Optical Path Length⚠ unverified
Physics / Optics · Compute the optical path length through a medium
Parameters
| Input | Symbol | Unit | Default | Description |
|---|---|---|---|---|
| n | n | — | 1.0 | Refractive index of the medium (dimensionless) |
| d | d | m | 1.0 | Physical path length through the medium |
| Output | Symbol | Unit | Description |
|---|---|---|---|
| result | OPL | m | Optical path length, in metres (m) |
The science & history
Understanding the Parameters
- $n$ — vacuum $n=1$; glass multiplies path.
- $d$ — physical thickness or path.
- OPL — differences in OPL determine interference (thin films, interferometers).
Derivation (Approaching a Proof)
Wave speed $c/n$; time to cross $d$ is $nd/c$, equal to vacuum path $nd$ at speed $c$. Hence OPL $= nd$.
History
OPL is the natural variable in Fermat’s principle and interferometry.
Related Concepts: Thin Film Thickness, Coherence Length, Snell's Law refraction angle
Notes: Registry calculator optical-path-length (unverified). Homogeneous medium segment.