CN-122018171-A - Method and device for axially shaping high aspect ratio microstructure by laser processing

CN122018171ACN 122018171 ACN122018171 ACN 122018171ACN-122018171-A

Abstract

The invention relates to the technical field of laser processing, in particular to a method and a device for axially shaping a microstructure with high aspect ratio by laser processing; the invention can accurately regulate and control the axial intensity distribution of the Bessel light beam by loading the complex coded hologram on the spatial light modulator, thereby realizing the preparation of the columnar voxel with adjustable height by single exposure. The voxel height can be continuously graded by only switching holograms which generate Bessel beams with different focal lengths, and the maximum transverse dimension is kept unchanged. The method does not need frequent axial mechanical scanning or power adjustment in processing, is beneficial to improving the processing efficiency and the operation stability, and is suitable for rapid processing of high aspect ratio microstructures such as microcolumns, microtubules, cell supports, binary diffraction devices and the like.

Inventors

XIE CHEN
LIU TONGYAN

Assignees

天津大学

Dates

Publication Date: 20260512
Application Date: 20260225

Claims (10)

1. The method for axially shaping the microstructure with the high aspect ratio by laser processing is characterized by comprising the following steps of: s1, generating initial laser by a femtosecond laser, and measuring the intensity distribution of an initial laser light field; s2, defining voxel parameters according to an aspect ratio microstructure based on the intensity distribution of the initial laser light field; step S3, calculating and generating a group of holograms of Bessel beams according to the voxel parameters, wherein the holograms are used for being loaded on a spatial light modulator, and the spatial light modulator modulates the emergent beam of the initial laser into the Bessel beam with controllable axial intensity distribution; S4, adjusting the processing energy of the Bessel beam through a light intensity attenuation device, and simultaneously adjusting an objective lens corresponding to the spatial light modulator to enable the objective lens to be aligned to a sample of a translation stage; step S5, controlling the translation stage to move, and simultaneously gradually replacing the holograms loaded in the spatial light modulator, projecting Bessel beams with different lengths at different processing points of the sample, wherein the Bessel beams are exposed at the processing points to generate voxels with corresponding heights; and step S6, performing post-processing on the voxels to obtain the Gao Zong wide-ratio microstructure with preset height distribution.
2. The method of axially shaping a laser machined high aspect ratio microstructure of claim 1 wherein the voxel parameters include: voxel diameter, which is the width of the voxel; voxel spacing, which is the distance between adjacent voxels; voxel height, which is the height distribution of the voxels.
3. The method of axially shaping a laser machined high aspect ratio microstructure according to claim 2, wherein the step of computationally obtaining the hologram of step S3 comprises: step S31, calculating initial surface phase distribution of the Bessel light beam, wherein the main lobe width of the Bessel light beam in the initial surface phase distribution is matched with the voxel diameter; Step S32, calculating and generating an axial intensity distribution curve of the Bezier beam, wherein the axial intensity distribution curve is matched with the voxel height; step S33, calculating and obtaining an initial complex amplitude distribution curve for realizing the axial intensity distribution curve in the Bessel light beam according to the axial intensity distribution curve; step S34, generating a plurality of holograms corresponding to the initial plane complex amplitude distribution curve by complex amplitude encoding.
4. The method for axially shaping a microstructure according to claim 3, wherein in said step S33, said method for calculating an initial complex amplitude distribution curve comprises the steps of setting said axial intensity distribution curve of said Bessel beam to be that of step S331 And the optical field of the Bessel beam is centered on the central axis of the beam The complex amplitude at this point is expressed as: ; Wherein z is the Bessel beam propagation distance, For the longitudinal component of the wave vector of the Bessel beam, r represents a radial coordinate and represents the distance from a certain point of the optical field to the central axis of the beam center; Step S332, according to the axial intensity distribution curve Solving the spatial spectrum of the initial plane by the following functional relation : ; Wherein k 0 is the wave number, Is the longitudinal spatial frequency; Step S333, obtaining the spatial frequency spectrum Substituting an angular spectrum propagation formula, calculating the light field complex amplitude distribution curve of an input plane ; The expression of the angular spectrum propagation formula is as follows: ; Where r is the radial coordinate of the device, In order to be a radial space frequency, A zero-order first class Bessel function; step S334, obtaining the initial surface complex amplitude distribution curve according to the light field complex amplitude distribution curve The method meets the following conditions: ; The initial complex amplitude distribution curve contains amplitude information And phase information X represents the abscissa on the initial surface and y represents the ordinate of the initial surface.
