ON THE PUMP INTENSITY DEPENDENCE OF PROBE NOISE, ABSORPTION AND DISPERSION IN A DRIVEN 2-LEVEL SYSTEM AT POINTS OF ZERO ABSORPTION AND IN THE DEAD-ZONE

We investigate the quantum noise gained by a weak probe laser interact ing with a driven two-level system at points of zero absorption and in the dead-zone. We find that in the Doppler-limit, maximum noise is ob tained at the extremum point of the probe dispersion curve as a functi on of the pump intensity. This implies that in this limit, the noise i s maximal at the transition point between focusing and defocusing. On the other hand, in the absence of Doppler broadening, this is true onl y for the case of a resonant pump.