Laser induced electron and sodium ion emission from single crystal NaNO3 at 1064 nm

Abstract

Wide band gap insulators irradiated with UV pulsed lasers have been shown to yield both photoinduced electrons and energetic positive ions suggesting occupied electronic states in the band gap. It is not obvious that similar experiments with near-IR wavelengths should yield detectable emissions. Here we report electron and Na+ ion emission from single crystal sodium nitrate (∼10 eV band gap) upon exposure to near-IR (1.16 eV) laser radiation. The fluence dependence of both ion and electron yields is highly nonlinear and the kinetic energies of the emitted ions can reach values up to 5 eV. Our data suggest that the observed emissions originate from defect sites and they are consistent with a model that requires multiple single photon charge transfer to ionize an electron trap and subsequently eject a nearby positive adion due to electrostatic repulsion. Further evidence for the role of defects in the observed ion emission are provided by two beam experiments; one beam (UV laser) is used to generate defects and the second beam (near-IR laser) is used to photodesorb the ions. Such experiments demonstrate that exposure of the sodium nitrate surfaces to UV laser radiation significantly increases the ion emission due to near-IR laser radiation.