Optical metrology features
Optical quantities and their measurement

Just like other areas of optics, metrology makes use of the various models that have been developed to account for the behavior of light, so we'll briefly review their essential features.

• The light ray model assumes that light propagates along lines, in the mathematical sense of the term: light rays. These lines are straight or, very exceptionally, curved. We'll link to it the alignments, angle and distance measurements by triangulation, such as those of Delambre and Méchain, which, at the height of the revolutionary turmoil, made it possible to establish the new standard of length, the metre.

• The more elaborate wave model depicts light as a wave, a periodic variation of a "light vector" or "Fresnel vector", perpendicular to the direction of propagation. In its simplest form (the scalar...