CN113237905A - Device and method for stabilizing pumping light beam of electron microscope system and electron microscope system - Google Patents
Device and method for stabilizing pumping light beam of electron microscope system and electron microscope system Download PDFInfo
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Abstract
本申请涉及电子显微镜技术领域，公开一种电镜系统泵浦光束的稳定装置及方法、电镜系统，目的是提供一种对入射至电镜内部的激光泵浦脉冲进行稳定的有效手段。电镜系统泵浦光束的稳定装置，包括：光斑探测组件，包括多通道光束探测器；光束稳定控制器，与光斑探测组件连接，用于每隔设定时间间隔，执行以下操作直至光斑位置漂移量小于或等于第一设定值：驱动光斑探测组件移动，使得多通道光束探测器到达电镜中物镜后焦面的电子束路径上；控制多通道光束探测器采集泵浦脉冲光斑信号，并根据当前采集的信号与初次采集的泵浦脉冲光斑信号计算得到光斑位置漂移量；当漂移量大于第一设定值时，根据漂移量对泵浦脉冲光束传播方向进行校正调节。
The present application relates to the technical field of electron microscopes, and discloses a device and method for stabilizing a pump beam of an electron microscope system, and an electron microscope system, with the purpose of providing an effective means for stabilizing laser pump pulses incident on the inside of the electron microscope. A device for stabilizing pump beams of an electron microscope system, including: a spot detection component, including a multi-channel beam detector; a beam stabilization controller, connected to the spot detection component, for performing the following operations every set time interval until the spot position drifts Less than or equal to the first set value: drive the spot detection component to move, so that the multi-channel beam detector reaches the electron beam path of the rear focal plane of the objective lens in the electron microscope; control the multi-channel beam detector to collect the pump pulse spot signal, and according to the current The collected signal and the pump pulse spot signal collected for the first time are calculated to obtain the spot position drift amount; when the drift amount is greater than the first set value, the propagation direction of the pump pulse beam is corrected and adjusted according to the drift amount.
Description
Technical Field
The application relates to the technical field of electron microscopes, in particular to a device and a method for stabilizing a pumping beam of an electron microscope system and the electron microscope system.
Background
The four-dimensional ultrafast transmission electron microscope developed by combining the ultrashort pulse laser and the conventional transmission electron microscope is an important characterization tool with high spatial and time resolution capability. The ultrafast transmission electron microscope mainly works in a pumping-detection mode, namely two paths of laser pulses are introduced into the transmission electron microscope, one path of laser pulses is pumping pulses and is used for exciting sample dynamics, the other path of laser pulses is detection pulses and is used for exciting a filament of an electron gun, and the generated electron pulses are imaged through a sample at a preset pumping/probe delay time point. To reduce the effect of the coulomb charge effect on temporal and spatial resolution, each probe pulse typically excites only a small number of electrons, and the increase in signal intensity is achieved by repeated accumulation of a pump/probe pulse sequence.
Different from the data recording mode of a conventional transmission electron microscope, the representation of the ultrafast transmission electron microscope needs to carry out continuous data acquisition under a series of different pumping/detection delay conditions, so that the evolution process information of electrons, crystal lattices and the like after the sample is excited on a time scale is extracted. For ultrafast bright field and dark field imaging, a single pumping/detection experiment usually requires several hours of acquisition time to obtain more comprehensive relaxation kinetic information of the sample. External electric fields, magnetic field changes, environmental vibrations and the like which are difficult to avoid in the process all affect the stability of laser pulses, and further the measurement precision of the transient process information of the sample is reduced. The instability of the detection pulse mainly affects the radiation dose of the electronic pulse, and the problem can be effectively solved by synchronously recording a time zero reference image (introducing a mechanical shutter in a pumping light path or controlling a delay line to return to a time zero point at fixed time intervals) during the collection of relaxation dynamics data to carry out intensity calibration. For the drift problem of the pump pulse, the current processing method is generally to stabilize the laser device or the external transmission optical path. However, the stabilization of the external optical path is not equivalent to the fixation of the region of action of the pump pulse incident on the electron microscope sample. The vibration of the ultrafast tem (with the inherent vibration frequency, amplitude, etc. different from the laser and the external light path) and the thermal drift caused by the mirror inside the lens barrel after the laser is continuously irradiated will cause the position of the pump light incident on the sample to change. Keeping the pumping light pulse and the sample action region constant in the ultrafast data acquisition process is very critical to the accurate extraction of the structure relaxation dynamics process information, but an effective means for stabilizing the laser pumping pulse incident into the transmission electron microscope is not available at present.
Disclosure of Invention
The application discloses a stabilizing device and a stabilizing method for a pumping beam of an electron microscope system and the electron microscope system, and aims to provide an effective means for stabilizing a laser pumping pulse incident into the electron microscope so as to improve the accuracy of data acquisition of the electron microscope system.
