Terahertz Components Made from Photopolymers: Dielectric Dispersion, Absorption, Geometry and Metrology

Vat photopolymerisation offers the geometric resolution needed for many terahertz quasi-optical components, but common photocurable polymers can exhibit substantial frequency-dependent absorption. The design problem is therefore inseparable from materials metrology. This review connects complex permittivity, refractive index, absorption coefficient and loss tangent to printed geometry, surface quality and measurement method. Published THz time-domain spectroscopy of commercial photopolymers demonstrates wide material-to-material variation, while recent stereolithography studies show that non-polar fillers such as PTFE can reduce absorption without abandoning high-resolution photopolymer processing. The review distinguishes bulk dielectric loss from geometry-induced scattering and reflection, and emphasises that nominal CAD dimensions are insufficient when feature size approaches the wavelength or when shrinkage alters phase delay. A qualification framework is proposed around frequency-resolved material properties, anisotropy, cure/post-cure state, dimensional metrology, surface condition and device-level S-parameter or optical measurements. The engineering objective is not to identify a universally “THz-transparent resin,” but to establish a traceable material-process-frequency window for each component. ER-425.