CN115026414A - Laser two-photon direct writing processing equipment and automatic focusing method thereof - Google Patents

Abstract

The invention relates to laser two-photon direct writing processing equipment and an automatic focusing method thereof. The processing equipment comprises: the laser device comprises a laser device, a light path adjusting component, an objective lens, a camera, a motion platform, a substrate and a controller. The base is used for bearing the material to be processed, the moving table is fixedly connected with the base, the objective lens is arranged between the base and the camera, and the light path adjusting component is arranged between the laser and the objective lens. According to the invention, the laser is started to emit laser by the controller, the camera is used for collecting the images of the substrate and the area where the material to be processed is located, and the equivalent diameter of the fluorescent light spot in each image is measured, so that the ideal value of the equivalent diameter of the fluorescent light spot is determined, the substrate is further controlled to lift until the equivalent diameter of the light spot reaches the ideal value, automatic focusing is completed, the focusing efficiency and the focusing precision of laser two-photon direct writing processing are improved, and the processing precision of the three-dimensional micro-nano structure is improved.

Description

Laser two-photon direct writing processing equipment and automatic focusing method thereof

Technical Field

The invention relates to the technical field of micro-nano structure processing, in particular to laser two-photon direct writing processing equipment and an automatic focusing method of the laser two-photon direct writing processing equipment.

Background

An ultrafast laser two-photon direct writing processing technology based on material two-photon absorption becomes an important means for processing a three-dimensional micro-nano structure. The two-photon absorption of the material refers to a nonlinear process that the material absorbs two photon energies simultaneously under the action of short-pulse and high-intensity ultrafast laser. The reaction area of the material can be limited at the focus of the laser processing equipment through two-photon absorption, so that ultra-high-precision three-dimensional micro-nano processing is realized.

In ultrafast laser two-photon direct writing processing, the interface between the two-photon material and the substrate is generally used as a processing reference plane. In order to ensure that the processed structure is not washed away after development, it is necessary to ensure that the focus is at the processing reference plane at the start of two-photon processing. In order to improve the micro-nano machining precision, the smaller the focus is, the higher the machining precision is; however, the smaller the focal point, the more difficult it is to position the initial machining focal point on the reference plane. Since the size of the focus in the optical axis direction is in the order of a single micron or submicron, a reference plane needs to be found accurately. At present, an initial focus is manually positioned on a reference surface by manpower, and the initial focus is searched by the experience of an operator and the manpower, so that the operation is inconvenient, the searching time is long, and errors can be caused.

Disclosure of Invention

Therefore, it is necessary to provide a laser two-photon direct writing processing apparatus and an automatic focusing method thereof for solving the problems of low focusing efficiency and poor accuracy in the ultrafast laser two-photon direct writing processing process.

The invention is realized by adopting the following technical scheme: a laser two-photon direct writing processing apparatus comprising: the laser device comprises a laser device, a light path adjusting component, an objective lens, a camera, a motion platform, a substrate and a controller.

The substrate is used for bearing a material to be processed, and the material to be processed is coated on the bottom surface of the substrate. The material to be processed fluoresces under the action of laser. The motion platform is fixedly connected with the substrate. The motion table has at least three degrees of freedom for driving the substrate to move up and down or horizontally. The camera is arranged above the substrate and is used for acquiring a fluorescence image of the substrate and the area where the material to be processed is located in real time. The objective lens is disposed between the substrate and the camera. The laser is focused by the objective lens to form a laser focus, and the laser focus is positioned in the substrate. The fluorescence emitted by the material to be processed under the action of laser is amplified by the objective lens and then acquired by the camera. The light path adjusting component is arranged between the laser and the objective lens and used for adjusting the energy and the phase of laser emitted by the laser, so that laser rays are vertically incident on the objective lens.

The controller is used for controlling the laser to emit laser and controlling the light path adjusting component to adjust the energy and the phase of the laser. The controller is also used for controlling the motion platform to adjust the vertical height of the substrate and acquiring an image for generating the fluorescent light spot in real time through the camera in the process of lifting the substrate. The controller is also used to measure the equivalent diameter of the fluorescent spot. The controller is also used for executing the following adjusting process according to the corresponding relation between the equivalent diameter of the light spot and the relative position of the focus: and determining the diameter of the corresponding light spot when the focus is at the ideal position, and taking the diameter as an ideal value of the size of the light spot. Judging the relation between the equivalent diameter of the facula and an ideal value under the current state: a. when the equivalent diameter of the light spot is larger than an ideal value, the controller generates a downward moving signal with a preset amplitude and controls the moving platform to drive the substrate to descend. b. When the equivalent diameter of the light spot is smaller than the ideal value, the controller generates an upward moving signal with a preset amplitude and controls the moving platform to drive the substrate to move upward. c. And when the equivalent diameter of the light spot is equal to the ideal value, confirming that the focusing is finished. The controller is also used for generating a corresponding femtosecond laser scanning strategy according to the three-dimensional micro-nano structure to be processed, adjusting the working parameters of the light path adjusting assembly and processing the required three-dimensional micro-nano structure on the material to be processed on the substrate.

