Polarization Combinations Research Articles

Coherent blue light enhancement via repumping laser in cesium vapor

We demonstrate the generation of coherent and collimated blue light (CBL) based on cesium (Cs) 6S<sub>1/2</sub>(<i>F</i> = 4)→6P<sub>3/2</sub>(<i>F'</i> = 5)→6D<sub>5/2</sub>(<i>F''</i> = 6)→7P<sub>3/2</sub>(<i>F'</i> = 5)→6S<sub>1/2</sub>(<i>F</i> = 4) diamond-type atomic system in a heated vapor cell. Two infrared pumping lasers with wavelengths at 852 nm (6S<sub>1/2</sub>→6P<sub>3/2</sub>) and 917 nm (6P<sub>3/2</sub>→6D<sub>5/2</sub>), provide step-wise excitation to the 6D<sub>5/2</sub> excited state, and induce strong two-photon coherence between the 6S<sub>1/2</sub> state and 6D<sub>5/2</sub> state. The atoms undergo a double cascade accompanied with the amplified spontaneous emission at 15.1 μm via the 7P<sub>3/2</sub> intermediate excited state, and produce a beam of 455 nm (7P<sub>3/2</sub>→6S<sub>1/2</sub>) CBL with highly spatiotemporal coherence through a parametric four-wave mixing process. We investigate the influence of experimental parameters such as polarization combination of the two pumping lasers, and their power, and the temperature of Cs vapor cell on the CBL. Especially, we add a beam of 894 nm laser operating at the 6S<sub>1/2</sub>(<i>F</i> = 3) →6P<sub>1/2</sub> transition as repumping laser, which can pump atoms back to the 6S<sub>1/2</sub>(<i>F</i> = 4) state from the 6S<sub>1/2</sub>(<i>F</i> = 3) state, thus significantly improving the power of CBL. This technique of the CBL enhancement via optical pumping is also useful for the other alkali metal atoms.

Ex vivo tolerization and M2 polarization of macrophages dampens both pro- and anti-inflammatory cytokine production in response to diabetic wound fluid stimulation

Monocytes/macrophages play a prominent role in cutaneous wound healing. Persistent inflammation in diabetic wounds is associated with the inability of monocytic cells to switch from a phagocytic M1 (classically activated) to an anti-inflammatory, pro-regenerative M2 (alternatively activated) phenotype and as consequence, the proliferative phase of healing does not commence. A targeted cell therapy approach could potentially restore the pathological wound microenvironment through paracrine signalling to enable healing. This study investigated whether in vitro pre-treatment of monocytic (J774.1 A) cells - using a combination of endotoxin-induced immune tolerance (Pam3CSK4) and M2 polarization (IL-4) - could make these cells impervious to the pathological wound microenvironment and enhance the release of anti-inflammatory cytokines/growth factors. The effect of Pam3CSK4-induced tolerance and IL-4-associated polarization was assessed independently and in combination, on the expression of intracellular (flow cytometry) and secreted (ELISA) cytokines (TNF-ɑ, IL-6, IL-10, TGF-β) with and without re-stimulation to define the optimal pre-treatment conditions. Successive pre-treatment approach consisting of endotoxin tolerance followed by IL-4 priming, dampened TNF-ɑ release and induced intracellular TGF-β production upon re-stimulation. To mimic a chronic wound microenvironment, the J774A.1 monocytes were differentiated into macrophages using GM-CSF prior to pre-treatment (optimal condition) and subsequently exposed to diabetic wound fluid. The data demonstrated that in the presence of wound fluid, the successive pre-treatment, promoted M2 polarization (CD206) of monocytic cells and significantly dampened the intracellular production of both pro-inflammatory (TNF-ɑ, IL-6) and anti-inflammatory (IL-10, TGF-β) cytokines.

