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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Terahertz Differential Absorption Spectroscopy Using Multi-Furcated Nd:YAG Microchip Laser for Gas Sensing
摘要： We demonstrate a frequency-domain differential absorption spectroscopy in the terahertz (THz) range for gas sensing applications. Our system is based on an injection-seeded THz-wave parametric generator driven by a multi-furcated Nd:YAG microchip laser. Within a single excitation cycle of the laser, the is-TPG generates up to three narrowband THz-wave pulses that are separated from each other in time by 78 μs and in frequency by 11 GHz, which is due to the spatial hole burning effect in the laser cavity. These pulses can be directly used to measure differential absorption signals, and first and second derivative spectra of target gas molecules without measuring reference spectra.
关键词： Nd:YAG microchip laser,gas sensing,differential absorption spectroscopy,THz-wave parametric generator,terahertz
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Miramar Beach, FL, USA (2019.8.19-2019.8.21)] 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Graphene Plasmonic Metasurface for Beam Forming and Gas Sensing
摘要： In this paper, we discuss application of tunable plasmon resonance in graphene for design of multi-purpose beam-forming metasurfaces without changing geometric features and dynamic label-free detection of trace gas at terahertz and mid-infrared frequencies.
关键词： metasurface,gas sensing,tunable,plasmonics
更新于2025-09-16 10:30:52
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Opportunities for photonic integrated circuits in optical gas sensors
摘要： In this article, the potential of photonic integrated circuits (PICs) for modern gas sensing applications is discussed. Optical detection systems can be found at the high-end of the currently available gas detectors, and PIC-based optical spectroscopic devices promise a significant reduction in size and cost. The performance of such devices is reviewed here. This discussion is not limited to one semiconductor platform, but includes several available platforms operating from the visible wavelength range up to the long wavelength infrared. The different platforms are evaluated regarding their capabilities in creating a fully integrated spectroscopic setup, including light source, interaction cell and detection unit. Advanced spectroscopy methods are assessed regarding their PIC compatibility. Based on the comparison of PICs with state-of-the-art bulk optical devices, it can be concluded that they can fill the application space of compact and low cost optical gas sensors.
关键词： gas sensing,indium phosphide,spectroscopy,silicon nitride,photonic integrated circuits,silicon photonics
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE SENSORS - Montreal, QC, Canada (2019.10.27-2019.10.30)] 2019 IEEE SENSORS - Room temperature gas sensors based on laser-annealed ZnO nanostructures for gaseous pollutants detection
摘要： To effectively control gaseous pollutants in air it is mandatory to fabricate reliable and non-expensive monitoring systems that can be easily deployed in urban areas. Sensing devices based on metal oxide nanostructures offer many advantages respect bulk material in detecting multiple hazardous gases such as, high stability, easy surface functionalization and temperature. Among diverse potentially nanostructures, ZnO nanorods can be obtained with low cost and simple process at a low manufacturing temperature opening the possibility to integrate the material with flexible substrates. Additionally, laser annealing procedure can be exploited to improve or tune the morphology and the electrical properties of these materials. In this work, we present a comparison between the performance of as deposited and laser-annealed devices in the detection of NO and NO2. Different sensors characteristics at increasing gas concentrations and dynamic behaviors are shown and discussed evaluating the mechanisms involved in the diverse pollutant detection. As result, the laser-annealed sensor exhibits a sensitivity one-order higher respect to as-grown sample in detecting NO (3.9x10-3 vs 2.7x10-4 [1/ppm]) while for NO2 sensitivity is more than four times higher (3.8x10-3 vs 8.4x10-4 [1/ppm]).
关键词： ZnO nanostructures,gaseous pollutants,room temperature gas sensing,laser annealing
更新于2025-09-16 10:30:52
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Low Energy Pulsed Laser Excitation in UV Enhances the Gas Sensing Capacity of Photoluminescent ZnO Nanohybrids
摘要： Nanohybrids, composed of luminescent zinc oxide (ZnO) nanoparticles dispersed in an inert polydimethylsiloxane (PDMS) matrix, exhibit an excellent ability to follow changes in the type and composition of their surrounding atmosphere. These changes are found to affect the UV photoluminescence (PL) emission of the ZnO-PDMS hybrids measured at room temperature. The influence of irradiation parameters, such as excitation intensity and wavelength, on the response of the ZnO-PDMS sensor against ethanol and oxygen, have been systematically investigated in a comparative study performed employing pulsed excitation at 248 and 355 nm. This study represents the first demonstration that the sensing performance of the PL-based ZnO sensors can be optimized by tuning the excitation parameters and it particularly illustrates that maintaining a low pump energy density is crucial for enhancing the sensitivity of the sensor achieving response values approaching 100%.
