High-transmittance and high-uniformity geometric phase grating element prepared by femtosecond pulse near-field normalization, method and application thereof

Abstract

The application discloses a high-transmittance and high-uniformity geometric phase grating element prepared by using femtosecond pulse near-field normalization, a method and application thereof, and belongs to the technical field of laser processing. The application utilizes the principle of femtosecond laser pulse near-field normalization to perform uniform processing in fused quartz, induces a new type of high-transmittance and high-uniformity birefringence structure, controls the change of the slow axis direction, thereby preparing a high-efficiency geometric phase grating with adjustable period, and realizes edge detection by using the light splitting characteristics of the geometric phase grating. The application is applied to optical image edge detection by using an innovative processing technology, solves the limitations of a traditional birefringence structure in transmittance and uniformity, and provides a solution with better performance and lower cost for the field of optical image edge detection.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser processing, and particularly relates to a high-transmittance and high-uniformity geometric phase grating element prepared by using femtosecond pulse near-field normalization, a method and application thereof. BACKGROUND

[0002] Birefringence structures are widely used in the field of optical element manufacturing. Edge detection is a basic problem in image processing and computer vision. Image edge detection can greatly reduce the amount of calculation while retaining important structural properties and eliminating weakly related information. Geometric phase elements made of birefringence structures have the advantages of miniaturization and integration compared to traditional edge detection systems composed of lenses and spatial filters, and are used as a new technology for optical image edge detection. In 2019, researchers used the birefringence structure of traditional femtosecond laser-induced in-vivo nanograting to construct a geometric phase metasurface that can perform optical differential calculation on image-carrying light beams and achieve edge detection through beam splitting.

[0003] However, the traditional nanograting birefringence structure coexists with positive and negative refractive index change regions, resulting in large overall scattering of the structure voxels, low transmittance, and poor uniformity of the voxels in long-range scanning. In this case, the ability of the camera to capture valid information is greatly reduced, and the accuracy of the measurement is also reduced.

[0004] Therefore, it is urgent to solve the problems of low transmittance and poor uniformity of the traditional birefringence structure to further improve the imaging effect of edge detection. SUMMARY

[0005] To solve the above-mentioned defects in the prior art, the application provides a high-transmittance and high-uniformity geometric phase grating element prepared by using femtosecond pulse near-field normalization, a method and application thereof. The application uses the principle of femtosecond laser pulse near-field normalization to uniformly process inside fused quartz, induces a new type of high-transmittance and high-uniformity birefringence structure, controls the change of its slow axis direction to prepare a high-efficiency geometric phase grating with adjustable period, and uses the light splitting characteristics of the geometric phase grating to achieve edge detection. The application applies innovative processing technology to optical image edge detection, solves the limitations of traditional birefringence structures in transmittance and uniformity, and provides a more optimal and lower-cost solution for the field of optical image edge detection.

[0006] The application is implemented by the following technical solutions:

[0007] In a first aspect, the application provides a method for preparing a high-transmittance and high-uniformity geometric phase grating element by using femtosecond pulse near-field normalization, which specifically includes the following steps:

[0008] Step one: the establishment of the laser processing optical path;

[0009] The specific steps are as follows: first, the femtosecond laser emitted by the laser passes through the energy regulation system composed of an electrically controlled half-wave plate HWP and a Glan prism P, and then passes through the polarization regulation system composed of a Pockels cell and a quarter-wave plate QWP; then the light beam passes through the beam expansion system composed of a concave lens L1 and a convex lens L2, and is projected onto the processing objective lens through the mirror M1, and is finally focused inside the sample to be processed; the LED illumination device is placed on the lower side of the sample stage, so that the white light emitted by the LED illumination device can penetrate the sample to be processed and then irradiate the objective lens OL; the white light is transmitted through the mirror M1 and then reflected by the mirror M2, and finally focused on the second convex lens L3, and a clear image is formed on the CCD sensor; the CCD sensor is connected to the industrial computer through a data line to observe the sample processing in real time;

[0010] Step two: leveling of the sample stage;

[0011] The specific steps are as follows: first, fix the sample to be processed on the three-dimensional displacement stage with an adjusting device; the adjusting device of the three-dimensional displacement stage includes X and Y axes in the horizontal direction and Z axis in the vertical direction; then, open the shutter in the processing optical path, focus the laser with the high-power objective lens, control the three-dimensional displacement stage to find the upper left corner of the sample to be processed, adjust the height of the displacement stage to focus the laser focal point on the upper surface of the sample, and record the Z-axis height of the surface at this time; similarly, find the upper right, lower left, and lower right surfaces of the sample and record the Z-axis height; adjust the adjusting device of the three-dimensional displacement stage according to the recorded surface Z-axis height data to make the surfaces at the four corners of the sample at the same Z-axis height; at this time, the sample stage to be processed has been leveled;

