve the speed and signal-to-noise ratio of two-photon imaging, we introduce a simple modification of a two-photon microscope, using a diffractive optical element (DOE) which splits the laser beam into several beamlets that can simultaneously scan the sample. We demonstrate the advantages of DOE scanning by enhancing the speed and sensitivity of two-photon calcium imaging of action potentials in neurons from neocortical brain slices. DOE scanning can easily improve the detection of time-varying signals in two-photon and other non-linear microscopic techniques. PMID:19636390

  4. Synthesis of Two-Photon Materials and Two-Photon Liquid Crystals

    NASA Technical Reports Server (NTRS)

    Subramaniam, Girija

    2001-01-01

    The duration of the grant was interrupted by two major accidents that the PI met with-- an auto accident in Pasadena, CA during her second summer at JPL which took almost eight months for recovery and a second accident during Fall 2000 that left her in crutches for the entire semester. Further, the time released agreed by the University was not given in a timely fashion. The candidate has been given post-grant expire time off. In spite of all these problems, the PI synthesized a number of new two-photon materials and studied the structure-activity correlation to arrive at the best-optimized structure. The PI's design proved to be one of the best in the sense that these materials has a hitherto unreported two-photon absorption cross section. Many materials based on PI's design was later made by the NASA colleague. This is Phase 1. Phase II of this grant is to orate liquid crystalline nature into this potentially useful materials and is currently in progress. Recent observations of nano- and pico-second response time of homeotropically aligned liquid crystals suggest their inherent potentials to act as laser hardening materials, i.e., as protective devices against short laser pulses. The objective of the current project is to exploit this potential by the synthesis of liquid crystals with high optical nonlinearity and optimizing their performance. The PI is trying structural variations to bring in liquid crystalline nature without losing the high two-photon cross section. Both Phase I and Phase II led to many invited presentations and publications in reputed journals like 'Science' and 'Molecular Crystals'. The list of presentations and reprints are enclosed. Another important and satisfying outcome of this grant is the opportunity that this grant offered to the budding undergraduate scientists to get involved in a visible research of international importance. All the students had a chance to learn a lot during research, had the opportunity to present their work at

  5. Two-photon interference of temporally separated photons.

    PubMed

    Kim, Heonoh; Lee, Sang Min; Moon, Han Seb

    2016-10-06

    We present experimental demonstrations of two-photon interference involving temporally separated photons within two types of interferometers: a Mach-Zehnder interferometer and a polarization-based Michelson interferometer. The two-photon states are probabilistically prepared in a symmetrically superposed state within the two interferometer arms by introducing a large time delay between two input photons; this state is composed of two temporally separated photons, which are in two different or the same spatial modes. We then observe two-photon interference fringes involving both the Hong-Ou-Mandel interference effect and the interference of path-entangled two-photon states simultaneously in a single interferometric setup. The observed two-photon interference fringes provide simultaneous observation of the interferometric properties of the single-photon and two-photon wavepackets. The observations can also facilitate a more comprehensive understanding of the origins of the interference phenomena arising from spatially bunched/anti-bunched two-photon states comprised of two temporally separated photons within the interferometer arms.

  6. Two-photon interference of temporally separated photons

    PubMed Central

    Kim, Heonoh; Lee, Sang Min; Moon, Han Seb

    2016-01-01

    We present experimental demonstrations of two-photon interference involving temporally separated photons within two types of interferometers: a Mach-Zehnder interferometer and a polarization-based Michelson interferometer. The two-photon states are probabilistically prepared in a symmetrically superposed state within the two interferometer arms by introducing a large time delay between two input photons; this state is composed of two temporally separated photons, which are in two different or the same spatial modes. We then observe two-photon interference fringes involving both the Hong-Ou-Mandel interference effect and the interference of path-entangled two-photon states simultaneously in a single interferometric setup. The observed two-photon interference fringes provide simultaneous observation of the interferometric properties of the single-photon and two-photon wavepackets. The observations can also facilitate a more comprehensive understanding of the origins of the interference phenomena arising from spatially bunched/anti-bunched two-photon states comprised of two temporally separated photons within the interferometer arms. PMID:27708380

  7. Two-photon interference of temporally separated photons

    NASA Astrophysics Data System (ADS)

    Kim, Heonoh; Lee, Sang Min; Moon, Han Seb

    2016-10-01

    We present experimental demonstrations of two-photon interference involving temporally separated photons within two types of interferometers: a Mach-Zehnder interferometer and a polarization-based Michelson interferometer. The two-photon states are probabilistically prepared in a symmetrically superposed state within the two interferometer arms by introducing a large time delay between two input photons; this state is composed of two temporally separated photons, which are in two different or the same spatial modes. We then observe two-photon interference fringes involving both the Hong-Ou-Mandel interference effect and the interference of path-entangled two-photon states simultaneously in a single interferometric setup. The observed two-photon interference fringes provide simultaneous observation of the interferometric properties of the single-photon and two-photon wavepackets. The observations can also facilitate a more comprehensive understanding of the origins of the interference phenomena arising from spatially bunched/anti-bunched two-photon states comprised of two temporally separated photons within the interferometer arms.

  8. Resonant enhancement of absorption in the superlens

    NASA Astrophysics Data System (ADS)

    Alekseyev, Leonid; Jacob, Zubin; Narimanov, Evgenii

    2007-03-01

    The Veselago lens (also known as the super lens) [1], which is a slab made of left handed material with ɛ=-1 and μ=-1 has interesting properties like perfect lensing [2] and cloaking [3]. When a source is placed in front of it there are regions of high field intensity in such a lens , known as anomalously localized resonant regions [3]. For practical applications of the superlens taking advantage of these properties, the effect of finite loss on the device performance is critical [4] . We calculate the absorption loss of dipole radiation by an ɛ<0 and μ<0 slab and find resonant enhancement of absorption in the superlensing regime. [1] V. G. Veselago, ``The electrodynamics of substances with simultaneously negative values of permittivity and permeability,'' Sov. Phys. Usp. 10, 509 (1968). [2] J. B. Pendry, ``Negative refraction makes a perfect lens,'' Phys. Rev. Lett. 85, 3966-3969 (2000). [3] Graeme W. Milton and Nicolae-Alexandry P. Nicorovici ``On the cloaking effects associated with anomalous localized resonance,'' Proc. R. Soc. A (2006) 462, 3027-3059. [4] V. A. Podolskiy and E. E. Narimanov, ``Near-sighted superlens,'' Opt. Lett. 30, 75-77 (2005)

  9. Neutron elastic backscattering with resonance enhancement

    SciTech Connect

    Gomberg, H.J.; McEllistrem, M.T.

    1993-12-31

    Reliable detection of explosives and narcotics depends on generating signatures of compounds which characterize them. Major explosives and also alkaloid narcotics contain unique concentrations of Carbon, Oxygen, and Nitrogen which provide specific elemental ratios and chemical signatures. Neutron-induced reaction methods are rapid and non-invasive means of probing container interiors for special element-ratio signatures which signal the presence of significant amounts of contraband. Among these reactions the highest probabilities occur for neutron from different light elements, allowing determination of relative abundance of these elements. The authors have already demonstrated signature for simulated explosives and simulated narcotics in experimental tests at 1-4 MeV at the University of Kentucky accelerator labs. Intensities of neutron scatter at angles near 150{degrees} from three different elements, C, N, and O, were determined. Fast neutron time-of-flight detection methods enabled measurement of neutron energies, and thus separation of scattering from the different elements. Making measurements on and off strong resonances for specific elements, increases PFD and reduces PFA. Measurements illustrating this resonance enhancement technique will be presented.

  10. Quantum homodyne tomography of a two-photon Fock state.

    PubMed

    Ourjoumtsev, Alexei; Tualle-Brouri, Rosa; Grangier, Philippe

    2006-06-02

    We present a continuous-variable experimental analysis of a two-photon Fock state of free-propagating light. This state is obtained from a pulsed nondegenerate parametric amplifier, which produces two intensity-correlated twin beams. Counting two photons in one beam projects the other beam in the desired two-photon Fock state, which is analyzed by using a pulsed homodyne detection. The Wigner function of the measured state is clearly negative. We developed a detailed analytic model which allows a fast and efficient analysis of the experimental results.

  11. Random access three-dimensional two-photon microscopy.

    PubMed

    Rózsa, Balázs; Katona, Gergely; Vizi, E Sylvester; Várallyay, Zoltán; Sághy, Attila; Valenta, Lásló; Maák, Pál; Fekete, Júlia; Bányász, Akos; Szipocs, Róbert

    2007-04-01

    We propose a two-photon microscope scheme capable of real-time, three-dimensional investigation of the electric activity pattern of neural networks or signal summation rules of individual neurons in a 0.6 mm x 0.6 mm x 0.2 mm volume of the sample. The points of measurement are chosen according to a conventional scanning two-photon image, and they are addressed by separately adjustable optical fibers. This allows scanning at kilohertz repetition rates of as many as 100 data points. Submicrometer spatial resolution is maintained during the measurement similarly to conventional two-photon microscopy.

  12. Scattering of two photons from two distant qubits: exact solution.

    PubMed

    Laakso, Matti; Pletyukhov, Mikhail

    2014-10-31

    We consider the inelastic scattering of two photons from two qubits separated by an arbitrary distance R and coupled to a one-dimensional transmission line. We present an exact, analytical solution to the problem, and use it to explore a particular configuration of qubits that is transparent to single-photon scattering, thus highlighting non-Markovian effects of inelastic two-photon scattering: strong two-photon interference and momentum dependent photon (anti)bunching. This latter effect can be seen as an inelastic generalization of the Hong-Ou-Mandel effect.

  13. Scattering of Two Photons from Two Distant Qubits: Exact Solution

    NASA Astrophysics Data System (ADS)

    Laakso, Matti; Pletyukhov, Mikhail

    2014-10-01

    We consider the inelastic scattering of two photons from two qubits separated by an arbitrary distance R and coupled to a one-dimensional transmission line. We present an exact, analytical solution to the problem, and use it to explore a particular configuration of qubits that is transparent to single-photon scattering, thus highlighting non-Markovian effects of inelastic two-photon scattering: strong two-photon interference and momentum dependent photon (anti)bunching. This latter effect can be seen as an inelastic generalization of the Hong-Ou-Mandel effect.

  14. Pulse-shaping based two-photon FRET stoichiometry.

    PubMed

    Flynn, Daniel C; Bhagwat, Amar R; Brenner, Meredith H; Núñez, Marcos F; Mork, Briana E; Cai, Dawen; Swanson, Joel A; Ogilvie, Jennifer P

    2015-02-09

    Förster Resonance Energy Transfer (FRET) based measurements that calculate the stoichiometry of intermolecular interactions in living cells have recently been demonstrated, where the technique utilizes selective one-photon excitation of donor and acceptor fluorophores to isolate the pure FRET signal. Here, we present work towards extending this FRET stoichiometry method to employ two-photon excitation using a pulse-shaping methodology. In pulse-shaping, frequency-dependent phases are applied to a broadband femtosecond laser pulse to tailor the two-photon excitation conditions to preferentially excite donor and acceptor fluorophores. We have also generalized the existing stoichiometry theory to account for additional cross-talk terms that are non-vanishing under two-photon excitation conditions. Using the generalized theory we demonstrate two-photon FRET stoichiometry in live COS-7 cells expressing fluorescent proteins mAmetrine as the donor and tdTomato as the acceptor.

  15. In vivo two-photon imaging of the mouse retina

    PubMed Central

    Sharma, Robin; Yin, Lu; Geng, Ying; Merigan, William H.; Palczewska, Grazyna; Palczewski, Krzysztof; Williams, David R.; Hunter, Jennifer J.

    2013-01-01

    Though in vivo two-photon imaging has been demonstrated in non-human primates, improvements in the signal-to-noise ratio (SNR) would greatly improve its scientific utility. In this study, extrinsic fluorophores, expressed in otherwise transparent retinal ganglion cells, were imaged in the living mouse eye using a two-photon fluorescence adaptive optics scanning laser ophthalmoscope. We recorded two orders of magnitude greater signal levels from extrinsically labeled cells relative to previous work done in two-photon autofluorescence imaging of primates. Features as small as single dendrites in various layers of the retina could be resolved and predictions are made about the feasibility of measuring functional response from cells. In the future, two-photon imaging in the intact eye may allow us to monitor the function of retinal cell classes with infrared light that minimally excites the visual response. PMID:24009992

  16. Three-dimensional two-photon imaging in polymeric materials

    NASA Astrophysics Data System (ADS)

    Belfield, Kevin D.; Schafer, Katherine J.; Andrasik, Stephen; Yavuz, Ozlem; Van Stryland, Eric W.; Hagan, David J.; Hales, Joel M.

    2002-01-01

    We report image formation via single and two-photon photoinduced fluorescence changes in a polymeric medium with two-photon fluorescence readout of multiplayer structures. Photoinduced acid generation in the presence of a two-photon fluorescent dye possessing strongly basic functional groups (7-benzothiazolyl-9,9-didecyl-2,2-(N,N- diphenylamino)fluorene underwent protonation upon exposure with UV or near-IR (740 nm fs pulses). Solution studies demonstrate formation of monoprotonated and diprotonated species upon irradiation, each resulting in distinctly different absorption and fluorescence properties. The fluorescence of the original, neutral, fluorophore is quenched upon monoprotonation with a concomitant increase in fluorescence at longer wavelengths due to the monoprotonated form. Hence, two channel two-photon fluorescence imaging provides 'positive' or 'negative' image readout capability. Results of solution and solid polymer thin films experiments are presented.

  17. Pulse-shaping based two-photon FRET stoichiometry

    PubMed Central

    Flynn, Daniel C.; Bhagwat, Amar R.; Brenner, Meredith H.; Núñez, Marcos F.; Mork, Briana E.; Cai, Dawen; Swanson, Joel A.; Ogilvie, Jennifer P.

    2015-01-01

    Förster Resonance Energy Transfer (FRET) based measurements that calculate the stoichiometry of intermolecular interactions in living cells have recently been demonstrated, where the technique utilizes selective one-photon excitation of donor and acceptor fluorophores to isolate the pure FRET signal. Here, we present work towards extending this FRET stoichiometry method to employ two-photon excitation using a pulse-shaping methodology. In pulse-shaping, frequency-dependent phases are applied to a broadband femtosecond laser pulse to tailor the two-photon excitation conditions to preferentially excite donor and acceptor fluorophores. We have also generalized the existing stoichiometry theory to account for additional cross-talk terms that are non-vanishing under two-photon excitation conditions. Using the generalized theory we demonstrate two-photon FRET stoichiometry in live COS-7 cells expressing fluorescent proteins mAmetrine as the donor and tdTomato as the acceptor. PMID:25836193

  18. Two-Photon Fluorescence Microscopy for Biomedical Research

    NASA Technical Reports Server (NTRS)

    Fischer, David; Zimmerli, Greg; Asipauskas, Marius

    2007-01-01

    This viewgraph presentation gives an overview of two-photon microscopy as it applies to biomedical research. The topics include: 1) Overview; 2) Background; 3) Principles of Operation; 4) Advantages Over Confocal; 5) Modes of Operation; and 6) Applications.

  19. Two-photon directed evolution of green fluorescent proteins

    NASA Astrophysics Data System (ADS)

    Stoltzfus, Caleb R.; Barnett, Lauren M.; Drobizhev, Mikhail; Wicks, Geoffrey; Mikhaylov, Alexander; Hughes, Thomas E.; Rebane, Aleksander

    2015-07-01

    Directed evolution has been used extensively to improve the properties of a variety of fluorescent proteins (FPs). Evolutionary strategies, however, have not yet been used to improve the two-photon absorption (2PA) properties of a fluorescent protein, properties that are important for two-photon imaging in living tissues, including the brain. Here we demonstrate a technique for quantitatively screening the two-photon excited fluorescence (2PEF) efficiency and 2PA cross section of tens of thousands of mutant FPs expressed in E. coli colonies. We use this procedure to move EGFP through three rounds of two-photon directed evolution leading to new variants showing up to a 50% enhancement in peak 2PA cross section and brightness within the near-IR tissue transparency wavelength range.

  20. The use of CNDO in spectroscopy. XV. Two photon absorption

    NASA Astrophysics Data System (ADS)

    Marchese, Francis T.; Seliskar, C. J.; Jaffé, H. H.

    1980-04-01

    Two-photon absorptivities have been calculated within the CNDO/S-CI molecular orbital framework of Del Bene and Jaffé utilizing the second order time dependent perturbation equations of Göppert-Mayer and polarization methods of McClain. Good agreement is found between this theory and experiment for transition energies, symmetries, and two-photon absorptivities for the following molecules: biphenyl, terphenyl, 2,2'-difluorobiphenyl, 2,2'-bipyridyl, phenanthrene, and the isoelectronic series: fluorene, carbazole, dibenzofuran.

  1. Malachite green derivatives for two-photon RNA detection.

    PubMed

    Lux, Jacques; Peña, Eduardo José; Bolze, Frédéric; Heinlein, Manfred; Nicoud, Jean-François

    2012-05-29

    The design, preparation and characterisation of a library of malachite green (MG) derivatives for two-photon RNA labelling is described. Some of these MG derivatives exhibit an increased affinity for an MG-aptamer, as well as improved two-photon sensitivity when compared to the classical malachite green chloride. The underlying mechanisms and potential benefits for in vivo RNA visualisation are discussed. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Antecedents of two-photon excitation laser scanning microscopy.

    PubMed

    Masters, Barry R; So, Peter T C

    2004-01-01

    In 1931, Maria Göppert-Mayer published her doctoral dissertation on the theory of two-photon quantum transitions (two-photon absorption and emission) in atoms. This report describes and analyzes the theoretical and experimental work on nonlinear optics, in particular two-photon excitation processes, that occurred between 1931 and the experimental implementation of two-photon excitation microscopy by the group of Webb in 1990. In addition to Maria Göppert-Mayer's theoretical work, the invention of the laser has a key role in the development of two-photon microscopy. Nonlinear effects were previously observed in different frequency domains (low-frequency electric and magnetic fields and magnetization), but the high electric field strength afforded by lasers was necessary to demonstrate many nonlinear effects in the optical frequency range. In 1978, the first high-resolution nonlinear microscope with depth resolution was described by the Oxford group. Sheppard and Kompfner published a study in Applied Optics describing microscopic imaging based on second-harmonic generation. In their report, they further proposed that other nonlinear optical effects, such as two-photon fluorescence, could also be applied. However, the developments in the field of nonlinear optical stalled due to a lack of a suitable laser source. This obstacle was removed with the advent of femtosecond lasers in the 1980s. In 1990, the seminal study of Denk, Strickler, and Webb on two-photon laser scanning fluorescence microscopy was published in Science. Their paper clearly demonstrated the capability of two-photon excitation microscopy for biology, and it served to convince a wide audience of scientists of the potential capability of the technique.

  3. Voigt spectral profiles in two-photon resonance fluorescence

    SciTech Connect

    Alexanian, Moorad; Bose, Subir K.

    2007-11-15

    A recent work on two-photon fluorescence is extended by considering the pump field to be a coherent state, which represents a laser field operating well above threshold. The dynamical conditions are investigated under which the two-photon spectrum gives rise, in addition to a Lorentzian line shape at the pump frequency, to two Voigt spectral sideband profiles. Additional conditions are found under which the Voigt profile behaves like either a Gaussian or a Lorentzian line shape.

  4. Two-photon photovoltaic effect in gallium arsenide.

    PubMed

    Ma, Jichi; Chiles, Jeff; Sharma, Yagya D; Krishna, Sanjay; Fathpour, Sasan

    2014-09-15

    The two-photon photovoltaic effect is demonstrated in gallium arsenide at 976 and 1550 nm wavelengths. A waveguide-photodiode biased in its fourth quadrant harvests electrical power from the optical energy lost to two-photon absorption. The experimental results are in good agreement with simulations based on nonlinear wave propagation in waveguides and the drift-diffusion model of carrier transport in semiconductors. Power efficiency of up to 8% is theoretically predicted in optimized devices.

  5. Two photon couplings of the lightest isoscalars from BELLE data

    SciTech Connect

    Dai, Ling -Yun; Pennington, Michael R.

    2014-07-07

    Amplitude Analysis of two photon production of ππ and K¯K, using S-matrix constraints and fitting all available data, including the latest precision results from Belle, yields a single partial wave solution up to 1.4 GeV. The two photon couplings of the σ/f0(500), f0(980) and f2(1270) are determined from the residues of the resonance poles.

  6. Two photon couplings of the lightest isoscalars from BELLE data

    DOE PAGES

    Dai, Ling -Yun; Pennington, Michael R.

    2014-07-07

    Amplitude Analysis of two photon production of ππ and K¯K, using S-matrix constraints and fitting all available data, including the latest precision results from Belle, yields a single partial wave solution up to 1.4 GeV. The two photon couplings of the σ/f0(500), f0(980) and f2(1270) are determined from the residues of the resonance poles.

  7. Two Photon Polymerization of Microneedles for Transdermal Drug Delivery

    PubMed Central

    Gittard, Shaun D.; Ovsianikov, Aleksandr; Chichkov, Boris N.; Doraiswamy, Anand; Narayan, Roger J.

    2010-01-01

    Importance of the field Microneedles are small-scale devices that are finding use for transdermal delivery of protein-based pharmacologic agents and nucleic acid-based pharmacologic agents; however, microneedles prepared using conventional microelectronics-based technologies have several shortcomings, which have limited translation of these devices into widespread clinical use. Areas covered in this review Two photon polymerization is a laser-based rapid prototyping technique that has been recently used for direct fabrication of hollow microneedles with a wide variety of geometries. In addition, an indirect rapid prototyping method that involves two photon polymerization and polydimethyl siloxane micromolding has been used for fabrication of solid microneedles with exceptional mechanical properties. What the reader will gain In this review, the use of two photon polymerization for fabricating in-plane and out-of-plane hollow microneedle arrays is described. The use of two photon polymerization-micromolding for fabrication of solid microneedles is also reviewed. In addition, fabrication of microneedles with antimicrobial properties is discussed; antimicrobial microneedles may reduce the risk of infection associated with formation of channels through the stratum corneum. Take home message It is anticipated that the use of two photon polymerization as well as two photon polymerization-micromolding for fabrication of microneedles and other microstructured drug delivery devices will increase over the coming years. PMID:20205601

  8. Uniform silica nanoparticles encapsulating two-photon absorbing fluorescent dye

    SciTech Connect

    Wu Weibing; Liu Chang; Wang Mingliang; Huang Wei; Zhou Shengrui; Jiang Wei; Sun Yueming; Cui Yiping; Xu Chunxinag

    2009-04-15

    We have prepared uniform silica nanoparticles (NPs) doped with a two-photon absorbing zwitterionic hemicyanine dye by reverse microemulsion method. Obvious solvatochromism on the absorption spectra of dye-doped NPs indicates that solvents can partly penetrate into the silica matrix and then affect the ground and excited state of dye molecules. For dye-doped NP suspensions, both one-photon and two-photon excited fluorescence are much stronger and recorded at shorter wavelength compared to those of free dye solutions with comparative overall dye concentration. This behavior is possibly attributed to the restricted twisted intramolecular charge transfer (TICT), which reduces fluorescence quenching when dye molecules are trapped in the silica matrix. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells with low cytotoxicity. - Graphical abstract: Water-soluble silica NPs doped with a two-photon absorbing zwitterionic hemicyanine dye were prepared. They were found of enhanced one-photon and two-photon excited fluorescence compared to free dye solutions. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells.

  9. Two-photon microscopy of cells and tissue.

    PubMed

    Rubart, Michael

    2004-12-10

    Two-photon excitation fluorescence imaging provides thin optical sections from deep within thick, scattering specimens by way of restricting fluorophore excitation (and thus emission) to the focal plane of the microscope. Spatial confinement of two-photon excitation gives rise to several advantages over single-photon confocal microscopy. First, penetration depth of the excitation beam is increased. Second, because out-of-focus fluorescence is never generated, no pinhole is necessary in the detection path of the microscope, resulting in increased fluorescence collection efficiency. Third, two-photon excitation markedly reduces overall photobleaching and photodamage, resulting in extended viability of biological specimens during long-term imaging. Finally, localized excitation can be used for photolysis of caged compounds in femtoliter volumes and for diffusion measurements by two-photon fluorescence photobleaching recovery. This review aims to provide an overview of the use of two-photon excitation microscopy. Selected applications of this technique will illustrate its excellent suitability to assess cellular and subcellular events in intact, strongly scattering tissue. In particular, its capability to resolve differences in calcium dynamics between individual cardiomyocytes deep within intact, buffer-perfused hearts is demonstrated. Potential applications of two-photon laser scanning microscopy as applied to integrative cardiac physiology are pointed out.

  10. X-ray two-photon absorption with high fluence XFEL pulses

    DOE PAGES

    Hoszowska, Joanna; Szlachetko, J.; Dousse, J. -Cl.; ...

    2015-09-07

    Here, we report on nonlinear interaction of solid Fe with intense femtosecond hard x-ray free-electron laser (XFEL) pulses. The experiment was performed at the CXI end-station of the Linac Coherent Light Source (LCLS) by means of high- resolution x-ray emission spectroscopy. The focused x-ray beam provided extreme fluence of ~105 photons/Å2. Two-photon absorption leading to K-shell hollow atom formation and to single K-shell ionization of solid Fe was investigated.

  11. X-ray two-photon absorption with high fluence XFEL pulses

    SciTech Connect

    Hoszowska, Joanna; Szlachetko, J.; Dousse, J. -Cl.; Błachucki, W.; Kayser, Y.; Milne, Ch.; Pajek, M.; Boutet, S.; Messerschmidt, M.; Williams, G.; Chantler, C. T.

    2015-09-07

    Here, we report on nonlinear interaction of solid Fe with intense femtosecond hard x-ray free-electron laser (XFEL) pulses. The experiment was performed at the CXI end-station of the Linac Coherent Light Source (LCLS) by means of high- resolution x-ray emission spectroscopy. The focused x-ray beam provided extreme fluence of ~105 photons/Å2. Two-photon absorption leading to K-shell hollow atom formation and to single K-shell ionization of solid Fe was investigated.

  12. Calculation of the spatial resolution in two-photon absorption spectroscopy applied to plasma diagnosis

    NASA Astrophysics Data System (ADS)

    Garcia-Lechuga, M.; Fuentes, L. M.; Grützmacher, K.; Pérez, C.; de la Rosa, M. I.

    2014-10-01

    We report a detailed characterization of the spatial resolution provided by two-photon absorption spectroscopy suited for plasma diagnosis via the 1S-2S transition of atomic hydrogen for optogalvanic detection and laser induced fluorescence (LIF). A precise knowledge of the spatial resolution is crucial for a correct interpretation of measurements, if the plasma parameters to be analysed undergo strong spatial variations. The present study is based on a novel approach which provides a reliable and realistic determination of the spatial resolution. Measured irradiance distribution of laser beam waists in the overlap volume, provided by a high resolution UV camera, are employed to resolve coupled rate equations accounting for two-photon excitation, fluorescence decay and ionization. The resulting three-dimensional yield distributions reveal in detail the spatial resolution for optogalvanic and LIF detection and related saturation due to depletion. Two-photon absorption profiles broader than the Fourier transform-limited laser bandwidth are also incorporated in the calculations. The approach allows an accurate analysis of the spatial resolution present in recent and future measurements.

  13. Two-photon fluorescent probe for cadmium imaging in cells.

    PubMed

    Liu, Yongyou; Dong, Xiaohu; Sun, Jian; Zhong, Cheng; Li, Boheng; You, Ximeng; Liu, Bifeng; Liu, Zhihong

    2012-04-21

    A novel two-photon excited fluorescent probe for cadmium (named as TPCd) was designed and synthesized utilizing a prodan (6-acetyl-2-methoxynaphthalene) derivative as the two-photon fluorophore and an o-phenylenediamine derivative as the Cd(2+) chelator, which possessed favorable photophysical properties and good water-solubility. The probe was designed with a photoinduced electron transfer (PET) mechanism and thus was weakly fluorescent itself. After binding with Cd(2+) which blocked the PET process, the fluorescence intensity of the probe was enhanced by up to 15-fold under one-photon excitation (OPE) and 27-fold under two-photon excitation (TPE), respectively. The two-photon action cross-section (Φδ) of the TPCd-Cd complex at 740 nm reached 109 GM compared to 3.6 GM for free TPCd, indicating the promising prospect of the probe in two-photon application. TPCd chelated Cd(2+) with 1 : 1 stoichiometry, and the apparent dissociation constant (K(d)) was 6.1 × 10(-5) M for the one-photon mode and 7.2 × 10(-5) M for the two-photon mode. The probe responded to Cd(2+) over a wide linear range from 0.1 to 30 μM with a detection limit of 0.04 μM. High selectivity of the probe towards Cd(2+) was acquired in Tris-HCl/sodium phosphate buffer. The probe was pH-independent in the biologically relevant pH range and non-toxic to living cells at reasonable concentration levels, warranting its in vivo applications. Through two-photon microscopy imaging, the probe was successfully applied to detect Cd(2+) uptake in living HepG2 cells.

  14. Resonance enhanced laser mass spectrometry for process- and environmental-analysis: Applications and perspectives

    NASA Astrophysics Data System (ADS)

    Zimmermann, Ralf; Heger, Hans Jörg; Dorfner, Ralph; Boesl, Ulrich; Kettrup, Antonius

    1998-12-01

    Laser induced Resonance-Enhanced Multi-Photon Ionization Time-Of-Flight Mass Spectrometry (REMPI TOFMS) is a highly selective as well as sensitive analytical technique, well suited for species selective, on-line monitoring of trace-substances. In this contribution some analytical applications of a mobile REMPI-TOFMS are presented. This includes REMPI-TOMS on-line analysis of coffee roasting gas and waste incineration flue gas as well as headspace measurements of pulp processing lye or rapid analysis of polycyclic aromatic hydrocarbons from soil samples via thermal desorption.

  15. Resonance enhanced laser mass spectrometry for process- and environmental-analysis: Applications and perspectives

    SciTech Connect

    Zimmermann, Ralf; Dorfner, Ralph; Kettrup, Antonius; Heger, Hans Joerg; Boesl, Ulrich

    1998-12-16

    Laser induced Resonance-Enhanced Multi-Photon Ionization Time-Of-Flight Mass Spectrometry (REMPI TOFMS) is a highly selective as well as sensitive analytical technique, well suited for species selective, on-line monitoring of trace-substances. In this contribution some analytical applications of a mobile REMPI-TOFMS are presented. This includes REMPI-TOMS on-line analysis of coffee roasting gas and waste incineration flue gas as well as headspace measurements of pulp processing lye or rapid analysis of polycyclic aromatic hydrocarbons from soil samples via thermal desorption.

  16. Three-dimensional microfabrication using two-photon polymerization

    NASA Astrophysics Data System (ADS)

    Cumpston, Brian H.; Ehrlich, Jeffrey E.; Kuebler, Stephen M.; Lipson, Matthew; Marder, Seth R.; McCord-Maughon, D.; Perry, Joseph W.; Roeckel, Harold; Rumi, Maria Cristina

    1998-09-01

    Photopolymerization initiated by the simultaneous absorption of two photons is unique in its ability to produce complex three-dimensional (3D) structures from a single, thick photopolymer film. Strong 3D confinement of the polymerization process is not possible in other polymer microfabrication techniques such as LIGA, rapid prototyping, and conventional photoresist technology. Two-photon polymerization also permits the fabrication of 3D structures and the definition of lithographic features on non-planar surfaces. We have developed a wide array of chromophores which hold great promise for 3D microfabrication, as well as other applications, such as two-photon fluorescence imaging and 3D optical data storage. These materials are based on a donor- (pi) -donor, donor-acceptor-donor, or acceptor-donor-acceptor structural motif. The magnitude of the two-photon absorption cross-section, (delta) , and the position of the two-photon absorption maximum, (lambda) (2)max, can be controlled by varying the length of the conjugated bridge and by varying the strength of the donor/acceptor groups. In this way, chromophores have been developed which exhibit strong two- photon absorption in the range of 500 - 975 nm, in some cases as high as 4400 X 10-50 cm4 s/photon-molecule. In the case of donor-(pi) -donor structures, quantum-chemical calculations show that the large absorption cross-sections arise from the symmetric re-distribution of charge from the donor end-groups to the conjugated bridge, resulting in an electronic excited-state which is more delocalized than the ground state. For many of these molecules, two-photon excitation populates a state which is sufficiently reducing that a charge transfer reaction can occur with acrylate monomers. The efficiency of these processes can be described using Marcus theory. Under suitable conditions, such reactions can induce radical polymerization of acrylate resins. Polymerization rates have been measured, and we show that these two-photon

  17. Two-photon flow cytometer with laser scanning Bessel beams

    NASA Astrophysics Data System (ADS)

    Wang, Yongdong; Ding, Yu; Ray, Supriyo; Paez, Aurelio; Xiao, Chuan; Li, Chunqiang

    2016-03-01

    Flow cytometry is an important technique in biomedical discovery for cell counting, cell sorting and biomarker detection. In vivo flow cytometers, based on one-photon or two-photon excited fluorescence, have been developed for more than a decade. One drawback of laser beam scanning two-photon flow cytometer is that the two-photon excitation volume is fairly small due to the short Rayleigh range of a focused Gaussian beam. Hence, the sampling volume is much smaller than one-photon flow cytometry, which makes it challenging to count or detect rare circulating cells in vivo. Bessel beams have narrow intensity profiles with an effective spot size (FWHM) as small as several wavelengths, making them comparable to Gaussian beams. More significantly, the theoretical depth of field (propagation distance without diffraction) can be infinite, making it an ideal solution as a light source for scanning beam flow cytometry. The trade-off of using Bessel beams rather than a Gaussian beam is the fact that Bessel beams have small concentric side rings that contribute to background noise. Two-photon excitation can reduce this noise, as the excitation efficiency is proportional to intensity squared. Therefore, we developed a two-photon flow cytometer using scanned Bessel beams to form a light sheet that intersects the micro fluidic channel.

  18. Confocal and Two-Photon Microscopy: Foundations, Applications and Advances

    NASA Astrophysics Data System (ADS)

    Diaspro, Alberto

    2001-11-01

    Confocal and Two-Photon Microscopy Foundations, Applications, and Advances Edited by Alberto Diaspro Confocal and two-photon fluorescence microscopy has provided researchers with unique possibilities of three-dimensional imaging of biological cells and tissues and of other structures such as semiconductor integrated circuits. Confocal and Two-Photon Microscopy: Foundations, Applications, and Advances provides clear, comprehensive coverage of basic foundations, modern applications, and groundbreaking new research developments made in this important area of microscopy. Opening with a foreword by G. J. Brakenhoff, this reference gathers the work of an international group of renowned experts in chapters that are logically divided into balanced sections covering theory, techniques, applications, and advances, featuring: In-depth discussion of applications for biology, medicine, physics, engineering, and chemistry, including industrial applications Guidance on new and emerging imaging technology, developmental trends, and fluorescent molecules Uniform organization and review-style presentation of chapters, with an introduction, historical overview, methodology, practical tips, applications, future directions, chapter summary, and bibliographical references Companion FTP site with full-color photographs The significant experience of pioneers, leaders, and emerging scientists in the field of confocal and two-photon excitation microscopy Confocal and Two-Photon Microscopy: Foundations, Applications, and Advances is invaluable to researchers in the biological sciences, tissue and cellular engineering, biophysics, bioengineering, physics of matter, and medicine, who use these techniques or are involved in developing new commercial instruments.

  19. Interference and complementarity for two-photon hybrid entangled states

    SciTech Connect

    Nogueira, W. A. T.; Santibanez, M.; Delgado, A.; Saavedra, C.; Neves, L.; Lima, G.; Padua, S.

    2010-10-15

    In this work we generate two-photon hybrid entangled states (HESs), where the polarization of one photon is entangled with the transverse spatial degree of freedom of the second photon. The photon pair is created by parametric down-conversion in a polarization-entangled state. A birefringent double-slit couples the polarization and spatial degrees of freedom of these photons, and finally, suitable spatial and polarization projections generate the HES. We investigate some interesting aspects of the two-photon hybrid interference and present this study in the context of the complementarity relation that exists between the visibility of the one-photon and that of the two-photon interference patterns.

  20. Tissue imaging using two-photon video rate microscopy

    NASA Astrophysics Data System (ADS)

    Kim, Ki H.; Buehler, Christof; Dong, Chen-Yuan; Masters, Barry R.; So, Peter T. C.

    1999-06-01

    Non-invasive optical diagnosis of cellular and extracellular structure and biochemistry in thick tissue is becoming a reality with the maturation of the two-photon imaging. Today, the slow imaging speed of typical two-photon microscopes is a major hurdle in realizing their clinical potential. We have developed a high-speed two-photon microscope optimized for acquiring 3-D tissue images in real time. The scanning speed improvement of this system is obtained by the use of an air bearing polygonal mirror. The maximum achievable scanning rate is 40 microseconds per line, which is about 100 times faster than conventional scanning microscopes. High-resolution fluorescence images were recorded in real-time by an intensified CCD camera. Using this instrument, we have monitored the movements of protozoas and mapped the collagen/elastin fiber structures in excised human skin.

  1. Two-photon interference between disparate sources for quantum networking

    PubMed Central

    McMillan, A. R.; Labonté, L.; Clark, A. S.; Bell, B.; Alibart, O.; Martin, A.; Wadsworth, W. J.; Tanzilli, S.; Rarity, J. G.

    2013-01-01

    Quantum networks involve entanglement sharing between multiple users. Ideally, any two users would be able to connect regardless of the type of photon source they employ, provided they fulfill the requirements for two-photon interference. From a theoretical perspective, photons coming from different origins can interfere with a perfect visibility, provided they are made indistinguishable in all degrees of freedom. Previous experimental demonstrations of such a scenario have been limited to photon wavelengths below 900 nm, unsuitable for long distance communication, and suffered from low interference visibility. We report two-photon interference using two disparate heralded single photon sources, which involve different nonlinear effects, operating in the telecom wavelength range. The measured visibility of the two-photon interference is 80 ± 4%, which paves the way to hybrid universal quantum networks. PMID:23783585

  2. Two-photon interference between disparate sources for quantum networking

    NASA Astrophysics Data System (ADS)

    McMillan, A. R.; Labonté, L.; Clark, A. S.; Bell, B.; Alibart, O.; Martin, A.; Wadsworth, W. J.; Tanzilli, S.; Rarity, J. G.

    2013-06-01

    Quantum networks involve entanglement sharing between multiple users. Ideally, any two users would be able to connect regardless of the type of photon source they employ, provided they fulfill the requirements for two-photon interference. From a theoretical perspective, photons coming from different origins can interfere with a perfect visibility, provided they are made indistinguishable in all degrees of freedom. Previous experimental demonstrations of such a scenario have been limited to photon wavelengths below 900 nm, unsuitable for long distance communication, and suffered from low interference visibility. We report two-photon interference using two disparate heralded single photon sources, which involve different nonlinear effects, operating in the telecom wavelength range. The measured visibility of the two-photon interference is 80 +/- 4%, which paves the way to hybrid universal quantum networks.

