To evaluate the effects of aerosol radiation forcing and laser atmospheric transport, it is necessary to know the parameters of aerosol light absorption characteristics and its vertical distribution. Thus, this paper presents a method based on a combination of field measurements and models to estimate the aerosol absorption coefficient distribution at vertical height. With the proposed method, the aerosol optical depth (AOD) and extinction profile at the entire layer are obtained via inversion with data observed using a sun-photometer and a LiDAR. Then, the aerosol absorption profile is obtained via selecting the corresponding aerosol modes as constraints from the moderate spectral resolution atmospheric transmittance algorithm and computer model (MODTRAN) and santa barbara DISORT atmospheric radiative transfer (SBDART) model. An inversion test is performed using data measured in a field experiment, and the results demonstrate that the proposed method is feasible and can be employed to obtain the vertical distribution of the aerosol absorption coefficient.

Based on an in-depth investigation on the randomness of the time series of the atmospheric extinction coefficient, this paper uses the monitoring data of atmospheric visibility, relative humidity (RH), the mass concentrations of particulate matter (PM10 and PM2.5), and NO2 content during autumn and winter in Chengdu from 2015 to 2017. In addition, the time series of the aerosol extinction coefficient in the corresponding period in Chengdu is obtained. The detection of nonstationarity in the aerosol extinction coefficient time series is conducted using generalized additive models for location, scale, and shape, followed by the covariate analysis of the aerosol extinction coefficient time series. The experimental results show that the aerosol extinction coefficient time series in Chengdu during autumn and winter are nonstationary, with nonlinear changes in their mean and variance. The mass concentration of fine particulate matter (PM2.5), RH, and aerosol component structure (PM2.5/PM10) are significant covariates of nonstationarity in the aerosol extinction coefficient series. Among them, PM2.5 contributes the most to the nonstationarity of the aerosol extinction coefficient series, followed by RH, and PM2.5/PM10 contributes the least. The explosive growth of aerosol extinction coefficient is closely related to the synergies of PM2.5, RH, and PM2.5/PM10.

Cirrus optical thickness is one of the cloud optical parameters that have great influence on global climate and earth radiation budget. In military, atmospheric science and other fields, there is a wide demand for cirrus optical parameter solving algorithm. Moderate-resolution imaging spectroradiometer (MODIS) data is used to solve cirrus parameters, and satellite multi-channel data is mostly used, so the data processing process is relatively complex. The RT3 model combined with MODIS cloud parameters was proposed to simulate and calculate cirrus reflectance, and a cirrus optical thickness lookup table was established. A simple algorithm was designed to achieve effective inversion of cirrus optical thickness. The correlation coefficient between the inversion results of cirrus optical thickness and the actual data measured by MODIS is 0.97, which verifies the reliability of cirrus optical thickness inversion. By selecting MODIS data at different time periods, the variation of cirrus optical thickness in different time and space ranges is analyzed, and the average error is less than 0.16, which further verifies the effectiveness of the RT3 model-based lookup table for inversion of cirrus optical thickness. The results are helpful to realize simple and effective inversion of cirrus optical properties worldwide.

In this study, using the extended Huygens-Fresnel principle and the improved Rytov method, a turbulence channel model based on the Gamma-Gamma intensity probability distribution is used to obtain the analytical expression of outage probability. On this basis, the outage probability characteristics of the heterodyne differential phase-shift keying (DPSK) modulation of Gaussian beam waves are studied in anisotropic turbulence. A performance study under different anisotropic ocean turbulence conditions is conducted. The effects of various turbulence parameters, i.e., the contributions of temperature and salinity to the power spectrum, the dissipation rate of kinetic energy per unit mass fluid, and the dissipation rate of mean-squared temperature, are investigated, and the transmission distance and data transmission rate on outage probability are analyzed. The analysis provides a theoretical basis for reducing the outage probability of Gaussian beam DPSK modulation and improving communication quality and reliability.

Humidity correction on atmospheric extinction coefficient is an important component of aerosol hygroscopicity research, which is also a key technical link for determining the mass concentration of near-ground particulate matter retrieved by satellite aerosol optical depth(AOD). Based on hourly PM2.5 mass concentration, atmospheric visibility, and relative humidity (RH) data collected in Chengdu from January to December 2016, the statistical relationship between the atmospheric extinction coefficient and particulate matter mass concentration, as well as its response characteristics with RH variation, are discussed in detail. The atmospheric extinction coefficient per unit mass follows a log-normal distribution when RH is less than 90%, and the shape and scale parameters of the distribution function exhibit a fluctuating growth as RH increases. Second, based on the log-normal distribution parameter of atmospheric extinction coefficient per unit mass under dry environmental conditions (RH ≤ 40%), the effect of humidity change on the probability distribution parameter of atmospheric extinction coefficient per unit mass is eliminated via mathematical transformation. Consequently, the principle and flow chart of humidity correction are proposed for the atmospheric extinction coefficient. Finally, the applicability based on the principle demonstrates that the correlation coefficient of PM2.5 mass concentration calculated by corrected atmospheric extinction coefficient and actual PM2.5 mass concentration is up to 0.90, significantly improving the corresponding humidity correction result using aerosol scattering hygroscopic growth factor method.

In a point diffraction interferometer (PDI), the shapes and positions of pinhole diffraction spots are determined by pinhole alignment conditions, and then the arrangement of subsequent optical path is affected. Based on Rayleigh-Sommerfeld diffraction theory, the pinhole diffraction intensity distribution for misaligned Gaussian beam incidence is studied. The mathematical expressions of different alignment errors including lateral shift, defocus, and tilt are given. The intensity distributions of pinholes with different diameters for different alignment errors are analyzed. The research results show that lateral shift alignment error does not affect the center position of diffraction spot, but it will change the shape of diffraction spot. With the increase of lateral shift alignment error, the first diffraction dark ring is with a crescent shape and gradually disappears in the direction of shift. Defocus alignment error has no obvious effect on position and shape of diffraction spots, but the intensity of diffraction light will decrease with the increase of defocusing amount. Tilt alignment error will cause the offset of the center position of diffraction spot, but it will not affect the shape of the diffraction spot. The offset direction is consistent with oblique incidence direction, and there is a linear relationship between the offset and tilt angle.

