Glossary

Absorption spectra
The intensity at which a given atom or molecule absorbs incident energy for a range of wavelengths
Active atom (active ion)
In a laser material, the atom (or ion) that actually lases
Active Medium (aka Gain material or Laser material)
The part of the laser where the lasing actually occurs and can refer to a solid, liquid, or gaseous material
Active Remote Sensing
Remote sensing using a light source that is part of the measurement equipment
Amplifier
A laser amplifier consists of a laser material complete with a population inversion which it will not lase on its own since it lacks feedback; an amplifier will increase the intensity of a laser beam injected into it
Beam radius
Size of the laser beam generally taken to be the radius at which the intensity drops to 1/e2 of its peak value
Birefringent filter
Wavelength tuning element that exploits the natural birefringent properties of some materials
Chiller (aka Cooler)
A device for removing waste heat from the laser, often a water cooler with a pump for circulating water around the gain material and pump
Coatings
Thin layers (about 1 micrometer) of material that are placed on an optical element to change its reflection and transmission
Coherence
A property of lasers where all of the light rays are in-phase with one another
Continuous wave
A laser that is on continuously from the time it is turned on until the time it is turned off Contrast a CW laser with a pulse laser
Crystal
A regular, periodic arrangement of atoms
Crystal Growth
A process by which laser quality crystals manufactured
Detector
An electro-optical element that converts light energy to electrical energy; detectors enable scientists to quantify the intensity of light and to sense light outside of the visible region of the electro-magnetic spectrum
Differential Absorption Lidar (DIAL)
A technique for determining range resolved concentrations of trace constituents of the atmosphere
Diffraction Limited
Nature’s limit on the quality of an optical system – the best an optical system can be
Diode laser (aka laser diode)
An electrically pumped semicoductor laser
Directionality
A layman’s term to discuss the property of a light source that describes how the light beam spreads as it travels through space
Divergence
A scientific term to discuss the property of a light source that describes how the light beam spreads (diverges) as it travels through space
Dopant
An atom or ion which replaces an atom in a crystal; the dopant will become the active atom or ion when the material is made into a laser rod
Doppler lidar
A lidar that exploits the doppler shift to determine wind speeds
Doppler shift
Change in frequency of light that results from motion of the source
Efficiency
A measure of the fraction of the input energy which is converted into output energy; depending on the context, the writer/speaker may be referring either to the efficiency of specific part of the laser or to the laser as a whole; when discussing the efficiency of the whole laser, the term wall plug efficiency is often used; the wall-plug efficiency equal to the output light energy divided by the electrical energy into the wall-plug
Electro-magnetic Spectrum
The range of wavelengths over which light extends
Emission spectra
The intensity at which a given atom or molecule emits energy for a range of wavelengths
Energy
Total amount of power emitted by the laser
Energy Level
Discrete energy states that an electron in orbit around an atom is allowed to have; electrons may jump to a higher energy level by absorbing a photon or it can jump to a lower energy level by emitting a photon
Etalon (aka Fabry-Perot Interferometer)
Frequency tuning device that exploits the properties of interference between two adjacent flat, parallel surfaces
Excitation Source (aka Pump)
An energy source that creates a population inversion in a laser or fluorescent material
Excited state
An atom in which one or more electrons are not in the ground state
Fabry-Perot Interferometer (aka Etalon)
Frequency tuning device that exploits the properties of interference between two adjacent flat, parallel surfaces
Feedback
A small portion of the light in a laser oscillator which does not exit the oscillator through output coupler; rather, the feedback passes through the laser material again to stimulate additional electrons to drop to the lower laser level
Fluoresence
The emission of light that accompanies the spontaneous transition of an electron from an excited state to a lower level
Frequency
Number of crests (or troughs) in a light wave that cross a particular point in space in one second; the frequency and wavelength are related by the equation wl * fr = c where wl = wavelength, fr = frequency, and c= speed of light
Gain material (aka Active Medium or Laser material)
The part of the laser where the lasing actually occurs and can refer to a solid, liquid, or gaseous material
Gamma Rays
Wavelength Less than 10-13 Meters
Gaussian beam
Lowest divergence, smallest radius laser beam possible for a given oscillator; it is is created when the laser is operating in the TEM00 mode
Global warming and cooling
Changes in the atmosphere’s temperature due to the presence of man-made atmospheric contaminants
Greenhouse gases
Atmospheric gases that trap the earth’s energy which leads to an increase in the earth’s temperature
Ground state
The minimum stable energy configuration of an atom; the ground state may coincide with the lower laser level
Host
Solid state laser material, often a crystal, that holds a dopant
Infra Red (IR)
Wavelength between 0.5 * 10-6 and 0.3 * 10-3 Meters
Injection seeding
