Wavefront correction and enhancement of the brightness of a phase image in a system comprising a phase-contrast interferometer and a nonlinear medium

It is suggested that a phase-contrast interferometer can be used in combination with a thin layer of a transparent nonlinear medium to narrow the angular distribution of a coherent laser beam. An experimental demonstration is reported of a fourfold increase in the axial brightness of a diverging He–Ne laser beam. A cell containing a liquid crystal and an additional layer, which absorbed partly the laser radiation and heated the liquid crystal, was used as the nonlinear medium. The experiments confirmed enhancement of the brightness of the phase image in the proposed system.