Based on the acousto-optic effect, transmission matrix method, and planar angular spectral expansion theory, the transmission model of Laguerre-Gaussian (LG) beams in an acousto-optically coupled coaxial atmospheric medium is established,and the acoustic field is used to change the refractive index of the atmospheric medium. Furthermore, effects of different acoustic frequencies and topological charges on the transmission characteristics of LG beams are investigated. Results show that the refractive index of the atmospheric medium is periodically and uniformly distributed after the plane acoustic field is perturbed,and the refractive index stratification period varies for different acoustic source frequencies. The phase distribution of the p-wave always appears on the central axis when LG beam transfers in the layered atmospheric medium. The phase distributions of the s-wave of the incident and transmitted fields remain the same and rotate from the center to the surroundings. The rotational direction of the s-wave phase and p-wave phase are opposite when the topological load of LG beam is opposite, and the phase distribution of p-wave changes. Different acoustic wave frequencies lead to varying refractive index distribution cycles in the transmission path of the LG beam, thereby affecting the phase characteristics of LG beam transmission in the layered medium generated by the acoustic field perturbation. Research results in this paper provide theoretical support for future experimental investigations into the impact of the acoustic field on the transmission characteristics of vortex light.

A comprehensive channel model for air ground optical communication is established for an uneven atmospheric environment with smoke and fog, and a discrete layered height model is used to analyze the differences between uplink and downlink communication. Experimental results indicate that a stable simulation can be achieved after reaching six layers of high layering. In an uneven atmospheric smoke and fog environment, optical signs passing through smoke near the ground can significantly reduce communication quality, in which the effect on the downlink is greater than that on the uplink. In general, the performance of the uplink is superior to that of the downlink. An increase in the receiving aperture affects the performance improvement of the uplink more significantly than that of the downlink. As the receiving diameter increases by 0.1 m, the bit error rate decreases by an order of magnitude. Increasing the receiving aperture degrades the communication performance of the downlink. Meanwhile, increasing the zenith angle deteriorates the communication performance of both the uplink and downlink. The results of this study can provide theoretical reference for air ground laser communication.

In biomimetic polarized-light navigation, atmospheric polarization modes can be used as directional benchmarks to achieve precise navigation and location. In the measurement of atmospheric polarization modes, when the direct sunlight lens or field of view is obstructed, the measurement will be interfered, thus resulting in reduced navigation accuracy. To reduce the effect of these perturbed areas on polarization-navigation accuracy, this study proposes an anti-interference algorithm based on the polarization angle and degree to eliminate interference and uses the Rayleigh scattering model to obtain the direction of the solar meridian for navigation orientation. Experimental results show that this method can not only accurately partition the interference area but also improve the accuracy of polarization navigation methods. For data with heading-angle errors exceeding 2.00° before and after anti-interference, the average heading-angle errors are 5.37° and 1.56°, respectively. For data with heading-angle errors of less than 2.00° before and after anti-interference, the average heading-angle errors are 1.13° and 0.59°, respectively.

Elucidating the dynamic relationship between aerosols and water vapor is crucial for revealing atmospheric processes, assessing environmental changes, and predicting climate system responses. Based on continuous lidar observations in Beijing during 2023, this study analyzed the correlation and variation patterns between aerosol backscatter ratio and water vapor mixing ratio profiles. Results reveal the consistency in the distribution and co-variation characteristics of aerosols and water vapor, where the correlation is significantly influenced by the season and both the heights and sources of air masses. Statistical analysis of the data shows that within the vertical range of 0.2?1 km, the correlation coefficient between the aerosol backscatter and water vapor mixing ratios exceeds 0.9, indicating a significant correlation. Notably, air masses from the northwest exhibit a higher correlation between these two factors as compared with other sources. Layered statistical results indicate that the correlation between aerosols and water vapor gradually weakens with increasing height. The seasonal statistics indicate that the correlation between the two profiles during autumn and winter is higher than that during spring and summer. These findings provide a new understanding of the interaction between aerosols and water vapor in the atmosphere, which is of great significance for improving atmospheric models and climate change predictions.

In response to the boundary value issue of the extinction coefficient in single-channel aerosol lidar inversion technology, an aerosol extinction coefficient inversion algorithm based on exponential iteration has been proposed to optimize the boundary value in the inversion calculation. The 4th-order convergent exponential iteration method is utilized to solve the nonlinear equation between the extinction coefficient boundary value and the backscattering signal of the lidar, and the Fernald method is used to invert the aerosol extinction coefficient. By using exponential iteration combined with the Fernald method, horizontal scanning data and vertical fixed-point detection data were inverted. The results were compared with those obtained from the Klett and Mie-Raman methods, which served as reference values to validate the performance of the exponential iteration method. The data analysis results indicate that, compared to the fixed-point iteration method, the exponential iteration method exhibits higher precision, faster convergence, and fewer iterations. The inversion error is approximately 14%, with around five iterations taking about 9 μs. This approach enables the rapid and accurate inversion of the extinction coefficient boundary values for horizontal scanning and vertical fixed-point detection signals from lidar.

