GAIN AND DIFFUSION IN AN INVERSIONLESS LASER

In this paper, a quantum theory of an inversionless laser is presented . The gain medium is considered to consist of three-level atoms in a c losed LAMBDA configuration, with a lower-level microwave coupling. By deriving an equation of motion for the reduced density matrix for the two modes of the field, gain and diffusion are studied. In particular, two mechanisms through which inversionless amplification takes place in the context of this model, namely, the suppression of absorption an d mode coupling, are discussed. Stable conditions for inversionless am plification and the attendant phase diffusion are discussed and a comp arison is made with conventional, inversion-based lasers. It is shown that lasing without inversion does not necessarily result in a reduced linewidth compared to a conventional laser.