Optical pathlength

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Definition

An optical pathlength is a measure of distance in a medium defined in terms of the number of wavelengths (for a given optical frequency) needed to cover the distance. As a result, optical pathlength scales with true distance and refractive index. In a homogeneous, isotropic medium, the optical pathlength between two points is defined as l=d*n, where d is the true distance and n is the refractive index.

Optical pathlength is often a more useful quantity to work with than true distance when designing optical devices such as resonators, Bragg reflectors and photonic crystals that rely on coherent scattering of light.