Abstract:This review introduces typical fractal structures and related control methods present in lasers, such as soliton fractals in single?pass optical fibers, fractals in vector soliton collisions, fractals in spin wave solitons, and fractals in breather lasers. It elucidates the characteristics of fractal lasers in mode?locked lasers, including high spectral density, strong anti?interference capabilities, high tuning precision, and the ability to achieve high?resolution femtosecond fiber combs. The paper discusses the issue of enhancing the resolution of femtosecond fiber combs, pointing out that using devil's staircase and Farey tree fractal structures in breather lasers, combined with intelligent tuning methods, can improve the detection resolution of femtosecond fiber combs. It forecasts the development directions of breather fractal combs in fields such as molecular spectroscopy and arbitrary optical wave synthesis. The paper suggests that by developing high?precision optical frequency domain locking technology, time?frequency phase holographic tracking detection technology, fractal spectrum correlation and phase noise analysis technology, and optimizing theoretical models, it is expected to further suppress comb noise and break through the spectral density limits.

Abstract:In this paper, the basic principle of luminescence thermometry and the composition of typical systems are introduced, with discussion on the measurement errors and uncertainty evaluation models of luminescence thermometry. The importance of measurement error analysis and measurement uncertainty evaluation in the research and application of luminescence thermometer is pointed out. In the analysis of measurement errors, it is crucial to comprehensively consider the influence of internal device parameters and the measurement environment on luminescence thermometry parameters, such as luminescence lifetime and intensity ratio. It can significantly minimize systematic errors and enhance the accuracy of temperature measurement to optimize the excitation light source, phosphors, detectors, data acquisition, and data processing schemes, along with to conduct thorough environmental factor analysis and calibration. Furthermore, to investigate the physical mechanisms that cause variations in the emission characteristics of phosphor due to factors other than temperature can lay a theoretical foundation for developing more adaptable luminescence thermometry materials. In the evaluation of measurement uncertainty, the uncertainty in temperature measurement based on luminescence lifetime and intensity ratio can be described using mathematical models. This quantified temperature measurement uncertainty serves as a basis for guiding the optimization and application of high?precision luminescence thermometry systems.

Abstract:In this paper, the reasons for low energy conversion efficiency of soliton microcomb pump are analyzed, and several proposed technical schemes to improve the pump light energy conversion efficiency of soliton microcombs are introduced, including pump energy circulation storage structure of normal?anomalous dispersion double?cavity coupled structure, super?mode resonance splitting structure of master?auxiliary microring coupled?cavity structure, pump feedback waveguide coupled microcavity interference structure, etc. The advantages and disadvantages of each scheme are analyzed. On this basis, the optimal design of the pump feedback waveguide coupling cavity is given, and the simulation result shows that the pump light conversion efficiency of the single soliton micro comb can exceed 25%. At the end of this paper, the low energy consumption generation schemes of soliton microcombs are summarized and prospected, providing theoretical references for the development and application of techniques to improve the pump energy conversion efficiency of microcavity soliton optical frequency combs.

Abstract:This paper reviews the latest developments and applications of optical techniques for measurements in scramjet combustor. Three categories of measurement methods are summarized: one?dimensional method, two?dimensional method and three?dimensional method. One?dimensional method can measure the combustion species concentration and temperature at a point or along a line in the combustion chamber, which is an important means to study the characteristics of combustion chemical reactions. Two?dimensional method can realize the planar measurement of flame structure or flow field information, and is an important approach to study the mixing of fuel and air, flame propagation, and the interaction between flame and turbulence, vortex and shock wave. The three?dimensional method is an important extension of the measurement ability of the two?dimensional method. It can overcome the line?of?sight limitation of the two?dimensional method, and realize the three?dimensional measurement of the combustion field. It is pointed out that endoscopy technology will be an important approach to meet the needs of optical testing in realistic combustion chamber. This paper summarizes the major problems encountered in the application of optical measurement in scramjet combustion chamber. Possible methods to improve the maturity of optical measurement in scramjet combustion chamber is prospected.

Abstract:The structural design and material selection of the piezoelectric layer, backing layer, matching layer, encapsulation layer, and interconnecting electrodes of flexible wearable piezoelectric ultrasound transducers are introduced, the advantages of the simulation design of the transducers using finite element analysis (FEA) technology are discussed, and key technologies in the transducers fabrication, such as electrode patterning, are described. The applications of this type of sensors in the fields of deep tissue imaging, haemodynamic monitoring, promoting the recovery of bone damage, and assisting transdermal drug delivery are analysed. The development direction of the sensors is outlooked, and it is pointed out that in the future, the measurement accuracy, safety and integration degree of flexible wearable piezoelectric ultrasound sensors can be further improved through the application of high?performance signal processing technology, improvement of ultrasound detection and imaging algorithm, and optimisation of the sensor structural design scheme, etc., so as to promote the marketable and industrial development of this kind of sensors.

