Showing papers on "Laser published in 1996"
TL;DR: Theoretical models and qualitative explanations of experimental results are presented in this paper for femtosecond laser ablation of solid targets by 0.2-5000 ps Ti: Sapphire laser pulses.
Abstract: Laser ablation of solid targets by 0.2–5000 ps Ti: Sapphire laser pulses is studied. Theoretical models and qualitative explanations of experimental results are presented. Advantages of femtosecond lasers for precise material processing are discussed and demonstrated.
2,513 citations
TL;DR: The results suggest that multiphoton interactions occur in the glasses and that it may be possible to write three-dimensional optical circuits in bulk glasses with such a focused laser beam technique.
Abstract: With the goal of being able to create optical devices for the telecommunications industry, we investigated the effects of 810-nm, femtosecond laser radiation on various glasses. By focusing the laser beam through a microscope objective, we successfully wrote transparent, but visible, round-elliptical damage lines inside high-silica, borate, soda lime silicate, and fluorozirconate (ZBLAN) bulk glasses. Microellipsometer measurements of the damaged region in the pure and Ge-doped silica glasses showed a 0.01–0.035 refractive-index increase, depending on the radiation dose. The formation of several defects, including Si E′ or Ge E′ centers, nonbridging oxygen hole centers, and peroxy radicals, was also detected. These results suggest that multiphoton interactions occur in the glasses and that it may be possible to write three-dimensional optical circuits in bulk glasses with such a focused laser beam technique.
2,500 citations
TL;DR: In this article, the InGaN multi-quantum-well (MQW) structure was used for laser diodes, which produced 215mW at a forward current of 2.3
Abstract: InGaN multi-quantum-well (MQW) structure laser diodes (LDs) fabricated from III-V nitride materials were grown by metalorganic chemical vapor deposition on sapphire substrates. The mirror facet for a laser cavity was formed by etching of III-V nitride films without cleaving. As an active layer, the InGaN MQW structure was used. The InGaN MQW LDs produced 215 mW at a forward current of 2.3 A, with a sharp peak of light output at 417 nm that had a full width at half-maximum of 1.6 nm under the pulsed current injection at room temperature. The laser threshold current density was 4 kA/cm2. The emission wavelength is the shortest one ever generated by a semiconductor laser diode.
2,100 citations
TL;DR: In this paper, the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime were reviewed, and the combination of device structure and material parameters provided sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence.
Abstract: Intracavity semiconductor saturable absorber mirrors (SESAM's) offer unique and exciting possibilities for passively pulsed solid-state laser systems, extending from Q-switched pulses in the nanosecond and picosecond regime to mode-locked pulses from 10's of picoseconds to sub-10 fs. This paper reviews the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime. The combination of device structure and material parameters for SESAM's provide sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence, in a compact structure with low insertion loss. We have been able to demonstrate, for example, passive modelocking (with no Q-switching) using an intracavity saturable absorber in solid-state lasers with long upper state lifetimes (e.g., 1-/spl mu/m neodymium transitions), Kerr lens modelocking assisted with pulsewidths as short as 6.5 fs from a Ti:sapphire laser-the shortest pulses ever produced directly out of a laser without any external pulse compression, and passive Q-switching with pulses as short as 56 ps-the shortest pulses ever produced directly from a Q-switched solid-state laser. Diode-pumping of such lasers is leading to practical, real-world ultrafast sources, and we will review results on diode-pumped Cr:LiSAF, Nd:glass, Yb:YAG, Nd:YAG, Nd:YLF, Nd:LSB, and Nd:YVO/sub 4/.
1,866 citations
Book•
10 Oct 1996
TL;DR: A survey of laser diagnostics can be found in this paper, where the authors present a survey of the field of laser diagnostic tools and their application in various fields, including: 1. Background Physics 3. Experimental Considerations 4. Application Considerations 5. Spontaneous Raman and Rayleigh Scattering 6. Coherent Anti-Stokes Raman Spectroscopy (CARS) 7. Laser-Induced Fluorescence (LIF) 8.
