Femtosecond pulse sequence customization system and method based on programmable control
By using components such as the SESAM mode-locked seed source and a high-bandwidth acousto-optic modulator, precise control of femtosecond pulse sequences was achieved, solving the problems of pulse selection and energy modulation in traditional systems and improving the flexibility and efficiency of high-precision material processing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- YUNNAN QIJING XINGUANG SEMICONDUCTOR EQUIPMENT CO LTD
- Filing Date
- 2026-02-06
- Publication Date
- 2026-05-15
AI Technical Summary
Traditional femtosecond laser pulse systems have difficulty in independently selecting or modulating the energy of individual pulses, which limits the flexibility and efficiency of high-precision material processing.
By employing a SESAM mode-locked seed source, a pulse sequence modulator, a MOPA power amplifier, and an RF drive module, combined with passive mode-locking, seed pulse selection, and time modulation, arbitrary combinations of 1 to 3000 pulses and optimized pulse energy distribution are achieved. Precise control is achieved through a high-bandwidth acousto-optic modulator and a diffraction grating.
It achieves precise control of energy within femtosecond pulse sequences, supports multiple energy distribution modes, improves the flexibility and accuracy of material processing, and controls timing jitter at the sub-picosecond level.
Smart Images
Figure CN122051772A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of femtosecond laser pulse processing technology, specifically relating to a femtosecond pulse sequence customization system and method based on programmable control. Background Technology
[0002] The energy injection time of a femtosecond laser pulse is much shorter than the energy transfer time between electrons and the crystal lattice in a material, causing the material to ionize or sublimate rapidly after absorbing energy. The heat does not have time to diffuse to the surrounding area, making it suitable for processing heat-sensitive materials such as polymers, biological tissues, and brittle materials, or for high-precision applications such as medical stents and micro-optical components.
[0003] Traditional femtosecond laser output is usually a continuous pulse sequence with a fixed repetition frequency or a pulse sequence with a fixed mode (such as burst mode). Among them, femtosecond laser pulse sequences with a repetition frequency of GHz (pulse interval less than 1 ns) are of great value in special processing fields such as high-efficiency material removal and nonlinear optical excitation.
[0004] Traditional femtosecond laser pulse optical systems, in single-pulse or fixed-sequence modes, are limited by the response time of electronic modulators (e.g., Acousto-Optic Modulator, AOM) (typically greater than 10 ns), making it difficult to independently select or modulate the energy of individual pulses. Therefore, this invention provides a femtosecond pulse sequence customization system and method based on programmable control. Summary of the Invention
[0005] The purpose of this invention is to provide a femtosecond pulse sequence customization system and method based on programmable control, which can combine passive mode-locking with precise selection of seed pulses and time modulation to achieve any combination of 1 to 3000 pulses, and with the pulse energy distribution optimization algorithm, achieve precise control of energy within the pulse sequence.
[0006] The specific technical solution adopted by this invention is as follows: A femtosecond pulse sequence customization system based on programmable control includes: SESAM mode-locked seed source, used to generate seed pulses; A pulse sequence modulator, connected to the SESAM mode-locked seed source, is configured to receive user-defined pulse sequence parameters and modulate the seed pulses into a customized pulse sequence with a preset number of pulses, pulse interval, and pulse energy envelope based on the parameters. The MOPA power amplifier is used to amplify the custom pulse sequence. The radio frequency driver module is used to generate nanosecond-level precise delay signals and uses a reference clock for system-wide timing synchronization, thereby ensuring the stability of the pulse sequence. A beam shaping and output module is used for collimation and focusing of the customized pulse sequence.
[0007] As an optional solution, the SESAM mode-locking seed source is based on a semiconductor saturable absorber mirror to achieve passive mode-locking, including the following steps: Phase 1: Self-starting seed formation: The SESAM structure absorbs and saturates a portion of the pulses within the laser cavity, allowing these pulses to pass through preferentially and be amplified by the gain medium, while the remaining pulses are absorbed and suppressed. This process is repeated to form an initial mode-locked seed pulse with concentrated energy. Phase Two: Seed Pulse Amplification and Q-Switching Mode Locking The initial mode-locked seed pulse is linearly amplified by the gain medium during the loop in the laser cavity. Its energy is continuously enhanced and is simultaneously affected by the interband and intraband effects of the SESAM structure, which manifests as Q-switching mode-locking. The pulse energy fluctuation causes the absorption characteristics of the SESAM structure to be dynamically adjusted, further screening and stabilizing the pulse sequence. Phase 3, Stabilizing Femtosecond Mode-Locked Output: When the pulse energy reaches a set level, the SESAM structure absorbs saturation. Due to the combined effect of the nonlinear amplification of the SESAM structure and the gain medium, the pulse is compressed and shaped, ultimately forming a stable femtosecond-level mode-locked pulse output.
