A multi-particle capture device and method for gaseous media

Abstract

This invention discloses a multi-particle trapping device and method for gaseous media. Based on a symmetrical optical tweezers array structure and wavefront modulation technology, the invention utilizes continuous adjustment of control signals via a control terminal to drive the dynamic deflection of a liquid crystal array on the surface of a spatial light modulator, thereby modulating the wavefront phase of the incident light field and achieving dynamic adjustment of the optical tweezers array. A two-dimensional hologram generated by the spatial light modulator is loaded onto a laser beam to construct the focal point of the arrayed optical tweezers. Combined with a symmetrical and conjugate dual-microscope objective structure, a stable three-dimensional potential well is formed. Furthermore, a high-precision calibration method ensures strict conjugation of the two optical paths, enabling high-speed microscopic image acquisition. This invention achieves spatial positioning and stable trapping of multiple gaseous particles, significantly improving the stability and spatial accuracy of the levitation array. Simultaneously, it can record particle trajectories and positional changes in real time, providing high temporal and spatial resolution data support for the study of gaseous particle dynamics.

Description

Technical Field

[0001] This invention belongs to the field of multi-particle suspension manipulation, specifically relating to a multi-particle capture device and method for gaseous media. Background Technology

[0002] In fields such as environmental science, atmospheric chemistry, drug delivery, and additive manufacturing, precise and controllable research on the behavior and interactions of micro / nanoparticles in the gas phase is of great significance. For example, the composition and distribution of atmospheric aerosols and industrial dust directly affect climate change and public health; precise delivery of drug particles to the lungs can improve the efficiency of inhalation therapy; and in micro / nano lithography and additive manufacturing processes, particle manipulation capabilities determine the precision of the finished product structure. However, traditional gas-phase particle research often relies on macroscopic methods such as collision chambers, airflow channels, or electrostatic deposition, making it difficult to achieve micron-scale positioning and dynamic control at the single-particle or array level. In recent years, with the development of optical manipulation technology, the precise manipulation of multiple particles has gradually become an important topic in micro / nano-scale research. In multiple fields such as optical micromanipulation, biophysics, materials science, and propellant research, spatial positioning, array construction, and dynamic control of particles have become important means to promote basic research and engineering applications. In particular, the manipulation of multiple particles in gaseous media not only helps to deepen the understanding of the transport and interaction mechanisms of suspended particles in the gas phase, but also serves cutting-edge applications such as aerosol dynamics, fuel particle combustion, and drug aerosol delivery. However, compared to optical tweezers systems widely used in liquid environments, achieving stable suspension and precise manipulation of multiple particles in a gaseous environment presents greater challenges due to the lack of viscous damping, stronger disturbances, and easier particle settling. Therefore, there is an urgent need to develop a highly flexible, high-resolution multi-particle trapping device suitable for gaseous environments, providing fundamental support for gaseous particle manipulation and measurement. Traditional single-objective optical tweezers structures mainly rely on refractive index matching and viscous damping in liquid media. In gaseous media, due to the large refractive index contrast, minimal gaseous damping, and susceptibility to environmental disturbances, single-path optical tweezers struggle to form a sufficiently deep optical trap, resulting in low gaseous particle trapping efficiency and poor stability.

[0003] With the development of spatial light modulators and computational holography, phase-modulated multi-point optical trap arrays can simultaneously generate tens to hundreds of independent optical traps on the focal plane, enabling parallel manipulation of multiple particles. However, existing solutions are mostly designed for liquid environments. In the gas phase, the particle size ranges widely (0.1 μm to 10 μm), and the system integration of high-refresh-rate phase control, high-speed imaging, and real-time feedback closed loops presents numerous technical challenges. In a liquid environment, particles are confined within a fixed focal plane of the microchannel, allowing the microscopic imaging system to accurately track their position. However, in the open gas phase, particles float freely in three-dimensional space. Due to the shallow depth of field of the microscope objectives, the camera struggles to determine the axial position of the particles. Neither manual operation of the three-dimensional displacement platform nor automatic control programs can accurately lock onto the target. Furthermore, the Brownian motion amplitude of particles in the gas phase is significantly higher than in the liquid environment, further increasing the difficulty of real-time tracking.

[0004] In contrast, the symmetric dual-beam optical tweezers create a symmetrical gradient force field along the propagation direction, which can balance the gravitational influence of particles at certain locations, enabling stable suspension of particles and preventing sedimentation or adhesion. The open dual-beam architecture has no physical barriers, and the optical trap force field generated by the ultra-long focal length objective can confine particles to a region far from the container surface. The reverse symmetric beam enhances the light intensity gradient in the focal region through interference effects, and its gradient force amplitude can be 3-5 times that of a single beam.

