Non-polarized Light Research Articles

A unique approach for investigating skin lesions and their relationship with TCM syndrome differentiation in alopecia areata

Background: Alopecia areata is also known as ‘oil wind’ in Chinese medicine. Alopecia areata is a debilitating autoimmune skindisease characterized by patches of non-scarring hair loss and inflammation that damages the scalp and body hair in a variable,often relapsing or permanent fashion. It is not quite obvious how the various Traditional Chinese Medicine (TCM) syndromes differentiate between the skin lesions under dermatoscopy caused by alopecia areata. Objective: This study aimed to provide a rational basis for TCM syndrome differentiation of alopecia areata and investigate the role of skin lesions in various TCM syndromes of alopecia areata under dermatoscopy. Methods: The dermatologist used a dermatoscope to take four images of the patient's skin lesion area and the skin lesion junction. Two of the images were captured with polarized light, while the other two were taken with non-polarized light. Patients with alopecia areata who had TCM syndrome differentiation were identified and examined using dermatoscopy. The occurrence of the yellow dot, white dot, exclamation mark hair and vascular sign, was determined and then statistically analyzed. Results: The positive rates of vascular signs relate to alopecia areata, exclamation mark hair relates to Qi-blood deficiency and white dot corresponded to liver and kidney deficiency. All the positive rates were statistically significant (P < 0.05). Compared to vascular sign, white dot sign, and Qi-blood deficiency syndrome groups, the positive rate of yellow dot syndrome was not significant (P>0.05) Conclusion: The findings suggest that particular skin lesions contribute to differentiating different TCM syndromes associated with alopecia areata. Skin lesions examined under dermatoscopy can assist in diagnosing the TCM syndromes associated with alopecia areata. Keywords: Dermatoscopic signs; Alopecia areata; TCM syndromes; Qi and blood deficiency; Liver and kidney deficiency.

The effects of side-chain flexibility on the photosensitivity of polyimide alignment film

ABSTRACT To examine the impact of side-chain flexibility on the photosensitivity of polyimide liquid crystal (LC) alignment films, two polyimides (OD-HAB-CA and OD-HAB6-CA) were synthesised. OD-HAB6-CA contains flexible hexamethylene side chains. This study demonstrates that the OD-HAB-CA alignment film can induce LC molecular alignment after 80 min of non-polarised ultraviolet light (NPUVL) irradiation. In contrast, the OD-HAB6-CA alignment film can achieve the same result after only 35 min of irradiation. This suggests that the flexibility of the side-chain can significantly improve the photosensitivity of the alignment film and shorten the required irradiation time. In addition, OD-HAB-CA and OD-HAB6-CA exhibit good thermal stability and light transmittance properties. The resulting LC cell have pretilt angles of 0.2° and 0.5°, respectively, which are suitable for in-plane switching mode LCDs.

The Linearly Polarized Light Effect on Maize Development

The main purpose of the work was to study the linearly polarized light impact on the maize plants development. The other purpose was to confirm the model proposed earlier. The methods used in this work include the development of LED light sources, the polarization parameter (degree of polarization) assessment and statistical analysis. Maize (Zea mays L.) plants, Hansatech FMS 1+ pulsed fluorimeter and software TXP Series Instrumentation were used. Plants were grown under white light (WW) with intensity of 200 µmol m–2 s–1. The morphometric parameters measured on the 21st day demonstrated that maize plants of different varieties grown under linearly polarized light developed better than under non-polarized light conditions. In addition, the fact was confirmed by chlorophyll fluorescence measurements. The mechanism has been proposed to explain significant polarized radiation impact on maize, according to which this impact depends on the shape and arrangement of the leaf epidermal cells. The monocotyledonous maize plants have leaves with an ordered arrangement of epidermal cells in comparison with dicotyledonous plants, which cells placed in chaotic order and have no certain shape. Thus, the maize cells layer can transform linearly polarized radiation into elliptically polarized radiation, thus latter should be more efficiently absorbed by the chiral chromophores of photosensitive structures in underlying photosynthetic cells.

