Advances in Intense Femtosecond Laser Filamentation in Air¹

S. L. Chin^a, T.-J. Wang^a, C. Marceau^a, J. Wu^b, J. S. Liu^c, O. Kosareva^d, *, N. Panov^d,
Y. P. Chen^a, J.-F. Daigle^a, S. Yuan^a, A. Azarm^a, W. W. Liu^e, T. Seideman^f,
H. P. Zeng^b, M. Richardson^g, R. Li^c, and Z. Z. Xu^c

^a Center for Optics, Photonics and Laser (COPL), Laval University, Quebec City, Qc G1 V 0A6, Canada

^b State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China

^c Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences, Jiading, Shanghai, China

^d International Laser Center, Dept. of Physics, Moscow State University, Moscow, Russia

^e Institute of Modern Optics, Nankai University, Tianjin, China

^f Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA

^g Townes Laser Institute, CREOL College of Optics and Photonics, University of Central Florida, Orlando, FL, USA

*e-mail: kosareva@physics.msu.ru

Received April 12, 2011; in final form, April 26, 2011; published online September 2, 2011

Abstract—This is a review of some recent development in femtosecond filamentation science with emphasis
on our collective work. Previously reviewed work in the field will not be discussed. We thus start with a very
brief description of the fundamental physics of single filamentation of powerful femtosecond laser pulses in air.
Intensity clamping is emphasized. One consequence is that the peak intensity inside one or more filaments
would not increase significantly even if one focuses the pulse at very high peak power even up to the peta-watt
level. Another is that the clamped intensity is independent of pressure. One interesting outcome of the high
intensity inside a filament is filament fusion which comes from the nonlinear change of index of refraction
inside the filament leading to cross beam focusing. Because of the high intensity inside the filament, one can
envisage nonlinear phenomena taking place inside a filament such as a new type of Raman red shift and the
generation of very broad band supercontinuum into the infrared through four-wave-mixing. This is what we call
by filamentation nonlinear optics. It includes also terahertz generation from inside the filament. The latter is
discussed separately because of its special importance to those working in the field of safety and security in
recent years. When the filamenting pulse is linearly polarized, the isotropic nature of air becomes birefringent
both electronically (instantaneous) and through molecular wave packet rotation and revival (delayed). Such
birefringence is discussed in detailed. Because, in principle, a filament can be projected to a long distance in
air, applications to pollution measurement as well as other atmospheric science could be earned out. We call
this filamentation atmospheric science. Thus, the following subjects are discussed briefly, namely, lightning
control, rain making, remote measurement of electric field, microwave guidance and remote sensing of pollut-
ants. A discussion on the higher order Kerr effect on the physics of filamentation is also given. This is a new
hot subject of current debate. This review ends on giving our view of the prospect of progress of this field of
filamentation in the future. We believe it hinges upon the development of the laser technology based upon the
physical understanding of filamentation and on the reduction in price of the laser system.

10.1134/S1054660X11190054

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