Complex Permittivity Extraction of Vacuum Windows for a Compact FEL-THz Source

Exact calculation of the power transmittance requires optical parameters of terahertz (THz) vacuum windows, widely used in the optical path in a vacuum electron system, such as the free electron laser (FEL) THz source. A method for extracting optical parameters of thick vacuum window materials based on THz-TDS was utilized for the determination of emitted power from the down-stream mirror of a compact FEL-THz facility at Huazhong University of Science and Technology (HUST). The real and imaginary part of permittivity for TPX and HRSi were extracted in a wide frequency range from 0.5 to 4.5 THz by the transmission-mode TDS measurement.