Nonlinear optical properties of LiNbO₃/Al₂O₃ films epitaxially grown by pulsed laser deposition

Abstract

Numerous epitaxial LiNbO₃ films, i.e., LiNbO₃(0001)/Al₂O₃(0001), LiNbO₃(0001)/Al₂O₃(1120), and LiNbO₃(1120)/Al₂O₃(1120) films, were grown by pulsed laser deposition. Low deposition temperatures below 450°C were used in order to reduce a Li deficient phase, LiNb₃O₈. Structural properties of the films, including twin formation, were investigated by X-ray θ-2θ scan and pole figure techniques. Nonlinear optical properties of these films were investigated using the Marker fringe and the Senarmont methods. The nonlinear optical coefficients related to the SHG, i.e., d ₃₁ and d ₃₃, were measured and their values were found to be very close to the LiNbO₃ single crystal values. It was also found that the SHG φ-scan can provide information on twin formations and in-plane orientation of the film. Electro-optic (EO) properties of the films were also studied. Films with different orientations display large differences in their EO properties: the epitaxial LiNbO₃(0001) films show little EO effects, but the LiNbO₃(1120) film shows a large quadratic EO behavior with an effective coefficient of 2.38×10^×15 m²/V².

Key Words:

• LiNbO₃ thin film
• pulsed laser deposition
• second harmonic generation
• electro-optic properties