Biomass Burning Plume from Simultaneous Observations of Polarization and Radiance at Different Viewing Directions with SGLI

The Earth Observation Satellite Global Change Observation Mission—Climate (GCOM)-C (SHIKISAI in Japanese), carrying a second-generation global imager (SGLI), was launched in 2017 by the Japan Aerospace Exploration Agency. The SGLI performs wide-swath multi-spectral measurements in 19 channels, from near-ultraviolet to thermal infrared (IR), including the red (674 nm; PL1 channel) and near-IR (869 nm; PL2 channel) polarization channels. This work aimed to demonstrate the advantages of SGLI, particularly the significance of simultaneous off-nadir polarized and nadir multi-spectral observations. The PL1 and PL2 channels were tilted at 45° for the off-nadir measurements, whereas the other channels took a straight downward view for the nadir measurements. As a result, the SGLI provided two-directional total radiance data at two wavelengths (674 and 869 nm) that were included in both off-nadir and nadir observations. Using these bidirectional data, an algorithm was applied to derive the altitude of the aerosol plume. Furthermore, because of the significance of the simultaneous observation of polarized and non-polarized light, the sensitivity difference between the radiance and polarized radiance was demonstrated. Severe wildfire events in Indonesia and California were considered as examples of specific applications. Herein, we present the results of our analysis of optically thick biomass-burning aerosol events. The results of the satellite-based analysis were compared with those of a chemical transport model. Exploring the SGLI’s unique capability and continuous 5-year global record paves the way for advanced data exploitation from future satellite missions as a number of multi-directional polarization sensors are programmed to fly in the late 2020s.

Strain-magneto-optics: Magnetoreflectivity in MnFe2O4 ferrite-spinel crystal

The single crystal of ferromagnetic magnetostrictive spinel MnFe2O4 was grown by the zone-floating method. The magnetic, magneto-elastic, optical, and magneto-optical properties of the MnFe2O4 ferrite-spinel were investigated in the infrared spectral range. A strain-magneto-optical phenomenon, which demonstrate the connection between magnetoreflection of non-polarized light and magnetostriction of MnFe2O4, was revealed. A maximum magnetoreflection of up to 1 % was observed at room temperature in a magnetic field of 2 kOe. Using the Kramers-Kronig method, the magnetorefractive effect and magnetooptical conductivity of MnFe2O4 were also calculated. The observed correlation between magnetoelastic and magneto-optical properties of MnFe2O4 was attributed to the significant contribution of linear magnetostriction to the magnetic anisotropy constant (ΔK/K1 ∼ 8 %) in the MnFe2O4 crystal. Additionally, a criterion of ΔK/K1 ∼ 1 % was proposed to evaluate the potential use of magnetostrictive materials in strain-magneto-optics.

Improved crystallinity and surface morphology of a-plane AlN grown on high temperature annealed AlN/sapphire template by pulsed-flow mode metal-organic vapor phase epitaxy

Preparing high quality non-polar aluminum nitride (AlN) templates is the key to improving the performance of non-polar deep-ultraviolet light-emitting diodes. In this study, we investigated the effect of buffer layer on the crystallinity and surface morphology of a-plane AlN films regrown by pulsed-flow mode (PM) metal-organic vapor phase epitaxy (MOVPE). Three buffer layers were compared including low-temperature AlN buffer layer grown by MOVPE (MO-buffer), sputtered AlN buffer layer (SP-buffer), and high-temperature annealed sputtered AlN buffer layer (HTA-buffer). It is found that the (11-20) plane x-ray rocking curve-full width at half maximum (XRC-FWHM) values of a-plane AlN films are significantly reduced after the regrowth process. Thanks to the high crystalline quality of HTA-buffer, AlN regrown on HTA-buffer exhibits the smallest (11-20) plane XRC-FWHM values of 1260/1440 arcsec along the [0001]/[1-100] direction. The mosaic tilt and basal plane stacking fault density are estimated to be 0.41° and 1.76 106 cm−1, respectively. The surface shows a uniform stripe-like pattern with the lowest root mean square value of 0.82 nm. Furthermore, the a-plane AlN epilayer regrown on HTA-buffer displays a weak in-plane stress anisotropy and high optical transmittance in the ultraviolet-visible region. Our work suggests that combining the PM regrowth with HTA-AlN buffer layer is a promising route to prepare high-quality a-plane AlN templates for efficient non-polar deep-ultraviolet light emitters.

