Revisited transition selection rules and laser emission in Nd3+ doped MgO:LiNbO3 crystal

Lithium niobate (LiNbO 3 ) crystals and devices have many important applications in laser frequency doubling and electro-optic frequency comb generation. Especially for Nd 3+ -doped LiNbO 3 , holding optical gain, electro-optic modulation, and frequency conversion concurrently, serves as the promising platform for on-chip integrated optical applications. However, despite of the first discovery over fifty years, the fundamental transition selection rules of Nd-doped LiNbO 3 crystal still remain elusive due to the complex Stark levels and undefined local symmetry. In this work, we present a comprehensive characterization of Nd:MgO:LiNbO 3 crystals, including crystal growth, optical spectrum, and transition selection rules. Based on the absorption spectrum and polarized fluorescence emission, we clarify the Stark splitting levels in Nd:MgO:LiNbO 3 crystal and give a panorama for 4 F 3/2 → 4 I 9/2 , 4 I 11/2 , 4 I 13/2 transitions. Meanwhile, we first employed the Γ 4 , Γ 5 , and Γ 6 irreducible representation to calibrate the Stark levels of Nd 3+ ions, which can establish a theoretical foundation for laser with different polarization characteristics in LiNbO 3 . Moreover, we performed the polarized laser generation at 1.08, 1.09, 1.38, and 1.4 μm to check the validity of fine energy level diagram and the electric-dipole selection rules by light polarization. To the best of our knowledge, this is the first report on laser oscillation at 1.4 μm in Nd:MgO:LiNbO 3 crystals.