Gain, yield and water vapor diagnostics in supersonic coils with different schemes of iodine injection

We report on a detailed experimental study of the gain and temperature in the resonator of a supersonic chemical oxygen-iodine laser operating without primary buffer gas and on preliminary power measurements in this laser. In particular, a study is carried out to find optimal values of the flow parameters corresponding to the maximum gain. The measurements are performed for slit nozzles with different numbers and positions of iodine injection holes. Using diode laser based diagnostic, the gain is studied as a function of the molar flow rates of various reagents, optical axis position along and across the flow and Mach number in the resonator. Maximum gain of 0.73%/cm is obtained at chlorine and secondary nitrogen flow rates of 15 mmole/s and 7 mmole/s, respectively, for a slit nozzle with transonic injection of iodine. The gain is found to be strongly inhomogeneous across the flow. For slit nozzle with iodine injection in the diverging part of the nozzle the values of the maximum gain are smaller than for the nozzles with transonic injection. Opening a leak downstream of the resonator in order to decrease the Mach number and increase the resonator pressure results in the decrease of the gain and dissociation fraction. The gain is a non-monotonous function of the iodine flow rate, whereas the temperature increases with increasing iodine flow. An analytical model is developed for calculating the iodine dissociation fraction Fand the number N of O₂(¹δ) molecules lost in the region of iodine dissociation per 1₂ molecule in slit nozzles. Preliminary power measurements are performed. For slit nozzle with iodine injection in the diverging part of the nozzle output power of 287 W with chemical efficiency of 21% was measured at 15.1 mmole/s of CI₂ with no primary buffer gas and secondary N₂ flow rate of 12.8 mmole/s. 21% efficiency is the highest reported chemical efficiency of a supersonic COIL operating without primary buffer gas.