[0012] Step three, design and parameter calculation of geometric phase grating element;

[0013] The specific steps are as follows: first, select the geometric phase grating period , element size and shape that match the actual needs; then, according to the phase gradient formula of one-dimensional grating , where x and y represent the position coordinates of the rectangular coordinate system in the two-dimensional plane, generate data to describe the phase distribution of the grating in the form of a two-dimensional array or matrix; then, determine the relationship between the phase and the slow axis angle of the birefringent structure by the formula , wherein the slow axis angle takes N discrete values within the range of 0-180°, corresponding to N kinds of oriented birefringent structures, to construct a geometric phase grating; finally, calculate the total phase retardation R of the geometric phase grating element by the formula , wherein, This indicates the wavelength of the light source in the detection optical path; and the required number of processing layers is determined by dividing the total phase delay obtained from the design by the phase delay of a single-layer birefringent structure.

[0014] Step 4: Preparation of homogeneous linear structures;

[0015] The specific steps are as follows: The height of the three-dimensional displacement stage is adjusted to ensure that the femtosecond laser is focused onto the predetermined processing area inside the sample; the initial pulse energy is modulated to deposit a seed pulse inside the sample; the electrically controlled half-wave plate (HWP) is rotated to adjust the polarization direction of the light and the energy of subsequent pulses is adjusted; a second point is induced from the initial seed using the near-field normalization principle, and then the second point is used as the seed to induce a third point, and so on; the scanning speed and exposure time are controlled to move the displacement stage during pulse radiation for line scanning processing; a uniform line structure is prepared, which is composed of a birefringent structure; the birefringent structure is a randomly distributed anisotropic nanopore structure.

[0016] Step 5: Fabrication of a geometric phase grating using femtosecond laser pulses;

[0017] Based on the fabrication of a uniform line structure, the line spacing is set, and a two-dimensional planar structure is formed. Then, the geometric phase grating is fabricated layer by layer from deep to shallow.

[0018] Furthermore, in step one, the sample to be processed is Corning Gorilla Glass 7979 with a thickness of 0.1-7 mm; the Pockels cell is a Leysop-1030nm electro-optic modulator manufactured by Resop GmbH, UK, with a beam expansion factor of 1.5-3 times; the objective lens OL used in laser processing is an objective lens manufactured by New Focus GmbH, with a numerical aperture NA of 0.1-0.65, a magnification of 10-60 ×, and a working distance of 10-14.0 mm; and a white LED light source is used for illumination.

[0019] Furthermore, in step four, the center wavelength of the femtosecond laser is 343-1030 nm, the pulse width is 100 fs-10 ps, ​​the repetition rate is 1 kHz-40 MHz, the pulse energy is 0.5-0.9 μJ, and the dot pitch is... The range is 0.8-2 μm, and the scanning speed is... The speed is 6-10 mm / s, and the single-point exposure time is... μs.

[0020] Furthermore, in step four, the number of seed pulses deposited inside the sample is 1-3; the diameter of the femtosecond laser-induced point is continuously adjustable in the range of 200nm-2μm with an adjustment accuracy of 50nm; the energy of subsequent pulses from the second point onwards is determined by the seed size and is set to 75%-150% of the initial pulse energy; to enable the near-field normalization principle to take effect, the displacement stage of subsequent pulses moves within 10-100nm.

[0021] Furthermore, in step five, the processing of each layer is carried out by scanning according to the phase distribution data in the .csv file. The .csv file is a .csv file that the processing system can recognize and process by converting the designed phase distribution matrix data into a .csv file through MATLAB software. It is used to control the slow axis angle of the birefringent structure, and thus control its phase.

[0022] In a second aspect, the present invention also provides a high-transmittance, high-uniformity geometric phase grating element prepared using the near-field normalization of femtosecond pulses, which is prepared by the method described in the first aspect.

[0023] Thirdly, this invention provides the application of high-transmittance, high-uniformity geometric phase grating elements prepared using femtosecond pulse near-field normalization in edge detection efficiency.

[0024] Furthermore, the application specifically includes the following steps:

[0025] Step A: Construct the test optical path and place the prepared geometric phase grating element on the focal plane between the first convex lens L1 and the second convex lens L2 to realize the Fourier transform of the beam.

