Science.gov

Sample records for 800-nm laser pulses

  1. Correlating Pulses from Two Spitfire, 800nm Lasers

    SciTech Connect

    Colby, Eric R.; Mcguinness, C.; Zacherl, W.D.; Plettner, T.; /Stanford U., Phys. Dept.

    2008-01-28

    The E163 laser acceleration experiments conducted at SLAC have stringent requirements on the temporal properties of two regeneratively amplified, 800nm, Spitfire laser systems. To determine the magnitude and cause of timing instabilities between the two Ti:Sapphire amplifiers, we pass the two beams through a cross-correlator and focus the combined beam onto a Hamamatsu G1117 photodiode. The photodiode has a bandgap such that single photon processes are suppressed and only the second order, two-photon process produces an observable response. The response is proportional to the square of the intensity. The diode is also useful as a diagnostic to determine the optimal configuration of the compression cavity.

  2. Switching of 800 nm femtosecond laser pulses using a compact PMN-PT modulator.

    PubMed

    Adany, Peter; Price, E Shane; Johnson, Carey K; Zhang, Run; Hui, Rongqing

    2009-03-01

    A voltage-controlled birefringent cell based on ceramic PMN-PT material is used to enable fast intensity modulation of femtosecond laser pulses in the 800 nm wavelength window. The birefringent cell based on a PMN-PT compound has comparatively high electro-optic response, allowing for a short interaction length of 3 mm and thus very small size, low attenuation of 0.16 dB, and negligible broadening for 100 fs optical pulses. As an application example, agile wavelength tuning of optical pulses is demonstrated using the soliton self-frequency shift in a photonic crystal fiber. By dynamically controlling the optical power into the fiber, this system switches the wavelength of 100 fs pulses from 900 nm to beyond 1120 nm with less than 5 micros time. In addition, a feedback system stabilizes the wavelength drift against external conditions resulting in high wavelength stability.

  3. Optical limiting property of a liquid malononitrile derivative on 800 nm laser pulses

    NASA Astrophysics Data System (ADS)

    Du, Juan; Wang, Liuheng; Xie, Na; Sun, Li; Wang, Xiaodong; Zhao, Yuxia; Wu, Feipeng

    2016-08-01

    A new liquid malononitrile derivative (LBDBP) has been synthesized by incorporating four tetraethylene glycol groups into the prototype scaffold of 2-[Bis-(4‧-diethylamino-biphenyl-4-yl)-methylene]-malononitrile (BDBP). The linear photophysical properties, optical/thermal stabilities and optical limiting behaviors of LBDBP and BDBP have been investigated. The results show that LBDBP has equivalent optical/thermal stability but much better solubility compared with BDBP. Its saturation concentration in DMF is increased to 0.075 M, while the corresponding datum for BDBP is only 0.01 M. The improved solubility of LBDBP insures a very significant optical limiting behavior. The saturated DMF solution of LBDBP can significantly reduce the intensity fluctuation of laser pulses in an 800 nm laser setup.

  4. Nonlinear absorption of femtosecond laser pulses (800 nm) by atmospheric air and water vapour

    SciTech Connect

    Kiselev, A M; Ponomarev, Yu N; Stepanov, A N; Tikhomirov, A B; Tikhomirov, B A

    2011-11-30

    Quantitative data on the nonlinear absorption cross sections of femtosecond Ti : Sapphire laser pulses in air and water vapour have been obtained. A photoacoustic spectrometer calibrated based on the calculated value of linear absorption of laser pulses with a wavelength of 800 nm and a spectral width of 17.7 nm is used to find the nonlinear absorption cross sections of water vapour and air: {sigma}{sub 2}{sup w} = (2.6{+-}0.4) Multiplication-Sign 10{sup -55} cm{sup 4} s and {sigma}{sub 2}{sup a} = (8.7{+-}1.0) Multiplication-Sign 10{sup -56} cm{sup 4} s, respectively. Based on measuring the absorption of femtosecond Ti : Sapphire laser pulses with a photoacoustic detector calibrated with the known linear absorption of ruby laser radiation by water vapour in air, the air nonlinear absorption cross section is found to be (8.2{+-}0.9) Multiplication-Sign 10{sup -56} cm{sup 4} s.

  5. Photoionization and photofragmentation of gaseous toluene using 80-fs, 800-nm laser pulses

    NASA Astrophysics Data System (ADS)

    Müller, A. M.; Uiterwaal, C. J. G. J.; Witzel, B.; Wanner, J.; Kompa, K.-L.

    2000-06-01

    This paper presents ion yields resulting from multiphoton ionization and fragmentation of gaseous toluene (C7H8) in the focus of an 80 fs Ti:sapphire laser beam (λ=800 nm) with a sufficiently small B-integral [Siegman, Lasers (University Science Books, Mill Valley, CA, 1986)]. The peak intensity was varied between 1.9×1013 and 2.8×1014W cm-2, and both linear and circular polarization were used. Over the whole range of intensities studied, only the singly charged parent ion and its fragment, C7H7+, are found. Although the Keldysh adiabaticity parameter equals 0.86 for the saturation intensity of ˜1×1014W cm-2, there is no indication of tunneling. The parent ion yield is found to be effectively proportional to the sixth power of the peak intensity. This is shown to be in good agreement with a multiple lowest-order perturbation multiphoton ionization model which takes into account successive channel closing for increasing peak intensities and orders up to 11 inclusive. On the assumption that the excess energy acquired by the toluene cation as a result of the interaction with the electromagnetic field is of the order of the ponderomotive energy for the intensity prevailing at the moment of the ionization, the internal energy distribution of the toluene cations created that is brought about by this multiple-order multiphoton ionization model is calculated. This internal energy distribution is in perfect agreement with the measured C7H7+ yield, if the rate-energy curve for the fragmentation of excited toluene cations as given by Golovin et al. [Sov. J. Chem. Phys. 2, 632 (1985)] is moderately reduced by a factor of 4.5.

  6. Comparison of glass processing using high-repetition femtosecond (800 nm) and UV (255 nm) nanosecond pulsed lasers

    NASA Astrophysics Data System (ADS)

    Karnakis, Dimitris M.; Knowles, Martyn R. H.; Alty, Kevin T.; Schlaf, Martin; Snelling, Howard V.

    2005-01-01

    Laser processing of glass is of significant commercial interest for microfabrication of "lab-on-a-chip" microfluidic devices. High repetition rate pulsed lasers have been investigated and provide adequate processing speeds but suffer from the inherent risk of laser-induced microcracking and other collateral damage induced in the glass. In this paper we present a comparative study between nanosecond deep UV (255nm) frequency doubled copper laser and femtosecond Ti:Sapphire (800nm) regenerative amplifier laser machining of borosilicate glass. Microchannel scribing and high aspect ratio hole drilling is demonstrated in thick glass using direct writing and mask projection techniques. The resulting material structure geometries have been examined using SEM microscopy and white light interferometry. The feasibility of glass laser machining and the significance of each laser type for this application are discussed.

  7. Ruby Emission in the Range 400-800 nm with Excitation by Continuous-Wave CO2 Laser Pulses

    NASA Astrophysics Data System (ADS)

    Marchenko, V. M.; Kiselev, V. V.

    2017-01-01

    Thermal emission spectra of ruby single crystals in the range 400-800 nm were studied experimentally as functions of the intensity at 10.6 μm of exciting pulses ( 0.5 s) from a continuous-wave electrical-discharge CO2 laser. Spectra at excitation intensity 1-20 kW/cm2 were superpositions of the thermal emission continuum of the sapphire crystal lattice in the range 600-800 nm and selective emission spectra of Cr3+ that were observed for the first time for ruby and consisted of R-lines at 695 nm; N-lines at 715 nm; 2 T 1, 4 T 2 → 4 A 2 transition bands at 672 and 643 nm; and 4 T 1, 2 T 2 → 4 A 2 transition bands at 530 and 490 nm that were not observed in the luminescence spectrum. Time dependences of the shapes of selective emission spectra, quenching and shifts of the R 1 line, and the temperature dependence of ruby luminescence spectra were investigated.

  8. High-brightness 800nm fiber-coupled laser diodes

    NASA Astrophysics Data System (ADS)

    Berk, Yuri; Levy, Moshe; Rappaport, Noam; Tessler, Renana; Peleg, Ophir; Shamay, Moshe; Yanson, Dan; Klumel, Genadi; Dahan, Nir; Baskin, Ilya; Shkedi, Lior

    2014-03-01

    Fiber-coupled laser diodes have become essential sources for fiber laser pumping and direct energy applications. Single emitters offer reliable multi-watt output power from a 100 m lateral emission aperture. By their combination and fiber coupling, pump powers up to 100 W can be achieved from a low-NA fiber pigtail. Whilst in the 9xx nm spectral range the single emitter technology is very mature with <10W output per chip, at 800nm the reliable output power from a single emitter is limited to 4 W - 5 W. Consequently, commercially available fiber coupled modules only deliver 5W - 15W at around 800nm, almost an order of magnitude down from the 9xx range pumps. To bridge this gap, we report our advancement in the brightness and reliability of 800nm single emitters. By optimizing the wafer structure, laser cavity and facet passivation process we have demonstrated QCW device operation up to 19W limited by catastrophic optical damage to the 100 μm aperture. In CW operation, the devices reach 14 W output followed by a reversible thermal rollover and a complete device shutdown at high currents, with the performance fully rebounded after cooling. We also report the beam properties of our 800nm single emitters and provide a comparative analysis with the 9xx nm single emitter family. Pump modules integrating several of these emitters with a 105 μm / 0.15 NA delivery fiber reach 35W in CW at 808 nm. We discuss the key opto-mechanical parameters that will enable further brightness scaling of multi-emitter pump modules.

  9. Generation of <7 fs pulses at 800 nm from a blue-pumped optical parametric amplifier at degeneracy.

    PubMed

    Siddiqui, A M; Cirmi, G; Brida, D; Kärtner, F X; Cerullo, G

    2009-11-15

    We generate ultrabroadband pulses at 800 nm from an optical parametric amplifier (OPA) pumped by the second harmonic of a Ti:sapphire system and working at degeneracy. The OPA is seeded by a white-light continuum generated from a near-IR OPA pumped by the same laser. Nearly transform-limited <7 fs pulses, fully characterized in amplitude and phase, are obtained with a chirped mirror compressor. The system fills the gap around 800 nm for broadband continuum seeded OPAs pumped by Ti:sapphire-based sources.

  10. Generation of Terahertz Radiation from Fe-doped InGaAsP Using 800 nm to 1550 nm Pulsed Laser Excitation

    NASA Astrophysics Data System (ADS)

    Hatem, O.; Freeman, J. R.; Cunningham, J. E.; Cannard, P. J.; Robertson, M. J.; Linfield, E. H.; Davies, A. G.; Moodie, D. G.

    2016-05-01

    We demonstrate efficient generation of terahertz (THz) frequency radiation by pulsed excitation, at wavelengths between 800 and 1550 nm, of photoconductive (PC) switches fabricated using Fe-doped InGaAsP wafers, grown by metal organic chemical vapor deposition (MOCVD). Compared to our previous studies of Fe-doped InGaAs wafers, Fe:InGaAsP wafers exhibited five times greater dark resistivity to give a value of 10 kΩ cm, and Fe:InGaAsP PC switches produced five times higher THz power emission. The effect of Fe-doping concentration (between 1E16 and 1.5E17 cm-3) on optical light absorption (between 800 and 1600 nm), on resistivity, and on THz emission is also discussed.

  11. Experimental study on 800 nm femtosecond laser ablation of fused silica in air and vacuum

    NASA Astrophysics Data System (ADS)

    Xu, Shi-zhen; Yao, Cai-zhen; Liao, Wei; Yuan, Xiao-dong; Wang, Tao; Zu, Xiao-tao

    2016-10-01

    Ablation rates of fused silica were studied as a function of femtosecond laser pulse fluences (0.7-41 J/cm2) in air and vacuum. The experiment was conducted by using a Ti:sapphire laser that emits radiation at 800 nm with a pulse width of 35 fs and a repetition rate of 10 Hz. The morphology and ablation depth of laser-induced damage crater were evaluated by using optical microscopy and scanning electron microscopy (SEM). Ablation rates were calculated from the depth of craters induced by multiple laser pulses. Results showed that two ablation regimes, i.e. non-thermal and thermal ablation co-existed in air and vacuum at low and moderate fluences. A drop of ablation rate was observed at high fluence (higher than 9.5 J/cm2) in air. While in vacuum, the ablation rate increased continuously with the increasing of laser fluence and much higher than that in air. The drop of ablation rate observed at high fluence in air was due to the strong defocusing effects associated with the non-equilibrium ionization of air. Furthermore, the laser-induced damage threshold (LIDT), which was determined from the relationship between crater area and the logarithm of laser energy, was found to depend on the number of incident pulses on the same spot, and similar phenomenon was observed in air and vacuum.

  12. Fabrication of nanostructures on silicon carbide surface and microgroove sidewall using 800-nm femtosecond laser

    NASA Astrophysics Data System (ADS)

    Khuat, Vanthanh; Chen, Tao; Dao, Vanluu

    2015-07-01

    Nanoripples and nanoparticles have been fabricated on the surface of a silicon carbide sample with the irradiation of an 800-nm femtosecond laser in an underwater environment. When a linearly polarized laser was used, the nanoripples were perpendicular to the polarization direction of the incident laser, and the period of the nanoripples was dependent on the number of pulses. When a circularly polarized laser was used, nanoparticles with a diameter of approximately 80 nm were formed. In addition, we observed two kinds of nanoripples on the sidewall of the silicon carbide microgroove fabricated by femtosecond laser irradiation followed by chemical wet etching. When the polarization direction was aligned perpendicular to the writing direction, ripples parallel to the surface of the sample were formed. We attribute the formation of this kind of ripple to interference of the incident laser and the reflected wave. When the polarization direction was aligned parallel to the writing direction, the ripples are perpendicular to the surface of the sample. We attribute the formation of this kind of ripple to interference of incident laser and bulk electron plasma wave. A scanning electron microscope equipped with an energy dispersive X-ray spectroscope was employed to characterize the morphology of the structures.

  13. High-harmonic inverse-free-electron-laser interaction at 800 nm.

    PubMed

    Sears, Christopher M S; Colby, Eric R; Cowan, Benjamin M; Siemann, Robert H; Spencer, James E; Byer, Robert L; Plettner, Tomas

    2005-11-04

    We present the first direct observation of a higher-order inverse-free-electron-laser (IFEL) interaction. Interaction at the fourth, fifth, and sixth harmonics is observed from an IFEL operating at 800 nm. The harmonic spacing, relative harmonic strength, and transverse beam overlap of the interaction are all in good agreement with tracking simulations.

  14. High-Harmonic Inverse-Free-Electron-Laser Interaction at 800 nm

    NASA Astrophysics Data System (ADS)

    Sears, Christopher M. S.; Colby, Eric R.; Cowan, Benjamin M.; Siemann, Robert H.; Spencer, James E.; Byer, Robert L.; Plettner, Tomas

    2005-11-01

    We present the first direct observation of a higher-order inverse-free-electron-laser (IFEL) interaction. Interaction at the fourth, fifth, and sixth harmonics is observed from an IFEL operating at 800 nm. The harmonic spacing, relative harmonic strength, and transverse beam overlap of the interaction are all in good agreement with tracking simulations.

  15. Fiber Bragg grating inscriptions in multimode fiber using 800 nm femtosecond laser

    NASA Astrophysics Data System (ADS)

    Rong, Qiangzhou; Qiao, Xueguang

    2015-09-01

    A short fiber Bragg grating (FBG) was successfully written in a multimode fiber (MMF) tube with core and cladding diameters of 105 μm and 125 μm using 800 nm femtosecond laser. A side-illumination technique was utilized to ensure the grating inscriptions regain over the core of MMF. Both fundamental mode and high-order modes of MMF are coupled at the core-mismatch junction and appear as two well-defined resonances in transmission. Femtosecond laserwritten three FBG-types present good thermostability up to 900 °C.

  16. Optical measurement of temperature in biological cells under infrared laser light exposure (λ=800 nm)

    NASA Astrophysics Data System (ADS)

    Moreau, David; Lefort, Claire; Leveque, Philippe; O'Connor, Rod P.

    2015-07-01

    Interest in the interaction between laser light and biological samples has gained momentum in recent years, particularly in neurobiology, where there is significant potential to stimulate neurons with infrared laser light. Despite recent reports showing the application of infrared light for neurostimulation, the underlying mechanism is still unknown. The two main hypotheses are based on thermal or electrostatic mechanisms. Here, a novel optical method is presented to make temperature measurements in human neural cells under infrared laser excitation (λ=800nm) using the dye Rhodamine B (RhB). The measurement of temperature is based on the property of RhB, a fluorescent dye whose fluorescence intensity decreases linearly with increases in temperature. We present and detail the setup and measurement procedure that has temporal resolution of few milliseconds, based around a fluorescent live-cell imaging microscope used for cellular microfluorimetry experiments.

  17. The 800-nm diode laser irradiation induces skin collagen synthesis by stimulating TGF-β/Smad signaling pathway.

    PubMed

    Dang, Yongyan; Liu, Bei; Liu, Lianxi; Ye, Xiyun; Bi, Xinling; Zhang, Yong; Gu, Jun

    2011-11-01

    The 800-nm diode laser is used clinically for hair removal and leg vein clearance. However, the effects of the laser on skin collagen synthesis have not been established. This study aims to research whether the 800-nm laser can be used for non-ablative rejuvenation and its possible mechanism by using an animal model. Eight 2-month-old rats were irradiated with the 800-nm diode laser at 20, 40, and 60 J/cm(2), respectively. Skin samples were taken for histological study and dermal thickness measurement at day 30 after laser irradiation. The expression of procollagen type I, III, IV, transforming growth factor-β (TGF-β), Smad2, 3, 4, and phosphorylated-Smad2, 3 in the rat skin was analyzed 24 h after completing all laser treatments by using RT-PCR and Western blot. Immunohistochemistry was performed to evaluate the content of type I collagen in the skin at day 30 after laser irradiation. The 800-nm diode laser treatments markedly improved the histological structure and increased dermal thickness compared to the non-irradiated controls. Laser irradiation at 40 J/cm(2) significantly up-regulated the expression of procollagen type I and IV, TGF-β and Smad2, 3, 4. The p-Smad2 and p-Smad3 levels were also enhanced in the laser-irradiated skin. The 800-nm laser is effective in improving skin structure and inducing skin new collagen expression. New collagen synthesis induced by the 800-nm laser was mediated by TGF-β/Smad signaling pathway. Thus, it seemed that the 800-nm laser could be used for non-ablative rejuvenation in the future.

  18. Writing of Bragg gratings through the polymer jacket of low-loss As2S3 fibers using femtosecond pulses at 800 nm.

    PubMed

    Bernier, M; El-Amraoui, M; Couillard, J F; Messaddeq, Y; Vallée, R

    2012-09-15

    Fiber Bragg gratings (FBG) were written through the polymer jacket of low-loss single mode As(2)S(3) chalcogenide fibers by using femtosecond laser pulses at 800 nm and a phase-mask. Peak reflectivity in excess of 99% was obtained at 3440 nm after 5 min of exposure. The resulting FBG maintained a peak reflectivity of 90% after 64 min of thermal annealing at 100 °C. This demonstration paves the way to the development of all-fiber mid-infrared laser sources.

  19. Fiber Bragg gratings inscriptions in multimode fiber using 800 nm femtosecond laser for high-temperature strain measurement

    NASA Astrophysics Data System (ADS)

    Yang, Tingting; Qiao, Xueguang; Rong, Qiangzhou; Bao, Weijia

    2017-08-01

    A short fiber Bragg grating (FBG) is successfully written in a multimode fiber (MMF) with core and cladding diameters of 50 μm and 125 μm using 800 nm femtosecond laser side-illumination technique. Three-type grating inscriptions can be realized at the different positions over the core of MMF by moving the focal-line position of laser beam. Both fundamental mode and higher-order modes of MMF are excited at the core-mismatch junction, resulting in two well-defined resonances in transmission. The strain measurement with a single core resonance mode is demonstrated experimentally at the ultra-high temperature. The result indicates that the strain sensitivity improved to 5.24 pm/με at the temperature of 600-900 °C, making it as a good candidate for the strain measurement at the high temperature environments.

  20. Fundamental research on the action mechanism of the 800 nm semiconductor laser on skin blackheads and coarse pores

    PubMed Central

    Lin, Jie; Jing, Li; Zhu, Hao; Dong, Fu-Sheng

    2017-01-01

    The aim of the study was to determine the mechanism of action of the 800 nm semiconductor laser on skin blackheads and coarse pores. A total of 24 healthy purebred short-haired male guinea pigs, weighing 350–400 g, were selected and smeared with 0.5 ml coal tar suspension evenly by injector once daily. Treatment was continued for 14 days to form an experimental area of 8×3 cm on the back of the guinea pigs. The animals were divided into the following groups: Normal control group (NC), low-dose laser treatment group (L-LS), high-dose laser treatment group (H-LS), and Q-switched Nd:YAG treatment group (QC). Samples were extracted 1, 7 and 14 days after surgery and hematoxylin and eosin staining was used to identify the following: Epidermis, dermis, sebaceous gland change and hair follicle damage; the expression of proliferating cell nuclear antigen (PCNA) of sebaceous gland cells using immunohistochemistry; sebaceous gland cell apoptosis using TUNEL; and the protein expression of caspase-3, Bax and Bcl-2 using western blot analysis. With the extension of time, we observed inflammatory cell infiltration, an increase in hair follicle distortion and necrosis of the surrounding hair follicles. The expression levels of PCNA of the L-LS, H-LS and QC groups decreased with time. Regarding the respective time points, the NC group was highest, the L-LS and H-LS groups were next highest and the H-LS group was lowest. The difference was statistically significant (P<0.05). The apoptotic rate of the L-LS, H-LS and QC groups increased with time. With regard to the respective time points, the NC group was lowest, the L-LS and QC groups were next lowest and the H-LS group was highest. The difference was statistically significant (P<0.05). The protein expression of caspase-3, Bax and Bcl-2 of the L-LS, H-LS and QC groups increased with time. Regarding the respective time points, caspase-3 and Bax protein expression of the NC group was lowest, the L-LS and QC groups were next lowest

  1. Transcranial Near-Infrared Laser Transmission (NILT) Profiles (800 nm): Systematic Comparison in Four Common Research Species

    PubMed Central

    Lapchak, Paul A.; Boitano, Paul D.; Butte, Pramod V.; Fisher, David J.; Hölscher, Thilo; Ley, Eric J.; Nuño, Miriam; Voie, Arne H.; Rajput, Padmesh S.

    2015-01-01

    Background and Purpose Transcranial near-infrared laser therapy (TLT) is a promising and novel method to promote neuroprotection and clinical improvement in both acute and chronic neurodegenerative diseases such as acute ischemic stroke (AIS), traumatic brain injury (TBI), and Alzheimer’s disease (AD) patients based upon efficacy in translational animal models. However, there is limited information in the peer-reviewed literature pertaining to transcranial near-infrared laser transmission (NILT) profiles in various species. Thus, in the present study we systematically evaluated NILT characteristics through the skull of 4 different species: mouse, rat, rabbit and human. Results Using dehydrated skulls from 3 animal species, using a wavelength of 800nm and a surface power density of 700 mW/cm2, NILT decreased from 40.10% (mouse) to 21.24% (rat) to 11.36% (rabbit) as skull thickness measured at bregma increased from 0.44 mm in mouse to 0.83 mm in rat and then 2.11 mm in rabbit. NILT also significantly increased (p<0.05) when animal skulls were hydrated (i.e. compared to dehydrated); but there was no measurable change in thickness due to hydration. In human calvaria, where mean thickness ranged from 7.19 mm at bregma to 5.91 mm in the parietal skull, only 4.18% and 4.24% of applied near-infrared light was transmitted through the skull. There was a slight (9.2-13.4%), but insignificant effect of hydration state on NILT transmission of human skulls, but there was a significant positive correlation between NILT and thickness at bregma and parietal skull, in both hydrated and dehydrated states. Conclusion This is the first systematic study to demonstrate differential NILT through the skulls of 4 different species; with an inverse relationship between NILT and skull thickness. With animal skulls, transmission profiles are dependent upon the hydration state of the skull, with significantly greater penetration through hydrated skulls compared to dehydrated skulls. Using

  2. S100a8/NF-κB signal pathway is involved in the 800-nm diode laser-induced skin collagen remodeling.

    PubMed

    Ren, Xiaolin; Ge, Minggai; Qin, Xiaofeng; Xu, Peng; Zhu, Pingya; Dang, Yongyan; Gu, Jun; Ye, Xiyun

    2016-05-01

    The 800-nm diode laser is widely used for hair removal and also promotes collagen synthesis, but the molecular mechanism by which dermis responses to the thermal damage induced by the 800-nm diode laser is still unclear. Ten 2-month-old mice were irradiated with the 800-nm diode laser at 20, 40, and 60 J/cm(2), respectively. Skin samples were taken for PCR, Western blot analysis, and histological study at day 3 or 30 after laser irradiation. The expression of S100a8 and its two receptors (advanced glycosylation end product-specific receptor, RAGE and toll-like receptor 4, TRL4) was upregulated at day 3 after laser treatments. P-p65 levels were also elevated, causing the increase of cytokine (tumor necrosis factor, TNF-α and interleukin 6, IL-6) and MMPs (MMP1a, MMP9). At day 30, PCR and Western blot analysis showed significant increase of type I and III procollagen in the dermis treated with laser. Importantly, skin structure was markedly improved in the laser-irradiated skin compared with the control. Thus, it seemed that S100a8 upregulation triggered NF-κB signal pathway through RAGE and TLR4, responding to laser-induced dermis wound healing. The involvement of the NF-κB pathway in MMP gene transcription promoted the turnover of collagen in the skin, accelerating new collagen synthesis.

  3. Long-term Comparison of a Large Spot Vacuum Assisted Handpiece vs the Small Spot Size Traditional Handpiece of the 800 nm Diode Laser.

    PubMed

    Youssef, Nour J; Rizk, Alain G; Ibrahimi, Omar A; Tannous, Zeina S

    2017-09-01

    BACKGROUND The 800 nm long-pulsed diode laser machine is safe and effective for permanent hair reduction. Traditionally, most long-pulsed diode lasers used for hair removal had a relatively small spot size. Recently, a long-pulsed diode laser with a large spot size and vacuum assisted suction handpiece was introduced. The treatment parameters of each type of handpiece differ. Short and long-term clinical efficacy, treatment associated pain, and patient satisfaction are important factors to be considered. This study aims to conduct a direct head to head comparison of both handpieces of the 800nm long-pulsed diode laser by evaluating long term hair reduction, treatment associated pain and patient satisfaction. Thirteen subjects were enrolled in this prospective, self-controlled, single-center study of axillary laser hair removal. The study involved 4 treatments using a long pulsed diode laser with a large spot size HS handpiece (single pass), HS handpiece (double pass), and a small spot size ET handpiece according to a randomized choice. The treatment sessions were done at 4-8 week intervals with follow up visits taken at 6 and 12 months after the last treatment session. Hair clearance and thickness analysis were assessed using macro hair count photographs taken at baseline visit, at each treatment session visit and at follow up visits. Other factors including pain, treatment duration, and patients' preference were secondary study endpoints. At 6 months follow up visits after receiving four laser treatments, there was statistically significant hair clearance in the three treatment arms with 66.1 % mean percentage hair reduction with the ET handpiece, 43.6% with the HSS (single pass) and 64.1 % with the HSD (double). However, at one year follow up, the results significantly varied from the 6 months follow up. The mean percentage hair reduction was 57.8% with the ET handpiece treated axillas (n=9), 16.5% with the HSS (single pass) handpiece treated axillas (n=7), and

  4. Direct writing of 150 nm gratings and squares on ZnO crystal in water by using 800 nm femtosecond laser.

    PubMed

    Liu, Jukun; Jia, Tianqing; Zhou, Kan; Feng, Donghai; Zhang, Shian; Zhang, Hongxin; Jia, Xin; Sun, Zhenrong; Qiu, Jianrong

    2014-12-29

    We present a controllable fabrication of nanogratings and nanosquares on the surface of ZnO crystal in water based on femtosecond laser-induced periodic surface structures (LIPSS). The formation of nanogrooves depends on both laser fluence and writing speed. A single groove with width less than 40 nm and double grooves with distance of 150 nm have been produced by manipulating 800 nm femtosecond laser fluence. Nanogratings with period of 150 nm, 300 nm and 1000 nm, and nanosquares with dimensions of 150 × 150 nm2 were fabricated by using this direct femtosecond laser writing technique.

  5. Broadband optical parametric chirped pulse amplification in K3B6O10Br crystal near 800 nm

    NASA Astrophysics Data System (ADS)

    Liu, Xiaodi; Xu, Lu; Zhang, Min; Pan, Shilie; Liang, Xiaoyan

    2017-09-01

    Broadband optical parametric chirped pulse amplification (OPCPA) of the K3B6O10Br (KBOB) crystal at a central wavelength of 800 nm has been demonstrated for the first time. Using type-1 non-collinear phase matching, a 52 nm FWHM bandwidth was achieved around 800 nm. The 0.25 mJ signal was amplified to 23.92 mJ at the pump intensity of 2.1 GW cm-2. The energy gain was 95.68. After compression, 15.31 mJ to 31.9 fs pulses were obtained. The results confirm that KBOB crystal is a potential alternative for efficient, broadband OPCPA near 800 nm.

  6. Mechanisms of the blue emission of NaYF4:Tm(3+) nanoparticles excited by an 800 nm continuous wave laser.

    PubMed

    Zhang, Hongxin; Jia, Tianqing; Shang, Xiaoying; Zhang, Shian; Sun, Zhenrong; Qiu, Jianrong

    2016-10-07

    A thorough understanding of energy transfer and upconversion (UC) processes between trivalent lanthanide (Ln(3+)) ions is essential and important for improving UC performance. However, because of the abundant energy states of Ln(3+) ions, UC mechanisms are very complicated, which makes it a challenge to exclusively verify and quantitatively evaluate the dominant process. In this study, the fundamental excitation processes of Tm(3+)-doped NaYF4 nanocrystals under 800 nm continuous wave (CW) laser excitation were experimentally investigated on the basis of the quantum transition principle. An 800 nm CW laser combined with other wavelength CW lasers, including 471 nm, 657 nm, 980 nm, and 1550 nm lasers, were designed to study in-depth the excitation processes of UC luminescence via simultaneous two-wavelength laser excitation. The results indicate that the excited state absorption of (3)H6→(3)H4∼∼(3)H5→(1)G4 is the dominant pathway of the 481 nm and 651 nm emission bands, and two kinds of energy transfer UC pathways, uniformly expressed as (1)G4 + (3)H4→(1)D2 + (3)F4, play the primary roles in the 456 nm emission band.

  7. IFEL-Chicane Based Microbuncher at 800nm

    NASA Astrophysics Data System (ADS)

    Sears, Christopher M. S.; Colby, Eric; Barnes, Christopher

    2004-12-01

    As a first stage to net acceleration in a laser based EM structure RF electron pulses must be microbunched to match the laser wavelength. We report on the design of an undulator and chicane for microbunching at 800nm using an inverse free electron laser (IFEL) interaction. This includes design considerations for the hardware itself, the laser IFEL interaction and bunching performance, and a full 3D particle tracking simulation to study the focusing effects and possible emittance growth due to the fringe fields of the magnets. The talk will close with a discussion of laser-electron beam diagnostics for overlap in the undulator and for diagnosing microbunching performance.

  8. Enhancement of 800 nm upconversion emission in a thulium doped tellurite microstructured fiber pumped by a 1560 nm femtosecond fiber laser

    NASA Astrophysics Data System (ADS)

    Jia, Zhixu; Yao, Chuanfei; Wang, Shunbin; Zheng, Kezhi; Xiong, Liangming; Luo, Jie; Lv, Dajuan; Qin, Guanshi; Ohishi, Yasutake; Qin, Weiping

    2016-04-01

    We report enhanced upconversion (UC) fluorescence in Tm3+ doped tellurite microstructured fibers (TDTMFs) fabricated by using a rod-in-tube method. Under the pumping of a 1560 nm femtosecond fiber laser, ultrabroadband supercontinuum light expanding from ˜1050 to ˜2700 nm was generated in a 4 cm long TDTMF. Simultaneously, intense 800 nm UC emission from the 3H4 → 3H6 transition of Tm3+ was observed in the same TDTMF. Compared to that pumped by a 1560 nm continuous wave fiber laser, the UC emission intensity was enhanced by ˜4.1 times. The enhancement was due to the spectral broadening in the TDTMF under the pumping of the 1560 nm femtosecond fiber laser.

  9. Fiber Bragg gratings inscribed using 800nm femtosecond laser and a phase mask in single- and multi-core mid-IR glass fibers.

    PubMed

    Suo, Rui; Lousteau, Joris; Li, Hongxia; Jiang, Xin; Zhou, Kaiming; Zhang, Lin; MacPherson, William N; Bookey, Henry T; Barton, James S; Kar, Ajoy K; Jha, Animesh; Bennion, Ian

    2009-04-27

    For the first time, Fiber Bragg grating (FBG) structures have been inscribed in single-core passive germanate and three-core passive and active tellurite glass fibers using 800 nm femtosecond (fs) laser and phase mask technique. With fs peak power intensity in the order of 10(11)W/cm(2), the FBG spectra with 2nd and 3rd order resonances at 1540 and 1033 nm in the germanate glass fiber and 2nd order resonances at approximately 1694 and approximately 1677 nm with strengths up to 14 dB in all three cores in the tellurite fiber were observed. Thermal responsivities of the FBGs made in these mid-IR glass fibers were characterized, showing average temperature responsivity approximately 20 pm/ degrees C. Strain responsivities of the FBGs in germanate glass fiber were measured to be 1.219 pm/microepsilon.

  10. Spectrally-broad coherent anti-Stokes Raman scattering hyper-microscopy utilizing a Stokes supercontinuum pumped at 800 nm.

    PubMed

    Porquez, Jeremy G; Cole, Ryan A; Tabarangao, Joel T; Slepkov, Aaron D

    2016-10-01

    We demonstrate spectral-focusing based coherent anti-Stokes Raman scattering (SF-CARS) hyper-microscopy capable of probing vibrational frequencies from 630 cm(-1) to 3250 cm(-1) using a single Ti:Sapphire femtosecond laser operating at 800 nm, and a commercially-available supercontinuum-generating fibre module. A broad Stokes supercontinuum with significant spectral power at wavelengths between 800 nm and 940 nm is generated by power tuning the fibre module using atypically long and/or chirped ~200 fs pump pulses, allowing convenient access to lower vibrational frequencies in the fingerprint spectral region. This work significantly reduces the instrumental and technical requirements for multimodal CARS microscopy, while expanding the spectral capabilities of an established approach to SF-CARS.

  11. Spectrally-broad coherent anti-Stokes Raman scattering hyper-microscopy utilizing a Stokes supercontinuum pumped at 800 nm

    PubMed Central

    Porquez, Jeremy G.; Cole, Ryan A.; Tabarangao, Joel T.; Slepkov, Aaron D.

    2016-01-01

    We demonstrate spectral-focusing based coherent anti-Stokes Raman scattering (SF-CARS) hyper-microscopy capable of probing vibrational frequencies from 630 cm−1 to 3250 cm−1 using a single Ti:Sapphire femtosecond laser operating at 800 nm, and a commercially-available supercontinuum-generating fibre module. A broad Stokes supercontinuum with significant spectral power at wavelengths between 800 nm and 940 nm is generated by power tuning the fibre module using atypically long and/or chirped ~200 fs pump pulses, allowing convenient access to lower vibrational frequencies in the fingerprint spectral region. This work significantly reduces the instrumental and technical requirements for multimodal CARS microscopy, while expanding the spectral capabilities of an established approach to SF-CARS. PMID:27867735

  12. Correlated Two-Electron Momentum Spectra for Strong-Field Nonsequential Double Ionization of He at 800 nm

    SciTech Connect

    Rudenko, A.; Ergler, Th.; Zrost, K.; Feuerstein, B.; Schroeter, C. D.; Moshammer, R.; Ullrich, J.; Jesus, V. L. B. de

    2007-12-31

    We report on a kinematically complete experiment on nonsequential double ionization of He by 25 fs 800 nm laser pulses at 1.5 PW/cm{sup 2}. The suppression of the recollision-induced excitation at this high intensity allows us to address in a clean way direct (e,2e) ionization by the recolliding electron. In contrast with earlier experimental results, but in agreement with various theoretical predictions, the two-electron momentum distributions along the laser polarization axis exhibit a pronounced V-shaped structure, which can be explained by the role of Coulomb repulsion and typical (e,2e) kinematics.

  13. Xe2 gerade Rydberg states observed in the afterglow of a microplasma by laser spectroscopy of a^3 {Σ }_u^ + ( {1_u,O_u^ - }) absorption in the green (545-555 nm) and near-infrared (675-800 nm)

    NASA Astrophysics Data System (ADS)

    Wagner, C. J.; Galvin, T. C.; Eden, J. G.

    2014-06-01

    Bound←bound transitions of the Xe dimer at small internuclear separation (R < 4.0 Å) have been observed in the 545-555 nm and 675-800 nm spectral regions by laser spectroscopy in the afterglow of a pulsed Xe microplasma with a volume of ˜160 nl. Transient suppression of Xe2 A^1 {Σ }_u^ + ( {O_u^ + }) to X^1 {Σ }_g^ + ( {O_g^ + }) emission in the vacuum ultraviolet (˜172 nm), induced by laser excitation of {Ω }_g leftarrow a^3 {Σ }_u^ + ( {1_u,O_u^ - }) [Rydberg←Rydberg] transitions of the molecule, has confirmed the existence of structure between 720 and 770 nm (reported by Killeen and Eden [J. Chem. Phys. 84, 6048 (1986)]) but also reveals red-degraded vibrational bands extending to wavelengths beyond 800 nm. Spectral simulations based on calculations of Franck-Condon factors for assumed {Ω }_g leftarrow a^3 {Σ }_u^ + transitions involving Ω = 0±,1 gerade Rydberg states suggest that the upper level primarily responsible for the observed spectrum is an Ω = 1 state correlated, in the separated atom limit, with Xe(5p6 1S0) + Xe(5p5 6p) and built on a predominantly A2Π3/2g molecular ion core. Specifically, the spectroscopic constants for the upper state of the 1_g leftarrow 1_u,O_u^ ± absorptive transitions are determined to be Te = 13 000 ± 150 cm-1, ω _e^' = 120 ± 10 cm^{ - 1}, ω _e^' x_e^' = 1.1 ± 0.4 cm^{ - 1}, De = 3300 ± 300 cm-1, and {Δ }R_e = R_e^' - R_e^' ' } = 0.3 ± 0.1 {Å} which are in general agreement with the theoretical predictions of the pseudopotential hole-particle formalism, developed by Jonin and Spiegelmann [J. Chem. Phys. 117, 3059 (2002)], for both the (5)1g and ( 3)O_g^ + states of Xe2. These spectra exhibit the most extensive vibrational development, and provide evidence for the first molecular core-switching transition, observed to date for any of the rare gas dimers at small R (<4 Ǻ). Experiments in the green (545-555 nm) also provide improved absorption spectra, relative to data reported in 1986 and 1999

  14. Two-photon fluorescence bioimaging with an all-semiconductor laser picosecond pulse source.

    PubMed

    Kuramoto, Masaru; Kitajima, Nobuyoshi; Guo, Hengchang; Furushima, Yuji; Ikeda, Masao; Yokoyama, Hiroyuki

    2007-09-15

    We have demonstrated successful two-photon excitation fluorescence bioimaging using a high-power pulsed all-semiconductor laser. Toward this purpose, we developed a pulsed light source consisting of a mode-locked laser diode and a two-stage diode laser amplifier. This pulsed light source provided optical pulses of 5 ps duration and having a maximum peak power of over 100 W at a wavelength of 800 nm and a repetition frequency of 500 MHz.

  15. Photostimulation of astrocytes with femtosecond laser pulses.

    PubMed

    Zhao, Yuan; Zhang, Yuan; Liu, Xiuli; Lv, Xiaohua; Zhou, Wei; Luo, Qingming; Zeng, Shaoqun

    2009-02-02

    The involvement of astrocytes in brain functions rather than support has been identified and widely concerned. However the lack of an effective stimulation of astrocytes hampers our understanding of their essential roles. Here, we employed 800-nm near infrared (NIR) femtosecond laser to induce Ca2+ wave in astrocytes. It was demonstrated that photostimulation of astrocytes with femtosecond laser pulses is efficient with the advantages of non-contact, non-disruptiveness, reproducibility, and high spatiotemporal precision. Photostimulation of astrocytes would facilitate investigations on information processing in neuronal circuits by providing effective way to excite astrocytes.

  16. Evaluation of the vacuum-assisted handpiece compared with the sapphire-cooled handpiece of the 800-nm diode laser system for the use of hair removal and reduction.

    PubMed

    Xia, Yang; Moore, Rachael; Cho, Sunghun; Ross, Edward V

    2010-12-01

    A handpiece with a 35 × 22-mm treatment window that uses vacuum technology has been designed for the diode laser system. Vacuum suction stretches the skin and brings the hair follicle closer to the surface with the intent to damage the hair follicle at a lower surface fluence. The objective of this study was to compare the degree of follicular thermal damage between the sapphire-cooled smaller handpiece at a higher fluence versus the larger vacuum-assisted handpiece at a lower fluence. Five male patients with Fitzpatrick skin types I-IV were enrolled in the study. Three test spots on the right back were treated with the vacuum-assisted laser handpiece at a setting of 10-12 J/cm², and 61-ms pulse duration. Three test spots on the left back were treated with the sapphire-cooled handpiece with a setting of 30-34 J/cm² and a pulse duration of 14-16 ms. A punch biopsy was obtained from one treated area for each handpiece type. The biopsies were sectioned horizontally and examined for the degree of thermal damage to the hair follicle at the level of the isthmus and the bulb. Immediate treatment response, pain score, and total treatment time were recorded. Biopsies from the skin treated with the sapphire-cooled handpiece and the vacuum-assisted handpiece showed the mean hair follicle diameter was 258.3 µm (SE [standard error] 41.7) and 225.1 µm (SE 17.1), respectively. The mean thermal damage diameter to hair diameter ratio was 0.91 (SE 0.10) and 0.72 (SE 0.12), respectively. The mean immediate treatment response, the mean pain severity, and the mean total treatment time were all lower for the vacuum-assisted handpiece. Treatment with the vacuum-assisted handpiece is faster and has a tendency to be more comfortable. Thermal damage to the hair follicle was greater with the sapphire-cooled handpiece.

  17. Ultrashort laser pulse driven inverse free electron laser accelerator experiment

    DOE PAGES

    Moody, J. T.; Anderson, S. G.; Anderson, G.; ...

    2016-02-29

    In this paper we discuss the ultrashort pulse high gradient Inverse Free Electron laser accelerator experiment carried out at the Lawrence Livermore National Laboratory which demonstrated gra- dients exceeding 200 MV/m using a 4 TW 100 fs long 800 nm Ti:Sa laser pulse. Due to the short laser and electron pulse lengths, synchronization was determined to be one of the main challenges in this experiment. This made necessary the implementation of a single-shot, non destructive, electro-optic sampling based diagnostics to enable time-stamping of each laser accelerator shot with < 100 fs accuracy. The results of this experiment are expected tomore » pave the way towards the development of future GeV-class IFEL accelerators.« less

  18. Ultrashort laser pulse driven inverse free electron laser accelerator experiment

    NASA Astrophysics Data System (ADS)

    Moody, J. T.; Anderson, S. G.; Anderson, G.; Betts, S.; Fisher, S.; Tremaine, A.; Musumeci, P.

    2016-02-01

    In this paper we discuss the ultrashort pulse high gradient inverse free electron laser accelerator experiment carried out at the Lawrence Livermore National Laboratory which demonstrated gradients exceeding 200 MV /m using a 4 TW 100 fs long 800 nm Ti :Sa laser pulse. Due to the short laser and electron pulse lengths, synchronization was determined to be one of the main challenges in this experiment. This made necessary the implementation of a single-shot, nondestructive, electro-optic sampling based diagnostics to enable time-stamping of each laser accelerator shot with <100 fs accuracy. The results of this experiment are expected to pave the way towards the development of future GeV-class IFEL accelerators.

  19. Efficient spectral-step expansion of a filamenting laser pulse.

    PubMed

    Théberge, Francis; Lassonde, Philippe; Payeur, Stéphane; Châteauneuf, Marc; Dubois, Jacques; Kieffer, Jean-Claude

    2013-05-01

    We report an efficient transfer of 800 nm energy into both the ultraviolet and the far infrared (IR) during the filamentation in air of an appropriately shaped laser pulse. The multiorder enhancement of the IR supercontinuum in the 3-5 μm atmospheric transmission windows was achieved thanks to spectral-step cascaded four-wave mixing occurring within the spectrum of the shaped femtosecond laser pulse. These results also point out the limit of the self-phase modulation model to explain the spectral broadening of a filamenting laser pulse.

  20. Isolated short attosecond pulse generation in an orthogonally polarized multicycle chirped laser field

    SciTech Connect

    Xu Junjie

    2011-03-15

    We theoretically demonstrate the generation of a high-order harmonic and isolated attosecond pulse in an orthogonally polarized laser field, which is synthesized by an 800-nm chirped laser pulse and an 800-nm chirp-free laser pulse. Owing to the instantaneous frequency increasingly reducing close to the center of the driving pulse, the extreme ultraviolet supercontinuum for the chirped synthesized field is even broader than that for an orthogonal chirp-free two-color laser field. It is found that the broadband supercontinuum spectrum can be achieved for the driving pulse with ten and above optical cycles. After phase compensation an isolated attosecond pulse with a duration of {approx}16 as is produced. Furthermore, the optimization of the chirping rate parameters is investigated to achieve cutoff extension and an isolated short attosecond pulse.

  1. Transforming graphite to nanoscale diamonds by a femtosecond laser pulse

    SciTech Connect

    Nueske, R.; Jurgilaitis, A.; Enquist, H.; Harb, M.; Larsson, J.; Fang, Y.; Haakanson, U.

    2012-01-23

    Formation of cubic diamond from graphite following irradiation by a single, intense, ultra-short laser pulse has been observed. Highly oriented pyrolytic graphite (HOPG) samples were irradiated by a 100 fs pulse with a center wavelength of 800 nm. Following laser exposure, the HOPG samples were studied using Raman spectroscopy of the sample surface. In the laser-irradiated areas, nanoscale cubic diamond crystals have been formed. The exposed areas were also studied using grazing incidence x-ray powder diffraction showing a restacking of planes from hexagonal graphite to rhombohedral graphite.

  2. 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.

  3. Filamentation of ultrashort laser pulses of different wavelengths in argon

    NASA Astrophysics Data System (ADS)

    Qi, Xiexing; Lin, Wenbin

    2017-02-01

    We investigate the filaments formed by the ultrashort laser pulses with different wavelengths of 400 nm, 586 nm and 800 nm propagating in argon. Numerical results show that, when the input power or the ratio of the input power to the critical power is given, the pulse with 400 nm wavelength has the largest on-axis intensity, as well as the narrowest filament and the most stable beam radius. These results indicate that the pulse with shorter wavelength is more suitable for the long-range propagation in argon.

  4. 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.

  5. Study of ambient air ionization with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Wang, Xiaolei; Zhang, Nan; Zhai, Hongchen; Zhu, Xiaonong

    2005-01-01

    The laser induced ionization of ambient air is studied experimentally with laser pulses whose durations range from 50 fs up to 10 ps at 800 nm. It is found that the minimum pulse energy for detectable air ionization follows the scaling law of ɛth varies direct as tpx, with 0.23 < x < 0.5, and x tends to rise for longer pulses within the range of 50 fs - 500 fs. For laser pulses from 0.7 ps to 10 ps, however, x is approximately equal to 0.8. The dependence of the critical intensity for air ionization on the beam spot size is also examined with a variety of focused laser beam spot sizes in the experiments.

  6. High-power Femtosecond Optical Parametric Amplification at 1 kHz in BiB(3)O(6) pumped at 800 nm.

    PubMed

    Petrov, Valentin; Noack, Frank; Tzankov, Pancho; Ghotbi, Masood; Ebrahim-Zadeh, Majid; Nikolov, Ivailo; Buchvarov, Ivan

    2007-01-22

    Substantial power scaling of a travelling-wave femtosecond optical parametric amplifier, pumped near 800 nm by a 1 kHz Ti:sapphire laser amplifier, is demonstrated using monoclinic BiB(3)O(6) in a two stage scheme with continuum seeding. Total energy output (signal plus idler) exceeding 1 mJ is achieved, corresponding to an intrinsic conversion efficiency of approximately 32% for the second stage. The tunability extends from 1.1 to 2.9 microm. The high parametric gain and broad amplification bandwidth of this crystal allowed the maintenance of the pump pulse duration, leading to pulse lengths less than 140 fs, both for the signal and idler pulses, even at such high output levels.

  7. Laser pulse shaping for generating uniform three-dimensional ellipsoidal electron beams.

    SciTech Connect

    Li, Y.; Chmnerisov, S.; Lewellen, J. W.

    2009-02-01

    A scheme of generating a uniform ellipsoidal laser pulse for high-brightness photoinjectors is discussed. The scheme is based on the chromatic aberration of a dispersive lens. Fourier optics simulation reveals the interplay of group velocity delay and dispersion in the scheme, as well as diffractions. Particle tracking simulation shows that the beam generated by such a laser pulse approaches the performance of that by an ideal ellipsoidal laser pulse and represents a significant improvement from the traditionally proposed cylindrical beam geometry. The scheme is tested in an 800-nm, optical proof-of-principle experiment at lower peak power with excellent agreement between the measurement and simulation.

  8. Diode laser based water vapor DIAL using modulated pulse technique

    NASA Astrophysics Data System (ADS)

    Pham, Phong Le Hoai; Abo, Makoto

    2014-11-01

    In this paper, we propose a diode laser based differential absorption lidar (DIAL) for measuring lower-tropospheric water vapor profile using the modulated pulse technique. The transmitter is based on single-mode diode laser and tapered semiconductor optical amplifier with a peak power of 10W around 800nm absorption band, and the receiver telescope diameter is 35cm. The selected wavelengths are compared to referenced wavelengths in terms of random error and systematic errors. The key component of modulated pulse technique, a macropulse, is generated with a repetition rate of 10 kHz, and the modulation within the macropulse is coded according to a pseudorandom sequence with 100ns chip width. As a result, we evaluate both single pulse modulation and pseudorandom coded pulse modulation technique. The water vapor profiles conducted from these modulation techniques are compared to the real observation data in summer in Japan.

  9. Cloning assay thresholds on cells exposed to ultrafast laser pulses

    NASA Astrophysics Data System (ADS)

    Koenig, Karsten; Riemann, Iris; Fischer, Peter; Becker, Thomas P.; Oehring, Hartmut; Halbhuber, Karl-Juergen

    1999-06-01

    The influence of the peak power, laser wavelength and the pulse duration of near infrared ultrashort laser pulses on the reproduction behavior of Chinese hamster ovary (CHO) cells has been studied. In particular, we determined the cloning efficiency of single cell pairs after exposure to ultrashort laser pulses with an intensity in the range of GW/cm2 and TW/cm2. A total of more than 3500 non- labeled cells were exposed to a highly focused scanning beam of a multiphoton laser microscope with 60 microsecond(s) pixel dwell time per scan. The beam was provided by a tunable argon ion laser pumped mode-locked 76 MHz Titanium:Sapphire laser as well as by a compact solid-state laser based system (Vitesse) at a fixed wavelength of 800 nm. Pulse duration (tau) was varied in the range of 100 fs to 4 ps by out-of- cavity pulse-stretching units consisting of SF14 prisms and blazed gratings. Within an optical (laser power) window CHO cells could be scanned for hours without severe impact on reproduction behavior, morphology and vitality. Ultrastructural studies reveal that mitochondria are the major targets of intense destructive laser pulses. Above certain laser power P thresholds, CHO cells started to delay or failed to undergo cell division and, in part, to develop uncontrolled cell growth (giant cell formation). The damage followed a P2/(tau) relation which is typical for a two- photon excitation process. Therefore, cell damage was found to be more pronounced at shorter pulses. Due to the same P2/(tau) relation for the efficiency of fluorescence excitation, two-photon microscopy of living cells does not require extremely short femtosecond laser pulses nor pulse compression units. Picosecond as well as femtosecond lasers can be used as efficient light sources in safe two photon fluorescence microscopy. Only in three photon fluorescence microscopy, femtosecond laser pulses are advantageous over picosecond pulses.

  10. Pulsed IR inductive lasers

    NASA Astrophysics Data System (ADS)

    Razhev, A. M.; Churkin, D. S.; Kargapol'tsev, E. S.

    2014-07-01

    Pulsed inductive discharge is a new alternative method of pumping active gas laser media. The work presents results of experimental investigations of near, mid, and far IR inductive gas lasers (H2, HF, and CO2) operating at different transitions of atoms and molecules with different mechanisms of formation of inversion population. The excitation systems of a pulsed inductive cylindrical discharge (pulsed inductively coupled plasma) and pulsed RF inductive discharge in the gases are developed. Various gas mixtures including H2, N2, He, Ne, F2, NF3, and SF6 are used. Characteristics of near IR H2 laser radiation are investigated. Maximal pulse peak power of 7 kW is achieved. The possibility of using a pulsed inductive discharge as a new method of pumping HF laser active medium is demonstrated. The pulsed RF inductive CO2 laser is created and a total efficiency of 17% is achieved.

  11. Cloning assay thresholds on cells exposed to ultrafast laser pulses

    NASA Astrophysics Data System (ADS)

    Koenig, Karsten; Riemann, Iris; Fischer, Peter; Becker, Thomas P.; Oehring, Hartmut; Halbhuber, Karl-Juergen

    1999-06-01

    The influence of the peak power, laser wavelength and the pulse duration of near infrared (NIR) ultrashort laser pulses on the reproduction behavior of Chinese hamster ovary (CHO) cells has been studied. In particular we determined the cloning efficiency of single cell pairs after exposure to ultrashort laser pulses with an intensity in the range of GW/cm2 and TW/cm2. A total of more than 3500 non- labeled cells were exposed to a highly focused scanning beam of a multiphoton laser microscope with 60 microsecond pixel dwell time per scan. The beam was provided by a tunable argon ion laser pumped mode-locked 76 MHz Titanium:Sapphire laser as well as by a compact solid-state laser based system (Vitesse) at a fixed wavelength of 800 nm. Pulse duration (tau) was varied in the range of 100 fs to 4 ps by out-of-cavity pulse- stretching units consisting of SF14 prisms and blazed gratings. Within an optical (laser power) window CHO cells could be scanned for hours without severe impact on reproduction behavior, morphology and vitality. Ultrastructural studies reveal that mitochondria are the major targets of intense destructive laser pulses. Above certain laser power P thresholds, CHO cells started to delay or failed to undergo cell division and, in part, to develop uncontrolled cell growth (giant cell formation). The damage followed a P2/(tau) relation which is typical for a two-photon excitation process. Therefore, cell damage was found to be more pronounced at shorter pulses. Due to the same P2/(tau) relation for the efficiency of fluorescence excitation, two- photon microscopy of living cells does not require extremely short femtosecond laser pulses nor pulse compression units. Picosecond as well as femtosecond layers can be used as efficient light sources in safe two photon fluorescence microscopy. Only in three photon fluorescence microscopy, femtosecond laser pulses are advantageous over picosecond pulses.

  12. Laser pulse stacking method

    DOEpatents

    Moses, Edward I.

    1992-01-01

    A laser pulse stacking method is disclosed. A problem with the prior art has been the generation of a series of laser beam pulses where the outer and inner regions of the beams are generated so as to form radially non-synchronous pulses. Such pulses thus have a non-uniform cross-sectional area with respect to the outer and inner edges of the pulses. The present invention provides a solution by combining the temporally non-uniform pulses in a stacking effect to thus provide a more uniform temporal synchronism over the beam diameter.

  13. Laser pulse stacking method

    DOEpatents

    Moses, E.I.

    1992-12-01

    A laser pulse stacking method is disclosed. A problem with the prior art has been the generation of a series of laser beam pulses where the outer and inner regions of the beams are generated so as to form radially non-synchronous pulses. Such pulses thus have a non-uniform cross-sectional area with respect to the outer and inner edges of the pulses. The present invention provides a solution by combining the temporally non-uniform pulses in a stacking effect to thus provide a more uniform temporal synchronism over the beam diameter. 2 figs.

  14. Laser fusion pulse shape controller

    DOEpatents

    Siebert, Larry D.

    1977-01-01

    An apparatus for controlling the pulse shape, i.e., the pulse duration and intensity pattern, of a pulsed laser system, and which is particularly well adapted for controlling the pellet ignition pulse in a laser-driven fusion reaction system. The apparatus comprises a laser generator for providing an optical control pulse of the shape desired, a pulsed laser triggered by the control pulse, and a plurality of optical Kerr-effect gates serially disposed at the output of the pulsed laser and selectively triggered by the control pulse to pass only a portion of the pulsed laser output generally corresponding in shape to the control pulse.

  15. Evidence of femtosecond-laser pulse induced cell membrane nanosurgery

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    The mechanism of femtosecond laser nanosurgical attachment is investigated in the following article. Using sub-10 femtosecond laser pulses with 800 nm central wavelength were used to attach retinoblastoma cells. During the attachment process the cell membrane phospholipid bilayers hemifuse into one shared phospholipid bilayer, at the location of attachment. Transmission electron microscopy was used in order to verify the above hypothesis. Based on the imaging results, it was concluded that the two cell membrane coalesce to form one single shared membrane. The technique of cell-cell attachment via femtosecond laser pulses could potentially serve as a platform for precise cell membrane manipulation. Manipulation of the cellular membrane is valuable for studying diseases such as cancer; where the expression level of plasma proteins on the cell membrane is altered.

  16. Pulsed Laser Propulsion.

    DTIC Science & Technology

    1978-10-01

    afforded by a pulsed laser propulsion system over a CW laser propulsion system are 1) simplicity in engine design as a result of permitting the laser...to engineering and weight considerations. The lower boundary of the corridor is set by propellant feed considerations. To the right of this boundary...example, a OOJ -5 per pulse laser operating at 7 x 10 sec between pulses (14, 285 pps) is capable of powering a 30 lb (135 Nt)thrust rocket engine that has

  17. 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.

  18. FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Conical Double Frequency Emission by Femtosecond Laser Pulses from DKDP

    NASA Astrophysics Data System (ADS)

    Zhang, Xi-Peng; Jiang, Hong-Bing; Tang, Shan-Chun; Gong, Qi-Huang

    2009-07-01

    Conical double frequency emission is investigated by femtosecond laser pulses at a wavelength of 800 nm in a DKDP crystal. It is demonstrated that the sum frequency of incident wave and its scattering wave accounts for the conical double frequency emission. The gaps on the conical rings are observed and they are very sensitive to the propagation direction, and thus could be used to detect the small angle deviation of surface direction.

