ABSTRACT
Soon after the first demonstration of ultrashort pulses, it appeared that although the pulse duration was very short, its peak power was still in the kilowatt range, too small to be used in most nonlinear optics experiments. Amplifiers were designed to increase the energy of the pulse, and multigigawatt pulses were obtained in 1982 (Fork et al., 1982; Migus et al., 1982). At that time, femtosecond lasers were based on dyes, and the pulses were amplified by simply sending them into a series of dye cells pumped by a nanosecond green laser. The efficiency was in general below 1%, and the pulse was hidden in a large amplified spontaneous emission (ASE) pedestal. In the meantime people were trying to decrease the duration of the pulse produced by a large-scale Nd:glass system. The main difficulties were linked to damage in the amplifier chain due to the very high peak power of the amplified short pulses.
