Two-beam optical interferometry is extremely valuable for quantitative space-time resolved refractive index measurements. Basically a two-beam optical interferometer consists of an intense light source, high quality plane mirrors, beam-splitters, and a photographic plate or viewing screen. A Mach-Zehnder interferometer arrangement utilizing coherent optical laser illumination is employed for spacetime resolved refractive index measurement of electron-ion gaseous plasmas produced in energetic pulsed pinches, laser-produced plasmas, and in media with thermal and concentration gradients. Double-pulsed Mach-Zehnder interferometry has been developed to provide effective infinite-fringe interferograms using relatively poor optics, simple alignments, low resolution films and a pulsed laser with a standard approximately 0.1A linewidth. Optical holographic techniques have been developed to record the total, three-dimensional picture onto a two-dimensional plate of film. As in optical interferometry, the intersection of a test and a reference beam results in an interference pattern--a hologram. For holographic interferometry, the photographic plate or film is exposed twice one exposure with and a second exposure without the experimental medium in the test beam. Recently, two-wavelength optical interferometry techniques were extended to two-wavelength optical holographic interferometry. Author
Sponsored by National Science Foundation, Washington, D. C.