Method for inducing same magnetization spot to face linear array at random

Abstract

The invention belongs to the technical field of magnetization spot array customization, and particularly relates to a method for inducing the same magnetization spot to face a linear array at will. A radiation field of a magnetic flow line source antenna in any orientation is superposed with a first-order spiral phase factor to reversely push and introduce a pupil field so as to construct a linear array in which pure transverse circularly polarized light focal spots are arranged along a specified space orientation, the number, the position, the spacing and the like of the focal spot array can be regulated and controlled, and the focal spots are in a near diffraction limit size; based on the inverse Faraday effect, the constructed novel focal spot array can induce a linear array in which super-diffraction limit magnetization spots are arranged along a specified space direction, and the number, the position and the spacing of the magnetization spots can be flexibly regulated and controlled; according to the method provided by the invention, the analytical expression of the entrance pupil vector light field can be obtained without a complicated optimization process, and the constructed novel magnetized spot array has wide application potential in the aspects of magneto-optical storage technology, parallel atom capture, confocal nuclear magnetic resonance microscopes and the like.

Description

Technical Field

[0001] The invention relates to the technical field of magnetized spot array customization, and in particular to a method for inducing the same magnetized spot to arbitrarily face a linear array. Background Art

[0002] Vector light fields are different from scalar light fields in that their polarization distribution on the same wavefront is related to the spatial position. By optimizing the amplitude, phase, and polarization state distribution of the vector light field on the entrance pupil plane of the focusing system, novel optical focal fields such as light needles, light bubbles, light pipes, and light chains can be formed after tight focusing. These novel optical focal fields have broad application potential in related fields, especially the light field with transverse circular polarization distribution can induce a photoinduced magnetization field that is the same or opposite to the propagation direction. Since high-resolution magnetization fields have broad application potential in magneto-optical storage technology, which is one of the important solutions to meet the huge data transmission, processing, and storage needs in the era of big data, photoinduced magnetization fields have attracted the attention of many research students.

[0003] In 2013, the research team of Min Gu successfully constructed a sub-wavelength diffraction pure longitudinal magnetization field with a size of 0.508λ in the focal area by tightly focusing an angularly polarized vortex beam and applying the optical focal field to an isotropic magneto-optical material. The team also achieved efficient reversal of the magnetization field by adjusting the phase direction of the vortex light. In 2014, the research team introduced a double-ring vortex binary filter with a π phase difference in the tight focusing system to modulate the angularly polarized light wavefront, thereby inducing the generation of an ultra-long pure longitudinal magnetic needle with a lateral resolution of 0.38λ and a length of 7.48λ. In 2017, the research group of Bao-Hua Jia reported the use of a 4π optical focusing device to focus two modulated vector beams to achieve a three-dimensional super-resolution pure longitudinal magnetization spot array. In the same year, the research group of Cheng-Wei Qiu proposed focusing six coherent circularly polarized beams in a 4π microscopy system to achieve a three-dimensional super-resolution pure longitudinal magnetization spot.

[0004] Most of the above publicly reported photoinduced magnetization fields or magnetization spot arrays are only along the longitudinal direction, with a single direction, and cannot achieve three-dimensional high-density super-resolution magneto-optical recording and storage, and generally require complex optimization design to obtain a complex entrance pupil vector light field. In 2018, Xiangping Li's research group used the radiation field of an orthogonal dipole pair to reversely construct a transverse circularly polarized light focal field to induce a three-dimensional specifiable magnetization field, but the full width at half maximum (FWHM) of this single magnetization field was 0.56λ´0.56λ´1.31λ, which did not exceed the diffraction limit. In view of the above-mentioned problems, the inventor of this case conducted an in-depth study on the problem, which led to the creation of this case. Summary of the invention