Expanding the measurement range of the optical fiber can substantially improve the applicability of pressure sensing system based on polarization properties . Accordingly, a sensing method based on the fusion of multiple Stokes parameters is proposed to expand the measurement range while ensuring high sensitivity. The polarization rotation axis of the sensor is obtained using theoretical simulations. Then, polarization controllers, a pressure device, and a polarimeter are used to achieve a sensing performance with a linearity of 99.8%, sensitivity of 0.1938 N-1, and measurement range of 28 N. The measurement range of the proposed multiparameter fusion method is five times larger than that of the methods based on single-parameter measurement, confirming the theoretical design. The proposed method can highly improve the performance and applicability of sensing systems based on polarization properties .

To study the probability distribution characteristics of a single-mode fiber coupling's receiving efficiency fluctuations during atmospheric laser communication, a calculation model of transient coupling efficiency disturbed by atmospheric turbulence was established, and the least dimensionless parameters affecting the statistical distribution of the fiber coupling efficiency were obtained. The results show that as the ratio of aperture radius to atmospheric coherence length increases, coupling efficiency decreases, whereas when coupling geometry parameters increase, coupling efficiency increases initially before decreasing, indicating a single maximum point.The transient coupling efficiency of space light to single-mode fiber was simulated using the Monte Carlo method and analyzed using the distribution characteristics. The dual Johnson SB distribution method was proposed to fit the probability density function of the transient coupling efficiency, and it was verified by the experimental data.The present results can provide references for optimized space-light parameter design in a single-mode fiber coupling system under different atmospheric turbulence intensities, supporting the realization of atmospheric laser communication systems with fiber coupling.

In this paper, a highly sensitive optical fiber temperature-sensing probe is prepared by integrating the conical polymer waveguide with an optical fiber using simple dipping and ultraviolet curing techniques. The experimental results show that the temperature sensitivity of the structure at low temperatures is 123.6 pm/°C, and the sensitivity observes a nonlinear increasing trend with an increase in temperature. Among them, the polymer waveguide has a compact structure, with an axial dimension of 300 μm and a minimum radial dimension of 2 μm. This prepared probe based on the waveguide has good temperature response characteristics and biocompatibility. It can also realize point detection and has significant application prospects in the field of biomedicine.

Aiming at the problem that the performance of free space optical communication links is easily affected by atmospheric turbulence, a multiple-input multiple-output (MIMO) polarization-coding method suitable for free space optical communication is constructed in this paper. The rapid construction of the polarization code adopts the universal partial sequence method, polarization-coding, modulation, and MIMO technologies are jointly optimized; the simulation analysis is performed under the atmospheric turbulence channel. The experimental results show that MIMO polarization-coding methods can improve system performance while maintaining low complexity under different construction methods and coding schemes. Under strong turbulence conditions and a bit error rate of 10-4, compared to the Monte Carlo method, the coding gain of the partial sequence method is about 0.2 dB. The computational complexity of offline construction is negligible. However, under strong and weak turbulence conditions, compared with the single-input single-output (SISO)-polar method, the coding gain of the MIMO (2×2)-polar method is about 1.1?1.6 dB, which has obvious diversity advantages.

In this study, the influential factors that impact the strain transfer rate of the optical fiber sensor are analyzed. The fiber sensors' ability to monitor strain distribution in structural materials depends on the bonding characteristic between the material and fiber. The strain transfer tip effect of the distributed fiber sensor is studied; the two parameters, paste length and colloidal shear modulus, are examined to assess the impact on the strain transfer rate. The results show that the strain transfer length can be increased by prolonging the length of the pasted fiber or increasing the shear modulus of the colloid. Adhesive with high shear modulus should be selected in the engineering application, and the paste length (greater than 5 cm) should be pasted at both ends of the paste measuring section to ensure that the strain results are accurate in the measuring section.

This article proposes and demonstrates a fiber optic sensor based on two cascaded Fabry-Perot interferometers (CFPIs) for simultaneous measurement of temperature and pressure. The sensor is made by fusion splicing of the single-mode fiber (SMF), hollow-core fiber (HCF), and double-hole fiber (DHF) in sequence. An air cavity FPI is formed in HCF and a silica cavity FPI is formed in DHF. The two FPIs are cascaded to form the mixed cavity FPI. The air cavity FPI is connected with the external environment via holes in the DHF, realizing sensing of air pressure with high sensitivity. At the same time, due to the thermo-optical effect and thermal expansion effect of the silica in the DHF, high sensitivity sensing is realized for temperature. In this article, in the air pressure measurement range of 0.1?0.6 MPa and the temperature measurement range of 60?260 °C, the sensitivity of the air cavity FPI to air pressure and temperature is 4 nm/MPa and 1 pm/°C, respectively, and the sensitivity of the mixed cavity FPI to air pressure and temperature is 0.5 nm/MPa and 9 pm/°C, respectively. The air cavity FPI and the mixing cavity FPI have different sensitivities to temperature and air pressure, and realize the dual parameter measurement of temperature and air pressure. At the same time, the sensing structure has simple manufacturing process, high integration, and high sensitivity.

