X-RAY PRODUCTION USING LASER-PLASMA ACCELERATORS

Bubble regime has been investigated using three-dimensional particle-in-cell simulations of ultra-relativistically intense laser pulses with duration a fraction of the plasma wavelength [1]. Electrons trapped inside the bubble experience an electrostatic force and undergo betatron motion. The present work analyzes the spontaneous radiation emitted by electrons undergoing betatron motion in the plasma bubble. Numerical simulations have been used to calculate the expected spectra and spatial distribution of the radiation. We discuss these theoretical results and an experiment at Strathclyde that is being set up to measure the betatron radiation. Laser-plasma accelerators and betatron oscillations: A light source capable of delivering pulses of X-rays with femtosecond duration should provide a new probe with a time resolution that would enable investigation of the evolution of molecular and solid state matter. Laser-plasma accelerators represent a new interesting way of generating short pulses of X-rays. The mechanism determining X-ray emission can be sketched through the following steps: - The propagation of intense laser pulses in underdense plasma generates plasma waves: laser wakefield acceleration (LWFA) occurs when a laser pulse travelling at a velocity close to the speed of light excites a trailing plasma wave or wake through the action of the ponderomotive force which expels electrons from regions of high laser intensity. - Electrons can be trapped in the wake and surf the electric field of the wake thus gaining energy from the wave . - If an intense laser pulse is ultra-relativistic and its duration shorter than the plasma wavelength, the ponderomotive force will expel plasma electrons radially and leave a cavitated (bubble) region behind the pulse, surrounded by a high electron density region. - Electrons are trapped at the rear of the bubble and accelerate along the laser axis, creating a beam with a radial and longitudinal size much smaller than the laser spot