Numerical technique for analyzing laser cavity acoustics and its application to a real laser design

Abstract

Pulsed chemical laser devices require a high degree of fluid homogeneity to meet electrical discharge and optical beam‐steering requirements. However, the lasing initiation process generates relatively large pressure and temperature (and thus, critically, density) disturbances which propagate upstream and downstream at fluid and acoustic velocities. These disturbances can interact with each other and with other system components and later return to the cavity to degrade subsequent lasing pulses. A quasi‐one‐dimensional numerical fluid analysis program has been developed, using the “discrete element” technique, which permits examination of the various forms of acoustic attenuation being considered for use in such systems. This technique has been used to establish fluid supply system characteristics for an actual 1000‐Hz pulse rate lasing system. A design was arrived at that could supply adequate acoustic attenuation within the required 1 ms. Some details of the numerical technique and correlation with experimental data will be presented. Major emphasis will be on the application of the technique to at least one particular laser system, and a generally applicable convective/acoustic design philosophy, which developed as a result of parameterization studies carried out using the numerical model.