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The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) satellite is a small magnetosphere–ionosphere link explorer developed cooperatively between China and Europe. It pioneers the use of X-ray imaging technology to perform large-scale imaging of the Earth’s magnetosheath and polar cusp regions. It uses a high-precision ultraviolet imager to image the overall configuration of the aurora and monitor changes in the source of solar wind in real time, using in situ detection instruments to improve human understanding of the relationship between solar activity and changes in the Earth’s magnetic field. The SMILE satellite is scheduled to launch in 2025. The European Incoherent Scatter Sciences Association (EISCAT)-3D radar is a new generation of European incoherent scatter radar constructed by EISCAT and is the most advanced ground-based ionospheric experimental device in the high-latitude polar region. It has multibeam and multidirectional quasi-real-time three-dimensional (3D) imaging capabilities, continuous monitoring and operation capabilities, and multiple-baseline interferometry capabilities. Joint detection by the SMILE satellite and the EISCAT-3D radar is of great significance for revealing the coupling process of the solar wind–magnetosphere–ionosphere. Therefore, we performed an analysis of the joint detection capability of the SMILE satellite and EISCAT-3D, analyzed the period during which the two can perform joint detection, and defined the key scientific problems that can be solved by joint detection. In addition, we developed Web-based software to search for and visualize the joint detection period of the SMILE satellite and EISCAT-3D radar, which lays the foundation for subsequent joint detection experiments and scientific research.

Solar wind charge exchange (SWCX) is the process of solar wind high-valence ions exchanging charges with neutral components and generating soft X-rays. Recently, detecting the SWCX emission from the magnetosphere is proposed as a new technique to study the magnetosphere using panoramic soft X-ray imaging. To better prepare for the data analysis of upcoming magnetospheric soft X-ray imaging missions, this paper compares the magnetospheric SWCX emission obtained by two methods in an XMM-Newton observation, during which the solar wind changed dramatically. The two methods differ in the data used to fit the diffuse X-ray background (DXB) parameters in spectral analysis. The method adding data from the ROSAT All-Sky Survey (RASS) is called the RASS method. The method using the quiet observation data is called the Quiet method, where quiet observations usually refer to observations made by the same satellite with the same target but under weaker solar wind conditions. Results show that the spectral compositions of magnetospheric SWCX emission obtained by the two methods are very similar, and the changes in intensity over time are highly consistent, although the intensity obtained by the RASS method is about \begin{document}$2.68\,\pm\, 0.56$\end{document} keV \begin{document}${\rm{cm}}^{-2} {\rm{s}}^{-1} {\rm{sr}}^{-1}$\end{document} higher than that obtained by the Quiet method. Since the DXB intensity obtained by the RASS method is about \begin{document}$2.84\,\pm\, 0.74$\end{document} keV \begin{document}${\rm{ cm}}^{-2} {\rm{s}}^{-1} {\rm{sr}}^{-1}$\end{document} lower than that obtained by the Quiet method, and the linear correlation coefficient between the difference of SWCX and DXB obtained by the two methods in different energy band is close to −1, the differences in magnetospheric SWCX can be fully attributed to the differences in the fitted DXB. The difference between the two methods is most significant when the energy is less than 0.7 keV, which is also the main energy band of SWCX emission. In addition, the difference between the two methods is not related to the SWCX intensity and, to some extent, to solar wind conditions, because SWCX intensity typically varies with the solar wind. In summary, both methods are robust and reliable, and should be considered based on the best available options.

