Ultrafast electronic pulse width measuring system and measuring method based on time amplification fringe scanning

Abstract

The invention discloses an ultrafast electronic pulse width measuring system and method based on time amplification fringe scanning. The problems that when the pulse width of an ultra-short electronic pulse is measured through an existing pulse width measurement technology, the measurement requirement for the length of an ultra-fast electronic pulse bunch with the electronic pulse width smaller than 100 femtoseconds is difficult to meet, the measurement precision is low, a measurement system is complex, and the cost is high are solved. According to the method, a time broadening effect is generated by utilizing a space charge effect and a vacuum dispersion effect of femtosecond-order ultrafast electronic pulse, the ultrafast electronic pulse is broadened to a picosecond order which can be detected by a traditional stripe scanning method, and the time broadening amount of the electronic pulse can be obtained by utilizing a space-time broadening theory; the pulse width of the broadened ultrafast electronic pulse is obtained through a stripe scanning deflection method, and the pulse width of the ultrafast electronic pulse can be obtained through inversion; the method provided by the invention can be used for accurately characterizing the femtosecond-order ultrafast electronic pulse ground pulse, and is high in time resolution, simple in system principle and easy to implement.

Description

Technical Field

[0001] The invention relates to a method for measuring the pulse width of an ultrafast electronic pulse, and in particular to a system and method for measuring the pulse width of an ultrafast electronic pulse based on time-amplified fringe scanning. Background Art

[0002] Ultrafast electron pulses are one of the main probes for studying the ultrafast dynamics of atoms or electrons in materials. Their pulse width directly affects the time resolution of ultrafast characterization instruments such as ultrafast electron diffraction devices and ultrafast electron microscopes. How to generate shorter ultrafast electron pulses has long been a hot topic in scientific research, and the corresponding ultrafast electron pulse width measurement technology has also attracted much attention. Currently, in the field of ultrafast electron pulse width measurement technology, the existing technologies mainly include:

[0003] In the paper Zhang W, Zhu D, Sui Y, et al. Streak camera calibration for bunch length measurement at BEPC II[J]. Radiation Detection Technology and Methods, 2021, 5: 466-473., an electron pulse measurement method based on a traditional streak camera is disclosed. The electrons arriving at different times are deflected to different spatial positions by using the time-varying deflection electric field on the deflection plate in the streak camera, and the electron pulse time series is converted into a recognizable spatial system. The pulse width of the electron pulse arriving at the deflection plate is then obtained by inverting the relationship between the change of the deflection electric field with time. The measurement accuracy of this method mainly depends on the streak camera. The time resolution of the most advanced commercial streak camera is 100fs, so it is difficult to meet the measurement requirements of the bunch length of ultrafast electron pulses with an electron pulse width of less than 100 femtoseconds.

[0004] In the paper Bai Jin, Chen Qushan, Fan Kuanjun. A bunch length measurement system based on RF deflection cavity [J]. Atomic Energy Science and Technology, 2019, 53(09): 1607-1611., a bunch length measurement system based on RF deflection cavity is disclosed. The RF deflection cavity will generate an eigenmode electric field under the excitation of external energy. When the electron pulse passes through the deflection cavity, it is deflected by the electric field in the cavity. Bunch slices with different longitudinal phases will be incident on different positions of the screen. The bunch length can be derived by analyzing the screen signal. This method can currently achieve bunch length diagnosis of tens of femtoseconds, but the synchronization problem of RF signals limits the improvement of the measurement accuracy of this scheme. At the same time, the RF source, cooling system, and signal synchronization system make the system more complicated and the operating cost is relatively high.