  19. TCSPC FLIM in the wavelength range from 800 nm to 1700 nm (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Becker, Wolfgang; Shcheslavsky, Vladislav

    2016-03-01

    Excitation and detection in the wavelength range above 800nm is a convenient and relatively inexpensive way to increase the penetration depth in optical microscopy. Moreover, detection at long wavelength avoids the problem that tissue autofluorescence contaminates the signals from endogenous fluorescence probes. FLIM at NIR wavelength may therefore be complementary to multiphoton microscopy, especially if the lifetimes of NIR fluorophores report biological parameters of the tissue structures they are bound to. Unfortunately, neither the excitation sources nor the detectors of standard confocal and multiphoton laser scanning systems are directly suitable for excitation and detection of NIR fluorescence. Most of these problems can be solved, however, by using ps diode lasers or Ti:Sapphire lasers at their fundamental wavelength, and NIR-sensitive detectors. With NIR-sensitive PMTs the detection wavelength range can be extended up to 900 nm, with InGaAs SPAD detectors up to 1700 nm. Here, we demonstrate the use of a combination of laser scanning, multi-dimensional TCSPC, and advanced excitation sources and detectors for FLIM at up to 1700 nm. The performance was tested at tissue samples incubated with NIR dyes. The fluorescence lifetimes generally get shorter with increasing absorption and emission wavelengths of the dyes. For the cyanine dye IR1061, absorbing around 1060 nm, the lifetime was found to be as short as 70 ps. Nevertheless the fluorescence decay could still be clearly detected. Almost all dyes showed clear lifetime changes depending on the binding to different tissue constituents.

  20. Nonlinear scattering in hard tissue studied with ultrashort laser pulses.

    PubMed

    Eichler, Jürgen; Kim, Beop-Min

    2002-01-01

    The back-scattered spectrum of ultrashort laser pulses (800 nm, 0.2 ps) was studied in human dental and other hard tissues in vitro below the ablation threshold. Frequency doubled radiation (SHG), frequency tripled radiation and two-photon fluorescence were detected. The relative yield for these processes was measured for various pulse energies. The dependence of the SHG signal on probe thickness was determined in forward and back scattering geometry. SHG is sensitive to linear polarization of the incident laser radiation. SHG in human teeth was studied in vitro showing larger signals in dentin than in cementum and enamel. In carious areas no SHG signal could be detected. Possible applications of higher harmonic radiation for diagnostics and microscopy are discussed.

  1. Pulsed inductive HF laser

    NASA Astrophysics Data System (ADS)

    Razhev, A. M.; Churkin, D. S.; Kargapol'tsev, E. S.; Demchuk, S. V.

    2016-03-01

    We report the results of experimentally investigated dependences of temporal, spectral and spatial characteristics of an inductive HF-laser generation on the pump conditions. Gas mixtures H2 - F2(NF3 or SF66) and He(Ne) - H2 - F2(NF3 or SF6) were used as active media. The FWHM pulse duration reached 0.42 μs. This value corresponded to a pulsed power of 45 kW. For the first time, the emission spectrum of an inductive HF laser was investigated, which consisted of seven groups of bands with centres around the wavelengths of 2732, 2736, 2739, 2835, 2837, 2893 and 2913 nm. The cross section profile of the laser beam was a ring with a diameter of about 20 mm and width of about 5 mm. Parameters of laser operation in the repetitively pulsed regime were sufficiently stable. The amplitude instability of light pulses was no greater than 5% - 6%.

  2. Optical Field Ionization of Atoms and Ions Using Ultrashort Laser Pulses

    NASA Astrophysics Data System (ADS)

    Fittinghoff, David Neal

    This dissertation research is an investigation of the strong optical field ionization of atoms and ions by 120-fs, 614-nm laser pulses and 130-fs, 800-nm laser pulses. The experiments have shown ionization that is enhanced above the predictions of sequential tunneling models for He^{+2}, Ne ^{+2} and Ar^ {+2}. The ion yields for He^ {+1}, Ne^{+1} and Ar^{+1} agree well with the theoretical predictions of optical tunneling models. Investigation of the polarization dependence of the ionization indicates that the enhancements are consistent with a nonsequential ionization mechanism in which the linearly polarized field drives the electron wavefunction back toward the ion core and causes double ionization through inelastic e-2e scattering. These investigations have initiated a number of other studies by other groups and are of current scientific interest in the fields of high-irradiance laser -matter interactions and production of high-density plasmas. This work involved: (1) Understanding the characteristic nature of the ion yields produced by tunneling ionization through investigation of analytic solutions for tunneling at optical frequencies. (2) Extensive characterization of the pulses produced by 614-nm and 800-nm ultrashort pulse lasers. Absolute calibration of the irradiance scale produced shows the practicality of the inverse problem--measuring peak laser irradiance using ion yields. (3) Measuring the ion yields (number of ions produced versus irradiance) for three noble gases using linear, circular and elliptical polarizations of laser pulses.

  3. Pulsed excimer laser processing

    NASA Astrophysics Data System (ADS)

    Wong, D.

    1985-06-01

    The status of pulsed excimer laser processing of PV cells is presented. The cost effective feasibility of fabricating high efficiency solar cells on Czochralski wafers using a pulsed excimer laser for junction formation, surface passivation, and front metallization. Laser annealing results were promising with the best AR coated cell having an efficiency of 16.1%. Better results would be expected with larger laser spot size because there was some degradation in open circuit voltage caused by laser spot overlap and edge effects. Surface heating and photolytic decomposition by the laser was used to deposit tungsten from the reaction of tungsten hexafluoride and hydrogen. The line widths were 5 to 10 mils, and the depositions passed the tape adhesion test. Thinner lines are practical using an optimized optical system.

  4. Pulsed excimer laser processing

    NASA Technical Reports Server (NTRS)

    Wong, D.

    1985-01-01

    The status of pulsed excimer laser processing of PV cells is presented. The cost effective feasibility of fabricating high efficiency solar cells on Czochralski wafers using a pulsed excimer laser for junction formation, surface passivation, and front metallization. Laser annealing results were promising with the best AR coated cell having an efficiency of 16.1%. Better results would be expected with larger laser spot size because there was some degradation in open circuit voltage caused by laser spot overlap and edge effects. Surface heating and photolytic decomposition by the laser was used to deposit tungsten from the reaction of tungsten hexafluoride and hydrogen. The line widths were 5 to 10 mils, and the depositions passed the tape adhesion test. Thinner lines are practical using an optimized optical system.

  5. Nanofabrication with pulsed lasers.

    PubMed

    Kabashin, Av; Delaporte, Ph; Pereira, A; Grojo, D; Torres, R; Sarnet, Th; Sentis, M

    2010-02-24

    An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser-matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics.

  6. Efficient 1 kHz femtosecond optical parametric amplification in BiB(3)O(6) pumped at 800 nm.

    PubMed

    Ghotbi, Masood; Ebrahim-Zadeh, Majid; Petrov, Valentin; Tzankov, Pancho; Noack, Frank

    2006-10-30

    We demonstrate efficient operation of a tunable femtosecond optical parametric amplifier based on BiB(3)O(6) pumped at 800 nm by a 1 kHz Ti:sapphire regenerative amplifier. The idler wavelength coverage extends to beyond 3 mum and the pulse duration at this wavelength is of the order of 110 fs. This new nonlinear borate crystal offers exceptionally high nonlinearity, making it a very promising candidate for power scaling of such frequency converters in the near-IR.

  7. Ionization of a multilevel atom by ultrashort laser pulses

    SciTech Connect

    Andreev, A. V.; Stremoukhov, S. Yu.; Shutova, O. A.

    2010-01-15

    Specific features of ionization of single atoms by laser fields of a near-atomic strength are investigated. Calculations are performed for silver atoms interacting with femtosecond laser pulses with wavelengths {lambda} = 800 nm (Ti:Sapphire) and {lambda} = 1.064 {mu}m (Nd:YAG). The dependences of the probability of ionization and of the form of the photoelectron energy spectra on the field of laser pulses for various values of their duration are considered. It is shown that the behavior of the probability of ionization in the range of subatomic laser pulse fields is in good agreement with the Keldysh formula. However, when the field strength attains values close to the atomic field strength, the discrepancies in these dependences manifested in a decrease in the ionization rate (ionization stabilization effect) or in its increase (accelerated ionization) are observed. These discrepancies are associated with the dependence of the population dynamics of excited discrete energy levels of the atom on the laser pulse field amplitude.

  8. FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Design of a High-Nonlinearity Single-Mode Holey Fiber with Flattened Dispersion around 800 nm

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Hou, Lan-Tian; Liu, Zhao-Lun; Zhou, Gui-Yao

    2009-11-01

    We numerically demonstrate a high-nonlinearity single-mode holey fiber with flattened dispersion around the Ti-Za laser band at 800 nm. The dispersion profile of the fiber has the shape of a quadratic curve, which reaches its maximum 5.96 ps.km-1 .nm-1 at 800 nm and its minimum -0.897 ps.km-1 .nm-1 at both 750 and 850 nm. The nonlinear coefficient is 170 W-1 km-1 at 800 nm and no higher order modes exit. A six-layer air-hole cladding ensures a loss less than 0.067 db/m in the 750 to 850 nm range. Two more air-hole rings will reduce the loss to below 0.1 db/km.

  9. Complicated high-order harmonic generation due to the falling edge of a trapezoidal laser pulse

    NASA Astrophysics Data System (ADS)

    Ahmadi, H.; Vafaee, M.; Maghari, A.

    2016-02-01

    High-order harmonic generation (HHG) is investigated for {{{H}}}2+ and its isotopologues under seven and ten-cycle trapezoidal laser pulses at an 800 nm wavelength and I = 4 × 1014 W cm-2 intensity. We numerically solved the full-dimensional electronic time-dependent Schrödinger equation (TDSE) with and without the Born-Oppenheimer approximation (BO). We show that contribution to the HHG spectrum from the trailing edge of a trapezoidal laser pulse can result in a redshift and complexity in the total HHG spectrum. This effect can be removed by considering different laser pulse durations and nuclear motion that is not possible for sin2 and Gaussian laser pulses. We have resolved the contributions to the redshift and other patterns in the HHG spectra into the different electronic and vibrational channels and the interference thereof.

  10. Pulsed inductive HF laser

    SciTech Connect

    Razhev, A M; Kargapol'tsev, E S; Churkin, D S; Demchuk, S V

    2016-03-31

    We report the results of experimentally investigated dependences of temporal, spectral and spatial characteristics of an inductive HF-laser generation on the pump conditions. Gas mixtures H{sub 2} – F{sub 2}(NF{sub 3} or SF6{sub 6}) and He(Ne) – H{sub 2} – F{sub 2}(NF{sub 3} or SF{sub 6}) were used as active media. The FWHM pulse duration reached 0.42 μs. This value corresponded to a pulsed power of 45 kW. For the first time, the emission spectrum of an inductive HF laser was investigated, which consisted of seven groups of bands with centres around the wavelengths of 2732, 2736, 2739, 2835, 2837, 2893 and 2913 nm. The cross section profile of the laser beam was a ring with a diameter of about 20 mm and width of about 5 mm. Parameters of laser operation in the repetitively pulsed regime were sufficiently stable. The amplitude instability of light pulses was no greater than 5% – 6%. (lasers)

  11. Pulsed laser beam intensity monitor

    SciTech Connect

    Cason, C.M.; Jones, R.W.

    1982-07-13

    A pulsed laser beam intensity monitor measures the peak power within a selectable cross section of a test laser beam and measures integrated energy of the beam during the pulse period of a test laser. A continuous wave laser and a pulsed ruby laser are coaxially arranged for simultaneously transmitting optical output energy through a crystal flat during the time a test laser pulse is transmitted through the flat. Due to stress birefringence in the crystal, the ruby laser pulse transmitted through the flat is recorded and analyzed to provide peak power information about the test laser output pulse, and the continuous wave laser output reflected from the crystal flat provides a measurement of energy during the test laser pulse.

  12. Propagation of ultrashort laser pulses in optically ionized gases

    SciTech Connect

    Morozov, A.; Luo, Y.; Suckewer, S.; Gordon, D. F.; Sprangle, P.

    2010-02-15

    Propagation of 800 nm, 120 fs laser pulses with intensities of 4x10{sup 16} W/cm{sup 2} in supersonic gas jets of N{sub 2} and H{sub 2} is studied using a shear-type interferometer. The plasma density distribution resulting from photoionization is resolved in space and time with simultaneously measured initial neutral density distribution. A distinct difference in laser beam propagation distance is observed when comparing propagation in jets of H{sub 2} and N{sub 2}. This is interpreted in terms of ionization induced refraction, which is stronger when electrons are produced from states of higher ionization potential. Three dimensional particle-in-cell simulations, based on directly solving the Maxwell-Lorentz system of equations, show the roles played by the forward Raman and ionization scattering instabilities, which further affect the propagation distance.

  13. Nanofabrication with Pulsed Lasers

    PubMed Central

    2010-01-01

    An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser–matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics. PMID:20672069

  14. Pulsed gas laser

    DOEpatents

    Anderson, Louis W.; Fitzsimmons, William A.

    1978-01-01

    A pulsed gas laser is constituted by Blumlein circuits wherein space metal plates function both as capacitors and transmission lines coupling high frequency oscillations to a gas filled laser tube. The tube itself is formed by spaced metal side walls which function as connections to the electrodes to provide for a high frequency, high voltage discharge in the tube to cause the gas to lase. Also shown is a spark gap switch having structural features permitting a long life.

  15. Correlated electron dynamics in nonsequential double ionization by orthogonal two-color laser pulses.

    PubMed

    Zhou, Yueming; Huang, Cheng; Tong, Aihong; Liao, Qing; Lu, Peixiang

    2011-01-31

    We have investigated the correlated electron dynamics in nonsequential double ionization (NSDI) of helium by the orthogonally polarized two-color pulses that consisted of an 800-nm and a 400-nm laser fields using the classical ensemble model. Depending on the relative phase of the two-color field, the electron momentum distributions along the polarization direction of the 800-nm field exhibit a surprisingly strong anticorrelated or correlated behavior. Back analysis reveals that recollisions eventually leading to NSDI are concentrated in a time window as short as several hundreds attoseconds with this scheme. By changing the relative phase of the two-color field, the revisit time of recolliding electron wave packet has been controlled with attosecond precision, which is responsible for the various correlated behaviors of the two electrons. Our results reveal that the orthogonally polarized two-color field can serve as a powerful tool to control the correlated electron dynamics in NSDI.

  16. Laser pulse sampler

    DOEpatents

    Vann, Charles

    1998-01-01

    The Laser Pulse Sampler (LPS) measures temporal pulse shape without the problems of a streak camera. Unlike the streak camera, the laser pulse directly illuminates a camera in the LPS, i.e., no additional equipment or energy conversions are required. The LPS has several advantages over streak cameras. The dynamic range of the LPS is limited only by the range of its camera, which for a cooled camera can be as high as 16 bits, i.e., 65,536. The LPS costs less because there are fewer components, and those components can be mass produced. The LPS is easier to calibrate and maintain because there is only one energy conversion, i.e., photons to electrons, in the camera.

  17. Laser pulse sampler

    DOEpatents

    Vann, C.

    1998-03-24

    The Laser Pulse Sampler (LPS) measures temporal pulse shape without the problems of a streak camera. Unlike the streak camera, the laser pulse directly illuminates a camera in the LPS, i.e., no additional equipment or energy conversions are required. The LPS has several advantages over streak cameras. The dynamic range of the LPS is limited only by the range of its camera, which for a cooled camera can be as high as 16 bits, i.e., 65,536. The LPS costs less because there are fewer components, and those components can be mass produced. The LPS is easier to calibrate and maintain because there is only one energy conversion, i.e., photons to electrons, in the camera. 5 figs.

  18. Laser pulse detector

    DOEpatents

    Mashburn, Douglas N.; Akerman, M. Alfred

    1981-01-01

    A laser pulse detector is provided which is small and inexpensive and has the capability of detecting laser light of any wavelength with fast response (less than 5 nanoseconds rise time). The laser beam is focused onto the receiving end of a graphite rod coaxially mounted within a close-fitting conductive, open-end cylindrical housing so that ablation and electric field breakdown of the resulting plasma occurs due to a bias potential applied between the graphite rod and housing. The pulse produced by the breakdown is transmitted through a matched impedance coaxial cable to a recording device. The cable is connected with its central lead to the graphite rod and its outer conductor to the housing.

  19. Laser pulse detector

    DOEpatents

    Mashburn, D.N.; Akerman, M.A.

    1979-08-13

    A laser pulse detector is provided which is small and inexpensive and has the capability of detecting laser light of any wavelength with fast response (less than 5 nanoseconds rise time). The laser beam is focused onto the receiving end of a graphite rod coaxially mounted within a close-fitting conductive, open-end cylindrical housing so that ablation and electric field breakdown of the resulting plasma occurs due to a bias potential applied between the graphite rod and housing. The pulse produced by the breakdown is transmitted through a matched impedance coaxial cable to a recording device. The cable is connected with its central lead to the graphite rod and its outer conductor to the housing.

  20. Mechanism for femtosecond laser pulse patterning of self-assembled monolayers on gold-coated substrates

    NASA Astrophysics Data System (ADS)

    Kirkwood, S. E.; Shadnam, M. R.; Amirfazli, A.; Fedosejevs, R.

    2007-04-01

    Self-assembled monolayer (SAM) patterning on gold thin films was performed using 800 nm, 118 fs laser pulses. SAM removal was ablative and was observed at fluences near the multishot ablation threshold for the thin gold film. Line widths six times smaller than the 2 e-folding intensity beam diameter were observed demonstrating sub-diffraction limited patterning with femtosecond lasers. Similar experimental results in air and N2 indicated that the removal process does not involve oxidation of the gold-sulfur bond as was claimed in the literature.

  1. Ultrahigh-resolution tethered OCT endoscopic capsule at 800 nm (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Li, Kaiyan; Mavadia-Shukla, Jessica; Liang, Wenxuan; Li, Xingde

    2017-02-01

    We present an ultrahigh-resolution, distal-scanning OCT capsule operating at 800 nm targeted towards gastrointestinal tract imaging. Among many others, one significant challenge in the 800-nm OCT capsule technology is the severe chromatic aberration in the imaging optics of the capsule. By combining commercial miniature lenses and customized diffractive lens, the achromatic focal shift was essentially eliminated (i.e. down to 1 µm) over a 3dB spectral bandwidth of 150 nm centered around 825 nm. We have achieved an axial resolution 2.7 µm. Initial proof-of-concept experiments with ex vivo pig esophagus demonstrated the excellent imaging performance of this 800-nm OCT capsule.

  2. 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.

  3. Ablation dynamics and shock wave expansion during laser processing of CFRP with ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Wiedenmann, Margit; Haist, Christoph; Freitag, Christian; Onuseit, Volkher; Weber, Rudolf; Graf, Thomas

    2014-03-01

    Carbon fibre reinforced plastics (CFRP) have a large potential in the automotive lightweight construction due to their low density and high mechanical stability. Compared with today's laser processing methods of metals the main issues in laser processing of CFRP are the very differing thermal, optical and mechanical properties of the components. To understand the process in detail, the ablation process of CFRP with ultrashort laser pulses was investigated. The shock wave and the vapor resulting from processing with single laser pulses were recorded. Shadow photography and luminescence photography with an ultra-high-speed camera was used to show the ablation process with a temporary resolution of up to 3 ns. The field of view was 250 μm × 250 μm. An ultrashort laser pulse with pulse duration of 4 ps and a wavelength of 800 nm was focused onto the workpiece. The energy content of the shock wave was calculated from the resulting images. The energy content of the shock wave was about 20 % of the incident energy and the speed of propagation of the shock wave was more than 2000 m/s. The high intensities in the range of 1013 W/cm2 lead to formation of a plasma plume which was clearly seen in the shadow photography images.

  4. Laser beam pulse formatting method

    DOEpatents

    Daly, Thomas P.; Moses, Edward I.; Patterson, Ralph W.; Sawicki, Richard H.

    1994-01-01

    A method for formatting a laser beam pulse (20) using one or more delay loops (10). The delay loops (10) have a partially reflective beam splitter (12) and a plurality of highly reflective mirrors (14) arranged such that the laser beam pulse (20) enters into the delay loop (10) through the beam splitter (12) and circulates therein along a delay loop length (24) defined by the mirrors (14). As the laser beam pulse (20) circulates within the delay loop (10) a portion thereof is emitted upon each completed circuit when the laser beam pulse (20) strikes the beam splitter (12). The laser beam pulse (20) is thereby formatted into a plurality of sub-pulses (50, 52, 54 and 56). The delay loops (10) are used in combination to produce complex waveforms by combining the sub-pulses (50, 52, 54 and 56) using additive waveform synthesis.

  5. Optical field ionization of atoms and ions using ultrashort laser pulses

    SciTech Connect

    Fittinghoff, David Neal

    1993-12-01

    This dissertation research is an investigation of the strong optical field ionization of atoms and ions by 120-fs, 614-run laser pulses and 130-fs, 800-nm laser pulses. The experiments have shown ionization that is enhanced above the predictions of sequential tunneling models for He+2, Ne+2 and Ar+2. The ion yields for He+1, Ne+1 and Ar+1 agree well with the theoretical predictions of optical tunneling models. Investigation of the polarization dependence of the ionization indicates that the enhancements are consistent with a nonsequential ionization mechanism in which the linearly polarized field drives the electron wavefunction back toward the ion core and causes double ionization through inelastic e-2e scattering. These investigations have initiated a number of other studies by other groups and are of current scientific interest in the fields of high-irradiance laser-matter interactions and production of high-density plasmas. This work involved: (1) Understanding the characteristic nature of the ion yields produced by tunneling ionization through investigation of analytic solutions for tunneling at optical frequencies. (2) Extensive characterization of the pulses produced by 614-nm and 800-ran ultrashort pulse lasers. Absolute calibration of the irradiance scale produced shows the practicality of the inverse problem--measuring peak laser irradiance using ion yields. (3) Measuring the ion yields for three noble gases using linear, circular and elliptical polarizations of laser pulses at 614-nm and 800-nm. The measurements are some of the first measurements for pulse widths as low as 120-fs.

  6. Crystallization of amorphous Si nanoclusters in SiO(x) films using femtosecond laser pulse annealings.

    PubMed

    Korchagina, T T; Gutakovsky, A K; Fedina, L I; Neklyudova, M A; Volodin, V A

    2012-11-01

    The SiO(x) films of various stoichiometries deposited on Si substrates with the use of the co-sputtering from two separate Si and SiO2 targets were annealed by femtosecond laser pulses. Femtosecond laser treatments were applied for crystallization of amorphous silicon nanoclusters in the silicon-rich oxide films. The treatments were carried out with the use of Ti-Sapphire laser with wavelength 800 nm and pulse duration about 30 fs. Regimes of crystallization of amorphous Si nanoclusters in the initial films were found. Ablation thresholds for SiO(x) films of various stoichiometries were discovered. The effect of laser assisted formation of a-Si nanoclusters in the non-stoichiometric dielectric films with relatively low concentration of additional Si atoms was also observed. This approach is applicable for the creation of dielectric films with semiconductor nanoclusters on non-refractory substrates.

  7. Frequency doubling and tripling of ultrashort laser pulses in biological tissues

    SciTech Connect

    Da Silva, L. B.; Eichler, J.; Joslin, E. J.; Kim, B.-M.

    1998-07-24

    Structural proteins such as collagen and elastin are known to generate second harmonic at high laser intensities. Second and third harmonic generations (SHG, THG) of 0.4 ps Ti-Sapphire laser radiation at 800 nm were observed in various biological tissues. Dependence of SHG on laser pulse energy and pulse width was investigated. Reflected second harmonic yield was measured for animal tissue in vitro and human skin in vivo. The yield varies about a factor of 20 for various areas of the skin while the scattered laser radiation (diffuse reflectance) varies only by a factor of 2. In some cases the THG efficiency was comparable to the SHG. Possible applications of higher harmonic radiation for diagnostics and microscopy are discussed.

  8. Design and construction of a PW ultrashort laser facility with ns, ps, and fs outputting pulses

    NASA Astrophysics Data System (ADS)

    Zhu, Qihua; Huang, Xiaojun; Wang, Xiao; Zeng, Xiaoming; Xie, Xudong; Wang, Fang; Wang, Fengrui; Lin, Donghui; Jiang, Dongbin; Wang, Xiaodong; Zhou, Kainan; Zuo, Yanlei; Zhang, Ying; Deng, Ying; Wei, Xiaofeng; Fan, Dianyuan

    2007-06-01

    A petawatt laser facility with three beams for fast ignition research and strong-field physics applications has been designed and is being constructed. The first beam (referred as SILEX-I) is a Ti:sapphire femto-second laser which pulse width is 30 fs, and till now, output power has reached to 330 TW. The other two beams are Nd 3+:glass lasers which output energy are larger than 1kJ and pulse width are about 1ps and 1ns respectively. By using the technology of OPA pumped by 800nm femtosecond laser and seeded by super-continuum white light (SWL), the three beams are synchronized with each other without jitter time. Tiled multilayer dielectric coating gratings are used for the compressor of the PW beam.

  9. Micro pulse laser radar

    NASA Technical Reports Server (NTRS)

    Spinhirne, James D. (Inventor)

    1993-01-01

    An eye safe, compact, solid state lidar for profiling atmospheric cloud and aerosol scattering is disclosed. The transmitter of the micro pulse lidar is a diode pumped micro-J pulse energy, high repetition rate Nd:YLF laser. Eye safety is obtained through beam expansion. The receiver employs a photon counting solid state Geiger mode avalanche photodiode detector. Data acquisition is by a single card multichannel scaler. Daytime background induced quantum noise is controlled by a narrow receiver field-of-view and a narrow bandwidth temperature controlled interference filter. Dynamic range of the signal is limited to optical geometric signal compression. Signal simulations and initial atmospheric measurements indicate that micropulse lider systems are capable of detecting and profiling all significant cloud and aerosol scattering through the troposphere and into the stratosphere. The intended applications are scientific studies and environmental monitoring which require full time, unattended measurements of the cloud and aerosol height structure.

  10. The Application of Ultrafast Laser Pulses to Laser Desorption Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Cui, Yang

    Ultrashort femtosecond laser pulses display exceptional performance for the selective ablation of materials, includes metals, semiconductors, and biological tissues. They do not damage the remaining unablated portion of a sample, which permits the possibility of depth profiling by repeat sampling at the same location. With sufficiently micro-focused fs laser pulse length beam, high lateral resolution mass spectrometry imaging is possible, while sample damage may degrade ultimate lateral resolution in some other methods. Combining imaging and depth profiling could ultimately leads to tomographical mass spectrometry or 3D imaging MS. Laser postionization, a "soft" ionization method, was combined with ultrafast laser desorption for enhanced molecular analysis. A customized femtosecond laser desorption/ablation postionization time-of-flight mass spectrometer was designed and built. The construction and performance of both phases including the VUV source are detailed. Instrument control software was written to operate this instrument, and many automated experiments were successfully demonstrated by this software. Elemental and molecular analysis was carried out on the instrument and demonstrated exceptional performance for fs laser pulse sampling of small areas. Studies demonstrated the imaging and depth profiling capability of fs-LDPI on metals, semiconductors and intact biofilm tissues. Attempts were made to reach the limit of lateral resolution of imaging by fs-LDPI-MS. The results showed similar lateral resolution of <2 mum for both fs 800 nm and 400 nm desorption beams. To improve the repetition rate for high speed imaging application, an alternative LDPI scheme was designed and constructed. The fs 800 beam was tripled to 267 nm and delivered into the ion source as an ionization laser, while a ns 349 nm pulse laser was used for desorption. Preliminary data showed certain intact molecular ions can be detected. Fragmentation tendency was measured against various

  11. Wavefront control to generate ultraviolet supercontinuum by filamentation of few-cycle laser pulses in argon.

    PubMed

    Wang, Zhanxin; Liu, Jiansheng; Li, Ruxin; Xu, Zhizhan

    2010-01-15

    We numerically demonstrated the filamentation dynamics of a 6 fs, 800 nm pulse focused in argon at atmospheric pressure by a zone plate and a concave mirror. In comparison with a concave mirror, the zone plate has a frequency-dependent focal length and can be used to control the wavefront of the laser beam in the frequency domain. A separate supercontinuum in the ultraviolet region extending from 250 to 300 nm and peaked at ~280 nm can be generated by using a proper zone plate.

  12. Femtosecond laser processing of fused silica and aluminum based on electron dynamics control by shaping pulse trains

    NASA Astrophysics Data System (ADS)

    Leng, Ni; Jiang, Lan; Li, Xin; Xu, Chuancai; Liu, Pengjun; Lu, Yongfeng

    2012-11-01

    The pulse train effects on femtosecond laser material processing are investigated from the viewpoint of electron dynamics on dielectrics with fused silica as a case study and metals with Al as a case study in air and water. During femtosecond laser (800 nm, 35 fs) pulse train (double pulses per train) processing of fused silica, a non-monotonic relationship between ablation size and pulse separation is observed with an abrupt rise in the range of 150-275 fs. It is assumed that this is due to the enhancement of photon-electron coupling efficiency and transition of the phase-change mechanism by adjusting the free electron density during pulse train ablation. Surface quality in Al is improved with less recast by designing the pulse energy distribution to adjust the electron/lattice temperature distribution. Furthermore, the positive effects on ablation quality by femtosecond pulse train technology are more significant in water than those in air.

  13. On the Feasibility of Depth Profiling of Animal Tissue by Ultrashort Pulse Laser Ablation

    PubMed Central

    Milasinovic, Slobodan; Liu, Yaoming; Bhardwaj, Chhavi; Melvin, Blaze M.T.; Gordon, Robert J.; Hanley, Luke

    2012-01-01

    Experiments were performed to examine the feasibility of MS depth profiling of animal tissue by ~75 fs, 800 nm laser pulses to expose underlying layers of tissue for subsequent MS analysis. Matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) was used to analyze phospholipids and proteins from both intact bovine eye lens tissue and tissue ablated by ultrashort laser pulses. Laser desorption postionization (LDPI-MS) with 10.5 eV single photon ionization was also used to analyze cholesterol and other small molecules in the tissue before and after laser ablation. Scanning electron microscopy was applied to examine the ablation patterns in the tissue and estimate the depth of the ablation craters. Ultrashort pulse laser ablation was found able to remove a layer of several tens of micrometers from the surface of eye lens tissue while leaving the underlying tissue relatively undamaged for subsequent MS analysis. MS analysis of cholesterol, phospholipids, peptides, and various unidentified species did not reveal any chemical damage caused by ultrashort pulse laser ablation for analytes smaller than ~6 kDa. However, a drop in intensity of larger protein ions was detected by MALDI-MS following laser ablation. An additional advantage was that ablated tissue displayed up to an order of magnitude higher signal intensities than intact tissue when subsequently analyzed by MS. These results support the use of ultrashort pulse laser ablation in combination with MS analysis to permit depth profiling of animal tissue. PMID:22482364

  14. Angular resolved photoionization of C60 by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  15. Laser pulse duration dependence of blister formation on back-radiated Ti thin films for BB-LIFT

    NASA Astrophysics Data System (ADS)

    Goodfriend, N. T.; Starinskiy, S. V.; Nerushev, O. A.; Bulgakova, N. M.; Bulgakov, A. V.; Campbell, E. E. B.

    2016-03-01

    The influence of the laser pulse duration on the mechanism of blister formation in the particle transfer technique, blister-based laser-induced forward transfer, was investigated. Pulses from a fs Ti:Sapphire laser (120 fs, 800 nm) and from a ns Nd:YAG laser (7 ns, 532 nm) were used to directly compare blister formation on thin titanium films of ca. 300 nm thickness, deposited on glass. The different blister morphologies were compared and contrasted by using optical microscopy and atomic force microscopy. The results provide evidence for different blister formation mechanisms: for fs pulses the mechanism is predominantly ablation at the metal-glass interface accompanied by confined plasma expansion and deformation of the remaining metal film; for ns pulses it is heating accompanied by thermal expansion of the metal film.

  16. High power ultrashort pulse lasers

    SciTech Connect

    Perry, M.D.

    1994-10-07

    Small scale terawatt and soon even petawatt (1000 terawatt) class laser systems are made possible by application of the chirped-pulse amplification technique to solid-state lasers combined with the availability of broad bandwidth materials. These lasers make possible a new class of high gradient accelerators based on the large electric fields associated with intense laser-plasma interactions or from the intense laser field directly. Here, we concentrate on the laser technology to produce these intense pulses. Application of the smallest of these systems to the production of high brightness electron sources is also introduced.

  17. Strong-field ionization and Coulomb explosion of argon clusters by few-cycle laser pulses

    NASA Astrophysics Data System (ADS)

    Mathur, D.; Rajgara, F. A.; Holkundkar, A. R.; Gupta, N. K.

    2010-08-01

    Energy distributions are measured for ions emitted upon Coulomb explosion of Arn clusters (n=400-900) upon irradiation by intense three-cycle pulses (10 fs) of 800-nm laser light of peak intensity 5×1014Wcm-2. With few-cycle pulses, there is insufficient time for the cluster to undergo expansion; this results in overall dynamics that are significantly different from those in the many-cycle regime. The peak ion energies are much lower than those obtained when 100-fs pulses of the same intensity are used; they are almost independent of the size of the cluster (over the range 400-900 atoms). Ion yields are measured to be larger in the direction that is perpendicular to the laser-polarization vector than along it. Model molecular dynamics calculations are used to qualitatively rationalize this unexpected anisotropy in terms of shielding by a spatially asymmetric electronic-charge cloud within the cluster.

  18. Laser system using ultra-short laser pulses

    DOEpatents

    Dantus, Marcos; Lozovoy, Vadim V.; Comstock, Matthew

    2009-10-27

    A laser system using ultrashort laser pulses is provided. In another aspect of the present invention, the system includes a laser, pulse shaper and detection device. A further aspect of the present invention employs a femtosecond laser and binary pulse shaping (BPS). Still another aspect of the present invention uses a laser beam pulse, a pulse shaper and a SHG crystal.

  19. Tailoring the surface plasmon resonance of embedded silver nanoparticles by combining nano- and femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Doster, J.; Baraldi, G.; Gonzalo, J.; Solis, J.; Hernandez-Rueda, J.; Siegel, J.

    2014-04-01

    We demonstrate that the broad surface plasmon resonance (SPR) of a single layer of near-coalescence silver nanoparticles (NPs), embedded in a dielectric matrix can be tailored by irradiation with a single nanosecond laser pulse into a distribution featuring a sharp resonance at 435 nm. Scanning electron microscopy studies reveal the underlying mechanism to be a transformation into a distribution of well-separated spherical particles. Additional exposure to multiple femtosecond laser pulses at 400 nm or 800 nm wavelength induces polarization anisotropy of the SPR, with a peak shift that increases with laser wavelength. The spectral changes are measured in-situ, employing reflection and transmission micro-spectroscopy with a lateral resolution of 4 μm. Spectral maps as a continuous function of local fluence can be readily produced from a single spot. The results open exciting perspectives for dynamically tuning and switching the optical response of NP systems, paving the way for next-generation applications.

  20. High-power pulsed lasers

    SciTech Connect

    Holzrichter, J.F.

    1980-04-02

    The ideas that led to the successful construction and operation of large multibeam fusion lasers at the Lawrence Livermore Laboratory are reviewed. These lasers are based on the use of Nd:glass laser materials. However, most of the concepts are applicable to any laser being designed for fusion experimentation. This report is a summary of lectures given by the author at the 20th Scottish University Summer School in Physics, on Laser Plasma Interaction. This report includes basic concepts of the laser plasma system, a discussion of lasers that are useful for short-pulse, high-power operation, laser design constraints, optical diagnostics, and system organization.

  1. Application of femtosecond ultrashort pulse laser to photodynamic therapy mediated by indocyanine green

    PubMed Central

    Sawa, M; Awazu, K; Takahashi, T; Sakaguchi, H; Horiike, H; Ohji, M; Tano, Y

    2004-01-01

    Backgrounds/aims: To evaluate treatment with high peak power pulse energy by femtosecond ultrashort pulse laser (titanium sapphire laser) delivered at an 800 nm wavelength for corneal neovascularisation using photodynamic therapy (PDT) mediated by indocyanine green (ICG). Methods: Using a gelatin solid as an in vitro corneal model, the safety of laser power was studied to determine if it degenerated gelatin with or without ICG. The authors then induced corneal neovascularisation in rabbit eyes by an intracorneal suturing technique. Fluorescein angiography was used to evaluate occlusion before PDT and 0, 1, 3, and 10 days after PDT. The authors performed light microscopy with haematoxylin eosin staining and transmission electron microscopy to determine thrombosis formation in the neovascular regions. Results: The threshold of peak laser power density ranged from 39 to 53 W/cm2. Laser irradiation was started 30 seconds after a 10 mg/kg ICG injection, and all irradiated segments were occluded at 0, 1, 3, and 10 days at 3.8 J/cm2. Light and electron microscopy documented thrombosis formation in the neovascular region. Conclusion: Femtosecond pulse laser enhanced by ICG can be used for PDT. Because of effective closure of corneal neovascularisation at a low energy level, the high peak power pulse energy of the femtosecond pulse laser might be more efficacious than continuous wave laser for use with PDT. PMID:15148220

  2. Periodic nanostructures on Si(100) surfaces generated by high-repetition rate sub-15 fs pulsed near-infrared laser light.

    PubMed

    Straub, Martin; Afshar, Maziar; Feili, Dara; Seidel, Helmut; König, Karsten

    2012-01-15

    Nanoscale rifts and ripples at a periodicity of 130 nm were generated on Si(100) surfaces immersed in water using tightly focused 800 nm 12 fs pulsed 85 MHz laser light at subnanojoule pulse energies. At radiant exposure close to the ablation threshold rifts were typically 20-50 nm in width and 70 nm in depth running perpendicular to the laser polarization. On increase of the irradiance, the rifts broadened and formed periodic ripples, whereas at highest exposure, a random nanoporous surface topology emerged. Rift and ripple formation is explained by laser-induced standing surface plasma waves, which result in periodic variation of dissipation and ablation.

  3. Proof of damage-free selective removal of thin dielectric coatings on silicon wafers by irradiation with femtosecond laser pulses

    SciTech Connect

    Rublack, Tino; Muchow, Markus; Schade, Martin; Leipner, Hartmut S.; Seifert, Gerhard

    2012-07-15

    The microstructural impact of selective femtosecond laser ablation of thin dielectric layers from monocrystalline silicon wafers was investigated. Various spots opened by 280 fs laser pulses at {lambda} = 1.03 {mu}m wavelength and 50 fs pulses at 800 nm, respectively, were analyzed in detail using Raman and transmission electron microscopy. The results show clearly that the thin dielectric films can be removed without any detectable modification of the Si crystal structure in the opened area. In contrast, in adjacent regions corresponding to laser fluence slightly below the breaking threshold, a thin layer of amorphous silicon with a maximum thickness of about 50 nm is found at the Si/SiO{sub 2} interface after laser irradiation. More than one pulse on the same position, however, causes structural modification of the silicon after thin film ablation in any case.

  4. Nonlinear refraction properties of nickel oxide thin films at 800 nm

    SciTech Connect

    Melo, Ronaldo P. Jr. de; Silva, Blenio J. P. da; Santos, Francisco Eroni P. dos; Azevedo, A.; Araujo, Cid B. de

    2009-11-01

    Measurements of the nonlinear refractive index, n{sub 2}, of nickel oxide films prepared by controlled oxidation of nickel films deposited on substrates of soda-lime glass are reported. The structure and morphology of the samples were characterized by scanning electron microscopy, atomic force microscopy, and x-ray diffractometry. Samples of excellent optical quality were prepared. The nonlinear measurements were performed using the thermally managed eclipse Z-scan technique at 800 nm. A large value of n{sub 2}approx =10{sup -12} cm{sup 2}/W and negligible nonlinear absorption were obtained.

  5. Megahertz pulse-burst alexandrite laser diagnostic systems

    NASA Astrophysics Data System (ADS)

    Luff, Jon David

    Megahertz pulse-burst laser systems coupled with megahertz-rate framing cameras have proven (over the last ten years) to be very robust in imaging of high-speed reacting and nonreacting supersonic flows. These Nd:YAG systems produce 20--30 pulses (at variable rates from 500 kHz to 1 MHz) with 50--100 mJ/pulse (lambda = 1064nm) and have been used with narrow, spectral-linewidth, iodine, atomic filters to image turbulence in supersonic boundary layers with great success (when operating at lambda = 532nm). To extend this pulse-burst capability at other wavelengths (wavelengths outside of the 5--30 GHz tuning range of Nd:YAG: lambda = 1064 nm fundamental, and lambda = 532 nm second harmonic), two unique, tunable, megahertz-rate alexandrite laser systems were designed and built. This dissertation documents these two systems and discusses the potential for tunable, megahertz, pulse-burst systems that have more tuning range than Nd:YAG. These tunable alexandrite systems substantially extend the wavelength range of pulse-burst laser technology, but, to date, have pulse-energy limitations. Tunable from 710 nm to 800 nm (in the fundamental), these lasers provide researchers one laser to reach multiple molecular or atomic resonances with variable pulse-burst pulse separations. The molecular and atomic species of interest in reacting and nonreacting flows are presented in Chapter 1, providing a road-map for the development of these tunable lasers. This dissertation presents the design and development of these systems, including mode control, Herriott cell design for pulse separation, and the megahertz-tuning ringmaster-oscillator. Chapter 2 covers the physics of alexandrite as a solid-state, lamp-pumped, tunable medium and compares it to the tunability of Ti:sapphire. Chapter 3 and 4 present the pulse-burst alexandrite systems. The first system, built in Princeton's Applied Physics group (PAPG) (Chapter 3), produced 1-5 mJ total pulse-packet energy of 20--30 pulses, or

  6. Formation of color centers and light scattering structures by femtosecond laser pulses in sodium fluoride

    NASA Astrophysics Data System (ADS)

    Bryukvina, L. I.; Pestryakov, E. V.; Kirpichnikov, A. V.; Martynovich, E. F.

    2014-11-01

    Modification of sodium fluoride crystal lattice by means of femtosecond laser pulses with λmax=800 nm, energy 0.5 mJ, duration 30 fs and repetition rate 1 kHz has been considered in the paper. Effective formation of simple and complex aggregate color centers and light scattering nanodefects in the channel of a laser beam in NaF crystal have been shown for the first time. Dependences of color centers concentration on the distance between the channel center and its periphery and along the channel have been presented. Influence of external focusing on color centers creation has been revealed. Explanations of the observed phenomena have been presented on the basis of nonlinear processes taking place under the effect of high-intensity femtosecond pulses.

  7. Propagation of ultrashort laser pulses in water: linear absorption and onset of nonlinear spectral transformation.

    PubMed

    Sokolov, Alexei V; Naveira, Lucas M; Poudel, Milan P; Strohaber, James; Trendafilova, Cynthia S; Buck, William C; Wang, Jieyu; Strycker, Benjamin D; Wang, Chao; Schuessler, Hans; Kolomenskii, Alexandre; Kattawar, George W

    2010-01-20

    We study propagation of short laser pulses through water and use a spectral hole filling technique to essentially perform a sensitive balanced comparison of absorption coefficients for pulses of different duration. This study is motivated by an alleged violation of the Bouguer-Lambert-Beer law at low light intensities, where the pulse propagation is expected to be linear, and by a possible observation of femtosecond optical precursors in water. We find that at low intensities, absorption of laser light is determined solely by its spectrum and does not directly depend on the pulse duration, in agreement with our earlier work and in contradiction to some work of others. However, as the laser fluence is increased, interaction of light with water becomes nonlinear, causing energy exchange among the pulse's spectral components and resulting in peak-intensity dependent (and therefore pulse-duration dependent) transmission. For 30 fs pulses at 800 nm center wavelength, we determine the onset of nonlinear propagation effects to occur at a peak value of about 0.12 mJ/cm(2) of input laser energy fluence.

  8. Optical absorption and photocurrent enhancement in semi-insulating gallium arsenide by femtosecond laser pulse surface microstructuring.

    PubMed

    Zhao, Zhen-Yu; Song, Zhi-Qiang; Shi, Wang-Zhou; Zhao, Quan-Zhong

    2014-05-19

    We observe an enhancement of optical absorption and photocurrent from semi-insulating gallium arsenide (SI-GaAs) irradiated by femtosecond laser pulses. The SI-GaAs wafer is treated by a regeneratively amplified Ti: Sapphire laser of 120 fs laser pulse at 800 nm wavelength. The laser ablation induced 0.74 μm periodic ripples, and its optical absorption-edge is shifted to a longer wavelength. Meanwhile, the steady photocurrent of irradiated SI-GaAs is found to enhance 50%. The electrical properties of samples are calibrated by van der Pauw method. It is found that femtosecond laser ablation causes a microscale anti-reflection coating surface which enhances the absorption and photoconductivity.

  9. Momentum spectra of electrons rescattered from rare-gas targets following their extraction by one- and two-color femtosecond laser pulses

    SciTech Connect

    Ray, D.; Chen Zhangjin; De, S.; Cao, W.; Le, A. T.; Lin, C. D.; Cocke, C. L.; Litvinyuk, I. V.; Kling, M. F.

    2011-01-15

    We have used velocity-map imaging to measure the three-dimensional momenta of electrons rescattered from Xe and Ar following the liberation of the electrons from these atoms by 45 fs, 800 nm intense laser pulses. Strong structure in the rescattering region is observed in both angle and energy, and is interpreted in terms of quantitative rescattering (QRS) theory. Momentum images have also been taken with two-color (800 nm + 400 nm) pulses on Xe targets. A strong dependence of the spectra on the relative phase of the two colors is observed in the rescattering region. Interpretation of the phase dependence using both QRS theory and a full solution to the time-dependent Schroedinger equation shows that the rescattered electrons provide a much more robust method for determining the relative phase of the two colors than do the direct electrons.

  10. Formation of colorized silicon by femtosecond laser pulses in different background gases

    NASA Astrophysics Data System (ADS)

    Yang, Hong-Dao; Li, Xiao-Hong; Li, Guo-Qiang; Wen, Cai; Qiu, Rong; Huang, Wen-Hao; Wang, Jun-Bo

    2011-08-01

    A single-crystal silicon(111) wafer surface fixed on an x- y translation stage is scanned with a focused femtosecond laser beam at a wavelength of 800 nm under different atmospheres (air, vacuum, and nitrogen). Different colors from different angles on the surface of the silicon then appear. From the result of the experiments, periodic ripple surface structures emerge on the surface of colorized silicon, and the phenomenon is more obvious in vacuum and nitrogen than in air. The periods of the surface structures on silicon are not the same in the different atmospheres. Under vacuum, the period is the longest and is closer to the wavelength of the laser irradiation. Different from metals, the range of energy density is smaller when the colorized silicon appears with femtosecond laser pulses. Through SEM, TEM, and AFM, we observe in detail the microstructures of colorized silicon that forms in air, vacuum, and nitrogen and analyze the possible physical mechanism. Finally, research into the optical reflection of the colorized silicon indicates that the reflectivity is not higher than 30% in the 250-800 nm range.

  11. Progress on developing a PW ultrashort laser facility with ns, ps, and fs outputting pulses

    NASA Astrophysics Data System (ADS)

    Zhu, Qihua; Huang, Xiaojun; Wang, Xiao; Zeng, Xiaoming; Xie, Xudong; Wang, Fang; Wang, Fengrui; Lin, Donghui; Wang, Xiaodong; Zhou, Kainan; Jiang, Dongbin; Deng, Wu; Zuo, Yanlei; Zhang, Ying; Deng, Ying; Wei, Xiaofeng; Zhang, Xiaomin; Fan, Dianyuan

    2008-03-01

    A petawatt laser facility with three beams for fast ignition research and strong-field physics applications has been designed and is being constructed. The first beam (referred as SILEX-I) is a Ti:sapphire femto-second laser which pulse width is 30 fs, and till now, output power has reached to 330 TW. The other two beams are Nd 3+:glass lasers which output energy are larger than 1kJ and pulse width are about 1ps and 1ns respectively. By using the technology of OPA pumped by 800nm femtosecond laser and seeded by super-continuum spectrum white light, the three beams are synchronized with each other without jitter time. By using the seeds from OPA pumped by femtosecond laser, and by using the pre-amplification stage of OPCPA, the signal to noise ratio of the Nd 3+:glass petawatt laser will reach to 10 8. Active methods are taken to control the gain narrowing effect of the Nd 3+:glass amplifiers, giving the option to compress the chirped pulse to ultrashort pulse with width less than 400fs. Tiled multilayer dielectric coating gratings are used for the compressor of the PW beam, which has been successfully demonstrated on a 100J picosecond Nd 3+:glass laser system.

  12. Dual-Laser-Pulse Ignition

    NASA Technical Reports Server (NTRS)

    Trinh, Huu; Early, James W.; Thomas, Matthew E.; Bossard, John A.

    2006-01-01

    A dual-pulse laser (DPL) technique has been demonstrated for generating laser-induced sparks (LIS) to ignite fuels. The technique was originally intended to be applied to the ignition of rocket propellants, but may also be applicable to ignition in terrestrial settings in which electric igniters may not be suitable.

  13. Generation of fluorescent CdSe nanocrystals by short-pulse laser fragmentation

    NASA Astrophysics Data System (ADS)

    Zholudov, Yu. T.; Sajti, C. L.; Slipchenko, N. N.; Chichkov, B. N.

    2015-12-01

    A simple liquid-phase laser fragmentation approach, resulting in the rapid transformation of CdSe microcrystals into colloidal quantum dots (QDs), is presented. Laser fragmentation is achieved by irradiating a CdSe suspension in dimethylformamide with intense infrared, picosecond laser pulses followed by surface passivation with oleylamine or different types of phosphines. The generated QDs reveal perfect colloidal stability preventing agglomeration and precipitation, and show characteristic QD absorption and fluorescence characteristics, whereas their emission properties strongly depend on the surface states and applied capping ligands. These QDs show distinct photoemission under 405-nm single-photon and 800-nm multi-photon excitations in the 560- to 610-nm spectral region corresponding to the QDs size of about 1.5-2 nm in diameter which is confirmed by transmission electron microscopy.

  14. Graphene Oxides as Tunable Broadband Nonlinear Optical Materials for Femtosecond Laser Pulses.

    PubMed

    Jiang, Xiao-Fang; Polavarapu, Lakshminarayana; Neo, Shu Ting; Venkatesan, T; Xu, Qing-Hua

    2012-03-15

    Graphene oxide (GO) thin films on glass and plastic substrates were found to display interesting broadband nonlinear optical properties. We have investigated their optical limiting activity for femtosecond laser pulses at 800 and 400 nm, which could be tuned by controlling the extent of reduction. The as-prepared GO films were found to exhibit excellent broadband optical limiting behaviors, which were significantly enhanced upon partial reduction by using laser irradiation or chemical reduction methods. The laser-induced reduction of GO resulted in enhancement of effective two-photon absorption coefficient at 400 nm by up to ∼19 times and enhancement of effective two- and three-photon absorption coefficients at 800 nm by ∼12 and ∼14.5 times, respectively. The optical limiting thresholds of partially reduced GO films are much lower than those of various previously reported materials. Highly reduced GO films prepared by using the chemical method displayed strong saturable absorption behavior.

  15. Depth profiling and imaging capabilities of an ultrashort pulse laser ablation time of flight mass spectrometer

    PubMed Central

    Cui, Yang; Moore, Jerry F.; Milasinovic, Slobodan; Liu, Yaoming; Gordon, Robert J.; Hanley, Luke

    2012-01-01

    An ultrafast laser ablation time-of-flight mass spectrometer (AToF-MS) and associated data acquisition software that permits imaging at micron-scale resolution and sub-micron-scale depth profiling are described. The ion funnel-based source of this instrument can be operated at pressures ranging from 10−8 to ∼0.3 mbar. Mass spectra may be collected and stored at a rate of 1 kHz by the data acquisition system, allowing the instrument to be coupled with standard commercial Ti:sapphire lasers. The capabilities of the AToF-MS instrument are demonstrated on metal foils and semiconductor wafers using a Ti:sapphire laser emitting 800 nm, ∼75 fs pulses at 1 kHz. Results show that elemental quantification and depth profiling are feasible with this instrument. PMID:23020378

  16. Formation and crystallization of silicon nanoclusters in SiN{sub x}:H films using femtosecond pulsed laser annealings

    SciTech Connect

    Korchagina, T. T. Volodin, V. A.; Chichkov, B. N.

    2010-12-15

    SiN{sub x}:H films of different compositions grown on glass and silicon substrates using plasma-chemical vapor deposition at a temperature of 380 deg. C have been subjected to pulsed laser annealings. The treatments are performed using titanium-sapphire laser radiation with a wavelength of 800 nm and a pulse duration of 30 fs. Structural changes in the films are studied using Raman spectroscopy. Amorphous silicon nanoclusters are detected in as-grown films with molar fractions of excess silicon of {approx}1/5 and larger. Conditions required for pulsed crystallization of nanoclusters were determined. According to the Raman data, no silicon clusters were detected in as-grown films with a small amount of excess silicon (x > 1.25). Pulsed treatments resulted in the formation of silicon nanoclusters 1-2 nm in size in these films.

  17. Modifying single-crystalline silicon by femtosecond laser pulses: an analysis by micro Raman spectroscopy, scanning laser microscopy and atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Bonse, J.; Brzezinka, K.-W.; Meixner, A. J.

    2004-01-01

    The surface modification of single-crystalline silicon induced by single 130 femtosecond (fs) Ti:sapphire laser pulses (wavelength 800 nm) in air is investigated by means of micro Raman spectroscopy (μ-RS), atomic force microscopy and scanning laser microscopy. Depending on the laser fluence, in some regions the studies indicate a thin amorphous top-layer as well as ablated and recrystallized zones. The single-pulse threshold fluences for melting, ablation and polycrystalline recrystallization are determined quantitatively. Several different topographical surface structures (rims and protrusions) are found. Their formation is discussed in the context of recent studies of the laser irradiation of silicon. In combination with a thin-film optical model, the thickness of the amorphous layer is determined by two independent and nondestructive optical methods to be in the order of several 10 nm.

  18. Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

    NASA Astrophysics Data System (ADS)

    Mirza, Inam; Bulgakova, Nadezhda M.; Tomáštík, Jan; Michálek, Václav; Haderka, Ondřej; Fekete, Ladislav; Mocek, Tomáš

    2016-12-01

    In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses.

  19. Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

    PubMed Central

    Mirza, Inam; Bulgakova, Nadezhda M.; Tomáštík, Jan; Michálek, Václav; Haderka, Ondřej; Fekete, Ladislav; Mocek, Tomáš

    2016-01-01

    In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses. PMID:27991543

  20. Ultrashort laser pulse beam shaping.

    PubMed

    Zhang, Shuyan; Ren, Yuhang; Lüpke, Gunter

    2003-02-01

    We calculated the temporal and spatial characteristics of an ultrashort laser pulse propagating through a diffractive beam-shaping system that converts a Gaussian beam into a beam with a uniform irradiance profile that was originally designed for continuous waves [Proc. SPIE 2863, 237(1996)]. The pulse front is found to be considerably curved for a 10-fs pulse, resulting in a temporal broadening of the pulse that increases with increasing radius. The spatial intensity distribution deviates significantly from a top-hat profile, whereas the fluence shows a homogeneous radial distribution.

  1. Adjustment of ablation shapes and subwavelength ripples based on electron dynamics control by designing femtosecond laser pulse trains

    NASA Astrophysics Data System (ADS)

    Yuan, Yanping; Jiang, Lan; Li, Xin; Wang, Cong; Lu, Yongfeng

    2012-11-01

    A quantum model is proposed to investigate femtosecond laser pulse trains processing of dielectrics by including the plasma model with the consideration of laser particle-wave duality. Central wavelengths (400 nm and 800 nm) strongly impact the surface plasmon field distribution, the coupling field intensity distribution (between the absorbed intensity and the surface plasma), and the distribution of transient localized free electron density in the material. This, in turn, significantly changes the localized transient optical/thermal properties during laser materials processing. The effects of central wavelengths on ablation shapes and subwavelength ripples are discussed. The simulation results show that: (1) ablation shapes and the spacing of subwavelength ripples can be adjusted by localized transient electron dynamics control using femtosecond laser pulse trains; (2) the adjustment of the radii of ablation shapes is stronger than that of the periods of subwavelength ripples.

  2. Femtosecond pulse laser ablation of chromium: experimental results and two-temperature model simulations

    NASA Astrophysics Data System (ADS)

    Saghebfar, M.; Tehrani, M. K.; Darbani, S. M. R.; Majd, A. E.

    2017-01-01

    In this work, the results of experimental and computational single- and multi-shot ablation threshold and the incubation effect of chromium metal sample, irradiated by ultrashort laser pulses, are presented. The experimental value of the ablation threshold is determined based on D2 method by measuring the outer ablation crater diameters as a function of incident laser pulse energy using 800 nm, 30 fs, laser pulses. The value of 0.19 ± 0.04 (J/cm2 ), is obtained for the single-shot ablation threshold fluence. The experimental results are compared with time-dependent heat flow calculations based on the two-temperature model and the effect of number and separation time of two consecutive laser pulses with the same total fluence is studied for the Cr target. Moreover, the role of pulse width and absorbed fluence in thermal equilibrium time between electrons and lattice is investigated in two-temperature model. The thermal equilibrium between electron and lattice is established after a few picoseconds for low fluences and after a few tens of picoseconds at higher fluences.

  3. Coaxial short pulsed laser

    DOEpatents

    Nelson, M.A.; Davies, T.J.

    1975-08-01

    This invention relates to a laser system of rugged design suitable for use in a field environment. The laser itself is of coaxial design with a solid potting material filling the space between components. A reservoir is employed to provide a gas lasing medium between an electrode pair, each of which is connected to one of the coaxial conductors. (auth)

  4. Anharmonic resonance absorption of short laser pulses in clusters: A molecular dynamics simulation study

    NASA Astrophysics Data System (ADS)

    Mahalik, S. S.; Kundu, M.

    2016-12-01

    Linear resonance (LR) absorption of an intense 800 nm laser light in a nano-cluster requires a long laser pulse >100 fs when Mie-plasma frequency ( ω M ) of electrons in the expanding cluster matches the laser frequency (ω). For a short duration of the pulse, the condition for LR is not satisfied. In this case, it was shown by a model and particle-in-cell (PIC) simulations [Phys. Rev. Lett. 96, 123401 (2006)] that electrons absorb laser energy by anharmonic resonance (AHR) when the position-dependent frequency Ω [ r ( t ) ] of an electron in the self-consistent anharmonic potential of the cluster satisfies Ω [ r ( t ) ] = ω . However, AHR remains to be a debate and still obscure in multi-particle plasma simulations. Here, we identify AHR mechanism in a laser driven cluster using molecular dynamics (MD) simulations. By analyzing the trajectory of each MD electron and extracting its Ω [ r ( t ) ] in the self-generated anharmonic plasma potential, it is found that electron is outer ionized only when AHR is met. An anharmonic oscillator model, introduced here, brings out most of the features of MD electrons while passing the AHR. Thus, we not only bridge the gap between PIC simulations, analytical models, and MD calculations for the first time but also unequivocally prove that AHR process is a universal dominant collisionless mechanism of absorption in the short pulse regime or in the early time of longer pulses in clusters.

  5. Intensity-resolved above-threshold ionization of xenon with short laser pulses

    NASA Astrophysics Data System (ADS)

    Hart, N. A.; Strohaber, J.; Kaya, G.; Kaya, N.; Kolomenskii, A. A.; Schuessler, H. A.

