Electron-phonon coupling effect is an important physical phenomenon for laser wavelength extension in solid-state laser materials. This review summarized the history of tunable solid-state lasers, namely, color-center, transition-metal, and rare-earth lasers, focusing on the spectral homogeneous broadening induced by the electron-phonon coupling effect. Recently, based on the multiphonon-coupling theory, an ultrabroadband laser emission far beyond the fluorescence spectrum was reported,thus greatly extending the available laser wavelengths. Moreover, various self-frequency doubling lasers were developed by combining the multiphonon-coupling and nonlinear-optical-conversion into one single crystal, thereby creating some low-cost and compact visible laser modules, covering the cyan-green-yellow-orange-red spectral range. These newly developed laser sources can meet the urgent demand of laser-based surgery and laser display applications, which can push and promote the rapid development of the all-solid-state laser technology.

Rare-earth-doped upconversion nanoparticles have attracted considerable attention because of their stable, narrowband, and multi-color luminescence, which features less crosstalk, photo-blinking, and photo-bleaching compared with quantum dots and organic dyes. However, rare-earth ions exhibit long luminescence decay times (ranging from microseconds to milliseconds), low quantum efficiency, weak luminescence intensity, and nondirectional far-field emission, restricting their application in time-dependent nanophotonic devices. Optical fields and electron excitations are coupled in plasmonic nanocavities, which is beneficial for significantly shortening the luminescence decay time, improving the quantum efficiency, enhancing the upconversion luminosity efficiency, and effectively controlling the emission direction. The paper reviews recent progress in nanocavity modulation of rare-earth ion luminescence, with a focus on the work of nanocavity modulation of rare-earth ions to achieve sub-50-ns ultrafast upconversion luminescence, and prospects for its applications in single-photon sources, quantum communication devices, and nanolasers.

In order to analyze and measure the radioactive content of samples more accurately and conveniently, a Monte Carlo application software tool (Geant4) is used to obtain the full energy peak efficiency curve of high-purity germanium (HPGe) detectors and thus to simulate and correct it in the measurement of radioactive samples. In particular, the different characteristic energies of a detector are measured in response to a point source 25 cm away from the HPGe probe. The experimental detection efficiency of γ-rays is compared with the simulation detection efficiency, and the influence of the dead layer on the detector efficiency of the HPGe crystal surface is studied by means of Geant4 simulations. The detection efficiency of the model is corrected by modifying the thickness of the upper and lower dead layers in turn, and the parameters of the Monte Carlo geometric model of the detector are optimized. Thereafter, the simulated efficiency of the optimized model is again compared with the measured efficiency of the point source, and the full energy peak efficiency curve of the HPGe detector in the range of 59.54‒1406 keV is obtained. The experimental measurement results show good agreement with the Monte Carlo simulations, exhibiting a relative error within 5%. The experimental results also demonstrate that the thickness of the dead layer on the surface of the HPGe crystal changes with the aging of the detector. After 7 years, the thickness of the dead layer increases from 0.5 mm to approximately 140 mm±0.05 mm.

In this study, we demonstrate the preparation of P-I-N type GaN ultraviolet (UV) detectors on self-supported substrates, and then investigate their forward current transport mechanisms. The results show that the electron diffusion current starts to dominate only when the forward voltage VF>2 V. Moreover, the effective forbidden bandwidth Eg~2.21 eV is much lower than the ideal value, which can be attributed to the energy band perturbation introduced by the conductive dislocations. An ideal factor n>2 when 1.35 V<VF<2 V indicates that the electron defect-assisted tunneling current is the dominant current component. The current has a negative temperature coefficient, which is primarily caused by the increase in the effective forbidden bandwidth of the electron once it is excited to a higher energy conduction band. In the VF<0.8 V and 0.8 V<VF<1.35 V regions, the current-voltage curves are power dependent; this behavior is consistent with the electron space charge confinement mechanism. The power factors are eight and four, respectively, and two different effective energy bandwidths, corresponding to two exponentially decaying defect state distributions, are obtained from the characteristic temperature.

