Optical properties of PVDF-TrFE and PVDF-TrFE-CTFE films in terahertz band

Polymers have enormous potential in the optoelectronic and biomedical fields due to flexibility, biocompatibility, and ease of fabrication. Recent developments in the use of terahertz (THz) waves for biomedical and security applications demand information on the optical properties of the polymers and polymer composites in this region. In the present work, transmission, refractive index (n), and extinction coefficient (k) of PVDF-TrFE (75/25 mol.) copolymer and PVDF-TrFE-CTFE (73/23/4 mol.) terpolymer films with different thicknesses (40 mu m, 60 mu m, 80 mu m) are measured by the THz-TDS system (up to 1 THz). PVDF copolymer and terpolymer films show average transmission of more than 90% irrespective of thickness. The average refractive index of PVDF-TrFE (75/25 mol.) copolymer and PVDF-TrFE-CTFE (73/23/4 mol.) terpolymer films are 1.50 +/- 0.04 and 1.45 +/- 0.05 respectively. The estimated extinction coefficient is considerably low for both polymer films for frequencies less than 0.6 THz. The average indices for PVDF-TrFE and PVDF-TrFE-CTFE films are close, however, the loss in PVDF-TrFE films is larger than the PVDF-TrFE-CTFE films. High transmission, low loss and ferroelectric properties make these PVDF based polymers highly desirable in light-wave manipulation, flexible electronic and solar devices.