Transmission coefficient
The transmission coefficient is used in physics and electrical engineering when wave propagation in a medium containing discontinuities is considered. A transmission coefficient describes the amplitude, intensity, or total power of a transmitted wave relative to an incident wave.
Different fields have different definitions for the term.
In optics, transmission is the property of a substance to permit the passage of light, with some or none of the incident light being absorbed in the process. If some light is absorbed by the substance, then the transmitted light will be a combination of the wavelengths of the light that was transmitted and not absorbed. For example, a blue light filter appears blue because it absorbs red and green wavelengths. If white light is shone through the filter, the light transmitted also appears blue because of the absorption of the red and green wavelengths.
The transmission coefficient is a measure of how much of an electromagnetic wave (light) passes through a surface or an optical element. Transmission coefficients can be calculated for either the amplitude or the intensity of the wave. Either is calculated by taking the ratio of the value after the surface or element to the value before.
In non-relativistic quantum mechanics, the transmission coefficient and related reflection coefficient are used to describe the behavior of waves incident on a barrier. The transmission coefficient represents the probability flux of the transmitted wave relative to that of the incident wave. It is often used to describe the probability of a particle tunneling through a barrier.
The transmission coefficient is defined in terms of the incident and transmitted probability current density J according to:
where Jinc is the probability current in the wave incident upon the barrier with normal unit vector and Jtrans is the probability current in the wave moving away from the barrier on the other side.
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