Mueller Matrix Polarimeter Research Articles

Evaluating backscattering polarized light imaging microstructural mapping capabilities through neural tissue and analogous phantom imaging.

Knowledge of fiber microstructure and orientation in the brain is critical for many applications. Polarized light imaging (PLI) has been shown to have potential for better understanding neural fiber microstructure and directionality due to the anisotropy in myelin sheaths surrounding nerve fibers of the brain. Continuing to advance backscattering based PLI systems could provide a valuable avenue for in vivo neural imaging. To assess the potential of backscattering PLI systems, the ability to resolve crossing fibers, and the sensitivity to fiber inclination and curvature are considered across different imaging wavelengths. Investigation of these areas of relative uncertainty is undergone through imaging potential phantoms alongside analogous regions of interest in fixed ferret brain samples with a five-wavelength backscattering Mueller matrix polarimeter. Promising phantoms are discovered for which the retardance, diattenuation and depolarization mappings are derived from the Mueller matrix and studied to assess the sensitivity of this polarimeter configuration to fiber orientations and tissue structures. Rich avenues for future study include further classifying this polarimeter's sensitivity to fiber inclination and fiber direction to accurately produce microstructural maps of neural tissue.

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.

Optimal Orientation Angle Configuration of Polarizers Exists in a 3 × 3 Mueller Matrix Polarimeter

A 3 × 3 Mueller matrix polarimeter, as one of the primary polarization measurement tools, has attracted intensive interest in various fields of polarization optics. In this paper, from a novel viewpoint with more mathematical analysis of the basic configuration and the working performance of a 3 × 3 Mueller matrix polarimeter, we systematically study the relationship between Mueller matrix measurement errors with the configuration and characteristics of polarizers in the polarimeter. We figure out that, mathematically, there is an optimal orientation angle configuration (0°, 60°, and 120°) of polarizers, which inherently ensures a minimal relative measurement error in general. Moreover, we interpret the internal source of such a robust error resistance under this optimized configuration mathematically for the first time. Simulation and practical experiments show the effectiveness of our mathematical analyses, and compared to the frequently used orientation angle configuration, the average relative error is reduced by up to 32% under such an optimized configuration.

Scene-adaptive spatially channeled imaging Mueller polarimeter.

A spatially adaptive Mueller matrix imaging polarimeter is described, simulated, and demonstrated with preliminary experiments. The system uses a spatial light modulator (SLM) in the polarization state generator (PSG) to create spatial carriers that controlled by the pattern written to the SLM. The polarization state analyzer (PSA) is a commercial division of focal plane imaging polarimeter. The PSG/PSA pair form a 9-channeled partial Mueller matrix polarimeter that measures a 3 × 3 sub-matrix of the Mueller matrix. We demonstrate that adapting the PSG modulation to the spatial frequency structure of the scene can reduce channel crosstalk and improve reconstruction accuracy. Initial experiments are performed that demonstrate the SLM's ability to produce sufficient modulation diversity to create the desired channel structure. Though there are several experimental challenges to obtain accurate Mueller matrix imagery, we demonstrate a system that adapts to the particular scene spatial frequency structure.

Snapshot imaging Mueller matrix polarimeter using modified Savart polariscopes.

We present a snapshot imaging Mueller matrix polarimeter using modified Savart polariscopes (MSP-SIMMP). The MSP-SIMMP contains both the polarizing optics and the analyzing optics encoding all Mueller matrix components of the sample into the interferogram by the spatial modulation technique. An interference model and the methods of reconstruction and calibration are discussed. To demonstrate the feasibility of the proposed MSP-SIMMP, the numerical simulation and the laboratory experiment of a design example are presented. The remarkable advantage of the MSP-SIMMP is easy to calibrate. Moreover, compared with conventional imaging Mueller matrix polarimeters with rotating parts, the advantage of the proposed instrument is simple, compact, snapshot-enabled, and stationary (no moving parts).

Multi-harmonic reconstruction of photoelastic modulator-based Mueller polarimeters using the complex Q-matrix.