[0005] Based on the above-mentioned technical requirements, this invention proposes a multi-particle dynamic capture device and method for gaseous media, which can achieve efficient, programmable, dynamic suspension and real-time imaging of particles in the gas phase without polluting the optical environment. Summary of the Invention

[0006] This invention provides a multi-particle capture device and method for gaseous media to solve the problem of multi-particle array suspension in the gas phase.

[0007] The present invention discloses a multi-particle trapping device for gaseous media, comprising a laser, a spatial light modulator, a beam splitter, a pair of microscope objectives, a suspension chamber, a high-speed microscopic imaging module, and an illumination module. The laser, spatial light modulator, beam splitter, and pair of microscope objectives constitute a coaxial optical path system. The pair of microscope objectives are symmetrically arranged on both sides of the suspension chamber, while the high-speed microscopic imaging module and illumination module are arranged opposite each other on the other two sides of the suspension chamber. The coaxial optical path formed by the illumination module and the high-speed microscopic imaging module is perpendicular to the coaxial optical path formed by the pair of microscope objectives. The pair of microscope objectives, the illumination module, and the high-speed microscopic imaging module are all positioned opposite the light windows on the sidewall of the suspension chamber. The laser beam emitted from the laser is boosted and expanded before reaching the spatial light modulator. A computer-generated hologram is loaded onto the spatial light modulator, and the input signal to the spatial light modulator is controlled by a host computer, which in turn controls the dynamic deflection of the liquid crystal array of the spatial light modulator, forming a dynamic light field distribution. The beam is then split by a beam splitter to form symmetrical or approximately symmetrical beams. These symmetrical or approximately symmetrical beams are then compressed and passed through two high numerical aperture microscope objectives to generate multifocal array optical tweezers in the suspension chamber, capturing and suspending multiple particles in the gaseous medium. The high-speed microscopic imaging module records the particle movement positions in real time and analyzes the particle motion parameters. The illumination module provides illumination for the high-speed microscopic imaging module.

[0008] Furthermore, the laser emitted by the laser is expanded by a set of lenses and the polarization direction of the laser is adjusted by a half-wave plate before being incident on the spatial light modulator.

[0009] Furthermore, the laser reflected by the spatial light modulator is split into two beams by a beam splitter in the optical module. The two laser beams are then condensed by two Kepler-type beam-shrinking optical paths and enter the microscope objective to generate a multifocal array optical tweezers in the suspension chamber.

[0010] Furthermore, the pair of microscope objectives are symmetrically arranged on both sides of the suspension chamber via two three-dimensional displacement mirror mounts. The suspension chamber is located at the focal plane of the two microscope objectives, and the two microscope objectives are symmetrical about the suspension chamber.

[0011] Preferably, the high-speed microscopic imaging module includes a high-speed image sensor and a microscopic imaging lens.

[0012] Preferably, the high-speed image sensor is a high-speed CMOS sensor or a high-speed CCD sensor.

[0013] Preferably, the spatial light modulator is a pure phase spatial light modulator or an amplitude-phase spatial light modulator.

[0014] Preferably, the microscope objective is a telephoto objective or a combination of microscope objectives;

[0015] Furthermore, the suspension chamber is a closed structure made of photosensitive resin, glass or metal. The side wall of the suspension chamber is provided with light windows. The particles are placed at the bottom of the suspension chamber and blown to the focal plane area by a micro airflow. Under the condition that the suspension chamber is kept closed, the particles are captured and stably suspended by symmetrical array optical tweezers.

[0016] Based on the above-mentioned device, the following multi-particle capture method for gaseous media is provided:

[0017] First, the laser is activated. The coaxial optical path system consisting of the laser, spatial light modulator, beam splitter, and a pair of microscope objectives generates two beams of reduced light.

[0018] Then, the two beams are initially calibrated using the interferometry method. The interferometry method is used to fine-tune the spatial angle of a pair of microscope objectives based on the interference pattern of the two beams, so that the two beams coincide precisely in the same spatial position and exhibit symmetrical or nearly symmetrical features, thereby achieving strict conjugate calibration of the dual-beam optical path.

[0019] After initial calibration, the two beam-shrink beams are precisely calibrated using a wavefront sensor via centroid extraction or maximum value extraction.

[0020] After calibration, a symmetrical or nearly symmetrical light beam is formed. This beam, after being narrowed, passes through two high numerical aperture microscope objectives to generate a multifocal array of optical tweezers within the suspension chamber, capturing and suspending multiple particles in the gaseous medium. During capture, the high-speed microscopic imaging module records the particle's position in real time and analyzes its motion parameters; the illumination module provides illumination for the high-speed microscopic imaging module.

