S. V. Bulanov

Highly efficient relativistic-ion generation in the laser-piston regime

The electromagnetic radiation pressure becomes dominant in the interaction of the ultra-intense electromagnetic wave with a solid material, thus the wave energy can be transformed efficiently into the energy of ions representing the material and the high density ultra-short relativistic ion beam is generated. This regime can be seen even with present-day technology, when an exawatt laser will be built. As an application, we suggest the laser-driven heavy ion collider.

Demonstration of laser-frequency upshift by electron-density modulations in a plasma wakefield.

Since the advent of chirped pulse amplification1 the peak power of lasers has grown dramatically and opened the new branch of high field science, delivering the focused irradiance, electric fields of which drive electrons into the relativistic regime. In a plasma wake wave generated by such a laser, modulations of the electron density naturally and robustly take the shape of paraboloidal dense shells, separated by evacuated regions, moving almost at the speed of light. When we inject another counter-propagating laser pulse, it is partially reflected from the shells, acting as relativistic flying (semi-transparent) mirrors, producing an extremely time-compressed frequency-multiplied pulse which may be focused tightly to the diffraction limit. This is as if the counterstreaming laser pulse bounces off a relativistically swung tennis racket, turning the ball of the laser photons into another ball of coherent X-ray photons but with a form extremely relativistically compressed to attosecond and zeptosecond levels. Here we report the first demonstration of the frequency multiplication detected from the reflection of a weak laser pulse in the region of the wake wave generated by the driver pulse in helium plasma. This leads to the possibility of very strong pulse compression and extreme coherent light intensification. This Relativistic Tennis with photon beams is demonstrated leading to the possibility toward reaching enormous electromagnetic field intensification and finally approaching the Schwinger field, toward which the vacuum nonlinearly warps and eventually breaks, producing electron-positron pairs.

Interaction of Electromagnetic Waves with Plasma in the Radiation-Dominated Regime

A study is made of the main regimes of interaction of relativistically strong electromagnetic waves with plasma under conditions in which the radiation from particles plays a dominant role. The discussion is focused on such issues as the generation of short electromagnetic pulses in the interaction of laser light with clusters and highly efficient ion acceleration in a thin plasma slab under the action of the ponderomotive pressure of the wave. An approach is developed for generating superintense electromagnetic pulses by means of up-to-date laser devices.

Relativistic Interaction of Laser Pulses with Plasmas

The lecture presents an introduction to the theory of the interaction of relativistically strong, ultra-short laser pulses with plasmas. The laser interaction with underdense plasmas and its application to the problem of charged particle acceleration, of laser frequency upshifting, of relativistic self focusing, and of the generation of a quasistatic magnetic field is discussed. The properties of nonlinear coherent structures such as relativistic solitons and vortices and the production of high harmonics are discussed. Over the last few years we have witnessed extremely fast progress in laser technology. The laser intensity / has increased by two orders of magnitude each couple of years and has now reached the value of > WW/cm in the radiation emitted by petawatt lasers [1]. The electric field of these pulses is of the order of ^ WV/cm and significantly exceeds the inter-atomic field. Such a large electric field fully ionizes the matter with which it interacts and can force the electrons in the plasma to oscillate with relativistic energy. In these regimes the specific features of the nonlinear dynamics of collisionless plasmas and their interaction with the electromagnetic waves become very important and attractive for theoretical studies [2], On the other hand, the increasing interest in the problems of the interaction of relativistically strong laser radiation with plasmas finds various broad applications in the development of new concepts of compact laser-based accelerators of charged particles [3]? powerful ultra-fast X-ray sources and controlled nuclear fusion in the framework of the Fast Ignition Concept [4]. They are also connected with the problems of the propagation of relativistically strong electromagnetic waves in space plasmas and with the mechanisms of acceleration of cosmic rays [5] and with the problems of high energy physics [6]. Particle acceleration by an ultra-intense laser pulse interacting with plasma also has practical applications to laser induced nuclear reactions [7]? ion injection into conventional accelerators, and hadrontherapy in medicine [8], When a petawatt laser pulse interacts with matter, conditions can be produced that were imagined to occur only in astrophysical objects. This opens the way for experimental plasma astrophysics to study the properties of matter under these extreme conditions [9]. In the relativistic range of amplitudes of the laser radiation, when its intensity is above 1.3 x lOW/cm, the ratio the electron quiver velocity in the laser field VE = eE/meu;to the speed of light ( VE / c) becomes close to one in the CP634, Science of Superstrong Field Inter actions, edited by K. Nakajima and M. Deguchi

