Wednesday, May 9, 2018

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

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 1×104  cm1 is resolvable.
Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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