Abstra ctA survey is made of interferometric techniques receiving the optical path 4 = fnds in real time. Using differential interferometry or a new phase coupling technique, I(Dt) can be obtained in a wide range of conditions. A variety of applications to gasdynamic problems is described.A laser beam traversing a flow gives information on the optical path 1 = f nds in the flow when it is brought to interference with a suitable reference beam. As in most cases the refractive index n can be related to one or more of the interesting flow parameters: density p, pressure p, temperature T, or electron density ne; laser interferometry is a suitable means for flow diagnostics.As is already described in [1 ] , it is the Wollaston prism differential interferometer that is especially well suited and offers great advantages in laser interferometry. The essential features of this technique will be described and demonstrated with a number of different applications to gasdynamic investigations.To overcome the limitations inherent in differential interferometry, a new phase coupling technique is now being developed in our laboratory. This leads to a new generation of laser interferometers having a wide range of applications especially in gasdynamics and related fields.Laser Differential Interferometer PrincipleThe optical system is based on a differential interferometer using Wollaston prisms as beam splitting elements. A continuous gas laser (He-Ne laser) is used as light source and photodiodes are used for registration. A schematic diagram of the arrangement is shown in Fig. 1.The linear polarization of the original laser beam is transformed into circular polarization using a A/4 plate. The laser beam is then split under a small angle c by means of a Wollaston prism. e is given by c = 2 tanalne-n ex or(1) where a is the prism angle and Inex -nor the difference between ordinary and extraordinary refractive index of the crystal. Quartz and calcite are used, the Inex -norI of which is 9.05 X 10-3 and 0.169, respectively. The partial beams leaving the Woilaston prism are polarized perpendicularly to each other. Their phase relation depends on the point at which the laser beam traverses the Wollaston prism so that it can be influenced by shifting the Wollaston prism. A lens of focal length f is placed at a distance f from the Wollaston prism. The partial beams run then parallel to each other in the test section. Their spacing a is a = 2f tan nex -nor -(
A small part of a focused laser beam in a Mach-Zehnder arrangement is used for the detection of highfrequency pressure waves. The interferometer is stabilized on an interference slope by means of a simple electro-optical feedback system. The method introduces only little perturbation to the pressure field and yields the true pressure history p(t) with a submicrosecond time resolution. Several examples of registrations show the capability of this ideal microphone.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.