Analysis of data generated by Mueller matrix polarimeters using two photoelastic modulators has been evolving with the improvements in data acquisition and digital signal processing (DSP). Historical processing of the temporal data generated by these devices has involved isolating the frequencies via hardware signal processing (e.g.,lock-in amplifiers) or the numerical computation of Fourier integrals of recorded temporal data. Both avenues have their advantages, but the DSP aspects of the latter provide greater flexibility in choice of harmonics for processing. While conventional processing uses one harmonic for each desired Mueller matrix element, recent work has demonstrated that theoretical improvements are possible by coherently combining the information in multiple harmonic channels for each element. We demonstrate some recent progress in DSP that enables these polarimeters' data to be more fully exploited by addressing two key issues in the Fourier domain: spectral leakage and phase recovery. Adequately addressing these issues enables numerical analysis of the temporal data in the complex Fourier domain and delivers Mueller matrix results in which spectral phase information is used to recover the matrix elements and determine their signs automatically. We explore the application of this complex analysis and how the precision and accuracy of the results are affected by common experimental and DSP limitations compared to the usual magnitude-only analysis in the Fourier domain. The multi-harmonic method can provide a theoretical factor of 1.3-1.7 improvement in instrumental precision, and our experimental results approach that theoretical range.

Characterization of cervical tissue using Mueller matrix polarimetry.

The cervix is composed of layers of squamous epithelium and connective tissue. The main component of the cervical connective tissue is collagen, which has specific orientations in different parts of the cervix and provides mechanical strength. Cervical pathologies such as cervical intraepithelial neoplasia (CIN), cancer, pregnancy, and spontaneous preterm birth (sPTB) allow for structural remodeling of both squamous epithelium and connective tissue. Mueller matrix (MM) polarimetry is an optical imaging technique that uses polarized light to characterize the morphologic changes in pathological cervix. In this study, advances in MM polarimetry in characterizing cervical tissue and associated pathologies were reviewed. In particular, the basic structure of the MM polarimeter is described. The interaction of polarized light with cervical tissue in terms of polarimetric parameters such as depolarization and birefringence is discussed. The assessment of cervical pathologies including CIN, cancer, pregnancy, and sPTB with MM polarimetry and the underlying reasons that produce the contrast in optical imaging are outlined. The clinical implementation of MM polarimetry, especially the Müller polarimetry colposcope, is also discussed. Finally, the challenges for MM polarimetry in cervical clinics are also speculated.

Self-registration of constant-step rotating Mueller matrix polarimeters.

Time-division framework is commonly used in Mueller matrix polarimeters (MPs), which takes extra numbers of images at the same position in an acquisition sequence. In this Letter, we utilize measurement redundancy to raise a unique loss function which can reflect and evaluate the degree of mis-registration of Mueller matrix (MM) polarimetric images. Further, we demonstrate that the constant-step rotating MPs have a self-registration loss function free from systematic errors. Based on this property, we propose a self-registration framework, which is able to apply efficient sub-pixel registration skipping the calibration procedure of MPs. It is demonstrated that the self-registration framework performs well for tissue MM images. By combining with other powerful vectorized super-resolution methods, the framework proposed in this Letter has the potential to handle more complicated registration problems.

Registration of polarimetric images for in vivo skin diagnostics.

.Significance: Mueller matrix (MM) polarimetry is a promising tool for the detection of skin cancer. Polarimetric in vivo measurements often suffer from misalignment of the polarimetric images due to motion, which can lead to false results.Aim: We aim to provide an easy-to-implement polarimetric image data registration method to ensure proper image alignment.Approach: A feature-based image registration is implemented for an MM polarimeter for phantom and in vivo human skin measurements.Results: We show that the keypoint-based registration of polarimetric images is necessary for in vivo skin polarimetry to ensure reliable results. Further, we deliver an efficient semiautomated method for the registration of polarimetric images.Conclusions: Image registration for in vivo polarimetry of human skin is required for improved diagnostics and can be efficiently enhanced with a keypoint-based approach.

