A system and method for controlling a femtosecond laser flattop beam

Abstract

The application relates to a femtosecond laser flat-top beam regulation system and method applied to the technical field of laser beam shaping, which comprises a femtosecond laser source, a beam expander, a light splitting module, a first and a second spatial light modulator (SLM), a light combining module, a real-time monitoring feedback module and a control unit. The core lies in that the basic flat-top beam generation and the high-speed dynamic modulation task are separated through the double-path parallel architecture of 'first SLM static shaping and second SLM dynamic compensation'. The control unit is configured to execute two kinds of intelligently cooperative working modes: a contour tracking mode to switch a pre-generated phase map sequence at a rate not lower than 1 kHz, so that the beam contour matches the special-shaped track in real time; and an online correction mode to generate a compensation phase map based on real-time feedback to correct spot distortion such as thermal lens effect. The application solves the problem that a single SLM system cannot simultaneously consider high-speed dynamic shaping and real-time anti-interference, and realizes the application of the femtosecond laser flat-top beam in high-end dynamic precision machining.

Description

Technical Field

[0001] This invention relates to the field of laser beam shaping technology, and more specifically, to a system and method for controlling a femtosecond laser flat-top beam. Background Technology

[0002] Flat-top laser beams (or homogenized beams) are widely used in laser processing, photolithography, and other fields due to their uniform energy distribution on the focal plane. Femtosecond lasers, with their ultrashort pulse widths and high peak power, offer significant advantages in precision cold processing. Combining these two technologies is an important direction for achieving high-quality processing results.

[0003] Currently, phase modulation methods based on spatial light modulators (SLMs) are one of the mainstream techniques for achieving flexible beam shaping. A typical approach involves using a single SLM, loading a static phase map calculated using algorithms such as Iterative Fourier Transform (GS) or Yang-Gu's algorithm, to shape a Gaussian beam into a flat-top beam in one step.

[0004] However, in applications involving femtosecond laser dynamic processing (such as 3D micro-carving, irregular contour cutting, and high-speed scanning), the aforementioned existing technologies have fundamental limitations: the system aims to generate a statically optimal flat-top beam. When processing requirements necessitate real-time changes in the beam profile along the motion trajectory, or require switching the beam shape at extremely high frequencies (e.g., above kHz), the single SLM system struggles to achieve truly high-speed dynamic shaping due to limitations in the SLM's refresh rate (typically 60-120Hz) and the computational time required for complex phase diagrams. This becomes a significant bottleneck restricting the application of femtosecond laser flat-top beam technology to high-end dynamic processing. Summary of the Invention

[0005] To address the prominent problem that existing femtosecond laser flat-top beam shaping technology is unable to meet the demands of high-speed dynamic processing, in the first aspect, this invention provides a femtosecond laser flat-top beam control system, comprising: a femtosecond laser source, a laser beam expander, a beam splitter, a first spatial light modulator, a second spatial light modulator, a beam combining module, a real-time monitoring and feedback module, and a control unit;

[0006] The beam splitter is used to split the expanded laser beam into a first beam and a second beam.

[0007] A first spatial light modulator is placed in the optical path of the first beam to load and maintain a static flat-top shaping phase diagram to form a basic flat-top beam.

[0008] The second spatial light modulator is set in the optical path of the second beam and is used to load a refreshable dynamic compensation phase map according to real-time control commands.

[0009] The beam combining module is used to combine two modulated beams into a single output.

[0010] The real-time monitoring and feedback module is used to collect the spot information of the output flat-top beam in real time;

[0011] The control unit is communicatively connected to the first spatial light modulator, the second spatial light modulator, and the real-time monitoring feedback module, respectively.

[0012] The control unit is configured to perform closed-loop dynamic control and is capable of operating in the following modes based on the processing status:

[0013] Contour tracking mode: In this mode, the control unit pre-generates a sequence of multiple dynamically compensated phase maps that are synchronized with the trajectory of the irregular contour of the workpiece, and switches the load to the second spatial light modulator at a rate of not less than 1 kHz, so that the contour of the flat-top beam matches the trajectory in real time.

