Sellmeier equation for the refractive index of ordinary light in 5 mol.% MgO-doped congruent lithium niobate

Congruent lithium niobate is a type of lithium niobate crystal with a mature growth process and is widely used in nonlinear optics research. Its refractive index accuracy will play a crucial role in the research and application of nonlinear optics. In this paper, we theoretically analyze the accuracy and reliability of nonlinear methods and experimentally measure the refractive index of ordinary light at different wavelengths and temperatures in a non-critical phase matching LN crystal by the sum-frequency generation and spontaneous parametric down-conversion processes, with the help of the existing accurate Sellmeier equation for the refractive index of extraordinary light. By fitting the refractive index of ordinary light, a new set of parameters for the Sellmeier equation is established. This equation shows excellent agreement with existing experimental results, and greatly extends the range of wavelengths and temperatures to 0.5-10 <i>μ</i> <i>m</i> and 20-250 ^∘ <i>C</i>.