High-energy coherent terahertz radiation emitted by wide-angle electron beams from a laser-wakefield accelerator

Abstract

High-charge electron beams produced by laser-wakefield accelerators are potentially novel, scalable sources of high-power terahertz radiation suitable for applications requiring high-intensity fields. When an intense laser pulse propagates in underdense plasma, it can generate femtosecond duration, self-injected picocoulomb electron bunches that accelerate on-axis to energies from 10s of MeV to several GeV, depending on laser intensity and plasma density. The process leading to the formation of the accelerating structure also generates non-injected, sub-picosecond duration, 1-2MeV nanocoulomb electron beams emitted obliquely into a hollow cone around the laser propagation axis. These wide-angle beams are stable and depend weakly on laser and plasma parameters. Here we perform simulations to characterise the coherent transition radiation emitted by these beams if passed through a thin metal foil, or directly at the plasma-vacuum interface, showing that coherent terahertz radiation with 10sμJ to mJ-level energy can be produced with an optical to terahertz conversion efficiency up to 10 −4 -10 −3 .

Ponderomotive and resonant effects in the acceleration of particles by electromagnetic modes

“…Even if one increases both amplitudes, keeping the two of them unequal with f ̸ = 1 limits the maximum velocity. On the other hand, when f = 1 the maximum, velocity can be as close to c as one wishes, all depending on the choice of the proper common mode amplitudes, whose extended range seen in the figure is compatible with the intensities generated in current petawatt and future exawatt highfrequency lasers [24] and self-focused infrared lasers of relativistically high intensities [25]. Color graded map for Gv π in terms of laser and wiggler amplitudes.…”

Compact radiation sources based on laser-driven plasma waves

“…We explore how high-quality [1][2][3][4] , femtosecond 5 to attosecond 6 duration, 1-10 kA peak current electron bunches can be accelerated to 0.1-10 GeV energies in millimetres to centimetres by a laser wakefield accelerator (LWFA) driven by a terawatt laser 1,7 . We also show that the un-trapped sheath electrons can lead to unprecedented 10s of nC bunches with energies of 1-5 MeV 8,9 , which can be transformed into THz radiation with high efficiency 9 , or used directly in imaging, radiation damage and pulsed radiolysis applications. The rapid development of LWFAs is leading to a paradigm shift in accelerator technology: the size of accelerators can now be reduced by many orders of magnitude compared with conventional technology, simply by taking advantage of space charge fields in plasma.…”

“…8 These 10s nC beams are quite divergent and therefore useful for imaging macroscopic objects 8 , as shown in Figure 4. The beams are also efficient emitters of THz radiation when passed through a thin metal foil or the plasma boundary 9 . Pulses of THz radiation with an energy in excess of several mJ are emitted with high efficiency using a very simple set up that requires little alignment 9 .…”

Coherent terahertz radiation emitted by wide-angle electron beams from a laser-wakefield accelerator

“…E-mail: d.a.jaroszynski@strath.ac.uk Theoretical studies indicate that these wide-angle beams can also produce mJ-level THz radiation. 15 Here we present numerical simulations to investigate the properties of this THz source. We show that the bunch duration of wide-angle beams is predicted to be longer than what is obtained from measurements and simulations of highenergy forward electron beams, resulting in the suppression of CTR at frequencies above 1-3 THz, depending on the geometry.…”