Time stretching drift tube and ultrafast diagnosis system

Abstract

The invention discloses a time stretching drift tube and an ultrafast diagnosis system, and relates to the technical field of ultrafast diagnosis. The time stretching drift tube comprises a photoelectric cathode, a first grid mesh, a second grid mesh, a micro-channel plate, a third grid mesh and an anode which are sequentially arranged in a vacuum device, a front-end acceleration region is formed between the photoelectric cathode and the first grid mesh, a deceleration region is formed between the first grid mesh and the second grid mesh, and a drift region is formed between the second grid mesh and the micro-channel plate; a rear-end first acceleration region is formed between the micro-channel plate and the third grid mesh, and a rear-end second acceleration region is formed between the third grid mesh and the anode; and a magnetic lens is arranged outside the vacuum device region corresponding to the drift region so as to apply radial constraint to electrons passing through the drift region. The time stretching drift tube can meet the linear stretching condition and has high time stretching precision under the large stretching multiplying power.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafast diagnosis, and in particular to a time-stretch drift tube and an ultrafast diagnosis system. Background Art

[0002] With the continuous advancement of science and technology, such as the rapid development of quantum computing, nanotechnology, biotechnology and other fields, higher and higher requirements are placed on the time resolution capability of ultrafast diagnostic equipment.

[0003] In the prior art, there are two main ways to improve the time resolution of ultrafast diagnostic equipment: one is to improve the time resolution of the equipment itself by improving the structure or devices of the diagnostic equipment; the other is to achieve the purpose of improving time resolution by using time stretching technology to make the electrons spatially widen. Due to the structural limitations of existing ultrafast diagnostic equipment, it is difficult to achieve a significant improvement in time resolution using the first approach, so the second approach is currently generally used to improve the time resolution of ultrafast diagnostic equipment. Among them, the time stretching technology mainly uses the velocity dispersion of electrons in the time stretching drift tube to stretch the electrical signal on the time scale.

[0004] However, the time-stretch drift tube in the prior art cannot strictly meet the linear stretching requirement and the time-stretching precision of electrons is low at a large stretching ratio. Summary of the invention

[0005] Based on this, it is necessary to provide a time-stretch drift tube and an ultrafast diagnostic system to address the above technical problems. The time-stretch drift tube has higher time-stretch accuracy at a larger stretch ratio.

[0006] The present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a time-stretch drift tube, comprising: a photocathode, a first grid, a second grid, a microchannel plate, a third grid and an anode sequentially arranged in a vacuum device;

[0008] The front-end acceleration zone is formed between the photocathode and the first grid, the deceleration zone is formed between the first grid and the second grid, and the drift zone is formed between the second grid and the microchannel plate; the rear-end first acceleration zone is formed between the microchannel plate and the third grid, and the rear-end second acceleration zone is formed between the third grid and the anode;

[0009] A photocathode, used to receive incident light and convert the incident light into electrons that enter the acceleration region;

[0010] The acceleration zone is loaded with a constant electric field so that electrons entering the acceleration zone at different times enter the deceleration zone at the same axial velocity;

[0011] The deceleration zone is loaded with a time-varying electric field so that the electrons entering the deceleration zone at different times enter the drift zone at different axial speeds;

[0012] The drift region is an equipotential region, so that electrons entering the drift region with different axial velocities are stretched on a time scale; a magnetic lens is arranged outside the vacuum device region corresponding to the drift region, so as to impose radial constraints on electrons passing through the drift region.

[0013] A rear first acceleration zone, for reducing the time dispersion of electrons emitted through the microchannel plate;

[0014] The second acceleration zone at the rear end is used to further reduce the electron time dispersion and prevent the anode from being disturbed by the induced current signal, and convert the electrons into electric pulse signals through the anode to be received by an external high-frequency oscilloscope.

[0015] In one embodiment, the time-stretch drift tube also includes a DC control module and a pulse control circuit; a constant potential is loaded to the photocathode, the first grid, the second grid, the input surface and the output surface of the microchannel plate, the third grid and the anode through the DC control module; a current is loaded to the magnetic lens through the DC control module or the pulse control circuit; a pulse current is loaded to the first grid through the pulse control circuit, and the voltage difference between the photocathode and the first grid is kept constant.

