Micro-nano particle optical control method and device based on circularly polarized light

Abstract

The invention relates to the technical field of optical control, in particular to a micro-nano particle optical control method and device based on circularly polarized light. The invention aims to solve the problem of insufficient flexibility of optical control. The optical control method comprises the following steps: pre-processing micro-nano particles to be controlled; the initial Gaussian beam is processed into a circular polarization tube type beam through a beam shaping module, a light guiding module and a polarization regulation and control module, and the micro-nano particles are irradiated from the position above the gas-liquid interface according to a preset mode; by adjusting the polarization regulation and control module and the light guide module, the motion direction, the motion speed and the stop position of the micro-nano particles are optically controlled. The optical control device comprises a control platform module, a laser emitting module, a light beam shaping module, a light guiding module, a polarization regulation and control module and an imaging monitoring module.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-nanoparticle manipulation, and more particularly to a micro-nanoparticle optical manipulation method and device based on circularly polarized light. BACKGROUND

[0002] Micro-nanoparticles often need to be transported and reversibly positioned with high precision and non-contact in the fields of biological detection, functional material construction, and micro-optical element integration. For this purpose, researchers have developed simple mechanical / centrifugal methods such as mechanical screening and density gradient centrifugation. However, the resolution of these methods is limited by the mesh aperture or the stability of the density gradient, and it is difficult to achieve sub-micron precision. Moreover, contact operations can cause mechanical damage.

[0003] Field force and field gradient methods can avoid direct contact, but each has its own limitations. For example, magnetic tweezers or electromagnetic manipulation require the particles to be magnetized or surface-modified, which complicates the system and limits its scope of application. In patent document CN114146890A, the acoustic tweezers technology uses a transducer array to emit focused and multi-angle plane ultrasound waves, combined with a time reversal algorithm to achieve particle manipulation. However, its positioning accuracy usually stays at the micron level and is easily affected by scattering attenuation in heterogeneous media. At the same time, the system is large in size and complex in electronic driving. In patent document CN114843002A, the photothermal diffusiophoresis device captures and moves particles over a large range through a local temperature gradient. However, the uneven distribution of the temperature field leads to large errors in the fine positioning of single particles, and the photothermal effect poses a potential risk of damage to temperature-sensitive samples.

[0004] In addition, optical mechanical methods can manipulate microparticles under label-free and non-contact conditions by utilizing the mechanical effects of the light field itself. Classic high numerical aperture optical tweezers rely on a three-dimensional gradient potential well to achieve capture, but the working distance is short and the efficiency of lateral transport on the gas-liquid interface is low. Patent document CN114496335A proposes to use an initial Gaussian beam to irradiate the interface at an angle, generating a unidirectional lateral optical force in the elliptical spot through the breaking of system symmetry, thereby driving the microparticles to move along the long axis of the spot. The feasibility of using lateral optical force for interface transport is verified. However, this scheme has the following shortcomings: the direction of the lateral optical force is fixedly coupled with the linear polarization vector, and if reverse transport or rapid stopping is required, the polarizer must be mechanically rotated or the incident angle must be changed, which is slow in response, and the force amplitude and direction are difficult to program independently.

[0005] In summary, existing interface microparticle manipulation techniques still cannot simultaneously meet the comprehensive requirements of high precision, fast reversible switching, and simple device. Especially in the context of multi-particle sequence assembly or reversible positioning, it is urgent to introduce new degrees of freedom of light field to improve the manipulation flexibility and simplify the system structure. SUMMARY

[0006] The present application aims to overcome at least one of the above-mentioned defects of the prior art, and provides a method and device for optical manipulation of micro-nanoparticles based on circularly polarized light, to solve the problem of insufficient flexibility of optical manipulation.

[0007] The first object of the present application is to provide a method for optical manipulation of micro-nanoparticles based on circularly polarized light, wherein a gas-liquid interface is prepared by a liquid medium and a gas medium, and the micro-nanoparticles to be manipulated are suspended in the liquid medium and partially exposed to the gas-liquid interface, and the micro-nanoparticles can move freely. The method is realized by an optical manipulation assembly, wherein the optical manipulation assembly comprises a light beam shaping module, a light guiding module, and a polarization control module. The method comprises the following steps: An initial Gaussian light beam is passed through the light guiding module, the light guiding module, and the polarization control module in a preset order, so that the initial Gaussian light beam is converted into a circularly polarized Gaussian light beam, and the micro-nanoparticles are irradiated from above the gas-liquid interface in a preset manner. The movement direction, movement speed, and residence position of the micro-nanoparticles are optically manipulated by adjusting the polarization control module and the light guiding module. The preset manner comprises: the circularly polarized Gaussian light beam forms an elliptical light spot with a major axis and a minor axis on the gas-liquid interface, the major axis is parallel to the gas-liquid interface and perpendicular to the propagation direction of the circularly polarized Gaussian light beam, and the micro-nanoparticles are bound to the major axis by a minor axis gradient force; and the incident angle formed by the circularly polarized Gaussian light beam and the normal line of the gas-liquid interface is in the range of (0°, 90°), and the circularly polarized Gaussian light beam induces the micro-nanoparticles to generate a transverse optical force parallel to the major axis.

