Precision Fresnel Biprism Interference Apparatus

Fresnel's Biprism Experiment is the fundamental example of common path interference by division of wavefront. Light from a slit passes through side-by-side prisms with very shallow angles to separate it into two almost parallel beams. When these beams are brought to overlapping by a convex lens, they interact as if they originated from two virtual sources side by side and generate equally-spaced fringes. The original version of the experiment by Fresnel is difficult to perform because it requires precise adjustment of the slit and prisms, a dark room, and a large amount of space to separate the fringes for easy viewing.