Showing papers in "Applied Physics B in 1988"
TL;DR: In this paper, the molecular continuum of xenon at 172 nm was obtained with an efficiency of close to 10% and model calculations for excimer formation and UV efficiencies in such discharges were presented.
Abstract: Dielectric-barrier (silent) discharges are ideally suited for efficient excitation of high-intensity UV radiation from excimers. The molecular continuum of xenon at 172 nm could be obtained with an efficiency of close to 10%. Model calculations for excimer formation and UV efficiencies in such discharges are presented. The possibility of obtaining many other wavelengths (e.g. KrF* at 248 nm and XeCl* at 308 nm) and the variety of conceivable geometries (plane or cylindrical) makes this new UV source an attractive choice for many photophysical and photochemical applications.
350 citations
TL;DR: In this article, a power-dependent reflection coefficient with fast time response and no frequency shift was proposed and analyzed, which utilizes a combination of a nonlinear crystal for second harmonic generation and a dichroic mirror with high reflectivity for the second harmonic and partial transmission.
Abstract: A device exhibiting a power-dependent reflection coefficient with fast time response and no frequency shift is proposed and analysed. It utilizes a combination of a nonlinear crystal for second harmonic generation and a dichroic mirror with high reflectivity for the second harmonic and partial transmission for the fundamental wavelenth. This device has been successfully used in a preliminary experiment to modelock a Nd:YAG laser.
148 citations
TL;DR: In this article, a convenient technique for the ultrashort-relaxation-time measurement using temporally incoherent light instead of short pulses can be applied to the studies of relaxation processes.
Abstract: A convenient technique for the ultrashort-relaxation-time measurement using temporally incoherent light instead of short pulses can be applied to the studies of relaxation processes. Theoretical studies on measuring various types of relaxation times by this method are summarized. We have applied this technique to the studies of the electronic dephasing in a polydiacetylene film, the vibrational dephasing in dimethylsulfoxide and the relaxation of optical Kerr effect in CS2 and nitrobenzene.
105 citations
TL;DR: In this article, the passive and hybrid Q-switching and mode-locking of solid-state lasers, dye lasers, semiconductor lasers and gas lasers is reviewed, and the dynamics of saturable absorbers and reverse saturation absorbers is illustrated.
Abstract: The passive and hybrid Q-switching and mode-locking of solid-state lasers, dye lasers, semiconductor lasers and gas lasers is reviewed. The dynamics of saturable absorbers and reverse saturable absorbers is illustrated. The nanosecond pulse generation by passive and hybrid Q-switching of low-gain active media is described. The picosecond and femtosecond pulse generation by passive and hybrid mode-locking in low-gain and high-gain active media is analysed. The performance data of passively and hybridly mode-locked cw femtosecond dye lasers are collected. The pulse shortening of ultra-fast pulses with saturable absorbers in intra-cavity and extra-cavity configurations is discussed.
96 citations
TL;DR: In this article, the authors explain laser cutting of gelatin and tissue with Er and CO2 lasers by combined action of evaporation, ejection of liquid and elastic deformation of the region of radiation impact.
Abstract: Laser cutting of gelatin and tissue with Er and CO2 lasers is explained by combined action of evaporation, ejection of liquid and elastic deformation of the region of radiation impact. It is shown that the ejection mechanism is more pronounced at 2.94 μm than at 10.6 μm. The use of high speed photography has revealed the influence of the temporal pulse shape. The experimental results are explained by a thermo-mechanical model.
80 citations
TL;DR: In this paper, a simple, achromatic, widely tunable distributed feedback dye laser arrangement is described, which makes use of a microscope objective, which images a transmission grating into the active medium.
Abstract: A simple, achromatic, widely tunable distributed feedback dye laser arrangement is described. It makes use of a microscope objective, which images a transmission grating into the active medium. With this arrangement subpicosecond operation and broad tunability (400–760 nm) is reported.
69 citations
TL;DR: Two-dimensional laser-induced fluorescence (2D-LIF) imaging of OH radicals, excited at 308 nm, has been employed to visualize the flame front in an internal combustion engine burning air/propane mixtures as discussed by the authors.