[0005] In the paper Pompili R, Cianchi A, Alesini D, et al. First single-shot and non-intercepting longitudinal bunch diagnostics for comb-like beam by means of electro-optic sampling [J]. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014, 740: 216-221., an electro-optic sampling method for electron beam bunch diagnosis is disclosed. When electrons pass through an electro-optic crystal, a birefringence effect is generated, and linearly polarized light becomes elliptically polarized light. The ellipticity is proportional to the electric field intensity, and the distribution of the Coulomb electric field of the bunch reflects the longitudinal distribution of the bunch. Although the electro-optic sampling method can achieve very high resolution in diagnosing the bunch length, it has strict requirements on laser technology, optical detection technology, etc., resulting in high system complexity, technical threshold and cost. Summary of the invention

[0006] The purpose of the present invention is to solve the technical problems that the existing pulse width measurement technology is difficult to meet the measurement requirements of the ultrafast electron pulse bunch length with an electron pulse width of less than 100 femtoseconds, the measurement accuracy is low, the measurement system is complex and the cost is high when measuring the pulse width of ultrashort (femtosecond or attosecond level) electron pulses, and to provide an ultrafast electron pulse width measurement system and a measurement method based on time-amplified fringe scanning.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] An ultrafast electronic pulse width measurement system based on time-amplified fringe scanning, which is special in that:

[0009] It includes a vacuum drift tube, a scanning deflection housing, a parallel deflection plate, a fluorescent screen, an electron bombardment CCD camera and a deflection control system;

[0010] The input end of the vacuum drift tube is used to be connected with the output end of the ultrafast electron pulse generating device, and the ultrafast electron pulse is input. After the ultrafast electron pulse is pulse-stretched in the vacuum drift tube, a stretched electron pulse is obtained; the output end of the vacuum drift tube is connected with the input end of the scanning deflection shell, and a slit is arranged between the two. The parallel deflection plate is arranged inside the scanning deflection shell, and the central axis of the vacuum drift tube is located between the two plates of the parallel deflection plate and is parallel to the two plates; wherein the slit is used to limit the size of the electron beam spot entering the parallel deflection plate to prevent the electron beam from being incident on the parallel deflection plate; the vacuum drift tube is used for the time amplification process of the ultrafast electron pulse, that is, the ultrafast electron pulse generates time and space broadening under the action of its own space charge effect, and the femtosecond-level electron pulse can be converted into a picosecond-level electron pulse through the time amplification process of the vacuum chamber, so that the traditional streak camera can detect the signal.

[0011] The input end of the deflection control system is connected to the signal output end of the ultrafast electronic pulse generating device, and the output end of the deflection control system is connected to the parallel deflection plates, for collecting the electrical signal outputted from the signal output end of the ultrafast electronic pulse generating device, and performing delay modulation to obtain a scanning bias signal synchronized with the time of the widened electronic pulse entering the parallel deflection plates, and inputting the synchronized scanning bias signal into the parallel deflection plates to form a scanning deflection field between the two plates of the parallel deflection plates;

[0012] The fluorescent screen is arranged at one end of the scanning deflection housing far away from the vacuum drift tube, and the outer side of the fluorescent screen is connected to the input end of the electron bombardment CCD camera.

[0013] Furthermore, the formula for pulse broadening of the ultrafast electron pulse by the vacuum drift tube (3) is:

[0014] t x =t0+Δt c ;

[0015] where t x is the pulse width of the stretched electron pulse, t0 is the pulse width of the ultrafast electron pulse generated by the ultrafast electron pulse generator, Δt c is the time stretching term, expressed as:

[0016]

[0017] Among them, t represents the electron drift time in the ultrafast electron pulse, v represents the ultrafast electron pulse speed, N represents the number of electrons in the ultrafast electron pulse, r represents the lateral radius of the ultrafast electron pulse, and m represents the mass of a single electron.

[0018] Furthermore, the deflection control system includes a signal synchronization system and a scanning circuit, the input end of the signal synchronization system is connected to the signal output end of the ultrafast electronic pulse generating device, and the output end of the signal synchronization system is connected to the scanning circuit and the parallel deflection plates in sequence. The signal synchronization system is used to collect the electrical signal output by the signal output end of the ultrafast electronic pulse generating device, and perform delay modulation to obtain an electrical signal synchronized with the broadened electronic pulse entering the parallel deflection plates. The synchronized electrical signal triggers the scanning circuit to generate a scanning bias signal, and the parallel deflection plates are used to produce a scanning deflection field according to the scanning bias signal.

[0019] Furthermore, the emission energy of the ultrafast electron pulse is 200 keV, the longitudinal length of the bunch is 30 fs, the transverse size of the bunch is 200 μm, and the number of electrons is 10,000.

