Chapter 3
Ultra-Short Pulse and Collisionless
Absorption
3.1 Ultra-Short Pulse in Non-relativistic Intensity
After the appearance of ultra-short pulse technology in the 1980s as described in
Chap. 1, the interaction of laser pulse of sub-picosecond duration with many solid
matters has been studied intensively. The physics of the ablation by ultrafast intense
laser, the removal of matter from solid surface or bulk, is of great fundamental and
practical interest. Many papers have been published regarding experimental results
and theoretical studies. The surface ablation of condensed matter under the irradiation of sub-picosecond laser pulses has a number of peculiar properties which
distinguish this process from the ablation induced by nanosecond and longer laser
pulses. In the absorption analysis, the penetration of laser field into solid density due
to skin effect should be considered, and consequently the properties of conductivity
in metal, insulator, and semiconductor become key physics to study laser absorption
and subsequent ablation phenomena.
Ultra-short laser interaction with solids opens interesting opportunities for the
study of optical and thermodynamic properties of matter with electron temperature
higher than the solid matter, namely, the state called warm dense matter (WDM).
The diagram showing the important phenomena in the considered intensity range is
given in Fig. 3.1 where pathways of the material from excitation, melting, and phase
transition to ablation are shown around the relevant timescale and intensity ranges
[1]. The intuitive image of Fig. 3.1 covers from about 10
10 W cm
À2 to above
10
14 W cm
À2 . At these intensities, a variety of phase transitions are observed near
solid surface. Excitation of the solid by electron heating takes place due to the laser
heating in pulse duration shown by red in the time scale in Fig. 3.1. Depending on
excitation strength, melting occurs roughly on a picosecond timescale. In semiconductors and insulators irradiated with high laser intensities, the loss of crystalline
order is possible within less than 1 picosecond. Laser-solid interaction in such
© Springer Nature Switzerland AG 2020
H. Takabe, The Physics of Laser Plasmas and Applications - Volume 1, Springer
Series in Plasma Science and Technology,
https://doi.org/10.1007/978-3-030-49613-5_3
81
Ultra-Short Pulse and Collisionless
Absorption
3.1 Ultra-Short Pulse in Non-relativistic Intensity
After the appearance of ultra-short pulse technology in the 1980s as described in
Chap. 1, the interaction of laser pulse of sub-picosecond duration with many solid
matters has been studied intensively. The physics of the ablation by ultrafast intense
laser, the removal of matter from solid surface or bulk, is of great fundamental and
practical interest. Many papers have been published regarding experimental results
and theoretical studies. The surface ablation of condensed matter under the irradiation of sub-picosecond laser pulses has a number of peculiar properties which
distinguish this process from the ablation induced by nanosecond and longer laser
pulses. In the absorption analysis, the penetration of laser field into solid density due
to skin effect should be considered, and consequently the properties of conductivity
in metal, insulator, and semiconductor become key physics to study laser absorption
and subsequent ablation phenomena.
Ultra-short laser interaction with solids opens interesting opportunities for the
study of optical and thermodynamic properties of matter with electron temperature
higher than the solid matter, namely, the state called warm dense matter (WDM).
The diagram showing the important phenomena in the considered intensity range is
given in Fig. 3.1 where pathways of the material from excitation, melting, and phase
transition to ablation are shown around the relevant timescale and intensity ranges
[1]. The intuitive image of Fig. 3.1 covers from about 10
10 W cm
À2 to above
10
14 W cm
À2 . At these intensities, a variety of phase transitions are observed near
solid surface. Excitation of the solid by electron heating takes place due to the laser
heating in pulse duration shown by red in the time scale in Fig. 3.1. Depending on
excitation strength, melting occurs roughly on a picosecond timescale. In semiconductors and insulators irradiated with high laser intensities, the loss of crystalline
order is possible within less than 1 picosecond. Laser-solid interaction in such
© Springer Nature Switzerland AG 2020
H. Takabe, The Physics of Laser Plasmas and Applications - Volume 1, Springer
Series in Plasma Science and Technology,
https://doi.org/10.1007/978-3-030-49613-5_3
81