[0008] As an alternative, the pulse sequence modulator is based on a high-bandwidth acousto-optic modulator to achieve pulse pickup and gating with a response time of less than 10ns. By driving an AWG through an FPGA, the pulse interval of 25 to 100ns can be continuously adjusted, enabling any combination of 1 to 3000 pulses.
[0009] As an optional solution, the pulse sequence modulator includes a diffraction grating, the specific structure of which is as follows: Lens L1 is used to collimate the pulse sequence output by the high-bandwidth acousto-optic modulator into parallel light; A grating G is disposed on the rear focal plane of the lens L1 to unfold the pulse time-domain information into a spatial spectrum. Lens L2 is disposed on the side of the grating G away from lens L1, and is used to image the spatial spectrum onto an adjustable aperture or spatial light modulator.
[0010] As an optional feature, the pulse sequence modulator is configured with a pulse energy distribution optimization algorithm, which includes the following three energy distribution modes: Flat pulse envelope: Each pulse maintains a consistent energy for uniform material removal; Increasing pulse envelope: Energy increases pulse by pulse, used for multi-level deep machining; Decreasing pulse envelope: Energy decreases pulse by pulse, used for precision surface finishing.
[0011] As an optional approach, the pulse energy distribution optimization algorithm specifically includes the following steps: Step 1: Receive user input and process parameters: Input the process target selection, pulse sequence parameters, and overall energy parameters; select a predefined envelope or a custom envelope; and set the total number of pulses. Pulse interval Total energy Energy dynamic range Output structured process requests; Step 2: Calculate the energy distribution coefficient vector in two cases: First case: Select a predefined envelope; for flat pulse envelopes: Generate coefficient vector. For the increasing pulse envelope: Generate coefficient vector Then, normalize the coefficient vector to make the average value 1. For the decreasing pulse envelope: generate a coefficient vector and normalize it. Second scenario: User-defined envelope. The system receives energy-pulse sequence curves uploaded by the user or graphically drawn, samples, smooths, and normalizes these curves to generate a coefficient vector. Output: Normalized energy distribution coefficient vector ; Step 3: Mapping to modulator drive signal: For MHz mode, voltage calculation is performed to generate an analog voltage waveform, while for GHz mode, the analog electrical signal is converted and a calibrated, synchronized modulator drive electrical signal is output. Step 4: Real-time monitoring and closed-loop feedback: Measure the actual energy distribution of the output pulse sequence in real time, compare the energy distribution with the target distribution, calculate the error vector, and output a more stable pulse sequence that has been optimized in real time. Step 5: Real-time monitoring and closed-loop feedback: Output control commands and start processing, send the final determined drive waveform parameters to the hardware, send a synchronous trigger signal, start laser output, and the system enters the monitoring state until the processing task is completed.
[0012] As an optional approach, in step three, voltage calculation is performed for the MHz mode, and the energy coefficient is calculated based on the "diffraction efficiency - drive RF power" calibration curve of the high-bandwidth acousto-optic modulator. Converted to the required radio frequency voltage amplitude Then there is Meanwhile, under the control of the FPGA, the AWG generates a length of The analog voltage waveform, each voltage amplitude The duration is exactly equal to the pulse interval. The rising / falling edge of the waveform is less than 10%.
[0013] As an optional approach, step three, for GHz mode, involves: converting the energy coefficient vector... Convolving with a template function representing the temporal shape of a single pulse generates a continuous pulse with a time length of approximately [missing information]. The analog time-domain waveform is fed into a DAC and converted into an analog electrical signal at a sampling rate greater than 10 GSa / s. Based on the fixed optical and electrical delays of the system, the output time of the analog signal is digitally compensated to ensure that it is precisely synchronized with the optical pulse. The output is a calibrated and synchronized modulator drive electrical signal.
[0014] As an optional solution, in step four, an online pulse energy detector is formed by using a high-speed photodiode and a sampling oscilloscope to measure the actual energy distribution of the output pulse sequence in real time. Meanwhile, step four uses a PID control algorithm or a lookup table correction algorithm to dynamically fine-tune the drive signal waveform to compensate for energy deviations caused by factors such as temperature drift and device nonlinearity.
