This plastic plano-convex lenses made with Polytetrafluoroethylene (Virgin White PTFE, Teflon®), has a low dielectric constant of approximately 1.96 @ 520 GHz and an index of refraction of 1.4. The low dielectric constant of PTFE ensures that the insertion loss is reasonably low. PTFE is usable for frequencies up to ~2 THz.
Material: PTFE Teflon®
Dielectric Constant: 1.96 at 520 GHz
Design Frequency: 500 GHz, n=1.4
Surface Irregularity: 10 µm, corresponding to λ/20 at 1.5 THz