Compact Radar Cross-Section Measurement Setup and Performance Evaluation

Abstract. Radar cross-section measurements require the background reflections to be much lower than the reflections of the device under test. Although, anechoic chambers with special target holders meet this requirement, they are expensive and still have imperfections. To further reduce background reflections or to measure in environments where an anechoic chamber is not suitable, digital signal processing can be used to reduce background reflections. In this paper, a complete signal processing chain realized in Matlab is proposed, involving time gating of the measured target response and a background subtraction technique. Furthermore, the proposed signal processing includes a calibration procedure with either a single known calibration target or multiple known targets to improve measurement uncertainties. A compact measurement setup, consisting of a vector network analyzer and two horn antennas, is used to evaluate the overall performance and the advantages of a multiple known target calibration in a practical manner. The calibrated setup is able to measure the radar cross-section in a frequency range from 2 to 12 GHz with a mean error of less than 0.2 dB for both, VV and HH polarization combinations. It could also be shown, that a multi target calibration can result in an improvement of the measurement uncertainty by about 2.5 %.

Investigation of 6S 1/2–8S 1/2 two-photon transition of cesium atoms by a single 822 nm laser

We experimentally investigate the 6S 1/2–8S 1/2 two-photon transition in cesium vapor by a single laser. A blue (455.5 and 459.3 nm) fluorescence signal is observed as a result of 822.5 nm laser beams illuminating the Cs vapor with a counter-propagating configuration. The dependences of the fluorescence intensity on the polarization combinations of the laser beams, laser power and vapor temperature are studied to obtain optimal experimental parameters. The frequency difference between the two hyperfine components of 4158 (7) MHz is measured with a Fabry–Perot interferometer as a frequency reference. Such a large spectral isolation and the insensitivity to the Earth’s magnetic field enable the 6S 1/2–8S 1/2 transition to be a stable frequency standard candidate for a frequency-doubled 1644 nm laser in the U-band window for quantum telecommunication.

Study of Integer Spin S = 1 in the Polar Magnet β-Ni(IO3)2.

Polar magnetic materials exhibiting appreciable asymmetric exchange interactions can potentially host new topological states of matter such as vortex-like spin textures; however, realizations have been mostly limited to half-integer spins due to rare numbers of integer spin systems with broken spatial inversion lattice symmetries. Here, we studied the structure and magnetic properties of the S = 1 integer spin polar magnet β-Ni(IO3)2 (Ni2+, d8, 3F). We synthesized single crystals and bulk polycrystalline samples of β-Ni(IO3)2 by combining low-temperature chemistry techniques and thermal analysis and characterized its crystal structure and physical properties. Single crystal X-ray and powder X-ray diffraction measurements demonstrated that β-Ni(IO3)2 crystallizes in the noncentrosymmetric polar monoclinic structure with space group P21. The combination of the macroscopic electric polarization driven by the coalignment of the (IO3)− trigonal pyramids along the b axis and the S = 1 state of the Ni2+ cation was chosen to investigate integer spin and lattice dynamics in magnetism. The effective magnetic moment of Ni2+ was extracted from magnetization measurements to be 3.2(1) µB, confirming the S = 1 integer spin state of Ni2+ with some orbital contribution. β-Ni(IO3)2 undergoes a magnetic ordering at T = 3 K at a low magnetic field, μ0H = 0.1 T; the phase transition, nevertheless, is suppressed at a higher field, μ0H = 3 T. An anomaly resembling a phase transition is observed at T ≈ 2.7 K in the Cp/T vs. T plot, which is the approximate temperature of the magnetic phase transition of the material, indicating that the transition is magnetically driven. This work offers a useful route for exploring integer spin noncentrosymmetric materials, broadening the phase space of polar magnet candidates, which can harbor new topological spin physics.