Abstract: Two-dimensional laser-induced fluorescence (2D-LIF) imaging of OH radicals, excited at 308 nm, has been employed to visualize the flame front in an internal combustion engine burning air/propane mixtures. Light sheet thicknesses down to 70 μm have been attained for excitation. Hydroxyl radicals were detected up to pressures of 7.5 bar at engine speeds of 500 rpm. An upper limit of 300 μm for the flame front thickness was obtained from line intensity profiles.
69 citations
TL;DR: In this article, major features of the AVLIS process are discussed with consideration of the process figures of merit, as well as some of the major features used in the process.
Abstract: Atomic Vapor Laser Isotope Separation (AVLIS) is a general and powerful technique applicable to many elements. A major present application to the enrichement of uranium for lightwater power reactor fuel has been under development at the Lawrence Livermore National Laboratory since 1973. In June 1985, the Department of Energy announced the selection of AVLIS as the technology to meet future U.S. needs for the internationally competitive production of uranium separative work. Major features of the AVLIS process will be discussed with consideration of the process figures of merit.
67 citations
TL;DR: In this article, a method for controlling nonradiative funnels to the ground state in many dyes is proposed to obtain faster saturable absorbers for sub-picosecond laser pulses.
Abstract: TICT states, accessible in twisted multichromophoric systems, are nonradiative funnels to the ground state in many dyes. By controlling these funnels, faster saturable absorbers for subpicosecond laser pulses can be developed. Oriented assemblies of TICT molecules, as in liquid crystalline polymers, are expected to exhibit light-induced macroscopic charge separation. Chemical approaches to supramolecular bistable species are also shown.
65 citations
TL;DR: In this paper, the frequency-doubled dye laser was replaced by KrF excimer laser of different beam properties, and the possibility of shifting the excimer wavelength 248.5 nm to the laser wavelength 193 nm was demonstrated.
Abstract: Wavelengths in the range from 188.9 to 197 nm have been obtained by type-I sum frequency generation (SFG) in β-BaB2O4. The fundamental beams were supplied by pulsed dye lasers one of which tuned between 780 and 950 nm and the other frequency-doubled at 497 nm. The possibility of shifting the excimer wavelength 248.5 nm to the excimer wavelength 193 nm has been demonstrated, replacing the frequency-doubled dye laser by KrF excimer lasers of different beam properties.
54 citations
TL;DR: In this paper, an approach to CARS, with considerable potential as a diagnostic for advanced airbreathing propulsion devices, is described and demonstrated, which employs both broadband and narrowband Stokes beams to generate CARS via two, two-color and two, three-color wave mixing processes.
Abstract: An approach to CARS, with considerable potential as a diagnostic for advanced airbreathing propulsion devices, is described and demonstrated. The technique is capable of providing simultaneous measurements of the major constitutents in H2/air combustion. The method employs both broadband and narrowband Stokes beams to generate CARS via two, two-color and two, three-color wave mixing processes. Temperature and concentration information are simultaneously available from N2, H2, and H2O. This permits the disappearance of fuel and appearance of product to be monitored. An analysis of the technique's capabilities and future improvements are discussed.
TL;DR: In this article, temperature and concentration measurements by Coherent anti-stokes Raman scattering (CARS) of molecular nitrogen, oxygen and methane were carried out and a comparison of corrected thermocouple and CARS temperature measurements in a high temperature furnace up to 2000 K was presented.
Abstract: Temperature and concentration measurements by Coherent Anti-Stokes Raman Scattering (CARS) of molecular nitrogen, oxygen and methane were carried out. A comparison of corrected thermocouple and CARS temperature measurements in a high-temperature furnace up to 2000 K is presented. The temperature dependent CARS spectra of N2 and O2 are evaluated by a simulation program. Agreement between CARS and thermocouple temperatures is obtained within 40 K for N2 and 80 K for O2. Good agreement is found between measurements and calculations of the decrease of CARS intensity with temperature. Various “quick-fit” methods for N2-and O2-temperature measurements from temperature sensitive spectral parameters were tested. Temperature dependent CARS spectra of thev1-fundamental of methane are recorded and the methane CARS intensity as function of temperature is measured.
