Physical optics of the laser-schlieren shock tube technique

The physical optics of the laser-schlieren technique for the measurement of rate processes in shock waves is examined in detail. The method utilizes the Kirchhoff-Huygens integral with the usual thin lens, paraxial, and Fresnel approximations, all of which are appropriate for the typical laser schlieren experiment. The resolution and sensitivity of the technique are defined for all detector separations, and a reliable method for locating the time origin in the schlieren signal is provided. Diffraction is found to have a significant effect on the shock front generated signal, and geometrical optics treatments of this signal are shown to be inadequate.