Light-triggered Modulation of Supramolecular Chirality.

Dynamically controlling the supramolecular chirality is of great significance in development of functional chiral materials, which is thus essential for the specific function implementation. As an external energy input, light is remote and accurate for modulating chiral assemblies. In non-polarized light control, some photochemically reactive units (e. g., azobenzene, ɑ-cyanostilbene, spiropyran, anthracene) or photo-induced directionally rotating molecular motors were designed to drive chiral transfer or amplification. Besides, photoexcitation induced assembly based physical approach was also explored recently to regulate supramolecular chirality beyond photochemical reactions. In addition, circularly polarized light was applied to induce asymmetric arrangement of organic molecules and asymmetric photochemical synthesis of inorganic metallic nanostructures, in which both wavelength and handedness of circularly polarized light have effects on the induced supramolecular chirality. Although light-triggered chiral assemblies have been widely applied in photoelectric materials, biomedical fields, soft actuator, chiral catalysis and chiral sensing, there is a lack of systematic review on this topic. In this review, we summarized the recent studies and perspectives in the constructions and applications of light-responsive chiral assembled systems, aiming to provide better knowledge for the development of multifunctional chiral nanomaterials.

Simple Visualization of Universal Ferroelastic Domain Walls in Lead Halide Perovskites.

Domain features and domain walls in lead halide perovskites (LHPs) have attracted broad interest due to their potential impact on optoelectronic properties of this unique class of solution-processable semiconductors. Using nonpolarized light and simple imaging configurations, ferroelastic twin domains and their switchings through multiple consecutive phase transitions are directly visualized. This direct optical contrast originates from finite optical reflections at the wall interface between two compositionally identical, orientationally different, optically anisotropic domains inside the material bulk. The findings show these domain walls serve as internal reflectors and steer energy transport inside halide perovskites optically. First-principles calculations show universal low domain-wall energies and modest energy barriers of domain switching, confirming their prevalent appearance, stable presence, and facile moving observed in the experiments. The generality of ferroelasticity in halide perovskites stems from their soft bonding characteristics. This work shows the feasibility of using LHP twin domain walls as optical guides of internal photoexcitations, capable of nonvolatile on-off switching and tunable positioning endowed by their universal ferroelasticity.

Characterization of vine, Vitis vinifera, leaves by Mueller polarimetric microscopy

In this work, we present the study of vine leaves, Vitis vinifera, performed by imaging polarimetry in the visible (at the wavelength of 530 nm). The purpose is to demonstrate, on a case study example, the high potential of imaging polarimetry and of polarimetric microscopy, in particular, for the characterization of vegetal tissues. The analysis of the Mueller matrix image of the sample provided by the polarimetric microscope by means of a matrix decomposition protocol yields a series of observables that are directly related to the fundamental physical properties that characterize the sample. Birefringence and dichroism are related to the structural properties of the medium and can be advantageously used as non-chemical, non-contact, non-destructive and non-toxic markers to highlight the presence of specific structures in the probed sample. Polarimetric images may also be used to enhance the contrast of the measured images. Specifically, we use the polarimetric properties and the depolarization indices to unveil the presence of structures such as raphides, some of them invisible under non-polarized light, and to investigate their properties.

The effects of polarized photobiomodulation on cellular viability, proliferation, mitochondrial membrane potential and apoptosis in human fibroblasts: Potential applications to wound healing.

