The atmospheric turbulence phase screen generated using the conventional power-spectrum-inversion method shows insufficient low-frequency sampling. Whereas the phase screen can be generated using the direct-summation method, the simulation speed is low owing to the significant amount of computations involved. Herein, a deep-learning technique is introduced to efficiently simulate an atmospheric turbulence phase screen by training a deep convolutional generative-adversarial network (DCGAN) model. The generator and discriminator loss functions converge to 0.07 and 0.98, respectively, and the trained model can be used to directly generate turbulent phase screens. Two methods for generating the atmospheric turbulence phase screen, i.e., the conventional numerical simulation and a simulation based on the DCGAN model, were used. A comparison between the two reveals that the DCGAN model can alleviate the shortcomings of the conventional simulation method at low frequencies and overcome the periodicity limitation. This method is applicable to the rapid generation of atmospheric turbulence phase screens as well as to image simulation and emulation.

Acoustic wave propagation in the atmosphere changes the atmospheric physical properties and affects the turbulence structure. In this study, COMSOL simulation was used to analyze the coherent acoustic field distribution of a line-array sound source at different source frequencies and acoustic wave transmission distances. Furthermore, a coherent acoustic wave generator was experimentally designed to perform horizontal transmission experiments of near-ground lasers in a coherent acoustic wave-disturbed atmospheric turbulence environment. The laser transmission characteristics in the original and coherent acoustic wave-disturbed atmospheric turbulence environments were compared via a crossover experiment. Moreover, the effects of changes in the height (i.e., acoustic wave transmission distance) between the laser optical path and acoustic source, the acoustic frequency of the acoustic source, and the acoustic pressure level on the transmission characteristics of the laser were analyzed. The results show that the coherent acoustic wave perturbation has a more obvious effect on the beam drift and light intensity flicker but none on the beam diameter. Different source frequencies and acoustic wave transmission distances will produce various acoustic field distributions; additionally, the effect of the coherent acoustic wave perturbation of atmospheric turbulence on the laser transmission characteristics of the impact is different. The larger the sound pressure level, the higher the effect of the coherent acoustic wave perturbation of atmospheric turbulence on the laser transmission characteristics of the impact. The results of this study provide a foundation for the use of acoustic waves to improve the atmospheric turbulence environment and quality of optical transmission.

Owing to their high sensitivity, high signal-to-noise ratio, and fast response speed, InGaAs/Si avalanche photodiodes (APDs) are utilized in various applications, including low light signal detection, long-distance fiber optic communication, laser ranging, and laser guidance. However, the high penetration dislocation density at the InGaAs/Si heterojunction interface, caused by the 7.7% lattice mismatch and maximum conduction band order between InGaAs and Si, results in large dark currents and complicates avalanche breakdown within APDs. To achieve high performance in InGaAs/Si APDs, this study introduces an eight-layer InGaAs gradient buffer at the InGaAs/Si bonding interface to reduce the charge carrier accumulation at the heterojunction interface. We have also innovatively added air grooves to the Si multiplication layer to replace the charge layer and modify the electric field. We investigat the influence of groove depth on the performance of the charge-free InGaAs/Si APDs at the bonding interface. Our research found that the current, recombination rate, impact ionization rate, electric field, and gain-bandwidth product of the InGaAs/Si APDs are optimized at groove depths of 150 and 300 nm. These findings provide theoretical guidance for the subsequent development of InGaAs/Si APDs with simplified processes, stable performance, and low noise.

Current wireless sensing systems based on Raman distributed-optical-fiber sensing systems are limited by technical bottlenecks such as unidirectional transmission of information and small transmission data volume. To overcome these bottlenecks, a wireless data transmission method and Raman distributed-optical-fiber temperature remote monitoring system were designed in this study. This system is based on a combination of a 4G wireless transmission module and a Raman distributed-optical-fiber sensing system. It is suitable for large-scale distributed sensing data. Results show that the proposed system displays field-monitoring results stably and in real-time in the remote control center. The bidirectional remote control of monitoring instructions was realized, and the monitoring results were analyzed. The proposed system is beneficial for reducing the cost of long-distance, real-time monitoring of distributed-optical-fiber in engineering application and improving the level of intelligent monitoring control and sensor monitoring efficiency.

We propose a diaphragm-based optical fiber sensor for pulse wave monitoring. A Fabry-Perot (F-P) cavity composed of a brass diaphragm and fiber end is utilized to form a sensor head. A parallel flat glass and linear charge-coupled device (CCD) are used as an optical demodulator. The mathematical model of optical cross-correlation demodulation is established. In an experiment, the monitoring system enables the real-time measurement of pulse waves from different subjects in different states. The obtained pulse wave, which has distinct feature points, is consistent with classical pulse wave theory. Hence, the research is significant for the development of digital pulse diagnosis technology.

This paper presents the design of a temperature-drift-resistant optoelectronic front-end for high sensitivity avalanche photodiode detectors (APD) to enhance the detection capability of weak backscattered Rayleigh light in distributed optical fiber acoustic sensing (DAS) systems and address the issue of poor avalanche gain temperature stability in APD. The optimal avalanche gain of the APD at different temperatures is measured and combined with APD bias voltage temperature auto-compensation and temperature control technology, to ensure that the APD always operates at the optimal avalanche gain state. Additionally, to address the wide dynamic range of the detected signal, a logarithmic amplification circuit is designed. Experimental results show that the circuit can achieve precise temperature auto-compensation of the APD bias voltage in the range of 0?50 ℃, with a bias voltage control error of only 0.04 V, temperature control error of 0.14 ℃, bandwidth of 1 MHz for the logarithmic amplification circuit, dynamic input range of up to 40 dB, and accurate detection of input optical power as low as 10 nW.

