This PDF file contains the front matter associated with SPIE Proceedings Volume 9509, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

The next few years will see next-generation high-power laser facilities (such as the Extreme Light Infrastructure) become operational, for which it is important to understand how interaction with intense laser pulses affects the bulk properties of a relativistic electron beam. At such high field intensities, we expect both radiation reaction and quantum effects to play a significant role in the beam dynamics. The resulting reduction in relative energy spread (beam cooling) at the expense of mean beam energy predicted by classical theories of radiation reaction depends only on the energy of the laser pulse. Quantum effects suppress this cooling, with the dynamics additionally sensitive to the distribution of energy within the pulse. Since chirps occur in both the production of high-intensity pulses (CPA) and the propagation of pulses in media, the effect of using chirps to modify the pulse shape has been investigated using a semi-classical extension to the Landau-Lifshitz theory. Results indicate that even large chirps introduce a significantly smaller change to final state predictions than going from a classical to quantum model for radiation reaction, the nature of which can be intuitively understood.

The 200TW ALLS laser system (30 fs, 5J) is used to accelerate electrons through laser wakefield and generate betatron emission in the 10keV range. Single shot phase contrast images of a series of nylon fibers with diameter ranging from 10μm to 400μm have been obtained in different geometries and are interpreted with a comprehensive model of x-ray propagation integrating the properties and geometries of the imaging beam line. A simple figure of merit, which can give indication on the interface sharpness of a phase object, is used to assess the quality of the imaging beam line.

We consider the Thomson and Compton scattering of high-energy electrons in an intense laser pulse. Our simulations show that energy losses due to radiation reaction cause the emitted radiation to be spread over a broader angular range than the case without these losses included. We explain this in terms of the effect of these energy losses on the particle dynamics. Finally, at ultra-high intensities, i.e. fields with a dimensionless parameter a₀~200, the energy of the emission spectrum is significantly reduced by radiation reaction and also the classical and QED results begin to differ. This is found to be due to the classical theory overestimating the energy loss of the electrons. Such findings are relevant to radiation source development involving the next generation of high-intensity laser facilities.

We report the results of experiments in which a single laser system is used to both accelerate electrons (0.5 GeV) and generate hard x-rays, by means of inverse Compton scattering. The x-rays are shown to have narrow bandwidth (50%) over a wide range of photon energies (50 keV -- 9 MeV). Results on the application of this novel source to x-ray radiography with high-resolution (< 5 micron) are also discussed.

In order to achieve the largest laser intensities, a plasma might be used as the amplification medium, thereby avoiding the material limits of conventional materials. The technique considered is resonant backward Raman amplification in plasma, wherein a short counter-propagating seed pulse, with frequency downshifted from a long pump pulse by the plasma frequency, absorbs the pump energy through a resonant decay interaction of the two counter-propagating light waves and a plasma wave. In the pump-depletion regime, the counter-propagating seed pulse assumes a self-contracting self-similar form, capturing the pump energy in a pulse of far shorter duration. This technique encounters limitations both at high laser seed output intensities and high pump laser intensities. At high seed output intensities, there are modulation instabilities that break up the output seed. At high pump intensities, the resonant interaction is interrupted by wavebreaking of the plasma wave. These limitations, while limiting, may not be as limiting as might be at first thought.

Envelope models offer the potential to dramatically reduce the computational overhead of particle-in-cell simulations of laser-plasma interactions. However, the associated approximations inevitably limit their applicability. We here derive the governing equations for an envelope model in order to gauge those limits. The approximations for electron response are shown to be exact in one dimension for the correct initial conditions. For multidimensional geometries, limits are placed on the canonical momentum perpendicular to the laser field, and on the amplitude of the laser field relative to the laser spot size. It is shown that those conditions are readily satisfied for the case of Raman amplification.

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 coherent, bright, short-wavelength radiation pulses. The new Scottish Centre for the Application of Plasma-based Accelerators (SCAPA) will develop a wide range of applications utilising such light sources. Electron bunches can be propagated through a magnetic undulator with the aim of generating fully coherent free-electron laser (FEL) radiation in the ultra-violet and Xrays spectral ranges. Demonstration experiments producing spontaneous undulator radiation have been conducted at visible and extreme ultra-violet wavelengths but it is an on-going challenge to generate and maintain electron bunches of sufficient quality in order to stimulate FEL behaviour. In the ALPHA-X beam line experiments, a Ti:sapphire femtosecond laser system with peak power 20 TW has been used to generate electron bunches of energy 80-150 MeV in a 2 mm gas jet laser-plasma wakefield accelerator and these bunches have been transported through a 100 period planar undulator. High peak brilliance, narrow band spontaneous radiation pulses in the vacuum ultra-violet wavelength range have been generated. Analysis is provided with respect to the magnetic quadrupole beam transport system and subsequent effect on beam emittance and duration. Requirements for coherent spontaneous emission and FEL operation are presented.

