Parametric study of small-signal gain in a slit nozzle, supersonic chemical oxygen-iodine laser operating without primary buffer gas

A detailed experimental study of the gain and temperature in the cavity of a supersonic chemical oxygen-iodine laser (COIL) is carried out to find opt imal values of the flow parameters corresponding to the maximum gain, It is found that high gain (> 0.7 % /cm) can be obtained in a COIL operating wit hout primary buffer gas and, hence, having a high gas temperature (>250 K) in the cavity. The measurements are performed for slit nozzles with differe nt numbers and positions of iodine injection holes. Using a diode laser-bas ed diagnostic, the gain is studied as a function of the molar flow rates of various reagents, with optical axis position along and across the flow, an d Mach number in the cavity. Maximum gain of 0.73%/cm is obtained at chlori ne and secondary nitrogen flow rates of 15 mmole/s and 7 mmole/s, respectiv ely, for a slit nozzle with transonic injection of iodine. The gain is foun d to he strongly inhomogeneous across the flow. For a slit nozzle with iodi ne injection in the diverging part of the nozzle, the values of the maximum gain are smaller than for nozzles with transonic injection. Opening a leak downstream of the cavity in order to decrease the Mach number and increase the cavity pressure results in a decrease of the gain and dissociation fra ction. The gain is a nonmonotonic function of the iodine flow rate, whereas the temperature increases with increasing iodine flow. An analytical model is del eloped for calculating in slit nozzles the iodine dissociation frac tion F and the number N of O-2((1)Delta) molecules lost in the region of io dine dissociation per I-2 molecule.