Interferometric signal and image processing by autoconvolution method

Interferometric methods are widely used in metrology, quality control and optical systems alignment(1,2). In precision measurement it is usually required to recover the interference fringes phase by non-linear data processing. As known the inherent property of equispaced fringes, Newton's rings and some other kinds of interference pattern is the symmetrical form of the function that describes the intensity distribution. Using such a priori information it is possible to calculate the shift of interference fringes with high sensitivity and noise-immunity without phase recovering using the linear transform only by signal autoconvolution(3,4). We have applied the autoconvolution method to measurement of fractional part of interference order for equispaced fringes(3) and to measurement of lateral displacement of Newton's rings(4). The first kind of interference fringes is usual e.g. for linear displacement measurement, the second one concerns the problems of lens centering and interferometer alignment. The autoconvolution method was realized by interferometric signal processing in spatial and spatial frequency domains. The accuracy and noise-immunity of autoconvolution method were verified.