Terahertz vibrational absorption resonances observed using on-chip terahertz circuits

A technique for measuring the vibrational absorption spectra of polycrystalline materials in the terahertz (THz) frequency range is demonstrated. We show that the evanescent electric field extending above lithographically-defined on-chip THz microstrip waveguides can be used to measure absorption resonances, offering higher sensitivity than typical free-space THz time-domain spectroscopy systems permit. The results indicate that on-chip THz systems could find new applications in the analysis, quality control, and identification of polycrystalline materials, such as pharmaceutical compounds.