Editing Active laser medium (section)

===Efficiency of the gain medium===
The efficiency of a '''gain medium''' can be defined as
<math>~ E =\frac{I_{\rm s} G}{I_{\rm p}A}~</math>.

Within the same model, the efficiency can be expressed as follows:
<math>~E =\frac{\omega_{\rm s}}{\omega_{\rm p}} \frac{1-V/p}{1+U/s}~</math>.

For efficient operation, both intensities—pump and signal—should exceed their saturation intensities:
<math>~\frac{p}{V}\gg 1~</math>, and <math>~\frac{s}{U}\gg 1~</math>.

The estimates above are valid for a medium uniformly filled with pump and signal light.  [[Spatial hole burning]] may slightly reduce the efficiency because some regions are pumped well, but the pump is not efficiently withdrawn by the signal in the nodes of the interference of counter-propagating waves.