Immersion interferometer for microscopic moiré interferometry

The basic sensitivity of moiré interferometry has been increased beyond the previously conceived theoretical limit. This is accomplished by creating the virtual reference grating inside a refractive medium instead of air, thus shortening the wavelength of light. Various optical configurations of moiré interferometry for operation in a refractive medium are introduced and one of them has been put into current practice. A very compact four-beamimmersion interferometer has been developed for microscopic viewing, which produces a basic sensitivity of 4.8 fringes per μm displacement (contour interval of 0.208 μm per fringe order), corresponding to moiré with 4800 lines per mm. Its configuration makes it inherently stable and relatively insensitive to environmental disturbances. An optical microscope is employed to obtain high spatial resolution. The method is demonstrated for deformation of a thick graphite/epoxy composite at the 0/90-deg ply interface. Paper was presented at the 1991 SEM Spring Conference on Experimental Mechanics held in Milwaukee, WI on June 9–13, 1991.