SPATIOTEMPORAL COUPLING OF LASER FLUCTUATIONS - OBSERVATIONS ON A LASER WITH INTERNAL FREQUENCY-CONVERSION

The amplitude of standing wave solid state lasers with frequency conve rsion inside the resonator can become unstable. We investigated the am plitude fluctuations of an end-pumped Nd:YAG-laser at low pump rates ( below 160% threshold pump power) and also above. Detecting the individ ual mode instabilities separately and comparing them with a theoretica l laser model, we can trace the origin of the mechanism leading to the observed fluctuations. At certain well defined discrete pump levels a bove 160% threshold the instabilities disappear. These stable emission states are associated with particular nonconventional mode patterns, some of them exhibiting a helical phase structure. Based on experiment al observations and computer simulations of pump induced resonator abe rrations we describe a mechanism for the emergence of the peculiar tra nsversal modes and laser fluctuations.