A vacuum optical tweezers system and method for non-spherical particles.

Abstract

This invention discloses a vacuum optical tweezers system and method for non-spherical particles. It includes a structured beam modulation module for wavefront modulation of an input linearly polarized laser beam to generate a multi-lobed structured beam, which is then incident into a vacuum trapping module. The vacuum trapping module focuses the incident multi-lobed structured beam to form an optical potential well, which is used to trap the non-spherical particles. This invention improves the trapping stability and attitude control accuracy of non-spherical particles in a vacuum environment and can be applied to fields such as precision mechanical measurement, high-performance sensing, and micro / nano structure physics research.

Description

Technical Field

[0001] This invention belongs to the field of vacuum optical tweezers, and particularly relates to a vacuum optical tweezers system and method for non-spherical particles. Background Technology

[0002] Optical tweezers is a technique that uses a focused laser beam to generate an optical potential well. By leveraging the combined effects of optical gradient forces and scattering forces, micro- and nano-scale particles are trapped within this potential well, enabling the capture and non-contact manipulation of microparticles. Optical tweezers offers significant advantages such as non-contact operation, high precision, and strong controllability. Building upon this foundation, vacuum optical tweezers extends the working environment of traditional optical tweezers from the liquid phase to a vacuum. By suspending microparticles in a vacuum, thermal noise caused by collisions with ambient gas molecules can be significantly reduced, allowing the microparticles to function as mechanical harmonic oscillators with a high quality factor. Therefore, vacuum optical tweezers not only has significant advantages in sensing extremely weak forces, acceleration, and torque, but also holds important application potential in cutting-edge physics fields such as macroscopic quantum states.

[0003] In the application research of vacuum optical tweezers, previous work has extended the optical trapping targets from traditional spherical particles to non-spherical particles with complex geometries. For example, the Geraci team at Northwestern University achieved stable optical trapping of high aspect ratio hexagonal prism particles in a vacuum environment using optical standing waves. The results show that, compared to spherical particles of the same mass, these non-spherical particles can achieve higher trapping frequencies and have lower photon recoil heating rates, thus providing a new experimental platform for cutting-edge research such as high-frequency gravitational wave detection and high-sensitivity mechanical sensing.

[0004] The above research indicates that non-spherical microparticles hold promise for improving the mechanical measurement sensitivity of vacuum optical tweezers systems and expanding their applications in precision measurement. Traditional vacuum optical tweezers systems typically employ Gaussian beams as the trapping beam. Because Gaussian beams have an approximately axisymmetric intensity distribution in the transverse plane, they are effective in trapping and stabilizing suspended spherical microparticles. However, for non-spherical microparticles with significant geometric anisotropy (such as ellipsoidal microparticles and nanorods), the optical potential trap formed by the Gaussian beam is insufficient to effectively constrain their rotational degrees of freedom, thus making it difficult to guarantee the particle's attitude stability. In particular, when the beam contains spin angular momentum or orbital angular momentum components, these angular momentum components can be transferred to the microparticle through the interaction between the light and the microparticle, thereby applying a spin torque or orbital torque, inducing rotational or unstable behavior in the microparticle, and potentially even causing the microparticle to escape from the optical trap.

[0005] Therefore, it is necessary to propose a new vacuum optical tweezers system for non-spherical particles. Summary of the Invention

[0006] To address the problem of traditional Gaussian beams failing to suppress rotational degrees of freedom and easily leading to attitude instability when capturing non-spherical particles, this invention aims to provide a vacuum optical tweezers system and method for non-spherical particles. This invention generates a multi-lobed structured beam through a structured beam modulation module and adjusts the phase encoding to match its angular intensity distribution with the rotational symmetry of the non-spherical particle, thereby utilizing optical gradient forces to achieve particle attitude locking and rotational stability control. Furthermore, when the non-spherical particle deflects relative to the angular intensity distribution of the multi-lobed structured beam, the optical gradient forces acting on its various parts exhibit an asymmetrical distribution in space, generating a restoring torque that causes the particle to tend to return to a stable orientation state consistent with the symmetry of the optical field. Through the action of this restoring torque, passive stability constraint on the non-spherical particle's attitude is achieved. This invention does not rely on a complex active feedback system and features simple structure, high stability, and strong adaptability.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] I. A vacuum optical tweezers system for non-spherical particles

[0009] The structured beam modulation module is used to modulate the wavefront of the input linearly polarized laser beam to generate a multi-lobed structured beam, which is then incident into the vacuum trapping module.

