Some remarks on radio-frequency holography

The extension of holographic techniques to radio frequencies offers new possibilities. The recording can be done by scanning an area with a probe. The reference wave can be replaced by a signal whose phase is varied with the probe position according to some program. Thus, "slow" reference waves (k > k0) can be simulated. Complex modulation schemes can also be used. A product detector can multiply the probe and the reference signal together and the recorded product can be used in the same manner as an intensity hologram. With two such "correlators," the probe signal can be obtained in phase and magnitude. Optical reconstruction can be done from this information.