A collimated terahertz wave excitation method and system for solid insulation space charge detection

Abstract

The present application relates to the technical field of terahertz space charge detection, and particularly relates to a collimated terahertz wave excitation method and system for solid insulation space charge detection. The method comprises determining target excitation parameters according to matching requirements of an excitation light beam and a photoconductive antenna, and adjusting power and spot size of the excitation light beam to the target excitation parameters; applying a bias voltage to the photoconductive antenna, and irradiating the photoconductive antenna with the adjusted excitation light beam to generate terahertz waves; collimating the terahertz waves through a collimating optical element to form a collimated terahertz wave beam; and focusing the collimated terahertz wave beam to a surface of a solid insulation sample to be detected by using a focusing optical element, so as to perform space charge detection. The present application effectively solves the problems of serious terahertz wave divergence and low radiation efficiency by optimizing excitation conditions of the photoconductive antenna and a collimating optical path, and significantly improves the signal-to-noise ratio and detection accuracy of solid insulation material space charge detection.

Description

Technical Field

[0001] This invention relates to the field of terahertz space charge detection technology, and in particular to a collimated terahertz wave excitation method and system for detecting space charge in solid insulation. Background Technology

[0002] Terahertz (THz) waves, a special band in the electromagnetic spectrum between microwaves and infrared, possess numerous excellent properties such as non-ionizing radiation, strong penetrating power, and high temporal resolution, demonstrating enormous application potential in cutting-edge scientific and engineering fields such as non-destructive testing of materials, spectral analysis, and space charge measurement. Currently, the accumulation and migration of space charge in solid insulating materials (such as polymers, epoxy resins, and ceramic dielectrics) has a decisive impact on their insulation performance and lifespan. However, traditional detection methods such as the pulse electroacoustic (PEA) method and the liquid-in-current (LIPP) method suffer from limitations such as contact-based detection, limited spatial resolution, and difficulty in real-time imaging.

[0003] In recent years, terahertz time-domain spectroscopy (THz-TDS) based on photoconductive antennas (PCA) has been used for solid-insulator space charge measurement research due to its non-contact and high-sensitivity characteristics. However, existing terahertz excitation optical paths generally suffer from problems such as: uncollimated excitation beam, severe terahertz wave divergence, low signal energy, unreasonable matching of photoconductive antenna bias and incident laser parameters, complex system optical path, difficult debugging, and poor stability. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, the first objective of this invention is to provide a collimated terahertz wave excitation method for space charge detection in solid-state insulation, comprising the following steps:

[0006] S1, determine the target excitation parameters according to the matching requirements between the excitation beam and the photoconductive antenna, and adjust the power and spot size of the excitation beam to the target excitation parameters; S2, apply a bias voltage to the photoconductive antenna and use the adjusted excitation beam to irradiate the photoconductive antenna to generate terahertz waves; S3, the terahertz wave is collimated by a collimating optical element to form a collimated terahertz beam; S4. The collimated terahertz beam is focused onto the surface of the solid insulating sample under test using focusing optical elements to perform space charge detection.

[0007] In one embodiment of the present invention, S1 further includes: S11, construct a device-level model that couples the semiconductor drift-diffusion equation with the Poisson equation, and solve for the current density distribution and the equivalent emitter electric dipole moment; S12, Construct a spatial-level model based on the equivalent transmitting electric dipole moment, and analyze the propagation law of terahertz waves in free space and optical elements; S13, based on the simulation output results of the device-level model and the space-level model, the target excitation parameters are deduced, and the power and spot size of the excitation beam are adjusted according to the target excitation parameters.

[0008] In one embodiment of the present invention, the Poisson equation is: ; The semiconductor drift-diffusion equation is as follows: ; ; Where ▽ is the gradient operator, ε Where is the dielectric constant. For electric potential, q For elementary charge, p Hole concentration n For electron concentration, The concentration of ionized donor impurities. The concentration of ionized acceptor impurities. For electron current density, R It is an SRH compound term. μ n For electron mobility, μ p Hole mobility D n The electron diffusion coefficient is... D p The hole diffusion coefficient is denoted as . Hole current density E For electric field strength, G The photogenerated carrier generation rate.