[0016] In one embodiment, the lengths of the front end acceleration zone, the deceleration zone, the rear end first acceleration zone and the rear end second acceleration zone are less than or equal to the first preset length, the length of the drift zone is less than or equal to the second preset length, and the first preset length is less than the second preset length; the difference between the lengths of the front end acceleration zone and the deceleration zone and the length of the drift zone is greater than the third preset length.

[0017] In one embodiment, the material of the photocathode is determined according to the wavelength band of the incident light.

[0018] In one embodiment, the calculation formula for the electron transit time through the front-end acceleration region is:

[0019] d 1 =v 0 t+a z t 2 / 2;

[0020]

[0021] a z =V pc e / md 1 ;

[0022] Among them, d 1 is the length of the front acceleration zone, v 0is the initial axial velocity of the electron, t is the transit time of the electron through the front acceleration zone, a z is the axial acceleration, E 0 is the axial initial energy of the electron, m is the mass of the electron, e is the charge of a single electron, V pc is the pressure difference in the front acceleration zone.

[0023] In one embodiment, the linear stretching condition of the drift region is:

[0024]

[0025] in, is the change of the potential of the first grid with time t, M is the linear stretching multiple of the drift region, U 1 (t) is the potential difference in the front acceleration zone, U 2 (t) is the potential difference in the deceleration zone, L is the length of the drift zone, m is the mass of the electron, and e is the charge of a single electron.

[0026] In one embodiment, the signal inversion formula of the time-stretch drift tube is expressed as:

[0027]

[0028] in, is the intensity distribution of the time-stretched drift tube input signal, Ψ(t′) is the signal intensity distribution after time stretching in the drift region, and M(t) is the linear stretching multiple of the drift region.

[0029] The present invention provides an ultrafast diagnostic system, which includes the time-stretch drift tube described in any embodiment of the first aspect.

[0030] At least one of the above technical solutions adopted by the present invention can achieve the following beneficial effects:

[0031] In the present invention, by setting a grid structure, the electrons have a good transmittance, and radial constraints are applied to the electrons in the drift region through a magnetic lens, so that the electrons will not expand radially while being stretched axially, thereby improving the time stretching accuracy. Moreover, after the electrons pass through the drift region for time stretching, the electrons are passed through the rear first acceleration region and the rear second acceleration region, thereby reducing the time dispersion caused by the electrons being emitted from the drift region, further improving the time stretching accuracy. Moreover, a third grid is set between the microchannel plate and the anode, which can effectively prevent the induced current formed by the electrons emitted from the microchannel plate at the anode, thereby improving the anti-interference ability of the rear end and effectively improving the accuracy of the electrical signal received by the anode. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0033] Figure 1 A schematic diagram of the structure of a time-stretch drift tube provided by the present invention;

[0034] Figure 2 A schematic diagram of the applied voltages of various components in a time-stretch drift tube provided by the present invention;

[0035] Figure 3 Schematic diagram of electronic time stretching in the drift region of a time stretch drift tube provided by the present invention

[0036] Figure 4 A schematic diagram of the deduction and inversion signal changes of a pulse signal provided by the present invention;

[0037] Figure 5 A schematic diagram of a current curve waveform collected by an anode at different triggering moments provided by the present invention.

[0038] Description of reference numerals:

[0039] 101. vacuum device; 102. photocathode; 103. first grid; 104. second grid; 105. microchannel plate; 106. third grid; 107. anode; 108. magnetic lens. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] The Compton Effect refers to the process in which incident high-energy photons are scattered by inelastic collisions with extranuclear electrons in the atoms of matter. High-energy photons (gamma rays, etc.) transfer part of their energy to electrons, causing them to break away from atoms and become recoil electrons, while the photon energy and direction of movement change. Inverse Compton scattering is similar to Compton scattering, both of which are scattering phenomena between photons and free electrons, but the direction of energy transfer is opposite. Compton scattering is the transfer of energy from photons to electrons, while inverse Compton scattering is the transfer of energy from electrons to photons.

[0042] Time stretching technology mainly uses the velocity dispersion of electrons in a vacuum drift tube to stretch electrical signals on a time scale. The application of this method can convert ultrashort pulse time scales into longer time scales.

