An Etymological Dictionary of Astronomy and Astrophysics

Two plane mirrors, fitted side by side at a small angle, used to create two mutually → coherent sources in a famous → interference experiment first suggested by A. Fresnel. A point source reflected at the mirrors appears as a pair of → virtual light sources, positioned close together, which interfere with each other due to their → coherence. This arrangement removes the problem that two separate light sources do not produce observable interference on account of their incoherence. Same as Fresnel’s double mirror. See also → Fresnel’s biprism, → Lloyd’s mirror.

See also: → Fresnel diffraction; → mirror.