An on-line measuring device and method for high-energy broadband pulsed laser field and far-field focal spot

Abstract

An on-line measuring device and method for high-energy broadband pulsed laser field and far-field focal spot: the broadband pulsed laser generated by a high-energy laser is first processed by an intensity attenuation system, and then reaches a beam splitting element; the light beam transmitted through the beam splitter passes through a coding plate, which codes and modulates the light beam, and then a single-frame diffraction image intensity formed after the coding plate modulation is recorded by a surface array light intensity detector; the light beam reflected by the beam splitting element is recorded by a spectral analysis unit. With the single-frame diffraction image intensity recorded by the surface array light intensity detector and the single-spectrum data recorded by the spectral analysis unit, the near-field complex amplitude (intensity and phase) distribution of the high-energy broadband pulsed laser field to be measured can be accurately reconstructed through a multi-modal light field reconstruction algorithm, and the far-field focal spot distribution can also be obtained. The method has the advantages of simple structure, low cost and strong environmental anti-interference ability.

Description

Technical Field

[0001] This invention relates to the field of high-energy laser measurement technology, specifically to an online measurement device and method for the optical field and far-field focal spot of a high-energy broadband pulsed laser, which is particularly suitable for the rapid reconstruction and monitoring of the optical field complex amplitude (including intensity and phase) distribution and far-field focusing characteristics of a high-power broadband pulsed laser system under real-time, high-precision, and anti-interference conditions. Background Technology

[0002] Laser inertial confinement fusion (ICF), as a key pathway to achieving controlled nuclear fusion and ushering in a new era of clean energy, has received significant attention from the scientific community. In ICF experiments, high-energy short-pulse broadband lasers play a crucial role, serving both as driving lasers to induce implosion and compression of the target pellet and as diagnostic light to acquire information about the fusion process, placing extremely stringent requirements on beam focusing characteristics. These high-energy short-pulse broadband lasers typically have bandwidths exceeding 10 nanometers, and their unique spectral characteristics make the optical field and far-field focal spot highly complex. Traditional optical field measurement methods are hampered by the incomplete coherence of broadband lasers, making it difficult to accurately reconstruct the complex amplitude distribution of the optical field. This results in an inability to accurately grasp the true state of the laser during transmission and focusing, posing a significant challenge to the repeatability and stability of physical experiments.

[0003] Currently, numerous researches have been conducted on measurement techniques for high-power pulsed lasers. For example, time slicing based on electro-optic deflectors, combined with single-frame diffraction images and phase retrieval algorithms, is used to reconstruct the dynamic optical field (e.g., Chinese patent application CN113340570A). These approaches primarily address the challenge of transient measurement under monochromatic / narrowband high-power, short-pulse conditions. However, when applied to broadband lasers, their inherent technical assumptions and designs reveal significant limitations:

[0004] The contradiction between the monochromatic / narrowband assumption and broadband reality: CN113340570A is applicable to narrowband light, and its algorithm model does not consider the incoherent superposition effect between different wavelength components. For broadband lasers, directly applying its algorithm will lead to distortion of the reconstructed complex amplitude distribution due to model mismatch, and the calculation error of the far-field focal spot will increase significantly, failing to reflect the true spectral synthesis effect.

[0005] The contradiction between time slicing and missing spectral information: These schemes acquire dynamic information by encoding in the time dimension, but do not simultaneously acquire the spectral distribution information of the pulse. For broadband lasers with variable spectral characteristics that have a decisive impact on the final focusing, the lack of spectral weighting, a key constraint, results in a reconstructed "dynamic light field" that is blurry or erroneous in the spectral dimension, making it unusable for accurate analysis of spectral-spatial coupling effects.

[0006] The contradiction between complex optical paths and environmental adaptability: Optical paths using high-speed active modulation elements such as electro-optic deflectors have extremely high requirements for synchronization control accuracy, environmental vibration and thermal stability. The system is complex and expensive. In online measurement scenarios with significant environmental disturbances, such as large ICF devices, its stability and reliability face challenges.