Photobiomodulation (PBM) is a widely used therapeutic intervention used to treat several chronic conditions. Despite this, fundamental research underpinning its effectiveness is lacking, highlighted by the lack of a definitive mechanism of action. Additionally, there are many treatment variables which remain underexplored, one of those being the effect of polarization the property of light that specifies the direction of the oscillating electric field. When applied to PBM, using linearly polarized light, when compared to otherwise identical non-polarized light, may enhance its biological efficacy. As such, we investigated the potential biological effects of polarized PBM when compared to non-polarized and non-irradiated controls in the domains of cellular viability, proliferation, apoptosis and mitochondrial membrane potential (ΔΨ) within cells exposed to oxidative stress. It was noted that polarized PBM, when compared to non-polarized PBM and non-irradiated controls, demonstrated mostly increased levels of cellular proliferation and ΔΨ, whilst decreasing the amount of cellular apoptosis. These results indicate that polarization may have utility in the clinical application of PBM. Future research is needed to further elucidate the underpinning mechanisms of PBM and polarization.

Method for hidden marking of transparent polypropylene film

Objectives. To quantitatively describe the thermochromic properties of films of isotactic polypropylene, a large-tonnage polymer widely used in the production of flexible packaging for goods and foodstuffs, as well as substantiate the possibility of covert labeling of transparent packaging.Methods. Differential scanning calorimetry, polarization photometry, infrared Fourier spectrometry, gravimetry, temperature control, physical and mechanical strength testing.Results. The identified thermochromic effect of dichroism in polarized light on industrial samples of transparent biaxially oriented film of isotactic polypropylene was studied. A change in the phase composition of the film-forming composition during short-term heating during marking was established. The absence of heat shrinkage and change in transparency in non-polarized light was shown, which provides the possibility of hidden recording of information and its contrast manifestation in a passing light stream at a certain arrangement of light filters.Conclusions. The causes and optimal conditions of the thermochromic effect are established. It is proposed to use local contact heat treatment of a polypropylene film for covert recording of information and marking of product packaging in order to protect against counterfeiting.

Orthogonal separation of arbitrary vector beams from non-polarized light waves based on a patterned liquid-crystal photo-alignment.

An effective method for orthogonally separating arbitrary vector polarized beams from non-polarized incident light waves is proposed in this Letter. A tunable patterned spatial distribution of liquid-crystal (LC) molecules can be effectively constructed based on both the initial photo-alignment and the electrically controlled birefringence of nematic LC materials. The LC photo-alignment over a smooth surface without any common nano-grooves leads to a highly efficient light-wave transformation by inducing a desired initial arrangement of LC directors and then acquiring extraordinary light waves with the needed, or even arbitrary, spatial polarization. The vector polarized beams can be highly converged according to a microhole-patterned electrode and a gradient refractive index distribution of the LC layer, which is driven and adjusted by an applied signal voltage. Due to the intrinsic polarization sensitivity of nematic LC materials, the formed gradient refractive index appearance only corresponds to extraordinary light waves. The proposed approach provides a way to achieve the orthogonal separation of arbitrary vector beams from non-polarized light waves. Moreover, it can be further utilized to generate and obtain arbitrary vector beams, as well as to perform adaptive light-beam convergence or even the focusing of arbitrary vector beams, which is expected to advance the development of vector beam generation and manipulation, thereby stimulating potential applications.

Improvement of the optical transmittance of a SiO2 surface by a femtosecond-laser-induced homogeneous nanostructure formation

It has been reported that periodic nanostructures with a period size of 200–330 nm can be formed on silicon suboxide (SiO x , x ≈ 1) with 800-nm, 100-fs laser pulses at a fluence much smaller than that needed for nanostructuring on glasses such as fused silica and borosilicate glass. We demonstrated that a homogeneous SiO2 nanostructure with a period of ∼240 nm can be produced using a two-step ablation process and heat treatment in air at 1000°C for 144 hours. Optical microscopic images of the nanostructured surface illuminated by non-polarized visible light show that the transmittance increases as the reflectivity decreases.

