An electronic speckle pattern interferometer suitable for use in an undergraduate laboratory is described. This interferometer can be built for a small fraction of the cost of a commercial version and is simple and inexpensive to build and understand. The interferometer is useful for visualizing the normal modes of vibrating objects as well as changes in index of refraction.
Thomas R. Moore, "A simple design for an electronic speckle pattern interferometer," American Journal of Physics 72, 1380-1384 (2004). With erratum, American Journal of Physics 73, 189 (2005).
American Journal of Physics