Method for measuring complex magneto-optical Kerr angle based on double-pointer weak measurement

Abstract

The invention belongs to the technical field of quantum optics, and discloses a double-pointer weak measurement-based complex magneto-optical Kerr angle measurement method, which comprises the following steps of: placing a sample to be measured between a weak coupling unit and a system front selection state unit or between the weak coupling unit and a system rear selection state unit, and reflecting an incident light beam from the surface of the sample; the system front selection state unit is adjusted, so that the light intensity signal acquired by the light signal acquisition unit is minimum; adjusting the pre-system selection state unit to enable the polarization state of the outgoing beam to be horizontal or vertical polarization, and adjusting the post-system selection state unit to enable the polarization state of the outgoing beam to be vertical or horizontal polarization; the external magnetic field intensity is adjusted, and meanwhile, the light spot mass center offset and the light intensity are received through the light information acquisition unit; and calculating a magneto-optical Kerr rotation angle and an ellipsometry rate. The method can be used for synchronously measuring the magneto-optical Kerr angle and the ellipsometry in one instrument state, and has extremely high sensitivity.

Description

Technical Field

[0001] This invention belongs to the field of quantum optics technology and relates to a method for measuring complex magneto-optical Kerr angles based on dual-pointer weak measurement. By utilizing the weak amplification characteristics of weak measurement technology, high-precision measurement of complex magneto-optical Kerr angles can be achieved. By combining dual-pointer technology, Kerr angles and ellipsoids can be measured simultaneously in one instrument state. It is suitable for high-precision measurement of magnetic and magneto-optical parameters of materials in the fields of materials science and magneto-optics. Background Technology

[0002] The magneto-optical Kerr effect refers to the physical phenomenon where the polarization plane and ellipticity of the reflected light change when a linearly polarized beam is reflected at a magnetic interface; it is essentially a complex effect. Based on the relationship between the magnetization direction and the incident plane, the magneto-optical Kerr effect can be divided into three types: transverse Kerr effect (TMOKE), longitudinal Kerr effect (LMOKE), and poloidal Kerr effect (PMOKE). With the development of spintronics, the magneto-optical Kerr effect has shown unique advantages in in-situ research of the magnetic properties of magneto-optical devices and thin films, and has been widely applied in fields such as magnetic measurement, magnetic domain imaging, magneto-optical ellipsometrics, and magneto-optical recording.

[0003] To study the magneto-optical Kerr effect and apply it to the study of material physical properties, such as the measurement of magneto-optical parameters, it is necessary to obtain the real part of the complex magneto-optical Kerr angle (magneto-optical Kerr rotation angle θ). K ) and the imaginary part (ellipticity ε) K ) to perform quantitative measurements. However, θ K and ε K They always coexist and contribute simultaneously to the detected magneto-optical Kerr signal. In conventional methods for measuring the magneto-optical Kerr effect, these two parameters can be measured separately by adjusting the phase using a quarter-wave plate. However, this not only reduces measurement efficiency but also introduces additional errors through the two measurement processes. Although θ can be obtained simultaneously by splitting the reflected light into multiple beams and performing multiple post-selection processes. K and ε K The signal improves measurement efficiency, but the measurements of these two parameters still come from different instrument states, which increases the complexity and cost of the optical system. Summary of the Invention

[0004] The purpose of this invention is to address the problem that existing technologies cannot simultaneously measure the magneto-optical Kerr rotation angle and ellipticity. It provides a method for measuring the complex magneto-optical Kerr angle based on dual-pointer weak measurement. Based on weak measurement technology, it amplifies the subtle polarization state changes caused by the magneto-optical Kerr effect. Furthermore, through dual-pointer technology using light intensity and amplified centroid, it enables simultaneous measurement of the magneto-optical Kerr rotation angle and ellipticity within a single instrument configuration, thereby improving the measurement accuracy and efficiency of the complex magneto-optical Kerr intersection.

