Beam Distortions in Laser Cavities

Posted on 2006-07-24 as a part of the Photonics Spotlight.

Permanent link: http://www.rp-photonics.com/spotlight_2006_07_24.html

Author: Dr. Rüdiger Paschotta, RP Photonics Consulting GmbH

Ref.: R. Paschotta, “Beam quality deterioration of lasers caused by intracavity beam distortions”, Opt. Express 14 (13), 6069 (2006)

It started with a curiosity, discovered more than three decades ago but not explained until very recently: when a mirror of a solid-state laser resonator is translated, there are often precisely defined positions where the beam quality of the laser output deteriorates strongly. It was soon recognized that these positions are related to certain frequency degeneracies of higher-order cavity modes, but it was not clear why certain degeneracies affect the beam quality much more strongly than others, and how exactly this is related to aberrations in the laser gain medium.

In the paper referenced above (which is freely accessible for the public), the mentioned curiosity is now well explained as a coherent mode coupling effect. More importantly, this analysis increased the overall understanding of how beam distortions within a laser resonator influence the beam quality. This has important practical implications: if you know how to design a laser resonator so that it is much less sensitive to thermal effects in the gain medium, you can realize high beam quality in an easier way than the conventional one, which means reducing the thermal effects as far as possible.