Terahertz Multi-Spectral Mueller Matrix Polarimetry on Leaf Using Only Orthogonal-Polarization Measurements

There has been a surge of emphasis on polarimetric imaging modalities recently, in which Mueller matrix polarimetry (MMP) is at the heart of our understanding of polarization properties of an imaged sample. However, the historiography of MMP, predominantly undertaken in optics, largely lost sight of the potential of terahertz radiation on interactions with the imaged samples, especially biological ones. In addition, studies of MMP are generally concerned with intensity-only measurements requiring at least 16 polarization combinations, which dramatically add to the time cost in the process of measurements. The proposed study sets out to examine the complete 4 × 4 MMP from 0.2 to 1 THz using only orthogonal polarizations for two-dimensional (2-D) and 3-D imaging on leaf. A modified THz time domain spectrometer with self-designed linear polarizers is utilized for measurements and data acquisition. The Mueller matrix polar decomposition and Mueller matrix transform are employed to facilitate extraction of polarization characteristics of the imaged leaf. The time-of-flight technique is adopted to assist in the 3-D reconstruction of the leaf. The results demonstrate the effectiveness and feasibility of the novel measurement synthesis approach and the modified system for accurate characterization of the sample. Meanwhile, the findings indicate that MMP is superior in feature extraction as well as contrast enhancement of the sample. The insights gained from this article may be of assistance to the characterization of biological samples with MMP at higher frequencies for future research.

Focusing characteristics of polarized second-harmonic emission at non-Ising polar domain walls

Non-Ising polar domain walls have recently emerged as individual two-dimensional materials exhibiting localized nonlinear optical emission. The analysis of this emitted light often requires focusing with high apertures. As a result, the vectorial properties of light come into play. This study provides an analytic treatment of the vector light fields’ effect on the polarized second-harmonic emission (SHG) arising at polar domain walls. While confined optical fields are expected to alter the SHG polarization response, we identify extrinsic and intrinsic properties capable of canceling focusing effects. We determine a precise combination of the fundamental wave polarization and orientation of the domain walls at which focusing effects are negligible. Furthermore, the perimeter defined by the domain walls intrinsic optical parameters below which focusing effects are negligible is extracted from a systematic focus-dependent analysis. Our study provides the necessary methodology and precautions to probe the internal structure of non-Ising domain walls with confined optical fields, and it can be extended to explore newly discovered ferroelectric topologic nanostructures.

Three-dimensional coupling structure for a high power laser diode module

A novel scheme involving a three-dimensional (3D) coupling structure is used to build a laser diode (LD) module that utilizes the fiber angle space more completely. Compared with the traditional 2D configuration, the number of LD’s is increased by 4, obtaining an increased efficiency of over 90%. Another advantage is that some costly optical elements used in the traditional polarization combination method are not necessary.

Interaction of Amyloid-β-(1-42) Peptide and Its Aggregates with Lipid/Water Interfaces Probed by Vibrational Sum-Frequency Generation Spectroscopy.

In this study, we use surface-sensitive vibrational sum-frequency generation (VSFG) spectroscopy to investigate the interaction between model lipid monolayers and Aβ(1-42) in its monomeric and aggregated states. Combining VSFG with atomic force microscopy (AFM) and thioflavin T (ThT) fluorescence measurements, we found that only small aggregates with probably a β-hairpin-like structure adsorbed to the zwitterionic lipid monolayer (DOPC). In contrast, larger aggregates with an extended β-sheet structure adsorbed to a negatively charged lipid monolayer (DOPG). The adsorption of small, initially formed aggregates strongly destabilized both monolayers, but only the DOPC monolayer was completely disrupted. We showed that the intensity of the amide-II' band in achiral (SSP) and chiral (SPP) polarization combinations increased in time when Aβ(1-42) aggregates accumulated at the DOPG monolayer. Nevertheless, almost no adsorption of preformed mature fibrils to DOPG monolayers was detected. By performing spectral VSFG calculations, we revealed a clear correlation between the amide-II' signal and the degree of amyloid aggregates (e.g., oligomers or (proto)fibrils) of various Aβ(1-42) structures. The calculations showed that only structures with a significant amyloid β-sheet content have a strong amide-II' intensity, in line with previous Raman studies. The combination of the presented results substantiates the amide-II(') band as a legitimate amyloid marker.

Probing size variations of molecular aggregates inside chlorosomes using single-object spectroscopy.

