  Though laser physics began at 1960s, its entropy evolution has not been
touched until very recently the Kraus-form solution of laser's master equation
is reported (Ann. Phys. 334 (2013)). We study the new physics based on the
discovery in this paper. We analyze time evolution of physical observables and
quantum optical properties in the laser process with arbitrary initial states,
such as the photon number, the second degree of coherence, etc. The evolution
of entropy of these states is also studied. Our results well conform with the
known behaviour of laser, which confirms that the master equation describes
laser suitably, and the Kraus-form operator solution is correct, elegant and
useful.

Quantum Physics