Are Indices of Polarimetric Purity Excellent Metrics for Object Identification in Scattering Media?

Polarization characteristics are significantly crucial for tasks in various fields, including the remote sensing of oceans and atmosphere, as well as the polarization LIDAR and polarimetric imaging in scattering media. Many polarimetric metrics (such as the degree of polarization, polarization angle diattenuation, and depolarization) have been proposed to enrich the characterization and improve the task performance in scattering media; yet, their related efficacy is limited, especially in high turbidity conditions. The indices of polarimetric purity (IPPs), including three different depolarization metrics, have been successfully applied to biomedical diagnosis. However, it is still debatable whether IPPs also are excellent metrics for identifying or distinguishing objects in scattering media. In this work, we seek to provide physical insights into the application of distinguishing and identifying different objects via IPPs. Imaging experiments are devised and performed on different objects, e.g., metals and plastics, under different turbidity levels, demonstrating the superiority of IPPs as excellent metrics for object identification in scattering conditions. The experimental results show that the IPPs images can enhance image contrast and improve discriminability, as well as break the limitation of traditional intensity-model imaging techniques when further combined with dehazing or enhancing algorithms. Importantly, as the used Mueller matrix (MM) and the related IPPs can also be obtained via other types of MM polarimeters (e.g., PolSAR and MM microscopy), the proposed solution and idea have potential for such applications as biomedical imaging, photogrammetry, and remote sensing.

Polarization Aberrations in High-Numerical-Aperture Lens Systems and Their Effects on Vectorial-Information Sensing

The importance of polarization aberrations has been recognized and studied in numerous optical systems and related applications. It is known that polarization aberrations are particularly crucial in certain photogrammetry and microscopy techniques that are related to vectorial information—such as polarization imaging, stimulated emission depletion microscopy, and structured illumination microscopy. Hence, a reduction in polarization aberrations would be beneficial to different types of optical imaging/sensing techniques with enhanced vectorial information. In this work, we first analyzed the intrinsic polarization aberrations induced by a high-NA lens theoretically and experimentally. The aberrations of depolarization, diattenuation, and linear retardance were studied in detail using the Mueller matrix polar-decomposition method. Based on an analysis of the results, we proposed strategies to compensate the polarization aberrations induced by high-NA lenses for hardware-based solutions. The preliminary imaging results obtained using a Mueller matrix polarimeter equipped with multiple coated aspheric lenses for polarization-aberration reduction confirmed that the conclusions and strategies proposed in this study had the potential to provide more precise polarization information of the targets for applications spanning across classical optics, remote sensing, biomedical imaging, photogrammetry, and vectorial optical-information extraction.

Ultrafast Mueller matrix polarimetry with 10 nanosecond temporal resolution based on optical time-stretch.

A fastest full Mueller matrix polarimeter, to the best of our knowledge, based on optical time-stretch has been proposed and demonstrated. Thanks to the time-stretch-based ultrafast spectra detection mechanism, its measurement time could reach 10 ns. Additionally, a novel, to the best of aour knowledge, simpler method to estimate its main systematic error has been proposed and verified. With the proposed method, static measurement of polarizer and wave plate is executed with a maximum coefficient error of below 0.1. Dynamic measurement of a free space electro-optic modulator as fast-changing phase retardation has also been executed to demonstrate the feasibility of the proposed system.

Removing the influence of the angle of incidence in a dual rotating retarder Mueller matrix polarimeter.

Due to the sensitivity of wave plates to the angle of incidence (AOI) of light, the accuracy of a dual rotating retarder Mueller matrix polarimeter is also influenced by the AOI. Unlike other conventional systematic errors, the phase retardance error of wave plates caused by AOI is a periodic perturbation rather than a constant. We propose a new method to eliminate the influence of AOI based on a numerical calibration method. To verify the reliability of the proposed calibration method, we measured various types of samples in a transmission Mueller matrix measuring system, such as air, dichroic samples, and birefringent samples, with different AOI conditions. It is demonstrated that the new calibration method can effectively eliminate the influence of AOI. After calibration, the maximum measurement error can be reduced to less than 0.02.