[0005] In response to the above problems, the present invention provides a method for constructing an arbitrarily oriented linear array of the same light focus spot based on the radiation field of an arbitrarily oriented magnetic streamline source antenna superimposed with a first-order spiral phase factor, and inducing an arbitrarily oriented linear array of the same magnetized spot in a magnetic material.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for inducing the same magnetization spot to arbitrarily face a linear array, the method comprising: A tight focusing system is established by two objective lenses with a confocal area; A magnetic flux source antenna is placed in the confocal area of ​​the tight focusing system; wherein the carrier magnetic flux of the magnetic flux source antenna has a uniform and in-phase phase distribution within its length range, and an amplitude distribution is a cosine square taper distribution with a period of N; The radiation field of the magnetic streamline source antenna is calculated, and on this basis, the spiral phase factor with the same spatial orientation is superimposed, and the radiation field radiates outward from the tight focusing system, and then propagates outward from the tight focusing system after being collimated by two identical high numerical aperture objective lenses, and the radiation field at the entrance pupil plane of the objective lens is obtained based on the bending effect of the lens on the radiation light. The radiation field at the entrance pupil plane of the objective lens is reversed by time reversal technology, propagated in the opposite direction, and focused to the origin of the confocal area of ​​the two objective lenses, so as to form a linear array optical focal field in which the focal spots of pure transverse circular polarization light are arranged along the specified spatial direction relative to the spatial direction of the magnetic streamline source antenna in the confocal area; wherein, the incident field phases of the entrance pupil planes on both sides of the tight focusing system differ by 180 degrees; Based on the inverse Faraday effect, magneto-optical material is placed in the confocal area of ​​two objective lenses. The linear array optical focal field of pure transverse circularly polarized light focal spots arranged along the specified spatial direction can induce a linear array photoinduced magnetization field of super-diffraction limit magnetization spots arranged along the specified spatial direction.

[0007] Furthermore, the tight focusing system is used to converge the incident fields of the entrance pupil surfaces on both sides to form a desired highly localized optical focal field in the confocal area and induce a target photoinduced magnetization field. The tight focusing system is composed of two identical high numerical aperture objective lenses that are confocal and have collinear optical axes. A reference rectangular coordinate system is established in the tight focusing system; wherein the common focus O of the two objective lenses is used as the origin of the rectangular coordinate system, the direction to the right of the collinear optical axis is used as the positive direction of the Z axis, and the Z axis is perpendicular to the focal plane XOY plane of the tight focusing system; wherein the X axis is vertically upward, and the Y axis is perpendicular to the XOZ plane.

[0008] Furthermore, the geometric length of the magnetic flux line source antenna is , the center point is located at the origin O of the rectangular coordinate system; The spatial orientation of the magnetic flux line source antenna is ,in and are the polar angle and azimuth angle of the line source antenna direction respectively; The magnetic flux of the magnetic flux line source antenna The mathematical expression of is as follows: (1) in, is the magnetic current amplitude, is the position variable of the magnetic streamline source.

[0009] Furthermore, the calculation process of the magnetic flux line source antenna radiation field specifically includes the following steps: firstly, the line source is calculated The length is The radiation field of the magnetic flux element is then integrated and accumulated along the geometric length of the source using the parallel ray method to obtain its radiation far field: (2) in: (3) (4) (5) (6) (7) (8) Among them, is a coefficient independent of the radiation pattern, is an imaginary unit, is the angular frequency, is the free space dielectric constant, is the wave impedance, is the wave number, and is the unit vector of the radiation field spherical coordinates, and They are the magnetic flux elements in and Directional factor of direction, is the array factor of the cosine square gradually tapered magnetic streamline source with amplitude of period N as a continuous line source.

[0010] Furthermore, along the spatial direction The calculation process of the spiral phase factor is as follows: 1) With the XYZ global coordinate system as the rotating whole, the origin O of the global coordinate is the rotation point, and the Z axis rotates along the oscillation direction of the magnetic dipole and the plane where OZ is located to direction, forming a rotated Axis; 2) The X-axis and Y-axis of the global coordinate system rotate synchronously to and axis, , and are the three principal axes of the local coordinate system after rotation; 3) the spatial direction is derived The spiral phase factor is: (9) in, is the topological charge number, is the local coordinate system after rotation plane azimuth; to induce the target magnetic field, the topological charge number in equation (9) The value must be ±1; In order to obtain the incident field required to induce the target magnetization field, the calculated coordinate system located at the origin and oriented in space is The radiation field of the magnetic streamline source antenna is superimposed with the spiral phase factor of the same spatial orientation shown in equation (9), and the expression of the radiation field after superposition is obtained as shown in equation (10).

