Laser parameters for the 10.8-µ N2O molecular laser

Measurements were made of the radiative lifetime for the 001-100 transition in N2O, the absolute population densities of the laser levels, and the saturation parameter in a typical flowing N2O-N2-He laser. These numbers are compared with the corresponding parameters in the CO2-N2-He system to explain the difference in their performance characteristics. In addition, dissociation of N2O in a discharge and power enhancement in the N2ON2-He laser by adding CO are discussed.     

A note on the sampling of zero crossings of two-dimensional signals

Curtis et al. applied a theorem due to Bezout to show that almost all continuous, periodic, band-limited two-dimensional signals can be reconstructed from at most 4(N1+ N2)²zero-crossing samples where N1and N2is the number of Fourier coefficients in the signal. In this letter we prove a new version of Bezout's theorem and apply it to the above problem to provide a more lenient sampling requirement of at most 8N1N2zero-crossing samples.     

Effects of gas flow on gain of 10.6 micron CO2laser amplifiers

Small-signal gain of flowing gas CO2laser amplifiers at 10.6 microns has been optimized for media including pure CO2CO2: N2, CO2: He, CO2: CO, CO2: O2, CO2: N2: He, CO2: CO : He, and CO2: CO : N2. Optimum gain of all flowing gas systems studied increases monotonically with increasing gas flow rate. In the low CO2flow rate region, 10 < RCO2: < 50 cm³/min, gas flow enhances the gain most for systems containing N2. Results provide strong evidence that the rapid increase in gain with flow rate in CO2: N2mixtures is due to removal by convection of the dissociated product CO. For 50 < RCO2< 200 cm³/min, a slow linear increase in gain of all gas mixtures with increasing flow rate occurs and is attributed to the cooling of gas temprature by convection. A stronger dependence of gainGon amplifier boreD, viz.,G propto I/D, was obtained for flowing gas media relative to that previously observed for nonflowing gas mixtures which is consistent with the proposed mechanism of gas cooling by convection. Highest gain values obtained were 7.8 and 6.2 dB/m with the flowing gas mixtures CO2: N2: He and CO2: CO : He, respectively, in a 12 mm bore water-cooled amplifier tube. Similarities between CO2: N2and CO2: CO systems suggest that pumping of the CO2laser by resonant transfer from CO* (upsilon = 1) can be significant.     

Behavior of first- and second-positive emission in the N2/SF6laser

Experimental results for the behavior of the emission of the discharge-excited first- and second-positive bands of N2and flow-tube measurements for the deactivation of theA^{3}Sigmamin{u}max{+}andB^{3}Pi_{g}levels of N2by SF6are presented. The results of both these experiments are used to explain the operating mechanisms of the N2/SF6laser.     

Improved operation of N2O TE lasers

The operation of a transversely excited N2O laser is improved by the addition of H2or CO to the discharge. The improvement is due to the effective nullification of the dissociative electron attachment reaction with N2O.     

A new oxidation-resistant self-aligned TiSi2process

This paper presents a thin amorphous Si (a-Si) on Ti as an oxidation-resistant material for a self-aligned TiSi2process. It is shown that a thin a-Si over Ti film will greatly suppress the interaction between Ti and ambient gases (N2and O2) during the thermal TiSi2formation cycle in conventional N2furnance while maintaining satisfactory self-aligned property after silicidation at a temperature below 630°C.     

Third-harmonic generation in a mixture of DBr and N2O

Third-harmonic generation of CO2P(24) 10.6 mum laser radiation was achieved in a mixture of DBr and N2O. The ratio of DBr and N2O used was 29:1. A frequency tripled signal was observed up to a total pressure of 4 atm.     

Gas additive effects in CO chemical lasers

The effects of gas additives on optical gain of the CO chemical laser (CL) have been measured for N2, SO2, H2, HF, CF4, CCl2F2, CO, OCS, N2O, and NO. One of the more unusual additives, NO, has been used to control the output spectrum of a laser oscillator by controlled sequential quenching of the high bands. The significance of these results for total power enhancement, output spectrum control, and alternate diluent use is discussed.     

