Method and apparatus for detecting small angular beam deviations

摘要

A method and apparatus for detecting small angular deviations of an input beam which utilizes a pair of diffraction gratings in series, both of which are operating in the Wood's anomaly region. As a result, the output intensity of the doubly diffracted input beam is at a maximum. Any deviation from the Wood's anomaly region by the input beam will substantially reduce the intensity of the output. This intensity variance is detected and utilized as an indication of a small angular deviation of the input beam.