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A new type of optical sensor based on "disorder"

Published in Nature Scientific Reports a research output by the University of Florence
A research team from the Department of Physics and Astronomy has developed and built a new class of optical sensor. The work was coordinated by Stefano Cavalieri and included Emilio Ignesti, Federico Tommasi, Lorenzo Fini and Fabrizio Martelli.  ("A new class of optical sensor: a random laser device" http://www.nature.com/articles/srep35225)

Optical sensors have been the subject of much research and development as means of investigation for a wide variety of materials. In particular, there is much interest in medical diagnostics with the objective of realising systems that reduce invasive to a minimum. The use of random laser is the innovation brought forward by this new type of sensor and it follows on the foundation studies carried out by the same research team.

"The core of the sensor exploits an optical source called random laser - comments Tommasi. Whereas a conventional laser is based on an ordinate active medium contained in an optical cavity usually formed by two mirrors, in a random laser light rays are amplified during their diffusion inside a disordered medium. The diffusion of light is a common optical phenomenon in our everyday life: we only need to take fog as an example. Even biological tissue is a light diffusing material. In order to make a random laser it is necessary to add to the diffusing medium the capacity to amplify light. Previous attempts to create a sensor based on random laser to investigate different materials - adds Tommasi - in particular biological tissues had the drawback of having to insert in the sample an active medium. In our specific case the idea was that of exploiting the sensor so that the active part is physically separated from the sample to analyse so that non invasive research is guaranteed."

"The structure of our sensor - comments Ignesti - is made up of a compact system based on spectral analysis of the random laser emissions from which we can get important information on the sample under investigation. As opposed to passive systems in which it is normally measured the attenuation of an optical signal propagating inside a diffusing medium, with our methodology it is the disorder of the investigated sample as such that allows the amplification of the signal."

In the near future this type of sensor could have applications in the biomedical diagnostic field for in-vivo analyses thanks to the fact that it is only minimally invasive. The researchers have already filed a patent in Italy on behalf of the University of Florence.


27 January 2017