The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a joint mission of the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS). Primary goals are investigating the dynamic response of the Earth's magnetosphere to the solar wind (SW) impact via simultaneous in situ magnetosheath plasma and magnetic field measurements, X-Ray images of the magnetosheath and magnetic cusps, and UV images of global auroral distributions. Magnetopause deformations associated with magnetosheath high speed jets (HSJs) under a quasi-parallel interplanetary magnetic field condition are studied using a three-dimensional (3-D) global hybrid simulation. Soft X-ray intensity calculated based on both physical quantities of solar wind proton and oxygen ions is compared. We obtain key findings concerning deformations at the magnetopause: (1) Magnetopause deformations are highly coherent with the magnetosheath HSJs generated at the quasi-parallel region of the bow shock, (2) X-ray intensities estimated using solar wind \begin{document}${\rm{H}}^+$\end{document} and self-consistent \begin{document}${\rm{O}}^{7+}$\end{document} ions are consistent with each other, (3) Visual spacecraft are employed to check the discrimination ability for capturing magnetopause deformations on Lunar and polar orbits, respectively. The SMILE spacecraft on the polar orbit could be expected to provide opportunities for capturing the global geometry of the magnetopause in the equatorial plane. A striking point is that SMILE has the potential to capture small-scale magnetopause deformations and magnetosheath transients, such as HSJs, at medium altitudes on its orbit. Simulation results also demonstrate that a lunar based imager (e.g., Lunar Environment heliospheric X-ray Imager, LEXI) is expected to observe a localized brightening of the magnetosheath during HSJ events in the meridian plane. These preliminary results might contribute to the pre-studies for the SMILE and LEXI missions by providing qualitative and quantitative soft X-ray estimates of dayside kinetic processes.

Earth’s magnetopause is a thin boundary separating the shocked solar wind plasma from the magnetospheric plasmas, and it is also the boundary of the solar wind energy transport to the magnetosphere. Soft X-ray imaging allows investigation of the large-scale magnetopause by providing a two-dimensional (2-D) global view from a satellite. By performing 3-D global hybrid-particle-in-cell (hybrid-PIC) simulations, we obtain soft X-ray images of Earth’s magnetopause under different solar wind conditions, such as different plasma densities and directions of the southward interplanetary magnetic field. In all cases, magnetic reconnection occurs at low latitude magnetopause. The soft X-ray images observed by a hypothetical satellite are shown, with all of the following identified: the boundary of the magnetopause, the cusps, and the magnetosheath. Local X-ray emissivity in the magnetosheath is characterized by large amplitude fluctuations (up to 160%); however, the maximum line-of-sight-integrated X-ray intensity matches the tangent directions of the magnetopause well, indicating that these fluctuations have limited impact on identifying the magnetopause boundary in the X-ray images. Moreover, the magnetopause boundary can be identified using multiple viewing geometries. We also find that solar wind conditions have little effect on the magnetopause identification. The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) mission will provide X-ray images of the magnetopause for the first time, and our global hybrid-PIC simulation results can help better understand the 2-D X-ray images of the magnetopause from a 3-D perspective, with particle kinetic effects considered.

The Soft X-ray Imager (SXI) is part of the scientific payload of the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) mission. SMILE is a joint science mission between the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS) and is due for launch in 2025. SXI is a compact X-ray telescope with a wide field-of-view (FOV) capable of encompassing large portions of Earth’s magnetosphere from the vantage point of the SMILE orbit. SXI is sensitive to the soft X-rays produced by the Solar Wind Charge eXchange (SWCX) process produced when heavy ions of solar wind origin interact with neutral particles in Earth’s exosphere. SWCX provides a mechanism for boundary detection within the magnetosphere, such as the position of Earth’s magnetopause, because the solar wind heavy ions have a very low density in regions of closed magnetic field lines. The sensitivity of the SXI is such that it can potentially track movements of the magnetopause on timescales of a few minutes and the orbit of SMILE will enable such movements to be tracked for segments lasting many hours. SXI is led by the University of Leicester in the United Kingdom (UK) with collaborating organisations on hardware, software and science support within the UK, Europe, China and the United States.