[0026] Step B: The laser beam first passes through the Glan prism P1, then sequentially through the object to be detected, a 4f optical system consisting of a first convex lens L1, a geometric phase grating element, and a second convex lens L2. The distance between the lenses is twice the focal length f, and the distance between the object and the first convex lens L1 of the 4f system is the focal length f. After passing through the 4f system, the linearly polarized light is split into left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP) with horizontal displacement, with the overlapping portion exhibiting linear polarization. The laser beam further passes through an analyzer P2, which filters the linearly polarized light in the overlapping area of ​​the image while retaining the circularly polarized light at the image edges. Finally, the edge information of the object is captured and analyzed by a CCD sensor connected to a PC. The distance between the CCD sensor and the second convex lens of the 4f system is the focal length f.

[0027] Furthermore, the lens of the 4f optical system is an MCX10610 plano-convex lens manufactured by Shenzhen Lubang Technology Co., Ltd., with a focal length of 10-50mm; the analyzer is an FLP51-VIS-M thin-film linear polarizer manufactured by Shenzhen Lubang Technology Co., Ltd.

[0028] Furthermore, by changing the period of the geometric phase grating, the angle between the emitted left-handed and right-handed circularly polarized light can be controlled, that is, the horizontal displacement of the two images can be controlled, thereby adjusting the resolution of image edge detection.

[0029] The principle of this invention is as follows:

[0030] The mechanism of near-field normalization-induced novel birefringent structures using femtosecond laser pulses: In line scanning machining using femtosecond laser pulses, the near-field enhancement effect shows that when the aperture is large, such as with a radius of 50 nm, the enhancement effect is weak. Only when very close to the nanoseed (<1 / 10 of the radius) is there a significant enhancement, and the width of the enhanced region is <1 / 2 of the radius. However, when the aperture of the seed structure is small, such as with a radius of 20 nm, the near-field enhancement region widens (>1 / 3 of the radius), and the width of the enhanced region is close to or even greater than the diameter. In this case, given the existing seed structure, by appropriately controlling the dot spacing and single-pulse energy during the scanning process, uniform machining can be achieved, ultimately inducing a birefringent structure with high uniformity and high transmittance. Specifically, because the energy is localized in the near field, the near-field propagation distance is ≤1 / 3 of the wavelength, and there is insufficient energy diffusion, avoiding the generation of positive refractive index change regions and structural scattering, thus increasing transmittance. The above mechanisms together constitute the near-field normalization principle, such as... Figure 2 As shown;

[0031] Mechanism for fabricating geometric phase gratings: Since the slow axis direction of the femtosecond excitation-induced birefringent structure is always perpendicular to the laser polarization direction, the polarization direction during the scanning process can be adjusted using an electro-optic modulator, thereby controlling the slow axis direction of the birefringent structure. This is achieved through device design. This allows us to determine the slow axis angle θ and laser polarization at each spatial location, and thus fabricate a geometric phase grating with an adjustable period by varying the slow axis direction.

[0032] The principle of edge detection using geometric phase gratings: the grating period can be determined from the grating's spectral dispersion characteristics. The beam splitting angle can be adjusted. The formula for the relationship between the two is: In the formula, The wavelength of light This is a diffraction order. Linearly polarized light illuminates the object and then, after incident on a geometric phase grating, exits as horizontally offset left-handed and right-handed circularly polarized light, overlapping in the middle and exhibiting linear polarization. An analyzer is then used to filter the linearly polarized light in the overlapping region of the image while retaining the circularly polarized light at the image edges, thus obtaining an image of the object's edge.

[0033] The principle behind improving edge detection efficiency: A novel birefringent structure fabricated using the near-field normalization of femtosecond laser pulses exhibits high uniformity and exhibits low light absorption and scattering, resulting in high transmittance and consequently high diffraction efficiency and image quality. Therefore, a geometric phase grating element constructed using this novel birefringent structure can uniformly enhance beam transmission efficiency during edge detection, thereby improving edge detection efficiency.

[0034] Compared with the prior art, the advantages of the present invention are as follows:

[0035] (1) The present invention utilizes the near-field normalization of femtosecond pulses to prepare a high-transmittance, high-uniformity birefringent structure, method and application. By utilizing the near-field normalization principle of femtosecond laser pulses, a high-transmittance birefringent structure was successfully prepared. This structure can effectively enhance the transmission efficiency of the beam, ensure that the effective information captured by the camera is not weakened, and reduce the system cost.

[0036] (2) The novel birefringent structure has excellent uniformity, which can ensure the uniformity of light intensity distribution during edge detection. This helps to avoid deviations in the detection results and improves the accuracy of edge detection.