[0043] Therefore, in response to the demand for ultrafast diagnostic equipment in the ultrafast field of various radiation detection such as inverse Compton scattering sources, laser plasma and Betatron radiation sources, that is, the need to extract as much physical information as possible, such as space-intensity, in the reaction process on the nanosecond or even sub-nanosecond time scale, a small time-stretch drift tube for ultrafast diagnostic systems is proposed. The time-stretch drift tube is a time-stretch drift tube with a new structure, which can achieve linear stretching while greatly improving the accuracy of the detection signal.

[0044] The technical solutions provided by various embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0045] Figure 1 Schematic diagram of the structure of a time-stretch drift tube in the present invention, which specifically includes: a photocathode 102, a first grid 103, a second grid 104, a microchannel plate 105, a third grid 106 and an anode 107 arranged in sequence in a vacuum device 101.

[0046] A front-end acceleration zone is formed between the photocathode 102 and the first grid 103, a deceleration zone is formed between the first grid 103 and the second grid 104, and a drift zone is formed between the second grid 104 and the microchannel plate 105; a rear-end first acceleration zone is formed between the microchannel plate 105 and the third grid 106, and a rear-end second acceleration zone is formed between the third grid 106 and the anode 106; a magnetic lens 108 is arranged outside the vacuum device area corresponding to the drift zone to impose radial constraints on electrons passing through the drift zone.

[0047] The photocathode is used to receive incident light and convert it into electrons to enter the acceleration zone; the front acceleration zone is loaded with a constant electric field so that electrons entering the acceleration zone at different times enter the deceleration zone at the same axial speed; the deceleration zone is loaded with a time-varying electric field so that electrons entering the deceleration zone at different times enter the drift zone at different axial speeds; the drift zone is an equipotential zone so that electrons entering the drift zone at different axial speeds are stretched on a time scale; the first acceleration zone at the rear end is used to reduce the time dispersion of electrons emitted through the microchannel plate; the second acceleration zone at the rear end further reduces the time dispersion of electrons while preventing the anode from causing interference due to the induced current signal, and converts the electrons into electrical pulse signals through the anode to be received by an external high-frequency oscilloscope. The anode is the receiving electrode of the electrons.

[0048] Specifically, the time stretching principle of the time stretching tube is as follows: visible light (incident light) irradiates the photocathode to generate photoelectrons, and the photoelectrons are accelerated by the cathode and the first grid M1 and enter the deceleration zone (from the first grid M1 to the second grid M2) where a time-varying electric field exists. Between the first grid M1 and the second grid M2, the photoelectrons are affected by the time-varying electric field, and the photoelectrons generated at different times enter the drift zone at different axial speeds, that is, the area from the second grid M2 to the input surface of the microchannel plate (MCP). Since the drift domain is an equipotential zone, the electrons move at a uniform speed in the axial direction, and the distance between electrons with different axial speeds is pulled apart to achieve time stretching. The time stretching technology can effectively reduce the time resolution requirements of the diagnostic equipment in the ultrafast diagnosis process. That is, the source signal only needs to cross the slope interval of the ramp loading signal to achieve a fixed stretching ratio, without determining the specific loading time, which will greatly simplify the physical system design and make signal synchronization easier. At the same time, the stretched signal only needs to undergo two steps of linear signal compression and amplification to conveniently obtain the source signal.

[0049] The physical process of electron motion in the time-stretch drift tube of the present invention is as follows: the photocathode receives incident light radiation, converts photons into electrons and retains its time-intensity information, the electrons generated by the photocathode enter the deceleration zone after axial acceleration through the front-end acceleration zone (loaded with an electrostatic field, i.e., a constant voltage), and the deceleration zone is loaded with a time-varying electric field, so that the electrons that enter the zone first are subjected to a smaller axial deceleration than the electrons that enter the zone later, so that the electrons at different times in the electron beam will produce velocity dispersion and enter the drift zone, and the drift zone, as the main action area of ​​time stretching, makes the electron beam fully stretched on the time scale, the stretched electron beam bombards the MCP input surface and is output from the MCP output surface after electron multiplication to enter the rear-end 1st-level acceleration zone (rear-end first acceleration zone), and then enters the rear-end 2nd-level acceleration zone (rear-end second acceleration zone) to bombard the anode and convert into an electrical pulse signal to be detected by an external high-frequency oscilloscope. Therefore, the photoelectrons generated by the photocathode successively experience the front-end acceleration zone, the deceleration zone, the drift zone, the MCP electron multiplication, the rear-end 1st-level acceleration zone and the rear-end 2nd-level acceleration zone.

