RADIATION IN WAVE-GUIDES AND CAVITIES - FUNDAMENTAL-ASPECTS OF 3-LEVEL SYSTEM DAMPING

A three-level ladder configuration is the most fundamental physical sy stem required for cw laser action. In this paper we present an exact q uantum calculation of three-level system radiation in simple waveguide s and cavities which covers weak and strong coupling. A small effect e xists even for a residual kind of cavity, a single reflecting wall. We show that Lower level relaxation has the same effect on upper level s pontaneous decay as cavity transmission losses. In contrast, the excit ation probability of a strong two-level dipole subject to pure polariz ation noise differs from the three-level system. This suggests that th e threshold behavior of microscopic lasers with small numbers of activ e atoms would depend not only on the amount but also on the origin of homogeneous broadening. Finally analytic expressions for the onset of strong coupling and the microlaser threshold are given and compared to the traditional laser threshold.