Depolarization and linear-retardance are the increasingly interesting polarization characteristics for disease diagnosis in clinic and scientific study. They can not only be obtained by Mueller polarimetry normally, but also the Stokes polarimetric imaging. Stokes polarimetric imaging with circularly polarized illumination can provide the main optical properties of tissues with a simpler device in a shorter time, which is much more attractive. Unfortunately, it is difficult to realize the standard circularly polarized illumination actually in experiments. In this paper, we establish a theoretical model to display the relationship between the nonstandard circularly polarized illumination and the accuracy of the measurement results. Compared to the measurement results by Mueller polarimetry, we found that the depolarizations measured are the same but retardances measured are not. And except the influence of the nonstandard circularly polarized illumination, the sample’s optical characteristics also affect the accuracy of the measured retardance. Additionally, we have conducted a comparative experiment between Mueller polarimetry and the Stokes polarimetric imaging to verify. According to the simulation and experiment, we have confirmed that Stokes polarimetric imaging has good performance in measuring most samples and broadband detection, but there is a large error for measuring strongly birefringent samples. Our work quantitatively analyzes the effect of nonstandard circularly polarized illumination on the accuracy of Stokes polarimetric imaging through theoretical derivation for the first time. It enriches the error theory of Stokes polarimetric imaging with circularly polarized illumination and lays a foundation for the improvement and application.
Polarization aberration of projection optics should be measured, controlled and compensated accurately in high numericalaperture image optical system, such as lithography tools for technical node of 14-5 nm. In this paper, we develop a threestep eigenvalue calibration method for polarization aberration measurement in-situ accurately. The whole system and subsystems can be calibrated by using the wide-view-angle quarter-wave plate as one of the reference samples. In addition, an experimental tool is developed to implement the proposed method, which is of significant importance to quantify and improve the properties of the projection optics in lithography.
The resolution and the field-of-view (FOV) of the Mueller microscope are mutually limiting. The increasing magnification exponentially reduces the FOV of microscopic images, which hinders the acquisition of high-resolution Mueller polarization images with large FOV. To address this problem, we propose a scanning splice method for the Mueller microscope. In this method, an optimized image stitching arithmetic, which specially restricts the selection of feature points to ensure the consistency of stitching results of multiple groups of images with the same position and different polarization states, is combined with Mueller polarization detection techniques. In addition, the combination involved can correct the slight jitter error of the system caused by the rotation of the wave plate during Mueller polarization detection. The experiment results demonstrate that this optimized arithmetic is more accurate than the traditional image stitching arithmetic. This research provides the possibility of the development of the whole slide scanning Mueller microscope.
An efficient method that allows spectral calibration for a Stokes polarimeter is presented in this paper. The calibration procedure only uses a reference polarizer to generate an arbitrary linear polarization state. The reference polarizer could also be calibrated while calibrating the Stokes polarimeter. In addition, this method does not involve the small-angle approximation and could avoid the influence of the initial azimuth error of the retarder and the reference polarizer. The experiment was carried out by a spectroscopy and a polarization state analyzer with a rotating wave plate. Experimental results show that the alignments of axis as well as the true retardation at a specific wavelength of the retarder are obtained.
Star test polarimeter can map the polarization state of incident light into an intensity distribution of the detection plane
by placing a space-variant phase retarder (SVPR) in the pupil plane of an optical system, which can achieve fast
acquisition of polarization information of incident light from a single irradiance image. However, subjected by the
system’s alignment and vibration, star test polarimetry need the calibration scheme with high robustness and fast speed.
This paper develops a fast calibration method for Star test polarimetry by measuring three intensity distribution of
orthogonal polarization state and an intensity distribution of left-handed circular polarization. Experimental results show
that the proposed method, combined with normalized least square (NLS), can rapidly calibrate the theoretical model to
accurately measure the polarization state of incident light.
Mueller polarization imaging technology can fully reflect the polarization characteristics of the sample, and can be used
as a method for imaging thin pathological sections of collagen tissue samples. So far, there has been no actual publication
about the detection of transplanted tendons using Mueller matrix imaging technology. In this paper, we apply the Mueller
imaging polarimeter for quantitative detection of rabbit transplanted tendon samples with or without tenocytes. The polar
decomposition parameters of the Mueller matrix of the rabbit tendon tissues are calculated and analyzed. Quantitative
analysis showed that tenocytes caused the decrease of tendon fibers retardance and the increase of standard deviation of
tendon fibers orientation. The experimental results indicate that the retardance and the orientation angle parameters of the
Mueller matrix can be used as quantitative indicators to distinguish rabbit tendon tissues with or without tenocytes and
can reveal the structural characteristics of collagen fiber bundles, which may provide more useful information for the
evaluation of tendon transplantation.