[0021] Due to the small particle size, light weight, sensitivity to spatial disturbances, and unstable motion of particles in gaseous media, traditional optical tweezers devices struggle to achieve stable array-based levitation (capture). This invention proposes a multi-particle capture device for gaseous media. Based on a symmetrical optical tweezers array structure and wavefront modulation technology, continuous adjustment of the control signal by a control terminal drives the dynamic deflection of the liquid crystal array on the surface of a spatial light modulator, thereby modulating the wavefront phase of the incident light field and achieving dynamic adjustment of the optical tweezers array. This enables the spatial positioning and stable levitation (capture) of multiple gaseous particles. By loading a two-dimensional hologram generated by the spatial light modulator onto a laser beam, an array-based optical tweezers focal point is constructed. Combined with a symmetrical and conjugate dual-microscope objective structure, a stable three-dimensional potential well is formed. Furthermore, high-precision optical calibration methods (such as interferometry and detector methods) ensure strict conjugation of the two optical paths, significantly improving the stability and spatial accuracy of the levitation array. Simultaneously, the device possesses high-speed microscopic image acquisition capabilities, enabling real-time recording of particle trajectories and positional changes, providing high temporal and spatial resolution data support for the study of gaseous particle dynamics. Compared to traditional single-optical tweezers systems, this invention provides a new method for array control and imaging of multiple gaseous particles in a micro-space, providing feasible technical support and experimental platform for research scenarios such as multi-particle interaction studies, aerosol manipulation, and microgravity condition simulation. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a block diagram of the overall structure of the device of the present invention;

[0024] Figure 2 for Figure 1 Preliminary calibration principle diagram for a moderately symmetrical or approximately symmetrical beam;

[0025] Figure 3 for Figure 1 Schematic diagram of the precise calibration principle for a symmetrical or approximately symmetrical beam;

[0026] Figure 4 The dot plot is for calibration using a wavefront sensor in Application Example 1;

[0027] Figure 5 The image shows the optical trap, suspended particles, and scattering pattern captured by using symmetrical optical tweezers to capture four toner particles in Application Example 1.

[0028] Figure 6The image shows the optical trap, suspended particles, and scattering pattern captured by using symmetrical optical tweezers to capture four carbon particles with increased spacing in Application Example 2.

[0029] Figure 7 The dot plot for calibration using a wavefront sensor in Application Example 3;

[0030] Figure 8 The image shows the optical trap, suspended particles, and scattering pattern captured by using symmetrical optical tweezers to capture six toner particles in Application Example 3. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0033] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0034] like Figure 1As shown, a multi-particle trapping device for gaseous media includes a laser, a spatial light modulator, a beam splitter, a pair of microscope objectives, a suspension chamber S, a high-speed microscopic imaging module, and an illumination module R. The laser, spatial light modulator, beam splitter, and pair of microscope objectives form a coaxial optical path system. The pair of microscope objectives are symmetrically arranged on both sides of the suspension chamber, and the high-speed microscopic imaging module and illumination module are arranged opposite each other on the other side of the suspension chamber. The coaxial optical path formed by the illumination module and the high-speed microscopic imaging module is perpendicular to the coaxial optical path formed by the pair of microscope objectives. The pair of microscope objectives, the illumination module, and the high-speed microscopic imaging module are all aligned with the light windows on the sidewall of the suspension chamber. The laser beam, after beam boosting and expansion, reaches the spatial light modulator. A computer-generated hologram is loaded onto the spatial light modulator, and the input signal to the modulator is modified by a host computer, thereby controlling the dynamic deflection of the modulator's liquid crystal array to form a dynamic light field distribution. The beam is then split by a beam splitter to form symmetrical or approximately symmetrical beams. Finally, the last pair of beams is reduced in size and passed through two high numerical aperture microscope objectives to generate multifocal array optical tweezers in the suspension chamber, capturing and suspending multiple particles in the gaseous medium. The high-speed microscopic imaging module records the particle movement positions in real time and analyzes the motion parameters. The illumination module provides illumination for the high-speed microscopic imaging module.

[0035] The suspension chamber, located on the axis of two symmetrical microscope objectives, provides a gaseous environment for microparticles at the focal plane of the objectives. The suspension chamber is a sealed structure, which can be made of materials such as photosensitive resin, glass, or metal. It features a suspension window perpendicular to the laser propagation direction and an imaging window parallel to the laser propagation direction; the windows can be made of highly transparent quartz glass. Microparticles are placed at the bottom of the suspension chamber and propelled to the focal plane region by a micro-airflow. While maintaining a sealed suspension chamber, symmetrical array optical tweezers are used to capture and stably suspend the microparticles.

[0036] In this embodiment, the laser emitted by the laser is expanded by the first lens L1 (focal length f1) and the second lens L2 (focal length f2) to match the input conditions of the spatial light modulator, expanding the laser beam to the target diameter D1 of the spatial light modulator. The distance between L1 and L2 is f1 + f2. After adjusting the polarization direction of the laser with a half-wave plate HWP, the first reflecting mirror M1 is incident on the spatial light modulator. The power of the laser can be adjusted by the internal modulation current.

