Springer Series in 120 OPTICAL SCIENCES founded by H.K.V.Lotsch Editor-in-Chief: W.T.Rhodes,Atlanta Editorial Board: A.Adibi,Atlanta T.Asakura,Sapporo T.W.Hänsch,Garching T.Kamiya,Tokyo F.Krausz,Garching B.Monemar,Linköping H.Venghaus,Berlin H.Weber,Berlin H.Weinfurter,München Springer Series in OPTICAL SCIENCES The Springer Series in Optical Sciences,under the leadership of Editor-in-Chief William T.Rhodes,Georgia Institute of Technology,USA,provides an expanding selection of research monographs in all major areas of optics:lasers and quantum optics,ultrafast phenomena,optical spectroscopy techniques,optoelectronics,quan- tum information,information optics,applied laser technology,industrial applications,and other topics of con- temporary interest. With this broad coverage oftopics,the series is ofuse to all research scientists and engineers who need up-to-date reference books. The editors encourage prospective authors to correspond with them in advance of submitting a manuscript. Submission ofmanuscripts should be made to the Editor-in-Chiefor one ofthe Editors.See also www.springer. com/series/624 Editor-in-Chief Ferenc Krausz Ludwig-Maximilians-Universität München William T.Rhodes Lehrstuhl für Experimentelle Physik Georgia Institute ofTechnology Am Coulombwall 1 School ofElectrical and Computer Engineering 85748 Garching,Germany Atlanta,GA 30332-0250,USA and E-mail:[email protected] Max-Planck-Institut für Quantenoptik Hans-Kopfermann-Straße I Editorial Board 85748 Garching,Germany E-mail:[email protected] Ali Adibi School ofElectrical and Computer Engineering Bo Monemar Van Leer Electrical Engineering Building Department ofPhysics Georgia Institute ofTechnology and Measurement Technology 777 Atlantic Drive NW Materials Science Division Atlanta,GA 30332-0250 Linköping University Email:[email protected] 58183 Linköping,Sweden E-mail:[email protected] Toshimitsu Asakura Hokkai-Gakuen University Herbert Venghaus Faculty ofEngineering Heinrich-Hertz-Institut 1-1,Minami-26,Nishi 11,Chuo-ku für Nachrichtentechnik Berlin GmbH Sapporo,Hokkaido 064-0926,Japan Einsteinufer 37 E-mail:[email protected] 10587 Berlin,Germany E-mail:[email protected] Theodor W.Hänsch Max-Planck-Institut für Quantenoptik Horst Weber Hans-Kopfermann-Strasse 1 Technische Universität Berlin 85748 Garching,Germany Optisches Institut E-mail:[email protected] Straβe des 17.Juni 135 10623 Berlin,Germany Takeshi Kamiya E-mail:[email protected] Ministry ofEducation,Culture,Sports Science and Technology Harald Weinfurter National Institution for Academic Degrees Ludwig-Maximilians-Universität München 3-29-1 Otsuka,Bunkyo-ku Sektion Physik Tokyo 112-0012,Japan Schellingstraβe 4/III E-mail:[email protected] 80799 München,Germany E-mail:[email protected] Hamlet Karo Avetissian Editor Relative Nonlinear Electrodynamics Interaction of Charged Particles with Strong and Super Strong Laser Fields With 23 Illustrations Prof.Dr.Hamlet Avetissian 1 Alex Manoukyan St. Department of Quantum Electronics Yerevan State University 375025 Yerevan,Armenia [email protected] Library ofCongress Control Number:2005935209 ISBN-10:0-387-30069-4 e-ISBN:0-387-30070-8 ISBN-13:978-0387-30069-6 Printed on acid-free paper. © 2006 Springer Science+Business Media,Inc. 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(EB) 9 8 7 6 5 4 3 2 1 springer.com Preface Withtheappearanceoflasershavecomerealpossibilitiesofrevealingnumer- ous nonlinear phenomena of diverse nature resulting from the interaction of strongelectromagneticfieldeitherwithmatterorwithfreechargedparticles. First attempts of investigators, especially experimentalists, were directed to- ward 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 monographs 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 experimen- tal results on atomic systems frequently had preceded the theoretical ones, theexperimentalinvestigationsonfreeelectronsbegangatheringpoweronly recently.Itisenoughtomentionthatthefirstexperimentsontheobservation 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. Whereas the experiments on atoms require only laser devices in common laboratories, the experiments on free electron beams require accelerators of charged particles and laser laborato- ries,i.e.,thisfieldisasynthesisofAcceleratorandLaserPhysics.Thesecond majorfactoristhesmallnessofthephoton–electroninteractioncrosssection incomparisonwiththephoton–atomone;revealingnonlinearphenomenaon freeelectronsthusrequireslaserfieldsofrelativisticintensities(e.g.,eventhe 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 Electro- dynamics — interaction of charged particles with laser fields of relativistic intensities—hascome.Inpresentingthecurrentstate-of-the-artinthisfield 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 electromag- netic processes in currently available coherent radiation fields of relativistic intensities. VI Preface Increasing interest in free–free transitions is connected with the realiza- tion of the two most important problems of modern physics, namely, the creation of shortwave coherent radiation sources — X-ray and γ-ray lasers — and high energy laser accelerators of charged particles. It is noteworthy that a great deal of the works on free–free transitions is 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 large number of reviews are devoted to this problem in the linear regime of amplification. However, particularly for the implemen- tation of X-ray lasers, the most promising candidate of which at the present time are FEL devices, the need for nonlinear mechanisms of generation of coherent radiation due to induced interaction of electron beam with strong laserfieldsmaybecrucial,comparedwiththecurrentundulator-basedFELs 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 typ- ically operating at optical or smaller frequencies. For the X-ray photons in expected X-ray FELs, the downshift in frequency as well as other quantum effectsbecomeimportant.Thus,becauseoftheabsenceofmirrors(resonator) or other drivers operable at these wavelengths, FEL systems currently un- der 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 re- quires 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 kilo- meters), nonlinear quantum mechanisms of generation