Surface profile measurement and stabilized Michelson interferometer

For the surface measurement the interferometers developed by Michelson, Mirau, Linnik, and etc., have been mainly used. Also it is important to stabilize the interferometer because the mapping of the interferogram is sensitively dependant on the stability conditions such as thermal drift, mechanical vibrations, and etc. In this work surface profile measurement has been investigated by using Vikhagen filtering method and Michelson interferometer. The stabilization of the interferometer has been done by fringe locking method. In this work 4-bucket algorithm has been applied to measure the surface profile. Explaining those simply, phase θ is shifted by θ = π/2 four times and four interference intensity fringes are obtained and the surface profile is calculated by using Borland C⁺⁺ program codes. Image noises originated from CCD camera, frame grabber, environmental experimental conditions, and etc., were eliminated by median filter and algorithm suggested by Vikhagen. Especially, noise filtering method by Vikhagen has advantage without convolution error by combining filtered image and π shifted images. Also we used path dependent two dimensional continuous scanning method. Michelson interferometer was used to measure surface roughness and PZT was automatically controlled in PC to shift the phase of the interferogram. The images were obtained from frame grabber through CCD. Images were treated by using MIL library and Borland C⁺⁺ program codes. The interferometer was stabilized by using fringe locking method, in which methods the reference mirror was pushed back to the original position of the fringe by applying the amplified error voltage when a fringe moves due to the environmental conditions. That stabilization was very effective in our harsh lab located on 17 stories.