[0037] (3) Compared with traditional bulky systems, the geometric phase grating element prepared by the present invention using a novel birefringent structure is easy to miniaturize and integrate. Attached Figure Description

[0038] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0039] Figure 1 This is a schematic diagram of the optical path of the novel geometric phase grating element fabricated in fused silica using the near-field normalization of femtosecond lasers according to the present invention.

[0040] In the diagram, HWP is an electrically controlled half-wave plate, P is a Glan prism, Pockels cell, QWP is a quarter-wave plate, L1 is a concave lens, L2 is the first convex lens, LED is an illumination lamp, M1 is the first reflector, M2 is the second reflector, a three-dimensional displacement stage (the adjustment device includes the horizontal X-axis, Y-axis and the vertical Z-axis), L3 is the second convex lens, and CCD is a camera.

[0041] Figure 2 This is a schematic diagram illustrating the principle of near-field normalization during line scanning processing in molten silica using a femtosecond laser, according to the present invention.

[0042] Figure 3 This is a schematic diagram illustrating the effect of the femtosecond laser pulse near-field normalization method on the structural morphology in this invention.

[0043] Among them, (a) is the processing result without adopting the femtosecond pulse near-field normalization principle;

[0044] (b) An electron microscope image of a line scanning process using this principle;

[0045] The results show that uniform lines can be fabricated using the near-field normalization principle of femtosecond pulses.

[0046] Figure 4 This is a schematic diagram of a novel birefringent structure fabricated in fused silica using the near-field normalization of a femtosecond laser, representing a randomly distributed anisotropic nanopore structure. The arrows indicate the direction of light polarization, and the nanopore structure is stretched along a direction perpendicular to the light polarization.

[0047] Figure 5 The line shape obtained by near-field normalization of femtosecond laser pulses according to the present invention;

[0048] Figure 6 A schematic diagram showing the phase delay R at different horizontal positions of a line processed using the near-field normalization of femtosecond laser pulses;

[0049] Figure 7 This is a birefringence microscope image showing the evolution of a femtosecond laser-induced birefringence structure with single-pulse energy; in the image, the bidirectional arrows indicate the direction of light polarization, the unidirectional arrows on the block structure indicate the slow axis direction of the birefringence structure, and the boxes indicate the processing pulse energy parameters corresponding to the selected novel birefringence structure.

[0050] Figure 8 This is a schematic diagram of a geometric phase grating;

[0051] Among them, (a) is the phase distribution diagram of a 1mm period geometric phase grating designed using MATLAB software, and the scale value represents the processing value in the .csv file that the processing system can recognize;

[0052] (b) is a birefringent microscope image of a geometric phase grating. The arrow indicates the slow axis direction of the birefringent structure, and the diameter is 2 mm.

[0053] Figure 9 This is a schematic diagram of the principle of beam splitting using a geometric phase grating.

[0054] In this system, linearly polarized light is incident on a geometric phase grating, and the outgoing light consists of left-hand circularly polarized light and right-hand circularly polarized light.

[0055] Figure 10 To test the beam splitting effect of the geometric phase grating;

[0056] The observed results show only positive and negative first-order diffraction spots, and no 0th-order or other-order diffraction spots; demonstrating the high-efficiency diffraction of the geometric phase grating, and the transmittance of the geometric phase grating element was measured to be 99%.

[0057] Figure 11 This is a schematic diagram of the test optical path for the edge detection method of a novel birefringent structure in molten quartz with a period of 1 mm geometric phase grating, which is based on the present invention.

[0058] In the diagram, the object is the object to be edge detected, P1 is the Glan prism, L1 is the first convex lens, L2 is the second convex lens (L1 and L2 form a 4f system), GPG is the geometric phase grating element, P2 is the analyzer, and CCD is the camera.

[0059] Figure 12 This is a test image of the edge detection of a periodic 1mm geometric phase grating in a fused silica body birefringent structure using near-field normalization induced by a femtosecond laser, according to the present invention.

