Showing papers on "Laser published in 2002"
Journal Article•
TL;DR: Schawlow and Townes as discussed by the authors proposed a technique for the generation of very monochromatic radiation in the infra-red optical region of the spectrum using an alkali vapour as the active medium.
Abstract: Schawlow and Townes1 have proposed a technique for the generation of very monochromatic radiation in the infra-red optical region of the spectrum using an alkali vapour as the active medium. Javan2 and Sanders3 have discussed proposals involving electron-excited gaseous systems. In this laboratory an optical pumping technique has been successfully applied to a fluorescent solid resulting in the attainment of negative temperatures and stimulated optical emission at a wave-length of 6943 A. ; the active material used was ruby (chromium in corundum). After demonstration in 1954 of the 'maser' principle (microwave amplification by stimulated emission of radiation), systems were sought in which the effect occurred in the infrared and visible spectrum. This goal was reached in 1960 when Theodore Maiman achieved optical laser action in ruby.
3,646 citations
TL;DR: The ability to count optical oscillations of more than 1015 cycles per second facilitates high-precision optical spectroscopy, and has led to the construction of an all-optical atomic clock that is expected eventually to outperform today's state-of-the-art caesium clocks.
Abstract: Extremely narrow optical resonances in cold atoms or single trapped ions can be measured with high resolution. A laser locked to such a narrow optical resonance could serve as a highly stable oscillator for an all-optical atomic clock. However, until recently there was no reliable clockwork mechanism that could count optical frequencies of hundreds of terahertz. Techniques using femtosecond-laser frequency combs, developed within the past few years, have solved this problem. The ability to count optical oscillations of more than 1015 cycles per second facilitates high-precision optical spectroscopy, and has led to the construction of an all-optical atomic clock that is expected eventually to outperform today's state-of-the-art caesium clocks.
2,612 citations
TL;DR: A monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure is reported, which is very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems.
Abstract: Semiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radio-frequency emitters enable wireless communications. But the terahertz region (1-10 THz; 1 THz = 10(12) Hz) between these ranges has remained largely underdeveloped, despite the identification of various possible applications--for example, chemical detection, astronomy and medical imaging. Progress in this area has been hampered by the lack of compact, low-consumption, solid-state terahertz sources. Here we report a monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure. The prototype demonstrated emits a single mode at 4.4 THz, and already shows high output powers of more than 2 mW with low threshold current densities of about a few hundred A cm(-2) up to 50 K. These results are very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems.
2,425 citations
TL;DR: It is demonstrated that by introducing a periodic microstructure into such a polar material (SiC) a thermal infrared source can be fabricated that is coherent over large distances (many wavelengths) and radiates in well defined directions.
Abstract: A thermal light-emitting source, such as a black body or the incandescent filament of a light bulb, is often presented as a typical example of an incoherent source and is in marked contrast to a laser. Whereas a laser is highly monochromatic and very directional, a thermal source has a broad spectrum and is usually quasi-isotropic. However, as is the case with many systems, different behaviour can be expected on a microscopic scale. It has been shown recently that the field emitted by a thermal source made of a polar material is enhanced by more than four orders of magnitude and is partially coherent at a distance of the order of 10 to 100nm. Here we demonstrate that by introducing a periodic microstructure into such a polar material (SiC) a thermal infrared source can be fabricated that is coherent over large distances (many wavelengths) and radiates in well defined directions. Narrow angular emission lobes similar to antenna lobes are observed and the emission spectra of the source depends on the observation angle--the so-called Wolf effect. The origin of the coherent emission lies in the diffraction of surface-phonon polaritons by the grating.
1,226 citations
TL;DR: A redshift that is strongly dependent on pump power supports the idea that the electron–hole plasma mechanism is primarily responsible for the gain at room temperature and is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet–blue coherent light sources.
