The conditions for the caustics emergence at the longitudinal optical sensing of stratified optically inhomogeneous media by structured laser beams which are visualized in a section as a family of geometric shapes. It was shown that in the observation plane at the exit of the medium projection of caustic surface appears as the extremums’ envelope of refractive displacement elements of the structure beam. This fact allows to experimentally determine the position of the caustic without registering intensity distribution in refractive image. Recorded geometric parameters of caustics are used to solve the inverse problem of refraction for reconstruction of the media physical characteristics, causing inhomogeneity of the refractive index. Experimental setup for pictures visualization of refraction of the structured laser radiation in the diffusion layer of the liquid is shown.