[0015] The method for customizing femtosecond pulse sequences includes the following steps: Infrared seed pulses (e.g., 1030 nm wavelength) with energies less than 350 fs are generated using a SESAM mode-locked seed source. The pulse energy can reach 10 μJ. A reflective SESAM structure, combined with concave mirror dispersion compensation, achieves pulse stability better than 0.1% RMS. Passive mode-locking is achieved using a semiconductor saturable absorber mirror, generating femtosecond seed pulses with stable phase characteristics and a damage threshold greater than 100 μJ / cm². 2 Response time: 0.5–5 ps; Pulse pickup and gating are achieved based on a high-bandwidth acousto-optic modulator with a response time of less than 10ns. By driving an AWG with an FPGA, the pulse interval can be continuously adjusted from 25 to 100ns, and the timing accuracy is maintained within the range of ±0.1ns. At the same time, a diffraction grating is used to shape the energy distribution of the pulse sequence, and the seed pulses are precisely screened and time-modulated to achieve any number of combinations of 1 to 3000 pulses. Simultaneously, precise control of energy within the pulse sequence is achieved through a pulse energy distribution optimization algorithm, supporting three typical energy distribution modes; The MOPA power amplifier was used to amplify the seed pulse, and microchannel water cooling was employed to control the operating temperature within a fluctuation range of ±1℃. A nanosecond-level precise delay signal is generated by an RF drive module, and a 100MHz reference clock is used for full system timing synchronization to ensure the long-term stability of the pulse sequence. The beam is collimated and focused using the beam shaping and output module to achieve the beam parameter M. 2 Less than 1.3.
[0016] The technical effects achieved by this invention are as follows: This invention achieves passive mode-locking based on a semiconductor saturable absorber mirror, generating femtosecond seed pulses with stable phase characteristics. The seed pulses are precisely selected and time-modulated by an acousto-optic modulator and an arbitrary waveform generator, enabling arbitrary combinations of 1 to 3000 pulses. Combined with a pulse energy distribution optimization algorithm, precise control of energy within the pulse sequence is achieved, thereby supporting three typical energy distribution modes: flat pulse envelope, increasing pulse envelope, and decreasing pulse envelope.
[0017] This invention employs an analog radio frequency driver to digitally control the interval of the pulse sequence, achieving fine adjustment of the pulse interval within the range of 25 to 100 ns. It utilizes a high-speed digital signal processor to generate a high-precision delay signal, controlling timing jitter at the sub-picosecond level. Attached Figure Description
[0018] Figure 1 This is a system block diagram of the signal transmission state of the femtosecond pulse sequence customization system in Embodiment 1 of the present invention; Figure 2 This is a flowchart of the femtosecond pulse sequence customization method in Embodiment 2 of the present invention.
[0019] The attached diagram lists the components represented by each number as follows: 1. SESAM mode-locked seed source; 2. Pulse sequence modulator; 3. MOPA power amplifier; 4. RF drive module; 5. Beam shaping and output module. Detailed Implementation
[0020] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.
[0021] Example 1: like Figure 1As shown, a femtosecond pulse sequence customization system based on programmable control includes a SESAM (Saturable Absorber Mirror) mode-locking seed source 1, a pulse sequence modulator 2, a MOPA power amplifier 3, an RF drive module 4, and a beam shaping and output module 5. During operation, the SESAM mode-locking seed source 1 achieves passive mode-locking based on a semiconductor saturable absorber mirror, generating femtosecond seed pulses with stable phase characteristics. The seed pulses are precisely selected and time-modulated to achieve any combination of 1 to 3000 pulses. The interval of the pulse sequence is digitally controlled to achieve fine adjustment of the pulse interval in the range of 25 to 100 ns, controlling the timing jitter at the sub-picosecond level. At the same time, through a self-developed pulse energy distribution optimization algorithm, the energy within the pulse sequence is precisely controlled, supporting three typical energy distribution modes.
[0022] See attached document Figure 1 SESAM mode-locking seed source 1 is used to generate infrared seed pulses (e.g., 1030 nm wavelength) with a pulse width of less than 350 fs and a pulse energy of up to 10 μJ. It adopts a reflective SESAM structure and combines concave mirror dispersion compensation to achieve pulse stability better than 0.1% RMS (Root Mean Square). Through self-starting mode-locking, the damage threshold is greater than 100 μJ / cm. 2 Response time is 0.5 to 5 ps.
