A magneto-optical Kerr effect-based measurement system and method

Abstract

The application discloses a kind of measurement system and method based on magneto-optical Kerr effect, belong to magnetic material measurement and imaging technical field, including three-dimensional displacement platform, optical path unit, electromagnetic unit and software control unit, three-dimensional displacement platform is in the magnetic field provided by electromagnetic unit;Optical path unit includes frame body and the laser generating device, focusing control device, differential signal measuring device and imaging device arranged in frame body interior;Linearly polarized light provided by laser generating device is focused to the sample surface fixed on three-dimensional displacement platform by focusing control device, sample surface reflects and returns focusing control device by reflected light, beam splitting obtains first reflected light and second reflected light, and the focusing control device can move up and down;Differential signal measuring device receives second reflected light to obtain electric signal, and transmit to software control unit;Imaging device receives first reflected light to realize the imaging of sample;Software control unit draws hysteresis loop according to the magnetic field intensity of the magnetic field and electric signal.

Description

Technical Field

[0001] This invention relates to a measurement system and method based on the magneto-optical Kerr effect, belonging to the field of magnetic material measurement and imaging technology. Background Technology

[0002] With the rapid development of information, medical, energy, and defense technologies, various components are constantly evolving towards intelligence, high integration, high-density storage, and ultra-fast transmission, leading to an increasing demand for high-performance magneto-optical devices. As magneto-optical devices develop, the requirements for magneto-optical material performance become increasingly stringent, making it increasingly urgent to improve the performance of existing magneto-optical materials and explore the development of new ones. Therefore, advanced measurement and imaging systems are needed to study the performance of magnetic materials. Magneto-optical characterization technology based on the magneto-optical Kerr effect achieves non-destructive testing of magnetic material performance by measuring the magneto-optical response generated by the interaction between light and material, and it has advantages such as high measurement accuracy, high sensitivity, and high temporal and spatial resolution. Therefore, magneto-optical Kerr effect characterization technology is an advanced method for characterizing the performance of magneto-optical materials, providing reliable theoretical and experimental basis for the research of magneto-optical material devices. However, the resolution of general magneto-optical Kerr effect measurement systems is at the millimeter level, and they can only measure some continuous-structure samples, which no longer meets modern needs.

[0003] Furthermore, hysteresis loops are an important characteristic of ferromagnetic and subferromagnetic materials. When the magnetic field strength changes periodically, the hysteresis phenomenon of strongly magnetic materials will form a closed magnetization curve, which indicates the relationship between the magnetization intensity M or magnetic induction intensity B and the magnetic field strength H during the repeated magnetization process of strongly magnetic materials. Different ferromagnetic materials have hysteresis loops of different shapes, and different shapes of hysteresis loops have different applications. Summary of the Invention

[0004] The purpose of this invention is to provide a measurement system and method based on the magneto-optical Kerr effect, which enables switching between two measurement modes, LMOKE and PMOKE, and allows for accurate measurement of the magneto-optical Kerr angle values ​​of the poloidal and longitudinal Kerr effects. This enables the study of the magnetic properties of materials in the micrometer region without causing any damage to the sample, greatly improving the resolution of the measurement system and reducing common-mode noise in the input optical signal.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] In a first aspect, the present invention provides a measurement system based on the magneto-optical Kerr effect, comprising a three-dimensional displacement stage, an optical path unit, an electromagnetic unit, and a software control unit, wherein the three-dimensional displacement stage is situated in a magnetic field provided by the electromagnetic unit;

[0007] The optical path unit includes a frame and a laser generator, a focusing control device, a differential signal measuring device, and an imaging device disposed inside the frame;

[0008] The laser generator provides linearly polarized light, which is focused onto the sample surface fixed on a three-dimensional displacement stage by a focusing control device. The sample surface reflects reflected light, which returns to the focusing control device and is split into a first reflected light and a second reflected light. The focusing control device can move up and down.

[0009] The differential signal measuring device receives the second reflected light to obtain an electrical signal and transmits it to the software control unit;

[0010] The imaging device receives the first reflected light to achieve image formation of the sample;

[0011] The software control unit draws the hysteresis loop based on the magnetic field strength and electrical signal of the magnetic field.