[0011] (10) Furthermore, the radiation field expression at the entrance pupil plane of the objective lens is shown in formula (11): (11) in, is the polar coordinate of the entrance pupil surface, is the distance between the entrance pupil observation point and the entrance pupil center, is the azimuth of the observation point on the entrance pupil plane, The component of the radiation field The component is bent; due to the bending of the radiation light by the lens, the objective lens that meets the sine condition is selected to form a focusing system, and its toe-cutting function is .

[0012] Furthermore, the focal field distribution of the confocal area can be calculated and quantitatively evaluated by Deby vector diffraction integral theory, and the calculation formula is: (12) in, is the spherical wavefront of the entrance pupil field after being bent by the objective lens, and its expression is shown in formula (13): (13) in , and are the unit vectors along the three principal axes of the rectangular coordinate system; is the cylindrical coordinate of the optical focal field; the constructed optical focal field is a pure transverse circular polarization near diffraction limit optical focal field along the spatial direction The number, position and spacing of the arranged linear array focal field are controlled by the parameters N and L0; the pure transverse direction is relative to the magnetic streamline source antenna space direction In terms of.

[0013] Furthermore, based on the inverse Faraday effect, the highly localized pure transverse circularly polarized near-diffraction-limited light focal field is directed toward the space The arranged linear array optical focal field can induce spatial orientation in magneto-optical materials. The same or opposite photoinduced magnetization field, which is calculated by equation (14): (14) in, and is the electric field vector of the focal field and its conjugate vector, is the coupling coefficient related to the magneto-optical material.

[0014] From the above description of the structure of the present invention, it can be seen that compared with the prior art, the present invention has the following advantages: The present invention utilizes the radiation field of a magnetic streamline source antenna in any orientation and superimposes a first-order spiral phase factor to reversely deduce the entrance pupil field, so as to realize the construction of a linear array of pure transverse circularly polarized light focal spots arranged along a specified spatial direction, the number, position, spacing, etc. of this light focal spot array can be controlled, and the focal spot is a near-diffraction limit size; based on the inverse Faraday effect, the novel light focal spot array constructed can induce a linear array of super-diffraction limit magnetized spots arranged along a specified spatial direction, and the number, position and spacing of the magnetized spots can also be flexibly controlled; the method proposed in the present invention can obtain an analytical expression of the entrance pupil vector light field without a complex optimization process, and the novel magnetized spot array constructed has broad application potential in magneto-optical storage technology, parallel atomic capture, confocal nuclear magnetic resonance microscopy, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 is a schematic diagram of an optical tight focusing system of the present invention; Figure 2 For Example 1 Normalized intensity and polarization distribution diagram of the constructed optical focal field in the Z=±0.75λ section, XZ and YZ planes; Figure 3 for Figure 2 The magnetization field induced by the optical focal field in the magnetic material; Figure 4 For Example 1 Normalized intensity and polarization distribution diagrams of the constructed optical focal field in the XY, XZ and YZ planes; Figure 5 for Figure 4 The magnetization field induced by the optical focal field in the magnetic material; Figure 6 The orientation parameter of the magnetic stream source in Example 2 is and Normalized intensity and polarization distribution diagrams of the constructed optical focal field in the Y=±0.625λ section, XZ and XY planes; Figure 7 for Figure 6 The magnetization field induced by the optical focal field in the magnetic material; Figure 8 For Example 3 When , the constructed linear array of light focal spots; Fig. 9 for Figure 8 The induced magnetized focal spot linear array. DETAILED DESCRIPTION

