Widely-Tunable Quantum Cascade-Based Sources for the Development of Optical Gas Sensors
SENSORS(2020)
Abstract
Spectroscopic techniques based on Distributed FeedBack (DFB) Quantum Cascade Lasers (QCL) provide good results for gas detection in the mid-infrared region in terms of sensibility and selectivity. The main limitation is the QCL relatively low tuning range (similar to 10 cm(-1)) that prevents from monitoring complex species with broad absorption spectra in the infrared region or performing multi-gas sensing. To obtain a wider tuning range, the first solution presented in this paper consists of the use of a DFB QCL array. Tuning ranges from 1335 to 1387 cm(-1) and from 2190 to 2220 cm(-1) have been demonstrated. A more common technique that will be presented in a second part is to implement a Fabry-Perot QCL chip in an external-cavity (EC) system so that the laser could be tuned on its whole gain curve. The use of an EC system also allows to perform Intra-Cavity Laser Absorption Spectroscopy, where the gas sample is placed within the laser resonator. Moreover, a technique only using the QCL compliance voltage technique can be used to retrieve the spectrum of the gas inside the cavity, thus no detector outside the cavity is needed. Finally, a specific scheme using an EC coherent QCL array can be developed. All these widely-tunable Quantum Cascade-based sources can be used to demonstrate the development of optical gas sensors.
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Key words
quantum cascade laser,widely tunable laser sources,mid-infrared laser sources,laser spectroscopy,QCL array,external-cavity systems,intra-cavity laser absorption spectroscopy,compliance voltage technique,gas sensors
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