Mueller matrix polarimetry is regarded as a promising technique to comprehensively provide the optical and
microstructural information of tissues. Especially, for pathological diagnosis, the Mueller matrix imaging can be used as a
powerful tool to detect the structural features of abnormal tissue areas on pathological sections. However, a comparative
study of the polarization characteristics of pathological sections with different preparation state is still needed to help
decide which kinds of sections can be effectively used for polarization imaging diagnosis. In this paper, we apply the
Mueller imaging polarimeter for quantitative detection of lung cancer section with the state of undewaxed, dewaxed and H-E
stained at cellular-level respectively. The Mueller matrix polar decomposition parameters of the lung cancer section are
calculated and analyzed. The results indicate that the polarization images of undewaxed section can reflect the
morphology and arrangement of cells. The polarization images of dewaxed is more suitable for the quantitative analysis
of tissue. The polarization images of stained sections are sensitive to the nucleus, which is suitable for the study of the
internal structure of the nucleus.
A channeled spectropolarimeter (CSP) measures spectrally resolved Stokes parameters from a snapshot. However, the reconstruction of Stokes parameters may suffer from noise and systemic errors, lowering the measurement accuracy. To accurately reconstruct Stokes parameters from the experimental data with random noise and residual systematic errors after calibration, we propose an adaptive linear reconstruction with regularizer (ALRR) for CSP. By modeling an l1-norm optimization problem with a 1-norm regularizer consisting of coefficients from the Legendre polynomials basis, together with an adaptive residual threshold considering the systematic errors and noise, Stokes parameters are reconstructed accurately in the presence of noise and systemic errors. Simulation results demonstrate the efficiency and noise-robustness of ALRR with a signal-to-noise ratio of 12 dB, while its self-adaption and accuracy are validated experimentally with a root-mean-square error of < 0.04. The proposed method can have important potential in real-time polarization measurement and processing for modulated polarimeters (i.e., Stokes CSP and Mueller CSP).
Mueller matrix polarization imaging system (MMPIS) is one of the most prospective tools that can provide a highresolution image of polarization properties for samples or systems. The MMPIS is composed of a laser source, polarization state generator (PSG), the sample, polarization state analyzer (PSA), a high-resolution imaging optics, collimating optics, and a CCD camera. Usually, the traditional eigenvalue calibration method (ECM) can be used to calibrate PSG and PSA. However, the imaging and collimating optics are not calibrated in MMPIS. For the highnumerical-aperture imaging system, the imaging and collimating optics can behave as polarization aberration modifying the tested sample’s polarization properties leading to the erroneous judgment which affects the measurement accuracy of the MMPIS. In this paper, the multi-step eigenvalue calibration method (MECM) is explored to calibrate MMPIS. For the MECM applied to calibrate MMPIS, the calibration samples are required to place in different positions of the light path and the ECM is adopted in each position. In this way, the Mueller matrices of PSG and PSA, as well as the Mueller matrices of imaging optics and collimating optics can be obtained through calculation. To evaluate the measurement accuracy of MMPIS, the sample with known polarization properties such as air is measured. The experimental results show that before calibrating the imaging optics and collimating optics the measurement accuracy of MMPIS is 0.0124, while after the measurement accuracy has been improved to 0.0046, which is 62.90% better than before. The MECM can be used for the requirements of high accuracy measurement.
Recently, micro-retarder arrays consisting of patterned liquid crystal polymer or sub-wavelength grating arrays with four different orientations are widely used in division of focal plane(DOFP)Stokes polarimeters. However, due to thermal sensitivity of liquid crystal, real-time calibration of the instruments is required to achieve high-precision detection under non-isothermal conditions. Sub-wavelength grating arrays require sophisticated process, and the study of the influence of grating structure errors on measurement accuracy has been rarely reported. To overcome these limitations, we design a quartz crystal micro-retarder array for DOFP full-Stokes polarimeter, which is composed of identical units with different retardances at four neighboring pixels. The retardance errors introduced by the errors of the substrate thickness (t) and etching depth (d) of the micro-retarder array are analyzed. Furthermore, the relationship among the measurement error, the instrument matrix error of Stokes polarimeter, and polarization state of incident light is established. Hereby, the influence of retardance error on the measurement error corresponding to incident light of different polarization state is analyzed. To reduce the measurement error of Stokes parameters to less than 0.02, the tolerances of t and d should be less than 0.11 μm and 0.09 μm, respectively. The micro-retarder array on quartz crystal is fabricated according to our design and tolerances analysis. Finally, the retardance characteristics of the micro-retarder arrays are characterized by the high accuracy (0.1%) Mueller polarimeter developed in house.
