基于单块晶体级联二阶非线性的超短激光脉冲脉宽压缩

Pulse-duration compression of ultra-short laser pulse by cascaded second-order nonlinearity

研究了基于单块偏硼酸钡(BBO)晶体的级联二阶非线性效应实现超短激光脉冲脉宽压缩的原理。采用分步傅里叶变换及四阶龙格-库塔算法对描述I类飞秒脉冲倍频过程的耦合波方程组进行了数值计算,定量分析了基频光与倍频光位相失配量、非线性晶体长度、入射基频光峰值光强和初始脉宽等因素对脉宽压缩效果的影响,并对实验参数进行了优化。采用单块BBO晶体,对中心波长为800nm、脉宽为140fs的超短激光脉冲开展了脉宽压窄的实验研究,获得了两倍以上的脉宽压缩倍率。对不同基频光峰值强度和不同初始脉宽下的实验结果与理论模拟结果进行了比较与分析,结果表明,倍频过程中的位相失配量、初始基频光峰值光强、脉冲啁啾,以及初始基频光脉宽等因素对脉冲压缩效果的影响较大。若要获得较高的压缩倍率,需要综合考虑上述多种因素。

The pulse-duration compression principle of a ultra-short laser pulse by cascaded second-or- der nonlinearity from a single 13-barium borate （BBO） crystal was studied theoretically and experimen- tally. By using the split-step Fourier transformation and fourth-order Runge-Kutta methods, the type I coupled wave equation＇s describing for Second Harmonic Generation （SHG） process of femtosecond pulse were simulated and calculated. The influences of the phase mismatch between fundamental har- monic（FH） and second harmonic（SH）pulses, the length of nonlinear crystal, peak intensity and the initial pulse-duration of the FH pulse on the pulse-duration compression were analyzed quantitatively and the experimental parameters were also optimized. Furthermore, the experiment of the pulse-width compression was performed for the ultra-short laser pulse with a center wavelength of 800 nm and a pulse width of 140 fs, and the pulse-width compression of more than two times was achieved. Finally, the experimental and simulation results for different fundamental peak intensities and initial pulse- widths were compared. Obtained results show that some factors like the phase mismatch between fun- damental harmonic（FH） and second harmonic（SH） pulses, peak intensity, pulse chirp and the initial pulse-duration of the FH pulse have much influence on the pulse compression, so these facts men- tioned above should be taken into consideration.