In many papers on laser dynamics theory, quantum Langevin equation of operators is converted to c-number stocastic differential equations, which is analyzed to obtain results. However, why this procedure is justified is not described in the papers, at least not satisfactory for me. I try to trace back to earlier literature, but still can't find a good explanation. Some of the papers I'm referring to are:
role of pumping statistics in laser dynamics Quantum Langevin approach, Phys. Rev. A
role of pumping statistics and dynamics of atomic polarization in quantum fluctuations of laser sources, Phys. Rev. A
laser theory with finite atom-field interacting time, Phys. Rev. A
sub-Poissonian processes in quantum optics, Rev. Mod. Phys.
Could anyone provide a brief answer? Or maybe direct me to a better reference.