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Enhanced brightness of a laser-driven x-ray and particle source by microstructured surfaces of silicon targets
摘要： The production of intense x-ray and particle sources is one of the most remarkable aspects of high energy laser interaction with a solid target. Wide application of these laser-driven secondary sources requires a high yield, which is partially limited by the amount of laser energy absorbed by the target. Here, we report on the enhancement of laser absorption and x-ray and particle flux by target surface modifications. In comparison to targets with flat front surfaces, our experiments show exceptional laser-to-target performance for our novel cone-shaped silicon microstructures. The structures are manufactured via laser-induced surface structuring. Spectral and spatial studies of reflectance and x-ray generation reveal significant increases of the silicon Ka line and a boost of the overall x-ray intensity, while the amount of reflected light decreases. Also, the proton and electron yields are enhanced, but both temperatures remain comparable to those of flat foil targets. We support the experimental findings with 2D particle in cell simulations to identify the mechanisms responsible for the strong enhancement. Our results demonstrate how custom surface structures can be used to engineer high power laser-plasma sources for future applications.
关键词： particle source,laser absorption,laser-driven x-ray,microstructured surfaces,x-ray generation,silicon targets
更新于2025-09-23 15:19:57
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Calculation of Direct Drive Targets for Megajoule Laser Facilities with Radiation in the Second and Third Harmonics of Nd Laser
摘要： The numerical results for cryogenic direct drive targets of megajoule facilities with radiation in the second and third harmonics of a Nd laser are presented. The calculations were performed with the 1D radiation hydrodynamics code ERA with the laser light absorption model that takes into account stimulated Brillouin scattering (SBS), generation of fast electrons in the processes of two-plasmon decay (TPD), and stimulated Raman scattering (SRS). The verification of the developed models was carried out on the basis of the comparison with experiments performed at the OMEGA and NIF facilities. The ignition margin (WQ) of nonuniform fusion targets with an allowance for energy losses due to radiation transfer and heat conduction from the hot spot was the objective of the target optimization. The calculations showed that SBS and target heating by fast electrons generated in TPD and SRS fatally reduce WQ of targets with a CH ablator for the megajoule laser with wavelength λ = 0.53 μm. The possibilities of decreasing these effects by replacing a CH ablator with a glass ablator and reducing the laser intensity upon increasing the target aspect ratio are considered. However, in both cases, WQ remains substantially below unity for the laser with wavelength λ = 0.53 μm. The ignition margin increases by a factor of ~2 upon transition from the second to the third harmonic of a Nd laser. A glass ablator almost eliminates fast electrons in calculation with the laser wavelength λ = 0.35 μm. In this case, if SBS is reduced by a factor of 3–4 via shifting the laser emission lines in the neighboring channels by Δλ ≈ 10–20 ?, the ignition margin WQ ~ 2 and a fusion energy yield of ~50 MJ are obtained in the 1D calculation for a laser energy of ~2 MJ and the third harmonic of a Nd laser.
关键词： megajoule laser facilities,two-plasmon decay,fast electron generation,direct drive targets,stimulated Raman scattering,thermonuclear ignition margin of target,stimulated Brillouin scattering
更新于2025-09-23 15:19:57
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Debris and shrapnel assessments for National Ignition Facility targets and diagnostics
摘要： High-energy laser experiments at the National Ignition Facility (NIF) can create debris and shrapnel capable of damaging laser optics and diagnostic instruments. The size, composition and location of target components and sacrificial shielding (e.g., disposable debris shields, or diagnostic filters) and the protection they provide is constrained by many factors, including: chamber and diagnostic geometries, experimental goals and material considerations. An assessment of the generation, nature and velocity of shrapnel and debris and their potential threats is necessary prior to fielding targets or diagnostics. These assessments may influence target and shielding design, filter configurations and diagnostic selection. This paper will outline the approach used to manage the debris and shrapnel risk associated with NIF targets and diagnostics and present some aspects of two such cases: the Material Strength Rayleigh-Taylor campaign and the Mono Angle Crystal Spectrometer (MACS).