[0014] Online correction mode: In this mode, the control unit matches the sampling frequency of the real-time monitoring feedback module with the refresh rate of the second spatial light modulator, and generates a dynamic compensation phase map based on the feedback control algorithm to compensate for the spot distortion caused by the transient thermal lensing effect caused by the interaction between the femtosecond laser and the material.

[0015] The control unit is also configured to automatically invoke or overlay an online correction mode for real-time compensation during contour tracking mode operation, based on spot information from the real-time monitoring feedback module indicating that the spot quality deviates from the preset target.

[0016] Furthermore, in contour tracking mode, the control unit is also configured to receive future trajectory segment information synchronized with the real-time position of the processing head from an external motion control system, and to preload the corresponding dynamic compensation phase map to the second spatial light modulator based on the information.

[0017] Furthermore, the control unit is also configured to: load a set of preset test phase maps onto the second spatial light modulator before the system starts processing or during the processing interval, and perform online self-calibration of the initial parameters of the static flat-top shaping phase map or the dynamic compensation algorithm based on the response results of the real-time monitoring feedback module.

[0018] Furthermore, the control unit is also configured to: when generating the dynamic compensation phase map, integrate the real-time monitoring value of the output pulse energy of the femtosecond laser source, and perform feedforward compensation on the dynamic compensation phase map.

[0019] Furthermore, in the online correction mode, the feedback control algorithm is an iterative learning control algorithm, which uses the periodic processing on the same processing trajectory to iteratively optimize the compensation amount of the thermal lensing effect.

[0020] Furthermore, the beam splitting module and the beam combining module are implemented by the same polarization beam splitting prism group, and a quarter-wave plate is provided in the optical path; the real-time monitoring feedback module includes a CCD camera, which collects and monitors the light spot through the beam splitter set in the output optical path of the beam combining module.

[0021] Furthermore, the static flat-top shaped phase diagram is generated using the Yang-Gu algorithm and optimized for the center wavelength and spectral bandwidth of the femtosecond laser.

[0022] The control unit is pre-set with target parameters characterizing an ideal flat-top beam, including the target energy distribution matrix of the beam, the target shape profile, and the allowable uniformity deviation threshold. The real-time monitoring and feedback module transmits the acquired beam image to the control unit. The control unit uses image processing algorithms to extract the actual energy distribution, shape profile, and size of the current beam in real time and compares them item by item with the target parameters. When the deviation of any characteristic parameter exceeds its corresponding threshold, the control unit determines that "the beam quality deviates from the preset target."

[0023] During contour tracking mode operation, if the aforementioned deviation occurs, the control unit does not interrupt contour tracking but immediately initiates the online correction mode calculation thread in parallel. This thread, based on the real-time monitored spot distortion characteristics, utilizes a built-in thermal lensing effect-phase compensation model to quickly calculate a compensation phase map to correct the distortion. Subsequently, the control unit performs complex superposition of this compensation phase map with the dynamic compensation phase map of the current frame in contour tracking mode to generate the final composite dynamic compensation phase map, which is then sent to the second spatial light modulator for loading. This process ensures that compensation for dynamic interference takes effect synchronously and seamlessly with the preset contour tracking.

[0024] Secondly, the present invention provides a method for controlling a femtosecond laser flat-top beam applied to the above-mentioned control system, comprising the following steps:

[0025] S10, Static initialization: Load and maintain a static flat-top shaping phase diagram on the first spatial light modulator to form a basic flat-top beam;

[0026] S20, Closed-loop dynamic control: During laser processing, based on the deviation between the real-time monitored spot information and the preset target parameters, a dynamic compensation phase map is generated and loaded into the second spatial light modulator to control the basic flat-top beam;

[0027] The S20 closed-loop dynamic control includes the following operating modes based on processing status calls or switches:

[0028] S21. Execute contour tracking mode: Based on the irregular contour trajectory of the workpiece, pre-generate a dynamic compensation phase map sequence and switch the loading at a rate of not less than 1kHz to make the flat-top beam contour match the trajectory in real time.

