Optically controlled coherent X-ray radiations from photo-excited nanotubes

Relativistic electrons propagating through a plasmonic medium such as photo-excited plasma channels with negative permittivities undergo betatron motions, emitting photons at oscillating resonance modes. The similar betatron radiation can be generated in X-ray regimes from electrons transported through optically pumped carbon nanotubes (CNTs). The X-ray radiation condition of 0.5 and 6 MeV electrons phase-matched with plasmonic waves in CNTs is analyzed with a theoretical model of the CNT dispersion relation. Based on the dispersion analysis, radiation intensities and the brilliance of the coherent X-ray source averaged over the pulse duration are estimated using a typical range of system parameters of conventional electron sources and tabletop femtosecond lasers. The assessment indicates that the average brilliance of the harmonic radiation can reach 1010-1013 photons/s/mm2/mrad2/0.1%BW with 0.5-6 MeV electrons and X-ray energy up to a few keV.