[0010] The vacuum trapping module is used to focus the incident multi-lobed structured beam to form an optical potential trap, which is used to trap non-spherical particles.

[0011] The vacuum optical tweezers system also includes:

[0012] Optical front end, used to generate linearly polarized laser beams.

[0013] The vacuum optical tweezers system also includes:

[0014] A particle imaging module is positioned between the structured beam modulation module and the vacuum capture module to collect and image the backscattered light from non-spherical particles within the vacuum capture module.

[0015] The vacuum optical tweezers system also includes:

[0016] The particle detection module is used to collect the forward scattered light of non-spherical particles and detect the motion signal of non-spherical particles; the particle detection module is located on the side of the vacuum capture module away from the structured beam modulation module.

[0017] The structured beam modulation module includes a phase modulation unit for wavefront modulation of the incident linearly polarized laser beam, thereby generating a multi-lobed structured beam with N angular intensity lobes on the cross-section, where N is a positive integer greater than or equal to 2.

[0018] The phase modulation unit is a device that realizes spatial phase or equivalent phase modulation.

[0019] The non-spherical particles have an M-fold rotational symmetry structure, where M is an integer greater than or equal to 2.

[0020] The angular intensity lobes N of the multi-lobed beam structure and the M-fold rotational symmetry of the non-spherical particle satisfy N=pM, where p is an integer greater than or equal to 1.

[0021] The non-spherical particle is a single non-spherical particle, or an equivalent variant of a single non-spherical particle, or a particle cluster consisting of multiple particles, or an equivalent variant of a particle cluster.

[0022] II. A method for capturing non-spherical particles in vacuum optical tweezers

[0023] The generated linearly polarized laser beam is phase-modulated to generate a multi-lobed beam, which is then incident into a vacuum trapping module. The vacuum trapping module focuses the incident multi-lobed beam to form an optical potential trap, which traps non-spherical particles.

[0024] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0025] 1. This invention generates a multi-lobed structured beam that matches the geometrically symmetrical non-spherical microparticles through a structured beam modulation module, forming an optical potential well with angular constraint in a vacuum environment. This effectively suppresses random rotation and attitude instability that easily occur when traditional Gaussian beams capture non-spherical microparticles, thereby improving the suspension stability and attitude control capability of non-spherical microparticles.

[0026] 2. Since the light intensity in the central region of the multi-lobed beam is low, it can reduce the heating effect of the trapping light field on the particles to a certain extent. At the same time, the multi-lobed beam that matches the particle size can produce a higher optical trap stiffness than the Gaussian beam, which helps to reduce the optical power required to achieve stable trapping, thereby reducing the risk of particles being heated, escaping and becoming unstable, improving the stability of trapping non-spherical particles in a high vacuum environment, and helping to improve the accuracy of mechanical quantity measurement.

[0027] 3. This invention mainly achieves the generation and control of multi-lobed structured beams through phase encoding, without the need for a complex active feedback control system. At the same time, this invention can flexibly change the angular intensity lobe number and symmetry of the multi-lobed structured beam by using phase encoding, thereby adapting to non-spherical particles or particle clusters with different morphologies. Combined with particle imaging and particle detection modules, it can achieve effective characterization of particle morphology and motion signals, and has broad application prospects in particle dynamics research and precision measurement. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings involved in the description of the embodiments are briefly described below. It should be understood that the following drawings only show some embodiments of this application and therefore should not be construed as limiting the scope of protection of this application.

[0029] In the accompanying drawings, the same or similar reference numerals indicate the same or similar components. The drawings are only used to illustrate the technical solution of this application, and the shape, size, proportion, and relative position of each component in the drawings are schematic representations and do not constitute a limitation on the scope of protection of this application.

[0030] Figure 1 This is a schematic diagram of the overall modules of the device of the present invention.

[0031] Figure 2 This is a schematic diagram of the specific optical path and structure of the device of the present invention.

[0032] Figure 3 This is a schematic diagram of the phase encoding loaded in the spatial light modulator of the present invention; wherein (a) is the phase distribution when the number of angular intensity lobes N is 2, (b) is the phase distribution when the number of angular intensity lobes N is 3, (c) is the phase distribution when the number of angular intensity lobes N is 4, (d) is the phase distribution when the number of angular intensity lobes N is 5, and (e) is the phase distribution when the number of angular intensity lobes N is 6.