Dual-rotator mueller matrix polarimeter for high-accuracy and high-precision measurements of glucose concentration

A Mueller matrix polarimeter incorporating two rotating retarders is proposed for determining the glucose concentration in aqueous solutions. In the proposed system, the accuracy and precision of the Mueller matrix measurements are enhanced through an effective compensation of both the systematic errors in the polarimeter and the environmental errors. Moreover, the synchronization of the two retarders is effectively controlled through the use of a simple discontinuous rotation strategy. The validity of the proposed compensation method is demonstrated numerically and experimentally using an air sample for illustration purposes. It is shown that the maximum error and maximum standard deviation of the measured Mueller matrix elements are ±0.0102 and ±0.0008, respectively. In addition, the response time is just 1 min. In experimental trials performed in the transmission mode using aqueous glucose samples, the maximum standard deviation of the optical rotation angle is found to be just 0.0388 degrees with a path length of 40 mm. Moreover, the extracted rotation angle varies linearly (R2 = 0.9176) with the glucose concentration over the concentration range of 100–500 mg/dL. Hence, the feasibility of the calibrated Mueller matrix polarimeter for glucose determination applications is confirmed.

A scattering similarity based calculation model for oil film identification

To identify oil spill at sea, a method of characterizing the scattering of the detected oil spill target is proposed, based on its polarization characteristics. Due to the unique feature that Mueller matrix is able to comprehensively describe polarization characteristics and has a close relation to the target itself, we propose to use a Mueller matrix polarimeter to calculate Mueller matrix. Combined with the conditions for physical realizability, the Mueller matrix is filtered to achieve a higher level of accuracy. Based on Pauli basis decomposition, the scattering similarity parameters (SSP) between the target and the typical scattering are studied. The formulas of SSP expressed by amplitude ratio and phase retardation in Fresnel reflection are derived, which help us discover the relationship among SSPs. A new concept of scattering similarity parameter difference (SSPD) is proposed and the relationship between SSPD and degree and polarization (DOP) is derived. The difference of SSPD curves between water and oil film is used to distinguish them, which can effectively detect oil spill.

CD Imaging at High Spatial Resolution at Diamond B23 Beamline: Evolution and Applications.

Circular Dichroism imaging in the 190–650 nm spectral region pionered at Diamond Light Source B23 beamline, has been made possible by the highly collimated microbeam generated at the beamline and has been used to study the homogeneity of the supramolecular structures of thin films of chiral materials deposited on fused quartz substrates. This facility has been expanded with the installation of a Mueller Matrix Polarimeter, MMP, coupled to the beamlight, of which a preliminary data will be discussed. In the solid state, the measurement of CD related to the supramolecular structure is hampered by the presence of circular birefringence, linear dichroism, and linear birefringence that can only be evaluated using the MMP technique. The ability to characterize the chiroptical property of thin chiral films prepared under a variety of conditions and protocols such as drop cast, spin coating, spray at different temperatures and concentrations will enable the determination of the critical parameters for reproducible, uniform and homogeneous specimen preparation, which is the sine qua non for any commercial application. This is of particular importance for optoelectronic materials, but it can also be extended to a broad variety of materials with applications from biosensors to biological tissues.

Validity of the product rule and its impact on the accuracy of a Mueller matrix polarimeter

In this work, we analyze the validity of the product rule and its impact on the accuracy of a Mueller matrix polarimeter. We demonstrate that the validity of the rule is essential to perform accurate measurements. The conditions for this rule to be valid in relation to different depolarization mechanisms are also discussed. The theoretical predictions are then experimentally verified by analyzing appropriately selected samples. Finally, we implement a real Mueller matrix polarimeter to show how its accuracy decreases when the product rule is not valid.

