Probing the suspended particles in natural water is significant for environmental monitoring and ecological research, such as early warning of water blooms and assessment of water quality. The particulate Mueller matrix polarimetry (PMP) based on polarized light scattering is established, which can be used to obtain the physical properties and polarization features of individual suspended particles in water. Previous researchers have measured the bulk Mueller matrix of water, in order to obtain information on suspended particles. However, there are many different suspended particles in the water, and the bulk Mueller matrix of water is difficult to know the properties of each particle and precisely retrieve the specific proportions of target suspended particles in the water. Recently, PMP can individually measure the suspended particles, and unlocks the potential of the Mueller matrix for the recognition and characterization of individual suspended particles in water. Powered by machine learning, many experimental results prove the potential abilities of PMP for the in-situ recognition and concentration proportions monitoring of different suspended particles in water.
The outbreak of red tide seriously affects marine ecology and exploitation of fishery resources, so it is necessary to monitor for suspended particles in seawater. Due to the characteristics of various types and great changes of suspended particles in seawater, a detailed classification method based on big data is needed, and polarized light technology has great potential in this respect. In this study, we have designed a prototype for measuring absorption and scattering properties based on polarized light illumination by adding polarization state generation module and polarization state analysis module on the base of a commercial instrument named AC-S. The prototype can measure the intrinsic optical properties of water for different incident polarized light, including water extinction coefficient c(λ) and absorption coefficient a(λ). In addition, the prototype can also measure the polarization scattering information of suspended particles, which is closely related to the complex refractive index, morphology and microstructure of particles. The polarization properties of water bodies are represented by Stokes vectors. The instrument is illuminated by LED with a central wavelength of 532 nm. During the measurement, a pump drives the sample through the flow tube for detection. The polarization generation module produces a specific incident polarization beam that is directed through an optical window into the flow tube. The light signal, which is absorbed and scattered by the suspended particles in the flow tube, is then received by the polarization analysis module, which completes the measurement of light intensity and polarization. The experimental results show that for the same sample, the inherent optical properties are different under different incident polarization states, which is closely related to the properties of particles in water. We have classified the polarization data of water bodies containing different particles with the help of support vector machine (SVM) algorithm, and all of them have obtained more than 90% classification accuracy.
Significance: Reflection Mueller matrix imaging is suitable for characterizing the microstructure of bulk specimens and probing dynamic processes in living animals, there are always demands for speed and accuracy for such applications to avoid possible artifacts and reveal a sample’s intrinsic properties.Aim: To demonstrate a design of collinear reflection Mueller matrix fast imaging microscope based on dual division of focal plane (DoFP) polarimeters (DoFPs-CRMMM) which has high measurement speed and accuracy.Approach: In DoFPs-CRMMM, to improve the measurement speed, we applied the dual DoFP polarimeters design on the collinear reflection system for the first time to achieve fast imaging in about 2 s. To improve the measurement accuracy, we improved the double-pass eigenvalue calibration method (dp-ECM) by background light correction, and explored the optimization of the set of reference samples.Results: DoFPs-CRMMM was applied to measure the standard polarization samples and monitor the tissue optical clearing process of an artificial layered bulk tissue. Results show that the system has satisfactory performance which can capture the variation of polarization properties during the dynamic process.Conclusions: We present the establishment and demo application of DoFPs-CRMMM. The measurement speed can be further accelerated for potential applications in monitoring dynamic processes or living biomedical systems.
A polarization microscope is a useful tool to reveal the optical anisotropic nature of a specimen and can provide abundant microstructural information about samples. We present a division of focal plane (DoFP) polarimeter-based polarization microscope capable of simultaneously measuring both the Stokes vector and the 3×4 Mueller matrix with an optimal polarization illumination scheme. The Mueller matrix images of unstained human carcinoma tissue slices show that the m24 and m34 elements can provide important information for pathological observations. The characteristic features of the m24 and m34 elements can be enhanced by polarization staining under illumination by a circularly polarized light. Hence, combined with a graphics processing unit acceleration algorithm, the DoFP polarization microscope is capable of real-time polarization imaging for potential quick clinical diagnoses of both standard and frozen slices of human carcinoma tissues.
Polarization has promising potential to retrieve the information of the steady samples, such as tissues. However, for the fast changing sample such as the suspended algae in the water, the kinetics of the particles also influence the scattered polarization. The present paper will show our recent results to extract the information about the kinetics of the suspended cylindrical particles by polarization measurements. The sample is the aqueous suspension of the glass fibers stirred by a magnetic stirrer. We measure the scattered polarization of the fibers by use of a simultaneous polarization measurement system and obtain the time series of two orthogonal polarization components. By use of correlation analysis, we obtain the time parameters from the auto-correlation functions of the polarization components, and observe the changes with the stirring speeds. Results show that these time parameters indicate the immigration of the fibers. After discussion, we find that they may further characterize the kinetics, including the translation and rotation, of the glass fibers in the fluid field.
Light scattering in atmosphere can change optical polarization properties. Analysis and Measurement on interaction of polarized light with atmospheric particulates can provide important information to evaluate the atmospheric composition and conditions. In this paper, we propose a polarization character focusing on the evaluation of soot content in the air, based on our polarized photon scattering simulation program. The simulation results demonstrate how the polarization parameter at a specific scattering angle can identify the soot particles from the other air pollutants. Compared with nonpolarization optical measurement, polarization characterization can enhance the contrast of distinguishing different type particles and also can be applied in a wide particle size range.