Phase-sensitive optical time-domain reflectometry (φ-OTDR) offers advantages such as high sensitivity, resistance to electromagnetic interference, and long transmission distance, and is widely used in fields such as rail transit, pipeline monitoring, marine acoustic-signal detection, and perimeter security. However, the performance of φ-OTDR systems is affected by laser, balanced photodetector, erbium-doped fiber amplifier, and environmental noises. Based on existing wavelet denoising algorithms, this study proposes a new adaptive threshold-calculation method and a new continuous low-error wavelet-threshold function using the wavelet coefficients in each layer wavelet transform as parameters for threshold calculation, as well as analyzes the performance of the new wavelet-threshold function. Experimental results show that compared with wavelet soft- and hard-threshold denoising algorithm, the improved adaptive wavelet-threshold denoising algorithm proposed herein offers better denoising effect.

The integration of high-speed communication and high-precision sensing is key in 6-Generation (6G) networks. A signal generation and transmission scheme for optical terahertz communication based on phase shift keying (PSK) and linear frequency modulation (LFM) is proposed, where geometric shaping (GS) technology is utilized to improve the communication capacity of integrated signals. Theoretical analysis was conducted on the generation, transmission, sensing, and communication principles of the GS-PSK-LFM integrated signal, and the ambiguity function of the integrated signal was analyzed. Based on MATLAB and VPI simulation environments, the communication and sensing performances of 8PSK-LFM and GS-8PSK-LFM formats at rates of 4 and 8 Gbaud were analyzed, as well as the effects of different DC offsets on the communication and sensing performances. The results show that the maximum peak-to-side lobe ratio (PSLR) of the proposed integrated signal theory is 10.5 dB at a rate of 4 Gbaud, and the distance resolution reaches 0.97 cm. Under a wireless channel-transmission distance of 50 m, the communication transmission rate can reach up to 24 Gbit/s, and the error rate is lower than the hard decision threshold of 3.8×10-3. At the same bit error rate, when combined with GS, the input optical power of the sensing signal photoelectric detector (PD) is reduced by a maximum of 0.43 dB compared with that of 8PSK-LFM. When the DC offset is 1, the communication and sensing performances are balanced. Thus, this may be considered in future scenarios where sensing is prioritized.

In this study, we develop a hydraulic sensing system employing a side-polished fiber (SPF) as the sensing medium. By side-polishing an ordinary single-mode fiber (SMF), birefringence is induced, thus resulting in a sensing unit whose fiber birefringence changes with the liquid depth. The polarization-analyzing optical-frequency-domain reflectometry technique is utilized to detect the Rayleigh backscattering light from the fiber. Signal demodulation is performed using a full-Mueller matrix-based distributed-polarization analysis method, thus enabling highly sensitive and spatially resolved birefringence measurements. Ultimately, the correlation between hydraulic pressure and fiber birefringence is established. The results show a linear correlation between the depth of side-polishing on the fiber and the induced birefringence. Moreover, with increasing hydrostatic pressure, the birefringence of the fiber sensing unit first decreases and then increases. The sensitivities for the decrease and increase in birefringence are -1.34×10-8 and 1.39×10-8 refractive index unit RIU/kPa (RIU is a unit of refractive index) for a fiber polishing depth of 40 μm. The technique proposes herein offered the possibility of achieving simultaneous multipoint hydraulic pressure sensing and presents a novel approach to implementing distributed/quasi-distributed hydraulic fiber optic sensing.

Distant space target laser ranging encounters challenges due to the non-cooperative nature of the targets, resulting in nonlinear temporal variations in the echo signals. This nonlinearity poses a significant constraint on the performance of conventional Poisson methods. In response to this, the paper proposes a recognition methodology tailored for nonlinear laser ranging signals. In the realm of feature construction, a genetic algorithm is employed to intricately generate a set of mathematical features for the echo data, thereby substantially reducing the required number of training samples. Regarding model selection, a random forest model is adopted, successfully achieving the classification of signals and noise under the condition of expeditious training. The comprehensive analysis of simulation and measured data shows that the proposed method has better results, thus verifying its effectiveness.

Wavelength is a crucial parameter for terahertz sources, and the Fabry-Perot (F-P) interferometric method is the preferred approach for measuring terahertz-source wavelengths. However, employing a high-resistance silicon wafer as the interference-cavity plane mirror presents challenges such as low reflectivity, a narrow applicable frequency band, and imprecise stripe precision; consequently, the demands of high-precision wavelength measurements cannot be satisfied. Hence, a series of interference chamber silicon-grid plane mirrors, which comprises high-resistance silicon wafers plated with a periodic metal grid, were designed and processed. These mirrors demonstrate a reflectivity exceeding 87% in the 0.08?0.53 THz band. The F-P interferometer successfully measures the wavelengths of 0.096 THz/0.14 THz avalanche sources and a 0.315 THz Schottky source, where optimal measurement results are yielded with wavelength errors of 0.16%, 0.33%, and 0.54%, respectively. Compared with measurements using high-resistance silicon wafers, this approach significantly improves the interference stripe precision and the half-peak width of the transmission peak. The simplicity of the structure facilitates ease of fabrication, thus contributing significantly to advancements in terahertz-wavelength measurement accuracy and related terahertz devices.

To measure the inner diameter of super large cylindrical shells with high accuracy, a visual detection system has been designed. This paper proposes a super large cylindrical shell diameter detection method based on noise classification, bilateral point cloud filtering, and cylinder feature fitting. First, point cloud data of the targeted cylindrical shell are obtained using a laser tracker. The noise in the point cloud data is classified into large-scale noise and small-scale noise. Various filtering algorithms are employed to remove the large-scale noise, whereas an improved bilateral filtering method is used to eliminate the small-scale noise. Second, a cylindrical-feature fitting method is proposed to measure the inner diameter of the cylindrical shell. Finally, real point cloud data of the super large cylindrical shell are collected for experimental verification. The experimental results show that the proposed method fits the cylinder more accurately than traditional tape measurement and roller detection methods. The error between the inner diameter of the cylinder obtained in the fitting experiment and the measured value is 0.21 mm, with a relative error of 0.003%. Compared to traditional measuring methods, the error is reduced by an order of magnitude. The detection time is less than 15 s, improving both detection efficiency and accuracy. The proposed detection method provides technical support for the online detection of the inner diameter of super large cylindrical shells.