In order to achieve the purpose, the application provides the following technical scheme:
a stabilizing device for a pump beam of an electron microscope system comprises:
the light spot detection assembly comprises a multi-channel light beam detector;
and the beam stabilization controller is connected with the light spot detection assembly and is used for executing the following pump beam correction operation at set time intervals until the light spot position drift amount is less than or equal to a first set value:
driving the light spot detection assembly to move, so that the multi-channel light beam detector reaches an electron beam path of a rear focal plane of an objective lens in an electron microscope;
controlling the multi-channel light beam detector to collect pumping pulse light spot signals, and calculating to obtain light spot position drift amount according to the currently collected pumping pulse light spot signals and the primarily collected pumping pulse light spot signals; and when the light spot position drift amount is larger than the first set value, correcting and adjusting the propagation direction of the pump pulse light beam according to the light spot position drift amount.
The utility model provides a stabilising arrangement of electron microscope system pump light beam utilizes multichannel beam detector to locate periodically at the objective back focal plane next-door neighbour with the sample and surveys pump laser pulse light spot position to calculate the drift volume through the comparison, later accurately rectifies the beam drift through feedback control, can satisfy the data acquisition required precision of electron microscope system up to light spot position drift volume. The device not only can effectively eliminate the beam instability generated when the laser and the coupling light path are influenced by the change of the external environment, but also can simultaneously correct the facula drift caused by the mechanical vibration of the electron microscope and the thermal drift of the reflecting mirror inside the lens cone, thereby fundamentally realizing the invariance of the action area of the pumping beam and the observed sample. Taking the time delay data acquisition work of an ultrafast transmission electron microscope as an example, the problem of instability of the pumping pulse is solved, which means that all the ultrafast data in the whole acquired time delay range accurately reflect the real structural relaxation dynamics behavior of the excited sample, and the intensive sampling (namely, the selection of a smaller time delay step length) can be carried out while a longer pumping/detection time delay range is adopted, so that more comprehensive and detailed relaxation process information of the sample can be obtained.
Optionally, the beam stabilization controller is further configured to: and when the light spot position drift amount is smaller than or equal to the first set value, driving the light spot detection assembly to move, so that the multi-channel light beam detector withdraws from the electron beam path.
Optionally, the light spot detection assembly further includes an objective diaphragm plate, the objective diaphragm plate includes a diaphragm hole, and the multi-channel beam detector is disposed on the objective diaphragm plate at a position avoiding the diaphragm hole;
the beam stabilization controller is further configured to: and after the multi-channel light beam detector is driven to leave the electron beam path, the diaphragm hole of the objective diaphragm plate is driven to reach the electron beam path of the rear focal plane of the objective in the electron microscope.
Optionally, the objective diaphragm plate is provided with a mounting through hole; the multi-channel beam detector is embedded in the mounting through hole of the objective lens diaphragm plate; and a positioning through hole is formed in the multi-channel beam detector.
Optionally, the electron microscope system comprises an electron image detector;
the light beam stabilization controller is electrically connected with the electronic image detector and is further used for: and after the multi-channel beam detector reaches an electron beam path of a back focal plane of an objective lens in an electron microscope, carrying out alignment operation of the positioning through hole and the electron beam, wherein the alignment operation comprises controlling the electron image detector to collect the intensity of the electron beam and driving the light spot detection assembly to move according to the intensity of the electron beam until the maximum value of the intensity of the electron beam is obtained.
Optionally, the light spot detection assembly comprises two multi-channel beam detectors;
the diameter of the first multi-channel beam detector is larger than the diameter of the pumping pulse light spot;
the diameter of the second multi-channel beam detector is smaller than the diameter of the pumping pulse light spot.
Optionally, the multi-channel beam detector is a CMOS.
Optionally, the beam stabilization controller includes a correction control module, a driving assembly, and a beam adjustment assembly;
the driving assembly is in transmission connection with the light spot detection assembly and is used for driving the light spot detection assembly to move;
the correction control module is electrically connected with the multi-channel beam detector and the driving assembly respectively and is used for: controlling a driving action of the driving assembly; controlling the multi-channel light beam detector to collect pumping pulse light spot signals, and calculating to obtain light spot position drift amount according to the currently collected pumping pulse light spot signals and the primarily collected pumping pulse light spot signals; when the light spot position drift amount is larger than a first set value, generating a light beam correction instruction according to the light spot position drift amount;
and the beam adjusting component is electrically connected with the correction control module and is used for correcting and adjusting the propagation direction of the pump pulse beam according to the beam correction instruction of the correction control module.
Optionally, the beam adjustment assembly includes two electric mirrors, and the electric mirrors are disposed on a path of the pumping pulse beam of the electron microscope.
Optionally, the light beam stabilization controller further includes a time delay data acquisition control module;
the time delay data acquisition control module is electrically connected with the correction control module and is further used for: interrupting the data acquisition work of the electron microscope at set time intervals, and sending a light beam correction operation instruction to the correction control module; after a successful correction instruction of the correction control module is received, controlling the electron microscope to continue data acquisition;
the correction control module is configured to: after receiving the correction operation instruction, controlling to execute the pump beam correction operation; and when the light spot position drift amount is smaller than or equal to the first set value in the pump light beam correction operation process, sending a correction success instruction to the time delay data acquisition control module.
Optionally, the first set value is 0 μm to 10 μm.
An electron microscope system comprises a laser, an electron microscope and a stabilizing device of the pumping beam of the electron microscope system, wherein the stabilizing device is used for stabilizing the pumping beam of the electron microscope system; the laser provides pumping pulses to the electron microscope, and the stabilizing device of the pumping beams of the electron microscope system is used for executing the correction operation of the pumping pulses.