3D Mueller matrix mapping of layered distributions of depolarisation degree for analysis of prostate adenoma and carcinoma diffuse tissues

Prostate cancer is the second most common cancer globally in men, and in some countries is now the most diagnosed form of cancer. It is necessary to differentiate between benign and malignant prostate conditions to give accurate diagnoses. We aim to demonstrate the use of a 3D Mueller matrix method to allow quick and easy clinical differentiation between prostate adenoma and carcinoma tissues with different grades and Gleason scores. Histological sections of benign and malignant prostate tumours, obtained by radical prostatectomy, were investigated. We map the degree of depolarisation in the different prostate tumour tissues using a Mueller matrix polarimeter set-up, based on the superposition of a reference laser beam with the interference pattern of the sample in the image plane. The depolarisation distributions can be directly related to the morphology of the biological tissues. The dependences of the magnitude of the 1st to 4th order statistical moments of the depolarisation distribution are determined, which characterise the distributions of the depolarisation values. To determine the diagnostic potential of the method three groups of histological sections of prostate tumour biopsies were formed. The first group contained 36 adenoma tissue samples, while the second contained 36 carcinoma tissue samples of a high grade (grade 4: poorly differentiated—4 + 4 Gleason score), and the third group contained 36 carcinoma tissue samples of a low grade (grade 1: moderately differentiated—3 + 3 Gleason score). Using the calculated values of the statistical moments, tumour tissues are categorised as either adenoma or carcinoma. A high level (> 90%) accuracy of differentiation between adenoma and carcinoma samples was achieved for each group. Differentiation between the high-grade and low-grade carcinoma samples was achieved with an accuracy of 87.5%. The results demonstrate that Mueller matrix mapping of the depolarisation distribution of prostate tumour tissues can accurately differentiate between adenoma and carcinoma, and between different grades of carcinoma. This represents a first step towards the implementation of 3D Mueller matrix mapping for clinical analysis and diagnosis of prostate tumours.

Mueller Matrix Polarimetric Imaging Analysis of Optical Components for the Generation of Cylindrical Vector Beams

In this work, we performed a Mueller matrix imaging analysis of two commercial optical components usually employed to generate and manipulate vector beams—a radial polarizer and a liquid-crystal q-plate. These two elements generate vector beams by different polarization mechanisms—polarizance and retardance, respectively. The quality of the vector beams relies on the quality of the device that generates them. Therefore, it is of interest to apply the well-established polarimetric imaging techniques to evaluate these optical components by identifying their spatial homogeneity in diattenuation, polarizance, depolarization, and retardance, as well as the spatial variation of the angles of polarizance and retardance vectors. For this purpose, we applied a customized imaging Mueller matrix polarimeter based on liquid-crystal retarders and a polarization camera. Experimental results were compared to the numerical simulations, considering the theoretical Mueller matrix. This kind of polarimetric characterization could be very helpful to the manufacturers and users of these devices.

Spectroscopic Mueller matrix polarimeter based on spectro-temporal modulation.

A spectroscopic Mueller matrix polarimeter based on spectro-temporal modulation with a compact, low-cost, and birefringent crystal-based configuration has been developed. The polarization state generator and polarization state analyzer in the system consists of a polarizer in front of two high-order retarders with equal thickness and a rotating achromatic quarter wave-plate followed by a fixed analyzer, respectively. It can acquire the 16 spectroscopic elements of the Mueller matrix in broadband with a faster measurement speed than that of the conventional spectroscopic Mueller matrix polarimeter based on a dual-rotating retarder. In addition, the spectral polarization modulation provided by the polarization state generator can produce five separate channels in the Fourier domain, which leads to a larger bandwidth of each channel than that of the existing spectral modulated spectroscopic Mueller matrix polarimeters. Experiment on the measurements of an achromatic quarter-wave plate oriented at different azimuths and SiO2 thin films deposited on silicon wafers with different thicknesses are carried out to show the feasibility of the developed spectroscopic Mueller matrix polarimeter.