Electro-optical detection system and method for simultaneous measurement of its sensitivity and bandwidth

Abstract

The application belongs to the technical field of electro-optic detection and ultrafast optical measurement, and particularly relates to an electro-optic detection system and a sensitivity and bandwidth synergistic measurement method thereof. The method comprises the following steps: dividing a pulsed laser into pump light and probe light, the pump light being used for disturbing a space charge to excite a transient electric field to be measured; making the probe light obliquely incident on an electro-optic sensor and being reflected by a sensor reflection surface to be emitted, and acquiring modulated probe light carrying transient electric field information; and changing a relative delay between the pump light and the probe light, step-by-step sampling and reconstructing the modulated probe light to realize measurement of the space charge. The system comprises a light splitting device, a reflection type electro-optic detection assembly, an optical sampling assembly and a controller, and the controller is configured to execute the method. The application realizes synergistic optimization of sensitivity and bandwidth, the measurement sensitivity reaches 200 mV / mm, the measurement bandwidth reaches 0.67 THz, and high-fidelity measurement of a picosecond level ultra-high frequency transient electric field signal can be realized.

Description

Technical Field

[0001] This application belongs to the field of electro-optic detection and ultrafast optical measurement technology, specifically involving electro-optic detection systems and methods for coordinating the measurement of their sensitivity and bandwidth. Background Technology

[0002] With the development of new power systems and the large-scale application of power electronic conversion equipment, the polarization conditions faced by insulating materials have shifted from traditional DC and power frequency AC to higher frequencies. Traditional evaluation techniques for insulation performance under DC and low-frequency AC conditions are no longer applicable. Under high-frequency polarization conditions, a large amount of space charge accumulates within the insulation system, easily causing severe distortion of the local electric field, which directly leads to changes in dielectric properties and the development of discharge phenomena. Therefore, space charge distribution has become a key indicator for reliably evaluating the high-frequency performance and state of insulating materials from a microscopic mechanism perspective.

[0003] To meet the demand for high spatiotemporal resolution space charge measurement, novel space charge measurement methods based on optoelectronics and electro-optic effects have been proposed. In electro-optic detection, the electric field information carried by the probe light can be demodulated using polarization detection to assess the space charge distribution. However, due to the extremely weak and ultra-high frequency characteristics of the transient electric field excited by space charge, traditional electro-optic detection systems face significant challenges in terms of measurement sensitivity and detection bandwidth. On the one hand, traditional electro-optic detection methods typically employ a transmission topology, resulting in extremely low spatial coverage between the probe spot and the sensor interface. This leads to an incident coupling coefficient of only about 0.1, further significantly attenuating the already weak electric field signal during detection, resulting in severely insufficient system sensitivity. On the other hand, even if the signal strength meets the requirements, the measurement of picosecond-level ultra-high frequency signals is still subject to severe waveform broadening or even distortion due to the inherent bandwidth limitations of photodetectors (MHz to GHz levels). Since these two difficulties stem from two extreme properties of the same signal, a single method can only solve one dimension of the problem and cannot simultaneously adapt to the characteristics of the signal being both weak and ultra-high frequency. Meanwhile, in the traditional electro-optic detection framework, there is an inherent contradiction between sensitivity and bandwidth: increasing the detector bandwidth usually introduces more noise and reduces the sensitivity of the detectable signal, while increasing the thickness of the sensing crystal or extending the working optical path can improve the signal strength, but will degrade the high-frequency response.

[0004] Therefore, existing electro-optic detection schemes have long been limited by the two intertwined problems of insufficient sensitivity and insufficient bandwidth when facing space charge measurement, and there is a lack of a technical solution that can simultaneously and systematically solve the above defects. Summary of the Invention

[0005] This application proposes a sensitivity and bandwidth coordinated measurement scheme for an electro-optic detection system, aiming to solve the two intertwined problems of insufficient sensitivity and insufficient bandwidth faced by existing electro-optic detection schemes when dealing with space charge measurement.

