CN104330430B - Apparatus for evaluating photoelectron emissivity of photocathode material, and evaluation method thereof - Google Patents

Abstract

The invention discloses a device for evaluating the photoelectron emission performance of a photocathode material and an evaluation method thereof. The evaluation device of the present invention includes: a vacuum chamber, a vacuum pumping system, a vacuum degree measuring system, a photocathode assembly, a power supply system, an optoelectronic imaging system, a data acquisition system, a laser excitation system and a focusing mirror. In the present invention, by setting a focusing mirror inside the vacuum chamber, the focus of the focusing mirror is located on the surface of the photocathode material, and by adjusting the incident position of the laser beam, the continuous change of the incident angle of the laser is realized, and the wavelength and polarization state of the laser can be changed. , all parameters of the photoelectron emission characteristics can be measured in situ. The method of the present invention saves a series of cumbersome steps of frequently adjusting the laser light path outside the vacuum chamber in the laser excitation mode with discrete angle incidence, only needs to change the incident position of the laser beam to change the incident angle, and overcomes the problems caused by the discrete angle incidence. Angle discontinuity problem.

Description

A device and method for evaluating photoelectron emission performance of photocathode materials

technical field

The invention relates to performance evaluation of photocathode materials, in particular to a device for evaluating the photoelectron emission performance of photocathode materials and an evaluation method thereof.

Background technique

Photocathode material is a kind of material with photoelectric effect, which can produce photoelectron emission under laser beam excitation, mainly including copper, magnesium, niobium and other metals, gallium arsenide, gallium nitride and other semiconductors and antimony-cesium, cesium-tellurium, Sodium-potassium-antimony and other binary or multi-element alkali metals. The photoelectron emission properties of photocathode materials mainly include quantum efficiency, total emission beam current, angular distribution of emitted electrons, energy dispersion of electrons, brightness and thermal emittance, etc.

The photocathode is one of the core components of photomultiplier tubes, electron accelerators, photoemission electron microscopes, and ultrafast electron microscopy technology with time resolution developed in the past ten years. The photoelectron emission performance of the photocathode materials used It has a key influence on the functional parameters of the above-mentioned equipment. For example, in order to obtain high-quality next-generation accelerator-based light sources, such as X-ray free electron lasers or energy recovery linear accelerator X-ray sources, the photocathode materials used in corresponding accelerators need to have the characteristics of high quantum efficiency and low thermal emittance; During the working process of the electron microscope, the thermal emittance of the pulsed electron beam excited by the pulsed laser on the surface of the photocathode material can determine the limit spatial resolution of the instrument's imaging, while the quantum efficiency and brightness of the photocathode material will restrict the signal intensity of the instrument's imaging .

After a photocathode material is manufactured through a complete process, it is necessary to conduct a quantitative evaluation of its photoelectron emission performance. Measurement conditions include: different laser incident angles, different laser wavelengths, different laser polarization states, and continuous or pulsed lasers; measurement parameters include: total photoelectron emission beam current, photoelectron angular distribution, photoelectron transverse momentum distribution, and brightness deduced from the above parameters and thermal emittance. The photoelectron emission performance parameters measured under different measurement conditions, on the one hand, provide a quantitative basis for judging the performance indicators of photocathode materials in related applications, and on the other hand, they can be used for the optimal design of photocathode material preparation process parameters.

However, since the photoelectron emission performance evaluation of photocathode materials needs to be carried out in ultra-high vacuum, controlling the continuous change of laser angle in ultra-high vacuum has always been an unsolved technical problem. The existing technology for controlling the laser angle is limited to opening multiple light-transmitting flanges with different angles on the wall of the vacuum chamber, so the angle change of the incident light is limited and the angle values are discrete values, so it cannot meet the needs of continuous different angles. Requirements for parameter measurement at laser incident angles.

Contents of the invention

In order to measure the photoelectron emission performance parameters of the photocathode material under the continuously changing laser incident angle and excitation light wavelength, the present invention provides a photocathode material photoelectron emission performance evaluation device and its evaluation method, which can be realized in different The photoelectron emission performance parameters of photocathode materials are measured at angle and wavelength.

An object of the present invention is to provide a device for evaluating the photoelectron emission performance of a photocathode material.

