Suspended particle is the main components of atmospheric aerosols, it is important to determine the composition, content, source, and concentration variation of suspended particles in the atmosphere. In this paper, we propose a new method based on the canonical correlation analysis(CCA) method to analyze the correlation between the polarized data and the concentration of suspended particles in the atmosphere. The new method can analyze very weak correlations between two sets of variables, which are both high-throughput and high-dimensional. Combined with the kernel probability density function, we can find out the elements that are more correlated in the two sets of variables. Firstly, the component of the suspended particles with the highest correlation between multi-angle polarized light data and suspended particles' concentration reference values are presented. Then, the concentration change of suspended particles in the atmosphere is predicted based on the measured polarized light data by the locally weighted linear regression(LWLR) method initially, the consistency of experimental data and predicted data verified the effectiveness of the new method.
Polarization is capable of probing microstructures and has unique sensitivity to fibrous anisotropic structure. Polarimetric imaging has demonstrated promising potential in diverse applications ranging from biomedicine, material science, and atmospheric remote sensing. The polarization properties of samples can be comprehensively described by a Mueller matrix (MM). However, the relationship between individual MM elements and properties of the sample is often not clear. There have been consistent efforts to derive polarization parameters from MM based on certain assumptions for better description of the samples, e.g., MM polar decomposition (MMPD), MM transformation (MMT) and MM differential decomposition. Usually, the MM imaging requires sequential measurements with different polarization states of incident light and the imaging process is time consuming. In addition, for movable samples, we cannot guarantee the consistency during the imaging. This may cause precision issues since the images cannot be well-registered. In this work, we built a statistical translation model to generate polarization parameters from a single Stokes vector which can be obtained by one-shot imaging. This will improve the imaging efficiency, simplify the optical system and avoid introducing errors by the image registration. In the model design, we adopted the generative adversarial network (GAN) where the generator is based on a U-net architecture. We demonstrated the effectiveness of our approach on liver tissue, blood smear and porous anodic alumina (PAA) film, and quantitatively evaluated the results by similarity assessment methods. The model can generate a parameter image within 0.1 second on a desktop computer, which shows the potential to achieve real-time performance.
Polarimetry is sensitive to the microstructures and has its advantages in characterizing the tissue microstructures. Our previous work on dynamic polarization changes with tissue clearing has investigated the tissue variations by using glycerol,saturated sucrose and formamide.In this study, we use a fast Mueller matrix microscope to quantitatively compare the different mechanisms of two clearing agents: glycerol and formamide. We obtain the temporal Mueller matrix images with an interval of 15 seconds and extract the temporal features of polarization parameters. Except the depolarization and linear retardance, we also analyze Mueller matrix transformation (MMT) parameters and rotation invariants derived from Mueller matrices. The former is used to characterize the microscale anisotropy of scattering media, and the latter is suitable for assessing the breaking of symmetries of scattering matrix. These Mueller matrix parameters convey the micro characteristic of biological tissues, and then help to explore and explain the microstructural changes of tissue properties by optical clearing.
A common polarization measurement system consists of a quarter-wave plate and a linear polarizer, and the rotation of the wave plate can provide different phase retardance. However, the rotating phase retarder will introduce some unwanted frequency components in the light intensity signal, which may affect the correct information extraction for dynamic observation of the optical process. In this work, we analyzed the effective working frequency band of the polarization measurement system and pointed out how to judge the reliability of dynamic periodic polarization signals. We present the parameter selection strategy of the cutoff frequency of the filter, sampling frequency and rotation angular velocity for a specific dynamic polarization change of scattered light. Finally, we apply our work in the polarization monitoring of tissue optical clearing and show the improvement of the measurement stability and accuracy.
Nebulization therapy is a common treatment for respiratory diseases. The particle size distribution and physicochemical properties of the atomized droplets of different nebulizers have a great impact on the treatment. Droplets larger than 5 microns and less than 10 microns generally can only reach the upper airway, those with 5-10 microns can reach the nasopharynx, those below 5 microns can reach the bronchi, and those smaller than one micron can enter the alveoli. This study provides a polarization measurement system for atomized droplets. In the experimental device, we used a 532 nm laser as the light source. In the incident module, we used a polarizer and a quarter wave plate to form a polarization generator to generate a specific incident polarization state. In the detection module, we measured the polarization scattering signals at four different angles, namely 30°, 60°, 85° and 115°. When the droplet passes through the scattering region, the trigger channel set in the forward direction of 10° first detects the signal, and then triggers the other four channels to complete the detection of the polarization signal. The liquid medicines we used in the experiment were sterile water, acetylcysteine, budesonide and sodium chloride solution. For different liquid medicines, we compared the nebulization effects of two nebulizers, oxygen-driven nebulizer and compressed air nebulizer. The suspended droplets produced by the nebulizer first pass through a pressure-stabilizing box with a built-in fan to realize the uniform dispersion of the atomized droplets, and then use the sheath flow device to realize single droplet detection according to the principle of hydrodynamic focusing. Experiments show that this method can obtain multidimensional polarization information for each measurement and enables fast real-time detection of the polarization scattering signal of liquid droplets.
Tissue optical clearing techniques have become more and more prominent in biomedical applications, since they can reduce scattering and improve the imaging depth, resolution and contrast. Polarization is sensitive to the microstructure of tissues, when apply the rapid Stokes imaging method to monitor the process of optical tissue clearing, we observe that the polarization parameters oscillate periodically during clearing. A series of experiments have been designed to verify the truth of oscillations, we first eliminate the influence of system noise by measuring air and other polarization optics, the system error is less than 1% and is stable, then we analyze the impacts from optical clearing agents, we take quartz plate, the quartz plate with saturated sucrose solution, the fact is that there are slight fluctuations in polarization parameters but no oscillations. However, when we test the porcine skin which immersed in optical clearing agents, there are significant oscillations which show periodicity in polarization parameter, the oscillation cycle is about 40s and the oscillation amplitudes become smaller with the increase of immersion time. Finally, we imaging the samples which have completed optical clearing and no oscillation is found. By these series experiments, we confirm the truth of oscillations of the polarization parameters during clearing, and we believe these are connected with the mechanisms of the clearing which need further study.
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