Glossary
Gaussian beams Theory and measurements

rayon de gorge: waist

Commonly used Anglicism meaning "neck" of the beam (characteristic of a Gaussian beam).

half width or radius

At a given z coordinate, the quantity defining the half-extent of the Gaussian ray for an intensity greater than or equal to e ^-2 = 13.5% of the maximum intensity.

half diffraction angle

Angle at the apex of a cone drawn by the Gaussian beam for a large z coordinate (characteristic of a Gaussian beam).

Rayleigh's length: longueur de Rayleigh

Dimension noted z _r for which the half-width of the beam is equal to $w_0\sqrt{2}$...