5. The method of axially shaping a laser machined high aspect ratio microstructure of claim 4 wherein the method of generating the hologram to achieve the initial face complex amplitude profile by complex amplitude encoding is: The amplitude information is encoded by a complex encoding method And the phase information Encoded as pure phase distribution The pure phase distribution The method meets the following conditions: ; where (m, n) is the pixel index of the spatial light modulator, To separate the blazed grating phases of the diffraction orders, Parameters for modulo operators Sum parameters The following respectively satisfy: ; ; By the pure phase distribution Acquiring the corresponding hologram; the said The method meets the following conditions: ; Wherein, the To measure the resulting amplitude of the incident light on the spatial light modulator, In order for the angle of the blaze to be such, Is the center wavelength of the incident light on the spatial light modulator.
6. A method of axially shaping a laser machined high aspect ratio microstructure according to claim 3, wherein in said step S32, said axial intensity profile is such that said Bessel beams having different axial intensities have the same maximum on-axis intensity above the threshold of aggregation of said sample in said step S4.
7. The method of claim 1, wherein the initial laser beam is collimated and expanded and polarization state modulated onto a spatial light modulator.
8. The method for processing the high aspect ratio microstructure by the axially shaped laser according to claim 1, wherein in the step S1, the measuring method for measuring the intensity distribution of the initial laser light field is that an image sensor is used for replacing and aligning the same spatial position where the spatial light modulator is located, the power of the initial laser is adjusted, the maximum light intensity of the initial laser is not saturated to the image sensor, and the intensity distribution of the actual light field of the initial laser is obtained according to the corresponding pixel of the image sensor.
9. The device for axially shaping the laser processing the high aspect ratio microstructure is characterized by comprising a femtosecond laser, a laser beam source and a laser beam source, wherein the femtosecond laser is used for emitting initial laser beam; the polarization state adjusting component is used for adjusting the polarization state of the initial laser; the collimating and beam expanding assembly is used for collimating and expanding the initial laser; A spatial light modulator for receiving the collimated and expanded beam and the polarization state adjusted initial laser light, the spatial light modulator being electrically connected to a computer, the computer loading a hologram obtained by performing a method of axially shaping the microstructure of the laser beam processing with high aspect ratio according to any one of claims 1 to 8 into the spatial light modulator, the spatial light modulator outputting a bessel beam with controllable axial intensity distribution; The asymmetric 4-F system is used for spatially filtering the Bessel light beam and focusing the filtered Bessel light beam through an objective lens; And the translation stage is used for receiving a sample, voxels with corresponding heights are generated by exposing the sample to the Bessel light beam focused by the objective lens, the translation stage is electrically connected with the computer, and the computer controls the movement of the translation stage.
10. The apparatus for axially shaping a laser processed high aspect ratio microstructure of claim 9, wherein the polarization state adjustment assembly comprises a polarization state adjustment element and a polarization beam splitter, the polarization state adjustment element and the polarization beam splitter modulating the initial laser light to a polarization state that matches the polarization sensitivity of the spatial light modulator; The collimation beam expansion assembly comprises a plano-convex lens and a plano-concave lens which are sequentially arranged; The initial laser after being regulated by the polarization state regulating component and the collimation and beam expansion component is turned into a light path by a reflector and is incident to the liquid crystal surface of the spatial light modulator at an off-axis incidence angle of 10 degrees; the asymmetric 4-F system comprises a tele lens and an iris diaphragm, and the Bessel light beam sequentially passes through the tele lens and the iris diaphragm and is transmitted to the objective lens.