In high-energy laser systems such as inertial confinement fusion systems, large-aperture optical components are widely used and transmittance is an important parameter for characterizing them. However, studies pertaining to the transmittance measurement of large-aperture spherical mirrors are few. Therefore, this paper proposes a curvature-radius-compensation technology to investigate the transmittance measurement of large-aperture spherical mirrors. First, the measurement scheme of a dual-beam single detector was adopted using the optical-power-ratio method. Second, to adapt to spherical mirrors with different curvature radii, a mathematical analytical solution was established to preliminarily adjust the angle and position of the mirror, compensate for curvature radius deviation, and finely adjust the curvature radius based on the displacement of light spot detected by the monitoring device. Subsequently, the compensation effect and factors affecting transmittance when measuring spherical mirrors with different curvatures were simulated and analyzed. The final simulation results show that proposed system can measure the transmittance of spherical mirrors with an effective aperture of less than 600 mm and a curvature radius of 1200 mm to ∞ at a measurement accuracy of 0.2%, thus satisfying the measurement requirements.

This study proposes a method for measuring the instantaneous relative frequency of a high-speed frequency-modulated continuous-wave (FMCW) laser signal based on a 3×3 fiber coupler. First, the operating principle of instantaneous relative frequency of the FMCW laser signal based on a 3×3 fiber coupler was theoretically analyzed. The study finds that the greater the delay difference between the two arms of the interferometer, the higher is the resolution of the measurement instantaneous relative frequency but the lower is the maximum sweep speed that can be measured. For example, when the delay between the two arms of the interferometer is 6.67×10?8 s (20 m optical path difference), the lower is the measurement speed. The maximum scanning speed is 7.5×1015 Hz/s. Next, the study constructed a high-speed FMCW laser signal instantaneous relative frequency measurement system based on a 3×3 fiber coupler. The FMCW laser signal with a sweep period of 22 μs and frequency range of 820 MHz was measured experimentally, and nonlinear correction was performed using a pre-distortion nonlinear correction method. The correction results reveal a residual nonlinearity of the FMCW laser signal of 1-r2=2.6326×10?5 and a root mean square frequency error of 1.23 MHz. The instantaneous frequency change measurement technology of the FMCW laser signal shows the advantages of high-speed and high-frequency resolution.

To improve the detection accuracy of gas concentration in tunable semiconductor laser absorption spectroscopy, an optimized variational mode decomposition combined wavelet packet denoising algorithm, based on the genetic algorithm (GA), was proposed. The proposed algorithm can solve the electrical and optical noises of the second harmonic signal in gas detection. Initially, GA optimized the decomposition mode number K and penalty factor α, and the optimal parameter combination was obtained. Then, the second harmonic signal was decomposed by the optimal parameter combination, and a series of intrinsic modes (IMF) was obtained. Pearson correlation coefficient was used to select the pure and noisy signals, and the noisy signal was denoised using a wavelet packet. Finally, the denoised signal was reconstructed with the pure one to obtain the second harmonic signal after denoising. Results show that compared with other noise reduction algorithms, the proposed algorithm can effectively remove the noise in the second harmonic signal, reduce the influence of external noise on the detection process, and improve the detection accuracy of gas concentration.

In recent years, forming Ti6Al4V aerospace parts by selective laser melting (SLM) technology has become an attractive research topic. However, pore defects that occur during the SLM process frequently lead to fatigue damage in the parts. The specifically designed experimental approach was applied to obtain fatigue life data when forming Ti6Al4V parts by SLM with different process parameter combinations. The SEM technique was used to measure the characteristic parameters of the fatigue source pore in the specimens, and the relationship between each characteristic parameter and fatigue life was analyzed. A fatigue life prediction model for SLM-formed Ti6Al4V parts was subsequently constructed based on characteristic parameters of the fatigue source pores using the random forest technique. The optimal model parameter combinations were obtained by utilizing stochastic search and k-fold cross-validation methods. The model prediction results are close to the 1.5 times error band, and the R2 and average relative errors are 0.914 and 29.1%, respectively. This indicates that the model exhibits high prediction accuracy.

To better guide the design of electrowetting liquid lenses, we propose a method for controlling their initial focal length. This method involves adjusting the microstructure of the electrode surface through low-power laser processing to change the contact angle of liquid lenses, thereby controlling the initial focal length. Using Wenzel theory, we derived the relationship between the initial focal length and geometric parameters (width and spacing) of the microstructural bumps. To validate this method, we conducted comparative experiments on three typical microstructures: cruciform, square, and concentric circular rings. Results show that the measured initial focal lengths of the concentric annular microstructures are consistent with the theoretical predictions. Additionally, these lenses have symmetrical shapes and smooth surfaces with no bumps. The centered radial microstructures are particularly effective for obtaining liquid lenses with good imaging qualities.

During laser direct energy deposition, the temperature distribution and flow state of the molten pool directly impact the quality of the deposited layer. Analyzing the dynamic behavior of the molten pool helps improve our understanding regarding the mechanism of molten pool formation, thereby reducing the occurrence of defects. This study established a coupled simulation model of the temperature and flow fields during laser direct energy deposition. The model considered the Marangoni effect and employed a dynamic mesh method to simulate molten pool morphology. Furthermore, this study investigated how different process parameters affect the temperature field and flow rate of the molten pool during single-pass single-layer deposition and the variations in the temperature field and morphology during the overlapping of multiple passes owing to asymmetric heat transfer. Results indicate that laser power, scanning speed, and powder feeding rate considerably affect the temperature field and flow rate of the molten pool, with laser power exhibiting the most substantial influence. Asymmetric heat transfer causes the temperature of different melt tracks to increase and then stabilize, leading to a consistent growth trend in the molten pool depth.

