WO2024229965A1 - Method for implementing arbitrarily spin-orientated focal spot beyond diffraction limit - Google Patents

Abstract

Disclosed is a method for implementing an arbitrarily spin-orientated focal spot beyond a diffraction limit. The method comprises: placing an orthogonal dipole pair in a space with a center point of a 4π optical focusing system as an original point, the phase difference in feed current of the dipole pair being π/2; spinning the orthogonal dipole pair around the original point; the 4π optical focusing system collecting a radiation field generated by the spun dipole pair, collimating the radiation field into an entrance pupil plane of the 4π optical focusing system, and utilizing a bending effect to obtain a radiation field of the entrance pupil plane; reversing the radiation field of the entrance pupil plane on the basis of the time inversion technology, and reversely transmitting and converging the radiation field towards a confocal area of two objective lenses from two sides of the entrance pupil plane of the 4π optical focusing system through relative π phase shift; and calculating on the basis of the Richards-Wolf vector diffraction theory to give focusing field data, so as to form an arbitrarily adjustable, arbitrarily spin-orientated focal spot beyond the diffraction limit in the confocal area of the two objective lenses. The spin-orientation of the focal spot beyond the diffraction limit generated by the method can be adjusted arbitrarily.

Description

A method for realizing arbitrary spin pointing to a super-diffraction-limited light focus Technical Field

The present invention relates to the technical field of generating a light focal spot, and in particular to a method for constructing a light focal spot with arbitrary spin pointing beyond the diffraction limit by utilizing the radiation field of a dipole pair.

Background Art

Light is an electromagnetic wave with two important dynamic parameters: linear momentum and angular momentum. Linear momentum and angular momentum play an important role in the interaction between light and matter, such as optical processing, optical capture, and optical manipulation. The angular momentum of light includes spin angular momentum and orbital angular momentum, which are related to the circular polarization state and vortex phase distribution of light, respectively. In the field of optical manipulation, controlling the spin angular momentum of light to make particles rotate around their own axis is an important optical manipulation method.

Generally, the rotation axis caused by the spin angular momentum of photons is parallel to the propagation direction of light, which is called longitudinal spin angular momentum. In 2012, scholars Konstantin Y. Bliokh and Franco Nori discovered transverse spin angular momentum perpendicular to the propagation direction in the evanescent field of vacuum and metal medium surface, which attracted the attention of many scholars. Later, spin angular momentum perpendicular to the propagation direction of light was discovered in surface plasmons, wave interference fields and focused light fields. The discovery of transverse spin angular momentum of photons has expanded the freedom of optical manipulation and has attracted extensive research in particle manipulation, photon spin-orbit coupling, quantum optical communication and other aspects.

In a tightly focused light field with a high numerical aperture, due to the bending effect of the lens on the focused light, there may be a longitudinal electric field component along the propagation direction of the light beam. This component and the transverse electric field component perpendicular to the propagation direction of the light beam can form a circular polarization state to form transverse spin angular momentum. Currently, there is no method reported in the public to achieve three-dimensional arbitrary adjustment of the spin angular momentum pointing of a light spot beyond the diffraction limit in a tightly focused light field. The arbitrary adjustment of the spin angular momentum pointing in three-dimensional space will greatly enhance the flexibility of photon control of particle rotation around an axis and expand its application space.

Summary of the invention

In view of the above problems, the present invention provides a method for realizing an arbitrary spin-pointing super-diffraction-limited light focus, which utilizes the radiation field of an orthogonal dipole pair, combined with time reversal technology and Richard-Wolf vector diffraction integral theory, to realize arbitrary adjustable spatial direction of the spin angular momentum in a tightly focused light field.

In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for realizing an arbitrary spin-pointing super-diffraction-limited light focal spot, the method comprising the following steps:

Step 1: Create a confocal area using two objective lenses Optical focusing system;

Step 2: Place a pair of orthogonal dipoles at In a space where the center point of the optical focusing system is the origin, the dipole pair is orthogonally placed in the space, and the phase difference of the feeding current of the dipole pair is π/2;

Step 3: The orthogonal dipole pairs are connected The optical focusing system rotates with the center point as the fulcrum;

Step 4: The optical focusing system collects and aligns the radiation field generated by the rotated dipole pair to The entrance pupil surface of the optical focusing system, and the radiation field of the entrance pupil surface is obtained based on the bending effect of the lens on the light;

Step 5: Based on the time reversal technique, the radiation field at the entrance pupil is inverted and the relative π phase shift is used to obtain The two sides of the entrance pupil plane of the optical focusing system propagate back and converge toward the confocal area of the two objective lenses, and the focusing field data is calculated using the vector diffraction integral theory to form a super-diffraction limited light focal spot with arbitrarily adjustable spin direction in the confocal area of the two objective lenses.