due to laser induced coherent interaction becomes 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 accelerators. Therefore, the nonlinear interaction of charged particles withstronglaserfieldswillbeconsideredingeneralaspectsfromthepointof 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 consid- eration of linear schemes of FELs taking also into account the existence of well-known monographs by T. Marshall (1987), C. Brau (1990), H. Freund Preface VII and T. Antonsen (1996), and E. Saldin, E. Schneidmiller, and M. Yurkov (1999) devoted especially to this problem. Besides the mentioned problems there is a third important problem con- cerningthequantumelectrodynamicvacuuminsuperstronglaserfields.With the appearance of superpower lasers of relativistic intensities in recent years, forwhichtheenergyofanelectronacquiredatawavelengthoflaserradiation exceedstheelectronrestenergy,multiphotonexcitationoftheDiracvacuum vianonlinearchannelsbecomesrealand,consequently,electron–positronpair production becomes available. It is a strongly nonlinear process in superin- tense laser fields, which occurs inevitably in all processes where the conser- vation laws for the pair production are permitted. Thus, while considering suchnonlinearprocesseswewillgivespecialconsiderationtothemultiphoton electron–positron pair production from superintense laser fields. Amongtheconsideredprocessesand,ingeneral,stimulatedprocesseswith the charged particles the coherent processes like Cherenkov, Compton, and undulatoressentiallydifferduetoapeculiarity,whichfundamentallychanges 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 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 open new possibilities for laser acceleration and FEL, since in these regimes the induced process pro- ceeds 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 ex- perimentaliststononlinearphenomenaof“reflection”andcaptureofcharged particles by a plane electromagnetic wave in Cherenkov, Compton, and un- dulator processes, which have been left in the shadows for more than three decades.ThisespeciallyrelatestotheexperimentsontheinducedCherenkov process made at SLAC by R. Pantell and collaborators since 1975 where the laser intensities were left below the critical value for the induced nonlin- ear Cherenkov process. It was necessary to increase the laser intensity a bit to reveal the existence of critical intensity and electron 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 cy- clotron resonance in an arbitrary 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. VIII Preface 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 reducing the particles’ acceleration and other coherent classical and quan- tum effects. As a periodic system with high coherency and having the same character of a particle motion, the crystal channel may be compared with an undulator — it is a “micro-undulator” with the space period much smaller thantheundulatorone.Wethusgiveconsiderationtotheinducedchanneling processingeneralaspectsofcoherentinteractionofrelativisticelectronsand positrons with a plane electromagnetic wave in a crystal. Concerning the consideration of induced noncoherent processes, please note that in the present 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 the nonlinear in- teraction,onecanreachtheeffectiveoutgrowthfromthepointofviewofthe above-mentioned problems. In particular, Stimulated Bremsstrahlung (SB) is of interest in plasma in the presence of an electromagnetic radiation field, sincebremsstrahlungisoneofthemajorelectrodynamicprocessesinplasma, andistheactualmechanismforplasmaheating(ascatteringcenterperforms the role of a third body for actual absorption/radiation of the wave photons by a charged particle). Besides, the role of SB is significant in the process of particleaccelerationwithplasma/laserfields,aswellasintheprocessofhigh harmonics generation in atomic/ionic systems through the continuum states in strong laser fields as an alternative means for implementation of coherent 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 superstrongradiationfieldsinregardtogeneralaspectswithnonlineareffects (nonrelativistic SB in various approximations has been considered in many monographs). We will also consider the coherent SB in crystals, which is of relativisticnatureinitself,havinginmindconsiderationofahigh-gainX-ray FEL scheme based on coherent bremsstrahlung in a crystal. Aseparatechapterhasbeendevotedtotheso-calledinducednonstation- ary 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 femtosecond laser pulses with any medium, which instantly turns into plasma. It is thus of certain in- teresttostudythenonlinearprocessesattheformationoflaserplasma.This Preface IX process may also be of great interest in astrophysics related to conversion of electromagnetic radiation frequencies in nonstationary plasma, in particular formationofhardγ-quantaofrelativisticenergies,electron–positronpairpro- duction, and other nonlinear processes at the abrupt variation of the matter properties in 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. I included only the ones that are most directly related to this monograph. Indeed, the problems discussed in this monograph do not exhaust the frame of induced nonlinear phenomena at the interaction of charged parti- cles with strong electromagnetic radiation. By considering a certain class of inducedprocesses,wehaveaimedatrevealingprincipalfeaturesofnonlinear behavior of a particle–strong wave interaction in coherent and noncoherent induced processes, which are of primary importance for the implementation of contemporary problems of FEL, laser accelerators, and electron–positron pair production from superintense laser fields. And if the consideration of thesenonlinearprocessesbasedonrelativisticclassicalandquantumtheories andthepresentationofthemainresultsarehelpfultospecialistsinthisfield, then the publication of this monograph will be justified. Inclosing,IwouldliketothankDr.G.Mkrtchianforassistanceinprepa- rationofthemanuscript,Dr.H.Koelsch,physicseditorSpringer-VerlagNew York, and associate editor V. Lipscy, for their patience and encouragement in the writing and publishing of the book. Yerevan, Armenia Hamlet K. Avetissian June 2005