THERMAL-EXPANSION COEFFICIENT MEASUREMENT BY DOUBLE-EXPOSURE SPECKLE PHOTOGRAPHY

Described is a method for the measurement of the lineal thermal expans ion coefficient of a sample in the form of a plate of an isotropic mat erial. The speckle of the sample is registered on a photographic plate before and after an increase of the temperature of the specimen. Then , two points or more on the photographic plate are illuminated by an u nexpanded laser beam, and the analysis of the Young fringes produced b y these points allows for the measurement of the translation, rotation and thermal expansion of the sample. The maximum diameter of the expl oring beam is analyzed and experimentally checked.