[0012] In conjunction with the first aspect, the laser generating device further includes a laser source, a first half-wave plate, and a first broadband polarization beam-splitting cubic prism. The laser source is used to provide laser light, and the first half-wave plate and the first broadband polarization beam-splitting cubic prism are sequentially arranged on the path of the laser beam toward the sample to polarize the laser light to obtain horizontally linearly polarized light.

[0013] In conjunction with the first aspect, the focusing control device further includes a second non-wideband polarizing beam-splitting cubic prism, an objective lens, and a one-dimensional displacement stage. The one-dimensional displacement stage is fixed at the bottom of the frame. The second non-wideband polarizing beam-splitting cubic prism is fixed on the one-dimensional displacement stage via its base. The objective lens is fixedly connected to the side of the second non-wideband polarizing beam-splitting cubic prism facing the three-dimensional displacement stage. The focusing control device can move up and down via the one-dimensional displacement stage, thereby realizing the up and down movement of the objective lens.

[0014] In conjunction with the first aspect, the differential signal measurement device further includes a second half-wave plate, a second broadband polarization beam splitter cube prism, a balanced photodetector, a second reflector, and a digital multimeter, wherein the balanced photodetector is provided with two windows;

[0015] The second half-wave plate and the second broadband polarization beam-splitting cubic prism are arranged in parallel on the path of the second reflected light. After passing through the second half-wave plate and the second broadband polarization beam-splitting cubic prism, the second reflected light is split into two light signals. One light signal directly enters one window of the balanced photodetector, and the other light signal enters the other window of the balanced photodetector after being refracted by the second reflector. This enables the differential signal measurement device to perform differential amplification processing on the two light signals and convert them into electrical signals, which are voltages.

[0016] The digital multimeter is connected to the balanced photodetector and the software control unit to read the voltage value output by the balanced photodetector and transmit it to the software control unit.

[0017] In conjunction with the first aspect, the differential signal measurement device further includes an aperture disposed between the second half-wave plate and the second broadband polarizing beam splitter prism for filtering out noise light.

[0018] In conjunction with the first aspect, the imaging device further includes a first non-wideband polarization beam splitting cubic prism, an LED lamp, and a CCD camera. The first non-wideband polarization beam splitting cubic prism is disposed in the path of the first reflected light. The light provided by the LED lamp illuminates the first non-wideband polarization beam splitting cubic prism and adds the first reflected light to achieve illumination of the first reflected light.

[0019] The first reflected light is split by the first broadband polarization beam-splitting cubic prism and then enters the window of the CCD camera to achieve image imaging of the sample.

[0020] In conjunction with the first aspect, the electromagnetic unit further includes a current source, a one-dimensional electromagnet, and a gaussmeter;

[0021] The current source is electrically connected to the one-dimensional electromagnet to provide current to the one-dimensional electromagnet, which is used to apply a magnetic field to the sample.

[0022] The gaussmeter is connected to the software control unit and is used to read the magnetic field strength and transmit it to the software control unit.

[0023] In a second aspect, the present invention also provides a measurement method based on the system described in any one of the first aspects, comprising:

[0024] The sample is fixed on the three-dimensional displacement stage. The three-dimensional displacement stage is adjusted so that the sample is at the focal point of the objective lens in the focusing control device. The current source in the electromagnetic unit is turned on so that the one-dimensional electromagnet applies a magnetic field to the sample. The magnetic field strength is measured by a gaussmeter.

[0025] The laser generator is turned on to obtain horizontal linearly polarized light. The linearly polarized light is focused onto the sample surface fixed on the three-dimensional displacement stage by the focusing control device. The sample surface reflects the reflected light, which returns to the focusing control device and is split into the first reflected light and the second reflected light.

[0026] An electrical signal is obtained by receiving the second reflected light through a differential signal measuring device;

[0027] The sample is imaged by receiving the first reflected light through the imaging device, and the hysteresis loop is drawn based on the magnetic field strength and electrical signal.

[0028] In conjunction with the second aspect, the electrical signal is further defined as the voltage value output by the balanced photodetector in the differential signal measuring device.

