Increase in the ratio of the energy of ultrashort laser pulses to the energy of the background radiation

It was established that nonlinear radiation losses occurred in neodymium-glass lasers generating ultrashort pulses. These lasers had bleachable dye cells and were operated at low values of the energy density in the resonator. The nonlinear losses and the finite relaxation time of the bleached state of the dye reduced the contrast of the laser radiation (the ratio of the energy of the ultrashort pulses to the energy of the background radiation). The contrast could be increased by more than two orders of magnitude by passing the radiation through a system with a stable two-component medium (an amplifier and a nonlinear absorber).