[0005] Weak measurement is a technique that significantly amplifies observables by constructing suitable pre- and post-selection states and weak coupling processes, ultimately achieving high-precision measurement of physical quantities through an amplified centroid pointer. Research shows that weak measurement techniques can effectively suppress technical noise, such as detector saturation correlation noise and beam jitter, and can achieve high-precision parameter measurement while maintaining low cost, thus having broad application prospects in the precision instrument industry. The dual-pointer weak measurement technique proposed in this invention further introduces intensity as a second pointer, combined with an amplified centroid pointer, enabling simultaneous extraction of the post-selection angle amplitude and phase. Therefore, it has certain application prospects for measuring complex parameters such as the complex magneto-optical Kerr angle.

[0006] Based on the above analysis, this invention provides a complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement, implemented using the following measurement device, which includes a light-emitting unit, a system pre-selection state unit, a weak coupling unit, a system post-selection state unit, and an optical information acquisition unit arranged sequentially along the optical path propagation direction; it includes the following steps:

[0007] (S1) Place the sample to be tested between the weakly coupled unit and the pre-selected state unit of the system, or between the weakly coupled unit and the post-selected state unit of the system, so that the incident beam is reflected from the sample surface.

[0008] (S2) Adjust the pre-selection state unit of the system to minimize the light intensity signal collected by the optical signal acquisition unit, and record the light intensity at this time as I0;

[0009] (S3) Adjust the pre-selection unit of the system to make the polarization state of the outgoing beam horizontal or vertical, and at the same time adjust the post-selection unit of the system to make the polarization state of the outgoing beam vertical or horizontal.

[0010] (S4) Adjust the external magnetic field strength, and at the same time receive the centroid offset of the light spot through the optical information acquisition unit. and light intensity I;

[0011] (S5) Based on the centroid offset of the light spot and the light intensity, calculate the magneto-optical Kerr rotation angle θ according to the following formula. K and ellipticity ε K ;

[0012] ; ;

[0013] in, This indicates the weak coupling strength generated by the weakly coupled unit; Indicates the uncertainty of the laser position; Indicates the correction of the center of mass. ; Indicates intensity contrast. .

[0014] In one possible implementation, the measuring device further includes a sample unit; the sample unit includes a stage and a magnetic field application device, wherein the sample to be tested is placed on the stage, and the stage is located within the magnetic field coverage area of ​​the magnetic field application device.

[0015] When the sample unit is placed between the weak coupling unit and the system pre-selection state unit, the optical path in the measuring device is as follows: the light beam emitted by the light-emitting unit is prepared into linearly polarized light by the system pre-selection state unit, and after being reflected by the surface of the sample to be measured in the sample unit, it passes through the weak coupling unit and the system post-selection state unit, and finally the light spot is received by the optical information acquisition unit.

[0016] When the sample unit is placed between the weak coupling unit and the system post-selection unit, the optical path in the measuring device is as follows: the light beam emitted by the light-emitting unit is prepared into linearly polarized light by the system pre-selection unit, and then incident on the surface of the sample to be measured in the sample unit through the weak coupling unit. The reflected light beam passes through the system post-selection unit and is finally received by the optical information acquisition unit.

[0017] In one implementation, the light-emitting unit includes a light source generator and an energy regulator disposed on its outgoing optical path. The light source generator is a laser or a laser diode; the energy regulator is one of a half-wave plate, a neutral density filter, or a variable beam splitter.

[0018] In one possible implementation, the system's pre-selection state unit comprises a first lens, a first polarization state selector, and a quarter-wave plate; the system's post-selection state unit comprises a second polarization state selector and a second lens. The first and second polarization state selectors may be the same or different, both being thin-film polarizers, wire-grid polarizers, or birefringent crystals. Both the first and second lenses are convex lenses.

[0019] In one possible implementation, the weakly coupled unit is a birefringent crystal.

[0020] In one possible implementation, the optical information acquisition unit is a charge-coupled device (CCD).

[0021] In one possible implementation, in step (S4), the direction of the magnetic field strength is adjusted to be parallel to the sample surface and parallel to the direction of the light incident plane; then, in step (S5), the magneto-optical Kerr rotation angle θ under the longitudinal Kerr effect (LMOKE) is obtained. K and ellipticity ε K ;

[0022] Alternatively, in step (S4), the direction of the magnetic field strength is adjusted to be parallel to the sample surface and perpendicular to the direction of the light incident surface; then the transverse Kerr effect (TMOKE) is characterized by the light intensity I.

