Standing Light Wave

(or stationary light wave). If two plane electromagnetic waves with equal amplitudes are propagating toward each other, the wave resulting from the superposition of the two waves is called a standing light wave. A standing light wave usually arises when a normally incident light wave is reflected from the flat surface of an ideal conductor or dielectric with a high index of refraction. At such a surface, the electric vector E of the standing light wave has a node, and the magnetic vector H has an antinode. In a free light wave, the phases of E and H are the same. In a standing light wave, however, the phases are shifted relative to each other by π/2. The nodes (and, accordingly, the antinodes) of the vectors E and H are separated in space by λ/2, where λ is the wavelength of the light. Energy is not transferred in a standing light wave but is only transformed from one form to another: from electrical energy to magnetic energy and vice versa.

Standing light waves were first obtained in 1890 by the German physicist O. Wiener. He showed that the photographic action of a light wave is related to its electric vector. Standing light waves were subsequently observed in investigations of the photoelectric effect, fluorescence (see), and other phenomena. The Lippmann process of color photography is based on the formation of standing light waves. Standing light waves arise in open resonators, which are important elements of some types of lasers.