In order to improve the phase measurement sensitivity of photonic optical interferometers in photon loss scenarios, a theoretical study of the sensitivity of photon coincidence measurement under photon loss has been carried out using a typical twin-Fock state as an input of a photonic Mach-Zehnder interferometer. Compared to parity measurement, the analysis shows that the photon coincidence measurement scheme is more robust to photon loss when using photon pairs as input, and the phase measurement sensitivity based on photon coincidence measurement can be very close to the quantum Cramr-Rao bound when the phase is between /4 and /2. The results show that the use of the photon coincidence measurement scheme can help to achieve ultra-high precision phase measurements in real-world environments, thus offering the possibility of breaking through the traditional scattering noise limit.

In order to solve the problems of low detection performance, large number of model parameters and difficult deployment in edge devices of the existing indoor vision aided algorithm, the YOLOv7-tiny network was improved and a new YOLOv7-ghost network model was proposed. Firstly, aiming at the problem of large number of model parameters, ghost bottleneck (GB) was introduced to replace partial pooling operation and efficient layer aggregation network (ELAN) to significantly reduce the number of model parameters. Secondly, by constructing a new high-performance lightweight module (C2f-global attention module), the global and local feature information were comprehensively considered to better capture the context information of nodes. Then, spatial pyramid pooling-fast and ghost bottleneck (SPPF-GB) module were introduced to recombine and compress the features to fuse the feature information of different scales and enhance the expression ability of features. Finally, deformable convolution network (DCN) was introduced in the head part to enhance the expression ability of receptive field, so as to capture more fine-grained target structure and background information around the target. The results show that, the parameters of the improved model decrease by 20.33%, the model size decreases by 18.70%, and mean average accuracy mAP@0.50 and mAP@0.50~0.95 increases by 1.2% and 3.3%, respectively. The network model not only ensures lightweight, but also greatly improves the detection accuracy, which is more conducive to the deployment of indoor scene target detection algorithm.

To achieve online rapid detection of steel wire meter liquid adjustment, filter paper enrichment was used to verify the feasibility of the enrichment method for steel wire meter liquid adjustment. On this basis, the influence of pH value on the detection results of laser induced breakdown spectroscopy (LIBS) technology was studied, and calibration curves were established by matching the pH values of standard samples to invert the Zn element in 7 surface adjustment liquids of a certain steel wire factory. Theoretical analysis and experimental verification were carried out. The results show that when Zn concentration is the same, there is a significant difference in LIBS spectral intensity with the change of pH value. The pH values of different types of steel wire table adjustment liquids cover -0.91~8.95. For samples with different pH values, the correlation coefficients are all above 0.98. The average relative error between the LIBS technology detection and the inductively coupled plasma mass spectrometry detection results of the seven types of adjustment liquids is -13.09%. LIBS technology combined with pH value matching to establish calibration curves can achieve rapid and accurate measurement of Zn element in steel wire surface adjustment solution. This study provides a methodological basis for the application of LIBS technology to the online detection of key elements in surface adjustment liquid during steel wire production.

In order to enhance the absorptivity of stainless steel surface in infrared band, nanosecond fiber laser was used to modify the morphology of stainless steel plate surface. The influences of process parameters on the geometrical dimensions of micro-crater, surface roughness and blackness were investigated systematically. The mechanism of laser enhanced absorptivity of stainless steel surface was obtained, and the method to improve the absorptivity and production efficiency was proposed. The results show that when other process parameters are fixed, the reduction of scanning speed leads to the overlap increase, inducing the depth of the micro-groove and the surface roughness of the sample increase. The mechanism of the absorptivity enhancement of stainless steel surface is the combined effect of laser-induced periodic surface structures (LIPSS) with light trapping effect and oxidation blackening, but the effect of light trapping of the LIPSS is more significant, therefore the absorptivity is proportional to the surface roughness Ra. When the scanning spacing is very small, the complex LIPSS with strong light trapping effect and the oxidation blackening caused by heat accumulation are produced, the surface roughness is very large, 92% absorptivity of infrared wavelength can be achieved. When the scanning spacing is suitable, the edge of the ablated micro-groove is not ablated by the pulse laser of next micro-groove, the sample surface is enough rough, high absorption and productivity can be obtained simultaneously. This research proposes a method to enhance the absorption of the metal surface.