We report a high-beam-quality diode-side-pumped Nd∶YAG intracavity-frequency-doubled laser. The thermal lensing effect of Nd∶YAG laser is compensated by using concave crystal rod. We have designed a convex-convex cavity based on the thermal focal length of the laser module to control the beam quality of the fundamental frequency laser. An acousto-optic Q-switching is used to modulate the fundamental frequency laser, and a type-II critical phase-matched lithium borate (LBO) crystal is used to generate frequency doubled laser. At a pump current of 21 A and a repetition frequency of 9 kHz, we obtain a 532 nm laser with an average power of 21.1 W and a pulse width of 60 ns. At maximum average power of the 532 nm laser, the beam quality has been measured to be Mx2×My2=1.33×1.36, and the power stability fluctuation within 1 hour is less than 3%.

To predict the flexural strength of stereolithography alumina ceramics and optimize the process parameters, a mathematical model is developed based on the response surface methodology. This model establishes the relationship between process parameters and the flexural strength of alumina bending specimens. Analysis of variance (ANOVA) and model validation is performed. The established model is used to analyze the effects and mechanisms of scanning speed, scanning spacing, slice thickness, and laser power, as well as their interactions on flexural strength of alumina ceramics, to determine the optimal response. The results show that the scanning spacing, scanning speed, laser power, and slice thickness significantly impact the flexural strength of alumina ceramics. The optimal combination of process parameters is scanning speed of 2382 mm/s, scanning spacing of 0.128 mm, slice thickness of 0.127 mm, and laser power of 206 mW. The flexural strength at this parameter combination is 302 MPa. The results of ANOVA and model validation demonstrate that the predicted values of the model closely match the real values, indicating high reliability.This model has good guiding significance for improving the mechanical properties of stereolithography alumina ceramics.

This study reports the preparation of 15-5PH martensitic stainless steel via laser-directed energy deposition (L-DED) and systematically analyzes its microstructure and properties in different directions. The research results indicate that the microstructure of 15-5PH martensitic stainless steel fabricated via laser-directed energy deposition is primarily composed of martensitic and a minute amount of austenitic phases. The extremely rapid heating and cooling during the formation process result in columnar grains growing epitaxially along the deposition direction. The microstructures in different regions parallel to the scanning direction differ significantly, with the central region of the sample experiencing prolonged thermal accumulation, thus resulting in coarser microstructures compared with the microstructures in the top and bottom regions. The microstructural variations along different forming directions result in anisotropic mechanical properties, with tensile strengths of 1000 MPa and 1014 MPa, yield strengths of 756 MPa and 883 MPa, and elongations of 8.7% and 7.4%, along the deposition direction and the direction parallel to the scanning direction, respectively.

pH-responsive hydrogels have garnered considerable attention in actuator manipulation, drug delivery, and tissue engineering because of their capacity to undergo structural or volumetric changes in response to acid/base alterations. The fabrication of microstructures of stimuli-responsive biomaterials is crucial in the development of biomedicine and tissue engineering. Bovine serum albumin (BSA) is commonly used in tissue engineering and drug delivery because of its non-toxic, biodegradable, and biocompatible properties. This study presents the macroscopic pH response of BSA-glycidyl methacrylate (BSA-GMA) hydrogels, the microscopic pH response of three-dimensional (3D) hydrogel microstructures polymerized by femtosecond laser direct writing, and cell viability studies. Femtosecond laser direct writing enables the creation of high-precision 3D structures of BSA-GMA hydrogels. The results indicate that the pH responsiveness of the BSA-GMA hydrogels increased with either increasing concentration or decreasing methacrylation degree of BSA-GMA. Unlike the BSA hydrogel, the photopolymerization of the BSA-GMA hydrogel by femtosecond laser direct writing does not deplete amino acid groups. Consequently, the 3D BSA-GMA hydrogel demonstrates a stronger pH response because it contains more amino and carboxyl groups. Furthermore, confocal fluorescence imaging and analysis of relative cell growth rates of chondrocytes on the BSA-GMA scaffolds indicate that the BSA-GMA hydrogel has good biocompatibility. These protein microstructures with controlled morphology and pH-responsive properties have potential applications in tissue engineering, biomedicine, and biosensors.

The temperature field during cladding under different cladding methods was simulated using the COMSOL software. Subsequently, using optimized process parameters, the Fe-based high-hardness and corrosion-resistant alloy was cladded on the blade of a 3Cr13 stainless-steel billet. The microstructure and microhardness of the two cladding layers were compared and analyzed. The results show that the simulated weld-pool morphology is consistent with the actual morphology. During top cladding, heat dissipates from the molten pool rapidly and the maximum temperature of the temperature field is 2271.1 K. During side cladding, the maximum temperature reaches 2349.7 K owing to heat accumulation. The microstructure of the top cladding layer from the bottom to the surface comprises a planar crystal, a small amount of cellular crystals, and dendrites. Meanwhile, the microstructure of the side cladding layer comprises a planar crystal, an equiaxed crystal, columnar dendrites, and dendrites from the bottom to the surface. The average microhardness of the top and side cladding layers is 783.8 HV and 688.5 HV, respectively.

In this study, laser-MIG hybrid welding and MIG welding were performed on aluminum-alloy crossbeam components of high-speed trains. Additionally, the weld formation as well as the microstructure and mechanical properties of the two welding methods were compared and investigated. The results show that both welding methods can achieve welds with good forming quality. Compared with MIG welding, laser-MIG hybrid welding offers a higher efficiency by approximately eight times while reducing the line energy by approximately 70%. The weld center of the two welding methods is a dendritic crystal. Compared with MIG welding, the laser-MIG hybrid welding features a columnar crystal in the fusion line at the weld side and the fusion zone is ambiguous. The hardness of the weld center resulting from laser-MIG hybrid welding is slightly higher than that from MIG welding. The lowest hardness achieved by laser-MIG hybrid welding is near the fusion line, whereas that achieved by MIG welding is in the weld area. The tensile strength of joints resulting from laser-MIG hybrid welding and MIG welding are 218.7 MPa and 177.0 MPa, respectively. The tensile specimens are fractured near the fusion line and weld zone, respectively, and both present the typical plastic fracture.

