Optoelectronic tweezer device for dielectric particle manipulation

Abstract

The application discloses an optoelectronic tweezers device for dielectric particle manipulation, and relates to the technical field of optoelectronic tweezers, and comprises an ultraviolet laser microscope light path, an ultraviolet laser sheet illumination light path, an imaging light path and a dielectric particle manipulation chip module; the dielectric particle manipulation chip module comprises a first lithium niobate wafer, a second lithium niobate wafer and a motion control device; the ultraviolet laser microscope light path irradiates the first lithium niobate wafer, and the ultraviolet laser sheet illumination light path irradiates the second lithium niobate wafer; the first lithium niobate wafer and the second lithium niobate wafer respectively generate photoelectrons after being irradiated; the photoelectrons generate laser converging light spots; the laser converging light spot generated by the first lithium niobate wafer is smaller than the laser converging light spot in the second lithium niobate wafer; a non-uniform electric field is generated in the dielectric particle manipulation chip; and the imaging light path is used for displaying particle information generated in the dielectric particle manipulation chip module. The device is simple in structure, and can flexibly, efficiently and accurately manipulate dielectric particles.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic tweezers technology, and more specifically to an optoelectronic tweezers device for manipulating dielectric particles. Background Technology

[0002] Optoelectronic tweezers (OET) technology is an emerging technique that utilizes the photoelectric effect to manipulate tiny objects (such as microspheres and particles). Developed from traditional optical tweezers, it combines optical and electrodynamic principles, enabling the capture, movement, rotation, and sorting of minute objects through precise control of light beams and electric fields. Relying on this photoinduced electrodynamic effect, OET offers significant advantages in micromanipulation, such as programmability, flexibility, versatility, high throughput, and ease of integration with other characterization systems, thus possessing broad application prospects.

[0003] When using optoelectronic materials (such as lithium niobate and lithium tantalate) as substrates, the virtual electrodes of optoelectronic tweezers can be preserved for a long time in the dark area. Furthermore, they can be erased and reused by heating and uniform illumination. Therefore, lithium niobate-based optoelectronic tweezers have become a research hotspot both domestically and internationally in recent years. In 2001, Sarkisov captured polystyrene microparticles on an x-cut iron-doped lithium niobate wafer. In 2011, Javier V et al. captured micron-sized calcium carbonate particles on the surface of a y-cut lithium niobate crystal. In 2013, Esseling et al. successfully achieved high-quality two-dimensional particle capture patterns by capturing charged particles (hydrofluoroether and GC particles) on a c-cut lithium niobate wafer. In 2015, Munoz-Martinez et al. successfully obtained two-dimensional particle capture patterns by immersing a laser-irradiated c-cut lithium niobate wafer in a dielectric particle (Ca2CO3) solution. In 2017, Chen et al. studied the dynamic dielectric electrophoresis behavior of insulating oil microdroplets using a single laser on a double c-cut lithium niobate device. While research on optoelectronic tweezers is relatively in-depth and extensive, there is still limited research on flexible and efficient manipulation of dielectric particles. Existing two-dimensional manipulation techniques for dielectric particles mostly involve single trapping patterns, failing to achieve flexible control. Furthermore, current research primarily relies on a single lithium niobate wafer and a single laser beam. Since the electric field of a single lithium niobate wafer is divergent, this significantly impacts the efficiency and precision of particle manipulation. Therefore, designing an optoelectronic tweezers device for flexible, efficient, and precise manipulation of dielectric particles is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides an optoelectronic tweezers device for manipulating dielectric particles, which can achieve flexible, efficient and precise manipulation of dielectric particles.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An optoelectronic tweezers device for manipulating dielectric particles includes: an ultraviolet laser microscope optical path, an ultraviolet laser sheet illumination optical path, an imaging optical path, and a dielectric particle manipulation chip module.

[0007] The dielectric particle manipulation chip module includes a first lithium niobate wafer, a second lithium niobate wafer, and a three-dimensional motion control device.

