A free electron laser device and imaging method for ultrafast dynamic imaging

Abstract

The present invention discloses a free electron laser device and imaging method for ultrafast dynamic imaging, belonging to the field of free electron laser technology. The device includes an undulator, a four-color magnetic compressor, an electron beam collector, a transmission grating and an X-ray CCD detector arranged along the path of the electron beam. The undulator has different dimensionless magnetic field parameters K, and a four-color magnetic compressor is arranged between each adjacent undulator. The electron beam collector is used to collect the electron beam, and the transmission grating performs wave splitting diffraction on the four beams of X-rays after passing through the sample, and then forms four diffraction images on the X-ray CCD detector. The beneficial effects of the present invention are as follows: the energy of the monoenergetic electron beam and the undulator parameters can be set to obtain the required X-ray photon energy, and the pulse energy can be controlled by the number of undulator modules in combination with the OK mechanism, so as to realize an "ultrafast dynamic movie" with a time resolution of picoseconds to femtoseconds, so as to be used to study the ultrafast dynamic process inside the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of free electron lasers, and in particular relates to a free electron laser device and an imaging method for ultrafast dynamic imaging. Background Art

[0002] Pulse X-ray photography flash has a wide range of applications in basic frontier science and national defense engineering. It is an important diagnostic tool for fluid dynamics experiments. For example, in implosion physics, flash photography and lead-shielded collimated cameras are used to photograph the implosion process of hollow gold sphere targets on a nanosecond time scale; in detonation physics, flash X-ray photography records the image of flying fragments, and the speed of the fragments can be determined by dividing the flight distance by the time difference; the dynamic deformation behavior of soft lead hitting thick glass at different time intervals is studied; finally, the propagation of detonation waves in sensitive high explosives with variable internal structures is studied. Therefore, flash X-ray photography is extremely urgent and important for studying the dynamic process of decomposing high-energy explosives and implosion compression of fissile materials.

[0003] At present, flash X-ray devices are constantly developing, upgrading and transforming. In the early stage, a beam of electrons produced X-rays through target shooting. After performance upgrade, it can run double pulses with a time interval of 1ms. The DARHT-II device uses a long pulse electron beam through a kicking device to cut the beam into four pulses with a certain time interval of 500ns, and the interval cannot be adjusted; compared with the DARHT-II device, the Shenlong II flash photography device has a smaller pulse interval (300-500ns) and can adjust the time interval of the three beam pulses.

[0004] From the number of pulses and pulse intervals, it can be seen that the development trend of flash X-ray photography light sources is from single-energy single pulse to multi-energy multi-pulse. Single-energy single-pulse light sources can only understand the motion state of an object at a certain moment, while multi-energy multi-pulse light sources can understand the dynamic changes of an object at different moments. This trend shows that researchers are in urgent need of a device that can provide multiple beams of rays with extremely short time intervals to achieve multiple flash photography. If ultrafast dynamic imaging of picosecond to femtosecond levels is to be achieved, the light source needs to have multi-energy and multi-pulse characteristics, and the pulse interval must reach the picosecond to femtosecond level. However, current flash X-ray photography has not yet met this requirement. Therefore, free electron laser (FEL) is seen as a potential solution. Based on the principle of free electron laser, the formula for the resonant wavelength of its radiation is:

[0005] ;

[0006] in, is the wavelength of radiation, is the undulator period, is the Lorentz factor of the electron beam, is the dimensionless magnetic field parameter of the undulator. By adjusting the undulator parameter or electron beam energy , which can generate multi-energy multi-pulse X-rays and provide a suitable light source for ultrafast dynamic imaging. Therefore, the methods for generating multi-energy multi-pulse X-ray light sources are mainly divided into multi-undulator schemes and multi-electron beam schemes. In the multi-electron beam scheme, a double-pulse laser irradiates the cathode plate to generate two electron beams, which are accelerated in the RF barrel of the acceleration cavity. According to the different RF cycles, the RF barrels are divided into single RF barrels and multi-RF barrels. The single RF barrel injects electron beams with different phases in the same RF cycle for acceleration, while the multi-RF barrel accelerates the two electron beams in different RF cycles.

