A system and method for spatiotemporal coupling of an x-ray free electron laser and a femtosecond laser

Abstract

The application provides a kind of X-ray free electron laser and femtosecond laser space-time coupling system and method, it is related to X-ray free electron laser and femtosecond laser field.The space-time coupling system of the application includes medium platform for placing coupling medium, X-ray source for emitting X-ray free electron laser, femtosecond laser system for emitting femtosecond laser and controlling femtosecond laser optical path, vacuum coaxial microscope for observing reflected light on coupling medium and data acquisition system for collecting various signals.The application can couple X-ray free electron laser and femtosecond laser.In the aspect of space coupling, multiple mirrors and lenses are provided, so that X-ray free electron laser and femtosecond laser can realize micron-level space coupling on coupling medium;In the aspect of time coupling, by the principle that X-ray free electron laser can cause refractive index mutation of coupling medium (the time scale of mutation is femtosecond), femtosecond-level time coupling of X-ray free electron laser and femtosecond laser is realized.

Description

Technical Field

[0001] This invention relates to the field of X-ray free-electron lasers and femtosecond lasers, and in particular to a spatiotemporal coupling system and method for X-ray free-electron lasers and femtosecond lasers. Background Technology

[0002] X-ray free-electron lasers (XLEs), characterized by femtosecond pulses, ultra-high brightness, and full coherence, are among the most advanced X-ray sources currently available. Their exceptional performance provides an advanced platform for cutting-edge research in physics, chemistry, materials science, and life sciences. In particular, the femtosecond pulse characteristics of XLEs offer unprecedented opportunities for conducting ultrafast scientific research.

[0003] Femtosecond laser-pumped X-ray free-electron laser detection is an important method for conducting time-resolved experiments, achieving time resolution down to the femtosecond scale. The key to conducting femtosecond laser-pumped X-ray free-electron laser detection experiments is achieving spatial and temporal overlap of the two laser beams.

[0004] To increase the flux density of irradiated samples, X-ray free-electron lasers typically need to be focused to the micrometer scale, thus requiring micrometer-level precision in spatial coupling. Simultaneously, the pulse width of both X-ray free-electron lasers and femtosecond pumped lasers is usually less than 100 fs, necessitating femtosecond-level precision in temporal coupling. Traditional methods for achieving spatiotemporal coupling between X-ray free-electron lasers and femtosecond pumped lasers require specialized equipment, increasing experimental complexity and making it difficult to achieve spatiotemporal coupling without altering the experimental optical path.

[0005] In summary, in order to facilitate the spatiotemporal coupling of X-ray free-electron lasers and femtosecond pumped lasers at the micrometer spatial scale and femtosecond time scale, it is essential to design a spatiotemporal coupling system and method for X-ray free-electron lasers and femtosecond pumped lasers based on coaxial microscope imaging. Summary of the Invention

[0006] To address the aforementioned and related issues, the first aspect of this invention provides a spatiotemporal coupling system for X-ray free-electron lasers and femtosecond lasers. This system can achieve micron-level spatial coupling and femtosecond-level temporal coupling between X-ray free-electron lasers and femtosecond pump lasers, with the spatial coupling method employing angular coupling.

[0007] The first aspect of this invention provides a spatiotemporal coupling system for an X-ray free-electron laser and a femtosecond laser, comprising a medium platform for placing a coupling medium and adjusting the relative position of the coupling medium; a vacuum coaxial microscope for observing and collecting reflected light on the coupling medium; the vacuum coaxial microscope includes an objective lens, a first reflecting mirror assembly, a lens assembly, a second reflecting mirror assembly, and an imaging device connected in sequence; the objective lens, the first reflecting mirror assembly, and the lens assembly form a first angle, and the lens assembly, the second reflecting mirror assembly, and the imaging device form a second angle; the first reflecting mirror assembly has an opening; and an X-ray source for emitting an X-ray free-electron laser; the X-ray free-electron laser passes through the first reflecting mirror assembly. An aperture and objective lens are used to form an X-ray free electron laser spot on the coupling medium; a femtosecond laser system, comprising a femtosecond laser source, an optical path adjustment module, a focusing lens, and a coupling mirror arranged sequentially along the femtosecond laser optical path; the femtosecond laser source is used to emit the femtosecond laser, the optical path adjustment module is used to adjust the optical path of the femtosecond laser, the focusing lens is used to focus the femtosecond laser, and the coupling mirror is used to reflect the femtosecond laser and form a femtosecond laser spot on the coupling medium that overlaps with the X-ray free electron laser spot; a data acquisition system, comprising a digital signal generator, an oscilloscope, and a processor; the digital signal generator and processor are electrically connected to the imaging equipment, and the oscilloscope is electrically connected to the coupling medium.

[0008] In one feasible embodiment, the optical path adjustment module includes a delay line and a moving module, the moving module being slidably disposed on the delay line; the moving module is provided with a first femtosecond laser reflector and a second femtosecond laser reflector arranged sequentially along the femtosecond laser optical path; the femtosecond laser after being reflected by the coupling mirror forms an angle with the coupling medium; a femtosecond laser shutter is also provided in the femtosecond optical path between the second femtosecond laser reflector and the coupling mirror, and an X-ray shutter is also provided in the X-ray free electron optical path between the X-ray free electron laser and the first reflector assembly.

[0009] In one feasible embodiment, the mobile module is provided with a first femtosecond laser reflector, a second femtosecond laser reflector, and a third femtosecond laser reflector arranged sequentially along the femtosecond laser optical path; an X-ray shutter and a coupling mirror are sequentially arranged in the optical path between the X-ray source and the first reflector assembly, and the coupling mirror is provided with a coupling mirror opening; the femtosecond laser reflected by the coupling mirror and the X-ray free electron laser passing through the coupling mirror are collinear.