A reflective fiber optic sensor that consists of one transmitting optical fiber and six receiving optical fibers with an inclined surface is developed to realize the online, nondestructive monitoring of the growth processes of moldson the surfaces of wooden cultural relics. A theoretical model of this sensor detection measurement is established, and the influences of the sensor structural parameters on its sensitivity are numerically simulated. The growth processes of Penicillium citrinum and Trichoderma longibrachiatum on the surfaces of wooden cultural relics are monitored online by the sensor. Results indicate that the sensor can accurately obtain the characteristic absorption peaks of Penicillium citrinum and Trichoderma longibrachiatum, which are 261 nm and 272 nm, respectively. The corresponding detection sensitivities are 6.49×10-4 AU/μm and 6.85×10-4 AU/μm (AU is a unit of absorbance), respectively. A good linear relationship is found between the sensor's output signal and the mold height. In addition, the growth of molds on the surfaces of wooden cultural relics can be inhibited via treatment by a sodium chloride solution with an 8% relative mass fraction. The proposed sensor can accurately identify the mold growing on the surfaces of wooden samples, and it has application prospect in the field of mold control for wooden cultural relics.

Hermite-Gaussian (HG) beam mode decomposition has important applications in quantum communications and super-resolution imaging. The traditional convolutional neural network based on deep learning can realize mode decomposition of light field intensity and phase based on a single intensity image of HG beams, and the system is simple. In this study, the mode decomposition and reconstruction of a Hermite-Gaussian intensity diagram based on the new network architecture of Swin Transformer are investigated. In an experiment, the superimposed light fields of six modes (where the weights and phases are random values) of HG00, HG10, HG01, HG20, HG11, and HG02 are used as the output light fields. Experimental results show that when six eigenmodes are involved, the weight prediction error of the scheme is 0.05 and the phase is 0.15. In reconstructing the intensity image using the predicted weights and phases, we find that the input intensity image is very similar to the predicted intensity image. This work is of certain significance for large-capacity quantum communications, spatial quantum measurements, and super-resolution imaging.

The orbital angular momentum (OAM) of vortex beams has important application prospects in free-space optical communications. During the propagation of vortex beams, atmospheric turbulence can affect the accurate detection of OAM modes. We propose and demonstrate the accurate detection of OAM modes using a shear interferometer and residual network model (ResNet-50) under different atmospheric turbulence conditions. We first derive the optical field intensity distribution of OAM beams after passing them through a shearing interferometer. We then introduce atmospheric turbulence theory and a residual network model suitable for the proposed physical model. Finally, we investigate the effects of training sample size on OAM recognition accuracy and OAM recognition accuracy under different turbulence intensity conditions. Results show that during the propagation of OAM beams, within the range of topological charge l of －4―4 and under weak atmospheric turbulence simulated by computers at Cn2=5×10-16 m-2/3, the OAM recognition accuracy is 100%. Under strong atmospheric turbulence simulated at Cn2=5×10-14 m-2/3, the OAM recognition accuracy is 92%.

Accurate measurement of beam quality in laser communication optical transceivers is crucial for their design, assembly, and application. This paper presents a large-aperture off-axis beam quality measurement system that utilizes complex amplitude reconstruction. The proposed system captures intensity and relative position information by focusing on an off-axis parabolic surface. The transport of intensity equation (TIE) is then employed to reconstruct the complex amplitude of the focused beam. Angular spectrum theory is applied to determine the beam's intensity distribution in space, thereby enabling rapid measurement of the beam quality factor M2. The proposed large-aperture off-axis focusing system effectively overcomes the aperture limitations of typical optical transceiver output beams. Optical simulations are used to analyze the system accuracy requirements to ensure precise measurements. The phase reconstruction process, achieved through purely numerical analysis using the TIE, is unaffected by amplitude variations in the focused beam field. Compared to ISO international standards, the proposed system achieves measurement accuracy with errors controlled within 4%. The experimental setup avoids the need for complex optical equipment, thus reducing the time required for multiple sampling steps. In addition, the proposed system provides a fast and accurate method for measuring laser communication optical transceivers, offering a technical means for dynamic quality detection.

A novel method for near-surface defect detection combining deep convolutional neural network (CNN) and support vector machine ensemble learning was proposed to address the challenge of quantitative recognition of surface defect depth and angle in laser ultrasonic testing. First, a finite element model was developed to simulate laser ultrasonic signals with various defect depths and angles. Second, wavelet transform was applied to perform time-frequency analysis of the signals, generating spectra that capture both time- and frequency-domain features. Finally, the time-frequency spectra were input into deep CNN and support vector machine models to predict defect depths and angles. Results reveal that the proposed model achieves high-precision predictions of defect depth and angle, with regression coefficients exceeding 0.98 and an average relative error between the true and predicted values below 13%. Notably, this prediction accuracy surpasses that of individual network models in ensemble learning, and other widely used CNN models and VRD ensemble neural network models.

Determining the types and sizes of surface defects is crucial for an evaluation of the surface quality of precision optical components. We propose a cascaded inversion algorithm based on a decision tree model to address the limitations of traditional inversion algorithms in terms of inversion dimension and scale when angle-resolved scattering signals are used to invert the structural characteristic parameters of surface defects. To construct the dataset needed to train the model, an electromagnetic simulation of the angle-resolved scattering system was established using the finite difference time domain method, and the dataset was obtained through simulation calculations. The inversion results for the test set data show that the proposed algorithm is able to predict the defect type and depth with a precision having an area under the curve of 0.99 and an average R2 of 0.932, expanding the inversion dimension. The algorithm also accurately predicts the width of defects at different defect depths with an average R2 of 0.997, increasing the scale of inversion. The proposed algorithm offers a new approach to the precise quantitative analysis of small defects on the surface of optical components.

