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1.
Optimum energy extraction from an electron-beam-pumped XeF(C A) laser is achieved with a five-component rare gas halide mixture. The characterization and modeling of laser action in such a gas mixture requires a knowledge of small-signal gain and absorption coefficients not only on the blue-green XeF(CA) transition, but also in the ultraviolet (UV) region for the competing XeF(BX) and KrF(BX ) transitions. The authors report gain measurements on the XeF(CA) transition and small-signal gain and absorption coefficients at or near both the XeF(BX ) (351 and 353 nm) and KrF(BX) (248 nm) transitions. A study of the gain for the UV and visible transitions as a function of Kr and Xe partial pressure is reported, and its impact on the XeF(CA) kinetics is discussed  相似文献   

2.
An XeF (CA) 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 (CA) laser. Also, by injecting a narrowband signal into the cavity, the XeF (CA) 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  相似文献   

3.
The scaling characteristics and medium properties of an injection-controlled XeF(CA) 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(CA) laser operation  相似文献   

4.
Fundamental processes affecting the operation and performance of electron beam-excited XeF(CA) 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(CA) properties, particularly net gain, under conditions for which the CA laser energy density and efficiency values are comparable to those of the UV XeF(BX) laser  相似文献   

5.
The laser performance and kinetic properties of the broadband CA 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 BX transition or the influence of the various buffer gases  相似文献   

6.
Efficient wavelength shifting by means of stimulated Raman scattering (SRS) in hydrogen and liquid nitrogen of the blue-green XeF( CA) 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  相似文献   

7.
Characteristics of an injection-controlled electron-beam pumped XeF(CA) 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  相似文献   

8.
The operation at a 1-Hz repetition frequency of an injection-controlled electron-beam-pumped XeF(CA) 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  相似文献   

9.
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  相似文献   

10.
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  相似文献   

11.
The application of an analytical model describing the injection control of pulsed laser systems is successfully demonstrated for the design of a scaled XeF(CA) excimer laser system. Enhancements to an earlier version o the model which improve the treatment of spatial beam overlap and saturation, unpumped volume, intracavity losses, and a noninteger number of roundtrips in the unstable resonator are described. These result in the accurate simulation of injection-controlled laser performance over a wide range of unstable resonator magnifications, mirror spacings, and intracavity optical losses. Excellent agreement between calculated and experimentally observed energies and temporal profiles of the injection-controlled laser output was obtained  相似文献   

12.
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  相似文献   

13.
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 CBSC provided R Cd,k-(1+CBSC), where Cd,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  相似文献   

14.
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(bX) chemical laser might exceed 0.5 MJ/m3. The bX 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  相似文献   

15.
How overshoot in the step response of a circuit involving an RLC line can be controlled using a combination of driver and line resistance that depends on the load capacitance is shown. The no-peak condition or its equivalent is used to relate line parameters to the driver and load impedances. This no-peak condition generalizes the impedance matching customarily used for lossless lines, i.e. it provides an alternative to the traditional choice RD=√ L/C. The results allow improved circuit response without risk of overshoot, for example, by reduction of driver resistance below √L/C for cases where line resistance is unavoidable and/or where load capacitance is not negligible compared to line capacitance. The algebraic formulas derived are more effective than case-by-case numerical simulations for analyzing scaling and technology issues, whether on-chip, or at the packaging, board, or system levels  相似文献   

16.
C-V characteristics of fully depleted SOI MOSFETs have been studied using a technique for measuring silicon-film thickness using a MOSFET. The technique is based on C-V measurements between the gate and source/drain at two different back-gate voltages, and only a large-area transistor is required. Using this technique, SOI film thickness mapping was made on a finished SIMOX wafer and a thickness variation of ±150 Å was found. This thickness variation causes as much as a 100-mV variation in the device threshold voltage. The silicon-film thickness variation and threshold-voltage variation across a wafer shows a linear correlation dependence for a fully depleted device. C-V measurements of the back-gate device yield the buried-oxide thickness and parasitic capacitances. The effects of GIDL (gate-induced drain leakage) current on C-V characteristics are also discussed  相似文献   

17.
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  相似文献   

18.
Decoding performance of Reed-Solomon (RS) coded M-ary FSK with noncoherent detection in a frequency-hopping spread spectrum mobile radio channel is theoretically analyzed. Exact formulas and an approximate one for evaluating word error rates (WERs) of error correction and error-and-erasure correction schemes on decoding the RS codes are derived. It is shown that with K symbol erasure and C symbol error detection, RS coded M-ary FSK achieves the equivalent diversity order of (K+1)(C+1)  相似文献   

19.
The asymptotic (M→∞) probability of symbol error Pe,m for M-ary orthogonal modulation in a Nakagami-m fading channel is given by the incomplete gamma function P(m, mx) where x=In 2/(Eb/N0) and Eb is the average energy per bit. For large signal-to-noise ratio this leads to a channel where the probability of symbol error varies as the inverse mth power of Eb/N0. These channels exist for all m⩾1/2. The special case of m=1 corresponds to Rayleigh fading, an inverse linear channel  相似文献   

20.
The usual approximate expression for measured fT =[gm/2π (Cgs+C gd)] is inadequate. At low drain voltages just beyond the knee of the DC I-V curves, where intrinsic f t is a maximum for millimeter-wave MODFETs, the high values of Cgd and Gds combine with the high gm to make terms involving the source and drain resistance significant. It is shown that these resistances can degrade the measured fT of a 0.30-μm GaAs-AlGaAs MODFET from an intrinsic maximum fT value of 73 GHz to a measured maximum value of 59 GHz. The correct extraction of maximum fT is essential for determining electron velocity and optimizing low-noise performance  相似文献   

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