The photocathode material photoelectron emission performance evaluation device of the present invention includes: a vacuum chamber, a vacuum pumping system, a vacuum degree measurement system, a photocathode assembly, a power supply system, a photoelectron imaging system, a data acquisition system, a laser excitation system, and a focusing mirror; Among them, the surface of the vacuum chamber is respectively connected to the vacuum pumping system and the vacuum degree measurement system through the flange port; the mechanical installation flange port and the power supply connection flange port are respectively arranged on the surface of the vacuum chamber, and the photocathode assembly is mechanically installed. The flange port enters the vacuum chamber and is installed on the connection fixture inside it. There are multiple electrodes in the power supply connection flange port. One end of the electrode is in the vacuum chamber and connected to the photocathode assembly. The other end of the electrode is in the vacuum chamber. The outside of the chamber is connected to the power system; the surface of the vacuum chamber is opposite to the photocathode assembly, and the photoelectron imaging system is installed through the flange opening of the observation window; a focusing mirror is set in the vacuum chamber, and the focus of the focusing mirror is located at the photocathode The surface of the photocathode material in the component; a laser incident flange is provided on the surface of the vacuum chamber, and a transparent material is installed to form an incident window. The laser excitation system located outside the vacuum chamber emits a laser beam through the incident window and enters the focusing mirror After reflection, it converges to the focal point; by changing the incident position of the laser beam, the angle of incident on the surface of the photocathode material is adjusted.

The photocathode assembly includes: a photocathode material, an anode, a photocathode material fixing frame and an anode fixing frame; wherein, the anode is a metal grid structure and is arranged on the anode fixing frame; the photocathode material is arranged on the photocathode material fixing frame, and the light The cathode material fixing frame is made of dielectric material; the photocathode material fixing frame and the anode fixing frame are respectively connected to the connection fixing frame inside the vacuum chamber through connectors, so that the photocathode assembly is installed in the vacuum chamber. The lateral size of the photocathode material needs to be smaller than that of the anode, and the distance between the surface of the photocathode material and the anode can be designed according to the requirements of the electric field. A cathode electrode and an anode electrode are installed in the power supply connection flange, and one end in the vacuum chamber is respectively connected to the photocathode material and the anode through a wire, the cathode electrode is connected to the power supply system at the end outside the vacuum chamber, and the anode electrode is in the vacuum chamber One end outside the room is grounded. After power supply, a uniform electric field with an intensity of megavolts per meter will be formed between the surface of the pre-measured photocathode material and the anode, which is used to longitudinally accelerate the photoelectrons excited by the incident laser on the surface of the photocathode material, making it bombard the photoelectrons In the imaging system, the longitudinal direction refers to the direction of the electric field; the transverse direction refers to the direction perpendicular to the electric field.

When the laser light is incident on the surface of the photocathode material, the generated photoelectrons are accelerated under the action of the electric field and do a parabolic motion. The present invention adopts the method of accelerating photoelectrons to make photoelectrons do parabolic motion, which has the following advantages: 1. The lateral spatial distribution range of photoelectrons is compressed, which is convenient for data reading; The physical quantity is simplified to a simple measurable physical quantity; 3. The photoelectron moving at high speed can effectively avoid the influence of magnetic field and stray electromagnetic field on the measurement data.

A laser incident flange is provided on the surface of the vacuum chamber, and a transparent material is installed to form an incident window. At the same time, a focusing mirror is installed in the vacuum chamber. The laser excitation system located outside the vacuum chamber emits a laser beam that enters the focus through the incident window. On the mirror, it is reflected to the surface of the photocathode material at the focal point, and the photocathode material is excited to generate photoelectrons. Continuously changing the incident position of the laser beam will continuously change the angle at which the laser beam is incident on the surface of the pre-measured photocathode material, thereby realizing continuous regulation of the angle at which the laser beam is incident on the surface of the photocathode material. The control of the excitation wavelength of the photocathode laser is realized by adjusting the output wavelength of the laser. A polarizer is introduced into the laser light path to realize the adjustment of the excitation polarization state of the photocathode laser.