Astronomical imaging technologies are basic tools for the exploration of the universe, providing basic data for the research of astronomy and space physics. The Soft X-ray Imager (SXI) carried by the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) aims to capture two-dimensional (2-D) images of the Earth’s magnetosheath by using soft X-ray imaging. However, the observed 2-D images are affected by many noise factors, destroying the contained information, which is not conducive to the subsequent reconstruction of the three-dimensional (3-D) structure of the magnetopause. The analysis of SXI-simulated observation images shows that such damage cannot be evaluated with traditional restoration models. This makes it difficult to establish the mapping relationship between SXI-simulated observation images and target images by using mathematical models. We propose an image restoration algorithm for SXI-simulated observation images that can recover large-scale structure information on the magnetosphere. The idea is to train a patch estimator by selecting noise–clean patch pairs with the same distribution through the Classification–Expectation Maximization algorithm to achieve the restoration estimation of the SXI-simulated observation image, whose mapping relationship with the target image is established by the patch estimator. The Classification–Expectation Maximization algorithm is used to select multiple patch clusters with the same distribution and then train different patch estimators so as to improve the accuracy of the estimator. Experimental results showed that our image restoration algorithm is superior to other classical image restoration algorithms in the SXI-simulated observation image restoration task, according to the peak signal-to-noise ratio and structural similarity. The restoration results of SXI-simulated observation images are used in the tangent fitting approach and the computed tomography approach toward magnetospheric reconstruction techniques, significantly improving the reconstruction results. Hence, the proposed technology may be feasible for processing SXI-simulated observation images.

The SMILE (Solar wind Magnetosphere Ionosphere Link Explorer) project (http://www.nssc.cas.cn/smile/, https://www.cosmos.esa.int/web/smile/mission) is a joint spacecraft mission of the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS) with an expected launch in 2025. SMILE aims to study the global interactions of solar wind–magnetosphere–ionosphere innovatively by imaging the Earth’s magnetosheath and cusps in soft X-rays and the northern auroral region in ultraviolet (UV) while simultaneously measuring plasma and magnetic field parameters in the solar wind and magnetosheath along a highly-elliptical and highly-inclined orbit. This special issue is composed of 22 articles, presenting recent progress in modeling and data analysis techniques developed for the SMILE mission. In this preface, we categorize the articles into the following seven topics and provide brief summaries: (1) instrument descriptions of the Soft X-ray Imager (SXI), (2) numerical modeling of the X-ray signals, (3) data processing of the X-ray images, (4) boundary tracing methods from the simulated images, (5) physical phenomena and a mission concept related to the scientific goals of SMILE-SXI, (6) studies of the aurora, and (7) ground-based support for SMILE.

Following our earlier work on tomographic reconstruction of the magnetosheath soft X-ray emissions with superposed epoch analysis of many images recorded from a single spacecraft we now explore the instantaneous reconstruction of the magnetosheath and magnetopause using a few images recorded simultaneously from a few spacecraft. This workis motivated by the prospect of possibly having two or three soft X-ray imagers in spacein the coming years, and that many phenomena which occur at the magnetopause boundary, such as reconnection events and pressure pulse responses, do not lend themselvesas well to superposed epoch analysis. If the reconstruction is successful — which we demonstrate in this paper that it can be — this collection of imagers can be used to reconstructthe magnetosheath and magnetopause from a single image from each spacecraft, allowing for high time resolution reconstructions. In this paper we explore the reconstruction using, two, three, and four spacecraft. We show that the location of the subsolar pointof the magnetopause can be determined with just two satellites, and that volume emissions of soft X-rays, and the shape of the boundary, can be reconstructed using three or more satellites.

