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.
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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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Common questions
What is the Optical Path Length formula?
Optical Path Length is written OPL = n ·d. 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. It belongs to Optics, under Wave Optics.
What are the units in OPL = n ·d?
In SI units, OPL is optical path length, measured in m; n is refractive index (dimensionless); d is geometric path length, measured in m.
How is the Optical Path Length formula derived?
Since wavelength decreases by factor n in a medium (λ_medium = λ_vacuum/n), the optical path length is n times the geometric path. The result is OPL = n ·d.