We theoretically investigate the possibility to use single-object spectroscopy to probe size variations of the bacteriochlorophyll aggregates inside chlorosomes. Chlorosomes are the light-harvesting organelles of green sulfur and non-sulfur bacteria. They are known to be the most efficient light-harvesting systems in nature. Key to this efficiency is the organization of bacteriochlorophyll molecules in large self-assembled aggregates that define the secondary structure inside the chlorosomes. Many studies have been reported to elucidate the morphology of these aggregates and the molecular packing inside them. It is widely believed that tubular aggregates play an important role. Because the size (radius and length) of these aggregates affects the optical and excitation energy transport properties, it is of interest to be able to probe these quantities inside chlorosomes. We show that a combination of single-chlorosome linear polarization resolved spectroscopy and single-chlorosome circular dichroism spectroscopy may be used to access the typical size of the tubular aggregates within a chlorosome and, thus, probe possible variations between individual chlorosomes that may result, for instance, from different stages in growth or different growth conditions.

Tripolarizated MIMO: Experimental Analysis and Modeling of Channel Properties in Both Indoor and Outdoor Scenarios

The tripolarized MIMO system can provide one more degree of freedom and have a more compacted size over a dual-polarized MIMO system, which is attractive for high-capacity wireless communication systems. In this paper, we analyze and model channel properties for tripolarized MIMO systems based on experimental channel measurements in typical indoor and outdoor scenarios. Firstly, channel measurement campaigns in the laboratory and the Urban Micro (UMi) scenarios on sub-6 GHz bands are presented. Then, based on measured data, path loss, delay spread (DS), and cross-polarization discrimination (XPD) for 9 polarization combinations are analyzed and modeled in a statistical way. Statistical results of these channel properties are also given. It is observed that channel properties of both large-scale fading and small-scale fading depend strongly on the polarization direction. Furthermore, we evaluate the performance of tripolarized MIMO systems by analyzing the Demmel condition number and channel capacity gain (CG). For both the indoor and the outdoor scenarios, it is found that colocated tripolarized antenna can bring a nearly threefold CG with respect to the unipolarized one. These results can give good insights into the design and evaluation of tripolarized MIMO systems.

Irrigated rice crop identification in Southern Brazil using convolutional neural networks and Sentinel-1 time series

Rice is one of the world’s staple food sources, with millions of tonnes produced and consumed every year. Therefore, mapping rice paddies is essential for agricultural management and ensuring food security. This study aimed to classify rice crops in southern Brazil using the SENTINEL-1 SAR time series and deep learning models, comparing two architectures (U-net and LinkNet) and four backbones (ResNet-34, ResNeXt-50, DenseNet-121, and VGG16). The time series construction considered ten images, each for a month, covering the rice planting cycle. The Convolutional Neural Network architectures were adapted to use multi-band data, allowing the extraction of features from all-temporal images. This approach provides capturing spatiotemporal information from rice plantations, which favors its detection. Besides, the research evaluated three data sets considering the polarizations: (a) VV-only, (b) VH-only, and (c) both VV and VH (VV + VH). The classification accuracies used to measure the performance of the models were the overall accuracy, F1-measure, area under the precision-recall curve (AUPRC), and the intersection over union (IoU). Results show that the VH + VV polarization combination yielded the best results, followed by VH-only and VV-only. The VV-only polarization had significantly worst results (nearly 10% less IoU than VH-only and nearly 15% less IoU compared to VV + VH). The results show that rice fields can be successfully classified with deep learning models and through our evaluation the LinkNet architecture with the ResNeXt-50 backbone showed the best results with an accuracy of 0.98, F1 of 0.93, AUPRC of 0.93, and IoU of 0.91.

