Freestanding Metal-Mesh Bandpass Filters with Wide Apertures for 2-5 THz

We report on the design and experimental characterization of metal-mesh bandpass filters for the 2 – 5 THz range. These filters are 3 - 5 μm thick freestanding copper films with a periodic array of either diamond-shaped or circular apertures. The simple aperture design enables robust engineering of the bandpass profile, achieving high peak power transmission (> 90 %) with a relatively narrow 3-dB bandwidth (5 - 15 %) across a wide THz frequency range (2 – 5 THz). Based on our numerical simulation results, we provide simple design equations for the filter design and experimentally demonstrate the bandpass filters with diamond-shaped apertures at 1.9 THz, 2.5 THz, and 4.7 THz. The measured transmission properties - center frequency, 3-dB bandwidth, and peak power transmission - agree well with the designed behavior. These filters are compatible with cryogenic operation and offer a cost-effective, high-performance solution for the THz bandpass filters in the 2-5 THz range.