To eliminate the influence of light source fluctuation in an optical object chromaticity measurement system, this study proposes a new algorithm for object chroma based on quadratic normalized coefficient and develope a measuring device. Based on the principle of no change in the original optical path, the device is installed at the back of a monochromator. The light from light source is divided into two parts: measurement beam and monitoring beam. Consequently, the measuring beam is normalized to the monitoring beam. Results obtains by changing the output current of the driving power to simulate the fluctuation of the light source using the proposed and conventional methods are compared. Experimental results show that the relative error of the proposed method is no more than 0.51%. Thus, the proposed method can effectively improve the stability and accuracy of the measurement system and eliminate the influence of the light source fluctuation.

For the measurement of chromatic aberration in high power laser systems, this article proposed a chromatic aberration measurement technology for ultrashort pulse laser system based on wavelength scanning holographic interferometry to obtain wavefront and defocus dispersion information at different wavelengths. Chromatic dispersion information of different wavelengths were obtained using a Zernike polynomial fitting. Chromatic aberration introduced by the chromatic aberration compensation unit was accurately measured. Results were in good agreement with the theoretical simulation results, defocus chromatic aberrations at longer and shorter wavelengths were negative and positive, respectively. The precision of proposed method was validated by comparing focal points at different wavelengths. Proposed method could effectively measure chromatic aberration in ultrashort pulse laser systems, and provide accurate data support for the precise control of chromatic aberration compensation.

A liquid crystal-integrated programmable metasurface beam deflector that exhibits a tunable deflection angle is designed, which combines a liquid crystal and Huygens resonant metasurface. Simulated results demonstrate that, compared with the same thickness liquid crystal, Huygens resonant metasurface increases the achievable range of phase control by a factor of ~1.87. Furthermore, a 32-channel liquid crystal-integrated metasurface beam deflector is encoded using periodic and arbitrary coding methods, thereby achieving beam scanning with a field of view of 20° and providing a potential solution for solid-state beam scanning.

To address challenges such as difficulty in integrating complex control system and controlling generating deterministic optical comb states for microcavity optical frequency comb, we propose a self-starting method for integrating microcavity optical frequency combs based on the forward and reverse frequency tuning principles. The integration of the microcavity optical frequency comb system and the deterministic generation of arbitrary optical frequency comb states are realized through high-speed acquisition of microcavity transmission spectra and real-time feedback control of pump optical frequency offsets. The system based on the layered design is compact, with dimensions constrained to 290 mm×195 mm×141 mm, and the average generation time for the optical frequency combs ranges from 1.2 s to 31.1 s. The proposed approach is poised to advance the development of microcavity optical frequency combs for applications in communications, time-frequency analysis, and precision measurements.

In view of the defect of the traditional proportional-integral-derivative control method, which needs to reset the controller parameters as the process parameters change, this study employs a reinforcement learning correction framework based on the Kriging model, where the framework is specifically designed to predict and control melt pool dimensions, thereby eliminating the need for parameter tuning. Through iterative learning of the effects of process parameters on melt pool dimensions, the framework corrects the embedded Kriging prediction model by enhancing its predictive performance and yielding more optimized process parameters. Experimental results demonstrate that this framework can mitigate the melt pool backflow effect, proficiently manage width errors, reduce cumulative height errors in formed components, and significantly enhance the dimensional accuracy of laser direct energy deposition components.

To achieve high power, short-pulse CO2 laser outputs, a 13.56 MHz radio frequency (RF)-excited axial fast-flow CO2 laser amplifier with an adjustable RF injection power of 0?88 kW is developed in this study. Additionally, a laser-amplification experimental device is created to investigate the gain performance of the amplifier. First, the six-temperature model theory is described and the laser-amplification kinetic equation is established and its output characteristics are calculated. Second, the relationship between amplifier RF injection power, CO2 proportion, non-dissociation ratio, and other parameters and the small-signal gain coefficient under three different cavity pressures is analyzed. When the amplifier cavity pressure is 8 kPa, the RF injection power is 50 kW, and the CO2 ratio is 14%, the maximum small-signal gain coefficient is obtained. As the RF injection power continues to increase, the small-signal gain coefficient first increases and then gradually saturates. Reasons contributing to the amplifier-gain saturation are analyzed theoretically. Based on experimental measurements, when the seed light input power is 110 W, the amplifier output power can exceed 3500 W. Finally, the evolution of the laser-pulse waveform during the gain-extraction stage is simulated and the time-domain variation characteristics of the small-signal gain coefficient are analyzed.

A linear frequency modulation laser is the core device of frequency modulated continuous wave (FMCW) lidar, and the frequency modulation linearity of the laser affects the ranging accuracy and resolution performance of FMCW lidar. This study first suppressed the frequency modulation nonlinearity of lasers and subsequently designed a distributed feedback (DFB) laser frequency modulation nonlinearity correction system based on a field programmable gate array (FPGA). Here, a pre-distortion iterative control learning algorithm acts as the core of the system. In real time, the system can detect the nonlinearity of the laser and optimize its injection current based on nonlinear distortion, thereby significantly reducing the frequency modulation nonlinearity of the DFB laser. A linear frequency modulation DFB laser with a scanning frequency of 5 kHz and a modulation bandwidth of 1.2 GHz is achieved using this method. The nonlinearity of the up and down sweep cycles of the DFB laser is reduced from 2.62% and 1.96% to 0.035% and 0.031%, respectively. Ranging experiments were conducted using the developed linear frequency modulation DFB laser, where the maximum error within 5 m is less than 14 mm.