Aiming at the problem of eccentricity error in shift-rotationn absolute measurement method in the detection process, a three-dimensional surface-based image registration eccentricity error correction method is proposed. First, the shift-rotation absolute measurement method is used to obtain the surface shape of the mirror under rotation 0° and rotation 180°. Then, the similarity function is constructed by using the 3D surface shape data to realize the registration of the tested mirror shape at 0° and 180°, so as to obtain the eccentricity error. The numerical simulation results show that the peak and valley value of the residual profile is 7.783 nm and the square mean root value is 0.578 nm before the correction of the eccentricity error. After correcting the eccentricity error, the peak and valley value of the residual profile is 0.034 nm, and the square mean root value is 0.004 nm. The results show that the correction method is feasible and can effectively improve the measurement accuracy of the shift-rotation method, which provides an important reference for the absolute measurement of high-precision optical element surface.

By studying the exit angle of light after passing through the prismatic absorbing medium, the relationship between among the exit angle, the incident angle, the real and imaginary parts of the complex refractive index in the glancing process can be obtained. Numerical simulation calculations show that when the apex angle and refractive index of the prism are constant and the imaginary part is larger, the greater the difference between the exit angle of the absorbing prism and the transparent prism, the greater the influence on the refractive index calculated by the inversion. When the apex angle is π/3 and the absorption imaginary part is 0.20, 0.10, and 0.01, the maximum relative errors of the calculated refractive index are about 5.0%, 2.5%, and 0.2%, respectively. When the imaginary part is constant, the smaller the output in the case of a large angle, the error caused by a prism with a large apex angle is small, and in the case of a large exit angle, the error caused by a prism with a small apex angle is small.

As the main detection tool in multi-field, large-aperture optoelectronic devices are characterized by strong detection capability and high resolution. However, limited by the optical principle, such devices show a strong dependence on precise focusing. Temperature focusing is a key operation for maintaining image quality. First, this study analyzes the theoretical relation between the temperature and the equivalent focal length of the system. Then, the shortcomings of the traditional compensation model are obtained via simulations. To accurately model the relation between the temperature and the focal length, the first-order Fourier function model is introduced for compensating the change in the focal length owing to the temperature. Finally, the linear compensation model and the first-order Fourier function model are compared based on application data. Results show that the fitting accuracy of temperature and focal length for first-order Fourier function model is higher than that for the linear compensation model. The first-order Fourier function model is simple and easy to implement. Moreover, it can be used for test and design of large-aperture optoelectronic devices and for temperature focusing.

Laguerre-Gaussian (LG0l) vortex beam carries optical angular momentum and provides additional multiplexing degrees of freedom, which significantly improve the optical communication capacity. The accurate measurement of the spot size of the LG0l vortex beam is of great significance owing to its application. The knife-edge method is an ideal method for measuring the spot size and waist radius of the beam for its advantages of low cost, convenience, high precision, and suitability for high-power measurement. However, previous studies on this method focused on the fundamental transverse mode Gaussian beam. Moreover, to the best of our knowledge, there is no research on the measurement of the LG0l vortex spot using the knife-edge method. In this study, the measurement of the spot size of the LG0l vortex beam based on the knife-edge method is investigated theoretically and experimentally. In the theoretical analysis, the principle for measuring the LG0l vortex beam is presented. In the experiment, the LG0l vortex beam is generated by modulating the fundamental Gaussian beam using spiral phase plate (SPP). The vortex beam spot is measured using the knife-edge method. The spot radii of LG0l vortex beams (l = 0, 1, and 2) are obtained after fitting the intensity distribution of the transverse field using the Mathematica program. According to the characteristics of the spot radii, we conclude that the spot radius remains unchanged during the transformation from the fundamental Gaussian beam to the LG0l vortex beamusing the SPP of lower order.

The welding surface defect is an important index for evaluating welding quality. This paper designs a welding surface defect detection system based on the principle of optical coherent ranging to solve the problem of low measurement accuracy of the existing detection methods. First, based on the principle of the Michelson interferometer, a broadband laser is used to scan a point on the welding surface to collect the interference light intensity of the reference and measurement arms. Second, the interference spectrum corresponding to the scanned point is determined using the collected light intensity. Finally, the optical path difference corresponding to the spectrum is calculated to determine the axial height of the scanned point relative to the reference mirror. The experimental results show that the axial measurement accuracy and the lateral resolution of the system can reach 10 μm and 13 μm, respectively. Moreover, it can accurately identify surface pores, lack of welds, welding seam misalignment, and other welding defects and accurately measure the geometry and determine the shape of the weld.

In order to further improve the sensitivity of the sensing system, a bi-parallel asymmetric Mach-Zehnder interferometer optical waveguide structure is designed on a lithium niobate wafer, and segmented electrodes are designed around the optical waveguide to achieve electro-optical modulation in the opposite direction. For this purpose, an integrated optical waveguide electric field sensor with a size of 78 mm×14 mm×7.5 mm is developed. The LTspice simulation software is used to design a cross-impedance balance photoelectric detection circuit, and the difference method is used to suppress common mode noise, so as to improve the sensitivity of the electric field sensor. The experimental results show that the time-domain measurable electric field intensity range of the sensing system is 33?3000 V/m, and the linear dynamic range is 35 dB, which is suitable for the time-domain measurement of weak electric fields.

In this study, an erbium-doped fiber femtosecond laser source based on divided-pulse amplification is introduced. Using a master-oscillator power-amplifier configuration, the seed pulse is first enhanced by a fiber preamplifier. Then, the preamplified pulse is divided into 64 replicas in sequence pulse dividers using polarization multiplexing. Finally, the seed pulse is simultaneously amplified and compressed in the main amplifier. A unique characteristic of divided-pulse amplification at 1.55 μm is that it can effectively reduce the nonlinearity-induced spectral distortion in the femtosecond pulse-amplification process for achieving pedestal-free pulse and finely control the nonlinear effect and managing the pump light intensity and fiber length in the spectrum-broadening process. In the pulse-amplification process, the pulse width could be compressed by the negative dispersion of fiber, thus, avoiding the use of grating or prism pairs. In the experiment, the low-nonlinearity and high-nonlinearity regions are investigated for the main amplifier. In the low-nonlinearity region, the amplified pulse achieves an average power of as high as 3 W with 830 fs pulse duration and 36.1 kW peak power. However, in the high-nonlinearity region, the amplified pulse achieves a pulse duration of as short as 137 fs with 1.54 W average power and 112 kW peak power. Furthermore, the contrast of 1560 nm femtosecond pulse is verified through optical frequency doubling in a periodically poled lithium niobate crystal. The optimized frequency doubling efficiency reaches up to 40.3%.

