Local Photorefractive Modification in Lithium Niobate Using Ultrafast Direct Laser Write Technique

In this work we demonstrate the possibility to form discrete homogeneously-altered refractive index regions of photorefractive origin in bulk of pure and iron doped lithium niobate crystals using femtosecond direct laser write technique. We show that nonlinear free charge generation and charge separation caused by the bulk photo-voltaic effect are the main contributing factors to the change in refractive index. Moreover, femtosecond pulse induced refractive index change can be by an order of magnitude higher than values reached with longer laser pulses. Additionaly, we show that with different recording algorithms a sufficient control on topological charge separation can be achieved in micrometer scale that lets implement reversible information recording procedures in lithium niobate crystal.