  3. Two-photon interference between disparate sources for quantum networking.

    PubMed

    McMillan, A R; Labonté, L; Clark, A S; Bell, B; Alibart, O; Martin, A; Wadsworth, W J; Tanzilli, S; Rarity, J G

    2013-01-01

    Quantum networks involve entanglement sharing between multiple users. Ideally, any two users would be able to connect regardless of the type of photon source they employ, provided they fulfill the requirements for two-photon interference. From a theoretical perspective, photons coming from different origins can interfere with a perfect visibility, provided they are made indistinguishable in all degrees of freedom. Previous experimental demonstrations of such a scenario have been limited to photon wavelengths below 900 nm, unsuitable for long distance communication, and suffered from low interference visibility. We report two-photon interference using two disparate heralded single photon sources, which involve different nonlinear effects, operating in the telecom wavelength range. The measured visibility of the two-photon interference is 80 ± 4%, which paves the way to hybrid universal quantum networks.

  4. Two-photon absorption of few-electron heavy ions

    SciTech Connect

    Surzhykov, A.; Indelicato, P.; Santos, J. P.; Amaro, P.; Fritzsche, S.

    2011-08-15

    The two-photon absorption of few-electron ions has been studied by using second-order perturbation theory and Dirac's relativistic equation. Within this framework, the general expressions for the excitation cross sections and rates are derived including a full account of the higher-order multipole terms in the expansion of the electron-photon interaction. While these expressions can be applied to any ion, independent of its particular shell structure, detailed computations are carried out for the two-photon absorption of hydrogen-, helium-, and berylliumlike ions and are compared with the available theoretical and experimental data. The importance of relativistic and nondipole effects in the analysis and computation of induced two-photon transitions is pointed out. Moreover, we discuss the potential of these transitions for atomic parity-violation studies in the high-Z domain.

  5. Adaptive optics two-photon scanning laser fluorescence microscopy

    NASA Astrophysics Data System (ADS)

    Zhou, Yaopeng; Bifano, Thomas; Lin, Charles

    2011-03-01

    Two-photon fluorescence microscopy provides a powerful tool for deep tissue imaging. However, optical aberrations from illumination beam path limit imaging depth and resolution. Adaptive Optics (AO) is found to be useful to compensate for optical aberrations and improve image resolution and contrast from two-photon excitation. We have developed an AO system relying on a MEMS Deformable Mirror (DM) to compensate the optical aberrations in a two-photon scanning laser fluorescence microscope. The AO system utilized a Zernike polynomial based stochastic parallel gradient descent (SPGD) algorithm to optimize the DM shape for wavefront correction. The developed microscope is applied for subsurface imaging of mouse bone marrow. It was demonstrated that AO allows 80% increase in fluorescence signal intensity from bone cavities 145um below the surface. The AO-enhanced microscope provides cellular level images of mouse bone marrow at depths exceeding those achievable without AO.

  6. Selective two-photon microscopy with shaped femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Pastirk, Igor; Dela Cruz, Johanna M.; Walowicz, Katherine A.; Lozovoy, Vadim V.; Dantus, Marcos

    2003-07-01

    Selective two-photon excitation of fluorescent probe molecules using phase-only modulated ultrashort 15-fs laser pulses is demonstrated. The spectral phase required to achieve the maximum contrast in the excitation of different probe molecules or identical probe molecules in different micro-chemical environments is designed according to the principles of multiphoton intrapulse interference (MII). The MII method modulates the probabilities with which specific spectral components in the excitation pulse contribute to the two-photon absorption process due to the dependence of the absorption on the power spectrum of E2(t) [1-3]. Images obtained from a number of samples using the multiphoton microscope are presented.

  7. Modulation of Attosecond Beating by Resonant Two-Photon Transition

    NASA Astrophysics Data System (ADS)

    Jiménez Galán, Álvaro; Argenti, Luca; Martín, Fernando

    2015-09-01

    We present an analytical model that characterizes two-photon transitions in the presence of autoionising states. We applied this model to interpret resonant RABITT spectra, and show that, as a harmonic traverses a resonance, the phase of the sideband beating significantly varies with photon energy. This phase variation is generally very different from the π jump observed in previous works, in which the direct path contribution was negligible. We illustrate the possible phase profiles arising in resonant two-photon transitions with an intuitive geometrical representation.

  8. A fluorescent benzothiazole probe with efficient two-photon absorption

    NASA Astrophysics Data System (ADS)

    Echevarria, Lorenzo; Moreno, Iván; Camacho, José; Salazar, Mary Carmen; Hernández, Antonio

    2012-11-01

    In this work, we report the two-photon absorption of 2-[4-(dimethylamino)phenyl]-1,3-benzothiazole-6-carbonitrile (DBC) in DMSO solution pumping at 779 nm with a 10 ns pulse laser-Nd:YAG system. The obtained two-photon absorption cross-section in DBC (407 ± 18 GM) is considerably high. Because DBC is a novel compound and have high values of fluorescence quantum yield, this result is expected to have an impact in biomolecules detection, diagnosis and treatment of cancer. Similar structures have previously been reported to show remarkable antitumour effects.

  9. Two-photon lasing by a superconducting qubit

    NASA Astrophysics Data System (ADS)

    Neilinger, P.; Rehák, M.; Grajcar, M.; Oelsner, G.; Hübner, U.; Il'ichev, E.

    2015-03-01

    We study the response of a magnetic-field-driven superconducting qubit strongly coupled to a superconducting coplanar waveguide resonator. We observed a strong amplification/damping of a probing signal at different resonance points corresponding to a one- and two-photon emission/absorption. The sign of the detuning between the qubit frequency and the probe determines whether amplification or damping is observed. The larger blue detuned driving leads to two-photon lasing, while the larger red detuning cools the resonator. Our experimental results are in good agreement with the theoretical model of qubit lasing and cooling at the Rabi frequency.

  10. Two-Photon Laser Scanning Stereomicroscopy for Fast Volumetric Imaging

    PubMed Central

    Yang, Yanlong; Yao, Baoli; Lei, Ming; Dan, Dan; Li, Runze; Horn, Mark Van; Chen, Xun; Li, Yang; Ye, Tong

    2016-01-01

    Bessel beams have been successfully used in two-photon laser scanning fluorescence microscopy to extend the depth of field (EDF), which makes it possible to observe fast events volumetrically. However, the depth information is lost due to integration of fluorescence signals along the propagation direction. We describe the design and implementation of two-photon lasers scanning stereomicroscopy, which allows viewing dynamic processes in three-dimensional (3D) space stereoscopically in real-time with shutter glasses at the speed of 1.4 volumes per second. The depth information can be appreciated by human visual system or be recovered with correspondence algorithms for some cases. PMID:27997624

  11. Spatial solitons in two-photon photorefractive media

    NASA Astrophysics Data System (ADS)

    Hou, Chunfeng; Pei, Yanbo; Zhou, Zhongxiang; Sun, Xiudong

    2005-05-01

    We provide a theory for spatial solitons due to the two-photon photorefractive effect based on the Castro-Camus model [Opt. Lett. 28, 1129 (2003)]. We present the evolution equation of one-dimensional spatial solitons in two-photon photorefractive media. In steady state and under appropriate external bias conditions, we obtain the dark and bright soliton solutions of the optical wave evolution equation, and also discuss the self-deflection of the bright solitons theoretically by taking into account the diffusion effect.

  12. Two-photon interference with non-identical photons

    NASA Astrophysics Data System (ADS)

    Liu, Jianbin; Zhou, Yu; Zheng, Huaibin; Chen, Hui; Li, Fu-li; Xu, Zhuo

    2015-11-01

    Two-photon interference with non-identical photons is studied based on the superposition principle in Feynman's path integral theory. The second-order temporal interference pattern is observed by superposing laser and pseudothermal light beams with different spectra. The reason why there is two-photon interference for photons of different spectra is that non-identical photons can be indistinguishable for the detection system when Heisenberg's uncertainty principle is taken into account. These studies are helpful to understand the second-order interference of light in the language of photons.

  13. Unconventional Photon Blockade Based on Two-Photon Tunneling

    NASA Astrophysics Data System (ADS)

    Zhou, Y. H.; Shen, H. Z.

    2017-09-01

    The study on the unconventional photon blockade mainly focus on Kerr nonlinearity. In this paper, we study the unconventional photon blockade based on another kind of nonlinearity, that is two-photon tunneling. The optimal conditions for strong antibunching are found by analytic calculations and numerical simulations, and the results are compared with the unconventional photon blockade based on Kerr nonlinearity, we find that the two-photon tunneling system has advantages for the larger antibunching area. Finally, we show that, after the symmetric-antisymmetric mode transformation, the two kinds of nonlinearities are equivalent from the perspective of photon antibunching.

  14. Two-photon in vivo imaging of retinal microstructures

    NASA Astrophysics Data System (ADS)

    Schejter, Adi; Farah, Nairouz; Shoham, Shy

    2014-02-01

    Non-invasive fluorescence retinal imaging in small animals is an important requirement in an array of translational vision applications. Two-photon imaging has the potential for long-term investigation of healthy and diseased retinal function and structure in vivo. Here, we demonstrate that two-photon microscopy through a mouse's pupil can yield high-quality optically sectioned fundus images. By remotely scanning using an electronically tunable lens we acquire highly-resolved 3D fluorescein angiograms. These results provide an important step towards various applications that will benefit from the use of infrared light, including functional imaging of retinal responses to light stimulation.

  15. Spatial solitons in two-photon photorefractive media

    SciTech Connect

    Hou Chunfeng; Pei Yanbo; Zhou Zhongxiang; Sun Xiudong

    2005-05-15

    We provide a theory for spatial solitons due to the two-photon photorefractive effect based on the Castro-Camus model [Opt. Lett. 28, 1129 (2003)]. We present the evolution equation of one-dimensional spatial solitons in two-photon photorefractive media. In steady state and under appropriate external bias conditions, we obtain the dark and bright soliton solutions of the optical wave evolution equation, and also discuss the self-deflection of the bright solitons theoretically by taking into account the diffusion effect.

  16. Quinoline-Derived Two-Photon Sensitive Quadrupolar Probes.

    PubMed

    Tran, Christine; Berqouch, Nawel; Dhimane, Hamid; Clermont, Guillaume; Blanchard-Desce, Mireille; Ogden, David; Dalko, Peter I

    2017-02-03

    Quadrupolar probes derived from 8-dimethylamino-quinoline (8-DMAQ) having a pegylated fluorene core were prepared and studied under "one-photon" (λ=365 nm) and "two-photon" (TP) (λ=730 nm) irradiation conditions. Compound 1 a was identified as the most efficient probe by UV activation that showed sequential release of acetic acid as a model. Although the probe showed high two-photon absorption it stayed inert under femtosecond irradiation conditions. Fast and selective photolysis was observed, however, by using picosecond irradiation conditions with a remarkably high TP uncaging cross-section (δu =2.3 GM).

  17. Two-photon photoassociation spectroscopy of an ultracold heteronuclear molecule

    NASA Astrophysics Data System (ADS)

    Dutta, Sourav; Pérez-Ríos, Jesús; Elliott, D. S.; Chen, Yong P.

    2017-01-01

    We report on two-photon photoassociation (PA) spectroscopy of ultracold heteronuclear LiRb molecules. This is used to determine the binding energies of the loosely bound levels of the electronic ground singlet and the lowest triplet states of LiRb. We observe strong two-photon PA lines with power broadened linewidths greater than 20 GHz at relatively low laser intensity of 30 W /c m2 . The implication of this observation on direct atom to molecule conversion using stimulated Raman adiabatic passage is discussed and the prospect for electronic ground-state molecule production is theoretically analyzed.

  18. Resonantly enhanced method for generation of tunable, coherent vacuum ultraviolet radiation

    DOEpatents

    Glownia, James H.; Sander, Robert K.

    1985-01-01

    Carbon Monoxide vapor is used to generate coherent, tunable vacuum ultraviolet radiation by third-harmonic generation using a single tunable dye laser. The presence of a nearby electronic level resonantly enhances the nonlinear susceptibility of this molecule allowing efficient generation of the vuv light at modest pump laser intensities, thereby reducing the importance of a six-photon multiple-photon ionization process which is also resonantly enhanced by the same electronic level but to higher order. By choosing the pump radiation wavelength to be of shorter wavelength than individual vibronic levels used to extend tunability stepwise from 154.4 to 124.6 nm, and the intensity to be low enough, multiple-photon ionization can be eliminated. Excitation spectra of the third-harmonic emission output exhibit shifts to shorter wavelength and broadening with increasing CO pressure due to phase matching effects. Increasing the carbon monoxide pressure, therefore, allows the substantial filling in of gaps arising from the stepwise tuning thereby providing almost continuous tunability over the quoted range of wavelength emitted.

  19. Resonantly enhanced method for generation of tunable, coherent vacuum-ultraviolet radiation

    DOEpatents

    Glownia, J.H.; Sander, R.K.

    1982-06-29

    Carbon Monoxide vapor is used to generate coherent, tunable vacuum ultraviolet radiation by third-harmonic generation using a single tunable dye laser. The presence of a nearby electronic level resonantly enhances the nonlinear susceptibility of this molecule allowing efficient generation of the vuv light at modest pump laser intensities, thereby reducing the importance of a six-photon multiple-photon ionization process which is also resonantly enhanced by the same electronic level but no higher order. By choosing the pump radiation wavelength to be of shorter wavelength than individual vibronic levels used to extend tunability stepwise from 154.4 to 124.6 nm, and the intensity to be low enough, multiple-photon ionization can be eliminated. Excitation spectra of the third-harmonic emission output exhibit shifts to shorter wavelength and broadening with increasing CO pressure due to phase matching effects. Increasing the carbon monoxide pressure, therefore, allows the substantial filling in of gaps arising from the stepwise tuning thereby providing almost continuous tunability over the quoted range of wavelength emitted.

  20. Two-photon absorbing porphyrins for oxygen microscopy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Esipova, Tatiana V.; Vinogradov, Sergei A.

    2016-03-01

    The ability to quantify oxygen in vivo in 3D with high spatial and temporal resolution is invaluable for many areas of the biomedical science, including ophthalmology, neuroscience, cancer and stem biology. An optical method based on oxygen-dependent quenching of phosphorescence is being developed, that allows quantitative minimally invasive real-time imaging of partial pressure of oxygen (pO2) in tissue. In the past, dendritically protected phosphorescent oxygen probes with controllable quenching parameters and defined bio-distributions have been developed. More recently our probe strategy has extended to encompass two-photon excitable oxygen probes, which brought about first demonstrations of two-photon phosphorescence lifetime microscopy (2PLM) of oxygen in vivo, providing new valuable information for neuroscience and stem cell biology. However, current two-photon oxygen probes suffer from a number of limitations, such as low brightness and high cost of synthesis, which dramatically reduce imaging performance and limit usability of the method. Here we present an approach to new bright phosphorescent chromophores with internally enhanced two-photon absorption cross-sections, which pave a way to novel proves for 2PLM. In addition to substantial increase in performance, the new probes can be synthesized by much more efficient methods, thereby greatly reducing the cost of the synthesis and making the technique accessible to a broader range of researchers across different fields.

  1. Imaging melanin by two-photon absorption microscopy

    NASA Astrophysics Data System (ADS)

    Ye, Tong; Yurtsever, Gunay; Fischer, Martin; Simon, John D.; Warren, Warren S.

    2006-02-01

    Multiphoton excitation fluorescence microscopy has proven to be a powerful method for non-invasive, in vivo, thick tissue imaging with molecular specificity. However, many important endogenous biomolecules do not fluoresce (NAD) or fluoresce with low efficiency (Melanin). In this report femtosecond pulse shaping methods are used to measure two-photon absorption (TPA) directly with very high sensitivity. Combining with the laser scanning microscope, this Two-photon Absorption Microscopy (TPAM) retains the penetration and localization advantages of two-photon fluorescence microscopy and permits direct observation of important endogenous molecular markers (melanin or hemoglobin) which are invisible in multiphoton fluorescence microscopy. We have demonstrated here for the first time that TPAM can successfully and more efficiently image melanoma cells and tissues and provide a good melanin contrast in optical sectioning of the melanoma lesions which are comparable to pathological histology. Combining with the two-photon fluorescence images acquired simultaneously, the distribution patterns of the melanocytes and their intratissue behavior could be studied without cutting the lesions from patients. TPAM will undoubtedly find the applications in the clinical diagnosis and biomedical research.

  2. Two-photon excitation endoscopy through a multimode optical fiber

    NASA Astrophysics Data System (ADS)

    Morales Delgado, Edgar E.; Psaltis, Demetri; Moser, Christophe

    2016-03-01

    The vast number of propagating solutions to the wave equation in multimode optical fibers represents a larger information capacity than provided by fiber bundles of the same diameter. Therefore, in the field of imaging, multimode fibers potentially allow the transmission of images with higher resolution. However, image transmission through multimode fibers is not direct as in the fiber bundle case, in which each of the fiber cores can relay a portion of the distal image. In multimode fiber transmission, a distribution of intensity is scrambled in time and space by the propagating modes, leading to a speckle-like pattern that does not resemble the initial distribution. Here, we demonstrate two-photon excitation imaging of fluorescent beads through a multimode optical fiber. We show that our method maintains the advantages of two-photon excitation microscopy compared to single-photon excitation such as reduced photo-bleaching, deeper penetration depth and sectioning capability. Our method is based on time-gated digital phase conjugation, which allows the generation of focused pulses on the other side of a multimode fiber. To acquire an image, the focused femtosecond pulse is scanned in a three-dimensional mesh, producing two-photon excitation on each spatial location of the sample. By collecting the fluorescence through the fiber, a 3D two-photon image is reconstructed.

  3. Two-Photon-Pumped Perovskite Semiconductor Nanocrystal Lasers.

    PubMed

    Xu, Yanqing; Chen, Qi; Zhang, Chunfeng; Wang, Rui; Wu, Hua; Zhang, Xiaoyu; Xing, Guichuan; Yu, William W; Wang, Xiaoyong; Zhang, Yu; Xiao, Min

    2016-03-23

    Two-photon-pumped lasers have been regarded as a promising strategy to achieve frequency up-conversion for situations where the condition of phase matching required by conventional approaches cannot be fulfilled. However, their practical applications have been hindered by the lack of materials holding both efficient two-photon absorption and ease of achieving population inversion. Here, we show that this challenge can be tackled by employing colloidal nanocrystals of perovskite semiconductors. We observe highly efficient two-photon absorption (with a cross section of 2.7 × 10(6) GM) in toluene solutions of CsPbBr3 nanocrystals that can excite large optical gain (>500 cm(-1)) in thin films. We have succeeded in demonstrating stable two-photon-pumped lasing at a remarkable low threshold by coupling CsPbBr3 nanocrystals with microtubule resonators. Our findings suggest perovskite nanocrystals can be used as excellent gain medium for high-performance frequency-up-conversion lasers toward practical applications.

  4. Ultrafast Laser Studies of Two-Photon Excited Fluorescence Intermittency in Single CdSe/ZnS Quantum Dots.

    PubMed

    Early, Kevin T; Nesbitt, David J

    2015-12-09

    Two-photon fluorescence microscopy of single quantum dots conditions has been reported by several groups, with contrasting observations regarding the kinetics and dynamics of fluorescence intermittency or "blinking". Here, we investigate the power dependence, kinetics, and statistics of two photon-excited fluorescence intermittency from single CdSe/ZnS quantum dots in a solid PMMA film as a function of sub-bandgap laser intensity at 800 nm. Fluorescence intermittency is observed at all excitation powers and a quadratic (n = 1.97(3)) dependence of the shot noise-limited fluorescence intensity on the incident laser power is verified, confirming essentially zero background contribution from one-photon excitation processes. Such analyses permit two photon absorption cross sections for single quantum dots to be extracted quantitatively from the data, which reveal good agreement with those obtained from previous two-photon FCS measurements. Strictly inverse power law-distributed off-state dwell times are observed for all excitation powers, with a mean power law exponent ⟨m(off)⟩ = 1.65(4) in excellent agreement with the behavior observed under one-photon excitation conditions. Finally, a superquadratic (n = 2.3(2)) rather than quartic (n = 4) power dependence is observed for the on-state blinking dwell times, which we kinetically analyze and interpret in terms of a novel 2 + 1 "hot" exciton ionization/blinking mechanism due to partially saturated 1-photon sub-bandgap excitation out of the two-photon single exciton state. The kinetic results are consistent with quantum dot photoionization quantum yields from "hot" exciton states (4(1) × 10(-6)) comparable with experimental estimates (10(-6)-10(-5)) of Auger ionization efficiencies out of the biexcitonic state.

  5. Synthesis, structure and two-photon absorption properties of a new multi-branched two-photon photopolymerization initiator

    NASA Astrophysics Data System (ADS)

    Yan, Yunxing; Tao, Xutang; Sun, Yuanhong; Yu, Wentao; Wang, Chuankui; Xu, Guibao; Yang, Jiaxiang; Wu, Yongzhong; Zhao, Xian; Jiang, Minhua

    2005-01-01

    A new free-radical photonpolymerization initiator Tris-[4-(2-pyridin-4-yl-vinyl)-phenyl]-amine (TPPA) has been synthesized and characterized by 1H NMR spectra, 13C NMR spectra and elemental analyses. X-ray diffraction analyses reveal that TPPA belongs to monoclinic system, P2 1/n space group with a=15.851 (3), b=9.7932 (18), c=20.084 (6) Å, α=90, β=107.241 (12), γ=90°, V=2977.6 (12) Å 3, Z=4, T=293 (2) K, Dc=1.237 g cm -3, R1=0.0569, wR=0.1245. The calculated two-photon absorption cross-section is 33.6×10 -50 cm 4 s photon -1. The experimental results confirm that TPPA is a good two-photon absorbing chromophore and operative two-photon photopolymerization initiator. When pumped with 820 nm laser irradiation, TPPA shows strong two-photon induced fluorescence. A microstructure has been fabricated under irradiation using a 200 fs, 76 MHz Ti: sapphire femtosecond laser at 820 nm. The possible photopolymerization mechanism is discussed.

  6. Intensity-resolved ionization yields of aniline with femtosecond laser pulses

    SciTech Connect

    Strohaber, J.; Hart, N.; Zhu, F.; Nava, R.; Pham, F.; Kolomenskii, A. A.; Paulus, G. G.; Schuessler, H. A.; Mohamed, T.; Schroeder, H.

    2011-12-15

    We present experimental results for the ionization of aniline and benzene molecules subjected to intense ultrashort laser pulses. Measured parent molecular ions yields were obtained using a recently developed technique capable of three-dimensional imaging of ion distributions within the focus of a laser beam. By selecting ions originating from the central region of the focus, where the spatial intensity distribution is nearly uniform, volumetric-free intensity-dependent ionization yields were obtained. The measured data revealed a previously unseen resonance-enhanced multiphoton ionization (REMPI)-like process. Comparison of benzene, aniline, and Xe ion yields demonstrates that the observed intensity-dependent structures are not due to geometric artifacts in the focus. Finally for intensities greater than {approx}3x10{sup 13} W/cm{sup 2}, we attribute the ionization of aniline to a stepwise process going through the {pi}{sigma}{sup *} state which sits three photons above the ground state and two photons below the continuum.

  7. Development of glucose sensor using two-photon adsorbed photopolymerization.

    PubMed

    Kim, Jong Min; Park, Jung-Jin; Lee, Haeng-Ja; Kim, Woo-Sik; Muramatsu, Hiroshi; Chang, Sang-Mok

    2010-01-01

    A novel glucose sensor was constructed, and its analytical potential examined. A chip-type three-electrode system for use in a flow-type electrochemical glucose sensor was fabricated using a UV lithography technique on a glass slide. An Ag/AgCl reference electrode was made by electroplating silver onto a Pt electrode and dipping in a saturated KCl solution for 30 min. In addition, a glucose-sensing electrode was fabricated using a two-photon adsorbed photopolymerization technique with a photo-reactive resin containing a glucose oxidase enzyme, ferrocene mediator, non-ionic surfactant, and carbon nanotubes. The cyclic voltammetry of the potassium ferrocyanide in the Pt sensor system showed a stable electrode condition. The response of the modified Pt sensor confirms the feasibility of using a two-photon adsorbed photopolymerization technique for the easy fabrication of functional biosensors.

  8. Two-photon-excited photoluminescence from porous silicon

    SciTech Connect

    Diener, J.; Shen, Y.R. |; Kovalev, D.I.; Polisski, G.; Koch, F.

    1998-11-01

    Two-photon-excited photoluminescence can be readily observed from porous silicon (PSi) with pulsed lasers. While its spectrum and lifetime are identical to those under one-photon excitation, it has a degree of polarization significantly higher than the latter and depending on the orientation of the input polarization with respect to the crystalline axes of the sample. The degree of polarization is a maximum when the input polarization is along [110] in the surface plane of PSi prepared from a Si (100) wafer and a minimum along [010]. The results can be understood from selective excitation of ellipsoidal nanoparticles by linearly polarized light and intrinsic anisotropy in two-photon excitation of crystalline Si. {copyright} {ital 1998} {ital The American Physical Society}

  9. One- and two-photon detachment of O-

    NASA Astrophysics Data System (ADS)

    Génévriez, Matthieu; Urbain, Xavier; Dochain, Arnaud; Cyr, Alain; Dunseath, Kevin M.; Terao-Dunseath, Mariko

    2016-08-01

    Cross sections for one- and two-photon detachment of O-(1 s22 s22 p5P2o) have been determined in a joint experimental and theoretical study. The absolute measurement is based on the animated-crossed-beam technique, which is extended to the case of pulsed lasers, pulsed ion beams, and multiphoton detachment. The ab initio calculations employ R -matrix Floquet theory, with simple descriptions of the initial bound state and the residual oxygen atom which reproduce well the electron affinity and ground-state polarizability. For one-photon detachment, the measured and computed cross sections are in good mutual agreement, departing significantly from previous reference experiments and calculations. The generalized two-photon detachment cross section, measured at the Nd:YAG laser wavelength, is in good agreement with the R -matrix Floquet calculations. Long-standing discrepancies between theory and experiment are thus resolved.

  10. Two-photon microscopy using fiber-based nanosecond excitation

    PubMed Central

    Karpf, Sebastian; Eibl, Matthias; Sauer, Benjamin; Reinholz, Fred; Hüttmann, Gereon; Huber, Robert

    2016-01-01

    Two-photon excitation fluorescence (TPEF) microscopy is a powerful technique for sensitive tissue imaging at depths of up to 1000 micrometers. However, due to the shallow penetration, for in vivo imaging of internal organs in patients beam delivery by an endoscope is crucial. Until today, this is hindered by linear and non-linear pulse broadening of the femtosecond pulses in the optical fibers of the endoscopes. Here we present an endoscope-ready, fiber-based TPEF microscope, using nanosecond pulses at low repetition rates instead of femtosecond pulses. These nanosecond pulses lack most of the problems connected with femtosecond pulses but are equally suited for TPEF imaging. We derive and demonstrate that at given cw-power the TPEF signal only depends on the duty cycle of the laser source. Due to the higher pulse energy at the same peak power we can also demonstrate single shot two-photon fluorescence lifetime measurements. PMID:27446680

  11. Two-Photon-Excited Fluorescence-Encoded Infrared Spectroscopy.

    PubMed

    Mastron, Joseph N; Tokmakoff, Andrei

    2016-11-23

    We report on a method for performing ultrafast infrared (IR) vibrational spectroscopy using fluorescence detection. Vibrational dynamics on the ground electronic state driven by femtosecond mid-infrared pulses are detected by changes in fluorescence amplitude resulting from modulation of a two-photon visible transition by nuclear motion. We examine a series of coumarin dyes and study the signals as a function of solvent and excitation pulse parameters. The measured signal characterizes the relaxation of vibrational populations and coherences but yields different information than conventional IR transient absorption measurements. These differences result from the manner in which the ground-state dynamics are projected by the two-photon detection step. Extensions of this method can be adapted for a variety of increased-sensitivity IR measurements.

  12. Combinatorial discovery of two-photon photoremovable protecting groups

    PubMed Central

    Pirrung, Michael C.; Pieper, Wolfgang H.; Kaliappan, Krishna P.; Dhananjeyan, Mugunthu R.

    2003-01-01

    A design principle for a two-photon photochemically removable protecting group based on sequential one-photon processes has been established. The expected performance of such groups in spatially directed photoactivation/photodeprotection has been shown by a kinetic analysis. One particular molecular class fitting into this design, the nitrobenzyl ethers of o-hydroxycinnamates, has been presented. An initial demonstration of two-photon deprotection of one such group prompted further optimization with respect to photochemical deprotection rate. This was accomplished by the preparation and screening of a 135-member indexed combinatorial library. Optimum performance for λ >350 nm deprotection in organic solvent was found with 4,5-dialkoxy and α-cyano substitution in the nitrobenzyl group and 4-methoxy substitution in the cinnamate. PMID:14557545

  13. Two-Photon In Vivo Imaging with Porous Silicon Nanoparticles.

    PubMed

    Kim, Dokyoung; Kang, Jinyoung; Wang, Taejun; Ryu, Hye Gun; Zuidema, Jonathan M; Joo, Jinmyoung; Kim, Muwoong; Huh, Youngbuhm; Jung, Junyang; Ahn, Kyo Han; Kim, Ki Hean; Sailor, Michael J

    2017-08-21

    A major obstacle in luminescence imaging is the limited penetration of visible light into tissues and interference associated with light scattering and autofluorescence. Near-infrared (NIR) emitters that can also be excited with NIR radiation via two-photon processes can mitigate these factors somewhat because they operate at wavelengths of 650-1000 nm where tissues are more transparent, light scattering is less efficient, and endogenous fluorophores are less likely to absorb. This study presents photolytically stable, NIR photoluminescent, porous silicon nanoparticles with a relatively high two-photon-absorption cross-section and a large emission quantum yield. Their ability to be targeted to tumor tissues in vivo using the iRGD targeting peptide is demonstrated, and the distribution of the nanoparticles with high spatial resolution is visualized. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Direct frequency comb two-photon laser cooling and trapping

    NASA Astrophysics Data System (ADS)

    Jayich, Andrew; Long, Xueping; Campbell, Wesley C.

    2016-05-01

    Generating and manipulating high energy photons for spectroscopy on electric dipole transitions of atoms and molecules with deeply bound valence electrons is difficult. Further, laser cooling of such species is even more challenging for lack of laser power. A possible solution is to drive two-photon transitions. This may alleviate the photon energy problem and open the door to cold, trapped samples of highly desirable species with tightly bound electrons. We perform a proof of principle experiment with rubidium by driving a two-photon transition with an optical frequency comb. We perform optical cooling and extend this technique to trapping, where we are able to make a magneto-optical trap in one dimension. This work is supported by the National Science Foundation CAREER program.

  15. Two-photon absorption of Zn(II) octupolar molecules.

    PubMed

    Mazzucato, Simone; Fortunati, Ilaria; Scolaro, Sara; Zerbetto, Michele; Ferrante, Camilla; Signorini, Raffaella; Pedron, Danilo; Bozio, Renato; Locatelli, Danika; Righetto, Stefania; Roberto, Dominique; Ugo, Renato; Abbotto, Alessandro; Archetti, Graziano; Beverina, Luca; Ghezzi, Sergio

    2007-06-21

    In this work we present an investigation of the non-linear optical (NLO) properties of two octupolar chromophores: [Zn(4,4'-bis(dibutylaminostyryl)-[2,2']-bipyridine)(3)](2+) and [Zn(4,4'-bis((E)-2-(N-(TEG)pyrrol-2-yl)vinyl)-[2,2']-bipyridine)(3)](2+) with Zn(ii) as the coordination center, using two-photon emission technique (TPE) in fs-pulse temporal regime. Compared to the free ligands, our results do not show a net increase in the two-photon absorption (TPA) cross-section for the octupolar complexes, once normalized to the ligand unit. This is in partial disagreement with a previous theoretical study investigating the first molecule where a significant increase of the TPA cross-section was predicted (X. J. Liu, et al., J. Chem. Phys., 2004, 120, 11 493).

  16. Two-photon interference from two blinking quantum emitters

    NASA Astrophysics Data System (ADS)

    Jöns, Klaus D.; Stensson, Katarina; Reindl, Marcus; Swillo, Marcin; Huo, Yongheng; Zwiller, Val; Rastelli, Armando; Trotta, Rinaldo; Björk, Gunnar

    2017-08-01

    We investigate the effect of blinking on the two-photon interference measurement from two independent quantum emitters. We find that blinking significantly alters the statistics in the Hong-Ou-Mandel second-order intensity correlation function g(2 )(τ ) and the outcome of two-photon interference measurements performed with independent quantum emitters. We theoretically demonstrate that the presence of blinking can be experimentally recognized by a deviation from the gD(2 )(0 ) =0.5 value when distinguishable photons from two emitters impinge on a beam splitter. Our findings explain the significant differences between linear losses and blinking for correlation measurements between independent sources and are experimentally verified using a parametric down-conversion photon-pair source. We show that blinking imposes a mandatory cross-check measurement to correctly estimate the degree of indistinguishability of photons emitted by independent quantum emitters.

  17. Two-photon microscopy using fiber-based nanosecond excitation.

    PubMed

    Karpf, Sebastian; Eibl, Matthias; Sauer, Benjamin; Reinholz, Fred; Hüttmann, Gereon; Huber, Robert

    2016-07-01

    Two-photon excitation fluorescence (TPEF) microscopy is a powerful technique for sensitive tissue imaging at depths of up to 1000 micrometers. However, due to the shallow penetration, for in vivo imaging of internal organs in patients beam delivery by an endoscope is crucial. Until today, this is hindered by linear and non-linear pulse broadening of the femtosecond pulses in the optical fibers of the endoscopes. Here we present an endoscope-ready, fiber-based TPEF microscope, using nanosecond pulses at low repetition rates instead of femtosecond pulses. These nanosecond pulses lack most of the problems connected with femtosecond pulses but are equally suited for TPEF imaging. We derive and demonstrate that at given cw-power the TPEF signal only depends on the duty cycle of the laser source. Due to the higher pulse energy at the same peak power we can also demonstrate single shot two-photon fluorescence lifetime measurements.

  18. Simultaneous two-photon excitation of photodynamic therapy agents

    SciTech Connect

    Wachter, E.A.; Fisher, W.G. |; Partridge, W.P.; Dees, H.C.; Petersen, M.G.

    1998-01-01

    The spectroscopic and photochemical properties of several photosensitive compounds are compared using conventional single-photon excitation (SPE) and simultaneous two-photon excitation (TPE). TPE is achieved using a mode-locked titanium:sapphire laser, the near infrared output of which allows direct promotion of non-resonant TPE. Excitation spectra and excited state properties of both type 1 and type 2 photodynamic therapy (PDT) agents are examined.

  19. Two-photon optical microscopy imaging of endothelial keratoplasty grafts.

    PubMed

    Lombardo, Marco; Parekh, Mohit; Serrao, Sebastiano; Ruzza, Alessandro; Ferrari, Stefano; Lombardo, Giuseppe

    2017-03-01

    To investigate the microstructure of endothelial keratoplasty grafts using two-photon optical microscopy. Six endothelial keratoplasty grafts obtained from human donor corneoscleral tissues and prepared by submerged hydrodissection technique were imaged by two-photon optical microscopy. In each graft, two liquid bubbles were created in order to investigate the presence of a conserved cleavage plane regardless of the volume of posterior stroma that remained attached to Descemet's membrane (DM); the first bubble (bubble A) was generated under DM and the second bubble (bubble B) injection was done in order to obtain a layer of deep stroma that kept the two bubbles separated. Six human donor corneoscleral tissues were used as controls. Second harmonic generation and two-photon emitted fluorescence signals were collected from each specimen. Dissection of stroma occurred along the posterior collagen lamellae at variable distance from DM, which ranged between 3 and 16 μm in bubble A and between 23 and 41 μm in bubble B. The residual stroma included, anteriorly, bands of collagen lamellae, and thin bundles of stromal collagen fibrils, posteriorly, which were tightly intertwining with the underlying DM. There was no anatomically distinct plane of separation between these pre-Descemetic stromal collagen bundles and the overlying collagen lamellae with this hydrodissection technique. Two-photon optical microscopy provided label-free high-resolution imaging of endothelial keratoplasty grafts, showing that the most posterior stroma changes organization at approximately 10 μm above the DM. The pre-Descemetic stromal collagen fibrils form an intertwined complex with DM, which cannot be separated using hydrodissection.

  20. Two-Photon Cavity Solitons in Active Optical Media

    SciTech Connect

    Vilaseca, R.; Torrent, M. C.; Garcia-Ojalvo, J.; Brambilla, M.; San Miguel, M.

    2001-08-20

    We show that broad-area cascade lasers with no absorbing intracavity elements support the spontaneous formation of two-dimensional bright localized structures in a dark background. These cavity solitons consist of islands of two-photon emission embedded in a background of single-photon emission. We discuss the mechanisms through which these structures are formed and interact, along with their properties and stability.

  1. Two-Photon Porphyrin Core Dendrimers for Optical Power Limiting

    DTIC Science & Technology

    2006-09-30

    Gryko (Polish Acad. Sci,), we studied 2PA of novel corroles [9]. 7. We studied the requirements imposed on organic photochromes for 2PA terabyte...imposed on organic photochromes for two-photon absorption (2PA) terabyte volumetric optical storage. We present a quantitative model of signal-to...noise ratio (SNR) and signal-to-background ratio (SBR) when 2PA-induced photochromic switching is used for writing, and 2PA-induced fluorescence is

  2. Development of Novel Two-Photon Absorbing Chromophores

    DTIC Science & Technology

    2006-08-01

    M. Urbas, Paul A. Fleitz, Joy E . Rogers, Jonathan E . Slagle, Daniel G. McLean, Richard L. Sutherland, Mark Brant , Douglas M. Krein, and...A. Fleitz (Exploratory Development, Hardened Materials Branch) Joy E . Rogers (UES) Jonathan E . Slagle (AT&T Government Solutions) Daniel G. McLean...Prescribed by ANSI Std. Z39-18 Invited Paper Development of novel two-photon absorbing chromophores Joy E . ~ o ~ e r s * " ’ ~ , Jonathan E . Slagle

  3. Two-photon Shack-Hartmann wavefront sensor.

    PubMed

    Xia, Fei; Sinefeld, David; Li, Bo; Xu, Chris

    2017-03-15

    We introduce a simple wavefront sensing scheme for aberration measurement of pulsed laser beams in near-infrared wavelengths (<2200  nm), where detectors are not always available or are very expensive. The method is based on two-photon absorption in a silicon detector array for longer wavelengths detection. We demonstrate the simplicity of such implementations with a commercially available Shack-Hartmann wavefront sensor and discuss the detection sensitivity of this method.

  4. Two-photon exchange corrections to the pion form factor

    DOE PAGES

    Peter G. Blunden; Melnitchouk, Wally; Tjon, John A.

    2010-01-06

    Here, we compute two-photon exchange corrections to the electromagnetic form factor of the pion, taking into account the finite size of the pion. Compared to the soft-photon approximation for the infrared divergent contribution which neglects hadron structure effects, the corrections are found to be ≲ 1% for small Q2 (Q2 < 0.1 GeV2), but increase to several percent for Q2 ≳ 1 GeV2 at extreme backward angles.

