Electron beam and pulsed laser attosecond scale delay diagnostic method

Abstract

This invention discloses an attosecond-level delay diagnosis method between electron beams and pulsed lasers, belonging to the technical field of delay diagnosis between electron beams and pulsed lasers. The method includes: adjusting the delay between a chirped pulsed laser a and a chirped electron beam b via a delay device; recording the positions of the delay devices corresponding to the appearance and end of the transverse modulation of the electron beam on an electron spectrometer to obtain the transverse modulation and energy spectrum of the chirped electron beam b; obtaining the chirped distribution of the chirped electron beam b using an electron beam chirped diagnostic reconstruction method based on laser transverse modulation of the electron beam; obtaining the angular distribution of the chirped electron beam b in the spatial domain based on [variable name missing]; determining the positive or negative value of the delay; performing a spatial domain Fourier transform on the angular distribution of the chirped electron beam b in the spatial domain; and further calculating the delay difference between the chirped electron beam b and the chirped pulsed laser a. This invention can diagnose attosecond-level delays between electron beams and pump pulses; the device is simple; and it has good scalability, extending to any wavelength band.

Description

Technical Field

[0001] This invention relates to the field of time delay diagnosis technology between electron beams and pulsed lasers, and particularly to an attosecond-level time delay diagnosis method between electron beams and pulsed lasers. Background Technology

[0002] Pump-probe technology, using ultrafast electron beams as the probe source, can diagnose ultrafast phenomena at the atomic and molecular structural levels, and has significant scientific implications in materials science and biology. This technique typically requires a pulsed laser as the pump pulse to excite the sample, followed by an ultrashort (picosecond to femtosecond) electron beam to diagnose the ultrafast dynamics within the sample. The temporal resolution of this technique depends on the electron beam pulse width and the time jitter between the electron beam and the pump pulse. Currently, with the development of electron beam pulse compression technology and novel plasma accelerators, the electron beam pulse width can be controlled to the femtosecond level. Research into attosecond-level electron beam generation schemes is also in full swing to explore even faster electron-level dynamics. On the other hand, the time jitter between the electron beam and the pump pulse is generally detected using terahertz schlieren technology, but this requires an additional complex terahertz source system, and its temporal resolution is currently limited to the femtosecond level. Therefore, developing a method capable of diagnosing attosecond-level time jitter is essential. Summary of the Invention

[0003] To address the shortcomings and deficiencies of existing technologies, this invention proposes an attosecond-level delay diagnostic method using electron beams and pulsed lasers.

[0004] Basic Idea of ​​the Invention

[0005] Based on the proposed patent [ZL202010564603.X], a tightly focused chirped pulse laser and a chirped electron beam are used to interact, and the transient energy chirped distribution of the electron beam is reconstructed, thereby obtaining the spatial distribution of the electron beam. By performing a spatial domain Fourier transform on the spatial distribution of the electron beam, the delay between the electron beam and the pump pulse can be obtained.

[0006] Brief introduction to the principle of the invention

[0007] According to the Lawson-Woodward theorem, since electrons traverse completely opposite electric fields before and after a symmetrical pulse focal length, the laser and electrons will not gain energy after interacting in an infinite spacetime. To overcome this limitation and achieve direct laser acceleration, many schemes have been proposed, such as using chirped laser pulses or confining the interaction region to obtain an asymmetric electromagnetic field. Furthermore, the momentum of the electron beam can be modulated by introducing obliquely incident laser light, which is widely used in free-electron laser devices for electron beam premodulation. Figure 1As shown, by introducing a beam whose propagation direction is at an angle of θ to the electron beam propagation direction... A pulsed laser interacts with an electron beam, and after the interaction, the electron beam will gain a path along... ( To delay time (where c is the speed of light in vacuum), the transverse momentum gain is periodically distributed longitudinally. This modulation can be achieved using divergence angle modulation. To describe it. The divergence angle distribution of the electron beam can be determined using an electron beam spectrometer. To make a diagnosis, because It is directly related to the laser field distribution, so Relationship, i.e., energy chirp distribution It can be done and The phase correlation between them is used to reconstruct the structure.

