Methods of applying laser interferometry to measure particle velocity history at the interface between a shocked specimen and a transparent window material are discussed. Particular emphasis is given to diffusely reflecting interface surfaces, to shock‐induced light polarization shifts which can occur in the window material, and to a transient loss of fringe contrast which occurs whenever the reflecting surface velocity is spattially nonuniform. It is shown that the loss of finge contrast can be used to provide time‐resolved measurements of the spatial variations in particle velocity.