retardance (original) (raw)
Author: the photonics expert (RP)
Definition: the difference in optical phase shifts between two polarization directions, e.g. for light transmitted through a sample or reflected at a surface
general opticsRelated: waveplates
Units: rad, λ
Formula symbol: Gamma\GammaGamma
Page views in 12 months: 1297
DOI: 10.61835/2jq Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn
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What is a Retardance?
When a light beam propagates through a birefringent medium, it experiences different changes in optical phase for the ordinary and extraordinary polarization components. The difference in those phase shifts is called retardance. It can be specified in radians (rad) or in degrees (°), alternatively in terms of wavelengths; a retardance of ($\lambda$), for example, corresponds to ($2 \pi$) or 360°.
In optics, a retardance is often introduced by inserting a waveplate — for example, a ($\pi$) retardance with a ($\lambda /2$) plate. With a Babinet–Soleil compensator or a Berek compensator, one can obtain an adjustable amount of retardance. Generally, optical elements for introducing a controlled amount of optical retardance are called retarders.
Retardation effects also occur upon reflection at a dielectric interface with non-normal incidence; here, the retardance can be calculated with Fresnel equations.
More complicated effects occur as a result of thermally induced birefringence, for example in a laser crystal, where both the amount of retardance and the axes directions generally depend on the position within the beam profile.
Note also that the retardance is generally wavelength-dependent. For achromatic waveplates, the wavelength dependence is minimized.
Frequently Asked Questions
This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).
What is optical retardance?
When a light beam propagates through a birefringent medium, its different polarization components experience different optical phase shifts. Retardance is the difference between those phase shifts.
How can a specific retardance be introduced into a light beam?
One can use optical elements called retarders. A common example is a waveplate, such as a half-wave plate which introduces a retardance of ($\pi$). For an adjustable amount of retardance, one may use a Babinet–Soleil compensator.
In which units is retardance specified?
Retardance can be specified in radians (rad) or degrees (°). Alternatively, it can be expressed in terms of wavelengths; for example, a retardance of ($\lambda$) corresponds to a phase difference of ($2\pi$) or 360°.
Does retardance only occur when light passes through a material?
No, retardation effects also occur upon reflection at a dielectric interface if the light is not hitting the surface at a normal angle. The amount of retardance can be calculated with Fresnel equations.
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