A device and method for measuring lithium niobate-based photovoltaic particle capture stability

Abstract

The application discloses a device and method for measuring the stability of particles captured by a lithium niobate-based photovoltaic tweezer, and is composed of a particle capturing system and a real-time particle position measuring system. The particle stability measurement first makes laser sweep across the particles on the pure lithium niobate chip. Due to the unique crystal characteristics of lithium niobate, the image recorded by the CCD camera below presents regular light and dark changes. The image is calculated to obtain the function relationship between the particle displacement information and the gray value change. Then the substrate is replaced with an iron-doped lithium niobate chip, the particles on the chip are captured by the particle capturing system, and the real-time particle position measuring system can calculate the real-time particle position information. The application can measure the stability of the particles captured by the lithium niobate-based photovoltaic tweezer under weak laser intensity, and also can measure the capturing stability of the particles under large light intensity by adding an attenuator, and has the characteristics of wide measurable light intensity range and real-time observation during the whole process.

Description

Technical Field

[0001] This invention relates to an apparatus and method for measuring the particle capture stability of lithium niobate-based photovoltaic tweezers. Specifically, it involves using an electric field generated by laser irradiation of a lithium niobate chip to capture particles, obtaining corresponding displacement information from the grayscale value changes of the captured image, thereby completing the measurement of particle capture stability. This invention belongs to the field of optical manipulation technology. Background Technology

[0002] Optoelectronic tweezers are tools that use photoelectric fields to grasp objects. They utilize the photovoltaic effect of crystals, requiring only weak light intensity to manipulate a large number of microspheres or particles. Optoelectronic tweezers greatly enrich the means of light-induced micromanipulation and are an important research tool for holding, manipulating, and microfabricating tiny particles such as cells, viruses, and biomolecules. In recent years, they have become a research hotspot both domestically and internationally in areas such as microfluidic chip laboratories and cell control.

[0003] Lithium niobate crystals possess piezoelectric, ferroelectric, electro-optic, and photorefractive properties, along with excellent thermal and chemical stability. Under laser irradiation, lithium niobate crystals exhibit a photovoltaic effect, generating photogenerated charges. Photogenerated photovoltaic electrons move directionally within the crystal, creating a photovoltaic electric field and realizing photoelectric tweezers. Therefore, photovoltaic tweezers manipulation based on lithium niobate crystals has emerged.

[0004] This invention discloses an apparatus and method for measuring the particle capture stability of lithium niobate-based photovoltaic tweezers. When a lithium niobate crystal is irradiated with a microwatt-level laser, the particles are captured at the center of the laser spot. The laser light passing through the lithium niobate crystal is then reflected into a CCD camera using a semi-transparent mirror. By processing the grayscale values ​​of the image and the particle displacement information, the real-time position information of the particles can be obtained, thus achieving the purpose of acquiring particle position information and measuring particle capture stability under microwatt-level light intensity. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method that is simple in structure, very convenient to operate, and capable of measuring the capture stability of lithium niobate-based photovoltaic tweezer particles under microwatt-level laser light intensity.

[0006] A device for measuring the particle capture stability of lithium niobate-based photovoltaic tweezers is characterized by: a particle capture system consisting of a CMOS image sensor 1, a filter 2, a laser 3, an electronic shutter 4, a translucent mirror 5, an objective lens 6, a lithium niobate chip 7, a three-dimensional transparent moving platform 8, a PC terminal 9, an objective lens 10, a translucent mirror 11, and a background light source 15; and a particle stability measurement system consisting of the laser 3, electronic shutter 4, translucent mirror 5, objective lens 6, lithium niobate chip 7, objective lens 10, translucent mirror 11, an attenuator 12, a phase retarder 13, and a CCD camera 14. The two systems enable simultaneous capture, manipulation, and stability measurement of microparticles.

