Scaling characteristics of the XeF (C→A)excimer laser

The scaling characteristics and medium properties of an injection-controlled XeF(C→A) laser pumped by a 10-ns-high current density electron beam have been investigated. A five-component laser gas mixture, consisting of F₂, NF₃ , Xe, Kr, and Ar was optimized for the scaled laser conditions, resulting in 0.8-J output pulses at 486.8 nm, corresponding to an energy density of small-signal-gain measurements combined with kinetic modeling permitted the characteristics of the dependence of net gain on the electron-beam energy deposition and gas mixture composition, resulting in an improved understanding of XeF(C→A) laser operation     

Injection control of a multipass amplification of a dischargeexcited XeF (C→A) laser

The laser performance and kinetic properties of the broadband C→A transition of the XeF*-exciplex have been studied under discharge excitation. With a pulsed dye laser as the injection source, amplified output pulses with an energy of up to 4 mJ have been obtained in the wavelength range from 450 to 520 nm. Injection of a well-defined seed pulse in an unstable confocal cavity has been developed into a useful technique for identification of subtle kinetic details of the complicated lasing process in XeF*, such as the role of the competitive narrow-band B→X transition or the influence of the various buffer gases     

Injection control of a long-pulse electron-beam pumped XeF (C→A) laser

An XeF (C→A) laser, pumped at a rate of 290 kW/cm³ with a 600-ns electron-beam pulse, has been operated as an injection-controlled oscillator. A stable cavity has been injected with radiation from a pulsed dye laser source. A significant reduction in laser turn-on time has been achieved, and the laser pulse duration has been extended to 500 ns (FWHM). As a consequence, the laser intrinsic efficiency and specific output energy have been increased by approximately 50%, to 1.8% and 3 J/L, respectively, which represent the best performance obtained thus far for any directly electrically excited XeF (C→A) laser. Also, by injecting a narrowband signal into the cavity, the XeF (C→A) laser linewidth has been reduced by more than two orders of magnitude, to less than 1.3 Å, the resolution of the spectrometer. The laser wavelength has been tuned from 478.6 to 486.8 nm, with less than a factor of two variation in output energy     

Characterization of an ultrahigh peak powerXeF(C→A) excimer laser system

The gain characteristics of an electron-beam pumped XeF(C→A) excimer amplifier operating in the blue-green spectral region were investigated for several laser pulse lengths. Saturation energy densities of 50 and 80 mJ/cm² were measured for injected laser pulse durations of 250 fs and ~100 ps, respectively. A gain bandwidth of 60 nm was observed with ~100-ps pulse injection. Using an optimized unstable resonator design, the laser amplifier has produced 275-mJ pulses with a pulse duration of 250 fs and a 2.5 times diffraction-limited beam quality, making the XeF(C→A) amplifier the first compact laser system in the visible spectral region to reach peak powers at the terawatt level     

Kinetic processes in electron beam-excited XeF (C40aA) laser media

Fundamental processes affecting the operation and performance of electron beam-excited XeF(C→A) laser media have been analyzed and modeled. Emphasis has been placed on conditions typical of high current density (~250A cm^-2), short pulse (~10 ns FWHM) e-beam excitation of high pressure (~6 atm) multicomponent mixtures comprised of Ar-Kr-Xe-NF₃-F₂ . Computation of the temporal evolution of excited and ionized species for such circumstances has permitted identification of the factors controlling XeF(C) formation and loss, and has resulted in the identification of the primary transient species that absorb radiation in the blue-green spectral region. The data so obtained serve to explain measured XeF(C→A) properties, particularly net gain, under conditions for which the C→ A laser energy density and efficiency values are comparable to those of the UV XeF(B→X) laser     

Performance characteristics of an injection-controlledelectron-beam pumped XeF(C→A) laser system

Characteristics of an injection-controlled electron-beam pumped XeF(C→A) laser are investigated with emphasis on efficient wideband tuning and scaling issues. Using a quasi-CW dye laser as an injection source, data are obtained that describe the laser characteristics over a wide parameter range. A high-Z electron-beam backscattering reflector inside the laser reaction cell improved the electron-beam energy deposition by 40%, resulting in an increase of the amplified laser output by more than a factor of four. Efficient and continuous wavelength tuning between 470 and 500 nm is achieved with an output energy density of ~1 J/l, and an intrinsic efficiency of ~1% throughout the entire tuning region     

