| The traditional surface error evaluation methods includes peak to valley value method, root mean square method and wave surface bump method etc. They have their own characteristics and the intrinsic link between each other. Intermediate frequency surface error evaluation is more and more widely concerned due to the application of high-power lasers. Compared to the shortage in the traditional intermediate frequency surface error evaluation, power spectral density method is applied to the new evaluation.The definition and physical significance of power spectral density are mainly discussed in this paper, which can be applied to evaluate the intermediate frequency surface error. The corresponding numerical method is proposed to calculate the power spectral density. Besides, we have talked about the applications in the intermediate frequency evaluation, PSD effective bandwidth and the calibration of interferometer. The calculation of one-dimensional PSD and two-dimensional PSD can be derived from the classical Fourier transform. According to the discretization of integral, we can build the discrete PSD mathematical model. Then, the relation between the PSD effective bandwidth and the sampling width has been discussed in detail. At last, the absolute "true" value of the measured wavefront can be obtained by means of the measurement of interferometer's frequency response.The software of power spectral density calculation is programmed in this paper, and this software has some commonality, with the function of any sampling sequence PSD calculation. It has modular design, fast Fourier transform algorithm and intuitive user interface. With the help of Visual C++ program, the software has good portability and functional development. At last, according to the contrast of two measurements and calculation results with the calculation result in Zygo Metropro software, we have verified the correctness of PSD calculation model and the appropriate selection of window function. |
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