[0008] The ultraviolet laser microscope optical path irradiates the first lithium niobate wafer, and the ultraviolet laser sheet illumination optical path irradiates the second lithium niobate wafer; the first and second lithium niobate wafers generate photoelectrons after irradiation; the photoelectrons generate a laser focusing spot.

[0009] The laser focusing spot generated by the first lithium niobate wafer is smaller than the laser focusing spot in the second lithium niobate wafer; a non-uniform electric field is generated in the dielectric particle manipulation chip module;

[0010] The imaging optical path is used to display particle information generated in the dielectric particle manipulation chip module.

[0011] Preferably, the optical path of the ultraviolet laser microscope includes:

[0012] The first laser, the first beam expander, the dichroic mirror, and the microscope objective;

[0013] The laser emitted by the first laser is used by the first beam expander to generate the first incident laser.

[0014] The first incident laser beam undergoes total internal reflection via a dichroic mirror and reaches the microscope objective.

[0015] The microscope objective focuses the first incident laser onto the surface of the first lithium niobate wafer.

[0016] Preferably, the ultraviolet laser sheet illumination optical path includes:

[0017] Second laser, second beam expander system, adjustable slit, converging lens;

[0018] The second laser emitted by the second laser is used by the second beam expander to generate a second incident laser.

[0019] The center point of the adjustable slit coincides with the main optical axis of the second laser, which is used to control the irradiation power of the second incident laser.

[0020] The converging lens always focuses the second incident laser onto the inside of the second lithium niobate wafer, and the converging point is located directly above the laser focal point generated by the microscope objective.

[0021] Preferably, the imaging optical path includes an illumination lamp, a filter, and a CMOS camera;

[0022] The lighting is used to provide a light source for the imaging optical path;

[0023] The filter is used to filter out laser light and to allow high transmission of light from the lighting fixture;

[0024] The CMOS camera can image the image collected by the microscope objective on the focal plane onto the CMOS camera's detection surface.

[0025] Preferably, the first incident laser is used to fill the microscope objective; the dichroic mirror is placed at a 45° angle to the first incident laser to perform total internal reflection of the first incident laser band and to achieve high transmission of the light from the illumination lamp; the optical axis of the microscope objective coincides with the principal optical axis of the first incident laser and focuses the laser onto the upper surface of the first lithium niobate wafer.

[0026] Preferably, the incident beam is used to fill the adjustable slit, the long side of which is parallel to the upper / lower surface of the second lithium niobate wafer, and the irradiation power of the second laser is controlled by adjusting the width of the adjustable slit.

[0027] Preferably, in the dielectric particle manipulation chip module, the focal plane of the microscope objective coincides with the upper surface of the first lithium niobate wafer;

[0028] The area of ​​the laser focusing spot obtained by the microscope objective is always smaller than the area of ​​the laser focusing spot in the second lithium niobate wafer.

[0029] The three-dimensional motion device is used to quasi-control the interlayer spacing and relative position of the dielectric particle manipulation chip module;

[0030] Both the first and second lithium niobate wafers are c-cut iron-doped lithium niobate wafers, and the two lithium niobate wafers are placed in parallel with the same polarization axis direction.

[0031] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a photoelectric tweezers device for manipulating dielectric particles, and the beneficial technical effects are:

[0032] (1) The photoelectric tweezers device proposed in this invention comprises two layers of C-cut iron-doped lithium niobate wafers and two induced laser beams. Both lithium niobate crystals are iron-doped lithium niobate. The incorporation of iron impurities introduces additional energy levels into the lithium niobate lattice, increasing the concentration of photogenerated carriers and the intensity of the built-in electric field, thereby improving the efficiency of photovoltaic generation. Furthermore, the lithium niobate wafers are placed parallel to each other with the same polarization axis direction. When the two laser beams are focused on the upper and lower lithium niobate wafers respectively, the -C surface of the wafer becomes positively charged and the +C surface becomes negatively charged, thus forming two electric field sources distributed vertically and with opposite polarities within the chip. Compared to the common single-layer C-cut lithium niobate generating a surface-diverging electric field, this manipulation device converges the electric field into a beam, effectively improving the optical manipulation efficiency. In addition, compared to a single-beam laser-induced optical path device, this manipulation device can focus the laser beam onto the two lithium niobate wafers respectively, fully inducing them to generate photo-excited electrons, significantly shortening the optical manipulation response time.