    2014-05-01

    We present intensity-resolved above-threshold ionization (ATI) spectra of xenon using an intensity scanning and deconvolution technique. Experimental data were obtained with laser pulses of 58 fs and a central wavelength of 800 nm from a chirped-pulse amplifier. Applying a deconvolution algorithm, we obtained spectra that have higher contrast and are in excellent agreement with characteristic two and ten Up cutoff energies contrary to that found for raw data. The retrieved electron-ionization probability is consistent with the presence of a second electron from double ionization. This recovered ionization probability is confirmed with a calculation based on the Perelomov, Popov, and Terent'ev tunneling ionization model [Sov. Phys. JETP 23, 924 (1966)]. Thus, the measurements of the photoelectron yields and the developed deconvolution technique allowed retrieval of more accurate spectroscopic information from the ATI spectra and ionization probability features that usually are concealed by volume averaging.

  6. Short pulse free electron laser amplifier

    DOEpatents

    Schlitt, Leland G.; Szoke, Abraham

    1985-01-01

    Method and apparatus for amplification of a laser pulse in a free electron laser amplifier where the laser pulse duration may be a small fraction of the electron beam pulse duration used for amplification. An electron beam pulse is passed through a first wiggler magnet and a short laser pulse to be amplified is passed through the same wiggler so that only the energy of the last fraction, f, (f<1) of the electron beam pulse is consumed in amplifying the laser pulse. After suitable delay of the electron beam, the process is repeated in a second wiggler magnet, a third, . . . , where substantially the same fraction f of the remainder of the electron beam pulse is consumed in amplification of the given short laser pulse in each wiggler magnet region until the useful electron beam energy is substantially completely consumed by amplification of the laser pulse.

  7. Formation of high spatial frequency ripples in stainless steel irradiated by femtosecond laser pulses in water

    NASA Astrophysics Data System (ADS)

    Huo, Yanyan; Jia, Tianqing; Feng, Donghai; Zhang, Shian; Liu, Jukun; Pan, Jia; Zhou, Kan; Sun, Zhenrong

    2013-05-01

    We report the formation of high spatial frequency ripples (HSFRs) in stainless steel irradiated by 50 fs, 800 nm, 1 kHz femtosecond laser pulses in water. The period of the HSFRs, Λ, is less than 0.2λ, where λ is the laser wavelength. We further conduct theoretical calculations to study the ultrafast dynamics, and find that double splitting of the low spatial frequency ripples (LSFRs, Λ > 0.45λ) plays a decisive role in the formation of HSFRs. Similar experiments are conducted in copper, however, no splitting of LSFRs is observed. The different experimental results on stainless steel and copper conducted in water and in air are also discussed.

  8. Generation of intense femtosecond optical vortex pulses with blazed-phase grating in chirped-pulse amplification system of Ti:sapphire laser

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chieh; Nabekawa, Yasuo; Midorikawa, Katsumi

    2016-11-01

    We demonstrate the generation of an intense femtosecond optical vortex (OV) pulse by employing an OV converter set between two laser amplifiers in a chirped-pulse amplification (CPA) system of a Ti:sapphire laser. The OV converter is composed of a liquid-crystal spatial light modulator (LC-SLM) exhibiting a blazed-phase computer-generated hologram, a concave mirror, and a flat mirror in the 4f setup. Owing to the intrinsic nature of the 4f setup, the OV converter is free from chromatic and topological-charge dispersions, which are always induced in a spiral phase plate conventionally used to convert an intense Gaussian laser pulse to an OV pulse, while we can avoid damage to the LC-SLM by the irradiation of a low-energy pulse before the second amplifier. We have increased the throughput of the OV converter to 42% by systematically investigating the diffraction efficiency of the blazed-phase hologram on the LC-SLM, which relaxes the gain condition required for the second amplifier. The combination of the high-throughput OV converter and the two-stage amplification enables us to generate OV pulses with an energy of 1.63 mJ and a pulse duration of 60 fs at a wavelength of 720 nm, at which the gain of the Ti:sapphire laser is only 60% of the peak gain around 800 nm.

  9. Investigation of a sodium-chloride-damage region by femtosecond laser

    NASA Astrophysics Data System (ADS)

    Gavasheli, Yu. O.; Komarov, P. S.; Ashitkov, S. I.; Savintsev, A. P.; Agranat, M. B.

    2016-12-01

    The damaged regions (craters) arising under optical destruction of a sodium-chloride surface by 40-fs pulses emitted from a terawatt titanium-sapphire laser system are investigated. The dependence of the sizes of the damaged spot and the crater depth on the laser-pulse energy are determined at a wavelength of 800 nm.

  10. Ultrashort-pulse laser machining

    SciTech Connect

    Banks, P S; Feit, M D; Nguyen, H T; Perry, M D; Rubenchik, A M; Sefcik, J A; Stuart, B C

    1998-09-01

    A new type of material processing is enabled with ultrashort (t < 10 ps) laser pulses. Cutting, drilling, sculpting of all materials (biologic materials, ceramics, sapphire, silicon carbide, diamond, metals) occurs by new mechanisms that eliminate thermal shock or collateral damage. High-precision machining to submicron tolerances is enabled resulting in high surface quality and negligible heat affected zone.

  11. Ultrashort-pulse lasers machining

    SciTech Connect

    Banks, P S; Feit, M D; Nguyen, H T; Perry, M D, Stuart, B C

    1999-01-22

    A new type of material processing is enabled with ultrashort (t < 10 psec) laser pulses. Cutting, drilling, sculpting of all materials (biologic materials, ceramics, sapphire, silicon carbide, diamond, metals) occurs by new mechanisms which eliminate thermal shock or collateral damage. High precision machining to submicron tolerances is enabled resulting in high surface quality and negligible heat affected zone.

  12. Pulsed Submillimeter Laser Program.

    DTIC Science & Technology

    1979-05-15

    flouride (CH3 F) located in a 7 cm absorption cell. The signal derived from the interaction occurring in this cell is used in conjunction with phase...methyl flouride it appears this technique can be generally applied to optimize the pump frequency for many other optically pumped FIR laser transitions...line of the 9 pm band with CH3 F. In Figure 37 is shown a simplified energy- level diagram of the prolate symmetric top methyl flouride molecule. The

  13. Developing Pulsed Fiber Lasers

    DTIC Science & Technology

    2007-06-15

    moving pupil imaging system. Y. Kawagoe et al. furthered the research in the early 80’s by using a rotating aperture at the Fourier ...dependent terms in Eq. 16 by their respective Fourier Series Eq. 16 can be written in the following form, ( ) ( ) ( ) ( )( ) ( ) ( ) ( )( )( ) 1 2 0...Asakura, “Speckle reduction by a rotating aperture at the Fourier transform plane,” Opt. Lasers in Eng., 3 197-218, (1982) [8] T. Iwai, N. Takai

  14. Intravital autofluorescence 2-photon microscopy of murine intestinal mucosa with ultra-broadband femtosecond laser pulse excitation: image quality, photodamage, and inflammation.

    PubMed

    Klinger, Antje; Krapf, Lisa; Orzekowsky-Schroeder, Regina; Koop, Norbert; Vogel, Alfred; Hüttmann, Gereon

    2015-11-01

    Ultra-broadband excitation with ultrashort pulses may enable simultaneous excitation of multiple endogenous fluorophores in vital tissue. Imaging living gut mucosa by autofluorescence 2-photon microscopy with more than 150 nm broad excitation at an 800-nm central wavelength from a sub-10 fs titanium-sapphire (Ti:sapphire) laser with a dielectric mirror based prechirp was compared to the excitation with 220 fs pulses of a tunable Ti:sapphire laser at 730 and 800 nm wavelengths. Excitation efficiency, image quality, and photochemical damage were evaluated. At similar excitation fluxes, the same image brightness was achieved with both lasers. As expected, with ultra-broadband pulses, fluorescence from NAD(P)H, flavines, and lipoproteins was observed simultaneously. However, nonlinear photodamage apparent as hyperfluorescence with functional and structural alterations of the tissue occurred earlier when the laser power was adjusted to the same image brightness. After only a few minutes, the immigration of polymorphonuclear leucocytes into the epithelium and degranulation of these cells, a sign of inflammation, was observed. Photodamage is promoted by the higher peak irradiances and/or by nonoptimal excitation of autofluorescence at the longer wavelength. We conclude that excitation with a tunable narrow bandwidth laser is preferable to ultra-broadband excitation for autofluorescence-based 2-photon microscopy, unless the spectral phase can be controlled to optimize excitation conditions.

  15. Intravital autofluorescence 2-photon microscopy of murine intestinal mucosa with ultra-broadband femtosecond laser pulse excitation: image quality, photodamage, and inflammation

    NASA Astrophysics Data System (ADS)

    Klinger, Antje; Krapf, Lisa; Orzekowsky-Schroeder, Regina; Koop, Norbert; Vogel, Alfred; Hüttmann, Gereon

    2015-11-01

    Ultra-broadband excitation with ultrashort pulses may enable simultaneous excitation of multiple endogenous fluorophores in vital tissue. Imaging living gut mucosa by autofluorescence 2-photon microscopy with more than 150 nm broad excitation at an 800-nm central wavelength from a sub-10 fs titanium-sapphire (Ti:sapphire) laser with a dielectric mirror based prechirp was compared to the excitation with 220 fs pulses of a tunable Ti:sapphire laser at 730 and 800 nm wavelengths. Excitation efficiency, image quality, and photochemical damage were evaluated. At similar excitation fluxes, the same image brightness was achieved with both lasers. As expected, with ultra-broadband pulses, fluorescence from NAD(P)H, flavines, and lipoproteins was observed simultaneously. However, nonlinear photodamage apparent as hyperfluorescence with functional and structural alterations of the tissue occurred earlier when the laser power was adjusted to the same image brightness. After only a few minutes, the immigration of polymorphonuclear leucocytes into the epithelium and degranulation of these cells, a sign of inflammation, was observed. Photodamage is promoted by the higher peak irradiances and/or by nonoptimal excitation of autofluorescence at the longer wavelength. We conclude that excitation with a tunable narrow bandwidth laser is preferable to ultra-broadband excitation for autofluorescence-based 2-photon microscopy, unless the spectral phase can be controlled to optimize excitation conditions.

  16. 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.

  17. Characterization of short pulse laser-produced plasmas at the Lawrence Livermore National Laboratory ultra short-pulse laser

    SciTech Connect

    Shepherd, R.; Price, D.; White, W.; Osterheld, A.; Walling, R.; Goldstein, W.; Stewart, R.; Gordan, S.

    1993-07-14

    The K-shell emission from porous aluminum targets is used to infer the density and temperature of plasmas created with 800 nm and 400 nm, 140 fs laser light. The laser beam is focused to a minimum spot size of 5 {mu}m with 800 nm light and 3 {mu}m with 400 nm light, producing a normal incidence peak intensity of 10{sup 18} Watts/cm{sup 2}. A new 800 fs x-ray streak camera is used to study the broadband x-ray emission. The time resolved and time integrated x-ray emission implies substantial differences between the porous target and the flat target temperature.

  18. Pulse transformer for GaAs laser

    NASA Technical Reports Server (NTRS)

    Rutz, E. M.

    1976-01-01

    High-radiance gallium arsenide (GaAs) laser operating at room temperature is utilized in optical navigation system. For efficient transformer-to-laser impedance match, laser should be connected directly to pulse transformer secondary winding.

  19. Single mode pulsed dye laser oscillator

    DOEpatents

    Hackel, R.P.

    1992-11-24

    A single mode pulsed dye laser oscillator is disclosed. The dye laser oscillator provides for improved power efficiency by reducing the physical dimensions of the overall laser cavity, which improves frequency selection capability. 6 figs.

  20. Single mode pulsed dye laser oscillator

    DOEpatents

    Hackel, Richard P.

    1992-01-01

    A single mode pulsed dye laser oscillator is disclosed. The dye laser oscillator provides for improved power efficiency by reducing the physical dimensions of the overall laser cavity, which improves frequency selection capability.

  1. Time-Resolved Studies of Molecular Dynamics Using - and Femto-Second Laser Pulses

    NASA Astrophysics Data System (ADS)

    Deliwala, Shrenik Mahendra

    1995-01-01

    This thesis presents the results of two experiments that measure the evolution of laser excited molecules. The experiment performed with 0.1-ps laser pulses elucidates the dynamics of desorption of O_2 and formation of CO_2 on a platinum surface. The experiment performed with nanosecond time resolution reveals the inter- and intra-molecular vibrational dynamics of infrared laser pumped molecules. Desorption of O_2 and formation of CO_2 were induced with subpicosecond laser pulses on a Pt(111) surface dosed with coadsorbed O_2 and CO. Fluence dependent yields obtained over a range of laser wavelengths from 267 to 800 nm, and pulse durations from 80 fs to 3.6 ps are presented. We observe a dependence of the nonlinear desorption yield on wavelength. Two-pulse correlation measurements show two different time-scales relevant to the desorption. The results show that nonthermal electrons play a role in the surface chemistry, and that an equilibrated pre-heating of the surface modes leads to enhanced desorption. In the second set of experiments reported in this thesis, time-resolved coherent anti-Stokes Raman spectroscopy was used to obtain the rovibrational energy distributions in polyatomic molecules following infrared multiphoton excitation. In addition to presenting new results on SF _6, we review previously obtained data on SO_2 and OCS. The data yield new details about infrared multiphoton excitation and intramolecular vibrational energy relaxation. In particular they show the significance of collisions in redistributing vibrational energy following excitation. The results also clearly show stronger inter-mode coupling and higher excitation in systems with increasing numbers of atoms per molecule. In addition, a detailed description is provided of the Ti:Sapphire based ultrashort pulsed amplified laser system. Both, the principles and the design of the laser system are discussed to serve as a manual for the femtosecond laser system constructed for the study of

  2. Ordered YBCO sub-micron array structures induced by pulsed femtosecond laser irradiation.

    PubMed

    Luo, C W; Lee, C C; Li, C H; Shih, H C; Chen, Y-J; Hsieh, C C; Su, C H; Tzeng, W Y; Wu, K H; Juang, J Y; Uen, T M; Chen, S P; Lin, J-Y; Kobayashi, T

    2008-12-08

    We report on the formation of organized sub-micron YBa(2)Cu(3)O(7) (YBCO) dots induced by irradiating femtosecond laser pulses on YBCO films prepared by pulse laser deposition with fluence in the range of 0.21 approximately 0.53 J/cm(2). The morphology of the YBCO film surface depends strongly on the laser fluences irradiated. At lower laser fluence (approximately 0.21 J/cm(2)) the morphology was pattern of periodic ripples with sub-micrometer spacing. Slightly increasing the laser fluence to 0.26 J/cm(2) changes the pattern into organized sub-micron dots with diameters ranging from 100 nm to 800 nm and height of 150 nm. Further increase of the laser fluence to over 0.32 J/cm(2), however, appeared to result in massive melting and led to irregular morphology. The mechanism and the implications of the current findings will be discussed. Arrays of YBCO sub-micron dots with T(c) = 89.7 K were obtained.

  3. Temperature dependent spectroscopic characterization of Tm:YAG crystals as potential laser medium for pulsed high energy laser amplifiers

    NASA Astrophysics Data System (ADS)

    Körner, Jörg; Reiter, Jürgen; Lühder, Tilman; Hein, Joachim; Jambunathan, V.; Lucianetti, Antonio; Mocek, Tomáš; Kaluza, Malte C.

    2017-05-01

    Similar to ytterbium doped laser materials laser operation with thulium doped media is possible within a quasi-three level scheme, which especially for pulse pumped lasers is a drawback for efficient laser operation, as a significant amount of energy is required to bleach out the laser medium. Since this energy cannot be extracted, it is lost for the amplification process. Hence, operation of such lasers at cryogenic temperatures seems to be an appropriate solution. For further modeling and derivation of design rules for future laser systems based on such a scheme reliable spectral data is needed. We will present absorption and emission measurements on Tm:YAG as a function of temperature in the range from 80 K to 300 K covering both the absorption bands around 800 nm and the emission bands up to 2.1 μm. The spectral measurements were carried out on two samples of Tm:YAG with doping levels of 2 at.% and 8 at.%. Precautions for reabsorption effects were taken to allow for accurate results over the whole measurement range. From these measurements we have derived absorption and emission cross sections and radiative lifetimes. By comparing the latter values to values obtained by highly accurate measurements of the lifetime using the pinhole method we could also estimate the quantum efficiency.

  4. Dark pulse emission of a fiber laser

    SciTech Connect

    Zhang, H.; Tang, D. Y.; Zhao, L. M.; Wu, X.

    2009-10-15

    We report on the dark pulse emission of an all-normal dispersion erbium-doped fiber laser with a polarizer in cavity. We found experimentally that apart from the bright pulse emission, under appropriate conditions the fiber laser could also emit single or multiple dark pulses. Based on numerical simulations we interpret the dark pulse formation in the laser as a result of dark soliton shaping.

  5. Morphology of ablation craters generated by ultra-short laser pulses in dentin surfaces: AFM and ESEM evaluation

    NASA Astrophysics Data System (ADS)

    Daskalova, A.; Bashir, S.; Husinsky, W.

    2010-11-01

    In this study, the surface morphology and structure of dentin after ablation by ultra-short pulses were evaluated using environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM). The dentin specimens examined were irradiated by a chirped-pulse-amplification (CPA) Ti:sapphire laser (800 nm) and the optimal conditions for producing various nanostructures were determined. Based on the ESEM results, it was possible to identify an energy density range as the ablation threshold for dentin. The laser-induced damage was characterized over the fluence range 1.3-2.1 J/cm 2. The results demonstrate that by selecting suitable parameters one can obtain efficient dentin surface preparation without evidence of thermal damage, i.e., with minimized heat affected zones and reduced collateral damage, the latter being normally characterized by formation of microcracks, grain growth and recrystallization in the heat affected zones.

  6. Simultaneous visible and near-infrared emission from a pulse-stretched alexandrite laser source

    NASA Astrophysics Data System (ADS)

    Boczar, Bruce; Thevar, Thanga; Rousseva, Ivelina; Kramer, Norman; Pryor, Brian; Frost, Rick

    2004-07-01

    An efficient method to make multi-spectral laser light having any selected pulsed duration in the range of 100 ns to 1 μs has been demonstrated in the laboratory. This laser system, based on the alexandrite tunable solid-state gain medium, which is tunable in its fundamental between 720 and 800 nm, was constructed near the gain maximum of 755 nm. A novel intracavity pulse-stretcher provides control of the pulse duration up to about 5 μs using the Pockels effect. In the demonstration prototype, however, the pulse duration was restricted to 500 ns to maintain the peak power needed for efficient nonlinear conversion. Following an amplification stage, Raman shifting in hydrogen gas was used to achieve efficient wavelength conversion to 1100 nm. The Raman shifted beam was frequency doubled to 550 nm using two BBO crystals arranged for walk-off compensation. The result was a convenient source of light whose spectral content, pulse duration, as well as other parameters, could be critically controlled.

  7. Third-order nonlinear optical response in transparent solids using ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Dota, K.; Dharmadhikari, J. A.; Mathur, D.; Dharmadhikari, A. K.

    2012-06-01

    The third-order optical nonlinearity, χ (3), is measured in transparent glasses (BK7 and fused silica) and crystals (BaF2 and quartz) using 36-fs, 800-nm laser pulses and the optical Kerr gate (OKE) technique; values are found to lie in the range 1.3-1.7×10-14 esu, in accordance with theoretical estimates. We probe the purely electronic response to the incident ultrashort laser pulse in fused silica and BK7 glass. In BaF2 and quartz, apart from the electronic response we also observe contribution from the nuclear response to the incident ultrashort pulses. We observe oscillatory modulations that persist for ˜400 fs. The response of the media (glasses and crystals) to ultrashort pulses is also measured using two-beam self-diffraction; the diffraction efficiency in the first-order grating is measured to be in the range of 0.06-0.13 %. Third harmonic generation due to self-phase matching in the transient grating geometry is measured as a function of temporal delay between the two incident ultrashort pulses, yielding the autocorrelation signal.

  8. Ultrashort-pulse laser calligraphy

    NASA Astrophysics Data System (ADS)

    Yang, Weijia; Kazansky, Peter G.; Shimotsuma, Yasuhiko; Sakakura, Masaaki; Miura, Kiyotaka; Hirao, Kazuyuki

    2008-10-01

    Control of structural modifications inside silica glass by changing the front tilt of an ultrashort pulse is demonstrated, achieving a calligraphic style of laser writing. The phenomena of anisotropic bubble formation at the boundary of an irradiated region and modification transition from microscopic bubbles formation to self-assembled form birefringence are observed, and the physical mechanisms are discussed. The results provide the comprehensive evidence that the light beam with centrosymmetric intensity distribution can produce noncentrosymmetric material modifications.

  9. Comparative study of femtosecond and nanosecond laser-induced breakdown spectroscopy of depleted uranium

    SciTech Connect

    Emmert, Luke A.; Chinni, Rosemarie C.; Cremers, David A.; Jones, C. Randy; Rudolph, Wolfgang

    2011-01-20

    We present spectra of depleted uranium metal from laser plasmas generated by nanosecond Nd:YAG (1064 nm) and femtosecond Ti:sapphire (800 nm) laser pulses. The latter pulses produce short-lived and relatively cool plasmas in comparison to the longer pulses, and the spectra of neutral uranium atoms appear immediately after excitation. Evidence for nonequilibrium excitation with femtosecond pulses is found in the dependence of spectral line intensities on the pulse chirp.

  10. Wakefield generation via two color laser pulses

    SciTech Connect

    Jha, Pallavi; Saroch, Akanksha; Kumar Verma, Nirmal

    2013-05-15

    The analytical study for the evolution of longitudinal as well as transverse electric wakefields, generated via passage of two color laser pulses through uniform plasma, has been presented in the mildly relativistic regime. The frequency difference between the two laser pulses is assumed to be equal to the plasma frequency, in the present analysis. The relative angle between the directions of polarization of the two laser pulses is varied and the wakefield amplitudes are compared. Further, the amplitude of the excited wakes by two color pulses are compared with those generated by a single laser pulse.

  11. Controlled assembly of high-order nanoarray metal structures on bulk copper surface by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Qin, Wanwan; Yang, Jianjun

    2017-07-01

    We report a new one-step maskless method to fabricate high-order nanoarray metal structures comprising periodic grooves and particle chains on a single-crystal Cu surface using femtosecond laser pulses at the central wavelength of 400 nm. Remarkably, when a circularly polarized infrared femtosecond laser pulse (spectrally centered at 800 nm) pre-irradiates the sample surface, the geometric dimensions of the composite structure can be well controlled. With increasing the energy fluence of the infrared laser pulse, both the groove width and particle diameter are observed to reduce, while the measured spacing-to-diameter ratio of the nanoparticles tends to present an increasing tendency. A physical scenario is proposed to elucidate the underlying mechanisms: as the infrared femtosecond laser pulse pre-irradiates the target, the copper surface is triggered to display anomalous transient physical properties, on which the subsequently incident Gaussian blue laser pulse is spatially modulated into fringe-like energy depositions via the excitation of ultrafast surface plasmon. During the following relaxation processes, the periodically heated thin-layer regions can be transferred into the metastable liquid rivulets and then they break up into nanodroplet arrays owing to the modified Rayleigh-like instability. This investigation indicates a simple integrated approach for active designing and large-scale assembly of complexed functional nanostructures on bulk materials.

  12. Compact KGd(WO4)2 picosecond pulse-train synchronously pumped broadband Raman laser.

    PubMed

    Gao, Xiao Qiang; Long, Ming Liang; Meng, Chen

    2016-08-20

    We demonstrate an efficient approach to realizing an extra-cavity, synchronously pumped, stimulated Raman cascaded process under low repetition frequency (1 kHz) pump conditions. We also construct a compact KGd(WO4)2 (KGW) crystal picosecond Raman laser that has been configured as the developed method. A pulse-train green laser pumped the corresponding 70 mm long KGW crystal Raman cavity. The pulse train contains six pulses, about 800 ps separated, for every millisecond; thus, it can realize synchronous pumping between pump pulse and the pumped Raman cavity. The investigated system produced a collinear Raman laser output that includes six laser lines covering the 532 to 800 nm spectra. This is the first report on an all-solid-state, high-average-power picosecond collinear multi-wavelength (more than three laser components) laser to our knowledge. This method has never been reported on before in the synchronously pumped stimulated Raman scattering (SRS) realm.

  13. Pulse shaping on the Nova laser system

    SciTech Connect

    Lawson, J.K.; Speck, D.R.; Bibeau, C.; Weiland, T.L.

    1989-02-06

    Inertial confinement fusion requires temporally shaped pulses to achieve high gain efficiency. Recently, we demonstrated the ability to produce complex temporal pulse shapes at high power at 0.35 microns on the Nova laser system. 2 refs., 2 figs.

  14. Generation of modulated microchip laser pulses

    NASA Astrophysics Data System (ADS)

    Almabouada, F.; Aiadi, K. E.; Louhibi, D.

    2015-01-01

    Modulated 532 nm laser pulses were generated by a Nd:YVO4 microchip laser and a KTP crystal end-pumped by a 808 nm laser diode. The interest in such works arise from the efficiency of this type of laser in several applications. To obtain the desired type of the modulated laser pulses, the electrical circuit of the laser diode was designed so as to enable varying their driving signal and current values. Different modulated signals were used, such as square wave, sine wave, and burst mode pulses. Varying the peak drive current, the duty cycle, and the number of pulses allowed us to adjust the laser energy. For the burst mode experiment, the pulse energy obtained was about 1.2 μJ.

  15. Experimental demonstration of joule-level non-collinear optical parametric chirped-pulse amplification in yttrium calcium oxyborate.

    PubMed

    Yu, Lianghong; Liang, Xiaoyan; Li, Jinfeng; Wu, Anhua; Zheng, Yanqing; Lu, Xiaoming; Wang, Cheng; Leng, Yuxin; Xu, Jun; Li, Ruxin; Xu, Zhizhan

    2012-05-15

    In this Letter, we report on what is, to our knowledge, the first experimental demonstration of yttrium calcium oxyborate (YCOB) for joule-level and broadband non-collinear optical parametric chirped-pulse amplification centered at 800 nm. Based on a Ti:sapphire chirped-pulse amplification front end, an amplified signal energy of 3.36 J was generated with a pump of 35 J in the crystal. Compressed pulse duration of 44.3 fs, with a bandwidth of 49 nm, was achieved. The results confirm that YCOB crystal is another potential alternative as a final amplifier besides Ti:sapphire in a petawatt laser at 800 nm.

  16. Nanodissection of human chromosomes with near-infrared femtosecond laser pulses.

    PubMed

    König, K; Riemann, I; Fritzsche, W

    2001-06-01

    Near-infrared laser pulses of a compact 80-MHz femtosecond laser source at 800 nm, a mean power of 15-100 mW, 170-fs pulse width, and millisecond beam dwell times at the target have been used for multiphoton-mediated nanoprocessing of human chromosomes. By focusing of the laser beam with high-numerical-aperture objectives of a scanning microscope to diffraction-limited spots and with light intensities of terawatts per cubic centimeter, precise submicrometer holes and cuts in human chromosomes have been processed by single-point exposure and line scans. A minimum FWHM cut size of ~100 nm during a partial dissection of chromosome 1, which is below the diffraction-limited spot size, and a minimum material removal of ~0.003mum (3) were determined by a scanning-force microscope. The plasma-induced ablated material corresponds to ~1/400 of the chromosome 1 volume and to ~65x10(3) base pairs of chromosomal DNA. A complete dissection could be performed with FWHM cut sizes below 200 nm. High-repetition-frequency femtosecond lasers at low mean power in combination with high-numerical-aperture focusing optics appear therefore as appropriate noncontact tools for nanoprocessing of bulk and (or) surfaces of transparent materials such as chromosomes. In particular, the noninvasive inactivation of certain genomic regions on single chromosomes within living cells becomes possible.

  17. Propagation of a short-pulse laser-driven electron beam in matter

    NASA Astrophysics Data System (ADS)

    Volpe, L.; Batani, D.; Birindelli, G.; Morace, A.; Carpeggiani, P.; Xu, M. H.; Liu, F.; Zhang, Y.; Zhang, Z.; Lin, X. X.; Liu, F.; Wang, S. J.; Zhu, P. F.; Meng, L. M.; Wang, Z. H.; Li, Y. T.; Sheng, Z. M.; Wei, Z. Y.; Zhang, J.; Santos, J. J.; Spindloe, C.

    2013-03-01

    We studied the transport of an intense electron beam produced by high intensity laser pulses through metals and insulators. Targets were irradiated at two different intensities, 1017 W/cm2 and 1019 W/cm2, at the laser facility Xtreme Light XL-III in Beijing, a Ti:Sa laser source emitting 40 fs pulses at 800 nm. The main diagnostic was Cu-Kα fluorescence imaging. Images of Kα spots have been collected for those two laser intensities, for different target thickness, and for different materials. Experimental results are analyzed taking into account both collisional and collective effects as well as refluxing at the edge of the target. The target temperature is evaluated to be Tc ˜ 6 eV for intensity I = 1017 W/cm2 (for all the tested materials: plastic, aluminium, and copper), and Tc ˜ 60 eV in aluminium and 120 eV in titanium for intensity I = 1019 W/cm2.

  18. Generation of skewed laser pulses for laser wakefield accelerators

    NASA Astrophysics Data System (ADS)

    Toth, C.; Faure, J.; Geddes, C. G. R.; van Tilborg, J.; Leemans, W. P.

    2002-11-01

    The effect of asymmetric laser pulses on electron yield from a laser wakefield accelerator has been experimentally studied (W.P. Leemans et al., submitted to Phys. Rev. Lett.) using > 10^19 cm-3 plasmas and a 10 TW, > 45 fs, Ti:Al_2O3 laser. The non-Gaussian laser pulse shapes were controlled through non-linear chirp with a grating pair compressor. Pulses (76 fs FWHM) with a steep rise (positive skew) were found to significantly enhance the electron yield compared to pulses with a gentle rise (negative skew). These results demonstrate that laser wakefield accelerator can be optimized using skewed laser pulses. Controlling the skewness of laser pulses can be done by appropriate choice of the higher order spectral phase coefficients. Details on how this is done using non-linear chirp using grating compressor, as well as an acousto-optic system (DAZZLER) will be presented.

  19. 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.

  20. Optimisation de l'émission du continuum femtoseconde de lumière blanche entre 600 nm et 800 nm

    NASA Astrophysics Data System (ADS)

    Ramstein, S.; Mottin, S.

    2005-06-01

    Un dispositif de spectroscopie avec résolution du temps de vol des photons en milieu diffus a été développé. Celui-ci repose sur l'utilisation d'un continuum de lumière blanche généré par focalisation d'un laser amplifié (830 nm, 1 kHz, 0.5 W, 170 fs) dans de l'eau déminéralisée. Afin d'optimiser spectralement et en puissance la source blanche sur la fenêtre spectrale 600 800 nm, une étude de la mise en forme spatio-temporelle avant autofocalisation de l'impulsion laser par le milieu a été menée. Cette mise en forme est effectuée de manière spatiale en changeant la focale de la lentille de focalisation et de manière temporelle en changeant le taux de compression de l'impulsion. L'étude montre que le cône de lumière émise possède plus de puissance dans la fenêtre spectrale d'intérêt pour des focales longues. Sur la fenêtre 600-800 nm, le rendement énergétique intégré varie de 5%, avec une focalef=6cm, à 15%, avec une focale f = 30 cm. La mise en forme temporelle montre des effets similaires avec les mêmes ordres de grandeur.

  1. Liquid assisted ablation of zirconium for the growth of LIPSS at varying pulse durations and pulse energies by femtosecond laser irradiation

    NASA Astrophysics Data System (ADS)

    Bashir, Shazia; Rafique, M. Shahid; Husinsky, Wolfgang

    2015-04-01

    Investigations have been performed to explore the optimized conditions for the growth of Laser Induced Periodic Surface Structures (LIPSS) by varying pulse durations and pulse energies during ultrashort pulsed laser ablation of zirconium (Zr). The Ti: Sapphire laser with central wavelength of 800 nm, maximum pulse energy of 1 mJ is used to ablate Zr targets in the wet environment of ethanol. Scanning Electron Microscope (SEM) analysis was performed for central as well as the peripheral ablated area to characterize nano and microstructures formed on the Zr surface. Raman spectroscopy was carried out to explore the chemical and compositional changes produced in laser ablated Zr. In order to explore the effect of varying pulse durations ranging from 25 to 100 fs, targets were exposed to 1000 succeeding pulses keeping the pulse energy constant at 600 μJ. The micrographs of peripheral ablated areas reveal the formation of nano scale ripples or Laser Induced Periodic Surface Structures (LIPSS) for all pulse durations. LIPSS are more distinct and well organized for the shortest pulse duration of 25 fs. Whereas, LIPSS become diffused and indistinct with the increase in the pulse duration. This is the clear indication that shortest pulse duration (in our case 25 fs) is most suitable for the growth of nanoscale ripples. In order to explore the effect of varying pulse energies on the growth of LIPSS, targets were exposed to 1000 succeeding pulses with energies ranging from 200 μJ to 600 μJ for a pulse duration of 25 fs. In the peripheral ablated areas LIPSS are grown for all pulse energies. For the lowest pulse energy of 200 μJ, LIPSS are distinct and well defined. For intermediate energies of 300 and 400 μJ they become diffused and indistinct. For higher pulse energies of 500 and 600 μJ, their appearance again becomes well defined and distinct. For central ablated areas LIPSS are grown but their appearance diffuses with increasing pulse energies. For the highest pulse

  2. Implications of transient changes of optical and surface properties of solids during femtosecond laser pulse irradiation to the formation of laser-induced periodic surface structures

    NASA Astrophysics Data System (ADS)

    Bonse, J.; Rosenfeld, A.; Krüger, J.

    2011-04-01

    The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon wafer surfaces by linearly polarized Ti:sapphire femtosecond laser pulses (pulse duration 130 fs, central wavelength 800 nm) is studied experimentally and theoretically. In the experiments, so-called low-spatial frequency LIPSS (LSFL) were found with periods smaller than the laser wavelength and an orientation perpendicular to the polarization. The experimental results are analyzed by means of a new theoretical approach, which combines the widely accepted LIPSS theory of Sipe et al. with a Drude model, in order to account for transient (intra-pulse) changes of the optical properties of the irradiated materials. It is found that the LSFL formation is caused by the excitation of surface plasmon polaritons, SPPs, once the initially semiconducting material turns to a metallic state upon formation of a dense free-electron-plasma in the material and the subsequent interference between its electrical field with that of the incident laser beam resulting in a spatially modulated energy deposition at the surface. Moreover, the influence of the laser-excited carrier density and the role of the feedback upon the multi-pulse irradiation and its relation to the excitation of SPP in a grating-like surface structure is discussed.

  3. Chemical aerosol detection using femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Alexander, Dennis R.; Rohlfs, Mark L.; Stauffer, John C.

    1997-07-01

    Many chemical warfare agents are dispersed as small aerosol particles. In the past, most electro-optical excitation and detection schemes have used continuous or pulsed lasers with pulse lengths ranging from nanoseconds to microseconds. In this paper, we present interesting ongoing new results on femtosecond imaging and on the time dependent solutions to the scattering problem of a femtosecond laser pulse interacting with a single small aerosol particle. Results are presented for various incident pulse lengths. Experimental imaging results using femtosecond pulses indicate that the diffraction rings present when using nanosecond laser pulses for imaging are greatly reduced when femtosecond laser pulses are used. Results are presented in terms of the internal fields as a function of time and the optical size parameter.

  4. Analysis of Picosecond Pulsed Laser Melted Graphite

    DOE R&D Accomplishments Database

    Steinbeck, J.; Braunstein, G.; Speck, J.; Dresselhaus, M. S.; Huang, C. Y.; Malvezzi, A. M.; Bloembergen, N.

    1986-12-01

    A Raman microprobe and high resolution TEM have been used to analyze the resolidified region of liquid carbon generated by picosecond pulse laser radiation. From the relative intensities of the zone center Raman-allowed mode for graphite at 1582 cm{sup -1} and the disorder-induced mode at 1360 cm{sup -1}, the average graphite crystallite size in the resolidified region is determined as a function of position. By comparison with Rutherford backscattering spectra and Raman spectra from nanosecond pulsed laser melting experiments, the disorder depth for picosecond pulsed laser melted graphite is determined as a function of irradiating energy density. Comparisons of TEM micrographs for nanosecond and picosecond pulsed laser melting experiments show that the structure of the laser disordered regions in graphite are similar and exhibit similar behavior with increasing laser pulse fluence.

  5. Time-resolved SFG study of formate on a Ni( 1 1 1 ) surface under irradiation of picosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Noguchi, H.; Okada, T.; Onda, K.; Kano, S. S.; Wada, A.; Domen, K.

    2003-03-01

    Time-resolved sum-frequency generation spectroscopy was carried out on a deuterated formate (DCOO) adsorbed on Ni(1 1 1) surface to investigate the surface reaction dynamics under instantaneous surface temperature jump induced by the irradiation by picosecond laser pulses. The irradiation of pump pulse (800 nm) caused the rapid intensity decrease of both CD and OCO stretching modes of bridged formate on Ni(1 1 1). Different temporal behaviors of intensity recovery between these two vibrational modes were observed, i.e., CD stretching mode recovered faster than OCO. This is the first result to show that the dynamics of adsorbates on metals strongly depends on the observed vibrational mode. From the results of temperature and pump fluence dependence, we concluded that the observed intensity change was not due to the decomposition or desorption, but was induced by a non-thermal process.

  6. Hydrogen migration within a water molecule: formation of HD+ upon irradiation of HOD with intense, ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Mathur, Deepak; Dharmadhikari, Aditya K.; Dharmadhikari, Jayashree A.; Vasa, Parinda

    2017-08-01

    We have carried out velocity map imaging experiments on HOD molecules irradiated by 10 fs long pulses of intense (˜1 PW cm-2) laser light (800 nm). We have detected HD+ ions as a signature of unimolecular hydrogen migration within the water molecule; ion momentum maps measured at different laser polarizations yield evidence that such hydrogen migration occurs on ultrafast timescales. We have been able to utilize the momentum maps to deduce that (i) the HD+ ion that is formed is vibrationally excited, and (ii) that the electronic state of the precursor HOD2+ dication has an essentially linear geometrical structure with elongated O-H and O-D bonds. Our results are in agreement with expectations from ab initio quantum chemical computations of potential energy surfaces of the lowest-energy states of HOD, HOD+ and HOD2+.

  7. Ultrashort Laser Pulses in Physics and Chemistry

    SciTech Connect

    Naskrecki, Ryszard

    2007-11-26

    Study of physical and chemical events accompanying light-matter interaction in pico- and femtosecond time scale have become possible with the use of ultrashort laser pulses. With the progress in generation of ultrashort laser pulses, the ultrafast optical spectroscopy, as a tool for dynamic study, is still evolving rapidly.

  8. Flexible pulse-controlled fiber laser

    PubMed Central

    Liu, Xueming; Cui, Yudong

    2015-01-01

    Controlled flexible pulses have widespread applications in the fields of fiber telecommunication, optical sensing, metrology, and microscopy. Here, we report a compact pulse-controlled all-fiber laser by exploiting an intracavity fiber Bragg grating (FBG) system as a flexible filter. The width and wavelength of pulses can be tuned independently by vertically and horizontally translating a cantilever beam, respectively. The pulse width of the laser can be tuned flexibly and accurately from ~7 to ~150 ps by controlling the bandwidth of FBG. The wavelength of pulse can be tuned precisely with the range of >20 nm. The flexible laser is precisely controlled and insensitive to environmental perturbations. This fiber-based laser is a simple, stable, and low-cost source for various applications where the width-tunable and/or wavelength-tunable pulses are necessary. PMID:25801546

  9. Flexible pulse-controlled fiber laser

    NASA Astrophysics Data System (ADS)

    Liu, Xueming; Cui, Yudong

    2015-03-01

    Controlled flexible pulses have widespread applications in the fields of fiber telecommunication, optical sensing, metrology, and microscopy. Here, we report a compact pulse-controlled all-fiber laser by exploiting an intracavity fiber Bragg grating (FBG) system as a flexible filter. The width and wavelength of pulses can be tuned independently by vertically and horizontally translating a cantilever beam, respectively. The pulse width of the laser can be tuned flexibly and accurately from ~7 to ~150 ps by controlling the bandwidth of FBG. The wavelength of pulse can be tuned precisely with the range of >20 nm. The flexible laser is precisely controlled and insensitive to environmental perturbations. This fiber-based laser is a simple, stable, and low-cost source for various applications where the width-tunable and/or wavelength-tunable pulses are necessary.

  10. Heating of solid targets with laser pulses

    NASA Technical Reports Server (NTRS)

    Bechtel, J. H.

    1975-01-01

    Analytical and numerical solutions to the heat-conduction equation are obtained for the heating of absorbing media with pulsed lasers. The spatial and temporal form of the temperature is determined using several different models of the laser irradiance. Both surface and volume generation of heat are discussed. It is found that if the depth of thermal diffusion for the laser-pulse duration is large compared to the optical-attenuation depth, the surface- and volume-generation models give nearly identical results. However, if the thermal-diffusion depth for the laser-pulse duration is comparable to or less than the optical-attenuation depth, the surface-generation model can give significantly different results compared to the volume-generation model. Specific numerical results are given for a tungsten target irradiated by pulses of different temporal durations and the implications of the results are discussed with respect to the heating of metals by picosecond laser pulses.

  11. Relativistic laser pulse compression in magnetized plasmas

    SciTech Connect

    Liang, Yun; Sang, Hai-Bo Wan, Feng; Lv, Chong; Xie, Bai-Song

    2015-07-15

    The self-compression of a weak relativistic Gaussian laser pulse propagating in a magnetized plasma is investigated. The nonlinear Schrödinger equation, which describes the laser pulse amplitude evolution, is deduced and solved numerically. The pulse compression is observed in the cases of both left- and right-hand circular polarized lasers. It is found that the compressed velocity is increased for the left-hand circular polarized laser fields, while decreased for the right-hand ones, which is reinforced as the enhancement of the external magnetic field. We find a 100 fs left-hand circular polarized laser pulse is compressed in a magnetized (1757 T) plasma medium by more than ten times. The results in this paper indicate the possibility of generating particularly intense and short pulses.

  12. Pulse shaper assisted short laser pulse characterization

    NASA Astrophysics Data System (ADS)

    Galler, A.; Feurer, T.

    2008-03-01

    We demonstrate that a pulse shaper is able to simultaneously act as an optical waveform generator and a short pulse characterization device when combined with an appropriate nonlinear element. We present autocorrelation measurements and their frequency resolved counterparts. We show that control over the carrier envelope phase allows continuous tuning between an intensity-like and an interferometric autocorrelation. By changing the transfer function other measurement techniques, for example STRUT, are easily realized without any modification of the optical setup.

  13. Temperature dependence of nanosecond laser pulse thresholds of melanosome and microsphere microcavitation

    NASA Astrophysics Data System (ADS)

    Schmidt, Morgan S.; Kennedy, Paul K.; Noojin, Gary D.; Thomas, Robert J.; Rockwell, Benjamin A.

    2016-01-01

    Melanosome microcavitation is the threshold-level retinal pigment epithelium (RPE) damage mechanism for nanosecond (ns) pulse exposures in the visible and near-infrared (NIR). Thresholds for microcavitation of isolated bovine RPE melanosomes were determined as a function of temperature (20 to 85°C) using single ns laser pulses at 532 and 1064 nm. Melanosomes were irradiated using a 1064-nm Q-switched Nd:YAG (doubled for 532-nm irradiation). For comparison to melanosome data, a similar temperature (20 to 65°C) dependence study was also performed for 532 nm, ns pulse exposures of black polystyrene microbeads. Results indicated a decrease in the microcavitation average radiant exposure threshold with increasing sample temperature for both 532- and 1064-nm single pulse exposures of melanosomes and microbeads. Threshold data and extrapolated nucleation temperatures were used to estimate melanosome absorption coefficients in the visible and NIR, and microbead absorption coefficients in the visible, indicating that melanin is a better absorber of visible light than black polystyrene. The NIR melanosome absorption coefficients ranged from 3713 cm-1 at 800 nm to 222 cm-1 at 1319 nm. These data represent the first temperature-dependent melanosome microcavitation study in the NIR and provide additional information for understanding melanosome microcavitation threshold dependence on wavelength and ambient temperature.

  14. Nonlinear dynamics of additive pulse modelocked lasers

    SciTech Connect

    Sucha, G.; Bolton, S.R.; Chemla, D.S.

    1995-04-01

    Nonlinear dynamics have been studied in a number of modelocked laser systems, primarily in actively modelocked systems. However, less attention has been paid to the dynamics of passively modelocked laser systems. With the recent revolutionary advances in femtosecond modelocked laser technology, the understanding of instabilities and dynamics in passively modelocked lasers is an important issue. Here, the authors present experimental and numerical studies of the dynamics of an additive-pulse modelocked (APM) color-center laser.

  15. Generation of an isolated sub-40-as pulse using two-color laser pulses: Combined chirp effects

    SciTech Connect

    Feng, Liqiang; Chu, Tianshu

    2011-11-15

    In this paper, we theoretically discuss the combined chirp effects on the isolated attosecond generation when a model Ar is exposed to an intense 5-fs, 800-nm fundamental chirped pulse combined with a weak 10-fs, 1200-nm controlling chirped pulse. It shows that for the case of the chirp parameters {beta}{sub 1} = 6.1 (corresponding to the 800-nm field) and {beta}{sub 2} = 4.0 (corresponding to the 1200-nm field), both the harmonic cutoff energy and the supercontinuum can be remarkably extended resulting in a 663-eV bandwidth. Moreover, due to the introduction of the chirps, the short quantum path is selected to contribute to the harmonic spectrum. Finally, by superposing a properly selected harmonic spectrum in the supercontinuum region, an isolated pulse as short as 31 as (5 as) is generated without (with) phase compensation.

  16. Optical Kerr effect of tRNA solution induced by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Kucia, Weronika E.; Sharma, Gargi; Joseph, Cecil S.; Sarbak, Szymon; Oliver, Cameron; Dobek, Andrzej; Giles, Robert H.

    2016-10-01

    The optical Kerr effect (OKE) in a transfer ribonucleic acid (tRNA) solution induced by femtosecond pulses of linearly polarized pump light (λi = 800 nm) and sounded by probe light (λp = 800 nm) was studied. The measurements were performed to find nonlinear optical parameters describing a single molecule (molecular Kerr constant K, mean nonlinear third order optical polarizability cpi) and to compare them with our previous OKE results obtained in ns and ps time range. The OKE experiment has proven to be an efficient method to obtain the nonlinear parameters of single molecules in solution, which reflects dynamic structure changes.

  17. Super-achromatic microprobe for ultrahigh-resolution endoscopic OCT imaging at 800 nm (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yuan, Wu; Alemohammad, Milad; Yu, Xiaoyun; Yu, Shaoyong; Li, Xingde

    2016-03-01

    In this paper, we report a super-achromatic microprobe made with fiber-optic ball lens to enable ultrahigh-resolution endoscopic OCT imaging. An axial resolution of ~2.4 µm (in air) can be achieved with a 7-fs Ti:Sapphire laser. The microprobe has minimal astigmatism which affords a high transverse resolution of ~5.6 µm. The miniaturized microprobe has an outer diameter of ~520 µm including the encasing metal guard and can be used to image small luminal organs. The performance of the ultrahigh-resolution OCT microprobe was demonstrated by imaging rat esophagus, guinea pig esophagus, and mouse rectum in vivo.

  18. Identifying spatially asymmetric high-order harmonic emission in the falling edge of an intense laser pulse

    NASA Astrophysics Data System (ADS)

    Vafaee, M.; Ahmadi, H.; Maghari, A.

    2017-01-01

    Two different induced effects of a laser falling edge on high-order harmonic generation (HHG) are resolved by numerically solving the full-dimensional electronic time-dependent Schrödinger equation beyond the Born-Oppenheimer approximation. The harmonic spectrum of {{{H}}}2+ and {{{T}}}2+ isotopes are compared to see the effects of a four-cycle falling edge of a 800 nm, 15-cycle trapezoidal laser pulse of I = 3 × {10}14 W cm-2 intensity on harmonic emission spectrum. The harmonic emission at the laser falling part is negligible for {{{H}}}2+ due to ionization suppression, but considerable for {{{T}}}2+. The falling edge of the laser pulse induces two effects on the HHG in {{{T}}}2+. The first well-known effect is non-adiabatic frequency redshift of generated odd-order harmonics. The second unknown one is spatially asymmetric harmonic emission, which appears as even harmonic orders. In order to clarify this new effect, spatial distribution of HHG and resolving HHG into different components are demonstrated. Asymmetric emission appears for both atoms and molecules as long as the harmonic emission of either the rising or falling edge of an intense trapezoidal or non-trapezoidal laser pulse is dominant.

  19. Pulsed laser nitriding of uranium

    NASA Astrophysics Data System (ADS)

    Zhang, Yongbin; Meng, Daqiao; Xu, Qinying; Zhang, Youshou

    2010-02-01

    Pulsed laser nitriding offers several advantages such as high nitrogen concentration, low matrix temperature, fast treatment, simple vacuum chamber and precise position control compare to ion implantation, which is favorable for radioactive material passivation. In this work, uranium metal was nitrided using an excimer laser for the first time. The nitrided layers are characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The nitride layer is composed mainly of UN and U 2N 3 and depends on nitriding process. The amount of nitride increases with energy density and pressure. The irradiated area has a wavy structure which increases the roughness, while scratches and asperities caused by sand paper polishing were eliminated. Scan speed has a profound influence on the nitride layer, at low speed U 2N 3 is more likely to form and the nitride layer tends to crack. XPS analysis shows that nitrogen has diffused into interior, while oxygen is only present on the surface. Ambient and humid-hot corrosion tests show the nitrided sample has good anticorrosion property.

  20. Pulse circuit apparatus for gas discharge laser

    DOEpatents

    Bradley, Laird P.

    1980-01-01

    Apparatus and method using a unique pulse circuit for a known gas discharge laser apparatus to provide an electric field for preconditioning the gas below gas breakdown and thereafter to place a maximum voltage across the gas which maximum voltage is higher than that previously available before the breakdown voltage of that gas laser medium thereby providing greatly increased pumping of the laser.

  1. High-power picosecond laser pulse recirculation.

    PubMed

    Shverdin, M Y; Jovanovic, I; Semenov, V A; Betts, S M; Brown, C; Gibson, D J; Shuttlesworth, R M; Hartemann, F V; Siders, C W; Barty, C P J

    2010-07-01

    We demonstrate a nonlinear crystal-based short pulse recirculation cavity for trapping the second harmonic of an incident high-power laser pulse. This scheme aims to increase the efficiency and flux of Compton-scattering-based light sources. We demonstrate up to 40x average power enhancement of frequency-doubled submillijoule picosecond pulses, and 17x average power enhancement of 177 mJ, 10 ps, 10 Hz pulses.

  2. High Power Picosecond Laser Pulse Recirculation

    SciTech Connect

    Shverdin, M Y; Jovanovic, I; Semenov, V A; Betts, S M; Brown, C; Gibson, D J; Shuttlesworth, R M; Hartemann, F V; Siders, C W; Barty, C P

    2010-04-12

    We demonstrate a nonlinear crystal-based short pulse recirculation cavity for trapping the second harmonic of an incident high power laser pulse. This scheme aims to increase the efficiency and flux of Compton-scattering based light sources. We demonstrate up to 36x average power enhancement of frequency doubled sub-millijoule picosecond pulses, and 17x average power enhancement of 177 mJ, 10 ps, 10 Hz pulses.

  3. Intense isolated attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses

    SciTech Connect

    Ma, Guangjin; Dallari, William; Borot, Antonin; Tsakiris, George D.; Veisz, Laszlo; Krausz, Ferenc; Yu, Wei

    2015-03-15

    We have performed a systematic study through particle-in-cell simulations to investigate the generation of attosecond pulse from relativistic laser plasmas when laser pulse duration approaches the few-cycle regime. A significant enhancement of attosecond pulse energy has been found to depend on laser pulse duration, carrier envelope phase, and plasma scale length. Based on the results obtained in this work, the potential of attaining isolated attosecond pulses with ∼100 μJ energy for photons >16 eV using state-of-the-art laser technology appears to be within reach.

  4. Generation of laser pulse trains for tests of multi-pulse laser wakefield acceleration

    NASA Astrophysics Data System (ADS)

    Shalloo, R. J.; Corner, L.; Arran, C.; Cowley, J.; Cheung, G.; Thornton, C.; Walczak, R.; Hooker, S. M.

    2016-09-01

    In multi-pulse laser wakefield acceleration (MP-LWFA) a plasma wave is driven by a train of low-energy laser pulses separated by the plasma period, an approach which offers a route to driving plasma accelerators with high efficiency and at high pulse repetition rates using emerging technologies such as fibre and thin-disk lasers. Whilst these laser technologies are in development, proof-of-principle tests of MP-LWFA require a pulse train to be generated from a single, high-energy ultrafast pulse. Here we demonstrate the generation of trains of up to 7 pulses with pulse separations in the range 150-170 fs from single 40 fs pulses produced by a Ti:sapphire laser.

  5. MOPA pulsed fiber laser for silicon scribing

    NASA Astrophysics Data System (ADS)

    Yang, Limei; Huang, Wei; Deng, Mengmeng; Li, Feng

    2016-06-01

    A 1064 nm master oscillator power amplifier (MOPA) pulsed fiber laser is developed with flexible control over the pulse width, repetition frequency and peak power, and it is used to investigate the dependence of mono-crystalline silicon scribe depth on the laser pulse width, scanning speed and repeat times. Experimental results indicate that long pulses with low peak powers lead to deep ablation depths. We also demonstrate that the ablation depth grows fast with the scanning repeat times at first and progressively tends to be saturated when the repeat times reach a certain level. A thermal model considering the laser pulse overlapping effect that predicts the silicon temperature variation and scribe depth is employed to verify the experimental conclusions with reasonably close agreement. These conclusions are of great benefits to the optimization of the laser material processing with high efficiency.

  6. Ultrashort-pulsed laser microstructuring of diamond

    NASA Astrophysics Data System (ADS)

    Shirk, Michael D.; Molian, Pal; Wang, Cai; Ho, Kai M.; Malshe, Ajay P.

    2000-11-01

    Precision microfabrication of diamond has many applications in the fields of microelectronics and cutting tools. In this work, and ultra-short pulsed Ti: Sapphire laser was used to perform patterning, hold drilling, and scribing of synthetic and CVD diamonds. Scanning electron microscopy, atomic force microscopy, profilometry, and Raman spectroscopy were employed to characterize the microstructures. A tight-binding molecular dynamics (TBMD) model was used to investigate atomic movements during ablation and predict thresholds for ablation. The ultra- short pulsed laser generated holes and grooves that were nearly perfect with smooth edges, little collateral thermal damage and recast layer. The most exciting observation was the absence of graphite residue that always occurs in the longer-pulsed laser machining. The ablation threshold for ultra-short pulsed laser was two orders of magnitude lower than that of longer-pulsed laser. Finite-difference thermal modeling showed that ultra-short pulses raised the electron temperatures of diamond in excess of 100,ooo K due to multiphoton absorption, absence of hydrodynamic motion, and lack of time for energy transfer from electrons to the lattice during the pulse duration. TBMD simulations, carried out on (111) and (100) diamond surfaces, revealed that ultra-short pulses peel carbon atoms layer-by -layer from the surface, leaving a smooth surface after ablation. However, longer pulses cause thermal melting resulting in graphite residue that anchors to the diamond surface following ablation.

  7. Picosecond pulsed diode ring laser gyroscope

    SciTech Connect

    Rosker, M.J.; Christian, W.R.; McMichael, I.C.

    1994-12-31

    An external ring cavity containing as its active medium a pair of InGaAsP diodes is modelocked to produce picosecond pulses. In such a laser, a small frequency difference proportional to the nonreciprocal phase shift (resulting from, e.g., the Sagnac effect) can be observed by beating together the counter propagating laser arms; the device therefore acts as a rotating sensor. In contrast to a conventional (cw) ring laser gyroscope, the pulsed gyroscope can avoid gain competition, thereby enabling the use of homogeneously broadened gain media like semiconductor diodes. Temporal separation of the pulses within the cavity also discriminates against frequency locking of the lasers. The picosecond pulsed diode ring laser gyroscope is reviewed. Both active and passive modelocking are discussed.

  8. Ultrafast pulsed Bessel beams for enhanced laser ablation of bone tissue for applications in LASSOS

    NASA Astrophysics Data System (ADS)

    Ashforth, Simon A.; Oosterbeek, Reece N.; Simpson, M. Cather

    2017-02-01

    Using a femtosecond pulsed laser system (pulse width = 100fs, repetition rate = 500 Hz, λ=800nm), a zero-order Bessel beam was generated using a LCOS-Spatial light modulator (LCOS-SLM) with an effective cone angle of 4.56°. Ablation threshold studies of fresh bovine and ovine load bearing cortical bone was identified using the method of least damage and found to be identical at φth = 0.15 +/- 0.03 J cm-2, irrespective of the target species. The ablation threshold is significantly reduced compared to the ablation threshold determined for Gaussian beams in bovine and ovine cortical bone (Load Bearing: φth = 0.91 +/- 0.03 J cm-2, Skull: φth = 1.19 +/- 0.06 J cm-2). Incubation effects were investigated and the incubation coefficient was determined to be ζ = 0.93 +/- 0.06, indicating no incubation effects are present. The relationship between tissue removal and the number of pulses applied was explored. By altering the translation rate of the sample under the Bessel region of the incident laser, the number of pulses applied at each point along the linear ablation features was varied. Cross sections of ablation features were measured using scanning electron microscopy (SEM) and maximum depths of the ablation features measured. The ablation rate of bovine and ovine cortical was found to be 2.69 - 13.21 +/- 0.05 μm pulse-1 and 2.49 - 12.79 +/- 0.03 μm pulse-1 respectively for fluence values ranging from 25.0 - 2.5 Jcm-2, significantly higher than those of Gaussian beams. Structural analysis of the ablation features using SEM and optical microscopy showed no signs of heat affected zone (HAZ) in the form of thermal shockwave cracking, molten debris deposition or charring of the tissue.

  9. Synthesized femtosecond laser pulse source for two-wavelength contouring with simultaneously recorded digital holograms.

    PubMed

    Hansel, Thomas; Steinmeyer, Günter; Grunwald, Ruediger; Falldorf, Claas; Bonitz, Jens; Kaufmann, Christian; Kebbel, Volker; Griebner, Uwe

    2009-02-16

    A dual-wavelength femtosecond laser pulse source and its application for digital holographic single-shot contouring are presented. The synthesized laser source combines sub-picosecond time scales with a wide reconstruction range. A center wavelength distance of the two separated pulses of only 15 nm with a high contrast was demonstrated by spectral shaping of the 50 nm broad seed spectrum centered at 800 nm. Owing to the resulting synthetic wavelength, the scan depth range without phase ambiguity is extended to the 100-microm-range. Single-shot dual-wavelength imaging is achieved by using two CMOS cameras in a Twyman-Green interferometer, which is extended by a polarization encoding sequence to separate the holograms. The principle of the method is revealed, and experimental results concerning a single axis scanner mirror operating at a resonance frequency of 0.5 kHz are presented. Within the synthetic wavelength, the phase difference information of the object was unambiguously retrieved and the 3D-shape calculated. To the best of our knowledge, this is the first time that single-shot two-wavelength contouring on a sub-ps time scale is reported.

  10. Injection locked oscillator system for pulsed metal vapor lasers

    DOEpatents

    Warner, Bruce E.; Ault, Earl R.

