IMMERSION INTERFEROMETER FOR MICROSCOPIC MOIRE INTERFEROMETRY

The basic sensitivity of moire 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 moire interferometry for operation in a retractive medium are introduced and one of them has been put into current practice. A very compact four-beam immersion interferometer has been developed for microscopic viewing, which produces a basic sensitivity of 4.8 fringes per-mu-m displacement (contour interval of 0.208-mu-m per fringe order), corresponding to moire 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.