In order to prepare wear-resistant titanium-based coating, a Ti-Al-N wear-resistant titanium-based coating was prepared on TC4 surface by laser cladding. The phase composition, microstructure evolution and hardness of the coating under different laser powers were observed and analyzed, and then the tribological properties of the composite coating in the air environment were analyzed. The results show that the strengthening phase of the coating is mainly composed of Ti2AlN, TiN, TiAl and TixAlly. The diffraction peak intensity of each phase changes with the increase of laser power, and the matrix phase is composed of (-TiAl+2-Ti3Al). The coating is metallurgically bonded to the substrate. With the increase of laser power, the microstructure gradually changes from dispersed columnar crystals to coarse dendrites, but when the laser power was 2.4 kW, the microstructure becomes fine again. The microhardness of the composite coating can reach 2.14 times that of the substrate. In the air friction environment, different samples are mainly abrasive wear, and the matrix wear is serious. The coatings under different laser powers greatly improve the wear resistance of the substrate. The minimum wear rate of the coating was 0.786×10-4 mm3·N-1·min-1, and the matrix was 1.34×10-4 mm3·N-1·min-1. Therefore, the coating performance can be adjusted by controlling the laser power, which provides basic support for the application of laser cladding high wear-resistant titanium-based composite coatings in aerospace and marine equipment.

Raman amplification can realize the distributed amplification of optical signals in optical fiber links, and has excellent amplification performance in terms of high gain and low noise, which is one of the key technologies in long-distance optical fiber communication systems. In recent years, in order to further extend the optical signal transmission distance based on Raman amplification, to reduce the relative intensity noise transfer via Raman amplification, to optimize and predict the performance parameters of Raman amplification system such as gain value, gain bandwidth and flatness, etc., a variety of novel fiber distributed Raman amplification technologies have been developed and applied. The research progress on the novel fiber distributed Raman amplification technology in recent years are reviewed, including high order distributed Raman amplification technology based on ultra-long distance fiber laser, low noise Raman amplification technology based on broadband incoherent pump source and intelligent distributed Raman amplification technology based on machine learning, which can sort out the development trends and improvement directions of fiber optic distributed Raman amplification technology.

In order to compare the application effect of two low altitude wind shear alerting algorithms of combined shear algorithm and the regional divergence algorithm on wind light detection and ranging (LiDAR) in complex wind fields, 15 wind shear cases caused by 3 typical weather processes of convective system, cold front, and momentum down at a typical plateau airport from 2017-12 to 2023-04 were selected for comparative analysis of the effectiveness of the recognition algorithms by using a wind LiDAR radar that is made in China. The results show that the accuracy of the combined shear algorithm and the regional divergence algorithm are 73.3% and 67.7%, respectively. The validity of low-level wind shear alarm obtained by the algorithm can last for more than 10 min. It can be seen that the combined shear algorithm is more advantageous in the identification of small-scale low-level wind shear. However, in the case of convective type and cold front type low-level wind shear with slow wind field change, the recognition rate of the two algorithms is not high. The research results of this paper have a good reference significance for equipment manufacturers to improve the low altitude wind shear alerting algorithm.

Point cloud noise reduction is crucial to the accuracy of light detection and ranging (LiDAR) imaging systems. In order to reduce the noise caused by receiver, multipath effect, external interference and atmospheric disturbances, a radius filtering method based on genetic algorithm was used for noise reduction, which optimized the key parameters of radius filtering (filtering radius and nearest-neighbor thresholds) by genetic algorithm. Validation in simple and complex scenes show that, the algorithm maintains denoising accuracy and point retention in simple scenes while slightly improving noise recall. The noise recall in complex scenes is improved by about 21% over traditional radius filtering and about 16% over statistical filtering, which is useful for point cloud radius filtering. The radius filtering based on genetic algorithm provides a novel and effective method for LiDAR data processing, which is valuable for improving the quality of LiDAR imaging.