[0007] Furthermore, existing traditional methods such as wavefront sensors and interferometers are also insufficient to achieve high-precision, real-time online measurement under conditions of strong vibration and wide spectrum.

[0008] Therefore, there is an urgent need to develop an online measurement technology for the optical field and focal spot of high-energy broadband pulsed lasers, capable of simultaneously acquiring spatial diffraction and spectral information in a single emission, and using efficient algorithms to achieve high-precision reconstruction of the complex amplitude and far-field distribution of the optical field. This method should possess characteristics such as compact structure, strong environmental robustness, and controllable cost to meet the pressing needs for real-time beam quality diagnosis and optimization in large laser facilities such as the ICF. Summary of the Invention

[0009] This invention addresses the problems of complex structure, weak environmental interference resistance, inaccurate broadband effect processing, and inability to achieve online real-time measurement in existing high-energy broadband pulsed laser light field and far-field focal spot measurement technologies. It proposes a measurement device and method for online measurement of high-energy broadband pulsed laser light field and far-field focal spot. By utilizing spatial diffraction mode data and spectral intensity mode data acquired synchronously from a single laser pulse, the light field is jointly solved through a multi-mode fusion iterative algorithm to reconstruct the near-field complex amplitude distribution and far-field focal spot distribution of the high-energy broadband pulsed laser light field.

[0010] To solve the above problems, the technical solution of the present invention is as follows:

[0011] An online measurement device for the optical field and far-field focal spot of a high-energy broadband pulsed laser, characterized in that it includes:

[0012] The following components are sequentially coaxially arranged along the optical axis of the broadband pulsed laser beam under test:

[0013] -Intensity attenuation system, used to attenuate the incident laser energy to the dynamic range of the array light intensity;

[0014] - A beam splitter, used to separate the attenuated beam into a transmitted beam and a reflected beam;

[0015] - A spatial encoder is disposed in the optical path of the transmitted beam to apply known spatial coding modulation to the beam wavefront;

[0016] - An array of light intensity detectors, located after the spatial encoder, is used to record the intensity of a single frame of diffraction image formed after modulation.

[0017] A spectral analysis unit is disposed on the reflected light path of the beam splitter and is used to synchronously acquire the spectral intensity distribution of the reflected beam with the area array light intensity detector.

[0018] The data processing unit is connected to the area array light intensity detector and the spectral analysis unit, respectively, and receives the intensity of the single-frame diffraction image and the spectral intensity distribution;

[0019] The data processing unit is configured to execute a multimodal optical field reconstruction algorithm, which: a) uses the intensity of the single-frame diffraction image as a spatial intensity constraint; b) uses the spectral intensity distribution as a spectral weight constraint; and c) during the iterative reconstruction process, simultaneously integrates the spatial intensity constraint and the spectral weight constraint, and reconstructs the near-field complex amplitude distribution and the corresponding far-field focal spot distribution of the broadband pulsed laser under test through a dynamic spectral weight correction mechanism.

[0020] Furthermore, the spatial encoder is an encoding board with a known modulation function, which is pseudo-randomly distributed in a two-dimensional plane. The spatial encoder is fixedly connected to the detection surface of the area array light intensity detector, and both are perpendicular to the optical axis. The distance L1 from the encoding board to the detection surface is a pre-calibrated fixed value.

[0021] Furthermore, the centers of the intensity attenuation system, the beam splitter, the spatial encoder, and the area array light intensity detector are all located on the optical axis, and the incident end of the spectral analysis unit is aligned with the center of the reflected beam.

