Polarized Light Research Articles

Impact on the Raman spectra of liquids when a polarized light source is used

The polarization state of the excitation light used in two Raman systems was controlled to study its effect in the unpolarized Raman spectra of unstructured samples. Both systems work in different regions of the electromagnetic spectrum (NIR and visible). Four polarization states (linear, linear at 45° and 90°, and circular) were used to excite liquid samples (ethanol, acetone, and their mixture). The results show that the Raman peaks intensities’ ratio varies according to the polarization state of the excitation light. Peaks related to functional groups and C-H stretching modes increase their intensity when circular polarization (CP) is applied. The latter may help to study liquid mixtures with low concentrations. Different polarizing light states give a more detailed spectroscopic analysis since it gathers more structural information of the samples tested in this work with an undefined structure.

Complex Raman Tensor in Helicity-Changing Raman Spectra of Black Phosphorus under Circularly Polarized Light.

In anisotropic two-dimensional materials, complex values of Raman tensors are necessary to explain the abnormal linearly polarized Raman spectra. In this work, we measured the helicity-changing Raman spectra of few-layer black phosphorus (BP) excited by circularly polarized light. We observed that the polarized Raman intensities of the Ag modes show a deflection angle that depends on the sample orientation, thickness, and laser excitation energy. To understand the deflection, we calculated the resonant Raman spectra by first-principles calculations, which give complex Raman tensors as a function of laser excitation energy. In particular, the phase difference between the elements of the complex Raman tensor is relevant to the deflection angle. The calculated results of monolayer BP reproduce the experimental helicity-resolved Raman spectra of few-layer BP satisfactorily.

Ultrafast Spin‐to‐Orbit and Orbit‐to‐Local‐Spin Conversions of Tightly Focused Hybridly Polarized Light Pulses

Spin–orbit interaction (SOI) has provided a new viable roadmap for the development of spin‐based photonics devices. However, existing strategies to control the SOI focus commonly on tailoring the spatial dimension of light fields yet neglecting the inherent temporal one. Herein, ultrafast temporal effects on both spin‐to‐orbit and orbit‐to‐local‐spin conversions based on the time‐assistant vectorial diffractive theory and the fast Fourier transformation are first presented. Such interconversions depend upon whether the incident hybridly vectorial light pulse carries vortex phase or not in a single high numerical aperture geometry. For the case of the absence of vortex phase, it is found that it enables orbit angular momentum‐carrying transverse component fields, and the resultant orbit angular momentum embedded within focused light fields remains constantly revolving as time elapses, which indicates that the controllable spin‐to‐orbit conversion occurs. By contrast, it is revealed that hybridly polarized vectorial‐vortex light pulses allow access to the locally excited circular polarization at the focus, and this induced local circular polarization is independent of ultrafast varying time, whereas the resulting spin angular momentum density components experience the alternation between the appearance and annihilation over time, thus giving rise to the tunable orbit‐to‐local‐spin conversion. These exotic ultrafast interconversions not only breathe a new life into the area of ultrafast photonics, but refresh our understanding on the paradigm of photonic SOI.

Near-infrared orthogonal polarized metalens

A metalens is a planar optical device that can accurately control the phase, polarization, and amplitude of light. Aiming at the application requirements of polarization imaging equipment for miniaturization, integration, and common field of view, we designed and fabricated two kinds of orthogonally polarized metalenses based on amorphous silicon and fused quartz. These metalenses can achieve orthogonal linear or circular polarization light imaging with a common field of view. The samples with a 2-mm diameter and 20-mm focal length were fabricated by electron beam exposure. The test results show that these metalenses can realize the imaging of orthogonal linearly or circularly polarized light simultaneously; the focusing efficiency is more than 50%, and the polarization contrast is >22 dB.

Selectively Regulating the Chiral Morphology of Amino Acid-Assisted Chiral Gold Nanoparticles with Circularly Polarized Light.

