EE5380: Principles of Photonics & Optical Engineering
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15 August 2015 Absorption coefficient
The absorption coefficient decides how far into a material, the light of a particular wavelength can penetrate before it is absorbed.
The photons that have an energy above the band gap, depends on the wavelength and its absorption coefficient is not constant. The likelihood of retaining a photon relies on upon the probability of having a photon and an electron connect so as to move starting with one energy band then onto the next. The absorption is relatively low for photons with energy very close to that of the band gap, as only those electrons directly at the…show more content… Because dn/dω and dε’/dω have the same sign, the index of refraction decreases with frequency in a spectral region of anomalous dispersion. Anomalous dispersion can be observed experimentally if the substance is not too opaque at the resonance frequency. E.g. certain dyes have absorption bands in the visible region of the spectrum and exhibit anomalous dispersion in the region of these bands. Prisms doped with these dyes produce a spectrum that is reversed, i.e. the longer wavelengths are refracted more than the shorter wavelengths. Aperture
A device that controls the amount of light admitted through an opening. In photography and digital photography, aperture is the unit of measurement that defines the size of the opening in the lens that can be adjusted to control the amount of light reaching the film or digital sensor. The size of the aperture is measured in F-stop. Aspherical
Aspherical lenses are lenses with complex curved surfaces, such as where the radius of curvature changes according to distance from the optical axis. It offers excellent aberration correction performance, which provides superior resolution, even with compact optics composed of a small number of elements.
In a system with astigmatism, the power of the optical system