Polarimetric Techniques Research Articles

Proposed method for phase retardation measurements using polarimetric techniques

Phase retardance elements such as quarter, half and full waveplates are essential elements in the most of the polarization systems. So, they should be determined precisely. Accurate determination of the phase retardation for these elements are necessary and critical due to its effect on the optical polarization measurements. In this paper we measure two-dimensional phase retardation distribution of half wave plate using four step phase shifting technique for accurate retardance measurements through the whole surface of the wave plate. By using this technique, four images are captured, which are related to different orientation of the azimuth angle of the analyzer, and mathematically analyzed to obtain the phase retardance measurements. The mean value of the phase retardance measurements is 182.57˚ with uncertainty 0.6˚.

Quantitative polarimetry Mueller matrix decomposition approach for diagnosing melanoma and non-melanoma human skin cancer

A simple and effective polarimetric technique is used to discriminate benign lesions from cancerous ones. This method is based on key polarimetric parameters of diattenuation, depolarization, and retardance. Several samples of human skin exhibiting three kinds of cancer as well as benign specimens are examined using a polarimetric technique and results are compared with pathology diagnosis. In this study polarimetric parameters are taken into account as a reliable diagnostic tool to distinguish the cancerous lesions precisely and non-invasively.

Mueller Matrix Polarimetry with Invariant Polarization Pattern Beams

A wide class of nonuniformly totally polarized beams that preserve their transverse polarization pattern during paraxial propagation was studied. Beams of this type are of interest, in particular, in polarimetric techniques that use a single input beam for the determination of the Mueller matrix of a homogeneous sample. In these cases, in fact, it is possible to test the sample response to several polarization states at once. The propagation invariance of the transverse polarization pattern is an interesting feature for beams used in these techniques, because the polarization state of the output beam can be detected at any transverse plane after the sample, without the use of any imaging/magnifying optical system. Furthermore, exploiting the great variety of the beams of this class, the ones that better fit specific experimental constrains can be chosen. In particular, the class also includes beams that present all possible polarization states across their transverse section (the full Poincaré beams (FPB)). The use of the latter has recently been proposed to increase the accuracy of the recovered Mueller matrix elements. Examples of FPBs with propagation-invariant polarization profiles and its use in polarimetry are discussed in detail. The requirement of invariance of the polarization pattern can be limited to the propagation in the far field. In such a case, less restrictive conditions are derived, and a wider class of beams is found.

High-accuracy polarimetric studies on lead germanate single crystals

A high-accuracy polarimetric technique has been used for the characterization of a lead germanate ferroelectric single crystal. The measurement results of the linear and circular birefringence in the [010] direction at a wavelength of 633 nm under the influence of an electric field are presented. Gyration–electric field hysteresis loops at alternative crystal positions in the polarization system have been used to determine the ellipticity of the eigenwaves. A temperature dependence of the gyration tensor component g 11 in the temperature range of 300–450 K was found.

A Validated Non-compendial Method for Determination of Haemodialysis Concentrate’s Contents and its Comparison with Compendial Method: Application of ISO 13958:2014 Standard

Background: Haemodialysis is a process to remove the waste products and excess fluids that build up in the human body when kidneys stop working. Haemodialysis concentrate consists of two parts, acid concentrate (Part A) that contains mineral ions (Na, K, Mg and Ca) and buffering agent acetic acid /citric acid whereas basic concentrate (Part B) comprises sodium bicarbonate alone or in combination with sodium chloride. Aim: Present research aimed to develop and validate a rapid method for the determination of cations and anions in haemodialysis concentrates in solution and powder form by choosing one technique among various suggested in ISO 13958:2014. Methods: The analysis was done by flame emission (flame photometer), atomic absorption spectrometer (AAS), polarimetric and titrimetric techniques. ICH guidelines were followed for method validation by addressing the linearity, accuracy, precision and detection limits (LOD and LOQ). Results and Discussion: The calibration curves were linear for Mg, Ca, K and Na with coefficient of determination (R2) ≥ 0.9978 and regression data indicating the excellent linearity for the selected concentration range for each content. The recovery results were obtained between the ranges 96.9-102.5 % which were good enough to justify the suitability of the proposed method for its intended applications. Statistical analysis indicated that there was no significant difference was observed between the proposed and compendial method at 95 % confidence of interval. Conclusion: The advantage of the proposed method over the compendial method by virtue of its economy and fast with reliable results because more reagents and chemicals are consumed in the compendial method.

