Testing the limits of the Stoney Equation for assessing stress in thin films from interferometric wavefront deformation measurements

摘要

We describe an optical measurement technique based on Carrier Frequency Interferometry (CFI) that allows to measure wavefront deformation of coated optics with high accuracy. The sensitivity of the method is considerably greater than phase shifting interferometry. The limits of validity of the Stoney equation in calculating stress in thin films is assessed using CFI. The evolution of stress in Ta_2O_5 films deposited by ion beam sputtering is also evaluated.