Spatial structure of radiation from a neodymium-glass four-wave feedback oscillator

A four-wave interaction with feedback was used in combination with a Faraday isolator to achieve unidirectional lasing in a neodymium glass. This improved greatly the transverse structure of the radiation and ensured a divergence close to the diffraction limit. The threshold value of the input energy was 12 mJ, the maximum reflection coefficient reached 25, and the maximum output energy was 0.5 J. A linear four-wave feedback resonator was proposed and investigated. In the strong discrimination region the transverse structure of the output radiation had a near-diffraction divergence. The threshold value of the input energy was then 16 mJ, the maximum reflection coefficient was 10, and the maximum output energy reached 0.4 J.