Technical Center: Laser Glossary of Terms

 

Phase

Waves are in phase with each other when all the troughs and peaks coincide and are "locked" together. The result is a reinforced wave in increased amplitude (brightness).

Photocoagulation

Use of the laser beam to heat tissue below vaporization temperatures with the principal objective being to stop bleeding and coagulate tissue.

Photometer

An instrument which measures luminous intensity.

Photon

In quantum theory, the elemental unit of light, having both wave and particle behavior. It has motion, but no mass or charge. The photon energy (E) is proportional to the EM wave frequency (v) by the relationship: E=hv; where h is Planck's constant (6.63 x10-34 Joule-sec).

Photosensitizers

Chemical substances or medications which increase the sensitivity of the skin or eye to irradiation by optical radiation, usually to UV.

Picosecond

A period of time equal to 10-12 seconds.

Pigment Epithelium

A layer of cells at the back of the retina containing pigment granules, i.e., a cloud of charged particles surrounding a laser impact.

Plasma

Shield The ability of plasma to stop transmission of laser light.

Pockel's Cell

An electro-optical crystal used as a Q-switch.

Point Source

Ideally, a source with infinitesimal dimensions. Practically, a source of radiation whose dimensions are small compared with the viewing distance.

Pointing Errors

Beam movement and divergence, due to instability within the laser or other optical distortion.

Polarization

Restriction of the vibrations of the electromagnetic field to a single plane, rather than the innumerable planes rotating about the vector axis. Various forms of polarization include random, linear, vertical, horizontal, elliptical, and circular.

Population Inversion

A state in which a substance has been energized, or excited, so that more atoms or molecules are in a higher excited state than in a lower resting state. This is a necessary prerequisite for laser action.

Power

The rate of energy delivery expressed in watts (joules per second). Thus: 1 Watt = 1 Joule/1 Sec.

Power Meter

An accessory used to measure laser beam power.

Protective Housing

A protective housing is a device designed to prevent access to radiant power or energy.

Pulse

A discontinuous burst of laser, light or energy, as opposed to a continuous beam. A true pulse achieves higher peak powers than that attainable in a CW output.

Pulse Duration

The "on" time of a pulsed laser. It may be measured in terms of millisecond, microsecond, or nanosecond as defined by half-peak-power points on the leading and trailing edges of the pulse.

Pulse Mode

Operation of a laser when the beam is intermittently on in fractions of a second.

Pulse Repetition Frequency (PRF)

The number of pulses produced per second by a laser.

Pulsed Laser

Laser which delivers energy in the form of a single or train of pulses.

Pump

To excite the lasing medium. (See Optical Pumping or Pumping.)

Pumped Medium

Energized laser medium.

Pumping

Addition of energy (thermal, electrical, or optical) into the atomic population of the laser medium, necessary to produce a state of population inversion.