[0010] In one feasible embodiment, the first reflector assembly includes a first reflector adjustment frame and a first reflector disposed in the first reflector adjustment frame; the second reflector assembly includes a second reflector adjustment frame and a second reflector disposed in the second reflector adjustment frame; the lens assembly includes a first sleeve, a lens, and a second sleeve connected in sequence; the imaging device includes a camera and a third sleeve; the objective lens, the first reflector adjustment frame, the first sleeve, the lens, the second sleeve, the second reflector adjustment frame, the third sleeve, and the camera are connected in sequence; the objective lens, the first reflector adjustment frame, and the first sleeve form a first angle, and the second sleeve, the second reflector adjustment frame, and the third sleeve form a second angle; the angles of the first angle and the second angle are both 90°.

[0011] In one feasible embodiment, the X-ray shutter has an aperture > 5 mm and an operating frequency ≥ 10 Hz; and / or, the femtosecond laser shutter has an aperture > 10 mm and an operating frequency ≥ 10 Hz; and / or, the objective lens has a magnification of 2 to 50 times and a resolution of 0.5 μm to 5 μm; and / or, the focusing lens has a diameter ≥ 25.4 mm and a focal length ≥ 200 to 1500 mm; and / or, the delay line has a travel ≥ 125 mm; and / or, the moving module has a movement accuracy ≤ 3 μm.

[0012] In one feasible implementation, the oscilloscope has a bandwidth ≥ 1 GHz; and / or, the digital signal generator has ≥ 4 channels and a timing accuracy ≤ 1 μs; and / or, the digital signal generator is electrically connected to the X-ray shutter, femtosecond laser shutter, and camera respectively via trigger cables; the oscilloscope is electrically connected to the coupling medium via a data acquisition cable; the trigger cable connector is BNC or Lemo, and the data acquisition cable connector is BNC or SMA.

[0013] In one feasible embodiment, the coupling medium is a fine coupling medium or a coarse coupling medium; the coarse coupling medium is a photodiode or an RF cable, and the fine coupling medium is selected from any one of silicon nitride, Ce:YAG crystal or gallium nitride single crystal.

[0014] In one feasible embodiment, the bandwidth of the photodiode is ≥5GHz, the bandwidth of the radio frequency cable is ≥5GHz, the thickness of the silicon nitride is >2μm, and the thickness of the Ce:YAG crystal is >10μm.

[0015] In one feasible embodiment, the medium platform includes a sample stage, a Z-axis adjustment mechanism, an X-axis adjustment structure, and a Y-axis adjustment mechanism arranged sequentially from top to bottom, with the coupling medium disposed on the sample stage; the overall load of the Z-axis adjustment mechanism, the X-axis adjustment structure, and the Y-axis adjustment mechanism is >0.2 kg; the stroke of the Z-axis adjustment mechanism is >±30 mm, and the resolution of the Z-axis adjustment mechanism is <1 μm; the stroke of the Y-axis adjustment mechanism is >±15 mm, and the resolution of the Y-axis adjustment mechanism is <1 μm; the stroke of the Z-axis adjustment mechanism is >±30 mm, and the resolution of the Z-axis adjustment mechanism is <1 μm.

[0016] A second aspect of the present invention provides a method of using the X-ray free-electron laser and femtosecond laser spatiotemporal coupling system as described in the first aspect of the present invention, characterized by comprising at least the following steps:

[0017] Step S1): Install the coupling medium on the medium platform;

[0018] Step S2): The X-ray source emits X-ray free laser light and forms an X-ray free electron laser spot on the coupling medium. The imaging device records the position of the X-ray free electron laser spot on the coupling medium.

[0019] Step S3): Stop emitting X-ray free electron laser; the femtosecond laser source emits femtosecond laser and forms a femtosecond laser spot on the coupling medium, and the imaging device records the position of the femtosecond laser spot on the coupling medium;

[0020] Step S4): Adjust the position or angle of the coupling mirror so that the positions of the femtosecond laser spot and the X-ray free electron laser spot on the coupling medium coincide;

[0021] Step S5): Simultaneously emit X-ray free-electron laser and femtosecond laser, and acquire the pulse signals of X-ray free-electron laser and femtosecond laser respectively with an oscilloscope;

[0022] Step S6): Continuously adjust the optical path adjustment module until the pulse signals of the X-ray free electron laser and the femtosecond laser coincide on the oscilloscope, and record two sets of reflected light data after each adjustment of the optical path adjustment module; the first set of reflected light data is the intensity of the reflected light from the femtosecond laser irradiating the coupling medium excited by the X-ray free electron laser; the second set of reflected light data is the intensity of the reflected light from the femtosecond laser irradiating the coupling medium only after the X-ray free electron laser is turned off.

[0023] Step S7): Normalize the two sets of data from each adjustment of the optical path adjustment module in step S6) and calculate the rate of change of reflectivity;

[0024] Step S8): Plot the curve of reflectivity as a function of the position of the delay line, with the absolute position of the optical path adjustment module as the x-axis and the rate of change of reflectivity at the corresponding position as the y-axis.