[0029] In conjunction with the second aspect, further, image formation of the sample is achieved by receiving the first reflected light through an imaging device, including:

[0030] The first reflected light is refracted into the window of the CCD camera through the first broadband polarizing beam-splitting cubic prism, thus achieving the imaging of the sample.

[0031] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0032] This invention provides a measurement system and method based on the magneto-optical Kerr effect. A linearly polarized light is provided by a laser generator, and then focused onto a sample surface fixed on a three-dimensional displacement stage by a focusing control device. The focusing control device can move vertically, and by adjusting the height of the objective lens within it, the angle of the laser incident on the sample can be adjusted, enabling switching between LMOKE and PMOKE measurement modes. This allows for precise measurement of the magneto-optical Kerr angle values ​​for both the poloidal and longitudinal Kerr effects, making this invention an ideal measurement system and method for studying the magnetic properties of magnetic thin films. It can be widely applied in magnetic nanotechnology, magnetic thin films, and other magnetic fields. The reflected light returns to the focusing control device and is then split into beams. The imaging device receives the first reflected light to image the sample, and the second reflected light enters the differential signal measurement device to obtain an electrical signal. Based on the magnetic field strength and the electrical signal, a hysteresis loop is plotted. This invention has good locality. Before the laser enters the magnetic field environment, the laser is focused by the objective lens, reducing its spot size to the micrometer level. This enables the study of the magnetic properties of materials in the micrometer region without causing any damage to the sample, greatly improving the resolution of the measurement system. Compared with the traditional MOKE measurement method, the differential signal measurement device in this invention can effectively reduce common-mode noise in the input optical signal, which is beneficial for suppressing noise and extracting weak signals. It has the characteristics of high sensitivity and noise suppression. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a measurement system based on the magneto-optical Kerr effect provided in an embodiment of the present invention;

[0034] Figure 2 This is a graph showing the voltage variation with the rotation angle of the electric rotary table, provided in an embodiment of the present invention.

[0035] Figure 3 This is a graph showing the variation of the relative voltage uncertainty with the rotation angle of the electric rotary table, provided in an embodiment of the present invention.

[0036] Figure 4 This is a voltage variation graph with the number of voltage recording points provided in an embodiment of the present invention;

[0037] Figure 5 This is a graph showing the change of voltage relative uncertainty with the number of voltage recording points provided in an embodiment of the present invention.

[0038] In the diagram, PBS1: First broadband polarization beam splitter cube prism; PBS2: Second broadband polarization beam splitter cube prism; BS1: First non-broadband polarization beam splitter cube prism; BS2: Second non-broadband polarization beam splitter cube prism; CCD: CCD camera; LED: LED light; PDB: Balanced photodetector. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0040] Example 1

[0041] The present invention provides a measurement system based on the magneto-optical Kerr effect, comprising a three-dimensional displacement stage, an optical path unit, an electromagnetic unit, and a software control unit, wherein the three-dimensional displacement stage is located in a magnetic field provided by the electromagnetic unit.

[0042] The optical path unit includes a frame and a laser generator, a focusing control device, a differential signal measuring device, and an imaging device disposed inside the frame.

[0043] like Figure 1 As shown, the laser generating device includes a laser source, two first reflecting mirrors, a first half-wave plate, and a first broadband polarizing beam-splitting cubic prism PBS1. The laser source provides laser light. The first reflecting mirror is set in the direction of laser emission. After the laser light is refracted by the first first reflecting mirror, the second first reflecting mirror is set in the emission path of the first refraction of the laser light. The laser light is refracted by the second first reflecting mirror so that the laser light enters the first half-wave plate perpendicularly. The first half-wave plate and the first broadband polarizing beam-splitting cubic prism PBS1 are sequentially set in the path of the laser light towards the sample to polarize the laser light and obtain horizontally linearly polarized light.

[0044] In this embodiment, the laser source is a laser (Changchun New Industries Optoelectronics, MLL-III-532-300mW, polarization ratio greater than 100:1, power continuously adjustable), and the wavelength of the generated laser is 532nm.