This study describes an extra-cavity frequency-doubled kilohertz multiwavelength laser for an atmospheric detection lidar that uses an LD pulse end-pumped Nd∶YAG laser crystal. It adopts an electro-optic Q-switching technique and a compact metastable cavity design to achieve a high dynamic-to-static ratio of 1064-nm fundamental frequency optical pulse output. Type Ⅰ phase-matched LBO crystal frequency doubling and type Ⅱ phase-matched LBO crystal sum-frequency outside the cavity were used to produce 355-nm sum-frequency light. Additionally, the influence factor of 355-nm sum-frequency light pulse energy was theoretically and experimentally investigated. A three-wavelength laser beam splitting output with a repetition frequency of 1 kHz was obtained for a frequency doubling conversion efficiency of 53%. The corresponding single-pulse energy was 1.18 mJ at 1064 nm, 1.06 mJ at 532 nm, and 0.73 mJ at 355 nm, and the pulse width was 3.49 ns at 1064 nm, 3.42 ns at 532 nm, and 3.02 ns at 355 nm; and the beam quality factors were Mx2 = 1.70, My2 = 1.75 at 1064 nm, Mx2 = 1.57, My2 = 1.41 at 532 nm, and Mx2 = 1.51, My2 = 1.38 at 355 nm.

A highly stable all-solid state ultraviolet laser with a center wavelength of 355 nm pumped by a laser diode (LD) with a center wavelength of 915 nm is demonstrated. LD with a central wavelength of 915 nm and linewidth of 5.3 nm is used as a pump source to end-pump Nd∶YVO4 crystal, and two LBO crystals are used as frequency doubling crystal and frequency tripling crystal in the laser. A stable all-solid state ultraviolet laser with a center wavelength of 355 nm is obtained by using V-shaped plane-convex unstable resonator structure and acousto-optic Q-switching mode. When the repetition rate is 30 kHz and the pump power is 45 W, the output power of the ultraviolet laser is 3.7 W, the pulse width is about 13 ns, optical-to-optical efficiency is 8.2%, the beam quality factor M2 is less than 1.2, and the output power stability (peak-to-peak value) is less than 4.5% in 6 hours of running time.

FeCrNiSi alloy cladding layer was prepared on GCr15 steel substrate using laser cladding technology. The effects of laser processing parameters on the microstructure, hardness and friction, and wear properties of the cladding layer were studied using the depth of field microscope, microhardness tester, and friction and wear tester. The primary dendrite size of the cladding layer was found to increase with an increase in laser power and scanning speed. However, the primary dendrite spacing first increases and then decreases with an increase in laser power, and the secondary dendrite spacing decreases gradually. The primary dendrite spacing first increases and then decreases with an increase in the scanning speed, whereas the secondary dendrite spacing first decreases and then increases. The surface hardness of the cladding layer increases with a decrease in laser power or an increase in the scanning speed. When the laser power and the scanning speed are 2400 W and 7 mm/s, respectively, the maximum hardness of the cladding layer is 781.5 HV, and the hardness value is 3.4 times that of the substrate. The wear mechanism of the cladding layer prepared using this process parameter evolves from abrasive and adhesive wear to fatigue-dominated wear mechanism.

The experimental study on the random characteristic of chaotic laser in the amplification process is carried out. A ring cavity structure is usually applied to generate chaotic laser based on the nonlinear Kerr effect in fiber. The outputs of chaotic laser with different powers are realized by controlling pump current, and they are amplified by ytterbium-doped fiber amplifier. Then, the random characteristic of chaotic laser in the amplification process is analyzed quantitatively by permutation entropy, skewness and kurtosis. The results show that the permutation entropy decreases with the increase of the pump current of the fiber amplifier and tends to a stable value. The skewness and kurtosis first increase and then decrease with the increase of the pump current of the fiber amplifier when the permutation entropy is similar, indicating that the random characteristic of the chaotic laser first decreases and then increases during the amplification process.

To explore the influence of the laser melting process on the comprehensive properties of stainless steel (SS) surface, we selected the LDF 4000-40 laser to treat the 0Cr17Ni12Mo2 SS surface and then used the optical and electron microscopes, an energy spectrum scanner, the microhardness and electrochemical analysis testers, and an abrasion testing machine to characterize the microstructure and performance. The results show that owing to the differences in heat transfer and cooling conditions in different regions, the macroscopic morphology of laser-melted SS is wavy at the interface with the matrix, the strengthened zone's surface layer comprises equiaxed crystals, the middle zone comprises equiaxed and columnar crystals, and the edge areas comprise flat crystals. Carbon, iron, and chromium elements are diffused in the strengthened zone. Because laser melting refines the microstructure, the highest microhardness of the strengthened layer is about 1.5 times higher than the highest hardness of the substrate. The strengthened layer has a stronger corrosion resistance than the substrate. However, once the strengthened layer is corroded, its corrosion rate is higher than that of the matrix. Owing to grain refinement and increased microhardness, the friction coefficient of the strengthened layer (0.29) is lower than that of the matrix (0.35), and the wear mechanism of the strengthened layer is abrasive wear.