    1988-01-01

    An injection locked oscillator system for pulsed metal vapor lasers is disclosed. The invention includes the combination of a seeding oscillator with an injection locked oscillator (ILO) for improving the quality, particularly the intensity, of an output laser beam pulse. The present invention includes means for matching the first seeder laser pulses from the seeding oscillator to second laser pulses of a metal vapor laser to improve the quality, and particularly the intensity, of the output laser beam pulse.

  11. Simulation of Double-Pulse Laser Ablation

    NASA Astrophysics Data System (ADS)

    Povarnitsyn, Mikhail E.; Itina, Tatian E.; Khishchenko, Konstantin V.; Levashov, Pavel R.

    2010-10-01

    We investigate the physical reasons of a strange decrease in the ablation depth observed in femtosecond double-pulse experiments with increasing delay between the pulses. Two ultrashort pulses of the same energy produce the crater which is less than that created by a single pulse. Hydrodynamicsimulation shows that the ablation mechanism is suppressed 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 modeling of the double-pulse ablation for different delays between pulses confirms this explanation.

  12. Compositional dependent response of silica-based glasses to femtosecond laser pulse irradiation

    NASA Astrophysics Data System (ADS)

    Seuthe, Thomas; Grehn, Moritz; Mermillod-Blondin, Alexandre; Bonse, Jörn; Eberstein, Markus

    2013-11-01

    Femtosecond laser pulse irradiation of inorganic glasses allows a selective modification of the optical properties with very high precision. This results in the possibility for the production of three-dimensional functional optical elements in the interior of glass materials, such as optical data storage, waveguide writing, etc. The influence of the chemical glass composition to the response upon ultrashort laser irradiation has not been studied systematically. For that, simple silicabased model glasses composed of systematically varying alkaline- and earth-alkaline components were prepared, irradiated on the surface and in the volume with single fs-laser pulses (~130 fs, 800 nm), and were subsequently analyzed by means of micro-Raman spectroscopy and quantitative phase contrast microscopy in order to account for changes in the glass structure and for alterations of the optical refractive index, respectively. The Raman spectroscopic studies of the laser-irradiated spots revealed no change in the average binding configuration (the so called Q-structure), but local changes of bond-angles and bond-lengths within the glass structure structure. Those changes are explained by structural relaxation of the glass network due to densification caused by a transient laser-induced plasma generation and the following shock wave and other thermal phenomena. Glasses with a low amount of network modifiers show changes in the Si-O network while glasses with a high amount of network modifiers react primarily via variation of the nonbridging oxygen ions. The results are discussed in terms of possible structural response mechanisms and conclusions are outlined regarding glass compositions with technical suitability for fs-laser modifications.

  13. Pulsed Laser Cladding of Ni Based Powder

    NASA Astrophysics Data System (ADS)

    Pascu, A.; Stanciu, E. M.; Croitoru, C.; Roata, I. C.; Tierean, M. H.

    2017-06-01

    The aim of this paper is to optimize the operational parameters and quality of one step Metco Inconel 718 atomized powder laser cladded tracks, deposited on AISI 316 stainless steel substrate by means of a 1064 nm high power pulsed laser, together with a Precitec cladding head manipulated by a CLOOS 7 axes robot. The optimization of parameters and cladding quality has been assessed through Taguchi interaction matrix and graphical output. The study demonstrates that very good cladded layers with low dilution and increased mechanical proprieties could be fabricated using low laser energy density by involving a pulsed laser.

  14. Limiting of microjoule femtosecond pulses in air-guided modes of a hollow photonic-crystal fiber

    SciTech Connect

    Konorov, S.O.; Serebryannikov, E.E.; Sidorov-Biryukov, D.A.; Bugar, I.; Chorvat, D. Jr.; Chorvat, D.; Bloemer, M.J.; Scalora, M.; Miles, R.B.; Zheltikov, A.M.

    2004-08-01

    Self-phase-modulation-induced spectral broadening of laser pulses in air-guided modes of hollow photonic-crystal fibers (PCFs) is shown to allow the creation of fiber-optic limiters for high-intensity ultrashort laser pulses. The performance of PCF limiters is analyzed in terms of elementary theory of self-phase modulation. Experiments performed with 100 fs microjoule pulses of 800 nm Ti:sapphire laser radiation demonstrate the potential of hollow PCFs as limiters for 10 MW ultrashort laser pulses and show the possibility to switch the limiting level of output radiation energy by guiding femtosecond pulses in different PCF modes.

  15. Fiber Laser Front Ends for High Energy, Short Pulse Lasers

    SciTech Connect

    Dawson, J; Messerly, M; Phan, H; Siders, C; Beach, R; Barty, C

    2007-06-21

    We are developing a fiber laser system for short pulse (1-10ps), high energy ({approx}1kJ) glass laser systems. Fiber lasers are ideal for these systems as they are highly reliable and enable long term stable operation.

  16. Short Pulse Laser Applications Design

    SciTech Connect

    Town, R J; Clark, D S; Kemp, A J; Lasinski, B F; Tabak, M

    2008-02-11

    We are applying our recently developed, LDRD-funded computational simulation tool to optimize and develop applications of Fast Ignition (FI) for stockpile stewardship. This report summarizes the work performed during a one-year exploratory research LDRD to develop FI point designs for the National Ignition Facility (NIF). These results were sufficiently encouraging to propose successfully a strategic initiative LDRD to design and perform the definitive FI experiment on the NIF. Ignition experiments on the National Ignition Facility (NIF) will begin in 2010 using the central hot spot (CHS) approach, which relies on the simultaneous compression and ignition of a spherical fuel capsule. Unlike this approach, the fast ignition (FI) method separates fuel compression from the ignition phase. In the compression phase, a laser such as NIF is used to implode a shell either directly, or by x rays generated from the hohlraum wall, to form a compact dense ({approx}300 g/cm{sup 3}) fuel mass with an areal density of {approx}3.0 g/cm{sup 2}. To ignite such a fuel assembly requires depositing {approx}20kJ into a {approx}35 {micro}m spot delivered in a short time compared to the fuel disassembly time ({approx}20ps). This energy is delivered during the ignition phase by relativistic electrons generated by the interaction of an ultra-short high-intensity laser. The main advantages of FI over the CHS approach are higher gain, a lower ignition threshold, and a relaxation of the stringent symmetry requirements required by the CHS approach. There is worldwide interest in FI and its associated science. Major experimental facilities are being constructed which will enable 'proof of principle' tests of FI in integrated subignition experiments, most notably the OMEGA-EP facility at the University of Rochester's Laboratory of Laser Energetics and the FIREX facility at Osaka University in Japan. Also, scientists in the European Union have recently proposed the construction of a new FI

  17. The interaction of intense ultrashort laser pulses with cryogenic He planar jets

    NASA Astrophysics Data System (ADS)

    Shihab, M.; Bornath, Th; Redmer, R.

    2017-04-01

    We study the interaction of intense ultrashort laser pulses with cryogenic He planar jets, i.e., slabs, using 2D3V relativistic particle-in-cell simulations. Of particular interest are laser intensities ({10}15{--}{10}20) W cm‑2, pulse lengths ≤100 fs, and the wave length regime ∼800 nm for which the slabs are initially transparent and subsequently inhomogeneously ionized. Pulses ≥slant {10}16 W cm‑2 are found to drive ionization along the slab and outside the laser spot, the ionization front propagates along the slab at a considerable fraction of the speed of light. Within the ionized region, there is a highly transient field which is a result of the charge-neutralizing disturbance at the slab-vacuum interface and which may be interpreted in terms of a two-surface-wave decay. The ionized region is predicted to reach solid-like densities and temperatures of few to hundreds of eV, i.e., it belongs to warm and hot dense matter regimes. Such extreme conditions are relevant for high-energy densities as found, e.g., in shock-wave experiments and inertial confinement fusion studies. The temporal evolution of the ionization is studied considering theoretically a pump–probe x-ray Thomson scattering scheme. We observe plasmon and non-collective modes that are generated in the slab, and their amplitude is proportional to the ionized volume. Our theoretical findings could be tested at free-electron laser facilities such as FLASH and the European XFEL (Hamburg) and the LCLS (Stanford).

  18. Role of the temperature dynamics in formation of nanopatterns upon single femtosecond laser pulses on gold

    NASA Astrophysics Data System (ADS)

    Gurevich, Evgeny L.; Levy, Yoann; Gurevich, Svetlana V.; Bulgakova, Nadezhda M.

    2017-02-01

    In this paper we investigate the role of two-temperature heating dynamics for formation of periodic structures on metal surfaces exposed to single ultrashort laser pulses.The results of two-temperature model (TTM) two-dimensional simulations are presented on the irradiation of gold by a single 800-nm femtosecond laser pulse the intensity of which is modulated in order to reproduce an initial electron temperature perturbation, which can arise from incoming and scattered surface wave interference. The growing (unstable) modes of the lattice temperature distribution along the surface may be significant in the laser induced periodic surface structures formation. After the end of the laser pulse and before the complete coupling between lattice and electrons occurs, the evolution of the amplitude of the subsequent modulation in the lattice temperature reveals different tendencies depending on the spatial period of the initial modulation. This instabilitylike behavior is shown to arise due to the perturbation of the electronic temperature which relaxes slower for bigger spatial periods and thus imparts more significant modulations to the lattice temperature. Small spatial periods of the order of 100 nm and smaller experience stabilization and fast decay from the more efficient lateral heat diffusion which facilitates the relaxation of the electronic temperature amplitude due to in-depth diffusion. An analytical instability analysis of a simplified version of the TTM set of equations supports the lattice temperature modulation behavior obtained in the simulations and reveals that in-depth diffusion length is a determining parameter in the dispersion relation of unstable modes. Finally, it is discussed how the change in optical properties can intensify the modulation-related effects.

  19. High-performance laser processing using manipulated ultrafast laser pulses

    NASA Astrophysics Data System (ADS)

    Sugioka, Koji; Cheng, Ya; Xu, Zhizhan; Hanada, Yasutaka; Midorikawa, Katsumi

    2012-07-01

    We employ manipulated ultrafast laser pulses to realize microprocessing with high-performance. Efficient microwelding of glass substrates by irradiation by a double-pulse train of ultrafast laser pulses is demonstrated. The bonding strength of two photostructurable glass substrates welded by double-pulse irradiation was evaluated to be 22.9 MPa, which is approximately 22% greater than that of a sample prepared by conventional irradiation by a single pulse train. Additionally, the fabrication of hollow microfluidic channels with a circular cross-sectional shape embedded in fused silica is realized by spatiotemporally focusing the ultrafast laser beam. We show both theoretically and experimentally that the spatiotemporal focusing of ultrafast laser beam allows for the creation of a three-dimensionally symmetric spherical peak intensity distribution at the focal spot.

  20. Pulsed laser irradiation of metal multilayers.

    SciTech Connect

    Adams, David Price; McDonald, Joel Patrick

    2010-11-01

    Vapor-deposited, exothermic metal-metal multilayer foils are an ideal class of materials for detailed investigations of pulsed laser-ignited chemical reactions. Created in a pristine vacuum environment by sputter deposition, these high purity materials have well-defined reactant layer thicknesses between 1 and 1000 nm, minimal void density and intimate contact between layers. Provided that layer thicknesses are made small, some reactive metal-metal multilayer foils can be ignited at a point by laser irradiation and exhibit subsequent high-temperature, self-propagating synthesis. With this presentation, we describe the pulsed laser-induced ignition characteristics of a single multilayer system (equiatomic Al/Pt) that exhibits self-propagating synthesis. We show that the thresholds for ignition are dependent on (i) multilayer design and (ii) laser pulse duration. With regard to multilayer design effects on ignition, there is a large range of multilayer periodicity over which ignition threshold decreases as layer thicknesses are made small. We attribute this trend of decreased ignition threshold to reduced mass transport diffusion lengths required for rapid exothermic mixing. With regard to pulse duration effects, we have determined how ignition threshold of a single Al/Pt multilayer varies with pulse duration from 10{sup -2} to {approx} 10{sup -13} sec (wavelength and spot size are held constant). A higher laser fluence is required for ignition when using a single laser pulse {approx} 100 fs or 1 ps compared with nanosecond or microsecond exposure, and we attribute this, in part, to the effects of reactive material being ablated when using the shorter pulse durations. To further understand these trends and other pulsed laser-based processes, our discussion concludes with an analysis of the heat-affected depths in multilayers as a function of pulse duration.

  1. Multiple laser pulse ignition method and apparatus

    DOEpatents

    Early, James W.

    1998-01-01

    Two or more laser light pulses with certain differing temporal lengths and peak pulse powers can be employed sequentially to regulate the rate and duration of laser energy delivery to fuel mixtures, thereby improving fuel ignition performance over a wide range of fuel parameters such as fuel/oxidizer ratios, fuel droplet size, number density and velocity within a fuel aerosol, and initial fuel temperatures.

  2. Laser glass marking: influence of pulse characteristics

    NASA Astrophysics Data System (ADS)

    Rolo, Ana; Coelho, João; Pires, Margarida

    2005-09-01

    Laser glass marking is currently used in several glass materials for different purposes, such as bar codes for product tracking, brand logos or just decoration. Systems with a variety of different laser sources, with inherent power ranges, wavelengths and pulse regimes have been used, namely CO2, Nd:YAG, Excimer, Ti-Sapphire lasers. CO2 Lasers systems, although being a reliable tool for materials processing, and very compact in the case of sealed low power lasers, are usually associated with a localized thermal loading on the material, causing brittle materials like glass to crack around the irradiated area. In this experimental study a pulsed CO2 laser was used to direct marking the glass surface. The temporal characteristics of the laser pulse--pulse length, period and duty cycle were varied, and glass materials with different thermal properties were used in order to correlate the marking process--cracking or softening with or without material removal with the laser and material characteristics. Glass materials with major industrial application, such as soda-lima, borosilicate (PYREX) glasses and crystal have been investigated. Laser marked areas have been characterized in terms of surface optical properties, like diffuse and direct reflectance and transmittance for white light, directly related with marked surface quality.

  3. Pulsed lasers in dentistry: sense or nonsense?

    NASA Astrophysics Data System (ADS)

    Koort, Hans J.; Frentzen, Matthias

    1991-05-01

    The great interest in the field of laser applications in dentistry provokes the question, if all these new techniques may really fulfill advantages, which are expected after initial in-vitro studies. Whereas laser surgery of soft oral tissues has been developed to a standard method, laser treatment of dental hard tissues and the bone are attended with many unsolved problems. Different laser types, especially pulsed lasers in a wide spectrum of wavelengths have been proofed for dental use. Today neither the excimer lasers, emitting in the far uv-range from 193 to 351 nm, nor the mid-infrared lasers like Nd:YAG (1,064 μm), Ho:YAG (2,1 μm) and Er:YAG (2,96 μm) or the C02-laser (10,6 μm) show mechanism of interaction more carefully and faster than a preparation of teeth with diamond drillers. The laser type with the most precise and considerate treatment effects in the moment is the short pulsed (15 ns) ArF-excimer laser with a wavelength of 193 nm. However this laser type has not yet the effectivity of mechanical instruments and it needs a mirror system to deliver the radiation. Histological results point out, that this laser shows no significant pathological alterations in the adjacent tissues. Another interesting excimer laser, filled with XeCI and emitting at a wavelength of 308 nm has the advantage to be good to deliver through quartz fibers. A little more thermal influence is to be seen according to the longer wavelength. Yet the energy density, necessary to cut dental hard tissues will not be reached with the laser systems available now. Both the pulsed Er:YAG- (2,94 μm, pulse duration 250 s) and the Ho:YAG -laser (2,1 μm, pulse duration 250 μs) have an effective coupling of the laser energy to hydrogeneous tissues, but they do not work sufficient on healthy enamel and dentine. The influence to adjacent healthy tissue is not tolerable, especially in regard of the thermal damage dentine and pulp tissues. Moreover, like the 193 nm ArF-excimer laser

  4. Evolution of laser pulse shape in a parabolic plasma channel

    NASA Astrophysics Data System (ADS)

    Kaur, M.; Gupta, D. N.; Suk, H.

    2017-01-01

    During high-intensity laser propagation in a plasma, the group velocity of a laser pulse is subjected to change with the laser intensity due to alteration in refractive index associated with the variation of the nonlinear plasma density. The pulse front sharpened while the back of the pulse broadened due to difference in the group velocity at different parts of the laser pulse. Thus the distortion in the shape of the laser pulse is expected. We present 2D particle-in-cell simulations demonstrating the controlling the shape distortion of a Gaussian laser pulse using a parabolic plasma channel. We show the results of the intensity distribution of laser pulse in a plasma with and without a plasma channel. It has been observed that the plasma channel helps in controlling the laser pulse shape distortion. The understanding of evolution of laser pulse shape may be crucial while applying the parabolic plasma channel for guiding the laser pulse in plasma based accelerators.

  5. Ultrashort pulse generation in semiconductor lasers

    NASA Technical Reports Server (NTRS)

    Auyeung, J.; Johnston, A. R.

    1981-01-01

    Techniques to generate picosecond optical pulses from semiconductor lasers are reviewed. Experimental methods and results of theoretical analysis of active modelocking are presented. It is shown that modelocking will achieve the shortest pulses; but the use of a cumbersome external cavity will probably limit its practical use. Short pulses produced by direct modulation such as gain switching are considerably broader than those obtained by passive modelocking. However, no external cavity is needed; and the simplicity of this method makes it important to be explored further. Recent experimental results are discussed where picosecond pulses from a buried heterostructure laser diode with ultrashort current pulses obtained from a comb generator are generated. Also, 28 ps pulses were obtained at 2.5 GHz repetition frequency, using the gain switching method. An analytical analysis based on the rate equations shows qualitative agreement with our experimental results.

  6. Pulsed Laser Illumination of Photovoltaic Cells

    NASA Technical Reports Server (NTRS)

    Yater, Jane A.; Lowe, Roland; Jenkins, Philip; Landis, Geoffrey A.

    1994-01-01

    In future space missions, free electron lasers (FEL) may be used to illuminate photovoltaic array receivers to provide remote power. The induction FEL and the radio-frequency (RF) FEL both produce pulsed rather than continuous output. In this work, we investigate cell response to pulsed laser light which simulates the RF FEL format, producing 50 ps pulses at a frequency of 78 MHz. A variety of Si, GaAs, CaSb and CdInSe2 (CIS) solar cells are tested at average incident powers between 4 mW/sq cm and 425 mW/sq cm. The results indicate that if the pulse repetition is high, cell efficiencies are only slightly reduced by using a pulsed laser source compared to constant illumination at the same wavelength. Because the pulse separation is less than or approximately equal to the minority carrier lifetime, the illumination conditions are effectively those of a continuous wave laser. The time dependence of the voltage and current response of the cells are also measured using a sampling oscilloscope equipped with a high frequency voltage probe and current transformer. The frequency response of the cells is weak, with both voltage and current outputs essentially dc in nature. Comparison with previous experiments shows that the RF FEL pulse format yields much more efficient photovoltaic conversion of light than does an induction FEL pulse format.

  7. Pulsed Laser Illumination of Photovoltaic Cells

    NASA Technical Reports Server (NTRS)

    Yater, Jane A.; Lowe, Roland; Jenkins, Philip; Landis, Geoffrey A.

    1994-01-01

    In future space missions, free electron lasers (FEL) may be used to illuminate photovoltaic array receivers to provide remote power. The induction FEL and the radio-frequency (RF) FEL both produce pulsed rather than continuous output. In this work, we investigate cell response to pulsed laser light which simulates the RF FEL format, producing 50 ps pulses at a frequency of 78 MHz. A variety of Si, GaAs, CaSb and CdInSe2 (CIS) solar cells are tested at average incident powers between 4 mW/sq cm and 425 mW/sq cm. The results indicate that if the pulse repetition is high, cell efficiencies are only slightly reduced by using a pulsed laser source compared to constant illumination at the same wavelength. Because the pulse separation is less than or approximately equal to the minority carrier lifetime, the illumination conditions are effectively those of a continuous wave laser. The time dependence of the voltage and current response of the cells are also measured using a sampling oscilloscope equipped with a high frequency voltage probe and current transformer. The frequency response of the cells is weak, with both voltage and current outputs essentially dc in nature. Comparison with previous experiments shows that the RF FEL pulse format yields much more efficient photovoltaic conversion of light than does an induction FEL pulse format.

  8. Pulse laser assist optical tweezers (PLAT) with long-duration pulse laser

    NASA Astrophysics Data System (ADS)

    Maeda, Saki; Sugiura, Tadao; Minato, Kotaro

    2011-07-01

    Optical tweezers is a technique to trap and to manipulate micron sized objects under a microscope by radiation pressure force exerted by a laser beam. Optical tweezers has been utilized for single-molecular measurements of force exerted by molecular interactions and for cell palpation. To extend applications of optical tweezers we have developed a novel optical tweezers system combined with a pulse laser. We utilize a pulse laser (Q-switched Nd: YAG laser, wavelength of 1064 nm) to assist manipulations by conventional optical tweezers with a continuous wave (CW) laser. The pulse laser beam is introduced into the same optics for conventional optical tweezers. In principle, instantaneous radiation force is proportional to instantaneous power of laser beam. As a result, pulse laser beam generates strong instantaneous force on an object to be manipulated. If the radiation force becomes strong enough to get over an obstacle structure and/or to be released from adhesion, the object will be free from these difficulties. We investigate the effect of pulse laser assistance with changing pulse duration of the laser. We report optimum pulse duration of 100 ns to 200 ns deduced from motion analysis of a particle in a beam spot. Our goal is to realize in-vivo manipulation and operation of a cell. For this purpose we need to reduce light energy of pulse laser beam and to avoid laser induced breakdown caused by strong light field. So we have developed a pulse laser with 160-ns pulse duration and have confirmed that availability on manipulation of living cells.

  9. Pulse-shaping circuit for laser excitation

    NASA Technical Reports Server (NTRS)

    Laudenslager, J. B.; Pacala, T. J.

    1981-01-01

    Narrower, impedence-matched pulses initiate stabler electric discharges for gas lasers. Discharges are more efficient, more compact, capable of high repetition rate, and less expensive than conventional electron-beam apparatus, but gas tends to break down and form localized arcs. Pulse-shaping circuit compresses width of high-voltage pulses from relatively-slow rise-time voltage generator and gradually grades circuit impedance from inherent high impedance of generator to low impedence of gas.

  10. Pressure wave charged repetitively pulsed gas laser

    DOEpatents

    Kulkarny, Vijay A.

    1982-01-01

    A repetitively pulsed gas laser in which a system of mechanical shutters bracketing the laser cavity manipulate pressure waves resulting from residual energy in the cavity gas following a lasing event so as to draw fresh gas into the cavity and effectively pump spent gas in a dynamic closed loop.

  11. Laser-induced periodic surface structures on zinc oxide crystals upon two-colour femtosecond double-pulse irradiation

    NASA Astrophysics Data System (ADS)

    Höhm, S.; Rosenfeld, A.; Krüger, J.; Bonse, J.

    2017-03-01

    In order to study the temporally distributed energy deposition in the formation of laser-induced periodic surface structures (LIPSS) on single-crystalline zinc oxide (ZnO), two-colour double-fs-pulse experiments were performed. Parallel or cross-polarised double-pulse sequences at 400 and 800 nm wavelength were generated by a Mach–Zehnder interferometer, exhibiting inter-pulse delays up to a few picoseconds between the sub-ablation 50-fs-pulses. Twenty two-colour double-pulse sequences were collinearly focused by a spherical mirror to the sample surface. The resulting LIPSS periods and areas were analysed by scanning electron microscopy. The delay-dependence of these LIPSS characteristics shows a dissimilar behaviour when compared to the semiconductor silicon, the dielectric fused silica, or the metal titanium. A wavelength-dependent plasmonic mechanism is proposed to explain the delay-dependence of the LIPSS on ZnO when considering multi-photon excitation processes. Our results support the involvement of nonlinear processes for temporally overlapping pulses. These experiments extend previous two-colour studies on the indirect semiconductor silicon towards the direct wide band-gap semiconductor ZnO and further manifest the relevance of the ultrafast energy deposition for LIPSS formation.

  12. Laser pulse shaping for high gradient accelerators

    NASA Astrophysics Data System (ADS)

    Villa, F.; Anania, M. P.; Bellaveglia, M.; Bisesto, F.; Chiadroni, E.; Cianchi, A.; Curcio, A.; Galletti, M.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Gatti, G.; Moreno, M.; Petrarca, M.; Pompili, R.; Vaccarezza, C.

    2016-09-01

    In many high gradient accelerator schemes, i.e. with plasma or dielectric wakefield induced by particles, many electron pulses are required to drive the acceleration of one of them. Those electron bunches, that generally should have very short duration and low emittance, can be generated in photoinjectors driven by a train of laser pulses coming inside the same RF bucket. We present the system used to shape and characterize the laser pulses used in multibunch operations at Sparc_lab. Our system gives us control over the main parameter useful to produce a train of up to five high brightness bunches with tailored intensity and time distribution.

  13. Quantifying pulsed laser induced damage to graphene

    SciTech Connect

    Currie, Marc; Caldwell, Joshua D.; Bezares, Francisco J.; Robinson, Jeremy; Anderson, Travis; Chun, Hayden; Tadjer, Marko

    2011-11-21

    As an emerging optical material, graphene's ultrafast dynamics are often probed using pulsed lasers yet the region in which optical damage takes place is largely uncharted. Here, femtosecond laser pulses induced localized damage in single-layer graphene on sapphire. Raman spatial mapping, SEM, and AFM microscopy quantified the damage. The resulting size of the damaged area has a linear correlation with the optical fluence. These results demonstrate local modification of sp{sup 2}-carbon bonding structures with optical pulse fluences as low as 14 mJ/cm{sup 2}, an order-of-magnitude lower than measured and theoretical ablation thresholds.

  14. Activated associative desorption of C + O → CO from Ru(001) induced by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Wagner, S.; Öström, H.; Kaebe, A.; Krenz, M.; Wolf, M.; Luntz, A. C.; Frischkorn, C.

    2008-12-01

    The femtosecond (fs)-laser-induced associative desorption of CO from a C/O coadsorbate on Ru(001) has been investigated. The recombination of the atomic reactants is found to originate predominantly from oxidation of isolated 'reactive' carbon atoms, whereas oxidation of surface carbon with carbon-carbon bonds is not observed. Due to the excess of oxygen atoms (C coverage in the few-percent range) the Cads + Oads → COgas formation exhibits first-order kinetics. For both excitation wavelengths 400 and 800 nm, a strongly nonlinear fluence (F) dependence of the CO desorption yield Y is observed with exponents n≈4 in a power law parametrization Y~langFrangn. Furthermore, excitation with 400 nm pulses leads to a significantly higher desorption yield as compared to 800 nm laser light with cross sections and desorption probabilities for 400 and 800 nm excitation of σeff=4.9×10-18 cm2, Pdes=0.17 and σeff=1.1×10-18 cm2, Pdes=0.07, respectively, at an absorbed fluence of langFrang=170 J m-2. This wavelength dependence is attributed to the shorter optical penetration of 400 nm light in the Ru substrate leading to higher surface temperatures at the same absorbed energy rather than to nonthermalized hot electrons. In addition, two-pulse-correlation measurements show a full-width at half-maximum of ~ 20 ps excluding a purely electron-driven reaction mechanism, which should exhibit a subpicosecond response time. However, careful qualitative and quantitative analyses based on frictional modelling of the adsorbate-substrate coupling reveals that the C-O association reaction is mediated by both substrate phonons and electrons. The electronic, i.e. nonadiabatic contribution with a coupling constant of ηel=1/500 fs-1 is responsible for the ultrafast activation of the reaction found in the frictional modelling to occur within ~1 ps after excitation. Similarities to the associative desorption of N2 (isoelectronic with CO) from N/Ru(001), a system for which density

  15. Pulsed solid state lasers for medicine

    NASA Astrophysics Data System (ADS)

    Kertesz, Ivan; Danileiko, A. Y.; Denker, Boris I.; Kroo, Norbert; Osiko, Vyacheslav V.; Prokhorov, Alexander M.

    1994-02-01

    The effect on living tissues of different pulsed solid state lasers: Nd:YAG ((lambda) equals 1.06 micrometers ) Er:glass (1.54 micrometers ), Ho:YAG (2.1 micrometers ) and Er:YAG (2.94 micrometers ) is compared with the continuous wave Nd:YAG- and CO2-lasers used in operating theaters. Portable Er:glass- and Er:YAG-lasers are developed for surgery/cosmetics and HIV-safe blood testing.

  16. Frequency modulation of semiconductor disk laser pulses

    SciTech Connect

    Zolotovskii, I O; Korobko, D A; Okhotnikov, O G

    2015-07-31

    A numerical model is constructed for a semiconductor disk laser mode-locked by a semiconductor saturable absorber mirror (SESAM), and the effect that the phase modulation caused by gain and absorption saturation in the semiconductor has on pulse generation is examined. The results demonstrate that, in a laser cavity with sufficient second-order dispersion, alternating-sign frequency modulation of pulses can be compensated for. We also examine a model for tuning the dispersion in the cavity of a disk laser using a Gires–Tournois interferometer with limited thirdorder dispersion. (control of radiation parameters)

  17. Classical dynamics of free electromagnetic laser pulses

    NASA Astrophysics Data System (ADS)

    Goto, S.; Tucker, R. W.; Walton, T. J.

    2016-02-01

    We discuss a class of exact finite energy solutions to the vacuum source-free Maxwell field equations as models for multi- and single cycle laser pulses in classical interaction with relativistic charged test particles. These solutions are classified in terms of their chiral content based on their influence on particular charge configurations in space. Such solutions offer a computationally efficient parameterization of compact laser pulses used in laser-matter simulations and provide a potential means for experimentally bounding the fundamental length scale in the generalized electrodynamics of Bopp, Landé and Podolsky.

  18. Photoimaging of the multiple filamentation of femtosecond laser pulses in poly(methyl methacrylate) doped with 2,2-difluoro-4-(9-anthracyl)-6-methyl-1,3,2-dioxaborine

    SciTech Connect

    Kulchin, Yu N; Vitrik, O B; Chekhlenok, A A; Zhizhchenko, A Yu; Proschenko, D Yu; Mirochnik, A G; Lyu Guohui

    2013-12-31

    We have studied the filamentation of femtosecond laser pulses (λ = 800 nm, ∼42 fs pulse duration) in poly(methyl methacrylate) doped with 2,2-difluoro-4-(9-anthracyl)-6-methyl-1,3,2- dioxaborine and the associated photomodification of the material. The results demonstrate that multiple filamentation occurs at pulse energies above 5 μJ. At a pulse energy of 1.5 mJ, it is accompanied by supercontinuum generation. The average filament length in PMMA is 9 mm and the filament diameter is ∼10 μm. An incident power density of ∼10{sup 12} W cm{sup -2} ensures inscription of the filament pattern owing to two-photon photochemical processes. Preliminary exposure to continuous light at λ = 400 nm enables an ordered filament pattern to be written. (interaction of laser radiation with matter)

  19. Pulsed infrared laser ablation and clinical applications

    NASA Astrophysics Data System (ADS)

    Chan, Kin Foong

    Sufficient light energy deposited in tissue can result in ablation and excessive thermal and mechanical damage to adjacent tissues. The goals of this research are to investigate the mechanisms of pulsed infrared laser ablation of tissue, to optimize laser parameters for minimizing unnecessary damage to healthy tissue, and to explore the potential of using pulsed infrared lasers for clinical applications, especially laser lithotripsy. A dual-channel optical low coherence reflectometer was implemented to measure the expansion and collapse velocities of a Q-switched Ho:YAG (λ = 2.12 μm) laser-induced cavitation in water. Cavitation wall velocities up to 11 m/s were measured with this technique, and the results were in fair agreement with those calculated from fast-flash photographic images. The dependence of ablation threshold fluence on calculus absorption was examined. Preliminary results indicated that the product of optical absorption and ablation threshold fluence, which is the heat of ablation, remained constant for a given urinary calculus type and laser pulse duration. An extended study examined the influence of optical absorption on pulsed infrared laser ablation. An analytical photothermal ablation model was applied and compared to experimental ablation results using an infrared free-electron laser at selected wavelengths between 2.12 μm and 6.45 μm Results were in good agreement with the model, and the ablation depths of urinary calculi were highly dependent upon the calculus optical absorption as well as light attenuation within the intrapulse ablation plume. An efficient wavelength for ablation corresponded to the wavelength of the Er:YAG laser (λ = 2.94 μm) suggested this laser should be examined for laser lithotripsy. Schlieren flash photography, acoustic transient measurements with a piezoelectric polyvinylidene-fluoride needle-hydrophone, mass loss measurements, and chemical analyses were employed to study the ablation mechanisms of the free

  20. Heat accumulation during pulsed laser materials processing.

    PubMed

    Weber, Rudolf; Graf, Thomas; Berger, Peter; Onuseit, Volkher; Wiedenmann, Margit; Freitag, Christian; Feuer, Anne

    2014-05-05

    Laser materials processing with ultra-short pulses allows very precise and high quality results with a minimum extent of the thermally affected zone. However, with increasing average laser power and repetition rates the so-called heat accumulation effect becomes a considerable issue. The following discussion presents a comprehensive analytical treatment of multi-pulse processing and reveals the basic mechanisms of heat accumulation and its consequence for the resulting processing quality. The theoretical findings can explain the experimental results achieved when drilling microholes in CrNi-steel and for cutting of CFRP. As a consequence of the presented considerations, an estimate for the maximum applicable average power for ultra-shorts pulsed laser materials processing for a given pulse repetition rate is derived.

  1. Single attosecond pulse generation in an orthogonally polarized two-color laser field combined with a static electric field

    SciTech Connect

    Xia Changlong; Zhang Gangtai; Wu Jie; Liu Xueshen

    2010-04-15

    We investigate theoretic high-order harmonic generation and single attosecond pulse generation in an orthogonally polarized two-color laser field, which is synthesized by a mid-infrared (IR) pulse (12.5 fs, 2000 nm) in the y component and a much weaker (12 fs, 800 nm) pulse in the x component. We find that the width of the harmonic plateau can be extended when a static electric field is added in the y component. We also investigate emission time of harmonics in terms of a time-frequency analysis to illustrate the physical mechanism of high-order harmonic generation. We calculate the ionization rate using the Ammosov-Delone-Krainov model and interpret the variation of harmonic intensity for different static electric field strengths. When the ratio of strengths of the static and the y-component laser fields is 0.1, a continuous harmonic spectrum is formed from 220 to 420 eV. By superposing a properly selected range of the harmonic spectrum from 300 to 350 eV, an isolated attosecond pulse with a duration of about 75 as is obtained, which is near linearly polarized.

  2. RF synchronized short pulse laser ion source

    SciTech Connect

    Fuwa, Yasuhiro Iwashita, Yoshihisa; Tongu, Hiromu; Inoue, Shunsuke; Hashida, Masaki; Sakabe, Shuji; Okamura, Masahiro; Yamazaki, Atsushi

    2016-02-15

    A laser ion source that produces shortly bunched ion beam is proposed. In this ion source, ions are extracted immediately after the generation of laser plasma by an ultra-short pulse laser before its diffusion. The ions can be injected into radio frequency (RF) accelerating bucket of a subsequent accelerator. As a proof-of-principle experiment of the ion source, a RF resonator is prepared and H{sub 2} gas was ionized by a short pulse laser in the RF electric field in the resonator. As a result, bunched ions with 1.2 mA peak current and 5 ns pulse length were observed at the exit of RF resonator by a probe.

  3. Pulsed laser illumination of photovoltaic cells

    NASA Technical Reports Server (NTRS)

    Yater, Jane A.; Lowe, Roland A.; Jenkins, Phillip P.; Landis, Geoffrey A.

    1994-01-01

    In future space missions, free electron lasers (FEL) may be used to illuminate photovoltaic array receivers to provide remote power. Both the radio-frequency (RF) and induction FEL provide FEL produce pulsed rather than continuous output. In this work we investigate cell response to pulsed laser light which simulates the RF FEL format. The results indicate that if the pulse repetition is high, cell efficiencies are only slightly reduced compared to constant illumination at the same wavelength. The frequency response of the cells is weak, with both voltage and current outputs essentially dc in nature. Comparison with previous experiments indicates that the RF FEL pulse format yields more efficient photovoltaic conversion than does an induction FEL pulse format.

  4. Fabrication of amorphous micro-ring arrays in crystalline silicon using ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Fuentes-Edfuf, Yasser; Garcia-Lechuga, Mario; Puerto, Daniel; Florian, Camilo; Garcia-Leis, Adianez; Sanchez-Cortes, Santiago; Solis, Javier; Siegel, Jan

    2017-05-01

    We demonstrate a simple way to fabricate amorphous micro-rings in crystalline silicon using direct laser writing. This method is based on the fact that the phase of a thin surface layer can be changed into the amorphous phase by irradiation with a few ultrashort laser pulses (800 nm wavelength and 100 fs duration). Surface-depressed amorphous rings with a central crystalline disk can be fabricated without the need for beam shaping, featuring attractive optical, topographical, and electrical properties. The underlying formation mechanism and phase change pathway have been investigated by means of fs-resolved microscopy, identifying fluence-dependent melting and solidification dynamics of the material as the responsible mechanism. We demonstrate that the lateral dimensions of the rings can be scaled and that the rings can be stitched together, forming extended arrays of structures not limited to annular shapes. This technique and the resulting structures may find applications in a variety of fields such as optics, nanoelectronics, and mechatronics.

  5. Concerted manipulation of laser plasma dynamics with two laser pulses

    NASA Astrophysics Data System (ADS)

    Braenzel, J.; Andreev, A. A.; Ehrentraut, L.; Sommer, D.; Schnürer, M.

    2017-05-01

    In this article we present experimental results from a counter-propagating two laser pulse experiment at high intensity and using ultrathin gold and plastic foil targets. We applied one laser pulse as a pre-pulse with an intensity of up to 1x1018 W/cm2. By this method we manipulated the pre-plasma of the foil target with which the stronger laser pulse with an intensity of 6x1019W/cm2 interacts. This alters significantly subsequent processes from the laser plasma interaction which we show the ion acceleration and high harmonic generation. On the one hand, the maximum kinetic ion energy and the maximum charge state for gold ions decline due to the pre-heating of the target in the time range of few ps, on the other hand the number of accelerated ions is increased. For the same parameter range we detected a significant raise of the high harmonic emission. Moreover, we present first experimental observations, that when the second laser pulse is applied as a counter-propagating post-pulse the energy distribution of accelerated carbon ions is charge selective altered. Our findings indicate that using this method a parametric optimization can be achieved, which promises new insights about the concurrent processes of the laser plasma dynamics.

  6. The effect of ultrafast laser wavelength on ablation properties and implications on sample introduction in inductively coupled plasma mass spectrometry

    PubMed Central

    LaHaye, N. L.; Harilal, S. S.; Diwakar, P. K.; Hassanein, A.; Kulkarni, P.

    2015-01-01

    We investigated the role of femtosecond (fs) laser wavelength on laser ablation (LA) and its relation to laser generated aerosol counts and particle distribution, inductively coupled plasma-mass spectrometry (ICP-MS) signal intensity, detection limits, and elemental fractionation. Four different NIST standard reference materials (610, 613, 615, and 616) were ablated using 400 nm and 800 nm fs laser pulses to study the effect of wavelength on laser ablation rate, accuracy, precision, and fractionation. Our results show that the detection limits are lower for 400 nm laser excitation than 800 nm laser excitation at lower laser energies but approximately equal at higher energies. Ablation threshold was also found to be lower for 400 nm than 800 nm laser excitation. Particle size distributions are very similar for 400 nm and 800 nm wavelengths; however, they differ significantly in counts at similar laser fluence levels. This study concludes that 400 nm LA is more beneficial for sample introduction in ICP-MS, particularly when lower laser energies are to be used for ablation. PMID:26640294

  7. The effect of ultrafast laser wavelength on ablation properties and implications on sample introduction in inductively coupled plasma mass spectrometry

    SciTech Connect

    LaHaye, N. L.; Harilal, S. S.; Diwakar, P. K.; Hassanein, A.; Kulkarni, P.

    2013-07-14

    We investigated the role of femtosecond (fs) laser wavelength on laser ablation (LA) and its relation to laser generated aerosol counts and particle distribution, inductively coupled plasma-mass spectrometry (ICP-MS) signal intensity, detection limits, and elemental fractionation. Four different NIST standard reference materials (610, 613, 615, and 616) were ablated using 400 nm and 800 nm fs laser pulses to study the effect of wavelength on laser ablation rate, accuracy, precision, and fractionation. Our results show that the detection limits are lower for 400 nm laser excitation than 800 nm laser excitation at lower laser energies but approximately equal at higher energies. Ablation threshold was also found to be lower for 400 nm than 800 nm laser excitation. Particle size distributions are very similar for 400 nm and 800 nm wavelengths; however, they differ significantly in counts at similar laser fluence levels. This study concludes that 400 nm LA is more beneficial for sample introduction in ICP-MS, particularly when lower laser energies are to be used for ablation.

  8. Short-pulse Laser Processing of CFRP

    NASA Astrophysics Data System (ADS)

    Weber, Rudolf; Freitag, Christian; Kononenko, Taras V.; Hafner, Margit; Onuseit, Volkher; Berger, Peter; Graf, Thomas

    Short-pulse lasers allow processing of carbon fiber reinforced plastics (CFRP) with very high quality, i.e. showing thermal damage in the range of only a few micrometers. Due to the usually high intensities and the short interaction times of such short pulses, only a small fraction of the incident laser energy is converted to residual heat which does not contribute to the ablation process. However, if the next pulse arrives before the material had time to cool down, i.e. this residual thermal energy did not sufficiently flow out of the interaction region, it encounters material which is still hot. This remaining energy and temperature is summing up during the sequence of pulses and is commonly referred to as "heat accumulation". Thermal damage in addition to the damage created by the process itself is induced, if the resulting temperature sum exceeds the damage temperatures of either the fibre or the plastic. The current paper presents the influence of the laser parameters such as pulse energy and repetition rate on this heat accumulation. An analytical model was used to describe the heat accumulation for different laser parameters. It describes the heat accumulation process and allows estimating the maximum number of pulses allowed at the same place before a detrimental temperature increase occurs.

  9. Stimulated crystallization of melt-quenched Ge{sub 2}Sb{sub 2}Te{sub 5} films employing femtosecond laser double pulses

    SciTech Connect

    Cotton, Rebecca L.; Siegel, Jan

    2012-12-15

    The phase transformation of Ge{sub 2}Sb{sub 2}Te{sub 5} films from the melt-quenched amorphous phase into the crystalline phase induced by 800 nm, 100 fs laser pulses has been studied. For partly amorphized films, progressive crystallization could be induced by single pulses, which can be explained by growth of already existing crystalline embryos. For completely amorphized films, it was not possible to induce crystallization with one or two consecutive pulses; three pulses being the threshold for the onset of crystallization. By employing a fs laser double pulse with an adjustable inter-pulse delay, partial crystallization could be triggered for a delay range of 200 fs-100 ps, while for longer delays no crystallization was possible. The time window for stimulated crystallization can be related to the relaxation dynamics of free electrons excited by the first pulse, which are further excited by the second pulse still remaining in the excited state. Our results indicate that the lifetime of excited electrons in melt-quenched amorphous Ge{sub 2}Sb{sub 2}Te{sub 5} is Almost-Equal-To 100 ps.

  10. Short-pulse laser amplification and saturation using stimulated Raman scattering

    NASA Astrophysics Data System (ADS)

    Dodd, E. S.; Ren, J.; Kwan, T. J. T.; Schmitt, M. J.; Lundquist, P. B.; Sarkisyan, S.; Nelson-Melby, E.

    2010-11-01

    Recent theoretical and experimental work has focused on using backward-stimulated Raman scattering (BSRS) in plasmas as a means of laser pulse amplification and compression [1,2,3]. We present initial computational and experimental work on SRS amplification in a capillary-discharge generated Xe plasma. The experimental set-up uses a 200 ps pump pulse with an 800 nm wavelength seeded by a 100 fs pulse from a broadband source and counter-propagates the pulses through a plasma of length 1 cm and diameter 0.1 cm. Results from initial experiments characterizing the plasma and on short-pulse amplification will be presented. Additionally, we present results from calculations using pF3d [4], and discuss the role of SRS saturation and determine the possible significance of electron trapping with a model implemented in pF3d [5]. [1] G. Shvets, N. J. Fisch, A. Pukhov, and J. Meyer-ter-Vehn, Phys. Rev. Lett. 81 4879 (1998). [2] V. M. Malkin, G. Shvets, and N. J. Fisch, Phys. Rev. Lett. 82 4448 (1999). [3] R. K. Kirkwood, E. Dewald, and C. Niemann, et al., Phys. Plasmas 14 113109 (2007). [4] R. L. Berger, B. F. Lasinski, T. B. Kaiser, et al., Phys. Fluids B 5 2243 (1993). [5] H. X. Vu, D. F. DuBois, and B. Bezzerides, Phys. Plasmas 14 012702 (2007). Supported by US DOE and LANS, LLC under contract DE-AC52-06NA25396. LA-UR-10-04787

  11. Ophthalmic applications of ultrashort pulsed lasers

    NASA Astrophysics Data System (ADS)

    Juhasz, Tibor; Spooner, Greg; Sacks, Zachary S.; Suarez, Carlos G.; Raksi, Ferenc; Zadoyan, Ruben; Sarayba, Melvin; Kurtz, Ronald M.

    2004-06-01

    Ultrashort laser pulses can be used to create high precision incision in transparent and translucent tissue with minimal damage to adjacent tissue. These performance characteristics meet important surgical requirements in ophthalmology, where femtosecond laser flap creation is becoming a widely used refractive surgery procedure. We summarize clinical findings with femtosecond laser flaps as well as early experiments with other corneal surgical procedures such as corneal transplants. We also review laser-tissue interaction studies in the human sclera and their consequences for the treatment of glaucoma.

  12. Inductive gas line for pulsed lasers

    DOEpatents

    Benett, William J.; Alger, Terry W.

    1985-01-01

    A gas laser having a metal inlet gas feed line assembly shaped as a coil, to function as an electrical inductance and therefore high impedance to pulses of electric current applied to electrodes at opposite ends of a discharge tube of a laser, for example. This eliminates a discharge path for the laser through the inlet gas feed line. A ferrite core extends through the coil to increase the inductance of the coil and provide better electric isolation. By elimination of any discharge breakdown through the gas supply, efficiency is increased and a significantly longer operating lifetime of the laser is provided.

  13. Inductive gas line for pulsed lasers

    DOEpatents

    Benett, W.J.; Alger, T.W.

    1982-09-29

    A gas laser having a metal inlet gas feed line assembly shaped as a coil, to function as an electrical inductance and therefore high impedance to pulses of electric current applied to electrodes at opposite ends of a discharge tube of a laser, for example. This eliminates a discharge path for the laser through the inlet gas feed line. A ferrite core extends through the coil to increase the inductance of the coil and provide better electric isolation. By elimination of any discharge breakdown through the gas supply, efficiency is increased and a significantly longer operating lifetime of the laser is provided.

  14. Nonequilibrium Interlayer Transport in Pulsed Laser Deposition

    SciTech Connect

    Tischler, Jonathan Zachary; Eres, Gyula; Larson, Ben C; Rouleau, Christopher M; Zschack, P.; Lowndes, Douglas H

    2006-01-01

    We use time-resolved surface x-ray diffraction measurements with microsecond range resolution to study the growth kinetics of pulsed laser deposited SrTiO3. Time-dependent surface coverages corresponding to single laser shots were determined directly from crystal truncation rod intensity transients. Analysis of surface coverage evolution shows that extremely fast nonequilibrium interlayer transport, which occurs concurrently with the arrival of the laser plume, dominates the deposition process. A much smaller fraction of material, which is governed by the dwell time between successive laser shots, is transferred by slow, thermally driven interlayer transport processes.

  15. Laser and intense pulsed light management of couperose and rosacea.

    PubMed

    Dahan, S

    2011-11-01

    Management of couperosis and rosacea has been totally renewed by laser and vascular laser techniques, with efficacy targeted on the telangiectases and to a lesser extent on the erythrosis. Laser management of hypertrophic rosacea or rhinophyma depends on surgical treatment with decortication, continuous CO(2) ablative laser or Erbium, fractionated at high power, then vascular laser treatment for the telangiectases: lasers with pulsed dye, KTP, or pulsed lights for red laser telangiectases and long pulse Nd-Yag laser for blue telangiectases. For papulopustular rosacea, vascular laser treatment (pulsed dye and KTP) and intense pulsed light will be begun once the inflammation has been treated. The major indication for vascular lasers and intense pulsed light is found in erythematotelangiectatic rosacea, with high efficacy for the telangiectases. Diffuse erythrosis is difficult to treat, requiring a high number of laser and/or intense pulsed light sessions. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

  16. [Laser and intense pulsed light management of couperose and rosacea].

    PubMed

    Dahan, S

    2011-09-01

    Management of couperosis and rosacea has been totally renewed by laser and vascular laser techniques, with efficacy targeted on the telangiectases and to a lesser extent on the erythrosis. Laser management of hypertrophic rosacea or rhinophyma depends on surgical treatment with decortication, continuous CO(2) ablative laser or Erbium, fractionated at high power, then vascular laser treatment for the telangiectases: lasers with pulsed dye, KTP, or pulsed lights for red laser telangiectases and long pulse Nd-Yag laser for blue telangiectases. For papulopustular rosacea, vascular laser treatment (pulsed dye and KTP) and intense pulsed light will be begun once the inflammation has been treated. The major indication for vascular lasers and intense pulsed light is found in erythematotelangiectatic rosacea, with high efficacy for the telangiectases. Diffuse erythrosis is difficult to treat, requiring a high number of laser and/or intense pulsed light sessions. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

  17. 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.}

  18. Pulsed laser illumination of photovoltaic cells

    NASA Technical Reports Server (NTRS)

    Yater, Jane A.; Lowe, Roland A.; Jenkins, Phillip P.; Landis, Geoffrey A.

    1995-01-01

    In future space missions, free electron lasers (FEL) may be used to illuminate photovoltaic receivers to provide remote power. Both the radio-frequency (RF) and induction FEL produce pulsed rather than continuous output. In this work we investigate cell response to pulsed laser light which simulates the RF FEL format. The results indicate that if the pulse repetition is high, cell efficiencies are only slightly reduced compared to constant illumination at the same wavelength. The frequency response of the cells is weak, with both voltage and current outputs essentially dc in nature. Comparison with previous experiments indicates that the RF FEL pulse format yields more efficient photovoltaic conversion than does an induction FEL format.

  19. Propagation of chirped laser pulses in a plasma channel

    SciTech Connect

    Jha, Pallavi; Malviya, Amita; Upadhyay, Ajay K.

    2009-06-15

    Propagation of an initially chirped, Gaussian laser pulse in a preformed parabolic plasma channel is analyzed. A variational technique is used to obtain equations describing the evolution of the phase shift and laser spot size. The effect of initial chirp on the laser pulse length and intensity of a matched laser beam propagating in a plasma channel has been analyzed. The effective pulse length and chirp parameter of the laser pulse due to its interaction with plasma have been obtained and graphically depicted. The resultant variation in laser frequency across the laser pulse is discussed.

  20. Ultrashort pulsed laser technology development program

    NASA Astrophysics Data System (ADS)

    Manke, Gerald C.

    2014-10-01

    The Department of Navy has been pursuing a technology development program for advanced, all-fiber, Ultra Short Pulsed Laser (USPL) systems via Small Business Innovative Research (SBIR) programs. Multiple topics have been published to promote and fund research that encompasses every critical component of a standard USPL system and enable the demonstration of mJ/pulse class systems with an all fiber architecture. This presentation will summarize published topics and funded programs.

  1. High harmonic generation with intense infrared few-cycle laser pulses

    NASA Astrophysics Data System (ADS)

    Legare, Francois

    2013-05-01

    Further shortening of attosecond pulse duration via high harmonic generation (HHG) can be achieved utilizing few-cycle pulses at wavelengths longer than 800 nm, because the HHG cut-off shifts towards higher photon energies proportional to the square of the laser wavelength. The IR spectral range at 1800 nm is accessed by choosing the narrow band Idler of a white light seeded optical parametric amplifier which enables passive carrier envelope phase (CEP) stabilization. Pulse compression is achieved via the combined action of nonlinear propagation in a hollow-core fiber (HCF) followed by subsequent linear propagation through fused silica (FS) in the anomalous dispersion regime, enabling sub-millijoule sub-two-cycle pulses. HHG spectra from Xenon and cyclohexadiene isomers will be presented demonstrating the benefit of using those ultrashort IR pulses for HHG spectroscopy. To amplify those pulses in the millijoule range, we introduce the concept of Fourier-plane Optical Parametric Amplification (FOPA). The key idea for amplification of octave-spanning spectra without loss of spectral width is to amplify the broad spectrum ``slice by slice.'' Opposed to traditional schemes where amplification takes place in time domain, we propose to amplify different spectral parts independently of each other in the spectral domain. The spectral dispersion is carried out according to a 4-f setup which performs an optical Fourier transformation of time domain input pulses into the spectral domain and vice versa. After amplification which takes place in the Fourier plane, the pulses are transformed back into the time domain. As a first demonstration, the FOPA was used to amplify 0.1 mJ sub-two-cycle pulses to 1.4 mJ denoting 14 fold amplification. Driving the process of HHG from Neon and Helium with those pulses have enabled to generate soft X-ray spectra extending beyond the Oxygen K-edge (~540 eV) denoting a first step towards the generation of isolated attosecond pulses in the water

  2. Modeling Pulsed Laser Melting of Embedded Nanoparticles

    NASA Astrophysics Data System (ADS)

    Sawyer, Carolyn Anne

    A model of pulsed laser melting of embedded nanoparticles is introduced. Pulsed laser melting (PLM) is commonly used to achieve a fast quench rate in nanoparticles; this model enables a better understanding of the influence of PLM on the size distribution of nanoparticles, which is crucial for studying or using their size-dependent properties. The model includes laser absorption according to the Mie theory, a full heat transport model, and rate equations for nucleation, growth, coarsening, and melting and freezing of nanoparticles embedded in a transparent matrix. The effects of varying the laser parameters and sample properties are studied, as well as combining PLM and rapid thermal annealing (RTA) processing steps on the same sample. A general theory for achieving narrow size distributions of nanoparticles is presented, and widths as narrow as 12% are achieved using PLM and RTA.

  3. Ceramic dentures manufactured with ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Werelius, Kristian; Weigl, Paul

    2004-06-01

    Conventional manufacturing of individual ceramic dental prosthesis implies a handmade metallic framework, which is then veneered with ceramic layers. In order to manufacture all-ceramic dental prosthesis a CAD/CAM system is necessary due to the three dimensional shaping of high strength ceramics. Most CAD/CAM systems presently grind blocks of ceramic after the construction process in order to create the prosthesis. Using high-strength ceramics, such as Hot Isostatic Pressed (HIP)-zirconia, this is limited to copings. Anatomically shaped fixed dentures have a sculptured surface with small details, which can't be created by existing grinding tools. This procedure is also time consuming and subject to significant loss in mechanical strength and thus reduced survival rate once inserted. Ultra-short laser pulses offer a possibility in machining highly complex sculptured surfaces out of high-strength ceramic with negligible damage to the surface and bulk of the ceramic. In order to determine efficiency, quality and damage, several laser ablation parameters such as pulse duration, pulse energy and ablation strategies were studied. The maximum ablation rate was found using 400 fs at high pulse energies. High pulse energies such as 200μJ were used with low damage in mechanical strength compared to grinding. Due to the limitation of available laser systems in pulse repetition rates and power, the use of special ablation strategies provide a possibility to manufacture fully ceramic dental prosthesis efficiently.

  4. Ultrashort pulse laser deposition of thin films

    DOEpatents

    Perry, Michael D.; Banks, Paul S.; Stuart, Brent C.

    2002-01-01

    Short pulse PLD is a viable technique of producing high quality films with properties very close to that of crystalline diamond. The plasma generated using femtosecond lasers is composed of single atom ions with no clusters producing films with high Sp.sup.3 /Sp.sup.2 ratios. Using a high average power femtosecond laser system, the present invention dramatically increases deposition rates to up to 25 .mu.m/hr (which exceeds many CVD processes) while growing particulate-free films. In the present invention, deposition rates is a function of laser wavelength, laser fluence, laser spot size, and target/substrate separation. The relevant laser parameters are shown to ensure particulate-free growth, and characterizations of the films grown are made using several diagnostic techniques including electron energy loss spectroscopy (EELS) and Raman spectroscopy.

  5. Approximately 800-nm-Thick Pinhole-Free Perovskite Films via Facile Solvent Retarding Process for Efficient Planar Solar Cells.

    PubMed

    Yuan, Zhongcheng; Yang, Yingguo; Wu, Zhongwei; Bai, Sai; Xu, Weidong; Song, Tao; Gao, Xingyu; Gao, Feng; Sun, Baoquan

    2016-12-21

    Device performance of organometal halide perovskite solar cells significantly depends on the quality and thickness of perovskite absorber films. However, conventional deposition methods often generate pinholes within ∼300 nm-thick perovskite films, which are detrimental to the large area device manufacture. Here we demonstrated a simple solvent retarding process to deposit uniform pinhole free perovskite films with thicknesses up to ∼800 nm. Solvent evaporation during the retarding process facilitated the components separation in the mixed halide perovskite precursors, and hence the final films exhibited pinhole free morphology and large grain sizes. In addition, the increased precursor concentration after solvent-retarding process led to thick perovskite films. Based on the uniform and thick perovskite films prepared by this convenient process, a champion device efficiency up to 16.8% was achieved. We believe that this simple deposition procedure for high quality perovskite films around micrometer thickness has a great potential in the application of large area perovskite solar cells and other optoelectronic devices.

  6. Compact pulsed laser having improved heat conductance

    NASA Technical Reports Server (NTRS)

    Yang, L. C. (Inventor)

    1977-01-01

    A highly efficient, compact pulsed laser having high energy to weight and volume ratios is provided. The laser utilizes a cavity reflector that operates as a heat sink and is essentially characterized by having a high heat conductivity, by being a good electrical insulator and by being substantially immune to the deleterious effects of ultra-violet radiation. Manual portability is accomplished by eliminating entirely any need for a conventional circulating fluid cooling system.

  7. Laser Cooling with Ultrafast Pulse Trains

    DTIC Science & Technology

    2011-08-08

    of the electron cutoff energy for a laser intensity of ~5.3 x 1014 W/cm2. Record-breaking atomic imaging resolution and first absorption imaging...unprecedented agreement between ab initio theory and experiment in this field by investigating ionisation of atomic hydrogen with few-cycle pulses [1]. Figure 1...2a). We have made a systematic study of the electron energy and laser intensity dependence of the CEP modulation depth and relative phase offset

  8. Tunable pulsed carbon dioxide laser

    NASA Technical Reports Server (NTRS)

    Megie, G. J.; Menzies, R. T.

    1981-01-01

    Transverse electrically-excited-atmosphere (TEA) laser is continuously tunable over several hundred megahertz about centers of spectral lines of carbon dioxide. It is operated in single longitudinal mode (SLM) by injection of beam from continuous-wave, tunable-waveguide carbon dioxide laser, which serves as master frequency-control oscillator. Device measures absorption line of ozone; with adjustments, it is applicable to monitoring of atmospheric trace species.

