Search

In many scenarios, it is really desirable but challenging for wide-field imaging to gather both the clear morphologies and fine details of the target. This paper realizes this imaging by a dual-mode imaging on optical parametric amplification (OPA) with a vortex laser pump. This design includes signal imaging and idler imaging, which have complementary point spread functions with each other. The signal acts as bright-field imaging to record morphologic information, whereas the idler does so for spiral phase contrast imaging to capture the featured details with high brightness and contrast, which has been experimentally confirmed with a target of herb tissue. By utilizing the coupling relation among the pump, signal, and idler, the information from the recorded signal and idler images can be merged, which allows us to reconstruct the target picture owning both high-contrast morphologies and high-brightness fine details. Due to high OPA gain, our imaging can work with weak illumination. Its field-of-view covers an area of 0.33 × 0.33 mm2 with a spatial resolution up to 228 lp/mm. This OPA imaging also provides an effective way for the imaging required nonlinear frequency conversion. [ABSTRACT FROM AUTHOR]

BackgroundThe electron beams produced by laser plasma acceleration have excellent quality for pulse lengths of the order of fs. Due to the existence of a strong laser field, there are difficulties in direct applications, and more applications need to transmit the electron beams to the application terminal. The energy spread leads to the generation of energy chirp of the electron beam in the transmission.PurposeThis study aims to explore the design of the beam optics to compress the pulse length and keep it on the fs scale.MethodsAn achromatic beamline consisting of bending magnets and quadrupole magnets was designed to compress the pulse length of electron beams. Critical parameters of an achromatic beamline were given by a derived formula. Transformation matrix was employed to investigate the differences of the pulse lengths in achromatic transmission and non-achromatic transmission. The pulse lengths of electron beams with different energies were scanned with different deflection angles (0.3 rad, 0.6 rad, 0.9 rad) and deflection radii (0.15 m, 0.25 m, 0.35 m) to study the influence of beamline parameters. Finally, the magnetic field gradients of the quadrupole lens were adjusted to realize the compression of electron beams with different energies in a beamline.ResultsComparing to non-achromatic transmission, the pulse lengths of electrons with the same energy and different initial divergence angles can be compressed effectively in the achromatic beamline. The larger the deflection angle or the deflection radius, the longer the pulse duration of the electron beam with higher energy (>25 MeV). By adjusting the magnetic field gradients of the quadrupole lens, the pulse lengths can be reduced from more than 100 fs to around 20 fs at higher energies.ConclusionsUsing a fixed-size achromatic beamline, combined with magnetic field strength adjustment, the pulse lengths of electron beams with different energies can be kept on the order of fs after transmission.

Two-dimensional tin sulfide (SnS), as a black phosphorus-analogue binary semiconductor, has received considerable attention in photonics and optoelectronics. Herein, the third-order nonlinearity susceptibility Im χ3 is enhanced from −(6.88 ± 0.10) × 10−14 esu to −(15.90 ± 0.27) × 10−14 esu by the size-related quantum confinement in layered SnS nanosheets. Due to the energy level alignment, a phonon-bottleneck effect is observed, which leads to a prolonged carrier lifetime. These results provide a platform for actively tuning the linear and nonlinear optics, and pave the way for designing SnS-based tunable and anisotropic optoelectronic devices.

This work presents TTFDNet, a transformer-based and transfer learning network for end-to-end depth estimation from single-frame fringe patterns in fringe projection profilometry. TTFDNet features a precise contour and coarse depth (PCCD) pre-processor, a global multi-dimensional fusion (GMDF) module and a progressive depth extractor (PDE). It utilizes transfer learning through fringe structure consistency evaluation (FSCE) to leverage the transformer's benefits even on a small dataset. Tested on 208 scenes, the model achieved a mean absolute error (MAE) of 0.00372 mm, outperforming Unet (0.03458 mm) models, PDE (0.01063 mm) and PCTNet (0.00518 mm). It demonstrated precise measurement capabilities with deviations of ~90 μm for a 25.4 mm radius ball and ~6 μm for a 20 mm thick metal part. Additionally, TTFDNet showed excellent generalization and robustness in dynamic reconstruction and varied imaging conditions, making it appropriate for practical applications in manufacturing, automation and computer vision. [ABSTRACT FROM AUTHOR]

In view of the problem that mountain tunnel construction is prone to collapse risk and disaster accidents, this paper proposes a fuzzy comprehensive evaluation method based on CRITIC and D-AHP combined weighting, which can effectively improve the accuracy of mountain tunnel collapse risk evaluation and reduce construction risks. This method combines the improved subjective weighting method D-number analytic hierarchy process and the more scientific and reasonable objective weighting method CRITIC method for combined weighting and uses game theory to optimize the weights, which improves its accuracy compared to traditional evaluation methods and makes up for the lack of subjective and objective weighting of a single evaluation method. The results show that the introduction of the D-number theory can reduce the impact of an uncertain environment on the evaluation results. The risk levels of the sample sections are all between three and four, which is consistent with the actual situation of the project, indicating that the evaluation model is feasible. [ABSTRACT FROM AUTHOR]

