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

Abstract

Singlet delta oxygen (SDO) yield, gain, 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. The flow rate through the M=3 laser cavity is 0.5 mole/sec, with a 10 cm gain path and steady-state run time of up to 10 sec. SDO yield and gain have been measured in a wide range of RF discharge powers, up to 4.5 kW. The results demonstrate that both yield and gain at high discharge powers nearly level off, approximately at 3.5% and 0.11 %/cm, respectively. Gain measurements at multiple axial locations in the supersonic section demonstrated that gain peaks 3 cm downstream of the nozzle exit and decreases to near transparency at the downstream end of the cavity. During operation, extensive separation bubbles formed near the top and the bottom walls of the supersonic flow channel. Gain measurements at two transverse locations detected negative gain (i.e. absorption) in the separation bubble at the conditions when significant gain was measured on the centerline, at the same axial location in the cavity. Laser power has been measured using two different resonator configurations, (i) two 99.9% output couplers on both resonator arms, 1.7 W, and (ii) 99.9% mirror on one arm and 99% output coupler on the other, 1.6 W. The latter result demonstrates that at the present conditions laser power can be coupled out without using high-reflectivity output couplers. Low c.w. output power may be due to strong transverse flow nonuniformity in the resonator, with significant absorption measured in the separation bubbles. Removing one of the angle step diffuser inserts significantly reduced flow separation, without reducing steady-state run time, and produced nearly uniform distribution of gain in the supersonic cavity, with 0.10-0.11 %/cm gain achieved over approximately 10 cm of the cavity length. This suggests that operation without diffuser inserts may result in higher gain and laser power.