Wide spectral range refractive indices of BBO crystal covering 0.2–2000 THz
Rukang Li, Guochun Zhang, Naixia Zhai, Binbin Zhou, Peter Uhd Jepsen
Abstract
Wide-range dispersive refractive indices from 0.2 to 2000 THz of the barium borate (BBO) crystal have been attained through joint research by density functional theory calculations and measurements by terahertz time-domain spectroscopy and minimum deviation methods in the THz and infrared-visible-ultraviolet (UV) and deep UV range. New parameters of the Sellmeier equations in the transparent windows in the IR to DUV and THz range are obtained by the least square fittings of the measured refractive indices together with the calculated data. Compared to previously reported models, the Sellmeier equations presented in this work more accurately capture the underlying electronic and vibrational transition mechanisms of the BBO crystal. Furthermore, these Sellmeier equations not only provide precise refractive index predictions but also achieve phase-matching angle predictions that are as accurate as or superior to those from earlier equations specifically tuned to observed PM angles.