This study experimentally demonstrates two types of ultra-broadband metamaterial absorbers with high performance in the visible-to-near-infrared range by using different anti-reflection coatings (i.e., SiO2 and Si3N4) and a multi-subcell Ti-SiO2-Ti metasurface. Compared to the bare metamaterial nanostructure, the absorption bandwidth of the coated metasurfaces exhibit increases of 594 nm and 1093 nm, respectively. Such improvements benefit from nearly perfect impedance matching to the free space enhanced by the anti-reflection coating, thin film interference, and excitations of different surface plasmon resonances. As a result, the absorber with SiO2 coating exhibits a measured bandwidth with an absorption of 0.9 ranging from 502 nm to 1892 nm, while the absorber with Si3N4 coating further broadens the bandwidth from 561 nm to 2450 nm. The measured average absorptions for both cases remain above 95% and 87%, respectively. Moreover, both nanostructures are robust to large incident angles of up to 60° for both TE and TM modes. Our findings highlight the promising potential of these absorbers for various applications, including solar energy harvesting, thermal emitters, and photodetectors. [ABSTRACT FROM AUTHOR]

Construction of the deep foundation pit (DFP) in subway stations is fraught with significant uncertainties, which may cause project delays due to discrepancies between single-indicator monitoring warning information and actual conditions at the site. Therefore, this article proposes a safety assessment method for DFP based on the Game-Cloud Model. An entirely quantitative assessment index system is established with on-site monitoring projects according to the design safety classification of DFP. Considering the one-sidedness of using a single method to determine the weights of assessment indices, game theory is introduced to calibrate the subjective and objective weights determined by the grey decision-making trial and evaluation laboratory (GDEMATEL) and the entropy method, respectively. Next, we use the forward cloud generator of the cloud model (CM) to generate the safety level membership function of the evaluation indicators. Finally, we quantitatively calculate the synthetic safety level of DFP using the comprehensive evaluation approach. A 19-day dynamic assessment was conducted on the actual engineering project by the proposed method. The results indicated that the synthetic safety level of the assessed area ranged between grades Ⅰ and Ⅱ, corresponding to Negligible and Acceptable in the acceptance criteria. Compared with the single-indicator monitoring warning results, it was more in line with on-site observation, which verified its reliability and practicality. [ABSTRACT FROM AUTHOR]

The construction of a subway deep foundation pit is complex and risky, thus multiple safety risk factors bring great challenges to evaluating the safety status accurately. Advanced monitoring technology equipment could obtain a large number of monitoring data, and how integrating complex and diversified monitoring data to assess the safety risk of foundation pits has become a new problem. Therefore, an intelligent multi-source fusion assessment model is proposed. This model is mainly used for solving risk probability distribution, deep learning, and intelligent prediction of monitoring indicators, and then evaluating safety status by fusing various parameters of multiple indicators. Thus, based on the data of deep learning and the measured multivariate data, the dynamic risk during foundation pit construction can be obtained. Moreover, a typical case study was performed through monitoring and carrying out the risk assessment which is located at the Martyrs' Lingyuan Station of Jinnan Metro Line R2, China. In this case, the PSO-SVM and LSTM models are used to predict the deformation trend, and the monitoring data is reliable with high precision. After multi-index fusion model calculation, the results show that the foundation pit structure is in a safe state, and the evaluation situation is basically consistent with the site. Consequently, the prediction of the new multi-source intelligent fusion risk assessment method is convincing. [ABSTRACT FROM AUTHOR]

The 1.7 μm band eye-safe laser sources have recently received lots of attention thanks to the development of various applications. Although a variety of lasing configurations operating in this band have been demonstrated, one still needs to seek a good candidate for particular applications with a reasonable compromise between the relative performance targets (e.g., stability, output power, and spectral purity) and the construction cost. Here, we demonstrate a high-power 1694 nm random fiber laser (RFL) in a cost-effective structure pumped by a high-powered 1565 nm RFL. The maximum output power reached the 10 W level, and the output showed extremely low-intensity fluctuations for both the short-time and long-time regimes. Meanwhile, an excellent spectral purity as high as 26.9 dB was also realized. This work provides one of the most attractive approaches for constructing high-performance 1.7 μm band laser sources for practical applications. [ABSTRACT FROM AUTHOR]

To study the dynamic response of shallow buried tunnel lining by drilling and blasting method, ABAQUS simulation software was used to establish a tunnel blasting finite element model based on the consideration of in situ stress. Dynamic static coupling numerical simulation was conducted to analyze the vibration response and stress response of tunnel lining. The simulation results were compared and analyzed with field monitoring data to obtain the dynamic response law of tunnel lining. The results show that in the same tunnel lining section, the vibration velocity response in the Y direction is the largest and the vibration velocity response in the Z direction is the smallest. The location of the peak particle velocity of the tunnel lining in three directions appears differently, and the location of the maximum MISES stress appears differently for different excavation sections. The arch shoulder is most affected by horizontal vibration in the X direction, and the vault is most affected by horizontal vibration in the Y direction. The dynamic response at the foot or arch shoulder position away from the lining section of the working face will show the "whip tip effect." A sudden change in MISES stress occurs at the location of the footing in the 315° direction of the liner section, and the liner is not uniformly stressed in this range. [ABSTRACT FROM AUTHOR]