[0037] The laser reflected from the spatial light modulator is split into two beams by the beam splitter BS, forming optical path A and optical path B;

[0038] Optical path A is a Keplerian beam-shrinking system, including a third lens L3 (focal length f3), a second mirror M2, and a fourth lens L4 (focal length f4). The second mirror M2 is located at the focal point of the third lens L3 and the fourth lens L4, and the distance between L3 and L4 is f3 + f4.

[0039] Optical path B is also a Keplerian beam-shrinking system, including a fifth lens L5 (focal length f5), a third reflecting mirror M3 and a sixth lens L6 (focal length f6). The third reflecting mirror M3 is located at the focal point of the fifth lens L5 and the sixth lens L6, and the distance between L5 and L6 is f5 + f6.

[0040] The third lens L3 and the fifth lens L5 have the same focal length, f3 = f5, and the fourth lens L4 and the sixth lens L6 have the same focal length, f4 = f6. This is used to shrink the beam-splitting spot to the entrance pupil diameter D2 of the microscope objective.

[0041] In this embodiment, a pair of microscope objectives are symmetrically positioned on either side of a suspension chamber via two three-dimensional displacement mirror mounts. The suspension chamber S is located at the focal plane of microscope objectives O1 and O2, and microscope objectives O1 and O2 are symmetrical about the suspension chamber S. The spatial angles of the two three-dimensional displacement mirror mounts are finely adjusted according to the beam splitting paths A and B. The beams after the beams are contracted by beam splitting paths A and B are highly compressed using the first microscope objective O1 and the second microscope objective O2 (magnification ≥ 20×), generating a multi-point array optical tweezers with reverse symmetry on the same focal plane.

[0042] Before use, the two beams are initially calibrated using interferometry. This calibration ensures that the two beams precisely overlap in the same spatial position and exhibit symmetrical or near-symmetrical characteristics. For example... Figure 2 As shown, based on the far-field interference principle of two opposing symmetrical beams at the exit of the beam splitter, optical paths A and B are propagated symmetrically through a Keplerian beam-shrinking system, a mirror, and a microscope objective, respectively, before returning to the same beam splitter exit, forming interference fringes on the far-field screen. Under the condition of satisfying the paraxial approximation of Fresnel diffraction, the contrast and spacing of these interference fringes directly reflect the degree of conjugation and relative aberration of the two wavefronts. By analyzing the interference pattern, the position of the beam splitter or microscope objective is finely adjusted using a high-precision three-dimensional displacement platform until the contrast of the interference fringes is maximized and the spacing is widest, thus achieving conjugation calibration of the dual-beam optical paths.

[0043] The two beams of light undergo far-field diffraction and superposition at the left exit of the beam splitter, and their intensity distribution can be expressed as:

[0044]

[0045] in For the spatial coordinates on the interference plane The light intensity distribution was measured at the location. Let be the complex amplitude field of optical path A at the interference plane. Its modulus square... This indicates the light intensity of a single beam A at that location. Let be the complex amplitude field of optical path B at the interference plane. Its modulus square... This indicates the light intensity of a single beam B at that location. This is an interference term that reflects the effect of the phase difference between the two light fields on the total light intensity. When the two beams are completely conjugate (the phase difference is zero), this term takes the maximum positive value, producing the stripes with the highest contrast.

[0046] Specifically as follows:

[0047] (1) Load a Gaussian noise scatter hologram onto the plane of the spatial light modulator to generate a test light field with wide spectrum characteristics;

[0048] (2) Optical path A: The beam passes through the beam splitter, is compressed by the Kepler-type beam shrinking system (lenses L3, L4), and is guided by the mirror into the left microscope objective, where it is focused to form a single light trap; after passing through the focal point, the beam continues to return to the left exit of the beam splitter via the beam shrinking system along the opposite path.

[0049] (3) Optical path B: It is split off by the beam splitter and guided into the right microscope objective through a beam-shrinking system and a mirror system equivalent to optical path A, forming an optical trap that propagates in opposite directions and symmetrically. After focusing, the beam returns to the left exit of the same beam splitter along the opposite path and is completely conjugate with optical path A.

[0050] (4) Collect the far-field interference pattern of the two beams at the exit on the left side of the beam splitter and evaluate the contrast of the interference fringes;

[0051] (5) Based on the deviation of the spacing and contrast of the interference fringes from the ideal value, the position of the beam splitter or microscope objective is finely adjusted by a high-precision three-dimensional displacement platform so that the fringe spacing is maximized and the contrast is high enough, thereby eliminating optical aberrations.

