Project 1.1

In this project, we will design and realise compact diode-based QEPAS sensors. The ESR will realise QEPAS sensing modules exploiting novel diode lasers operating in the range 2-2.5 μm The diode lasers will be based on the buried-grating design pioneered by UM in the GaSb technology. In this device, a grating is etched in the waveguide before regrowth of the top-cladding layer. The ESR will be involved in the design, processing and characterisation of the diode lasers. He/she will qualify their operability on the QEPAS set-ups of UM before implementing them in UNIBA sensing systems. The first part of QEPAS related activity will be dedicated to the design and the realisation of the spectrophone to be accommodated into the gas cell. The spectrophone will be composed by a highly innovative custom-made quartz tuning fork (QTF) and a single micro-resonator tube for the sound wave enhancement. Resonance frequencies lower than 32 kHz and high quality factors are required to be able to efficiently detect slow relaxing gases of interest for environmental monitoring, such as methane (CH₄), sulphur dioxide (SO₂) and carbon dioxide (CO₂). The spacing between the two prongs will also play a central role for the final sensor sensitivity. It will be crucial to avoid that a portion of the laser radiation hits the QTF prongs or the micro-resonator tube; otherwise an undesirable non-zero thermo-elastic background noise signal will arise, strongly limiting sensor performance. Thus, the prong spacing will be optimised with respect to the beam profile quality of the developed laser sources. The ESR will also use telecoms lasers as an alternative.

In the second part, we will develop an ultra-compact QEPAS system characterised by a compact size (<1dm³) and low-power consumption (<1 W). Possible gas targets are H₂O, CH₄, CO₂ or O₃. To further increase the ruggedness of the sensors, solid core fibres will be used to optically coupled the laser source with the QEPAS module. One of the optical windows of the ADM will be substituted with a dedicated fibre connector, thereby realising an opticless sensing system. The possibility to work at atmospheric pressure will relax constraints related to gas pressure and flow controllers. The QEPAS ADM will also include the gas inlet and outlet ports. An important part of the project will be the realisation of dedicated software and control electronics to allow autonomous sensor operation. In the last period of the PhD project the realised sensors will be implemented on a drone to test the capability to measure target gas concentrations in air and in real-time.