[0025] The present invention provides a spatiotemporal coupling system for X-ray free-electron laser and femtosecond laser, which has the following beneficial effects:

[0026] 1) This invention enables the coupling of X-ray free-electron lasers and femtosecond lasers. In terms of spatial coupling, this invention employs multiple mirrors and lenses to achieve micrometer-level spatial coupling between the X-ray free-electron laser and the femtosecond laser on the coupling medium. In terms of temporal coupling, it utilizes the principle that the X-ray free-electron laser causes a sudden change in the refractive index of the fine coupling medium (the time scale of the change is femtosecond) to achieve femtosecond-level temporal coupling between the X-ray free-electron laser and the femtosecond laser.

[0027] 2) The spatial coupling of the present invention is divided into angular coupling and collinear coupling. The switching between angular coupling and collinear coupling can be achieved by simply replacing and adjusting the femtosecond laser coupler and the third femtosecond laser reflector. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of Embodiment 1 of the present invention.

[0029] Figure 2 This is a schematic diagram of the overall structure of Embodiment 2 of the present invention.

[0030] Figure Labels

[0031] Vacuum coaxial microscope 1

[0032] Objective lens 11

[0033] First reflecting mirror assembly 12

[0034] First reflector adjustment bracket 12.1

[0035] First reflecting mirror 12.2

[0036] Lens assembly 13

[0037] First sleeve 13.1

[0038] Lens 13.2

[0039] Second sleeve 13.3

[0040] Second reflector assembly 14

[0041] Second reflector adjustment bracket 14.1

[0042] Second reflecting mirror 14.2

[0043] Imaging equipment 15

[0044] Camera 15.1

[0045] Third sleeve 15.2

[0046] Media Platform 2

[0047] Sample stage 21

[0048] Z-axis adjustment mechanism 22

[0049] X-axis adjustment mechanism 23

[0050] Y-axis adjustment mechanism 24

[0051] X-ray source 3

[0052] X-ray shutter 31

[0053] Femtosecond laser source 4

[0054] Optical path adjustment module 41

[0055] First femtosecond laser reflector 42

[0056] Second femtosecond laser reflector 43

[0057] Third femtosecond laser reflector 44

[0058] Femtosecond laser shutter 45

[0059] Focusing lens 46

[0060] Coupled mirror 47

[0061] Data Acquisition System 5

[0062] Digital Signal Generator 51

[0063] Oscilloscope 52

[0064] Processor 53 Detailed Implementation

[0065] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In the description of the present invention, it should be noted that the terms "left side", "right side", "upper side", "lower side", "above", "below", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0066] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0067] Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0068] This invention provides a spatiotemporal coupling system for X-ray free-electron lasers and femtosecond lasers, see reference. Figure 1 and Figure 2 The system includes a dielectric platform 2, which is used to place the coupling medium and adjust the relative position of the coupling medium. The coupling medium is further divided into two types: the first type is a coarse coupling medium, such as a photodiode and an RF cable, preferably the bandwidth of the photodiode is ≥5GHz and the bandwidth of the RF cable is ≥5GHz; the second type is a fine coupling medium, such as silicon nitride, Ce:YAG crystal and gallium nitride single crystal, preferably the thickness of the silicon nitride is >2μm and the thickness of the Ce:YAG crystal is ≥10μm.

[0069] Continue reading Figure 1 and Figure 2 The system also includes a vacuum coaxial microscope 1 for observing and collecting reflected light on a coupling medium. The vacuum coaxial microscope 1 comprises an objective lens 11, a first reflecting mirror assembly 12, a lens assembly 13, a second reflecting mirror assembly 14, and an imaging device 15 connected in sequence. The objective lens 11, the first reflecting mirror assembly 12, and the lens assembly 13 form a first angle, preferably 90°. The lens assembly 13, the second reflecting mirror assembly 14, and the imaging device 15 form a second angle, preferably 90°. The first reflecting mirror assembly 12 has a first reflecting mirror assembly opening.

[0070] Continue reading Figure 1 and Figure 2 It also includes an X-ray source 3 that emits X-ray free electron lasers, the X-ray free electron lasers passing through the opening of the first reflector assembly and the objective lens 11 and forming an X-ray free electron laser spot on the coupling medium.

[0071] Continue reading Figure 1 and Figure 2It also includes a femtosecond laser system, which includes a femtosecond laser source 4, an optical path adjustment module 41, a focusing lens 46, and a coupling mirror 47 arranged sequentially along the femtosecond laser optical path. The femtosecond laser source 4 is used to emit femtosecond laser, the optical path adjustment module 41 is used to adjust the optical path of the femtosecond laser, the focusing lens 46 is used to focus the femtosecond laser, and the coupling mirror 47 is used to reflect the femtosecond laser and form a femtosecond laser spot on the coupling medium that overlaps with the X-ray free electron laser spot.

[0072] Continue reading Figure 1 and Figure 2 It also includes a data acquisition system 5, which includes a digital signal generator 51, an oscilloscope 52 and a processor 53. The digital signal generator 51 and the processor 53 are electrically connected to the imaging device 15, and the oscilloscope 52 is electrically connected to the coupling medium.

[0073] Further, see Figure 1 and Figure 2 The first reflector assembly 12 includes a first reflector adjustment frame 12.1 and a first reflector 12.2 disposed within the first reflector adjustment frame 12.1. The lens assembly 13 includes a first sleeve 13.1, a lens 13.2, and a second sleeve 13.3 connected in sequence. The second reflector assembly 14 includes a second reflector adjustment frame 14.1 and a second reflector 14.2 disposed within the second reflector adjustment frame 14.1. The imaging device 15 includes a camera 15.1 and a third sleeve 15.2, one end of which is connected to the working end of the camera 15.1, and the other end of which is connected to the second reflector adjustment frame 14.1. As a supplement, the overall shape of the vacuum coaxial microscope 1 is Z-shaped, and the connection relationship from bottom to top is as follows: objective lens 11 → first reflecting mirror adjustment frame 12.1 → first sleeve 13.1 → lens 13.2 → second sleeve 13.3 → second reflecting mirror adjustment frame 14.1 → third sleeve 15.2 → camera 15.1. See also... Figure 1 and Figure 2 The first reflector assembly opening includes a first reflector adjustment bracket opening in the first reflector adjustment bracket 12.1 and a first reflector opening in the first reflector 12.2.

