The use of a laser for various applications depends upon the beam properties of laser,
such as direction, divergence, and wavelength or frequency characteristics, which can be
adjusted by the laser components. The features affecting the beam properties of laser
include: size of the gain medium, location, separation and reflectivity of the mirrors of
the optical cavity, and presence of losses in the beam path within the cavity. Some of
these features determine the unique properties of the laser beam, referred to as laser
modes. The laser modes are wavelike properties relating to the oscillating character of the
beam as the beam passes back and forth through the amplifier and grows at the expense
of existing losses. The development of laser modes involves an attempt by competing
light beams of similar wavelengths to fit an exact number of their waves into the
optical cavity. For example, a laser mode of green light having a wavelength of exactly 5
x 10-5 cm will fit exactly 1,000,000 full cycles of oscillations between laser cavity mirrors
separated by a distance of exactly 50 cm. Most lasers have several modes operating
simultaneously in the form of both longitudinal and transverse modes which give rise to
a complex frequency and spatial structure within the beam which otherwise appears as
simple pencil-like beam of light.