Chapter 1
Introduction
The laser invented in 1960 is now widely used for our life, in science researches, etc.
Its technology is still progressing, and its applications have spread over very wide
fields from industrial applications to fundamental research. The topics of this book
are focused on the physics of the plasma interacting with intense and ultra-intense
lasers. It is studied mainly on how laser energy is converted to the energy of matter in
the state of plasma. It is the topic of plasma heating by laser irradiation and/or laser
absorption due to the interaction with matters. The laser intensity discussed in the
book is extremely intense in the range of 10
13 W/cm
2
– 10
22 W/cm
2 . The pulse
durations of such intense lasers are from nanoseconds to sub-picoseconds. The total
energy of such laser pulses is about 1 ~ 10
6 joule. Such lasers are roughly called high
and ultra-high power lasers; the brief history of technology progress of which is
given, for example, in [1].
It is intuitively clear how it is intense by comparing the laser power to the energy
flux by the sun which is of the order of W/cm
2 . When such high-power lasers
irradiate on any matters, they are soon evaporated and ionized to become plasma
before the main part of the laser photons irradiates the matters. Most of the laser
photons interact with the laser-produced plasmas. This is the reason for the name of
physics as the laser-plasma interaction.
There are typically two types of such high-power lasers. One is high-power laser
delivering sub-kilo joule to a few Mega Joule of photon energy with the pulse
duration of nanosecond (ns: 10
À9 s) rage. Such a laser is focused on solid materials
with its focused intensity of 10
13–16 W/cm
2 . The focusing diameter is of ~100 μm to
several mm, roughly speaking. The intensity and pulse width are designed so that
most of the laser energy is converted to the thermal energy of plasma. The physics of
laser energy absorption is discussed in this text.
Since the plasma expands with the ion sound velocity, extremely high pressure is
generated in the plasma near the surface by the confinement of absorbed energy due
© 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_1
1
Introduction
The laser invented in 1960 is now widely used for our life, in science researches, etc.
Its technology is still progressing, and its applications have spread over very wide
fields from industrial applications to fundamental research. The topics of this book
are focused on the physics of the plasma interacting with intense and ultra-intense
lasers. It is studied mainly on how laser energy is converted to the energy of matter in
the state of plasma. It is the topic of plasma heating by laser irradiation and/or laser
absorption due to the interaction with matters. The laser intensity discussed in the
book is extremely intense in the range of 10
13 W/cm
2
– 10
22 W/cm
2 . The pulse
durations of such intense lasers are from nanoseconds to sub-picoseconds. The total
energy of such laser pulses is about 1 ~ 10
6 joule. Such lasers are roughly called high
and ultra-high power lasers; the brief history of technology progress of which is
given, for example, in [1].
It is intuitively clear how it is intense by comparing the laser power to the energy
flux by the sun which is of the order of W/cm
2 . When such high-power lasers
irradiate on any matters, they are soon evaporated and ionized to become plasma
before the main part of the laser photons irradiates the matters. Most of the laser
photons interact with the laser-produced plasmas. This is the reason for the name of
physics as the laser-plasma interaction.
There are typically two types of such high-power lasers. One is high-power laser
delivering sub-kilo joule to a few Mega Joule of photon energy with the pulse
duration of nanosecond (ns: 10
À9 s) rage. Such a laser is focused on solid materials
with its focused intensity of 10
13–16 W/cm
2 . The focusing diameter is of ~100 μm to
several mm, roughly speaking. The intensity and pulse width are designed so that
most of the laser energy is converted to the thermal energy of plasma. The physics of
laser energy absorption is discussed in this text.
Since the plasma expands with the ion sound velocity, extremely high pressure is
generated in the plasma near the surface by the confinement of absorbed energy due
© 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_1
1