A femtosecond ultrafast diffraction imaging system and method based on X-ray free electron laser

Abstract

The application provides a femtosecond ultrafast diffraction imaging system and method based on an X-ray free electron laser, and relates to the field of X-ray free electron lasers. The X-ray free electron laser femtosecond ultrafast diffraction imaging system provided by the application comprises an X-ray light source for emitting X-ray free electron laser; a light path focusing mechanism arranged on the light path of the X-ray free electron laser and used for focusing the X-ray free electron laser; a light control mechanism arranged on the light path of the X-ray free electron laser focused by the light path focusing mechanism and forming a light control slit; a sample target arranged at the focal point of the X-ray free electron laser; a sample target arranged at the focal point of the X-ray free electron laser; a single photon response detection mechanism arranged in the diffraction light path generated after the X-ray free electron laser bombards the sample and used for collecting a diffraction pattern; and a phase workstation electrically connected with the single photon response detection mechanism and used for collecting diffraction pattern data and performing phase recovery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of X-ray free electron laser experiment, and particularly to a femtosecond ultrafast diffraction imaging system and method based on X-ray free electron laser. BACKGROUND

[0002] X-ray free electron laser is a scientific research device based on linear electron accelerator, which can generate femtosecond pulse width, ultra-high brightness and full coherent X-ray laser, and the wavelength can cover the range from far infrared to X-ray band, providing unprecedented opportunities for frontier scientific research in physics, chemistry, life science and material science. Therefore, developing advanced methodology based on X-ray free electron laser can not only expand the ability and level of methodology, but also be widely applied in basic scientific research, which has wide practical significance. Among them, coherent diffraction imaging is an advanced lens-free imaging method, which can realize three-dimensional imaging of micron-sized crystals, and the spatial resolution can reach ten nanometers, and has high resolution for atomic displacement and strain in the crystal, and has wide application prospect. The energy of soft X-ray band free electron laser is generally between 100 and 1000 eV, which is suitable for diffraction research of long period structure.

[0003] Crystal structure is a periodic structure formed by ordered arrangement of atoms, and similar to this is superlattice structure, which is a periodic structure formed by ordered arrangement of small particles with similar shape. Superlattice structure is simple to control and suitable for performance regulation, and has wide application prospect in engineering, chemical industry and optics. At the same time, superlattice structure has rich topological structure, which is suitable for research and development in topological field. For example, the Nobel Prize in 2016 was awarded to the achievements in two-dimensional topology. However, due to the time resolution of detection means, related researches are mostly concentrated in the time scale of microsecond, and have no ability to solve key scientific problems in faster time scale, and electron microscope with strict requirements for samples is used. For example, the speed of electron transfer in atom is usually less than 1 picosecond, and the time scale of magnetic phase transition is usually several tens of picoseconds. Therefore, how to study superlattice structure in faster time scale has always been a difficult problem.

[0004] In summary, there is a need for an imaging system capable of studying superlattice structure in femtosecond scale. SUMMARY

[0005] In order to solve the above problems, the present application provides a femtosecond ultrafast diffraction imaging system of X-ray free electron laser, which can study superlattice structure in femtosecond scale.

[0006] The application provides a femtosecond ultrafast diffraction imaging system of an X-ray free electron laser, which comprises an X-ray light source for emitting an X-ray free electron laser; an optical path focusing mechanism arranged on an optical path of the X-ray free electron laser and used for focusing the X-ray free electron laser; a light control mechanism arranged on an optical path of the X-ray free electron laser focused by the optical path focusing mechanism and forming a light control slit, and used for controlling a light transmission amount of the X-ray free electron laser; a sample target arranged at a focal point of the X-ray free electron laser; the sample target comprises a plurality of target areas, and samples are arranged in the target areas; the X-ray free electron laser forms a diffraction light path after forming a light spot on the samples; a single photon response detection mechanism is arranged in the diffraction light path generated after the X-ray free electron laser bombards the samples, and is used for collecting a diffraction pattern; and a phase workstation is electrically connected with the single photon response detection mechanism, and is used for collecting diffraction pattern data and performing phase recovery.

[0007] In an implementable embodiment, the optical path focusing mechanism comprises a first focusing mirror and a second focusing mirror arranged in the optical path of the X-ray free electron laser; the first focusing mirror and the second focusing mirror are arranged relative to a light beam of the X-ray free electron laser and focus the X-ray free electron laser on the sample target.