[0023] The self-starting process of SESAM mode-locked seed source 1 can be divided into the following three stages: Phase 1: Self-starting seed formation: When the initial light intensity inside the laser cavity is weak, the interband transition effect of the SESAM structure plays a dominant role. Due to energy fluctuations, light pulses of different intensities will randomly appear inside the cavity. The SESAM structure absorbs and saturates the strong pulses (increases transmittance), allowing them to pass through preferentially and be amplified by the gain medium; while the weak pulses are absorbed and suppressed. This process repeats itself, gradually forming an initial mode-locked seed pulse with concentrated energy. Phase Two: Seed Pulse Amplification and Q-Switching Mode Locking The initial seed pulse is linearly amplified by the gain medium during the loop within the laser cavity, and the energy continuously increases. At this time, the interband and intraband effects of the SESAM structure work together, resulting in Q-switching mode-locking. The pulse energy fluctuations cause the absorption characteristics of the SESAM structure to be dynamically adjusted, further screening and stabilizing the pulse sequence. Q-switching technology controls the quality factor (Q value) of the laser cavity to achieve energy accumulation and instantaneous release. For example, in the high Q value stage, by inserting components such as saturable absorbers, electro-optic modulators, or acousto-optic modulators, the cavity loss is increased, making it impossible for the laser to form stable oscillations. At this time, the gain medium (such as doped crystals or optical fibers) is continuously pumped, and energy is accumulated in the medium in the form of population inversion. In the low Q value stage, when the energy accumulates to the threshold, the cavity loss is suddenly reduced (such as the saturable absorber being "bleached" or the modulator switch being turned on), and the Q value rises sharply. The accumulated energy is released in the form of ultrashort pulses, forming high peak power laser pulses. Mode-locking technology, when energy accumulates to a certain level, the interband transition effect of the SESAM structure is "bleached" (absorption saturation), or the modulator switch is turned on, the cavity loss suddenly decreases, and the cavity light intensity increases sharply. Nonlinear effects (such as Kerr lens or the intraband thermal balance effect of SESAM structure) begin to dominate, forcing all longitudinal modes to synchronize phase and forming a mode-locked pulse. Phase 3, Stabilizing Femtosecond Mode-Locked Output: When the pulse energy is high enough, the SESAM structure is completely "bleached" (absorption saturation), the interband transition effect can be ignored, and the intraband thermal equilibrium effect dominates. At this point, the SESAM structure and the nonlinear amplification of the gain medium work together to compress and shape the pulse, ultimately forming a stable femtosecond-level mode-locked pulse output.
[0024] See attached document Figure 1 The pulse sequence modulator 2 is based on a high-bandwidth acousto-optic modulator to achieve pulse pickup and gating with a response time of less than 10ns. It drives an AWG (Arbitrary Waveform Generator) through an FPGA (Field Programmable Gate Array) to achieve continuous adjustment of the pulse interval from 25 to 100ns, with timing accuracy maintained within the range of ±0.1ns. At the same time, a diffraction grating is used to shape the energy distribution of the pulse sequence, and it supports custom pulse amplitude envelope.
[0025] In this embodiment, a high-bandwidth acousto-optic modulator of the Brimrose or Gooch & Housego model is used, with a bandwidth of not less than 200MHz, ensuring that the rise / fall time is not greater than 5ns, and that it can match the light wavelength (such as 1064nm or 1550nm) and diffraction efficiency greater than 80%. It is paired with a high-speed RF switch of the Mini-Circuits ZASW-2-50DR+ model to control the RF signal on and off, keeping the switching time within the range of less than 5ns. At the same time, it is necessary to ensure that the RF signal source has a bandwidth of greater than 200MHz, which is consistent with the center frequency of the high-bandwidth acousto-optic modulator (for example, set to 80MHz). This embodiment also selects a Keysight M8195A AWG device with a bandwidth of not less than 1GSa / s and a sampling rate of not less than 5GSa / s, paired with a Xilinx Kintex-7 or Intel Cyclone 10 GX FPGA. The NCO (numerically controlled oscillator) generates pulse interval parameters in steps of 25 to 100 ns, converts the parameters into AWG sampling point addresses, dynamically updates the waveform buffer, uses a high-precision timer (such as the HMC built into the FPGA) to trigger the AWG output, monitors the AWG output with a Keysight Infiniium UXR high-speed oscilloscope, and fine-tunes the FPGA trigger delay to ensure that the error between the actual interval and the set value is less than 0.1 ns. Regarding the selection of the diffraction grating, considering the requirement of diffraction efficiency greater than 80%, this embodiment uses a Thorlabs GR25-0608 blazed grating with a line density of not less than 1200 lines / mm and a 4f shaping optical path. The pulse sequence output from the high-bandwidth acousto-optic modulator is collimated into parallel light through lens L1 (f=500mm). The grating G is placed at the rear focal plane of lens L1 to unfold the pulse time-domain information into a spatial spectrum. Lens L2 (f=500mm) images the spectrum onto an adjustable aperture (A) or a spatial light modulator (SLM). A beam splitter and a power meter can be added at the end of the optical path to monitor the pulse energy after shaping in real time.