[0022] Second, the present invention also provides a method for online measurement of the high-energy broadband pulsed laser light field and far-field focal spot using the above-mentioned device, characterized in that the method includes the following steps:

[0023] Step S1. Calibration and parameter calibration: Establish the measurement optical path, calibrate the modulation function T(x,y) of the spatial encoder and its detection surface distance L1 to the area array light intensity detector, and input it into the data processing unit;

[0024] Step S2. Synchronous multimodal data acquisition: When the high-energy broadband pulsed laser to be tested is emitted, the area array intensity detector and the spectral analysis unit are simultaneously triggered to acquire the intensity of a single frame diffraction image. and normalized spectral intensity distribution ;

[0025] Step S3: Multimodal fusion light field reconstruction: The intensity of the single-frame diffraction image is... and spectral intensity distribution The data is input to the data processing unit, and the following iterative algorithm is executed:

[0026] S31: Based on the aforementioned spectral intensity distribution The multi-wavelength complex amplitude optical field is initialized based on the profile of the high-energy broadband pulsed laser beam to be measured.

[0027] S32: Perform forward propagation calculations on the optical field for each wavelength component, sequentially passing through: Fourier transform, spatial constraints, inverse Fourier transform, propagation to the coding plane, multiplication by the modulation function T(x,y), and propagation to the detector plane to obtain the estimated complex amplitude at each wavelength;

[0028] S33: Perform diffraction-spectral dual-mode constraint correction. This step includes:

[0029] (1) Calculate the composite estimated intensity of the incoherent superposition of the estimated intensities of each wavelength;

[0030] (2) Combine the synthesized estimated intensity with the intensity of the recorded single-frame diffraction image. Compare and calculate the global intensity correction factor;

[0031] (3) Calculate the energy percentage of each wavelength component in the synthesized optical field in the current iteration;

[0032] (4) Perform dynamic correction of spectral weights: compare and correct the energy percentage with the target spectral weights to generate a spectral weight correction factor;

[0033] (5) Combine the global intensity correction factor and the spectral weight correction factor to jointly correct the amplitude of the light field at each wavelength;

[0034] S34: Backpropagate the corrected light field to the initial plane, apply spatial support domain constraints, and update the light field estimate;

[0035] S35: Repeat S32-S34 until the convergence condition is met;

[0036] S4: Output the results. Output the near-field complex amplitude distribution obtained from the final iteration, and obtain the far-field focal spot distribution through Fourier transform.

[0037] Furthermore, in step S33, the global intensity correction factor is calculated using the following formula:

[0038]

[0039] In the formula, This is the global amplitude correction factor for the nth iteration; The intensity of a single frame of diffraction image; The synthesized broadband intensity of the nth iteration; The regularization constant is 1, a very small positive number. Its function is to ensure the stability of numerical calculations and prevent errors caused by the combined intensity. When the estimated value of some pixels is close to zero, the denominator being zero or too small can cause the formula calculation result to overflow or produce a large error.

[0040] Furthermore, the dynamic correction of spectral weights in step S33 specifically includes:

[0041] The formula for calculating the energy percentage of each wavelength is as follows:

[0042] ,

[0043] In the formula, This is a provisional estimate of the total energy of the k-th wavelength in the nth iteration; This represents the amplitude distribution of the k-th wavelength after global correction in the n-th iteration.

[0044] The formula for calculating the spectral weighting correction factor is as follows:

[0045]

[0046] In the formula, This is the spectral scaling correction factor for the k-th wavelength in the nth iteration; The target spectral intensity weight for the k-th wavelength; This is a provisional estimate of the total energy of the k-th wavelength in the nth iteration; Temporarily estimate the sum of the total energy for all wavelengths; The regularization constant is 2, a very small positive number, whose main function is to prevent the current energy percentage of a certain wavelength from being affected. When the value is very close to zero, the denominator becomes too small, resulting in a small correction factor. To prevent computational instability or overflow, ensure numerical robustness.

[0047] The amplitude is corrected using the spectral weighting correction factor, as shown in the following formula:

[0048] ;

[0049] In the formula, This represents the final corrected amplitude of the k-th wavelength in the nth iteration. This is the spectral scaling correction factor for the k-th wavelength in the nth iteration; This represents the amplitude distribution of the k-th wavelength after global spatial correction in the nth iteration.

