Search Results (132)

Optical materials are widely used in large optical systems such as lithography machines and astronomical telescopes. However, optical materials inevitably produce subsurface damage (SSD) during lapping and polishing processes, degrading the laser damage threshold and impacting the service life of the optical system. The large surface roughness of the lapped optical materials further increases the difficulty of the nondestructive detection of SSD. Quantum dots (QDs) show great development potential in the nondestructive detection of SSD in lapped materials. However, existing QD-based SSD detection methods ignore the polarization sensitivity of QDs to excitation light, which affects the detection accuracy of SSD. To address this problem, this paper explores the fluorescence polarization properties of QDs in the SSD of optical materials. First, the detection principle of SSD based on the fluorescence polarization of QDs is investigated. Subsequently, a fluorescence polarization detection system is developed to analyze the fluorescence polarization properties of QDs in SSD. Finally, the SSD is detected based on the studied polarization properties. The results show that the proposed method effectively improves the detection rate of SSD by 10.8% and thus provides guidance for evaluating the quality of optical material and optimizing optical material processing technologies. The research paradigm is equally applicable to biomedicine, energy, optoelectronics, and the environment, where QDs have a wide range of applications. Full article

Near-infrared (NIR) photoelectric synaptic devices show great potential in studying NIR artificial visual systems integrating excellent optical characteristics and bionic synaptic plasticity. However, NIR synapses based on transition metal dichalcogenides (TMDCs) suffer from low stability and poor environmental performance. Thus, an environmentally friendly NIR synapse was fabricated based on lanthanide-doped upconversion nanoparticles (UCNPs) and two-dimensional (2D) WSe₂ via solution spin coating technology. Biological synaptic functions were simulated successfully through 975 nm laser regulation, including paired-pulse facilitation (PPF), spike rate-dependent plasticity, and spike timing-dependent plasticity. Handwritten digital images were also recognized by an artificial neural network based on device characteristics with a high accuracy of 97.24%. In addition, human and animal identification in foggy and low-visibility surroundings was proposed by the synaptic response of the device combined with an NIR laser and visible simulation. These findings might provide promising strategies for developing a 24/7 visual response of humanoid robots. Full article

Road traffic emissions are still a significant contributor to air pollution, which causes adverse health effects. Remote emission sensing (RES) is a state-of-the-art technique that continuously monitors the emissions of thousands of vehicles in traffic. Automatic number plate recognition (ANPR) systems are an essential part of RES systems to identify the registered owners of high-emitting vehicles. Recognizing number plates on L-vehicles (two-wheelers) with a standard ANPR system is challenging due to differences in size and placement across various categories. No ANPR system is designed explicitly for Category L vehicles, especially mopeds. In this work, we present an automatic number plate detection and recognition system for Category L vehicles (L-ANPR) specially developed to recognize L-vehicle number plates of various sizes and colors from different categories and countries. The cost-effective and energy efficient L-ANPR system was implemented on roads during remote emission measurement campaigns in multiple European cities and tested with hundreds of vehicles. The L-ANPR system recognizes Category L vehicles by calculating the size of each passing vehicle using photoelectric sensors. It can then trigger the L-ANPR detection system, which begins detecting license plates and recognizing license plate numbers with the L-ANPR recognizing system. The L-ANPR system’s license plate detection model is trained using thousands of images of license plates from various types of Category L vehicles across different countries, and the overall detection accuracy with test images exceeded 90%. The L-ANPR system’s character recognition is designed to identify large characters on standard number plates as well as smaller characters in various colors on small, moped license plates, achieving a recognition accuracy surpassing 70%. The reasons for false recognitions are identified and the solutions are discussed in detail. Full article

Two-dimensional (2D) van der Waals materials have been actively investigated for broadband, high-sensitivity, low-power-consumption photodetection owing to their highly customizable band structures and fast interfacial charge transfers. Studying photocurrent generation mechanisms provides insights into charge carrier dynamics in WSe₂-based detectors, linking spatial factors (e.g., photocurrent generation/collection) with interfacial band alignment. Here, we employ scanning photocurrent microscopy to spatially resolve the processes of photocurrent generation and collection in WSe₂-based composite structures. Photocurrent polarity and magnitude at interface reflects interfacial band alignment and potential gradients at metal–WSe₂ and WSe₂–In₂Se₃ junctions. Strong electric fields at metal–WSe₂ interfaces drive more efficient electron–hole separation and yield higher photocurrents, compared with WSe₂–In₂Se₃ interfaces. The photodetector exhibits broadband detection capabilities from visible to infrared light, achieving a high responsivity of 17.7 A/W and an excellent detectivity of 3.7 × 10¹² Jones, as well as fast response times of <113 µs. Furthermore, object imaging with a resolution better than 0.5 mm was successfully demonstrated, highlighting the potential of this photoresponse for practical imaging applications. This work reveals that photocurrent is distributed with a clear dependence on device configuration, offering a new avenue for optimizing 2D material-based photoelectric devices. Full article

