Probing electron acceleration and x-ray emission in laser-plasma accelerators

Abstract

International audienceWhile laser-plasma accelerators have demonstrated a strong potential in the acceleration of electrons up to giga-electronvolt energies, few experimental tools for studying the acceleration physics have been developed. In this paper, we demonstrate a method for probing the acceleration process. A second laser beam, propagating perpendicular to the main beam, is focused on the gas jet few nanosecond before the main beam creates the accelerating plasma wave. This second beam is intense enough to ionize the gas and form a density depletion, which will locally inhibit the acceleration. The position of the density depletion is scanned along the interaction length to probe the electron injection and acceleration, and the betatron X-ray emission. To illustrate the potential of the method, the variation of the injection position with the plasma density is studied

Hard X Rays from Laser-Wakefield Accelerators in Density Tailored Plasmas

“…Plasma density profiles were estimated using a Normarsky interferometer. A second laser pulse (300 mJ / 30 fs) was used as a machining beam to estimate where electrons are injected and where x-ray radiation is produced along the laser propagation axis [18,19].…”

“…x-ray emission regions using the method described in [18]. We have found that the plasma lengths, over which Betatron radiation is produced, were 1.5 ± 0.5 mm for the up-ramp density, and 2 ± 0.5 mm for the constant density cases.…”

“…The critical energy shifts from 5 to 10 keV and the flux is enhanced by a factor 3. In order to verify, that the signal enhancement results from the change of electron orbits associated with the up-ramp density, we have estimated the x-ray emission regions using the method described in [18]. We have found that the plasma lengths, over which Betatron radiation is produced, were 1.5 ± 0.5 mm for the up-ramp density, and 2 ± 0.5 mm for the constant density cases.…”

“…was used as a machining beam to estimate where electrons are injected and where x-ray radiation is produced along the laser propagation axis [18,19].…”

Enhancement of laser-driven betatron x-rays by a density-depressed plasma structure

“…In this paper, we used a plasma structure of a density depression with a tunable length and position to enhance the betatron radiation generated from LWFA via ionization injection. The density depression is produced by using a technique of transverse laser machining [36,37] that has been applied in the enhancement of relativistic harmonic generation [38], and the optimization of LWFA [39,40] and betatron radiation [41]. By utilizing the density depression in a proper position, the amplitude of the betatron oscillation is increased after the accelerated electron passing through the depression, and therefore a bright betatron x-ray beam has been produced with a significant enhancement both in the critical energy and the photon number.…”