[0060] (a) is the original image of the object to be detected captured without the addition of an analyzer; (b) is the image of the edge portion of the object. Detailed Implementation

[0061] To clearly and completely describe the technical solution and its specific working process of the present invention, the specific embodiments of the present invention are as follows, in conjunction with the accompanying drawings:

[0062] Example 1

[0063] This embodiment provides a method for preparing a high-transmittance, high-uniformity birefringent structure using the near-field normalization of femtosecond pulses, specifically including the following steps:

[0064] Step 1: Setting up the laser processing optical path, such as... Figure 1 As shown;

[0065] The specific steps are as follows: First, the femtosecond laser emitted from the laser is passed through an energy control system consisting of an electrically controlled half-wave plate (HWP) and a Glan prism (P), and then through a polarization control system consisting of a Pockels cell and a quarter-wave plate (QWP). The beam then passes through a beam expander system consisting of a concave lens (L1) and a convex lens (L2), and is projected onto the processing objective lens via a reflector (M1), ultimately focusing onto the interior of the sample to be processed. An LED illumination device is placed under the sample stage to allow the white light emitted by the LED to penetrate the sample and illuminate the objective lens (OL). After being transmitted through reflector (M1), the white light is reflected again by reflector (M2) and finally focused onto the second convex lens (L3), forming a clear image on the CCD sensor. The CCD sensor is connected to an industrial computer via a data cable to monitor the sample processing in real time.

[0066] Step 2: Leveling the sample stage;

[0067] The specific steps are as follows: First, fix the 2mm thick fused silica sample to be processed onto a three-dimensional displacement stage equipped with an adjustment device. The adjustment device of the three-dimensional displacement stage includes the horizontal X-axis, Y-axis, and vertical Z-axis. Then, open the shutter in the processing optical path, and the laser is focused by the high-power objective lens. Control the three-dimensional displacement stage to find the upper left corner of the sample to be processed. By adjusting the height of the moving stage, the laser focus is focused on the upper surface of the sample, and the Z-axis height of the surface at the upper left corner of the sample is recorded. Similarly, find the upper right, lower left, and lower right surfaces of the sample and record their Z-axis heights. Adjust the adjustment device of the three-dimensional displacement stage according to the recorded surface Z-axis height data so that the surfaces at the four corners of the sample are at the same Z-axis height. At this point, the sample stage is leveled.

[0068] Step 3: Design and parameter calculation of geometric phase grating elements;

[0069] The specific steps are as follows: First, use MATLAB software to design a geometric phase grating with a period of 1mm and a circular grating with a diameter of 2mm, such as... Figure 8 As shown in (a). The phase distribution matrix data designed in MATLAB software is converted into a .csv file that the machining system can recognize and process. The slow axis angle of the birefringent structure takes 180 discrete values ​​within the range of 0-180°, corresponding to 180 orientations of the birefringent structure. The machining file with the .csv extension is then imported into the machining control program. The required phase delay is calculated as follows: The number of processing layers is determined by dividing the total phase delay of the design by the phase delay of the single-layer birefringent structure.

[0070] The .csv file is generated by converting the designed phase distribution matrix data into a .csv file that the processing system can recognize and process using MATLAB software. It is used to control the slow axis angle of the birefringent structure, thereby controlling its phase.

[0071] Step 4: Preparation of homogeneous linear structures;

[0072] The specific steps are as follows: First, by adjusting the height of the moving stage, the femtosecond laser is precisely focused onto the predetermined processing area inside the sample. The femtosecond laser parameters are: pulse width 300 fs, repetition rate 200 kHz, scanning speed 6 mm / s, spot spacing 1 μm, and single-point exposure time 266 μs. Calculations show that the stage moves 30 nm for each laser pulse, meeting the 10-100 nm requirement for near-field modulation. Points are induced by the femtosecond laser, and these points are connected to form a line for line scanning. The parameter selection is based on the near-field normalization principle of femtosecond laser pulses and the interaction mechanism with fused silica to ensure the effective induction of novel birefringent structures. The processed line structure is characterized using a birefringent microscope, revealing significant birefringence characteristics, such as... Figure 5 As shown, this image was acquired using a birefringent microscope, and the arrow indicates the slow axis direction of the novel birefringent structure. Further data analysis was performed on the phase retardation R at different horizontal positions, such as... Figure 6 As shown, the results indicate that the phase delay of the novel birefringent structure fabricated using the near-field normalization of femtosecond laser pulses has almost no fluctuation, i.e., it has high uniformity; through the above steps, a uniform line structure was successfully fabricated.

[0073] Step 5: Determining the parameters for preparing the geometric phase grating using femtosecond laser pulses;

[0074] Based on the fabrication of a uniform line structure, with a line spacing of 1 μm, a sweeping process was performed to form a block structure. The program controlled a Pockels cell to select four polarizations as a group, fabricating five groups of block structures with pulse energies of 0.9 μJ, 0.8 μJ, 0.7 μJ, 0.6 μJ, and 0.5 μJ respectively. The fabricated block structures were characterized using a birefringence microscope, revealing birefringence structures, such as... Figure 7 As shown. A parameter window for a high-transmittance birefringent structure was found, and the novel birefringent parameter with a suitable phase retardation was determined to be a pulse energy of 0.6 μJ.

[0075] Step 6: Fabrication of a geometric phase grating using femtosecond laser pulses;

[0076] Based on the fabrication of a uniform line structure, the line spacing is set, and a two-dimensional planar structure is formed. Then, the geometric phase grating is fabricated layer by layer from deep to shallow.

[0077] After processing, the processing quality was tested using a birefringence microscope to ensure that the phase distribution and phase retardation met the design requirements. The birefringence microscope image is shown below. Figure 8 As shown in (b).

[0078] In this embodiment, the sample to be processed is Corning Gorilla Glass 7979 with a thickness of 0.1-7 mm; the Pockels cell is a Leysop-1030nm electro-optic modulator manufactured by Resop GmbH, UK, and the beam expander has a magnification of 1.5-3 times; the objective lens OL used for laser processing is a New Focus objective lens with a numerical aperture NA=0.16, magnification of 10×, and working distance of 14.0 mm; the illumination source is a white LED light source.

[0079] Example 2

[0080] This embodiment provides an application of high-transmittance, high-uniformity birefringent structures prepared using femtosecond pulse near-field normalization in edge detection efficiency, specifically including the following steps:

[0081] Step A: Test the efficiency of the geometric phase grating;

[0082] The test optical path uses a 532 nm wavelength laser. The test process first involves passing the laser through a Glan prism, then incident on a geometric phase grating. The beam splitting principle of this grating is as follows: Figure 9 As shown, the emitted beam is split into left-handed and right-handed circularly polarized light with horizontal displacement. The test results are as follows: Figure 10 As shown, the observed result is that only positive and negative first-order diffraction spots are present, while no 0th-order or other-order diffraction spots are present. This phenomenon proves that the geometric phase grating has a high-efficiency beam splitting capability, which can effectively decompose the incident beam into the desired polarization state while suppressing unwanted diffraction orders.

[0083] Step B: Edge detection;

[0084] The specific steps are as follows: Figure 11As shown, the laser beam first passes through a Glan prism P1, then sequentially through the object to be detected, a 4f optical system consisting of a first convex lens L1, a geometric phase grating element, and a second convex lens L2. The distance between the lenses is twice the focal length f, and the distance between the object and the first convex lens L1 of the 4f system is the focal length f. The geometric phase grating element prepared in step A is placed on the focal plane between the first and second lenses to achieve a Fourier transform of the beam. After passing through the 4f system, the linearly polarized light is split into left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP) with horizontal displacement, with the overlapping portion exhibiting linear polarization. The laser beam further passes through an analyzer P2, which filters the linearly polarized light in the overlapping area of ​​the image while retaining the circularly polarized light at the image edges. Finally, the edge information of the object is captured and analyzed by a CCD sensor connected to a PC. The distance between the CCD sensor and the second convex lens of the 4f system is the focal length f.

[0085] In this embodiment, the lens of the 4f optical system is an MCX10610 plano-convex lens manufactured by Shenzhen Lubang Technology Co., Ltd., with a focal length of 10-50mm; the analyzer is an FLP51-VIS-M thin-film linear polarizer manufactured by Shenzhen Lubang Technology Co., Ltd.

[0086] By changing the period of the geometric phase grating, the angle between the emitted left-handed and right-handed circularly polarized light can be controlled, thus controlling the horizontal displacement of the two images and adjusting the resolution of image edge detection.

[0087] The birefringent microscope is an Olympus BX53 optical microscope equipped with the Oosight imaging system. The specific method for determining the novel birefringent structure is to utilize the characteristic that the structure has a transmittance of up to 99% in the visible light range. Specifically, the structure cannot be seen under an optical microscope, but it can be seen under a birefringent microscope.

[0088] Without an analyzer, the original image of the object to be detected was first acquired, such as... Figure 12 As shown in (a); an analyzer is inserted into the optical path to specifically filter the linearly polarized light in the overlapping portion of the left-hand circularly polarized (LCP) and right-hand circularly polarized (RCP) images, leaving the circularly polarized light component at the edge, thereby obtaining an image of the object's edge, as shown in (a). Figure 12 As shown in (b).