[0033] Figure 4 The following are theoretical simulation light intensity distribution diagrams of the multi-lobed beam structure in the present invention on the Fourier plane of the 4F optical system; wherein, (a) is the theoretical simulation light intensity distribution diagram when the number of angular intensity lobes N is 2, (b) is the theoretical simulation light intensity distribution diagram when the number of angular intensity lobes N is 3, (c) is the theoretical simulation light intensity distribution diagram when the number of angular intensity lobes N is 4, (d) is the theoretical simulation light intensity distribution diagram when the number of angular intensity lobes N is 5, and (e) is the theoretical simulation light intensity distribution diagram when the number of angular intensity lobes N is 6.

[0034] Figure 5 The above are experimentally measured light intensity distribution diagrams of the multi-lobed beam structure in the Fourier plane of the 4F optical system in this invention; wherein, (a) is the experimentally measured light intensity distribution diagram when the number of angular intensity lobes N is 2, (b) is the experimentally measured light intensity distribution diagram when the number of angular intensity lobes N is 3, (c) is the experimentally measured light intensity distribution diagram when the number of angular intensity lobes N is 4, (d) is the experimentally measured light intensity distribution diagram when the number of angular intensity lobes N is 5, and (e) is the experimentally measured light intensity distribution diagram when the number of angular intensity lobes N is 6.

[0035] Figure 6The light intensity distribution diagrams of the optical potential well focal plane obtained from the close-focusing simulation are shown below. Among them, (a) is the light intensity distribution diagram of the optical potential well focal plane when the number of angular intensity lobes N is 2, (b) is the light intensity distribution diagram of the optical potential well focal plane when the number of angular intensity lobes N is 3, (c) is the light intensity distribution diagram of the optical potential well focal plane when the number of angular intensity lobes N is 4, (d) is the light intensity distribution diagram of the optical potential well focal plane when the number of angular intensity lobes N is 5, and (e) is the light intensity distribution diagram of the optical potential well focal plane when the number of angular intensity lobes N is 6.

[0036] Figure 7 These are schematic diagrams of typical non-spherical particle morphologies; where (a) is a schematic diagram of a non-spherical particle morphology with 2-fold rotational symmetry, (b) is a schematic diagram of a non-spherical particle morphology with 3-fold rotational symmetry, (c) is a schematic diagram of a non-spherical particle morphology with 4-fold rotational symmetry, (d) is a schematic diagram of a non-spherical particle morphology with 5-fold rotational symmetry, and (e) is a schematic diagram of a non-spherical particle morphology with 6-fold rotational symmetry.

[0037] In the diagram: Optical front end 1, Structured beam modulation module 2, Vacuum trapping module 3, Particle imaging module 4, Particle detection module 5, Laser source 101, First half-wave plate 102, First polarizing beam splitter 103, Second half-wave plate 104, First convex lens 105, Second convex lens 106, Spatial light modulator 201, Third convex lens 202, Fourth convex lens 203, Mirror 204, Vacuum cavity 301, High numerical aperture objective lens 302, Non-spherical particle 303, Collecting lens 304, Second polarizing beam splitter 401, Faraday rotator 402, Camera 403, Neutral density filter 501, Fifth convex lens 502, Quadrant detector 503. Detailed Implementation

[0038] The exemplary embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the following embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit the scope of protection of this application. Those skilled in the art can make various equivalent substitutions or improvements to the described embodiments without departing from the technical concept of this application, and such substitutions or improvements should all fall within the scope of protection of this application.

[0039] In the following description, unless otherwise stated, the same reference numerals in different figures denote the same or similar parts or functional units. The figures are for illustrative purposes only, and the shape, size, scale, and relative position of the parts in the figures can be appropriately adjusted according to actual needs, and should not be construed as limiting the scope of protection of this application.

[0040] The singular forms “a,” “the,” or “the” used in the specification and claims also include the plural forms where appropriate, unless the context clearly specifies otherwise. Furthermore, the terms “first,” “second,” “third,” etc., used in the specification are only for distinguishing objects of the same kind and do not indicate any limitation on order or priority.

[0041] like Figure 1 As shown, the vacuum optical tweezers system for matching the topography of multi-lobe structures of non-spherical microparticles proposed in this invention includes:

[0042] The structured beam modulation module 2 is used to perform wavefront modulation on the input linearly polarized laser beam to generate a multi-lobe structured beam and incident it into the vacuum trapping module 3.

[0043] Specifically, the structured beam modulation module 2 includes a phase modulation unit for wavefront modulation of the incident linearly polarized laser beam, thereby generating a multi-lobed structured beam with N angular intensity lobes on the cross-section, where N is a positive integer greater than or equal to 2.