A method for stabilizing a pumping beam of an electron microscope system comprises the following steps:
in the data acquisition working process of the electron microscope, the following pump beam correction operation is executed at set time intervals until the drift amount of the light spot position is less than or equal to a first set value:
driving a multi-channel beam detector to an electron beam path of a rear focal plane of an objective lens in an electron microscope, and controlling the multi-channel beam detector to acquire a pumping pulse light spot signal;
calculating to obtain a light spot position drift amount according to the currently acquired pumping pulse light spot signal and the primarily acquired pumping pulse light spot signal, and comparing the light spot position drift amount with a first set value; and when the light spot position drift amount is larger than the first set value, correcting and adjusting the propagation direction of the pump pulse light beam according to the light spot position drift amount.
Optionally, the method further includes:
and when the light spot position drift amount is smaller than or equal to the first set value, driving the multi-channel light beam detector to withdraw from the electron beam path, and continuing to acquire electron microscope data.
Optionally, when the diameter of the multi-channel beam detector is larger than the diameter of the pump pulse spot; according to the pumping pulse facula signal of current collection and the pumping pulse facula signal calculation of first collection obtain facula position drift volume, specifically include:
and determining the profile information of the pumping pulse light spot according to the currently acquired pumping pulse light spot signal, and comparing the currently determined profile information with the profile information of the primarily acquired pumping pulse light spot signal to obtain the light spot position drift amount.
Optionally, when the diameter of the multi-channel beam detector is smaller than or equal to the diameter of the pump pulse spot; according to the pumping pulse facula signal of current collection and the pumping pulse facula signal calculation of first collection obtain facula position drift volume, specifically include:
determining the intensity information of the pumping pulse light spot according to the currently acquired pumping pulse light spot signal, and comparing the currently determined intensity information with the intensity information of the primarily acquired pumping pulse light spot signal;
if the difference value between the currently determined intensity information and the intensity information of the primarily acquired pumping pulse spot signal is larger than a second set value, the pumping laser beam correction operation is executed again; in the re-executed pump laser beam correction operation, the diameter of the multi-channel beam detector is larger than the diameter of the pump pulse spot, and the re-executed pump laser beam correction operation specifically includes: and determining the profile information of the pumping pulse light spot according to the currently acquired pumping pulse light spot signal, and comparing the currently determined profile information with the profile information of the primarily acquired pumping pulse light spot signal to obtain the light spot position drift amount.
Drawings
Fig. 1 is a schematic structural diagram of a stabilizing device for a pump beam of an electron microscope system according to an embodiment of the present disclosure;
fig. 2 is a schematic structural diagram of an electron microscope system according to an embodiment of the present disclosure;
fig. 3 is a block diagram illustrating a structure of a stabilizing device for a pump beam of an electron microscope system according to an embodiment of the present disclosure;
fig. 4 is a schematic structural diagram of a light spot detection assembly in a stabilizing apparatus for a pump beam of an electron microscope system according to an embodiment of the present disclosure;
fig. 5 is a schematic structural diagram of an objective diaphragm plate in a device for stabilizing a pump beam of an electron microscope system according to an embodiment of the present disclosure;
fig. 6 is a schematic structural diagram of a multi-channel beam detector in a device for stabilizing a pump beam of an electron microscope system according to an embodiment of the present disclosure;
fig. 7 is a schematic structural diagram of a multi-channel beam detector in a device for stabilizing a pump beam of an electron microscope system according to another embodiment of the present disclosure;
fig. 8 is a flowchart of a method for stabilizing a pump beam of an electron microscope system according to an embodiment of the present disclosure.
Detailed Description
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, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
As shown in fig. 1, fig. 2 and fig. 3, an embodiment of the present application provides a device for stabilizing a pump beam of an electron microscope system, where the device includes:
the light spot detection assembly 1 comprises a multi-channel light beam detector 3;
and the beam stabilization controller 2 is connected with the light spot detection assembly 1 and is used for performing the following pump beam correction operation at set time intervals until the light spot position drift amount is smaller than or equal to a first set value:
driving the light spot detection assembly 1 to move, so that the multi-channel light beam detector 3 reaches an electron beam Q path of a focal plane behind an objective lens 41 in an electron microscope 4;
controlling a multi-channel light beam detector 3 to collect pumping pulse S light spot signals, and calculating to obtain light spot position drift amount according to the currently collected pumping pulse S light spot signals and the primarily collected pumping pulse S light spot signals; and when the light spot position drift amount is larger than a first set value, correcting and adjusting the propagation direction of the pumping pulse S light beam according to the light spot position drift amount.
