Modern laser sources nowadays deliver ultrashort light pulses reaching few cycles in duration, high energies beyond the Joule level and peak powers exceeding several terawatt (TW). When such pulses propagate through optically-transparent media, they first self-focus in space and grow in intensity, until they generate a tenuous plasma by photo-ionization. For free electron densities and beam intensities below their breakdown limits, these pulses evolve as self-guided objects, resulting from successive equilibria between the Kerr focusing process, the chromatic dispersion of the medium, and the defocusing action of the electron plasma. Discovered one decade ago, this self-channeling mechanism reveals a new physics, widely extending the frontiers of nonlinear optics. Implications include long-distance propagation of TW beams in the atmosphere, supercontinuum emission, pulse shortening as well as high-order harmonic generation. This review presents the landmarks of the 10-odd-year progress in this field. Particular emphasis is laid to the theoretical modeling of the propagation equations, whose physical ingredients are discussed from numerical simulations. Differences between femtosecond pulses propagating in gaseous or condensed materials are underlined. Attention is also paid to the multifilamentation instability of broad, powerful beams, breaking up the energy distribution into small-scale cells along the optical path. The robustness of the resulting filaments in adverse weathers, their large conical emission exploited for multipollutant remote sensing, nonlinear spectroscopy, and the possibility to guide electric discharges in air are finally addressed on the basis of experimental results.
The universality of filamentation-caused challenges of ultrafast laser energy deposition in semiconductors
Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学）；Laboratoire Hubert Curien, Université Jean Monnet（让·莫内大学于贝尔·居安实验室）；First Light Imaging S.A.S.（第一束光成像有限公司）；Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology—Hellas (FORTH)（希腊基础研究与技术基金会电子结构与激光研究所）；University of Crete（克里特大学）；Fraunhofer Institute for Applied Optics and Precision Engineering IOF（弗劳恩霍夫应用光学和精密工程研究所）
Université Bourgogne Europe, CNRS（勃艮第欧洲大学）；University of Calabria（卡拉布里亚大学）；University of Limoges, CNRS（利摩日大学）；Niccolò Cusano University（尼古拉·库萨诺大学）；Sapienza Universit‘a di Roma（罗马第一大学）
