Universal nanosecond range pulse contrast measurement for a kJ-class petawatt laser.

A single-shot measuring apparatus with optical limiting for temporal pulse contrast of kJ-class petawatt lasers in the nanosecond range is proposed. A temporal linear filter comprising an electro-optical switch, a polarizer, a temporal nonlinear filter composed of cascaded SHG crystals, and a dichromatic mirror are, respectively, used as an optical limiting apparatus for contrast measurement of nanosecond and picosecond pulses to improve dynamic range and temporal resolution. The apparatus has been applied to pulse contrast measurements at the SG-II petawatt facility, achieving a high dynamic range of 1010 and a fast time resolution of 107 ps in the 350 ns range. This technique can also be universally applied to the limiting of the main pulse of varying pulse widths to diagnose pre-pulses during generation and transmission.

Experimental study on measuring pulse duration in the far field for high-energy petawatt lasers.

We study the feasibility of measuring pulse duration in the far field in high-energy petawatt lasers using single-shot autocorrelation. This single-shot autocorrelation technique makes use of parametric upconversion in media with randomly oriented ferroelectric domains, which supports transverse second-harmonic generation with two counter-propagating fundamental beams. We show that this technique possesses a large time window, capable of measuring pulses with temporal duration ranging from a sub-picosecond to tens of picoseconds. We test the performance of this technique in the presence of multipulse structures, intensity modulations in the near field, and spatial-temporal coupling in fundamental beams. We also investigate the influence of beam pointing discrepancy on the measurement. Our study can serve as a preliminary experiment for robustly characterizing pulse duration in high-energy petawatt lasers.

Temporal characterization of petawatt class laser at Shen Guang II facility.

Temporal characterization is important to diagnose and measure a petawatt (PW) class laser. We obtained the V curve of the pulse width versus the grating position using pulse width measurement with a mirror image configuration. The temporal range for pulse width was 18 ps with a resolution of 0.05 ps. We measured the pulse contrast between the -60 ps and -6 ps PW class laser within a single shot in the Shen Guang II facility. We measured the pulse contrast between the -91 ps and -60 ps PW class laser after expanding the temporal range. The temporal range was 70 ps, with a dynamic range of eight orders of magnitude.

Noncritically phase-matched fourth-harmonic generation of Nd:glass lasers and design of final optics assembly.

The noncritically phase-matched (NCPM) fourth-harmonic generation (FHG) with partially deuterated dihydrogen phosphate (KD*P) crystal at an Nd:glass laser radiation wavelength of 1053.1 nm has been confirmed. NCPM FHG has been achieved in 70% and 65% deuterated KD*P crystal at the temperature of 17.7°C and 29.3°C, respectively. The angular acceptance of 70% and 65% deuterated KD*P crystals fixed at their NCPM temperature were measured, which were 53 and 55 mrad, respectively. The application of the NCPM FHG in a high-power laser facility for inertial confinement fusion is also discussed. Based on the theoretical analysis, the NCPM KD*P can be placed after the focus lens; thus, the laser-induced damage of a fused-silica lens at ultraviolet can be avoided.

Studies on design of 351 nm focal plane diagnostic system prototype and focusing characteristic of SGII-upgraded facility at half achievable energy performance.

In order to obtain the intensity distribution of a 351 nm focal spot and smoothing by spectral dispersion (SSD) focal plane profile of a SGII-upgraded facility, a type of off-axis imaging system with three spherical mirrors, suitable for a finite distance source point to be imaged near the diffraction limit has been designed. The quality factor of the image system is 1.6 times of the diffraction limit tested by a 1053 nm point source. Because of the absence of a 351 nm point source, we can use a Collins diffraction imaging integral with respect to λ=351 nm, corresponding to a quality factor that is 3.8 times the diffraction limit at 351 nm. The calibration results show that at least the range of ±10 mrad of view field angle and ±50 mm along the axial direction around the optimum object distance can be satisfied with near diffraction limited image that is consistent with the design value. Using this image system, the No. 2 beam of the SGII-upgraded facility has been tested. The test result of the focal spot of final optics assembly (FOA) at 351 nm indicates that about 80% of energy is encompassed in 14.1 times the diffraction limit, while the output energy of the No. 2 beam is 908 J at 1053 nm. According to convolution theorem, the true value of a 351 nm focal spot of FOA is about 12 times the diffraction limit because of the influence of the quality factor. Further experimental studies indicate that the RMS value along the smoothing direction is less than 15.98% in the SSD spot test experiment. Computer simulations show that the quality factor of the image system used in the experiment has almost no effect on the SSD focal spot test. The image system can remarkably distort the SSD focal spot distribution under the circumstance of the quality factor 15 times worse than the diffraction limit. The distorted image shows a steep slope in the contour of the SSD focal spot along the smoothing direction that otherwise has a relatively flat top region around the focal spot center.