Further, in step 1, the The optical focusing system consists of two high numerical aperture objective lenses with exactly the same dimensions and optical parameters. The optical axes of the two objective lenses are on the same straight line and are placed confocally.

In the A reference rectangular coordinate system is established in the optical focusing system; wherein the origin O of the reference rectangular coordinate system is the common focus of the two objective lenses; and the direction of the optical axis is axis, and Axis perpendicular to flat; The axis is vertically upward. Axis perpendicular to flat.

Further, in step 1, a pair of orthogonal dipole pairs are placed at The specific setting method in the space with the center point of the optical focusing system as the origin is: place one of the dipoles at axis, and the other dipole is placed On axis.

Further, in step 2, the orthogonal dipole pairs are The center point of the optical focusing system is used as the fulcrum for rotation. The specific setting method of rotation is: point P is any point in the reference rectangular coordinate system, then the spherical coordinate value of point P is ,in is the distance between point P and the origin O, For ray OP and The angle of the positive axis, For ray OP in Projection of the plane and Angle of the positive axis;

The reference rectangular coordinate system The axis revolves around the origin O The plane formed by the axis and the ray OP rotates one step horn, The axis rotates to point to OP; the ray OP is used as the new coordinate system after rotation Axis, at the same time The shaft rotates synchronously to axis, The shaft rotates synchronously to Axis, that is, the spatial position of the dipole pair changes with the reference rectangular coordinate system Axis and The axes rotate synchronously, and the rotated dipole pairs are located at the new coordinate system Axis and axis.

Furthermore, in step 3, the radiation field generated by the rotated dipole pair is calculated as follows:

Axes and reference rectangular coordinate system , and The angles of the axes are , and , Axes and reference rectangular coordinate system , and The angles of the axes are , and , after detailed derivation, we get:

(1)

(2)

The dipole is located on the x, y and z axes of the reference rectangular coordinate system, and its radiation fields are , and , the calculation formulas are as follows:

(3)

(4)

(5)

C is a constant that is independent of the direction of the radiation field;

After rotation, The radiated field of the dipole about the axis is:

(6)

After rotation, The radiated field of the dipole about the axis is:

(7)

Considering that the phase difference of the feeding current of the dipole pair is π/2, the radiation field of the dipole pair is:

(8)

in Is an imaginary unit.

Furthermore, in step 4, the radiation field of the entrance pupil plane is calculated as follows:

According to the bending effect of the lens on light, the radiation field at the entrance pupil surface is obtained as follows:

(9)

in, is the polar coordinate of the entrance pupil surface, is the apodization function of the objective lens, is the radiation field of the dipole pair.

Furthermore, in step 5, based on the Richard-Wolf vector diffraction integral theory, the electric field distribution in the confocal area can be calculated:

(10)

Where j is the imaginary unit, λ is the wavelength, is the maximum convergence angle of the objective lens, is the radiation field at the entrance pupil surface, is the polar coordinate of the entrance pupil surface, is the apodization function of the objective lens.

Further, in step 5, the spin angular momentum density of the focal field is calculated based on the calculated electric field in the confocal area. , the spin angular momentum density The calculation formula is as follows:

(11)

Among them, and is the electric field vector of the focal field and its conjugate vector, and is the magnetic field vector of the focal field and its conjugate vector, is a Gaussian unit, To take the imaginary part operation;

Then, the spin angular momentum density of the focal field is calculated. To quantitatively evaluate the spin orientation of the electric field in the confocal region, the spin angular momentum of the electric field in the confocal region is calculated by equation (11): of , and The three components , and , which can be quantitatively evaluated and , and The angle between the axes, i.e. the direction angle .