[0052] (6) Repeat steps (4) to (5) until the contrast of the interference fringes reaches the maximum and the fringe spacing meets the design requirements, thereby completing the conjugate calibration of the dual-beam optical path.

[0053] After initial calibration, this embodiment uses a Shack-Hartmann wavefront sensor for precise calibration.

[0054] like Figure 3 As shown, after coarse calibration of the optical path, a Shack-Hartmann wavefront sensor can be set up for precise calibration. The Shack-Hartmann wavefront sensor is fixed to the exit plane of optical path A, ensuring that the microlens array surface of the sensor is perpendicular to the propagating optical axis. At this point, a Gaussian noise scatter hologram is loaded with the spatial light modulator to generate a broadband coherent test optical field. An aperture needs to be placed in optical path B to completely block it, preventing interference with optical path A.

[0055] The laser is activated, causing the beam from optical path A to pass through the beam-shrinking system, mirror, and microscope objective, forming a spot array on the sensor's microlens array. The sensor control software records the spot image corresponding to each microlens unit; for a high-resolution sensor, multiple square regions may correspond to one spot array. The spot image output by the sensor is divided into N microlens unit regions, and the pixel intensity distribution within the i-th region is denoted as... Extract the center coordinates of the light spot for each microlens unit region. There are two methods for centroid extraction:

[0056] One method is the maximum intensity method, which takes the pixel region in which each point forms a light spot as the target centroid, and the region with the largest gray value amplitude. That is, directly take the position of the brightest pixel in the area;

[0057] The second method is the centroid-weighted method, which takes the weighted average position of all pixels within a single spot pixel region: , Subsequently, based on the definition of an ideal reference lattice, the offset vector and error index are calculated. For each acquired light spot center, the offset vector relative to the corresponding reference point is calculated: , The overall error index is obtained by accumulating the Euclidean lengths of each offset vector. This is done to quantify the deviation of optical path A from the ideal reference. Using image processing tools such as OpenCV, and based on the statistical distribution of each offset vector, the X, Y, Z translation, pitch, and deflection knobs of a three-dimensional displacement platform are used to fine-tune the microscope objective or beam splitter to reduce system aberrations and angular errors. After each adjustment, the above steps are repeated until... If the light converges to a preset threshold or fails to decrease further, optical path A is considered to have completed the correction, and the final dot matrix will be... As a reference optical path dot matrix.

[0058] The control software saves the set of point coordinates obtained after optical path A correction and locks the positions of the three-dimensional platform and optical components to ensure that the reference optical path remains stable.

[0059] Move the Shack-Hartmann wavefront sensor to the exit position of optical path B, repeat the above steps, and extract the center of the light spot. The offset and error of optical path B are calculated: , , Similarly, by using a three-dimensional displacement platform and optical element knobs, the optical path B is adjusted according to the offset vector, and the above steps are repeated after each adjustment until the lattice height of the optical path B and the optical path A coincide, thus achieving strict conjugate calibration of the two optical paths.

[0060] The illumination module is perpendicular to the coaxial optical path formed by the microscope objectives O1 and O2. Simultaneously, the illumination module is spatially aligned with the suspension chamber S.

[0061] The high-speed microscopy imaging module is perpendicular to the suspended optical path (set opposite to the illumination module). The module includes a high-speed image sensor and a microscopic imaging lens. The microscopic imaging lens is connected to the high-speed image sensor via a standard camera F-mount. The microscopic imaging lens consists of two parts: the first part is the optical barrel, which in this embodiment uses a NAVITAR 2X F-MOUNT 1-62922; the second part is the imaging lens, which in this embodiment uses a Mitutoyo MPlan Apo 10×, with a focal length of 200mm and a numerical aperture of 0.28.

[0062] Based on the aforementioned device, an arrayed optical tweezers focal point is constructed by loading a two-dimensional hologram generated by a spatial light modulator onto a laser beam. Combined with a symmetrical and conjugate dual-microscope structure, a stable three-dimensional potential well is formed, enabling the spatial positioning and stable suspension of multiple gaseous particles. Real-time acquisition of the suspension chamber using a high-speed microscopic imaging module allows for the recording of particle trajectories and positional changes, providing high temporal and spatial resolution data support for the study of particle dynamics in gaseous media.

[0063] Application Example 1

[0064] First, a pure phase-type spatial light modulator is used to generate four optical potential wells at the conjugate focal planes of the two microscope objectives, and then a strict conjugate calibration of the dual optical paths is performed according to the "dot matrix contrast" calibration method.