Laser initiated explosions and chemiluminescence

Explosions can be induced in mixtures of SF6with appropriate fuels, by a single pulse of a free running CO2laserapprox 1.5 mus [full width at half maximum (FWHM)]. A typical threshold for initiation of reaction was somewhat above 4 J for a 1:1 mixture of SF6and SiH4, at a total pressure of 10 torr, with the unfocused beam illuminating 8 cm²of cell area. High levels of luminosity were generated covering both the near ultraviolet, visible, and infrared. The spectral and temporal characteristics of the following fuels and fuel-oxidizer combinations (with SF6present) are summarized: the most prominent emitter from SiH4is S*2, B³Sigma-_{u}; Sn(CH3)4+ N2O [SnO*; SnF*] ; Pb(CH3)4+ N2O [PbO*; PbF*; PbS*] ; Bi(CH3)3+ N2O [BiF*]; B2H6with and without N2O [BO*; BO*2; S*2]. Several atomic lines were also recorded. Estimates of the energy density deposited by the laser pulse suggest that initiation of rapid reaction was primarily due to attack of superexcited SF6by highly reducing radical species.     

Lasing in N2O and CO2isotope mixtures pumped by blackbody radiation

The use of N2O and CO2isotopes as active species for a blackbody radiation pumped laser has been experimentally demonstrated and theoretically analyzed. The results obtained for mixtures containing N2O,¹³C¹⁶O2, and¹²C¹⁸O2are presented. For the first time, continuous lasing action with blackbody radiation pumping has been obtained for this species. Two active species mixtures were tested, obtaining up to a 100 percent increase in output power due toupsilon-upsilontransfer. A simple model was developed and gain calculations are presented.     

A TE duolaser providing simultaneous lasing on CO2and N2O transitions

Simultaneous laser action on CO2and N2O transitions has been achieved in a helical resistor-pin-type transversely excited (TE) laser. The laser emits typically a power of 10-100 kW in a 700-ns-long pulse which consists basically of two overlapping pulses, the peaks of which do not coincide, and which can be associated with the CO2and N2O emission, respectively. The conditions of optimal operation are described and the effects of some parameter changes are indicated.     

Analysis of chemical degradation products in an e-beam pumped rare-gas halide laser

Chemical degradation products created during the operation of ane-beam pumped, repetitively pulsed XeF laser with closed flow cycle capability are reported. From an initial lasing mixture of Ar/Xe/NF3, the degraded gas was found to contain N2F2(N2F4), CO2, nitrogen oxides, CF4, and SiF4. Gaseous species were identified by their infrared and ultraviolet absorption spectra. Also present was a solid material tentatively thought to consist of fluorocarbons and aluminum fluorides. The observed gas chemistry suggests methods for improving laser performance by prevention of contaminant buildup.     

Electron energy distribution in CO2laser discharges

Electrical plasma parameters of the CO2laser were investigated by probe and high-frequency techniques. The electron energy distribution function was measured by the second derivative method. The relatively high-pressure effect on the electron probe current was taken into account when analyzing the experimental curves. The influence of the addition of N2, He, Xe and the influence of CO2dissociation on the plasma discharge properties were studied. Calculations of the pumping rates to vibrational levels taking part in creating inversion show that the influence on output power of a CO2laser usually observed with the addition of N2and He cannot be explained by a changing of the electron component of the plasma. The increase of output power and efficiency with addition of Xe to the CO2laser is connected with an essential changing of plasma parameters of the electron component.     

A study of the spontaneous emission from CO2-N2-He-H2laser discharges C3πu-B3πgemission bands of N2

Results of spectroscopic investigations of the spontaneous emission of CO2lasers are presented. The band head emission in the Second Positive System (C^{3}pi_{u}- B^{3}pi_{g}) of N2is studied as a function of discharge current and laser output power. The observed changes of the band head intensities are described in terms of the vibrational energy distribution in theC^{3}pi_{u}electronic state of N2. A simple model is developed by which the influence of the laser process can be understood. The excitation properties of theC^{3}pi_{u}state are in reasonable qualitative agreement with the predictions of this model.     