Metagenomic comparison of intestinal microbiota between normal and liver fibrotic rhesus macaques (Macaca mulatta).

Liver fibrosis is an important pathological process in chronic liver disease and cirrhosis. Recent studies have found a close association between intestinal microbiota and the development of liver fibrosis. To determine whether there are differences in the intestinal microbiota between rhesus macaques with liver fibrosis (MG) and normal rhesus macaques (MN), fecal samples were collected from 8 male MG and 12 male MN. The biological composition of the intestinal microbiota was then detected using 16S rRNA gene sequencing. The results revealed statistically significant differences in ASVs and Chao1 in the alpha-diversity and the beta-diversity of intestinal microbiota between MG and MN. Both groups shared Prevotella and Lactobacillus as common dominant microbiota. However, beneficial bacteria such as Lactobacillus were significantly less abundant in MG (P = 0.02). Predictive functional analysis using PICRUSt2 gene prediction revealed that MG exhibited a higher relative abundance of functions related to substance transport and metabolic pathways. This study may provide insight into further exploration of the mechanisms by which intestinal microbiota affect liver fibrosis and its potential future use in treating liver fibrosis.

Metabolic dysfunction-associated steatotic liver disease: ferroptosis related mechanisms and potential drugs.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is considered a "multisystem" disease that simultaneously suffers from metabolic diseases and hepatic steatosis. Some may develop into liver fibrosis, cirrhosis, and even hepatocellular carcinoma. Given the close connection between metabolic diseases and fatty liver, it is urgent to identify drugs that can control metabolic diseases and fatty liver as a whole and delay disease progression. Ferroptosis, characterized by iron overload and lipid peroxidation resulting from abnormal iron metabolism, is a programmed cell death mechanism. It is an important pathogenic mechanism in metabolic diseases or fatty liver, and may become a key direction for improving MASLD. In this article, we have summarized the physiological and pathological mechanisms of iron metabolism and ferroptosis, as well as the connections established between metabolic diseases and fatty liver through ferroptosis. We have also summarized MASLD therapeutic drugs and potential active substances targeting ferroptosis, in order to provide readers with new insights. At the same time, in future clinical trials involving subjects with MASLD (especially with the intervention of the therapeutic drugs), the detection of serum iron metabolism levels and ferroptosis markers in patients should be increased to further explore the efficacy of potential drugs on ferroptosis.

A personalized prediction model for urinary tract infections in type 2 diabetes mellitus using machine learning.

Patients with type 2 diabetes mellitus (T2DM) are at higher risk for urinary tract infections (UTIs), which greatly impacts their quality of life. Developing a risk prediction model to identify high-risk patients for UTIs in those with T2DM and assisting clinical decision-making can help reduce the incidence of UTIs in T2DM patients. To construct the predictive model, potential relevant variables were first selected from the reference literature, and then data was extracted from the Hospital Information System (HIS) of the Sichuan Academy of Medical Sciences and Sichuan Provincial People's Hospital for analysis. The data set was split into a training set and a test set in an 8:2 ratio. To handle the data and establish risk warning models, four imputation methods, four balancing methods, three feature screening methods, and eighteen machine learning algorithms were employed. A 10-fold cross-validation technique was applied to internally validate the training set, while the bootstrap method was used for external validation in the test set. The area under the receiver operating characteristic curve (AUC) and decision curve analysis (DCA) were used to evaluate the performance of the models. The contributions of features were interpreted using the SHapley Additive ExPlanation (SHAP) approach. And a web-based prediction platform for UTIs in T2DM was constructed by Flask framework. Finally, 106 variables were identified for analysis from a total of 119 literature sources, and 1340 patients were included in the study. After comprehensive data preprocessing, a total of 48 datasets were generated, and 864 risk warning models were constructed based on various balancing methods, feature selection techniques, and a range of machine learning algorithms. The receiver operating characteristic (ROC) curves were used to assess the performances of these models, and the best model achieved an impressive AUC of 0.9789 upon external validation. Notably, the most critical factors contributing to UTIs in T2DM patients were found to be UTIs-related inflammatory markers, medication use, mainly SGLT2 inhibitors, severity of comorbidities, blood routine indicators, as well as other factors such as length of hospital stay and estimated glomerular filtration rate (eGFR). Furthermore, the SHAP method was utilized to interpret the contribution of each feature to the model. And based on the optimal predictive model a user-friendly prediction platform for UTIs in T2DM was built to assist clinicians in making clinical decisions. The machine learning model-based prediction system developed in this study exhibited favorable predictive ability and promising clinical utility. The web-based prediction platform, combined with the professional judgment of clinicians, can assist to make better clinical decisions.