[0009] In one embodiment of the present invention, S13 further includes: S131 uses a Glan-Taylor prism to split and adjust the power of a femtosecond laser. The transmitted energy and the rotation angle satisfy a cosine square relationship, thus achieving continuous power control. S132 uses a focusing lens to adjust the focal length of the emitted light spot and optimize the spot size; S133, the adjusted power and spot size are input as the target excitation parameters to subsequent steps to ensure the matching requirements between the excitation beam and the photoconductive antenna.

[0010] In one embodiment of the present invention, S2 further includes: S21, a photoconductive antenna with interdigitated electrodes and a GaAs substrate is used, and a DC bias voltage is applied to the photoconductive antenna; S22, the photoconductive antenna is irradiated with the adjusted excitation beam to generate terahertz waves, and the acceleration direction of the photogenerated carriers is consistent with the polarization direction of the terahertz waves.

[0011] In one embodiment of the present invention, S3 further includes: S31, an off-axis parabolic mirror is used as the collimating optical element to form a collimating beam; S32, The photoconductive antenna and the off-axis parabolic mirror are arranged in the same focal plane to ensure collimated output of terahertz waves; S33, the terahertz wave is collimated by the off-axis parabolic mirror to form a collimated terahertz beam to achieve low divergence output.

[0012] In one embodiment of the present invention, S4 further includes: S41, using a TPX lens as the focusing optical element, the collimated beam is focused onto the sample; S42, the collimated terahertz beam is focused onto the surface of the solid insulating sample to be tested, and the space charge is detected by using the focused terahertz beam, so as to realize non-contact detection and imaging of space charge in solid insulating materials.

[0013] To achieve the above objectives, a second aspect of the present invention provides a collimated terahertz wave excitation system for space charge detection in solid-state insulation, characterized in that it comprises: The simulation analysis module is used to determine the target excitation parameters based on the matching requirements between the excitation beam and the photoconductive antenna. A laser system is used to adjust the power and spot size of the excitation beam to the target excitation parameters, and to apply a bias voltage to the photoconductive antenna. The adjusted excitation beam is used to irradiate the photoconductive antenna to generate a terahertz wave. The terahertz wave is collimated by a collimating optical element to form a collimated terahertz beam, and the collimated terahertz beam is focused onto the surface of the solid insulating sample under test by a focusing optical element for space charge detection.

[0014] In one embodiment of the present invention, the simulation analysis module includes: The device-level analysis module is used to analyze the effects of different excitation spot sizes, bias voltages, and material parameters on the terahertz transient radiation field, and to obtain the current density distribution and the equivalent emission electric dipole moment. The space-level analysis module is used to analyze the focusing performance and energy transmission efficiency of terahertz waves emitted by photoconductive antennas in space. The analysis module is used to infer the target excitation parameters based on the simulation output results of the device-level model and the space-level model.

[0015] To achieve the above objectives, a third aspect of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method described in the first aspect.

[0016] The methods, systems, and storage media of this invention can significantly improve the excitation efficiency and collimation of terahertz waves, reduce the beam divergence angle, and improve energy coupling efficiency, thereby enhancing the signal-to-noise ratio and measurement accuracy of solid-insulated space charge detection.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a flowchart of a collimated terahertz wave excitation method for space charge detection in solid insulation according to an embodiment of the present invention; Figure 2 This is a structural diagram of a collimated terahertz wave excitation system for solid-insulator space charge detection according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the electric field at the device level of the photoconductive antenna according to an embodiment of the present invention; Figure 4 This is a schematic diagram of space-level simulation of photoconductive antenna and terahertz wave space propagation according to an embodiment of the present invention. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0021] The following description, with reference to the accompanying drawings, describes a collimated terahertz wave excitation method and system for detecting space charge in solid insulation according to an embodiment of the present invention.

[0022] Example 1 Figure 1 This is a flowchart of a collimated terahertz wave excitation method for solid-insulating space charge detection according to an embodiment of the present invention.

[0023] like Figure 1 As shown, the collimated terahertz wave excitation method for solid-insulator space charge detection includes the following steps: S1. Establish device-level and space-level simulation models, and optimize and determine the excitation spot size and optical path structure parameters based on carrier dynamics characteristics and electromagnetic wave propagation laws.

