Effect of partially coherence of high power fiber laser on coherent combination

Coherent combination of multiple fiber laser is an effective method to get high power laser with excellent beam quality. However, recently developed high power fiber lasers have relatively long linewidths, which means degradation of coherence and disaduentage of coherent combination. The far-field energy distribution of coherent combining high power fiber laser beam array was calculated using pseudo-partially coherent beam(PPCB) model. The results show that when the linewidths of single fiber laser beam get larger, the far-field pattern hardly changes, but the peak power and Strehl value of far-field spot reduce, which means the degradation of the combined beam. The linewidth of single fiber laser should be no more than 5 nm to keep the Strehl ratio larger than 0.8.