[0007] The multi-undulator scheme is divided into a split undulator and a fresh slice scheme. The split undulator divides the undulator into two sections and uses a magnetic compressor to introduce a time delay, thereby generating pulses of different colors in each section. Since the same electron beam is used to generate pulses of two colors, neither pulse can achieve full saturation. The fresh slice scheme controls the electron beam slices so that each slice is independently lasered in a different undulator, thereby achieving pulse saturation of each undulator. The advantages of the multi-electron beam scheme include the ability to independently generate lasers for each color, high radiation power, and a short required undulator length. However, the disadvantages of this scheme are that the tunability of the pulses in the spectral and temporal domains is limited; the device is complex and it is difficult to ensure the phase synchronization of multiple electron beams; and the pointing of the two pulses cannot be independently controlled. In contrast, the multi-undulator scheme has greater flexibility in the coordination of the time interval and wavelength interval of the pulses. However, for the split undulator, the radiation power of different colors is difficult to achieve saturation, while the fresh slice scheme is not limited by this. It should be noted that when the fresh slice scheme is used to generate more than three X-ray beams, the large lateral expansion of the tilted electron beam may lead to the loss of the electron beam, thereby increasing the complexity and difficulty of the operation. Summary of the invention

[0008] The purpose of the embodiments of the present invention is to provide a free electron laser device and imaging method for ultrafast dynamic imaging, which can generate a multi-energy, multi-pulse, high time resolution (picosecond to femtosecond level) and time interval controllable light source, which can be used for multiple (3-4) ultrafast dynamic imaging to observe the state of ultrafast moving objects at different times, thereby solving at least one technical problem involved in the background technology.

[0009] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0010] An embodiment of the present invention provides a free electron laser device for ultrafast dynamic imaging, comprising an undulator A, a first four-color magnetic compressor, an undulator B, a second four-color magnetic compressor, an undulator C, a third four-color magnetic compressor, an undulator D, an electron beam collector, a transmission grating and an X-ray CCD detector, which are sequentially arranged along the path of the electron beam, wherein the undulator A, the undulator B, the undulator C and the undulator D have different dimensionless magnetic field parameters K, wherein:

[0011] The electron beam passes through the undulator A to generate a wavelength of The first beam of X-rays is then passed through the first four-color magnetic compressor at the same time. The first beam of X-rays is not affected by the magnetic field of the first four-color magnetic compressor and propagates along a straight line, while the electron beam is deflected by the magnetic field of the first four-color magnetic compressor to produce a time delay. The delayed electron beam passes through the undulator B to produce a wavelength of The electron beam and the second beam of X-rays then pass through the second four-color magnetic compressor at the same time. The second beam of X-rays continues to propagate in a straight line. The electron beam is deflected by the magnetic field of the second four-color magnetic compressor to produce a time delay. The delayed electron beam passes through the undulator C to produce a wavelength of The electron beam and the third X-ray beam then pass through the third four-color magnetic compressor at the same time. The third X-ray beam continues to propagate in a straight line. The electron beam is deflected by the magnetic field of the third four-color magnetic compressor to produce a time delay. The delayed electron beam passes through the undulator D to produce a wavelength of The fourth X-ray beam, , the delay time between adjacent X-rays ranges from 100fs to 10ps; the electron beam passing through the undulator D is received by the electron beam collector, and the first X-ray, the second X-ray, the third X-ray, and the fourth X-ray passing through the undulator D sequentially pass through the sample to excite and capture the ultrafast dynamic process in the sample, and then pass through the transmission grating to generate corresponding diffraction angles as well as ,and Finally, the X-ray CCD detector forms the corresponding diffraction angle and time The first diffraction image is formed, and then in the time range of picoseconds to femtoseconds, the second beam of X-rays forms a corresponding diffraction angle on the X-ray CCD detector. and time The second diffraction image, the third beam of X-rays forms a corresponding diffraction angle on the X-ray CCD detector and time The third diffraction image, the fourth beam of X-rays forms a corresponding diffraction angle on the X-ray CCD detector and time The fourth diffraction image is obtained, thereby obtaining four ultrafast dynamic process imaging images with time intervals from femtoseconds to picoseconds, reflecting the motion state of the sample at different times.