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 invention integrates the radiation field of the orthogonal dipole pair, the time reversal technology and the Richard-Wolf vector diffraction integral theory, and designs the orthogonal dipole pair with the center point located at The center point of the focusing system is the origin of the reference rectangular coordinate system; the dipole pairs are placed orthogonally in space, and the phase difference of the feeding current is π/2; the spatial direction of the normal line of the plane where the dipole pair is located is Can be set arbitrarily, among which is the angle between the normal and the Z axis (optical axis), is the angle between the projection of the normal on the XOY plane and the X axis; the radiation field of the dipole pair is The focusing system collects and aligns Focus the entrance pupil of the system; invert the radiation field at the entrance pupil and use a relative π phase shift from The optical focusing system's pupils on both sides propagate back and converge toward the confocal area, and a super-diffraction-limited light focal spot with arbitrarily adjustable spin orientation can be formed in the confocal area, and its light intensity 3D profile is a short ellipsoid with a major axis of 0.48λ and a minor axis of 0.41λ; therefore, the method of the present invention does not require a complicated optimization process, and the spin orientation of the generated super-diffraction-limited light focal spot can be arbitrarily adjusted. The light focal spot customized according to the method of the present invention has broad application potential in the fields of optical manipulation and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 is a schematic diagram of the present invention. Schematic diagram of the optical focusing system;

FIG2 is a 3D profile diagram of light intensity according to the first embodiment of the present invention;

FIG3 is a side view of the XOY plane of the light intensity 3D profile of the first embodiment of the present invention;

FIG4 is a side view of the XOZ plane of the light intensity 3D profile of the first embodiment of the present invention;

FIG5 is a YOZ plane side view of the light intensity 3D profile of the first embodiment of the present invention;

FIG6 is a diagram showing the light intensity and polarization state distribution of an XOY cross section of the first embodiment of the present invention;

FIG7 is a diagram showing the light intensity and polarization state distribution of the XOZ cross section of the first embodiment of the present invention;

FIG. 8 is a diagram of the second embodiment of the present invention when setting parameters 3D contour diagram of the light intensity of the confocal area spot;

FIG. 9 is a diagram of the second embodiment of the present invention when setting parameters The light intensity distribution and polarization state distribution diagram of the YOZ cross section of the confocal area light spot;

FIG. 10 is a diagram of the second embodiment of the present invention when setting parameters 3D contour diagram of the light intensity of the confocal area spot;

FIG. 11 is a diagram of the second embodiment of the present invention when setting parameters The XOZ cross-sectional light intensity distribution and polarization state distribution diagram of the confocal area spot;

FIG12 is a 3D profile diagram of light intensity of Embodiment 3 of the present invention;

FIG. 13 is a diagram showing the light intensity distribution and polarization state distribution of the YOZ cross section of the third embodiment of the present invention.

DETAILED DESCRIPTION

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.

Referring to FIG1 , a method for realizing an arbitrary spin-pointing super-diffraction-limited light focal spot is provided, the method comprising the following steps:

Created by two objectives with a confocal area Optical focusing system: a pair of orthogonal dipole pairs are placed at In a space with the center point of the optical focusing system as the origin, the dipole pair is placed orthogonally in the space, and the phase difference of the feeding current of the dipole pair is π/2; the orthogonal dipole pair is placed as The optical focusing system rotates with the center point as the fulcrum; The optical focusing system collects and aligns the radiation field generated by the rotated dipole pair to The entrance pupil of the optical focusing system is used to obtain the radiation field of the entrance pupil according to the bending effect of the lens on the light. Based on the time reversal technology, the radiation field of the entrance pupil is reversed and the relative π phase shift is used to obtain the radiation field of the entrance pupil. The two sides of the entrance pupil plane of the optical focusing system propagate back and converge toward the confocal area of the two objective lenses, and the focusing field data is obtained by using vector diffraction integral and theoretical calculation, so as to form a super-diffraction limited light focal spot with arbitrarily adjustable spin direction in the confocal area of the two objective lenses.

The invention integrates the radiation field of the orthogonal dipole pair, the time reversal technology and the Richard-Wolf vector diffraction integral theory, and designs the orthogonal dipole pair with the center point located at The center point of the optical focusing system is the origin of the reference rectangular coordinate system; the dipole pairs are placed orthogonally in space, and the phase difference of the feeding current is π/2; the spatial direction of the normal line of the plane where the dipole pair is located Can be set arbitrarily, among which is the angle between the normal and the Z axis (optical axis), is the angle between the projection of the normal on the XOY plane and the X axis; the radiation field of the dipole pair is The optical focusing system collects and aligns The entrance pupil of the optical focusing system; invert the radiation field at the entrance pupil and use a relative π phase shift from The optical focusing system's pupils on both sides propagate back and converge toward the confocal area, and a super-diffraction-limited light focal spot with arbitrarily adjustable spin orientation can be formed in the confocal area, and its light intensity 3D profile is a short ellipsoid with a major axis of 0.48λ and a minor axis of 0.41λ; therefore, the method of the present invention does not require a complicated optimization process, and the spin orientation of the generated super-diffraction-limited light focal spot can be arbitrarily adjusted. The light focal spot customized according to the method of the present invention has broad application potential in the fields of optical manipulation and the like.