[0006] The first aspect of this application provides a method for coordinating the measurement of sensitivity and bandwidth of an electro-optic detection system, including: The pulsed laser is divided into a pump light and a probe light. The pump light is used to disturb the space charge to excite the transient electric field to be measured. The probe light is incident at an angle onto the electro-optic sensor and reflected by the sensor's reflective surface before exiting, thereby acquiring modulated probe light carrying transient electric field information; By altering the relative delay between the pump light and the probe light, the modulated probe light is progressively sampled and reconstructed to rebuild the high-bandwidth waveform of the transient electric field signal, thereby enabling the measurement of the space charge.

[0007] In some embodiments of this application, the electro-optic sensor includes a sensing crystal; The process of obliquely incidenting the probe light onto the electro-optic sensor and then reflecting it off the sensor's reflective surface to obtain the modulated probe light carrying transient electric field information includes: The probe light is incident on the electro-optic sensor at a Brewster angle corresponding to the refractive index of the sensing crystal, and is reflected by the reflective surface before exiting, so as to ensure that the p-state polarized light achieves zero-loss transmission at the sensor interface and obtains the modulated probe light carrying transient electric field information. Brewster's Corner Calculated using the following formula: , in, The refractive index of the sensing crystal is [value missing]. The refractive index of air.

[0008] In some embodiments of this application, the crystal material of the sensing crystal is determined based on the dual influence of the electro-optic coefficient of the crystal material and the sensor thickness on the system sensitivity; The optimal crystal thickness is determined based on the crystal material, the beam propagation distance, and the electric field strength.

[0009] In some embodiments of this application, the sensing crystal is a lithium niobate crystal, and the reflective surface is coated with a high-reflectivity aluminum film; The thickness of the sensing crystal is 2 mm.

[0010] In some embodiments of this application, the probe light is incident on the electro-optic sensor at an angle of 66° and is reflected by the reflective surface before exiting, thereby acquiring modulated probe light carrying transient electric field information.

[0011] In some embodiments of this application, the pulsed laser is a femtosecond pulsed laser; The stepwise sampling of the modulated probe light by changing the relative delay between the pump light and the probe light includes: By changing the optical path of the probe light through a step delay line, a fixed time delay is generated between each pulse as a sampling interval, and the picosecond-level pulse width electric field signal is sampled step by step.

[0012] In some embodiments of this application, the stepwise sampling and reconstruction of the modulated probe light includes: The signal obtained by stepwise sampling is reconstructed by a lock-in amplifier to restore the original high-bandwidth signal.

[0013] In some embodiments of this application, the method is applied to the transient electric field measurement of space charge in solid insulating materials.

[0014] In some embodiments of this application, the electro-optic detection system has picosecond-level pulse width electric field tracking capability, a minimum detection electric field strength threshold of 200 mV / mm, a measurement bandwidth of 0.67 THz, and a theoretical equivalent spatial resolution of 3.6 nm.

[0015] A second aspect of this application provides an electro-optical detection system, comprising: A beam splitter is used to split a pulsed laser into a pump beam and a probe beam, wherein the pump beam is used to perturb the space charge to excite the transient electric field to be measured. A reflective electro-optic detection component is used to obliquely incident the detection light onto the electro-optic sensor and then emit it after being reflected by the reflective surface of the electro-optic sensor, thereby acquiring modulated detection light carrying transient electric field information. The reflective electro-optic detection component includes the electro-optic sensor, which has a reflective surface. An optical sampling component is used to progressively sample and reconstruct the modulated probe light by changing the relative delay between the pump light and the probe light to reconstruct the high-bandwidth waveform of the transient electric field signal, thereby realizing the measurement of the space charge, wherein the optical sampling component includes a delay device; A controller configured to perform the method described in the first aspect of the embodiments of this application.

