Femtosecond laser autocorrelator with automatic calibration function and measuring method thereof

Abstract

According to the femtosecond laser autocorrelator with the automatic calibration function and the measuring method thereof, the femtosecond laser autocorrelator has the advantages of being high in measuring speed, high in precision, easy and convenient to operate and small in size, the inherent stability of a light path is fundamentally improved through an integrated light-machine unit, and the measurement accuracy is improved. The light path state sensing unit realizes real-time in-situ monitoring of multiple parameters such as light beam quality and element poses, the adaptive optical unit can dynamically compensate wavefront distortion and optimize phase matching, and the intelligent control processing unit drives the whole system to complete an intelligent process from automatic optimization calibration, signal acquisition processing to pulse reconstruction calculation. Through the combined action of the characteristics, the inherent defects that a traditional instrument depends on manual adjustment, is easily interfered by the environment, is low in measurement efficiency, is insufficient in stability and the like are effectively overcome, and the femtosecond laser pulse measuring device is particularly suitable for rapid, accurate and reliable measurement requirements on femtosecond laser pulses in laboratories and industrial sites.

Description

Technical Field

[0001] This invention relates to the field of femtosecond laser technology, and in particular to a femtosecond laser autocorrelator with automatic calibration function and its measurement method. Background Technology

[0002] Femtosecond laser pulses, with their extremely short pulse widths and extremely high peak power, play an irreplaceable role in ultrafast spectroscopy, precision micromachining, biomedical imaging, and fundamental physics research. Accurate measurement of the femtosecond laser pulse width is crucial for ensuring the performance and reliability of these applications. The autocorrelation method is one of the most widely used and mature techniques for measuring femtosecond pulse width. Its basic principle is to split the pulse to be measured and introduce an adjustable time delay, then reconcile them in a nonlinear crystal to generate a frequency-doubled signal. By measuring the change in the intensity of this frequency-doubled signal as a function of the delay time (i.e., the autocorrelation curve), the width of the original pulse can be indirectly derived.

[0003] Traditional femtosecond laser autocorrelators are typically assembled from a series of discrete optical components. A typical structure includes an aperture for beam shaping, a beam splitter, a delay line composed of multiple mirrors, a frequency doubling crystal, a focusing lens, and a photodetector (such as a photodiode or CCD). During measurement, the optical path difference is continuously scanned by precisely moving the mirrors in the delay line to obtain the autocorrelation curve point by point. While this architecture based on discrete components and mechanical scanning has become relatively mature after long-term development, it has revealed several inherent defects in practical applications. First, because a large number of discrete components are assembled through mechanical structures, the stability of the optical path is heavily dependent on assembly precision and environmental conditions. Even minor vibrations, temperature drifts, or stress changes can easily cause optical path misalignment, leading to measurement reference drift. Therefore, before, during, and after measurement, operators often need to manually adjust the optical path based on experience, which is time-consuming, labor-intensive, and requires a high level of expertise from the operator. Secondly, scanning measurement is essentially a time-for-precision tradeoff. Obtaining high-resolution autocorrelation curves requires long scanning times, making true single-shot (single-pulse) measurements impossible. This is not only inefficient but also makes it difficult to capture non-repeatable or low-repetition-frequency pulse events. Furthermore, the entire system is bulky; components such as the optical platform and mechanical delay line make the instrument cumbersome, failing to meet the portability requirements of field or integrated applications. In addition, traditional instruments generally lack real-time monitoring capabilities of the optical path itself. Whether the beam quality is optimal, the component positions are accurate, and the phase matching conditions of the frequency doubling crystal are optimal are all in a "blind adjustment" state, directly affecting the signal-to-noise ratio, repeatability, and final accuracy of the measurement.

