Brilliant femtosecond-laser-driven hard X-ray flashes from carbon nanotube plasma

Brilliant X- and γ-ray sources with ultrashort duration are widely pursued in fundamental science, industry and medicine. Compact femtosecond X-ray sources based on relativistic electrons accelerated by the laser wakefield in gases have performed outstandingly. Their energy conversion efficiency from laser to hard X-ray photons (>10 keV) is, however, limited to 10−7–10−5. Here we report the high-yield generation of hard X-ray flashes from targets made of carbon nanotubes, instead of gases. Orders-of-magnitude more electrons, accelerated to relativistic energy, are strongly wiggled inside a micrometre-scale, near-critical density plasma formed by the nanotube target, emitting 1012 high-energy photons per shot. The yield of hard X-rays exceeds 1010 photons per joule, corresponding to an unprecedented efficiency of 10−3. Irradiated by upcoming 10-PW-class lasers, such targets can deliver 10-MeV photons with brightness outperforming existing sources by two orders of magnitude.