Nanopatterned silicon exhibiting partial polarization and chirality

In this paper, we report a study on Si nanopatterns, fabricated as a one-dimensional (1D) Si nanograting with a sub-wavelength (≈200 nm) period. Unpolarized light normally incident on the nanopatterned Si becomes partially polarized and chiral over the entire visible range of 380–740 nm. The degree and the state of polarization of light were measured using polarimetric and ellipsometric techniques. The analysis showed that the reflected light is partially linearly polarized and at the same time a slight chirality (Ŝ3≠0) is observed. Although the polarization of the reflected light is related to the 1D nanograting anisotropy, the chiral transformation of the light could be related to a micrometer-scale chiral substructure on the Si nanopatterned surface. This structure results from the dynamic polarization rotation of the femtosecond laser pulses in their filaments in liquid carbon disulfide near the Si surface during the interferential plasmonic self-organization of the surface nanorelief. These results could underline a key enabling process for the fabrication of polarization-sensitive metasurface-based sensors or devices within the common complementary metal-oxide semiconductor (CMOS)-compatible technology.

Sentinel-1 Polarimetry to Map Apple Orchard Damage after a Storm

Climate change increases extreme whether events such as floods, hailstorms, or storms, which can affect agriculture, causing damages and economic loss within the agro-food sector. Optical remote sensing data have been successfully used in damage detections. Cloud conditions limit their potential, especially while monitoring floods or storms that are usually related to cloudy situations. Conversely, data from the Polarimetric Synthetic Aperture Radar (PolSAR) are operational in all-weather conditions and are sensitive to the geometrical properties of crops. Apple orchards play a key role in the Italian agriculture sector, presenting a cultivation system that is very sensitive to high-wind events. In this work, the H-α-A polarimetric decomposition technique was adopted to map damaged apple orchards with reference to a stormy event that had occurred in the study area (NW Italy) on 12 August 2020. The results showed that damaged orchards have higher H (entropy) and α (alpha angle) values compared with undamaged ones taken as reference (Mann–Whitney one-tailed test U = 14,514, p < 0.001; U = 16604, p < 0.001 for H and α, respectively). By contrast, A (anisotropy) values were significantly lower for damaged orchards (Mann–Whitney one-tailed test U = 8616, p < 0.001). Based on this evidence, the authors generated a map of potentially storm-damaged orchards, assigning a probability value to each of them. This map is intended to support local funding restoration policies by insurance companies and local administrations.

3-D Characterization of Urban Areas Using High-Resolution Polarimetric SAR Tomographic Techniques and a Minimal Number of Acquisitions

This article addresses the 3-D reconstruction of urban areas using a minimal number of Synthetic Aperture Radar (SAR) acquisitions, that is, a set of three images, characterized by intermediate spatial resolution features. In such extreme conditions, conventional tomographic techniques reveal unadapted to refined 3-D imaging purposes, either due to the resulting intrinsic coarse vertical resolution, or to the low dimensionality of the data set, that prevents any separation of complex mixed scattering patterns. A new high-resolution (HR) tomographic estimator, based on a polarimetric signal subspace fitting criterion, is proposed to overcome these limitations, as this method adapts to the statistical behavior of the backscattered signals using robust metrics. The optimization of the corresponding focusing criterion is led through a new polarimetric alternating projection algorithm, characterized by a low computational cost, which may also be used to optimize the polarimetric the deterministic maximum likelihood criterion. The proposed polarimetric signal subspace fitting technique is shown to outperform the other studied HR techniques over both simulated signals and data acquired by the DLR’s ESAR sensor at L-band over Dresden city, Germany. Finally full-rank polarimetric tomographic estimators are proposed that generalize nonparametric polarimetric estimators, and permit to estimate second-order polarimetric representations in 3-D, instead of unitary rank target vector with their conventional versions. This approach makes it possible to characterize polarimetric scattering mechanisms in 3-D.