Chiral nanomaterials have attracted increasing attention due to their versatile optical properties. Although circularly polarized (CP) light can serve as an inducer, it has negligible effects because of the short lifetime of the plasmonic states. Here, we propose that the site-selective chirality regulation on the morphology of cysteine (cys) amino acid-assisted chiral gold nanoparticles (cys-chiral AuNPs) can be realized through CP light irradiation. This can result in the increased or decreased circular dichroism (CD) signal intensity. The site-selective growth mechanism of the cys-chiral AuNPs is elucidated with light-matter interactions through the opposite rotation of right(R)/left(L) CP light. The site-selective chirality growth of the cys-chiral AuNPs is ascribed to the morphology evolution induced by the synergy of cys and R/L-CP light, which is clearly analyzed and elucidated with high CD intensities. This work provides a promising alternative strategy to produce high-chirality nanomaterials that can be applied in biomedicine and enantiomer photocatalytic reaction.

Polarization State Variation Induced by the Circularly Polarized Light Scattering in LiNbO3：Fe Crystal（Invited）

Polarization State Variation Induced by the Circularly Polarized Light Scattering in LiNbO3：Fe Crystal（Invited）

Giant ooids of microbial origin from the Zhangxia Formation (Cambrian Miaolingian Series) in North China

The role of microorganisms in the formation of giant ooids is one of the areas of long-term controversy in ooidal research, but it has not been confirmed conclusively. Abundant giant ooids developed in the Zhangxia Formation of the Cambrian Miaolingian Series in North China. Giant ooids in the study area were examined by using Polarized Light Microscopy and Field Emission Environmental Scanning Electron Microscopy. The nuclei of the ooids consist of micritic pellets or radial ooids with diameters less than 2 mm and are formed in a weak-agitating seawater environment. Their cortices are concentric, and are characterized by the alternations of the dark laminae of micritic calcite or Girvanella filaments and light laminae of microsparry calcite. In the environments of inter-bank sea with the alternating development of medium and low energy and chiefly weak-agitating conditions, giant ooids were formed under the joint action of Girvanella filamentous growth, biologically-induced calcification and/or biologically-influenced calcification and inorganic calcium carbonate precipitation. The microfossils of Girvanella are distributed in inner and outer cortices of giant ooids, especially dense in the latter. This distinctly indicates that microbes play a significant role in the formation of giant ooids, and also provides a vital example for discussing the microbial origin of giant ooids.

Photoresponsivity of Asymmetrical Dihydropyrene Under Circularly Polarized Light Irradiation

Photoresponsivity of Asymmetrical Dihydropyrene Under Circularly Polarized Light Irradiation

A Double Layer Laminated Film of Cellulose Nanocrystals and Dye Displaying Vibrant Circularly Polarized Light

A Double Layer Laminated Film of Cellulose Nanocrystals and Dye Displaying Vibrant Circularly Polarized Light

Lead‐Free Chiral 2D Double Perovskite Microwire Arrays for Circularly Polarized Light Detection

AbstractThe realization of polarized photodetection vigorously accelerates the development of applications in quantum communication, medicine, imaging, and sensing. Polarized light detection has been realized based on chiral perovskites, but the high concentrations of toxic lead and instability in those reported perovskites impose difficulties for their commercial applications. Furthermore, the precise patterning of perovskite arrays with high crystallinity is in high demand for the integration of optoelectronic devices. Herein, pure (001)‐orientated lead‐free chiral 2D double perovskite single‐crystalline microwire arrays are fabricated by the capillary‐bridge confined assembly technique. Perovskite microwire arrays present remarkable environmental stability under ambient conditions. With the synergy of the excellent crystallinity and sensitive circular‐polarization absorption of chiral perovskite microwire arrays, outstanding circularly polarized light photodetectors are realized, with responsivity exceeding 52 mA W−1 and detectivity exceeding 3.9 × 1011 Jones.

Local Growth Mediated by Plasmonic Hot Carriers: Chirality from Achiral Nanocrystals Using Circularly Polarized Light.

