A New Mixing Gasdynamic Laser

Abstract

A mixing gasdynainic laser (MGDL) incorporating a screen nozzle has been developed and demonstrated in a shock tube simulator. This concept has been shown to extend the specific power and efficiency of the conventional gasdynamic laser by a large factor and, at the same time, avoid the persistent, large-scale flow nonuniformities exhibited in earlier mixing laser concepts. Through the mixing of supersonic streams of N2 (2000 K and 66 atnt), with adjacent supersonic streams providing CO2 and H2O from very small orifices, gains of 1.5%/cm and 30 kJ/Ib of stored energy have been measured in the laser cavity. Time-resolved interferometric measurements have shown the mixing process and decay of turbulence to occur rapidly, before appreciable loss of stored energy, dtse to the small characteristic scale of the mixing. Essentially complete mixing and flow homogeneity (2% Ap/p} were achieved 15 cm downstream of the nozzle exit plane. Measured output specific powers of up to 11.8 kj/lb were extracted with a muliimode resonator. The results obeyed scaling taws that predict 15-20 kJ/Ib extractable from a larger device. The effects of impurities such as hydrogen and carbon monoxide that may appear in the combustion products of fuels have been determined. Smalt signal gains of 1.25%/cm and available energies of 27 kJ/lb were measured from a typical mixture of 75 N2/22 CO/3 H2 at 2300 K mixed with 10% CO2/1% H2O in the laser cavity. Based on the agreement of these measurements with an analytic model, an extractable specific power of greater than 20 k,f/8b can be predicted for a well-designed, large-scale laser device.