[0029] S22. Execute online correction mode: By matching the monitoring sampling and phase map refresh frequency, and based on the feedback control algorithm, a dynamic compensation phase map is generated to compensate for the transient thermal lensing effect;

[0030] During the operation of the S21 contour tracking mode, the S22 online correction mode is automatically invoked or superimposed for real-time compensation based on the spot information that indicates that the spot quality deviates from the preset target, as monitored in real time.

[0031] Furthermore, in the S21 contour tracking mode, the method also includes: receiving future trajectory segment information synchronized with the real-time position of the processing head, and preloading the corresponding dynamic compensation phase map in a forward-looking manner based on the information.

[0032] Furthermore, the method also includes an online self-calibration step: before the static initialization of S10 or during the interval of the closed-loop dynamic control of S20, a set of preset test phase diagrams are loaded into the second spatial light modulator, and the initial parameters of the static flat-top shaping phase diagram or the dynamic compensation algorithm are calibrated according to the monitoring response results.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention employs a dual-parallel architecture of "first SLM static shaping and second SLM dynamic compensation," physically separating the computationally complex basic flat-top shaping task from the dynamic compensation task requiring rapid response. This allows the system to independently modulate the beam shape or wavefront in real time at a high refresh rate of no less than 1kHz while maintaining a high-precision basic flat-top beam. This solves the bottleneck problem of existing single SLM systems being unable to be applied to high-speed dynamic processing due to refresh rate and computational latency, enabling femtosecond laser flat-top beams to be effectively applied to dynamic scenarios such as high-speed scanning and irregular contour processing.

[0035] 2. The two core operating modes of contour tracking and online correction in the system of this invention are not simply parallel, but organically integrated through an intelligent collaborative mechanism based on real-time feedback. This enables the system not only to actively track preset complex processing trajectories, but also to perceive and compensate for dynamic aberrations caused by thermal lensing effects and other factors in real time during processing. It elevates the open-loop controlled flat-top beam system into a control system capable of closed-loop correction of dynamic aberrations based on real-time feedback, significantly improving process stability and consistency of processing results under harsh conditions such as deep etching and high-repetition-rate processing.

[0036] 3. A multi-level, high-precision closed-loop control system was constructed, expanding the system's capability boundaries. Based on the aforementioned core dynamic control capabilities, this invention introduces a series of optimization modules to build a more complete system ecosystem:

[0037] The forward-looking preloading overcomes the delay in the control system and ensures precise synchronization of ultra-high-speed contour tracking;

[0038] The online self-calibration function can automatically correct the system's static error and SLM drift during processing intervals, ensuring the system's basic accuracy and reliability during long-term operation;

[0039] Energy feedforward compensation, through the integration of laser energy monitoring, achieves advance suppression of major known disturbances;

[0040] Iterative learning optimization is designed for repetitive processing tasks, and can automatically accumulate experience and improve compensation accuracy and efficiency.

[0041] These modules work together to enable the system to achieve higher standards in terms of dynamic response capability, long-term stability, and final machining accuracy.

[0042] 4. The dynamic flat-top beam control capability achieved by this invention directly targets the urgent needs of femtosecond lasers in high-end precision manufacturing fields such as OLED irregular shape cutting, glass micro-nano 3D engraving, and high-performance medical device processing. It provides these industries with a reliable tool to break through the existing bottlenecks in processing efficiency and precision, and has important industrialization and promotion value. Attached Figure Description

[0043] Figure 1 This is a structural block diagram of the femtosecond laser flat-top beam control system in the first embodiment of the present invention;

[0044] Figure 2 This is a schematic flowchart of the femtosecond laser flat-top beam control method in the second embodiment of the present invention. Detailed Implementation

[0045] The following detailed description of two embodiments of the present invention is provided in conjunction with the accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0046] First implementation method:

[0047] Figure 1 A femtosecond laser flat-top beam control system is shown, comprising a femtosecond laser source, a laser beam expander, a beam splitter, a first spatial light modulator, a second spatial light modulator, a beam combiner, and a real-time monitoring and feedback module arranged sequentially along the optical path. The entire system is coordinated and controlled by a control unit.