Simultaneous HCN and H2O laser emission in mixtures containing H, C, N, and O

Simultaneous laser emission at 337 and 118 μ has been observed in a pulsed discharge through a mixture of N2, O2, and either CH4or (C2H5)2O. Earlier observation of a laser line at 469 μ is rejected and explained.     

Stimulated rotational Raman scattering in the atmosphere

Theoretical and experimental information in the literature is used to calculate the gain coefficient for stimulated rotational Raman scattering by atmospheric N2and O2. The dependence on laser wavelength and polarization, as well as on the pressure and altitude is discussed. It is pointed out that because of pressure broadening, the gain coefficient is independent of altitude up to an altitude of 40-50 km, where the Raman transition becomes Doppler broadened. The 1 percent conversion threshold for vertical propagation from the ground up is calculated for various transitions and laser beam characteristics. The highest-gain transition, theS(8) transition of N2, is shown to have a 1 percent conversion intensity threshold of ∼ 1.2 MW/cm2for linearly polarized light at a wavelength of 400 nm.     

Direct optical pumping of high-pressure CO2and N2O lasers with a pulsed HF pump laser

Pulsed HF laser radiation has been used for direct optical excitation of CO2and N2O lasers at 10 and 5 atm gas pressures, respectively, which are the pressures required for continuous laser frequency tuning between the line centers in these gases. The maximum demonstrated quantum efficiency is about 14 percent, which seems to be limited by the formation of pressure waves in the gas, in addition to losses in the resonator optics. We find that quantum efficiencies close to unity are theoretically feasible with a low-loss resonator, and by using a sufficiently short pump pulse to avoid a serious influence from pressure waves. The excitation scheme can be used with any of the CO2and N2O laser isotopes.     

Absorption in the near-ultraviolet wing of the Kr2F*(410 nm) band

An intracavity laser technique has been used to study the absorption of electron-beam pumped Ne/Kr/F2gas mixtures (196 and 300 K) in the "blue wing" of the Kr2F emission continuum. The experiments were conducted at 358 nm using theupsilon' = 0 rightarrow upsilon" = 1transition of the N2(C rightarrow B) laser. Comparing the results with the predictions of a computer model, the species primarily responsible for absorption have been identified as Ne+2, Kr+2, and Kr2F*. The photoabsorption cross sections for Ne+2and Kr2F (Kr+2F-) at 358 nm have been estimated to be8.1 cdot 10^{-19}and5.4 cdot 10^{-18}cm², respectively. The Kr2F* absorption cross section is roughly 20 percent of that reported for Kr+2at the same wavelength. The fluorescence efficiency of Kr2F* ine-beam excited 94.93 percent Ne/5 percent Kr/0.07 percent F2(P_{total} = 4000torr) gas mixtures has been found to be a factor of 2.8 higher than that of the N2(C rightarrow B) band in Ar/5 percent N2mixtures. Also, the rate constant for quenching of Kr2F* by F2was measured to be(4.1 pm 0.5) cdot 10^{-10}cm³. s^-1at 300 K and(3.0 pm 0.5) cdot 10^{-10}cm². s^-1at 196 K.     

New CW FIR laser action by Stark tuning from optically pumped CH3OH and CH3OD

Fifteen new CW FIR laser lines are reported from Stark tuned CO2optically pumped CH3OH and CH3OD. Four new CW laser lines have also been observed from zero field optically pumped CH3OD, three with a CO2laser, and one with an N2O laser.     

Pulsed N2O molecular laser studies

The afterglow pulse-gain technique was used to measure the relaxation of the 00°1 upper laser level in N2O from 300 to 700°K. The rate constantk_{N_{2}O}(torr^-1s^-1) varies with temperature aslog10k_{N_{2}O} = 4.53 - 10.9T^{-1/3}. Measurements of the relaxation time at 300°K agree with the fluorescence technique results of Yardley [1]. Gain studies were also made with gas mixtures in a nonflowing system. Single-pulsed N2O + CO + He mixtures at 300°K showed considerable peak gain. However, subsequent pulses of these mixtures show that the gain is reduced because of the chemical reaction forming CO2. Measurements of this transformation from one molecular laser mixture to another are discussed.