[0050] Among them, except for the magnetic lens, all other components of the time-stretch drift tube are in a high vacuum environment, that is, in a vacuum device. The high vacuum state inside the vacuum device is about 10 -5 Pa. The magnetic lens is a long magnetic lens, and the long magnetic lens may include two, which are respectively placed on the upper and lower sides outside the drift region.

[0051] Optionally, the material of the photocathode is determined based on the wavelength band of the incident light. The incident light irradiates the photocathode to generate photoelectrons through the external photoelectric effect. The material of the photocathode can be selected based on the wavelength band of the incident light, and there are materials such as gold, potassium sodium cesium antimony compound (KNaCsSb) or gallium arsenide (GaAs). Similarly, the photocathode is made on the inner surface of the input window. For example, different input window materials will selectively transmit light waves of different wavelengths. Quartz glass is transparent to ultraviolet light, but ordinary glass is not transparent to ultraviolet light. The input window material needs to be selected based on the wavelength band of the incident light, such as leaded glass, quartz glass, etc.

[0052] The stretched electron beam is multiplied by the MCP element and accelerated in the two-stage acceleration zone at the rear end, and then bombards the anode (the anode material can be made of metal materials such as aluminum or gold) and is collected by an external high-frequency oscilloscope. The function of the rear third grid M3 is to provide the rear-end acceleration electric field and shield the anode receiving stage induced current signal, improve the accuracy of the collected signal, and reduce interference.

[0053] The overall size of the time-stretching drift tube is about Ф75mm×150mm, which is much smaller than a series of diagnostic equipment such as traditional pulse stretching and framing tubes.

[0054] By studying the head and tail electrons in the emitted electron beam, the entire generation and transport process of electrons in the time-stretch drift tube is analyzed, including the acceleration of electrons emitted from the photocathode in the front acceleration zone, the deceleration in the deceleration zone, the stretching in the drift zone, the multiplication in the MCP device, the acceleration of electrons in the rear first acceleration zone, and the acceleration of electrons in the rear second acceleration zone bombarding the metal anode to form an electrical pulse signal which is detected and recorded by an external high-frequency oscilloscope.

[0055] A constant electric field is loaded between the photocathode and M1, which can effectively reduce the time dispersion caused by the axial energy distribution of the electrons emitted by the photocathode, so that the electrons entering the deceleration zones of M1 and M2 at different times have almost the same axial velocity. At the same time, based on the grid structure, the ramp pulse can effectively pass through the core area of ​​electron movement, forming an effective time-varying deceleration electric field, thereby forming velocity dispersion.

[0056] The time-stretch drift tube also includes a DC control module and a pulse control circuit; a constant potential is applied to the photocathode, the first grid, the second grid, the input surface and the output surface of the microchannel plate, the third grid and the anode through the DC control module; a current is applied to the magnetic lens through the DC control module or the pulse control circuit; a pulse current is applied to the first grid through the pulse control circuit, and the voltage difference between the photocathode and the first grid is kept constant.

[0057] The pressure difference between the photocathode and the first grid is kept constant. At this time, a time-varying deceleration electric field is generated between the first grid and the second grid. The axial acceleration of the electrons in the front acceleration zone is consistent and does not change with the time when the electrons are generated. It is only related to the axial component of the initial energy distribution of the electrons.

[0058] Alternatively, if Figure 2 As shown, a constant voltage of -2V can be loaded on the photocathode through a DC control module, a constant voltage of -1V can be loaded on the input surfaces of the first grid, the second grid and the microchannel plate respectively, a constant voltage of 0V can be loaded on the output surface of the microchannel plate, a constant voltage of 1V can be loaded on the third grid, and a constant voltage of 2V can be loaded on the anode; current can be loaded on the magnetic lens through a DC control module or a pulse control circuit, and the magnetic lens can determine the current according to the loaded current and the number of windings to ensure that the magnetic field strength is 120Gauss; the pulse current loaded on the first grid by the pulse control circuit is a ramp pulse.

[0059] Furthermore, in the present invention, the first grid, the second grid and the third grid adopt a grid structure with a grid width of 10um+ / -0.5um and a grid size of 40um+ / -0.5um, which can well ensure the formation of an electric field while ensuring an electron transmittance of more than 60%.