  5. Two-photon injection of polaritons in semiconductor microstructures.

    PubMed

    Leménager, Godefroy; Pisanello, Ferruccio; Bloch, Jacqueline; Kavokin, Alexey; Amo, Alberto; Lemaitre, Aristide; Galopin, Elisabeth; Sagnes, Isabelle; De Vittorio, Massimo; Giacobino, Elisabeth; Bramati, Alberto

    2014-01-15

    We experimentally demonstrate that two-photon pumping of "dark" excitons in quantum wells embedded in semiconductor microcavities can result in exciton-polariton injection and photon lasing. In the case of a semiconductor micropillar pumped at half of the exciton frequency, we observe a clear threshold behavior, characteristic of the vertical cavity surface emitting laser transition. These results are interpreted in terms of stimulated emission of terahertz photons, which allows for conversion of "dark" excitons into exciton-polaritons.

  6. Two-photon exchange in elastic electron–proton scattering

    DOE PAGES

    Afanasev, A.; Blunden, P. G.; Hasell, D.; ...

    2017-04-17

    Here, we review recent theoretical and experimental progress on the role of two-photon exchange (TPE) in electron-proton scattering at low to moderate momentum transfers. We make a detailed comparison and analysis of the results of competing experiments on the ratio of e+p to e-p elastic scattering cross sections, and of the theoretical calculations describing them. A summary of the current experimental situation is provided, along with an outlook for future experiments.

  7. On the role of entanglement in two-photon metrology

    NASA Astrophysics Data System (ADS)

    Stefanov, André

    2017-06-01

    The role of entanglement in metrology with photon pairs is investigated. We consider the situations where either one photon only interacts with a probe, or where both photons interact with two independent systems. Based on arguments from quantum information theory, we show that the presence of entanglement in the state cannot lead to results, which could not be obtained with separable states. This shows that entanglement can only provide advantages when genuine two-photon interactions are present.

  8. Improved deep two-photon calcium imaging in vivo.

    PubMed

    Birkner, Antje; Tischbirek, Carsten H; Konnerth, Arthur

    2016-12-21

    Two-photon laser scanning calcium imaging has emerged as a useful method for the exploration of neural function and structure at the cellular and subcellular level in vivo. The applications range from imaging of subcellular compartments such as dendrites, spines and axonal boutons up to the functional analysis of large neuronal or glial populations. However, the depth penetration is often limited to a few hundred micrometers, corresponding, for example, to the upper cortical layers of the mouse brain. Light scattering and aberrations originating from refractive index inhomogeneties of the tissue are the reasons for these limitations. The depth penetration of two-photon imaging can be enhanced through various approaches, such as the implementation of adaptive optics, the use of three-photon excitation and/or labeling cells with red-shifted genetically encoded fluorescent sensors. However, most of the approaches used so far require the implementation of new instrumentation and/or time consuming staining protocols. Here we present a simple approach that can be readily implemented in combination with standard two-photon microscopes. The method involves an optimized protocol for depth-restricted labeling with the red-shifted fluorescent calcium indicator Cal-590 and benefits from the use of ultra-short laser pulses. The approach allows in vivo functional imaging of neuronal populations with single cell resolution in all six layers of the mouse cortex. We demonstrate that stable recordings in deep cortical layers are not restricted to anesthetized animals but are well feasible in awake, behaving mice. We anticipate that the improved depth penetration will be beneficial for two-photon functional imaging in larger species, such as non-human primates.

  9. Two-Photon Absorption in Organometallic Bromide Perovskites.

    PubMed

    Walters, Grant; Sutherland, Brandon R; Hoogland, Sjoerd; Shi, Dong; Comin, Riccardo; Sellan, Daniel P; Bakr, Osman M; Sargent, Edward H

    2015-09-22

    Organometallic trihalide perovskites are solution-processed semiconductors that have made great strides in third-generation thin film light-harvesting and light-emitting optoelectronic devices. Recently, it has been demonstrated that large, high-purity single crystals of these perovskites can be synthesized from the solution phase. These crystals' large dimensions, clean bandgap, and solid-state order have provided us with a suitable medium to observe and quantify two-photon absorption in perovskites. When CH3NH3PbBr3 single crystals are pumped with intense 800 nm light, we observe band-to-band photoluminescence at 572 nm, indicative of two-photon absorption. We report the nonlinear absorption coefficient of CH3NH3PbBr3 perovskites to be 8.6 cm GW(-1) at 800 nm, comparable to epitaxial single-crystal semiconductors of similar bandgap. We have leveraged this nonlinear process to electrically autocorrelate a 100 fs pulsed laser using a two-photon perovskite photodetector. This work demonstrates the viability of organometallic trihalide perovskites as a convenient and low-cost nonlinear absorber for applications in ultrafast photonics.

  10. Two-photon excited fluorescence emission from hemoglobin

    NASA Astrophysics Data System (ADS)

    Sun, Qiqi; Zeng, Yan; Zhang, Wei; Zheng, Wei; Luo, Yi; Qu, Jianan Y.

    2015-03-01

    Hemoglobin, one of the most important proteins in blood, is responsible for oxygen transportation in almost all vertebrates. Recently, we discovered two-photon excited hemoglobin fluorescence and achieved label-free microvascular imaging based on the hemoglobin fluorescence. However, the mechanism of its fluorescence emission still remains unknown. In this work, we studied the two-photon excited fluorescence properties of the hemoglobin subunits, heme/hemin (iron (II)/(III) protoporphyrin IX) and globin. We first studied the properties of heme and the similar spectral and temporal characteristics of heme and hemoglobin fluorescence provide strong evidence that heme is the fluorophore in hemoglobin. Then we studied the fluorescence properties of hemin, globin and methemoglobin, and found that the hemin may have the main effect on the methemoglobin fluorescence and that globin has tryptophan fluorescence like other proteins. Finally, since heme is a centrosymmetric molecule, that the Soret band fluorescence of heme and hemoglobin was not observed in the single photon process in the previous study may be due to the parity selection rule. The discovery of heme two-photon excited fluorescence may open a new window for heme biology research, since heme as a cofactor of hemoprotein has many functions, including chemical catalysis, electron transfer and diatomic gases transportation.

  11. Recent two-photon physics results from ARGUS

    NASA Astrophysics Data System (ADS)

    Živko Representing Argus Collaboration, Tomi

    1995-07-01

    Two photon production of π+π+π0π-π-, K+K-π+π-, K+K-π+π0π-, π+π0π-, and π+π- has been studied using the ARGUS detector at the e+e- storage ring DORIS II at DESY. A partial wave analysis was performed on the five-pion and three-pion final states. In the reaction γγ→ωρ0 is showed that the partial-wave with spin and parity (JP,Jz)=(2+,±2) dominates. The cross section and angular distributions of the reaction γγ→φρ0→K+K-π+π- were measured for the first time. The production of the vector-meson pair φω is observed in the two-photon reaction γγ→K+K-π+π0π-. The two-photon width of the tensor meson a2(1320) was measured in the decay channel π+π0π-. An upper limit, significantly lower than indicated by previous experiments was set on the radiative width of the π2(1670) meson. An upper limit was set on the radiative width of the f0(975)in the decay channel π+π-.

  12. Temporal coherence and indistinguishability in two-photon interference effects

    SciTech Connect

    Jha, Anand Kumar; O'Sullivan, Malcolm N.; Chan, Kam Wai Clifford; Boyd, Robert W.

    2008-02-15

    We show that temporal two-photon interference effects involving the signal and idler photons created by parametric down-conversion can be fully characterized in terms of the variations of two length parameters--called the biphoton path-length difference and the biphoton path-asymmetry-length difference--which we construct using the six different length parameters that a general two-photon interference experiment involves. We perform an experiment in which the effects of the variations of these two parameters can be independently controlled and studied. In our experimental setup, which does not involve mixing of signal and idler photons at a beam splitter, we further report observations of Hong-Ou-Mandel- (HOM-)like effects both in coincidence and in one-photon count rates. As an important consequence, we argue that the HOM and the HOM-like effects are best described as observations of how two-photon coherence changes as a function of the biphoton path-asymmetry-length difference.

  13. Image enhancement with two-photon laser scanning microscopy

    NASA Astrophysics Data System (ADS)

    Wang, Chun-Ming

    1998-07-01

    Although confocal microscopy provides an efficient means of fluorescence imaging, many obstacles including extensive photobleaching and limited penetration depths limit its application. Emergence of two-photon laser scanning microscopy (TPLSM), with limited excitation volume, successfully overcomes those difficulties. Not only is TPLSM shown to have much less photobleaching and better penetration depths than CLSM, but also it is capable of doing UV imaging without using special UV optical elements. Several different aspects of TPLSM are discussed in the dissertation. The progress of 3-D fluorescence microscopy, a historical retrospective of two-photon excitation, the physics of two-photon excitation and our instrument setup are discussed in the first chapter. In chapter II, a qualitative and quantitative confirmation of two-photon excitation, optical transfer efficiency, point spread function and resolution, signal-to-noise ratio, and two-photon excitation spectrum are presented. Chapter III shows the comparison between TPLSM and CLSM. Although CLSM has slightly better resolution than TPLSM, TPLSM has much less photobleaching and toxicity, greater penetration depth, less signal cross talk, and better signal collecting efficiency. Image deconvolution techniques with CLSM and TPLSM are discussed in chapter IV. Using this image processing methods and acquired PSF, we improved the resolution of CLSM and TPLSM dramatically. These deblurring techniques were applied to study the positions of proteins in the pre- and postsynaptic compartments of rat hippocampal culture cells. The improved resolution enabled us to distinguish the positions of Synapsin I, CaM Kinase II, and PSD-95, which could only be done with electron microscopy before. In chapter V, image degradation due to brain tissue scattering is discussed. Emission signals with long wavelengths were shown to have better resolution and image contrast because of less tissue scattering. This result shows the necessity

  14. Two-Photon Fluorescence Microscope for Microgravity Research

    NASA Technical Reports Server (NTRS)

    Fischer, David G.; Zimmerli, Gregory A.; Asipauskas, Marius

    2005-01-01

    A two-photon fluorescence microscope has been developed for the study of biophysical phenomena. Two-photon microscopy is a novel form of laser-based scanning microscopy that enables three-dimensional imaging without many of the problems inherent in confocal microscopy. Unlike one-photon optical microscopy, two-photon microscopy utilizes the simultaneous nonlinear absorption of two near-infrared photons. However, the efficiency of two-photon absorption is much lower than that of one-photon absorption, so an ultra-fast pulsed laser source is typically employed. On the other hand, the critical energy threshold for two-photon absorption leads to fluorophore excitation that is intrinsically localized to the focal volume. Consequently, two-photon microscopy enables optical sectioning and confocal performance without the need for a signal-limiting pinhole. In addition, there is a reduction (relative to one-photon optical microscopy) in photon-induced damage because of the longer excitation wavelength. This reduction is especially advantageous for in vivo studies. Relative to confocal microscopy, there is also a reduction in background fluorescence, and, because of a reduction in Rayleigh scattering, there is a 4 increase of penetration depth. The prohibitive cost of a commercial two-photon fluorescence-microscope system, as well as a need for modularity, has led to the construction of a custom-built system (see Figure 1). This system includes a coherent mode-locked titanium: sapphire laser emitting 120-fs-duration pulses at a repetition rate of 80 MHz. The pulsed laser has an average output power of 800 mW and a wavelength tuning range of 700 to 980 nm, enabling the excitation of a variety of targeted fluorophores. The output from the laser is attenuated, spatially filtered, and then directed into a confocal scanning head that has been modified to provide for side entry of the laser beam. The laser output coupler has been replaced with a dichroic filter that reflects the

  15. Near-threshold photoelectron angular distributions from two-photon resonant photoionization of He

    NASA Astrophysics Data System (ADS)

    O'Keeffe, P.; Mihelič, A.; Bolognesi, P.; Žitnik, M.; Moise, A.; Richter, R.; Avaldi, L.

    2013-01-01

    Two-photon resonant photoionization of helium is investigated both experimentally and theoretically. Ground state helium atoms are excited to the 1s4p, 1s5p and 1s6p 1P states by synchrotron radiation and ionized by a synchronized infrared pulsed picosecond laser. The photoelectron angular distributions of the emitted electrons are measured using a velocity map imaging (VMI) spectrometer. The measured asymmetry parameters of the angular distribution allow the phase differences and the ratios of the dipole matrix elements of the 1sɛs and 1sɛd channels to be determined. The experimental results agree with the calculated values obtained in a configuration-interaction calculation with a Coulomb-Sturmian basis set. The effects of the radiative decay of the intermediate state and the static electric field of the VMI spectrometer on the measurements are discussed.

  16. Resonant two-photon absorption of extreme-ultraviolet free-electron-laser radiation in helium

    SciTech Connect

    Nagasono, Mitsuru; Suljoti, Edlira; Pietzsch, Annette; Hennies, Franz; Wellhoefer, Michael; Hoeft, Jon-Tobias; Martins, Michael; Wurth, Wilfried; Foehlisch, Alexander; Treusch, Rolf; Feldhaus, Josef; Schneider, Jochen R.

    2007-05-15

    We have investigated the nonlinear response of helium to intense extreme-ultraviolet radiation from the free-electron laser in Hamburg (FLASH). We observe a spectral feature between 24 and 26 eV electron kinetic energy in photoemission which shows a quadratic fluence dependence. The feature is explained as a result of subsequent processes involving a resonant two-photon absorption process into doubly excited levels of even parity (N=5 and 6), radiative decay to the doubly excited states in the vicinity of the He{sup +} (N=2) ionization threshold and finally the photoionization of the inner electron by the radiation of the next microbunches. This observation suggests that even-parity states, which have been elusive to be measured with the low pulse energy of synchrotron radiation sources, can be investigated with the intense radiation of FLASH. This also demonstrates a first step to bring nonlinear spectroscopy into the xuv and soft-x-ray regime.

  17. Imaging multiphoton ionization and dissociation of rotationally warm CO via the B+Σ1 and E1Π electronic states

    NASA Astrophysics Data System (ADS)

    Sun, Z.-F.; Scheidsbach, R. J. A.; Suits, A. G.; Parker, D. H.

    2017-07-01

    Pathways for formation of C+ and O+ ions when applying (2 + 1) resonance enhanced multiphoton ionization (REMPI) of CO via the B1Σ+ and E1Π electronic states are characterized with the velocity map imaging technique. By employing an unskimmed pulsed valve, it was possible to obtain sharp images for a wide range of initial CO J-states. Most of the atomic ion production pathways could be assigned as one- or two-photon dissociation of a series of vibrational levels of the CO+ X2Σ+ and A2Π states. Large enhancements in dissociation of particular CO+ vibrational states in these progressions could be accurately assigned to accidental resonances of the REMPI laser with CO+ X2Σ+ -B2Σ+ transitions.

  18. Two-photon imaging and analysis of neural network dynamics

    NASA Astrophysics Data System (ADS)

    Lütcke, Henry; Helmchen, Fritjof

    2011-08-01

    The glow of a starry night sky, the smell of a freshly brewed cup of coffee or the sound of ocean waves breaking on the beach are representations of the physical world that have been created by the dynamic interactions of thousands of neurons in our brains. How the brain mediates perceptions, creates thoughts, stores memories and initiates actions remains one of the most profound puzzles in biology, if not all of science. A key to a mechanistic understanding of how the nervous system works is the ability to measure and analyze the dynamics of neuronal networks in the living organism in the context of sensory stimulation and behavior. Dynamic brain properties have been fairly well characterized on the microscopic level of individual neurons and on the macroscopic level of whole brain areas largely with the help of various electrophysiological techniques. However, our understanding of the mesoscopic level comprising local populations of hundreds to thousands of neurons (so-called 'microcircuits') remains comparably poor. Predominantly, this has been due to the technical difficulties involved in recording from large networks of neurons with single-cell spatial resolution and near-millisecond temporal resolution in the brain of living animals. In recent years, two-photon microscopy has emerged as a technique which meets many of these requirements and thus has become the method of choice for the interrogation of local neural circuits. Here, we review the state-of-research in the field of two-photon imaging of neuronal populations, covering the topics of microscope technology, suitable fluorescent indicator dyes, staining techniques, and in particular analysis techniques for extracting relevant information from the fluorescence data. We expect that functional analysis of neural networks using two-photon imaging will help to decipher fundamental operational principles of neural microcircuits.

  19. Hyperspectral imaging of microalgae using two-photon excitation.

    SciTech Connect

    Sinclair, Michael B.; Melgaard, David Kennett; Reichardt, Thomas A.; Timlin, Jerilyn Ann; Garcia, Omar Fidel; Luk, Ting Shan; Jones, Howland D. T.; Collins, Aaron M.

    2010-10-01

    A considerable amount research is being conducted on microalgae, since microalgae are becoming a promising source of renewable energy. Most of this research is centered on lipid production in microalgae because microalgae produce triacylglycerol which is ideal for biodiesel fuels. Although we are interested in research to increase lipid production in algae, we are also interested in research to sustain healthy algal cultures in large scale biomass production farms or facilities. The early detection of fluctuations in algal health, productivity, and invasive predators must be developed to ensure that algae are an efficient and cost-effective source of biofuel. Therefore we are developing technologies to monitor the health of algae using spectroscopic measurements in the field. To do this, we have proposed to spectroscopically monitor large algal cultivations using LIDAR (Light Detection And Ranging) remote sensing technology. Before we can deploy this type of technology, we must first characterize the spectral bio-signatures that are related to algal health. Recently, we have adapted our confocal hyperspectral imaging microscope at Sandia to have two-photon excitation capabilities using a chameleon tunable laser. We are using this microscope to understand the spectroscopic signatures necessary to characterize microalgae at the cellular level prior to using these signatures to classify the health of bulk samples, with the eventual goal of using of LIDAR to monitor large scale ponds and raceways. By imaging algal cultures using a tunable laser to excite at several different wavelengths we will be able to select the optimal excitation/emission wavelengths needed to characterize algal cultures. To analyze the hyperspectral images generated from this two-photon microscope, we are using Multivariate Curve Resolution (MCR) algorithms to extract the spectral signatures and their associated relative intensities from the data. For this presentation, I will show our two-photon

  20. Two-photon inner-shell transitions in molybdenum

    NASA Astrophysics Data System (ADS)

    Bannett, Yigal B.; Freund, Isaac

    1984-07-01

    The two-photon x-ray emission spectra of inner-shell transitions in metallic Mo have been studied using large-area energy-dispersive Si(Li) detectors and fast, computer-controlled, time-coincidence electronics. The discrete energy-summation spectrum displays a peak at 17.1 keV corresponding to the expected 2s-->1s transition, as well as a second, more intense peak at 19.7 keV. Based upon very recent analytical H-atom calculations by Florescu, this latter peak is tentatively identified as due primarily to 3d-->1s transitions. The continuous two-photon spectrum has also been measured on an absolute intensity scale and compared with a frozen-orbital calculation based upon direct summation of the second-order perturbation expansion for the relevant matrix elements. For the 2s-->1s transition, excellent quantitative agreement is found using the self-consistent-field Hartree-Fock wave functions of Clementi and Roetti. The same calculation predicts that the 3s-->1s transition is of negligible relative amplitude. Because the calculational method is inapplicable to d states, a simple closure approximation is developed which is found to be reasonably good for both the 2s and 3s two-photon transitions, but apparently fails for the 3d transition since it predicts a result which is relatively much too small. Our data are the first for inner-shell transitions and it is anticipated that further developments in both instrumentation and in theory will yield a new, rich, multiphoton inner-shell spectroscopy.

  1. Two-photon absorption spectra of carotenoids compounds

    NASA Astrophysics Data System (ADS)

    Vivas, Marcelo Gonçalves; Silva, Daniel Luiz; Boni, Leonardo de; Zalesny, Robert; Bartkowiak, Wojciech; Mendonca, Cleber Renato

    2011-05-01

    Carotenoids are biosynthetic organic pigments that constitute an important class of one-dimensional π-conjugated organic molecules with enormous potential for application in biophotonic devices. In this context, we studied the degenerate two-photon absorption (2PA) cross-section spectra of two carotenoid compounds (β-carotene and β-apo-8'-carotenal) employing the conventional and white-light-continuum Z-scan techniques and quantum chemistry calculations. Because carotenoids coexist at room temperature as a mixture of isomers, the 2PA spectra reported here are due to samples containing a distribution of isomers, presenting distinct conjugation length and conformation. We show that these compounds present a defined structure on the 2PA spectra, that peaks at 650 nm with an absorption cross-section of approximately 5000 GM, for both compounds. In addition, we observed a 2PA band at 990 nm for β-apo-8'-carotenal, which was attributed to a overlapping of 11Bu+-like and 21Ag--like states, which are strongly one- and two-photon allowed, respectively. Spectroscopic parameters of the electronic transitions to singlet-excited states, which are directly related to photophysical properties of these compounds, were obtained by fitting the 2PA spectra using the sum-over-states approach. The analysis and interpretations of the 2PA spectra of the investigated carotenoids were supported by theoretical predictions of one- and two-photon transitions carried out using the response functions formalism within the density functional theory framework, using the long-range corrected CAM-B3LYP functional.

  2. Two-Photon Fluorescence Microscopy Developed for Microgravity Fluid Physics

    NASA Technical Reports Server (NTRS)

    Fischer, David G.; Zimmerli, Gregory A.; Asipauskas, Marius

    2004-01-01

    Recent research efforts within the Microgravity Fluid Physics Branch of the NASA Glenn Research Center have necessitated the development of a microscope capable of high-resolution, three-dimensional imaging of intracellular structure and tissue morphology. Standard optical microscopy works well for thin samples, but it does not allow the imaging of thick samples because of severe degradation caused by out-of-focus object structure. Confocal microscopy, which is a laser-based scanning microscopy, provides improved three-dimensional imaging and true optical sectioning by excluding the out-of-focus light. However, in confocal microscopy, out-of-focus object structure is still illuminated by the incoming beam, which can lead to substantial photo-bleaching. In addition, confocal microscopy is plagued by limited penetration depth, signal loss due to the presence of a confocal pinhole, and the possibility of live-cell damage. Two-photon microscopy is a novel form of laser-based scanning microscopy that allows three-dimensional imaging without many of the problems inherent in confocal microscopy. Unlike one-photon microscopy, it utilizes the nonlinear absorption of two near-infrared photons. However, the efficiency of two-photon absorption is much lower than that of one-photon absorption because of the nonlinear (i.e., quadratic) electric field dependence, so an ultrafast pulsed laser source must typically be employed. On the other hand, this stringent energy density requirement effectively localizes fluorophore excitation to the focal volume. Consequently, two-photon microscopy provides optical sectioning and confocal performance without the need for a signal-limiting pinhole. In addition, there is a reduction in photo-damage because of the longer excitation wavelength, a reduction in background fluorescence, and a 4 increase in penetration depth over confocal methods because of the reduction in Rayleigh scattering.

  3. Adaptive optical two-photon microscopy using autofluorescent guide stars.

    PubMed

    Tao, Xiaodong; Norton, Andrew; Kissel, Matthew; Azucena, Oscar; Kubby, Joel

    2013-12-01

    We demonstrate a fast, direct wavefront-sensing method for dynamic in vivo adaptive optical two-photon microscopy. By using a Shack-Hartmann wavefront sensor and open-loop control, the system provides high-speed wavefront measurement and correction. To measure the wavefront in the middle of a Drosophila embryo at early stages, autofluorescence from endogenous fluorophores in the yolk were used as reference guide stars. The method was tested through live imaging of a Drosophila embryo. The aberration in the middle of the embryo was measured directly for the first time. After correction, the contrast and signal intensity of the structure in the middle of the embryo was improved.

  4. Two Photon Absorption Laser Induced Fluorescence for Fusion Class Plasmas

    NASA Astrophysics Data System (ADS)

    Elliott, Drew B.

    Neutral hydrogen particles play an important role in many fusion systems. The edge region of fusion plasmas is strongly influenced by these neutral particles and is of growing importance because of the challenges of plasma material interaction. A two photon absorption laser induced fluorescence diagnostic at West Virginia University has been constructed to measure the local density and velocity distribution of these neutral particles. The diagnostic measures the ground state of hydrogen isotopes by way of two photon absorption from the 1s to 3d state and subsequent single photon emission to the 2 p state. These measurements are absolutely calibrated by comparing the integrated emission spectra to that of a measurement performed on a known density of calibration gas and knowing the relative absorption cross sections for the two species. Measurements were performed on deuterium atoms in the Helicity Injected Torus with Steady Induction 3 and calibrated using the standard krypton calibration scheme. Measured neutral densities were well below predicted values and the measurement process identified a flaw in the krypton calibration scheme. A new calibration scheme using xenon gas was developed to eliminate any possibility of chromatic aberration through refractive optics. This new xenon calibration scheme required measurement of the relative absorption cross section between the 5p6 to 4p 57f to 5p55 d Xe scheme and the 4p6 to 4 p55p to 4p 55s Kr scheme, then comparison of the Xe to Kr relative cross section to the Kr to H relative cross section to determine the overall Xe to H relative absorption cross section. Doppler free two photon absorption laser induced fluorescence measurements were also performed on the compact helicon for waves and instabilities experiment (CHEWIE), for hydrogen, deuterium, and krypton neutrals. The Doppler free technique increased signal intensity and narrowed the measured spectral width of the absorption line. The Doppler free technique

  5. Two-photon spectroscopy of excitons with entangled photons.

    PubMed

    Schlawin, Frank; Mukamel, Shaul

    2013-12-28

    The utility of quantum light as a spectroscopic tool is demonstrated for frequency-dispersed pump-probe, integrated pump-probe, and two-photon fluorescence signals which show Ramsey fringes. Simulations of the frequency-dispersed transmission of a broadband pulse of entangled photons interacting with a three-level model of matter reveal how the non-classical time-bandwidth properties of entangled photons can be used to disentangle congested spectra, and reveal otherwise unresolved features. Quantum light effects are most pronounced at weak intensities when entangled photon pairs are well separated, and are gradually diminished at higher intensities when different photon pairs overlap.

  6. Two-photon quantum interference in plasmonics: theory and applications.

    PubMed

    Gupta, S Dutta; Agarwal, G S

    2014-01-15

    We report perfect two-photon quantum interference with near-unity visibility in a resonant tunneling plasmonic structure in folded Kretschmann geometry. This is despite absorption-induced loss of unitarity in plasmonic systems. The effect is traced to perfect destructive interference between the squares of amplitude reflection and transmission coefficients. We further highlight yet another remarkable potential of coincidence measurements as a probe with better resolution as compared to standard spectroscopic techniques. The finer features show up in both angle resolved and frequency resolved studies.

  7. Two-photon excitation microscopy with spatial light modulator

    NASA Astrophysics Data System (ADS)

    Matsumoto, Naoya; Konno, Alu; Inoue, Takashi; Toyoda, Haruyoshi; Miwa, Toshiyuki; Nakamura, Kazuhiro; Okazaki, Shigetoshi

    2017-04-01

    We attempted to observe deep regions in biological samples through two-photon excitation microscopy adopting a spatial light modulator (SLM). The SLM is used for correcting spherical aberration (SA) caused by the refractive-index mismatch between the immersion medium and sample. In the observation of fluorescent beads in transparent epoxy resin, the fluorescence intensity from a scan with SA correction was 50 times that from a scan without SA correction. After that, we observed blood vessels in a mouse brain, which became transparent with a clearing agent.

  8. Polarization rotation under two-photon Raman resonance for magnetometry

    SciTech Connect

    Pradhan, S.; Behera, R.; Das, A. K.

    2012-04-23

    The polarization rotation and coherent population trapping signal arising due to two photon process using linearly polarized light are found to be significantly enhanced for a Zeeman degenerate system. The zero crossing of the dispersive profile is found to be shifting proportional to the applied magnetic field, albeit the absorptive profile position remains invariant for a slightly imbalanced orthogonal circular polarization component. It provides an alternative method for precise measurement of vector magnetic field without requirement of a bias field. The use of polarization rotation signal for magnetic field measurement offers added advantage due to improved signal to noise ratio.

  9. Two Photon Decays of Charmonia from Lattice QCD

    SciTech Connect

    Jozef Dudek; Robert Edwards

    2006-07-12

    We make the first calculation in lattice QCD of two-photon decays of mesons. Working in the charmonium sector, using the LSZ reduction to relate a photon to a sum of hadronic vector eigenstates, we compute form-factors in both the space-like and time-like domains for the transitions {eta}{sub c} {yields} {gamma}*{gamma}* and {chi}{sub c0} {yields} {gamma}*{gamma}*. At the on-shell point we find approximate agreement with experimental world-average values.

  10. Pulse front adaptive optics in two-photon microscopy.

    PubMed

    Sun, Bangshan; Salter, Patrick S; Booth, Martin J

    2015-11-01

    Adaptive optics has been extensively studied for the correction of phase front aberrations in optical systems. In systems using ultrafast lasers, distortions can also exist in the pulse front (contour of constant intensity in space and time), but until now their correction has been mostly unexplored due to technological limitations. In this Letter, we apply newly developed pulse front adaptive optics, for the first time to our knowledge, to practical compensation of a two-photon fluorescence microscope. With adaptive correction of the system-induced pulse front distortion, improvements beyond conventional phase correction are demonstrated.

  11. Nonlinear Dual-Comb Spectroscopy with Two-Photon Excitation

    NASA Astrophysics Data System (ADS)

    Meek, S. A.; Hipke, A.; Hansch, T. W.; Picque, N.

    2013-06-01

    Dual frequency comb spectroscopy has proven to be a powerful method for acquiring broadband, high resolution spectra with measurement times that are much shorter than in traditional moving-mirror Fourier transform spectroscopy. Because the measurements are carried out with femtosecond lasers, this technique has great potential for decreasing the measurement times and improving the signal-to-noise ratio of nonlinear spectroscopic measurements, such as two-photon excitation or Raman processes. In the case of two-photon excitation, an entire spectrum can be obtained at a given signal level using dual-comb spectroscopy in the same time that a measurement of a single transition frequency would be obtained with a continuous laser of the same average power. In this presentation, I will show the latest results in extending the dual-comb technique to two-photon excitation spectroscopy, with measurements on gas-phase rubidium and liquid-phase dye samples. In our realization of dual-comb spectroscopy, two frequency combs with slightly different repetition rates are combined on a beam splitter and directed into a sample, and we measure the intensity of the resulting fluorescence as a function of time. Because of the different repetition rates, the time delay between a pulse from the first comb and the next pulse from the second comb changes linearly with time, simulating the action of the moving mirror in a traditional Michelson interferometer. The Fourier transform of the measured time-domain interferogram produces a radio-frequency spectrum that can be directly converted to a broadband optical spectrum through a linear scaling of the frequency. To achieve the highest possible resolution, it is necessary to compensate the residual relative fluctuations of the repetition rate and the carrier-envelope offset frequency of the frequency combs. Measuring RF beatnotes of each comb with two CW lasers provides two error signals that can be used to correct the recorded interferograms

  12. Two-photon photoassociative spectroscopy of ultracold Sr88

    NASA Astrophysics Data System (ADS)

    Martinez de Escobar, Y. N.; Mickelson, P. G.; Pellegrini, P.; Nagel, S. B.; Traverso, A.; Yan, M.; Côté, R.; Killian, T. C.

    2008-12-01

    We present results from two-photon photoassociative spectroscopy of the least-bound vibrational level of the XΣg+1 state of the Sr288 dimer. Measurement of the binding energy allows us to determine the s -wave scattering length a88=-1.4(6)a0 . For the intermediate state, we use a bound level on the metastable S01-P13 potential, which provides large Franck-Condon transition factors and narrow one-photon photoassociative lines that are advantageous for observing quantum-optical effects such as Autler-Townes resonance splittings.

  13. Metastable Krypton Beam Source via Two-Photon Pumping Technique

    SciTech Connect

    Wong, W.W.; Young, L.

    2003-01-01

    Metastable beams of rare gas atoms have wide applications in chemical analysis of samples, as well as in aiding understanding of fundamental processes and physical attributes. Most current sources of metastable rare gas atomic beams, however, are limited in their flux density, which greatly reduces their utility in applications such as low level trace analysis and precision measurements. Previous work has demonstrated feasibility of metastable krypton production via two-photon pumping, and this paper extends that possibility into beam form. Further optimization on this scheme, moreover, promises 100-fold increase of metastable krypton flux density over that of an rf-driven discharge.

  14. Nonlocal Pancharatnam phase in two-photon interferometry

    SciTech Connect

    Mehta, Poonam; Samuel, Joseph; Sinha, Supurna

    2010-09-15

    We propose a polarized intensity interferometry experiment, which measures the nonlocal Pancharatnam phase acquired by a pair of Hanbury-Brown-Twiss photons. The setup involves two polarized thermal sources illuminating two polarized detectors. Varying the relative polarization angle of the detectors introduces a two-photon geometric phase. Local measurements at either detector do not reveal the effects of the phase, which is an optical analog of the multiparticle Aharonov-Bohm effect. The geometric phase sheds light on the three-slit experiment and suggests ways of tuning entanglement.

  15. Two-photon physics as a probe of hadron dynamics

    SciTech Connect

    Brodsky, S.J.

    1981-05-01

    Two-photon collisions provide an ideal laboratory for testing many features of quantum chromodynamics, especially the interplay between the vector-meson-dominated and point-like hadronic interactions of the photon. A number of QCD applications are discussed, including: jet and single-particle production at large transverse momentum; the photon structure function and its relationship to the ..gamma.. ..-->.. q anti q wave function; and the possible role of gluonium states in the ..gamma gamma.. ..-->.. rho/sup 0/rho/sup 0/ channel. Evidence that even low momentum transfer photon-hadron interactions are sensitive to the point-like ..gamma.. ..-->.. q anti q coupling is discussed.

  16. Two-photon exclusive processes in quantum chromodynamics

    SciTech Connect

    Brodsky, S.J.

    1986-07-01

    QCD predictions for ..gamma gamma.. annihilation into single mesons, meson pairs, and baryon pairs are reviewed. Two-photon exclusive processes provide the most sensitive and practical measure of the distribution amplitudes, and thus a critical confrontation between QCD and experiment. Both the angular distribution and virtual photon mass dependence of these amplitudes are sensitive to the shapes of the phi (chi, Q). Novel effects involving the production of qq anti q anti q states at threshold are also discussed, and a new method is presented for systematically incorporating higher-order QCD corrections in ..gamma gamma.. reactions.

  17. Microphotonic parabolic light directors fabricated by two-photon lithography

    SciTech Connect

    Atwater, J. H.; Spinelli, P.; Kosten, E.; Parsons, J.; Van Lare, C.; Van de Groep, J.; Garcia de Abajo, J.; Polman, A.; Atwater, H. A.

    2011-10-10

    We have fabricated microphotonic parabolic light directors using two-photon lithography, thin-film processing, and aperture formation by focused ion beam lithography. Optical transmission measurements through upright parabolic directors 22 μm high and 10 μm in diameter exhibit strong beam directivity with a beam divergence of 5.6°, in reasonable agreement with ray-tracing and full-field electromagnetic simulations. The results indicate the suitability of microphotonic parabolic light directors for producing collimated beams for applications in advanced solar cell and light-emitting diode designs.

  18. Two-Photon Exchange in (Semi-)Inclusive DIS

    SciTech Connect

    Schlegel, M.; Metz, A.

    2009-08-04

    In this note we consider effects of a Two-Photon Exchange (TPE) in inclusive DIS and semi-inclusive DIS (SIDIS). In particular, transverse single spin asymmetries are generated in inclusive DIS if more than one photon is exchanged between the lepton and the hadron. We briefly summarize the TPE in DIS in the parton model and extend our approach to SIDIS, where a new leading twist sin(2{phi}) contribution to the longitudinal beam spin asymmetry shows up. Possible TPE effects for the Sivers and the Collins asymmetries in SIDIS are power-suppressed.

  19. Two-Photon Exchange in (Semi-)Inclusive DIS

    SciTech Connect

    Schlegel, Marc; Metz, Andreas

    2009-01-01

    In this note we consider effects of a Two-Photon Exchange (TPE) in inclusive DIS and semi-inclusive DIS (SIDIS). In particular, transverse single spin asymmetries are generated in inclusive DIS if more than one photon is exchanged between the lepton and the hadron. We briefly summarize the TPE in DIS in the parton model and extend our approach to SIDIS, where a new leading twist $\\sin(2\\phi)$ contribution to the longitudinal beam spin asymmetry shows up. Possible TPE effects for the Sivers and the Collins asymmetries in SIDIS are power-suppressed.

  20. Two-photon exchange corrections to the pion form factor

    SciTech Connect

    Peter G. Blunden; Melnitchouk, Wally; Tjon, John A.

    2010-01-06

    Here, we compute two-photon exchange corrections to the electromagnetic form factor of the pion, taking into account the finite size of the pion. Compared to the soft-photon approximation for the infrared divergent contribution which neglects hadron structure effects, the corrections are found to be ≲ 1% for small Q2 (Q2 < 0.1 GeV2), but increase to several percent for Q2 ≳ 1 GeV2 at extreme backward angles.

  1. Two-photon exchange in electron-trinucleon elastic scattering

    NASA Astrophysics Data System (ADS)

    Kobushkin, A. P.; Timoshenko, Ju. V.

    2013-10-01

    We discuss two-photon exchange (TPE) in elastic electron scattering off the trinucleon systems, 3He and 3H. The calculations are done in the semirelativistic approximation with the trinucleon wave functions obtained with the Paris and CD-Bonn nucleon-nucleon potentials. An applicability area of the model is wide enough and includes the main part of kinematical domain where experimental data exist. All three TPE amplitudes (generalized form factors) for electron 3He elastic scattering are calculated. We find that the TPE amplitudes are a few times more significant in the scattering of electrons off 3He then in the electron-proton scattering.

  2. Imaging nanowire plasmon modes with two-photon polymerization

    SciTech Connect

    Gruber, Christian; Trügler, Andreas; Hohenester, Ulrich; Ditlbacher, Harald; Hohenau, Andreas; Krenn, Joachim R.; Hirzer, Andreas; Schmidt, Volker

    2015-02-23

    Metal nanowires sustain propagating surface plasmons that are strongly confined to the wire surface. Plasmon reflection at the wire end faces and interference lead to standing plasmon modes. We demonstrate that these modes can be imaged via two-photon (plasmon) polymerization of a thin film resist covering the wires and subsequent electron microscopy. Thereby, the plasmon wavelength and the phase shift of the nanowire mode picked up upon reflection can be directly retrieved. In general terms, polymerization imaging is a promising tool for the imaging of propagating plasmon modes from the nano- to micro-scale.

  3. Rate for annihilation of galactic dark matter into two photons

    NASA Technical Reports Server (NTRS)

    Giudice, Gian F.; Griest, Kim

    1989-01-01

    A calculation of the cross section for neutralino-neutralino annihilation into two photons is performed and applied to dark matter in the galactic halo to find the counting rate in a large gamma ray detector such as EGRET (Energetic Gamma Ray Experiment Telescope) or ASTROGAM. Combining constraints from particle accelerators with the requirement that the neutralinos make up the dark matter, it is found that rates of over a few dozen events per year are unlikely. The assumptions that go into these conclusions are listed. Other particle dark matter candidates which could give larger and perhaps observable signals are suggested.

  4. Acetylene-substituted two-photon absorbing molecules with rigid elongated pi-conjugation: synthesis, spectroscopic properties and two-photon fluorescence cell imaging applications.