[0024] Further, step S1 includes: S11, construct a device-level model that couples the semiconductor drift-diffusion equation with the Poisson equation, and solve for the current density distribution and the equivalent emitter electric dipole moment.

[0025] Specifically, this invention establishes device-level and space-level simulation models to predict the radiation and propagation of terahertz waves through numerical simulation. The simulation consists of two levels: the device-level model characterizes the dynamics of charge carriers inside the photoconductive antenna and solves for the current density distribution based on semiconductor physics equations; the space-level model analyzes the propagation of terahertz waves based on the equivalent current source output from the device level. Through joint simulation of the two levels, the optimal excitation spot size and optical path structure parameters are determined by reverse engineering.

[0026] As one implementation method, a multiphysics simulation software is used to construct the model. The device-level simulation employs a coupled model of "semiconductor drift-diffusion equation + Poisson equation," and the equation set includes:

[0027]

[0028]

[0029] ▽ represents the gradient operator. ε Where is the dielectric constant. For electric potential, q For elementary charge, p Hole concentration n For electron concentration, The concentration of ionized donor impurities. The concentration of ionized acceptor impurities. For electron current density, R It is an SRH compound term. μ nFor electron mobility, μ p Hole mobility D n The electron diffusion coefficient is... D p The hole diffusion coefficient is denoted as . Hole current density E For electric field strength, G The photogenerated carrier generation rate.

[0030] S12, Construct a spatial-level model based on the equivalent transmitting electric dipole moment, and analyze the propagation law of terahertz waves in free space and optical elements.

[0031] The geometric model is based on the equivalent current source of the device-level output to analyze the propagation, collimation and focusing of terahertz waves in free space and optical elements.

[0032] In the geometric model, the finger width, finger spacing, and thickness of the interdigitated electrodes are modeled according to the actual dimensions. The laser source in the geometric model is defined using a spatiotemporal double Gaussian model of femtosecond pulse parameters to define laser excitation, and the generation rate formula is: ; Where η: quantum efficiency (efficiency of converting photons into electron-hole pairs), α780: absorption coefficient (corresponding to 780 nm laser wavelength). Planck constant, ω: angular frequency of light, I0: peak intensity of laser light, x, y, z represent the three-dimensional directions in space, ω0: waist radius of the beam, τp: pulse width (FWHM), t represents time.

[0033] By combining antenna geometry with the definition of laser excitation, the selection of optical path components can be guided.

[0034] By establishing a joint simulation model at the device and space levels, the radiation characteristics and propagation behavior of terahertz waves can be accurately predicted during the system design phase, avoiding the long development cycle and debugging difficulties caused by traditional trial-and-error methods. Optimizing the determined excitation spot size and optical path structure parameters significantly improves the excitation efficiency and collimation of terahertz waves, laying the foundation for high signal-to-noise ratio detection of space charge in the future.

[0035] S13, based on the simulation output results of the device-level model and the space-level model, the target excitation parameters are deduced, and the power and spot size of the excitation beam are adjusted according to the target excitation parameters.

[0036] Specifically, S131 uses a Glan-Taylor prism to split and adjust the power of the femtosecond laser. The transmitted energy and the rotation angle satisfy a cosine square relationship, thus achieving continuous power control. S132 uses a focusing lens to adjust the focal length of the emitted light spot and optimize the spot size; S133, the adjusted power and spot size are input as the target excitation parameters to subsequent steps to ensure the matching requirements between the excitation beam and the photoconductive antenna.

[0037] S2, control the output power of the pulsed laser source and focus the laser beam to the excitation spot size through the focusing lens, so as to irradiate the effective excitation area of ​​the photoconductive antenna.

[0038] Further, step S2 includes: S21, a photoconductive antenna with interdigitated electrodes and a GaAs substrate is used, and a DC bias voltage is applied to the photoconductive antenna.

[0039] Specifically, a photoconductive antenna structure comprising interdigitated electrodes and a GaAs substrate is first constructed. The GaAs substrate thickness is set to... The dielectric constant is set to 12.9. The material physical parameters are configured with electron mobility... Hole mobility The carrier lifetime is 0.2–1 ps. The finger width, finger spacing, and thickness of the interdigitated electrodes are modeled according to the actual dimensions, and the non-light-receiving area is covered with opaque metallization to form a clear and effective excitation area and avoid noise caused by stray light excitation.