[0016] In order to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0017] like Figure 1 As shown, a method for inducing the same magnetization spot to arbitrarily face a linear array, the method comprising: establishing a tight focusing system by two objective lenses with a confocal area; placing a magnetic streamline source antenna in the confocal area of ​​the tight focusing system; wherein the carrier magnetic flux of the magnetic streamline source antenna has a uniform and in-phase phase distribution within its length range, and an amplitude distribution is a cosine square taper distribution with a period N; calculating the radiation field of the magnetic streamline source antenna, and on this basis superimposing a spiral phase factor of the same spatial direction, the radiation field radiates outward of the tight focusing system, and propagates outward of the tight focusing system after being collimated by two identical high numerical aperture objective lenses, and according to the bending effect of the lens on the radiation light, the radiation field is obtained. The radiation field at the entrance pupil plane of the objective lens; the radiation field at the entrance pupil plane of the objective lens at this time is reversed by time reversal technology, propagated in the opposite direction, and focused to the origin of the common focal area of ​​the two objective lenses, so as to form a linear array optical focal field in which the focal spots of pure transverse circular polarized light are arranged along the specified spatial direction relative to the spatial direction of the magnetic streamline source antenna in the common focal area; wherein, the incident field phases of the entrance pupil planes on both sides of the tight focusing system differ by 180 degrees; based on the inverse Faraday effect, magneto-optical materials are placed in the common focal area of ​​the two objective lenses, and the linear array optical focal field in which the focal spots of pure transverse circular polarized light are arranged along the specified spatial direction can induce a linear array photo-induced magnetization field in which the super-diffraction limit magnetization spots are arranged along the specified spatial direction in the magneto-optical material.

[0018] The present invention utilizes the radiation field of a magnetic streamline source antenna in any orientation and superimposes a first-order spiral phase factor to reversely deduce the entrance pupil field, so as to realize the construction of a linear array of pure transverse circularly polarized light focal spots arranged along a specified spatial orientation, the number, position, spacing, etc. of this light focal spot array can be controlled, and the focal spot is a near-diffraction limit size; based on the inverse Faraday effect, the novel light focal spot array constructed can induce a linear array of super-diffraction limit magnetized spots arranged along a specified spatial orientation, and the number, position and spacing of the magnetized spots can also be flexibly controlled; the method proposed in the present invention can obtain an analytical expression of the entrance pupil vector light field without a complex optimization process, and the novel magnetized spot array constructed has broad application potential in magneto-optical storage technology, parallel atomic capture, confocal nuclear magnetic resonance microscopy, etc.

[0019] The specific implementation steps of the method of the present invention are now introduced in detail: Step 1: Build a tight focusing system: like Figure 1 As shown, the tight focusing system is composed of two identical high numerical aperture objective lenses that are confocal and collinearly placed with their optical axes; the confocal point O of the two objective lenses is used as the origin of the global coordinate system, the direction to the right of the collinear optical axis is used as the positive direction of the Z axis, and the Z axis is perpendicular to the focal plane XOY plane of the tight focusing system; the X axis is vertically upward, and the Y axis is perpendicular to the XOZ plane; the tight focusing system is used to converge the incident fields of the entrance pupil surfaces on both sides to form a desired highly localized optical focal field in the focal area and induce a target photoinduced magnetization field.

[0020] Step 2: Set up the magnetic flux line source antenna: A magnetic flux source antenna is set at the origin of the tight focusing system shown in step 1, and its geometric length is , the spatial orientation is ,in and are the polar angle and azimuth angle of the line source antenna direction respectively; The carrier magnetic current of the magnetic stream source is evenly distributed in phase within its length range, and the amplitude distribution is a cosine square gradually decreasing distribution with a period of N. The mathematical expression of is as follows: (1) in, is the magnetic current amplitude, is the position variable of the magnetic streamline source.

[0021] Step 3: Solve the radiation field of the magnetic stream source antenna in step 2: To solve the radiation field of the magnetic flux line source antenna in step 2, first calculate the line source The length is The radiation field of the magnetic flux element is then integrated and accumulated along the geometric length of the source using the parallel ray method to obtain its radiation far field: (2) in: (3) (4) (5) (6) (7) (8) Among them, is a coefficient independent of the radiation pattern, is an imaginary unit, is the angular frequency, is the free space dielectric constant, is the wave impedance, is the wave number, and is the unit vector of the radiation field spherical coordinates, and They are the magnetic flux elements in and Directional factor of direction, is the array factor of the cosine square gradually tapered magnetic streamline source with amplitude of period N as a continuous line source.

