Diffraction Calculation Method

Calculating diffraction of light correctly is a most important content in the research of optic information processing. However, it is a difficult problem to complete diffraction calculation correctly. In recent years, with the rapid development of digital information processing techniques, diffraction calculation may be accomplished conveniently. There are various fast algorithms of calculating diffraction integral in space range and frequency range.In this thesis, we have summarized three numerical evaluation methods of calculating diffraction integral in space range and two fast Fourier transform (FFT) methods in frequency range. The methods of calculating diffraction integral in space range are discussed chiefly. The graphs are given by comparing with the three polynomial approximations of Fresnel functions, and comparison results are analyzed specifically. The results show: the curves are so similar that the maximal relative error between them is less than 6%. The algebraic methods of diffraction calculation replace integrals by algebraic expressions, so the computational efficiency can be improved highly.In order to validating the approximate algorithm of Collins' formula, the diffraction images for a light wave that passes a thin lens from a quadrate aperture are simulated theoretically and compared with the experimental results. It is shown that the experimental results are in agreement with the computation results. Therefore, this approximate method is applied to the measurement of the lens focus, and the focus error between using this approximate method and traditional method is 0.7%.