A reflective fiber-optic spectral sensor is developed to realize online nondestructive monitoring of the growth process of Aspergillus versicolor on the surfaces of paper cultural relics. The sensor consists of one tapered input and six receiving fibers. First, the principle of sensor measurement of mold microorganisms on the surfaces of paper cultural relics is established. Then, the morphological characteristics of Aspergillus versicolor on the surfaces of paper samples are derived. Finally, the growth process of Aspergillus versicolor on the surfaces of paper samples is monitored online by the sensor. The results indicate that the sensor can accurately obtain the characteristic absorption peaks (295 nm and 390 nm) of Aspergillus versicolor. When the height of Aspergillus versicolor is in the range of 101.1‒596.0 μm, the output signal of the sensor has a linear relationship with the growth height of Aspergillus versicolor, and the detection limit reaches 10 μm.

In free-space optical communication, vortex-superimposed beams with different radius combinations can transmit more information at the same channel overhead. However, the vortex beam undergoes phase disturbances owing to atmospheric turbulence, affecting the ability to identify its orbital angular momentum (OAM) modes. Existing models cannot precisely identify OAM superimposed beam modes perturbed by random atmospheric turbulence. Therefore, a deep learning recognition method based on attention mechanism is proposed. The attention mechanism module is embedded in VGG-16 to improve the perception performance of the model for superimposed beam modes in different states. In addition, the atmospheric turbulence is simulated using the power spectrum inversion method to simulate the actual state of turbulence, and subharmonics are used to compensate for the low-frequency information of the random turbulence screen. An OAM superimposed beam dataset affected by random turbulence is established, and the proposed model is trained using this dataset. The experimental results show that under the condition of unknown atmospheric turbulence intensity, the accuracy of the proposed method compared to those of traditional methods improves by up to 4.46%. This demonstrates the effectiveness of the model for identifying OAM superimposed beams. In addition, the proposed model exhibits good robustness and generalization ability. This study provides a new method for identifying OAM modes.

Based on the broad application prospect of distributed optical fiber sensing technology in the field of perimeter security, the modulation mechanism and demodulation principle of vibration signals on single-mode optical fiber are deduced and analyzed in detail, and a set of distributed acoustic sensor (DAS) system based on phase sensitive time domain reflectometer is constructed. A complete piezoelectric ceramic vibration signal detection experiment and voice and footstep signal detection experiment are designed. The intensity and phase demodulation of vibration signals are realized by moving difference summation and orthogonal demodulation algorithm. In the voice detection experiment, the sensitivity of optical fiber to sound waves is improved by using an iron semi-closed hollow cylinder. The subjective mean opinion value survey of the original voice and the repeated voice is made to verify the quality of the speech signal. The footstep signals collected by DAS system are analyzed and interpreted in the time domain and frequency domain, and the relevant features of the single-step signal is extracted and explained. The experiments prove that this system can realize complex voice and footstep signal detection in the transmission distance of 2 km, and the spatial resolution can reach 2.2 m, which can be well applied to voice and footstep monitoring in the perimeter security.

Typically, the realization of strain vector sensing based on traditional optical fiber sensing is difficult. To address this, in this study, a multi-core optical fiber strain vector sensing system based on an in-phase and quadrature (IQ) modulated optical frequency domain reflector (OFDR) is designed and verified. The IQ modulation technique is used to perform a linear frequency sweep of the light source, and the strain vector information of a seven-core fiber after bending is obtained from the OFDR system using the spatial structure relation of multi-core fibers. Experimental results demonstrate that the spatial resolution of the bending strain is 28.35 cm in an 87 m seven-core fiber with a sweep frequency of 990 MHz. When the bending curvature of the optical fiber is 1.78 m-1, the angular resolution is 29°. Moreover, the simulation analysis indicates that when the sweep frequency range increases to 10 GHz, a theoretical angular resolution of 1.02° can be achieved, which can further improve the system performance.

