Spatial structure of the fundamental mode of a loop cavity with gain-grating holograms

An analysis is made of an increase in the radiation divergence in a self-starting laser system with four-wave mirrors based on saturated-gain gratings in the active medium of an Nd : YAlO₃ laser. The experimental results obtained lead to the conclusion that in such systems with a loop cavity the full phase conjugation does not occur because at least two gain gratings shifted in phase by π are formed in the active medium of the laser.