Maximum Permissible Exposure

Abbreviated MPE.  The level of laser radiation to which an unprotected person may be exposed without adverse biological changes to the eye or skin.

Meniscus Lens

The lens used primarily in CO2 lasers by Coherent, Inc. It has one side convex, the other concave.

Metastable

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.)

Micrometer

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).

Mode

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.

Modulation

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

Monochromatic Light

Theoretically, light consisting of just one wavelength. Since no light is completely monochromatic, it usually consists of a very narrow band of wavelengths. Lasers provide the narrowest bands.