A Grating Scale for Noise Free Natural Interference Fringe Suitable for Compact Displacement Measuring Grating Interferometer
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A state of the art grating interferometer using the natural interference pattern from first order diffraction beams whose fringe periodicity changes half of the grating pitch whose movement or phase information gives the desired displacement measurement. In order to use such fringe it is essential to suppress zero and even order diffraction order beams which is done, generally, by introducing a half wave path difference from two phase zones on each grating element zone in a binary phase grating with 50% fill factor. The presence of 3rd order beam restricts the placement of detector closer to the grating scale and so putting restriction on compactness of interferometer. A grating element groove structure is proposed which eliminates intensities in even 3rd and 6th order enabling placement of detector far closer to increase compactness of set-up.
KeywordsBinary Grating Grating Element Groove Depth
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