CN113654462B - Method and device for monitoring position of detection light spot of ultrafast electron microscope - Google Patents
Method and device for monitoring position of detection light spot of ultrafast electron microscope Download PDFInfo
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Abstract
The invention relates to a device and a method for monitoring the position of a detection light spot of an ultrafast electron microscope, wherein the device comprises a femtosecond detection laser pulse, a reflecting mirror, a laser focusing lens, a beam splitter, a CCD camera and an optical flange window; after the femtosecond detection laser pulse is reflected by the reflecting mirror, focusing is carried out by the laser focusing lens, and the focused laser is incident into the beam splitter to be split into two beams; a beam of focused laser emitted by the beam splitter enters the CCD camera at a certain angle according to the beam splitting ratio to present a facula image; the other beam of focused laser emitted by the beam splitter is used as detection laser pulse to be normally incident to the tip of the photocathode filament of the electron gun of the ultra-fast electron microscope from the optical flange window, and the filament is excited to generate detection photoelectron pulse. The invention provides a novel and convenient way for quickly and accurately obtaining the real-time state of the detection laser spot acting on the tip of the filament to generate photoelectron detection pulse.
Description
Technical Field
The invention relates to a method and a device for monitoring the position of a detection light spot of an ultrafast electron microscope, and relates to the technical field of ultrafast electron microscope detection.
Background
An ultrafast electron microscope is an ultrafast imaging technology based on a pump-detection principle and combining advantages of high spatial resolution of an electron microscope (a transmission electron microscope or a scanning electron microscope) and high time resolution of femtosecond laser, can simultaneously have ultrahigh space-time resolution, and is an important development direction of an electron microscope characterization technology. Taking an ultrafast scanning electron microscope technology as an example, the method mainly relies on the pump-detection principle of femtosecond pulse laser, combines the unique advantage of short electron wavelength of high-energy electron beams emitted by a scanning electron microscope to realize scanning secondary electron imaging with ultrahigh time resolution, and is widely applied to ultrafast carrier dynamics research of various materials including metals, photoelectric semiconductors, organic polymer films and the like. One of the core steps of the ultrafast scanning electron microscope technology is that femtosecond laser pulse in ultraviolet band passes through an optical flange window pre-installed on an electron gun lens barrel of a scanning electron microscope, the tip of an electron gun photocathode is excited by utilizing Einstein photoelectric effect to generate an photoelectron pulse sequence, pulse electrons enter the scanning electron microscope lens barrel after being accelerated, and then reach the surface of a sample after being converged and scanned and deflected by an electromagnetic lens to excite secondary electrons, and the secondary electrons are collected by a secondary electron detector to carry out time resolution detection. However, since the electron gun itself is very narrow in space and the internal filament is very thin (especially, the radius of curvature of the field emission filament tip is in the order of hundred nanometers), the position where the detection laser is incident inside the electron gun cannot be directly observed by naked eyes. Therefore, the difficulty of focusing the ultraviolet femtosecond laser to a diameter of only tens of micrometers and precisely irradiating the tip of a fine filament on the order of hundred nanometers is great.
The method and the device for generating pulse photoelectrons by utilizing the photocathode of an ultraviolet detection pulse laser generator in the existing ultra-fast electron microscope research mainly utilize red visible light which directly reflects the outline and the position of a filament and is emitted by the photocathode due to heating in a conventional thermal emission or thermal field emission mode to calibrate the light path. Specifically, red light emitted by the lamp filament sequentially passes through an optical flange window of the electron gun and a focusing lens arranged in front of the optical flange window of the electron gun to enter a pre-arranged digital microscope or a long-focus camera, and clear red lamp filament images can be directly displayed on a display screen connected with the camera by finely adjusting the receiving angle and the focus of the digital microscope or the camera; then, according to the principle that two points are used for determining a straight line, two diaphragms with adjustable aperture sizes are sequentially added between the digital microscope and the focusing lens, and the fact that the red light spots of the filament observed in the digital microscope when each diaphragm is changed in size are uniformly scaled by taking the center of the diaphragm as the center of a circle is ensured, so that the red light emitted by the filament is determined to enter the optical path of the digital microscope through the optical flange and the focusing lens. Finally, according to the principle of reversibility of the light path, the reflecting mirror in the light path is adjusted to enable the ultraviolet detection femtosecond laser to pass through the centers of the two positioning diaphragms, and the ultraviolet detection femtosecond laser returns according to the original path of the light path for transmitting the red light by the filament and is incident to the tip of the filament to generate pulse photoelectrons for detection and imaging. Although the method can realize that the photocathode of the excitation electron gun generates pulse photoelectrons, because the tip of the filament is too small, it is still very difficult to determine whether the laser strikes the filament only through two common positioning diaphragms placed in the light path, and each calibration needs to take a great deal of time to finely tune the reflecting mirror in the front light path to find the position of the ultraviolet femtosecond laser irradiating the tip of the filament in a blind scanning mode, so that the process is rough and complex, time-consuming and labor-consuming. Because the femtosecond laser light path is easily affected by external conditions such as temperature, humidity, mechanical vibration and the like of surrounding environment, the directivity of the light path is difficult to keep stable for a long time, so that a mirror of the light path needs to be frequently fine-tuned to ensure optimal pulse photoelectron emission efficiency. Because of the fact that a detector capable of directly showing the specific condition of the incident detection laser spot is not provided, whether the detection laser really acts on the tip of the filament at all times can not be further judged, and the optimal excitation efficiency is achieved.