Extended shortwave infrared (eSWIR) detectors operating at high temperatures are widely utilized in planetary science. A high-performance eSWIR based on pBin InAs/GaSb/AlSb type-II superlattice (T2SL) grown on a GaSb substrate is demonstrated. It achieves the optimization of the device’s optoelectronic performance by adjusting the p-type doping concentration in the AlAs_0.1Sb_0.9/GaSb barrier. Experimental and TCAD simulation results demonstrate that both the device’s dark current and responsivity grow as the doping concentration rises. Here, the bulk dark current density and bulk differential resistance area are extracted to calculate the bulk detectivity for evaluating the photoelectric performance of the device. When the barrier concentration is 5 × 10¹⁶ cm⁻³, the bulk detectivity is 2.1 × 10¹¹ cm·Hz^1/2/W, which is 256% higher than the concentration of 1.5 × 10¹⁸ cm⁻³. Moreover, at 300 K (−10 mV), the 100% cutoff wavelength of the device is 1.9 μm, the dark current density is 9.48 × 10⁻⁶ A/cm², and the peak specific detectivity is 7.59 × 10¹⁰ cm·Hz^1/2/W (at 1.6 μm). An eSWIR focal plane array (FPA) detector with a 320 × 256 array scale was fabricated for this purpose. It demonstrates a remarkably low blind pixel rate of 0.02% and exhibits an excellent imaging quality at room temperature, indicating its vast potential for applications in infrared imaging. Full article

Two-dimensional materials have emerged as core components for next-generation optoelectronic devices due to their quantum confinement effects and tunable electronic properties. Indium selenide (InSe) demonstrates breakthrough photoelectric performance, with its remarkable light-responsive characteristics spanning from visible to near-infrared regions, offering application potential in high-speed imaging, optical communication, and biosensing. This study investigates the doping characteristics of InSe using first-principles calculations, focusing on the doping and adsorption behaviors of Argentum (Ag) and Bismuth (Bi) atoms in InSe and their effects on its electronic structure. The research reveals that Ag atoms preferentially adsorb at interlayer vacancies with a binding energy of −2.19 eV, forming polar covalent bonds. This reduces the band gap from the intrinsic 1.51 eV to 0.29–1.16 eV and induces an indirect-to-direct band gap transition. Bi atoms doped at the center of three Se atoms exhibit a binding energy of −2.06 eV, narrowing the band gap to 0.19 eV through strong ionic bonding, while inducing metallic transition at inter-In sites. The introduced intermediate energy levels significantly reduce electron transition barriers (by up to 60%) and enhance carrier separation efficiency. This study links doping sites, electronic structures, and photoelectric properties through computational simulations, offering a theoretical framework for designing high-performance InSe-based photodetectors. It opens new avenues for narrow-bandgap near-infrared detection and carrier transport optimization. Full article

Developing advanced materials with enhanced performance through the doping of nanoclusters is a promising strategy. However, there remains an insufficient understanding of the specific effects induced by such doped nanoclusters, particularly regarding the structural evolution pattern after doping with rare-earth elements and their impact on performance. To solve this problem, we used first-principles calculation to study the structural evolution pattern and spectroscopic properties of anionic TbGe_n (n = 6–17) nanoclusters through the ABCluster global search technique coupled with the mPW2PLYP double-hybrid density functional theory. The results revealed that the geometrical evolution pattern is from the typical Tb-linked structures (for n = 10–13, in which Tb acts as a linker connecting two germanium sub-clusters) to Tb-centered cage configurations (for n = 14–17). The simulated photoelectron spectroscopy of anionic TbGe₁₆ agrees well with its experimental counterpart. Furthermore, we calculated properties such as infrared spectroscopy, Raman spectroscopy, ultraviolet–visible (UV–vis) spectra, magnetism, charge transfer, the HOMO-LUMO gap, and relative stability. The results suggest that TbGe₁₂⁻ and TbGe₁₆⁻ clusters, with their remarkable stability and tunable photothermal properties, can serve as ideal building blocks for developing novel functional nanomaterials. These clusters demonstrate promising applications in solar photothermal conversion, photoelectric conversion, and infrared imaging technologies through their distinct one- and three-dimensional architectures, respectively. Full article