Based on the traditional distributed optical fiber sensing technology that uses back Rayleigh scattering, a linear sweep pulse modulation method for micro-seismic detection is proposed. The rectangular pulse in the modulation system is first transformed into a linear sweep pulse, and long-distance and high-spatial-resolution sensing is realized by compressing the pulse and matching filtering. Through simulation and experimental verifications, a narrow line-width laser with a line width of approximately 10 kHz is selected as the light source. Electro-optical and acousto-optical modulations determine the frequency scanning range and time as 5.6‒5.8 GHz and 2 μs, respectively. Linear sweep signal modulation obtains a sensing distance of 10 km, and the intensity range of the received back Rayleigh scattering signal is -60~-50 dBm.

In order to quickly detect hydrogen leaks, there is an urgent need to develop a safer and lower concentration detection lower limit hydrogen sensor. This article assembles a micro cantilever beam probe coated with palladium film with a single-mode fiber end face, and designs an easy to prepare and low-cost fiber optic hydrogen sensor. The experimental results show that the sensor has an ultra-high hydrogen response sensitivity of about -9.887 μm/%, while also having an ultra-low detection lower limit as low as 1.76×10-3% and excellent repeatability. Under the conditions of trace hydrogen volume fraction, the sensor exhibits excellent linear response to hydrogen volume fraction, which is of great significance for trace gas detection and has important application value in hydrogen energy batteries, nuclear power plants, and space exploration.

Angular spectrum method has distortion problem in the long-distance diffraction calculation because of the calculation error caused by the reduction of effective spectrum components and spectrum aliasing. Based on the frequency sampling characteristics of the band-limited angular spectrum method, an improved scaling angular spectrum method is proposed. Then, the method is applied to the diffraction field simulation of large-size square telephoto lenses, circular axicon lenses and diffractive optical elements. The results show that compared with the original band-limited angular spectrum method and the scaling angular spectrum method, the diffraction field obtained by the improved method has higher resolution and no edge distortion. Our research indicates that the improved method has important application potential in the precise calculation of large size, long distance and small diffraction fields.

With the development of advanced light sources, surface smoothness is becoming crucial for large-sized and high-precision mirrors. In this study, a two-dimensional (2D) absolute metrology method is developed that is based on the laser interferometer translational shear method for high aspect ratio rectangular flat mirrors used in X-rays. In this method, translational measurements in orthogonal directions are replaced with multiple shifted measurements in a single direction. In addition, a multi-matrix augmented zonal method reconstruction algorithm is derived to obtain the absolute surface shape of high-precision rectangular flat mirrors. Through simulations, the root mean square (RMS) of the residuals between the reconstructed absolute surface shape and initial surface shape is 0.03 nm (~λ/20000) without considering noise. Surface shape recovery under different numbers of translations and translation distances when considering Gaussian noise is then simulated and analyzed, and an experimental verification is performed for a rectangular plane mirror of 120 mm×40 mm. The measured absolute surface shape recovery is determined as 1.07 nm (λ/591) using the RMS of the absolute surface shape residual obtained by the three-plane method. Both simulations and experiments show that the proposed method can effectively obtain the 2D absolute surface shape of a high-precision rectangular planar mirror. Unidirectional translation thus lays the foundation for establishing multi-aperture stitching measurements based on absolute measurements.

When dual beams are used to measure the roll angle, the angle between the double-collimated beams is easily disturbed by environmental changes, mechanical deformation, and other factors, which seriously affect measurement accuracy. The roll angle measured by the dual beam is sensitive to the spot position. By contrast, the roll angle measured by polarization depends on the polarization state of the incident light and is relatively less affected by laser angle drift. Therefore, to improve the accuracy of the roll error in five-degree-of-freedom measurements at long distances, a polarization-based roll angle optical path is proposed. The path is used to measure the roll angle of the sensor at different positions, calculate the angle between the dual beams, and perform calibrations, thus improving measurement accuracy. The test results show that in the measurement range of 0.75‒2.00 m, the roll angle measurement error after compensation is reduced by 88.97%. This meets the long-distance roll angle measurement requirements for high precision and easy installation.