Description

Method and device for axially shaping high aspect ratio microstructure by laser processing Technical Field The invention relates to the technical field of laser processing, in particular to a method and a device for axially shaping a microstructure with high aspect ratio by laser processing. Background The High Aspect Ratio (HAR) microstructure has become a core research object and a key technical challenge in the micro-nano manufacturing field due to its great application potential in the fields of micro-electro-mechanical systems, micro-optics, biology, metamaterials and the like. Typical features of such structures are that their longitudinal dimensions are much larger than their lateral dimensions, which places extremely high demands on resolution, aspect ratio capability, efficiency and three-dimensional morphology controllability of the processing technology. Currently, the processing method for realizing the HAR microstructure can be mainly divided into the following categories of the traditional micro-nano processing technology, namely the Deep Reactive Ion Etching (DRIE) is represented, and the structure with steep side wall and extremely high depth-to-width ratio can be realized on a silicon wafer, but is difficult to be applied to non-silicon materials or realize the processing of true three-dimensional arbitrary shapes. The femtosecond laser direct writing and modification technology comprises the steps of performing laser scanning modification in a transparent material, and selectively removing a modified region by wet etching. The method can manufacture micro-channels in hard and brittle materials such as glass, but has great difficulty in controlling the roughness and the shape accuracy of the side wall, and is difficult to realize any three-dimensional design. And (3) femtosecond laser direct writing, namely focusing the femtosecond laser by using a high numerical aperture objective lens, and scanning and polymerizing the photoresist point by using a three-dimensional moving sample stage. Although the method can realize complex three-dimensional molding with submicron resolution, the method takes a very long time to manufacture a single high aspect ratio microstructure. The femtosecond laser is shaped into a long focal depth beam through a conical lens or a spatial light modulator, so that the high aspect ratio micro-column structure can be efficiently processed, however, the focal depth, the transverse size and the focal position of the beam are usually coupled, and adjusting one parameter (such as the focal depth) often causes linkage change of other parameters (such as the focal position), so that the total exposure power needs to be frequently adjusted or the sample is moved in the depth direction, and the highly programmable manufacturing of the complex HAR micro-structure cannot be realized in a fixed focal plane. Therefore, in the field of femto-second laser preparation of high depth-to-depth ratio microstructures, a programmable, efficient and simple-to-operate solution is required to be developed. Disclosure of Invention Compared with the prior art, the application aims to provide the method for processing the high aspect ratio microstructure by the axial shaping laser, which can avoid adjusting parameter coupling linkage. In order to achieve the above purpose, the present invention provides the following technical solutions: a method for axially shaping a laser processing high aspect ratio microstructure comprises the following steps: S1, generating initial laser by a femtosecond laser, and measuring the intensity distribution of an initial laser light field; s2, defining voxel parameters according to the microstructure of the high aspect ratio based on the intensity distribution of the initial laser light field; s3, calculating and generating a group of holograms of Bessel beams according to voxel parameters, wherein the holograms are used for being loaded on a spatial light modulator, and the spatial light modulator modulates an emergent beam of initial laser into the Bessel beams with controllable axial intensity distribution; s4, adjusting the processing energy of the Bessel beam through the light intensity attenuation device, and simultaneously adjusting an objective lens corresponding to the spatial light modulator to align the objective lens to the sample of the translation stage; S5, controlling the translation stage to move, simultaneously gradually replacing holograms loaded in the spatial light modulator, projecting Bessel beams with different lengths at different processing points of the sample, and exposing the Bessel beams at the processing points to generate voxels with corresponding heights; And S6, performing post-processing on the voxels to obtain the high aspect ratio microstructure with preset height distribution. The technical scheme has the following technical effects: According to the technical scheme, the complex coding hologram is loaded on the spatial ligh