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Sample records for femtosecond pulse pairs

  1. Spatiotemporal control of degenerate multiphoton fluorescence microscopy with delay-tunable femtosecond pulse pairs

    NASA Astrophysics Data System (ADS)

    Das, Dhiman; Bhattacharyya, Indrajit; Goswami, Debabrata

    2016-07-01

    Selective excitation of a particular fluorophore in an ensemble of different fluorophores with overlapping fluorescence spectra is shown to be dependent on the time delay of femtosecond pulse pairs in multiphoton fluorescence microscopy. In particular, the two-photon fluorescence behavior of the Texas Red and DAPI dye pair inside Bovine Pulmonary Artery Endothelial (BPAE) cells depends strongly on the center wavelength of the laser, as well as the delay between two identical laser pulses in one-color femtosecond pulse-pair excitation scheme. Thus, we present a novel design concept using pairs of femtosecond pulses at different central wavelengths and tunable pulse separations for controlling the image contrast between two spatially and spectrally overlapping fluorophores. This femtosecond pulse-pair technique is unique in utilizing the variation of dye dynamics inside biological cells as a contrast mode in microscopy of different fluorophores.

  2. Towards a turn-key femtosecond laser: Elimination of grating-pair stretchers from chirped-pulse amplification systems

    SciTech Connect

    Kane, S.; Squier, J.

    1995-11-01

    The authors have demonstrated for the first time a method for compensating second and third-order dispersion in the normal dispersion regime. They show that a pair of gratings written on to dielectric slabs can produce third-order dispersion which is opposite in sign to that of a traditional grating pair. Their calculations indicate that this grating pair can compensate for very large amounts of material dispersion in a compact geometry, making possible the expansion, amplification, and compression of sub-100-fs pulses in simple and robust systems. In addition, this grating pair can be used as a compact intracavity dispersion compensator, significantly reducing the size and complexity of femtosecond sources.

  3. Femtosecond polarization pulse shaping.

    PubMed

    Brixner, T; Gerber, G

    2001-04-15

    We report computer-controlled femtosecond polarization pulse shaping where intensity, momentary frequency, and light polarization are varied as functions of time. For the first time to our knowledge, a pulse shaper is used to modulate the degree of ellipticity as well as the orientation of the elliptical principal axes within a single laser pulse by use of a 256-pixel two-layer liquid-crystal display inside a zero-dispersion compressor. Interferometric stability of the setup is not required. Complete pulse characterization is achieved by dual-channel spectral interferometry. This technology has a large range of applications, especially in the field of quantum control. PMID:18040384

  4. Femtosecond pulse shaping using plasmonic snowflake nanoantennas

    SciTech Connect

    Tok, Ruestue Umut; Sendur, Kuersat

    2011-09-15

    We have theoretically demonstrated femtosecond pulse manipulation at the nanoscale using the plasmonic snowflake antenna's ability to localize light over a broad spectrum. To analyze the interaction of the incident femtosecond pulse with the plasmonic nanoantenna, we first decompose the diffraction limited incident femtosecond pulse into its spectral components. The interaction of each spectral component with the nanoantenna is analyzed using finite element technique. The time domain response of the plasmonic antenna is obtained using inverse Fourier transformation. It is shown that the rich spectral characteristics of the plasmonic snowflake nanoantenna allow manipulation of the femtosecond pulses over a wide spectrum. Light localization around the gap region of the nanoantenna is shown for femtosecond pulses. As the alignment of incident light polarization is varied, different antenna elements oscillate, which in turn creates a different spectrum and a distinct femtosecond response.

  5. High energy femtosecond pulse compression

    NASA Astrophysics Data System (ADS)

    Lassonde, Philippe; Mironov, Sergey; Fourmaux, Sylvain; Payeur, Stéphane; Khazanov, Efim; Sergeev, Alexander; Kieffer, Jean-Claude; Mourou, Gerard

    2016-07-01

    An original method for retrieving the Kerr nonlinear index was proposed and implemented for TF12 heavy flint glass. Then, a defocusing lens made of this highly nonlinear glass was used to generate an almost constant spectral broadening across a Gaussian beam profile. The lens was designed with spherical curvatures chosen in order to match the laser beam profile, such that the product of the thickness with intensity is constant. This solid-state optics in combination with chirped mirrors was used to decrease the pulse duration at the output of a terawatt-class femtosecond laser. We demonstrated compression of a 33 fs pulse to 16 fs with 170 mJ energy.

  6. Photoemission using femtosecond laser pulses

    SciTech Connect

    Srinivasan-Rao, T.; Tsang, T.; Fischer, J.

    1991-10-01

    Successful operation of short wavelength FEL requires an electron bunch of current >100 A and normalized emittance < 1 mm-mrad. Recent experiments show that RF guns with photocathodes as the electron source may be the ideal candidate for achieving these parameters. To reduce the emittance growth due to space charge and RF dynamics effects, the gun may have to operate at high field gradient (hence at high RF frequency) and a spot size small compared to the aperture. This may necessitate the laser pulse duration to be in the subpicosecond regime to reduce the energy spread. We will present the behavior of metal photocathodes upon irradiation with femtosecond laser beams, comparison of linear and nonlinear photoemission, and scalability to high currents. Theoretical estimate of the intrinsic emittance at the photocathode in the presence of the anomalous heating of the electrons, and the tolerance on the surface roughness of the cathode material will be discussed.

  7. Programmable femtosecond laser pulses in the ultraviolet

    SciTech Connect

    Hacker, M.; Feurer, T.; Sauerbrey, R.; Lucza, T.; Szabo, G.

    2001-06-01

    Using a combination of a zero-dispersion compressor and spectrally compensated sum-frequency generation, we have produced amplitude-modulated femtosecond pulses in the UV at 200 nm. {copyright} 2001 Optical Society of America

  8. Encoding and decoding of femtosecond pulses.

    PubMed

    Weiner, A M; Heritage, J P; Salehi, J A

    1988-04-01

    We demonstrate the spreading of femtosecond optical pulses into picosecond-duration pseudonoise bursts. Spreading is accomplished by encoding pseudorandom binary phase codes onto the optical frequency spectrum. Subsequent decoding of the spectral phases restores the original pulse. We propose that frequency-domain encoding and decoding of coherent ultrashort pulses could form the basis for a rapidly reconfigurable, code-division multiple-access optical telecommunications network. PMID:19745879

  9. Holographic capture of femtosecond pulse propagation

    SciTech Connect

    Centurion, Martin; Pu Ye; Psaltis, Demetri

    2006-09-15

    We have implemented a holographic system to study the propagation of femtosecond laser pulses with high temporal (150 fs) and spatial resolutions (4 {mu}m). The phase information in the holograms allows us to reconstruct both positive and negative index changes due to the Kerr nonlinearity (positive) and plasma formation (negative), and to reconstruct three-dimensional structure. Dramatic differences were observed in the interaction of focused femtosecond pulses with air, water, and carbon disulfide. The air becomes ionized in the focal region, while in water long plasma filaments appear before the light reaches a tight focus. In contrast, in carbon disulfide the optical beam breaks up into multiple filaments but no plasma is measured. We explain these different propagation regimes in terms of the different nonlinear material properties.

  10. Hemifusion of cells using femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Katchinskiy, Nir; Godbout, Roseline; Goez, Helly R.; Elezzabi, Abdulhakem Y.

    2015-03-01

    Attachment of single cells via hemifusion of cellular membranes using femtosecond laser pulses is reported in this manuscript. This is a method to attach single cells using sub-10 femtosecond laser pulses, with 800 nm central wavelength delivered from a Ti:Sapphire laser is described. A fluorescent dye, Calcein AM, was used to verify that the cell's cytoplasm did not migrate from a dyed cell to a non-dyed cell, in order to ascertain that the cells did not go through cell-fusion process. An optical tweezer was used in order to assess the mechanical integrity of the attached joint membranes. Hemifusion of cellular membranes was successful without initiating full cell fusion. Attachment efficiency of 95% was achieved, while the cells' viability was preserved. The attachment was performed via the delivery of one to two trains of sub-10 femtosecond laser pulses lasting 15 milliseconds each. An ultrafast reversible destabilization of the phospholipid molecules in the cellular membranes was induced due to a laser-induced ionization process. The inner phospholipid cell membrane remained intact during the attachment procedure, and cells' cytoplasm remained isolated from the surrounding medium. The unbounded inner phospholipid molecules bonded to the nearest free phospholipid molecule, forming a joint cellular membrane at the connection point. The cellular membrane hemifusion technique can potentially provide a platform for the creation of engineered tissue and cell cultures.

  11. Pulse front tilt measurement of femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Dimitrov, Nikolay; Stoyanov, Lyubomir; Stefanov, Ivan; Dreischuh, Alexander; Hansinger, Peter; Paulus, Gerhard G.

    2016-07-01

    In this work we report experimental investigations of an intentionally introduced pulse front tilt on femtosecond laser pulses by using an inverted field correlator/interferometer. A reliable criterion for the precision in aligning (in principle) dispersionless systems for manipulating ultrashort pulses is developed, specifically including cases when the pulse front tilt is a result of a desired spatio-temporal coupling. The results obtained using two low-dispersion diffraction gratings are in good qualitative agreement with the data from a previously developed analytical model and from an independent interferometric measurement.

  12. Femtosecond pulses propagation through pure water

    NASA Astrophysics Data System (ADS)

    Naveira, Lucas; Sokolov, Alexei; Byeon, Joong-Hyeok; Kattawar, George

    2007-10-01

    Recently, considerable attention has been dedicated to the field of optical precursors, which can possibly be applied to long-distance underwater communications. Input beam intensities have been carefully adjusted to keep experiments in the linear regime, and some experiments have shown violation of the Beer-Lambert law. We are presently carrying out experiments using femtosecond laser pulses propagating through pure water strictly in the linear regime to study this interesting and important behavior. We are also employing several new and innovative schemes to more clearly define the phenomena.

  13. Chirped femtosecond pulse scattering by spherical particles

    NASA Astrophysics Data System (ADS)

    Kim, Dal-Woo; Xiao, Gang-Yao; Lee, Tong-Nyong

    1996-05-01

    Generalized Lorentz-Mie formulas are used to study the scattering characteristics when a chirped femtosecond pulse illuminates a spherical particle. For a linear chirped Gaussian pulse with the envelope function g( tau ) = exp[- pi (1 + ib) tau 2], dimensionless parameter b is defined as a chirp. The calculation illustrated that even for pulses with a constant carrier wavelength ( lambda 0 = 0.5 mu m) and pulse-filling coefficient (l0 = 1.98), the efficiencies for extinction and scattering differ very much between the carrier wave and the different chirped pulses. The slowly varying background of the extinction and the scattering curves is damped by the chirp. When the pulse is deeply chirped, the maxima and minima of the background curves reduce to the point where they disappear, and the efficiency curves illustrate a steplike dependence on the sphere size. Another feature is that the only on the amount of chirp (|b|), regardless of upchirp (b greater than 0) or downchirp (b less than 0).

  14. Optical reprogramming with ultrashort femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Uchugonova, Aisada; Breunig, Hans G.; Batista, Ana; König, Karsten

    2015-03-01

    The use of sub-15 femtosecond laser pulses in stem cell research is explored with particular emphasis on the optical reprogramming of somatic cells. The reprogramming of somatic cells into induced pluripotent stem (iPS) cells can be evoked through the ectopic expression of defined transcription factors. Conventional approaches utilize retro/lenti-viruses to deliver genes/transcription factors as well as to facilitate the integration of transcription factors into that of the host genome. However, the use of viruses may result in insertional mutations caused by the random integration of genes and as a result, this may limit the use within clinical applications due to the risk of the formation of cancer. In this study, a new approach is demonstrated in realizing non-viral reprogramming through the use of ultrashort laser pulses, to introduce transcription factors into the cell so as to generate iPS cells.

  15. Femtosecond molecular dynamics of tautomerization in model base pairs

    NASA Astrophysics Data System (ADS)

    Douhal, A.; Kim, S. K.; Zewail, A. H.

    1995-11-01

    HYDROGEN bonds commonly lend robustness and directionality to molecular recognition processes and supramolecular structures1,2. In particular, the two or three hydrogen bonds in Watson-Crick base pairs bind the double-stranded DNA helix and determine the complementarity of the pairing. Watson and Crick pointed out3, however, that the possible tautomers of base pairs, in which hydrogen atoms become attached to the donor atom of the hydrogen bond, might disturb the genetic code, as the tautomer is capable of pairing with different partners. But the dynamics of hydrogen bonds in general, and of this tautomerization process in particular, are not well understood. Here we report observations of the femtosecond dynamics of tautomerization in model base pairs (7-azaindole dimers) containing two hydrogen bonds. Because of the femtosecond resolution of proton motions, we are able to examine the cooperativity of formation of the tautomer (in which the protons on each base are shifted sequentially to the other base), and to determine the characteristic timescales of the motions in a solvent-free environment. We find that the first step occurs on a timescale of a few hundred femtoseconds, whereas the second step, to form the full tautomer, is much slower, taking place within several picoseconds; the timescales are changed significantly by replacing hydrogen with deuterium. These results establish the molecular basis of the dynamics and the role of quantum tunnelling.

  16. Optical gene transfer by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Konig, Karsten; Riemann, Iris; Tirlapur, Uday K.

    2003-07-01

    Targeted transfection of cells is an important technique for gene therapy and related biomedical applications. We delineate how high-intensity (1012 W/cm2) near-infrared (NIR) 80 MHz nanojoule femtosecond laser pulses can create highly localised membrane perforations within a minute focal volume, enabling non-invasive direct transfection of mammalian cells with DNA. We suspended Chinese hamster ovarian (CHO), rat kangaroo kidney epithelial (PtK2) and rat fibroblast cells in 0.5 ml culture medium in a sterile miniaturized cell chamber (JenLab GmbH, Jena, Germany) containing 0.2 μg plasmid DNA vector pEGFP-N1 (4.7 kb), which codes for green fluorescent protein (GFP). The NIR laser beam was introduced into a femtosecond laser scanning microscope (JenLab GmbH, Jena, Germany; focussed on the edge of the cell membrane of a target cell for 16 ms. The integration and expression efficiency of EGFP were assessed in situ by two-photon fluorescence-lifetime imaging using time-correlated single photon counting. The unique capability to transfer foreign DNA safely and efficiently into specific cell types (including stem cells), circumventing mechanical, electrical or chemical means, will have many applications, such as targeted gene therapy and DNA vaccination.

  17. Micromachining soda-lime glass by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Jia, Wei; Yu, Jian; Chai, Lu; Wang, Ching-Yue

    2015-08-01

    The physical process of forming a modified region in soda-lime glass was investigated using 1 kHz intense femtosecond laser pulses from a Ti: sapphire laser at 775 nm. Through the modifications induced by the femtosecond laser radiation using selective chemical etching techniques, we fabricated reproducible and defined microstructures and further studied their morphologies and etching properties. Moreover, a possible physical mechanism for the femtosecond laser modification in soda-lime glass was proposed.

  18. Kilohertz generation of high contrast polarization states for visible femtosecond pulses via phase-locked acousto-optic pulse shapers

    SciTech Connect

    Seiler, Hélène; Walsh, Brenna; Palato, Samuel; Kambhampati, Patanjali; Thai, Alexandre; Forget, Nicolas; Crozatier, Vincent

    2015-09-14

    We present a detailed analysis of a setup capable of arbitrary amplitude, phase, and polarization shaping of broadband visible femtosecond pulses at 1 kHz via a pair of actively phase stabilized acousto-optic programmable dispersive filters arranged in a Mach-Zehnder interferometer geometry. The setup features phase stability values around λ/225 at 580 nm as well as degrees of polarization of at least 0.9 for any polarization state. Both numbers are important metrics to evaluate a setup's potential for applications based on polarization-shaped femtosecond pulses, such as fully coherent multi-dimensional electronic spectroscopy.

  19. Quenching Plasma Waves in Two Dimensional Electron Gas by a Femtosecond Laser Pulse

    NASA Astrophysics Data System (ADS)

    Shur, Michael; Rudin, Sergey; Greg Rupper Collaboration; Andrey Muraviev Collaboration

    Plasmonic detectors of terahertz (THz) radiation using the plasma wave excitation in 2D electron gas are capable of detecting ultra short THz pulses. To study the plasma wave propagation and decay, we used femtosecond laser pulses to quench the plasma waves excited by a short THz pulse. The femtosecond laser pulse generates a large concentration of the electron-hole pairs effectively shorting the 2D electron gas channel and dramatically increasing the channel conductance. Immediately after the application of the femtosecond laser pulse, the equivalent circuit of the device reduces to the source and drain contact resistances connected by a short. The total response charge is equal to the integral of the current induced by the THz pulse from the moment of the THz pulse application to the moment of the femtosecond laser pulse application. This current is determined by the plasma wave rectification. Registering the charge as a function of the time delay between the THz and laser pulses allowed us to follow the plasmonic wave decay. We observed the decaying oscillations in a sample with a partially gated channel. The decay depends on the gate bias and reflects the interplay between the gated and ungated plasmons in the device channel. Army Research Office.

  20. Cornea surgery with nanojoule femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Koenig, Karsten; Wang, Bagui; Riemann, Iris; Kobow, Jens

    2005-04-01

    We report on a novel optical method for (i) flap-generation in LASIK procedures as well as (ii) for flap-free intrastromal refractive surgery based on nanojoule femtosecond laser pulses. The near infrared 200 fs pulses for multiphoton ablation have been provided by ultracompact turn-key MHz laser resonators. LASIK flaps and intracorneal cavities have been realized with high precision within living New Zealand rabbits using the system FemtoCutO (JenLab GmbH, Jena, Germany) at 800 nm laser wavelength. Using low-energy sub-2 nJ laser pulses, collateral damage due to photodisruptive and self-focusing effects was avoided. The laser ablation system consists of fast galvoscanners, focusing optics of high numerical aperture as well as a sensitive imaging system and provides also the possibility of 3D multiphoton imaging of fluorescent cellular organelles and SHG signals from collagen. Multiphoton tomography of the cornea was used to determine the exact intratissue beam position and to visualize intraocular post-laser effects. The wound healing process has been investigated up to 90 days after instrastromal laser ablation by histological analysis. Regeneration of damaged collagen structures and the migration of inflammation cells have been detected.

  1. Modeling crater formation in femtosecond-pulse laser damage from basic principles.

    PubMed

    Mitchell, Robert A; Schumacher, Douglass W; Chowdhury, Enam A

    2015-05-15

    We present the first fundamental simulation method for the determination of crater morphology due to femtosecond-pulse laser damage. To this end we have adapted the particle-in-cell (PIC) method commonly used in plasma physics for use in the study of laser damage and developed the first implementation of a pair potential for PIC codes. We find that the PIC method is a complementary approach to modeling laser damage, bridging the gap between fully ab-initio molecular dynamics approaches and empirical models. We demonstrate our method by modeling a femtosecond-pulse laser incident on a flat copper slab for a range of intensities. PMID:26393696

  2. Noncontact microsurgery of living cell membrane using femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Ilina, I. V.; Ovchinnikov, A. V.; Sitnikov, D. S.; Chefonov, O. V.; Agranat, M. B.; Mikaelyan, A. S.

    2013-06-01

    Near-infrared femtosecond laser pulses were applied to initiate reversible permeabilization of cell membrane and inject extrinsic substances into the target cells. Successful laser-based injection of a membrane impermeable dye, as well as plasmid DNA was demonstrated.

  3. Femtosecond spectroscopy with vacuum ultraviolet pulse pairs

    SciTech Connect

    Allison, Tom; Wright, Travis; Stooke, Adam; Khurmi, Champak; van Tilborg, Jeroen; Liu, Yanwei; Falcone, Roger; Belkacem, Ali

    2011-06-17

    We combine different wavelengths from an intense high-order harmonics source with variable delay at the focus of a split-mirror interferometer to conduct pump-probe experiments on gas-phase molecules. We report measurements of the time resolution (< 44fs) and spatial profiles (4 {micro}m x 12 {micro}m) at the focus of the apparatus. We demonstrate the utility of this two-color, high-order-harmonic technique by time resolving molecular hydrogen elimination from C{sub 2} H{sub 4} excited into its absorption band at 161nm.

  4. Pulse energy dependence of subcellular dissection by femtosecond laser pulses

    NASA Technical Reports Server (NTRS)

    Heisterkamp, A.; Maxwell, I. Z.; Mazur, E.; Underwood, J. M.; Nickerson, J. A.; Kumar, S.; Ingber, D. E.

    2005-01-01

    Precise dissection of cells with ultrashort laser pulses requires a clear understanding of how the onset and extent of ablation (i.e., the removal of material) depends on pulse energy. We carried out a systematic study of the energy dependence of the plasma-mediated ablation of fluorescently-labeled subcellular structures in the cytoskeleton and nuclei of fixed endothelial cells using femtosecond, near-infrared laser pulses focused through a high-numerical aperture objective lens (1.4 NA). We find that the energy threshold for photobleaching lies between 0.9 and 1.7 nJ. By comparing the changes in fluorescence with the actual material loss determined by electron microscopy, we find that the threshold for true material ablation is about 20% higher than the photobleaching threshold. This information makes it possible to use the fluorescence to determine the onset of true material ablation without resorting to electron microscopy. We confirm the precision of this technique by severing a single microtubule without disrupting the neighboring microtubules, less than 1 micrometer away. c2005 Optical Society of America.

  5. Tailoring the plasma channel generated by femtosecond laser pulse

    NASA Astrophysics Data System (ADS)

    Wang, Haitao; Fan, Chengyu; Zhang, Pengfei; Jia, Wei

    2015-02-01

    By investigating the spatial and temporal variations of the propagating pulses, we have shown for the first time that the lattice waveguides can induce nonlinear effects to tailor the plasma channel generated by a femtosecond laser pulse. Different types of the spatiotemporal localized nonlinear light bullet’s propagating configurations have been predicted. By adjusting the parameters of the modulation potential, longer continuum filaments and reshaped laser pulses can be obtained, due to the focusing nonlinearity of the lattice modulation index.

  6. Precise micromachining of materials using femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Garasz, K.; Tański, M.; Barbucha, R.; Kocik, M.

    2015-06-01

    We present the results of the experimental parametric study on efficiency, accuracy and quality of femtosecond laser micromachining of different materials. The laser micromachining process was performed with a solid-state Yb:KYW laser. The laser generates 500 fs pulses of three different wavelengths, repetition rate from 100 to 900 kHz and output power up to 50 W. This allows to perform a complex research for a wide range of parameters and materials. Laser micromachining is a process based on a laser ablation phenomenon, i.e. total evaporation of material from the target surface during laser irradiation. It is the most precise method of material removal. Applying a femtosecond laser in the process, allows the use of ultra short pulses, with a duration of 10-15 seconds, while maintaining a high laser power. The concentration of energy within a single pulse is sufficiently high to cause the detachment of particles from the irradiated target without any thermal interactions with the surrounding material. Therefore, the removal of the material occurs only in the laser focus. This allows to avoid most of the unwanted effects of the heat affected zone (HAZ). It has been established, that the quality of laser ablation process using femtosecond pulses is much higher than while using the long pulsed lasers (i.e. nanosecond). The use of femtosecond laser pulses creates therefore an attractive opportunity for high quality micromachining of many groups of materials.

  7. Materials processing with a tightly focused femtosecond laser vortex pulse.

    PubMed

    Hnatovsky, Cyril; Shvedov, Vladlen G; Krolikowski, Wieslaw; Rode, Andrei V

    2010-10-15

    In this Letter we present the first (to our knowledge) demonstration of material modification using tightly focused single femtosecond laser vortex pulses. Double-charge femtosecond vortices were synthesized with a polarization-singularity beam converter based on light propagation in a uniaxial anisotropic medium and then focused using moderate- and high-NA optics (viz., NA=0.45 and 0.9) to ablate fused silica and soda-lime glass. By controlling the pulse energy, we consistently machine micrometer-size ring-shaped structures with <100nm uniform groove thickness. PMID:20967085

  8. Wavelength Effects In Femtosecond Pulsed Laser Ablation And Deposition

    SciTech Connect

    Castillejo, Marta; Nalda, Rebeca de; Oujja, Mohamed; Sanz, Mikel

    2010-10-08

    Ultrafast pulsed laser irradiation of solid materials is highly attractive for the micro-and nanostructuring of substrates and for the fabrication of nanostructured deposits. Femtosecond laser pulses promote efficient material removal with reduced heat transfer and high deposition rates of nanometer scale particles free of microscopic particulates. Most of the studies to date have been performed with light pulses centered around the peak wavelength of the Titanium:Sapphire laser, around 800 nm. Analysis of the process over a broader range of wavelengths can provide important information about the processes involved and serve as experimental tests for advanced theoretical models. We report on our current investigations on the effect that laser wavelength of femtosecond pulses has on the superficial nanostructuring induced on biopolymer substrates, and on the characteristics of nanostructured deposits grown by pulsed laser deposition from semiconductor targets.

  9. Suppression of Ablation in Femtosecond Double-Pulse Experiments

    SciTech Connect

    Povarnitsyn, M. E.; Khishchenko, K. V.; Levashov, P. R.; Itina, T. E.

    2009-11-06

    We report the physical reasons of a curious decrease in the crater depth observed for long delays in experiments with two successive femtosecond pulses. Detailed hydrodynamic modeling demonstrates that the ablation mechanism is dumped when the delay between the pulses exceeds the electron-ion relaxation time. In this case, the interaction of the second laser pulse with the expanding target material leads to the formation of the second shock wave suppressing the rarefaction wave created by the first pulse. The evidence of this effect follows from the pressure and density profiles obtained at different delays after the first laser pulse.

  10. Geometrical limitations in grating pair pulse compression

    SciTech Connect

    Brorson, S.D.; Haus, H.A.

    1988-01-01

    Optical-pulse compression using gratings has become a standard technique for producing ultrafast pulses outside a laser cavity. Short pulses produced by a mode-locked laser are focused into an optical fiber. There, self-phase modulation and group velocity dispersion act to broaden the bandwidth of the pulse and impart to it a negative chirp. A pair of diffraction gratings are placed following the fiber. Different frequencies follow different paths through the grating pair; if they are properly oriented, the gratings can compensate for the linear chirp of the pulse. In this way the spectral components of the pulse are compressed in time. The net effect of the system is to produce an output pulse that is shorter than the input pulse because of the additional frequencies generated in the fiber.

  11. Femtosecond laser pulse induced birefringence in optically isotropic glass.

    SciTech Connect

    Vawter, Gregory Allen; Luk, Ting Shan; Guo, Junpeng; Yang, Pin; Burns, George Robert

    2003-07-01

    We used a regeneratively amplified Ti:sapphire femtosecond laser to create optical birefringence in an isotropic glass medium. Between two crossed polarizers, regions modified by the femtosecond laser show bright transmission with respect to the dark background of the isotropic glass. This observation immediately suggests that these regions possess optical birefringence. The angular dependence of transmission through the laser-modified region is consistent with that of an optically birefringent material. Laser-induced birefringence is demonstrated in different glasses, including fused silica and borosilicate glass. Experimental results indicate that the optical axes of laser-induced birefringence can be controlled by the polarization direction of the femtosecond laser. The amount of laser-induced birefringence depends on the pulse energy level and number of accumulated pulses.

  12. Generating long sequences of high-intensity femtosecond pulses.

    PubMed

    Bitter, M; Milner, V

    2016-02-01

    We present an approach to creating pulse sequences extending beyond 150 ps in duration, comprised of 100 μJ femtosecond pulses. A quarter of the pulse train is produced by a high-resolution pulse shaper, which allows full controllability over the timing of each pulse. Two nested Michelson interferometers follow to quadruple the pulse number and the sequence duration. To boost the pulse energy, the long train is sent through a multipass Ti:sapphire amplifier, followed by an external compressor. A periodic sequence of 84 pulses of 120 fs width and an average pulse energy of 107 μJ, separated by 2 ps, is demonstrated as a proof of principle. PMID:26836087

  13. Heating of a metal nanofilm during femtosecond laser pulse absorption

    SciTech Connect

    Bezhanov, S G; Kanavin, A P; Uryupin, S A

    2014-09-30

    We have studied the temperature evolution of electrons and the lattice of a metal nanofilm interacting with a femtosecond s- or p-polarised pulse. It is shown that even if the film thickness is greater than the skin-layer depth, the temperature distribution during the pulse action may be close to the uniform one because of the high electron thermal conductivity, which leads to a rapid redistribution of energy over the film thickness. (nanostructures)

  14. Probing Molecular Dynamics at Attosecond Resolution with Femtosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Tong, X. M.; Zhao, Z. X.; Lin, C. D.

    2003-12-01

    The kinetic energy distribution of D+ ions resulting from the interaction of a femtosecond laser pulse with D2 molecules is calculated based on the rescattering model. From analyzing the molecular dynamics, it is shown that the recollision time between the ionized electron and the D+2 ion can be read from the D+ kinetic energy peaks to attosecond accuracy. We further suggest that a more precise reading of the clock can be achieved by using shorter fs laser pulses (about 15fs).

  15. Spectral compression of femtosecond pulses using chirped volume Bragg gratings.

    PubMed

    Nejbauer, Michał; Kardaś, Tomasz M; Stepanenko, Yuriy; Radzewicz, Czesław

    2016-06-01

    In this Letter, we demonstrate a 360 fold spectral bandwidth reduction of femtosecond laser pulses using the method of sum frequency generation of pulses with opposite chirps. The reduction has been achieved in a compact setup in which a single chirped volume Bragg grating replaces conventional stretcher and compressor units. Starting with 180 fs pulses, we have obtained, with a 30% overall efficiency, pulses longer than 100 ps with the spectral bandwidth of 0.23  cm-1 (7 GHz). We also discuss our method on theoretical grounds. PMID:27244372

  16. Efficient reflection grisms for pulse compression and dispersion compensation of femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Gibson, Emily A.; Gaudiosi, David M.; Kapteyn, Henry C.; Jimenez, Ralph; Kane, Steve; Huff, Rachel; Durfee, Charles; Squier, Jeff

    2006-11-01

    Efficient reflection grisms for pulse-compression and material-dispersion compensation have been designed and demonstrated in a 40 fs, 300 μJ, 5 kHz downchirped pulse amplification system for the first time to our knowledge. A grism design for 800nm femtosecond laser pulse dispersion compensation applications is realized by using standard, commercial diffraction gratings.