IBM1
TL;DR: In this article, the entrainment in a jet expansion of material vaporized with a laser pulse from a surface below but closely adjacent to the jet orifice was investigated, and the results can be used to optimize the overlap of the concentration pulse with a skimmer or other probe.
Abstract: We have investigated the entrainment in a jet expansion of material vaporized with a laser pulse from a surface below but closely adjacent to the jet orifice Jets of He and Ar were used as carriers, and perylene was the test substance Its distribution in space and time far from the nozzle was measured by laser-induced fluorescence and one-dimensional imaging with an optical multichannel analyzer The width of the perylene concentration profile was found to be much narrower than the width of the gas expansion, especially in He This makes it possible to extract a useful portion of the entrained material through a skimmer Depending on the values of experimental parameters, the center of the profile first appears above, on, or below the jet axis and then moves lower with time Effects of several parameters on shape and time-dependent position of the profile were investigated The results can be used to optimize the overlap of the concentration pulse with a skimmer or other probe
TL;DR: In this article, the authors summarized some recent developments in this rapidly expanding field and summarized some of the potential applications in different areas of technology and applied it in various areas of science.
Abstract: Chemical processing of materials with lasers is a new and interdisciplinary field with many already realized and potential applications in different areas of technology This overview summarizes some recent developments in this rapidly expanding field
TL;DR: In this paper, an analytical expression of the ion-cloud temperature is established taking space-charge effects into account and involving only physical parameters which can be easily measured, and the validity of this approximate expression is discussed and it is compared to numerically established results.
Abstract: The use of a stored ion cloud in an rf quadrupole trap has shown its possibilities as a high-performance frequency standard. The most important source of systematic error of such a standard is the second-order Doppler shift, an effect of special relativity, which produces a relative frequency shift approximated by the ratio of the mean kinetic energy to the rest mass energy of an ion. Assuming that the ion cloud can be characterized by a temperatureT, the determination ofT is of paramount importance in evaluating the second-order Doppler shift. In this paper, an analytical expression of the ion-cloud temperature is established taking space-charge effects into account and involving only physical parameters which can be easily measured. The validity of this approximate expression is discussed and it is compared to numerically established results published elsewhere.
ENEA1
TL;DR: In this paper, a direct measurement of the electron-density time evolution in the active medium of a self-sustained XeCl laser discharge has been performed by means of the holographic interferometry technique.
Abstract: A direct measurement of the electron-density time evolution in the active medium of a self-sustained XeCl laser discharge has been performed by means of the holographic interferometry technique. The time and space resolved behaviour of the discharge seems to confirm that the halogen depletion instability and the hot spots developing in the cathode region are the basic mechanisms which determine the premature termination of the output laser pulse.
TL;DR: In this article, the third-order nonlinear susceptibility components and the effective thirdorder non-linear susceptibility of type II phase-matched (ooe→e) third-harmodic generation were determined.
Abstract: The third-harmonic generation of picosecond light pulses in a calcite crystal is studied experimentally and theoretically. A passively mode-locked Nd: phosphate glass laser is used in the experiments. The third-order nonlinear susceptibility components and the effective third-order nonlinear susceptibility of type II phase-matched (ooe→e) thirdharmodic generation are determined.
TL;DR: In this paper, the effect of free-carrier screening on the absorption and refraction in the vicinity of the band-gap at room temperature was investigated on a 1μm slab.
Abstract: We report on large optical nonlinearities due to specific many-body effects in high-density electron-hole pair systems. On bulk CdS we study the effect of free-carrier screening on the absorption and refraction in the vicinity of the band-gap at room temperature. Steady-state saturable absorption at mW-power levels and four-wave mixing with first-order efficiencies as large as 2% of the incoming light are demonstrated on a 1μm slab. On CuBr microcrystallites embedded in glass we investigate the changes of the exciton absorption caused by many-exciton effects both at cryo and room temperature. In contrast to bulk semiconductors, we observe a blue shift of the exciton peak at resonant optical excitation. In addition, strong saturation of absorption with very large contrast shows up. We find Lorentzian saturation intensities in the 100 kW/cm2 range.