关键词： diagnostics,shrapnel,debris,National Ignition Facility,targets
更新于2025-09-23 15:19:57
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[IEEE 2018 IEEE 3rd International Conference on Signal and Image Processing (ICSIP) - Shenzhen, China (2018.7.13-2018.7.15)] 2018 IEEE 3rd International Conference on Signal and Image Processing (ICSIP) - Radar Target Discrimination with F-CNN: Fewer Parameters and Higher Accuracy
摘要： In order to discriminate the real targets, the clutter and the dense multi-false targets, we propose a factorized convolutional neural network-based algorithm for radar targets discrimination. We factorized convolutional neural network model with depthwise separable convolution. To reduce the parameters of the model, we factorized convolutional neural network by reducing the numbers of both convolutional filters and connection nodes of fully connected layers. The result of the measured data demonstrates that, as compared with the existing model, the simplified factorized convolutional neural network has higher discrimination rate for the real targets, the clutter and the dense multi-false targets, and its parameters are less than ten percent counterpart of a recent proposed model.
关键词： targets discrimination,dense multi-false targets,radar anti-jamming,factorized convolutional neural network
更新于2025-09-19 17:15:36
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Geospatial Target Detection from High-Resolution Remote-Sensing Images Based on PIIFD Descriptor and Salient Regions
摘要： Geospatial target detection from visible remote-sensing images is considered as one of the most important issues in the analysis of aerial and satellite imagery. Development of remote-sensing techniques and enhancing resolution of images provide an opportunity to advance automatic analysis. The proposed methods of geospatial target detection have faced to a variety of challenges. Recently, local features are extensively used which play a very effective role in dealing with these issues. High intensity variations between targets and backgrounds in different images are the most critical challenges. Most proposed local feature descriptors are not able to deal with this amount of intensity variations and are accompanied with errors when facing them. In this paper, PIIFD descriptor has been applied to cope with intense intensity variations, as this descriptor is symmetrical against contrast. The proposed framework to automatically detect geospatial targets includes a supervised approach based on local features extraction and description and consists of three main steps including training, image searching, and geospatial target detection. In the training step, local features are extracted by UR-SIFT algorithm that properly matches with remote-sensing images and are described by the PIIFD descriptor. Due to the large dimensions of the extracted features, the SABOVW model has been used for quantization purpose. This model uses soft assignment of features to codebook, and the presentation provided by this model is used to train SVM classi?er. In the second step, for the sake of computational ef?ciency, the salient regions of the image are detected by combining the saliency models, which reduces the image space to search the geospatial targets. In the third step, the salient regions are scanned by the sliding window approach and a descriptor of each position is generated. Eventually, the process of detection of geospatial targets will be carried out by applying the trained SVM model to each window. In order to evaluate the ef?ciency of the PIIFD descriptor, its performance is compared with descriptors such as SIFT, DAISY, LSS, and LBP. The results showed better performance of the PIIFD descriptor in detection of geospatial targets.
关键词： Saliency models,Local features,Airplane targets,Detector,Descriptor,SABOVW model
更新于2025-09-19 17:15:36
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A universal photoelectrochemical biosensor for dual microRNAs detection based on two CdTe nanocomposites
摘要： Various diseases are closely related with simultaneous changes of multiple miRNAs expressions levels. It’s of great significance to develop photoelectrochemical (PEC) biosensors for multiple miRNAs detection for both clinical diagnosis and biological mechanisms research. In this work we designed a novel PEC biosensor for simultaneous dual miRNAs detection for the first time. Two nanocomposites CdTe loaded on carbon nitrides nanosheets (CdTe-C3N4) with anodic photocurrent and CdTe loaded on 3D graphene hydrogel (CdTe-3DGH) with cathodic photocurrent were prepared and showed enhanced PEC performances. Photocurrents of the two nanocomposites can be clearly distinguished at corresponding critical voltage. Then probe DNA1 and DNA2 were combined with the CdTe-3DGH and CdTe-C3N4 NCs through covalent binding respectively. With the competition hybridization reaction between target miRNAs and the complementary DNA (cDNA), concentrations of miRNA141 and miRNA21 may be sensitively quantified by the respective photocurrents change. Compared with traditional PEC biosensors, this design didn’t require any additional equipment and can provide a higher detection efficiency, which has a good universality and expansibility for the fabrication of multiplex PEC assays.
