Hollow-Core Metallic Waveguide-Based Molecular Sensing in Terahertz to Mid-Infrared Spectral Range

Hollow-core metallic waveguides can simultaneously serve as efficient transmission media in the terahertz (THz) region and gas absorption cells at the mid-infrared (MIR) band. Here, we report a molecular sensing and detection platform in MIR to THz wavelength based on hollow-core metallic waveguides. The inner silver film of such flexible waveguides is fabricated by electroless liquid phase chemical deposition, and low transmission loss of the waveguide is experimentally observed. The MIR absorption spectroscopy of bovine serum albumin is experimentally demonstrated on the waveguides in the region of 2800-1000 cm ^{-{1}} . The output THz beam profiles from the waveguides demonstrate a single-mode spatial intensity distribution under different bias currents of quantum cascade lasers operated at the frequency of 2.58 THz. Sensing of glucose solution with a series of concentrations is presented for the waveguides with 5 cm length by making full use of the hollow-core structure. The atomic force microscopy (AFM) results indicate that the amorphous glucose molecules play a key role in the surface roughness of silver coating and the effect of waveguide length on the intensity of absorption is discussed. Hollow-core metallic waveguides will enable a general approach to detect various biological molecules in both THz and MIR ranges.