Im studying gain saturation for homogeneous and inhomogeneously broaded transistions. Im a little confused bout the logistics of laser operation regarding the gain in the cavity. So from ground state, the atoms are optically pumped to produce population inversion(4 level system) where stimulated emission occurs and we have lasing operation. obviously here there is a optical gain, the input photons are amplified by multiple passes through medium. Im told gain saturation occurs where there is so much stimulated emission that population inversion runs out and gain reduces to the threshold (=1). So saturation occurs after a very short time? ie does the system go from steady state population inversion, where gain is >1, to steady state N1=N2, where gain=1?