[0060] A constant electric field is loaded between the photocathode and the first grid M1, which can effectively reduce the time dispersion caused by the axial energy distribution of the electrons emitted by the photocathode, so that the electrons entering the deceleration zone of the first grid M1 and the second grid M2 at different times have almost the same axial speed. At the same time, based on the grid structure, the ramp pulse can effectively pass through the core area of ​​the electron movement to form an effective time-varying deceleration electric field, thereby forming velocity dispersion. When the ramp pulse is transmitted on the second grid M2, the central area where the electrons pass can also generate a good time-varying electric field.

[0061] The time stretching of the electron beam is mainly concentrated in the drift region. At the same time, the transit time of the electrons is mainly concentrated in the drift region, which is in the nanosecond order. Therefore, it is necessary to impose radial constraints on the electron beam. Otherwise, the electron beam spot will expand radially due to the space charge effect, etc., and eventually the electron beam spot acting on the anode signal receiving electrode will become larger, that is, the electron transit time dispersion will increase, resulting in large errors in the detection results. Therefore, a magnetic lens is set outside the drift region to impose radial constraints on the electrons passing through the drift region to improve the accuracy of time stretching of the time stretch drift tube.

[0062] The microchannel plate MCP is used for electrical signal enhancement, so the time-stretch drift tube of the present invention can be used for the detection of weak signals.

[0063] The advantages of setting the third grid M3 are: ① Based on the energy distribution of MCP emitted electrons, most of them are low-energy electrons, so their axial emission speed is relatively low, which will lead to an increase in time dispersion. The existence of the M3 structure plays a post-acceleration role, which is used to reduce the accuracy of the detection results caused by the time dispersion of MCP emitted electrons; ② The existence of M3 can effectively prevent the induced current formed by MCP emitted electrons at the anode, that is, it has anti-interference ability, which can effectively improve the accuracy and sensitivity of the electrical signal received by the receiving electrode.

[0064] In one embodiment, the lengths of the front end acceleration zone, the deceleration zone, the rear end first acceleration zone and the rear end second acceleration zone are less than or equal to the first preset length, the length of the drift zone is less than or equal to the second preset length, and the first preset length is less than the second preset length; the difference between the lengths of the front end acceleration zone and the deceleration zone and the length of the drift zone is greater than the third preset length.

[0065] Furthermore, the length of the front acceleration zone and the deceleration zone is much shorter than the length of the drift zone. For example, the difference between the length of the front acceleration zone and the deceleration zone and the length of the drift zone can be set to be greater than the third preset length. The third preset length, the second preset length and the third preset length can all be set according to requirements. For example, the lengths of the front acceleration zone, the deceleration zone, the rear first acceleration zone and the rear second acceleration zone are all no greater than 2 mm, and the length of the drift zone is no greater than 120 mm.

[0066] In one embodiment, the calculation formula for the electron transit time through the front-end acceleration region is:

[0067] d 1 =v 0 t+a z t 2 / twenty one)

[0068]

[0069] a z =V pc e / md 1 (3)

[0070] Among them, d 1 is the length of the front acceleration zone, v 0 is the initial axial velocity of the electron, t is the transit time of the electron through the front acceleration zone, a z is the axial acceleration, E 0 is the axial initial energy of the electron, m is the mass of the electron, e is the charge of a single electron, V pc is the pressure difference in the front acceleration zone.

[0071] In one embodiment, the linear stretching condition of the drift region is:

[0072]

[0073] in, is the change of the potential of the first grid with time t, M is the linear stretching multiple of the drift region, U 1 (t) is the potential difference in the front acceleration zone, U 2 (t) is the potential difference in the deceleration zone, L is the length of the drift zone, m is the mass of the electron, and e is the charge of a single electron.

[0074] Specifically, the linear stretching condition of the drift region is derived as follows:

[0075] Compared with the drift region, the length of the front acceleration region and the deceleration region is much smaller than that of the drift region, and the speed difference between the head and tail electrons of the electron bunch has not reached the maximum. Therefore, the main stretching area of ​​the electron beam is the drift region. The linear stretching of the drift region is analyzed, such as Figure 3 As shown, Figure 3 Schematic diagram of electron time stretching in the drift region. dt is the time difference between the first and last electrons when the electron bunch enters the drift region. The drift time of the first electron of the electron bunch from entering the drift region to completely leaving the drift region is t 0 , the tail electron drift time is t 1 , M is the time stretching multiple of the drift region.

