Search

In this work, a novel diagnostic technique for carbon monoxide (CO) number density measurements in a nitrogen buffer mixture at elevated pressures up to 5 bar was developed and tested. The technique utilizes 2 + 1 resonance enhanced multi-photon ionization (REMPI) of CO induced by a femtosecond laser pulse at 230.1 nm, followed by detection of the number of REMPI-induced electrons using the microwave scattering (MS) method (REMPI-MS technique). Dependences of the number of REMPI-generated electrons on CO number density and laser energy were measured and analyzed in conjunction with a four energy level model of the CO molecule. The number of REMPI-induced electrons scaled linearly with CO number density up to about 5 × 1018 cm−3 and was independent of the buffer gas pressure up to 5 bar. Higher CO number densities caused saturation onset associated with laser beam energy loss while travelling through the gaseous mixture due to two-photon absorption and photoionization. The number of REMPI-induced electrons was found to scale cubically with the laser pulse energy for the tested energy range of 8–20 μJ (intensity in the focal region about 7–18 GW/cm2), which is consistent with the operation regime where the number density of excited CO molecules increases throughout the laser pulse duration and does not saturate in time. The linear scaling region of the REMPI-MS signal can be used for a CO number density diagnostic after appropriate calibration of the system.

Intracavity optogalvanic detection of 14C utilizes the narrow band specificity of 14CO2 laser resonances in the infrared spectrum, coupled with greatly enhanced sensitivity from amplified effective path lengths in optical cavities. Background (nonresonant) interactions are also enhanced in such cavities, making proper separation of signals from background imperative. Intracavity Optogalvanic Spectroscopy (ICOGS) is similar to cavity ring-down spectroscopy (CRDS) with certain crucial differences. An ICOGS model, based on a basic CO2 laser and optogalvanic effect physics, is presented. Experimental results using a laboratory instrument with a continuous flow of small CO2 samples in a buffer gas illustrate the model. It is shown that acquisition of optimized signal-to-background ratios for the quantitation of 14CO2 in samples of order 10 μg is achievable, considerably smaller than with CRDS.

This paper presents a detailed model of cluster formation from a supersaturated atomic vapor in an inert buffer gas. The population balance equations for the cluster size distribution are based on the Smoluchowski coagulation equation and take into account (i) convective diffusion of clusters, (ii) cluster loss to walls of an aggregation chamber, and (iii) formation of fractal-like aggregates. The model predictions are confronted to experimental observations, and they agree with experimental data on Cu particle formation in NC200-UHV nanocluster source. The model can be used as an aid in tuning the experimental parameters for attaining a desired nanoparticle size distribution.

Electron density measurements have been made in steady-state plasmas in a spherical inertial electrostatic confinement (IEC) discharge using microwave interferometry. Plasma cores interior to two cathodes, having diameters of 15 and 23 cm, respectively, were probed over a transverse range of 10 cm with a spatial resolution of about 1.4 cm for buffer gas pressures from 0.2 to 6 Pa in argon and deuterium. The transverse profiles are generally flat, in some cases with eccentric symmetric minima, and give mean densities of from approx. = 0.4 to 7x 10(exp 10)/cu cm, the density generally increasing with the neutral gas pressure. Numerical solutions of the 1-D Poisson equation for EC plasmas are reviewed and energy distribution functions are identified which give flat transverse profiles. These functions are used with the plasma approximation to obtain solutions which also give densities consistent with the measurements, and a double potential well solution is obtained which has minima qualitatively similar to those observed. Explicit consideration is given to the compatibility of the solutions interior and exterior to the cathode, and to grid transparency. Deuterium fusion neutron emission rates were also measured and found to be isotropic, to within the measurement error, over two simultaneous directions. Anisotropy was observed in residual emissions during operation with non-fusing hydrogen-1. The deuterium rates are consistent with predictions from the model.

Laser operation on the Au-II 282.3 nm ultraviolet transition is obtained using a high-voltage segmented hollow-cathode discharge tube. The metal vapor is produced by means of cathode sputtering. A small amount of argon is added to the helium buffer gas in order to achieve higher sputtering yield. Measurements of the laser power and small signal gain indicate that the optimal partial concentration of argon is in the range of 0.25%–0.75%. Quasi-continuous wave output power of 100 mW is obtained from a 34-cm-long active region while the highest small-signal gain is 52% m−1. To explain the basic features of the laser operation we present a model of the segmented hollow-cathode discharge. All the discharge characteristics are calculated in a self-consistent way except the temperature of slow electrons. The trajectories of fast electrons emitted from the cathode are followed by Monte Carlo simulation. Rate equations of ion, metastable and metal atom densities are solved in the negative glow, while another Monte...