The processing equipment designs a focusing control method by analyzing the corresponding relation between the position information of the laser focus relative to the substrate and the maximum diameter of the fluorescent light spot acquired in real time, so that the position information of the laser focus relative to the substrate is correspondingly determined according to the maximum diameter of the fluorescent light spot, and the substrate is controlled to be driven to generate displacement, so that the laser focus and the substrate are positioned at ideal positions. According to the invention, the relative position of the laser focus and the substrate is controlled and adjusted through the comparison of the fluorescent light spot images, so that automatic focusing is completed, the focusing efficiency and the focusing precision of two-photon direct writing processing are improved, and the processing precision of the three-dimensional micro-nano structure is improved.

In one embodiment, the method for calculating the ideal value of the spot size comprises the following steps: setting a ratio according to the property of the material to be processed; selecting the maximum value of the equivalent diameter of the light spot as a reference value; taking the product of the ratio and the reference value as an ideal value; wherein, when the photoresist is used as the material to be processed, the ratio is 2/3.

In one embodiment, the optical path adjusting assembly includes a half-wave plate, a Glan laser prism, a beam expander, an attenuator plate, and a beam splitter. The half-wave plate is arranged in the incident direction of the laser light and is used for adjusting the phase of the laser light. The Glan laser prism is arranged on the emission path of the laser and used for converting laser light into polarized light. The beam expander is arranged in the emergent direction of the polarized light and used for converting the polarized light into collimated laser beams. The attenuation sheet is vertically arranged on the light path of the collimated laser beam and used for adjusting the energy of the collimated laser beam. The spectroscope is arranged on the emergent path of the collimated laser beam and used for reflecting the collimated laser beam to enable the collimated laser beam to vertically enter the objective lens. The beam splitter is also used to transmit the fluorescence emitted by the material to be processed into the camera.

In one embodiment, the beam splitter is a dichroic mirror having the characteristics of reflecting infrared light with wavelength of 750-850nm and transmitting visible light with wavelength of 400-700 nm.

In one embodiment, the laser is a femtosecond laser, and the center wavelength of the laser emitted by the femtosecond laser is 800 nm. Laser emitted by the femtosecond laser is totally reflected when being incident on the dichroic mirror, so that the energy of the laser is kept, and the interference of other light rays is eliminated.

In one embodiment, the motion stage comprises a driver, a motion mechanism and an object stage, wherein the driver is electrically connected with the controller, and the driver is also electrically connected with the motion mechanism. The movement mechanism is fixedly connected with the objective table. The objective table is detachably connected with the base. The driver can receive the control command of the controller and control the motion mechanism to adjust the position of the object stage.

In one embodiment, the camera is a CCD camera, and the CCD camera includes a lens, a CCD module and an image processor electrically connected in sequence. The lens is used for collecting optical signals emitted by the substrate and the material to be processed. The CCD module is used for converting the optical signal into an electric signal. The image processor is used for converting the electric signals into digital signals and converting the digital signals into fluorescence images. The image collected by the CCD camera has the characteristics of high definition and convenient transmission.

The invention also provides an automatic focusing method of the laser two-photon direct writing processing equipment, which comprises the following steps:

s1: placing a material to be processed with a fluorescent effect on the bottom surface of the substrate;

s2: emitting laser for focusing and focusing the laser to form a laser focus, and moving the substrate until the bottom surface of the substrate is positioned below the laser focus;

s3: moving the substrate upwards until the laser focus is completely positioned in the material to be processed;

s4: in the process of moving the substrate upwards, acquiring images of the substrate and the area where the material to be processed is located in real time as fluorescence images;

s5: measuring the equivalent diameter of the light spot in each fluorescence image;

s6: and executing the following adjusting process according to the corresponding relation between the equivalent diameter of the light spot and the relative position of the focus: determining the equivalent diameter of the corresponding light spot when the focus is positioned at the ideal position, and taking the equivalent diameter as an ideal value of the equivalent diameter of the light spot; judging the relation between the equivalent diameter of the facula and an ideal value under the current state: when the equivalent diameter of the light spot is larger than an ideal value, a controller generates a downward moving signal with a preset amplitude and controls a moving platform to drive a substrate to descend; when the equivalent diameter of the light spot is smaller than an ideal value, the controller generates an upward moving signal with a preset amplitude and controls the moving platform to drive the substrate to move upward; and thirdly, confirming that focusing is finished when the equivalent diameter of the light spot is equal to the ideal value.