[0004] In recent years, although some improvements have attempted to introduce motorized translation stages to replace manual adjustments or optimize data processing through algorithms, their core hardware remains fundamentally based on a discrete, open-loop, and passive response paradigm. These improvements have not fundamentally resolved the core contradictions of optical path dynamic stability, measurement real-time performance, and operational intelligence. For example, current technologies still cannot detect and compensate for wavefront distortion and pointing drift of the beam in real time during measurement, nor can they automatically maintain optimal phase-matching conditions when the environment changes. Therefore, how to construct a femtosecond laser autocorrelator with self-state awareness, the ability to actively maintain optimal operating conditions, and the capability for rapid automatic calibration and single-shot measurement has become a pressing technical challenge in this field, and is of great significance for promoting the wider and more reliable industrial and scientific research applications of ultrafast laser technology. Summary of the Invention

[0005] The purpose of this invention is to provide a femtosecond laser autocorrelator with automatic calibration function and its measurement method to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a femtosecond laser autocorrelator with automatic calibration function, comprising:

[0008] An integrated optomechanical unit fixes the core optical components within a base, forming a unique and stable internal optical path channel;

[0009] The optical path state sensing unit is used to monitor the beam quality, component pose, and environmental parameters inside the integrated optomechanical unit in real time.

[0010] An adaptive optics unit is used to dynamically adjust the beam wavefront or the state of optical elements based on feedback from the optical path state sensing unit.

[0011] The intelligent control and processing unit is connected to the integrated optomechanical unit, the optical path state sensing unit and the adaptive optics unit respectively, and is used to execute the automatic calibration process, process the sensing data, drive adaptive adjustment and calculate the pulse width based on the autocorrelation signal;

[0012] The user interaction and display unit is connected to the intelligent control and processing unit and is used for parameter setting and result display.

[0013] Preferably, the integrated optomechanical unit includes:

[0014] The input adjustment and beam splitting module is used to receive and collimate the femtosecond laser pulse to be measured, and split it into a first beam and a second beam.

[0015] The delay and beam combining module includes a mirror assembly driven by a precision translation stage, used to introduce an adjustable optical path delay for the first beam and guide the first beam and the second beam to spatial overlap;

[0016] The frequency doubling and detection module, which includes a frequency doubling crystal and a matrix CCD, is used to convert the overlapping beam into a frequency doubling signal and acquire its spatial intensity distribution;

[0017] The optical elements of the input adjustment and beam splitting module, the delay and beam combining module, and the frequency doubling and detection module are integrated on the same base using micro-optical technology.

[0018] Preferably, the optical path state sensing unit includes:

[0019] A mirror pose sensor is integrated into the mirror assembly of the delay and beam combining module and the precision translation stage, and is used to provide real-time feedback on the spatial position and angle of the mirror.

[0020] A beam quality analyzer is installed in the optical path before or after the frequency doubling crystal to monitor the position, intensity distribution and wavefront information of the beam spot after beam combining in real time.

[0021] A crystal state sensor is attached to the frequency doubling crystal to monitor the crystal temperature and angle.

[0022] Preferably, the adaptive optics unit includes:

[0023] At least one deformable mirror is disposed in the optical path of the input adjustment and beam splitting module or the delay and beam combining module, and is used to dynamically adjust the surface shape of the mirror under the drive of the intelligent control and processing unit to compensate for beam wavefront distortion.

[0024] An electric rotary table, which carries the frequency doubling crystal, is used to automatically adjust the phase matching angle of the crystal based on feedback from the crystal state sensor and the wavelength of the laser to be measured.

[0025] Preferably, the intelligent control and processing unit is used to perform:

[0026] Receive real-time data from the mirror pose sensor and the beam quality analyzer;

[0027] Based on the real-time data, adjustment instructions for the shape of the deformable reflective mirror and the position of the precision translation stage are generated through a control algorithm;

[0028] The deformable mirror and the precision translation stage are driven to perform adjustments to optimize the beam overlap quality and wavefront, thereby completing the automatic optical path calibration.

[0029] This invention also provides a measurement method for a femtosecond laser autocorrelator with automatic calibration function, comprising the following steps:

[0030] S1. System self-calibration: The intelligent control and processing unit initiates a closed-loop control process, using the data from the optical path state sensing unit and the adjustments from the adaptive optics unit to automatically find the optimal optical path state and complete delay calibration and beam optimization;

[0031] S2. Single pulse measurement: Under the optimized optical path state, the matrix CCD is triggered to acquire the spatial intensity distribution of the frequency harmonic signal of the pulse under test in a single acquisition.

