Results of small-signal gain measurements on a supersonic chemical oxygen iodine laser with an advanced nozzle bank

High-resolution diode laser spectroscopy has been used to probe the gain in the active medium formed by an advanced supersonic chemical oxygen iodine laser (COIL), ejector nozzle bank. The probe beam was directed through the medium at 90degrees (normal) to the flow velocity and at an angle of 27.5degrees away from normal incidence. Analysis of the small-signal gain spectrum allowed for the determination of the gain, average gas velocity, static pressure, and temperature. The dependence of gain, temperature, and gas velocity on the primary nitrogen molar flow rate and basic hydrogen peroxide temperature was obtained. A maximum small-signal gain of 7 x 10(-3) cm(-1), average gas velocity of 575 m/s, static temperature of 172 K were measured for flow rates of 270 mmole/s of primary nitrogen, 39.2 mmole/s of chlorine, 11 mmole/s of secondary nitrogen, and 0.8 mmole/s of iodine. Estimation of the static pressure in the flow core from spectroscopic data is very close to the static sidewall pressure. The role of transverse velocity components in the gas flow and their effect on the interpretation of gain profiles is discussed.