We have studied, both experimentally and numerically, the radiometric efficiency of low-pressure barium–argon positive column discharges. Using a 14 mm inner diameter alumina discharge tube to reduce chemical reactivity, we have operated discharges with Ba vapor pressures corresponding to a range of oven temperatures from 600 to 800 °C, Ar buffer gas pressures of 0.5 and 5 Torr, and currents of 100–800 mA. The spectral power distribution has been determined by examining the visible radiation emitted perpendicular to the discharge axis from a small aperture in the side of the alumina discharge tube. Absolute emitted powers were determined by comparison to a calibrated tungsten–quartz–halogen lamp. The measured efficiencies for production of visible radiation from the positive column ranged from 2.5% to 52%. These efficiencies correspond to luminous efficacies ranging from 6 to 97 lm/W. Strong emission on Ba ion lines at 455.4, 493.4, 614.2, and 649.7 nm contributed significantly to the best efficiency, 52%, and yielded a white light. A numerical model, incorporating a substantial number of excited levels and atomic processes, has been used to examine the same conditions. The model reproduces most of the major experimental trends.

We report the results of an experimental and theoretical study on the feasibility of a barium low pressure discharge as a potential new light source. Barium has a strong neutral resonance line at 553.5 nm, near the center of the eye’s response curve, as well as several red and blue lines from barium ions. Due to the strong reactivity of barium with a wide variety of standard lamp materials, experiments were performed in arc tubes lined with yttria (Y2O3). A wide range of parameter space was explored in buffer gas pressure (1–30 Torr), gas type (argon, neon, and krypton), barium temperature (400–760 °C), and arc current (0.05–1.0 A). The numerical model qualitatively predicted the influence of these parameters on light output. However, the predicted efficacies of up to 100 lm/W were considerably higher than the measured values. The best positive column efficacy achieved was 50 lm/W in a sealed yttria lined quartz tube with 5 Torr argon operating at 400 mA at 760 °C. Possible reasons for this discrepancy ar...

A two-dimensional model has been used to understand the physics and process engineering issues associated with a conceptual 300 mm Cu internal-coil ionized physical vapor deposition reactor. It has been found that inductive coupling from the coil is the primary source of plasma production. Since the coil is in direct contact with the plasma, a significant fraction of the coil power is deposited in the gas capacitively as well. This results in sputtering of the Cu coil, which tends to improve Cu flux uniformity at the outer edges of the wafer. Since the Cu ionization threshold is much lower than Ar, Cu+ density is comparable to Ar+ density even though ground state Cu density is much smaller than Ar. Significant fraction of the neutral Cu flux to the wafer is in the metastable or athermal state. The effects of several actuators, reactor dimensions, and buffer gas on important plasma and process quantities have also been investigated. Electron density in the reactor and Cu ionization fraction increases with ...

The dynamics of debris in a buffer gas after ejection from the solid target during laser–plasma soft x-ray generation is studied. Analytical formulas for the flight range of cylindrical and spherical debris are derived using the incompressible flow theory. The validity range of the formulas and the related error margins are discussed. Finally, the flight range formula for spherical particles is extended to two times the Mach number at the expenses of a somewhat higher error margin (up to 25%).

Ionized metal physical vapor deposition (IMPVD) is a process in which sputtered metal atoms from a magnetron target are ionized by a secondary plasma before depositing onto the substrate. The sputtered metal atoms and neutralized ions reflected from the target have higher kinetic energies than the buffer gas and so are not in thermal equilibrium. These nonthermal (inflight) species can dominate the total metal species density at low pressures (

The decay rate of the Hg 61P1 level was measured as a function of cold spot temperature (Hg density) and buffer gas pressure in cylindrical, sealed fused silica cells. The decay rates were obtained using a time-resolved laser-induced 185 nm fluorescence experiment with multi-step excitation. Cold spot temperatures from 25 to 100 °C were studied. The Hg densities for this temperature range and with no buffer gas yield the lowest possible decay rates due to radiation trapping with partial frequency redistribution. Decay rates with argon buffer gas pressures of 3 and 30 Torr were also studied. The results are in agreement with published data from a discharge afterglow experiment. Monte Carlo simulations of radiation transport in the cells, including the effects of hyperfine and isotope structure, the effects of foreign gas broadening, and partial frequency redistribution are compared to the experimental data. Reasonably good agreement is obtained, however there is evidence of quenching of Hg 61P1 atoms in co...

The operation of a metal–vapor buffer-gas hollow cathode discharge is re-examined using modeling techniques that have been developed for electronegative plasma discharges. It is shown that a previously developed global model can be extended to give spatially resolved densities as well as more accurate values for the plasma parameters. A numerical calculation for a neon–copper (Ne–Cu) discharge is used to illustrate the results of the modeling technique. The density profiles of the neutral and ion components, and their variation with the buffer gas pressure, are similar to those found by numerical solution of the complete equations.

