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# glossary

**Laser**: acronym of : « light amplification by stimulated emission of radiation » ; device emitting spatially and temporally coherent light radiation based on the stimulated emission**Waist**: position along the propagation axis where a laser beam has the smallest size**Wavelength ( of a light wave )**: distance between two consecutive identical states of the electric ( or magnetic ) field**Embedded gaussian beam**: beam with a gaussian intensity distribution used to simulate a real beam from the gaussian fundamental mode ; characterized by the M-square coefficient representing the ratio between its divergence and that of the fundamental gaussian mode with the same waist size**M square factor (M2)**: ratio between the divergence of an embedded gaussian beam and that of the fundamental mode of a laser (gaussian mode) with the same waist size and at the same wavelength**Rayleigh range**: for gaussian or embedded gaussian beams, distance in the propagation direction from the waist to a position where the beam radius is increased by a factor of square root of 2**Divergence**: defines the maximum angle between the light rays of a beam**Wavefront radius**: radius of curvature of the wavefront of a spherical wave