[0016] In summary, the electro-optic detection system and its sensitivity and bandwidth co-measurement method provided in the embodiments of this application, by employing a reflective detection topology, allow the detection light to be incident obliquely onto the electro-optic sensor and reflected by the reflective surface before exiting (interface transmittance is approximately 0.95), thus avoiding the problem of significant signal attenuation caused by the extremely low incident coupling coefficient (approximately 0.1) in transmission topologies, and solving the problem of insufficient sensitivity. Secondly, by introducing optical sampling measurement and using step delay lines to progressively sample and reconstruct, the detection bandwidth is increased from the MHz / GHz level to the THz level, solving the problem of insufficient bandwidth. The above technical features are not simply superimposed, but rather, in response to the dual extreme characteristics of the signal being both weak and ultra-high frequency in the space charge measurement scenario, they together form a complete closed loop of pre-enhancement and post-bandwidth limitation breakthrough, achieving unexpected technical effects such as a jump in measurement sensitivity from 800V / mm to 200mV / mm and an increase in measurement bandwidth from 28.6MHz to 0.67THz. Attached Figure Description

[0017] The features and advantages of this application will become clearer with reference to the accompanying drawings, which are illustrative and should not be construed as limiting the application in any way. In the drawings: Figure 1 This is a schematic diagram of the electro-optical detection system provided in the embodiments of this application; Figure 2 This is a schematic diagram of the sensitivity and bandwidth collaborative optimization framework of the electro-optic detection system adapted for space charge measurement provided in the embodiments of this application; Figure 3 This is a flowchart illustrating a method for coordinating the measurement of sensitivity and bandwidth of an electro-optic detection system according to some embodiments of this application; Figure 4 This is according to one embodiment of the present application. Figure 3 The response characteristics of the cooperative measurement method shown are under a picosecond pulse electric field; Figure 5 This is a system architecture diagram of an electro-optical detection system according to some embodiments of this application. Detailed Implementation

[0018] In the following detailed description, numerous specific details of this application are illustrated by example to provide a thorough understanding of the relevant disclosure. However, it will be apparent to those skilled in the art that this application can be practiced without these details. It should be understood that the terms “system,” “apparatus,” “unit,” and / or “module” used in this application are one way of distinguishing different parts, elements, sections, or components at different levels in a sequential arrangement. However, these terms may be replaced with other expressions if other expressions can achieve the same purpose.

[0019] It should be understood that when a device, unit, or module is referred to as being "on," "connected to," or "coupled to" another device, unit, or module, it may be directly connected to or coupled to, or communicate with, other devices, units, or modules, or there may be intermediate devices, units, or modules present, unless the context explicitly indicates otherwise. For example, the term "and / or" as used herein includes any one and all combinations of one or more of the relevant listed items.

[0020] The terminology used in this application is for the purpose of describing specific embodiments only and is not intended to limit the scope of this application. As shown in the specification and claims of this application, unless the context clearly indicates otherwise, words such as "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate that explicitly identified features, integrals, steps, operations, elements, and / or components are included, and such expressions do not constitute an exclusive list, and other features, integrals, steps, operations, elements, and / or components may also be included.

[0021] Referring to the following description and accompanying drawings, these and other features and characteristics, operating methods, functions of related structural elements, combinations of parts, and economics of manufacture of this application can be better understood, wherein the description and drawings form part of the specification. However, it is clearly understood that the drawings are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this application. It is understood that the drawings are not drawn to scale.

[0022] Various structural diagrams are used in this application to illustrate various variations of the embodiments according to this application. It should be understood that the preceding or following structures are not intended to limit this application. The scope of protection of this application is determined by the claims.

[0023] In space charge measurement based on the electro-optic effect, the measured signal is the transient electric field excited by the space charge after laser perturbation. This electric field has two extreme characteristics: first, it is extremely weak, with the field strength typically on the order of mV / mm; second, it has an extremely narrow pulse width (on the order of picoseconds), corresponding to a spectral bandwidth on the order of THz. These two characteristics are interdependent, placing extremely high demands on both the sensitivity and detection bandwidth of the electro-optic detection system.

