Gain and output power measurements in an electrically excited oxygen–iodine laser with a scaled discharge

Abstract

Singlet delta oxygen (SDO) yield, small signal gain, and output power have been measured in a scaled electric discharge excited oxygen–iodine laser. Two different types of discharges have been used for SDO generation in O2–He–NO flows at pressures up to 90 Torr, crossed nanosecond pulser/dc sustainer discharge and capacitively coupled transverse RF discharge. The total flow rate through the laser cavity with a 10 cm gain path is approximately 0.5 mole s−1, with steady-state run time at a near-design Mach number of M = 2.9 of up to 5 s. The results demonstrate that SDO yields and flow temperatures obtained using the pulser-sustainer and the RF discharges are close. Gain and static temperature in the supersonic cavity remain nearly constant, γ = 0.10–0.12% cm−1 and T = 125–140 K, over the axial distance of approximately 10 cm. The highest gain measured is 0.122% cm−1 at T = 140 K. Positive gain measured in the supersonic inviscid core extends over approximately one half to one third of the cavity height, with absorption measured in the boundary layers near top and bottom walls of the cavity. Laser power has been measured using (i) two 99.9% mirrors on both sides of the resonator, 2.5 W, and (ii) 99.9% mirror on one side and 99% mirror on the other side, 3.1 W. Gain downstream of the resonator is moderately reduced during lasing (by up to 20–30%) and remains nearly independent of the axial distance, by up to 10 cm. This suggests that only a small fraction of power available for lasing is coupled out, and that additional power may be coupled in a second resonator. Preliminary laser power measurements using two transverse resonators operating at the same time (both using 99.9–99% mirror combinations) demonstrated lasing at both axial locations, with the total power of 3.8 W.