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.

Polarimetric Calibration of L-Band UAVSAR Data

The polarimetric distortion in the PolSAR datasets causes the polarimetric decomposition and classification techniques to produce wrong outputs, which result in misinterpreting the scattering phenomenon and the ground targets. The most important polarimetric distortions in airborne PolSAR datasets are the channel imbalance and crosstalk. The minimization of these polarimetric distortions using polarimetric calibration techniques is very important to carry out the quantitative analysis using PolSAR data and time-series analysis and to compare the results between different sensors. The objective of this study was to implement the external polarimetric calibration of the L-band UAVSAR system using trihedral corner reflectors. The polarimetric distortion matrix (PDM) was formulated after considering the crosstalk and channel imbalance polarimetric distortions to derive the scattering matrix free from all kinds of polarimetric distortions from the observed scattering matrix. The channel imbalance between different polarization channels was estimated with the help of trihedral corner reflectors and homogeneously distributed targets. The crosstalk parameters were estimated by assuming the scattering reciprocity constraint, which is valid in the case of monostatic radars. The scattering matrix free from polarimetric distortions was derived from the PDM after estimating the polarimetric distortions. The polarimetric signatures and the coherency matrix behaviour of the trihedral corner reflectors were used to analyse the ground target characterization improvement after polarimetric calibration.

Design of an endomicroscope including a resonant fiber-based microprobe dedicated to endoscopic polarimetric imaging for medical diagnosis

We report on a novel endomicroscope, to the best of our knowledge, designed for achieving full 4×4 Mueller polarimetric images of biological tissues through a fiber endoscope for medical diagnosis. The polarimetric technique is based on a previously published two-wavelength differential method (TWDM). A key component of the endomicroscope is a resonant fiber-based microprobe including a highly-selective fiber Bragg grating (FBG), free of detrimental polarimetric effects, photo written in the core of the fiber, near the output face. By means of the TWDM, and using the specially designed microprobe (diameter 2.9 mm, length 30 mm), full Mueller images of 250×250 pixels were produced at the rate of 1 image/2 s through a 2 m single mode fiber, paving the way to in vivo applications in polarimetric endomicroscopy.

Application of Polarimetric-SAR Decompositions on RADARSAT-2 Fine Quad-Pol Images to Enhance the Performances of Ships Detection Algorithms

Remote sensing of vessels is an important tool for ship safety and security at sea. In this work, we are interested in improving ships detection using polarimetric Synthetic Aperture Radar (SAR). To develop the appropriate method, different processing techniques are applied on Pol-SAR images such as fusion and polarimetric decompositions and we use adaptive threshold detectors to assess the performances of the processing techniques. The data exploited in this work were acquired on a port area of the city of Vancouver by using RADARSAT-2 satellite. In this paper it is shown first that when exploiting single polarization, the HH channel provides the highest score of detection probability (PD) of 87.2% for a false alarm probability (PFA) of 0.05%, and this while using the cell averaging constant false alarm rate (CA-CFAR) detector. The result is obtained comparatively with other polarizations (HV, VV) and detection algorithms. Second, the fusion of polarimetric channels achieves its best performances with the CA-CFAR detector, comparatively with the two parameters (2P)-CFAR and generalized likelihood ratio test (GLRT). Third, we find that among the conventional polarimetric techniques, the singular value decomposition (SVD) combined with CA-CFAR detector gives the best results and achieves a detection probability of 91% for a false alarm of 0.05%. This result was obtained by comparing the performances of other combinations of decompositions (Pauli, Freeman, Yamaguchi), fusion and ships detection algorithms. In this paper, we obtain with the proposed approach an increase of 3.8% in detection probability for false alarm probability of 0.05%.