Accurate 3-D understory information obtained by terrestrial laser scanning usually requires the registration of multi-station scanning point cloud data. In order to reduce the need for additional equipment or functions when collecting forest laser scanning data, a forest laser scanning data registration method using smartphone positioning and orientation data was proposed. Firstly, initial transformation parameters were calculated based on the positioning and orientation from the smartphone. Then search space was generated from the initial transformation parameters, and different parameters were further evaluated by the proposed two-level objective functions using stem positions to obtain final registration result. During the evaluation process, stem positions were filtered by the distance between two scanner positions. The results of the registration test conducted on six pairs of measuring stations showe that the average rotation angle error 4.3′, horizontal and vertical translation errors obtained are 8.3 mm and 35 mm, respectively. The proposed method can improve the registration accuracy and efficiency and has high stability, and smartphone can provide effective auxiliary information for registration with canopy height (less than 11.5 m).

In order to construct a unidirectional traveling-wave ring resonator or non-planar ring resonator that utilizes the magneto-optical effect of the laser gain medium itself without additional magneto-optical crystals, so as to meet the application requirements of preparing continuous wave single-frequency 1.5 m solid-state lasers with power greater than watts, the Verdet constants of Er, Yb∶YAl3(BO3)4 crystals were experimentally investigated by means of magneto-optical modulation technique combined with balanced detection. The Verdet constants of Er, Yb∶YAl3(BO3)4 crystals at different doped atomic fractions and temperatures were obtained. The results show that the measured Verdet constants of Er, Yb∶YAl3(BO3)4 crystals with different doped atomic fractions of Yb ions, namely 10%, 15% and 25%, are 48.11°/(T·m), 33.05°/(T·m) and 10.88°/(T·m), respectively. When the temperature of Er, Yb∶YAl3(BO3)4 crystal with a Yb3+ doped atomic fractions of 25% is increased from 13 ℃ to 38 ℃, the Verdet constant showes a nonlinear decrease from 11.40°/(T·m) to 10.15°/(T·m). The Verdet constant of the Er, Yb∶YAl3(BO3)4 crystal is comparable with that of the yttrium aluminum garnet crystal. Moreover, the crystal exhibits paramagnetism. The magneto-optic rotation performance of the gain medium can be improved by either employing the low doped crystal or lowering the crystal temperature. This study provides a reference for the construction of continuous wave single frequency solid-state lasers without additional magneto-optical crystals.

For the photoelectric detection technology of music signal, an improved harmonic reconstruction algorithm was proposed to reduce the system noise while retaining the timbre of music. Firstly, the priori signal-to-noise ratio of the signal was calculated, and Wiener filter for noise reduction processing was constructed. Then a comb filter design scheme was proposed to address the characteristic of multiple harmonic components in music signals. After performing the inverse Fourier transform on the power spectrum of the music signal, the number of sampling points within one fundamental period of the music signal was determined. The number of samples was used as the node parameter of the comb filter, and the harmonic enhancement of the music signal was thus accomplished. The noise reduction effect was theoretically analyzed through the calculation of the priori signal-to-noise ratio, and then the noise reduction effect of different noise reduction algorithms was obtained through experimental verification. The results show that the algorithm can perform denoising well. Compared with the traditional harmonic reconstruction algorithm, the performance of reducing the log-spectral distortion of music signal is improved by more than 50% when the signal-to-noise ratio is -5 dB, 0 dB and 5 dB, and the timbre of the music signal can be well preserved. This study provides a reference for timbre analysis and evaluation in performances of different types of musical instruments.

To solve the problem of large overshooting and long time needed for stabilization of fast steering mirror (FSM) under traditional proportion-integration-differentiation (PID) control, adaptive fuzzy algorithm was introduced to optimize the control and improve the control performance. Based on the structure and working principle of the voice coil actuator (VCA) fast steering mirror, a closed-loop control model was constructed. The membership function and domain in the controller were optimized, and the adaptive fuzzy incremental PID controller was implemented through field-programmable gate array (FPGA). Simulations and physical tests were conducted. The results show that the adaptive fuzzy incremental PID controller can achieve “zero overshoot” and “zero oscillation” in the overall closed-loop process. At the same time compared with the traditional PID controller, the time required for system stabilization has been shortened by 17.5%, and the system bandwidth has been increased by 16.7%. This method can effectively improve the control effect of the fast steering mirror and can be applied to other systems requiring high-precision control.