In one embodiment, the corresponding relationship between the equivalent diameter of the light spot and the relative position of the focus is as follows: and I, when no light spot exists in the fluorescence image, the laser focus is completely positioned in the substrate. And II, when light spots appear in the fluorescence image and gradually increase, the laser focus starts to contact the material to be processed and gradually moves to the interface between the substrate and the material to be processed. And III, when the light spot in the fluorescence image reaches the maximum value and does not change any more, the laser focus is positioned at the interface of the substrate and the material to be processed and gradually moves into the material to be processed.

In one embodiment, the method for calculating the ideal value of the spot size includes: setting a ratio according to the property of the material to be processed; selecting the maximum value of the equivalent diameter of the facula as a reference value; the product of the ratio and the reference value is taken as an ideal value.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention designs a focusing control method by analyzing the corresponding relation between the position information of the laser focus relative to the substrate and the maximum diameter of the fluorescent light spot acquired in real time, so that the position information of the laser focus relative to the substrate is correspondingly determined according to the maximum diameter of the fluorescent light spot, and the substrate is controlled and driven to generate displacement, so that the laser focus and the substrate are positioned at ideal positions. According to the invention, the relative position of the laser focus and the substrate is controlled and adjusted through the comparison of the fluorescent light spot images, so that automatic focusing is completed, the focusing efficiency and the focusing precision of two-photon direct writing processing are improved, and the processing precision of the three-dimensional micro-nano structure is improved.

2. The invention adopts the substrate which does not emit fluorescence same as the material to be processed under the action of the laser to bear the material to be processed, so that the obtained fluorescence spots are easier to distinguish, and the measurement of the maximum diameter of the fluorescence spots is facilitated.

3. The image acquired by the CCD camera has the characteristics of high definition and convenience in transmission, and the focusing efficiency and precision can be improved.

Drawings

FIG. 1 is a schematic view of a processing apparatus according to embodiment 1 of the present invention;

FIG. 2 is a schematic diagram of the optical path adjusting assembly of FIG. 1;

FIG. 3 is a flow chart of an auto focus method of the processing tool of FIG. 1;

FIG. 4 is a diagram illustrating the auto-focusing method of FIG. 3;

FIG. 5 is a graph showing the relationship between the maximum diameter of the spot of the fluorescence in FIG. 3 and the position information of the laser focus;

FIG. 6 is a schematic diagram of the position of the laser focus in FIG. 5 relative to the material to be processed;

FIG. 7 is a comparison of the spot images of FIG. 3;

FIG. 8 is a comparative diagram of the spot images when the laser focus is at different positions;

fig. 9 is a comparison graph of micro-nano structure processing effects with different positions as processing reference planes.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

It will be understood that when an element is referred to as being "mounted on" another element, it can be directly on the other element or intervening elements may also be present. When a component is referred to as being "disposed on" another component, it can be directly on the other component or intervening components may also be present. When an element is referred to as being "secured to" another element, it can be directly secured to the other element or intervening elements may also be present.

Unless defined otherwise, 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 invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "or/and" includes any and all combinations of one or more of the associated listed items.

Referring to fig. 1 and 2, fig. 1 is a schematic structural diagram of a processing apparatus according to the present embodiment; fig. 2 is a schematic structural diagram of the optical path adjusting assembly in fig. 1. This embodiment still provides a laser two-photon directly writes processing equipment, and processing equipment includes: the laser device comprises a laser device, a light path adjusting component, an objective lens, a camera, a motion platform, a substrate and a controller.

The laser is used for emitting laser light. In this embodiment, a ChameleonVision-S femtosecond laser is adopted, the central wavelength of the laser is 800nm, the pulse width is 75fs, and the repetition frequency is 80 MHz. Of course, in other embodiments, a pulsed laser or a continuous laser, etc. may be used.

