Rapid, High-Resolution Trace-Gas Detection in the 7–8 μm Window Using a Multiplexed Quantum Cascade Laser Platform for broadband Sensing Applications

Trace gases and warfare agents, ranging from greenhouse gases like methane to chemical warfare agents like sarin, all possess unique rotational-vibrational fingerprints in the mid-infrared. Their detection is, however, generally hindered by spectral broadening. We describe a high-resolution spectroscopic system to overcome this, covering the significant 7–8 μm spectral window. Our method uses a novel optical set up based on an ultra-widely tunable, multiplexed, continuous-wave quantum cascade laser (QCL) in the 6.88–11.05 μm range. This enables precise targeting of narrow absorption features in the 6.88–7.6 μm region. To achieve the best possible spectral fidelity, the entire equipment is mounted in a custom designed vacuum chamber, eliminating atmospheric background absorption. We present a platform for rapid, high-resolution detection of trace gases and toxic chemical species by precision spectroscopy of their rotational–vibrational transitions in the mid-IR, exploiting the broad tunability of a multiplexed QCL source with combination of a vacuum-isolated environment. Our next step involves designing mid-infrared optical parametric oscillators (OPOs), broadband light sources that generate signal and idler through frequency conversion of a pump laser via nonlinear harmonic generation.