Highly anisotropic transient optical response of charge density wave order in ZrTe3_3

Low dimensionality in CDW systems leads to anisotropic optical properties, in both equilibrium and non-equilibrium conditions. Here we perform polarized two-color pump probe measurements on a quasi-1D material ZrTe$_3$, in order to study the anisotropic transient optical response in the CDW state. Profound in-plane anisotropy is observed with respect to polarization of probe photons. Below $T_\mathrm{CDW}$ both the quasi-particle relaxation signal and amplitude mode (AM) oscillation signal are much larger with $\mathbf{E}_\mathrm{pr}$ nearly parallel to $a$ axis ($\mathbf{E}_\mathrm{pr} \parallel a$) than for $\mathbf{E}_\mathrm{pr}$ parallel to $b$ axis ($\mathbf{E}_\mathrm{pr} \parallel b$). This reveals that $\mathbf{E}_\mathrm{pr} \parallel a$ signal is much more sensitive to the variation of the CDW gap. Interestingly, the lifetime of the AM oscillations observed with $\mathbf{E}_\mathrm{pr} \parallel b$ is longer than $\mathbf{E}_\mathrm{pr} \parallel a$. Moreover, at high pump fluence where the electronic order melts and the AM oscillations vanish for $\mathbf{E}_\mathrm{pr} \parallel a$ , the AM oscillatory response still persists for $\mathbf{E}_\mathrm{pr} \parallel b$. We discuss possible origins that lead to such unusual discrepancy between the two polarizations.Comment: 6 pages, 4 figure

Optical studies of structural phase transition in the vanadium-based kagome metal ScV6Sn6

In condensed matter physics, materials with kagome lattice exhibit exotic emergent quantum states, including charge density wave (CDW), superconductivity and magnetism. Very recently, hexagonal kagome metal ScV6Sn6 was found to undergo fascinating first-order structural phase transition at around 92 K and a 3x3x3 CDW modulation. The bulk electronic band properties are enlightened for comprehending the origin of the structural phase transition. Here, we perform a optical spectroscopy study on the monocrystalline compound across the transition temperature. The structural transition gives rise to the abrupt changes of optical spectra without observing gap development behavior. The optical measurements revealed a sudden reconstruction of the band structure after transition. We emphasize that the phase transition is of the first order and distinctly different from the conventional density-wave type condensation. Our results provide insight into the origin of the structural phase transition in the new kagome metal compound.Comment: 7 pages, 4 figure

Pump-induced terahertz conductivity response and peculiar bound state in Mn3Si2Te6

We report the significant enhancement on ultrafast terahertz optical conductivity and the unexpected formation of a polaronic-like state in semiconductor Mn3Si2Te6 at room temperature. With the absorption of pump photons, the low-frequency terahertz photoconductivity spectrum exhibits a significant rise, quickly forming a broad peak and subsequently shifting to higher energy. The short-lived nature of the broad peak, as well as the distribution of optical constants, strongly points towards a transient polaron mechanism. Our study not only provides profound insights into the remarkable photoelectric response of Mn3Si2Te6 but also highlights its significant potential for future photoelectric applications

Development of China’s first space-borne aerosol-cloud high-spectral-resolution lidar: retrieval algorithm and airborne demonstration

Aerosols and clouds greatly affect the Earth’s radiation budget and global climate. Light detection and ranging (lidar) has been recognized as a promising active remote sensing technique for the vertical observations of aerosols and clouds. China launched its first space-borne aerosol-cloud high-spectral-resolution lidar (ACHSRL) on April 16, 2022, which is capable for high accuracy profiling of aerosols and clouds around the globe. This study presents a retrieval algorithm for aerosol and cloud optical properties from ACHSRL which were compared with the end-to-end Monte-Carlo simulations and validated with the data from an airborne flight with the ACHSRL prototype (A2P) instrument. Using imaging denoising, threshold discrimination, and iterative reconstruction methods, this algorithm was developed for calibration, feature detection, and extinction coefficient (EC) retrievals. The simulation results show that 95.4% of the backscatter coefficient (BSC) have an error less than 12% while 95.4% of EC have an error less than 24%. Cirrus and marine and urban aerosols were identified based on the airborne measurements over different surface types. Then, comparisons were made with U.S. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) profiles, Moderate-resolution Imaging Spectroradiometer (MODIS), and the ground-based sun photometers. High correlations (R > 0.79) were found between BSC (EC) profiles of A2P and CALIOP over forest and town cover, while the correlation coefficients are 0.57 for BSC and 0.58 for EC over ocean cover; the aerosol optical depth retrievals have correlation coefficient of 0.71 with MODIS data and show spatial variations consistent with those from the sun photometers. The algorithm developed for ACHSRL in this study can be directly employed for future space-borne high-spectral-resolution lidar (HSRL) and its data products will also supplement CALIOP data coverage for global observations of aerosol and cloud properties

