Compensation of Gain Narrowing by Self-Phase Modulation in High-Energy Ultrafast Fiber Chirped-Pulse Amplifiers

We propose a method to compensate gain narrowing by use of the self-phase modulation effect in a femtosecond fiber chirped-pulse amplifier (CPA). An engineering rule is derived to determine the stretched pulse duration that allows this compensation. Simulations are carried out to validate this idea. A tradeoff is found between achievable pulse duration and output energy, but we show that this technique allows the generation of 100 fs pulses even for high-gain systems, with output energies of the order of 100 ¿ J. An experimental proof of principle demonstrates the generation of 112 fs, 10 ¿J pulses, the shortest high-energy pulse, to our knowledge, generated by a fiber CPA system.