[0076] Among them, t i The time when the electrons entering the drift region from the second grid M2 reach the input surface of the microchannel plate MCP is t' i , then:

[0077]

[0078] Where L is the length of the drift region, eV(t i ) is t i The axial energy of the incident electron at time t, ignoring the influence of the electron's space charge effect, the axial velocity of the electron when it enters the drift region is related to the electron's axial energy. a , t b (t a <t b ) When the electron emitted from M2 reaches the MCP input surface, the time stretching ratio is:

[0079]

[0080] Taking the limit on both sides of formula (8), if we want M(t a , t b ) is a constant, that is, linear stretching, then:

[0081]

[0082] Inferred:

[0083]

[0084] Solve the differential equation:

[0085] [V(t)′] 2 =K 2 V(t) 3 (11)

[0086]

[0087] V(t) is the voltage value of the first grid M1.

[0088] Calculated from the initial condition V(0) = 1 kV, U 1 (t) = 1 kV, M2 potential Finally, the M1 potential is obtained for:

[0089]

[0090] Substituting M = 50 and formula (13) back into formula (10), we get K ≈ 5.8 × 10 8 , and obtain the linear stretching condition:

[0091]

[0092] In one embodiment, the signal inversion formula of the time-stretch drift tube is expressed as:

[0093]

[0094] in, is the intensity distribution of the time-stretched drift tube input signal, Ψ(t′) is the signal intensity distribution after time stretching in the drift region, and M(t) is the linear stretching multiple of the drift region.

[0095] If it is an ideal linear stretching process, the inversion signal will be the accurate source signal. Assume that the source signal is at t a to b The time interval enters the drift region, and the intensity distribution is Then the time interval when the interval signal reaches the end of the drift region after being stretched is t′ a to t′ b , the corresponding intensity distribution is Ψ(t′ a →t′ b ). According to the law of conservation of charge and t′ b -t′a / t b -t a =M(t), taking the limit on both sides, we get formula (15).

[0096] In an exemplary embodiment, a Gaussian reference source signal is defined as follows: half-width 10 ps, ​​standard deviation σ=4.25 ps, μ=20 ps, The deduction and inversion of pulse signals are as follows Figure 4 As shown, the reference source signal is Figure 4 As shown in Figure (a), using electromagnetic simulation (Computer Simulation Technology, CST) software, the anode collector signal is obtained under the conditions of 1 kV voltage of the photocathode, the length of the drift region L = 100 mm, and the signal trigger time ttrig = 20 ps. The source signal obtained after inversion is as follows Figure 4 As shown in Figure (b), the curve obtained after inversion is basically consistent with the reference source signal curve.

[0097] Considering the single pulse cases at different triggering moments, the pulse generation time is within the linear stretching electric pulse time window, e.g. Figure 5 As shown, the anode collector current curves at different triggering times are obtained. The triggering time ranges from 0ps to 100ps, with an interval step of 10ps. Figure 5 It can be seen that the current curve waveforms between 10ps and 40ps are relatively consistent, and the stretching multiple is relatively stable.

[0098] The present invention provides a small time-stretch drift tube for ultrafast diagnostic systems, which is intended to meet the requirements of more efficient detection and low-cost system construction in ultrafast test diagnosis of devices such as inverse Compton scattering sources, laser plasmas, and Betatron radiation sources, and to simplify system design. The small time-stretch drift tube is based on the time-stretch principle and utilizes linear stretching conditions. The source signal only needs to cross the slope interval of the ramp loading signal to achieve a fixed stretching ratio. There is no need to determine the specific loading time, which greatly simplifies the physical system design and makes signal synchronization easier. At the same time, the stretched signal only needs to undergo two steps of linear signal compression and amplification to conveniently obtain the source signal. The present invention reduces costs, reduces volume (miniaturization), and improves the integration of beam diagnosis, providing an innovative solution for experimental research and industrial applications in related fields.

[0099] The present invention is based on the time stretching principle. By calculating the motion state of electrons in the space field, the physical design of a small time stretching drift tube is carried out, and detailed linear stretching conditions are obtained through numerical calculations. The original signal can be inverted according to the electric pulse model received by the anode, thereby realizing the detection of picosecond or even femtosecond pulse rays under a larger stretching ratio.

