Межзонный двухфотонный линейно-циркулярный дихроизм в полупроводниках в приближении Кейна

Interband two-photon optical transitions are classified and expressions are obtained for the matrix elements in a narrow-gap semiconductor depending on the band parameters, degree of polarization, and light frequency. It is shown that the main contribution to two-photon linear-circular dichroism in narrow-gap semiconductors is made by optical transitions proceeding from the subband of light holes to the conduction band. The dependences of the partial coefficients of interband two-photon absorption of light, which differ from each other by the types of optical transitions, are analyzed depending on the degree of polarization of the light, and a quantitative analysis of the coefficient of linear-circular dichroism of two-photon absorption of light is carried out. Expressions are obtained for the spectral dependence of the coefficient of interband two-photon absorption of light in narrow-gap semiconductors in the Kane model.

Polarization Characterization of LEDs by Stokes Parameters Measurements

Stokes parameters have been measured by using a polarimeter consisting of a rotating phase plate before a fixed polarizer for bullet-shaped red, green and blue LEDs at 3 different directions of 0°, 45° and 90° from the principal axis. The degree of polarization is minimum at the observation angle 0° (observed head-on) for all colors as expected but has non-zero values (1-9%). As for the possible cause for the partial polarization, it is likely to be brought by striae inside the transparent epoxy resin that can be easily visible. Data at observation angle 90° have features common for all colors; the degree of polarization is highest, the long axis azimuth of the polarization ellipse is nearly in the horizontal direction, and the ellipticity is small. These features can be explained as follows. At observation angle 90°, only small fraction of the beam emitted nearly horizontally is detected possibly through multireflection (the plane of incidence is in the vertical plane) inside the top- and bottom-surfaces (in the horizontal direction) of the chip substrate. Since the reflectance for s-polarization (horizontal component) is higher than that for p-polarization, the emerging beam becomes horizontally polarized. The hypotheses that geometrical asymmetry generates polarization is experimentally supported.

Spatio-Temporal Pattern and Influence Mechanism of Cultivated Land System Resilience: Case from China

The study of cultivated land systems from the perspective of resilience is of great significance for the innovation of the research paradigm of cultivated land use and the rational utilization and protection of cultivated land. This study aims to explain the theoretical connotations of cultivated land system resilience (CLSR), construct an evaluation system and zoning rules for CLSR, and take 30 provinces of China as case study areas to explore the influencing factors of CLSR, so as to provide a reliable governance plan for the sustainable development of cultivated land. The results show that: (1) CLSR refers to a sustainable development ability that CLS—by adjusting the structure and scale of internal elements—absorbs and adapts to internal and external disturbances and shocks to the maximum possible extent, abandons the original inapplicable state, creates a new recovery path, achieves a new balance, and avoids system recession. (2) The overall CLSR of the 30 provinces showed an upward trend, and the degree of polarization of the distribution pattern was gradually intensified and experienced a transition process from “leading by resource and ecological resilience—equilibrium of each resilience—leading by production and scale structural resilience”. (3) In the north, east, and south coastal areas of China, CLSR mainly consists of the major evolution areas and the stable development areas; the potential excitation areas of CLSR are mainly concentrated in the central and western regions of China; the CLSR-sensitive lag areas and degraded vulnerable areas are mainly distributed in the northwest and southwest of China. (4) Water resource endowment has a strong influence on CLSR, while social economy mainly influences CLSR through ‘economic foundation-superstructures’ and ‘economic development-factor agglomeration’. (5) According to the different CLSR zones, CLSR was strengthened mainly from the aspects of driving factor agglomeration, building factor free-flow systems, and multi-means support.

Polarization control of attosecond pulses using bi-chromatic elliptically polarized laser

We study the high harmonic generation (HHG) using elliptically polarized two-color driving fields. The HHG via bi-chromatic counter-rotating laser fields is a promising source of circularly polarized ultrashort XUV radiation at the attosecond time scale. The ellipticity or the polarization of the attosecond pulses can be tweaked by modifying the emitted harmonics' ellipticity, which can be controlled by varying the driver fields. A simple setup is used to control the polarization of the driving fields, which eventually changes the ellipticity of the attosecond pulses. A well-defined scaling for the ellipticity of the attosecond pulse as a function of the rotation angle of the quarter-wave plate is also deduced by solving the time-dependent Schr\"odinger equation (TDSE) in two dimensions. The scaling can further be explored to obtain the attosecond pulses of the desired degree of polarization, ranging from linear to elliptical to circular polarization.

