PhysRefPhysics reference
Category
Optics

Optical Path Length

The optical path length accounts for the change in wavelength when light travels through a medium. It equals the distance light would travel in vacuum in the same number of wavelengths.

Variables

OPL
Optical path length
m
n
Refractive index
unitless
d
Geometric path length
m

Derivation

Since wavelength decreases by factor n in a medium (λ_medium = λ_vacuum/n), the optical path length is n times the geometric path.

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