The content of Bromine was measured by X-ray fluorescence approach in order to study the spatial distribution characteristics of Bromine in seawater and analyze the reasons that affect the distribution of Bromine near the Eastern shore of Leizhou Peninsula. First, the calibration curve of standard solution is obtained by small-focus X-ray fluorescence spectrometer and direct injection method, and the linear fitting equation is derived from the relationship between the fluorescence intensity and the mass concentration of Bromine, to detect the mass concentration of Bromine in coastal waters. Then, we further analyze the influences of the land runoff, tide and the structure of circulation on the distribution of Bromine in seawater in the east of Leizhou Peninsula based on the spatial variation of Bromine mass concentration in water, the spatial distribution of land runoff, tide and the structure of circulation. The Bromine mass concentration of 18 stations in the east of Leizhou Peninsula is in the range of 50.79?62.11 mg/L derived by the X-ray fluorescence spectrometry approach, and the results indicate that the content of Bromine in this area is less than that in the ocean and varies greatly with space. In this area, the Bromine content almost increases with the distance between the sampling site and two-bays-one-island (Zhanjiang bay, Leizhou bay and Naozhou island) increasing. In addition, in the south of this area and the entrance of Qiongzhou Strait, for the complex influences of currents, the Bromine content increases along the flow direction of Qiongzhou Strait. The variation of Bromine mass concentration in coastal waters demonstrates that the distribution of Bromine is uneven, and the uneven distribution fact of Bromine is mainly caused by the land runoff, tide, alongshore current near Western Guangdong, Qiongzhou Strait current, and cyclonic circulation.

Existing theoretical models of skylight polarization patterns have problems that only consider the influence of the sun or the moon alone and could not adequately describe the polarization patterns of the sky during the transition between dawn and dusk in clear weather. Therefore, a modelling method of skylight polarization patterns under the influence of dawn and twilight is proposed. The method introduces the influence of the sun and the moon and calculates the Stokes vectors using the position of the sun and the moon. Considering the factors of multiple scattering of atmospheric particles in the actual sky, the influence weights of the sun and the moon are determined by Stokes vector optimization. In addition, the obtained angle of polarization is used to characterize the skylight polarization patterns. The experimental results show that the simulation results of the proposed model and the measured angle of polarization have the same distribution and variation characteristics, and maintain a high degree of similarity, which can effectively characterize the skylight polarization patterns influenced by dawn and twilight.

The high-precision reconstruction of an underwater neighborhood sound field is crucial for studying and analyzing the structural characteristics of neighborhood sound field and improving the underwater acoustic sensing performance. The deflection effect of the laser beam passing through the acoustic field carries the gradient and pressure information of the acoustic field when the laser beam width is much smaller than the acoustic wave wavelength. This study provides a data sensing basis for sound field reconstruction by employing the Kirchhoff integral theorem. The calculation method of a virtual extended acoustic field aperture is presented herein by using the density of the laser sensing acoustic field, which further approaches the theoretical requirement of the infinite integral interval in the Kirchhoff integral theorem. The results of the proposed sound field reconstruction ideas and methods are verified in an underwater neighborhood space. The results show that, compared with direct acoustic holography, the proposed acoustic field reconstruction method improves the peak signal-to-noise ratio by 5.5 dB, thereby providing a new feasible idea for developing high-precision neighborhood acoustic field sensors.

Space-borne Mie lidar is the most widely used instrument to profile aerosols in the global scale. However, due to the variation of atmospheric aerosol types, the retrieval model for aerosol extinction coefficients from lidar signals assumes a prior aerosol model, which impedes the further improvement of retrieval accuracy. As such, an iteration algorithm for aerosol extinction coefficient profiling from space-board dual-wavelength lidar observation is proposed. First, the initial extinction-to-backscatter ratio (i.e., lidar ratio) is obtained based on a prior aerosol mode and the aerosol extinction coefficient and optical depth at two channels are then retrieved. Moreover, with the relationship built between aerosol optical depth and aerosol mass column, the total aerosol mass columns at two channels are estimated. Finally, by applying the constraints that the two-channel observations correspond to the same aerosol mass column, the lidar ratio and the optical parameters are optimized iteratively based on lidar observation extensively. Due to the limitation of the channel number of the dual-wavelength lidar, the method is only applicable to the two-type mixed aerosol model. The accuracy and the applicability of the method are evaluated based on the background information of aerosol profiles in Baotou, Inner Mongolia, China. The retrieval results from the empirically estimated lidar ratio are taken as the control group. The results show that the proposed method yields mean accuracy improvement of extinction coefficient at 532 nm and 1064 nm channels by 21.16% and 3.00%, respectively. The method is also applied to CALIOP data to further validate the application potential of the proposed retrieval model.

In order to solve the problem of low light absorption of silicon nanowire photodetector, we construct a hexagonal silicon nanowire structure of photodetector. We cover the structure with zero-bandgap graphene and add Au grating at the same time, and finally use COMSOL software to model and analyze the structure. It is shown that in the optical band range between 0.5 μm and 1.5 μm, the graphene coverage and the Au grating can effectively enhance the light absorption performance of the device. What is more, the thickness of both graphene and Au grating has an effect on the performance of the device.

The optical spectrometer, an instrument used to detect and analyze spectra with various wavelength components of incident light, has a growing demand for applications in fundamental research, industrial production and daily life. Conventional spectrometers based on precise optical dispersion components usually necessitate large volume and weight, which hardly meet the trend of miniaturization and low cost for diverse applications. We realize a filter-array-based computational reconstructive optical spectrometer through combining a series Cs0.1MA0.9PbX3 (X is Cl, Br, I) perovskite materials with different visible light absorption characteristics prepared by spin coating method and complementary metal oxide semiconductor sensor. Considering the spectral response of the perovskite film array, the non-negative Tikhonov regularization method is used to reconstruct the spectra. Finally, the designed optical spectrometer is tested and verified, which exhibits a spectral resolution of 27 nm at 500 nm wavelength and achieves a certain spectral resolution within the visible range.

A vertical-structure photodetector based on two-dimensional perovskite (PEA)2(MA)4Pb5I16[PEA is C6H5(CH2)NH3, MA is CH3NH3] is fabricated and its property is analyzed. The photocurrent of the device reaches a maximum when the thickness of the two-dimensional perovskite thin film is 280 nm, while at 500 nm, the external quantum efficiency reaches 90%, the responsivity reaches 0.37 A/W, and the detectivity reaches 3.4×1012 Jones(1 Jones=1 cm?Hz1/2/W). The response time of the device does not continue to decrease as the thickness of two-dimensional perovskite thin film decreases, but reaches a minimum at the thickness of 80 nm due to the effect of carrier transit time and the quality of perovskite thin film. By fixing the thickness of the two-dimensional perovskite film at 80 nm, we finally achieve a response time of 113 ns by reducing the effective area of the device. This work is of great significance to promote the development of low-cost and fast-response photodetectors.

This study aims to improve the recognition of perimeter intrusion events of the optical fiber sensing system under complex outdoor conditions. An intrusion event recognition method based on improved singular spectrum analysis and genetic algorithm optimized bidirectional long-short-term memory neural network (GA-BiLSTM) is proposed. First, the improved singular spectrum analysis was used to iteratively denoise the optical fiber sensing signal and its components. The signal contribution rate was used to determine the order of signal reconstruction, which controls the denoising process of the signal components, thereby completing the denoising of the optical fiber sensing signal. To recognize intrusion events, the genetic algorithm was used to optimize the parameters of the neural network. Subsequently, a bi-directional long-short-term memory neural network was constructed to extract the spatial characteristics of optical fiber signals. An intrusion event recognition experiment was carried out using the measured optical fiber sensing signals of six events, i.e., climbing, running, knocking, static, windy, and rainy days. The experimental results show that the improved singular spectrum analysis, when applied to the dual Mach-Zehnder fiber perimeter sensing system, exhibits superior denoising performance compared to ordinary singular spectrum analysis. The average signal-to-noise ratio of the consequent signal improved by 12.79 dB. However, the mean root mean square error was slightly reduced. Moreover, the GA-BiLSTM method increased the average recognition rate of intrusion events by 5.7%, with the recognition accuracy rate reaching up to 98.1%.