Atomic emission spectroscopy of turntable electrode (RDE-AES) is widely used in oil detection because of its simple operation, no need for sample preparation, and high reliability. However, the arc is the primary light source used in this technology. The instability of the arc caused by the change in the discharge gap induced by electrode wear and other factors leads to errors between the analysis results of the last collected spectral data and the actual situation. Herein, a method using atomic emission spectrometry with an oil detection device based on the “double turntable” electrode structure is proposed. In other words, the rod electrode in the traditional “rod turntable” electrode structure is replaced by a turntable electrode that can rotate. Its significant advantage is that it reduces the detection error caused by electrode wear. For its structural physical modeling, the process of arc excitation is simulated by COMSOL multi physical field simulation software. Further, the changing rules of electrode gap, oil film thickness, and external excitation on the arc excitation effect are explored using the control variable method. The effects of the influencing factors on the arc excitation time and instantaneous excitation temperature are obtained, and the parameters are optimized according to the simulation results. The simulation results show that the excitation effect of the “double turntable" electrode structure is significantly improved compared with the traditional structure, and the excitation time and temperature are improved to a certain extent. In particular, the arc excitation effect is stable in mass testing, which verifies the progressiveness and practicability of this method. It also provides analytical support for in-depth research on oil detection using the method based on turntable electrode atomic emission spectrometry.

As an indispensable indicator in the development of optical components, laser-induced damage threshold (LIDT) is still the direction of research to improve the accuracy of its measurement results. In this paper, an optimal allocation method of damage test points based on Monte Carlo method is proposed to improve the accuracy of LIDT fitting results. According to the limited irradiation test area and irradiation spot size of the test sample, a nonlinear degenerate defect damage model is simulated, and the sensitivity analysis of the influence of test points change on the fitting LIDT results at different fluence levels is analyzed. Then, according to the setting parameters of damage model, a model is established to generate relevant damage data. The number of test points at each specified fluence level is changed by the control variable method, with the number of test points unchanged at the rest of the fluences.The Monte Carlo method is used to perform multiple simulation calculations on all damage data. The relationship curve between the standard deviation of the fitting results and the test points is drawn, so as to calculate the sensitivity of the corresponding test points to the standard deviation of the damage threshold fitting result. Finally, a more reasonable allocation of test points under each fluence is carried out with this sensitivity as the weight. The results show that the standard deviation of the fitting result of the sensitivity weight method is 0.272 J/cm2, which is about 31% lower than the standard deviation of 0.395 J/cm2 in the standard distribution method.

Railways have become the main transportation artery in our country, and many railway tunnels are distributed because of the diversity of geographical conditions. There are many structural safety monitoring methods for railway tunnels. However, traditional monitoring methods have certain limitations. Based on the current research which focuses on optical sensing, the optical video replacement technology with excellent accuracy and high economic feasibility is organically combined with fiber grating sensing technology, and the optical sensing is applied to the safety monitoring of railway tunnels during operation. Through the analysis of monitoring data in static and traffic conditions, combined with the simulation model, the application of optical sensing in railway tunnel monitoring during operation is preliminarily discussed to provide a reference for related engineering technologies.

Tin droplet generator is a crucial submodules of the light source used in laser-pulsed plasma extreme ultraviolet lithography. Such a light source requires a tin droplet target with high repetition rate, small diameter, and good stability. This study presents our recent progress on the droplet generator, encompassing the droplet diameter, repetition rate, spacing between adjacent droplets, and position stability. The generated tin droplets exhibit a diameter of ~40 μm, spacing of 230 μm between the adjacent droplets, and stable operating time of 5 h at a repetition rate of 100 kHz. Within a 10 s interval, the calculated standard deviation of the droplet positions in the vertical and horizontal directions are approximately 2 μm and 1 μm, respectively. However, the aspects of droplet usability, such as the droplet diameter, operating time, and long-term position stability require further improvement.