[0065] The calibration process is as follows:

[0066] Calibration was performed using a Shack-Hartmann wavefront sensor with a microlens array size of 21×18 and a lens aperture of 300μm. The image sensor used had dimensions of 6.656mm×5.325mm, a pixel size of 5.2μm, and a maximum frame rate of 25fps. The calibration steps are as follows:

[0067] (1) Fix the microlens array surface of the Shack–Hartmann wavefront sensor perpendicular to the exit of optical path A to ensure that the sensor completely covers the light spot area emitted from the microscope objective; preload a Gaussian noise scatter hologram on the plane of the spatial light modulator to generate a wide-spectrum test light field, start the laser and introduce the beam into optical path A through the beam splitter.

[0068] (2) 10–20 frames of light spot array images are continuously acquired by the built-in or external CMOS sensor to reduce the impact of single-frame noise; the acquired multi-frame images are superimposed or median filtered to generate an average spot array with high signal-to-noise ratio for subsequent accurate positioning.

[0069] (3) Divide the averaged image into 21×18 sub-regions according to the microlens unit, and calculate the center coordinates of the spot using the maximum intensity method for each region.

[0070] (4) The measured center coordinates With a pre-calculated ideal reference lattice Compare and fine-tune the position of the beam splitter or microscope objective along the X, Y, and Z axes and in the pitch and yaw directions. After each fine-tuning, evaluate the deviation until the maximum offset value is lower than the preset threshold (10 μm in this example). Confirm that optical path A has completed high-precision conjugate correction and save the final dot matrix as a reference.

[0071] (5) Move the sensor to the exit of optical path B, repeat the above steps to collect and extract the center of the light spot. Compare it one by one with the reference dot matrix of optical path A, and repeat the calibration steps of optical path A to adjust the optical elements of optical path B until their offset converges to the same threshold, thus completing the entire calibration process.

[0072] Figure 4 (a) shows the dot matrix generated on the focal plane of the Shack-Hartmann sensor after fine-tuning and calibration of optical path A using the three-dimensional adjustment knob. Figure 4 (b) shows the dot matrix generated on the focal plane of the Shack-Hartmann sensor after fine-tuning and calibration by the three-dimensional adjustment knob of the optical path B. In this example, the pixel clock of the Shack-Hartmann sensor used is 43MHz, the frame rate is 25fps, and the exposure time is 8.085ms.

[0073] Subsequently, carbon powder particles are blown into the bottom of the suspension chamber via a micro-airflow, and the sealing cover is quickly closed to maintain a stable gas phase environment. The maximum output power is obtained by adjusting the laser current knob to 6.5 A (corresponding to an output power of 2 W), and the capture device is activated and enters the capture state.

[0074] A Phantom high-speed camera paired with a Navitar macro lens was used to capture video of the suspended area within the focal plane of the microscope objective. Figure 5 (a) shows the projected positions of the four optical traps in the xOy plane; Figure 5 (b) shows a static image of four toner particles successfully captured under bright field conditions; Figure 5Image (c) is the captured image recorded solely by the scattered light from the particles under dark conditions. During the experiment, the exposure time of the high-speed CMOS sensor was adjusted to 1900 μs, the frame rate was 500 fps, and the resolution was 640×480. Symmetrical optical tweezers successfully suspended four carbon particles with diameters of approximately 1–5 μm on the focal plane, and during a continuous 5-minute video observation, the center position drift of each of the four particles was less than 0.5 μm. Figure 5 As can be seen, this invention can achieve stable capture and suspension of four carbon powder particles in an air medium. This result verifies the feasibility of symmetrical optical tweezers in a non-liquid environment, breaking through the limitation of traditional optical tweezers relying on high-refractive-index liquid media; the particle suspension stability stems from the uniform depth of the three-dimensional potential well formed by beam interference and the symmetrical distribution of gradient forces, effectively suppressing lateral escape caused by radiation pressure; at the same time, the scattering loss in the air medium is extremely low, significantly improving the stiffness of the optical well and the capture lifetime.

[0075] Application Example 2

[0076] Four-point holograms with increased lateral spacing (potential well spacing adjusted from 5 μm to 10 μm) were sequentially loaded into a pure phase-type spatial light modulator, and the conjugate calibration of the dual optical paths was completed according to the "dot matrix comparison" method in Application Example 1. Subsequently, carbon powder particles were blown into the bottom of the suspension chamber and sealed. The laser current was adjusted to 6.5 A (corresponding to an output power of 2 W) to enter the capture mode. Similar to the capture process in Application Example 1, the capture device was started.