[0024] Traditional electro-optic detection systems typically employ a transmission topology, where the probe light penetrates along the sensor's normal, resulting in an incident coupling coefficient α of only around 0.1. This leads to a significant further attenuation of the already weak electric field signal during detection, resulting in severely insufficient system sensitivity. Furthermore, in the signal readout stage, traditional schemes use balanced detectors for direct photoelectric conversion. However, limited by the inherent bandwidth of balanced detectors (MHz to GHz levels), picosecond-level ultra-high-frequency signals experience waveform broadening or even distortion. In contrast, femtosecond pulsed lasers, due to their extremely narrow pulse width, have been introduced into the field of ultrafast optical measurement, offering the possibility of achieving high time-resolution signal detection.

[0025] As described in the background section, the space charge measurement scheme based on the traditional electro-optic detection system has the following defects: insufficient sensitivity due to the low incident coupling coefficient of the transmission topology (about 0.1), and difficulty in measuring picosecond-level ultra-high frequency signals due to the inherent bandwidth limitation of the detector (MHz to GHz level). Moreover, the above two defects originate from two extreme properties of the same signal, and a single method cannot solve them at the same time.

[0026] To systematically address the aforementioned deficiencies, this application proposes an electro-optic detection system and its sensitivity and bandwidth coordinated measurement scheme. The aim is to achieve high-fidelity measurement of transient electric field signals with both "weak" and "ultra-high frequency" extreme characteristics by integrating reflective electro-optic detection topology with optical sampling measurement.

[0027] like Figure 1 (A schematic diagram of the electro-optic detection system provided in this application embodiment) shows that this application constructs a measurement system that integrates reflective electro-optic detection with optical sampling. Its core is: the probe light is incident at an inclined angle onto an electro-optic sensor with a reflective surface, and after reflection, it exits, thereby acquiring modulated probe light carrying transient electric field information at the front end with high light energy utilization; subsequently, the modulated probe light enters the optical sampling module, and the relative delay between the pump light and the probe light is changed by a step delay line, achieving signal reconstruction through step-by-step sampling at the back end.

[0028] Based on the above system architecture, this application further implements the following: Figure 2(A schematic diagram of the sensitivity and bandwidth co-optimization framework of the electro-optic detection system adapted for space charge measurement provided in this application embodiment) shows a four-step optimization method. This method unfolds from two core dimensions: Step S1 (detection topology optimization) replaces the transmission topology with a reflective detection topology, increasing the light energy utilization rate from approximately 0.1 to approximately 0.95, solving the problem of insufficient sensitivity; Step S4 (detection bandwidth optimization) introduces optical sampling measurement, replacing traditional direct photoelectric conversion with a stepwise sampling method, increasing the detection bandwidth from the MHz / GHz level to the THz level, solving the problem of insufficient bandwidth. Steps S2 (sensor parameter optimization) and S3 (detection angle optimization) are preferred methods, further achieving incremental performance improvements through sensor parameter optimization and Brewster angle matching. The above S1 and S4 are not independent but form a closed loop around the same modulated probe light, resulting in front-end enhancement and back-end bandwidth breakthrough—S1 provides a measurable signal basis for S4, and S4 enables the ultrafast signal captured by S1 to be read out without distortion. Both are adapted to the dual extreme characteristics of the signal being both weak and ultra-high frequency.

[0029] Figure 3 This is a flowchart illustrating a method for coordinating the measurement of sensitivity and bandwidth of an electro-optic detection system according to some embodiments of this application. Figure 3 As shown, the method includes: S310 divides the pulsed laser into pump light and probe light, wherein the pump light is used to disturb the space charge to excite the transient electric field to be measured.

