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.
A bistatic lidar has been assembled at the HIPAS Observatory in Alaska (64.9 degree(s) N latitude and 146.8 degree(s) W) around a 2.7 m diameter rotating Liquid Mirror Telescope (LMT) with parabolic mercury reflecting surface. The LMT is isolated in a tower under a float glass skylight for operation when outside temperature can be at -40 degree(s)C. The lidar operates in conjunction with a 70MW (Effective Radiated Power) Radio Frequency array and ionospheric heater, which has been shown to perturb the arctic ionosphere and the electrojet. Bistatic laser illuminators include a Doubled YAG pumped dye laser (presently tuned to the 590 nm sodium D<SUB>2</SUB> resonance), an Excimer pumped dye laser (also tuned to the D<SUB>2</SUB> line), and a Doubled Alexandrite laser for future N<SUB>2</SUB> and Ca<SUP>+</SUP> detection. Observations include sporadic Na formation due to the aurora, detection of Leonid's meteor trails (starting at 180 km) and changes in the sodium layer due to the HIPAS-RF heater. The 590 nm lidar is now being modified to detect polar stratospheric clouds during the summer. Ozone and OH can be detected in the future with the 308 nm wavelength of the excimer laser. A more recent application will use the LMT to focus a several hundred Joule - nanosecond duration laser pulse to 100 km altitudes, for the purpose of creating multi kilometer long plasma columns in the sky for direct electroject modification experiments. The 1057 nm laser pulse will be generated by surplus Nova components; namely, 9.2 cm and 15 cm disk amplifiers in a double pass SBS configuration.
The advent of inexpensive large aperature near diffraction limited Liquid Mirror Telescopes (LMT's) makes possible applications not sensitive to their near vertical viewing nature; such as, astronomical surveys, space debris surveys, lidar collectors, and laser radiation concentrators, for plasma creation experiments in the sky. LMTs are easily an order of magnitude less expensive than a polished glass reflectors, which are only approximations to the naturally perfect parabolic surtace created by a rotating liquid. Highly reflecting liquid mercury is easily cleaned and safe when handled correctly.