Formation of Carrier Frequency Holograms with an On-axis Reference Beam

In this method, a transmission grating is placed in front of the photographic plate. The hologram is formed in four exposures. After each exposure, the grating is translated by a quarter of its spatial period and the phase of the reference beam is shifted by 90 degrees . An analysis shows that such a hologram is equivalent to one formed with an off-axis reference beam. Experimentally, holograms with carrier frequencies as high as 94 lines/mm gave good reconstructions. The new method should be advantageous when holograms are to be formed with sources of short coherence length or through phase distorting media.