14 dicembre 2020

Projects for Master Degree

PolySense Labs offer several Master Thesis Projects within the research topics:


  • Quartz-Enhanced Photoacoustic Spectroscopy

  • Photothermal Spectroscopy

  • Tunable Diode Laser Spectroscopy

  • Optical Gas Sensing

The projects are classified in three types:

  • The Experimental Master’s thesis option requires that the student complete an original research project in the laboratory. This includes the realization of an experimental setup, measurements and data analysis. The students will work with sophisticated laboratory instruments and facilities.
  • A Theoretical Master’s thesis option comes with a focus on a theoretical subject. The empirical study is taken as the topic for the master’s program. The student is required to discuss unresolved aspects with numerical simulations as well to develop novel models.
  • The hybrid Theoretical/Experimental Master’s thesis proposes a good overlap between theory and experiment. It includes numerical simulations supported by an experimental investigation. The experimental part is expected to validate the theoretical model and to gather data for modifying them.

Here you can see the current thesis projects that are available at the Physics Department – PolySense Laboratories for 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





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





Title: Tunable laser absorption spectroscopy exploiting a quartz tuning fork as optical detector

Type of Thesis: 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: Vincenzo Spagnolo/Angelo Sampaolo





Title: Study of acoustic coupling between millimeter-size resonator tubes and a quartz tuning fork

Type of Thesis: Theoretical/Experimental

Description: Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a spectroscopic technique aimed at trace gas detection, exploiting the photoacoustic effect that occurs in an absorbing gas. The core of any QEPAS sensor is a spectrophone, composed by a quartz tuning fork (QTF) and a pair of resonator tubes located on both sides of QTF prongs. Resonator tubes act as an organ pipe acoustic resonator and can enhance the intensity of the acoustic field between the QTF prongs up to 60 times. For a selected QTF, the geometric parameters influencing the spectrophone performance are the internal diameter and the length of the two tubes. The project aims to develop a theoretical model capable of predicting both the optimal internal diameter and length of the tubes of a QEPAS spectrophone as a function of the QTF prongs geometry. The theoretical model will be based on the open-end correction of resonators, the divergence of the sound field exiting one tube, and its acoustic coupling with the other tube. To test and validate the model, a set of QEPAS spectrophones will be realized and positioned in an acoustic detection module for QEPAS sensing of a gas species in the mid-infrared spectral range. The experimental data will be compared with theoretical prediction.

Referents: Vincenzo Spagnolo/Pietro Patimisco





Title: Photoacoustic signal generation via a light pulse train excitation in an unbounded gas medium

Type of Thesis: Theoretical

Description: Photoacoustic Spectroscopy is based on the detection of the acoustic signal generated by the absorption of light in the gas. The simplest model uses a two-level energy scheme based on optical absorption and no-radiative desorption. The deposited heat power density caused by no-radiative relaxation represents the source term of the acoustic wave equation. In quartz-enhanced photoacoustic spectroscopy (QEPAS), the acoustic wave is detected by a spectrophone, composed by a quartz tuning fork acoustically coupled with a pair of acoustic resonators acting as organ pipe. The photoacoustic signal is usually generated by a weak sinusoidal modulation of light intensity, which produces periodic sound due to the periodic localized heating of the gas. If a pulsed laser excitation regime is used, the dynamic is completely different. This project aims to extend the simple two-level model for describing the heat power generation process for pulsed illumination. The model will describe the effects of the duration and the peak intensity of the light pulse on photoacoustic signal generation. It is expected that the light intensity distribution can modify the profile of the heat pulse which in turns affects the shape of the sound pulse. The effect of an excitation by a pulse train on acoustic resonators will be argued.

Referents: Angelo Sampaolo/Marilena Giglio





Title: Quartz-enhanced photoacoustic spectroscopy for methane isotopologues detection

Type of Thesis: Experimental

Description: In the petrochemical industry and oil exploration carbon isotopic compositions of methane and wet gas components are used to investigate the gas origin and its source rock maturity. Both origin and possible generation processes of natural gas can be reflected by isotopic composition of hydrocarbon components. In particular a measurement of the isotopic ratio of carbon and hydrogen of methane helps to identify the thermogenic and biogenic origin of natural gases and isotopic fractionation associated with sinks that can be used to quantify the global methane budget. The project aims to realize a quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor for detection of two well-separated, not overlapping absorption lines of 12CH4 and 13CH4 by using a single laser source. Both 12CH4 and 13CH4 are spherical rotors, that show similar vibrational-rotational line patterns, shifted by 10 cm-1 due to the C mass difference. Attention will be also given regarding the possible large dependence that a ratio in intensity has on the temperature through ground-state energies and broadening coefficients. The sensor capability in measuring variation of the 13CH4/12CH4 abundance ratio will be determined.

