Gain diagnostic in a supersonic COIL with transonic injection of iodine

Measurements of die gain and temperature in the resonator of a supersonic chemical oxygen-iodine laser (COIL) with transonic injection of I₂, using diode laser based diagnostics, are reported. The measurements were carried out for a grid nozzle and two slit nozzles with different number and diameters of injection holes. Maximum gain of 0.54%/cm was obtained for a slit nozzle with the same total cross section of the injection holes as for the grid nozzle (for the later the maximum gain was only 0.34%/cm). The gain is found to be nonmonotonous function of the iodine flow rate, whereas the temperature increases with increasing iodine flow. The gain also increases with increasing O₂(¹Δ) yield. The measured temperatures in the resonator corresponding to the maximum gain are rather high (> 300 K).