Optically pumped microplasma rare gas laser.

The optically pumped rare-gas metastable laser is a chemically inert analogue to three-state optically pumped alkali laser systems. The concept requires efficient generation of electronically excited metastable atoms in a continuous-wave (CW) electric discharge in flowing gas mixtures near atmospheric pressure. We have observed CW optical gain and laser oscillation at 912.3 nm using a linear micro-discharge array to generate metastable Ar(4s, 1s(5)) atoms at atmospheric pressure. We observed the optical excitation of the 1s(5) → 2p(9) transition at 811.5 nm and the corresponding fluorescence, optical gain and laser oscillation on the 2p(10) ↔ 1s(5) transition at 912.3 nm, following 2p(9)→2p(10) collisional energy transfer. A steady-state kinetics model indicates efficient collisional coupling within the Ar(4s) manifold.

Cs 894.3 nm laser pumped by photoassociation of Cs-Kr pairs: excitation of the Cs D(2) blue and red satellites.

Lasing on the D(1) transition (6P1/22-->6S1/22) of Cs has been observed by photoassociating Cs-Kr atomic pairs with a tunable, pulsed dye laser. Pumping of the blue or red satellites of the Cs D(2) line (62P3/2<==>62S1/2), peaking at approximately 841.1 nm and approximately 853 nm (respectively) in Cs/Kr/C(2)H(6) gas mixtures, provides a photodissociation laser in which the CsKr excimer parent molecule is not, at any point in the pumping process, in a bound electronic state. Relative to the absorbed pump pulse energy, laser slope efficiencies greater than or approximately 5% have been measured when the Cs number density is in the range of 5x10(14)-1.5x10(15) cm(-3) and the pump wavelength is 841.1 nm. Direct photoexcitation of the Cs 6P3/22 state at 852.1 nm under these conditions is a less efficient pathway for pumping the 894.3 nm laser, presumably as a result of competing nonlinear optical processes such as 1+2 resonantly enhanced multiphoton ionization of the alkali atom.

Hyperspectral infrared imaging of HF(v, J) chemiluminescence and gain in chemically reacting flowfields.

This paper presents results from investigations of chemically reacting flowfields and optical gain profiles in HF chemical laser media by infrared hyperspectral imaging. Subsonic and supersonic chemiluminescent F+H2 reacting flowfields, produced in high-fluence microwave-driven reactors, were imaged at a series of wavelengths, 2.6-3.1 microm, by a low-order, spectrally scanning Fabry-Perot interferometer mated to an infrared camera. The resulting hyperspectral data cubes define the spectral and spatial distributions of the emission. Spectrally resolved images at high spatial resolution were processed to determine spatial distributions of the excited-state concentrations of the product HF(v, J) molecules, as well as spatial distributions of small-signal gain on specific laser transitions. Additional high-resolution Fourier transform spectroscopy and spectral fitting analysis determined detailed excited-state distributions in the reacting flowfields. The measurements showed that energetic HF(v, J) state distributions were generated by both the supersonic and fast-flow subsonic mixing schemes. In particular, the subsonic reactor produced a spatially distributed field of inverted, near-nascent state populations, with small-signal gains near 2-3%/cm.

Kinetics for the reactions of O- and O2- with O2(a1Deltag) measured in a selected ion flow tube at 300 K.

The kinetics of the reactions of O- and O2- with O2(a1Deltag) have been studied at 300 K in a selected ion flow tube (SIFT). The O2(a1Deltag) concentrations have been determined using emission at 1270 nm from the O2(a1Deltag, v=0-->X3Sigmag-, v=0) transition measured with an InGaAs detector calibrated against absolute spectrally dispersed emission measurements. The rate constants measured for O- and O2- are 1.1x10(-10) and 6.6x10(-10) cm3 s-1, respectively, with uncertainties of +/-35%. The O2- reaction only produces electrons and can be described as Penning detachment, while the O- reaction has been found to produce both O2- and e-. The O2- branching fraction has a lower limit of approximately 0.30. Comparison of the present results to previous measurements found in the literature provides a resolution to a previous discrepancy in the rate constant values.

Application of Balanced Detection to Absorption Measurements of Trace Gases with Room-Temperature, Quasi-cw Quantum-Cascade Lasers.

Distributed-feedback quantum-cascade (QC) lasers are expected to form the heart of the next-generation mid-IR laser absorption spectrometers, especially as they are applied to measurements of trace gases in a variety of environments. The incorporation of room-temperature-operable, single-mode QC lasers should result in highly compact and rugged sensors for real-world applications. We report preliminary results on the performance of a laser absorption spectrometer that uses a QC laser operating at room temperature in a quasi-cw mode in conjunction with balanced ratiometric detection. We have demonstrated sensitivities for N(2)O [10 parts in 10(6) volume-mixing ratio for a 1-m path (ppmv-m)] and NO [520 parts in 10(9) volume-mixing ratio for a 1-m path (ppbv-m)] at 5.4 mum. System improvements are described that are expected to result in a 2 orders of magnitude increase in sensitivity.

Spectral signatures of micron-sized particles in the Shuttle optical environment.

Solar-illuminated particulates surrounding the space Shuttle have been observed repeatedly in Shuttle missions. Even very low particulate loadings can interfere optically with measurements of earth limb emissions. Depending on wavelength and particle size, the important optical contributions can be scattering of solar radiation, scattering of earth radiation, and particle self-emission, all of which can exhibit significant spectral structure. We examine predicted particle brightnesses for ice particles as functions of wavelength through the visible and IR and as functions of particle size between the volume absorption and geometric scattering regimes. Predicted brightnesses are compared to expected atmospheric limb radiances in various spectral bandpasses to illustrate conditions in which earth limb sensors would be affected and the means for identifying particulate contributions.

Rocketborne cryogenic (10 K) high-resolution interferometer spectrometer flight HIRIS: auroral and atmospheric IR emission spectra.

A Michelson interferometer spectrometer cooled to 10 degrees by liquid helium was flown into an IBC class III aurora on 1 April 1976 from Poker Flat, Alas. The sensor, HIRIS, covered the spectral range 455-2500 wave numbers (4-22 microm) with a spectral resolution of 1.8 cm(-1) and an NESR of 5 x 10-12 W/cm2 scrm(-1) at 1000 cm(-1). An atmospheric emission spectrum was obtained every 0.7 sec over an altitude range of 70-125 km. Atmospheric spectra were obtained of CO2 (nu3), NO (Deltanu = 1), O3 (nu3) and CO2 (nu2). Auroral produced excitations were observed for each band, this being the first known measurement of auroral enhancements of O3 (nu3), 9.6 microm, and CO2 (nu2), 15 microm, emissions.