    PubMed

    Liu, Bo; Zhang, Hai-Li; Liu, Jun; Huang, Zhen-Li; Zhao, Yuan-Di; Luo, Qing-Ming

    2007-09-01

    Two asymmetrical molecules with substituted acetylene as central rigid elongated conjugation are reported as potential chromophores for two-photon microscopic imaging. These molecules consist of a typical D-pi-A structure, have different donors (D), the same pi-conjugated center (pi) and the same acceptor (A). Structural characterization and spectroscopic properties, including single-photon (linear) absorption, quantum yields, single-photon fluorescence, and two-photon absorption spectra, were studied in solvents with different polarity. These acetylene-substituted molecules were found to have high two-photon absorption cross-sections (for example, 690 GM for molecule 1 in toluene), which were determined by a two-photon induced fluorescence method using a femtosecond Ti: sapphire laser as excitation source. Single- and two-photon cellular imaging experiments demonstrate that the substituted acetylene derivatives could be one kind of promising two-photon fluorescence probes for cellular imaging.

  5. High-order dispersion effects in two-photon interference

    NASA Astrophysics Data System (ADS)

    Mazzotta, Zeudi; Cialdi, Simone; Cipriani, Daniele; Olivares, Stefano; Paris, Matteo G. A.

    2016-12-01

    Two-photon interference and Hong-Ou-Mandel (HOM) effect are relevant tools for quantum metrology and quantum information processing. In optical coherence tomography, the HOM effect is exploited to achieve high-resolution measurements with the width of the HOM dip being the main parameter. On the other hand, applications like dense coding require high-visibility performance. Here we address high-order dispersion effects in two-photon interference and study, theoretically and experimentally, the dependence of the visibility and the width of the HOM dip on both the pump spectrum and the downconverted photon spectrum. In particular, a spatial light modulator is exploited to experimentally introduce and manipulate a custom phase function to simulate the high-order dispersion effects. Overall, we show that it is possible to effectively introduce high-order dispersion effects on the propagation of photons and also to compensate for such effect. Our results clarify the role of the different dispersion phenomena and pave the way for optimization procedures in quantum technological applications involving PDC photons and optical fibers.

  6. Simultaneous two-photon excitation of photodynamic therapy agents

    NASA Astrophysics Data System (ADS)

    Wachter, Eric A.; Partridge, W. P., Jr.; Fisher, Walter G.; Dees, Craig; Petersen, Mark G.

    1998-07-01

    The spectroscopic and photochemical properties of several photosensitive compounds are compared using conventional single-photon excitation (SPE) and simultaneous two-photon excitation (TPE). TPE is achieved using a mode-locked titanium:sapphire laser, the near infrared output of which allows direct promotion of non-resonant TPE. Excitation spectra and excited state properties of both type I and type II photodynamic therapy (PDT) agents are examined. In general, while SPE and TPE selection rules may be somewhat different, the excited state photochemical properties are equivalent for both modes of excitation. In vitro promotion of a two-photon photodynamic effect is demonstrated using bacterial and human breast cancer models. These results suggest that use of TPE may be beneficial for PDT, since the technique allows replacement of visible or ultraviolet excitation with non- damaging near infrared light. Further, a comparison of possible excitation sources for TPE indicates that the titanium:sapphire laser is exceptionally well suited for non- linear excitation of PDT agents in biological systems due to its extremely short pulse width and high repetition rate; these features combine to effect efficient PDT activation with minimal potential for non-specific biological damage.

  7. Temperature dependence of the two photon absorption in indium arsenide

    SciTech Connect

    Berryman, K.W.; Rella, C.W.

    1995-12-31

    Nonlinear optical processes in semiconductors have long been a source of interesting physics. Two photon absorption (TPA) is one such process, in which two photons provide the energy for the creation of an electron-hole pair. Researchers at other FEL centers have studied room temperature TPA in InSb, InAs, and HgCdTe. Working at the Stanford Picosecond FEL Center, we have extended and refined this work by measuring the temperature dependence of the TPA coefficient in InAs over the range from 80 to 350 K at four wavelengths: 4.5, 5.06, 6.01, and 6.3 microns. The measurements validate the functional dependence of recent band structure calculations with enough precision to discriminate parabolic from non-parabolic models, and to begin to observe smaller effects, such as contributions due to the split-off band. These experiments therefore serve as a strong independent test of the Kane band theory, as well as providing a starting point for detailed observations of other nonlinear absorption mechanisms.

  8. Imaging of Protein Crystals with Two-Photon Microscopy

    SciTech Connect

    Padayatti, Pius; Palczewska, Grazyna; Sun, Wenyu; Palczewski, Krzysztof; Salom, David

    2012-05-02

    Second-order nonlinear optical imaging of chiral crystals (SONICC), which portrays second-harmonic generation (SHG) by noncentrosymmetric crystals, is emerging as a powerful imaging technique for protein crystals in media opaque to visible light because of its high signal-to-noise ratio. Here we report the incorporation of both SONICC and two-photon excited fluorescence (TPEF) into one imaging system that allows visualization of crystals as small as 10 {mu}m in their longest dimension. Using this system, we then documented an inverse correlation between the level of symmetry in examined crystals and the intensity of their SHG. Moreover, because of blue-green TPEF exhibited by most tested protein crystals, we also could identify and image SHG-silent protein crystals. Our experimental data suggest that the TPEF in protein crystals is mainly caused by the oxidation of tryptophan residues. Additionally, we found that unspecific fluorescent dyes are able to bind to lysozyme crystals and enhance their detection by TPEF. We finally confirmed that the observed fluorescence was generated by a two-photon rather than a three-photon process. The capability for imaging small protein crystals in turbid or opaque media with nondamaging infrared light in a single system makes the combination of SHG and intrinsic visible TPEF a powerful tool for nondestructive protein crystal identification and characterization during crystallization trials.

  9. Positron/Electron Annihilation via the Two-Photon Pathway

    NASA Astrophysics Data System (ADS)

    Gauthier, Isabelle

    When a positron/electron pair annihilate via the two-photon pathway, the emitted photons are momentum correlated. This correlation ensures that they move along a straight line path in opposite directions. An experiment performed in 2004 by Dr. V.D. Irby measured the time interval between detection of the photons. He observed a decay in the number of counts with increasing detection time interval, which he described using a Lorentzian, the line width of which at full-width half-maximum is measured to be 120ps. The data collected by Irby is interesting because current theory predicts that because the source is so localized (the effective source width used by Irby is safely within 5rnrn) the photons should be detected within a time interval of Deltat=d/c where d is the thickness of the source. This time interval corresponds to 17ps. This thesis fits the results to an exponential, and shows that this exponentially decaying nature of the coincidence time interval is characteristic of the entanglement of the two photons. We find that the wavefunctions of the photons decoheres in space according to how long the particle pair took to decay (which is exponential), and that the probability of simultaneous detection depends on the exponential of the product of the lifetime of positronium and the detection time interval.

  10. Multidimensional two-photon imaging of diseased skin

    NASA Astrophysics Data System (ADS)

    Cicchi, R.; Sestini, S.; De Giorgi, V.; Massi, D.; Lotti, T.; Pavone, F. S.

    2008-02-01

    We used combined two photon intrinsic fluorescence (TPE), second harmonic generation microscopy (SHG), fluorescence lifetime imaging microscopy (FLIM), and multispectral two photon emission detection (MTPE) to investigate different kinds of human cutaneous ex-vivo skin lesions. Morphological and spectroscopic analyses allowed to characterize both healthy and pathological skin samples, including tumors, as well as to discriminate between healthy and diseased tissue, in a good agreement with common routine histology. In particular, we examined tissue samples from normal and pathological scar tissue (keloid), and skin tumors, including basal cell carcinoma (BCC) and malignant melanoma (MM). By using combined TPE-SHG microscopy we investigated morphological features of different skin regions, as BCC, tumor-stroma interface, healthy dermis, fibroblastic proliferation, and keloids. The SHG to autofluorescence aging index of dermis (SAAID) score was used to characterize each region, finding differences between BCC, healthy skin, tumor-stroma interface, keloids, and fibroblastic proliferation. Further comparative analysis of healthy skin and neoplastic samples was performed using FLIM. In particular, BCC showed a blue-shifted fluorescence emission, a higher absorption at 800 nm excitation wavelength, and a slightly longer mean fluorescence lifetime. MM showed a lifetime distribution similar to the corresponding melanocytic nevus (MN) lifetime distribution for the slow lifetime component, and different for the fast lifetime component.

  11. Theory of Two-Photon Absorptions in Graphene Fragments

    NASA Astrophysics Data System (ADS)

    Aryanpour, K.; Shukla, A.; Mazumdar, S.; Sandhu, A.; Roberts, A.

    2012-02-01

    Electron-electron correlations in graphene is currently an active field of research [1-3]. The carbon atoms in graphene have the same sp^2 hybridization as in strongly correlated π-conjugated polymer systems. The low energy behavior in graphene however appears to be reasonably described within the one-electron Dirac massless fermions model. Historically, the occurrence of the lowest two-photon state below the optical one-photon state provided the strongest proof for strong electron correlations in linear polyenes [4]. We systematically study the Coulomb interaction effects on the ground state and nonlinear absorptions in graphene fragments as a function of system size, beginning from the smallest stable fragment coronene. We report high order calculations of one- vs two-photon spin singlet and triplet states, in coronene, hexabenzocoronene and other molecular fragments that clearly indicate the strong role of electron-electron interactions. We will discuss the implications of our work on molecular systems for the thermodynamic limit of graphene. [4pt] [1] Siegel David A.; et al., PNAS, v108, 28, 11365-11369 (2011)[0pt] [2] Gr"onqvist J. H.; et al., arXiv: 1107.5653v1[0pt] [3] Uchoa B.; et al., arXiv: 1109.1577v1[0pt] [4] Ramasesha S.; et al., J. Chem. Phys. 80, 3278 (1984)

  12. Nonresonant two-photon transitions in length and velocity gauges

    NASA Astrophysics Data System (ADS)

    Jentschura, U. D.

    2016-08-01

    We reexamine the invariance of two-photon transition matrix elements and corresponding two-photon Rabi frequencies under the "gauge" transformation from the length to the velocity gauge. It is shown that gauge invariance, in the most general sense, only holds at exact resonance, for both one-color as well as two-color absorption. The arguments leading to this conclusion are supported by analytic calculations which express the matrix elements in terms of hypergeometric functions, and ramified by a "master identity" which is fulfilled by off-diagonal matrix elements of the Schrödinger propagator under the transformation from the velocity to the length gauge. The study of the gauge dependence of atomic processes highlights subtle connections between the concept of asymptotic states, the gauge transformation of the wave function, and infinitesimal damping parameters for perturbations and interaction Hamiltonians that switch off the terms in the infinite past and future [of the form exp(-ɛ |t |)] . We include a pertinent discussion.

  13. Double-Pomeron and two-photon processes at RHIC

    SciTech Connect

    Chung, S.U.; Weygand, D.P.; Willutzki, H.J.

    1991-11-01

    Double-Pomeron processes have been shown to be an important and novel source of hadron production at moderate energies at the ISR. These processes are expected to provide glue-rich hadrons from 1 GeV to 10 GeV or more, encompassing the states consisting of u, d, s and b quarks. The double-pomeron cross sections for central hadroproduction are calculated for p {times} p and Au {times} Au at RHIC. Two-photon production of hadrons in the central region begins to dominate or at least become comparable to the double-Pomeron processes as the Z of the beams increases from p to Au. Since photons couple to charge, these hadroproductions involve mainly quarkonia and multiquark states. Therefore, a comparative study of these processes is expected to provide new insights into the constituents of hadronic matter. The two-photon processes are calculated following the recipe given by Cahn and Jackson. The paper starts out with a thorough discussion of the relevant kinematics, phase space and Regge amplitudes.

  14. Two-photon multiplane imaging of neural circuits (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yang, Weijian; Miller, Jae-eun K.; Carrillo-Reid, Luis; Pnevmatikakis, Eftychios; Paninski, Liam; Peterka, Darcy S.; Yuste, Rafael

    2016-03-01

    Imaging the neuronal activity throughout the brain with high temporal and spatial resolution is an important step in understanding how the brain works. Two-photon laser scanning microscopy with fluorescent calcium indicators has enabled this type of experiments in vivo. Most of these microscopes acquire images serially, with a single laser beam, limiting the overall imaging speed. To overcome this limit, multiple beamlets can be used to image in parallel multiple regions. Here, we demonstrate a novel scheme of a two-photon laser-scanning microscope that can simultaneously record neuronal activity at multiple planes of the sample with a single photomultiplier tube. A spatial light modulator is used to generate the designated multiple beamlets, and a constrained non-negative matrix factorization algorithm is used to demix the signals from multiple scanned planes. We simultaneously record neuronal activity of multiple layers of a mouse cortex at 10 fps in vivo. This novel imaging scheme provides a powerful tool for mapping the brain activity.

  15. Two-Photon-Induced Fluorescence of Isomorphic Nucleobase Analogs

    PubMed Central

    Lane, Richard S. K.; Jones, Rosemary; Sinkeldam, Renatus W.

    2014-01-01

    Five isomorphic fluorescent uridine mimics have been subjected to two-photon (2P) excitation analysis to investigate their potential applicability as non-perturbing probes for the single-molecule detection of nucleic acids. We find that small structural differences can cause major changes in the two-photon excitation probability, with the 2P cross sections varying by over one order of magnitude. Two of the probes, both furan-modified uridine analogs, have the highest 2P cross sections (3.8 GM and 7.6 GM) reported for nucleobase analogs, using a conventional Ti:sapphire laser for excitation at 690 nm; they also have the lowest emission quantum yields. In contrast, the analogs with the highest reported quantum yields have the lowest 2P cross sections. The structure-photophysical property relationship presented here is a first step towards the rational design of emissive nucleobase analogs with controlled 2P characteristics. The results demonstrate the potential for major improvements through judicious structural modifications. PMID:24604669

  16. One-step theory of two-photon photoemission

    NASA Astrophysics Data System (ADS)

    Braun, J.; Rausch, R.; Potthoff, M.; Ebert, H.

    2016-09-01

    A theoretical frame for two-photon photoemission is derived from the general theory of pump-probe photoemission, assuming that not only the probe but also the pump pulse is sufficiently weak. This allows us to use a perturbative approach to compute the lesser Green function within the Keldysh formalism. Two-photon photoemission spectroscopy is a widely used analytical tool to study nonequilibrium phenomena in solid materials. Our theoretical approach aims at a material-specific, realistic, and quantitative description of the time-dependent spectrum based on a picture of effectively independent electrons as described by the local-density approximation in band-structure theory. To this end we follow Pendry's one-step theory of the photoemission process as close as possible and heavily make use of concepts of relativistic multiple-scattering theory, such as the representation of the final state by a time-reversed low-energy electron diffraction state. The formalism allows for a quantitative calculation of the time-dependent photocurrent for moderately correlated systems like simple metals or more complex compounds like topological insulators. An application to the Ag(100) surface is discussed in detail.

  17. Two-Photon Imaging of Microbial Immunity in Living Tissues

    PubMed Central

    Herz, Jasmin; Zinselmeyer, Bernd H.; McGavern, Dorian B.

    2013-01-01

    The immune system is highly evolved and can respond to infection throughout the body. Pathogen-specific immune cells are usually generated in secondary lymphoid tissues (e.g., spleen, lymph nodes) and then migrate to sites of infection where their functionality is shaped by the local milieu. Because immune cells are so heavily influenced by the infected tissue in which they reside, it is important that their interactions and dynamics be studied in vivo. Two-photon microscopy is a powerful approach to study host-immune interactions in living tissues, and recent technical advances in the field have enabled researchers to capture movies of immune cells and infectious agents operating in real time. These studies have shed light on pathogen entry and spread through intact tissues as well as the mechanisms by which innate and adaptive immune cells participate in thwarting infections. This review focuses on how two-photon microscopy can be used to study tissue-specific immune responses in vivo, and how this approach has advanced our understanding of host-immune interactions following infection. PMID:22846498

  18. Two-Photon Holographic Stimulation of ReaChR

    PubMed Central

    Chaigneau, Emmanuelle; Ronzitti, Emiliano; Gajowa, Marta A.; Soler-Llavina, Gilberto J.; Tanese, Dimitrii; Brureau, Anthony Y. B.; Papagiakoumou, Eirini; Zeng, Hongkui; Emiliani, Valentina

    2016-01-01

    Optogenetics provides a unique approach to remotely manipulate brain activity with light. Reaching the degree of spatiotemporal control necessary to dissect the role of individual cells in neuronal networks, some of which reside deep in the brain, requires joint progress in opsin engineering and light sculpting methods. Here we investigate for the first time two-photon stimulation of the red-shifted opsin ReaChR. We use two-photon (2P) holographic illumination to control the activation of individually chosen neurons expressing ReaChR in acute brain slices. We demonstrated reliable action potential generation in ReaChR-expressing neurons and studied holographic 2P-evoked spiking performances depending on illumination power and pulse width using an amplified laser and a standard femtosecond Ti:Sapphire oscillator laser. These findings provide detailed knowledge of ReaChR's behavior under 2P illumination paving the way for achieving in depth remote control of multiple cells with high spatiotemporal resolution deep within scattering tissue. PMID:27803649

  19. Femtosecond two-photon-excited fluorescence of melanin

    NASA Astrophysics Data System (ADS)

    Teuchner, Klaus; Mueller, Susanne; Freyer, Wolfgang; Leupold, Dieter; Altmeyer, Peter; Stuecker, Markus; Hoffmann, Klaus

    2003-02-01

    Spectral and time-resolved fluorescence studies of different eumelanins (natural, synthetic, enzymatic) in solution have been carried out by two-photon excitation at 800 nm, using 80 fs pulses with photon flux densities <= 1027 cm-2.s-1. Whereas all samples show monotonously decreasing absorption between near UV and near IR, their fluorescence behavior indicates strong heterogeneity. With respect to the also measured one-photon excited fluorescence (OPF) of melanin at 400 nm, the overall spectral shape of the two-photon excited fluorescence (TPF) is red-shifted. Both OPF and TPF exhibit three-exponential decay with a shortest component # 200 ps. As is also shown, the fluorescence properties of melanin are dependent on the micro-environment. This allows the hypothesis, that the process of malignant transformation in skin tissue could be reflected in the fluorescence, provided the melanin in skin is selectively excited. The latter is realized by the described stepwise absorption of two 800 nm photons. In this way, indeed characteristic differences between the TPF spectra of healthy tissue, nevus cell nevi and malignant melanoma have been found.

  20. Resolution in two-photon infrared vision (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Artal, Pablo; Komar, Katarzyna; Gambin, Adrian; Manzanera, Silvestre; Wojtkowski, Maciej

    2017-02-01

    Human subjects can detect infrared light at wavelengths over 1000 nm perceived as visible of the corresponding half wavelength. This is due to a two-photon process and requires the use of pulsed light sources well focused within the retina. We have developed an experimental system to measure, for the first time, the visual resolution of the eye when is stimulated with infrared (1043 nm) and compared with visible light (543 nm). Scanner mirrors were used to project letters of different sizes onto the retina in both wavelengths. Subjects performed a visual test to determine the smallest letter size that was distinguishable for each wavelength for a range of defocus values. An additional optical path was used to record the retinal images of the spot after reflection in the retina and double-pass through the optical media. The best visual acuity was obtained at different defocus locations corresponding to the chromatic difference between green and infrared. Although, there was some individual variability, visual acuity was found to be similar both in visible and infrared. The use of two-photon infrared vision may have some potential applications for vision in those cases were the optical media is opaque to visible wavelengths while keeping some transparency in the infrared.

  1. One- and two-photon absorption of highly conjugated multiporphyrin systems in the two-photon Soret transition region

    NASA Astrophysics Data System (ADS)

    Fisher, Jonathan A. N.; Susumu, Kimihiro; Therien, Michael J.; Yodh, Arjun G.

    2009-04-01

    This study presents a detailed investigation of near-infrared one- and two-photon absorption (TPA) in a series of highly conjugated (porphinato)zinc(II) compounds. The chromophores interrogated include meso-to-meso ethyne-bridged (porphinato)zinc(II) oligomers (PZnn species), (porphinato)zinc(II)-spacer-(porphinato)zinc(II) (PZn-Sp-PZn) complexes, PZnn structures featuring terminal electron-releasing and -withdrawing substituents, related conjugated arrays in which electron-rich and -poor PZn units alternate, and benchmark PZn monomers. Broadband TPA cross-section measurements were performed ratiometrically using fluorescein as a reference. Superficially, the measurements indicate very large TPA cross-sections (up to ˜104GM; 1GM =1×10-50cm4sphoton-1) in the two-photon Soret (or B-band) resonance region. However, a more careful analysis of fluorescence as a function of incident photon flux suggests that significant one-photon absorption is present in the same spectral region for all compounds in the series. TPA cross-sections are extracted for the first time for some of these compounds using a model that includes both one-photon absorption and TPA contributions. Resultant TPA cross-sections are ˜10GM. The findings suggest that large TPA cross-sections reported in the Soret resonance region of similar compounds might contain significant contributions from one-photon absorption processes.

  2. Time-Resolved Measurement of Interatomic Coulombic Decay Induced by Two-Photon Double Excitation of Ne2

    NASA Astrophysics Data System (ADS)

    Takanashi, T.; Golubev, N. V.; Callegari, C.; Fukuzawa, H.; Motomura, K.; Iablonskyi, D.; Kumagai, Y.; Mondal, S.; Tachibana, T.; Nagaya, K.; Nishiyama, T.; Matsunami, K.; Johnsson, P.; Piseri, P.; Sansone, G.; Dubrouil, A.; Reduzzi, M.; Carpeggiani, P.; Vozzi, C.; Devetta, M.; Negro, M.; Faccialà, D.; Calegari, F.; Trabattoni, A.; Castrovilli, M. C.; Ovcharenko, Y.; Mudrich, M.; Stienkemeier, F.; Coreno, M.; Alagia, M.; Schütte, B.; Berrah, N.; Plekan, O.; Finetti, P.; Spezzani, C.; Ferrari, E.; Allaria, E.; Penco, G.; Serpico, C.; De Ninno, G.; Diviacco, B.; Di Mitri, S.; Giannessi, L.; Jabbari, G.; Prince, K. C.; Cederbaum, L. S.; Demekhin, Ph. V.; Kuleff, A. I.; Ueda, K.

    2017-01-01

    The hitherto unexplored two-photon doubly excited states [Ne*(2 p-13 s )]2 were experimentally identified using the seeded, fully coherent, intense extreme ultraviolet free-electron laser FERMI. These states undergo ultrafast interatomic Coulombic decay (ICD), which predominantly produces singly ionized dimers. In order to obtain the rate of ICD, the resulting yield of Ne2+ ions was recorded as a function of delay between the extreme ultraviolet pump and UV probe laser pulses. The extracted lifetimes of the long-lived doubly excited states, 390 (-130 /+450 ) fs , and of the short-lived ones, less than 150 fs, are in good agreement with ab initio quantum mechanical calculations.

  3. Fluorescent Pluronic nanodots for in vivo two-photon imaging.

    PubMed

    Maurin, Mathieu; Vurth, Laeticia; Vial, Jean-Claude; Baldeck, Patrice; Marder, Seth R; Van der Sanden, Boudewijn; Stephan, Olivier

    2009-06-10

    We report the synthesis of new nanosized fluorescent probes based on bio-compatible polyethylene-polypropylene glycol (Pluronic) materials. In aqueous solution, mini-emulsification of Pluronic with a high fluorescent di-stryl benzene-modified derivative, exhibiting a two-photon absorption cross section as high as 2500 Goeppert-Mayer units at 800 nm, leads to nanoparticles exhibiting a hydrodynamic radius below 100 nm. We have demonstrated that these new probes with luminescence located in the spectral region of interest for bio-imaging (the yellow part of the visible spectrum) allow deep (500 microm) bio-imaging of the mice brain vasculature. The dose injected during our experiments is ten times lower when compared to the classical commercial rhodamine-B isothicyanate-Dextran system but gives similar results to homogeneous blood plasma staining. The mean fluorescent signal intensity stayed constant during more than 1 h.

  4. Fluorescent Pluronic nanodots for in vivo two-photon imaging

    NASA Astrophysics Data System (ADS)

    Maurin, Mathieu; Vurth, Laeticia; Vial, Jean-Claude; Baldeck, Patrice; Marder, Seth R.; Sanden, Boudewijn Van der; Stephan, Olivier

    2009-06-01

    We report the synthesis of new nanosized fluorescent probes based on bio-compatible polyethylene-polypropylene glycol (Pluronic) materials. In aqueous solution, mini-emulsification of Pluronic with a high fluorescent di-stryl benzene-modified derivative, exhibiting a two-photon absorption cross section as high as 2500 Goeppert-Mayer units at 800 nm, leads to nanoparticles exhibiting a hydrodynamic radius below 100 nm. We have demonstrated that these new probes with luminescence located in the spectral region of interest for bio-imaging (the yellow part of the visible spectrum) allow deep (500 µm) bio-imaging of the mice brain vasculature. The dose injected during our experiments is ten times lower when compared to the classical commercial rhodamine-B isothicyanate-Dextran system but gives similar results to homogeneous blood plasma staining. The mean fluorescent signal intensity stayed constant during more than 1 h.

  5. High contrast two-photon imaging of fingermarks

    PubMed Central

    Stoltzfus, Caleb R.; Rebane, Aleksander

    2016-01-01

    Optically-acquired fingermarks are widely used as evidence across law enforcement agencies as well as in the courts of law. A common technique for visualizing latent fingermarks on nonporous surfaces consists of cyanoacrylate fuming of the fingerprint material, followed by impregnation with a fluorescent dye, which under ultra violet (UV) illumination makes the fingermarks visible and thus accessible for digital recording. However, there exist critical circumstances, when the image quality is compromised due to high background scattering, high auto-fluorescence of the substrate material, or other detrimental photo-physical and photo-chemical effects such as light-induced damage to the sample. Here we present a novel near-infrared (NIR), two-photon induced fluorescence imaging modality, which significantly enhances the quality of the fingermark images, especially when obtained from highly reflective and/or scattering surfaces, while at the same time reducing photo-damage to sensitive forensic samples. PMID:27053515

  6. Two-photon fluorescence stereomicroscopy with Bessel beams

    NASA Astrophysics Data System (ADS)

    Yang, Yanlong; Lei, Ming; Zheng, Juanjuan; Li, Runze; Yan, Shaohui; Yao, Baoli; Ye, Tong

    2013-02-01

    Three dimensional distributions of cells can be usually acquired by optical sectioning methods, such as multiphoton excitation and confocal fluorescence laser scanning microscopy. Though the lateral scan rates can reach up to several kHz, the relatively slow axial scan comprises the speed of real-time imaging of a volume. Here we propose a three dimensional imaging method that uses Bessel beams as excitation in multiphoton fluorescence microscopy. The extended focus of the Bessel beam allows recording a volume of cells without scanning the depth. The depth information can be retrieved by recording a pair of parallax views of the same volume. We have demonstrated the stereoscope capability on a homebuilt two-photon fluorescence microscope.

  7. Two-photon quantum walk in a multimode fiber

    PubMed Central

    Defienne, Hugo; Barbieri, Marco; Walmsley, Ian A.; Smith, Brian J.; Gigan, Sylvain

    2016-01-01

    Multiphoton propagation in connected structures—a quantum walk—offers the potential of simulating complex physical systems and provides a route to universal quantum computation. Increasing the complexity of quantum photonic networks where the walk occurs is essential for many applications. We implement a quantum walk of indistinguishable photon pairs in a multimode fiber supporting 380 modes. Using wavefront shaping, we control the propagation of the two-photon state through the fiber in which all modes are coupled. Excitation of arbitrary output modes of the system is realized by controlling classical and quantum interferences. This report demonstrates a highly multimode platform for multiphoton interference experiments and provides a powerful method to program a general high-dimensional multiport optical circuit. This work paves the way for the next generation of photonic devices for quantum simulation, computing, and communication. PMID:27152325

  8. Arbitrary-scan imaging for two-photon microscopy

    NASA Astrophysics Data System (ADS)

    Botcherby, Edward; Smith, Christopher; Booth, Martin; Juskaitis, Rimas; Wilson, Tony

    2010-02-01

    In this paper, we present details of a scanning two-photon fluorescence microscope we have built with a nearisotropic scan rate. This means that the focal spot can be scanned at high speed along any direction in the specimen, without introducing systematic aberrations. We present experimental point spread function measurements for this system using an Olympus 0.8 NA 40X water dipping objective lens that demonstrates an axial range of operation greater than 200 μm. We give details of a novel actuator device used to displace the focusing element and demonstrate axial scan responses up to 3.5 kHz. Finally, we present a bioscience application of this system to image dendritic processes that follow non-linear paths in three-dimensional space. The focal spot was scanned along one such process at 400 Hz with an axial range of more than 90 μm.

  9. Improving in vivo two photon microscopy without adaptive optics

    NASA Astrophysics Data System (ADS)

    Estrada, Gerardo

    Two photon microscopy is one of the fastest growing methods of in-vivo imaging of the brain. It has the capability of imaging structures on the scale of 1mum. At this scale the wavelength of the imaging field (usually near infra-red), is comparable to the size of the structures being imaged, which makes the use of ray optics invalid. A better understanding is needed to predict the result of introducing different media into the light path. We use Wolf's integral, which is capable of fulfilling these needs without the shortcomings of ray optics. We predict the effects of aberrating media introduced into the light path like glass cover-slips and then correct the aberration using the same method. We also create a method to predict aberrations when the interfaces of the media in the light-path are not aligned with the propagation direction of the wavefront.

  10. Clinical multiphoton tomography and clinical two-photon microendoscopy

    NASA Astrophysics Data System (ADS)

    König, Karsten; Bückle, Rainer; Weinigel, Martin; Elsner, Peter; Kaatz, Martin

    2009-02-01

    We report on applications of high-resolution clinical multiphoton tomography based on the femtosecond laser system DermaInspectTM with its flexible mirror arm in Australia, Asia, and Europe. Applications include early detection of melanoma, in situ tracing of pharmacological and cosmetical compounds including ZnO nanoparticles in the epidermis and upper dermis, the determination of the skin aging index SAAID as well as the study of the effects of anti-aging products. In addition, first clinical studies with novel rigid high-NA two-photon 1.6 mm GRIN microendoscopes have been conducted to study the effect of wound healing in chronic wounds (ulcus ulcera) as well as to perform intrabody imaging with subcellular resolution in small animals.

  11. High contrast two-photon imaging of fingermarks

    NASA Astrophysics Data System (ADS)

    Stoltzfus, Caleb R.; Rebane, Aleksander

    2016-04-01

    Optically-acquired fingermarks are widely used as evidence across law enforcement agencies as well as in the courts of law. A common technique for visualizing latent fingermarks on nonporous surfaces consists of cyanoacrylate fuming of the fingerprint material, followed by impregnation with a fluorescent dye, which under ultra violet (UV) illumination makes the fingermarks visible and thus accessible for digital recording. However, there exist critical circumstances, when the image quality is compromised due to high background scattering, high auto-fluorescence of the substrate material, or other detrimental photo-physical and photo-chemical effects such as light-induced damage to the sample. Here we present a novel near-infrared (NIR), two-photon induced fluorescence imaging modality, which significantly enhances the quality of the fingermark images, especially when obtained from highly reflective and/or scattering surfaces, while at the same time reducing photo-damage to sensitive forensic samples.

  12. On the two-photon width of the δ(980)

    NASA Astrophysics Data System (ADS)

    Narison, S.

    1986-07-01

    The two-photon width of the δ(980) is evaluated using three-point function sum rules which are able to predict accurately the anomalous π0 --> γ and non-anomalous δ --> ηπ decay rates. The prediction, though smaller than previous results based on vector meson dominance, is still higher than the present Crystal Ball data. An analysis of the three-point function with one-gluon exchange cannot support the previous successful explanation of the data within the four-quark scheme. On leave of absence from Laboratoire de Physique Mathématique, Université des Sciences et Techniques du Languedoc, Place Eugène Batailon, F-34100 Montpellier Cedez, France.

  13. Two-photon quantum walk in a multimode fiber.

    PubMed

    Defienne, Hugo; Barbieri, Marco; Walmsley, Ian A; Smith, Brian J; Gigan, Sylvain

    2016-01-01

    Multiphoton propagation in connected structures-a quantum walk-offers the potential of simulating complex physical systems and provides a route to universal quantum computation. Increasing the complexity of quantum photonic networks where the walk occurs is essential for many applications. We implement a quantum walk of indistinguishable photon pairs in a multimode fiber supporting 380 modes. Using wavefront shaping, we control the propagation of the two-photon state through the fiber in which all modes are coupled. Excitation of arbitrary output modes of the system is realized by controlling classical and quantum interferences. This report demonstrates a highly multimode platform for multiphoton interference experiments and provides a powerful method to program a general high-dimensional multiport optical circuit. This work paves the way for the next generation of photonic devices for quantum simulation, computing, and communication.

  14. High contrast two-photon imaging of fingermarks.

    PubMed

    Stoltzfus, Caleb R; Rebane, Aleksander

    2016-04-07

    Optically-acquired fingermarks are widely used as evidence across law enforcement agencies as well as in the courts of law. A common technique for visualizing latent fingermarks on nonporous surfaces consists of cyanoacrylate fuming of the fingerprint material, followed by impregnation with a fluorescent dye, which under ultra violet (UV) illumination makes the fingermarks visible and thus accessible for digital recording. However, there exist critical circumstances, when the image quality is compromised due to high background scattering, high auto-fluorescence of the substrate material, or other detrimental photo-physical and photo-chemical effects such as light-induced damage to the sample. Here we present a novel near-infrared (NIR), two-photon induced fluorescence imaging modality, which significantly enhances the quality of the fingermark images, especially when obtained from highly reflective and/or scattering surfaces, while at the same time reducing photo-damage to sensitive forensic samples.

  15. Two-photon excited UV fluorescence for protein crystal detection

    SciTech Connect

    Madden, Jeremy T.; DeWalt, Emma L.; Simpson, Garth J.

    2011-10-01

    Complementary measurements using SONICC and TPE-UVF allow the sensitive and selective detection of protein crystals. Two-photon excited ultraviolet fluorescence (TPE-UVF) microscopy is explored for sensitive protein-crystal detection as a complement to second-order nonlinear optical imaging of chiral crystals (SONICC). Like conventional ultraviolet fluorescence (UVF), TPE-UVF generates image contrast based on the intrinsic fluorescence of aromatic residues, generally producing higher fluorescence emission within crystals than the mother liquor by nature of the higher local protein concentration. However, TPE-UVF has several advantages over conventional UVF, including (i) insensitivity to optical scattering, allowing imaging in turbid matrices, (ii) direct compatibility with conventional optical plates and windows by using visible light for excitation, (iii) elimination of potentially damaging out-of-plane UV excitation, (iv) improved signal to noise through background reduction from out-of-plane excitation and (v) relatively simple integration into instrumentation developed for SONICC.

  16. Measurement of two-photon exchange effects in CLAS

    NASA Astrophysics Data System (ADS)

    Rimal, Dipak; Raue, Brian; Adikaram, Dasuni; Weinstein, Lawrence

    2014-03-01

    There is a significant discrepancy between the Rosenbluth and the polarization transfer measurements of the proton's electric to magnetic form factor ratio GEp/GEp. One possible explanation of this discrepancy is the contribution from two-photon exchange (TPE) effects, which are not typically accounted for in standard radiative corrections. The ratio of positron-proton to electron-proton elastic scattering cross sections, R =σ/(e+ p) σ (e- p) , provides a model independent measurement of the TPE contribution to elastic electron-proton scattering. We measured this ratio at Jefferson Lab using a mixed electron-positron beam. Both electrons and positrons were elastically scattered from a liquid hydrogen target. The resulting scattered particles were detected in CLAS. The experimental details and results will be discussed. U.S. Dept. of Energy.

  17. Two-photon exchange effect studied with neural networks

    SciTech Connect

    Graczyk, Krzysztof M.

    2011-09-15

    An approach to the extraction of the two-photon exchange (TPE) correction from elastic ep scattering data is presented. The cross-section, polarization transfer (PT), and charge asymmetry data are considered. It is assumed that the TPE correction to the PT data is negligible. The form factors and TPE correcting term are given by one multidimensional function approximated by the feedforward neural network (NN). To find a model-independent approximation, the Bayesian framework for the NNs is adapted. A large number of different parametrizations is considered. The most optimal model is indicated by the Bayesian algorithm. The obtained fit of the TPE correction behaves linearly in {epsilon} but it has a nontrivial Q{sup 2} dependence. A strong dependence of the TPE fit on the choice of parametrization is observed.

  18. Superparamagnetic microrobots: fabrication by two-photon polymerization and biocompatibility.

    PubMed

    Suter, Marcel; Zhang, Li; Siringil, Erdem C; Peters, Christian; Luehmann, Tessa; Ergeneman, Olgac; Peyer, Kathrin E; Nelson, Bradley J; Hierold, Christofer

    2013-12-01

    This work presents the fabrication and controlled actuation of swimming microrobots made of a magnetic polymer composite (MPC) consisting of 11-nm-diameter magnetite (Fe3O4) nanoparticles and photocurable resin (SU-8). Two-photon polymerization (TPP) is used to fabricate the magnetic microstructures. The material properties and the cytotoxicity of the MPC with different nanoparticle concentrations are characterized. The live/dead staining tests indicate that MPC samples with varied concentrations, up to 10 vol.%, have negligible cytotoxicity after 24 h incubation. Fabrication parameters of MPC with up to 4 vol.% were investigated. We demonstrate that the helical microdevices made of 2 vol.% MPC were capable of performing corkscrew motion in water applying weak uniform rotating magnetic fields.

  19. Two-photon quantum interference for an undergraduate lab

    NASA Astrophysics Data System (ADS)

    Ourjoumtsev, A.; Dheur, M.-C.; Avignon, T.; Jacubowiez, L.

    2015-11-01

    We present a simple setup allowing undergraduate students to reproduce the Hong-Ou-Mandel experiment during a half-day labwork session and observe the coalescence of two indistinguishable photons merging on a balanced beamsplitter. This two-photon interference effect, fundamentally related to the bosonic character of the photons, is commonly used in the fields of quantum communication and computing to test the indistinguishability of two single-photon wavepackets. The setup makes use of very few optical elements and requires little alignement that can be performed by students themselves. It allows them to gather essential experimental skills related to parametric crystals, fibre optics and single-photon detection, and to transpose abstract concepts of quantum physics to a hands-on experiment in the lab.

  20. Anomalous two-photon spectral features in warm rubidium vapor

    NASA Astrophysics Data System (ADS)

    Perrella, C.; Light, P. S.; Milburn, T. J.; Kielpinski, D.; Stace, T. M.; Luiten, A. N.

    2016-09-01

    We report observation of anomalous fluorescence spectral features in the environs of a two-photon transition in a rubidium vapor when excited with two different wavelength lasers that are both counterpropagating through the vapor. These features are characterized by an unusual trade-off between the detunings of the driving fields. Three different hypothetical processes are presented to explain the observed spectra: a simultaneous three-atom and four-photon collision, a four-photon excitation involving a light field produced via amplified spontaneous emission, and population pumping perturbing the expected steady-state spectra. Numerical modeling of each hypothetical process is presented, supporting the population pumping process as the most plausible mechanism.

