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Dipartimento di Fisica - Politecnico di Milano

A portable fiber-laser device for hyperspectral detection of water contaminants to counter water-related terrorism

Description of the activity
The risk of chemical and biological attacks on water systems is of growing concern. It is vital to have an integrated device allowing for fast and extensive monitoring of water network and supplies to reduce vulnerabilities and ultimately the overall risk for population.
The activity is aimed to develop a highly accurate, sensitive, reliable and portable device for in-line detection of water contaminants at trace levels (ppm- and ppb-levels) to guarantee real time monitoring of water safety and integration to any water
infrastructures.  Students will gain expertise in laser physics, spectroscopy, and fiber-format laser sources.



The device developed within this activity is a spectrometer composed of two fiber laser sources, a flow-cell (cuvette) for inline analysis of water, a high-sensitivity photodetector, and a data acquisition board. The laser beam will be passed through the flow-cell filled with water and then focused onto the photodetector for acquisition of a temporal trace (interferogram) through the acquisition board. The interferogram is continuously processed by the acquisition board to detect potential contaminants even at very low concentration.
The spectrometer will be based on the technique called Dual-Comb Coherent Anti-Stokes Raman Scattering (Dual-Comb CARS), using two optical frequency comb (OFC) laser sources to simultaneously probe broad spectral bandwidth at high resolution with a single photodetector in the so-called fingerprint region of molecules, where all the fundamental spectral features and identity of molecules resides.


The activity will be focussed on the detection of cyanide (CN-). More specifically, experiments will be carried out on benzonitrile (C7H5CN), an aromatic organic compound belonging to the class of organic nitriles which do not readily release cyanide ions upon contact with water, and so has low toxicities. The chemical structure of a benzonitrile molecule is shown in Fig. 2, where the cyanide ion can be seen linked to the rest of the molecule while retaining the speificity of its C-N chemical bonding. The prominent peak at 2100 cm-1 in the Raman spectrum of benzonitrile (Fig. 3) is due to the cyanide ion; this peak will be targeted in the dual-comb CARS experiment to reveal the presence of CN traces in water.


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