Abstract:

Abstract:

Abstract:

Abstract:This paper introduces the current development status of high?performance cold atomic clocks serving as frequency standards，elaborates on the fundamental principles, performance specifications, applications in metrology and other fields, and development trends of fountain clocks and optical clocks. The analysis focuses on the impact of atomic clock technology advancements on the redefinition of the "second", explores the evolutionary pathways and current status of the redefinition of the "second". It is pointed out that the performance of atomic clocks can be improved by increasing the coherent interaction time, reducing the atomic temperature, and optimizing the uncertainty evaluation strategy. It is proposed that the uncertainty level of atomic clocks can be further improved and their application scope expanded by implementing integrated space?time measurements, optimizing the evaluation methods for gravitational redshift, and establishing high?level intercontinental remote comparison links.

Abstract:In order to solve the problems of wide linewidth of the vertical cavity surface emitting laser (VCSEL) used in traditional miniature and chip scale coherent population trapping (CPT) atomic clocks, a micro external cavity diode laser (ECDL) for CPT rubidium atomic clocks with a wavelength of 795 nm was designed using a self?developed laser chip and millimeter sized optical components. The laser has a size of less than 1 cm³ and features narrow linewidth and good direct modulation characteristics. Based on this ECDL, a miniature atomic clock with non?VCSEL light source has been achieved for the first time, with a short?term frequency stability of 3.70 × 10^-11@1 s and 1.35 × 10^-12@1 000 s. This is of great significance for the subsequent realization of high?performance miniature or even chip?scale atomic clock products.

Abstract:An integrated system for laser frequency locking of atomic interferometers was developed in order to improve the miniaturization and stability of atomic interferometers. The integrated circuit system is used for frequency stabilized spectral signal acquisition, modulation and demodulation, and ZYNQ is used to complete the digital Proportional Integration Differentiation (PID) function to realize the low?noise and fast locking of the laser frequency. The integrated modem module has a circuit area of only 77 mm × 113 mm, which is capable of meeting the laser locking requirements for use in most alkaline atomic energy stages. Experiments were conducted to verify the performance of the integrated system for laser frequency locking in atomic interferometers, and the results show that: the frequency fluctuation after laser frequency locking is 98.81 kHz@7 h; the re?locking time of the laser frequency is 600 μs@100 MHz; and there is no de?locking in a long?term measurement of 100 h. This system provides a strong support for promoting the application of atomic interferometer in complex environments such as geological research and resource exploration.

Abstract:Cells perceive physical properties such as stiffness, elasticity, and topological structure of the microenvironment through the extracellular matrix, and utilize mechanosensitive proteins to respond to mechanical stimuli, thereby regulating behaviors such as proliferation, differentiation, and migration. Therefore, precise measurement of mechanical forces between cells and the matrix is crucial for studying mechanosensing and signal transduction. To measure the traction forces exerted by tumor cells on the matrix during migration, this study employs Traction Force Microscopy (TFM) technology. By real?time monitoring of the displacement of fluorescent microspheres embedded in the matrix and combining the mechanical properties of the matrix, high?precision traction force measurement at the subcellular scale is achieved using forward and inverse methods. The measurement results showed that tumor cells exerted traction forces of approximately 431.9 Pa in the protrusion regions and 153.9 Pa in the cell body regions during migration on the constructed matrix. This technology, with its advantages of high resolution, non?invasiveness, and real?time in situ detection, provides a new research approach for mechanical measurements at the micro?nano scale.

Abstract:To study the nonlinear impact of calibration errors on the positioning accuracy of a robot's end?effector, a linkage analysis of end?effector pose calibration errors for a six?degree?of?freedom robot was conducted. Using the modified Denavit?Hartenberg model (MDH) constraints, a kinematic parameter model for a six?degree?of?freedom robot was established to analyze the spatial geometric relationships of the end?effector's pose transformation. The sources of robot calibration errors were examined, and the functional relationships between the coordinate systems of the measurement system were derived. Based on this, a calibration error propagation model for the robot's end?effector pose was constructed. A calibration system for a six?degree?of?freedom robot was set up to conduct experiments. Experimental results indicate that the primary sources of calibration error in robotic end?effector positioning include link length errors, joint offset errors, joint twist angle errors, and zero?position errors. The combined calibration error was measured as 2.66 mm, with relative uncertainties in the x, y, and z directions of 0.09%, 0.37% and 0.46% respectively. The research findings provide technical references for achieving precise positioning control of the robot's end?effector.