The laser excitation system includes a laser, a reflector and a displacement device. The laser emits a laser beam to the reflector, and the reflector is installed on the displacement device. The displacement device drives the mirror to move, thereby driving the optical path of the laser beam to move, and realizing the continuous incident position of the laser beam. Variety.

The vacuum chamber is made of non-magnetic metal material, and the vacuum degree in the vacuum chamber is better than 5x10 ^-9 τ. The surface of the vacuum chamber is connected to the vacuum pumping system and the vacuum degree measuring system through the flange port, the inside of the vacuum chamber is evacuated, and the vacuum degree in the vacuum chamber is maintained and controlled through real-time and accurate vacuum degree measurement.

The flange mouth adopts a knife-edge flange, and the middle is sealed with a copper ring. This structure can realize ultra-high vacuum under high temperature conditions.

The optoelectronic imaging system includes a transparent observation window, fluorescent screen and image acquisition device; the observation window is installed on the surface of the vacuum chamber through the flange opening of the observation window; the fluorescent screen is installed on the inner side of the observation window through the mounting bracket; the image acquisition device is installed on the outside of the viewing window. The observation window is made of quartz glass; the fluorescent screen is made of yttrium aluminum garnet (Ce:YAG) single crystal fluorescent screen, which will emit light under the bombardment of photoelectrons, and is used to obtain images of the lateral distribution of photoelectrons. An image acquisition device is installed outside the vacuum chamber to record the image formed by photoelectron bombardment. Compared with the fluorescent screen of ordinary glass evaporated phosphor, the use of single crystal fluorescent screen has the following advantages: the brightness of the fluorescent screen is higher, which is conducive to the observation of imaging details; the surface will not absorb a lot of gas, which is conducive to the maintenance of ultra-high vacuum; Phosphor screen life is much longer than phosphor screens.

The data acquisition system is connected to the vacuum chamber through the data acquisition flange port on the surface of the vacuum chamber, including vacuum mechanical transmission rod, position adjustment frame, lead electrode, Faraday cup, ammeter and computer; among them, the data acquisition flange port is installed Vacuum mechanical transmission rod, one end of the vacuum mechanical transmission rod is located in the vacuum chamber, connected to the position adjustment frame, and a Faraday cup is installed on the position adjustment frame; the other end of the vacuum mechanical transmission rod is located outside the vacuum chamber, through the external operation of the vacuum chamber The vacuum mechanical transmission rod regulates the displacement of the position adjustment frame. The Faraday cup is a small metal cylinder, sealed at both ends, and a small hole is opened on one of the ends. When the photoelectron enters the small metal cylinder through the small hole, it will be completely absorbed by the small metal cylinder, which is used to test the size of the photoelectron beam. There is a lead electrode in the data acquisition flange, one end of the lead electrode is in the vacuum chamber, and is connected to the metal wire fixed at the end of the Faraday cup; the other end of the lead electrode is outside the vacuum chamber, connected to the ammeter outside the vacuum chamber, the ammeter Connected to a computer, the collected beam data can be recorded in real time. Outside the vacuum chamber, the position of the Faraday cup located inside the vacuum chamber can be regulated by the position adjustment knob of the vacuum mechanical transmission rod, so that the Faraday cup is located directly in front of the photocathode assembly, that is, directly in front of the anode of the photocathode assembly. Measurement of the total photoelectron emission beam current will be achieved.

An inspection window flange is set next to the data acquisition flange, and the inspection window is installed to observe and detect the installation position of the photocathode assembly, the position where the laser beam is incident on the focusing mirror and the surface of the photocathode material.

Further, on the surface of the vacuum chamber, a plurality of fixed laser incident flange ports are provided, distributed at regular intervals, and a transparent material is installed in each fixed laser incident flange port to form a window for introducing The laser emitted by the laser, by controlling the laser optical path, makes the laser incident on the surface of the photocathode material in the photocathode assembly from the transparent window on the fixed laser flange at different positions, and realizes different laser incident angles. The fixed laser entrance flange is used as a backup system for adjusting the laser incident angle. When using the laser incident window, the focusing mirror can be kept in place, and only half of the windows can be used at this time; if all the windows are used, the focusing mirror needs to be replaced. remove.

