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Quasi-optics are essential components of terahertz (THz) systems, used to direct and manipulate THz radiation. High-resolution additive manufacturing (AM) techniques, such as vat photopolymerization (VP), enable the low-cost production of complex quasi-optical components with optically smooth surfaces and fine geometric features with dimensions comparable to wavelengths in the THz region. However, VP-produced quasi-optics are often inefficient owing to significant absorption losses, with commercially available photopolymers exhibiting absorption coefficients ranging between 19 – 27 cm –1 at 1 THz. Polytetrafluoroethylene (PTFE) is highly transparent in the THz region, making it a promising filler material to reduce the absorption of photopolymers. However, no previous studies have reported the development of a PTFE composite suitable for processing via VP. In this study, PTFE powder-filled composites were formulated containing PTFE-to-photocurable-resin ratios ranging from 1:10–4:10, corresponding to approximately 9.0 % and 28.5 % by weight, respectively. Samples were manufactured via VP and characterised from 0.5 to 2.0 THz using a THz time-domain spectroscopy system. The results demonstrated a correlation between higher PTFE ratios and a reduction in the absorption coefficient of the samples from 0.5 to 2.0 THz, with the 4:10 sample having an absorption coefficient of 15.3 ± 0.3 cm –1 at 1 THz, 27.8 % lower than that of the neat resin (21.2 ± 0.4 cm –1 ). Additionally, experimental results were shown to agree well with a Maxwell Garnett effective medium approximation-based calculation of the THz optical properties of AM composites. These findings highlight the potential of non-polar polymer fillers to enhance the transparency of photopolymers to THz radiation, potentially supporting the future development of more efficient VP-produced quasi-optical components. • PTFE-filled photopolymer composites were developed for stereolithography systems. • The ∼30 wt% PTFE composite had 27.8 % less absorption at 1 THz than the base resin. • The Maxwell Garnett model matched experimental results with high accuracy. • Non-polar fillers can enhance the THz transparency of photopolymers. • Improves the efficiency of THz optics made via stereolithography.
Phillips et al. (Tue,) studied this question.