14
S. L. Chin
and a partial cascade/avalanche ionization [7] would have taken place resulting in
a local plasma within the laser’s pulse duration; i.e. the plasma was created almost
instantaneously. The plasma would expand quickly and explode the wood material.
The explosion has generated a lot of wood dust particles flying out of the surface
[64]. This would mean that the flying wood particles would carry away most of the
energy in the plasma in the form of kinetic energy. Hence, not much heat would
be left on the surface; i.e. ‘cold’ cutting. The ‘cold’ surface would not interact with
ambient oxygen; hence, no oxidation or charring of the wood was observed [62–64].
1.10 Filament Induced Discharge Guiding, Condensation,
Precipitation and Air Motion (Wind)
During the ‘instantaneous’ excitation events (fs time scale) in a filament in air (see
Sect. 1.2), energy is fed from the laser pulse into the interaction processes and get
‘stored’ temporarily in the filament zone. Soon after this, a series of relaxations take
place in the sense that the excitation energy will be released. Radiative relaxation
of molecules will emit radiations out of the system. Collisions in events such as
plasma recombination, rotational relaxation, chemical reaction, and so on take place
at different times. The fast relaxation in the fs, ps and ns time scale has led to
the phenomena and applications such as fluorescence, harmonics generation, 4WM,
molecular alignment, etc. Some phenomena such as molecular alignment through
the excitation of rotational wave packets [9] and the generation of THz wave due to
plasma oscillation and 4WM [65] were not discussed.
Meanwhile, the recombination of the plasma and the relaxation of all the excited
molecules would result in a sudden non-uniform heating resulting in a very high
temperature (more than one thousand degrees Kelvin) in the filament’s axial zone
while near the filament’s surface, it was around ambient temperature [66]. This high
temperature gradient would give rise to a sudden expansion of the filament zone in the
microsecond time scale [66]. This would result in a shock wave propagating outward
from the filament. The shock wave would propagate and decay into an acoustic wave
in the microsecond to millisecond time scale. The filament zone would become a
thermally hot zone. The pressure in this hot zone would be lower than the ambient
pressure [66]. This low pressure zone had been shown to be physically responsible for
guiding discharge in air in relation to the dream of using filament to guide lightning
[67]. This is because the electrical conductivity of the low pressure zone is high.
It would thus become a discharge channel in a high voltage zone guiding corona
discharge [68–70]. An excellent recent review is given by J.-P. Wolf on using short
laser pulse for weather control [36].
The pressure in the low pressure hot zone would return to ambient pressure in
a few microseconds [71]. Its size would expand to a few times the original size
in about 500 µs [66]. This expanded hot zone would relax thermodynamically;
i.e. convection would follow. Convection means heat conduction together with gas
S. L. Chin
and a partial cascade/avalanche ionization [7] would have taken place resulting in
a local plasma within the laser’s pulse duration; i.e. the plasma was created almost
instantaneously. The plasma would expand quickly and explode the wood material.
The explosion has generated a lot of wood dust particles flying out of the surface
[64]. This would mean that the flying wood particles would carry away most of the
energy in the plasma in the form of kinetic energy. Hence, not much heat would
be left on the surface; i.e. ‘cold’ cutting. The ‘cold’ surface would not interact with
ambient oxygen; hence, no oxidation or charring of the wood was observed [62–64].
1.10 Filament Induced Discharge Guiding, Condensation,
Precipitation and Air Motion (Wind)
During the ‘instantaneous’ excitation events (fs time scale) in a filament in air (see
Sect. 1.2), energy is fed from the laser pulse into the interaction processes and get
‘stored’ temporarily in the filament zone. Soon after this, a series of relaxations take
place in the sense that the excitation energy will be released. Radiative relaxation
of molecules will emit radiations out of the system. Collisions in events such as
plasma recombination, rotational relaxation, chemical reaction, and so on take place
at different times. The fast relaxation in the fs, ps and ns time scale has led to
the phenomena and applications such as fluorescence, harmonics generation, 4WM,
molecular alignment, etc. Some phenomena such as molecular alignment through
the excitation of rotational wave packets [9] and the generation of THz wave due to
plasma oscillation and 4WM [65] were not discussed.
Meanwhile, the recombination of the plasma and the relaxation of all the excited
molecules would result in a sudden non-uniform heating resulting in a very high
temperature (more than one thousand degrees Kelvin) in the filament’s axial zone
while near the filament’s surface, it was around ambient temperature [66]. This high
temperature gradient would give rise to a sudden expansion of the filament zone in the
microsecond time scale [66]. This would result in a shock wave propagating outward
from the filament. The shock wave would propagate and decay into an acoustic wave
in the microsecond to millisecond time scale. The filament zone would become a
thermally hot zone. The pressure in this hot zone would be lower than the ambient
pressure [66]. This low pressure zone had been shown to be physically responsible for
guiding discharge in air in relation to the dream of using filament to guide lightning
[67]. This is because the electrical conductivity of the low pressure zone is high.
It would thus become a discharge channel in a high voltage zone guiding corona
discharge [68–70]. An excellent recent review is given by J.-P. Wolf on using short
laser pulse for weather control [36].
The pressure in the low pressure hot zone would return to ambient pressure in
a few microseconds [71]. Its size would expand to a few times the original size
in about 500 µs [66]. This expanded hot zone would relax thermodynamically;
i.e. convection would follow. Convection means heat conduction together with gas