[0023] Alternatively, in step (S4), the direction of the magnetic field strength is adjusted to be perpendicular to the sample surface; then, in step (S5), the magneto-optical Kerr rotation angle θ under the poloidal Kerr effect (PMOKE) is obtained. K and ellipticity ε K .

[0024] In one possible implementation, in step (S4), the spot centroid offset... It is the offset of the centroid of the light spot currently received by the optical information acquisition unit relative to the centroid position when the optical information acquisition unit receives two light spots with completely equal intensity (denoted as the centroid of the light spot at this time is 0). It can be read directly by the optical information acquisition unit, or it can be obtained through a formula. Calculated.

[0025] Compared with existing technologies, the complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement provided by this invention has the following gain effects:

[0026] (1) The present invention uses weak measurement technology, which can amplify the slight change in polarization state caused by the magneto-optical Kerr effect by nearly 10,000, and has extremely high sensitivity;

[0027] (2) The invention uses dual-pointer technology (including magnified centroid and intensity) to simultaneously measure magneto-optical Kerr angle and ellipticity in one instrument state, which not only reduces testing costs but also avoids additional errors caused by multiple measurement processes;

[0028] (3) The magneto-optical Kerr effect is divided into the poloidal Kerr effect (PMOKE), longitudinal Kerr effect (LMOKE), and transverse Kerr effect (TMOKE). Both PMOKE and LMOKE will cause the generation of complex magneto-optical Kerr angles, while TMOKE will cause changes in the intensity of reflected light. The method of the present invention is not only applicable to the measurement of complex magneto-optical Kerr angles in PMOKE and LMOKE, but also applicable to the measurement of light intensity in TMOKE, and has good universality. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other embodiments and their drawings can be obtained based on the embodiments shown in these drawings without creative effort.

[0030] Figure 1 A schematic diagram of a complex magneto-optical Kerr angle measuring device based on dual-pointer weak measurement provided by the present invention;

[0031] Figure 2This is a schematic diagram of the complex magneto-optical Kerr angle measurement results under the longitudinal Kerr effect obtained by the complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement in Example 1;

[0032] Figure 3 This is a schematic diagram of the complex magneto-optical Kerr angle measurement results under the poloidal Kerr effect obtained by the complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement in Example 2;

[0033] Figure 4 The results (a) and (b) are the measurement results of the centroid offset of the light spot under the transverse Kerr effect obtained by the complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement in Example 3. Detailed Implementation

[0034] The technical solutions of various embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The complex magneto-optical Kerr angle measurement device based on dual-pointer weak measurement used in the following embodiments, such as Figure 1 As shown, it includes a light-emitting unit 1, a system pre-selection state unit 2, a sample unit 3, a weak coupling unit 4, a system post-selection state unit 5, and a light information acquisition unit 6 arranged sequentially along the light path propagation direction.

[0036] The light-emitting unit 1 consists of a light source generator and an energy regulator located in the beam emission direction. The light source generator is a collimated laser, and the laser position uncertainty of the collimated laser is... Micrometer; the energy regulator is a half-wave plate.

[0037] The system front selection unit 2 includes a first lens, a first polarization state selector, and a quarter-wave plate arranged in sequence; the system rear selection unit 5 includes a second polarization state selector and a second lens arranged in sequence; both the first polarization state selector and the second polarization state selector are Glan polarizers; both the first lens and the second lens are convex lenses.

[0038] Sample unit 3 includes a stage and a magnetic field application device, on which the sample to be tested is placed. The magnetic field application device uses an electromagnet. The stage is located within the magnetic field coverage area of ​​the magnetic field application device.

[0039] The weakly coupled unit 4 is a birefringent crystal. The beam obtained by the birefringent crystal has a lateral splitting distance of 30 micrometers, that is... =30 micrometers.

[0040] The optical information acquisition unit 6 is a charge-coupled device (CCD).

