Chapter 1
Femtosecond Laser Filamentation
Induced Phenomena and Applications
See Leang Chin
Abstract The temporal evolution of a filament is followed. The physical processes
evolve from quantum effect in the fs time scale through chemistry in the ps and
ns time scale to classical physics in the microsecond to second time scale. A few
applications and phenomena arising from each step of the physical evolution are
discussed briefly.
1.1 Introduction
Since the accidental discovery, in 1995, of long distance self-focusing of a femtosecond (fs) Ti-sapphire laser pulse in air [1] by the Michigan group led by Prof.
Gerard Mourou, Nobel Laureate 2018, a new sub-field of nonlinear optics, namely,
filamentation, was born [2–7]. Filamentation is a phenomenon of the propagation
of a powerful fs laser pulse in a high density transparent medium such as atmospheric pressure air or condensed media. The most popular laser used in these works
is the Ti-sapphire laser. We shall limit the discussion in the present work to the
propagation of this laser in air. The wavelength of the Ti-sapphire laser is around
800 nm; hence, its single photon energy is around 1.55 eV. This photon energy is
much smaller than the ionization potentials of the molecules in air (the ionization
potential of oxygen molecule is 12.1 eV and that of nitrogen molecule, 15.6 eV).
Self-focusing of the laser pulse would result in a self-focal region in which the intensity is so high that tunnel ionization of the O 2 and N 2 molecules occurs [8]. The
negative index of refraction of the plasma will defocus the laser pulse and stop the
self-focusing. HOKE (Nonlinear Higher Order Kerr Effect) would probably not play
a competitive role before ionization because of the fast rise of the laser pulse to a
high field regime. The latter corresponds to the rapid onset of the non-perturbative
regime. That is to say, the perturbative description (hence, the HOKE effect) cannot
be used anymore [9]. Many physical processes are involved from the birth to the
S. L. Chin (B)
Center for Optics, Photonics and Lasers (COPL), Laval University, Quebec City, Canada
e-mail: slchin@phy.ulaval.ca
© Springer Nature Switzerland AG 2020
K. Yamanouchi and D. Charalambidis (eds.), Progress in Ultrafast
Intense Laser Science XV, Topics in Applied Physics 136,
https://doi.org/10.1007/978-3-030-47098-2_1
1
Femtosecond Laser Filamentation
Induced Phenomena and Applications
See Leang Chin
Abstract The temporal evolution of a filament is followed. The physical processes
evolve from quantum effect in the fs time scale through chemistry in the ps and
ns time scale to classical physics in the microsecond to second time scale. A few
applications and phenomena arising from each step of the physical evolution are
discussed briefly.
1.1 Introduction
Since the accidental discovery, in 1995, of long distance self-focusing of a femtosecond (fs) Ti-sapphire laser pulse in air [1] by the Michigan group led by Prof.
Gerard Mourou, Nobel Laureate 2018, a new sub-field of nonlinear optics, namely,
filamentation, was born [2–7]. Filamentation is a phenomenon of the propagation
of a powerful fs laser pulse in a high density transparent medium such as atmospheric pressure air or condensed media. The most popular laser used in these works
is the Ti-sapphire laser. We shall limit the discussion in the present work to the
propagation of this laser in air. The wavelength of the Ti-sapphire laser is around
800 nm; hence, its single photon energy is around 1.55 eV. This photon energy is
much smaller than the ionization potentials of the molecules in air (the ionization
potential of oxygen molecule is 12.1 eV and that of nitrogen molecule, 15.6 eV).
Self-focusing of the laser pulse would result in a self-focal region in which the intensity is so high that tunnel ionization of the O 2 and N 2 molecules occurs [8]. The
negative index of refraction of the plasma will defocus the laser pulse and stop the
self-focusing. HOKE (Nonlinear Higher Order Kerr Effect) would probably not play
a competitive role before ionization because of the fast rise of the laser pulse to a
high field regime. The latter corresponds to the rapid onset of the non-perturbative
regime. That is to say, the perturbative description (hence, the HOKE effect) cannot
be used anymore [9]. Many physical processes are involved from the birth to the
S. L. Chin (B)
Center for Optics, Photonics and Lasers (COPL), Laval University, Quebec City, Canada
e-mail: slchin@phy.ulaval.ca
© Springer Nature Switzerland AG 2020
K. Yamanouchi and D. Charalambidis (eds.), Progress in Ultrafast
Intense Laser Science XV, Topics in Applied Physics 136,
https://doi.org/10.1007/978-3-030-47098-2_1
1