Plasmonic nanocrystals and their assemblies are excellent tools to create functional systems, including systems with strong chiral optical responses. Here we study the possibility of growing chiral plasmonic nanocrystals from strictly nonchiral seeds of different types by using circularly polarized light as the chirality-inducing mechanism. We present a novel theoretical methodology that simulates realistic nonlinear and inhomogeneous photogrowth processes in plasmonic nanocrystals, mediated by the excitation of hot carriers that can drive surface chemistry. We show the strongly anisotropic and chiral growth of oriented nanocrystals with lowered symmetry, with the striking feature that such chiral growth can appear even for nanocrystals with subwavelength sizes. Furthermore, we show that the chiral growth of nanocrystals in solution is fundamentally challenging. This work explores new ways of growing monolithic chiral plasmonic nanostructures and can be useful for the development of plasmonic photocatalysis and fabrication technologies.

Transfer-matrix method of circular polarization light in an axionic photonic insulator

The photonic analog of an axioniclike system (or electronic topological insulator) is called an axionic photonic crystal. These materials are classified by three physical properties: permittivity $\ensuremath{\epsilon}$, permeability $\ensuremath{\mu}$, and the topological parameter $\ensuremath{\theta}$. As a particular case, crystals with periodic $\ensuremath{\epsilon}$ and $\ensuremath{\mu}$ are the so-called photonic crystals. In this paper, we employ a transfer-matrix treatment to study the propagation of light waves in an axionic photonic crystal composed of alternating building layers $A$ and $B$. We present numerical results for the photonic band structure as a function of the ratio between permittivities $R={\ensuremath{\epsilon}}_{B}/{\ensuremath{\epsilon}}_{A}$, layer thicknesses $X={d}_{B}/{d}_{A}$, and topological parameters $\ensuremath{\delta}={\ensuremath{\pi}}^{2}{({\ensuremath{\theta}}_{A}\ensuremath{-}{\ensuremath{\theta}}_{B})}^{2}/{\ensuremath{\alpha}}^{2}$. Our numerical results reveal that the band-gap features (width, center position, upper and lower frequencies) depend on the three parameters $\ensuremath{\epsilon}$, $\ensuremath{\mu}$, and $\ensuremath{\theta}$, but with the dependence on $\ensuremath{\theta}$ being stronger. In particular, as far as the band-gap width is concerned, we find that $X$ and $R$ work against each other; that is, as $X$ increases, $R$ must decreases for a wide band-gap emergence and vice versa. More interesting, however, are the results for the topological parameter $\ensuremath{\theta}$. We show that the presence of $\ensuremath{\theta}$ produces a photonic band gap (PBG) which depends only on the $\ensuremath{\delta}$ term. The widening of this PBG is slightly asymmetrical and monotonic as a function of $\ensuremath{\delta}$. It was also found that $\ensuremath{\delta}$ has no influence on the center position of the PBG. Our results open possibilities for technological applications of axionic photonic crystals with regard to the controlling and confinement of the propagation of light.

Full-Range Optical Imaging of Planar Collagen Fiber Orientation Using Polarized Light Microscopy.

A novel method for semiautomated assessment of directions of collagen fibers in soft tissues using histological image analysis is presented. It is based on multiple rotated images obtained via polarized light microscopy without any additional components, i.e., with just two polarizers being either perpendicular or nonperpendicular (rotated). This arrangement breaks the limitation of 90° periodicity of polarized light intensity and evaluates the in-plane fiber orientation over the whole 180° range accurately and quickly. After having verified the method, we used histological specimens of porcine Achilles tendon and aorta to validate the proposed algorithm and to lower the number of rotated images needed for evaluation. Our algorithm is capable to analyze 5·105 pixels in one micrograph in a few seconds and is thus a powerful and cheap tool promising a broad application in detection of collagen fiber distribution in soft tissues.

Role of Restored Underwater Images in Underwater Imaging Applications

Underwater images are extremely sensitive to distortion occurring in an aquatic underwater environment, with absorption, scattering, polarization, diffraction and low natural light penetration representing common problems caused by sea water. Because of these degradation of quality, effectiveness of the acquired images for underwater applications may be limited. An effective method of restoring underwater images has been demonstrated, by considering the wavelengths of red, blue, and green lights, attenuation and backscattering coefficients. The results from the underwater restoration method have been applied to various underwater applications; particularly, edge detection, Speeded Up Robust Feature detection, and image classification that uses machine learning. It has been shown that more edges and more SURF points can be detected as a result of using the method. Applying the method to restore underwater images in image classification tasks on underwater image datasets gives accuracy of up to 89% using a simple machine-learning algorithm. These results are significant as it demonstrates that the restoration method can be implemented on underwater system for various purposes.