The utility model provides a stabilising arrangement of electron microscope system pump beam utilizes multichannel beam detector 3 to locate periodically at the focus face behind objective 41 that is close to with sample 40 and survey pump laser pulse S facula position to through the comparison calculation drift volume, later through feedback control to carry out the accuracy correction to the beam drift, until facula position drift volume can satisfy the data acquisition required precision of electron microscope system. The device not only can effectively eliminate the beam instability generated when the laser and the coupling light path are influenced by the change of the external environment, but also can simultaneously correct the facula drift caused by the mechanical vibration of the electron microscope and the thermal drift of the reflecting mirror inside the lens cone, thereby fundamentally realizing the invariance of the action area of the pumping beam and the observed sample. Taking the time delay data acquisition work of an ultrafast transmission electron microscope as an example, the problem of instability of the pumping pulse is solved, which means that all the ultrafast data in the whole acquired time delay range accurately reflect the real structural relaxation dynamics behavior of the excited sample, and the intensive sampling (namely, the selection of a smaller time delay step length) can be carried out while a longer pumping/detection time delay range is adopted, so that more comprehensive and detailed relaxation process information of the sample can be obtained.
Specifically, as shown in fig. 2, the electron beam Q, which is emitted after the probe pulse R excites the filament 42 of the electron gun, acts on the sample together with the beam of the pump pulse S, and the spot detection assembly 1 is located on the beam path of the pump pulse S when moving to the beam path of the electron beam Q.
In some embodiments, the adjusting the propagation direction of the pump pulse beam according to the spot position drift amount may specifically include the following methods: and calculating a feedback control signal capable of offsetting the light spot position drift amount according to the light spot position drift amount, and accordingly adjusting the deflection angle of the external transmission light path reflector to change the propagation direction of the pump light so as to realize drift correction.
In some embodiments, the spot position drift amount may be calculated by using a two-dimensional cross-correlation algorithm, that is, a cross-correlation function between a current spot signal recorded in the pumping detection process and an initially acquired reference signal is calculated, and an argument corresponding to a maximum value of the cross-correlation function is a drift amount of the pump pulse S along the X/Y direction after passing through the sample 40. The feedback control method may be selected from a proportional-integral-derivative method, a robust feedback method, and a velocity feedback control method.
In some embodiments, the electron microscope may be an ultrafast transmission electron microscope, and the data acquisition operation of the electron microscope is generally a time delay data acquisition operation; such as continuous data acquisition experiments performed under pump/probe experimental conditions. Of course, the electron microscope and the data acquisition work thereof are not limited thereto, and can be selected according to actual requirements.
In some embodiments, as shown in fig. 1 and 2, the beam stabilization controller 2 is further configured to: when the light spot position drift amount is smaller than or equal to a first set value, the light spot detection assembly 1 is driven to move, so that the multi-channel light beam detector 3 is withdrawn from the path of the electron beam Q.
In other words, after the pump beam calibration operation is successfully completed, the multi-channel beam probe 3 needs to be removed from the path of the electron beam Q to continue the data acquisition of the electron microscope 4 itself.
In some embodiments, as shown in fig. 1, 2 and 3, the beam stabilization controller 2 may include a calibration control module 21, a drive assembly 23, and a beam adjustment assembly 22.
In some embodiments of the present disclosure, the driving assembly 23 is in transmission connection with the light spot detecting assembly 1, and is used for driving the light spot detecting assembly 1 to move.
Illustratively, the drive assembly includes a high-precision motor, which may be, for example, a linear servo motor with fast dynamic response, good stability, and high precision of repeated positioning. Specifically, the light spot detection assembly is driven by a high-precision motor and can reciprocate in a two-dimensional plane formed by a focal plane behind the objective lens, so that the positioning through hole of the multi-channel light beam detector is aligned with the path of the electron beam.
In some embodiments of the present disclosure, as shown in fig. 1, 2 and 3, the calibration control module 21 is electrically connected to the multi-channel beam detector 3 and the driving assembly 23, respectively, for: controlling the driving action of the driving assembly 23; and controlling the multi-channel light beam detector 3 to collect pumping pulse S light spot signals, obtaining light spot position drift amount according to the currently collected pumping pulse S light spot signals and the primarily collected pumping pulse S light spot signals, and generating a light beam correction instruction according to the light spot position drift amount when the light spot position drift amount is larger than a first set value.
In some embodiments of the present disclosure, as shown in fig. 1, 2 and 3, the beam adjustment assembly 22 is electrically connected to the calibration control module 21, and is configured to perform calibration adjustment on the beam propagation direction of the pump pulse S according to the beam calibration command of the calibration control module 21.
Illustratively, the beam conditioning assembly 22 may include two motorized mirrors 220, and the motorized mirrors 220 are disposed on the beam path of the pumping pulse S of the galvano-mirror 4.
Illustratively, upon receiving the beam correction command, the motorized mirror 220 electrically controls the pitch and yaw to bring the pump pulse S to the target position.
Specifically, the beam adjustment assembly 22 includes two motorized mirrors 220, which can achieve the operations of pure translation of the light beam and the like, and better control the beam spot position.
Specifically, the calibration control module 21 first sends a control command to the driving assembly 23 to drive the multi-channel beam probe 3 to reach the electron beam Q path of the back focal plane of the objective lens 41 through the driving assembly 23; then, the correction control module 21 sends an instruction to the multi-channel beam detector 3 to control the multi-channel beam detector 3 to perform light spot acquisition operation; then, the correction control module 21 calculates and obtains the light spot position drift amount through the collected light spots, and generates a light beam correction instruction (feedback control signal) according to the light spot position drift amount when the light spot position drift amount is larger than a first set value; finally, the correction control module 21 sends a beam correction command to the beam adjustment assembly 22 to control the beam adjustment assembly 22 to perform position correction.