[0033] (2) This invention proposes using two laser beams to ultimately generate two light spots of different sizes. The upper laser beam is converged by a slit and a converging lens, while the lower laser beam is converged by a microscope objective. Since the microscope objective is generally more effective at focusing laser light than a conventional convex lens, the excited area of ​​the upper lithium niobate crystal is more dispersed, resulting in a lower charge density, while the excited area of ​​the lower lithium niobate crystal is more concentrated, resulting in a higher charge density. This creates a non-uniform electric field in the chip interlayer. Dielectric particles in the non-uniform electric field experience dielectric force, thereby achieving efficient particle manipulation. Furthermore, the smaller excited area of ​​the lower lithium niobate layer effectively improves the precision of optical manipulation.

[0034] (3) This invention proposes to use a three-dimensional motion control device to precisely control the interlayer spacing and spatial position of the lithium niobate chip. During the operation, the laser is fixed, and the chip can move along the planned path in the x-axis and y-axis directions. The particles respond quickly at the laser irradiation point, and the charge at this point does not disappear immediately after the laser leaves. The particles can be captured on the lower surface of the wafer along the path irradiated by the laser, thereby realizing flexible particle manipulation. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the optoelectronic tweezers device provided by the present invention;

[0037] Figure 2 A schematic diagram of the electric field generated by laser irradiation on two horizontally placed c-cut lithium iron niobate sheets (+c face up) according to an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram illustrating the polarization of polystyrene microspheres under dielectric electrophoretic force in a non-uniform electric field, as provided in an embodiment of the present invention.

[0039] In the figure: 1-1 First ultraviolet laser, 1-2 First lens, 1-3 Second lens, 1-4 Dichroic mirror, 1-5 Microscope objective, 1-6 Illumination lamp, 1-7 Filter, 1-8 CMOS camera, 2-1 Second ultraviolet laser, 2-2 Third lens, 2-3 Fourth lens, 2-4 Adjustable slit, 2-5 Converging lens, 3-1 First lithium iron niobate wafer, 3-2 Second lithium iron niobate wafer, 3-3 Three-dimensional motion control device. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0041] like Figure 1 As shown, this embodiment of the invention discloses an optoelectronic tweezers device for manipulating dielectric particles, including: an ultraviolet laser microscope optical path, an ultraviolet laser sheet illumination optical path, an imaging optical path, and a dielectric particle manipulation chip module;

[0042] The dielectric particle manipulation chip module includes a first lithium niobate wafer 3-1, a second lithium niobate wafer 3-2, and a three-dimensional motion control device 3-3;

[0043] The ultraviolet laser microscope optical path irradiates the first lithium niobate wafer 3-1, and the ultraviolet laser sheet illumination optical path irradiates the second lithium niobate wafer 3-2; the first lithium niobate wafer 3-1 and the second lithium niobate wafer 3-2 generate photoelectrons after irradiation; the photoelectrons generate a laser focusing spot.

[0044] The laser focusing spot generated by the first lithium niobate wafer 3-1 is smaller than the laser focusing spot generated by the second lithium niobate wafer 3-2; a non-uniform electric field is generated in the dielectric particle manipulation chip module;

[0045] The imaging optical path is used to display particle information generated in the dielectric particle manipulation chip module.

[0046] Furthermore, in this embodiment of the invention, the ultraviolet laser microscope optical path and the ultraviolet laser sheet illumination optical path use ultraviolet lasers. When the lithium niobate wafer is irradiated by two ultraviolet lasers, it will generate photo-excited electrons due to the photovoltaic effect. Moreover, the laser focusing spot in the first lithium niobate wafer 3-1 is smaller than the laser focusing spot in the second lithium niobate wafer 3-2. Therefore, a non-uniform electric field will be generated in the control chip, thereby realizing the directional control of dielectric particles.