[0048] The pulsed laser emitted from the femtosecond laser source is collimated and expanded by a beam expander, and then split into a first beam and a second beam with orthogonal polarization by a beam splitter. The first beam is incident on a first spatial light modulator, which loads and maintains a static flat-top shaped phase diagram according to instructions from the control unit. This phase diagram is generated by optimizing the center wavelength (e.g., 1030 nm) and spectral bandwidth (e.g., ±10 nm) of the femtosecond laser using the Yang-Gu algorithm. Its function is to ensure that the reflected first beam forms a basic flat-top beam with uniform energy distribution on the target plane (e.g., energy fluctuation in the top uniform region is better than ±5%).

[0049] The second beam, after passing through a quarter-wave plate, is incident on the second spatial light modulator. The core function of the second spatial light modulator is to load and rapidly refresh the dynamic compensation phase map according to real-time instructions from the control unit. The second beam, loaded with the dynamic compensation phase map, returns along the same path, and after passing through the quarter-wave plate again, its polarization state rotates by 90°, becoming the same as the first beam. At this point, the beam combining module efficiently combines the two beams, outputting the final controlled beam to the processing head. The beam splitting module and the beam combining module can be implemented using the same polarization beam splitter prism group. The real-time monitoring feedback module typically includes a CCD or CMOS camera, an image acquisition card, and a processing unit. It acquires a portion of the output beam for analysis through a beam splitter located in the optical path after the beam combining module.

[0050] The key concept of this invention lies in separating the computationally complex, non-frequently changing basic flat-top shaping task from the high-speed, dynamically changing compensation modulation task through the parallel configuration of dual spatial light modulators, on the physical optical path. This fundamentally overcomes the response speed bottleneck of single spatial light modulator systems in dynamic scenes caused by refresh rate (typically 60-120Hz) and computational resource limitations.

[0051] The control unit is the core of the entire system. The real-time monitoring and feedback module acquires light spot images from the final output optical path and calculates light spot information in real time (such as energy distribution matrix, centroid position, second moment size, low-order Zernike aberration coefficients obtained through mode fitting algorithm, etc.), and feeds it back to the control unit.

[0052] The control unit is configured to perform closed-loop dynamic control and can operate in the following two core working modes based on the processing status:

[0053] Contour Tracking Mode: This mode is enabled when the machining task involves high-speed cutting of irregular contours (such as the contour of a curved mobile phone screen). The trajectory analysis module of the control unit pre-discretes the machining trajectory in the CAD drawing into a dense sequence of points (e.g., point spacing of 1μm). For each point on the trajectory, a dynamic compensation phase map is generated based on rapid calculations using geometric optics principles or scalar diffraction theory, aligning the center of the flat-top beam with that point and matching the beam contour direction with the tangent direction of the trajectory. All these phase maps are arranged in a pre-generated sequence according to the machining order. During machining, the synchronous control module receives real-time position signals from the external motion control system and, at a rate of not less than 1kHz (e.g., 1.2kHz), accurately retrieves the corresponding phase map from the sequence and loads it onto the second spatial light modulator, enabling the output flat-top beam contour to match the motion trajectory in real time.

[0054] Online Correction Mode: This mode is specifically designed to combat dynamic aberrations generated during processing, most typically the transient thermal lensing effect caused by changes in refractive index due to localized thermal expansion of the material. In this mode, the aberration analysis module of the control unit analyzes the distortion characteristics of the feedback spot at a frequency matching the refresh rate of the second spatial light modulator (e.g., assessing defocus by calculating changes in the second moment size of the spot, or assessing astigmatism by ellipticity). Subsequently, a dynamic compensation phase map capable of compensating for this distortion is calculated based on the feedback control algorithm and applied.