[0030] This application uses a femtosecond pulsed laser as the light source, whose ultrashort pulse width characteristics provide a high-temporal-resolution sampling basis for optical sampling measurements. For example... Figure 1 As shown, the femtosecond pulsed laser is split into pump light by a beam splitter. Figure 1 (labeled as excitation laser) and probe light ( Figure 1 (The image is labeled as a probe laser). The pump light is used to disturb space charges to excite the transient electric field to be measured, while the probe light is used to sense this transient electric field. The pump light and probe light are transmitted through different optical paths, and their relative delay is adjusted by a delay device so that the probe light senses the transient electric field at different times, thereby achieving equivalent time sampling of the transient electric field signal.

[0031] S320, the probe light is obliquely incident on the electro-optic sensor and reflected by the sensor's reflective surface before exiting, thereby acquiring modulated probe light carrying transient electric field information.

[0032] This step aims to replace the traditional transmission topology with a reflective probe topology, so that the probe light is incident on the electro-optic sensor at an inclined angle and reflected by the reflective surface before exiting. This improves the energy coupling efficiency and measurement sensitivity of the probe laser, thereby acquiring modulated probe light carrying transient electric field information, and providing a measurable signal basis for subsequent optical sampling.

[0033] like Figure 2 As shown, the detection topology is first optimized. That is, the transmission topology is abandoned and a reflection detection topology is adopted to eliminate the limitation of the incident coupling coefficient and improve the detection laser energy coupling and measurement efficiency.

[0034] Specifically, such as Figure 1 As shown, in the transmission mode, the detection laser orthogonally penetrates the sensor along the side normal; while in the reflection mode, the beam is obliquely coupled at a specific tilt angle and is extracted after being reflected by the sensing interface on the side of the sample.

[0035] In the transmission method, since only the beam component penetrating the electro-optic medium undergoes polarization evolution under field intensity modulation during the measurement process, while the polarization state of the remaining free space beam components remains constant, the output differential light intensity of the balanced detector should be: in, Defined as the incident coupling coefficient, it is used to quantify the spatial coverage ratio between the detection spot and the sensor device; The effective interaction length, in a transmission topology, is strictly equal to the geometric length of the sensor. To balance the differential light intensity output by the detector.

[0036] In the reflection method, the probe light is at an angle... Coupled to the sensor interface, Fresnel reflection occurs on the upper surface of the sensor, forming the first reflected beam; the remaining components refract into the sensor, undergo total internal reflection at the lower surface, and then exit, forming the second reflected beam carrying the sensing information. Only the reflected light path entering the interior of the medium undergoes birefringence modulation caused by space charge perturbation, while the polarization state of the reflected light from the air interface remains unchanged. Therefore, the light intensity difference in the reflection detection topology is: , in, This represents the effective optical path length of the probe light within the medium under the reflection topology, and its value varies with the incident angle. Change comes with change.

[0037] When the incident angle satisfies the following critical matching condition, the effective reflected optical path reaches the theoretical upper limit, and this maximum value converges exactly to the axial physical length of the sensor: , Under this critical matching condition, the effective interactive optical path lengths of the transmission and reflection topologies are equivalent, and the difference in system measurement efficiency then depends entirely on the incident coupling coefficient. With interface transmittance The ratio of the two is significant. Transmission topologies are limited by a low incident coupling coefficient (approximately 0.1), while reflection architectures possess relatively high interface transmittance (approximately 0.95). Therefore, the overall measurement efficiency of reflection-based detection topologies far surpasses that of transmission topologies, exhibiting extremely high space charge detection sensitivity.

[0038] Subsequently, sensing parameters were optimized. Based on the dual influence of the crystal electro-optic coefficient and sensor thickness on system sensitivity, the optimal sensing material was selected, and the optimal crystal thickness, balancing beam propagation distance and electric field strength, was determined. Experimental and theoretical analysis showed that sensitivity is positively correlated with the electro-optic coefficient. This embodiment uses trigonal lithium niobate with an ilmenite structure (…). The crystal has an electro-optic coefficient as high as 30.4 pm / V, and its response amplitude is the largest and there is no waveform broadening under high frequency and narrow pulse electric field.