TL;DR: In this paper, a pulsed laser operating in the range 680-800 nm was used for wave mixing and stimulated processes in pure potassium and mixed sodium-potassium vapors.
Abstract: We report observations of several wave-mixing and stimulated processes in pure potassium and mixed sodium-potassium vapors which are excited by a pulsed laser operating in the range 680–800 nm. When the laser is tuned to the potassium two-photon 4S→6S transition, we observe stimulated emission on the various cascade transitions as well as four- and six-wave mixing. When the laser is tuned over the range 747 to 753 nm, which is well away from all atomic transitions, we observe strong forward and weak backward emission at the potassium 3D3/2→4P1/2 transition wavelength (1.17 μm). However, this latter emission is only observed in the mixed sodium-potassium vapor. We present data on the excitation spectrum, forward to backward asymmetry, temporal dependence, and the laser power dependence of this emission. We speculate that twophoton photodissociation of the NaK molecule is responsible for this emission.
TL;DR: In this article, the authors discuss the use of laser light to study the dynamics of chemical reactions, to stimulate chemical reactions and finally to analyze substance and the unique properties of the laser light (high power, monochromaticity, short duration, directivity and temporal coherence) provide quite new instrumental possibilities in all these problems.
Abstract: Many methods and achievements in chemistry are based on using the interactive of light with atoms and molecules. It is sufficient to mention photochemistry, flashphotolysis, spectrochemistry and others. The advent of laser amplified the connection between chemistry and light. Today laser light has become a very versatile and effective tool, first, to study the dynamics of chemical reactions, secondly, to stimulate chemical reactions and finally, to analyze substance. The unique properties of laser light (high power, monochromaticity, short duration, directivity and temporal coherence) provide quite new instrumental possibilities in all these problems.
TL;DR: In this paper, the generation of tunable vacuum ultraviolet radiation by anti-Stokes Raman scattering of ultraviolet dye-laser radiation in cold hydrogen has been investigated and the scattering efficiency of XeCl laser and Nd:YAG laser pumped commercial dye lasers and the influence of different beam profiles has been studied.
Abstract: The generation of tunable vacuum ultraviolet radiation by anti-Stokes Raman scattering of tunable ultraviolet dye-laser radiation in cold hydrogen has been investigated. The scattering efficiency of XeCl laser and Nd:YAG laser pumped commercial dye lasers and the influence of different beam profiles has been studied. Up to 12 anti-Stokes orders down to 129 nm were observed with output powers between about 20 kW at λ=191 nm and somewhat less than 100 W at λ=129 nm. The efficiency of transversely pumped lasers with an intensity peaked in the center of the beam profile was found to be higher than doughnut shaped intensity distributions. The cooling of the active gas to liquid nitrogen temperatures improved the output pulse energies 3 to 5 times on average. It was found that this intensity increase was caused mainly by the narrowing of the Raman linewidth upon cooling.
TL;DR: In this article, a steady-state, chemiluminescence technique has been used to measure effective rate constants for vibrational relaxation as a function of vibrational level for KrF* in collisions with He, Ne, and Ar and XeCl* with Ar.
Abstract: A steady-state, chemiluminescence technique has been used to measure effective rate constants for vibrational relaxation as a function of vibrational level for KrF* in collisions with He, Ne, and Ar and XeCl* with Ar. The effective rate constants reported include contributions to relaxation due to intersystem crossing between theB andC states, in addition to direct relaxation within theB state. The relevance of these results to the understanding of previous measurements in KrF and XeCl lasers is discussed.
TL;DR: In this article, the currentvoltage characteristics of a gas field ion source (GFIS) have been measured for hydrogen and all rare gases, and the maximum currents in a GFIS have been found to a few 100 nA.