  1. Two-photon transition form factor of c ¯ quarkonia

    NASA Astrophysics Data System (ADS)

    Chen, Jing; Ding, Minghui; Chang, Lei; Liu, Yu-xin

    2017-01-01

    The two-photon transition of c ¯c quarkonia are studied within a covariant approach based on the consistent truncation scheme of the quantum chromodynamics Dyson-Schwinger equation for the quark propagator and the Bethe-Salpeter equation for the mesons. We find the decay widths of ηc→γ γ and χc 0 ,2→γ γ in good agreement with experimental data. The obtained transition form factor of ηc→γ γ* for a wide range of spacelike photon-momentum-transfer squared is also in agreement with the experimental findings of the BABAR experiment. As a by-product, the decay widths of ηb,χb 0 ,2→γ γ and the transition form factor of ηb,χc 0 ,b 0→γ γ* are predicted, which await experimental testing.

  2. Two-photon fluorescence microscopy of corneal riboflavin absorption.

    PubMed

    Gore, Daniel M; Margineanu, Anca; French, Paul; O'Brart, David; Dunsby, Chris; Allan, Bruce D

    2014-04-17

    To correct for attenuation in two-photon fluorescence (TPF) measurements of riboflavin absorption in porcine corneas. Two-photon fluorescence imaging of riboflavin was performed using excitation at a wavelength of 890 nm, with fluorescence signal detected between 525 and 650 nm. TPF signal attenuation was demonstrated by imaging from either side of a uniformly soaked corneoscleral button. To overcome this attenuation, a reservoir of dextran-free 0.1% wt/vol riboflavin 5'-monophosphate in saline and hydroxypropyl methylcellulose (HPMC) was placed on top of porcine corneas (globe intact-epithelium removed). TPF imaging was performed through this reservoir with image stacks acquired at 10-μm steps through the cornea repeated at regular intervals for up to 60 minutes. A novel correction method was applied to achieve corneal riboflavin concentration measurements in whole eyes (n = 4). Significant attenuation of the TPF signal was observed in all eyes, with the signal decreasing approximately linearly with depth in uniformly soaked tissue. Cross-sectional TPF images taken of excised corneal strips confirmed the tissue was uniformly soaked so that the decrease in signal was not due to spatial variations in riboflavin concentration. After correcting for signal attenuation, we observed increased riboflavin concentrations with longer soak duration, with the mean (standard deviation) maximum tissue concentration recorded at 0.094% (± 0.001) wt/vol [1.36 mg/mL]. Uniform riboflavin absorption was achieved after a minimum 50 minutes. Following a standard corneal cross-linking soak of 30 minutes, a mean stromal concentration of 0.086% (± 0.001) wt/vol [1.25 mg/mL] was achieved at a depth of 300 μm. The accuracy of TPF measurements of corneal riboflavin absorption can be increased by applying a correction for depth-related signal attenuation.

  3. Two-photon patterning of optical waveguides in flexible polymers

    NASA Astrophysics Data System (ADS)

    Bichler, Sabine; Feldbacher, Sonja; Woods, Rachel; Satzinger, Valentin; Schmidt, Volker; Jakopic, Georg; Langer, Gregor; Kern, Wolfgang

    2009-08-01

    Over the last few years two-photon based photo-processes have become an important method to generate 3D microstructures in organic materials without the use of masks and molds. The present work deals with the fabrication of optical waveguides in a flexible polysiloxane matrix for data transmission on printed circuit boards (PCB). In the developed system the waveguide core is formed by two-photon induced photo polymerization (TPIP) of selected monomers, which are dissolved in a silicone matrix. Through the photo-induced polymerization an interpenetrating network is generated, resulting in a refractive index change between the illuminated waveguide cladding and the illuminated core material. Because of the optical transparency, flexibility, chemical and thermal stability polysiloxanes were chosen as optical matrix material. Different types of phenyl methacrylates with a high refractive index were used as monomers. In order to obtain a high contrast in refractive index, the monomers were removed from non-illuminated regions in a vacuum process after laser exposure. The written optical waveguides were evidenced by phase contrast microscopy, revealing an excellent structuring behaviour of the developed material. Optical techniques e.g. cut-back measurements and light extraction tests were applied to characterize the inscribed waveguide structures and to detect the resulting optical loss. To determine the refractive index change upon UV-irradiation spectroscopic ellipsometry was applied. Thus, a difference of Δn=0.02 between the non-illuminated cladding and the illuminated core material was detected. Further, prototypes of optical interconnects on PCBs were fabricated by inscription of a waveguide bundle between a mounted laser and photo diode, resulting in the desired increase of the transmitted photocurrent after TPA structuring. In conclusion, the obtained results demonstrate that fully flexible optical interconnects are accessible by the developed process.

  4. A precise measurement of the two-photon exchange effect

    NASA Astrophysics Data System (ADS)

    Moteabbed, Maryam

    The two-photon exchange phenomenon is believed to be responsible for the discrepancy observed between the ratio of proton electric and magnetic form factors, measured by the Rosenbluth and polarization transfer methods. This disagreement is about a factor of three at Q 2 of 5.6 GeV2. The precise knowledge of the proton form factors is of critical importance in understanding the structure of this nucleon. The theoretical models that estimate the size of the two-photon exchange (TPE) radiative correction are poorly constrained. This factor was found to be directly measurable by taking the ratio of the electron-proton and positron-proton elastic scattering cross sections, as the TPE effect changes sign with respect to the charge of the incident particle. A test run of a modified beamline has been conducted with the CEBAF Large Acceptance Spectrometer (CLAS) at Thomas Jefferson National Accelerator Facility. This test run demonstrated the feasibility of producing a mixed electron/positron beam of good quality. Extensive simulations performed prior to the run were used to reduce the background rate that limits the production luminosity. A 3.3 GeV primary electron beam was used that resulted in an average secondary lepton beam of 1 GeV. As a result, the elastic scattering data of both lepton types were obtained at scattering angles up to 40 degrees for Q2 up to 1.5 GeV2. The cross section ratio displayed an epsilon dependence that was Q2 dependent at smaller Q2 limits. The magnitude of the average ratio as a function of epsilon was consistent with the previous measurements, and the elastic (Blunden) model to within the experimental uncertainties. Ultimately, higher luminosity is needed to extend the data range to lower epsilon where the TPE effect is predicted to be largest.

  5. Classes of two-photon states defined by linear interactions and destructive two-photon quantum interference in a single mode

    NASA Astrophysics Data System (ADS)

    Lund, A. P.

    2015-11-01

    We describe a two-photon quantum interference effect which differs from the Hong-Ou-Mandel effect in that the destructive quantum inference occurs on a component of the state where two photons are in a single output mode while maintaining the two-photon events in the alternative mode. This effect is manifestly nonclassical but requires more sophisticated technology to observe than the Hong-Ou-Mandel effect. The theory outlined in this paper can also be used to classify two-photon states into classes which are related by the ability to transform the states within the class by using only linear optical interactions. This theory shows that there is an infinite number of these classes of two photon states when there are two or more modes which can support the photons.

  6. A Dipolar Anthracene Dye: Synthesis, Optical Properties and Two-photon Tissue Imaging.

    PubMed

    Moon, Hyunsoo; Jun, Yong Woong; Kim, Dokyoung; Ryu, Hye Gun; Wang, Taejun; Kim, Ki Hean; Huh, Youngbuhm; Jung, Junyang; Ahn, Kyo Han

    2016-09-20

    Two-photon microscopy is a powerful tool for studying biological systems. In search of novel two-photon absorbing dyes for bioimaging, we synthesized a new anthracene-based dipolar dye (anthradan) and evaluated its two-photon absorbing and imaging properties. The new anthradan, 9,10-bis(o-dimethoxy-phenyl)-anthradan, absorbs and emits at longer wavelengths than acedan, a well-known two-photon absorbing dye. It is also stable under two-photon excitation conditions and biocompatible, and thus used for two-photon imaging of mouse organ tissues to show bright, near-red fluorescence along with negligible autofluorescence. Such an anthradan thus holds promise as a new class of two-photon absorbing dyes for the development of fluorescent probes and tags for biological systems. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Resonantly enhanced selective photochemical etching of GaN

    NASA Astrophysics Data System (ADS)

    Trichas, E.; Kayambaki, M.; Iliopoulos, E.; Pelekanos, N. T.; Savvidis, P. G.

    2009-04-01

    Wavelength dependent photochemical etching of GaN films reveals a strong resonant enhancement of the photocurrent at the GaN gap, in close agreement with the excitonic absorption profile of GaN. The corresponding etching rate of GaN strongly correlates with the measured photocurrent. No photocurrent, nor etching is observed for AlGaN films under same excitation conditions. The method could pave the way to the development of truly selective etching of GaN on AlGaN for the fabrication of nitride based optoelectronic devices.

  8. Two-Photon Ghost Image and Interference-Diffraction

    NASA Technical Reports Server (NTRS)

    Shih, Y. H.; Sergienko, A. V.; Pittman, T. B.; Strekalov, D. V.; Klyshko, D. N.

    1996-01-01

    One of the most surprising consequences of quantum mechanics is entanglement of two or more distance particles. The two-particle entangled state was mathematically formulated by Schrodinger. Based on this unusual quantum behavior, EPR defined their 'physical reality' and then asked the question: 'Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?' One may not appreciate EPR's criterion of physical reality and insist that 'no elementary quantum phenomenon is a phenomenon until it is a recorded phenomenon'. Optical spontaneous parametric down conversion (SPDC) is the most effective mechanism to generate an EPR type entangled two-photon state. In SPDC, an optical beam, called the pump, is incident on a birefringent crystal. The pump is intense enough so that nonlinear effects lead to the conversion of pump photons into pairs of photons, historically called signal and idler. Technically, the SPDC is said to be type-1 or type-2, depending on whether the signal and idler beams have parallel or orthogonal polarization. The SPDC conversion efficiency is typically on the order of 10(exp -9) to 10(exp -11), depending on the SPDC nonlinear material. The signal and idler intensities are extremely low, only single photon detection devices can register them. The quantum entanglement nature of SPDC has been demonstrated in EPR-Bohm experiments and Bell's inequality measurements. The following two experiments were recently performed in our laboratory, which are more closely related to the original 1935 EPR gedankenezperiment. The first experiment is a two-photon optical imaging type experiment, which has been named 'ghost image' by the physics community. The signal and idler beams of SPDC are sent in different directions, so that the detection of the signal and idler photons can be performed by two distant photon counting detectors. An aperture object (mask) is placed in front of the signal photon detector and illuminated by the signal beam through a

  9. Resonant two-photon ionization spectroscopy of jet-cooled tantalum carbide, TaC.

    PubMed

    Krechkivska, Olha; Morse, Michael D

    2010-08-07

    The optical spectrum of diatomic TaC has been investigated for the first time, with transitions recorded in the range from 17,850 to 20,000 cm(-1). Six bands were rotationally resolved and analyzed to obtain ground and excited state parameters, including band origins, upper and lower state rotational constants and bond lengths, Fermi contact parameter b(F) for the ground state, and lambda doubling parameters for the excited states. The ground state of TaC was found to be X (2)Sigma(+), originating from the 1sigma(2)2sigma(2)1pi(4)3sigma(1) electronic configuration, in which only the valence orbitals arising from the Ta(5d+6s) and C(2s+2p) orbitals are listed. All of the rotationally resolved and analyzed bands were found to originate from the ground state, giving B(0)"=0.489 683(83) cm(-1), r(0)"=1.749 01(15) A, and b(F)"=0.131 20(36) cm(-1) (1sigma error limits) for (181)Ta (12)C. Comparison of the Fermi contact parameter to the atomic value shows that the 3sigma orbital is approximately 75% Ta 6s in character. The other group 5 transition metal carbides, VC and NbC, have long been known to have 1sigma(2)2sigma(2)1pi(4)1delta(1), (2)Delta ground states, with low-lying 1sigma(2)2sigma(2)1pi(4)3sigma(1), (2)Sigma(+) excited states. The emergence of a different ground state in TaC, as compared to VC and NbC, is due to the relativistic stabilization of the 6s orbital in Ta. This lowers the energy of the 6s-like 3sigma orbital in TaC, causing the 1sigma(2)2sigma(2)1pi(4)3sigma(1), (2)Sigma(+) state to fall below the 1sigma(2)2sigma(2)1pi(4)1delta(1), (2)Delta state.

  10. Two-photon absorption spectroscopy of stilbene and phenanthrene: Excited-state analysis and comparison with ethylene and toluene

    NASA Astrophysics Data System (ADS)

    de Wergifosse, Marc; Elles, Christopher G.; Krylov, Anna I.

    2017-05-01

    Two-photon absorption (2PA) spectra of several prototypical molecules (ethylene, toluene, trans- and cis-stilbene, and phenanthrene) are computed using the equation-of-motion coupled-cluster method with single and double substitutions. The states giving rise to the largest 2PA cross sections are analyzed in terms of their orbital character and symmetry-based selection rules. The brightest 2PA transitions correspond to Rydberg-like states from fully symmetric irreducible representations. Symmetry selection rules dictate that totally symmetric transitions typically have the largest 2PA cross sections for an orientationally averaged sample when there is no resonance enhancement via one-photon accessible intermediate states. Transition dipole arguments suggest that the strongest transitions also involve the most delocalized orbitals, including Rydberg states, for which the relative transition intensities can be rationalized in terms of atomic selection rules. Analysis of the 2PA transitions provides a foundation for predicting relative 2PA cross sections of conjugated molecules based on simple symmetry and molecular orbital arguments.

  11. Two-Photon Absorption in Conjugated Energetic Molecules.

    PubMed

    Bjorgaard, Josiah A; Sifain, Andrew E; Nelson, Tammie; Myers, Thomas W; Veauthier, Jacqueline M; Chavez, David E; Scharff, R Jason; Tretiak, Sergei

    2016-07-07

    Time-dependent density functional theory (TD-DFT) was used to investigate the relationship between molecular structure and the one- and two-photon absorption (OPA and TPA, respectively) properties of novel and recently synthesized conjugated energetic molecules (CEMs). The molecular structures of CEMs can be strategically altered to influence the heat of formation and oxygen balance, two factors that can contribute to the sensitivity and strength of an explosive material. OPA and TPA are sensitive to changes in molecular structure as well, influencing the optical range of excitation. We found calculated vertical excitation energies to be in good agreement with experiment for most molecules. Peak TPA intensities were found to be significant and on the order of 10(2) GM. Natural transition orbitals for essential electronic states defining TPA peaks of relatively large intensity were used to examine the character of relevant transitions. Modification of molecular substituents, such as additional oxygen or other functional groups, produces significant changes in electronic structure, OPA, and TPA and improves oxygen balance. The results show that certain molecules are apt to undergo nonlinear absorption, opening the possibility for controlled, direct optical initiation of CEMs through photochemical pathways.

  12. Two-photon absorption in conjugated energetic molecule

    DOE PAGES

    Bjorgaard, Josiah August; Sifain, Andrew; Nelson, Tammie Renee; ...

    2016-06-03

    Time-dependent density functional theory (TD-DFT) is used to investigate the relationship between molecular structure and one- and two-photon absorption (OPA and TPA, respectively) properties in novel and recently synthesized conjugated energetic molecules (CEMs). The molecular structure of CEMs can be strategically altered to influence the heat of formation and oxygen balance, two factors that can contribute to the sensitivity and strength of an explosive material. OPA and TPA are sensitive to changes in molecular structure as well, influencing optical range of excitation. We find calculated vertical excitation energies in good agreement with experiment for most molecules. Peak TPA intensities aremore » significant and on the order of 102 GM. Natural transition orbitals for essential electronic states defining TPA peaks of relatively large intensity to examine the character of relevant transitions. Minor modification of molecular substituents, such as additional oxygen and other functional groups, produces significant changes in electronic structure, OPA, TPA, and improves the oxygen balance. Results show that select molecules are apt to nonlinear absorption, opening the possibility for controlled, direct optical initiation of CEMs through photochemical pathways.« less

  13. Two-photon autofluorescence spectroscopy of oral mucosa tissue

    NASA Astrophysics Data System (ADS)

    Edward, Kert; Shilagard, Tuya; Qiu, Suimin; Vargas, Gracie

    2011-03-01

    The survival rate for individuals diagnosed with oral cancer is correlated with the stage of detection. Thus the development of novel techniques for the earliest possible detection of malignancies is of critical importance. Single photon (1P) autofluorescence spectroscopy has proven to be a powerful diagnostic tool in this regard, but 2P (two photon) spectroscopy remains essentially unexplored. In this investigation, a spectroscopic system was incorporated into a custom-built 2P laser scanning microscope. Oral cancer was induced in the buccal pouch of Syrian Golden hamsters by tri-weekly topical application of 9,10-dimethyl-1,2-benzanthracene (DMBA).Three separated sites where investigated in each hamster at four excitation wavelengths from 780 nm to 890 nm. A Total of 8 hamsters were investigated (4 normal and 4 DMBA treated). All investigated sites were imaged via 2p imaging, marked for biopsy, processed for histology and H&E staining, and graded by a pathologist. The in vivo emission spectrum for normal, mild/high grade dysplasia and squamous cell carcinoma is presented. It is shown that the hamsters with various stages of dysplasia are characterized by spectral differences as a function of depth and excitation wavelength, compared to normal hamsters.

  14. Two-Photon-Exchange Effects and Δ (1232) Deformation

    NASA Astrophysics Data System (ADS)

    Zhou, Hai-Qing; Yang, Shin Nan

    The two-photon-exchange (TPE) contribution in ep to epπ 0 with W = MΔ and small Q2 is calculated and its corrections to the ratios of electromagnetic transition form factors REM = E1 + (3/2)/M1 + (3/2) and RSM = S1 + (3/2)/M1 + (3/2), are analysed. A simple hadronic model is used to estimate the TPE amplitude. Two phenomenological models, MAID2007 and SAID, are used to approximate the full ep to epπ 0 cross sections which contain both the TPE and the one-photon-exchange (OPE) contributions. The genuine OPE amplitude is then extracted from an integral equation by iteration. We find that the TPE contribution is not sensitive to whether MAID or SAID is used as input in the region with Q2 < 2 GeV2. It gives small correction to REM while for RSM, the correction is about -10% at small ɛ and about 1% at large ɛ for Q2 ≈ 2.5 GeV2. The large correction from TPE at small ɛ must be included in the analysis to get a reliable extraction of RSM.

  15. Two-Photon-Absorption Scheme for Optical Beam Tracking

    NASA Technical Reports Server (NTRS)

    Ortiz, Gerardo G.; Farr, William H.

    2011-01-01

    A new optical beam tracking approach for free-space optical communication links using two-photon absorption (TPA) in a high-bandgap detector material was demonstrated. This tracking scheme is part of the canonical architecture described in the preceding article. TPA is used to track a long-wavelength transmit laser while direct absorption on the same sensor simultaneously tracks a shorter-wavelength beacon. The TPA responsivity was measured for silicon using a PIN photodiode at a laser beacon wavelength of 1,550 nm. As expected, the responsivity shows a linear dependence with incident power level. The responsivity slope is 4.5 x 10(exp -7) A/W2. Also, optical beam spots from the 1,550-nm laser beacon were characterized on commercial charge coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) imagers with as little as 13.7 microWatts of optical power (see figure). This new tracker technology offers an innovative solution to reduce system complexity, improve transmit/receive isolation, improve optical efficiency, improve signal-to-noise ratio (SNR), and reduce cost for free-space optical communications transceivers.

  16. Photodynamic therapy by nonresonant two-photon excitation

    NASA Astrophysics Data System (ADS)

    Koenig, Karsten; Riemann, Iris; Fischer, Peter

    1999-07-01

    Intracellular photodynamic reactions by nonlinear excitation of porphyrin photosensitizers have been induced using near infrared ultrashort laser pulses at 200 fs pulse width, 80 MHz pulse repetition rate and 2 mW mean laser power. In particular, a highly focused 780 nm pulsed laser scanning beam was employed at a frame rate of 1/16 s-1 (60 microsecond(s) pixel dwell time) to expose Photofrin-labeled and aminolevulinic acid (ALA)-labeled Chinese hamster ovary cells. Intracellular accumulation and photobleaching of the fluorescent photosensitizers protoporphyrin IX and Photofrin have been studied by non-resonant two-photon fluorescence excitation. Subsequent scanning of the sensitizer-labeled cells resulted in reduced cloning efficiency of 50% and 0% after about 13 scans (approximately equals 10 mJ) and 50 scans, respectively, in the case of Photofrin accumulation (5 (mu) g/ml) and after about 24 scans and 100 scans in the case of ALA administration (1.5 mg/ml). Live/dead assays revealed the loss of vitality of most of cells after 50 scans for Photofrin-labeled cells and 100 scans for ALA-labeled cells. Sensitizer-free control cells could be scanned more than 250 times (1.1 h) without impact on the reproduction behavior, morphology, and vitality.

  17. Two-photon polymerization for fabrication of biomedical devices

    NASA Astrophysics Data System (ADS)

    Ovsianikov, Aleksandr; Doraiswamy, Anand; Narayan, R.; Chichkov, B. N.

    2007-01-01

    Two-photon polymerization (2PP) is a novel technology which allows the fabrication of complex three-dimensional (3D) microstructures and nanostructures. The number of applications of this technology is rapidly increasing; it includes the fabrication of 3D photonic crystals [1-4], medical devices, and tissue scaffolds [5-6]. In this contribution, we discuss current applications of 2PP for microstructuring of biomedical devices used in drug delivery. While in general this sector is still dominated by oral administration of drugs, precise dosing, safety, and convenience are being addressed by transdermal drug delivery systems. Currently, main limitations arise from low permeability of the skin. As a result, only few types of pharmacological substances can be delivered in this manner [7]. Application of microneedle arrays, whose function is to help overcome the barrier presented by the epidermis layer of the skin, provides a very promising solution. Using 2PP we have fabricated arrays of hollow microneedles with different geometries. The effect of microneedle geometry on skin penetration is examined. Our results indicate that microneedles created using 2PP technique are suitable for in vivo use, and for integration with the next generation of MEMS- and NEMS-based drug delivery devices.

  18. Improving the fidelity of two-photon absorption reference standards

    NASA Astrophysics Data System (ADS)

    de Reguardati, S.; Pahapill, J.; Rammo, M.; Rebane, A.

    2017-02-01

    Reference standards with well-defined femtosecond two-photon absorption (2PA) properties facilitate accurate measurement of nonlinear-optical spectra by bypassing tedious characterization of the photon flux. The 2PA standards are increasingly used for developing advanced multi-photon fluorescent probes and, since recently, also for probing intra- and intermolecular electrostatic interactions. We have recently reported 2PA cross section values of a set of common organic dyes in different solvents in 680-1050 nm wavelength range with estimated accuracy of 8%. In the present work, we aim at further improving the accuracy and fidelity of the absolute 2PA cross section data by comparing in a pair-wise manner the relative 2PA efficiency of nine standards with partially overlapping absorption- and fluorescence emission spectra. We measure the relative 2PA-induced fluorescence for each pair under identical excitation conditions, which allows revealing inconsistencies potentially present in the previously published data due to errors in estimating the excitation laser beam spatial- and temporal profile, pulse energy and other critical parameters. Our current measurements confirmed and in some cases improved previously reported error margins thus improving the fidelity of the reference data. We also present refined 2PA cross section data on 9-Chloroanthracene in dichloromethane.

  19. Two photon absorption in high power broad area laser diodes

    NASA Astrophysics Data System (ADS)

    Dogan, Mehmet; Michael, Christopher P.; Zheng, Yan; Zhu, Lin; Jacob, Jonah H.

    2014-03-01

    Recent advances in thermal management and improvements in fabrication and facet passivation enabled extracting unprecedented optical powers from laser diodes (LDs). However, even in the absence of thermal roll-over or catastrophic optical damage (COD), the maximum achievable power is limited by optical non-linear effects. Due to its non-linear nature, two-photon absorption (TPA) becomes one of the dominant factors that limit efficient extraction of laser power from LDs. In this paper, theoretical and experimental analysis of TPA in high-power broad area laser diodes (BALD) is presented. A phenomenological optical extraction model that incorporates TPA explains the reduction in optical extraction efficiency at high intensities in BALD bars with 100μm-wide emitters. The model includes two contributions associated with TPA: the straightforward absorption of laser photons and the subsequent single photon absorption by the holes and electrons generated by the TPA process. TPA is a fundamental limitation since it is inherent to the LD semiconductor material. Therefore scaling the LDs to high power requires designs that reduce the optical intensity by increasing the mode size.

  20. Two-photon resonant optical processes in atomic potassium

    NASA Astrophysics Data System (ADS)

    Zhang, P.-L.; Schawlow, A. L.

    1984-12-01

    Two-photon resonant four-wave and six-wave optical processes in ns 2S(1/2) (n = 7-20) states of K atoms are investigated experimentally, using 0.1-3-mJ 20-pm-linewidth 575-665-nm pulses from a dye laser pumped by a frequency-doubled Nd:YAG laser to excite K vapor at (0.47-3.55) x 10 to the 16th/cu cm in a steel heat-pipe oven at 300-380 C. The UV-range coherent lines are detected by a 1-m spectrometer, photomultiplier tube, and boxcar; and the results are presented in extensive tables and graphs and characterized in terms of a theoretical model of wave-mixing processes and parametric oscillations, based on the wave equation, atomic polarization, and phase-match conditions. About 100 lines are detected, of which 70 are identified with six-wave processes and 15 with four-wave processes. The strongest lines are found near the mP-4S transitions anad have components frequency shifted relative to the atomic transitions; these lines are attributed to parametric oscillation.

  1. Two-photon holographic optogenetics of neural circuits (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yang, Weijian; Carrillo-Reid, Luis; Peterka, Darcy S.; Yuste, Rafael

    2016-03-01

    Optical manipulation of in vivo neural circuits with cellular resolution could be important for understanding cortical function. Despite recent progress, simultaneous optogenetic activation with cellular precision has either been limited to 2D planes, or a very small numbers of neurons over a limited volume. Here we demonstrate a novel paradigm for simultaneous 3D activation using a low repetition rate pulse-amplified fiber laser system and a spatial light modulator (SLM) to project 3D holographic excitation patterns on the cortex of mice in vivo for targeted volumetric 3D photoactivation. This method is compatible with two-photon imaging, and enables the simultaneous activation of multiple cells in 3D, using red-shifted opsins, such as C1V1 or ReaChR, while simultaneously imaging GFP-based sensors such as GCaMP6. This all-optical imaging and 3D manipulation approach achieves simultaneous reading and writing of cortical activity, and should be a powerful tool for the study of neuronal circuits.

  2. Two-photon excited photoconversion of cyanine-based dyes

    NASA Astrophysics Data System (ADS)

    Kwok, Sheldon J. J.; Choi, Myunghwan; Bhayana, Brijesh; Zhang, Xueli; Ran, Chongzhao; Yun, Seok-Hyun

    2016-03-01

    The advent of phototransformable fluorescent proteins has led to significant advances in optical imaging, including the unambiguous tracking of cells over large spatiotemporal scales. However, these proteins typically require activating light in the UV-blue spectrum, which limits their in vivo applicability due to poor light penetration and associated phototoxicity on cells and tissue. We report that cyanine-based, organic dyes can be efficiently photoconverted by nonlinear excitation at the near infrared (NIR) window. Photoconversion likely involves singlet-oxygen mediated photochemical cleavage, yielding blue-shifted fluorescent products. Using SYTO62, a biocompatible and cell-permeable dye, we demonstrate photoconversion in a variety of cell lines, including depth-resolved labeling of cells in 3D culture. Two-photon photoconversion of cyanine-based dyes offer several advantages over existing photoconvertible proteins, including use of minimally toxic NIR light, labeling without need for genetic intervention, rapid kinetics, remote subsurface targeting, and long persistence of photoconverted signal. These findings are expected to be useful for applications involving rapid labeling of cells deep in tissue.

  3. Results from the OLYMPUS Two-Photon Exchange Experiment

    NASA Astrophysics Data System (ADS)

    O'Connor, Colton; Olympus Collaboration

    2017-01-01

    Measurements of the proton's electric-to-magnetic form factor ratio obtained by different methods disagree significantly in a way that depends on Q2. The OLYMPUS experiment was designed to empirically quantify two-photon exchange in lepton-proton scattering, an effect that, in some models, can fully account for this disagreement. This was achieved at the DORIS storage ring at DESY by measuring the ratio of the elastic cross-sections for positron-proton and electron-proton scattering with alternating 2.01 GeV lepton beams incident on an internal hydrogen gas target. Data were collected with an integrated luminosity of over 4.0 fb-1 using a large-acceptance toroidal spectrometer and multiple luminosity monitoring systems, allowing for precise results (<1% uncertainty) over the range of 0.6 <=Q2 <= 2.2 (GeV/ c)2. This work is supported by DOE Grant DE-FG02-94ER40818.

  4. Two-photon absorption in conjugated energetic molecule

    SciTech Connect

    Bjorgaard, Josiah August; Sifain, Andrew; Nelson, Tammie Renee; Myers, Thomas Winfield; Veauthier, Jacqueline Marie; Chavez, David E.; Scharff, Robert Jason; Tretiak, Sergei

    2016-06-03

    Time-dependent density functional theory (TD-DFT) is used to investigate the relationship between molecular structure and one- and two-photon absorption (OPA and TPA, respectively) properties in novel and recently synthesized conjugated energetic molecules (CEMs). The molecular structure of CEMs can be strategically altered to influence the heat of formation and oxygen balance, two factors that can contribute to the sensitivity and strength of an explosive material. OPA and TPA are sensitive to changes in molecular structure as well, influencing optical range of excitation. We find calculated vertical excitation energies in good agreement with experiment for most molecules. Peak TPA intensities are significant and on the order of 102 GM. Natural transition orbitals for essential electronic states defining TPA peaks of relatively large intensity to examine the character of relevant transitions. Minor modification of molecular substituents, such as additional oxygen and other functional groups, produces significant changes in electronic structure, OPA, TPA, and improves the oxygen balance. Results show that select molecules are apt to nonlinear absorption, opening the possibility for controlled, direct optical initiation of CEMs through photochemical pathways.

  5. Two-photon absorption in conjugated energetic molecule

    SciTech Connect

    Bjorgaard, Josiah August; Sifain, Andrew; Nelson, Tammie Renee; Myers, Thomas Winfield; Veauthier, Jacqueline Marie; Chavez, David E.; Scharff, Robert Jason; Tretiak, Sergei

    2016-06-03

    Time-dependent density functional theory (TD-DFT) is used to investigate the relationship between molecular structure and one- and two-photon absorption (OPA and TPA, respectively) properties in novel and recently synthesized conjugated energetic molecules (CEMs). The molecular structure of CEMs can be strategically altered to influence the heat of formation and oxygen balance, two factors that can contribute to the sensitivity and strength of an explosive material. OPA and TPA are sensitive to changes in molecular structure as well, influencing optical range of excitation. We find calculated vertical excitation energies in good agreement with experiment for most molecules. Peak TPA intensities are significant and on the order of 102 GM. Natural transition orbitals for essential electronic states defining TPA peaks of relatively large intensity to examine the character of relevant transitions. Minor modification of molecular substituents, such as additional oxygen and other functional groups, produces significant changes in electronic structure, OPA, TPA, and improves the oxygen balance. Results show that select molecules are apt to nonlinear absorption, opening the possibility for controlled, direct optical initiation of CEMs through photochemical pathways.

  6. Mobile laser lithography station for microscopic two-photon polymerization

    NASA Astrophysics Data System (ADS)

    Leinenbach, F.; Breunig, H. G.; König, K.

    2015-03-01

    We present a mobile laser lithography station for 3D structuring by microscopic two-photon polymerization. For structuring the Coherent Vitara UBB titanium:sapphire femtosecond laser is used, which has a power output of 500mW and generates pulses with a central wavelength of 810nm. The laser pulses have a tunable bandwidth from 50nm to 250nm. The pulses are temporally compressed using chirped mirrors to a minimum duration of less than 15fs at the sample. The laser power reaching the sample can be motionless controlled by a combination of a liquid crystal retarder and a polarizer within milliseconds. The sample is placed onto a microscope stage which has a movement range of 300µm in the X, Y and Z direction with an accuracy of 2nm. Sample imaging is possible with a microscope camera simultaneous to the structuring. The pulses are focused by a 40X microscope objective (1.3NA) onto the sample. To operate the lithography station, we developed a LabVIEW-based software which controls sample position, laser power and objective height and as well as the microscope camera. Furthermore, CAD data can be read and converted into sample position data. By combining all these components, a fully automatic structuring of a sample with sub-micrometer precision is possible.

  7. Two-photon excited photoconversion of cyanine-based dyes.

    PubMed

    Kwok, Sheldon J J; Choi, Myunghwan; Bhayana, Brijesh; Zhang, Xueli; Ran, Chongzhao; Yun, Seok-Hyun

    2016-03-31

    The advent of phototransformable fluorescent proteins has led to significant advances in optical imaging, including the unambiguous tracking of cells over large spatiotemporal scales. However, these proteins typically require activating light in the UV-blue spectrum, which limits their in vivo applicability due to poor light penetration and associated phototoxicity on cells and tissue. We report that cyanine-based, organic dyes can be efficiently photoconverted by nonlinear excitation at the near infrared (NIR) window. Photoconversion likely involves singlet-oxygen mediated photochemical cleavage, yielding blue-shifted fluorescent products. Using SYTO62, a biocompatible and cell-permeable dye, we demonstrate photoconversion in a variety of cell lines, including depth-resolved labeling of cells in 3D culture. Two-photon photoconversion of cyanine-based dyes offer several advantages over existing photoconvertible proteins, including use of minimally toxic NIR light, labeling without need for genetic intervention, rapid kinetics, remote subsurface targeting, and long persistence of photoconverted signal. These findings are expected to be useful for applications involving rapid labeling of cells deep in tissue.

  8. Synergistic Two-Photon Absorption Enhancement in Photosynthetic Light Harvesting

    NASA Astrophysics Data System (ADS)

    Chen, Kuo-Mei; Chen, Yu-Wei; Gao, Ting-Fong

    2012-06-01

    The grand scale fixation of solar energies into chemical substances by photosynthetic reactions of light-harvesting organisms provides Earth's other life forms a thriving environment. Scientific explorations in the past decades have unraveled the fundamental photophysical and photochemical processes in photosynthesis. Higher plants, green algae, and light-harvesting bacteria utilize organized pigment-protein complexes to harvest solar power efficiently and the resultant electronic excitations are funneled into a reaction center, where the first charge separation process takes place. Here we show experimental evidences that green algae (Chlorella vulgaris) in vivo display a synergistic two-photon absorption enhancement in their photosynthetic light harvesting. Their absorption coefficients at various wavelengths display dramatic dependence on the photon flux. This newly found phenomenon is attributed to a coherence-electronic-energy-transfer-mediated (CEETRAM) photon absorption process of light-harvesting pigment-protein complexes of green algae. Under the ambient light level, algae and higher plants can utilize this quantum mechanical mechanism to create two entangled electronic excitations adjacently in their light-harvesting networks. Concerted multiple electron transfer reactions in the reaction centers and oxygen evolving complexes can be implemented efficiently by the coherent motion of two entangled excitons from antennae to the charge separation reaction sites. To fabricate nanostructured, synthetic light-harvesting apparatus, the paramount role of the CEETRAM photon absorption mechanism should be seriously considered in the strategic guidelines.

  9. Two-photon excited photoconversion of cyanine-based dyes

    PubMed Central

    Kwok, Sheldon J. J.; Choi, Myunghwan; Bhayana, Brijesh; Zhang, Xueli; Ran, Chongzhao; Yun, Seok-Hyun

    2016-01-01

    The advent of phototransformable fluorescent proteins has led to significant advances in optical imaging, including the unambiguous tracking of cells over large spatiotemporal scales. However, these proteins typically require activating light in the UV-blue spectrum, which limits their in vivo applicability due to poor light penetration and associated phototoxicity on cells and tissue. We report that cyanine-based, organic dyes can be efficiently photoconverted by nonlinear excitation at the near infrared (NIR) window. Photoconversion likely involves singlet-oxygen mediated photochemical cleavage, yielding blue-shifted fluorescent products. Using SYTO62, a biocompatible and cell-permeable dye, we demonstrate photoconversion in a variety of cell lines, including depth-resolved labeling of cells in 3D culture. Two-photon photoconversion of cyanine-based dyes offer several advantages over existing photoconvertible proteins, including use of minimally toxic NIR light, labeling without need for genetic intervention, rapid kinetics, remote subsurface targeting, and long persistence of photoconverted signal. These findings are expected to be useful for applications involving rapid labeling of cells deep in tissue. PMID:27029524

  10. Review of two-photon exchange in electron scattering

    SciTech Connect

    J. Arrington, P. G. Blunden, W. Melnitchouk

    2011-10-01

    We review the role of two-photon exchange (TPE) in electron-hadron scattering, focusing in particular on hadronic frameworks suitable for describing the low and moderate Q^2 region relevant to most experimental studies. We discuss the effects of TPE on the extraction of nucleon form factors and their role in the resolution of the proton electric to magnetic form factor ratio puzzle. The implications of TPE on various other observables, including neutron form factors, electroproduction of resonances and pions, and nuclear form factors, are summarized. Measurements seeking to directly identify TPE effects, such as through the angular dependence of polarization measurements, nonlinear epsilon contributions to the cross sections, and via e+p to e-p cross section ratios, are also outlined. In the weak sector, we describe the role of TPE and gamma-Z interference in parity-violating electron scattering, and assess their impact on the extraction of the strange form factors of the nucleon and the weak charge of the proton.

  11. Measurement of two-photon exchange effect with CLAS

    SciTech Connect

    Raue, Brian A

    2010-08-01

    The structure of the proton is one the most important and most studied topics in nuclear physics. However, discrepant measurements of the proton's electromagnetic form factor ratio, GE/GM, seriously jeopardize a definitive understanding of the proton's structure. Measurements of GEGM using the Rosenbluth separation technique disagree with those using polarization transfer methods by about a factor of three at Q2~5.6 GeV2. It has been hypothesized that this discrepancy is due to two-photon exchange (TPE) effects that are not part of the usual radiative corrections. Theoretical corrections for the TPE effect are difficult due to the fact that a large number of excited nucleon states can contribute to the process. However, the TPE effect can be directly determined by measuring the ratio of the positron-proton to electron-proton elastic scattering cross sections, R = sigma(e+)/sigma(e-), as the TPE effect changes sign with respect to the charge of the incident particle. A brief test run of a modified beamline and the CLAS detector at Jefferson Lab has resulted in the most precise measurements of the R to date. We will present results from the test run covering Q2<0.8 GeV2 and 0.78<=epsilon<=0.97. In addition, the test run demonstrated the feasibility of producing a mixed electron/positron beam of good quality so that the measurements can be extended up to Q2~3.0 GeV2.

  12. Perturbative QCD predictions for two-photon exchange

    SciTech Connect

    Borisyuk, Dmitry; Kobushkin, Alexander

    2009-02-01

    We study two-photon exchange (TPE) in the elastic electron-nucleon scattering at high Q{sup 2} in the framework of perturbative quantum chromodynamics. The obtained TPE amplitude is of order {alpha}/{alpha}{sub s} with respect to Born approximation. Its shape and value are sensitive to the choice of nucleon wave function, thus study of TPE effects can provide important information about nucleon structure. With the wave functions based on quantum chromodynamics sum rules, TPE correction to the electron-proton cross section has a negative sign, is almost linear in {epsilon}, and grows logarithmically with Q{sup 2} up to 7% at Q{sup 2}=30 GeV{sup 2}. The results of existing hadronic calculations, taking into account just the nucleon intermediate state, can be smoothly connected with the perturbative quantum chromodynamics result near Q{sup 2}{approx}3 GeV{sup 2}. Above this point two methods disagree, which implies that the hadronic approach becomes inadequate at high Q{sup 2}. Other relevant observables, such as the electron/positron cross section ratio, are also discussed.