  17. High-speed photorefractive keratectomy with femtosecond ultraviolet pulses

    NASA Astrophysics Data System (ADS)

    Danieliene, Egle; Gabryte, Egle; Vengris, Mikas; Ruksenas, Osvaldas; Gutauskas, Algimantas; Morkunas, Vaidotas; Danielius, Romualdas

    2015-05-01

    Femtosecond near-infrared lasers are widely used for a number of ophthalmic procedures, with flap cutting in the laser-assisted in situ keratomileusis (LASIK) surgery being the most frequent one. At the same time, lasers of this type, equipped with harmonic generators, have been shown to deliver enough ultraviolet (UV) power for the second stage of the LASIK procedure, the stromal ablation. However, the speed of the ablation reported so far was well below the currently accepted standards. Our purpose was to perform high-speed photorefractive keratectomy (PRK) with femtosecond UV pulses in rabbits and to evaluate its predictability, reproducibility and healing response. The laser source delivered femtosecond 206 nm pulses with a repetition rate of 50 kHz and an average power of 400 mW. Transepithelial PRK was performed using two different ablation protocols, to a total depth of 110 and 150 μm. The surface temperature was monitored during ablation; haze dynamics and histological samples were evaluated to assess outcomes of the PRK procedure. For comparison, analogous excimer ablation was performed. Increase of the ablation speed up to 1.6 s/diopter for a 6 mm optical zone using femtosecond UV pulses did not significantly impact the healing process.

  18. Enhancement of peak intensity in a filament core with spatiotemporally focused femtosecond laser pulses

    SciTech Connect

    Zeng Bin; Chu Wei; Li Guihua; Zhang Haisu; Ni Jielei; Gao Hui; Liu Weiwei; Yao Jinping; Cheng Ya; Xu Zhizhan; Chin, See Leang

    2011-12-15

    We demonstrate that the peak intensity in the filament core, which is inherently limited by the intensity clamping effect during femtosecond laser filamentation, can be significantly enhanced using spatiotemporally focused femtosecond laser pulses. In addition, the filament length obtained by spatiotemporally focused femtosecond laser pulses is {approx}25 times shorter than that obtained by a conventional focusing scheme, resulting in improved high spatial resolution.

  19. Colorizing metals with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Vorobyev, A. Y.; Guo, Chunlei

    2008-01-01

    For centuries, it had been the dream of alchemists to turn inexpensive metals into gold. Certainly, it is not enough from an alchemist's point of view to transfer only the appearance of a metal to gold. However, the possibility of rendering a certain metal to a completely different color without coating can be very interesting in its own right. In this work, we demonstrate a femtosecond laser processing technique that allows us to create a variety of colors on a metal that ultimately leads us to control its optical properties from UV to terahertz.

  20. Colorizing metals with femtosecond laser pulses

    SciTech Connect

    Vorobyev, A. Y.; Guo Chunlei

    2008-01-28

    For centuries, it had been the dream of alchemists to turn inexpensive metals into gold. Certainly, it is not enough from an alchemist's point of view to transfer only the appearance of a metal to gold. However, the possibility of rendering a certain metal to a completely different color without coating can be very interesting in its own right. In this work, we demonstrate a femtosecond laser processing technique that allows us to create a variety of colors on a metal that ultimately leads us to control its optical properties from UV to terahertz.

  1. Femtosecond pulse sequences used for optical manipulation of molecular motion.

    PubMed

    Weiner, A M; Leaird, D E; Wiederrecht, G P; Nelson, K A

    1990-03-16

    Optical control over elementary molecular motion is enhanced with timed sequences of femtosecond (10(-15) second) pulses produced by pulse-shaping techniques. Appropriately timed pulse sequences are used to repetitively drive selected vibrations of a crystal lattice, in a manner analogous to repetitively pushing a child on a swing with appropriate timing to build up a large oscillation amplitude. This process corresponds to repetitively "pushing" molecules along selected paths in the lattice. Amplification of selected vibrational modes and discrimination against other modes are demonstrated. Prospects for more extensive manipulation of molecular and collective behavior and structure are clearly indicated. PMID:17843793

  2. Electron transfer of carbonylmetalate radical pairs: femtosecond visible spectroscopy of optically excited ion pairs

    SciTech Connect

    Wen, X.; Spears, K.G.; Wiederrecht, G.P.; Wasielewski, M.R.

    1997-02-01

    Charge transfer excitation at 640 nm of the cobaltocenium tetracarbonylcobaltate ion pair, [Cp{sub 2}Co{sup +}{vert_bar}Co(CO){sub 4}{sup -}], was monitored in 1,2- dichloroethane solution by femtosecond transient visible absorption spectroscopy. The absorption prepares a neutral radical pair that can undergo spontaneous back electron transfer, and which shows a double peaked spectrum with features at 760 and 815 nm at 3 ps delay time. Transient decay times of 5.8{+-}0.5 ps were measured by monitoring the decay of Co(CO){sub 4} at 757 nm and 780 nm, and these are assigned to the back electron transfer step. The ET kinetics are consistent with the previously reported rates of electron transfer that were measured for specific vibrational states by picosecond transient IR.

  3. Nanosecond component in a femtosecond laser pulse

    SciTech Connect

    Shneider, M. N.; Semak, V. V.; Zhang Zhili

    2012-11-15

    Experimental and computational results show that the coherent microwave scattering from a laser-induced plasma can be used for measuring the quality of a fs laser pulse. The temporal dynamics of the microwave scattered signal from the fs-laser induced plasma can be related to the effect of nanosecond tail of the fs laser pulse.

  4. The effect of pre-pulse on the gratings coded by two interfered femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Han, Yanhua; Fan, Guanghua; Qu, Shiliang

    2016-07-01

    The effect of pre-pulse on the gratings coded with two interfered femtosecond pulses is studied on silica glass. The results show that the modulation depth of the gratings is deeper than that in absence of pre-pulse, and decreases with increased arrival time of pre-pulse. For the arrival time within 120-200 fs, the free electrons produced by pre-pulse can act as seed electrons for the subsequent interfered pulses to multiply, thus deepening the depth of the gratings. With the arrival time beyond 200 fs, the self-trapped excitons can provide seed electrons for the subsequent pulse multiplying, thus deepening the gratings.

  5. Rapid microfabrication of transparent materials using filamented femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Butkus, S.; Gaižauskas, E.; Paipulas, D.; Viburys, Ž.; Kaškelyė, D.; Barkauskas, M.; Alesenkov, A.; Sirutkaitis, V.

    2014-01-01

    Microfabrication of transparent materials using femtosecond laser pulses has showed good potential towards industrial application. Maintaining pulse energies exceeding the critical self-focusing threshold by more than 100-fold produced filaments that were used for micromachining purposes. This article demonstrates two different micromachining techniques using femtosecond filaments generated in different transparent media (water and glass). The stated micromachining techniques are cutting and welding of transparent samples. In addition, cutting and drilling experiments were backed by theoretical modelling giving a deeper insight into the whole process. We demonstrate cut-out holes in soda-lime glass having thickness up to 1 mm and aspect ratios close to 20, moreover, the fabrication time is of the order of tens of seconds, in addition, grooves and holes were fabricated in hardened 1.1 mm thick glass (Corning Gorilla glass). Glass welding was made possible and welded samples were achieved after several seconds of laser fabrication.

  6. Optimally enhanced optical emission in laser-induced air plasma by femtosecond double-pulse

    NASA Astrophysics Data System (ADS)

    Chen, Anmin; Li, Suyu; Li, Shuchang; Jiang, Yuanfei; Shao, Junfeng; Wang, Tingfeng; Huang, Xuri; Jin, Mingxing; Ding, Dajun

    2013-10-01

    In laser-induced breakdown spectroscopy, a femtosecond double-pulse laser was used to induce air plasma. The plasma spectroscopy was observed to lead to significant increase of the intensity and reproducibility of the optical emission signal compared to femtosecond single-pulse laser. In particular, the optical emission intensity can be optimized by adjusting the delay time of femtosecond double-pulse. An appropriate pulse-to-pulse delay was selected, that was typically about 50 ps. This effect can be especially advantageous in the context of femtosecond laser-induced breakdown spectroscopy, plasma channel, and so on.

  7. Optimally enhanced optical emission in laser-induced air plasma by femtosecond double-pulse

    SciTech Connect

    Chen, Anmin; Li, Suyu; Li, Shuchang; Jiang, Yuanfei; Ding, Dajun; Shao, Junfeng; Wang, Tingfeng; Huang, Xuri; Jin, Mingxing

    2013-10-15

    In laser-induced breakdown spectroscopy, a femtosecond double-pulse laser was used to induce air plasma. The plasma spectroscopy was observed to lead to significant increase of the intensity and reproducibility of the optical emission signal compared to femtosecond single-pulse laser. In particular, the optical emission intensity can be optimized by adjusting the delay time of femtosecond double-pulse. An appropriate pulse-to-pulse delay was selected, that was typically about 50 ps. This effect can be especially advantageous in the context of femtosecond laser-induced breakdown spectroscopy, plasma channel, and so on.

  8. Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon.

    PubMed

    Derrien, Thibault J-Y; Krüger, Jörg; Itina, Tatiana E; Höhm, Sandra; Rosenfeld, Arkadi; Bonse, Jörn

    2013-12-01

    The formation of near-wavelength laser-induced periodic surface structures (LIPSS) on silicon upon irradiation with sequences of Ti:sapphire femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied theoretically. For this purpose, the nonlinear generation of conduction band electrons in silicon and their relaxation is numerically calculated using a two-temperature model approach including intrapulse changes of optical properties, transport, diffusion and recombination effects. Following the idea that surface plasmon polaritons (SPP) can be excited when the material turns from semiconducting to metallic state, the "SPP active area" is calculated as function of fluence and double-pulse delay up to several picoseconds and compared to the experimentally observed rippled surface areas. Evidence is presented that multi-photon absorption explains the large increase of the rippled area for temporally overlapping pulses. For longer double-pulse delays, relevant relaxation processes are identified. The results demonstrate that femtosecond LIPSS on silicon are caused by the excitation of SPP and can be controlled by temporal pulse shaping. PMID:24514516

  9. Low-dispersion, high-gain femtosecond optical pulse amplifier.

    PubMed

    Rodenberger, D C; Grossman, C H; Garito, A F

    1990-05-01

    We demonstrate a novel amplifier for femtosecond optical pulses. The output of a colliding-pulse mode-locked laser is amplified to 0.3 microJ per pulse at a repetition rate of 8 kHz by using 1 W of pump power from a copper-vapor laser. Our high-efficiency amplifier focuses the beam for four gain passes through a thin dye stream that uses a Z configuration with matched focusing. Because of low group-velocity dispersion, the output pulses are only slightly broadened, from 63 to 73 fsec, and may be used directly to generate a white-light continuum without pulse compression after amplification. PMID:19767988

  10. Femtosecond laser pulse train interaction with dielectric materials

    NASA Astrophysics Data System (ADS)

    Dematteo Caulier, O.; Mishchik, K.; Chimier, B.; Skupin, S.; Bourgeade, A.; Javaux Léger, C.; Kling, R.; Hönninger, C.; Lopez, J.; Tikhonchuk, V.; Duchateau, G.

    2015-11-01

    The interaction of trains of femtosecond microjoule laser pulses with dielectric materials by means of a multi-scale model is investigated. Theoretical predictions are directly confronted with experimental observations in soda-lime glass. It is shown that due to the low heat conductivity, a significant fraction of the laser energy can be accumulated in the absorption region. Depending on the pulse repetition rate, the material can be heated to high temperatures even though the single pulse energy is too low to induce a significant material modification. Regions heated above the glass transition temperature in the simulations correspond very well to zones of permanent material modifications observed in the experiments. It turns out that pulse-to-pulse variations of the laser absorption are negligible and of minor influence to permanent material modifications.

  11. Vector-dispersion compensation and pulse pedestal cancellation in a femtosecond nonlinear amplification fiber laser system.

    PubMed

    Xie, Chen; Liu, Bowen; Niu, Hailiang; Song, Youjian; Li, Yi; Hu, Minglie; Zhang, Yueguang; Shen, Weidong; Liu, Xu; Wang, Chingyue

    2011-11-01

    We report on a femtosecond nonlinear amplification fiber laser system using a vector-dispersion compressor, which consists of a transmission grating pair and multipass cell based Gires-Tournois interferometer mirrors. The mirror is designed with nearly zero group-delay dispersion and large negative third-order dispersion. As a result, the third-order dispersion of the compressor can be adjusted independently to compensate the nonlinear phase shift of amplified pulses to reduce the pulse pedestal. With this scheme, the system outputs 44  fs laser pulses with little wing at 26.6  W output average power and 531  nJ pulse energy, corresponding to 10.8  MW peak power. PMID:22048347

  12. Femtosecond laser microchannels fabrication based on electrons dynamics control using temporally or spatially shaped pulses

    NASA Astrophysics Data System (ADS)

    Yan, Xueliang; Hu, Jie; Li, Xiaowei; Xia, Bo; Liu, Pengjun; Lu, Yongfeng; Jiang, Lan

    2014-11-01

    With ultrashort pulse durations and ultrahigh power densities, femtosecond laser presents unique advantages of high precision and high quality fabrication of microchannels in transparent materials. In our study, by shaping femtosecond laser pulse energy distribution in temporal or spatial domains, localized transient electrons dynamics and the subsequent processes, such as phase changes, can be controlled, leading to the dramatic increases in the capability of femtosecond laser microchannels fabrication. The temporally shaped femtosecond laser pulse trains can significantly enhance the material removal rate in both water-assisted femtosecond laser drilling and femtosecond laser irradiation followed by chemical etching. Besides, high-aspect-ratio and small-diameter microchannels are drilled by spatially shaped femtosecond laser pulses.

  13. Energy deposition dynamics of femtosecond pulses in water

    SciTech Connect

    Minardi, Stefano Pertsch, Thomas; Milián, Carles; Couairon, Arnaud; Majus, Donatas; Tamošauskas, Gintaras; Dubietis, Audrius; Gopal, Amrutha

    2014-12-01

    We exploit inverse Raman scattering and solvated electron absorption to perform a quantitative characterization of the energy loss and ionization dynamics in water with tightly focused near-infrared femtosecond pulses. A comparison between experimental data and numerical simulations suggests that the ionization energy of water is 8 eV, rather than the commonly used value of 6.5 eV. We also introduce an equation for the Raman gain valid for ultra-short pulses that validates our experimental procedure.

  14. Alexandrite-pumped alexandrite regenerative amplifier for femtosecond pulse amplification

    SciTech Connect

    Hariharan, A.; Fermann, M.E.; Stock, M.L.; Harter, D.J.; Squier, J.

    1996-01-01

    We demonstrate a regenerative amplifier incorporating alexandrite as the gain medium that is pumped by an alexandrite laser. Temperature-altered gain permitted the 728-nm alexandrite pump laser, operating at room temperature, to pump a 780{endash}800-nm alexandrite laser that was maintained at elevated temperatures. 200-fs pulses from a Ti:sapphire oscillator were amplified to the millijoule level. This system also amplified femtosecond pulses from a frequency-doubled Er-doped fiber laser. {copyright} {ital 1996 Optical Society of America.}

  15. Patterning of silica microsphere monolayers with focused femtosecond laser pulses

    SciTech Connect

    Cai Wenjian; Piestun, Rafael

    2006-03-13

    We demonstrate the patterning of monolayer silica microsphere lattices with tightly focused femtosecond laser pulses. We selectively removed microspheres from a lattice and characterized the effect on the lattice and the substrate. The proposed physical mechanism for the patterning process is laser-induced breakdown followed by ablation of material. We show that a microsphere focuses radiation in its interior and in the near field. This effect plays an important role in the patterning process by enhancing resolution and accuracy and by reducing the pulse energy threshold for damage. Microsphere patterning could create controlled defects within self-assembled opal photonic crystals.

  16. Self-phase modulation of femtosecond pulses in hollow photonic-crystal fibres

    SciTech Connect

    Konorov, Stanislav O; Zheltikov, Aleksei M; Sidorov-Biryukov, D A; Bugar, I; Chorvat, D J; Beloglazov, V I; Skibina, N B; Shcherbakov, Andrei V; Chorvat, D; Mel'nikov, L A

    2004-01-31

    Self-phase modulation of femtosecond laser pulses in hollow-core photonic-crystal fibres is experimentally studied. Photonic-crystal fibres allowing single-mode waveguide regimes of nonlinear-optical interactions to be implemented with maximum transmission for 800-nm femtosecond pulses are designed and fabricated. A radical enhancement of self-phase modulation is demonstrated for submicrojoule femtosecond pulses of Ti:sapphire-laser radiation propagating through hollow photonic-crystal fibres. (optical fibres)

  17. Pulsed digital holography system recording ultrafast process of the femtosecond order

    NASA Astrophysics Data System (ADS)

    Wang, Xiaolei; Zhai, Hongchen; Mu, Guoguang

    2006-06-01

    We report, for the first time to our knowledge, a pulsed digital microholographic system with spatial angular multiplexing for recording the ultrafast process of the femtosecond order. The optimized design of the two sets of subpulse-train generators in this system makes it possible to implement a digital holographic recording with spatial angular multiplexing of a frame interval of the femtosecond order, while keeping the incident angle of the object beams unchanged. Three pairs of amplitude and phase images from the same view angle digitally reconstructed by the system demonstrated the ultrafast dynamic process of laser-induced ionization of ambient air at a wavelength of 800 nm, with a time resolution of 50 fs and a frame interval of 300 fs.

  18. Nonequilibrium screening and exciton dynamics probed by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Peyghambarian, N.; Koch, S. W.

    1993-02-01

    Our efforts were aimed at the study of nonequilibrium properties of a high-density electron-hole-pair system, which was generated resonantly by femtosecond laser excitation. The investigation consisted of joint theoretical and experimental approaches. Using state of the art femtosecond experimental techniques, we studied extremely rapid physical phenomena. We have succeeded not only in completing the proposed tasks, but have also initiated some new projects and obtained very interesting results. During the last three years in this program, we have published three physical Review Letters, nine Physical Reviews, several other papers in good journals such as Appl. Phys. Lett., J. Opt. Soc. Am., etc., nineteen invited presentations at important conferences, and several contributed papers at international conferences. The list of publications is given in the next section. Here, we summarize the highlights of our achievements during the last three years of this contract.

  19. Testing of a femtosecond pulse laser in outer space

    PubMed Central

    Lee, Joohyung; Lee, Keunwoo; Jang, Yoon-Soo; Jang, Heesuk; Han, Seongheum; Lee, Sang-Hyun; Kang, Kyung-In; Lim, Chul-Woo; Kim, Young-Jin; Kim, Seung-Woo

    2014-01-01

    We report a test operation of an Er-doped fibre femtosecond laser which was conducted for the first time in outer space. The fibre-based ultrashort pulse laser payload was designed to meet space-use requirements, undergone through ground qualification tests and finally launched into a low-earth orbit early in 2013. Test results obtained during a one-year mission lifetime confirmed stable mode-locking all the way through although the radiation induced attenuation (RIA) in the Er-doped gain fibre caused an 8.6% reduction in the output power. This successful test operation would help facilitate diverse scientific and technological applications of femtosecond lasers in space and earth atmosphere in the near future. PMID:24875665

  20. Testing of a femtosecond pulse laser in outer space

    NASA Astrophysics Data System (ADS)

    Lee, Joohyung; Lee, Keunwoo; Jang, Yoon-Soo; Jang, Heesuk; Han, Seongheum; Lee, Sang-Hyun; Kang, Kyung-In; Lim, Chul-Woo; Kim, Young-Jin; Kim, Seung-Woo

    2014-05-01

    We report a test operation of an Er-doped fibre femtosecond laser which was conducted for the first time in outer space. The fibre-based ultrashort pulse laser payload was designed to meet space-use requirements, undergone through ground qualification tests and finally launched into a low-earth orbit early in 2013. Test results obtained during a one-year mission lifetime confirmed stable mode-locking all the way through although the radiation induced attenuation (RIA) in the Er-doped gain fibre caused an 8.6% reduction in the output power. This successful test operation would help facilitate diverse scientific and technological applications of femtosecond lasers in space and earth atmosphere in the near future.

  1. Focal spot analysis of radially polarized femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Sun, Wenchao; Hu, Wenhua; Qi, Junli; Wang, Weiming; Liao, Jiali; Yi, Wenjun; Jia, Hui; Li, Xiujian

    2014-09-01

    When radially polarized light beams focus through high numerical-aperture lens, there will be a very strong longitudinal component of the light field near the focus. And, under the condition of certain system parameters, they can shape a spot which is over the focusing spot of the diffraction limit, which are the superiorities that linearly polarized light and circularly polarized light do not have. Besides, what we have found in the experiment is that radially polarized femtosecond laser pulses own the same superiorities, which provides the basis for using the focusing characteristics of radially polarized light beams under the condition of shorter and more powerful laser pulses. So far, although people have studied a lot on radially polarized light beams, this kind of light beams' focusing characters are rarely researched. What is worse, most research of its focusing characters still stays in the stage of theoretical simulation,and it seems that none of people have really studied it by the way of experiments. This article is precisely based on this. On the basis of predecessors' a lot of theoretical research, the article pays more attention on analyzing radially polarized light beams' focusing character through experiments. What's more, the article, based on femtosecond laser pulses, compares the differences of the focusing nature among linearly polarized light, circularly polarized light and radially polarized light. And it gets the conclusion that radially polarized femtosecond laser pulses have better focusing character in longitudinal light field, confirming the feasibility that radially polarized light beams can be used in the fields of pulling, catching, and accelerating particles, metal cutting and high-density storage.

  2. [INVITED] Control of femtosecond pulsed laser ablation and deposition by temporal pulse shaping

    NASA Astrophysics Data System (ADS)

    Garrelie, Florence; Bourquard, Florent; Loir, Anne--Sophie; Donnet, Christophe; Colombier, Jean-Philippe

    2016-04-01

    This study explores the effects of temporal laser pulse shaping on femtosecond pulsed laser deposition (PLD). The potential of laser pulses temporally tailored on ultrafast time scales is used to control the expansion and the excitation degree of ablation products including atomic species and nanoparticles. The ablation plume generated by temporally shaped femtosecond pulsed laser ablation of aluminum and graphite targets is studied by in situ optical diagnostic methods. Taking advantage of automated pulse shaping techniques, an adaptive procedure based on spectroscopic feedback regulates the irradiance for the enhancement of typical plasma features. Thin films elaborated by unshaped femtosecond laser pulses and by optimized sequence indicate that the nanoparticles generation efficiency is strongly influenced by the temporal shaping of the laser irradiation. The ablation processes leading either to the generation of the nanoparticles either to the formation of plasma can be favored by using a temporal shaping of the laser pulse. Insights are given on the possibility to control the quantity of the nanoparticles. The temporal laser pulse shaping is shown also to strongly modify the laser-induced plasma contents and kinetics for graphite ablation. Temporal pulse shaping proves its capability to reduce the number of slow radicals while increasing the proportion of monomers, with the addition of ionized species in front of the plume. This modification of the composition and kinetics of plumes in graphite ablation using temporal laser pulse shaping is discussed in terms of modification of the structural properties of deposited Diamond-Like Carbon films (DLC). This gives rise to a better understanding of the growth processes involved in femtosecond-PLD and picosecond-PLD of DLC suggesting the importance of neutral C atoms, which are responsible for the subplantation process.

  3. A versatile femtosecond stimulated Raman spectroscopy setup with tunable pulses in the visible to near infrared

    SciTech Connect

    Zhu, Liangdong; Liu, Weimin; Fang, Chong

    2014-07-28

    We demonstrate a versatile and efficient setup to perform femtosecond stimulated Raman spectroscopy (FSRS). Technical innovations are implemented to achieve the wavelength tunability for both the picosecond narrowband Raman pump pulse and femtosecond broadband Raman probe pulse. Using a simplified one-grating scheme in a home-built second harmonic bandwidth compressor followed by a two-stage noncollinear optical parametric amplifier, we tune the Raman pump pulse from ca. 480 to 750 nm. To generate the suitable Raman probe pulse in tandem, we rely on our recently demonstrated broadband up-converted multicolor array technique that readily provides tunable broadband laser sidebands across the visible to near-infrared range. This unique setup has unparalleled flexibility for conducting FSRS. We measure the ground-state Raman spectra of a cyclohexane standard using tunable pump-probe pairs at various wavelengths across the visible region. The best spectral resolution is ∼12 cm{sup −1}. By tuning the pump wavelength closer to the electronic absorption band of a photoacid pyranine in water, we observe the pre-resonantly enhanced Raman signal. The stimulated Raman gain of the 1627 cm{sup −1} mode is increased by over 15 times.

  4. Measurements of Intense Femtosecond Laser Pulse Propagation in Air

    NASA Astrophysics Data System (ADS)

    Ting, Antonio

    2004-11-01

    Intense femtosecond pulses generated from chirped pulse amplification (CPA) lasers can deliver laser powers many times above the critical power for self-focusing in air. Catastrophic collapse of the laser pulse is usually prevented by the defocusing of the plasma column formed when the laser intensity gets above the threshold for multiphoton ionization. The resultant laser/plasma filament can extend many meters as the laser pulse propagates in the atmosphere. We have carried out a series of experiments both for understanding the formation mechanisms of the filaments and the nonlinear effects such as white light and harmonics generation associated with them. Many applications of these filaments such as remote atmospheric breakdown, laser induced electrical discharge and femtosecond laser material interactions require direct measurements of their characteristics. Direct measurements of these filaments had been difficult because the high laser intensity ( ˜10^13 W/cm^2) can damage practically any optical diagnostics. A novel technique was invented to obtain the first absolute measurements of laser energy, transverse profile, fluence and spectral content of the filaments. We are investigating a ``remote atmospheric breakdown'' concept of remotely sensing chemical and biological compounds. A short intense laser pulse can be generated at a remote position by using the group velocity dispersion (GVD) of the air to compress an initially long, frequency negatively chirped laser pulse to generate the air breakdown and filaments. We have observed that nonlinear contributions to the laser spectrum through self-phase modulation can lead to modification of the linear GVD compression. We have also observed the generation of ultraviolet (UV) radiations from these filaments in air and the induced fluorescence by the UV radiation of a surrogate biological agent. These and other results such as laser induced electrical discharges will be presented.

  5. Localized waveguide formation in germanosilicate fiber transmitting femtosecond IR pulses

    PubMed Central

    Tu, Haohua; Koh, Yee Lin; Marks, Daniel L.; Boppart, Stephen A.

    2010-01-01

    Transmission of intense femtosecond 825 nm pulses progressively produces a waveguide at the entrance of a heavily Ge-doped silicate fiber. The waveguide behaves as a multimillimeter long-fiber bandpass filter that scatters away light with wavelengths shorter or longer than 850 nm. This phenomenon has been correlated with the ~800 nm photosensitivity producing type I-IR fiber Bragg gratings in side-written lightly Ge-doped silicate fibers and low-loss waveguides in pure silica bulk glass. A model incorporating color center formation is proposed to understand the underlying mechanism. PMID:20548798

  6. Molecular rovibrational dynamics investigated by two-photon wavepacket interferometry with phase-locked pulse pairs

    NASA Astrophysics Data System (ADS)

    Cao, Ying; Zhang, Liang; Yang, Yan; Sun, Zhenrong; Wang, Zugeng

    2007-07-01

    Time-resolved two-photon fluorescence spectra have been investigated based on wavepacket interferometry (WPI), and the wavepacket dynamics of the excited states for 4-dicyanomethylene-2-methyl-6- p-dimethyl-aminostryryl-4H-pyran (DCM) is determined by phase-locked femtosecond pulse pairs. A relative phase between the femtosecond pulse pairs can be maintained as the delay line scanning, and so the two-photon fluorescence signals will be observed to appear periodically recurring features. It indicates the constructive or destructive interference between two-photon wavepackets on the molecular excited states. The experimental results show that the phase-locked WPI has the potential applications in the wavepacket dynamics of the complicated molecular systems.

  7. Femtosecond decay dynamics of intact adenine and thymine base pairs in a supersonic jet.

    PubMed

    Kim, Nam Joon; Chang, Jinyoung; Kim, Hyung Min; Kang, Hyuk; Ahn, Tae Kyu; Heo, Jiyoung; Kim, Seong Keun

    2011-07-11

    We investigated the decay dynamics of the DNA base pairs adenine-adenine (A(2)), adenine-thymine (AT), and thymine-thymine (T(2)) produced in a supersonic jet by femtosecond (fs) time-resolved photoionization spectroscopy. The base pair was excited by a fs pump pulse at 267 nm and the population change of its excited state was monitored by non-resonant three-photon ionization using a fs probe pulse at 800 nm after a certain time delay. All of the transients recorded in the mass channel of the parent ion exhibited a tri-exponential decay, with time constants ranging from 100 fs to longer than 100 ps. Most of these time constants coincide well with the previous values deduced indirectly from the transients of protonated adenine (AH(+)) and thymine (TH(+)), which were assumed to be produced by fragmentation of the base-pair ions. Notably, for the transient of T(2), we observed a new decay component with a time constant of 2.3 ps, which was absent in the transient of TH(+). We suggest that the new decay component arises from the decay of stacked T(2) dimers that are mostly ionized to T(2)(+), whereas the decay signal recorded in the mass channel of TH(+) is merely from the relaxation of hydrogen-bonded T(2) dimers. From the amplitude of the new decay component, the population of the stacked T(2) dimers relative to the hydrogen-bonded dimers was estimated to be ∼2 % in the supersonic jet, which is about fifteen times higher than the theoretical value. PMID:21710523

  8. Trident Pair Production in Strong Laser Pulses

    SciTech Connect

    Ilderton, Anton

    2011-01-14

    We calculate the trident pair production amplitude in a strong laser background. We allow for finite pulse durations, while still treating the laser fields nonperturbatively in strong-field QED. Our approach reveals explicitly the individual contributions of the one-step and two-step processes. We also expose the role gauge invariance plays in the amplitudes and discuss the relation between our results and the optical theorem.

  9. Filamentation of Beam-Shaped Femtosecond Laser Pulses

    SciTech Connect

    Polynkin, Pavel; Kolesik, Miroslav; Moloney, Jerome

    2010-10-08

    When ultra-intense and ultra-short optical pulses propagate in transparent dielectrics, the dynamic balance between multiple linear and nonlinear effects results in the generation of laser filaments. These peculiar objects have numerous interesting properties and can be potentially used in a variety of applications from remote sensing to the optical pulse compression down to few optical cycles to guiding lightning discharges away from sensitive sites. Materializing this practical potential is not straightforward owing to the complexity of the physical picture of filamentation. In this paper, we discuss recent experiments on using beam shaping as a means of control over the filament formation and dynamics. Two particular beam shapes that we have investigated so far are Bessel and Airy beams. The diffraction-free propagation of femtosecond Bessel beams allows for the creation of extended plasma channels in air. These extended filaments can be used for the generation of energetic optical pulses with the duration in the few-cycle range. In the case of filamentation of femtosecond Airy beams, the self-bending property of these beams allows for the creation of curved filaments. This is a new regime of the intense laser-pulse propagation in which the linear self-bending property of the beam competes against the nonlinear self-channeling. The bent filaments generated by ultra-intense Airy beams emit forward-propagating broadband radiation. Analysis of the spatial and spectral distribution of this emission provides for a valuable tool for analyzing the evolution of the ultra-intense optical pulse along the optical path.

