An ultrafast laser processing device and method based on complex amplitude modulation type composite light field shaping element

Abstract

This invention discloses an ultrafast laser processing apparatus and method based on a complex amplitude-modulated composite optical field shaping element, belonging to the field of optical field shaping technology. It includes: a substrate; a metasurface and diffractive optical elements formed on the substrate, with the metasurface and diffractive optical elements located on opposite sides of the substrate. The metasurface includes multiple superatomic pillars, and the diffractive optical elements include multiple structural units. The superatomic pillars and structural units are arranged in a one-to-one correspondence to form a unit group for complex amplitude modulation of the incident beam. This invention achieves complete complex amplitude modulation through the synergy of the metasurface and diffractive optical elements, significantly reducing speckle crosstalk, and integrating beam shaping functionality into a centimeter-scale element, replacing traditional bulky optical systems. It has advantages such as high optical field shaping quality and functional integration, and is suitable for ultrafast laser precision processing.

Description

Technical Field

[0001] This invention belongs to the field of optical field shaping technology, specifically relating to an ultrafast laser processing device and method based on a complex amplitude-modulated composite optical field shaping element. Background Technology

[0002] Ultrafast lasers, with their ultrashort pulse characteristics, can interact with matter through nonlinear effects, enabling maskless manufacturing. Compared to traditional photolithography, ultrafast laser direct writing technology has made significant contributions to interdisciplinary research fields such as nanophotonics, biomedicine, sensing and imaging, optoelectronics, and artificial intelligence photonics. Meanwhile, ultrafast lasers also have industrial applications spanning ophthalmic surgery, precision glass cutting, fiber optic sensor manufacturing, and additive manufacturing.

[0003] Current ultrafast laser direct writing technology mainly employs a point-by-point scanning serial processing mode. This involves moving the sample via a displacement stage, allowing the focused laser spot to scan point by point along a preset path to form the desired pattern. However, the manufacturing efficiency of large-area patterned structures is severely limited. Simultaneously, the field-of-view limitations of traditional imaging optics and the limited precision of the displacement platform result in stitching defects and proximity effect errors in the laser processing of large-area patterned structures. Therefore, there is an urgent need to develop beam shaping technology to modulate the laser energy to a spatial distribution that matches the target patterned structure, thereby achieving high-throughput, large-area precision manufacturing.

[0004] For example, Chinese patent CN114355616A proposes a high-throughput multi-slot two-photon laser direct writing system. This system uses a beam-expanding and homogenizing module to shape the Gaussian distribution into a flat-top beam, and a beam-combining module to combine multiple sub-slots into a multi-slot, enabling large-area micro / nano fabrication. Another example is Chinese patent CN118778380A, which discloses a high-throughput two-photon direct writing device based on controllable multi-slot grayscale writing. This device obtains a uniform intensity focal array through the coordinated control of a microlens array and a digital micromirror array, and achieves high-precision grayscale writing by controlling the rotation angle and the spacing between the lines.

[0005] While these advanced technologies can generate high-throughput dot lattices, they still rely on scanning methods for processing, and the processing efficiency needs further improvement. Furthermore, the optical systems of these devices are extremely complex, typically requiring sequential processing through discrete modules such as a dot lattice shaping module, a 4f system, and a focusing objective. This makes optical path adjustment difficult, and even minute alignment deviations between lens groups can significantly impact the final beam quality, thus reducing processing quality and accuracy.

[0006] Therefore, there is an urgent need for a composite optical field shaping element that can overcome the above-mentioned defects: on the one hand, improve processing efficiency; on the other hand, solve speckle crosstalk problem; and at the same time, reduce optical path complexity and alignment deviation sensitivity. Summary of the Invention

[0007] This invention provides an ultrafast laser processing device and method based on a complex amplitude-modulated composite optical field shaping element. By independently controlling the amplitude and part of the phase of the incident beam through the radius and height of the superatomic column, and combining the height of the structural unit to fully compensate for the remaining phase, it realizes the full amplitude and full phase control of the incident beam and the direct generation of patterned structured light. This solves the problems of speckle crosstalk caused by phase singularities, as well as the complex optical path and sensitivity to alignment deviation caused by the numerous discrete optical modules in existing laser processing systems.

[0008] The technical solution adopted in this invention is as follows: A composite optical field shaping element based on complex amplitude modulation includes: Base; A metasurface and a diffractive optical element are formed on the substrate, the metasurface and the diffractive optical element are respectively located on both sides of the substrate, the metasurface is used to receive the incident light beam and includes multiple superatomic pillars, and the diffractive optical element includes multiple structural units; The superatomic pillars are arranged in a one-to-one correspondence with the structural units to form a unit group, which is used to perform complex amplitude control on the incident beam. The radius and height of the superatomic pillars are set according to the energy distribution of the target pattern structured light, and are used to control the amplitude and phase of the incident beam. The height of the structural unit of the diffractive optical element is set according to the energy distribution of the target pattern structured light, and is used to perform phase compensation on the beams controlled by the superatomic pillars in the same unit group.

[0009] The composite optical field shaping element based on complex amplitude modulation used in this invention also has the following additional technical features: Each of the said unit groups is paired with the incident beam After complex amplitude modulation, the resulting optical field is: , in, This indicates a unit group with amplitude modulation capability; The radius of the superatomic column; The height of the superatomic column; The height of the structural unit; For arbitrary polarized incident beams; The transmittance of the composite optical field shaping element is determined by... Adjust the settings accordingly; Represents the imaginary unit; The phase delay of the composite optical field shaping element. ,in To control the phase of the incident beam using the superatomic pillars, by changing... , To regulate, To compensate for the phase of the beam through the structural unit, by changing... To implement regulation.