This study examines the auxiliary effects of an ultrasonic vibration physical field on laser polishing and explores how ultrasonic amplitude and laser parameters influence the surface roughness of zirconia ceramics. By employing a response surface experimental design, this study aims to optimize the surface roughness. Zirconia ceramics are polished using a pulsed laser, and the study evaluates the surface roughness, hardness, friction and wear coefficients, and changes in the surface element composition.Resultsindicate that the optimal process parameters for ultrasonic-assisted laser polishing of zirconia ceramics are as follows: laser power is 75.9 W, pulse frequency is 3.28 kHz, scanning speed is 345 mm/s, ultrasound amplitude is 25%, and vibration frequency is 19.42 kHz. Pulsed laser polishing alone reduces the surface roughness from 2.479 to 0.595 μm. When combined with ultrasonic vibration, the surface roughness decreases further to 0.477 μm, resulting in an overall reduction of 80.7%. Additionally, ultrasonic vibration induces residual compressive stress within the remelted layer, leading to a narrower vertical crack width than that generated by laser polishing alone. Although ultrasonic-assisted laser polishing slightly increases surface hardness, it does not notably alter the content of surface elements.

In this paper, the controllable frequency-tuning and laser output characteristics of a single-longitudinal-mode distributed Bragg reflector (DBR) fiber laser with a piezoelectric ceramic that axially stretches across a DBR fiber resonant cavity are investigated. Our theoretical analysis shows that this tuning scheme can effectively prevent the occurrence of mode hopping during frequency tuning, which is beneficial for obtaining a wider frequency-tuning range without mode hopping. Additionally, experimental results verify that this tuning mechanism can achieve fast and controllable frequency tuning of the DBR fiber laser over a wide range without mode hopping. The maximum mode-hop-free frequency-tuning range obtained in our experiment is as high as 116 GHz. During the frequency-tuning process, changes in the linewidth and relative intensity noise of the laser are not significant; furthermore, large fluctuations in the output laser power can be effectively suppressed using a boost fiber-optic amplifier.

Based on a two-dimensional axisymmetric thermal and mechanical simplified model of a quantum well infrared photodetector under 8.2 μm long-wave infrared mono-pulse laser irradiation, the transient temperature and stress-field distribution of the detector under various pulse widths were calculated using the finite-element method. In addition, variations in the thresholds of the detector for thermal decomposition, melting, and stress-induced damages under laser irradiation with the pulse width ranging from 1 to 300 ns were preliminarily determined. Results show that damage thresholds exhibit a downward trend as the laser pulse width decreases. Specifically, when the pulse width reduced from 300 to 1 ns, the decomposition damage threshold decreases by 23.10% (from 3.16 to 2.43 J/cm2), melting damage threshold decreases by 23.27% (from 5.50 to 4.22 J/cm2), and stress-induced damage threshold decreases by 44.62% (from 8.92 to 4.94 J/cm2).

The T800 cobalt-based alloy has excellent high-temperature wear resistance and is widely used for surface strengthening of aero-engine hot-end components. In this paper, benefiting from the advantages of laser direct deposition technology, defect-free T800 cobalt-based alloy wear blocks are successfully prepared on K417G substrate. To investigate the microstructure and properties of the laser direct-deposited T800 cobalt-based alloy wear blocks, microstructure and microhardness analyses are performed on the wear blocks, comparing the results with those of the conventional overlay wear blocks of a part. The experimental results show that the microhardness of laser direct-deposited wear block from the top of the wear to the base material displays a continuous non-linear decreasing trend, and the hardness of heat-affected zone without surfacing welding is higher than that of wear-resistant block. The microhardness of laser direct-deposited wear block is as high as 704 HV, which is much higher than the 340 HV of the surfacing wear block. The thermal influence of laser direct-deposited wear block on the base material is small, and the depth of heat-affected zone is about 180 μm, which is much smaller than the heat-affected zone of the surfacing.

In this study, a Fe-Mn-Cr-Ni medium entropy alloy is fabricated using selective laser melting. By varying the laser power and scanning speed, the surface imperfections and quality of the alloy samples with different energy density are evaluated. The result shows that as the bulk energy density increases, the relative density of the samples initially increases and then decreases, whereas the surface roughness initially decreases and then increases. Under a low bulk energy density (≤77.38 J/mm3), the powder on the alloy surface is sintered together owing to insufficient melting, thus resulting in a protruded surface. The main internal defects are spheroidization defects caused by powder non-fusion. Under a high bulk energy density (≥104.76 J/mm3), the droplets generate during the forming process splash and accumulate on the surface of the sample, thus causing a keyhole effect within the alloy and inducing microcracks. The hardness of the formed block first increases and then decreases as the bulk energy density increases. The sample with a bulk energy density of 88.44 J/mm3 exhibits the highest relative density (99.5%) and superior forming quality. Additionally, it exhibits as Vickers hardness of 211 HV, a tensile strength of 549 MPa, and an elongation of 21.8%.

