1 Dipartimento Interateneo di Fisica, Università degli studi di Bari Aldo Moro e Politecnico di Bari, Via Amendola 173, Bari I-70126, Italy2 Department of Electrical and Computer Engineering, Rice University, 6100 Main Street, Houston, TX 77005, USA3 NEST, CNR-Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa I-56127, Italy4 Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, UK
* Author to whom correspondence should be addressed.
Academic Editor: Markus W. Sigrist
Received: 8 February 2016 / Revised: 14 March 2016 / Accepted: 23 March 2016 / Published: 25 March 2016
We report on a quartz-enhanced photoacoustic (QEPAS) sensor for methanol (CH3OH) detection employing a novel quartz tuning fork (QTF), specifically designed to enhance the QEPAS sensing performance in the terahertz (THz) spectral range. A discussion of the QTF properties in terms of resonance frequency, quality factor and acousto-electric transduction efficiency as a function of prong sizes and spacing between the QTF prongs is presented. The QTF was employed in a QEPAS sensor system using a 3.93 THz quantum cascade laser as the excitation source in resonance with a CH3OH rotational absorption line located at 131.054 cm−1. A minimum detection limit of 160 ppb in 30 s integration time, corresponding to a normalized noise equivalent absorption NNEA = 3.75 × 10−11 cm−1W/Hz½, was achieved, representing a nearly one-order-of-magnitude improvement with respect to previous reports.