[0012] Optionally, the energy range of the electron beam is 0.8 GeV to 14 GeV.

[0013] Optionally, the first four-color magnetic compressor, the second four-color magnetic compressor, and the third four-color magnetic compressor are all C-type magnetic compressors.

[0014] Optionally, the C-type magnetic compressor includes a plurality of bending magnets that generate a magnetic field to cause the electron beam to bend differently at different time delays.

[0015] Optionally, the dimensionless magnetic field parameter K of undulator A, undulator B, undulator C, and undulator D ranges from 0.5 to 4, and the period The value range is 30mm to 100mm.

[0016] Optionally, the magnetic field value range of the first four-color magnetic compressor, the second four-color magnetic compressor, and the third four-color magnetic compressor is 0.5-6T.

[0017] Optionally, a linear accelerator is also included for generating the electron beam and accelerating the electron beam to a required energy.

[0018] Optionally, the undulator A is divided into undulator modules A1 to A1. N , used to generate a wavelength of The undulator B is divided into undulator modules B1 to undulator modules B N , used to generate a wavelength of The undulator C is divided into undulator modules C1 to undulator modules C N , used to generate a wavelength of The undulator D is divided into undulator modules D1 to D N , used to generate a wavelength of The fourth X-ray beam, and , the wavelength difference between adjacent X-rays is 0.3 nanometers or 3 nanometers.

[0019] Optionally, the undulator module includes a sub-undulator, an OK magnetic compressor and a quadrupole iron.

[0020] The present invention also provides an imaging method of a free electron laser device based on the ultrafast dynamic imaging, comprising the following steps:

[0021] Step 1, adjusting the electron beam energy, the dimensionless magnetic field parameter K and the magnetic field size of the four-color magnetic compressor;

[0022] Step 2, using an electron beam to traverse the undulator A, the first four-color magnetic compressor, the undulator B, the second four-color magnetic compressor, the undulator C, the third four-color magnetic compressor and the undulator D multiple times, to generate four beams of X-rays with different wavelengths at different times;

[0023] Step 3, combining the OK mechanism, adjusting the pulse energy of the four X-ray beams by the number of undulator modules;

[0024] Step 4: Four X-ray beams with different wavelengths at different times pass through the sample in sequence to stimulate and capture the ultrafast dynamic process in the sample;

[0025] Step five: Use a transmission grating to separate X-rays of different wavelengths in space. Arrange the wavelengths from small to large and symmetrically expand them around the zero order. Use an X-ray CCD detector to record and analyze multiple diffraction images to reconstruct the motion state of the sample under X-rays of different wavelengths, indirectly reflecting the dynamic evolution process of the sample in the order of tens of femtoseconds to picoseconds.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] According to the experimental requirements, the present invention can set the monoenergetic electron beam energy and the undulator parameters to obtain the required X-ray photon energy, and control the pulse energy by combining the OK mechanism through the number of undulator modules. At the same time, the delay parameters of the four-color magnetic compressor can also be set according to the requirements of high-time resolution dynamic imaging. These three adjustment methods can customize suitable multi-energy multi-pulse X-rays as the light source for ultrafast imaging. The customized four beams of X-rays pass through the sample in turn and are separated by a transmission grating, and finally generate four diffraction images similar to the "flash photography" effect on the X-ray CCD detector, realizing an "ultrafast dynamics movie" with a time resolution of picoseconds to femtoseconds, which can be used to study ultrafast dynamic processes inside matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0029] Figure 1 A schematic diagram of the structure of a free electron laser device for ultrafast dynamic imaging provided by the present invention;

[0030] Figure 2A schematic diagram of the imaging process of the free electron laser device for ultrafast dynamic imaging provided by the present invention;

[0031] Figure 3 This is a schematic diagram of the structure of a free electron laser device for ultrafast dynamic imaging provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0033] See also Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a free electron laser device for ultrafast dynamic imaging, including an undulator A, a first four-color magnetic compressor 2, an undulator B, a second four-color magnetic compressor 3, an undulator C, a third four-color magnetic compressor 4, an undulator D, an electron beam collector 5, a transmission grating 6 and an X-ray CCD detector 7, which are arranged in sequence along the travel path of the electron beam 1.

