Coherent optical noise suppression.
The performance of coherent optical spatial filtering systems is often limited by lens noise. Imperfections in the optical components generate noisy diffraction patterns when illuminated by spatially coherent light. This random noise often masks useful signals in the output images. Coherent noise can be reduced by decreasing the spatial coherence of the illumination system. Unfortunately, reducing spatial coherence also reduces the frequency discrimination capabilities of the system; a filter cannot operate on a given spatial frequency without significantly affecting an adjacent frequency. This paper presents a technique for time averaging coherent optical noise without reducing the spatial frequency discrimination capability associated with a laser illumination system. Experimental results are given for noise suppression by both a reduction in spatial coherence and by the noise averaging technique. The improved frequency discrimination of the latter technique is also demonstrated.