Wideband-tunable high-power radiation by SRS of aXeF(C→A) excimer laser

Efficient wavelength shifting by means of stimulated Raman scattering (SRS) in hydrogen and liquid nitrogen of the blue-green XeF( C→A) excimer laser was demonstrated. Energy conversion into the first Stokes line with an efficiency of 38% was achieved. Continuously tunable radiation of 523-579 nm and of 578-650 nm with pulse energies ranging from 100 to 210 mJ was generated in liquid nitrogen and hydrogen, respectively. A peak power of 35 MW at 549.0 nm was obtained     

Chemically produced XeF(B) electronic excited state

Ultraviolet (UV) emission has been observed in the reactions of XeF₂+F₂+SiH₄ and XeF₂+F₂+F+B₂H₆. The emission spectra have been identified with the B²Σ→X²Σ transition of XeF. The emission intensity has also been examined as functions of the XeF₂, F₂, SiH₄, and Ar concentrations. Possible mechanisms of XeF(B) production are discussed     

Computer model of the electron-beam excited XeF(B-X) laser

The authors report results on the computer simulation of electron-beam pumped XeF lasers user common conditions, as well as under elevated temperature and high pumping rates that are known to improve laser performance. The Boltzmann equation for the electron energy distribution function and the chemical kinetics equations were solved in a consistent manner. The model took into account five vibrational levels of the electronic B state and seven levels for the C and X states of the XeF molecule. The model used gives reasonable agreement with the results of small signal gain measurements. A method of taking into account the finite rate of rotational relaxation makes it possible to obtain time dependencies of the lasing power in different spectral bands that qualitatively agree with those measured in experiments at different temperatures and pump rates     

Time-resolved studies of the C-A transition inavalanche discharges: fluorescence and gain-loss studies

Time-resolved XeF C-A fluorescence and gain-loss studies were conducted in an avalanche discharge using arc-type UV preionization in a variety of devices that deliver peak powers from 1 to 13 MW/cm³ in time intervals from 10 to 30 ns. The results coupled with extensive fluorescence measurements give indications of the possibility of developing a successful XeF C-A transition avalanche discharge tester. Fluorescence studies giving relative upper state densities as a function of different gas mixtures correlate well with the peak gain observed. Thus, relative peak fluorescence intensities are a good gauge for the best mixture for C -A transition lasing     

Repetitively pulsed operation of an injection-controlled high-powerXeF(C→A) excimer laser

The operation at a 1-Hz repetition frequency of an injection-controlled electron-beam-pumped XeF(C→A) excimer laser system is reported. A compact, halogen-compatible, closed flow loop incorporating a transverse inline fan was used for gas circulation. In single-laser-shot operation, the timing between an electron beam and the injection dye laser was carefully adjusted to obtain an optimum laser pulse energy stability. An improved output-laser energy of 1.2 J per pulse with an intrinsic efficiency of 1.1% at 486.8 nm was achieved with a large-aperture unstable resonator. Interferograms taken during and after an electron-beam pump pulse to determine the minimum optical cavity recovery time of this device indicate that stable laser output energy performance at repetition rates of up to 25 Hz could be achieved with the present flow loop     

Confidence bounds for Pr{X>Y} in 1-way ANOVArandom model

Approximate confidence bounds for reliability, R=Pr{X >Y|X,Y}, are obtained, where X and Y are independent normal (Gaussian) random variables, and X and Y are vectors of measurements for X and Y, respectively. Balanced 1-way ANOVA (analysis of variants) random effect models are assumed for the populations of X and Y. Confidence bounds are derived for R under three cases for standard deviations, σ_x and σ_y. An example shows how the results are used     