[0089] The results show that this implementation utilizes the femtosecond pulse near-field enhancement and normalization effect in the seed-modified region. By rationally adjusting the scanning speed and power, the continuous modification caused by near-field enhancement localizes energy within the newly formed nanostructure. This results in anisotropic nanostructures, and because the near-field modulation effect keeps the size on the nanometer scale, it does not introduce scattering effects. Consequently, the prepared high-transmittance, high-uniformity birefringent structure exhibits excellent accuracy in edge detection. In contrast, under non-near-field normalization conditions, the induced non-novel birefringent structures, due to the lack of energy control and the rarity of keeping the spacing within the near-field enhancement range, result in structures that grow drastically to the micrometer scale. Scattering directly changes from Rayleigh scattering to Mie scattering, leading to low transmittance and poor uniformity. When used as a device, the strong scattered light causes uneven light intensity distribution during edge detection, resulting in strong speckle patterns. Especially when detecting complex-shaped objects, this makes it impossible to accurately capture and reconstruct edge information or generates false information, reducing the accuracy of edge detection.

[0090] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0091] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0092] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for fabricating high-transmittance, high-uniformity geometrical phase grating elements using femtosecond pulse near-field normalization, characterized in that, Specifically, the steps include the following: Step 1: Setting up the laser processing optical path; The specific steps are as follows: First, the femtosecond laser emitted from the laser passes through the energy control system consisting of an electrically controlled half-wave plate (HWP) and a Glan prism (P), and then passes through the polarization control system consisting of a Pockels cell and a quarter-wave plate (QWP). After that, the beam passes through the beam expansion system consisting of a concave lens (L1) and a convex lens (L2), and then is projected onto the processing objective lens through a reflecting mirror (M1), and finally focused into the interior of the sample to be processed. The LED lighting device is placed on the lower side of the sample stage so that the white light emitted by the LED lighting device can penetrate the sample to be processed and illuminate the objective lens OL. After being transmitted through the reflector M1, the white light is reflected again by the reflector M2 and finally focused on the second convex lens L3, forming a clear image on the CCD sensor. The CCD sensor is connected to the industrial control computer through a data cable to observe the sample processing in real time. Step 2: Leveling the sample stage; The specific steps are as follows: First, fix the sample to be processed onto a three-dimensional displacement stage equipped with an adjustment device; the adjustment device of the three-dimensional displacement stage includes the horizontal X-axis, Y-axis, and vertical Z-axis; then, open the shutter in the processing optical path, the laser is focused by the high-power objective lens, and the three-dimensional displacement stage is controlled to find the upper left corner of the sample to be processed. By adjusting the height of the moving stage, the laser focus is made to focus on the upper surface of the sample, and the Z-axis height of the surface at the upper left corner of the sample is recorded at this time; similarly, find the upper right, lower left, and lower right surfaces of the sample, and record the Z-axis height; adjust the adjustment device of the three-dimensional displacement stage according to the recorded surface Z-axis height data so that the surfaces at the four corners of the sample are at the same Z-axis height; at this time, the sample stage is leveled. Step 3: Design and parameter calculation of the geometric phase grating element; The specific steps are as follows: First, select a geometric phase grating period that matches the actual requirements. Component size and shape; Subsequently, based on the phase gradient formula of a one-dimensional grating In the formula, x and y represent the position coordinates in a Cartesian coordinate system on a two-dimensional plane, generating data to describe the phase distribution of the grating, presented in the form of a two-dimensional array or matrix; then, through the formula... Determine the phase angle with the slow axis of the birefringent structure The relationship is as follows: the slow axis angle takes N discrete values ​​within the range of 0-180°, corresponding to N birefringent structures with different orientations, to construct a geometric phase grating; finally, the geometric phase grating is constructed using the formula... The total phase delay R of the geometric phase grating element is calculated, where, This indicates the wavelength of the light source in the detection optical path; and the required number of processing layers is determined by dividing the total phase delay obtained from the design by the phase delay of a single-layer birefringent structure. Step 4: Preparation of homogeneous linear structures; The specific steps are as follows: The height of the three-dimensional displacement stage is adjusted to ensure that the femtosecond laser is focused onto the predetermined processing area inside the sample; the initial pulse energy is modulated to deposit a seed pulse inside the sample; the electrically controlled half-wave plate (HWP) is rotated to adjust the polarization direction of the light and the energy of subsequent pulses is adjusted; a second point is induced from the initial seed using the near-field normalization principle, and then the second point is used as the seed to induce a third point, and so on; the scanning speed and exposure time are controlled to move the displacement stage during pulse radiation for line scanning processing; a uniform line structure is prepared, which is composed of a birefringent structure; the birefringent structure is a randomly distributed anisotropic nanopore structure. Step 5: Fabrication of a geometric phase grating using femtosecond laser pulses; Based on the fabrication of a uniform line structure, the line spacing is set, and a two-dimensional planar structure is formed. Then, the geometric phase grating is fabricated layer by layer from deep to shallow.