Therefore, in the current common method for generating pulse photoelectrons by exciting an electron gun photocathode by using ultraviolet femtosecond pulse laser in the ultrafast electron microscopy technology, the problems that accurate positioning cannot be realized and the accurate position of the femtosecond detection laser acting on the electron gun photocathode tip cannot be visually monitored always exist. In order to obtain the optimal pulse photoelectron emission efficiency and ensure stable pulse photoelectron emission for a long time, development of a method and a device capable of directly monitoring the real-time position of an ultraviolet femtosecond pulse laser spot is urgently needed, so that an ultrafast electron microscope can stably operate for a long time and acquire clear ultrafast kinetic information.
Disclosure of Invention
In view of the above problems, it is an object of the present invention to provide a device for monitoring the position of a probe light spot of an ultrafast electron microscope, which can realize the function of monitoring the position and shape of a femto-second probe laser light spot on an ultrafast scanning electron microscope or an ultrafast transmission electron microscope in real time, so as to obtain the pulse photoelectrons with the best yield to detect the dynamic process of an ultrafast carrier after a sample is excited.
The second purpose of the invention is to provide a method for monitoring the position of the detection light spot of the ultra-fast electron microscope, and the method can be popularized to monitoring the position of the pumping light spot of the ultra-fast electron microscope.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
in a first aspect, the invention provides a device for monitoring the position of a detection light spot of an ultrafast electron microscope, which comprises a femtosecond detection laser pulse, a reflecting mirror, a laser focusing lens, a beam splitter, a CCD camera and an optical flange window;
after the femtosecond detection laser pulse is reflected by the reflecting mirror, focusing is carried out by the laser focusing lens, and focused laser is incident into the beam splitter to be split into two beams;
a beam of focused laser emitted by the beam splitter enters the CCD camera at a certain angle according to the beam splitting ratio to present a facula image;
and the other beam of focused laser emitted by the beam splitter is used as a detection laser pulse to be normally incident to the tip of a photocathode filament of an electron gun of the ultra-fast electron microscope from the optical flange window, and the filament is excited to generate a detection photoelectron pulse.
Further, a collimation diaphragm is arranged between the reflecting mirror and the laser focusing lens.
Further, when the optical flange window is positioned below the electron gun suppression electrode of the ultra-fast electron microscope, the ultra-fast electron microscope further comprises a three-dimensional electronic control reflector, and detection laser pulses incident through the optical flange window are reflected to the tip of the photocathode filament through the three-dimensional electronic control reflector.
Further, the femtosecond detection laser pulse is obtained by frequency-tripled or frequency-quadrupled pulse laser of near infrared femtosecond laser with fundamental frequency.
Further, the laser focusing lens is a plane convex lens made of ultraviolet-grade fused quartz, the front surface and the rear surface of the plane convex lens are plated with ultraviolet antireflection films, and laser is perpendicularly incident from the curved surface center of the plane convex lens and focused on the tip of a filament at the rear focal point of the plane convex lens, so that ultra-fast detection photoelectron pulses with the same repetition frequency are excited and generated.
Further, the beam splitter adopts an ultraviolet fused quartz beam splitter.
Further, the optical flange window is provided with lead glass plated with an ultraviolet antireflection film.
Further, the surface of the reflecting mirror is plated with a dielectric film or an aluminum film, and the reflecting mirror is arranged on the three-dimensional precise electric adjustable mirror frame.
Further, the laser focusing lens is arranged on the three-dimensional small precision mechanical displacement table and is used for adjusting the incident angle and position of the detection light path.
