Optical Autocorrelator with Special Application to MTF Measurement

An optical autocorrelator is described which is based on a modified Sagnac two-mirror interferometer that operates in the zero-fringe mode. The real-time radiant flux output is the square of the autocorrelation of the aperture function. In a particular application, when the aperture function is the pupil function of a lens under test, the autocorrelator output is the MTF of the lens. The system is not limited in focal length; aperature size is limited only by the sizes of the beam splitters and mirrors. Experimental results are given with comparison data for both infinite-conjugate MTF and the autocorrelation of an annular aperture. Methods of adapting the system for measurement of the phase of the transfer function and for finite conjugate testing are also described.