title: Enhancing the sensitivity of mid-IR quantum cascade laser-based cavity-enhanced absorption spectroscopy using RF current perturbation.
abstract: The sensitivity of mid-IR quantum cascade laser (QCL) off-axis cavity-enhanced absorption spectroscopy (CEAS), often limited by cavity mode structure and diffraction losses, was enhanced by applying a broadband RF noise to the laser current. A pump-probe measurement demonstrated that the addition of bandwidth-limited white noise effectively increased the laser linewidth, thereby reducing mode structure associated with CEAS. The broadband noise source offers a more sensitive, more robust alternative to applying single-frequency noise to the laser. Analysis of CEAS measurements of a CO(2) absorption feature at 1890  cm(-1) averaged over 100 ms yielded a minimum detectable absorption of 5.5×10(-3)  Hz(-1/2) in the presence of broadband RF perturbation, nearly a tenfold improvement over the unperturbed regime. The short acquisition time makes this technique suitable for breath applications requiring breath-by-breath gas concentration information.
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Manfred
authors.forename: James M R
authors.initials: JM
authors.lastname: Kirkbride
authors.forename: Luca
authors.initials: L
authors.lastname: Ciaffoni
authors.forename: Robert
authors.initials: R
authors.lastname: Peverall
authors.forename: Grant A D
authors.initials: GA
authors.lastname: Ritchie
mesh_terms: D065966:Absorption, Physicochemical; D007259:Infrared Rays; D007834:Lasers; D013057:Spectrum Analysis