Strong stimulated cascade emission and coherent four‐wave parametric radiations are observed. By proper observation of the excitation spectra, the cascade emission and the coherent four‐wave mixing parametric processes can be identified. The effect of the buffer gas pressure on the intensity and the pulse compression of the emitted radiation were investigated. Cascade inversionless coherent radiation emission with absorption reduction and third order nonlinear susceptibility enhancement due to the presence of a strong internally generated field are discussed for the 4p–4s strong emission observed.

The generation of excimer radiation in mixtures of the rare‐gases Kr or Xe together with chlorine gas has been investigated by a dielectric barrier discharge. The characteristics of the emission spectra of the excimers formed, centered around 222 and 308 nm, were obtained for different gas mixtures and total gas pressures using an ultraviolet (UV) monochromator. The influence of the gas mixture, chlorine gas concentration, total gas pressure, and buffer gas dependence of the UV intensity has been investigated using chemical actinometry. Conversion efficiencies (from input electrical to output optical energy) as high as 15% can be achieved under optimal conditions. This low‐cost and high‐power excimer lamp system can provide an interesting alternative to conventional UV lamps for industrial large‐scale UV processes.

This investigation focuses on low‐pressure S2 molecular rf discharges for use as diffuse radiators. Cylindrical fused silica S2–Ar and S2–Ne lamps have been tested at 13.56 MHz and the absolute radiative efficiencies have been measured. The radiation is emitted primarily between 2800 and 3500 A. The UV radiative efficiencies were studied as a function of input power, buffer gas pressure, discharge radius, and applied external cooling. The maximum observed efficiency for a low power density, diffuse rf discharge is 7%. The measured UV efficiencies of the 13.56 MHz discharges are somewhat lower than those of low‐pressure S2–Ar dc discharges. A reentrant lamp design has been tested as well and no improvements in efficiency were observed.

The dc positive column sulfur (S) and S–Ar discharges have been studied over a wide range of operating conditions. Even though the equilibrium partial pressure of S2 is low in the 50 °C–200 °C temperature range investigated here, the primary radiating molecule in these discharges is S2. Electronic collisions dissociate S8 to produce the radiating S2 molecules at densities far in excess of the equilibrium density. The majority of the spectral emission occurs in the 2800–3500 A range. The spectrum observed from these discharges corresponds nicely to that obtained from dc discharges at much higher temperatures. The radiation output has been studied as a function of input power, wall temperature, buffer gas pressure, discharge radius, and cold spot temperature. The absolute efficiency of the discharge in generating near‐ultraviolet radiation has been measured and the results are presented for many areas of the multidimensional parameter space. The maximum efficiency of ultraviolet and visible emission obtaine...

The hot restrike is one of the biggest challenges in operating ceramic metal halide lamps with mercury as buffer gas. Compared to a cold lamp, the pressure within a ceramic burner is two orders of magnitude higher during steady state operation due to the high temperature of the ceramic tube and the resulting high mercury vapour pressure. Room temperature conditions are achieved after 300 s of cooling down in a commercial burner, enclosed in an evacuated outer bulb. At the beginning of the cooling down, ignition voltage rises up to more than 14 kV. A significant reduction of the hot-restrike voltage can be achieved by using a so called active antenna. It is realized by a conductive sleeve surrounding the burner at the capillary of the upper electrode. The antenna is connected to the lower electrode of the lamp, so that its potential is extended to the vicinity of the upper electrode. An increased electric field in front of the upper electrode is induced, when an ignition pulse is applied to the lamp electr...

Replicas of a mask are etched in Si wafers with a micrometer lateral resolution and typical depths of 200 nm by irradiation with filtered synchrotron radiation using cutoff wavelengths of 105, 122, and 150 nm. An excellent selectivity and anisotropy is obtained by suppressing the spontaneous etching of the XeF2 etch gas (typical 10−2 mbar) with O2 or Ar buffer gas (typical 1 mbar). The efficiency of etching increases by more than two orders of magnitude by reducing the wavelength from longer than 150 nm to the spectral range of 105–122 nm. The number of removed Si atoms per incident photon reaches a value above unity for the short wavelengths. This very high quantum efficiency, which exceeds that in the visible spectral range by more than four orders of magnitude, is attributed to selective electronic excitation of a thin fluorosilyl layer on top of the Si wafer. The low probability of absorption in this layer implies a reaction efficiency far above unity.