[0010] The phase modulation of the incident beam by the superatomic column is specifically as follows: The effective refractive index of the metasurface can be controlled by adjusting the radius of the superatomic pillars. By combining the wavelength of the incident beam with the height of the superatomic column, the phase of the incident beam can be modulated. , in, To adjust the phase of the incident beam, The wavelength of the incident beam is 1. The effective refractive index of the superatomic column is controlled by adjusting the radius of the superatomic column. The height of the superatomic column.

[0011] The modulation of the incident beam amplitude by the superatomic column is specifically as follows: By adjusting the height and radius of the superatomic pillars, the resonant detuning is controlled to regulate the transmittance of the composite optical field shaping element, thereby controlling the amplitude of the incident beam.

[0012] The phase compensation of the beam after modulation by the diffractive optical element for the corresponding superatomic column in the same unit group is specifically as follows: , in, The phase used to compensate for the beam. The wavelength of the incident beam is 1. The effective refractive index of the diffractive optical element is... The height of the structural unit of the diffractive optical element.

[0013] The transmittance range of the composite light field shaping element is 0 to 1. The phase compensation range achieved by adjusting the diffractive optical element is 0-2. .

[0014] The substrate is a structure made of fused silica. The superatomic pillars are structures made of anisotropic dielectric materials, with periodicity. The amplitude and phase of the incident beam can be controlled by changing the radius and height of the superatomic column.

[0015] A second aspect of the present invention provides an ultrafast laser processing apparatus, comprising: Ultrafast laser source, used to emit laser beams; Beam expanders are used to increase the size of laser beams. A polarization control component is used to adjust the polarization state of a laser beam. The ultrafast laser source, the beam expander, and the polarization control component are arranged coaxially along the incident light path. Beam splitters are used to change the incident direction of laser beams; The aforementioned composite optical field shaping element; A displacement stage for carrying a workpiece, wherein the composite optical field shaping element and the displacement stage are coaxially arranged along the imaging optical path; The laser beam emitted from the ultrafast laser source passes sequentially through the beam expander, the polarization control component, and the beam splitter along the incident optical path. After the beam splitter changes its direction, it is incident on the composite optical field shaping element along the imaging optical path. After being modulated by the composite optical field shaping element, it forms a patterned structured light on the workpiece surface.

[0016] The ultrafast laser processing device also includes: Dichroic mirrors are used to filter out interfering light. Tube lens; The near-infrared camera, the displacement stage, the composite light field shaping element, the beam splitter, the dichroic mirror, the tube lens, and the near-infrared camera are coaxially arranged along the imaging optical path so that the light beam reflected from the workpiece surface passes through the composite light field shaping element, the beam splitter, the dichroic mirror, and the tube lens before entering the near-infrared camera for imaging.

[0017] A third aspect of the present invention provides an ultrafast laser processing method for controlling the composite optical field shaping element, comprising: Determine the shape and energy distribution of the target pattern structured light To obtain the complex amplitude distribution required for the composite optical field shaping element. ; , in, The amplitude to be controlled for the composite optical field shaping element; The phase that needs to be controlled for the composite optical field shaping element. ,in For the modulation of the phase of metasurface, To compensate for the phase of diffractive optical elements; Indicates focal length; , indicating the point of the composite light field shaping element To pattern structured light spot The distance; Represents the imaginary unit; The wavelength of the incident beam; For wave vector, ; According to the required amplitude adjustment The transmittance of the composite optical field shaping element was determined through normalization. To determine the radius of the superatomic column. and height ; Based on the radius of the superatom column and height The phase of the incident beam controlled by the metasurface is obtained, and combined with the phase that the composite optical field shaping element needs to control, the compensation phase of the diffractive optical element is obtained, so as to determine the structural unit height H of the diffractive optical element.

[0018] Due to the adoption of the above technical solution, the beneficial effects achieved by this invention are as follows: In this invention, the amplitude and phase are directly modulated through the synergy of the metasurface layer of the composite optical field shaping element and the diffractive optical element (DOE). The metasurface modulates the amplitude and part of the phase, while the DOE independently compensates for the remaining phase, thus achieving complete complex amplitude modulation. This avoids the generation of phase singularities and reduces speckle crosstalk, as it eliminates the need for a pure phase iteration algorithm. Furthermore, the metasurface can utilize different metaatomic pillars to arbitrarily control the phase and amplitude of the incident light wave, enabling complex amplitude encoding and generating patterned structured light of arbitrary shapes and grayscale, thus achieving single-pass direct-write patterned structures.

[0019] Furthermore, by integrating the metasurface and DOE on both sides of the substrate, the complex amplitude shaping function of the beam is integrated into a single element. It eliminates the need for the 4f imaging module and objective focusing module of the existing spatial light modulator (SLM), compressing the originally large and complex optical path system into a centimeter-level module. This significantly reduces the system's debugging difficulty and sensitivity to alignment errors, which is beneficial for the miniaturization and portable deployment of the processing system.

[0020] Therefore, it can better adapt to the requirements of industrial-grade ultrafast laser processing, can be mass-produced and used, and has the characteristics of low cost and high stability, thus getting rid of the constraints of high cost and complex optical path calibration. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the structure of the composite optical field shaping element based on complex amplitude modulation according to one embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the metasurface according to one embodiment of the present invention; Figure 3 This is a transmission and phase distribution diagram of the superatomic column at different heights and radii according to one embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the diffractive optical element according to one embodiment of the present invention; Figure 5 This is a phase distribution diagram of the structural unit of the diffractive optical element at different heights according to one embodiment of the present invention; Figure 6 This is a binary intensity structured light and its amplitude and phase diagram according to one embodiment of the present invention; Figure 7 This invention provides an 8-bit grayscale structured light and its amplitude and phase diagram according to one embodiment of the present invention. Figure 8 This is a schematic diagram of the structure of the ultrafast laser processing device according to one embodiment of the present invention.

[0022] in: 1. Ultrafast laser source; 2. Beam expander; 3. Polarization control components; 4. Beam splitter; 5. Composite optical field shaping element; 51. Metasurface; 511. Superatomic column; 52. Substrate; 53. Diffractive optical element; 531. Structural unit; 6. Workpiece; 7. Displacement stage; 8. Dichroic mirror; 9. Tube lens; 10. Near-infrared camera. Detailed Implementation

[0023] To more clearly illustrate the overall concept of the present invention, a detailed description will be provided below with reference to the accompanying drawings and examples.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0025] like Figure 1 , Figure 2 and Figure 4 As shown, a composite optical field shaping element 5 based on complex amplitude modulation includes: Base 52; A metasurface 51 and a diffractive optical element 53 are formed on the substrate 52. The metasurface 51 and the diffractive optical element 53 are located on both sides of the substrate 52. The metasurface 51 is used to receive the incident light beam and includes a plurality of superatomic pillars 511. The diffractive optical element 53 includes a plurality of structural units 531. The superatomic pillars 511 and the structural units 531 are arranged in a one-to-one correspondence to form a unit group, which is used to perform complex amplitude control on the incident beam. The radius and height of the superatomic pillar 511 are set according to the energy distribution of the target pattern structured light, and are used to control the amplitude and phase of the incident beam. The structural unit height of the diffractive optical element 53 is set according to the energy distribution of the target pattern structured light, and is used to perform phase compensation on the beam after the beam is controlled by the corresponding superatomic pillar 511 in the same unit group.

[0026] It should be noted that the composite light field shaping element 5 based on complex amplitude modulation provided in this application integrates the metasurface 51 and the diffractive optical element 53 on both sides of the same substrate 52. The amplitude and part of the phase of the incident beam are controlled by the radius and height of the superatomic pillars 511 in each unit group, and the remaining phase is compensated by the height of the corresponding structural unit 531, thereby achieving complete control of the amplitude and phase of the incident beam and generating the required patterned structured light in one go.

[0027] The composite optical field shaping element 5 includes a substrate 52, a metasurface 51 formed on the substrate 52, and a diffractive optical element 53 formed on the substrate 52. The metasurface 51 and the diffractive optical element 53 are located on opposite sides of the substrate 52. The metasurface 51 is used to receive the incident light beam and is composed of multiple superatomic pillars 511 arranged periodically along the surface of the substrate 52. The diffractive optical element 53 is composed of structural units 531 that periodically correspond to the metasurface 51. The overall size of the entire composite optical field shaping element 5 is on the centimeter scale, requiring no external power supply or computer control, and can be mass-produced and used after being prefabricated at the factory.

[0028] The metasurface 51 is composed of multiple cylindrical superatomic pillars 511. Each superatomic pillar 511 has a specific radius and height. By varying the radius and height of each superatomic pillar 511, the amplitude and phase of the incident beam can be simultaneously controlled.

[0029] Specifically, the modulation of the incident beam by the metasurface 51 is based on the following two physical effects. First, phase modulation is based on the transmission phase effect. When the incident beam passes through the metaatomic pillar 511, its phase delay depends on the effective refractive index and height of the metaatomic pillar 511. The effective refractive index of the metaatomic pillar 511 is mainly determined by its radius; therefore, by changing the radius of the metaatomic pillar 511, the effective refractive index can be modulated; by changing the height of the metaatomic pillar 511, the amount of phase delay can be further adjusted. The combined effect of radius and height allows for flexible phase adjustment over a wide range.

[0030] Secondly, amplitude can be controlled based on the Fabry-Perot resonance effect. Variations in the height and radius of the superatom pillar 511 alter the detuning of the Fabry-Perot resonance, thereby precisely controlling the transmittance. By rationally designing the radius and height of each superatom pillar 511, arbitrary target transmittance can be obtained, enabling arbitrary control of the incident beam amplitude distribution.

[0031] Since the metaatom pillar 511 adopts a cylindrical structure and does not exhibit birefringence, the aforementioned amplitude and phase modulation characteristics are independent of the polarization state of the incident beam. That is, when light of any polarization state is incident, the metasurface 51 can output according to the preset transmittance and phase delay. This simplifies the control requirements for the polarization state of the incident light and improves the applicability of the system.

[0032] The diffractive optical element 53 is located on the other side of the substrate 52, opposite to the metasurface 51. The diffractive optical element 53 is composed of multiple structural units 531, each structural unit 531 corresponding to a metaatomic pillar 511 on the metasurface 51. By setting different heights for each structural unit 531, the phase delay introduced by that unit can be independently controlled.

[0033] This means that the diffractive optical element 53 can independently provide any desired phase delay, unaffected by amplitude modulation. This characteristic allows the diffractive optical element 53 to precisely compensate for the phase deviation generated by the metasurface 51 in achieving the target amplitude distribution, thereby ensuring that the total phase delay of the entire composite optical field shaping element 5 is exactly equal to the phase distribution required by the design.

