optical path length difference (OPD)

The difference in optical path length between two paths, it's important for determining phase differences.

Synonyms: optical path difference

Related MicroscopyU Article

Specimen Optical Path Length Variations

Phase contrast microscopy interprets differences in specimen optical path length as fluctuations in light intensity, which are readily observed as variations in contrast through the microscope. This interactive tutorial explores the effects of refractive index and thickness changes on the apparent overall optical path length, and demonstrates how two specimens can have different combinations of these variables but still display the same path length.