Abstract

So far quantum-mechanical laser theories used approaches based on different but equivalent formulations either relying on a density matrix description or on the Fokker–Planck equation [1, 2]. In all these descriptions an important approximation and assumption have been used since: The outcoupling of photons out of the laser resonator was modeled by a loss term in analogy to what an equivalent intra-cavity absorption of photons would cause to the laser quantum state, i.e., an uncorrelated loss of single photons, thereby incorporating the finite cavity Q-factor into the description of the laser. Although this procedure is consistent in terms of energy and average photon number it lacks the fact that a typical dielectric laser output mirror is not just a uncorrelated photon extracting device like an absorbing or scattering object. As the output coupler is a beam splitter it has a complex action on the incoming intra-cavity photon state. The photon state, therefore, reflected back into the laser resonator is not just shifted to a lower average photon number but is a rather complex combination of various number states that are binomially distributed.

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