[0040] In one embodiment, the substrate material of the interdigitated electrode is GaAs with a thickness of 200–500 μm; material parameters: μn = 2000 cm⁻¹ 2 / V·s,μp=200cm 2 / V·s; Carrier lifetime 0.2–1ps; Dielectric constant 12.9.

[0041] As one implementation method, a femtosecond laser source is configured such that its output wavelength is... Pulse width is Power is The repetition frequency is And the emitted light spot is approximately A vertically polarized laser beam is used as the initial input light source.

[0042] Simultaneously, the initial input light source is incident on a Glan-Taylor prism for beam splitting and power adjustment. This is achieved by adjusting the angle of the Glan-Taylor prism. Using the transmitted energy and angle to satisfy Based on the relationship, the attenuation of the vertically polarized laser beam is controlled to obtain a power-controlled laser beam, which serves as the input for subsequent focusing processing. Next, the power-controlled laser beam is focused onto the excitation spot size using a focusing lens. Specifically, when the optical path distance parameter is determined, a focal length of approximately [missing information] is selected. The focusing lens will reduce the emitted light spot to approximately The laser beam is focused to The size of the excitation spot is determined. Finally, the focused laser beam is irradiated onto the effective excitation region of the photoconductive antenna to complete the preparation and delivery of the excitation light, ensuring that photogenerated carriers are generated within the effective region.

[0043] S22, the photoconductive antenna is irradiated with the adjusted excitation beam to generate terahertz waves. The acceleration direction of the photogenerated carriers is consistent with the polarization direction of the terahertz waves, thereby generating terahertz waves. The terahertz waves output from this process have polarization characteristics consistent with the bias field, serving as the input signal for subsequent collimation processing.

[0044] This implementation achieves precise matching of incident light spot size and power through the coordinated control of the Glan-Taylor prism and the focusing lens, effectively solving the problem of low terahertz radiation efficiency caused by unoptimized excitation spot of photoconductive antenna, and significantly improving the signal-to-noise ratio of the space charge detection system.

[0045] S3, apply a bias voltage to the photoconductive antenna, use the irradiated laser beam to excite photogenerated carriers and accelerate them under the action of the bias electric field to generate terahertz waves.

[0046] Further, step S3 includes: S31, an off-axis parabolic mirror is used as the collimating optical element to form a collimating beam.

[0047] Specifically, this invention uses an off-axis parabolic mirror as the collimating optical element. The input source is the initial terahertz wave radiated by the photoconductive antenna under the combined action of the bias voltage and the excitation beam, and this beam has a large spatial divergence angle in its initial state.

[0048] In one implementation, the off-axis parabolic mirror (OAP) has a diameter / focal length of 50.8 mm and is 90° off-axis, forming a collimating beam.

[0049] S32, the photoconductive antenna and the off-axis parabolic mirror are arranged in the same focal plane to ensure collimated output of terahertz waves and improve the signal-to-noise ratio.

[0050] S33, the terahertz wave is collimated by the off-axis parabolic mirror to form a collimated terahertz beam to achieve low divergence output.

[0051] This embodiment achieves efficient collimated transmission of terahertz waves through the cofocal arrangement of a specific-specification off-axis parabolic mirror and a photoconductive antenna. Its beneficial effects include a significant reduction in the divergence angle of the terahertz beam, an increase in the field strength on the sample surface and the system signal-to-noise ratio, thereby optimizing the sensitivity and imaging quality of space charge detection in solid insulating materials.

[0052] S4 uses collimating optical elements to collimate the generated terahertz waves, and then uses focusing optical elements to focus the collimated terahertz waves onto the surface of the solid insulating material to be tested.

[0053] Further, step S4 includes: S41, using a TPX lens as the focusing optical element, focuses the collimated beam onto the sample.

[0054] In one implementation, the TPX lens has a diameter of 50.8 mm and a focal length of 100 mm.

[0055] After the collimated terahertz beam is incident on the TPX lens, the lens converges the beam based on its material refractive index characteristics, refocusing the parallel-propagating collimated beam onto a specific focal plane. The output is a focused terahertz beam, with its focal point precisely falling on the surface of the solid insulating sample under test. With this configuration, the terahertz wave energy is highly concentrated on the sample surface, significantly improving the surface field strength and signal-to-noise ratio, and optimizing energy transmission efficiency.