The ion-channel laser (ICL) has been proposed as an alternative to the free-electron laser (FEL), replacing the deflection of electrons by the periodic magnetic field of an undulator with the periodic betatron motion in an ion channel. Ion channels can be generated by passing dense energetic electron bunches or intense laser pulses through plasma. The ICL has potential to replace FELs based on magnetic undulators, leading to very compact coherent X-ray sources. In particular, coupling the ICL with a laser plasma wakefield accelerator would reduce the size of a coherent light source by several orders of magnitude. An important difference between FEL and ICL is the wavelength of transverse oscillations: In the former it is fixed by the undulator period, whereas in the latter it depends on the betatron amplitude, which therefore has to be treated as variable. Even so, the resulting equations for the ICL are formally similar to those for the FEL with space charge taken into account, so that the well-developed formalism for the FEL can be applied. The amplitude dependence leads to additional requirements compared to the FEL, e.g. a small spread of betatron amplitudes. We shall address these requirements and the resulting practical considerations for realizing an ICL, and give parameters for operation at UV fundamental wavelength, with harmonics extending into X-rays.

The linac-based Terahertz source at the SPARC_LAB test facility is able to generate highly intense Terahertz broadband pulses via coherent transition radiation (CTR) from high brightness electron beams. The THz pulse duration is typically down to 100 fs RMS and can be tuned through the electron bunch duration and shaping. The measured stored energy in a single THz pulse has reached 40 μJ, which corresponds to a peak electric field of 1.6 MV/cm at the THz focus. Here we present the main features, in particular spatial and spectral distributions and energy characterizations of the SPARC_LAB THz source, which is very competitive for investigations in Condensed Matter, as well as a valid tool for electron beam longitudinal diagnostics.

Over the last two decades, BNL’s ATF has pioneered the use of high-peak power CO₂ lasers for research in advanced accelerators and radiation sources. Our recent developments in ion acceleration, Compton scattering, and IFELs have further underscored the benefits from expanding the landscape of strong-field laser interactions deeper into the midinfrared (MIR) range of wavelengths. This extension validates our ongoing efforts in advancing CO₂ laser technology, which we report here. Our next-generation, multi-terawatt, femtosecond CO₂ laser will open new opportunities for studying ultra-relativistic laser interactions with plasma in the MIR spectral domain. We will address new regimes in the particle acceleration of ions and electrons, as well as the radiations sources, ranging from THz to gamma- rays, that are enabled by the emerging ultra-fast CO₂ lasers.

In this paper we consider X-Ray and EUV Transition radiation propagating in backward direction which is generated by the ultrarelativistic electron bunch crossing the target. The target consists of periodical set of thin wires with the rectangular cross-section. We obtain the analytical expressions for distribution of the energy of the transition radiation per solid angle and frequency. In high frequency region (X-Ray, EUV), where the wavelength of radiation is less than length of a beam, the main part of radiation is incoherent. In this case the radiation from electron bunches is described by the so called incoherent form-factor. We obtain and analyse the expression for incoherent form-factor. In this work we show that incoherent form-factor arises always when the size of a target is finite and that it depends on the ratio between the transversal size of the bunch and the production of wavelength and Lorentz-factor of the charged particles. The coherent effects of target and the electron bunch play an important role in increasing the intensity of radiation and also change the spatial distribution of radiation.

Absorption in the medium, i.e. an imaginary part of the dielectric permittivity, can lead to arising of Cherenkov radiation at high frequencies – X-Ray and XUV. In this paper X-Ray Diffraction radiation from a bunch of ultra-relativistic electrons moving near an absorbing target is investigated theoretically. In these conditions the Cherenkov radiation arises even when trajectories of the particles does not cross the target. The spatial distribution of the radiation usually represents the cone with the axis in forward direction with thickness proportional to the imaginary part of dielectric permittivity. In this paper it is shown that taking into account the refraction and reflection of the waves at the surface of the target leads to essential changes in spatial distribution of radiation. We give analytical description of the XUV Cherenkov and diffraction radiation from the bunch of charged particles. We show that the spatial distribution of radiation is not symmetrical in relation to the top face of the target.