[0039] For thickness While increasing the thickness can extend the optical path, it significantly weakens the electric field of the space charge distribution inside the crystal. Based on the experimentally determined inflection point of sensitivity decrease, a crystal thickness of 2 mm was selected. At this thickness, the weights of the optical path extension and the weakening of the electric field are optimally balanced, and diffuse reflection interference caused by an excessively thin crystal is avoided.

[0040] Furthermore, the detection angle is optimized through optical path angle matching. The theoretical Brewster angle is calculated based on the refractive index of the selected sensing crystal, and the incident angle of the detection light is adjusted to this optimal angle to ensure... Zero-loss transmission of polarized light. Ideally, the incident light is set to be parallel to the plane of incidence. When polarized light is projected onto a medium surface at exactly the Brewster angle, the interface will only reflect light with perpendicular vibrations. polarization components, The polarization component achieves near-zero-loss transmission, completely penetrating into the sensing crystal to respond to the electric field signal excited by space charge. For practical testing environments, a polarizer is used to control the polarization state of the light source. State-polarized light. When it is incident at a Brewster angle, the probe light can be transmitted into the sensor with maximum efficiency; conversely, increasing or decreasing the incident angle will increase the energy loss caused by reflection. Therefore, the system's detection sensitivity to the electric field of the charge reaches its theoretical peak near the Brewster angle.

[0041] The formula for calculating the optimal incident angle of the probe light uses the Brewster angle calculation formula: , in, The refractive index of the sensing crystal, The refractive index is denoted by air. For lithium niobate crystals, the optimal incident angle of the probe light is approximately 66°.

[0042] like Figure 1 As shown, the modulated probe light emitted after being reflected by the electro-optic sensor sequentially enters a quarter-wave plate, a Wollaston prism, and a balanced detector to convert the transient electric field information into a measurable electrical signal.

[0043] S330, by changing the relative delay between the pump light and the probe light, the modulated probe light is sampled and reconstructed step by step to reconstruct the high-bandwidth waveform of the transient electric field signal, thereby realizing the measurement of the space charge.

[0044] This step optimizes the detection bandwidth to read the signal from the modulated probe light carrying transient electric field information acquired in S320. As shown in S320, although the modulated probe light acquired through the reflective detection topology has a measurable signal strength, the pulse width of its carried electric field information is extremely narrow (picosecond level). If a traditional balanced detector is used for direct photoelectric conversion, the signal will suffer severe waveform broadening or even distortion due to the inherent bandwidth of the detector (MHz to GHz level). Therefore, this step introduces delay-line-based optical sampling measurement, using sampling laser pulses to progressively sample and reconstruct the modulated probe light, thus overcoming the bandwidth limitations of traditional balanced detectors.

[0045] like Figure 1 As shown, the probe light split in S310 is incident on the electro-optic sensor after its optical path is altered by a step delay line. The modulated probe light, after reflection, is then converted into an electrical signal by a quarter-wave plate, a Wollaston prism, and a balanced detector. The pump light split in S310 is used to perturb space charges to excite the transient electric field to be measured, providing a repeatable time reference for the measurement process. By successively changing the position of the step delay line to alter the optical path of the probe light, the delay of the probe light relative to the pump light changes sequentially, thus sampling at different time points of the transient electric field waveform. After multiple cycles of progressive sampling, all sampling points are reconstructed into the original high-bandwidth signal by a lock-in amplifier, thereby achieving distortion-free measurement of picosecond-level pulse-width transient electric field signals.

[0046] To verify the output response of the collaborative measurement method described in this application under picosecond pulse width signals, one embodiment of this application uses a photoconductive antenna to generate a picosecond pulse width electric field based on the photogenerated carrier effect. Figure 4 Given Figure 3 The output response of the cooperative measurement method shown is under a 200 mV / mm picosecond pulse width electric field. Figure 4As can be seen, the proposed collaborative measurement method responds well under picosecond pulse electric fields. Measurement of picosecond pulse electric fields was achieved with a pulse width of 1.5 ps, and the waveform showed no significant distortion. This demonstrates that the bandwidth of the proposed collaborative measurement method has the potential to reach the THz level. Optical sampling measurement mitigates the detector bandwidth limitations imposed by direct measurement; each sampling is equivalent to acquiring a DC signal, effectively reducing noise levels and further improving measurement sensitivity.

