Accumulated laser-photoneutron generation

We present repeated generation of photoneutrons by double-pulse irradiation of ultrathin foils. A ~ mJ prepulse turns a foil into a 100-μm scale plasma plume from which a beam of MeV electrons is generated by the main pulse. Neutrons are generated in a secondary metal target placed downstream to the electron beam. We utilize an automated target system capable of delivering ultrathin foils to the laser focus at an average rate of 0.1 Hz. With 153 consecutive laser shots taken over the course of 24 min, we generated a total 2.6 × 10 7 neutrons. We present a method for evaluating how the number of photoneutrons scales with the laser intensity in this experimental scenario, which we validate against the measured yields.