Fe-Cr-Mo-Si alloy powder was added to the surface of Q235 steel to prepare a wear-resistant iron-based cladding layer by using 3 kW fiber-coaxial laser cladding equipment. The Fe-Cr-Mo-Si cladding layer's microstructure, hardness, and friction-wear behavior were studied using a metallographic microscope, Vickers hardness tester, and friction and wear testing machine. The results show that the microstructure of the Fe-Cr-Mo-Si cladding layer is uniform and dense without pores, cracks, and other defects. The cladding layer is composed of dendritic crystals. A fine planar crystal structure is formed at the bonding surface of the cladding layer and Q235 steel, and the cladding layer and the substrate exhibit good metallurgical bonding. The average hardness of the cladding layer reaches 642.2 HV, which is four times the substrate's hardness. When the load is 50 N, the average friction coefficients of the cladding layer and the substrate are 0.621 and 0.512, respectively, and the wear mass loss of the cladding layer is 14.6% of the substrate. The friction coefficient decreases as load increases, whereas the size of the wear outline increases as load increases. The results show that the wear mechanism of the cladding layer is abrasive wear and adhesive wear, while that of the substrate is mainly adhesive wear and fatigue spalling wear. The laser cladding of Fe-Cr-Mo-Si alloy powder on Q235 steel can improve wear resistance significantly.

Selective laser melting (SLM) is a new way to manufacture complex NiTi shape memory alloy parts and has become one of the research hotspots in the field of smart materials. In this paper, an optical microscope, a scanning electron microscope, an X-ray diffractometer, a differential scanning calorimeter, and a universal material testing machine were used to investigate the effect of hatch spacing (h) on the relative density, microstructure, phase-transformation behavior, and mechanical properties of a NiTi alloy fabricated using the SLM process. The results demonstrate that when the line energy density was within the range of 100?250 J/m, a continuous and stable single track could be obtained. As the hatch spacing decreased from 115 to 64 μm, the content of NiTi (B2) phase and the surface roughness decreased while the relative density and the transformation temperature gradually increased. The NiTi sample fabricated with h=77 μm exhibited the best overall performance. The relative density, compressive strength, and tensile strength were 98.5%, 3351 MPa, and 839 MPa, respectively. After the first compression cycle, the recoverable strain was 5.99% and the strain recovery rate was 97%. After the 10th and 20th compression cycles, the recoverable strain remained 5.77% and 5.75%, respectively.

Herein, a 2024 aluminum alloy coated with a 150 μm epoxy primer was cleaned using a nanosecond pulsed laser with different pulse frequencies. Moreover, the surface morphology, surface roughness, cleaning thickness, and cleaning mechanism were analyzed. Experimental results show that the surface roughness (Ra) was slightly affected by the pulse frequency and was about 3 μm. Furthermore, the cleaning depth was calculated under different pulse frequencies; the results show that the cleaning depth reached about 130 μm at a pulse frequency of 10 kHz. The effect of the laser frequency on the ablative amount and thermal stress was studied during laser cleaning via numerical simulations. Numerical simulation results show that the ablative amount decreased with the increase in the frequency and the maximum decrease in ablative amount was >9% when the pulse frequency was 5?25 kHz. The trigger threshold of the peeling mechanism was approximately 1.64 J/cm2 based on the linear fitting calculation of the maximum thermal stress and pulse energy density. When the pulse energy density was greater than 1.64 J/cm2, it was difficult to accumulate heat as the frequency increased, which weakened the ablation mechanism. However, as the frequency increased, the peeling mechanism was enhanced; thus, a good cleaning effect could be obtained.

High power continuous green lasers have important applications in laser displaying, biomedicine, non-ferrous metal processing, and other fields. These research issues have become hot topics in the laser field. Therefore, to achieve high power and high efficiency continuous green laser output, a high-power fiber laser is built by using a narrow-band fiber grating, and the frequency doubling technology is studied by using the laser as the fundamental laser source. The fundamental frequency fiber laser with a bandwidth less than 50 pm is obtained, and the output power can reach 100 W. Based on this fundamental frequency laser, 532 nm green laser output of 11.6 W is achieved by using a one-way frequency doubling KTP crystal, and the frequency doubling efficiency is 11.6%. Linearly polarized laser is obtained by polarizing the fundamental frequency laser with a polarizing prism. The frequency doubling experiment of p-polarized laser passing through a polarizing prism is carried out. The output power of 532 nm frequency doubling laser is 7.3 W and the frequency doubling efficiency is 14.2%. These experiments show that the frequency doubling efficiency of fiber lasers can be improved by controlling the spectral bandwidth of fundamental frequency laser via the narrow linewidth grating. The 532 nm green laser can be obtained by doubling the frequency of the s-polarized laser reflected by the polarizing prism. The green laser power can be increased to more than 14 W by combining two green laser beams via the laser beam combination technology.

A carrier and a catalyst, i.e., porous carbon fiber prepared by the etching template method and ferroferric oxide (Fe3O4), respectively, were uniformly mixed and vacuum-filtered to prepare a photothermal membrane (PTM) with interfacial heating and photo-Fenton catalytic properties. The material was characterized using X-ray diffractometer, scanning electron microscope, specific surface-area and porosity tester, and ultraviolet-visible spectrometer. Additionally, the effects of pH, hydrogen peroxide dosage, and solar radiation density on the degradation efficiency of the material were studied. The experimental results show that the degradation rate of RhB reached 100% after 80 min of reaction when the initial concentration of RhB was 10 mg/L, the pH value was 5,the dosage amount of H2O2 was 300 μL, and the solar radiation density was 3 kW/m2. The catalytic efficiency of the photothermal membrane was 92% after 10 experimental cycles, indicating the high stability of the PTM.