Abstract: There is much current interest in the optical properties of semiconductor nanowires, because the cylindrical geometry and strong two-dimensional confinement of electrons, holes and photons make them particularly attractive as potential building blocks for nanoscale electronics and optoelectronic devices, including lasersand nonlinear optical frequency converters. Gallium nitride (GaN) is a wide-bandgap semiconductor of much practical interest, because it is widely used in electrically pumped ultraviolet-blue light-emitting diodes, lasers and photodetectors. Recent progress in microfabrication techniques has allowed stimulated emission to be observed from a variety of GaN microstructures and films. Here we report the observation of ultraviolet-blue laser action in single monocrystalline GaN nanowires, using both near-field and far-field optical microscopy to characterize the waveguide mode structure and spectral properties of the radiation at room temperature. The optical microscope images reveal radiation patterns that correlate with axial Fabry-Perot modes (Q approximately 10(3)) observed in the laser spectrum, which result from the cylindrical cavity geometry of the monocrystalline nanowires. A redshift that is strongly dependent on pump power (45 meV microJ x cm(-2)) supports the idea that the electron-hole plasma mechanism is primarily responsible for the gain at room temperature. This study is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet-blue coherent light sources.
1,207 citations
TL;DR: It is demonstrated that a laser-based sampling system, consisting of a few-femtosecond visible light pulse and a synchronized sub-feminine soft X-ray pulse, allows us to trace the relaxation dynamics of core-excited atoms directly in the time domain with attosecond resolution.
Abstract: The characteristic time constants of the relaxation dynamics of core-excited atoms have hitherto been inferred from the linewidths of electronic transitions measured by continuous-wave extreme ultraviolet or X-ray spectroscopy. Here we demonstrate that a laser-based sampling system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows us to trace these dynamics directly in the time domain with attosecond resolution. We have measured a lifetime of 7.9(-0.9)(+1.0) fs of M-shell vacancies of krypton in such a pump-probe experiment.
1,204 citations
Journal Article•
TL;DR: In this article, a detailed analysis of the laser properties of Ti:Al2O3 is presented, including absorption and fluorescence spectra and lifetime as a function of temperature.
Abstract: Spectroscopic measurements and laser performance of Ti:Al2O3 are discussed in detail. Data on absorption and fluorescence spectra and fluorescence lifetime as a function of temperature are presented. Laser characteristics observed with pulsed-dye-laser, frequency-doubled Nd:YAG-laser, and argon-ion-laser pumping are covered and show that nearly quantum-limited conversion of pump radiation can be achieved, along with tuning over the wavelength range 660–986 nm.
1,131 citations
TL;DR: This work demonstrates a micrometre-scale, nonlinear Raman source that has a highly efficient pump–signal conversion (higher than 35%) and pump thresholds nearly 1,000 times lower than shown before, which represents a route to compact, ultralow-threshold sources for numerous wavelength bands that are usually difficult to access.
Abstract: The ability to confine and store optical energy in small volumes has implications in fields ranging from cavity quantum electrodynamics to photonics. Of all cavity geometries, micrometre-sized dielectric spherical resonators are the best in terms of their ability to store energy for long periods of time within small volumes. In the sphere, light orbits near the surface, where long confinement times (high Q) effectively wrap a large interaction distance into a tiny volume. This characteristic makes such resonators uniquely suited for studies of nonlinear coupling of light with matter. Early work recognized these attributes through Raman excitation in microdroplets-but microdroplets have not been used in practical applications. Here we demonstrate a micrometre-scale, nonlinear Raman source that has a highly efficient pump-signal conversion (higher than 35%) and pump thresholds nearly 1,000 times lower than shown before. This represents a route to compact, ultralow-threshold sources for numerous wavelength bands that are usually difficult to access. Equally important, this system can provide a compact and simple building block for studying nonlinear optical effects and the quantum aspects of light.
1,060 citations
TL;DR: In this paper, the authors used three-dimensional particle-in-cell simulations to study laser wake field acceleration (LWFA) at highly relativistic laser intensities, and observed ultra-short electron bunches emerging from laser wake fields driven above the wave-breaking threshold by few-cycle laser pulses shorter than the plasma wavelength.
