The method of laser Doppler visualization and measurement of 2D velocity vector field in flows with minimization of influence of a multi–particle scattering is discussed. The investigated section in the flow is illuminated with a laser sheet. Our approach is based on reception of a pair wise difference of normalized frequency–demodulated images of a laser sheet in light beams scattered in various directions. The 2D velocities field is formed from linear combinations of images of the laser sheet in frequency–demodulated light scattered in directions orthogonal to it.

The methods of Hilbert optics widely use in tasks of visualization and measurement of phase optical density in fluids. In this work, the problem of vortex rings generation upon sudden opening of a cylindrical chamber containing a gas at elevated pressure is considered. At diffraction of pressure front on an aperture in a wall the vortical rings propagated in the opposite directions from the wall have been detected by optical Hilbert methods.