[0020] Furthermore, the slit width is 20 μm, and the distance from the slit to the parallel deflection plate is 4 mm.

[0021] Furthermore, the outer side of the fluorescent screen is connected to the input end of the electron bombardment CCD camera through optical coupling glue.

[0022] At the same time, the present invention also provides an ultrafast electron pulse width measurement method based on time-amplified fringe scanning, the special feature of which is that the ultrafast electron pulse width measurement system based on the above-mentioned time-amplified fringe scanning includes the following steps:

[0023] S1, disconnect the deflection control system, turn on the ultrafast electronic pulse generating device to generate ultrafast electronic pulses, and input the ultrafast electronic pulses into the vacuum drift tube, calculate the time stretching term of the ultrafast electronic pulses according to the parameters of the ultrafast electronic pulses, use the time stretching term to stretch the ultrafast electronic pulses in the vacuum drift tube, and output the stretched electronic pulses;

[0024] S2, the broadened electron pulse passes through the slit and the parallel deflection plate in turn and is incident on the fluorescent screen to form a fringe-like spot. The image of the fringe-like spot is collected by the electron bombardment CCD camera, and the longest size σ of the fringe-like spot is calculated. s ;

[0025] S3, restore access to the deflection control system, collect the output end electrical signal of the ultrafast electronic pulse generating device through the deflection control system, and delay modulate the output end electrical signal to output a scanning bias signal that is synchronized with the time of the widened electronic pulse entering the parallel deflection plate; input the scanning bias signal to the parallel deflection plate to form a scanning deflection field between the two plates of the parallel deflection plate; the widened electronic pulse in the parallel deflection plate is deflected when output and incident on the fluorescent screen to form a quasi-stripe light spot, and the image of the quasi-stripe light spot is collected by the electron bombardment CCD camera, and the longest size of the quasi-stripe light spot is obtained as σ d ;

[0026] S4, the size of the fringe-like spot σ s and the size of the fringe-like spot is σ d The pulse width of the stretched electron pulse is calculated, and the pulse width of the ultrafast electron pulse is calculated based on the pulse width of the stretched electron pulse and the time stretching term.

[0027] Furthermore, the specific process of S1 is:

[0028] S11, disconnect the deflection control system, turn on the ultrafast electron pulse generating device to generate ultrafast electron pulses, and input them into the vacuum drift tube;

[0029] S12. Calculate the time broadening term Δt of the ultrafast electron pulse based on the parameters of the ultrafast electron pulse c , the formula is:

[0030]

[0031] Wherein, t represents the electron drift time in the ultrafast electron pulse, v represents the ultrafast electron pulse velocity, N represents the number of electrons in the ultrafast electron pulse, r represents the lateral radius of the ultrafast electron pulse, and m represents the mass of a single electron;

[0032] S13. The time stretching term is used in the vacuum drift tube to stretch the ultrafast electron pulse. The expression is:

[0033] t x =t0+Δt c ;

[0034] Wherein, x is the pulse width of the stretched electron pulse, and t0 is the pulse width of the ultrafast electron pulse generated by the ultrafast electron pulse generating device;

[0035] S14, output pulse width is t x The stretched electron pulse.

[0036] Further, in S4, the size σ of the striated light spot is s and the size of the fringe-like spot is σ d The formula for calculating the pulse width of the stretched electron pulse is:

[0037]

[0038] Among them, v scan is the scanning speed of the fringe scanning deflection system.

[0039] Further, in S4, the formula for calculating the pulse width of the ultrafast electron pulse according to the pulse width of the stretched electron pulse and the time stretching term is:

[0040] t0=t x -Δt c .

[0041] Beneficial effects of the present invention:

[0042] 1. The present invention discloses an ultrafast electron pulse width measurement system and method based on time-amplified fringe scanning. Based on the time-space broadening theory of non-relativistic electron pulses and the traditional fringe scanning deflection method, it can accurately characterize the pulses of ultrafast electron pulses in the femtosecond range. It has high time resolution, simple system principle and is easy to implement.