[0041] The optical path in the above device is as follows: the light beam emitted by the light-emitting unit 1 is prepared into linearly polarized light by the system pre-selection state unit 2, and after being reflected by the surface of the sample to be tested in the sample unit 3, it passes through the weak coupling unit 4 and the system post-selection state unit 5, and finally the light spot is received by the optical information acquisition unit 6.

[0042] Example 1

[0043] This embodiment provides a complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement, which is performed using the above-mentioned measuring device according to the following steps:

[0044] (S1) Place the sample to be tested between the weakly coupled unit and the pre-selected state unit of the system, so that the incident beam is reflected from the sample surface;

[0045] (S2) Adjust the pre-selection state unit of the system to minimize the light intensity signal collected by the optical signal acquisition unit, and record the light intensity at this time as I0;

[0046] (S3) Adjust the front selection unit of the system to make the polarization state of the outgoing beam horizontal, and at the same time adjust the rear selection unit of the system to make the polarization state of the outgoing beam vertical.

[0047] (S4) Adjust the external magnetic field strength and make the direction of the magnetic field strength parallel to the sample surface and parallel to the direction of light incident, so as to generate the longitudinal Kerr effect; at the same time, the optical information acquisition unit receives the centroid offset of the light spot. and light intensity I;

[0048] (S5) Based on the centroid offset of the light spot and the light intensity, calculate the magneto-optical Kerr rotation angle θ under the longitudinal Kerr effect (LMOKE) according to the following formula. K and ellipticity ε K ;

[0049] ; ;

[0050] in, This indicates the weak coupling strength generated by the weakly coupled unit; Indicates the uncertainty of the laser position; Indicates the correction of the center of mass. ; Indicates intensity contrast. .

[0051] Figure 1 The magneto-optical Kerr rotation angle θ under the longitudinal Kerr effect is given. K and ellipticity ε KA schematic diagram showing the variation with magnetic field strength shows that the magneto-optical Kerr rotation angle θ can be achieved using the method of this invention. K and ellipticity ε K Synchronous measurement.

[0052] Example 2

[0053] This embodiment provides a complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement, which is performed using the above-mentioned measuring device according to the following steps:

[0054] (S1) Place the sample to be tested between the weakly coupled unit and the pre-selected state unit of the system, so that the incident beam is reflected from the sample surface;

[0055] (S2) Adjust the pre-selection state unit of the system to minimize the light intensity signal collected by the optical signal acquisition unit, and record the light intensity at this time as I0;

[0056] (S3) Adjust the front selection unit of the system to make the polarization state of the outgoing beam horizontal, and at the same time adjust the rear selection unit of the system to make the polarization state of the outgoing beam vertical.

[0057] (S4) Adjust the external magnetic field strength and make the direction of the magnetic field strength perpendicular to the sample surface to generate the poloidal Kerr effect; at the same time, receive the centroid offset of the light spot through the optical information acquisition unit. and light intensity I;

[0058] (S5) Based on the centroid offset of the light spot and the light intensity, calculate the magneto-optical Kerr rotation angle θ under the poloidal Kerr effect (PMOKE) according to the following formula. K and ellipticity ε K ;

[0059] ; ;

[0060] in, This indicates the weak coupling strength generated by the weakly coupled unit; Indicates the uncertainty of the laser position; Indicates the correction of the center of mass. ; Indicates intensity contrast. .

[0061] Figure 2 The magneto-optical Kerr rotation angle θ under the poloidal Kerr effect is given. K and ellipticity ε K A schematic diagram showing the variation with magnetic field strength shows that the magneto-optical Kerr rotation angle θ can be achieved using the method of this invention. K and ellipticity ε K Synchronous measurement.

[0062] Example 3

[0063] This embodiment provides a complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement, which is performed using the above-mentioned measuring device according to the following steps:

[0064] (S1) Place the sample to be tested between the weakly coupled unit and the pre-selected state unit of the system, so that the incident beam is reflected from the sample surface;

[0065] (S2) Adjust the pre-selection state unit of the system to minimize the light intensity signal collected by the optical signal acquisition unit, and record the light intensity at this time as I0;

[0066] (S3) Adjust the front selection unit of the system to make the polarization state of the outgoing beam horizontal, and at the same time adjust the rear selection unit of the system to make the polarization state of the outgoing beam vertical.