  10. Analysis of femtosecond quantum control mechanisms with colored double pulses

    SciTech Connect

    Vogt, Gerhard; Nuernberger, Patrick; Selle, Reimer; Dimler, Frank; Brixner, Tobias; Gerber, Gustav

    2006-09-15

    Fitness landscapes based on a limited number of laser pulse shape parameters can elucidate reaction pathways and can help to find the underlying control mechanism of optimal pulses determined by adaptive femtosecond quantum control. In a first experiment, we employ colored double pulses and systematically scan both the temporal subpulse separation and the relative amplitude of the two subpulses to acquire fitness landscapes. Comparison with results obtained from a closed-loop experiment demonstrates the capability of fitness landscapes for the revelation of possible control mechanisms. In a second experiment, using transient absorption spectroscopy, we investigate and compare the dependence of the excitation efficiency of the solvated dye molecule 5,5{sup '}-dichloro-11-diphenylamino-3,3{sup '}-diethyl-10,12-ethylene thiatricarbocyanine perchlorate (IR140) on selected pulse shapes in two parametrizations. The results show that very different pulse profiles can be equivalently adequate to maximize a given control objective. Fitness landscapes thus provide valuable information about different pathways along which a molecular system can be controlled with shaped laser pulses.

  11. Moving picture recording and observation of femtosecond light pulse propagation using a rewritable holographic material

    NASA Astrophysics Data System (ADS)

    Yamamoto, Seiji; Takimoto, Tetsuya; Tosa, Kazuya; Kakue, Takashi; Awatsuji, Yasuhiro; Nishio, Kenzo; Ura, Shogo; Kubota, Toshihiro

    2011-08-01

    We succeeded in recording and observing femtosecond light pulse propagation as a form of moving picture by means of light-in-flight recording by holography using a rewritable holographic material, for the first time. We used a femtosecond pulsed laser whose center wavelength and duration were 800 nm and ˜120 fs, respectively. A photo-conductor plastic hologram was used as a rewritable holographic material. The femtosecond light pulse was collimated and obliquely incident to the diffuser plate. The behavior of the cross-section between the collimated femtosecond light pulse and the diffuser plate was recorded on the photo-conductor plastic hologram. We experimentally obtained a spatially and temporally continuous moving picture of the femtosecond light pulse propagation for 58.3 ps. Meanwhile, we also investigated the rewritable performance of the photo-conductor plastic hologram. As a result, we confirmed that ten-time rewriting was possible for a photo-conductor plastic hologram.

  12. Femtosecond pulsed laser deposition of biological and biocompatible thin layers

    NASA Astrophysics Data System (ADS)

    Hopp, B.; Smausz, T.; Kecskeméti, G.; Klini, A.; Bor, Zs.

    2007-07-01

    In our study we investigate and report the femtosecond pulsed laser deposition of biological and biocompatible materials. Teflon, polyhydroxybutyrate, polyglycolic-acid, pepsin and tooth in the form of pressed pellets were used as target materials. Thin layers were deposited using pulses from a femtosecond KrF excimer laser system (FWHM = 450 fs, λ = 248 nm, f = 10 Hz) at different fluences: 0.6, 0.9, 1.6, 2.2, 2.8 and 3.5 J/cm 2, respectively. Potassium bromide were used as substrates for diagnostic measurements of the films on a FTIR spectrometer. The pressure in the PLD chamber was 1 × 10 -3 Pa, and in the case of tooth and Teflon the substrates were heated at 250 °C. Under the optimized conditions the chemical structure of the deposited materials seemed to be largely preserved as evidenced by the corresponding IR spectra. The polyglycolic-acid films showed new spectral features indicating considerable morphological changes during PLD. Surface structure and thickness of the layers deposited on Si substrates were examined by an atomic force microscopy (AFM) and a surface profilometer. An empirical model has been elaborated for the description of the femtosecond PLD process. According to this the laser photons are absorbed in the surface layer of target resulting in chemical dissociation of molecules. The fast decomposition causes explosion-like gas expansion generating recoil forces which can tear off and accelerate solid particles. These grains containing target molecules without any chemical damages are ejected from the target and deposited onto the substrate forming a thin layer.

  13. Ultrasmall Silver Nanopores Fabricated by Femtosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Zhao, Jimin; Bian, F.; Tian, Y. C.; Wang, R.; Yang, H. X.; Xu, Hongxing; Meng, Sheng

    2012-02-01

    Ultrasmall nanopores in silver thin films with a diameter of about 2 nm have been fabricated using femtosecond laser ablation in liquid [1]. Ultrafast laser pulse ablation generates highly nonequilibrium excitated states, from which silver thin films emerge and progressively grow with the assistance of capping agent molecules. During this growth process, capping agent molecules are enclaves within the film, leaving individual ultrasmall pores in the thin film. Our first-principles calculations show that the pore size is critically determined by the dimension of the confined molecules. Furthermore, by using smaller capping agent molecules, we were able to fabricate smaller nanopores with 1.6nm diameter. Our approach advances the capability of optical methods in making nanoscale structures with potential applications in areas such as near-field aperture probes, imaging masks, magnetic plasmonic resonances, and biosensing with individual nanopores. [4pt] [1] F. Bian, Y. C. Tian, R. Wang, H. X. Yang, H. X. Xu, Sheng Meng, and Jimin Zhao, Ultrasmall Silver Nanopores Fabricated by Femtosecond Laser Pulses, Nano Lett. 11, 3251--3257 (2011).

  14. Transient light absorption induced in glassby femtosecond laser pulses

    SciTech Connect

    Blonskii, I V; Kadan, V N; Pavlov, I A; Kryuchkov, N N; Shpotyuk, O I

    2009-10-31

    The dynamics of the transient light absorption induced in K8 optical glass by filamented femtosecond laser pulses have been studied using time-resolved transmitted-light microscopy at wavelengths from 450 to 700 nm. The transient absorption measured as a function of probe beam wavelength is compared to that predicted by the Drude plasma model. We conclude that, just 450 fs after a pump pulse, the transient absorption is dominated by transient electronic states, presumably, self-trapped excitons, with an excitation energy of 2.6 - 2.7 eV. These states are filled with free-carriers from a long-lived plasma, which acts as a 'carrier reservoir'. The relaxation of transient absorption has two components. The slow component, with {tau}{sub 1} {approx} 17-17.5 ps, is governed by the plasma thermalisation time, whereas the second, with {tau}{sub 1} >> 300 ps, is determined by the plasma lifetime. (nonlinear optical phenomena)

  15. Nonlinear Raman-Nath diffraction of femtosecond laser pulses.

    PubMed

    Vyunishev, A M; Slabko, V V; Baturin, I S; Akhmatkhanov, A R; Shur, V Ya

    2014-07-15

    We study the nonlinear Raman-Nath diffraction (NRND) of femtosecond laser pulses in a 1D periodic nonlinear photonic structure. The calculated second-harmonic spectra represent frequency combs for different orders of transverse phase matching. These frequency combs are in close analogy with the well-known spectral Maker fringes observed in single crystals. The spectral intensity of the second harmonic experiences a redshift with a propagation angle, which is opposite the case of Čerenkov nonlinear diffraction. We analyze how NRND is affected by the group-velocity mismatch between fundamental and second-harmonic pulses and by the parameters of the structure. Our experimental results prove the theoretical predictions. PMID:25121694

  16. Microcrystal delivery by pulsed liquid droplet for serial femtosecond crystallography.

    PubMed

    Mafuné, Fumitaka; Miyajima, Ken; Tono, Kensuke; Takeda, Yoshihiro; Kohno, Jun Ya; Miyauchi, Naoya; Kobayashi, Jun; Joti, Yasumasa; Nango, Eriko; Iwata, So; Yabashi, Makina

    2016-04-01

    A liquid-droplet injector has been developed that delivers pristine microcrystals to an X-ray irradiation area for conducting serial femtosecond crystallography (SFX) with an X-ray free-electron laser (XFEL). By finely tuning the pulsed liquid droplets in time and space, a high hit rate of the XFEL pulses to microcrystals in the droplets was achieved for measurements using 5 µm tetragonal lysozyme crystals, which produced 4265 indexable diffraction images in about 30 min. The structure was determined at a resolution of 2.3 Å from <0.3 mg of protein. With further improvements such as reduction of the droplet size, liquid droplets have considerable potential as a crystal carrier for SFX with low sample consumption. PMID:27050131

  17. Continuous and Pulsed THz generation with molecular gas lasers and photoconductive antennas gated by femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Cruz, Flavio C.; Nogueira, T.; Costa, Leverson F. L.; Jarschel, Paulo F.; Frateschi, Newton C.; Viscovini, Ronaldo C.; Vieira, Bruno R. B.; Guevara, Victor M. B.; Pereira, Daniel

    2008-04-01

    We report THz generation based on two systems: 1) continuous-wave (cw) laser generation in molecular gas lasers, and 2) short pulse generation in photoconductive antennas, gated by femtosecond near-infrared Ti:sapphire lasers. With the first system, we have generated tens of monochromatic cw laser lines over the last years, extending roughly from 40 microns to several hundred microns. This is done by optical pumping of gas lasers based on polar molecules such as methanol and its isotopes. In the second system, under development, pulsed THz radiation is generated by a photoconductive antenna built in a semi-insulating GaAs substrate excited by femtosecond pulses from a near-infrared (800 nm) Ti:sapphire laser.

  18. Compression of Electron Pulses for Femtosecond Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Zandi, Omid; Yang, Jie; Centurion, Martin

    2014-05-01

    Our goal is to improve the temporal resolution in electron diffraction experiments to 100 fs by compressing the electron pulses using a time-varying electric field. The compressed pulse can be used for a better understanding of the dynamics of molecules under study. A bunch of 3 million electrons is generated at a photocathode by femtosecond UV laser pulses and accelerated to 100 keV in a static electric field. Then, the longitudinal component of the electric field of a microwave cavity is employed to compress the bunch. The cavity's frequency and phase are accurately tuned in such a way that the electric field is parallel to the bunch motion at its arrival and antiparallel to it at its exit. Compression in the transverse directions is done by magnetic lenses. Simulations have been done to predict the bunch profile at different positions and times by General Particle Tracer code. A streak camera has been built to measure the duration of the pulses. It uses the electric field of a discharging parallel plate capacitor to rotate the bunch so that angular spreading of the bunch is proportional to its duration. The capacitor is discharged by a laser pulse incident on a photo switch.

  19. Optical measurement on quantum cascade lasers using femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Cai, Hong

    Quantum cascade lasers (QCLs) as the state-of-the-art mid-infrared (mid-IR) coherent sources have been greatly developed in aspects such as output power, energy efficiency and spectral purity. However, there are additional applications of QCLs in high demand, namely mode-locking, mid-IR modulation, etc. The inherent optical properties and ultrafast carrier dynamics can lead to solutions to these challenges. In this dissertation, we further characterize QCLs using mid-IR femtosecond (fs) pulses generated from a laser system consisting of a Ti:sapphire oscillator, a Ti:sapphire regenerative amplifier, an optical parametric amplifier and a difference frequency generator. We study the Kerr nonlinearity of QCLs by coupling resonant and off-resonant mid-IR fs pulses into an active QCL waveguide. We observe an increase in the spectral width of the transmitted fs pulses as the coupled mid-IR pulse power increases. This is explained by the self-phase modulation effect due to the large Kerr nonlinearity of QCL waveguides. We further confirm this effect by observing the intensity dependent far-field profile of the transmitted mid-IR pulses, showing the pulses undergo self-focusing as they propagate through the active QCL due to the intensity dependent refractive index. The finite-difference time-domain simulations of QCL waveguides with Kerr nonlinearity incorporated show similar behavior to the experimental results. The giant Kerr nonlinearity investigated here may be used to realize ultrafast pulse generation in QCLs. In addition, we temporally resolved the ultrafast mid-infrared transmission modulation of QCLs using a near-infrared pump/mid-infrared probe technique at room temperature. Two different femtosecond wavelength pumps are used with photon energy above and below the quantum well (QW) bandgap. The shorter wavelength pump modulates the mid-infrared probe transmission through interband transition assisted mechanisms, resulting in a high transmission modulation depth

  20. Satellite observations of transionospheric pulse pairs

    SciTech Connect

    Holden, D.N.; Munson, C.P.; Devenport, J.C.

    1995-04-15

    The BLACKBEARD payload aboard the ALEXIS satellite has been making broadband observations in the VHF band of the radio spectrum. Since November of 1993 several hundred unusual signals have been recorded. The peculiar nature of these bursts of radio noise is that they have a duration of approximately 10 {mu}sec, are typically 20 to 40 dB brighter than the average background, and occur in pairs separated by approximately 50 {mu}sec. The authors have dubbed these emissions TransIonospheric Pulse Pairs, or TIPP events. They do not know what the source of these emissions is, but the dispersion of these signals is consistent with an origin at or near the earth`s surface. The satellite field of view and time of day when TIPP events are generally detected are consistent with regions of thunderstorm activity such as south-central Africa or Indonesia. 4 refs., 5 figs.

  1. Tunable, high-repetition-rate, femtosecond pulse generation in the ultraviolet.

    PubMed

    Ghotbi, M; Esteban-Martin, A; Ebrahim-Zadeh, M

    2008-02-15

    We report efficient generation of tunable femtosecond pulses in the ultraviolet (UV) by intracavity doubling of a visible femtosecond optical parametric oscillator (OPO). The OPO, based on a 400 microm BiB3O6 crystal and pumped at 415 nm in the blue, can provide visible femtosecond signal pulses across 500-710 nm. Using a 500 microm crystal of beta-BaB2O4 internal to the OPO cavity, efficient frequency doubling of the signal pulses into the UV is achieved, providing tunable femtosecond pulses across 250-355 nm with up to 225 mW of average power at 76 MHz. Cross-correlation measurements result in UV pulses with durations down to 132 fs for 180 fs blue pump pulses. PMID:18278105

  2. Phenomenology of transionospheric pulse pairs: Further observations

    SciTech Connect

    Massey, R.S.; Holden, D.N.; Shao, X.

    1998-11-01

    We report on further observations of transionospheric pulse pairs (TIPPs), which are the most powerful transient radio signals observed by the Blackbeard broadband digital radio receiver on the ALEXIS satellite. The source of these signals is unknown but appears to be associated with thunderstorm activity. The signals do not resemble those reported for known lightning processes. We have previously reported observations of these events in the frequency band 28{endash}95 MHz. In this paper we report observations of TIPPs in the 117- to 166-MHz band, with the subsatellite point situated over the contiguous United States. The main results are that the measured pulse parameter statistics are nearly the same as reported for the low-frequency events, with the exception that the pulse separation distribution is biased toward smaller values in the high-frequency observations. The radiated power does not drop off appreciably even at 166 MHz, which further constrains the possible size and timescale of the source(s). We also report results of experiments designed to measure the apparent reflectivity of dry, flat ground at frequencies around 100 MHz. We find that the apparent reflectivity can exceed 90{percent}. This result helps to explain how the second pulse in a TIPP can have so much energy relative to the first. {copyright} 1998 American Geophysical Union

  3. Generation of individually modulated femtosecond pulse string by multilayer volume holographic gratings.

    PubMed

    Yan, Xiaona; Gao, Lirun; Yang, Xihua; Dai, Ye; Chen, Yuanyuan; Ma, Guohong

    2014-10-20

    A scheme to generate individually modulated femtosecond pulse string by multilayer volume holographic grating (MVHG) is proposed. Based on Kogelnik's coupled-wave theory and matrix optics, temporal and spectral expressions of diffracted field are given when a femtosecond pulse is diffracted by a MVHG. It is shown that the number of diffracted sub-pulses in the pulse string equals to the number of grating layers of the MVHG, peak intensity and duration of each diffracted sub-pulse depend on thickness of the corresponding grating layer, whereas pulse interval between adjacent sub-pulses is related to thickness of the corresponding buffer layer. Thus by modulating parameters of the MVHG, individually modulated femtosecond pulse string can be acquired. Based on Bragg selectivity of the volume grating and phase shift provided by the buffer layers, we give an explanation on these phenomena. The result is useful to design MVHG-based devices employed in optical communications, pulse shaping and processing. PMID:25401645

  4. Filamentation of femtosecond laser pulses as a source for radiotherapy

    NASA Astrophysics Data System (ADS)

    Meesat, Ridthee; Allard, Jean-François; Belmouaddine, Hakim; Brastaviceanu, Tiberius; Tremblay, Luc; Paquette, Benoit; Jay-Gerin, Jean-Paul; Wagner, J. Richard; Lepage, Martin; Houde, Daniel

    2011-08-01

    Here, we report that intense ultra-short laser pulses produce a plasma of low energy electrons (LEEs) by the inverse Bremsstrahlung effect and multiphoton ionization process. The phenomena show five striking characteristics. First, the self-focusing of ultra-short laser pulses creates a plasma of LEEs (6.5 eV), which is concentrated in filaments through an avalanche process. Second, kinetically hot 6.5 eV electrons interact with surrounding molecules resulting in reactive radical species. Third, the dose rate reaches an enormous level of ~2.8 × 1011 Gy/s as determined by a cericcerous sulfate dosimetry and this leads to an ultra-high deposition of energy of between 4.6 × 107 to 8.16 × 107 keV/μm. Fourth, filaments of variable length are produced by femtosecond pulses depending on the pulse duration as determined by a tissue-equivalent radiation polymer gel dosimeter and imaged by magnetic resonance imaging (MRI). These results reveal that one of the very interesting novelty of filamentation is the very low entrance dose, similar to proton irradiation. Lastly, filamentary irradiation results in the decomposition of thymidine in the absence and the presence of oxygen similar to the radiolysis of water.

  5. Fibonacci-like photonic structure for femtosecond pulse compression.

    PubMed

    Makarava, L N; Nazarov, M M; Ozheredov, I A; Shkurinov, A P; Smirnov, A G; Zhukovsky, S V

    2007-03-01

    The compression of femtosecond laser pulses by linear quasiperiodic and periodic photonic multilayer structures is studied both experimentally and theoretically. We compare the compression performance of a Fibonacci and a periodic structure with similar total thickness and the same number of layers, and find the performance to be higher in the Fibonacci case, as predicted by numerical simulation. This compression enhancement takes place due to the larger group velocity dispersion at a defect resonance of the transmission spectrum of the Fibonacci structure. We demonstrate that the Fibonacci structure with the thickness of only 2.8 microm can compress a phase-modulated laser pulse by up to 30%. The possibility for compression of laser pulses with different characteristics in a single multilayer is explored. The operation of the compressor in the reflection regime has been modeled, and we show numerically that the reflected laser pulse is subjected to real compression: not only does its duration decrease but also its amplitude rises. PMID:17500811

  6. Active compensation of large dispersion of femtosecond pulses for precision laser ranging.

    PubMed

    Lee, Sang-Hyun; Lee, Joohyung; Kim, Young-Jin; Lee, Keunwoo; Kim, Seung-Woo

    2011-02-28

    We describe an active way of compensation for large dispersion induced in the femtosecond light pulses travelling in air for laser ranging. The pulse duration is consistently regulated at 250 fs by dispersion control, allowing sub-micrometer resolution in measuring long distances by means of time-of-flight measurement. This method could facilitate more reliable applications of femtosecond pulses for satellite laser ranging, laser altimetry and active LIDAR applications. PMID:21369227

  7. Sub-diffraction limited structuring of solid targets with femtosecond laser pulses.

    PubMed

    Korte, F; Adams, S; Egbert, A; Fallnich, C; Ostendorf, A; Nolte, S; Will, M; Ruske, J P; Chichkov, B; Tuennermann, A

    2000-07-17

    Possibilities to produce sub-diffraction limited structures in thin metal films and bulk dielectric materials using femtosecond laser pulses are investigated. The physics of ultrashort pulse laser ablation of solids is outlined. Results on the fabrication of sub-micrometer structures in 100-200 nm chrome-coated surfaces by direct ablative writing are reported. Polarization maintaining optical waveguides produced by femtosecond laser pulses inside crystalline quartz are demonstrated. PMID:19404368

  8. Fabrication of optical cavities with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Lin, Jintian; Song, Jiangxin; Tang, Jialei; Fang, Wei; Sugioka, Koji; Cheng, Ya

    2014-03-01

    We report on fabrication of three-dimensional (3D) high-quality (Q) whispering-gallery-mode microcavities by femtosecond laser micromachining. The main fabrication procedures include the formation of on-chip freestanding microdisk through selective material removal by femtosecond laser pulses, followed by surface smoothing processes (CO2 laser reflow for amorphous glass and focused ion beam (FIB) sidewall milling for crystalline materials) to improve the Q factors. Fused silica microcavities with 3D geometries are demonstrated with Q factors exceeding 106. A microcavity laser based on Nd:glass has been fabricated, showing a threshold as low as 69μW via free space continuous-wave optical excitation at the room temperature. CaF2 crystalline microcavities with Q factor of ~4.2×104 have also been demonstrated. This technique allows us to fabricate 3D high-Q microcavities in various transparent materials such as glass and crystals, which will benefit a broad spectrum of applications such as nonlinear optics, quantum optics, and bio-sensing.

  9. Multiterawatt femtosecond laser system with kilohertz pulse repetition rate

    SciTech Connect

    Petrov, V V; Pestryakov, E V; Laptev, A V; Petrov, V A; Kuptsov, G V; Trunov, V I; Frolov, S A

    2014-05-30

    The basic principles, layout and components are presented for a multiterawatt femtosecond laser system with a kilohertz pulse repetition rate f, based on their parametric amplification and laser amplification of picosecond radiation that pumps the stages of the parametric amplifier. The results of calculations for a step-by-step increase in the output power from the LBO crystal parametric amplifier channel up to the multiterawatt level are presented. By using the developed components in the pump channel of the laser system, the parameters of the regenerative amplifier with the output energy ∼1 mJ at the wavelength 1030 nm and with f = 1 kHz are experimentally studied. The optical scheme of the diode-pumped multipass cryogenic Yb:Y{sub 2}O{sub 3} laser ceramic amplifier is developed and its characteristics are determined that provide the output energy within the range 0.25 – 0.35 J. (lasers)

  10. Ferroelectric domain engineering by focused infrared femtosecond pulses

    SciTech Connect

    Chen, Xin; Shvedov, Vladlen; Sheng, Yan; Karpinski, Pawel; Koynov, Kaloian; Wang, Bingxia; Trull, Jose; Cojocaru, Crina; Krolikowski, Wieslaw

    2015-10-05

    We demonstrate infrared femtosecond laser-induced inversion of ferroelectric domains. This process can be realised solely by using tightly focused laser pulses without application of any electric field prior to, in conjunction with, or subsequent to the laser irradiation. As most ferroelectric crystals like LiNbO{sub 3}, LiTaO{sub 3}, and KTiOPO{sub 4} are transparent in the infrared, this optical poling method allows one to form ferroelectric domain patterns much deeper inside a ferroelectric crystal than by using ultraviolet light and hence can be used to fabricate practical devices. We also propose in situ diagnostics of the ferroelectric domain inversion process by monitoring the Čerenkov second harmonic signal, which is sensitive to the appearance of ferroelectric domain walls.

  11. Laser surface and subsurface modification of sapphire using femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Eberle, G.; Schmidt, M.; Pude, F.; Wegener, K.

    2016-08-01

    Two methods to process sapphire using femtosecond laser pulses are demonstrated, namely ablation (surface), and in-volume laser modification followed by wet etching (subsurface). Firstly, the single and multipulse ablation threshold is determined and compared with previous literature results. A unique application of ablation is demonstrated by modifying the entrance aperture of water jet orifices. Laser ablation exhibits advantages in terms of geometric flexibility and resolution, however, defects in the form of edge outbreaks and poor surface quality are evident. Secondly, the role of material transformation, polarisation state and formation of multi-focus structures after in-volume laser modification is investigated in order to explain their influence during the wet etching process. Laser scanning and electron microscopy as well as electron backscatter diffraction measurements supported by ion beam polishing are used to better understand quality and laser-material interactions of the two demonstrated methods of processing.

  12. Multiterawatt femtosecond laser system with kilohertz pulse repetition rate

    NASA Astrophysics Data System (ADS)

    Petrov, V. V.; Pestryakov, E. V.; Laptev, A. V.; Petrov, V. A.; Kuptsov, G. V.; Trunov, V. I.; Frolov, S. A.

    2014-05-01

    The basic principles, layout and components are presented for a multiterawatt femtosecond laser system with a kilohertz pulse repetition rate f, based on their parametric amplification and laser amplification of picosecond radiation that pumps the stages of the parametric amplifier. The results of calculations for a step-by-step increase in the output power from the LBO crystal parametric amplifier channel up to the multiterawatt level are presented. By using the developed components in the pump channel of the laser system, the parameters of the regenerative amplifier with the output energy ~1 mJ at the wavelength 1030 nm and with f = 1 kHz are experimentally studied. The optical scheme of the diode-pumped multipass cryogenic Yb:Y2O3 laser ceramic amplifier is developed and its characteristics are determined that provide the output energy within the range 0.25 - 0.35 J.

  13. Realizing Ultrafast Electron Pulse Self-Compression by Femtosecond Pulse Shaping Technique.

    PubMed

    Qi, Yingpeng; Pei, Minjie; Qi, Dalong; Yang, Yan; Jia, Tianqing; Zhang, Shian; Sun, Zhenrong

    2015-10-01

    Uncorrelated position and velocity distribution of the electron bunch at the photocathode from the residual energy greatly limit the transverse coherent length and the recompression ability. Here we first propose a femtosecond pulse-shaping method to realize the electron pulse self-compression in ultrafast electron diffraction system based on a point-to-point space-charge model. The positively chirped femtosecond laser pulse can correspondingly create the positively chirped electron bunch at the photocathode (such as metal-insulator heterojunction), and such a shaped electron pulse can realize the self-compression in the subsequent propagation process. The greatest advantage for our proposed scheme is that no additional components are introduced into the ultrafast electron diffraction system, which therefore does not affect the electron bunch shape. More importantly, this scheme can break the limitation that the electron pulse via postphotocathode static compression schemes is not shorter than the excitation laser pulse due to the uncorrelated position and velocity distribution of the initial electron bunch. PMID:26722884

  14. Pulse reshaping in nearly resonant interaction of femtosecond pulses with dense rubidium vapor

    NASA Astrophysics Data System (ADS)

    Vdović, Silvije; Skenderović, Hrvoje; Pichler, Goran

    2016-07-01

    Propagation of intense femtosecond pulses resonant with the atomic rubidium vapor results in phenomenon known as conical emission. The origin of this phenomenon is connected with self-phase modulation in time domain accompanied with spatial self-focusing for blue-detuned pulses. When the laser central wavelength is red-detuned the self-defocusing occurs. Using frequency-resolved optical gating measurements and simple modeling of pulse propagation within the linear dispersion theory it is shown that the retrieved phase of the propagated pulse, and the associated instantaneous frequency, shows evidence of both linear dispersion and self-phase modulation. These results are consistent with the theory of the intensity dependent nonlinear refraction index in medium where linear dispersion contributes significantly to pulse reshaping.

  15. Femtosecond pulse damage thresholds of dielectric coatings in vacuum

    SciTech Connect

    Michelle D. Shinn, Duy N. Nguyen, Luke A. Emmert ,Paul Schwoebel, Dinesh Patel, Carmen S. Menoni, Wolfgang Rudolph

    2011-03-01

    At 10-7 Torr, the multiple femtosecond pulse damage threshold, F(?), is about 10% of the single pulse damage fluence F(1) for hafnia and silica films compared to about 65% and 50%, respectively, at 630 Torr. In contrast, the single-pulse damage threshold is pressure independent. The decrease of F(?) with decreasing air pressure correlates with the water vapor and oxygen content of the ambient gas with the former having the greater effect. The decrease in F(?) is likely associated with an accumulation of defects derived from oxygen deficiency, for example vacancies. From atmospheric air pressure to pressures of {approx}3 x 10{sup -6} Torr, the damage 'crater' starts deterministically at the center of the beam and grows in diameter as the fluence increases. At pressure below 3x10-6 Torr, damage is initiated at random 'sites' within the exposed area in hafnia films, while the damage morphology remains deterministic in silica films. A possible explanation is that absorbing centers are created at predisposed sample sites in hafnia, for example at boundaries between crystallites, or crystalline and amorphous phases.

  16. Minimum visible retinal lesions from pico- and femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Roach, William P.; Toth, Cynthia A.; Stein, Cindy D.; Noojin, Gary D.; Stolarski, David J.; Cain, Clarence P.

    1994-08-01

    Threshold measurements for Minimum Visible Lesions (MVL) at the retina are reported for femtosecond (fs) and picosecond (ps) laser pulses in Rhesus monkey eyes using visible wavelengths. The 50% probability for damage (ED50) dosages are calculated for 1 hour and 24 hour post-exposures at the 95% confidence level. The ED50 values are found to decrease with pulsewidth down to 600 fs. At 90 fs the ED50 dosages were noted to increase slightly when compared with the 3 ps and 600 fs values. Fluorescein angiography (FA) was accomplished at both 1 hour and 24 hour post-exposure and did not demonstrate lower threshold for damage, which has been the case for MVL's created with longer pulse durations (>= nanoseconds). At the 90 fs pulse duration, MVLs were not observed below 0.1 (mu) J. At energies greater than 0.1 (mu) J, both MVL and the absence of MVL's were observed up to 1.4 (mu) J. Above 1.4 (mu) J all energies delivered showed MVL development. Out of 138 data points taken at 90 fs, 94 were between 0.1 and 14 (mu) J, and the observed lesions are distributed with approximately 50% probability throughout this energy rate.

  17. Interaction of femtosecond laser pulses with tempera paints

    NASA Astrophysics Data System (ADS)

    Gaspard, Solenne; Oujja, Mohamed; Moreno, Pablo; Méndez, Cruz; García, Ana; Domingo, Concepción; Castillejo, Marta

    2008-12-01

    For the implementation of femtosecond (fs) laser cleaning methodologies of light-sensitive substrates as those encountered in artistic paintings, the interaction between fs laser pulses and painting components has to be well characterized. In this work, the modifications induced by fs laser irradiation of paints are examined in unvarnished aged model temperas. Irradiation at fluences below or above the ablation thresholds by 120 fs pulses at 795 nm from a Ti:Sapphire laser of unpigmented and traditional artist's pigment temperas (cinnabar and chrome yellow) is shown to result in various degrees of discolouration and changes of the laser-induced fluorescence signal. Fourier transform FT-Raman (at 1064 nm) and micro-Raman (at 785 nm) spectroscopic measurements were carried out to assess the changes induced. Noticeable modifications of the Raman bands of the pigments are absent while build-up of extra bands of amorphous carbon (indicative of carbonization or charring) does not take place, in contrast with previous observations upon irradiation with 248 nm, 25 ns pulses. It is concluded that IR fs irradiation provides a high degree of control over the induced modifications, a feature of interest in the design of new laser restoration schemes.

  18. Femtosecond pulsed laser ablation of GaAs

    NASA Astrophysics Data System (ADS)

    Trelenberg, T. W.; Dinh, L. N.; Saw, C. K.; Stuart, B. C.; Balooch, M.