  9. Propagation of ultrashort laser pulses through water.

    PubMed

    Li, Jianchao; Alexander, Dennis R; Zhang, Haifeng; Parali, Ufuk; Doerr, David W; Bruce, John C; Wang, Hao

    2007-02-19

    In this paper, propagation of ultrashort pulses through a long 3.5 meter water channel was studied. Of particular interest was the attenuation of the beam at various lengths along the variable path length and to find an explanation of why the attenuation deviates from typical Beer Lambert law around 3 meters for ultrashort laser pulse transmission. Laser pulses of 10 fs at 75 MHz, 100 fs at 80 MHz and 300 fs at 1 KHz were employed to investigate the effects of pulse duration, spectrum and repetition rate on the attenuation after propagating through water up to 3 meters. Stretched pulse attenuation measurements produced from 10 fs at a frequency of 75 MHz were compared with the 10 fs attenuation measurements. Results indicate that the broad spectrum of the ultrashort pulse is the dominant reason for the observed decrease in attenuation after 3 meters of travel in a long water channel. The repetition rate is found not to play a significant role at least for the long pulse scenario in this reported attenuation studies.

  10. Ultrafast pulsed laser utilizing broad bandwidth laser glass

    DOEpatents

    Payne, S.A.; Hayden, J.S.

    1997-09-02

    An ultrafast laser uses a Nd-doped phosphate laser glass characterized by a particularly broad emission bandwidth to generate the shortest possible output pulses. The laser glass is composed primarily of P{sub 2}O{sub 5}, Al{sub 2}O{sub 3} and MgO, and possesses physical and thermal properties that are compatible with standard melting and manufacturing methods. The broad bandwidth laser glass can be used in modelocked oscillators as well as in amplifier modules. 7 figs.

  11. Ultrafast pulsed laser utilizing broad bandwidth laser glass

    DOEpatents

    Payne, Stephen A.; Hayden, Joseph S.

    1997-01-01

    An ultrafast laser uses a Nd-doped phosphate laser glass characterized by a particularly broad emission bandwidth to generate the shortest possible output pulses. The laser glass is composed primarily of P.sub.2 O.sub.5, Al.sub.2 O.sub.3 and MgO, and possesses physical and thermal properties that are compatible with standard melting and manufacturing methods. The broad bandwidth laser glass can be used in modelocked oscillators as well as in amplifier modules.

  12. Direct Coulomb explosion imaging of coherent rotational dynamics induced by few-cycle laser pulses in light and heavy hydrogen

    NASA Astrophysics Data System (ADS)

    Bocharova, Irina; Magrakvelidze, Maia; Ranitovic, Predrag; Ray, Dipanwita; Cocke, Lewis; Litvinyuk, Igor

    2008-05-01

    We followed fast evolution of angular distributions for H2 and D2 molecules after their interaction with 8 fs 800 nm laser pulses. The rotating molecules were exploded by another few-cycle probe pulse time-delayed for up to 10 ps in respect to the pump. For neutral molecules we observed coherent rotational dynamics characterized by periodic revivals without noticeable decoherence within the 10 ps time-scale. For D2 up to 4 rotational states were involved in the wavepackets for each of the two spin isomers. In light hydrogen the resulting dynamics was dominated by beating of just two rotational states. The experimental data are in excellent agreement with our numerical simulations obtained by solving time-dependent Schr"odinger equation. For molecules that were ionized by the pump pulse we observed both vibrational and rotational dynamics. Time-dependent angular distributions for the molecular ions exhibit transient alignment only soon after the pulse (20 fs for H2^+ and 40 fs for D2^+) with no consequent revivals within the next 10 ps.

  13. Electromagnetic Pulses at Short-Pulse Laser Facilities

    SciTech Connect

    Brown, Jr., C G; Throop, A; Eder, D; Kimbrough, J

    2007-08-28

    Electromagnetic Pulse (EMP) is a known issue for short-pulse laser facilities, and will also be an issue for experiments using the advanced radiographic capability (ARC) at the National Ignition Facility (NIF). The ARC diagnostic uses four NIF beams that are compressed to picosecond durations for backlighting ignition capsules and other applications. Consequently, we are working to understand the EMP due to high-energy (MeV) electrons escaping from targets heated by short-pulse lasers. Our approach is to measure EMP in the Titan short-pulse laser at Lawrence Livermore National Laboratory (LLNL) and to employ that data to establish analysis and simulation capabilities. We have installed a wide variety of probes inside and outside the Titan laser chamber. We have high-frequency B-dots and D-dots, a photodiode, and fast current-viewing and integrating current transformers. The probe outputs are digitized by 10 and 20 Gsample/s oscilloscopes. The cables and oscilloscopes are well shielded to reduce noise. Our initial measurement campaign has yielded data useful mainly from hundreds of MHz to several GHz. We currently are supplementing our high-frequency probes with lower-frequency ones to obtain better low-frequency data. In order to establish analysis and simulation capabilities we are modeling the Titan facility using various commercial and LLNL numerical electromagnetic codes. We have simulated EMP generation by having a specified number of electrons leave the target and strike the chamber wall and other components in the chamber. This short impulse of electrons has a corresponding broad spectrum, exciting high-frequency structure in the resulting EMP. In this paper, we present results of our initial measurement campaign and comparisons between the measurements and simulations.

  14. Electromagnetic Pulses at Short-Pulse Laser Facilities

    SciTech Connect

    Brown, C G; Throop, A; Eder, D; Kimbrough, J

    2008-02-04

    Electromagnetic Pulse (EMP) is a known issue for short-pulse laser facilities, and will also be an issue for experiments using the advanced radiographic capability (ARC) at the National Ignition Facility (NIF). The ARC diagnostic uses four NIF beams that are compressed to picosecond durations for backlighting ignition capsules and other applications. Consequently, we are working to understand the EMP due to high-energy (MeV) electrons escaping from targets heated by short-pulse lasers. Our approach is to measure EMP in the Titan short-pulse laser at Lawrence Livermore National Laboratory (LLNL) and to employ that data to establish analysis and simulation capabilities. We have installed a wide variety of probes inside and outside the Titan laser chamber. We have high-frequency B-dot and D-dot probes, a photodiode, and fast current-viewing and integrating current transformers. The probe outputs are digitized by 10 and 20 Gsample/s oscilloscopes. The cables and oscilloscopes are well shielded to reduce noise. Our initial measurement campaign has yielded data useful mainly from several hundreds of MHz to several GHz. We currently are supplementing our high-frequency probes with lower-frequency ones to obtain better low-frequency data. In order to establish analysis and simulation capabilities we are modeling the Titan facility using various commercial and LLNL numerical electromagnetics codes. We have simulated EMP generation by having a specified number of electrons leave the target and strike the chamber wall and other components in the chamber. This short impulse of electrons has a correspondingly broad spectrum, exciting high-frequency structure in the resulting EMP. In this paper, we present results of our initial measurement campaign and comparisons between the measurements and simulations.

  15. Modulated Pulsed Laser Sources for Imaging Lidars

    DTIC Science & Technology

    2007-10-01

    manufactured by QPC. This C-mount device has a monolithic semiconductor amplifier allowing the package to output up to 1.5 Watts at 1064 nm with linewidths ɘ.1...pulsed driver based on the avalanche transistor circuit being used for gain switching, a 1064 nm DFB laser manufactured by QPC and a DBR -style laser...available now that may provide the needed power. An example of such a laser is the QPC C-mount monolithic oscillator/amplifier which can output 1.5

  16. Chemically-Assisted Pulsed Laser-Ramjet

    NASA Astrophysics Data System (ADS)

    Horisawa, Hideyuki; Kaneko, Tomoki; Tamada, Kazunobu

    2010-10-01

    A preliminary study of a chemically-assisted pulsed laser-ramjet was conducted, in which chemical propellant such as a gaseous hydrogen/air mixture was utilized and detonated with a focused laser beam in order to obtain a higher impulse compared to the case only using lasers. CFD analysis of internal conical-nozzle flows and experimental measurements including impulse measurement were conducted to evaluate effects of chemical reaction on thrust performance improvement. From the results, a significant improvement in the thrust performances was confirmed with addition of a small amount of hydrogen to propellant air, or in chemically-augmented operation.

  17. Lasers and Intense Pulsed Light Hidradenitis Suppurativa.

    PubMed

    Saunte, Ditte M; Lapins, Jan

    2016-01-01

    Lasers and intense pulsed light (IPL) treatment are useful for the treatment of hidradenitis suppurativa (HS). Carbon dioxide lasers are used for cutting or vaporization of the affected area. It is a effective therapy for the management of severe and recalcitrant HS with persistent sinus tract and scarring, and can be performed under local anesthesia. HS has a follicular pathogenesis. Lasers and IPL targeting the hair have been found useful in treating HS by reducing the numbers of hairs in areas with HS. The methods have few side effects, but the studies are preliminary and need to be repeated. Copyright © 2016 Elsevier Inc. All rights reserved.

  18. Chemically-Assisted Pulsed Laser-Ramjet

    SciTech Connect

    Horisawa, Hideyuki; Kaneko, Tomoki; Tamada, Kazunobu

    2010-10-13

    A preliminary study of a chemically-assisted pulsed laser-ramjet was conducted, in which chemical propellant such as a gaseous hydrogen/air mixture was utilized and detonated with a focused laser beam in order to obtain a higher impulse compared to the case only using lasers. CFD analysis of internal conical-nozzle flows and experimental measurements including impulse measurement were conducted to evaluate effects of chemical reaction on thrust performance improvement. From the results, a significant improvement in the thrust performances was confirmed with addition of a small amount of hydrogen to propellant air, or in chemically-augmented operation.

  19. Pulse solid state lasers in aesthetic surgery

    NASA Astrophysics Data System (ADS)

    Dobryakov, Boris S.; Greben'kova, Ol'ga B.; Gulev, Valerii S.

    1996-04-01

    The emission of a pulse-periodic laser on alumo-ittrium garnet applied for preventive and medical treatment of a capsule contracture round implanted prostheses in xenoplastics is described in the present paper. The results obtained testify to a high efficiency of suggested method.

  20. Pulsed cyclic laser based on dissociative excitation

    SciTech Connect

    Celto, J.E.; Schimitschek, E.J.

    1980-10-14

    A pulsed laser produces emitted laser energy by dissociative excitation of metal dihalide and cyclic recombination. A metal dihalide selected from subgroup ii-b of the periodic table of elements is contained within an elongate sealed enclosure. Two elongate electrodes having external terminals are supported in parallel relationship within the enclosure, forming a gap parallel to the principal axis of the enclosure. A source of pulsed electric power is connected to the terminals of the two electrodes, producing repetitive transverse electric discharges across the gap. An inert buffer gas is included within the enclosure for aiding electric discharge uniformity, and to provide vibrational relaxation of the lasing medium in its electronic states. The buffer gas is ionized by a third electrode within the enclosure connected to a source of pulses which immediately precede the pulses applied to the first and second electrode so that the lasing medium is preionized immediately prior to the principal electric discharge. Two reflective surfaces, one of which is only partially reflective, are aligned with the principal axis of the laser assembly for producing an optical resonator for the emitted laser energy.

  1. Ultrashort Pulse (USP) Laser-Matter Interactions

    DTIC Science & Technology

    2013-03-05

    unlimited 2D electron wavepacket quantum simulation Source: Luis Plaja, U Salamanca 31 Direct Frequency Comb Spectroscopy in the Extreme...intensity short pulse laser interacting with structured targets yields an enhancement in the number and energy of hot electron. • Monte Carlo

  2. Pulsed laser deposition: Prospects for commercial deposition of epitaxial films

    SciTech Connect

    Muenchausen, R.E.

    1999-03-01

    Pulsed laser deposition (PLD) is a physical vapor deposition (PVD) technique for the deposition of thin films. The vapor source is induced by the flash evaporation that occurs when a laser pulse of sufficient intensity (about 100 MW/cm{sup 2}) is absorbed by a target. In this paper the author briefly defines pulsed laser deposition, current applications, research directed at gaining a better understanding of the pulsed laser deposition process, and suggests some future directions to enable commercial applications.

  3. Extension of harmonic cutoff in a multicycle chirped pulse combined with a chirp-free pulse

    SciTech Connect

    Xu Junjie; Zeng Bin; Yu Yongli

    2010-11-15

    We demonstrate high-order harmonic generation in a wave form synthesized by a multicycle 800-nm chirped laser pulse and a chirp-free laser pulse. Compared with the case of using only a chirped pulse, both the harmonic cutoff and the extreme ultraviolet supercontinuum can be extended when a weak chirp-free pulse is combined with the chirped pulse. When chirp-free pulse intensity grows, the cutoff energy and bandwidth of the supercontinuum grow as well. It is found that the broad supercontinuum can be achieved for a driving pulse with long duration even though the driving pulse reaches 10 optical cycles. An isolated attosecond pulse with duration of about 59 as is obtained, and after appropriate phase compensation with a duration of about 11 as. In addition, by performing time-frequency analyses and the classical trajectory simulation, the difference in supercontinuum generation between the preceding wave form and a similar wave form synthesized by an 800-nm fundamental pulse and a 1600-nm subharmonic pulse is investigated.

  4. Selective breaking of bonds in water with intense, 2-cycle, infrared laser pulses

    SciTech Connect

    Mathur, D. Dharmadhikari, A. K.; Dota, K.; Dey, D.; Tiwari, A. K.; Dharmadhikari, J. A.; De, S.; Vasa, P.

    2015-12-28

    One of the holy grails of contemporary science has been to establish the possibility of preferentially breaking one of several bonds in a molecule. For instance, the two O–H bonds in water are equivalent: given sufficient energy, either one of them is equally likely to break. We report bond-selective molecular fragmentation upon application of intense, 2-cycle pulses of 800 nm laser light: we demonstrate up to three-fold enhancement for preferential bond breaking in isotopically substituted water (HOD). Our experimental observations are rationalized by means of ab initio computations of the potential energy surfaces of HOD, HOD{sup +}, and HOD{sup 2+} and explorations of the dissociation limits resulting from either O–H or O–D bond rupture. The observations we report present a formidable theoretical challenge that need to be taken up in order to gain insights into molecular dynamics, strong field physics, chemical physics, non-adiabatic processes, mass spectrometry, and time-dependent quantum chemistry.

  5. Laser zona dissection using short-pulse ultraviolet lasers

    NASA Astrophysics Data System (ADS)

    Neev, Joseph; Tadir, Yona; Ho, Peter D.; Whalen, William E.; Asch, Richardo H.; Ord, Teri; Berns, Michael W.

    1992-06-01

    The interaction of pulsed ultraviolet radiation with the zona pellucida of human oocytes which had failed to fertilize in standard IVF cycles, was investigated. Two lasers were studied: a 100 ps pulsed Nd:YAG with a nonlinear crystal emitting light at 266 nm, and a 15 ns XeCl excimer laser with 308 nm radiation. Incisions in the zona were made by aiming the beam tangentially to the oocyte. The results indicate superior, high precision performance by the excimer laser creating trenches as narrow as 1 micrometers and as shallow as 1 micrometers . The incision size was found to be sensitive to the laser's energy and to the position of the microscope's objective focal plane, but relatively insensitive to the laser pulse repetition rate. Once the minimum spot size was defined by the system parameters, the laser beam was used to curve out any desired zona shape. This laser microsurgery technique as applied to partial zone dissection or zona drilling could prove very useful as a high-precision, non-contact method for treatments of low fertilization rate and for enhancing embryo implantation rates in patients undergoing IVF treatments.

  6. Femtosecond-pulsed laser micromachining of a 4H SiC wafer for MEMS pressure sensor diaphragms and via holes

    NASA Astrophysics Data System (ADS)

    Dong, Yuanyuan; Nair, Rajeev; Molian, Raathai; Molian, Pal

    2008-03-01

    The challenging issues in conventional microfabrication of SiC pressure sensor diaphragms from bulk wafers are low etch rates, thicker (>40 µm) diaphragms, low spatial resolutions, rough surfaces and substantial contamination. In via hole drilling of SiC, the critical concern is the low drilling speed (nm per minute). In this work, femtosecond (fs)-pulsed laser ablation was conducted to overcome some of these deficiencies. Circular diaphragms (0.5 to 1 mm) by trepanning mode and via holes (30-50 µm) by percussion drilling mode were micromachined in 250 µm thick 4H-SiC single crystals using an 800 nm wavelength, 120 fs, 1 mJ Ti:sapphire laser. Pulse energy, number of pulses and scan rate were varied to obtain a high etch rate and high quality features. Results showed that the etch rates are 2-10 µm per pulse, diaphragm thicknesses are 20-200 µm, surface roughness is 1-2 µm Ra and via hole drilling speeds are up to 25 µm per second. The etch depth control was well within ± 1%. High aspect ratio features with excellent spatial resolutions were obtained due to the absence of thermal damages such as a recast layer and contamination. Thus, femtosecond-pulsed laser ablation by virtue of its unique characteristics such as multiphoton ionization and the absence of lattice heating offers high speed, precision and accuracy in micromachining 4H-SiC wafers.

  7. Spatially modulated laser pulses for printing electronics.

    PubMed

    Auyeung, Raymond C Y; Kim, Heungsoo; Mathews, Scott; Piqué, Alberto

    2015-11-01

    The use of a digital micromirror device (DMD) in laser-induced forward transfer (LIFT) is reviewed. Combining this technique with high-viscosity donor ink (silver nanopaste) results in laser-printed features that are highly congruent in shape and size to the incident laser beam spatial profile. The DMD empowers LIFT to become a highly parallel, rapidly reconfigurable direct-write technology. By adapting half-toning techniques to the DMD bitmap image, the laser transfer threshold fluence for 10 μm features can be reduced using an edge-enhanced beam profile. The integration of LIFT with this beam-shaping technique allows the printing of complex large-area patterns with a single laser pulse.

  8. High power parallel ultrashort pulse laser processing

    NASA Astrophysics Data System (ADS)

    Gillner, Arnold; Gretzki, Patrick; Büsing, Lasse

    2016-03-01

    The class of ultra-short-pulse (USP) laser sources are used, whenever high precession and high quality material processing is demanded. These laser sources deliver pulse duration in the range of ps to fs and are characterized with high peak intensities leading to a direct vaporization of the material with a minimum thermal damage. With the availability of industrial laser source with an average power of up to 1000W, the main challenge consist of the effective energy distribution and disposition. Using lasers with high repetition rates in the MHz region can cause thermal issues like overheating, melt production and low ablation quality. In this paper, we will discuss different approaches for multibeam processing for utilization of high pulse energies. The combination of diffractive optics and conventional galvometer scanner can be used for high throughput laser ablation, but are limited in the optical qualities. We will show which applications can benefit from this hybrid optic and which improvements in productivity are expected. In addition, the optical limitations of the system will be compiled, in order to evaluate the suitability of this approach for any given application.

  9. Group velocity and pulse lengthening of mismatched laser pulses in plasma channels

    SciTech Connect

    Schroeder, Carl; Benedetti, Carlo; Esarey, Eric; van Tilborg, Jeroen; Leemans, Wim

    2011-07-07

    Analytic solutions are presented to the non-paraxial wave equation describing an ultra-short, low-power, laser pulse propagating in aplasma channel. Expressions for the laser pulse centroid motion and laser group velocity are derived, valid for matched and mismatchedpropagation in a parabolic plasma channel, as well as in vacuum, for an arbitrary Laguerre-Gaussian laser mode. The group velocity of amismatched laser pulse, for which the laser spot size is strongly oscillating, is found to be independent of propagation distance andsignificantly less than that of a matched pulse. Laser pulse lengthening of a mismatched pulse owing to laser mode slippage isexamined and found to dominate over that due to dispersive pulse spreading for sufficiently long pulses. Analytic results are shown tobe in excellent agreement with numerical solutions of the full Maxwell equations coupled to the plasma response. Implications for plasmachannel diagnostics are discussed.

  10. Laser-pulse compression using magnetized plasmas

    DOE PAGES

    Shi, Yuan; Qin, Hong; Fisch, Nathaniel J.

    2017-02-28

    Proposals to reach the next generation of laser intensities through Raman or Brillouin backscattering have centered on optical frequencies. Higher frequencies are beyond the range of such methods mainly due to the wave damping that accompanies the higher-density plasmas necessary for compressing higher frequency lasers. However, we find that an external magnetic field transverse to the direction of laser propagation can reduce the required plasma density. Using parametric interactions in magnetized plasmas to mediate pulse compression, both reduces the wave damping and alleviates instabilities, thereby enabling higher frequency or lower intensity pumps to produce pulses at higher intensities and longermore » durations. Finally, in addition to these theoretical advantages, our method in which strong uniform magnetic fields lessen the need for high-density uniform plasmas also lessens key engineering challenges or at least exchanges them for different challenges.« less

  11. Laser-pulse compression using magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Shi, Yuan; Qin, Hong; Fisch, Nathaniel J.

    2017-02-01

    Proposals to reach the next generation of laser intensities through Raman or Brillouin backscattering have centered on optical frequencies. Higher frequencies are beyond the range of such methods mainly due to the wave damping that accompanies the higher-density plasmas necessary for compressing higher frequency lasers. However, we find that an external magnetic field transverse to the direction of laser propagation can reduce the required plasma density. Using parametric interactions in magnetized plasmas to mediate pulse compression, both reduces the wave damping and alleviates instabilities, thereby enabling higher frequency or lower intensity pumps to produce pulses at higher intensities and longer durations. In addition to these theoretical advantages, our method in which strong uniform magnetic fields lessen the need for high-density uniform plasmas also lessens key engineering challenges or at least exchanges them for different challenges.

  12. Phase Noise Comparision of Short Pulse Laser Systems

    SciTech Connect

    S. Zhang; S. V. Benson; J. Hansknecht; D. Hardy; G. Neil; Michelle D. Shinn

    2006-12-01

    This paper describes the phase noise measurement on several different mode-locked laser systems that have completely different gain media and configurations including a multi-kW free-electron laser. We will focus on the state of the art short pulse lasers, especially the drive lasers for photocathode injectors. A comparison between the phase noise of the drive laser pulses, electron bunches and FEL pulses will also be presented.

  13. Double nanosecond pulses generation in ytterbium fiber laser

    SciTech Connect

    Veiko, V. P.; Samokhvalov, A. A. Yakovlev, E. B.; Zhitenev, I. Yu.; Kliushin, A. N.; Lednev, V. N.; Pershin, S. M.

    2016-06-15

    Double pulse generation mode for nanosecond ytterbium fiber laser was developed. Two sequential 60-200 ns laser pulses with variable delay between them were generated by acousto-optic modulator opening with continuous diode pumping. A custom radio frequency generator was developed to produce two sequential “opening” radio pulses with a delay of 0.2–1 μs. It was demonstrated that double pulse generation did not decrease the average laser power while providing the control over the laser pulse power profile. Surprisingly, a greater peak power in the double pulse mode was observed for the second laser pulse. Laser crater studies and plasma emission measurements revealed an improved efficiency of laser ablation in the double pulse mode.

  14. Double nanosecond pulses generation in ytterbium fiber laser

    NASA Astrophysics Data System (ADS)

    Veiko, V. P.; Lednev, V. N.; Pershin, S. M.; Samokhvalov, A. A.; Yakovlev, E. B.; Zhitenev, I. Yu.; Kliushin, A. N.

    2016-06-01

    Double pulse generation mode for nanosecond ytterbium fiber laser was developed. Two sequential 60-200 ns laser pulses with variable delay between them were generated by acousto-optic modulator opening with continuous diode pumping. A custom radio frequency generator was developed to produce two sequential "opening" radio pulses with a delay of 0.2-1 μs. It was demonstrated that double pulse generation did not decrease the average laser power while providing the control over the laser pulse power profile. Surprisingly, a greater peak power in the double pulse mode was observed for the second laser pulse. Laser crater studies and plasma emission measurements revealed an improved efficiency of laser ablation in the double pulse mode.

  15. Dark and bright pulse passive mode-locked laser with in-cavity pulse-shaper.

    PubMed

    Schröder, Jochen B; Coen, Stéphane; Sylvestre, Thibaut; Eggleton, Benjamin J

    2010-10-25

    We demonstrate the integration of a spectral pulse-shaper into a passive mode-locked laser cavity for direct control of the output pulse-shape of the laser. Depending on the dispersion filter applied with the pulse-shaper we either observe a bright or dark "soliton-like" pulse train. The results demonstrate the strong potential of an in-cavity spectral pulse-shaper as an experimental tool for controlling the dynamics of passively mode-locked lasers.

  16. Pulsed Power for Solid-State Lasers

    SciTech Connect

    Gagnon, W; Albrecht, G; Trenholme, J; Newton, M

    2007-04-19

    Beginning in the early 1970s, a number of research and development efforts were undertaken at U.S. National Laboratories with a goal of developing high power lasers whose characteristics were suitable for investigating the feasibility of laser-driven fusion. A number of different laser systems were developed and tested at ever larger scale in pursuit of the optimum driver for laser fusion experiments. Each of these systems had associated with it a unique pulsed power option. A considerable amount of original and innovative engineering was carried out in support of these options. Ultimately, the Solid-state Laser approach was selected as the optimum driver for the application. Following this, the Laser Program at the Lawrence Livermore National Laboratory and the University of Rochester undertook aggressive efforts directed at developing the technology. In particular, at Lawrence Livermore National Laboratory, a series of laser systems beginning with the Cyclops laser and culminating in the present with the National Ignition Facility were developed and tested. As a result, a large amount of design information for solid-state laser pulsed power systems has been documented. Some of it is in the form of published papers, but most of it is buried in internal memoranda, engineering reports and LLNL annual reports. One of the goals of this book is to gather this information into a single useable format, such that it is easily accessed and understood by other engineers and physicists for use with future designs. It can also serve as a primer, which when seriously studied, makes the subsequent reading of original work and follow-up references considerably easier. While this book deals only with the solid-state laser pulsed power systems, in the bibliography we have included a representative cross section of papers and references from much of the very fine work carried out at other institutions in support of different laser approaches. Finally, in recent years, there has

  17. Laser-Induced Damage with Femtosecond Pulses

    NASA Astrophysics Data System (ADS)

    Kafka, Kyle R. P.

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

  18. Simultaneous time-space resolved reflectivity and interferometric measurements of dielectrics excited with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Garcia-Lechuga, M.; Haahr-Lillevang, L.; Siegel, J.; Balling, P.; Guizard, S.; Solis, J.

    2017-06-01

    Simultaneous time-and-space resolved reflectivity and interferometric measurements over a temporal span of 300 ps have been performed in fused silica and sapphire samples excited with 800 nm, 120 fs laser pulses at energies slightly and well above the ablation threshold. The experimental results have been simulated in the frame of a multiple-rate equation model including light propagation. The comparison of the temporal evolution of the reflectivity and the interferometric measurements at 400 nm clearly shows that the two techniques interrogate different material volumes during the course of the process. While the former is sensitive to the evolution of the plasma density in a very thin ablating layer at the surface, the second yields an averaged plasma density over a larger volume. It is shown that self-trapped excitons do not appreciably contribute to carrier relaxation in fused silica at fluences above the ablation threshold, most likely due to Coulomb screening effects at large excited carrier densities. For both materials, at fluences well above the ablation threshold, the maximum measured plasma reflectivity shows a saturation behavior consistent with a scattering rate proportional to the plasma density in this fluence regime. Moreover, for both materials and for pulse energies above the ablation threshold and delays in the few tens of picoseconds range, a simultaneous "low reflectivity" and "low transmission" behavior is observed. Although this behavior has been identified in the past as a signature of femtosecond laser-induced ablation, its origin is alternatively discussed in terms of the optical properties of a material undergoing strong isochoric heating, before having time to substantially expand or exchange energy with the surrounding media.

  19. Post pulse shutter for laser amplifier

    DOEpatents

    Bradley, Laird P. [Livermore, CA; Carder, Bruce M. [Antioch, CA; Gagnon, William L. [Berkeley, CA

    1981-03-17

    Apparatus and method for quickly closing off the return path for an amplified laser pulse at the output of an amplifier so as to prevent damage to amplifiers and other optical components appearing earlier in the chain by the return of an amplified pulse. The apparatus consists of a fast retropulse or post pulse shutter to suppress target reflection and/or beam return. This is accomplished by either quickly placing a solid across the light transmitting aperture of a component in the chain, such as a spatial filter pinhole, or generating and directing a plasma with sufficiently high density across the aperture, so as to, in effect, close the aperture to the returning amplified energy pulse.

  20. Post pulse shutter for laser amplifier

    DOEpatents

    Bradley, L.P.; Carder, B.M.; Gagnon, W.L.

    1981-03-17

    Disclosed are an apparatus and method for quickly closing off the return path for an amplified laser pulse at the output of an amplifier so as to prevent damage to amplifiers and other optical components appearing earlier in the chain by the return of an amplified pulse. The apparatus consists of a fast retropulse or post pulse shutter to suppress target reflection and/or beam return. This is accomplished by either quickly placing a solid across the light transmitting aperture of a component in the chain, such as a spatial filter pinhole, or generating and directing a plasma with sufficiently high density across the aperture, so as to, in effect, close the aperture to the returning amplified energy pulse. 13 figs.

  1. Laser-supported detonation waves and pulsed laser propulsion

    SciTech Connect

    Kare, J. )

    1990-07-30

    A laser thermal rocket uses the energy of a large remote laser, possibly ground-based, to heat an inert propellant and generate thrust. Use of a pulsed laser allows the design of extremely simple thrusters with very high performance compared to chemical rockets. The temperatures, pressures, and fluxes involved in such thrusters (10{sup 4} K, 10{sup 2} atmospheres, 10{sup 7} w/cm{sup 2}) typically result in the creation of laser-supported detonation (LSD) waves. The thrust cycle thus involves a complex set of transient shock phenomena, including laser-surface interactions in the ignition of the LSD wave, laser-plasma interactions in the LSD wave itself, and high-temperature nonequilibrium chemistry behind the LSD wave. The SDIO Laser Propulsion Program is investigating these phenomena as part of an overall effort to develop the technology for a low-cost Earth-to-orbit laser launch system. We will summarize the Program's approach to developing a high performance thruster, the double-pulse planar thruster, and present an overview of some results obtained to date, along with a discussion of the many research question still outstanding in this area.

  2. Laser-supported detonation waves and pulsed laser propulsion

    SciTech Connect

    Kare, J.T.

    1989-01-01

    A laser thermal rocket uses the energy of a large remote laser, possibly ground-based, to heat an inert propellant and generate thrust. Use of a pulsed laser allows the design of extremely simple thrusters with very high performance compared to chemical rockets. The temperatures, pressures, and fluxes involved in such thrusters (10{sup 4} K, 10{sup 2} atmospheres, 10{sup 7} w/cm{sup 2}) typically result in the creation of laser-supported detonation (LSD) waves. The thrust cycle thus involves a complex set of transient shock phenomena, including laser-surface interactions in the ignition if the LSD wave, laser-plasma interactions in the LSD wave itself, and high-temperature nonequilibrium chemistry behind the LSD wave. The SDIO Laser Propulsion Program is investigating these phenomena as part of an overall effort to develop the technology for a low-cost Earth-to-orbit laser launch system. We will summarize the program's approach to developing a high performance thruster, the double-pulse planar thruster, and present an overview of some results obtained to date, along with a discussion of the many research questions still outstanding in this area. 16 refs., 7 figs.

  3. Selective laser melting of copper using ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Kaden, Lisa; Matthäus, Gabor; Ullsperger, Tobias; Engelhardt, Hannes; Rettenmayr, Markus; Tünnermann, Andreas; Nolte, Stefan

    2017-09-01

    Within the field of laser-assisted additive manufacturing, the application of ultrashort pulse lasers for selective laser melting came into focus recently. In contrast to conventional lasers, these systems provide extremely high peak power at ultrashort interaction times and offer the potential to control the thermal impact at the vicinity of the processed region by tailoring the pulse repetition rate. Consequently, materials with extremely high melting points such as tungsten or special composites such as AlSi40 can be processed. In this paper, we present the selective laser melting of copper using 500 fs laser pulses at MHz repetition rates emitted at a center wavelength of about 1030 nm. To identify an appropriate processing window, a detailed parameter study was performed. We demonstrate the fabrication of bulk copper parts as well as the realization of thin-wall structures featuring thicknesses below 100 {μ }m. With respect to the extraordinary high thermal conductivity of copper which in general prevents the additive manufacturing of elements with micrometer resolution, this work demonstrates the potential for sophisticated copper products that can be applied in a wide field of applications extending from microelectronics functionality to complex cooling structures.

  4. Comparison of amplified spontaneous emission pulse cleaners for use in chirped pulse amplification front end lasers

    SciTech Connect

    Dawson, J; Siders, C; Phan, H; Kanz, V; Barty, C

    2007-07-02

    We compare various schemes for removing amplified spontaneous emission from seed laser pulses. We focus on compact schemes that are compatible with fiber laser front end systems with pulse energies in the 10nJ-1{micro}J range and pulse widths in the 100fs-10ps range. Pre-pulse contrast ratios greater than 10{sup 9} have been measured.

  5. On-axis pulsed laser deposition of hybrid perovskite films for solar cell and broadband photo-sensor applications

    NASA Astrophysics Data System (ADS)

    Bansode, Umesh; Ogale, Satishchandra

    2017-04-01

    High quality hybrid perovskite films are grown by the pulsed laser deposition (PLD) process through target stoichiometry and gas ambient control in the commonly used on-axis geometry which is compatible with PLD of other materials such as metal oxides. The use of an off-stoichiometric target and a momentum softening gas mixture of argon and hydrogen (90%:10%) is shown to yield dense films in the on-axis geometry with excellent stoichiometry and optical quality. The band gap can be easily tuned from 1.6 to 2.3 eV with either mixed halide composite target or successive depositions of inter-diffusing MAPbBr3 and MAPbI3 layers. A photosensor based on PLD grown MAPbI3 is shown to render impressive performance over the broad range of wavelengths from 375 to 800 nm at a voltage of 5 V bias. A planar heterojunction solar cell based on the dry-processed on-axis PLD grown film exhibits a champion conversion efficiency of 10.9%. A heterostructure comprising in situ pulsed laser deposited Cu2O (p-type) followed by the hybrid perovskite film shows a rectifying characteristic and photoresponse.

  6. 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.

  7. Laser-Material Interaction of Powerful Ultrashort Laser Pulses

    SciTech Connect

    Komashko, A

    2003-01-06

    Laser-material interaction of powerful (up to a terawatt) ultrashort (several picoseconds or shorter) laser pulses and laser-induced effects were investigated theoretically in this dissertation. Since the ultrashort laser pulse (USLP) duration time is much smaller than the characteristic time of the hydrodynamic expansion and thermal diffusion, the interaction occurs at a solid-like material density with most of the light energy absorbed in a thin surface layer. Powerful USLP creates hot, high-pressure plasma, which is quickly ejected without significant energy diffusion into the bulk of the material, Thus collateral damage is reduced. These and other features make USLPs attractive for a variety of applications. The purpose of this dissertation was development of the physical models and numerical tools for improvement of our understanding of the process and as an aid in optimization of the USLP applications. The study is concentrated on two types of materials - simple metals (materials like aluminum or copper) and wide-bandgap dielectrics (fused silica, water). First, key physical phenomena of the ultrashort light interaction with metals and the models needed to describe it are presented. Then, employing one-dimensional plasma hydrodynamics code enhanced with models for laser energy deposition and material properties at low and moderate temperatures, light absorption was self-consistently simulated as a function of laser wavelength, pulse energy and length, angle of incidence and polarization. Next, material response on time scales much longer than the pulse duration was studied using the hydrocode and analytical models. These studies include examination of evolution of the pressure pulses, effects of the shock waves, material ablation and removal and three-dimensional dynamics of the ablation plume. Investigation of the interaction with wide-bandgap dielectrics was stimulated by the experimental studies of the USLP surface ablation of water (water is a model of

  8. Method and apparatus for the production of pre pulse free smooth laser radiation pulses of variable pulse duration

    SciTech Connect

    Witte, K. J.; Fill, E.; Scrlac, W.

    1985-04-30

    The pulse duration of an iodine laser is adjusted between 400 ps and 20 ns primarily by changing the resonator length in the range of about 2 cm to about 100 cm and secondarily by the ratio of excitation energy to threshold energy of the laser. Iodine laser pulses without pre-pulse and substructure are achieved in that the gas pressure of the laser gas of the iodine laser is adapted to the resonator length in order to limit the band width of the amplification and thus the band width of the pulse to be produced. The longer are the laser pulses to be produced the lower is the pressure chosen. A prerequisite for the above results is that the excitation of the iodine laser occurs extremely rapidly. This is advantageously achieved by photo-dissociation of a perfluoroalkyl iodide as CF/sub 3/I by means of laser providing sufficiently short output pumping pulses, e.g. an excimer laser, as a KrF laser or XeCl laser or a frequency-multiplied Nd-glass or Nd-YAG laser, or a N/sub 2/ laser (in combination with t-C/sub 4/F/sub 9/I as laser medium). In addition to the substantial advantage of the easy variability of the pulse duration the method additionally has a number of further advantages, namely pre-pulse-free rise of the laser pulse up to the maximum amplitude; exchange of the laser medium between two pulses is not necessary at pulse repetition rates below about 1 hertz; high pulse repetion rates obtainable with laser gas regeneration; switching elements for isolating a laser oscillator from a subsequent amplifier cascade for the purpose of avoiding parasitic oscillations are not as critical as with flashlamp-pumped lasers.

  9. Laser-driven hydrothermal process studied with excimer laser pulses

    NASA Astrophysics Data System (ADS)

    Mariella, Raymond; Rubenchik, Alexander; Fong, Erika; Norton, Mary; Hollingsworth, William; Clarkson, James; Johnsen, Howard; Osborn, David L.

    2017-08-01

    Previously, we discovered [Mariella et al., J. Appl. Phys. 114, 014904 (2013)] that modest-fluence/modest-intensity 351-nm laser pulses, with insufficient fluence/intensity to ablate rock, mineral, or concrete samples via surface vaporization, still removed the surface material from water-submerged target samples with confinement of the removed material, and then dispersed at least some of the removed material into the water as a long-lived suspension of nanoparticles. We called this new process, which appears to include the generation of larger colorless particles, "laser-driven hydrothermal processing" (LDHP) [Mariella et al., J. Appl. Phys. 114, 014904 (2013)]. We, now, report that we have studied this process using 248-nm and 193-nm laser light on submerged concrete, quartzite, and obsidian, and, even though light at these wavelengths is more strongly absorbed than at 351 nm, we found that the overall efficiency of LDHP, in terms of the mass of the target removed per Joule of laser-pulse energy, is lower with 248-nm and 193-nm laser pulses than with 351-nm laser pulses. Given that stronger absorption creates higher peak surface temperatures for comparable laser fluence and intensity, it was surprising to observe reduced efficiencies for material removal. We also measured the nascent particle-size distributions that LDHP creates in the submerging water and found that they do not display the long tail towards larger particle sizes that we had observed when there had been a multi-week delay between experiments and the date of measuring the size distributions. This is consistent with transient dissolution of the solid surface, followed by diffusion-limited kinetics of nucleation and growth of particles from the resulting thin layer of supersaturated solution at the sample surface.

  10. Pulsed laser radiation therapy of skin tumors

    SciTech Connect

    Kozlov, A.P.; Moskalik, K.G.

    1980-11-15

    Radiation from a neodymium laser was used to treat 846 patients with 687 precancerous lesions or benign tumors of the skin, 516 cutaneous carcinomas, 33 recurrences of cancer, 51 melanomas, and 508 metastatic melanomas in the skin. The patients have been followed for three months to 6.5 years. No relapses have been observed during this period. Metastases to regional lymph nodes were found in five patients with skin melanoma. Pulsed laser radiation may be successfully used in the treatment of precancerous lesions and benign tumors as well as for skin carcinoma and its recurrences, and for skin melanoma. Laser radiation is more effective in the treatment of tumors inaccessible to radiation therapy and better in those cases in which surgery may have a bad cosmetic or even mutilating effect. Laser beams can be employed in conjunction with chemo- or immunotherapy.

  11. Pulse Compression Techniques for Laser Generated Ultrasound

    NASA Technical Reports Server (NTRS)

    Anastasi, R. F.; Madaras, E. I.

    1999-01-01

    Laser generated ultrasound for nondestructive evaluation has an optical power density limit due to rapid high heating that causes material damage. This damage threshold limits the generated ultrasound amplitude, which impacts nondestructive evaluation inspection capability. To increase ultrasound signal levels and improve the ultrasound signal-to-noise ratio without exceeding laser power limitations, it is possible to use pulse compression techniques. The approach illustrated here uses a 150mW laser-diode modulated with a pseudo-random sequence and signal correlation. Results demonstrate the successful generation of ultrasonic bulk waves in aluminum and graphite-epoxy composite materials using a modulated low-power laser diode and illustrate ultrasound bandwidth control.

  12. Nd3+ sensitized up/down converting dual-mode nanomaterials for efficient in-vitro and in-vivo bioimaging excited at 800 nm.

    PubMed

    Li, Xiaomin; Wang, Rui; Zhang, Fan; Zhou, Lei; Shen, Dengke; Yao, Chi; Zhao, Dongyuan

    2013-12-18

    Core/shell1/shell2/shell3 structured NaGdF4:Nd/NaYF4/NaGdF4:Nd,Yb,Er/NaYF4 nanocrystals were well designed and synthesized, each of the parts assume respective role and work together to achieve dual-mode upconverting (UC) and downconverting (DC) luminescence upon the low heat effect 800-nm excitation. Nd(3+), Yb(3+), Er(3+) tri-doped NaGdF4:Nd,Yb,Er UC layer [NIR (800 nm)-to-Visible (540 nm)] with a constitutional efficient 800 nm excitable property were achieved for the in-vitro bioimaging with low auto-fluorescence and photo-damage effects. Moreover, typical NIR (800 nm)-to-NIR (860-895 nm) DC luminescence of Nd(3+) has also been realized with this designed nanostructure. Due to the low heat effect, high penetration depth of the excitation and the high efficiency of the DC luminescence, the in-vivo high contrast DC imaging of a whole body nude mouse was achieved. We believe that such dual-mode luminescence NCs will open the door to engineering the excitation and emission wavelengths of NCs and will provide a new tool for a wide variety of applications in the fields of bioanalysis and biomedical.

  13. GEOS-1 laser pulse return shape analysis

    NASA Technical Reports Server (NTRS)

    Felsentreger, T. L.

    1972-01-01

    An attempt has been made to predict the shape of the laser return pulse from the corner cube retroreflectors on the GEOS-1 spacecraft. The study is geometrical only, and neglects factors such as optical interference, atmospheric perturbations, etc. A function giving the intensity of the return signal at any given time has been derived. In addition, figures are given which show the predicted return pulse shape as a function of time, the angle between the beam and the spin axis, and an in-plane angle (designating the orientation of the intersection of the planar waves with the plane of the corner cubes).

  14. Nanosecond laser ablation for pulsed laser deposition of yttria

    NASA Astrophysics Data System (ADS)

    Sinha, Sucharita

    2013-09-01

    A thermal model to describe high-power nanosecond pulsed laser ablation of yttria (Y2O3) has been developed. This model simulates ablation of material occurring primarily through vaporization and also accounts for attenuation of the incident laser beam in the evolving vapor plume. Theoretical estimates of process features such as time evolution of target temperature distribution, melt depth and ablation rate and their dependence on laser parameters particularly for laser fluences in the range of 6 to 30 J/cm2 are investigated. Calculated maximum surface temperatures when compared with the estimated critical temperature for yttria indicate absence of explosive boiling at typical laser fluxes of 10 to 30 J/cm2. Material ejection in large fragments associated with explosive boiling of the target needs to be avoided when depositing thin films via the pulsed laser deposition (PLD) technique as it leads to coatings with high residual porosity and poor compaction restricting the protective quality of such corrosion-resistant yttria coatings. Our model calculations facilitate proper selection of laser parameters to be employed for deposition of PLD yttria corrosion-resistive coatings. Such coatings have been found to be highly effective in handling and containment of liquid uranium.

  15. High speed sampling circuit design for pulse laser ranging

    NASA Astrophysics Data System (ADS)

    Qian, Rui-hai; Gao, Xuan-yi; Zhang, Yan-mei; Li, Huan; Guo, Hai-chao; Guo, Xiao-kang; He, Shi-jie

    2016-10-01

    In recent years, with the rapid development of digital chip, high speed sampling rate analog to digital conversion chip can be used to sample narrow laser pulse echo. Moreover, high speed processor is widely applied to achieve digital laser echo signal processing algorithm. The development of digital chip greatly improved the laser ranging detection accuracy. High speed sampling and processing circuit used in the laser ranging detection system has gradually been a research hotspot. In this paper, a pulse laser echo data logging and digital signal processing circuit system is studied based on the high speed sampling. This circuit consists of two parts: the pulse laser echo data processing circuit and the data transmission circuit. The pulse laser echo data processing circuit includes a laser diode, a laser detector and a high sample rate data logging circuit. The data transmission circuit receives the processed data from the pulse laser echo data processing circuit. The sample data is transmitted to the computer through USB2.0 interface. Finally, a PC interface is designed using C# language, in which the sampling laser pulse echo signal is demonstrated and the processed laser pulse is plotted. Finally, the laser ranging experiment is carried out to test the pulse laser echo data logging and digital signal processing circuit system. The experiment result demonstrates that the laser ranging hardware system achieved high speed data logging, high speed processing and high speed sampling data transmission.

  16. Electron acceleration by a propagating laser pulse in vacuum

    SciTech Connect

    Wang Fengchao; Shen Baifei; Zhang Xiaomei; Li Xuemei; Jin Zhangying

    2007-08-15

    Electrons accelerated by a propagating laser pulse of linear or circular polarization in vacuum have been investigated by one-dimensional particle-in-cell simulations and analytical modeling. A stopping target is used to stop the laser pulse and extract the energetic electrons from the laser field. The effect of the reflected light is taken into account. The maximum electron energy depends on the laser intensity and initial electron energy. There is an optimal acceleration length for electrons to gain maximum energy where electrons meet the peak of the laser pulse. The optimal acceleration length depends strongly on the laser pulse duration and amplitude.

  17. Pulse-burst laser systems for fast Thomson scattering (invited)

    SciTech Connect

    Den Hartog, D. J.; Ambuel, J. R.; Holly, D. J.; Robl, P. E.; Borchardt, M. T.; Falkowski, A. F.; Harris, W. S.; Parke, E.; Reusch, J. A.; Stephens, H. D.; Yang, Y. M.

    2010-10-15

    Two standard commercial flashlamp-pumped Nd:YAG (YAG denotes yttrium aluminum garnet) lasers have been upgraded to ''pulse-burst'' capability. Each laser produces a burst of up to 15 2 J Q-switched pulses (1064 nm) at repetition rates of 1-12.5 kHz. Variable pulse-width drive (0.15-0.39 ms) of the flashlamps is accomplished by insulated gate bipolar transistor (IGBT) switching of electrolytic capacitor banks. Direct control of the laser Pockels cell drive enables optimal pulse energy extraction, and up to four 2 J laser pulses during one flashlamp pulse. These lasers are used in the Thomson scattering plasma diagnostic system on the MST reversed-field pinch to record the dynamic evolution of the electron temperature profile and temperature fluctuations. To further these investigations, a custom pulse-burst laser system with a maximum pulse repetition rate of 250 kHz is now being commissioned.

  18. Pulse-burst laser systems for fast Thomson scattering (invited).

    PubMed

    Den Hartog, D J; Ambuel, J R; Borchardt, M T; Falkowski, A F; Harris, W S; Holly, D J; Parke, E; Reusch, J A; Robl, P E; Stephens, H D; Yang, Y M

    2010-10-01

    Two standard commercial flashlamp-pumped Nd:YAG (YAG denotes yttrium aluminum garnet) lasers have been upgraded to "pulse-burst" capability. Each laser produces a burst of up to 15 2 J Q-switched pulses (1064 nm) at repetition rates of 1-12.5 kHz. Variable pulse-width drive (0.15-0.39 ms) of the flashlamps is accomplished by insulated gate bipolar transistor (IGBT) switching of electrolytic capacitor banks. Direct control of the laser Pockels cell drive enables optimal pulse energy extraction, and up to four 2 J laser pulses during one flashlamp pulse. These lasers are used in the Thomson scattering plasma diagnostic system on the MST reversed-field pinch to record the dynamic evolution of the electron temperature profile and temperature fluctuations. To further these investigations, a custom pulse-burst laser system with a maximum pulse repetition rate of 250 kHz is now being commissioned.

  19. Pulsed laser triggered high speed microfluidic switch

    NASA Astrophysics Data System (ADS)

    Wu, Ting-Hsiang; Gao, Lanyu; Chen, Yue; Wei, Kenneth; Chiou, Pei-Yu

    2008-10-01

    We report a high-speed microfluidic switch capable of achieving a switching time of 10 μs. The switching mechanism is realized by exciting dynamic vapor bubbles with focused laser pulses in a microfluidic polydimethylsiloxane (PDMS) channel. The bubble expansion deforms the elastic PDMS channel wall and squeezes the adjacent sample channel to control its fluid and particle flows as captured by the time-resolved imaging system. A switching of polystyrene microspheres in a Y-shaped channel has also been demonstrated. This ultrafast laser triggered switching mechanism has the potential to advance the sorting speed of state-of-the-art microscale fluorescence activated cell sorting devices.

  20. Nanosecond pulsed laser blackening of copper

    NASA Astrophysics Data System (ADS)

    Tang, Guang; Hourd, Andrew C.; Abdolvand, Amin

    2012-12-01

    Nanosecond (12 ns) pulsed laser processing of copper at 532 nm resulted in the formation of homogenously distributed, highly organized microstructures. This led to the fabrication of large area black copper substrates with absorbance of over 97% in the spectral range from 250 nm to 750 nm, and a broadband absorbance of over 80% between 750 nm and 2500 nm. Optical and chemical analyses of the fabricated black metal are presented and discussed. The employed laser is an industrially adaptable source and the presented technique for fabrication of black copper could find applications in broadband thermal radiation sources, solar energy absorbers, irradiative heat transfer devices, and thermophotovoltaics.

  1. Control of XeF laser output by pulse injection

    NASA Technical Reports Server (NTRS)

    Pacala, T. J.; Christensen, C. P.

    1980-01-01

    Injection locking is investigated as a means for control of optical pulse duration and polarization in a XeF laser. Intense short-pulse generation in the ultraviolet is achieved by injection of a low-level 1-ns optical pulse into a XeF oscillator. Control of laser output polarization by injection locking is demonstrated and studied as a function of injected signal level. Enhancement of XeF electric-discharge laser efficiency by injection pulse 'priming' is observed.

  2. 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.

  3. Plasma generated during underwater pulsed laser processing

    NASA Astrophysics Data System (ADS)

    Hoffman, Jacek; Chrzanowska, Justyna; Moscicki, Tomasz; Radziejewska, Joanna; Stobinski, Leszek; Szymanski, Zygmunt

    2017-09-01

    The plasma induced during underwater pulsed laser ablation of graphite is studied both experimentally and theoretically. The results of the experiment show that the maximum plasma temperature of 25000 K is reached 20 ns from the beginning of the laser pulse and decreases to 6500 K after 1000 ns. The observed OH absorption band shows that the plasma plume is surrounded by the thin layer of dissociated water vapour at a temperature around 5500 K. The hydrodynamic model applied shows similar maximum plasma temperature at delay times between 14 ns and 30 ns. The calculations show also that already at 14th ns, the plasma electron density reaches 0.97·1027 m-3, which is the critical density for 1064 nm radiation. At the same time the plasma pressure is 2 GPa, which is consisted with earlier measurements of the peak pressure exerted on a target in similar conditions.

  4. Pulse switching for high energy lasers

    NASA Technical Reports Server (NTRS)

    Laudenslager, J. B.; Pacala, T. J. (Inventor)

    1981-01-01

    A saturable inductor switch for compressing the width and sharpening the rise time of high voltage pulses from a relatively slow rise time, high voltage generator to an electric discharge gas laser (EDGL) also provides a capability for efficient energy transfer from a high impedance primary source to an intermediate low impedance laser discharge network. The switch is positioned with respect to a capacitive storage device, such as a coaxial cable, so that when a charge build-up in the storage device reaches a predetermined level, saturation of the switch inductor releases or switches energy stored in the capactive storage device to the EDGL. Cascaded saturable inductor switches for providing output pulses having rise times of less than ten nanoseconds and a technique for magnetically biasing the saturable inductor switch are disclosed.

  5. Short-pulse laser materials processing

    SciTech Connect

    Stuart, B.C.; Perry, M.D.; Myers, B.R.; Banks, P.S.; Honea, E.C.

    1997-06-18

    While there is much that we have learned about materials processing in the ultrashort-pulse regime, there is an enormous amount that we don`t know. How short does the pulse have to be to achieve a particular cut (depth, material, quality)? How deep can you cut? What is the surface roughness? These questions are clearly dependent upon the properties of the material of interest along with the short-pulse interaction physics. From a technology standpoint, we are asked: Can you build a 100 W average power system ? A 1000 W average power system? This proposal seeks to address these questions with a combined experimental and theoretical program of study. Specifically, To develop an empirical database for both metals and dielectrics which can be used to determine the pulse duration and wavelength necessary to achieve a specific machining requirement. To investigate Yb:YAG as a potential laser material for high average power short-pulse systems both directly and in combination with titanium doped sapphire. To develop a conceptual design for a lOOW and eventually 5OOW average power short-pulse system.

  6. Laser pulse stretcher method and apparatus

    DOEpatents

    Hawkins, Jon K.; Williams, William A.

    1990-01-01

    The output of an oscillator stage of a laser system is monitored by a photocell which is coupled to a feedback section to control a Pockels Cell and change the light output of the oscillator stage. A synchronizing pulse is generated in timed relation to the initiation of operation of the oscillator stage and is applied to a forward feed section which cooperates with the feedback section to maintain the light output constant for an extended time interval.

  7. Magnetron Sputtered Pulsed Laser Deposition Scale Up

    DTIC Science & Technology

    2003-08-14

    2:721-726 34 S. J. P. Laube and E. F. Stark, “ Artificial Intellegence in Process Control of Pulsed Laser Deposition”, Proceedings of...The model would be based on mathematical simulation of real process data, neural-networks, or other artificial intelligence methods based on in situ...Laube and E. F. Stark, Proc. Symp. Artificial Intel. Real Time Control, Valencia, Spain, 3-5 Oct. ,1994, p.159-163. International Federation of

  8. Metal-Silicide Formation With Laser Pulses

    NASA Astrophysics Data System (ADS)

    Luches, Armando; Leggieri, Gilberto; D'Anna, Emilia

    1989-05-01

    The most relevant results obtained in the field of the synthesis of metal suicides with pulsed lasers in the nanosecond regime are reviewed. Particular emphasis is given to the results obtained in our laboratories. Formation of stable and metastable compounds, their structure and the surface morphology of the irradiated materials are discussed. The reaction kinetics is investigated through a comparison of the experimental results with the temperatures of the irradiated samples, calculated by solving the heat diffusion equation.

  9. Rectangular Pulsed Laser-Electromagnetic Hybrid Accelerator

    SciTech Connect

    Kishida, Yoshiaki; Katayama, Masahiro; Horisawa, Hideyuki

    2010-10-13

    Experimental investigation of impulse-bit and propellant consumption rate, or mass shot, per single pulse discharge was conducted to characterize the thrust performance of the rectangular laser-electromagnetic hybrid acceleration thruster with various propellant materials. From the result, alumina propellant showed significantly superior performance. The largest values of the measured impulse-bit, specific impulse and thrust efficiency were 49 {mu}Nsec, 6,200 sec and 22%, respectively.

  10. Large grain growth of Ge-rich Ge1-xSnx (x ≈ 0.02) on insulating surfaces using pulsed laser annealing in flowing water

    NASA Astrophysics Data System (ADS)

    Kurosawa, Masashi; Taoka, Noriyuki; Ikenoue, Hiroshi; Nakatsuka, Osamu; Zaima, Shigeaki

    2014-02-01

    We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge1-xSnx (x < 0.02) on SiO2 crystallized by pulsed laser annealing (PLA) in air and water. Despite the very low Sn content of 2%, Sn atoms within the GeSn layers play a role in preventing ablation and aggregation of the layers during these PLA. Raman and electron backscatter diffraction measurements demonstrate achievement of large-grain (˜800 nmϕ) growth of Ge0.98Sn0.02 polycrystals by using PLA in water. These polycrystals also show a tensile-strain of ˜0.68%. This result opens up the possibility for developing GeSn-based devices fabricated on flexible substrates as well as Si platforms.

  11. First in vivo animal studies on intraocular nanosurgery and multiphoton tomography with low-energy 80-MHz near-infrared femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Konig, Karsten; Wang, Bagui; Krauss, Oliver; Riemann, Iris; Schubert, Harald; Kirste, Sigrun; Fischer, Peter

    2004-07-01

    We report on a method for refractive laser surgery based on low-energy femtosecond laser pulses provided by ultracompact turn-key non-amplified laser systems. An additional excimer laser is not required for ablation of the stroma. The novel method has the potential to be used for (i) optical flap creation as well as stroma ablation and (ii) for non-invasive flap-free intrastromal ablation. In addition, 3D multiphoton imaging of the cornea can be performed. In particular, we used sub-nanojoule near infrared 80 MHz femtosecond laser pulses for multiphoton imaging of corneal structures with ultrahigh resolution (< 1μm) as well as for highly precise intraocular refractive surgery. Imaging based on two-photon excited cellular autofluorescence and SHG formation in collagen structures was performed at GW/cm2 intensities, whereas destructive optical breakdown for nanoprocessing occurred at TW/cm2 light intensities. These high intensities were realized with sub-nJ pulses within a subfemtoliter intrastromal volume by diffraction-limited focussing with high NA objectives and beam scanning 50 to 140 μm below the epithelial surface. Multiphoton tomography of the cornea was used to determine the target of interest and to visualize intraocular post-laser effects. Histological examination with light- and electron microscopes of laser-exposed porcine and rabbit eyes reveal a minimum intratissue cut size below 1 μm without destructive effects to surrounding collagen structures. LASIK flaps and intracorneal cavities could be realized with high precision using 200 fs, 80 MHz, sub-nanojoule pulses at 800 nm. First studies on 80 MHz femtosecond laser surgery on living rabbits have been performed.

  12. Picosecond pulse measurements using the active laser medium

    NASA Technical Reports Server (NTRS)

    Bernardin, James P.; Lawandy, N. M.

    1990-01-01

    A simple method for measuring the pulse lengths of synchronously pumped dye lasers which does not require the use of an external nonlinear medium, such as a doubling crystal or two-photon fluorescence cell, to autocorrelate the pulses is discussed. The technique involves feeding the laser pulses back into the dye jet, thus correlating the output pulses with the intracavity pulses to obtain pulse length signatures in the resulting time-averaged laser power. Experimental measurements were performed using a rhodamine 6G dye laser pumped by a mode-locked frequency-doubled Nd:YAG laser. The results agree well with numerical computations, and the method proves effective in determining lengths of picosecond laser pulses.

  13. Pulsed-discharge carbon dioxide lasers

    NASA Technical Reports Server (NTRS)

    Willetts, David V.

    1990-01-01

    The purpose is to attempt a general introduction to pulsed carbon dioxide lasers of the kind used or proposed for laser radar applications. Laser physics is an excellent example of a cross-disciplinary topic, and the molecular spectroscopy, energy transfer, and plasma kinetics of the devices are explored. The concept of stimulated emission and population inversions is introduced, leading on to the molecular spectroscopy of the CO2 molecule. This is followed by a consideration of electron-impact pumping, and the pertinent energy transfer and relaxation processes which go on. Since the devices are plasma pumped, it is necessary to introduce a complex subject, but this is restricted to appropriate physics of glow discharges. Examples of representative devices are shown. The implications of the foregoing to plasma chemistry and gas life are discussed.

