Abstract

A method for recording achromatic volume holograms is described. These are of interest for their high diffraction efficiency and ability to be realized in real time using nonlinear optics. Such volume holograms may be used in applications including image reconstruction, distortion compensation, and phase conjugation. The polychromatic object field passes through a fixed tilted grating. A telescope images the undiffracted and first-order beams onto the holographic recording medium tilted by the same angle as the fixed grating. Proper tilt of the dispersive recording medium makes the system volume achromatic and the fixed grating tilt makes the system achromatic at the surface of the recording medium. In a typical experiment a 5-mm thick crystal of photorefractive barium titanate might be used. The undiffracted portion of the beam is spatially filtered so that it may be used as a plane wave reference beam. Alternatively, if there is a point source in the object field everything else in the field may be filtered out of the undiffracted beam so that the undiffracted beam may be used as a reference beam to cancel phase aberrations of the exterior system. This is similar to previous monochromatic experiments in which a reference beam is passed through the same distortion as the object beam so that a distortion compensated hologram may be written.¹

© 1989 Optical Society of America