One of the promising methods for manufacturing high-aperture and inf-wavelength diffractive optical elements (DOE) is direct laser writing on thin metal films in regime of through oxidation. The amplitude diffractive metal/oxide structure is formed directly by localized laser heating without post-processing using liquid or dry etching. Optical diffractometry based on an analysis of the diffraction pattern obtained from a locally illuminated region of the grating is quite suitable indirect method for inspecting the metal/oxide gratings with a infmicron period. Measurement of the angular distribution of diffraction orders allows determining local period of the DOE structure, and measuring the intensity distribution over all diffraction orders allows determining the duty cycle of the grating. In this paper, the configurations of instrumentation schemes of metal/oxide gratings monitoring and algorithms for processing of diffraction patterns formed at illuminating the metal/oxide gratings by probe laser beam are considered.