[0043] 2. The ultrafast electronic pulse width measurement system based on time-amplified fringe scanning of the present invention is simple and low-cost, and can be widely used in various electronic pulse width measurement experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a structural schematic diagram of an embodiment of an ultrafast electronic pulse width measurement system based on time-amplified fringe scanning of the present invention;

[0045] Figure 2 This is a schematic diagram of the evolution of the pulse width of an ultrafast electron pulse during the amplification process over time in step S1 of an embodiment of an ultrafast electron pulse pulse width measurement method based on time-amplified fringe scanning of the present invention.

[0046] In the figure, 1-ultrafast electron pulse generating device; 2-ultrafast electron pulse; 3-vacuum drift tube; 4-scanning deflection shell; 5-parallel deflection plate; 6-fluorescent screen; 7-electron bombardment CCD camera; 8-output electrical signal; 9-signal synchronization system; 10-scanning circuit; 11-scanning bias voltage signal; 12-slit. DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] This embodiment is an ultrafast electronic pulse width measurement system based on time-amplified fringe scanning, such as Figure 1 As shown, it includes a vacuum drift tube 3, a scanning deflection housing 4, a parallel deflection plate 5, a fluorescent screen 6, an electron bombardment CCD camera 7 and a deflection control system;

[0049] The input end of the vacuum drift tube 3 inputs the ultrafast electron pulse 2 of the order of hundreds of femtoseconds generated by the ultrafast electron pulse generating device 1, and the ultrafast electron pulse 2 is pulse stretched in the vacuum drift tube 3 to obtain a stretched electron pulse; a slit 12 is provided between the output end of the vacuum drift tube 3 and the scanning deflection housing 4, and a parallel deflection plate 5 is provided inside the scanning deflection housing 4, and the central axis of the vacuum drift tube 3 is located between the two plates of the parallel deflection plate 5 and is parallel to the two plates;

[0050] The ultrafast electron pulse 2 generated by the ultrafast electron pulse generating device 1 has an emission energy of 200 keV, a bunch longitudinal length of 30 fs, a bunch transverse size of 200 μm, and an electron number of 10,000.

[0051] The vacuum drift tube 3 used in this embodiment has a length of 39.5 cm and a diameter of 5 cm. When the ultrafast electron pulse is pulse-broadened in the vacuum drift tube 3, the formula is:

[0052] t x =t0+Δt c ;

[0053] where t x is the pulse width of the stretched electron pulse, t0 is the pulse width of the ultrafast electron pulse generated by the ultrafast electron pulse generating device 1, Δt c is the time stretching term, expressed as:

[0054]

[0055] Among them, Δt c is the time broadening term, t represents the electron drift time in the ultrafast electron pulse, v represents the ultrafast electron pulse velocity, N represents the number of electrons in the ultrafast electron pulse, r represents the lateral radius of the ultrafast electron pulse, and m represents the mass of a single electron.

[0056] The width of the slit 12 is 20 μm, and the distance from the slit 12 to the parallel deflection plate 5 is 4 mm.

[0057] The distance between the ultrafast electron pulse 2 and the parallel deflection plate 5 is the vacuum drift distance. In this embodiment, the vacuum drift distance is close to 40 cm. The electron pulse of the order of hundreds of femtoseconds will be widened to 1-2 picoseconds after passing through the vacuum drift tube 3.

[0058] The parallel deflection plates 5 have a length of 50 mm, a width of 20 mm, and a spacing of 2 mm.

[0059] The input end of the signal synchronization system 9 is connected to the output end of the ultrafast electronic pulse generating device 1, and the output end of the signal synchronization system 9 is connected to the scanning circuit 10 and the parallel deflection plate 5 in sequence, so as to collect the output electrical signal 8 of the output end of the ultrafast electronic pulse generating device 1, and obtain an electrical signal synchronized with the widened electronic pulse entering the parallel deflection plate. The synchronized electrical signal triggers the scanning circuit to generate a scanning bias signal, which is input into the parallel deflection plate 5 to form a scanning deflection field between the two plates of the parallel deflection plate 5; and is used to offset the widened electronic pulse entering the parallel deflection plate 5.

[0060] The scanning circuit 10 provides a time-varying scanning electric field with a peak value of 1000V to the parallel deflection plates 5 .