Frequency and polarization emission properties of a photon-pair source based on a photonic crystal fiber

In this work, we experimentally demonstrate a photon-pair source with correlations in the frequency and polarization degrees of freedom. We base our source on the spontaneous four-wave mixing (SFWM) process in a photonic crystal fiber. We show theoretically that the two-photon state is the coherent superposition of up to six distinct SFWM processes, each corresponding to a distinct combination of polarizations for the four waves involved and giving rise to an energy-conserving pair of peaks. Our experimental measurements, both in terms of single and coincidence counts, confirm the presence of these pairs of peaks, while we also present related numerical simulations with excellent experiment-theory agreement. We explicitly show how the pump frequency and polarization may be used to effectively control the signal-idler photon-pair properties, defining which of the six processes can participate in the overall two-photon state and at which optical frequencies. We analyze the signal-idler correlations in frequency and polarization, and in terms of fiber characterization, we input the SFWM-peak experimental data into a genetic algorithm which successfully predicts the values of the parameters that characterize the fiber cross section, as well as predict the particular SFWM process associated with a given pair of peaks. We believe our work will help advance the exploitation of photon-pair correlations in the frequency and polarization degrees of freedom.

Physics-based optimization of Landau parameters for ferroelectrics: application to BZT–50BCT

In analogy to thermochemical parameter optimization in the CALculation of PHAse Diagrams (CALPHAD) approach that relies on a wide variety of experimental measurements, a thermodynamic parameter optimization strategy to describe the polarization response with single-crystal Landau coefficients is documented herein to bridge the gap between CALPHAD, Landau theory and the generality of phase field theory. As an example, anisotropic Landau coefficients are obtained by starting from experimental parameters for Pb-free 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–50BCT). Thermodynamic parameters are optimized separately for the rhombohedral (R) and tetragonal (T) ferroelectric phases using a combination of single-crystal and polycrystalline polarization and permittivity data. Parameters are validated against dielectric permittivity as a function of temperature from single-crystal and polycrystalline samples. The optimized parameters correctly predict the sequence of phase transitions as a function of temperature and the paraelectric–ferroelectric transition at 355.5 K is within the experimentally reported range. An upper thermodynamic limit is predicted for R + T metastable coexistence at 302.3 K in agreement with the experimentally measured transition to a stable single T phase for this chemistry at 302 K. The detailed parameter optimization procedure enables the identification of single-crystal tensor properties from experimental measurements for a wide variety of chemistries.

Theoretical study of micro-structure fabrication by multi-beam laser interference lithography with different polarization combinations

In this study, we systematically and comprehensively investigated the influence of polarization angle on the fabrication of micro-structures by multi-beam laser interference lithography. Using theoretical analysis and simulation, we studied the effect of different polarization combinations, i.e. transverse electric (TE) and transverse magnetic (TM) polarization combinations, on the characteristics of the micro-structures fabricated by three-, four-, and six-beam laser interference lithography. We successfully obtained micro-structures with different periodic patterns such as honeycomb dots, quasi-elliptic dots, different square dots, and quasi-triangular dots. The simulation results illustrate that polarization affects the formation of interference patterns, pattern contrasts, and periods. The methods discussed herein are simple, low cost, and allow excellent control over structural parameters, and hence are useful for the micro-structure manufacturing industry.

Sub-Millimeter-Wave Polarization-Independent Spatial Power Divider for a Two-Port Dual-Polarized Antenna

An antenna system is proposed that uses a novel polarization-independent spatial power divider to align the beams from two orthogonally oriented dual-polarized feeds. This antenna system uses a common aperture for transmitting and receiving and provides high port isolation while maintaining compatibility with fully polarimetric radar. Unlike conventional two antenna radar systems, a radar using this antenna does not suffer from the parallax problem. The spatial power divider is designed using an all-dielectric metasurface approach and is fabricated on a silicon wafer using standard micromachining technology. The measured device exhibits at most 0.9 dB of difference between the reflection and transmission for both transverse electric and transverse magnetic incident waves at 45° incidence, over a band from 221 to 250 GHz. Conical horns are fabricated as feeds and together with the spatial power divider, a focusing lens, and microwave absorbers, are assembled in a three-dimensional-printed housing to complete the antenna system. Its measured gain is approximately 39 dB for each port and polarization, and isolation between ports is at least 40 dB for all polarization combinations over the band of interest.