[0008] In the present application, by introducing the spin angular momentum carried by the circularly polarized Gaussian beam and setting the non-zero incident angle of the incident angle number ∈ (0°, 90°), the spin-orbit coupling effect can be generated at the gas-liquid interface with discontinuous refractive index, and then the transverse optical force along the long axis direction of the elliptical light spot is induced for the micro-nano particles suspended in the gas-liquid interface. In this way, the suspended particles can be driven to produce displacement in a specific direction on the interface. Wherein, by switching the circular polarization direction of the circularly polarized Gaussian beam through the polarization control module, the direction of the transverse optical force can be reversed, but the spot pattern remains unchanged. This feature ensures that the micro-nano particles can be reversibly transported under the driving of the bidirectional optical force, effectively avoiding the interference caused by the incident light re-adjustment or platform movement. In addition, the micro-nano particles are bound by a strong gradient force in the short axis direction of the elliptical light spot, and their displacement mainly occurs in the long axis direction; by adjusting the incident angle of the circularly polarized Gaussian beam through the light guiding module, combined with adjusting the power of the initial Gaussian beam, the amplitude of the transverse optical force can be continuously controlled, so as to realize the accurate control of the particle movement speed and the termination position. In this way, the amplitude and direction of the transverse optical force are decoupled, a two-degree-of-freedom control capability is realized, and the control efficiency and positioning accuracy are improved.

[0009] Further, the incident angle ∈ is [5°, 75°].

[0010] Tests show that the incident angle based on the present application helps to induce more significant transverse optical force.

[0011] Further, the radius of the micro-nano particle is 200 nm-50 µm.

[0012] Further, the difference between the refractive index of the micro-nano particle and the refractive index of the gas is greater than 0.05.

[0013] Further, the micro-nano particle is a polystyrene particle or a silica particle.

[0014] Further, the length of the long axis is 100-500 um, the length of the short axis is 10-100 um, and the ratio of the length of the long axis to the length of the short axis is 3-15.

[0015] Based on the long and short axis parameters of the present application, the gradient force in the long axis direction can be avoided to interfere with the transverse optical force, and the manipulation effect of the transverse optical force on the micro-nano particle is optimized.

[0016] Further, the maximum light intensity of the elliptical light spot covering the area of the gas-liquid interface is not less than 1 mW.µm⁻².

[0017] Further, the liquid medium is any one of pure water, ethanol, and low-concentration buffer solution.

[0018] A second objective of this invention is to provide a micro / nano particle optical manipulation device based on circularly polarized light, comprising: The control platform module is used to carry out the preparation of gas-liquid interfaces through liquid and gas media, wherein the micro-nano particles to be controlled are suspended in the liquid media and partially exposed at the gas-liquid interface, and the micro-nano particles can move freely. Laser emission module, used to emit the initial Gaussian beam; An optical manipulation component includes a beam shaping module, a light guiding module, and a polarization control module. The optical manipulation component is used to convert an initial Gaussian beam passing through the beam shaping module, the light guiding module, and the polarization control module in a preset sequence into a circularly polarized Gaussian beam, and then irradiate the micro / nano particles from above the gas-liquid interface in a preset manner. The polarization control module and the light guiding module are further configured to control the direction of motion, speed of motion, and position of the micro / nano particles. The preset method includes: the circularly polarized Gaussian beam forms an elliptical spot with a major axis and a minor axis at the gas-liquid interface, the major axis being parallel to the gas-liquid interface and perpendicular to the propagation direction of the circularly polarized Gaussian beam, and the micro / nanoparticles being bound to the major axis by a minor axis gradient force; and the angle of incidence formed by the circularly polarized Gaussian beam and the normal to the gas-liquid interface having degrees ∈ (0°, 90°), and the circularly polarized Gaussian beam inducing the micro / nanoparticles to generate a transverse optical force parallel to the major axis.

[0019] Furthermore, the polarization control module includes a polarizer, λ / 2 wave plate and λ / 4 waveplate, the polarizer, the λ / 2 waveplate, the aforementioned λ The 4-wave plates are coaxial and arranged sequentially along the propagation direction of the initial Gaussian beam.

[0020] In this invention, a polarizer is used to transform the polarization state of an initial Gaussian beam into a reliable linearly polarized Gaussian beam, through... λ / 2 waveplates adjust the rotation direction of polarized light to achieve polarization angle adjustment; λ A / 4 waveplate is used to convert a linearly polarized Gaussian beam into a circularly polarized Gaussian beam, or to adjust the rotation of the beam to left- or right-hand circular polarization, thereby controlling the direction of the optical force in the optical field. It can be understood that by adjusting... λ / 2 waveplate and λ The angle of the 4-wave plate allows for flexible adjustment of the polarization state of the beam, thereby enabling precise control of the particle's motion direction.

[0021] Further, the light beam shaping module comprises at least one cylindrical lens and at least one convex lens, the cylindrical lens and the convex lens are coaxial and arranged in sequence along the propagation direction of the initial Gaussian light beam.

[0022] Further, the laser exit module outputs an initial Gaussian light beam with a wavelength of 400-800 nm; and / or, The output mode of the laser exit module is single longitudinal mode output; and / or, The output power of the laser exit module ranges from 0 to 5 W, and / or, The polarization extinction ratio of the laser exit module is greater than or equal to 20 dB.

[0023] Further, it further comprises an imaging module for monitoring the position and motion trajectory of the micro-nanoparticles and imaging.

[0024] Compared with the prior art, the beneficial effects of the present application are: (1) Through the spin-orbit coupling effect induced by the spin angular momentum of the circularly polarized Gaussian light beam and the refractive index jump of the gas-liquid interface, asymmetric light scattering of the particles at the interface is caused, a direction reversible lateral optical force is constructed, and high-response, low-energy micro-particle transport control is realized.

[0025] (2) The amplitude and direction of the optical force are decoupled, the direction of the optical force is determined by the polarization rotation direction, the amplitude is controlled by the incident angle and the laser power, and the double-degree-of-freedom control ability is realized.

[0026] (3) Without the help of photothermal layers, acoustic arrays or magnetic control systems, high-precision and multi-particle programming assembly can be realized, and the micro-nanoparticle optical manipulation device and the operation process are significantly simplified.

[0027] (4) The micro-nanoparticle optical manipulation device has a simple structure, is suitable for various optical platforms, has good scalability and integration, and is suitable for various optical manipulation application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The flowchart of the micro-nanoparticle optical manipulation method based on circularly polarized light of the present application.

[0029] Figure 2 The schematic diagram of the micro-nanoparticle optical manipulation device based on circularly polarized light of the present application.

[0030] Figure 3 The near-field scattering field diagram of the polystyrene micro-nanoparticle in the test example under different circular polarization directions, wherein, Figure 3 (a) is the near-field scattering field diagram under the right-handed circular polarization direction, Figure 3 (b) is the near-field scattering field diagram under the left-handed circular polarization direction.

[0031] Figure 4 Fig. 1 shows the variation diagram of the lateral optical force of polystyrene micro-nanoparticles in the test example with different circular polarization rotations and incident angles.

[0032] Fig. 1 shows the variation diagram of the lateral optical force of polystyrene micro-nanoparticles in the test example with different circular polarization rotations and incident angles. DETAILED DESCRIPTION

[0033] The drawings of the present application are only used for illustrative description, and cannot be understood as a limitation on the present application. In order to better illustrate the following embodiments, some components of the drawings may be omitted, enlarged or reduced, and do not represent the actual product size; it can be understood by those skilled in the art that some well-known structures in the drawings and their descriptions may be omitted.

[0034] In addition, in the present application, unless otherwise explicitly specified and limited, the terms "connection", "fixation" and the like should be broadly understood, for example, "fixation" can be fixed connection, or detachable connection, or integral; can be directly connected, or indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0035] In addition, the description of "first", "second" and the like in the present application is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor within the scope of protection required by the present application.

[0036] Example 1 As shown in Figure 1 The present application first provides a micro-nanoparticle optical manipulation method based on circularly polarized light, the steps are as follows: S0. Preprocessing the micro-nanoparticles to be manipulated, first preparing a stable gas-liquid interface through a liquid medium and a gas medium, the micro-nanoparticles to be manipulated are suspended in the liquid medium and partially exposed to the gas-liquid interface, ensuring that the micro-nanoparticles can move freely; S1. Shape the initial Gaussian beam into an elliptical beam, specifically, shape the initial Gaussian beam emitted by the laser emitting module into an elliptical beam with an elliptical cross section through the beam shaping module; S2. The elliptical light beam is converted into a circularly polarized Gaussian light beam after sequentially passing through the light guiding module and the polarization control module, and irradiates the micro-nano particles from above the gas-liquid interface in a preset manner, that is, the incident light beam for irradiating the micro-nano particles is a circularly polarized Gaussian light beam, and the projection section is elliptical; The preset manner includes: the incident light beam forms an elliptical spot with a major axis and a minor axis on the gas-liquid interface, the major axis is parallel to the gas-liquid interface and perpendicular to the propagation direction of the circularly polarized Gaussian light beam, and the micro-nano particles are bound on the major axis by the short-axis gradient force; and through the guiding action of the light guiding module, the incident angle formed by the circularly polarized Gaussian light beam and the normal line of the gas-liquid interface is in the range of (0°, 90°), thereby inducing the micro-nano particles to generate transverse optical force parallel to the major axis; S3. The micro-nano particles are optically manipulated by the optical module. In specific implementation, the polarization control module and the light guiding module 3 are adjusted to optically manipulate the movement direction, movement speed and residence position of the micro-nano particles.

[0037] In some embodiments, the elliptical light beam can be first converted into a circularly polarized Gaussian light beam by the polarization control module, and then be obliquely incident on the micro-nano particles by the adjusting action of the light guiding module. In other embodiments, the initial Gaussian light beam emitted by the laser emission module can be first converted into a circularly polarized Gaussian light beam by the polarization control module, and then be shaped into an elliptical light beam by the beam shaping module, and then be obliquely incident on the micro-nano particles by the adjusting action of the light guiding module. In addition, in other embodiments, the beam shaping module can be arranged between the light guiding module and the polarization control module, or arranged after the light guiding module and the polarization control module. It should be noted that the order of the initial Gaussian light beam passing through the beam shaping module, the light guiding module and the polarization control module can be flexibly adjusted according to actual conditions, as long as a circularly polarized Gaussian light beam can be obtained and the micro-nano particles can be irradiated from above the gas-liquid interface in the preset manner. Those skilled in the art will easily understand that this will not be described here.

[0038] It is necessary to emphasize that since the light guiding module usually includes a mirror, the mirror may be silver-coated or coated with a dielectric film, which will change the polarization of the reflected light. Therefore, in a preferred embodiment, the polarization control module is arranged after the light guiding module, which is more conducive to obtaining the expected polarization effect. Of course, according to the type of the mirror, the regulation of the polarization by the mirror can be measured, so if the polarization control module is arranged before the light guiding module, the polarization can be designed according to the regulation of the polarization by the mirror, so that the expected polarization can be achieved after the mirror.

[0039] In some embodiments, the micro-nanoparticles are isotropic particles, preferably transparent particles with a refractive index greater than that of the medium liquid, such as polystyrene, silica, etc., and the difference between the refractive index of the micro-nanoparticles and the refractive index of the gas is greater than 0.05, and the particle size of the micro-nanoparticles ranges from 200 nm to 50 µm, to ensure sufficient optical force response and manipulation stability. More preferably, the liquid medium is pure water, deionized water, ethanol or a low-concentration buffer solution, and the gas medium is air, and the interface requires to be clean and stable, without obvious flow and vibration, to avoid airflow and background noise causing disturbance to the microparticles.

[0040] In some embodiments, in step S2, the length of the long axis of the elliptical light spot is 100-500 µm, and the length of the short axis is 10-100 µm, and the ratio of the length of the long axis to the length of the short axis is 3-15, so that the gradient force in the long axis direction can be avoided to interfere with the transverse optical force, and the manipulation effect of the transverse optical force on the micro-nanoparticles can be optimized.

[0041] In some embodiments, in step S3, the motion direction of the micro-nanoparticles can be switched by the polarization control module, and in a preferred embodiment, the operation of the polarization control module can also be controlled by the control system module, so that the motion direction of the micro-nanoparticles can be switched more quickly. Specifically, the positive and negative directions of the long axis can be switched; the incident angle can be adjusted by adjusting the inclination angle of the light guiding module 3, so as to control the amplitude of the transverse optical force, and further control the motion speed of the micro-nanoparticles. In addition, there is a positive correlation between the power of the initial Gaussian beam and the amplitude of the transverse optical force, so the power of the initial Gaussian beam can also be adjusted to jointly control the motion speed of the micro-nanoparticles. It can be understood that the micro-nanoparticles finally stay in the region with the strongest light field, and form a sequenced micro-assembly structure. When all the micro-nanoparticles are positioned, the micro-nanoparticles can also be locked by reducing the laser power or by switching the position of the elliptical light spot to stop the action of the transverse optical force, so that the particles naturally remain in their final positions, and the micro-assembly process is completed.

[0042] The optical manipulation principle of the present application is as follows: by introducing the spin angular momentum carried by the circularly polarized Gaussian beam and setting a non-zero incident angle of the incident angle number ∈ (0°, 90°), the spin-orbit coupling effect can be generated at the gas-liquid interface with discontinuous refractive index. Specifically, due to the spin angular momentum carried by the circularly polarized Gaussian beam, when interacting with the tilted interface and the scattering field, the spin angular momentum is partially converted into the orbital angular momentum, resulting in asymmetric distribution of light momentum in the transverse direction, and further inducing the micro-nano particles suspended in the gas-liquid interface to generate transverse optical force along the long axis direction of the elliptical light spot. In this way, the suspended particles can be driven to move in a specific direction on the interface. Wherein, by switching the circular polarization direction of the incident light beam through the polarization control module, the direction of the transverse optical force can be reversed, but the light spot pattern remains unchanged. This feature ensures that the micro-nano particles can be reversibly transported under the driving of the bidirectional optical force, effectively avoiding the interference caused by the adjustment of the incident light or the movement of the platform. In addition, the micro-nano particles are bound by a strong gradient force in the short axis direction of the elliptical light spot, and their displacement mainly occurs in the long axis direction. By adjusting the incident angle of the incident light beam through the light guiding module, combined with adjusting the power of the initial Gaussian beam, the amplitude of the transverse optical force can be continuously controlled, so as to realize the accurate control of the particle movement speed and the termination position. In this way, the amplitude and direction of the transverse optical force are decoupled, the two-degree-of-freedom control ability is realized, and the control efficiency and positioning accuracy are improved.

