Snapshot imaging Mueller matrix polarimeter using polarization gratings

Abstract

A snapshot imaging Mueller matrix polarimeter (SIMMP) is theoretically described and empirically demonstrated through simulation. Spatial polarization fringes are localized onto a sample by incorporating polarization gratings (PGs) into a polarization generator module. These fringes modulate the Mueller matrix (MM) components of the sample, which are subsequently isolated with PGs in an analyzer module. The MM components are amplitude modulated onto spatial carrier frequencies which, due to the PGs, maintain high visibility in spectrally broadband illumination. An interference model of the SIMMP is provided, followed by methods of reconstruction and calibration. Lastly, a numerical simulation is used to demonstrate the system's performance in the presence of noise. . A sample's MM is often characterized by time-sequentially changing the polarization state of both the generated and analyzed light using rotating polarization elements. By measuring the intensity under at least 16 unique combinations of generated and analyzed polarization states, the 16 Mueller matrix components can be calculated. However, more measurements are often taken to increase the measured signal-to-noise ratio (SNR) and to optimize the condition number of the system's measurement matrix [4,5]. Since a conventional MM imaging polarimeter uses temporal scanning, intensity variations caused by sample motion must be minimized and often require an image registration scheme [6]. Misregistration is also caused by systematic errors, such as beam-wander from the rotating optical elements. This further increases the complexity in applications where MM imaging polarimetry may be beneficial, especially for in vivo biomedical imaging of scenes with low inherent contrast [6].To eliminate the need for image registration and capture all information in a single measurement (i.e., a snapshot), we propose to combine a technique for channeled Mueller matrix spectropolarimetry [7] with an imaging channeled polarimeter based on polarization gratings (PGs) [8,9]. The layout of the snapshot imaging Mueller matrix polarimeter (SIMMP) is depicted in Fig. 1. It contains both a generator and analyzer module. In the generator module, the source is either spatially incoherent quasi-monochromatic light or spectrally broadband illumination that is collimated by lens f 1 . Transmission of this light through the linear polarizer (P 1 ) makes the incident normalized Stokes vector S in S 0;in x; y∕2 1 0 1 0 T , where the superscript T represents the transpose operation and S 0;in is the total incident power. Transmission of this light through PGs L 1 through L 4 enables the second re-imaging lens (f 2 ) to localize polarization interference fringes [10,11] onto the sample. These fringes modulate the Mueller matrix Mx; y of the sample by two spatial carrier frequencies, the field of which is then collimated by lens f 3 into the analyzing optics. It should be mentioned that Mx; y is assumed to have no wavelength dependence over the spectral range of the measurement. The 4 beams...

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