[0047] Specifically, the optical path of the ultraviolet laser microscope includes:

[0048] First laser 1-1, first beam expander system, dichroic mirror 1-4 and microscope objective 1-5;

[0049] The laser emitted by the first laser 1-1 is used by the first beam expander system to generate the first incident laser.

[0050] The first incident laser beam undergoes total internal reflection via dichroic mirrors 1-4 and is directed to microscope objective 1-5;

[0051] The microscope objective 1-5 focuses the first incident laser onto the upper surface of the first lithium niobate wafer 3-1.

[0052] Specifically, the ultraviolet laser sheet illumination optical path includes:

[0053] Second laser 2-1, second beam expander system, adjustable slit 2-4, converging lens 2-5;

[0054] The second laser emitted by the second laser 2-1 is used by the second beam expander system to generate a second incident laser.

[0055] The center point of the adjustable slit 2-4 coincides with the main optical axis of the second laser, and is used to control the irradiation power of the second incident laser.

[0056] The converging lens 2-5 always focuses the second incident laser onto the inside of the second lithium niobate wafer 3-2, and the converging point is located directly above the laser focal point generated by the microscope objective 1-5.

[0057] Furthermore, in this embodiment of the invention, the first beam expanding system includes convex lens 1-2 and convex lens 1-3; the second beam expanding system includes convex lens 2-2 and convex lens 2-3.

[0058] Specifically, the imaging optical path includes illumination lamps 1-6, filters 1-7, and CMOS cameras 1-8;

[0059] Illumination lamps 1-6 are used to provide a light source for the imaging optical path;

[0060] The filters 1-7 are used to filter out laser light and to allow high transmission of light from the lighting lamps 1-6;

[0061] The CMOS camera 1-8 can image the image on the focal plane collected by the microscope objective 1-5 onto the detection surface of the CMOS camera 1-8.

[0062] Furthermore, in this embodiment of the invention, the CMOS camera 1-8 is an infinity imaging camera, which can image the image on the focal plane collected by the microscope objective 1-5 onto the camera detection surface, thereby enabling simultaneous particle manipulation and observation.

[0063] Specifically, the first incident laser is used to fill the microscope objective 1-5; the dichroic mirror 1-4 is placed at a 45° angle to the first incident laser to perform total internal reflection of the first incident laser band and to achieve high transmission of the light from the illumination lamp 1-6; the optical axis of the microscope objective 1-5 coincides with the principal optical axis of the first incident laser and focuses the laser onto the upper surface of the first lithium niobate wafer 3-1.

[0064] Specifically, the second incident laser is used to fill the adjustable slit 2-4, the long side of which is parallel to the upper / lower surface of the second lithium niobate wafer 3-2. The adjustable slit 2-4 controls the irradiation power of the second laser 2-1 by adjusting its width.

[0065] Specifically, in the dielectric particle manipulation chip module, the focal plane of the microscope objective 1-5 coincides with the upper surface of the first lithium niobate crystal 3-1.

[0066] The area of ​​the laser focusing spot obtained by the microscope objectives 1-5 is always smaller than the area of ​​the laser focusing spot in the second lithium niobate wafer 3-2.

[0067] The three-dimensional motion device 3-3 is used to control the interlayer spacing and relative position of the quasi-control dielectric particle manipulation chip module;

[0068] Both the first lithium niobate wafer 3-1 and the second lithium niobate wafer 3-2 are c-cut iron-doped lithium niobate wafers. The two lithium niobate wafers are placed in parallel and have the same polarization axis direction.