Synthesis of dielectric polymers with bipyridyl ligand and metal complex by ring-opening metathesis polymerization

Block copolymers with bipyridyl ligand and metal ion complex were synthesized by ring-opening metathesis polymerization. The combination of high dipolar polarization induced by bis(trifluoromethyl) group in polymer, the long-range polaron hopping process produced by the introduction of metal-bipyridyl side group, and the self-assembled nanostructure significantly improved the dielectric properties of polymers. The iridium(III)-contained block copolymer exhibited outstanding comprehensive dielectric and energy storage performance with high dielectric constant of 23.0–20.3 and low dielectric loss of 0.032–0.013 at 102–106 Hz, and high polarizability of 3.14 μC cm−2 at 280 MV m−1. Besides, the released-stored energy density reached 4.17/4.86 J cm−3 accompanied with the charge-discharge efficiency of 86%. Therefore, it would have potential applications as a metal-organic dielectric material with good dielectric and energy storage properties.

Simultaneous perfect polarization of spin and valley using monolayer MoS2 modulated by light and spin Zeeman field

Perfect polarization of spin and valley is found to coexist in the proposed junction of monolayer MoS2. The junction consists of two barriers modulated by off-resonant circularly polarized light and spin Zeeman field, respectively. By appropriately altering the modulation, we can achieve all four combinations of simultaneous perfect spin and valley polarization, which are , , , and . Moreover, we have found that by continuously tuning the light illuminating the junction, the valley polarization will abruptly dive from 100% to −100%. The spin polarization exhibits similar features when we tune the spin Zeeman field. Thus, the valley switching effect and the spin switching effect are realized in monolayer MoS2 by varying the circularly polarized light and spin Zeeman field. These results demonstrate the modulated monolayer MoS2’s potential as a vital tool in spintronics and valleytronics.

Study on the director arrangement of cholesteric liquid crystals with planar texture in PAN and TN cells

The director arrangement of cholesteric liquid crystals with planar texture (CLCPT) in PAN and TN cells is demonstrated in this paper. First, two types of director arrangements of CLCPT in PAN and TN cell were presented according to experience and their expressions were developed by using the liquid crystal (LC) elasticity theory, also the theoretical expressions for reflectance and transmittance at a certain incident angle of the CLCPT cell corresponding to four kinds of polarization combinations (Rpp, Rps, Rsp, Rss, Tpp, Tps, Tsp, Tss) were deduced based on the multilayer optical theory. Then the fully leaky optical guided wave (FLOGW) method was introduced to prove the correctness of the two types of director arrangements presented above. During the implementation of this method, 8 different CLCPT cell samples were made considering the natural pitch of CLC, cell thickness and anchoring direction of cell substrates. Further, the experimental and theoretical curves for Rpp and Rss variation with incident angle of each sample were obtained and fitted correspondingly. Thus, by analyzing the fitting results, the director arrangement characteristics of the CLCPT in PAN and TN cells were demonstrated experimentally.

A New Suppression approach of FWM Crosstalk Effect in Optical Communication Link based on Polarization combiner Method

To meet the growing needs of internet data, optical communication systems have become the backbone of modern communications networks. At the present time, the dense wavelength division multiplexing (DWDM) technique has been used to increase the number of channels, but the nonlinear effects have a great impact that limits the performance of doubling the DWDM system. The four wave mixing (FWM) is the most harmful and dangerous as the effect of FWM increases on the system the greater the optical connection distances. The new approach of pairing groups of different optical signals was investigated to suppress the FWM effect. The simulation was conducted for an 8-channel system with a total data rate (80Gb/s). A comparative study was conducted on the suppression of FWM by the difference in the power inputs (-0.5 to 20) dBm. The robustness of the proposed technique was examined using two forms of modulation (Carrier Suppressed Return to Zero (CSRZ) and Duo Binary Modulation class -1(DBM-1)) techniques, with optical fiber system of (1,2,5) spans, each of length 60 Km, with spacing between the channels 50GHz. The power of FWM was significantly reduced with the CSRZ & DBM-1 techniques to less than (47.97%, 41.38 %) respectively, at an input power of 12.5 dBm. The performance of the proposed system with the polarization technique was improved by the rate of the quality factor (Q-factor of (91.59%, 78.67%) for the same sequence of modulation.