H. Avetissian – Relativistic Nonlinear Electrodynamics (2nd edition, 2016)

Автор: H. Avetissian
Название книги: Relativistic Nonlinear Electrodynamics (2nd edition)
Формат: PDF
Жанр: Физика
Страницы: 514
Качество: Изначально компьютерное, E-book

This revised edition of the author’s classic 2006 text offers a comprehensively updated review of the field of relativistic nonlinear electrodynamics. It explores the interaction of strong and super-strong electromagnetic/laser radiation with the electromagnetic quantum vacuum and diverse types of matter – including free charged particles and antiparticles, acceleration beams, plasma and plasmous media. The appearance of laser sources of relativistic and ultra-relativistic intensities over the last decade has stimulated investigation of a large class of processes under such super-strong radiation fields.

Revisions for this second edition reflect these developments and the book includes new chapters on Bremsstrahlung and nonlinear absorption of superintense radiation in plasmas, the nonlinear interaction of relativistic atoms with intense laser radiation, nonlinear interaction of strong laser radiation with Graphene, and relativistic nonlinear phenomena in solid-plasma targets under supershort laser pulses of ultrarelativistic intensities.

The only book devoted to the subject of relativistic nonlinear electrodynamics, this second edition will be a valuable resource for graduate students and researchers involved in any aspect of the field, including those working with intense x-ray – gamma-ray lasers, the new generation of small size laser-plasma accelerators of superhigh energies and high-brightness particle beams.

About a decade has passed since the writing of the book “Relativistic Nonlinear
Electrodynamics.” On the one hand, this is a short time period for substantial
advancements in a science like physics, on the other hand, the unprecedented
development of laser technologies during the last decade, specifically, the implementation
of ultrashort laser sources and subcycle pulses of relativistic intensities
exceeding the intra-atomic fields, have become real. This radically changes the
practical situation in high energy radiation-matter physics, related in particular to
the creation of superpower X-ray–γ-ray coherent sources, new type—laser–plasma
accelerators of enormous energies, laser-induced nuclear fusion, production of
antimatter from vacuum, etc. It is noteworthy the realization of relativistic
solid-plasma-targets/nanolayers under ultrashort superintense laser pulses, making
available the implementation of high brightness electron and ion beams of solid
densities and high energies. In turn, the emergence of such superstrong electromagnetic
fields has rapidly initiated extensive fundamental investigations in the
area of Relativistic Nonlinear Electrodynamics, revealing various new nonlinear
phenomena in the fields approaching to Schwinger one for vacuum Quantum
Electrodynamics (QED).
Concerning the degree of nonlinearity in strong radiation–matter interaction
processes, it has been revealed that exotic cases of condensed matter possessing
huge electromagnetic nonlinearity at which nonlinear effects occur at rather small
intensities of exciting field compare to ordinary free–free or bound–bound transitions.
The best example of such type of matter is graphene. Thus, nonlinear excitation
of the Dirac sea in graphene occurs at a billion time smaller intensities of
external radiation field than it is necessary for excitation of the electron–positron
vacuum and, in general, for revealing of nonlinear effects in ordinary materials.
Therefore, the present book was completed with the new material regarding the
unique nonlinear properties of graphene in strong laser fields.
Besides, in this book we added new material concerning the relativistic quantum
theory of scattering on the arbitrary potential field beyond the Born and ordinary
eikonal approximations. Thus, we developed a new—Generalized Eikonal Approximation (GEA)—in both elastic and inelastic scattering theory for spinor
and scalar particles scattering on the short-range and long-range potential fields of
arbitrary form, as well as in the presence of superstrong laser radiation of arbitrary
intensities. The latter—Stimulated Bremsstrahlung (SB)—apart from its important
role in laser-induced processes of Above-Threshold Ionization (ATI) of atoms and
High Harmonic Generation (HHG), is considered here as a basic process for
nonlinear absorption of superpower electromagnetic radiation in plasma.