[0069] Furthermore, in this embodiment of the invention, the focal plane of the microscope objective 1-5 coincides with the upper surface of the first lithium niobate wafer 3-1; the area of ​​the laser focusing spot obtained by the microscope objective 1-5 is always smaller than the area of ​​the laser focusing spot in the second lithium niobate wafer 3-2. When the ultraviolet laser irradiates the c-cut iron-doped lithium niobate wafer, a large number of photo-induced electrons moving along the c-axis are generated inside, making the -c surface of the lithium niobate wafer positively charged and the +c surface negatively charged. This generates two electric field sources with opposite polarities distributed vertically in the control chip. Since the illumination area on the first lithium niobate wafer 3-1 is small and the illumination area on the second lithium niobate wafer 3-2 is large, a non-uniform electric field is generated between the first lithium niobate wafer 3-1 and the second lithium niobate wafer 3-2. The dielectric particles achieve directional movement under the drive of the dielectric force generated by the non-uniform electric field, thereby achieving the purpose of precise particle control.

[0070] The expression for the dielectric force experienced by a dielectric particle in a non-uniform electric field in this invention is as follows:

[0071]

[0072] In the formula, r is the particle radius, ε m Let ω be the dielectric constant of the medium, and α(ω) be the Klausius-Mossotti factor. The gradient of the square of the electric field intensity reflects the degree of non-uniformity of the electric field;

[0073] The expression for α(ω) is:

[0074]

[0075] Formula ε * This is a unified expression for the complex dielectric constant, where j is the imaginary unit, σ is the conductivity, and ω is the angular frequency of the electric field. (Subscripted) These refer to the complex dielectric constants of the particle and the medium, respectively, and their expressions and ε. * The forms are the same; for easier understanding, it can also be written as... In this invention, a lithium niobate substrate is irradiated with a laser at an angular frequency ω→0, ε * Since the imaginary part approaches infinity, the expression for the dielectric force at this point is:

[0076]

[0077] In the formula, σ p and σ m These represent the electrical conductivity of the particle and the medium, respectively.

[0078] It can be seen that the sign of Re[α(ω)] is determined by σ p and σm The difference determines when σ p Greater than σ m When Re[α(ω)] is positive, F EDP When σ is positive, the particle experiences an attractive force; conversely, when σ is positive, the particle experiences an attractive force. p Less than σ m When Re[α(ω)] is negative, F EDP When the value is negative, the particle experiences a repulsive force.

[0079] In another embodiment of the present invention, taking polystyrene microspheres as the manipulated particles and insulating oil as the buffer solution as an example, the working process of the particle-manipulated photoelectric tweezers device of the present invention specifically includes the following steps:

[0080] Step 1: Fix two lithium niobate wafers horizontally on the three-dimensional motion control device, with both of them facing upwards (the conductivity of polystyrene microspheres is greater than that of insulating oil). Take an appropriate amount of liquid medium containing uniform polystyrene particles and drop it onto the surface of the first lithium niobate wafer 3-1. Adjust the spacing between the chip layers using the three-dimensional motion device 3-3.

[0081] Step 2: Start the ultraviolet laser 1-1. The incident laser beam is expanded by the beam expansion system composed of lenses 1-2 and 1-3, and then reflected by the dichroic mirror 1-4 to generate a converging solid Gaussian spot in the microscope objective 1-5, which is then focused on the upper surface of the first lithium niobate wafer 3-1.

[0082] Step 3: Start the ultraviolet laser 2-1. The incident laser beam is expanded by the beam expanding system composed of lenses 2-2 and 2-3. Then, it is transformed into sheet illumination through the adjustable slit 2-4 and the power is adjusted. Subsequently, the laser is focused into the second lithium niobate wafer 3-2 by the converging lens 2-5. By adjusting the position of the converging lens, the focal spot on the second lithium niobate wafer is located directly above the focal spot in the first lithium niobate wafer.

[0083] Step Four: As Figure 2 As shown, when a laser beam shines on iron-doped lithium niobate wafers 3-1 and 3-2, electrons inside the wafers easily escape from the Fe... 2+ / 3+ Electrons excited from the trap move along the positive direction (+c) of the lithium niobate polarization axis, causing a large number of excited electrons to accumulate on the +c surface of the c-cut lithium niobate, while leaving a large number of positive charges on the -c surface. Furthermore, due to the different spot sizes of the two induced lasers, a pattern is formed in the chip interlayer as follows: Figure 2 The non-uniform electric field shown;

[0084] Step 5: As Figure 3As shown, polystyrene microspheres are polarized in a non-uniform electric field, resulting in the separation of positive and negative charges. The field strength is stronger where the positive charge is located and weaker where the negative charge is located. The forces at the two polarized ends are not equal, and the resultant force is the dielectric force. Furthermore, the conductivity of polystyrene microspheres is greater than that of insulating oil. Under the action of the positive dielectric force, the polystyrene microspheres are captured at the first lithium niobate spot.

