Photonics Dictionary: A

A dispersion relation defined in order to value the reciprocal amount of dispersion. It is defined as the refractivity over the difference in index values of the shortest and longest visible...

An instrument that uses optical filtration in order to measure the transmittance for a discrete range or specific number of wavelengths.

The transfer of energy from an incident electromagnetic energy field with wavelength or frequency to an atomic or molecular medium.

A group of frequencies or wavelengths on the electromagnetic spectrum which exhibits resonance or energy contributions near and in relation to a peak resonance wavelength.

An optical lens manufactured to control the transmission of light over a specified wavelength range. Low absorption lenses are produced which are anti-reflection coated for UV, VIS and IR wavelengths...

The wavelength or frequency corresponding to an absorption resonance with a given molecular or atomic species. The line spectrum will vary with the element as well as the molecular compound.

An absorption peak refers to a sharp increase or spike in the absorption of electromagnetic radiation at a particular wavelength or energy level. It is a distinctive feature in the absorption...

Measures the absorption or sample transmittance over a range of specified wavelengths. Sample may be placed within the device and the transmission measured to an accuracy of given percent. The...

Experimental method of measuring the transmission of a given sample as a function of the wavelength.

Fraction absorption over a specified range of wavelengths.

The measured change in absorption at a single wavelength while altering experimental parameters such as the incident intensity or pulse width.

A broadband continuum resonator that confines a wide range of wavelengths. From the optical confinement a single wavelength may be released by means of a tuning grating.

An achromat, in the context of optics, refers to a type of lens or lens system designed to reduce chromatic aberration. Chromatic aberration is an optical phenomenon where different colors of light...

A lens consisting of two or more elements, usually of crown and flint glass, that has been corrected for chromatic aberration with respect to two selected wavelengths. Also known as achromat.

Cemented prisms of differing refractive indices which refract incident light and, due to differing refractive indices, will not spatially separate individual wavelengths.

Light diffracted by a solid (usually quartz in crystal or fused form) traversed by acoustic waves. If the ultrasonic wavelength is larger than the diameter of the light beam, the diffraction orders...

Any fluorescence in which the wavelength of the emitted light differs from that of the absorbed light.

A 2-million W, 2.7-µm-wavelength hydrogen-fluoride laser used as a directed energy weapon.

The coefficient Å in Angstrom's formula for the dispersing coefficient for dust present in the atmosphere. The formula is expressed as S × Ål-B where l represents wavelength and B...

An angstrom, symbolized by the Ångström or Å, is a unit of length used to express atomic and molecular dimensions. It is equal to 0.1 nanometers or 1 × 10-10 meters. The...

Dispersion that occurs when the medium's index of refraction decreases as the frequency of the propagating light increases. For a given medium, some wavelength ranges may produce anomalous dispersion...

A spectral phenomenon in which the degree of the photoresponse of an illuminated semiconductor is determined by the wavelength composition of the incident light.

An antireflection coating (AR coating) is a thin film or coating applied to optical surfaces, such as lenses or windows, to minimize unwanted reflections and increase the transmission of light...

An aspheric mirror is an optical mirror surface that deviates from the shape of a perfect sphere, having a non-spherical surface profile. Unlike traditional spherical mirrors, which have a curved...

A range of wavelengths within which radiation transmitted through the atmosphere suffers relatively little absorption by atmospheric gases.

The area of optics in which the wave nature of a particle is exploited to carry out very accurate interferometry and other optical techniques with atoms instead of photons. In this process, particles...

An atomic absorption spectrometer (AAS) is an analytical instrument used to determine the concentration of specific chemical elements in a sample by measuring the absorption of light at...

Attenuated total reflectance (ATR) spectroscopy is a technique used in analytical chemistry to obtain IR spectra of samples. It is particularly useful for analyzing solid and liquid samples without...

The green line, in the spectrum of the aurora borealis, that has a wavelength of 5577 Å; it is caused by a forbidden transition in oxygen.

Autofluorescence refers to the natural emission of fluorescence exhibited by certain biological structures or molecules when exposed to light. Unlike fluorescence that results from the application of...

In fiber optics, the use of a detector to study the range of refractive indices achieved at various wavelengths. This information is calculated electronically to establish the divergence between...

A lens aberration that causes axial light rays having different wavelengths to focus at various points along the axis.