A table-top laser-based source of short, collimated, ultra-relativistic positron beams

We present here the first experimental evidence of the generation of ultra-short (35 fs), highly collimated (3 mrad) and ultra relativistic (150 MeV) positron beams following the interaction of a laser-wakefield accelerated electron beam with high-Z solid targets. The modest laser parameters (25 TW) make this the first demonstration of a table top source of relativistic positron beams. We anticipate that these beams will be also of direct relevance to the laboratory study of astrophysical leptonic jets.