The light path adjusting component is used for adjusting the energy and the emission direction of the laser and converting the laser into a collimated laser beam. The light path adjusting component comprises a half-wave plate, a Glan laser prism, a beam expander, an attenuation plate and a spectroscope. The half-wave plate is arranged in the incident direction of the laser light and is used for adjusting the phase of the laser light. The half-wave plate is a birefringent crystal with a thickness such that when light of normal incidence is transmitted, the phase difference between ordinary light (o-light) and linearly polarized light (e-light) is equal to pi or an odd multiple of pi. The Glan laser prism is arranged on the emission path of the laser and used for converting laser light into polarized light. The glan laser prism is a birefringent polarizing device made of natural calcite crystals, and the main component of the glan laser prism is rhombohedral crystals of CaCO 3. An unbiased collimated laser beam is input to the glan laser prism, and a linearly polarized light beam (e-beam) can be obtained. The glan laser prism has higher transmittance and polarization purity than other polarizing plates. The beam expander is arranged in the emergent direction of the polarized light and used for converting the polarized light into a collimated laser beam. The beam expander is a lens assembly capable of changing the diameter and divergence angle of the laser beam. The laser light emitted from the laser has a certain divergence angle, and the adjustment by the beam expander changes the laser beam into a collimated (parallel) laser beam. The attenuation sheet is vertically arranged on the light path of the collimated laser beam and used for adjusting the energy of the collimated laser beam. The light intensity can be attenuated by making the substance into sheet by using the absorption characteristic of the substance to the light and placing the sheet on the light path adjusting component, and the sheet element is called as an optical attenuation sheet. The amount of light passing through the attenuation sheet depends on the type of material and also on the thickness of the material. The spectroscope is arranged on the emergent path of the collimated laser beam and used for reflecting the collimated laser beam to enable the collimated laser beam to vertically enter the objective lens. The spectroscope is also used to transmit fluorescence emitted from the material to be processed into the camera. In this embodiment, the beam splitter is a dichroic mirror, and has the characteristics of reflecting infrared light with wavelength of 750-850nm and transmitting visible light with wavelength of 400-700 nm. The laser with the wavelength of 800nm emitted by the laser is reflected by the reflector and then vertically enters the objective lens, and other visible light is directly transmitted, so that the influence on the processing or focusing process is avoided. In addition, the wavelength of the fluorescence emitted by the material to be processed is generally between 450-600nm, and the fluorescence can also be directly transmitted from the spectroscope and captured by the camera, so that the definition of fluorescence imaging can be improved, and the interference of the fluorescence on laser processing can be avoided. Of course, in other embodiments, the optical path adjusting assembly may be replaced by a corresponding optical fiber component, as long as the laser light can be converted into a collimated laser beam and perpendicularly incident on the objective lens.

The objective lens is arranged between the substrate and the camera, can focus laser emitted by the laser to form a laser focus, and the position of the objective lens is arranged according to the distance between the objective lens and the laser focus, so that the initial position of the substrate covers the whole laser focus. The fluorescence emitted by the material to be processed can be magnified and observed through the objective lens. The camera can acquire a fluorescence image of the substrate and the material to be processed through the objective lens. In this embodiment, an objective lens of 50 times is used, and the numerical aperture NA of the objective lens is 0.8. The laser focus of the laser focused by the objective lens is ellipsoid. Of course, in other embodiments, the magnification and numerical aperture of the objective lens may be higher or lower, as long as the straight laser beam can be focused and the focal point is incident on the material to be processed.

The substrate is used for bearing a material to be processed and the material to be processed is positioned below the substrate. The material to be processed fluoresces under the action of laser. In this embodiment, a glass slide is used as a substrate. The material to be processed is coated on the bottom surface of the slide. Under the action of laser, the glass slide emits fluorescence which is obviously different from the material to be processed. Of course, in other embodiments, the substrate may be made of transparent material such as plastic or silicon wafer, or may be made of opaque material, but the substrate must have sufficient light transmission performance so that the focal point of the laser can fall on the material to be processed through the substrate.

The camera may be arranged directly above the objective lens. The beam splitter is located between the camera and the objective lens. The fluorescence emitted by the material to be processed under the action of the laser reversely passes through the objective lens and is transmitted to the lens of the camera through the spectroscope. The camera can acquire the fluorescence image in real time through the objective lens. The camera of the present embodiment is a CCD camera. The CCD camera has the characteristics of small volume, light weight, no influence of a magnetic field and vibration and impact resistance. The CCD camera comprises a lens, a CCD module and an image processor which are electrically connected in sequence. The lens is used for collecting optical signals emitted by the slide or the material to be processed. The CCD module is used for converting the optical signal into an electric signal. The image processor is used for converting the electric signals into digital signals and converting the digital signals into fluorescence images. The image collected by the CCD camera has the characteristics of high definition and convenient transmission. Of course, in other embodiments, the camera may be replaced by a photoelectric conversion element such as a photodiode or a phototriode, as long as the optical signal emitted from the substrate and the material to be processed can be converted into an image or an electrical signal.