[0047] It should be noted that, Figure 2 The optimization of sensing parameters and detection angle in this application is the preferred implementation method, which aims to further improve the intrinsic sensitivity and light energy utilization of the system. Those skilled in the art can choose to implement or omit the above preferred steps according to specific application requirements.

[0048] In this application, the reflective probe topology used in probe topology optimization and the optical sampling measurement introduced by probe bandwidth optimization together constitute a complete measurement link for signals that are both weak and ultra-high frequency: probe topology optimization raises the weak electric field signal to a signal-to-noise ratio level that can be subsequently sampled, providing a measurable signal basis for probe bandwidth optimization; probe bandwidth optimization, on the other hand, achieves THz-level signal fidelity reconstruction through optical sampling, enabling the ultrafast signal captured by probe topology optimization to be read out without distortion. From the perspective of optical path configuration, the above two are physically inseparable and cascaded—the probe light generated from the same femtosecond pulse laser beam must first obtain electric field modulation through the reflective topology before entering the optical sampling module for delayed sampling and reconstruction; if the reflective topology is removed, there will be no modulated signal to be sampled in optical sampling; if optical sampling is removed, the ultra-high frequency modulated signal captured by the reflective topology cannot be read out with fidelity due to the detector bandwidth limitation. The two are interdependent and indispensable.

[0049] Figure 5 This is a system architecture diagram of an electro-optical detection system according to some embodiments of this application. Figure 5 As shown, the electro-optic detection system includes a controller, a beam splitter, a reflective electro-optic detection component, and an optical sampling component.

[0050] The controller, as the core of the system, is configured to execute... Figure 3 The sensitivity and bandwidth coordinated measurement method of the electro-optic detection system is implemented by controlling the beam splitter, the reflective electro-optic detection component, and the optical sampling component to achieve each step of the method.

[0051] The beam splitter is used to split the pulsed laser into pump light and probe light, wherein the pump light is used to disturb the space charge to excite the transient electric field to be measured. The reflective electro-optic detection component is used to obliquely incident the detection light onto the electro-optic sensor and then emit it after being reflected by the reflective surface of the electro-optic sensor, thereby acquiring modulated detection light carrying transient electric field information. The reflective electro-optic detection component includes the electro-optic sensor, which has a reflective surface. The optical sampling component is used to progressively sample and reconstruct the modulated probe light by changing the relative delay between the pump light and the probe light, so as to reconstruct the high-bandwidth waveform of the transient electric field signal, thereby realizing the measurement of the space charge, wherein the optical sampling component includes a delay device.

[0052] like Figure 5 As shown, the controller is connected to the beam splitter, the reflective electro-optical detection component and the optical sampling component through a bidirectional data path to achieve closed-loop control of each module.

[0053] In summary, the electro-optic detection system and its sensitivity and bandwidth co-measurement method provided in the embodiments of this application, by employing a reflective detection topology, allow the detection light to be incident obliquely onto the electro-optic sensor and reflected by the reflective surface before exiting (interface transmittance is approximately 0.95), thus avoiding the problem of significant signal attenuation caused by the extremely low incident coupling coefficient (approximately 0.1) in transmission topologies, and solving the problem of insufficient sensitivity. Secondly, by introducing optical sampling measurement and using step delay lines to progressively sample and reconstruct, the detection bandwidth is increased from the MHz / GHz level to the THz level, solving the problem of insufficient bandwidth. The above technical features are not simply superimposed, but rather, in response to the dual extreme characteristics of the signal being both weak and ultra-high frequency in the space charge measurement scenario, they together form a complete closed loop of pre-enhancement and post-bandwidth limitation breakthrough, achieving unexpected technical effects such as a jump in measurement sensitivity from 800V / mm to 200mV / mm and an increase in measurement bandwidth from 28.6MHz to 0.67THz.