[0032] S3. Signal preprocessing: Denoise and background subtraction are performed on the acquired intensity distribution data;

[0033] S4. Pulse Reconstruction and Pulse Width Calculation: Based on the preprocessed data, an algorithm model is used to reconstruct the time-domain shape of the original pulse and calculate its pulse width;

[0034] S5. Result Output: The pulse shape, pulse width value, and measurement quality evaluation parameters are presented through the user interaction and display unit.

[0035] Preferably, in step S1, finding the optimal optical path state specifically includes:

[0036] S11. Control the precision translation stage to scan, while using the reflector pose sensor to record the precise position, and using the matrix CCD to collect the frequency harmonic signal intensity at the corresponding position;

[0037] S12. Based on the acquired signal, the peak search algorithm is used to identify the first self-coherence point position x1 and the second self-coherence point position x2;

[0038] S13. Calculate the center position x0 = (x1 + x2) / 2, and control the precision translation stage to move to x0;

[0039] S14. Read the data from the beam quality analyzer and adjust the surface shape of the deformable mirror to achieve the optimal beam-combining spot quality index.

[0040] Preferably, in step S3, the noise reduction uses a moving average filter, with the following formula:

[0041] ;

[0042] in, This is the filtered spatial intensity distribution function. Spatial location coordinates, For the size of the filter window, , The filter window half-width, For summation index variables, This is the original spatial intensity distribution function.

[0043] Preferably, in step S4, a multi-model fitting strategy is adopted, including a Gaussian model and a hyperbolic secant model;

[0044] The method for calculating pulse width using a Gaussian model is as follows:

[0045] S41. Assuming the impulse is Gaussian, the autocorrelation function is modeled as follows:

[0046] ;

[0047] in, It is the autocorrelation function. For time delay, , At the speed of light, The standard deviation parameter of the Gaussian function;

[0048] S42. The least squares method is used to fit the net signal intensity after background subtraction, which is then substituted into the Gaussian model. The formula is:

[0049] ;

[0050] in, The amplitude;

[0051] S43. Calculate the pulse width using the following formula:

[0052] ;

[0053] in, The pulse is full width at half maximum (FWHM).

[0054] The method for calculating pulse width using the hyperbolic secant model is as follows:

[0055] S44. If it is a hyperbolic secant pulse, the formula for calculating the pulse width is:

[0056] ;

[0057] in, is the characteristic width parameter of the hyperbolic secant function.

[0058] Preferably, after step S5, the method further includes:

[0059] S6. Measurement result verification: Calculate the coefficient of variation based on multiple consecutive measurement results. When the coefficient of variation is less than the preset threshold, the measurement result is deemed reliable.

[0060] The present invention achieves the following beneficial technical effects compared to the prior art:

[0061] This invention provides a femtosecond laser autocorrelator with automatic calibration and its measurement method. By introducing a collaborative architecture of an integrated optomechanical unit, an optical path state sensing unit, an adaptive optics unit, and an intelligent control processing unit, a closed-loop intelligent measurement system integrating "sensing-decision-execution" is constructed, thereby achieving fully automatic, high-precision, and high-stability single-shot measurement of femtosecond laser pulse width. This invention features fast measurement speed, high accuracy, simple operation, and compact size. The integrated optomechanical unit fundamentally improves the inherent stability of the optical path; the optical path state sensing unit enables real-time in-situ monitoring of multiple parameters such as beam quality and component pose; the adaptive optics unit dynamically compensates for wavefront distortion and optimizes phase matching; and the intelligent control processing unit drives the entire system to complete the intelligent process from automatic optimization calibration and signal acquisition and processing to pulse reconstruction calculation. These features work together to effectively overcome the inherent drawbacks of traditional instruments, such as reliance on manual adjustment, susceptibility to environmental interference, low measurement efficiency, and insufficient stability. It is particularly suitable for the rapid, accurate, and reliable measurement needs of femtosecond laser pulses in laboratories and industrial settings. Attached Figure Description

[0062] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0063] Figure 1 This is a structural diagram of a femtosecond laser autocorrelator with automatic calibration function provided by the present invention;

[0064] Figure 2 The flowchart illustrates the measurement method of the femtosecond laser autocorrelator with automatic calibration function provided by this invention. Detailed Implementation

[0065] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0066] The purpose of this invention is to provide a femtosecond laser autocorrelator with automatic calibration function and its measurement method. Its core lies in realizing automatic calibration, rapid measurement and accurate calculation of femtosecond laser pulse width through the integration of intelligent modules and algorithm optimization.

