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ETH Zurich - D-MAVT - IET - LEC - Research - Power, Energy & Turbomachinery - Turbomachinery: Glossary

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Absorption Coefficient:
Factor describing light’s ability to be absorbed per unit of path length.

Anode:
An electrical element in laser excitation which attracts electrons from a cathode.

Beam:
A collection of rays that may be parallel, convergent, or divergent.

Beam delivery system:
The use of optics, such as mirrors, lenses, and optical fibers, arranged in such a way that a laser beam can be precisely directed to a specific locations.

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).

Beam divergence:
The tendency of a laser beam to expand in diameter as it moves away from the source, measured in milliradians (1 milliradian = 3.4 minutes-of-arc or approximately 1 mil) at specified points. 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.

Brightness:
A measure of the luminous intensity achievable by a laser, directly related to the focusability of a particular wavelength of laser light.

Cathode:
The negative electrode of a gas laser providing electrons for an electrical discharge.

Cavity:
The laser resonator, or tube, in which the lasing process occurs.

Coherence:
A property of electromagnetic waves which are in phase in both time and space. Coherent light has monochromaticity and low beam divergence, and can be concentrated to high power densities.

Continuous Wave (CW):
Laser power with a constant, steady-state laser with a continuous output that is greater than or equal to 0.25 s.

Depth of Focus:
The distance over which the focused laser spot has a constant diameter and thus constant irradiance.

Divergence:
The angular measurement of laser beam spread with distance. The projected dot of a laser will increase in size the farther it is projected. Laser divergence is measured in milliradians (mrad).

EUV extreme ultraviolet:
Extreme Ultraviolet radiation (EUV or XUV) is high-energy ultraviolet radiation, generally defined to be electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths from 120 nm down to 10 nm, and therefore (by the Planck–Einstein equation) having photons with energies from 10 eV up to 124 eV. EUV is naturally generated by the solar corona and artificially by plasma and synchroton light sources.

Excitation:
Energizing the material into a state of population inversion.

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

Focal Point:
Distance between the focusing lens and the point on the optical axis to which parallel rays of light are converged by the laser. The focal point of a laser beam is the point of highest energy concentration.

Focus:
As a noun, the point where rays of light meet which have been reflected by a mirror or refracted by a lens, giving rise to an image of the source. As a verb, to adjust focal length for the clearest image and smallest spot size.

Infrared Radiation (IR):
Invisible electromagnetic radiation with wave lengths ranging between 0.70 to 1000 micrometers. This region is often broken up into IR-A, IR-B, and IR-C.

Laser Medium (Active Medium):
Material used to emit the laser light and for which the laser is named.

Monochromatic:
Light consisting of theoretically just one wavelength. Lasers do provide the narrowest of bandwidths that can be achieved, however no light has only a single frequency since it will have some bandwidth.

Nd:YAG:
(neodymium-doped yttrium aluminium garnet; Nd:Y3Al5O12) is a crystal that is used as a lasing medium for solid-state lasers. The dopant, triply ionized neodymium, typically replaces yttrium in the crystal structure of the yttrium aluminium garnet (YAG), since they are of similar size. Generally the crystalline host is doped with around 1% neodymium by atomic percent.

Near Field Imaging:
A solid-state laser imaging technique offering control of spot size and hole geometry, adjustable working distance, uniform energy distribution, and a wide range of spot sizes.

Neodymium (Nd):
The rare earth element that is the active element in Nd:YAG lasers and Nd:Glass lasers.

Opacity:
The degree to which light is not allowed to travel through a material.

Pockel’s Cell:
An electro-optical crystal used as a Q-switch.

Power Meter:
An accessory used to measure laser beam power.

Q-switch:
A device that acts as a shutter to move in and out of the beam path at regular intervals so that a large amount of energy is stored and then released in a burst of energy.

Refraction:
The change of direction of propagation of any wave, such as an electromagnetic wave, when it passes from one medium to another in which the wave velocity is different. The bending of incident rays as they pass from one medium to another (e.g., air to glass).

Solid Angle:
The ratio of the area on the surface of a sphere to the square of the radius of that sphere. It is expressed in steradians (sr).

Spot Size:
The mathematical measurement of the radius of the laser beam.

Ultraviolet lithography:
Ultraviolet lithography is a process commonly used in integrated circuit fabrication to selectively remove parts from a thin film of substrate. As the name implies this technique uses a source of UV radiation placed behind a mask and the image of this mask is projected onto a UV sensitive chemical photo-resist coated semiconductor wafer using optical lenses.

Alternative LEC Glossaries:

General Glossary | Wind Energy Glossary | Turbomachinery Glossary | Plasma Science Glossary |Instrumentation Glossary

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