Wave Front

In an electromagnetic energy field emanating from a source, the wavefront is a surface connecting all field points that are equidistant from the source.

Wave Number

The number of waves per unit distance of radiant energy of a given wavelength; the reciprocal of the wavelength of light. Units given in cm^-1

WavePlate

Wave plates, also known as retardation plates, are birefringent optical elements with two optic axes, one fast and one slow. The incoming beam is separated into mutually orthogonal polarized beams that are recombined with a phase difference that is a function of the thickness of the material and the wavelength of the light. If the phase difference is exactly 1/4 cycle, the plate is called a quarter-wave plate. If the phase difference is exactly 1/2 cycle, the plate is called a half-wave plate.

Wavelength

Electromagnetic radiation propagates as a sinusoidal wave. The wavelength of the wave is the length of one complete cycle. The velocity (v) of the wave is determined by the equation frequency of a wave are related by the equation

v = n x l

where n is the frequency of the wave and l is the wavelength.

Window

A piece of glass with plane parallel surfaces used to admit light into an optical system and to exclude dirt and moisture. In a laser system if the windows are to be mounted perpendicualr to the direction of propogation of the beam, they are often coated with an antireflection coating to reduce losses. In many lasers, uncoated windows are mounted at Brewster's angle. At Brewster's angle, beams with the polarization direction parallel to the surface experience significant reflection losses (approximately 4% per surface) but beams with the orthogonal polarization have near zero losses. The differential losses between the two orientations typically forces the laser into linear polarization.