The modulated grating hologram

A phase and amplitude, off-axis hologram was synthesized from three computer-generated transmission masks, using a multiple-exposure holographic recording method. Each of the masks controls one fixed-phase component of the complex hologram transmittance. The basic grating is generated optically, relieving the computer of the burden of drawing details the size of each fringe. The maximum information capacity of the computer plotting device can then be applied to the generation of the grating modulation function. By this method, large digital holograms (25 mm by 25 mm) were synthesized in dichromated gelatin. The recording method is applicable to virtually any holographic medium. The modulated grating hologram was designed primarily for the application of spatial filtering, in which the requirement is a hologram with large dynamic range and large free spectral range.