[0061] The electron pulse will drift 300 mm after being emitted from the parallel deflection plate 5 and will be incident on the fluorescent screen 6 .

[0062] One end of the scanning deflection housing 4 away from the vacuum drift tube 3 is connected to a fluorescent screen 6, and the fluorescent screen 6 is connected to an electron bombardment CCD camera 7 through an optical coupling glue.

[0063] A method for measuring the pulse width of an ultrafast electron pulse based on time-amplified fringe scanning, based on an ultrafast electron pulse pulse width measurement system based on time-amplified fringe scanning, comprises the following steps:

[0064] S1, disconnect the deflection control system, turn on the ultrafast electron pulse generating device 1 to generate ultrafast electron pulses, and input them into the vacuum drift tube 3, calculate the time stretching term of the ultrafast electron pulse, use the time stretching term to stretch the ultrafast electron pulse, and output the stretched electron pulse; the specific process is:

[0065] S11, turning on the ultrafast electronic pulse generating device 1 to generate an ultrafast electronic pulse 2, with a pulse width of t0;

[0066] S12. Calculate the time broadening term of ultrafast electron pulses. The formula is:

[0067]

[0068] Among them, Δt c is the time broadening term, t represents the electron drift time in the ultrafast electron pulse, v represents the ultrafast electron pulse velocity, N represents the number of electrons in the ultrafast electron pulse, r represents the lateral radius of the ultrafast electron pulse, and m represents the mass of a single electron;

[0069] S13, the time stretching term is used to time stretch the ultrafast electron pulse, and the expression is:

[0070] t x =t0+Δt c ;

[0071] Among them, tx is to widen the pulse width of the electronic pulse, t0 is the pulse width of the ultrafast electronic pulse generated by the ultrafast electronic pulse generating device 1;

[0072] S14, output pulse width is t x The stretched electron pulse.

[0073] S2, the stretched electron pulse passes through the slit 12 and the parallel deflection plate 5 in turn and is incident on the fluorescent screen 6 to form a fringe-like light spot. The image of the fringe-like light spot is collected by the electron bombardment CCD camera 7, and the longest size σ of the fringe-like light spot is calculated. s ;

[0074] S3, restore access to the deflection control system, collect the output end electrical signal of the ultrafast electronic pulse generating device 1 through the deflection control system, and use the signal synchronization system 9 to delay and modulate the output end electrical signal of the ultrafast electronic pulse generating device 1, so that the signal is synchronized with the time of the broadened electronic pulse entering the parallel deflection plate 5, and then input into the scanning circuit 10 as a trigger signal, and the time-varying scanning bias signal 11 generated by the scanning circuit 10 is input into the parallel deflection plate 5, and a scanning deflection field is formed between the two plates of the parallel deflection plate 5; the broadened electronic pulse in the parallel deflection plate 5 is deflected when output, and is incident on the fluorescent screen 6 to form a quasi-fringe light spot, and the image of the quasi-fringe light spot is collected by the electron bombardment CCD camera 7, and the longest size of the quasi-fringe light spot is calculated as σ d ;

[0075] S4, the size of the fringe-like spot σ s and the size of the fringe-like spot is σ d , according to the correspondence between spatial information and time information, the pulse width of the broadened electronic pulse is calculated as follows:

[0076]

[0077] Among them, v scan is the scanning speed of the fringe scanning deflection system.

[0078] The pulse width of the ultrafast electron pulse is calculated based on the pulse width of the stretched electron pulse and the time stretching term; the formula is:

[0079] t0=t x -Δt c .

[0080] The ultrafast electron pulse width measurement system and method based on time-amplified fringe scanning of this embodiment are used to measure the ultrafast electron pulse. The evolution process of the pulse width of the ultrafast electron pulse during the time amplification process is as follows: Figure 2As shown, the left side of the horizontal axis 700mm is the evolution of the pulse width of the electron pulse in the ultrafast electron pulse generating device during acceleration, collimation, focusing and pulse compression; the right side is the time amplification process of the ultrashort electron pulse during vacuum drift. After 40cm of time broadening, the pulse width at the deflection plate is 592fs (RMS), i.e. 1.394ps (FWHM). At this time, the current general streak camera can be used to measure the pulse width of the electron pulse after broadening, thereby achieving the measurement requirement of the ultrafast electron pulse bunch length less than 100 femtoseconds.