Abstract: 1. Survey of Laser Diagnostics 2. Background Physics 3. Experimental Considerations 4. Application Considerations 5. Spontaneous Raman and Rayleigh Scattering 6. Coherent Anti-Stokes Raman Spectroscopy (CARS) 7. Laser-Induced Fluorescence (LIF) 8. Coherent Methods for Minor Species 9. Field Techniques
1,736 citations
Book•
14 Jun 1996
TL;DR: In this article, the theory of nonlinear optics frequency doubling and mixing optical parametric generation, amplification, and oscillation characterization of second order nonlinear optical materials properties of selected second-order nonlinearoptical materials is discussed.
Abstract: Elements of the theory of nonlinear optics frequency doubling and mixing optical parametric generation, amplification, and oscillation characterization of second order nonlinear optical materials properties of selected second order nonlinearoptical materials nonlinear index of refraction characterization of nonlinear refractive index materials optical properties of selected third order nonlinear optics materials nonlinear absorption experimental techniques in nonlinear absorption ultrafast characterization techniques laser flash photolysis nonlinear absorption properties of selected materials stimulated Raman scattering stimulated Brillouin scattering properties of selected stimulated light-scattering materials theelectro-optic effect.
1,563 citations
TL;DR: In this article, a three-color, solid-state, volumetric display based on two-step, two-frequency upconversion in rare earth-doped heavy metal fluoride glass is described.
Abstract: A three-color, solid-state, volumetric display based on two-step, two-frequency upconversion in rare earth-doped heavy metal fluoride glass is described. The device uses infrared laser beams that intersect inside a transparent volume of active optical material to address red, green, and blue voxels by sequential two-step resonant absorption. Three-dimensional wire-frame images, surface areas, and solids are drawn by scanning the point of intersection of the lasers around inside of the material. The prototype device is driven with laser diodes, uses conventional focusing optics and mechanical scanners, and is bright enough to be seen in ambient room lighting conditions. QuickTime movie of the three-dimensional display.
1,410 citations
TL;DR: In this paper, a novel material, GaInNAs, that can be formed on GaAs to drastically improve the temperature characteristics in long-wavelength-range laser diodes is proposed.
Abstract: We propose a novel material, GaInNAs, that can be formed on GaAs to drastically improve the temperature characteristics (T0) in long-wavelength-range laser diodes. The feasibility of our proposal is demonstrated experimentally.
1,384 citations
TL;DR: An overview of the physics issues relevant to the plasma wakefield accelerator, the plasma beat-wave accelerator, including the self-modulated regime, and wakefield accelerators driven by multiple electron or laser pulses is given in this article.
Abstract: An overview is given of the physics issues relevant to the plasma wakefield accelerator, the plasma beat-wave accelerator, the laser wakefield accelerator, including the self-modulated regime, and wakefield accelerators driven by multiple electron or laser pulses. Basic properties of linear and nonlinear plasma waves are discussed, as well as the trapping and acceleration of electrons in the plasma wave. Formulas are presented for the accelerating field and the energy gain in the various accelerator configurations. The propagation of the drive electron or laser beams is discussed, including limitations imposed by key instabilities and methods for optically guiding laser pulses. Recent experimental results are summarized.
1,066 citations
Book•
01 Jan 1996
TL;DR: The literature abounds with texts on the subject of lasers as mentioned in this paper, but the treatment of ultrashort lasers in such books is cursory, if included at all, since the intricacies of femtosecond pulse generation go beyond what is commonly considered fundamental.
Abstract: The literature abounds with texts on the subject of lasers. Any one book could provide a beginning graduate student with the tools necessary to understand lasers and their interaction with matter. However, the treatment of ultrashort lasers in such books is cursory, if included at all, since the intricacies of femtosecond pulse generation go beyond what is commonly considered fundamental.
972 citations
TL;DR: A novel method for three-dimensional optical data storage that has submicrometer size resolution, provides a large contrast in index of refraction, and is applicable to a wide range of transparent materials is presented.