[0067] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0068] Example 1:

[0069] Figure 1 The overall system architecture of the autocorrelator of this invention is demonstrated. The system, with an intelligent control and processing unit at its core, coordinates the integrated optomechanical unit, optical path state sensing unit, adaptive optics unit, and user interaction and display unit to work together as an organic whole. The femtosecond laser pulse to be measured first enters the integrated optomechanical unit. This unit is not a simple combination of multiple discrete components in the traditional sense, but rather, through micro-optical processes or precision machining techniques, core optical functional modules such as input adjustment and beam splitting, delay and beam combining, frequency doubling and detection are fixed in a highly integrated manner within a base with a low coefficient of thermal expansion and high mechanical stability. This design forms an inherently stable optical path system, minimizing errors introduced by independent component assembly and adjustment and misalignment caused by environmental perturbations at the physical level, laying a solid foundation for highly repeatable measurements.

[0070] In the integrated optomechanical unit, the input conditioning and beam splitting module receives and collimates the pulse to be measured, which is then split into a first beam and a second beam of similar intensity by a beam splitter. The delay and beam combining module is key to introducing time delay. One beam has a mirror group driven by a precision translation stage along its path. By precisely controlling the position of the translation stage, the optical path of the beam can be linearly changed, thereby introducing the required time delay τ between the two beams. The two beams are finally guided to the spatial coincidence point of the frequency doubling and detection module. The core of this module is a frequency doubling crystal. When the two femtosecond pulses coincide perfectly in time and space, a sum-frequency or frequency doubling effect occurs, generating a detection signal with a shorter wavelength. This signal is then captured by a high-sensitivity matrix CCD, recording the spatial distribution of the frequency-doubled light intensity. The entire optical path, from input to detection, is completed within the integrated substrate. The external interface includes only a laser input port and electrical signal / data lines, achieving miniaturization and packaging of the system.

[0071] However, relying solely on the robustness of the physical structure is insufficient to handle all disturbances. Therefore, this invention introduces an optical path state sensing unit. This unit comprises multiple embedded sensors: a mirror pose sensor is integrated onto a precision translation stage and the mirror it supports, monitoring the mirror's precise spatial position and angle in real time and in situ, with feedback accuracy down to the sub-micron and microradian level; a beam quality analyzer (which can be a miniaturized Shack-Hartmann wavefront sensor or a combination of a microlens array with a high dynamic range and a camera) is cleverly placed in the optical path before or after the frequency doubling crystal to continuously monitor the centroid position of the combined beam spot, the uniformity of light intensity distribution, and crucial wavefront phase information; and a crystal state sensor (which can be a high-precision patch temperature sensor and angle encoder) is closely attached to the frequency doubling crystal to monitor its operating temperature and incident angle relative to the beam in real time. All this sensor data is transmitted in real time to the intelligent control and processing unit via a high-speed data bus.

[0072] Perception is essential for decision-making and execution. The adaptive optics unit serves as the system's "executor." Deformable mirrors (which can be MEMS-based or piezoelectric ceramic-driven continuous-surface deformable mirrors) are strategically deployed in the optical path. Under the command of the intelligent control and processing unit, their mirror surface shape can be dynamically and precisely altered, actively correcting wavefront distortion of the incident beam caused by atmospheric turbulence, optical element aberrations, or mechanical vibrations, ensuring that the beam quality reaching the frequency doubling crystal remains close to the diffraction limit. Simultaneously, the motorized rotary stage carrying the frequency doubling crystal automatically fine-tunes the crystal's angle based on temperature data from the crystal state sensor and a pre-set wavelength-phase matching angle database to compensate for phase mismatch caused by temperature drift or wavelength changes, consistently maintaining the frequency doubling conversion efficiency near its optimal value.