The motion platform is fixedly connected with the substrate. The motion table has at least three degrees of freedom for driving the substrate to move up and down or horizontally. The motion stage includes a drive, a motion mechanism, and an object stage. The driver is electrically connected with the controller and the motion mechanism. The movement mechanism is fixedly connected with the objective table. The objective table is detachably connected with the base. The driver can receive the control command of the controller and control the motion mechanism to adjust the position of the object stage. The moving mechanism can be an electric cylinder, a linear stepping motor, an oil cylinder or an air cylinder and the like. The PI-E545 three-dimensional nanometer mobile station is adopted in the embodiment, the displacement can be accurate to the nanometer level, the control is stable, quick and accurate, and the method is widely applied to micro-nano-level precision machining. Of course, in other embodiments, the motion stage may be other micro-scale or nano-scale motion stage, as long as the relative position of the laser focal point and the material to be processed can be adjusted according to the control instruction.

The controller is used for controlling the laser to emit laser and controlling the light path adjusting component to adjust the energy and the phase of the laser. In the focusing process of the processing equipment, the laser absorbs energy through the attenuation sheet, so that a laser focus with lower energy is formed through the focusing of the objective lens, and the damage to the shape or the structure of a material to be processed is avoided. The controller is also used for controlling the motion table to adjust the vertical height of the substrate and acquiring a fluorescence image in real time in the process of lifting the substrate. In the process that the substrate moves from the lowest position of the motion table to the highest position of the motion table, the camera acquires optical signals of the substrate and the material to be processed in real time according to preset shooting frequency, the camera or the controller can convert the optical signals into electric signals, then the electric signals are converted into digital signals, the digital signals are converted into digital images, and finally corresponding fluorescence images are generated in the controller. The controller is also used to measure the equivalent diameter of the spot in the fluorescence image. The fluorescence emitted by the material to be processed forms a spot in the fluorescence image, which is clearly distinguished from other background light such as visible light, fluorescence of other objects, or reflected laser light. And adding a circumscribed circle on the outer side of the light spot through measurement software stored in the controller, and further taking the diameter of the circumscribed circle as the equivalent diameter of the light spot. The controller is also used for executing the following adjusting process according to the corresponding relation between the equivalent diameter of the light spot and the relative position of the focus: and determining the diameter of the corresponding light spot when the focus is at the ideal position as an ideal value of the size of the light spot. The method for calculating the ideal value of the spot size comprises the following steps: setting a ratio according to the property of the material to be processed; selecting the maximum value of the equivalent diameter of the light spot as a reference value; the product of the ratio and the reference value is taken as an ideal value. This example used photoresist (SZ2080) as the material to be processed, and the photoresist was placed on a glass slide and baked using a hot oven for 15 minutes before processing. The ratio of the ideal value of the spot to the reference value in the fluorescence image obtained by applying the photoresist was 2/3. Of course, in other embodiments, the material to be processed may be replaced by other photosensitive materials having fluorescence effect or doped with fluorescence effect substances, such as photosensitive resin, photosensitive hydrogel, and the like, and accordingly, the ratio thereof may be adjusted accordingly. Judging the relation between the equivalent diameter of the facula and the ideal value under the current state: a. when the equivalent diameter of the light spot is larger than the ideal value, the controller generates a downward moving signal with a preset amplitude and controls the moving platform to drive the substrate to descend. b. When the equivalent diameter of the light spot is smaller than the ideal value, the controller generates an upward moving signal with a preset amplitude and controls the moving platform to drive the substrate to move upward. c. And confirming that the focusing is finished when the equivalent diameter of the light spot is equal to the ideal value. The controller is also used for generating a corresponding femtosecond laser scanning strategy according to the three-dimensional micro-nano structure to be processed, adjusting the working parameters of the assembly and processing the required three-dimensional micro-nano structure in the material to be processed on the substrate. In this process, the laser energy is adjusted by a glan laser prism and a half-wave plate, and the laser energy may also be adjusted by using an attenuator plate. Laser with proper energy enters the objective lens through the spectroscope, so that the material to be processed is subjected to two-photon direct writing processing. And developing the sample structure to remove the part of the sample material exceeding the three-dimensional micro-nano structure to be processed, and further correcting the sample structure to obtain the three-dimensional micro-nano structure consistent with the three-dimensional micro-nano structure to be processed.