  13. Two-photon interference of polarization-entangled photons in a Franson interferometer.

    PubMed

    Kim, Heonoh; Lee, Sang Min; Kwon, Osung; Moon, Han Seb

    2017-07-18

    We present two-photon interference experiments with polarization-entangled photon pairs in a polarization-based Franson-type interferometer. Although the two photons do not meet at a common beamsplitter, a phase-insensitive Hong-Ou-Mandel type two-photon interference peak and dip fringes are observed, resulting from the two-photon interference effect between two indistinguishable two-photon probability amplitudes leading to a coincidence detection. A spatial quantum beating fringe is also measured for nondegenerate photon pairs in the same interferometer, although the two-photon states have no frequency entanglement. When unentangled polarization-correlated photons are used as an input state, the polarization entanglement is successfully recovered through the interferometer via delayed compensation.

  14. Dynamical modeling of pulsed two-photon interference

    NASA Astrophysics Data System (ADS)

    Fischer, Kevin A.; Müller, Kai; Lagoudakis, Konstantinos G.; Vučković, Jelena

    2016-11-01

    Single-photon sources are at the heart of quantum-optical networks, with their uniquely quantum emission and phenomenon of two-photon interference allowing for the generation and transfer of nonclassical states. Although a few analytical methods have been briefly investigated for describing pulsed single-photon sources, these methods apply only to either perfectly ideal or at least extremely idealized sources. Here, we present the first complete picture of pulsed single-photon sources by elaborating how to numerically and fully characterize non-ideal single-photon sources operating in a pulsed regime. In order to achieve this result, we make the connection between quantum Monte-Carlo simulations, experimental characterizations, and an extended form of the quantum regression theorem. We elaborate on how an ideal pulsed single-photon source is connected to its photocount distribution and its measured degree of second- and first-order optical coherence. By doing so, we provide a description of the relationship between instantaneous source correlations and the typical experimental interferometers (Hanbury-Brown and Twiss, Hong-Ou-Mandel, and Mach-Zehnder) used to characterize such sources. Then, we use these techniques to explore several prototypical quantum systems and their non-ideal behaviors. As an example numerical result, we show that for the most popular single-photon source—a resonantly excited two-level system—its error probability is directly related to its excitation pulse length. We believe that the intuition gained from these representative systems and characters can be used to interpret future results with more complicated source Hamiltonians and behaviors. Finally, we have thoroughly documented our simulation methods with contributions to the Quantum Optics Toolbox in Python in order to make our work easily accessible to other scientists and engineers.

  15. Two-photon excitation photodynamic therapy with Photofrin

    NASA Astrophysics Data System (ADS)

    Karotki, Aliaksandr; Khurana, Mamta; Lepock, James R.; Wilson, Brian C.

    2005-09-01

    Photodynamic therapy (PDT) based on simultaneous two-photon (2-γ) excitation has a potential advantage of highly targeted treatment by means of nonlinear localized photosensitizer excitation. One of the possible applications of 2-γ PDT is a treatment of exodus age-related macular degeneration where highly targeted excitation of photosensitizer in neovasculature is vital for reducing collateral damage to healthy surrounding tissue. To investigate effect of 2-γ PDT Photofrin was used as an archetypal photosensitizer. First, 2-γ absorption properties of Photofrin in the 750 - 900 nm excitation wavelength range were investigated. It was shown that above 800 nm 2-γ interaction was dominant mode of excitation. The 2-γ cross section of Photofrin was rather small and varied between 5 and 10 GM (1 GM = 10-50 cm4s/photon) in this wavelength range. Next, endothelial cells treated with Photofrin were used to model initial effect of 2-γ PDT on neovasculature. Ultrashort laser pulses provided by mode-locked Ti:sapphire laser (pulse duration at the sample 300 fs, repetition rate 90 MHz, mean laser power 10 mW, excitation wavelength 850 nm) were used for the excitation of the photosensitizer. Before 2-γ excitation of the Photofrin cells formed a single continuous sheet at the bottom of the well. The tightly focused laser light was scanned repeatedly over the cell layer. After irradiation the cell layer of the control cells stayed intact while cells treated with photofrin became clearly disrupted. The light doses required were high (6300 Jcm(-2) for ~ 50% killing), but 2-γ cytotoxicity was unequivocally demonstrated.

  16. Voltage-sensitive rhodol with enhanced two-photon brightness.

    PubMed

    Kulkarni, Rishikesh U; Kramer, Daniel J; Pourmandi, Narges; Karbasi, Kaveh; Bateup, Helen S; Miller, Evan W

    2017-03-14

    We have designed, synthesized, and applied a rhodol-based chromophore to a molecular wire-based platform for voltage sensing to achieve fast, sensitive, and bright voltage sensing using two-photon (2P) illumination. Rhodol VoltageFluor-5 (RVF5) is a voltage-sensitive dye with improved 2P cross-section for use in thick tissue or brain samples. RVF5 features a dichlororhodol core with pyrrolidyl substitution at the nitrogen center. In mammalian cells under one-photon (1P) illumination, RVF5 demonstrates high voltage sensitivity (28% ΔF/F per 100 mV) and improved photostability relative to first-generation voltage sensors. This photostability enables multisite optical recordings from neurons lacking tuberous sclerosis complex 1, Tsc1, in a mouse model of genetic epilepsy. Using RVF5, we show that Tsc1 KO neurons exhibit increased activity relative to wild-type neurons and additionally show that the proportion of active neurons in the network increases with the loss of Tsc1. The high photostability and voltage sensitivity of RVF5 is recapitulated under 2P illumination. Finally, the ability to chemically tune the 2P absorption profile through the use of rhodol scaffolds affords the unique opportunity to image neuronal voltage changes in acutely prepared mouse brain slices using 2P illumination. Stimulation of the mouse hippocampus evoked spiking activity that was readily discerned with bath-applied RVF5, demonstrating the utility of RVF5 and molecular wire-based voltage sensors with 2P-optimized fluorophores for imaging voltage in intact brain tissue.

  17. Determining the Quark Charges by One and Two Photon Processes.

    NASA Astrophysics Data System (ADS)

    Janah, Arjun

    1982-05-01

    Testable predictions are presented, which may be used to decide between the gauge theories of integer and fractionally charged quarks (icq and fcq). Two distinctive features of icq are exploited, namely (a) presence of color non-singlet components in weak and electromagnetic currents and (b) possible liberation of color non-singlet states above a threshold energy. Consequences are sought in lepton-hadron interaction processes, taking into account the known "color-suppression" effect. Single photon/weak-boson processes such as (nu)N (--->) (nu)X distinguish between icq and fcq only above color-threshold. Experimental consequences of color-liberation in the above process are obtained. It is found that the gluon-parton contribution survives color-suppression to produce a significant rise in the structure functions when color-threshold is exceeded. Two-photon processes such as e('+)e('-) (--->) e('+)e('-) + 2 jets distinguish between the two theories even below color threshold. To obtain the icq predictions for this process, one must take into account (a) the (momentum -dependent) color suppression and (b) the added contribution from pair production of charged gluons. This is done, and it is observed that: (i) in icq, the ratio R('(gamma)(gamma)(2 jet)) is not simply a number given by the quark charges; it depends on the gluon mass, on kinematics and on the particular differential cross-section considered; (ii) the deviation of icq cross-sections from the fcq values depends crucially on whether one includes "untagged" events; if this is done, the deviation is large; the charged gluon contribution is mainly responsible for this deviation; the quark contribution is smaller than naively expected. Finally, comparison is made with experimental data on e('+)e('-) (--->) e('+)e('-) + 2 jets. Here, icq is found to be in better agreement than fcq, for a broad range of gluon masses. A suitably modified equivalent photon approximation is employed.

  18. Two photon microscopy for studies of xenobiotics in human skin

    NASA Astrophysics Data System (ADS)

    Simonsson, Carl; Smedh, Maria; Jonson, Charlotte; Karlberg, Ann-Therese; Ericson, Marica B.

    2007-07-01

    For successful uptake and distribution of drugs from transdermal formulations, it is important to understand the skin barrier function. Innovative advances in modern microscopy have provided valuable tools to study the interaction between the skin and xenobiotics. Two-photon microscopy (TPM) allows non-invasive visualization of fluorescent compounds in the skin. The advantages of TPM over conventional confocal microscopy are better light penetration into highly scattering and absorbing tissue such as human skin, improved detection efficiency, limited out of focus photobleaching and reduced phototoxic effects. We present TPM as an alternative non-invasive in vitro method to study chemical penetration enhancement of fluorescent model drugs. The permeability of sulforhodamine B (SRB) through human epidermis was measured with vertical diffusion cells. The absorption was visualized using TPM after 24 h passive diffusion. We have evaluated variations in physicochemical parameters controlling dermal drug uptake induced by the penetration enhancer oleic acid according to methods previously described by Yu et al. Optical sectioning by TPM was compared with cryosectioning. Oleic acid significantly increased penetration of sulforhodamine. TPM images demonstrate a four-fold increase in the partition coefficient. In addition, a six-fold increase in the concentration gradient was found over stratum corneum. Better light penetration and detection efficiency increase maximum imaging depth in TPM compared to conventional confocal microscopy, however loss of signal due to scattering and absorption is still significant and will affect distribution profiles generated by optical sectioning. A true concentration profile cannot be established without better knowledge about signal losses in the skin.

  19. Measurement of two-photon exchange effect with CLAS

    SciTech Connect

    Raue, Brian A.

    2010-08-05

    The structure of the proton is one the most important and most studied topics in nuclear physics. However, discrepant measurements of the proton's electromagnetic form factor ratio, G{sub E}/G{sub M}, seriously jeopardize a definitive understanding of the proton's structure. Measurements of G{sub E}G{sub M} using the Rosenbluth separation technique disagree with those using polarization transfer methods by about a factor of three at Q{sup 2{approx}}5.6 GeV{sup 2}. It has been hypothesized that this discrepancy is due to two-photon exchange (TPE) effects that are not part of the usual radiative corrections. Theoretical corrections for the TPE effect are difficult due to the fact that a large number of excited nucleon states can contribute to the process. However, the TPE effect can be directly determined by measuring the ratio of the positron-proton to electron-proton elastic scattering cross sections, R = {sigma}(e{sup +})/{sigma}(e{sup -}), as the TPE effect changes sign with respect to the charge of the incident particle. A brief test run of a modified beamline and the CLAS detector at Jefferson Lab has resulted in the most precise measurements of the R to date. We will present results from the test run covering Q{sup 2}<0.8 GeV{sup 2} and 0.78{<=}{epsilon}{<=}0.97. In addition, the test run demonstrated the feasibility of producing a mixed electron/positron beam of good quality so that the measurements can be extended up to Q{sup 2{approx}}3.0 GeV{sup 2}.

  20. Reaction-based two-photon probes for mercury ions: fluorescence imaging with dual optical windows.

    PubMed

    Rao, Alla Sreenivasa; Kim, Dokyoung; Wang, Taejun; Kim, Ki Hean; Hwang, Sekyu; Ahn, Kyo Han

    2012-05-18

    For fluorescent imaging of mercury ions in living species, two-photon probes with dual optical windows are in high demand but remain unexplored. Several dithioacetals were evaluated, and a probe was found, which, upon reaction with mercury species, yielded a two-photon dye; this conversion accompanies ratiometric emission changes with a 97-nm shift, enabling fluorescent imaging of both the probe and mercury ions in cells by one- and two-photon microscopy for the first time.

  1. Two-photon decay of excited levels in hydrogen: The ambiguity of the separation of cascades and pure two-photon emission

    SciTech Connect

    Labzowsky, L.; Solovyev, D.; Plunien, G.

    2009-12-15

    The problem of the evaluation of the two-photon decay width of excited states in hydrogen is considered. Two different approaches to the evaluation of the width including cascades channels are employed: the summation of the transition probabilities for various decay channels and the evaluation of the imaginary part of the Lamb shift. As application, the two-photon decay channels for the 3s level of the hydrogen atom are evaluated, including the cascade transition probability 3s-2p-1s. An important role is assigned to the two-photon decays in astrophysics context, since processes of this kind provide a possibility for the decoupling of radiation and matter in the early universe. We demonstrate the ambiguity of separation of the 'pure' two-photon contribution and criticize the existing methods for such a separation.

  2. Two Photon Absorption Laser Induced Fluorescence of Helium Ions in a Microwave Assisted Helicon Source

    NASA Astrophysics Data System (ADS)

    Scime, Earl

    2014-10-01

    The spectroscopic measurement of helium ion velocity distribution functions in a low temperature plasma is problematic for a number of reasons. First and foremost is the difficulty in accessing the UV and soft x-ray transitions to the ground state. Conventional laser induced fluorescence on ions in plasmas is routinely performed in argon, neon, xenon, and barium. Two-photon absorption laser induced fluorescence (TALIF) on neutrals has been demonstrated in hydrogen, nitrogen, and oxygen plasmas. We have successfully performed LIF on helium atoms and have had some hints of success with laser absorption spectroscopy on excited states of helium ions, the n = 5 to n = 6 transition in the infrared (1012 nm). Here we report a new approach using TALIF to access the n = 2 to n = 6 transition of singly ionized helium. The fluorescence path at 656 nm completes the three-level sequence. To obtain the electron temperatures necessary to create a sufficient population of metastable helium ions trapped in the 2S state, we have increased the electron temperature of a helicon plasma with 1.2 kW of microwaves at 2.45 GHz. Here we report emission spectroscopy measurements that confirm the increase in excited state population densities and preliminary TALIF measurements on helium ions. This work is funded by the US Department of Energy through Grant DE-SC0004736.

  3. Vibrational resonance enhanced broadband multiphoton absorption in a triphenylamine derivative

    SciTech Connect

    Lu Changgui; Cui Yiping; Huang Wei; Yun Binfeng; Wang Zhuyuan; Hu Guohua; Cui Jing; Lu Zhifeng; Qian Ying

    2007-09-17

    Multiphoton absorption of 2,5-bis[4-(2-N,N-diphenylaminostyryl)phenyl]-1,3,4-oxadiazole was experimentally studied by using femtosecond laser pulses. This material demonstrates a very broad multiphoton absorption band of around 300 nm width with two peaks of 1250 and 1475 nm. The first peak results from the three-photon absorption process while the second is attributed to the vibrational resonance enhanced four-photon absorption process. Combination of these two processes provides a much broader multiphoton absorption band. In this letter, the analytical solution to nonlinear transmission of a three-photon absorption process is also given when the incident beam has a Gaussian transverse spatial profile.

  4. Two-photon vibrational spectroscopy for biosciences based on surface-enhanced hyper-Raman scattering

    PubMed Central

    Kneipp, Janina; Kneipp, Harald; Kneipp, Katrin

    2006-01-01

    Two-photon excitation is gaining rapidly in interest and significance in spectroscopy and microscopy. Here we introduce a new approach that suggests versatile optical labels suitable for both one- and two-photon excitation and also two-photon-excited ultrasensitive, nondestructive chemical probing. The underlying spectroscopic effect is the incoherent inelastic scattering of two photons on the vibrational quantum states called hyper-Raman scattering (HRS). The rather weak effect can be strengthened greatly if HRS takes place in the local optical fields of gold and silver nanostructures. This so-called surface-enhanced HRS (SEHRS) is the two-photon analogue to surface-enhanced Raman scattering (SERS). SEHRS provides structurally sensitive vibrational information complementary to those obtained by SERS. SEHRS combines the advantages of two-photon spectroscopy with the structural information of vibrational spectroscopy and the high-sensitivity and nanometer-scale local confinement of plasmonics-based spectroscopy. We infer effective two-photon cross-sections for SEHRS on the order of 10−46 to 10−45 cm4·s, similar to or higher than the best “action” cross-sections (product of the two-photon absorption cross-section and fluorescence quantum yield) for two-photon fluorescence, and we demonstrate HRS on biological structures such as single cells after incubation with gold nanoparticles. PMID:17088534

  5. Description of the states of two-photon interference in an optical gating Michelson interferometer

    NASA Astrophysics Data System (ADS)

    Pongophas, Ekkarat; Sriklin, Watthana; Sinsarp, Asawin; Suwanna, Sujin; Chunwachirasiri, Withoon; Singhsomroje, Wisit

    2016-01-01

    We investigate the interference of two photons in an optical gating Michelson interferometer. The phenomenon is studied using two different representations of photons: the space-time domain and a step-by-step two-photon state evolution. Both representations lead to identical results. The evolution analysis describes the result by the interference of four two-photon traveling states, whereas the space-time domain analysis reveals that the classical interference of the high-intensity light source is identical to two-photon interference in the quantum regime, except for a multiplicative factor of (n2), where n is the number of photons.

  6. Two-photon induced photoluminescence and singlet oxygen generation from aggregated gold nanoparticles.

    PubMed

    Jiang, Cuifeng; Zhao, Tingting; Yuan, Peiyan; Gao, Nengyue; Pan, Yanlin; Guan, Zhenping; Zhou, Na; Xu, Qing-Hua

    2013-06-12

    Metal nanoparticles have potential applications as bioimaging and photosensitizing agents. Aggregation effects are generally believed to be adverse to their biomedical applications. Here we have studied the aggregation effects on two-photon induced photoluminescence and singlet oxygen generation of Au nanospheres and Au nanorods of two different aspect ratios. Aggregated Au nanospheres and short Au nanorods were found to display enhanced two-photon induced photoluminescence and singlet oxygen generation capabilities compared to the unaggregated ones. The two-photon photoluminescence of Au nanospheres and short Au nanorods were enhanced by up to 15.0- and 2.0-fold upon aggregation, and the corresponding two-photon induced singlet oxygen generation capabilities were enhanced by 8.3 and 1.8-fold, respectively. The two-photon induced photoluminescence and singlet oxygen generation of the aggregated long Au nanorods were found to be lower than the unaggregated ones. These results support that the change in their two-photon induced photoluminescence and singlet oxygen generation originate from aggregation modulated two-photon excitation efficiency. This finding is expected to foster more biomedical applications of metal nanoparticles as Au nanoparticles normally exist in an aggregated form in the biological environments. Considering their excellent biocompatibility, high inertness, ready conjugation, and easy preparation, Au nanoparticles are expected to find more applications in two-photon imaging and two-photon photodynamic therapy.

  7. Two-photon absorption and nonlinear polariton effects in organic crystals

    SciTech Connect

    Johnson, C.K.

    1981-01-01

    Two-photon excitation (TPE) and second harmonic generation (SHG) have been studied in phenanthrene crystals at low temperatures (2 to 6K) in order to investigate mechanisms of two-photon absorption (TPA), the relationship between TPE and SHG, and polariton effects. The transition studied is of special interest because it is both one- and two-photon allowed in the dipole approximation. Consequently, polariton states and SHG play a role in the two-photon process. In the polariton model, both TPA and SHG are understood as resulting from the process of polariton fusion.

  8. Impressive europium red emission induced by two-photon excitation for biological applications.

    PubMed

    Lo, Wai-Sum; Kwok, Wai-Ming; Law, Ga-Lai; Yeung, Chi-Tung; Chan, Chris Tsz-Leung; Yeung, Ho-Lun; Kong, Hoi-Kuan; Chen, Chi-Hang; Murphy, Margaret B; Wong, Ka-Leung; Wong, Wing-Tak

    2011-06-20

    Three triazine-based europium(III) complexes were synthesized that demonstrated strong two-photon induced europium emission with a high two-photon absorption cross-section. The modified triazine ligand of complex 3 initiated over 100% enhancement of the two-photon absorption cross-section (σ(2): 320 GM) when compared with complex 1 (σ(2): 128 GM) in a solution of DMSO. Europium complex 3 is also stable in vitro, and power-dependence curves were obtained in vitro to confirm the two-photon-induced f-f emission in HeLa cells. © 2011 American Chemical Society

  9. Two-photon absorption and spectroscopy of the lowest two-photon transition in small donor-acceptor-substituted organic molecules

    NASA Astrophysics Data System (ADS)

    Beels, Marten T.; Biaggio, Ivan; Reekie, Tristan; Chiu, Melanie; Diederich, François

    2015-04-01

    We determine the dispersion of the third-order polarizability of small donor-acceptor substituted organic molecules using wavelength-dependent degenerate four-wave mixing experiments in solutions with varying concentrations. We find that donor-acceptor-substituted molecules that are characterized by extremely efficient off-resonant nonlinearities also have a correspondingly high two-photon absorption cross section. The width and shape of the first two-photon resonance for these noncentrosymmetric molecules follows what is expected from their longest wavelength absorption peak, and the observed two-photon absorption cross sections are record high when compared to the available literature data, the size of the molecule, and the fundamental limit for two-photon absorption to the lowest excited state, which is essentially determined by the number of conjugated electrons and the excited-state energies. The two-photon absorption of the smallest molecule, which only has 16 electrons in its conjugated system, is one order of magnitude larger than for the molecule called AF-50, a reference molecule for two-photon absorption [O.-K. Kim et al., Chem. Mater. 12, 284 (2000), 10.1021/cm990662r].

  10. Two-Photon Probes for pH: Detection of Human Colon Cancer using Two-Photon Microscopy.

    PubMed

    Hong, Seung Taek; Kim, Tae Hyeong; Choi, Ji-Woo; Park, Seong Jun; Kwon, Sung An; Paik, Kyu Cheol; Han, Man So; Kim, Eun Sun; Chun, Hoon Jai; Heo, Jung-Nyoung; Cho, Bong Rae

    2017-09-19

    We have developed two-photon (TP) pH-sensitive probes (BH-2 and BHEt-1) that exhibit absorption and emission maxima at 370 and 466 nm, and TP absorption cross-section values of 51 and 61 GM (1 GM = 10(-50)cm(4)s/photon), respectively, at 750 nm and pH 3.0 in a universal buffer (0.1 M citric acid, 0.1 M KH2PO4, 0.1 M Na2B4O7, 0.1 M Tris, 0.1 M KCl)/1,4-dioxane (7/3) solution. The TPM images of CCD-18co (a normal colon cell line) and HCT116 cells (a colon cancer cell line) labeled with BH-2 were too dim to be distinguished. When the same cells were labeled with BHEt-1, however, the TPM image of the HCT116 cells was much brighter than that of CCD-18co cells, and the relative proportion of the acidic vesicles (Pacid) of the former was 5-fold larger than that of latter. BHEt-1 could also differentiate HepG2 cells (a human liver cancer cell line) from LX-2 cells (a human hepatic stellate cell line) with a 6-fold larger Pacid value. Human colon cancer tissues labeled with BHEt-1 showed similar results, demonstrating much brighter TPM images and 6-fold larger Pacid values compared to normal tissue. These results suggest the potential utility of BHEt-1 for detecting colon cancer in human tissues using TPM.

  11. [Two-photon microscopy of the cornea using intrinsic contrast].

    PubMed

    Krüger, A; Hovakimyan, M; Ramírez, D F; Stachs, O; Lubatschowski, H; Wree, A; Guthoff, R; Heisterkamp, A

    2009-12-01

    Three-dimensional imaging of the cornea under physiological conditions is best performed with intrinsic contrast mechanisms for the visualisation of cells and extracellular matrix. However, the unique transparency of the cornea goes along with a lack of contrast for the extracellular matrix (ECM) in reflective mode microscopy and optical coherence tomography. Femtosecond laser-based non-linear microscopy provides novel contrast mechanisms for the visualisation of ECM. The confinement of the non-linear contrast to the focus volume provides an intrinsic sectioning property for 3D imaging. Further advantages of the infrared light are lower phototoxicity and higher penetration depth into the tissue. For the visualisation of the cornea and its layered substructures two non-linear contrast mechanisms are of main interest: Two-photon excited autofluorescence of NAD(P)H in the cytoplasma and second harmonic generation (SHG) in the collagen-I fibres of the stroma. Ex-vivo corneas of the rabbit were imaged to demonstrate the abilities of non-linear microscopy. Using the autofluorescence of NAD(P)H the corneal epithelium with squamous cells, wing cells and basal cells is visualised in three dimensions without additional exogenoeus staining. Stromal keratocytes are also imaged using the NAD(P)H autofluoresecence. The layered structure of lamella in the stroma is visible after virtual resclicing of the 3D volume data. The en-face SHG images detected through the transparent cornea in forward direction show areas of parallel streaks, which increase in size and periodically alter in orientation (90 degrees , 45 degrees) with increasing depth from anterior to posterior. These streaks are not visible in the backward SHG signal. First results on rabbit corneas, which were cross-linked with Rivoflavin and UV application showed a signature of treatment five weeks post treatment. There were zones in the stroma totally lacking NAD(P)H autofluorescence and the abundance of keratocytes was

  12. Hybrid Theranostic Platform for Second Near-IR Window Light Triggered Selective Two-Photon Imaging and Photothermal Killing of Targeted Melanoma Cells.

    PubMed

    Tchounwou, Christine; Sinha, Sudarson Sekhar; Viraka Nellore, Bhanu Priya; Pramanik, Avijit; Kanchanapally, Rajashekhar; Jones, Stacy; Chavva, Suhash Reddy; Ray, Paresh Chandra

    2015-09-23

    Despite advances in the medical field, even in the 21st century cancer is one of the leading causes of death for men and women in the world. Since the second near-infrared (NIR) biological window light between 950 and 1350 nm offers highly efficient tissue penetration, the current article reports the development of hybrid theranostic platform using anti-GD2 antibody attached gold nanoparticle (GNP) conjugated, single-wall carbon nanotube (SWCNT) for second near-IR light triggered selective imaging and efficient photothermal therapy of human melanoma cancer cell. Reported results demonstrate that due to strong plasmon-coupling, two-photon luminescence (TPL) intensity from theranostic GNP attached SWCNT materials is 6 orders of magnitude higher than GNP or SWCNT alone. Experimental and FDTD simulation data indicate that the huge enhancement of TPL intensity is mainly due to strong resonance enhancement coupled with the stronger electric field enhancement. Due to plasmon coupling, the theranostic material serves as a local nanoantennae to enhance the photothermal capability via strong optical energy absorption. Reported data show that theranostic SWCNT can be used for selective two-photon imaging of melanoma UACC903 cell using 1100 nm light. Photothermal killing experiment with 1.0 W/cm(2) 980 nm laser light demonstrates that 100% of melanoma UACC903 cells can be killed using theranostic SWCNT bind melanoma cells after just 8 min of exposure. These results demonstrate that due to plasmon coupling, the theranostic GNP attached SWCNT material serves as a two-photon imaging and photothermal source for cancer cells in biological window II.

  13. Ionization Measurement and Spectroscopy of ThS and ThS^+

    NASA Astrophysics Data System (ADS)

    Bartlett, J. H.; Heaven, M. C.

    2013-06-01

    Gas-phase thorium sulfide has been produced via laser ablation of thorium in a jet-cooled expansion of 0.1% H_2S/He carrier gas. Electronic spectra have been recorded for the first time by laser-induced fluorescence (LIF) over the region 17500-23650 cm^{-1}. Resonance-enhanced multiphoton ionization (REMPI) was used in conjunction with a Wiley-McLaren time-of-flight mass spectrometer to confirm LIF assigments of seven rotationally-resolved bands belonging to ThS. Dispersing fluorescence from the {[22.13]}^1Π-{X}^1Σ_g transition revealed a vibrational progression of the ground electronic state of ThS, for which the vibrational constants were ω_e = 520.0(7) cm^{-1} and ω_eχ_e = 11.0(9) cm^{-1}. An accurate value for the ionization potential of ThS as well as term energies of ThS^+ up to v^+ = 7 in the ^2Σ^+ ground state and v^+ = 3 in the ^2Δ_{3/2} first excited state have been obtained using two-photon pulsed-field ionization zero kinetic energy photoelectron spectroscopy (PFI-ZEKE). Vibrational constants for these states have also been detemined. High-level electronic structure calculations performed for ThS and ThS^+ gave term energies and molecular parameters that are in excellent agreement with the experimental results. The change in bond characteristics upon ionization of ThS is found to be consistent with that observed for HfO, HfS, and ThO.

  14. Two-photon fluorescence probes for imaging of mitochondria and lysosomes.

    PubMed

    Yang, Wanggui; Chan, Pui Shan; Chan, Miu Shan; Li, King Fai; Lo, Pik Kwan; Mak, Nai Ki; Cheah, Kok Wai; Wong, Man Shing

    2013-04-28

    Novel biocompatible cyanines show not only a very large two-photon cross-section of up to 5130 GM at 910 nm in aqueous medium for high-contrast and -brightness two-photon fluorescence live cell imaging but also highly selective subcellular localization properties including localization of mitochondria and lysosomes.

  15. Two-Photon Photoexcited Photodynamic Therapy and Contrast Agent with Antimicrobial Graphene Quantum Dots.

    PubMed

    Kuo, Wen-Shuo; Chang, Chia-Yuan; Chen, Hua-Han; Hsu, Chih-Li Lilian; Wang, Jiu-Yao; Kao, Hui-Fang; Chou, Lawrence Chao-Shan; Chen, Yi-Chun; Chen, Shean-Jen; Chang, Wen-Tsan; Tseng, Shih-Wen; Wu, Ping-Ching; Pu, Ying-Chih

    2016-11-09

    A graphene quantum dot (GQD) used as the photosensitizer with high two-photon absorption in the near-infrared region, a large absolute cross section of two-photon excitation (TPE), strong two-photon luminescence, and impressive two-photon stability could be used for dual modality two-photon photodynamic therapy (PDT) and two-photon bioimaging with an ultrashot pulse laser (or defined as TPE). In this study, a GQD efficiently generated reactive oxygen species coupled with TPE, which highly increased the effective PDT ability of both Gram-positive and -negative bacteria, with ultralow energy and an extremely short photoexcitation time generated by TPE. Because of its two-photon properties, a GQD could serve as a promising two-photon contrast agent for observing specimens in depth in three-dimensional biological environments while simultaneously proceeding with PDT action to eliminate bacteria, particularly in multidrug-resistant (MDR) strains. This procedure would provide an efficient alternative approach to easily cope with MDR bacteria.

  16. Effect of morphology and solvent on two-photon absorption of nano zinc oxide

    SciTech Connect

    Kavitha, M.K.; Haripadmam, P.C.; Gopinath, Pramod; Krishnan, Bindu; John, Honey

    2013-05-15

    Highlights: ► ZnO nanospheres and triangular structures synthesis by novel precipitation technique. ► The effect of precursor concentration on the size and shape of nano ZnO. ► Open aperture Z-scan measurements of the ZnO nanoparticle dispersions. ► Nanospheres exhibit higher two photon absorption coefficient than triangular nanostructures. ► Nanospheres dispersed in water exhibit higher two photon absorption coefficient than its dispersion in 2-propanol. - Abstract: In this paper, we report the effect of morphology and solvent on the two-photon absorption of nano zinc oxide. Zinc oxide nanoparticles in two different morphologies like nanospheres and triangular nanostructures are synthesized by novel precipitation technique and their two-photon absorption coefficient is measured using open aperture Z-scan technique. Experimental results show that the zinc oxide nanospheres exhibit higher two-photon absorption coefficient than the zinc oxide triangular nanostructures. The zinc oxide nanospheres dispersed in water exhibit higher two-photon absorption coefficient than that of its dispersion in 2-propanol. The zinc oxide nanospheres dispersed in water shows a decrease in two-photon absorption coefficient with an increase in on-axis irradiance. The result confirms the dependence of shape and solvent on the two-photon absorption of nano zinc oxide.

  17. Two-photon absorption of BF2-carrying compounds: insights from theory and experiment.

    PubMed

    Bednarska, Joanna; Zaleśny, Robert; Wielgus, Małgorzata; Jędrzejewska, Beata; Puttreddy, Rakesh; Rissanen, Kari; Bartkowiak, Wojciech; Ågren, Hans; Ośmiałowski, Borys

    2017-02-22

    This communication presents a structure-property study of a few novel pyridine-based difluoroborate compounds with a N-BF2-O core, which exhibit outstanding fluorescence properties. To exploit their potential for two-photon bioimaging, relationships between the two-photon action cross section and systematic structural modifications have been investigated and unravelled.

  18. Two-dimensional two-photon absorbing chromophores and solvent effects on their cross-sections

    NASA Astrophysics Data System (ADS)

    Zheng, Lixin; Jen, Alex K.

    2003-02-01

    A series of 2-dimensional two-photon absorbing chromophores and their 1-dimensional analogs were studied. The influence of the solvents on the linear absorption, photoluminescence and two-photon absorption cross-sections were also examined for these chromophores. The stoke's shift increase with increasing solvent polarity, that can be adequately described by Lippert equation. Two-photon absorption cross sections were measured with femtosecond pulses by the two-photon-induced fluorescence technique. It was observed that two-photon cross-sections were also strongly dependent on the solvents, however no simple correlation with solvent polarity was found in this study. Interestingly, a linear relationship was observed in these chromophores between the molar extinction coefficient and the two-photon cross section when plotted in log-log formats. Understanding of the relationship may provide a better insight of the two-photon absorption processes, and potentially will contribute to the design of highly efficient two-photon absorbing chromophores.

  19. A GSH-activatable ruthenium(ii)-azo photosensitizer for two-photon photodynamic therapy.

    PubMed

    Zeng, Leli; Kuang, Shi; Li, Guanying; Jin, Chengzhi; Ji, Liangnian; Chao, Hui

    2017-02-07

    A glutathione (GSH)-activatable ruthenium(ii)-azo photosensitizer was prepared. The complex had low toxicity towards cells under dark conditions. It exhibited excellent phototoxicity under two-photon excitation (810 nm) and thus was developed as a two-photon photodynamic anticancer agent for cancer therapy.

  20. Interplay between resonant enhancement and quantum path dynamics in harmonic generation in helium

    NASA Astrophysics Data System (ADS)

    Camp, Seth; Schafer, Kenneth J.; Gaarde, Mette B.

    2015-07-01

    We present a theoretical study of the influence of resonant enhancement on quantum path dynamics in the generation of harmonics above and below the ionization threshold in helium. By varying the wavelength and intensity of the driving field from 425 to 500 nm and from 30 to 140 TW /cm 2 , respectively, we identify enhancements of harmonics 7, 9, and 11 that correspond to multiphoton resonances between the ground state and the Stark-shifted 1 s 2 p ,1 s 3 p , and 1 s 4 p excited states. A time-frequency analysis of the emission shows that both the short and the long quantum path contributions to the harmonic yield are enhanced through these bound-state resonances. We analyze the subcycle time structure of the ninth harmonic yield in the vicinity of the resonances and find that on resonance the long trajectory contribution is phase shifted by approximately π /4 . Finally, we compare the single atom and the macroscopic response of a helium gas and find that while the subcycle time profiles are slightly distorted by propagation effects, the phase shift of the long-trajectory contribution is still recognizable.

  1. Two-photon excitation microscopy for the study of living cells and tissues.

    PubMed

    Benninger, Richard K P; Piston, David W

    2013-06-01

    Two-photon excitation microscopy is an alternative to confocal microscopy that provides advantages for three-dimensional and deep tissue imaging. This unit will describe the basic physical principles behind two-photon excitation and discuss the advantages and limitations of its use in laser-scanning microscopy. The principal advantages of two-photon microscopy are reduced phototoxicity, increased imaging depth, and the ability to initiate highly localized photochemistry in thick samples. Practical considerations for the application of two-photon microscopy will then be discussed, including recent technological advances. This unit will conclude with some recent applications of two-photon microscopy that highlight the key advantages over confocal microscopy and the types of experiments which would benefit most from its application.

  2. Bis(pyrene)-Doped Cationic Dipeptide Nanoparticles for Two-Photon-Activated Photodynamic Therapy.

    PubMed

    Sun, Bingbing; Wang, Lei; Li, Qi; He, Pingping; Liu, Huiling; Wang, Hao; Yang, Yang; Li, Junbai

    2017-08-25

    At present, one of main problems for photodynamic therapy (PDT) is how to improve the treatment depth. Two-photon activated (TPA) developed recently provide a possible solution for it. In this work, we report the energy-transferring assembled cationic dipeptide nanoparticles for two-photon activated photodynamic therapy (TPA-PDT). In the nanoparticles, the coencapsulated two-photon fluorescent dye bis(pyrene) (BP) is an energy donor, and a photosensitizer rose bengal (RB) is an acceptor based on an intraparticle fluorescence resonance energy transfer (FRET) mechanism. BP in the nanoparticles can be excited by one- or two- photon laser. And then, the energy of BP was transferred to RB, which highly enhanced the generation of singlet oxygen. The cellular experiments indicated that this nanosystem can induce the cytotoxicity under one- and two-photon irradiation, which allows further applications of FRET-based biomaterials for TPA-PDT.

  3. Description of states of two-photon interference in optical gating Michelson interferometer

    NASA Astrophysics Data System (ADS)

    Pongophas, Ekkarat; Sinsarp, Asawin; Suwanna, Sujin; Chunwachirasiri, Withoon; Singhsomroje, Wisit

    2015-07-01

    The interference of two photons in the optical gating Michelson interferometer is investigated. The phenomenon is studied using two different representations of photons: the space-time domain and a step-by-step two photon state evolution. Both representations lead to an equivalent description of the two-photon states which is the interference of four cases of two-photon traveling states, as implied by the evolution analysis. Additionally, the space-time domain analysis reveals that the classical interference of high-intensity light source is identical to the two-photon interference in the quantum regime except for a multiplicative factor of (n 2), where n is the number of photons.

  4. Optimizing single-nanoparticle two-photon microscopy by in situ adaptive control of femtosecond pulses

    SciTech Connect

    Li, Donghai; Deng, Yongkai; Chu, Saisai; Jiang, Hongbing; Wang, Shufeng; Gong, Qihuang

    2016-07-11

    Single-nanoparticle two-photon microscopy shows great application potential in super-resolution cell imaging. Here, we report in situ adaptive optimization of single-nanoparticle two-photon luminescence signals by phase and polarization modulations of broadband laser pulses. For polarization-independent quantum dots, phase-only optimization was carried out to compensate the phase dispersion at the focus of the objective. Enhancement of the two-photon excitation fluorescence intensity under dispersion-compensated femtosecond pulses was achieved. For polarization-dependent single gold nanorod, in situ polarization optimization resulted in further enhancement of two-photon photoluminescence intensity than phase-only optimization. The application of in situ adaptive control of femtosecond pulse provides a way for object-oriented optimization of single-nanoparticle two-photon microscopy for its future applications.

  5. Two-Photon Excitation Microscopy for the Study of Living Cells and Tissues

    PubMed Central

    Benninger, Richard K.P.; Piston, David W.