[0008] In an implementable embodiment, the light control mechanism comprises a first baffle and a second baffle arranged in the optical path of the X-ray free electron laser, and the light control slit is formed between the first baffle and the second baffle.

[0009] In an implementable embodiment, the sample target comprises an adjusting mechanism and a sample target arranged above the adjusting mechanism; the sample target comprises a plurality of target areas, and samples are arranged in the target areas.

[0010] In an implementable embodiment, the single photon response detector comprises a supporting platform and a single photon response detector arranged on the supporting platform; the single photon response detector comprises a first diffraction light plate, a zero-order diffraction light plate and a second diffraction light plate arranged in the diffraction light path; the first diffraction light plate and the second diffraction light plate are arranged relative to the light beam of the X-ray free electron laser and are located in a diffraction light region of the diffraction light path, the zero-order diffraction light plate is arranged in a straight-through region of the diffraction light path, and a light baffle is further arranged in front of the zero-order diffraction light plate.

[0011] In an implementable embodiment, a diameter of the light spot of the X-ray free electron laser on the sample target is 1-20 μm.

[0012] In an implementable embodiment, materials of the first focusing mirror and the second focusing mirror are independently selected from KB mirrors, Fresnel zone plates or X-ray combined refractive lenses.

[0013] In one feasible embodiment, the materials of the first baffle and the second baffle are independently selected from single crystal silicon, boron carbide or tungsten carbide; and / or the width of the light-controlling slit is greater than 50 μm, the movement accuracy of the first baffle and the second baffle is less than 1 μm, and the movement resolution of the first baffle and the second baffle is less than 0.2 μm.

[0014] In one feasible embodiment, the operating frequency of the single-photon response detector is greater than 2 Hz, and the resolution of the single-photon response detector is greater than 2k.

[0015] In one feasible embodiment, the sample target is a silicon nitride thin film window; and / or the number of the target areas is 10 to 30.

[0016] In a feasible implementation manner, the distance between the light control mechanism and the sample target is 100-1000 mm.

[0017] The present invention provides a femtosecond ultrafast diffraction imaging system for X-ray free electron laser, which has the following beneficial effects: the present invention utilizes femtosecond pulses of X-ray free electron laser and adopts a method combining plane wave coherent diffraction imaging and Bragg coherent diffraction imaging to study the three-dimensional morphology and strain structure changes of superlattices at the femtosecond level. It can realize continuous observation of superlattice materials at the femtosecond level, carry out ultrafast experiments to study key dynamic behaviors, observe changes in the three-dimensional morphology of samples on a femtosecond time scale, and quantitatively analyze the distribution of the strain field inside the crystal, and can accurately capture changes in the crystal structure in three-dimensional space and ultrafast time scales. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a side view of the overall structure of the present invention.

[0019] Figure 2 Schematic diagram of the structure of the sample target in the present invention.