The controller may be stored in a computer. The controller can be a program, software or a U disk, and also can be a singlechip or other equipment with an operation function. The computer can also comprise a display, and the display is used for displaying the spot image, the maximum diameter of the spot or the position information of the laser focus in real time, so that an operator can conveniently observe the relative position of the laser focus and the material to be processed in real time.

Please refer to fig. 3 and fig. 4. FIG. 3 is a flow chart of an auto-focusing method of the processing apparatus of FIG. 1; FIG. 4 is a diagram illustrating the auto-focusing method of FIG. 3. The embodiment also provides an automatic focusing method of the laser two-photon direct writing processing equipment. The focusing method comprises the following steps:

s1: the material to be processed having a fluorescent effect is placed on the bottom surface of the substrate. The material to be processed can be directly selected from materials with fluorescence effect, or fluorescent materials can be added into materials without fluorescence effect to form fluorescent polymers, so that fluorescence is emitted under the action of laser.

S2: and emitting laser for focusing and focusing the laser to form a laser focus, and moving the substrate until the bottom surface of the substrate is positioned below the laser focus. The laser light required for focusing may be a single emitted laser light or a common laser light with the machining process. When the focusing process and the processing process share the laser, the laser needs to reduce energy through the light path adjusting component in the focusing process, so that the shape or the structure of the material to be processed is prevented from being damaged.

S3: and moving the substrate upwards until the laser focus is completely positioned in the material to be processed. The laser focus moves from the substrate to the material to be processed, and the fluorescence effect generated by the laser focus gradually changes.

S4: and acquiring fluorescence images of the substrate and the area where the material to be processed is positioned in real time during the process of moving the substrate upwards. The method of acquiring a fluorescence image includes: optical signals of the substrate and the material to be processed are collected. The optical signal is converted into an electrical signal. The electrical signal is converted to a digital signal. The digital signal is converted into a fluorescence image. The optical signal includes visible light and invisible light, the fluorescence emitted by the material to be processed has a characteristic that is clearly distinguished from other light, and the fluorescence emitted by the material to be processed forms a light spot in the fluorescence image through photoelectric conversion and is clearly distinguished from other light.

S5: the maximum diameter of the spot was measured in each fluorescence image as the spot equivalent diameter. The method for measuring the equivalent diameter of the light spot comprises the following steps: and adding a circumscribed circle on the outer side of the light spot of each fluorescence image through a preset measuring program, and further taking the diameter of the circumscribed circle as the equivalent diameter of the light spot.

S6: and executing the following adjusting process according to the corresponding relation between the equivalent diameter of the light spot and the relative position of the focus: and determining the diameter of the corresponding light spot when the focus is at the ideal position as an ideal value of the size of the light spot. The ideal value calculation method comprises the following processes: comparing all the spot equivalent diameters, and taking the maximum value of the spot equivalent diameters as a reference value. And calculating the product of the reference value and a preset ratio as an ideal value. Judging the relation between the equivalent diameter of the facula and the ideal value under the current state: when the equivalent diameter of the light spot is larger than the ideal value, the controller generates a downward moving signal with a preset amplitude and controls the moving platform to drive the substrate to descend. And secondly, when the equivalent diameter of the light spot is smaller than the ideal value, the controller generates an upward moving signal with a preset amplitude and controls the moving platform to drive the substrate to move upward. And thirdly, confirming that focusing is finished when the equivalent diameter of the light spot is equal to the ideal value.

Referring to fig. 5, fig. 6 and fig. 7, fig. 5 is a graph showing the relationship between the maximum diameter of the fluorescent spot in fig. 3 and the position information of the laser focus; FIG. 6 is a schematic diagram of the position of the laser focus in FIG. 5 relative to the material to be processed; fig. 7 is a comparison of the spot images of fig. 3. The corresponding relation between the equivalent diameter of the light spot and the relative position of the focus comprises the following steps: and I, when the fluorescent light spot does not appear, the laser focus is positioned in the substrate. And II, when the fluorescent light spot begins to appear, most of the laser focus is positioned in the substrate and begins to contact the material to be processed. And III, when the fluorescent light spot is gradually enlarged until the fluorescent light spot is not enlarged, moving the laser focus to the interface of the substrate and the material to be processed and gradually moving the laser focus to the material to be processed.