Another object of the present invention is to provide a method for evaluating the photoelectron emission performance of a photocathode material.

The evaluation method of photocathode material photoelectron emission performance of the present invention comprises the following steps:

1) Install the pre-measured photocathode material into the photocathode assembly through the photocathode material fixing frame, then enter the photocathode assembly into the vacuum chamber through the mechanical installation flange port, and install it on the internal connection fixing frame, and finally Connect and fix the mechanical installation flange port with the vacuum chamber;

2) Connect the power supply system and the external electrode of the vacuum chamber corresponding to the flange port of the power supply connection with a conductive connecting wire, provide the cathode voltage for the photocathode material in the photocathode assembly, and ground the anode, and use the conductive connecting wire to connect the vacuum chamber The surface of the chamber is grounded;

3) Start the vacuum chamber pumping system to evacuate the inside of the ultra-high vacuum chamber, and at the same time, measure the vacuum degree in the ultra-high vacuum chamber in real time through the vacuum degree measurement system;

4) When the vacuum degree of the vacuum chamber is better than 5×10 ^-9 τ, turn on the power supply system to supply power to the photocathode material, so that a uniform electric field is generated between the surface of the photocathode material and the anode, and the cathode voltage is slowly applied, and finally the electric field strength Reaching the order of megavolts per meter;

5) Turn on the laser excitation system to generate a laser beam, and properly adjust the optical path so that the laser beam is incident on the surface of the pre-measured photocathode material. At this time, the photocathode material generates photoelectron emission. The mesh of the metal grid structure, through the equipotential free field of the vacuum chamber, bombards the opposite fluorescent screen or the Faraday cup to form the horizontal distribution image of photoelectrons, that is, the lateral position on the fluorescent screen represents the horizontal position of photoelectrons emitted by the photocathode material. distribution, or measure the total photoelectron emission beam current;

6) By adjusting the incident position of the laser beam, change the position of the incident to the focusing mirror, thereby changing the incident angle, and by adjusting the wavelength and polarization state of the laser beam, use the image acquisition device to record the photoelectron lateral distribution image under different measurement conditions , use the Faraday cup to measure the total photoelectron emission beam, and obtain the photoelectron angular distribution data through the photoelectron lateral distribution image; then use the electric field parameters to deduce the photoelectron transverse momentum distribution data and thermal emittance data; and then use the total photoelectron emission beam parameters to deduce Photoelectron emission brightness data, thus, the total photoelectron emission beam current, photoelectron angular distribution, photoelectron transverse momentum distribution and deduced from the above parameters can be measured under different laser incident angles, different laser wavelengths, and different laser polarization state measurement conditions. Brightness and thermal emittance;

7) After the measurement of the photoelectron emission performance parameters of the photocathode material is completed, the cathode voltage is slowly reduced, and finally the power supply system that provides the cathode voltage to the photocathode material is turned off.

The invention is used for the rapid test of the photoelectron emission performance of the photocathode material. After assembling the measured photocathode material into the photocathode assembly, no secondary adjustment is required, and only one vacuum pumping system needs to be started until the ultra-high vacuum is reached in the vacuum chamber. After that, all the parameters of the photoelectron emission characteristics can be obtained by in-situ measurement, and the test content is complete, the cycle is short, and the efficiency is high.

Advantages of the present invention:

In the present invention, a focusing mirror is arranged inside the vacuum chamber, and the focus of the focusing mirror is located on the surface of the photocathode material. By adjusting the incident position of the laser beam, the continuous change of the incident angle is realized, and the wavelength and polarization state of the laser can be changed. Under different laser incident angles, different laser wavelengths, and different laser polarization state measurement conditions, the total photoelectron emission beam current, photoelectron angular distribution, photoelectron transverse momentum distribution, and brightness and thermal emittance deduced from the above parameters can be measured. The method of the present invention saves a series of cumbersome steps of frequently adjusting the laser light path outside the vacuum chamber in the discrete angle incident laser excitation mode, only needs to change the position of the laser beam to change the incident angle, and overcomes the problems caused by the discrete angle incident Angle discontinuity problem.