[0067] (S4) Adjust the external magnetic field strength and make the direction of the magnetic field strength parallel to the sample surface and perpendicular to the direction of the light incident surface to generate a transverse Kerr effect; at the same time, receive the centroid offset of the light spot through the optical information acquisition unit. and light intensity I.

[0068] Figure 3 The centroid shift of the light spot under the transverse Kerr effect is given. The diagram illustrates the variation of light intensity I with magnetic field strength. The diagram shows the shift in the centroid of the light spot. The change is not significant, but the light intensity increases linearly with the magnetic field strength, indicating that the method of the present invention can effectively measure the light intensity, thus proving the effectiveness of the method of the present invention in the measurement of complex magneto-optical Kerr angle.

[0069] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for measuring the complex magneto-optical Kerr angle based on dual-pointer weak measurement, implemented using a measurement device comprising a light-emitting unit, a system pre-selection state unit, a weak coupling unit, a system post-selection state unit, and an optical information acquisition unit arranged sequentially along the optical path propagation direction; characterized in that, The complex magneto-optical Kerr angle measurement method includes the following steps: (S1) Place the sample to be tested between the weakly coupled unit and the pre-selected state unit of the system, or between the weakly coupled unit and the post-selected state unit of the system, so that the incident beam is reflected from the sample surface. (S2) Adjust the pre-selection state unit of the system to minimize the light intensity signal collected by the optical signal acquisition unit, and record the light intensity at this time as I0; (S3) Adjust the pre-selection unit of the system to make the polarization state of the outgoing beam horizontal or vertical, and at the same time adjust the post-selection unit of the system to make the polarization state of the outgoing beam vertical or horizontal. (S4) Adjust the external magnetic field strength, and at the same time receive the centroid offset of the light spot through the optical information acquisition unit. and light intensity I; (S5) Based on the centroid offset of the light spot and the light intensity, calculate the magneto-optical Kerr rotation angle θ according to the following formula. K and ellipticity ε K ; ； ； in, This indicates the weak coupling strength generated by the weakly coupled unit; Indicates the uncertainty of the laser position; Indicates the correction of the center of mass. ; Indicates intensity contrast. .

2. The complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement according to claim 1, characterized in that, The measuring device also includes a sample unit; the sample unit includes a stage and a magnetic field application device, the sample to be tested is placed on the stage, and the stage is located within the magnetic field coverage area of ​​the magnetic field application device.

3. The complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement according to claim 1, characterized in that, The light-emitting unit includes a light source generator and an energy regulator disposed on its outgoing light path. The light source generator is a laser or a laser diode; the energy regulator is one of a half-wave plate, a neutral density filter, or a variable beam splitter.

4. The complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement according to claim 1, characterized in that, The system's front selection unit consists of a first lens, a first polarization state selector, and a quarter-wave plate; the system's rear selection unit consists of a second polarization state selector and a second lens.

5. The complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement according to claim 4, characterized in that, The first polarization state selector and the second polarization state selector may be the same or different, both of which are thin-film polarizers, wire grid polarizers or birefringent crystals; the first lens and the second lens are both convex lenses.

6. The complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement according to claim 1, characterized in that, The weakly coupled unit is a birefringent crystal; the optical information acquisition unit is a charge-coupled device (CCD).

7. The complex magneto-optical Kerr angle measurement method based on dual-pointer weak measurement according to any one of claims 1 to 6, characterized in that, In step (S4), the direction of the magnetic field strength is adjusted to be parallel to the sample surface and parallel to the direction of the light incident plane; then, in step (S5), the magneto-optical Kerr rotation angle θ under the longitudinal Kerr effect is obtained. K and ellipticity ε K ; Alternatively, in step (S4), the direction of the magnetic field strength is adjusted to be parallel to the sample surface and perpendicular to the direction of the light incident surface; then the transverse Kerr effect is characterized by the light intensity I. Alternatively, in step (S4), the direction of the magnetic field strength is adjusted to be perpendicular to the sample surface; then, the magneto-optical Kerr rotation angle θ under the poloidal Kerr effect is obtained through step (S5). K and ellipticity ε K .

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