Structural, optical and femtosecond third-order nonlinear optical properties of LiNbO < inf > 3 < /inf > thin films

Abstract

LiNbO3 thin films were deposited by means of Al:ZnO as intermediate layer using pulsed laser deposition and their structural, linear and nonlinear optical (NLO) properties were investigated. The films were found to be polycrystalline, (110) orientation for Al:ZnO/fused silica and (300) orientation for Al:ZnO/quartz substrates. The films demonstrated a transparency of > 80% in the visible and near-infrared region. The NLO studies were performed with the Z-scan technique using ∼150 fs, 80 MHz pulses at 800 nm. The studies revealed that the polycrystalline LiNbO3films and (300) LiNbO3films demonstrated reverse saturable absorption while a transition to saturable absorption was observed in the case of (110) LiNbO3. The presence of two-photon absorption is attributed to the indirect transition via intermediate defect levels which is related to the structural asymmetry. The large nonlinearity in refractive index could be a result of the strain induced ferroelectric polarization. The magnitude of the third order optical nonlinearity of all films was ∼10−11 e.s.u. which is orders of magnitude higher than the value obtained for single crystal Z-cut LiNbO3.