Optoacoustic sensors for trace gas sensing
The research aims to develop optical sensor for detection of gas species of interest for industrial, enviromental, biomedical and security applications. Special attention is devoted to the study of gas exhaust produced by diesel engine.
Tuning Fork QEPAS cell
The Polysense (http://polysense.poliba.it) gas sensing group lead by Prof. Spagnolo has demonstrated ability to detect several type of gas species.
The technique used is based on photoacoustic effect and infrared and Thz Quantum Cascade Lasers. The photoacoustic effect is the generation of an acoustic wave in a specially designed gas cell that arises from the selective absorption of modulated light of appropriate wavelength by the target component of a gas mixture. The amplitude of this sound wave is directly proportional to the gas concentration. In standard photoacoustic spectroscopy (PAS) the generated sound detected using a sensitive microphone if the laser beam is modulated in the audio frequency range.
In the last few years in the framework of a collaboration with the Laser Science Group of the Rice University lead by Prof.Frank K. Tittel, and THORLABS GmbH we developed innovative photoacoustic sensors based on the use of tuning forks as acoustic transducer. The basic idea of this approach, called quartz enhanced photoacoustic (QEPAS), is to invert the common PAS approach and accumulate the acoustic energy not in a gas filled cell, but in the resonant transducer. Such an approach removes restrictions imposed on the gas cell by acoustic resonance conditions . The employed tuning forks are typically identical to that used in wristwatches, however recently we designed and realized new QTFs with improved geometry in terms of optoacoustic coupling efficiency .
We achieved several scientific breakthroughs such as the realization of the first mid-IR fiber coupled QEPAS sensor with record sensitivity (few tens of ppt) , the realization of first QEPAS sensor operating in the THz spectral range , the realization of the first intracavity-QEPAS sensors, coupling a QTF in a build-up optical cavity , the realization of the first QEPAS sensor employing QTF overtone flecural modes  .
Using these approaches, we developed gas sensors for different type of gas species: nitric oxide (NO) , Nitrous oxide (N2O) , Sulphur hexafluoride (SF6) [2,7], carbon dioxide (CO2) , hydrazine (N2H4), hydrogen peroxide (H2O2), methane (CH4) , methanol (CH3OH)  and hydrogen sulfide (H2S, in near, mid-IR and THz ranges [5,12]).
These sensors can be used for applications that require fast response time (< 1 s), such as gas leak detection  and breath analysis, but also for environmental monitoring  and industrial process control .
Recently we start to implement the realized custom QTFs in QEPAS sensor and achiving improved sensing performances [1-5, 15] and realize the first simultaneous dual-gas QEPAS sensors 
 H. Zheng, L. Dong, A. Sampaolo, P. Patimisco, W. Ma, L. Zhang, W. Yin,L. Xiao, V. Spagnolo, S. Jia, F.K. Tittel, "Overtone resonance enhanced single-tube on-beam quartz enhanced photoacoustic spectrophone", Applied Physics Letters 109, 111103 (2016).
 A. Sampaolo, P. Patimisco, M. Giglio, L. Chieco, G. Scamarcio, F.K. Tittel, and V. Spagnolo, "Highly sensitive gas leak detector based on a quartz-enhanced photoacoustic SF6 sensor", Optics Express 24, 15872-15881 (2016).
 P. Patimisco, A. Sampaolo, L. Dong, M. Giglio, G. Scamarcio, F. K. Tittel, and V. Spagnolo, "Analysis of the electro-elastic properties of custom quartz tuning forks for optoacoustic gas sensing", Sensors and Actuators B 227, 539-546 (2016).
 A. Sampaolo, P. Patimisco, L. Dong, A. Geras, G. Scamarcio, T. Starecki, F. K. Tittel, and V. Spagnolo, "Quartz-enhanced photoacoustic spectroscopy exploiting tuning fork overtone modes", Applied Physics Letters 107, 231102 (2015).
 V. Spagnolo, P. Patimisco, R. Pennetta, A. Sampaolo, G. Scamarcio, M.S. Vitiello and F.K. Tittel, "THz Quartz-enhanced photoacoustic sensor for H2S trace gas detection", Optics Express 23, pp. 7574-7582 (2015)
 P. Patimisco, G. Scamarcio, F.K. Tittel, V. Spagnolo, “Quartz-Enhanced Photoacoustic Spectroscopy: A Review,” Sensors 14, 6165-6205 (2014).
 V. Spagnolo, P. Patimisco, S. Borri, G. Scamarcio, B.E. Bernacki, and J. Kriesel,” Part-per-trillion level SF6 detection using a quartz enhanced photoacoustic spectroscopy-based sensor with single-mode fiber-coupled quantum cascade laser excitation,” Opt. Lett. 37, 4461–4463 (2012).
 S. Borri, P. Patimisco, A. Sampaolo, M.S. Vitiello, H.E. Beere, D.A. Ritchie, G. Scamarcio and V. Spagnolo, "Terahertz quartz enhanced photo-acoustic sensor", Appl. Phys. Lett. 103, 021105 (2013).
 Borri, S.; Patimisco, P.; Galli, I.; Mazzotti, D.; Giusfredi, G.; Scamarcio, G.; de Natale, P.; Spagnolo, V. Intracavity Quartz-Enhanced Photoacoustic sensor. Appl. Phys. Lett. 104, 091114 (2014).
 L. Dong, V. Spagnolo, R. Lewicki, F.K. Tittel, “Ppb-level detection of nitric oxide using an external cavity quantum cascade laser based QEPAS sensor”, Optics Express, 19, 24037-24045
 M. Jahjah, W. Kiang, N.P. Sanchez, W. REi, P. Patimisco, V. Spagnolo, S.C. Herndon, R.J. Griffin, F.K. Tittel, "Atmospheric CH4 and N2O measurements near Greater Houtson area landfills using QCL-based QEPAS sensor system during DISCOVERY-AQ 2013", Optics Letters 39, 957 (2014).
 M. Siciliani de Cumis, S. Viciani, S. Borri, P. Patimisco, A. Sampaolo, G. Scamarcio, P. De Natale, F. D'Amato, V. Spagnolo, Opt. Express 22, 28222-28231, (2015)
 H. Wu, A. Sampaolo, L. Dong, P. Patimisco, X. Liu, H. Zheng, X. Yin, W. Ma, L. Zhang, W. Yin, V. Spagnolo, S. Jia, and F.K. Tittel, "Quartz enhanced photoacoustic H2S gas sensor based on a fiber-amplifier source and a custom tuning fork with large prong spacing", Appl. Phys. Lett. 107, 111104 (2015).
 P. Patimisco, A. Sampaolo, H. Zheng, L. Dong, F.K. Tittel, V. Spagnolo, "Quartz–enhanced photoacoustic spectrophones exploiting custom tuning forks: a review", Advances in Physics X 2, 169-187 (2016).
 P. Patimisco, A. Sampaolo, L. Dong, F.K. Tittel, V. Spagnolo, “Recent advances in quartz enhanced photoacoustic sensing, Appl. Phys. Rev. 5, 011106 (2018).
 H. Wu, X. Yin, L. Dong, K. Pei, A. Sampaolo, P. Patimisco, H. Zheng, W. Ma, L. Zhang, W. Yin, L. Xiao, V. Spagnolo, S. Jia, and Frank K. Tittel, "Simultaneous dual-gas QEPAS detection based on a fundamental and overtone combined vibration of quartz tuning fork", Applied Physics Letters 110, 121104 (2017).