  14. Shock profile induced by short laser pulses

    NASA Astrophysics Data System (ADS)

    Couturier, S.; de Rességuier, T.; Hallouin, M.; Romain, J. P.; Bauer, F.

    1996-06-01

    Standard 25-μm-thick polyvinilydene fluoride (PVDF) piezoelectric gauges and new 450-μm-thick P(VDF 70%, TrFE 30%) piezoelectric copolymer have been used to record shock profiles at the back face of metallic targets irradiated by laser pulses of 2.5 and 0.6 ns duration at a 1.06 μm wavelength. The records are fully explained with simplified space-time diagram analysis. The pressure profile applied at the front face of the target has been determined from these records combined with numerical simulations of wave propagation through the target. A numerical code describing the interaction of laser with matter (FILM) has also been used for computing the applied pressure. Both methods lead to very close results. The peak pressure dependence on incident laser intensity is determined up to 30 GPa at 1012 W/cm2.

  15. Pulsed Nd-YAG laser in endodontics

    NASA Astrophysics Data System (ADS)

    Ragot-Roy, Brigitte; Severin, Claude; Maquin, Michel

    1994-12-01

    The purpose of this study was to establish an operative method in endodontics. The effect of a pulsed Nd:YAG laser on root canal dentin has been examined with a scanning electron microscope. Our first experimentation was to observe the impacts carried out perpendicularly to root canal surface with a 200 micrometers fiber optic in the presence of dye. Secondarily, the optical fiber was used as an endodontic instrument with black dye. The irradiation was performed after root canal preparation (15/100 file or 40/100 file) or directly into the canal. Adverse effects are observed. The results show that laser irradiation on root canal dentin surfaces induces a nonhomogeneous modified dentin layer, melted and resolidified dentin closed partially dentinal tubules. The removal of debris is not efficient enough. The laser treatment seems to be indicated only for endodontic and periapical spaces sterilization after conventional root canal preparation.

  16. Ultrafast laser pulses for medical applications

    NASA Astrophysics Data System (ADS)

    Lubatschowski, Holger; Heisterkamp, Alexander; Will, Fabian; Serbin, Jesper; Bauer, Thorsten; Fallnich, Carsten; Welling, Herbert; Mueller, Wiebke; Schwab, Burkard; Singh, Ajoy I.; Ertmer, Wolfgang

    2002-04-01

    Ultrafast lasers have become a promising tool for micromachining and extremely precise ablation of all kinds of materials. Due to the low energy threshold, thermal and mechanical side effects are limited to the bu micrometers range. The neglection of side effects enables the use of ultrashort laser pulses in a broad field of medical applications. Moreover, the interaction process based on nonlinear absorption offers the opportunity to process transparent tissue three dimensionally inside the bulk. We demonstrate the feasibility of surgical procedures in different fields of medical interest: in ophthalmology intrastromal cutting and preparing of cornael flaps for refractive surgery in living animals is presented. Besides, the very low mechanical side effects enables the use of fs- laser in otoralyngology to treat ocecular bones. Moreover, the precise cutting quality can be used in fields of cardiovascular surgery for the treatment of arteriosklerosis as well as in dentistry to remove caries from dental hard tissue.

  17. Enhanced Photoacoustic Beam Profiling of Pulsed Lasers

    NASA Astrophysics Data System (ADS)

    González, M.; Santiago, G.; Paz, M.; Slezak, V.; Peuriot, A.

    2013-09-01

    An improved version of a photoacoustic beam profiler of pulsed lasers is presented. The new model resorts to high-bandwidth condenser microphones to register higher-order, excited acoustic modes, thus enabling more accurate profiling. In addition, Xe was used as a buffer gas since its high atomic weight further reduces the eigenfrequencies. Furthermore, a new gas-handling system makes up for some deficiencies found in the first model. The system was calibrated using the Airy pattern generated with a pinhole illuminated by a frequency-doubled Nd:YAG laser that excited traces. Once calibrated, the beam profile of a TEA laser was obtained, using ethylene as the absorbing species. This profiler returns more accurate profiles than thermal paper.

  18. Corneal and skin laser exposures from 1540-nm laser pulses

    NASA Astrophysics Data System (ADS)

    Johnson, Thomas E.; Mitchell, Michael A.; Rico, Pedro J.; Fletcher, David J.; Eurell, Thomas E.; Roach, William P.

    2000-06-01

    Mechanisms of tissue damage are investigated for skin and cornea exposures from 1540 nm ('eye safe') laser single pulses of 0.8 milli-seconds. New skin model data point out the advantages of using the Yucatan mini-pig versus the Yorkshire pig for in-vivo skin laser exposures. Major advantages found include similarities in thickness and melanin content when compared with human skin. Histology from Yucatan mini-pig skin exposures and the calculation of an initial ED50 threshold indicate that the main photon tissue interaction may not be solely due to water absorption. In-vitro corneal equivalents compared well with in-vivo rabbit cornea exposure under similar laser conditions. In-vivo and in-vitro histology show that initial energy deposition leading to damage occurs intrastromally, while epithelial cells show no direct injury due to laser light absorption.

  19. Electron beam switched discharge for rapidly pulsed lasers

    DOEpatents

    Pleasance, Lyn D.; Murray, John R.; Goldhar, Julius; Bradley, Laird P.

    1981-01-01

    Method and apparatus for electrical excitation of a laser gas by application of a pulsed voltage across the gas, followed by passage of a pulsed, high energy electron beam through the gas to initiate a discharge suitable for laser excitation. This method improves upon current power conditioning techniques and is especially useful for driving rare gas halide lasers at high repetition rates.

  20. Ultrashort-pulse laser generated nanoparticles of energetic materials

    SciTech Connect

    Welle, Eric J.; Tappan, Alexander S.; Palmer, Jeremy A.

    2010-08-03

    A process for generating nanoscale particles of energetic materials, such as explosive materials, using ultrashort-pulse laser irradiation. The use of ultrashort laser pulses in embodiments of this invention enables one to generate particles by laser ablation that retain the chemical identity of the starting material while avoiding ignition, deflagration, and detonation of the explosive material.

  1. Influence of ambient pressure on the ablation hole in femtosecond laser drilling Cu.

    PubMed

    Wang, Qinxin; Chen, Anmin; Li, Suyu; Qi, Hongxia; Qi, Ying; Hu, Zhan; Jin, Mingxing

    2015-09-20

    The holes were drilled by femtosecond laser pulse (800 nm, 100 fs) on Cu sheets at different ambient pressures. The pressure range was from 1 Pa to atmospheric pressure. The number of pulses to drill through the target, the stable photodiode signal, and the hole diameter were obtained as functions of ambient pressure. The morphology of the hole was observed by a scanning electron microscope (SEM). The result showed that the ambient pressure had significant influence on the morphology of the hole.

  2. In vitro perforation of human epithelial carcinoma cell with antibody-conjugated biodegradable microspheres illuminated by a single 80 femtosecond near-infrared laser pulse.

    PubMed

    Terakawa, Mitsuhiro; Tsunoi, Yasuyuki; Mitsuhashi, Tatsuki

    2012-01-01

    Pulsed laser interaction with small metallic and dielectric particles has been receiving attention as a method of drug delivery to many cells. However, most of the particles are attended by many risks, which are mainly dependent upon particle size. Unlike other widely used particles, biodegradable particles have advantages of being broken down and eliminated by innate metabolic processes. In this paper, the perforation of cell membrane by a focused spot with transparent biodegradable microspheres excited by a single 800 nm, 80 fs laser pulse is demonstrated. A polylactic acid (PLA) sphere, a biodegradable polymer, was used. Fluorescein isothiocyanate (FITC)-dextran and short interfering RNA were delivered into many human epithelial carcinoma cells (A431 cells) by applying a single 80 fs laser pulse in the presence of antibody-conjugated PLA microspheres. The focused intensity was also simulated by the three-dimensional finite-difference time-domain method. Perforation by biodegradable spheres compared with other particles has the potential to be a much safer phototherapy and drug delivery method for patients. The present method can open a new avenue, which is considered an efficient adherent for the selective perforation of cells which express the specific antigen on the cell membrane.

  3. Nonlinear optical studies on 4-(ferrocenylmethylimino)-2-hydroxy-benzoic acid thin films deposited by matrix-assisted pulsed laser evaporation (MAPLE)

    NASA Astrophysics Data System (ADS)

    Matei, Andreea; Marinescu, Maria; Constantinescu, Catalin; Ion, Valentin; Mitu, Bogdana; Ionita, Iulian; Dinescu, Maria; Emandi, Ana

    2016-06-01

    We present results on a new, laboratory synthesized ferrocene-derivative, i.e. 4-(ferrocenylmethylimino)-2-hydroxy-benzoic acid. Thin films with controlled thickness are deposited by matrix-assisted pulsed laser evaporation (MAPLE), on quartz and silicon substrates, with the aim of evaluating the nonlinear optical properties for potential optoelectronic applications. Dimethyl sulfoxide was used as matrix, with 1% wt. concentration of the guest compound. The frozen target is irradiated by using a Nd:YAG laser (4ω/266 nm, 7 ns pulse duration, 10 Hz repetition rate), at low fluences ranging from 0.1 to 1 J/cm2. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to probe the surface morphology of the films. Fourier transform infrared (FTIR) and Raman spectroscopy reveal similar structure of the thin film material when compared to the starting material. The optical properties of the thin films are investigated by spectroscopic-ellipsometry (SE), and the refractive index dependence with respect to temperature is studied. The second harmonic generation (SHG) potential is assessed by using a femtosecond Ti:sapphire laser (800 nm, 60-100 fs pulse duration, 80 MHz repetition rate), at 200 mW maximum output power, revealing that the SHG signal intensity is strongly influenced by the films' thickness.

  4. Pulse shape control in a dual cavity laser: numerical modeling

    NASA Astrophysics Data System (ADS)

    Yashkir, Yuri

    2006-04-01

    We present a numerical model of the laser system for generating a special shape of the pulse: a steep peak at the beginning followed by a long pulse tail. Laser pulses of this nature are required for various applications (laser material processing, optical breakdown spectroscopy, etc.). The laser system consists of two "overlapped" cavities with different round-trip times. The laser crystal, the Q-switching element, the back mirror, and the output coupler are shared. A shorter pulse is generated in a short cavity. A small fraction of this pulse is injected into the long cavity as a seed. It triggers generation of the longer pulse. The output emission from this hybrid laser produces a required pulse shape. Parameters of the laser pulse (ratios of durations and energies of short- and long- pulse components) can be controlled through cavity length and the output coupler reflection. Modelling of the laser system is based on a set of coupled rate equations for dynamic variables of the system: the inverse population in an active laser media and photon densities in coupled cavities. Numerical experiments were provided with typical parameters of a Nd:YAG laser to study the system behaviour for different combinations of parameters.

  5. Tailored terahertz pulses from a laser-modulated electron beam.

    PubMed

    Byrd, J M; Hao, Z; Martin, M C; Robin, D S; Sannibale, F; Schoenlein, R W; Zholents, A A; Zolotorev, M S

    2006-04-28

    We present a new method to generate steady and tunable, coherent, broadband terahertz radiation from a relativistic electron beam modulated by a femtosecond laser. We have demonstrated this in the electron storage ring at the Advanced Light Source. Interaction of an electron beam with a femtosecond laser pulse copropagating through a wiggler modulates the electron energies within a short slice of the electron bunch with about the same duration of the laser pulse. The bunch develops a longitudinal density perturbation due to the dispersion of electron trajectories, and the resulting hole emits short pulses of temporally and spatially coherent terahertz pulses synchronized to the laser. We present measurements of the intensity and spectra of these pulses. This technique allows tremendous flexibility in shaping the terahertz pulse by appropriate modulation of the laser pulse.

  6. Tailored Terahertz Pulses from a Laser-Modulated Electron Beam

    SciTech Connect

    Byrd, J.M.; Hao, Z.; Martin, M.C.; Robin, D.S.; Sannibale, F.; Schoenlein, R.W.; Zholents, A.A.; Zolotorev, M.S.

    2006-04-28

    We present a new method to generate steady and tunable, coherent, broadband terahertz radiation from a relativistic electron beam modulated by a femtosecond laser. We have demonstrated this in the electron storage ring at the Advanced Light Source. Interaction of an electron beam with a femtosecond laser pulse copropagating through a wiggler modulates the electron energies within a short slice of the electron bunch with about the same duration of the laser pulse. The bunch develops a longitudinal density perturbation due to the dispersion of electron trajectories, and the resulting hole emits short pulses of temporally and spatially coherent terahertz pulses synchronized to the laser. We present measurements of the intensity and spectra of these pulses. This technique allows tremendous flexibility in shaping the terahertz pulse by appropriate modulation of the laser pulse.

  7. Pulsed laser fluorometry for environmental monitoring

    SciTech Connect

    Saunders, G. C.; Martin, J. C.; Jett, J. H.; Wilder, M. E.; Martinez, A.; Bentley, B. F.; Lopez, J.; Hutson, L.

    1990-01-01

    A compact pulsed laser fluorometer has been incorporated into a continuous flow system developed to detect acetylcholinesterase (AChE) inhibitors and/or primary amine compounds in air and water. A pulsed nitrogen laser pumped dye laser excites fluorescent reactants which flow continuously through a quartz flow cell. Data are collected, analyzed, and displayed using a Macintosh II personal computer. For detection of cholinesterase inhibitors the fluorogenic substrate N methylindoxyl acetate is used to monitor the activity of immobilized enzyme. Presence of inhibitors results in a decrease of steady state fluorescence. Detection of compounds containing primary amines is based on their reaction with fluorescamine to rapidly produce intensely fluorescent products. Compounds of interest to our research were amino acids, peptides, and proteins. An increase in steady state fluorescence could be cause to evaluate the reasons for the change. The detection limit of the protein, bovine serum albumin (BSA) in water is 10 ppT. Nebulized BSA concentrated by the LANL air sampler can be detected at sub ppT original air concentration. 16 refs., 14 figs., 3 tabs.

  8. Landau damping of a driven plasma wave from laser pulses

    SciTech Connect

    Bu Zhigang; Ji Peiyong

    2012-01-15

    The interaction between a laser pulse and a driven plasma wave with a phase velocity approaching the speed of light is studied, and our investigation is focused on the Gaussian laser pulse. It is demonstrated that when the resonance condition between the plasma wave and the laser pulse is satisfied, the Landau damping phenomenon of the plasma wave originated from the laser pulse will emerge. The dispersion relations for the plasma waves in resonance and non-resonance regions are obtained. It is proved that the Landau damping rate for a driven plasma wave is {gamma}>0 in the resonance region, so the laser pulse can produce an inverse damping effect, namely Landau growth effect, which leads an instability for the plasma wave. The Landau growth means that the energy is transmitted from the laser pulse to the plasma wave, which could be an effective process for enhancing the plasma wave.

  9. Nanosecond double-pulse fiber laser with arbitrary sub-pulse combined based on a spectral beam combining system

    NASA Astrophysics Data System (ADS)

    Hu, Man; Zheng, Ye; Yang, Yifeng; Chen, Xiaolong; Liu, Kai; Zhao, Chun; Wang, Jianhua; Qi, Yunfeng; He, Bing; Zhou, Jun

    2017-05-01

    In order to improve the processing efficiency and quality of nanosecond pulse laser drilling, a new double-pulse technique is put forward. Two single pulse lasers with different pulse duration or different repetition rate are spectrally combined by a home-made polarization-independent multilayer dielectric reflective diffraction grating. The pulse energy of single lasers and the inter-pulse separation can both be set at one's option. Then, double-pulse lasers represent two closely conjoint pulses with tunable pulse duration and tunable repetition rate and tunable pulse energy and tunable inter-pulse separation are obtained.

  10. Optimizing chirped laser pulse parameters for electron acceleration in vacuum

    SciTech Connect

    Akhyani, Mina; Jahangiri, Fazel; Niknam, Ali Reza; Massudi, Reza

    2015-11-14

    Electron dynamics in the field of a chirped linearly polarized laser pulse is investigated. Variations of electron energy gain versus chirp parameter, time duration, and initial phase of laser pulse are studied. Based on maximizing laser pulse asymmetry, a numerical optimization procedure is presented, which leads to the elimination of rapid fluctuations of gain versus the chirp parameter. Instead, a smooth variation is observed that considerably reduces the accuracy required for experimentally adjusting the chirp parameter.

  11. Transportation of megawatt millijoule laser pulses via optical fibers?

    NASA Astrophysics Data System (ADS)

    Tauer, Johannes; Kofler, Heinrich; Schwarz, Elisabeth; Wintner, Ernst

    2010-04-01

    Laser ignition is considered to be one of the most promising future concepts for internal combustion engines. It combines the legally required reduction of pollutant emissions and higher engine efficiencies. The igniting plasma is generated by a focused pulsed laser beam. Having pulse durations of a few nanoseconds, the pulse energy E p for reliable ignition amounts to the order of 10 mJ. Different methods of laser ignition with an emphasis on fiber-based systems will be discussed and evaluated.

  12. K-shell emission from 140 femtosecond laser-produced plasmas created from porous aluminum targets

    SciTech Connect

    Shepherd, R.; Price, D.; White, B.; Osterheld, A.; Walling, R.; Slaughter, D.; Stewart, R.; Gordan, S.

    1992-06-05

    The K-shell emission from flat and porous aluminum targets is used to infer the efficiency of creating a high temperature (>100eV), thermal plasma with 800 nm, 140 fs laser light. The K-shell emission from flat aluminum targets is fond to be significantly less than that of the porous targets, implying a lower temperature and less efficient coupling between the target and ultra-short pulse laser light.

  13. Evaluation of pulsed laser ablation in liquids generated gold nanoparticles as novel transfection tools: efficiency and cytotoxicity

    NASA Astrophysics Data System (ADS)

    Willenbrock, Saskia; Durán, María. Carolina; Barchanski, Annette; Barcikowski, Stephan; Feige, Karsten; Nolte, Ingo; Murua Escobar, Hugo

    2014-03-01

    Varying transfection efficiencies and cytotoxicity are crucial aspects in cell manipulation. The utilization of gold nanoparticles (AuNP) has lately attracted special interest to enhance transfection efficiency. Conventional AuNP are usually generated by chemical reactions or gas pyrolysis requiring often cell-toxic stabilizers or coatings to conserve their characteristics. Alternatively, stabilizer- and coating-free, highly pure, colloidal AuNP can be generated by pulsed laser ablation in liquids (PLAL). Mammalian cells were transfected efficiently by addition of PLAL-AuNP, but data systematically evaluating the cell-toxic potential are lacking. Herein, the transfection efficiency and cytotoxicity of PLAL AuNP was evaluated by transfection of a mammalian cell line with a recombinant HMGB1/GFP DNA expression vector. Different methods were compared using two sizes of PLAL-AuNP, commercialized AuNP, two magnetic NP-based protocols and a conventional transfection reagent (FuGENE HD; FHD). PLAL-AuNP were generated using a Spitfire Pro femtosecond laser system delivering 120 fs laser pulses at a wavelength of 800 nm focusing the fs-laser beam on a 99.99% pure gold target placed in ddH2O. Transfection efficiencies were analyzed after 24h using fluorescence microscopy and flow cytometry. Toxicity was assessed measuring cell proliferation and percentage of necrotic, propidium iodide positive cells (PI %). The addition of PLAL-AuNP significantly enhanced transfection efficiencies (FHD: 31 %; PLAL-AuNP size-1: 46 %; size-2: 50 %) with increased PI% but no reduced cell proliferation. Commercial AuNP-transfection showed significantly lower efficiency (23 %), slightly increased PI % and reduced cell proliferation. Magnetic NP based methods were less effective but showing also lowest cytotoxicity. In conclusion, addition of PLAL-AuNP provides a novel tool for transfection efficiency enhancement with acceptable cytotoxic side-effects.

  14. Pulsed holmium laser ablation of cardiac valves

    SciTech Connect

    Lilge, L.; Radtke, W.; Nishioka, N.S. )

    1989-01-01

    Ablation efficiency and residual thermal damage produced by pulsed holmium laser radiation were investigated in vitro for bovine mitral valves and human calcified and noncalcified cardiac valves. Low-OH quartz fibers (200 and 600 microns core diameter) were used in direct contact perpendicular to the specimen under saline or blood. Etch rate was measured with a linear motion transducer. Radiant exposure was varied from 0 to 3 kJ/cm{sup 2}. For 200-microns fibers, the energy of ablation was approximately 5 kJ/cm{sup 3} in noncalcified and 15 kJ/cm{sup 3} in calcified valves. Etch rates were dependent on mechanical tissue properties. Maximum etch rate at 1,000 J/cm{sup 2} was 1-2 mm/pulse at 3 Hz repetition rate. Microscopic examination revealed a zone of thermal damage extending 300 microns lateral into adjacent tissue. Thermal damage was independent of radiant exposure beyond twice threshold.

  15. Investigation of a Pulsed 1550 nm Fiber Laser System

    DTIC Science & Technology

    2015-12-15

    14. ABSTRACT There is a strong need for a pulsed laser system at eye safe wavelengths for illuminator applications . High power pulsed 1550 nm fiber...system at eye safe wavelengths for illuminator applications . High power pulsed 1550 nm fiber lasers systems are able to generate, shaped, pulses at...for illuminator applications . Considerations which impact the wavelength to be used are the transmissivity of the atmosphere and the responsivity of

  16. Optical penetration sensor for pulsed laser welding

    DOEpatents

    Essien, Marcelino; Keicher, David M.; Schlienger, M. Eric; Jellison, James L.

    2000-01-01

    An apparatus and method for determining the penetration of the weld pool created from pulsed laser welding and more particularly to an apparatus and method of utilizing an optical technique to monitor the weld vaporization plume velocity to determine the depth of penetration. A light source directs a beam through a vaporization plume above a weld pool, wherein the plume changes the intensity of the beam, allowing determination of the velocity of the plume. From the velocity of the plume, the depth of the weld is determined.

  17. Pulsed laser deposition—invention or discovery?

    NASA Astrophysics Data System (ADS)

    Venkatesan, T.

    2014-01-01

    The evolution of pulsed laser deposition had been an exciting process of invention and discovery, with the development of high Tc superconducting films as the main driver. It has become the method of choice in research and development for rapid prototyping of multicomponent inorganic materials for preparing a variety of thin films, heterostructures and atomically sharp interfaces, and has become an indispensable tool for advancing oxide electronics. In this paper I will give a personal account of the invention and development of this process at Bellcore/Rutgers, the opportunity, challenges and mostly the extraordinary excitement that was generated, typical of any disruptive technology.

  18. Metallic Clusters in Strong Femtosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Suraud, Eric; Reinhard, P.-G.; Ullrich, Carsten A.

    1998-03-01

    We present a theoretical study of the electron response of a Na_9^+ cluster excited by strong femtosecond laser pulses.(C. A. Ullrich, P.-G. Reinhard, and E. Suraud, J. Phys. B 30), 5043 (1997) Our approach is based on time-dependent density functional theory within the adiabatic local density approximation, including a recently developed self-interaction correction scheme. We investigate numerically the full electronic dipolar response and multiphoton ionization of the cluster and discuss the ionization mechanism. A strong correlation between induced electronic dipole oscillations and electron emission is observed, leading to a pronounced resonant enhancement of ionization at the frequency of the Mie plasmon.

  19. Generating Submillimeter-Wave Frequencies From Laser Pulses

    NASA Technical Reports Server (NTRS)

    Spencer, Michael G.; Maserjian, Joseph

    1994-01-01

    Semiconductor photoconductive switches generate electrical pulses containing submillimeter-wavelength carrier signals (frequency between 300 and 3,000 GHz) and harmonics thereof when illuminated with short-rise-time pulses from lasers. Device of this type used as local oscilator in heterodyne submillimeter-wave receiver. Electrical output of device coupled via transmission line, waveguide, or antenna to mixer circuitry of receiver. Phase delays between optically activated semiconductor switches determine output carrier frequencies. N electrical pulses generated by each laser pulse. Thus, fundamental output frequency is N times laser-pulse-repetition rate.

  20. Improved pulse laser ranging algorithm based on high speed sampling

    NASA Astrophysics Data System (ADS)

    Gao, Xuan-yi; Qian, Rui-hai; Zhang, Yan-mei; Li, Huan; Guo, Hai-chao; He, Shi-jie; Guo, Xiao-kang

    2016-10-01

    Narrow pulse laser ranging achieves long-range target detection using laser pulse with low divergent beams. Pulse laser ranging is widely used in military, industrial, civil, engineering and transportation field. In this paper, an improved narrow pulse laser ranging algorithm is studied based on the high speed sampling. Firstly, theoretical simulation models have been built and analyzed including the laser emission and pulse laser ranging algorithm. An improved pulse ranging algorithm is developed. This new algorithm combines the matched filter algorithm and the constant fraction discrimination (CFD) algorithm. After the algorithm simulation, a laser ranging hardware system is set up to implement the improved algorithm. The laser ranging hardware system includes a laser diode, a laser detector and a high sample rate data logging circuit. Subsequently, using Verilog HDL language, the improved algorithm is implemented in the FPGA chip based on fusion of the matched filter algorithm and the CFD algorithm. Finally, the laser ranging experiment is carried out to test the improved algorithm ranging performance comparing to the matched filter algorithm and the CFD algorithm using the laser ranging hardware system. The test analysis result demonstrates that the laser ranging hardware system realized the high speed processing and high speed sampling data transmission. The algorithm analysis result presents that the improved algorithm achieves 0.3m distance ranging precision. The improved algorithm analysis result meets the expected effect, which is consistent with the theoretical simulation.

  1. Long pulse chemical laser. Final technical report

    SciTech Connect

    Bardon, R.L.; Breidenthal, R.E.; Buonadonna, V.R.

    1989-02-01

    This report covers the technical effort through February, 1989. This effort was directed towards the technology associated with the development of a large scale, long pulse DF-CO{sub 2} chemical laser. Optics damage studies performed under Task 1 assessed damage thresholds for diamond-turned salt windows. Task 2 is a multi-faceted task involving the use of PHOCL-50 for laser gain measurements, LTI experiments, and detector testing by LANL personnel. To support these latter tests, PHOCL-50 was upgraded with Boeing funding to incorporate a full aperture outcoupler that increased its energy output by over a factor of 3, to a full kilojoule. The PHOCL-50 carbon block calorimeter was also recalibrated and compared with the LANL Scientech meter. Cloud clearing studies under Task 3 initially concentrated on delivering a Boeing built Cloud Simulation Facility to LANL, and currently involves design of a Cold Cloud Simulation Facility. A Boeing IRAD funded theoretical study on cold cloud clearing revealed that ice clouds may be easier to clear then warm clouds. Task 4 involves the theoretical and experimental study of flow system design as related to laser beam quality. Present efforts on this task are concentrating on temperature gradients induced by the gas filling process. General support for the LPCL field effort is listed under Task 5, with heavy emphasis on assuring reliable operation of the Boeing built Large Slide Valve and other device related tests. The modification of the PHOCL-50 system for testing long pulse DF (4{mu}m only) chemical laser operation is being done under Task 6.

  2. Pulsed laser surface hardening of ferrous alloys.

    SciTech Connect

    Xu, Z.; Reed, C. B.; Leong, K. H.; Hunter, B. V.

    1999-09-30

    A high power pulsed Nd:YAG laser and special optics were used to produce surface hardening on 1045 steel and gray cast iron by varying the process parameters. Unlike CO{sub 2} lasers, where absorptive coatings are required, the higher absorptivity of ferrous alloys at the Nd:YAG laser wavelength eliminates the necessity of applying a coating before processing. Metallurgical analysis of the treated tracks showed that very fine and hard martensitic microstructure (1045 steel) or inhomogeneous martensite (gray cast iron) were obtained without surface melting, giving maximum hardness of HRC 61 and HRC 40 for 1045 steel and gray cast iron respectively. The corresponding maximum case depths for both alloys at the above hardness are 0.6 mm. Gray cast iron was more difficult to harden without surface melting because of its lower melting temperature and a significantly longer time-at-temperature required to diffuse carbon atoms from the graphite flakes into the austenite matrix during laser heating. The thermal distortion was characterized in term of flatness changes after surface hardening.

  3. Pulsed HF laser ablation of dentin

    NASA Astrophysics Data System (ADS)

    Papagiakoumou, Eirini I.; Papadopoulos, Dimitris N.; Makropoulou, Mersini I.; Khabbaz, Maruan G.; Serafetinides, Alexander A.

    2005-03-01

    The interaction of a TEA (Transversally Excited Atmospheric pressure) corona preionized oscillator double amplifier HF (hydrogen fluoride) laser beam with dentin tissue is reported. Pulses of 39 ns in the wavelength range of 2.65-3.35 μm and output energies in the range of 10-45 mJ, in a predominantly TEM00 beam were used to interact with dentin tissue. Ablation experiments were conducted with the laser beam directly focused on the tissue. Several samples of freshly extracted human teeth were used, cut longitudinally in facets of about 1mm thick and stored in phosphate buffered saline after being cleaned from the soft tissue remains. The experimental data (ablation thresholds, ablation rates) are discussed with respect to the ablation mechanism(s). Adequate tissue removal was observed and the ablation behavior was, in the greates part of the available fluences, almost linear. From the microscopic examination of teh samples, in a scanning electron microscope (SEM), the irradiated surfaces displayed oval craters (reflecting the laser beam shape) with absence of any melting or carbonization zone. It is suggested that the specific laser removes hard tissue by a combined photothermal and plasma mediated ablation mechanism, leaving a surface free from thermal damage and with a well-shaped crater.

  4. Laser-Based Pulsed Photoacoustic Ammonia Detection

    NASA Astrophysics Data System (ADS)

    Vallespi, Arturo; Slezak, Verónica; Peuriot, Alejandro; Santiago, Guillermo

    2013-09-01

    Detecting ammonia traces is relevant in health, manufacturing, and security areas, among others. As ammonia presents a strong absorption band (the mode) around 10 m, some of the physical properties which may influence its detection by means of pulsed photoacoustic (PA) spectroscopy with a TEA laser have been studied. The characteristics of the ammonia molecule and the laser intensity may result in a nonlinear dependence of the PA signal amplitude on the laser fluence. Ammonia absorption can be described as a simple two-level system with power broadening. As is a polar molecule, it strongly undergoes adsorption phenomena in contact with different surfaces. Therefore, physical adsorption-desorption at the cell’s wall is studied. A theoretical model, based on Langmuir’s assumptions, fits well to the experimental results with stainless steel. Related to these studies, measurements led to the conclusion that, at the used fluenced values, dissociation by multiphotonic absorption at the 10P(32) laser line may be discarded. A calibration of the system was performed, and a detection limit around 190 ppb (at 224 ) was achieved.

  5. Studies on high-quality electron beams and tunable x-ray sources produced by laser wakefield accelerators

    NASA Astrophysics Data System (ADS)

    Zeng, Ming; Luo, Ji; Chen, Min; Sheng, Zheng-Ming

    2016-11-01

    The applications of laser wake field accelerators (LWFA) rely heavily on the quality of produced high energy electron beams and X-ray sources. We present our recent progress on this issue. Firstly we propose a bichromatic laser ionization injection scheme for obtaining high quality electron beams. With the laser pulse combinations of 800 nm and 267 nm, or 2400 nm and 800 nm in wavelengths, electron beams with energy spread of 1% or lower can be produced. Secondly we propose polarization tunable X-ray sources based on LWFA. By shooting a laser pulse into a preformed plasma channel with a skew angle referring to the channel axis, the plasma channel can act as a helical undulator for elliptically polarized X-rays.

  6. 25 years of pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Lorenz, Michael; Ramachandra Rao, M. S.

    2014-01-01

    It is our pleasure to introduce this special issue appearing on the occasion of the 25th anniversary of pulsed laser deposition (PLD), which is today one of the most versatile growth techniques for oxide thin films and nanostructures. Ever since its invention, PLD has revolutionized the research on advanced functional oxides due to its ability to yield high-quality thin films, multilayers and heterostructures of a variety of multi-element material systems with rather simple technical means. We appreciate that the use of lasers to deposit films via ablation (now termed PLD) has been known since the 1960s after the invention of the first ruby laser. However, in the first two decades, PLD was something of a 'sleeping beauty' with only a few publications per year, as shown below. This state of hibernation ended abruptly with the advent of high T c superconductor research when scientists needed to grow high-quality thin films of multi-component high T c oxide systems. When most of the conventional growth techniques failed, the invention of PLD by T (Venky) Venkatesan clearly demonstrated that the newly discovered high-T c superconductor, YBa2Cu3O7-δ , could be stoichiometrically deposited as a high-quality nm-thin film with PLD [1]. As a remarkable highlight of this special issue, Venkatesan gives us his very personal reminiscence on these particularly innovative years of PLD beginning in 1986 [2]. After Venky's first paper [1], the importance of this invention was realized worldwide and the number of publications on PLD increased exponentially, as shown in figure 1. Figure 1. Figure 1. Published items per year with title or topic PLD. Data from Thomson Reuters Web of Knowledge in September 2013. After publication of Venky's famous paper in 1987 [1], the story of PLD's success began with a sudden jump in the number of publications, about 25 years ago. A first PLD textbook covering its basic understanding was soon published, in 1994, by Chrisey and Hubler [3]. Within a

  7. PHASE NOISE COMPARISON OF SHORT PULSE LASER SYSTEMS

    SciTech Connect

    Shukui Zhang; Stephen Benson; John Hansknecht; David Hardy; George Neil; Michelle D. Shinn

    2006-08-27

    This paper describes phase noise measurements of several different laser systems that have completely different gain media and configurations including a multi-kW free-electron laser. We will focus on state-of-the-art short pulse lasers, especially drive lasers for photocathode injectors. Phase noise comparison of the FEL drive laser, electron beam and FEL laser output also will be presented.

  8. Reshaping of intense laser pulse with a capillary

    SciTech Connect

    Cao Lihua; Yu Wei; Yu, M. Y.; Wang Xin; Gu Yuqiu; He, X. T.

    2009-09-15

    The reshaping of intense laser pulse by vacuum capillary is studied by particle-in-cell simulation. It is shown that as an intense laser pulse propagates from free space into a capillary, its profile is reshaped due to laser-plasma interaction near the entrance of capillary. As a result, the free-space mode is self-consistently converted into a capillary mode. Only the relatively low-intensity periphery of the reshaped pulse interacts with the capillary-wall plasma, so that the high-intensity center of the pulse can propagate in the narrow vacuum channel over a distance much larger than the Rayleigh length. The mechanism is then applied to reshape a radially imperfect laser pulse having two wings around the center spot. Most of the output light energy is concentrated in the center spot, and the wings are almost completely removed. That is, the quality of the laser pulse can be greatly improved by a capillary.

  9. Stabilization of CO2 laser short-pulse oscillation by tickle pulse for dot processing

    NASA Astrophysics Data System (ADS)

    Tokita, Daisaku; Sakurada, Noriyo; Ishii, Yoshio; Kubota, Yuzuru; Watanabe, Kazuhiro

    2005-03-01

    Image drawing using a laser system has been attempted by Segmented Pixel Drawing (SPD) method and Laser Plastic Coloring (LPC) method in our laboratory. Laser dot processing by a short pulse oscillation of a CO2 laser is used for these laser methods. Stable short pulse oscillation is required for an accurate image drawing. That oscillation has a tendency to be unstable because of its long oscillation interval. A tickle pulse is known as one of a technique which is conventionally used for a continuous pulse oscillation of a CO2 laser in order to make rising rate of laser oscillation quick. In this study, this tickle pulse has been improved and applied to the short pulse oscillation in order to stable short pulse oscillation and high accurate laser dot processing. In the result, processed dots are appeared bigger with less variation in their sizes with the improved tickle pulse case compared with the conventional case. Short pulse oscillation is stabilized by these improved tickle pulse. Reproducibility and accuracy ofthe SPD method and LPC method might be realized by this stabilized dot processing.

  10. Production of Picosecond, Kilojoule, and Petawatt Laser Pulses via Raman Amplification of Nanosecond Pulses

    SciTech Connect

    Trines, R. M. G. M.; Bingham, R.; Norreys, P. A.; Fiuza, F.; Fonseca, R. A.; Silva, L. O.

    2011-09-02

    Raman amplification in plasma has been promoted as a means of compressing picosecond optical laser pulses to femtosecond duration to explore the intensity frontier. Here we show for the first time that it can be used, with equal success, to compress laser pulses from nanosecond to picosecond duration. Simulations show up to 60% energy transfer from pump pulse to probe pulse, implying that multikilojoule ultraviolet petawatt laser pulses can be produced using this scheme. This has important consequences for the demonstration of fast-ignition inertial confinement fusion.

  11. Pulsed laser deposition of pepsin thin films

    NASA Astrophysics Data System (ADS)

    Kecskeméti, G.; Kresz, N.; Smausz, T.; Hopp, B.; Nógrádi, A.

    2005-07-01

    Pulsed laser deposition (PLD) of organic and biological thin films has been extensively studied due to its importance in medical applications among others. Our investigations and results on PLD of a digestion catalyzing enzyme, pepsin, are presented. Targets pressed from pepsin powder were ablated with pulses of an ArF excimer laser ( λ = 193 nm, FWHM = 30 ns), the applied fluence was varied between 0.24 and 5.1 J/cm 2. The pressure in the PLD chamber was 2.7 × 10 -3 Pa. The thin layers were deposited onto glass and KBr substrates. Our IR spectroscopic measurements proved that the chemical composition of deposited thin films is similar to that of the target material deposited at 0.5 and 1.3 J/cm 2. The protein digesting capacity of the transferred pepsin was tested by adapting a modified "protein cube" method. Dissolution of the ovalbumin sections proved that the deposited layers consisted of catalytically active pepsin.

  12. Nanosecond pulsed laser texturing of optical diffusers

    NASA Astrophysics Data System (ADS)

    Alqurashi, Tawfiq; Sabouri, Aydin; Yetisen, Ali K.; Butt, Haider

    2017-02-01

    High-quality optical glass diffusers have applications in aerospace, displays, imaging systems, medical devices, and optical sensors. The development of rapid and accurate fabrication techniques is highly desirable for their production. Here, a micropatterning method for the fast fabrication of optical diffusers by means of nanosecond pulsed laser ablation is demonstrated (λ=1064 nm, power=7.02, 9.36 and 11.7 W and scanning speed=200 and 800 mm s-1). The experiments were carried out by point-to-point texturing of a glass surface in spiral shape. The laser machining parameters, the number of pulses and their power had significant effect on surface features. The optical characteristics of the diffusers were characterized at different scattering angles. The features of the microscale structures influenced average roughness from 0.8 μm to 1.97 μm. The glass diffusers scattered light at angles up to 20° and their transmission efficiency were measured up to ˜97% across the visible spectrum. The produced optical devices diffuse light less but do so with less scattering and energy losses as compared to opal diffusing glass. The presented fabrication method can be applied to any other transparent material to create optical diffusers. It is anticipated that the optical diffusers presented in this work will have applications in the production of LED spotlights and imaging devices.

  13. Relation Between Discharge Length and Laser Pulse Characteristics in Longitudinally Excited CO2 Laser

    NASA Astrophysics Data System (ADS)

    Uno, Kazuyuki; Dobashi, Kazuma; Akitsu, Tetsuya; Jitsuno, Takahisa

    2013-04-01

    A longitudinally excited CO2 laser pumped by a fast discharge emits a short laser pulse, similarly to TEA and Q-switched CO2 lasers. We investigated the relation between the discharge length and the laser pulse characteristics to develop a longitudinally excited CO2 laser producing a high spike laser pulse. We examined discharge lengths of 30, 45, and 60 cm, using the same mirrors and the same excitation circuit with the same input energy. A longer discharge length increased the discharge volume and improved the laser output energy. However, the longer discharge length caused a long discharge formation time (a slow fall time of the discharge voltage) due to the higher discharge impedance, which resulted in a long laser pulse tail. Therefore, the longitudinally excited CO2 laser had optimum conditions for obtaining a high spike laser pulse effectively.

  14. Pulse-shape control of two-color interference in high-order-harmonic generation

    NASA Astrophysics Data System (ADS)

    Hamilton, K. R.; van der Hart, H. W.; Brown, A. C.

    2017-01-01

    We report on calculations of harmonic generation by neon in a mixed (800-nm + time-delayed 400-nm) laser pulse scheme. In contrast with previous studies we employ a short (few-cycle) 400-nm pulse, finding that this affords control of the interference between electron trajectories contributing to the cutoff harmonics. The inclusion of the 400-nm pulse enhances the yield and cutoff energy, both of which exhibit a strong dependence on the time delay between the two pulses. Using a combination of time-dependent R -matrix theory and a classical trajectory model, we assess the mechanisms leading to these effects.

  15. Few-cycle pulse compression through cascade of bulk media and hollow-core fiber

    NASA Astrophysics Data System (ADS)

    Wang, D.; Li, D. X.; Chen, X. W.; Leng, Y. X.; Xu, Z. Z.

    2010-06-01

    We experimentally demonstrated a new few-cycle pulse compression technique through the cascade of bulk media and hollow-core fiber (HCF) and this compression system has been intensively studied. The pulses with the duration of ˜5 fs and the energy of 0.33 mJ near 800 nm have been generated by compressing the ˜40 fs input pulse from a commercial laser system. In principle, this technique allows compression of pulses with duration of picoseconds to a few cycles (sub-7 fs) and the output can be above 1 mJ.

  16. Stimulated brillouin backscatter of a short-pulse laser

    SciTech Connect

    Hinkel, D.E.; Williams, E.A.; Berger, R.L.

    1994-11-03

    Stimulated Brillouin backscattering (SBBS) from a short-pulse laser, where the pulse length is short compared to the plasma length, is found to be qualitatively different than in the long pulse regime, where the pulse length is long compared to the plasma length. We find that after an initial transient of order the laser pulse length transit time, the instability reaches a steady state in the variables x{prime} = x {minus} V{sub g}t, t{prime} = t, where V{sub g} is the pulse group velocity. In contrast, SBBS in a long pulse can be absolutely unstable and grows indefinitely, or until nonlinearities intervene. We find that the motion of the laser pulse induces Doppler related effects that substantially modify the backscattered spectrum at higher intensities, where the instability is strongly coupled (i.e. , has a growth rate large compared to the ion acoustic frequency).

  17. A new pulsed laser deposition technique: Scanning multi-component pulsed laser deposition method

    SciTech Connect

    Fischer, D.; Jansen, M.; Fuente, G. F. de la

    2012-04-15

    The scanning multi-component pulsed laser deposition (PLD) method realizes uniform depositions of desired coatings by a modified pulsed laser deposition process, preferably with a femto-second laser-system. Multi-component coatings (single or multilayered) are thus deposited onto substrates via laser induced ablation of segmented targets. This is achieved via horizontal line-scanning of a focused laser beam over a uniformly moving target's surface. This process allows to deposit the desired composition of the coating simultaneously, starting from the different segments of the target and adjusting the scan line as a function of target geometry. The sequence and thickness of multilayers can easily be adjusted by target architecture and motion, enabling inter/intra layer concentration gradients and thus functional gradient coatings. This new, simple PLD method enables the achievement of uniform, large-area coatings. Case studies were performed with segmented targets containing aluminum, titanium, and niobium. Under the laser irradiation conditions applied, all three metals were uniformly ablated. The elemental composition within the rough coatings obtained was fixed by the scanned area to Ti-Al-Nb = 1:1:1. Crystalline aluminum, titanium, and niobium were found to coexist side by side at room temperature within the substrate, without alloy formation up to 600 deg. C.

  18. A new pulsed laser deposition technique: scanning multi-component pulsed laser deposition method.

    PubMed

    Fischer, D; de la Fuente, G F; Jansen, M

    2012-04-01

    The scanning multi-component pulsed laser deposition (PLD) method realizes uniform depositions of desired coatings by a modified pulsed laser deposition process, preferably with a femto-second laser-system. Multi-component coatings (single or multilayered) are thus deposited onto substrates via laser induced ablation of segmented targets. This is achieved via horizontal line-scanning of a focused laser beam over a uniformly moving target's surface. This process allows to deposit the desired composition of the coating simultaneously, starting from the different segments of the target and adjusting the scan line as a function of target geometry. The sequence and thickness of multilayers can easily be adjusted by target architecture and motion, enabling inter/intra layer concentration gradients and thus functional gradient coatings. This new, simple PLD method enables the achievement of uniform, large-area coatings. Case studies were performed with segmented targets containing aluminum, titanium, and niobium. Under the laser irradiation conditions applied, all three metals were uniformly ablated. The elemental composition within the rough coatings obtained was fixed by the scanned area to Ti-Al-Nb = 1:1:1. Crystalline aluminum, titanium, and niobium were found to coexist side by side at room temperature within the substrate, without alloy formation up to 600 °C.

  19. Threshold for permanent refractive index change in crystalline silicon by femtosecond laser irradiation

    NASA Astrophysics Data System (ADS)

    Bachman, D.; Chen, Z.; Fedosejevs, R.; Tsui, Y. Y.; Van, V.

    2016-08-01

    An optical damage threshold for crystalline silicon from single femtosecond laser pulses was determined by detecting a permanent change in the refractive index of the material. This index change could be detected with unprecedented sensitivity by measuring the resonant wavelength shift of silicon integrated optics microring resonators irradiated with femtosecond laser pulses at 400 nm and 800 nm wavelengths. The threshold for permanent index change at 400 nm wavelength was determined to be 0.053 ± 0.007 J/cm2, which agrees with previously reported threshold values for femtosecond laser modification of crystalline silicon. However, the threshold for index change at 800 nm wavelength was found to be 0.044 ± 0.005 J/cm2, which is five times lower than the previously reported threshold values for visual change on the silicon surface. The discrepancy is attributed to possible modification of the crystallinity of silicon below the melting temperature that has not been detected before.

  20. Ultrafast laser-induced damage and the influence of spectral effects

    NASA Astrophysics Data System (ADS)

    Gulley, Jeremy R.

    2012-12-01

    Numerous studies have investigated the prerequisite role of photoionization in ultrafast laser-induced damage (LID) of bulk dielectrics. This study examines the role of spectral width and instantaneous laser frequency in LID using a frequency dependent multiphoton ionization (MPI) model and numerical simulation of initially 800 nm laser pulses propagating through fused silica. Assuming a band gap of 9 eV, MPI by an 800 nm field is a six-photon process, but when the instantaneous wavelength is greater than 827 nm an additional photon is required for photoionization, reducing the probability of the event by many orders of magnitude. Simulation results suggest that this frequency dependence can significantly impact the onset of LID and ultrashort pulse filamentation in solids.

  1. New methods of generation of ultrashort laser pulses for ranging

    NASA Technical Reports Server (NTRS)

    Jelinkova, Helena; Hamal, Karel; Kubecek, V.; Prochazka, Ivan

    1993-01-01

    To reach the millimeter satellite laser ranging accuracy, the goal for nineties, new laser ranging techniques have to be applied. To increase the laser ranging precision, the application of the ultrashort laser pulses in connection with the new signal detection and processing techniques, is inevitable. The two wavelength laser ranging is one of the ways to measure the atmospheric dispersion to improve the existing atmospheric correction models and hence, to increase the overall system ranging accuracy to the desired value. We are presenting a review of several nonstandard techniques of ultrashort laser pulses generation, which may be utilized for laser ranging: compression of the nanosecond pulses using stimulated Brillouin and Raman backscattering; compression of the mode-locked pulses using Raman backscattering; passive mode-locking technique with nonlinear mirror; and passive mode-locking technique with the negative feedback.

  2. Analysis on the characteristics of pulsed laser proximity fuze's echo

    NASA Astrophysics Data System (ADS)

    Wang, Kun; Chen, Huimin

    2011-06-01

    With the rapid development of semiconductor technology and laser technology, a kind of proximity fuze named pulsed laser proximity fuze has been applied. Compared with other fuzes, pulsed laser proximity fuze has high ranging precision and strong resistance to artificial active interference. It is an important development tendency of proximity fuze. The paper analyze the characteristic of target echo of laser signal, and then make theoretical analysis and calculation on the laser signal transmission in the smog. Firstly, use the pulse width of 10ns semiconductor laser fuze to do typical targets experiment, to get the echo information of target distance is 5m; then to do smog interference experiment, by comparing the pulse width amplitude and backscattering signal amplitude of laser fuze in simulation and experiment, analyzing the effect of anti-clutter, providing the evidence for the subsequent of circuit of signal amplification and processing.

  3. Generation of ultrashort electron bunches by colliding laser pulses.

    PubMed

    Schroeder, C B; Lee, P B; Wurtele, J S; Esarey, E; Leemans, W P

    1999-05-01

    A proposed laser-plasma-based relativistic electron source [E. Esarey et al., Phys. Rev. Lett. 79, 2682 (1997)] using laser-triggered injection of electrons is investigated. The source generates ultrashort electron bunches by dephasing and trapping background plasma electrons undergoing fluid oscillations in an excited plasma wake. The plasma electrons are dephased by colliding two counterpropagating laser pulses which generate a slow phase velocity beat wave. Laser pulse intensity thresholds for trapping and the optimal wake phase for injection are calculated. Numerical simulations of test particles, with prescribed plasma and laser fields, are used to verify analytic predictions and to study the longitudinal and transverse dynamics of the trapped plasma electrons. Simulations indicate that the colliding laser pulse injection scheme has the capability to produce relativistic femtosecond electron bunches with fractional energy spread of order a few percent and normalized transverse emittance less than 1 mm mrad using 1 TW injection laser pulses.

  4. Absolute X-ray yield studies from Xe-clusters with ultrashort Ti:Sa laser pulses at 2×1018 W/cm2

    NASA Astrophysics Data System (ADS)

    Nickles, P. V.; Ter-Avetisyan, S.; Stiel, H.; Sandner, W.; Schnürer, M.

    2002-04-01

    High intensity (~2×1018 W/cm2) laser excited large Xe-clusters (105…106 atoms per cluster) have been studied concerning scaling and absolute EUV-emission in a wavelength range between 7 nm and 15 nm. Ultrashort (50 fs) pulses from a Ti:Sa multi-TW laser at 800 nm wavelength were applied in the experiments. Characterized cluster target variations in combination with different laser irradiation have been used for EUV-yield optimization. Maximum emission as a function of the backing pressure and a spatial emission anisotropy covering a factor of 2 is discussed with a simple model of the source geometry and EUV-radiation absorption. High charge states and strong x-ray yield from laser heated clusters are considered due to collisional and optical field ionization processes. Circularly polarized laser light instead of linear polarization results in a factor of 2.5 higher emission in the 11 nm to 15 nm wavelength range. This indicates the initial influence of optical field ionization for the interaction parameter range used and contrasts to collisional heating which seems to influence preferentially higher ionization states. An absolute emission efficiency at 13.4 nm of up to 0.5% in 2π sr and 2.2% bandwidth has been measured. .

  5. Spatially resolved analysis of Kα x-ray emission from plasmas induced by a femtosecond weakly relativistic laser pulse at various polarizations.

    PubMed

    Cristoforetti, G; Anania, M P; Faenov, A Ya; Giulietti, A; Giulietti, D; Hansen, S B; Koester, P; Labate, L; Levato, T; Pikuz, T A; Gizzi, L A

    2013-02-01

    Spatially resolved K-shell spectroscopy is used here to investigate the interaction of an ultrashort laser pulse (λ=800 nm, τ=40 fs) with a Ti foil under intense irradiation (Iλ(2)=2×10(18)Wμm(2)cm(-2)) and the following fast electron generation and transport into the target. The effect of laser pulse polarization (p, s, and circular) on the Kα yield and line shape is probed. The radial structure of intensity and width of the lines, obtained by a discretized Abel deconvolution algorithm, suggests an annular distribution of both the hot electron propagation into the target and the target temperature. An accurate modeling of Kα line shapes was performed, revealing temperature gradients, going from a few eV up to 15-20 eV, depending on the pulse polarization. Results are discussed in terms of mechanisms of hot electron generation and of their transport through the preplasma in front of the target.

  6. Glass drilling by longitudinally excited CO2 laser with short laser pulse

    NASA Astrophysics Data System (ADS)

    Uno, Kazuyuki; Yamamoto, Takuya; Akitsu, Tetsuya; Jitsuno, Takahisa

    2015-03-01

    We developed a longitudinally excited CO2 laser that produces a short laser pulse. The laser was very simple and consisted of a 45-cm-long alumina ceramic pipe with an inner diameter of 9 mm, a pulse power supply, a step-up transformer, a storage capacitance, and a spark-gap switch. The laser pulse had a spike pulse and a pulse tail. The energy of the pulse tail was controlled by adjusting medium gas. Using three types of CO2 laser pulse with the same spike-pulse energy and the different pulse-tail energy, the characteristics of the hole drilling of synthetic silica glass was investigated. Higher pulse-tail energy gave deeper ablation depth. In the short laser pulse with the spike-pulse energy of 1.2 mJ, the spike pulse width of 162 ns, the pulse-tail energy of 24.6 mJ, and the pulse-tail length of 29.6 μs, 1000 shots irradiation produced the ablation depth of 988 μm. In the hole drilling of synthetic silica glass by the CO2 laser, a crack-free process was realized.

  7. System for rapidly tuning a low pressure pulsed laser

    SciTech Connect

    Fox, J.A.; Ahl, J.L.

    1989-09-19

    This patent describes a system for rapidly tuning a low pressure pulsed laser over multiple wavelengths. The system comprising: a low pressure one electrode pair discharge region in a laser cavity having a laser trigger means connected to the electrode pair for initiating low pressure discharge within the discharge region; a quarterwave plate and a Q-switch in optical alignment with the one electrode pair discharge region along the laser optical axis; a fixed laser output coupler at the discharge region end of the laser cavity; and a rotatable grating means for wavelength switching the at least two high gain Q-switched pulses.

  8. Pulse front adaptive optics: a new method for control of ultrashort laser pulses.

    PubMed

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

    2015-07-27

    Ultrafast lasers enable a wide range of physics research and the manipulation of short pulses is a critical part of the ultrafast tool kit. Current methods of laser pulse shaping are usually considered separately in either the spatial or the temporal domain, but laser pulses are complex entities existing in four dimensions, so full freedom of manipulation requires advanced forms of spatiotemporal control. We demonstrate through a combination of adaptable diffractive and reflective optical elements - a liquid crystal spatial light modulator (SLM) and a deformable mirror (DM) - decoupled spatial control over the pulse front (temporal group delay) and phase front of an ultra-short pulse was enabled. Pulse front modulation was confirmed through autocorrelation measurements. This new adaptive optics technique, for the first time enabling in principle arbitrary shaping of the pulse front, promises to offer a further level of control for ultrafast lasers.

  9. Solitary Nanostructures Produced by Ultrashort Laser Pulse.

    PubMed

    Inogamov, Nail A; Zhakhovsky, Vasily V; Khokhlov, Viktor A; Petrov, Yury V; Migdal, Kirill P

    2016-12-01

    Laser-produced surface nanostructures show considerable promise for many applications while fundamental questions concerning the corresponding mechanisms of structuring are still debated. Here, we present a simple physical model describing those mechanisms happened in a thin metal film on dielectric substrate irradiated by a tightly focused ultrashort laser pulse. The main ingredients included into the model are (i) the film-substrate hydrodynamic interaction, melting and separation of the film from substrate with velocity increasing with increase of absorbed fluence; (ii) the capillary forces decelerating expansion of the expanding flying film; and (iii) rapid freezing into a solid state if the rate of solidification is comparable or larger than hydrodynamic velocities. The developed model and performed simulations explain appearance of microbump inside the focal spot on the film surface. The model follows experimental findings about gradual transformation of the bump from small parabolic to a conical shape and to the bump with a jet on its tip with increasing fluence. Disruption of the bump as a result of thinning down the liquid film to a few interatomic distances or due to mechanical break-off of solid film is described together with the jetting and formation of one or many droplets. Developed theory opens door for optimizing laser parameters for intended nanostructuring in applications.

  10. 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.

  11. Near-threshold femtosecond laser fabrication of one-dimensional subwavelength nanogratings on a graphite surface

    NASA Astrophysics Data System (ADS)

    Golosov, E. V.; Ionin, A. A.; Kolobov, Yu. R.; Kudryashov, S. I.; Ligachev, A. E.; Makarov, S. V.; Novoselov, Yu. N.; Seleznev, L. V.; Sinitsyn, D. V.; Sharipov, A. R.

    2011-03-01

    Superimposed one-dimensional quasiperiodic gratings with multiple periods Λ ≈ 110-800 nm well below or comparable to the pump laser wavelength of 744 nm, and ridge orientations perpendicular to the linear polarization of infrared femtosecond laser pulses, were fabricated after multiple near-threshold laser shots on a planar surface of quasimonocrystalline graphite in ambient air. The broad range of the grating periods corresponds to the large number of spatial Fourier harmonics of the final nanorelief (up to m=7th order, Λm≈800 nm/m=110-800 nm), qualitatively representing the nonsinusoidal profile of the laser-induced intermediate surface relief (the set of periodic, broadly spaced narrow nanotrenches), which provides the corresponding multiangle diffraction of the incident femtosecond laser pulses. Experimental measurements and modeling of the transient optical constants of the photoexcited graphite justify the excitation, at the first stage, of the first-order (Λ1≈800 nm) surface plasmon-polaritonic (SPP) wave on the photo-excited initial planar graphite surface becoming metallic via photo-generation of dense electron hole plasma (˜1021 cm-3). Such an SPP wave provides intermediate nanorelief in the form of the nonsinusoidal surface grating via its interference with the incident laser wave, resulting under near-threshold laser irradiation conditions in the highly localized surface ablation of the material in the interference maxima. During the next stage, the multiperiod subwavelength nanogratings develop through the multiangle diffraction of the multiple incident laser pulses on the intermediate nonsinusoidal surface grating.

  12. Intra-tissue Refractive Index Shaping (IRIS) of the cornea and lens using a low-pulse-energy femtosecond laser oscillator

    PubMed Central

    Ding, Li; Knox, Wayne H.; Bühren, Jens; Nagy, Lana J.; Huxlin, Krystel R.

    2009-01-01

    Purpose To assess the optical effect of high-repetition-rate, low energy femtosecond laser pulses on lightly-fixed corneas and lenses. Methods Eight corneas and eight lenses were extracted post-mortem from normal, adult cats. They were lightly fixed and stored in a solution that minimized swelling and opacification. An 800nm Ti:Sapphire femtosecond laser oscillator with a 27fs pulse duration and 93MHz repetition rate was used to inscribe gratings consisting of 20-40 lines, each 1μm wide, 100μm long and 5μm apart, 100μm below the tissue surface. Refractive index changes in the micromachined regions were calculated immediately and after one month of storage by measuring the intensity distribution of diffracted light when the gratings were irradiated with a 632.8nm He-Ne laser. Results Periodic gratings were created into the stromal layer of the corneas and the cortex of the lenses by adjusting the laser pulse energy until visible plasma luminescence and bubbles were no longer generated. The gratings had low scattering loss and could only be visualized using phase microscopy. Refractive index changes measured 0.005±0.001 to 0.01±0.001 in corneal tissue and 0.015±0.001 to 0.021±0.001 in the lenses. The gratings and refractive index changes were preserved after storing the micromachined corneas and lenses for one month. Conclusions These pilot experiments demonstrate a novel application of low-pulse-energy, MHz femtosecond lasers in modifying the refractive index of transparent ocular tissues without apparent tissue destruction. Although it remains to be verified in living tissues, the stability of this effect suggests that the observed modifications are due to long-term molecular and/or structural changes. PMID:18641284

  13. Pulse-shaping of gain-switched pulse from multimode laser diode using fiber Sagnac interferometer.

    PubMed

    Wada, Kenji; Takamatsu, Shuji; Watanebe, Hideyuki; Matsuyama, Tetsuya; Horinaka, Hiromichi

    2008-11-24

    We propose a pulse-tail elimination and pulse shortening method using an optical interferometer, which is effective for picosecond chirped pulses from gain-switched multimode laser diodes. In a numerical simulation, when the delay distance between a chirped pulse and its replica in an optical interferometer matches two times the round-trip optical length of the laser cavity, the pulse-front and -rear tail parts are effectively eliminated from the input chirped pulse after passing through the optical interferometer. Using this method with a fiber Sagnac interferometer, a 33 ps pulse with a long-tail emitted from a gain-switched 1540 nm multimode laser diode was linearly transformed into a 20 ps pulse with a substantially reduced tail.