Retina-like photoimaging devices with features such as a wide-field-of-view and high spatial resolution have wide application prospects in retinal prosthetics and remote sensing. However, the fabrication of flexible and conformal surfaces is hindered by the incompatible microfabrication processes of traditional rigid, silicon-based substrates. A kirigami strategy for hemispherical surface assembly is proposed to construct a MoS₂-based retina-like photodetector array. The device is first fabricated on a flat polyimide (PI) substrate and then tailored using a laser. By approximating the spherical surface using planar sectors, the laser-cut PI film can tightly adhere to the PDMS spherical shell without significant wrinkles. The responsivity and specific detectivity of our conformal photodetector can reach as high as 247.9 A/W and 6.16 × 10¹¹ Jones, respectively. The array integrates 180 pixels on a spherical crown with a radius of 11 mm, and a hollow letter “T” is successfully recognized. Comprehensive experimental results in this work reveal the utility of our device for photoelectric detection and imaging. We believe that our work provides a new methodology for the exploitation of 2D material-based retinal image sensors. Full article

Intensified complementary metal-oxide semiconductor (ICMOS) sensors involve multiple steps, including photoelectric conversion and photoelectric multiplication, each of which introduces noise that significantly impacts image quality. To address the issues of insufficient denoising performance and poor model generalization in ICMOS image denoising, this paper proposes a systematic solution. First, we established an experimental platform to collect real ICMOS images and introduced a novel noise generation network (LD-NGN) that accurately simulates the strong sparsity and spatial clustering of ICMOS noise, generating a multi-scene paired dataset. Additionally, we proposed a new noise evaluation metric, KL-Noise, which allows a more precise quantification of noise distribution. Based on this, we designed a denoising network specifically for ICMOS images, MAST-Net, and trained it using the multi-scene paired dataset generated by LD-NGN. By capturing multi-scale features of image pixels, MAST-Net effectively removes complex noise. The experimental results show that, compared to traditional methods and denoisers trained with other noise generators, our method outperforms both qualitatively and quantitatively. The denoised images achieve a peak signal-to-noise ratio (PSNR) of 35.38 dB and a structural similarity index (SSIM) of 0.93. This optimization provides support for tasks such as image preprocessing, target recognition, and feature extraction. Full article

This study evaluates the measurement uncertainty of the wave buoy calibration device using a vertical lifting method to ensure the accuracy and reliability of wave buoy measurements for marine research. The calibration device employs a linear motor-driven vertical displacement system, integrating a standard steel tape for wave height measurement and a photoelectric switch-based time calibration module for wave period verification. To address the limitations of traditional instruments, the device utilizes a 0.1 mm laser beam and image processing software to enhance the resolution of the standard steel tape, reducing the smallest division measurement from 1 mm to 0.1 mm. Additionally, a high-precision time calibration method synchronizes the time of the motor’s upper computer software and a frequency meter, minimizing indication error. Key uncertainty sources, including repeatability, environmental temperature effects, and the smallest division measure of instrument, were systematically analyzed. Results demonstrate that the extended measurement uncertainty (k = 2) for wave heights of 0.03 m and 40 m are 0.058 mm and 1.088 mm, respectively, while the uncertainty for a 30 s wave period is 3 ms. These values meet the stringent accuracy requirements (0.5% of measured values) for calibrating advanced wave buoys like the Directional Waverider 4. The proposed device provides a robust solution for validating wave buoy performance, offering significant practical value for oceanographic studies and coastal engineering applications. Full article