Nickel tetracarbonyl [Ni(CO)4] molecules were used as a probe to investigate the coverage of a heated polycrystalline nickel surface with nitrogen adspecies. For this purpose, the deposition kinetics of nickel (Ni) microstructures from the thermal decomposition of nickel tetracarbonyl was investigated as a function of the partial pressure of nitrogen (N2), used as buffer gas. The laser‐induced chemical vapor deposition technique was used to produce polycrystalline nickel lines in an atmosphere of pure Ni(CO)4 or a [Ni(CO)4+N2] mixture. The deposition process was performed on polysilicon/silicon dioxide/〈100〉 monosilicon substrates. As a heat source, a cw argon‐ion laser was used. The laser‐induced surface temperature was varied in the range 500–850 °C. For Ni(CO)4 partial pressures typically below 0.3 mbar, the nickel deposition rate was found to decrease as the N2 partial pressure increases. For higher Ni(CO)4 partial pressures, the deposition rate was found to be independent of the N2 partial pressure. ...

Addition of helium to an Ar/Xe gas mixture has been shown to significantly improve the fission‐fragment excited 1.73 μm atomic xenon laser performance. Using narrow band dielectric laser cavity mirrors to suppress the 2.03 μm atomic xenon transition, the 1.73 μm laser power efficiency varied between 1% and 3% for total pressures of 520–1550 Torr, He/Ar ratios of 3/1–16/1, and pump rates of 5–40 W/cm3. For a constant energy loading, the FWHM of the laser pulse with respect to the pump pulse increased by a factor of 2.5 when argon was replaced by helium. Small signal gain varied between 0.1%/cm and 1.0%/cm. The implication of helium substitution on the Ar/Xe laser kinetics is discussed.

Polarization Raman microprobe spectroscopy is used to study crystalline silicon heated to the melting point by a tightly focused cw laser beam, which is either fixed or scanned across the surface. By examining optical phonons in solid silicon, the real‐time Raman spectrum monitors the progress of silicon flow during melting and the trench depth during melt‐assisted etching. Raman peaks lie between 482 cm−1, which is the Raman shift for silicon uniformly heated to the melting point (1690 K), and ∼510 cm−1, which is the Raman shift for c‐Si heated just to the melting point and probed by the same beam. During laser melting with a static laser, the Raman spectrum of scattered light with z(x,y)z polarization has two peaks, while the z(x,x)z spectrum has one peak. This shows that at the beginning of melting in vacuum by a static laser there is a central region with solid silicon floating in the melt, which is surrounded by hot solid material. Because of the flow of the molten semiconductor, the temperature profile changes, causing the Raman spectrum to change rapidly. Laser melting of c‐Ge and thin films of silicon in vacuum is also studied, as is the melting of c‐Si by a static laser in the presence of an inert buffer gas. The presence of an inert buffer is shown to affect the temperature profile very strongly during melting and also during laser heating at lower laser powers when no melting occurs. During scanned laser melting and etching, the Raman spectrum has a single peak using either polarization configuration. Raman analysis during melting of silicon by a scanning laser shows that the average temperature in the probed region is much higher when there is a gas‐phase argon buffer present (and no etching) than when there is an etching mixture of argon/chlorine gas (and etching). Along with these real‐time Raman measurements, the reflection of the incident laser was monitored, and post‐process Raman analysis and profilometry were also performed to characterize surface changes due to melting and etching.

The results of a parametric study of a copper hollow anode cathode laser operating on the He‐Cu+ infrared lines are reported. The discharge voltage, the small‐signal unsaturated gain on the 780.8‐nm transition, and the ground‐state copper atom concentration each exhibit a universal dependence on the ratio J/p of the discharge current density to the total pressure of the helium‐argon buffer gas mixture. The laser output power dependencies (780.8 and 782.5 nm) on J/p, while not resulting in universal curves, have common threshold values of J/p. The threshold value of J/p for the 782.5‐nm line is approximately twice that for the 780.8‐nm line.

A theoretical study investigating the effect of superfluorescent emission on the operation of an optically pumped CF4 laser is reported. The coupled space‐ and time‐dependent rate equations for the molecular population densities and the photon fluxes have been numerically solved to study the dependence of the superfluorescent emission contents in the CF4‐laser output on the various laser parameters such as the temperature, pressure, pumping rate, and the feedback factors. We have studied the effect of the temporal shape of the CO2 pump pulse on the superfluorescent emission and the laser‐pulse energies. Our calculations indicate that a considerable reduction in the superfluorescent emission is possible by shaping the pump CO2‐laser pulse and by choosing the laser operating parameters appropriately. We have also investigated the effect of the addition of buffer gas on the superfluorescent emission and laser emission.