[0050] Furthermore, the joint correction in step S33 specifically includes:

[0051] By keeping the estimated phase of each wavelength channel on the plane of the area array optical intensity detector unchanged, and replacing the optical field function with the corrected amplitude, a new planar optical field of the area array optical intensity detector is constructed. , where i is the imaginary unit;

[0052] Furthermore, in step S34, the radius of the spatial support domain constraint adopts a dynamic adjustment strategy, using a larger constraint radius in the initial iteration and gradually decreasing to the actual beam size as the number of iterations increases.

[0053] Furthermore, the convergence condition is that the relative error between the synthesized estimated intensity and the measured diffraction intensity image is less than a preset threshold ε. th , where ε th ≤10 -3 .

[0054] Compared with the prior art, the technical effects of the present invention are as follows:

[0055] 1) Using two heterogeneous data sources, namely the intensity of a single-frame diffraction image recorded by an area array light intensity detector and the intensity distribution of a one-dimensional spectrum recorded by a spectrometer, a high-energy broadband pulsed laser light field and far-field focal spot are reconstructed by a multimodal algorithm.

[0056] 2) In the iterative phase retrieval loop, spatial intensity constraints of the diffraction image and spectral weight constraints of the measured spectrum are introduced simultaneously, and the two work synergistically through a dynamic correction mechanism. The optical field information that traditional methods require tens to hundreds of pulse scans to obtain is compressed into a single pulse measurement.

[0057] 3) Its structure is simple and has excellent anti-environmental interference performance. It is suitable for online measurement work in the limited space of high-power laser devices. Compared with commonly used laser beam measuring instruments, this device is not only cheaper and more accurate, but also has better application potential and a broad market prospect.

[0058] 4) Unlike schemes such as CN113340570A that rely solely on a single spatial diffraction image, this invention simultaneously acquires a single frame of spatial diffraction image and a one-dimensional spectral intensity distribution. For the first time, it obtains the necessary spatial and spectral heterogeneous information to describe the light field in a single pulse measurement, providing a fundamental data basis for solving the measurement challenge of incoherent superposition in broadband lasers. Compared to CN113340570A, which aims to recover the temporal evolution sequence of the light field, this invention aims to and can directly obtain an accurate static complex amplitude distribution incorporating all spectral components and its corresponding far-field focal spot in a single measurement. This has irreplaceable value for evaluating the overall focusing performance of broadband lasers and analyzing chromatic aberration effects, especially meeting the diagnostic needs of fields such as ICF for the combined spectral and spatial characteristics of the beam. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the online measurement device for the high-energy broadband pulsed laser light field and far-field focal spot of the present invention.

[0060] In the diagram: 1-High-energy laser, 2-Intensity attenuation system, 3-Beam splitter, 4-Encoding board, 5-Area array light intensity detector, 6-Spectrometer, 7-Computer.

[0061] Figure 2 Flowchart for the calculation and reconstruction of the high-energy broadband pulsed laser light field and far-field focal spot. Detailed Implementation

[0062] The present invention will be further described below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention should not be limited by these embodiments.

[0063] Please refer to the following first. Figure 1 , Figure 1 This is a schematic diagram of an online measurement device for the optical field and far-field focal spot of a high-energy broadband pulsed laser. As shown in the figure, the steps of this embodiment of the invention are as follows:

[0064] I. Debugging of the measuring device:

[0065] according to Figure 1 As shown, a measuring device is constructed, arranged along the principal optical axis of the high-energy laser 1 to be tested:

[0066] An intensity attenuation system 2 is placed after the output port of the high-energy laser 1. This attenuation system 2 consists of two stages of attenuators. The first stage is a reflective adjustable attenuator (e.g., based on a combination of a Glan prism and a half-wave plate) used for coarse energy adjustment; the second stage is a set of neutral density filters with fixed magnification used for fine attenuation and to prevent damage to subsequent optical components. This ensures that the single-pulse energy density incident on the detector plane is below its damage threshold and that the light intensity signal is within the detector's linear response region. A beam splitter 3 is placed on the optical axis of the attenuated beam. In this embodiment, the beam splitter 3 can be a broadband beam splitter with approximately 50% reflectivity and 50% transmittance for the operating wavelength range (e.g., visible to near-infrared). The transmitted light path (main measurement light path) is used for optical field reconstruction, and the reflected light path (auxiliary measurement light path) is used for spectral analysis.