[0008] First, the momentum modulation process of the electron beam during the interaction between the laser and the electron beam is studied. For electrons on the axis (x=y=0), in the laser polarization direction (x), due to... The momentum modulation of these electrons in the laser polarization direction (x) is as follows: Assuming the electron is a relativistic electron with energy in the MeV range, i.e. For tiny laser tilt angles In the case of the z-axis, the electric field on the axis can be expressed as follows under the paraxial approximation:

[0009] (1)

[0010] in: , , , , For the initial phase, , combined The initial delay time is transverse momentum gain of electrons for:

[0011] (2)

[0012] in: , For laser treatment of waist spots, Let be the Rayleigh length. To achieve maximum momentum gain for the electron beam, it is necessary to make To maximize, let according to formula (2) It can be obtained The angle that is maximized is Simultaneously, it is assumed. It is worth noting... exist Within the range Horizontal, which means momentum modulation in Deviation In larger cases, this is still very significant; therefore, introducing a tilted laser beam to drive transverse momentum modulation of the electron beam is a robust approach.

[0013] Furthermore, the modulation intensity of the electron beam after the interaction ends It depends on the field that the electron traverses. Due to the stronger ( ) field and less phase mismatch, Corresponding to the situation The amplitude will be much higher than The situation at that time, and It has the same envelope as the laser pulse, therefore Furthermore, the laterally separated electrons (on-axis and off-axis) have the same modulation phase, and the modulation period is the same as that of the laser field. If the previous period is consistent, then Therefore, we can assume that momentum modulation satisfies ,in To modulate the amplitude, the interaction time should be as short as possible to achieve instantaneous reconstruction. To obtain a shorter interaction time, the laser needs to be tightly focused to reduce its Rayleigh length. .

[0014] How to reconstruct the transient energy chirp of an electron beam is a key problem that needs to be solved. When the pulsed laser has a linear chirp distribution, its frequency satisfies the following relationship: The momentum distribution of the electron beam modulated by this pulsed laser will change longitudinally after the interaction process ends: ,in This refers to the initial momentum of the electron beam before interaction. For relativistic electron beams generated after injection into a plasma accelerator, after being transversely modulated, the following condition is generally satisfied: Therefore, the divergence modulation curve of the electron beam and It will be directly related to: ,in Furthermore, in order to reconstruct the entire electron beam cluster, the laser pulse width... Should be greater than ,in Electron beam pulse width, The relative delay from the laser pulse center to the electron beam center, if we choose the electron beam center as the origin of the delay time... Then we have:

[0015] (3)

[0016] In the experiment, Diagnosis can be performed using electron beam spectroscopy, and the resulting divergence modulation can be analyzed. and calculable The phase relationship between them can be deconstructed The correlation between them, i.e., the chirp distribution of the electron beam. To obtain the dispersion angle phase The dispersion modulation curve obtained from the experiment needs to be... Envelope normalization is performed, followed by logarithmic calculation, and then... The correlation between them can be obtained from the following phase relationship: .

[0017] Based on the transverse modulation of the chirped electron beam b The chirp distribution of the reconstructed chirped electron beam b The angular distribution of the chirped electron beam b in the spatial domain was obtained. Angular distribution of the chirped electron beam b in the spatial domain Perform a Fourier transform in the spatial domain to obtain

[0018] (4)

[0019] get center frequency The time delay difference between the chirped electron beam b and the chirped pulsed laser a is... for

[0020] (5)

[0021] like Figure 2 The reconstructed electron beam space is called the distribution. and corresponding The frequency domain spectral distribution diagram is shown. The time resolution of this method depends on the period of the pulsed laser. By using efficient frequency doubling techniques and other means, the pulsed laser period can be compressed to the attosecond level, thereby enabling attosecond-level delay diagnosis.

