啁啾系数对飞秒脉冲的分裂及光谱性质的影响

Effect of Chirp Coefficient on Pulse Splitting and Spectral Properties of Femtosecond Pulse

利用预估校正-时域有限差分法求得不含慢变包络近似和旋转波近似的全波Maxwell-Bloch方程的数值解,在Λ型三能级原子介质中研究了啁啾系数C对传播中的飞秒Gauss型脉冲分裂情况及光谱性质的影响.结果表明:面积小于等于3π的啁啾脉冲在介质中不出现分裂,但脉冲啁啾会引起脉冲频谱的震荡;对于4π面积啁啾脉冲,啁啾系数C较小时脉冲在介质中发生分裂,C较大的脉冲不再产生分裂,即分裂的子脉冲数量减少;随着C增大,脉冲中心频率附近频谱震荡愈加剧烈,高频成分的范围及强度明显减小;对于大面积8π脉冲,脉冲分裂情况与4π情况相似,但随C增大,脉冲高频成分的范围和强度没有明显变化,而高频成分中的峰值分布却显著不同.

The effect of chirp coefficient （C） on pulse splitting and spectral properties of femtosecond Gaussian pulse propagating in a three-level A-type atomic medium were investigatedby using the numerical solution of the full Maxwell-Bloch equations without the slowly varying envelope and the rotating-wave approximations. It is shown that, when area of the chirped pulse is smaller than or equal to 3n, regardless of size of the C, pulse splitting doesn＇t occur, but the oscillation of the spectral component near the central frequency becomes more severe with the increasing of the C; when the 4n area pulse with smaller value of C propagates in the mediums, pulse splitting occurs, but the splitting doesn＇t occur for the 4n area pulse with bigger value of C; and the oscillation of the spectral component near the central frequency becomes more severe and the pulse spectral bandwidth and the strength of the spectral component with higher frequency decrease obviously with the increasing of the C. For the pulse with larger area 8n, the case of pulse splitting is similar to 47t pulse, the pulse spectral bandwidth and the strength of the spectral component with higher frequency are not varied evidently with the increasing of the C,but distributions of peak values of the spectral component with higher frequency are very different for the puls with different values of the C.