[0044] A phase modulation unit is a device that realizes spatial phase or equivalent phase modulation, including but not limited to one or more of spatial light modulators, diffractive optical elements, metasurface devices, and deformable mirrors.

[0045] One feasible implementation method is, for example Figure 2 As shown, the phase modulation unit includes a spatial light modulator 201, a third convex lens 202, a fourth convex lens 203, and a reflector 204 arranged sequentially along the optical axis. The spatial light modulator 201 is loaded with phase encoding to achieve phase modulation of the incident linearly polarized laser beam; the aperture and polarization direction of the linearly polarized laser beam incident on the structured beam modulation module 2 meet the requirements of the spatial light modulator 201. The third convex lens 202 and the fourth convex lens 203 constitute a conjugate transmission assembly, used for conjugate transmission of the beam modulated by the spatial light modulator 201, and for spatial alignment and optical path extension of the modulated beam; the beam transmitted by the conjugate transmission assembly is reflected by the reflector 204, and after passing through the particle imaging module 4, finally reaches the front focal plane of the high numerical aperture objective lens 302 of the vacuum optical tweezers system. The conjugate transmission assembly is a 4F optical system or an equivalent conjugate optical system.

[0046] Within the pixel plane of the spatial light modulator 201, a polar coordinate system is established with the optical axis as the center, and the polar angle is denoted as . Its value range is [0, 2π). The polar angle interval is divided into N angular sectors, corresponding to the generation of a multi-lobed beam with N angular intensity lobes. The polar angle interval corresponding to the k-th sector... Defined as:

[0047]

[0048] Further define the sector indicator function :

[0049]

[0050] The phase distribution loaded by the spatial light modulator 201 is a piecewise constant phase function. :

[0051]

[0052] Where, θ k Let be the phase code value corresponding to the k-th sector. mod 2π means that the phase is modulo 2π, that is, when the phase value exceeds 2π, subtract an integer multiple of 2π so that the final phase value falls into the interval [0, 2π).

[0053] Phase encoding value θ k The parity of the sector number N is set as follows:

[0054] When N is even, alternating binary phase encoding is used, as shown in the following formula:

[0055]

[0056] When N is odd, arithmetic phase encoding is used, as shown in the following formula:

[0057]

[0058] Through the aforementioned angular segmented phase encoding, the incident linearly polarized laser beam, after propagation and focusing, forms a multi-lobed structure beam with N angular intensity lobes in its cross-section. This allows the optical potential well to form an angular intensity distribution in the transverse plane that matches the rotational symmetry of the non-spherical particle. In other words, the optical potential well maintains a structure with N angular intensity lobes in its cross-section, enabling the non-spherical particle 303 to be captured and suspended within the trapping region of the optical potential well, and providing angular constraint on the non-spherical particle 303.

[0059] The vacuum trapping module 3 is used to focus the incident multi-lobed structured beam to form an optical potential trap, which is used to trap and suspend non-spherical particles 303.

[0060] In one feasible implementation, the vacuum capture module 3 includes an optical trap generating element and a collecting lens 304 disposed within a vacuum cavity 301. The optical trap generating element and the collecting lens 304 are spaced apart along the optical axis. The optical trap generating element is disposed near the structured beam modulation module 2, and the collecting lens 304 is disposed near the particle detection module 5. The optical trap generating element is used to focus a multi-lobed structured beam to form an optical potential trap, thereby capturing and suspending non-spherical particles 303 in a vacuum environment. The optical potential trap is disposed between the optical trap generating element and the collecting lens 304.

[0061] The optical axis of the optical trap generating element can be set to be vertically upward, so that the optical potential trap formed by its convergence will cause the direction of the axial scattering force on the non-spherical particle 303 to be opposite to the direction of gravity. Gravity will partially cancel out the axial scattering force, thereby achieving stable suspension of the non-spherical particle 303 in a vacuum environment.

[0062] A multi-lobed beam has a lower intensity in the central region, with its energy concentrated primarily in multiple symmetrically distributed angular intensity lobes. After being focused by an optical trap generating element, the multi-lobed beam can generate a series of adjacent local optical traps, which can apply optical forces and moments in multiple directions to non-spherical particles. With proper optical design, non-spherical particles can be trapped at the beam center; if the particle rotates, the gradient forces generated by the surrounding angular intensity lobes will exert a restoring moment on the particle, maintaining its stable attitude and orientation during the trapping process.