Keyhole instability is an important factor influencing defect formation in deep-penetration laser welding. This study investigates the use of 304 stainless steel as the welding material and examines the influence of spot spacing on keyhole behavior during dual-beam laser welding with a 50∶50 energy ratio. A high-speed camera was used for this intensive investigation. This study explores how a dual-beam laser source enhances keyhole stability by analyzing keyhole morphology and porosity. Results indicate that as the spot spacing increases from 0 to 1.800 mm, a single keyhole splits into two, with keyhole stability initially increasing and then decreasing. The most stable keyhole is achieved at a spot spacing of 0.450 mm, as indicated by a standard deviation in keyhole depth variation of 0.03. This improvement is mainly due to a noticeable reduction in the nonuniform evaporation of the metal liquid and an increase in the distance between the keyhole front and back walls.

The laser cutting of wafers is critical in the manufacturing process, with the polarization state of the beam significantly affecting the efficiency and quality of wafer cutting. Utilizing a liquid crystal spatial light modulator (SLM) in conjunction with combinations of half-wave and quarter-wave plates allows one to achieve dynamic control over the polarization state of the beam by dynamically loading various grayscale patterns onto the SLM. Based on this concept, three methodologies were implemented for cutting monocrystalline silicon carbide (SiC), ensuring that the polarization state of the beam remains parallel, perpendicular, or oriented 43° to the processing path direction. The results indicate that when the polarization state of the beam is parallel to the processing-path direction, the material cutting edge exhibits superior light absorption, thus resulting in the highest ablation efficiency. Additionally, the heat-affected zones on the top and bottom surfaces of the wafer, the edge chipping sizes, and the cross-sectional roughness are minimized, thus facilitating the attainment of more efficient and higher-quality wafer cutting.

To improve the wear resistance of titanium alloy blades used in aircraft engines, three composite materials, namely micro-TiN/Ti6Al4V, nano-TiN/Ti6Al4V, and micro/nano-TiN/Ti6Al4V, were prepared via laser-directed energy deposition. Micro-TiN partially melted and dispersed within the Ti6Al4V matrix, leading to particle strengthening. Meanwhile, nano-TiN completely dissolved and solidified within the Ti6Al4V matrix, leading to solid solution strengthening. With variations in the melt-pool temperature and nitrogen content, primary and eutectic TixN phases formed in the nano-TiN/Ti6Al4V and micro/nano-TiN/Ti6Al4V structures, exhibiting dendritic, flower-like, and whisker-like microstructures that promoted grain refinement. The microhardness values (wear rates) of the micro-, micro/nano-, and nano-TiN/Ti6Al4V composite materials were 510 HV0.2 (7.8 mg), 565 HV0.2 (6.9 mg), and 604 HV0.2 (5.3 mg), respectively. Compared with that of Ti6Al4V, the microhardness values of micro-, micro/nano-, and nano-TiN/Ti6Al4V increased by 19.4%, 32.1%, and 41.5%, respectively, and the wear rates decreased by 13.3%, 23.3%, and 41.1%, respectively. Notably, nano-TiN/Ti6Al4V exhibited the highest microhardness value and optimal wear resistance.

This article presents the design of a spaceborne line laser capable of projecting a single line shape for in-orbit measurement of thermal deformations on the surfaces of synthetic aperture radar antenna arrays. The laser incorporates a heat dissipation structure and adheres to resistance theory, making it suitable for the rigorous thermal vacuum environments encountered in space. Its beam width remains under 3 mm at a distance of 4.5 m, and the directional shift following continuous operation for 5 min is less than 25 μrad. Functioning effectively within a temperature range of 0?30 ℃, the laser exhibits high flatness, broad coverage, and remarkable stability. This design offers a novel technical reference for future in-orbit measurements of large-scale structural deformations.

This study utilizes a computational fluid dynamics (CFD) model to conduct high-speed laser cladding on flat plates, outer shafts, and inner shafts. The research aims to investigate the influence of process parameters on the clad morphology and molten pool. The differences in the dynamic evolution of molten pools during single and multi-pass cladding on different workpieces are analyzed. The results indicate that as the cladding speed increases, the molten pool gradually decreases in size. With the same process parameters applied, the molten pool on the flat plate is the largest, and the width and height of the clad layer decrease with the increase in cladding speed. With identical process parameters, the clad layer on the flat plate has the smallest width and the highest height; meanwhile, the clad layer width and height on the outer shaft are both smaller than those on the inner shaft. During the multi-pass cladding process, the molten pool increases in size with the addition of cladding passes. It is noteworthy that starting from the second pass, each scanned pass leads to an increase in the clad layer width greater than the set hatch spacing, and this increase further grows with the increase in the number of scanning passes. On the outer and inner shafts, the molten pool exhibits flow in different flow dynamics due to the effect of gravity, while on the flat plate, gravity has a relatively minor impact on molten pool flow. In the longitudinal section of the clad layer center on flat plates, outer shafts, and inner shafts, the dynamic evolution of molten pools follows a similar flow pattern. The liquid inside the molten pool flows towards the end of the pool under the combined effects of Marangoni force and surface tension. The maximum flow velocities of the molten pool are 0.931 m/s, 0.964 m/s, and 1.385 m/s, with the lowest flow velocity observed on the flat plate and the highest on the inner shaft. The temperature gradient decreases as the cladding speed increases. Under equivalent cladding speeds, the highest temperature gradient is observed on the flat plate, whereas the lowest temperature gradient is noted on the inner shaft.

