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The damage threshold measurement device is an important technical indicator of high-power laser technology, mainly used for the development and testing of high-power laser optical components. The synchronous trigger module serves as a controller for controlling the timing between modules, and is one of the key technologies in the development of damage threshold devices. A synchronous triggering module and method for laser damage threshold measurement device are introduced. A hardware solution based on FPGA as the main control chip has been designed. By setting synchronization trigger parameters through the upper computer control software, the width of each output synchronization signal and the timing between each signal can be controlled, which can greatly improve the accuracy and efficiency of synchronization trigger. Through experimental verification, the adjustment accuracy between synchronous pulse signals is 2ns, and the minimum width of synchronous pulse signals is 10 ns, which meets the needs of laser damage threshold measurement devices.
The damage threshold measurement device is an important technical indicator of high-power laser technology, mainly used for the development and testing of high-power laser optical components. The synchronous trigger module serves as a controller for controlling the timing between modules, and is one of the key technologies in the development of damage threshold devices. A synchronous triggering module and method for laser damage threshold measurement device are introduced. A hardware solution based on FPGA as the main control chip has been designed. By setting synchronization trigger parameters through the upper computer control software, the width of each output synchronization signal and the timing between each signal can be controlled, which can greatly improve the accuracy and efficiency of synchronization trigger. Through experimental verification, the adjustment accuracy between synchronous pulse signals is 2ns, and the minimum width of synchronous pulse signals is 10 ns, which meets the needs of laser damage threshold measurement devices.
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Abstract:
In order to solve the problem that the current beam quality analyzer can only be used to evaluate the beam quality of small caliber and low power lasers, an experimental study on the attenuation and compression technique of high power laser beam quality measurement was carried out. A device for measuring wave aberration and beam quality of the compressed beam laser was built, and an experiment was carried out to determine the influence of the assembly error on beam quality. The experimental results show that with the increase of the field of view, the measurement deviation of 1/3 fold beam reduction module at 1.2° field of view is less than 5%. A polarization splitting device was built and the influence of attenuation components on beam stability was studied. The experimental results show that the stability of the quasi-single-mode laser with random polarization is more susceptible to the depolarization of the attenuated component than that of the multi-mode laser. A high power laser beam quality measuring device with high reflection type and wedge-plate type was built to measure the beam quality of 1 kW quasi-single mode laser. The experimental results show that in the high reflection measuring device, the depolarization occurs when the beam passes through the high reflector, which results in a smaller beam quality measurement result, and the measurement result of the wedge-plate measuring device is closer to the real result.
In order to solve the problem that the current beam quality analyzer can only be used to evaluate the beam quality of small caliber and low power lasers, an experimental study on the attenuation and compression technique of high power laser beam quality measurement was carried out. A device for measuring wave aberration and beam quality of the compressed beam laser was built, and an experiment was carried out to determine the influence of the assembly error on beam quality. The experimental results show that with the increase of the field of view, the measurement deviation of 1/3 fold beam reduction module at 1.2° field of view is less than 5%. A polarization splitting device was built and the influence of attenuation components on beam stability was studied. The experimental results show that the stability of the quasi-single-mode laser with random polarization is more susceptible to the depolarization of the attenuated component than that of the multi-mode laser. A high power laser beam quality measuring device with high reflection type and wedge-plate type was built to measure the beam quality of 1 kW quasi-single mode laser. The experimental results show that in the high reflection measuring device, the depolarization occurs when the beam passes through the high reflector, which results in a smaller beam quality measurement result, and the measurement result of the wedge-plate measuring device is closer to the real result.
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Abstract:
In recent years, with the demand and development of high-power, high-energy laser systems, the anti-laser capability of optical films has become one of the bottlenecks restricting the development of high-quality laser systems. Based on different preparation methods and process parameters, the damage threshold of the film will have an important impact. In this paper, the methods for improving the damage threshold of the film before, during and after plating are briefly introduced, including the film material selection、Membrane system design、solvent cleaning、ion beam cleaning、preparation method、ion beam post-processing、laser pretreatment、etc.
