Photo-assisted proton exchange and chemical etching on Fe-doped lithium niobate crystals

We report the photo-assisted proton exchange and chemical etching on Fe-doped LiNbO3 crystals. Selective proton exchange and chemical etching are realized through the 455nm-laser irradiation on the crystal surface in pyrophosphoric acid. Optical microscopy and Micro-IR spectroscopy analysis show that the hydrogen incorporation is confined spatially by the laser irradiation. Moreover, under the laser irradiation, + z surface is found to be more easily etched than –z surface. This unexpected etching anisotropy is attributed to the photogalvanic effect of the crystal.