[0074] There are two ways to achieve spatial coupling between X-ray free-electron lasers and femtosecond lasers: collinear coupling and angular coupling. Both of these coupling methods can achieve spatial coupling, so the desired coupling mode can be selected according to the actual situation. Implementation 1 is angular coupling, and implementation 2 is collinear coupling.

[0075] Example 1

[0076] This embodiment provides a spatiotemporal coupling system for an X-ray free-electron laser and a femtosecond laser. The spatial coupling method adopts angular coupling. Angular coupling means that a certain angle is formed between the optical axis of the X-ray free-electron laser irradiating the coupling medium and the optical axis of the femtosecond laser reflected onto the coupling medium.

[0077] See Figure 1 The optical path adjustment module 41 includes a delay line and a moving module. The moving module is slidably mounted on the delay line. A first femtosecond laser reflector 42 and a second femtosecond laser reflector 43 are sequentially arranged along the femtosecond laser optical path on the moving module. The femtosecond laser, after being reflected by the coupling mirror 47, forms an angle with the coupling medium. A femtosecond laser shutter 45 is also provided in the femtosecond laser optical path between the second femtosecond laser reflector 43 and the coupling mirror 47. An X-ray shutter 31 is also provided in the X-ray free electron laser optical path between the X-ray free electron laser and the first reflector assembly 12. In this embodiment, the optical paths of the X-ray free electron laser and the femtosecond laser are as follows:

[0078] X-ray free electron laser optical path: X-ray source 3 → X-ray shutter 31 → First reflector assembly 12 (first reflector assembly opening) → Objective lens 11 → Coupling medium.

[0079] Femtosecond laser optical path: Femtosecond laser source 4 → First femtosecond laser reflector 42 → Second femtosecond laser reflector 43 → Focusing lens 46 → Femtosecond laser shutter 45 → Coupler reflector 47 → Coupler medium.

[0080] It is worth noting that this embodiment uses angular coupling to achieve spatial coupling. Therefore, there is no overlap between the femtosecond laser optical path and the X-ray free electron laser optical path. After being reflected by the coupling mirror 47, the femtosecond laser hits the coupling medium at an angle. This angle can be controlled by controlling the angle of the coupling mirror 47, and is generally maintained between 90° and 120°.

[0081] See Figure 1 and Figure 2 The digital signal generator 51 is electrically connected to the X-ray shutter 31, the femtosecond laser shutter 45, and the imaging device 15, respectively. The oscilloscope 52 is electrically connected to the coupling medium, and the data acquisition unit is electrically connected to the imaging device 15. Additionally, the digital signal generator 51 acts as a trigger, providing trigger signals to the X-ray shutter 31, the femtosecond laser shutter 45, and the imaging device 15 to trigger the opening and closing of the X-ray shutter 31 and the femtosecond laser shutter 45, as well as the exposure of the imaging device 15.

[0082] This embodiment also provides a method of use, as described below:

[0083] Step S1): Install the coupling medium on the media platform 2. Further, install the coarse coupling medium and the fine coupling medium on the media platform 2 respectively, and place them in relatively suitable positions.

[0084] Step S2): The X-ray source 3 emits an X-ray free electron laser and forms an X-ray free electron laser spot on the coupling medium. The imaging device 15 records the position of the X-ray free electron laser spot on the coupling medium.

[0085] Furthermore, the X-ray shutter 31 is triggered by the digital signal generator 51, opening the X-ray shutter 31 so that the X-ray free electron laser emitted by the X-ray source 3 can form an X-ray free electron laser light path along the path X-ray shutter 31 → first reflector assembly 12 (first reflector assembly opening) → objective lens 11, thereby irradiating the coarse coupling medium.

[0086] Furthermore, a trigger signal is provided to the imaging device 15 via the digital signal generator 51, causing the imaging device 15 to be exposed to image the fluorescence irradiated by the X-ray free electron laser on the coarse coupling medium, and the position of the X-ray spot is recorded. Specifically, the fluorescence forms a fluorescence light path along the path of objective lens 11 → first reflecting mirror assembly 12 → lens assembly 13 → second reflecting mirror assembly 14 → imaging device 15, and is thus captured by the imaging device 15.

[0087] Step S3): Stop emitting X-ray free electron laser; femtosecond laser source 4 emits femtosecond laser and forms a femtosecond laser spot on the coupling medium, and imaging device 15 records the position of the femtosecond laser spot on the coupling medium.

[0088] Furthermore, the digital signal generator 51 provides a trigger signal for the femtosecond laser shutter 45, opening the femtosecond laser shutter 45 so that the femtosecond laser emitted by the femtosecond laser source 4 can form a femtosecond laser optical path along the path of the first femtosecond laser reflector 42 → the second femtosecond laser reflector 43 → the femtosecond laser shutter 45 → the focusing lens 46 → the coupling reflector 47, thereby irradiating the coarse coupling medium.