Distributed optical fiber acoustic sensing (DAS) signal has problems with strong noise and difficult recognition. To solve these problems, a deep residual shrinkage network based on new threshold function (DRSN-NTF) is proposed. DRSN-NTF uses new threshold function instead of soft threshold function on the basis of deep residual shrinkage network (DRSN), which makes it more capable in signal noise processing and classification recognition. DAS system is used to collect the experimental data of perimeter intrusion events, and six groups of experiment with different signal-to-noise ratios (0 dB?5 dB) are designed by adding Gaussian white noise. The experimental results of the four models are compared to investigate the recognition effect of DRSN-NTF. The results show that the average test accuracy of DRSN-NTF is 1.05% higher than that of DRSN in the case of strong noise. With the reduction of the signal-to-noise ratio, the difference between the test accuracy of DRSN-NTF and that of DRSN increases, indicating that DRSN-NTF is more capable in signal noise processing and classification recognition, which can lead to relatively higher recognition accuracy. Therefore, DRSN-NTF is more suitable for recognition of DAS signal.

At present, the recognition of vibration events by distributed fiber optic vibration sensing is easy to overfit and the generalization ability is insufficient. We propose a distributed fiber optic vibration recognition method based on fractional Fourier transform (FrFT). The method uses FrFT for the time-frequency conversion of the time-domain vibration signals, which means adding a new analysis dimension compared with the traditional time-domain method. Compared with the traditional time-frequency domain method, this method not only solves the problem of mutual constraints of time resolution and frequency resolution but also enhances the feature richness of time-frequency data. It is more conducive to the learning of deep models and can effectively prevent model overfitting. Outdoor field experiments show that the recognition accuracy of the FrFT method reaches 98.5%, and the accuracy can still maintain more than 98% on the special generalization test set. At the same time, a more reliable evaluation index f1-score is introduced. The f1-score is the harmonic mean of precision and recall. It is used to comprehensively evaluate precision and recall. The f1-score of each event recognized by this method is higher than 0.975.

The additional phase noise of a sub-Hz linewidth laser transmitted in the fiber to excite the Hz-linewidth transition of erbium is actively compensated for using the fundamental laser of the cooling laser in the ultracold erbium atom system. To perform heterodyne beat detection and implement the compensation feedback without affecting the power of the original sub-Hz linewidth laser (1299 nm), we injecte the broad-linewidth fundamental laser of the cooling light at a similar wavelength (1166 nm) from the output end of the fiber. The phase noise of the narrow-linewidth laser caused by temperature and vibration in fiber transmission is suppressed when the noise of the two lasers is almost the same. The linewidth of the beat frequency signal of the transmitted laser is narrowed from 14.6 Hz to 11.6 mHz and the stability of the optical-frequency transmission link is improved from 1.6×10-16 to 6.5×10-19 in 1000 s, meeting the optical-frequency transfer needs of a start-of-the-art optical clock. This optical-frequency transfer scheme can be used as an alternative where the power of the transmitted laser is insufficient or physical space is limited. The scheme is also applicable for simplifying the source setup on branching optical-fiber networks.

This paper proposes a long-distance sensing system using ultra-weak fiber Bragg grating arrays. By taking advantages of the discrete distribution and high signal-to-noise ratio of ultra-weak fiber Bragg gratings, this system employs a segmented acquisition method to decrease the requirements for data caching and computing capabilities. For spatial demodulation of the 10 km sensing section, ZYNQ (ZYNQ-7035 All Programmable SoC) embedded hardware is used. To design the input pulse power and Raman fiber amplifier configuration with power balance and dynamic segmented gain control, the OptiSystem software is employed to simulate and analyze the power budget of the system. An experimental system is constructed and validated, showing that the system's operating range can reach 50 km, the fluctuation of sensing signal intensity is less than 2.2 dB, the spatial resolution is 1.5 m, the demodulation speed is 0.3 Hz, the remote demodulation accuracy is within 6 pm, and the measurement accuracy for temperature and strain is ±0.15 ℃ and ±5.5 με, respectively. The overall system performance outperforms traditional Brillouin optical time-domain reflectometer and exhibits good scalability while demonstrating significant technical advantages in long-distance fiber temperature and strain sensing.

A coherent demodulation scheme based on injection locking local laser and optical phase compensation is proposed. The local oscillator (LO) is recovered by injection locking, and the signal is demodulated via homodyne coherent detection. Using the proportional-integral-derivative (PID) algorithm to control the piezoelectric ceramic (PZT) enables the optical phase compensation. The results demonstrate that the fluctuation of optical phase difference does not exceed ±4.8°. The modulation, transmission, and demodulation experiments of a dual-user 400-Mbit/s pseudo-random binary sequence (PRBS) in the ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) are implemented. Additionally, the bit error rate (BER) test is conducted.

Recently, with the development of new-generation mobile communication systems, the demand for high data rates and large bandwidth is increasing. In this study, we proposed a second-order Raman fiber amplifier designed with two second-order pumps and four first-order pumps to amplify the C+L full-band signal light using a tellurium-based optical fiber as the transmission medium, which can effectively alleviate optical communication network challenges due to bandwidth growth. First, a simplified second-order Raman coupled wave equation is solved numerically, and then the pumping parameters of the second-order Raman fiber amplifier are optimized using a cooperative search algorithm to improve output performance. Meanwhile, the performance of first- and second-order Raman fiber amplifiers under the same pump parameter configuration is analyzed. Additionally, the influence of two key factors, that is, second-order pump optical power and fiber length on the average output gain and gain flatness of a designed second-order tellurium-based Raman fiber amplifier are investigated. Experimental results show that the average output gain of the designed second-order tellurium-based fiber Raman amplifier is 27.3601 dB and the gain flatness is 0.6601 dB in the ultrawide bandwidth range of 1530?1630 nm.

Time delay estimation for analog signals is more susceptible to noise than that for demodulated signals, which increases false positives and conceals the correct peak value. The singular spectral decomposition method combined with improved generalized cross-correlation function is proposed to reduce the influence of Gaussian noise on the time delay estimation results. Simulink simulation results show that the proposed method can obtain fault-type and distance information in the same order of magnitude accuracy for lower transmission frequency requirements than demodulation signal time delay estimation. Multiple experimental verifications in the -5 dB Gaussian noise environment can yield that, compared to the results of the secondary correlation method, the absolute value of the main peak side-lobe ratio increases by more than 0.6756 dB, and the ratio of the peak value of misjudgment to the peak value of the fault point decreases by more than 0.2710. This also improves in different degrees under other conditions.

A dual-peak resonance long-period fiber grating (LPFG) based on CO2 laser technology is proposed to investigate a highly sensitive refractive index sensor. First, dual-peak resonance LPFGs with grating periods of 196 and 73 μm are fabricated in conventional single-mode fiber and 80 μm bend-insensitive single-mode fiber, respectively,using a CO2 laser after etching cladding. This demonstrates the possibility of fabricating an LPFG on a single-mode fiber with a shorter grating period using CO2 laser micromachining technology. Dual-peak resonance LPFGs with grating periods of 110 and 115 μm are directly fabricated in two 80 μm single-mode fibers using a CO2 laser. The results show that the dual-peak resonance LPFGs fabricated in two 80 μm thin single-mode fibers exhibit advantages of deep attenuation loss, low loss, and high refractive index sensitivity. Based on its excellent performance, the dual-peak resonance LPFG based on CO2 laser technology is a prospective sensor applicable to fields such as biological, chemical, and environmental parameter detection. In addition, a simple-operation low-cost method for fabricating dual-peak resonance LPFGs is proposed.

