![]() ![]() 21 proposed a light-induced thermoelastic spectroscopy (LITES) technique for ultra-high sensitive trace gas detection. Thus, an optimum sensing approach would rely on direct absorption, to level off the influence of the gas matrix fluctuations, and on tuning forks as sharply resonant transducers to sense the light intensity variations. The main drawback of the photoacoustic technique, with respect to direct absorption approaches, consists in the fact that the concentration fluctuations of each component in the gas matrix affect the signal arising from the energy relaxation of the excited target molecule 19. The main advantages in implementing QEPAS consist in i) avoiding the use of optical detectors, high compactness and robustness also thanks to the implementation of optical fibers 18. This was possible thanks to the design and realization of custom tuning forks staring from 2015 16, 17. This upgrade of the photoacoustic approach is referred as quartz-enhanced photoacoustic spectroscopy (QEPAS) 14 and since 2002 has demonstrated comparable performances with respect to light absorption spectroscopic approaches relying on multipass cells or optical cavities in several diverse applications 15. In photoacoustic spectroscopy gas detection QTFs have demonstrated great performances acting as piezoelectric sound transducer and replacing the microphones typically employed in PAS. Due to the advantage of a high quality factor Q >10,000 at standard atmospheric pressure, QTFs have proved to be a suitable piezoelectric sensor for atomic force microscopy 7, 8, near-field scanning optical microscope 9, femto-newton force sensing 10, alternating gradient magnetometer 11, magnetic force microscopy 12 and electric field intensity distribution detection 13. To overcome these limitations, a sensitive, compact and low-cost alternative to optical detectors can be represented by the quartz tuning forks (QTFs). Although the above mentioned photodetectors can reach fairly low values of Noise Equivalent Power (NEP), they are characterized by a limited detection bandwidth, a high cost and unreliable performances in harsh environments. bolometers, pyroelectrics and Golay Cells, or photonic detectors, such as photoconductive, photovoltaic and photoemissive devices 4- 6. Commercially available infrared photodetectors can be categorized in thermal detectors, i.e. The Lambert-Beere law rules the light absorption through a gas sample, but the sensor capability in detecting small intensity variation of the transmitted light are substantially determined by the performances of the optical detector employed. Laser absorption spectroscopy is a well-established technique for gas sensing, widely used in environmental monitoring 1, industrial process control 2, diagnostic and biomedical applications 3. The detection limits achieved for the QTF were comparable or even lower down to one order of magnitude with respect to market-available photodetectors. Once identified the most performant resonator, this QTF was implemented in a TDLAS setup and it was combined with laser diodes, interband- and quantum-cascade laser sources emitting from 1 μm to 10.5 μm and targeting different gas spacies. The role of the strain field, accumulation time and working pressure of the quartz resonator in this Light-Induced Thermo-Elastic Spectroscopy (LITES) approach was then evaluated for a whole set of tuning forks. ![]() In this work we present an extensive study on quartz tuning forks (QTFs) used as photodetectors, exploiting the opto-thermo-elastic energy conversion arising from the laser radiation-QTF interaction. The main limitations of tunable diode laser absorption spectroscopy (TDLAS) sensors are represented by the high cost, limited detection bandwidth and low adaptability of photodetectors to work in harsh environments. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |