CN-119291825-B - High-transmittance high-uniformity geometric phase grating element prepared by utilizing femtosecond pulse near-field normalization, method and application thereof

CN119291825BCN 119291825 BCN119291825 BCN 119291825BCN-119291825-B

Abstract

The invention discloses a high-transmittance and high-uniformity geometric phase grating element prepared by utilizing femtosecond pulse near-field normalization, a method and application thereof, belonging to the technical field of laser processing, wherein the invention utilizes the principle of femtosecond laser pulse near-field normalization to uniformly process inside fused quartz, the novel high-transmittance and high-uniformity double-refraction structure is induced, the slow axis direction change is controlled, so that the high-efficiency geometric phase grating with adjustable period is prepared, and the edge detection is realized by utilizing the spectroscopic characteristic of the geometric phase grating. The invention is applied to optical image edge detection through an innovative processing technology, solves the limitation of the traditional double refraction structure on transmittance and uniformity, and provides a solution with better performance and lower cost for the field of optical image edge detection.

Inventors

WANG LEI
ZHANG XIN
CHEN QIDAI
SUN HONGBO

Assignees

吉林大学

Dates

Publication Date: 20260512
Application Date: 20241025

Claims (10)

1. The method for preparing the geometric phase grating element with high transmittance and high uniformity by utilizing the near field normalization of the femtosecond pulse is characterized by comprising the following steps: step one, constructing a laser processing light path; The method comprises the steps of enabling femtosecond laser emitted by a laser to sequentially pass through an energy regulation and control system composed of an electric control half-wave plate HWP and a gram prism P, sequentially pass through a polarization regulation and control system composed of a Prke box and a quarter-wave plate QWP, enabling light beams to pass through a beam expanding system composed of a concave lens L 1 and a convex lens L 2 , then projecting the light beams to the front of a processing objective lens through a reflecting mirror M 1 , finally focusing the light beams to the inside of a sample to be processed, arranging an LED lighting device at the lower side of a sample table, facilitating white light emitted by the LED lighting device to penetrate through the sample to be processed and then irradiate the sample OL, enabling the white light beams to be reflected again through a reflecting mirror M 2 after being transmitted through a reflecting mirror M 1 , finally focusing the light beams to a second convex lens L 3 , and forming a clear image on a CCD sensor, connecting the CCD sensor with an industrial personal computer through a data line, and observing the processing condition of the sample in real time; step two, leveling a sample table; firstly, fixing a sample to be processed on a three-dimensional displacement table with an adjusting device, wherein the adjusting device of the three-dimensional displacement table comprises an X axis, a Y axis and a Z axis in the vertical direction in the horizontal direction, then opening a light gate in a processing light path, focusing laser by a high-power objective lens, controlling the three-dimensional displacement table to find the upper left corner of the sample to be processed, focusing a laser focus on the upper surface of the sample by adjusting the height of the moving table, and recording the Z axis heights of the surface at the upper left corner of the sample at the moment; step three, designing a geometric phase grating element and calculating parameters; firstly, selecting geometric phase grating period matched with actual requirement Element size and shape, then, according to the phase gradient formula of the one-dimensional grating Wherein x, y represent the position coordinates of rectangular coordinate system on two-dimensional plane, generating data for describing grating phase distribution, and presenting in two-dimensional array or matrix form, then passing through formula To determine the phase Slow axis angle with birefringent structure Wherein the angle of the slow axis takes N discrete values within the range of 0-180 DEG, and the geometrical phase grating is constructed corresponding to N oriented birefringent structures, finally, the geometrical phase grating is obtained by the formula The total phase retardation R of the geometric phase grating element is calculated, wherein, The total phase delay amount obtained by design is divided by the phase delay amount of the single-layer double-refraction structure to determine the required processing layer number; step four, preparing a uniform line structure; The method comprises the specific steps of ensuring that femtosecond laser focuses on a preset processing area inside a sample by adjusting the height of a three-dimensional displacement table, modulating initial pulse energy, depositing seed pulses inside the sample, rotating an electric control half wave plate HWP to adjust the polarized light direction, adjusting the energy of subsequent pulses, inducing a second point by the initial seed according to a near-field normalization principle, inducing a third point by taking the second point as a seed, and the like, controlling the scanning speed and the exposure time to enable the displacement table to move in pulse irradiation to perform line scanning processing, and preparing a uniform line structure, wherein the line structure consists of a birefringent structure, and the birefringent structure is an anisotropic nano hole structure which is randomly distributed; preparing a geometric phase grating by femtosecond laser pulse; on the basis of processing uniform line structures, the line spacing is set, a two-dimensional plane structure is formed by processing, and then the geometric phase grating is prepared by processing layer by layer from deep to shallow.
