Angular selection of radiation in regenerative amplification in a laser with an unstable resonator

Experimental and theoretical investigations were made of the angular distribution of amplified external radiation injected off-axially into an unstable resonator containing an active medium. Feasibility of angular selection of the external signal was demonstrated. The calculations agreed with the experimental results and made it possible to estimate the role of the frequency effects and also to identify the requirements in respect of the parameters needed to maximize radiation selection.