[0007] A method for measuring the particle capture stability of lithium niobate-based photovoltaic tweezers is characterized by the following: First, a lithium niobate chip is used as the basis. A laser beam passes through the lithium niobate chip and is incident on a CCD camera, which captures a unique crystal image of the lithium niobate chip. Two perpendicular black bands in the image form a black cross, dividing a series of concentric bright circles with proportionally increasing spacing into four equal parts, forming a crystal image with interlocking outer rings and a central circle divided into four right-angled sectors. This image does not change with two-dimensional translation of the lithium niobate chip. Mapping this image to a two-dimensional coordinate system, the black cross corresponds to the coordinate axes, and the four divisions correspond to the four quadrants. This coordinate system corresponds to a two-dimensional coordinate system established with the center of the laser spot on the upper surface of the lithium niobate crystal as the origin. When a portion of the circular laser spot is blocked by a particle and cannot be incident on the lithium niobate chip, the brightness of the corresponding quadrant portion of the crystal image presented by the CCD camera will darken. As the particle approaches the center of the laser spot from different positions, the brightness of the corresponding quadrant portion of the crystal image will become increasingly darker. Furthermore, the inner circular right-angled sectors in the corresponding quadrants will also be proportionally reduced. The image is imported into a PC for grayscale value calculation. The grayscale values ​​of the divided first, second, third, and fourth quadrant regions are integrated and recorded as 11, 12, 13, and 14 respectively. The particles on the surface of the lithium niobate chip have exactly one x and one y coordinate in a two-dimensional coordinate system established with the center point of the laser spot as the origin. Correspondingly, we can obtain the real-time position information of the particles. The specific operation steps of this method are as follows: First, using a pure lithium niobate chip as a substrate, a small amount of oil-soluble solution containing the particles to be tested is dropped onto the substrate. A three-dimensional transparent moving platform is slowly moved laterally from left to right along the x-axis via a PC. Since the pure lithium niobate chip cannot capture the particles, the laser can completely scan the particles on the substrate, and the CCD camera below records the entire process. Because the particles block the laser from left to right, the relationship between the real-time displacement information of the particles and the change in grayscale value is defined as follows:

[0008]

[0009] Here, A is the proportionality constant; k = 2πn s / λ,n s Let λ be the solvent refractive index, λ be the laser beam, and α = 0.0074d. 3 Where d is the particle diameter; w is the laser beam waist radius; and x is the known displacement of the particle center from the laser spot center in each frame. Through the previous lateral scan, we obtain the specific value of the scaling factor A, thus obtaining the relationship between particle displacement information and grayscale values. At this point, when we use a lithium iron niobate crystal to capture particle position information, the particle displacements on the x-axis and y-axis are respectively:

[0010]

[0011]

[0012] The PC computer processes the grayscale values ​​of each frame of the image. The real-time displacement information of the particles along the x and y axes can be obtained from the function curve, thus completing the measurement of the particle capture stability. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a device and method for measuring the particle capture stability of lithium niobate-based photovoltaic tweezers.

[0014] Figure 2 The image of the crystal captured by a CCD camera when it is pure lithium niobate and there are no particles obstructing the view.

[0015] Figure 3 When the lithium niobate is pure, the lateral movement of the particles on its surface is controlled so that the laser sweeps across the particles, and the particle displacement and gray value change function image are calculated.

[0016] Figure 4 This is a process diagram illustrating one embodiment of the present invention for capturing microspheres on an iron-doped lithium niobate chip.

[0017] Figure 5 This is a particle location distribution diagram obtained by capturing microspheres on an iron-doped lithium niobate chip according to the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments and accompanying drawings.

[0019] A device and method for measuring the particle capture stability of photoelectric tweezers. A small amount of transformer oil solution containing 1µm polystyrene microspheres is dropped onto a pure lithium niobate chip 7, which is then placed on a three-dimensional transparent moving platform 8. An electronic shutter 4 and a background light source 14 are opened, and a 473nm laser 3 is adjusted to output 10µW of laser light. The laser beam passes through the electronic shutter 4, is reflected by a dichroic mirror 5, and enters a 100x oil immersion objective lens 6, focusing the laser light onto the surface of the pure lithium niobate chip 7. A PC 11 sends a signal to the three-dimensional transparent moving platform 8, and a CCD camera 1 observes the 1µm polystyrene particles on the pure lithium niobate chip as they slowly move laterally from left to right. The laser light then sweeps laterally across the particles on the pure lithium niobate substrate. Simultaneously, the laser light passes through a 20x objective lens 10, is reflected by a dichroic mirror 11, passes through an attenuator 12, and enters a monochrome CCD camera 13. The PC 9 processes the data to obtain the relationship between particle displacement information and grayscale value changes, calculating the ratio A = 0.14042, and plotting it as a function graph.

[0020] The electronic shutter 4 is closed, and the chip is replaced with an iron-doped lithium niobate chip. A small amount of transformer oil solution containing 1µm polystyrene microspheres is dropped onto the iron-doped lithium niobate chip 7. The electronic shutter 4 is then opened, and the particles are captured at the laser spot. Subsequently, the monochrome CCD camera 13 records the entire process of the particles shaking at the laser spot during capture. After processing by the PC 9, the grayscale value changes of each frame are obtained. Then, the displacements of the particles along the x-axis and y-axis were obtained as follows:

[0021]

[0022]

[0023] This allows us to obtain real-time particle location information and complete the measurement of particle capture stability.

