Terahertz transmissive quarter-wave plate based on free-standing T-shaped metasurface

Kameshkov et al. (2026) present a terahertz quarter-wave plate built as a free-standing metal metasurface of T-shaped elements. Because the design has no supporting substrate, it avoids the losses and design complications a substrate brings. The plate converts linearly polarised THz radiation into circularly polarised light, and it achieves near-pure circular polarisation at around 0.60 THz. The team characterised the device by THz time-domain spectroscopy from 0.4 to 0.8 THz. A free-standing tungsten wire-grid polariser from Purewave Polarizers was placed in front of the sample at a fixed orientation. It purified the polarisation of the incident beam, so the measured circular polarisation could be attributed to the metasurface alone.