| The distribution of space charge is crucial to the evaluation of the operational performance and operating condition of insulating materials.Since the space charge distribution of insulating materials varies greatly under different operating environments,the development of charge measurement techniques for different insulation environments is an important way to achieve reliable evaluation of the insulation performance and operating condition of electrical equipment.In the current research,the existing charge measurement methods can realize the test under the working frequency and DC conditions,but it is still difficult to test under the high frequency and transient pulse stress conditions,which is mainly due to the insufficient measurement resolution and speed.Therefore,the development of optoelectronic space charge measurement methods with nanometer-level measurement resolution and microsecond-level measurement speed potential is an important means to achieve space charge measurement under high-frequency and transient pulse stress conditions.Therefore,the research on the topology of optoelectronic space charge measurement and THz excitation generation device has high theoretical significance and application value.In this paper,we propose and optimize the topology design of space charge measurement based on elliptical polarization detection principle.The paper firstly selects the optical rectification method as the excitation generator of the space charge measurement scheme in optoelectronics through simulation modeling,and proposes two topologies of elliptical polarization detection principle,reflection method and transmission method,based on the radiation characteristics of its excitation THz wave.Further,with the polarization state description method of Stokes vector and Mueller matrix,the detection feasibility of reflection and transmission method measurement topologies is theoretically derived,and it is concluded that the sensing sensitivity of reflection method is better than that of transmission method when the thickness of the elasto-optical sensor is thin.To verify the correctness of the theoretical derivation,an elliptical polarization measurement platform under two topologies is experimentally constructed,and a piezoelectric actuator is selected as an elastic wave simulation generator,and the results confirm the sensitivity advantage of the reflection method for topology measurement.Meanwhile,during the measurement process,the experiments initially realized the selection of sensor material and the exclusion of repeatability error,and found that the mechanical properties of fused silica crystal are more excellent than other materials when it is used as the elasto-optical sensing material,and the measurement linearity error and repeatability error are less than 5%during the test.After determining the optical measurement topology design,this paper proposes the corresponding THz radiation conversion mechanism characterization model for the charge measurement requirement and optimizes its generation device parameters.The paper firstly derives the time domain and frequency domain characterization equations for nonlinear media under isotropic and anisotropic conditions using Maxwell’s set of equations under nonlinear media conditions.Based on the fact that the optical rectification effect belongs to the special differential frequency effect in the second-order nonlinear effect,the modeling deduces the electric field strength characterization of the nonlinear crystal at the millimeter level,and it is concluded that the optimization result of the crystal thickness is approximately the same under the conditions of whether the dielectric loss and the photoelectric field change with time are considered,and it is determined to be 1 mm.meanwhile,due to the inverse relationship between the femtosecond laser pulse width and the center frequency of the radiated terahertz wave,combined with the The THz excitation requirement of optoelectronics is combined with the 400 fs pulse width laser as the excitation laser.In addition,for the effect of laser incidence angle,the article chose to take<110>crystal-oriented crystals as an example,and concluded that the best results were obtained when the pump light was vertically incident on ZnTe crystals at an angle of 55°to the z-axis.Further,the article realizes the THz generation device construction and charge perturbation experimental testing.Based on the optimized parameters of the THz excitation generator obtained in the previous paper,the ORIGAMI XP femtosecond laser is selected as the excitation pulse laser and the THz camera is used as the detection device in this paper.Using the THz camera measurement to obtain the image pixel value proportional to the THz radiation energy,the average power of the THz excitation spot focusing focus is obtained to be about W level.Meanwhile,in order to realize the experimental test of space charge perturbation,this paper proposes an improved ring electrode structure test platform based on the electroacoustic pulse method.Through the corresponding software simulation,the center pressure drop of the ring electrode is smaller and the decay is more uniform,which has a greater advantage compared with the contralateral design.After completing the design,assembly and calibration of the test platform,the experiments focus the THz radiation spot on the test specimen and conclude that THz radiation can achieve charge perturbation under the exclusion of optical pressure and possible optical effects.In summary,this paper proposes a new topology design for space charge measurement in optoelectronics and investigates the conversion mechanism of THz excitation generation to achieve parameter optimization of high power and narrow pulse width THz radiation generation device.The THz radiation generation and detection device is constructed,and the design of charge perturbation test platform is proposed to derive the rationality of THz radiation as charge perturbation excitation.Therefore,the experimental tests and theoretical analysis in this paper can lay the foundation for the subsequent space charge measurement in optoelectronics. |
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