ABSTRACT: Microplastics have attracted global concern. The environmental-weathering processes control their fate, transport, transformation, and toxicity to wildlife and human health, but their impacts on biogeochemical redox processes remain largely unknown. Herein, multiple spectroscopic and electrochemical approaches in concert with wet-chemistry analyses were employed to characterize the redox properties of weathered microplastics. The spectroscopic results indicated that weathering of phenol–formaldehyde resins (PFs) by hydrogen peroxide (H2O2) led to a slight decrease in the content of phenol functional groups, accompanied by an increase in semiquinone radicals, quinone, and carboxylic groups. Electrochemical and wet-chemistry quantifications, coupled with microbial–chemical characterizations, demonstrated that the PFs exhibited appreciable electron-donating capacity (0.264–1.15 mmol e– g–1) and electron-accepting capacity (0.120–0.300 mmol e– g–1). Specifically, the phenol groups and semiquinone radicals were responsible for the electron-donating capacity, whereas the quinone groups dominated the electron-accepting capacity. The reversible redox peaks in the cyclic voltammograms and the enhanced electron-donating capacity after accepting electrons from microbial reduction demonstrated the reversibility of the electron-donating and -accepting reactions. More importantly, the electron-donating phenol groups and weathering-induced semiquinone radicals were found to mediate the production of H2O2 from oxygen for arsenite oxidation. In addition to the H2O2-weathered PFs, the ozone-aged PF and polystyrene were also found to have electron-donating and arsenite-oxidation capacity. This study reports important redox properties of microplastics and their effect in mediating contaminant transformation. These findings will help to better understand the fate, transformation, and biogeochemical roles of microplastics on element cycling and contaminant fate.

The coupling between solar wind and the magnetosphere and the dynamic processes in geo-space are the basic driving factors of space weather. Understanding these processes on the system level is essential to the studies of space physics and space weather. Recent solar wind charge exchange (SWCX) X-ray emission discoveries provide a novel approach to detect the large-scale magnetosphere through soft X-ray imaging. SWCX occurs when high-charge heavy ions such as C6+, N7+, O7+, and O8+ in the solar wind interact with neutral atoms or molecules, such as neutral hydrogen atoms in near-Earth space, neutral hydrogen and helium atoms in the heliosphere, and H2O and CO2 molecules on comets and other planets. Solar wind ions become excited by receiving one or more electrons, and then return to the ground state by releasing one or more photons in the soft X-ray band. The characteristics of the SWCX emissions include the X-ray spectrum showing line emissions corresponding to different species of solar wind particles and neutrons, and fast time variations closely related to solar wind variations. The SWCX soft X-ray emission of the Earth's magnetosphere mainly occurs in the magnetosheath on the dayside and the cusp regions. Therefore, the magnetosphere can be remotely imaged using large-scale soft X-ray imaging technology, allowing the fundamental modes of the interaction between the solar wind and magnetosphere to be recognized on a systematic scale.In this context, the European Space Agency (ESA) and Chinese Academy of Sciences (CAS) jointly proposed the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE). SMILE was approved in 2016 and implemented thereafter. SMILE aims to provide remote sensing measurements of the magnetopause and bow shock around the subsolar region, part of the cusp regions, and the aurora, as well as simultaneous in situ observations of the solar wind plasma and magnetic field. SMILE is planned to be launched in 2024–2025. Other missions have also been proposed to image the Earth's magnetosphere, such as the GEOspace X-ray imager (GEO-X) in Japan, Lunar Environment heliospherics X-ray Imager (LEXI) in the United States, and Lunar-based soft X-ray imager (LSXI) in China.With the advent of soft X-ray imaging missions to detect the magnetopause, evaluating the expected soft X-ray images and developing appropriate techniques to extract 3-dimentional boundary information from the 2-dimentional images is essential. Global magnetohydrodynamic (MHD) and instrument simulations are used to generate expected X-ray images under different solar wind conditions with different viewing geometries. Based on these images, several approaches have been developed to analyze the signals, composing the 'arsenal' or 'toolkit' for magnetopause reconstruction. Each approach has its own advantages and disadvantages, applicable to different situations.This paper introduces the mechanism of magnetospheric X-ray emission, reviews the research on the observational evidence and characteristics of SWCX X-ray emissions, summarizes the progress of simulation studies, presents the missions (or concept) of the magnetospheric X-ray detection, and discusses the possibility of future implementation of X-ray imaging for detecting other planets.