Abstract: We present a novel method for three-dimensional optical data storage that has submicrometer size resolution, provides a large contrast in index of refraction, and is applicable to a wide range of transparent materials. Bits are recorded by use of a 0.65-N.A. objective to focus 100-fs laser pulses inside the material. The laser pulse produces a submicrometer-diameter structurally altered region with high contrast in index of refraction. We record binary information by writing such bits in multiple planes and read it out with a microscope objective with a short depth of field. We demonstrate data storage and retrieval with 2-microm in-plane bit spacing and 15-microm interplane spacing (17 Gbits/cm(3)). Scanning electron microscopy and atomic force microscopy show structural changes confined to an area 200 nm in diameter.
Book•
31 Mar 1996
TL;DR: In this paper, the authors present a survey of the latest developments in laser spectroscopy, focusing on the following: Absorption and emission of light, Widths and profiles of Spectral Lines, Spectroscopic Instrumentation, and Spectroscopy of Collision Processes.
Abstract: Introduction.- Absorption and Emission of Light.- Widths and Profiles of Spectral Lines.- Spectroscopic Instrumentation.- Lasers as Spectroscopic Light Sources.- Doppler-Limited Absorption and Fluorescence Spectroscopy with Lasers.- Nonlinear Spectroscopy.- Laser Raman Spectroscopy.- Laser Spectroscopy in Molecular Beams.- Optical Pumping and Double-Resonance Techniques.- Time-Resolved Laser Spectroscopy.- Coherent Spectroscopy.- Laser Spectroscopy of Collision Processes.- New Developments in Laser Spectroscopy.- Applications of Laser Spectroscopy.- References.- Index.
TL;DR: In this paper, a scheme for exploiting the nonresonant second-order nonlinearities in electrooptic media to extend the bandwidth of coherent spectroscopy in the far-infrared using ultrafast laser pulses was presented.
Abstract: We present a scheme for exploiting the nonresonant second‐order nonlinearities in electro‐optic media to extend the bandwidth of coherent spectroscopy in the far‐infrared using ultrafast laser pulses. Using optical rectification and electro‐optic sampling in 〈110〉 ZnTe for the generation and coherent detection of freely propagating THz radiation, respectively, we have demonstrated spectral sensitivity beyond 3 THz. This was accomplished by achieving phase matching for both optical rectification and electro‐optic sampling over a broad range of THz frequencies.
TL;DR: The confocal optical microscopy technique as discussed by the authors is a technique for increasing the contrast of microscope images, particularly in thick specimens, by restricting the observed volume, the technique keeps overlying or nearby scatterers from contributing to the detected signal.
Abstract: Confocal optical microscopy is a technique for increasing the contrast of microscope images, particularly in thick specimens. By restricting the observed volume, the technique keeps overlying or nearby scatterers from contributing to the detected signal. The price for this is that the instrument must observe only one point at a time (in the scanning laser version) or a group of separated points with very little light (in the disc version). This paper describes how the confocal advantage comes about and how it is implemented in actual instruments.
TL;DR: A nonhomogeneous distribution of indium tetra(tert-butyl)phthalocyanine chloride along the beam path substantially enhances the excited-state absorption, yielding an optical limiter with a linear transmittance of 0.70 that can attenuate 8-nanosecond, 532-nanometer laser pulses by factors of up to 540.
Abstract: Molecules with weak ground-state absorption that form strongly absorbing excited states can be used in optical limiters, which can protect sensors or human eyes from optical damage. Phthalocyanine complexes bearing heavy atoms or paramagnetic groups or in solvents containing heavy atoms show optical limiting enhanced by excited triplet-state absorption. A nonhomogeneous distribution of indium tetra(tert-butyl)phthalocyanine chloride along the beam path substantially enhances the excited-state absorption, yielding an optical limiter with a linear transmittance of 0.70 that can attenuate 8-nanosecond, 532-nanometer laser pulses by factors of up to 540.
TL;DR: In this article, the interaction of intense, femtosecond laser radiation with the large (50{endash}200 A) clusters produced in pulsed gas jets was examined.
