Han, MolongSmith, DanielHock Ng, SoonVilagosh, ZoltanAnand, VijayakumarKatkus, TomasReklaitis, IgnasMu, HaoranRyu, MeguyaMorikawa, JunkoVongsvivut, JitrapornAppadoo, DominiqueJuodkazis, Saulius2024-03-282024-03-282022https://doi.org/10.3390%2Fmi13081170https://hdl.handle.net/10062/97408THz band-pass filters were fabricated by femtosecond-laser ablation of 25-μm-thick micro-foils of stainless steel and Kapton film, which were subsequently metal coated with a ∼70 nm film, closely matching the skin depth at the used THz spectral window. Their spectral performance was tested in transmission and reflection modes at the Australian Synchrotron’s THz beamline. A 25-μm-thick Kapton film performed as a Fabry–Pérot etalon with a free spectral range (FSR) of 119 cm−1, high finesse Fc≈17, and was tuneable over ∼10μm (at ∼5 THz band) with β=30∘ tilt. The structure of the THz beam focal region as extracted by the first mirror (slit) showed a complex dependence of polarisation, wavelength and position across the beam. This is important for polarisation-sensitive measurements (in both transmission and reflection) and requires normalisation at each orientation of linear polarisation.enAttribution-NonCommercial-NoDerivatives 4.0 InternationalTHz filterssynchrotron infraredanisotropyinfo:eu-repo/semantics/article