[0089] Step S4): Adjust the position or angle of the coupling mirror 47 so that the positions of the femtosecond laser spot and the X-ray free electron laser spot on the coupling medium coincide.

[0090] Furthermore, by adjusting the angle of the coupling mirror 47, the position of the femtosecond laser spot coincides with the position of the X-ray free electron laser spot, thereby achieving spatial coupling between the X-ray free electron laser and the femtosecond laser.

[0091] Step S5): Simultaneously emit X-ray free electron laser and femtosecond laser, and oscilloscope 52 acquires the pulse signals of X-ray free electron laser and femtosecond laser respectively.

[0092] Furthermore, the fine coupling medium is switched to a coarse coupling medium, and the photosensitive area on the coarse coupling medium is moved to the point where the X-ray free electron laser spot and the femtosecond laser spot overlap. Subsequently, the trigger signals for the X-ray shutter 31 and the femtosecond laser shutter are provided by the digital signal generator 51, and the X-ray shutter 31 and the femtosecond laser shutter are opened simultaneously. The pulse signals of the two beams are then acquired by the oscilloscope 52.

[0093] Step S6): Continuously adjust the optical path adjustment module 41 until the pulse signals of the X-ray free electron laser and the femtosecond laser coincide on the oscilloscope 52, and record two sets of reflected light data after each adjustment of the optical path adjustment module 41; the first set of reflected light data is the intensity of reflected light from the femtosecond laser irradiating the coupling medium excited by the X-ray free electron laser; the second set of reflected light data is the intensity of reflected light from the femtosecond laser irradiating the coupling medium after the X-ray free electron laser is turned off.

[0094] Furthermore, the femtosecond laser moving module is adjusted so that the first femtosecond laser reflector 42 and the second femtosecond laser reflector 43 can move along the direction of the femtosecond laser delay line, thereby increasing or decreasing the optical path of the femtosecond laser until the pulse signals of the X-ray free electron laser and the femtosecond laser coincide on the oscilloscope 52, achieving picosecond precision time coupling.

[0095] Furthermore, the coarse coupling medium is switched to a fine coupling medium. The principle is that X-ray free-electron laser irradiation on the coarse coupling medium generates photocarriers, causing a change in the refractive index of the coarse coupling medium, which in turn changes the intensity of the femtosecond laser reflection. The femtosecond laser moving module is moved within a range of ±5mm, with a step size of no more than 10μm.

[0096] Furthermore, with each step of movement, the X-ray shutter 31 and the femtosecond laser shutter 45 are simultaneously opened, and the coarse coupling medium is imaged and acquired through the imaging device 15. Simultaneously, the reflection intensity of the femtosecond laser is measured using the processor 53, with at least 100 pulses acquired. Subsequently, the X-ray shutter 31 is closed, and the same number of images are acquired at the same location, again with at least 100 pulses acquired using the processor 53. This process is repeated until all data within a ±5mm range has been acquired.

[0097] Step S7): Normalize the two sets of data from each adjustment of the optical path adjustment module 41 in step S6) and calculate the rate of change of reflectivity;

[0098] Step S8): Plot the reflectivity variation curve as a function of the delay line position, using the absolute position of the optical path adjustment module 41 as the x-axis and the rate of change of reflectivity at the corresponding position as the y-axis. Further, plot the reflectivity variation curve as a function of the delay line position, using the absolute position of the femtosecond laser movement module on the femtosecond laser delay line as the x-axis and the rate of change of reflectivity at the corresponding position as the y-axis. Find the position where the reflectivity first changes, thus achieving time zero-point coincidence between the femtosecond laser and the X-ray free electron laser at the femtosecond level. It is worth noting that when the X-ray free electron laser irradiates the fine coupling medium, it causes a sudden change in the refractive index of the fine coupling medium (the time scale of the change is femtosecond). If, at the same time, the femtosecond laser also irradiates the fine coupling medium, the intensity of the reflected or transmitted light from the femtosecond laser in that region will change abruptly due to the refractive index change caused by the X-ray free electron laser. Therefore, by measuring the abrupt change point of the reflected laser, it is possible to determine whether the X-ray free electron laser and the femtosecond laser have achieved time coincidence.

[0099] Example 2

[0100] This embodiment provides a spatiotemporal coupling system for an X-ray free-electron laser and a femtosecond laser. The spatial coupling method employs collinear coupling, meaning that the X-ray free-electron laser path and the femtosecond laser path partially overlap and become collinear. The main difference between this embodiment and Embodiment 1 lies in the configuration of the femtosecond laser system.

[0101] See Figure 2 The moving module is equipped with a first femtosecond laser reflector 42, a second femtosecond laser reflector 43, and a third femtosecond laser reflector 44 arranged sequentially along the femtosecond laser optical path. An X-ray shutter 31 and a coupling mirror 47 are sequentially disposed in the optical path between the X-ray source 3 and the first reflector assembly 12. The coupling mirror 47 has a coupling mirror opening. The femtosecond laser reflected by the coupling mirror 47 and the X-ray free-electron laser passing through the coupling mirror 47 are collinear. In this embodiment, the optical paths of the X-ray free-electron laser and the femtosecond laser are as follows:

[0102] X-ray free electron laser optical path: X-ray source 3 → X-ray shutter 31 → coupling mirror 47 (coupler mirror opening) → first mirror assembly 12 (first mirror assembly opening) → objective lens 11 → coupling medium.

