Spatially resolved temperature diagnostic for the chemical oxygen-iodine laser based on a variant of saturation spectroscopy

Abstract

The Chemical Oxygen-Iodine Laser (COIL) depends upon a supersonic mixing nozzle to produce optical gain on the 2P1/2 - 2P3/2 atomic iodine transition at l equals 1.315 mm. The translational temperature in the gain generator is particularly important, as the yield of singlet oxygen required to reach lasing threshold decreases from 17 percent at room temperature to 6 percent at T equals 150K. We have demonstrated an optical technique for measuring the gas temperature in the COIL supersonic expansion region with a spatial resolution of less than 12 mm3 using a novel variant of saturated laser spectroscopy. The sub-Doppler hyperfine spectrum of the visible I 2 (Chi) 1 (Sigma) g + yields B 3 (Pi) (O u + ) transition exhibits 15 or 21 transitions and has been recorded using laser saturation spectroscopy with a resolution of about 10 MHz. Pressure broadening of the hyperfine components and cross-relaxation effects have been studied and depend significantly on rotational level. By altering the saturation spectroscopy apparatus so that the pump and probe beams are nearly co-propagating, a Doppler profile, limited to the iodine sample in the volume of the overlapped beams, is obtained. Temperature, as derived from the Doppler profile, is spatially resolved and used to examine the flow from a small supersonic nozzle assembly.