Monitoring Strain-Controlled Exciton-Phonon Coupling in Layered MoS2 by Circularly Polarized Light.

The modulation of exciton-phonon coupling by strain greatly affects the optical and optoelectronic properties of two-dimensional (2D) materials. Although photoluminescence and optical absorption spectra have been used to characterize the overall change of exciton-phonon coupling under strain, there has been no effective method to distinguish the evolution of the major contributions of exciton-phonon coupling, that is, deformation potential (DP) and Fröhlich interaction (FI). Here we report the direct monitoring of the evolution of DP and FI under strain in layered MoS2 using circularly polarized Raman spectroscopy. We found that the relative proportions of DP and FI can be well evaluated by the circular polarization ratio of the E2g1 mode for strained MoS2. Further, we demonstrated that the strain control of DP and FI in MoS2 is dominated by the excitonic effect. Our method can be extended to other 2D semiconductors and would be helpful for manipulating exciton-phonon couplings by strain.

Single-Shot Quantitative Polarization Imaging of Complex Birefringent Structure Dynamics.

Polarization light microscopes are powerful tools for probing molecular order and orientation in birefringent materials. While a number of polarization microscopy techniques are available to access steady-state properties of birefringent samples, quantitative measurements of the molecular orientation dynamics on the millisecond time scale have remained a challenge. We propose polarized shearing interference microscopy (PSIM), a single-shot quantitative polarization imaging method, for extracting the retardance and orientation angle of the laser beam transmitting through optically anisotropic specimens with complex structures. The measurement accuracy and imaging performance of PSIM are validated by imaging a birefringent resolution target and a bovine tendon specimen. We demonstrate that PSIM can quantify the dynamics of a flowing lyotropic chromonic liquid crystal in a microfluidic channel at an imaging speed of 506 frames per second (only limited by the camera frame rate), with a field-of-view of up to 350 × 350 μm2 and a diffraction-limit spatial resolution of ~2 μm. We envision that PSIM will find a broad range of applications in quantitative material characterization under dynamical conditions.

The role of dual energy computed tomography in the differentiation of acute gout flares and acute calcium pyrophosphate crystal arthritis

ObjectivesTo analyse the diagnostic impact of dual energy computed tomography (DECT) in acute gout flares and acute calcium pyrophosphate (CPP) crystal arthritis when compared to the gold standard of arthrocentesis with compensated polarised light microscopy. Microscopy results were also compared to musculoskeletal ultrasound (MUS), conventional radiographs, and the suspected clinical diagnosis (SCD).MethodsThirty-six patients with a suspected gout flare (n = 24) or acute CPP crystal arthritis (n = 11, n = 1 suffered from neither) who received a DECT and underwent arthrocentesis were included. Two independent readers assessed DECT images for signs of monosodium urate crystals or calcium pyrophosphate deposition.ResultsSensitivity of DECT for gout was 63% (95% CI 0.41–0.81) with a specificity of 92% (0.41–0.81) while sensitivity and specificity for acute CPP arthritis were 55% (0.23–0.83) and 92% (0.74–0.99), respectively. MUS had the highest sensitivity of all imaging modalities with 92% (0.73–0.99) and a specificity of 83% (0.52–0.98) for gout, while sensitivity and specificity for acute CPP crystal arthritis were 91% (0.59–1.00) and 92% (0.74–0.99), respectively.ConclusionDECT is an adequate non-invasive diagnostic tool for acute gout flares but might have a lower sensitivity than described by previous studies. Both MUS and SCD had higher sensitivities than DECT for acute gout flares and acute CPP crystal arthritis.Key Points• DECT offers a lower sensitivity for acute gout flares than previously described.• DECT sensitivity for acute CPP crystal arthritis is less than the already validated ultrasound.