[0034] The metasurface 51 and the diffractive optical element 53 work together to ensure that the final transmittance and total phase of the composite optical field shaping element 5 perfectly match the inversion calculation results, thereby accurately forming the target pattern structured light on the focal plane. This composite optical field shaping element 5 does not rely on a pure phase iteration algorithm, avoiding speckle crosstalk caused by phase singularities. At the same time, it integrates the functions of the beam shaper, 4f system, and focusing objective, which are separate in traditional laser processing systems, into a single module, significantly reducing system complexity and alignment difficulty.

[0035] As a preferred embodiment of the present invention, each of the unit groups corresponds to the incident beam. After complex amplitude modulation, the resulting optical field is: , in, This indicates a unit group with amplitude modulation capability; The radius of the superatomic column; The height of the superatomic column 511; The height of the structural unit 531; For arbitrary polarized incident beams; To determine the transmittance of the composite light field shaping element 5, by changing... To regulate; Represents the imaginary unit; The phase delay of the composite optical field shaping element 5, ,in To control the phase of the incident beam through the superatomic column 511, by changing... To regulate, To compensate for the phase of the beam through the structural unit 531, by changing... To implement regulation.

[0036] When an incident beam of arbitrary polarization When the light is incident perpendicularly on the metasurface 51 of the composite optical field shaping element 5, the emitted beam can be uniformly represented as... .

[0037] Since the entire composite light field shaping element 5 is composed of multiple unit groups, and the emitted light fields of each unit group are spatially arranged, the desired target pattern structured light is ultimately formed on the focal plane. This is achieved by independently selecting different [specific parameters] for each unit group. , , By combining these elements, the desired amplitude and phase information can be obtained separately.

[0038] like Figure 6 As shown, for binary intensity structured light, the amplitude and phase distributions are obtained by solving based on the intensity distribution of the light field. A composite light field shaping element 5 is designed based on the amplitude and phase distributions. When a light source with a wavelength of 1030 nm is incident, structured light with an SDU pattern is obtained on the plane of the workpiece 6. Figure 7 As shown, for 8-bit grayscale structured light, the amplitude and phase distribution are obtained by solving based on the intensity distribution of the light field. Based on the amplitude and phase distribution, a composite element structure is designed. When a light source with a wavelength of 1030nm is incident, a lotus flower pattern structured light is obtained on the plane of workpiece 6.

[0039] In addition, transmittance This determines the amplitude attenuation factor of the incident beam after passing through this unit group. This is achieved by changing the radius of the superatomic column 511. and height This results in higher transmittance. Variation. In one embodiment, the amplitude of the incident beam is controlled by changing the radius and height of the superatomic column 511, specifically as follows: By adjusting the height and radius of the superatomic column 511, the resonant detuning is changed, thereby altering the transmittance of the composite optical field shaping element 5 and controlling the amplitude of the incident beam.

[0040] This embodiment utilizes the inherent Fabry-Perot resonance effect of each superatomic pillar 511 in the metasurface 51. By adjusting the radius and height of the superatomic pillars 511, the resonance detuning is changed, thereby controlling the transmittance of the composite optical field shaping element 5, ultimately achieving arbitrary distribution control of the incident beam amplitude. This aims to solve the problem that traditional optical field control elements cannot directly and independently control the amplitude distribution.

[0041] It is understandable that the Fabry-Perot resonance is a multiple reflection interference phenomenon formed between the two end faces of the superatomic pillar 511. When the wavelength of the incident light and the geometry of the superatomic pillar 511 satisfy certain matching conditions, the resonance is enhanced and the transmittance approaches 1; when the resonance conditions are deviated from (i.e., the detuning increases), the transmittance decreases.

[0042] Specifically, the amplitude of the incident beam after modulation is: , in, Indicates the non-resonant background transmission term. Indicates the intensity of resonant scattering. This indicates the resonant linewidth or equivalent loss. The wavelength of the Fabry-Perot resonance is determined by the geometric parameters of the superatomic column 511. For the... Longitudinal Fabry-Perot resonance, , in, It is the effective refractive index of the superatomic column 511. It is the equivalent reflection phase at the interface between the top of the superatomic column 511 and the air. The equivalent reflection phase is caused by the mode mismatch between the bottom of the superatomic column 511 and the substrate. This is the resonance order.

[0043] Due to the radius of superatoms It will change the degree of lateral constraint in the pattern, thereby changing , and And height By directly altering the longitudinal optical path length within the cavity, the Fabry-Perot resonance wavelength can be written as... , Finally, at a fixed operating wavelength Below, the transmission amplitude is, .

[0044] It should be noted that the transmittance of the composite light field shaping element 5 ranges from 0 to 1. The DOE transmittance is approximately 1; therefore, the height and radius of the superatomic pillar 511 together determine the transmittance of the composite light field shaping element 5. By adjusting these two parameters, the resonant detuning can be continuously changed, thus allowing the transmittance to vary arbitrarily between 0 and 1.

[0045] Specifically, when the radius and height make the resonant wavelength exactly equal to the working wavelength, the detuning is 0 and the transmittance reaches its maximum (close to 1); when the radius or height deviates from the resonant condition, the absolute value of the detuning increases, the resonant intensity weakens, and the transmittance gradually decreases to 0.

[0046] transmittance It does not regulate the phase; it is related to the phase factor. They are independent of each other and together constitute the complex amplitude. Phase delay This represents the phase change of the incident beam after passing through structural unit 531. In this application, the total phase delay is a linear superposition of two parts: , in, The phase modulation amount is provided by the superatomic pillars 511 in the metasurface 51. In one embodiment, the phase modulation of the incident beam by the superatomic pillars 511 is specifically as follows: The effective refractive index of the metasurface 51 can be controlled by adjusting the radius of the superatomic pillar 511. By adjusting the height of the superatomic column 511 in conjunction with the wavelength of the incident beam, the phase of the incident beam can be controlled. , in, To adjust the phase of the incident beam, The wavelength of the incident beam is 1. The effective refractive index of metasurface 51 is controlled by the radius of the superatomic pillar 511. The height of the superatomic column 511.