[0020] Reference numerals

[0021] X-ray source 1

[0022] Optical path focusing mechanism 2

[0023] First focusing mirror 21

[0024] Second focusing mirror 22

[0025] Light control mechanism 3

[0026] First baffle 31

[0027] Second baffle 32

[0028] Light control slit 33

[0029] Sample target 4

[0030] Target area 41

[0031] Sample 42

[0032] Single-photon response detection mechanism 5

[0033] Support platform 51

[0034] Single-photon response detector 52

[0035] First diffraction light plate 52.1

[0036] Zero-order diffraction light plate 52.2

[0037] Second diffraction light plate 52.3

[0038] Light barrier 53

[0039] Phase workstation 6

[0040] Fine adjustment mechanism 7

[0041] Coarse adjustment mechanism 8

[0042] Angle adjustment mechanism 9 DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application. In the description of the present application, it should be noted that the terms "left side", "right side", "upper side", "lower side", "upper", "lower" and the like indicate the orientation or positional relationship shown in the drawings, and are only used for the purpose of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" are only used for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0044] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integrally connected, can be mechanical connection, can also be electrical connection, can be directly connected, can also be indirectly connected through an intermediate medium, and can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0045] In addition, in the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0046] The embodiment of the present application provides a femtosecond ultrafast diffraction imaging system based on X-ray free electron laser, referring to Figure 1 , comprising: an X-ray source 1 for emitting X-ray free electron laser; a light path focusing mechanism 2 arranged on the light path of the X-ray free electron laser for focusing the X-ray free electron laser; a light control mechanism 3 arranged on the light path of the X-ray free electron laser focused by the light path focusing mechanism 2 and forming a light control slit 33, for controlling the light transmission amount of the X-ray free electron laser; a sample target 4 arranged at the focal point of the X-ray free electron laser, the sample target 4 comprising a plurality of target areas 41, a sample 42 being arranged in the target area 41, and the X-ray free electron laser forming a diffraction light path after forming a spot on the sample 42; a single photon response detection mechanism 5 arranged in the diffraction light path generated after the sample 42 is bombarded by the X-ray free electron laser, for collecting diffraction patterns; a phase workstation 6 electrically connected with the single photon response detection mechanism 5, for collecting diffraction pattern data and performing phase recovery, and the phase workstation 6 is usually a computer. The present application utilizes femtosecond pulses of X-ray free electron laser, adopts a method combining plane wave coherent diffraction imaging and Bragg coherent diffraction imaging, studies the three-dimensional morphology and strain structure changes of superlattice in femtosecond order, can realize continuous observation of superlattice material in femtosecond order, carries out key dynamic behavior of ultrafast experimental research, can observe the change of three-dimensional morphology of the sample 42 in femtosecond time scale, and quantitatively analyzes the distribution of strain field in the crystal, and can accurately capture the change of crystal structure in three-dimensional space and ultrafast time scale.

[0047] In the femtosecond ultrafast diffraction imaging system provided by the embodiment of the present application, referring to Figure 1The light path focusing mechanism 2 comprises a first focusing mirror 21 and a second focusing mirror 22 arranged in the light path of the X-ray free electron laser, and the first focusing mirror 21 and the second focusing mirror 22 are arranged relative to the light beam of the X-ray free electron laser and focus the X-ray free electron laser on the sample target 4. In the present application, the focal length of the X-ray free electron laser is adjusted by adjusting the angles of the first focusing mirror 21 and the second focusing mirror 22, so as to ensure that the focal length of the X-ray free electron laser can be located at the position of the sample target 4. Generally, the included angle between the first focusing mirror 21, the second focusing mirror 22 and the X-ray free electron laser is the same. Further, the materials of the first focusing mirror 21 and the second focusing mirror 22 are independently selected from KB mirrors, Fresnel zone plates or X-ray compound refractive lenses, and the KB mirrors are preferred because the light propagation efficiency of the KB mirrors is the highest and the light intensity of the focused light spot is higher.

[0048] In the femtosecond ultrafast diffraction imaging system provided by the embodiment of the present application, referring to Figure 1 The light control mechanism 3 comprises a first baffle 31 and a second baffle 32 arranged in the light path of the X-ray free electron laser, and the light control slit 33 is formed between the first baffle 31 and the second baffle 32. In use, the first baffle 31 and the second baffle 32 are simultaneously close to or away from the light beam of the X-ray free electron laser. The middle region of the X-ray free electron laser is a fully coherent part, and the edge region is non-coherent stray light. The function of the light control slit 33 is to allow the fully coherent part of the X-ray free electron laser to pass through and filter out the stray light of the X-ray free electron laser. In a specific embodiment, the materials of the first baffle 31 and the second baffle 32 are independently selected from single crystal silicon, boron carbide or tungsten carbide, and the tungsten carbide is preferred. In a specific embodiment, the width of the light control slit is > 50 μm, where the width refers to the gap width between the first baffle 31 and the second baffle 32. The moving precision of the first baffle 31 and the second baffle 32 is < 1 μm, where the moving precision refers to the minimum step length when moving. The moving resolution of the first baffle 31 and the second baffle 32 is < 0.2 μm, where the moving resolution refers to the error value when moving.