[0034] The undulator A, undulator B, undulator C, and undulator D have different dimensionless magnetic field parameters K. In a specific embodiment, the dimensionless magnetic field parameter K has a value range of 0.5 to 4. The undulator period The value range is 30mm to 100mm.

[0035] The electron beam 1 passes through the undulator A to generate a wavelength of The first X-ray beam is then passed through the first four-color magnetic compressor 2 simultaneously by the electron beam 1 and the first X-ray beam. The first X-ray beam is not affected by the magnetic field of the first four-color magnetic compressor 2 and propagates along a straight line, while the electron beam 1 is deflected by the magnetic field of the first four-color magnetic compressor 2 to produce a time delay. The delayed electron beam 1 passes through the undulator B to produce a wavelength of The electron beam 1 and the second beam of X-rays then pass through the second four-color magnetic compressor 3 at the same time. The second beam of X-rays continues to propagate in a straight line. The electron beam 1 is deflected under the magnetic field of the second four-color magnetic compressor 3 to produce a time delay. The delayed electron beam 1 passes through the undulator C to produce a wavelength of The electron beam 1 and the third X-ray beam then pass through the third four-color magnetic compressor 4 at the same time. The third X-ray beam continues to propagate in a straight line. The electron beam 1 is deflected under the magnetic field of the third four-color magnetic compressor 4 to produce a time delay. The delayed electron beam 1 passes through the undulator D to produce a wavelength of The fourth X-ray beam, , the delay time between adjacent X-rays ranges from 100fs to 10ps; the electron beam 1 passing through the undulator D is received by the electron beam collector 5, and the first X-ray, the second X-ray, the third X-ray, and the fourth X-ray passing through the undulator D sequentially pass through the sample 8 to excite and capture the ultrafast dynamic process in the sample 8, and then pass through the transmission grating 6 to generate corresponding diffraction angles as well as ,and Finally, the X-ray CCD detector 7 forms a corresponding diffraction angle and time The first diffraction image is formed, and then in the time range of picoseconds to femtoseconds, the second beam of X-rays forms a corresponding diffraction angle on the X-ray CCD detector. and time The second diffraction image, the third beam of X-rays forms a corresponding diffraction angle on the X-ray CCD detector and time The third diffraction image, the fourth beam of X-rays forms a corresponding diffraction angle on the X-ray CCD detector and time The fourth diffraction image is obtained, thereby obtaining four ultrafast dynamic process imaging images with time intervals ranging from femtoseconds to picoseconds, reflecting the motion state of sample 8 at different times.

[0036] In a specific embodiment, the energy range of the electron beam 1 is 0.8 GeV to 14 GeV.

[0037] The first four-color magnetic compressor 2, the second four-color magnetic compressor 3, and the third four-color magnetic compressor 4 are all C-type magnetic compressors, and the magnetic field value range is 0.5-6 T. The C-type magnetic compressor includes a plurality of bending magnets that generate magnetic fields to make the electron beam bend differently at different time delays.

[0038] The device further comprises a linear accelerator (not shown) for generating the electron beam 1 and accelerating the electron beam to a desired energy.

[0039] Recombination Figure 2 and Figure 3 As shown, the undulator A is divided into undulator modules A1 to A1. N , used to generate a wavelength of The undulator B is divided into undulator modules B1 to undulator modules B N , used to generate a wavelength of The undulator C is divided into undulator modules C1 to undulator modules C N , used to generate a wavelength of The undulator D is divided into undulator modules D1 to D N , used to generate a wavelength of The fourth X-ray beam, and , the wavelength difference between adjacent X-rays is 0.3 nanometers or 3 nanometers.

[0040] In a specific embodiment, the undulator module includes a sub-undulator a, an OK magnetic compressor b and a quadrupole iron c.