In this study, the effects of laser power and cleaning speed on the surface macro- and micromorphology of Q235B carbon steel after the rust layer was cleaned with a continuous laser at 1080 nm, are investigated. Moreover, the effect of different process parameters on roughness is analyzed, and cross-sectional metallographic observations, element content, and compound analysis of the cleaned sample surface are carried out. From hardness test and electrochemical analysis, it is found that the minimum roughness of sample surface is 3.94 μm, and the laser cleaning effect is the best when the cleaning speed is constant at 100 mm·s-1, laser power is 4 kW, Fe content is the highest, and O content is the lowest. When the laser power is constant at 7 kW, and the cleaning speed increases from 100 mm·s-1 to 500 mm·s-1, the surface roughness of the specimen first decreases and then increases. The minimum roughness is 3.68 μm when the cleaning speed is 400 mm·s-1, at which time the laser can completely clean the rust layer in a single scan, and its cleaning efficiency is 20.6 m2·h-1. A remelted layer is generated on the surface of the cleaned substrate, which improves the corrosion resistance of the substrate surface after cleaning the rust layer, and its hardness is approximately 4 times higher than that of the steel when the laser power is 7 kW and the cleaning speed is 100 mm·s-1. A continuous rectangular spot laser cleaning model is created using Ansys software and its results are compared with the experimental results to determine the parameters and estimate their effects for the high power continuous laser cleaning process.

Ti6Al4V powder added TiB2 particles with a mass fraction of 0%~5% was melted using selective laser melting to produce the in-situ TiB/Ti6Al4V composites to study the forming properties, microstructure evolution, and mechanical properties of samples with different TiB2 additions. When the mass fraction of TiB2 added was 1%, the α′-Ti in the microstructure of the sample gradually disappeared, and a dispersedly distributed unit cell like TiB was observed. Further addition of TiB2 caused the strengthening method of the material to evolve from dispersion strengthening to whisker strengthening. Simultaneously, TiB in the grain boundary was enriched to form a dendritic structure and a network structure. The in-situ TiB as a nucleation point can remarkably enhance the hardness and friction performances of the TiB/Ti6Al4V sample under the action of fine grain strengthening, solid solution strengthening, and whisker strengthening. As a result, the microhardness of the sample increased from (336.8±6.64) HV to (498.07±12.56) HV, and the wear mechanism of the sample changed from adhesive wear to abrasive wear. When the mass fraction of TiB2 added was 1%, better wear performance was obtained.

We present a method for all-optical control of silica whispering-gallery-mode microspheres with laser-induced graphene (LIG). Polyimide (PI) films are carbonized to LIG under CO2 laser irradiation. A 980 nm laser is used as a pump light to irradiate the LIG surface, and the transmission and reflection spectra of microcavities are studied. Experimental results show that the tuning scheme maintains a Q factor of approximately 108 throughout the tuning process, with a tuning range and sensitivity of approximately 1.09 nm and approximately 8.8 pm/mW, respectively. This scheme has the advantages of having no mechanical interference, an ultrahigh-Q factor, and a wide tuning range, thus extending all-optical tuning to applications in cavity quantum dynamics, nonlinear optics, and low-threshold lasers.

When using picosecond lasers, black patterns of varying contrasts are obtained on the surface of aluminum alloys by changing the laser marking parameters. In this study, the surface of experimental marking samples is measured using a laser scanning microscope, and the mechanism of picosecond laser blackening is analyzed through the theoretical modeling of electromagnetic waves. Consequently, a dense peak-valley morphology with different maximum height values on the micro-nano scale is formed on the surface of the laser marking samples. The results indicate that a larger maximum height of the micro-nano peak-valley morphology on the sample surface causes a lower surface reflectivity and the formation of black patterns with higher contrasts. Additionally, the contrast obtained using the sample gray value is almost equal to that obtained via theoretical modeling, which proves that the above phenomenon is the main reason for the laser blackening of aluminum alloys.