In recent years, with the demand and development of high-power, high-energy laser systems, the anti-laser capability of optical films has become one of the bottlenecks restricting the development of high-quality laser systems. Based on different preparation methods and process parameters, the damage threshold of the film will have an important impact. In this paper, the methods for improving the damage threshold of the film before, during and after plating are briefly introduced, including the film material selection、Membrane system design、solvent cleaning、ion beam cleaning、preparation method、ion beam post-processing、laser pretreatment、etc.
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Abstract:
The laser warning system performs warning positioning by extracting the relevant parameters of incoming laser, and its angle positioning accuracy is directly related to the battlefield survivability. In order to effectively improve the angle positioning accuracy of the laser warning system, this paper proposes an algorithm for high-precision measurement of incoming laser parameters based on the principle of grating diffraction laser warning. Firstly, the laser warning system is calibrated, and the 0-level spot center of the diffraction spot calibration image is accurately extracted by Gaussian fitting. The laser angle of the future attack is fitted with the spot center of the corresponding angle. According to the fitting result, the angle parameters of the incoming laser corresponding to the diffraction image of the spot at any angle are determined. The experimental results show that the azimuth measurement error is better than 0.29°, and the pitch measurement error is better than 0.38°. The algorithm effectively improves the measurement accuracy of the laser warning system.
The laser warning system performs warning positioning by extracting the relevant parameters of incoming laser, and its angle positioning accuracy is directly related to the battlefield survivability. In order to effectively improve the angle positioning accuracy of the laser warning system, this paper proposes an algorithm for high-precision measurement of incoming laser parameters based on the principle of grating diffraction laser warning. Firstly, the laser warning system is calibrated, and the 0-level spot center of the diffraction spot calibration image is accurately extracted by Gaussian fitting. The laser angle of the future attack is fitted with the spot center of the corresponding angle. According to the fitting result, the angle parameters of the incoming laser corresponding to the diffraction image of the spot at any angle are determined. The experimental results show that the azimuth measurement error is better than 0.29°, and the pitch measurement error is better than 0.38°. The algorithm effectively improves the measurement accuracy of the laser warning system.
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Abstract:
Choosing the light source with high uniformity and high stability is the key technology for the radiometric calibration of solar absolute radiometer. The existing light source in the laboratory cannot meet the uniformity and stability at the same time. Therefore, this paper proposes to obtain a highly uniform and stable surface light source through galvanometer scanning. Firstly, the two-dimensional laser scanning mode is established, and the optical system with fast scanning galvanometer and off-axis mirror as the core is designed; Secondly, according to the galvanometer scanning system, the driver is established, the control software is developed, and three scanning paths are designed; Finally, the appropriate scanning path is selected for experimental verification and its uniformity and stability are tested. The experimental results show that the non-uniformity of the scanning spot of the galvanometer is better than ± 1%, the divergence angle is less than ± 0.26°, and the stability of the light source is better than 0.02%. The feasibility of the laser galvanometer scanning light source as the irradiance calibration light source of the absolute radiometer is verified, which provides key technical support and experimental basis for achieving high-precision solar irradiance calibration.
Choosing the light source with high uniformity and high stability is the key technology for the radiometric calibration of solar absolute radiometer. The existing light source in the laboratory cannot meet the uniformity and stability at the same time. Therefore, this paper proposes to obtain a highly uniform and stable surface light source through galvanometer scanning. Firstly, the two-dimensional laser scanning mode is established, and the optical system with fast scanning galvanometer and off-axis mirror as the core is designed; Secondly, according to the galvanometer scanning system, the driver is established, the control software is developed, and three scanning paths are designed; Finally, the appropriate scanning path is selected for experimental verification and its uniformity and stability are tested. The experimental results show that the non-uniformity of the scanning spot of the galvanometer is better than ± 1%, the divergence angle is less than ± 0.26°, and the stability of the light source is better than 0.02%. The feasibility of the laser galvanometer scanning light source as the irradiance calibration light source of the absolute radiometer is verified, which provides key technical support and experimental basis for achieving high-precision solar irradiance calibration.
