Self-compression of ferntosecond laser pulses in normally dispersive solid material

实验研究了正色散固体介质中的激光脉冲自压缩现象，证明了无需任何外加色散补偿情况下，固体透明介质中的自聚焦传输过程可使高功率飞秒激光脉冲实现时域脉冲压缩，并详细研究了输出脉冲的时域和频域特性随入射脉冲强度的演化规律．实验结果表明脉冲自压缩量随入射脉冲强度的增加呈递增趋势，然而当入射光强增大到足以引起超连续谱及锥形辐射产生时，脉冲时域形状会发生分裂．此外还发现发散光束入射情况下同样可以观察到脉冲自压缩现象．We have experimentally demonstrated the self-compression of gegawatt high power femtosecond laser pulses in normally dispersive solid bulk media. It was proved that high-power femtosecond laser pulses can be compressed during the self-focusing propagation in the transparent nonlinear medium. The self-compression behavior was investigated in detail under a variety of experimental conditions, and the temporal and spectral characteristics of resulted pulses are found to be significantly affected by the input pulse intensity, with higher intensity corresponding to shorter compressed pulse. However, the output pulse is split into two peaks when the input intensity is high enough to lead to supercontinuum and conical emission. By the propagation in a piece of BK7 glass, a self-compression from 50fs to 20fs is achieved, with a compression factor of about 2.5. Moreover, we find that pulse self-compression can be achieved with a divergent input laser beam into the glass