SIMULTANEOUS 2-WAVELENGTH HOLOGRAPHIC-INTERFEROMETRY IN A SUPERORBITAL EXPANSION TUBE FACILITY

A new variation of holographic interferometry has been utilized to per form simultaneous two-wavelength measurements, allowing quantitative a nalysis of the heavy particle and electron densities in a superorbital facility. An air test gas accelerated to 12 km/s was passed over a cy lindrical model, simulating reentry conditions encountered by a space vehicle on a superorbital mission. Laser beams with two different wave lengths have been overlapped, passed through the test section, and sim ultaneously recorded on a single holographic plate. Reconstruction of the hologram generated two separate interferograms at different. angle s from which the quantitative measurements were made. With this techni que, a peak electron concentration of (5.5 +/- 0.5) x 10(23) m(-3) was found behind a bow shock on a cylinder. (C) 1997 Optical Society of A merica.