On Unstable Resonators Producing Compact Output Beam

A class of unstable laser resonators producing output beams with a continuous compact aperture by a simple manner, without involving special optical components is described. These resonators are composed of spherical mirrors and belong to unstable optical ones both for positive and negative branches. Space distributions of the cavity lasing modes and output characteristics of such resonators for a fast-flow discharge CO2 laser are investigated numerically. The results demonstrate very favourable prospects for using this type of resonators.