The specific implementation steps of the method of the present invention are now introduced in detail:

(1) Placement of dipole pairs:

The optical focusing system consists of two high numerical aperture objective lenses with exactly the same dimensions and optical parameters. The optical axes of the two objective lenses are on the same straight line and are placed confocally.

exist A reference rectangular coordinate system is established in the optical focusing system; the origin O of the reference rectangular coordinate system is the common focus of the two objective lenses; the direction of the optical axis is axis, and Axis perpendicular to flat; The axis is vertically upward. Axis perpendicular to flat;

Place an orthogonal pair of dipoles at The specific setting method in the space with the center point of the optical focusing system as the origin is: place one of the dipoles at axis, and the other dipole is placed On the axis, the feeding currents of the dipole pairs differ in phase by π/2.

(2) Rotating coordinate system:

Point P is an arbitrary point in the reference rectangular coordinate system, and its spherical coordinate value is ,in is the distance between point P and the origin O, For ray OP and The angle of the positive axis, For ray OP in Projection of the plane and Angle of the positive axis.

The reference rectangular coordinate system The axis revolves around the origin O The plane formed by the axis and the ray OP rotates one step horn, The axis rotates to point to OP; the ray OP is used as the new coordinate system after rotation Axis, at the same time The shaft rotates synchronously to axis, The shaft rotates synchronously to Axis; the spatial position of the dipole pair varies with the reference rectangular coordinate system Axis and The axes rotate synchronously, and the rotated dipole pairs are located at Axis and Axis, as shown in Figure 1.

(3) Calculate the radiation field of the rotated dipole pair:

Axes and reference rectangular coordinate system , and The angles of the axes are , and , Axes and reference rectangular coordinate system , and The angles of the axes are , and , after detailed derivation, we get:

(1)

(2)

The dipole is located at the reference rectangular coordinate system , and axis, and their radiation fields are , and , the calculation formulas are as follows:

(3)

(4)

(5)

C is a constant that is independent of the direction of the radiation field;

After rotation, The radiated field of the dipole about the axis is:

(6)

After rotation, The radiated field of the dipole about the axis is:

(7)

Considering that the phase difference of the feeding current of the dipole pair is π/2, the radiation field of the dipole pair is:

(8)

in Is an imaginary unit.

(4) Calculate the radiation field at the entrance pupil surface:

The reference rectangular coordinate system The plane is the confocal plane of two objectives with the same high numerical aperture, forming Optical focusing system; To calculate the radiation field at the entrance pupil, the bending effect of the lens on the light must be considered; if the apodization function of the objective lens is , then the radiation field at the entrance pupil surface can be obtained as:

(9)

in is the polar coordinate of the entrance pupil surface.

(5) Reverse and tightly focus the radiation field of the dipole pair:

Based on the time reversal technology, the above radiation field is reversed at the entrance pupil plane of the objective lens. The phases of the incident fields on both sides are different by π and propagate in the opposite direction, converging and focusing on the confocal area of the two objective lenses. Based on the Richard-Wolf vector diffraction integral theory, the electric field distribution in the confocal area can be calculated:

(10)

Where j is the imaginary unit, λ is the wavelength, is the maximum convergence angle of the objective lens, is the radiation field at the entrance pupil surface, is the polar coordinate of the entrance pupil surface, is the apodization function of the objective lens.

(6) Calculate the spin orientation of the electric field in the confocal region:

Calculate the spin angular momentum density of the focal field using the generated focal field data To quantitatively evaluate the spin orientation of the electric field in the confocal area and the spin angular momentum density The calculation formula is as follows:

(11)

In the formula and is the electric field vector of the focal field and its conjugate vector, and is the magnetic field vector of the focal field and its conjugate vector, is a Gaussian unit, is the operation of taking the imaginary part; here only the electric field in the confocal area is calculated; the spin angular momentum of the electric field in the confocal area is calculated by equation (11): of , and The three components , and , which can be quantitatively evaluated and , and The angle between the axes, i.e. the direction angle .

The following examples are given to demonstrate the effectiveness of the method proposed by the present invention.

