Highly sensitive trace-gas sensors are required in a large range of applications, such as biological, environmental, industrial, and fundamental physics. Photoacoustic spectroscopy has the advantages of compactness and robustness and is characterized by a high degree of flexibility in its configuration, in particular in the selection of the laser source and the transducer. Here we report the experimental characterization of new silicon-based Micro electro-mechanical systems (MEMS) structures to be applied as acoustic-to-voltage transducers in a photo-acoustic-based sensor. In our setup, a 4.5 μm continuous wave quantum cascade laser is used to address strong N2O roto-vibrational transition, and the detection of MEMS oscillations is performed via a balanced interferometric readout.
In the race toward increasingly high-performance trace-molecule sensors, one of the most significant steps forward in the last decade for photoacoustic sensors was their combination with high-finesse optical cavities. Validated with different configurations, this technique demonstrated enhanced sensitivities below the part-per-trillion level (ppt) and record dynamic ranges. Here we present our advanced cantilever-based photoacoustic setup, based on a custom-made silicon cantilever embedded in a doubly-resonant configuration. The combination of a high-quality-factor acoustic resonator and a high-finesse optical cavity allows a final sensitivity enhancement by several orders of magnitude. The sensor was tested on strong N2O transitions around 4.5 μm wavelength with a continuous-wave quantum cascade laser.
We describe the development and the first characterization of a compact trace-gas sensor based on cantilever photoacoustic spectroscopy (CEPAS). The sensor was characterized in order to find the optimal operating parameters (pressure, molecule absorption line and laser modulated frequency). N2O was selected as test molecule. A quality factor of 200 at 10 mbar of cell pressure were determined. Furthermore, the first test measurements showed a minimum detection level of hundreds of ppb with integration time of 30 ms.
Interband and Quantum Cascade Lasers are key sources for MIR molecular sensing. Understanding their noise features and stabilizing their emission is of fundamental importance for applications like precision spectroscopy and metrology. High-Q crystalline Whispering Gallery Mode Resonators have proven to be powerful tools for characterization and stabilization of lasers from the UV to the MIR. Here, we report our recent results on Whispering Gallery Mode Resonators used for frequency characterization, stabilization and linewidth narrowing of Interband and Quantum Cascade Lasers. These results pave the way to new classes of compact MIR sources usable in Space missions, Metrology and Fundamental Physics.
The synthesis of complex nanostructures that combine materials and dimensionality, promises the ability to identify novel designs and architectures with enhanced properties that could be used in new devices. One of the building blocks in nanomaterials are nanowires, which offer several possibilities to get complex nanostructures. We present two kinds of morphologies based on oxide nanowires obtained by a thermal evaporation method. The common feature of both morphologies is a central oxide nanowire and, depending on the growth parameters, nanowires with either nanocrystallites or nano/microrods attached to the central wire are obtained. We have previously reported the fabrication of several single oxide nanowires and in particular, gallium oxide (β-Ga2O3) and zinc germanate oxide (Zn2GeO4) nanowires. Here we report the shape evolution of these nanowires by the suitable modification of the growth parameters. The addition of tin oxide (SnO2) to the precursors and variation of the thermal treatments duration result in the formation of the above-mentioned complex nanostructures. Structural and chemical characterizations were performed by electron microscopy techniques and Raman spectroscopy. The results shed light on the understanding of the driving mechanisms that lead to the formation of complex oxide nanostructures.
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