[0047] When the incident beam passes perpendicularly through a height of , radius is When considering the superatomic column 511, the superatomic column 511 can be regarded as a segment of length 511. A dielectric waveguide. When a light beam propagates within it, its phase change is determined by the propagation constant. With distance The product of these factors determines the propagation constant. For the fundamental mode, the propagation constant is related to the refractive index of the material and the transverse dimension of the waveguide. The effective refractive index of the superatomic pillar 511 is defined. It represents the equivalent refractive index of the waveguide structure for the accumulation of optical wave phase.

[0048] Effective refractive index of superatomic column 511 Depends on its radius When the radius is small, the effective refractive index of the superatomic column 511 is closer to the refractive index of the surrounding medium, resulting in a relatively low effective refractive index. As the radius increases, the light field becomes more localized within the high-refractive-index column, and the effective refractive index gradually increases, approaching the bulk refractive index of the column material. Therefore, changing the height and radius of the superatomic column 511 alters the total phase delay. .

[0049] It should be noted that for a given transmittance, such as Figure 3 As shown, complete phase control from 0 to 2π cannot be achieved, therefore, an integrated DOE is needed to compensate for the transport phase of metasurface 51. The compensation phase is provided by the diffractive optical element 53. In one embodiment, the phase compensation of the beam after modulation of the corresponding superatomic column 511 in the same unit group by the diffractive optical element is specifically as follows: , in, The phase used to compensate for the beam. The wavelength of the incident beam is 1. The effective refractive index of the diffractive optical element is... The height of the structural unit 531.

[0050] In this embodiment, the diffractive optical element 53 is treated as an independent phase modulation layer by changing the height of its structural unit 531. This introduces a precisely controllable phase delay. This compensates for the phase deviation caused by the metasurface in achieving the target amplitude distribution, and ultimately achieves complete complex amplitude control of the composite optical field shaping element 5.

[0051] In this application, the effective refractive index can be considered as a fixed design constant. Therefore, With height Linear relationship, phase Follow It increases linearly.

[0052] It should be noted that the range for phase compensation by adjusting the diffractive optical element 53 is 0-2. .because It can be from 0 to It can take any value within the range, thus fully compensating for any phase deviation generated by the metasurface 51. Typically, it will... The design scope is set to make Cover at least one complete Period, for example when When the phase changes from 1 μm to 3.3 μm, the phase change can reach ,like Figure 5 As shown.

[0053] This implementation method is through and Independent adjustment allows for the synthesis of any desired complex amplitude distribution, theoretically enabling the generation of patterned structured light of arbitrary shape and grayscale (including binary and 8-bit grayscale). Unlike pure phase methods, it eliminates the need for iterative calculations, thereby reducing phase singularities and the resulting speckle noise, and significantly improving the quality of the emitted beam.

[0054] Furthermore, since cylindrical superatoms do not exhibit birefringence, the element is insensitive to the polarization state of incident light.

[0055] In a preferred embodiment of the present invention, the substrate 52 is a structure made of fused silica.

[0056] The superatomic pillar 511 is a structure made of anisotropic dielectric material, periodically... The amplitude and phase of the incident beam can be controlled by changing the radius and height of the superatomic column 511.

[0057] Fused silica was selected as the substrate material. Silicon carbide (SiC) was selected as the material for the superatomic pillars 511. SiC possesses high hardness, high thermal conductivity, and good chemical stability, and high aspect ratio nanopillar structures can be obtained through plasma etching. Other anisotropic dielectric materials, such as silicon nitride (Si3N4), titanium dioxide (TiO2), or amorphous silicon, can also be used if necessary. These materials all have high refractive indexes and low absorption characteristics, and there are no restrictions on their selection.

[0058] For incident wavelength ,cycle The subwavelength condition is met, thus eliminating visible light-order diffraction and reducing interference from higher-order diffraction spots on the fabricated pattern. The 650nm period allows the radius of the superatomic pillars to vary from 50nm to 300nm, and the height from 400nm to 1500nm, achieving a transmittance of 0–1 and a wide phase range through Fabry-Perot resonance and transport phase.

[0059] A second aspect of the present invention provides an ultrafast laser processing apparatus, such as... Figure 8 As shown, it includes: Ultrafast laser source 1, used to emit laser beams; Beam expander 2 is used to increase the size of the laser beam; The polarization control component 3 is used to adjust the polarization state of the laser beam. The ultrafast laser source 1, the beam expander 2, and the polarization control component 3 are arranged coaxially along the incident light path. Beam splitter 4 is used to change the incident direction of the laser beam; The composite optical field shaping element 5; The displacement stage 7 is used to support the workpiece 6, and the composite optical field shaping element 5 and the displacement stage 7 are coaxially arranged along the imaging optical path. The laser beam emitted from the ultrafast laser source 1 passes sequentially through the beam expander 2, the polarization control component 3, and the beam splitter 4 along the incident optical path. After the beam splitter 4 changes its direction, it is incident on the composite optical field shaping element 5 along the imaging optical path. After being modulated by the composite optical field shaping element 5, it forms a patterned structured light on the surface of the workpiece 6.

[0060] This application aims to construct an ultrafast laser processing system that is compact in structure, has a simple optical path, high processing accuracy, and is easy to deploy in industry.

