Single shot source size measurement of laser driven proton beams with active plasma lens*

Using an active plasma lens we demonstrate a single-shot method to measure the energy-dependent source size of laser driven proton beams. The active plasma lens acts as an imaging system, yielding magnified proton beam spots at a distance of 1.5 meters behind the target. A simple Monte Carlo code is used to simulate the transport and retrieve the source size from the measurement. In the energy range of 3 to 7 MeV we show the measured proton beam source size is 210 to 60 micrometers, with an incident laser spot size of 52 micrometers and a peak laser intensity of 2*1 \textasciicircum 19 W/cm \textasciicircum 2.