Investigation of the properties of a laser with an unstable resonator and additional feedback

An experimental investigation was made of the properties of a neodymium glass laser with an unstable resonator and an additional mirror which covered part of the optical beam cross section to reduce the stimulated emission threshold. The results were compared with the case of a conventional low-magnification unstable resonator. It was found that radiation with a low angular divergence cannot be obtained from a laser with an unstable resonator and additional feedback.