To simplify the calculation, the parameter C that is independent of the light focal field shape and polarization is normalized in the embodiments listed, that is, C=1; to converge the reverse radiation field of the dipole pair, the high numerical aperture objective lens convergence angle is taken as ,Right now The objective lens that satisfies the sine condition is used as the objective lens of the embodiment of the present invention, and its apodization function .

Example 1: Generating a Z-axis spin-pointing super-diffraction-limited light focal spot:

The dipole pair is placed as shown in Figure 1, and the parameters are set. , the light intensity of the confocal area is calculated The 3D shape contour diagram when , is shown in Figure 2, and its XOY, XOZ and YOZ plane views are shown in Figures 3, 4 and 5 respectively. It can be found that its light intensity distribution contour is a short ellipsoid rotated around the Z axis, and the light focal spot is a sub-wavelength size; the light intensity and polarization state distribution of the XOY and XOZ cross sections are shown in Figures 6 and 7 respectively.

It can be seen from Figure 6 that the light intensity distribution at the center of the focal spot XOY section is a perfect circular distribution, and the polarization at the center of the focal spot is a circular polarization distribution. It can be judged that its spin direction is along the Z axis. By analyzing and calculating the spin density of the data in the central area of the focal field through formula (11), the direction angle of the central area can be obtained as , that is, along the positive direction of the Z axis, according to the set parameters Determination; It can be seen from FIG7 that the light intensity distribution at the center of the focal spot XOZ cross section is an elliptical distribution, and the polarization at the center of the focal spot is linear polarization in the X direction; Analysis of the data in FIG6 and FIG7 shows that the light intensity profile of the focal spot is a short ellipsoid, the half-maximum full width of the short axis is 0.41λ, the half-maximum full width of the long axis is 0.48λ, and the volume of the focal spot is 0.0422λ ³ , which is a super-diffraction-limited light focal spot.

Example 2: Generating X-axis and Y-axis spin-pointing super-diffraction-limited light focal spots:

When setting parameters , the light intensity of the confocal area is calculated The 3D shape contour diagram is shown in Figure 8, and the light intensity distribution and polarization state distribution in the YOZ plane are shown in Figure 9.

When setting parameters , the light intensity of the confocal area is calculated The 3D shape profile diagram is shown in Figure 10, and the light intensity distribution and polarization state distribution in the XOZ plane are shown in Figure 11.

As shown in Figures 8 and 10, the 3D shape of the focal spot is similar to that in Example 1, which are rotating bodies rotating around the X-axis and the Y-axis respectively; as shown in Figures 9 and 11, the central area of the focal spot is positive circular polarization, and the two rotation directions are opposite. By analyzing and calculating the spin density of the data in the central area of the focal field, the direction angle of the central area can be obtained as and , that is, the spin points along the positive direction of the X-axis and Y-axis respectively, according to the parameters set Decide.

Example 3: Generating a light focal spot with spin pointing to a non-axial direction:

In order to generate a light focal spot with spin pointing in a non-axial direction, the value of the direction parameter cannot be the same as in Example 1 and Example 2. Without loss of generality, For example, the light intensity of the confocal area is calculated. The 3D shape contour diagram is shown in Figure 12; the YOZ plane light intensity distribution and polarization state distribution are shown in Figure 13.

It can be seen from Figure 12 that the light intensity distribution is a short ellipsoid, and the direction of the short ellipsoid is non-axial; at the same time, it can be seen from Figure 13 that the focal spot has an elliptically polarized distribution in the YOZ plane, not a perfect circular distribution; based on the focal field data of the YOZ plane, the spin density in the X, Y, and Z directions is calculated, and the direction angle of the central area of the focal spot is , the corresponding spatial orientation is , by the set parameters Decide.

In summary, it can be seen from Examples 1, 2 and 3 that the method proposed by the present invention can be easily adjusted by adjusting the spatial pointing parameters The purpose of controlling the spin angular momentum direction of the super-diffraction limited light focus is achieved.