Abstract: We examine the interaction of intense, femtosecond laser radiation with the large (50{endash}200 A) clusters produced in pulsed gas jets. Both experiment and simulation show that the plasmas produced during these interactions exhibit electron temperatures far in excess of that predicted by above-threshold ionization theory for a low-density gas. Efficient heating of the clusters by the laser is followed by rapid expansion of the clusters and long-lived x-ray emission from hot, decaying, underdense plasma. {copyright} {ital 1996 The American Physical Society.}
TL;DR: OCT represents a promising new technology for imaging vascular microstructure with a level of resolution not previously achieved with the use of other imaging modalities, and can be performed with a catheter integrated with a relatively inexpensive optical fiber.
Abstract: Background Optical coherence tomography (OCT) is a recently developed medical diagnostic technology that uses back-reflected infrared light to perform in situ micron scale tomographic imaging. In this work, we investigate the ability of OCT to perform micron scale tomographic imaging of the internal microstructure of in vitro atherosclerotic plaques. Methods and Results Aorta and relevant nonvascular tissue were obtained at autopsy. Two-dimensional cross-sectional imaging of the exposed surface of the arterial segments was performed in vitro with OCT. A 1300-nm wavelength, superluminescent diode light source was used that allows an axial spatial resolution of 20 μm. The signal-to-noise ratio was 109 dB. Images were displayed in gray scale or false color. Imaging was performed over 1.5 mm into heavily calcified tissue, and a high contrast was noted between lipid- and water-based constituents, making OCT attractive for intracoronary imaging. The 20-μm axial resolution of OCT allowed small structural details...
TL;DR: In this paper, the authors used time-resolved photography to measure the position of the bubble front and the bubble wall as a function of time and the photographs were used to determine the shock front and bubble wall velocity as well as the shock wave pressure.
Abstract: Shock wave emission and cavitation bubble expansion after optical breakdown in water with Nd:YAG laser pulses of 30‐ps and 6‐ns duration is investigated for energies between 50 μJ and 10 mJ which are often used for intraocular laser surgery. Time‐resolved photography is applied to measure the position of the shock front and the bubble wall as a function of time. The photographs are used to determine the shock front and bubble wall velocity as well as the shock wave pressure as a function of time or position. Calculations of the bubble formation and shock wave emission are performed using the Gilmore model of cavitation bubble dynamics and the Kirkwood–Bethe hypothesis. The calculations are based on the laser pulse duration, the size of the plasma, and the maximally expanded cavitation bubble, i.e., on easily measurable parameters. They yield the dynamics of the bubble wall, the pressure evolution inside the bubble, and pressure profiles in the surrounding liquid at fixed times after the start of the laser...
TL;DR: Different couplings between a single ion trapped in a harmonic potential and an environment are designed and the variation of the laser frequencies and intensities allows one to design the coupling and select the master equation describing the motion of the ion.
Abstract: We show how to design different couplings between a single ion trapped in a harmonic potential and an environment. The coupling is due to the absorption of a laser photon and subsequent spontaneous emission. The variation of the laser frequencies and intensities allows one to ``engineer'' the coupling and select the master equation describing the motion of the ion.
Book•
01 Jan 1996
TL;DR: In this paper, the authors discuss the use of Ln3+ Ions in the creation of a new generation of IONS in the form of an Activator Ions.