[0022] Technical solution of the present invention

[0023] An attosecond-level delay diagnostic method using electron beams and pulsed lasers includes the following steps:

[0024] S1. By adjusting the delay between the chirped pulse laser a and the chirped electron beam b through the delay device (1), the positions of the delay device (1) corresponding to the appearance and end of the transverse modulation of the electron beam on the electron spectrometer (3) are recorded. An arbitrary value in the middle is taken for the experiment. The transverse modulation of the chirped electron beam b at this time is obtained through the electron spectrometer (3). and its energy spectrum ;

[0025] S2, through transverse modulation of the chirped electron beam b and its energy spectrum The chirp distribution of the chirped electron beam b was obtained using an electron beam chirp diagnostic reconstruction method based on laser transverse modulation of the electron beam. ;

[0026] S3. Based on the transverse modulation of the chirped electron beam b The chirp distribution of the reconstructed chirped electron beam b The angular distribution of the chirped electron beam b in the spatial domain was obtained. ;

[0027] S4. Determination of delay positive or negative: The chirp parameters of the chirped pulse laser a... Adjust to 0, repeat step S1, and obtain the transverse modulation of the chirped electron beam b at this time. and its energy spectrum ,and Compared to the situation where, in the use In the case of <0 pulse laser, if the modulation curve is in the high-energy region The shorter the modulation period, the more significant the delay positive and negative parameters. Conversely ;

[0028] S5. Angular distribution of the chirped electron beam b in the spatial domain Perform a Fourier transform in the spatial domain to obtain The time delay difference between the chirped electron beam b and the chirped pulsed laser a is obtained using the following formula. :

[0029]

[0030] in: for The center frequency, denoted as α, is the center frequency of the chirped pulsed laser a.

[0031] Furthermore, the delay unit (1) is composed of four planar reflectors, and the delay unit (1) is controlled by a translation stage, with a delay control accuracy of 20 nanometers.

[0032] Furthermore, the spectral phase and intensity distribution of the chirped pulsed laser a are measured using FROG or SPIDER to obtain the center frequency of the chirped pulsed laser a. and chirp parameters .

[0033] The beneficial effects of this invention are:

[0034] 1. It can diagnose the attosecond-level delay between the electron beam and the pump pulse. Currently, there is no other solution that can achieve attosecond-level jitter time diagnosis.

[0035] 2. The device is simple and does not require redesigning a complex device. It can be realized by relying on commonly used, mature, stable and reliable components such as parabolic mirrors and electron spectrometers.

[0036] 3. It has good scalability, and the pulsed laser used can be extended to any wavelength band. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the electron beam and pulsed laser attosecond-level delay diagnostic method device according to an embodiment of the present invention.

[0038] Figure 2 The reconstructed electron beam spatial angular distribution in this embodiment of the invention. and corresponding The frequency domain spectrum distribution diagram. Detailed Implementation

[0039] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0040] This invention provides an attosecond-level delay diagnostic method and apparatus using electron beams and pulsed lasers (as shown in the attached diagram). Figure 1 (As shown). The chirped pulsed laser a, after being focused by time delay 1 and parabolic mirror 2, interacts with the chirped electron beam b. The energy spectrum and transverse divergence angle distribution of the chirped electron beam b are then diagnosed by electron spectrometer 3. The time-delay diagnostic method includes the following steps:

[0041] S1. By adjusting the delay between the chirped pulse laser a and the chirped electron beam b through the delay device (1), the positions of the delay device (1) corresponding to the appearance and end of the transverse modulation of the electron beam on the electron spectrometer (3) are recorded. An arbitrary value in the middle is taken for the experiment. The transverse modulation of the chirped electron beam b at this time is obtained through the electron spectrometer (3). and its energy spectrum ;

[0042] The spectral phase and intensity distribution of the chirped pulsed laser a were measured using FROG or SPIDER to obtain the center frequency of the chirped pulsed laser a. and chirp parameters ;

[0043] Establish the diagnostic optical path: After being focused by the delay unit 1 and the parabolic mirror 2, the chirped pulsed laser a interacts with the chirped electron beam b, and then the chirped electron beam b, which is modulated laterally, is freely transmitted into the electron spectrometer 3.

