Nuclear collision induced lattice swelling and refractive-index modification in ion-irradiated yttrium orthoaluminate crystal

This work reports the study of lattice damage behavior in yttrium orthoaluminate (YAlO3) crystal irradiated with medium-energy (6.0 MeV) and relatively high-energy (20.0 MeV) Si ions through complementary characterization techniques including Rutherford backscattering/channeling spectroscopy, transmission electron microscopy and X-ray diffraction. The results clearly demonstrate that under Si-ion irradiation over the energy range from a few MeV up to tens of MeV, the nuclear energy loss (elastic collisions between injected ions and target atoms) along ion trajectory would play a dominant role in lattice damage and swelling, which leads to the decrease of refractive index in the nuclear energy deposition region and the waveguide formation in YAlO3 crystal. By contrast, the electronic energy loss (ionization and electronic excitation) over the corresponding ion energy range would not produce obvious lattice damage, and therefore could not significantly modify the refractive index in YAlO3 crystal. Utilizing optical-coupling measurements and iWKB-procedure simulation, the modified refractive-index profile in ion irradiation region has been reconstructed, and the obtained corresponding relationship between the refractive-index profile and SRIM-simulated dpa profile further confirms the nuclear-energy-loss induced lattice swelling and refractive-index decrease behaviors in ion-irradiated YAlO3 crystal, consisting with the microstructure characterization results.