[0041] The present invention also provides an imaging method of a free electron laser device based on the ultrafast dynamic imaging, comprising the following steps:

[0042] Step 1, adjusting the electron beam energy, the dimensionless magnetic field parameter K and the magnetic field size of the four-color magnetic compressor;

[0043] Step 2, using the electron beam 1 to traverse the undulator A, the first four-color magnetic compressor 2, the undulator B, the second four-color magnetic compressor 3, the undulator C, the third four-color magnetic compressor 4 and the undulator D multiple times, to generate four beams of X-rays with different wavelengths at different times;

[0044] Step 3, combining the OK mechanism, adjusting the pulse energy of the four X-ray beams by the number of undulator modules;

[0045] Step 4, four beams of X-rays with different wavelengths at different times pass through the sample 8 in sequence to excite and capture the ultrafast dynamic process in the sample 8;

[0046] Step five, use the transmission grating 6 to separate the X-rays of different wavelengths in space, arrange the wavelengths from small to large, and expand symmetrically with the zero order as the center. Use the X-ray CCD detector 7 to record and analyze multiple diffraction images, reconstruct the motion state of the sample under X-rays of different wavelengths, and indirectly reflect the dynamic evolution process of the sample in the order of tens of femtoseconds to picoseconds.

[0047] The free electron laser device and imaging method based on the ultrafast dynamic imaging provided by the present invention are described in detail below with reference to specific embodiments.

[0048] Example 1

[0049] See also Figure 1 As shown, in Example 1, the free electron laser device includes a linear accelerator (not shown), an undulator A, a first four-color magnetic compressor 2, an undulator B, a second four-color magnetic compressor 3, an undulator C, a third four-color magnetic compressor 4, an undulator D and an electron beam collector 5. The appropriate electron beam energy, dimensionless magnetic field parameter K and undulator period are determined according to the specific requirements of the radiation photon wavelength. For example, the wavelengths of multi-pulse multi-energy X-rays are 1.13, 1.43, 1.73, and 2.03 nm, respectively, and the corresponding electron beam energy is 3.17 GeV. The undulator period is is 38mm, and the corresponding values ​​of the dimensionless magnetic field parameter K are 1.1, 1.4, 1.6, and 1.8 respectively. When the electron beam 1 passes through the undulator A and moves at high speed, it generates radiation at the resonant wavelength. This radiation is a high-energy X-ray pulse, that is, the first beam of X-rays is formed. Then, the electron beam 1 and the first beam of X-rays pass through the first four-color magnetic compressor 2 at the same time. In the first four-color magnetic compressor 2, X-rays propagate along a straight path without deflection, while the electron beam 1 is deflected due to the action of the magnetic field, resulting in an additional path relative to the straight path. Therefore, there is a time delay for the electron beam 1 relative to the first beam of X-rays. The delayed electron beam 1 passes through the undulator B, where it continues to radiate photons and generates a second beam of X-rays. The method of delaying the electron beam 1 indirectly causes a time interval (delay) between the first beam of X-rays and the second beam of X-rays, and the time interval can be adjusted by adjusting the magnetic field size of the four-color magnetic compressor. Its parameter range is 0.5-6T, and the corresponding delay parameter range is , that is, in the range of 100fs to 10ps.

[0050] Then, the electron beam 1 and the second beam of X-rays pass through the second four-color magnetic compressor at the same time, and the electron beam 1 is deflected. Similarly, the electron beam 1 is delayed relative to the second beam of X-rays. After that, the electron beam 1 reaches the undulator C and continues to oscillate and radiate photons, generating a third beam of X-rays, and the time interval between the second beam of X-rays and the third beam of X-rays is also due to the delay of the electron beam 1 in the second four-color magnetic compressor 3. Finally, when the third beam of X-rays and the electron beam 1 pass through the third four-color magnetic compressor 4 at the same time, the electron beam 1 is deflected again. At this time, the electron beam 1 controlled by the third four-color magnetic compressor 4 is behind the third beam, the second beam, and the first beam of X-rays. Subsequently, the electron beam 1 passes through the undulator D and radiates photons at the resonance wavelength to form the last beam of X-rays. Therefore, a monoenergetic electron beam must traverse the combination of the undulator and the four-color magnetic compressor multiple times to generate four beams of X-ray pulses, and the time interval between adjacent X-rays can reach the femtosecond to picosecond level. In addition, the electron beam 1 is effectively collected and managed by the electron beam collector 5.