To provide a larger area and larger regional selectivity of light stimulation in the application of optogenetics, a multi-channel optogenetic stimulation system with a simple structure, wireless control of stimulation parameters and independent control was developed by our research group. A μLED chip was used as the light source, and lithography and micro-welding technology were used to fabricate a blue light stimulator with an array light source. The wireless control function of the stimulator was realised using the wireless communication module. The size and weight of the photic stimulator were 46 mm × 30 mm and 7.134 g, respectively. The results showed that the maximum output optical power of the optrode's surface was 24.6 mW, which met the requirements of activating neurones by ChR2. The adjustable range of the output optical frequency was 1-500 Hz, while the maximum output error was less than 1%. The adjustable range of the duty cycle was 0-100%, while the maximum distance of the wireless communication was 50 m. This system can be used in the fields of optogenetic regulation, cell culture and fields that require a large area of light. Finally, it provides an effective tool for the regulation and research of neural circuits.

Based on the two-mode traveling wave model, the nonlinear dynamics of a semiconductor ring laser (SRL) subject to phase conjugate cross optical feedback is numerically studied. It is found that the SRL shows low frequency anti-phase oscillation when the phase changes of these two modes are desynchronized, and the oscillation period increases with the increase of feedback time. In contrast, in the case that the phase changes are synchronized, the two-mode output of the SRL can be one-periodic, multiply-periodic and chaotic by changing injection intensity. In addition, the time-delay signature (TDS) of the generated chaotic signal is identified by the autocorrelation function (ACF), and the corresponding bandwidth is calculated by using the power spectrum. It is found that the TDS first decreases and then increases with the increase of feedback strength, however the bandwidth increases approximately linearly, which indicates that by properly adjusting the feedback strength, the TDS of chaotic signals can be well suppressed and these signals can be used for secure communications and random number generation.

In order to compare the collimation effect of TIR (Total Internal Reflection) lens and free-form reflector for LED (Light-Emitting Diode) light source. Based on TracePro, the effective range and spot diameter of LED light source are simulated under TIR lens and reflector of the same caliber, and the collimation characteristics of TIR lens and reflector of the same caliber are compared. The results show that with the increase of aperture, the range increases, and the light pattern goes through three stages, and the corresponding light spot has three forms, namely rectangular shape, double peak shape and hump shape. After the light source passes through the reflector, the spot diameter is smaller and there is lag effect. The range of LED light source after passing through the TIR lens is longer, but the difference is small. When the aperture of the spot is too large, both optical systems form rings.

Dry etching is required to microfabricate 4H-SiC-based microelectromechanical system (MEMS) devices, such as pressure sensors and microwave power semiconductor devices. The processing efficiency can be boosted by improving the etching rate. However, adjusting the etching rate of 4H-SiC by manipulating etching process parameters not only changes the etched surface roughness, but also impacts the surface roughness of the etched surface. To achieve excellent pattern morphology and improve the etching mask lift-off quality while simultaneously improving the etching rate and reducing the surface roughness need of 4H-SiC, we optimized the photolithography process parameters, including exposure mode, exposure time, and development time, to meet the development need of 4H-SiC MEMS devices. We investigated the effects of etching process parameters (such as etching gas content, chamber pressure, and radio-frequency power) on etching rate and surface roughness in reactive ion etching (RIE) with SF6 and O2 as etching gas and Ni as an etching mask. The results show that a flat atomic surface can be achieved by optimizing etching process parameters. The etching rate of 4H-SiC is 292.3 nm/min and root-mean-square (RMS) roughness is 0.56 nm when the flow of SF6 and O2 is 330 and 30 mL/min, respectively, the chamber pressure is 4 Pa, and RF power is 300 W. High-quality etched surfaces with a high etching rate can be obtained using optimized etching process parameters.

Considering the combat demands of an individual soldier and focusing on the poor imaging quality and very short exit pupil distance of current transmission sniper rifle scopes, a long-eye distance high-precision imaging sniper rifle scope is designed. Based on the design indices of the system, the objective and eyepiece sets are decomposed and the optical focal degree is calculated. The optical path of the scope is designed using ZEMAX software. The objective and eyepiece sets of the scope adopted a telecentric optical path. The magnification of the system is 10×, the diameters of the incoming pupil and exit pupil are 50 mm and 5 mm, respectively, the field of view angle is 2.2°, the distance of the exit pupil is 87.89 mm, and the length of the mechanical cylinder is 403.76 mm. The design results show that the imaging quality of the objective lens and ocular lens is excellent. Moreover, the modulation transfer function value of the whole optical path after docking is greater than 0.85 at Nyquist frequency of 16.67 lp/mm, which meets the requirements of a military sniper rifle scope.

In order to realize a high-integration and high-stability three-dimensional optical chip, it is necessary to systematically study the coupling characteristics of three-dimensional spatial waveguides. This paper mainly studies the coupling between waveguides in three-dimensional integrated optical chips. The electromagnetic field distribution of the waveguide array under different architectures is simulated by full-wave simulation. The coupling efficiency between parallel waveguides and crossed waveguides is analyzed, which is related to and the waveguide spacing, the refractive index of the surrounding medium, the working wavelength and the angle. In parallel waveguides, when the center-to-center spacing between the waveguides on two SiO2 substrates is 0.76 μm and the coupling length is 72.5 μm, the coupling efficiency between the waveguides in the vertical direction reaches 0.997. In crossed waveguides, the coupling efficiency between the waveguides is very sensitive to the angle between the waveguides. When the angle is greater than 10°, no coupling occurs between the waveguides, so the coupling between the waveguides can be controlled by adjusting the angle between the waveguides.

