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Improved laser Sensing in multiple scattering media using polarization

Type of activity
Competitive project
Funding entity
Funding entity code
163.350,00 €
Start date
End date
Fluidics, Laser Sensing, Lidar Imagers, OFI, Optical Engineering, Optical Metrology, Photonics, Polarization, Scattering, cámaras lidar, dispersión, fluídica, fotónica, ingeniería óptica, metrología óptica, sensores láser
Laser sensing in its many approaches is a key technology in multiple future applications, e.g. enabling the ubiquity of information
generation expected for the Internet of Things. Most laser sensing techniques, however, become limited when multiple scattering media is
present. There the laser beam loses partially its coherence, is depolarized, or becomes spread radiometrically degrading its performance
as sensor. Such problem initially appeared in biophotonics, where the presence of highly scattering tissue complicates the laser sensing
process. In tissue optics, statistical methods based on Monte Carlo (MC) and finite element (FEM) models are used to solve the radiative
transfer equation (RTE) to model light propagation in scattering media. However, interoperable software tools which enable to combine the
FEM and MC approaches, and the effect of macro and microscale events in electromagnetic fields have appeared in the last years, and
may be applied to model scattering. Further, polarization effects in scattering media are already used qualitatively in imaging instruments
(the dermatoscope) or in atmospheric lidar (characterization of clouds). In our past project of the Plan Nacional, we used MC methods to
introduce depth-sectioning features to Optical Feedback Interferometry (OFI) sensors. Within this project, we will extend this know-how
into the detailed solution of the RTE and depolarization events to time dependent signals (pulsed or modulated sources). The goal of the
project is the quantification of depolarization and radiometric data in multiple scattering media to develop new laser sensing strategies, or
to complement existing ones. From the theoretical point of view, novel tools will be used to build models of the interaction of laser light with
multiple scattering media to predict the performance of the sensors of interest. Basic geometric models (flat surfaces and uniform media
with multiple scatterers) will be used as starting point to understand the physics of real-world situations and get acquainted with the novel
tools, and to validate the proposed models. A controlled experimental testbed for multiple scattering media (solids,fluids and gases) will be
built to check the predictions of the models. The findings of the theoretical models will be used to build two proof-of-concept instruments
targetting specific applications. A first one will implement a polarization-enhanced OFI sensor applied to the measurement of changes in
parameters in a flowing fluid, to monitor flow of liquids and gases in multiple scattering media. This will be applied to the analysis of the
state of conservation of blood bags or liquid aliments, such as milk. A second proof-of-concept will focus on the problems of lidar imagers
in multiple scattering media, such as e.g dense fog, dust, smoke or rain. Lidar imagers are key technologies in the new generations of
automated vehicles, and its behavior in harsh atmospheric conditions is a problem currently not solved. Laser pulses in scattering media
are delayed and dispersed, affecting the reliability of the measurements, which may be quantified radiometrically. Besides, polarimetric
measurements may identify the density and type of the scattering element in the environment. The application of the models to lidar
imaging setups will contribute to improve the accuracy of the measurements and to widen the reliability of lidar imagers.