To address the shortcomings of existing frequency-stabilized lasers with low frequency stability and short stabilization periods, a laser frequency stabilization system is designed based on the first-harmonic saturable absorption scheme. The saturation absorption method was used to obtain the saturation absorption spectra of 87Rb D2 line F = 2 and 85Rb F = 3 in the rubidium gas chamber. To obtain an error signal reflecting the changes in laser frequency, modulation and demodulation techniques were applied. Additionally, automatic locking of the laser frequency was achieved by keeping the laser temperature unchanged and controlling current. In addition to the frequency stabilization scheme, the study designed a differential current/voltage conversion circuit, spectral conditioning circuit, and low-noise negative-feedback composite amplifier constant-current source circuit based on the Howland structure. These components facilitate the spectral signal conversion, demodulation, and drive and feedback control of the LD. Furthermore, a peak detection procedure based on minimum convolutional root-mean-square is designed and developed using QT uplink and data acquisition card, incremental PID, and other procedures. The experiment used the saturated absorption spectrum of the 87Rb D2 line F=2 in the cross peak CO32- to stabilize the frequency of a 780 nm semiconductor laser. The results demonstrate successful power-on auto-locking with frequency stability analysis yielding a second-level stability index of 1.64×10-10.

Flow cytometry allows for the simultaneous detection of multiple cellular markers. It serves as a crucial tool for the efficient analysis of cells and a comprehensive understanding of cellular functions and disease mechanisms. The optical fixtures and components of the multichannel flow cytometry laser platform are susceptible to minor displacements due to environmental temperature, which can lead to deviations in spot spacing and changes in laser delay, ultimately affecting the accuracy of detection results. A laser platform with combined heating and heat dissipation for temperature control is designed to mitigate these effects. Finite element simulation is used to analyze the steady-state temperature distribution of the laser platform at different environmental temperatures, and spot spacing at different environmental temperatures is measured using a digital microscope. Finally, the instrument resolution is evaluated using the coefficient of variation of the full peak width. Experimental results show that after adding the temperature control system, the maximum temperature difference between the laser platform and the laser diode decreases by 4.7 ℃, and the maximum relative deviation in spot spacing is also reduced to 0.86%. The coefficient of variation of the full peak width is ≤2.4%, surpassing the YY/T 0588—2017 industry standard for flow cytometry, which requires a variation of the full peak width of ≤3.0%.

To realize wide-range optical beam scanning with low sidelobes, we design a multi-circular optical phased array with a minimum spacing of 18 μm between adjacent array elements and an operating wavelength of 1550 nm by optimizing the position of the array elements and the excitation of the array elements using a modified genetic algorithm and a convex optimization algorithm. The optimization is performed in two steps: first, the genetic algorithm is improved to optimize the distribution of ring spacing at a specific elevation angle, which yields a low peak sidelobe level over a wide beam steering range; subsequently, the excitation-amplitude distribution of the array elements is optimized using the convex optimization algorithm for different steering angles, which further reduces the peak sidelobe level. Using this combined optimization, scanning ranges of -45° to 45° and 0° to 360° are achieved in the elevation and azimuth directions, respectively, and the peak sidelobe level reduced to -20.47 dB, with a maximum far-field divergence angle of 0.146°. To verify the effectiveness of the algorithm, a small-scale multi-circular optical phased array containing 64 array elements is developed, and an experimental system is constructed for experimental verification. The experimental results are consistent with the optimization results of the algorithm.

Aiming at the problem of accurate matching between measuring distance and tracking control parameters in current laser tracking and measurement technology, a laser precision tracking and control system based on range adaptive tracking strategy is developed. According to the motor tracking control parameters calibrated at different distances, the range adaptive parameter model based on least square polynomial fitting is constructed, and the tracking control parameters matching with any distance within the calibration distance range are obtained, and the stable tracking of long-distance targets is realized. Tracking control parameter calibration experiments, circular track tracking performance verification experiments and target track coordinate measurement experiments are carried out for the developed system. The experimental results show that the designed tracking system can stably track and measure the moving target with the range of 50 m, with not less than 500 mm/s tracking speed, and it can be applied to the precision tracking and measurement of long-distance dynamic targets.

During the launch process of space telescope, vibrations can cause irreversible harm to the main mirror. Passive vibration reduction methods are ideal for high-frequency vibrations, but they are less effective for low-frequency vibrations. To effectively suppress transmission of low-frequency vibrations, an active isolation device is introduced. The proposed method employs an active vibration isolation control strategy based on acceleration feedback. This study is carried out in three aspects, which are the design of a permanent magnet spring force actuator, anlysis of main mirror's harmonic response, and experimental verification of active vibration reduction system. Results indicate that, with the introduction of active vibration reduction system, the amplitude of low-frequency vibrations in the experimental system decreases by ~50%.

To solve the problem of digital light processing (DLP) light curing 3D printer image distortion and aberration, a optical micro-projection distortion correction method based on moving least squares method (MLS) is proposed. This method identifies error regions based on pixel-level images captured by a plate camera, and selects control points, and calculates target moving points. By using these two sets of pixel coordinate points to determine the image error, the MLS algorithm, which combines area control and compute unified device architecture (CUDA) acceleration, maps the control point coordinates to the target moving point coordinates, producing an inverse aberration map. This inverse aberration map is then used to correcte the aberration. Experimental results show that this method can correct micro-projection distortion in DLP optical machine. The final correction error reaches 0.5 pixel in accuracy, which improves the projection quality. This advancement significantly benefits the light-curing 3D printing industry.

To solve the problem of insufficient pixel dynamic range, a high dynamic range pixel structure using charge distribution and lateral overflow integrated capacitor (LOFIC) technology is proposed. By splitting LOFIC capacitances and increasing the direct overflow path for a photogenerated charge, the collected overflow charge is distributed between two split capacitors according to the capacitance value during exposure period, and the larger capacitance is dynamically refreshed to realize the compression of high light signal voltage, which enhances the pixel's full-well capacity (FWC) and dynamic range. The adjustment of the number of charge distribution and dynamic refresh and the ratio of capacitance splitting can realize different extensions of dynamic range. In this study, a 6 μm×6 μm pixel is designed based on a 110 nm complementary metal oxide semiconductor process with a high conversion gain (HCG) of 128 μV/e- and an overall LOFIC capacitance of 31.36 fF. Simulation results show that the pixel has a FWC of 1.43 Me- when the capacitance boosting factor is 7, and dynamic range can be up to 116.8 dB. Compared with traditional LOFIC pixel, proposed dynamic range is extended by 16.6 dB. The results indicate that charge distribution LOFIC pixel can achieve higher dynamic range under limited capacitance conditions.