[0026] To meet the diverse processing needs of users employing femtosecond laser pulses, this embodiment incorporates a pulse energy distribution optimization algorithm on top of the pulse sequence modulator 2. This enables precise control of energy within the pulse sequence and supports three typical energy distribution modes (as a predefined library), including: Flat pulse envelope: Each pulse maintains a consistent energy, suitable for uniform material removal; Increasing pulse envelope: Energy increases pulse by pulse, suitable for multi-level deep machining; Decreasing pulse envelope: Energy decreases pulse by pulse, suitable for precision surface finishing.
[0027] The pulse energy distribution optimization algorithm includes the following steps: Step 1: Receive user input and process parameters; Enter the following parameters: (a) Process target selection: Select flat pulse envelope, increasing pulse envelope, or decreasing pulse envelope from the predefined library, or select custom; (b) Pulse sequence parameters: Set the total number of pulses Pulse interval ; (c) Overall energy parameters: Total energy Or average single pulse energy Energy dynamic range ; Output: Structured process request; Step 2: Calculate the energy distribution coefficient vector in two cases; First scenario: Select a predefined envelope; Flat pulse envelope: generating coefficient vector (length is) ); Increasing pulse envelope (linear): Generates coefficient vector Then normalize it to make the average value 1; Decreasing pulse envelope (linear): Generates a coefficient vector and normalizes it; Second scenario: User-defined envelope; Receive energy-pulse sequence curves uploaded by users or graphically plotted; The energy-pulse sequence curve is sampled, smoothed, and normalized to generate a coefficient vector. ; Output: Normalized energy distribution coefficient vector ; Step 3: Map to modulator drive signal; For MHz mode (high bandwidth acousto-optic modulator driver): Voltage calculation: Based on the "diffraction efficiency - drive RF power" calibration curve of the high-bandwidth acousto-optic modulator, the energy coefficient is... Converted to the required radio frequency voltage amplitude Then there is ; Waveform generation: Under the control of the FPGA, the AWG generates a waveform of length [length missing]. The analog voltage waveform, each voltage amplitude The duration is exactly equal to the pulse interval. The rising / falling edge of the waveform is less than 10%; For GHz mode (AOPDF / EOM driver): Waveform synthesis: The algorithm converts the energy coefficient vector Convolving with a template function (such as a Gaussian shape) representing the time-domain shape of a single pulse generates a continuous pulse with a time length of approximately [missing information]. The simulated time-domain waveform; Digital-to-analog conversion: The waveform data is fed into an ultra-high-speed DAC and converted into an analog electrical signal at a sampling rate greater than 10 GSa / s; Time delay alignment: The algorithm digitally compensates for the output time of the analog signal based on the fixed optical and electrical delays of the system, ensuring that it is precisely synchronized with the optical pulse; Output: A calibrated, synchronized modulator drive electrical signal; Step 4: Real-time monitoring and closed-loop feedback; An online pulse energy detector is composed of a high-speed photodiode and a sampling oscilloscope, which is used to measure the actual energy distribution of the output pulse sequence in real time. The measured energy distribution is compared with the target distribution, and the error vector is calculated. The drive signal waveform is dynamically fine-tuned by using a PID control algorithm or a lookup table correction algorithm to compensate for energy deviations caused by factors such as temperature drift and device nonlinearity. The PID control algorithm or the lookup table correction algorithm are well-known technologies to those skilled in the art, and will not be described redundantly in this embodiment. Output: A more stable pulse sequence optimized in real time; Step 5: Real-time monitoring and closed-loop feedback; Output control commands and start processing; The final determined drive waveform parameters are sent to the hardware (AWG or high-speed DAC). Send a synchronization trigger signal to start laser output; The system enters monitoring mode until the processing task is completed.