Equivalent time sampling is an important technology in the field of high-speed optical waveform testing and quality evaluation. It uses low actual sampling rates for exchanging higher bandwidth and vertical resolution; hence, it is incapable of using filtering, averaging, and other methods for equalization when measuring signals with random and discontinuous characteristics. Therefore, herein, a recursive neural network-based equivalent time sampling signal equalization method is proposed. By training the recursive network model, an equivalent time equalizer is established, and the method is validated by processing equivalent time sampling signals of optical digital communication and light detection and ranging (LiDAR) waveforms. The results show that compared with the input waveform, the eye graph related parameters that characterize the quality of optical communication, i.?e., eye height, eye width, and jitter, exhibit considerable improvements. For linear frequency modulation LiDAR signals, enhancing the waveform amplitude spectrum response solves the problem of equalization processing for equivalent time sampling signals.

A Laguerre-Gaussian beam can be converted into a Hermite-Gaussian beam using a tilted lens. In this work, a position mapping relationship was derived between the incident Laguerre-Gaussian beam array and the Hermite-Gaussian beam array converted by the tilted lens. When the tilted lens is rotated around an arbitrary axis by a certain angle, the positions of the two beam arrays will be symmetrical about that axis. In the experiments, Laguerre-Gaussian beam arrays of 1×1, 2×2, 3×3, 3×1, and 1×3 were generated using a spatial light modulator and converted into Hermite-Gaussian beam arrays via a tilted lens, and the above theoretical analysis was verified through comparison of the distributions of the two beam arrays. The experimental results are in perfect agreement with the theoretical analysis. Based on the theoretical results and the position distribution of the Hermite-Gaussian beam array, the topological charge of the Laguerre-Gaussian beam array can be detected. This work provides clearer theoretical guidance for the orbital angular momentum detection of Laguerre-Gaussian beam arrays.

As the large angle deflection of a mirror is difficult to measure in an electromagnetic galvanometer system, a photoelectric mirror-angle-sensing device based on the quadrant photoelectric detector (PD) and LED was designed. First, the basic principle of mirror angle detection was analyzed, and based on the LED Lambertian radiation model, the mathematical model between the true value and the calculated value of the mirror deflection angle was established. Second, the system detection range was defined with the nonlinearity as the evaluation standard. Then, the influence of the detector's horizontal position, distance between the center of the mirror and the LED, and half-power angle of the LED on the detection range of the system were simulated and analyzed. Finally, an experimental platform was built for verification. The simulation and experimental results show that the established mathematical model is effective for mirror angle detection using Lambertian LED. With reduced distance between the detector and the LED, increased distance between the center of the mirror and the LED, and increased half-power angle of the LED, the angle detection range of the system can be improved.

Photoelectric theodolites are important instruments for measuring the attitude of flying targets. We present a method for determining the attitude measurement accuracy of a photoelectric theodolite using a real time kinematic carrier phase difference technology (RTK) positioning unmanned aerial vehicle (UAV). The method uses the line formed between the center point of the UAV RTK antenna and a reference point as the axis of the attitude angle to be measured, calculates the included angle between that axis and the datum plane through the RTK positioning value, and uses the angle as the standard attitude against which the attitude measurement accuracy of the photoelectric theodolite is tested. In this paper, the principle of measuring attitude precision is introduced, the uncertainty in RTK and measuring precision are analyzed, and the rule of equipment distribution is discussed. Theoretical analysis and experimental results show that the proposed method can be used for measurement of the attitude accuracy of photoelectric theodolites.

We propose a method based on X-ray absorption spectra (XAS),which allows the calculation of each channel in the energy spectrum. The theoretical absorption energy spectrum of the sample is obtained using the attenuation coefficient curve of the sample elements and the background energy spectrum of the radiation source, and compares with the actual absorption energy spectrum of the sample. The energy spectrum is fitted and the element surface density is calculated with the annealing algorithm. The results show that the standard deviation of repeated experiments when measuring a single element is low and the measurement uncertainty is in the order of 10-4 g/cm2. This system can also be used for the measurement of the areal density of multi-element thin films, meeting the requirements of non-destructive and highly stable measurements of metal thin films in inertial confinement fusion experiments.

We propose a new phase retrieval algorithm based on the combination of the Monge-Ampère equation and the iterative angular spectrum algorithm. Since the iterative angular spectrum algorithm is highly dependent on the initial value, we utilize the solution of the Monge-Ampère equation to initialize it, which is expected to yield more accurate results than the solution of the transport of intensity equation. To avoid the algorithm becoming stuck in local minima and iteration stagnation, we adopt an alternating iteration strategy between the traditional iterative angular spectrum algorithm and hybrid input-output algorithm. The effectiveness of the hybrid algorithm is demonstrated by numerical experiments.

We report a single-beam triaxial atomic magnetometer based on cross bias magnetic field. Based on Bloch equation, the theory of single-beam scheme to achieve triaxial magnetic field detection is studied. To achieve triaxial magnetic field detection, the method of using cross bias magnetic field to rotate the atomic spin polarization direction is proposed and experimentally verified. By using only one single modulation magnetic field, it is possible to suppress low frequency noise and avoid the problem of magnetic field cross-talk. The experimental results show that the system response bandwidth to the magnetic field along X-axis is 90 Hz and the system sensitivity is 21 fT/(Hz1/2) under the zero-field condition. The system response bandwidth to the magnetic field along Y-axis is 130 Hz and the system sensitivity is 26 fT/(Hz1/2) when a bias magnetic field of 34 nT is applied in the Z-axis. The system response bandwidth to the magnetic field along Z-axis is 128 Hz and the system sensitivity is 29 fT/(Hz1/2) when a bias magnetic field of 38 nT is applied in the Y-axis. The proposed triaxial atomic magnetometer has the advantages of small size, simple structure and low fabrication cost, and is expected to be used in the biomedical and other fields.

In order to realize the high-precision measurement of pulsed laser echo signal parameters, a weak laser signal detection system that can analyze the pulse width, real-time power and energy parameters of the signal is designed by using full waveform sampling technology. The system hardware platform uses a low-noise wide-dynamic range analog front-end for signal preprocessing. The system realizes data quantization and dynamic time-domain latch based on field programmable gate array, analog to digital converter and other modules. In order to reduce the cost of the hardware platform, a multi-frame accumulation algorithm based on nonuniform periodic trigger signal is proposed to reduce the distortion of waveform reconstruction caused by high discreteness of data on low sampling rate platform. By fitting and compensating the quantized data, the algorithm improves the calculation accuracy of the system laser signal parameters. The system detects the parameters of a pulsed laser with 3 ns pulse width and 9 μW peak power and compared with the high sampling rate platform. The results show that the calculation error of the proposed system for laser signal pulse width is about 0.041 ns, peak power calculation error is about 0.53 μW, energy integration error is about 4.52 fJ and uncertainty of repeated measurement with all parameters is less than 8%.

The single-photon detection technique has unique advantages, such as high sensitivity, low timing jitter, and low power consumption. Thus, its applications in laser ranging and imaging are becoming increasingly widespread. In this paper, we introduce a low-cost high-precision single-photon ranging system, in which a narrow pulse laser generated by the laser diode with a pulse width of 160 ps and a low timing jitter single-photon detector based on a multi-pixel photon counter with a timing jitter of 417 ps are used to reduce the overall timing jitter of the system. The ranging experiment results show that within the 2-meter ranging range, the distance measurement accuracy of the single-photon ranging system could reach 370 μm@RMS. The experimental device adopts a coaxial optical path design, with a simple structure and easy integration, providing a feasible solution for achieving a miniaturized, low-power, high-precision single photon ranging system.

