Nonlinear absorber characteristics and their effects on discrimination amplifiers

In an effort to suppress the background intensity surrounding short laser pulses we have investigated the behavior of various discrimination amplifiers. These amplifiers are made up of a sequence of bleachable dyes and amplifiers having an over-all small-signal gain below unity and a large-signal gain above unity. The characteristics of such amplifiers depend strongly on the dye transmission which is itself a function of the particular spatial and temporal profile of the laser pulse propagated through it. This characteristic was investigated experimentally and theoretically. We found 84% transmission at 100 times the saturation intensity of a dye of initial transmission T0=0.2. As a consequence, typical experimental pulse profiles reduce the background suppression efficiency of discrimination amplifiers considerably. However, background suppression of over 2000 is attainable.