Abstract: We use three-dimensional particle-in-cell simulations to study laser wake field acceleration (LWFA) at highly relativistic laser intensities. We observe ultra-short electron bunches emerging from laser wake fields driven above the wave-breaking threshold by few-cycle laser pulses shorter than the plasma wavelength. We find a new regime in which the laser wake takes the shape of a solitary plasma cavity. It traps background electrons continuously and accelerates them. We show that 12-J, 33-fs laser pulses may produce bunches of 3×1010 electrons with energy sharply peaked around 300 MeV. These electrons emerge as low-emittance beams from plasma layers just 700-μm thick. We also address a regime intermediate between direct laser acceleration and LWFA, when the laser-pulse duration is comparable with the plasma period.
1,055 citations
TL;DR: In this paper, the current status of research and development on laser shock processing of metals, also known as laser peening, using Q-switched high power lasers is reviewed and the influence of processing parameters on the laser-induced shock waves in metal components are discussed and analyzed.
933 citations
TL;DR: This review focuses on the nature of the non-thermal transitions in semiconductors under femtosecond laser excitation.
Abstract: Soon after it was discovered that intense laser pulses of nanosecond duration from a ruby laser could anneal the lattice of silicon, it was established that this so-called pulsed laser annealing is a thermal process. Although the radiation energy is transferred to the electrons, the electrons transfer their energy to the lattice on the timescale of the excitation. The electrons and the lattice remain in equilibrium and the laser simply 'heats' the solid to the melting temperature within the duration of the laser pulse. For ultrashort laser pulses in the femtosecond regime, however, thermal processes (which take several picoseconds) and equilibrium thermodynamics cannot account for the experimental data. On excitation with femtosecond laser pulses, the electrons and the lattice are driven far out of equilibrium and disordering of the lattice can occur because the interatomic forces are modified due to the excitation of a large (10% or more) fraction of the valence electrons to the conduction band. This review focuses on the nature of the non-thermal transitions in semiconductors under femtosecond laser excitation.
TL;DR: The results demonstrate the potential of quantum cascade lasers as continuous wave mid-infrared light sources for high-resolution spectroscopy, chemical sensing applications, and free-space optical communication systems.
Abstract: Continuous wave operation of quantum cascade lasers is reported up to a temperature of 312 kelvin. The devices were fabricated as buried heterostructure lasers with high-reflection coatings on both laser facets, resulting in continuous wave operation with optical output power ranging from 17 milliwatts at 292 kelvin to 3 milliwatts at 312 kelvin, at an emission wavelength of 9.1 micrometers. The results demonstrate the potential of quantum cascade lasers as continuous wave mid-infrared light sources for high-resolution spectroscopy, chemical sensing applications, and free-space optical communication systems.
TL;DR: An electron generated by x-ray photoionization can be deflected by a strong laser field and this phase dependence can be used to measure the duration and chirp of single sub100-attosecond x-rays.
Abstract: An electron generated by x-ray photoionization can be deflected by a strong laser field Its energy and angular distribution depends on the phase of the laser field at the time of ionization This phase dependence can be used to measure the duration and chirp of single sub100-attosecond x-ray pulses
TL;DR: This review describes recent progress on plastic optical fiber lasers and amplifiers with lanthanides and focuses especially on the design and selection of plastic optical Fiber and chelate materials.