In a second aspect, the present invention provides a method for monitoring the position of a probe spot of an ultrafast electron microscope, comprising:
the femto-second detection laser pulse is beaten near the tip of the photocathode filament of the ultra-fast electron microscope through a rough adjustment reflector, whether an optoelectronic image appears or not is observed, and if the optoelectronic image is beaten on the photocathode filament, the optoelectronic image is generated;
regulating and controlling the angle and the specific position of the femtosecond detection laser on the tip of the photocathode filament through a fine-tuning laser focusing lens, if the resolution ratio of the photoelectron image is relatively highest, the brightness and the contrast ratio are relatively highest, and the image quality is kept stable, the laser is considered to be on the tip of the photocathode filament, at the moment, a light spot presented by a CCD camera is determined to be an optimal light spot, and the position and the size of the optimal light spot are recorded;
and (3) monitoring the change condition of the spot parameters (position, shape, size, intensity and the like) displayed on the CCD camera in real time, judging whether the femtosecond detection laser acts on the photocathode tip, and if the size and the position of the spot are inconsistent with the optimal spot, adjusting the optical path to basically keep consistency with the optimal spot, namely ensuring that the femtosecond laser pulse always strikes the photocathode filament tip.
Due to the adoption of the technical scheme, the invention has the following advantages:
1. the invention utilizes the combination device of the ultraviolet focusing lens, the ultraviolet beam splitter and the CCD camera (charge coupled device) to realize the accurate positioning of the specific position of the ultra-fast photocathode of the electron gun of the ultra-fast electron microscope, thereby monitoring the position of the ultra-fast photocathode of the electron gun, where the detection pulse laser spot is hit, in real time, so as to ensure that the ultra-fast electron microscope is in the state of optimal and stable photoelectron pulse excitation efficiency at all times;
2. the invention can be used for accurately judging whether the femtosecond ultraviolet detection laser strikes the tip of the photocathode filament of the electron microscope, namely, the quality and the position of a light spot displayed on a CCD camera are observed in real time, so that the best position of the detection laser acting on the tip of the filament is kept as much as possible by fine adjustment of optical path components such as a reflector, a focusing lens and the like in an incident optical path, and finally, the imaging effect of the ultrafast electron microscope is best;
in conclusion, the invention provides a novel and convenient way for quickly and accurately obtaining the real-time state of the detection laser spot acting on the tip of the filament to generate photoelectron detection pulse, and provides a guarantee for finally realizing ultra-fast electron microscopic imaging based on a pumping-detection mechanism and analyzing the ultra-fast dynamic process related to the structure and energy carriers in the material.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Like parts are designated with like reference numerals throughout the drawings. In the drawings:
FIG. 1 is a schematic diagram of a monitoring device for detecting light spots by an ultrafast electron microscope, wherein ultraviolet femtosecond laser excites a photocathode of an electron gun from the side;
FIG. 2 is a schematic diagram of a monitoring device for detecting light spots by an ultra-fast electron microscope, wherein the ultra-fast electron microscope excites a photocathode of an electron gun from bottom to top by ultraviolet femtosecond laser according to the embodiment of the invention;
FIG. 3 is a method workflow diagram of an embodiment of the present invention;
FIG. 4 is a physical diagram of a probe spot of about 50 μm in diameter focused on a photocathode in accordance with an embodiment of the present invention.
Detailed Description
Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only, and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "includes," "including," and "having" are inclusive and therefore specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order described or illustrated, unless an order of performance is explicitly stated. It should also be appreciated that additional or alternative steps may be used.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
For ease of description, spatially relative terms, such as "inner," "outer," "lower," "upper," and the like, may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.
The invention provides a device and a method for monitoring the position of a detection light spot of an ultrafast electron microscope, wherein the device comprises a femtosecond detection laser pulse, a reflecting mirror, a laser focusing lens, a beam splitter, a CCD camera and an optical flange window; after the femtosecond detection laser pulse is reflected by the reflecting mirror, focusing is carried out by the laser focusing lens, and the focused laser is incident into the beam splitter to be split into two beams; a beam of focused laser emitted by the beam splitter enters the CCD camera at a certain angle according to the beam splitting ratio to present a facula image; the other beam of focused laser emitted by the beam splitter is used as detection laser pulse to be normally incident to the tip of the photocathode filament of the electron gun of the ultra-fast electron microscope from the optical flange window, and the filament is excited to generate detection photoelectron pulse. The invention provides a method and a device for monitoring the accurate action of ultraviolet femtosecond detection laser pulses on the optimal excitation site of the photocathode tip of an electron gun in an ultrafast electron microscope system in real time, and relates to an ultrafast electron microscope technology which combines a femtosecond laser light path system based on a pumping-detection principle and a field emission or thermal emission high-resolution electron microscope (a transmission electron microscope or a scanning electron microscope), which is mainly used for detecting the ultrafast dynamics process of excited state energy carriers in a material and can simultaneously have ultrahigh space-time resolution.