[0045] In this embodiment, the reflector is manufactured by LBTEK (Lubang Technology), with an operating wavelength of 400nm-750nm; the first half-wave plate is manufactured by LBTEK (Lubang Technology), with an operating wavelength of 405nm-1550nm.

[0046] In this embodiment, the first broadband polarization beam-splitting cubic prism PBS1 is a broadband polarization beam-splitting cubic prism with a working wavelength of 420nm-680nm and an extinction ratio of >1000:1.

[0047] After passing through the first half-wave plate, the laser beam is separated into two beams of transmitted p-polarized light and refracted s-polarized light by the first broadband polarization beam-splitting cubic prism PBS1, with perpendicular polarization directions. Based on the definition of a plane containing input and reflected beams, the beam whose polarization vector is parallel to this plane is called p-polarized light, while the beam whose polarization vector is perpendicular to this plane is called s-polarized light. In this invention, only the transmitted p-polarized light needs to be used to enter the subsequent optical path, while the refracted s-polarized light is removed by refraction through the first broadband polarization beam-splitting cubic prism PBS1.

[0048] like Figure 1 As shown, the focusing control device includes a second non-wideband polarizing beam-splitting cubic prism BS2, an objective lens, and a one-dimensional displacement stage. The one-dimensional displacement stage is fixed to the bottom of the frame. The second non-wideband polarizing beam-splitting cubic prism BS2 is fixed to the one-dimensional displacement stage via its base. The objective lens is fixedly connected to the side of the second non-wideband polarizing beam-splitting cubic prism BS2 facing the three-dimensional displacement stage. The projected p-polarized light is focused by the objective lens after passing through the second non-wideband polarizing beam-splitting cubic prism BS2. This improves the resolution of the system and, through lens refraction, generates an incident angle for LMOKE measurement.

[0049] In this embodiment, the objective lens is a 20x objective lens (Mitutoyo M Plan Apo series, Japan).

[0050] The one-dimensional displacement stage can move the second non-wideband polarizing beam splitter cubic prism BS2 and the objective lens fixed on it up and down, thereby realizing two measurement modes: LMOKE (longitudinal magneto-optical Kerr effect) and PMOKE (polar magneto-optical Kerr effect). The main difference between the two modes lies in the incident surface and the direction of the magnetic field. Therefore, the two modes can be switched by adjusting the incident angle and the sample direction.

[0051] When using the LMOKE measurement mode, the sample needs to be fixed on a three-dimensional displacement stage. The sample is then adjusted to the focal point of the objective lens using the three-dimensional displacement stage. The incoming light must enter from the edge of the objective lens and be refracted by the objective lens before entering the magnetic field.

[0052] When using PMOKE measurement mode, the sample needs to be fixed on a three-dimensional displacement stage. The sample is then adjusted to the focal point of the objective lens using the three-dimensional displacement stage. The incoming light must enter from the center of the objective lens and be refracted by the objective lens before entering the magnetic field. By changing the direction of the sample, the magnetic field magnetization intensity is made perpendicular to the surface of the medium.

[0053] After the light is reflected from the sample surface, it becomes reflected light. The reflected light is then split into first reflected light and second reflected light by the second non-wideband polarization beam splitter prism BS2 in the focusing control device.

[0054] like Figure 1 As shown, the differential signal measurement device includes a second half-wave plate, an aperture, a second broadband polarization beam splitter cubic prism PBS2, a balanced photodetector PDB, a second reflector, and a digital multimeter. The balanced photodetector PDB has two windows, and the aperture is used to filter out noise light.

[0055] The second half-wave plate and the second broadband polarization beam-splitting cubic prism PBS2 are arranged in parallel on the path of the second reflected light. After passing through the second half-wave plate and the second broadband polarization beam-splitting cubic prism PBS2, the second reflected light is split into two light signals. One light signal directly enters one window of the balanced photodetector PDB, and the other light signal enters the other window of the balanced photodetector PDB after being refracted by the second reflector. In order to ensure signal collection, the laser spot is controlled to hit the exact center of the window collection area in this embodiment. The balanced photodetector PDB performs differential amplification on the two light signals and converts them into electrical signals, which are voltages.

[0056] The digital multimeter is connected to the balanced photodetector PDB and the software control unit to read the voltage value output by the balanced photodetector PDB and transmit it to the software control unit.

