Abstract-High-temperature terahertz intrawaveguide spectroscopy using hollow-core sapphire photonic crystal waveguide

Gleb M. Katyba,  Vladimir N. Kurlov,  Kirill I. Zaytsev,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11065/2526292/High-temperature-terahertz-intrawaveguide-spectroscopy-using-hollow-core-sapphire-photonic/10.1117/12.2526292.short

An ability to use sapphire hollow-core terahertz (THz) waveguides for high-temperature intrawaveguide spectroscopy was studied experimentally. We assembled an experimental setup, which employs the principles of THz intrawaveguide spectroscopy and uses a backward wave oscillator, as a continuous-wave THz source with tunable output frequency, and a Golay cell, as a detector of THz wave intensity. In this setup, the sapphire shaped crystal serves simultaneously as an optical waveguide and as a sample cuvette; the analyte is placed in its central hollow channel. We applied the setup for high-temperature measurements of sodium nitrite (NaNO₂) powder. The observed results demonstrate an ability to sense melting of NaNO₂-powder; justifying a prospect of sapphire waveguides in THz measurements in harsh environments, at high temperatures and pressures.

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Abstract- Design and Characterization Low-Loss Modes in Dielectric-Coated Hollow-Core Waveguides at THz Frequency

Asmar Aming,   B. M. Azizur Rahman

https://ieeexplore.ieee.org/document/8327807/

Designs of hollow-core rectangular, circular, and elliptical waveguides with inner coating of silver and polystyrene (PS) are presented for low-loss terahertz guidance. The PS thickness deposited over silver is optimized to achieve the lowest possible loss for each waveguide at the frequency of 2.5 THz. The mode also tends to be a near-Gaussian in shape, easy for coupling to transmitter and receiver. The lowest propagation loss of 0.13 dB/m is obtained for the mode in a circular waveguide with 2200 μm bore diameter by using a full-vectorial finite element method. It is also shown here that rectangular and elliptical waveguides with a similar core area offer a lower loss value for the Hy21 mode and the LP02 mode, respectively, compared to a circular waveguide. Besides this optimized rectangular waveguide not only shows a minimum loss of 0.09 dB/m but with 4 times higher loss for the other polarization, hence the polarization state of the signal can also be maintained in this waveguide.