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Abstract:
In order to solve the problem that the amount of visibility parameters at home and abroad cannot be absolutely traced, we proposed the quantitative value reclaiming method of traceability to the amount of geometry using the working principle, structural characteristics, and environmental conditions. We design a transmitted visibility instrument as the main standard device to calibrate the transmitted visibility instrument effectively, which promotes the development of the visible value to trace the origin system. The main standard device uses precision mechanical processing process, which follows the absolute traceability method of geometric parameter measurement. It can greatly reduce the measurement uncertainty of the transmission rate. The combined traceability chain solves the problem of unable to reproduce and accurately measure the existing technology. In addition, the use of cone shadowing body can avoid the introduction of other sources of uncertainty except rotating factors, which greatly improves the calibration capability of the visibility instrument resolution.
In order to solve the problem that the amount of visibility parameters at home and abroad cannot be absolutely traced, we proposed the quantitative value reclaiming method of traceability to the amount of geometry using the working principle, structural characteristics, and environmental conditions. We design a transmitted visibility instrument as the main standard device to calibrate the transmitted visibility instrument effectively, which promotes the development of the visible value to trace the origin system. The main standard device uses precision mechanical processing process, which follows the absolute traceability method of geometric parameter measurement. It can greatly reduce the measurement uncertainty of the transmission rate. The combined traceability chain solves the problem of unable to reproduce and accurately measure the existing technology. In addition, the use of cone shadowing body can avoid the introduction of other sources of uncertainty except rotating factors, which greatly improves the calibration capability of the visibility instrument resolution.
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Abstract:
In the analysis and design of Nd:YAG Q-switched lasers, researchers usually choose to ignore the influence of laser lower level lifetime on pulse waveform. When the laser pulse width is much larger than the laser lower level lifetime, this approximation generally does not bring much deviation. When the pulse width reaches the nanosecond level, the influence of the lower level lifetime of the Nd:YAG crystal about 30 nanoseconds on the pulse waveform will become very serious. The theoretical analysis model of the influence of Nd:YAG lower level lifetime on the output pulse waveform was established, and the output waveform of the narrow pulse width Q-switched Nd:YAG laser was simulated. The results show that in the case of narrow pulse width laser output, the lifetime of the lower energy level of the laser will lead to the tail peak of the Q-switched pulse after the main peak, and the tail peak energy can reach more than 100 % of the main peak energy. At the same time, the experimental system of Nd:YAG acousto-optic Q-switched laser was established. The Q-switched pulse waveform was measured under the condition of approximate simulation calculation, and the tail peak phenomenon consistent with the simulation results was observed. The correctness of the theoretical model was verified by experiments.
In the analysis and design of Nd:YAG Q-switched lasers, researchers usually choose to ignore the influence of laser lower level lifetime on pulse waveform. When the laser pulse width is much larger than the laser lower level lifetime, this approximation generally does not bring much deviation. When the pulse width reaches the nanosecond level, the influence of the lower level lifetime of the Nd:YAG crystal about 30 nanoseconds on the pulse waveform will become very serious. The theoretical analysis model of the influence of Nd:YAG lower level lifetime on the output pulse waveform was established, and the output waveform of the narrow pulse width Q-switched Nd:YAG laser was simulated. The results show that in the case of narrow pulse width laser output, the lifetime of the lower energy level of the laser will lead to the tail peak of the Q-switched pulse after the main peak, and the tail peak energy can reach more than 100 % of the main peak energy. At the same time, the experimental system of Nd:YAG acousto-optic Q-switched laser was established. The Q-switched pulse waveform was measured under the condition of approximate simulation calculation, and the tail peak phenomenon consistent with the simulation results was observed. The correctness of the theoretical model was verified by experiments.