[0055] As an example, a simplified feedback control algorithm is implemented as follows: Let the monitored change in the spot radius be the error. The controller uses a proportional-integral (PI) control law, and its output is the defocus phase amount that needs to be compensated. :

[0056] ;

[0057] Among them, the proportionality coefficient and integral coefficient This phase quantity can be determined through system calibration experiments. It is converted into the corresponding Zernike defocus term polynomial and a corresponding dynamic compensation phase map is generated.

[0058] Implementation of the collaborative mechanism:

[0059] The key advantage of this invention lies in the intelligent coordination of the two modes described above. The control unit is pre-set with target parameters characterizing an ideal flat-top beam, including the target energy distribution matrix of the beam spot, the target shape profile (e.g., circular, square), and an allowable uniformity deviation threshold (e.g., an energy uniformity threshold set to 90%). During contour tracking mode operation, the control unit continuously compares the real-time extracted actual parameters of the current beam spot with the target parameters. When the deviation of any characteristic parameter exceeds its corresponding threshold (e.g., the calculated circumferential energy uniformity decreases from the initial 95% to 88%, below the preset 90% threshold), the control unit determines that "the beam spot quality deviates from the preset target."

[0060] At this point, the system does not interrupt contour tracking. The control unit immediately starts the calculation thread for online correction mode in parallel. Based on the real-time monitored spot distortion characteristics, this thread uses the built-in thermal lensing effect-phase compensation model to quickly calculate the compensation phase map used to correct the distortion.

[0061] As a concrete example of this model, it can be simplified into a linear response model. Assume the monitored spot radius expansion is... Equivalent defocusing amount introduced by thermal lens Proportional, that is:

[0062] ;

[0063] in This is the scaling factor obtained through prior system calibration. To compensate for this defocus, a second spatial light modulator is needed to apply a wavefront conjugate to it, with a compensating phase distribution. It can be represented as:

[0064] ;

[0065] in The wavelength is the laser wavelength. The control unit performs rapid calculations based on this model.

[0066] Subsequently, the control unit performs a crucial "complex superposition" operation: this operation involves algebraically adding the phase values ​​of corresponding pixels of the compensated phase map matrix calculated in the online correction mode to the dynamic compensated phase map matrix currently required in the contour tracking mode, generating a composite dynamic compensated phase map, which is then sent to the second spatial light modulator for loading. This process achieves "tracking and correction simultaneously," ensuring that contour tracking accuracy and spot quality remain stable throughout the entire high-speed dynamic processing.

[0067] The specific implementation of the optimized functional modules:

[0068] To achieve higher accuracy and robustness, the control unit also integrates the following optimization modules:

[0069] Forward-looking preloading module: To overcome system control delay, this module receives "future trajectory segment information" (e.g., trajectory points in the next 2ms) provided by the motion control system. For example, when the processing head moves to point A, the module has already predicted that it will go to points B and C, and retrieves the dynamic compensation phase map corresponding to points B and C from the pre-generated sequence in advance, loading it into the image buffer of the second spatial light modulator to achieve near-zero delay switching.

[0070] Online self-calibration module: Before the start of daily processing or during long-term operation intervals, the system performs a self-calibration process. The control unit controls the second spatial light modulator to sequentially load a set of known test phase maps covering the entire modulation range (such as Zernike aberration modes such as tilt, defocus, and astigmatism), and records the actual spot shifts or shape changes generated through the monitoring feedback module.

[0071] The specific calibration and correction process can be briefly described as follows: Let $N$ types of test phase maps be loaded to form a matrix. The monitored changes in the corresponding light spot features form a matrix. The system response matrix is ​​fitted using a system identification algorithm (such as the least squares method). , making Then, calculations were performed. generalized inverse For the initial static error that needs to be corrected (Measured without any compensated phase map), can be calculated A corrected phase map is obtained. This corrected phase map can be directly superimposed on the static phase map of the first spatial light modulator, or used to correct the initial parameters of the compensation model in the online correction algorithm.

