This PDF file contains the front matter associated with SPIE Proceedings Volume 8075, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Recently electromagnetic cascades that can develop in strong laser field have attracted much attention. In this paper we analyze equations for the distribution functions of cascade particles (electrons, positrons and hard photons). The approximate scaling laws for these equations are found. The dependence of cascade characteristics on laser parameters is discussed. The comparison of the obtained results with results of numerical simulations is given.

The radiative and quantum effects in laser plasmas are discussed. The self-consistent numerical model based on particle-in-cell and Monte-Carlo methods are developed. First we analyze the spectra of Compton backscattered photons and betatron radiation in the classical and quantum regimes. Then we address an interaction between intense laser pulse and relativistic electron beam. Finally we discuss the electron-positron pair plasma production in extremely-intense laser field. It is shown that such plasma can be an efficient source of energetic gammaquanta.

The possibility of employing strong optical and x-ray laser fields to investigate processes in the realm of classical and quantum electrodynamics as well as nuclear quantum optics is considered. In the first part we show on the theoretical side how modern strong optical laser fields can be employed to test the fundamental classical equations of motion of the electron which include radiation reaction, i.e., the effect of the radiation emitted by the electron on its own motion. Then, we clarify the quantum origin of radiation reaction and discuss a new radiation regime where both quantum and radiation effects dominate the electron dynamics. The second part is dedicated to the possibility of controlling nuclear transitions with coherent x-ray light. In particular, we investigate the resonant driving of nuclear transitions by super-intense x-ray laser fields considering parameters of upcoming high-frequency coherent light sources. As relevant application, the controlled pumping or release of energy stored in long-lived nuclear states is discussed.

The upcoming γ facilities MEGa-Ray (Livermore) and ELI-NP (Bucharest) will have a 10⁵ times higher γ flux F₀ = 10¹³/s and a ~30 times smaller band width (ΔE_γ/E_γ = BW ≈ 10^-3) than the presently best γ beam facility. They will allow to extract a small γ beam of about 30 - 100 μm radius 1 m behind the γ production point, containing the dominant γ energy band width. One can collimate the γ beam down to Θ_BW = √ BW/ γe , where γe = E_e/ m_ec² is a measure of the energy E_e of the electron beam, from which the γ beam is produced by Compton back-scattering. Due to the γ energy - angle correlation, the angular collimation results at the same time in a reduction of the γ beam band width without loss of "good" γ quanta, however, the primary γ flux F₀is reduced to about F_coll ≈ F₀ · 1.5 · ΔE_γ/E_γ. For γ rays in the (0.1-100) MeV range, the negative real part δ of the index of refraction n = 1- δ + iβ from coherent Rayleigh scattering (virtual photo effect) dominates over the positive δ contributions from coherent virtual Compton scattering and coherent virtual pair creation scattering (Delbrück scattering). The very small absolute value |δ| ≈ 10^-6 - 10^-9 of the index of refraction of matter for hard X-rays and γ-rays and its negative sign—in contrast to usual optics—results in a very different γ-ray optics, e.g. focusing lenses become concave and we use stacks of N optimized lenses. It requires very small radii of curvature of the γ lenses and thus very small γ beam radii. This leads to a technical new solution, where the primary γ beam is subdivided into M γ beamlets, which do not interfere with each other, but contribute with their independent intensities. We send the γ beamlets into a two-dimensional array of closely packed cylindrical parabolic refractive lenses, where N ≈ 10³ lenses with very small radius of curvature are stacked behind each other, leading to contracted beam spots in one dimension. With a second 1D lens system turned by 90⁰, we can obtain small spots for each of the beamlets. While focusing the beamlets to a much smaller spot size, we can bend them effectively with micro wedges to e.g. parallel beamlets. We can monochromatize these γ beamlets within the rocking curve of a common Laue crystal, using an additional angle selection by a collimator to reach a strongly reduced band width of 10^-4 - 10^-6. We propose the use of a further lens/wedge arrays or Bragg reflection to superimpose the beamlets to a very small total γ beam spot. Many experiments gain much from the high beam resolution and the smaller focal spot. This new γ optics requires high resolution diagnostics, where we want to optimize the focusing, using very thin target wires of a specific nuclear resonance fluorescence (NRF) isotope to monitor the focusing for the resonance energy. With such beams we can explore new nuclear physics of higher excited states with larger level densities. New phenomena, like the transition from chaotic to regular nuclear motion, weakly-bound halo states or states decaying by tunneling can be studied. The higher level density also allows to probe parity violating nuclear forces more sensitively. This γ optics improves many applications, like a more brilliant positron source, a more brilliant neutron source, higher specific activity of medical radioisotopes or NRF micro-imaging.

Radiation Friction or Reaction (RR) effects are important for highly relativistic electrons in superintense electromagnetic fields and are thus expected to play a crucial role in next-term experiments. It is therefore important to include RR in particle-in-cell (PIC) simulations of laser-plasma by an appropriate modeling, keeping the essential RR effects into account while retaining at the same time the capability to perform large-scale simulations. We describe a suitable approach, based on the Landau-Lifshitz equation, which allows the insertion of RR in PIC codes in a modular way and with a very reduced computational cost. Properties of the kinetic equation with RR which is effectively solved by the PIC method are also discussed. We then present the results of multi-dimensional PIC simulations, mainly on radiation pressure acceleration of thin foil targets, addressing the importance of RR effects and showing the strong role played by the laser pulse polarization.