关键词： ZnO photoluminescence,ethanol sensing,optical sensor,ZnO nanoparticles,gas sensing,oxygen sensing,ZnO-PDMS nanocomposite
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Extended-Cavity-Quantum-Cascade-Laser-Voltage Intracavity Sensing and Application to Atmospheric Gas Detection
摘要： Laser spectrometers based on Quantum Cascade Lasers (QCL) provide good results for gas sensing in terms of sensibility and selectivity thanks to the characteristics of these sources. Distributed feedback (DFB) configuration provides narrow linewidth that enhances selectivity and their emission in the mid-IR enables to reach the fundamental absorption bands of molecules. The main limitation of these sources is their narrow tuning range (~ 10 cm-1) that prevents from monitoring complex species with broad absorption spectra or realizing multi-gas sensing. To obtain a broader tuning range, one solution consists of QCL DFB array with an arrayed waveguide grating to perform multi-species spectroscopy [1]. A more common technique is to implement the laser in an external cavity system. In GSMA, a commercial Extended-Cavity Quantum Cascade Laser emitting at 10.5 μm has been used to demonstrate photoacoustic gas sensing of heavy molecules such as butane [2] and a lab-made EC-QCL emitting at 7.5 μm was developed for detection of acetone and POCl3 in gas phase [3]. Moreover, the use of an external cavity allows the possibility to perform Intra-Cavity Laser Absorption Spectroscopy (ICLAS). In this method the sample is placed within the laser resonator. Absorption lines of the sample imprint signatures on the spectrum because they influence it during many round trips. The cavity output light is detected to perform spectroscopy. The used QCL developed by mirSense is operated in cw operation at room temperature and emits from 7.4 to 7.8 μm. A technique using the QCL compliance voltage [4] called EVIS (EC-QCL Voltage Intracavity Sensing) is used to retrieve the spectrum of the gas inside the cavity. This way no detector outside the cavity is needed. With gas inside the cavity, losses rise implies a variation of intracavity intensity thus a variation of laser voltage. The large wavenumber sweeping is performed through the grating rotation and the variation of QCL current supply permits to obtain a small wavelength variation. In order to suppress the QCL mode hops influence, a current ramp is applied so that the small wavelength total variation is equal to 1 QCL mod hop. Then QCL voltage is recorded during the current ramp, for all grating positions, and a numerical treatment is performed to improve the signal. Fig. 1 presents a result of this measurement (on the left) compared with the absorption coefficient calculated from the HITRAN database [www.hitran.org] (on the right). This measurement corresponds to a cavity filled with 0.3% of CH4 in air (containing water vapor) at atmospheric pressure. This preliminary result shows a good agreement between the voltage difference and the calculated absorption coefficient. The resolution is estimated to approx. 0.1 cm-1.
关键词： Quantum Cascade Lasers,gas sensing,ICLAS,Intra-Cavity Laser Absorption Spectroscopy,EVIS,EC-QCL Voltage Intracavity Sensing,QCL
更新于2025-09-12 10:27:22
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Terahertz differential absorption spectroscopy using multifurcated subnanosecond microchip laser
摘要： Using spectral multifurcated oscillations in a passively Q-switched microchip laser, we demonstrate frequency-domain differential absorption spectroscopy in the terahertz (THz) frequency region. Within a single quasi-continuous-wave (QCW) excitation, a microchip laser comprising a 7-mm-long Nd:YAG/Cr:YAG composite ceramic provides up to three subnanosecond pulses with a 1064-nm wavelength and a 50-Hz QCW repetition rate. We have observed that the longitudinal mode of double and triple pulses shows stable bifurcation and trifurcation, respectively, induced by a spatial hole burning effect within the laser cavity. These pulses are directly used to drive an injection-seeded THz-wave parametric generator based on a MgO-doped LiNbO3 crystal, thereby generating up to three monochromatic, self-frequency-switched THz-wave pulses separated from each other in frequency by a free spectral range of the laser cavity. By precisely tuning one of the THz-wave frequencies to the gas absorption line, multifurcated THz-wave pulses facilitate the measurement of differential absorption signals every 20 ms without any active frequency modulation. We also show that first- and second-order derivative spectra of gas absorption can be derived from a single frequency sweep of multifurcated pulses without a reference spectrum and computational derivation. Our approach paves the way toward realization of a THz differential absorption lidar for use in fast gas sensing applications.