[0063] Furthermore, by adjusting the number of lobes in the multi-lobed beam according to the rotational symmetry order of the non-spherical particle to be captured, the angular intensity distribution can be matched with the rotational symmetry of the non-spherical particle, thereby enabling attitude locking and rotational stability control in a vacuum environment.

[0064] Furthermore, due to the lower light intensity in the central region, the multi-lobed beam structure helps to reduce the thermal effect of the trapping light field on the particles; when the size of the light trap is matched with the particle size, the trapping light field forms a high intensity gradient in the particle edge region, thereby generating a higher light trap stiffness than that of a Gaussian beam, which helps to reduce the light power required for trapping, thereby reducing the heating effect and the risk of particle escape.

[0065] Therefore, the above characteristics enable multi-lobed beams to exhibit higher stability when capturing non-spherical particles in a high vacuum environment, which is beneficial for achieving higher accuracy in mechanical quantity measurement.

[0066] The collecting lens 304 collects and collimates the forward scattered light of the non-spherical particles 303, and directs the forward scattered light into the particle detection module 5 located behind the vacuum cavity 301.

[0067] Vacuum cavity 301 provides a vacuum environment for the optically suspended non-spherical particles 303. An optical window coated with an antireflective film is provided on the cavity wall of vacuum cavity 301 to allow light beams to pass through and enter or exit its interior. The surface of this optical window is preferably coated with an antireflective film optimized for a 1064 nm wavelength to reduce optical loss and improve beam transmission efficiency. Vacuum cavity 301 also has a vacuum gauge interface and a vacuum pump assembly interface. The vacuum gauge interface connects to a vacuum gauge for real-time monitoring of the vacuum level inside the cavity; the vacuum pump assembly interface connects to a vacuum pump assembly via a vacuum valve for evacuating vacuum from vacuum cavity 301.

[0068] Optionally, the light trap generating element is a high numerical aperture objective lens 302. The high numerical aperture objective lens 302 is a microscope objective lens with a numerical aperture of 0.8, or other microscope objectives with a numerical aperture of not less than 0.6 can also be used.

[0069] In one feasible implementation, the vacuum optical tweezers system further includes:

[0070] Optical front end 1, used to generate a linearly polarized laser beam.

[0071] In one feasible embodiment, the optical front end 1 includes a laser source 101, a first half-wave plate 102, a first polarizing beam splitter 103, a second half-wave plate 104, a first convex lens 105, and a second convex lens 106 arranged sequentially along the optical axis. The laser beam generated by the laser source 101 passes sequentially through the first half-wave plate 102 and the first polarizing beam splitter 103 to obtain a linearly polarized beam with a defined polarization direction. The second half-wave plate 104 is used to adjust the polarization angle of the linearly polarized beam to match the spatial light in the structured beam modulation module 2. The polarization requirements of the modulator 201 are adjusted to improve the modulation efficiency of the spatial light modulator 201. The beam after being adjusted by the second half-wave plate 104 passes through the first convex lens 105 and the second convex lens 106 in sequence. The first convex lens 105 and the second convex lens 106 form a beam expander group to expand the beam so that the diameter of the collimated output beam matches the effective modulation area of ​​the spatial light modulator, thereby improving the utilization efficiency of the spatial light modulator 201 and allowing the expanded beam (i.e., the linearly polarized laser beam) to be incident on the structured beam modulation module 2.

[0072] The laser source 101 is used to generate a continuous laser beam with a wavelength of 1064 nm. This laser source is preferably a low-noise, high-stability continuous laser, suitable for optical tweezers trapping experiments.

[0073] In one feasible implementation, the vacuum optical tweezers system further includes:

[0074] The particle imaging module 4, located between the structured beam modulation module 2 and the vacuum capture module 3, is used to collect the backscattered light of the non-spherical particles 303 in the vacuum capture module 3 and perform imaging, and analyze the morphological characteristics of the non-spherical particles 303 based on the imaging results.

[0075] In one feasible implementation, the particle imaging module 4 includes a second polarizing beam splitter 401, a Faraday rotator 402, and a camera 403. The transmission polarization direction of the second polarizing beam splitter 401 is consistent with the polarization direction of the incident beam emitted from the structured beam modulation module 2, allowing the incident beam to pass through the second polarizing beam splitter 401 while maintaining its original polarization direction. The Faraday rotator 402 is disposed between the second polarizing beam splitter 401 and the vacuum trapping module 3, and is used to rotate the polarization direction of the transmitted incident beam by 45°. When the backscattered light generated by the non-spherical particles 303 returns along the original optical path and passes through the Faraday rotator 402 again, its polarization direction is rotated by 90° relative to the initial polarization direction of the incident beam, thereby being reflected at the second polarizing beam splitter 401, achieving polarization separation between the incident beam and the backscattered light.

