A large aperture inexpensive interferometer for routine flow measurements

A description is given of an interferometer which has been shown to produce good infinite fringe interferograms of large flow fields without the use of extremely high-quality optics. The method is no more sensitive to temperature and vibration than a conventional schlieren system. An attractive feature is that a schlieren can be converted to an interferometer simply by using a laser source and by replacing the knife-edge with a suitable spatial filter. This interferometer makes it possible to construct relatively low-cost, large-aperture interferometers work in a normal laboratory environment. Because of the brightness of the source and the low losses encountered in the system, it is possible to record real-time interferograms to study unsteady phenomena or to record interferograms of a steady flow with a continuously changing view angle