In order to solve the problem of semiconductor laser wavelength drift leading to output wavelength deviation, a dual-loop distributed feedback (DFB) laser two-stage temperature control system was proposed. Based on the internal temperature control system of the semiconductor laser, an external environmental temperature loop control system was introduced to ensure that the laser can operate within a stable temperature range. With an embedded processor as the main controller, a digital proportional-integral-derivative control algorithm was adopted. Combined with pulse width modulation and low-cost H-bridge chips to control the heating and cooling of thermoelectric coolers (TEC), precise control of the laser two-stage temperature was achieved. Temperature stability experiments were carried out by changing the control temperature of the laser while keeping the environmental temperature constant and changing the environmental temperature while keeping the laser operating temperature constant. The results indicate that the temperature control precision of this system can reach up to ±0.03 ℃. Wavelength stability experiments were conducted with a near-infrared DFB laser, and the results showe that the maximum wavelength error of the laser in 120 min is 0.0036 nm. Under constant current conditions, the correlation coefficient between laser output wavelength and temperature is higher than 0.9996. The temperature control system has the characteristics of high precision, low cost and compact size, and has certain application prospects in molecular spectroscopy, gas detection, fiber optics communication, and other fields.

Laser diode were easily affected by temperature, vibration and other external factors during free-running operation, and the frequency stability of the output laser was difficult to meet the technical requirements of the fields such as quantum precision measurement, high-precision spectroscopy and laser communication. In order to obtain output laser with stable frequency, a frequency-stabilized laser diode was designed, which was constructed based on the ultra precision energy level structure of the D2 transition line of 133Cs atoms and the principle of saturated absorption. The atomic transitionline of |62S1/2, F=4〉→|62P3/2, F′=5〉 was taken as the reference standard of the frequency locked loop (FLL). The results show that, the out-put laser frequency was stabilized by feedback control method. The frequency stability is measured to be 3.88×10-12 at the integration time of 1 s, and the lowest frequency stability is 1.70×10-12 at the integration time of 16 s. The long-term frequency fluctuation of 12 h is less than 140 kHz measured from the beat frequency signal. The linewidth is 438.41 kHz@10 s. The responding rms power stability is 6.11×10-4. The volume of the whole device is 9×103 cm3. The combination of saturated absorption spectroscopy and feedback control can significantly reduce the frequency fluctuation of free-running semiconductor lasers. The laser has good performance in some key indicators such as frequency stabilization. It has been miniaturized, which makes it easy to move and maintain. And it operates stably for a long time and is capable of meeting the technical requirements for frequency-locked laser light sources in applications such as quantum measurements.

The emergence of photoacoustic imaging has expanded the application of biomedical imaging technology in cells, tissues, and living organisms to monitor a variety of physiological processes in complex internal environments. Photoacoustic imaging is essentially 3-D imaging, involving three spatial dimensions. By adding time or frequency dimensions, richer tissue information can be obtained, enabling qualitative and quantitative analysis of target morphological structures and functional components. This article reviews the research progress of 4-D (3-D+time or 3-D+spectrum), 5-D (3-D+time+spectrum) photoacoustic imaging technology and photoacoustic spectral unmixing technology. and The current problems were summarized. The clinical application prospects and possible development directions in the future were predicted.

In order to enhance the detection sensitivity of aerosol particle spectrometers, a method that two photodetectors were used to separately detect the side-scattered light of small particles and the forward-scattered light of large particles was employed. A miniaturized high-sensitivity aerosol particle spectrometer based on light scattering was designed and developed. Polystyrene standard microspheres were used to test the signal response of the particle spectrometer. Comparative observations were conducted with similar foreign products for 24 h, showing good concentration correlation and consistent trend between the two instruments during the test period. The results indicate that, the developed aerosol particle spectrometer has a minimum resolution particle size interval of 20 nm, and it is characterized by small size and light weight. This study provides important reference for aerosol detection using small unmanned aerial vehicles.

