Gd:LiNbO3 (Gadolinium-doped Lithium Niobate) is a type of lithium niobate crystal that is doped with gadolinium ions. Lithium niobate is a widely used material in the field of photonics due to its excellent electro-optic, acousto-optic, and nonlinear optical properties. Gadolinium doping enhances the nonlinear optical properties of lithium niobate and makes it an attractive material for use in a variety of optical and microwave applications, including frequency conversion, modulation, and phase-matching. Some of the applications of Gd:LiNbO3 include second harmonic generation, optical parametric oscillation, and wavelength conversion.