[0057] In this embodiment, the balanced photodetector PDB is manufactured by Thorlabs, model PDB210A, with an operating wavelength of 320 nm-1060 nm; the digital multimeter is manufactured by Keithley, model DMM7510.

[0058] like Figure 1 As shown, the imaging device includes a first non-wideband polarization beam splitter cubic prism BS1, an LED lamp, and a CCD camera. The first non-wideband polarization beam splitter cubic prism BS1 is positioned in the path of the first reflected light. The light provided by the LED lamp illuminates the first non-wideband polarization beam splitter cubic prism BS1 and adds the first reflected light to achieve illumination of the first reflected light.

[0059] The first reflected light is split by the first broadband polarization beam splitter PBS1 and enters the window of the CCD camera to achieve image imaging of the sample.

[0060] In this embodiment, sample control is achieved through a three-dimensional displacement stage (Zhuoli Hanguang, PSM25A-65C, 25 mm stroke) and the angle of the sample rod. First, the thin-film sample is fixed on an aluminum sample rod, which is then mounted on the fixed stage of the three-dimensional displacement stage via a standard Ø12.7 mm rod holder (Lubang Technology, PH-xxB series). The standard Ø12.7 mm rod holder extends completely to the bottom, meeting the minimum beam height requirement, and can hold the standard Ø12.7 mm rod. The groove on the inner wall of the holder fits tightly with the rod, preventing the rod from sliding or rolling and improving the stability of the system. The sample rod can rotate 360 ​​degrees within the rod holder to adjust the sample angle, and simultaneously, in conjunction with the three-dimensional displacement stage, the thin-film sample is moved to the area between the magnetic poles, which is also the focal point of the objective lens.

[0061] The electromagnetic unit includes a current source, a one-dimensional electromagnet, and a gaussmeter; the current source and the one-dimensional electromagnet are electrically connected to provide current to the one-dimensional electromagnet, which is used to apply a magnetic field to the sample; the gaussmeter is connected to the software control unit to read the magnetic field strength and transmit it to the software control unit.

[0062] In this embodiment, the imaging resolution of the CCD camera is measured using a calibration ruler, wherein the minimum interval of the calibration ruler is 10 μm.

[0063] The resolution of the system measurement is determined by the spot size of the incident laser. The resolution of a typical magneto-optical Kerr effect measurement system is at the millimeter level, and it can only measure some samples with continuous structures. The measurement system provided in this embodiment of the invention focuses the laser through an objective lens before the laser enters the magnetic field environment, reducing its spot size to the micrometer level, which greatly improves the resolution of the measurement system.

[0064] A half-wave plate (wavelength 523nm) is placed in the reflected light path and fixed on an electric rotary stage (Zhuoli Hanguang, TBR60L). The step resolution of the electric rotary stage is 0.00125 deg, or 1.25 mdeg. The corresponding polarization plane of the linearly polarized light rotates by 2.5 mdeg. Therefore, the resolution of the polarization angle or the minimum measurable polarization angle is 2.5 mdeg * measurement uncertainty. The measurement uncertainty is defined as the deviation of the voltage measurement value from the expected voltage.

[0065] like Figure 2 As shown in the figure, this embodiment of the invention provides a graph of voltage variation with the rotation angle of the electric rotary table. The straight line in the graph is the result of linear fitting, and the relative error is as follows: Figure 3 As shown.

[0066] like Figure 3As shown in the figure, the embodiment of the present invention provides a graph of the relative voltage uncertainty as a function of the rotation angle of the electric rotary table. The relative voltage uncertainty is the output signal voltage minus the linear expectation value, and then divided by the output signal voltage. It is within ±3%, so the minimum measurable polarization angle is 2.5mdeg*3%=0.075mdeg. However, this uncertainty does not exclude the uncertainty of the angle rotation, which can be measured by fixing the rotation angle of the half-wave plate.