[0081] In the ultrafast electron pulse width measurement system and measurement method based on time-amplified fringe scanning of the present invention, after time stretching an ultrafast electron pulse less than 100 femtoseconds, an electric field is applied to deflect the time-stretched ultrafast electron pulse, and the light spot information before and after the electric field is applied on the fluorescent screen is collected to calculate the ultrafast electron pulse width, which can accurately characterize the pulse of ultrafast electron pulses in the femtosecond order, has high time resolution, and the system principle is simple and easy to implement.

[0082] The above description is only a specific embodiment of the present invention, and a comparison of the effects of the specific embodiments and the related comparative examples, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An ultrafast electronic pulse width measurement system based on time-amplified fringe scanning, characterized in that: It comprises a vacuum drift tube (3), a scanning deflection housing (4), a parallel deflection plate (5), a fluorescent screen (6), an electron bombardment CCD camera (7) and a deflection control system; The input end of the vacuum drift tube (3) is used to be connected to the output end of the ultrafast electron pulse generating device (1) to input the ultrafast electron pulse, and after the ultrafast electron pulse is pulse-stretched in the vacuum drift tube (3), a stretched electron pulse is obtained; the output end of the vacuum drift tube (3) is connected to the input end of the scanning deflection housing (4), and a slit (12) is provided between the two; the parallel deflection plate (5) is provided inside the scanning deflection housing (4), and the central axis of the vacuum drift tube (3) is located between the two plates of the parallel deflection plate (5) and is parallel to the two plates; The deflection control system has an input end connected to a signal output end of an ultrafast electronic pulse generating device (1), and an output end connected to a parallel deflection plate (5), and is used to collect an electrical signal output from the signal output end of the ultrafast electronic pulse generating device (1), and to perform delay modulation to obtain a scanning bias signal that is synchronized with the time of the widened electronic pulse entering the parallel deflection plate (5), and to input the synchronized scanning bias signal into the parallel deflection plate (5), so as to form a scanning deflection field between two plates of the parallel deflection plate (5); The fluorescent screen (6) is arranged at one end of the scanning deflection housing (4) away from the vacuum drift tube (3), and the outer side of the fluorescent screen (6) is connected to the input end of the electron bombardment CCD camera (7).

2. The ultrafast electronic pulse width measurement system based on time-amplified fringe scanning according to claim 1, characterized in that: The formula for pulse broadening of the ultrafast electron pulse by the vacuum drift tube (3) is: t x =t0+Δt c ; where t x is the pulse width of the extended electron pulse, t0 is the pulse width of the ultrafast electron pulse generated by the ultrafast electron pulse generating device (1), Δt c is the time stretching term, expressed as: Among them, t represents the electron drift time in the ultrafast electron pulse, v represents the ultrafast electron pulse speed, N represents the number of electrons in the ultrafast electron pulse, r represents the lateral radius of the ultrafast electron pulse, and m represents the mass of a single electron.

3. The ultrafast electron pulse width measurement system based on time-amplified fringe scanning according to claim 1, characterized in that: The deflection control system comprises a signal synchronization system (9) and a scanning circuit (10); the input end of the signal synchronization system (9) is connected to the signal output end of the ultrafast electronic pulse generating device (1); the output end of the signal synchronization system (9) is connected to the scanning circuit (10) and the parallel deflection plate (5) in sequence; the signal synchronization system (9) is used to collect the electrical signal output from the signal output end of the ultrafast electronic pulse generating device (1), and perform delay modulation to obtain an electrical signal synchronized with the broadened electronic pulse entering the parallel deflection plate (5); the synchronized electrical signal triggers the scanning circuit (10) to generate a scanning bias signal; and the parallel deflection plate (5) is used to generate a scanning deflection field according to the scanning bias signal.

4. The ultrafast electronic pulse width measurement system based on time-amplified fringe scanning according to claim 1, characterized in that: The emission energy of the ultrafast electron pulse is 200 keV, the longitudinal length of the bunch is 30 fs, the transverse size of the bunch is 200 μm, and the number of electrons is 10,000.

