Compact tunable Compton x-ray source from laser-plasma accelerator and plasma mirror

摘要

We present an in-depth experimental-computational study of the parametersnecessary to optimize a tunable, quasi-monoenergetic, efficient, low-backgroundCompton backscattering (CBS) x-ray source that is based on the self-alignedcombination of a laser-plasma accelerator (LPA) and a plasma mirror (PM). Themain findings are: (1) an LPA driven in the blowout regime by 30 TW, 30 fslaser pulses producesnot only a high-quality, tunable, quasi-monoenergeticelectron beam, but also a high-quality, relativistically intense (a0~1) spentdrive pulse that remains stable in profile and intensity over the LPA tuningrange. (2) A thin plastic film near the gas jet exit retro-reflects the spentdrive pulse efficiently into oncoming electrons to produce CBS x-rays withoutdetectable bremsstrahlung background. Meanwhile anomalous far-field divergenceof the retro-reflected light demonstrates relativistic "denting" of the PM.Exploiting these optimized LPA and PM conditions, we demonstratequasi-monoenergetic (50% FWHM energy spread), tunable (75 to 200 KeV) CBSx-rays, characteristics previously achieved only on more powerful laser systemsby CBS of a split-off, counter-propagating pulse. Moreover, laser-to-x-rayphoton conversion efficiency ~6e12 exceeds that of any previous LPA-basedquasi-monoenergetic Compton source. Particle-in-cell simulations agree wellwith the measurements.