    2004-01-01

    The properties of femtosecond-pulsed laser deposited GaAs nanoclusters were investigated. Nanoclusters of GaAs were produced by laser ablating a single crystal GaAs target in vacuum or in a buffer gas using a Ti-sapphire laser with a 150 fs minimum pulse length. For in-vacuum deposition, X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) revealed that the average cluster size was approximately 7 nm for laser pulse lengths between 150 fs and 25 ps. The average cluster size dropped to approximately 1.5 nm at a pulse length of 500 ps. It was also observed that film thickness decreased with increasing laser pulse length. A reflective coating, which accumulated on the laser admission window during ablation, reduced the amount of laser energy reaching the target for subsequent laser shots and developed more rapidly at longer pulse lengths. This observation indicates that non-stoichiometric (metallic) ablatants were produced more readily at longer pulse lengths. The angular distribution of ejected material about the target normal was well fitted to a bi-cosine distribution of cos 47 θ+ cos 4 θ for ablation in vacuum using 150 fs pulses. XPS and AES revealed that the vacuum-deposited films contained excess amorphous Ga or As in addition to the stoichiometric GaAs nanocrystals seen with XRD. However, films containing only the GaAs nanocrystals were produced when ablation was carried out in the presence of a buffer gas with a pressure in excess of 6.67 Pa. At buffer gas pressure on the order of 1 Torr, it was found that the stoichiometry of the ablated target was also preserved. These experiments indicate that both laser pulse length and buffer gas pressure play important roles in the formation of multi-element nanocrystals by laser ablation. The effects of gas pressure on the target's morphology and the size of the GaAs nanocrystals formed will also be discussed.

  19. Quasi-steady-state air plasma channel produced by a femtosecond laser pulse sequence

    PubMed Central

    Lu, Xin; Chen, Shi-You; Ma, Jing-Long; Hou, Lei; Liao, Guo-Qian; Wang, Jin-Guang; Han, Yu-Jing; Liu, Xiao-Long; Teng, Hao; Han, Hai-Nian; Li, Yu-Tong; Chen, Li-Ming; Wei, Zhi-Yi; Zhang, Jie

    2015-01-01

    A long air plasma channel can be formed by filamentation of intense femtosecond laser pulses. However, the lifetime of the plasma channel produced by a single femtosecond laser pulse is too short (only a few nanoseconds) for many potential applications based on the conductivity of the plasma channel. Therefore, prolonging the lifetime of the plasma channel is one of the key challenges in the research of femtosecond laser filamentation. In this study, a unique femtosecond laser source was developed to produce a high-quality femtosecond laser pulse sequence with an interval of 2.9 ns and a uniformly distributed single-pulse energy. The metre scale quasi-steady-state plasma channel with a 60–80 ns lifetime was formed by such pulse sequences in air. The simulation study for filamentation of dual femtosecond pulses indicated that the plasma channel left by the previous pulse was weakly affected the filamentation of the next pulse in sequence under our experimental conditions. PMID:26493279

  20. Quasi-steady-state air plasma channel produced by a femtosecond laser pulse sequence.

    PubMed

    Lu, Xin; Chen, Shi-You; Ma, Jing-Long; Hou, Lei; Liao, Guo-Qian; Wang, Jin-Guang; Han, Yu-Jing; Liu, Xiao-Long; Teng, Hao; Han, Hai-Nian; Li, Yu-Tong; Chen, Li-Ming; Wei, Zhi-Yi; Zhang, Jie

    2015-01-01

    A long air plasma channel can be formed by filamentation of intense femtosecond laser pulses. However, the lifetime of the plasma channel produced by a single femtosecond laser pulse is too short (only a few nanoseconds) for many potential applications based on the conductivity of the plasma channel. Therefore, prolonging the lifetime of the plasma channel is one of the key challenges in the research of femtosecond laser filamentation. In this study, a unique femtosecond laser source was developed to produce a high-quality femtosecond laser pulse sequence with an interval of 2.9 ns and a uniformly distributed single-pulse energy. The metre scale quasi-steady-state plasma channel with a 60-80 ns lifetime was formed by such pulse sequences in air. The simulation study for filamentation of dual femtosecond pulses indicated that the plasma channel left by the previous pulse was weakly affected the filamentation of the next pulse in sequence under our experimental conditions. PMID:26493279

  1. Photoassociation and coherent transient dynamics in the interaction of ultracold rubidium atoms with shaped femtosecond pulses. I. Experiment

    SciTech Connect

    Mullins, Terry; Salzmann, Wenzel; Goetz, Simone; Albert, Magnus; Eng, Judith; Wester, Roland; Weidemueller, Matthias; Weise, Fabian; Merli, Andrea; Weber, Stefan M.; Sauer, Franziska; Woeste, Ludger; Lindinger, Albrecht

    2009-12-15

    We experimentally investigate various processes present in the photoassociative interaction of an ultracold atomic sample with shaped femtosecond laser pulses as an detailed extension of previous work [W. Salzmann et al., Phys. Rev. Lett. 100, 233003 (2008)]. We demonstrate the photoassociation of pairs of rubidium atoms into electronically excited, bound molecular states using spectrally cut femtosecond laser pulses tuned below the rubidium D{sub 1} or D{sub 2} asymptote. Time-resolved pump-probe spectra reveal oscillations of the molecular formation rate, which are due to coherent transient dynamics in the electronic excitation. The oscillation frequency corresponds to the detuning of the spectral cut position to the asymptotic transition frequency of the rubidium D{sub 1} or D{sub 2} lines, respectively. Measurements of the molecular photoassociation signal as a function of the pulse energy reveal a nonlinear dependence and indicate a nonperturbative excitation process. Chirping the association laser pulse allowed us to change the phase of the coherent transients. Furthermore, a signature for molecules in the electronic ground state is found, which is attributed to molecule formation by femtosecond photoassociation followed by spontaneous decay. In a subsequent article [A. Merli et al., Phys. Rev. A 80, 063417 (2009)] quantum mechanical calculations are presented, which compare well with the experimental data and reveal further details about the observed coherent transient dynamics.

  2. Femtosecond pulses generated from a synchronously pumped chromium-doped forsterite laser

    NASA Technical Reports Server (NTRS)

    Seas, A.; Petricevic, V.; Alfano, R. R.

    1993-01-01

    Kerr lens mode-locking (KLM) has become a standard method to produce femtosecond pulses from tunable solid state lasers. High power inside the laser resonator propagating through the laser-medium with nonlinear index of refraction, coupled with the stability conditions of the laser modes in the resonator, result in a passive amplitude modulation which explains the mechanism for pulse shortening. Recently, chromium doped forsterite was shown to exhibit similar pulse behavior. A successful attempt to generate femtosecond pulses from a synchronously pumped chromium-doped forsterite laser with intracavity dispersion compensation is reported. Stable, transform limited pulses with duration of 105 fs were routinely generated, tunable between 1240 to 1270 nm.

  3. Two-photon fluorescence excitation spectroscopy by pulse shaping ultrabroad-bandwidth femtosecond laser pulses

    SciTech Connect

    Xu Bingwei; Coello, Yves; Lozovoy, Vadim V.; Dantus, Marcos

    2010-11-10

    A fast and automated approach to measuring two-photon fluorescence excitation (TPE) spectra of fluorophores with high resolution ({approx}2 nm ) by pulse shaping ultrabroad-bandwidth femtosecond laser pulses is demonstrated. Selective excitation in the range of 675-990 nm was achieved by imposing a series of specially designed phase and amplitude masks on the excitation pulses using a pulse shaper. The method eliminates the need for laser tuning and is, thus, suitable for non-laser-expert use. The TPE spectrum of Fluorescein was compared with independent measurements and the spectra of the pH-sensitive dye 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) in acidic and basic environments were measured for the first time using this approach.

  4. Live cell opto-injection by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Baumgart, J.; Bintig, W.; Ngezahayo, A.; Ertmer, W.; Lubatschowski, H.; Heisterkamp, A.

    2007-02-01

    Fluorescence imaging of cells and cell organelles requires labeling by fluorophores. The labeling of living cells is often done by transfection of fluorescent proteins. Viral vectors are transferring the DNA into the cell. To avoid the use of viruses, it is possible to perforate the cell membrane for example by electro-shocks, the so called electroporation, so that the fluorescent proteins can diffuse into the cell. This method causes cell death in up to 50% of the treated cells because the damage of the outer membrane is too large. A less lethal perforation of the cell membrane with high efficiency can be realized by femtosecond (fs) laser pulses. Transient pores are created by focusing the laser beam for some milliseconds on the membrane. Through this pore, the proteins can enter into the cell. This was demonstrated in a proof of principle experiment for a few cells, but it is essential to develop an opto-perforation system for large numbers of cells in order to obtain statistically significant samples for biological experiments. The relationship between pulse energy, irradiation time, repetition rate and efficacy of the transfer of a chromophor into the cells as well as the viability of the cells was analysed. The cell viability was observed up to 90 minutes after manipulation.

  5. Infrared antireflection DLC films by femtosecond pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Wang, Shuyun; Guo, Yanlong; Wang, Xiaobing; Cheng, Yong; Wang, Huisheng; Liu, Xu

    2009-05-01

    Diamond-like Carbon(DLC) films are deposited by Ti:Sapphire femtosecond pulsed laser(800nm, 120fs-2ps, 3.3W, 1-1000Hz) at room temperature. The substrate is n-type Si(100), and the target is 99.999%-purity graphite. After a great lot of experiments, optimal technical parameters, which are 1000Hz repetition frequency, 120fs pulse-width, 5cm-distance between target and underlay and 1014W/cm2 power-density, were used to deposite 443nm thick DLC film. Raman spectrum measurement shows a broad peak with a center at 1550 cm-1 for all films, similar to those of typical diamond-like carbon films prepared using other methods. And sp3-bond content reaches 67% analyzed by XPS. There is no nick on the film when scraped 105 times by a RS-5600 friction test machine under the pressure of 9.8N. The infrared transmittance increases along with the oxygen pressure when between 0.03 Pa and 2 Pa. The result shows that oxygen is effective in etching sp2-bond content. The extreme infrared transmittance of Si slice deposited DLC film on single surface is higher than 64% at 3-5μm, superior to 53% when being uncoated.

  6. Generation of electromagnetic pulses from plasma channels induced by femtosecond light strings.

    PubMed

    Cheng, C C; Wright, E M; Moloney, J V

    2001-11-19

    We present a model that elucidates the physics underlying the generation of an electromagnetic pulse from a femtosecond laser induced plasma channel. The radiation pressure force from the laser pulse spatially separates the ionized electrons from the heavier ions and the induced dipole moment subsequently oscillates at the plasma frequency and radiates an electromagnetic pulse. PMID:11736337

  7. Adiabatic femtosecond pulse compression and control by using quadratic cascading nonlinearity

    NASA Astrophysics Data System (ADS)

    Zeng, Xianglong; Ashihara, Satoshi; Shimura, Tsutomu; Kuroda, Kazuo

    2008-01-01

    We experimentally demonstrate that adiabatic compression of femtosecond pulse can be achieved by employing the management of quadratic cascading nonlinearity in quasi-phase-matching gratings. Cascading nonlinearity is not a simple analogy with third-order optical nonlinearity in term of the engineering properties of the magnitude and focusing (or defocusing) nonlinearity. Femtosecond pulse compression is investigated based on type-I (e: o + o) collinear QPM geometry of aperiodically poled MgO-doped LiNbO 3 (MgO: LN). Group-velocity-matching condition is chosen to generate quadratic femtosecond soliton consisting of fundamental (FF) and second harmonic (SH) pulses. Adiabatic-like compression process is observed in the length of 50 mm linearly chirped QPM. Cascading nonlinearity is local managed, instead of dispersion management used in fiber adiabatic soliton compression. Quadratic soliton including FF and SH pulses are obtained from the compression of 95 fs FF pulse in the initial experiments. Dependence on the phase mismatch and group velocity mismatch, cascading nonlinearity has a flexible property and presents a new challenge for exploring femtosecond pulse shaping and control. The demonstrated pulse compression and control based on cascading nonlinearity is useful for generation of shorter pulses with clean temporal profiles, efficient femtosecond second harmonic generation and group-velocity control.

  8. Laser ranging by time-of-flight measurement of femtosecond light pulses

    NASA Astrophysics Data System (ADS)

    Kim, Young-Jin

    2014-04-01

    Time-of-flight (TOF) measurement of femtosecond light pulses was investigated for laser ranging of long distances with sub-micrometer precision in the air. The bandwidth limitation of the photo-detection electronics used in timing femtosecond pulses was overcome by adopting a type-II nonlinear second-harmonic crystal that permits producing the balanced optical cross-correlation signal between two overlapped light pulses. This method offered a sub-femtosecond timing resolution in determining the temporal offset between two pulses through lock-in control of the pulse repetition rate with reference to the atomic clock. The exceptional ranging capability was verified by measuring various distances from 1.5 m to 700 m. This method is found suited for terrestrial land surveying and space missions of formation-flying satellites.

  9. Optical Response of Metal Nanoantennas to Femtosecond Pulses

    NASA Astrophysics Data System (ADS)

    Biswas, Sushmita; Heberle, Albert

    2007-03-01

    Nanoscale metal antennas are promising devices for focusing light down to dimensions much smaller than the wavelength of light. This focusing can lead to strong optical enhancement of the response of single molecules or quantum dots placed in the antenna gap, as well as strong nonlinearities. The optical response of such antenna, however, is not well understood yet. Here, we will present results of our investigations of the linear and nonlinear optical response of silver nanoscale bowtie antennas to excitation with near-infrared pulses from a femtosecond Ti:sapphire laser. The antennas were fabricated with electron beam lithography and a lift-of process on glass substrates and semiconductor materials. They have lengths of a few hundred nanometers and gaps between 10 and 100 nanometers. We will discuss polarization dependence of the excitation sensitivity, second harmonic generation and other nonlinear effects. References: [1] P. Muhlschlegel et al., Science ,1607(2005). [2] J.N. Farahani et al., Phys. Rev. Lett. 95,017402(2005).

  10. Phase and intensity characterization of femtosecond pulses from a chirped-pulse amplifier by frequency-resolved optical gating

    SciTech Connect

    Kohler, B.; Yakovlev, V.V.; Wilson, K.R.; Squier, J.; DeLong, K.W.; Trebino, R.

    1995-03-01

    Frequency-resolved optical gating (FROG) measurements were made to characterize pulses from a Ti:sapphire chirped-pulse amplified laser system. By characterizing both the pulse intensity and the phase, the FROG data provided the first direct observation to our knowledge of residual phase distortion in a chirped-pulse amplifier. The FROG technique was also used to measure the regenerative amplifier dispersion and to characterize an amplitude-shaped pulse. The data provide an experimental demonstration of the value of FROG for characterizing complex pulses, including tailored femtosecond pulses for quantum control.

  11. Separating pairing from quantum phase coherence dynamics above the superconducting transition by femtosecond spectroscopy

    PubMed Central

    Madan, I.; Kurosawa, T.; Toda, Y.; Oda, M.; Mertelj, T.; Kusar, P.; Mihailovic, D.

    2014-01-01

    In classical superconductors an energy gap and phase coherence appear simultaneously with pairing at the transition to the superconducting state. In high-temperature superconductors, the possibility that pairing and phase coherence are distinct and independent processes has led to intense experimental search of their separate manifestations. Using femtosecond spectroscopy methods we now show that it is possible to clearly separate fluctuation dynamics of the superconducting pairing amplitude from the phase relaxation above the critical transition temperature. Empirically establishing a close correspondence between the superfluid density measured by THz spectroscopy and superconducting optical pump-probe response over a wide region of temperature, we find that in differently doped Bi2Sr2CaCu2O8+δ crystals the pairing gap amplitude monotonically extends well beyond Tc, while the phase coherence shows a pronounced power-law divergence as T → Tc, thus showing that phase coherence and gap formation are distinct processes which occur on different timescales. PMID:25014162

  12. Observation of Optical Pulse and Material Dynamics on the Femtosecond Time-Scale

    SciTech Connect

    Omenetto, F.; Luce, B.; Siders, C.W.; Taylor, A.J.

    1999-09-13

    The widespread availability of lasers that generate pulses on the femtosecond scale has opened new realms of investigation in the basic and applied sciences, rendering available excitations delivering intensities well in excess of 10{sup 21} W/cm{sup 2}, and furnishing probes capable of resolving molecular relaxation timescales. As a consequence and a necessity, sophisticated techniques to examine the pulse behavior on the femtosecond scale have been developed and are of crucial importance to gain insight on the behavior of physical systems. These techniques will be discussed with specific application to guided pulse propagation and ionization dynamics of noble gases.

  13. Measurement of temperature rises in the femtosecond laser pulsed three-dimensional atom probe

    SciTech Connect

    Cerezo, A.; Smith, G.D.W.; Clifton, P.H.

    2006-04-10

    A previous Letter [B. Gault et al., Appl. Phys. Lett. 86, 094101 (2005)] interpreted measurements of the field evaporation enhancement under femtosecond pulsed laser irradiation of a field emitter in terms of a direct electric field enhancement by the intrinsic field of the laser light. We show that, on the contrary, the field evaporation enhancement is predominantly a thermal heating effect. Indirect measurements of the peak specimen temperature under irradiation by femtosecond laser pulses are consistent with temperature rises obtained using longer laser pulses in a range of earlier work.

  14. Fabrication of a periodic structure with a high refractive-index difference by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Takeshima, Nobuhito; Kuroiwa, Yutaka; Narita, Yoshihiro; Tanaka, Shuhei; Hirao, Kazuyuki

    2004-08-01

    A microfabrication process using ultrafast laser pulses in glass was investigated. We investigated the formation of semiconductors by the irradiation of glasses with femtosecond laser pulses. ZnS- or PbS-doped SiO2-Al2O3-B2O3-CaO-ZnO-Na2O-K2O glasses were prepared by a melting method and irradiated by femtosecond laser pulses. Periodic structures in the sample glasses with a high refractive index difference were produced by femtosecond laser pulses. The maximum relative refractive index difference between the irradiated area and the nonirradiated areas was 20%. Diffraction gratings were also fabricated inside the ZnS- or PbS-doped silicate glasses. The diffraction efficiency of these gratings was approximately 90% in the infrared region.

  15. Femtosecond strong-field quantum control with sinusoidally phase-modulated pulses

    SciTech Connect

    Wollenhaupt, M.; Praekelt, A.; Sarpe-Tudoran, C.; Liese, D.; Bayer, T.; Baumert, T.

    2006-06-15

    The quantum control of the ionization of potassium atoms using shaped intense femtosecond laser pulses is investigated. We use sinusoidal phase modulation as a prototype for complex shaped pulses to investigate the physical mechanism of the strong-field quantum control by shaped femtosecond light fields. The influence of all parameters characterizing the sinusoidal phase modulation on strong-field-induced dynamics is studied systematically in experiment and theory. Our results are interpreted in terms of the selective population of dressed states (SPODS) which gives a natural physical picture of the dynamics in intense laser fields. We show that modulated femtosecond pulses in combination with photoelectron spectroscopy are a versatile tool to prepare and to probe SPODS. The decomposition of the excitation and ionization process induced by shaped pulses into elementary physically transparent steps is discussed.

  16. Numerical simulation of impurity desorption induced by nanosecond and femtosecond laser pulses

    SciTech Connect

    Chi Yinsheng; Lin Xiaohui; Chen Minhua; Chen Yunfei

    2006-08-01

    A model based on a stochastic process was developed to study the impurity molecule desorption from a substrate induced by nanosecond and femtosecond lasers. The dynamics of adsorbed molecules irradiated by the laser pulses can be considered to be a Brownian motion in the bath of excited energy carriers. A two-step model was used to describe the nonequilibrium heating process induced by the femtosecond laser pulses. The difference between the desorption processes induced by nanosecond and femtosecond lasers was discussed based on the numerical results for the desorption of CO molecules from a Ru surface. Results indicate that the femtosecond laser is a much better tool for desorption than the nanosecond laser.

  17. Observations in collinear femtosecond-nanosecond dual-pulse laser-induced breakdown spectroscopy.

    PubMed

    Scaffidi, J; Pearman, W; Carter, J C; Angel, S M

    2006-01-01

    In the work reported herein, we have combined a short-lived femtosecond laser-induced plasma (LIP) and a longer-lived nanosecond LIP in a collinear pulse configuration to examine the source(s) of atomic emission and signal-to-noise enhancement in dual-pulse laser-induced breakdown spectroscopy (LIBS). Initial studies indicate that the primary source of dual-pulse LIBS enhancement in the collinear configuration may in large part be a matter of pulse focus; focusing on the sample surface, for example, yields atomic emission enhancements whose lifetime correlates reasonably well with the femtosecond LIP emissive lifetime, suggesting that plasma-plasma coupling may play an important role at that pulse focus. At a second "optimal" focal position above the sample surface, alternatively, atomic emission and signal-to-noise enhancements correlate quite well with the nitrogen and oxygen atomic emission reductions previously seen following use of a femtosecond air spark and a nanosecond ablative pulse in the orthogonal dual-pulse configuration, suggesting that pressure or number density reductions due to femtosecond LIP formation in air may be significant at that pulse focus. PMID:16454914

  18. Measurement of ablation threshold of oxide-film-coated aluminium nanoparticles irradiated by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Chefonov, O. V.; Ovchinnikov, A. V.; Il'ina, I. V.; Agranat, M. B.

    2016-03-01

    We report the results of experiments on estimation of femtosecond laser threshold intensity at which nanoparticles are removed from the substrate surface. The studies are performed with nanoparticles obtained by femtosecond laser ablation of pure aluminium in distilled water. The attenuation (or extinction, i.e. absorption and scattering) spectra of nanoparticles are measured at room temperature in the UV and optical wavelength ranges. The size of nanoparticles is determined using atomic force microscopy. A new method of scanning photoluminescence is proposed to evaluate the threshold of nanoparticle removal from the surface of a glass substrate exposed to IR femtosecond laser pulses with intensities 1011 – 1013 W cm-2.

  19. Double pulse laser-induced breakdown spectroscopy with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Piñon, V.; Fotakis, C.; Nicolas, G.; Anglos, D.

    2008-10-01

    This paper presents results obtained in a study of collinear geometry double pulse femtosecond LIBS analysis of solids in ambient environment. LIBS signal enhancement of 3-10 fold, accompanied by significant improvement of signal reproducibility, in comparison with the single pulse case, has been found in different samples such as brass, iron, silicon, barium sulfate and aluminum when an optimum temporal separation between the two ablating pulses is used. The influence of the delay between pulses in the LIBS signal intensity was investigated and two intervals of interaction were established. A first transient regime from 0 to 50 ps, in which the LIBS signal increases until reaching a maximum, and a second regime that ranges from 50 to 1000 ps (maximum inter-pulse delay investigated) in which the signal enhancement remains constant. Emissions from both ionized and neutral atoms show the same pattern of enhancement with a clear tendency of lines arising from higher energy emissive states to exhibit higher enhancement factors.

  20. Modification of Carbon Nanotube Templates Using Femtosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Chang, Won-Seok; Yoo, Byung-Hyun; Cho, Sung-Hak

    2008-08-01

    Selective modification of carbon nanotubes (CNTs) on Si substrates was performed using a femtosecond laser. The high shock wave generated by the femtosecond laser effectively removed the CNTs without damage to the Si substrate. This process has many advantages because it is performed without chemicals and is easily applied to large-area patterning. The CNTs grown by plasma-enhanced chemical vapor deposition (PECVD) have a catalyst cap at the end of the nanotube due to the tip-growth mode mechanism. For the application of an electron emission and a bio sensor, the catalyst cap is usually chemically removed, which damages the surface of the wall of the CNTs. However, precise control of the femtosecond laser power and focal position can solve this problem. Furthermore, selective cutting of carbon nanotube using a femtosecond laser does not cause any phase change in the CNTs, as usually shown in focused ion beam irradiation of the CNTs.

  1. Morphological effects of nanosecond- and femtosecond-pulsed laser ablation on human middle ear ossicles

    NASA Astrophysics Data System (ADS)

    Ilgner, Justus F. R.; Wehner, Martin M.; Lorenzen, Johann; Bovi, Manfred; Westhofen, Martin

    2006-01-01

    We evaluate the feasibility of nanosecond-pulsed and femtosecond-pulsed lasers for otologic surgery. The outcome parameters are cutting precision (in micrometers), ablation rate (in micrometers per second), scanning speed (in millimeters per second), and morphological effects on human middle ear ossicles. We examine single-spot ablations by a nanosecond-pulsed, frequency-tripled Nd:YAG laser (355 nm, beam diameter 10µm, pulse rate 2 kHz, power 250 mW) on isolated human mallei. A similar system (355 nm, beam diameter 20µm, pulse rate 10 kHz, power 160-1500 mW) and a femtosecond-pulsed CrLi:SAF-Laser (850 nm, pulse duration 100 fs, pulse energy 40 µJ, beam diameter 36 µm, pulse rate 1 kHz) are coupled to a scanner to perform bone surface ablation over a defined area. In our setups 1 and 2, marginal carbonization is visible in all single-spot ablations of 1-s exposures and longer: With an exposure time of 0.5 s, precise cutting margins without carbonization are observed. Cooling with saline solution result is in no carbonization at 1500 mW and a scan speed of 500 mm/s. Our third setup shows no carbonization but greater cutting precision, although the ablation volume is lower. Nanosecond- and femtosecond-pulsed laser systems bear the potential to increase cutting precision in otologic surgery.

  2. Observation of voids and optical seizing of voids in silica glass with infrared femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Watanabe, Wataru; Toma, Tadamasa; Yamada, Kazuhiro; Nishii, Junji; Hayashi, Ken-ichi; Itoh, Kazuyoshi

    2000-11-01

    Many researchers have investigated the interaction of femtosecond laser pulses with a wide variety of materials. The structural modifications both on the surface and inside the bulk of transparent materials have been demonstrated. When femtosecond laser pulses are focused into glasses with a high numerical-aperture objective, voids are formed. We demonstrate that one can seize and move voids formed by femtosecond laser pulses inside silica glass and also merge two voids into one. We also present clear evidence that a void is a cavity by showing a scanning-electron-microscope image of cleft voids: we clove through the glass along a plane that includes the laser-ablated thin line on the surface and the voids formed inside. The optical seizing and merging of voids are important basic techniques for fabricate micro-optical dynamic devices, such as the rewritable 3-D optical storage.

  3. A new multifunctional device for femtosecond pulse characterization with a wide operating range

    NASA Astrophysics Data System (ADS)

    Li, F. J.; Zhang, S. X.; Liu, Q. F.; Zhao, G. K.; Liu, J.

    2014-01-01

    We demonstrate a novel and simple device for femtosecond pulse characterization, which combines the frequency-resolved optical gating (FROG) and the self-referenced spectral interferometry (SRSI) methods in the frequency-resolved optical gating and self-referenced spectral interferometry (FASI) method. It was found that the comparative advantages of FROG and SRSI can complement each other. Therefore FASI can be used to characterize femtosecond pulses in different conditions, which may need different devices when using either the FROG or the SRSI method independently. With our multifunctional FASI device, the TG-FROG, SHG-FROG and TG-SRSI methods were used to fully characterize femtosecond pulses at 800 nm with different dispersions. The experimental results obtained by all three methods were compared with each other and also with the calculated data. These results proved the reliability and the wide operating range of our FASI device.

  4. Realizing up-conversion fluorescence tuning in lanthanide-doped nanocrystals by femtosecond pulse shaping method

    PubMed Central

    Zhang, Shian; Yao, Yunhua; Shuwu, Xu; Liu, Pei; Ding, Jingxin; Jia, Tianqing; Qiu, Jianrong; Sun, Zhenrong

    2015-01-01

    The ability to tune color output of nanomaterials is very important for their applications in laser, optoelectronic device, color display and multiplexed biolabeling. Here we first propose a femtosecond pulse shaping technique to realize the up-conversion fluorescence tuning in lanthanide-doped nanocrystals dispersed in the glass. The multiple subpulse formation by a square phase modulation can create different excitation pathways for various up-conversion fluorescence generations. By properly controlling these excitation pathways, the multicolor up-conversion fluorescence can be finely tuned. This color tuning by the femtosecond pulse shaping technique is realized in single material by single-color laser field, which is highly desirable for further applications of the lanthanide-doped nanocrystals. This femtosecond pulse shaping technique opens an opportunity to tune the color output in the lanthanide-doped nanocrystals, which may bring a new revolution in the control of luminescence properties of nanomaterials. PMID:26290391

  5. Two-octave spectral broadening of subnanojoule Cr:forsterite femtosecond laser pulses in tapered fibers

    NASA Astrophysics Data System (ADS)

    Akimov, D. A.; Ivanov, A. A.; Alfimov, M. V.; Bagayev, S. N.; Birks, T. A.; Wadsworth, W. J.; Russell, P. St. J.; Fedotov, A. B.; Pivtsov, V. S.; Podshivalov, A. A.; Zheltikov, A. M.

    Spectral broadening of femtosecond Cr:forsterite laser pulses is enhanced due to the use of tapered fibers. Supercontinuum generation with unamplified subnanojoule femtosecond Cr:forsterite laser pulses is observed for the first time. With 40-fs 0.6-nJ pulses of 1.25-μm Cr:forsterite laser radiation coupled into a tapered fiber having a taper waist diameter of about 2 μm and a taper waist length of 90 mm, we observed the spectra spanning more than two octaves at the output of the fiber in the regime of anomalous group-velocity dispersion. This result opens the way for the creation of compact femtosecond Cr:forsterite laser plus tapered fiber systems for optical metrology and biomedical applications.

  6. Space-selective laser joining of dissimilar transparent materials using femtosecond laser pulses

    SciTech Connect

    Watanabe, Wataru; Onda, Satoshi; Tamaki, Takayuki; Itoh, Kazuyoshi; Nishii, Junji

    2006-07-10

    We report on the joining of dissimilar transparent materials based on localized melting and resolidification of the materials only around the focal volume due to nonlinear absorption of focused femtosecond laser pulses. We demonstrate the joining of borosilicate glass and fused silica, whose coefficients of thermal expansion are different. The joint strength and the transmittance through joint volume were investigated by varying the translation velocity of the sample and the pulse energy of the irradiated laser pulses.

  7. Surface mico-structures on amorphous alloys induced by vortex femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Ran, Ling-Ling; Qu, Shi-Liang; Guo, Zhong-Yi

    2010-03-01

    This paper investigates the generation of self-organized surface structures on amorphous alloys by vortex femtosecond laser pulses. The scanning electron microscope characterizations show that the as-formed structures are periodic ripples, aperiodic ripples, and 'coral-like' structures. Optimal conditions for forming these surface structures are determined in terms of pulses number at a given pulse energy. The applicable mechanism is suggested to interpret the formation and evolution of the 'coral-like' structures.

  8. Investigation of the spectra of luminescence and Raman scattering in water and chlorophyll "a" excited by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Biryukova, Yu. S.; Ilyin, A. A.; Golik, S. S.; Mayor, A. Y.