Computational Modeling of Chromatin Fiber to Characterize Its Organization Using Angle-Resolved Scattering of Circularly Polarized Light.

Understanding the structural organization of chromatin is essential to comprehend the gene functions. The chromatin organization changes in the cell cycle, and it conforms to various compaction levels. We investigated a chromatin solenoid model with nucleosomes shaped as cylindrical units arranged in a helical array. The solenoid with spherical-shaped nucleosomes was also modeled. The changes in chiral structural parameters of solenoid induced different compaction levels of chromatin fiber. We calculated the angle-resolved scattering of circularly polarized light to probe the changes in the organization of chromatin fiber in response to the changes in its chiral parameters. The electromagnetic scattering calculations were performed using discrete dipole approximation (DDA). In the chromatin structure, nucleosomes have internal interactions that affect chromatin compaction. The merit of performing computations with DDA is that it takes into account the internal interactions. We demonstrated sensitivity of the scattering signal’s angular behavior to the changes in these chiral parameters: pitch, radius, the handedness of solenoid, number of solenoid turns, the orientation of solenoid, the orientation of nucleosomes, number of nucleosomes, and shape of nucleosomes. These scattering calculations can potentially benefit applying a label-free polarized-light-based approach to characterize chromatin DNA and chiral polymers at the nanoscale level.

Uncertainty analysis of calibration source with adjustable degree of polarization in a wide dynamic range

In order to satisfy the requirements of pre-launch laboratory calibration with high accuracy for polarization remote sensor, an innovative high precision polarimetric calibration instrument with adjustable degree of linear polarization (DoLP) in a wide dynamic range called adjustable polarization light source (APOLS) has been developed. APOLS consists of a collimated light source (CLS) and a polarization state adjuster (PSA). The PSA contains four parallel K9 glass plates, which can be orientated from 0° to 65° accurately controlled by electromechanical driving mechanism whose rotation accuracy is better than ±5″. Regarding the DoLP of APOLS, its adjustment range is from 0 to 0.72 within the spectral range from 460 to 2000 nm. The theoretical model of APOLS was established to describe the DoLP produced by multiple refraction of transmitted light. Meanwhile, the major systematic factors contributing to the DoLP uncertainty such as refractive index and absorption of K9 glass, incident angle, instability and parallelism of light source were analyzed. By using the spectro-polarimetric analyzer (SPOLA), the uncertainty evaluation experiments of APOLS were carried out. The results showed that when the DoLP value was in the range of 0.26 to 0.72, the uncertainty was less than 0.5%, and when the DoLP value was in the range of 0.003 to 0.26, the uncertainty was in the range of 8.5993% to 0.5534%. Moreover, the uncertainty was in the range of 0.0027% to 0.0032% when the uncertainty of the CLS was not considered. The consistency evaluation between APOLS and SPOLA ranged from -0.36 to 0.6 indicates the experimental results are satisfying. It can be concluded that the APOLS significantly improved the dynamic range and accuracy of the polarimetric calibration instrument.

Periodic integration-based polarization differential imaging for underwater image restoration

Underwater image restoration is extensively used in many applications, such as ocean exploration and underwater rescue. With the development of polarization imaging technology, polarization differential imaging (PDI) has gradually become one of the most effective tools for image restoration in the underwater environment. To eliminate the interferences of inconsistent polarization direction and image noise in conventional PDI systems, we propose a new underwater image restoration method based on the periodic integration of polarization images. The method replaces one or two pairs of orthogonal polarization images with the integration of a series of polarization images in PDI system to achieve underwater image restoration. Firstly, we captured a series of polarization images in different polarization directions during a complete variation cycle of image intensity. Then, these polarization images are accumulated together, and the result is approximately regarded as the intensity integration of polarization light in the dimension of polarization direction. Finally, we can calculate the polarization degree of each pixel and obtain a clear polarization differential image. Compared with the existing PDI methods based on one or two pairs of orthogonal polarization images, both qualitative and quantitative experimental results show that the proposed method has better performance in texture enhancement and noise suppression.