[0043] The second aspect of the present application provides a micro-nano particle optical manipulation device based on circularly polarized light, referring to Figure 2 The micro-nano particle 7 optical manipulation device based on circularly polarized light comprises: A manipulation platform module 6 carries a gas-liquid interface prepared by a liquid medium and a gas medium, and the micro-nano particles 7 to be manipulated are suspended in the liquid medium and partially exposed to the gas-liquid interface, and the micro-nano particles 7 can move freely; A laser exit module 1 is used for emitting an initial Gaussian beam; A beam shaping module 2 is used for shaping the initial Gaussian beam into an incident light beam with an elliptical cross section; A light guiding module 3 is used for guiding the incident light beam to obliquely irradiate the micro-nano particles 7, and for adjusting the incident angle of the incident light beam; A polarization control module 4 is used for converting the incident light beam into a circularly polarized Gaussian beam, and for adjusting the rotation direction of the circularly polarized Gaussian beam; An imaging monitoring module 5 is used for monitoring the position and motion trajectory of the micro-nano particles 7, and for imaging.

[0044] In specific implementation, the operation platform module 6 includes a three-dimensional displacement platform with sub-micron level moving precision and a transparent sample container. The three-dimensional displacement platform is used to install a sample cell carrying liquid and particles, and can be finely adjusted in X, Y and Z axes to realize accurate alignment of the elliptical light spot and the position of the micro-nano particles 7, which helps to maintain the liquid surface in a static state to avoid interface disturbance to the particle operation.

[0045] In specific implementation, the laser emission module 1 outputs an initial Gaussian beam with a wavelength of 400-800 nm, a single longitudinal mode output, an output power range of 0-5 W, and a polarization extinction ratio of ≥20 dB. The initial Gaussian beam can be a perfect linearly polarized Gaussian beam reflected by a He-Ne laser and a diode laser, a linearly polarized Gaussian beam with a reduced polarization degree, or a non-polarized or randomly polarized Gaussian beam. It can be understood that no matter what type of Gaussian beam it is, it can be converted into a circularly polarized Gaussian beam by the polarization control module 4 in the prior art, and no further description is needed here.

[0046] In specific implementation, the beam shaping module 2 includes at least one cylindrical lens and at least one convex lens, which are coaxial and arranged in sequence along the propagation direction of the initial Gaussian beam.

[0047] In specific implementation, the polarization control module 4 includes a polarizer, λ a / 2 wave plate and λ a / 4 wave plate, which are coaxial and arranged in sequence along the propagation direction of the initial Gaussian beam. The polarizer is used to convert the polarization state of the initial Gaussian beam into a reliable linearly polarized Gaussian beam, which is adjusted by the / 2 wave plate to adjust the rotation direction of the polarized light and realize the adjustment of the polarization angle. λ The / 4 wave plate is used to convert the linearly polarized Gaussian beam into a circularly polarized Gaussian beam, or adjust the rotation direction of the beam to left-handed or right-handed circular polarization, so as to control the direction of the optical force in the light field. It can be understood that by adjusting the angles of the / 2 wave plate and the / 4 wave plate, the polarization state of the beam can be flexibly adjusted to realize accurate control of the motion direction of the microparticles. λ λ λ λ λ

[0048] In specific implementation, the imaging monitoring module 5 is composed of a CCD camera, an imaging objective lens and synchronous illumination, which can realize full-process tracking and image recording of the micro-nano particles 7 placed at the gas-liquid interface, and analyze the motion speed and motion time of the particles.

[0049] ​​​​​In some embodiments, the circularly polarized light-based micro-nanoparticle 7 optical manipulation device further comprises a control system module 8 and a computer 9 module. In actual application, the control system module 8 and the computer 9 form an automatic control and data acquisition core, and are electrically connected with the laser emission module 1, the light guiding module 3, the polarization control module 4, and the manipulation platform module 6. Exemplarily, the control system adopted by the control system module 8 is based on an FPGA or microcontroller architecture, and executes instructions such as power adjustment, polarization state switching, and platform position control of the initial Gaussian light beam; the computer 9 end is used for user interaction, data processing, real-time control instruction sending, and image processing result visualization. It should be pointed out that the FPGA or microcontroller architecture is prior art in the field, and will not be described here.

[0050] The circularly polarized light-based micro-nanoparticle 7 optical manipulation device of the present application cooperates with each module to form a complete micro-particle active transport and assembly system. The control process is as follows: the computer 9 presets a particle target position sequence, the system judges the position deviation according to the real-time image of the current particle, and dynamically adjusts the polarization state and the direction of the incident angle, so as to drive the particle to move along the set trajectory to the target area, and finally realizes positioning locking by adjusting to linear polarization.

[0051] Test example This test example takes polystyrene micro-nanoparticles as an example to verify the circularly polarized light-based micro-nanoparticle optical manipulation method and device.

[0052] Exemplarily, in step S0, the stable gas-liquid interface is prepared by a liquid medium and a gas medium, and the micro-nanoparticles to be manipulated are suspended in the liquid medium and partially exposed to the gas-liquid interface. Specifically, a quartz glass piece with a size of 40 mm × 25 mm × 1 mm is taken, ultrasonic cleaning is performed in deionized water and anhydrous ethanol for 10 minutes each, and then nitrogen blowing is performed for drying, ready for use. About 0.8 mL of deionized water is added to the surface of the quartz piece to form a stable liquid surface, ensuring that it is dust-free and bubble-free, so that the deionized water-air interface is the gas-liquid interface. Then, 0.2 μL of polystyrene (PS) suspension is added to the liquid surface using a 10 μL pipette, and the polystyrene micro-nanoparticles are suspended in the deionized water-air interface. When implemented, the polystyrene micro-nanoparticles are monodisperse spherical particles with a refractive index n = 1.59, a particle size r = 500 nm, and a concentration controlled within 10 5 μL to ensure that the polystyrene micro-nanoparticles on the deionized water-air interface are loosely distributed in a single layer in the observation area.

[0053] Exemplarily, step S1 is specifically: an initial Gaussian light beam is emitted by the laser emission module 1, and the laser emission module 1 emits an initial Gaussian light beam with a wavelength λ=532nm, continuous output power P=1W solid-state laser, the initial output is linearly polarized Gaussian beam, the beam shaping module 2 includes coaxially arranged cylindrical lens ( f =100mm) and convex lens ( f = 60 mm), the initial linearly polarized Gaussian beam is shaped into an elliptical beam with an elliptical cross section by the beam shaping module 2.

[0054] Exemplarily, in step S2, under the guidance of the light guiding module 3, the elliptical beam is converted into a circularly polarized Gaussian beam after passing through the polarization regulation module 4, and is obliquely incident on the polystyrene micro-nano particles on the gas-liquid interface at an incident angle θ, and then the handedness of the circularly polarized Gaussian beam is switched by the polarization regulation module 4 to realize the reversible movement and manipulation of the polystyrene micro-nano particles. Specifically, the elliptical beam obtained by the beam shaping module 2 is obliquely incident on the sample area by the light guiding module 3, and is converted into a circularly polarized Gaussian beam after being modulated by the polarization regulation module 4 composed of a polarizer and a wave plate combination (λ / 2 wave plate and λ / 4 wave plate) and then irradiated on the sample. For ease of understanding, the directions involved in the present application are described by means of a three-dimensional coordinate system, specifically, the x-axis, the y-axis and the z-axis are perpendicular to each other, wherein the xy plane is parallel to the gas-liquid interface, and the z-axis is the normal line of the plane where the gas-liquid interface is located. The circularly polarized Gaussian beam projects an elliptical light spot on the gas-liquid interface (the surface of deionized water), with the long axis in the y direction and the short axis in the x direction. In the xy plane, the elliptical light spot has a long axis of about 160μm and a short axis of about 45μm. The focal point of the light spot is located directly above the liquid surface to ensure that the light field interacts sufficiently with the gas-liquid interface. In the present test example, the incident circularly polarized Gaussian beam is located in the xz plane, and the fast axis angle α of the λ / 4 wave plate can be adjusted to switch between left-handed circular polarization (LCP) and right-handed circular polarization (RCP), thereby exciting a direction-controllable transverse scattering light field.

[0055] Exemplarily, in step S3, by adjusting the power and polarization state of the incident beam, the polystyrene micro-nano particles can be driven, reversibly positioned and assembled based on the transverse optical force. When implementing, the incident power P can be continuously adjusted in the range of 0-5W; in the present test example, under the condition that the incident angle θ ∈(0°,90°)°, the direction of the transverse optical force can be instantaneously reversed by controlling the system module 8 to switch the circular polarization handedness, thereby driving the polystyrene micro-nano particles to move along the yThe axis (the long axis of the elliptical light spot) moves back and forth, and after the polystyrene micro-nanoparticles reach the target assembly position, the circularly polarized Gaussian beam is switched back to neutral polarization by the polarization control module 4 to realize positioning locking. The transverse optical force is generated by the fact that the particles are partially submerged in the liquid surface, surrounded by asymmetric refractive index (about 1.0 in air and about 1.33 in water), and the asymmetric scattering distribution is formed by the spin-orbit coupling effect of the circularly polarized Gaussian beam at the interface, so that the transverse optical force is excited in the direction of the long axis (the direction of the arrow in the figure) y Transverse optical force is excited in the direction of the long axis F y .