Mueller matrix images(MMI) contain complete polarization information of the media. Mueller matrix decomposition technique, where Mueller matrix polar decomposition(MMPD) and differential decomposition(MMDD) are widely used to decompose MMI, is the key to extract intrinsic polarimetry characteristics of biological tissues. For the decomposition of biological tissue MMI, Satish et al. expressed that MMDD was more suitable for Mueller matrix polarimetric analysis of tissues, while Alali et al. pointed out that MMDD did not offer a great advantage over MMPD. To deal with this problem, we explore how to choose the appropriate decomposition method to accurately extract the polarization information in biological tissues. The experimental results indicate that the linear retardance and optical rotation images obtained from two decomposition methods are different if tissues exhibit significant linear retardance and optical rotation effects simultaneously. According to the physical model of MMDD that the occurrence of polarization effects is orderindependent, MMDD should be applied to MMI of tissues to obtain accurate polarization characteristics in this situation. The biological tissue has low optical rotation in most cases in which the polarimetric images extracted from two decomposition methods are nearly identical, so MMPD and MMDD both can accurately acquire the polarimetric properties of tissues. Meanwhile, comparing the runtime of two decomposition methods to process MMI, we find the processing speed of MMDD is much faster than MMPD. Thus, we summarize that MMDD method is more suitable for the decomposition of the biological tissue MMI, with the advantages of both fast and accurate, which is significant in diagnosis of clinical.
Channeled spectropolarimeter (CSP) measures the spectrally resolved Stokes vector of light from only one single spectral acquisition, which makes it possible to accurately measure dynamic events. The accurate reconstruction of Stokes vector plays a key role in this snapshot technique shifting the main burden of measurement to computational work. The state-ofthe-art algorithm runs the Fourier transform of the channeled spectrum or linear operator model of the system and its pseudo-inverse to reconstruct Stokes vector. However, they may suffer from the lack of signal-to-noise ratio (SNR) then reduce the accuracy of reconstruction. To accurately reconstruct Stokes vector from noise-contaminated data, we propose an effective method called fast compressed channeled spectropolarimeter (FCCSP). In our FCCSP method, the spectrum from spectrometer is seen as the compressive representation of Stokes vector, thus the FCCSP algorithm is to solve an underdetermined problem, where we reconstruct the 4N×1 Stokes vector from only N×1 spectral data acquisition points. Simulation results show that our FCCSP method is more accurate to reconstruct Stokes vector changing gradually with wavelength from noise-contaminated spectrum than Fourier and linear operator methods. Besides, it is faster and more memory and computation-friendly than other compressed CSP method.
Vortex beams have drawn much attention for their distinct properties. When vortex beams propagate along optical axis, they exhibit complicated physical phenomena. Under tight focusing condition, we investigate the defocusing behavior of two superposed vortex beams with opposite but arbitrary topological charge. The results reveal that the intensity distribution of the focus will be petal-shaped if the two topological charges have opposite sign, where the number of intensity lobes in the focal plane is |m− n + 2| . Meanwhile, we find that the focusing intensity of topological charge m = −n would not appear the helical structure when a defocusing occurs. Otherwise, the defocusing would result in the helical structure of intensity when m ≠ −n , and the rotation of helical structure depends on the sign of m + n . Of which clockwise rotation of defocus intensity is related to the negative m + n , and anti-clockwise direction corresponds to the positive m + n . Furthermore, the helical degree of the helical intensity also depends on the magnitude of m + n . The interesting results obtained in this paper will lead to further advances in the field of optical vortices.
Optical vortices have been applied in many fields for their distinct properties. In this paper, we explore the focusing intensity distribution of the radially and azimuthally polarized vortex beam (VB) with varying beam waist parameter. The results reveal that low beam waist parameter is beneficial to form a super-resolution spot. In the condition of the high beam waist parameter, the focusing intensity of radially and azimuthally polarized VB along the longitudinal direction would split to multi-spots. Meanwhile, the focal plane intensity distribution become non-symmetrical as well as expansion when the beam waist parameter increase. Therefore, appropriate beam waist must be chosen for the two kind beam in actually application. Furthermore, we also investigate the focal properties affected with helical phase TC. The results reveal that the focal spot size of radially polarized VB along the longitudinal gradually increases with the order of helical phase. The peak intensity ratio of the longitudinal and transverse field of radially polarized VB holds a maximum value when helical phase order l = 0 and becomes to minimum when l =1 , then gradually increases with the order of helical phase. For the azimuthally polarized VB, when l =1 , the focal intensity would exhibit an excellent small solid spot. The results obtained in this paper are useful for application of radially and azimuthally polarized VB.
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