Abstract: Organic dye-doped polymers have been widely investigated as gain media in solid-state dye lasers. Dye molecules which have large absorption and induced emission cross sections due to allowed π-π transitions are ideal active dopants for the generation and amplification of intense light pulses. However, continuous wave operation is not feasible with organic dyes because of the triplet losses. On the other hand, lanthanide ions that have long metastable state lifetimes are widely used in silica glass-based fiber amplifiers and for both continuous and pulsed lasers. It has been more than 30 years since the first lanthanide lasers were reported.1-3 During this period a wide variety of lanthanide lasers and amplifiers have been investigated, and extensive progress has been made by many researchers. Many reviews have been written concentrating primarily on the physical and chemical properties of lanthanides in many matrices for laser action.4-8 Recently, several books have focused on lanthanide-doped fiber amplifiers for optical communications.9-11 The success of lanthanide-doped fiber amplifiers has inspired thousands of publications and continues to motivate research on the many diverse components that are required in these systems. Optical links are now used primarily in applications such as telecommunications with single-mode silica optical fibers, which have the ability to provide high-bandwidth and long-distance communications. However, as the demand for bandwidth increases in the office and home, it has become increasingly important to develop very low cost optical links that can be readily installed by users. Plastic optical fibers (POF) have received increasing attention because of their clear technical advantages over glass fibers, such as flexibility and a large core diameter, which enables efficient connection and coupling resulting in a low-cost system for a local area network. Recently a low-loss (100 db/km), highbandwidth 5.12 GHz for 100 m transmission graded index plastic optical fiber (GI-POF) has been developed.12 Also, an all fluorinated POF, whose low loss region is extended to the visible and near-infrared, has been successfully prepared.13 Plastic optical fiber amplifiers (POFA) that generate signal light in the visible and near-infrared are potentially important because of their adaptability for POF-based short span optical local distribution networks. This review describes recent progress on plastic optical fiber lasers and amplifiers with lanthanides. We focus especially on the design and selection of plastic optical fiber and chelate materials.
Journal Article•
TL;DR: In this article, an algorithm which estimated position, height, and crown diameter of individual trees was proposed to detect and measure individual trees in a high-resolution airborne laser scanner data.
Abstract: High-resolution airborne laser scanner data offer the possibility to detect and measure individual trees. In this study an algorithm which estimated position, height, and crown diameter of individu ...
TL;DR: In this paper, the mechanism of ablation of solids by intense femtosecond laser pulses is described in an explicit analytical form, and the formulas for ablation thresholds and ablation rates for metals and dielectrics, combining the laser and target parameters, are derived and compared to experimental data.
Abstract: The mechanism of ablation of solids by intense femtosecond laser pulses is described in an explicit analytical form. It is shown that at high intensities when the ionization of the target material is complete before the end of the pulse, the ablation mechanism is the same for both metals and dielectrics. The physics of this new ablation regime involves ion acceleration in the electrostatic field caused by charge separation created by energetic electrons escaping from the target. The formulas for ablation thresholds and ablation rates for metals and dielectrics, combining the laser and target parameters, are derived and compared to experimental data. The calculated dependence of the ablation thresholds on the pulse duration is in agreement with the experimental data in a femtosecond range, and it is linked to the dependence for nanosecond pulses.
TL;DR: In this article, the initial modification and ablation of crystalline silicon with single and multiple Ti:sapphire laser pulses of 5 to 400 fs duration was investigated, and the authors found the phenomena amorphization, melting, re-crystallization, nucleated vaporization, and Ablation to occur with increasing laser fluence down to the shortest pulse durations.
Abstract: We investigated the initial modification and ablation of crystalline silicon with single and multiple Ti:sapphire laser pulses of 5 to 400 fs duration. In accordance with earlier established models, we found the phenomena amorphization, melting, re-crystallization, nucleated vaporization, and ablation to occur with increasing laser fluence down to the shortest pulse durations. We noticed new morphological features (bubbles) as well as familiar ones (ripples, columns). A nearly constant ablation threshold fluence on the order of 0.2 J/cm2 for all pulse durations and multiple-pulse irradiation was observed. For a duration of ≈100 fs, significant incubation can be observed, whereas for 5 fs pulses, the ablation threshold does not depend on the pulse number within the experimental error. For micromachining of silicon, a pulse duration of less than 500 fs is not advantageous.
TL;DR: Calculations and measurements are reported that confirm the production of high-power broadband THz radiation from subpicosecond electron bunches in an accelerator, several orders of magnitude higher than any existing source, which could enable various new applications.