Abstract: Current-voltage characteristics of a gas field ion source (GFIS) have been measured for hydrogen and all rare gases. The parameter set included tip temperature, tip radius and gas temperature and pressure. This investigation has been made to get a complete overview of the field ion currents (FIC) and to estimate the maximum currents in a GFIS, which have been found to a few 100 nA. This estimate allows also a feasibility study of a GFIS, modified by a supertip, a small protuberance on the emitter surface.
TL;DR: The reliability and numerical stability of the model calculations depend on the way in which the collision terms of the Boltzmann equation and the e-HCl collision rates are evaluated as mentioned in this paper.
Abstract: Measurements of current, voltage, and laser emission of an X-ray preionized selfsustained XeCl* laser discharge using Ne:Xe:HCl gas mixtures are compared with predictions of spatially homogeneous model calculations. As a prerequisite an accurate and detailed model of the electrical circuit is developed. For current and voltage measurements electro-optical methods are used. Corrections to the measurements and the reliability of the final data are discussed in detail. Using collision cross sections from the recent literature and stepwise vibrational excitation of HCl up tov=3 reproduces the electrical conductivities measured in a large field of parameters. The reliability and numerical stability of the model calculations depend on the way in which the e-HCl collision terms of the Boltzmann equation and the e-HCl collision rates are evaluated. The predicted total laser pulse energies are too small, but the shape and timing of the pulse correspond to the experimental values.
TL;DR: In this article, the infrared emission spectrum of the plume produced by KrF excimer laser ablation of polyimide films in air and in He was measured in the 680 to 1580 cm−1 wavenumber range.
Abstract: The infrared emission spectrum of the plume produced by KrF excimer laser ablation of polyimide films in air and in He was measured in the 680 to 1580 cm−1 wavenumber range. Using 400 mJ/cm2 laser pulses of 248 nm and 35 ns duration yielded a strong emission band characteristic of thev2 transitions of hot HCN molecules. Band counters calculations were carried out of thev2 emission expected from HCN in thermal equilibrium at various temperatures. They indicate that except for a slight deviation of the measured data from thermal equilibrium, the best fit of the observed results is obtained at a plume temperature of 2250±150K.
TL;DR: In this paper, a table-top excimer laser system was used to irradiate solid targets at intensities of up to 4×1015 W/cm2, where the X-ray conversion efficiencies were between 1-5%.
Abstract: A table-top excimer laser system generating sub-ps pulses was used to irradiate solid targets at intensities of up to 4×1015 W/cm2. Soft X-ray spectra of various materials were measured. The X-ray conversion efficiencies were between 1–5%. Streak camera measurements showed instrument-limited X-ray pulse duration of a few ps.
TL;DR: In this paper, the photoablation of polystyrene (PS) and polymethylmethacrylate (PMMA) was studied in real-time during the uv laser pulse at 193 nm.
Abstract: The photoablation of polystyrene (PS) and polymethylmethacrylate (PMMA) was studied in real-time during the uv laser pulse at 193 nm. The transmission and total reflection of thin polymer layers on quartz glass substrates was measured time-resolved. From the results for the strongly absorbing PS it can be concluded that the emission of material starts within the first few nanoseconds of the laser pulse. Photoablation of PMMA, which is a relatively weak absorber at 193 nm, is accompanied by strong modifications of the transmission by the first several ten laser pulses.
ENEA1
TL;DR: In this paper, the spectral and time dependence of the luminescence emitted by fragments after the multiple-photon decomposition of silane was studied and compared with previous results and interpretations.
Abstract: A systematic study of spectral and time dependence of the luminescence emitted by fragments after ir multiple-photon decomposition of silane, is presented. Data obtained at various silane pressure (1–35 Torr) and pulsed CO2 laser fluences are discussed and compared with previous results and interpretations.
TL;DR: In this article, the pulses from a colliding-pulse mode-locked dye laser (100 fs, 20 pJ) are amplified to 0.2 mJ and self-phase modulated in an excimer laser pumped dye amplifier.
Abstract: The pulses from a colliding-pulse mode-locked dye laser (100 fs, 20 pJ) are amplified to 0.2 mJ and self phase modulated in an excimer laser pumped dye amplifier. Suitable chirp compensation leads to nearly bandwidth-limited pulses of about 50 fs duration.