Laser wakefield acceleration: towards compact electron accelerator and ultrashort coherent light sources

Modern accelerators are built on radio-frequency technologies. Accelerating fields as high as ~50MV/m can be achieved. With fields beyond that, the metallic rf-cavitites break down. In order to accelerate GeV beam energies, accelerating cavities of 100s meters is thus a must. Recently, the laser wakefield acceleration emerges as a new technique, holding the promise to greatly shrink the size of future accelerators. It operates with a plasma medium, instead of metallic cavities. The plasma is ionized matter (i.e., already broken down), but it can be perturbed to have regular wave structures bearing super-strong fields (~100GV/m), 3 orders of magnitude larger than with rf-cavitites. Thus, a plasma-based accelerator can achieve GeV acceleration in just millimeters. High-intensity short-pulse lasers can be used to drive the perturbation, creating laser wake waves in an gaseous plasma. This acceleration has normally produced femtosecond narrow electron bunches, which are drivers for femtosecond incoherent x-ray sources.

Here, we show under proper plasma density control, it is possible to generate attosecond (3 orders of magnitude shorter than femtoseconds) electron beams of wide diameters. Such an attosecond electron sheet can radiate super-strong fully coherent attosecond light pulses when it undergoes radial contraction in the plasma wake. It can also serve as an ultrarelativistic flying mirror for the generation of coherent x-ray lights via Thomson backscattering.

F.-Y. Li, Z.-M. Sheng, Y. Liu, J. Meyer-ter-Vehn, W. B. Mori, W. Lu, and J. Zhang, Dense attosecond electron sheets from laser wakefields using an up-ramp density transition, Phys. Rev. Lett. 110, 135002 (2013).

F.-Y. Li, Z.-M. Sheng, M. Chen, L.-L. Yu, J. Meyer-ter-Vehn, W. B. Mori, and J. Zhang, Radially polarized, half-cycle, attosecond pulses from laser wakefields through coherent synchrotronlike radiation, Phys. Rev. E 90,043104 (2014).

F.-Y. Li, Z.-M. Sheng, M. Chen, H.-C. Wu, Y. Liu, J. Meyer-ter-Vehn, W. B. Mori, and J. Zhang, Coherent kilo-electron-volt backscattering from plasma-wave boosted relativistic electron mirrors, Appl. Phys. Lett. 105, 161102 (2014).

J. Mu, F.-Y. Li, M. Zeng, M. Chen, Z.-M. Sheng, and J. Zhang, Robust relativistic electron mirrors in laser wakefields for enhanced Thomson backscattering, Appl. Phys. Lett. 103, 261114 (2013).

Y. Liu, F.-Y. Li, M. Zeng, M. Chen, and Z.-M. Sheng, Ultra-intense attosecond pulses emitted from laser wakefields in non-uniform plasmas, Laser and Particle Beams, 31, 233 (2013).

M. Chen, J. Luo, F.-Y. Li, F. Liu, Z.-M. Sheng, and J. Zhang, Tunable synchrotron-like radiation from centimeter scale plasma channels, Light: Science & Applications, 5, e16015 (2016).

X. Yang, E. Brunetti, D. Reboredo Gil, G. Welsh, F.-Y. Li, et al., Three electron beams from a laser-plasma wakefield accelerator and the energy apportioning question, Scientific Reports, 7, 43910 (2017).