[0049] In the femtosecond ultrafast diffraction imaging system provided by the embodiment of the present application, referring to Figure 1 The fine adjustment mechanism 7, the coarse adjustment mechanism 8 and the angle adjustment mechanism 9 are sequentially arranged below the sample target 4. The coarse adjustment mechanism 8 and the fine adjustment mechanism 7 can realize the movement of the sample target 4 in three directions of XYZ. The resolution of the fine adjustment mechanism 7 is ≤ 10 nm, and the resolution of the coarse adjustment mechanism 8 is ≤ 1 μm. The moving direction can be referred to Figure 1The angle adjusting mechanism 9 can realize the rotation adjustment of the sample target 4 around the three directions of XYZ, the rotation along the X and Y axes aims to find the diffraction surface of the sample 42, the rotation along the Z axis is the scanning direction, and the resolution of the angle adjusting mechanism 9 is ≤0.1°. In a specific embodiment, the stroke of the coarse adjusting mechanism 8 in the X and Y directions is >±100 mm, the stroke in the Z direction is >±50 mm, and the overall load is >0.6 kg; the stroke of the fine adjusting mechanism 7 in the X and Y directions is >±10 μm, the resolution is ≤10 nm, the stroke in the Z direction is >±5 μm, the resolution is ≤10 nm, and the overall load is >0.5 kg; the rotation range of the angle adjusting mechanism 9 along the X and Y axes is >15°, the resolution is better than 0.1°, the rotation range along the Z axis is >360°, the resolution is better than 0.001°, and the overall load is >1 kg. In a preferred embodiment, the angle adjusting mechanism 9 can use the integrated angle displacement table of Huber Company, which comprises a two-axis arc angle displacement table 5203.80 and a single-axis rotation displacement table 480 connected in a top-down manner; the coarse adjusting mechanism 8 can use the integrated linear displacement table of Huber Company, which comprises an XY displacement table 5102.50 and a Z displacement table 2103.D40 connected in a top-down manner; and the fine adjusting mechanism 7 can use the integrated piezoelectric displacement table of SmarAct Company, which comprises an XY displacement table PLF3232-xy.60 and a Z displacement table PLF3232-z.60 connected in a top-down manner.

[0050] In the femtosecond ultrafast diffraction imaging system provided in the embodiments of the present application, referring to Figure 1 The sample target 4 comprises an adjusting mechanism and a sample target 4 arranged above the adjusting mechanism, and the sample target 4 comprises a plurality of target areas 41, and the sample 42 is arranged in the target areas 41. As an illustration, when the X-ray free electron laser passes through the sample 42, the diffraction path is generated, and the diffraction paths generated for different samples 42 are different. Therefore, in order to collect different diffraction paths, different samples 42 need to be arranged in the plurality of target areas 41. The spot of the X-ray free electron laser is usually located on the sample 42 in one target area 41, that is, the X-ray free electron laser usually irradiates one sample 42 in each experiment. In order to make the spot of the X-ray free electron laser fall on different samples 42, the position of the sample target 4 can be moved by controlling the fine adjusting mechanism 7 and the coarse adjusting mechanism 8, so that different samples 42 are aligned with the spot of the X-ray free electron laser. In a specific embodiment, the sample target 4 is a silicon nitride thin film window. In another specific embodiment, the number of the target areas 41 is 10-30, and preferably 25.

[0051] In the femtosecond ultrafast diffraction imaging system provided in the embodiments of the present application, referring to Figure 1The single-photon response detector comprises a support platform 51 and a single-photon response detector 52 arranged on the displacement table, wherein the single-photon response detector 52 comprises a first diffraction light plate 52.1, a zero-order diffraction light plate 52.2 and a second diffraction light plate 52.3 arranged in a diffraction light path; the first diffraction light plate 52.1 and the second diffraction light plate 52.3 are arranged relative to the light beam of the X-ray free electron laser and located in a diffraction light region of the diffraction light path; the zero-order diffraction light plate 52.2 is arranged in a straight-through region of the diffraction light path, and a light blocking plate 53 is further arranged in front of the zero-order diffraction light plate 52.2. After the X-ray free electron laser passes through the sample target 4, a diffraction light path is formed, which is divided into two regions, i.e., a diffraction light region and a straight-through light region. The diffraction light in the diffraction light region is incident on the first diffraction light plate 52.1 and the second diffraction light plate 52.3 and forms a light spot, and this part of the light spot is a Bragg diffraction pattern of the sample 42. The diffraction light in the straight-through light region is first incident on the light blocking plate 53, then the light wave bypasses the light blocking plate 53 to form secondary diffraction light again, the secondary diffraction light is incident on the zero-order diffraction light plate 52.2 and forms a light spot, and the light spot formed by the secondary diffraction light is a zero-order diffraction pattern of the sample 42. In an embodiment, the working frequency of the single-photon response detector 52 is greater than 2 Hz, the pixel size is greater than 2K pixels, the distance between the single-photon response detector 52 and the sample target 4 is 100-1000 mm, and the step precision is less than 1 mm. As an illustration, the distance between the single-photon response detector 52 and the sample target 4 is usually determined by the size of the sample 42, and needs to satisfy that the sampling frequency is greater than the Nyquist frequency, and generally requires that the oversampling rate is greater than 2. In actual measurement, generally at least two pixel sizes are required for each diffraction edge. For example, for a 2 mm-sized sample 42, a 15 mm pixel size detector is placed at 166 mm, and an oversampling rate of 30 can be achieved. The embodiment also provides a use method of the femtosecond ultrafast diffraction imaging system based on the X-ray free electron laser, which at least comprises the following steps:

[0052] 1) Preparation and calibration of the light path, the position of the sample target 4 is adjusted to align the center of the light spot with the sample 42; since the light spot of the X-ray free electron laser used in the experiment is in the micron level, the position of the light spot on the sample 42 needs to be determined before the experiment, which will help to screen the experimental sample 42 of interest during the experiment; by controlling the coarse adjustment mechanism 8, the fine adjustment mechanism 7 and the angle adjustment mechanism 9, the position and angle of the sample target 4 relative to the light spot can be adjusted, and the sample 42 to be measured in the sample target 4 can be moved to the center of the light spot.

[0053] 2) Collecting diffraction spots, the sample 42 is bombarded by the X-ray free electron, and the Bragg diffraction pattern and the zero-order diffraction pattern are collected by the single-photon response detector 52.

[0054] 3) Phase retrieval, phase retrieval is performed on the Bragg diffraction pattern and the zeroth order diffraction pattern to obtain high-resolution topography imaging and internal strain imaging, respectively. The mainstream method of phase retrieval is to use an iterative algorithm to cycle the diffraction spots in reciprocal space and direct space to perform fast Fourier transform. The constraint in reciprocal space is the amplitude information obtained from the diffraction pattern, and the constraint in direct space is the estimated crystal boundary. In each cycle in reciprocal space, the amplitude is rewritten as the amplitude of the measured diffraction pattern, while the phase information is retained. After a sufficient number of iterative cycles, the algorithm converges to obtain the final reconstruction result. Through this method, the three-dimensional topographic structure of the sample 42 can be obtained, and the theoretical limit resolution can reach the size of the superlattice unit, generally in the range of several nanometers to several tens of nanometers. As an illustration, the core of phase retrieval is an image processing algorithm, and there are many image processing algorithms that can achieve phase retrieval. Here, they will not be listed one by one.

[0055] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the technical field, several improvements and replacements can be made without departing from the technical principles of the present application, and these improvements and replacements should also be considered as the protection scope of the present application.

Claims

1. An X-ray free electron laser based femtosecond ultrafast diffraction imaging system, characterized in that, The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device.

2. The femtosecond ultrafast diffraction imaging system of claim 1, wherein: The application relates to an X-ray free electron laser device.

3. The femtosecond ultrafast diffraction imaging system of claim 1 or 2, wherein: The application relates to an X-ray free electron laser device.

4. The femtosecond ultrafast diffractive imaging system of claim 1, wherein: The application relates to an X-ray free electron laser device.

5. The femtosecond ultrafast diffractive imaging system of claim 2, wherein: The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. The application relates to an X-ray free electron laser device. 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The femtosecond ultrafast diffractive imaging system of claim 3, wherein: The material of the first baffle (31) and the second baffle (32) is independently selected from single crystal silicon, boron carbide or tungsten carbide; and / or, the width of the light control slit (33) is > 50 μm, the moving precision of the first baffle (31) and the second baffle (32) is < 1 μm, and the moving resolution of the first baffle (31) and the second baffle (32) is < 0.2 μm.

7. The femtosecond ultrafast diffractive imaging system of claim 1, wherein: The working frequency of the single-photon response detector (52) is > 2 Hz, and the resolution of the single-photon response detector (52) is > 2 k.

8. The femtosecond ultrafast diffractive imaging system of claim 1, wherein: The diameter of the X-ray free electron laser spot on the sample target (4) is 2-20 μm; and / or, the number of the target regions (41) is 10-30; and / or, the distance between the light control mechanism (3) and the sample target (4) is 100-1000 mm.

9. A method for using the femtosecond ultrafast diffraction imaging system according to any one of claims 1-8, comprising at least the following steps: 1) Preparation and calibration of the optical path, adjusting the position of the sample target (4) to align the center of the spot with the sample (42); 2) Collecting diffraction spots, using X-ray free electron to bombard the sample (42), and collecting the Bragg diffraction pattern and the zero-order diffraction pattern by the single-photon response detector (52); 3) Phase recovery, performing phase recovery on the Bragg diffraction pattern and the zero-order diffraction pattern to obtain high-resolution topographic imaging and internal strain imaging, respectively.

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