Description of drawings

Fig. 1 is the structural representation of photocathode material photoelectron emission performance evaluation device of the present invention, and wherein, (a) is a side view, and (b) is the sectional view along A-A ' line in (a);

Fig. 2 is the partially enlarged sectional view of the photocathode assembly and the focusing mirror of the photocathode material photoelectron emission performance evaluation device of the present invention;

3 is a schematic diagram of the relationship between the incident position and incident angle of the laser beam of the photocathode material photoelectron emission performance evaluation device of the present invention;

Fig. 4 is a schematic diagram of the power supply connection flange port of the photocathode material photoelectron emission performance evaluation device of the present invention;

5 is a partial cross-sectional view of the data acquisition system of the photocathode material photoelectron emission performance evaluation device of the present invention.

detailed description

The present invention will be further described through the embodiments below in conjunction with the accompanying drawings.

As shown in Figure 1, the photocathode material photoelectron emission performance evaluation device of the present embodiment comprises: vacuum chamber 1, vacuum pumping system 10, vacuum degree measuring system, photocathode assembly 2, power supply system, photoelectron imaging system 3, data Acquisition system 8, laser excitation system 4 and focusing mirror 5, focusing mirror 5 adopts a rotating parabolic reflector; wherein, the surface of vacuum chamber 1 is connected to vacuum pumping system 10 and vacuum degree measuring system through flange ports respectively; The surface of the vacuum chamber 1 is respectively provided with a mechanical installation flange port 21 and a power supply connection flange port 71. The photocathode assembly 2 enters the vacuum chamber 1 through the mechanical installation flange port 21, and is installed on the connection fixing frame 26 inside it. Above, an anode electrode 73 and a cathode electrode 72 are arranged in the power supply connection flange port 71, one end of the electrode is in the vacuum chamber 1, connected to the photocathode assembly 2, and the other end of the electrode is outside the vacuum chamber 1, and connected to the power supply The system is connected; the surface of the vacuum chamber 1 is opposite to the photocathode assembly 2, and the photoelectron imaging system 3 is installed through the observation window flange opening 31; The surface of the cathode material 22 is parallel to the axis of rotational symmetry of the rotating parabolic mirror, and the focus of the rotating parabolic mirror is located on the surface of the photocathode material 22; the surface of the vacuum chamber 1 is provided with a laser incident flange port 41, and a quartz glass The incident window is formed, and the laser excitation system 4 located outside the vacuum chamber emits a laser beam through the incident window parallel to the surface of the photocathode material 22 and is incident on the rotating parabolic mirror, and is reflected to the surface of the photocathode material 22 at the focal point; by changing the laser The distance between the beam and the surface of the photocathode material changes the angle of incidence on the surface of the photocathode material; the data acquisition system 8 is set on the top of the vacuum chamber 1 , and an inspection window flange 91 is set beside it.

The optoelectronic imaging system comprises a transparent observation window 32, a fluorescent screen 33 and an image acquisition device; the observation window 32 is installed on the surface of the vacuum chamber through the observation window flange opening 31; the fluorescent screen 33 is installed on the inside of the observation window 32 by a mounting frame; the image acquisition The device is installed on the outside of the observation window through the mounting bracket.

Quartz glass is installed in the laser incident flange port 41 to form an incident window, and the diameter of the incident window is larger than the size of the rotating parabolic reflector perpendicular to the axis of rotational symmetry.

In this embodiment, the focusing mirror 5 adopts a rotating parabolic reflector, the focus of which is located on the surface of the photocathode material, the quasi-focal length is 50mm, and the mirror projection length in the direction of the axis of rotational symmetry is 22.75mm, perpendicular to the axis of rotational symmetry The projection length of the plane (that is, the surface of the photocathode material or the surface of the anode in the photocathode assembly) is 43mm, from the intersection line of the positive focal plane and the rotating paraboloid inward (the direction along the rotational symmetry axis of the paraboloid pointing to the apex is defined as The mirror surface between 2mm in the inner direction) is partially cut off to avoid blocking photoelectron emission. On the surface of the vacuum chamber 1, eight fixed laser incident flange ports 61 are provided, distributed at regular intervals, with the center of the photocathode material as the center, and the interval angle between two adjacent fixed laser incident flange ports is 18. degrees or 15 degrees. Quartz glass is installed in each fixed laser incident flange to form a laser incident fixed window, which is used to introduce the laser emitted by the laser outside the vacuum chamber. The laser is incident on the photocathode material from different laser incident fixed windows. Different angles to the surface of the photocathode material realize discrete different laser incident angles.