Investigation on the Effects of Polarization Orientation Angle Shift in the UAVSAR Polarimetric Decomposition

The polarization orientation angle (POA) shift results in higher cross-polarization intensity in the HV and VH channels making the reflection asymmetrical. The L-band quad-pol dataset acquired over the Fujiyama mountain, Japan by the Uninhabited Aerial Vehicle Synthetic Aperture Radar of JPL/NASA was used in this study to analyse the effect of POA shift in the polarimetric decomposition techniques. The dataset was first compensated for the POA shift using the circular polarization algorithm, and a mean polarization orientation angle shift of − 4.23° was estimated. The Yamaguchi 3-component model-based decomposition and the H/A/Alpha eigenvector-based decomposition techniques were performed on the dataset before and after POA compensation. It was found that there was an overestimation of volume scattering component and underestimation of double-bounce scattering component before POA compensation in the Yamaguchi 3-component decomposition technique. After the POA compensation, there was a significant reduction in the volume scattering component observed at the non-vegetated areas and increase in double-bounce scattering in the same areas. There was no considerable change observed in the surface scattering component because of its roll invariant nature. Since the H/A/Alpha decomposition parameters were also independent of the orientation angle change because of their roll invariance property, there was no change observed in those parameters after POA compensation.

Geometrical Phase Optical Components: Measuring Geometric Phase without Interferometry

Optical components that are based on Pancharatnam–Berry phase feature a polarization-dependent diffraction that can be used to fabricate lenses and gratings with unique properties. In recent years, the great progress made in the fabrication of the metasurfaces that are required for these optical components has lowered their cost and has made them widely available. One of the often-overlooked properties of optical components based on geometrical phases (GPs) is that, contrary to dynamical phases, their phase can be measured while using a polarimetric technique without the need to resort to interferometry methods. This is possible because the Pancharatnam–Berry phase is not controlled by an optical path difference; it results from a space variant polarization manipulation. In this work, we apply Mueller matrix microscopy in order to measure the geometrical phase of GP lenses and polarization gratings. We show that a single space resolved Mueller matrix measurement with micrometric resolution is enough to obtain a full characterization phase-profile of these GP-based optical components and evaluate their performance.

Polarimetric studies of L-arginine-doped potassium dihydrogen phosphate single crystals

Conoscopic interference patterns, channelled spectra and polarimetric techniques have been used for the characterization of pure and doped (with L-arginine amino acid) potassium dihydrogen phosphate (KDP) single crystals. Experimental polarimetric data have been obtained for the frequently used wavelength of 633 nm and for two close wavelengths of 532 and 543 nm in a high-accuracy dual-wavelength polarimeter. The measurement of eigenwave ellipticity in the [100] and [010] directions and between 295 and 340 K shows small differences in the absolute values of the specific optical rotations of KDP crystals doped with L-arginine in the range of 0.7–3.8 wt%. It is found that the gyration tensor component g 11, specific optical rotation and eigenwave ellipticity show different dispersion in the visible spectral region.

Investigation of the optical beam shifts for monolayer MoS2 using polarimetric technique

The spatial and angular Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts are examined for fundamental Gaussian beam (633 nm) reflected from a monolayer of MoS2 using the ‘Stokes polarimetric’ technique. This technique enables us to promptly determine the magnitudes of the reflection coefficients and their relative phase differences which gives the optical beam shifts. The GH and IF shifts are measured with different polarization basis along with varying angle of incidence. This is a precision technique depending only upon the polarization components of the light beam and is quite independent of the fluctuations of the light intensity. The response of GH and IF shifts for MoS2 substrate is significant and thus may open up new possibilities in the optical applications of 2D materials.