[0073] The intelligent control and processing unit is typically composed of a high-performance embedded industrial computer or an FPGA / DSP combination. It runs complex control algorithms, signal processing algorithms, and pulse width calculation algorithms. Its primary task is to execute a fully automated calibration process: it drives a precision translation stage to scan and simultaneously reads the absolute position of the pose sensor and the relative light intensity signal acquired by the matrix CCD. Through a built-in peak search algorithm, the unit can automatically identify the precise positions x1 and x2 corresponding to two feature points on the autocorrelation curve. Then, it calculates the center position x0 = (x1 + x2) / 2 and controls the translation stage to move to x0, completing the initial delay calibration. Next, the unit reads data from the beam quality analyzer and calculates the driving voltage to be applied to the deformable mirror using a closed-loop control algorithm (which can be a control algorithm based on Zernike mode coefficient feedback) to correct the observed wavefront aberrations and optimize beam quality indicators such as the Strell ratio. The entire process requires no manual intervention and can be completed within seconds, achieving intelligent calibration from "coarse adjustment" to "fine adjustment."

[0074] After completing the above intelligent calibration, the system enters a high-precision test-ready state. At this point, the operator initiates a single-shot measurement via user interaction and display unit (which can be a touchscreen or connected host computer software). Figure 2 The measurement process shown involves the intelligent control and processing unit triggering the matrix CCD to perform a single exposure, acquiring the spatial intensity distribution of the harmonic signal generated by the current pulse under test. Subsequently, the unit performs signal preprocessing on the raw data: firstly, a moving average filter is used to suppress random noise, as shown in the formula:

[0075] ;

[0076] in, Filtered spatial intensity distribution function Spatial location coordinates, For the size of the filter window, , The filter window half-width, For summation index variables, The original spatial intensity distribution function is used; then, the background light intensity distribution, which was measured beforehand under conditions without laser input, is subtracted to obtain the net signal intensity distribution. This preprocessing significantly improves the signal-to-noise ratio of the data.

[0077] Next comes pulse reconstruction and pulse width calculation. The intelligent control and processing unit employs a multi-model fitting strategy to enhance adaptability. It simultaneously uses a Gaussian function model and a hyperbolic secant square function model to perform nonlinear least-squares fitting of the net signal intensity distribution. Specifically, the spatial coordinates are expressed using the relational formula... The time delay is converted and substituted into the mathematical expressions of both models for fitting. The fitting process aims to find a set of model parameters that minimizes the sum of squared residuals between the calculated model values ​​and the measured data. After fitting, the unit compares the goodness of fit of the two models and automatically selects the model with the better fit as the final shape description of the measured pulse.

[0078] Specifically, the method for calculating the pulse width using the Gaussian model is as follows:

[0079] Assuming the pulse is Gaussian, the autocorrelation function is modeled as follows:

[0080] ;

[0081] in, It is the autocorrelation function. For time delay, , At the speed of light, The standard deviation parameter of the Gaussian function;

[0082] The net signal intensity after background subtraction is fitted using the least squares method and substituted into the Gaussian model, as shown in the formula:

[0083] ;

[0084] in, The amplitude;

[0085] The formula for calculating pulse width is:

[0086] ;

[0087] in, The pulse is full width at half maximum (FWHM).

[0088] The method for calculating pulse width using the hyperbolic secant model is as follows:

[0089] If it is a hyperbolic secant pulse, the pulse width is calculated using the following formula:

[0090] ;

[0091] in, This is the characteristic width parameter of the hyperbolic secant function. This multi-model adaptive selection mechanism effectively avoids systematic calculation errors caused by a preset single impulse model.

[0092] Finally, all results (including the reconstructed pulse time-domain shape curve, calculated pulse width values, fitting error estimates, and key optical path state parameters) are clearly presented on the user interaction and display unit. To further ensure the reliability of the measurement results, the method may also include a result verification step: the system can automatically perform several (e.g., three) rapid single-shot measurements consecutively and calculate the coefficient of variation of the obtained pulse width results. If the coefficient of variation is lower than the user-set threshold, a "measurement reliable" message will be displayed on the interface; otherwise, the user may be prompted to check the stability of the laser source or re-execute the calibration process.