Design and Implementation of Continuous Zoom Control System Based on Fractional Order PID Controller
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Abstract:
Continuous zoom system is a kind of photoelectric imaging device that can continuously switch the field of view, and continuously detect and identify the target. It has the characteristics of fast and stable. Aiming at its high accuracy and high stability control requirements, a design method of fractional-order PID(proportion integration differentiation) controller based on internal mode control is proposed. The proposed controller has only three tuning parameters which can be obtained from desired gain crossover frequency and phase margin. The proposed fractional-order PID controller outperforms traditional PID controller. The simulation results show that the fractional-order PID has the characteristics of strong anti-interference and robustness. In addition, there is no overshoot and no static error after digital realization. Finally, the digital fractional-order PID is applied to actual continuous zoom system, and the system can obtain clear and stable images, which verifies the effectiveness of the control strategy.
Continuous zoom system is a kind of photoelectric imaging device that can continuously switch the field of view, and continuously detect and identify the target. It has the characteristics of fast and stable. Aiming at its high accuracy and high stability control requirements, a design method of fractional-order PID(proportion integration differentiation) controller based on internal mode control is proposed. The proposed controller has only three tuning parameters which can be obtained from desired gain crossover frequency and phase margin. The proposed fractional-order PID controller outperforms traditional PID controller. The simulation results show that the fractional-order PID has the characteristics of strong anti-interference and robustness. In addition, there is no overshoot and no static error after digital realization. Finally, the digital fractional-order PID is applied to actual continuous zoom system, and the system can obtain clear and stable images, which verifies the effectiveness of the control strategy.
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Abstract:
In order to solve the problems of high cost, large volume, vertical color difference and distortion correction of most existing ultra short focal projection equipment,an ultra-short focal micro projection lens based on DMD chip is designed, and its tolerance analysis and thermal analysis are carried out.The system consists of seven lenses, greatly simplifying the structure and reducing the cost. The F number of the system is 1.7, the focal length is 1.65 mm, the optical length is 79.39 mm, the projection ratio is 0.16, and the system has the characteristics of large aperture, large field of view and miniaturization. The design results show that the MTF of the full field of view is larger than 0.65 at the space cutoff frequency of 93 lp/mm, which is close to the diffraction limit. The vertical color difference of the system is controlled within 1.2 μm, the maximum distortion is −2.17%, and the full-field relative illuminance is greater than 0.95, which satisfies the design requirements.
In order to solve the problems of high cost, large volume, vertical color difference and distortion correction of most existing ultra short focal projection equipment,an ultra-short focal micro projection lens based on DMD chip is designed, and its tolerance analysis and thermal analysis are carried out.The system consists of seven lenses, greatly simplifying the structure and reducing the cost. The F number of the system is 1.7, the focal length is 1.65 mm, the optical length is 79.39 mm, the projection ratio is 0.16, and the system has the characteristics of large aperture, large field of view and miniaturization. The design results show that the MTF of the full field of view is larger than 0.65 at the space cutoff frequency of 93 lp/mm, which is close to the diffraction limit. The vertical color difference of the system is controlled within 1.2 μm, the maximum distortion is −2.17%, and the full-field relative illuminance is greater than 0.95, which satisfies the design requirements.
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Abstract:
Laser particle size analyzer has been widely used in the measurement of particle size distribution in various fields due to its advantages of fast speed and non-contact. However, the relationship between the angular distribution of scattered light and particle size is complex. In order to obtain the consistent relative accuracy under different particle sizes, the measurement range of particle size distribution will be small and cannot meet the requirements of wide distribution particle size measurement. According to the Fresnel principle of Mie scattering approximation, it was proposed to use the catadioptric optical path. The particle scattering signal was divided into two beams by the splitter, and the transmitted as well as reflected scattering signals were collected by two sets of compound lenses and two photodetectors, respectively. The combined signal was inversed to obtain the particle size distribution, thereby improving the range of particle size measurement. Two kinds of standard particles and their mixtures were used in the experiment. The results show that the relative error of the volume median diameter D50 measured by a single standard particle is not greater than 7.9%, and the correct peak distribution can also be obtained for mixed particles.
