**Aperture**

An opening through which radiation can pass.

**Attenuation**

The decease in the radiant flux of any optical beam as it passes through and absorbing and/or scattering medium.

**Beam diameter**

The distance between diametrically opposed points in the cross section of a circular beam where the power-per-unit area is 1/e2 or 13.5% of the peak.

**Beam divergence**

Angle of beam spread measured in radians or milliradians (1 milliradian = 3.4 minutes-of-arc or approximately 1 mil). For small angles where the chord is approximately equal to the arc, the increase in the diameter of the beam is numerically equal to 1/1000th of the range in meters multiplied by the number of milliradians of beam divergence. That is, at 1000 meters range, a beam divergence of 2 milliradians would produce a beam diameter 2 meters wider than the emergent beam diameter.

**Boresight**

The boresight is a measure of the deviation of the optical axis of the laser beam with respect to the mechanical axis of the laser housing.

**Collimation**

The process by which a divergent beam of radiation is converted to a parallel beam. A diode laser focused at more than ~115 cm (~45 inches) is said to be “collimated” for all practical purposes.

**CW Laser**

Continuous-wave laser, as distinguished from a pulsed laser. A laser emitting for a period in excess of 0.25 second.

**Depth-of-Field**

The depth-of-field (DOF) is defined as the distance through which satisfactory definition can be maintained when a lens is in focus at a particular distance. In other words, this value lets the user know the range over which there will be a significant difference in line thickness. There is a general agreement that “satisfactory definition” is maintained as long as the image size remains smaller than 1.4 times its smallest size. This distance is also called the Rayleigh range. The DOF is therefore equal to twice the Rayleigh range of the focusing system.

**Divergence**

The increase in the diameter of the laser beam with distance from the exit aperture. (The value gives the full angle at the point where the laser radiant exposure of irradiance is 1/e of the maximum value. For the purpose of this guide, divergence is taken as the full angle expressed in radians], or the change in beam diameter measured between those points which includes the radiant exposure or irradiance equal to 1/e of the maximum value. The angular extent of a beam which contains all the radius vectors of the polar curve of radiant intensity having length rated at 36.8% of maximum. Sometimes this also referred to as “beam spread,” but the two are not always equivalent.)

**Fan Angle**

The fan angle is the angular spread of the laser beam, as defined by in equation below:-

FA = 2 Arctan (L/2D)

Where L is the length of the line and D is the distance between the laser and the target.

**Focus**

The focus is the point on the optical axis of a lens or optical system to which parallel rays will converge. All Global laser dot, line or cross lasers are user-adjustable for focus, allowing the adjustment of the line thickness (or focus) at the desired projection distance.

**Hertz (Hz)**

Unit of frequency, i.e. “cycles per second.”

**IEC**

IEC is the International Electrotechnical Commission. An organization that publishes the IEC 60825-1 laser safety standard.

Infrared (IR.)

The invisible portion of the electromagnetic spectrum that lies between 0.75 and 1000um.

**Laser**

A source of an intense, coherent, directional beam of optical radiation. Also, and acronym for: Light Amplification by Stimulated Emission of Radiation. A laser usually is composed of an energy source, a resonant cavity, and an active lasing medium.

**Laser device**

Either a laser or a laser system.

Laser Diode Module

An assembly of electrical, mechanical, and optical components that includes a laser.

**Light**

Visible radiation. In this guide, wavelengths between 400 and 700 nm. The Commission International de la Eclairage (International Commission on Illumination) define this spectral region as 380-400 nm to 760-780 nm.

**Limiting aperture**

The maximum circular area over which irradiance and radian exposure can be averaged.

**Modulation**

A change in the output level generated by a change in supplied voltage.

Micrometer (um)

Formerly termed “micron,” a measure of length equal to 10-9 meters = 1000 nanometers.

**Nanometer (nm)**

Unit of length equal to 10-9 m or 0.001 um.

**Optical radiation**

UV, visible, and IR radiation (100nm to 1mm).

**Output power and output energy**

The laser output power is used primarily to rate CW lasers since the energy delivered per unit time remains relatively constant (output measured in watts). The power output level of CW lasers is usually expressed in milliwatts (mW=1/1000 watt) or Watts.

**Radian**

A unit of angular measure equal to the angle subtended at the center of a circle by a chord whose length is equal to the radius of the circle. (1 radian=57.3 degrees or 2p radians= 360 degrees.)

**Rayleigh scattering**

Scattering of radiation in the course of its passage through a medium containing particles, the sized of which are small compared with the wavelength of the radiation.

**Semiconductor or injection laser**

A class of lasers which at present produce relatively low CW power outputs. Also known as a “diode laser.” Similar to a light-emitting diode, except that the optical radiation emission is coherent and more monochromatic.

**Ultraviolet (UV) radiation**

Electromagnetic radiation with wavelengths between soft X-rays and visible violet light, often broken down into UV-A(315-400nm), UV-B (280-315 nm), and UV-C (100-280nm). UV radiation of wavelengths less than 180nm are transmitted very poorly through air.

**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 400 and 700 nm.

**Watt (W)**

The unit of power, or radiant flux.

**Wavelength**

Electromagnetic energy is transmitted in the form of a sinusoidal wave. The wavelength is the physical distance covered by one cycle of this wave. Wavelength is inversely proportional to the frequency.