关键词： photoelectrochemical,microRNA,dual targets,biosensor
更新于2025-09-19 17:15:36
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Coincidence-Pumping Upconversion Detector Based on Passively Synchronized Fiber Laser System
摘要： The Sentinel-1A is the first of two satellites that composes the Sentinel-1 radar mission. Both satellites operate a C-band synthetic aperture radar (SAR) system to give continuity to the European SAR program. SAR is a flexible sensor able to fulfil users/applications requirements in terms of resolution and coverage thanks to different operational modes and polarizations. With the in-orbit availability of very-high-resolution X-band SAR sensors, the Sentinel-1 satellites have been designed to achieve wide coverage at medium to high resolution. The interferometric wide swath (IWS) mode implemented with the terrain observation with progressive scan (TOPS) technique is the standard acquisition mode over European waters and land masses. IWS in dual-polarization (VV/VH) combination offers 250-km swath at 5 m × 20 m (range × azimuth) spatial resolution. These specifications are in line with the needs of the European Maritime and Security Agency (EMSA) for oil spill and ship detection applications included in the CleanSeaNet program. The main goals of this paper are: assessment of medium-to-high-resolution C-band Sentinel-1 data with very-high-resolution X-band TerraSAR-X data for maritime targets detection; synergetic use of multiplatforms satellite SAR data for target features extraction; evaluation of polarimetric target detectors for the available co-polarization and cross-polarization Sentinel-1A IWS VV/VH products. The objectives are achieved by means of real, almost coincident C-band and X-band SAR data acquired by Sentinel-1A and TerraSAR-X satellites over Gulf of Naples and Catania (South Italy). Furthermore, the obtained results are supported by recorded ground truth vessel reports via terrestrial automatic identification system (AIS) stations located in the area.
关键词： multipolarization,targets detection,Multifrequency,synthetic aperture radar (SAR)
更新于2025-09-19 17:13:59
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Study of laser-driven magnetic fields with a continuous wave Faraday rotation diagnostic
摘要： Magnetic ?elds driven by a laser in coil targets were studied for laser energies of (cid:2)25 J and two pulse durations of 2.8 ns and 70 ps. Axial magnetic ?elds in the coils were measured by continuous wave Faraday rotation diagnostics. The diagnostics indicated magnetic ?elds of 6–14 T in the coil and currents of 10–20 kA. Magnetic ?elds were compared for similar laser targets, focusing conditions, and laser energies. A 30-times increase in the intensity of the laser beam by reducing the pulse duration resulted in an increase in the magnetic ?eld and current by a factor of 2. The relaxation time of the magnetic pulse was on the sub-microsecond scale.
关键词： coil targets,magnetic field measurement,laser-driven magnetic fields,pulse duration,Faraday rotation diagnostics
更新于2025-09-19 17:13:59
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Establishment of a New Quantitative Evaluation Model of the Targetsa?? Geometry Distribution for Terrestrial Laser Scanning
摘要： The precision of target-based registration is related to the geometry distribution of targets, while the current method of setting the targets mainly depends on experience, and the impact is only evaluated qualitatively by the findings from empirical experiments and through simulations. In this paper, we propose a new quantitative evaluation model, which is comprised of the rotation dilution of precision (rDOP, assessing the impact of targets’ geometry distribution on the rotation parameters) and the translation dilution of precision (tDOP, assessing the impact of targets’ geometry distribution on the translation parameters). Here, the definitions and derivation of relevant formulas of the rDOP and tDOP are given, the experience conclusions are theoretically proven by the model of rDOP and tDOP, and an accurate method for determining the optimal placement location of targets and the scanner is proposed by calculating the minimum value of rDOP and tDOP. Furthermore, we can refer to the model (rDOP and tDOP) as a unified model of the geometric distribution evaluation model, which includes the DOP model in GPS.
关键词： targets’ geometry distribution,target-based registration,terrestrial laser scanning,precision of the registration
更新于2025-09-19 17:13:59
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Efficient absorption of laser light by nano-porous materials with well-controlled structure
摘要： The absorption of high-power nanosecond laser pulses in a porous matter is investigated through theoretical and numerical calculations. The effects of structural properties of the porous target such as size of pores and thickness of solid elements on the laser absorption are investigated. The time and space-dependent absorption coefficient of the laser created partially homogenized plasma is used in a plasma hydrodynamic code to reproduce the laser absorption and plasma formation processes in a porous matter. It is observed that the structural characteristics of the porous material can be optimized to significantly increase the laser energy absorption. For porous targets with pore sizes in the range 30–60 nm a value around 1000 nm could be desirable for the wall thickness to increase the laser absorption efficiency to more than 90%. The results can be advantageous in production of efficient laser absorber targets which are desirable in advanced applications such as inertial confinement fusion and laser-plasma x-ray sources.
关键词： laser produced plasma,laser–matter interaction,plasma absorption coefficient,porous targets
更新于2025-09-19 17:13:59