[0077] The acquisition section used a Phantom high-speed camera with a Navitar macro lens, with an exposure time of 1900 μs, a frame rate of 500 fps, and a resolution of 640×480, to photograph the suspended area within the focal plane of the microscope objective. Figure 6 (a) shows the projection of four optical traps in the xOy plane, where the two on the left exhibit typical defocus blur characteristics due to their lateral position deviating from the focal plane. This optical blur can serve as an indicator of the three-dimensional distribution of particles relative to the focal plane. Figure 6 (b) provides the same as Figure 6 (a) Distribution of scattered light corresponding to the carbon powder; Figure 6 (c) shows the particle scattering profile recorded under bright field conditions; Figure 6 In (d), an aggregated state can be observed where two adhered carbon particles are trapped in the same potential well. According to... Figure 6 As shown in (e), alternating bright and dark interference fringes can also be observed after the scattered light from the particles is superimposed. From Figure 6 As can be seen, by adjusting the light field and increasing the spacing between the four light traps, the capture and suspension of four carbon powder particles with a larger spacing can be achieved, indicating that the present invention has high stability in light field control and particle manipulation in the gaseous medium.

[0078] Application Example 3

[0079] In this example, a new hologram is loaded into a pure phase-type spatial light modulator. Six hexagonally symmetrically distributed optical potential wells are generated at the conjugate focal planes of the two microscope objectives through phase modulation. The "dot matrix contrast" calibration method is used to complete the strict conjugate calibration of the dual optical paths.

[0080] The optical path was calibrated using a Shack-Hartmann wavefront sensor. The calibration process is as follows:

[0081] A microlens array of 21×18 pixels with a lens aperture of 300μm was selected. The image sensor used measures 6.656mm×5.325mm, with a pixel size of 5.2μm and a maximum frame rate of 25fps. The calibration steps are as follows:

[0082] (1) Fix the microlens array surface of the Shack–Hartmann wavefront sensor perpendicular to the exit of optical path A to ensure that the sensor completely covers the light spot area emitted from the microscope objective; preload a Gaussian noise scatter hologram on the plane of the spatial light modulator to generate a wide-spectrum test light field, start the laser and introduce the beam into optical path A through the optical module.

[0083] (2) 10–20 frames of light spot array images are continuously acquired by the built-in or external CMOS sensor to reduce the impact of single-frame noise; the acquired multi-frame images are superimposed or median filtered to generate an average spot array with high signal-to-noise ratio for subsequent accurate positioning.

[0084] (3) Divide the averaged image into 21×18 sub-regions according to the microlens unit, and calculate the center coordinates of the spot using the maximum intensity method for each region.

[0085] (4) The measured center coordinates ( , (and a pre-calculated ideal reference lattice) , The beam splitter or microscope objective is finely adjusted along the X, Y, and Z axes and in the pitch and yaw directions. After each fine adjustment, the deviation is evaluated until the maximum offset value is lower than the preset threshold (10 μm in this example). The optical path A is confirmed to have completed high-precision conjugate correction, and the final dot matrix is ​​saved as a reference.

[0086] (5) Move the sensor to the exit of optical path B, repeat the above steps to collect and extract the center of the light spot ( , Then, compare it one by one with the reference dot matrix of optical path A, and repeat the calibration steps of optical path A to adjust the optical elements of optical path B until their offset converges to the same threshold, thus completing the entire calibration process.

[0087] Figure 7 (a) shows the dot matrix generated on the focal plane of the Shack-Hartmann sensor after fine-tuning and calibration of optical path A using the three-dimensional adjustment knob. Figure 7 In the middle (b), the dot matrix generated on the focal plane of the Shack-Hartmann sensor after the optical path B is finely adjusted and calibrated by the three-dimensional adjustment knob is shown. In this example, the pixel clock of the Shack-Hartmann sensor used is 26MHz, the frame rate is 10.12fps, and the exposure time is 6.223ms.

[0088] Subsequently, the carbon powder particles are blown into the bottom of the suspension chamber through a micro-airflow and quickly sealed. The laser current is adjusted to 6.5 A (corresponding to an output power of about 2 W) to start the capture device and enter the capture state.

[0089] The Phantom high-speed camera, in conjunction with the Navitar macro lens, was used to capture images of the focal plane area. The exposure time was 1900 μs, the frame rate was 500 fps, and the resolution was 640×480. Figure 8 Figure 8(a) shows the projected positions of the six optical traps in the xOy plane; in the bright-field image of Figure 8(b), the six carbon powder particles captured by the six optical traps can be clearly observed. In the potential trap in the fourth quadrant, due to the non-uniform particle size and the slight change in the gas phase refractive index, a single potential trap simultaneously binds two submicron-sized carbon powder particles. Figure 8 The scattered light image shown in (c) reveals concentric ring diffraction patterns around the defocused particles, in addition to the symmetrical optical tweezers interference fringes. Under dark-field conditions, the geometric profile of the particles deviating from the focal plane acts as a dynamic aperture stop, causing Fresnel diffraction of the incident light and forming a ring structure. The entire observation lasted 5 minutes, recording the trapping and scattering characteristics of carbon powder particles by the six-light-trap array. Figure 8 As can be seen from this, the present invention can achieve stable capture and suspension of six carbon powder particles in an air medium, indicating that the required number of array optical traps for the control of the light field has the ability to stably capture and suspend particles in a gaseous medium that meet the target number.