MobileSkin: Classification of Skin Lesion Images Acquired Using Mobile Phone-Attached Hand-Held Dermoscopes

Dermoscopy is the visual examination of the skin under a polarized or non-polarized light source. By using dermoscopic equipment, many lesion patterns that are invisible under visible light can be clearly distinguished. Thus, more accurate decisions can be made regarding the treatment of skin lesions. The use of images collected from a dermoscope has both increased the performance of human examiners and allowed the development of deep learning models. The availability of large-scale dermoscopic datasets has allowed the development of deep learning models that can classify skin lesions with high accuracy. However, most dermoscopic datasets contain images that were collected from digital dermoscopic devices, as these devices are frequently used for clinical examination. However, dermatologists also often use non-digital hand-held (optomechanical) dermoscopes. This study presents a dataset consisting of dermoscopic images taken using a mobile phone-attached hand-held dermoscope. Four deep learning models based on the MobileNetV1, MobileNetV2, NASNetMobile, and Xception architectures have been developed to classify eight different lesion types using this dataset. The number of images in the dataset was increased with different data augmentation methods. The models were initialized with weights that were pre-trained on the ImageNet dataset, and then they were further fine-tuned using the presented dataset. The most successful models on the unseen test data, MobileNetV2 and Xception, had performances of 89.18% and 89.64%. The results were evaluated with the 5-fold cross-validation method and compared. Our method allows for automated examination of dermoscopic images taken with mobile phone-attached hand-held dermoscopes.

Clinical and Dermatoscopic Signs of Micromelanoma - A Review of the Literature

Introduction: Micromelanoma, also called a small-sized melanoma, in the scientific literature is commonly defined as a skin melanoma with a diameter of 3 mm or less, although definitions of 5 mm or less can also be found.
 Objectives: The aim of this study was to identify the clinical and dermatoscopic features that characterize skin micromelanomas.
 Materials and Methods: The study was carried out by searching relevant articles using keyword “micromelanoma” in the following electronic databases – PubMed, Wiley, Scopus, Web of science, ScienceDirect, EBSCOhost, and Google Scholar. The search was performed in the period from January 20th, 2022, to January 31st, 2022. The search had a limit of English language.
 Results: According to the published literature, micromelanomas are most often diagnosed in women, since in reviewed studies 43 – 81.8% of patients were women. People diagnosed with micromelanoma are mostly in the age group of 40 to 59 years. Clinically micromelanomas are most frequently seen as dark or light brown macules in diameter of 3 – 4 mm located on the lower extremities and as lesions that had developed de novo. The most common diagnostic methods used for micromelanoma diagnostics are physical skin examination and dermatoscopy – polarized light and nonpolarized light. The most widely used diagnostic dermatoscopic algorithm is the 7 – point checklist. Diagnostic accuracy shown for dermatoscopic algorithms is in the range of 48.2 – 65.9%, showing that not all micromelanomas can be diagnosed with diagnostic dermatoscopic algorithms and other characteristics must be considered. The dermatoscopic pattern for micromelanomas is variable – spitzoid, globular, reticular, and structureless, of which spitzoid is the most common. The most common melanoma-specific dermatoscopic signs seen in micromelanomas are irregular dots/globules (25.0 – 88.4% of micromelanomas), atypical network (40.0 – 77.0% of micromelanomas), atypical blotches (16.6 – 38.4% of micromelanomas), and pseudopods (3.4 – 46.0% of micromelanomas). Less frequently other melanoma specific dermatoscopic features – regression, blue – white veil and asymmetric multicomponent dermatoscopic pattern can be observed. Micromelanomas often present asymmetry in structure and color and frequently have two colors dermatoscopically. Micromelanomas rarer than larger melanomas have atypical vessels – dotted, linear, or polymorphous (3.8 – 32.0% of micromelanomas).
 Conclusions: Micromelanoma can develop in people of any age and gender, but most commonly it develops after the age of 40 and in women. Micromelanoma develops mainly as a de novo lesion on the lower extremities and has a diameter of 1 to 5 mm at the time of presentation. Dermatoscopically, micromelanomas often have melanoma-specific dermatoscopic features, and therefore dermatoscopy aids in diagnosing micromelanoma.