[0093] In a specific application embodiment, this invention is used to measure a pulse with a center wavelength of 800 nm output from a Ti:Sapphire femtosecond laser amplifier. After the system is powered on, "automatic calibration" is initiated with a single click via the touchscreen. Within approximately 5 seconds, the system completes the positioning of the translation stage and optimization of the deformable mirror shape, and the status indicator light turns green. After injecting the pulse to be measured, clicking "single measurement" instantly captures the signal using the matrix CCD, and the intelligent control unit completes data processing and calculation within milliseconds. The screen displays the pulse width as "98.7±1.2 fs (CV<1.5%)" and plots a smooth Gaussian fitting curve. The entire operation requires no manual optical path adjustment, significantly improving measurement efficiency and reliability, making it particularly suitable for rapid quality inspection of pulse states on laser processing lines or for capturing unstable pulses in ultrafast laboratories.

[0094] In summary, this invention, through high-level hardware integration and intelligent empowerment, transforms femtosecond laser pulse width measurement from an experience-dependent craft into a reliable, efficient, and easy-to-use automated process. The integrated optomechanical unit provides a stable physical structure, the optical path state sensing unit provides keen perception, the adaptive optics unit brings flexible execution, and the intelligent control and processing unit enables intelligent decision-making. This closed-loop system, formed by the collaboration of these four components, fundamentally solves the pain points of traditional technologies and represents an important direction for the development of femtosecond laser measurement technology towards intelligence, precision, and portability.

[0095] It should be noted that the components mentioned in the above embodiments are all general standard parts or components known to those skilled in the art. Their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0096] This invention has illustrated its principles and implementation methods using specific examples. The descriptions of these embodiments are merely illustrative of the method and its core ideas; furthermore, those skilled in the art will recognize that modifications may be made to the specific implementation methods and application scope based on the principles of this invention. Therefore, the content of this specification should not be construed as limiting the invention.

Claims

1. A femtosecond laser autocorrelator with automatic calibration function, characterized in that, include: An integrated optomechanical unit fixes the core optical components within a base, forming a unique and stable internal optical path channel; The optical path state sensing unit is used to monitor the beam quality, component pose, and environmental parameters inside the integrated optomechanical unit in real time. An adaptive optics unit is used to dynamically adjust the beam wavefront or the state of optical elements based on feedback from the optical path state sensing unit. The intelligent control and processing unit is connected to the integrated optomechanical unit, the optical path state sensing unit and the adaptive optics unit respectively, and is used to execute the automatic calibration process, process the sensing data, drive adaptive adjustment and calculate the pulse width based on the autocorrelation signal; The user interaction and display unit is connected to the intelligent control and processing unit and is used for parameter setting and result display.

2. The femtosecond laser autocorrelator with automatic calibration function according to claim 1, characterized in that, The integrated optomechanical unit includes: The input adjustment and beam splitting module is used to receive and collimate the femtosecond laser pulse to be measured, and split it into a first beam and a second beam. The delay and beam combining module includes a mirror assembly driven by a precision translation stage, used to introduce an adjustable optical path delay for the first beam and guide the first beam and the second beam to spatial overlap; The frequency doubling and detection module, which includes a frequency doubling crystal and a matrix CCD, is used to convert the overlapping beam into a frequency doubling signal and acquire its spatial intensity distribution; The optical elements of the input adjustment and beam splitting module, the delay and beam combining module, and the frequency doubling and detection module are integrated on the same base using micro-optical technology.

3. The femtosecond laser autocorrelator with automatic calibration function according to claim 2, characterized in that, The optical path state sensing unit includes: A mirror pose sensor is integrated into the mirror assembly of the delay and beam combining module and the precision translation stage, and is used to provide real-time feedback on the spatial position and angle of the mirror. A beam quality analyzer is installed in the optical path before or after the frequency doubling crystal to monitor the position, intensity distribution and wavefront information of the beam spot after beam combining in real time. A crystal state sensor is attached to the frequency doubling crystal to monitor the crystal temperature and angle.

