Dominant-mode laser beam as Gauss-Schell model beam

Lasers that are equipped with stable optical resonators having large to very large Fresnel numbers and uniform active medium with respect to gain and refractive index, are running multimode, and the highest order transverse mode has the largest mode coefficient. By using this dominant mode feature and an incoherent superposition of the coherent modes, a simple approximate relation was inferred, that allows to estimate beam quality factor M 2 from the geometrical data of the cavity. A way to evaluate the global degree of coherence of dominant mode laser beams by using a Gauss-Schell model beam having the same beam quality factor M 2 , is proposed.