Strong nonlinear optical response and transient symmetry switching in Type-II Weyl semimetal β\beta-WP2

The topological Weyl semimetals with peculiar band structure exhibit novel nonlinear optical enhancement phenomena even for light at optical wavelengths. While many intriguing nonlinear optical effects were constantly uncovered in type-I semimetals, few experimental works focused on basic nonlinear optical properties in type-II Weyl semimetals. Here we perform a fundamental static and time-resolved second harmonic generation (SHG) on the three dimensional Type-II Weyl semimetal candidate $\beta$-WP$_2$. Although $\beta$-WP$_2$ exhibits extremely high conductivity and an extraordinarily large mean free path, the second harmonic generation is unscreened by conduction electrons, we observed rather strong SHG response compared to non-topological polar metals and archetypal ferroelectric insulators. Additionally, our time-resolved SHG experiment traces ultrafast symmetry switching and reveals that polar metal $\beta$-WP$_2$ tends to form inversion symmetric metastable state after photo-excitation. Intense femtosecond laser pulse could optically drive symmetry switching and tune nonlinear optical response on ultrafast timescales although the interlayer coupling of $\beta$-WP$_2$ is very strong. Our work is illuminating for the polar metal nonlinear optics and potential ultrafast topological optoelectronic applications.Comment: 8 pages, 5 figure

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health

Numerical study of vortex eccentricity in a gas cyclone

This paper presents a numerical study of the vortex eccentricity in a gas cyclone and its effect on the performance of the cyclone. The gas flow in the cyclone was modeled as an unsteady flow by the Navier–Stokes equations with the Reynolds Stress Model (RSM) as the turbulence model. The particles were modelled by the Lagrangian particle tracking (LPT) approach in an unsteady gas flow. Gas cyclones with the same dimensions and total flow rates but different numbers of inlets were simulated with the inlet velocity varying from 12 to 20 m/s. The vortex eccentricities in different cases were analyzed in terms of radial deviation and angular deviation. In addition, the frequency of the precessing vortex core (PVC) was analyzed by the fast Fourier transform (FFT). The results show that the vortex center in the single inlet cyclone has a great eccentricity and its precession center is also different from the geometric center, which reduces the particle collection efficiency. The increase in the symmetry of the inlet causes only a very small increase in the pressure drop in the simulated cases, but it can significantly reduce the vortex eccentricity, particularly by eliminating the eccentricity of the PVC center. The improvement of the vortex eccentricity can generally increase the collection efficiency for particles greater than 2.0 µm. The increase of the collection efficiency is mainly because the symmetrical vortex can restrain the short-circuiting flow of particles. The results can improve the understanding of the vortex flow in gas cyclones which may guide the optimization of gas cyclones. © 201

Vortex characteristics of a gas cyclone determined with different vortex identification methods

This paper characterizes the vortex flow field in a gas cyclone based on different vortex identification methods, including vorticity method, Q criterion, λ2 criterion, Ω method and Liutex method. Analysis and comparison of isosurfaces of different vortex identification methods indicate that except vorticity method, the vortex core, the eddy flow and the short-circuit flow can be identified directly by other methods. But the small scale vortices, such as top ash ring, can only be fully recognized by Liutex method. The contours demonstrate that the magnitude of five vortex parameters is the largest in the vortex core, followed by the short-circuit flow, and the eddy flow is the smallest. But only Liutex method can predict the vortex core center and identify the most severe vortex eccentricity is in the bottom of vortex finder, the lower part of the cone and the hopper. The work not only improves the understanding of the vortex structure in a gas cyclone, which can critically affects cyclone performance, but also reveals the differences in the commonly used vortex characterization methods