Direct laser writing of metastable modifications in lithium niobate crystal with ultrashort laser pulses

This work demonstrates that direct laser writing (DLW) is an excellent technique for metastable modification formation in the bulk of pure and iron doped LiNbO₃ crystals. Using laser pulses generated with Ti:sapphire and Yb:KGW femtosecond laser systems, it is possible to induce photorefractive modifications that appear only in the proximity of laser focus and allows employing all crystal volume for data or photonic device inscription. By correctly choosing laser parameters and writing algorithms simple or complex geometry regions with homogeneously modified refractive index can be formed. The magnitude of refractive index change can be controlled by varying total radiant exposure. We show that uneven charge distribution in the crystal can be rearranged multiple times with the same writing laser beam thus implementing possibility to locally erase or change previously recorded data.