    2015-11-01

    The Raman spectra of femtosecond laser pulses in distilled and tap water, and luminescence spectra of aqueous solutions containing dissolved organic matter, chlorophyll "a" and biological objects excited by ultra-short laser pulses was investigated.

  9. Characterization of ultraviolet femtosecond pulse propagation in aluminum-coated capillary fibers

    SciTech Connect

    Thoegersen, Jan; Madsen, Esben Svitzer Yates; Holmegaard, Lotte; Jensen, Svend Knak; Keiding, Soeren Rud; Matsuura, Yuji; Miyagi, Mitsunobu

    2005-08-01

    We demonstrate that hollow core fibers with aluminum-coated bores of {phi}=0.7 mm and {phi}=1.0 mm are well suited for guiding high-power ultraviolet femtosecond pulses. We consider 1-m-long fibers in two geometries: straight and bent with a 30-cm radius of curvature. The straight fibers transmit approximately 60% of the power at 200 nm and 85% at 266 nm, while the corresponding numbers for the bent fibers are 25% and 35%. The duration of the femtosecond pulses increases by 10% and 50% per meter at 200 and 266 nm, respectively. The broadening increases to a factor of two when the fiber is bent. The maximum transmitted pulse energy at 266 nm is 100 {mu}J corresponding to 0.5 GW or an intensity of 10{sup 11} W/cm{sup 2}. However, this value is limited only by the 266 nm pulse generation and is expected to go even higher. The applicability of the powerful femtosecond pulses from the fiber is demonstrated by an experiment in which water is ionized by two-photon absorption. This experiment indicates the potential of using aluminized hollow core fibers in medical therapy with ultraviolet femtosecond pulses.

  10. The formation of an intense filament controlled by interference of ultraviolet femtosecond pulses

    SciTech Connect

    Wang Yongdong; Zhang Yisan; Chen Peng; Shi Liping; Lu Xin; Wu Jian; Ding Liang'en; Zeng Heping

    2011-03-14

    We experimentally investigated the formation of a wavelength-scale photonic plasma grating induced by interference-assisted coalescence of two noncollinear ultraviolet femtosecond laser pulses. The period of the created plasma grating decreased with the crossing angle of the interacting laser pulses. For a proper small crossing angle, the noncollinear ultraviolet filaments were coalesced and an intense single ultraviolet filament was formed with a diameter of 5 {mu}m which was below the focused limitation. This may provide a way to control ultraviolet femtosecond filamentation.

  11. Wavelength-dependent femtosecond pulse amplification in wideband tapered-waveguide quantum well semiconductor optical amplifiers.

    PubMed

    Xia, Mingjun; Ghafouri-Shiraz, H

    2015-12-10

    In this paper, we study the wavelength-dependent amplification in three different wideband quantum well semiconductor optical amplifiers (QWAs) having conventional, exponentially tapered, and linearly tapered active region waveguide structures. A new theoretical model for tapered-waveguide QWAs considering the effect of lateral carrier density distribution and the strain effect in the quantum well is established based on a quantum well transmission line modeling method. The temporal and spectral characteristics of amplified femtosecond pulse are analyzed for each structure. It was found that, for the amplification of a single femtosecond pulse, the tapered-waveguide QWA provides higher saturation gain, and the output spectra of the amplified pulse in all three structures exhibit an apparent redshift and bandwidth narrowing due to the reduction of carrier density; however, the output spectrum in the tapered-waveguide amplifier is less distorted and exhibits smaller bandwidth narrowing. For the simultaneous amplification of two femtosecond pulses with different central frequencies, in all the three structures, two peaks appear in the output spectra while the peak at the frequency closer to the peak frequency of the QWA gain spectrum receives higher amplification due to the frequency (wavelength) dependence of the QWA gain. At a low peak power level of the input pulse, the bandwidth of each window in the tapered structure is larger than that of the conventional waveguide structure, which aggravates the spectrum alias in the amplification of femtosecond pulses with different central frequencies. As the peak powers of the two pulses increase, the spectrum alias in the conventional waveguide becomes more serious while there are small changes in the tapered structures. Also, we have found that in the amplification of a femtosecond pulse train, the linear-tapered QWAs exhibit the fastest gain recovery as compared with the conventional and exponentially tapered QWAs. PMID

  12. Synthesis of Optical Frequencies and Ultrastable Femtosecond Pulse Trains from an Optical Reference Oscillator

    NASA Astrophysics Data System (ADS)

    Bartels, A.; Ramond, T. M.; Diddams, S. A.; Hollberg, L.

    Recently, atomic clocks based on optical frequency standards have been demonstrated [1,2]. A key element in these clocks is a femtosecond laser that downconverts the petahertz oscillation rate into countable ticks at 1 GHz. When compared to current microwave standards, these new optical clocks are expected to yield an improvement in stability and accuracy by roughly a factor of 1000. Furthermore, it is possible that the lowest noise microwave sources will soon be based on atomically-stabilized optical oscillators that have their frequency converted to the microwave domain via a femtosecond laser. Here, we present tests of the ability of femtosecond lasers to transfer stability from an optical oscillator to their repetition rates as well as to the associated broadband frequency comb. In a first experiment, we phase-lock two lasers to a stabilized laser diode and find that the relative timing jitter in their pulse trains can be on the order of 1 femtosecond in a 100 kHz bandwidth. It is important to distinguish this technique from previous work where a femtosecond laser has been stabilized to a microwave standard [3,4] or another femtosecond laser [5]. Furthermore, we extract highly stable microwave signals with a fractional frequency instability of 2×10-14 in 1 s by photodetection of the laser pulse trains. In a second experiment, we similarly phase-lock the femtosecond laser to an optical oscillator with linewidth less than 1 Hz [6]. The precision with which we can make the femtosecond frequency comb track this reference oscillator is then tested by a heterodyne measurement between a second stable optical oscillator and a mode of the frequency comb that is displaced 76 THz from the 1 Hz-wide reference. From this heterodyne signal we place an upper limit of 150 Hz on the linewidth of the elements of the frequency comb, limited by the noise in the measurement itself.

  13. Construction and characterization of ultraviolet acousto-optic based femtosecond pulse shapers

    SciTech Connect

    Mcgrane, Shawn D; Moore, David S; Greenfield, Margo T

    2008-01-01

    We present all the information necessary for construction and characterization of acousto optic pulse shapers, with a focus on ultraviolet wavelengths, Various radio-frequency drive configurations are presented to allow optimization via knowledgeable trade-off of design features. Detailed performance characteristics of a 267 nm acousto-optic modulator (AOM) based pulse shaper are presented, Practical considerations for AOM based pulse shaping of ultra-broad bandwidth (sub-10 fs) amplified femtosecond pulse shaping are described, with particular attention paid to the effects of the RF frequency bandwidth and optical frequency bandwidth on the spatial dispersion of the output laser pulses.

  14. LASERS: Efficient source of femtosecond pulses and its use for broadband supercontinuum generation

    NASA Astrophysics Data System (ADS)

    Tausenev, Anton V.; Kryukov, P. G.; Bubnov, M. M.; Likhachev, M. E.; Romanova, E. Yu; Yashkov, M. V.; Khopin, V. F.; Salganskii, M. Yu

    2005-07-01

    A femtosecond Er3+-doped fibre laser system is developed and studied. The system contains a master oscillator operating in the pulse stretching regime, an amplifier of chirped pulses, and a device for pulse compression. The laser emits 1.55-μm, 100-fs, 90-mW pulses with a pulse repetition rate of 25 MHz. The setup was used for supercontinuum generation in an optical fibre heavily doped with GeO2. The width of the generated supercontinuum was close to an octave.

  15. Efficient source of femtosecond pulses and its use for broadband supercontinuum generation

    SciTech Connect

    Tausenev, Anton V; Kryukov, P G; Bubnov, M M; Likhachev, M E; Romanova, E Yu; Yashkov, M V; Khopin, V F; Salganskii, M Yu

    2005-07-31

    A femtosecond Er{sup 3+}-doped fibre laser system is developed and studied. The system contains a master oscillator operating in the pulse stretching regime, an amplifier of chirped pulses, and a device for pulse compression. The laser emits 1.55-{mu}m, 100-fs, 90-mW pulses with a pulse repetition rate of 25 MHz. The setup was used for supercontinuum generation in an optical fibre heavily doped with GeO{sub 2}. The width of the generated supercontinuum was close to an octave. (lasers)

  16. Control of laser induced reactions in solids using selected photon energies and pulse pairs

    NASA Astrophysics Data System (ADS)

    Hess, Wayne; Joly, Alan; Beck, Kenneth; Gerrity, Daniel; Dickinson, J. Thomas; Sushko, Peter; Shluger, Alexander

    2002-03-01

    Laser control of reaction dynamics is an intensely studied area of chemical physics. Sophisticated quantum and optimal control schemes have been developed to overcome difficulties associated with rapid energy redistribution from laser-prepared initial states. Experiment and theory have demonstrated how specific product pathways can be selected by irradiation with one or more laser beams. Although most laser control research has focused on small gas-phase molecules, product and quantum state control of laser desorption from solids is possible using delayed pulse pairs, selected pulse duration or by judicious choice of laser wavelength. Theory indicates that it is possible to excite the surface of ionic crystals, over the bulk, using tunable laser sources.[1] We recently demonstrated control of ion emission from MgO surfaces[2] using femtosecond pulse pairs and nearly exclusive emission of hyperthermal Br (2P3/2) from laser excited KBr.[3] Here, we explore the mechanism of laser desorption in experiments using delayed pulse pairs and tunable single pulses. The first laser pulse induces formation of transient species and the second pulse then excites the intermediate state to induce desorption of selected species or quantum states. Selective desorption raises the intriguing prospect of selective surface modification. The principles described here should be extendable to other alkali halides and metal oxides. References: [1] A.L. Shluger, P.V. Sushko, and L.N. Kantorovich, Phys. Rev. B. 59, (1999) 2417. [2] K.M. Beck, A.G. Joly, and W.P. Hess, Sur. Sci. 451, 166 (2000). [3] W. P. Hess, A. G. Joly, K. M. Beck, D. P. Gerrity, P. V. Sushko, and A. L. Shluger, J. Chem. Phys. 115, 9463 (2001).

  17. Understanding Femtosecond-Pulse Laser Damage through Fundamental Physics Simulations

    NASA Astrophysics Data System (ADS)

    Mitchell, Robert A., III

    It did not take long after the invention of the laser for the field of laser damage to appear. For several decades researchers have been studying how lasers damage materials, both for the basic scientific understanding of highly nonequilibrium processes as well as for industrial applications. Femtosecond pulse lasers create little collateral damage and a readily reproducible damage pattern. They are easily tailored to desired specifications and are particularly powerful and versatile tools, contributing even more industrial interest in the field. As with most long-standing fields of research, many theoretical tools have been developed to model the laser damage process, covering a wide range of complexities and regimes of applicability. However, most of the modeling methods developed are either too limited in spatial extent to model the full morphology of the damage crater, or incorporate only a small subset of the important physics and require numerous fitting parameters and assumptions in order to match values interpolated from experimental data. Demonstrated in this work is the first simulation method capable of fundamentally modeling the full laser damage process, from the laser interaction all the way through to the resolidification of the target, on a large enough scale that can capture the full morphology of the laser damage crater so as to be compared directly to experimental measurements instead of extrapolated values, and all without any fitting parameters. The design, implementation, and testing of this simulation technique, based on a modified version of the particle-in-cell (PIC) method, is presented. For a 60 fs, 1 mum wavelength laser pulse with fluences of 0.5 J/cm 2, 1.0 J/cm2, and 2.0 J/cm2 the resulting laser damage craters in copper are shown and, using the same technique applied to experimental crater morphologies, a laser damage fluence threshold is calculated of 0.15 J/cm2, consistent with current experiments performed under conditions similar

  18. Single-shot measurement of the spectral envelope of broad-bandwidth terahertz pulses from femtosecond electron bunches

    SciTech Connect

    van Tilborg, Jeroen; Toth, Csaba; Matlis, Nicholas; Plateau, Guillaume; Leemans, Wim

    2011-06-17

    We present a new approach (demonstrated experimentally and through modeling) to characterize the spectral envelope of a terahertz (THz) pulse in a single shot. The coherent THz pulse is produced by a femtosecond electron bunch and contains information on the bunch duration. The technique, involving a single low-power laser probe pulse, is an extension of the conventional spectral encoding method (limited in time resolution to hundreds of femtoseconds) into a regime only limited in resolution by the laser pulse length (tens of femtoseconds). While only the bunch duration is retrieved (and not the exact charge profile), such a measurement provides a useful and critical parameter for optimization of the electron accelerator.

  19. Characterization of the optical components fabricated by femtosecond pulses in transparent materials

    NASA Astrophysics Data System (ADS)

    Mazule, Lina; Liukaityte, Simona; Sabonis, Vytautas; Gertus, Titas; Mikutis, Mindaugas; Paipulas, Domas; Puodziunas, Tomas; Sirutkaitis, Valdas

    2013-09-01

    We report optical characterization of the different optical components fabricated in transparent materials by bulk refractive index modification or surface ablation by femtosecond pulses. The methods used for characterization of the components with refractive index modification fabricated in fused silica by high repetition rate femtosecond KGW:Yb laser were transmission and diffraction measurements at 532 and 632.8 nm wavelengths, and total integrated scattering (TIS) at 532 mn wavelength. The combined characterization methods were sufficient for modification process optimization and allowed creation of the Bragg gratings with diffraction efficiency in range from 55 to 90% and low scattering losses. The forward and backward TIS measurements of the radial polarization converter showed that forward scattering is more than five times as high as backward scattering. Solar cells with modified surface by femtosecond pulse ablation were investigated by TIS and Volt-Ampere measurements. The current increase is registered with growth of the scattering loses in the solar cells.

  20. Nanosurgery with near-infrared 12-femtosecond and picosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Uchugonova, Aisada; Zhang, Huijing; Lemke, Cornelius; König, Karsten

    2011-03-01

    Laser-assisted surgery based on multiphoton absorption of NIR laser light has great potential for high precision surgery at various depths within the cells and tissues. Clinical applications include refractive surgery (fs-LASIK). The non-contact laser method also supports contamination-free cell nanosurgery. Here we apply femtosecond laser scanning microscopes for sub-100 nm surgery of human cells and metaphase chromosomes. A mode-locked 85 MHz Ti:Sapphire laser with an M-shaped ultrabroad band spectrum (maxima: 770 nm/830 nm) with an in situ pulse duration at the target ranging from 12 femtoseconds up to 3 picoseconds was employed. The effects of laser nanoprocessing in cells and chromosomes have been quantified by atomic force microscopy (AFM) and electron microscopy. These studies demonstrate the potential of extreme ultrashort femtosecond laser pulses at low mean milliwatt powers for sub-100 nm surgery.

  1. Femtosecond Er-doped fiber laser based on divided-pulse nonlinear amplification

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Li, Wenxue; Li, Lang; Hao, Qiang; Zhao, Jian; Zeng, Heping

    2016-02-01

    A high-power erbium-doped fiber amplifier was realized by using a spatially and temporally divided pulse amplification technique. Pulse amplification and compression were simultaneously achieved in a double-clad Er-doped fiber by controlling the pulse gain and dispersion, generating a slope efficiency of 19.2% for the divided pulse amplification. The spectrum and pulse evolutions for nonlinear amplification and compression in the double-clad gain fiber were studied both in theory and experiment. Then 680 mW near-infrared femtosecond laser pulses were obtained by using 0.45 m single-mode fiber to compress amplified pulses. Frequency doubling was further carried out with a periodically poled lithium niobate (PPLN) crystal, generating 790 nm laser pulses with 110 mW average power and 95.7 fs pulse duration.

  2. Low threshold power density for the generation of frequency up-converted pulses in bismuth glass by two crossing chirped femtosecond pulses.

    PubMed

    Zhang, Hang; Liu, Hui; Si, Jinhai; Yi, Wenhui; Chen, Feng; Hou, Xun

    2011-06-20

    We investigated the generation of frequency up-converted femtosecond laser pulses by nondegenerate cascaded four-wave mixing (CFWM) in a bismuth-oxide glass (BI glass). Broad-bandwidth light pulses with different propagation directions were simultaneously obtained by using two small-angle crossing femtosecond laser pulses in BI glass. Experimental results show that the threshold power density for the generation of broad-bandwidth femtosecond pulses in BI glass is one order of magnitude lower than that in fused silica. PMID:21716439

  3. Reflection of a probe pulse and thermal emission of electrons produced by an aluminum film heated by a femtosecond laser pulse

    SciTech Connect

    Bezhanov, S. G.; Ionin, A. A.; Kanavin, A. P.; Kudryashov, S. I.; Makarov, S. V.; Seleznev, L. V.; Sinitsyn, D. V.; Uryupin, S. A.

    2015-06-15

    It is shown that an experimental decrease in the reflection of a probe femtosecond pulse from an aluminum film heated by a higher-power femtosecond pulse can be quantitatively described taking into account the inhomogeneous distribution of the laser pulse field in the film and the evolution of the electron and lattice temperature during absorption of the heating inhomogeneous field. Analysis of the electron temperature evolution on the heated film surface combined with modern concepts about the influence of a surface volume charge on thermal emission gave the relation between the amount of emitted electrons and experimental data on the heating of the aluminum film by the femtosecond pulse.

  4. Noncontact microsurgery and delivery of substances into stem cells by means of femtosecond laser pulses

    SciTech Connect

    Il'ina, I V; Ovchinnikov, A V; Sitnikov, D S; Chefonov, O V; Agranat, M B

    2014-06-30

    We have studied the efficiency of microsurgery of a cell membrane in mesenchymal stem cells and the posterior cell viability under the localised short-time action of femtosecond IR laser pulses aimed at noncontact delivery of specified substances into the cells. (extreme light fields and their applications)

  5. Investigation of temporal contrast effects in femtosecond pulse laser micromachining of metals.

    SciTech Connect

    Campbell, Benjamin (Pennsylvania State University, Freeport, PA); Palmer, Jeremy Andrew

    2006-06-01

    Femtosecond pulse laser drilling has evolved to become a preferred process for selective (maskless) micromachining in a variety of materials, including metals, polymers, semiconductors, ceramics, and living tissue. Manufacturers of state-of-the-art femtosecond laser systems advertise the inherent advantage of micromachining with ultra short pulses: the absence of a heat affected zone. In the ideal case, this leads to micro and nano scale features without distortion due to melt or recast. However, recent studies have shown that this is limited to the low fluence regime in many cases. High dynamic range autocorrelation studies were performed on two commercial Ti:sapphire femtosecond laser systems to investigate the possible presence of a nanosecond pedestal in the femtosecond pulse produced by chirped pulse amplification. If confirmed, nanosecond temporal phenomena may explain many of the thermal effects witnessed in high fluence micromachining. The material removal rate was measured in addition to feature morphology observations for percussion micro drilling of metal substrates in vacuum and ambient environments. Trials were repeated with proposed corrective optics installed, including a variable aperture and a nonlinear frequency doubling crystal. Results were compared. Although the investigation of nanosecond temporal phenomena is ongoing, early results have confirmed published accounts of higher removal rates in a vacuum environment.

  6. Local field enhancement on metallic periodic surface structures produced by femtosecond laser pulses

    SciTech Connect

    Ionin, Andrei A; Kudryashov, Sergei I; Ligachev, A E; Makarov, Sergei V; Mel'nik, N N; Rudenko, A A; Seleznev, L V; Sinitsyn, D V; Khmelnitskii, R A

    2013-04-30

    Periodic surface structures on aluminium are produced by femtosecond laser pulses for efficient excitation of surface electromagnetic waves using a strong objective (NA = 0.5). The local electromagnetic field enhancement on the structures is measured using the technique of surface-enhanced Raman scattering from pyridine molecules. (extreme light fields and their applications)

  7. Propagation of femtosecond pulses in a hollow-core revolver fibre

    NASA Astrophysics Data System (ADS)

    Yatsenko, Yu P.; Krylov, A. A.; Pryamikov, A. D.; Kosolapov, A. F.; Kolyadin, A. N.; Gladyshev, A. V.; Bufetov, I. A.

    2016-07-01

    We have studied for the first time the propagation of femtosecond pulses through an optical fibre with an air-filled hollow core and a cladding in the form of one ring of noncontacting cylindrical capillaries for high-power radiation transmission in the 1.55-μm telecom range. Numerical analysis results demonstrate that the parameters of the fibre enable radiation transmission in the form of megawatt-power Raman solitons through up to a 25-m length of the fibre and tuning of the emission wavelength over 130 nm. We have experimentally demonstrated femtosecond pulse transmission through fibres up to 5 m in length in the linear propagation regime, without distortions of the pulse spectrum, with a dispersion-induced temporal pulse broadening within 20%.

  8. Comparative study of the ablation of materials by femtosecond and pico- or nanosecond laser pulses

    SciTech Connect

    Kononenko, Taras V; Konov, Vitalii I; Garnov, Sergei V; Danielius, R; Piskarskas, A; Tamosauskas, G; Dausinger, F

    1999-08-31

    A series of studies was carried out on the ablation of steel, Si{sub 3}N{sub 4} ceramic, and diamond in air by femtosecond (200 and 900 fs) pulses of different wavelengths (532 and 266 nm) and in a wide energy density range (1 - 10{sup 3} J cm{sup -2}). The ablation rates were measured for different geometries of the irradiation surface [a shallow crater and a channel with a high (up to 10) aspect ratio]. The ablation rates (in a shallow crater) and the morphologies of the irradiated surface were compared for femtosecond and longer (220 ps, 7 ns) pulses. The role of the laser-generated plasma in the ablation of materials by subpicosecond pulses as well as the prospects for the practical application of ultrashort laser pulses in the processing of materials are analysed. (interaction of laser radiation with matter. laser plasma)

  9. Single-shot ablation threshold of chromium using UV femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Banerjee, S. P.; Fedosejevs, R.

    2014-07-01

    Single-shot ablation threshold for thin chromium film was studied using 266 nm, femtosecond laser pulses. Chromium is a useful material in the nanotechnology industry and information on ablation threshold using UV femtosecond pulses would help in precise micromachining of the material. The ablation threshold was determined by measuring the ablation crater diameters as a function of incident laser pulse energy. Absorption of 266 nm light on the chromium film was also measured under our experimental conditions, and the absorbed energy single-shot ablation threshold fluence was 46 ± 5 mJ/cm2. The experimental ablation threshold fluence value was compared to time-dependent heat flow calculations based on the two temperature model for ultrafast laser pulses. The model predicts a value of 31.6 mJ/cm2 which is qualitatively consistent with the experimentally obtained value, given the simplicity of the model.

  10. Irreversible modification of magnetic properties of Pt/Co/Pt ultrathin films by femtosecond laser pulses

    SciTech Connect

    Kisielewski, J.; Dobrogowski, W.; Kurant, Z.; Stupakiewicz, A.; Tekielak, M.; Maziewski, A.; Kirilyuk, A.; Kimel, A.; Rasing, Th.; Baczewski, L. T.; Wawro, A.

    2014-02-07

    Annealing ultrathin Pt/Co/Pt films with single femtosecond laser pulses leads to irreversible spin-reorientation transitions and an amplification of the magneto-optical Kerr rotation. The effect was studied as a function of the Co thickness and the pulse fluence, revealing two-dimensional diagrams of magnetic properties. While increasing the fluence, the creation of two branches of the out-of-plane magnetization state was found.

  11. Physical origin of nanograting formation on fused silica with femtosecond pulses

    SciTech Connect

    Liang, Feng Vallée, Réal

    2014-09-29

    We present a comprehensive analysis of physical evolution of nanograting formation based on an experiment performed with femtosecond pulses focused under moderate focusing conditions and where pulse energy is slowly increased as the focused beam is moved along the sample surface. The results demonstrate that nanograting inscription is initiated at the location of the maximum plasma density and evolves through local intensity side lobes, whose locations are self-regulated in a closed feedback loop, in agreement with the plasmonic model.

  12. Impact of spatial inhomogeneities on on-axis pulse reconstruction in femtosecond filaments

    NASA Astrophysics Data System (ADS)

    Brée, Carsten; Kretschmar, Martin; Nagy, Tamas; Kurz, Heiko G.; Morgner, Uwe; Kovačev, Milutin

    2015-05-01

    We demonstrate a strong influence of the spatial beam profile on the vacuum-propagated on-axis pulse shapes for a femtosecond filament in argon. The effects can be minimized by transmitting the filament into the far-field by a laser drilled pinhole setup. Using this method, we can monitor the pulse compression dynamics along the entire longitudinal extension of the filament, including the ionization-induced plasma channel.

  13. Optimization of two tailored rectangular femtosecond laser pulses in methane dissociation

    NASA Astrophysics Data System (ADS)

    Sadighi-Bonabi, R.; Dehghani, Z.; Irani, E.

    2010-05-01

    Based on the quantum mechanics principles and classically calculated dressed potential surfaces by using field assisted dissociation model the dissociation probability for CH4+ molecule exposed with a 100 femtosecond 8 Jcm-2 Ti:sapphire laser pulses is calculated. Using the gradient optimization method two tailored rectangular laser pulses for controlling the dissociation of C-H bond of CH4+ molecule along laser pulse direction is found. In the proposed optimization method, the complicacy of solving Schrodinger wave equation is reduced by using classical method and in contrast to the usual controlling and pulse shaping methods of chemical reactions, the experimental data is not needed and this reduces the controlling costs.

  14. Generation of elliptically polarized nitrogen ion laser fields using two-color femtosecond laser pulses

    PubMed Central

    Li, Ziting; Zeng, Bin; Chu, Wei; Xie, Hongqiang; Yao, Jinping; Li, Guihua; Qiao, Lingling; Wang, Zhanshan; Cheng, Ya

    2016-01-01

    We experimentally investigate generation of nitrogen molecular ion () lasers with two femtosecond laser pulses at different wavelengths. The first pulse serves as the pump which ionizes the nitrogen molecules and excites the molecular ions to excited electronic states. The second pulse serves as the probe which leads to stimulated emission from the excited molecular ions. We observe that changing the angle between the polarization directions of the two pulses gives rise to elliptically polarized laser fields, which is interpreted as a result of strong birefringence of the gain medium near the wavelengths of the laser. PMID:26888182

  15. Kerr self-cleaning of femtosecond-pulsed beams in graded-index multimode fiber.

    PubMed

    Liu, Zhanwei; Wright, Logan G; Christodoulides, Demetrios N; Wise, Frank W

    2016-08-15

    We observe a nonlinear spatial self-cleaning process for femtosecond pulses in graded-index (GRIN) multimode fiber (MMF). Pulses with ∼80 fs duration at 1030 nm are launched into GRIN MMF with 62.5 μm core. The near-field beam profile at the output end of the fiber evolves from a speckled pattern to a centered, bell-shaped transverse structure with increasing pulse energy. The experimental observations agree well with numerical simulations, which show that the Kerr nonlinearity underlies the process. This self-cleaning process may find applications in ultrafast pulse generation and beam-combining. PMID:27519060

  16. Accumulation of Raman gain between closely spaced pulse pairs.

    PubMed

    Marshall, L R; Piper, J A

    1990-12-01

    The short-pulse conversion efficiency of stimulated Raman scattering in Pb vapor is increased from 15% to 35% by using a novel technique that employs a closely spaced pair of pump pulses. The second pulse scatters off the coherent excitation induced in the medium by the first pulse, with a resultant enhancement in efficiency. To our knowledge these results give the first observation of such long-lived cooperative phenomena in stimulated Raman scattering. We have also observed this phenomenon in H(2) and show that this technique is readily applicable to other Raman-active media. PMID:19771085

  17. Acoustic experimental investigation of interaction femtosecond laser pulses with gas-aerosol media and biological tissues

    NASA Astrophysics Data System (ADS)

    Bochkarev, N. N.; Kabanov, A. M.; Stepanov, A. N.

    2008-02-01

    Using two optical acoustic approaches we experimentally investigated spatial location of filament zone of propagation channel of focused laser radiation. For femtosecond pulses passing in air it was shown that nonlinear focus length had spatial scale of 1/P at initial power P moderate for self-focusing and at optical system focus distance significantly lower than Rayleigh beam length. The results of experimental optical acoustic investigation of femto- and nanosecond pulses attenuation by some biological tissues (muscular tissue, adipose tissue, cutaneous covering, milk) and optical breakdown thresholds on these one are presented. It was shown that penetration depth of short laser pulse radiation into biological tissues is the same as for longer one. However, amplitude of acoustic response to a process of interaction of femtosecond laser pulse with biological tissue is larger in several times than that to interaction with nanosecond pulses of the same power and spectral distribution. The obtained of threshold values can be interesting for tabulation of limit allowable levels of irradiation at work with laser radiation. Such values are unknown for femtosecond laser pulses today.

  18. Selective metallization on insulator surfaces with femtosecond laser pulses.

    PubMed

    Xu, Jian; Liao, Yang; Zeng, Huidan; Zhou, Zenghui; Sun, Haiyi; Song, Juan; Wang, Xinshun; Cheng, Ya; Xu, Zhizhan; Sugioka, Koji; Midorikawa, Katsumi

    2007-10-01

    We report selective metallization on surfaces of insulators (glass slides and lithium niobate crystal) based on femtosecond laser modification combined with electroless plating. The process is mainly composed of four steps: (1) formation of silver nitrate thin films on the surfaces of glass or crystal substrates; (2) generation of silver particles in the irradiated area by femtosecond laser direct writing; (3) removal of unirradiated silver nitrate films; and (4) selective electroless plating in the modified area. We discuss the mechanism of selective metallization on the insulators. Moreover, we investigate the electrical and adhesive properties of the copper microstructures patterned on the insulator surfaces, showing great potential of integrating electrical functions into lab-on-a-chip devices. PMID:19550542

  19. Femtosecond pulse laser notch shaping via fiber Bragg grating for the excitation source on the coherent anti-Stokes Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Oh, Seung Ryeol; Kwon, Won Sik; Kim, Jin Hwan; Kim, Kyung-Soo; Kim, Soohyun

    2015-03-01

    Single-pulse coherently controlled nonlinear Raman spectroscopy is the simplest method among the coherent anti-Stokes Raman spectroscopy systems. In recent research, it has been proven that notch-shaped femtosecond pulse laser can be used to collect the coherent anti-Stokes Raman signals. In this study, we applied a fiber Bragg grating to the notch filtering component on the femtosecond pulse lasers. The experiment was performed incorporating a titanium sapphire femtosecond pulse laser source with a 100 mm length of 780-HP fiber which is inscribed 30 mm of Bragg grating. The fiber Bragg grating has 785 nm Bragg wavelength with 0.9 nm bandwidth. We proved that if the pulse lasers have above a certain level of positive group delay dispersion, it is sufficient to propagate in the fiber Bragg grating without any spectral distortion. After passing through the fiber Bragg grating, the pulse laser is reflected on the chirped mirror for 40 times to make the transform-limited pulse. Finally, the pulse time duration was 37 fs, average power was 50mW, and showed an adequate notch shape. Furthermore, the simulation of third order polarization signal is performed using MATLAB tools and the simulation result shows that spectral characteristic and time duration of the pulse is sufficient to use as an excitation source for single-pulse coherent anti-Stokes Raman spectroscopy. In conclusion, the proposed method is more simple and cost-effective than the methods of previous research which use grating pairs and resonant photonic crystal slab.