In some embodiments, as shown in fig. 3, the device for stabilizing the pump beam of the electron microscope system may further include a time delay data acquisition control module 24, and the time delay data acquisition control module 24 may control the data acquisition operation of the electron microscope.
Illustratively, the time delay data acquisition control module 24 may specifically perform automatic acquisition and storage of relaxation dynamics information of the sample under a series of pumping/detection time delay conditions by controlling an electronic image detector and a time delay line in an electron microscope.
Illustratively, the time delay data acquisition control module 24 may be electrically connected to the calibration control module 21, and further configured to: interrupting the data acquisition work of the electron microscope at set time intervals, and sending a light beam correction operation instruction to a correction control module; and after receiving a successful correction instruction of the correction control module, controlling the electron microscope to continue data acquisition.
Accordingly, a correction control module 21 for: after receiving the correction operation instruction, controlling to execute the pump beam correction operation; and when the spot position drift amount is less than or equal to the first set value in the pump beam correction operation process, a successful correction instruction is sent to the time delay data acquisition control module 24.
In some embodiments of the present disclosure, the interaction process between the delay data acquisition control module 24 and the correction control module 21 may specifically include the following procedures: as shown in fig. 3, the time delay data acquisition control module 24 controls the data acquisition work of the electron microscope; after a preset periodic time interval condition is reached, the time delay data acquisition control module 24 interrupts current data acquisition, issues an instruction to the correction control module 21 to perform pumping light beam detection correction, and specifically includes controlling the multi-channel light beam detector 3 to enter an electronic light path, acquiring a light spot signal, then obtaining position drift information by comparing with a reference signal initially acquired, calculating a corresponding feedback control signal according to the position drift information, transmitting the feedback control signal to the light beam adjusting assembly 22 on an external transmission light path, and changing the propagation direction of pumping light through the light beam adjusting assembly 22 to realize drift correction. After the correction is successful, the correction control module 21 controls the multi-channel beam detector 3 to withdraw from the electron beam path, and returns a successful correction instruction to the time delay data acquisition control module 24. After receiving the instruction, the delay data acquisition control module 24 continues the current pump detection data acquisition operation.
For example, the time delay data acquisition control module 24 may be designed integrally with the beam correction control module 21.
Specifically, the stabilizing device and the beam stabilizing controller provided by the embodiment of the application integrate the functions of time delay sequence data acquisition control, pump light spot position detection, automatic pump light pulse direction calibration and the like of an electron microscope into a whole, and the drift detection and calibration process of the pump light pulses and the acquisition process of the time delay data are automatically completed by the integration of the beam stabilizing controller, so that manual operation is not needed, and full-automatic control operation can be realized.
In some embodiments, as shown in fig. 1, 4 and 5, the light spot detecting assembly 1 further includes an objective diaphragm plate 11, the objective diaphragm plate 11 includes a diaphragm aperture 10, and the multi-channel beam detector 3 is disposed on the objective diaphragm plate 11 at a position avoiding the diaphragm aperture 10. The aperture is in the micron range, typically 10 μm to 100 μm.
Specifically, as shown in fig. 4, the light spot detecting assembly may further include a diaphragm holder 12 and a diaphragm fixing plate 13, where the diaphragm holder 12 and the diaphragm fixing plate 13 are used to fix the objective diaphragm plate 11.
Further, the beam stabilization controller is further configured to: after the multi-channel light beam detector is driven to leave the electron beam path, the diaphragm hole of the objective lens diaphragm plate is driven to reach the electron beam path of the objective lens back focal plane in the electron microscope.
Illustratively, as shown in fig. 5, the objective diaphragm plate 11 may be a configuration of four diaphragm holes 10, for example, four apertures having diameters of 40 μm, 50 μm, 70 μm, and 100 μm, respectively.
Specifically, the multi-channel beam detector and an objective lens diaphragm plate for electron diffraction beam spot selection are integrated in a light spot detection assembly, driven by a driving assembly and can reciprocate in a two-dimensional plane formed by a rear focal plane of an objective lens. Furthermore, the introduction of the multi-channel beam detector does not affect the normal function of the ultrafast transmission electron microscope, can reduce the influence of the stabilizing device on the electron microscope system to the maximum extent, and simplifies the detection and correction operation of the pump pulse beam as much as possible. In addition, the multi-channel detector is arranged on the objective diaphragm plate, and can be conveniently detached, checked and replaced.
Illustratively, the objective diaphragm plate can be made by Focused Ion Beam (FIB) nanomachining technology, and is made of Mo or metal alloy.
In some embodiments of the present disclosure, as shown in fig. 5, 6 and 7, the objective diaphragm plate 11 is provided with a mounting through hole; the multi-channel beam detector 3 is embedded in the mounting through hole of the objective lens diaphragm plate 11; the multi-channel beam detector 3 is provided with a positioning through hole 30.
Illustratively, as shown in FIGS. 6 and 7, the positioning through-holes 30 may have a diameter of 1 μm to 2 μm. In addition, the positioning through hole 30 may be provided in the center of the multi-channel beam probe 3.
