Diffraction-limited holography

Experimental determinations of the size of the Airy disk for real image reconstructions of holograms of limited extent have yielded values comparable with those given by diffraction limitation. The holograms used are transmission, side-band holograms of low carrier frequency and are constructed in the far field of the object (~3-microm extent). In reconstruction, the real image is focused, with unit magnification, onto a rotating ground-glass plate and viewed through a microscope with 400x magnification. Comparisons of the reconstructed image with the actual object are made for holographic speeds ranging from f/10 to f/2 using visual, photographic, and photoelectric recordings. Photographic resolution tests, using standard bar patterns, yield a value of 1.05 for the ratio of the observed radius of the Airy disk to that corresponding to diffraction limitation. These tests are in disagreement with photoelectric measurements, the discrepancy being quantitatively ascribable to contrast enhancement in the film.