As shown in Figure 2, the photocathode assembly 2 includes: a photocathode material 22, an anode 23, a photocathode material fixing frame 24 and an anode fixing frame 25; wherein, the anode 23 is a metal grid structure and is arranged on the anode fixing frame 25; The photocathode material 22 is arranged on the photocathode material fixing frame 24, and the photocathode material fixing frame 24 adopts dielectric material; 26, so that the photocathode assembly is installed in the vacuum chamber 1. The geometrical position between the photocathode material and the anode is determined with a distance of 5 mm, so that the incident laser beam parallel to the axis of rotational symmetry is incident on the surface of the photocathode material 22 and produces photoelectrons that bombard the optoelectronic imaging system 3 . One end of the photocathode material 22 and the anode 23 inside the vacuum chamber are respectively connected to the cathode electrode 72 and the anode electrode 73 in the power supply connection flange port 71 through wires, and the cathode electrode 72 is connected to the power supply system at one end outside the vacuum chamber. The anode electrode 73 is grounded at one end outside the vacuum chamber. After power supply, a uniform electric field with an intensity of megavolts per meter will be formed between the surface of the pre-measured photocathode material and the anode, which is used to accelerate photoelectrons vertically and compress the lateral distribution range of photoelectrons.

As shown in FIG. 3 , the photocathode material 22 is parallel to the rotational symmetry axis of the rotating parabolic mirror, and the focal point is located on the surface of the photocathode material 22 . The laser excitation system 4 includes a laser 42, a reflector 43 and a displacement device 44. The laser 42 sends a laser beam to the reflector 43, and after reflection, it is incident on the rotating parabolic reflector. The reflector 43 is installed on the displacement device 44 and is driven by the displacement device 44. The mirror 43 moves along a direction perpendicular to the axis of rotational symmetry, thereby driving the optical path of the laser beam to move, and realizing the continuous change of the distance L between the laser beam and the surface of the photocathode material 22 . Continuously changing the distance L between the laser beam and the surface of the photocathode material 22 will continuously change the incident angle θ of the beam incident on the surface of the photocathode material, thereby realizing continuous adjustment of the angle of the laser beam incident on the surface of the photocathode material.

As shown in Figure 4, the power supply connection flange port 71 adopts a knife-edge flange, and the middle is sealed with a copper ring, and the cathode electrode 72 and the anode electrode 73 are sealed by ceramics 74, and one end of the cathode electrode 72 and the anode electrode 73 is in the vacuum chamber, respectively. Connect to the photocathode material 22 and the anode 23 of the photocathode assembly, the other end is outside the vacuum chamber, the other end of the cathode electrode 72 is connected to the power supply system, in order to provide the cathode voltage for the photocathode material 22, the other end of the anode electrode 73 is connected to the ground connect.

As shown in Figure 5, the data acquisition system 8 is connected to the vacuum chamber through the data acquisition flange port 81 on the surface of the vacuum chamber, including a vacuum mechanical transmission rod 82, a position adjustment frame 83, lead electrodes, a Faraday cup 84, an ammeter and computer. Install the vacuum mechanical transmission rod 82 through the data acquisition flange port 81, one end of the vacuum mechanical transmission rod 82 is located in the vacuum chamber 1, connect the position adjustment frame 83, and install the Faraday cup 84 in the position adjustment; the vacuum mechanical transmission rod 82 The other end is located outside the vacuum chamber 1 , and the displacement of the position adjusting frame 83 is regulated by operating the vacuum mechanical transmission rod outside the vacuum chamber 1 . The Faraday cup 84 is a small metal tube, both ends are sealed respectively, and a small hole is opened on one of the ends. When the photoelectron enters the small metal tube through the small hole, it will be completely absorbed by the small metal tube, and is used to test the photoelectron beam current. There is a lead electrode in the data acquisition flange, one end of the lead electrode is in the vacuum chamber, and is connected to the metal wire fixed at the end of the Faraday cup; the other end of the lead electrode is outside the vacuum chamber, connected to the ammeter outside the vacuum chamber, the ammeter Connected to a computer, the collected beam data can be recorded in real time. Outside the vacuum chamber, the vacuum thread 85 of the position adjustment knob of the vacuum mechanical transmission rod pushes the vacuum mechanical transmission rod to realize the mechanical transmission inside and outside the vacuum chamber, so that the position of the Faraday cup located inside the vacuum chamber can be regulated, so that Faraday The cup is located directly in front of the photocathode assembly, that is, directly in front of the anode of the photocathode assembly, at this time the measurement of the total photoelectron emission beam will be realized. On the position adjustment frame 83, a position adjustment rod 86 is installed. Before installing the photocathode assembly and starting the vacuum pumping system, adjust the position adjustment rod 86 to realize the alignment of the Faraday cup, so that the position of the small hole of the Faraday cup is in the connection fixing frame 26 on the mechanical central axis.