[0067] A spatial encoder and an area array light intensity detector 5 are sequentially installed in the transmission optical path of the beam splitter 3. In this embodiment, the spatial encoder is a binary random phase plate as the encoding plate 4, whose phase distribution function T(x, y) is known and has been precisely calibrated by an independent interferometer. The encoding plate 4 adopts a phase of... and random distribution Or the space intensity is and 1 random distribution The smallest unit size is 9µm, and the distance from the plane of the encoder plate 4 to the area array light intensity detector 5 is... The area array intensity detector 5 has a resolution of 4096 pixels × 4096 pixels and a minimum unit size of 9µm. The spectrometer 6 has a spectral range of 200-1100nm and an optical resolution of 0.75nm full width at half maximum (FWHM). The area array intensity detector 5 acquires the intensity of a single frame diffraction image formed by the encoding plate 4. The output of the area array intensity detector 5 is connected to the input of the computer 7. The encoding plate 4 and the area array intensity detector 5 are fixed together by a rigid mechanical bracket to ensure that their relative position (distance L1) remains constant and that the surface of the encoding plate 4 is parallel to the photosensitive surface of the area array intensity detector 5. A spectral analysis unit is installed on the reflected light path of the beam splitter 3. In this embodiment, a fiber optic spectrometer 6 is used to synchronously record the spectrum of the beam. During installation, its entrance slit position needs to be finely adjusted to ensure that it accurately acquires the central part of the laser beam reflected by the beam splitter 3. The output of the spectrometer 6 is connected to the input of the computer 7.

[0068] Adjust the intensity attenuation system 2, beam splitter 3, encoder 4, and area array intensity detector 5 to ensure that the center of all optical components is located on the principal optical axis of the laser under test. Simultaneously, ensure that the detector facet of the spectrometer 6 is directly facing the center of the reflected beam. The debugging goal is to ensure that the laser beam can completely pass through the beam splitter 3 and encoder 4 and illuminate the effective photosensitive area of ​​the area array intensity detector 5, while the reflected beam can completely enter the receiving aperture of the spectrometer 6.

[0069] Besides binary random phase plates, sinusoidal phase gratings and pseudo-random intensity masks can also achieve similar modulation functions, provided their modulation function T(x,y) is known. Spectral analysis elements can also be snapshot spectrometers equipped with photodiode arrays to achieve higher time resolution.

[0070] II. Implementation Steps of the Measurement Method

[0071] After the measuring device is set up and calibrated, online measurements should be performed according to the following procedure:

[0072] Step S10: Data Synchronization Acquisition

[0073] Start the high-energy laser 1 to emit a broadband pulse laser to be tested.

[0074] The computer 7 synchronously triggers the area array intensity detector 5 and the spectrometer 6. The area array intensity detector 5 records the intensity of a single frame diffraction image formed on its photosensitive surface by a broadband laser beam modulated by the encoder 4, denoted as . Spectrometer 6 simultaneously records the spectral curve of the pulsed laser. After dark background subtraction and intensity normalization by computer, the normalized spectral intensity distribution is obtained, denoted as... .