Maize/peanut intercropping is practiced widely to increase land productivity and considered a sustainable way for using and saving resources through peanut’s complementary N source via biological N2 fixation. Our study aims to understand how maize/peanut intercropping affects the nodulation of peanuts under water-limiting conditions and different nitrogen inputs. A two-year micro-plot experiment in 2015–2016 and a two-year field experiment in 2017–2018 were conducted to quantify nodulation in maize/peanut intercropping and sole peanut cropping under four N fertilization rates (N-free, low, medium, and high N) in rain-fed water-limited conditions. In the micro-plot experiment, intercropped peanuts increased nodule biomass compared to sole peanuts. The nodule number of intercropped peanuts was 51.6% (p = 0.001) higher than that of sole cropped peanuts, while nodule weights did not differ at high N fertilization rates and were lower in the no-N fertilization control. However, the results were different in the field experiment. Both the nodule number and single weight of the sole cropped peanut were 48.7% (p = 0.020) and 58.9% (p = 0.014) higher than that of the intercropped peanut. The ratio of the nodule weight to aboveground dry matter at the beginning peg in the dry year of 2017 was lower in intercropping than sole cropping, especially at low N fertilization rates. The potential increase in nodulation found in a well-controlled micro-plot environment might be limited by strong water and light competitions in field conditions. The results could contribute to the understanding of interspecific interactions in cereal/legume intercropping.

Imaging has been an important strategy for exploring space weather. The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a joint Chinese Academy of Sciences (CAS) and European Space Agency (ESA) mission, aiming at studying the interaction between Earth’s magnetosphere and solar wind near the subsolar point via soft X-ray imaging. As the boundary of Earth’s magnetosphere, magnetopause is a significant detection target to mirror solar wind’s change for the SMILE mission. In preparation for inverting three-dimensional magnetopause, we proposed an OESA-UNet model to detect the magnetopause position. The model obtains magnetopause with a U-shaped structure, in an end-to-end manner. Inspired by attention mechanisms, these blocks are integrated into ours. OESA-UNet captures low and high-level feature maps by adjusting the receptive field for precise localization. Adaptively pre-processing the image provides a prior for the network. Availability metrics are designed to determine whether it can serve three-dimensional inversion. Lastly, we provided ablation and comparison experiments by qualitative and quantitative analysis. Our recall, precision, and f1 score are 93.8%, 92.1%, and 92.9%, respectively, with an average angle deviation of 0.005 under the availability metrics. Results indicate that OESA-UNet outperforms other methods. It can better serve the purpose of magnetopause tracing from an X-ray image.

Abstract Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a novel self-standing mission dedicated to observing the solar wind–magnetosphere coupling via simultaneous in situ solar wind/magnetosheath plasma and magnetic field measurements, soft X-ray images of the magnetosheath and polar cusps, and UV images of global auroral distributions. While analyzing the observed images after the launch of SMILE, it will be a challenging task to reconstruct the 3-dimensional surface of the magnetopause from 2-dimensional images. Therefore, one of the most important key issues about SMILE is the reconstruction of magnetopause from X-ray images. This paper will review four main approaches have been developed so far, namely, the boundary fitting approach (BFA), the tangent fitting approach (TFA), the tangential direction approach (TDA), and the computed tomography approach (CTA). We will discuss their scope of application and pros and cons, and hopefully inspire future efforts.

Plasma flow vorticity is ubiquitous in space and plays a key role in material mixing and energy transfer. The five THEMIS satellites orbiting in different regions of the terrestrial magnetotail provide an unprecedented opportunity to study the temporal–spatial evolution characteristics of a plasma flow vortex on large spatial scales. We present an analysis of the flow vorticity that occurred between 05:50 and 06:30 UT on 2009 March 23 during a quiet time of the terrestrial magnetotail. The uneven distributions of the density and temperature of the vortex observed by the three near-Earth satellites (THA, THD, and THE) indicate that the plasma in the solar wind gradually mixed into the near-Earth magnetotail through a series of nonequilibrium processes. Both the flow vortices and dipolarization observed by the three near-Earth satellites were about 10 minutes earlier than those observed by the two satellites (THB and THC) in the mid-magnetotail. Further analysis of the relationship between vorticity, field-aligned current, and energy transport reveals that the flow vortex interacted with the surrounding plasma during its tailward propagation. The field-aligned current related to the vorticity could only generate a pseudo-breakup of the aurora in the ionosphere. Thus, we speculate that this flow vortex mainly transports mass and energy from the solar wind to the near-magnetotail, propagates tailward to the mid-magnetotail, and heats the encountered plasma by dissipating its bulk flow and dominant thermal energy. These results shed light on the mass mixing, energy transport, and dissipation of the plasma flow vortex during quiet levels of geomagnetic activity on large spatial scales.