[0028] See attached document Figure 1 The MOPA power amplifier 3 includes a pre-amplifier single-mode fiber amplifier and a two-stage large mode area (20 / 400μm) double-clad fiber power amplifier. The maximum output power can reach 100W and the single pulse energy is 500μJ. Under 100kHz conditions, this embodiment adopts microchannel water cooling technology for the MOPA power amplifier 3 to control the operating temperature within ±1℃ range, effectively suppressing the thermal lensing effect.
[0029] The system includes a pre-amplifier for seed light pre-amplification to maintain beam quality, a first-stage large mode area (LMA) double-clad fiber power amplifier (configured with a core diameter of 20μm and an inner cladding diameter of 400μm) for initial power enhancement, and a second-stage large mode area (LMA) double-clad fiber power amplifier (configured with a core diameter of 22μm and an inner cladding diameter of 440μm) for final power amplification.
[0030] See attached document Figure 1 The RF drive module 4 generates nanosecond-level precise delay signals through a high-speed analog RF generator with a bandwidth greater than 200MHz, and uses a 100MHz reference clock for full system timing synchronization to ensure the long-term stability of the pulse sequence.
[0031] See attached document Figure 1 The beam shaping and output module 5 uses the Galilean telescope system to collimate and focus the beam, achieving beam parameter M. 2 It has a wavelength of less than 1.3 and provides a standard FC / APC fiber optic output interface, supporting multiple wavelength conversion units, such as wavelength conversion between 515nm and 343nm.
[0032] See attached document Figure 1 The entire system's clock is derived from the same rubidium atomic clock and synchronized using digital phase-locked loop technology, keeping clock drift below 1 ppm / year. The FPGA / AWG generates MHz gated signals for a high-bandwidth acousto-optic modulator. Simultaneously, a DAC (ultra-high-speed digital-to-analog converter) under the control of the FPGA and atomic clock generates GHz analog modulation signals corresponding to optical pulses, driving AOPDF (acousto-optic programmable dispersion filter) or EOM (electro-optic modulator). Alternatively, an analog RF driver is used to digitally control the pulse sequence interval, achieving fine adjustment of the pulse interval within the range of 25–100 ns. The key lies in using a DSP (high-speed digital signal processor) to generate high-precision delay signals, controlling timing jitter at the sub-picosecond level.
[0033] As an optional implementation, the FPGA integrates a "delay alignment algorithm" to ensure that the MHz gated signal and the GHz modulated signal are precisely synchronized with the optical pulse in time, with jitter of less than 10ps.
[0034] This embodiment also provides a mode switching process, the specific steps of which are as follows: When the user switches the mode from "MHz adjustable interval mode" to "GHz fixed interval mode" through the software interface, the above-mentioned femtosecond pulse sequence customization system completes the following automatic reconfiguration in less than 1ms: Hardware path switching: The seed optical path is switched from "MHz mode modulation chain" (high bandwidth acousto-optic modulator as the main modulator) to "GHz mode modulation chain" (high bandwidth acousto-optic modulator as the gate, AOPDF / EOM as the main modulator) through an optical switch. Control parameter loading: The FPGA loads the driver firmware for GHz mode, and the AWG and high-speed DAC call the corresponding waveform parameters; Clock synchronization switching: The system master clock synchronization network performs fast relocking to ensure that the GHz modulation signal and the 1GHz repetition frequency of the seed laser are in the same source and phase; Status confirmation and output: After the self-test system confirms that the operating points of each modulator are normal, it outputs a customized GHz pulse sequence.
[0035] Example 2: like Figure 2 As shown, the femtosecond pulse sequence customization method, applied to the femtosecond pulse sequence customization system provided in Example 1, includes the following steps: Infrared seed pulses (e.g., 1030 nm wavelength) with an energy of less than 350 fs are generated using SESAM mode-locked seed source 1. The pulse energy can reach 10 μJ. A reflective SESAM structure, combined with concave mirror dispersion compensation, achieves pulse stability better than 0.1% RMS. Passive mode-locking is achieved based on a semiconductor saturable absorber mirror, generating femtosecond seed pulses with stable phase characteristics and a damage threshold greater than 100 μJ / cm². 2 Response time: 0.5–5 ps; Pulse pickup and gating are achieved based on a high-bandwidth acousto-optic modulator with a response time of less than 10ns. By driving an AWG with an FPGA, the pulse interval can be continuously adjusted from 25 to 100ns, and the timing accuracy is maintained within the range of ±0.1ns. At the same time, a diffraction grating is used to shape the energy distribution of the pulse sequence, and the seed pulses are precisely screened and time-modulated to achieve any number of combinations of 1 to 3000 pulses. Simultaneously, precise control of energy within the pulse sequence is achieved through a pulse energy distribution optimization algorithm, supporting three typical energy distribution modes; The MOPA power amplifier 3 was used to amplify the seed pulse, and the operating temperature was controlled within a fluctuation range of ±1℃ by using microchannel water cooling. The RF drive module 4 generates a nanosecond-level precise delay signal, and a 100MHz reference clock is used for full system timing synchronization to ensure the long-term stability of the pulse sequence. The beam is collimated and focused by the beam shaping and output module 5 to achieve the beam parameter M. 2 Less than 1.3.