[0051] The gain of a free electron laser decreases significantly as the energy dispersion of the electron beam 1 increases, especially when the RMS energy dispersion of the electron beam 1 Greater than the Pierce parameter of FEL , for X-ray FELs, the range is . Figure 1 The four-color magnetic compressor in the method cannot effectively adjust the quality of the electron beam 1 because the momentum compression parameters of the four-color magnetic compressor need to be precisely set. Although the momentum compression parameters are precisely set , the resonant radiation wavelength of electron beam 1 in undulator A is , density modulation is performed by the first four-color magnetic compressor 2 to enhance the wavelength The first X-ray beam micro-bunching effect, but in the undulator A, the wavelength needs to be destroyed The micro-bunching effect of the first X-ray beam reshapes the wavelength The micro-bunching effect of the second X-ray beam causes the resonant radiation to emit a wavelength of Therefore, the total energy of the X-ray pulse output by the undulator beamline is not high, and the required time delay cannot be set, because there is a two-fold relationship between the dispersion function and the delay function, that is, This solution is inseparable from the regulation and delay process of the electron beam 1.

[0052] Therefore, in order to improve the gain of FEL, the present invention uses an optical klystron (OK mechanism) to optimize the performance of the free electron laser device, such as Figure 2 and Figure 3 As shown, in Figure 1 In the basic solution, the device is modified in combination with the OK mechanism. The undulator A, undulator B, undulator C, and undulator D are respectively divided into multiple undulator modules. Taking undulator A as an example, the specific configuration includes: undulator A extends from undulator module A1 to undulator module A N , the wavelength produced is The first X-ray beam, correspondingly, undulator B produces a wavelength of The second X-ray beam, produced by undulator C, has a wavelength of The third X-ray beam, produced by undulator D, has a wavelength of The fourth X-ray beam. Each undulator module is mainly composed of three parts: sub-undulator a, OK magnetic compressor b and quadruple iron c. Among them, the momentum compression parameter of OK magnetic compressor b is To design accurately, the formula needs to be satisfied and ( When the electron beam 1 first passes through the undulator module A1, the sub-undulator a generates resonant radiation with a wavelength of , and performs energy modulation. Subsequently, the OK magnetic compressor b converts the energy modulation into density modulation, enhancing the micro-bunching effect of the electron beam 1. Then, the electron beam 1 is focused by the quadruple iron c to ensure that it maintains stable quality when entering the next module. This process is repeated in the subsequent undulator modules, and the electron beam 1 passes through each undulator module one by one, and finally in the undulator module A. N Further enhance the coherent radiation and improve the wavelength of FEL Similarly, for wavelength , and The processing is also carried out in a similar manner, gradually enhancing the gain of each wavelength. By adjusting the number of undulator modules, the pulse energy of each X-ray beam can be flexibly controlled, thereby significantly improving the performance of this free electron laser device. The four-color magnetic compressor is used to adjust the time interval between electron beam 1 and X-rays.

[0053] Therefore, the present invention divides the magnetic compressor into an independent four-color magnetic compressor with a delay function and an OK magnetic compressor with a dispersion function, so that the delay function and the dispersion function operate independently, thereby achieving the purpose of regulating the time interval between adjacent X-ray pulses and adjusting the quality of the electron beam.

[0054] The present invention sets the energy of the monoenergetic electron beam and the undulator parameter K according to the experimental requirements to obtain the required X-ray pulse photon energy. The delay parameters of the four-color magnetic compressor can also be set according to the requirements of high-time resolution dynamic imaging to achieve ultrafast dynamic imaging from picoseconds to femtoseconds. For example, the energy range of the electron beam 1 is 0.8GeV to 14GeV, the dimensionless magnetic field parameter K ranges from 0.5 to 4, and the undulator period is The range is from 30mm to 100mm, the X-ray pulse photon energy range is from 0.4nm to 20nm, and the delay parameter range of the four-color magnetic compressor is arrive In addition, the present invention can also improve the FEL gain through the OK mechanism. The generation of multi-energy multi-pulse X-rays can promote the realization of ultrafast dynamic imaging from femtosecond to picosecond levels and help us study the ultrafast dynamic processes inside matter.

