Optics and Laser Technology最新文献

With the development of artificial intelligence technology, the demand for image quality in machine vision systems is increasing. However, current research mainly focuses on chromaticity and light environment indicators, and cannot fundamentally solve the problem. To solve this problem, we established a machine vision optimal spectral calculation model from the perspective of physical energy, designed a narrowband spectral experiment, and analyzed it using JS divergence. The results showed that the calculated optimal spectrum significantly improved the image brightness and JS divergence compared to Standard White, with a maximum increase of 135.66% in image brightness and 82% in JS divergence. Research has found a significant linear correlation between the brightness value of machine vision images and the irradiance with a coefficient of 1, but not with the illumination. It was also found that the divergence of JS is not related to the irradiance, but has a significant linear correlation with the difference in spectral distribution with a coefficient of 1. These findings will provide a new basis and ideas for the light environment design of machine vision systems, provide new methods for improving system image quality, and have a significant positive impact on deep learning of the machine vision system.

Digital holographic microscopy (DHM) has been widely used in the biological and medical fields as an important tool for observing microstructures. However, the imaging quality of DHM is impacted by various random noises introduced by the light source and optical components as well as the experimental environment. In order to reduce the effect of random noise, this paper proposes an adaptive filtering and total directional variation (TDV) method based on the change of principal component analysis (PCA) transform domain to reduce the phase noise. The performance of the proposed method is tested by experiments, showing that it can effectively reduce the random noise of the phase image and retain details of the image well.

Non-destructive and real-time monitoring of the detailed growth process is essential for the manufacture of multilayer nanofilms. In this paper, the process of a layer of transparent nanosheets growing on the top surface of nanoporous anodized alumina (NpAA) is monitored by reflectance interference spectroscopy (RIfS) combining theoretical simulation and experimental detection. The main influencing factors on the properties of RIfS and effective optical thickness (EOT) are investigated systematically and in detail, where both NpAA and nanosheets parameters are changed individually as well as simultaneously. The experimental results for ∼ 1 μm thickness of (ZnO-ZnCl₂) nanosheets growing on the NpAA measured with a home-made RIfS system are in good agreement with the simulation data. We have shown that both the modeling and the experimental methodologies proposed have a high accuracy and a simplicity highly suitable in the fields of non-destructive, in situ and real-time monitoring of the fabrication process of transparent multi-layer composites, and can be readily employed to determine the nano structured thin film growth.

Hydrogen possesses vast potential for development and application. However, its low density and high diffusion coefficient render it prone to leakage during storage and transportation. It is necessary to conduct a safe and effective high sensitivity real-time leak detection for hydrogen. In this study, a telemetry system for hydrogen leakage based on Raman spectroscopy was built, simulating the scene of hydrogen leakage from the pipeline to the atmosphere through the air knife, and the actual concentration of hydrogen leakage into the air was measured directly. Based on the method of theoretical analysis and numerical simulation, the time-domain variation characteristics and influencing factors of the measured Raman scattering signal are analyzed, and the leakage concentration measured by the system is simulated and verified. The results show that the system has good measurement effectiveness. In the concentration range below the hydrogen explosion limit, the hydrogen leakage was measured at different leakage conditions with distance 1–5 m and leakage flow 0.25–3 L/min. The results show that the lower limit of concentration measurement of the system is 0.07 vol%. When the hydrogen concentration before leakage is the hydrogen explosion limit of 4.0 vol%, the minimum measurable leakage flow is 0.5 L/min, and the farthest measurement distance is 5 m. This study provides an intuitive and powerful reference for the engineering application of long-range portable measurement of hydrogen leakage based on Raman scattering spectroscopy.

Laser systems have demonstrated the potential to create micro-features that significantly influence the friction and wear characteristics of challenging-to-machine workpiece surfaces. This study examines the potential benefits of laser texturing the surface at high temperatures to make the Hastelloy C-276 superalloy more resistant to wear and reduce friction, which is commonly used in high-temperature applications in industries such as aerospace, automotive, semiconductor, and nuclear. A total of 72 laser textured surfaces are produced using a 50 W nanosecond pulsed fiber laser, with the aim of improving the overall efficiency and reliability of Hastelloy C-276. The research aims to study the influence of laser power, pulse frequency, and scan speed on the surface properties of Hastelloy C-276 at various temperatures, including room temperature, 100 °C, and 200 °C. A simultaneous heating apparatus is developed for elevated-temperature surface texturing, and the surface topography is evaluated using parameters such as R_a, R_sk, R_ku, and R_z. Additionally, micro-structural analysis is performed using scanning electron microscopy and atomic force microscopy. The findings indicate that modifying the scan speed and pulse frequency leads to enhanced surface properties when using fiber laser technology to generate surface textures on Hastelloy alloy while applying concurrent heating. Furthermore, the influence of laser power on the properties of the surface at elevated temperatures is found to be negligible. This study contributes to the understanding of the influence of laser parameters on laser-textured surfaces of Hastelloy C-276, particularly at elevated temperatures, thereby providing valuable insights for improving the performance of this superalloy in high-temperature applications.