  14. Clutter discrimination algorithm simulation in pulse laser radar imaging

    NASA Astrophysics Data System (ADS)

    Zhang, Yan-mei; Li, Huan; Guo, Hai-chao; Su, Xuan; Zhu, Fule

    2015-10-01

    Pulse laser radar imaging performance is greatly influenced by different kinds of clutter. Various algorithms are developed to mitigate clutter. However, estimating performance of a new algorithm is difficult. Here, a simulation model for estimating clutter discrimination algorithms is presented. This model consists of laser pulse emission, clutter jamming, laser pulse reception and target image producing. Additionally, a hardware platform is set up gathering clutter data reflected by ground and trees. The data logging is as clutter jamming input in the simulation model. The hardware platform includes a laser diode, a laser detector and a high sample rate data logging circuit. The laser diode transmits short laser pulses (40ns FWHM) at 12.5 kilohertz pulse rate and at 905nm wavelength. An analog-to-digital converter chip integrated in the sample circuit works at 250 mega samples per second. The simulation model and the hardware platform contribute to a clutter discrimination algorithm simulation system. Using this system, after analyzing clutter data logging, a new compound pulse detection algorithm is developed. This new algorithm combines matched filter algorithm and constant fraction discrimination (CFD) algorithm. Firstly, laser echo pulse signal is processed by matched filter algorithm. After the first step, CFD algorithm comes next. Finally, clutter jamming from ground and trees is discriminated and target image is produced. Laser radar images are simulated using CFD algorithm, matched filter algorithm and the new algorithm respectively. Simulation result demonstrates that the new algorithm achieves the best target imaging effect of mitigating clutter reflected by ground and trees.

  15. Spectral compression of single-photon-level laser pulse

    PubMed Central

    Li, Yuanhua; Xiang, Tong; Nie, Yiyou; Sang, Minghuang; Chen, Xianfeng

    2017-01-01

    We experimentally demonstrate that the bandwidth of single photons laser pulse is compressed by a factor of 58 in a periodically poled lithium niobate (PPLN) waveguide chip. A positively chirped single photons laser pulse and a negatively chirped classical laser pulse are employed to produce a narrowband single photon pulse with new frequency through sum-frequency generation. In our experiment, the frequency and bandwidth of single photons at 1550 nm are simultaneously converted. Our results mark a critical step towards the realization of coherent photonic interface between quantum communication at 1550 nm and quantum memory in the near-visible window. PMID:28240245

  16. Spectral compression of single-photon-level laser pulse

    NASA Astrophysics Data System (ADS)

    Li, Yuanhua; Xiang, Tong; Nie, Yiyou; Sang, Minghuang; Chen, Xianfeng

    2017-02-01

    We experimentally demonstrate that the bandwidth of single photons laser pulse is compressed by a factor of 58 in a periodically poled lithium niobate (PPLN) waveguide chip. A positively chirped single photons laser pulse and a negatively chirped classical laser pulse are employed to produce a narrowband single photon pulse with new frequency through sum-frequency generation. In our experiment, the frequency and bandwidth of single photons at 1550 nm are simultaneously converted. Our results mark a critical step towards the realization of coherent photonic interface between quantum communication at 1550 nm and quantum memory in the near-visible window.

  17. Evolution of chirped laser pulses in a magnetized plasma channel

    SciTech Connect

    Jha, Pallavi; Hemlata,; Mishra, Rohit Kumar

    2014-12-15

    The propagation of intense, short, sinusoidal laser pulses in a magnetized plasma channel has been studied. The wave equation governing the evolution of the radiation field is set up and a variational technique is used to obtain the equations describing the evolution of the laser spot size, pulse length and chirp parameter. Numerical methods are used to analyze the simultaneous evolution of these parameters. The effect of the external magnetic field on initially chirped as well as unchirped laser pulses on the spot size, pulse length and chirping has been analyzed.

  18. Ultrashort-pulse laser system for hard dental tissue procedures

    NASA Astrophysics Data System (ADS)

    Neev, Joseph; Da Silva, Luiz B.; Feit, Michael D.; Perry, Michael D.; Rubenchik, Alexander M.; Stuart, Brent C.

    1996-04-01

    In spite of intensive research, lasers have not replaced conventional tools in many hard tissue applications. Ultrashort pulse lasers offer several advantages in their highly per-pulse-efficient operation, negligible thermal and mechanical damage and low noise operation. Possible development of optimal laser systems to replace the high-speed dental drill is discussed. Applications of ultrashort pulse systems for dental procedures are outlined. Selection criteria and critical parameters are considered, and are compared to the conventional air-turbine drill and to long and short pulsed systems.

  19. Tailored terahertz pulses from a laser-modulated electronbeam

    SciTech Connect

    Byrd, J.M.; Hao, Z.; Martin, M.C.; Robin, D.S.; Sannibale, F.; Schoenlein, R.W.; Zholents, A.A.; Zolotorev, M.S.

    2006-03-06

    We present a new method to generate steady and tunable,coherent, broadband terahertz radiation from a relativistic electron beammodulated by a femtosecond laser. We have demonstrated this in theelectron storage ring at the Advanced Light Source. Interaction of anelectron beam with a femtosecond laser pulse copropagating through awiggler modulates the electron energies within a short slice of theelectron bunch with about the same duration of the laser pulse. The bunchdevelops a longitudinal density perturbation due to the dispersion ofelectron trajectories, and the resulting hole emits short pulses oftemporally and spatially coherent terahertz pulses synchronized to thelaser. We present measurements of the intensity and spectra of thesepulses. This technique allows tremendous flexibility in shaping theterahertz pulse by appropriate modulation of the laser pulse.

  20. Laser Pulse-Stretching Using Multiple Optical Ring-Cavities

    NASA Technical Reports Server (NTRS)

    Kojima, Jun; Nguyen, Quang-Viet; Lee, Chi-Ming (Technical Monitor)

    2002-01-01

    We describe a simple and passive nanosecond-long (ns-long) laser 'pulse-stretcher' using multiple optical ring-cavities. We present a model of the pulse-stretching process for an arbitrary number of optical ring-cavities. Using the model, we optimize the design of a pulse-stretcher for use in a spontaneous Raman scattering excitation system that avoids laser-induced plasma spark problems. From the optimized design, we then experimentally demonstrate and verify the model with a 3-cavity pulse-stretcher system that converts a 1000 mJ, 8.4 ns-long input laser pulse into an approximately 75 ns-long (FWHM) output laser pulse with a peak power reduction of 0.10X, and an 83% efficiency.

  1. Mid-ultraviolet pulsed laser micromachining of SiC

    NASA Astrophysics Data System (ADS)

    Qi, Litao; Li, Mingxing; Lin, Haipeng; Hu, Jinping; Tang, Qingju; Liu, Chunsheng

    2014-11-01

    This paper provides an investigation of the ablation behavior of single crystal 4H-SiC and 6H-SiC wafer to improve the manufacturability and high-temperature performance of SiC using laser applications. 266nm pulsed laser micromachining of SiC was investigated. The purpose is to establish suitable laser parametric regime for the fabrication of high accuracy, high spatial resolution and thin diaphragms for high-temperature MEMS pressure sensor applications. Etch rate, ablation threshold and quality of micromachined features were evaluated. The governing ablation mechanisms, such as thermal vaporization, phase explosion, and photomechanical fragmentation, were correlated with the effects of pulse energy. The ablation threshold is obtained with ultraviolet pulsed laser ablation. The results suggested ultraviolet pulsed laser's potential for rapid manufacturing. Excellent quality of machined features with little collateral thermal damage was obtained in the lower pulse energy range. The leading material removal mechanisms under these conditions were discussed.

  2. Ultrafast pulse lasers jump to macro applications

    NASA Astrophysics Data System (ADS)

    Griebel, Martin; Lutze, Walter; Scheller, Torsten

    2016-03-01

    Ultrafast Lasers have been proven for several micro applications, e.g. stent cutting, for many years. Within its development of applications Jenoptik has started to use ultrafast lasers in macro applications in the automotive industry. The JenLas D2.fs-lasers with power output control via AOM is an ideal tool for closed loop controlled material processing. Jenoptik enhanced his well established sensor controlled laser weakening process for airbag covers to a new level. The patented process enables new materials using this kind of technology. One of the most sensitive cover materials is genuine leather. As a natural product it is extremely inhomogeneous and sensitive for any type of thermal load. The combination of femtosecond pulse ablation and closed loop control by multiple sensor array opens the door to a new quality level of defined weakening. Due to the fact, that the beam is directed by scanning equipment the process can be split in multiple cycles additionally reducing the local energy input. The development used the 5W model as well as the latest 10W release of JenLas D2.fs and achieved amazing processing speeds which directly fulfilled the requirements of the automotive industry. Having in mind that the average cycle time of automotive processes is about 60s, trials had been done of processing weakening lines in genuine leather of 1.2mm thickness. Parameters had been about 15 cycles with 300mm/s respectively resulting in an average speed of 20mm/s and a cycle time even below 60s. First samples had already given into functional and aging tests and passed successfully.

  3. Single-grating laser pulse stretcher and compressor.

    PubMed

    Lai, M; Lai, S T; Swinger, C

    1994-10-20

    Stretching and compressing of laser pulses is demonstrated with a single-grating apparatus. A laser pulse of 110 fs is stretched to 250 ps and then recompressed to 115 fs. The apparatus exploits a two-level structure: one level for stretching and the other for compressing. This single-grating configuration shows significant simplification in structure and alignment over existing multiple-grating systems. Such a stretcher-compressor is particularly suitable for use with chirped-pulse amplification in which laser wavelength tuning is desirable. Only one rotational adjustment is rquired to restore the alignment of the entire stretcher and compressor when the laser wavelength is changed.

  4. Dark pulse generation in fiber lasers incorporating carbon nanotubes.

    PubMed

    Liu, H H; Chow, K K

    2014-12-01

    We demonstrate the generation of dark pulses from carbon nanotube (CNT) incorporated erbium-doped fiber ring lasers with net anomalous dispersion. A side-polished fiber coated with CNT layer by optically-driven deposition method is embedded into the laser in order to enhance the birefringence and nonlinearity of the laser cavity. The dual-wavelength domain-wall dark pulses are obtained from the developed CNT-incorporated fiber laser at a relatively low pump threshold of 50.6 mW. Dark pulses repeated at the fifth-order harmonic of the fundamental cavity frequency are observed by adjusting the intra-cavity polarization state.

  5. Method and circuit for shaping laser output pulses

    NASA Technical Reports Server (NTRS)

    Barnes, Norman P. (Inventor)

    1990-01-01

    The invention is a method and circuit for shaping laser pulses 17' in which a laser medium 12' in a laser resonator 10' that includes a Q-switch 14' and polarizer 13' which act in combination to control the loss of the resonator 10' and provide the laser output 17' representative of such loss. An optical diode 22' senses the level of the output pulse 17' and provides an output signal 23' that when amplified is used with a control voltage from a supply 29' provide a control signal 19' which is applied to Q-switch 14' to control the shape of the output pulse 17' by adjusting its length.

  6. Self-compression of 2 microm laser filaments.

    PubMed

    Bergé, Luc

    2008-12-22

    We numerically study the filamentation of ultrashort laser pulses at 2 microm carrier wavelength in noble gases (argon, xenon) and in air. Compared with filamentation in the near-visible domain (800 nm), mid-infrared optical sources with durations close to a single cycle can be generically produced at various pressures and powers near the self-focusing threshold. The mechanism by which self-compression takes place mainly involves optical self-focusing, pulse steepening and plasma defocusing. On-axis spectra and spectral phases are discussed. Delivering single-cycled pulses at long wavelengths has important applications in the generation of high-order harmonics and isolated attosecond pulses.

  7. Simultaneous phase, amplitude, and polarization control of femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Lindinger, A.; Weber, S. M.; Plewicki, M.; Weise, F.

    2012-12-01

    We present a serial pulse shaper design which allows us to shape the phase, amplitude, and polarization of fs laser pulses independently and simultaneously. The capabilities of this setup are demonstrated by implementing a method for generating parametrically tailored laser pulses. This method is applied on the ionization of NaK molecules by feedback loop optimization, employing a temporal sub pulse encoding. Moreover, we introduce and characterize a further development of this common path pulse shaper scheme for full control of all light field parameters.

  8. High energy protons generation by two sequential laser pulses

    SciTech Connect

    Wang, Xiaofeng; Shen, Baifei E-mail: zhxm@siom.ac.cn; Zhang, Xiaomei E-mail: zhxm@siom.ac.cn; Wang, Wenpeng; Xu, Jiancai; Yi, Longqing; Shi, Yin

    2015-04-15

    The sequential proton acceleration by two laser pulses of relativistic intensity is proposed to produce high energy protons. In the scheme, a relativistic super-Gaussian (SG) laser pulse followed by a Laguerre-Gaussian (LG) pulse irradiates dense plasma attached by underdense plasma. A proton beam is produced from the target and accelerated in the radiation pressure regime by the short SG pulse and then trapped and re-accelerated in a special bubble driven by the LG pulse in the underdense plasma. The advantages of radiation pressure acceleration and LG transverse structure are combined to achieve the effective trapping and acceleration of protons. In a two-dimensional particle-in-cell simulation, protons of 6.7 GeV are obtained from a 2 × 10{sup 22 }W/cm{sup 2} SG laser pulse and a LG pulse at a lower peak intensity.

  9. Pulsed laser deposition vs. matrix assisted pulsed laser evaporation for growth of biodegradable polymer thin films

    NASA Astrophysics Data System (ADS)

    Mercado, A. L.; Allmond, C. E.; Hoekstra, J. G.; Fitz-Gerald, J. M.

    2005-08-01

    Thin films of poly (lactide-co-glycolide) (PLGA), a biodegradable polymer, were deposited on Si wafers by both conventional pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE) using chloroform (CHCl3) as a matrix solvent. This research represents an initial study to investigate the deposition characteristics of each technique at comparable conditions to gain insight into the transport and degradation mechanisms of each approach. The deposited materials were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), and gel permeation chromatography (GPC) with refractive index (RI) detection. While FTIR and NMR results do not show a measurable departure from the native, in sharp contrast GPC results show a significant change (up to 95%) in molecular weight for both deposition methods. This result makes it clear that it is possible to overlook substantial degradation when incomplete chemical analysis is conducted.

  10. Investigation of laser-driven proton acceleration using ultra-short, ultra-intense laser pulses

    SciTech Connect

    Fourmaux, S.; Gnedyuk, S.; Lassonde, P.; Payeur, S.; Pepin, H.; Kieffer, J. C.; Buffechoux, S.; Albertazzi, B.; Capelli, D.; Antici, P.; Levy, A.; Fuchs, J.; Lecherbourg, L.; Marjoribanks, R. S.

    2013-01-15

    We report optimization of laser-driven proton acceleration, for a range of experimental parameters available from a single ultrafast Ti:sapphire laser system. We have characterized laser-generated protons produced at the rear and front target surfaces of thin solid targets (15 nm to 90 {mu}m thicknesses) irradiated with an ultra-intense laser pulse (up to 10{sup 20} W Dot-Operator cm{sup -2}, pulse duration 30 to 500 fs, and pulse energy 0.1 to 1.8 J). We find an almost symmetric behaviour for protons accelerated from rear and front sides, and a linear scaling of proton energy cut-off with increasing pulse energy. At constant laser intensity, we observe that the proton cut-off energy increases with increasing laser pulse duration, then roughly constant for pulses longer than 300 fs. Finally, we demonstrate that there is an optimum target thickness and pulse duration.

  11. Studies of Photosynthesis Using a Pulsed Laser

    PubMed Central

    De Vault, Don; Chance, Britton

    1966-01-01

    The rate of oxidation of cytochrome following absorption of a short pulse of light from a ruby laser in the photosynthetic bacterium Chromatium has been measured spectrophotometrically. The half-time is about 2 μsec at room temperature increasing to 2.3 msec at about 100°K and constant at the latter value to 35°K or below. The temperature dependence above 120°K corresponds to an activation energy of 3.3 kcal/mole; that below 100°K to less than 80 cal/mol: essentially a temperature-independent electron transport reaction. Since the slowness below 100°K indicates the presence of a barrier, the lack of activation energy is taken to mean penetration by quantum-mechanical “tunneling.” PMID:5972381

  12. Computer Modeling of Pulsed Chemical Lasers.

    DTIC Science & Technology

    1983-12-31

    laser pulse was by photolysis of molecular fluorine using flashlamps. The initiation reaction pro- ceeded as: F2 + hvP = 2F (1.4) with Vp being an... MEN a~ji -U-O--- C C, ca. 04 ( i’ c4 CL viM m0 LA 04 016 166 Elm1 E FI ozF LA- 10 --- - -6’~ 167 =VE 0.ik 0ww 1 68 -wl MAIN t...# r Al w YVfaia we. a...0m NoJ IS-90I IRA -. OEM 179 180 MIN im, IUAINNE Ililm MINE 17i mmm mums NOW1911mmoImm, man .AKE-# 0 ON1 INA 0 Suffillan Ellmmm MEN IFIRM 0 W-mv- um I

  13. Approaches to solar cell design for pulsed laser power receivers

    NASA Technical Reports Server (NTRS)

    Jain, Raj K.; Landis, Geoffrey A.

    1993-01-01

    Using a laser to beam power from Earth to a photovoltaic receiver in space could be a technology with applications to many space missions. Extremely high average-power lasers would be required in a wavelength range of 700-1000 nm. However, high-power lasers inherently operate in a pulsed format. Existing solar cells are not well designed to respond to pulsed incident power. To better understand cell response to pulsed illumination at high intensity, the PC-1D finite-element computer model was used to analyze the response of solar cells to continuous and pulsed laser illumination. Over 50 percent efficiency was calculated for both InP and GaAs cells under steady-state illumination near the optimum wavelength. The time-dependent response of a high-efficiency GaAs concentrator cell to a laser pulse was modeled, and the effect of laser intensity, wavelength, and bias point was studied. Three main effects decrease the efficiency of a solar cell under pulsed laser illumination: series resistance, L-C 'ringing' with the output circuit, and current limiting due to the output inductance. The problems can be solved either by changing the pulse shape or designing a solar cell to accept the pulsed input. Cell design possibilities discussed are a high-efficiency, light-trapping silicon cell, and a monolithic, low-inductance GaAs cell.

  14. Synthesis and characterization of amorphous SiO2 nanowires via pulsed laser deposition accompanied by N2 annealing

    NASA Astrophysics Data System (ADS)

    Li, Hui; Guan, Leilei; Xu, Zhuoqi; Zhao, Yu; Sun, Jian; Wu, Jiada; Xu, Ning

    2016-12-01

    Amorphous SiO2 nanowires are successfully fabricated on fused silica substrates covered by nickel/carbon catalyst bilayers via a method of pulsed laser deposition accompanied by annealing in ambient N2. The field emission scanning electron microscopy images show that the optimum annealing temperature for the growth of SiO2 nanowires is about 1200 °C and the grown SiO2 nanowires become denser, longer and more uniform with the increment of annealing duration. The results of transmission electron microscopy and high-resolution transmission electron microscopy show that the grown nanowires are amorphous and have dark spheres on their tops. The analyses of energy dispersive X-ray spectroscopy reveal that the nanowires are composed of SiO2 and the dark spheres on their tops contain little nickel. It is inferred that nickel, carbon and CO are the key elements to promote the SiO2 nanowire growth in the solid-liquid-solid mode. Transmission spectra demonstrate that the as-grown nanowire thin films can have about 94% average transmittance in the range of 350-800 nm, meanwhile the photoluminescence spectra of the as-grown SiO2 nanowire samples show stable ultraviolet emission centered at about 363 nm with a shoulder at about 393 nm.

  15. Fabrication of p-type SnO2 films via pulsed laser deposition method by using Sb as dopant

    NASA Astrophysics Data System (ADS)

    Yu, Shihui; Zhang, Weifeng; Li, Linngxia; Xu, Dan; Dong, Helei; Jin, Yuxin

    2013-12-01

    p-Type transparent conducting antimony-doped tin oxide (ATO) thin films were successfully fabricated on quartz glass substrates by pulsed laser deposition using a 20 at.% Sb doped SnO2 ceramic target. The growth temperature was varied from 500 to 800 °C, after deposition, the thin films were rapidly annealed at 500 °C in air for 2 h. Several analytical tools such as X-ray diffraction (XRD), Hall measurements, four-point probe, field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible-near infrared (UV-Vis-NIR) spectrophotometer were used to explore the causes of the changes in optoelectronic properties and surface micrographs. The Sb-doped SnO2 film prepared at 700 °C possessed the lowest resistivity of 0.87 Ω cm with a Hall mobility of 0.65 cm2 v-1 s-1 and hole concentration of 1.01 × 1019 cm-3, while the average transmittance is about 85% in the visible light region (400-800 nm). Furthermore, SnO2-based p-n homojunction was fabricated by deposition of a Sb-doped p-type SnO2 layer on a Sb-doped n-type SnO2 layer.

  16. Laser nanoablation of diamond surface at high pulse repetition rates

    NASA Astrophysics Data System (ADS)

    Kononenko, V. V.; Gololobov, V. M.; Pashinin, V. P.; Konov, V. I.

    2016-10-01

    The chemical etching of the surface of a natural diamond single crystal irradiated by subpicosecond laser pulses with a high repetition rate (f ≤slant 500 {\\text{kHz}}) in air is experimentally investigated. The irradiation has been performed by the second-harmonic (515 {\\text{nm}}) radiation of a disk Yb : YAG laser. Dependences of the diamond surface etch rate on the laser energy density and pulse repetition rate are obtained.

  17. Electron beam-switched discharge for rapidly pulsed lasers

    DOEpatents

    Pleasance, L.D.; Murray, J.R.; Goldhar, J.; Bradley, L.P.

    1979-12-11

    A method and apparatus are designed for electrical excitation of a laser gas by application of a pulsed voltage across the gas, followed by passage of a pulsed, high energy electron beam through the gas to initiate a discharge suitable for laser excitation. This method improves upon current power conditioning techniques and is especially useful for driving rare gas halide lasers at high repetition rates.

  18. CO{sub 2} laser pulse shortening by laser ablation of a metal target

    SciTech Connect

    Donnelly, T.; Mazoyer, M.; Lynch, A.; O'Sullivan, G.; O'Reilly, F.; Dunne, P.; Cummins, T.

    2012-03-15

    A repeatable and flexible technique for pulse shortening of laser pulses has been applied to transversely excited atmospheric (TEA) CO{sub 2} laser pulses. The technique involves focusing the laser output onto a highly reflective metal target so that plasma is formed, which then operates as a shutter due to strong laser absorption and scattering. Precise control of the focused laser intensity allows for timing of the shutter so that different temporal portions of the pulse can be reflected from the target surface before plasma formation occurs. This type of shutter enables one to reduce the pulse duration down to {approx}2 ns and to remove the low power, long duration tails that are present in TEA CO{sub 2} pulses. The transmitted energy is reduced as the pulse duration is decreased but the reflected power is {approx}10 MW for all pulse durations. A simple laser heating model verifies that the pulse shortening depends directly on the plasma formation time, which in turn is dependent on the applied laser intensity. It is envisaged that this plasma shutter will be used as a tool for pulse shaping in the search for laser pulse conditions to optimize conversion efficiency from laser energy to useable extreme ultraviolet (EUV) radiation for EUV source development.

  19. CO2 laser pulse shortening by laser ablation of a metal target.

    PubMed

    Donnelly, T; Mazoyer, M; Lynch, A; O'Sullivan, G; O'Reilly, F; Dunne, P; Cummins, T

    2012-03-01

    A repeatable and flexible technique for pulse shortening of laser pulses has been applied to transversely excited atmospheric (TEA) CO(2) laser pulses. The technique involves focusing the laser output onto a highly reflective metal target so that plasma is formed, which then operates as a shutter due to strong laser absorption and scattering. Precise control of the focused laser intensity allows for timing of the shutter so that different temporal portions of the pulse can be reflected from the target surface before plasma formation occurs. This type of shutter enables one to reduce the pulse duration down to ~2 ns and to remove the low power, long duration tails that are present in TEA CO(2) pulses. The transmitted energy is reduced as the pulse duration is decreased but the reflected power is ~10 MW for all pulse durations. A simple laser heating model verifies that the pulse shortening depends directly on the plasma formation time, which in turn is dependent on the applied laser intensity. It is envisaged that this plasma shutter will be used as a tool for pulse shaping in the search for laser pulse conditions to optimize conversion efficiency from laser energy to useable extreme ultraviolet (EUV) radiation for EUV source development.

  20. CO2 laser pulse shortening by laser ablation of a metal target

    NASA Astrophysics Data System (ADS)

    Donnelly, T.; Mazoyer, M.; Lynch, A.; O'Sullivan, G.; O'Reilly, F.; Dunne, P.; Cummins, T.

    2012-03-01

    A repeatable and flexible technique for pulse shortening of laser pulses has been applied to transversely excited atmospheric (TEA) CO2 laser pulses. The technique involves focusing the laser output onto a highly reflective metal target so that plasma is formed, which then operates as a shutter due to strong laser absorption and scattering. Precise control of the focused laser intensity allows for timing of the shutter so that different temporal portions of the pulse can be reflected from the target surface before plasma formation occurs. This type of shutter enables one to reduce the pulse duration down to ˜2 ns and to remove the low power, long duration tails that are present in TEA CO2 pulses. The transmitted energy is reduced as the pulse duration is decreased but the reflected power is ˜10 MW for all pulse durations. A simple laser heating model verifies that the pulse shortening depends directly on the plasma formation time, which in turn is dependent on the applied laser intensity. It is envisaged that this plasma shutter will be used as a tool for pulse shaping in the search for laser pulse conditions to optimize conversion efficiency from laser energy to useable extreme ultraviolet (EUV) radiation for EUV source development.

  1. Dielectric breakdown induced by picosecond laser pulses

    NASA Technical Reports Server (NTRS)

    Smith, W. L.; Bechtel, J. H.; Bloembergen, N.

    1976-01-01

    The damage thresholds of transparent optical materials were investigated. Single picosecond pulses at 1.06 microns, 0.53 microns and 0.35 microns were obtained from a mode locked Nd-YAG oscillator-amplifier-frequency multiplier system. The pulses were Gaussian in space and time and permitted the determination of breakdown thresholds with a reproducibility of 15%. It was shown that the breakdown thresholds are characteristic of the bulk material, which included nine alkali halides, five different laser host materials, KDP, quartz, sapphire and calcium fluoride. The extension of the damage data to the ultraviolet is significant, because some indication was obtained that two- and three-photon absorption processes begin to play a role in determining the threshold. Throughout the visible region of the spectrum the threshold is still an increasing function of frequency, indicating that avalanche ionization is the dominant factor in determining the breakdown threshold. This was confirmed by a detailed study of the damage morphology with a high resolution microscope just above the threshold. The influence of self focusing is discussed, and evidence for beam distortion below the power threshold for complete self focusing is presented, confirming the theory of Marburger.

  2. Laser ablation of borosilicate glass with high power shaped UV nanosecond laser pulses

    NASA Astrophysics Data System (ADS)

    von Witzendorff, Philipp; Bordin, Andrea; Suttmann, Oliver; Patel, Rajesh S.; Bovatsek, James; Overmeyer, Ludger

    2016-03-01

    The application of thin borosilicate glass as interposer material requires methods for separation and drilling of this material. Laser processing with short and ultra-short laser pulses have proven to enable high quality cuts by either direct ablation or internal glass modification and cleavage. A recently developed high power UV nanosecond laser source allows for pulse shaping of individual laser pulses. Thus, the pulse duration, pulse bursts and the repetition rate can be set individually at a maximum output power of up to 60 W. This opens a completely new process window, which could not be entered with conventional Q-switched pulsed laser sources. In this study, the novel pulsed UV laser system was used to study the laser ablation process on 400 μm thin borosilicate glass at different pulse durations ranging from 2 - 10 ns and a pulse burst with two 10 ns laser pulses with a separation of 10 ns. Single line scan experiments were performed to correlate the process parameters and the laser pulse shape with the ablation depth and cutting edge chipping. Increasing the pulse duration within the single pulse experiments from 2 ns to longer pulse durations led to a moderate increase in ablation depth and a significant increase in chipping. The highest material removal was achieved with the 2x10 ns pulse burst. Experimental data also suggest that chipping could be reduced, while maintaining a high ablation depth by selecting an adequate pulse overlap. We also demonstrate that real-time combination of different pulse patterns during drilling a thin borosilicate glass produced holes with low overall chipping at a high throughput rate.

  3. Formation of sub-200 nm nanostructure on Fe film irradiated by femtosecond laser

    NASA Astrophysics Data System (ADS)

    Liu, Kaijun; Li, Xiaohong; Xie, Changxin; Wang, Kai; Zhou, Qiang; Qiu, Rong

    2017-09-01

    In this article, we report the formation of two kinds of laser induced periodic surface structures (LIPSSs) with direction perpendicular to laser polarization on the Fe films irradiated by 800 nm femtosecond laser pulses. High-spatial frequency LIPSSs (HSFLs) with periods of 150-230 nm are observed with small laser pulse number less than 100. Low-spatial frequency LIPSSs (LSFLs) with periods of 500-640 nm appear abruptly when increasing the pulse number to a specific pulse number varied with laser fluence, and the periods of LSFLs have a tendency to decrease when the pulse number exceeds some specific values varied for different laser fluences. The formation of high- and low-spatial frequency periodic structures may be related to the surface plasmon polaritons excited by laser on surface iron oxides film or iron film.

  4. Laser pulsing in linear Compton scattering

    DOE PAGES

    Krafft, G. A.; Johnson, E.; Deitrick, K.; ...

    2016-12-16

    Previous work on calculating energy spectra from Compton scattering events has either neglected considering the pulsed structure of the incident laser beam, or has calculated these effects in an approximate way subject to criticism. In this paper, this problem has been reconsidered within a linear plane wave model for the incident laser beam. By performing the proper Lorentz transformation of the Klein-Nishina scattering cross section, a spectrum calculation can be created which allows the electron beam energy spread and emittance effects on the spectrum to be accurately calculated, essentially by summing over the emission of each individual electron. Such anmore » approach has the obvious advantage that it is easily integrated with a particle distribution generated by particle tracking, allowing precise calculations of spectra for realistic particle distributions in collision. The method is used to predict the energy spectrum of radiation passing through an aperture for the proposed Old Dominion University inverse Compton source. In addition, as discussed in the body of the paper, many of the results allow easy scaling estimates to be made of the expected spectrum. A misconception in the literature on Compton scattering of circularly polarized beams is corrected and recorded.« less

  5. Laser pulsing in linear Compton scattering

    NASA Astrophysics Data System (ADS)

    Krafft, G. A.; Johnson, E.; Deitrick, K.; Terzić, B.; Kelmar, R.; Hodges, T.; Melnitchouk, W.; Delayen, J. R.

    2016-12-01

    Previous work on calculating energy spectra from Compton scattering events has either neglected considering the pulsed structure of the incident laser beam, or has calculated these effects in an approximate way subject to criticism. In this paper, this problem has been reconsidered within a linear plane wave model for the incident laser beam. By performing the proper Lorentz transformation of the Klein-Nishina scattering cross section, a spectrum calculation can be created which allows the electron beam energy spread and emittance effects on the spectrum to be accurately calculated, essentially by summing over the emission of each individual electron. Such an approach has the obvious advantage that it is easily integrated with a particle distribution generated by particle tracking, allowing precise calculations of spectra for realistic particle distributions "in collision." The method is used to predict the energy spectrum of radiation passing through an aperture for the proposed Old Dominion University inverse Compton source. Many of the results allow easy scaling estimates to be made of the expected spectrum.

  6. Hemocompatible, pulsed laser deposited coatings on polymers.

    PubMed

    Lackner, Juergen M; Waldhauser, Wolfgang; Major, Roman; Major, Boguslaw; Bruckert, Franz

    2010-02-01

    State-of-the-art non-thrombogenic blood contacting surfaces are based on heparin and struggle with the problem of bleeding. However, appropriate blood flow characteristics are essential for clinical application. Thus, there is increasing demand to develop new coating materials for improved human body acceptance. Materials deposited by vacuum coating techniques would be an excellent alternative if the coating temperatures can be kept low because of the applied substrate materials of low temperature resistance (polymers). Most of the recently used plasma-based deposition techniques cannot fulfill this demand. However, adequate film structure and high adhesion can be reached by the pulsed laser deposition at room temperature, which was developed to an industrial-scaled process at Laser Center Leoben. Here, this process is described in detail and the resulting structural film properties are shown for titanium, titanium nitride, titanium carbonitride, and diamond-like carbon on polyurethane, titanium and silicon substrates. Additionally, we present the biological response of blood cells and the kinetic mechanism of eukaryote cell attachment. In conclusion, high biological acceptance and distinct differences for the critical delamination shear stress were found for the coatings, indicating higher adhesion at higher carbon contents.

  7. Ablation of steel using picosecond laser pulses in burst mode

    NASA Astrophysics Data System (ADS)

    Lickschat, Peter; Demba, Alexander; Weissmantel, Steffen

    2017-02-01

    Results obtained in picosecond laser processing of steel applying the burst mode are presented. Using the burst mode, pulse trains, i.e., bursts, consisting of a number of picosecond pulses with an inter-pulse delay of 12.5 ns and 10 ps pulse duration are applied for material processing. Small cavities with sizes in the range of the laser beam diameter made by single-burst ablation are compared to quadratic cavities of 0.5 × 0.5 mm² produced by multiburst ablation and simultaneous scanning of the laser beam across the steel sample surface. The ablated volume per pulse within the burst was calculated either from the ablated volume per burst or from the ablation depth of the quadratic cavities. With the second to fourth pulses in the bursts, a reduction of the ablated volume per pulse in comparison with the first pulse in the bursts (i.e., to the use of single pulses) was found for both single- and multiburst ablation, which is assumed to be due to plasma shielding. By contrast, the ablated volume per pulse within the bursts increases for the fifth to eighth pulses. Heat accumulation effect and the influence of the heated plasma can be assumed to be the reason for these higher ablation rates. SEM micrographs also show that there is a higher melt ejection out of the laser processed area. This is indicated by the formation of bulges about the ablated area.

  8. Monotonically chirped pulse evolution in an ultrashort pulse thulium-doped fiber laser.

    PubMed

    Haxsen, Frithjof; Wandt, Dieter; Morgner, Uwe; Neumann, Jörg; Kracht, Dietmar

    2012-03-15

    We report on monotonically positively chirped pulse operation of a hybridly mode-locked thulium fiber laser. Dispersion management was realized with a small-core, high-NA fiber providing normal dispersion in the 2 μm wavelength region. The laser delivered pulses with 0.7 nJ energy at the 1927 nm center wavelength and sub-500-fs pulse duration after compression.

  9. Optimizing Atom Probe Analysis with Synchronous Laser Pulsing and Voltage Pulsing.

    PubMed

    Zhao, Lu; Normand, Antoine; Houard, Jonathan; Blum, Ivan; Delaroche, Fabien; Latry, Olivier; Ravelo, Blaise; Vurpillot, Francois

    2017-04-01

    Atom probe has been developed for investigating materials at the atomic scale and in three dimensions by using either high-voltage (HV) pulses or laser pulses to trigger the field evaporation of surface atoms. In this paper, we propose an atom probe setup with pulsed evaporation achieved by simultaneous application of both methods. This provides a simple way to improve mass resolution without degrading the intrinsic spatial resolution of the instrument. The basic principle of this setup is the combination of both modes, but with a precise control of the delay (at a femtosecond timescale) between voltage and laser pulses. A home-made voltage pulse generator and an air-to-vacuum transmission system are discussed. The shape of the HV pulse presented at the sample apex is experimentally measured. Optimizing the delay between the voltage and the laser pulse improves the mass spectrum quality.

  10. Multichannel optoacoustic spectroscopy of molecular gases with pulsed lasers

    NASA Astrophysics Data System (ADS)

    Ponomarev, Iu. N.

    1989-05-01

    The linear and nonlinear absorption of laser radiation by H20 and CO2 is studied using dual-channel optoacoustic spectroscopy (OAS) with pulsed ruby and CO2 lasers. The possibility of VT-relaxation time determination is studied with allowance made for its dependence on laser radiation intensity. The advantages of the OAS method are outlined.

  11. Optical pulse generation using fiber lasers and integrated optics

    SciTech Connect

    Wilcox, R.B.; Browning, D.F.; Burkhart, S.C.; VanWonterghem, B.W.

    1995-03-27

    We have demonstrated an optical pulse forming system using fiber and integrated optics, and have designed a multiple-output system for a proposed fusion laser facility. Our approach is an advancement over previous designs for fusion lasers, and an unusual application of fiber lasers and integrated optics.

  12. Bismuth thin films obtained by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Flores, Teresa; Arronte, Miguel; Rodriguez, Eugenio; Ponce, Luis; Alonso, J. C.; Garcia, C.; Fernandez, M.; Haro, E.

    1999-07-01

    In the present work Bi thin films were obtained by Pulsed Laser Deposition, using Nd:YAG lasers. The films were characterized by optical microscopy. Raman spectroscopy and X-rays diffraction. It was accomplished the real time spectral emission characterization of the plasma generated during the laser evaporation process. Highly oriented thin films were obtained.

  13. Pulsed Laser Deposition of Gallium Arsenide.

    NASA Astrophysics Data System (ADS)

    Leppert, Valerie Jean

    Recent applications of pulsed laser deposition to the growth of various types of thin films suggest that it may be successfully used for III-V semiconductors. The goal of this work is to characterize the growth of GaAs using PLD and to determine the scope of the technique for this material. Therefore, laser ablation of GaAs is characterized here using spectroscopic analysis of the optical emission lines from the laser plasma plume. Additionally, the influence of growth conditions on GaAs films grown on a range of substrates is examined. In-situ analysis of the GaAs plume revealed that atomic, rather than molecular, arsenic is a major constituent of the GaAs plume. This may explain why no arsenic overpressure was needed to grow stoichiometric material. Nonlinear behavior of Ga emission intensity with laser power density indicated that several ablation mechanisms may be at work. EDAX studies indicate that deposited material is stoichiometric. Single crystal GaAs was grown on GaAs, Si and InP using PLD. A deposition rate of 0.65 mu m/hr was obtained. Defects consisting of dislocations, twinning and stacking faults were observed. An increase in laser power density decreased the minimum temperature for good film growth. Films were smooth overall, but suffered from an occasional inclusion of macroparticulates. Methods for screening particles were examined. The optimum growth temperature for GaAs/GaAs growth was 470^circC, but good films could be obtained as low as 335^circ C. GaAs/Si underwent a transition from a (110) oriented film to single crystal (100) film at 470 ^circC. Photoluminescence was obtained for the GaAs/GaAs and GaAs/InP systems. Well oriented films of GaAs (110) on an amorphous substrate (fused silica) were obtained for the first time using PLD at temperatures as low as 288^ circC. The effects of deposition temperature, deposition time, background gas, annealing, MOCVD overlayer and shadow masking were examined.

  14. Incubation and nanostructure formation on n- and p-type Si(1 0 0) and Si(1 1 1) at various doping levels induced by sub-nanojoule femto- and picosecond near-infrared laser pulses

    NASA Astrophysics Data System (ADS)

    Schüle, M.; Afshar, M.; Feili, D.; Seidel, H.; König, K.; Straub, M.

    2014-09-01

    N- and p-doped Si(1 0 0) and Si(1 1 1) surfaces with dopant concentrations of 2 × 1014-1 × 1019 cm-3 were irradiated by tightly focused 85-MHz repetition rate Ti:sapphire laser light (central wavelength 800 nm, bandwidth 120 nm) at pulse durations of 12 fs to 1.6 ps. Dependent on pulse peak intensity and exposure time nanorifts, ripples of period 130 nm as well as sponge-like randomly nanoporous surface structures were generated with water immersion and, thereafter, laid bare by etching off aggregated oxide nanoparticles. The same structure types emerged in air or water with transform-limited 100-fs pulses. At a pulse length of 12 fs pronounced incubation occurred with incubation coefficients S = 0.66-0.85, whereas incubation was diminished for picosecond pulses (S > 0.95). The ablation threshold strongly rose with dopant concentration. At similar doping level it was higher for n-type than for p-type samples and for Si(1 0 0) compared to Si(1 1 1) surfaces. These observations are attributed to laser-induced defect states in the bandgap which participate in photoexcitation, deactivation of dopants by complex formation, and different densities of interface states at the boundary with the ultrathin native silicon dioxide surface layer. The threshold increase with pulse length revealed predominant single-photon excitation as well as multiphoton absorption.

  15. 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.

  16. Ultrashort laser pulse interaction with photo-thermo-refractive glass

    NASA Astrophysics Data System (ADS)

    Siiman, Leo A.

    Photo-thermo-refractive (PTR) glass is an ideal photosensitive material for recording phase volume holograms. It is a homogeneous multi-component silicate glass that demonstrates all the advantages of optical glass: thermal stability, high laser damage threshold, and a wide transparency range. Moreover the ability to record phase patterns (i.e. spatial refractive index variations) into PTR glass has resulted in the fabrication of volume holograms with diffraction efficiency greater than 99%. The conventional method of recording a hologram in PTR glass relies on exposure to continuous-wave ultraviolet laser radiation. In this dissertation the interaction between infrared ultrashort laser pulses and PTR glass is studied. It is shown that photosensitivity in PTR glass can be extended from the UV region to longer wavelengths (near-infrared) by exposure to ultrashort laser pulses. It is found that there exists a focusing geometry and laser pulse intensity interval for which photoionization and refractive index change in PTR glass after thermal development occur without laser-induced optical damage. Photoionization of PTR glass by IR ultrashort laser pulses is explained in terms of strong electric field ionization. This phenomenon is used to fabricate phase optical elements in PTR glass. The interaction between ultrashort laser pulses and volume holograms in PTR glass is studied in two laser intensity regimes. At intensities below ˜10 12 W/cm2 properties such as diffraction efficiency, angular divergence, selectivity, and pulse front tilt are shown to agree with the theory of linear diffraction for broad spectral width lasers. A volume grating pair arrangement is shown to correct the laser pulse distortions arising from pulse front tilt and angular divergence. At higher intensities of irradiation, nonlinear generation and diffraction of third harmonic is observed for three types of interactions: sum-frequency generation, front-surface THG generation, and THG due to

  17. Generation of 1.5 cycle 0.3 TW laser pulses using a hollow-fiber pulse compressor.

    PubMed

    Park, Juyun; Lee, Jae-Hwan; Nam, Chang Hee

    2009-08-01

    Pulse compression in a differentially pumped neon-filled hollow fiber was used to generate high-power few-cycle laser pulses. The pulse compression process was optimized by adjusting gas pressure and laser chirp to produce the shortest laser pulses. Precise dispersion control enabled the generation of laser pulses with duration of 3.7 fs and energy of 1.2 mJ. This corresponds to an output of 1.5 cycle, 0.3 TW pulses at a 1 kHz repetition rate using positively chirped 33 fs laser pulses.

  18. Application of Yb:YAG short pulse laser system

    DOEpatents

    Erbert, Gaylen V.; Biswal, Subrat; Bartolick, Joseph M.; Stuart, Brent C.; Crane, John K.; Telford, Steve; Perry, Michael D.

    2004-07-06

    A diode pumped, high power (at least 20W), short pulse (up to 2 ps), chirped pulse amplified laser using Yb:YAG as the gain material is employed for material processing. Yb:YAG is used as the gain medium for both a regenerative amplifier and a high power 4-pass amplifier. A single common reflective grating optical device is used to both stretch pulses for amplification purposes and to recompress amplified pulses before being directed to a workpiece.

  19. Fiber Optic Solutions for Short Pulse Lasers

    SciTech Connect

    Beach, R; Dawson, J; Liao, Z; Jovanovic, I; Wattellier, B; Payne, S; Barty, C P

    2003-01-29

    For applications requiring high beam quality radiation from efficient, compact and rugged sources, diffraction limited fiber lasers are ideal, and to date have been demonstrated at average CW power levels exceeding 100 W with near diffraction limited: output. For conventional single-core step-index single-mode fibers, this power level represents the sealing limit because of nonlinear and laser damage considerations. Higher average powers would exceed nonlinear process thresholds such as the Raman and stimulated Brillouin scattering limit, or else damage the fiber due to the high intensity level in the fiber's core. The obvious way to increase the average power capability of fibers is to increase the area of their core. Simply expanding the core dimensions of the fiber allows a straightforward power sealing due to enhanced nonlinear and power handling characteristics that scale directly with the core area. Femtosecond, chirped-pulse, fiber lasers with pulse energies greater than 1mJ have been demonstrated in the literature [2] using this technique. This output energy was still limited by the onset of stimulated Raman scattering. We have pursued an alternative and complimentary approach which is to reduce the intensity of light propagating in the core by distributing it more evenly across the core area via careful design of the refractive index profile [3]. We have also sought to address the primary issue that results from scaling the core. The enhanced power handling capability comes at the expense of beam quality, as increasing the core diameter in standard step index fibers permits multiple transverse modes to lase simultaneously. Although this problem of multimode operation can be mitigated to some extent by appropriately designing the fiber's waveguide structure, limitations such as bend radius loss, sensitivity to thermally induced perturbations of the waveguide structure, and refractive index control, all become more stringent as the core diameter grows

  20. A laser spectrometer and wavemeter for pulsed lasers

    NASA Technical Reports Server (NTRS)

    Mckay, J. A.; Laufer, P. M.; Cotnoir, L. J.

    1989-01-01

    The design, construction, calibration, and evaluation of a pulsed laser wavemeter and spectral analyzer are described. This instrument, called the Laserscope for its oscilloscope-like display of laser spectral structure, was delivered to NASA Langley Research Center as a prototype of a laboratory instrument. The key component is a multibeam Fizeau wedge interferometer, providing high (0.2 pm) spectral resolution and a linear dispersion of spectral information, ideally suited to linear array photodiode detectors. Even operating alone, with the classic order-number ambiguity of interferometers unresolved, this optical element will provide a fast, real-time display of the spectral structure of a laser output. If precise wavelength information is also desired then additional stages must be provided to obtain a wavelength measurement within the order-number uncertainty, i.e., within the free spectral range of the Fizeau wedge interferometer. A Snyder (single-beam Fizeau) wedge is included to provide this initial wavelength measurement. Difficulties in achieving the required wide-spectrum calibration limit the usefulness of this function.

  1. Generation of high-power nanosecond pulses from laser diode-pumped Nd:YAG lasers

    NASA Technical Reports Server (NTRS)

    Chan, Kinpui

    1988-01-01

    Simulation results are used to compare the pulse energy levels and pulse energy widths that can be achieved with LD-pumped Nd:YAG lasers for both the pulse-transmission mode (PTM) and pulse-reflection mode (PRM) Q-switching methods for pulse energy levels up to hundreds of microjoules and pulse widths as short as 1 ns. It is shown that high-power pulses with pulse widths as short as 1 ns can be generated with PTM Q-switched in LD-pumped Nd:YAG lasers. With the PRM Q-switching method, pulse widths as short as 2 ns and pulse energy at the level of a few hundred microjoules can also be achieved but require pumping with 8-10-mJ AlGaAs laser diode arrays.

  2. Dynamics of plasma formation, relaxation, and topography modification induced by femtosecond laser pulses in crystalline and amorphous dielectrics

    SciTech Connect

    Puerto, D.; Siegel, J.; Gawelda, W.; Galvan-Sosa, M.; Solis, J.; Ehrentraut, L.; Bonse, J.

    2010-05-15

    We have studied plasma formation and relaxation dynamics along with the corresponding topography modifications in fused silica and sapphire induced by single femtosecond laser pulses (800 nm and 120 fs). These materials, representative of high bandgap amorphous and crystalline dielectrics, respectively, require nonlinear mechanisms to absorb the laser light. The study employed a femtosecond time-resolved microscopy technique that allows obtaining reflectivity and transmission images of the material surface at well-defined temporal delays after the arrival of the pump pulse which excites the dielectric material. The transient evolution of the free-electron plasma formed can be followed by combining the time-resolved optical data with a Drude model to estimate transient electron densities and skin depths. The temporal evolution of the optical properties is very similar in both materials within the first few hundred picoseconds, including the formation of a high reflectivity ring at about 7 ps. In contrast, at longer delays (100 ps-20 ns) the behavior of both materials differs significantly, revealing a longer lasting ablation process in sapphire. Moreover, transient images of sapphire show a concentric ring pattern surrounding the ablation crater, which is not observed in fused silica. We attribute this phenomenon to optical diffraction at a transient elevation of the ejected molten material at the crater border. On the other hand, the final topography of the ablation crater is radically different for each material. While in fused silica a relatively smooth crater with two distinct regimes is observed, sapphire shows much steeper crater walls, surrounded by a weak depression along with cracks in the material surface. These differences are explained in terms of the most relevant thermal and mechanical properties of the material. Despite these differences the maximum crater depth is comparable in both material at the highest fluences used (16 J/cm{sup 2}). The

  3. Three-dimensional optical coherence tomography at 1050 nm versus 800 nm in retinal pathologies: enhanced performance and choroidal penetration in cataract patients.

    PubMed

    Povazay, Boris; Hermann, Boris; Unterhuber, Angelika; Hofer, Bernd; Sattmann, Harald; Zeiler, Florian; Morgan, James E; Falkner-Radler, Christiane; Glittenberg, Carl; Blinder, Susanne; Drexler, Wolfgang

    2007-01-01

    Frequency domain optical coherence tomography (FD-OCT), based on an all-reflective high-speed InGaAs spectrometer, operating in the 1050 nm wavelength region for retinal diagnostics, enables high-speed, volumetric imaging of retinal pathologies with greater penetration into choroidal tissue is compared to conventional 800 nm three-dimensional (3-D) ophthalmic FD-OCT systems. Furthermore, the lower scattering at this wavelength significantly improves imaging performance in cataract patients, thereby widening the clinical applicability of ophthalmic OCT. The clinical performance of two spectrometer-based ophthalmic 3-D OCT systems compared in respect to their clinical performance, one operating at 800 nm with 150 nm bandwidth (approximately 3 microm effective axial resolution) and the other at 1050 nm with 70 nm bandwidth (approximately 7 microm effective axial resolution). Results achieved with 3-D OCT at 1050 nm reveal, for the first time, decisive improvements in image quality for patients with retinal pathologies and clinically significant cataract.

  4. Recent progress in picosecond pulse generation from semiconductor lasers

    NASA Technical Reports Server (NTRS)

    Auyeung, J. C.; Johnston, A. R.

    1982-01-01

    This paper reviews the recent progress in producing picosecond optical pulses from semiconductor laser diodes. The discussion concentrates on the mode-locking of a semiconductor laser diode in an external resonator. Transform-limited optical pulses ranging from several picoseconds to subpicosecond durations have been observed with active and passive mode-locking. Even though continuing research on the influence of impurities and defects on the mode-locking process is still needed, this technique has good promise for being utilized in fiber-optic communication systems. Alternative methods of direct electrical and optical excitation to produce ultrashort laser pulses are also described. They can generate pulses of similar widths to those obtained by mode-locking. The pulses generated will find applications in laser ranging and detector response measurement.

  5. 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.

  6. Recent progress in picosecond pulse generation from semiconductor lasers

    NASA Technical Reports Server (NTRS)

    Auyeung, J. C.; Johnston, A. R.

    1982-01-01

    This paper reviews the recent progress in producing picosecond optical pulses from semiconductor laser diodes. The discussion concentrates on the mode-locking of a semiconductor laser diode in an external resonator. Transform-limited optical pulses ranging from several picoseconds to subpicosecond durations have been observed with active and passive mode-locking. Even though continuing research on the influence of impurities and defects on the mode-locking process is still needed, this technique has good promise for being utilized in fiber-optic communication systems. Alternative methods of direct electrical and optical excitation to produce ultrashort laser pulses are also described. They can generate pulses of similar widths to those obtained by mode-locking. The pulses generated will find applications in laser ranging and detector response measurement.

  7. Short-pulse laser interactions with disordered materials and liquids

    SciTech Connect

    Phinney, L.M.; Goldman, C.H.; Longtin, J.P.; Tien, C.L.

    1995-12-31

    High-power, short-pulse lasers in the picosecond and subpicosecond range are utilized in an increasing number of technologies, including materials processing and diagnostics, micro-electronics and devices, and medicine. In these applications, the short-pulse radiation interacts with a wide range of media encompassing disordered materials and liquids. Examples of disordered materials include porous media, polymers, organic tissues, and amorphous forms of silicon, silicon nitride, and silicon dioxide. In order to accurately model, efficiently control, and optimize short-pulse, laser-material interactions, a thorough understanding of the energy transport mechanisms is necessary. Thus, fractals and percolation theory are used to analyze the anomalous diffusion regime in random media. In liquids, the thermal aspects of saturable and multiphoton absorption are examined. Finally, a novel application of short-pulse laser radiation to reduce surface adhesion forces in microstructures through short-pulse laser-induced water desorption is presented.

  8. Response of silicon solar cell to pulsed laser illumination

    NASA Technical Reports Server (NTRS)

    Willowby, D.; Alexander, D.; Edge, T.; Herren, K.

    1993-01-01

    The response of silicon solar cell(s) to pulsed laser illumination is discussed. The motivation was due to the interest of Earth to space/Moon power beaming applications. When this work began, it was not known if solar cells would respond to laser light with pulse lengths in the nanosecond range and a repetition frequency in the kHz range. This is because the laser pulse would be shorter than the minority carrier lifetime of silicon. A 20-nanosecond (ns) full width half max (FWHM) pulse from an aluminum-gallium/arsenide (Al-Ga-As) diode laser was used to illuminate silicon solar cells at a wavelength of 885 nanometers (nm). Using a high-speed digital oscilloscope, the response of the solar cells to individual pulses across various resistive loads was observed and recorded.

  9. LIBS using dual- and ultra-short laser pulses.

    PubMed

    Angel, S M; Stratis, D N; Eland, K L; Lai, T; Berg, M A; Gold, D M

    2001-02-01

    Pre-ablation dual-pulse LIBS enhancement data for copper, brass and steel using ns laser excitation are reported. Although large enhancements are observed for all samples, the magnitude of the enhancement is matrix dependent. Whereas all of the dual-pulse studies used ns laser excitation we see interesting effects when using ps and fs laser excitation for single-pulse LIBS. LIBS spectra of copper using 1.3 ps and 140 fs laser pulses show much lower background signals compared to ns pulse excitation. Also, the atomic emission decays much more rapidly with time. Because of relatively low backgrounds when using ps and fs pulses, non-gated detection of LIBS is shown to be very effective. The plasma dissipates quickly enough using ps and fs laser pulses, that high pulse rates, up to 1,000 Hz, are effective for increasing the LIBS signal, for a given measurement time. Finally, a simple near-collinear dual-pulse fiber-optic LIBS probe is shown to be useful for enhanced LIBS measurements.

  10. Laser induced breakdown spectroscopy with picosecond pulse train

    NASA Astrophysics Data System (ADS)

    Lednev, Vasily N.; Pershin, Sergey M.; Sdvizhenskii, Pavel A.; Grishin, Mikhail Ya; Davydov, Mikhail A.; Stavertiy, Anton Ya; Tretyakov, Roman S.

    2017-02-01

    Picosecond pulse train and nanosecond pulse were compared for laser ablation and laser induced breakdown spectroscopy (LIBS) measurements. A detailed study revealed that the picosecond pulse train ablation improved the quality of laser craters (symmetric crater walls and the absence of large redeposited droplets), which was explained by a smaller heat affected zone and suppression of melt splash. Greater plasma dimensions and brighter plasma emission were observed by gated imaging for picosecond pulse train compared to nanosecond pulse ablation. Increased intensity of atomic and ionic lines in gated and time integrated spectra provided better signal-to-noise ratio for picosecond pulse train sampling. Higher temperature and electron density were detected during first microsecond for the plasma induced by the picosecond pulse train. Improved shot-to-shot reproducibility for atomic/ionic line intensity in the case of picosecond pulse train LIBS was explained by more effective atomization of target material in plasma and better quality of laser craters. Improved precision and limits of detections were determined for picosecond pulse train LIBS due to better reproducibility of laser sampling and increased signal-to-noise ratio.

  11. Synchronous pulse generation in a multicavity fiber laser system

    NASA Astrophysics Data System (ADS)

    Gómez-Pavón, L. C.; Martí-Panameño, E.; Gómez-de la Fuente, O.; Luis-Ramos, A.

    2006-09-01

    We report the experimental synchronous pulse generation in a multicavity fiber laser system with two Erbium-doped fiber laser cavities. We have demonstrated that through the evanescent fields interaction between one cavity with active modulation and other one in continuous wave it is possible to generate more intense pulses in both cavities. Moreover, the synchronous pulse generation between cavities is achieved with an appropriate selection of pump intensity, modulation frequency and coupling ratio. We found that the pulse intensity is 2.5 times greater and the pulse duration lowers than a single Erbium-doper fiber laser. Furthermore, by means of the synchronous diagram we determined the synchronization strength in temporal pulse emission between cavities.

  12. Characterization of nonlinear properties of black phosphorus nanoplatelets with femtosecond pulsed Z-scan measurements.

    PubMed

    Zheng, Xin; Chen, Runze; Shi, Gang; Zhang, Jianwei; Xu, Zhongjie; Cheng, Xiang'ai; Jiang, Tian

    2015-08-01

    The nonlinear properties of black phosphorus (BP) nanoplatelets (NPs) have been characterized with Z-scan measurements under 800-nm femtosecond pulsed laser excitation. A transition from saturable absorption (SA) to reverse saturable absorption (RSA) with the increase of laser intensity was observed in the open-aperture (OA) measurements. Simultaneously, closed-aperture (CA) measurements were carried out to investigate the nonlinear refractive index of BP NPs together, and a value of n(2) ≃(6.8±0.2)×10(-13) m2/W was obtained. The nonlinear absorption properties were analyzed according to the band structure of BP. A theoretical analysis based on SA and two-photon absorption (TPA) was used to determine the nonlinear absorption coefficients from the experimental results, and the TPA coefficient at 800 nm was estimated about (4.5±0.2)×10(-10) m/W.

  13. Ponderomotive acceleration of electrons by a self focused laser pulse

    SciTech Connect

    Singh, Rohtash; Sharma, A. K.