[0022] Step 4: Superimpose the spiral phase factor of the corresponding direction on the radiation field of step 3: Along the spatial direction The calculation process of the spiral phase factor is as follows: 1) Take the XYZ global coordinate system as the rotating whole, such as Figure 1 The origin O of the global coordinates shown is the rotation point, and the Z axis rotates along the oscillation direction of the magnetic dipole and the plane where OZ is located to direction, forming a rotated Axis; 2) The X-axis and Y-axis of the global coordinate system rotate synchronously to and axis, , and are the three principal axes of the local coordinate system after rotation; 3) the spatial direction is derived The spiral phase factor is: (9) in is the topological charge number, is the local coordinate system after rotation plane azimuth; to induce the target magnetic field, the topological charge number in equation (9) The value must be ±1; In order to obtain the incident field required to induce the target magnetization field, the coordinate system calculated in step (2) is located at the origin and oriented in space. The radiation field of the magnetic streamline source antenna is superimposed with the spiral phase factor of the same spatial orientation shown in equation (9), and the expression of the radiation field after superposition is obtained as shown in equation (10).

[0023] (10) Step 5: derive the vector light field at the pupil based on the total radiation field in step 4; Step 4: The calculated superimposed radiation field radiates outward from the confocal area, and propagates outward after being collimated by two identical high numerical aperture objective lenses. Due to the bending of the radiation light by the lens, an objective lens that satisfies the sine condition is selected to form a focusing system, and its apodization function is: , then the radiation field at the entrance pupil of the objective can be obtained as: (11) in is the polar coordinate of the entrance pupil surface, is the distance between the entrance pupil observation point and the entrance pupil center, is the azimuth of the observation point on the entrance pupil plane, The component of the radiation field The weight is bent.

[0024] Step 6: Reverse the light path, focus in the opposite direction, and calculate the focal field distribution of the focal area: Based on the time reversal technology, the radiation field at the entrance pupil of the objective lens is calculated by reversing step (5), propagating in the opposite direction, and converging toward the origin of the confocal region of the two objective lenses, and the expected focal field will be formed in the confocal region; at this time, the incident field phases of the entrance pupils on both sides of the tight focusing system differ by 180 degrees; the distribution of the focal field in the confocal region can be calculated and quantitatively evaluated by the Deby vector diffraction integral theory, and the calculation formula is: (12) in, is the spherical wavefront of the entrance pupil field after being bent by the objective lens, and its expression is shown in formula (13): (13) in, , and are the unit vectors along the three principal axes of the rectangular coordinate system. is the cylindrical coordinate of the optical focal field; the characteristics of the tightly focused optical field are quantitatively evaluated by equations (12) and (13); the optical focal field constructed in this application is a purely transverse circularly polarized near-diffraction-limited optical focal field along the spatial direction The number, position and spacing of the arranged linear array focal field are controlled by the parameters N and L0; the pure transverse direction here is relative to the spatial orientation of the magnetic streamline source antenna In terms of.

[0025] Step 7: Calculate the photoinduced magnetization field induced by the tightly focused light field in step 6 on the magneto-optical material: Based on the inverse Faraday effect, Figure 1 The magneto-optical material is set at the confocal area position, and the highly localized pure transverse circular polarization near diffraction limit array light focal field constructed in step 6 induces a spatial orientation-related optical field on the magneto-optical material. The same or opposite photoinduced magnetization field (depending on the topological charge The magnetization field is calculated by equation (14): (14) Among them, and is the electric field vector of the focal field and its conjugate vector, is the coupling coefficient related to the magneto-optical material; the near diffraction limit array optical focal field constructed by step 6 of the present application can induce a spatial orientation The super-diffraction-limited photoinduced magnetization spot is oriented along the space Novel magnetization fields in linear arrangement.

[0026] Several specific examples are given below to demonstrate the effectiveness of the method proposed by the present invention.

[0027] To simplify the calculation, the parameters C and γ that are independent of the shape and polarization of the optical focal field and the induced magnetization field are normalized in the examples listed, that is, C=1, γ=1; to converge all the radiation fields of the magnetic streamline source antenna after the superposition of the spiral phase factor, the high numerical aperture objective lens convergence angle is taken as ,Right now ; Topological charge The signs of are different, and the induced magnetic field directions are opposite. =1; the objective lens that satisfies the sine condition is used as the objective lens used in the embodiment of the present invention.

[0028] Example 1: Inducing a pure longitudinal super-diffraction-limited photoinduced magnetization field linear array: Let the magnetic streamline source be placed along the Z axis, with its orientation parameter ,make and , the Z-axis light focus linear array and the induced Z-axis linear array of the same magnetized spot are calculated by equations (12), (13) and (14). Their characteristics are as follows: Figure 2 and Figure 3 shown.

[0029] Figure 2 For Normalized intensity and polarization distribution diagram of the focal field constructed at Z=±0.75λ section, XZ and YZ planes. It can be seen that the central area of ​​the focal spot at Z=±0.75λ section is a pure circular polarization distribution, and the X and Y polarization distributions are respectively X and Y in the XZ and YZ planes; the number of focal spots arranged along the Z axis is 2, which is the same as the parameter N; the spacing of the focal spots is 1.5λ, which is numerically equal to ; The full width at half maximum (FWHM) of the light intensity of the two light focal spots along their lateral and longitudinal directions are 0.41λ, 0.41λ and 0.6λ respectively, which are near-diffraction-limited light focal spots. Figure 3 for Figure 2 The magnetization field induced by the focal field of the light in the magnetic material is shown in Figure 1. It can be seen that the induced magnetization field is a binary array formed by the same pure longitudinal polarization magnetization spots arranged along the Z axis, and the regularity of their spacing and positions is the same as Figure 2 The focal field is consistent with that of the magnetized spot. The full width at half maximum (FWHM) of the magnetic field intensity along the transverse and longitudinal directions are measured to be 0.28λ, 0.28λ and 0.44λ respectively, which is a super-diffraction limited magnetized spot.

[0030] Figure 4 For Normalized intensity and polarization distribution diagram of the focal field constructed in the XY, XZ and YZ planes. It can be seen that the central area of ​​the focal spot is a pure circular polarization distribution, and the X and Y polarization distributions are respectively in the XZ and YZ planes; the number of focal spots arranged along the Z axis is 3, which is the same as the parameter N, and they are arranged symmetrically about the origin; the spacing of the focal spots is 4λ / 3, which is numerically equal to The full width at half maximum (FWHM) of the intensity of the three light spots along their lateral and longitudinal directions are 0.42λ, 0.42λ and 0.54λ, respectively, which are near-diffraction-limited light spots. Figure 5 for Figure 4 The magnetization field induced by the focal field of the light in the magnetic material is shown in Figure 1. It can be seen that the induced magnetization field is a three-element array of the same pure longitudinal polarization magnetization spots arranged along the Z axis, and the regularity of their spacing and positions is the same as Figure 4 The optical focal field is consistent with that of the magnetized spot. The full width at half maximum (FWHM) of the magnetic field intensity along the transverse and longitudinal directions are measured to be 0.29λ, 0.29λ and 0.39λ respectively, which is a super-diffraction limited magnetized spot.

[0031] Example 2: Inducing a pure transverse super-diffraction-limited photoinduced magnetization field linear array: Let the parameters of the magnetic streamline source be , the orientation parameter is , that is, the line source is placed on the X-axis, and the X-axis linear array of light focal spots and the X-axis linear array of the same magnetized spots induced by them are calculated by equations (12), (13) and (14). Their characteristics are as follows: Figure 6 and Figure 7shown.

[0032] Figure 6 is the direction parameter of the magnetic streamline source and Normalized intensity and polarization distribution diagram of the focal field constructed at Y=±0.625λ section, XZ and XY planes. It can be seen that the central area of ​​the focal spot cross section is a pure circular polarization distribution, and the Z and Y linear polarization distributions are respectively in the XZ and XY planes; the number of focal spots arranged along the X axis is 4, which is the same as the parameter N; the spacing of the focal spots is 1.25λ, which is numerically equal to The full width at half maximum (FWHM) of the light intensity of the two light focal spots along their lateral and longitudinal directions are 0.42λ, 0.42λ and 0.52λ respectively, which are near-diffraction-limited light focal spots. Figure 7 for Figure 6 The magnetization field induced by the focal field of the light in the magnetic material is shown in Figure 1. It can be seen that the induced magnetization field is a four-element array formed by the same pure X-linear polarization magnetization spots arranged along the X axis, and the regularity of their spacing and positions is the same as Figure 6 The focal field is consistent with that of the magnetized spot. The full width at half maximum (FWHM) of the magnetic field intensity in the transverse and longitudinal directions of the magnetized spot is measured to be 0.30λ, 0.30λ and 0.38λ respectively, which is a super-diffraction-limited magnetized spot. In this example, the azimuth angle of the magnetic stream source antenna in the XY plane is changed. , we can construct a An array of linearly arranged super-diffraction-limited magnetized spots.

