Polarimeter for measuring the properties of birefringent media in reflective mode

The effect of pupil size on the measurement of corneal birefringence properties: preliminary study

We used a partial Mueller matrix polarimeter to measure the corneal anisotropic properties at three pupil sizes (dilated, natural, and constricted). The geometrical parameters of first order isochromes were described by quadrilaterals. These parameters are statistically significantly different between the three pupil sizes. The pupillary size changes do not influence the azimuth angle distribution α. The retardation R and birefringence distributions show asymmetry in the nasal-temporal cross-section. There are differences between pupil sizes for both nasal and temporal parts of the cornea for these distributions. Iridial light scattering and diffraction might be the reason for these differences.

Partial Mueller matrix polarimeter using liquid crystal modulators

A simple partial Mueller polarimeter is described, consisting of two linear polarizers and two liquid crystal variable retarders. The measurement leads to an incomplete Mueller-Scierski matrix, in which the elements from the third row and the third column are simultaneously missing. The proposed procedure for determining information about the birefringent medium from such an incomplete matrix is based on numerical methods and carrying out measurements with the rotated azimuthal sample. Acquired from the obtained results, the missing elements of the Mueller-Scierski matrix are reconstructed. The correctness of the method was verified by numerical simulations and test measurements.

Birefringent properties of the cornea measured by a Mueller type polarimeter in healthy adults and children

Mueller type polarimeter was used for in vivo measurements of the anisotropic parameters (retardation and azimuth angle) of corneas. To determine birefringence, corneal thickness was measured with a Scheimpflug camera (Corvist ST). The retardation distributions in the nasal-temporal cross-section in both children (N=7) and adults (N=38) groups occurred asymmetrical. The asymmetry in birefringence distributions was observed only in adults group. The geometrical analysis of the first order isochromes in both age groups showed the asymmetry of its shapes. The changes of symmetry in birefringent properties with age may have potential relationship with changing corneal biometry.

In vivo measurements of corneal birefringence properties using the one-way reflective Mueller polarimetry

This work presents the results of in vivo measurements of human corneal birefringence properties using the one-way reflective polariscope, in which the same module is used to generate and analyze the light polarization state. Data analysis was performed with the use of Mueller polarimetry techniques. The distribution of the azimuth angle and the phase retardation was determined on the paracentral and limbal areas. The results indicate growth of the phase retardation magnitude and the radial orientation of the azimuth angle in the cornea's peripheral region, which confirms our assumptions and the results presented by other researchers.

Method of signal processing in a time-division LWIR image polarimetric sensor

We report on the method of signal processing in a passive long-wave infrared (LWIR) image polarimetric sensor. The method enables the detection of natural and manmade targets. It includes the error related to the rotation of the polarizing element during an image reading as well as permits the polarimeter operation without a classical phase synchronization loop. In addition, to verify the proposed method, a prototype of a time-division polarimetric system that operates in the 8-12 µm band and is based on an uncooled microbolometric detector array was designed and developed. The entire system enabled us to successfully detect a few types of artificial objects from the distance of several tens of meters. The maximum image refresh rate was 5.45 Hz and could be further increased.