关键词： differential absorption spectroscopy,terahertz,gas sensing,microchip laser,multifurcated oscillations
更新于2025-09-12 10:27:22
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Controlled joule-heating of suspended glassy carbon wires for localized chemical vapor deposition
摘要： This paper demonstrates for the first time localized chemical vapor deposition of WO3-x on a suspended glassy carbon wire. A process based on the photopatterning of an SU-8 scaffold, the near-field electrospinning of an SU-8 fiber, and their pyrolysis yields a monolithic carbon structure featuring a glassy carbon wire of known diameter and length, suspended on a glassy carbon scaffold. The temperature required for the deposition of WO3-x is generated by passing current through the wire, which causes Joule heating. The deposition starts in the midpoint of the wire, and extends to its ends as the current is increased. The thickness and length of the coating are functions of the imposed current. The evolution of the coating can be monitored in real time by measuring the voltage vs current characteristic of the wire. We have deposited WO3-x coatings with thickness from 71 nm to 1.4 μm, in glassy carbon wires with diameters between 780 nm and 2.95 μm. The coatings are uniform and polycrystalline. The suspended glassy carbon wire is a generic platform for the deposition of many transition metal oxide (TMO) coatings, and opens the door to carbon-TMO structures for applications including catalysis and gas sensing.
关键词： glassy carbon wire,gas sensing,localized chemical vapor deposition,WO3-x,catalysis,Joule heating,transition metal oxide
更新于2025-09-12 10:27:22
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Multi-Purpose Nanovoid Array Plasmonic Sensor Produced by Direct Laser Patterning
摘要： We demonstrate a multi-purpose plasmonic sensor based on a nanovoid array fabricated via inexpensive and highly-reproducible direct femtosecond laser patterning of thin glass-supported Au films. The proposed nanovoid array exhibits near-IR surface plasmon (SP) resonances, which can be excited under normal incidence and optimised for specific applications by tailoring the array periodicity, as well as the nanovoid geometric shape. The fabricated SP sensor offers competitive sensitivity of ≈ 1600 nm/RIU at a figure of merit of 12 in bulk refractive index tests, as well as allows for identification of gases and ultra-thin analyte layers, making the sensor particularly useful for common bioassay experiments. Moreover, isolated nanovoids support strong electromagnetic field enhancement at lattice SP resonance wavelength, allowing for label-free molecular identification via surface-enhanced vibration spectroscopy.
关键词： refractive index and gas sensing,nanovoid arrays,direct femtosecond laser printing,plasmonic sensors
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Ring Interband Cascade Lasers for Environmental Monitoring
摘要： Interband cascade lasers (ICLs) combine the concept of quantum cascade lasers (QCLs) and conventional photodiodes, because they rely on the voltage-efficient in-series connection of multiple active regions as in QCLs as well as the long upper-level recombination lifetimes of photodiodes. The distinctive low power consumption of ICLs makes them especially attractive for mobile applications in the mid-infrared, such as process control, medical applications and spectroscopy. As a first proof of principle we present ICLs fabricated into ring-shaped cavities. A second order distributed feedback (DFB) grating is used for the light outcoupling of our ring ICLs, in vertical direction through the GaSb substrate. The first demonstrated devices with a waveguide width of 10 μm and 400 μm outer diameter show light emission at a wavelength of ~3.7 μm. A pulsed threshold current density <1 kA/cm2 is measured at 20°C. We are currently working on the second generation of such ring ICLs with smaller waveguides for better suppression of higher order lateral modes and larger outer diameter (e.g. 800 μm) for increased optical output power. The newly developed devices are used in a project for trace gas sensing via the principle of photothermal interferometry.
关键词： Interband cascade lasers,trace gas sensing,distributed feedback grating,photothermal interferometry,ring-shaped cavities
更新于2025-09-12 10:27:22