Abstract: Terahertz (THz) radiation, which lies in the far-infrared region, is at the interface of electronics and photonics. Narrow-band THz radiation can be produced by free-electron lasers and fast diodes. Broadband THz radiation can be produced by thermal sources and, more recently, by table-top laser-driven sources and by short electron bunches in accelerators, but so far only with low power. Here we report calculations and measurements that confirm the production of high-power broadband THz radiation from subpicosecond electron bunches in an accelerator. The average power is nearly 20 watts, several orders of magnitude higher than any existing source, which could enable various new applications. In particular, many materials have distinct absorptive and dispersive properties in this spectral range, so that THz imaging could reveal interesting features. For example, it would be possible to image the distribution of specific proteins or water in tissue, or buried metal layers in semiconductors; the present source would allow full-field, real-time capture of such images. High peak and average power THz sources are also critical in driving new nonlinear phenomena and for pump-probe studies of dynamical properties of materials.
TL;DR: A theoretical analysis and experimentally demonstrate a Pancharatnam-Berry phase-based diffraction grating for laser radiation at a wavelength of 10.6microm.
Abstract: Space-variant Pancharatnam-Berry phase optical elements based on computer-generated subwavelength gratings are presented. By continuously controlling the local orientation and period of the grating we can achieve any desired phase element. We present a theoretical analysis and experimentally demonstrate a Pancharatnam-Berry phase-based diffraction grating for laser radiation at a wavelength of 10.6microm.
TL;DR: Submicrometer-resolution OCT is demonstrated in vitro on human colorectal adenocarcinoma cells HT-29, a novel light source that has great potential for development of spectroscopic OCT because its spectrum covers the absorption bands of several biological chromophores.
Abstract: Optical coherence tomography (OCT) with unprecedented submicrometer axial resolution achieved by use of a photonic crystal fiber in combination with a compact sub-10-fs Ti:sapphire laser (Femtolasers Produktions) is demonstrated for what the authors believe is the first time The emission spectrum ranges from 550 to 950 nm (?c=725 nm , Pout=27 mW) , resulting in a free-space axial OCT resolution of ~075 ?m , corresponding to ~05 ?m in biological tissue Submicrometer-resolution OCT is demonstrated in vitro on human colorectal adenocarcinoma cells HT-29 This novel light source has great potential for development of spectroscopic OCT because its spectrum covers the absorption bands of several biological chromophores
TL;DR: It is shown that a gain in maximum electron energy of up to 200 megaelectronvolts can be achieved, along with an improvement in the quality of the ultrashort electron beam in the forced laser wake field regime.
Abstract: Plasmas are an attractive medium for the next generation of particle accelerators because they can support electric fields greater than several hundred gigavolts per meter. These accelerating fields are generated by relativistic plasma waves-space-charge oscillations-that can be excited when a high-intensity laser propagates through a plasma. Large currents of background electrons can then be trapped and subsequently accelerated by these relativistic waves. In the forced laser wake field regime, where the laser pulse length is of the order of the plasma wavelength, we show that a gain in maximum electron energy of up to 200 megaelectronvolts can be achieved, along with an improvement in the quality of the ultrashort electron beam.
TL;DR: In this paper, the authors reviewed the current available semiconductor laser sources for spectroscopy in the near and mid-infrared spectral region based upon gallium arsenide, indium phosphite, antimonides and lead-salt containing compounds.
TL;DR: The generation of cavity solitons in vertical cavity semiconductor microresonators that are electrically pumped above transparency but slightly below lasing threshold is demonstrated and it is shown that the generated optical spots can be written, erased and manipulated as objects independent of each other and of the boundary.
Abstract: Cavity solitons are localized intensity peaks that can form in a homogeneous background of radiation. They are generated by shining laser pulses into optical cavities that contain a nonlinear medium driven by a coherent field (holding beam). The ability to switch cavity solitons on and off1,2 and to control their location and motion3 by applying laser pulses makes them interesting as potential ‘pixels’ for reconfigurable arrays or all-optical processing units. Theoretical work on cavity solitons2,3,4,5,6,7 has stimulated a variety of experiments in macroscopic cavities8,9,10 and in systems with optical feedback11,12,13. But for practical devices, it is desirable to generate cavity solitons in semiconductor structures, which would allow fast response and miniaturization. The existence of cavity solitons in semiconductor microcavities has been predicted theoretically14,15,16,17, and precursors of cavity solitons have been observed, but clear experimental realization has been hindered by boundary-dependence of the resulting optical patterns18,19—cavity solitons should be self-confined. Here we demonstrate the generation of cavity solitons in vertical cavity semiconductor microresonators that are electrically pumped above transparency but slightly below lasing threshold20. We show that the generated optical spots can be written, erased and manipulated as objects independent of each other and of the boundary. Numerical simulations allow for a clearer interpretation of experimental results.
