A thin layer of a homogeneously oriented nematic liquid crystal (NLC) can be used as an unusual recording medium for the materials testing in order to visualize the distribution of the weak power physical fields, local modifications and microrelef defects on the surface, and the structural inhomogeneities in the bulk. The initial NLC molecular ordering represents the basis for the external fields visualization. The ordering may be disturbed locally under the influence of the thermal, electric, or magnetic fields, molecular interactions, or electromagnetic irradiation. The recording of these areas becomes possible if the NLC deformed structure is illuminated in the transition or reflection mode, and the interference pattern to appear is studied in the crossed polarizers in comparison with the background structure . The light intensity over NLC layer I(x,y) modulated by the defovried structure is described by the equation I(x,y) = Io sin4[6(x,y)/2], where phase delay o = f(n, nd, ne, no, H); n, nd are the refractive indices of a nondeformed and deformed NLC layers; no, ne are the refractive indices of the NLC layer for the ordinary and extraordinary polarizations, H - the NLC layer thickness.