Finally, it should be noted that the purpose of publishing the implementation is to help further understand the present invention, but those skilled in the art can understand that various replacements and modifications can be made without departing from the spirit and scope of the present invention and the appended claims. It is possible. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the protection scope of the present invention is subject to the scope defined in the claims.

Claims (8)

1. A photocathode material photoelectron emission performance evaluation device, characterized in that, the evaluation device includes: vacuum chamber, vacuum pumping system, vacuum degree measurement system, photocathode assembly, power supply system, photoelectron imaging system, data acquisition system, laser excitation system, and focusing mirror; wherein, the surface of the vacuum chamber is connected to the vacuum pumping system and the vacuum degree measurement system through flange ports; the mechanical installation flange port and the power supply connection method are respectively arranged on the surface of the vacuum chamber The blue port, the photocathode assembly enters the vacuum chamber through the mechanical installation flange port, and is installed on the internal connection fixture. There are multiple electrodes in the power supply connection flange port, and one end of the electrode is in the vacuum chamber, connected to the The photocathode assembly, the other end of the electrode is outside the vacuum chamber and connected to the power supply system; the surface of the vacuum chamber is opposite to the photocathode assembly, and the optoelectronic imaging system is installed through the flange opening of the observation window; the focusing plane is set in the vacuum chamber The focal point of the focusing mirror is located on the surface of the photocathode material in the photocathode assembly; a laser incident flange is provided on the surface of the vacuum chamber, and a transparent material is installed to form an incident window, and the laser excitation system located outside the vacuum chamber emits The laser beam is incident on the focusing mirror through the incident window for reflection, and converges to the focal point after reflection; by changing the incident position of the laser beam, the angle of incident on the surface of the photocathode material is adjusted. 2. The evaluation device according to claim 1, wherein the photocathode assembly comprises: a photocathode material, an anode, a photocathode material fixing frame and an anode fixing frame; wherein, the anode is a metal grid structure and is arranged on On the anode fixing frame; the photocathode material is arranged on the photocathode material fixing frame, and the photocathode material fixing frame is made of a dielectric material; the photocathode material fixing frame and the anode fixing frame are respectively connected to the connection fixing frame inside the vacuum chamber through connectors , so that the photocathode assembly is installed in the vacuum chamber. 3. The evaluation device according to claim 1, wherein the laser excitation system includes a laser, a reflector and a displacement device, the laser emits a laser beam to the reflector, and the reflector is installed on the displacement device and driven by the displacement device The mirror moves, thereby driving the optical path of the laser beam to move, and realizing the continuous change of the incident position of the laser beam. 4. evaluation device as claimed in claim 1, is characterized in that, described optoelectronic imaging system comprises transparent observation window, fluorescent screen and image acquisition device; Observation window is installed on the surface of vacuum chamber by observation window flange mouth; Fluorescent screen Installed on the inside of the observation window through the installation frame; the image acquisition device is installed on the outside of the observation window through the installation frame. 5. The evaluation device according to claim 1, wherein the data acquisition system is connected to the vacuum chamber through a data acquisition flange on the surface of the vacuum chamber, including a vacuum mechanical transmission rod, a position adjustment frame, a lead wire Electrode, Faraday cup, ammeter and computer; among them, the vacuum mechanical transmission rod is installed through the data acquisition flange, one end of the vacuum mechanical transmission rod is located in the vacuum chamber, connected to the position adjustment frame, and the Faraday cup is installed in the position adjustment plus; the vacuum mechanical The other end of the transmission rod is located outside the vacuum chamber, and the displacement of the position adjustment frame is regulated by operating the vacuum mechanical transmission rod outside the vacuum chamber; a lead electrode is arranged in the mouth of the data acquisition flange, and one end of the lead electrode is inside the vacuum chamber. The metal wire fixed at the end of the Faraday cup is connected; the other end of the lead electrode is outside the vacuum chamber, connected to the ammeter outside the vacuum chamber, and the ammeter is connected to the computer. 