SPATIAL HOMOGENEITIES EVALUATION OF FERROFLUID THIN PLATES POLARIMETRIC CHARACTERISTICS FOR ACTIVE IMAGERY

When a static magnetic field perpendicular to the propagation direction of a laser beam is applied to a magnetic liquid, linear birefringence and dichroism can be present in this material (dichroism appears only for particular preparation conditions of ferrofluid samples). Linear birefringence is used to realize an adjustable wave plate for polarimetric modulation applications in active imagery. A set of linear birefringence measurements are made using a continuous laser source and the results show the possibility for such a material to realize polarimetric modulation, but with inhomogeneities induced by temperature effects. To extend the utilization of such polarimetric property in active imagery, the spatial distribution of this polarimetric characteristic must be homogeneous. A measurement method is developed in the case of an imagery application using a pulsed laser beam; in this case, the temperature effects that could appear with a continuous laser source are removed. The results show the possibility to develop ferrofluids as homogeneous adjustable wave plates for which it is possible to obtain polarimetric modulation for different wavelength.