Specific imaging of caustics upon refraction of structured laser radiation in stratified media

Conditions for caustic formation upon longitudinal probing of stratified optically inhomogeneous media by structured laser beams that are visualized in the cross section as families of geometrical figures are studied. In the plane of observation at the exit from the medium, the projection of the caustic surface is imaged as an envelope of extrema of refractive deflection of beam-structure elements. This circumstance makes it possible to experimentally determine the caustic position in the absence of intensity measurements in the refraction image. The measured geometrical parameters of caustics are employed in the solution of the inverse problem of refraction to reconstruct physical parameters of the medium that control nonuniformity of refractive index.