THz Filters Made by Laser Ablation of Stainless Steel and Kapton Film

THz band-pass filters were fabricated by femtosecond-laser ablation of 25-mu m-thick micro-foils of stainless steel and Kapton film, which were subsequently metal coated with a similar to 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-mu m-thick Kapton film performed as a Fabry-Perot etalon with a free spectral range (FSR) of 119 cm(-1), high finesse F-c approximate to 17, and was tuneable over similar to 10 mu m (at similar to 5 THz band) with beta = 30 degrees 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.