Journal Article•
TL;DR: In this paper, 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: This review describes recent research to understand and utilize laser ablation for direct solid sampling, with emphasis on sample introduction to an inductively coupled plasma (ICP).
TL;DR: A white-light seeded optical parametric amplifier is suggested as a self-stabilized source of few-cycle pulses, in which the phase of the electric field is exactly reproduced in each laser shot.
Abstract: The phase link between signal, idler, and pump waves in a parametric interaction allows generation of an idler pulse with a phase independent of that of the input pulse. We suggest the use of a white-light seeded optical parametric amplifier as a self-stabilized source of few-cycle pulses, in which the phase of the electric field is exactly reproduced in each laser shot.
TL;DR: In this article, a new generation of solid-state laser and optical materials on the basis of highly transparent nanocrystalline yttrium aluminium garnet Y3Al5O12 (YAG) ceramics was developed and adequately characterized.
TL;DR: In the scheme proposed, a beam of fast ions accelerated by a laser pulse can be integrated in the installations intended for proton therapy, ensuring that the irradiation of the surrounding healthy tissues and organs is minimal.
Abstract: The feasibility of using laser plasma as a source of high-energy ions for the purposes of proton therapy is discussed The proposal is based on the efficient ion acceleration observed in recent laboratory and numerical experiments on the interaction of high-power laser radiation with gaseous and solid targets The specific dependence of proton energy losses in biological tissues (the Bragg peak) promotes the solution of one of the main problems of radiation therapy, namely, the irradiation of a malignant tumor with a sufficiently strong and homogeneous dose, ensuring that the irradiation of the surrounding healthy tissues and organs is minimal In the scheme proposed, a beam of fast ions accelerated by a laser pulse can be integrated in the installations intended for proton therapy
TL;DR: In this paper, an experimental study is presented to evaluate the effectiveness of micro-surface structure, produced by laser texturing, to improve tribological properties of reciprocating automotive components, including piston rings and cylinder linings.
Abstract: An experimental study is presented to evaluate the effectiveness of micro-surface structure, produced by laser texturing, to improve tribological properties of reciprocating automotive components. The test rig and test specimens are described and some test results are presented. Good correlation is found with theoretical prediction of friction reduction on a simple, yet representative, test specimen. Potential benefit of the laser surface texturing under conditions of lubricant starvation is also presented. Finally, friction reduction with actual production piston rings and cylinder liner segments is demonstrated. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002
TL;DR: In this article, the two-wave mixing is measured in a standard geometry (29) with the two beams having external angles of 30 and 60 to the sample normal and beam variance 1:1.
Abstract: For transient ellipsometry, the sample is placed between crossed polarizers at an angle of 54 between the sample normal and the laser beam. A laser diode at a wavelength k = 905 nm is employed and the residual birefringence of the sam- ple is compensated by a crystal compensator. The transmission through the el- lipsometry setup is measured in response to a step function of the electric field applied to the sample with a rise time of ~100 ls. The two-wave mixing is measured in a standard geometry (29) with the two beams having external angles of 30 and 60 to the sample normal and beam ra- tio 1:1. The laser source is a Kr ion laser at a wavelength of 647 nm. The time transients are measured by opening a shutter for both beams with a switching time of about 150 ls. After the measurements, the gratings are erased by a larg- er, non-Bragg matched erasing beam. In the beam fanning experiments, the same setup as in the two-wave mixing is used except only one beam is present. The angle of the beam to the sample normal is 60 and the applied electric field is inverted compared to two-wave mixing to enhance the fanning. Additionally, an aperture is placed in the beam path 50 cm behind the sample, which clips only 5 % of the unperturbed beam.