New material has been included devoted to relativistic atoms in strong laser
fields considering multiphoton excitation of atoms with high charge numbers and
highly charged ions, taking into account the fine structure of relativistic atoms–ions
with accompanying coherent effects; nonlinear acceleration of atoms by powerful
laser pulses, as well as relativistic theory of ATI of atoms/highly charged ions and
HHG on these quantum systems by laser radiation of relativistic intensities.
So, while the present book is introduced as a second edition of the monograph
“Relativistic Nonlinear Electrodynamics” published in 2006, this book includes
new material with five new chapters (Chaps. 10–14), a new paragraph (5.7), and
some numerical treatment of considered processes for actual nonplanar laser pulses.
Now let us introduce briefly the content of this book to the reader.
With the appearance of lasers have come real possibilities for revealing
numerous nonlinear phenomena of diverse nature resulting from the interaction of
strong electromagnetic field either with matter or with free charged particles. First
attempts of investigators, especially experimentalists, were directed toward studying
the processes of interaction of laser radiation with matter, which led to the rapid
formation of a new field—Nonlinear Optics. The numerous published books on this
subject are evidence of that. The situation regarding the processes of interaction of
laser radiation with free charged particles (free–free transitions) is different.
Whereas the experimental results on atomic systems frequently had preceded the
theoretical ones, the experimental investigations on free electrons began gathering
power only recently. It is enough to mention that the first experiments on the
observation of multiphoton exchange between free electrons and laser radiation
started in 1975 (the Cherenkov and bremsstrahlung processes), whereas due to the
progress of Nonlinear Optics, the precision laser spectroscopy of superhigh resolution
on atomic systems had already been established. This situation is explained
by two objective factors. While the experiments on atoms require only laser devices
in common laboratories, the experiments on free electron beams require accelerators
of charged particles and laser laboratories, i.e., this field is a synthesis of
Accelerator and Laser Physics. The second major factor is the smallness of the
photon–electron interaction cross section in comparison with the photon–atom one;
revealing nonlinear phenomena on free electrons, this requires laser fields of relativistic
intensities (e.g., even the observation of the second harmonic in nonlinear
Compton scattering). Such superpower femtosecond laser sources have appeared
only recently. Hence, the time for experimental development of this branch of
Nonlinear Electrodynamics—covering interaction of charged particles with laser
fields of relativistic intensities—has come. In presenting the current state of the art
in this field and gathering up-to-date theoretical material in this book we have pursued the goal of stimulating the laser-driven experiments on relativistic electron
beams and comprehensive theoretical investigations of nonlinear electromagnetic
processes in currently available coherent radiation fields of relativistic intensities.
Increasing interest in free–free transitions is connected with the realization of the
two most important problems of modern physics, namely the creation of shortwave
coherent radiation sources—X-ray and γ-ray lasers—and small size laser-plasma
accelerators of superhigh energies. It is noteworthy that a great deal of the work on
free–free transitions are related to the Free Electron Laser (FEL) problem, i.e., to the
discussion of concrete schemes of relativistic electron beam radiation amplification
in coherent systems, such as the undulator, and to the search for their optimization.
A small number of monographs and a large number of reviews are devoted to this
problem in the linear regime of amplification. However, particularly for the
implementation of X-ray lasers, the most promising candidate of which at the
present time is still FEL devices, the need for nonlinear mechanisms of generation
of coherent radiation due to induced interaction of electron beam with strong laser
fields may be crucial, compared with the current undulator-based FELs in the linear
regime of amplification. On the other hand, the present FELs operate in the classical
regime where the electron wave packet size over the interaction length is less than a
wavelength of radiation. This means that the photon frequency shift due to the
electron quantum recoil must be less than the gain bandwidth. This condition is
satisfied for current FELs typically operating at optical or smaller frequencies. For
the X-ray photons in expected X-ray FELs, the downshifts in frequency as well as
other quantum effects become important. Thus, because of the absence of mirrors
(resonator) or other drivers operable at these wavelengths, FEL systems currently
under consideration for X-ray sources, operate in the so-called Self-Amplified
Spontaneous Emission (SASE) regime in which the initial shot noise on an electron
beam is amplified over the course of propagation through a long wiggler. In turn,
large pulse-to-pulse variations arise in both output power and radiation spectrum,
and quantum effects on the start-up from noise will be important.