4. The femtosecond laser autocorrelator with automatic calibration function according to claim 3, characterized in that, The adaptive optics unit includes: At least one deformable mirror is disposed in the optical path of the input adjustment and beam splitting module or the delay and beam combining module, and is used to dynamically adjust the surface shape of the mirror under the drive of the intelligent control and processing unit to compensate for beam wavefront distortion. An electric rotary table, which carries the frequency doubling crystal, is used to automatically adjust the phase matching angle of the crystal based on feedback from the crystal state sensor and the wavelength of the laser to be measured.

5. The femtosecond laser autocorrelator with automatic calibration function according to claim 4, characterized in that, The intelligent control and processing unit is used to perform: Receive real-time data from the mirror pose sensor and the beam quality analyzer; Based on the real-time data, adjustment instructions for the shape of the deformable reflective mirror and the position of the precision translation stage are generated through a control algorithm; The deformable mirror and the precision translation stage are driven to perform adjustments to optimize the beam overlap quality and wavefront, thereby completing the automatic optical path calibration.

6. The measurement method of the femtosecond laser autocorrelator with automatic calibration function according to any one of claims 1-5, characterized in that, Includes the following steps: S1. System self-calibration: The intelligent control and processing unit initiates a closed-loop control process, using the data from the optical path state sensing unit and the adjustments from the adaptive optics unit to automatically find the optimal optical path state and complete delay calibration and beam optimization; S2. Single pulse measurement: Under the optimized optical path state, the matrix CCD is triggered to acquire the spatial intensity distribution of the frequency harmonic signal of the pulse under test in a single acquisition. S3. Signal preprocessing: Denoise and background subtraction are performed on the acquired intensity distribution data; S4. Pulse Reconstruction and Pulse Width Calculation: Based on the preprocessed data, an algorithm model is used to reconstruct the time-domain shape of the original pulse and calculate its pulse width; S5. Result Output: The pulse shape, pulse width value, and measurement quality evaluation parameters are presented through the user interaction and display unit.

7. The measurement method of the femtosecond laser autocorrelator with automatic calibration function according to claim 6, characterized in that, Step S1, finding the optimal optical path state specifically includes: S11. Control the precision translation stage to scan, while using the reflector pose sensor to record the precise position, and using the matrix CCD to collect the frequency harmonic signal intensity at the corresponding position; S12. Based on the acquired signal, the peak search algorithm is used to identify the first self-coherence point position x1 and the second self-coherence point position x2; S13. Calculate the center position x0 = (x1 + x2) / 2, and control the precision translation stage to move to x0; S14. Read the data from the beam quality analyzer and adjust the surface shape of the deformable mirror to achieve the optimal beam-combining spot quality index.

8. The measurement method of the femtosecond laser autocorrelator with automatic calibration function according to claim 6, characterized in that, In step S3, noise reduction uses a moving average filter, with the following formula: ; in, This is the filtered spatial intensity distribution function. Spatial location coordinates, For the size of the filter window, , The filter window half-width, For summation index variables, This is the original spatial intensity distribution function.

9. The measurement method of the femtosecond laser autocorrelator with automatic calibration function according to claim 6, characterized in that, In step S4, a multi-model fitting strategy is adopted, including Gaussian model and hyperbolic secant model; The method for calculating pulse width using a Gaussian model is as follows: S41. Assuming the impulse is Gaussian, the autocorrelation function is modeled as follows: ; in, It is the autocorrelation function. For time delay, , At the speed of light, The standard deviation parameter of the Gaussian function; S42. The least squares method is used to fit the net signal intensity after background subtraction, which is then substituted into the Gaussian model. The formula is: ； in, The amplitude; S43. Calculate the pulse width using the following formula: ； in, The pulse is full width at half maximum (FWHM). The method for calculating pulse width using the hyperbolic secant model is as follows: S44. If it is a hyperbolic secant pulse, the formula for calculating the pulse width is: ； in, is the characteristic width parameter of the hyperbolic secant function.

10. The measurement method of the femtosecond laser autocorrelator with automatic calibration function according to claim 6, characterized in that, Following step S5, the following is also included: S6. Measurement result verification: Calculate the coefficient of variation based on multiple consecutive measurement results. When the coefficient of variation is less than the preset threshold, the measurement result is deemed reliable.

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