2. The method for preparing the high-transmittance and high-uniformity geometric phase grating element by utilizing the near-field normalization of femtosecond pulses according to claim 1, wherein in the first step, a sample to be processed is 7979 glass manufactured by Corning company, the thickness is 0.1-7mm, a Prinsepia box is a Leysop-1030nm electro-optical modulator manufactured by Leippu company, the beam expansion multiple of a beam expansion system is 1.5-3 times, an objective lens OL adopted by laser processing is an objective lens manufactured by New Focus company, the numerical aperture NA=0.1-0.65, the amplification multiple is 10-60×, the working distance is 10-14.0 mm, and an illumination light source is a white LED light source.
3. The method for fabricating a high transmittance, high uniformity geometric phase grating device according to claim 1, wherein in step four, the femtosecond laser has a center wavelength of 343-1030nm, a pulse width of 100fs-10ps, a repetition frequency of 1kHz-40MHz, a pulse energy of 0.5-0.9 μJ, and a dot spacing 0.8-2 Μm, scanning speed 6-10Mm/s, single-point exposure time of μs。
4. The method for preparing the high-transmittance high-uniformity geometric phase grating element by utilizing the near-field normalization of femtosecond pulses according to claim 1, wherein in the fourth step, the number of seed pulses deposited in a sample is 1-3, the diameter of a femtosecond laser-induced spot is continuously adjustable within the range of 200nm-2 mu m, the adjustment precision is 50nm, the energy of a subsequent pulse from a second spot is determined by the size of the seed and is set to 75-150% of the energy of an initial pulse, the principle of near-field normalization is enabled, and the moving distance of a displacement table of the subsequent pulse is within 10-100 nm.
5. The method for fabricating a high transmittance, high uniformity geometric phase grating element using femtosecond pulsed near field normalization of claim 1, wherein in step five, processing of each layer is performed by sweeping according to phase distribution data in a csv file, which is a csv file that is recognized and processed by a processing system by converting designed phase distribution matrix data into a MATLAB software, for controlling a slow axis angle of a birefringent structure, thereby controlling a phase thereof.
6. High transmittance, high uniformity geometric phase grating element prepared using femtosecond pulsed near field normalization, characterized by being prepared by the method of any one of claims 1-5.
7. The use of a high transmittance, high uniformity geometric phase grating element fabricated using femtosecond pulsed near-field normalization as recited in claim 6 for edge detection efficiency.
8. The use of a high transmittance, high uniformity geometric phase grating element fabricated using femtosecond pulsed near field normalization as defined in claim 7 for edge detection efficiency, said use comprising the steps of: Step A, a test light path is built, and a prepared geometric phase grating element is placed on a focal plane between a first convex lens L 1 and a second convex lens L 2 so as to realize Fourier transform of light beams; Step B, the laser beam firstly passes through a gram prism P 1 , then sequentially passes through a 4f optical system formed by a first convex lens L 1 , a geometric phase grating element and a second convex lens L 2 , wherein the distance between the lenses is twice as long as the lens focal length f, the distance between the object and the first convex lens L 1 of the 4f system is the lens focal length f, after passing through the 4f system, the linearly polarized light is divided into left circularly polarized light LCP and right circularly polarized light RCP with horizontal displacement offset, the overlapping part of the linearly polarized light is represented as linear polarization, the laser further passes through an analyzer P 2 , the linearly polarized light in the overlapping area in the middle of the image can be filtered, meanwhile, the circularly polarized light at the edge of the image is reserved, and finally, the edge information of the object is captured and analyzed through a CCD sensor connected with a computer PC, wherein the distance between the CCD sensor and the second convex lens of the 4f system is the lens focal length f.
9. The application of the geometric phase grating element with high transmittance and high uniformity prepared by utilizing the near field normalization of femtosecond pulses in the aspect of edge detection efficiency, according to claim 8, wherein the lens of the 4f optical system is an MCX10610 type plano-convex lens manufactured by Shenzhen Feng technology Co., ltd, the focal length is 10-50mm, and the analyzer is an FLP51-VIS-M type thin film linear polarizer manufactured by Shenzhen Feng technology Co., ltd.
10. The application of the geometric phase grating element with high transmittance and high uniformity prepared by utilizing the near field normalization of femtosecond pulses in the aspect of edge detection efficiency, as claimed in claim 8, is characterized in that the included angle between outgoing left-handed circularly polarized light and right-handed circularly polarized light can be regulated and controlled by changing the period of the geometric phase grating, namely, the horizontal displacement of two images is controlled, and further, the resolution of image edge detection can be adjusted.