[0072] Energy feedforward compensation module: The system receives a real-time monitoring signal of the output pulse energy of the femtosecond laser source. This module incorporates an experimentally calibrated empirical mapping relationship between energy and thermal effects. For example, the following relationship was experimentally established on a specific material: [The module compensates for the preset defocusing amount in the phase diagram.] Proportional to energy deviation:

[0073] ;

[0074] in The coefficients obtained through linear regression (unit: ), This is the standard processing energy. When fluctuations in the laser pulse energy are detected, the module proactively predicts changes in the intensity of the thermal lensing effect based on this mapping relationship, and directly superimposes the corresponding feedforward compensation amount onto the dynamically compensated phase diagram generated by the online correction mode.

[0075] Iterative learning control module: For repetitive processes performed on the same trajectory (such as batch micro-perforation), this algorithm is applied in online correction mode. During the initial processing, the system records each processing position. The corresponding optimal compensation phase diagram calculated by the online correction mode. After processing is complete, the iterative learning controller is updated according to the following rules:

[0076] ;

[0077] in, For the first The second processing is in the first Point residual aberration feedback signals (such as spot distortion variables). For learning gain ( After several iterations, It will converge to an optimal value, which can be directly called in subsequent repeated processing to improve consistency and efficiency.

[0078] The second implementation method: a method for controlling the flat-top beam of a femtosecond laser.

[0079] Figure 2 A method for controlling a femtosecond laser flat-top beam applied to the above system is shown, comprising the following steps:

[0080] S10, Static Initialization: Load and maintain the static flat-top shaped phase map generated by the Yang-Gu algorithm on the first spatial light modulator to form the basic flat-top beam.

[0081] S20. Closed-loop dynamic control: During laser processing, based on the deviation between the real-time monitored spot information and the preset target parameters, a dynamic compensation phase map is generated and loaded into the second spatial light modulator to control the basic flat-top beam. This core step includes the following collaborative working modes:

[0082] S21. Execute contour tracking mode: Based on the irregular contour trajectory of the workpiece, pre-generate a sequence consisting of multiple dynamic compensation phase maps, and switch the loading at a rate of not less than 1kHz to make the flat-top beam contour match the trajectory in real time.

[0083] S22. Execute online correction mode: By matching the monitoring sampling and phase map refresh frequency, and based on the feedback control algorithm, a dynamic compensation phase map is generated to compensate for transient thermal lensing effects.

[0084] During the operation of S21 mode, the actual parameters of the light spot are continuously compared with the preset target parameters (such as energy uniformity). When the deviation exceeds the threshold, S22 mode is automatically triggered, and the phase value of the corresponding pixel is added to the phase map of S21 mode to generate a composite phase map for loading, thereby achieving synchronous tracking and correction.

[0085] The method may also include the following optimization steps:

[0086] In S21 mode, the system receives future trajectory segment information synchronized with the real-time position of the processing head, and preloads the corresponding phase map from the pre-generated sequence based on this information.

[0087] Before step S10 or during the processing interval of step S20, an online self-calibration step is performed: a set of preset test phase diagrams are loaded into the second spatial light modulator, the system transfer function is calibrated in reverse according to the monitoring response results, and the initial parameters of the static flat-top shaping phase diagram or dynamic compensation algorithm are calibrated accordingly.

[0088] Example 1:

[0089] To illustrate the effectiveness of the system of the present invention, the following embodiments are provided. The specific parameters used in these embodiments are for illustrative purposes only and should not be construed as limiting the present invention.

[0090] Using the control system of this invention, a piece of silicon glass with a thickness of 0.7 mm is cut into an irregular contour (including a complex curve with a line width of 10 μm and a radius of curvature of 50 μm).