[0067] With a fixed half-wave plate deflection angle, the voltage uncertainty measurement results are as follows:

[0068] like Figure 4 As shown in the figure, the embodiment of the present invention provides a voltage variation graph with the number of voltage recording points. A series of voltage steps can be seen, each step corresponding to a half-wave plate deflection angle rotation of 1.25 mdeg (optical polarization plane rotation of 2.5 mdeg); the voltage relative uncertainty is defined as the deviation of the voltage from the average value when the half-wave plate is fixed.

[0069] Cut Figure 4 The voltage step at one end has a total of 25 measurements. When the average output signal voltage is 0.01365V, the voltage relative uncertainty is ±0.25%, as shown in Figure 5.

[0070] The average signal voltage changes from 0.01365 V to 0.016417 V, a change of 0.002767 V, corresponding to a rotation of 2.5 mdeg in the polarization plane. Therefore, the relative angular uncertainty is 2.5 * 0.25% * (0.01365 / 0.002757) = 0.03 mdeg.

[0071] The result verified by fixing the half-wave plate is that the minimum uncertainty of the polarization angle is 0.03 mdeg.

[0072] Example 2

[0073] The measurement method provided in this embodiment of the invention includes:

[0074] The sample is fixed on the three-dimensional displacement stage. The three-dimensional displacement stage is adjusted so that the sample is at the focal point of the objective lens in the focusing control device. The current source in the electromagnetic unit is turned on so that the one-dimensional electromagnet applies a magnetic field to the sample. The magnetic field strength is measured by a gaussmeter.

[0075] The laser generator is turned on to obtain horizontal linearly polarized light. The linearly polarized light is focused onto the sample surface fixed on the three-dimensional displacement stage by the focusing control device. The sample surface reflects the reflected light, which returns to the focusing control device and is split into the first reflected light and the second reflected light.

[0076] An electrical signal is obtained by receiving the second reflected light through a differential signal measuring device;

[0077] The sample is imaged by receiving the first reflected light through the imaging device, and the hysteresis loop is plotted based on the magnetic field strength and electrical signal.

[0078] The electrical signal is the voltage value output by the balanced photodetector in the differential signal measurement device.

[0079] Imaging a sample by receiving the first reflected light through an imaging device includes:

[0080] The first reflected light is refracted through the first broadband polarization beam-splitting cubic prism PBS1 into the window of the CCD camera, thus achieving the imaging of the sample.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A measurement system based on the magneto-optical Kerr effect, characterized in that, It includes a three-dimensional displacement stage, an optical path unit, an electromagnetic unit, and a software control unit. The three-dimensional displacement stage is located in the magnetic field provided by the electromagnetic unit. The optical path unit includes a frame and a laser generator, a focusing control device, a differential signal measuring device, and an imaging device disposed inside the frame; The laser generator provides linearly polarized light, which is focused onto the sample surface fixed on a three-dimensional displacement stage by a focusing control device. The sample surface reflects reflected light, which returns to the focusing control device and is split into a first reflected light and a second reflected light. The focusing control device can move up and down. The differential signal measuring device receives the second reflected light to obtain an electrical signal and transmits it to the software control unit; The imaging device receives the first reflected light to achieve image formation of the sample; The software control unit draws the hysteresis loop based on the magnetic field strength and electrical signal of the magnetic field; The focusing control device includes a second non-wideband polarization beam splitting cubic prism, an objective lens, and a one-dimensional displacement stage. The one-dimensional displacement stage is fixed at the bottom of the frame. The second non-wideband polarization beam splitting cubic prism is fixed on the one-dimensional displacement stage via its base. The objective lens is fixedly connected to the side of the second non-wideband polarization beam splitting cubic prism facing the three-dimensional displacement stage. The one-dimensional displacement stage can move the second non-wideband polarization beam splitting cubic prism BS2 and the objective lens fixed on it up and down, thereby realizing two measurement modes: LMOKE and PMOKE. When measuring a sample, the sample is fixed on a three-dimensional displacement stage. When the LMOKE measurement mode is required, the height of the objective lens is adjusted using a one-dimensional displacement stage so that linearly polarized light enters from the edge of the objective lens, is refracted by the objective lens, and then enters the magnetic field. The sample is then adjusted to the focal point of the objective lens using a three-dimensional displacement stage to achieve the LMOKE measurement mode. When the PMOKE measurement mode is required, the height of the objective lens is adjusted using a one-dimensional displacement stage so that linearly polarized light enters from the center of the objective lens, is refracted by the objective lens, and then enters the magnetic field. The sample is then adjusted to the focal point of the objective lens using a three-dimensional displacement stage to achieve the PMOKE measurement mode.