[0085] Step 6: Adjust CMOS camera 1-8 to infinity imaging, and image the image on the focal plane collected by the microscope objective onto the detection surface of CMOS camera 1-8 to see the particle manipulation state clearly in real time.

[0086] Step 7: Adjust the three-dimensional motion control device 3-3 to control the lithium niobate chip to move slowly along the set path. Repeat steps 4 and 5. Under the action of dielectrophoresis force, the particles are continuously captured at the laser irradiation point of the first lithium niobate wafer, thus showing a flexible form of particle manipulation.

[0087] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0088] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An optoelectronic tweezer device for dielectric particle manipulation, characterized by, The application relates to a dielectric particle manipulation chip module and a dielectric particle manipulation chip module. The dielectric particle manipulation chip module comprises a first lithium niobate wafer, a second lithium niobate wafer and a three-dimensional motion control device. The first lithium niobate wafer and the second lithium niobate wafer generate photo-excited electrons after being irradiated. The laser converging light spot generated by the first lithium niobate wafer is smaller than the laser converging light spot in the second lithium niobate wafer. An uneven electric field is generated in the dielectric particle manipulation chip module. The imaging light path is used for displaying particle information generated by the dielectric particle manipulation chip module. The ultraviolet laser microscope light path comprises a first ultraviolet laser, a first beam expander system, a dichroic mirror and a microscope objective. The first ultraviolet laser generates first incident laser through the first beam expander system. The first incident laser is totally reflected to the microscope objective through the dichroic mirror. The microscope objective converges the first incident laser to the upper surface of the first lithium niobate wafer. The ultraviolet laser sheet illumination light path comprises a second ultraviolet laser, a second beam expander system, an adjustable slit and a converging lens. The second ultraviolet laser generates second incident laser through the second beam expander system. The center point of the adjustable slit coincides with the main optical axis of the second laser, and is used for controlling the irradiation power of the second incident laser. The converging lens always converges the second incident laser in the second lithium niobate wafer, and the converging point is located directly above the laser focal point generated by the microscope objective. The three-dimensional motion control device is used for accurately controlling the spacing and relative position of the dielectric particle manipulation chip module. The imaging light path comprises an illumination lamp, a filter and a CMOS camera. The illumination lamp is used for providing a light source for the imaging light path.

2. The optoelectronic tweezer device for dielectric particle manipulation according to claim 1, wherein, The filter is used for filtering out laser and highly transmitting the light wave band of the illumination lamp. The CMOS camera images the image on the focal plane collected by the microscope objective to the detection surface of the CMOS camera. The first incident laser is used for filling the microscope objective. The dichroic mirror is placed at an angle of 45 degrees with the first incident laser, and is used for totally reflecting the first incident laser and highly transmitting the light of the illumination lamp.

3. The optoelectronic tweezer device for dielectric particle manipulation according to claim 2, wherein, The optical axis of the microscope objective coincides with the main optical axis of the first incident laser, and converges the laser to the upper surface of the first lithium niobate wafer.

4. The optoelectronic tweezer device for dielectric particle manipulation according to claim 1, wherein, The second incident laser is used for filling the adjustable slit.

5. The optoelectronic tweezer device for dielectric particle manipulation according to claim 1, wherein, The focal plane of the microscope objective coincides with the upper surface of the first lithium niobate wafer. The laser converging light spot area obtained by the microscope objective is always smaller than the laser converging light spot area in the second lithium niobate wafer. The first lithium niobate wafer and the second lithium niobate wafer are both c-cut iron-doped lithium niobate wafers, and the two lithium niobate wafers are placed in parallel and have consistent polarization axis directions.

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