[0076] The camera 403 includes an imaging lens and an image sensor. The backscattered light reflected by the second polarizing beam splitter 401 is focused by the imaging lens and imaged onto the image sensor to image the non-spherical particles 303.

[0077] In one feasible implementation, the vacuum optical tweezers system further includes:

[0078] The particle detection module 5 is used to collect the forward scattered light of the non-spherical particles 303 and detect the motion signal of the non-spherical particles 303; the particle detection module 5 is located on the side of the vacuum capture module 3 away from the structured beam modulation module 2.

[0079] In one feasible implementation, the particle detection module 5 includes a neutral density filter 501, a fifth convex lens 502, and a quadrant detector 503. The forward scattered light generated by the non-spherical particle 303 is first attenuated by the neutral density filter 501 to prevent detector overload. Then, it is converged and focused by the fifth convex lens 502 so that the forward scattered light is incident on the detection center of the quadrant detector 503. The quadrant detector 503 is used to convert the optical signal carrying the motion information of the non-spherical particle 303 into an electrical signal to realize the real-time detection of the spatial displacement and motion state of the non-spherical particle 303.

[0080] The non-spherical particles 303 have three-dimensional dimensions ranging from hundreds of nanometers to tens of micrometers. The non-spherical particles 303 exhibit M-fold rotational symmetry, where M is an integer greater than or equal to 2. M represents the highest order of rotational symmetry that allows the particle to maintain its geometric shape when rotated around the symmetry axis; that is, the non-spherical particle 303 retains its geometric shape when rotated by an angle that is an integer multiple of 2π / M around the symmetry axis. The non-spherical particles 303 can be a single non-spherical particle, an equivalent variant of a single non-spherical particle, a particle cluster composed of multiple particles, or an equivalent variant of a particle cluster. When the non-spherical particles 303 are a particle cluster or an equivalent variant of a particle cluster, the particle cluster moves as a rigid whole, and its overall shape characterizes the geometric shape of the non-spherical particles 303. An equivalent variant refers to a particle that, while maintaining M-fold rotational symmetry, can still achieve the same trapping function after undergoing minor deformation. Minor deformation includes, but is not limited to, changes in size ratio, edge rounding, or local surface morphology changes. Local surface morphology changes include changes in surface roughness, local protrusions or depressions, and the introduction or adjustment of microstructure textures.

[0081] Based on the device structure, the generation method of the multi-lobed beam structure and its matching relationship with the morphology of non-spherical particles are further explained.

[0082] The incident laser beam is phase-modulated using a spatial light modulator 201 to generate a multi-lobed structured beam with an angular intensity distribution. Specifically, a pre-designed phase code is loaded onto the spatial light modulator 201, so that the incident laser beam, after reflection modulation, forms a structured beam with an angular segmented phase distribution. Figure 3 of (a), Figure 3 (b) Figure 3 (c) Figure 3 (d) and Figure 3 (e) gives the phase coding distribution for angular intensity lobe numbers N=2 to N=6.

[0083] The beam modulated by the spatial light modulator 201 enters the 4F optical system, and the 4F optical system realizes the conjugate transmission of the light field. The modulated beam forms a multi-lobed structure beam with multiple angular intensity lobes at the Fourier plane of the 4F system. Figure 4 of (a), Figure 4 (b) Figure 4 (c) Figure 4 (d) and Figure 4 (e) presents the simulation results of the theoretical light intensity distribution of the multi-lobed structure beam at the Fourier plane of the 4F optical system when the number of angular intensity lobes N=2 to N=6; the light intensity distributions are all normalized, that is, normalized with the maximum light intensity as 1. Figure 5 of (a), Figure 5 (b) Figure 5 (c) Figure 5 (d) and Figure 5 (e) presents the actual intensity distribution results for the multi-lobed beam structure with angular intensity lobes N=2 to N=6, which were measured by a beam analyzer. Theoretical calculations and experimental measurements show that when the spatial light modulator 201 is loaded with phase encoding that satisfies the angular segmented modulation condition, the beam can form a symmetrical intensity structure with N angular intensity lobes in the transverse plane. After being tightly focused by the high numerical aperture objective lens 302, an optical potential well with corresponding angular symmetry can be formed near the focal point.

[0084] In this embodiment, by reasonably selecting the number of angular intensity lobes N, the angular intensity distribution of the optical potential well can be matched with the geometry of the non-spherical particle 303, thereby generating an angular constraint effect on the non-spherical particle 303 and achieving stable locking of the particle's attitude. When the non-spherical particle 303 has M-fold rotational symmetry, the number of angular intensity lobes N of the multi-lobed structure beam can be selected to satisfy N=pM, where M represents the highest rotational symmetry order of the non-spherical particle 303, and p is an integer greater than or equal to 1, serving as an adjustment coefficient. Preferably, p=1, in which case the number of angular intensity lobes of the multi-lobed structure beam is the same as the rotational symmetry order of the non-spherical particle 303, thereby matching the angular intensity distribution of the optical field with the rotational symmetry of the particle. For example, when the non-spherical particle 303 is an ellipsoid with 2-fold rotational symmetry, a multi-lobed structure beam with N=2 or N=4 can be selected to match the optical field distribution with the rotational symmetry of the particle.

[0085] Figure 6 of (a), Figure 6 (b) Figure 6 (c) Figure 6 (d) and Figure 6 (e) presents the optical potential well focal plane intensity distribution of multi-lobed beams with angular intensity lobe numbers N=2 to N=6, respectively. The results are obtained by the Debye integral method. Figure 7 (a) is a schematic diagram of the morphology of a non-spherical particle with two-fold rotational symmetry. Figure 7 (b) is a schematic diagram of the morphology of a non-spherical particle with 3-fold rotational symmetry. Figure 7 (c) is a schematic diagram of the morphology of a non-spherical particle with 4-fold rotational symmetry. Figure 7 (d) is a schematic diagram of the morphology of a non-spherical particle with 5-fold rotational symmetry. Figure 7Figure (e) is a schematic diagram of the morphology of a non-spherical particle with six rotational symmetries. By reasonably selecting the number of angular intensity lobes that matches the particle's symmetry, the captured non-spherical particle can be made to align its geometric symmetry axis with the symmetry direction of the optical field under the action of the optical gradient force, thereby achieving stable constraint on the particle's attitude. By adjusting the phase encoding parameters loaded on the spatial light modulator 201, the number of angular intensity lobes of the multi-lobed structured beam can be flexibly adjusted, thus enabling the structured beam to adapt to non-spherical particles with different morphologies and different rotational symmetry orders. It should be noted that the particle morphology shown in the figure is only a schematic example to illustrate typical cases of different symmetries and does not constitute any limitation on the particle shape applicable to this invention.

[0086] The implementation process of the system of the present invention may include the following steps:

[0087] 1) Turn on the laser source 101, and adjust the first half-wave plate 102 and the second half-wave plate 104 to make the output beam have a preset power and polarization direction;

[0088] 2) Start the spatial light modulator 201 and load the phase encoding of the multi-lobed structured beam so that the modulated structured beam forms a light trap trapping region in the vacuum cavity 301.

[0089] 3) Activate the microparticle support device to allow the non-spherical microparticles 303 to enter the optical trap capture area and be stably captured under the combined action of optical gradient force, optical scattering force and gravity.

[0090] 4) Turn on the vacuum pump unit connected to the vacuum chamber 301, open the vacuum valve, and evacuate the vacuum chamber 301 to gradually reduce the air pressure inside the vacuum chamber 301 to the predetermined value.

[0091] 5) Turn on the camera 403 and adjust the focus of the lens to make the non-spherical particles 303 clearly imaged on the image sensor;

[0092] 6) Fine-tune the position of the quadrant detector 503 so that the forward scattered light from the particles converges at the center of the quadrant detector 503 after passing through the neutral density filter 501 and the fifth convex lens 502, and record the displacement signal of the non-spherical particles 303.

[0093] 7) The displacement data is processed based on the motion signal of the non-spherical particles 303 to obtain the power spectral density of the particle displacement and calculate the optical trap stiffness to evaluate the capture stability. On this basis, the air pressure in the vacuum cavity 301 can be gradually reduced and the motion signal of the non-spherical particles 303 can be continuously recorded. By comparing the changes in power spectral density under different air pressure conditions, the dynamic behavior of the particles and the capture stability can be further analyzed.

[0094] The present invention proposes a method for capturing non-spherical particles in vacuum optical tweezers, comprising:

[0095] The generated linearly polarized laser beam is wavefront modulated to generate a multi-lobed structure beam, which is then incident into the vacuum trapping module 3. The vacuum trapping module 3 focuses the incident multi-lobed structure beam to form an optical potential trap, which traps and suspends non-spherical particles 303.

