Optical depth, or optical thickness, is a measure of transparency. Optical depth is defined as the negative natural logarithm of the fraction of radiation (e.g., light) that is not scattered or absorbed on a path. Hence optical depth is dimensionless, and in particular is not a length, though it is a monotonically increasing function of path length, and approaches zero as the path length approaches zero.
Read more about Optical Depth: Formulations
Famous quotes containing the words optical and/or depth:
“There is an optical illusion about every person we meet.”
—Ralph Waldo Emerson (1803–1882)
“It is thus that the few rare lucid well-disposed people who have had to struggle on the earth find themselves at certain hours of the day or night in the depth of certain authentic and waking nightmare states, surrounded by the formidable suction, the formidable tentacular oppression of a kind of civic magic which will soon be seen appearing openly in social behavior.”
—Antonin Artaud (1896–1948)