We describe a numerical method for obtaining a nondepolarizing estimate from an experimental Mueller matrix, a necessary preliminary step in determining the Jones matrix and the polarization properties of the sample under study. The proposed method, being a variant of the general virtual experiment approach, is based on minimizing the least squares distance between the light intensities virtually generated by the effectively measured Mueller matrix of the sample and by its nondepolarizing estimate, while taking into account the exact phenomenological description of the polarimetric instrument used. It can be applied to complete, as well as to partial (12-element) experimental Mueller matrices. The application of the method is illustrated on experimental examples and its performance is compared to that of alternative approaches.
The complete polarimetric responses of oblique- and square- lattices of metal subwavelength hole arrays that display extraordinary optical transmission were examined. The Mueller scattering matrices were measured at normal and oblique incidence for plane wave illumination using a polarimeter employing four photoelastic modulators. The oblique array has strong natural optical activity combined with asymmetric (non-reciprocal) transmission of circularly polarized light. At oblique incidence the square lattice also shows asymmetric transmission at non-normal incidence, whenever the plane of incidence does not coincide with a mirror line. Symmetry considerations associated with non-reciprocal transmission are emphasized in a comparison with the complete polarimetric response of dissymmetric gold gammadion arrays.
Mueller matrix microscopy is the natural generalization of polarization microscopy. It provides images of the
Mueller matrix of a sample with micrometric resolution. In this work we describe a Mueller matrix microscope
that uses the dual rotating compensator technique to simultaneously determine all the elements of its transmission
or reflection Mueller matrix. The instrument uses two compensators that rotate at different frequencies and
every Mueller matrix element is determined by using a digital frequency demodulation technique that does the
frequency-analysis of the time dependent intensity captured at every pixel of the CCD detector. Transmission
and reflection measurements are illustrated with experimental examples.
Photoelastic modulators (PEMs) are among the most robust and precise polarization modulation devices,
but the high frequency free-running nature of PEMs challenges their incorporation into relatively slow CCD and
CMOS imaging systems. Current methods to make PEMs compatible with imaging suffer from low light throughput
or use high cost intensified CCDs. They are not ideal for some analyses (microscopy, reflectivity, fluorescence,
etc.), and likely cannot be extended to polarimeters with more than two PEMs. We propose to modulate the light
source with a square wave derived from particular linear combinations of the elementary PEM frequencies and
phases. The real-time synthesis of the square waves can be achieved using a field programmable gate array (FPGA).
Here we describe the operating principle.