Radar reflectivity signatures and possible lead times of warnings for very large hail in Poland based on data from 2007-2015

Abstract Hail involving very large hailstones (maximum diameter ≥ 5 cm), is a rare but very hazardous phenomenon in Poland, and can be forecast using reflectivity signatures. Every year, Poland experiences from one to over a dozen storms with such large hailstones. Despite the current recommendations regarding polarimetric techniques used in hail risk monitoring, Poland does not have a fully polarimetric radar network. Therefore it is essential to check hail detection capabilities using only reflectivity techniques based on individual radar systems involving hail detection algorithms such as Waldvogel et al. (1979) or Vertically Integrated Liquid thresholds connected with manual signature analysis to get better warning decisions. This study is aimed to determine the reflectivity features, thresholds and lead times for nowcasting of severe storms with very large hailstones in Poland, using data from the Polish radar system and from the European Severe Weather Database for the period 2007–2015. Most incidents involving very large hailstones were linked to supercell storms with distinctive reflectivity signatures, however, some storms with extremely large hailstones presented very poorly developed signatures. These signatures enabled the prediction of hail involving very large hailstones approximately 29 minutes before it fell. The Lemon (1980) criterion and WER were found to be the best hail predictors for Polish radar system conditions.

Soil-Permittivity Estimation Under Grassland Using Machine-Learning and Polarimetric Decomposition Techniques

The estimation of soil permittivity under fully covered grassland is a challenging task that can be approached by either model-based polarimetric decomposition techniques or data-driven machine-learning (ML) methods. In this study, we test the benefits and limitations of those techniques when individually or jointly applied to estimate the permittivity of the top soil (lower than 5-cm depth) from the L-band full-polarimetric SAR data. Training (needed for the ML approach) and reference data for accuracy assessment are based on the soil-permittivity measurements from an in situ sensor network. The applied polarimetric decomposition approaches are unable to estimate high soil-permittivity ranges (permittivity higher than 25-30) under the full-cover grassland leading to an underestimation compared with the in situ values. Purely data-driven ML techniques, here a case-adapted Random Forest (RF) architecture, applied directly to the SAR data achieve similar results as the decomposition approaches, where estimation quality mostly depends on the quality of the training set. The combination of both techniques works best and is able to represent high soil-permittivity ranges. The joint estimation decreases the mean absolute error drastically compared with applying any of the two approaches alone (i.e., from 4.88 and 4.99 of an informed physical model and ML on SAR only to 3.35).

Simple method for the characterization of birefringence of single-mode optical fibers

Over the past few decades, various laboratories have worked on non-destructive methods for the evaluation of residual birefringence of single-mode optical fibers. Among them, polarimetric methods allowing the measurement of polarization eigenmodes represent the best option when it is necessary either to understand or to control the evolution of the state of polarization of light along the fiber. In this work, we present a polarimetric technique based on the use of Mueller calculus and the Poincaré sphere. This is a simple, precise, and non-destructive method allowing the measurement of the azimuth and ellipticity angles of the polarization eigenmode, as well as the total retardation angle modulus-π.

Ship Recognition from Chaff Clouds with Sophisticated Polarimetric Decomposition

Ship recognition from chaff cloud jamming is challenging since they have similar dimensions and radar cross sections. In this paper, a polarimetric recognition technique with sophisticated polarimetric decomposition is proposed. To this end, a seven-component model-based decomposition is first put forward by integrating three sophisticated scattering models, thus the dominant and local scattering of ships can be characterized accurately. According to the derived scattering contributions, a robust discrimination feature is then designed based on the concept of contrast and suppression. Coupled with the average scattering angle estimated from eigen-based decomposition, the constructed feature vector is inputted into the support vector machine and the recognition is finally fulfilled. The proposed method is tested on simulated and real polarimetric radar data and the results demonstrate that the proposed method achieves the highest recognition rate of over 98%, which outperforms the state-of-the-art methods.