Radiation Lifetime in a Cavity
Laser radiation in a cavity will have a finite lifetime because of losses at the cavity walls. The decay of a radiation mode can be expressed as
For cavity dimension L and reflection coefficient a, the time to make n reflections is
After n reflections, the radiation intensity is
which gives for the lifetime:
Using the series approximation
This cavity lifetime is one of the parameters which determines the pumping power which must be used to maintain a given level of radiation from a laser.