Laser particle size analyzer has been widely used in the measurement of particle size distribution in various fields due to its advantages of fast speed and non-contact. However, the relationship between the angular distribution of scattered light and particle size is complex. In order to obtain the consistent relative accuracy under different particle sizes, the measurement range of particle size distribution will be small and cannot meet the requirements of wide distribution particle size measurement. According to the Fresnel principle of Mie scattering approximation, it was proposed to use the catadioptric optical path. The particle scattering signal was divided into two beams by the splitter, and the transmitted as well as reflected scattering signals were collected by two sets of compound lenses and two photodetectors, respectively. The combined signal was inversed to obtain the particle size distribution, thereby improving the range of particle size measurement. Two kinds of standard particles and their mixtures were used in the experiment. The results show that the relative error of the volume median diameter D50 measured by a single standard particle is not greater than 7.9%, and the correct peak distribution can also be obtained for mixed particles.
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Abstract:
An inverted 3-FOV Schmidt telescope based on 3-facet mirror is developed, and its key technical problems are studied. Based on the geometric symmetry of the regular triangular pyramid, the relationship between the angle of the visual axis of the three fields of view and the angle of the facet mirror is derived, and a 3-facet mirror is designed to realize the multi-field observation function. The influence of the gravity deformation of the primary mirror of the inverted Schmidt telescope on the image quality is analyzed by the finite element method; The influence of the key parameters of the testing optical path on the processing error of Schmidt corrector is expounded; The stray light of optical system is studied by Monte Carlo method. The whole optical system is tested experimentally, and a 3-facet mirror is actually developed. The included angle between the mirrors is 133.08°, which can observe three fields of view perpendicular to each other at the same time. The test result of the telescope optical system is PV = 0.614 λ, RMS=0.105 λ (λ = 632.8 nm). The system can be used to measure the earth attitude in space, which expands the application of Schmidt telescope.
An inverted 3-FOV Schmidt telescope based on 3-facet mirror is developed, and its key technical problems are studied. Based on the geometric symmetry of the regular triangular pyramid, the relationship between the angle of the visual axis of the three fields of view and the angle of the facet mirror is derived, and a 3-facet mirror is designed to realize the multi-field observation function. The influence of the gravity deformation of the primary mirror of the inverted Schmidt telescope on the image quality is analyzed by the finite element method; The influence of the key parameters of the testing optical path on the processing error of Schmidt corrector is expounded; The stray light of optical system is studied by Monte Carlo method. The whole optical system is tested experimentally, and a 3-facet mirror is actually developed. The included angle between the mirrors is 133.08°, which can observe three fields of view perpendicular to each other at the same time. The test result of the telescope optical system is PV = 0.614 λ, RMS=0.105 λ (λ = 632.8 nm). The system can be used to measure the earth attitude in space, which expands the application of Schmidt telescope.
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Abstract:
In response to the issue of accuracy in measuring the elevation of spatial coordinate points relative to a reference point, a new elevation measurement method based on a physical horizontal reference plane is proposed. By utilising the concepts of laser triangulation and leveraging the geometric features of measuring light pathways, a high-precision elevation measurement system was built. This technique employed a physical horizontal reference. Within a Lambertian scattering light field, an analysis was done to determine the influence of tilt angle modifications on the centroid displacement of laser energy. An related error correction model was built, which permitted tilt angle compensation for elevation data by the use of a tilt angle sensor. Additionally, an autonomously constructed calibration platform was deployed for verification studies targeted at calibrating the suggested elevation measuring system. The findings demonstrate that the proposed combined elevation measuring technique achieves a repeatable measurement error within a fluctuation range of ±20 μm across a 500 mm measurement range. Compared to the single laser displacement sensor measurement methodology, the combined elevation measuring method considerably lowers the fluctuation of measurement errors. It is capable of supporting precise measurements of spatial coordinate points in any orientation and effectively boosting the performance of laser displacement sensors in the area of elevation measurement, consequently giving more genuine and effective measurement results.