[0103] Femtosecond laser optical path: Femtosecond laser source 4 → First femtosecond laser mirror 42 → Second femtosecond laser mirror 43 → Third femtosecond laser mirror 44 → Focusing lens 46 → Femtosecond laser shutter 45 → Coupler mirror 47 → First mirror assembly 12 (first mirror assembly opening) → Objective lens 11 → Coupler medium

[0104] It is worth noting that this embodiment uses collinear coupling to achieve spatial coupling. Therefore, there is an overlapping part between the femtosecond laser optical path and the X-ray free electron laser optical path. The overlapping part is "first reflector assembly 12 (first reflector assembly opening) → objective lens 11 → coupling medium".

[0105] This embodiment also provides a method of use, as described below:

[0106] Step S1): Install the coupling medium on the media platform 2. Further, install the coarse coupling medium and the fine coupling medium on the media platform 2 respectively, and place them in relatively suitable positions.

[0107] Step S2): The X-ray source 3 emits an X-ray free electron laser and forms an X-ray free electron laser spot on the coupling medium. The imaging device 15 records the position of the X-ray free electron laser spot on the coupling medium.

[0108] Furthermore, the X-ray shutter 31 is triggered by the digital signal generator 51, opening the X-ray shutter 31 so that the X-ray free electron laser emitted by the X-ray source 3 can form an X-ray free electron laser light path along the path X-ray shutter 31 → first reflector assembly 12 (first reflector assembly opening) → objective lens 11, thereby irradiating the coarse coupling medium.

[0109] Furthermore, a trigger signal is provided to the imaging device 15 via the digital signal generator 51, causing the imaging device 15 to be exposed to image the fluorescence irradiated by the X-ray free electron laser on the coarse coupling medium, and the position of the X-ray spot is recorded. Specifically, the fluorescence forms a fluorescence light path along the path of objective lens 11 → first reflecting mirror assembly 12 → lens assembly 13 → second reflecting mirror assembly 14 → imaging device 15, and is thus captured by the imaging device 15.

[0110] Step S3): Stop emitting X-ray free electron laser; femtosecond laser source 4 emits femtosecond laser and forms a femtosecond laser spot on the coupling medium, and imaging device 15 records the position of the femtosecond laser spot on the coupling medium.

[0111] Furthermore, the digital signal generator 51 provides a trigger signal for the femtosecond laser shutter 45, opening the femtosecond laser shutter 45 so that the femtosecond laser emitted by the femtosecond laser source 4 can form a femtosecond laser optical path along the path of the first femtosecond laser reflector 42 → the second femtosecond laser reflector 43 → the femtosecond laser shutter 45 → the focusing lens 46 → the coupling reflector 47, thereby irradiating the coarse coupling medium.

[0112] Step S4): Adjust the position or angle of the coupling mirror 47 so that the positions of the femtosecond laser spot and the X-ray free electron laser spot on the coupling medium coincide.

[0113] Furthermore, the position of the coupling mirror 47 is adjusted so that the position of the femtosecond laser spot coincides with the position of the X-ray free electron laser spot, thereby achieving spatial coupling between the X-ray free electron laser and the femtosecond laser.

[0114] Step S5): Simultaneously emit X-ray free electron laser and femtosecond laser, and oscilloscope 52 acquires the pulse signals of X-ray free electron laser and femtosecond laser respectively.

[0115] Furthermore, the fine coupling medium is switched to a coarse coupling medium, and the photosensitive area on the coarse coupling medium is moved to the point where the X-ray free electron laser spot and the femtosecond laser spot overlap. Subsequently, the trigger signals for the X-ray shutter 31 and the femtosecond laser shutter are provided by the digital signal generator 51, and the X-ray shutter 31 and the femtosecond laser shutter are opened simultaneously. The pulse signals of the two beams are then acquired by the oscilloscope 52.

[0116] Step S6): Continuously adjust the optical path adjustment module 41 until the pulse signals of the X-ray free electron laser and the femtosecond laser coincide on the oscilloscope 52, and record two sets of reflected light data after each adjustment of the optical path adjustment module 41; the first set of reflected light data is the intensity of reflected light from the femtosecond laser irradiating the coupling medium excited by the X-ray free electron laser; the second set of reflected light data is the intensity of reflected light from the femtosecond laser irradiating the coupling medium after the X-ray free electron laser is turned off.

[0117] Furthermore, the femtosecond laser moving module is adjusted so that the first femtosecond laser reflector 42 and the second femtosecond laser reflector 43 can move along the direction of the femtosecond laser delay line, thereby increasing or decreasing the optical path of the femtosecond laser until the pulse signals of the X-ray free electron laser and the femtosecond laser coincide on the oscilloscope 52, achieving picosecond precision time coupling.

[0118] Furthermore, the coarse coupling medium is switched to a fine coupling medium. The principle is that X-ray free-electron laser irradiation on the coarse coupling medium generates photocarriers, causing a change in the refractive index of the coarse coupling medium, which in turn changes the intensity of the femtosecond laser reflection. The femtosecond laser moving module is moved within a range of ±5mm, with a step size of no more than 10μm.

[0119] Furthermore, with each step of movement, the X-ray shutter 31 and the femtosecond laser shutter 45 are simultaneously opened, and the coarse coupling medium is imaged and acquired through the imaging device 15. At the same time, the reflection intensity of the femtosecond laser is measured using the processor 53, with at least 100 pulses acquired. Subsequently, the X-ray shutter 31 is closed, and the same number of images are acquired at the same location, again with the processor 53 measuring the reflection intensity of the femtosecond laser, acquiring at least 100 pulses. This process is repeated until all data within a ±5mm range has been acquired.

