THESIS PROJECTS COMPLETED AT LABORATORY POLYSENSE IN 2021
Title: Measurement of vibrational-translational relaxation rates of methane isotopes by using quartz-enhanced photoacoustic spectroscopy
Type of Thesis: Theoretical/Experimental
Description: Quartz-enhanced photoacoustic spectroscopy (QEPAS) is an indirect optical absorption technique based on the detection of sound waves generated by absorption of modulated optical radiation from gas target molecules by using a quartz-tuning fork (QTF). A crucial aspect in QEPAS detection is the dependence of the QEPAS signal on the radiation-to-sound conversion efficiency, which affects the acoustic waves generation within the gas. It is mainly determined by the transfer rate of the vibrational energy of excited analytes molecules to kinetic energy (translation) of the surrounding molecules (V-T relaxation). This master thesis project aims at measuring the V-T relaxation rate of methane isothopes in a defined gas matrix, employing custom-made, low frequency QTFs operating at different gas pressures. The dependence of the QEPAS signal as well as the resonance properties on the gas pressure of the QTF must be modelled to retrieve the radiation-to-sound conversion efficiency.
Referents: Marilena Giglio/Vincenzo Spagnolo
COMPLETED by Dr Mariagrazia OLIVIERI on 10/26/2021
Title: Multi-gas detection exploiting a Vernier-effect quantum cascade laser employed as light source in quartz-enhanced photoacoustic spectroscopy
Type of Thesis: Experimental
Description: Quantum cascade lasers (QCLs) are excellent mid-infrared light sources for gas spectroscopy. They offer single-mode, high spectral purity emission with high continuous-wave output power levels in a compact device. However, due to narrow spectral tunability, a single QCL is usually used to target only one gas species or at most two. In this project, multi-gas detection will be accomplished by using a non-commercial Vernier-effect based QCL developed in collaboration with Alpes Laser. The source prototype is characterized by the possibility of a direct temperature tuning over the two distributed Bragg reflectors with an accurate control of the emission wavelength, thus resulting in a wide-tunable source emitting in a single beam. The source was designed to match the absorption features of four gas species in the atmosphere, i.e. water (H2O), carbon monoxide (CO), nitrous oxide (N2O) and carbon dioxide (CO2). The research plan aims to explore the potentiality of the Vernier-QCL as a suitable source for quartz-enhanced photoacoustic spectroscopy for multi-gas detection, including an experimental study of electro-opto-spectral source properties.
Referents: Pietro Patimisco/Marilena Giglio
COMPLETED by Dr Raffaele DE PALO on 07/20/2021
THESIS PROJECTS COMPLETED AT LABORATORY POLYSENSE IN 2022
Title: Multi-wavelength mid-infrared quantum cascade laser integrated photonic circuits
Type of Thesis: Theoretical/Experimental
Description: The work will focus on the development of integrated photonic circuits based on mid-infrared quantum cascade lasers that can provide emission lines for sensing of gases with widely spaced target absorption lines. The student will design the laser active region and waveguide layers to enable low-threshold laser operation at target wavelengths. The student will also analyze and design distributed feedback gratings for single-mode emission at target wavelengths. The student will then fabricate multi-wavelength distributed feedback lasers from the wafers grown in the institute per his design specifications and characterize the devices in continuous-wave operation at room temperature. Finally, the student will theoretically analyze the design of the passive photonic system for coupling laser emission and combining the emission of the lasers to a single output.
Referents: Pietro Patimisco/Mikhail Belkin
COMPLETED by Dr Edoardo DE TOMA on 26/04/2022
Title: Development of partial least squares regression tool for complex gas mixtures analysis in quartz-enhanced photoacoustic spectroscopy
Type of Thesis: Theoretical/Experimental
Description:Multivariate analysis (MVA) is a well-established tool to investigate physical systems made up of several components. Among different MVA methods, partial least squares regression (PLSR) stands out for its ability to deal with correlated and noisy experimental data. In optical gas sensing, measurement of single component concentration in a multi-component mixture is a crucial issue when several absorbing gases can compete one each other. For gas samples containing different absorbers species, spectral features belonging to different gas targets can overlap, requiring appropriate tools to identify and isolate each single component. The project aims to combine the quartz-enhanced photoacoustic spectroscopy (QEPAS) with PLSR to identify gas components in a mixture with strongly overlapping and/or interfering absorption features over the full spectral dynamic range of a laser source. An algorithm based on PLSR will be developed to retrieve absolute concentrations of gas components in the mixture. Then, the algorithm will be tested with a QEPAS sensor for spectroscopic analysis of complex gas mixtures.