In this paper, we present a figure-eight all-polarization maintaining thulium-doped mode-locked fiber laser based on a nonlinear optical loop mirror operating at noise-like pulse regimes. The total cavity length is 34.5 m, and the calculated net group delay dispersion is estimated to be ∼−2.616 ps2. At the maximum pump power, stable noise-like pulse centered at 1943 nm with a spectral full width at half maximum of 32 nm, a pulse energy of 13.51 nJ, and a coherence spike width of 236 fs is generated at a repetition rate of 5.96 MHz with the signal-to-noise ratio ∼64 dB. The polarization extinction ratio is > 15 dB at any mode-locking operation. The slope efficiency and the output power fluctuation of the laser are 5.16% and 0.039%, respectively. The laser does not require polarization state controllers, and it holds very high stability, which is insensitive to temperature changes or mechanical vibrations. Through further amplification, it will be a good laser source for real-time interrogation of fiber Bragg gratings and supercontinuum generation.

We systematically studied several of the most traditional hollow-core anti-resonant fiber (HC-ARF) structures, with the aim of achieving low confinement loss, single-mode performance, and high insensitivity to bending in the 2 µm band. Moreover, the propagation loss of fundamental mode (FM), higher-order mode (HOMs), and the higher-order mode extinction ratio (HOMER) under different geometric parameters were studied. Analysis showed that the confinement loss of the six-tube nodeless hollow-core anti-resonant fiber at 2 µm was 0.042 dB/km, and its higher-order mode extinction ratio was higher than 9000. At the same time, a confinement loss of 0.040 dB/km at 2 µm was achieved in the five-tube nodeless hollow-core anti-resonant fiber, and its higher-order mode extinction ratio was higher than 2700.

Extracting the peak value of the X-ray signal in the original magnetopause detection method of soft X-ray imaging (SXI) for the SMILE satellite is problematic because of the unclear interface of the magnetosphere system under low solar wind density and the short integration time. Herein, we propose a segmentation algorithm for soft X-ray images based on depth learning, we construct an SXI simulation dataset, and we segment the magnetospheric system by learning the spatial structure characteristics of the magnetospheric system image. Then, we extract the maximum position of the X-ray signal and calculate the spatial configuration of the magnetopause using the tangent fitting approach. Under a uniform universe condition, we achieved a pixel accuracy of the maximum position of the photon number detected by the network as high as 90.94% and contained the position error of the sunset point of the 3D magnetopause below 0.2 RE. This result demonstrates that the proposed method can detect the peak photon number of magnetospheric soft X-ray images with low solar wind density. As such, its use improves the segmentation accuracy of magnetospheric soft X-ray images and reduces the imaging time requirements of the input image.

Warmer and drier conditions are increasing the frequency of forest fires, which in turn produce pyrogenic carbon. Here the authors show that accumulation of pyrogenic carbon can suppress post-fire methane production in northern peatlands and can effectively buffer fire-derived greenhouse gas emissions.