[0056] S42, the collimated terahertz beam is focused onto the surface of the solid insulating sample to be tested, and the space charge is detected by using the focused terahertz beam, so as to realize non-contact detection and imaging of space charge in solid insulating materials.

[0057] like Figure 3 As shown, under femtosecond laser pulse excitation, transient charge carriers are generated in the photoconductive material, forming transient currents under the action of an applied bias electric field, thus generating a strong electric field distribution in the electrode gap region. The electric field is mainly concentrated in the gap region between the interdigitated electrodes, exhibiting the following characteristics: the electric field shows a significant enhancement at the electrode edges (tip effect), with the local field strength reaching its maximum value; the electric field vector direction is mainly distributed along the electrode gap direction, indicating the dominant direction of charge carrier drift; the electric field decays rapidly with distance from the electrode gap, exhibiting typical local field distribution characteristics; the central excitation region corresponds to the laser irradiation position and is the main source region of terahertz radiation.

[0058] This distribution indicates that the terahertz radiation of the device mainly originates from the transient photocurrent changes at the electrode gap, providing a basis for subsequent modeling of the equivalent electric dipole moment.

[0059] like Figure 4As shown, the simulation, based on the equivalent current source or equivalent electric dipole moment model extracted at the device level, calculates the far-field radiation intensity distribution at different frequencies (0.3-1.2 THz) in free space. The results show that the terahertz radiation exhibits an approximately isotropic symmetrical distribution, consistent with short dipole radiation characteristics; the radiation intensity is highest in the normal direction (approximately 90°), exhibiting a typical dipole radiation main lobe structure; the radiation pattern shape is basically consistent at different frequencies, but the radiation intensity varies with frequency; the high-frequency component (e.g., above 1 THz) radiation is stronger, indicating that the device possesses good high-frequency response capability; the radiation pattern shows a smooth change without obvious sidelobes, indicating that the antenna structure has good directional stability. These results verify that the established space-level model can effectively describe the propagation law of terahertz waves in free space and can be used for further analysis of collimation and focusing characteristics in optical systems.

[0060] This embodiment effectively improves the terahertz field strength and signal-to-noise ratio on the sample surface and optimizes energy transmission efficiency by focusing with a TPX lens with specific parameters, thereby achieving highly sensitive non-contact detection and imaging of space charge in solid insulating materials.

[0061] Example 2 like Figure 2 As shown, a collimated terahertz wave excitation system 10 for solid-insulator space charge detection includes: The simulation analysis module 100 is used to determine the target excitation parameters based on the matching requirements between the excitation beam and the photoconductive antenna.

[0062] The laser system 200 is used to adjust the power and spot size of the excitation beam to the target excitation parameters, apply a bias voltage to the photoconductive antenna, irradiate the photoconductive antenna with the adjusted excitation beam to generate a terahertz wave, collimate the terahertz wave with a collimating optical element to form a collimated terahertz beam, and focus the collimated terahertz beam onto the surface of the solid insulating sample to be tested with a focusing optical element for space charge detection.

[0063] The simulation analysis module includes: The device-level analysis module 101 is used to analyze the effects of different excitation spot sizes, bias voltages and material parameters on the terahertz transient radiation field, and to obtain the current density distribution and the equivalent emission electric dipole moment. Space-level analysis module 102 is used to analyze the focusing performance and energy transmission efficiency of terahertz waves emitted by photoconductive antennas in space; Analysis module 103 is used to infer the target excitation parameters based on the simulation output results of the device-level model and the space-level model.

[0064] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-described method for excitation of collimated terahertz waves for space charge detection in solid-state insulation.

[0065] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0066] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A collimated terahertz wave excitation method for space charge detection in solid-state insulation, characterized in that the steps include... include: S1, determine the target excitation parameters according to the matching requirements between the excitation beam and the photoconductive antenna, and adjust the power and spot size of the excitation beam to the target excitation parameters; S2, apply a bias voltage to the photoconductive antenna and irradiate the photoconductive antenna with the adjusted excitation beam to generate terahertz waves; S3, the terahertz wave is collimated by a collimating optical element to form a collimated terahertz beam; S4. The collimated terahertz beam is focused onto the surface of the solid insulating sample under test using focusing optical elements to perform space charge detection.

