The generation of laser-driven dense relativistic electron layers from ultra-thin foils and their use for coherent Thomson backscattering is discussed, applying analytic theory and one-dimensional particle-in-cell simulation. The blow-out regime is explored in which all foil electrons are separated from ions by direct laser action. The electrons follow the light wave close to its leading front. Single electron solutions are applied to initial acceleration, phase switching, and second-stage boosting. Coherently reflected light shows Doppler-shifted spectra, chirped over several octaves. The Doppler shift is found to be proportional to γ_x^2=1/(1-β_x^2), where β_x is the electron velocity component in normal direction of the electron layer which is also the direction of the driving laser pulse. Due to transverse electron momentum p_y, the Doppler shift by 4*γ_x^2=4*γ^2/(1+(p_y/mc)^2) ~= 2*γis significantly smaller than full shift of 4*γ^2. Methods to turn p_y -> 0 and to recover the full Doppler shift are proposed and verified by 1D-PIC simulation. These methods open new ways to design intense single attosecond pulses.
A proposal for a novel source of isolated attosecond XUV -- soft X-ray pulses with a well controlled carrier-envelope phase difference (CEP) is presented in the framework of nonlinear Thomson-backscattering. Based on the analytic solution of the Newton-Lorentz equations, the motion of a relativistic electron is calculated explicitly, for head-on collision with an intense fs laser pulse. By using the received formulae, the collective spectrum and the corresponding temporal shape of the radiation emitted by a mono-energetic electron bunch can be easily computed. For certain suitable and realisti…
Numerical calculations of a high brilliance synchrotron source and on issues with characterizing strong radiation damping effects in non-linear Thomson/Compton backscattering experiments
大量的理论计算研究了辐射反作用力对强场反向传播电子束-激光相互作用中辐射分布的影响，但是这些影响--包括量子校正--是否能在与真实的聚束和聚焦场的相互作用中观察到，正如许多即将提出的实验所希望的那样？我们提出了数值计算的角度分辨辐射光谱的电子束团的参数类似于激光尾场加速实验中产生的，与强烈的，超短激光脉冲相互作用。对于我们的参数，辐射阻尼对\emph{photons}的角分布和能量分布的影响是不容易辨别的一个"现实的"中等发射度电子束。然而，使用这种反向传播的光束-激光器几何形状的实验应该能够通过测量\emph{electron beam}性质来测量使用当前激光系统的这种效应。此外，该源的亮度非常高，峰值光谱亮度超过$10^{29}$光子$\,$ s $^{-1}$ mm $^{-2}$ mrad $^{-2}(0.1$ %带宽$)^{-1}$，效率约为2%，峰值能量为10 MeV。
Acceleration of ultra-thin electron layer. Analytical treatment compared with 1D-PIC simulation
在本文中，我们应用分析模型[V. V. Kulagin et al.，Phys. Plasmas 14，113101（2007）]来描述通过示意性单周期激光脉冲对超薄电子层的加速，并与一维粒子单元（1D-PIC）模拟进行比较。这是在创建一个相干后向散射的相对论镜的背景下，并补充了这EPJD卷中的两篇相关论文。该模型被证明是重现的1D-PIC结果几乎定量的几个激光周期足够的超短探测脉冲的后向散射的短时间。
Experimental demonstration of Flying-Focus enhanced Thomson scattering
Queen’s University Belfast（贝尔法斯特女王大学）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器）；University of Hamburg（汉堡大学）；Gérard Mourou Center for Ultrafast Optical Science, University of Michigan（密歇根大学杰拉德·穆鲁超快光学科学中心）；Laboratory for Laser Energetics, University of Rochester（罗切斯特大学激光能源实验室）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；ELI Beamlines Facility, The Extreme Light Infrastructure ERIC（极端光基础设施欧洲研究联盟ELI光束线设施）
Experimental observation of nonlinear Thomson scattering
一个世纪前，J. J. Thomson证明了电子对低强度光的散射是一个线性过程（即，散射光的频率与入射光的频率相同）并且光的磁场不起作用。今天，随着超高峰值功率激光器的发明，现在有可能产生足够的光子密度来研究相对论范围内的汤姆逊散射。随着光强度的增加，电子在散射过程中的速度也会增加，当激光强度接近10^18 W/cm ^2时，电子的速度接近光速。在这个极限下，光的磁场对电子运动的影响应该与它的电场的影响相当，并且由于相对论修正，电子质量应该增加。因此，在这样的高场中的电子被预测为非线性地以8字形模式而不是直线移动，从而以入射激光频率的谐波辐射光子，每个谐波都有自己独特的角分布。在这封信中，我们报告了有史以来第一次直接实验证实这些预测，以前被称为非线性汤姆逊散射的主题。扩展这些结果相干相对论谐波产生可能最终导致新的桌面X射线源。