The notion of a cold Born-Infeld plasma is reviewed and the dispersion relation for a right-handed circularly polarized electromagnetic plane wave is given. The maximum amplitude (wave-breaking limit) of large amplitude longitudinal plane waves is summarized.

Raman scattering is a three wave interaction in which a high frequency electromagnetic wave gives up energy to an electromagnetic wave at lower frequency and a Langmuir wave. This process has been suggested as a way of amplifying a short laser pulse by having it interact with a counter-propagating long pulse. I shall describe the essential theory behind this, discuss some of the e¤ects which may act to limit its e¤ectiveness and give a brief account of current progress.

Raman backscattering (RBS) in plasma has been proposed as a way of amplifying and compressing high intensity laser pulses for more than a decade. Not like the chirped pulse ampliffication (CPA) laser system, in which the laser intensity is limited by the damage threshold of conventional media, plasma is capable of tolerating ultrahigh laser intensities, together with RBS which is enable to transfer laser energy efficiently from a higher frequency pulse to a lower one, this scheme opens a scenario of the next generation of laser amplifiers. Experimental investigation has been carried out with a long (250 ps) pump pulse and a counter-propagating short (70 fs) probe pulse interacting in an under-dense preformed capillary plasma channel. Energy transfer from the pump pulse to the probe was observed. The guiding property was studied and the energy gain dependence of pump and probe energy were recorded.

The influence of wavebreaking on Raman amplification is investigated. A phenomenological modification is added to a set of slowly varying envelope equations, and found to give good agreement to particle-in-cell simulations for cold plasma in the wavebreaking regime. For warm plasma, good agreement is not found using the warm wavebreaking limit. However, the PIC simulations show that the decreased wavebreaking limit does have a significant impact on amplification. The limitations of our model are discussed, and possible future work outlined.

Improved performance of Free Electron Laser (FEL) light sources in terms of timing stability, pulse shape and spectral properties of the amplified FEL pulses is of interest in many fields of science. A promising scheme is direct seeding with High-Harmonic Generation (HHG) in a noble gas target. A Free-Electron-Laser seeded by an external XUV-source is planned for FLASH II at DESY in Hamburg. The requirements for the XUV/soft X-ray source can be summarized as follows: A repetition rate of at least 100 kHz in a 10 Hz burst is needed at variable wavelengths from 10 to 40 nm and pulse energies of several nJ within single harmonics. This application requires a laser amplifier system with exceptional parameters, mJ-level pulse energy, sub-10 fs pulse duration at 100 kHz (1 MHz) burst repetition rate. A new OPCPA system is under development in order to meet these requirements, and very promising results has been achieved. In parallel to this development, a new High- Harmonic Generation concept is necessary to sustain the high average power of the driving laser system and for the need of high conversion efficiencies. Highest conversion efficiency in High Harmonic Generation has been shown using gas-filled capillary targets, up to now. For our application, only a free-jet target is applicable for high harmonic generation at high repetition rate, to overcome damage threshold limitations of HHG target optics. A new multi-jet target is under development and first tests show a good performance of this nozzle configuration.

The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) programme is developing laserplasma accelerators for the production of ultra-short electron bunches with subsequent generation of high brilliance, short-wavelength radiation pulses. Ti:sapphire laser systems with peak power in the range 20-200 TW are coupled into mm- and cm-scale plasma channels in order to generate electron beams of energy 50-800 MeV. Ultra-short radiation pulses generated in these compact sources will be of tremendous benefit for time-resolved studies in a wide range of applications across many branches of science. Primary mechanisms of radiation production are (i) betatron radiation due to transverse oscillations of the highly relativistic electrons in the plasma wakefield, (ii) gamma ray bremsstrahlung radiation produced from the electron beams impacting on metal targets and (iii) undulator radiation arising from transport of the electron beam through a planar undulator. In the latter, free-electron laser action will be observed if the electron beam quality is sufficiently high leading to stimulated emission and a significant increase in the photon yield. All these varied source types are characterised by their high brilliance arising from the inherently short duration (~1-10 fs) of the driving electron bunch.

The ion-channel laser (ICL) has been proposed as an alternative to the free-electron laser (FEL), replacing the deflection of electrons in an undulator by betatron oscillations in an ion channel. The aim of this study is to describe the ICL in terms of the well-developed formalism for the FEL in the steady-state, while taking into account the dependence of the resonance between oscillations and emitted field on the oscillation amplitude. Numerical solutions for experimentally relevant parameters show similarities and differences between both devices. The ICL has potential to replace FELs based on magnetic undulators, leading to very compact coherent X-ray sources. Furthermore, coupling the ICL with a laser plasma wakefield accelerator would reduce the size of a coherent light sources by several orders of magnitude.

A compact gamma-ray source using laser-accelerated electron beam is being under development at KAERI for nuclear applications, such as, radiography, nuclear activation, photonuclear reaction, and so on. One of two different schemes, Bremsstrahlung radiation and Compton backscattering, may be selected depending on the required specification of photons and/or the energy of electron beams. Compton backscattered gamma-ray source is tunable and quasimonochromatic and requires electron beams with its energy of higher than 100 MeV to produced MeV photons. Bremsstrahlung radiation can generate high energy photons with 20 - 30 MeV electron beams, but its spectrum is continuous. As we know, laser accelerators are good for compact size due to localized shielding at the expense of low average flux, while linear RF accelerators are good for high average flux. We present the design issues for a compact gamma-ray source at KAERI, via either Bremsstrahlung radiation or Compton backscattering, using laser accelerated electron beams for the potential nuclear applications.