Abstract: LASER INSULATING CRYSTALS AND THEIR STIMULATED EMISSION Development of Crystal-Laser Physics (Short Historical Remarks) Fluorine- and Oxygen-Containing Laser Crystalline Hosts and Their Activator Ions Other Laser Crystals Stimulated-Emission Channels of Activated Insulating Laser Crystals Stimulated Emission 4fN-4fN and 4fN-15d1-4fN Channels of Ln3+ Ions Laser Channels of Ln2+ and U3+ Ions Laser Channels of Cr3+, Cr4+, Ti3+, and Mn5+ Ions Laser Channels of TM2+ Activators Crystalline Laser Hosts for Obtaining Generation of Ln3+ Activators at New Wavelengths References ENERGY LEVELS AND OPTICAL-TRANSITION INTENSITIES OF GENERATING ACTIVATORS IN INSULATING LASER CRYSTALS Stark-Level Structure of Lasing Activator Ions Basic Concepts of Modern Crystal-Field Theory Stark-Level Energies of Generating Ions in Laser Insulating Crystals (Experimental Data) References Intensity of Radiative Transitions of Ln3+ Activators in Insulating Laser Crystals Electric Dipole Transitions Judd-Ofelt Intensity Parameters Wi Magnetic Dipole Transitions Spectroscopic-Quality Parameters of Insulating Laser Crystals with Ln3+ Activators References Multiphonon 4fN-4fN Nonradiative Transitions of Ln3+ Activators in Laser Crystals Principal Mechanisms of the Modern Theory of Nonradiative Relaxation of Ln3+ Ions in Crystals Energy-Gap Law - Dependence of WJJc on DEJJc References MULTILEVEL OPERATING LASER SCHEMES FOR THE EXCITATION OF STIMULATED EMISSION IN ACTIVATED CRYSTALS Cascade Operating Schemes for Crystalline Lasers Cascade Laser Schemes for Crystals Doped with Ln3+ Activators Features of Cascade Generation of the Ln3+ Ions in Crystals Cross-Cascade Laser Schemes for Crystals Doped with Ln3+ Activators References Sensitizing, Deactivating, and Feed-Flowing Operating Schemes for Crystalline Lasers Sensitizing Laser Schemes Deactivating Laser Schemes Feed-Flowing Laser Schemes Laser Action of Unlike Ln3+ Ion-Doped Crystals References Stepwise Laser Operating Schemes for Crystals Doped with Ln3+ Activator Ions Upconversion and Stimulated Emission of Ln3+ Ions in Crystals at High-Level Energy Excitation Upconversion Operating Laser Schemes for Er3+ Ion-Doped Crystals Operating Laser Schemes with Stepwise Absorption of Pump Quanta for YAlO3 and LiYF4 Crystals Doped with Er3+ Ions References Cross-Relaxation Operating Schemes for Crystalline Lasers Cross-Relaxation Laser Operating Schemes with Quantum Efficiency Equal to 1 Cross-Relaxation Laser Operating Schemes with Quantum Efficiency Equal to 2 Cross-Relaxation Laser Operating Schemes with Quantum Efficiency Equal to 3 Three-Micron 5I6 (R)yy5I7 Laser Channel of Ho3+ Ions in the BaYb2F8 Crystal References Laser Operating Schemes with Strong Depopulation of the Ground States of Generating Ln3+ Ions Ground-State Lifting - a Way to Increase Crystalline-Laser Efficiency Laser Action of Ln3+ Ions in Insulating Crystals Under Condition of Ground-State-Level Depletion Photon-Avalanche Phenomena in Laser Crystals with Ln3+ Activators References NOVEL AND PROMISING TECHNOLOGIES IN THE PHYSICS AND TECHNIQUE OF CRYSTALLINE LASERS New Generation of Crystalline Lasers Laser Action of Crystals Doped with Ln3+ Ions under Selective Laser Pumping Miniature Crystalline Lasers with High Density of Waveguiding Laser Pumping Crystalline Lasers with Self-Frequency Conversion Solar-Pumped Crystalline Lasers References Concluding Remarks The Current State in Laser-Diode-Pumped Crystalline Laser Development (Table Data) Up-to-Date Survey of Crystalline Upconversion Lasers (Table Data) Praseodymium Crystalline Lasers for the Creation of "White" Laser Light References Appendix A: Crystalline Hosts and Lasing Ions Index
15 Jun 1996-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the role of laser shock processing (LSP) on the cyclic properties of A356, Al12Si and 7075 aluminium alloys was evaluated, and major contributors to the fatigue performance improvements were investigated in order to determine the optimum shock conditions.