Description

High-transmittance high-uniformity geometric phase grating element prepared by utilizing femtosecond pulse near-field normalization, method and application thereof Technical Field The invention belongs to the technical field of laser processing, and particularly relates to a high-transmittance and high-uniformity geometric phase grating element prepared by utilizing femtosecond pulse near-field normalization, a method and application thereof. Background Birefringent structures are widely used in the field of optical element fabrication. Edge detection is a fundamental problem in image processing and computer vision, and the image edge detection eliminates weak related information while retaining important structural attributes, so that the calculated amount can be greatly reduced. Compared with the traditional edge detection system consisting of a lens and a spatial filter, the geometric phase element manufactured by utilizing the birefringent structure has the advantage of easy miniaturization and integration, and is used for optical image edge detection as an emerging technical means. In 2019, researchers construct a method based on geometric phase super surface by using a traditional double refraction structure based on femto-second laser-induced in-vivo nanometer grating, and the method can perform optical differential calculation on a light beam carrying image information and split the light beam to realize edge detection. However, in the conventional nano grating double-refraction structure, due to the coexistence of the positive refractive index change region and the negative refractive index change region, the whole body of the structural voxels is scattered greatly, and the problems of low transmittance and poor whole body uniformity of voxels scanned for a long distance exist. In this case, the ability of the camera to capture valid information is greatly reduced, as is the accuracy of the measurement. Therefore, there is a need to solve the problems of low transmittance and poor uniformity of the conventional birefringent structure, so as to further improve the imaging effect of edge detection. Disclosure of Invention Aiming at the defects in the prior art, the invention provides a high-transmittance and high-uniformity geometric phase grating element prepared by utilizing the near-field normalization of femtosecond pulses, a method and application thereof, the invention utilizes the near-field normalization principle of femtosecond laser pulses to uniformly process the inside of fused quartz, the novel high-transmittance and high-uniformity double-refraction structure is induced, the slow axis direction change is controlled, so that the high-efficiency geometric phase grating with adjustable period is prepared, and the edge detection is realized by utilizing the spectroscopic characteristic of the geometric phase grating. The invention is applied to optical image edge detection through an innovative processing technology, solves the limitation of the traditional double refraction structure on transmittance and uniformity, and provides a solution with better performance and lower cost for the field of optical image edge detection. The invention is realized by the following technical scheme: In a first aspect, the present invention provides a method for preparing a geometric phase grating element with high transmittance and high uniformity by using femtosecond pulse near field normalization, which specifically comprises the following steps: step one, constructing a laser processing light path; The method comprises the steps of enabling femtosecond laser emitted by a laser to sequentially pass through an energy regulation and control system composed of an electric control half-wave plate HWP and a gram prism P, sequentially pass through a polarization regulation and control system composed of a Prke box and a quarter-wave plate QWP, enabling light beams to pass through a beam expanding system composed of a concave lens L 1 and a convex lens L 2, then projecting the light beams to the front of a processing objective lens through a reflecting mirror M 1, finally focusing the light beams to the inside of a sample to be processed, arranging an LED lighting device at the lower side of a sample table, facilitating white light emitted by the LED lighting device to penetrate through the sample to be processed and then irradiate the sample OL, enabling the white light beams to be reflected again through a reflecting mirror M 2 after being transmitted through a reflecting mirror M 1, finally focusing the light beams to a second convex lens L 3, and forming a clear image on a CCD sensor, connecting the CCD sensor with an industrial personal computer through a data line, and observing the processing condition of the sample in real time; step two, leveling a sample table; firstly, fixing a sample to be processed on a three-dimensional displacement table with an adjusting device, wherein the adjusting device of