[0036] The above description is merely an optional embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention, unless otherwise specified or limited, shall be implemented according to conventional means in the art.
Claims
1. A femtosecond pulse sequence customization system based on programmable control, characterized in that, include: SESAM mode-locked seed source (1) is used to generate seed pulses; The pulse sequence modulator (2), connected to the SESAM mode-locked seed source (1), is configured to receive user-defined pulse sequence parameters and modulate the seed pulses into a customized pulse sequence with a preset number of pulses, pulse interval and pulse energy envelope based on the parameters; MOPA power amplifier (3) is used to amplify the custom pulse sequence; The radio frequency drive module (4) is used to generate nanosecond-level precise delay signals and uses a reference clock to synchronize the timing of the entire system, thereby ensuring the stability of the pulse sequence. The beam shaping and output module (5) is used for collimation and focusing of the customized pulse sequence.
2. The femtosecond pulse sequence customization system according to claim 1, characterized in that, The SESAM mode-locking seed source (1) achieves passive mode-locking based on a semiconductor saturable absorber mirror, including the following steps: Phase 1: Self-starting seed formation: The SESAM structure absorbs and saturates a portion of the pulses within the laser cavity, allowing these pulses to pass through preferentially and be amplified by the gain medium, while the remaining pulses are absorbed and suppressed. This process is repeated to form an initial mode-locked seed pulse with concentrated energy. Phase Two: Seed Pulse Amplification and Q-Switching Mode Locking The initial mode-locked seed pulse is linearly amplified by the gain medium during the loop in the laser cavity. Its energy is continuously enhanced and is simultaneously affected by the interband and intraband effects of the SESAM structure, which manifests as Q-switching mode-locking. The pulse energy fluctuation causes the absorption characteristics of the SESAM structure to be dynamically adjusted, further screening and stabilizing the pulse sequence. Phase 3, Stabilizing Femtosecond Mode-Locked Output: When the pulse energy reaches a set level, the SESAM structure absorbs saturation. Due to the combined effect of the nonlinear amplification of the SESAM structure and the gain medium, the pulse is compressed and shaped, ultimately forming a stable femtosecond-level mode-locked pulse output.
3. The femtosecond pulse sequence customization system according to claim 1, characterized in that: The pulse sequence modulator (2) is based on a high-bandwidth acousto-optic modulator to achieve pulse pickup and gating, with a response time of less than 10ns. It drives an AWG via an FPGA to achieve continuous adjustment of the pulse interval from 25 to 100ns, and realizes any combination of 1 to 3000 pulses.
4. The femtosecond pulse sequence customization system according to claim 1, characterized in that, The pulse sequence modulator (2) includes a diffraction grating, the specific structure of which is as follows: Lens L1 is used to collimate the pulse sequence output by the high-bandwidth acousto-optic modulator into parallel light; A grating G is disposed on the rear focal plane of the lens L1 to unfold the pulse time-domain information into a spatial spectrum. Lens L2 is disposed on the side of the grating G away from lens L1, and is used to image the spatial spectrum onto an adjustable aperture or spatial light modulator.
5. The femtosecond pulse sequence customization system according to claim 1, characterized in that, The pulse sequence modulator (2) is equipped with a pulse energy distribution optimization algorithm, which includes the following three energy distribution modes: Flat pulse envelope: Each pulse maintains a consistent energy for uniform material removal; Increasing pulse envelope: Energy increases pulse by pulse, used for multi-level deep machining; Decreasing pulse envelope: Energy decreases pulse by pulse, used for precision surface finishing.
