High finesse optical cavity coupled with a quartz-enhanced photoacoustic spectroscopic sensor

Year: 2015

Authors: Patimisco P., Borri S., Galli I., Mazzotti D., Giusfredi G., Akikusa N., Yamanishi M., Scamarcio G., De Natale P., Spagnolo V.

Autors Affiliation: Istituto Nazionale di Ottica (INO) – CNR, UOS Sesto Fiorentino and European Laboratory for Non-linear Spectroscopy (LENS), via Carrara 1, 50019 Sesto Fiorentino, Italy;
Istituto di Fotonica e Nanotecnologie (IFN) – CNR and Dipartimento Interateneo di Fisica, Università e Politecnico di Bari, via Amendola 176, 70126 Bari, Italy;
Development Bureau Laser Device R&D Group, Hamamatsu Photonics KK, Shizuoka 434-8601, Japan;
Central Research Laboratories, Hamamatsu Photonics KK, Shizuoka 434-8601, Japan.

Abstract: An ultra-sensitive and selective quartz-enhanced photoacoustic spectroscopy (QEPAS) combined with a high-finesse cavity sensor platform is proposed as a novel method for trace gas sensing. We call this technique Intra-cavity QEPAS (I-QEPAS). In the proposed scheme, a single-mode continuous wave quantum cascade laser (QCL) is coupled into a bow-tie optical cavity. The cavity is locked to the QCL emission frequency by means of a feedback-locking loop that acts directly on a piezoelectric actuator mounted behind one of the cavity mirrors. A power enhancement factor of similar to 240 was achieved, corresponding to an intracavity power of similar to 0.72 W. CO2 was selected as the target gas to validate our sensor. For the P(42) CO2 absorption line, located at 2311.105 cm(-1), a minimum detection limit of 300 parts per trillion by volume at a total gas pressure of 50 mbar was achieved with a 20 s integration time. This corresponds to a normalized noise equivalent absorption of 3.2 x 10(-10) W cm(-1) Hz(-1/2), comparable with the best results reported for the QEPAS technique on much faster relaxing gases. A comparison with standard QEPAS performed under the same experimental conditions confirms that the I-QEPAS sensitivity scales with the intracavity laser power enhancement factor.

Journal/Review: ANALYST

Volume: 140 (3)      Pages from: 736  to: 743

More Information: This work was financially supported by the Italian Ministry for University and Research through the Italian national projects PON01_02238, PON02_00675, PON02_00576 and the project \”Active Ageing@home\”; within the National Technological Cluster (CTN) venture in the PON-2013-FESR framework.
DOI: 10.1039/c4an01158a

Citations: 34
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