Field-widened Michelson interferometer for measuring velocities of diffuse back surfaces of shocked specimens

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Abstract
A classical Michelson spectrometer with different length arms used to study the velocity of a diffusing surface illuminated by a laser beam gives a signal whose modulation M decreases rapidly with increasing sensitivity of the apparatus and roughness of the surface. Using the Fraunhofer diffraction theory, a formula connecting these parameters has been established. It proves the advantage of the field‐widened interferometer, and we have set up an original specimen where M=1 provided that all the points of the illuminated area move at the same velocity. For a disordered displacement of these points, the signal of this interferometer is more complicated; a particular case is solved and experimentally verified in connection with the free surface velocity of a fixed aluminum disk submitted to the impact of a thin plate projected with inaccurate parallelism.
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