Referents: Angelo Sampaolo/Christine Holzl
COMPLETED by Dr Aldo Francesco Pio CANTATORE on 28/09/2022
Title: Study of optical coupling of quantum cascade lasers with hollow-core waveguides for low-loss single-mode output
Type of Thesis: Theoretical/Experimental
Description:Hollow-core waveguides (HCWs) are the best candidate for the transmission of infrared laser radiation, as they offer good flexibility for easy handling and high output beam quality with low propagation loss. The HCWs structure is composed of a hollow glass capillary tube with a metallic/dielectric structure deposited inside the bore. The bore size, typically < 1 mm, determines the overall losses and mode quality of the HCW, whereas the thickness of the dielectric layer determines the spectral response. The single mode propagation and mode filtering capabilities are strongly dependent on the fiber diameter, the laser wavelength, and the coupling conditions. The project aims ay studying the optical coupling between a collimated laser beam and a HCW in the mid-infrared range. The theoretical analysis of optical mode structure in dielectric hollow-core waveguide will be studied in detail. Propagation losses will be analyzed as a function of the laser beam launch conditions into the fiber, and propagation losses predicted by using fundamental waveguide theory.
Referents: Marilena Giglio/Pietro Patimisco
COMPLETED by Dr Riccardo ROMANELLI on 28/09/2022
Title: Dual gas detection exploiting two resonance modes of a quartz tuning fork
Type of Thesis: Experimental
Description:Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) exploits the photoacoustic effect occurring in the modulated light absorption of a gas sample, by employing a quartz tuning fork as a sharply resonant microphone. Based on an indirect absorption, QEPAS sensing does not need any optical detector and the sound wave detection is wavelength independent. This makes QEPAS technique suitable for multi-gas detection. The development of custom QTFs opened the way to exploit QEPAS technique in wavelength-modulation division multiplexing (WMDM) scheme configuration. If the QTF frequency of the in-plane flexural mode is decreased to a few kHz, the frequency of the in-plane first overtone mode, which is ∼6.2 times higher than the fundamental one, becomes accessible for QEPAS operation. This project aims at realizing a simultaneous dual-gas QEPAS detection exploiting a custom QTF and two laser sources operating in the infrared range, used as the excitation sources for the fundamental and the first overtone mode of a bare QTF and simultaneous detection of two gas species.
Referents: Marco Grande/Angelo Sampaolo
COMPLETED by Dr Luigi MELCHIORRE on 13/06/2022
THESIS PROJECTS COMPLETED AT LABORATORY POLYSENSE IN 2023
Title: 3-wavelength source based on beam combining of quantum cascade lasers for selective multi-color laser spectroscopy
Type of Thesis: Experimental
Description:Laser absorption spectroscopy (LAS) is a promising gas sensing technique capable of providing high-bandwidth, species-specific sensing, and highly quantitative measurements. Usually, single mode distributed feedback (DFB) diode lasers are employed as a light source to target a single, interference-free absorption line, allowing high selectivity and sensitivity. Apart from specific cases in which two or more absorption lines can be covered within its dynamic current range, DFB lasers do not represent the optimal choice for multi-gas detection. A feasible approach is to employ several laser sources, each one targeting the absorption feature of a single component of the gas mixture. In this case, the light sources are shined in sequence. This project aims at using a multi-wavelength tabletop box including 3 DFB quantum cascade lasers (QCLs). The three-wavelength laser module prototype will contain 3 different commercially available QCL chips with a single collimated beam output produced using dichroitic beam combiners in the module. The three-wavelength laser module will be used as light source in a quartz-enhanced photoacustic spectroscopy sensor to target, in sequence, three different gas species: NO2 at 6.25 um, SO2 at 7.41 um and NH3 at 9.06 um.
Referents: Pietro Patimisco/Andrea Zifarelli
COMPLETED by Dr Nicoletta ARDITO on 27/09/2023
Title: Design and development of lithium niobate microfluidic device for particle manipulation based on fs-laser technology
Type of Thesis: Theoretical/Experimental
Description: Microfluidics has received considerable attention in recent years for particles manipulation. Microfluidic devices realized on piezoelectric crystals offers the possibility for generating electrically induced surface forces (such as surface acoustic waves) for particles sorting. In this thesis work, simulations based on the finite element method (FEM) will be performed for modelling piezoelectric LiNbO3 substrate and optimizing the microfluidic geometries. A preliminary study on the ablation threshold during multi-pulse ultrafast laser ablation of LiNbO3 will be performed. Then, a rapid prototyping method based on fs-laser technology will be adopted to fabricate the microfluidic channels, following the geometries prompted by the numerical modelling.