This article describes a 1397 nm narrow-linewidth-filter-type external-cavity semiconductor laser (IF-ECDL) suitable for spaceborne strontium clock ultra-stable laser sources. Effective suppression of technical noise, such as mechanical vibration and temperature fluctuations during laser operation, has been achieved by designing an integrated laser configuration and using an invar-based external cavity. The linewidth of the proposed 1397 nm laser is measured as approximately 6 kHz, which is close to the linewidth limit determined by the current source noise of the laser. It is the narrowest linewidth of discrete-device-type ECDLs reported heretofore. In addition, the laser can output optical power higher than 60 mW and provide a mode-hop-free frequency tuning range of more than 11 GHz with only piezoelectric transducer (PZT) scanning. Furthermore, it has quite high power and frequency stability. In addition to satellite-borne optical clock applications, this laser is also expected to become an ideal light source for the fields of precision measurement, quantum physics, and other applications that require narrow-linewidth laser light sources.

This study systematically investigated the effects of different annealing heat treatment processes on the tensile properties of selective laser melted (SLM) 316L stainless steel in different build directions. The results show that significant tensile property anisotropy is present in the SLM specimens in different build directions. The elongation of the 0°, 45°, and 90° specimens significantly increase by 20.21%, 31.54%, and 16.93%, respectively, whereas the ultimate tensile strength values slightly decrease by 7.05%, 3.35%, and 2.19%, respectively, after annealing heat treatment at 950 °C for 0.5 h. In addition, the average sizes of the cellular grains of the 0°, 45°, and 90° specimens are reduced by 34%, 51%, and 46%, respectively, and the average dislocation densities decrease by 5.71%, 10.00%, and 43.62%, respectively. Recrystallization occurs in the SLM specimens in different build directions. The synergistic effects of fine grain strengthening, low dislocation density, and recrystallization contribute to the significant improvements in toughness and anisotropy of the SLM specimens in different build directions. Finally, the enhancement mechanism of annealing heat treatment on the anisotropy of the SLM 316L stainless steel in different build directions is revealed.

Temperature is a common and significant physical quantity, particularly under harsh conditions such as a high voltage or strong electric/magnetic fields. In this study, we developed an all-fiber-optic temperature sensor based on a fiber-end microstructure doped with quantum dots (QDs). The microstructure was fabricated on a fiber tip using two-photon polymerization technology. The results show that the fluorescence intensity of the QD microstructure is reduced with an increase in temperature, and the peak position of photoluminescence exhibits a linear change in the temperature range of 26?70 ℃. The developed sensor exhibits a high-temperature sensitivity of 135 pm/℃. The proposed method has enormous potential for the development of fiber-end temperature sensors.

It is crucial to optimize the size of Au@semiconductor core-shell nanospheres for the application of nanoparticles in biological imaging. In this study, the influence of the core radius and shell thickness of Au@ semiconductor core-shell nanospheres on their backscattering spectra is quantitively analyzed using Mie scattering theory and a refractive index size correction model for metal nanoparticles. The results indicate that by changing the size parameters, the resonance wavelength of Au@semiconductor nanospheres can be tuned to within the first near-infrared biological window. Moreover, the size of Au@semiconductor nanospheres is optimized at three commonly used laser wavelengths (800 nm, 830 nm, and 900 nm). The results show that the optimal core radius and shell thickness are 60?80 nm and 18?20 nm, respectively. Au@TiO2 nanospheres exhibit good backscattering ability among the three types of nanoparticles. Given the presence of certain errors in the material preparation process, a size range is also determined when the volume backscattering coefficient is greater than 95% of its maximum value. Finally, the influence of biological tissue refractive index and incident laser wavelength on the optimization results is analyzed. Research has shown that an increase in the refractive index of biological tissues leads to an enhancement of backscattering ability, whereas an increase in the wavelength of the incident laser weakens backscattering ability. Hence, optimized Au@semiconductor nanospheres can serve as ideal contrast agents in biological imaging.

To achieve a sufficient light dose and control the light field distribution in capsule under battery-powered, experiments are conducted using digestive tract tumor cell model and tumor-bearing mice model. The killing effects of Gaussian, non-uniform, and uniform light fields produced by light-emitting diode (LED) arrays on tumors are compared, identifying the effect of uniform light field as the optimum. To achieve an LED array with a uniform light field output under capsule size, a three-dimensional mathematical model of the LED array's light field is established to deduce optimum irradiation distance and spatial distribution of the capsule light source. The model indicates that an equilateral triangle LED array with a distribution radius of 7 mm can achieve uniform light field when the irradiation distance range is 7.1?8.8 mm, the optimum irradiation distance is 7.8 mm. The fit between the real LED array results and the mathematical model output is excellent, with a fit coefficient of 0.9934. Results show that the capsule-based photodynamic therapy light source with LED array can achieve uniform light field within the working distance and complete the photodynamic effect. This study successfully developes a prediction model for LED array light field distribution, provids a useful research tool for the medical application of LED light sources.

Ultrathin freestanding thin-film filters with high transmittance in the extreme ultraviolet band can be prepared using metallic as well as nonmetallic materials. However, improper process parameters and experimental conditions can directly cause film rupture during preparation. This study performed a finite element simulation of the key preparation steps of freestanding thin films and calculated the equivalent stress on the film under different conditions. The results indicate that the thin film sample, when placed perpendicularly to the liquid surface, experiences the minimum equivalent stress. During liquid transfer, higher fluid flow velocity leads to greater equivalent stress on the thin film. Further, the equivalent stress on the thin film is mostly distributed near the inner-diameter edge of the external support frame. The improved preparation process based on these simulation results is more stable than the original process, reducing the negative impacts of adverse process conditions and parameters on the thin-film transfer process, as well as the uncertainty caused by human factors. In addition, the repeatability of the film preparation process is improved, and the yield of the ultrathin freestanding extreme ultraviolet thin-film filters is enhanced.