Abstract: Subjecting target metallic samples to a very short pulse (about 20 ns) of intense (GW cm−2) laser light generates, through a surface plasma, a high-pressure stress wave propagating to the first millimetre in depth, which is commonly called laser shock processing (LSP). The purpose of this work was to evaluate the role of this novel process on the cyclic properties of A356, Al12Si and 7075 aluminium alloys. Major contributors to the fatigue performance improvements were investigated in order to determine the optimum shock conditions. These were mainly compressive residual stress (RS) levels for which a large range of incident shock conditions was performed. We showed that stress levels were very sensitive to the laser fluence and the number of local impacts, and experimental RS measurements were found to be in good agreement with analytical modelling results. In comparison, a conventional shot peening (SP) treatment was found to lead to higher surface hardening and RS levels, but with a very detrimental roughening not observed after LSP. High cycle (107) fatigue tests carried out on laser- processed, shot-peened and untreated notched samples illustrated the efficiency of LSP as a new, promising method to improve the fatigue limits σD of structures, especially in comparison with enhancements displayed by SP (+22% vs. +10%). According to crack detection electric measurements, fatigue performance improvements with LSP mainly occurred during the crack initiation stage.
TL;DR: In this article, the absorption and emission properties of transition metal (TM)-doped zinc chalcogenides have been investigated to understand their potential application as room-temperature, mid-infrared tunable laser media.
Abstract: The absorption and emission properties of transition metal (TM)-doped zinc chalcogenides have been investigated to understand their potential application as room-temperature, mid-infrared tunable laser media. Crystals of ZnS, ZnSe, and ZnTe, individually doped with Cr/sup 2+/, Co/sup 2+/, Ni/sup 2+/, or Fe/sup 2+/ have been evaluated. The absorption and emission properties are presented and discussed in terms of the energy levels from which they arise. The absorption spectra of the crystals studied exhibit strong bands between 1.4 and 2.0 /spl mu/m which overlap with the output of strained-layer InGaAs diodes. The room-temperature emission spectra reveal wide-band emissions from 2-3 /spl mu/m for Cr and from 2.8-4.0 /spl mu/m for Co, Cr luminesces strongly at room temperature; Co exhibits significant losses from nonradiative decay at temperatures above 200 K, and Ni and Fe only luminesce at low temperatures, Cr/sup 2+/ is estimated to have the highest quantum yield at room temperature among the media investigated with values of /spl sim/75-100%. Laser demonstrations of Cr:ZnS and Cr:ZnSe have been performed in a laser-pumped laser cavity with a Co:MgF/sub 2/ pump laser. The output of both lasers were determined to peak at wavelengths near 2.35 /spl mu/m, and both lasers demonstrated a maximum slope efficiency of approximately 20%. Based on these initial results, the Cr/sup 2+/ ion is predicted to be a highly favorable laser ion for the mid-IR when doped into the zinc chalcogenides; Co/sup 2+/ may also serve usefully, but laser demonstrations yet remain to be performed.
TL;DR: The relation between the conditions for the onset of equilibrium and nonequilibrium excitonic condensates and a different type of laser without inversion which utilizes many-body coherences is discussed.
Abstract: We analyze elementary properties of exciton and polariton lasers --- devices that generate coherent optical and matter waves using final-state stimulation of exciton-phonon scattering. First we discuss the relation between the conditions for the onset of equilibrium and nonequilibrium excitonic condensates. Provided that the thermal de Broglie wavelength ${\ensuremath{\lambda}}_{\mathit{T}}$ exceeds the exciton Bohr radius ${\mathit{a}}_{\mathit{B}}$, an exciton laser operates without electronic population inversion. In contrast to previous proposals, this is a different type of laser without inversion which utilizes many-body coherences. When the excitonic character of the polariton branch vanishes, a polariton laser becomes indistinguishable from a photon laser. \textcopyright{} 1996 The American Physical Society.
TL;DR: The realization of a whispering-gallery-mode laser based on neodymium-doped silica micro-spheres with potential as a permanent microlaser operating with a few active ions at liquid-helium temperature is reported.
Abstract: We report on the realization of a whispering-gallery-mode laser based on neodymium-doped silica microspheres. Absorbed pump powers at threshold are as low as 200 nW. The linear variation of the threshold with the loss factor of the cavity mode has also been observed. We discuss the potential of this system as a permanent microlaser operating with a few active ions at liquid-helium temperature.