Predicting three-month fasting blood glucose and glycated hemoglobin changes in patients with type 2 diabetes mellitus based on multiple machine learning algorithms.

Fasting blood glucose (FBG) and glycosylated hemoglobin (HbA1c) are key indicators reflecting blood glucose control in type 2 diabetes mellitus (T2DM) patients. The purpose of this study is to establish a predictive model for blood glucose changes in T2DM patients after 3 months of treatment, achieving personalized treatment.A retrospective study was conducted on type 2 diabetes mellitus real-world medical data from 4 cities in Sichuan Province, China from January 2015 to December 2020. After data preprocessing, data inputting, data sampling, and feature screening, 16 kinds of machine learning methods were used to construct prediction models, and 5 prediction models with the best prediction performance were screened respectively. A total of 100,000 cases were included to establish the FBG model, and 2,169 cases were established to establish the HbA1c model. The best prediction model both of FBG and HbA1c finally obtained are realized by ensemble learning and modified random forest inputting, the AUC values are 0.819 and 0.970, respectively. The most important indicators of the FBG and HbA1c prediction model were FBG and HbA1c. Medication compliance, follow-up outcome, dietary habits, BMI, and waist circumference also had a greater impact on FBG levels. The prediction accuracy of the models of the two blood glucose control indicators is high and has certain clinical applicability.HbA1c and FBG are mutually important predictors, and there is a close relationship between them.

Phase control requirements of high intensity laser beam combining.

Aiming at getting the general requirements of the beam combine for ignition scale laser facilities, the analytical expressions including the factors affecting the combine results are derived. The physical meanings of every part are illustrated. Based on these expressions, the effects of the factors, including the beam configuration, piston error, and tip/tilt error, are studied analytically and numerically. The results show that the beam configuration cannot affect the Strehl ratio (SR) of the combined beam, but it influences the FWHM of the main peak and the ratio of the main peak and the side peak. The beam separation should be no more than 1.24 times the individual beam width for the multibeam combine, and be close to the individual beam width for the two-beam combine as much as possible. The piston error can change the characteristics of the combine beam focus, including the peak intensity, the focal spot morphology, the fractional energy contained within a certain area, and the center of mass. For the two-beam combine, a piston error less than 2π/5 rad is suitable, and for the multibeam combine, the standard deviation of the piston error should be no more than 2π/10 rad. The tip/tilt error has a great influence on the combined results. It affects the superposition degree of the focal spots of the combined elements directly. A requirement of 0.5~1 µrad for the standard deviation of the tip/tilt error is adequate.

Accuracy of single-shot autocorrelation measurements of petawatt laser pulses.

At the Shen Guang II (SGII) Petawatt Laser Facility, measurements of large-energy, single-shot laser pulses sometimes feature asymmetric autocorrelation signals, causing uncertainty in the measurement of compressed pulses. This study presents a method for defining and describing the asymmetry of autocorrelation signals. We discuss two sources of asymmetry: the nonuniform distribution of the near field excited by a beam, and the rotation of autocorrelator arms from the cylinder lens. The pulsewidth of an asymmetric autocorrelation signal is shorter than its real width. After updating the autocorrelator, the single-shot autocorrelator for the SGII petawatt laser exhibits a measurement uncertainty of below 12.3%. Recommendations on reducing asymmetry in large-energy, single-shot autocorrelation are discussed.

Fractional Fourier transform of flat-topped multi-Gaussian beams.

The fractional Fourier transform (FRFT) of the flat-topped multi-Gaussian beam (FMGB) is investigated based on the three kinds of FRFT optical systems: Lohmann I, Lohmann II, and quadratic graded-index systems. The analytical expressions for the FRFT of the FMGB are derived based on the propagation of the FMGB through the three systems. By introducing a hard-edge aperture function, the analytical expressions for the FRFT of the FMGB carried out by the apertured FRFT optical systems are presented. The FRFT characteristics of the FMGB for the three kinds of FRFT optical systems with and without apertures are discussed in detail. Results show that the three types of FRFT optical systems have the same function when the apertures are ignored but that significantly different characteristics are exhibited when the apertures appear.

