Photonics Dictionary

The equation devised by Sir G.B. Airy for the analysis of light diffraction near a caustic surface: (d2f/dz2) - zf = 0 where z represents the independent variable, and f is the value of the function.

The perceived brightness difference between light and dark areas on a target.

The angular subtense of the field of view in the image space of a telescope, as differentiated from that in the object space (the true field).

The perceived brightness of an object being viewed at some distance, especially through an optical instrument.

The visual perception of motion when fixed stimuli are exposed in rapid temporal and spatial succession.

The angle subtended by an object, determined by the size of the object and its distance from the viewer.

The point at which decreasing current supplied to a laser results in the extinguishing of the laser discharge.

A technique whereby two laser beams, one at an excitation wavelength and the second at a wavelength that produces Stokes Raman scattering, interact coherently in a sample, producing a strong...

A fiber optic communications system that works on the principles of homodyning or heterodyning. The transmitting laser produces an optical wave that is modulated in amplitude, phase or frequency by...

A coherent fiber bundle (CFB), also known as a coherent fiber optic bundle, is an assembly of multiple optical fibers arranged in a specific geometric pattern to maintain the spatial coherence of...

A light source that is capable of producing radiation with waves vibrating in phase. The laser is an example of a coherent light source.

The manifestation of light from scatterers outside the plane of the object in coherent light systems. The output of these systems is often marred by this noise.

The use of phase conjugation or other methods to increase the power density of a laser beam under adverse atmospheric conditions.

Radiation in which the phase relationship between any two points in the radiation field has a constant difference, or is exactly the same in either the spatial or the temporal mode throughout the...

A condition during laser operation when laser output can no longer be increased by additional electric current.

A sudden, brief increase in current or voltage in a circuit that can damage sensitive components and instruments. Preventive measures include slow-starter circuits, filtering and static control.

The current that flows in a photodetector when there is no optical radiation incident on the detector and operating voltages are applied.

A lidar (light detection and ranging) technique used in pollution monitoring. Two light beams are emitted simultaneously, one at a wavelength that will be absorbed by the target particles, and the...

Differential interference contrast (DIC) microscopy, also known as Nomarski interference contrast microscopy, is an optical imaging technique used in microscopy to enhance the contrast of transparent...

A device that produces an interferogram that can be directly related to the temperature gradient and thereby provides a direct measure of the convective heat transfer coefficients.

The variation in attenuation among the propagating modes of an optical fiber.

A variation in propagation delay caused by differences in group velocity among modes of an optical fiber. Also called multimode group delay, this effect is commonly due to imperfections or any...

A type of phase-shift keying using a one-bit delay line.

A method of coding image data by storing in memory only differences in brightness of each pixel from that of its nearest horizontal neighbors: that is, it is the change in brightness rather than the...

The slope of the curve when output is plotted against input for quantum efficiency in a device.

The measurement of the spectrum bands formed by a spectroscopic sample, based on the differences between the sample and the reference cell it is placed in.

The minimum electrical current input needed to initiate lasing.

The positive ion current created in an electron tube as a result of the collisions between electrons and residual gas molecules.

In optics, the term denoting the lack of a fixed phase relationship between two waves. If two incoherent waves are superimposed, interference effects cannot last longer than the individual coherent...

A bundle of filaments of optical glass or other transparent materials that transmit only light, not optical images. The arrangement of the individual fibers in the bundle is not sufficiently regular...

The production of holograms initially from either conventional photographs or incoherent optical equipment.

A Laurent polarimeter is an instrument used in optics for measuring the rotation of plane-polarized light caused by optically active substances. Optical rotation, also known as optical activity, is a...

The force acting upon a charged particle as it moves in a magnetic field, proportional to the particle's charge and velocity.

The Lorentz oscillator model is a theoretical model used in physics to describe the response of a charged particle (such as an electron) to an oscillating electric field. It is particularly employed...

In a laser diode, the photocurrent produced by a photodiode that detects the emission from the rear facet of the semiconductor chip. It can be used to provide feedback control of the forward current...

A function that quantifies the performance degradation of coherent communications systems, imaging systems and all systems that rely on the spot size of a laser beam that has propagated along an...

Any noise or current fluctuation that prevents precise measurement of the signal current. Both dark current and signal current have random fluctuations that affect the arrival of pulses. Thermal...

An assembly of optical fibers that will not transmit coherent images or information because the relationship of the fibers on either end of the assembly is random; Noncoherent fiber bundles are...

Radiation having waves that are out of phase in space and/or time.

The current that flows through a photosensitive device, such as a photodiode, as the result of exposure to radiant power.

The electron stream emitted by a phototube when the cathode is exposed to light.

A method of determining prism power at any point on a lens. Prism power equals the product of the dioptric power and the distance, in centimeters, from the optical center.

Capable of being penetrated by some form of radiation.

Measures by heterodyning interferometry the local slope of a vibrating sample. The method allows the reconstruction of a three dimensional map of the surface in order to determine the slope and...

An aperture consisting of a semitransparent central region whose amplitude transmittance only is varied, and the relative phase difference between the central and annular region is fixed as p -...

A photocathode that receives radiation from one side and emits a photoelectric current from the opposite side.