Wideband Refractive Index Extraction of Low-loss Materials with the Combined TDS-FTIR Method

A method to obtain the optical constants of low loss materials in a wide frequency range was proposed based on the measured transmission data from THz-TDS and FTIR. With anchoring phase points from TDS, the phase spectrum lost in FTIR original data was successfully retrieved and the complex refractive index was acquired with standard iterative method (Nelder-Mead and Newton-Raphson). As an example, the refractive index and extinction coefficient of HRSi were extracted from 0.5 to 10 THz with both iterative method and analytic formula. Good agreement between TDS and FTIR results in the overlapped frequency range was realized.