Optical Properties of Materials
Author: the photonics expert Dr. Rüdiger Paschotta (RP)
Definition: properties of materials which define their effects on light
- optical properties of materials
Related: optical materialsoptical properties of devices
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DOI: 10.61835/pte Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn
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Optical materials have a range of properties describing their effects on light. This article presents a brief overview:
| Property | Symbol | Units | Definition |
|---|---|---|---|
| Absorptance | ($A$) | 1 | the fraction of incoming radiant flux which is absorbed by an object |
| Absorption coefficient | ($\alpha$) | m−1, cm−1 | a logarithmic measure for the distributed absorption in a medium |
| Absorption length | ($L_\textrm{abs}$) | m | the length over which absorption reduces the optical intensity to 1/e of its initial value |
| Birefringence | the polarization dependence of the refractive index of a medium | ||
| Chromatic dispersion | the frequency dependence of the phase velocity in a transparent medium | ||
| Dichroism | wavelength-dependent transmission, alternatively polarization-dependent absorption | ||
| Emissivity | ($\epsilon$) | 1 | a measure of how strongly an object emits and absorbs thermal radiation |
| Group delay dispersion | ($D_2$) | s2 | the frequency dependence of the group delay, or (quantitatively) the corresponding derivative with respect to angular frequency |
| Group index | ($n_\textrm{g}$) | 1 | the ratio of the vacuum velocity of light to the group velocity in a medium |
| Opacity | ($\kappa$) | 1 or m2/kg | the property of a substance or an object not to transmit light or at least to attenuate it |
| Optical activity | the ability of a transparent substance to exhibit polarization rotation or circular dichroism | ||
| Polarization beat length | ($L_\textrm{B}$) | m | the period of interference effects in a birefringent medium |
| Principal dispersion | ($n_\textrm{F} - n_\textrm{C}$) | 1 | a crude measure for chromatic dispersion of a transparent optical material |
| Propagation losses | %/cm, dB/m | losses of optical energy during propagation of light | |
| Refractive index | ($n$) | 1 | a measure of the reduction in the velocity of light in a medium |
| Sellmeier formula | an equation for calculating the wavelength-dependent refractive index of a medium | ||
| Thermo-optic coefficient | ($\partial n/\partial T$) | K–1 | derivative of refractive index with respect to temperature |
| Transparency | the property of a material to transmit light without strong absorption and scattering |
Most optical properties depend on the wavelength of light, sometimes also on the polarization and (for non-isotropic media) on the direction of propagation.
For laser gain media, additional quantities come into play, such as absorption and emission cross-sections.
Concerning nonlinearities, there are various additional possibly relevant quantities, such as nonlinear coefficients related to nonlinear polarization and cross-sections for Raman scattering.