[0061] The ultrafast laser source 1 is used to emit ultrashort pulse laser beams. Typically, a femtosecond fiber laser or a solid-state laser with a center wavelength of 1030 nm can be used. This source provides the high peak power density required for processing to excite nonlinear absorption or material modification.

[0062] The beam expander 2 is placed after the laser source to expand the beam waist diameter of the laser beam so that the spot size matches the effective aperture of the composite optical field shaping element 5.

[0063] The beam expander 2 has an adjustable magnification. By adjusting the magnification, the diameter of the expanded spot is made slightly larger than the effective aperture of the composite optical field shaping element 5, so as to make full use of the modulation region of the element.

[0064] The polarization control component 3 is used to adjust the polarization state of the incident laser beam. This component includes at least one of a linear polarizer, a half-wave plate, or a quarter-wave plate. Since the composite optical field shaping element 5 of this invention is insensitive to polarization, the polarization control component 3 is not strictly necessary. However, in certain special applications, the polarization state can be flexibly adjusted to optimize the processing effect according to actual processing needs.

[0065] For example, using a quarter-wave plate to convert linearly polarized light into circularly polarized light can create a symmetrical energy distribution in different directions for the processed light spot. The polarization control component 3 should be mounted on a rotating frame for online adjustment.

[0066] Beam splitter 4 is used to change the propagation direction of the laser beam, while simultaneously achieving non-coaxiality between the incident optical path and the imaging optical path. In this embodiment, beam splitter 4 reflects the laser from the light source to the optical axis direction where the composite optical field shaping element 5 is located, and transmits the reflected light returning from the surface of the workpiece 6 to the near-infrared camera.

[0067] The composite light field shaping element 5, integrated into the device, fully modulates the amplitude and phase of the incident light beam and directly focuses it to generate the target pattern structured light. The plane of the composite light field shaping element 5 is perpendicular to the imaging optical path. The pattern structured light modulated by the composite light field shaping element 5 is projected onto the workpiece surface to achieve workpiece processing.

[0068] The displacement stage 7 is used to support the workpiece 6 and can realize three-dimensional (X, Y, Z) precision motion. The displacement stage 7 can be a one-dimensional to three-dimensional electrically driven displacement platform for positioning the workpiece 6.

[0069] The laser beam emitted from the ultrafast laser source 1 is first expanded in size by the beam expander 2, then adjusted to the desired polarization state by the polarization control component 3, and then incident on the beam splitter 4. The beam splitter 4 guides the beam to the imaging optical path, so that the beam is incident perpendicularly on the composite optical field shaping element 5. After being modulated by the composite optical field shaping element 5, the emitted beam directly carries the amplitude information of the target pattern and is focused on the surface of the workpiece 6 placed on the displacement stage 7, forming pattern structured light and completing the single exposure processing.

[0070] Traditional processing apparatuses based on spatial light modulators (SLMs) must image the SLM plane onto the back focal plane of the objective lens or the workpiece plane using a 4f system. This requires at least two lenses (or lens groups) and an additional objective lens, resulting in a complex optical path system and cumbersome debugging. In this application, the composite light field shaping element 5 achieves complex amplitude modulation of the light field, reducing the number of components used and significantly reducing space occupation and focusing difficulty.

[0071] Furthermore, since the composite light field shaping element 5 does not require a pure phase iteration algorithm, there will be no speckle noise caused by phase singularities in the outgoing light field, and the edge sharpness, uniformity and repeatability of the processed pattern are optimized.

[0072] Moreover, the displacement stage 7 remains stationary during processing, and the entire pattern structure light can be processed onto the workpiece 6 with only one laser pulse. The processing time is independent of the pattern area, which improves efficiency compared to point-by-point scanning or multi-point parallel scanning.

[0073] As a preferred embodiment of the present invention, such as Figure 8 As shown, it also includes a dichroic mirror 8, used to filter interfering light; Tube lens 9; The near-infrared camera 10, the displacement stage 7, the composite light field shaping element 5, the beam splitter 4, the dichroic mirror 8, the tube lens 9, and the near-infrared camera 10 are arranged coaxially along the imaging optical path so that the light beam reflected from the surface of the workpiece 6 enters the near-infrared camera 10 for imaging after passing through the composite light field shaping element 5, the beam splitter 4, the dichroic mirror 8, and the tube lens 9.

[0074] This implementation aims to solve the problem that the processing area cannot be directly detected and the processing effect is difficult to judge during ultrafast laser processing.

[0075] The dichroic mirror 8 filters out interfering light, enhancing the imaging effect. The focal length of the tube lens 9 is matched with the target surface size and required magnification of the near-infrared camera 10, together forming the imaging system. The near-infrared camera 10 captures the weak reflection signals in ultrafast laser processing to achieve imaging.

[0076] The displacement stage 7, the composite light field shaping element 5, the beam splitter 4, the dichroic mirror 8, the cylindrical lens 9, and the near-infrared camera 10 are coaxially arranged along the imaging optical path so that the light beam reflected from the surface of the workpiece 6 passes through the composite light field shaping element 5, the beam splitter 4, the dichroic mirror 8, and the cylindrical lens 9 before entering the near-infrared camera 10 for imaging. That is, the light reflected from the surface of the workpiece 6 propagates in the opposite direction to the incident processing beam. After the processing beam is modulated and focused onto the surface of the workpiece 6 by the composite light field shaping element 5, part of the light is reflected by the surface of the workpiece 6.