5. The ultrafast electron pulse width measurement system based on time-amplified fringe scanning according to claim 1, characterized in that: The width of the slit (12) is 20 μm, and the distance from the slit (12) to the parallel deflection plate (5) is 4 mm.

6. The ultrafast electron pulse width measurement system based on time-amplified fringe scanning according to claim 1, characterized in that: The outer side of the fluorescent screen (6) is connected to the input end of the electron bombardment CCD camera (7) through optical coupling glue.

7. A method for measuring the pulse width of ultrafast electron pulses based on time-amplified fringe scanning, characterized in that: An ultrafast electronic pulse width measurement system based on time-amplified fringe scanning according to any one of claims 1 to 6 comprises the following steps: S1, disconnecting the deflection control system, turning on the ultrafast electron pulse generating device (1) to generate an ultrafast electron pulse, and inputting the ultrafast electron pulse into the vacuum drift tube (3), calculating the time stretching term of the ultrafast electron pulse according to the parameters of the ultrafast electron pulse, using the time stretching term to stretch the ultrafast electron pulse in the vacuum drift tube (3), and outputting the stretched electron pulse; S2, the broadened electron pulse passes through the slit (12) and the parallel deflection plate (5) in sequence and is incident on the fluorescent screen (6), forming a striated light spot. The image of the striated light spot is collected by the electron bombardment CCD camera (7), and the longest size σ of the striated light spot is obtained. s ; S3, restore access to the deflection control system, collect the output end electrical signal of the ultrafast electron pulse generating device (1) through the deflection control system, and delay modulate the output end electrical signal to output a scanning bias signal that is synchronized with the time of the expanded electron pulse entering the parallel deflection plate (5); input the scanning bias signal to the parallel deflection plate (5), and form a scanning deflection field between the two plates of the parallel deflection plate (5); the expanded electron pulse in the parallel deflection plate (5) is deflected when output, and is incident on the fluorescent screen (6) to form a quasi-stripe light spot, and the image of the quasi-stripe light spot is collected by the electron bombardment CCD camera (7), and the longest size of the quasi-stripe light spot is obtained as σ d ; S4, the size of the fringe-like spot σ s and the size of the fringe-like spot is σ d The pulse width of the stretched electron pulse is calculated, and the pulse width of the ultrafast electron pulse is calculated based on the pulse width of the stretched electron pulse and the time stretching term.

8. The method for measuring the pulse width of an ultrafast electron pulse based on time-amplified fringe scanning according to claim 7, characterized in that: The specific process of S1 is as follows: S11, disconnecting the deflection control system, turning on the ultrafast electron pulse generating device (1) to generate ultrafast electron pulses, and inputting the ultrafast electron pulses into the vacuum drift tube (3); S12. Calculate the time broadening term Δt of the ultrafast electron pulse based on the parameters of the ultrafast electron pulse c , the formula is: Wherein, t represents the electron drift time in the ultrafast electron pulse, v represents the ultrafast electron pulse velocity, N represents the number of electrons in the ultrafast electron pulse, r represents the transverse radius of the ultrafast electron pulse, and m represents the mass of a single electron; S13, in the vacuum drift tube (3), a time stretching term is used to stretch the ultrafast electron pulse, and the expression is: t x =t0+Δt c ; Among them, t x is to widen the pulse width of the electronic pulse, t0 is the pulse width of the ultrafast electronic pulse generated by the ultrafast electronic pulse generating device (1); S14, output pulse width is t x The stretched electron pulse.

9. The method for measuring the pulse width of ultrafast electron pulses based on time-amplified fringe scanning according to claim 7, characterized in that: In S4, the size σ of the fringe-like spot s and the size of the fringe-like spot is σ d The formula for calculating the pulse width of the stretched electron pulse is: Among them, v scan is the scanning speed of the fringe scanning deflection system.

10. The method for measuring the pulse width of ultrafast electron pulses based on time-amplified fringe scanning according to claim 9, characterized in that: In S4, the formula for calculating the pulse width of the ultrafast electron pulse according to the pulse width of the stretched electron pulse and the time stretching term is: t0=t x -Δt c 。

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