Claims

1. A device for measuring the particle trapping stability of lithium niobate-based photovoltaic tweezers, characterized in that: In the device, a particle capture system is composed of a CMOS image sensor (1), a filter (2), a laser (3), an electronic shutter (4), a first semi-transparent mirror (5), a first objective lens (6), a pure lithium niobate chip, a three-dimensional transparent moving platform (8), a PC (9), a second objective lens (10), a second semi-transparent mirror (11), and a background light source (15); a particle real-time position measurement system is composed of a laser (3), an electronic shutter (4), a first semi-transparent mirror (5), a first objective lens (6), an iron-doped lithium niobate chip, a three-dimensional transparent moving platform (8), a second objective lens (10), a second semi-transparent mirror (11), an attenuator (12), a phase delayer (13), and a black and white CCD camera (14). The microparticle capture and stability measurement are performed simultaneously through two systems. During the measurement, a pure lithium niobate chip with microparticles on its upper surface is placed on a three-dimensional transparent moving platform (8). The laser beam of the laser (3) passes through the electronic shutter (4), is reflected by the first semi-transparent mirror (5), and enters the first objective lens (6), so that the laser is focused on the upper surface of the pure lithium niobate chip. The PC (9) moves the three-dimensional transparent moving platform (8), and the microparticles on the pure lithium niobate chip are observed to move slowly from left to right through the CMOS image sensor (1). The laser then sweeps across the particle on the pure lithium niobate chip horizontally. At the same time, the laser passes through the pure lithium niobate chip and the three-dimensional transparent moving platform (8), passes through the second objective lens (10), and passes through the second semi-transparent mirror. After reflection by the semi-reflective mirror (11), the light passes through the attenuator (12) and enters the black-and-white CCD camera (14). The PC (9) processes the image acquired by the black-and-white CCD camera (14). By analyzing the image changes when the microparticles are not captured and when they are captured, the relationship between the real-time displacement information of the microparticles and the gray value change is obtained. The gray value is the gray value of the unique crystal image of the lithium niobate chip acquired by the black-and-white CCD camera (14). Subsequently, the electronic shutter (4) is closed, the chip in the device is replaced with an iron-doped lithium niobate chip, the microparticles are placed on the surface of the iron-doped lithium niobate chip, the electronic shutter (4) is opened, and the laser beam of the laser (3) passes through the electronic shutter (4), is reflected by the first semi-reflective mirror (5), and enters the second... An objective lens (6) is used to focus the laser onto the surface of the lithium iron niobate chip, and the microparticles are captured at the laser spot. At the same time, the laser passes through the lithium iron niobate chip and the three-dimensional transparent moving platform (8), passes through the second objective lens (10), is reflected by the second semi-transparent mirror (11), passes through the attenuator (12), and enters the black and white CCD camera (14). The black and white CCD camera (14) records the entire process of the particles shaking at the laser spot when capturing the microparticles. The gray value change of each frame image is obtained by processing the data on the PC (9). The displacement of the microparticles on the X and Y axes is obtained by using the relationship between the real-time displacement information of the microparticles and the gray value change, and the real-time position information of the microparticles is obtained, thus completing the measurement of the microparticle capture stability.

2. A method for measuring the particle trapping stability of lithium niobate-based photovoltaic tweezers, characterized in that... The method includes: First, using a pure lithium niobate chip as a substrate, a small amount of oil-soluble solution containing the particles to be tested is dropped onto the substrate. The substrate is placed on a three-dimensional transparent moving platform. The three-dimensional transparent moving platform is slowly moved laterally from left to right along the X-axis via a PC. At this time, the laser beam can completely scan the particles on the substrate. The camera below the substrate then records the image of the entire process. Since the microparticles block the laser from left to right, the image changes when the microparticles are not captured and when they are captured are analyzed via the PC to obtain the relationship between the real-time displacement information of the microparticles and the gray value change. Next, using an iron-doped lithium niobate chip as a substrate, a small amount of oil-soluble solution containing the particles to be tested is dropped onto the substrate. The iron-doped lithium niobate chip is captured by irradiating it with a laser. The PC processes the images acquired by the camera located below the chip. The grayscale value of the frame image is used to obtain the real-time displacement information of the microparticles on the X and Y axes, based on the relationship between the obtained real-time displacement information of the microparticles and the grayscale value change. This allows for the measurement of the stability of the photovoltaic tweezers in capturing microparticles. The grayscale value is the grayscale value of the unique crystal image of the lithium niobate-based chip captured by the camera. The crystal image is a conic interferogram of the lithium niobate-based chip. This image is mapped to a two-dimensional coordinate system, with the black cross in the image corresponding to the coordinate axes. The part of the image divided equally by the black cross corresponds to the four quadrants. When the microparticles on the lithium niobate-based chip undergo displacement changes in the two-dimensional coordinate system established with the center of the laser spot as the origin, the integral of the grayscale value in the four quadrants of the crystal image will change accordingly. This allows for the obtaining of the relationship between the real-time displacement information of the microparticles and the grayscale value change, thereby completing the measurement of the stability of the microparticle capture.

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