[0077] The reflected light returns along its original path, first passing through the composite light field shaping element 5 again, and then reaching the beam splitter 4, propagating in the reverse direction of the imaging light path. Next, the light passes through the dichroic mirror 8, which filters out incompletely attenuated stray light from the processing laser. The filtered beam then enters the cylindrical lens 9, which images the intermediate image of the workpiece 6 surface onto the photosensitive surface of the near-infrared camera 10. Finally, the near-infrared camera 10 receives the image and displays the processed area image of the workpiece 6 surface in real time on a computer monitor or its built-in display screen.

[0078] This embodiment provides near-infrared imaging that is coaxial with the imaging optical path, which can clearly see the surface of the workpiece 6 and the projection of the pattern structure light, and detect the processing accuracy.

[0079] A third aspect of the present invention provides an ultrafast laser processing method for controlling the composite optical field shaping element 5, comprising: Determine the shape and energy distribution of the target pattern structured light The complex amplitude distribution required for the composite optical field shaping element 5 is obtained. ; , in, The amplitude to be adjusted for the composite optical field shaping element 5; The phase to be adjusted for the composite optical field shaping element 5. ,in For the phase modulation of metasurface 51, Phase compensation for diffractive optical element 53; Indicates focal length; , representing pattern structured light spots 5 points to the composite light field shaping element The distance; Represents the imaginary unit; The wavelength of the incident beam; For wave vector, ; According to the required amplitude adjustment The transmittance of the composite light field shaping element 5 was determined through normalization. To determine the radius of the superatomic column 511. and height ; Based on the radius of the superatomic column 511 and height The phase of the incident beam controlled by the metasurface 51 is obtained, and the phase to be controlled by the composite optical field shaping element 5 is combined to obtain the compensation phase of the diffractive optical element 53, so as to determine the structural unit height H of the diffractive optical element 53.

[0080] This application aims to establish a precise mapping method from a target light field to a physical structure, enabling the composite light field shaping element 5 to generate the required structured light according to a preset pattern.

[0081] First, based on the processing requirements, the spatial intensity distribution of the structured light for the target pattern is defined. This distribution can be any two-dimensional function, such as a binary pattern, like... Figure 6 The image is set to the letters SDU, where the intensity value is 0 or 1; a grayscale pattern, such as... Figure 7 The lotus pattern shown has an intensity value that varies continuously between 0 and 255.

[0082] After the target pattern is input, the Rayleigh-Sommerfeld diffraction integral formula is used. , The complex amplitude distribution at the composite optical field shaping element 5 is derived from the target intensity distribution. Specifically, each point on the target focal plane is considered as a spherical secondary wavelet source, and their coherent superposition at the composite optical field shaping element 5 forms the desired complex amplitude distribution. Since the formula includes distance... Sum of coefficients It considers both propagation amplitude attenuation and phase delay, thus enabling precise calculation of the complex amplitude that the composite optical field shaping element 5 should provide under full-space propagation conditions. Specifically, in the formula... This indicates that the composite light field shaping element 5 is designed to focus the patterned light field to a distance of [missing information]. On the plane.

[0083] The obtained amplitude distribution Normalization is performed so that its maximum value corresponds to the transmittance. ,Right now: , This refers to the target transmittance (range 0-1) required for each unit group of the composite optical field shaping element 5. Then, using a pre-established design database, i.e., the transmittance and the radius of the superatomic pillars obtained through simulation... ,high The mapping relationship is used to select a set of mapping relationships for each superatomic column. This makes the actual transmittance as close as possible to the target transmittance. .

[0084] Within the radius of the selected superatom column 511 and height Then, the phase contribution of this unit group to the incident beam can be obtained. It can be read directly from the database. The total phase required by the composite optical field shaping element 5 is... Therefore, the phase that needs to be compensated by the structural unit 531 of the diffractive optical element 53 is: , Usually Normalization to Between. Then, utilizing the linear relationship between the height and phase of the diffractive optical element 53 structural unit: , The required structural element height can be obtained by inverse solving: , in, This is the effective refractive index of the structural unit 531 of the diffractive optical element 53. Therefore, the effective refractive index of each structural unit 531 is... The value is uniquely determined.

[0085] The calculated radius of each superatom column ,high and the height of the corresponding diffractive optical element 53 structural unit The design is then converted into a standardized graphic design format. Next, metasurfaces and diffractive optical elements are fabricated on both sides of the substrate using electron beam lithography or laser direct-write lithography combined with dry etching. The final result is an integrated composite optical field shaping element 5 that perfectly matches the design.

[0086] The prepared composite optical field shaping element 5 is installed in the aforementioned ultrafast laser processing device, and an ultrafast laser of a preset wavelength is incident. The surface of the workpiece 6 is placed at its back focal length. At this point, precise target pattern structured light can be obtained in a single exposure, completing the processing.

[0087] Traditional pure phase methods rely on iterative algorithms to infer the phase, which inevitably produces phase singularities, leading to speckle in the reconstructed optical field. This application directly calculates the complex amplitude distribution of the object plane based on the target optical field, eliminating the need for pure phase iterative algorithms and avoiding the generation of phase singularities, thereby reducing speckle crosstalk.

[0088] Grayscale lithography requires different exposure doses at different locations. Traditional methods require multiple exposures, mask repositioning, or point-by-point scanning using deformable mirrors, resulting in low efficiency. This application directly provides the energy distribution corresponding to different grayscale levels through amplitude modulation, which can be completed in a single exposure, significantly reducing processing time.

[0089] For any parts not mentioned in this invention, existing technologies can be used or referenced.