A laser beam that is injected into a second slave laser that induces the second laser to lase; often the master laser has a low power, narrow spectral linewidth output and the slave oscillator is intended to greatly amplify the injection beam
Intensity
The rate at which radiant energy is transmitted per unit area
Laser
Light Amplification by the Stimulated Emission of Radiation, an electro-optical device for producing a high power, monochromatic, low divergence, coherent light source
Laser Material (aka Gain Material or Laser material)
The part of the laser where the lasing actually occurs and can refer to a solid, liquid, or gaseous material
Lattice
The regular arrangement of atoms or ions in a crystal
Lidar
The optical analog to radar; a radar system that operates using visible, near IR or UV light
Lifetime
(1) The length of time an electron can be expected to remain in a given energy level (2) The length of time before an electro-optical component can be expected to fail, often given in shots
Light
An oscillating electric which generates an oscillating magnetic field; the resulting electro-magnetic wave propagates through space in a direction that is perpendicular to both the electric and magnetic fields
Line width
The range of wavelengths at which a laser lases
Lower Laser Level
The lower energy state that is directly involved in the lasing process
Metastable energy level
“Somewhat stable” energy level; thhe length of time an electron can be expected to reside in a metastable energy level (lifetime) is much greater than the time it can be expected to reside in other excited states; the lifetime to a metastable state is typically 10-3 seconds while the lifetime for other excited states is typically 10-8 seconds
Meter
A unit of length = about 39.37 inches
Micron, micrometer = 1 millionth of a meter
Nanometer = 1 billionth of a meter
Microwave
Wavelength between 3 mm and 10 cm
Mode
Spatial and temporal energy distributions in which a given laser resonator will lase
Monochromaticity
The property of a laser where the laser emits energy over a very narrow wavelength range, literally, one color
Non-linear crystal
Optical materials which can be used to shorten the wavelength (increase the frequency) of incident light
Normal mode
A laser that does not contain a Q-switch
Optical Parametric Oscillator (OPO)
A technique for increasing an existing laser beam’s wavelength
Oscillator
A laser gain medium place in an optical system which will provide feedback
Output Coupler
Optical element that enables some light to exit the laser oscillator
Passive Remote Sensing
Remote sensing naturally occurring radiation
Polarization
The process of confining the electric vector of a light to one direction
Polarizer
A material which converts linearly polarized light to circularly polarized light
Population inversion
The situation in which the upper laser level contains more electrons than the lower laser level
Power
The rate at which energy is transferred
Power density (aka Irradiance)
The rate at which energy is transferred for a given volume
Pulse width
Time duration of a laser pulse
Pump
A device such as a flashlamp or a laser diode used to create a population inversion in a laser material
Pump Level
Energy level into which the pump excites electrons; the pump level may coincide with the upper laser level; often, electrons in the pump level drop to the upper laser level
Q-switch
An optical on-off switch
Radio waves and TV
Wavelength greater than 30 cm
Reflectivity
Fraction of incident energy which is reflected by a surface
Remote Sensing
Any technique for measuring, observing, or monitoring a process or item without physically touching the item under observation
Repetition rate
Number of pulses per second
Resonator
A laser in which, to simplify its analysis, the gain medium has been removed
Sensitizer
A atom or ion added to the laser material which does not in itself lase but which increases the amount of energy in the upper laser level
Shot
Another name for a laser pulse
Solid State Laser
A laser whose gain medium is made from a solid as opposed to a liquid or gas
Spectra
The pattern, the wavelength and intensity, at which each molecule and atom absorbs and emits radiation is unique to that atom or molecule; this pattern is called a spectra and can be used to identify an atom or molecule
Spectrometer
A device for measuring spectra
Spontaneous Emission
The radiation which results when an electron in an excited state drops to a lower energy level without any external radiation stimulating the process
Stable resonator
A resonator in which the light beam retraces the same path each trip through the resonator
Stimulated Emission
The radiation which results when an electron in an excited state drops to a lower energy level with external radiation stimulating the process
Telescope
A device to focusing collimated light to a small point
Tunable
A laser with an adjustable wavelength
Ultra-Violet (UV)
Wavelength between 10-9 and 0.4 * 10-6 Meters
Unstable resonator
A resonator in which the light beam retraces a different path each trip through the resonator
Upper Laser Level
A metastable (somewhat stable) energy level which is the higher energy state that is involved directly in the lasing process
Vertical Profile
Variation in a parameter as a function of height
Visible
Wavelength between 0.4 * 10-6 and 0.5 * 10-6 Meters
Vortex
A region within a body of fluid in which the fluid elements have an angular velocity
Wavelength
The distance between two successive peaks (or troughs) of an electro-magnetic wave
Wind sheer
Place at which two air masses, each traveling in different directions with different speeds, meet resulting in a rapid change in wind direction and speed
X-ray
Wavelength between 10-13 and 10-9 Meters