In response to the issue of accuracy in measuring the elevation of spatial coordinate points relative to a reference point, a new elevation measurement method based on a physical horizontal reference plane is proposed. By utilising the concepts of laser triangulation and leveraging the geometric features of measuring light pathways, a high-precision elevation measurement system was built. This technique employed a physical horizontal reference. Within a Lambertian scattering light field, an analysis was done to determine the influence of tilt angle modifications on the centroid displacement of laser energy. An related error correction model was built, which permitted tilt angle compensation for elevation data by the use of a tilt angle sensor. Additionally, an autonomously constructed calibration platform was deployed for verification studies targeted at calibrating the suggested elevation measuring system. The findings demonstrate that the proposed combined elevation measuring technique achieves a repeatable measurement error within a fluctuation range of ±20 μm across a 500 mm measurement range. Compared to the single laser displacement sensor measurement methodology, the combined elevation measuring method considerably lowers the fluctuation of measurement errors. It is capable of supporting precise measurements of spatial coordinate points in any orientation and effectively boosting the performance of laser displacement sensors in the area of elevation measurement, consequently giving more genuine and effective measurement results.
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Abstract:
Particle velocity is an important parameter for analyzing the propagation law of stress waves in a solid medium. Combining the laser Doppler effect and an all-fiber interferometric velocimetry system, a measurement method of stress wave particle velocity in solid medium based on fiber coated probe is proposed. The fiber coated probe was embedded in the polymethyl methacrylate(PMMA) at the same radius from the burst center, and the miniature explosive ball with 0.125 g TNT equivalent was used as the explosion source to fill in the center cavity and generate stress wave. Based on the time-frequency analysis method of the short-time Fourier transform, the velocity of the optical fiber end surface can be calculated from the collected signal, and then the medium particle velocity can be deduced. In the experiment,the velocity of the data measured by different fiber coated probes was 22.648 m/s and 23.505 m/s. The relative difference between the resulting particle velocity and the data obtained by the traditional circular particle speedometer method is less than 5.00%, which indicates the feasibility of the method.
Particle velocity is an important parameter for analyzing the propagation law of stress waves in a solid medium. Combining the laser Doppler effect and an all-fiber interferometric velocimetry system, a measurement method of stress wave particle velocity in solid medium based on fiber coated probe is proposed. The fiber coated probe was embedded in the polymethyl methacrylate(PMMA) at the same radius from the burst center, and the miniature explosive ball with 0.125 g TNT equivalent was used as the explosion source to fill in the center cavity and generate stress wave. Based on the time-frequency analysis method of the short-time Fourier transform, the velocity of the optical fiber end surface can be calculated from the collected signal, and then the medium particle velocity can be deduced. In the experiment,the velocity of the data measured by different fiber coated probes was 22.648 m/s and 23.505 m/s. The relative difference between the resulting particle velocity and the data obtained by the traditional circular particle speedometer method is less than 5.00%, which indicates the feasibility of the method.
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Abstract:
In order to overcome the molding technology of high-steep spherical optical parts, a sub-aperture grinding method was proposed, taking hemispherical and hyper-hemispherical infrared optical domes as the research object. The traditional generating method grinding forming theory is expanded, the spherical surface is discretized into a series of sub-aperture rings, the grinding wheel "steps" along the ring, and a complete spherical surface is obtained by splicing and forming. In this paper, the transformation relationship between the forming spherical surface and the position coordinates of the three-axis machine tool is analyzed, the machining motion trajectory is simulated, and the radius error compensation verification experiment and the variable feed parameter optimization experiment are carried out. A method of variable radius grinding is proposed to solve the problem of over-cutting of hyper-hemisphere machining materials. The forming process test was carried out on the hot-pressed zinc sulfide and magnesium-aluminum spinel spherical dome with aspect ratios of 0.5 (hemisphere) and 0.55 (hyper-hemisphere) respectively. The sag height difference of each point on the processing surface less than 4 μm, and the surface roughness Ra<1.5 μm. The results show that the method is feasible and provides an effective solution for deep high gradient spherical processing.
