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
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.
Your notes
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- n = 1.5 (Refractive index)
- d = 3 m (Geometric path length)
Result: OPL = 4.5 m
Other optics formulas with the same quantities
- Refractive Index (Refraction) shares Refractive index
- Apparent Depth (Refraction) shares Refractive index
- Prism Minimum Deviation (Prisms) shares Refractive index
Where this formula is listed
- Optics formulas, under Wave Optics, alongside Double-Slit Interference, Fringe Spacing, Single-Slit Diffraction, Diffraction Grating and Resolving Power of Grating.
- In the optics list it comes after Thin Film Interference and before Constructive Interference Condition.
- Optics formula sheet, one of 34 formulas printed with symbol keys and SI units.
- The full formula index, grouped by category and topic.
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.