Example 1
As shown in fig. 1, the device for monitoring the position of a light spot of an ultrafast electron microscope provided in this embodiment is a detection light path of an ultrafast electron microscope in which ultraviolet femtosecond laser excites a photocathode of an electron gun from a side surface, and includes a high-repetition-rate femtosecond laser 1, an ultraviolet reflector 2, collimating diaphragms 3 and 4, an ultraviolet laser focusing lens 5, an ultraviolet beam splitter 6, a CCD camera 7 and an optical flange window 8.
The near infrared femtosecond pulse laser generated by the high repetition rate femtosecond laser 1 can be divided into two beams according to a power ratio of 1:1 (for example, the method is not limited thereto, and the beam splitting ratio can be set according to the need): one beam is usually subjected to frequency doubling or frequency tripling to obtain pumping laser for the dynamic process of a sample in a laser generator mirror, and the other beam is subjected to frequency tripling or frequency quadrupling to obtain detection laser with the wavelength in an ultraviolet band for exciting a photocathode of an electron gun of an electron microscope to generate pulse photoelectrons for ultra-fast dynamic imaging and detection, wherein the embodiment mainly focuses on the description of the process and specifically comprises the following steps:
after being reflected by an ultraviolet reflecting mirror 2, the femtosecond ultraviolet detection laser pulse sequentially passes through two collimating diaphragms 3 and 4 and is focused by an ultraviolet laser focusing lens 5, the focused laser is incident on an ultraviolet beam splitting mirror 6 at a set angle such as a 45-degree angle and is split into two beams according to a certain power ratio (the reflection and the transmittance can be 1:9 or 2:8 and the like without limitation), and one focused laser reflected by the ultraviolet beam splitting mirror 6 is vertically incident into a CCD camera 7 to present a facula image; the transmitted laser through the ultraviolet beam splitter 6 is used as a detection laser pulse to be normally incident on a photocathode filament tip 9 of an electron gun of the electron microscope from an optical flange window 8, and the electro-optic effect of Einstein is utilized to excite the filament tip to generate a detection photoelectron pulse.
In some preferred embodiments of the present invention, the femtosecond detection laser pulse used for exciting the photocathode of the electron gun of the electron microscope is a pulse laser with ultraviolet band (which can meet the requirements of work function of most photocathode filament materials) obtained by frequency tripled or frequency quadrupled by near infrared femtosecond laser (1030 nm) with fundamental frequency, and meets certain basic conditions such as pulse width, heavy frequency, single pulse energy, polarization direction, etc., for example, the pulse width range can be 250-300fs, the heavy frequency range can be 200KHz-25MHz, the single pulse energy is 1-10nJ, and the polarization direction is parallel to the filament, i.e. the vertical polarization direction.
In some preferred embodiments of the present invention, the ultraviolet laser focusing lens 5 is a plano-convex lens made of ultraviolet-grade fused quartz with both front and rear surfaces coated with an ultraviolet antireflection film, allowing the laser light in the deep ultraviolet band to be totally transmitted and effectively avoiding the generation of laser-induced fluorescence. The detection laser is vertically incident from the curved surface center of the plano-convex lens and focused on the tip of the filament at the back focus of the plano-convex lens, and is used for exciting and generating ultra-fast detection photoelectron pulses with the same repetition frequency. Because the area of the focusing light spot is small and the average power density is high, pulse photoelectrons can be effectively excited to be generated for dynamic information imaging and detection.
In some preferred embodiments of the invention, the electron gun photocathode is primarily directed to a schottky thermal field emission photocathode (which may also be a conventional thermal emission tungsten cathode, yttrium iridium oxide (Y) 2 O 3 -Ir) cathode, lanthanum hexaboride (LaB) 6 ) Cathode, schottky cold field emission cathode, etc., as examples and without limitation), its hot field cathode filament is installed at the center of the grid hole and at a proper distance, the filament is made of single crystal tungsten W material and the tip (radius of curvature about 300nm to 500 nm) is like a "Y" needle point, and a small group of metal oxide (e.g., zirconia ZrO) is coated on the upper part of the tip in order to effectively reduce the electron work function in single crystal tungsten to about 2.5 eV. Because the work function of electrons after photoexcitation is typically affected by the crystal orientation of the surface of the material away, the schottky thermal field emission cathode is typically<100>The crystal orientation, and thus the lowest possible work function and high photoelectron emissivity.
