Mueller polarimetry can be integrated into almost any active imaging or spectroscopic system, and thus can provide polarimetric information at any spatial scale
Basically, to convert an active imaging system or a spectrophotometer into a polarimeter, one has to add a Polarization State Generator (PSG) in the illumination arm, and a Polarization State Analyzer, or PSA, in the detection arm.
All our polarimeters but one make use of liquid crystals (LCs) in their PSGs and PSAs, as these devices fast, easy to use and are very well suited for imaging applications, with wide angular acceptances and minimal aberrations.Imaging polarimeters
We implemented two polarimetric microscopes, one operating in reflection and the other in transmission, with very similar designs.
These instruments can image either the sample itself (real space imaging), or the back focal plane of the objective (conoscopic imaging), In this latter mode the instrument is
equivalent to a 2D goniometric polarimeter, with azimuthal angle spanning the full 0°-360° range, and polar angle 0°- 60°.
This development was an essential part of Sami Ben Hatit’s thesis
, defended in 2009.Schematic representation of the polarimetric Microscope mounted in reflection configuration.Macroscopic Imager Polarimeter
We also developed a macroscopic imaging polarimeter, shown in the figure, to study surgical samples. This instrument, currently operating at the Pathology Department of Institut Mutualiste Montsouris (IMM), has been considerably upgraded by Stanislas Deby during his 3 years “apprentissage”.
The new version, compatible with in vivo examination of uterine cervix (polarimetric colposcope), acquires the 16 raw images in 80 ms, without degrading the measurement accuracy.
Polarimetric imager for macroscopic samples. Left : optical outline of the instrument, Right : photo of the instrument being used to image a colon sample at Pathology department of Institut Mutualiste MontsourisSpectroscopic PolarimetersPolarimeter based on Liquid Crystal Devices
The first Mueller Ellipsometer worked under only one wavelength, but we have recently developed an instrument that works in the whole visible spectral range. Moreover, it has the advantage of a particularly simple conception: The polarization states generator (PSG) and analyzer (PSA) are identical and are composed by a polarizer, a wavelength film and two ferroelectric liquid crystals, oriented and piloted in an optimized way. A CCD camera is also included in order to separate all the spectral components at the same time. More details can be found here
Enric Garcia-Caurel finalized a broad band polarimeter based on rotatable Fresnel rhombs optimized to work in the mid-infrared spectral range between 2 μm and 16 μm. The system is based on achromatic components (grid polarizer and total internal reflection retarder).
The broadband polarimeter can be used to study for instance: doping levels of transparent conducting oxydes, to characterize the optical properties of low-E coatings, or to characterize the chemical composition of thin fimms made of organic molecules.
An advanced version of this instrument, working inside of a vacuum chamber, is going to be integrated in a characterization platform at LTM
(Grenoble) within the Equipex IMPACT.
Functional schema of the broadband Polarimeter. The polarization state generator includes a linear polarizer and a V-shaped achromatic retarder. The same elements can be found in the polarization state analyzer, but in reverse order.
Fiber Based Polarimeter
This instrument is designed to provide pointwise full Mueller matrix measurements via a single mode fiber, with endoscopic applications as the final goal. The project is being run in partnership (ANR IMULE project, nov 2011- oct. 2014) with XLIM (Limoges, Dominique Pagnoux) and Institut Mutualiste Montsouris (Pathology Department, Pierre Validire)