This letter discusses the effect of nitric oxide on gain and output power of a pulser-sustainer discharge excited oxygen iodine laser. Adding small amounts of NO to the laser mixture ͑a few hundreds of ppm͒ considerably increases gain and output power due to ͑i͒ O atom titration and resultant slower I * atom quenching and ͑ii͒ improved stability of the dc sustainer discharge, which allows stable operation at significantly higher discharge powers. Gain on the 1315 nm iodine atom transition and laser power in the M = 3 transverse laser cavity are 0.049% / cm and 1.24 W, at a flow temperature of T = 100 K.

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 O 2-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.

The paper presents the results of iodine vapour dissociation measurements in a high voltage, nanosecond pulse duration, repetitively pulsed discharge, used as an auxiliary (‘side’) discharge in an electric discharge excited oxygen–iodine laser. The side discharge, sustained in a high-pressure iodine vapour/helium mixture remained stable in the entire range of experimental conditions. Iodine dissociation fraction generated in the side discharge and measured in the laser cavity is up to 50%. However, the experiments showed that additional iodine dissociation generated in the side discharge only moderately increases laser gain, by 10–15%. Parametric gain optimization by varying main discharge pressure, O2 and NO fractions in the flow, I2 flow rate, pulsed discharge frequency and sustainer discharge power, with the side discharge in operation produces gain up to 0.08% cm−1. Two parameters that critically affect gain are the energy loading per molecule in the discharge and the NO flow rate controlling the O atom concentration in the flow. In particular, operation at the main discharge pressure of 60 Torr results in significantly higher gain than at 100 Torr, 0.080% cm−1 versus 0.043% cm−1, due to higher discharge energy loading per molecule at the lower pressure. Laser output power measured at the gain optimized conditions is 1.4 W.

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