To address problems arising from focusing through scattering media, this paper proposes a genetically assisted harmony search (GAHS) algorithm for wavefront modulation to achieve greater and more stable light-intensity enhancement while maintaining high noise resistance. The main innovation of GAHS algorithm is the combination of the genetic-algorithm cross-directional optimization process with the retrieval method of the harmony search algorithm, which improves the algorithm's optimization ability while ensuring the globality of the algorithm optimization through the traversal process of the harmony algorithm, thereby improving the algorithm's adaptability. Experimental results show that the GAHS algorithm can efficiently complete single- and multi-point wavefront focusing, thus forming a bright and visible light spot at the specified target position; additionally, the focusing gain increases with the number of modulation modules. A simulation model was constructed. In an environment with different noise levels, the GAHS algorithm was compared with the original harmony search algorithm and other classical optimization algorithms. The results show that the GAHS algorithm presents a higher enhancement level than the original algorithm in a noisy environment and has a higher enhancement upper limit compared with other classical algorithms, thus demonstrating its effectiveness as well as potential in imaging and light manipulation through scattering media.

Magnetic field control provides a valuable method for manipulating atomic energy levels and interactions in quantum precision measurements during the interaction between atoms and light. In high-precision quantum sensing experiments, precise measurement cannot be achieved without the cooperation between magnetic field systems and optical detection systems. In order to meet the magnetic field requirements of different optical detection systems, a set of fast switching magnetic field systems and alternating magnetic field systems were developed, and this device was combined with Lee-Whiting coils to achieve kHz alternating magnetic field signals. In the experiment, the frequency adjustment of the alternating magnetic field can be achieved by adjusting the size of the inductance and capacitance components, as well as increasing the adjustable range of the components to expand the frequency spectrum of the alternating magnetic field. The experimental results have demonstrated the feasibility of this method in generating alternating magnetic fields, which can be used for the study of cold atomic absorption spectroscopy under alternating magnetic fields.

This paper investigates the photon antifocusing effect in a four-wave mixing coupled system embedded with a two-level atom. Through analytical analysis of the system, we obtain the optimal conditions for achieving photon blockade. Subsequently, numerical results are obtained by solving the main equation in the steady-state limit. Our findings reveal that the analytical optimal conditions are consistent with the numerical results, demonstrating that this system can realize nontraditional photon blockade. Further, a detailed discussion is presented on the influence of various system parameters on achieving nontraditional photon blockade. The results indicate that the four-wave mixing coupling interaction and atom-cavity coupling coefficient significantly enhance the nontraditional photon blockade effect.

A twin beam is a type of bright entangled optical field that has important applications in the field of quantum information. An optical beam with a spatial structure similar to a Bessel distribution possesses the property of self-healing, and its Bessel distribution can be recovered after encountering an obstacle. In this study, a low-threshold non-degenerate optical parametric oscillator with a threshold of 60 mW was proposed and developed. Based on the proposed non-degenerate optical parametric oscillator that works above the threshold, we generated a twin beam exhibiting a Gaussian distribution, yielding a power of 8 mW and an intensity difference squeezing of 5.1 dB. Subsequently, we prepared a twin beam with zero-order Bessel distribution, featuring 5 dB intensity difference squeezing, using a Bessel converter. Furthermore, we investigated its self-healing property after encountering an obstacle. The results showed that while the Bessel distribution of the twin beam was recovered, the intensity difference squeezing decreased due to obstacle-induced loss. Thus, the results of this study serve as a reference for the application of twin beams with Bessel distribution.

By embedding quantum bits into satellites, low-orbit quantum satellites enable highly secure communications, thus protecting information from eavesdropping and tampering. Currently, quantum-satellite resources are few, and two decision-making attributes of candidate quantum satellites are prioritized, i.e., service time and signal strength, to reasonably allocate the existing quantum-satellite resources such that the normal business requirements of end-users are satisfied. In this study, to minimize the interference of X-ray flares, a star-ground quantum-communication-link fading model under the interference of X-ray flares was constructed, and a quantum-satellite resource scheduling strategy based on a hybrid-immunity and simulated-annealing algorithm was proposed by combining the remaining service time of quantum satellites and their signal strengths based on three decision-making attributes, which were used as the objective function of the system model. The results show that the strategy offers better convergence stability and load balancing than the unimproved-immune and simulated-annealing algorithm, thus providing useful reference for the efficient utilization of quantum-satellite resources and the switching of low-orbit quantum satellites under the interference of X-ray flares.

Lithography is a critical process in advanced integrated circuit manufacturing, transferring circuit patterns from a mask to semiconductor wafers through optical diffraction-interference and photochemical reactions. With the continuous advancement of Moore's Law, the critical dimensions in lithography are gradually shrinking, approaching the resolution limits of lithography equipment. This transition exacerbates the optical proximity effect, leading to deviations between the lithographic images on the wafer and the intended mask patterns. To address this, computational lithography has become essential for correcting these deviations over the past two decades. Recently, inverse lithography technology (ILT) has emerged as a significant advancement. Unlike traditional methods, ILT employs pixel-by-pixel correction and has been integrated into mass production, enhancing process windows, pattern fidelity, and uniformity. This paper introduces the operational principles of ILT, reviews its progress and achievements, explores its applications in various scenarios, and discusses the associated challenges and requirements in process applications. Additionally, it details the mask manufacturing process flow, the challenges in ILT mask production, and the current solutions, concluding with potential future directions for ILT development.