Specifically, the multi-channel beam detector can be positioned through the positioning through hole, so that the positions of the multi-channel beam detector on the back focal plane of the objective lens are consistent in each pump pulse beam correction operation.
In addition, the multi-channel light beam detector integrated on the objective diaphragm plate can be used for positioning and calibrating the initial position of a pump light spot after the external coupling optical path is adjusted in a large range by combining the scanning function of the electric reflector. The method is faster and more effective than the common positioning methods such as carbon film ablation and the like.
Illustratively, as shown in fig. 2 and 3, the electron microscope system includes an electron image detector 43. The beam stabilization controller 2, which may be electrically connected to the electronic image detector 43, is configured to: after the multi-channel beam detector 3 reaches the path of the electron beam Q on the focal plane behind the objective lens 41 in the electron microscope 4, the alignment operation of the positioning through hole 30 and the electron beam Q is performed, wherein the alignment operation comprises controlling the electron image detector 43 to collect the intensity of the electron beam Q and driving the light spot detection assembly 1 to move according to the intensity of the electron beam Q until the maximum value of the intensity of the electron beam Q is obtained. Illustratively, the correction control module 21 in the beam stabilization controller 2 is electrically connected to the electronic image detector 43 to perform the above control operation.
Specifically, when the electron image detector 43 acquires the maximum intensity of the electron beam Q, that is, it indicates that the positioning through hole of the multi-channel beam detector is aligned with the path of the electron beam Q, the operation of acquiring the pumping pulse S spot signal may be started. In addition, since the alignment operation is performed after the multi-channel beam probe 3 is driven to the electron beam Q path of the back focal plane of the objective lens 41 each time, it can be ensured that the positions of the multi-channel beam probe on the back focal plane of the objective lens are consistent in each pump pulse beam calibration operation.
For example, when a beam correction operation is first performed, a multi-channel beam detector is driven into the electron beam path by a high precision motor, and an electron image detector receives an electron image signal. The high-precision motor drives the optical detector to scan along a two-dimensional plane until the electron image intensity is maximum, namely the position of the electron beam centered in the positioning through hole is used as a reference position; and carrying out positioning adjustment on the multi-channel beam detector at each subsequent beam correction operation, namely carrying out alignment operation of the positioning through hole and the electron beam.
In some embodiments, as shown in fig. 5, the spot detection assembly comprises two multi-channel beam detectors 3, both multi-channel beam detectors 3 being arranged on the objective diaphragm plate 11. Specifically, as shown in fig. 6, the diameter of the first multi-channel beam detector 3 is larger than the spot diameter of the pump pulse; as shown in fig. 7, the diameter of the second multi-channel beam detector 3 is smaller than or equal to the pump pulse spot diameter.
Illustratively, both multi-channel beam detectors employ CMOS.
Illustratively, the multi-channel beam detector is selected from a CMOS which is resistant to electron beam irradiation, and the surface of the detector can be further coated with a light attenuation coating, for example, the coating material can be an aluminum, copper or gold thin film to protect the surface of the detector from being damaged.
Illustratively, the diameter of the beam receiving surface of the first multi-channel beam detector is much larger than the diameter of the light spot, and may be less than or equal to 3 mm, for example, 0.5mm to 2 mm; the diameter of the beam receiving surface of the second multi-channel beam detector is slightly smaller than the diameter of the light spot, and can be in the micron order, for example, tens of microns. The two multi-channel beam detectors may then be no more than 0.5mm thick, taking into account physical space constraints at the back focal plane of the objective lens.
For example, the first multi-channel beam detector has a length by width by height dimension of less than 1mm by 0.5 mm;
the second multi-channel beam detector has a length by width by height dimension of less than 0.065mm by 0.5 mm.
In some embodiments, the set time interval may be determined according to the actual situation of the time delay data sampling, for example, the operation of detecting and correcting the pump beam may be performed every 20 minutes for 20 minutes.
In some embodiments, the first set value is 0 μm to 10 μm, for example, the first set value may be set to 5 μm, that is, when the spot position drift amount is greater than 5 μm, the propagation direction of the pump pulse beam is adjusted, otherwise, the data acquisition of the electron microscope is continued.
In addition, as shown in fig. 2, an embodiment of the present application further provides an electron microscope system, where the electron microscope system includes a laser 5, an electron microscope 4, and a stabilizing device for the pump beam of the electron microscope system as described above, where the laser 5 provides the pump pulse S to the electron microscope 4, and the stabilizing device for the pump beam of the electron microscope system is used to perform a calibration operation of the pump pulse S.
Illustratively, referring to FIG. 2, the electron microscope system of the present disclosure may be an ultrafast transmission electron microscope system. The laser 5 is used for generating pulse laser, and is divided into a detection pulse R and a pumping pulse S after passing through a beam splitter; the transmission electron microscope 4 comprises an electron microscope cavity, a filament 42, a condenser 44, an objective 41, an objective diaphragm 11, a selective area diaphragm 45, an intermediate mirror 46, a projection lens 47 and the like.
Illustratively, referring to fig. 1 and 2, the galvano-mirror system further includes a one-dimensional motorized displacement stage 6 disposed in the optical path between the laser 5 and the tem 4. The two motorized mirrors 220 in the stabilizing device may be located in the light path before and after the motorized stage 6, respectively.