To further suppress the effects of assembly error disturbance on the output performance of a fast steering mirror control system and to improve the tracking accuracy of the system, a disturbance suppression method with internal and external disturbance observation links based on the principle of disturbance observation is proposed. The effects of the assembly error of the fast steering mirror on the accuracy of the control system were analyzed, and an equivalent mathematical model of the unbalance torque disturbance was developed. The inner loop interference observation link was used to suppress medium- and high-frequency disturbances, whereas the outer loop interference observation link was used to compensate for the medium- and low-frequency disturbance amplification of the inner loop interference observation link and provide medium- and low-frequency disturbance suppression. The input and error signal transmission process of the proposed disturbance suppression method were analyzed, and the control parameters of each controller of the suppression system were designed. A virtual prototype simulation test platform was built to test the performance of the control system. The results show that the adjustment time error of the virtual prototype system is 0.54% before and after the double interference observation link is added. For a 15-Hz equivalent disturbance, the disturbance suppression capability is improved by 25.23%. Theoretical and experimental results show that the introduction of a double disturbance observation links can effectively suppress the disturbance of the assembly error.

To reduce the maximum temperature and improve the temperature uniformity of a laser heating surface, a comprehensive heat dissipation method for jet impingement strengthening of the surface is proposed. In this study, a performance evaluation factor (PEC) that considers both heat dissipation and flow resistance characteristics was introduced for numerical research and compared with traditional microchannel heat dissipation characteristics. Results show that reducing the impact distance causes the boundary layer in the impact zone to become thinner, increases the transverse flow velocity, and moves the vortex center to the central entrance, thereby improving the heat transfer efficiency. The reduced impact distance not only reduces the maximum temperature of the system, it also achieves temperature uniformity. A comparison with traditional microchannel heat dissipation characteristics reveals that the PEC reaches its maximum at a dimensionless jet impingement distance of 0.25, making this system suitable for heat dissipation of laser heat sources. In addition, the results of thermal stress and strain analysis indicate that under the yield limit of the same material, the highest laser heat flux density that the system can withstand is significantly greater than that of the microchannel cooling system, resulting in better heat transfer performance and greater applicability.

With rising energy demand, oil and gas drilling activities are increasing. Laser drilling has great application value in the energy field and is expected to realize the manufacture of downhole in-situ glass casing to replace traditional metal casing, resulting in time and money savings for oil and gas drilling projects. The stable formation of laser irradiation rock vitrification is a key factor in achieving glass casing. In this study, the influencing factors and mechanisms of laser ablation granite vitrification are investigated based on laser scanning granite experiments, combined with phase detection and numerical simulation. The results show that after laser scanning, the constituent minerals of granite melt and fragment according to the ease of melting, and part of the surface is transformed into dark glass. The high-speed airflow can effectively remove rock debris and dust, improve the laser efficiency, and increase the adhesion of rock glass. Granite is susceptible to temperature fracture, and its low scanning speed and airflow auxiliary conditions favor the formation of vitrification. In practical engineering applications, the temperature action of the rock can be controlled via the scanning speed and auxiliary high-speed airflow to form stable rock glass, and create an in-situ vitrification well wall that firmly covers the hard rock surface. This study focuses on the vitrification mechanism of laser-acting rocks, and provides an important reference for expanding the engineering application of laser drilling.

We study the packaging method and key technologies of thin-disk laser, and report on our home-made thin-disk module comprising a YAG/Yb∶YAG composite thin-disk crystal with 5 mm diameter, which is glued onto a diamond heat sink. The multi-pass pumping scheme of the thin-disk module is analyzed and a numerical simulation model of thermal effect is established. The thermal focal length of the thin-disk crystal is measured to be approximately 445.6 mm at pump power density of 2.2 kW/cm2 and pump wavelength of 940 nm. A continuous wave laser based on the thin-disk module is realized and it delivers fundamental mode output of 18.75 W at the pump power of 70 W. The slope efficiency and optical-to-optical efficiency are 36.59% and 26.79%, respectively.

In order to obtain the optimal parameters of laser cladding process parameters of austenitic stainless steel alloy on hydraulic prop steel surface, the process parameters laser power, scanning speed, powder feeding speed are selected as input variables, and the quality of cladding layer is used as evaluation index to establish a mathematical model. 16 groups of orthogonal experiments are designed. Using adaptive chaotic particle swarm optimization algorithm to perform optimization, and the macro-morphology and microstructure of the cladding layer are analysed by experiments to verify the rationality and accuracy of the optimized process parameters. Two groups of specimens with similar comprehensive evaluation values are compared. The results show that the best combination of process parameters are laser power of 1200 W, scanning speed of 13 mm/s, and the powder feeding speed of 1.72 g/min. Using adaptive chaotic particle swarm optimization algorithm to optimize the process parameters can effectively improve the macroscopic defects and surface properties of the cladding layer, which proves the feasibility of the optimization algorithm in the field of laser cladding.

Low reflectivity and superhydrophilicity are ideal conditions for improving the performance of electronic devices, graphene as a new superconducting material has been widely used in the field of electronic information. At present, the realization of low reflection and superhydrophilicity mostly depends on the microstructure design and processing of graphite surface by femtosecond laser, and the high processing cost limits its further development. Therefore, we propose a low-cost, low-reflectivity graphite surface microstructure processing method based on picosecond laser. The effects of laser processing parameters on the micro-morphology, reflectivity and hydrophilicity of graphite surface are systematically studied through experiments. The results show that the reflectance of graphite samples with microstructured surfaces is significantly reduced after laser processing. In addition, the contact angle of graphite samples is effectively regulated, and the generation of graphene oxide on the surface of graphite samples after processing is verified. Using ultraviolet picosecond laser prepare microstructures on the graphite surface has the advantages of high efficiency, controllability and low cost, and provides technical support for its potential application in the preparation of surface functional components.

A three-mode non-mode selective photonic lantern (PL) with mode conversion and lossless transmission characteristic is used to achieve coherent beam combining of a diode laser at 976 nm. Compared with the conventional spatial aperture coherent beam combining of diode lasers, the proposed beam combining field does not produce side flaps and has high beam quality. By simulating the beam combining characteristics of the PL and building a complete beam combining experimental system, final 976 nm diode laser fundamental mode output power reached 99.7 mW with a conversion efficiency of 33.2%. The experimental results show that this beam combining system achieves mode conversion and enables the diode laser to output in fundamental mode, demonstrating a promising method for coherent beam combining of diode lasers.

To improve the wear resistance of ductile iron, TiC-Ni25 metal composite coatings are prepared by laser fusion coating using insitu generation and direct TiC addition. The effects of different Ti additions on the microstructure, microhardness and friction and wear properties of TiC-Ni25 composite coatings at 25 ℃, 200 ℃ and 400 ℃ are respectively investigated. The results show that Ti, which has strong thermal conductivity and promotes graphitization, reduces the generation of lysite in the bonding area between the composite coating and the matrix. And Ti, which is a strong carbide forming element, also promotes the in situ generation of TiC, which plays a role for combination of fine grain strengthening, intergranular strengthening and diffusion strengthening in the coating. The addition of Ti improves the wear resistance of the coating, controlls the porosity and cracks defects of the composite coating. Due to the competition between the hardness enhancement of TiC generated insitu and the toughening effect of enriched Ti, the microhardness of the 5%Ti-10%TiC-Ni composite coating is higher than that of 2%Ti-10%TiC-Ni and 8%Ti-10%TiC-Ni coatings. The friction and wear properties of the 5%Ti-10%TiC-Ni composite coating are excellent at above temperatures because of the formation of dense oxide film, which strengthens the protection of the wear area. The increases in friction coefficient, wear volume and wear rate of the composite coatings at 200 ℃ are due to the formation of rough oxide film, which reduces the wear resistance. The main wear mechanisms of the composite coatings are abrasive wear and slight adhesive wear at 25 ℃, and oxidation wear, fatigue wear and adhesive wear at 200 ℃ and 400 ℃.

