Irradiation-assisted photoelastic domain wall formation in X- and Y-cut lithium niobate

Irradiation-assisted photoelastic domain wall formation in single-crystalline X- and Y-cut lithium niobate (LNO) is studied at low displacement doses, namely, up to a maximum of 2.5×10⁻² dpa and annealed at 270 °C. The formation of surface ridges (or striations) is observed and quantified using atomic force and optical microscopy. In spite of the different crystallographic orientation of the two single-crystals a correlation between the density of surface defects and the displacement dose is established phenomenologically which means that the displacement damage and its consequent defect accumulation behavior prior to annealing (‘incubation phase’) defines to which extent the lattice undergoes an irreversible mechanical deformation immediately after annealing. This ridge formation mechanism assisted by irradiation and moderate annealing constitutes a fine tool to modify the near-surface structure and the local optical properties of LNO and hence it allows one to potentially micromachine new photonic devices.