Optical Path Difference (OPD)
Optical path difference is the phase shift which happens between two previously coherent sources when passed through different mediums. For example a wave passed through glass will appear to travel a greater distance than an identical wave in air. This is because the source in the glass will have experienced a greater number of wavelengths due to the higher refractive index of the glass.
The OPD can be calculated from the following equation:
where d1 and d2 are the distances of the ray passing through medium 1 or 2, n1 is greater refractive index (e.g., glass) and n2 is the smaller refractive index (e.g., air).
Read more about this topic: Optical Path Length
Famous quotes containing the words optical, path and/or difference:
“People who have realized that this is a dream imagine that it is easy to wake up, and are angry with those who continue sleeping, not considering that the whole world that environs them does not permit them to wake. Life proceeds as a series of optical illusions, artificial needs and imaginary sensations.”
—Alexander Herzen (1812–1870)
“The broken ridge of the hills
was the line of a lover’s shoulder,
his arm-turn, the path to the hills,
the sudden leap and swift thunder
of mountain boulders, his laugh.”
—Hilda Doolittle (1886–1961)
“I see less difference between a city and a swamp than formerly.”
—Henry David Thoreau (1817–1862)