2. The method for fabricating high-transmittance, high-uniformity geometrical phase grating elements using femtosecond pulse near-field normalization as described in claim 1, characterized in that, In step one, the sample to be processed is Corning Gorilla Glass 7979 with a thickness of 0.1-7 mm; the Pockels cell is a Leysop-1030nm electro-optic modulator manufactured by Resop GmbH, UK, and the beam expansion system has a beam expansion factor of 1.5-3 times; the objective lens OL used for laser processing is an objective lens manufactured by New Focus, with a numerical aperture NA of 0.1-0.65, a magnification of 10-60 ×, and a working distance of 10-14.0 mm; the illumination source is a white LED light source.

3. The method for fabricating high-transmittance, high-uniformity geometrical phase grating elements using femtosecond pulse near-field normalization as described in claim 1, characterized in that... In step four, the center wavelength of the femtosecond laser is 343-1030 nm, the pulse width is 100 fs-10 ps, ​​the repetition rate is 1 kHz-40 MHz, the pulse energy is 0.5-0.9 μJ, and the spot spacing is... The range is 0.8-2 μm, and the scanning speed is... The speed is 6-10 mm / s, and the single-point exposure time is... μs.

4. The method for fabricating high-transmittance, high-uniformity geometrical phase grating elements using femtosecond pulse near-field normalization as described in claim 1, characterized in that, In step four, the number of seed pulses deposited inside the sample is 1-3; the diameter of the femtosecond laser-induced point is continuously adjustable in the range of 200nm-2μm with an adjustment accuracy of 50nm; the energy of subsequent pulses from the second point onwards is determined by the seed size and is set to 75%-150% of the initial pulse energy; to make the near-field normalization principle work, the displacement stage of subsequent pulses moves within 10-100nm.

5. The method for fabricating a high-transmittance, high-uniformity geometrical phase grating element using femtosecond pulse near-field normalization as described in claim 1, characterized in that... In step five, the processing of each layer is carried out by scanning the lines according to the phase distribution data in the .csv file. The .csv file is a .csv file that the processing system can recognize and process by converting the designed phase distribution matrix data into a .csv file through MATLAB software. It is used to control the slow axis angle of the birefringent structure, and thus control its phase.

6. A high-transmittance, high-uniformity geometrical phase grating element fabricated using the near-field normalization of femtosecond pulses, characterized in that... It is prepared by the method according to any one of claims 1-5.

7. The application of the high transmittance and high uniformity geometric phase grating element fabricated using femtosecond pulse near-field normalization as described in claim 6 in edge detection efficiency.

8. The application of the high-transmittance, high-uniformity geometrical phase grating element fabricated using femtosecond pulse near-field normalization as described in claim 7 in edge detection efficiency, characterized in that... The application specifically includes the following steps: Step A: Construct the test optical path and place the prepared geometric phase grating element on the focal plane between the first convex lens L1 and the second convex lens L2 to realize the Fourier transform of the beam. Step B: The laser beam first passes through the Glan prism P1, then sequentially through the object to be detected, a 4f optical system consisting of a first convex lens L1, a geometric phase grating element, and a second convex lens L2. The distance between the lenses is twice the focal length f, and the distance between the object and the first convex lens L1 of the 4f system is the focal length f. After passing through the 4f system, the linearly polarized light is split into left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP) with horizontal displacement, with the overlapping portion exhibiting linear polarization. The laser beam further passes through an analyzer P2, which filters the linearly polarized light in the overlapping area of ​​the image while retaining the circularly polarized light at the image edges. Finally, the edge information of the object is captured and analyzed by a CCD sensor connected to a PC. The distance between the CCD sensor and the second convex lens of the 4f system is the focal length f.

9. The application of the high-transmittance, high-uniformity geometrical phase grating element fabricated using femtosecond pulse near-field normalization as described in claim 8 in edge detection efficiency, characterized in that... The lens of the 4f optical system is an MCX10610 plano-convex lens manufactured by Shenzhen Lubang Technology Co., Ltd., with a focal length of 10-50mm; the analyzer is an FLP51-VIS-M thin-film linear polarizer manufactured by Shenzhen Lubang Technology Co., Ltd.

10. The application of the high-transmittance, high-uniformity geometrical phase grating element fabricated using femtosecond pulse near-field normalization as described in claim 8 in edge detection efficiency, characterized in that... By changing the period of the geometric phase grating, the angle between the emitted left-handed and right-handed circularly polarized light can be controlled, thus controlling the horizontal displacement of the two images and adjusting the resolution of image edge detection.

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