File:BouncingRay.png

The ray of ASE, bouncing in an active mirror due to the w:total internal reflection; at the pumped region of size $L$, such a ray may have length of order of $2L$. Most of rays are much shorter than $2L$, but due to the exponential growth of the intensity in the gain medium the long rays give significant contribution to the depletion of gain.

This picture have been presented at Third Laser Ceramics Symposium 2007, Paris – Auditorium Curie – CNRS – 3 rue Michel-Ange, 75016 Pari;

http://www.ils.uec.ac.jp/~dima/CONF/2007/PARIS/50.pdf

This pic is available also at Wikisource, http://commons.wikimedia.org/wiki/File:BouncingRay.png