# Laser Physics: Steady state gain

1. Nov 15, 2011

### Niles

Hi

In almost every book on photonics I've seen, the following expression for the steady state gain is derived

1 + flux/fluxsaturation = gsmall signal/g,

where I by flux mean intracavity flux and g is the gain. When talking about lasers, then in the very same books (e.g. Saleh/Teich) the authors argue that when lasing begins, the intracavity photon flux increases, hence by the above expression the gain decreases until it settles on its steady state value (which is equal to losses). What I find to be confusing is that the above expression only holds for steady state, but Saleh/Teich (and others) use it to argue that gain decreases until it reaches steady state.

How can they use our steady state expression above to describe the dynamical behavior too?

Best,
Niles.