Buffer gases to increase the efficiency of an optically pumped far infrared D2O laser

The effects of buffer gas additives on the performance of an optically pumped D2O laser operating at 385 μm have been investigated both experimentally and by numerical simulation. Three gases, sulphur hexafluoride, carbon tetrafluoride, andn-hexane, were found to produce an increase of up to 40 percent in the pumping efficiency, as well as significant lengthening of the far infrared pulse. Under optimum conditions, 2.6 J in a 1 μs long pulse have been obtained. The buffer gases are shown to eliminate the vibrational deexcitation bottleneck, which in pure D2O leads to an accumulation of population in the upper vibrational leve and, hence, a reduction in the efficiency of absorption of the pump beam. Comparison of the observed buffer gas effects with the predictions of a numerical simulation code based on a rate equation model gives information about the constants for vibrational and rotational relaxation rates due to D2O-D2O and D2O-buffer gas collisions.     

Observation of new FIR superradiant lines from optically pumped D2O

Four new laser lines from optically pumped D2O vapor are reported at wavelengths of 235 μm, 280 μm, 97 μm, and 98 μm, the latter having a quantum conversion efficiency of 38 percent.     

Backward and foreward FIR emmission characteristics drom D2O in both Raman and laser regimes

Laser emission spectra for the 66 and 116 μ D2O lines pumped by the 9.66 μP32CO2line in both backward and forward directions have been obtained. Forward spectra are predominantly Raman dominated, except for a narrow pressure region near 2 torr where the 116 μ line is laser-like. Backward spectra appear to be entirely laser-like showing narrower bandwidths and constant frequency. The shape of the pulse outlines in different directions and pressures confirm the findings of the emission spectra. Total FIR energy emission is also asymetric, being significantly greater in the forward direction.     

The identification of candidate transitions for optically pumped far infrared lasers: Methyl halides and D2O

Two hundred and forty-four candidate transitions for optically pumped far infrared lasers have been identified in C¹²H3F, C¹³H3F, C¹²D3F, C¹²H3Cl³⁵, C¹²H3Cl³⁷, C¹²H3Br⁷⁹, C¹²H3Br⁸¹, and D2O using as candidate pump lines, 781 in number, the isotopic forms of CO2, the sequence and hot bands of C¹²O2¹⁶, and the N2O bands. The dominant transition parameters responsible for strong emission from TEA, CW, and long pulse modes of operation were identified by a correlation between known experimental behavior and the pertinent transition parameters, the results being that strong TEA laser emission correlates with ground state population while strong CW and long pulse emission correlate with absorption coefficient. The candidate transitions were subsequently selected on the basis of these parameters using calculated transitions and assignments based on band data from high resolution laser-Stark spectroscopy and measured candidate pump frequencies.     

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.     

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.     

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.     

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.     

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.     

Assignment of laser lines in optically pumped submillimeter lasers: HDCO, D2CO

Respectively, three and eight laser lines have been precisely measured and assigned in asymmetric-top molecules HDCO and D2CO. Frequency calculations of rotational transitions use parameters obtained from microwave studies. For frequency calculations of rovibrational transitions, vibrational energies derived from infrared band analysis have been also taken into account. The assignment is confirmed by infrared radio frequency double resonance experiments inside the submillimeter laser cavity.     

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.     

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.     

Additional CW far infrared laser lines from CO2laser pumped cis 1,2 C2H2F2

Six new CW far infrared laser lines are reported for the cis 1, 2 C2H2F2molecule optically pumped by a CO2laser. Of these, two have high conversion efficiencies in the 1-2 percent range.     

Enhancement of laser action in H2O by the addition of helium

The power output of a water vapor laser operating in the region from 28 to 119 μ has been increased at least five times by the addition of helium. The optimum mixture was 1.2-torr H2O and 4.6-torr He.     

Small-signal gain and time-resolved spectroscopy of the D2-F2/CO2pulsed chemical transfer laser system

Measurements made of the small-signal gain and time-resolved spectral output of a flash-initiated D2-F2/CO2chemical transfer laser system are reported. Small-signal gain measurements indicate a possible lack of rotational equilibration among the rotational levels of the CO2during the DF-CO2V-V energy transfer process. Time-resolved spectral output of this system, operated as a laser oscillator, is presented as verification of the small-signal gain results.     

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.     

New CW far-infrared laser lines from CO2laser-pumped CD3OH

Twenty-one new CW far-infrared laser lines have been observed from the CD3OH molecule pumped by a CO2laser. The wavelengths of these new lines fall in the short wavelength range from 34.5 to 287 μm.     

New far-infrared laser lines in N15H3

Several isotopes of NH3have been studied as laser candidates, including ND2H, NH2D, ND3, and N¹⁵H3. Lasing was observed in N¹⁵H3at 15.08 and 15.91 μ. Tentative assignments of transitions to the2nu_{2} rightarrow nu_{2}vibrational levels have been made. Enhanced energy output was observed in N¹⁴H3with the addition of helium.     

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.