  20. Tailoring the filamentation of intense femtosecond laser pulses with periodic lattices

    SciTech Connect

    Panagiotopoulos, P.; Tzortzakis, S.; Efremidis, N. K.; Papazoglou, D. G.; Couairon, A.

    2010-12-15

    We show numerically that by using periodic lattices the filamentation of intense femtosecond laser pulses, otherwise a result of competing nonlinear effects, can be well controlled with respect to its properties. The diffraction induced by the lattice provides a regularizing mechanism to the nonlinear self-action effects involved in filamentation. We demonstrate a new propagation regime of intense lattice solitons bridging the field of spatial solitons with that of femtosecond laser filamentation. The effective filamentation control is expected to have an important impact on numerous applications.

  1. Linear micromirror array for broadband femtosecond pulse shaping in phase and amplitude

    NASA Astrophysics Data System (ADS)

    Weber, Stefan M.; Waldis, Severin; Noell, Wilfried; Kiselev, Denis; Extermann, Jérôme; Bonacina, Luigi; Wolf, Jean-Pierre; de Rooij, Nico F.

    2009-02-01

    We are developing a linear array of micromirrors designed for optical, femtosecond laser pulse shaping. It is a bulkmicromachined device, capable of retarding or diminishing certain laser frequencies in order to perform phase and amplitude modulation within a frequency band spanning the UV to the near-infrared. The design consists of a linear array of mirrors fixed on either side by springs. They feature two degrees of freedom: Out-of-plane motion for phase shifting and rotational motion for binary amplitude modulation, both realized using vertical comb drives. The first applications will include femtosecond discrimination experiments on biomolecules.

  2. Micro/Nano-Structuring of Medical Stainless Steel using Femtosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Lin, C. Y.; Cheng, C. W.; Ou, K. L.

    The medical stainless steel (SUS 304) surface is irradiated by femtosecond laser pulses with linear or circular polarization to form nanostructure-covered conical microstructures. The mean spacing of the conical microstructures and the type of the nanostructure can be controlled by the laser-processing parameters. The liquid test (water and normal-saline solution) demonstrates that the process provides a fast single-step structuring method to generate hydrophobic-enhanced metal parts. The biocompatibility test demonstrated that the femtosecond laser micro/nano- structuring surfaces have excellent biocompatibility properties compared to an untreated surface.

  3. Spatial and temporal dependence of interspark interactions in femtosecond-nanosecond dual-pulse laser-induced breakdown spectroscopy.

    PubMed

    Scaffidi, Jon; Pearman, William; Lawrence, Marion; Carter, J Chance; Colston, Bill W; Angel, S Michael

    2004-09-20

    A femtosecond air spark has recently been combined with a nanosecond ablative pulse in order to map the spatial and temporal interactions of the two plasmas in femtosecond-nanosecond orthogonal preablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS). Good spatial and temporal correlation was found for reduced atomic emission from atmospheric species (nitrogen and oxygen) and increased atomic emission from ablated species (copper and aluminum) in the femtosecond-nanosecond plasma, suggesting a potential role for atmospheric pressure or nitrogen/oxygen concentration reduction following air spark formation in generating atomic emission enhancements in dual-pulse LIBS. PMID:15473246

  4. Spatial and Temporal Dependence of Interspark Interactions in Femtosecond-Nanosecond Dual-Pulse Laser-Induced Breakdown Spectroscopy

    NASA Astrophysics Data System (ADS)

    Scaffidi, Jon; Pearman, William; Lawrence, Marion; Chance Carter, J.; Colston, Bill W., Jr.; Angel, S. Michael

    2004-09-01

    A femtosecond air spark has recently been combined with a nanosecond ablative pulse in order to map the spatial and temporal interactions of the two plasmas in femtosecond-nanosecond orthogonal preablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS). Good spatial and temporal correlation was found for reduced atomic emission from atmospheric species (nitrogen and oxygen) and increased atomic emission from ablated species (copper and aluminum) in the femtosecond-nanosecond plasma, suggesting a potential role for atmospheric pressure or nitrogen/oxygen concentration reduction following air spark formation in generating atomic emission enhancements in dual-pulse LIBS.

  5. Tuning etch selectivity of fused silica irradiated by femtosecond laser pulses by controlling polarization of the writing pulses

    SciTech Connect

    Yu Xiaoming; Zeng Bin; Liao Yang; He Fei; Cheng Ya; Xu Zhizhan; Sugioka, Koji; Midorikawa, Katsumi

    2011-03-01

    We report on experimental study on chemical etch selectivity of fused silica irradiated by femtosecond laser with either linear or circular polarization in a wide range of pulse energies. The relationships between the etch rates and pulse energies are obtained for different polarization states, which can be divided into three different regions. A drop of the etch rate for high pulse energy region is observed and the underlying mechanism is discussed. The advantage of using circularly polarized laser is justified owing to its unique capability of providing a 3D isotropic etch rate.

  6. Control of grating-coupled ultrafast surface plasmon pulse and its nonlinear emission by shaping femtosecond laser pulse

    NASA Astrophysics Data System (ADS)

    Toma, Kazunori; Masaki, Yuta; Kusaba, Miyuki; Hirosawa, Kenichi; Kannari, Fumihiko

    2015-09-01

    Spatiotemporal nanofocusing of ultrafast surface plasmon polaritons (SPPs) coupled on a metal Au tapered tip with a curvature radius of a few tens of nanometers is deterministically controlled based on the measured plasmon response function. We control the SPP pulse shape and the second harmonic generation at the apex of the Au tapered tip by shaping the excitation femtosecond laser pulses based on the response function. We also adapted a similar control scheme for coherent anti-Stokes Raman scattering (CARS) and achieved selective CARS excitation of a single Raman mode of carbon nanotubes with only a single excitation laser pulse at the apex of the tip.

  7. Characterization of femtosecond-laser pulse induced cell membrane nanosurgical attachment.

    PubMed

    Katchinskiy, Nir; Godbout, Roseline; Elezzabi, Abdulhakem Y

    2016-07-01

    This article provides insight into the mechanism of femtosecond laser nanosurgical attachment of cells. We have demonstrated that during the attachment of two retinoblastoma cells using sub-10 femtosecond laser pulses, with 800 nm central wavelength, the phospholipid molecules of both cells hemifuse and form one shared phospholipid bilayer, at the attachment location. In order to verify the hypothesis that hemifusion takes place, transmission electron microscope images of the cell membranes of retinoblastoma cells were taken. It is shown that at the attachment interface, the two cell membranes coalesce and form one single membrane shared by both cells. Thus, further evidence is provided to support the hypothesis that laser-induced ionization process led to an ultrafast reversible destabilization of the phospholipid layer of the cellular membrane, which resulted in cross-linking of the phospholipid molecules in each membrane. This process of hemifusion occurs throughout the entire penetration depth of the femtosecond laser pulse train. Thus, the attachment between the cells takes place across a large surface area, which affirms our findings of strong physical attachment between the cells. The femtosecond laser pulse hemifusion technique can potentially provide a platform for precise molecular manipulation of cellular membranes. Manipulation of the cellular membrane is an important procedure that could aid in studying diseases such as cancer; where the expression level of plasma proteins on the cell membrane is altered. PMID:27446703

  8. Characterization of femtosecond-laser pulse induced cell membrane nanosurgical attachment

    PubMed Central

    Katchinskiy, Nir; Godbout, Roseline; Elezzabi, Abdulhakem Y.

    2016-01-01

    This article provides insight into the mechanism of femtosecond laser nanosurgical attachment of cells. We have demonstrated that during the attachment of two retinoblastoma cells using sub-10 femtosecond laser pulses, with 800 nm central wavelength, the phospholipid molecules of both cells hemifuse and form one shared phospholipid bilayer, at the attachment location. In order to verify the hypothesis that hemifusion takes place, transmission electron microscope images of the cell membranes of retinoblastoma cells were taken. It is shown that at the attachment interface, the two cell membranes coalesce and form one single membrane shared by both cells. Thus, further evidence is provided to support the hypothesis that laser-induced ionization process led to an ultrafast reversible destabilization of the phospholipid layer of the cellular membrane, which resulted in cross-linking of the phospholipid molecules in each membrane. This process of hemifusion occurs throughout the entire penetration depth of the femtosecond laser pulse train. Thus, the attachment between the cells takes place across a large surface area, which affirms our findings of strong physical attachment between the cells. The femtosecond laser pulse hemifusion technique can potentially provide a platform for precise molecular manipulation of cellular membranes. Manipulation of the cellular membrane is an important procedure that could aid in studying diseases such as cancer; where the expression level of plasma proteins on the cell membrane is altered. PMID:27446703

  9. Ablation of femural bone with femtosecond laser pulses--a feasibility study.

    PubMed

    Liu, Yifei; Niemz, Markolf

    2007-09-01

    Although lasers are nowadays widely accepted as a popular scalpel of minimally invasive surgery (MIS), one of the most common orthopedic surgeries-the replacement of the knee joint-is still performed using an ordinary oscillating saw. Since ultra-short laser pulses are usually considered to be inefficient regardless of their high precision, the newest development of femtosecond laser systems has not yet been clinically applied to any mass ablation situation. However, thin disk Yb:KYW lasers meanwhile provide sufficient output power to ablate bone tissue within a reasonable time frame. Our results mainly focus on ablation rates obtained at different spot distances, repetition rates and pulse energies. It is shown that femtosecond laser pulses at high repetition rates are a promising tool for orthopedic surgery. PMID:17242869

  10. Targeted transfection of stem cells with sub-20 femtosecond laser pulses.

    PubMed

    Uchugonova, Aisada; König, Karsten; Bueckle, Rainer; Isemann, Andreas; Tempea, Gabriel

    2008-06-23

    Multiphoton microscopes have become important tools for non-contact sub-wavelength three-dimensional nanoprocessing of living biological specimens based on multiphoton ionization and plasma formation. Ultrashort laser pulses are required, however, dispersive effects limit the shortest pulse duration achievable at the focal plane. We report on a compact nonlinear laser scanning microscope with sub-20 femtosecond 75 MHz near infrared laser pulses for nanosurgery of human stem cells and two-photon high-resolution imaging. Single point illumination of the cell membrane was performed to induce a transient nanopore for the delivery of extracellular green fluorescent protein plasmids. Mean powers of less than 7 mW (<93 pJ) and low millisecond exposure times were found to be sufficient to transfect human pancreatic and salivary gland stem cells in these preliminary studies. Ultracompact sub-20 femtosecond laser microscopes may become optical tools for nanobiotechnology and nanomedicine including optical stem cell manipulation. PMID:18575499

  11. Wavelength-switchable femtosecond pulse fiber laser mode-locked by silica-encased gold nanorods

    NASA Astrophysics Data System (ADS)

    Wang, Xude; Luo, Zhichao; Liu, Meng; Tang, Rui; Luo, Aiping; Xu, Wencheng

    2016-04-01

    A wavelength-switchable femtosecond pulse fiber laser is demonstrated by using a saturable absorber (SA) of silica-encased gold nanorods (GNRs@SiO2). The GNRs@SiO2 SA presents a modulation depth of 4.5% and nonsaturable loss of 32.1%. By properly adjusting the cavity parameters, femtosecond mode-locked pulses centered at 1535.6 nm and 1560.5 nm could be achieved alternately. The durations of pulses at the two wavelengths are measured to be ~403 fs and ~426 fs, respectively. The achieved results indicated that the GNRs@SiO2 could indeed be a promising nonlinear material with excellent photothermal stability and saturable absorption, which could satisfy the requirements for different photonic devices and applications.

  12. Optimizing single-nanoparticle two-photon microscopy by in situ adaptive control of femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Li, Donghai; Deng, Yongkai; Chu, Saisai; Jiang, Hongbing; Wang, Shufeng; Gong, Qihuang

    2016-07-01

    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.

  13. Acoustic Pulses in Iron Observed by Femtosecond X-ray Diffraction

    NASA Astrophysics Data System (ADS)

    Henighan, Tom; Bonetti, Stefano; Granitzka, Patrick; Zhu, Diling; Parkin, Stuart; Trigo, Mariano; Reis, David; Durr, Herman

    2014-03-01

    Interest in improving the performance of memory storage devices has fueled recent discoveries in novel mechanisms for manipulating magnetic spins on ultrafast timescales, including magnetoacoustics. Direct measurement of ionic motion could allow one to observe the coupling between the magnetic spins and lattice dynamics in a crystal. In this talk, I will discuss recent results on time-resolved acoustics observed by time-resolved diffuse X-ray scattering in a 25 nm thick alpha-iron crystal of high quality. Acoustic pulses are generated using a femtosecond optical laser which provides an impulsive strain in the crystal. The ensuing phonon dynamics are resolved by scattering of femtosecond X-ray pulses provided by the Linac Coherent Light Source. In particular, we observe terahertz oscillations in the Fourier components of the acoustic pulses imaged by the detector.

  14. Silica Nanowire Growth on Photonic Crystal Fiber by Pulsed Femtosecond Laser Deposition

    NASA Astrophysics Data System (ADS)

    Langellier, Nicholas; Li, Chih-Hao; Furesz, Gabor; Glenday, Alex; Phillips, David; Zhang, Huiliang; Noah Chang, Guoqing; Kaertner, Franz; Szentgyorgyi, Andrew; Walsworth, Ronald

    2012-06-01

    We present a new method of nanowire fabrication using pulsed laser deposition. An 800 mW 1 GHz femtosecond Ti:Sapphire laser is guided into a polarization-maintaining photonic crystal fiber (PCF). The PCF, with a core tapered to 1.7 micron diameter, converts femtosecond laser pulses centered at 800 nm into green light with a spectrum down to 500 nm. The PCF is enclosed in a cylindrical tube with glass windows, sealed in a class 100 clean room with silicone-based RTV adhesive. The high power of each laser pulse in a silica-rich environment leads to growth of a silica nanowire at the output end of the PCF. SEM analysis shows that the nanowire is 720 nm in diameter and grows at a rate of about 0.6 um/s. Details of nanowire performance along with potential applications will be presented.

  15. Amplitude autocorrelation of femtosecond laser pulses using linear photogalvanic effect in sillenite crystals

    NASA Astrophysics Data System (ADS)

    Grachev, A. I.; Romashko, R. V.; Kulchin, Yu. N.; Golik, S. S.; Nippolainen, E.; Kamshilin, A. A.

    2012-06-01

    We demonstrate excitation of the linear photogalvanic current in a Bi12TiO20 crystal by two orthogonally polarized femtosecond laser pulses with detecting the electrical current via charge accumulation on the sample electrodes. Such a setup was used to implement an interferometric autocorrelation technique for characterization of ultrashort light pulses. Integration of the detected current in femtosecond time domain leads to vanishing of a bipolar component of the photogalvanic current which arises due to a pulse chirping. The advantage of the proposed technique is that it produces the electric field correlation function directly without the need for data processing using a compact, robust, and non-expensive detector in the form of a photoconductive cell of a non-centrosymmetric crystal.

  16. Auditory detection of paired pulses by a dolphin in the presence of a pulse jam

    NASA Astrophysics Data System (ADS)

    Sukhoruchenko, M. N.

    2004-07-01

    From behavioral studies of a bottlenose dolphin ( Tursiops truncatus), the audibility thresholds were measured for a single pair of equal-amplitude pulses, i.e., clicks, presented to the dolphin in combination with a pulse jam. The pulse jam consisted of pairs of identical pulses with a pulse spacing τj within the pairs and a pair repetition rate f j. Series of pulses were interrupted by a pause R>1/ f j, within which the pulse jam was absent while a pair of test pulses was supplied to one of the two channels at random. Each series had a duration T, and the total stimulation cycle was J= T+ R. The dependence of the test pair detection threshold on the pulse spacing τj was studied at different fixed values of the pulse spacing in the test pair: τt=50, 100, 200, and 500 µs. Preliminary measurements performed with τj=τt=100 µs were used to adjust the parameters of the pulse jam. The threshold shift at τj=τt=100 µs reached 35 dB above the audibility threshold of the test pair in the absence of the pulse jam. On both sides of the point τj=τt=100 µs the thresholds decreased with varying τj to approximately 20 dB above the detection threshold of the test pair in the absence of the jam. However, in the course of training, the threshold curves gradually shifted downwards approaching the detection level of the test pair in the absence of the jam and becoming progressively flatter (the selectivity with respect to the pulse jam vanished). A decrease in the pause duration R restored the dependence of the test pair detection threshold on τj. In this case, a statistically significant maximum was obtained at τj=τt for τj within the critical interval (for τt<500 µs). Beyond the critical interval (for τt>500 µs), even with the smallest pause duration ( R=15 ms), no dependence of the test pair detection thresholds on τj could be observed.

  17. Luminescence of black silicon fabricated by high-repetition rate femtosecond laser pulses

    SciTech Connect

    Chen Tao; Si Jinhai; Hou Xun; Kanehira, Shingo; Miura, Kiyotaka; Hirao, Kazuyuki

    2011-10-01

    We studied the photoluminescence (PL) from black silicon that was fabricated using an 800 nm, 250 kHz femtosecond laser in air. By changing the scan velocity and the fluence of the femtosecond laser, the formation of the PL band between the orange (600 nm) and red bands (near 680 nm) could be controlled. The red band PL from the photoinduced microstructures on the black silicon was observed even without annealing due to the thermal accumulation of high-repetition rate femtosecond laser pulses. The orange band PL was easily quenched under 532 nm cw laser irradiation, whereas the red band PL was more stable; this can be attributed to ''defect luminescence'' and ''quantum confinement'', respectively.

  18. Long distance measurement with femtosecond pulses using a dispersive interferometer.

    PubMed

    Cui, M; Zeitouny, M G; Bhattacharya, N; van den Berg, S A; Urbach, H P

    2011-03-28

    We experimentally demonstrate long distance measurements with a femtosecond frequency comb laser using dispersive interferometry. The distance is derived from the unwrapped spectral phase of the dispersed interferometer output and the repetition frequency of the laser. For an interferometer length of 50 m this approach has been compared to an independent phase counting laser interferometer. The obtained mutual agreement is better than 1.5 μm (3×10(-8)), with a statistical averaging of less than 200 nm. Our experiments demonstrate that dispersive interferometry with a frequency comb laser is a powerful method for accurate and non-incremental measurement of long distances. PMID:21451683

  19. Self-guiding supercontinuum generation and damage in bulk materials induced by femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Sirutkaitis, Valdas; Gaizauskas, Eugenijus; Kudriashov, Viacheslav; Barkauskas, Martynas; Vaicaitis, Virgilijus; Grigonis, Rimantas; Piskarskas, Algis S.

    2003-05-01

    The dynamics of multiple pulse laser-induced damage in the form of cracking or nonlinear coloration in bulk materials (fused silica and borosilicate K8 glass) was studied under the irradiation by femtosecond pulses at 800 nm wavelength. A Ti:sapphire chirped pulse amplification system with ~130-fs pulse duration and ~1-mJ pulse energy at 1-kHz repetition rate was used in the experiment. Self-guided propagation of femtosecond pulses over greater than 1-cm lengths accompanied by intensive supercontinuum generation was observed and studied in an interaction geometry where the laser beam was focused in the middle of the thick (~4 cm) sample. The pulse energy value at which self-guided propagation and supercontinuum generation in fused silica was observed was ~60 times lower than the laser-induced damage threshold. The nonlinear coloration in K8 glass was present at pulse energy values which exceeded the threshold for self-guided propagation. Numerical simulations involving self-focusing, temporal dispersion and multiphoton absorption were found to be in good agreement with the experimental results.

  20. Fifth-order intensity autocorrelations based on six-wave mixing of femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Gaižauskas, Eugenijus; Steponkevičius, KÈ©stutis; Vaičaitis, Virgilijus

    2016-02-01

    It is shown both experimentally and by numerical simulations that fifth-order intensity autocorrelations of femtosecond laser pulses can be obtained from two-beam noncollinear six-wave mixing in air. A numerical analysis of competing direct and six-wave-assisted third-harmonic-generation pathways showed that these measurements are suitable for the background-free temporal characterization of laser pulses. Reshaping of the pulse and 10 fs subpulse formation during the primary stages of light filamentation were observed using the proposed method.

  1. Real-time study of bulk damage formation in glass initiated by intense femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Kudriašov, V.; Gaižauskas, E.; Sirutkaitis, V.

    2005-12-01

    Dynamics of damage formation by focusing intense femtosecond pulses inside the fused silica glass is studied in wide energy range. Damage usually is initiated in the zone near geometrical focus, which is preceded by the zone where beam propagates in the form of multiple filaments. For high repetition rate pulses damage appears as an extended narrow track along the beam path, which forms due to the propagation of the initial damage zone toward the laser source. For low repetition rate pulses extended damage tracks don't form.

  2. Optical waveguide writing in photochromic material: photoinduced optical properties by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Gutiérrez, J. M.; Camacho-López, S.; Cano-Lara, M.; Rodríguez, A.; Balderas-Navarro, R. E.; Elizalde, L. E.; Ledezma, R.

    2011-09-01

    We report on the interaction of high repetition rate (MHz) Ti: sapphire laser pulses with a spiropyran polymer (MIC1). Such a polymer is photochromic, wich has potential applications in integrated optical devices. A thin film of polymer deposited on a glass substrate is irradiated with ultrashort pulses (66 fs) from a Ti: sapphire laser. We demonstrate that it is possible to induce an absorption band in the visible by the use of femtosecond pulses via a two-photon excitation process; this might be useful to accomplish waveguide-like structures formation with photochromic response.

  3. Fine-pitched microgratings encoded by interference of UV femtosecond laser pulses.

    PubMed

    Kamioka, Hayato; Miura, Taisuke; Kawamura, Ken-ichi; Hirano, Masahiro; Hosono, Hideo

    2002-01-01

    Fine-pitched microgratings are encoded on fused silica surfaces by a two-beam laser interference technique employing UV femtosecond pulses from the third harmonics of a Ti:sapphire laser. A pump and prove method utilizing a laser-induced optical Kerr effect or transient optical absorption change has been developed to achieve the time coincidence of the two pulses. Use of the UV pulses makes it possible to narrow the grating pitches to an opening as small as 290 nm, and the groove width of the gratings is of nanoscale size. The present technique provides a novel opportunity for the fabrication of periodic nanoscale structures in various materials. PMID:12908258

  4. ICAN as a new laser paradigm for high energy, high average power femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Brocklesby, W. S.; Nilsson, J.; Schreiber, T.; Limpert, J.; Brignon, A.; Bourderionnet, J.; Lombard, L.; Michau, V.; Hanna, M.; Zaouter, Y.; Tajima, T.; Mourou, Gérard

    2014-05-01

    The application of petawatt lasers to scientific and technological problems is advancing rapidly. The usefulness of these applications will depend on being able to produce petawatt pulses at much higher repetition rates than is presently possible. The International Coherent Amplification Network (ICAN) consortium seeks to design high repetition rate petawatt lasers using large scale coherent beam combination of femtosecond pulse amplifiers built from optical fibres. This combination of technologies has the potential to overcome many of the hurdles to high energy, high average power pulsed lasers, opening up applications and meeting societal challenges.

  5. Optical cell cleaning with NIR femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Uchugonova, Aisada; Breunig, Hans Georg; Batista, Ana; König, Karsten

    2015-03-01

    Femtosecond laser microscopes have been used as both micro and nanosurgery tools. The optical knock-out of undesired cells in multiplex cell clusters shall be further reported on in this study. Femtosecond laser-induced cell death is beneficial due to the reduced collateral side effects and therefore can be used to selectively destroy target cells within monolayers, as well as within 3D tissues, all the while preserving cells of interest. This is an important characteristic for the application in stem cell research and cancer treatment. Non-precise damage compromises the viability of neighboring cells by inducing side effects such as stress to the cells surrounding the target due to the changes in the microenvironment, resulting from both the laser and laser-exposed cells. In this study, optimum laser parameters for optical cleaning by isolating single cells and cell colonies are exploited through the use of automated software control. Physiological equilibrium and cellular responses to the laser induced damages are also investigated. Cell death dependence on laser focus, determination and selectivity of intensity/dosage, controllable damage and cell recovery mechanisms are discussed.

  6. Femtosecond-Laser-Pulse Characterization and Optimization for CARS Microscopy

    PubMed Central

    Piazza, Vincenzo; de Vito, Giuseppe; Farrokhtakin, Elmira; Ciofani, Gianni; Mattoli, Virgilio

    2016-01-01

    We present a simple method and its experimental implementation to determine the pulse durations and linear chirps of the pump-and-probe pulse and the Stokes pulse in a coherent anti-Stokes Raman scattering microscope at sample level without additional autocorrelators. Our approach exploits the delay line, ubiquitous in such microscopes, to perform a convolution of the pump-and-probe and Stokes pulses as a function of their relative delay and it is based on the detection of the photons emitted from an appropriate non-linear sample. The analysis of the non-resonant four-wave-mixing and sum-frequency-generation signals allows for the direct retrieval of the pulse duration on the sample and the linear chirp of each pulse. This knowledge is crucial in maximizing the spectral-resolution and contrast in CARS imaging. PMID:27224203

  7. Femtosecond-Laser-Pulse Characterization and Optimization for CARS Microscopy.

    PubMed

    Piazza, Vincenzo; de Vito, Giuseppe; Farrokhtakin, Elmira; Ciofani, Gianni; Mattoli, Virgilio

    2016-01-01

    We present a simple method and its experimental implementation to determine the pulse durations and linear chirps of the pump-and-probe pulse and the Stokes pulse in a coherent anti-Stokes Raman scattering microscope at sample level without additional autocorrelators. Our approach exploits the delay line, ubiquitous in such microscopes, to perform a convolution of the pump-and-probe and Stokes pulses as a function of their relative delay and it is based on the detection of the photons emitted from an appropriate non-linear sample. The analysis of the non-resonant four-wave-mixing and sum-frequency-generation signals allows for the direct retrieval of the pulse duration on the sample and the linear chirp of each pulse. This knowledge is crucial in maximizing the spectral-resolution and contrast in CARS imaging. PMID:27224203

  8. Fiber delivery of femtosecond pulses from a Ti:sapphire laser.

    PubMed

    Clark, S W; Ilday, F O; Wise, F W

    2001-09-01

    We propose a way to deliver nanojoule-energy, 100-fs pulses at 800 nm through a few meters of standard optical fiber. Pulses from a mode-locked laser are compressed temporally, and then spectrally, to produce the desired pulses at the end of the fiber. Initial experiments agree well with calculations and demonstrate the benefits of this technique: For an energy of ~0.5 nJ , the delivered pulses are ~5 times shorter than those delivered by other techniques. The issues that must be addressed to scale the technique up to delivered pulse energies of 5 nJ are identified, and the apparatus employs only readily available components. Thus we expect it to find use in the many applications that would benefit from fiber delivery of femtosecond pulses. PMID:18049595

  9. Femtosecond pulsed laser ablation to enhance drug delivery across the skin.

    PubMed

    Garvie-Cook, Hazel; Stone, James M; Yu, Fei; Guy, Richard H; Gordeev, Sergey N

    2016-01-01

    Laser poration of the skin locally removes its outermost, barrier layer, and thereby provides a route for the diffusion of topically applied drugs. Ideally, no thermal damage would surround the pores created in the skin, as tissue coagulation would be expected to limit drug diffusion. Here, a femtosecond pulsed fiber laser is used to porate mammalian skin ex vivo. This first application of a hollow core negative curvature fiber (HC-NCF) to convey a femtosecond pulsed, visible laser beam results in reproducible skin poration. The effect of applying ink to the skin surface, prior to ultra-short pulsed ablation, has been examined and Raman spectroscopy reveals that the least, collateral thermal damage occurs in inked skin. Pre-application of ink reduces the laser power threshold for poration, an effect attributed to the initiation of plasma formation by thermionic electron emission from the dye in the ink. Poration under these conditions significantly increases the percutaneous permeation of caffeine in vitro. Dye-enhanced, plasma-mediated ablation of the skin is therefore a potentially advantageous approach to enhance topical/transdermal drug absorption. The combination of a fiber laser and a HC-NCF, capable of emitting and delivering femtosecond pulsed, visible light, may permit a compact poration device to be developed. PMID:26449289

  10. In-vivo laser-induced bubbles in the primate eye with femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Cain, Clarence P.; DiCarlo, Cheryl D.; Noojin, Gary D.; Amnotte, Rodney E.; Rockwell, Benjamin A.; Roach, William P.

    1996-05-01

    Threshold measurements for laser-induced breakdown (LIB) and bubble generation for femtosecond laser pulsewidths have been made in vivo for rhesus monkey eyes. These LIB thresholds are compared with model-predicted thresholds for water and minimum visible lesion thresholds in Dutch Belted rabbit and rhesus monkey eyes. LIB thresholds in biological materials including vitreous, normal saline, tap water, and ultrapure water have been measured and reported using an artificial eye. We have recorded on video the first LIB causing bubble formation in any eye in vivo using albino rabbit eyes, pigmented rabbit eyes, and rhesus monkey eyes. External optics were used to focus the image within the vitreous and the bubbles generated were clearly formed anterior to the retina within the vitreous humor. The length of time that the bubbles are visible depends on the pulse energy delivered and may last for several seconds. However, for pulse energies near thresholds, the bubbles have a very short lifetime and may be seen on the video for only one frame. The plasma formation at the breakdown site acts as a limiting mechanism for energy transmission and may explain why high-energy femtosecond pulses at energies up to 100 microjoules sometimes do not cause severe damage to the retina. This fact may also explain why it is so difficult to product hemmorrhagic lesions in either the rabbit or primate eye with 100-femtosecond laser pulses.

  11. Simulation of the temperature increase in porcine cadaver iris during direct illumination by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Sun, Hui; Kurtz, Ronald M.; Juhasz, Tibor

    2012-03-01

    As a model for laser exposure of the iris during femtosecond corneal surgery, we simulated the temperature rise in porcine cadaver iris during direct illumination by the femtosecond laser. The temperature increase induced by a 60 kHz iFS Advanced Femtosecond Laser (AMO Inc., Santa Ana, CA) in porcine cadaver iris was simulated using COMSOL (Comsol Inc., Burlington, MA) finite element software. Temperature increases up to 2.45 °C (corresponding to 2 μJ laser pulse energy and 24 second illumination) were observed in the porcine cadaver iris from the simulation with little variation in temperature profiles compared with specimens for the same laser energy illumination in experiment. : The commercial iFS Advanced Femtosecond Laser operating with pulse energies at approximately the lower limit of the range evaluated in this study would be expected to result in a 1.23 °C temperature increase and, therefore, does not present a safety hazard to the iris.

