Angle of Diffraction (AOD)

The angle at which light is diffracted from a grating. Measured from normal (perpendicular) incidence to the grating surface.

Angle of Incidence (AOI)

The angle at which light enters a grating. Measured from normal (perpendicular) incidence to the grating surface.


The useful wavelength range of a grating, spectrometer, or system.

Center Wavelength (CWL)

The wavelength for which a grating is designed to operate at peak efficiency.


Full Width at Half Maximum. A measure of the width of a peak, the distance from the right to the left flank of a peak at half the height of the peak maximum

Optical Coherence Tomography (OCT)

An imaging technique that uses light to capture micrometer-resolution images from light interference within optical scattering media. See our OCT Tutorial.

p-polarized Light

Light that oscillates parallel to the plane of incidence.

Polarization Dependent Loss (PDL)

Losses that vary, in an optical component, at different states of polarization. The difference is expressed in decibels between the maximum and minimum loss.

Raman Shift

A change in frequency undergone by monochromatic light scattered by the molecules of substance whose characteristics determine the amount of change. Cf Raman Wavenumber.

Raman Spectroscopy

A spectroscopic technique used to observe vibrational, rotational, and other low-frequency modes in a system.

Raman Wavenumber

Raman shifts are typically reported in wavenumbers, which have units of inverse length as this value is directly related to excitation wavelength.


In spectrometers the width of the peak for an input consisting only of a single wavelengh for example from an atomic emission source. Often dependent on the wavelength, then usually specified as the average across the spectral range.

s-polarized Light

Light that oscillates perpendicular to the plane of incidence.

Spatial Frequency

A characteristic of any structure that is periodic across position in space such as the line spacing in surface relief grating or the fringe spacing in a volume phase grating.

Surface Relief Grating

A grating whose structure is machined or etched onto the surface of grating medium or substrate.

Volume Phase Grating (VPG)

A grating whose structure is in the volume of the medium. The grating is formed by periodic differences in the index of refraction in the medium.

Volume Phase Holographic Grating (VPHG)

A volume phase grating written using holographic techniques.

Wavelength (λ)

The distance between successive crests of a wave such as an electromagnetic wave or light. Typically expressed in nanometers (nm) or microns (µm), and indicated by a lowercase Greek lambda (λ).

Wavenumber (ṽ)

The spatial frequency of a wave, either in cycles per unit distance or radians per unit distance. Typically expressed in inverse centimeters (1/cm or cm⁻¹). (Wikipedia)