[0054] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application. The appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for coordinating the measurement of sensitivity and bandwidth of an electro-optic detection system, characterized in that, include: The pulsed laser is divided into a pump light and a probe light. The pump light is used to disturb the space charge to excite the transient electric field to be measured. The probe light is incident at an angle onto the electro-optic sensor and reflected by the sensor's reflective surface before exiting, thereby acquiring modulated probe light carrying transient electric field information; By altering the relative delay between the pump light and the probe light, the modulated probe light is progressively sampled and reconstructed to rebuild the high-bandwidth waveform of the transient electric field signal, thereby enabling the measurement of the space charge.

2. The method according to claim 1, characterized in that: The electro-optic sensor includes a sensing crystal; The process of obliquely incidenting the probe light onto the electro-optic sensor and then reflecting it off the sensor's reflective surface to obtain the modulated probe light carrying transient electric field information includes: The probe light is incident on the electro-optic sensor at a Brewster angle corresponding to the refractive index of the sensing crystal, and is reflected by the reflective surface before exiting, so as to ensure that the p-state polarized light achieves zero-loss transmission at the sensor interface and obtains the modulated probe light carrying transient electric field information. Brewster's Corner Calculated using the following formula: ， in, The refractive index of the sensing crystal is given. The refractive index of air.

3. The method according to claim 2, characterized in that: The crystal material of the sensing crystal is determined based on the dual influence of the electro-optic coefficient of the crystal material and the sensor thickness on the system sensitivity; The optimal crystal thickness is determined based on the crystal material, the beam propagation distance, and the electric field strength.

4. The method according to claim 3, characterized in that: The sensing crystal is a lithium niobate crystal, and the reflective surface is coated with a high-reflectivity aluminum film. The thickness of the sensing crystal is 2 mm.

5. The method according to claim 4, characterized in that: The probe light is incident on the electro-optic sensor at an angle of 66° and is reflected by the reflective surface before exiting, thereby acquiring modulated probe light carrying transient electric field information.

6. The method according to claim 1, characterized in that: The pulsed laser is a femtosecond pulsed laser; The stepwise sampling of the modulated probe light by changing the relative delay between the pump light and the probe light includes: By changing the optical path of the probe light through a step delay line, a fixed time delay is generated between each pulse as a sampling interval, and the picosecond-level pulse width electric field signal is sampled step by step.

7. The method according to claim 6, characterized in that, The stepwise sampling and reconstruction of the modulated probe light includes: The signal obtained by stepwise sampling is reconstructed by a lock-in amplifier to restore the original high-bandwidth signal.

8. The method according to any one of claims 1-7, characterized in that: The method is applied to the transient electric field measurement of space charge in solid insulating materials.

9. The method according to any one of claims 1-7, characterized in that: The electro-optic detection system has picosecond-level pulse width electric field tracking capability, a minimum detection electric field strength threshold of 200mV / mm, a measurement bandwidth of 0.67THz, and a theoretical equivalent spatial resolution of 3.6nm.

10. An electro-optical detection system, characterized in that, include: A beam splitter is used to split a pulsed laser into a pump beam and a probe beam, wherein the pump beam is used to perturb the space charge to excite the transient electric field to be measured. A reflective electro-optic detection component is used to obliquely incident the detection light onto the electro-optic sensor and then emit it after being reflected by the reflective surface of the electro-optic sensor, thereby acquiring modulated detection light carrying transient electric field information. The reflective electro-optic detection component includes the electro-optic sensor, which has a reflective surface. An optical sampling component is used to progressively sample and reconstruct the modulated probe light by changing the relative delay between the pump light and the probe light to reconstruct the high-bandwidth waveform of the transient electric field signal, thereby realizing the measurement of the space charge, wherein the optical sampling component includes a delay device; A controller configured to perform the method as described in any one of claims 1-9.

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