Numeral analysis of spectral shaping based on superstructure fiber Bragg grating in high-power Nd:glass chirped pulse amplification system

Using the genetic algorithm, we design a superstructure fiber Bragg grating (SSFBG) to pre-compensate gain narrowing and gain saturation effects in a high-power Nd:glass chirped pulse amplification system. An inverse engineering operation of chirped pulse amplification processing is used to calculate the target spectrum of the seed pulse and then the response function of the SSFBG can be obtained. Some numerical simulations are given to realize a 20 μJ, 15 nm ultrashort seed pulse to the hundreds Joules, 8 nm optimal fourth order super-Gaussian chirped pulses in a high power Nd:glass amplification system. The results show that the gain narrowing and gain saturation effects will be reduced largely when a SSFBG, which has a proper refractive index modulation distribution, chirp coefficient and length, is used. It is believed that this proposed method will provide a theoretical direction for the future experiment. Moreover, it will also be useful and flexible for the spectral transform in other chirped pulse application areas.