[0044] S2, through transverse modulation of the chirped electron beam b and its energy spectrum The chirp distribution of the chirped electron beam b was obtained using an electron beam chirp diagnostic reconstruction method based on laser transverse modulation of the electron beam. ;

[0045] S3. Based on the transverse modulation of the chirped electron beam b The chirp distribution of the reconstructed chirped electron beam b The angular distribution of the chirped electron beam b in the spatial domain was obtained. ;

[0046] S4. Determination of delay positive or negative: The chirp parameters of the chirped pulse laser a... Adjust to 0, repeat step S1, and obtain the transverse modulation of the chirped electron beam b at this time. and its energy spectrum ,and Compared to the situation where, in the use In the case of <0 pulse laser, if the modulation curve is in the high-energy region The shorter the modulation period, the more significant the delay positive and negative parameters. Conversely ;

[0047] S5. Angular distribution of the chirped electron beam b in the spatial domain Perform a Fourier transform in the spatial domain to obtain The time delay difference between the chirped electron beam b and the chirped pulsed laser a is obtained using the following formula. :

[0048]

[0049] in: for The center frequency, denoted as α, is the center frequency of the chirped pulsed laser a.

[0050] Furthermore, the delay unit 1 is composed of four planar reflectors, and the delay unit 1 is controlled by a translation stage, with a delay control accuracy of 20 nanometers.

[0051] In summary, this invention proposes a method for diagnosing the ultrashort delay between an electron beam and a pulsed laser using tightly focused chirped pulsed lasers. This method can effectively achieve laser period-level precision delay diagnosis between ultrashort electron beams and pulsed lasers. By using efficient frequency doubling technology to obtain pulsed lasers with attosecond periods, attosecond-level delay diagnosis can be achieved. This method can be applied to the optimization and control of compact electron accelerators and makes attosecond ultrafast electron diffraction time jitter detection possible, which has significant scientific implications for further exploration and research on attosecond beamline sources and attosecond structure dynamics.

[0052] The specific embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A diagnostic method for attosecond-level delay of electron beam and pulsed laser, wherein a chirped pulsed laser a is focused by a delay unit (1) and a parabolic mirror (2) and interacts with a chirped electron beam b, and the energy spectrum and transverse divergence angle distribution of the chirped electron beam b are diagnosed by an electron spectrometer (3), characterized in that, Includes the following steps: S1. By adjusting the delay between the chirped pulse laser a and the chirped electron beam b through the delay device (1), the positions of the delay device (1) corresponding to the appearance and end of the transverse modulation of the electron beam on the electron spectrometer (3) are recorded. An arbitrary value in the middle is taken for the experiment. The transverse modulation of the chirped electron beam b at this time is obtained through the electron spectrometer (3). and its energy spectrum ; S2, through transverse modulation of the chirped electron beam b and its energy spectrum The chirp distribution of the chirped electron beam b was obtained using an electron beam chirp diagnostic reconstruction method based on laser transverse modulation of the electron beam. ; S3. Based on the transverse modulation of the chirped electron beam b The chirp distribution of the reconstructed chirped electron beam b The angular distribution of the chirped electron beam b in the spatial domain was obtained. ; S4. Determination of delay positive or negative: The chirp parameters of the chirped pulse laser a... Adjust to 0, repeat step S1, and obtain the transverse modulation of the chirped electron beam b at this time. and its energy spectrum ,and Compared to the situation where, in the use In the case of <0 pulse laser, if the modulation curve is in the high-energy region The shorter the modulation period, the more significant the delay positive and negative parameters. Conversely ; S5. Angular distribution of the chirped electron beam b in the spatial domain Perform a Fourier transform in the spatial domain to obtain The time delay difference between the chirped electron beam b and the chirped pulsed laser a is obtained using the following formula. : in: for The center frequency, denoted as α, is the center frequency of the chirped pulsed laser a.

2. The electron beam and pulsed laser attosecond-level delay diagnostic method according to claim 1, characterized in that, The delay unit (1) consists of four planar mirrors. The delay unit (1) is controlled by a translation stage, and the delay control accuracy is 20 nanometers.

3. The electron beam and pulsed laser attosecond-level delay diagnostic method according to claim 1, characterized in that, The spectral phase and intensity distribution of the chirped pulsed laser a were measured using FROG or SPIDER to obtain the center frequency of the chirped pulsed laser a. and chirp parameters .

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