In the process of processing the micro-nano structure, spot images of the laser focus at different positions are respectively selected, and the obtained spot image contrast image is shown in fig. 8. According to the preset three-dimensional structure, the laser focus is located in the substrate, the material to be processed and the ideal position are respectively used as processing reference surfaces to process the micro-nano structure, and the obtained micro-nano structure comparison graph is shown in fig. 9. Referring to fig. 8 and 9, fig. 8 is a comparison diagram of spot images when the laser focus is located at different positions; fig. 9 is a comparison graph of micro-nano structure processing effects with different positions as processing reference planes. Wherein, fig. 8a is a fluorescent spot image when the laser focus is located on the substrate, and there is no fluorescent spot in the image. Fig. 8b is an image of a fluorescent spot as the laser focus begins to contact the material to be processed, and the fluorescent spot begins to appear. Fig. 8c is a fluorescent light spot image when the laser focus is located at the interface between the material to be processed and the substrate, and the fluorescent light spot equivalent diameter reaches the reference value. Fig. 8d is an image of a fluorescent spot when the laser focus is at an ideal position, and the spot equivalent diameter of the fluorescent spot reaches an ideal value. It can be seen that, in the actual processing process, the corresponding relationship between the spot image and the laser focus is basically consistent with the corresponding relationship in the focusing control method. Fig. 9a is a schematic diagram of the micro-nano structure when the laser focus is completely located in the substrate as the processing reference plane, and the finally formed micro-nano structure is partially lost. Fig. 9b is a schematic diagram of the micro-nano structure when the laser focus is located at the interface between the substrate and the material to be processed as the processing reference plane, and the finally formed micro-nano structure is the same as the design structure. Fig. 9c is a schematic diagram of the micro-nano structure when the laser focus is completely in the material to be processed as the processing reference plane, and the finally formed micro-nano structure is completely lost. After verification, when the equivalent diameter of the fluorescent light spot in the light spot image reaches an ideal value, the laser focus is just positioned at an ideal processing position, and the micro-nano structure processed at the ideal processing position is the same as the design structure.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is specific and detailed, but not to be understood as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A laser two-photon direct writing processing device adopts laser to process a material to be processed into a micro-nano structure, and the processing device comprises a laser; characterized in that, the processing equipment still includes:

a substrate for carrying a material to be processed; the material to be processed is positioned below the substrate; the material to be processed emits fluorescence under the action of laser;

the moving table is fixedly connected with the substrate, has at least three degrees of freedom and is used for driving the substrate to generate lifting or horizontal movement;

the camera is arranged above the substrate and is used for acquiring images of the underlying substrate and a material area to be processed in real time;

an objective lens disposed between the substrate and the camera;

the optical path adjusting component is arranged between the laser and the objective lens and is used for adjusting the energy and the phase of laser emitted by the laser and enabling laser rays to be projected onto a substrate below through the objective lens; and

a controller to: (1) controlling the laser to emit laser, and simultaneously controlling the light path adjusting component to adjust the energy and the phase of the laser; (2) controlling the motion table to adjust the vertical height of the substrate, and acquiring an image for generating a fluorescent light spot in real time through a camera in the process of lifting the substrate; (3) measuring the equivalent diameter of the fluorescent light spot; (4) and executing the following adjusting process according to the corresponding relation between the equivalent diameter of the light spot and the relative position of the focus: determining the equivalent diameter of the corresponding light spot when the focus is positioned at the ideal position, and taking the equivalent diameter as an ideal value of the size of the light spot; judging the relation between the equivalent diameter of the facula and the ideal value under the current state: a. when the equivalent diameter of the light spot is larger than the ideal value, the controller generates a downward moving signal with a preset amplitude and controls the moving platform to drive the substrate to descend; b. when the equivalent diameter of the light spot is smaller than the ideal value, the controller generates an upward moving signal with a preset amplitude and controls the moving platform to drive the substrate to move upward; c. when the equivalent diameter of the light spot is equal to the ideal value, confirming that focusing is finished; (5) and generating a corresponding femtosecond laser scanning strategy according to the three-dimensional micro-nano structure to be processed, adjusting the working parameters of the light path adjusting assembly, and processing the required three-dimensional micro-nano structure on the material to be processed on the substrate.

2. The laser two-photon direct writing processing apparatus according to claim 1, wherein the calculation method of the ideal value of the spot size includes: setting a ratio according to the property of the material to be processed; selecting the maximum value of the equivalent diameter of the light spot as a reference value; taking the product of the ratio and the reference value as an ideal value; wherein, when the photoresist is used as the material to be processed, the ratio is set to 2/3.