Broadband low-coherence light is expected to overcome the laser-plasma instability in inertial confinement fusion. However, achieving an efficient third-harmonic generation of broadband low-coherence light remains a significant technical problem in engineering applications. Currently, limited research has been done on the third-harmonic generation of broadband low-coherence light. In this study, the characteristics of the broadband low-coherence light are introduced, along with the frequency conversion processes involving second-harmonic and sum frequency generation. Subsequently, the fundamental challenges for an efficient third-harmonic generation with broadband low-coherence light are presented and an overview of the developmental history, principles, and limitations of various broadband third-harmonic generation schemes is provided. In experiments on the frequency conversion of low-coherence light, the acceptance bandwidth and nonlinear coefficients of commonly used nonlinear frequency-conversion crystals are compared for reference. Finally, some suggestions for potential breakthrough directions are proposed for an efficient third-harmonic generation of broadband low-coherence light.

Recently, several researchers have demonstrated the potential of fiber optic Raman technology for biomedical applications. With improving optical component performance and emerging new technologies, the design of fiber optic Raman probes is constantly evolving, leading to diverse applications and functions. Herein, the latest developments in fiber optic Raman probes, focusing on their structural design and material selection, are reviewed. This includes fiber selection and arrangement, probe size, objective selection, and system construction. Moreover, this article highlights the recent practical applications of fiber optic Raman probes in biomedicine and summarizes the approaches and methodologies for designing and constructing clinically specific probes. Moreover, the ideas and directions for future applications and development of fiber optic Raman technology are clarified.

As China continues its ascent toward becoming an aerospace power, the application of semiconductor lasers in the space environment is gradually increasing. However, the space environment imposes unique and extremely harsh operational conditions, with which the semiconductor lasers must cope to maintain their reliability. In this paper, the current research status on semiconductor lasers for space applications is reviewed, focusing on their thermal, vibration, and irradiation reliability. Furthermore, we identify existing problems and propose future research directions of semiconductor laser reliability for space applications to lay ground for subsequent applied research. Addressing the identified problems and implementing the proposed research directions will not only help to better understand the performance of semiconductor lasers in the space environment but also promote the development of China's space industry.

To address issues of low accuracy and low robustness in predicting heterogeneous samples, this study focuses on Polygonatum sibiricum polysaccharide and proposes a model transfer algorithm based on homogeneous samples. By incorporating a hybrid modeling strategy, different physical-state mixed prediction models were established. Stacking ensemble learning was employed to establish base prediction models, and a radial basis function (RBF) neural network was introduced as the transfer function in transfer near-infrared spectroscopy. It was used to fit the nonlinear mapping relationship of spectra from samples with different physical states. By adjusting the size of absorbance matrix window, the network fitting effect was optimized and the near-infrared spectroscopy transfer function was determined. Results indicate that the mixed prediction model corrected using the RBF achieves fitting coefficient (R2) of 0.991, root mean square error (RMSE) of 0.497%, and mean absolute error (MAE) of 0.383% for testing set. Proposed nonlinear transfer algorithm effectively manages sample complexity, reduces the effects of sample surface morphology and moisture on modeling, and enhances the accuracy and generalizability of mixed prediction model for Polygonatum sibiricum polysaccharide content.

X-ray fluorescence spectrometry is employed to conduct three tests on each of 80 blade samples, resulting in a total of 240-set spectral data. After preprocessing, feature elements are selected based on the ratio of the relative standard deviation of elements among samples to the mean relative standard deviation from three tests. These chosen feature elements included Fe, Cr, Mn, Cu, Ni, Ti, Pb, Ca, Mo, Zn, Ga, and Nb. Subsequently, data for 12 feature elements are subjected to Z-score standardization to eliminate dimensional differences among elements. Visual analysis and principal component analysis are then performed. Finally, a Bayesian-optimized random forest algorithm is employed for the classification and identification of these 80 samples, and it achieves an accuracy rate of 95%. Cross-validation results in an average accuracy of 92.5% with a standard deviation of 1.02%. Results of this research demonstrate that the combination of X-ray fluorescence spectrometry and the random forest algorithm can effectively achieve sample identification, provid a method by which to trace the brands and series of blade evidence from crime scenes, and offer valuable leads for investigative purposes.

A novel auxiliary ion source with a dual-chamber structure featuring a heated filament was proposed and designed in this study. This innovation overcomes the limitations of current filament-based ion sources, which cannot accommodate oxidative gases as process gases or support extended filament operation time. The ion source presented herein is suitable for the assisted fabrication of oxide films and fulfills certain functions of an activator. To validate the efficacy of proposed ion source, a series of experiments were designed. Two common oxide films utilized in optoelectronics-tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2) were selected as the deposition materials. By systematically adjustmenting the parameters, including the ion source's current, voltage, bias, and the flow rate of the working gas, as well as employing spectrophotometric techniques to quantify the optical characteristics such as the transmissivity, refractive index, and absorbance of deposited films, the effects of these parameters on the optical properties of the films were investigated. Experiment results conclusively affirm the effectiveness of the ion source design, where its ability to enhance the quality of the resultant films is demonstrated.

We proposed a femtosecond laser reconstruction method based on a multi-output residual neural network. Using this method, we performed quality analysis and pulse inversion on the trace of frequency-resolved optical gating method. Furthermore, we optimized the inversion results using a local weighted regression method. Results show that the trace quality recognition model in the preprocessing stage of proposed algorithm achieves an accuracy of 98.14%. Compared with retrieved amplitude N-grid algorithmic (RANA), the proposed algorithm's reconstruction result has an average relative error of ~4.6%. The average calculation time of the proposed algorithm is ~0.037 s, indicating that the calculation speed is more than an order of magnitude faster than that of the RANA. Additionally, the proposed algorithm has strong noise immunity, demontrating the feasibility of the residual neural network in femtosecond pulse inversion. This method is important for the rapid reconstruction of femtosecond pulse lasers and improving stability at low signal-to-noise ratios.