[0055] Example 2

[0056] See more specifically Figure 2 As shown, the present invention can use four X-ray light sources generated by free electron laser to perform multiple "flash photography", and the wavelengths of the four X-ray light sources are respectively , , and ,and , the wavelength difference between adjacent X-rays is 0.3 nanometers or 3 nanometers, and the time interval between adjacent X-rays is in the picosecond to femtosecond level. They pass through the sample 8 in sequence, exciting and capturing the ultrafast dynamic process in the sample. When these X-rays pass through the high line density transmission grating 6, according to the grating equation:

[0057] ;

[0058] in, is the grating period, is the diffraction angle, is the diffraction order, is the wavelength. X-rays of different wavelengths will be separated in space. According to the dispersion theory, the wavelengths are arranged in order from small to large, and are symmetrically spread out with the zero order as the center. Since the wavelength of each X-ray beam is different, the transmission grating 6 produces different diffraction angles for these X-rays ( ). The X-ray CCD detector 7 records these diffraction images, among which the first diffraction image is formed by the first beam of X-rays on the X-ray CCD detector 7, and the corresponding diffraction angle is , the corresponding time is Then, in the time range from picoseconds to femtoseconds, the second beam of X-rays forms a second diffraction image, corresponding to a diffraction angle of , the corresponding time is . In chronological order, the corresponding time is formed in sequence and time The third and fourth diffraction images are obtained. X-rays of different energies can capture the sample state at different times. The transmission grating 6 disperses the X-rays of different energies to separate them. Then, four diffraction images are recorded by the X-ray CCD detector 7. Each diffraction image represents the sample state at different times, corresponding to time , , and , reflecting the dynamic evolution process of sample 8 at different times. In addition, the material of transmission grating 6 can be selected according to the energy characteristics of multi-energy multi-pulse X-rays to improve the ultrafast dynamic imaging resolution and optimize the imaging effect, as shown in Table 1.

[0059] Table 1 Transmission grating parameters

[0060]

[0061] In summary, the transmission grating 6 can distinguish X-rays of different energies, and then the X-ray CCD detector 7 records and analyzes four diffraction images at different times. Therefore, the present invention uses multi-pulse multi-energy X-rays to obtain four ultrafast dynamic process imaging pictures with time intervals of femtoseconds to picoseconds, reflecting the motion state of the sample 8 at different times.

[0062] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0063] In addition, it should be noted that the scope of the methods and systems in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0064] The embodiments of the present invention are described above, but the present invention is not limited to the above-mentioned specific implementation modes. The above-mentioned specific implementation modes are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A free electron laser device for ultrafast dynamic imaging, characterized in that: The invention comprises an undulator A, a first four-color magnetic compressor, an undulator B, a second four-color magnetic compressor, an undulator C, a third four-color magnetic compressor, an undulator D, an electron beam collector, a transmission grating and an X-ray CCD detector, which are sequentially arranged along the traveling path of the electron beam. The undulator A, the undulator B, the undulator C and the undulator D have different dimensionless magnetic field parameters K, wherein: The electron beam passes through the undulator A to generate a wavelength of The first beam of X-rays is then passed through the first four-color magnetic compressor at the same time. The first beam of X-rays is not affected by the magnetic field of the first four-color magnetic compressor and propagates along a straight line, while the electron beam is deflected by the magnetic field of the first four-color magnetic compressor to produce a time delay. The delayed electron beam passes through the undulator B to produce a wavelength of The electron beam and the second beam of X-rays then pass through the second four-color magnetic compressor at the same time. The second beam of X-rays continues to propagate in a straight line. The electron beam is deflected by the magnetic field of the second four-color magnetic compressor to produce a time delay. The delayed electron beam passes through the undulator C to produce a wavelength of The electron beam and the third X-ray beam then pass through the third four-color magnetic compressor at the same time. The third X-ray beam continues to propagate in a straight line. The electron beam is deflected by the magnetic field of the third four-color magnetic compressor to produce a time delay. The delayed electron beam passes through the undulator D to produce a wavelength of The fourth X-ray beam, , the delay time between adjacent X-rays ranges from 100fs to 10ps; the electron beam passing through the undulator D is received by the electron beam collector, and the first X-ray, the second X-ray, the third X-ray, and the fourth X-ray passing through the undulator D sequentially pass through the sample to excite and capture the ultrafast dynamic process in the sample, and then pass through the transmission grating to generate corresponding diffraction angles as well as ,and Finally, the X-ray CCD detector forms the corresponding diffraction angle and time The first diffraction image is formed, and then in the time range of picoseconds to femtoseconds, the second beam of X-rays forms a corresponding diffraction angle on the X-ray CCD detector. and time The second diffraction image, the third beam of X-rays forms a corresponding diffraction angle on the X-ray CCD detector and time The third diffraction image, the fourth beam of X-rays forms a corresponding diffraction angle on the X-ray CCD detector and time The fourth diffraction image is obtained, thereby obtaining four ultrafast dynamic process imaging images with time intervals from femtoseconds to picoseconds, reflecting the motion state of the sample at different times.