A two‐dimensional, time‐dependent model has been developed to determine the coupled fluid dynamic and charged particle transport behavior of a flowing gas, nuclear pumped laser cavity. Stationary results are presented for a typical cavity that uses a flowing He buffer gas pumped with charged particles produced by the 10B(n,α)7Li reaction. The boron is coated on fuel plates mounted parallel to the flow direction. The effects of changing the buffer gas inlet flow velocity and outlet pressure are investigated. For a fixed inlet velocity, the results presented show that the gradients of the charged particle energy deposition and density increase in magnitude primarily in the direction perpendicular to the gas flow, i.e., normal to the fuel plates, as the outlet pressure is increased. With increasing inlet velocity and a fixed outlet pressure, the density variations decrease, whereas the variations in energy deposition increase in the direction perpendicular to the flow and decrease in the direction parallel t...

The output characteristics of an optically pumped titanium vapor laser on various buffer gas species and pressures have been measured, and the role of buffer gas on the laser output is accordingly discussed. He, Ne, Ar, and Kr are used as buffer gases. The optimum condition for the maximum output energy is 4 Torr of He with 10 μs delay time.

Anomalous optogalvanic line shapes were observed in a commercial hollow cathode lamp containing argon buffer gas. Deviations from Gaussian line shapes were particularly strong for transitions originating from the 3P2 metastable level of argon. The anomalous line shapes can be described reasonably well by the assumption that two regions in the discharge are excited simultaneously, each giving rise to a purely Gaussian line shape, but with different polarities, amplitudes, and linewidths.

Using He, Ne, and Ar buffer gases, lasing performances of a compact Blumlein‐type XeBr laser at 282 nm have been studied. The maximum energy of 0.64 mJ and the maximum power of 190 kW have been obtained with 4‐atm Xe/HBr/Ne mixture. He‐based mixture has been inferior to Ne‐based mixture both in the output energy and in the gas lifetime. Atmospheric‐pressure operation has been possible only by an Ar buffer gas. These buffer‐gas dependences have been similar to those of XeCl lasers.

A model is developed for self-consistently calculating the gas temperature in a direct current argon glow discharge, used for analytical spectroscopy. The power input into the argon gas due to elastic (i.e., kinetic energy transfer) collisions of Ar+ ions, and fast Ar atoms, sputtered Cu atoms and electrons with the argon gas atoms is calculated with Monte Carlo models. This power input is used in a heat transfer model to calculate the gas temperature. The amount of power input, the contributions of the various input sources, and the resulting gas temperature are calculated for a wide range of voltages, pressures, and currents, typically applied in analytical spectroscopy. It is found that the temperature can increase significantly at high voltages, pressures, and currents (up to a factor of 3 compared to absolute room temperature).

An XeCl excimer laser was operated at the high repetition rate of 2.5 kHz, which can circulate the laser gas uniformly and efficiently. The characteristics of the gas flow rate and the average laser power versus the repetition rate were investigated in both He and Ne buffer gas mixtures. In He buffer gas, the average laser power saturates at 1.3 kHz and, thereafter, drops abruptly. On the other hand, stable operation at the highest repetition rate, 2.5 kHz, has been attained in Ne buffer at a gas flow rate of 54 m/s with an average laser power of 87 W.

Ti vapor is produced in a He buffer gas. Ti metal is irradiated by a pulsed YAG laser, and its vapor is optically pumped by a N2 laser at 337 nm. Laser lines at 551.4, 472.3, and 471.0 nm from the Ti 3D01 level which is connected to the ground state by the 337‐nm resonance line. Laser lines are reported for the first time at 551.5, 551.3, 431.5, and 547.4 nm from the 3D02, 3D03, or 3G05 levels which are not optically connected to the ground state by the 337 nm line. The laser transitions from the 3D02, 3D03, or 3G05 levels are observed only in a He‐Ti mixture.

The stopping power of a buffer gas against laser-plasma debris is quantitatively assessed by means of visualization techniques. For ablation of planar tin targets in an Ar ambient, an expanding wavefront was visualized, whose translation energy was rapidly reduced within a few millimeters above the target surface. The fastest debris component was along the normal to the target with an initial kinetic energy of 1.1 keV. The buffer gas efficiency changed in a line-of-sight-dependent way, thermalizing more efficiently the on-axis components. The maximum stopping power of the gas buffer was determined as high as 0.4 keV/mm. Due to the reduction in stopping power, nonlinearly with the debris kinetic energy, a gas buffer thickness of 10 mm is required at the studied atmospheric pressure in order to mitigate high energy debris below a fiducial threshold of 0.1 keV.

