Optical Path Length - Optical Path Difference (OPD)

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:

    The convent, which belongs to the West as it does to the East, to antiquity as it does to the present time, to Buddhism and Muhammadanism as it does to Christianity, is one of the optical devices whereby man gains a glimpse of infinity.
    Victor Hugo (1802–1885)

    The sweetest and most inoffensive path of life leads through the avenues of science and learning; and whoever can either remove any obstructions in this way, or open up any new prospect, ought so far to be esteemed a benefactor to mankind.
    David Hume (1711–1776)

    ... [woman suffrage] has made little difference beyond doubling the number of voters. There is no woman’s vote as such. They divide up just about as men do.
    Alice Roosevelt Longworth (1884–1980)