An optical injection scheme into the laser wakefield accelerator by preceding injection pulse is investigated by means of 3D numerical particle-in-cell simulations. Quasimonoenergetic hundred-pC electron bunches as short as 6 fs can be generated. Optimal beam separation distance is found at the intersection point of the injection beam bubble with the collection volume for transverse injection into the accelerator beam bubble. It approximately corresponds to the plasma wavelength. The main advantage of this scheme is the localized injection of high charge. This injection mechanism can be useful…
We study the effects of laser pulse focussing on the spectral properties of Thomson scattered radiation. Modelling the laser as a paraxial beam we find that, in all but the most extreme cases of focussing, the temporal envelope has a much bigger effect on the spectrum than the focussing itself. For the case of ultra-short pulses, where the paraxial model is no longer valid, we adopt a sub-cycle vector beam description of the field. It is found that the emission harmonics are blue shifted and broaden out in frequency space as the pulse becomes shorter. Additionally the carrier envelope phase be…
Twisted Laguerre-Gaussian lasers, with orbital angular momentum and characterised by doughnut shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high gradient positron acceleration. The production of ultrahigh intensity twisted laser pulses …
We report the experimental results of simultaneous measurements on the electron and X-ray spectra from near-critical-density (NCD) double-layer targets irradiated by relativistic femtosecond pulses at the intensity of 5E19 W/cm^2. The dependence of the electron and X-ray spectra on the density and thickness of the NCD layer was studied. For the optimal targets, electrons with temperature of 5.5 MeV and X-rays with critical energy of 5 keV were obtained. 2D particle-in-cell simulations based on the experimental parameters confirm the electrons are accelerated in the plasma channel through direc…
On extreme field limits in high power laser matter interactions: radiation dominant regimes in high intensity electromagnetic wave interaction with electrons
Plasmas with anisotropic electron velocity distribution functions are needed for the controlled study of kinetic plasma instabilities in the laboratory. We demonstrate that such plasma can be produced using ultrashort laser pulses via optical-field ionization (OFI). We experimentally show this control by using Thomson scattering as a diagnostic to probe the characteristic electron velocity distributions using linearly and circularly polarized laser pulses to ionize helium. Furthermore the He plasma produced by a circularly polarized light pulse exhibits the onset of the electron streaming inst…
We study the interaction of intense ultrashort laser pulses with cryogenic He jets using 2d/3v relativistic Particle-in-Cell simulations (XOOPIC). Of particular interest are laser intensities $(10^{15}-10^{20})$ W/cm$^2$, pulse lengths $\le 100$ fs, and the frequency regime $\sim 800$ nm for which the jets are initially transparent and subsequently not homogeneously ionized. Pulses $\ge 10^{16}$ W/cm$^2$ are found to drive ionization along the jet and outside the laser spot, the ionization-front propagates along the jet at a fraction of the speed of light. Within the ionized region, there is a…
We consider backscattering of laser pulses in strongly-magnetized plasma mediated by kinetic magnetohydrodynamic waves. Magnetized low-frequency scattering, which can occur when the external magnetic field is neither perpendicular nor parallel to the laser propagation direction, provides an instability growth rate higher than Raman scattering and a frequency downshift comparable to Brillouin scattering. In addition to the high growth rate, which allows smaller plasmas, and the 0.1-2\% frequency downshift, which permits a wide range of pump sources, MLF scattering is an ideal candidate for ampl…
