Improvement to Sellmeier equation for periodically poled LiNbO3 crystal using mid-infrared difference-frequency generation

Improvement to the Sellmeier equation for the extraordinary index of periodically poled LiNbO3 crystal (PPLN) is reported. The equation has been improved based on a continuous tunable mid-infrared radiation realizing in a PPLN crystal using difference-frequency-generation (DFG) and quasi-phase-matching (QPM) technique. The improved equation is suitable to estimate the QPM conditions of PPLN crystal for temperatures between 25 °C and 180 °C and mid-infrared wavelengths ranging from 2.8 μm to 4.8 μm.