Taking accurate measurements of the state of polarization (SOP) is the key for the success of polarization sensitive techniques which can provide rich information on the microstructure of complex scattering media, such as biological tissues. For static or slow varying samples, SOP measurements can be achieved by time-sequential recoding of different polarization components controlled by rotating polarizers and wave plates or temporal modulation devices such as photoelastic modulators or liquid crystal variable retarders. When the sample is moving or changing its status quickly, polarization components recoded at different time may correspond to different SOPs, which can lead to significant errors in the final results. Simultaneous polarization measurements are necessary for probing such dynamic samples. In this paper, using the simultaneously recorded polarization components, we are able to mimic time sequential polarization schemes and evaluate the errors. The results show that the kinetics of the sample will affect the systematic error and an increase in the statistical errors of the measured degree of polarization (DOP). We change the kinetics of samples with different stirring speed, which is indicated by the characteristic time of the auto-correlation function. It is also demonstrated that the simultaneously recorded polarization components reveals additional information on the orientation of fibrous scatterers as well as their translation and rotation kinetics.
We present both the two-dimensional backscattering point-illumination and surface-illumination Mueller matrices for the anisotropic sphere-cylinder scattering media. The experimental results of the microsphere-silk sample show that the Mueller matrix elements of an anisotropic scattering medium are different from those of an isotropic medium. Moreover, both the experiments and Monte Carlo simulations show that the directions of the fibrous scatterers have prominent effects on the Mueller matrix elements. As the fibrous samples rotate, the surface-illumination Mueller matrix measurement results for the m12, m21, m13, m31, m22, m23, m32, and m33 elements represent periodical variations. Experiments on skeletal muscle and porcine liver tissue samples confirm that the periodical changes for the surface-illumination Mueller matrix elements are closely related to the well aligned fibrous scatterers. The m22, m23, m32, and m33 elements are powerful tools for quantitative characterization of anisotropic scattering media, including biological tissues.
We present both the two-dimensional backscattering point-illumination and surface-illumination Mueller matrices for the anisotropic sphere-cylinder scattering media. The experimental results of the microsphere-silk sample show that the Mueller matrix elements of an anisotropic scattering medium are different from those of an isotropic medium. Moreover, both the experiments and Monte Carlo simulations show that the directions of the fibrous scatterers have prominent effects on the Mueller matrix elements. As the fibrous samples rotate, the surface-illumination Mueller matrix measurement results for the m12, m21, m13, m31, m22, m23, m32, and m33 elements represent periodical variations. Experiments on skeletal muscle and porcine liver tissue samples confirm that the periodical changes for the surface-illumination Mueller matrix elements are closely related to the well aligned fibrous scatterers. The m22, m23, m32, and m33 elements are powerful tools for quantitative characterization of anisotropic scattering media, including biological tissues.
We have developed a sphere-cylinder birefringence model (SCBM) for anisotropic media. The new model is based on a previously published sphere-cylinder scattering model (SCSM), but the spherical and cylindrical scatterers are embedded in a linearly birefringent medium. A Monte Carlo simulation program for SCBM was also developed by adding a new module to the SCSM program to take into account the effects of birefringence. Simulations of the backscattering Mueller matrix demonstrate that SCBM results in better agreement with experimental results than SCSM and is more suitable to characterize fibrous tissues such as skeletal muscle. Using Monte Carlo simulations, we also examined the characteristics of two-dimensional backscattering Mueller matrix of SCBM and analyzed the influence of linear birefringence.
We acquired polarized reflectance images and Mueller matrix of fresh bovine skeletal muscle. Using
polarization-dependent Monte Carlo simulations based on a sphere-cylinder scattering model, we are able to reproduce
the characteristic features in the experiment results. We also simulate the changes of reflectance profile during stretching
and rigor process, which are regarded as the changes of cylinders' diameter and the cylinder-sphere ratio in our model.
The good agreement between simulations and experiments indicates that the unique pattern of polarized reflectance of
skeletal muscles can also be due to scattering of well aligned fibrous myofibrils rather than coherent diffraction on the
sarcomeres. It provides another angle to understand the interaction between photons and skeletal muscle and a proper
model which characterizes the microstructure of the skeletal muscle. In addition, we give a parameter K calculated from
the M12 element of Mueller matrix. The K-value is sensitive to different parameters in sphere-cylinder scattering model,
therefore it is expected to use for monitoring the states of the skeletal muscle.
Linear differential polarization imaging can improve image quality and characterize the polarization properties of
biological tissues. Degree of polarization imaging (DOPI) yields images based on photons backscattered from the
superficial layers, but shows different measurement results for different incident polarization or sample orientations. The
rotating linear polarization imaging (RLPI) method can characterize the anisotropic properties of tissues, by recording
the linear differential polarization as a function of multi-incident and multi-detection polarization angles and gives a set
of new parameters insensitive to incident polarization angles. The physical meanings, dependence on the incident
polarization angles and the imaging depth of the parameters of the rotating linear polarization imaging will be compared
with those of degree of polarization imaging, which indicate the application potential of the two linear differential
polarization imaging methods in tissue imaging and medical diagnosis.
A novel rotating linear polarization imaging technique is developed to characterize the anisotropic properties of tissues. Differences of orthogonal linear polarization with different incident and detection polarization angles are fitted to an analytical function to retrieve a set of parameters. Experiments with different tissues and Monte Carlo simulations indicate that two of the parameters, G and φ3/2, are correlated to the anisotropic property and the orientation angle of the fibrous structure in the media. The technique can be used for clinical diagnosis.
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