Flexible Terahertz Gas Sensing Platform: Combining Hollow Waveguide Gas Cells with an Opto-Electronic Light Source

We present a robust platform for molecular gas sensing in the terahertz (THz) range. It combines near-infrared electro-optic modulation and photomixing to create a spectrally adaptable terahertz source, with a new generation of substrateintegrated hollow waveguides (iHWGs) providing freedom in the optical absorption path design. Results show low propagation losses qualifying iHWGs for proper THz waveguiding and flexible sensing. The latter is demonstrated by the measurement of various rotational transitions of nitrous oxide (N
2
O). A fast frequency sideband modulation technique leads to reduced measurement times and increased photometric accuracy compared to a standard wavelength tuning method.