6. The evaluation device according to claim 1, further comprising a plurality of fixed laser incident flange ports, distributed at regular intervals on the surface of the vacuum chamber, installed in each fixed laser incident flange port There is a transparent material forming the window. 7. The evaluation device according to claim 1, wherein the focusing mirror adopts a rotating parabolic mirror, and the surface of the photocathode material in the photocathode assembly is parallel to the axis of rotational symmetry of the rotating parabolic mirror, located in a vacuum The laser excitation system outside the chamber emits a laser beam that is incident on the rotating parabolic mirror through the incident window parallel to the surface of the photocathode material, and is reflected to the surface of the photocathode material at the focal point. 8. an evaluation method of photocathode material photoelectron emission performance, it is characterized in that, described evaluation method comprises the following steps: 1) Install the pre-measured photocathode material into the photocathode assembly through the photocathode material fixing frame, then enter the photocathode assembly into the vacuum chamber through the mechanical installation flange port, and install it on the internal connection fixing frame, and finally Connect and fix the mechanical installation flange port with the vacuum chamber; 2) Connect the power supply system and the external electrode of the vacuum chamber corresponding to the flange port of the power supply connection with a conductive connecting wire, provide the cathode voltage for the photocathode material in the photocathode assembly, and ground the anode, and use the conductive connecting wire to connect the vacuum chamber The surface of the chamber is grounded; 3) Start the vacuum chamber pumping system to evacuate the inside of the ultra-high vacuum chamber, and at the same time, measure the vacuum degree in the ultra-high vacuum chamber in real time through the vacuum degree measurement system; 4) When the vacuum degree of the vacuum chamber is better than 5×10 ^-9 τ, turn on the power supply system to supply power to the photocathode material, so that a uniform electric field is generated between the surface of the photocathode material and the anode, and the cathode voltage is slowly applied, and finally the electric field strength Reaching the order of megavolts per meter; 5) Turn on the laser excitation system to generate a laser beam, and properly adjust the optical path so that the laser beam is incident on the surface of the pre-measured photocathode material. At this time, the photocathode material generates photoelectron emission. The mesh of the metal grid structure, through the equipotential free field of the vacuum chamber, bombards the opposite fluorescent screen or the Faraday cup to form the horizontal distribution image of photoelectrons, that is, the lateral position on the fluorescent screen represents the horizontal position of photoelectrons emitted by the photocathode material. distribution, or measure the total photoelectron emission beam current; 6) By adjusting the incident position of the laser beam, change the position of the incident to the focusing mirror, thereby changing the incident angle, and by adjusting the wavelength and polarization state of the laser beam, use the image acquisition device to record the photoelectron lateral distribution image under different measurement conditions , use the Faraday cup to measure the total photoelectron emission beam, and obtain the photoelectron angular distribution data through the photoelectron lateral distribution image; then use the electric field parameters to deduce the photoelectron transverse momentum distribution data and thermal emittance data; and then use the total photoelectron emission beam parameters to deduce Photoelectron emission brightness data, thus, the total photoelectron emission beam current, photoelectron angular distribution, photoelectron transverse momentum distribution and deduced from the above parameters can be measured under different laser incident angles, different laser wavelengths, and different laser polarization state measurement conditions. Brightness and thermal emittance; 7) After the measurement of the photoelectron emission performance parameters of the photocathode material is completed, the cathode voltage is slowly reduced, and finally the power supply system that provides the cathode voltage to the photocathode material is turned off.