Estimation of Rock Characteristics Based on Polarization Spectra: Surface Roughness, Composition, and Density

Surface polarization characteristics provide crucial structural information of the Earth's surface. As two key elements of the natural geographical environment, rocks and soils play an important role in the study of surface processes. Inherent surface characteristics, such as surface roughness, composition, and density are critical parameters for the remote monitoring of land surfaces as they affect the polarization characteristics of scattered light waves. In this study, we investigated the relationship between surface roughness, composition, and density, and the polarization spectra of limestone-dolomite series rock. Results reveal a power function relationship between the surface roughness and the degree of polarization peaks among different detection zenith and azimuth angles. The depth and position of the absorbing waveband are significantly correlated with the characteristic component contents. The rock density was determined via the polarized reflection spectra, with the Earth's surface density calculations associated with a 2.6% divergence from the current recognized data. Our results demonstrate the ability of polarized spectra to retrieve surface roughness, composition, and density, with potential for further development in future work.

Swallowtail Butterflies Use Multiple Visual Cues to Select Oviposition Sites

Flower-foraging Japanese yellow swallowtail butterflies, Papilio xuthus, exhibit sophisticated visual abilities. When ovipositing, females presumably attempt to select suitable leaves to support the growth of their larval offspring. We first established that butterflies indeed select particular leaves on which to lay eggs; when presented with a single Citrus tree, butterflies significantly favored two out of 102 leaves for oviposition. These preferences were observed across many individuals, implying that they were not merely idiosyncratic, but rather based on properties of the leaves in question. Because the butterflies descended towards the leaves rather directly from a distance, we hypothesized that they base their selection on visual cues. We measured five morphological properties (height, orientation, flatness, roundness, and size) and four reflective features (green reflectance, brightness, and degree and angle of linear polarization). We found that the number of eggs laid upon a leaf was positively correlated with its height, flatness, green reflectance, and brightness, and negatively correlated with its degree of polarization, indicating that these features may serve as cues for leaf selection. Considering that other studies report ovipositing butterflies’ preference for green color and horizontally polarized light, butterflies likely use multiple visual features to select egg-laying sites on the host plant.

In situ measurements of reef squid polarization patterns using two-dimensional polarization data mapped onto three-dimensional tessellated surfaces

Reef squids belong to a group reputed for polarization sensitivity, yet polarization patterns of reef squid have not been quantified in situ . To quantify polarization patterns from video polarimetric data, we developed a protocol to map two-dimensional polarization data onto squid-shaped three-dimensional tessellated surfaces. This protocol provided a robust data container used to investigate three-dimensional regions-of-interest, producing data lineouts derived from the squid's geometry. This protocol also extracted polarimeter and squid body orientations and the solar heading from polarization images. When averaged over the solar heading, the ventral midline gave a low degree of polarization (2.4 ± 5.3%), and the area between the ventral and flank midlines had higher values (9.0 ± 5.3%). These averaged data had a large discontinuity in the angle of polarization (AoP) at the mantle's ventral midline (64 ± 55°), with larger discontinuities measured on individual squid. Ray-tracing calculations demonstrated that the AoP pattern was not related to the squid's surface-normal geometry. However, the AoP followed virtual striation axes on the squid's surface oriented 24° to the squid's long axis, similar in angle (27°) to the striations of birefringent collagen fibres documented in other squid species’ skin.

Polarimetric Dehazing Method Based on Image Fusion and Adaptive Adjustment Algorithm

To improve the robustness of current polarimetric dehazing scheme in the condition of low degree of polarization, we report a polarimetric dehazing method based on the image fusion technique and adaptive adjustment algorithm which can operate well in many different conditions. A splitting focus plane linear polarization camera was employed to grab the images of four different polarization directions, and the haze was separated from the hazy images by low-pass filtering roughly. Then the image fusion technique was used to optimize the method of estimating the transmittance map. To improve the quality of the dehazed images, an adaptive adjustment algorithm was introduced to adjust the illumination distribution of the dehazed images. The outdoor experiments have been implemented and the results indicated that the presented method could restore the target information obviously, and both the visual effect and quantitative evaluation have been enhanced.