Finally, the absence of resonators at X-ray wavelengths requires a single-pass
high-gain FEL, which in the linear regime will have an extremely large size. Hence,
to reach the required gain on distances much smaller than the coherent length in the
linear regime of amplification, which would reduce greatly the present size of
projected X-ray lasers (several kilometers), nonlinear quantum mechanisms of
generation due to laser-induced coherent interaction become of prime importance.
On the other hand, the inverse problem of laser-induced nonlinear FEL schemes is
the problem of creation of novel accelerators of charged particles of superhigh
energies—laser-plasma accelerators. Therefore, the nonlinear interaction of charged
particles with strong laser fields will be considered in general aspects from the point
of view of both nonlinear quantum FEL schemes and classical laser accelerator
problems. At the same time, we will not overload the material of this book, the
subject of which is nonlinear electromagnetic processes, with the consideration of
linear schemes of FELs taking also into account the existence of well-known books
by T. Marshall (1987), C. Brau (1990), H. Freund and T. Antonsen (1996), and E. Saldin, E. Schneidmiller, and M. Yurkov (1999) devoted especially to this
problem.
Besides the mentioned problems there is another important problem concerning
the quantum electrodynamic vacuum in superstrong laser fields. With the appearance
of superpower lasers of relativistic intensities in recent years, for which the
energy of an electron acquired at a wavelength of laser radiation exceeds the
electron rest energy, multiphoton excitation of the Dirac vacuum via nonlinear
channels becomes real and, consequently, electron–positron pair production
becomes available. It is a strongly nonlinear process in superintense laser fields,
which occurs inevitably in all processes where the conservation laws for the pair
production are permitted. Thus, while considering such nonlinear processes we will
give special consideration to the multiphoton electron–positron pair production
from superintense laser fields.
Among the considered processes and, in general, stimulated processes with the
charged particles, coherent processes like Cherenkov, Compton, and undulator
essentially differ due to a peculiarity that fundamentally changes the common
picture of electromagnetic processes in dielectric media, and in vacuum—the
presence of a second wave or an undulator. Because of the coherent character of the
corresponding spontaneous radiation process (the existence of certain coherence
condition for radiation) in the presence of an external electromagnetic wave a
critical value of the wave field exists above which a plane wave becomes a potential
barrier or well for a particle and specific threshold nonlinear phenomena arise. The
latter opens new possibilities for laser acceleration and FEL, since in these regimes
the induced process proceeds only in one direction: the inverse concurrent process
of radiation in acceleration regime, and absorption process for the FEL regime are
absent. Therefore, we expect that this book will help to direct the attention of
experimentalists to nonlinear phenomena of “reflection” and capture of charged
particles by a plane electromagnetic wave in Cherenkov, Compton, and undulator
processes, which have been left in the shadows for more than four decades. This
especially relates to the experiments on the induced Cherenkov process made at
SLAC by R. Pantell and collaborators since 1975, where the laser intensities were
left below the critical value for the induced nonlinear Cherenkov resonance. It was
necessary to increase the laser intensity slightly to reveal the existence of critical
intensity and electron shock acceleration due to the “reflection” phenomenon,
proving thereby the peculiarity of the induced Cherenkov process with its nonlinear
threshold nature.
It is worth emphasizing another threshold phenomenon of nonlinear cyclotron
resonance in an arbitrary dispersive medium—dielectric or plasma. That is so-called
electron hysteresis, which can serve as an actual mechanism for laser acceleration of
charged particle beams in plasma media where the use of superpower laser fields is
not restricted and significant acceleration may be reached.