With the advancements in the field of infrared micro-optical technologies, the preparation of infrared micro-optical devices with high precision has attracted increased attention. There are many shortcomings in the traditional preparation technology. However, the femtosecond laser is suitable for preparing infrared micro-optical components because of its ultra-fast characteristics. Taking lens array, compound eye, grating, optical waveguide and photonic crystal as examples, the development of infrared micro-optical components with the femtosecond laser using different materials and manufacturing methods is introduced. The materials used are the infrared semiconductor, chalcogenide glass, and infrared polymer. The methods used are the femtosecond laser-induced chemical etching, femtosecond laser-assisted wet etching, and femtosecond laser-assisted dry etching. The applications and specific cases are discussed, and the future development trend of this technology is presented.

In order to explore the influence of technological parameters on the cutting section quality in the process of thick plate laser cutting, the 30000 W ultra-high power fiber laser cutting machine independently developed by Penta laser was used to carry out four factors and five levels orthogonal tests on 304 stainless steel with a thickness of 40 mm, and the residual results were analyzed. The influence law of each process parameter on the cutting section index (upper and lower slit width, perpendicularity and the roughness value of the upper, middle and lower plates) was obtained. The results show that the influence of slit width on the upper surface is defocus amount, auxiliary gas pressure, laser power, and cutting speed. The influence of perpendicularity is cutting speed, defocus amount, laser power, and auxiliary gas pressure. The primary and secondary effects of roughness are as follows laser power, defocus amount, auxiliary gas pressure, and cutting speed. The results of the residual analysis show that the optimized process parameters of ultra-high power laser cutting 304 stainless steel with 40 mm thickness are as follows laser power 20000 W, cutting speed 200 mm/min, auxiliary gas pressure 18 bar, and defocus amount +11 mm.

To improve the energy extraction efficiency of the high repetition rate and short pulse CO2 master-oscillator power-amplification system in the light source of laser plasma extreme ultraviolet lithography, it is necessary to study the coupling matching characteristics between the beam intensity cross-section distribution of the seed beam and the gain distribution of the laser amplifier. Based on the Euler-Lagrange formula and Frantz-Nodvik equation, the optimal intensity distribution function of the seed beam under a specific gain distribution is solved by variational method. The effects of the seed beam width, intensity distribution, and gain distribution of the laser amplifier on the power extraction are examined. The results of numerical simulation show that for the laser amplifier with a gain radius of 1 cm, the optimal beam radius of the fundamental mode Gaussian beam with a pulsed seed light power of 500 W is 0.67 cm, and the optimal beam width of the low-power seed light is not equal to the gain width of the amplifier. The optimal beam radius of the higher-order super-Gaussian beam with a pulsed seed power of 2000 W is close to the gain region radius. The optimal beam radius corresponding to the 8-order super-Gaussian beam is 0.9 cm, and the power extraction value is 3409 W. The higher-order gain distribution and the matched super-Gaussian beam can significantly enhance the energy extraction value of the amplifier. The results of this study will provid e theoretical guidance for designing pulsed CO2 main-oscillation power amplifier systems.

In order to address the poor flexibility of traditional rust recognition methods when applied to different images of rust in the process of rust removal by laser, a rust detection method based on a multi-layer perception (MLP) neural network is proposed. A machine vision inspection system for laser cleaning is built, and the MLP neural network is used to identify rust images. The results show that the MLP neural network model has a coverage rate of more than 95% and a false recognition rate of less than 6% for identifying rust from images with different degrees of rust captured under different lighting conditions. The open operation of the image eliminates small misidentified areas, and the minimum external rectangle, which is used as the region of interest for laser cleaning, is generated according to the visual inspection results. The coverage rate of the final region of interest is close to 100%. This method can improve the detection efficiency of rust removal by laser and promote the automation of this process.

