Unstable condition in which the energy of a molecule is at some discrete level above the lowest, or ground state. It is this condition which is necessary for emission of photons in a laser. (From quantum theory.)

A “MY-kro’ mee-ter” is a unit of length equal to one millionth of a meter, or one micron. (Not to be confused with my-KROM’-a-ter, a measuring instrument used with a telescope, microscope, or laser for fine focusing).

One thousandth of a Joule.

A particular functioning arrangement, setup, or condition for laser operation, such as continuous emission, pulses, or grouped pulses. Mode also describes the cross-sectional shape of the beam. See Transverse Electromagnetic Mode, abbreviated TEM.

The ability to superimpose an external signal on the output beam of the laser as a control.