To address the demands and challenges of rapidly advancing millimeter-wave radar technology for broadband and high-gain antenna design, we propose a novel hourglass-shaped slot structure. We develope a W-band high-gain broadband substrate integrated waveguide (SIW) antenna with a multiresonant hourglass-shaped slot array, which is optimized using genetic algorithms to balance the impedance bandwidth and radiation efficiency. The simulation results indicate that the SIW slot array excited multiple resonant frequencies, leading to bandwidth expansion. The antenna achieves a -10 dB impedance bandwidth from 76.32 to -100.39 GHz, with a relative bandwidth of 27.24% and coverage of 68.8% of the W-band. In addition, the radiation efficiency is 93%, with a maximum gain of 19.6 dBi. Despite its small size, the antenna offers considerable improvements in the gain and efficiency. The voltage standing wave ratio at the resonant frequency point is less than 1.2, and the return loss is below -20 dB. This antenna features a wide-frequency band, low profile, high gain, and ease of integration, making it suitable for wireless communication and millimeter-wave applications.

Light recycling is a method for developing high-power-density incoherent light sources, which combines significant challenges and high efficiency. However, the high processing difficulty and cost of traditional light recycling channels limit their widespread application. For this purpose, a spherical reflective film-coated light recycling lens is proposed, adopting a design method that is easy to model and process. This lens can be flexibly combined and matched, and it is suitable for LED chips of any wavelength, making it especially ideal for high-power-density LED applications. Simulations and experimental comparisons of three standard wavelengths were conducted in the industrial and medical fluorescence detection fields, namely 365 nm, 385 nm, and 455 nm. Among them, the measured values of far-field power-density enhancement in the 385 nm wavelength range are 19.56%?25.19%, which can meet the needs of some enterprises for increasing light source power density. This work innovatively demonstrates a design method for high-power-density lenses and presents an experimental process for a high-power-density light recycling channel. Thanks to the analysis and demonstration of experimental results, this concept provides new paths and design ideas for lighting enterprise designers, with potentially significant economic benefits.

To reduce the impact of Joule heating on the spatial resolution of long magnetic lens framing cameras, this paper developed a pulse current generator based on thyristors and Marx circuits for use in solenoid long magnetic lenses, and studied the relationship between output pulse current and circuit parameters. Based on the current triggering characteristics of thyristors and the inductance characteristics of long magnetic lenses, self triggering circuits and diode freewheeling circuits were designed to reduce the cost of driving circuits and protection circuits. When the charging voltage is 200 V, the solenoid load resistance is 0.94 Ω, and the inductance is 5.25 mH, the Marx generator with four parallel circuits and four stages in series on each circuit outputs a peak pulse current of -337.5 A and a full width at half maximum of 8.89 ms. When used to excite a long magnetic lens, it can generate a pulse magnetic field with a peak value of 0.57 T and a full width at half maximum of 3.31 ms.

In order to study the abnormal transmission phenomenon of C-type curved metal arrays with circular holes, the transmission spectrum and electric field distribution are obtained through experiments. The process of generating and transmitting optical lattices is analyzed for the C-type curved metal circular hole arrays. It is found that C-type curved metal circular hole arrays based on waveguide and tunneling modes exhibit anomalous transmission mechanisms, with tunneling mode evolving from waveguide mode and maximum transmission decreasing with increasing bending degree. There are three main reasons for this: first, the reflectivity of the C-type curved metal circular hole array is at a relatively high level at the maximum transmittance; second, the efficiency of electric field coupling in the metal circular hole array is reduced due to the waist variation of the light field with Gaussian like distribution in the optical lattice above the array and the deviation between the centers of the light field and circular hole; finally, the significant bending effect of C-type circular hole leads to large electric field transmission losses.

In this study, the vectorial properties of spatiotemporal optical vortices are investigated by combining them with polarization singularity, and a spatiotemporally polarized singular light field is proposed, which is a polarized singular light field in the spatial domain and features vortex phases in the spatiotemporal domain. Using the superposition of two orthogonal circularly polarized beams, three types of spatiotemporally polarized singularities, namely, C-point, V-point, and higher-order spatiotemporally polarized singularities are realized. The effect of the spiral phase of the spatiotemporal domain on the spatiotemporally polarized singularities in the spatial domain is investigated. The results show that the spiral phase must exist in the same plane as the spatiotemporal domain of the two superimposed beams; otherwise, the polarized singular structure in the spatial domain will be destroyed. This study provides better understanding into the physical properties of spatiotemporal optical vortices and provides a theoretical basis for their applied research.

The non-equilibrium effects induced by the energy flow that accompanies heat exchange between the system and its environment play a pivotal role in quantum information processing tasks. The information and energy that a quantum system exchange with its surroundings cause coherence decay and energy transfer. In this study, we used the non-Markovian quantum state diffusion method to study the dynamical evolution properties of coherence and energy flow in a five-qubit Heisenberg XXX spin chain system at thermal equilibrium. We examined the case in which the system was coupled to a common non-Markovian bosonic bath and introduced a pseudo-pure state as the initial state for the evolution of the system dynamics. Finally, we analyzed the effects of environmental memory effects, noise intensity, temperature, and magnetic field strength on quantum coherence and energy flow. Numerical simulation results show that, as the environmental correlation coefficient increases, the coherence of the system is enhanced. Energy flow back from the environment to the system may be feasible with the help of non-Markovian memory effects.

