Effective focal length (EFL)

Distance from the principal point to the focal point of a lens.

Electric vector

The electric field associated with a light wave that has both direction and amplitude.

Electromagnetic radiation

The propagation of varying electric and magnetic fields through space at the velocity of light.

Electromagnetic spectrum

The range of frequencies and wavelengths emitted by atomic systems. The total spectrum includes radio waves as well as short cosmic rays. Wavelengths cover a range from 1 Hz to perhaps as high as 1020 Hz.

Electromagnetic wave

A disturbance that propagates outward from an electric charge that oscillates or is accelerated. Includes radio waves, X-rays, gamma rays, and infrared, ultraviolet, and visible light.

Electron

Negatively charged particle of an atom.

Electrostatic discharge (ESD)

The sudden transfer of accumulated static charge (typically of high voltage at low current) from one object to another. ESD can be extremely harmful to semiconductor diodes, causing failure or a significant decrease in lifetime. Users of semiconductor lasers should always wear antistatic devices when working with these devices.

Embedded laser

A laser with an assigned class number higher than the inherent capability of the laser system in which it is incorporated, whereby the system’s lower classification is appropriate to the engineering features limiting accessible emission.

Emergent beam diameter

Diameter of the laser beam at the exit aperture of the system in centimeters (cm) defined at 1/e or 1/e² irradiance points.

Emission

Act of giving off radiant energy by an atom or molecule.

Emissivity

The ratio of the radiant energy emitted by any source to that emitted by a blackbody at the same temperature.

Emittance

The rate at which emission occurs.

Emitter size

The size of the emitter of a laser diode expressed in microns. Typical sizes are 1um by 3µm for low power index-guided diodes. High power gain-guided laser diodes have emitter sizes from 1µm by 50µm to 1µm by 500µm. Bars and arrays are typically made up of several 1µm by 500µm gain-guided “chips” spaced evenly across distances of up to 10mm (10,000µm).

Enclosed laser device

Any laser or laser system located within an enclosure that does not permit hazardous optical radiation emission from the enclosure. The laser inside is termed an “embedded laser.”

Energy

The product of power (Watts) and duration (seconds). One Watt second = one Joule.

Energy (Q)

The capacity for doing work. Energy is commonly used to express the output from pulsed lasers and is generally measured in Joules (J). The product of power (Watts) and duration (seconds). One Watt second = one Joule.

Energy source

High voltage electricity, radiowaves, flashes of light, or another laser used to excite the laser medium.

Enhanced pulsing

Electronic modulation of a laser beam to produce high peak power at the initial stage of the pulse. Allows rapid vaporization of the material without heating the surrounding area. Such pulses are many times the peak power of the CW mode (also called “superpulse”).

Excimer

“Excited Dimer.” A gas mixture used as the active medium in a family of lasers emitting ultraviolet light.

Excitation

Energizing a material into a state of population inversion.

Excited state

Atom with an electron in a higher energy level than it normally occupies.

Exempted laser product

In the U.S., a laser device exempted by the U.S. Food and Drug Administration from all or some of the requirements of 21 CFR 1040.

Extended source

An extended source of radiation that can be resolved into a geometrical image in contrast with a point source of radiation, which cannot be resolved into a geometrical image. A light source whose diameter subtends a relatively large angle from an observer.