Claims

1. A multi-particulate capture device oriented toward a gas phase medium, characterized by, The system includes a laser, a spatial light modulator, a beam splitter, a pair of microscope objectives, a suspension chamber, a high-speed microscopic imaging module, and an illumination module. The laser, spatial light modulator, beam splitter, and pair of microscope objectives form a coaxial optical path system. The pair of microscope objectives are symmetrically arranged on both sides of the suspension chamber, while the high-speed microscopic imaging module and illumination module are arranged opposite each other on the other two sides. The coaxial optical path formed by the illumination module and the high-speed microscopic imaging module is perpendicular to the coaxial optical path formed by the pair of microscope objectives. The pair of microscope objectives, the illumination module, and the high-speed microscopic imaging module are all positioned opposite the optical windows on the sidewall of the suspension chamber. The laser beam is transmitted through... After beam lifting and expansion, the light reaches the spatial light modulator. A computer-generated hologram is loaded onto the spatial light modulator, and the input signal to the spatial light modulator is controlled by a host computer, which in turn controls the dynamic deflection of the liquid crystal array of the spatial light modulator, forming a dynamic light field distribution. The beam is then split by a beam splitter to form symmetrical or approximately symmetrical beams. These symmetrical or approximately symmetrical beams are then narrowed and passed through two high numerical aperture microscope objectives to generate multifocal array optical tweezers in the suspension chamber, capturing and suspending multiple particles in the gaseous medium. The high-speed microscopic imaging module records the particle motion positions in real time and analyzes the particle motion parameters. The illumination module provides illumination for the high-speed microscopic imaging module.

2. The gas phase media oriented multi-particulate capture device of claim 1, wherein, The laser emitted by the laser is expanded by a set of lenses and the polarization direction of the laser is adjusted by a half-wave plate before being incident on the spatial light modulator.

3. The gas phase media oriented multi-particulate capture device of claim 1, wherein, The laser reflected by the spatial light modulator is split into two beams by a beam splitter in the optical module. The two laser beams are then condensed by two Kepler-type beam-shrinking optical paths and enter the microscope objective to generate a multifocal array optical tweezers in the suspension chamber.

4. The gas phase media oriented multi-particulate capture device of claim 1, wherein, The pair of microscope objectives are symmetrically arranged on both sides of the suspension chamber via two three-dimensional displacement mirror mounts. The suspension chamber is located at the focal plane of the two microscope objectives, and the two microscope objectives are symmetrical about the suspension chamber.

5. The gas phase media oriented multi-particulate capture device of claim 1, wherein, The aforementioned high-speed microscopic imaging module includes a high-speed image sensor and a microscopic imaging lens.

6. The gas phase media oriented multi-particulate capture device of claim 1, wherein, High-speed image sensors are either high-speed CMOS sensors or high-speed CCD sensors.

7. The gas phase media oriented multi-particulate capture device of claim 1, wherein, The spatial light modulator is either a pure phase type spatial light modulator or an amplitude phase type spatial light modulator.

8. The gas phase media oriented multi-particulate capture device of claim 1, wherein, The microscope objective is a long focal length objective or a combination of microscope objectives.

9. The multi-particle suspension device for gaseous media as described in claim 1, characterized in that: The suspension chamber is a closed structure made of photosensitive resin, glass or metal. The side wall of the suspension chamber is provided with light windows. The particles are placed at the bottom of the suspension chamber and blown to the focal plane area by micro-airflow. Under the condition that the suspension chamber is kept closed, the particles are captured and stably suspended by symmetrical array optical tweezers.

10. A multi-particle capture method for a gaseous medium using any one of the apparatuses of claims 1 to 9, characterized in that, Specifically: First, the laser is activated. The coaxial optical path system consisting of the laser, spatial light modulator, beam splitter, and a pair of microscope objectives generates two beams of reduced light. Then, the two beams are initially calibrated using the interferometry method. The interferometry method is used to fine-tune the spatial angle of a pair of microscope objectives based on the interference pattern of the two beams, so that the two beams coincide precisely in the same spatial position and exhibit symmetrical or nearly symmetrical features, thereby achieving strict conjugate calibration of the dual-beam optical path. After initial calibration, the two beam-shrink beams are precisely calibrated using a wavefront sensor via centroid extraction or maximum value extraction. After calibration, a symmetrical or nearly symmetrical light beam is formed. This beam, after being narrowed, passes through two high numerical aperture microscope objectives to generate a multifocal array of optical tweezers within the suspension chamber, capturing and suspending multiple particles in the gaseous medium. During capture, the high-speed microscopic imaging module records the particle's position in real time and analyzes its motion parameters; the illumination module provides illumination for the high-speed microscopic imaging module.

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