Quantum theory of microchip lasers with intracavity SRS-conversion

Quantum theory of diode-pumped passively Q-switched microchip lasers with intracavity transient and quasi-stationary stimulated Raman scattering (SRS) conversion has been developed, where dynamics of Raman medium excitation, collective vibration dephasing, and intracavity multiwave mixing of the laser, Stokes and anti-Stokes waves are taken into account. By means of canonical transformation we construct the Hamiltonian describing the intracavity electromagnetic field, the Raman medium and their interaction. A branching set of coupled Heisenberg–Langevin dynamic equations has been obtained for the amplitudes of the generated laser, Stokes and anti-Stokes waves, the collective vibration amplitudes and the population of the excited states of the Raman medium. It is shown that the ordinary phenomenological and quasi-stationary semi-classical models for this class of lasers are the special cases of the developed here quantum description. The simulations based on the presented theory match well experimental data on the dependence of the duration and energy of the Stokes pulses on the pump power.