Two-Level Laser Dynamics with a Noiseless Vacuum Reservoir
  We analyze the quantum properties of the light generated by a two-level laser in which the two-level atoms available in a closed cavity are pumped to the upper level by means of electron bombardment. We consider the case in which the two-level laser is coupled to a vacuum reservoir via a single-port mirror and seek to carry out our analysis by putting the noise operators associated with the vacuum reservoir in normal order. It is found that the two-level laser generates coherent light when operating well above threshold and chaotic light when operating at threshold. Moreover, we have established that a large part of the total mean photon number is confined in a relatively small frequency interval. 
Fesseha Kassahun
quant-ph