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THz Filters Made by Laser Ablation of Stainless Steel and Kapton Film
(2022) Han, Molong; Smith, Daniel; Hock Ng, Soon; Vilagosh, Zoltan; Anand, Vijayakumar; Katkus, Tomas; Reklaitis, Ignas; Mu, Haoran; Ryu, Meguya; Morikawa, Junko; Vongsvivut, Jitraporn; Appadoo, Dominique; Juodkazis, Saulius
THz 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.