[0120] Step S7): Normalize the two sets of data from each adjustment of the optical path adjustment module 41 in step S6) and calculate the rate of change of reflectivity;

[0121] Step S8): Plot the reflectivity variation curve as a function of the delay line position, using the absolute position of the optical path adjustment module 41 as the x-axis and the rate of change of reflectivity at the corresponding position as the y-axis. Further, plot the reflectivity variation curve as a function of the delay line position, using the absolute position of the femtosecond laser movement module on the femtosecond laser delay line as the x-axis and the rate of change of reflectivity at the corresponding position as the y-axis. Find the position where the reflectivity first changes, thus achieving time zero-point coincidence between the femtosecond laser and the X-ray free electron laser at the femtosecond level. It is worth noting that when the X-ray free electron laser irradiates the fine coupling medium, it causes a sudden change in the refractive index of the fine coupling medium (the time scale of the change is femtosecond). If, at the same time, the femtosecond laser also irradiates the fine coupling medium, the intensity of the reflected or transmitted light from the femtosecond laser in that region will change abruptly due to the refractive index change caused by the X-ray free electron laser. Therefore, by measuring the abrupt change point of the reflected laser, it is possible to determine whether the X-ray free electron laser and the femtosecond laser have achieved time coincidence.

[0122] The following are supplementary explanations for the two embodiments described above:

[0123] Additionally, the X-ray shutter 31 has an aperture > 5 mm and an operating frequency ≥ 10 Hz; preferably, the aperture is 6 mm and the operating frequency is 10 Hz. The femtosecond laser shutter 45 has an aperture > 10 mm and an operating frequency ≥ 10 Hz; preferably, the aperture is 10 mm and the operating frequency is 10 Hz. The focusing lens 46 has a diameter ≥ 25.4 mm and a focal length ≥ 200–1500 mm; preferably, the diameter is 25.4 mm and the focal length is 1000 mm. The delay line has a travel ≥ 125 mm; preferably, the travel is 325 mm. The moving module has a moving accuracy ≤ 3 μm; preferably, the moving accuracy is 1 μm.

[0124] Further, see Figure 1 and Figure 2The medium platform 2 includes a sample stage 21 and a three-dimensional adjustment mechanism. The three-dimensional adjustment mechanism includes a Z-axis adjustment mechanism, an X-axis adjustment mechanism, and a Y-axis adjustment mechanism arranged sequentially from top to bottom. The sample stage 21 is mounted on the Z-axis adjustment mechanism. In a specific embodiment, the Z-axis adjustment mechanism, X-axis adjustment mechanism, and Y-axis adjustment mechanism all use related products developed by SmarAct, wherein the Z-axis adjustment mechanism uses model SLC-24105, the X-axis adjustment mechanism uses model SLC-24105, and the Y-axis adjustment mechanism uses model SLC-2445. Preferably, the overall load of the Z-axis adjustment mechanism, X-axis adjustment mechanism, and Y-axis adjustment mechanism is >0.2kg; the stroke of the Z-axis adjustment mechanism is >±30mm, and the resolution of the Z-axis adjustment mechanism is <1μm; the stroke of the Y-axis adjustment mechanism is >±15mm, and the resolution of the Y-axis adjustment mechanism is <1μm; the stroke of the Z-axis adjustment mechanism is >±30mm, and the resolution of the Z-axis adjustment mechanism is <1μm.

[0125] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A spatiotemporal coupling system for X-ray free-electron laser and femtosecond laser, characterized in that, include: A media platform for placing the coupling medium and adjusting the relative position of the coupling medium; A vacuum coaxial microscope is used to observe and collect reflected light on the coupling medium; the vacuum coaxial microscope includes an objective lens, a first reflecting mirror assembly, a lens assembly, a second reflecting mirror assembly, and an imaging device connected in sequence; the objective lens, the first reflecting mirror assembly, and the lens assembly form a first angle, and the lens assembly, the second reflecting mirror assembly, and the imaging device form a second angle; the first reflecting mirror assembly has an opening; An X-ray source is used to emit X-ray free-electron laser; the X-ray free-electron laser passes through the opening of the first reflector assembly and the objective lens and forms an X-ray free-electron laser spot on the coupling medium; A femtosecond laser system includes a femtosecond laser source, an optical path adjustment module, a focusing lens, and a coupling mirror arranged sequentially along the femtosecond laser optical path; the femtosecond laser source is used to emit femtosecond laser light, the optical path adjustment module is used to adjust the optical path of the femtosecond laser light, the focusing lens is used to focus the femtosecond laser light, and the coupling mirror is used to reflect the femtosecond laser light and form a femtosecond laser spot on the coupling medium that overlaps with the X-ray free electron laser spot; A data acquisition system, comprising a digital signal generator, an oscilloscope, and a processor; the digital signal generator and the processor are electrically connected to the imaging device, and the oscilloscope is electrically connected to the coupling medium.

2. The spatiotemporal coupling system according to claim 1, characterized in that: The optical path adjustment module includes a delay line and a moving module, the moving module being slidably disposed on the delay line; the moving module is provided with a first femtosecond laser reflector and a second femtosecond laser reflector arranged sequentially along the femtosecond laser optical path; the femtosecond laser, after being reflected by the coupling reflector, forms an angle with the coupling medium; The femtosecond laser reflector and the coupling reflector are further provided with a femtosecond laser shutter in the femtosecond optical path, and the X-ray free electron laser and the first reflector assembly are further provided with an X-ray shutter in the X-ray free electron optical path.