Propagation of flat-topped multi-Gaussian beams through a double-lens system with apertures.

A general model for different apertures and flat-topped laser beams based on the multi-Gaussian function is developed. The general analytical expression for the propagation of a flat-topped beam through a general double-lens system with apertures is derived using the above model. Then, the propagation characteristics of the flat-topped beam through a spatial filter are investigated by using a simplified analytical expression. Based on the Fluence beam contrast and the Fill factor, the influences of a pinhole size on the propagation of the flat-topped multi-Gaussian beam (FMGB) through the spatial filter are illustrated. An analytical expression for the propagation of the FMGB through the spatial filter with a misaligned pinhole is presented, and the influences of the pinhole offset are evaluated.

Propagation of flat-topped multi-Gaussian beams through an apertured ABCD optical system.

The generalized analytical expression for the propagation of flat-topped multi-Gaussian beams through a misaligned apertured ABCD optical system is derived. Using this analytical expression, the propagation characteristics of flat-topped multi-Gaussian beams through a spatial filter are investigated. The analytical formula of the electric field distribution in the focal plane is also derived for revealing the effects of the misalignment parameters clearly. It is found that different misalignment parameters have different influences on the electric field distributions of the beam focus spot and the output beam characteristics. The intensity distribution of the beam is mainly determined by the misalignment matrix element E, and the phase distribution is affected by the misalignment matrix elements G and E.

Characteristics of beam alignment in a high power four-pass laser amplifier.

Beam alignment is used to control the pointing, rotation, and position of a beam automatically. We give an overview of the beam alignment system for a four-pass amplifier system. The coupling relationships between dependent quantities and deviations thereof for parameters of key optical elements are analyzed using matrix optics techniques. The rotation characteristics of a near field are discussed. The characteristics of the four-pass adjustment in the cavity spatial filter are shown and the output characteristics are provided. Finally, we develop an adjustment procedure.

Laboratory Study on Disconnection Events in Comets.

When comets interacting with solar wind, straight and narrow plasma tails will be often formed. The most remarkable phenomenon of the plasma tails is the disconnection event, in which a plasma tail is uprooted from the comet's head and moves away from the comet. In this paper, the interaction process between a comet and solar wind is simulated by using a laser-driven plasma cloud to hit a cylinder obstacle. A disconnected plasma tail is observed behind the obstacle by optical shadowgraphy and interferometry. Our particle-in-cell simulations show that the difference in thermal velocity between ions and electrons induces an electrostatic field behind the obstacle. This field can lead to the convergence of ions to the central region, resulting in a disconnected plasma tail. This electrostatic-field-induced model may be a possible explanation for the disconnection events of cometary tails.

Demonstration of laser-produced neutron diagnostic by radiative capture gamma-rays.

We report a new scenario of the time-of-flight technique in which fast neutrons and delayed gamma-ray signals were both recorded in a millisecond time window in harsh environments induced by high-intensity lasers. The delayed gamma signals, arriving far later than the original fast neutron and often being ignored previously, were identified to be the results of radiative captures of thermalized neutrons. The linear correlation between the gamma photon number and the fast neutron yield shows that these delayed gamma events can be employed for neutron diagnosis. This method can reduce the detecting efficiency dropping problem caused by prompt high-flux gamma radiation and provides a new way for neutron diagnosing in high-intensity laser-target interaction experiments.

Formation and evolution of a pair of collisionless shocks in counter-streaming flows.

A pair of collisionless shocks that propagate in the opposite directions are firstly observed in the interactions of laser-produced counter-streaming flows. The flows are generated by irradiating a pair of opposing copper foils with eight laser beams at the Shenguang-II (SG-II) laser facility. The experimental results indicate that the excited shocks are collisionless and electrostatic, in good agreement with the theoretical model of electrostatic shock. The particle-in-cell (PIC) simulations verify that a strong electrostatic field growing from the interaction region contributes to the shocks formation. The evolution is driven by the thermal pressure gradient between the upstream and the downstream. Theoretical analysis indicates that the strength of the shocks is enhanced with the decreasing density ratio during both flows interpenetration. The positive feedback can offset the shock decay process. This is probable the main reason why the electrostatic shocks can keep stable for a longer time in our experiment.