[0090] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0091] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A composite optical field shaping element based on complex amplitude modulation, characterized in that, include: Base; A metasurface and a diffractive optical element are formed on the substrate, the metasurface and the diffractive optical element are respectively located on both sides of the substrate, the metasurface is used to receive the incident light beam and includes multiple superatomic pillars, and the diffractive optical element includes multiple structural units; The superatomic pillars are arranged in a one-to-one correspondence with the structural units to form a unit group, which is used to perform complex amplitude control on the incident beam. The radius and height of the superatomic pillars are set according to the energy distribution of the target pattern structured light, and are used to control the amplitude and phase of the incident beam. The height of the structural unit of the diffractive optical element is set according to the energy distribution of the target pattern structured light, and is used to perform phase compensation on the beams controlled by the superatomic pillars in the same unit group.

2. The composite optical field shaping element based on complex amplitude modulation as described in claim 1, characterized in that, Each of the said unit groups is paired with the incident beam After complex amplitude modulation, the resulting optical field is: ， in, This indicates a unit group with amplitude regulation capability; The radius of the superatomic column; The height of the superatomic column; The height of the structural unit; For arbitrary polarized incident beams; To determine the transmittance of the composite optical field shaping element, by changing... To regulate; Represents the imaginary unit; The phase delay of the composite optical field shaping element. ,in To control the phase of the incident beam using the superatomic pillars, by... Adjust the settings accordingly. To compensate for the phase of the beam through the structural unit, by changing... To implement regulation.

3. The composite optical field shaping element based on complex amplitude modulation according to claim 2, characterized in that, The phase modulation of the incident beam by the superatomic column is specifically as follows: The effective refractive index of the metasurface can be controlled by adjusting the radius of the superatomic pillars. By combining the wavelength of the incident beam with the height of the superatomic column, the phase of the incident beam can be modulated. ， in, To adjust the phase of the incident beam, The wavelength of the incident beam is 1. The effective refractive index of the superatomic column is controlled by adjusting the radius of the superatomic column. The height of the superatomic column.

4. The composite optical field shaping element based on complex amplitude modulation as described in claim 2, characterized in that, The modulation of the incident beam amplitude by the superatomic column is specifically as follows: By adjusting the height and radius of the superatomic pillars, the resonant detuning is controlled to regulate the transmittance of the composite optical field shaping element, thereby controlling the amplitude of the incident beam.

5. The composite optical field shaping element based on complex amplitude modulation according to claim 2, characterized in that, The phase compensation of the beam after modulation by the diffractive optical element for the corresponding superatomic column in the same unit group is specifically as follows: ， in, The phase used to compensate for the beam. The wavelength of the incident beam is 1. The effective refractive index of the diffractive optical element is... The height of the structural unit of the diffractive optical element.

6. The composite optical field shaping element based on complex amplitude modulation according to claim 2, characterized in that, The transmittance range of the composite light field shaping element is 0 to 1. The phase compensation range achieved by adjusting the diffractive optical element is 0-2. .

7. The composite optical field shaping element based on complex amplitude modulation according to claim 1, characterized in that, The substrate is a structure made of fused silica. The superatomic pillars are structures made of anisotropic dielectric materials, with periodicity. The amplitude and phase of the incident beam can be controlled by changing the radius and height of the superatomic column.

8. An ultrafast laser processing device, characterized in that, include: Ultrafast laser source, used to emit laser beams; Beam expanders are used to increase the size of laser beams. A polarization control component is used to adjust the polarization state of a laser beam. The ultrafast laser source, the beam expander, and the polarization control component are arranged coaxially along the incident light path. Beam splitters are used to change the incident direction of laser beams; The composite light field shaping element according to any one of claims 1 to 7; A displacement stage for carrying a workpiece, wherein the composite optical field shaping element and the displacement stage are coaxially arranged along the imaging optical path; The laser beam emitted from the ultrafast laser source passes sequentially through the beam expander, the polarization control component, and the beam splitter along the incident optical path. After the beam splitter changes its direction, it is incident on the composite optical field shaping element along the imaging optical path. After being modulated by the composite optical field shaping element, it forms a patterned structured light on the workpiece surface.

9. The ultrafast laser processing apparatus according to claim 8, characterized in that, Also includes: Dichroic mirrors are used to filter out interfering light. Tube lens; The near-infrared camera, the displacement stage, the composite light field shaping element, the beam splitter, the dichroic mirror, the tube lens, and the near-infrared camera are coaxially arranged along the imaging optical path so that the light beam reflected from the workpiece surface passes through the composite light field shaping element, the beam splitter, the dichroic mirror, and the tube lens before entering the near-infrared camera for imaging.

10. An ultrafast laser processing method, characterized in that, For controlling the composite optical field shaping element according to any one of claims 1 to 7, comprising: Determine the energy distribution of structured light on the target pattern To obtain the complex amplitude distribution required for the composite optical field shaping element. ; ， in, The amplitude to be controlled for the composite optical field shaping element; The phase that needs to be controlled for the composite optical field shaping element. ,in For the modulation of the phase of metasurface, To compensate for the phase of diffractive optical elements; Indicates focal length; , indicating the point of the composite light field shaping element To pattern structured light spot The distance; Represents the imaginary unit; The wavelength of the incident beam; For wave vector, ; According to the required amplitude adjustment The transmittance of the composite optical field shaping element was determined through normalization. To determine the radius of the superatomic column. and height ; Based on the radius of the superatom column and height The phase modulation of the incident beam by the metasurface is obtained. The phase to be regulated by the composite optical field shaping element The compensated phase of the diffractive optical element is obtained. To determine the structural unit height H of the diffractive optical element.

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