2. The free electron laser device for ultrafast dynamic imaging according to claim 1, characterized in that: The energy range of the electron beam is 0.8 GeV to 14 GeV.

3. The free electron laser device for ultrafast dynamic imaging according to claim 2, characterized in that: The first four-color magnetic compressor, the second four-color magnetic compressor, and the third four-color magnetic compressor are all C-type magnetic compressors.

4. The free electron laser device for ultrafast dynamic imaging according to claim 3, characterized in that: The C-type magnetic compressor includes a plurality of bending magnets which generate a magnetic field to cause the electron beam to bend differently at different time delays.

5. The free electron laser device for ultrafast dynamic imaging according to claim 1, characterized in that: The dimensionless magnetic field parameter K of undulator A, undulator B, undulator C, and undulator D ranges from 0.5 to 4, and the period The value range is 30mm to 100mm.

6. The free electron laser device for ultrafast dynamic imaging according to claim 5, characterized in that: The magnetic field value ranges of the first four-color magnetic compressor, the second four-color magnetic compressor, and the third four-color magnetic compressor are all 0.5-6T.

7. The free electron laser device for ultrafast dynamic imaging according to claim 1, characterized in that: Also included is a linear accelerator for generating the electron beam and accelerating the electron beam to a desired energy.

8. The free electron laser device for ultrafast dynamic imaging according to claim 1, characterized in that: The undulator A is divided into undulator modules A1 to A1. N , used to generate a wavelength of The undulator B is divided into undulator modules B1 to undulator modules B N , used to generate a wavelength of The undulator C is divided into undulator modules C1 to undulator modules C N , used to generate a wavelength of The undulator D is divided into undulator modules D1 to D N , used to generate a wavelength of The fourth X-ray beam, and , the wavelength difference between adjacent X-rays is 0.3 nanometers or 3 nanometers.

9. The free electron laser device for ultrafast dynamic imaging according to claim 8, characterized in that: The undulator module includes a sub-undulator, an OK magnetic compressor and a quadrupole iron.

10. An imaging method of a free electron laser device for ultrafast dynamic imaging based on any one of claims 1 to 9, characterized in that: The steps include: Step 1, adjusting the electron beam energy, the dimensionless magnetic field parameter K and the magnetic field size of the four-color magnetic compressor; Step 2, using an electron beam to traverse the undulator A, the first four-color magnetic compressor, the undulator B, the second four-color magnetic compressor, the undulator C, the third four-color magnetic compressor and the undulator D multiple times, to generate four beams of X-rays with different wavelengths at different times; Step 3, combining the OK mechanism, adjusting the pulse energy of the four X-ray beams by the number of undulator modules; Step 4: Four X-ray beams with different wavelengths at different times pass through the sample in sequence to stimulate and capture the ultrafast dynamic process in the sample; Step five: Use a transmission grating to separate X-rays of different wavelengths in space. Arrange the wavelengths from small to large and symmetrically expand them around the zero order. Use an X-ray CCD detector to record and analyze multiple diffraction images to reconstruct the motion state of the sample under X-rays of different wavelengths, indirectly reflecting the dynamic evolution process of the sample at the order of hundreds of femtoseconds to several picoseconds.

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