[0096] This invention utilizes a spatial light modulator to load phase encoding onto a multi-lobed structured beam, forming an optical potential well with angular constraint capabilities in a vacuum environment. This enables stable capture and attitude control of non-spherical particles. Compared to traditional Gaussian beam optical tweezers, the multi-lobed structured beam forms an optical potential well structure with angular intensity distribution in the transverse plane, thereby improving the angular constraint capability for non-spherical particles and achieving attitude locking. Simultaneously, a particle imaging module allows for real-time imaging observation of the morphological characteristics of non-spherical particles, and a particle detection module enables high-precision detection of their motion state, thus achieving quantitative analysis of particle dynamics.

[0097] Through the above structure and method, this embodiment utilizes the spatial light modulator 201 to generate a multi-lobed beam with an adjustable angular intensity distribution, enabling the angular structure of the optical potential well to match the geometry of the non-spherical particle, thereby improving the attitude stability of the non-spherical particle in the vacuum optical levitation system and providing a new experimental implementation method for the study and precision measurement of non-spherical particle dynamics.

[0098] The specific embodiments described in this specification may be given different names, and the above content is merely illustrative. All equivalent changes or improvements made based on the concept, structure, features, and principles of this invention should be included within the scope of protection of this invention. Any modifications, additions, or similar methods made by those skilled in the art based on the concept of this invention, as long as they do not depart from the structure of this invention or exceed the definition of the claims, should be considered within the scope of protection of this invention.

Claims

1. A vacuum optical tweezers system for non-spherical particles, characterized in that, The vacuum optical tweezers system includes: The structured beam modulation module (2) is used to perform wavefront modulation on the input linearly polarized laser beam to generate a multi-lobe structured beam and incident it into the vacuum trapping module (3); The vacuum trapping module (3) is used to focus the incident multi-lobed structure beam to form an optical potential trap, which is used to trap a non-spherical particle (303). The non-spherical microparticle (303) has an M-fold rotational symmetry structure, where M is an integer greater than or equal to 2; The angular intensity lobes N of the multi-lobed beam structure and the M-fold rotational symmetry of the non-spherical particle satisfy N=pM, where p is an integer greater than or equal to 1.

2. The system according to claim 1, wherein The vacuum optical tweezers system also includes: Optical front end (1) is used to generate a linearly polarized laser beam.

3. A system for vacuum optical tweezers of non-spherical microparticles according to claim 1 or 2, characterized in that, The vacuum optical tweezers system also includes: A particle imaging module (4) is set between the structured beam modulation module (2) and the vacuum capture module (3) to collect the backscattered light of non-spherical particles (303) in the vacuum capture module (3) and perform imaging.

4. The system according to claim 1 or 2, wherein The vacuum optical tweezers system also includes: The particle detection module (5) is used to collect the forward scattered light of non-spherical particles (303) and detect the motion signal of non-spherical particles (303); the particle detection module (5) is located on the side of the vacuum capture module (3) away from the structured beam modulation module (2).

5. The system of claim 1, wherein the vacuum optical tweezers system is used for non-spherical microparticles. The structured beam modulation module (2) includes a phase modulation unit for wavefront modulation of the incident linearly polarized laser beam, thereby generating a multi-lobed structured beam with N angular intensity lobes on the cross section, where N is a positive integer greater than or equal to 2.

6. The system of claim 5, wherein the vacuum optical tweezers system is used for non-spherical microparticles. The phase modulation unit is a device that realizes spatial phase or equivalent phase modulation.

7. The system of claim 1, wherein the vacuum optical tweezers system is used for non-spherical microparticles. The non-spherical particle (303) is a single non-spherical particle, or an equivalent variant of a single non-spherical particle, or a particle cluster consisting of multiple particles, or an equivalent variant of a particle cluster.

8. A method of trapping non-spherical microparticles in a vacuum optical tweezer, characterized by, include: Obtain the M value for non-spherical particles, where the non-spherical particles have an M-fold rotational symmetry structure, and M is an integer greater than or equal to 2; The angular intensity lobes N of the multi-lobed structured beam are determined, and the angular intensity lobes N of the multi-lobed structured beam and the M-fold rotational symmetry of the non-spherical particle satisfy N=pM, where p is an integer greater than or equal to 1. The generated linearly polarized laser beam is phase-modulated to generate a multi-lobed structure beam and is incident into the vacuum trapping module (3). The vacuum trapping module (3) focuses the incident multi-lobed structure beam to form an optical potential trap, which traps a non-spherical particle (303).

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