M

M² value

Describes the deviation of the laser beam from a theoretical, ideal Gaussian beam profile. For a theoretical Gaussian beam, the M² value is equal to 1.0. For a typical laser beam, the M² value is greater than 1.0. Collimated TEM₀₀ diode laser beams typically have an M² value ranging from 1.1 to 1.7.

Maintenance

Performance of those adjustments or procedures specified in user information provided by the manufacturer with the laser or laser system, which are to be performed by the user to ensure the intended performance of the product. It does not include operation or service as defined in this glossary.

Maximum permissable exposure (MPE)

The level of laser radiation to which a person may be exposed without hazardous effect or adverse biological changes in the eye or skin.

Meniscus lens

A lens that has one side convex and the other concave.

Metastable state

The state of an atom, just below a higher excited state, that an electron occupies momentarily before destabilizing and emitting light. The upper of the two lasing levels.

Micrometer

A unit of length in the International System of Units (SI) equal to one- millionth of a meter. Often referred to as a “micron.”

Micron

An abbreviated expression for micrometer, which is the unit of length equal to one-millionth of a meter. See micrometer.

Microprocessor

A digital chip (computer) that operates, controls, and monitors lasers.

Milliradian (mrad)

1/1000 of a radian (1×10<sup-3radians). Usually used to specify the divergence of a laser beam.

Mode

A term used to describe how the power of a laser beam is geometrically distributed across the cross-section of the beam. Also used to describe the operating mode of a laser (e.g., continuous or pulsed).

Mode locked

A method of producing laser pulses in which short pulses (approximately 10- to 12-second) are produced and emitted in bursts or a continuous train.

Modulated lasers

Allow users to vary the output power of a laser by varying a control voltage. The laser is activated only when needed. Beam modulation may be used to synchronize a laser with an analytical instrument or camera. Several of our laser diode modules employ one of two types of modulation: analog or TTL.

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. No light is absolutely single frequency since it will have some bandwidth. Lasers provide the narrowest of bandwidths that can be achieved.

Multimode

Laser emission at several closely spaced frequencies.