Automated Quantitative Mapping of Ore Minerals by Multispectral Reflected-light Microscopy

ABSTRACT An innovative multispectral reflected-light microscopy system is able to automatically identify ore minerals by measuring their specular reflectance with non-polarized light in a number of spectral bands, and comparing the values obtained with a reference database. In this way it can provide quantitative mineralogical mapping comparable to that obtained from automated mineralogy systems based on SEM-EDS (Scanning Electron Microscopy with Energy-Dispersive X-Ray Spectroscopy), at a fraction of the cost and with less stringent environmental and operational requirements. The new system, called AMCO (for Automated Microscopic Characterization of Ores), consists of an instrument and two proprietary software applications: amcoCapture, to acquire multispectral images of a polished section prepared from an ore sample, and amcoAnalysis, to process these images and extract different types of mineralogical information from them.

Fractal Dimension Analysis of Melanocytic Nevi and Melanomas in Normal and Polarized Light-A Preliminary Report.

Clinical diagnosis of pigmented lesions can be a challenge in everyday practice. Benign and dysplastic nevi and melanomas may have similar clinical presentations, but completely different prognoses. Fractal dimensions of shape and texture can describe the complexity of the pigmented lesion structure. This study aims to apply fractal dimension analysis to differentiate melanomas, dysplastic nevi, and benign nevi in polarized and non-polarized light. A total of 87 Eighty-four patients with 97 lesions were included in this study. All examined lesions were photographed under polarized and non-polarized light, surgically removed, and examined by a histopathologist to establish the correct diagnosis. The obtained images were then processed and analyzed. Area, perimeter, and fractal dimensions of shape and texture were calculated for all the lesions under polarized and non-polarized light. The fractal dimension of shape in polarized light enables differentiating melanomas, dysplastic nevi, and benign nevi. It also makes it possible to distinguish melanomas from benign and dysplastic nevi under non-polarized light. The fractal dimension of texture allows distinguishing melanomas from benign and dysplastic nevi under polarized light. All examined parameters of shape and texture can be used for developing an automatic computer-aided diagnosis system. Polarized light is superior to non-polarized light for imaging texture details.

(Invited) One-Dimensionally Aligned Quantum Rods for Generation of Highly-Pure Circularly Polarized Light with High Light Intensity