  12. Communication: The electronic structure of matter probed with a single femtosecond hard x-ray pulse.

    PubMed

    Szlachetko, J; Milne, C J; Hoszowska, J; Dousse, J-Cl; Błachucki, W; Sà, J; Kayser, Y; Messerschmidt, M; Abela, R; Boutet, S; David, C; Williams, G; Pajek, M; Patterson, B D; Smolentsev, G; van Bokhoven, J A; Nachtegaal, M

    2014-03-01

    Physical, biological, and chemical transformations are initiated by changes in the electronic configuration of the species involved. These electronic changes occur on the timescales of attoseconds (10(-18) s) to femtoseconds (10(-15) s) and drive all subsequent electronic reorganization as the system moves to a new equilibrium or quasi-equilibrium state. The ability to detect the dynamics of these electronic changes is crucial for understanding the potential energy surfaces upon which chemical and biological reactions take place. Here, we report on the determination of the electronic structure of matter using a single self-seeded femtosecond x-ray pulse from the Linac Coherent Light Source hard x-ray free electron laser. By measuring the high energy resolution off-resonant spectrum (HEROS), we were able to obtain information about the electronic density of states with a single femtosecond x-ray pulse. We show that the unoccupied electronic states of the scattering atom may be determined on a shot-to-shot basis and that the measured spectral shape is independent of the large intensity fluctuations of the incoming x-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shot capability and limitations of HEROS, which enables the technique to track the electronic structural dynamics in matter on femtosecond time scales, making it an ideal probe technique for time-resolved X-ray experiments. PMID:26798772

  13. Communication: The electronic structure of matter probed with a single femtosecond hard x-ray pulse

    PubMed Central

    Szlachetko, J.; Milne, C. J.; Hoszowska, J.; Dousse, J.-Cl.; Błachucki, W.; Sà, J.; Kayser, Y.; Messerschmidt, M.; Abela, R.; Boutet, S.; David, C.; Williams, G.; Pajek, M.; Patterson, B. D.; Smolentsev, G.; van Bokhoven, J. A.; Nachtegaal, M.

    2014-01-01

    Physical, biological, and chemical transformations are initiated by changes in the electronic configuration of the species involved. These electronic changes occur on the timescales of attoseconds (10−18 s) to femtoseconds (10−15 s) and drive all subsequent electronic reorganization as the system moves to a new equilibrium or quasi-equilibrium state. The ability to detect the dynamics of these electronic changes is crucial for understanding the potential energy surfaces upon which chemical and biological reactions take place. Here, we report on the determination of the electronic structure of matter using a single self-seeded femtosecond x-ray pulse from the Linac Coherent Light Source hard x-ray free electron laser. By measuring the high energy resolution off-resonant spectrum (HEROS), we were able to obtain information about the electronic density of states with a single femtosecond x-ray pulse. We show that the unoccupied electronic states of the scattering atom may be determined on a shot-to-shot basis and that the measured spectral shape is independent of the large intensity fluctuations of the incoming x-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shot capability and limitations of HEROS, which enables the technique to track the electronic structural dynamics in matter on femtosecond time scales, making it an ideal probe technique for time-resolved X-ray experiments. PMID:26798772

  14. Control and understanding of the formation of micro/nanostructured metal surfaces using femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Zuhlke, Craig A.

    An application of femtosecond lasers that has developed, in recent years, is the functionalization of surfaces. With femtosecond laser ablation micro and nano-scale features can be created in a single step without affecting the bulk material. In this dissertation micro/nanostructuring of metal surfaces, specifically nickel and SS316, was carried out using femtosecond laser pulses. By varying the fluence (between 0.01 and 3.18 J/cm2), and pulse count (between 1 and 20,000 pulses) incident on the metal surface, a number of surface morphologies were produced. It was demonstrated that a number of these morphologies can be separated in regions based on fluence and shot number. The effects of other parameters were studied in less detail, including: polarization, stationary versus rastering pulses, atmosphere during processing (processing in nitrogen and oxygen), and lens aberrations. Two morphologies from femtosecond laser ablation of metals are demonstrated for the first time: spike shaped microstructures that have peaks above the original surface, and pyramid shaped structures (with a much lower aspect ratio than commonly published morphologies) covered in thick layers of nanoparticles. Similarities and differences are shown between the commonly published relief structures, with a blunt, round top (mounds) and the protruding spikes. This work shows that the morphologies are formed through a balance between fluid flow, nanoparticle/material redeposition and preferential etching. It can be observed by watching the development of individual microstructures with increasing pulse count, what role each of these processes plays in their development. Mounds, spikes, and pyramids each have a different balance of these processes, leading to the uniqueness of each morphology. As an application of these processes, studies were completed to utilize the high surface areas of these micro/nanostructures to produce ultracapacitor electrodes. This proved to be challenging, due to the

  15. Measurement of the Optical Coherence of a Femtosecond Pulsed Laser by Shearing Interferometry with a Double-Frequency Grating

    NASA Astrophysics Data System (ADS)

    Ming, Hai; Qian, Jiang-yuan; Xie, Jian-ping; A, B. Fedotov; X, Xiao; M, M. T. Loy

    1998-01-01

    Shearing interferometry of an ion-etched holographic double-frequency grating is used to measure the optical coherence of femtosecond pulsed lasers. The experimental results show that the optical coherence of the femtosecond light beam is not only related to the spectral width and size of the light source but is also related to the pulse duration and mode-locked laser state. The results of theoretical analysis and numerical calculation are also given. Application of this research is also discussed.

  16. Effect of atomic density on propagation and spectral property of femtosecond chirped Gaussian pulses

    NASA Astrophysics Data System (ADS)

    Wang, Zhendong; Gao, Feng

    2015-05-01

    We theoretically investigate the effect of the atomic densities N on propagation and spectral property of femtosecond chirped Gaussian pulse in a three-level Λ-type atomic medium by using the numerical solution of the full Maxwell- Bloch equations. It is shown that, when the positive chirped pulse with area 3π, propagate in the medium with smaller N, pulse splitting doesn't occur and many small oscillations at the trailing edge of the pulse appear, in addition, the level |2< population ρ22 of the pulse exhibits an oscillation feature with time evolution, moreover, the spectral component near the central frequency of the pulse shows an oscillation characteristic too, and the propagation and spectral property of the negative chirped 3π pulse is very similar to that of the positive chirped 3π pulse. For the positive chirped 3π pulse pulses, propagate in the medium with larger N, pulse splitting also doesn't occur but many small oscillations both at leading edge and the trailing edge of the pulse appear, and the population ρ22 of the pulse only exhibits an scarcely oscillation feature with time evolution, at the same time many oscillations both in blue shift and red shift components of the pulse appear but the spectral component near the central frequency of the pulse oscillate more severely, and the propagation and spectral property of the negative chirped 3π pulse is very similar to that of the positive chirped 3π pulse, but comparing with the case of the negative chirped 3π pulse, the propagation of the positive chirped 3π pulse is delayed at the same distance and the delayed time becomes longer with the distance increasing.

  17. Prepulse effect on intense femtosecond laser pulse propagation in gas

    SciTech Connect

    Giulietti, Antonio; Tomassini, Paolo; Galimberti, Marco; Giulietti, Danilo; Gizzi, Leonida A.; Koester, Petra; Labate, Luca; Ceccotti, Tiberio; D'Oliveira, Pascal; Auguste, Thierry; Monot, Pascal; Martin, Philippe

    2006-09-15

    The propagation of an ultrashort laser pulse can be affected by the light reaching the medium before the pulse. This can cause a serious drawback to possible applications. The propagation in He of an intense 60-fs pulse delivered by a Ti:sapphire laser in the chirped pulse amplification (CPA) mode has been investigated in conditions of interest for laser-plasma acceleration of electrons. The effects of both nanosecond amplified spontaneous emission and picosecond pedestals have been clearly identified. There is evidence that such effects are basically of refractive nature and that they are not detrimental for the propagation of a CPA pulse focused to moderately relativistic intensity. The observations are fully consistent with numerical simulations and can contribute to the search of a stable regime for laser acceleration.

  18. Extreme rotational excitation with long sequences of intense femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Bitter, Martin; Milner, Valery

    2015-05-01

    We present an experimental approach to rotational excitation of molecules capable of creating ultra-broad rotational wave packets inaccessible with other methods, including the technique of an optical centrifuge. Our approach is based on an impulsive excitation by a long sequence of more than 20 laser pulses with peak intensities within each pulse exceeding 1013 W/cm2. The method overcomes the three obstacles on the way towards extreme rotational excitation: (i) the strong-field effects associated with a single-pulse scheme, (ii) the centrifugal distortion and Anderson localization in a multi-pulse approach, and (iii) the bandwidth limitation of an optical centrifuge. In oxygen, we demonstrate the ability to populate rotational states with an angular momentum N ~ 250 ℏ , more than twice higher than previously achieved with the centrifuge. Precise timing of the pulses and their spectral broadening due to molecular phase modulation, essential to this technique, are demonstrated and discussed.

  19. Femtosecond spatial pulse shaping at the focal plane.

    PubMed

    Martínez-Matos, Ó; Vaveliuk, P; Izquierdo, J G; Loriot, V

    2013-10-21

    Spatial shaping of ultrashort laser beams at the focal plane is theoretically analyzed. The description of the pulse is performed by its expansion in terms of Laguerre-Gaussian orthonormal modes. This procedure gives both a comprehensive interpretation of the propagation dynamics and the required signal to encode onto a spatial light modulator for spatial shaping, without using iterative algorithms. As an example, pulses with top-hat and annular spatial profiles are designed and their dynamics analyzed. The interference of top-hat pulses is also investigated finding potential applications in high precision pump-probe experiments (without using delay lines) and for the creation of subwavelength ablation patterns. In addition, a novel class of ultrashort pulses possessing non-stationary orbital angular momentum is also proposed. These exotic pulses provide additional degrees of freedom that open up new perspectives in fields such as laser-matter interaction and micro-machining. PMID:24150344

  20. Ablation and nanostructuring of metals by femtosecond laser pulses

    SciTech Connect

    Ashitkov, S I; Komarov, P S; Ovchinnikov, A V; Struleva, E V; Agranat, M B; Zhakhovskii, V V; Inogamov, N A

    2014-06-30

    Using an interferometric continuous monitoring technique, we have investigated the motion of the surface of an aluminium target in the case of femtosecond laser ablation at picosecond time delays relative to the instant of laser exposure. Measurements of the temporal target dispersion dynamics, molecular dynamics simulation results and the morphology of the ablation crater have demonstrated a thermomechanical (spall) nature of the disruption of the condensed phase due to the cavitation-driven formation and growth of vapour phase nuclei upon melt expansion, followed by the formation of surface nanostructures upon melt solidification. The tensile strength of heated aluminium in a condensed state has been determined experimentally at an expansion rate of ∼10{sup 9} s{sup -1}. (extreme light fields and their applications)

  1. Adaptive control of lasers and their interactions with matter using femtosecond pulse shaping

    NASA Astrophysics Data System (ADS)

    Efimov, Anatoly

    Coherent control of chemical reactions, atomic and molecular systems, lattice dynamics, and electronic motion rely on femtosecond laser sources capable of producing programmable arbitrarily shaped waveforms. To enter the time scale of natural dynamic processes in many systems, femtosecond pulse shaping techniques must be extended to the ultrashort pulse domain (<50 fs). Concurrently, reliable high-fidelity amplification of shaped waveforms is required in many applications. We demonstrate ultrabroad bandwidth pulse shaping of 13 fs pulses with Fourier-domain phase-only filtering using a liquid crystal array. We further demonstrate the amplification of shaped pulses in a multipass chirped pulse amplifier (CPA) system to produce millijoule-level optical waveforms with 30 fs resolution. Recently, a new approach to coherent control of physical systems was introduced, which, instead of relying on formidable theoretical calculations of complex system dynamics, makes use of an appropriate experimental feedback from the system itself to control its evolution. We apply this adaptive feedback approach for enhancement of ionization rates in a femtosecond plasma with the goal of minimization of phase distortions in the amplifier system. With the help of a learning algorithm and survival principles of nature, we teach our laser to control its own phase by using spectral blueshifting in a rapidly created plasma as a feedback to the algorithm. Control of lattice vibrations has long been sought as a means of studying phonon-related processes in solids. In addition, generation and control of large-amplitude optical phonon modes may open a path to femtosecond time- resolved studies of structural phase transitions and production of ultrashort shaped X-ray pulses. We perform pump-probe phase-resolved measurements and control of optical A1g mode in sapphire through shaped-pulse impulsive stimulated Raman scattering (ISRS). We chose this material as a candidate for possible nonlinear

  2. Analysis of strained surface layers of ZnO single crystals after irradiation with intense femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Schneider, Andreas; Wolverson, Daniel; Sebald, Kathrin; Hodges, Chris; Kuball, Martin; Voss, Tobias

    2013-05-01

    Structural modifications of ZnO single crystals that were created by the irradiation with femtosecond laser pulses at fluences far above the ablation threshold were investigated with micro-Raman spectroscopy. After light-matter interaction on the femtosecond time scale, rapid cooling and the pronounced thermal expansion anisotropy of ZnO are likely to cause residual strains of up to 1.8% and also result in the formation of surface cracks. This process relaxes the strain only partially and a strained surface layer remains. Our findings demonstrate the significant role of thermoelastic effects for the irradiation of solids with intense femtosecond laser pulses.

  3. Webcam autofocus mechanism used as a delay line for the characterization of femtosecond pulses

    SciTech Connect

    Castro-Marín, Pablo; Kapellmann-Zafra, Gabriel; Garduño-Mejía, Jesús Rosete-Aguilar, Martha; Román-Moreno, Carlos J.

    2015-08-15

    In this work, we present an electromagnetic focusing mechanism (EFM), from a commercial webcam, implemented as a delay line of a femtosecond laser pulse characterization system. The characterization system consists on a second order autocorrelator based on a two-photon-absorption detection. The results presented here were performed for two different home-made femtosecond oscillators: Ti:sapph @ 820 nm and highly chirped pulses generated with an Erbium Doped Fiber @ 1550 nm. The EFM applied as a delay line represents an excellent alternative due its performance in terms of stability, resolution, and long scan range up to 3 ps. Due its low power consumption, the device can be connected through the Universal Serial Bus (USB) port. Details of components, schematics of electronic controls, and detection systems are presented.

  4. Femtosecond X-ray Pulse Temporal Characterization in Free-Electron Lasers Using a Transverse Deflector

    SciTech Connect

    Ding, Y.; Behrens, C.; Emma, P.; Frisch, J.; Huang, Z.; Loos, H.; Krejcik, P.; Wang, M-H.; /SLAC

    2011-12-13

    We propose a novel method to characterize the temporal duration and shape of femtosecond x-ray pulses in a free-electron laser (FEL) by measuring the time-resolved electron-beam energy loss and energy spread induced by the FEL process, with a transverse radio-frequency deflector located after the undulator. Its merits are simplicity, high resolution, wide diagnostic range, and non-invasive to user operation. When the system is applied to the Linac Coherent Light Source, the first hard x-ray free-electron laser in the world, it can provide single-shot measurements on the electron beam and x-ray pulses with a resolution on the order of 1-2 femtoseconds rms.

  5. Webcam autofocus mechanism used as a delay line for the characterization of femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Castro-Marín, Pablo; Kapellmann-Zafra, Gabriel; Garduño-Mejía, Jesús; Rosete-Aguilar, Martha; Román-Moreno, Carlos J.

    2015-08-01

    In this work, we present an electromagnetic focusing mechanism (EFM), from a commercial webcam, implemented as a delay line of a femtosecond laser pulse characterization system. The characterization system consists on a second order autocorrelator based on a two-photon-absorption detection. The results presented here were performed for two different home-made femtosecond oscillators: Ti:sapph @ 820 nm and highly chirped pulses generated with an Erbium Doped Fiber @ 1550 nm. The EFM applied as a delay line represents an excellent alternative due its performance in terms of stability, resolution, and long scan range up to 3 ps. Due its low power consumption, the device can be connected through the Universal Serial Bus (USB) port. Details of components, schematics of electronic controls, and detection systems are presented.

  6. Nanosurgery of cells and chromosomes using near-infrared twelve-femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Uchugonova, Aisada; Lessel, Matthias; Nietzsche, Sander; Zeitz, Christian; Jacobs, Karin; Lemke, Cornelius; König, Karsten

    2012-10-01

    Laser-assisted surgery based on multiphoton absorption of near-infrared laser light has great potential for high precision surgery at various depths within the cells and tissues. Clinical applications include refractive surgery (fs-LASIK). The non-contact laser method also supports contamination-free cell nanosurgery. In this paper we describe usage of an ultrashort femtosecond laser scanning microscope for sub-100 nm surgery of human cells and metaphase chromosomes. A mode-locked 85 MHz Ti:Sapphire laser with an M-shaped ultrabroad band spectrum (maxima: 770 nm/830 nm) and an in situ pulse duration at the target ranging from 12 fs up to 3 ps was employed. The effects of laser nanoprocessing in cells and chromosomes have been quantified by atomic force microscopy. These studies demonstrate the potential of extreme ultrashort femtosecond laser pulses at low mean milliwatt powers for sub-100 nm surgery of cells and cellular organelles.

  7. Webcam autofocus mechanism used as a delay line for the characterization of femtosecond pulses.

    PubMed

    Castro-Marín, Pablo; Kapellmann-Zafra, Gabriel; Garduño-Mejía, Jesús; Rosete-Aguilar, Martha; Román-Moreno, Carlos J

    2015-08-01

    In this work, we present an electromagnetic focusing mechanism (EFM), from a commercial webcam, implemented as a delay line of a femtosecond laser pulse characterization system. The characterization system consists on a second order autocorrelator based on a two-photon-absorption detection. The results presented here were performed for two different home-made femtosecond oscillators: Ti:sapph @ 820 nm and highly chirped pulses generated with an Erbium Doped Fiber @ 1550 nm. The EFM applied as a delay line represents an excellent alternative due its performance in terms of stability, resolution, and long scan range up to 3 ps. Due its low power consumption, the device can be connected through the Universal Serial Bus (USB) port. Details of components, schematics of electronic controls, and detection systems are presented. PMID:26329240

  8. Femtosecond Pulse Characterization as Applied to One-Dimensional Photonic Band Edge Structures

    NASA Technical Reports Server (NTRS)

    Fork, Richard L.; Gamble, Lisa J.; Diffey, William M.

    1999-01-01

    The ability to control the group velocity and phase of an optical pulse is important to many current active areas of research. Electronically addressable one-dimensional photonic crystals are an attractive candidate to achieve this control. This report details work done toward the characterization of photonic crystals and improvement of the characterization technique. As part of the work, the spectral dependence of the group delay imparted by a GaAs/AlAs photonic crystal was characterized. Also, a first generation an electrically addressable photonic crystal was tested for the ability to electronically control the group delay. The measurement technique, using 100 femtosecond continuum pulses was improved to yield high spectral resolution (1.7 nanometers) and concurrently with high temporal resolution (tens of femtoseconds). Conclusions and recommendations based upon the work done are also presented.

  9. Plasma channels during filamentation of a femtosecond laser pulse with wavefront astigmatism in air

    NASA Astrophysics Data System (ADS)

    Dergachev, A. A.; Ionin, A. A.; Kandidov, V. P.; Mokrousova, D. V.; Seleznev, L. V.; Sinitsyn, D. V.; Sunchugasheva, E. S.; Shlenov, S. A.; Shustikova, A. P.

    2014-12-01

    We have demonstrated experimentally and numerically the possibility of controlling parameters of plasma channels formed during filamentation of a femtosecond laser pulse by introducing astigmatism in the laser beam wavefront. It is found that weak astigmatism increases the length of the plasma channel in comparison with the case of aberration-free focusing and that strong astigmatism can cause splitting of the plasma channel into two channels located one after another on the filament axis.

  10. Optical field emission from resonant gold nanorods driven by femtosecond mid-infrared pulses

    SciTech Connect

    Kusa, F.; Echternkamp, K. E.; Herink, G.; Ropers, C.; Ashihara, S.

    2015-07-15

    We demonstrate strong-field photoelectron emission from gold nanorods driven by femtosecond mid-infrared optical pulses. The maximum photoelectron yield is reached at the localized surface plasmon resonance, indicating that the photoemission is governed by the resonantly-enhanced optical near-field. The wavelength- and field-dependent photoemission yield allows for a noninvasive determination of local field enhancements, and we obtain intensity enhancement factors close to 1300, in good agreement with finite-difference time domain computations.

  11. Plasma channels during filamentation of a femtosecond laser pulse with wavefront astigmatism in air

    SciTech Connect

    Dergachev, A A; Kandidov, V P; Shlenov, S A; Ionin, A A; Mokrousova, D V; Seleznev, L V; Sinitsyn, D V; Sunchugasheva, E S; Shustikova, A P

    2014-12-31

    We have demonstrated experimentally and numerically the possibility of controlling parameters of plasma channels formed during filamentation of a femtosecond laser pulse by introducing astigmatism in the laser beam wavefront. It is found that weak astigmatism increases the length of the plasma channel in comparison with the case of aberration-free focusing and that strong astigmatism can cause splitting of the plasma channel into two channels located one after another on the filament axis. (interaction of laser radiation with matter. laser plasma)

  12. Role of multiple shots of femtosecond laser pulses in periodic surface nanoablation

    SciTech Connect

    Miyaji, Godai; Miyazaki, Kenzo

    2013-08-12

    Using a pump and probe technique, we observed time-dependent change in reflectivity of crystalline silicon surface to study the dynamic process of periodic surface nanostructure formation in femtosecond (fs) laser ablation. The results have shown that multiple shots of low-fluence fs laser pulses play the crucial role in the non-thermal process for nanostructuring through the increasing bonding structure change to amorphous silicon and resulting decrease in the ablation threshold.

  13. Simulation of photon acceleration upon irradiation of a mylar target by femtosecond laser pulses

    SciTech Connect

    Andreev, Stepan N; Rukhadze, Anri A; Tarakanov, V P; Yakutov, B P

    2010-01-31

    Acceleration of protons is simulated by the particle-in-cell (PIC) method upon irradiation of mylar targets of different thicknesses by femtosecond plane-polarised pulsed laser radiation and at different angles of radiation incidence on the target. The comparison of the results of calculations with the experimental data obtained in recent experiments shows their good agreement. The optimal angle of incidence (458) at which the proton energy achieves its absolute maximum is obtained. (effects of laser radiation on matter)

  14. Noncontact microsurgery of cell membranes using femtosecond laser pulses for optoinjection of specified substances into cells

    SciTech Connect

    Il'ina, I V; Ovchinnikov, A V; Chefonov, O V; Sitnikov, D S; Agranat, Mikhail B; Mikaelyan, A S

    2013-04-30

    IR femtosecond laser pulses were used for microsurgery of a cell membrane aimed at local and short-duration change in its permeability and injection of specified extracellular substances into the cells. The possibility of noncontact laser delivery of the propidium iodide fluorescent dye and the pEGFP plasmid, encoding the green fluorescent protein, into the cells with preservation of the cell viability was demonstrated. (extreme light fields and their applications)

  15. The interaction of intense femtosecond laser pulses with solid targets

    SciTech Connect

    Klem, D.E.; Darrow, C.; Lane, S.; Perry, M.D.

    1992-12-30

    The absorption of 800 fsec Nd-glass laser pulses obliquely incident on solid targets is measured at intensities up to 10[sup 18] W/cm[sup 2]. The associated production of hard x-rays is also measured.

  16. The interaction of intense femtosecond laser pulses with solid targets

    SciTech Connect

    Klem, D.E.; Darrow, C.; Lane, S.; Perry, M.D.

    1992-12-30

    The absorption of 800 fsec Nd-glass laser pulses obliquely incident on solid targets is measured at intensities up to 10{sup 18} W/cm{sup 2}. The associated production of hard x-rays is also measured.

  17. Microstructuring of fused silica using femtosecond laser pulses of various wavelengths

    NASA Astrophysics Data System (ADS)

    Pfeiffer, Manuel; Engel, Andy; Reisse, Guenter; Weissmantel, Steffen

    2015-11-01

    Experimental results on ablation and microstructuring of fused silica (Corning 7980 HPFS Standard Grade) using femtosecond laser pulses will be presented. In particular, the ablation behavior of the material at the laser wavelengths of 775, 387 and 258 nm was investigated. The qualities of selected microstructures produced at the different wavelengths are compared with respect to roughness, crack formation and exactness. The investigations were carried out using an automated microstructuring system equipped with a femtosecond laser Clark-MXR CPA 2010 (1 mJ maximum pulse energy, 1 kHz repetition rate and 150 fs pulse duration). Layer-by-layer ablation is realized for producing 3D microstructures, where the layer thickness depends on the ablated depth per laser pulse. Those ablation depths depend on the material and the laser parameters and were determined for the three wavelengths in preparatory investigations. Therefore, the laser fluence and the pulse-to-pulse distance were varied independently. We will present the results of our fundamental studies on fs-laser ablation at the three wavelengths and show several structures, such as pyramids, half spheres and cones. Best results were obtained at 258 nm wavelength. There, the exactness was highest and the roughness of the surfaces of the structures was lowest. In addition, absolutely no crack formation occurred.

  18. Rotational excitation of molecules with long sequences of intense femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Bitter, M.; Milner, V.

    2016-01-01

    We investigate the prospects of creating broad rotational wave packets by means of molecular interaction with long sequences of intense femtosecond pulses. Using state-resolved rotational Raman spectroscopy of oxygen, subject to a sequence of more than 20 laser pulses with peak intensities exceeding 1013W /cm2 per pulse, we show that the centrifugal distortion is the main obstacle on the way to reaching high rotational states. We demonstrate that the timing of the pulses can be optimized to partially mitigate the centrifugal limit. The cumulative effect of a long pulse sequence results in a high degree of rotational coherence, which is shown to cause an efficient spectral broadening of probe light via cascaded Raman transitions.

  19. Magnetic phases in Pt/Co/Pt films induced by single and multiple femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Kisielewski, J.; Kurant, Z.; Sveklo, I.; Tekielak, M.; Wawro, A.; Maziewski, A.

    2016-05-01

    Ultrathin Pt/Co/Pt trilayers with initial in-plane magnetization were irradiated with femtosecond laser pulses. In this way, an irreversible structural modification was introduced, which resulted in the creation of numerous pulse fluence-dependent magnetic phases. This was particularly true with the out-of-plane magnetization state, which exhibited a submicrometer domain structure. This effect was studied in a broad range of pulse fluences up to the point of ablation of the metallic films. In addition to this single-pulse experiment, multiple exposure spots were also investigated, which exhibited an extended area of out-of-plane magnetization phases and a decreased damage threshold. Using a double exposure with partially overlapped spots, a two-dimensional diagram of the magnetic phases as a function of the two energy densities was built, which showed a strong inequality between the first and second incoming pulses.

  20. The role of light-induced nanostructures in femtosecond laser micromachining with vector and scalar pulses.

    PubMed

    Hnatovsky, Cyril; Shvedov, Vladlen G; Krolikowski, Wieslaw

    2013-05-20

    In this article we compare the results of micromachining of fused silica and silicon with tightly focused scalar (viz., circularly and linearly polarized) and vector (viz., azimuthally and radially polarized) femtosecond laser pulses. We show that drilling with radially polarized pulses produces holes with smoother and better-delineated walls compared with the other polarizations used, whereas linearly polarized pulses can machine 20-nm wide single grooves in fused silica when the electric field of the pulse is aligned perpendicular to the cutting direction. The observed polarization-controlled micromachining is due to the formation of sub-diffraction-limited nanostructures that are optically produced in the multi-pulse irradiation regime. PMID:23736485

  1. UV laser removal of varnish on tempera paints with nanosecond and femtosecond pulses.

    PubMed

    Oujja, Mohamed; García, Ana; Romero, Carolina; Vázquez de Aldana, Javier R; Moreno, Pablo; Castillejo, Marta

    2011-03-14

    Two laser cleaning approaches based on ablation by ultraviolet laser pulses of femtosecond (fs) and nanosecond (ns) durations for the removal of shellac varnish from egg-yolk based tempera paints are investigated. Laser irradiation effects, induced on the varnish layer and on the underlying temperas by multiple pulses in the fs domain at 398 and 265 nm and single pulses in the ns domain at 213 nm, were examined following a spectroanalytical approach. By using optical microscopy, colorimetry and laser induced fluorescence it was found that irradiation of the varnished temperas with fs pulses changes the texture of the varnish surface and results in degradation of the underlying coloured paint. In contrast, operating with pulses of 15 ns at the highly absorbed wavelength of 213 nm, controlled micrometric layer removal of the varnish is possible without noticeable modification of the coloured temperas. These results widen the choice of laser conditions for painting restoration. PMID:21264373

  2. Retinal hemorrhagic lesions from femtosecond visible laser pulses

    NASA Astrophysics Data System (ADS)

    Stein, Cindy D.; Toth, Cynthia A.; Cain, Clarence P.; Noojin, Gary D.; Stolarski, David J.; Rockwell, Benjamin A.; Roach, William P.

    1994-08-01

    We present our clinical evaluation of hemorrhagic and non-hemorrhagic 90 fs single pulses in rabbits and primates. The rabbit and primate eye present unique in vivo models for evaluation of retinal and choroidal laser induced hemorrhages with distinct differences in their retinal anatomy. We found two different hemorrhagic events to occur in the posterior pole with delivery of 90 fs pulses. First, in the Dutch Belted rabbit, we found large amounts of energy per pulse (from 20 to 60 times ED50) were required for formation of subretinal hemorrhages. Second, in the Rhesus monkey, we found significant numbers of small intraretinal hemorrhages from relatively low energy 90 fs pulses. Both the Dutch Belted rabbit and the Rhesus monkey failed to consistently show subretinal hemorrhagic lesions form very high pulse energies. Our findings suggest more energy absorption at the level of the retinal circulation than the choroidal circulation with our pulse parameters. The effects of the laser on the retinal circulation may be due to the use of a wavelength of 580 nm. At this wavelength the oxyhemoglobin to melanin absorption ratio is nearly at its peak (approximately 0.40), perhaps allowing improved absorption in the retinal vasculature. One precaution with this finding, however, are the distinct differences between primate and non-primate ocular systems. Further studies are required to resolve the differences in damage at the level of the RPE and choroid between rabbits and primates.

