Simultaneous mid-infrared quantum cascade laser dual comb Faraday rotation and absorption spectroscopy

Abstract Faraday rotation spectroscopy and absorption spectroscopy are performed simultaneously in a dual comb spectroscopy arrangement with quantum cascade laser combs operating at ∼8 μ m. The system uses free-running laser combs that provide ∼70 cm −1 spectral coverage and ∼2 MHz spectral resolution. Detection of NO 2 in an equilibrium mixture with N 2 O 4 and N 2 O is used to demonstrate selective measurements of paramagnetic NO 2 in the presence of spectrally interfering diamagnetic species.