[0091] System parameters: Femtosecond laser source center wavelength 1030nm, repetition rate 200kHz, single pulse energy 25μJ. The first SLM is a 1920x1152 pixel reflective phase-type SLM, and the loaded static phase map is optimized for these parameters. The second SLM is a 512x512 pixel high-speed pure phase-type SLM, with a refresh rate set to 1.2kHz. The real-time monitoring feedback module is a high-speed CMOS camera, with the sampling frame rate synchronized with the SLM refresh rate. The preset target uniformity threshold in the control unit is 90%.

[0092] Comparison object: A comparison system that uses only a single (same as the first SLM model) SLM to run a static flat-top shaping phase map and is unable to perform kHz-level dynamic phase map refresh.

[0093] Process and Results:

[0094] Contour tracking fidelity: In the contour tracking mode of the system of this invention, a sequence containing 10,000 frames of dynamically compensated phase maps is pre-generated. During processing, the control unit switches the phase maps at a rate of 1.2 kHz. Based on the system architecture and control principle of this invention, theoretical calculations predict that when scanning along a complex curve at a speed of 500 mm / s, a contour tracking error of less than ±0.5 μm can be achieved. In contrast, the comparative system, limited by its SLM's global refresh rate of 60 Hz, will have a significantly increased theoretical tracking error under the same conditions.

[0095] Thermal effect suppression capability: After 3 minutes of continuous processing, the system of this invention triggers online correction mode when the energy uniformity drops to 88% (below the 90% threshold). Based on the aforementioned simplified thermal lens-phase compensation model, the system can suppress the longitudinal drift of the spot focus caused by thermal accumulation within ±1.5μm and control the fluctuation of the spot diameter within ±2%. In contrast, for the comparative system, based on the same thermal model, under open-loop processing, the focus drift may exceed 25μm and the spot diameter expansion may exceed 20%.

[0096] Collaborative processing effect: At sharp corners of irregular contours (where laser dwell time is slightly longer and local heat accumulation is likely to occur), the system automatically superimposes online corrections. Based on comprehensive simulation results, this collaborative mechanism predicts that the taper of the processed sidewall in this feature area can be improved from approximately 5° under traditional open-loop processing to approximately 3°, and the depth of the heat-affected zone can be reduced from approximately 2μm to approximately 1μm, thereby achieving a more uniform processing quality across the entire irregular contour.

[0097] It should be noted that the above implementation methods and embodiments are merely preferred examples of the present invention, used to illustrate the principles and core advantages of the present invention. Based on the core concept of the present invention—"dynamic closed loop and pattern collaboration under dual SLM division of labor"—various adaptive changes and improvements made by those skilled in the art within the described system architecture, method principle, and algorithm framework should be included within the protection scope of the present invention.

Claims

1. A control system for a femtosecond laser flat-top beam, characterized in that, include: Femtosecond laser source, laser beam expander, beam splitter, first spatial light modulator, second spatial light modulator, beam combiner, real-time monitoring and feedback module and control unit; The beam splitting module is used to split the expanded laser beam into a first beam and a second beam. The first spatial light modulator is disposed in the optical path of the first beam to load and maintain a static flat-top shaping phase diagram to form a basic flat-top beam; The second spatial light modulator is disposed on the optical path of the second beam and is used to load a refreshable dynamic compensation phase map according to real-time control commands; The beam combining module is used to combine two modulated beams into a common beam for output. The real-time monitoring and feedback module is used to collect the spot information of the output flat-top beam in real time. The control unit is communicatively connected to the first spatial light modulator, the second spatial light modulator, and the real-time monitoring feedback module, respectively. The control unit is configured to perform closed-loop dynamic control and is capable of operating the following modes based on the processing status: Contour tracking mode: In this mode, the control unit pre-generates a sequence of multiple dynamically compensated phase maps that are synchronized with the trajectory of the irregular contour of the workpiece, and switches the load to the second spatial light modulator at a frequency of not less than 1 kHz, so that the flat-top beam contour matches the trajectory in real time. Online correction mode: In this mode, the control unit matches the sampling frequency of the real-time monitoring feedback module with the refresh rate of the second spatial light modulator, and generates a dynamic compensation phase map based on the feedback control algorithm to compensate for the spot distortion caused by the transient thermal lensing effect caused by the interaction between the femtosecond laser and the material. The control unit is also configured to: during the operation of the contour tracking mode, automatically invoke or superimpose the online correction mode for real-time compensation based on the spot information indicating that the spot quality deviates from the preset target fed back by the real-time monitoring feedback module; In the contour tracking mode, the control unit is also configured to: receive future trajectory segment information synchronized with the real-time position of the processing head from an external motion control system, and preload the corresponding dynamic compensation phase map to the second spatial light modulator in a forward-looking manner based on the information; The control unit is also configured to: load a set of preset test phase maps onto the second spatial light modulator before the system starts processing or during the processing interval, and perform online self-calibration of the initial parameters of the static flat-top shaping phase map or the dynamic compensation algorithm based on the response result of the real-time monitoring feedback module.

