INTERFERENCE PHENOMENA IN DOPPLER-BROADENED QUANTUM TRANSITIONS - AMPLIFICATION OF INTENSE RADIATION WITHOUT POPULATION-INVERSION

We study the effect of nonlinear interference processes on quantum tra nsitions in intense resonant electromagnetic fields with allowance for changes in level populations, relaxation processes, incoherent excita tion, and Doppler broadening of the transitions, on the absorption, am plification, and refraction of the interacting fields. The theory is g eneralized to the case of nonlinear interference interaction of two in tense fields in open and closed three-level quantum systems. Using the density matrix, we derive general expressions in the case of stationa ry interaction that make it possible to analyze the optical characteri stics for various configurations of the interfering transitions by a s imple substitution of parameters. The possibility of amplifying light without saturated population inversion in a resonant transition is dis cussed. We formulate the conditions for such amplification and use exa mples to show that under appropriate changes in the initial level popu lations and the intensity of the auxiliary light, the inversionless am plification coefficient does not decrease with increasing intensity of the amplified radiation. We also show that allowance for these accomp anying processes greatly affects the choice of optimal conditions for interference in optical transitions. As an illustration we list the re sults of a numerical analysis of possible experiments. (C) 1998 Americ an Institute of Physics.