The electron microscope system comprises a stabilizing device for the pumping light beam of the electron microscope system, which can effectively eliminate the instability of the light beam generated when the laser and the coupling light path are influenced by the change of the external environment, and more importantly, can simultaneously correct the light spot drift caused by the mechanical vibration of the electron microscope and the thermal drift of a reflector inside a lens cone, thereby fundamentally realizing the invariance of the action area of the pumping light beam and an observed sample. Taking the time delay data acquisition work of an ultrafast transmission electron microscope as an example, the problem of instability of the pumping pulse is solved, which means that all the ultrafast data in the whole acquired time delay range accurately reflect the real structural relaxation dynamics behavior of the excited sample, and the intensive sampling (namely, the selection of a smaller time delay step length) can be carried out while a longer pumping/detection time delay range is adopted, so that more comprehensive and detailed relaxation process information of the sample can be obtained.
In addition, an embodiment of the present application further provides a method for stabilizing a pump beam of an electron microscope system, where the method includes the following steps, as shown in fig. 8:
in the data acquisition working process of the electron microscope, the following pump beam correction operation is executed at set time intervals until the drift amount of the light spot position is less than or equal to a first set value:
102, controlling a multi-channel light beam detector to collect pumping pulse light spot signals, and calculating to obtain light spot position drift amount according to the currently collected pumping pulse light spot signals and the primarily collected pumping pulse light spot signals; comparing the light spot position drift amount with a first set value;
and 103, when the light spot position drift amount is larger than a first set value, correcting and adjusting the propagation direction of the pump pulse light beam according to the light spot position drift amount.
Specifically, the method for stabilizing the pump beam of the electron microscope system provided by the embodiment of the present application can be specifically realized based on the electron microscope system provided by the embodiment of the present application. The method for stabilizing the pump beam has the same embodiments and the same beneficial effects as the electron microscope system provided by the embodiment of the application, and details are not repeated here.
In some embodiments, the method for stabilizing the pump beam of the electron microscope system further includes, as shown in fig. 8:
and 104, when the light spot position drift amount is smaller than or equal to a first set value, driving the multi-channel light beam detector to withdraw from the electron beam path, and executing 105, namely, continuing to acquire the electron microscope data.
Illustratively, as shown in fig. 8, after the correction adjustment is performed on the propagation direction of the pump pulse beam in step 103, the step 102 may be repeated until the obtained spot position drift amount is less than or equal to the first set value.
In some embodiments, when the diameter of the multi-channel beam detector is larger than the pump pulse spot diameter; step 102, may include the steps of:
and determining the profile information of the pumping pulse light spot according to the currently acquired pumping pulse light spot signal, and comparing the currently determined profile information with the profile information of the primarily acquired pumping pulse light spot signal to obtain the light spot position drift amount.
Illustratively, the diameter of the multi-channel beam detector is larger than the diameter of the pumping pulse light spot, image information of the whole light spot can be acquired, and further the drift amount of the light spot position can be determined through the light spot profile image information.
For example, the multichannel beam detector with a larger diameter may specifically adopt the first multichannel beam detector in the stabilizing device for the pump beam of the electron microscope system.
For example, in this embodiment of the application, a specific process of the operation of the electron microscope system may include the following steps:
step 201, putting in a sample, starting a pumping detection mode, and adjusting the experimental sample in a conventional imaging system mode.
Step 202, a high-precision motor drives a multi-channel optical detector (a first multi-channel optical detector) to an electronic optical path, and a beam stabilization controller controls the multi-channel optical detector to collect a spot profile signal after a pump pulse penetrates through a sample, stores the spot profile signal and sets the spot profile signal as an initial value.
And 203, driving the diaphragm hole of the objective diaphragm plate to an electronic light path by the high-precision motor, and collecting the time delay data of the electronic microscope. The acquisition and correction operation of the spot signal is periodically carried out in the process of pumping/detection data acquisition.
Step 204, the step of each spot position collecting and correcting operation includes:
firstly, a first multi-channel optical detector is arranged in an electronic optical path on a back focal plane of an objective lens, and positioning adjustment is carried out.
Then, the first multi-channel optical detector records the light spot profile of the pump pulse after the pump pulse penetrates through the sample, the measured light spot profile signal is compared with the initial value of the light spot profile signal, the position drift amount is calculated, and the position drift amount is compared with a first set value.
When the light spot position drift amount is larger than a first set value, a feedback control signal capable of offsetting the light spot position drift amount is further calculated through the position drift amount, and accordingly, the deflection angle of the external transmission light path reflector is adjusted to change the propagation direction of the pump light, and drift correction is achieved.
And when the drift amount of the light spot position is smaller than a first set value, withdrawing the multi-channel optical detector from the electron beam path, and continuing to acquire data of the electron microscope.