The above are only preferred embodiments of the present invention and are 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 (4)

A method for realizing arbitrary spin pointing to a super-diffraction-limited light focal spot, characterized in that the method comprises the following steps: Step 1: Create a confocal area using two objective lenses Optical focusing system; The optical focusing system consists of two high numerical aperture objective lenses with exactly the same dimensions and optical parameters. The optical axes of the two objective lenses are on the same straight line and are placed confocally. In the A reference rectangular coordinate system is established in the optical focusing system; wherein the origin O of the reference rectangular coordinate system is the common focus of the two objective lenses; and the direction of the optical axis is axis, and Axis perpendicular to flat; The axis is vertically upward. Axis perpendicular to flat; Place an orthogonal pair of dipoles at The specific setting method in the space where the center point of the optical focusing system is the origin is: place one of the dipoles at axis, and the other dipole is placed on axis; Step 2: Place a pair of orthogonal dipoles at In a space with the center point of the optical focusing system as the origin, the dipole pair is orthogonally placed in the space, and the phase difference of the feeding current of the dipole pair is π/2; the orthogonal dipole pair is placed in a The center point of the optical focusing system is used as the fulcrum for rotation; the specific setting method of rotation is: point P is an arbitrary point in the reference rectangular coordinate system, and its spherical coordinate value is ,in is the distance between point P and the origin O, For ray OP and The angle of the positive axis, For ray OP in Projection of the plane and Angle of the positive axis; The reference rectangular coordinate system The axis revolves around the origin O The plane formed by the axis and the ray OP rotates one step horn, The axis rotates to point to OP; the ray OP is used as the new coordinate system after rotation Axis, at the same time The shaft rotates synchronously to axis, The shaft rotates synchronously to Axis, that is, the spatial position of the dipole pair changes with the reference rectangular coordinate system Axis and The axes rotate synchronously, and the rotated dipole pairs are located at the new coordinate system Axis and axis; Step 3: The orthogonal dipole pairs are connected The optical focusing system rotates with the center point as the fulcrum; the radiation field generated by the rotated dipole pair is calculated as follows: Axes and reference rectangular coordinate system , and The angles of the axes are , and , Axes and reference rectangular coordinate system , and The angles of the axes are , and , after detailed derivation, we get: (1) (2) The dipole is located on the x, y and z axes of the reference rectangular coordinate system, and its radiation fields are , and , the calculation formulas are as follows: (3) (4) (5) C is a constant that is independent of the direction of the radiation field; After rotation, The radiated field of the dipole about the axis is: (6) After rotation, The radiated field of the dipole about the axis is: (7) Considering that the phase difference of the feeding current of the dipole pair is π/2, the radiation field of the dipole pair is: (8) in is an imaginary unit; Step 4: The optical focusing system collects and aligns the radiation field generated by the rotated dipole pair to The entrance pupil surface of the optical focusing system, and the radiation field of the entrance pupil surface is obtained based on the bending effect of the lens on the light; Step 5: Based on the time reversal technique, the radiation field at the entrance pupil is inverted and the relative π phase shift is used to obtain The two sides of the entrance pupil plane of the optical focusing system propagate back and converge toward the confocal area of the two objective lenses, and the focusing field data is calculated using the vector diffraction integral theory to form a super-diffraction limited light focal spot with arbitrarily adjustable spin direction in the confocal area of the two objective lenses. The method for realizing an arbitrary spin-directed super-diffraction-limited light focal spot according to claim 1 is characterized in that: in step 4, the calculation method of the radiation field of the entrance pupil plane is specifically as follows: According to the bending effect of the lens on light, the radiation field at the entrance pupil surface is obtained as follows: (9) in, is the polar coordinate of the entrance pupil surface, is the apodization function of the objective lens, is the radiation field of the dipole pair. The method for realizing an arbitrary spin-pointing super-diffraction-limited light focal spot according to claim 2 is characterized in that: in step 5, based on the Richard-Wolf vector diffraction integral theory, the electric field distribution in the confocal area can be calculated: (10) Where j is the imaginary unit, λ is the wavelength, is the maximum convergence angle of the objective lens, is the radiation field at the entrance pupil surface, is the polar coordinate of the entrance pupil surface, is the apodization function of the objective lens. The method for realizing a super-diffraction-limited light focal spot with arbitrary spin pointing according to claim 3 is characterized in that: in step 5, the spin angular momentum density of the focal field is calculated based on the calculated confocal area electric field. , the spin angular momentum density The calculation formula is as follows: (11) Among them, and is the electric field vector and its conjugate vector in the confocal region, and is the magnetic field vector of the focal field and its conjugate vector, is a Gaussian unit, To take the imaginary part operation; Then, the spin angular momentum density of the focal field is calculated. To quantitatively evaluate the spin orientation of the electric field in the confocal region, the spin angular momentum of the electric field in the confocal region is calculated by equation (11): of , and The three components , and , which can then be quantitatively evaluated and , and The angle between the axes, i.e. the direction angle .