Referents: Vincenzo Spagnolo/Marilena Giglio





Title: Quartz-enhanced photoacoustic sensor with wide dynamic range operation from percent to part-per-billion

Type of Thesis: Experimental

Description: Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) is indirect absorption technique where the photo-induced acoustic wave generated in an absorbing medium is detected by a spectrophone, composed by a quartz tuning fork (QTF) and a pair of millimeter-size resonator tubes located on both sides of QTF. The two tubes act as acoustic resonator and amplify the sound wave nearby the QTF. It can be shown that the acoustic wave intensity is proportional to the gas concentration and thus a wide dynamic linear range can be supposed. In practice, the optimization of QEPAS spectrophone for low concentrations detection makes it inevitably unusable for high concentrations, primarily for non-linearity and signal saturation effects. This project aims to design and realize an innovative QEPAS module composed by a bare QTF, for high concentration measurements, and a spectrophone, for low concentrations. Both two QTFs and tubes must be aligned along the same optical axis in order to allow laser beam to pass through without touching any of them.  The QEPAS module will be tested with an absorbing gas varying its concentration from percent to part-per-billion range.

Referents: Angelo Sampaolo/Pietro Patimisco





Title: Development of partial least squares regression tool for complex gas mixtures analysis in quartz-enhanced photoacoustic spectroscopy

Type of Thesis: Theoretical/Experimental


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 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. The ultimate precision and accuracy will be compared with standard MLR approach.

Referents: Angelo Sampaolo/Marilena Giglio





Title: Photothermal Spectroscopy exploiting a Fabry-Pérot interferometer for local temperature changes detection

Type of Thesis: Experimental


The photoacoustic and photothermal effects arise from the absorption of modulated light in a gas sample. If the gas molecules absorb light emitted from a modulated source, modulated gas heating with the same periodicity and intensity proportional to the number of the absorbing molecules will occur. The periodic heat release causes a local change in density, involving the generation of a diffusive thermal localized wave, which decays exponentially from the excitation region and the generation of acoustic modes, which can propagate far from the excitation area. Photothermal Spectroscopy (PTS) detects localized thermal perturbations within a gas sample by probing its refractive index changes. The project aims to use a Fabry-Pérot interferometer to detect the refractive index changes in the gas sample. The refractive index change induces a phase shift in the electromagnetic wave that can be measured by the interferometer. With a selected gas species, a calibration procedure will assess the PTS sensor transfer function, the ultimate detection limit and the normalized noise equivalent absorption, to be compared with state-of-the-art gas sensors.

Note: The Master Thesis Project will be developed within the OPTAPHI European Project (https://www.optaphi.eu/projects/project-1-2/) and it plans to spend a research period at Institute of Chemical Technologies and Analytics in Technical University of Wien (https://www.cta.tuwien.ac.at/division_environmental_analytics_process_analytics_and_sensors/process_analytics/focus_of_research/)

Referents: Vincenzo Spagnolo/Pietro Patimisco




Title: Study of water influence on environmental monitoring of methane by using a quartz-enhanced photoacoustic spectroscopy sensor

Type of Thesis: Experimental


Quartz-enhanced photoacoustic spectroscopy (QEPAS) for methane detection is based on the absorption of modulated laser light by the methane molecules. The energy of the excited roto-vibrational states of CH4 is released via inelastic collisions among the surrounding molecules, generating a pressure wave detected by a spectrophone.  Thus, excited methane molecules relax through different channels via collisions with any kind of molecule composing the mixture. For environmental monitoring of methane, the mixture is mainly composed by nitrogen (~ 78%), oxygen (~ 20%) and water vapor that can vary in a large dynamic range. As a result, a variation of water concentration in air causes a variation in the QEPAS methane signal not related to a change in the CH4 concentration. The project aims to study the influence of water vapor on methane detection by simultaneously measuring both CH4 and H2O concentration levels. Since variations of water vapor in gas matrix produces changes in methane relaxation rate, a theoretical and experimental study of CH4 relaxation in a humidified matrix is mandatory for the realization of a reliable outdoor CH4 QEPAS sensor.

Referents: Vincenzo Spagnolo/Marilena Giglio





Within the European Innovation Action with topic “Advancing photonics technologies and application driven photonics components and the innovation ecosystem” and sub-topic “Smart Photonic Sensing for Environmental Pollution Detection”,

PolySenSe is pleased to inform that soon Master Thesis Projects will be available to be developed within the European Project PASSEPARTOUT “Photonic Accurate and Portable Sensor Systems Exploiting Photo-Acoustic and Photo-Thermal Based Spectroscopy for Real-Time Outdoor Air Pollution Monitoring”.

PASSEPARTOUT aims to develop hyperspectral optical sensors based on Quartz Enhanced Photoacoustic Spectroscopy and Photothermal Interferometry for a wide range of ambient pollutants. PASSEPARTOUT will realize the first 3D mobile optical gas analyzer network capable of operating in an urban area. Innovative and high-performance technologies for high accuracy and flexible environmental air quality monitoring will be built on robust drone-mounted, low-cost vehicle-mounted and stationary sensors. The network will provide real-time information about the concentration of polluting gases (NOx, SO2, NH3, CH4, CO and CO2) and black carbon within urban areas, around landfills and seaports with extremely high precision and good spatial resolution. The collected data will be combined with weather data and analyzed in a Cloud, exploiting machine learning algorithms.