Referents: Annalisa Volpe/Pietro Patimisco
COMPLETED by Dr Felice SFREGOLA on 27/09/2023
Title: Hydrogen detection based on wavelength modulation and multipass absorption spectroscopy
Type of Thesis: Experimental
Description: The development of new sources of clean and renewable energy have become trategic for most countries. Among them, hydrogen (H2) has the advantages of being clean, green, pollution-free, abundant, and has a high combustion efficiency. Thus, it is considered to have a promising future. However, H2 is a flammable and explosive gas. Therefore, real-time monitoring of H2 concentration in atmosphere is crucial to monitor potential H2 leakage. In recent years, various H2 sensing methods have been continuously emerging: electrochemical sensors, resistance-based sensor and mechanical sensors. Such sensors suffer poor sensitivity and interference from humidity, with the disadvantages of complicated hysteresis, poor repeatability, a non-zero baseline. Optical gas sensors are very promising, but the lack of suitable laser sources and the weak optical absorption of H2 limit the sensitivity of H2 detection. In this project, a tunable diode laser spectroscopy based on the wavelength modulation spectroscopy and a Herriott multipass gas cell with an optical length of 10 meters is proposed as optical sensing technique to target the strongest H2 absorption line located at 2.12 um.
Referents: Angelo Sampaolo/Giansergio Menduni
COMPLETED by Dr Bohdan BASYUK on 20/07/2023
Title: Calibration-free wavelength-modulation spectroscopy with first and second harmonic detection
Type of Thesis: Theoretical
Description: Tunable diode laser-absorption spectroscopy has matured into a robust and convenient means of measuring a wide variety of gas parameters, such as the concentration. Light emitted from tunable diode sources is passed through a gaseous test sample to a detector, and the absorption of light can be related to the gas concentration. In wavelength modulation spectroscopy (WMS), the laser wavelength is modulated sinusoidally and the nonuniform absorption gives rise to components in the detector signal at the harmonics of the original frequency. One of the key drawbacks to applying traditional WMS in practical environments for concentration measurements is the need to calibrate the WMS signals to a known mixture and condition in order to recover the absolute concentration or temperature. For most real-world environments and field-deployable sensors, this is difficult and impractical, and may involve the need for additional equipment and complexity in the sensor system. The aim of this project is to model the transmission coefficient for the laser light through the absorbing medium in terms of a Fourier series to retrieve the WMS-1f and -2f signals, in order to take into account for laser intensity as well as for the inclusion of laser-specific tuning characteristics in the spectral-absorption model.
Referents: Pietro Patimisco
COMPLETED by Dr Tesfay GEBRU on 12/12/2023
THESIS PROJECTS COMPLETED AT LABORATORY POLYSENSE IN 2024
Title: Tunable laser absorption spectroscopy exploiting a quartz tuning fork as optical detector
Type of Thesis: Theoretical/Experimental
Description:A quartz tuning fork (QTF) can be used as light detector exploiting light-induced thermo-elastic effect occurring within the quartz crystal. When the radiation hits the surface of the QTF, photothermal energy is generated because of light absorption by the quartz. Due to the thermo-elastic conversion, elastic deformations put prongs into vibration if the laser is intensity-modulated at one of the QTF resonance frequencies. Mechanical vibrations induce local strain and charges are generated via inverse piezoelectric effect. Thus, the QTF acts as a photodetector. This project aims to realize a gas sensor based on direct absorption spectroscopy in wavelength modulation and a QTF as optical detector. The light transmitted by a gas cell will be focused on the QTF surface where the maximum strain occurs. The photogenerated signal will be studied as a function of operating conditions, namely the laser spot position, the light intensity and the ambient conditions of the QTF. With the best conditions, the sensor transfer function as well as its sensitivity will be determined by a calibration procedure. Then, the ultimate detection limit and the normalized noise equivalent absorption will be evaluated and compared with state-of-the-art gas sensors.
Referents: Andrea Zifarelli/Pietro Patimisco
COMPLETED by Dr Lavinia Anna MONGELLI on 18/04/2024