  3. Reversible permeabilization using high-intensity femtosecond laser pulses: applications to biopreservation.

    PubMed

    Kohli, Vikram; Acker, Jason P; Elezzabi, Abdulhakem Y

    2005-12-30

    Non-invasive manipulation of live cells is important for cell-based therapeutics. Herein we report on the uniqueness of using high-intensity femtosecond laser pulses for reversibly permeabilizing mammalian cells for biopreservation applications. When mammalian cells were suspended in a impermeable hyperosmotic cryoprotectant sucrose solution, femtosecond laser pulses were used to transiently permeabilize cells for cytoplasmic solute uptake. The kinetics of cells exposed to 0.2, 0.3, 0.4, and 0.5 M sucrose, following permeabilization, were measured using video microscopy, and post-permeabilization survival was determined by a dual fluorescence membrane integrity assay. Using appropriate laser parameters, we observed the highest cell survival for 0.2 M sucrose solution (>90%), with a progressive decline in cell survival towards higher concentrations. Using diffusion equations describing the transport of solutes, the intracellular osmolarity at the inner surface of the membrane (x = 10 nm) and to a diffusive length of x = 10 microm was estimated, and a high loading efficiency (>98% for x = 10 nm and >70% for x = 10 microm) was calculated for cells suspended in 0.2 M sucrose. This is the first report of using femtosecond laser pulses for permeabilizing cells in the presence of cryoprotectants for biopreservation applications. PMID:16189821

  4. Two-photon lithography and nanoprocessing with picojoule extreme ultrashort 12 femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    König, Karsten; Uchugonova, Aisada; Schug, Michael; Zhang, Huijing; Saremi, Sumarie; Feili, Dara; Seidel, Helmut

    2010-02-01

    A compact ultra-broadband femtosecond laser scanning microscope with 12 femtoseconds pulse width at the focal plane of a high NA objective has been employed in material nanoprocessing. The laser works at 85 MHz with an M-shaped emission spectrum with maxima at 770 nm and 827 nm. Different motorized setups based on the introduction of chirped mirrors, flint glass wedges, and glass blocks have been realized to vary the in situ pulse length from 12 femtoseconds up to 3 picoseconds. Nanoprocessing was performed in silica, photoresists, glass, polymers, and biological structures. Mean powers as low as 2 mW were sufficient to realize plasma-mediated cutting effects in human chromosomes with sub-80 nm cut width. Using a mean power of 7-9 mW, transient nanoholes were "drilled" in the cellular membrane for targeted transfection of stem cells and the introduction of μRNA probes. Region of interest (ROI) scanning have been used for optical cleaning of human adult stem cell populations and blood cell suspensions. 3D two-photon nanolithography based on the ultrabroad band laser pulses was realized with the photoresist SU-8. Multiphoton sub-20fs microscopes may become novel non-invasive 3D tools for highly precise nanoprocessing of inorganic and organic targets.

  5. Ultra-broadband Superradiant Pulses from Femtosecond Laser Pumped InP based Quantum Well Laser Diode

    NASA Astrophysics Data System (ADS)

    Liu, Jingjing

    Laser techniques, such as gain / Q switching, mode-locking, have successfully overcome the energy restriction of gain clamping in the stead-state operated lasers, and allowed the generation of giant pulses with short pulse durations. However, gain saturation further limits the amount of stored energy in a gain medium, and therefore limits the possible maximum pulse energy obtained by laser techniques. Here we circumvent both gain clamping and the capacity limitation of energy storage by operating the double-quantum-well laser diode chips on ultrafast gain-switching model using femtosecond (fs) laser pulses as the optical pump. The advantage of our pumping approach is that the fs pulse can instantly produce a very large number of carriers, and therefore enable the formation of non-equilibrium coherent e-h BCS-like condensate state in a large energy region from the lowest QW subband edges to the highest subband and then obtain the ultra-broadband superradiant pulses. Superradiance (SR) or the coherent spontaneous emission is not a new quantum optics phenomenon, which has been proposed in 1954 by R. Dicke, even earlier than the invention of laser. It is famous as by its ultrashort duration, high peak power, high coherence and high timing jitter. Recently, femtosecond SR pulses have been generated from semiconductors. This investigation has revived both theoretical and experimental studies of SR emission. In this thesis, we have demonstrated the generation of intense, delayed SR pulses from the InP based double quantum well laser diode at room temperature. The 1040 nm femtosecond laser was applied as the optical pumping source, and when the pump power is high enough, the cooperative recombination of e-h pairs from higher order quantum energy levels can occur to generate SR bursts earlier than the cooperative emission from the lower quantum energy levels. Then, ultra-broadband TM polarized SR pulses have been firstly generated at room temperature. Our experiments also

  6. Femtosecond laser ablation of sapphire on different crystallographic facet planes by single and multiple laser pulses irradiation

    NASA Astrophysics Data System (ADS)

    Qi, Litao; Nishii, Kazuhiro; Yasui, Motohiro; Aoki, Hikoharu; Namba, Yoshiharu

    2010-10-01

    Ablation of sapphire on different crystallographic facet planes by single and multiple laser pulses irradiation was carried out with a femtosecond pulsed laser operating at a wavelength of 780 nm and a pulse width of 164 fs. The quality and morphology of the laser ablated sapphire surface were evaluated by scanning electron microscopy and atomic force microscopy. For single laser pulse irradiation, two ablation phases were observed, which have a strong dependency on the pulse energy. The volume of the ablated craters kept an approximately linear relationship with the pulse energy. The threshold fluences of the two ablation phases on different crystallographic facet planes were calculated from the relationship between the squared diameter of the craters and pulse energy. With multiple laser pulses irradiation, craters free of cracks were obtained in the 'gentle' ablation phase. The threshold fluence for N laser pulses was calculated and found to decrease inversely to the number of laser pulses irradiating on the substrate surface due to incubation effect. The depth of the craters increased with the number of laser pulses until reaching a saturation value. The mechanism of femtosecond laser ablation of sapphire in two ablation phases was discussed and identified as either phase explosion, Coulomb explosion or particle vaporization. The choice of crystallographic facet plane has little effect on the process of femtosecond laser ablation of sapphire when compared with the parameters of the femtosecond laser pulses, such as pulse energy and number of laser pulses. In the 'gentle' ablation phase, laser-induced periodic surface structures (LIPSS) with a spatial period of 340 nm were obtained and the mechanism of the LIPSS formation is discussed. There is a potential application of the femtosecond laser ablation to the fabrication of sapphire-based devices.

  7. Full characterization of RF compressed femtosecond electron pulses using ponderomotive scattering.

    PubMed

    Gao, Meng; Jean-Ruel, Hubert; Cooney, Ryan R; Stampe, Jonathan; de Jong, Mark; Harb, Maher; Sciaini, German; Moriena, Gustavo; Dwayne Miller, R J

    2012-05-21

    High bunch charge, femtosecond, electron pulses were generated using a 95 kV electron gun with an S-band RF rebunching cavity. Laser ponderomotive scattering in a counter-propagating beam geometry is shown to provide high sensitivity with the prerequisite spatial and temporal resolution to fully characterize, in situ, both the temporal profile of the electron pulses and RF time timing jitter. With the current beam parameters, we determined a temporal Instrument Response Function (IRF) of 430 fs FWHM. The overall performance of our system is illustrated through the high-quality diffraction data obtained for the measurement of the electron-phonon relaxation dynamics for Si (001). PMID:22714191

  8. Demonstration of acceleration of relativistic electrons at a dielectric microstructure using femtosecond laser pulses.

    PubMed

    Wootton, Kent P; Wu, Ziran; Cowan, Benjamin M; Hanuka, Adi; Makasyuk, Igor V; Peralta, Edgar A; Soong, Ken; Byer, Robert L; Joel England, R

    2016-06-15

    Acceleration of electrons using laser-driven dielectric microstructures is a promising technology for the miniaturization of particle accelerators. Achieving the desired GV m-1 accelerating gradients is possible only with laser pulse durations shorter than ∼1  ps. In this Letter, we present, to the best of our knowledge, the first demonstration of acceleration of relativistic electrons at a dielectric microstructure driven by femtosecond duration laser pulses. Using this technique, an electron accelerating gradient of 690±100  MV m-1 was measured-a record for dielectric laser accelerators. PMID:27304266

  9. Demonstration of acceleration of relativistic electrons at a dielectric microstructure using femtosecond laser pulses

    DOE PAGESBeta

    Wootton, Kent P.; Wu, Ziran; Cowan, Benjamin M.; Hanuka, Adi; Makasyuk, Igor V.; Peralta, Edgar A.; Soong, Ken; Byer, Robert L.; England, R. Joel

    2016-06-02

    Acceleration of electrons using laser-driven dielectric microstructures is a promising technology for the miniaturization of particle accelerators. Achieving the desired GV m–1 accelerating gradients is possible only with laser pulse durations shorter than ~1 ps. In this Letter, we present, to the best of our knowledge, the first demonstration of acceleration of relativistic electrons at a dielectric microstructure driven by femtosecond duration laser pulses. Furthermore, using this technique, an electron accelerating gradient of 690±100 MV m–1 was measured—a record for dielectric laser accelerators.

  10. Temporally focused femtosecond laser pulses for low numerical aperture micromachining through optically transparent materials

    PubMed Central

    Vitek, Dawn N.; Adams, Daniel E.; Johnson, Adrea; Tsai, Philbert S.; Backus, Sterling; Durfee, Charles G.; Kleinfeld, David; Squier, Jeffrey A.

    2010-01-01

    Temporal focusing of spatially chirped femtosecond laser pulses overcomes previous limitations for ablating high aspect ratio features with low numerical aperture (NA) beams. Simultaneous spatial and temporal focusing reduces nonlinear interactions, such as self-focusing, prior to the focal plane so that deep (~1 mm) features with parallel sidewalls are ablated at high material removal rates (25 µm3 per 80 µJ pulse) at 0.04-0.05 NA. This technique is applied to the fabrication of microfluidic devices by ablation through the back surface of thick (6 mm) fused silica substrates. It is also used to ablate bone under aqueous immersion to produce craniotomies. PMID:20721196

  11. Protons acceleration in thin CH foils by ultra-intense femtosecond laser pulses

    SciTech Connect

    Kosarev, I. N.

    2015-03-15

    Interaction of femtosecond laser pulses with the intensities 10{sup 21}, 10{sup 22 }W/cm{sup 2} with CH plastic foils is studied in the framework of kinetic theory of laser plasma based on the construction of propagators (in classical limit) for electron and ion distribution functions in plasmas. The calculations have been performed for real densities and charges of plasma ions. Protons are accelerated both in the direction of laser pulse (up to 1 GeV) and in the opposite direction (more than 5 GeV). The mechanisms of forward acceleration are different for various intensities.

  12. Theoretical analysis of fluorescence signals in filamentation of femtosecond laser pulses in nitrogen molecular gas

    SciTech Connect

    Arevalo, E.; Becker, A.

    2005-10-15

    We study numerically and analytically the role of the combined effect of self-focusing, geometrical focusing, and the plasma defocusing in the formation of the fluorescence signal during the filamentation of a Ti:sapphire laser pulse in nitrogen molecular gas. Results of numerical simulations are used to estimate the number of excited ions in the focal volume, which is proportional to the fluorescence signal. We find good agreement between the theoretical results and the experimental data, showing that such data can be used to get further insight into the effective focal volume during filamentation of femtosecond laser pulses in transparent media.

  13. Temperature distribution in dental tissue after interaction with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Pike, Pavlina; Parigger, Christian; Splinter, Robert; Lockhart, Peter

    2007-12-01

    Algebraic and numerical solutions are presented of the temperature rise in dental tissue due to interaction with ultrashort optical radiation. Results of the studies with femtosecond laser pulses show agreement between theory and experiment. A temperature rise of typically 5 K is found for a 40 millisecond train of 7 nJ, 70 fs laser pulses at a repetition rate of 80 MHz. The peak irradiance in our experimental studies was limited to 3×106 W/cm2. Applications include photoacoustic imaging and tomography of dental tissue.

  14. Cell perforation mediated by plasmonic bubbles generated by a single near infrared femtosecond laser pulse.

    PubMed

    Boutopoulos, Christos; Bergeron, Eric; Meunier, Michel

    2016-01-01

    We report on transient membrane perforation of living cancer cells using plasmonic gold nanoparticles (AuNPs) enhanced single near infrared (NIR) femtosecond (fs) laser pulse. Under optimized laser energy fluence, single pulse treatment (τ = 45 fs, λ = 800 nm) resulted in 77% cell perforation efficiency and 90% cell viability. Using dark field and ultrafast imaging, we demonstrated that the generation of submicron bubbles around the AuNPs is the necessary condition for the cell membrane perforation. AuNP clustering increased drastically the bubble generation efficiency, thus enabling an effective laser treatment using low energy dose in the NIR optical therapeutical window. PMID:26199220

  15. Nonadiabatic alignment of van der Waals--force-bound argon dimers by femtosecond laser pulses

    SciTech Connect

    Wu, J.; Vredenborg, A.; Ulrich, B.; Schmidt, L. Ph. H.; Meckel, M.; Voss, S.; Sann, H.; Kim, H.; Jahnke, T.; Doerner, R.

    2011-06-15

    We demonstrated that the weak van der Waals-force-bound argon dimer can be nonadiabatically aligned by nonresonant femtosecond laser pulses, showing periodic alignment and anti-alignment revivals after the extinction of the laser pulse. Based on the measured nonadiabatic alignment trace, the rotational constant of the argon dimer ground state is determined to be B{sub 0}= 0.05756 {+-} 0.00004 cm{sup -1}. Noticeable alignment dependence of frustrated tunneling ionization and bond-softening induced dissociation of the argon dimer are observed.

  16. Temporal lenses for attosecond and femtosecond electron pulses

    PubMed Central

    Hilbert, Shawn A.; Uiterwaal, Cornelis; Barwick, Brett; Batelaan, Herman; Zewail, Ahmed H.

    2009-01-01

    Here, we describe the “temporal lens” concept that can be used for the focus and magnification of ultrashort electron packets in the time domain. The temporal lenses are created by appropriately synthesizing optical pulses that interact with electrons through the ponderomotive force. With such an arrangement, a temporal lens equation with a form identical to that of conventional light optics is derived. The analog of ray diagrams, but for electrons, are constructed to help the visualization of the process of compressing electron packets. It is shown that such temporal lenses not only compensate for electron pulse broadening due to velocity dispersion but also allow compression of the packets to durations much shorter than their initial widths. With these capabilities, ultrafast electron diffraction and microscopy can be extended to new domains,and, just as importantly, electron pulses can be delivered directly on an ultrafast techniques target specimen. PMID:19541639

  17. Generating femtosecond X-ray pulses using an emittance-spoiling foil in free-electron lasers

    NASA Astrophysics Data System (ADS)

    Ding, Y.; Behrens, C.; Coffee, R.; Decker, F.-J.; Emma, P.; Field, C.; Helml, W.; Huang, Z.; Krejcik, P.; Krzywinski, J.; Loos, H.; Lutman, A.; Marinelli, A.; Maxwell, T. J.; Turner, J.

    2015-11-01

    Generation of femtosecond to sub-femtosecond pulses is attracting much attention in X-ray free-electron laser user community. One method is to use a slotted, emittance-spoiling foil which was proposed before (P. Emma et al., Phys. Rev. Lett. 92, 074801 (2004)) and has been widely used at the Linac Coherent Light Source. Direct experimental characterization of the slotted-foil performance was previously unfeasible due to a lack of appropriate diagnostics. With a recently installed X-band radio-frequency transverse deflector, we are able to characterize the electron bunch spoiling effect and X-ray pulse when using the slotted foil. We show that few-femtosecond X-ray pulses are generated with flexible control of the single-pulse duration or double-pulse separation with comparison to the theoretical model.

  18. Generating femtosecond X-ray pulses using an emittance-spoiling foil in free-electron lasers

    SciTech Connect

    Ding, Y. Coffee, R.; Decker, F.-J.; Emma, P.; Field, C.; Huang, Z.; Krejcik, P.; Krzywinski, J.; Loos, H.; Lutman, A.; Marinelli, A.; Maxwell, T. J.; Turner, J.; Behrens, C.; Helml, W.

    2015-11-09

    Generation of femtosecond to sub-femtosecond pulses is attracting much attention in X-ray free-electron laser user community. One method is to use a slotted, emittance-spoiling foil which was proposed before (P. Emma et al., Phys. Rev. Lett. 92, 074801 (2004)) and has been widely used at the Linac Coherent Light Source. Direct experimental characterization of the slotted-foil performance was previously unfeasible due to a lack of appropriate diagnostics. With a recently installed X-band radio-frequency transverse deflector, we are able to characterize the electron bunch spoiling effect and X-ray pulse when using the slotted foil. We show that few-femtosecond X-ray pulses are generated with flexible control of the single-pulse duration or double-pulse separation with comparison to the theoretical model.

  19. Frequency conversion of high-intensity, femtosecond laser pulses

    SciTech Connect

    Banks, P S

    1997-06-01

    Almost since the invention of the laser, frequency conversion of optical pulses via non- linear processes has been an area of active interest. However, third harmonic generation using ~(~1 (THG) in solids is an area that has not received much attention because of ma- terial damage limits. Recently, the short, high-intensity pulses possible with chirped-pulse amplification (CPA) laser systems allow the use of intensities on the order of 1 TW/cm2 in thin solids without damage. As a light source to examine single-crystal THG in solids and other high field inter- actions, the design and construction of a Ti:sapphire-based CPA laser system capable of ultimately producing peak powers of 100 TW is presented. Of special interest is a novel, all-reflective pulse stretcher design which can stretch a pulse temporally by a factor of 20,000. The stretcher design can also compensate for the added material dispersion due to propagation through the amplifier chain and produce transform-limited 45 fs pulses upon compression. A series of laser-pumped amplifiers brings the peak power up to the terawatt level at 10 Hz, and the design calls for additional amplifiers to bring the power level to the 100 TW level for single shot operation. The theory for frequency conversion of these short pulses is presented, focusing on conversion to the third harmonic in single crystals of BBO, KD*P, and d-LAP (deuterated I-arginine phosphate). Conversion efficiencies of up to 6% are obtained with 500 fs pulses at 1053 nm in a 3 mm thick BBO crystal at 200 GW/cm 2. Contributions to this process by unphasematched, cascaded second harmonic generation and sum frequency generation are shown to be very significant. The angular relationship between the two orders is used to measure the tensor elements of C = xt3)/4 with Crs = -1.8 x 1O-23 m2/V2 and .15Cri + .54Crs = 4.0 x 1O-23 m2/V2. Conversion efficiency in d-LAP is about 20% that in BBO and conversion efficiency in KD*P is 1% that of BBO. It is calculated

  20. Dynamics of water trimer in femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Wang, Zhiping; Zhang, Fengshou; Xu, Xuefeng; Wang, Yanbiao; Qian, Chaoyi

    2016-07-01

    With the help of the time-dependent local-density approximation (TDLDA) coupled non-adiabatically to molecular dynamics (MD), we studied both the static properties and irradiation dynamics of water trimer subject to the short and intense femtosecond laser field. It is shown that the optimized geometry and the optical absorption strength of the water trimer accord well with results in literature. Three typical possible irradiated scenarios of water trimer which are “normal oscillation”, “dissociation and formation” and “pure OH dissociation” are exhibited by investigating the ionization and the level depletion related to electrons as well as the OH bonds, proton-transfer, the intermolecular distance and the kinetic energy connected with ions. In three scenarios, the behaviors of water trimer can be attributed to the sequential combination of responses of the electrons emission, the proton-transfer, OH vibration and rotation, OH dissociation and hydroxyl formation, respectively. The relevant time scales of the first proton-transfer and OH dissociation are identified as 13 fs and 10-20 fs, respectively. The study of kinetic energies of ions show that the kinetic energies of the remaining ions are all below 4.5 eV and outgoing hydrogen ions carry a kinetic energy about 5-12 eV. Furthermore, it is found that in the tunneling ionization situations the depletion is fairly shared between the various levels except the most deep occupied electronic level while in the multiphotonic ionization case the electron loss comes from all single-electron levels and the HOMO level contributes the most.

  1. Temporal femtosecond pulse shaping dependence of laser-induced periodic surface structures in fused silica

    SciTech Connect

    Shi, Xuesong; Jiang, Lan; Li, Xin Zhang, Kaihu; Yu, Dong; Yu, Yanwu; Lu, Yongfeng

    2014-07-21

    The dependence of periodic structures and ablated areas on temporal pulse shaping is studied upon irradiation of fused silica by femtosecond laser triple-pulse trains. Three types of periodic structures can be obtained by using pulse trains with designed pulse delays, in which the three-dimensional nanopillar arrays with ∼100–150 nm diameters and ∼200 nm heights are first fabricated in one step. These nanopillars arise from the break of the ridges of ripples in the upper portion, which is caused by the split of orthogonal ripples in the bottom part. The localized transient electron dynamics and corresponding material properties are considered for the morphological observations.

  2. Intensity evaluation using a femtosecond pulse laser for absolute distance measurement.

    PubMed

    Wu, Hanzhong; Zhang, Fumin; Li, Jianshuang; Cao, Shiying; Meng, Xiangsong; Qu, Xinghua

    2015-06-10

    In this paper, we propose a method of intensity evaluation based on different pulse models using a femtosecond pulse laser, which enables long-range absolute distance measurement with nanometer precision and large non-ambiguity range. The pulse cross-correlation is analyzed based on different pulse models, including Gaussian, Sech(2), and Lorenz. The DC intensity and the amplitude of the cross-correlation patterns are also demonstrated theoretically. In the experiments, we develop a new combined system and perform the distance measurements on an underground granite rail system. The DC intensity and amplitude of the interference fringes are measured and show a good agreement with the theory, and the distance to be determined can be up to 25 m using intensity evaluation, within 64 nm deviation compared with a He-Ne incremental interferometer, and corresponds to a relative precision of 2.7×10(-9). PMID:26192864

  3. High-energy infrared femtosecond pulses generated by dual-chirped optical parametric amplification.

    PubMed

    Fu, Yuxi; Takahashi, Eiji J; Midorikawa, Katsumi

    2015-11-01

    We demonstrate high-energy infrared femtosecond pulse generation by a dual-chirped optical parametric amplification (DC-OPA) scheme [Opt. Express19, 7190 (2011)]. By employing a 100 mJ pump laser, a signal pulse energy exceeding 20 mJ at a wavelength of 1.4 μm was achieved before dispersion compensation. A total output energy of 33 mJ was recorded. Under a further energy scaling condition, the signal pulse was compressed to an almost transform-limited duration of 27 fs using a fused silica prism compressor. Since the DC-OPA scheme is efficient and energy scalable, design parameters for obtaining 100 mJ level infrared pulses are presented, which are suitable as driver lasers for the energy scaling of high-order harmonic generation with sub-keV photon energy. PMID:26512524

  4. MHz-ultrasound generation by chirped femtosecond laser pulses from gold nano-colloidal suspensions.

    PubMed

    Masim, Frances Camille P; Hsu, Wei-Hung; Tsai, Chih-Hung; Liu, Hao-Li; Porta, Matteo; Nguyen, Mai Thanh; Yonezawa, Tetsu; Balčytis, Armandas; Wang, Xuewen; Juodkazis, Saulius; Hatanaka, Koji

    2016-07-25

    Strong absorption of femtosecond laser pulses in Au nano-colloidal suspensions was used to generate coherent ultrasound signals at 1-20 MHz frequency range. The most efficient ultrasound generation was observed at negative chirp values and was proportional to the pulse duration. Maximization of a dimensionless factor A ≡ αc0tp defined as the ratio of pulse duration tp and the time required for sound at speed c0 to cross the optical energy deposition length (an inverse of the absorption coefficient α) given by 1/(αc0). Chirp controlled pulse duration allows effective enhancement of ultrasound generation at higher frequencies (shorter wavelengths) and is promising for a high spatial resolution acoustic imaging. PMID:27464156

  5. Drilling of aluminum and copper films with femtosecond double-pulse laser

    NASA Astrophysics Data System (ADS)

    Wang, Qinxin; Luo, Sizuo; Chen, Zhou; Qi, Hongxia; Deng, Jiannan; Hu, Zhan

    2016-06-01

    Aluminum and copper films are drilled with femtosecond double-pulse laser. The double-pulse delay is scanned from -75 ps to 90 ps. The drilling process is monitored by recording the light transmitted through the sample, and the morphology of the drilled holes is analyzed by optical microscopy. It is found that, the breakthrough time, the hole evolution during drilling, the redeposited material, the diameters of the redeposited area and the hole, change as functions of double-pulse delay, and are different for the two metals. Along the double-pulse delay axis, three different time constants are observed, a slow one of a few tens of picoseconds, a fast one of a few picoseconds, and an oscillation pattern. Results are discussed based on the mechanisms of plasma shielding, electron-phonon coupling, strong coupling of laser with liquid phase, oxidation of aluminum, laser induced temperature and pressure oscillations, and the atomization of plume particles.

  6. Magneto-optical imaging of magnetic domain pattern produced by intense femtosecond laser pulse irradiation

    NASA Astrophysics Data System (ADS)

    Sinha, Jaivarhan; Mohan, Shyam; Banerjee, S. S.; Kahaly, S.; Kumar, G. Ravindra

    2009-03-01

    An important and intriguing area of research is laser plasma generated giant magnetic field pulses. Interaction of ultrashort high intensity laser pulses with matter involves several mechanisms for generating ultrastrong magnetic fields. By irradiating a magnetic recordable tape constituting of γ-Fe2O3 particles with an intense p-polarized femtosecond laser pulses (˜ 10^16 W cm-2, 100fs), we have found complex magnetic field patterns stored in the tape. We image the local magnetic field distribution around the irradiated region [1] using the high sensitivity magneto-optical imaging technique. We understand the complex magnetic domains patterns recoded on the tape in terms of interesting instabilities [1] generated in the plasma produced during the irradiation of the tape with intense laser pulses. [0pt] [1] Jaivardhan Sinha, Shyam Mohan, S. S Banerjee, S. Kahaly, G. Ravindra Kumar, Phys. Rev. E 77, 046118(2008). *satyajit@iitk.ac.in

  7. Direct mapping of recoil in the ion-pair dissociation of molecular oxygen by a femtosecond depletion method.

    PubMed

    Baklanov, Alexey V; Janssen, Liesbeth M C; Parker, David H; Poisson, Lionel; Soep, Benoit; Mestdagh, Jean-Michel; Gobert, Olivier

    2008-12-01

    Time-resolved dynamics of the photodissociation of molecular oxygen, O(2), via the (3)Sigma(u) (-) ion-pair state have been studied with femtosecond time resolution using a pump-probe scheme in combination with velocity map imaging of the resulting O(+) and O(-) ions. The fourth harmonic of a femtosecond titanium-sapphire (Ti:sapphire) laser (lambda approximately 205 nm) was found to cause three-photon pumping of O(2) to a level at 18.1 eV. The parallel character of the observed O(+) and O(-) images allowed us to conclude that dissociation takes place on the (3)Sigma(u) (-) ion-pair state. The 815 nm fundamental of the Ti:sapphire laser used as probe was found to cause two-photon electron photodetachment starting from the O(2) ion-pair state, giving rise to (O((3)P)+O(+)((4)S)) products. This was revealed by the observed depletion of the yield of the O(-) anion and the appearance of a new O(+) cation signal with a kinetic energy E(transl)(O(+)) dependent on the time delay between the pump and probe lasers. This time-delay dependence of the dissociation dynamics on the ion-pair state has also been simulated, and the experimental and simulated results coincide very well over the experimental delay-time interval from about 130 fs to 20 ps where two- or one-photon photodetachment takes place, corresponding to a change in the R(O(+),O(-)) interatomic distance from 12 to about 900 A. This is one of the first implementations of a depletion scheme in femtosecond pump-probe experiments which could prove to be quite versatile and applicable to many femtosecond time-scale experiments. PMID:19063560

  8. Laser induced periodic surface structuring on Si by temporal shaped femtosecond pulses.

    PubMed

    Almeida, G F B; Martins, R J; Otuka, A J G; Siqueira, J P; Mendonca, C R

    2015-10-19

    We investigated the effect of temporal shaped femtosecond pulses on silicon laser micromachining. By using sinusoidal spectral phases, pulse trains composed of sub-pulses with distinct temporal separations were generated and applied to the silicon surface to produce Laser Induced Periodic Surface Structures (LIPSS). The LIPSS obtained with different sub-pulse separation were analyzed by comparing the intensity of the two-dimensional fast Fourier Transform (2D-FFT) of the AFM images of the ripples (LIPSS). It was observed that LIPSS amplitude is more emphasized for the pulse train with sub-pulses separation of 128 fs, even when compared with the Fourier transform limited pulse. By estimating the carrier density achieved at the end of each pulse train, we have been able to interpret our results with the Sipe-Drude model, that predicts that LIPSS efficacy is higher for a specific induced carrier density. Hence, our results indicate that temporal shaping of the excitation pulse, performed by spectral phase modulation, can be explored in fs-laser microstructuring. PMID:26480419

  9. Material processing with 12 femtosecond picojoule laser pulses

    NASA Astrophysics Data System (ADS)

    König, Karsten; Licht, Martin; Straub, Martin; Uchugonova, Aisada

    2012-03-01

    Extremely short near infrared laser pulses (e.g. 10 fs) offer the possibility of precise sub-100nm processing without collateral side effects. Furthermore, the can be employed to excite a variety of absorbers simultaneously due to their broad 100 nm emission band. We demonstrate two-photon fluorescence imaging of green and red fluorescent proteins in living cells as well as two-photon nanolithography with 12 fs laser pulses (750-850 nm) at low microwatt mean power using an 85 MHz laser resonator. At a minimum of 400 μW mean power, direct nanoprocessing in blood cells was realized. Multiphoton ablation in biological specimens follows a P2/τ relation. We were able to create sub-100nm ripples in silicon wafers, to cut glass, gold, and polymers as well as to create transient nanoholes in the membranes of living stem cells and cancer cells for targeted transfection.

  10. Micro-processing of polymers and biological materials using high repetition rate femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Ding, Li

    High repetition rate femtosecond laser micro-processing has been applied to ophthalmological hydrogel polymers and ocular tissues to create novel refractive and diffractive structures. Through the optimization of laser irradiation conditions and material properties, this technology has become feasible for future industrial applications and clinical practices. A femtosecond laser micro-processing workstation has been designed and developed. Different experimental parameters of the workstation such as laser pulse duration, focusing lens, and translational stages have been described and discussed. Diffractive gratings and three-dimensional waveguides have been fabricated and characterized in hydrogel polymers, and refractive index modifications as large as + 0.06 have been observed within the laser-irradiated region. Raman spectroscopic studies have shown that our femtosecond laser micro-processing induces significant thermal accumulation, resulting in a densification of the polymer network and increasing the localized refractive index of polymers within the laser irradiated region. Different kinds of dye chromophores have been doped in hydrogel polymers to enhance the two-photon absorption during femtosecond laser micro-processing. As the result, laser scanning speed can be greatly increased while the large refractive index modifications remain. Femtosecond laser wavelength and pulse energy as well as water and dye concentration of the hydrogels are optimized. Lightly fixed ocular tissues such as corneas and lenses have been micro-processed by focused femtosecond laser pulses, and refractive index modifications without any tissue-breakdown are observed within the stromal layer of the corneas and the cortex of the lenses. Living corneas are doped with Sodium Fluorescein to increase the two-photon absorption during the laser micro-processing, and laser scanning speed can be greatly increased while inducing large refractive index modifications. No evidence of cell death