3. The laser two-photon direct writing processing apparatus according to claim 1, wherein the optical path adjusting assembly comprises a half-wave plate, a glan laser prism, a beam expander, an attenuator plate, and a beam splitter; the half-wave plate is arranged in the incidence direction of the laser and used for adjusting the phase of the laser; the Glan laser prism is arranged on an emission path of the laser and used for converting the laser into polarized light; the beam expander is arranged in the emergent direction of the polarized light and used for converting the polarized light into a collimated laser beam; the attenuation sheet is vertically arranged on the light path of the collimated laser beam and is used for adjusting the energy of the collimated laser beam; the spectroscope is arranged on an emergent path of the collimated laser beam and used for reflecting the collimated laser beam to enable the collimated laser beam to vertically enter the objective lens; the spectroscope is also used for transmitting fluorescence emitted by a material to be processed into the camera.

4. The apparatus as claimed in claim 3, wherein the beam splitter is a dichroic mirror having the characteristics of reflecting infrared light with wavelength of 750 and 850nm and transmitting visible light with wavelength of 400 and 700 nm.

5. The laser two-photon direct writing processing apparatus according to claim 4, wherein the laser is a femtosecond laser that emits laser light having a center wavelength of 800 nm.

6. The laser two-photon direct writing processing apparatus according to claim 1, wherein the motion stage comprises a driver, a motion mechanism, and an object stage, the driver being electrically connected to the motion mechanism; the movement mechanism is fixedly connected with the objective table; the driver is used for respectively controlling the movement mechanism to adjust the position of the object stage according to the control instruction of the controller; the base is detachably connected to the objective table.

7. The laser two-photon direct writing processing apparatus according to claim 1, wherein the camera is a CCD camera; the CCD camera comprises a lens, a CCD module and an image processor which are electrically connected in sequence; the lens is used for collecting optical signals emitted by the substrate and the material to be processed; the CCD module is used for converting the optical signal into an electric signal; the image processor is used for converting the electric signals into digital signals and converting the digital signals into the fluorescence images.

8. An auto-focusing method of a laser two-photon direct writing processing apparatus applied to the laser two-photon direct writing processing apparatus according to any one of claims 1 to 7, comprising the steps of:

s1: placing a material to be processed with a fluorescent effect on the bottom surface of the substrate;

s2: emitting laser for focusing and focusing the laser to form a laser focus, and moving the substrate until the bottom surface of the substrate is positioned below the laser focus;

s3: moving the substrate upwards until the laser focus is completely positioned in the material to be processed;

s4: in the process of moving the substrate upwards, acquiring images of the substrate and the area where the material to be processed is located in real time as fluorescence images;

s5: measuring the equivalent diameter of the light spot in each fluorescence image;

s6: and executing the following adjusting process according to the corresponding relation between the equivalent diameter of the light spot and the relative position of the focus: determining the equivalent diameter of the corresponding light spot when the focus is positioned at the ideal position, and taking the equivalent diameter as an ideal value of the equivalent diameter of the light spot; judging the relation between the equivalent diameter of the facula and the ideal value under the current state: when the equivalent diameter of the light spot is larger than the ideal value, a controller generates a downward moving signal with a preset amplitude and controls the moving platform to drive the substrate to descend; when the equivalent diameter of the light spot is smaller than the ideal value, a controller generates an upward moving signal with a preset amplitude and controls the moving platform to drive the substrate to move upward; and thirdly, confirming that focusing is finished when the equivalent diameter of the light spot is equal to the ideal value.

9. The auto-focusing method of two-photon laser direct writing processing equipment according to claim 8, wherein in S6, the equivalent diameter of the light spot is related to the relative position of the focus by: when no light spot exists in the fluorescence image, the laser focus is completely positioned in the substrate; II, when light spots appear in the fluorescence image and gradually increase, the laser focus starts to contact the material to be processed and gradually moves to an interface between the substrate and the material to be processed; and III, when the light spot in the fluorescence image reaches the maximum value and does not change any more, the laser focus is positioned at the interface of the substrate and the material to be processed and gradually moves into the material to be processed.

10. The auto-focusing method of a laser two-photon direct writing processing apparatus according to claim 8, wherein the calculation method of the ideal value of the spot size in S6 includes: setting a ratio according to the property of the material to be processed; selecting the maximum value of the equivalent diameter of the light spot as a reference value; and taking the product of the ratio and the reference value as an ideal value.

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