The working environment of an infrared optical lens is complicated and often affected by external loads. A finite element analysis model is established in ANSYS for a long-wave infrared optical lens, and half-sine impact simulation analysis with a peak acceleration of 100g and duration of 6 ms is conducted. The rigid-body displacement, peak to valley (PV), and root mean square (RMS) values of the extracted data are calculated, and the Zernike polynomial is used to fit the lens surface shape after impact to estimate the Zernike coefficient. Correspondingly, the impact on the performance of the infrared optical lens is analyzed. Based on the response surface method, the infrared optical lens is optimized, simulations on the impact of the optimized model are conducted, and comparative analysis is performed. The results show that the maximum deformation and the maximum equivalent stress of the lens after impact are reduced due to the optimization of the infrared optical lens; additionally, the PV and RMS values, which represent the changes in the surface shape of the lens, decrease. Thus, optimizing the structure can reduce the impact to a certain extent.

Silicon-based micro-ring resonators (MRRs) are widely used in photonic integration because of their excellent spectral selectivity, compact footprint, and low power consumption. However, MRR wavelength shifts caused by manufacturing errors and the high thermal sensitivity of silicon-based devices can lead to unstable operation. Therefore, a corresponding wavelength-locking scheme must be implemented in practice. In this paper, we propose an MRR wavelength-locking system based on differential evolution and digital perturbation. The output optical power is taken as the monitoring variable, and the optimal heating power is searched for the target signal wavelength based on a differential evolution algorithm in the global search stage. Moreover, the error signal is demodulated based on a digital perturbation algorithm in the local locking stage to increase or decrease the heating power to eliminate the interference of ambient temperature fluctuations. After theoretical derivation and experimental verification, it is found that the proposed differential evolution algorithm is approximately four times faster than the traditional step-by-step scanning method for searching for the optimal heating power. We verify the stable locking of the resonant wavelength of the MRR under a 5 ℃ ambient temperature change within 400 s.

In this work, we fabricate silver nanoparticle arrays with a small size, high density, and controllable surface densities in a specific range using a rapid thermal annealing method. Based on the far-field optical reflection and transmission spectra of the silver nanoparticle arrays that are experimentally measured and according to a theoretical numerical conversion, the absorption, scattering, and extinction properties of the silver nanoparticle arrays are investigated. The results show that the resonance wavelength derived from the localized surface plasmon tends to redshift with an increase in surface density of the silver nanoparticle arrays (i.e., decreased nanoparticle spacing). In addition, the redshift is more pronounced for stronger coupling interactions between neighboring nanoparticles. This method provides a helpful reference for analyzing localized surface plasmon properties, primarily for small high-density metal nanoparticle arrays with non-negligible inter-particle coupling interactions.

Quantum satellite communication is an important part of global quantum secure communication network. In order to study the effect of snowfall on quantum satellite communication performance, first, based on the Gamma spectrum distribution function of snow particles and Mie scattering theory, the energy attenuation model of light quantum in snowfall environment is established. Then the relationship between the parameters such as snowfall intensity and the fidelity of the satellite-ground link, the channel establishment rate and the channel entanglement is studied, and the numerical simulation is carried out. Finally, in order to accurately simulate the impact of snow interference on the communication performance of satellite-ground links, a weighted noise channel model is introduced, and the impact of snow on the weighted noise channel capacity is analyzed. The results show that the snowfall intensity has a significant effect on the quantum energy and fidelity of light. When the transmission distance is 4.1 km and the snowfall intensity increases from 2.82 mm/d to 8.71 mm/d, the entanglement decreases from 0.738 to 0.206. When the snowfall intensity increases from 3.75 mm/d to 8.25 mm/d, the channel establishment rate decreases from 16.84 pair/s to 7.76 pair/s. When the transmission distance is 2.5 km and the snowfall intensity increases from 4.0 mm/d to 8.5 mm/d, the weighted noise channel capacity decreases from 0.6207 to 0.3547. Therefore, the impact of snowfall on quantum satellite communication system cannot be ignored, and corresponding adjustment strategies should be taken to ensure the reliability and effectiveness of communication according to the snowfall level.

