Abstract-Gas spectroscopy with integrated frequency monitoring through self-mixing in a terahertz quantum-cascade laser

Rabi Chhantyal-Pun, Alexander Valavanis, James T. Keeley, Pierluigi Rubino, Iman Kundu, Yingjun Han, Paul Dean, Lianhe Li, A. Giles Davies, and Edmund H. Linfield

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-10-2225

We demonstrate a gas spectroscopy technique, using self-mixing in a 3.4 terahertz quantum-cascade laser (QCL). All previous QCL spectroscopy techniques have required additional terahertz instrumentation (detectors, mixers, or spectrometers) for system pre-calibration or spectral analysis. By contrast, our system self-calibrates the laser frequency (i.e., with no external instrumentation) to a precision of 630 MHz (0.02%) by analyzing QCL voltage perturbations in response to optical feedback within a 0–800 mm round-trip delay line. We demonstrate methanol spectroscopy by introducing a gas cell into the feedback path and show that a limiting absorption coefficient of ∼1×10−4  cm−1$\sim 1\times {10}^{-4}{\mathrm{cm}}^{-1}$ is resolvable.

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