Rate measurement in shock waves with the laser-schlieren technique

The paper discusses the laser-schlieren or narrow laser beam deflection technique in some detail, with particular reference to its application to very fast processes. The optics of the beam-shock wave interaction is examined using the scalar formulation of Huygens' principle (Kirchoff integral), with the shock density profile introduced as a transmission coefficient. The accuracy with which the signal generated by a differential detector will reproduce the variation of the refractive index gradient in a reactive shock is discussed in terms of this formulation. The response of such a detector to passage of a curved shock in a rare gas is also determined employing the shock-curvature theory of de Boer. These calculations are in good agreement with experiment and locate the 'time origin' - coincidence of shock leading edge and beam center - on the 'positive' portion of the signal near zero-crossing.