In this study, we investigate the influence of the forming process on the types, sizes, and quantities of internal defects in a GH3536 alloy fabricated via laser selective melting. We test the microstructure, density, and defect quantity, along with the defect type, size distribution, and quantity of the alloy. The research shows that a change in the process parameters gradually increases the energy density, with the density of the formed parts gradually increasing before stabilizing. The sample is uniform and dense without defects within 79.17?92.59 J/mm3 of the energy density. With the gradual increase or decrease in the energy density, the internal defects of the sample are mainly pore-type defects with a pore size <0.1 mm. When the energy density ≤48.87 J/mm3, non-fusion and micro cracks primarily constitute the internal defects of the sample.

Laser powder bed fusion (LPBF) technology is one of the most widely used forming technologies in the field of metal additive manufacturing because of its high forming accuracy, low surface roughness, and excellent performance of the formed parts. In this paper, we review the factors influencing powder packing density in LPBF technology, which is a key part of LPBF technology. First, the methods of powder bed quality characterization and evaluation, such as image analysis, X-ray in-situ monitoring, and sampling method, are summarized. On this basis, the influence of powder particle size, powder morphology, powder preparation method, powder recycling, and powder recoating process parameters on the powder bed packing density is described from powder characteristics and powder recoating process, respectively. Among them, the particle size distribution and morphology of the powder are the key factors affecting the powder packing density, and the wider single-peak distribution and the bimodal distribution of coarse and fine particles are favorable to improve the powder packing density; the closer the powder morphology is to spherical shape, the better the powder flowability is, which is favorable to improve the powder spreading homogeneity. The powder packing density and spreading homogeneity together will improve the powder bed packing density and the density of formed samples. The change of powder recoating process conditions can influence the powder spreading quality and packing density, among which controlling reasonable recoating speed, choosing roller type scraper, and increasing the roughness of substrate will further improve the powder bed packing density. Finally, this paper presents the prospect of methods and techniques to further improve the powder bed density.

The immunity of topological states against backscattering and structural defects provides them with a unique advantage in the exploration and design of high-precision low-loss optical devices. However, the operating bandwidth of the topological states in certain photonic structures is difficult to actively tune and flexibly reconfigure. In this study, we propose a valley topological photonic crystal (TPC) comprising two inverse honeycomb photonic crystals, consisting of hexagonal silicon and Ge2Sb2Te5 (GST) rods. When GST transitions from the amorphous phase to the crystalline phase, the edge band of the TPC appears as a significant redshift and is inversed from a"∪"to an"∩"shape with topological phase transition, which enables active tuning of the operating bandwidth and propagation direction of topological edge states. Both the topological edge and corner states in a triangular structure constructed using TPCs can be simultaneously adjusted and reconfigured via GST phase transition, along with a change in the group number of corner states. Using the adjustability of topological edge states and electromagnetic coupling between two different topological bearded interfaces, we develop a multichannel optical router with a high tuning degree of freedom, where channels can be actively reconfigured and their on/off states can be freely switched. Our study provides a strategy for the active regulation of topological states and may be beneficial for the development of reconfigurable topological optical devices.

The use of light-induced micro-motors or micro-propellers, showcasing non-contact and non-damaging characteristics, is garnering increased attention in biomedical, micro-machine, and environmental fields. The High-order Poincaré (HOP) beam, as a vector beam, provides a controllable driving force with adjustable orbital angular momentum and spin angular momentum. In this study, we present the spin of a self-assembled micro-propeller structure propelled by the HOP beam, enabling flexible control over rotation velocity and direction. Our findings reveal that modifications to the total angular momentum of the driving beam field or alterations in the micro-propeller blade structure can influence rotation velocity. This research offers an efficient and versatile approach for applications in optical micromanipulation and micromachinery.

Due to low costs and exceptional photoelectric properties, perovskite solar cell materials have attracted great attention. During the fabrication of perovskite light-absorbing layers, dual-source vapor-deposited perovskite thin films suffer from long-standing issues of unknown growth mechanism and inferior crystallization quality, which negatively impacts the optical absorbance and charge carrier lifetimes of perovskite thin films, impeding the performance development of vapor-deposited perovskite solar cell devices. By utilizing bulky organic cations with different radii, this work designs quasi two-dimensional perovskite materials, and apply them as buffering templates at the perovskite/hole transport layer interfaces, thus manipulating the crystal growth process of vapor-deposited perovskite grains. The modified crystallization patterns result in vertically grown perovskite grains with columnar shapes, which notably enhances light-absorbing properties and carrier lifetimes of perovskite layers, boosting the power conversion efficiency from 16.21% to 19.55% on perovskite solar cells. The abovementioned results have provided valuable references to the vapor-deposited perovskite films and photovoltaic devices with outstanding optoelectronic performance.

Being an important part of planar heterojunction perovskite solar cells (PSCs), electron transport layer (ETL) plays important roles in enhancing the photovoltaic performance and stability of PSCs. Despite the two most commonly used ETL materials, titanium dioxide (TiO2) and tin oxide (SnO2) all being nanoparticles and fabricated through solution method, TiO2 suffers from low electron mobility, large device hysteresis, weak chemical stability and high-temperature processing. By comparison, SnO2 owns the advantages of excellent optoelectronic properties, greater stability because of its chemical inertness and low-temperature processability. We focus on the stability and interfacial charge extraction in PSCs based on SnO2 ETL. First, physical properties and advantages of SnO2 are reviewed. Then, starting from the preparation and film formation methods of SnO2 (e.g. chemical bath deposition, solution spin-coating, etc.), we further discuss the bulk and surface defects of SnO2. Finally, targeting the defect profiles of SnO2 ETL, we emphasize regulatory approaches to enhance the device stability and carrier extraction in PSCs based on interfacial passivation, bulk doping and double-ETL structures. This review article contributes to the further advancements of device performance and stability of PSCs, and provides insights for the practical application of this emerging photovoltaic technology.

We present a theoretical study of the one-dimensional modulational instability of a broad optical beam propagating in a biased photorefractive crystal with both linear and quadratic electro-optic effects (Kerr effect) under steady-state conditions. One-dimensional modulational instability growth rates are obtained by treating the space-charge field equation globally and locally. Both theoretical reasoning and numerical simulation show that both the global and local modulational instability gains are governed simultaneously by the strength and the polarity of external bias field and by the ratio of the intensity of the broad beam to that of the dark irradiance. Under a strong bias field, the results obtained using these two methods are in good agreement in the low spatial frequency regime. Moreover, the instability growth rate increases with the bias field, and the maximum instability growth occurs when ratio of light intensity to dark irradiance is 0.88.

Biological compound eyes have excellent optical properties, including large field of view, small size, no aberrations, and sensitivity to moving objects. Sensitivity to moving objects is crucial for flying insects that chase small, fast-moving targets. Inspired by the sensitivity of compound eyes possessed by insects to moving objects, we prepared a single-layer bionic compound eye with five ommatidia, each consisting of a Fresnel lens. Using femtosecond laser two-photon polymerization processing technology and soft lithography technology, a flexible bionic compound eye with high accuracy and repeatability was prepared. Experimental results show that the prepared bionic compound eye could obtain high-quality images and be used to track moving targets.

