optical path length (OPL)

The distance that light would travel through a vacuum to maintain an equivalent phase with light traveling through some medium. For example, light passing through a cell experiences a longer optical path length than light that does not.

See also: optical path length difference

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Specimen Optical Path Length Variations

Explore the effects of changes to refractive index and thickness on optical path length, and discover how two specimens can have different combinations of these variables but still display the same path length.