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Issue 3, 2015
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High finesse optical cavity coupled with a quartz-enhanced photoacoustic spectroscopic sensor

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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 ∼240 was achieved, corresponding to an intracavity power of ∼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 × 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.

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

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Article information


Submitted
27 Jun 2014
Accepted
24 Nov 2014
First published
24 Nov 2014

Analyst, 2015,140, 736-743
Article type
Paper
Author version available

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

P. Patimisco, S. Borri, I. Galli, D. Mazzotti, G. Giusfredi, N. Akikusa, M. Yamanishi, G. Scamarcio, P. De Natale and V. Spagnolo, Analyst, 2015, 140, 736
DOI: 10.1039/C4AN01158A

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