Broken strand damage of the high-voltage cable may be caused due to environmental problems in use. And the existing detection technology cannot meet the requirements for detecting the broken strand damage of the part of the cable wrapped by the clamp on the high-voltage piezoelectric tower under the electrification condition. In order to solve the existing problems, laser ultrasound, a new non-contact laser ultrasonic detection method was adopted to detect the broken strand damage of a cable. The propagation of laser ultrasonic guided wave in high voltage cable was studied theoretically. The influence of small radius r, large radius R and axial pitch L on the dispersion curve of high voltage cable spiral structure was analyzed. A transient model was established to study the physical problem of laser excitation of ultrasonic guided waves in lossless cables. The amplitude and dispersion characteristics of the basic order modes L(0,1), T(0,1) and F(1,1) of helical structures were analyzed by means of B-scan and 2-D Fourier transform signal analysis. The results show that L(0,1), F(1,1) modes in the frequency range of 0 kHz~100 kHz are the most suitable detection modes when using laser ultrasound to detect high-voltage cables. This result is helpful to the research of non-destructive testing of high voltage cables by non-contact laser ultrasound technology.

The current aircraft inlet pipe leakage monitoring system primarily employs eutectic salt electric superheat detectors as temperature sensing units. A linear array optical fiber sensor probe was investigated for detecting leaks in the aircraft inlet pipe, aiming to overcome the existing technical bottlenecks of the system such as poor electromagnetic compatibility, low measurement accuracy, and slow response time. The fiber grating array parameter design and package structure design were carried out by mathematical modeling and simulation methods, and experimental verification and mathematical analysis were carried out. The research demonstrates that the sensor probe has a certain strain immunity and vibration resistance ability with a temperature sensing accuracy of 0.1 m and positioning accuracy of 1.0 m. A temperature measurement accuracy within ±3 ℃ over a working temperature range from 0 ℃~180 ℃ was achieved. The results of this study provide a new idea for remote distributed and lightweight aircraft bleed air leakage temperature measurement instead of eutectic salt leak detection sensors.

To solve the problem of “kiss bonding” and “weak bonding” which cannot be detected by conventional nondestructive testing technology, a self-designed variable pulse width Nd∶YAG laser was selected. Three surface treatment methods and two kinds of adhesives were used to prepare the bonded structures of 4.68 MPa, 17.69 MPa, 21.35 MPa. The fixed laser parameters were used to verify the bonded structures by laser shock experiment. The results show that when the laser pulse width is 30 ns, spot diameter is 4 mm and laser energy is 8 J, the 3M DP460 adhesive with the tensile strength of 37 MPa does not have spalling damage, while the 3M DP810 adhesive with the tensile strength of 15 MPa has spalling damage. With the increase of laser energy, the interface debonding area of 4.68 MPa bonded structure increases from 12.5 mm2 to 50.0 mm2, while no obvious damage is found in 21.35 MPa bonded structure, indicating that under appropriate laser parameters, laser spalling technology can be used as a non-destructive testing method to effectively detect “weak bonding” and “kiss bonding” at the bonding interface. This study provides a reference for the application of laser spalling technology in the field of interface bonding strength detection of bonded structures.

To achieve a laser capable of functioning in applications such as distance measurement and target designation, two methodologies were primarily utilized: The simulation analysis of the ray transfer matrix for the telescope cavity and the theoretical calculation of steady-state thermal resistance to analyze both the internal heat transfer and surface heat dissipation processes. Through rigorous theoretical examination and empirical validation, a compact solid-state electro-optical Q-switched air-cooled near-fundamental mode laser capable of operating at an ambient temperature of 40 ℃ was successfully developed. Output laser at 1064 nm was characterized by a repetition rate of 10 Hz, a single pulse energy of 100 mJ, a beam quality factor M2 of 1.31, a pulse duration of 10 ns, and a divergence angle of 0.6 mrad. The findings demonstrate that this laser is optimally suited for applications that demand lasers with high single-pulse energy, peak power, and exceptional beam quality, such as in laser ranging and targeting. This advancement holds significant implications for the evolution of laser-based distance measurement and target indication technologies.