A proposed chemically pumped laser based on theb→X transition in O2

Simple kinetics calculations demonstrate that the well-known electronic energy pooling reaction involving O₂(a ¹Δ) is capable of producing an effective population inversion in O₂(b¹Σ). The densities of O₂(a¹Δ) which are potentially achievable suggest that the extractable energy storage density of an O ₂(b→X) chemical laser might exceed 0.5 MJ/m³. The b→X emission lifetime measurements conducted under conditions of high relative O₂( b¹Σ) density reveal no evidence of rapid self-quenching effects which would be potentially detrimental to laser performance. The relatively long energy storage times predicted, together with freedom from reagent mixing requirements, make such a laser an attractive alternative to other existing and proposed short wavelength chemical lasers     

Modeling and experimental results for C(V) in anabrupt isotype n Al0.5Ga0.5As/GaAs heterojunction

The differential capacitance C of an abrupt isotype n Al_0.5 Ga_0.5As/GaAs heterojunction has been modeled by directly calculating the dependence of the space charge on the voltage V at its terminals. The electron charge distribution was calculated considering the 2-D electron gas by simultaneously solving the Schrodinger and the Poisson equations, DX centers included. Results from this model predict an asymmetric bell-shape dependence of C on V, with a maximum near the contact potential, and are in good agreement with experiment. This further provides experimental evidence of Γ-Γ and X-X valley coupling for electrons traveling across the heterojunction. For voltage values not too close to the contact potential, it was possible to find a simple method, based on a total depletion, that gives a good fit to experiment     

Robustness of mean E{X} and R charts

The effect of nonnormality on E{X} and R charts is reported. The effect of departure from normality can be examined by comparing the probabilities that E{X} and R lie outside their three-standard-deviation and two-standard-deviation control limits. Tukey's λ-family of symmetric distributions is used because it contains a wide spectrum of distributions with a variety of tail areas. The constants required to construct E{X} and R charts for the λ-family are computed. Control charts based on the assumption of normality give inaccurate results when the tails of the underlying distribution are thin or thick. The validity of the normality assumption is examined by using a numerical example     

The (d,k) subcode of a linear block code

A simple technique employing linear block codes to construct (d,k) error-correcting block codes is considered. This scheme allows asymptotically reliable transmission at rate R over a BSC channel with capacity C_BSC provided R ⩽C_d,k-(1+C_BSC), where C_d,k is the maximum entropy of a (d,k ) source. For the same error-correcting capability, the loss in code rate incurred by a multiple-error correcting (d,k) code resulting from this scheme is no greater than that incurred by the parent linear block code. The single-error correcting code is asymptotically optimal. A modification allows the correction of single bit-shaft errors as well. Decoding can be accomplished using off-the-shelf decoders. A systematic (but suboptimal) encoding scheme and detailed case studies are provided     

The SIR-C/X-SAR synthetic aperture radar system

The SIR-C/X-SAR synthetic aperture radar, a three-frequency radar to be flown on the Space Shuttle in September 1993, is described. The SIR-C system is a two-frequency radar operating at 1250 MHz (L-band) and 5300 MHz (C-band), and is designed to get four-polarization radar imagery at multiple surface angles. The X-band synthetic aperture radar (X-SAR) system is an X-band imaging radar operating at 9600 MHz. The discussion covers the mission concept; system design; hardware; RF electronics; digital electronics; command, timing, and telemetry, and testing     

On (k, t)-subnormal covering codes

The concept of a (k, t)-subnormal covering code is defined. It is discussed how an amalgamated-direct-sumlike construction can be used to combine such codes. The existence of optimal (q, n, M) 1 codes C is discussed such that by puncturing the first coordinate of C one obtains a code with (q, 1)-subnorm 2     

Interpretation and control of C-V measurementsusing pattern recognition and expert system techniques

The authors demonstrate how a pattern-recognition system can be applied to the interpretation of capacitance-voltage (C-V ) curves on an MOS test structure. By intelligently sequencing additional measurements it is possible to accurately extract the maximum amount of information available from C-V and conductance-voltage (G-V) measurements. The expert system described, (CV-EXPERT), is completely integrated with the measurement, instrumentation, and control software and is thus able to call up a sequence of individually tailored tests for the MOS test structure under investigation. The prototype system is able to correctly identify a number of process faults, including a leaky oxide, as shown. Improvements that could be gained from developing rules to coordinate G-V, capacitance-time, and doping profile measurements simply by recognizing the important factors in the initial C- V measurement are illustrated