As is known, the spontaneous radiation of relativistic electrons and positrons
channeled in a crystal is of great interest due to two major factors: the radiation is in
the X-ray and γ-ray domains, and its spectral intensity noticeably exceeds that of
other radiation sources in the short-wave range. Thus, induced channeling radiation in the presence of an external wave field becomes important as a potential source
for short-wave coherent radiation. On the other hand, due to the induced channeling
effect the inverse process—absorption of the wave photons by the particles—will
also take place leading the particles’ acceleration and other coherent classical and
quantum effects. As a periodic system with high coherency and having the same
character as a particle motion, the crystal channel may be compared with an
undulator—it is a “micro-undulator” with the space period much smaller than the
undulator one. We thus give consideration to the induced channeling process in
general aspects of coherent interaction of relativistic electrons and positrons with a
plane electromagnetic wave in a crystal.
Concerning the consideration of induced noncoherent processes, please note that
in this book we included only induced processes related to plasma media where
they provide actual energy conversion between the particles and transverse electromagnetic
wave and, due to nonlinear interaction, one can reach the effective
outgrowth for the aforementioned problems having as origin the real energy
exchange between the particles and laser beams. From this point of view SB, being
an inevitable induced process in laser-plasma system, is the actual mechanism for
absorption of plane electromagnetic radiation by plasma electrons at the scattering
on the ions. So, it has a significant role in the problems of plasma heating,
laser-plasma accelerator, as well as HHG in atomic/ionic systems through the
continuum states in strong laser fields as an alternative means for implementation of
coherent VUV–X-ray sources, which has witnessed significant experimental
advancement in recent years. However, the consideration of these processes is
beyond the scope of this book. We will consider here the relativistic SB in strong
and superstrong radiation fields in regard to general aspects with nonlinear effects
(nonrelativistic SB in various approximations has been considered in many books).
We will also consider the case of coherent SB process in crystals, which is of
relativistic nature by itself, having in mind consideration of a high-gain X-ray FEL
scheme based on coherent bremsstrahlung in the crystals.
A separate chapter has been devoted to the so-called induced nonstationary
transition effect based on the spontaneous transition radiation effect in a medium at
the abrupt variation of its properties, to describe the nonlinear particle–strong wave
interaction processes in plasma. Such a situation takes place inevitably at the
interaction of superintense ultrashort laser pulses with any medium, which instantly
turns into plasma. It is thus of certain interest to study the nonlinear processes at the
formation of laser plasma. This process may also be of great interest in astrophysics
related to conversion of electromagnetic radiation frequencies in nonstationary
plasma, in particular formation of hard γ-quanta of relativistic energies, electron–
positron pair production, and other nonlinear processes at the abrupt variation of the
matter properties in high energy cosmic objects.
In order not to overload the reader, the references on a given subject are presented
separately in each chapter. My apologies go to all authors whose works are
not covered in this book. We included only the ones that are most directly related to
this book Indeed, the problems discussed in this book do not exhaust the frame of induced
nonlinear phenomena at the interaction of charged particles or condensed matter
with strong and superstrong electromagnetic radiation. By considering a certain
class of induced processes, we have aimed at revealing the principal features of
nonlinear behavior of a particle/matter–strong wave interaction in laser-induced
processes, which are of primary importance for the implementation of contemporary
problems, the most significant of which are creation of powerful X-ray–γ-ray
lasers, laser-plasma accelerators, and production of high density antimatter from
superintense laser fields of ultra-relativistic intensities. And if the presentation of
relativistic nonlinear theory of interaction of charged particles, QED vacuum,
condensed matter, and specific quantized systems with strong and superstrong
electromagnetic fields are helpful to specialists in this field, then the publication of
this book will be justified.
In closing, I would like to thank Dr. G. Mkrtchian for assistance in preparation
of the manuscript, and Dr. Tom Spicer, Senior Physics Editor, Springer-Verlag
New York, for his efforts in the publishing of this book