Testing device and testing method for optical thin film stress

The invention provides a testing device and a testing method for optical thin film stress. Surface sound waves with the same frequency are generated at specific positions of the front surface and the back surface of a prepared long-strip sample by a surface sound wave generator; the surface sound waves are used as a diffraction grating for incident light; when a film is not plated, the wavelengths of the surface sound waves on the front surface and the back surface of a substrate are equal and the symmetrical diffraction grating is formed, and diffraction zero-grade or +/-1-grade light intensity is uniformly distributed; after the film is plated, the substrate is bent by the stress; the sound wave speeds on the two surfaces are changed so that the wavelengths of the sound waves on the front surface and the back surface are different and the diffraction grating is not symmetrical, and furthermore, the zero-grade or +/-1-grade light intensity is not uniformly distributed; the light intensity is periodically distributed and is converted into the bending curvature of the substrate according to the size of the period; and the stress of a thin film is calculated according to a Stoney formula. The testing device has the advantages of simple structure, simplicity in manufacturing and high sensitivity; and the system errors of a traditional substrate bending method are eliminated, and the testing device can be applied to the detection of the stress of all the thin films prepared on the transparent substrate.