Hyperbolic metamaterials (HMMs) have attracted wide attention owing to the exotic physical attributes and great application potential. The optical functional devices based on HMM have been the focuses of research. In this work, we propose and numerically analyze a terahertz (THz) HMM device consisting of a graphene-dielectric HMM, aluminum metamaterials composed of square patches, and an interjacent hollow cavity. Both the spectral characteristics and potential applications based on the device are numerically explored and displayed. Due to the impedance matching condition achieved at the top-air interface, the THz device features a single band absorption of 0.95, centered at 0.896 THz. Also, the absorption ability of the device demonstrates a strong robustness to wide incident angles up to 70° for the two orthogonal incident polarizations. In addition, the device is capable of functioning as a THz sensor if the dielectric hollow cavity is replaced by a microfluid cavity design. The sensing capacity of the device is numerically assessed as well, which discloses a maximum refractive index sensitivity of 400 GHz/RIU. Such a novel THz device composed of a graphene HMM offer a feasible option for future multi-functional devices in integrated optics.

To explore the mechanism of material removal, this paper conducts a systematic study on picosecond laser processing of zirconia by using both theory and experiment. Comparing the multivariate lattice heat capacity of the Einstein and Debye models, two-temperature model (TTM) is developed to improve the accuracy of the temperature field. Then, to verify the effectiveness of TTM proposed, ablation experiments are performed by single-pulse picosecond laser on zirconia at different laser energy density. The results show that the measured craters profiles are well agree with the simulated melting/vaporization temperature distribution. Micro-morphology is significantly affected by phase transition induced by temperature rise. Moreover, the results confirmed that increased temperature can lead to transition in zirconia crystal structure and oxygen vacancies. Finally, the effect of coupling temperature variations on the elemental and physical phase variations are focused to investigate, which can help to optimize the processing quality due to crystalline phase transitions. This study provides guidance for optimizing picosecond laser processing of zirconia.

This study investigated the hydrogen embrittlement behaviors of three laser welding joints for the 1500 MPa Al-Si coated steel using slow strain rate tensile and hydrogen concentration experiments. The results show that LW-HT is fractured in the fusion zone without hydrogen charging because the δ-ferrite reduces the mechanical properties. With the increase in hydrogen concentration, the fracture location is still FZ. The fusion zone of LWF-HT is composed of martensite and retained austenite, and when the hydrogen concentration is 3.4 ppm, retained austenite traps many hydrogen atoms. The newly formed martensite during tensile inheriting the high hydrogen concentration in retained austenite causes cleavage in the fusion zone. When the hydrogen concentration is 13.6 ppm, most hydrogen segregates at the prior austenite grain boundaries, causing an intergranular fracture in the fusion zone. The fusion zone of LWF-HS is composed of martensite and carbide, and grain refinement and nanoscaled Fe₃C can reduce HE susceptibility. With the increase in hydrogen concentration, the fracture location is still base materials. The significantly increased hydrogen concentration compared to LWF-HT is mainly trapped in carbides without reducing the banding force of dislocations and grain boundaries. This work provides a scientific basis and technical direction for realizing high-quality laser wire-filling welding of Al-Si coated steel.

Long-distance light detection and ranging (LiDAR) has been highly demanded for applications on unmanned vehicles and drones. CMOS-fabricated single-photon avalanche diodes (SPADs) play a key role in the receiver end due to their high photo-sensitivity and readiness for system-on-chip integration. However, the large amounts of involved components together with the diverse ranging conditions make engineering and optimizing these modules a daunting challenge. In this work, we have developed an analytical model for calculating minimum ranging time from the physical parameters for a photon-counting LiDAR. The experimental verifications of the model have been performed and a good consistency has been obtained. Our work enables architecture design and optimization for making low-cost high-performance SPAD LiDARs.

We report the effect of radio frequency (RF) acetylene plasma on the dynamics and composition of titanium (Ti) plasma plume in a plasma-enhanced pulsed laser deposition (PEPLD) system. The titanium target, mounted inside a capacitively coupled RF discharge, was ablated by using a nanosecond Nd:YAG pulsed laser at 1064 nm with a power density of 2.65 GW/cm². The experiments were performed at different operating pressures of acetylene. Fast imaging and optical emission spectroscopy were employed to study the physics behind the pulsed laser deposition in both (PLD) and PEPLD systems. A nonlinear dependence of the plasma plume evolution was observed over a range of pressure. Different expansion regimes correspond to the pressure of the experiments. The plume expansion velocity ranges between 6 × 10³ m/s and 30 × 10³ m/s. Emission spectra reveal the presence of C II and Ti II lines depending on the experimental conditions. The presence of background RF plasma leads to substantial enhancement of the emission intensity of the C II spectral lines. In addition, with increasing RF power and background pressure, the intensities of the C II spectral lines increase; whereas the intensities of the Ti II spectral lines decrease with the increase in RF power. Plasma temperature was estimated from the Ti II lines using the Boltzmann plot method, whereas the electron density was estimated from the Stark-broadened Ti II line at 454.9 nm. The calculated densities and temperatures lie between 10¹⁷–10¹⁸ cm⁻³ and 0.8–2.0 eV, respectively. These results show the effects of the different backgrounds (either neutral or RF plasma) on the propagation of the laser-produced plasma (LPP), which we propose to be useful in the thin film deposition process using PLD.