Converting non-polarized visible light (natural light) into circular polarized (CP) light is currently an important issue because of the attractive properties of CP light such as acceleration of photosynthesis and enhancement of conversion efficiency of photovoltaics[1,2]. Until now, various methods for creating CP visible light, such as filtration by circular polarizer, selective reflection by chiral liquid crystal structures, and circular polarized luminescence (CPL) from chiral luminophores[3], have been reported. However, creation of highly-pure CP visible light with high light intensity is still considered as challenging issue. In this presentation, we propose an approach for creating highly-pure CP visible light with high light intensity by converting linearly polarized luminescence (LPL) using quarter-wave plate.In this work, we put spotlight on colloidal semiconductor quantum rods (QRs) because of its unique advantages described as follows: (1) Absorption coefficient and emission quantum yield are relatively high. (2) Sharp emission peaks are expected. (3) Variety of QRs with different emission colors can be excited by irradiation of single-wavelength light. We selected CdSe/CdS core/shell QRs as LPL generating 1D nanostructure. CdSe/CdS core/shell QRs were synthesized by hot-injection method. As shown in Figure 1a, the obtained suspension showed orange-colored strong emission under UV light irradiation. TEM image of the dried sample of the QRs toluene suspension indicates that the average length, average width of the obtained rod-like nanostructures were about 30 nm and 4.5 nm, respectively. After QRs/toluene suspension was mixed with poly(ethylene-co-vinyl acetate) (EVA)/toluene solution, the mixture was casted on glass slide and dried it under air. Then, the prepared composite polymer film was stretched in one direction and was attached on glass slide. When the luminescence from the QRs/EVA stretched film was observed under the linear polarizer placed in parallel direction to the stretching direction, the observed light was brighter than that of perpendicular direction (Figure 1c). By measuring the photoluminescence of parallel (I//) and perpendicular (I⊥) components under depolarized excitation at 450 nm, the QRs/EVA stretched film showed clear LPL property with constant ratio (CR) = 5.4, defined as CR = I// / I⊥ (Figure 1b). Furthermore, when the QRs/EVA stretched film was combined with a quarter-wave plate placed at 45° to the stretching direction and was observed through the right-handed (RH) or left-handed (LH) circular polarizer, brighter light was observed through LH circular polarizer (Figure 1d). By quantitative evaluation of RH- and LH-CP light components, total emission includes 82% of LH-CP light and 18% of RH-CP light (Figure 1e). These results indicate that the combination of the QRs/EVA stretched film and quarter-wave plate generate highly-pure CP light which can be distinguished by the naked eye (Figure 2d). Interestingly, the handedness of CP light can be switched by simply changing the angle between fast axis of the quarter-wave plate and stretching direction of LPL films (Figure 1f). In this presentation, we will also discuss about multiplexing of optical information by using CP light conversion.[1] W. Qin et. al., J. Phys. Chem., 2018, 122, 12566-12571. [2] B. Hu et. al., ACS Photonics, 2017, 4, 2821-2827. [3] P. Duan, M. Liu et. al., Adv. Mater. 2020, 32, 1900110. Figure 1

High-quality deformed lying helix in chiral LC on surface with periodic alignment prepared by two-step optical treatment

ABSTRACT We propose a method for creating a periodic planar-homeotropic alignment (PHA) of liquid crystal (LC) on a film prepared by spin-coating a solution of a mixture of a photosensitive organic azo dye and a surfactant. Irradiation by polarised and non-polarised ultraviolet light provides areas with reliable planar and homeotropic LC alignment, respectively. Using a photomask, gratings with PHA are created, and optical properties of the LC cells based upon them are investigated. For the first time, the characteristic fine features of the field-induced transition of the initially standing chiral LC helix into a Deformed Lying Helix (DLH) configuration with the spiral axis lying in the LC layer plane are visualised and studied. The observed optical images illustrate the high-quality DLH pattern. Numerical simulations of the DLH reveal the peculiarities of the obtained structure and how it is formed.

Absorption of nonpolarized light by a two-dimensional ensemble of spherical silver particles under oblique illumination

The problem of absorption of nonpolarized (natural) light by a two-dimensional ensemble (monolayer) of spherical particles under oblique illumination is considered. The solution is based on the statistical theory of multiple scatteing of waves. The written equations make it possible to find the optimal conditions for the absorption of directed light to increase the absorption efficiency of monolayers with a periodic and partially ordered spatial arrangement of particles. The results of the calculations are presented for the absorption coefficient of polarized and natural light by ensembles of silver particles in a nonabsorbing medium. The particle size and monolayer filling factor are chosen so as to illustrate the dependence of absorption on the angle of incidence under conditions of resonance effects caused by the spatial organization of particles. It is shown that in the region of the resonant absorption peak a normally illuminated monolayer with a triangular lattice of silver particles can absorb almost an order of magnitude more incident light than a partially ordered layer. The absorption coefficient of a monolayer under directional oblique illumination can be almost an order of magnitude larger than under normal illumination. The results can be used to optimize the design of opto-electronic devices based on particulate layers.