A high-flat broadband optical frequency comb (OFC) signal generation scheme is proposed, and the mechanism and simulation analysis of the signal generation mechanism and method of high-flat and wideband electro-optical comb are carried out. In the simulation analysis, the dual-drive Mach-Zehnder modulator is used to generate the optical frequency comb signal, the phase modulator is used to further increase the number of comb lines, and finally the flatness is improved by jointly optimizing the drive signal power and DC bias voltage of the Mach-Zehnder modulator. The simulation results show that the scheme can generate a broadband comb signal with a bandwidth of 1.08 THz, with a tone-to-noise ratio of 60 dB and a flatness of 0.5 dB. The proposed scheme is applied to the optical carrier terahertz communication system, and the transmission performance of single-channel and multi-channel 16th-order quadrature amplitude modulation (16QAM) terahertz signals in the case of back-to-back (BTB) or 10 km optical fiber transmission is verified by simulation. The results show that the bit error rate in each of the above cases is lower than the threshold of forward error correction code.

High-resolution imaging in space cameras requires a long focal length, leading to increased distance between the primary and secondary mirrors. Consequently, this results in a larger camera volume and inefficient space utilization. To decrease the launch cost and envelope size of the space camera during launch, a high-precision, repeatable secondary mirror deployment mechanism is designed based on the four-link space structure for the coaxial three-mirror optical system. The mechanism's error was analyzed, and finite element analysis was conducted to evaluate its reliability. Additionally, a repeatability test plan was devised to ensure the mechanism's consistency. Following the folding of the secondary mirror deployment mechanism, the optical axis direction length of the space camera is reduced from 875 mm to 324 mm, achieving a 63% compression in volume. In its unfolded state, the mechanism exhibits a fundamental frequency of 96.64 Hz. The maximum deviation in repeated unfolding displacement is measured at 15.61 μm, and the maximum inclination deviation is 16.89″. These results demonstrate the mechanism's effectiveness in minimizing the space camera's volume and meeting the in-orbit requirements, attributable to its locked state fundamental frequency. Furthermore, the mechanism maintains the optical system's repeatability and can accommodate the payload conditions of micro and nano satellites, making it an ideal solution for aerospace applications.

With the development of processing technology and the increasing requirement of spatial resolution, the slit widths of linear zone plate have become increasingly small. For slits with different widths on the linear zone plate, the incident uniform plane wave can excite one or more waveguide modes, resulting in inter-mode dispersion and phase differences. Even if there is only single-mode transmission in the slits, the effective refractive index of the fundamental mode is related to the width of the slit, which leads to phase difference of slits with different widths at the exit. To eliminate these phase differences, we propose an equal-width single-mode slit waveguide linear zone plate, study its focusing effect in the extreme ultraviolet band, and establish the corresponding Gaussian far-field analytical model. Numerical simulations based on finite element software confirm the distribution of the Gaussian mode field of fundamental mode, and a calculation based on the Fresnel diffraction integral further confirms the validity of the far-field analytical model. As one example, we design an equal-width single-mode slit waveguide linear zone plate and calculate its normalized one-dimensional light field distribution in the focal plane.

A novel rigid support structure is proposed in this paper to solve the contradiction between thermal stability and structural stiffness in small- and medium-aperture space mirrors assembled using traditional flexible supports. Additionally, a high-precision secondary mirror assembly with a clear aperture of ?214 mm is developed for a high-resolution space camera. The combination of a mirror body, cone, support cylinder, and rigid base plate is adopted to realize heat dissipation by extending and optimizing the transmission path of the thermal stress within the assembly. The secondary mirror assembly with a rigid support structure weighs 2.6 kg, and the surface accuracy change has a root-mean-square (RMS) value of 2.573 nm in the simulation under the condition of a 4 °C uniform temperature rise. The inclination and displacement of the mirror body subjected to the gravity test are 2.028" and 0.566 μm, respectively, revealing the outstanding advantages of the proposed scheme over traditional flexible support systems. The measured surface accuracy RMS value of the secondary mirror is 0.0181λ (λ=632.8 nm), and the changes in the surface accuracy at 16 and 24 °C do not exceed 0.0025λ. The fundamental frequency of the assembly reaches 502.1 Hz, and the surface accuracy of the secondary mirror remains relatively unchanged after rapid heat cycles and large-scale vibrations. In the assembling tolerance test, the secondary mirror is only slightly deformed under 0.02 mm unevenness. The proposed rigid support structure can significantly improve the working performance of small- and medium-aperture mirrors and has broad application prospects in the optomechanical structural design of remote sensors.

Mode converter, achieving the mode conversion task from fundamental mode to higher-order mode, is a key component for the on-chip multimode transmission and mode division multiplexing transmission. Here, we propose an array of V-shaped silicon mode converter based on the thin film lithium niobate (TFLN) waveguide. The mode conversion structure is consisted of an array of V-shaped silicon, where it is deposited atop the TFLN waveguide. Based on such structure, we conduct detailed structural analyses and optimizations, where the required conversion length is only 11 μm and the central wavelength is 1550 nm for the mode conversion from input TE0 mode to output TE1 mode. The mode conversion efficiency, crosstalk, and insertion loss are 96.8%, -28.6 dB, and 0.78 dB, respectively. We further extend the device structure and obtain the mode conversion from input TE0 mode to output TE2 mode in the same length, where the mode conversion efficiency, crosstalk, and insertion loss are 91.3%, -?14.3 dB, and 1 dB, respectively. If we further extend the device structure, other higher-order modes can also be obtained. We believe the proposed device structure and scheme could benefit the multimode transmission for the TFLN waveguide and boost the development of photonic integrated components and circuits based on the TFLN platform.

The COVID-19 pandemic since 2019 has brought huge impacts and economic losses to the world. AlGaN-based deep-ultraviolet light emitting diode (DUV-LED) as a new and efficient sterilization device has attracted broad research attentions. The transparent electrode covering deep-UV band plays an important role in improving the performance of deep-UV LEDs. Here, we propose a novel core-shell structure Cu@metal nanosilks (Cu@metal NSs) network electrode with high transparency (>90%) to enhance the output power of deep-UV LED. In addition, based on the optimized design of integrated array module of deep-UV LEDs, a 180 mW DUV-LED sterilization device is fabricated. The device shows high inactivation performance for Escherichia coli and Staphylococcus aureus (>99.99%) and for COVID-19 virus (>99.9%). This work provides a novel method for improving the performance of deep-UV LEDs and pushing forward the efficient sterilization applications.

A design and research scheme for a reconfigurable microwave photonic mixer is proposed. The scheme can reconstruct and generate a linear frequency modulation signal, a frequency conversion signal, or a phase shift signal only by changing the driving signal and direct-current bias voltage. The generated linear frequency-modulated signal has three bands, and the bandwidth can be increased to four times at most. Up and down conversion signals can be generated at the same time. The obtained phase shift signal can be continuously tuned at 0?360°. The simulation results show that the scheme can generate linear frequency-modulated signals with a frequency of 11 GHz and a bandwidth of 2 GHz, a frequency of 18 GHz and a bandwidth of 4 GHz, and a frequency of 29 GHz and a bandwidth of 2 GHz. The pulse compression performance is good. It can simultaneously generate an up-conversion signal with a frequency of 32 GHz and a down-conversion signal with a frequency of 8 GHz, and the electric stray suppression ratio is higher than 30 dB. It can also generate a continuously adjustable phase-shift signal with a 0?360° phase, and the power fluctuation is within 0.1 dB. The system has a spurious free dynamic range of 114.1 dB?Hz2/3.

Based on the axial cone mirror and the Rayleigh-Sommerfeld vector diffraction theory, a detailed theoretical analysis of the generation of non-diffracted light and the light field after the generation is carried out. The spatial light field distribution and the on-axis light intensity distribution curve of the two non-diffracted beams are simulated by numerical simulation, and based on the processing technology of the conical mirror, the light field analysis of the conical angle of the conical mirror and the beam emitted from the first and second axis conical mirrors are carried out. The results show that when the conical angle of the first-axis conical mirror is smaller than that of the second-axis conical mirror, the light intensity of the outgoing beam in the interference coincidence region is a coupled superposition of the two parts of the light field, and a new non-diffracted beam is generated; conversely, the two diffraction-free beams do not coincide and continue to maintain their respective non-diffracted characteristics. Second, the outgoing beams are distributed in concentric rings along a cross-section perpendicular to the transmission direction, and the radius of the concentric rings varies with the transmission distance. In this paper, the intensity distribution, beam distribution and ring diameter of the two non-diffracted beams are tuned both theoretically and numerically, which is an important guideline for the application of non-diffracting beams in large scale space precision measurements and particle micromanipulation.