2. The femtosecond laser flat-top beam control system according to claim 1, characterized in that, The control unit is further configured to: when generating the dynamic compensation phase diagram, integrate the real-time monitoring value of the output pulse energy of the femtosecond laser source, and perform feedforward compensation on the dynamic compensation phase diagram.

3. The femtosecond laser flat-top beam control system according to claim 1, characterized in that, In the online correction mode, the feedback control algorithm is an iterative learning control algorithm that uses the periodic processing on the same processing trajectory to iteratively optimize the compensation amount for the thermal lensing effect.

4. The femtosecond laser flat-top beam control system according to claim 1, characterized in that, The beam splitting module and the beam combining module are implemented by the same polarization beam splitting prism group, and a quarter-wave plate is provided in the optical path; the real-time monitoring feedback module includes a CCD camera, which collects the monitoring light spot by means of the beam splitter set in the output optical path of the beam combining module.

5. The femtosecond laser flat-top beam control system according to claim 1, characterized in that, The static flat-top shaped phase diagram is generated using the Yang-Gu algorithm and optimized for the center wavelength and spectral bandwidth of the femtosecond laser.

6. A method for controlling a femtosecond laser flat-top beam, applied to the control system as described in any one of claims 1-5, characterized in that, Includes the following steps: S10, Static initialization: Load and maintain the static flat-top shaping phase diagram on the first spatial light modulator to form a basic flat-top beam; S20, Closed-loop dynamic control: During the laser processing, based on the deviation between the real-time monitored spot information and the preset target parameters, a dynamic compensation phase map is generated and loaded into the second spatial light modulator to control the basic flat-top beam; The S20 closed-loop dynamic control includes the following working modes based on processing status invocation or switching: S21. Execute contour tracking mode: Based on the irregular contour trajectory of the workpiece to be processed, pre-generate a dynamic compensation phase map sequence and switch the loading at a frequency of not less than 1kHz so that the flat top beam contour matches the trajectory in real time. S22. Execute online correction mode: By matching the monitoring sampling and phase map refresh frequency, and based on the feedback control algorithm, a dynamic compensation phase map is generated to compensate for the transient thermal lensing effect; During the operation of the S21 contour tracking mode, the S22 online correction mode is automatically invoked or superimposed for real-time compensation based on the spot information indicating that the spot quality deviates from the preset target, as monitored in real time.

7. The control method according to claim 6, characterized in that, In the S21 contour tracking mode, the method further includes: receiving future trajectory segment information synchronized with the real-time position of the processing head, and preloading the corresponding dynamic compensation phase map in a forward-looking manner based on the information.

8. The control method according to claim 6, characterized in that, The method further includes an online self-calibration step: before the static initialization of S10 or during the interval of the closed-loop dynamic control of S20, a set of preset test phase diagrams are loaded onto the second spatial light modulator, and the initial parameters of the static flat-top shaping phase diagram or the dynamic compensation algorithm are calibrated according to the monitoring response results.

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