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Two holographic methods for flatness testing with subwavelength or multiple-wavelength sensitivities

Two holographic methods suited for the measurement of flatness deviation are presented. The first one takes advantage of the basic holographic interferometry arrangement usually meant for deformation analysis of rough bodies. Simple modifications allow flatness measurements of polished surfaces with sub-wavelength sensitivity. Secondly, a new desensitized interferometer is described allowing the measurement of rougher objects, more frequently encountered in engineering practice. The key component of this interferometer is a diffractive optical element produced by recording two wave interference patterns. Desensitization factors ranging from 1 to 100 with respect to a Fizeau interferometer can be achieved. Harness checks of computer disks demonstrate the possibilities of both interferometers. Deformation measurements performed with the desensitized interferometer are presented.