2. The measurement system based on the magneto-optical Kerr effect according to claim 1, characterized in that, The laser generating device includes a laser source, a first half-wave plate, and a first broadband polarization beam-splitting cubic prism. The laser source is used to provide laser light, and the first half-wave plate and the first broadband polarization beam-splitting cubic prism are sequentially arranged on the path of the laser light towards the sample to polarize the laser light and obtain horizontally linearly polarized light.

3. The measurement system based on the magneto-optical Kerr effect according to claim 1, characterized in that, The differential signal measurement device includes a second half-wave plate, a second broadband polarization beam splitter cube prism, a balanced photodetector, a second reflector, and a digital multimeter. The balanced photodetector has two windows. The second half-wave plate and the second broadband polarization beam-splitting cubic prism are arranged in parallel on the path of the second reflected light. After passing through the second half-wave plate and the second broadband polarization beam-splitting cubic prism, the second reflected light is split into two light signals. One light signal directly enters one window of the balanced photodetector, and the other light signal enters the other window of the balanced photodetector after being refracted by the second reflector. This enables the differential signal measurement device to perform differential amplification processing on the two light signals and convert them into electrical signals, which are voltages. The digital multimeter is connected to the balanced photodetector and the software control unit to read the voltage value output by the balanced photodetector and transmit it to the software control unit.

4. The measurement system based on the magneto-optical Kerr effect according to claim 3, characterized in that, The differential signal measurement device also includes an aperture disposed between the second half-wave plate and the second broadband polarizing beam splitter prism for filtering out noise light.

5. A measurement system based on the magneto-optical Kerr effect according to claim 2, characterized in that, The imaging device includes a first non-wideband polarization beam splitting cubic prism, an LED lamp, and a CCD camera. The first non-wideband polarization beam splitting cubic prism is positioned in the path of the first reflected light. The light provided by the LED lamp illuminates the first non-wideband polarization beam splitting cubic prism and adds the first reflected light to achieve illumination of the first reflected light. The first reflected light is split by the first broadband polarization beam-splitting cubic prism and then enters the window of the CCD camera to achieve image imaging of the sample.

6. The measurement system based on the magneto-optical Kerr effect according to claim 1, characterized in that, The electromagnetic unit includes a current source, a one-dimensional electromagnet, and a gaussmeter. The current source is electrically connected to the one-dimensional electromagnet to provide current to the one-dimensional electromagnet, which is used to apply a magnetic field to the sample. The gaussmeter is connected to the software control unit and is used to read the magnetic field strength and transmit it to the software control unit.

7. A measurement method based on the system according to any one of claims 1 to 6, characterized in that, include: The sample is fixed on the three-dimensional displacement stage. The three-dimensional displacement stage is adjusted so that the sample is at the focal point of the objective lens in the focusing control device. The current source in the electromagnetic unit is turned on so that the one-dimensional electromagnet applies a magnetic field to the sample. The magnetic field strength is measured by a gaussmeter. The laser generator is turned on to obtain horizontal linearly polarized light. The linearly polarized light is focused onto the sample surface fixed on the three-dimensional displacement stage by the focusing control device. The sample surface reflects the reflected light, which returns to the focusing control device and is split into the first reflected light and the second reflected light. An electrical signal is obtained by receiving the second reflected light through a differential signal measuring device; The sample is imaged by receiving the first reflected light through the imaging device, and the hysteresis loop is drawn based on the magnetic field strength and electrical signal.

8. The measurement method according to claim 7, characterized in that, The electrical signal is the voltage value output by the balanced photodetector in the differential signal measurement device.

9. The measurement method according to claim 7, characterized in that, Imaging a sample by receiving the first reflected light through an imaging device includes: The first reflected light is refracted into the window of the CCD camera through the first broadband polarizing beam-splitting cubic prism, thus achieving the imaging of the sample.

Images