In some preferred embodiments of the present invention, the ultraviolet beam splitter 6 employs an ultraviolet fused silica beam splitter, which is installed between the ultraviolet laser focusing lens 5 and the optical flange window 8, has a certain beam splitting ratio when the detected femtosecond laser is incident on the surface thereof at a certain angle (for example, typically at an angle of 45 °), and has an electromagnetic wave response band mainly covering about 200nm to 450nm, and has low light absorptivity and good thermal stability in this wavelength range. Normally, one side of the ultraviolet fused quartz beam splitting sheet is flat, the other side of the ultraviolet fused quartz beam splitting sheet is provided with a protrusion with a certain radian, and the whole ultraviolet fused quartz beam splitting sheet is wedge-shaped, so that unnecessary interference caused by front and rear surface reflection can be effectively reduced.
In some preferred embodiments of the invention, a CCD camera 7 is mounted on an additional bread board outside the electron gun near the optical flange window 8 for collecting another fraction of the reflected beam-splitting laser light split from the probe laser beam of the excitation photocathode by an ultraviolet beam splitter 6. Since the small part of the split laser light and the laser light acting on the photocathode tip come from the same main light path, the split laser light collected by the CCD camera 7 can completely reflect the real state of the detection laser acting on the photocathode tip in real time.
In some preferred embodiments of the invention, the optical flange window 8 has a plumbitized glass mounted thereon with an ultraviolet anti-reflection film on the surface.
In some preferred embodiments of the present invention, the surface of the ultraviolet reflecting mirror 2 is coated with a dielectric film, such as a multilayer dielectric film (totally reflecting ultraviolet laser and being resistant to laser light) or an aluminum film of different refractive indexes on a BK7 substrate having a surface accuracy of λ/10. Further, the ultraviolet reflecting mirror 2 may be disposed on a three-dimensional precision electric adjustable mirror bracket, for initially adjusting the incident angle and position of the detection laser when the detection light path is set up, so that the detection laser passes through the centers of the collimation diaphragms 3,4 and the ultraviolet laser focusing lens 5 respectively and then reaches the filament basically, and for calibrating and optimizing the detection laser at any time during the use of the light path after the light path is set up, the optimum point where the detection laser strikes the tip of the filament is achieved.
In some preferred embodiments of the present invention, the size of the openings of the collimating diaphragms 3 and 4 can be adjusted, so as to determine the incidence direction of the detection laser, and fix the detection light path to facilitate the subsequent collimation of the light path at any time.
In some preferred embodiments of the present invention, the ultraviolet laser focusing lens 5 is placed on the three-dimensional small-sized precise electric displacement table 10, the incident angle and position of the detection light path are finely adjusted and controlled by adjusting the X axis and the Y axis of the electric displacement table 10, so that the detection light path can vertically penetrate through the center of the ultraviolet laser focusing lens 5 to be converged at the filament tip, and the focusing position of the detection laser is changed by adjusting the Z axis of the electric displacement table 10, so that the filament tip is located near the focus as much as possible, and the photoelectron excitation efficiency is improved.
Example 2
The device for monitoring the position of the detection light spot of the ultrafast electron microscope provided in this embodiment is a detection light path of the ultrafast electron microscope in which the light path of the detection laser excites the photocathode of the electron gun from bottom to top, unlike embodiment 1, the photoelectron excitation mode is that the focused detection laser is reflected upward to the tip of the photocathode by the fixed mirror 11 placed in the lens barrel as shown in fig. 2 to generate pulse photoelectrons, so the detection laser light spot monitoring device constructed for this excitation mode is that the detection laser light enters the mirror 11 after being focused by the ultraviolet laser focusing lens 5 and is split into two beams by the ultraviolet beam splitter 6, wherein the reflected beams enter the CCD camera 7, and the lens beams enter the lens barrel side optical flange window 8 (at this time, the optical flange window 8 is located below the suppression electrode 12) to be reflected upward as the detection laser pulse excitation photocathode to generate detection pulse electron beams. In the same way, the laser spot of the reflected beam on the screen of the CCD camera 7 can reflect the actual condition of the transmitted beam acting on the tip of the filament in real time, and further the excitation of the optimal pulse photoelectron beam can be maintained by adjusting the ultraviolet reflecting mirror 2 and the ultraviolet laser focusing lens 5 on the mechanical displacement table.
