QUANTUM CORRECTIONS TO SEMICLASSICAL LASER THEORY

We suggest a method for successive quantum corrections (in powers of the Planck constant hBAR) to laser field characteristics. The Lagrangian formalism and the representation of the effective potential for the laser have been used. The analogy between the laser and the lambda-phi-4 theory has been established: the laser below, at and above the threshold corresponds to a relativistic particle with positive, zero and imaginary mass, respectively. For a sample calculation, corrections to linewidth, output power and phase diffusion which are due to the internal quantum nature of the laser light have been analytically derived. The bifurcation on the threshold turns out to be a semi-classical effect because the internal quantum fluctuations do not change the value of the threshold.