Scintillators in High-Power Laser-Driven Experiments

Nowadays, it is possible to accelerate bunches of particles in the interaction of ultrahigh intensity (UHI) laser pulses with matter. Electrons, protons, ions, and high-energy photon beams can be produced in experiments and reach kinetic energies close to hundreds of mega-electron-volts for protons and giga-electron-volts for electrons and for the associated Bremsstrahlung photons. At these energies, these beams can induce a large variety of nuclear reactions, which can be detected and studied using gamma-ray spectroscopy techniques. At standard accelerator facilities, scintillator detectors are commonly used to perform prompt gamma-ray spectrometry studies. However, during laser-matter interactions, high fluxes of X-rays (mostly soft) are generated, which lead to instantaneous huge energy deposits (similar to 1 μJ) in these scintillators. Depending on the laser characteristics (energy and pulse duration), the detector recovery time after these X-ray flashes can reach several milliseconds, which makes any prompt or 'in beam' measurement impossible. The origin of this long-duration signal is investigated in the case of a LaBr₃ crystal coupled to different photodetectors. While it was impossible using standard photomultiplier tubes to detect γ-ray emissions before a few milliseconds after a laser shot, we could, using a hybrid photodiode, resolve single gamma-ray emission a few tens of microseconds after the laser shot. Furthermore, we have also shown that the LaBr₃ scintillator presents an unexpected long-lived light emission (afterglow). Directions are suggested for future studies in order to minimize the effects of this afterglow emission. (authors)