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.     

PassivelyQ-switched N2O laser

Freon 12 and SF6have been used to passivelyQswitch laser transitions fromR(17)toP(36)in the00deg1-10deg0N2O band. Pulses having a half-intensity width of 0.75 μs with peak powers 10-20 times the CW power were observed.     

Active mode locking of a high-pressure pulsed N2O laser

Experimental results on the active mode locking of a transversely excited N2O laser at subatmospheric pressures are presented. Nanosecond pulses of 10.8-μ radiation were produced with typical peak-power outputs in the 100-kW range.     

Higher order harmonics of CO2and N2O laser difference frequencies

The generation of the fourth and fifth harmonics of the difference frequency between two 28-THz laser lines, by a tungsten-nickel diode, was observed.     

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.     

Photopreionization of the 3371-Å pulsed N2laser

Photopreionization of the 3371-Å pulsed N2laser by use of a seed gas of low ionization threshold and flashlamp excitation is observed to result in increased laser output and reproducibility. Preionization also increases the range of permissible operating pressures, enabling operation with atmospheric-pressure mixtures of N2and He without reduced intensity.     

385 µmD2O laser linewidth measurements to -60 dB

First linewidth measurements over a 60 dB dynamic range of a pulsed, high-power, optically pumped far infrared laser are presented. These measurements were made possible by using a 385 μmD2O laser with an N2O absorption filter and a sensitive heterodyne receiver. Studying a 385 μmD2O laser oscillator we find that the low-level linewidth (<-20 dB) can be explained by the ac Stark effect due to the high-power pump field. Also, we have not observed any frequency pulling of the main Raman emission frequency due to the strong pump and FIR laser fields.     

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.     

Collisionally induced lasing in CO2and N2O using vibrationally excited CO

Continuous-wave oscillation has been observed on a number of P-branch transitions belonging to the     

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.     

4.9-µ He-Air-CH4-(CO) laser

Low-vibrational-levelP(J)_{upsilon,upsilon'}CO laser emissions have been measured from He-air-CH4mixtures. The CW lines below 5.0μ were measured in air to occur at 4.8836, 4.8935, 4.8974, 4.9072, 4.9366, 4.9466, 4.9670, and 4.9778μ. These emissions are tentatively identified to result from transitions as low asupsilon = 3 : 2. Such emissions were relatively more frequent with CH4than with CO specifically.     

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.     

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.     

Near single-line operation of a free-burning CS2/O2/N2O flame laser with a nondispersive optical cavity

The CS2/O2/N2O flame laser has been operated for the first time under conditions in which the spectral output is nearly single line. This transition is theP_{10-9}(17) of CO at 5.4265 μm, the same transition which was observed to oscillate in single-line fashion by Hirose et al. in an electrically initiated CO chemical laser. It is suggested that the unique behavior of this line may be due to its close proximity to aPbranch transition in an adjacent band, namely theP_{9-8}(23) line, such that the gain profiles of the two lines overlap. Calculations suggest that at the conditions of these experiments, the separation of the line centers for this pair is about 0.3 Å or less. TheP_{10-9}(17) transition was also found to be totally absent under certain conditions of high multiline power, particulary at low O2and N2O flows. This may be due to absorption by a high-bandRbranch transition at 5.4266 μm, namely theR_{15-16}(32) line.     

Optical pumping by CO2and N2O lasers: New CW FIR emissions in 1,1-difluoroethane

53 new CW FIR laser lines are reported in 1,1-difluoroethane optically pumped near 10 μm by CO2and N2O lasers. The emission spectrum initially reported in the literature consisted of four lines between 770 and 458 μm and has now been extended to the 2.39 mm- 319 μm region. The reason for this extension, especially to the long wavelengths, is analyzed.     

The F + H2O chemical laser

Laser oscillation, restricted by energy limitations to transitions from first vibrationallevel to ground state, has been observed from HF produced by the reaction of the F atom on H2O initiated by pulsed electric discharge in flowing mixed F2-H20-He gases at 10 torr.     

CO2laser preamplifier capabilities for low-level 10.6-µm direct-detection receivers

We examine the potential of CO2laser preamplifiers for sensitivity enhancement in low-level, direct-detection 10.6-μm receivers. For the condition in which a gain-dependent competition exists between the background noise and amplifier spontaneous emission noise (assuming negligible thermal noise), the analysis predicts an optimum useful SNR enhancement of only 6 dB for a blackbody background field of 300 K and 4.1 dB for a background of 260 K, when the amplifier gain bandwidth perp-line is 100 MHz and the infrared (IR) filter bandwidth is 0.10 μm. Based on preselected choice of gain and bandwidth, a two-stage, water-cooled, flowing-gas amplifier of optimized design was constructed. A maximum gain of 3.12 dB was attained forP(20)with a He : CO2: N2mixture of 5.0 : 1.0 : 0.6 at a coolant temperature of 285 K and a slow gas refresh rate of 0.2 volumes/s. Using a fast-flow system with 12-volume/s refresh rate, we measured an amplifier gain of 3.9 dB, close to the design estimate of 4.1 dB. With a calibrated HgCdTe detector,f/4cold shield, and narrow-band (0.25 μm) cold filter, a spontaneous emission flux density ofsim 1.0 times 10^{14}photons/ cm². s was measured at the 3.12-dB gain level, in close agreement with the theoretical estimate. Excess noise resulting from amplifier discharge was undetectable above the basic detector noise.     

A comparative study of D2O oscillators emitting at 385 µm

The generation of single-mode pulses of far-infrared (FIR) radiation of duration up to 700 ns at 385 μm has been achieved using a confocal unstable resonator with D2O as an active medium. Future volumetric scaling to the power levels necessary for measuring ion temperature in tokamak plasmas by Thomson scattering appears encouraging. A comparison between the performance of the unstable resonator and two hemispherical resonators is reported.     

An atomic Rydberg state 16-µ laser

A 16 μ laser operating on the 626-cm^-1transition between the6D_{3/2} rightarrow 7P_{1/2}states in potassium vapor has been demonstrated. This laser features an extremely high gain, a favorable branching ratio, and a laser-enhanced cascade process.     

A 16-µm source for laser isotope enrichment

A potentially efficient, high-energy 16-μm source is proposed based on stimulated rotational Raman scattering in H2or D2using a TEA CO2laser source. The calculated pump energy threshold for rotational Raman scattering on theS(0) 354.33 cm^-1Raman line of H2at 77 K and 1 atm pressure is 3.1 J.