To satisfy the application requirements of laser rangefinders in terrain mapping, shallow coastal detection, and other fields, this study proposes a set of echo reception systems suitable for airborne laser rangefinders. The system measures the absolute distance between the device and sea surface via time-to-digital technology, as well as the relative distance of multiple targets via analog-to-digital converter technology, thus enabling the reception and measurement of echoes from the sea surface and seabed in shallow coastal areas. To address the issue of ranging accuracy affected by errors in the travel time of laser echo signals, this paper proposes an automatic parameter-control algorithm that can automatically adjust the circuit gain and comparator thresholds based on the echo signal. Additionally, the Levenberg-Marquardt (LM) algorithm is used to decompose the echoes, thus effectively improving the accuracy of multitarget echo decomposition. By constructing an experimental system for testing, the results show that the root mean square error of the system for measuring single targets does not exceed 2.89 cm and the accuracy of echo decomposition for dual targets does not exceed 2.56 cm.

Lasers of ~900 nm band can be used for pumping Yb3+-doped laser materials and atmospheric sensing. Moreover, the frequency doubling of ～900 nm lasers leads to deep-blue lasers of ~450 nm, which are crucial for underwater communication, biomedical applications, and laser processing. Because of their good integrability, tunability, and high beam quality, ~900 nm lasers based on Nd3+-doped silica fibers have attracted increasing research attention. However, overcoming the competition from the ~1060 nm transition of Nd3+ is necessary to realize ~900 nm fiber lasers. In this study, we review common techniques for suppressing the ~1060 nm parasitic oscillation in ~900 nm fiber lasers by focusing on an active enhancement scheme for ~900 nm emission we proposed previously. Using this scheme, the obtained ~900 nm emission intensity of Nd3+-doped silica fibers is higher than its ~1060 nm intensity. A 113.5 W high-power laser output at 927 nm, high-frequency ultrashort pulsed laser at 920 nm, single-frequency lasers at 890 nm and 910 nm, and picosecond pulsed laser at 920 nm with an average power of 10 W class have been achieved in all-fiber structures using self-developed Nd3+-doped silica fibers. This result will lay the foundation for the application of an all-fiber laser at ~900 nm.

With the rapid advancement of the semiconductor industry, there is a growing demand for improved polishing quality and efficiency for third-generation comprehensive band-gap power semiconductor materials, particularly silicon carbide (SiC). As a result, it is crucial to explore efficient surface manufacturing technologies to meet the urgent needs of the industry. This study compares common polishing techniques for SiC materials and summarizes the mechanisms of laser polishing and various laser surface modification-assisted polishing methods. Additionally, recent research progress in laser-based surface polishing technology for SiC materials is reviewed, focusing on the challenges posed by the material's high hardness, brittleness, and chemical inertness. Laser-based surface polishing offers several advantages, including efficiently removing SiC surface materials, avoiding subsurface damage, and facilitating industrial automation. Two promising development directions are summarized for highly efficient and nondestructive ultraprecision polishing technology for SiC materials in the current semiconductor industry. One of the development directions involves combining laser technology with chemical mechanical polishing (CMP). The other focuses on integrating multi-energy fields with laser polishing or laser-assisted CMP technology. Finally, the potential development of laser polishing and laser-assisted CMP technology, along with the underlying mechanisms, is discussed. This study provides a novel perspective and valuable reference for the highly effective and high-quality polishing of third-generation comprehensive band-gap power semiconductor materials, such as SiC, with substantial implications for the industry.

Recently, there has been a growing interest in using artificial intelligence (AI) technology to design metamaterial devices. This approach reduces the reliance on traditional design methods that require expertise in electromagnetics theory and simulation, resulting in a more efficient design cycle. Despite the progress made in this field, device design in the terahertz band remains relatively underdeveloped. This paper scrutinizes traditional design methods of terahertz metamaterial devices from the perspective of device function and focuses on the current research status of tunable multifunctional metamaterial devices. The article discusses how artificial intelligence techniques, such as machine learning, evolutionary algorithms, and deep learning, can aid in the optimization of metamaterial devices based on structural parameters and electromagnetic response. Finally, this section discusses future developments and challenges in the field, providing useful references for researchers engaged in related studies.

To meet the requirements of demultiplexing in wavelength division multiplexing (WDM) systems for medium- and high-quality signal transmission, this study investigates two aspects: the elimination of crosstalk and the improvement in the wavelength drift of concave echelle grating (CEG) demultiplexing devices. The design used to eliminate crosstalk is summarized into three structures: Roland circle, non-Roland circle, and multiple grating cascade are presented and analyzed. To improve the wavelength shift, two methods—compensating polarization and flattening passband, are evaluated. Further, in introducing the demultiplexing principles, we review the research progress on crosstalk elimination and wavelength shift improvements and analyze the advantages for the proposed methods of eliminating crosstalk and improving wavelength shift. Additionally, the conditions for eliminating crosstalk and wavelength shift improvements are identified, and the potential future development directions of demultiplexers are discussed.

