DOUBLE-EXPOSURE SPECKLE PHOTOGRAPHY WITH 3 SLABS FOR THERMAL-EXPANSION TENSOR MEASUREMENT

Three mutually perpendicular slabs are cut from a block of material wh ich is anisotropic from a thermal expansion standpoint. The three slab s are placed in a thermostatic bath and illuminated with HeNe laser li ght, and their speckle is registered. The set of slabs is subjected to a temperature increase, and a second speckle on the same photographic plate is exposed. Observation of the Young fringes at three points of each slab with a narrow laser beam provides ample possibilities for c alculating the material's thermal expansion tenser components. The met hod provides the tenser calculation with one photographic plate only.