In order to overcome the molding technology of high-steep spherical optical parts, a sub-aperture grinding method was proposed, taking hemispherical and hyper-hemispherical infrared optical domes as the research object. The traditional generating method grinding forming theory is expanded, the spherical surface is discretized into a series of sub-aperture rings, the grinding wheel "steps" along the ring, and a complete spherical surface is obtained by splicing and forming. In this paper, the transformation relationship between the forming spherical surface and the position coordinates of the three-axis machine tool is analyzed, the machining motion trajectory is simulated, and the radius error compensation verification experiment and the variable feed parameter optimization experiment are carried out. A method of variable radius grinding is proposed to solve the problem of over-cutting of hyper-hemisphere machining materials. The forming process test was carried out on the hot-pressed zinc sulfide and magnesium-aluminum spinel spherical dome with aspect ratios of 0.5 (hemisphere) and 0.55 (hyper-hemisphere) respectively. The sag height difference of each point on the processing surface less than 4 μm, and the surface roughness Ra<1.5 μm. The results show that the method is feasible and provides an effective solution for deep high gradient spherical processing.
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Abstract:
In order to measure the resonance wavelength of plasma grating, the sensitivity of grating parameters to stress is studied, a new type of stress-sensitive polydimethylsiloxane (PDMS) thin film plasma grating is proposed. Based on the principle of finite difference time domain (FDTD), a simulation model of periodic plasma grating structure is established. With the help of periodic boundary conditions, by applying stress to the grating and changing the parameters of the plasma grating (i.e. period, duty cycle and Au film thickness) to achieve the measurement of the resonance wavelength, the sensitivity of the grating parameters to the force is studied; and compare the simulation result with the theoretical value to get the relative error. The relative error is calculated by comparing the simulation result with the theoretical value. The results show that when the grating period is 0.7 μm, the duty cycle is 55%, and the gold film thickness is 0.02 μm, the response to force is most sensitive at this time; Secondly, comparing the resonance peak wavelength at different periods obtained by simulation with the theoretical calculation value, the results of the two are consistent; When the period is 0.7 μm, the wavelength of the resonance peak is 1.251 μm, and the relative error obtained by theory and simulation is less than 2%, and the result is more accurate. This method plays an important role in the fields of monochromator, spectrometer and sensor.
In order to measure the resonance wavelength of plasma grating, the sensitivity of grating parameters to stress is studied, a new type of stress-sensitive polydimethylsiloxane (PDMS) thin film plasma grating is proposed. Based on the principle of finite difference time domain (FDTD), a simulation model of periodic plasma grating structure is established. With the help of periodic boundary conditions, by applying stress to the grating and changing the parameters of the plasma grating (i.e. period, duty cycle and Au film thickness) to achieve the measurement of the resonance wavelength, the sensitivity of the grating parameters to the force is studied; and compare the simulation result with the theoretical value to get the relative error. The relative error is calculated by comparing the simulation result with the theoretical value. The results show that when the grating period is 0.7 μm, the duty cycle is 55%, and the gold film thickness is 0.02 μm, the response to force is most sensitive at this time; Secondly, comparing the resonance peak wavelength at different periods obtained by simulation with the theoretical calculation value, the results of the two are consistent; When the period is 0.7 μm, the wavelength of the resonance peak is 1.251 μm, and the relative error obtained by theory and simulation is less than 2%, and the result is more accurate. This method plays an important role in the fields of monochromator, spectrometer and sensor.