Abstract:This paper introduces the principle, application and development status of the strain field measurement system based on Digital Image Correlation (DIC), expounds the necessity of calibrating the system, and introduces the principles of representative calibration methods for DIC strain field measurement systems, such as four point bending calibration method, uniaxial tension calibration method, vertical loading calibration method and speckle transformation calibration method. The calibration dimension, calibration range, device cost, device complexity, metrological traceability and measurement uncertainty of various calibration methods are discussed, and the advantages and disadvantages of each calibration technology are compared and analyzed. It is pointed out that the accuracy of existing calibration methods can be improved by improving sensor performance, optimizing the measurement optical path, and enhancing the speckle quality. The development direction of calibration technology for strain field measurement systems based on DIC is discussed, and it is pointed out that future research should focus on the reliable generation and reproduction of large deformation fields, three?dimensional visualization of speckle patterns, and organic fusion of multiple calibration data to further broaden the scope of application of strain field calibration and effectively reduce the uncertainty in the measurement process.

Abstract:In order to solve the problem of non?destructive, online, and in?service quantitative monitoring / testing of Brinell hardness of alloy steel component, by building and using an advanced critical refractive longitudinal wave parameter testing device, we have carried out experiments on quantitatively evaluating the near surface Brinell hardness of alloy steel using ultrasonic critical refracted longitudinal waves, measured the critical refracted longitudinal wave propagation characteristic parameters in alloy steel calibration specimens, and calculated the detection parameters required for evaluating Brinell hardness, namely acoustic velocity and attenuation coefficient. In the experiment, we altered the front edges distance between the receiving and transmitting probes and the calibrating specimen microstructure, studied the influence of above changes on the ultrasonic propagation characteristic parameters, confirmed the sensitive detecting parameter for evaluating alloy steel calibration specimen Brinell hardness, and finally established the calibration mapping relationship models between the near surface Brinell hardness of 45^# steel calibration specimens and the critical refractive longitudinal wave characteristic parameters, verified its hardness prediction accuracy. The test result shows that the wave detection parameters are different in sensitivity to the calibrated specimen Brinell hardness, there is a strong correlation relationship between the acoustic velocity and the Brinell hardness, and the error of the establishing Brinell hardness prediction model is less than 10%. The attenuation coefficient cannot be used to evaluate the near surface Brinell hardness of 45^# steel specimens. This study provides some reference for evaluating the Brinell hardness of alloy steel components by ultrasonic non?destructive testing methods.

Abstract:To improve the response performance of magneto electric vibration sensors in the low frequency range, a low?frequency extension method for magneto electric vibration sensors based on hysteresis compensation is proposed. Firstly, the working principle and mathematical model of the magneto electric vibration sensor were analyzed to identify the key parameters that affect the low?frequency measurement performance of the sensor. Then a second?order hysteresis compensation circuit was designed, a low?frequency compensation filtering link was introduced to optimize the transfer functions of input and output, and MATLAB software was used for simulation verification. Finally, a vibration comparison testing system was established for experimental verification. The results showed that the low?frequency extension method of magneto electric vibration sensor based on hysteresis compensation can extend the measurement bandwidth of a magneto electric vibration sensor with a natural frequency of 2.02 Hz to 0.202 Hz, verifying the feasibility of this method and providing important technical support for promoting the application of small magneto electric vibration sensors in low?frequency measurement scenarios.

Abstract:Under the background of domestic scientific instruments, in order to change the situation that the optically detected magnetic?state?selection cesium atomic clock still depends on imported lasers, three domestic distributed?feedback laser (DFB?LD) tubes were applied to the optically detected magnetic?state?selection cesium atomic clock, and the heterodyne beat?note measurement were conducted. In addition, the differences between these lasers and TOPTICA Photonics DFB?LD were analyzed. The experiment results show that the linewidth of the domestic laser is 1.999 MHz ± 6 kHz, and its frequency stability is 1 × 10^-11@100 s; the domestic lasers can achieve the standard specification (1.45 × 10^-12@100 s) on the domestic cesium beam tube, which provides ideas and references for further improving the performance of domestic lasers. Narrowing the domestic laser linewidth will be required in the future to achieve higher specifications of the compact cesium beam clock.

Abstract:This paper introduces the digital transformation status and achievements of domestic and foreign aviation maintenance enterprises under the wave of digitalization, analyzes the elements and organization of testing and metrology business in aircraft operation and maintenance, proposes a digital construction method for testing and metrology business, including resource digitization, data digitization, process digitization, and signature digitization, around the goal of improving maintenance work quality and efficiency while ensuring safety, and discusses the expected effects , providing ideas for establishing a unified digital standard in the civil aviation maintenance field.

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