    2013-01-01

    Two-photon excitation microscopy is an alternative to confocal microscopy that provides advantages for three-dimensional and deep tissue imaging. This unit will describe the basic physical principles behind two-photon excitation and discuss the advantages and limitations of its use in laser-scanning microscopy. The principal advantages of two-photon microscopy are reduced phototoxicity, increased imaging depth, and the ability to initiate highly localized photochemistry in thick samples. Practical considerations for the application of two-photon microscopy will then be discussed, including recent technological advances. This unit will conclude with some recent applications of two-photon microscopy that highlight the key advantages over confocal microscopy and the types of experiments which would benefit most from its application. PMID:23728746

  6. Two-photon absorption in a series of 2,6-disubstituted BODIPY dyes.

    PubMed

    Barros, Leonardo W T; Cardoso, Thiago A S; Bihlmeier, Angela; Wagner, Danny; Kölmel, Dominik K; Hörner, Anna; Bräse, Stefan; Brito Cruz, Carlos H; Padilha, Lazaro A

    2017-08-16

    We report on the two-photon absorption spectra of a series of 2,6-disubstituted BODIPY dyes. Depending on the substituents, we observe increasing two-photon absorption cross sections with values up to 350 GM compared to 70 GM in the unsubstituted dye. Quantum chemical calculations are performed to assign the absorption bands and to understand the factors controlling the size of the two-photon absorption cross section. Both the maximum of the two-photon absorption band as well as the red-shift of the whole spectrum correlate with the ability of the substituents to extend the π-electron system of the dye. The above-mentioned intense two-photon absorption band corresponds to the absorption of photons with 1.3 eV, which is at the first near-infrared transparency window for biological tissues. The dyes could thus be suitable for bio-imaging applications.

  7. Charge transfer enhances two-photon absorption in transition metal porphyrins.

    PubMed

    Humphrey, Jonathan L; Kuciauskas, Darius

    2006-03-29

    Two-photon absorption processes were investigated in electropolymerized Fe(III), Mn(III), and Co(II) 5,10,15,20-tetrakis-(4-hydroxytetraphenyl)porphyrin films. Degenerate four wave mixing (DFWM) spectroscopy with 100 fs pulses in the near-IR spectral region was used. Metalloporphyrins with strong charge transfer (CT) transitions in the linear absorption spectra also show enhanced two-photon absorption. (Metalloporphyrin two-photon absorption cross section, delta, increases >10 times over that for the metal free porphyrin.) This effect was attributed to a two-photon induced charge transfer between the metal ion's d orbitals and the pi-system of the porphyrin. Correlation of one- and two-photon absorption properties of transition metal porphyrins suggests a new and simple approach to improve organic materials for photonic applications.

  8. Strong field ionization rates simulated with time-dependent configuration interaction and an absorbing potential

    SciTech Connect

    Krause, Pascal; Sonk, Jason A.; Schlegel, H. Bernhard

    2014-05-07

    Ionization rates of molecules have been modeled with time-dependent configuration interaction simulations using atom centered basis sets and a complex absorbing potential. The simulations agree with accurate grid-based calculations for the ionization of hydrogen atom as a function of field strength and for charge resonance enhanced ionization of H{sub 2}{sup +} as the bond is elongated. Unlike grid-based methods, the present approach can be applied to simulate electron dynamics and ionization in multi-electron polyatomic molecules. Calculations on HCl{sup +} and HCO{sup +} demonstrate that these systems also show charge resonance enhanced ionization as the bonds are stretched.

  9. pH Effect on Two-Photon Cross Section of Highly Fluorescent Dyes Using Femtosecond Two-Photon Induced Fluorescence.

    PubMed

    Makhal, Krishnandu; Goswami, Debabrata

    2017-01-01

    Effect of solution pH on two-photon absorption cross-section of highly fluorescent Coumarin and Rhodamine dyes with high repetition rate femtosecond laser pulses at 780 nm is presented using two-photon induced fluorescence technique. A correspondence in the measured two-photon and single-photon cross-section values is seen when the pH changes from acidic to basic conditions (pH = 2-10) for solutions in 1:1 water-ethanol binary mixture. By plotting changes in the single-photon and two-photon fluorescence in this pH range, the excited state pKa values are found. The ground state pKa values are also affected by the protonation deprotonation equilibrium as a result of variation in pH from acidic to basic, which are characterized by changes in absorbance spectra. Most of these single-photon and two-photon induced fluorescence spectra show characteristic blue shifts. Different fluorescence quantum yields calculated at each pH reflect a change in structure corresponding to their associated properties as a result of acid base equilibrium.

  10. Evaluation of the exothermicity of the chemi-ionization reaction Sm + O → SmO+ + e-

    NASA Astrophysics Data System (ADS)

    Cox, Richard M.; Kim, JungSoo; Armentrout, P. B.; Bartlett, Joshua; VanGundy, Robert A.; Heaven, Michael C.; Ard, Shaun G.; Melko, Joshua J.; Shuman, Nicholas S.; Viggiano, Albert A.

    2015-04-01

    The exothermicity of the chemi-ionization reaction Sm + O → SmO+ + e- has been re-evaluated through the combination of several experimental methods. The thermal reactivity (300-650 K) of Sm+ and SmO+ with a range of species measured using a selected ion flow tube-mass spectrometer apparatus is reported and provides limits for the bond strength of SmO+, 5.661 eV ≤ D0(Sm+-O) ≤ 6.500 eV. A more precise value is measured to be 5.725 ± 0.07 eV, bracketed by the observed reactivity of Sm+ and SmO+ with several species using a guided ion beam tandem mass spectrometer (GIBMS). Combined with the established Sm ionization energy (IE), this value indicates an exothermicity of the title reaction of 0.08 ± 0.07 eV, ˜0.2 eV smaller than previous determinations. In addition, the ionization energy of SmO has been measured by resonantly enhanced two-photon ionization and pulsed-field ionization zero kinetic energy photoelectron spectroscopy to be 5.7427 ± 0.0006 eV, significantly higher than the literature value. Combined with literature bond energies of SmO, this value indicates an exothermicity of the title reaction of 0.14 ± 0.17 eV, independent from and in agreement with the GIBMS result presented here. The evaluated thermochemistry also suggests that D0(SmO) = 5.83 ± 0.07 eV, consistent with but more precise than the literature values. Implications of these results for interpretation of chemical release experiments in the thermosphere are discussed.

  11. Resonantly Enhanced Emission from a Luminescent Nanostructured Waveguide

    NASA Astrophysics Data System (ADS)

    Inada, Yasuhisa; Hashiya, Akira; Nitta, Mitsuru; Tomita, Shogo; Tsujimoto, Akira; Suzuki, Masa-Aki; Yamaki, Takeyuki; Hirasawa, Taku

    2016-09-01

    Controlling the characteristics of photon emission represents a significant challenge for both fundamental science and device technologies. Research on microcavities, photonic crystals, and plasmonic nanocavities has focused on controlling spontaneous emission by way of designing a resonant structure around the emitter to modify the local density of photonic states. In this work, we demonstrate resonantly enhanced emission using luminescent nanostructured waveguide resonance (LUNAR). Our concept is based on coupling between emitters in the luminescent waveguide and a resonant waveguide mode that interacts with a periodic nanostructure and hence outcouples via diffraction. We show that the enhancement of resonance emission can be controlled by tuning the design parameters. We also demonstrate that the enhanced emission is attributable to the accelerated spontaneous emission rate that increases the probability of photon emission in the resonant mode, accompanied by enhanced the local density of photonic states. This study demonstrates that nanostructured luminescent materials can be designed to exhibit functional and enhanced emission. We anticipate that our concept will be used to improve the performance of a variety of photonic and optical applications ranging from bio/chemical sensors to lighting, displays and projectors.

  12. Resonantly Enhanced Emission from a Luminescent Nanostructured Waveguide

    PubMed Central

    Inada, Yasuhisa; Hashiya, Akira; Nitta, Mitsuru; Tomita, Shogo; Tsujimoto, Akira; Suzuki, Masa-aki; Yamaki, Takeyuki; Hirasawa, Taku

    2016-01-01

    Controlling the characteristics of photon emission represents a significant challenge for both fundamental science and device technologies. Research on microcavities, photonic crystals, and plasmonic nanocavities has focused on controlling spontaneous emission by way of designing a resonant structure around the emitter to modify the local density of photonic states. In this work, we demonstrate resonantly enhanced emission using luminescent nanostructured waveguide resonance (LUNAR). Our concept is based on coupling between emitters in the luminescent waveguide and a resonant waveguide mode that interacts with a periodic nanostructure and hence outcouples via diffraction. We show that the enhancement of resonance emission can be controlled by tuning the design parameters. We also demonstrate that the enhanced emission is attributable to the accelerated spontaneous emission rate that increases the probability of photon emission in the resonant mode, accompanied by enhanced the local density of photonic states. This study demonstrates that nanostructured luminescent materials can be designed to exhibit functional and enhanced emission. We anticipate that our concept will be used to improve the performance of a variety of photonic and optical applications ranging from bio/chemical sensors to lighting, displays and projectors. PMID:27682993

  13. Nonlinear theory of a two-photon correlated-spontaneous-emission laser: A coherently pumped two-level--two-photon laser

    SciTech Connect

    Lu, N.; Zhao, F.; Bergou, J.

    1989-05-15

    We develop a nonlinear theory of a two-photon correlated-spontaneous-emission laser (CEL) by using an effective interaction Hamiltonian for a two-level system coupled by a two-photon transition. Assuming that the active atoms are prepared initially in a coherent superposition of two atomic levels involved in the two-photon transition, we derive a master equation for the field-density operator by using our quantum theory for coherently pumped lasers. The steady-state properties of the two-photon CEL are studied by converting the field master equation into a Fokker-Planck equation for the antinormal-ordering Q representation of the field-density operator. Because of the injected atomic coherence, the drift and diffusion coefficients become phase sensitive. This leads to laser phase locking and an extra two-photon CEL gain. The laser field can build up from a vacuum in the no-population-inversion region, in contrast to an ordinary two-photon laser for which triggering is needed. We find an approximate steady-state solution of the Q representation for the laser field, which consists of two identical peaks of elliptical type. We calculate the phase variance and, for any given mean photon number, obtain the minimum variance in the phase quadrature as a function of the initial atomic variables. Squeezing of the quantum noise in the phase quadrature is found and it exhibits the following features: (1) it is possible only when the laser intensity is smaller than a certain value; (2) it becomes most significant for small mean photon number, which is achievable in the no-population-inversion region; and (3) a maximum of 50% squeezing can be asymptotically approached in the small laser intensity limit.

  14. Precise Two-Photon Photodynamic Therapy using an Efficient Photosensitizer with Aggregation-Induced Emission Characteristics.

    PubMed

    Gu, Bobo; Wu, Wenbo; Xu, Gaixia; Feng, Guangxue; Yin, Feng; Chong, Peter Han Joo; Qu, Junle; Yong, Ken-Tye; Liu, Bin

    2017-07-01

    Two-photon photodynamic therapy (PDT) is able to offer precise 3D manipulation of treatment volumes, providing a target level that is unattainable with current therapeutic techniques. The advancement of this technique is greatly hampered by the availability of photosensitizers with large two-photon absorption (TPA) cross section, high reactive-oxygen-species (ROS) generation efficiency, and bright two-photon fluorescence. Here, an effective photosensitizer with aggregation-induced emission (AIE) characteristics is synthesized, characterized, and encapsulated into an amphiphilic block copolymer to form organic dots for two-photon PDT applications. The AIE dots possess large TPA cross section, high ROS generation efficiency, and excellent photostability and biocompatibility, which overcomes the limitations of many conventional two-photon photosensitizers. Outstanding therapeutic performance of the AIE dots in two-photon PDT is demonstrated using in vitro cancer cell ablation and in vivo brain-blood-vessel closure as examples. This shows therapy precision up to 5 µm under two-photon excitation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Two-photon absorption and two-photon circular dichroism of L-tryptophan in the near to far UV region

    NASA Astrophysics Data System (ADS)

    Vesga, Yuly; Hernandez, Florencio E.

    2017-09-01

    Herein we report on the first measurements of the two-photon absorption (TPA) spectrum of L-tryptophan in DMSO solution in the near to far UV region and the two-photon circular dichroism (TPCD) signal corresponding to a transition at 200 nm. We demonstrate the application of the Double L-scan technique in the near to far UV region to perform polarization dependent TPA measurements of chiral molecules. TPCD measurements below 400 nm reveal that chiral molecules in solution, such as tryptophan/DMSO, can undergo photochemical reactions in front of prolonged exposure to UV radiation.

  16. In vivo two-photon imaging of retina in rabbits and rats.

    PubMed

    Jayabalan, Gopal Swamy; Wu, Yi-Kai; Bille, Josef F; Kim, Samuel; Mao, Xiao Wen; Gimbel, Howard V; Rauser, Michael E; Fan, Joseph T

    2017-05-05

    The purpose of this study was to evaluate the retina using near-infrared (NIR) two-photon scanning laser ophthalmoscopy. New Zealand white rabbits, albino rats, and brown Norway rats were used in this study. An autofluorescence image of the retina, including the retinal cells and its associated vasculatures was obtained by a real-time scan using the ophthalmoscope. Furthermore, the retinal vessels, nerve fiber layers and the non-pigmented retina were recorded with two-photon fluorescein angiography (FA); and the choroidal vasculatures were recorded using two-photon indocyanine green angiography (ICGA). Two-photon ICGA was achieved by exciting a second singlet state at ∼398 nm. Simultaneous two-photon FA and two-photon ICGA were performed to characterize the retinal and choroidal vessels with a single injection. The minimum laser power threshold required to elicit two-photon fluorescence was determined. The two-photon ophthalmoscope could serve as a promising tool to detect and monitor the disease progression in animal models. Moreover, these high-resolution images of retinal and choroidal vessels can be acquired in a real-time scan with a single light source, requiring no additional filters for FA or ICGA. The combination of FA and ICGA using the two-photon ophthalmoscope will help researchers to characterize the retinal diseases in animal models, and also to classify the types (classic, occult or mixed) of choroidal neovascularization (CNV) in macular degeneration. Furthermore, the prototype can be adapted to image the retina of rodents and rabbits. Copyright © 2017. Published by Elsevier Ltd.

  17. Correlated two-photon generation by diamond atomic system in Yb atoms

    NASA Astrophysics Data System (ADS)

    Yoon, Tai Hyun; Song, Minsoo

    2011-05-01

    We study a non-degenerate correlated two-photon generation with narrow bandwidths of 50 MHz by using a diamond atomic system in the collimated Yb atomic beam. We excited the 6s2 1S0 atoms into the 6s7s 1S0 excited state by the resonant two-photon transition via the intermediate 6s6p 1P1 state. Then, the excited atoms decay spontaneously into the 6s2 1S0 ground state via the inter-combination 6s6p 3P1 state. We are focusing on the closed-loop two-photon absorption/excitation path through which correlated two photons having the wavelengths of 611.3 nm (Stokes) and 556.8 nm (anti-Stokes) can be generated efficiently. We performed first a two-photon absorption spectroscopy for the 1S0-1P1-1S0 two-photon transitions. An ECDL at 399 nm was used to excite the 1S0-1P1 transition and another ECDL at 1077 nm was used to excite the 1P1-1S0 transition. From the spontaneous two-photon emission process, we were able to detect correlated two-photons at 611.3 nm and 555.8 nm at the plane perpendicular to the excitation beams, and parallel to the Yb atomic beam. We detected a few times of 106 photons per second both at the idler and signal beams at the condition of two-photon resonance with the detection solid angle of only 0.01 sr. We also performed an optical switching and modulation experiments of the photon-pair by optically switching and frequency modulation of the 399-nm driving field.

  18. Two-photon absorption of [2.2]paracyclophane derivatives in solution: A theoretical investigation

    NASA Astrophysics Data System (ADS)

    Ferrighi, Lara; Frediani, Luca; Fossgaard, Eirik; Ruud, Kenneth

    2007-12-01

    The two-photon absorption of a class of [2.2]paracyclophane derivatives has been studied using quadratic response and density functional theories. For the molecules investigated, several effects influencing the two-photon absorption spectra have been investigated, such as side-chain elongation, hydrogen bonding, the use of ionic species, and solvent effects, the latter described by the polarizable continuum model. The calculations have been carried out using a recent parallel implementation of the polarizable continuum model in the DALTON code. Special attention is given to those aspects that could explain the large solvent effect on the two-photon absorption cross sections observed experimentally for this class of compounds.

  19. Two-Photon Optical Interrogation of Individual Dendritic Spines with Caged Dopamine

    PubMed Central

    2013-01-01

    We introduce a novel caged dopamine compound (RuBi-Dopa) based on ruthenium photochemistry. RuBi-Dopa has a high uncaging efficiency and can be released with visible (blue-green) and IR light in a two-photon regime. We combine two-photon photorelease of RuBi-Dopa with two-photon calcium imaging for an optical imaging and manipulation of dendritic spines in living brain slices, demonstrating that spines can express functional dopamine receptors. This novel compound allows mapping of functional dopamine receptors in living brain tissue with exquisite spatial resolution. PMID:23672485

  20. Two-photon Anderson localization in a disordered quadratic waveguide array

    NASA Astrophysics Data System (ADS)

    Bai, Y. F.; Xu, P.; Lu, L. L.; Zhong, M. L.; Zhu, S. N.

    2016-05-01

    We theoretically investigate two-photon Anderson localization in a χ (2) waveguide array with off-diagonal disorder. The nonlinear parametric down-conversion process would enhance both the single-photon and the two-photon Anderson localization. In the strong disorder regime, the two-photon position correlation exhibits a bunching distribution around the pumped waveguides, which is independent of pumping conditions and geometrical structures of waveguide arrays. Quadratic nonlinearity can be supplied as a new ingredient for Anderson localization. Also, our results pave the way for engineering quantum states through nonlinear quantum walks.

  1. Cyanines as new fluorescent probes for DNA detection and two-photon excited bioimaging.

    PubMed

    Feng, Xin Jiang; Wu, Po Lam; Bolze, Frédéric; Leung, Heidi W C; Li, King Fai; Mak, Nai Ki; Kwong, Daniel W J; Nicoud, Jean-François; Cheah, Kok Wai; Wong, Man Shing

    2010-05-21

    A series of cyanine fluorophores based on fused aromatics as an electron donor for DNA sensing and two-photon bioimaging were synthesized, among which the carbazole-based biscyanine exhibits high sensitivity and efficiency as a fluorescent light-up probe for dsDNA, which shows selective binding toward the AT-rich regions. The synergetic effect of the bischromophoric skeleton gives a several-fold enhancement in a two-photon absorption cross-section as well as a 25- to 100-fold enhancement in two-photon excited fluorescence upon dsDNA binding.

  2. The two-photon exchange contribution to elastic electron-nucleon scattering at large momentum transfer

    SciTech Connect

    Andrei V. Afanasev; Stanley J. Brodsky; Carl E. Carlson; Yu-Chun Chen; Marc Vanderhaeghen

    2005-01-01

    We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer by using a quark-parton representation of virtual Compton scattering. We thus can relate the two-photon exchange amplitude to the generalized parton distributions which also enter in other wide angle scattering processes. We find that the interference of one- and two-photon exchange contribution is able to substantially resolve the difference between electric form factor measurements from Rosenbluth and polarization transfer experiments.

  3. Dispersion spreading of biphotons in optical fibers and two-photon interference.

    PubMed

    Brida, G; Chekhova, M V; Genovese, M; Gramegna, M; Krivitsky, L A

    2006-04-14

    We present the first observation of two-photon polarization interference structure in the second-order Glauber correlation function of two-photon light generated via type-II spontaneous parametric down-conversion. In order to obtain this result, two-photon light is transmitted through an optical fiber and the coincidence distribution is analyzed by means of the start-stop method. Beyond the experimental demonstration of an interesting effect in quantum optics, these results also have considerable relevance for quantum communications.

  4. Nonsequential two-photon absorption from the K shell in solid zirconium

    NASA Astrophysics Data System (ADS)

    Ghimire, Shambhu; Fuchs, Matthias; Hastings, Jerry; Herrmann, Sven C.; Inubushi, Yuichi; Pines, Jack; Shwartz, Sharon; Yabashi, Makina; Reis, David A.

    2016-10-01

    We report the observation of nonsequential two-photon absorption from the K shell of solid Zr (atomic number Z =40 ) using intense x-ray pulses from the Spring-8 Angstrom Compact Free-Electron Laser (SACLA). We determine the generalized nonlinear two-photon absorption cross section at the two-photon threshold in the range of 3.9-57 ×10-60cm4s bounded by the estimated uncertainty in the absolute intensity. The lower limit is consistent with the prediction of 3.1 ×10-60cm4s from the nonresonant Z-6 scaling for hydrogenic ions in the nonrelativistic, dipole limit.

  5. A Two-Photon Fluorescent Probe for Lysosomal Thiols in Live Cells and Tissues

    PubMed Central

    Fan, Jiangli; Han, Zhichao; Kang, Yao; Peng, Xiaojun

    2016-01-01

    Lysosome-specific fluorescent probes are exclusive to elucidate the functions of lysosomal thiols. Moreover, two-photon microscopy offers advantages of less phototoxicity, better three dimensional spatial localization, deeper penetration depth and lower self-absorption. However, such fluorescent probes for thiols are still rare. In this work, an efficient two-photon fluorophore 1,8-naphthalimide-based probe conjugating a 2,4-dinitrobenzenesulfonyl chloride and morpholine was designed and synthesized, which exhibited high selectivity and sensitivity towards lysosomal thiols by turn-on fluorescence method quantitatively and was successfully applied to the imaging of thiols in live cells and tissues by two-photon microscopy. PMID:26794434

  6. Dicke coherent narrowing in two-photon and Raman spectroscopy of thin vapor cells

    SciTech Connect

    Dutier, Gabriel; Todorov, Petko; Hamdi, Ismahene; Maurin, Isabelle; Saltiel, Solomon; Bloch, Daniel; Ducloy, Martial

    2005-10-15

    The principle of coherent Dicke narrowing in a thin vapor cell, in which sub-Doppler spectral line shapes are observed under a normal irradiation for a {lambda}/2 thickness, is generalized to two-photon spectroscopy. Only the sum of the two wave vectors must be normal to the cell, making the two-photon scheme highly versatile. A comparison is provided between the Dicke narrowing with copropagating fields, and the residual Doppler broadening occurring with counterpropagating geometries. The experimental feasibility is discussed on the basis of a first observation of a two-photon resonance in a 300-nm-thick Cs cell. Extension to the Raman situation is finally considered.

  7. Study of Two-Photon Reseonant Four Wave Sum Mixing in Xeon and its Competition with the Four Wave Difference Mixing

    NASA Astrophysics Data System (ADS)

    Al-Basheer, W.; Shi, Y. J.

    2009-06-01

    The two-photon resonant four wave sum- and difference-mixing in Xe gaseous medium was studied by subjecting a variety of molecular samples, including acetone, furan, triethylamine (TEA), and dimethylsilacyclobutane (DMSCB), to the laser sources produced from the four wave mixing processes for ionization. Ionization of acetone-h6, acetone-d6, furan-h4, furan-h4, and DMSCB samples showed similar behaviour. It is demonstrated that in a vacuum ultraviolet (VUV) spectral region of 103 - 109 nm four-wave sum mixing in Xe can only occur in ten discontinued regions, all of which are to the blue of a Xe atomic transition. Study of the TEA sample with its ionization potential lower than the photon energy of the VUV radiation from the difference mixing illustrated the competition between the sum- and difference-mixing occurring simultaneously in the Xe gas cell.

  8. An Amphiphilic BODIPY-Porphyrin Conjugate: Intense Two-Photon Absorption and Rapid Cellular Uptake for Two-Photon-Induced Imaging and Photodynamic Therapy.

    PubMed

    Zhang, Tao; Lan, Rongfeng; Gong, Longlong; Wu, Baoyan; Wang, Yuzhi; Kwong, Daniel W J; Wong, Wai-Kwok; Wong, Ka-Leung; Xing, Da

    2015-11-02

    The new amphiphilic BODPY-porphyrin conjugate BZnPP and its precursor BZnPH were synthesised, and their linear and two-photon photophysical properties, together with their cellular uptake and photo-cytotoxicity, were studied. This amphiphilic conjugate consists of a hydrophobic BODIPY moiety and a hydrophilic tetra(ethylene glycol) chain bridging a cationic triphenylphosphonium group to an amphiphilic porphyrin ZnP through acetylide linkers at its meso positions. A large two-photon absorption cross-section (σ=1725 GM) and a high singlet oxygen quantum yield (0.52) were recorded. Intense linear- and two-photon-induced red emissions were also observed for both BZnPP and BZnPH. Further in vitro studies showed that BZnPP exhibited very efficient cellular uptake and strong photocytotoxic but weak dark cytotoxic properties towards human breast carcinoma MCF-7 cells. In summary, the two-photon-induced emission and the potent photo-cytotoxicity of BZnPP make it an efficacious dual-purpose tumour-imaging and photodynamic therapeutic agent in the tissue-transparent spectral windows. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Note: Derivation of two-photon circular dichroism—Addendum to “Two-photon circular dichroism” [J. Chem. Phys. 62, 1006 (1975)

    SciTech Connect

    Friese, Daniel H.

    2015-09-07

    This addendum shows the detailed derivation of the fundamental equations for two-photon circular dichroism which are given in a very condensed form in the original publication [I. Tinoco, J. Chem. Phys. 62, 1006 (1975)]. In addition, some minor errors are corrected and some of the derivations in the original publication are commented.

  10. Y-shaped two-photon absorbing molecules with an imidazole-thiazole core

    NASA Technical Reports Server (NTRS)

    Feng, Ke; De Boni, Leonardo; Misoguti, Lino; Mendonca, C. R.; Meador, Michael; Hsu, Fu-Lian; Bu, Xiu R.

    2004-01-01

    Two new classes of two-photon absorbing Y-shaped molecules have been developed to possess an imidazole-thiazole core and a stilbene-type conjugation pathway with either nitro or sulfonyl as terminal electron-accepting group.

  11. Measurement of Two-Photon Absorption Cross Section of Metal Ions by a Mass Sedimentation Approach

    PubMed Central

    Ma, Zhuo-Chen; Chen, Qi-Dai; Han, Bing; Liu, Xue-Qing; Song, Jun-Feng; Sun, Hong-Bo

    2015-01-01

    The photo-reduction of metal ions in solution induced by femtosecond laser is an important and novel method for fabricating three-dimensional metal microstructures. However, the nonlinear absorption cross section of metal ions remains unknown because its measurement is difficult. In the present study, a method based on Two-Photon Excited Sedimentation (TPES) is proposed to measure the two-photon absorption cross section (TPACS) of metal ions in solution. The power-squared dependence of the amount of sediment on the excitation intensity was confirmed, revealing that 800 nm femtosecond laser induced reduction of metal ions was a two photon absorption process. We believe that the proposed method may be applied to measure the TPACS of several metal ions, thereby opening a new avenue towards future analysis of two-photon absorption materials. PMID:26657990

  12. Experimental observation of sub-Rayleigh quantum imaging with a two-photon entangled source

    SciTech Connect

    Xu, De-Qin; Song, Xin-Bing; Li, Hong-Guo; Zhang, De-Jian; Wang, Hai-Bo; Xiong, Jun Wang, Kaige

    2015-04-27

    It has been theoretically predicted that N-photon quantum imaging can realize either an N-fold resolution improvement (Heisenberg-like scaling) or a √(N)-fold resolution improvement (standard quantum limit) beyond the Rayleigh diffraction bound, over classical imaging. Here, we report the experimental study on spatial sub-Rayleigh quantum imaging using a two-photon entangled source. Two experimental schemes are proposed and performed. In a Fraunhofer diffraction scheme with a lens, two-photon Airy disk pattern is observed with subwavelength diffraction property. In a lens imaging apparatus, however, two-photon sub-Rayleigh imaging for an object is realized with super-resolution property. The experimental results agree with the theoretical prediction in the two-photon quantum imaging regime.

  13. Experimental observation of sub-Rayleigh quantum imaging with a two-photon entangled source

    NASA Astrophysics Data System (ADS)

    Xu, De-Qin; Song, Xin-Bing; Li, Hong-Guo; Zhang, De-Jian; Wang, Hai-Bo; Xiong, Jun; Wang, Kaige

    2015-04-01

    It has been theoretically predicted that N-photon quantum imaging can realize either an N-fold resolution improvement (Heisenberg-like scaling) or a √{ N } -fold resolution improvement (standard quantum limit) beyond the Rayleigh diffraction bound, over classical imaging. Here, we report the experimental study on spatial sub-Rayleigh quantum imaging using a two-photon entangled source. Two experimental schemes are proposed and performed. In a Fraunhofer diffraction scheme with a lens, two-photon Airy disk pattern is observed with subwavelength diffraction property. In a lens imaging apparatus, however, two-photon sub-Rayleigh imaging for an object is realized with super-resolution property. The experimental results agree with the theoretical prediction in the two-photon quantum imaging regime.

  14. Two-photon fluorescence correlation spectroscopy with high count rates and low background using dielectric microspheres

    PubMed Central

    Aouani, Heykel; Schön, Peter; Brasselet, Sophie; Rigneault, Hervé; Wenger, Jérôme

    2010-01-01

    Two-photon excitation fluorescence is a powerful technique commonly used for biological imaging. However, the low absorption cross section of this non-linear process is a critical issue for performing biomolecular spectroscopy at the single molecule level. Enhancing the two-photon fluorescence signal would greatly improve the effectiveness of this technique, yet current methods struggle with medium enhancement factors and/or high background noise. Here, we show that the two-photon fluorescence signal from single Alexa Fluor 488 molecules can be enhanced up to 10 times by using a 3 µm diameter latex sphere while adding almost no photoluminescence background. We report a full characterization of the two-photon fluorescence enhancement by a single microsphere using fluorescence correlation spectroscopy. This opens new routes to enhance non-linear optical signals and extend biophotonic applications. PMID:21258531

  15. Plasmonic-enhanced two-photon fluorescence with single gold nanoshell

    NASA Astrophysics Data System (ADS)

    Zhang, TianYue; Lu, GuoWei; Shen, HongMing; Perriat, P.; Martini, M.; Tillement, O.; Gong, QiHuang

    2014-06-01

    Single gold nanoshell with mutilpolar plasmon resonances is proposed to enhance two-photon fluorescence efficiently. The single emitter single nanoshell configuration is studied systematically by employing the finite-difference time-domain method. The emitter located inside or outside the nanoshell at various positions leads to a significantly different enhancement effect. The fluorescent emitter placed outside the nanoshell can achieve large fluorescence intensity given that both the position and orientation of the emission dipole are optimally controlled. In contrast, for the case of the emitter placed inside the nanoshell, it can experience substantial two-photon fluorescence enhancement without strict requirements upon the position and dipole orientations. Metallic nanoshell encapsulating many fluorescent emitters should be a promising nanocomposite configuration for bright two-photon fluorescence label. The results provide a comprehensive understanding about the plasmonic-enhanced two-photon fluorescence behaviors, and the nanocomposite configuration has great potential for optical detecting, imaging and sensing in biological applications.

  16. Dye-doped sol-gel materials for two-photon absorption induced fluorescence

    NASA Astrophysics Data System (ADS)

    Canva, Michael; Roger, Gisèle; Cassagne, Florence; Lévy, Yves; Brun, Alain; Chaput, Frédéric; Boilot, Jean-Pierre; Rapaport, Alexandra; Heerdt, Céline; Bass, Michael

    2002-01-01

    Two-photon absorption (TPA) and subsequent fluorescence properties of laser dyes are retained when doped into solid state sol-gel materials. These properties were demonstrated to be applicable in true 3D displays.

  17. Fluorescence upconversion properties of a class of improved pyridinium dyes induced by two-photon absorption

    NASA Astrophysics Data System (ADS)

    Xu, Guibao; Hu, Dawei; Zhao, Xian; Shao, Zongshu; Liu, Huijun; Tian, Yupeng

    2007-06-01

    We report the fluorescence upconversion properties of a class of improved pyridinium toluene- p-sulfonates having donor- π-acceptor (D- π-A) structure under two-photon excitation at 1064 nm. The experimental results show that both the two-photon excited (TPE) fluorescence lifetime and the two-photon pumped (TPP) energy upconversion efficiency were increased with the enhancement of electron-donating capability of the donor in the molecule. It is also indicated that an overlong alkyl group tends to result in a weakened molecular conjugation, leading to a decreased two-photon absorption (TPA) cross section. By choosing the donor, we can obtain a longest fluorescence lifetime of 837 ps, a highest energy upconversion efficiency of ˜6.1%, and a maximum TPA cross-section of 8.74×10 -48 cm 4 s/photon in these dyes.

  18. Two-photon vibrational excitation of air by long-wave infrared laser pulses

    NASA Astrophysics Data System (ADS)

    Palastro, J. P.; Peñano, J.; Johnson, L. A.; Hafizi, B.; Wahlstrand, J. K.; Milchberg, H. M.

    2016-08-01

    Ultrashort long-wave infrared (LWIR) laser pulses can resonantly excite vibrations in N2 and O2 through a two-photon transition. The absorptive vibrational component of the ultrafast optical nonlinearity grows in time, starting smaller than but quickly surpassing the electronic, rotational, and vibrational refractive components. The growth of the vibrational component results in a novel mechanism of third-harmonic generation, providing an additional two-photon excitation channel, fundamental + third harmonic. The original and emergent two-photon excitations drive the resonance exactly out of phase, causing spatial decay of the absorptive vibrational nonlinearity. This nearly eliminates two-photon vibrational absorption. Here we present simulations and analytical calculations demonstrating how these processes modify the ultrafast optical nonlinearity in air. The results reveal nonlinear optical phenomena unique to the LWIR regime of ultrashort pulse propagation in the atmosphere.

  19. Two-photon absorption properties of a new series of 2CTσ chromophores

    NASA Astrophysics Data System (ADS)

    Zhou, Yu-fang; Meng, Fan-qing; Zhao, Xian; Xu, Dong; Jiang, Min-hu

    2000-10-01

    We have designed and synthesized a new series of two-photon ASPT-like charge transfer moieties linked by σ-bond spacers to N-position of pyridine cycle. Both theoretical and experimental results show there is no linear absorption in 600-1300 nm, so two-photon properties can be expected in this range. Two-photon absorption (TPA) cross-sections were calculated by using INDO/CI and SOS methods. The results show that those compounds possess large cross-sections as well as appropriate absorption wavelengths. Also the magnitude of the cross-section changes regularly with the number of the σ-bond spacers. These imply that they are good candidates for two-photon devices.

  20. Super-resolution two-photon microscopy via scanning patterned illumination

    NASA Astrophysics Data System (ADS)

    Urban, Ben E.; Yi, Ji; Chen, Siyu; Dong, Biqin; Zhu, Yongling; DeVries, Steven H.; Backman, Vadim; Zhang, Hao F.

    2015-04-01

    We developed two-photon scanning patterned illumination microscopy (2P-SPIM) for super-resolution two-photon imaging. Our approach used a traditional two-photon microscopy setup with temporally modulated excitation to create patterned illumination fields. Combing nine different illuminations and structured illumination reconstruction, super-resolution imaging was achieved in two-photon microscopy. Using 2P-SPIM we achieved a lateral resolution of 141 nm, which represents an improvement by a factor of 1.9 over the corresponding diffraction limit. We further demonstrated super-resolution cellular imaging by 2P-SPIM to image actin cytoskeleton in mammalian cells and three-dimensional imaging in highly scattering retinal tissue.

  1. Y-shaped two-photon absorbing molecules with an imidazole-thiazole core

    NASA Technical Reports Server (NTRS)

    Feng, Ke; De Boni, Leonardo; Misoguti, Lino; Mendonca, C. R.; Meador, Michael; Hsu, Fu-Lian; Bu, Xiu R.

    2004-01-01

    Two new classes of two-photon absorbing Y-shaped molecules have been developed to possess an imidazole-thiazole core and a stilbene-type conjugation pathway with either nitro or sulfonyl as terminal electron-accepting group.

  2. Method and apparatus for producing laser radiation following two-photon excitation of a gaseous medium

    DOEpatents

    Bischel, William K. [Menlo Park, CA; Jacobs, Ralph R. [Livermore, CA; Prosnitz, Donald [Hamden, CT; Rhodes, Charles K. [Palo Alto, CA; Kelly, Patrick J. [Fort Lewis, WA

    1979-02-20

    Method and apparatus for producing laser radiation by two-photon optical pumping of an atomic or molecular gaseous medium and subsequent lasing action. A population inversion is created as a result of two-photon absorption of the gaseous species. Stark tuning is utilized, if necessary, in order to tune the two-photon transition into exact resonance. In particular, gaseous ammonia (NH.sub.3) or methyl fluoride (CH.sub.3 F) is optically pumped by a pair of CO.sub.2 lasers to create a population inversion resulting from simultaneous two-photon excitation of a high-lying vibrational state, and laser radiation is produced by stimulated emission of coherent radiation from the inverted level.

  3. Method and apparatus for producing laser radiation following two-photon excitation of a gaseous medium

    DOEpatents

    Bischel, W.K.; Jacobs, R.R.; Prosnitz, D.P.; Rhodes, C.K.; Kelly, P.J.

    1979-02-20

    Method and apparatus are disclosed for producing laser radiation by two-photon optical pumping of an atomic or molecular gaseous medium and subsequent lasing action. A population inversion is created as a result of two-photon absorption of the gaseous species. Stark tuning is utilized, if necessary, in order to tune the two-photon transition into exact resonance. In particular, gaseous ammonia (NH[sub 3]) or methyl fluoride (CH[sub 3]F) is optically pumped by a pair of CO[sub 2] lasers to create a population inversion resulting from simultaneous two-photon excitation of a high-lying vibrational state, and laser radiation is produced by stimulated emission of coherent radiation from the inverted level. 3 figs.

  4. The two-photon excitation cross section of 6MAP, a fluorescent adenine analogue.

    PubMed

    Stanley, Robert J; Hou, Zhanjia; Yang, Aiping; Hawkins, Mary E

    2005-03-03

    6MAP is a fluorescent analogue of adenine that undergoes Watson-Crick base pairing and base stacking in double-stranded DNA. The one-photon absorption spectrum of 6MAP is characterized by a maximum around 330 nm with moderate quantum yield fluorescence centered at about 420 nm. To take advantage of this probe for confocal and single-molecule microscopy, it would be advantageous to be able to excite the analogue via two photons. We report the first determination of the two-photon excitation cross section and spectrum for 6MAP from 614 to 700 nm. The power dependence of the fluorescence indicates that emission results from the absorption of two photons. The one-photon and two-photon emission line shapes are identical within experimental error. A study of the concentration dependence of the fluorescence yield for one-photon excitation shows no measurable quenching up to about 5 microM. The maximum in the two-photon excitation spectrum gives a two-photon cross section, delta(TPE), of 3.4 +/- 0.1 Goeppert-Mayer (G.M.) at 659 nm, which correlates well with the one-photon absorption maximum. This compares quite favorably with cross sections of various naturally fluorescent biological molecules such as flavins and nicotiamide. In addition, we have also obtained the two-photon-induced fluorescence emission spectrum of quinine sulfate. It is approximately the same as that for one-photon excitation, suggesting that two-photon excitation of quinine sulfate may be used for calibration purposes.

