Spatial coherence of light beams in lasers with feedback

It is demonstrated for the first time that the formation of spatially coherent laser beams is influenced strongly by interference effects in the laser resonator and by amplification. Lasers with lumped and distributed feedback are considered. A relationship is established between the natural angular broadening Δθ of beams and the natural laser line width. The theoretical estimates of Δθ are in agreement with the experimental data for He-Ne lasers.