Antirelaxation surface coatings allow long spin relaxation times in alkali-metal cells without buffer gas, enabling faster diffusion of the alkali atoms throughout the cell and giving larger signals due to narrower optical linewidths. Effective coatings were previously unavailable for operation at temperatures above 80 C. We demonstrate that octadecyltrichlorosilane (OTS) can allow potassium or rubidium atoms to experience hundreds of collisions with the cell surface before depolarizing, and that an OTS coating remains effective up to about 170 C for both potassium and rubidium. We consider the experimental concerns of operating without buffer gas and with minimal quenching gas at high vapor density, studying the stricter need for effective quenching of excited atoms and deriving the optical rotation signal shape for atoms with resolved hyperfine structure in the spin-temperature regime. As an example of a high-temperature application of antirelaxation coated alkali vapor cells, we operate a spin-exchange relaxation-free atomic magnetometer with sensitivity of 6 fT/sqrt(Hz) and magnetic linewidth as narrow as 2 Hz., Comment: 8 pages, 5 figures. The following article appeared in Journal of Applied Physics and may be found at http://link.aip.org/link/?jap/106/114905

The electrical characteristics (voltage, electric field, charged particle densities, dissipated power, particle energy, etc.) are analyzed in the case of low pressure (0.5 and 1 Torr) radio-frequency (rf) discharges in nitrous oxide (N2O)/Helium (He) mixtures. An optimized and validated particle model has been used for these analyses in the case of gradual dilutions of N2O with He buffer gas. A specific care is carried on the power density evolution and variation which show a complex behavior as a function of He proportion (up to 85%). These analyses are based on a microscopic approach enabling one to show the contribution of the different inelastic processes mainly between electrons and respectively N2O and He gases. This approach enables also one to show the discharge region (the positive column or the plasma region) where the power is preferentially dissipated. The power density variation is found to be mainly proportional to the electron density variation. The latter is dependent on the different proc...

The production of hyperpolarized gases by spin-exchange optical pumping (SEOP) requires exact knowledge of the alkali metal’s D1 absorption profile and the degree to which it is broadened and shifted by varying buffer gas composition and pressure. We have measured these parameters for cesium (Cs) in the presence of Xe, N2, and H4e perturber gases at densities up to 10 amagats. The effects of these gases are important as Cs is attracting increasing interest for SEOP applications. Our measurements were made using simple white-light illumination of the Cs vapor while characterizing the D1 (6S1/2 to 6P1/2) and D2 (6S1/2 to 6P3/2) resonances using a high-resolution optical spectrometer. For the Cs D1 resonance at T=120 °C, we report shifts from the 894.59 nm vacuum wavelength caused by H3e, H4e, N2, and Xe of −0.017±0.003, −0.013±0.002, 0.026±0.002, and 0.029±0.002 nm/amagat. We also report the shifts for the D2 resonance as well as pressure broadening coefficients for both resonances.

One of the serious problems in the laser-produced plasma for an extreme ultraviolet (EUV) light source used for the next generation lithography is the generation of fast ions that damage the EUV collector optics. In this study, the mitigation of fast ions from a laser-produced Sn plasma by a H2 background gas was investigated. It has been confirmed that H2 buffer gas at a pressure of 13.3Pa has little influence on the transmission of 13.5nm light with an optical path length of 200mm. The sputtering of a dummy mirror by the fast ions generated from the laser-produced Sn plasma and their mitigation were investigated by visualizing the spatial distributions of sputtered atoms using the laser-induced fluorescence (LIF) imaging method. It was evaluated that the sputtering rate by the fast ions was reduced to less than approximately 5% by H2 gas with a column density of 1.2×1021l∕m2. The dynamics and the chemical reaction of the plasma plume containing the high energy and high density ions in a H2 background ga...

The excitation mechanism of buffer gas in the laser-ablation process was investigated by time- and space-resolved emission spectroscopies. A silicon disk was ablated in neon gas at a pressure of 1 torr by the fundamental beam output of a Nd: yttrium aluminum garnet laser (1064 nm). The time-resolved emission spectra showed the generation of excited silicon ions Sin+*(n=1−3) and excited neon neutrals Ne* to the 2p1 level immediately after laser irradiation. Excitation of Ne to the 2pn(n=2−10) levels was delayed by 150 ns. The temporal evolutions of the space-resolved emission from Ne* indicated excitation by fast (

The performance of externally controlled, high‐pressure, diffuse discharges as switching elements in pulse power systems is strongly determined by the recombination and attachment processes in the fill gas. To obtain high control efficiency and fast response of the diffuse discharge switch the discharge must be attachment dominated with the attachment rate coefficient increasing with field strength. An electron‐beam controlled diffuse discharge system was constructed to study the behavior of pulsed discharges in the submicrosecond range in gas mixtures containing N2 as a buffer gas and small additives of electronegative gases. The results of experiments in N2 plus N2O were compared with values obtained with a Monte Carlo code and a rate equation calculation.