With the advent of soft X-ray imaging enabling global magnetopause detection, it is critical to use reconstruction techniques to derive the 3-dimensional magnetopause location from 2-dimensional X-ray images. One of the important assumptions adopted by most techniques is that the direction with maximum soft X-ray emission is the tangent direction of the magnetopause, which has not been validated in observation so far. This paper analyzes a magnetospheric solar wind charge exchange (SWCX) soft X-ray event detected by XMM–Newton during relatively stable solar wind and geomagnetic conditions. The tangent direction of the magnetopause is determined by an empirical magnetopause model. Observation results show that the maximum SWCX soft X-ray intensity gradient tends to be the tangent of the magnetopause’s inner boundary, while the maximum SWCX soft X-ray intensity tends to be the tangent of the magnetopause’s outer boundary. Therefore, it is credible to use the assumption that the tangent direction of the magnetopause is the maximum SWCX soft X-ray intensity or its gradient when reconstructing the 3-dimensional magnetopause location. In addition, since these two maxima tend to be the inner and outer boundaries of the magnetopause, the thickness of magnetopause can also be revealed by soft X-ray imaging.

This work studies the dynamic response of solar wind charge exchange (SWCX) soft X-ray emission in the Earth’s magnetosphere to the solar wind proton flux. Unlike previous studies that attempted to use complex magnetohydrodynamic models to match the details of observed SWCX of a necessarily limited number of cases, this work focuses on determining the changes over individual observations in a much larger sample. To provide the cleanest test, we selected XMM-Newton observations when the solar wind proton flux changed suddenly by a factor greater than 1.5 and calculated the correlation coefficient between the SWCX emission in the 0.5–0.7 keV band and the proton flux. We find that the dynamical response is weak when the solar wind proton flux is low (

An all-fiber wavelength-tunable narrow-linewidth polarization-maintaining (PM) Tm-doped fiber master oscillator power amplifier (MOPA) system is presented. We demonstrate an all-fiber ring cavity Tm-doped fiber master-oscillator (MO) with a tuning range of 110 nm (from 1925 to 2034 nm). The maximum output power of 459 mW is obtained at 1992.9 nm for 16 W of launched pump power at 793 nm, corresponding to a slope efficiency of 5.6% concerning launched pump power. By using a one-stage Tm-doped fiber amplifier combined with a high gain of >10 dB, the maximum slope efficiency is 12.6% and the output power is 5.65 W at 1993 nm. The 3 dB linewidth is less than 0.5 nm, M2 ≈ 1.25, and the polarization extinction ratio (PER) reaches 21.4 dB. The influence of different active fiber lengths on laser amplification is also studied.

In this paper, an improved mathematical model is proposed by taking the factors of high-energy photons and temperature into consideration, which is verified and explained by the experimental data in our experiments and other papers. By fitting and analyzing the experimental data, we can quantitatively determine the relationship between the pump power Pλ and the photon frequency ν in the fiber core, the core area A and the temperature T of the fiber core and PD loss, and explain the mechanism of the PD phenomenon to a certain extent. We believe that the excitation of color centers by high-energy photons is the main reason for photodarkening. Furthermore, there is a positive correlation between the power of high-energy photons and the photodarkening rate, and the temperature is positively correlated with the saturated photodarkening absorption.

Mid-infrared (MIR) ultrashort laser pulses have a wide range of applications in the fields of environmental monitoring, laser medicine, food quality control, strong-field physics, attosecond science, and some other aspects. Recent years have seen great developments in MIR laser technologies. Traditional solid-state and fiber lasers focus on the research of the short-wavelength MIR region. However, due to the limitation of the gain medium, they still cannot cover the long-wavelength region from 8 to 20 µm. This paper summarizes the developments of 8–20 μm MIR ultrafast laser generation via difference frequency generation (DFG) and reviews related theoretical models. Finally, the feasibility of MIR power scaling by nonlinear-amplification DFG and methods for measuring the power of DFG-based MIR are analyzed from the author’s perspective.

In this paper, we summarize the research on photodarkening in optical fibers. The causes of photodarkening in fiber, the influence of photodarkening on fiber laser, the experimental device of photodarkening, and the mathematical model used to study the phenomenon of photodarkening are described in detail. At the end of the paper, we summarize the means and methods to suppress photodarkening.

Electron transfer reactions govern most biogeochemical processes, yet we have a limited knowledge of the electrochemistry of pyrogenic carbon, a major component of organic matter. Here, the authors quantify electron transfers between pyrogenic carbon and mineral phases under different pyrolysis temperatures.