Asymptotic analysis of convergent Gaussian beam reflected from a liquid-solid interface

The nonspecular effects principally appearing at a Rayleigh incidence neighborhood show a distortion of the reflected caustic with respect to geometric acoustic results. This distortion is studied qualitatively, and its physical representation is given. In particular, the lateral and focal shifts thus exhibited confirm previous results. By means of asymptotic methods (the steepest-descent method and the adequate version of Ludwig at the caustic neighborhood) based upon the short wave hypothesis, the acoustic reflected field is evaluated at each point of the space considered. The study is of interest in connection with the use of focusing transducers to limit diffusion effects during the nondestructive evaluation of materials