[0056] Figure 3 It is shown in this test example that when the polystyrene micro-nanoparticles with a radius of 500 nm are at the air-water interface and are irradiated by right-handed and left-handed circularly polarized light beams with an incident angle of 75°, the near-field scattering field distribution of the polystyrene micro-nanoparticles in the θ plane is formed. yz

[0057] Among them, Figure 3 (a) shows the scattering field distribution under right-handed circularly polarized (RCP) Gaussian light irradiation. In the figure, the central white circle represents the position of the polystyrene micro-nanoparticles, and half of the polystyrene micro-nanoparticles are in the air and half are in the water. When the polystyrene micro-nanoparticles are irradiated by right-handed circularly polarized (RCP) Gaussian light, the scattering field around the polystyrene micro-nanoparticles presents an asymmetric distribution in the plane perpendicular to the propagation direction of the incident light. Above and below the polystyrene micro-nanoparticles, the light field intensity presents a clear intensity contrast region, indicating that the electromagnetic field distribution has obvious asymmetry in the up-down direction of the polystyrene micro-nanoparticles. This asymmetry is mainly due to the fact that the polystyrene micro-nanoparticles are located on the interface with discontinuous refractive index, which breaks the symmetry of the scattering field in the yz direction, thereby generating a transverse optical force in the y direction, thereby driving the polystyrene micro-nanoparticles to stably transport in the –y direction.

[0058] Figure 3 (b) shows the scattering field distribution under left-handed circularly polarized (LCP) light irradiation, which presents a mirror symmetry relationship opposite to that under right-handed circularly polarized Gaussian light. The scattering intensity in the upper region of the particles is stronger, and the scattering intensity in the lower region is weaker, and the transverse optical force generated is in the y direction, pushing the particles to move in the y direction. It can be seen that the near-field scattering field of right-handed and left-handed circularly polarized Gaussian light has mirror symmetry in the direction, and the polarization rotation direction directly determines the transport direction of the microparticles, verifying the reversibility and accuracy of polarization control in microparticle manipulation.

[0059] Further, to verify the change of the transverse optical force with the incident angle, Figure 4 ​The test example demonstrates the changes in transverse optical power of a 500 nm radius polystyrene particle under different circular polarization directions (LCP and RCP) and incident angles. Figure 4 In the diagram, the black line (LCP) represents the transverse optical force variation under left-handed circularly polarized Gaussian light illumination. This variation increases with the incident angle. θ As the angle of incidence increases from 0° to 15°, the transverse optical force remains negative, indicating that the particles are driven by optical force along the –y direction. When the incident angle exceeds 15°, the transverse optical force rapidly turns positive and gradually increases with the increase of the incident angle, reaching its maximum value in the +y direction at an incident angle of 75°. The gray line (RCP) represents the change in transverse optical force under right-handed circularly polarized Gaussian light. With the change of the incident angle, its trend is opposite to that of LCP, that is, the optical force is positive in the incident angle range of 0° to 15°, i.e., the optical force is in the +y direction; when the incident angle is in the range of 15° to 90°, the optical force gradually becomes negative, and reaches its minimum value at 75°, i.e., its maximum value in the –y direction. Overall, the optical force change trends of LCP and RCP are the same, but they are mirror images of each other in magnitude and direction, demonstrating the control effect of polarization direction on the particle's motion direction and mechanical response. In particular, the corresponding transverse optical force is more significant when the degree of the incident angle is ∈ [5°, 75°].

[0060] Furthermore, the motion trajectory of polystyrene micro / nano particles is recorded in real time using a CCD (2048×2048 resolution, 30 fps) in the imaging monitoring module 5. Combined with image processing algorithms, the particle path coordinates are extracted, enabling dynamic quantitative analysis of the transport behavior of the polystyrene micro / nano particles. Experiments show that, under controlled conditions of 1 W laser power, 500 nm particle radius, and 75° incident angle, the average transport velocity of the polystyrene micro / nano particles is 6.2 μm / s, the maximum lateral displacement reaches 140 μm, and the positioning accuracy is better than ±0.2 μm.

[0061] Further, by controlling the circular polarization rotation and the steering platform module 6 through the control system module 8 and the computer 9, the assembly of multiple particles can be precisely controlled. In this process, first, by adjusting the laser power and the incident angle, the polystyrene micro-nano particles are moved along the preset trajectory to the center of the light spot one by one. The gradient force in the optical field ensures the precise aggregation of the polystyrene micro-nano particles along the long axis direction of the light spot, and the transverse optical force undertakes the task of transporting the particles, pushing the polystyrene micro-nano particles to move stably along the long axis direction of the light spot to the target position. In the experiment, the multiple polystyrene micro-nano particles can complete the precise transportation from the starting position to the target position within 30 seconds. The polystyrene micro-nano particles finally stay in the region with the strongest optical field and form a sequenced micro-assembly structure. When all the polystyrene micro-nano particles complete positioning, the power of the linearly polarized Gaussian beam emitted by the laser emission module 1 can be appropriately reduced, or the particle locking can be achieved by switching the light spot position, stopping the transverse optical force, so that the polystyrene micro-nano particles naturally remain in their final position, and the micro-assembly process is completed. Experimental verification shows that by adjusting the laser parameters, the micro-assembly operation has good repeatability and stability, and provides an effective solution for high-precision micro-nano scale assembly.

