Measuring the Roughness Parameters of Ground and Polished Optical Surfaces by High-Precision Laser Interferometry Methods

Methods and instruments for controlling the roughness parameters of the optical surface profiles with different root-mean-square deviations sigma at different stages of the technological processing are discussed. An infrared laser interferometry method has been developed and justified, which is based on the Kirchhoff approximation upon scattering of plane electromagnetic wave lambda by a phase screen under condition sigma >> lambda. The analytical relation between the contrast of the video image of an interference pattern recorded with a designed unequal-arm Twyman-Green interferometer with a working wavelength of 10.6 mu m and the root-mean-square deviation has been obtained. The dynamic interferometry technique for controlling local nanometer deviations of the surfaces of optical components from a specified profile has been implemented and experimentally confirmed for the case when sigma >> lambda under the production vibration conditions using the algorithm for calculating the objective function: the 1D power spectral density. We report on the theoretical and experimental studies on the determination of the local root-mean-square deviations of the surfaces of optical parts with a diameter of up to 100 mm with regard to the nonexcluded systematic and random components of the objective function determination error.