Ultrafast laser welding of transparent materials has been widely used in sensors, microfluidics, optics, etc. However, the existing ultrafast laser welding depths are limited by the short laser Rayleigh length, which makes it difficult to realize the joining of transparent materials in the millimeter depth range and becomes a new challenge. Based on temporal shaping, we realized Burst mode ultrafast laser output with different sub-pulse numbers and explored the effect of different Burst modes on the welding performance using high-speed shadow in situ imaging. The experimental results show that the Burst mode femtosecond laser (twelve sub-pulses with a total energy of 28.9 μJ) of 238 fs, 1035 nm and 1000 kHz can form a molten structure with a maximum depth of 5 mm inside the quartz, and the welding strength can be higher than 18.18 MPa. In this context, we analyzed the transient process of forming teardrop molten structures inside transparent materials using high-speed shadow in situ imaging detection and systematically analyzed the fracture behavior of the samples. In addition, we further reveal the Burst femtosecond laser welding mechanism of transparent materials comprehensively by exploring the difference in welding performance under the effect of Burst modes with different sub-pulse numbers. This paper is the first to realize molten structures in the range of up to 5 mm, which is expected to provide a new welding method for curved surfaces and large-size transparent materials, helping to improve the packaging strength of photoelectric devices and the window strength of aerospace materials. Full article

Local feature descriptors are a critical problem in computer vision; the majority of current approaches find it difficult to achieve a balance between descriptiveness, robustness, compactness, and efficiency. This paper proposes the local discrete feature histogram (LDFH), a novel local feature descriptor, as a solution to this problem. The LDFH descriptor is constructed based on a robust local reference frame (LRF). It partitions the local space based on radial distance and calculates three geometric features, including the normal deviation angle, polar angle, and normal lateral angle, in each subspace. These features are then discretized to generate three feature statistical histograms, which are combined using a weighted fusion strategy to generate the final LDFH descriptor. Experiments on public datasets demonstrate that, compared with the existing methods, LDFH strikes an excellent balance between descriptiveness, robustness, compactness, and efficiency, making it suitable for various scenes and sensor datasets. Full article

Since photodetectors are widely used in a variety of applications, such as imaging, optical communication, security and safety, motion detection, environmental sensing, and more, they are a crucial part of many technologies. The performance of photodetectors has significantly improved due to the advanced development of third-generation semiconducting materials caused by the novel pyro-phototronic effect. This effect; induced by localized heating under pulsed incident light, enhances the generation, separation, and collection of charge carriers within photodetectors. The combined pyroelectric and photoelectric effects resulting from this process are collectively termed the pyro-phototronic effect. It is crucial to understand how the pyro-phototronic effect affects the optoelectronic processes that take place during photodetection. This review addresses the latest advancements in photodetector performance by presenting the pyro-phototronic effect for a range of semiconductors. We provide a comprehensive summary of the pyro-phototronic effect in different semiconducting materials and outline recent developments in photodetectors. Full article

Monolayer MoS₂ has been widely researched in high performance phototransistors for its high carrier mobility and strong photoelectric conversion ability. However, some defects in MoS₂, such as vacancies or impurities, provide more possibilities for carrier recombination; thus, restricting the formation of photocurrents and resulting in decreased responsiveness. Herein, all-inorganic CsPbBr₃ perovskite quantum dots (QDs) with high photoelectric conversion efficiency and light absorption coefficients are introduced to enhance the responsivity of a 2D MoS₂ phototransistor. The CsPbBr₃/MoS₂ heterostructure has a type II energy band, and it has a high responsivity of ~1790 A/W and enhanced detectivity of ~2.4 × 10¹¹ Jones. Additionally, the heterostructure CsPbBr₃/MoS₂ enables the synergistic effect mechanism of photoconduction and photogating effects with the gate tunable photo-response, which could also contribute to an improved performance of the MoS₂ phototransistor. This work provides new strategies for performance phototransistors and is expected to play an important role in many fields, such as optical communication, environmental monitoring and biomedical imaging, and promote the development and application of related technologies. Full article

In order to improve the imaging quality of the vehicle photoelectric servo system, image motion compensation under the vehicle platform is studied. Based on the principle of image motion compensation, combined with coordinate system transformation and velocity vector decomposition, the angular velocity compensation formula of a fast mirror in dynamic scanning imaging of a vehicle photoelectric servo system is obtained. A discrete sliding mode control algorithm based on the Kalman filter is proposed. The proposed algorithm and the discrete sliding mode control algorithm are simulated and compared to verify the system control performance. The simulation results show that the designed algorithm improves control accuracy by 76.3%, reduces overshoot by 75%, and improves response time by 31.25% compared with the discrete sliding mode control algorithm. The experimental platform is built to verify the experimental results. The experimental results show that the speed stability accuracy of the fast mirror is better than 19 μrad, which is 74.37% higher than that of the traditional control scheme. This study provides a reference for the follow-up study of image motion compensation in a vehicle photoelectric servo system. Full article