Example 3
The invention utilizes the reflected laser facula which is presented by the CCD camera 7 in real time to completely copy the condition that the transmitted laser facula is in the electron gun, realizes the complete visualization of the condition that the detection laser acts on the photocathode to generate detection photoelectrons, replaces the original low-efficiency mode of scanning detection laser in a large range to blindly find the tip of the filament, and can be used as an accurate basis for efficiently and directly monitoring the real condition that the detection laser facula acts on the tip of the photocathode.
As shown in fig. 3, the method for monitoring the position of a light spot detected by an ultrafast electron microscope according to the present embodiment includes the following steps:
s1, the ultraviolet femtosecond laser is shot near the tip of a photocathode filament through a rough adjustment motor-driven reflector 2, at the moment, an optoelectronic image can appear, and if the ultraviolet femtosecond laser is shot on the photocathode filament, the optoelectronic image can be generated.
Specifically, on the existing electron microscope operation software, the filament does not emit thermal electron imaging by setting filament parameters, and imaging can only be performed by detecting photoelectrons generated by laser excitation, namely, whether the detection laser is irradiated on the filament or not is judged by detecting the laser through a switch, and whether photoelectron images appear or not is judged: when the detection laser is turned off, the electron microscope window is completely black, and no secondary electron image exists; when the detection laser is turned on, a secondary electron image appears in the electron microscope window immediately, at this time, the detection laser strikes the photocathode filament to excite pulse photoelectron to obtain a photoelectron image, at this time, the condition of poor image quality may appear, the poor image quality means that the image resolution is not high, the overall brightness and contrast of the image are lower and the like because of weak photoelectron signals.
S2, fine-adjusting the ultraviolet laser focusing lens 5 to regulate and control the angle and specific position of the ultraviolet femtosecond laser on the photocathode filament tip 12.
Specifically, the incident angle and position of the detection light path are finely regulated and controlled by adjusting the X axis and the Y axis of the electric displacement table 10, so that the detection light path can vertically penetrate through the center of the ultraviolet laser focusing lens 5 to be converged at the filament tip, and the focusing position of the detection laser is changed by adjusting the Z axis of the electric displacement table 10, so that the filament tip is positioned near the lens focus as much as possible, and the photoelectron excitation efficiency is improved.
If the optoelectronic image resolution is relatively highest, the brightness and contrast are relatively greatest, and the image quality remains stable, indicating that the filament tip is hit, the optoelectronic excitation efficiency is highest, and if not hit, the optoelectronic signal is weak and the image quality is poor. Because different thicknesses of the focusing lens are different in refractive index and different in focusing degree, excitation can be finally realized through the fine tuning method to generate a large number of pulse photoelectrons, namely, the state of maximum contrast, strongest brightness and highest resolution of a photoelectron image is optimized, and clearer ultrafast carrier dynamics information can be detected.
S3, when the image quality is kept optimal and stable for a long time, the laser is considered to strike the tip of the photocathode filament, at the moment, the light spot displayed by the CCD camera 7 is determined to be the optimal light spot, the position and the size of the optimal light spot are recorded, the change of the light spot parameters of the CCD camera 7 is monitored in real time when the laser is used, whether the femtosecond detection laser acts on the tip of the photocathode filament is judged, and if the size and the position of the light spot are inconsistent with the optimal light spot, the optical path is regulated to be consistent with the optimal light spot, namely the fact that the femtosecond laser pulse always strikes the tip of the photocathode filament is ensured.
Specifically, the photoelectronic image is marked with the position and the size of the best light spot (the shape of the best light spot is relatively round, the intensity is in gaussian distribution and relatively strong) on the computer screen synchronously connected with the CCD camera 7, the two laser beams obtained by beam splitting are identical in behavior and property because the two laser beams are from the same laser beam, that is, although the two finally focused light spots may not be identical, the change trend of the shape, the size, the position, the intensity distribution and the like of the light spot is identical, the change trend is the same, the change trend can be used as a monitoring standard, the conditions of monitoring the position, the shape, the intensity and the like of the detected light spot in real time can be realized through the circle, and the situation that the laser beam is precisely hit at the tip of the photocathode filament can be considered as long as the light spot is adjusted to the marked position of the circle in the follow-up. This is because the transmitted laser beam incident on the photocathode filament obtained by the beam splitting of the detection laser beam and the reflected beam entering the CCD camera 7 are both from the same pulse laser beam, when the main optical path is changed (the ultraviolet mirror 2 or the ultraviolet laser focusing lens 5 is adjusted), the change is completely consistent, including the basic parameters such as the position, shape, size and intensity of the light spot, and the main laser beam does not pass through other optical elements after one beam splitting, so that any distortion of information can be effectively avoided. As shown in fig. 4, the spot of the ultraviolet femtosecond detection laser with the diameter of about 50 μm focused on the photocathode and presented on the screen of the CCD camera 7 in real time includes information such as spot position, shape, size and intensity distribution, so that the position and size of the ultraviolet femtosecond laser acting on the tip of the photocathode can be directly judged, the incidence direction and the locus of the detection laser can be adjusted in time, and finally, the imaging quality of the detection photoelectron pulse is optimal, and clear ultrafast kinetic information is obtained.