[0033] Example 3: Inducing a super-diffraction-limited photoinduced magnetization field in an arbitrary direction linear array: To further illustrate the convenience and effectiveness of the method of the present invention in inducing the generation of a linear array of magnetized spots in any direction beyond the diffraction limit, unlike Example 1 and Example 2, the linear array of magnetized spots induced in this example is not located in the three main planes. Without loss of generality, let the parameters of the magnetic streamline source be , the spatial orientation formed by the five light spots is obtained as The linear array focal field is When the 3D shape is as follows Figure 8 As shown in Figure 2, the induced magnetic focus linear array is as follows: Fig. 9 As shown. Figure 5 It can be seen that the direction parameter of the magnetic streamline source is determines the spatial orientation of the target array, N determines the number of light focal spots and magnetized spots, and N jointly determine the focal spot Specific positions and spacings on the straight lines shown.

[0034] The results presented in Example 1, Example 2 and Example 3 indicate that the method proposed in the present invention can be used to construct a rich linear array of super-diffraction-limited magnetized spots, and the constructed novel magnetized spot array has broad application potential in magneto-optical storage technology, parallel atomic capture, confocal nuclear magnetic resonance microscopy, etc.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for inducing the same magnetized spot to arbitrarily face a linear array, characterized in that: The method comprises: A tight focusing system is established by two objective lenses with a confocal area; A magnetic flux source antenna is placed in the confocal area of ​​the tight focusing system; wherein the carrier magnetic flux of the magnetic flux source antenna has a uniform and in-phase phase distribution within its length range, and an amplitude distribution is a cosine square taper distribution with a period of N; The radiation field of the magnetic streamline source antenna is calculated, and on this basis, the spiral phase factor with the same spatial orientation is superimposed, and the radiation field radiates outward from the tight focusing system, and then propagates outward from the tight focusing system after being collimated by two identical high numerical aperture objective lenses, and the radiation field at the entrance pupil plane of the objective lens is obtained based on the bending effect of the lens on the radiation light. The radiation field at the entrance pupil plane of the objective lens is reversed by time reversal technology, propagated in the opposite direction, and focused to the origin of the confocal area of ​​the two objective lenses, so as to form a linear array optical focal field in which the focal spots of pure transverse circular polarization light are arranged along the specified spatial direction relative to the spatial direction of the magnetic streamline source antenna in the confocal area; wherein, the incident field phases of the entrance pupil planes on both sides of the tight focusing system differ by 180 degrees; Based on the inverse Faraday effect, magneto-optical material is placed in the confocal area of ​​two objective lenses. The linear array optical focal field of pure transverse circularly polarized light focal spots arranged along the specified spatial direction can induce a linear array photoinduced magnetization field of super-diffraction limit magnetization spots arranged along the specified spatial direction.

2. A method for inducing the same magnetization spot to arbitrarily face a linear array according to claim 1, characterized in that: The tight focusing system is used to converge the incident fields of the entrance pupil surfaces on both sides to form a desired highly localized optical focal field in the confocal area and induce a target photoinduced magnetization field. The tight focusing system is composed of two identical high numerical aperture objective lenses that are confocal and have collinear optical axes. A reference rectangular coordinate system is established in the tight focusing system; wherein the common focus O of the two objective lenses is used as the origin of the rectangular coordinate system, the direction to the right of the collinear optical axis is used as the positive direction of the Z axis, and the Z axis is perpendicular to the focal plane XOY plane of the tight focusing system; wherein the X axis is vertically upward, and the Y axis is perpendicular to the XOZ plane.