3. The spatiotemporal coupling system according to claim 2, characterized in that: The moving module is provided with a first femtosecond laser reflector, a second femtosecond laser reflector, and a third femtosecond laser reflector arranged sequentially along the femtosecond laser optical path; the X-ray shutter and the coupling mirror are sequentially arranged in the optical path between the X-ray source and the first reflector assembly, and the coupling mirror is provided with a coupling mirror opening; The femtosecond laser reflected by the coupling mirror and the X-ray free electron laser passing through the coupling mirror are collinear.

4. The spatiotemporal coupling system according to claim 2 or 3, characterized in that: The first reflector assembly includes a first reflector adjustment frame and a first reflector disposed in the first reflector adjustment frame; the second reflector assembly includes a second reflector adjustment frame and a second reflector disposed in the second reflector adjustment frame; the lens assembly includes a first sleeve, a lens, and a second sleeve connected in sequence; the imaging device includes a camera and a third sleeve; The objective lens, the first mirror adjustment frame, the first sleeve, the lens, the second sleeve, the second mirror adjustment frame, the third sleeve, and the camera are connected in sequence; the objective lens, the first mirror adjustment frame, and the first sleeve form the first angle, and the second sleeve, the second mirror adjustment frame, and the third sleeve form the second angle; the angles of the first angle and the second angle are both 90°.

5. The spatiotemporal coupling system according to claim 3, characterized in that: The aperture of the X-ray shutter is >5mm, and the operating frequency is ≥10 Hz; And / or, the aperture of the femtosecond laser shutter is >10 mm and the operating frequency is ≥10 Hz; And / or, the objective lens has a magnification of 2 to 50 times and a resolution of 0.

5. m~5 m; And / or, the diameter of the focusing lens is ≥25.4 mm and the focal length is ≥200~1500 mm; And / or, the travel of the delay line is ≥ 125 mm; And / or, the movement accuracy of the moving module is ≤3 m.

6. The spatiotemporal coupling system according to claim 4, characterized in that: The oscilloscope has a bandwidth ≥ 1 GHz; and / or the digital signal generator has ≥ 4 channels and a time accuracy ≤ 1 GHz. s; And / or, the digital signal generator is electrically connected to the X-ray shutter, the femtosecond laser shutter, and the camera respectively via trigger cables; the oscilloscope is electrically connected to the coupling medium via a data acquisition cable; the connector of the trigger cable is BNC or Lemo, and the connector of the data acquisition cable is BNC or SMA.

7. The spatiotemporal coupling system according to any one of claims 1 to 3, characterized in that: The coupling medium is either a fine coupling medium or a coarse coupling medium; the coarse coupling medium is a photodiode or an RF cable, and the fine coupling medium is selected from any one of silicon nitride, Ce:YAG crystal, or gallium nitride single crystal.

8. The spatiotemporal coupling system according to claim 7, characterized in that: The bandwidth of the photodiode is ≥5 GHz, and the bandwidth of the radio frequency cable is ≥5 GHz; the thickness of the silicon nitride is >2. m, the thickness of the Ce:YAG crystal is ≥10 m. m.

9. The spatiotemporal coupling system according to any one of claims 1 to 3, characterized in that: The medium platform includes a sample stage, a Z-axis adjustment mechanism, an X-axis adjustment structure, and a Y-axis adjustment mechanism arranged sequentially from top to bottom, and the coupling medium is disposed on the sample stage; The overall load of the Z-axis adjustment mechanism, the X-axis adjustment structure, and the Y-axis adjustment mechanism is >0.2 kg; the stroke of the Z-axis adjustment mechanism is >±30 mm; and the resolution of the Z-axis adjustment mechanism is <1. m; the stroke of the Y-axis adjustment mechanism is > ±15 mm, and the resolution of the Y-axis adjustment mechanism is <1. m; the stroke of the Z-axis adjustment mechanism is > ±30 mm, and the resolution of the Z-axis adjustment mechanism is <1. m.

10. A method of using the X-ray free-electron laser and femtosecond laser spatiotemporal coupling system as described in claim 1, characterized in that, At least the following steps are included: Step S1): Mount the coupling medium on the media platform; Step S2): The X-ray source emits an X-ray free electron laser and forms an X-ray free electron laser spot on the coupling medium. The imaging device records the position of the X-ray free electron laser spot on the coupling medium. Step S3): Stop emitting X-ray free electron laser; the femtosecond laser source emits femtosecond laser and forms a femtosecond laser spot on the coupling medium, and the imaging device records the position of the femtosecond laser spot on the coupling medium; Step S4): Adjust the position or angle of the coupling mirror so that the positions of the femtosecond laser spot and the X-ray free electron laser spot on the coupling medium coincide; Step S5): Simultaneously emit X-ray free-electron laser and femtosecond laser, and acquire the pulse signals of X-ray free-electron laser and femtosecond laser respectively with an oscilloscope; Step S6): Continuously adjust the optical path adjustment module until the pulse signals of the X-ray free electron laser and the femtosecond laser coincide on the oscilloscope, and record two sets of reflected light data after each adjustment of the optical path adjustment module; the first set of reflected light data is the intensity of the reflected light from the femtosecond laser irradiating the coupling medium excited by the X-ray free electron laser; the second set of reflected light data is the intensity of the reflected light from the femtosecond laser irradiating the coupling medium only after the X-ray free electron laser is turned off. Step S7): Normalize the two sets of data from each adjustment of the optical path adjustment module in step S6) and calculate the rate of change of reflectivity; Step S8): Plot the curve of reflectivity as a function of the position of the delay line, with the absolute position of the optical path adjustment module as the abscissa and the rate of change of reflectivity at the corresponding position as the ordinate.

Images