The parametric dependence of the output energies and efficiencies for the Raman conversion of the radiation from a long‐pulse 1‐J XeCl excimer laser in Pb vapor was investigated. The effects of atom depletion and buffer gas on the stimulated Raman scattering output were discussed in detail. Multipeak structures of the waves of the Raman‐shifted pulses were observed which could be attributed to the coherent effects in Raman scattering. A computer model was introduced to explain the multipeak structures of the stimulated Raman scattering waveforms.

The time evolution of ground‐ and metastable‐state copper atom concentrations and the laser energy in a bust‐mode CuBr laser were measured as a function of temperature, buffer gas species, and repetition rate within the burst. The concentrations were measured by monitoring the absorption of the 244.2‐ and 510.6‐nm atomic copper lines. The optimum time separations of the electrical pulses within the burst were found to be 80 and 235 μ for helium and argon buffer gases, respectively. A correlation was found between the time dependences of the laser energy and ground‐state density within the burst. Accumulation was found to occur in the copper atom ground state but not in the metastable 2D5/2 level.

A uniform electron density is produced by two‐photon ionization of trace trimethylamine in the N2 buffer gas of atmospheric pressure using ArF laser photons. The transient conduction pulses induced by the electron motion between parallel electrodes under various applied electric fields are observed. The duration of the electron transient pulse is shortened when the electron attacher O2, N2O, or CF4 is added to the buffer gas. Electron attachment rate constants are obtained from the ratios of the transient current with and without attachers at various times after the laser pulses. For O2 and N2O, the electron attachment rate constants measured in this experiment agree with previous values measured by different methods. The apparent rate constants for the attachment of low‐energy electrons by CF4 are measured. The electron drift velocity is found to increase when CF4 is added to N2. The present method is applicable for the measurement of the electron attachment rate associated with the production of short‐lived negative ions.

A kinetic model of the sustained discharge Ar/HgBr2 laser is developed from an experimental base. The choice of Ar as the buffer gas is supported by measurements of the specific fluorescence and laser efficiency in the buffer mixtures (Ar, Ar+5% Xe, Ne+10% Xe, Ne+10% N2). A computational treatment of the coupled photon and kinetic equations is described. Gain measurements determine a peak HgBr (B‐X) stimulated emission cross section of 1.6×10−16 cm2±20% at 502 nm. Absorption measurements between 515 and 530 nm show the presence of a large, broad band absorption tentatively assigned to HgBr+2 with a cross section of 2×10−18 cm2. An upper bound of 5×10−9 cm3 sec−1 is placed on the rate constant for electron collisional quenching of the HgBr(B) state. The laser extraction efficiency of 65% is modeled by a lower level collisional deactivation by Ar with a rate constant 6.0×10−12 cm3 sec−1. Discharge impedance is measured as a function of E/N and the ionizing electron beam current density. Using the new data a...

Previous studies of a commerical passive gas cell Rb87 frequency standard showed a strong dependence of the output frequency νRb upon the microwave power Pμλ. A major conclusion of that work was that the dependence of νRb upon Pμλ was due to a line inhomogeneity effect. The line inhomogeneity interpretation suggested that substituting a wall coating for the usual buffer gas would reduce the dependence upon Pμλ. As a part of the present work, a wall coating (a form of paraffin) was used and a reduction of this dependence by a factor of 100 was obtained. The present work has led to a more convincing theoretical demonstration of the line inhomogeneity effect. The paper discusses some of the details of the analytical procedure. There are certain major requirements that a wall coating would have to satisfy if it is to be superior to the usual buffer gas, and these are discussed in the text. The advantages demonstrated by the present work indicate that further studies are warranted to determine if an improved standard could be built based on a wall coating.

Rates of photothermal gold deposition onto alumina substrates heated by a focused argon‐ion laser beam were measured by determining the time required for deposits to grow through the focal spot of a HeNe laser probe beam directed parallel to the substrate. Deposition rates from 0.25 to 6 μm/s were measured for deposits with heights ranging from 5 to 100 μm. Rates of gold deposition using dimethyl gold hexafluoroacetylacetonate as a precursor depend linearly on the gold precursor partial pressure and for a wide variety of conditions do not depend on the laser power or focal spot diameter. A theory is presented to describe reactant mass transfer‐controlled deposition with and without buffer gas. Comparison of measured with calculated growth rates showed that gold deposition rates using dimethyl gold hexafluoroacetylacetonate as a precursor were transport limited for the conditions studied. Theory and experiment also showed that the deposition rate decreases inversely with increasing buffer gas pressure abov...

