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Miracles of the off-axis interference pattern

The development of the wave nature of light, over the last 430 years, resulted in the off-axis or Leith hologram. Earlier contributions were expressions for the resolution of microscopes and telescopes and the first color photographs. X-ray diffraction by crystals and recorded photographically (actually "holograms" recorded without a reference beam) eventually produced images of atoms in crystals. D. Gabor was the first to add an in line reference beam to a diffraction pattern by passing a coherent beam through a tenuous scene. Interference between the light scattered by the scene and the unperturbed beam was recorded (as in crystallography by a photographic plate, the hologram). The message was reconstructed when the plate was re illuminated with colored light. It is believed that the off axis reference beam was discovered during the classified development of side looking radars. The invention of the visible helium neon laser clarified the importance of the off axis hologram which produces 3D imagery with continuous parallax (miracle #1) of the recorded scene. It was found that the off axis hologram reconstructed the amplitude and phase of the original wavefront, making possible interferometric comparisons (miracle #2). Reconstruction of the conjugate wavefront was achieved by reversing the direction of the reconstructing beam (miracle #3). Phase conjugated holograms makes possible 3D microscopes and can be used to correct different optical systems. In hind sight, it could be said that the off axis or Leith hologram was too obvious, as are all other great discoveries.