  5. Two-Photon Laser Micro-Nano Fabrication; Understanding from Single-Voxel Level

    DTIC Science & Technology

    2003-04-01

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP014231 TITLE: Two-Photon Laser Micro - Nano Fabrication; Understanding...758 @ 2003 Materials Research Society LL4.6 Two-Photon Laser Micro - Nano Fabrication; Understanding from Single-Voxel Level Satoshi Kawatal and Hong...spatial resolution by the radical quenching effect [8, 9], improvement of fabrication efficiency by using 3D vector scanning [9], 3D micro -diagnosis by

  6. Fast two-photon neuronal imaging and control using a spatial light modulator and ruthenium compounds

    NASA Astrophysics Data System (ADS)

    Peterka, Darcy S.; Nikolenko, Volodymyr; Fino, Elodie; Araya, Roberto; Etchenique, Roberto; Yuste, Rafael

    2010-02-01

    We have developed a spatial light modulator (SLM) based microscope that uses diffraction to shape the incoming two-photon laser source to any arbitrary light pattern. This allows the simultaneous imaging or photostimulation of different regions of a sample with three-dimensional precision at high frame rates. Additionally, we have combined this microscope with a new class of two photon active neuromodulators with Ruthenium BiPyridine (RuBi) based cages that offer great flexibility for neuronal control.

  7. Serial two-photon tomography: an automated method for ex-vivo mouse brain imaging

    PubMed Central

    Ragan, Timothy; Kadiri, Lolahon R.; Venkataraju, Kannan Umadevi; Bahlmann, Karsten; Sutin, Jason; Taranda, Julian; Arganda-Carreras, Ignacio; Kim, Yongsoo; Seung, H. Sebastian

    2011-01-01

    Here we describe an automated method, which we call serial two-photon (STP) tomography, that achieves high-throughput fluorescence imaging of mouse brains by integrating two-photon microscopy and tissue sectioning. STP tomography generates high-resolution datasets that are free of distortions and can be readily warped in 3D, for example, for comparing multiple anatomical tracings. This method opens the door to routine systematic studies of neuroanatomy in mouse models of human brain disorders. PMID:22245809

  8. Two-photon neuronal and astrocytic stimulation with azobenzene-based photoswitches.

    PubMed

    Izquierdo-Serra, Mercè; Gascón-Moya, Marta; Hirtz, Jan J; Pittolo, Silvia; Poskanzer, Kira E; Ferrer, Èric; Alibés, Ramon; Busqué, Félix; Yuste, Rafael; Hernando, Jordi; Gorostiza, Pau

    2014-06-18

    Synthetic photochromic compounds can be designed to control a variety of proteins and their biochemical functions in living cells, but the high spatiotemporal precision and tissue penetration of two-photon stimulation have never been investigated in these molecules. Here we demonstrate two-photon excitation of azobenzene-based protein switches and versatile strategies to enhance their photochemical responses. This enables new applications to control the activation of neurons and astrocytes with cellular and subcellular resolution.

  9. Two-Photon Neuronal and Astrocytic Stimulation with Azobenzene-Based Photoswitches

    PubMed Central

    2015-01-01

    Synthetic photochromic compounds can be designed to control a variety of proteins and their biochemical functions in living cells, but the high spatiotemporal precision and tissue penetration of two-photon stimulation have never been investigated in these molecules. Here we demonstrate two-photon excitation of azobenzene-based protein switches and versatile strategies to enhance their photochemical responses. This enables new applications to control the activation of neurons and astrocytes with cellular and subcellular resolution. PMID:24857186

  10. Absolute frequency measurement of rubidium 5S-7S two-photon transitions.

    PubMed

    Morzyński, Piotr; Wcisło, Piotr; Ablewski, Piotr; Gartman, Rafał; Gawlik, Wojciech; Masłowski, Piotr; Nagórny, Bartłomiej; Ozimek, Filip; Radzewicz, Czesław; Witkowski, Marcin; Ciuryło, Roman; Zawada, Michał

    2013-11-15

    We report the absolute frequency measurements of rubidium 5S-7S two-photon transitions with a cw laser digitally locked to an atomic transition and referenced to an optical frequency comb. The narrow, two-photon transition, 5S-7S (760 nm), insensitive to first-order in a magnetic field, is a promising candidate for frequency reference. The performed tests yielded more accurate transition frequencies than previously reported.

  11. Two-Photon Exchange in Elastic Electron-Proton Scattering: A QCD Factorization Approach

    SciTech Connect

    Kivel, Nikolai; Vanderhaeghen, Marc

    2009-08-28

    We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer Q{sup 2}. It is shown that the leading two-photon exchange amplitude behaves as 1/Q{sup 4}, and can be expressed in a model independent way in terms of the leading twist nucleon distribution amplitudes. Using several models for the nucleon distribution amplitudes, we provide estimates for existing data and for ongoing experiments.

  12. DURIP97 Instrumentation for Characterization of Two-Photon Absorbing Organic Materials

    DTIC Science & Technology

    2007-11-02

    Room Bl 15 Boiling AFB DC 20332- 8050 5 . FUNDING NUMBERS AFOSR Grant F49620-97-1-0200 8. PERFORMING ORGANIZATION REPORT NUMBER 11. SUPPLEMENTARY...REPORT 1 Final Technical ...u DATES CUVCHED 4/1/97 - 3/ 31 /98 4. TITLE AND SUBTITLE DURIP97 Instrumentation for Characterization of Two-Photon...in great demand for variety-of applications including, two-photon excited fluorescence microscopy (7- 4), optical limiting ( 5 - 7), three-dimensional

  13. Two-Photon Entanglement and EPR Experiments Using Type-2 Spontaneous Parametric Down Conversion

    NASA Technical Reports Server (NTRS)

    Sergienko, A. V.; Shih, Y. H.; Pittman, T. B.; Rubin, M. H.

    1996-01-01

    Simultaneous entanglement in spin and space-time of a two-photon quantum state generated in type-2 spontaneous parametric down-conversion is demonstrated by the observation of quantum interference with 98% visibility in a simple beam-splitter (Hanburry Brown-Twiss) anticorrelation experiment. The nonlocal cancellation of two-photon probability amplitudes as a result of this double entanglement allows us to demonstrate two different types of Bell's inequality violations in one experimental setup.

  14. Nonlocality of high-dimensional two-photon orbital angular momentum states

    SciTech Connect

    Aiello, A.; Oemrawsingh, S. S. R.; Eliel, E. R.; Woerdman, J. P.

    2005-11-15

    We propose an interferometric method to investigate the nonlocality of high-dimensional two-photon orbital angular momentum states generated by spontaneous parametric down conversion. We incorporate two half-integer spiral phase plates and a variable-reflectivity output beam splitter into a Mach-Zehnder interferometer to build an orbital angular momentum analyzer. This setup enables testing the nonlocality of high-dimensional two-photon states by repeated use of the Clauser-Horne-Shimony-Holt inequality.

  15. Highly Selective Two-Photon Fluorescent Probe for Ratiometric Sensing and Imaging Cysteine in Mitochondria.

    PubMed

    Niu, Weifen; Guo, Lei; Li, Yinhui; Shuang, Shaomin; Dong, Chuan; Wong, Man Shing

    2016-02-02

    A novel ratiometric mitochondrial cysteine (Cys)-selective two-photon fluorescence probe has been developed on the basis of a merocyanine as the fluorophore and an acrylate moiety as the biothiol reaction site. The biocompatible and photostable acrylate-functionalized merocyanine probe shows not only a mitochondria-targeting property but also highly selective detection and monitoring of Cys over other biothiols such as homocysteine (Hcy) and glutathione (GSH) and hydrogen sulfide (H2S) in live cells. In addition, this probe exhibits ratiometric fluorescence emission characteristics (F518/F452), which are linearly proportional to Cys concentrations in the range of 0.5-40 μM. More importantly, the probe and its released fluorophore, merocyanine, exhibit strong two-photon excited fluorescence (TPEF) with two-photon action cross-section (Φσmax) of 65.2 GM at 740 nm and 72.6 GM at 760 nm in aqueous medium, respectively, which is highly desirable for high contrast and brightness ratiometric two-photon fluorescence imaging of the living samples. The probe has been successfully applied to ratiometrically image and detect mitochondrial Cys in live cells and intact tissues down to a depth of 150 μm by two-photon fluorescence microscopy. Thus, this ratiometric two-photon fluorescent probe is practically useful for an investigation of Cys in living biological systems.

  16. Two-photon fluorescent probes for biological Mg(2+) detection based on 7-substituted coumarin.

    PubMed

    Yin, Haijing; Zhang, Buchang; Yu, Haizhu; Zhu, Lin; Feng, Yan; Zhu, Manzhou; Guo, Qingxiang; Meng, Xiangming

    2015-05-01

    Two novel water-soluble coumarin-based compounds (OC7, NC7) were designed and synthesized as two-photon fluorescent probes for biological Mg(2+) detection. The compounds feature a β-keto acid as a high selective binding site for Mg(2+) and the coumarin framework as the two-photon fluorophore. OC7 and NC7 show significant "off-on" detecting signals (9.05-fold and 23.8-fold fluorescence enhancement) and lower detection limits compared with previous reported two-photon fluorescent probes for Mg(2+). Moreover, OC7-Mg(2+) and NC7-Mg(2+) exhibit large two-photon absorption cross sections (340 and 615 GM) at the near-infrared wavelengths (740 and 860 nm), which indicates that the probes are very suitable for detection of Mg(2+) in vivo. Both OC7 and NC7 are pH-insensitive and of low cytotoxicity and can be applied to image intracellular Mg(2+) under two-photon microscopy (TPM). Our results provide a strategy to modify the coumarin fluorophore to get better two-photon fluorescent properties. And the results also suggest that electronic density of β-keto acid plays a very important role in the recognition of Mg(2+).

  17. Two-Photon and Second Harmonic Microscopy in Clinical and Translational Cancer Research

    PubMed Central

    PERRY, SETH W.; BURKE, RYAN M.; BROWN, EDWARD B.

    2012-01-01

    Application of two-photon microscopy (TPM) to translational and clinical cancer research has burgeoned over the last several years, as several avenues of pre-clinical research have come to fruition. In this review, we focus on two forms of TPM—two-photon excitation fluorescence microscopy, and second harmonic generation microscopy—as they have been used for investigating cancer pathology in ex vivo and in vivo human tissue. We begin with discussion of two-photon theory and instrumentation particularly as applicable to cancer research, followed by an overview of some of the relevant cancer research literature in areas that include two-photon imaging of human tissue biopsies, human skin in vivo, and the rapidly developing technology of two-photon microendoscopy. We believe these and other evolving two-photon methodologies will continue to help translate cancer research from the bench to the bedside, and ultimately bring minimally invasive methods for cancer diagnosis and treatment to therapeutic reality. PMID:22258888

  18. Two Photon Absorption in II-VI Semiconductors: The Influence of Dimensionality and Size.

    PubMed

    Scott, Riccardo; Achtstein, Alexander W; Prudnikau, Anatol; Antanovich, Artsiom; Christodoulou, Sotirios; Moreels, Iwan; Artemyev, Mikhail; Woggon, Ulrike

    2015-08-12

    We report a comprehensive study on the two-photon absorption cross sections of colloidal CdSe nanoplatelets, -rods, and -dots of different sizes by the means of z-scan and two-photon excitation spectroscopy. Platelets combine large particle volumes with ultra strong confinement. In contrast to weakly confined nanocrystals, the TPA cross sections of CdSe nanoplatelets scale superlinearly with volume (V(∼2)) and show ten times more efficient two-photon absorption than nanorods or dots. This unexpectedly strong shape dependence goes well beyond the effect of local fields. The larger the particles' aspect ratio, the greater is the confinement related electronic contribution to the increased two-photon absorption. Both electronic confinement and local field effects favor the platelets and make them unique two-photon absorbers with outstanding cross sections of up to 10(7) GM, the largest ever reported for (colloidal) semiconductor nanocrystals and ideally suited for two-photon imaging and nonlinear optoelectronics. The obtained results are confirmed by two independent techniques as well as a new self-referencing method.

  19. Rapid prototyping of electrochromatography chips for improved two-photon excited fluorescence detection.

    PubMed

    Hackl, Claudia; Beyreiss, Reinhild; Geissler, David; Jezierski, Stefan; Belder, Detlev

    2014-04-15

    In the present study, we introduce two-photon excitation at 532 nm for label-free fluorescence detection in chip electrochromatography. Two-photon excitation at 532 nm offers a promising alternative to one-photon excitation at 266 nm, as it enables the use of economic chip materials instead of fused silica. In order to demonstrate these benefits, one-photon and two-photon induced fluorescence detection are compared in different chip layouts and materials with respect to the achievable sensitivity in the detection of polycyclic aromatic hydrocarbons (PAHs). Customized chromatography chips with cover or bottom slides of different material and thickness are produced by means of a rapid prototyping method based on liquid-phase lithography. The design of thin bottom chips (180 μm) enables the use of high-performance immersion objectives with low working distances, which allows one to exploit the full potential of two-photon excitation for a sensitive detection. The developed method is applied for label-free analysis of PAHs separated on a polymer monolith inside polymer glass sandwich chips made from fused silica or soda-lime glass. The obtained limits of detection range from 40 nM to 1.95 μM, with similar sensitivities in fused silica thin bottom chips for one-photon and two-photon excitation. In deep-UV non- or less-transparent devices two-photon excitation is mandatory for label-free detection of aromatics with high sensitivity.

  20. Spatial-mode two-photon interference at a beam splitter

    SciTech Connect

    Deng, L.-P.; Dang, G.-F.; Wang, K.

    2006-12-15

    We present a general theory on the interference of a two-photon wave packet associated with spatial modes at a beam splitter. We find that the topological symmetry of the two-photon angular spectrum governs the nature of the two-photon interference. We distinguish between the coalescence interference and anticoalescence interference according to the decrease or increase of the coincidence probability in the absence of interference, respectively, and demonstrate that the symmetric and antisymmetric two-photon angular spectra are responsible for perfect coalescence interference and anticoalescence interference, respectively. Then we prove that anticoalescence interference never occurs for two independent photons, and it turns out that anticoalescence interference is the signature of two-photon entanglement. On the basis of this feature, we propose a special Mach-Zehnder interferometer, incorporated with two spiral phase plates, which can change the interference from a coalescence to an anticoalescence type only for a two-photon entangled state. The scheme is simple and straightforward compared with a test of Bell's inequality.

  1. Role of laser-driven electron multi-scattering in resonance-enhanced below-threshold harmonic generation of He atoms

    NASA Astrophysics Data System (ADS)

    Li, Peng-Cheng; Chu, Shih-I.

    2014-05-01

    We perform an ab initio study of the resonance-enhanced harmonic generation of He atoms below the ionization threshold by solving the time-dependent Schr ∖''odinger equation and Maxwell's equation simultaneously. An accurate angular-momentum-dependent model potential is constructed for the description of the He atoms low-lying and Rydberg states. We find that the process of laser-driven electron multi-scattering can play a crucial role in resonance-enhanced below-threshold harmonic generation. This result is confirmed by simulations with an extended semiclassical model and time-frequency analysis of macroscopic harmonic spectra by means of the synchrosqueezed transform based on short time Fourier transform. Our results emphasize that the laser-driven electron multi-scattering must be taken into account to fully understand the quantum path contribution related to resonance-enhanced below-threshold harmonic spectra. This work was partially supported by DOE and by MOE-NSC-NTU-Taiwan.

  2. Enhanced two-photon fluorescence imaging and therapy of cancer cells via Gold@bridged silsesquioxane nanoparticles.

    PubMed

    Croissant, Jonas; Maynadier, Marie; Mongin, Olivier; Hugues, Vincent; Blanchard-Desce, Mireille; Chaix, Arnaud; Cattoën, Xavier; Wong Chi Man, Michel; Gallud, Audrey; Gary-Bobo, Magali; Garcia, Marcel; Raehm, Laurence; Durand, Jean-Olivier

    2015-01-21

    A two-photon photosensitizer with four triethoxysilyl groups is synthesized through the click reaction. This photosensitizer allows the design of bridged silsesquioxane (BS) nanoparticles through a sol-gel process; moreover, gold core BS shells or BS nanoparticles decorated with gold nanospheres are synthesized. An enhancement of the two-photon properties is noted with gold and the nanoparticles are efficient for two-photon imaging and two-photon photodynamic therapy of cancer cells.

  3. An experimental study of nonclassical effects in two-photon interferometry

    NASA Astrophysics Data System (ADS)

    Liang, Junlin

    Two-photon interferometry is a relatively new field with applications ranging from precise measurements of optical phase shifts to fundamental tests of quantum mechanics. In contrast to conventional single-photon interferometry, two-photon interferometry typically involves measuring correlations between two detectors placed in two different output ports of an interferometer. Of particular interest is two-photon interferometry with entangled photon pairs, in which case it is often possible to observe effects that are not possible with classical fields. Because these entanglement effects are becoming increasingly important in Quantum Information Processing (QIP) applications, there is currently a strong need for further exploration of new ideas, basic physics, and experimental techniques of two-photon interferometry. Contained herein are the results of three new two-photon interferometry experiments using entangled photon pairs produced by a Type-I Parametric Down-Conversion (PDC) source. In the first experiment, we demonstrate a new technique for compensating for two-photon interferometer beamsplitter asymmetries by manipulating the polarization degree of freedom in the system. Roughly speaking, projective polarization measurements are used to re-balance the magnitude of various two-photon amplitudes that were made distinguishable by non-ideal refection and transmission coefficients of a key beamsplitter. In the second experiment, we utilize a short coherence-length continuous-wave (CW) PDC pump laser to explore two-photon interferometry in a new intermediate regime between the more familiar extremal cases which use either a long coherence-length CW pump or an ultra-short pulsed pump laser. These results provide new insight into the role of PDC pump coherence in two-photon interferometry. Finally, we use two-photon interferometry to experimentally investigate entangled "photon holes", which is a new form of entanglement that arises from the correlated absence of

  4. Laser-induced ionization of Na vapor

    SciTech Connect

    Wu, R.C.Y.; Judge, D.L.; Roussel, F.; Carre, B.; Breger, P.; Spiess, G.

    1982-01-01

    The production of Na/sub 2//sup +/ ions by off-resonant laser excitation in the 5800-6200A region mainly results from two-photon absorption by the Na/sub 2/ molecule to highly excited gerade states followed by (a) direct ionization by absorbing a third photon or (b) coupling to the molecular Na/sub 2/ D/sup 1/PI..mu.. Rydberg state which is subsequently ionized by absorbing a third photon. This mechanism, i.e., a two-photon resonance three photon ionization process, explains a recent experimental observation of Roussel et al. It is suggested that the very same mechanism is also responsible for a similar observation reported by Polak-Dingels et al in their work using two crossed Na beams. In the latter two studies the laser-induced associative ionization processes were reported to be responsible for producing the Na/sub 2//sup +/ ion. From the ratio of molecular to atomic concentration in the crossed beam experiment of Polak-Dingels et al we estimate that the cross section for producing Na/sub 2//sup +/ through laser-induced associative ionization is at least four orders of magnitude smaller than ionization through the two-photon resonance three photon ionization process in Na/sub 2/ molecules.

  5. Laser-induced ionization of Na vapor

    NASA Astrophysics Data System (ADS)

    Wu, C. Y. Robert; Judge, D. L.; Roussel, F.; Carré, B.; Breger, P.; Spiess, G.

    1982-09-01

    The production of Na2+ ions by off-resonant laser excitation in the 5800-6200Å region mainly results from two-photon absorption by the Na2 molecule to highly excited gerade states followed by (a) direct ionization by absorbing a third photon or (b) coupling to the molecular Na2 D1Πu Rydberg state which is subsequently ionized by absorbing a third photon. This mechanism, i.e., a two-photon resonance three photon ionization process, explains a recent experimental observation of Roussel et al. It is suggested that the very same mechanism is also responsible for a similar observation reported by Polak-Dingels et al in their work using two crossed Na beams. In the latter two studies the laser-induced associative ionization processes were reported to be responsible for producing the Na2+ ion. From the ratio of molecular to atomic concentration in the crossed beam experiment of Polak-Dingels et al. we estimate that the cross section for producing Na2+ through laser-induced associative ionization is at least four orders of magnitude smaller than ionization through the two-photon resonance three photon ionization process in Na2 molecules.

  6. Evaluation of the exothermicity of the chemi-ionization reaction Sm + O → SmO{sup +} + e{sup −}

    SciTech Connect

    Cox, Richard M; Kim, JungSoo; Armentrout, P. B. E-mail: mheaven@emory.edu; Bartlett, Joshua; VanGundy, Robert A.; Heaven, Michael C. E-mail: mheaven@emory.edu; Ard, Shaun G.; Shuman, Nicholas S.; Viggiano, Albert A. E-mail: mheaven@emory.edu; Melko, Joshua J.

    2015-04-07

    The exothermicity of the chemi-ionization reaction Sm + O → SmO{sup +} + e{sup −} has been re-evaluated through the combination of several experimental methods. The thermal reactivity (300–650 K) of Sm{sup +} and SmO{sup +} with a range of species measured using a selected ion flow tube-mass spectrometer apparatus is reported and provides limits for the bond strength of SmO{sup +}, 5.661 eV ≤ D{sub 0}(Sm{sup +}-O) ≤ 6.500 eV. A more precise value is measured to be 5.72{sub 5} ± 0.07 eV, bracketed by the observed reactivity of Sm{sup +} and SmO{sup +} with several species using a guided ion beam tandem mass spectrometer (GIBMS). Combined with the established Sm ionization energy (IE), this value indicates an exothermicity of the title reaction of 0.08 ± 0.07 eV, ∼0.2 eV smaller than previous determinations. In addition, the ionization energy of SmO has been measured by resonantly enhanced two-photon ionization and pulsed-field ionization zero kinetic energy photoelectron spectroscopy to be 5.7427 ± 0.0006 eV, significantly higher than the literature value. Combined with literature bond energies of SmO, this value indicates an exothermicity of the title reaction of 0.14 ± 0.17 eV, independent from and in agreement with the GIBMS result presented here. The evaluated thermochemistry also suggests that D{sub 0}(SmO) = 5.83 ± 0.07 eV, consistent with but more precise than the literature values. Implications of these results for interpretation of chemical release experiments in the thermosphere are discussed.

  7. Piezoelectric resonance enhanced microwave and optoelectronic interactive devices

    NASA Astrophysics Data System (ADS)

    McIntosh, Robert

    Electro-optic (EO) devices that modulate optical signals by electric fields are an integrative part of the photonics industry and device optimization is an important area of research. As applications move to large bandwidth and higher frequency, low electro-optic effects and the requirement for large dimension become restrictive for microwave-optical devices. Both experimental and computational evaluations indicate that strain and polarization distribution have a significant impact on electromagnetic wave propagation resulting from a resonant structure; however, no systematic study or fundamental understandings are available. This dissertation research has been carried out to study and further develop the subject of piezoelectric resonance enhanced electro-acoustic-optic process, in order to improve the sensitivity and efficiency of electro-optic sensors and to explore novel applications. Many finite element models have been constructed for evaluating the mechanisms of the phenomena and the effectiveness of the device structure. The enhancement in transmission is found to be directly related to the strain-coupled local polarization. At piezoelectric resonance oscillating dipoles or local polarizations become periodic in the material and have the greatest impact on transmission. Results suggest that the induced charge distribution by a piezoelectric material at certain resonant frequencies is effective for aiding or impeding the transmission of a propagating wave. The behavior of both piezoelectric-defined (or intrinsic piezoelectric materials) and engineered periodic structures are reported. The piezoelectric response of the surface displacement of samples is investigated using an ultra-high frequency laser Doppler vibrometer. A two dimensional view of the surface is obtained and the surface displacement, velocity and acceleration are compared to the electro-optic response under the resonant condition. A study of the acousto-optic (AO) effect in a family of oxide

  8. Measurement of degenerate two-photon absorption spectra of a series of developed two-photon initiators using a dispersive white light continuum Z-scan

    NASA Astrophysics Data System (ADS)

    Ajami, Aliasghar; Husinsky, Wolfgang; Tromayer, Maximilian; Gruber, Peter; Liska, Robert; Ovsianikov, Aleksandr

    2017-08-01

    To achieve efficient micro- and nanostructuring based on two-photon polymerization (2PP), the development and evaluation of specialized two-photon initiators (2PIs) are essential. Hence, a reliable method to determine the two-photon absorption (2PA) spectra of the synthesized 2PIs used for 2PP structuring is crucial. A technique by which absolute visible-to-near-infrared 2PA spectra of degenerate nature can be determined via performing a single dispersive white-light continuum (WLC) Z-scan has been realized. Using a dispersed white light beam containing 8 fs pulses at wavelengths ranging from 650 nm to 950 nm, the nonlinear transmittance as a function of the sample position can be measured for all spectral components by performing a single scan along the laser beam propagation direction. In this work, the 2PA spectrum of three different 2PIs was determined using this technique. 2PP structuring was also accomplished using the developed 2PIs at different wavelengths. Tuning the wavelength of the laser to match the peak of the 2PA spectra of the developed 2PIs resulted in lower intensity thresholds and facilitated higher structuring speeds. As an example, using M2CMK 2PI for 2PP, the scanning speed can be increased up to 5 folds when the laser wavelength is tuned to 760 nm (i.e., 2PA maximum) instead of the conventionally used 800 nm.

  9. A multidimensional screening method for the selection of two-photon enhanced fluorescent proteins

    NASA Astrophysics Data System (ADS)

    Stoltzfus, Caleb; Barnett, Lauren; Rebane, Aleksander; Hughes, Thomas; Drobizhev, Mikhail; Wicks, Geoffrey; Mikhailov, Alexandr

    2014-03-01

    Two-photon excitation of fluorescent proteins (FPs) is widely used in imaging whole organisms or living tissues. Many different FPs are now available but these proteins have only been optimized for their one-photon properties. We have developed a technique for screening entire libraries of E. coli colonies expressing FPs that utilizes multiple wavelengths of linear excitation as well as two-photon excitation. Single mutations in a particular protein that affect one or twophoton properties are easily identified, providing new views of structure/function relationships. An amplified femtosecond Ti:sapphire laser and a spectrally filtered lamp source are used to acquire the fluorescence signals of up to ~1000 E. coli colonies on a standard Petri dish. Automation of the analysis and acquisition of the fluorescent signals makes it feasible to rapidly screen tens of thousands of colonies. In a proof of principle experiment with the commonly used EGFP, we used two rounds of error prone PCR and selection to evolve new proteins with shifted absorption and increased two-photon cross sections at 790nm. This method of screening, coupled with careful measurements of photo bleaching dynamics and two-photon cross sections, should make it possible to optimize a wide variety of fluorescent proteins and biosensors for use in two-photon microscopes.

  10. Properties and chemical environment effects of alkylamino styryl pyrazine two-photon fluorophores

    NASA Astrophysics Data System (ADS)

    Collette, Jeremy C.; Harper, Aaron W.

    2003-11-01

    Advancement over the past decade of materials based on two-photon absorption has been phenomenal; yet, a need for greater understanding of multi-photon processes remains. Questions of design to maximize two-photon absorbance cross-sections and quantum yields have been addressed quantitatively. However, effects of the chemical environment on the absorption and emission processes in these chromophores are largely unexplored. This study presents the effects of 26 different solvents on the absorption and emission characteristics of a set of six new alkylamino-substituted styryl pyrazines. The solvatochromic comparison method is employed to derive structure-optical property relationships within this family of fluorophores, and the effects of solvent polarity, hydrogen bonding and inductive and dispersive forces are discussed. Electrostatic and transition moments are measured and their contributions to two-photon absorbance cross-sections (δTPA) are discussed. Symmetric D-π-A-π-D molecular architecture is thought to play a very important role in increasing δTPA by disrupting the degeneracy of excited states and increasing one- and two-photon transition probabilities. The coupling of strong electron donors to strong electron acceptors with symmetric D-π-A-π-D molecular architecture is shown to produce fluorophores with exceptional two-photon activities.

  11. Sub-diffraction positioning of a two-photon excited and optically trapped quantum dot.

    PubMed

    Jauffred, Liselotte; Kyrsting, Anders; Arnspang, Eva C; Reihani, S Nader S; Oddershede, Lene B

    2014-06-21

    Colloidal quantum dots are luminescent long-lived probes that can be two-photon excited and manipulated by a single laser beam. Therefore, quantum dots can be used for simultaneous single molecule visualization and force manipulation using an infra-red laser. Here, we show that even a single optically trapped quantum dot, performing restricted Brownian motion within the focal volume, can be two-photon excited by the trapping laser beam and its luminescence can be detected by a camera. After two-photon excitation for a time long enough, the emitted light from the quantum dot is shown to blueshift. A quantum dot is much smaller than a diffraction limited laser focus and by mapping out the intensity of the focal volume and overlaying this with the positions visited by a quantum dot, a quantum dot is shown often to explore regions of the focal volume where the intensity is too low to render two-photon absorption likely. This is in accordance with the observation that a trapped quantum dot is only fluorescing 5-10 percent of the time. The results are important for realizing nano-scale quantum dot control and visualization and for correct interpretation of experiments using two-photon excited quantum dots as markers.

  12. Pseudopotential calculations and photothermal lensing measurements of two-photon absorption in solids

    SciTech Connect

    White, W.T. III

    1985-11-04

    We have studied two-photon absorption in solids theoretically and experimentally. We have shown that it is possible to use accurate band structure techniques to compute two-photon absorption spectra within 15% of measured values in a wide band-gap material, ZnS. The empirical pseudopotential technique that we used is significantly more accurate than previous models of two-photon absorption in zinc blende materials, including present tunneling theories (which are essentially parabolic-band results in disguise) and the nonparabolic-band formalism of Pidgeon et al. and Weiler. The agreement between our predictions and previous measurements allowed us to use ZnS as a reference material in order to validate a technique for measuring two-photon absorption that was previously untried in solids, pulsed dual-beam thermal lensing. With the validated technique, we examined nonlinear absorption in one other crystal (rutile) and in several glasses, including silicates, borosilicates, and one phosphate glass. Initially, we believed that the absorption edges of all the materials were comparable; however, subsequent evidence suggested that the effective band-gap energies of the glasses were above the energy of two photons in our measurement. Therefore, we attribute the nonlinear absorption that we observed in glasses to impurities or defects. The measured nonlinear absorption coefficients were of the order of a few cm/TW in the glasses and of the order of 10 cm/GW in the crystals, four orders of magnitude higher than in glasses. 292 refs.

  13. Enhanced Size Selection in Two-Photon Excitation for CsPbBr3 Perovskite Nanocrystals.

    PubMed

    Chen, Junsheng; Chábera, Pavel; Pascher, Torbjörn; Messing, Maria E; Schaller, Richard; Canton, Sophie; Zheng, Kaibo; Pullerits, Tõnu

    2017-10-05

    Cesium lead bromide (CsPbBr3) perovskite nanocrystals (NCs), with large two-photon absorption (TPA) cross-section and bright photoluminescence (PL), have been demonstrated as stable two-photon-pumped lasing medium. With two-photon excitation, red-shifted PL spectrum and increased PL lifetime is observed compared with one-photon excitation. We have investigated the origin of such difference using time-resolved laser spectroscopies. We ascribe the difference to the enhanced size selection of NCs by two-photon excitation. Because of inherent nonlinearity, the size dependence of absorption cross-section under TPA is stronger. Consequently, larger size NCs are preferably excited, leading to longer excited-state lifetime and red-shifted PL emission. In a broad view, the enhanced size selection in two-photon excitation of CsPbBr3 NCs is likely a general feature of the perovskite NCs and can be tuned via NC size distribution to influence their performance within NC-based nonlinear optical materials and devices.

  14. Molecular engineering of two-photon fluorescent probes for bioimaging applications

    NASA Astrophysics Data System (ADS)

    Liu, Hong-Wen; Liu, Yongchao; Wang, Peng; Zhang, Xiao-Bing

    2017-03-01

    During the past two decades, two-photon microscopy (TPM), which utilizes two near-infrared photons as the excitation source, has emerged as a novel, attractive imaging tool for biological research. Compared with one-photon microscopy, TPM offers several advantages, such as lowering background fluorescence in living cells and tissues, reducing photodamage to biosamples, and a photobleaching phenomenon, offering better 3D spatial localization, and increasing penetration depth. Small-molecule-based two-photon fluorescent probes have been well developed for the detection and imaging of various analytes in biological systems. In this review, we will give a general introduction of molecular engineering of two-photon fluorescent probes based on different fluorescence response mechanisms for bioimaging applications during the past decade. Inspired by the desired advantages of small-molecule two-photon fluorescent probes in biological imaging applications, we expect that more attention will be devoted to the development of new two-photon fluorophores and applications of TPM in areas of bioanalysis and disease diagnosis.

  15. Titanium: Sapphire laser as an excitation source in two-photon spectroscopy

    SciTech Connect

    Fisher, W.G.; Wachter, E.A.; Armas, M.; Seaton, C.

    1997-02-01

    The passively mode-locked titanium:sapphire laser provides new opportunities for acquiring two-photon spectral data in the near-infrared, a region not commonly accessible to synchronously pumped dye lasers. This source generates pulses with peak powers near 100 kW at average powers over 1 W and is capable of yielding two-photon signals roughly two orders of magnitude larger than is possible with synchronously pumped dye lasers. However, the multimode output of this laser exhibits significant temporal and spectral pulse profile variations as the laser wavelength is tuned. As a consequence, peak powers of the titanium:sapphire laser can vary independently from average power across the tuning range. This wavelength dependence, coupled with the quadratic dependence of the two-photon signal upon the instantaneous power of the laser, precludes simple average power correction of nonlinear spectral band shapes. Here, we investigate the key properties of the titanium:sapphire laser as an excitation source for two-photon spectroscopy. We also identify a chemical reference suitable for obtaining source-corrected excitation spectra in the near-infrared using a double-beam, ratiometric approach; this is based on a source-independent two-photon excitation spectrum for the laser dye coumarin-480 that has been obtained with a single-frequency titanium:sapphire laser. From these data, correction factors are generated for correction of multimode source data. {copyright} {ital 1997} {ital Society for Applied Spectroscopy}

  16. Long-Term Two-Photon Imaging in Awake Macaque Monkey.

    PubMed

    Li, Ming; Liu, Fang; Jiang, Hongfei; Lee, Tai Sing; Tang, Shiming

    2017-03-08

    Successful application of two-photon imaging with genetic tools in awake macaque monkeys will enable fundamental advances in our understanding of higher cognitive function at the level of molecular and neuronal circuits. Here we report techniques for long-term two-photon imaging in awake macaque monkeys. Using genetically encoded indicators including GCaMP5 and GCaMP6s delivered by AAV2/1 into the visual cortex, we demonstrate that high-quality two-photon imaging of large neuronal populations can be achieved and maintained in awake monkeys for months. Simultaneous intracellular recording and two-photon calcium imaging confirm that fluorescence activity is linearly proportional to neuronal spiking activity across a wide range of firing rates (10 Hz to 150 Hz). By providing two-photon imaging access to cortical neuronal populations at single-cell or single dendritic spine resolution in awake monkeys, the techniques reported can help bridge the use of modern genetic and molecular tools and the study of higher cognitive function.

  17. Molecular engineering of two-photon fluorescent probes for bioimaging applications.

    PubMed

    Liu, Hong-Wen; Liu, Yongchao; Wang, Peng; Zhang, Xiao-Bing

    2017-03-22

    During the past two decades, two-photon microscopy (TPM), which utilizes two near-infrared photons as the excitation source, has emerged as a novel, attractive imaging tool for biological research. Compared with one-photon microscopy, TPM offers several advantages, such as lowering background fluorescence in living cells and tissues, reducing photodamage to biosamples, and a photobleaching phenomenon, offering better 3D spatial localization, and increasing penetration depth. Small-molecule-based two-photon fluorescent probes have been well developed for the detection and imaging of various analytes in biological systems. In this review, we will give a general introduction of molecular engineering of two-photon fluorescent probes based on different fluorescence response mechanisms for bioimaging applications during the past decade. Inspired by the desired advantages of small-molecule two-photon fluorescent probes in biological imaging applications, we expect that more attention will be devoted to the development of new two-photon fluorophores and applications of TPM in areas of bioanalysis and disease diagnosis.

  18. Sulfonated aluminum phthalocyanines for two-photon photodynamic cancer therapy: the effect of the excitation wavelength

    NASA Astrophysics Data System (ADS)

    Wang, J.; Li, W.; Yu, H. B.; Cheung, N. H.; Chen, J. Y.

    2014-03-01

    Sulfonated aluminum phthalocyanine (AlPcS) is a well-studied photosensitizer which has been widely used in research and in clinical applications of the photodynamic therapy of cancers. Conventionally, one-photon excitation was used, but it was unknown whether two-photon excitation of AlPcS was equally effective. In this study, the two-photon absorption cross sections of AlPcS at near infrared wavelengths were deduced from femtosecond (fs) laser-induced fluorescence. We found that the two-photon absorption cross section of AlPcS was strongly dependent on the excitation wavelength. It was about 19 GM when excited at 800 nm, but grew to 855 GM when excited at 750 nm. The 750 nm fs-laser-induced fluorescence images of AlPcS in human nasopharyngeal carcinoma cells were clearly visible while the corresponding images were very dim when excited at 800 nm. Singlet oxygen production was 13 times higher when excited at 750 nm relative to 800 nm. Our subsequent in vitro experiments showed that 750 nm two-photon excitation with an unfocused fs laser beam damaged cancer cells in a light-dose-dependent manner typical of photodynamic therapy (PDT). The killing at 750 nm was about 9-10 times more efficient than at 800 nm. These results demonstrated for the first time that AlPcS has good potential for two-photon PDT of cancers.

  19. A theoretical investigation of two typical two-photon pH fluorescent probes.

    PubMed

    Xu, Zhong; Ren, Ai-Min; Guo, Jing-Fu; Liu, Xiao-Ting; Huang, Shuang; Feng, Ji-Kang

    2013-01-01

    Intracellular pH plays an important role in many cellular events, such as cell growth, endocytosis, cell adhesion and so on. Some pH fluorescent probes have been reported, but most of them are one-photon fluorescent probes, studies about two-photon fluorescent probes are very rare. In this work, the geometrical structure, electronic structure and one-photon properties of a series of two-photon pH fluorescent probes have been theoretically studied by using density functional theory (DFT) method. Their two-photon absorption (TPA) properties are calculated using the method of ZINDO/sum-over-states method. Two types of two-photon pH fluorescent probes have been investigated by theoretical methods. The mechanisms of the Photoinduced Charge Transfer (PCT) probes and the Photoinduced Electron Transfer (PET) probes are verified specifically. Some designed strategies of good two-photon pH fluorescent probes are suggested on the basis of the investigated results of two mechanisms. For the PCT probes, substituting a stronger electron-donating group for the terminal methoxyl group is an advisable choice to increase the TPA cross section. For the PET probes, the TPA cross sections increase upon protonation.

  20. Selective two-photon excitation of a vibronic state by correlated photons.

    PubMed

    Oka, Hisaki

    2011-03-28

    We theoretically investigate the two-photon excitation of a molecular vibronic state by correlated photons with energy anticorrelation. A Morse oscillator having three sets of vibronic states is used, as an example, to evaluate the selectivity and efficiency of two-photon excitation. We show that a vibrational mode can be selectively excited with high efficiency by the correlated photons, without phase manipulation or pulse-shaping techniques. This can be achieved by controlling the quantum correlation so that the photon pair concurrently has two pulse widths, namely, a temporally narrow width and a spectrally narrow width. Though this concurrence is seemingly contradictory, we can create such a photon pair by tailoring the quantum correlation between two photons.