1. Apparatus for providing successively accessible interference patterns comprising: optical memory means having a storage material for storing frequency holes in at least two spatial dimensions and a frequency dimension, the frequency holes forming interference patterns in at least two spatial dimensions wherein the frequency dimension includes a series of different interference patterns, the optical memory means further having transparent electrode means on two surfaces of the storage material for applying an electric field across the storage material; means for directing an optical beam of wavelength .lambda. onto the storage means; and control means for varying the electric field potential across the storage material thereby shifting different interference patterns into resonance with the optical beam to provide an optical output of the stored interference patterns.