Laser terminology

Apparent Power/Brightness:

The intensity of light as it appears to the human eye. The eye is most sensitive to wavelengths (colors) in the center of the visible spectrum. Hence, green light will appear brighter than any other color of light of the same power or magnitude.

Beam Diameter

The distance between diametrically opposed points in the cross section of a circular beam where the intensity is reduced by a factor of 1/e (0.368) of the peak level (for safety standards). The value is normally chosen at 1/e² (0.135) of the peak level for manufacturing specifications.

Beam Divergence

Angle of beam spread measured in radians or meliorations. For small angles where the cord is approximately equal to the arc, the beam divergence can be closely approximated by the ratio of the cord length (beam diameter) divided by the distance (range) from the laser aperture. The longer the distance a laser beam travels, the more it spreads, or diverges.

Coherence

A term describing light as waves which are in phase in both time and space. Monochrome and low divergence are two properties of coherent light.

Constant Wave (CW)

The output of a laser that is operated in a continuous (pulse duration >0.25s) rather than a pulsed mode.

Diode

A device through which current can pass freely only in one direction. The diode is arguably one of the most important components in a laser. Oftentimes the lifetime of a laser is based on the quality of the diode.

Failsafe Interlock

An interlock where the failure of a single mechanical or electrical component of the interlock will cause the system to go into, or remain in, a safe mode.

Frequency

The number of light waves passing a fixed point in a given unit of time, or the number of complete vibrations in that period of time.

Heat Sink

A substance or device used to dissipate or absorb unwanted heat energy.

KTP

Potassium Titanyl Phosphate. A crystal used to change the wavelength of a ND:YVO4 laser from 1064nm (infrared) to 532nm (green).

Laser

An acronym for Light A mplification by Stimulated Emission of Radiation. A laser is a cavity, with mirrors at the ends, filled with material such as crystal, glass, liquid, gas, or dye. A device which produces an intense beam of light with the unique properties of coherence, collimator, and monochrome.

Laser Class

The Food & Drug Administration (FDA) regulates, as the name implies, foods and drugs. However, they also regulate all radiation emitting products, which include lasers. The subgroup of the FDA in charge of regulating radiation emitting products is the Center for Devices of Radiological Health (CDRH). They have divided lasers into several classes based on output power.

Laser Diode Module

A complete laser package including the circuitry, a laser diode, and all optical components assembled into a protective housing. The only additional requirement to power the laser diode module is an appropriately matched power supply.

Longitudinal or Axial Mode

Determines the wavelength bandwith produced by a given laser system controlled by the distance between the two mirrors of the laser cavity. Individual longitudinal modes are produced by standing waves within a laser cavity.

M²

A measurement of laser quality. M² is a single number that describes the beam's quality in comparison to a theoretically perfect Giessen beam, and that can be used to predict a real, non-Gaussian beam's behavior in an optics system.

Milliampere (mA)

A unit of current equal to one thousandth (10 ^-3) of an ampere. The current draw of a laser is often measured in milliamperes (mA) or amps (A).

Milliradian (mrad)

A unit of angular distance equal to one thousandth (10 ^-3) of a radian. It is used to measure laser beam divergence.

Milliwatt (mW)

A unit of power equal to one thousandth (10 ^-3) of a watt. It is used to measure the output power of most low to mid-power lasers. Generally lasers that exceed 999mW are measured in watts. For example, a 1000mW laser would have a power output specification of 1W.

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, such as continuous or pulsed.

Modulation

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

MTTF

Mean Time To Failure. This is an approximation of the average lifetime expected out of a laser diode.

Nanometer

A metric unit a length equal to one billionth of a meter. It is used to measure the wavelength of most lasers. For example, some common red lasers include 635nm, 650nm, and 660nm. Common green lasers are 532nm and 557nm. Commone blue lasers are 457nm and 473nm. A much larger wavelength, such as 1064nm, would be an infrared laser.

ND:YVO4 Laser

Neodymium: Yttrium Vanadium Quadroxide. A synthetic crystal used as a laser medium to produce 1064nm light.

Operating Current

The range of specified current required to operate a laser. Laser operating current is measured in Amps (A) or milliamperes (mA).

Operating Voltage

The range of specified input voltage required to operate a laser. Laser operating voltage is measured in volts (V).

Output Power

The energy per second measured in watts emitted from the laser in the form of coherent light. Laser output power is measured in watts (W) or milliwatts (mW).

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.

Protective Housing

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

Pumping

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

Stability

The ability of a laser system to resist changes in its operating characteristics. Temperature, electrical, dimensional, and power stability are included.

TEM_oo

The lowest order mode possible with a bell-shaped (Gaussian) distribution of light across the laser beam.

Visible Radiation (light)

Electromagnetic radiation which can be detected by the human eye. It is commonly used to describe wavelengths which lie in the range between 400nm and 750nm. The peak of the human spectral response is about 555nm.

Volt (V)

The SI unit of potential difference and electromotive force. Generally used to measure the input voltage of a laser power supply.

Wavelength

The length of the light wave, usually measured from crest to crest, which determines its color. Common units of measurement are the micrometer (micron), the nanometer, and (earlier) the Angstrom unit.