TL;DR: Results are presented for multiphoton Compton scattering in which up to four laser photons interact with an electron, in agreement with theoretical calculations.
Abstract: Nonlinear Compton scattering has been observed in the collision of a low-emittance 46.6-GeV electron beam with terawatt pulses from a Nd:glass laser at 1054 and 527 nm wavelengths in an experiment at the Final Focus Test Beam at SLAC. Peak laser intensities of ${10}^{18}\phantom{\rule{0ex}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$ have been achieved, corresponding to a value of 0.6 for the parameter $\ensuremath{\eta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}e{E}_{\mathrm{rms}}/m{\ensuremath{\omega}}_{0}c$. Results are presented for multiphoton Compton scattering in which up to four laser photons interact with an electron, in agreement with theoretical calculations.
TL;DR: In this article, the generation of harmonics by interaction of an ultrashort laser pulse with a step boundary of a plane overdense plasma layer is studied at intensities Iλ2=1017 −1019 W −2μm2 for normal and oblique incidence and different polarizations.
Abstract: The generation of harmonics by interaction of an ultrashort laser pulse with a step boundary of a plane overdense plasma layer is studied at intensities Iλ2=1017–1019 W cm−2 μm2 for normal and oblique incidence and different polarizations. Fully relativistic one‐dimensional particle‐in‐cell (PIC) simulations are performed with high spectral resolution. Harmonic emission increases with intensity and also when lowering the plasma density. The simulations reveal strong oscillations of the critical surface driven by the normal component of the laser field and by the ponderomotive force. It is shown that the generation of harmonics can be understood as reflection from the oscillating surface, taking full account of retardation. Describing the oscillations by one or more Fourier components with adjustable amplitudes, model spectra are obtained that well reproduce the PIC spectra. The model is based on relativistic cold plasma equations for oblique incidence. General selection rules concerning polarization of odd and even harmonics depending on incident polarization are derived.
02 Jun 1996
TL;DR: The design and performance of a prototype single-mode fiber-optic scanning OCT catheter with a diameter of 1 mm is described, which will permit micron scale, cross-sectional medical diagnostic imaging in tissues such as the vascular system, the gastrointestinal tract, the urinary tract, and the respiratory tract.
Abstract: Summary form only given. In order to apply OCT for imaging of internal organ systems, a flexible, small diameter, catheter/endoscope, which is capable of delivering, focusing, scanning, and collecting a single-spatial-mode optical beam, must be constructed. In this summary, we describe the design and performance of a prototype single-mode fiber-optic scanning OCT catheter with a diameter of 1 mm. OCT imaging may be performed at 1.3-micron wavelengths using either a superluminescent laser diode source or a Kerr-lens mode-locked Cr:forsterite laser, which provides high powers for high-speed imaging. This device is an enabling technology for OCT and will permit micron scale, cross-sectional medical diagnostic imaging in tissues such as the vascular system, the gastrointestinal tract, the urinary tract, and the respiratory tract.
01 Jan 1996
TL;DR: In this article, a review of the state of the art in spatially and temporally precise laser diagnostics for temperature and species is presented, including two-dimensional implementations, their state of maturity assessed, and major remaining research issues identified.
Abstract: Nonintrusive laser probing of unsteady combustion processes provides the capability for the remote, in—situ, spatially and temporally precise measurement of, among other parameters, gas temperature and species concentrations. The predominant spatially—precise laser diagnostics for temperature and species include spontaneous Raman scattering (RS) and coherent anti-Stokes Raman spectroscopy (CARS) for measurements of major, i.e., ≥~ 1%, constituents, and laser—induced fluorescence spectroscopy (LIFS) and degenerate four wave mixing (DFWM) for minor, ppm level, species. Rayleigh scattering can provide total density measurements. These techniques are reviewed, including two-dimensional implementations, their state of maturity assessed, and major remaining research issues identified.
TL;DR: In this article, the authors studied the effect of sub-picosecond laser radiation on the energy and pulse duration of solid targets irradiated by Ti:sapphire laser radiation in the range of 10 9 − 5 × 10 16 W cm 2.