[0062] Obviously, the above embodiments of the present application are only examples for clearly illustrating the technical solutions of the present application, and are not intended to limit the specific embodiments of the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the claims of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for optical manipulation of micro- and nano-particles based on circularly polarized light, characterized in that, A gas-liquid interface is prepared by a liquid medium and a gas medium, and a micro-nano particle to be manipulated is suspended in the liquid medium and partially exposed to the gas-liquid interface, and the micro-nano particle can move freely; The method is implemented by an optical manipulation assembly, and the optical manipulation assembly comprises a light beam shaping module, a light guiding module, and a polarization control module; The method comprises: An initial Gaussian beam is passed through the light beam shaping module, the light guiding module, and the polarization control module in a preset order, so that the initial Gaussian beam is converted into a circularly polarized Gaussian beam, and the circularly polarized Gaussian beam irradiates the micro-nano particle from above the gas-liquid interface in a preset manner; The movement direction, movement speed, and residence position of the micro-nano particle are optically manipulated by adjusting the polarization control module and the light guiding module; The preset manner comprises: the circularly polarized Gaussian beam forms an elliptical spot with a major axis and a minor axis on the gas-liquid interface, the major axis is parallel to the gas-liquid interface and perpendicular to the propagation direction of the circularly polarized Gaussian beam, and the micro-nano particle is bound to the major axis by a minor axis gradient force; and the angle of incidence of the circularly polarized Gaussian beam with respect to the normal line of the gas-liquid interface is in the range of (0°, 90°), so as to induce the micro-nano particle to generate a transverse optical force parallel to the major axis.

2. The method of claim 1, wherein, The angle of incidence is in the range of [5°, 75°].

3. The method of claim 1, wherein, The radius of the micro-nano particle is 200 nm-50 µm, and / or, The difference between the refractive index of the micro-nano particle and the refractive index of the gas is greater than 0.05; and / or, The micro-nano particle is a polystyrene particle or a silica particle.

4. The method of claim 1, wherein, The length of the major axis is 100-500 um, the length of the minor axis is 10-100 um, and the ratio of the length of the major axis to the length of the minor axis is 3-15.

5. The method of claim 1, wherein, The maximum light intensity of the elliptical spot covering the area of the gas-liquid interface is not less than 1 mW.µm⁻².

6. The method of claim 1, wherein, The liquid medium is any one of pure water, ethanol, and a low-concentration buffer solution.

7. A device for optical manipulation of micro- and nano-particles based on circularly polarized light, characterized in that, It comprises: A manipulation platform module is configured to carry a gas-liquid interface prepared by a liquid medium and a gas medium, wherein a micro-nano particle to be manipulated is suspended in the liquid medium and partially exposed to the gas-liquid interface, and the micro-nano particle can move freely; A laser exit module is configured to emit an initial Gaussian beam; An optical manipulation assembly comprises a light beam shaping module, a light guiding module, and a polarization control module, and is configured to convert an initial Gaussian beam passed through the light beam shaping module, the light guiding module, and the polarization control module in a preset order into a circularly polarized Gaussian beam, and irradiate the micro-nano particle from above the gas-liquid interface in a preset manner; wherein the polarization control module and the light guiding module are further configured to manipulate the movement direction, movement speed, and residence position of the micro-nano particle. The preset mode includes: the circularly polarized Gaussian light beam forms an elliptical spot with a major axis and a minor axis on the gas-liquid interface, the major axis is parallel to the gas-liquid interface and perpendicular to the propagation direction of the circularly polarized Gaussian light beam, and the micro-nano particles are bound on the major axis by the minor axis gradient force; and the incident angle of the circularly polarized Gaussian light beam with the normal of the gas-liquid interface is between 0° and 90°, and the circularly polarized Gaussian light beam induces the micro-nano particles to generate transverse optical force parallel to the major axis.

8. The apparatus of claim 7, wherein, The polarization control module includes a polarizer, λ / 2 wave plate and λ / 4 waveplate, the polarizer, the λ / 2 waveplate, the aforementioned λ / 4 waveplates are coaxial and arranged sequentially along the propagation direction of the initial Gaussian beam; and / or The light beam shaping module includes at least one cylindrical lens and at least one convex lens, and the cylindrical lens and the convex lens are coaxial and arranged in sequence along the propagation direction of the initial Gaussian light beam.

9. The apparatus of any of claims 7, wherein, The laser exit module outputs an initial Gaussian light beam with a wavelength of 400-800 nm; and / or, The output mode of the laser exit module is single longitudinal mode output; and / or, The output power range of the laser exit module is 0-5 W, and / or, The polarization extinction ratio of the laser exit module is greater than or equal to 20 dB.

10. The device of any of claims 7-9, wherein, Further comprising an imaging monitoring module for monitoring the position and motion trajectory of the micro-nano particles and imaging.

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