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Register a new userDemonstration of the synchrotron-type spectrum of laser-produced Betatron radiation
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Betatron X-ray radiation in laser-plasma accelerators is produced when electrons are accelerated and wiggled in the laser-wakefield cavity. This femtosecond source, producing intense X-ray beams in the multi kiloelectronvolt range has been observed at different interaction regime using high power laser from 10 to 100 TW. However, none of the spectral measurement performed were at sufficient resolution, bandwidth and signal to noise ratio to precisely determine the shape of spectra with a single laser shot in order to avoid shot to shot fluctuations. In this letter, the Betatron radiation produced using a 80 TW laser is characterized by using a single photon counting method. We measure in single shot spectra from 8 to 21 keV with a resolution better than 350 eV. The results obtained are in excellent agreement with theoretical predictions and demonstrate the synchrotron type nature of this radiation mechanism. The critical energy is found to be Ec = 5.6 pm 1 keV for our experimental conditions. In addition, the features of the source at this energy range open novel perspectives for applications in time-resolved X-ray science.
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Development of x-ray phase contrast imaging applications with a laboratory scale source have been limited by the long exposure time needed to obtain one image. We demonstrate, using the Betatron x-ray radiation produced when electrons are accelerated and wiggled in the laser-wakefield cavity, that a high quality phase contrast image of a complex object (here, a bee), located in air, can be obtained with a single laser shot. The Betatron x-ray source used in this proof of principle experiment has a source diameter of 1.7 microns and produces a synchrotron spectrum with critical energy E_c=12.3 +- 2.5 keV and 10^9 photons per shot in the whole spectrum.
Direct laser acceleration (DLA) of electrons in a plasma of near critical electron density (NCD) and associated synchrotron-like radiation are discussed for moderate relativistic laser intensity (the normalized laser amplitude $a_0$ $leq$ 4.3) and ps-long pulse. This regime is typical for kJ PW-class laser facilities designed for high energy density research. Currently, in experiments at the PHELX laser it was demonstrated that interaction of 10$^{19}$ W/cm$^{2}$ sub-ps laser pulse with sub-mm long NCD plasma results in generation of high-current well-directed super-ponderomotive electrons with effective temperature that is 10$times$ higher than the ponderomotive potential [O. Rosmej et al., PPCF 62, 115024 (2020)]. Three-dimensional Particle-In-Cell simulations provided a good agreement with the measured electron energy distribution and were used in the current work to study synchrotron radiation of the DLA accelerated electrons. The resulting x-ray spectrum with a critical energy of 5 keV reveals an ultra-high photon number of 7$times$10$^{11}$ in the 1-30 keV photon energy range at the focused laser energy of 20 J. Numerical simulations of a betatron x-ray phasecontrast imaging based on the DLA process for the parameters of a PHELIX laser is presented. The results are of interest for applications in high energy density (HED) experiments, which require a picosecond x-ray pulse and a high photon flux.
Electrons at the surface of a plasma that is irradiated by a laser with intensity in excess of $10^{23}~mathrm{W}mathrm{cm}^{-2}$ are accelerated so strongly that they emit bursts of synchrotron radiation. Although the combination of high photon and electron density and electromagnetic field strength at the plasma surface makes particle-particle interactions possible, these interactions are usually neglected in simulations of the high-intensity regime. Here we demonstrate an implementation of two such processes: photon absorption and stimulated emission. We show that, for plasmas that are opaque to the laser light, photon absorption would cause complete depletion of the multi-keV region of the synchrotron photon spectrum, unless compensated by stimulated emission. Our results motivate further study of the density dependence of QED phenomena in strong electromagnetic fields.
Betatron x-ray source from laser plasma interaction combines high brightness, few femtosecond duration and broad band energy spectrum. However, despite these unique features the Betatron source has a crippling drawback preventing its use for applications. Its properties significantly vary shot-to-shot and none of the developments performed so far resolved this problem. In this letter we present a simple method that allows to produce stable and bright Betatron x-ray beams. In addition, we demonstrate that this scheme provides polarized and easily tunable radiation. Experimental results show that the pointing stability is better than 10% of the beam divergence, with flux fluctuation of the order of 20% and a polarization degree reaching up to 80%
The emission characteristics of intense laser driven protons are controlled using ultra-strong (of the order of 10^9 V/m) electrostatic fields varying on a few ps timescale. The field structures are achieved by exploiting the high potential of the target (reaching multi-MV during the laser interaction). Suitably shaped targets result in a reduction in the proton beam divergence, and hence an increase in proton flux while preserving the high beam quality. The peak focusing power and its temporal variation are shown to depend on the target characteristics, allowing for the collimation of the inherently highly divergent beam and the design of achromatic electrostatic lenses.
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