Finally, it should be noted that the above embodiments are merely illustrative of the technical solution of the present invention, and not limiting thereof; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may be modified or some technical features may be replaced with other technical solutions, which may not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
The method can also be popularized to the information of the position, the shape, the size, the intensity distribution and the like of the pumping light spot of the ultra-fast electron microscope.
Claims (9)
1. The device for monitoring the position of the detection light spot of the ultra-fast electron microscope is characterized by comprising a femtosecond detection laser pulse, a reflecting mirror, a laser focusing lens, a beam splitter, a CCD camera and an optical flange window;
after the femtosecond detection laser pulse is reflected by the reflecting mirror, focusing is carried out by the laser focusing lens, and focused laser is incident into the beam splitter to be split into two beams;
a beam of focused laser emitted by the beam splitter vertically enters the CCD camera to present a facula image;
the other beam of focused laser emitted by the beam splitter is used as a detection laser pulse to be normally incident to the tip of a photocathode filament of an electron gun of the ultra-fast electron microscope from the optical flange window, and the filament is excited to generate a detection photoelectron pulse; when the optical flange window is positioned below the electron gun suppression electrode of the ultra-fast electron microscope, the ultra-fast electron microscope further comprises a three-dimensional electronic control reflector, and detection laser pulses incident through the optical flange window are reflected to the tip of the photocathode filament through the three-dimensional electronic control reflector.
2. The device for monitoring the position of a light spot detected by an ultrafast electron microscope as recited in claim 1, wherein a collimating diaphragm is disposed between the reflecting mirror and the laser focusing lens.
3. The device for monitoring the position of a light spot detected by an ultrafast electron microscope according to claim 1, wherein the femtosecond detection laser pulse is obtained by multiplying the near infrared femtosecond laser with a fundamental frequency by three or four times.
4. A device for monitoring the position of a light spot of an ultrafast electron microscope according to any one of claims 1 to 3, wherein the laser focusing lens is a plano-convex lens made of ultraviolet fused quartz, the front and rear surfaces of which are coated with ultraviolet antireflection films, and laser is perpendicularly incident from the curved center of the plano-convex lens and focused on the tip of a filament at the rear focal point of the plano-convex lens, so as to excite and generate ultrafast detection photoelectron pulses with the same repetition frequency.
5. A device for monitoring the position of a light spot detected by an ultrafast electron microscope according to any one of claims 1 to 3, wherein the beam splitter adopts an ultraviolet fused quartz beam splitter.
6. A device for monitoring the position of a light spot detected by an ultrafast electron microscope according to any one of claims 1 to 3, wherein the optical flange window is provided with a leaded glass plated with an ultraviolet antireflection film.
7. A device for monitoring the position of a light spot detected by an ultrafast electron microscope according to any one of claims 1 to 3, wherein the surface of the reflecting mirror is plated with a dielectric film or an aluminum film, and the reflecting mirror is arranged on a three-dimensional precise electric adjustable mirror frame.
8. A device for monitoring the position of a light spot detected by an ultrafast electron microscope according to claims 1 to 3, wherein the laser focusing lens is arranged on a three-dimensional small precision mechanical displacement table and is used for adjusting the incident angle and position of a detection light path.
9. A method of monitoring an apparatus for detecting spot position based on an ultrafast electron microscope as recited in any one of claims 1 to 8, comprising:
the femto-second detection laser pulse is beaten near the tip of the photocathode filament of the ultra-fast electron microscope through a rough adjustment reflector, whether an optoelectronic image appears or not is observed, and if the optoelectronic image is beaten on the photocathode filament, the optoelectronic image is generated;
regulating and controlling the angle and the specific position of the femtosecond detection laser on the tip of the photocathode filament through a fine-tuning laser focusing lens, if the resolution ratio of the photoelectron image is relatively highest, the brightness and the contrast ratio are relatively highest, and the image quality is kept stable, the laser is considered to be on the tip of the photocathode filament, at the moment, a light spot presented by a CCD camera is determined to be an optimal light spot, and the position and the size of the optimal light spot are recorded;
and (3) monitoring the change condition of the light spot parameters displayed on the CCD camera in real time, judging whether the femtosecond detection laser acts on the photocathode tip, and if the size and the position of the light spot are inconsistent with the optimal light spot, adjusting the light path to keep consistency with the optimal light spot, namely ensuring that the femtosecond laser pulse always strikes the photocathode filament tip.