6. The femtosecond pulse sequence customization system according to claim 5, characterized in that, The pulse energy distribution optimization algorithm specifically includes the following steps: Step 1: Receive user input and process parameters: Input the process target selection, pulse sequence parameters, and overall energy parameters; select a predefined envelope or a custom envelope; and set the total number of pulses. Pulse interval Total energy Energy dynamic range Output structured process requests; Step 2: Calculate the energy distribution coefficient vector in two cases: First case: Select a predefined envelope; for flat pulse envelopes: Generate coefficient vector. For the increasing pulse envelope: Generate coefficient vector Then, normalize the coefficient vector to make the average value 1. For the decreasing pulse envelope: generate a coefficient vector and normalize it. Second scenario: User-defined envelope. The system receives energy-pulse sequence curves uploaded by the user or graphically drawn, samples, smooths, and normalizes these curves to generate a coefficient vector. Output: Normalized energy distribution coefficient vector ; Step 3: Mapping to modulator drive signal: For MHz mode, voltage calculation is performed to generate an analog voltage waveform, while for GHz mode, the analog electrical signal is converted and a calibrated, synchronized modulator drive electrical signal is output. Step 4: Real-time monitoring and closed-loop feedback: Measure the actual energy distribution of the output pulse sequence in real time, compare the energy distribution with the target distribution, calculate the error vector, and output a more stable pulse sequence that has been optimized in real time. Step 5: Real-time monitoring and closed-loop feedback: Output control commands and start processing, send the final determined drive waveform parameters to the hardware, send a synchronous trigger signal, start laser output, and the system enters the monitoring state until the processing task is completed.
7. The femtosecond pulse sequence customization system according to claim 6, characterized in that: In step three, for the MHz mode, voltage calculation is performed, and the energy coefficient is calculated based on the diffraction efficiency-drive RF power calibration curve of the high-bandwidth acousto-optic modulator. Converted to the required radio frequency voltage amplitude Then there is Meanwhile, under the control of the FPGA, the AWG generates a length of The analog voltage waveform, each voltage amplitude The duration is equal to the pulse interval The rising and falling edges of the waveform are less than 10%.
8. The femtosecond pulse sequence customization system according to claim 6, characterized in that: In step three, for the GHz mode, the energy coefficient vector is... Convolving with a template function representing the temporal shape of a single pulse generates a continuous pulse with a time length of [missing information]. The analog time-domain waveform is fed into a DAC and converted into an analog electrical signal at a sampling rate greater than 10 GSa / s. Based on the fixed optical and electrical delays of the system, the output time of the analog signal is digitally compensated to ensure that it is precisely synchronized with the optical pulse, and the calibrated and synchronized modulator drive electrical signal is output.
9. The femtosecond pulse sequence customization system according to claim 6, characterized in that: In step four, an online pulse energy detector is formed by a high-speed photodiode and a sampling oscilloscope to measure the actual energy distribution of the output pulse sequence in real time. Meanwhile, step four uses a PID control algorithm or a lookup table correction algorithm to dynamically fine-tune the drive signal waveform to compensate for energy deviations caused by factors such as temperature drift and device nonlinearity.
10. A femtosecond pulse sequence customization method, applied to the femtosecond pulse sequence customization system according to any one of claims 1-9, characterized in that, The customization method includes the following steps: Infrared seed pulses with an energy of less than 10 μJ are generated by a SESAM mode-locked seed source (1). A reflective SESAM structure is adopted, and combined with concave mirror dispersion compensation, the pulse stability is better than 0.1% RMS. Passive mode-locking is achieved based on a semiconductor saturable absorber mirror to generate femtosecond seed pulses with stable phase characteristics. Pulse pickup and gating are achieved based on a high-bandwidth acousto-optic modulator with a response time of less than 10ns. By driving an AWG with an FPGA, the pulse interval can be continuously adjusted from 25 to 100ns, and the timing accuracy is maintained within the range of ±0.1ns. At the same time, a diffraction grating is used to shape the energy distribution of the pulse sequence, and the seed pulses are precisely screened and time-modulated to achieve any number of combinations of 1 to 3000 pulses. Simultaneously, precise control of energy within the pulse sequence is achieved through a pulse energy distribution optimization algorithm, supporting three typical energy distribution modes; The MOPA power amplifier (3) was used to amplify the seed pulse. The operating temperature was controlled within the fluctuation range of ±1℃ by using microchannel water cooling. A nanosecond-level precise delay signal is generated by the radio frequency drive module (4), and a 100MHz reference clock is used for full system timing synchronization to ensure the long-term stability of the pulse sequence. The beam is collimated and focused by the beam shaping and output module (5) to achieve the beam parameter M. 2 Less than 1.3.