1 Femtosecond Laser Filamentation Induced Phenomena and Applications
15
motion and mixing. The time scale could last up to 90 ms [66]. Air flow would occur;
i.e. wind would be induced by filamentation.
The thermodynamic relaxation of the filament zone described in the preceding
paragraph would have practical consequences depending on the environment in
which the filament is formed and depending on the performance of the laser. For
example, if a high repetition rate (1 kHz, for example) fs Ti-sapphire laser were used
to generate filaments inside a cloud chamber, the resultant air motion would become
a turbulence [35, 72, 73]. In these experiments [35, 72–75], the humidity inside the
cloud chamber (0.5 m × 0.5 m × 0.2 m) was high (saturated or sub-saturated). The
bottom plate was at a temperature of −46 °C while at the top, room temperature
was maintained [35]. The large temperature gradient plus the air turbulence would
induce condensation and precipitation [34–36, 72–75]. This is because the turbulence
would mix up the moist air with a large temperature gradient such that after mixing,
super-saturation would result in the region around the filament. Chemicals such as
HNO 3 –H 2 O as well as the background impurities would act as cloud condensation
nuclei and grow in the super-saturated environment. At high repetition rate, a quasicontinuous build-up of the condensation would result in the formation of large size
water/ice droplets that would fall down to the bottom of the cloud chamber [74]. If
the repetition rate were slow (e.g. 10 Hz), only condensation would be seen because
the growth of the water droplets into large size particles could not be sustained at
low repetition rate of excitation. Condensation had been observed not only in a cloud
chamber but also in the field (see [36] and references therein). Filamentation induced
precipitation could be used as an alternative way to remove environmental pollutants.
1.11 Conclusion
This paper gives an overview of a limited number of applications/phenomena arising
at different stages of the temporal evolution of a fs Ti-sapphire laser filament (mostly
in air). The mechanism of these applications/phenomena vary from quantum physics
in the short time scale (fs) through chemistry in the intermediate time scale (ps to ns)
to classical physics in the long time scale (µs to s). It is hoped that the brief analysis
would stimulate new ideas for the discovery of new phenomena and applications.
Acknowledgements The author would like to thank Prof. Nobuaki Nakashima and Prof. Tomoyuki
Yatsuhashi of Osaka City University, Japan, Dr. S. Abbas Hosseini of Citrogene, Calif., USA and
Prof. Olga Kosareva of Moscow State University for generously sharing their scientific knowledge
with the author. This work was supported by the Center for Optics, Photonics and Laser (COPL),
Laval University, Quebec City, Canada.
15
motion and mixing. The time scale could last up to 90 ms [66]. Air flow would occur;
i.e. wind would be induced by filamentation.
The thermodynamic relaxation of the filament zone described in the preceding
paragraph would have practical consequences depending on the environment in
which the filament is formed and depending on the performance of the laser. For
example, if a high repetition rate (1 kHz, for example) fs Ti-sapphire laser were used
to generate filaments inside a cloud chamber, the resultant air motion would become
a turbulence [35, 72, 73]. In these experiments [35, 72–75], the humidity inside the
cloud chamber (0.5 m × 0.5 m × 0.2 m) was high (saturated or sub-saturated). The
bottom plate was at a temperature of −46 °C while at the top, room temperature
was maintained [35]. The large temperature gradient plus the air turbulence would
induce condensation and precipitation [34–36, 72–75]. This is because the turbulence
would mix up the moist air with a large temperature gradient such that after mixing,
super-saturation would result in the region around the filament. Chemicals such as
HNO 3 –H 2 O as well as the background impurities would act as cloud condensation
nuclei and grow in the super-saturated environment. At high repetition rate, a quasicontinuous build-up of the condensation would result in the formation of large size
water/ice droplets that would fall down to the bottom of the cloud chamber [74]. If
the repetition rate were slow (e.g. 10 Hz), only condensation would be seen because
the growth of the water droplets into large size particles could not be sustained at
low repetition rate of excitation. Condensation had been observed not only in a cloud
chamber but also in the field (see [36] and references therein). Filamentation induced
precipitation could be used as an alternative way to remove environmental pollutants.
1.11 Conclusion
This paper gives an overview of a limited number of applications/phenomena arising
at different stages of the temporal evolution of a fs Ti-sapphire laser filament (mostly
in air). The mechanism of these applications/phenomena vary from quantum physics
in the short time scale (fs) through chemistry in the intermediate time scale (ps to ns)
to classical physics in the long time scale (µs to s). It is hoped that the brief analysis
would stimulate new ideas for the discovery of new phenomena and applications.
Acknowledgements The author would like to thank Prof. Nobuaki Nakashima and Prof. Tomoyuki
Yatsuhashi of Osaka City University, Japan, Dr. S. Abbas Hosseini of Citrogene, Calif., USA and
Prof. Olga Kosareva of Moscow State University for generously sharing their scientific knowledge
with the author. This work was supported by the Center for Optics, Photonics and Laser (COPL),
Laval University, Quebec City, Canada.