2. The method as described in claim 1, characterized in that, S1 further includes: S11, construct a device-level model that couples the semiconductor drift-diffusion equation with the Poisson equation, and solve for the current density distribution and the equivalent emitter electric dipole moment; S12, Construct a spatial-level model based on the equivalent transmitting electric dipole moment, and analyze the propagation law of terahertz waves in free space and optical elements; S13, based on the simulation output results of the device-level model and the space-level model, the target excitation parameters are deduced, and the power and spot size of the excitation beam are adjusted according to the target excitation parameters.

3. The method according to claim 2, characterized in that, The Poisson equation is: ； The semiconductor drift-diffusion equation is as follows: ； ； Where ▽ is the gradient operator, ε Where is the dielectric constant. For electric potential, q For elementary charge, p Hole concentration, n For electron concentration, The concentration of ionized donor impurities. The concentration of ionized acceptor impurities. For electron current density, R It is an SRH compound term. μ n For electron mobility, μ p Hole mobility D n The electron diffusion coefficient is... D p The hole diffusion coefficient is denoted as . Hole current density E For electric field strength, G The photogenerated carrier generation rate.

4. The method according to claim 1, characterized in that, S13 further includes: S131 uses a Glan-Taylor prism to split and adjust the power of a femtosecond laser. The transmitted energy and the rotation angle satisfy a cosine square relationship, thus achieving continuous power control. S132 uses a focusing lens to adjust the focal length of the emitted light spot and optimize the spot size; S133, the adjusted power and spot size are input as the target excitation parameters to subsequent steps to ensure the matching requirements between the excitation beam and the photoconductive antenna.

5. The method as described in claim 1, characterized in that, S2 further includes: S21, a photoconductive antenna with interdigitated electrodes and a GaAs substrate is used, and a DC bias voltage is applied to the photoconductive antenna; S22, the photoconductive antenna is irradiated with the adjusted excitation beam to generate terahertz waves, and the acceleration direction of the photogenerated carriers is consistent with the polarization direction of the terahertz waves.

6. The method as described in claim 1, characterized in that, S3 further includes: S31, an off-axis parabolic mirror is used as the collimating optical element to form a collimating beam; S32, The photoconductive antenna and the off-axis parabolic mirror are arranged in the same focal plane to ensure collimated output of terahertz waves; S33, the terahertz wave is collimated by the off-axis parabolic mirror to form a collimated terahertz beam to achieve low divergence output.

7. The method as described in claim 1, characterized in that, S4 further includes: S41, using a TPX lens as the focusing optical element, the collimated beam is focused onto the sample; S42, the collimated terahertz beam is focused onto the surface of the solid insulating sample to be tested, and the space charge is detected by using the focused terahertz beam to realize non-contact detection and imaging of space charge in solid insulating materials.

8. A collimated terahertz wave excitation system for detecting space charge in solid-state insulation, characterized in that, include: The simulation analysis module is used to determine the target excitation parameters based on the matching requirements between the excitation beam and the photoconductive antenna. A laser system is used to adjust the power and spot size of the excitation beam to the target excitation parameters, and to apply a bias voltage to the photoconductive antenna. The adjusted excitation beam is used to irradiate the photoconductive antenna to generate a terahertz wave. The terahertz wave is collimated by a collimating optical element to form a collimated terahertz beam, and the collimated terahertz beam is focused onto the surface of the solid insulating sample under test by a focusing optical element for space charge detection.

9. The system as described in claim 8, characterized in that, The simulation analysis module includes: The device-level analysis module is used to analyze the effects of different excitation spot sizes, bias voltages, and material parameters on the terahertz transient radiation field, and to obtain the current density distribution and the equivalent emission electric dipole moment. The space-level analysis module is used to analyze the focusing performance and energy transmission efficiency of terahertz waves emitted by photoconductive antennas in space. The analysis module is used to infer the target excitation parameters based on the simulation output results of the device-level model and the space-level model.

10. A computer-readable storage medium storing a computer program that, when executed by a processor, implements the method as claimed in any one of claims 1-7.

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