Synthesis of fiber Bragg grating for gain-narrowing compensation in high-power Nd: Glass chirped pulse amplification system

We propose and analyze theoretically a method to compensate gain-narrowing effect by using the spectral shaping technology based on superstructure fiber Bragg grating (SSFBG) in high-power Nd:glass chirped pulse amplification system. The target spectrum is firstly calculated from hundreds joules amplified chirped Gaussian or super-Gaussian pulse by an inverse engineering operation. A genetic algorithm is used to design the SSFBG and obtain the index modulation distribution of grating which can transform the initial seed pulse to the target spectrum. The numerically simulations show that the spectral narrowing effect of chirped pulse amplification will be reduced largely and the ideal pulse spectrum (Gaussian or super-Gaussian) is also obtained. It is believed that this proposed method will provide a theoretical direction for the following experiment. Moreover, it will also be useful and flexible for the spectral transform in other chirped pulse application areas.