In other embodiments, when the diameter of the multi-channel beam detector is less than or equal to the pump pulse spot diameter; step 102, may include the steps of:
determining the intensity information of the pumping pulse light spot according to the currently acquired pumping pulse light spot signal, and comparing the currently determined intensity information with the intensity information of the primarily acquired pumping pulse light spot signal;
if the difference value between the currently determined intensity information and the intensity information of the primarily acquired pumping pulse light spot signals is larger than a second set value, performing the pumping laser beam correction operation again, wherein in the performed pumping laser beam correction operation again, the diameter of the multi-channel light beam detector is larger than the diameter of the pumping pulse light spots; the re-executed pump laser beam correction operation step specifically includes: and determining the profile information of the pumping pulse light spot according to the currently acquired pumping pulse light spot signal, and comparing the currently determined profile information with the profile information of the primarily acquired pumping pulse light spot signal to obtain the light spot position drift amount.
Specifically, the reading of the spot intensity information by the pixel combination mode of the multi-channel beam detector is much faster than the reading of the whole image (spot profile information) pixel by pixel, and the signal-to-noise ratio can be improved. In addition, the time-consuming cross-correlation operation process in the contour information processing can be omitted. Therefore, by collecting the spot intensity information, the size of the spot position drift amount can be quickly evaluated. However, since it is difficult to specify a specific value of the spot position drift amount by comparing the spot intensities, if it is estimated that the spot position drift amount is large by the evaluation of the spot intensity information, the specific value of the spot position drift amount is specified by further comparison calculation of the spot profile information, and correction adjustment is performed. It should be noted that the 'first set value' is a reference value of the preset spot position drift amount, and belongs to a length unit; the 'second set value' is a reference value of a preset spot intensity variation, which belongs to the light intensity unit.
Illustratively, the diameter of the multi-channel beam detector is smaller than or equal to the diameter of the pumping pulse light spot, at this time, the intensity information of the light spot can be obtained, and the drift amount of the position of the light spot can be rapidly estimated through the intensity information of the light spot; if the drift amount estimated through the light spot intensity information is large, a large-diameter multi-channel light beam detector is adopted to obtain the outline image of the light spot again, the specific value of the drift amount of the light spot position is determined through comparison of the light spot outline information, and whether light beam correction adjustment is carried out or not is determined according to the determined drift amount of the light spot position; and if the drift amount estimated through the light spot intensity information is small, the light beam correction adjustment is not needed, and the data acquisition work of the electron microscope can be directly continued.
For example, the second setting value may be determined according to the actual conditions such as the intensity of the pumping pulse, and the selection of the first setting value; for example, the second setting value may be set to 5% of the intensity of the initially acquired pump pulse light spot signal, that is, as long as the variation value of the currently acquired light spot intensity relative to the initially acquired pump pulse light spot intensity is greater than 5%, the profile of the light spot is obtained again by using the large-diameter multi-channel beam detector, and the light spot position drift amount is determined. Otherwise, the light spot position drift amount can be directly determined to be less than or equal to the first set value.
Specifically, the method steps of the present embodiment are suitable for the situation where the external environment changes, the mechanical vibration and the thermal drift of the optical element have less influence.
The multi-channel beam detector with a smaller diameter may specifically adopt a second multi-channel beam detector in the stabilizing device for the pump beam of the electron microscope system.
For example, in this embodiment of the application, a specific process of the operation of the electron microscope system may include the following steps:
step 301, putting in a sample, starting a pumping detection mode, and adjusting the experimental sample in a conventional imaging system mode.
Step 302, a high-precision motor sequentially drives a multichannel optical detector with a larger diameter (a first multichannel optical detector) and a multichannel optical detector with a smaller diameter (a second multichannel optical detector) to an electronic optical path, a light beam stabilization controller respectively controls the two multichannel optical detectors to collect a light spot profile signal and a light spot intensity signal after a pump pulse penetrates through a sample, the light spot profile signal and the light spot intensity signal are stored, and the two signals are respectively set as a first initial value and a second initial value.
And 303, driving the diaphragm hole of the objective diaphragm plate to an electronic light path by the high-precision motor, and acquiring the time delay data of the electronic microscope. The acquisition and correction operation of the spot signal is periodically carried out in the process of pumping/detection data acquisition.
Step 304, each step of spot position acquisition and correction operation includes:
firstly, a second multi-channel optical detector is arranged in an electronic optical path on a focal plane behind an objective lens, the intensity of a light spot of a pump pulse after penetrating through a sample is recorded through the second multi-channel optical detector, and a measured light spot intensity signal is compared with a second initial value (the initial value of the light spot intensity signal);
if the difference between the measured spot intensity signal and the second initial value is greater than a second set value, executing the step of spot position acquisition and correction operation in the step 204;
if the difference value between the measured spot intensity signal and the second initial value is smaller than or equal to a second set value, directly determining that the spot position drift amount of the currently acquired pumping pulse spot signal and the initially acquired pumping pulse spot signal is smaller than a first set value; and then, the multi-channel optical detector is controlled to withdraw from the electron beam path, and the data acquisition work of the electron microscope is continued.
It should be noted that the present disclosure is applicable to dynamic change processes in fast and ultra-fast time scales, such as femtoseconds, picoseconds or nanoseconds, and the like, and at the same time, the present disclosure can be applied to almost all material characterization of transmission electron microscopes. The order of the steps is not limited to that listed above and may be varied or rearranged as desired, unless specifically stated or necessary to occur in sequence. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.
It will be apparent to those skilled in the art that various changes and modifications may be made in the embodiments of the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.
Claims (16)
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