All-laser-driven Thomson X-ray sources

Abstract

We discuss the development of a new generation of accelerator-based hard X-ray sources driven exclusively by laser light. High-intensity laser pulses serve the dual roles: first, accelerating electrons by laser-driven plasma wakefields, and second, generating X-rays by inverse Compton scattering. Such all-laser-driven X-rays have recently been demonstrated to be energetic, tunable, relatively narrow in bandwidth, short pulsed and well collimated. Such characteristics, especially from a compact source, are highly advantageous for numerous advanced X-ray applications – in metrology, biomedicine, materials, ultrafast phenomena, radiology and fundamental physics.

Keywords:

• laser plasma X-ray
• scattering
• electron accelerator

Disclosure statement

No potential conflict of interest was reported by the author.

Notes

1. A light pulse propagates in plasma at the group velocity, $v_g=c\sqrt{1-{\mathit{\omega }}_p^2/{\mathit{\omega }}_0^2}$, where ω_p is the plasma frequency, defined by ${\mathit{\omega }}_p^{}=\sqrt{n_e{q}^2/{\mathit{\epsilon }}_0{m}_e}$, and n_e is the plasma density. In highly under-dense plasmas, v_g ∼ c, since in this case ${\mathit{\omega }}_p^2\ll {\mathit{\omega }}_0^2$, or n_e $\ll$ n_c, where n_c is the critical density, the density at which ${\mathit{\omega }}_0^{}={\mathit{\omega }}_p$.

2. When relativistic electrons, with v ≈ c, are accelerated, their kinetic energy increases much more rapidly than does their velocity, since the relativistic kinetic energy is ≈ γm₀c².

3. Photon energy spectral densities, or photon energy per unit bandwidth (MeV/MeV), can be peaked due to the nonuniform photon energy weighting. However, the same spectrum may not be peaked when plotted as photon number spectral density, photon number per unit bandwidth (MeV⁻¹), which has even energy weighting.

Additional information

Funding

This work was supported by the Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) [award number DE-FG02-05ER15663] (ultrafast x-ray science); the Air Force Office for Scientific Research [FA9550-11-1-0157]; the Department of Homeland Security Domestic Nuclear Detection Office [competitively awarded contract number HSHQDC-13-C-B0036]; National Strategic Research Institute [FA4600-12-D-9000]. This support does not constitute an express or implied endorsement on the part of the Government.