The spatiotemporal optical vortex has attracted the attention of researchers due to its unique property of carrying transverse orbital angular momentum. Compared with ordinary vortex beams, it can provide additional degrees of freedom and marks a higher level of modulation of light fields. Based on the spatiotemporal-spatial optical vortex with spiral phases in both spatiotemporal and spatial domains, the spatiotemporal-spatiotemporal optical vortex and spatiotemporal-spatiotemporal-spatial optical vortex with spiral phases on two different spatiotemporal planes are numerically simulated. According to the concentric situation between different vortices in the usual spatiotemporal optical vortex, by introducing parameters to modulate the position of the center of the spatiotemporal domain vortex, we have achieved the goal of eccentricity between different vortices and numerically simulated eccentric double vortex and eccentric triple vortex. This research enriches the mode of spatiotemporal optical vortices and provides a theoretical basis for their subsequent research.

In practical applications of high-speed quantum random number generators, using Toeplitz matrices as a post-processing method to extract the randomness of quantum random numbers has become a major technology roadmap. However, Toeplitz matrices are more suitable for hardware calculations than for software calculations and typically require that specialized field programmable gate array (FPGA) circuits be constructed for fast calculations. Based on the quantum random generator of spontaneous emission amplification (ASE), a fast post-processing method based on a simple hash function is proposed. The time complexity of this method is only O(N), which is less than O(NlogN) of a Toeplitz matrix, and compared with another commonly used post-processing method, least significant bit (LSB) post-processing has higher efficiency in random number extraction. The random number calculated by the proposed post-processing method in the experiment passes the randomness test of the national institute of standards and technology (NIST) in the United States.

Evolution process and properties of wave-particle quantum walk (QW) are studied by theoretical calculation and quantum simulator's simulation. Quantum control can contribute to the realization of QWs in quantum wave-particle superposition state with a relative phase between walkers. The post-selection operation is used to realize the continuous transitions of QW from the state of waves with multi-path coherence to the state of particles without coherence in two different ways: coherence and mixing. Due to quantum interference, there are essential differences between coherence and mixing, and their specific features are characterized by position variance. We also demonstrate the coherent wave-particle QWs in the real quantum simulator. When the walker is in the wave-particle coherent state, two completely different properties can be observed simultaneously through one measurement. By adjusting the relative phase in the wave-particle coherent state, the diffusion rate of the walker can be controlled.

To solve existing difficulties in the current laser ranging receiving optical system, that is, the system has sufficient light input while ensuring its low manufacturing cost and light miniaturization, a large relative aperture receiving optical system is analyzed and designed based on the Lagrange invariant theory. The proposed system uses a six-piece Galilean standard spherical mirror, and an avalanche photodiode (APD) with a photosensitive surface diameter of 0.5 mm, to detect an echo light signal. The optimized system consists of an entrance pupil diameter of 50 mm, a relative aperture of 1∶0.9, a total system length of 114.9 mm, and a Lagrange invariant of 125 mrad·mm, which not only obtains sufficient light input, but also addresses low-cost miniaturization requirements. To reduce the stray light influence, the lens hood and barrel fence structure are further designed. Stray light simulation tracking results indicate that the stray light suppression outside the 20°‒85° off axis angle field of view meets the laser ranging system requirements. Under the premise of receiving an optical system with a Lagrange invariant of 125 mrad·mm, the ranging range comprehensively increased by 21 times after adding the optical system. This confirms that the receiving optical system has significant application value.

To address the lidar odometer output trajectory drift problem for a wide range of outdoor building map scenes, a continuous motion prediction algorithm based on the normal distribution transformation is proposed to improve the estimation accuracy of the initial value of point cloud matching under the condition that only lidar is used to construct the odometer. Frame and local map matching is used instead of inter-frame matching. The drift of the motion trajectory is then effectively suppressed. The simulation results are verified by two different scenarios of the Kitti dataset. The improved lidar odometer algorithm reduces the global average errors of two trajectories by 27.93% and 36.66%, while the maximum Z-axis deviation of the two trajectories is reduced by 70.29% and 82.52%. The improved lidar odometer can stably and effectively suppress the motion trajectory drift.

Because ultra-intense ultra-short laser has a large beam in space and a short pulse in time, the spatiotemporal coupling effect, for example the pulse-front distortion, frequently appears, which leads to a separation between the pulse-front and the phase-front in space-time, such as the pulse-front tilt or curvature, and is not conducive to obtaining the expected high focused intensity. However, when this pulse-front distortion (control) is applied in the X-shape optical wave-packet, a new degree of freedom is introduced for freely controlling the group-velocity and the group-acceleration of the optical wave-packet, enabling superluminal, subluminal, accelerating, decelerating, and even dynamically-controllable group velocities. By reviewing the pulse-front distortion (control)'s adverse effects in the ultra-intense ultra-short lasers and its special performances in the X-shape optical wave-packets, we try to provide some reflections on the cross-application of the same optical phenomenon in different research directions.

Optical frequency domain reflectometer (OFDR) is a distributed optical fiber measurement technology. The scanning laser is injected into the optical fiber link, and the position and intensity of the reflection points on the optical fiber link are located by analyzing the Rayleigh backscattering scattering light in the frequency domain. Because of its high precision, high spatial resolution and other characteristics, it is widely used in aerospace, intelligent structure, material processing, optical network monitoring, biomedicine and other high precision measurement and manufacturing fields. In this paper, the basic principle of OFDR is described. The research progress of key technologies to improve OFDR performance is introduced. Finally, the application of OFDR in different fields and to the future development trend are summarized and prospected.

Laser warning technologies are important components of optoelectronic countermeasures that detect and warn regarding hazardous laser signals, effectively improving the survival capabilities of crucial platforms such as aircrafts, ships, and satellites. These technologies also hold considerable importance in related fields. Based on their detection principles, these technologies can be categorized into four types: coherent recognition, spectral recognition, grating diffraction, and imaging technologies. This study summarizes the current development status of laser warning technologies and equipment domestically and globally and includes a comparative analysis of the performance and development trends of various laser warning technologies.

In laser shock processing (LSP) technology, as the driving source and energy source of shock loads, the different selection of laser pulse parameters determines the laser absorption mechanism, energy deposition, and even the plasma explosion behavior. This plays an important role in determining the morphological characteristics of shock loads and the surface strengthening effect of materials. This paper provides a review of the mechanisms and influencing laws of various laser parameters involved in LSP technology in laser driven shock effects, as well as the current research and cognitive status in process allocation. The importance of laser time profile in plasma explosion behavior and shock loading characteristics is reviewed, as well as the current status that Gaussian-like profiles that output from Q-switched laser is commonly used in LSP. It also points out that optimizing the laser time profile can improve the conversion efficiency of laser energy to mechanical energy. And it is possible that shock load characteristics can be accurately manipulated by adjusting laser time profiles.

The output beam of the laser resonator is Gaussian, which makes it often unable to be used directly. It is necessary to improve the uniformity through beam shaping to meet the application requirements. Starting from the characteristics of optical system, this paper summarizes three main laser beam shaping technologies, including aperture method, field mapper method, and multi-aperture beam focusing method, respectively introduces the basic principle, application range, and main realization methods of three laser beam shaping technologies, and expounds the typical application and research progress of different laser beam shaping methods. Finally, the current problems and future development of laser beam shaping technology are comprehensively discussed. This review has certain reference significance for the research of laser beam shaping technology.