Abstract:In order to meet the demand for high?precision automatic detection of multiple wafer defects during the manufacturing process of micro light emitting diode (Micro?LED) chips, a large?field?of?view polarisation dual?channel Micro?LED wafer defects automatic optical inspection system has been designed. The system integrates microscopic imaging technology with polarisation imaging technology, thereby enhancing the contrast of Micro?LED wafer defect images and enhancing the detection accuracy. The system utilises infinite conjugate microscopic objectives and barrel lenses, which expand the image area of wafer samples captured in a single exposure and improve the detection efficiency. Experiments have been conducted to verify the performance of the large?field?of?view dual?channel Micro?LED wafer defect optical inspection system, and the results demonstrate that: the system's magnification is 20, the illumination uniformity is up to 91.6%, and the maximum image field?of?view is 33 mm; The modulation transfer function (MTF) curve of the system is close to the diffraction limit at the Nyquist frequency of 31 lp / mm, which can satisfy the object resolving power of 0.8 μm. The system has been shown to enhance the information entropy, edge intensity, standard deviation and average gradient of polarimetric images in comparison to traditional grey?scale images by 25.6%, 24.9%, 33% and 173.3%, respectively. The large?field?of?view dual?channel Micro?LED wafer defect optical inspection system has been demonstrated to capture the characteristic information of different types of defects in real time, with high recognition efficiency, low missed detection rate and other advantages, providing a strong support for the high?precision inspection of Micro?LED wafer production quality.

Abstract:Frequency Scanning Interferometry (FSI) absolute distance measurement technology exhibits significant potential for applications in advanced manufacturing and aerospace technology. To address the issue of significant measurement errors in traditional FSI systems under high?dynamic conditions, this paper proposes an FSI distance measurement method based on electro?optical intensity?phase cascade modulation. Based on the theoretical derivation of the amplification effect of optical path difference variation in traditional FSI systems, a double?sideband FSI distance measurement system with electro?optical intensity?phase cascade modulation was designed. The system employs a single photodetector for photoelectric detection of the frequency?scanning interference signal, and uses all?phase fast Fourier transform (APFFT) to extract the phase information of the interference signal with high precision, enabling the simultaneous high?accuracy measurement of both absolute distance and relative displacement of the target. Simulation results show that the standard deviation of the absolute distance measurement of this method can reach below 10 μm, and the standard deviation of the relative displacement measurement can reach below 10 nm, which effectively verifies the feasibility and accuracy of the proposed method.

Abstract:In order to research high precision and high speed laser measurement technology, this study explores precision ranging using a femtosecond optical frequency comb based on electro-optic sampling timing detection technology. The optical frequency comb ranging system integrates a fiber Sagnac interferometer, electro-optic modulators with dynamic phase bias, non-reciprocal static phase biasing units, and optical pulse time-of-flight detection, offering advantages of high precision and speed. The system achieves a 45 nm single-point ranging uncertainty within a 26 ms integration time. Coupled with a two-dimensional scanning translation stage, it enables precise measurements of step heights on gauge blocks and surface morphology of coins. Additionally, it dynamically detects the diffuse reflections from a metallic film 3 m away influenced by nearby speaker sound waves, faithfully reproducing the played music signals. This study demonstrates the great potential of electro-optic sampling timing detection technology in high precision and high speed distance measurement, playing a significant role in advancing the field of precision ranging.

Abstract:Cavity optomechanical sensors, as a focal point at the intersection of technology and science, are pivotal for improving sensing resolution across diverse applications. This research modulates the intracavity optical field mode volume by adjusting the optical fiber coupling state to achieve controllable optomechanical coupling, leading to a strong coupling lock state. Within a chip?scale optomechanical sensor resonator system constructed from two?dimensional photonic crystals, the study successfully demonstrated the enhancement of mechanical quality factor (Q?factor) and the suppression of system noise through controllable optomechanical coupling. Experimental results indicate that in the strong optomechanical coupling lock state, the mechanical Q?factor is increased by approximately 10 times compared to the weak coupling state, and system noise is significantly reduced by about 26 dB. Moreover, the optomechanical accelerometer sensor, based on this scheme, achieves a sensitivity of 126.58 mV / g under a 6 kHz acceleration drive. This study not only validates the potential of controllable optomechanical coupling in enhancing mechanical Q?factor and reducing system noise, but also offers new perspectives for the design and application of optomechanical systems, significantly advancing the development in photonic and micro?nano mechanical systems.

Abstract:To solve the problems of low precision and poor reliability of traditional contact sensors in the detection of high?voltage cable suspension, a non?contact displacement detection system of high?voltage cable suspension differential mutual inductance is developed by applying the principle of electromagnetic induction and adopting the differential mutual inductance measurement technology through the coordinated work of the transmitting circuit and receiving circuit, which realizes the high?precision detection of the position of the cable core. The transmitting circuit drives the transmitting coil by enhancing the 85 kHz sinusoidal signal, and the receiving circuit converts the received signal into ± 5 V direct voltage signal and 4 ~ 20 mA current signal. To effectively suppress the radiated interference, which is mainly concentrated in the receiving coil and its transmission path, a combination of shielded transmission line and band?pass filter is used to minimize the noise effect. The experimental results show that the best performance of sensor linearity and sensitivity is achieved in the displacement range of ± 30 mm, with linearity up to 97.49% and sensitivity up to 35.93 mV / mm. This system significantly improves the detection accuracy of high?voltage cables, overcomes the limitations of the traditional detection methods, and demonstrates good stability and reliability.