In the seam tracking based on structured light vision, strong noise such as arc and spatter generated in the welding process would greatly reduce the visibility of the weld, resulting in tracking failure. In order to solve this problem, a seam tracking algorithm based on the improved kernel correlation filter was proposed to better adapt to the strong noise environment. Firstly, the initial feature points of the weld were obtained. Based on the gray distribution characteristics of the weld laser stripe, the centerline of the weld laser stripe was extracted by Steger algorithm. Then the center line was filtered and derived to obtain the initial feature points of the weld. Finally, the initial feature points of the weld were used as the initial input, and the improved kernel correlation filter was applied to learn and track the weld feature points. The results show that, the average error of the algorithm is 0.305 mm, and the maximum tracking error is 0.479 mm in the case of strong noise interference, which achieves good tracking effect and effectively avoids tracking drift. This study provides a useful reference for high-precision seam tracking.

The refractive index structure constant, as one of the key indicators characterizing atmospheric turbulence intensity, is measured by the temperature pulsation meter. Research on its measurement uncertainty is of significant importance. Based on the principle of the temperature pulsation meter, a tungsten filament with a diameter of 10 m, a resistance value of 90 and a temperature coefficient of variation of 4.5×10-3/K were used as the measuring sensor to obtain the average temperature different coefficient. The measurement uncertainty of refractive index structure constant was derived from an integrated analysis of parameters including pressure, temperature and distance. Experimental data indicates that within the true value range of 10-13 to 10-16 near the ground, the calculated measurement uncertainty remains within 1%, demonstrating its reliability. The result is very effective for improving the measurement resolution of temperature pulsation meter, and it is also a new idea for controlling the measurement uncertainty of temperature pulsation meter.

There are a huge demand for fast and efficient demolition workers in rescue operations. Laser cutting showed great potential because of its characteristics of non-contact, high speed, and high precision. In order to explore the application of laser cutting technology in the rescue and demolition of Q235 steel plate, taking 8 mm and 15 mm thick Q235 steel plate as the research object, the high-power fiber laser was used for long-distance cutting experiment. The theoretical analysis and experiment verified the influence of laser power and cutting speed on the cutting quality. The results show that, for 8 mm thick steel plate, the optimal cutting effect can be obtained when the distance between the laser head and the workpiece is 10 m, the cutting speed is 2.00 mm/s, and the laser power is 10 kW, respectively; for 15 mm thick steel plate, the distance between the laser head and the workpiece is 13 m, the cutting speed is 2.25 mm/s, and the laser power is 13 kW. The hardness test results also reveal the influence of laser power on the hardness of the material after cutting, indicating that laser cutting not only changed the geometry of the material, but also may affect its mechanical properties. This result is helpful for the laser cutting technology in the field of rescue and demolition, and provides optimized process parameters for practical application.

In order to improve the quality and efficiency of laser paint removal, acrylic paint layer was sprayed on the surface of 2024 aluminum alloy and cleaning test was carried out. The surface morphology, element energy spectrum, and roughness of the sample after paint removal were observed and analyzed by orthogonal test method, and the influence degree of each laser parameter on paint removal effect was studied. The best combination of process parameters was obtained by verification test comparison. The results show that, among the five main parameters, the laser power has the most significant influence on the paint removal thickness. When the paint layer can be basically removed by a single scan, the paint removal effect can not be obviously improved by simply increasing the laser power. Under the appropriate combination of parameters, the paint layer of about 200 m on the surface of aluminum alloy can be completely removed without damaging the substrate. This study provides some reference for laser paint removal process.

In order to make the laser power of flexible printed circuit (FPC) board laser drilling equipment in domestic industry real-time monitoring, stable and dynamic adjustment, an embedded power monitoring and automatic control method based on domestic GD32 chip as the core was adopted. Theoretical analysis and experimental verification were carried out. The results show that the mean squared error of the fitted line between the set power of the laser and the actual monitoring power is less than 0.05626, and the laser power fluctuation is less than 2%. The results show that the method is feasible for FPC laser drilling equipment.