The safety hazard and economic losses caused by marine corrosion have posed major challenges in shipping. With the introduction of relevant laws and regulations that require the shipping industry to improve the cleaning needs of ships and monitor their corroded parts, the issues of low efficiency, low precision, varying degrees of substrate damage, chemical pollution, resource waste, and occupational hazards of traditional rust removal have become prominent. Laser derusting technology is a noncontact green derusting method with the advantages of high efficiency, low costs, and automation. This paper introduces the research status of laser rust removal techniques and describes the typical laser rust removal methods and mechanisms, the combined application of laser derusting, and other related technologies. The development prospects of laser derusting technology in shipping is presented. The findings afford a reference for the future application of laser derusting technology in ships.

Usually, lasers can be used for speech signal detection in non-contact and long-distance scenarios. Consequently, the remote laser speech detection technology has broad application prospects in laser interception, multi-mode monitoring, intrusion detection, search and rescue operations, laser microphones, and other fields. In this paper, we review research advances in the remote laser speech signal detection technology from the perspectives of remote laser vibration detection systems and detected signal analysis and processing methods; moreover, we expound the future development prospects of this technology.

To explore the scattering characteristics of aerosol particles in the near infrared band, the optical scattering characteristics of two hypothetical structures having mixed core-shell particles and the same aerosol particles in black carbon and sulfate aerosols are investigated by using discrete dipole approximation. A core-shell particle model with black carbon as the core and ammonium sulfate as the shell is constructed to simulate the extinction efficiency factor, scattering efficiency factor, absorption efficiency factor, asymmetry factor, and single scattering albedo of the particles at several incident wavelengths (875, 1020, 1640, and 2000 nm) in specific incident directions with varied effective particle sizes. The numerical results show that the extinction, scattering, and absorption efficiency factors of mononuclear shell particle, two-core cluster particle, and three-core cluster particle initially increase and then decrease with an increasing effective particle size at the same incident wavelength. In addition, the differences in the scattering and extinction efficiency factors of the three particles are less than 10%. With an increase in the number of nuclear particles, the radius of the particle structure increases, and the peak of the efficiency factor shifts backward. At the four different wavelengths, the asymmetry factor of the multi-nucleated cluster particles is 0.1777, 0.1960, 0.2900, and 0.3131 larger than that of the mononuclear shell particles on average, and the average difference between the asymmetry factors of the two types of multi-nucleated particles is 0.096. At the same effective particle size, the single scattering albedo of mononuclear shell particles is higher than that of multi-core particles; the larger the wavelength, the more distinct is the difference. The results are useful for further analyses of the optical scattering characteristics of complex atmospheric aerosol particles and monitoring of pollutants and climate.

One of the benefits of using terahertz (THz) spectra in characterizing weak interactions is that their anharmonicity can help us to understand the macroscopic properties of crystals. In this study, 2,6-diamino-3,5-dinitropyrazine (ANPZ) was adopted to analyze the anharmonic mechanism of terahertz spectra. First, the temperature-induced anharmonicity was obtained from the THz spectral measurement under heating. Next, density functional theory was used to identify the vibration properties of each absorption. Vibration mode decomposition was then employed to deeply analyze the origins of these anharmonic differences. The results show that the softening of the special intermolecular hydrogen bonding is responsible for the strong anharmonicity. Furthermore, the displacement properties of the atomic temperature factor calculated based on phonon and quasi-simple harmonic approximations also verify the above conclusion. The present study demonstrates that THz spectroscopy can provide insight into the response of hydrogen bonding under heating and can be used as a scientific analysis method for understanding the macroscopic properties of crystals.

In order to satisfy the requirements of information encryption security in the information era, this paper presents a method of information encryption based on laser-induced breakdown spectroscopy (LIBS) technology. The information to be encrypted was written on white paper with an aqueous solution prepared from zinc gluconate tablets and deionized water. By analyzing the LIBS spectra of white paper and of white paper coated with aqueous zinc gluconate solution, the spectral lines of Zn I at 328.23 nm, 472.22 nm, and 481.05 nm were used to decrypt the information. The LIBS spectra of different positions on the white paper containing the encrypted information were obtained by scanning, and the contrast of the spatial distribution of spectral intensity was improved by baseline correction, normalization, and spectral superposition, allowing the encrypted information to be interpreted more clearly and completely. The experimental results show that this method achieves efficient extraction of hidden information with zinc gluconate tablets commonly used in daily life, and has the advantages of high security, low cost, and convenient production. It provides a new idea for LIBS in the field of information encryption, and has value for certain potential applications.

Microstructure and mechanical properties of heat-resistant steel will deteriorate during the service process. The real-time monitoring of the aging state is of great significance for safe operation and production. In this study, a portable laser-induced breakdown spectroscopy (LIBS) device is used to quickly diagnose the aging grade of T91 steel, while the obtained spectral features are dimensionally reduced and the modeling method is optimized. Principal component analysis (PCA) and linear discriminant analysis (LDA) are used to optimize and simplify the spectral features. Finally, after dimensionality reduction, the data are used to evaluate the aging grade model based on the K-nearest neighbor and the support vector machine (SVM) algorithms. Further, the influence of key parameter selection on the model performance is studied. The results show that the spectral data reduced by LDA can achieve a better clustering distribution and improve the accuracy of the evaluation model. In addition, the LDA-SVM model can achieve 94.58% accuracy, which is the highest among all the mentioned aging grade evaluation models. The result demonstrates that the modeling method can efficiently realize the aging grade evaluation of T91 steel based on portable LIBS.

To investigate the variation in indoor carbon dioxide (CO2) volume fractions and their relationship with human activities, this study designs an open-path tunable diode laser absorption spectroscopy (TDLAS) sensing system to monitor indoor CO2 volume fractions. A distributed feedback (DFB) laser with a central wavelength of 2004 nm is employed as the excitation light source to measure the R(16) characteristic absorption line of carbon dioxide. The Levenberg-Marquardt method of nonlinear least squares fitting is employed to fit the measured spectra, allowing for volume fraction measurements without requiring calibration. Comparative measurements with a commercial XENSIVTM PAS CO2 sensor yield a high correlation (R2=0.89). The results indicate that the daily average indoor CO2 volume fraction is 4.63×10-4, slightly surpassing outdoor levels, whereas the fluctuation range of indoor CO2 volume fraction within a day is 3.86×10-4?5.66×10-4. Indoor CO2 volume fraction is volume fractions influenced by ventilation and indoor human activities, and the daily volume fraction trends are highly correlated with working hours. At a personnel density of 0.005 persons/m3, the growth rate of CO2 volume fraction is measured at 2.3×10-5 h-1. Therefore, timely ventilation is recommended for crowded indoor environments to prevent elevated CO2 volume fractions that may cause discomfort.

Recently, tunneling delay time in attosecond experiments leads to discussions about the nonadiabaticity in tunneling process. Under strong field condition, the tunneling delay time usually can be predicted by Keldysh parameter. However, this prediction will fail when we use a few-cycle orthogonal polarized two-color laser field with an envelope. At this time, the initial momentum of photoelectron and the energy consumed in the tunneling process are two important factors that affect the tunneling delay time. Therefore, we find the relationship between these two factors with ionization probability under the above-mentioned laser field. By changing the field intensity ratio and phase difference of the orthogonal polarized two-color lasers, their influence on the tunneling delay time is identified separately, meanwhile, the regulation of tunneling delay time is achieved. Finally, we find that the energy consumed in the tunneling process is a dominant factor influencing the tunneling delay time. These findings contribute to the quantitative analysis of non-adiabatic tunneling delay time and provide new ideas for regulating the ultrafast non-adiabatic tunneling process.