In order to facilitate the ignition of the gas discharge plasma, a high open circuit voltage is required to drive the constant current source. At the same time, because of the negative resistance effect of gas discharge, the voltage required to maintain the discharge after ignition is far less than the ignition voltage, and the surplus voltage after ignition will result in a large power consumption of the constant-current source. In view of this, a circuit scheme to reduce power consumption of a constant current source for glow-discharge drive is proposed, and its working principle is analyzed in detail. In this scheme, a constant current source with an open circuit voltage slightly higher than the maintenance voltage of gas discharge is used to reduce power consumption, and a high-voltage pulse piezoelectric ceramic is used to ensure reliable ignition of gas discharge. The constant current source and the high-voltage pulse circuit work in parallel after being isolated by high-voltage silicon stack. Experimental results show that when the circuit works normally, the power consumption can be reduced by about 50%. The sample precision test of the galvanized sheet is carried out on the direct current glow discharge experimental platform, and it is found that the relative standard deviation (RSD) of the test results of Cu, Si, and Mo contents (spectral line intensity) are all greater than 2%.

To increase the laser damage threshold, an ion-beam assisted electron-beam formation method is used for preparing high-reflection films with three wavelengths of 355, 532, and 1064 nm. First, Lambda 950 spectrophotometer is used to test the spectral performance of the film sample. Then, the influence of different substrate materials and substrate cleaning processes on the laser damage threshold of the film are verified. Finally, the weak absorption capacity of the film and the laser damage threshold under different working vacuum degrees are studied systematically, and the relationship between the weak absorption capacity of the film and the laser damage threshold is analyzed. Additionally, the relationship between the weak absorption of the thin film and the laser damage threshold value is analyzed. The results show that the reflectance at the three wavelengths meets the requirement of optical performance indicators for the solid-state 355-nm ultraviolet laser. The laser damage threshold of the film and weak absorption value do not correspond to each other when the working vacuum increases to a certain level. However, an optimal value indicates that the high-reflection film can be used as the mirror in an all-solid-state 355-nm laser.

Spectrally encoded Mueller matrix measurement has the advantages of high measurement speed, compact structure, low loss, and no moving parts. Furthermore, all elements in the Mueller matrix can be obtained with only a single measurement. The main principle of this method is to use a set of phase retarders with a specific thickness ratio to modulate the Mueller matrix elements to the frequency channel of the spectrum; then, the Mueller matrix is demodulated through the Fourier transform of the spectrum. However, the thickness or phase error of the retarders causes a large error in the demodulated Mueller matrix elements. In this work, we theoretically obtained the general expression of light intensity with phase error and then calculated the phase error using a single sample. This method can avoid the influence of the different initial phases of different samples and improve the calculation accuracy of the phase error. We calculated the influence of phase errors of the retarders via simulation and experimentally verified the feasibility of the error calculation and calibration methods.

Based on entanglement swapping, a scheme to generate the maximum entangled state by means of an entangled V-type three-level atomic system partially interacting with an entangled two-mode cavity field is proposed. In the scheme, the entanglement between the atom and the cavity field without any initial interaction can be achieved by measuring only a single atomic state without joint measurement. In the process of atom-cavity interaction, the cavity is only virtually excited and there is no energy exchange between the atom and the cavity, so the requirements of system on cavity quality are greatly relaxed. The results show that when the interaction time between the atom and the cavity field is 1.4675 ×10-5 s, the maximum entangled state with fidelity of 92.8% can be obtained. Moreover, the feasibility of the scheme is also discussed.

Cavity ring-down absorption spectroscopy is a direct absorption spectroscopy detection technology with high sensitivity, strong selectivity, and fast response speed. This technology has the smallest noise absorption coefficient of 10-12 cm-1·Hz-1/2 due to continuous improvement and expansion of excitation light source, cavity structure, and modulation method etc. The working principle, technical characteristics, and typical applications of cavity ring-down absorption spectroscopy detection equipment are summarized in this study, and the effects of the excitation light source, cavity structure, and modulation methods on cavity ring-down spectroscopy detection technology are analyzed. Finally, the technology's application prospect is prospected by merging the typical applications of cavity ring-down absorption spectroscopy in different fields.

With the unique advantages of high processing accuracy, high efficiency, no pollution, and wide range of application materials, laser processing has become the first choice for micro-hole fabrication, especially in the processing of high-quality micro-holes. The advantages and research significance of laser processing micro-holes are introduced. The quality characteristics of laser processing micro-holes (such as depth-diameter ratio, taper, roundness, and recast layer) are summarized. The current research status of micro-hole quality of laser processing is reviewed and discussed. The impact of drilling methods, laser process parameters (such as pulse width, wavelength, and repetition frequency), and processing environment (such as vacuum, gas, and liquid) on the quality of laser processing micro-holes and the reasons for the impact are discussed. The development direction of laser processing of micro-holes and the focus of future research are summarized.

As semiconductor lasers have excellent characteristics including wide output wavelength range, simple structure, and easy to be integrated, they are widely used in medical, sensing, optical communications, military, and aerospace fields. With the increase of application requirements and output optical power, the reliability of lasers suffers from severe challenges. This paper reviews the failure mechanism of semiconductor lasers and analyzes the five effective failure detection and analysis methods of photoluminescence technology, electroluminescence technology, cathodoluminescence technology, infrared thermal imaging, and emission microscope. Furthermore, this paper summarizes and suggests the improvement measurements of the failure induced by the active area, cavity surface, welding, and operating environment. These will provide effective suggestions for the research and production of semiconductor lasers.

At present, the rapid development of micro-machining and finishing technology has put forward higher requirements for miniaturization processing technology: the processing scale needs to be improved to the micron or even nanometer scale, and three-dimensional micro-machining can be achieved inside the material. Femtosecond laser can break through the limit of diffraction limit and machining limit, and is the hot spot of advanced manufacturing technology. In this paper, the development and mechanism of femtosecond laser machining are reviewed, and the mechanism of laser machining is described from the Coulomb explosion model, microexplosion model, color center model and two-photon ionization model. For femtosecond laser ultrafast action process, simulation is the main means to analyze the machining mechanism and study the laser and material action process. The characteristics and application range of the two-temperature model, molecular dynamics model and composite model used in femtosecond laser simulation are analyzed in order to provide a basis for the theoretical research of femtosecond laser machining. Finally, the existing problems of femtosecond laser machining technology are pointed out, and the development of this technology is prospected.