[0075] S20 data preprocessing:

[0076] Read the intensity of a single frame of diffraction image from the record ;

[0077] Read spectral intensity distribution The continuous spectrum is then discretized into K wavelength channels to obtain the discrete spectral weights {λ}. k , S k},and Where k = 1, 2, ..., K, S k =S(λ k ),

[0078] λ k S is the center wavelength of the k-th wavelength channel; k The normalized spectral intensity of the k-th wavelength channel;

[0079] Based on the intensity of the recorded single-frame diffraction image An approximate contour is obtained, and an initial spatial amplitude distribution is defined. ;

[0080] Initialize the complex amplitude field:

[0081] According to the spectral intensity weight S k The initial spatial amplitude distribution is assigned to each wavelength channel. ;

[0082] For each wavelength channel, a random phase distribution ϕ in the range of [-0.1π, 0.1π] is introduced. rand (x,y), forming the initial complex amplitude field for each wavelength channel: , where i is the imaginary unit;

[0083] S30 performs multimodal fusion iterative reconstruction

[0084] (a) Propagation in the forward direction to the detector plane:

[0085] Perform a Fast Fourier Transform on the initial optical field of each wavelength channel An initial spatial support domain constraint is applied in the transform domain. ,in The focal plane constraint function is typically a circular aperture function with a radius parameter of . The radius gradually increases with the number of iterations n; then the result is subjected to an inverse fast inverse Fourier transform. ;

[0086] Using the angular spectrum propagation formula, the spatial domain light field is propagated to the 4-plane of the encoding board. ,in, Represents the angular spectral propagation factor;

[0087] On the 4-plane of the encoder, multiply the optical field function by the known encoder modulation function. That is, phase distribution;

[0088] Continuing with the angular spectrum propagation formula, the modulated light field is propagated from the plane of the encoder plate 4 to the plane of the area array intensity detector 5, yielding the estimated complex amplitude field of the k-th wavelength channel. ;

[0089] (b) Diffraction-spectral dual-mode constraint and correction:

[0090] Multi-wavelength estimation is combined with the intensity I of a single-frame diffraction image recorded. CCD and spectral data S k To achieve fusion constraints, assuming complete incoherence between wavelength channels, the superposition of estimated light intensities for all wavelength channels on the plane of the area array intensity detector 5 is calculated. ;

[0091] The synthesized estimated light intensity is compared with the intensity of the recorded single-frame diffraction image to calculate the global intensity correction factor. , where δ is a very small positive value used to prevent division by zero;

[0092] Applying the global intensity correction factor to apply spectral constraints, the initial amplitude correction is as follows: ;

[0093] Spectral weighting correction: (i) Calculate the proportion of energy of each wavelength channel to the total energy. (ii) Calculate its relationship with the target spectrum S. k Matched spectral weighting correction factor: (iii) Applying the spectral weighting correction factor, the final corrected amplitude is obtained: ;

[0094] Keeping the estimated phase of each wavelength channel on the plane of the area array optical intensity detector unchanged, the optical field function is replaced with the corrected amplitude to construct a new plane optical field for the area array optical intensity detector. ;

[0095] (c) Backpropagation and demodulation:

[0096] by As a new constraint, reverse angular spectrum propagation is performed independently for each wavelength channel, propagating back from the plane of the area array intensity detector 5 to the plane of the encoding board 4, to obtain the optical field of the encoding board plane. ;

[0097] In order to remove the influence of the encoder modulation and suppress noise, Wiener filtering is used for optical field demodulation on plane 4 of the encoder board. , where β is the noise suppression factor (usually selected between 0.5 and 2.0, its role is to balance signal fidelity and noise suppression during the demodulation process);

[0098] (d) Backpropagate to the initial plane and update:

[0099] The demodulated light field The reverse angular spectrum propagates back to the Fourier transform output plane. ;

[0100] Perform a fast Fourier transform on the light field ;

[0101] Spatial constraints are applied at the focal plane, with a region radius R. n The value can be gradually increased with each iteration to improve convergence, thus obtaining the initial estimate for the (n+1)th iteration. ;

[0102] S37. Repeat steps (a) to (d) for multiple iterations;

[0103] At the end of each iteration, the reconstruction error of the synthesized broadband intensity image is calculated: ;

[0104] When reconstruction error < 10 -3 When the preset convergence threshold is reached, the iteration stops. This refers to the calculated and reconstructed high-energy broadband pulsed laser focal spot distribution;

[0105] Perform a fast inverse Fourier transform on the laser focal plane optical field. , This refers to the calculated and reconstructed high-energy broadband pulsed laser light field distribution.