3. A method for inducing the same magnetization spot to arbitrarily face a linear array according to claim 2, characterized in that: The geometric length of the magnetic flux line source antenna is , the center point is located at the origin O of the rectangular coordinate system; The spatial orientation of the magnetic flux line source antenna is ,in and are the polar angle and azimuth angle of the line source antenna direction respectively; The magnetic flux of the magnetic flux line source antenna The mathematical expression of is as follows: （1） in, is the magnetic current amplitude, is the position variable of the magnetic streamline source.

4. The method of inducing the same magnetization spot to arbitrarily face a linear array according to claim 1, characterized in that: The calculation process of the magnetic flux line source antenna radiation field specifically includes the following steps: firstly, the line source is calculated The length is The radiation field of the magnetic flux element is then integrated and accumulated along the geometric length of the source using the parallel ray method to obtain its radiation far field: （2） in: (3) （4） （5） （6） （7） （8） Among them, is a coefficient independent of the radiation pattern, is an imaginary unit, is the angular frequency, is the free space dielectric constant, is the wave impedance, is the wave number, and is the unit vector of the radiation field spherical coordinates, and They are the magnetic flux elements in and Directional factor of direction, is the array factor of the cosine square gradually tapered distributed magnetic streamline source with amplitude of period N as a continuous line source.

5. The method of inducing the same magnetized spot to arbitrarily face a linear array according to claim 1, characterized in that: Along the spatial direction The calculation process of the spiral phase factor is as follows: 1) With the XYZ global coordinate system as the rotating whole, the origin O of the global coordinate is the rotation point, and the Z axis rotates along the oscillation direction of the magnetic dipole and the plane where OZ is located to direction, forming a rotated Axis; 2) The X-axis and Y-axis of the global coordinate system rotate synchronously to and axis, , and are the three principal axes of the local coordinate system after rotation; 3) the spatial direction is derived The spiral phase factor is: （9） in, is the topological charge number, is the local coordinate system after rotation plane azimuth; to induce the target magnetic field, the topological charge number in equation (9) The value must be ±1; In order to obtain the incident field required to induce the target magnetization field, the calculated coordinate system located at the origin and oriented in space is The radiation field of the magnetic streamline source antenna is superimposed with the spiral phase factor of the same spatial orientation shown in formula (9), and the expression of the radiation field after superposition is obtained as shown in formula (10): （10）。 6. A method for inducing the same magnetization spot to arbitrarily face a linear array according to claim 1, characterized in that: The radiation field expression at the entrance pupil plane of the objective lens is shown in formula (11): （11） in, is the polar coordinate of the entrance pupil surface, is the distance between the entrance pupil observation point and the entrance pupil center, is the azimuth of the observation point on the entrance pupil plane, The component of the radiation field The component is bent; due to the bending of the radiation light by the lens, the objective lens that meets the sine condition is selected to form a focusing system, and its toe-cutting function is .

7. The method of inducing the same magnetization spot to arbitrarily face a linear array according to claim 1, characterized in that: The focal field distribution of the confocal area can be calculated and quantitatively evaluated by Deby vector diffraction integral theory, and the calculation formula is: （12） in, is the spherical wavefront of the entrance pupil field after being bent by the objective lens, and its expression is shown in formula (13): （13） in , and are the unit vectors along the three principal axes of the rectangular coordinate system; is the cylindrical coordinate of the optical focal field; the constructed optical focal field is a pure transverse circular polarization near diffraction limit optical focal field along the spatial direction The number, position and spacing of the arranged linear array focal field are controlled by the parameters N and L0; the pure transverse direction is relative to the magnetic streamline source antenna space direction In terms of.

8. The method of inducing the same magnetized spot to arbitrarily face a linear array according to claim 1, characterized in that: Based on the inverse Faraday effect, a highly localized pure transverse circularly polarized near-diffraction-limited light focal field is directed in the spatial direction. The arranged linear array optical focal field can induce spatial orientation in magneto-optical materials. The same or opposite photoinduced magnetization field, which is calculated by equation (14): （14） in, and is the electric field vector of the focal field and its conjugate vector, is the coupling coefficient related to the magneto-optical material.

Images