An isolated ultra-short γ-ray pulse is a unique tool for measuring ultrafast-physics process, such as imaging of intra-nuclear dynamics and inner-shell electron dynamics. Here, we propose an all-optical efficient scheme for generating isolated ultra-short γ-ray pulse from a laser-driven nanofoil. When a few-cycle circularly polarized laser pulse with an intensity of 10 22 W/cm 2 irradiates a nanofoil, the electrons in the nanofoil are pushed forward collectively, forming a single relativistic electron sheet (RES) with the charge of nC. The electrons are substantially accelerated to high energies by the super-ponderomotive force of the laser. Then a counter-propagating laser pulse with a peak intensity of 10 21 W/cm 2 collides with the RES, resulting in the generation of an isolated sub-femtosecond γ-ray pulse via nonlinear Compton scattering. The effects of laser polarization on the polarization degree of γ-rays is investigated by using a proof-of-principle calculation. It is shown that a highly-polarized isolated γ-ray pulse with the cut-off energy of 100 MeV can be eventually generated in a head-on colliding configuration when the scattering laser is a linearly polarized laser. Such an isolated ultra-short polarized γ-ray source would provide critical applications in high energy physics, laboratory astrophysics and nuclear physics.

Radioisotopes are indispensable agents in medical diagnosis and treatment, among which 62, 64Cu and 68Ga are medical isotopes widely used in positron emission tomography (PET) imaging. Experiments of generating these radioisotopes via laser-induced photonuclear reactions were performed on the XingGuangIII laser facility of the Laser Fusion Research Center (LFRC) at Mianyang. Large-charge (Q_e ~ 40 nC) MeV electron (e–) beams were generated with 100 TW picosecond (ps) laser pulses. The e– beams then impinge on a metal stack composed of Ta foil and activation plates (natural Cu and Ga2O3), producing high-energy bremsstrahlung radiations and isotopes 62, 64Cu and 68Ga, respectively. The characteristic emissions of the produced 62, 64Cu and 68Ga were off-line detected and the production yields of 62, 64Cu and 68Ga were obtained to be the order of 106 per laser shot. The dependence of radioisotope production efficiency (per e–) on electron temperature (T_e) is investigated through Geant4 simulations. It is found that the production efficiency increases with the T_e and then reaches a saturation value of 8 × 10−5 for 62Cu and 10–5 for 68Ga at T_e ~ 10 MeV. The prospect of producing medically isotopes 62, 64Cu and 68Ga is further evaluated by using table-top femtosecond laser system of high repetition. Considering a repetition rate of 100 Hz, it is expected that the activity can reach 0.2 GBq for 62Cu, 0.1 GBq for 64Cu and 0.05 GBq for 68Ga, respectively. Such activity would meet the required dose for clinical PET imaging, indicating the great potential to produce medical radioisotopes with an all-optical, high-repetition laser system.