The features of the phase object visualization in the field of coherent laser radiation predicted in the first Rytov approximation

We concern the problem of laser beam diffraction by a phase object with and without radiation absorption. In terms of a plane optical wave passing through the object, we solve the scalar Helmholtz wave equation in the first Rytov approximation and discuss the consequences of the equation obtained in such an approximation. By taking into account the wave diffraction spreading, numerous features of the phase object visualization in the field of coherent laser radiation are predicted. We reveal the fundamental relationships between the Fourier spectra of the object dielectric permittivity and diffracted wave characteristics described in terms of the wave intensity and phase shift in free space. The findings are of a general nature and can be useful in optical imaging of various objects.