    2010-12-15

    Ponderomotive acceleration of electrons by a short laser pulse undergoing relativistic self-focusing in a plasma is investigated. The saturation in nonlinear plasma permittivity causes periodic self-focusing of the laser. The periodicity lengths are different for different axial segments of the pulse. As a result, pulse shape is distorted. An electron initially on the laser axis and at the front of the self-focusing pulse gains energy from the pulse until it is run over by the pulse peak. By the time electron reaches the tail, if pulse begins diverging, the deceleration of the electron is slower and the electron is left with net energy gain. The electrons slightly off the laser axis see a radial ponderomotive force too. Initially, when they are accelerated by the pulse front the acceleration is strong as they are closer to the axis. When they see the tail of the pulse (after being run by the pulse), they are farther from the axis and the retardation ponderomotive force is weaker. Thus, there is net energy gain.

  14. Femtosecond pulse generation from a Ti3+:sapphire laser near 800  nm with voltage reconfigurable graphene saturable absorbers.

    PubMed

    Baylam, Isınsu; Ozharar, Sarper; Kakenov, Nurbek; Kocabas, Coskun; Sennaroglu, Alphan

    2017-04-01

    We experimentally show that a voltage-controlled graphene-gold supercapacitor saturable absorber (VCG-gold-SA) can be operated as a fast saturable absorber with adjustable linear absorption at wavelengths as low as 795 nm. This was made possible by the use of a novel supercapacitor architecture, consisting of a high-dielectric electrolyte sandwiched between a graphene and a gold electrode. The high-dielectric electrolyte allowed continuous, reversible adjustment of the Fermi level and, hence, the optical loss of the VCG-gold-SA up to the visible wavelengths at low bias voltages of the order of a few volts (0-2 V). The fast saturable absorber action of the VCG-gold-SA and the bias-dependent reduction of its loss were successfully demonstrated inside a femtosecond Ti3+:sapphire laser operating near 800 nm. Dispersion compensation was employed by using dispersion control mirrors and a prism pair. At a bias voltage of 1.2 V, the laser operated with improved power performance in comparison with that at zero bias, and the VCG-gold-SA initiated the generation of nearly transform-limited pulses as short as 48 fs at a pulse repetition rate of 131.7 MHz near 830 nm. To the best of our knowledge, this represents the shortest wavelength where a VCG-gold-SA has been employed as a mode locker with adjustable loss.

  15. Efficient photoassociation with a train of asymmetric laser pulses

    SciTech Connect

    Zhang Wei; Wang Gaoren; Cong Shulin

    2011-04-15

    The photoassociation (PA) dynamics implemented by a train of asymmetric slowly turned-on and rapidly turned-off (STRT) laser pulses is investigated theoretically with Cs{sub 2} as an example. A higher PA efficiency is achieved by optimizing the parameters of the STRT pulse train. The PA reaction goes partly beyond the scope of the PA window. Numerical calculations show that an efficient population accumulation in the PA process can be realized with the STRT laser-pulse train which is available in the current experiment based on laser mode-lock and shaping technology.

  16. Airborne bathymetric charting using pulsed blue-green lasers

    NASA Technical Reports Server (NTRS)

    Kim, H. H.

    1977-01-01

    Laboratory and airborne experiments have proven the feasibility and demonstrated the techniques of an airborne pulsed laser system for rapidly mapping coastal water bathymetry. Water depths of 10 plus or minus 0.25 m were recorded in waters having an effective attenuation coefficient of 0.175 m. A 2-MW peak power Nd:YAG pulsed laser was flown at an altitude of 600 m. An advanced system, incorporating a mirror scanner, a high pulsed rate laser, and a good signal processor, could survey coastal zones at the rate of several square miles per hour.

  17. Airborne bathymetric charting using pulsed blue-green lasers.

    PubMed

    Kim, H H

    1977-01-01

    Laboratory and airborne experiments have proven the feasibility and demonstrated the techniques of an airborne pulsed laser system for rapidly mapping coastal water bathymetry. Water depths of 10 +/- 0.25 m were recorded in waters having an effective attenuation coefficient of 0.175 m(-1). A2-MW peak power Nd:YAG pulsed laser was flown at an altitude of 600 m. An advanced system, incorporating a mirror scanner, a high pulsed rate laser, and a good signal processor, could survey coastal zones at the rate of several square miles per hour.

  18. Safe Operation and Alignment of the Variable Pulse Width Laser at the US Army Research Laboratory

    DTIC Science & Technology

    2016-02-01

    pulse at pulse widths between 50 µs to 10 ms. Maximum energy output is only achieved by proper alignment and laser operation. This report provides...not included in the operator’s manual. 15. SUBJECT TERMS pulse width, laser energy , laser alignment, peak power, laser operation 16. SECURITY...Acknowledgments v 1. Introduction 1 2. Energy Output of the Variable Pulse Width Laser 1 3. Operation of the Variable Pulse Width Laser 2 4

  19. All-fiber ring Raman laser generating parabolic pulses

    SciTech Connect

    Kruglov, V. I.; Mechin, D.; Harvey, J. D.

    2010-02-15

    We present theoretical and numerical results for an all-fiber laser using self-similar parabolic pulses ('similaritons') designed to operate using self-similar propagation regimes. The similariton laser features a frequency filter and a Sagnac loop which operate together to generate an integrated all-fiber mode-locked laser. Numerical studies show that this laser generates parabolic pulses with linear chirp in good agreement with analytical predictions. The period for propagating similariton pulses in stable regimes can vary from one to two round trips for different laser parameters. Two-round-trip-period operation in the mode-locked laser appears at bifurcation points for certain cavity parameters. The stability of the similariton regimes has been confirmed by numerical simulations for large numbers of round trips.

  20. Velocity measurement using frequency domain interferometer and chirped pulse laser

    NASA Astrophysics Data System (ADS)

    Ishii, K.; Nishimura, Y.; Mori, Y.; Hanayama, R.; Kitagawa, Y.; Sekine, T.; Sato, N.; Kurita, T.; Kawashima, T.; Sunahara, A.; Sentoku, Y.; Miura, E.; Iwamoto, A.; Sakagami, H.

    2017-02-01

    An ultra-intense short pulse laser induces a shock wave in material. The pressure of shock compression is stronger than a few tens GPa. To characterize shock waves, time-resolved velocity measurement in nano- or pico-second time scale is needed. Frequency domain interferometer and chirped pulse laser provide single-shot time-resolved measurement. We have developed a laser-driven shock compression system and frequency domain interferometer with CPA laser. In this paper, we show the principle of velocity measurement using a frequency domain interferometer and a chirped pulse laser. Next, we numerically calculated spectral interferograms and show the time-resolved velocity measurement can be done from the phase analysis of spectral interferograms. Moreover we conduct the laser driven shock generation and shock velocity measurement. From the spectral fringes, we analyze the velocities of the sample and shockwaves.

  1. High-charge energetic ions generated by intersecting laser pulses

    SciTech Connect

    Yang, L.; Deng, Z. G.; Yu, M. Y.; Wang, X. G.

    2016-08-15

    Ion acceleration from the interaction of two intersecting intense laser pulses with an overdense plasma is investigated using a three-dimensional particle-in-cell simulation. It is found that, comparing with the single-pulse case, the charge of the resulting energetic ion bunch can be increased by more than an order of magnitude without much loss of quality. Dependence of the ion charge on the interaction parameters, including separation distance and incidence angles of the lasers, is considered. It is shown that the charge of the accelerated ion bunch can be optimized by controlling the degree of laser overlapping. The improved performance can be attributed to the enhanced laser intensity as well as stochastic heating of the accelerated electrons. Since at present the intensity of readily available lasers is limited, the two pulse scheme should be useful for realizing higher laser intensity in order to achieve higher-energy target normal sheath acceleration ions.

  2. Pulse Splitting in Short Wavelength Seeded Free Electron Lasers

    SciTech Connect

    Labat, M.; Couprie, M. E.; Joly, N.; Bruni, C.

    2009-12-31

    We investigate a fundamental limitation occurring in vacuum ultraviolet and extreme ultraviolet seeded free electron lasers (FELs). For a given electron beam and undulator configuration, an increase of the FEL output energy at saturation can be obtained via an increase of the seed pulse duration. We put in evidence a complex spatiotemporal deformation of the amplified pulse, leading ultimately to a pulse splitting effect. Numerical studies of the Colson-Bonifacio FEL equations reveal that slippage length and seed laser pulse wings are core ingredients of the dynamics.

  3. Propagation of Complex Laser Pulses in Optically Dense Media

    NASA Astrophysics Data System (ADS)

    Fetterman, M. R.; Davis, J. C.; Goswami, D.; Yang, W.; Warren, W. S.

    1999-05-01

    Ultrafast laser pulses with complex envelopes (amplitude and frequency modulated) are used to excite an optically dense column of rubidium vapor. Pulse reshaping, stimulated emission dynamics, and residual electronic excitation in the Rb vapor are all shown to depend strongly on the laser pulse shape. Pulses that produce adiabatic passage in the optically thin limit exhibit more complex behavior in optically thick samples, including an unexpected dependence on the sign of the frequency sweep. Numerical solutions of the Maxwell-Bloch equations are shown to account for our results.

  4. The affect of erbium hydride on the conversion efficience to accelerated protons from ultra-shsort pulse laser irradiated foils

    SciTech Connect

    Offermann, Dustin Theodore

    2008-01-01

    This thesis work explores, experimentally, the potential gains in the conversion efficiency from ultra-intense laser light to proton beams using erbium hydride coatings. For years, it has been known that contaminants at the rear surface of an ultra-intense laser irradiated thin foil will be accelerated to multi-MeV. Inertial Confinement Fusion fast ignition using proton beams as the igniter source requires of about 1016 protons with an average energy of about 3MeV. This is far more than the 1012 protons available in the contaminant layer. Target designs must include some form of a hydrogen rich coating that can be made thick enough to support the beam requirements of fast ignition. Work with computer simulations of thin foils suggest the atomic mass of the non-hydrogen atoms in the surface layer has a strong affect on the conversion efficiency to protons. For example, the 167amu erbium atoms will take less energy away from the proton beam than a coating using carbon with a mass of 12amu. A pure hydrogen coating would be ideal, but technologically is not feasible at this time. In the experiments performed for my thesis, ErH3 coatings on 5 μm gold foils are compared with typical contaminants which are approximately equivalent to CH1.7. It will be shown that there was a factor of 1.25 ± 0.19 improvement in the conversion efficiency for protons above 3MeV using erbium hydride using the Callisto laser. Callisto is a 10J per pulse, 800nm wavelength laser with a pulse duration of 200fs and can be focused to a peak intensity of about 5 x 1019W/cm2. The total number of protons from either target type was on the order of 1010. Furthermore, the same experiment was performed on the Titan laser, which has a 500fs pulse duration, 150J of energy and can be focused to about 3 x 1020 W/cm2. In this experiment 1012 protons were seen from both erbium hydride and

  5. High pulse energy 2 µm femtosecond fiber laser.

    PubMed

    Wan, Peng; Yang, Lih-Mei; Liu, Jian

    2013-01-28

    In the paper, a 2 µm high energy fs fiber laser and amplification system is presented based on Tm doped fibers. The seed laser was designed to generate pulse train at 2024 nm at a repetition rate of 2.5 MHz. An AOM was used as a pulse picker to further lower the repetition rate down to 100 kHz. Two-stage fiber pre-amplifiers and a high energy large mode area (LMA) fiber amplifier were used to boost pulse energy up to 54 µJ before pulse compressor with chirped pulse amplification technique. After compressor, pulse energy of 36.7µJ and pulse duration of 910 fs and were obtained.

  6. Measuring spatiotemporal intensity-and-phase complexity of multimode fiber output pulses

    NASA Astrophysics Data System (ADS)

    Guang, Zhe; Rhodes, Michelle; Trebino, Rick

    2016-03-01

    We demonstrate ultrashort pulse spatiotemporal field measurement for multimode optical fibers, using a singleframe characterization technique, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH). We measure STRIPED FISH traces and retrieve the pulse field E(x,y,t) or equivalently E(x,y,ω), to generate movies revealing the field structure induced by propagating modes, due to their differences in field spatial distribution, modal propagation velocity and modal dispersion inside the fiber. We launch femtosecond pulses near 800nm from Ti: Sapphire laser to investigate linearly polarized modes LP01, LP11, LP02 and LP21 in multimode fibers.

  7. Sub-20 fs μJ-energy pulses tunable down to the near-UV from a 1 MHz Yb-fiber laser system.

    PubMed

    Bradler, Maximilian; Riedle, Eberhard

    2014-05-01

    Optical parametric amplifiers render widely tunable ultrashort pulses, but for full spectral coverage, complex mixing schemes are needed. In particular, the blue and near-UV part of the spectrum is not directly reached with the 800 nm pump from Ti:sapphire systems or the 1030 nm pump of Yb-based lasers. We combine third harmonic pumping at 343 nm with seeding by a second harmonic (SH) pumped continuum to tune a noncollinear optical parametric amplifier down to 395 nm. Together with a SH pumped branch, the full range from 395 to 970 nm is covered with 20 fs pulse length or less. Pulse energies up to the μJ-level with an average power of up to 200 mW at 200 kHz and 480 mW at 1 MHz are achieved. With additional frequency doubling, the full range down to 210 nm is reached without gap. Two-photon absorption in the amplifier crystal is discussed as the critical issue in UV-pumped systems.

  8. Optimization and control of electron beams from laser wakefield accelerations using asymmetric laser pulses

    NASA Astrophysics Data System (ADS)

    Gopal, K.; Gupta, D. N.

    2017-10-01

    Optimization and control of electron beam quality in laser wakefield acceleration are explored by using a temporally asymmetric laser pulse of the sharp rising front portion. The temporally asymmetric laser pulse imparts stronger ponderomotive force on the ambient plasma electrons. The stronger ponderomotive force associated with the asymmetric pulse significantly affects the injection of electrons into the wakefield and consequently the quality of the injected bunch in terms of injected charge, mean energy, and emittance. Based on particle-in-cell simulations, we report to generate a monoenergetic electron beam with reduced emittance and enhanced charge in laser wakefield acceleration using an asymmetric pulse of duration 30 fs.

  9. LASERS: Electric-discharge XeCl laser emitting 10-J, 300-ns pulses

    NASA Astrophysics Data System (ADS)

    Konovalov, I. N.; Losev, V. F.; Panchenko, Yu N.; Ivanov, N. G.; Sukhov, M. Yu

    2005-03-01

    The development of a long-pulse electric-discharge XeCl laser with the 9 × 6 × 100 cm active volume is reported. Laser is excited by using a double circuit with a pulsed charged storage capacitor consisting of paper-oil capacitors forming the pulse-shaping line. The storage capacitor is switched by a multichannel extended gap. The laser mixture was preionised by X-rays. The laser generated the 10-J output pulses with the FWHM of 300 ns, and a uniform intensity distribution over the exit aperture.

  10. Stabilizing laser energy density on a target during pulsed laser deposition of thin films

    DOEpatents

    Dowden, Paul C.; Jia, Quanxi

    2016-05-31

    A process for stabilizing laser energy density on a target surface during pulsed laser deposition of thin films controls the focused laser spot on the target. The process involves imaging an image-aperture positioned in the beamline. This eliminates changes in the beam dimensions of the laser. A continuously variable attenuator located in between the output of the laser and the imaged image-aperture adjusts the energy to a desired level by running the laser in a "constant voltage" mode. The process provides reproducibility and controllability for deposition of electronic thin films by pulsed laser deposition.

  11. Hydroxyapatite thin films grown by pulsed laser deposition and matrix assisted pulsed laser evaporation: Comparative study

    NASA Astrophysics Data System (ADS)

    Popescu-Pelin, G.; Sima, F.; Sima, L. E.; Mihailescu, C. N.; Luculescu, C.; Iordache, I.; Socol, M.; Socol, G.; Mihailescu, I. N.

    2017-10-01

    Pulsed Laser Deposition (PLD) and Matrix Assisted Pulsed Laser Evaporation (MAPLE) techniques were applied for growing hydroxyapatite (HA) thin films on titanium substrates. All experiments were conducted in a reaction chamber using a KrF* excimer laser source (λ = 248 nm, τFWHM ≈ 25 ns). Half of the samples were post-deposition thermally treated at 500 °C in a flux of water vapours in order to restore crystallinity and improve adherence. Coating surface morphologies and topographies specific to the deposition method were evidenced by scanning electron, atomic force microscopy investigations and profilometry. They were shown to depend on deposition technique and also on the post-deposition treatment. Crystalline structure of the coatings evaluated by X-ray diffraction was improved after thermal treatment. Biocompatibility of coatings, cellular adhesion, proliferation and differentiation tests were conducted using human mesenchymal stem cells (MSCs). Results showed that annealed MAPLE deposited HA coatings were supporting MSCs proliferation, while annealed PLD obtained films were stimulating osteogenic differentiation.

  12. Over 0.5 MW green laser from sub-nanosecond giant pulsed microchip laser

    NASA Astrophysics Data System (ADS)

    Zheng, Lihe; Taira, Takunori

    2016-03-01

    A sub-nanosecond green laser with laser head sized 35 × 35 × 35 mm3 was developed from a giant pulsed microchip laser for laser processing on organic superconducting transistor with a flexible substrate. A composite monolithic Y3Al5O12 (YAG) /Nd:YAG/Cr4+:YAG/YAG crystal was designed for generating giant pulsed 1064 nm laser. A fibercoupled 30 W laser diode centered at 808 nm was used with pump pulse duration of 245 μs. The 532 nm green laser was obtained from a LiB3O5 (LBO) crystal with output energy of 150 μJ and pulse duration of 268 ps. The sub-nanosecond green laser is interesting for 2-D ablation patterns.

  13. Ablation characteristics of quantum square pulse mode dental erbium laser

    NASA Astrophysics Data System (ADS)

    Lukač, Nejc; Suhovršnik, Tomaž; Lukač, Matjaž; Jezeršek, Matija

    2016-01-01

    Erbium lasers are by now an accepted tool for performing ablative medical procedures, especially when minimal invasiveness is desired. Ideally, a minimally invasive laser cutting procedure should be fast and precise, and with minimal pain and thermal side effects. All these characteristics are significantly influenced by laser pulse duration, albeit not in the same manner. For example, high cutting efficacy and low heat deposition are characteristics of short pulses, while vibrations and ejected debris screening are less pronounced at longer pulse durations. We report on a study of ablation characteristics on dental enamel and cementum, of a chopped-pulse Er:YAG [quantum square pulse (QSP)] mode, which was designed to reduce debris screening during an ablation process. It is shown that in comparison to other studied standard Er:YAG and Er,Cr:YSGG laser pulse duration modes, the QSP mode exhibits the highest ablation drilling efficacy with lowest heat deposition and reduced vibrations, demonstrating that debris screening has a considerable influence on the ablation process. By measuring single-pulse ablation depths, we also show that tissue desiccation during the consecutive delivery of laser pulses leads to a significant reduction of the intrinsic ablation efficacy that cannot be fully restored under clinical settings by rehydrating the tooth using an external water spray.

  14. Transient thermal analysis of semiconductor diode lasers under pulsed operation

    NASA Astrophysics Data System (ADS)

    Veerabathran, G. K.; Sprengel, S.; Karl, S.; Andrejew, A.; Schmeiduch, H.; Amann, M.-C.

    2017-02-01

    Self-heating in semiconductor lasers is often assumed negligible during pulsed operation, provided the pulses are `short'. However, there is no consensus on the upper limit of pulse width for a given device to avoid-self heating. In this paper, we present an experimental and theoretical analysis of the effect of pulse width on laser characteristics. First, a measurement method is introduced to study thermal transients of edge-emitting lasers during pulsed operation. This method can also be applied to lasers that do not operate in continuous-wave mode. Secondly, an analytical thermal model is presented which is used to fit the experimental data to extract important parameters for thermal analysis. Although commercial numerical tools are available for such transient analyses, this model is more suitable for parameter extraction due to its analytical nature. Thirdly, to validate this approach, it was used to study a GaSb-based inter-band laser and an InP-based quantum cascade laser (QCL). The maximum pulse-width for less than 5% error in the measured threshold currents was determined to be 200 and 25 ns for the GaSb-based laser and QCL, respectively.

  15. Pulsed infrared laser irradiation of biological tissue: effect of pulse duration and repetition rate

    NASA Astrophysics Data System (ADS)

    Jansen, E. Duco; Chundru, Ravi K.; Samanani, Salim A.; Tibbetts, Todd A.; Welch, Ashley J.

    1993-07-01

    Pulsed laser ablation is a trade off between minimizing thermal damage (for relatively long pulses) and mechanical damage (for relatively short pulses) to tissue adjacent to the ablation crater. Often it is not known what the optimal laser parameters are for a specific application, since clinically used parameters have at least partially been dictated by physical limitations of the laser devices. We recently obtained a novel type of cryogenic continuous wave holmium:YAG laser ((lambda) equals 2.09 micrometers ) with a galvanometric drive outcouple mirror that acts as a Q-switch. This unique device provides pulse repetition rates from a few Hz up to kHz and the pulse length is variable from microsecond(s) to ms. The effect of pulse duration and repetition rate on the thermal response of chicken breast is documented using temperature measurements with a thermal camera. We varied the pulse width from 10 microsecond(s) to 5 ms and fond that these pulse durations can be considered impulses of thermalized optical energy. In this paper some theoretical considerations of the pulse length will be described that support the experimental data. It was also found that even at 1 pulse per second thermal superposition occurs, indicating a much longer thermal relaxation time than predicted by a simple time constant model.

  16. Ultrafast laser photoinscription of polarization sensitive devices in bulk silica glass.

    PubMed

    Cheng, G; Mishchik, K; Mauclair, C; Audouard, E; Stoian, R

    2009-06-08

    Ultrashort pulsed laser irradiation of bulk fused silica may result under specific energetic conditions in the self-organization of subwavelength material redistribution regions within the laser trace. The modulated structures have birefringent properties and show unusual anisotropic light scattering and reflection characteristics. We report here on the formation of waveguiding structures with remarkable polarization effects for infrared light. The photoinscription process using 800 nm femtosecond laser pulses is accompanied by third harmonic generation and polarization dependent anisotropic scattering of UV photons. The photowritten structures can be arranged in three-dimensional patterns generating complex propagation and polarization effects due to the anisotropic optical properties.

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

  18. Synchronization of sub-picosecond electron and laser pulses

    SciTech Connect

    Rosenzweig, J.B.; Le Sage, G.P.

    1999-07-01

    Sub-picosecond laser-electron synchronization is required to take full advantage of the experimental possibilities arising from the marriage of modern high intensity lasers and high brightness electron beams in the same laboratory. Two particular scenarios stand out in this regard, injection of ultra-short electron pulses in short wavelength laser-driven plasma accelerators, and Compton scattering of laser photons from short electron pulses. Both of these applications demand synchronization, which is sub-picosecond, with tens of femtosecond synchronization implied for next generation experiments. The design of a microwave timing modulator system is now being investigated in more detail. (AIP) {copyright} {ital 1999 American Institute of Physics.}

  19. Synchronization of sub-picosecond electron and laser pulses

    SciTech Connect

    Rosenzweig, J. B.; Le Sage, G. P.

    1999-07-12

    Sub-picosecond laser-electron synchronization is required to take full advantage of the experimental possibilities arising from the marriage of modern high intensity lasers and high brightness electron beams in the same laboratory. Two particular scenarios stand out in this regard, injection of ultra-short electron pulses in short wavelength laser-driven plasma accelerators, and Compton scattering of laser photons from short electron pulses. Both of these applications demand synchronization, which is sub-picosecond, with tens of femtosecond synchronization implied for next generation experiments. The design of a microwave timing modulator system is now being investigated in more detail.

  20. Acceleration Mechanism Of Pulsed Laser-Electromagnetic Hybrid Thruster

    SciTech Connect

    Horisawa, Hideyuki; Mashima, Yuki; Yamada, Osamu

    2011-11-10

    A fundamental study of a newly developed rectangular pulsed laser-electromagnetic hybrid thruster was conducted. Laser-ablation plasma in the thruster was induced through laser beam irradiation onto a solid target and accelerated by electrical means instead of direct acceleration only by using a laser beam. The performance of the thrusters was evaluated by measuring the ablated mass per pulse and impulse bit. As results, significantly high specific impulses up to 7,200 s were obtained at charge energies of 8.6 J. Moreover, from the Faraday cup measurement, it was confirmed that the speed of ions was accelerated with addition of electric energy.

  1. Excitation and Control of Plasma Wakefields by Multiple Laser Pulses

    NASA Astrophysics Data System (ADS)

    Cowley, J.; Thornton, C.; Arran, C.; Shalloo, R. J.; Corner, L.; Cheung, G.; Gregory, C. D.; Mangles, S. P. D.; Matlis, N. H.; Symes, D. R.; Walczak, R.; Hooker, S. M.

    2017-07-01

    We demonstrate experimentally the resonant excitation of plasma waves by trains of laser pulses. We also take an important first step to achieving an energy recovery plasma accelerator by showing that a plasma wave can be damped by an out-of-resonance trailing laser pulse. The measured laser wakefields are found to be in excellent agreement with analytical and numerical models of wakefield excitation in the linear regime. Our results indicate a promising direction for achieving highly controlled, GeV-scale laser-plasma accelerators operating at multikilohertz repetition rates.

  2. Parabolic similariton Yb-fiber laser with triangular pulse evolution

    NASA Astrophysics Data System (ADS)

    Wang, Sijia; Wang, Lei

    2016-04-01

    We propose a novel mode-locked fiber laser design which features a passive nonlinear triangular pulse formation and self-similar parabolic pulse amplification intra cavity. Attribute to the nonlinear reshaping progress in the passive fiber, a triangular-profiled pulse with negative-chirp is generated and paved the way for rapid and efficient self-similar parabolic evolution in a following short-length high-gain fiber. In the meanwhile, the accompanied significantly compressed narrow spectrum from this passive nonlinear reshaping also gives the promise of pulse stabilization and gain-shaping robustness without strong filtering. The resulting short average intra-cavity pulse duration, low amplified spontaneous emission (ASE) and low intra-cavity power loss are essential for the low-noise operation. Simulations predict this modelocked fiber laser allows for high-energy ultra-short transform-limited pulse generation exceeding the gain bandwidth. The output pulse has a de-chirped duration (full-width at half maximum, FWHM) of 27 fs. In addition to the ultrafast laser applications, the proposed fiber laser scheme can support low-noise parabolic and triangular pulse trains at the same time, which are also attractive in optical pulse shaping, all-optical signal processing and high-speed communication applications.

  3. Metal Processing with Ultra-Short Laser Pulses

    SciTech Connect

    Banks, P S; Feit, M D; Komashko, A M; Perry, M D; Rubenchik, A M; Stuart, B C

    2000-05-01

    Femtosecond laser ablation has been shown to produce well-defined cuts and holes in metals with minimal heat effect to the remaining material. Ultrashort laser pulse processing shows promise as an important technique for materials processing. We will discuss the physical effects associated with processing based experimental and modeling results. Intense ultra-short laser pulse (USLP) generates high pressures and temperatures in a subsurface layer during the pulse, which can strongly modify the absorption. We carried out simulations of USLP absorption versus material and pulse parameters. The ablation rate as function of the laser parameters has been estimated. Since every laser pulse removes only a small amount of material, a practical laser processing system must have high repetition rate. We will demonstrate that planar ablation is unstable and the initially smooth crater bottom develops a corrugated pattern after many tens of shots. The corrugation growth rate, angle of incidence and the polarization of laser electric field dependence will be discussed. In the nonlinear stage, the formation of coherent structures with scales much larger than the laser wavelength was observed. Also, there appears to be a threshold fluence above which a narrow, nearly perfectly circular channel forms after a few hundred shots. Subsequent shots deepen this channel without significantly increasing its diameter. The role of light absorption in the hole walls will be discussed.

  4. Silicon cell culture templates with nanotopography: periodic nanostructures and random nanoporous topologies generated by high-repetition rate sub-15 fs pulsed near-infrared laser light

    NASA Astrophysics Data System (ADS)

    Straub, Martin; Uchugonova, Aisada; Koch, Marcus; König, Karsten

    2012-03-01

    In recent years a variety of studies has demonstrated that artificially generated microenvironments can exert a strong influence on cell growth, cell adhesion, proliferation, and differentiation behavior in the culture dish. In particular, cells tend to adapt themselves to elongated micro- and nanostructures. Thus, nanostructured substrates are of significant interest in the biological and biomedical sciences as adhesion and development of cells can be controlled via the topological surface properties. In contrast to earlier approaches relying on electron beam or nanoimprint lithography, nanostructures were produced on Si(100) surfaces using sub-15 femtosecond high-resolution laser scanning microscopy. Laser processing was performed with the silicon surface immersed in water followed by hydrofluoric acid etching in order to remove silicon oxide residues. Ripples of at a periodicity of 150 nm as well as random nanoporous surface arrangements were generated by Ti:Sapphire laser light of centre wavelength 800 nm (bandwidth 120 nm, repetition rate 85 MHz) at picojoule pulse energies. Growth of Chinese hamster ovary (CHO) cells revealed good adhesion to the silicon substrates. Importantly, alignment of cells along the direction of ripples was observed, whereas randomly nanoporous surfaces did not induce any preferences in cell orientation.

  5. Pulsed laser deposition of ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Sengupta, Somnath; McKnight, Steven H.; Sengupta, Louise C.

    1997-05-01

    It has been shown that in bulk ceramic form, the barium to strontium ratio in barium strontium titanium oxide (Ba1- xSrxTiO3, BSTO) affects the voltage tunability and electronic dissipation factor in an inverse fashion; increasing the strontium content reduces the dissipation factor at the expense of lower voltage tunability. However, the oxide composites of BSTO developed at the Army Research Laboratory still maintain low electronic loss factors for all compositions examined. The intent of this study is to determine whether such effects can be observed in the thin film form of the oxide composites. The pulsed laser deposition (PLD) method has been used to deposit the thin films. The different compositions of the compound (with 1 wt% of the oxide additive) chosen were: Ba0.3Sr0.7TiO3, Ba0.4Sr0.6TiO3, Ba0.5Sr0.5TiO3, Ba0.6Sr0.4TiO3, and Ba0.7Sr0.3TiO3. The electronic properties investigated in this study were the dielectric constant and the voltage tunability. The morphology of the thin films were examined using the atomic force microscopy. Fourier transform Raman spectroscopy was also utilized for optical characterization of the thin films. The electronic and optical properties of the thin films and the bulk ceramics were compared. The results of these investigations are discussed.

  6. Power Enhancement Cavity for Burst-Mode Laser Pulses

    SciTech Connect

    Liu, Yun

    2015-01-01

    We demonstrate a novel optical cavity scheme and locking method that can realize the power enhancement of picosecond UV laser pulses operating at a burst mode with arbitrary burst (macropulse) lengths and repetition rates.

  7. Schwinger vacuum pair production in chirped laser pulses

    SciTech Connect

    Dumlu, Cesim K.

    2010-08-15

    The recent developments of high intensity ultrashort laser pulses have raised the hopes of observing Schwinger vacuum pair production which is one of the important nonperturbative phenomena in QED. The quantitative analysis of realistic high intensity laser pulses is vital for understanding the effect of the field parameters on the momentum spectrum of the produced particles. In this study, we analyze chirped laser pulses with a subcycle structure, and investigate the effects of the chirp parameter on the momentum spectrum of the produced particles. The combined effect of the chirp and carrier phase of the laser pulse is also analyzed. These effects are qualitatively explained by investigating the turning-point structure of the potential within the framework of the complex WKB scattering approach to pair production.

  8. Vector self-pulsing in erbium-doped fiber lasers.

    PubMed

    Sergeyev, Sergey V

    2016-10-15

    Insight into instabilities of fiber laser regimes leading to complex self-pulsing operations is an opportunity to unlock the high power and dynamic operation tunability of lasers. Though many models have been suggested, there is no complete covering of self-pulsing complexity observed experimentally. Here, I further generalized our previous vector model of erbium-doped fiber laser and, for the first time, to the best of my knowledge, map tunability of complex vector self-pulsing on Poincare sphere (limit cycles and double scroll polarization attractors) for laser parameters, e.g., power, ellipticity of the pump wave, and in-cavity birefringence. Analysis validated by extensive numerical simulations demonstrates good correspondence to the experimental results on complex self-pulsing regimes obtained by many authors during the last 20 years.

  9. Pulsed excimer laser processing for cost-effective solar cells

    NASA Technical Reports Server (NTRS)

    Wong, D.

    1984-01-01

    The goal was to demonstrate the cost effectiveness feasibility of fabricating 16% efficient solar cells on 125 mm diameter Cz wafers using pulsed excimer laser for junction formation, surface passivation, and front metallization.

  10. Pulse laser assisted optical tweezers for biomedical applications.

    PubMed

    Sugiura, Tadao; Maeda, Saki; Honda, Ayae

    2012-01-01

    Optical tweezers which enables to trap micron to nanometer sized objects by radiation pressure force is utilized for manipulation of particles under a microscope and for measurement of forces between biomolecules. Weak force of optical tweezers causes some limitations such as particle adhesion or steric barrier like lipid membrane in a cell prevent further movement of objects. For biomedical applications we need to overcome these difficulties. We have developed a technique to exert strong instantaneous force by use of a pulse laser beam and to assist conventional optical tweezers. A pulse laser beam has huge instantaneous laser power of more than 1000 times as strong as a conventional continuous-wave laser beam so that the instantaneous force is strong enough to break chemical bonding and molecular force between objects and obstacles. We derive suitable pulse duration for pulse assist of optical tweezers and demonstrate particle manipulation in difficult situations through an experiment of particle removal from sticky surface of glass substrate.

  11. Chirped pulse inverse free-electron laser vacuum accelerator

    DOEpatents

    Hartemann, Frederic V.; Baldis, Hector A.; Landahl, Eric C.

    2002-01-01

    A chirped pulse inverse free-electron laser (IFEL) vacuum accelerator for high gradient laser acceleration in vacuum. By the use of an ultrashort (femtosecond), ultrahigh intensity chirped laser pulse both the IFEL interaction bandwidth and accelerating gradient are increased, thus yielding large gains in a compact system. In addition, the IFEL resonance condition can be maintained throughout the interaction region by using a chirped drive laser wave. In addition, diffraction can be alleviated by taking advantage of the laser optical bandwidth with negative dispersion focusing optics to produce a chromatic line focus. The combination of these features results in a compact, efficient vacuum laser accelerator which finds many applications including high energy physics, compact table-top laser accelerator for medical imaging and therapy, material science, and basic physics.

  12. Pulsed lasers on plasmas produced by electron beams and discharges

    SciTech Connect

    Tarasenko, Viktor F; Yakovlenko, Sergei I

    2003-02-28

    The use of electron beams for pumping dense gases made it possible to obtain lasing on atomic and molecular transitions in different spectral ranges and to develop high-power pulsed lasers. N.G. Basov and coworkers made a substantial contribution to the formation and advancement of this field. A brief review of the research on efficient elevated-pressure active media and high-power pulsed lasers utilising plasmas produced both by an electron beam and an electron-beam-controlled discharge is presented. These are excimer and exciplex lasers, lasers utilising atomic transitions in xenon and neon, an Ar -N{sub 2} mixture laser, a molecular nitrogen ion laser, and a high-pressure CO{sub 2} laser. Data obtained in the investigation of the radiation of rare-gas halide complexes are given. (special issue devoted to the 80th anniversary of academician n g basov's birth)

  13. Longitudinally excited CO2 laser with short laser pulse for hard tissue drilling

    NASA Astrophysics Data System (ADS)

    Uno, Kazuyuki; Hayashi, Hiroyuki; Akitsu, Tetsuya; Jitsuno, Takahisa

    2014-02-01

    We developed a longitudinally excited CO2 laser that produces a short laser pulse with a circular beam and a low divergence angle. The laser was very simple and consisted of a 45-cm-long alumina ceramic pipe with an inner diameter of 9 mm, a pulse power supply, a step-up transformer, a storage capacitance, and a spark-gap switch. The laser pulse had a spike pulse width of 103 ns and a pulse tail length of 32.6 μs. The beam cross-section was circular and the full-angle beam divergence was 1.7 mrad. The laser was used to drill ivory samples without carbonization at fluences of 2.3-7.1 J/cm2. The drilling depth of the dry ivory increased with the fluence. The drilling mechanism of the dry ivory was attributed to absorption of the laser light by the ivory.

  14. Laser shaping of a relativistic circularly polarized pulse by laser foil interaction

    SciTech Connect

    Zou, D. B.; Zhuo, H. B.; Yu, T. P.; Yang, X. H.; Shao, F. Q.; Ma, Y. Y.; Yin, Y.; Ouyang, J. M.; Ge, Z. Y.; Zhang, G. B.; Wang, P.

    2013-07-15

    Laser shaping of a relativistic circularly polarized laser pulse in ultra-intense laser thin-foil interaction is investigated by theoretical analysis and particle-in-cell simulations. It is found that the plasma foil as a nonlinear optical shutter has an obvious cut-out effect on the laser temporal and spatial profiles. Two-dimensional particle-in-cell simulations show that the high intensity part of a Gaussian laser pulse can be well extracted from the whole pulse. The transmitted pulse with longitudinal steep rise front and transverse super-Gaussian profile is thus obtained which would be beneficial for the radiation pressure acceleration regime. The Rayleigh-Taylor-like instability is observed in the simulations, which destroys the foil and results in the cut-out effect of the pulse in the rise front of a circularly polarized laser.

  15. Effect of Pulse Length on Engraving Efficiency in Nanosecond Pulsed Laser Engraving of Stainless Steel

    NASA Astrophysics Data System (ADS)

    Manninen, Matti; Hirvimäki, Marika; Poutiainen, Ilkka; Salminen, Antti

    2015-10-01

    Dependency of laser pulse length on the effectiveness of laser engraving 304 stainless steel with nanosecond pulses was investigated. Ytterbium fiber laser with pulse lengths from 4 to 200 ns was used at a constant average power of 20 W. Measured criteria for effective laser engraving were high material removal rate (MRR), good visual quality of the engraved surface, and low processing temperature. MRR was measured by weighing the samples prior and after the engraving process. Visual quality was evaluated from magnified images. Surface temperature of the samples was measured by two laser spot-welded K-type thermocouples near the laser-processed area. It was noticed that MRR increases significantly with longer pulse lengths, while the quality decreases and processing temperature increases. Some peculiar process behavior was noticed. With short pulses (<20 ns), the process temperature steadily increased as the engraving process continued, whereas with longer pulses the process temperature started to decrease after initially jumping to a specific level. From visually analyzing the samples, it was noticed that the melted and resolidified bottom structure had cracks and pores on the surface when 50 ns or longer pulse lengths were used.

  16. Effect of pulse duty cycle on Inconel 718 laser welds

    NASA Technical Reports Server (NTRS)

    McCay, M. H.; McCay, T. D.; Dahotre, N. B.; Sharp, C. M.; Sedghinasab, A.; Gopinathan, S.

    1989-01-01

    Crack sensitive Inconel 718 was laser pulse welded using a 3.0 kW CO2 laser. Weld shape, structure, and porosity were recorded as a function of the pulse duty cycle. Within the matrix studied, the welds were found to be optimized at a high (17 ms on, 7 ms off) duty cycle. These welds were superior in appearance and lack of porosity to both low duty cycle and CW welds.

  17. Long Pulse Narrowband XeCl Laser Studies

    DTIC Science & Technology

    1990-03-15

    longest pulse width obtained with an e-beam pumped excimer laser . The kinetics processes of the long pulse narrowband were investigated by measurements...electrically triggered switch driven by a small Marx bank which produces the high voltage trigger required. This allows a high standoff voltage and...Phys. Lett 45, p. 507 (1984). 13 M. W. Taylor, J. Goldhar, and J. R. Murray, "Dylux: an instant image photographic material suitable for UV laser beam

  18. Repetitively pulsed Cr:LiSAF laser for lidar applications

    SciTech Connect

    Shimada, Tsutomu; Early, J.W.; Lester, C.S.; Cockroft, N.J.

    1994-03-01

    A Cr:LiSAF laser has been successfully operated at time averaged powers up to 11 W and at pulse repetition rates to 12 Hz. During Q-switch operation, output energy as high as 450 mJ (32 ns FWHM) was obtained. Finally, line narrowed Q-switched pulses (< 0.1 nm) from the Cr:LiSAF laser were successfully used as a tunable light source for lidar to measure atmospheric water content.

  19. Rapid scanning autocorrelator for measurements of picosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Harde, H.; Burggraf, H.

    1981-08-01

    A rapid scanning autocorrelation interferometer for measurements of picosecond laser pulses is described which uses a rotating prism as scanning device in one arm of the interferometer to permit continuous display of autocorrelation traces at audio frequencies on an oscilloscope. Scan widths of more than 500 ps with high linearity can be achieved. Autocorrelation measurements of picosecond pulses from a synchronously pumped mode-locked dye laser are presented.

  20. Supression of laser breakdown by pulsed nonequilibrium ns discharge

    NASA Astrophysics Data System (ADS)

    Starikovskiy, A. Y.; Semenov, I. E.; Shneider, M. N.

    2016-10-01

    The avalanche ionization induced by infrared laser pulses was investigated in a pre-ionized argon gas. Pre-ionization was created by a high-voltage pulsed nanosecond discharge developed in the form of a fast ionization wave. Then, behind the front of ionization wave additional avalanche ionization was initiated by the focused Nd-YAG laser pulse. It was shown that the gas pre-ionization inhibits the laser spark generation. It was demonstrated that the suppression of laser spark development in the case of strong gas pre-ionization is because of fast electron energy transfer from the laser beam focal region. The main mechanism of this energy transfer is free electrons diffusion.

  1. Interaction of cold atoms with short laser pulses.

    NASA Astrophysics Data System (ADS)

    Chamberlin, Karen; Lilla, Derek; Taylor, Kyle; Zick, Kevin; Taft, Greg; Nguyen, Hai

    2006-05-01

    We present a powerful diagnostic system to observe the interaction of ultrafast laser pulses with trapped ^87Rb atoms. The ionization of cold atoms and the formation of cold molecules in an intense laser field in the μK temperature range open new branches of research in chemistry, metrology, and quantum physics. However, the interaction of cold atoms with short laser pulses and the subsequent ionization or molecule formation are processes which are not well understood and can be easily misinterpreted. In our proposed experimental setup, an existing ultrafast laser system at the University of Wisconsin-Stevens Point will be used in conjunction with Magneto Optical Trap Recoil Ion Momentum Spectroscopy (MOTRIMS) to directly measure the products formed by the interaction of ultrafast laser pulses with the cold trapped ^87Rb atoms.

  2. High power repetitive TEA CO2 pulsed laser

    NASA Astrophysics Data System (ADS)

    Yang, Guilong; Li, Dianjun; Xie, Jijiang; Zhang, Laiming; Chen, Fei; Guo, Jin; Guo, Lihong

    2012-07-01

    A high power repetitive spark-pin UV-preionized TEA CO2 laser system is presented. The discharge for generating laser pulses is controlled by a rotary spark switch and a high voltage pulsed trigger. Uniform glow discharge between two symmetrical Chang-electrodes is realized by using an auto-inversion circuit. A couple of high power axial-flow fans with the maximum wind speed of 80 m/s are used for gas exchange between the electrodes. At a repetitive operation, the maximum average output laser power of 10.4 kW 10.6 μm laser is obtained at 300 Hz, with an electro-optical conversion efficiency of 15.6%. At single pulsed operation, more pumping energy and higher gases pressures can be injected, and the maximum output laser energy of 53 J is achieved.

  3. Three-stage compression of nanosecond laser pulses

    SciTech Connect

    Akulinichev, V.V.; Mavrichev, M.E.; Pivinskii, E.G.

    1994-04-01

    Three-stage compression of 8-ns pulses of a Nd:YAG laser was investigated. One of the stages used SBS (Stimulated Brillouin Scattering) in CCl4 and the other two used backward SRS (Stimulated Raman Scattering) in compressed methane. Conditions for substantial enhancement of the energy stability of picosecond pulses formed by the output compression stage were found. 8 refs.

  4. Magnetization in ruby induced by a short laser pulse

    SciTech Connect

    Usmanov, R.G.; Khaimovich, E.P.

    1995-09-01

    Specific features of formation of nonequilibrium magnetization in ruby crystal excited by a laser pulse are experimentally studied. It is shown theoretically that the circularly polarized light pulse induces orientation of the medium and its magnetization. Changes of the magnetization direction induced by an external magnetic field are analyzed. 11 refs., 3 figs.

  5. Experimental verification of physical model of pulsed laser welding

    SciTech Connect

    Jellison, J.L.; Keicher, D.M.

    1990-01-01

    Whereas most experimental and theoretical studies of the role of convection in fusion welding have been concerned with continuous heat sources, a pulsed heat source is the focus of this study. This is primarily an experimental study of the pulsed Nd:YAG laser welding of austenitic stainless steels. 12 refs., 9 figs.

  6. High Average Power, High Energy Short Pulse Fiber Laser System

    SciTech Connect

    Messerly, M J

    2007-11-13

    Recently continuous wave fiber laser systems with output powers in excess of 500W with good beam quality have been demonstrated [1]. High energy, ultrafast, chirped pulsed fiber laser systems have achieved record output energies of 1mJ [2]. However, these high-energy systems have not been scaled beyond a few watts of average output power. Fiber laser systems are attractive for many applications because they offer the promise of high efficiency, compact, robust systems that are turn key. Applications such as cutting, drilling and materials processing, front end systems for high energy pulsed lasers (such as petawatts) and laser based sources of high spatial coherence, high flux x-rays all require high energy short pulses and two of the three of these applications also require high average power. The challenge in creating a high energy chirped pulse fiber laser system is to find a way to scale the output energy while avoiding nonlinear effects and maintaining good beam quality in the amplifier fiber. To this end, our 3-year LDRD program sought to demonstrate a high energy, high average power fiber laser system. This work included exploring designs of large mode area optical fiber amplifiers for high energy systems as well as understanding the issues associated chirped pulse amplification in optical fiber amplifier systems.

  7. Fabrication of micro-convex domes using long pulse laser

    NASA Astrophysics Data System (ADS)

    Wang, Xingsheng; Zhang, Yongnian; Wang, Ling; Xian, Jieyu; Jin, Meifu; Kang, Min

    2017-01-01

    Micro-convex domes inspired from nature can be machined by chemical and physical routes to achieve specific functions. Laser surface texturing (LST) is the front runner among the current material micro-processing technologies. However, most of the studies relating to LST dealt with the formation of micro-dimples. In this paper, LST using long pulse laser was used to create micro-convex domes on 304L stainless steel. Spherical-cap-shaped domes with diameters of 30-75 μm and height of 0.9-5.5 μm were created through LST. The effects of laser-processing parameters on surface morphologies of the created convex domes were investigated. The height of the convex dome increased at first and then decreased with the increasing laser power. The change tendency of the height with the pulse duration varied at different laser powers. The diameter of the convex dome increased almost linearly with the laser power or pulse duration. The superior micro-convex domes were achieved at a pulse energy of 5.6 mJ with a laser power of 80 W and pulse duration of 70 μs.

  8. Excitability in semiconductor microring lasers: Experimental and theoretical pulse characterization

    SciTech Connect

    Gelens, L.; Coomans, W.; Van der Sande, G.; Verschaffelt, G.; Mashal, L.; Beri, S.; Danckaert, J.

    2010-12-15

    We characterize the operation of semiconductor microring lasers in an excitable regime. Our experiments reveal a statistical distribution of the characteristics of noise-triggered optical pulses that is not observed in other excitable systems. In particular, an inverse correlation exists between the pulse amplitude and duration. Numerical simulations and an interpretation in an asymptotic phase space confirm and explain these experimentally observed pulse characteristics.

  9. Influence of the main pulse and prepulse intensity on high-order harmonic generation in silver plasma ablation

    SciTech Connect

    Elouga Bom, L. B.; Kieffer, J.-C.; Ozaki, T.; Ganeev, R. A.; Suzuki, M.; Kuroda, H.

    2007-03-15

    We present experimental studies of high-order harmonic generation in silver plasma ablation performed with the Ti:sapphire laser beams of the Advanced Laser Light Source (800 nm wavelength, 360 mJ total energy). We have independently varied the intensity of the prepulse (which creates the plasma ablation) and the intensity of the main pulse (which generates the harmonics), and studied their influence on the harmonic spectrum. We show here that the presence of doubly ionized atoms in the ablation, created either by a strong prepulse intensity or with the irradiation of the main pulse, is ineffective for the generation of harmonics.

  10. Fiber laser pumped high power mid-infrared laser with picosecond pulse bunch output.

    PubMed

    Wei, Kaihua; Chen, Tao; Jiang, Peipei; Yang, Dingzhong; Wu, Bo; Shen, Yonghang

    2013-10-21

    We report a novel quasi-synchronously pumped PPMgLN-based high power mid-infrared (MIR) laser with picosecond pulse bunch output. The pump laser is a linearly polarized MOPA structured all fiberized Yb fiber laser with picosecond pulse bunch output. The output from a mode-locked seed fiber laser was directed to pass through a FBG reflector via a circulator to narrow the pulse duration from 800 ps to less than 50 ps and the spectral FWHM from 9 nm to 0.15 nm. The narrowed pulses were further directed to pass through a novel pulse multiplier through which each pulse was made to become a pulse bunch composing of 13 sub-pulses with pulse to pulse time interval of 1.26 ns. The pulses were then amplified via two stage Yb fiber amplifiers to obtain a linearly polarized high average power output up to 85 W, which were then directed to pass through an isolator and to pump a PPMgLN-based optical parametric oscillator via quasi-synchronization pump scheme for ps pulse bunch MIR output. High MIR output with average power up to 4 W was obtained at 3.45 micron showing the feasibility of such pump scheme for ps pulse bunch MIR output.

  11. Synchronization of Sub-Picosecond Electron and Laser Pulses

    SciTech Connect

    Rosenzweig, J.B.; Le Sage G.P.

    2000-08-15

    Sub-picosecond laser-electron synchronization is required to take full advantage of the experimental possibilities arising from the marriage of modern high intensity lasers and high brightness electron beams in the same laboratory. Two particular scenarios stand out in this regard, injection of ultra-short electron pulses in short wavelength laser-driven plasma accelerators, and Compton scattering of laser photons from short electron pulses. Both of these applications demand synchronization, which is subpicosecond, with tens of femtosecond synchronization implied for next-generation experiments. Typically, an RF electron accelerator is synchronized to a short pulse laser system by detecting the repetition signal of a laser oscillator, adjusted to an exact subharmonic of the linac RF frequency, and multiplying or phase locking this signal to produce the master RF clock. Pulse-to-pulse jitter characteristic of self-mode-locked laser oscillators represents a direct contribution to the ultimate timing jitter between a high intensity laser focus and electron beam at the interaction point, or a photocathode drive laser in an RF photoinjector. This timing jitter problem has been addressed most seriously in the context of the RF photoinjector, where the electron beam properties are sensitive functions of relative timing jitter. The timing jitter achieved in synchronized photocathode drive laser systems is near, or slightly below one picosecond. The ultimate time of arrival jitter of the beam at the photoinjector exit is typically a bit smaller than the photocathode drive-laser jitter due to velocity compression effects in the first RF cell of the gun. This tendency of the timing of the electron beam arrival at a given spatial point to lock to the RF lock is strongly reinforced by use of magnetic compression.

  12. ULTRASHORT LIGHT PULSES: Formation of subfemtosecond laser pulses in aperiodically poled nonlinear-optical crystals

    NASA Astrophysics Data System (ADS)

    Shutov, I. V.; Novikov, A. A.; Chirkin, A. S.

    2008-03-01

    The method of synthesis of ultrashort laser pulses in nonlinear aperiodically poled crystals based on the simultaneous generation of several higher optical harmonics is considered. The interaction of four waves with multiple frequencies involving three mutually coupled nonlinear three-frequency processes is studied. It is shown that by introducing intense laser radiation into a crystal, pulses of duration of the order of a few hundreds of attoseconds can be produced at the crystal output.

  13. Pulsed laser processing of electronic materials in micro/nanoscale

    NASA Astrophysics Data System (ADS)

    Hwang, David Jen

    2005-08-01

    Time-resolved pump-and-probe side-view imaging has been performed to investigate the energy coupling to the target specimen over a wide range of fluences. Plasmas generated during the laser ablation process are visualized and the decrease of the ablation efficiency in the high fluence regime (>10 J/cm2) is attributed to the strong interaction of the laser pulse with the laser-induced plasmas. The high intensity ultra-short laser pulses also trigger volumetric multi-photon absorption (MPA) processes that can be beneficial in applications such as three-dimensional bulk modification of transparent materials. Femtosecond laser pulses were used to fabricate straight and bent through-channels in the optical glass. Drilling was initiated from the rear surface to preserve consistent absorbing conditions of the laser pulse. Machining in the presence of a liquid solution assisted the debris ejection. Drilling process was further enhanced by introducing ultrasonic waves, thereby increasing the aspect ratio of drilled holes and improving the quality of the holes. In conventional lens focusing schemes, the minimum feature size is determined by the diffraction limit. Finer resolution is accomplished by combining pulsed laser radiation with Near-field Scanning Optical Microscopy (NSOM) probes. Short laser pulses are coupled to a fiber-based NSOM probes in order to ablate thin metal films. A detailed parametric study on the effects of probe aperture size, laser pulse energy, temporal width and environment gas is performed. The significance of lateral thermal diffusion is highlighted and the dependence of the ablation process on the imparted near-field distribution is revealed. As a promising application of laser ablation in nanoscale, laser induced breakdown spectroscopy (LIBS) system has been built up based on NSOM ablation configuration. NSOM-LIBS is demonstrated with nanosecond pulsed laser excitation on Cr sample. Far-field collecting scheme by top objective lens was chosen as

  14. Phase and Frequency Control of Laser Arrays for Pulse Synthesis

    DTIC Science & Technology

    2015-01-02

    passively mode-locked vertical-external-cavity surface- emitting lasers ( VECSELs ) [5, 6], quantum dot lasers with tapered gain sections [7], and...Ritchie, B. Kunert, B. Heinen, and W. Stolz, Ř.35 kW peak power femtosecond pulse mode-locked VECSEL for supercontinuum generation," Opt. Express 21

  15. Profile of Laser-Produced Acoustic Pulse in a Liquid.

    DTIC Science & Technology

    1983-10-12

    Tam, AppL Phys. Lett. 40, 310 (1982). 7. G. C. Wetsel , Jr., in Acoustic Imaging, Vol. 12, edited by E. A. Ash and C. R. Hill (Plenum, New York, 1982...p. 137. 8. G. C. Wetsel , "Photothermal Excitation of Elastic Waves by 10 ns Laser Pulses and Detection by Photoelastic Laser Beam Deflection," to

  16. CONTROLLING THE CHARACTERISTICS OF LASER LIGHT: Possibility of generating femtosecond laser pulses by a deflection method

    NASA Astrophysics Data System (ADS)

    Isaakyan, A. R.; Kolchin, K. V.; Makshantsev, B. I.

    1993-05-01

    The transmission of a laser beam through a multiple-prism traveling-wave deflector is examined theoretically. Femtosecond laser pulses can be generated through the use of such a deflector. Possibilities for using a deflector to measure the shape of pulses with a femtosecond time resolution are discussed.

  17. Applying laser pulse stretching technique on photoacoustic imaging for efficiently delivering laser energy

    NASA Astrophysics Data System (ADS)

    Wang, Tianheng; Kumavor, Patrick D.; Zhu, Quing

    2012-02-01

    High-energy and short-duration outputs from lasers are desirable to improve the photoacoustic image quality when imaging deeply-seated lesions. In many clinical applications, optical fibers are used to couple the high-energy laser pulse to tissue. These high peak intensity pulses can damage an optical fiber input face if the damage threshold is exceeded. It is necessary to reduce the peak intensity to minimize the fiber damage and to delivery sufficient light for imaging. In this paper, a laser-pulse-stretching technique is introduced to reduce the peak intensity of laser pulses. To demonstrate the technique, an initial 17ns pulse was stretched to 37ns by a ring-cavity laser-pulse-stretching system, and the laser peak power reduced to 42%. The stretched pulse increased the fiber damage threshold by 1.5-fold. Three ultrasound transducers centered at 1.3MHz, 3.5MHz, 6MHz frequencies were simulated and the results showed that the photoacoustic signal of 0.5mm-diameter target obtained with 37ns pulse was about 98%, 91% and 80% respectively using the same energy as with the 17ns pulse. Simulations were validated using a broadband hydrophone. Quantitative comparisons of photoacoustic images obtained with three corresponding ultrasound transducers showed that the image quality was not affected by stretching the pulse.

  18. Subpicosecond and picosecond laser ablation of dental enamel: comparative analysis

    NASA Astrophysics Data System (ADS)

    Rode, Andrei V.; Madsen, Nathan R.; Kolev, Vesselin Z.; Gamaly, Eugene G.; Luther-Davies, Barry; Dawes, Judith M.; Chan, A.

    2004-06-01

    We report the use of sub-picosecond near-IR and ps UV pulsed lasers for precision ablation of freshly extracted human teeth. The sub-picosecond laser wavelength was ~800nm, with pulsewidth 150 fs and pulse repetition rate of 1kHz; the UV laser produced 10 ps pulses at 266 nm with pulse rate of ~1.2x105 pulses/s; both lasers produced ~1 W of output energy, and the laser fluence was kept at the same level of 10-25 J/cm2. Laser radiation from both laser were effectively absorbed in the teeth enamel, but the mechanisms of absorption were radically different: the near-IR laser energy was absorbed in a plasma layer formed through the optical breakdown mechanism initiated by multiphoton absorption, while the UV-radiation was absorbed due to molecular photodissociation of the enamel and conventional thermal deposition. The rise in the intrapulpal temperature was monitored by embedded thermocouples, and was shown to remain low with subpicosecond laser pulses, but risen up to 30°C, well above the 5°C pain level with the UV-laser. This study demonstrates the potential for ultra-short-pulsed lasers to precision and painless ablation of dental enamel, and indicated the optimal combination of laser parameters in terms of pulse energy, duration, intensity, and repetition rate, required for the laser ablation rates comparable to that of mechanical drill.

  19. Pulse-duration dependent sequential double ionization by elliptically polarized laser pulses

    NASA Astrophysics Data System (ADS)

    Tong, Aihong; Deng, Yongju; Liu, Dan

    2016-05-01

    Using a fully classical model, we have studied sequential double ionization of argon driven by elliptically polarized laser pulses at intensities well in the over-barrier ionization region. The results show that the joint electron momentum distributions in the minor elliptical direction depend strongly on the pulse duration. From pulse number N = 4 to 10, the clustering regions of the joint electron momentum increase with the pulse duration. For even larger pulse durations, the clustering region does not increase further but the population of the joint electron momentum in these regions changes with the pulse duration. Back analysis of double ionization trajectories shows the phenomenon of multiple ionization bursts and the pulse duration-dependent multiple ionization bursts of the second electron is responsible for the evolution of the joint electron momentum distribution with the pulse duration.

  20. Pulsed CO laser for isotope separation of uranium

    SciTech Connect

    Baranov, Igor Y.; Koptev, Andrey V.

    2012-07-30

    This article proposes a technical solution for using a CO laser facility for the industrial separation of uranium used in the production of fuel for nuclear power plants, employing a method of laser isotope separation of uranium with condensation repression in a free jet. The laser operation with nanosecond pulse irradiation can provide an acceptable efficiency in the separating unit and a high efficiency of the laser with the wavelength of 5.3 {mu}m. In the present work we also introduce a calculation model and define the parameters of a mode-locked CO laser with a RF discharge in the supersonic stream. The average pulsed CO laser power of 3 kW is sufficient for efficient industrial isotope separation of uranium in one stage.