Champeaux Stéphanie, Bergé Luc
Département de Physique Théorique et Appliquée, CEA/DAM Ile de France, Boîte Postale 12, F-91680 Bruyères-le-Châtel, France.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Dec;68(6 Pt 2):066603. doi: 10.1103/PhysRevE.68.066603. Epub 2003 Dec 11.
The nonlinear propagation of femtosecond pulses in pressure-gas cells filled with argon is investigated. By increasing the pressure for reaching peak power levels close to the threshold for self-focusing, it is shown that either group-velocity dispersion or multiphoton ionizing (MPI) sources can become key players for arresting the beam collapse. For input powers noticeably above critical, MPI rapidly dominates and the formation of self-guided filaments of light occurs. We discuss the dynamical role of MPI in shortening the pulse duration up to the optical cycle limit. Two different wavelength domains are commented. The influence of space-time focusing and self-steepening effects is furthermore discussed. Their respective roles in promoting shock structures are studied and shown to still promote pulse shortening in suitable power regimes. Finally, spectral broadening is analyzed and proven to be more important for large laser wavelengths. Numerical integration of the propagation equations is explained in the light of analytical arguments.
研究了飞秒脉冲在充满氩气的压力气室中的非线性传播。通过增加压力以达到接近自聚焦阈值的峰值功率水平，结果表明群速度色散或多光子电离（MPI）源都可能成为阻止光束坍缩的关键因素。对于明显高于临界值的输入功率，MPI迅速起主导作用，并且会形成自导光丝。我们讨论了MPI在将脉冲持续时间缩短至光学周期极限方面的动态作用。评论了两个不同的波长范围。此外，还讨论了时空聚焦和自陡峭效应的影响。研究了它们在促进激波结构方面各自的作用，并表明在合适的功率范围内仍能促进脉冲缩短。最后，分析了光谱展宽，并证明其对于较大激光波长更为重要。根据解析论证对传播方程的数值积分进行了解释。