Schwinger Limit Attainability with Extreme Power Lasers

High intensity colliding laser pulses can create abundant electron-positron pair plasma [A. R. Bell and J. G. Kirk, Phys. Rev. Lett. 101, 200403 (2008)], which can scatter the incoming electromagnetic waves. This process can prevent one from reaching the critical field of quantum electrodynamics at which vacuum breakdown and polarization occur. Considering the pairs are seeded by the Schwinger mechanism, it is shown that the effects of radiation friction and the electron-positron avalanche development in vacuum depend on the electromagnetic wave polarization. For circularly polarized colliding pulses, these effects dominate not only the particle motion but also the evolution of the pulses. For linearly polarized pulses, these effects are not as strong. There is an apparent analogy of these cases with circular and linear electron accelerators to the corresponding constraining and reduced roles of synchrotron radiation losses.

Relativistic laser-matter interaction and relativistic laboratory astrophysics

AbstractThe paper is devoted to the prospects of using the laser radiation interaction with plasmas in the laboratory relativistic astrophysics context. We discuss the dimensionless parameters characterizing the processes in the laser and astrophysical plasmas and emphisize a similarity between the laser and astrophysical plasmas in the ultrarelativistic energy limit. In particular, we address basic mechanisms of the charged particle acceleration, the collisionless shock wave and magnetic reconnection and vortex dynamics properties relevant to the problem of ultrarelativistic particle acceleration.

Controlled electron injection into the wake wave using plasma density inhomogeneity

The electron injection, for the laser wake field accelerator, controlled through the plasma density inhomogeneity is studied on a basis of analytical estimates and two- and three-dimensional particle-in-cell simulations. The injection scheme requires a concordance of the density scale length and laser intensity. It is shown that at a sloping inhomogeneity of plasma the wave breaking produces stronger singularity of the electron density than at a density discontinuity, but develops slower. With the help of simulations for a moderate laser intensity, we demonstrate the optimal plasma density gradient, where the electron injection into the wake wave forms the electron beam with low divergence, small energy spread and high energy.

Nonlinear Thomson scattering in the strong radiation damping regime

The motion of an electron can be strongly influenced by the radiation emitted by the electron during the interaction with petawatt class lasers focused to small spot sizes. In order to study this problem we have numerically integrated the equation of motion of a single electron interacting with an intense electromagnetic wave and calculated the backscattered spectra. Large differences are found between the case where damping is included and not included. In particular, the first harmonic of the backscattered radiation is downshifted and the overall amplitude of the spectra is smaller than in the case with no damping. An analytical expression for the downshift is obtained and found to agree fairly well with the numerical calculations.

Frequency multiplication of light back-reflected from a relativistic wake wave

A method of coherent high-frequency electromagnetic radiation generation, proposed by Bulanov, Esirkepov, and Tajima [Phys. Rev. Lett. 91, 085001 (2003)], is experimentally demonstrated. This method is based on the radiation frequency multiplication during reflection at a mirror flying with relativistic velocity. The relativistic mirror is formed by the electron density modulations in a strongly nonlinear wake wave, excited in an underdense plasma in the wake behind an ultrashort laser pulse. In our experiments, the reflection of a countercrossing laser pulse from the wake wave is observed. The detected frequency multiplication factor is in the range from 55 to 114, corresponding to a reflected radiation wavelength from 7 to 15nm. This may open a way towards tunable high-intensity sources of ultrashort coherent electromagnetic pulses in the extreme ultraviolet and x-ray spectral regions. Parameters of the reflecting wake wave can be determined using the reflected radiation as a probe.

Soft x-ray source for nanostructure imaging using femtosecond-laser-irradiated clusters

The intense soft x-ray light source using the supersonic expansion of the mixed gas of He and CO2, when irradiated by a femtosecond Ti:sapphire laser pulse, is observed to enhance the radiation of soft x-rays from the CO2 clusters. Using this soft x-ray emissions, nanostructure images of 100-nm-thick Mo foils in a wide field of view (mm2 scale) with high spatial resolution (800nm) are obtained with high dynamic range LiF crystal detectors. The local inhomogeneities of soft x-ray absorption by the nanometer-thick foils is measured with an accuracy of less than ±3%.