title: Investigation of hollow cylindrical metal terahertz waveguides suitable for cryogenic environments.
abstract: The field of terahertz (THz) waveguides continues to grow rapidly, with many being tailored to suit the specific demands of a particular final application. Here, we explore waveguides capable of enabling efficient and accurate power delivery within cryogenic environments (< 4 K). The performance of extruded hollow cylindrical metal waveguides made of un-annealed and annealed copper, as well as stainless steel, have been investigated for bore diameters between 1.75 - 4.6 mm, and at frequencies of 2.0, 2.85 and 3.4 THz, provided by a suitable selection of THz quantum cascade lasers. The annealed copper resulted in the lowest transmission losses, < 3 dB/m for a 4.6 mm diameter waveguide, along with 90° bending losses as low as ~2 dB for a bend radius of 15.9 mm. The observed trends in losses were subsequently analyzed and related to measured inner surface roughness parameters. These results provide a foundation for the development of a wide array of demanding low-temperature THz applications, and enabling the study of fundamental physics.
authors.forename: R
authors.initials: R
authors.lastname: Wallis
authors.forename: R Degl
authors.initials: RD
authors.lastname: Innocenti
authors.forename: D S
authors.initials: DS
authors.lastname: Jessop
authors.forename: O
authors.initials: O
authors.lastname: Mitrofanov
authors.forename: C M
authors.initials: CM
authors.lastname: Bledt
authors.forename: J E
authors.initials: JE
authors.lastname: Melzer
authors.forename: J A
authors.initials: JA
authors.lastname: Harrington
authors.forename: H E
authors.initials: HE
authors.lastname: Beere
authors.forename: D A
authors.initials: DA
authors.lastname: Ritchie