[0100] The invention proposes a small time-stretch drift tube for use in an ultrafast diagnostic system, whose time-stretch characteristic is linear time-stretch, so as to simplify the physical design of the corresponding diagnostic system and facilitate inversion to obtain source signal information.

[0101] In an exemplary embodiment, an ultrafast diagnostic system is provided. The system includes the time-stretch drift tube described in any one of the above embodiments.

[0102] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the present invention.

Claims

1. A time-stretch drift tube, characterized in that: include: A photocathode, a first grid, a second grid, a microchannel plate, a third grid and an anode are sequentially arranged in the vacuum device; The front-end acceleration zone is formed between the photocathode and the first grid, the deceleration zone is formed between the first grid and the second grid, and the drift zone is formed between the second grid and the microchannel plate; the rear-end first acceleration zone is formed between the microchannel plate and the third grid, and the rear-end second acceleration zone is formed between the third grid and the anode; The photocathode is used to receive incident light and convert the incident light into electrons that enter the acceleration region; The acceleration zone is loaded with a constant electric field so that electrons entering the acceleration zone at different times enter the deceleration zone at the same axial speed; The deceleration zone is loaded with a time-varying electric field so that electrons entering the deceleration zone at different times enter the drift zone at different axial speeds; The drift region is an equipotential region, so that electrons entering the drift region with different axial velocities are stretched on a time scale; a magnetic lens is arranged outside the vacuum device region corresponding to the drift region, so as to impose radial constraints on electrons passing through the drift region. The rear first acceleration zone is used to reduce the time dispersion of electrons emitted through the microchannel plate; The rear second acceleration zone is used to further reduce electron time dispersion and prevent the anode from causing interference due to the induced current signal, and converts electrons into electrical pulse signals through the anode to be received by an external high-frequency oscilloscope.

2. The time-stretch drift tube according to claim 1, characterized in that: The time-stretch drift tube further comprises a DC control module and a pulse control circuit; a constant potential is applied to the photocathode, the first grid, the second grid, the input surface and the output surface of the microchannel plate, the third grid and the anode through the DC control module; a current is applied to the magnetic lens through the DC control module or the pulse control circuit; The pulse control circuit is used to load a pulse current to the first grid, and the voltage difference between the photocathode and the first grid is kept constant.

3. The time-stretch drift tube according to claim 1, characterized in that: The lengths of the front-end acceleration zone, the deceleration zone, the rear-end first acceleration zone and the rear-end second acceleration zone are less than or equal to a first preset length, the length of the drift zone is less than or equal to a second preset length, and the first preset length is less than the second preset length; the differences between the lengths of the front-end acceleration zone and the deceleration zone and the length of the drift zone are both greater than a third preset length.

4. The time-stretch drift tube according to claim 1, characterized in that: The material of the photocathode includes gold, potassium sodium cesium antimony compound or gallium arsenide.

5. The time-stretch drift tube according to claim 1, characterized in that: The calculation formula for the electron transit time through the front-end acceleration zone is: d1=v0t+az t 2 / 2; a z =V pc e / md1; Wherein, d1 is the length of the front acceleration zone, v0 is the initial axial velocity of the electron, t is the transit time of the electron through the front acceleration zone, a z is the axial acceleration, E0 is the axial initial energy of the electron, m is the mass of the electron, e is the charge of a single electron, V pc is the pressure difference in the front acceleration zone.

6. The time-stretch drift tube according to claim 1, characterized in that: The linear stretching condition of the drift region is: in, is the change of the potential of the first grid with time t, M is the linear stretching multiple of the drift region, U1(t) is the potential difference in the front acceleration region, U2(t) is the potential difference in the deceleration region, L is the length of the drift region, m is the electron mass, and e is the charge of a single electron.

7. The time-stretch drift tube according to claim 1, characterized in that: The signal inversion formula of the time-stretch drift tube is expressed as: in, is the intensity distribution of the time-stretched drift tube input signal, Ψ(t′) is the signal intensity distribution after time stretching in the drift region, and M(t) is the linear stretching multiple of the drift region.

8. An ultrafast diagnostic system, characterized in that: The system comprises the time-stretch drift tube according to any one of claims 1-7.

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