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Abstract:
A general model of fiber Bragg grating (FBG) acceleration detector has been established for the two-point package model. The sensitivity and the resonance frequency's analytical expressions of the acceleration detector have been deduced theoretically, and the influence factors which affecting the sensitivity and resonance frequency have been researched deeply, the acceleration detector’s response characteristics have been discussed, which would be affected by the ratio, that the package fiber stiffness to the structure stiffness. Based on this basis, the restrictive relation between the sensitivity and the resonance frequency have been analyzed, among the equivalent mass and the ratio have been in the range of 0~100 g, 0~1 and 0~100, respectively. And the resonance frequency’s change rule within the scope of 0~500 Hz (low-medium frequency) and 0~1200 Hz (medium-high frequency) also has been studied. Furthermore, the package fibers have been chosen 10 mm and 60 mm as examples to analyze the influence to the above two mentioned, the sensitivity of each simulation would reach up to ~1 000 pm/G, and the quality factor has been introduced. This study has played a significant role in the design and comprehensive performance evaluation of the acceleration detector, and provided a theoretical reference for the optimization of structural parameters to it.
A general model of fiber Bragg grating (FBG) acceleration detector has been established for the two-point package model. The sensitivity and the resonance frequency's analytical expressions of the acceleration detector have been deduced theoretically, and the influence factors which affecting the sensitivity and resonance frequency have been researched deeply, the acceleration detector’s response characteristics have been discussed, which would be affected by the ratio, that the package fiber stiffness to the structure stiffness. Based on this basis, the restrictive relation between the sensitivity and the resonance frequency have been analyzed, among the equivalent mass and the ratio have been in the range of 0~100 g, 0~1 and 0~100, respectively. And the resonance frequency’s change rule within the scope of 0~500 Hz (low-medium frequency) and 0~1200 Hz (medium-high frequency) also has been studied. Furthermore, the package fibers have been chosen 10 mm and 60 mm as examples to analyze the influence to the above two mentioned, the sensitivity of each simulation would reach up to ~1 000 pm/G, and the quality factor has been introduced. This study has played a significant role in the design and comprehensive performance evaluation of the acceleration detector, and provided a theoretical reference for the optimization of structural parameters to it.
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Abstract:
In order to solve the problem of image clarity and contrast degradation in fog scene image restoration, a single image defogging algorithm based on residual learning and guided filtering was proposed. The residual network was constructed by using foggy images and corresponding clear images. Multi-scale convolution is used to extract more detailed haze features. Taking advantage of the anisotropy of the guided filter, the image after the residual network is filtered to maintain the image edge characteristics, and a clearer fog-free image is obtained. The experimental results show that, compared with DCP algorithm, CAP algorithm, SRCNN algorithm, DehazeNet algorithm and MSCNN algorithm, On synthetic foggy images, the PSNR reaches 27.840 3/dB at the highest, the SSIM value reaches 0.979 6 at the highest, and the running time on natural foggy images reaches 0.4 s at the lowest. and the subjective evaluation and objective evaluation are better than other comparison algorithms. Proposed to fog algorithm not only to the fog effect is better, and faster, with strong practical value.
In order to solve the problem of image clarity and contrast degradation in fog scene image restoration, a single image defogging algorithm based on residual learning and guided filtering was proposed. The residual network was constructed by using foggy images and corresponding clear images. Multi-scale convolution is used to extract more detailed haze features. Taking advantage of the anisotropy of the guided filter, the image after the residual network is filtered to maintain the image edge characteristics, and a clearer fog-free image is obtained. The experimental results show that, compared with DCP algorithm, CAP algorithm, SRCNN algorithm, DehazeNet algorithm and MSCNN algorithm, On synthetic foggy images, the PSNR reaches 27.840 3/dB at the highest, the SSIM value reaches 0.979 6 at the highest, and the running time on natural foggy images reaches 0.4 s at the lowest. and the subjective evaluation and objective evaluation are better than other comparison algorithms. Proposed to fog algorithm not only to the fog effect is better, and faster, with strong practical value.
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