Laser additive manufacturing (LAM) is widely used in the fields of aviation, chemistry, medicine, and biology in recent because of its advantages in terms of small batches, complex structures, short cycles, and low costs. Among them, selective laser melting (SLM) is an extremely important technology that is widely used because of its advantages of high-precision control, high density, and a wide range of available materials. However, during the additive forming process, owing to factors such as temperature gradient changes and metal phase transformation, it is easy to generate large residual tensile stress as well as a large number of small pores, cracks, and other defects. To effectively solve such problems, laser shock peening (LSP), which is an advanced material modification technology, is widely used in the post-processing of additive manufacturing. This article discusses the research and application of LSP on SLM in recent years, highlighting the feasibility and future prospects of low-energy laser shock peening (LE-LSP) in SLM applications.

Because of their rapid onset, strong toxicity, and wide range damage, biological and chemical warfare agents pose a severe threat to human health. Therefore, achieving rapid and highly sensitive detection of such agents is crucial for maintaining national security and preventing or managing public safety emergencies. Surface-enhanced Raman scattering (SERS) technique offers high sensitivity, rapid speed, and simple operation, making it promising for identifying and detecting biological and chemical warfare agents. This review summarizes the advancements in the detection of biological and chemical warfare agents using SERS technique, and highlights its advantages and future prospects in the detection of such agents.

With the rapid development of aerospace and nuclear energy technologies, there is an urgent need for optical fibers with excellent anti-radiation properties. Specialized optical fibers are crucial for applications in space communication and sensing, space measurement and acquisition, and satellite-to-ground communication However, radiation in extreme environments can damage fibers, reduce their transmission capacity, and compromise their stability and safety. This paper reviews the relevant literature on improving the anti-radiation performance of optical fibers and presents the current status of efforts to improve the anti-radiation performance of these fibers. Existing methods include altering the core or cladding materials and implementing various pre-treatments. By comparing the mechanisms and influence of these approaches, it is evident that combining multiple methods can remarkably improve the anti-radiation performance of transmission optical fibers. Specifically, combining pre-irradiation, H2 and D2 loading, annealing, photobleaching, and appropriate doping elements substantially improves the fiber anti-radiation performance. These findings offer a reliable approach for deploying optical fibers in extreme environments, and their successful implementation paves the way for future optical fiber research and applications, where more innovative and efficient methods can be explored to continually enhance optical fiber reliability and stability under extreme conditions.

When the peak power of the pulse satisfies certain conditions, it will cause the transverse intensity distribution at the output end of the gradient refractive index multimode fiber to transform from speckle to bell shaped beam. This is a special nonlinear phenomenon caused by the spatiotemporal nonlinear interaction between multiple transverse modes, known as Kerr beam self-cleaning (BSC). When this process occurs, it exhibits a strong mode self purification process: the energy of high-order modes is transferred to the fundamental mode, that is, the energy exchange between modes. At this time, the energy of high-order modes continuously transfers to the fundamental mode and is stably stored in the fundamental mode. Its significant characteristics are: improving the brightness of the output beam and robustness to fiber bending and compression.These features enable us to overcome the limitations of multimode fibers in terms of low output beam quality, which is extremely promising for a host of technological applications. We introduced this phenomenon from its discovery to recent research progress, and summarized its mechanism and explanation.

A three-dimensional Monte Carlo method (3D MCM)-based extinction model is proposed. In this model, the incident light beam is assumed to be composed of discrete photons, and Mie scattering theory is employed to describe how light scatters off individual particles. This approach enables the prediction of a particle system's extinction spectrum by counting all events after photons enter the system. The traditional extinction model, Lambert-Beer (LB) model, is calculated simultaneously, and a measuring device is built to verify the model. The comparison shows a root mean square error of <0.003 between the results of the 3D MCM and LB model, and <0.015 between the results of the 3D MCM and experimental model. These findings confirm the predictive accuracy of 3D MCM for characterizing extinction spectrum, thus expanding its applicability to various scenarios. 3D MCM model is successfully applied to the mixed particle system, and the prediction for extinction spectrum under non-parallel beam incidence is realized.

To address the problems of low detection accuracy, complex detection process, and insufficient applicability of traditional titration analysis process, an automatic titration system based on continuous spectral analysis was designed. With the core of a ball screw-driven injection pump pushing rod motion control, a visible spectrometer, a self-built data algorithm, and a high-precision titration system were adopted to improve the efficiency and accuracy of titration analysis. The relationship between the continuous transmission spectrum of solution and consumed volume of titration solution was investigated, and the end point of titration was automatically identified via the abrupt change observed in the correlation coefficient curve of solution spectrum. In this study, two types of titration were selected to test the accuracy and repeatability of the continuous spectral titration system. Results indicate that the overall relative error of the system is less than 0.5% and relative standard deviation is less than 0.3%. Furthermore, the proposed system demonstrates superior detection accuracy and repeatability compared with standard manual titration.

This study investigates the photogenerated carrier dynamics in gallium antimonide (GaSb) crystals using reflective optical pumping-terahertz detection technology. First, we examined fluctuations in terahertz time-domain peak intensity caused by varying the energy density pump light at a wavelength of 400 nm. Based on results of this examination, we derived the recombination time of photogenerated carriers in GaSb crystal. Next, we recorded the terahertz time-domain spectrum of GaSb crystals under different energy-density pump light conditions at a wavelength of 400 nm. This helped in calculating the GaSb conductivity in the terahertz frequency band. Finally, by leveraging the Drude-Smith model, we conducted conductivity fitting and extracted key parameters, including the Smith parameter and carrier scattering time. This study provides valuable insights into GaSb material modification and related detector manufacturing.