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

Abstract

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.