Персона: Бухарский, Николай Дмитриевич
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Characterization of bright betatron radiation generated by direct laser acceleration of electrons in plasma of near critical density
Directed x-rays produced in the interaction of sub-picosecond laser pulses of moderate relativistic intensity with plasma of near-critical density are investigated. Synchrotron-like (betatron) radiation occurs in the process of direct laser acceleration (DLA) of electrons in a relativistic laser channel when the electrons undergo transverse betatron oscillations in self-generated quasi-static electric and magnetic fields. In an experiment at the PHELIX laser system, high-current directed beams of DLA electrons with a mean energy ten times higher than the ponderomotive potential and maximum energy up to 100 MeV were measured at 1019 W/cm2 laser intensity. The spectrum of directed x-rays in the range of 5ў??60 keV was evaluated using two sets of Ross filters placed at 0‚ш and 10‚ш to the laser pulse propagation axis. The differential x-ray absorption method allowed for absolute measurements of the angular-dependent photon fluence. We report 1013 photons/sr with energies andamp;gt;5 keV measured at 0‚ш to the laser axis and a brilliance of 1021 photons sў??1 mmў??2 mradў??2 (0.1%BW)ў??1. The angular distribution of the emission has an FWHM of 14‚шў??16‚ш. Thanks to the ultra-high photon fluence, point-like radiation source, and ultra-short emission time, DLA-based keV backlighters are promising for various applications in high-energy-density research with kilojoule petawatt-class laser facilities.