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Citations (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1379262A (en) * | 2002-05-17 | 2002-11-13 | 中国科学院上海光学精密机械研究所 | Observing microscope for scanning probe microscope equipment |
| JP2004158365A (en) * | 2002-11-08 | 2004-06-03 | Keyence Corp | Electron microscope, method for operating electron microscope, operating program of electron microscope and computer readable recording medium |
| JP2008084734A (en) * | 2006-09-28 | 2008-04-10 | National Institute For Materials Science | Electron beam generator, and method for irradiating cathode tip part with laser beam |
| JP2008249478A (en) * | 2007-03-30 | 2008-10-16 | Toray Res Center:Kk | Cathode luminescence apparatus and analysis method using the same |
| CN106645236A (en) * | 2016-10-20 | 2017-05-10 | 中国科学院物理研究所 | Ultra-fast transmission electron microscope system and use method thereof |
| CN108474932A (en) * | 2015-11-01 | 2018-08-31 | 霍华德休斯医学研究所 | Big visual field, high-resolution microscope |
| US10338013B1 (en) * | 2018-01-25 | 2019-07-02 | Kla-Tencor Corporation | Position feedback for multi-beam particle detector |
| CN112379129A (en) * | 2020-11-16 | 2021-02-19 | 付学文 | High-space-time resolution multi-mode carrier dynamics measurement system and measurement method |
| CN112505001A (en) * | 2020-11-25 | 2021-03-16 | 华中科技大学 | Device and method for dynamically measuring transparent material under femtosecond laser loading |
| JP2021048114A (en) * | 2019-09-20 | 2021-03-25 | 株式会社ホロン | Scanning electron microscope and secondary electron detection method for scanning electron microscope |
| CN112587302A (en) * | 2021-03-04 | 2021-04-02 | 季华实验室 | Femtosecond laser real-time dynamic positioning focusing system and method |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4014917B2 (en) * | 2002-04-11 | 2007-11-28 | 株式会社キーエンス | Electron microscope and operation method of electron microscope |
-
2021
- 2021-08-23 CN CN202110977982.XA patent/CN113654462B/en active Active
Patent Citations (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1379262A (en) * | 2002-05-17 | 2002-11-13 | 中国科学院上海光学精密机械研究所 | Observing microscope for scanning probe microscope equipment |
| JP2004158365A (en) * | 2002-11-08 | 2004-06-03 | Keyence Corp | Electron microscope, method for operating electron microscope, operating program of electron microscope and computer readable recording medium |
| JP2008084734A (en) * | 2006-09-28 | 2008-04-10 | National Institute For Materials Science | Electron beam generator, and method for irradiating cathode tip part with laser beam |
| JP2008249478A (en) * | 2007-03-30 | 2008-10-16 | Toray Res Center:Kk | Cathode luminescence apparatus and analysis method using the same |
| CN108474932A (en) * | 2015-11-01 | 2018-08-31 | 霍华德休斯医学研究所 | Big visual field, high-resolution microscope |
| CN106645236A (en) * | 2016-10-20 | 2017-05-10 | 中国科学院物理研究所 | Ultra-fast transmission electron microscope system and use method thereof |
| US10338013B1 (en) * | 2018-01-25 | 2019-07-02 | Kla-Tencor Corporation | Position feedback for multi-beam particle detector |
| JP2021048114A (en) * | 2019-09-20 | 2021-03-25 | 株式会社ホロン | Scanning electron microscope and secondary electron detection method for scanning electron microscope |
| CN112379129A (en) * | 2020-11-16 | 2021-02-19 | 付学文 | High-space-time resolution multi-mode carrier dynamics measurement system and measurement method |
| CN112505001A (en) * | 2020-11-25 | 2021-03-16 | 华中科技大学 | Device and method for dynamically measuring transparent material under femtosecond laser loading |
| CN112587302A (en) * | 2021-03-04 | 2021-04-02 | 季华实验室 | Femtosecond laser real-time dynamic positioning focusing system and method |
Non-Patent Citations (1)
| Title |
|---|
| Laser-free GHz stroboscopic transmission electron microscope: Components, system integration, and practical considerations for pump-probe measurements;Fu Xuewen;《REVIEW OF SCIENTIFIC INSTRUMENTS》;全文 * |
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