Owing to their unique optical and electronic properties, two-dimensional (2D) materials have demonstrated broad promising applications in optoelectronic devices. Molybdenum disulfide (MoS2), a representative 2D material, has shown remarkable advantages in the field of photodetection because of its atomic-level interfaces and thickness-dependent tunable band structure. However, after many years of extensive studies, MoS2 devices have reached a bottleneck in terms of performance. To further improve the performance of MoS2 devices, various methods, such as band engineering, ferroelectric polarization, and plasmon resonance, have been investigated. However, a thorough review of such studies has not been conducted. In this paper, we briefly summarize the latest theoretical and practical research into MoS2 photodetectors. The principles, structure design, preparation, and optoelectronic characteristics of the new MoS2 photodetectors based on the three aforementioned methods were reviewed. This comprehensive review can broaden the existing understanding of MoS2 devices and provide important guidelines for future applications.

In order to characterize the near-infrared polarization characteristics of typical satellite surface materials, the reflection characteristics of the target surfaces are described based on the microplane element model and considering the specular scattering and diffuse scattering comprehensively. The specular coefficient and diffuse reflectance are introduced to clarify the influence of the two kinds of reflection on the polarization degree, and the masking effect of the actual rough surface is considered. A more perfect model of multi-parameter polarization bidirectional reflection distribution function is established, and the expression of polarization degree of optical reflection suitable for rough material surface is deduced. The near-infrared polarization experiments of typical satellite surface materials are carried out, and the multi-parameter values of satellite surface materials are retrieved from the experimental data by using genetic algorithm, and then the polarization information simulation curve is obtained. The results show that the simulated values of the multi-parameter polarization bidirectional reflection distribution function are in good agreement with the experimental values, and the polarization characteristics of different satellite surface materials have great differences in distribution.

A microwave instantaneous frequency measurement scheme based on single lightpath polarization multiplexing technology was proposed. This technique requires only a dual-polarization dual-drive Mach-Zehnder modulator to provide the pump light and probe light needed for stimulated Brillouin scattering. Compared with the previous dual-channel Brillouin scattering technique, the proposed technique offers the advantages of a simple structure, compression system volume, stable and controllable pump light and detection light interference, and improved system stability. The unknown microwave signal was modulated using carrier suppression double sideband modulation as the pump light, and the swept-frequency detection signal was phase modulated as the scanning detection light. Moreover, the conversion from phase modulation to intensity modulation was realized using the stimulated Brillouin scattering effect. The microwave signal instantaneous frequency was measured by establishing a mapping relationship between the scanning frequency and the output optical power. Theoretical and simulation models were established to study the influence of the pump light wavelength jitter, DC bias point drift, phase drift of electric phase shifter, and polarization state shift of pump light and probe light on frequency measurement accuracy. Research results show that the proposed scheme can measure the frequency of microwave signals above 30 GHz. Furthermore, the maximum absolute measurement error does not exceed 30 MHz, while the relative measurement error is less than 2%. The frequency measurement range can be increased by increasing the scanning range of the frequency sweep detection signal and the modulation frequency range of the modulator. The proposed scheme has the advantages of a compact structure, stable performance, and simple operation and has a wide application prospect in low-cost and wide-spectrum radar detection.

In this paper, the molar absorptivity of carbonate ions is calculated by measuring the infrared absorption spectra of 30-100 mmol/L low-concentration sodium carbonate aqueous solutions. The infrared absorption spectra of 30-100 mmol/L sodium carbonate aqueous solutions were measured using the infrared single attenuated total reflection (ATR) accessory based on zinc selenide. The simulated pure water ATR spectrum was used as the baseline to adjust the infrared absorption spectra of the sodium carbonate aqueous solutions. The Kramers-Kronig formula was used to calculate the refractive indices and extinction coefficients of the sodium carbonate solutions. Furthermore, the effective optical pathlengths and the molar absorptivities of the low-concentration sodium carbonate aqueous solutions were calculated. The calculated maximum molar absorptivity of carbonate ions is 2421.99 L/(mol·cm).

The classical film stack (0.5LH0.5L)n induces half-wave holes due to its inhomogeneity of refractive index. In the design of film structures, the film possessing a homogeneous refractive index is usually assumed. When its optical thickness is half of the central wavelength, the film can be regarded as an absent layer. Unfortunately, in the practical fabrication, there exists some inhomogeneity in the refractive index of the film, which causes the optical thickness of the film inconsistent with theoretical design, and thus half-wave holes occur. Here the basic periodic structure of the film is optimized. The optical admittance of the optimized film structure at half wave is no longer affected by the refractive index inhomogeneity. On this basis, a harmonic beam splitting film is designed and fabricated that effectively eliminates the half-wave hole phenomena. The theoretical and experimental spectral curves are in a good agreement.

In order to explore the computational performance of the existing CIECAM02 and CIECAM16 color appearance models on the color vision differences of individual observers, five lighting sources with different spectral power distribution and 24 colors of the GretagMacbeth ColorChecker standard color card are selected, and 208 sets of individual observer color matching functions are used. The color vision difference of individual observers is quantified. For all selected lighting sources and color centers, the average value of CIECAM-UCS color difference of individual observer and standard observer CIE1964 is the same, which is 1.29. At the same time, in the two color appearance models, the observer variability(the mean color difference from the mean) is relatively consistent, and the observer variability under the white LED light source is relatively large. In addition, the maximum value at color patch blue is 2.49 (2.32). It suggested that the individual differences were larger in this observation condition. The results can provide some basic data and calculation basis for the optimization of color appearance model.