The Modified Unified Expansion Theory (MUET), which can be simultaneously a
pplied to large and small correlation time cases, are obtained by means of
improving the accuracy of calculation. We investigate the colored-loss-nois
e model and colored-gain-noise model for a single-mode laser, and the analy
tic expressions of the probability are obtained through the MUET. Compariso
n shows that the results of the MUET are in better agreement with the simul
ation results than the results of the other theory.