Studies are reported of stable glow discharges in high‐pressure Hg vapors (?2 amagats) produced by a 20‐nsec ionizing electron beam pulse. The discharges were very stable and operated for 4–5 μsec after the e‐beam initiating pulse at E/N values up to 8×10−17 V cm2 and discharge current densities of 4 A/cm2. Power loadings of 3–6 kW/cm3 were typically obtained. An electron recombination coefficient of 7.4×10−9 cm3 sec−1 was measured. Strong continuum radiation from both the visible (4900 A) and UV (3350 A) bands of molecular Hg were observed. Absorption measurements from 4000 to 6764 A are presented. No gain in this spectral region was ever detected. A peak absorption cross section at 4800 A was estimated to be 2×10−16 cm2. The implication of this absorption on other potential laser systems employing Hg as a buffer gas are discussed.

The rate constants for quenching of metastable He, Ne, Ak, Kr, and Xe by copper atoms have been measured at room temperature and found to be (0.93

The laser output characteristics, such as the pulse width, peak power, pulse energy, and average power of a discharge‐heated copper vapor laser, which has a discharge tube of inner diameter 4.2 cm and length 150 cm, are investigated under such conditions as the charging voltage of 14.5 kV, laser tube temperature of 1450 °C, pulse repetition rate range from 0.5 to 9.5 kHz, and buffer gas pressures of 20 and 75 Torr. Comparing the widths of the laser pulses obtained at the buffer gas of 20 Torr with that obtained at 75 Torr, it is found that the rates of relaxation of metastable atoms at these two buffer gas pressures are comparable, even though the cooling mechanisms of the electrons, the collisional deexcitation partners of metastable atoms, are different. From the dependencies of the pulse energy on the pulse repetition rate, it is found that the prepulse electron density should be higher than the value of 1013 cm−3 for efficient pumping of this laser. The dependencies of the average power on the pulse r...

Recent experiments have demonstrated that the finite rate of vibrational relaxation in the formation of KrF affects the saturation characteristics of the KrF(B) state during extraction of laser light. We have assembled a collisional radiative model using calculated Einstein A coefficients for the lowest twenty KrF states and an approximate calculation of the rate of vibrational energy transfer between KrF and a buffer gas. The model describes the flow of excitation through the vibrational levels of KrF, and demonstrates the effects of vibrational relaxation on KrF(B) saturation and spectra. The results of these calculations agree qualitatively with the published experimental results. In addition, we find that, due to the relaxation kinetics of KrF, Kr2F, a major absorber, is not truly saturable.

An rf wave applied to an optically pumped Na vapor in a high‐density He+N2 buffer gas, situated in a magnetic field gradient, can produce localized bright fringes due to local rf magnetic resonance. We examine in this paper the features of optical pumping in a dense alkali‐helium‐nitrogen vapor mixture, and investigate how such systems can be optimized for use as a simple real‐time rf spectrum analyzer (for broadcast rf waves) with a wide frequency range (dc to several GHz). We derive the optimum values of the optical pumping rate, helium density, sodium density, and nitrogen density which are necessary in order to produce sharp, high‐contrast, and bright fringes, and have accurate and unambiguous rf frequency spectra determinations with fast dynamic response. Samples of observed rf frequency spectra are presented, and the observed spectrum of a sinusoidal FM wave compares satisfactorily with the theoretical spectrum. The observed rf resolution bandwidth is about equal to the optical pumping rate, which is about 1 kHz in this study (rf frequency ∼1 MHz). Similar resolution can be obtained in the microwave range.

We report on the influence of xenon buffer gas on the shape of the self‐reversed Na‐D lines emitted by high‐pressure sodium (HPS) arcs. In a previous paper we have reported experimental results on the collisional broadening of the Na‐D line wings by xenon at high temperatures [M. J. Jongerius, J. Phys. B 20, 3345 (1987)]. These results are used to calculate the relative wavelength positions Δλr and Δλb of the red and blue Na‐D self‐reversal maximum, respectively, as functions of the Na/Hg amalgam temperature. The additional broadening by xenon leads to a strong asymmetry in the shape of the Na‐D emission lines and a distinct maximum in Δλr/Δλb because of the Na‐Xe satellite at 590.9 nm. The presence of this maximum in Δλr/Δλb is confirmed by experiments in which the shape of the Na‐D emission lines is measured as a function of the arc power. The maximum value of Δλr/Δλb can be used as a measure of the xenon pressure in the arc. Furthermore, Δλr and Δλb can be used to obtain values for the sodium and mercu...

The electron‐attachment rate constants of HCl diluted in Ar and N2 were measured as a function of the reduced electric field E/N. These data were converted to the electron‐attachment cross section of HCl using the electron‐energy distribution functions of pure Ar and N2. The dependence of the electron‐attachment rate constant and the mean electron energy on the fraction of HCl in each buffer gas was investigated. A comparison of the current result with both available experimental data and theoretical calculations is made.