Gain Distribution and Output Power Measurements in a Scaled Electric Discharge Excited Oxygen-Iodine Laser

Abstract

Singlet delta oxygen (SDO) yield, gain in the supersonic cavity, and output power have been measured in a scaled-up electric discharge excited oxygen-iodine laser. The laser is using 5 kW transverse RF discharge operated at pressures of up to P0=90 torr to generate singlet delta oxygen in an oxygen-helium flow doped with NO. The total flow rate through the M=3 laser cavity is approximately 0.5 mole/sec, with a 10 cm gain path and steady-state run time at near design Mach number of M=2.9 of up to 5 sec. Gain and static temperature measurements vs. axial distance in the supersonic cavity demonstrated near uniform gain and temperature distributions, γ=0.10-0.12 % cm and T=125-140 K, over the distance of approximately 10 cm. Highest gain measured is 0.122 %/cm at T=140 K. Positive gain is measured in the supersonic inviscid core extending 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 two different resonator configurations, (i) two 99.9% output couplers on both resonator sides, 2.5 W, and (ii) a 99.9% mirror on one side and a 99% output coupler on the other side, 3.1 W. Gain measurements downstream of the resonator during lasing demonstrate moderate gain reduction at these conditions. Gain downstream of the resonator remains nearly independent of the axial distance, by up to 10 cm, suggesting 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 locations, with the total power of 3.8 W. The results demonstrate that only a small fraction of power stored in the flow and available for lasing is coupled out.