On the basis of different light guiding principles, hollow-core microstructure fibers can be divided into hollow-core photonic band gap fibers and hollow-core anti-resonant fibers. For these two types of fibers, scattering loss caused by the roughness of the inner wall of the air hole is one of the sources of loss. Scattering loss is the main source of loss in hollow-core photonic bandgap fibers. In hollow-core anti-resonant fibers, scattering loss is also one of the important reasons for loss during operation in the short-wavelength region. To reduce the scattering loss of hollow-core microstructure optical fibers, in-depth research on the roughness of the inner wall of the air hole is necessary. Therefore, in this paper, research progress on the relevant theory, measurement technologies, and suppression methods for the roughness of the inner wall of the air hole in hollow-core microstructure optical fibers are described. Further, relevant theory and experimental results are summarized, and important future research directions are suggested.

Based on earlier reports in the lithography technology field and global list of "highly-cited scientists", the research time and distribution characteristics of countries, research institutions, research funding institutions, and high-level basic research talents in the lithography technology are analyzed. Based on these two aspects, a bibliometric analysis of published works in the lithography technology field was performed to investigate the research direction, themes, and development trends in this field. The results show that the output of lithography technology papers is currently declining, and the United States has a leading edge in this research field. Research on optical lithography and masking, photoresist and electron beam lithography, extreme ultraviolet (EUV) lithography, and other technical topics is still dominated by foreign institutions. China has launched research on emerging themes, including high-numerical-aperture EUV lithography, guided self-assembly lithography, graphene-based materials, and machine learning applications. This study proposes suggestions for improving the overall layout, involved research institutions, enterprise strength, and talent mechanism of lithography technology research and development to provide a scientific basis for decision-making and research directions in related fields.

In recent years, Thulium-doped fiber laser has attracted more and more attention because of its compact structure, near diffraction limit beam quality, and high quantum efficiency. Among these laser sources, high power continuous wave (CW) thulium-doped fiber lasers have been widely used in many fields, such as medical treatment, military security, space communication, air pollution detection, material processing, and so on. In the past 20 years, high power CW thulium-doped fiber lasers have developed rapidly, and the highest output power has reached kilowatt level. In this paper, the high power CW thulium-doped fiber lasers reported in the past are reviewed from the aspects of oscillator and amplification system, and some views on the future development trend are given.

In order to meet the wide demands of single longitudinal mode continuous wave laser in various fields such as optical communication, optical sensing, precision measurement, quantum technology, and atomic physics etc., the stability and signal-to-noise ratio of the single longitudinal mode laser has to be improved. This paper discusses the intensity noise which plays a major role in output stability of a single longitudinal mode laser, and shows its main source and generation mechanism. On this basis, combined with comparative analysis of various methods, this paper gives the recent developments of suppression means of intensity noise. Aimed at improving output stability of single longitudinal mode fiber laser in high power laser facility, relevant study using semiconductor optical amplifier is given, which suppressed the intensity noise.

Space division multiplexing (SDM) is a critical technology that can increase the capacity of existing single-mode fiber optic communication systems by tens of times. It is worth studying as an effective means to overcome the capacity bottleneck of traditional single-mode fiber optic communication systems. This overview introduces the key technologies and research progress of the multiplexer/demultiplexer, fiber amplifier, few-mode fiber, and optical transmission system integrated device in strong coupling communication systems with few-mode fibers. This overview also introduces some of the more classic or latest experiments in strong coupling communication systems with few-mode fibers, and discusses the future research directions of few-mode optical transmission system.

Terahertz time-domain spectroscopy (THz-TDS) is used to quantify and analyze the spectral characteristics of four gastrointestinal drugs: Enteritis capsules, Bismuth Citrate Potassium capsules, Rabeprazole Sodium enteric tablets, and Bifidobacterium Triptans capsules in the 0.25?2.40 THz band. Terahertz waves are sensitive to weak structural changes and can accurately identify drugs containing the same excipients. The experimental results show that the spectra of the four drugs are distinctly different; thus, THz-TDS technology cannot be used to identify drug components and classify drug effects. Additionally, there are evident differences in the spectral characteristics compared with those of the failed drugs manifested by the shift, addition, and disappearance of absorption peaks. The experimental study provides reference data for drug identification and efficacy identification by THz-TDS.