[0106] Experimental results show that the device of the present invention successfully realizes the measurement of the high-energy pulsed broadband laser light field and far-field focal spot. A single-frame diffraction image intensity is recorded online by an array light intensity detector and a single-spectral data is recorded online by a spectrometer. Then, the near-field complex amplitude distribution of the high-energy broadband pulsed laser light field under test can be accurately reconstructed by a multi-modal light field reconstruction algorithm. At the same time, the far-field focal spot distribution can also be deduced.

[0107] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. An online measurement device for the optical field and far-field focal spot of a high-energy broadband pulsed laser, characterized in that, include: The following components are sequentially coaxially arranged along the optical axis of the broadband pulsed laser beam under test: -Intensity attenuation system, used to attenuate the incident laser energy to the dynamic range of the array light intensity; - A beam splitter, used to separate the attenuated beam into a transmitted beam and a reflected beam; - A spatial encoder is disposed in the optical path of the transmitted beam to apply known spatial coding modulation to the beam wavefront; - An array of light intensity detectors, located after the spatial encoder, is used to record the intensity of a single frame of diffraction image formed after modulation. A spectral analysis unit is disposed on the reflected light path of the beam splitter and is used to synchronously acquire the spectral intensity distribution of the reflected beam with the area array light intensity detector. The data processing unit is connected to the area array light intensity detector and the spectral analysis unit, respectively, and receives the intensity of the single-frame diffraction image and the spectral intensity distribution; The data processing unit is configured to execute a multimodal optical field reconstruction algorithm, which: a) uses the intensity of the single-frame diffraction image as a spatial intensity constraint; b) uses the spectral intensity distribution as a spectral weight constraint; c) during the iterative reconstruction process, calculates a global intensity correction factor based on the deviation between the intensity of the single-frame diffraction image and the synthesized estimated intensity, and calculates a spectral weight correction factor based on the deviation between the current energy proportion of each wavelength and the target spectral weight, thereby jointly correcting the amplitude of each wavelength component and reconstructing the near-field complex amplitude distribution and the corresponding far-field focal spot distribution of the broadband pulsed laser under test.

2. The online measurement device for the high-energy broadband pulsed laser field and far-field focal spot according to claim 1, characterized in that: The spatial encoder is an encoding board with a known modulation function, which is pseudo-randomly distributed in a two-dimensional plane. The spatial encoder is fixedly connected to the detection surface of the area array light intensity detector, and both are perpendicular to the optical axis. The distance L1 from the encoding board to the detection surface is a pre-calibrated fixed value.

3. The online measurement device for the high-energy broadband pulsed laser field and far-field focal spot according to claim 1 or 2, characterized in that: The centers of the intensity attenuation system, the beam splitter, the spatial encoder, and the area array light intensity detector are all located on the optical axis, and the incident end of the spectral analysis unit is aligned with the center of the reflected beam.

4. An online measurement method for the optical field and far-field focal spot of a high-energy broadband pulsed laser, implemented based on the online measurement device as described in any one of claims 1-3, characterized in that, The method includes the following steps: Step S1. Calibration and parameter calibration: Establish the measurement optical path, calibrate the modulation function T(x,y) of the spatial encoder and its detection surface distance L1 to the area array light intensity detector, and input it into the data processing unit; Step S2. Synchronous multimodal data acquisition: When the high-energy broadband pulsed laser to be tested is emitted, the area array intensity detector and the spectral analysis unit are simultaneously triggered to acquire the intensity of a single frame diffraction image. and normalized spectral intensity distribution ; Step S3: Multimodal fusion light field reconstruction: The intensity of the single-frame diffraction image is... and spectral intensity distribution The data is input to the data processing unit, and the following iterative algorithm is executed: S31: Based on the aforementioned spectral intensity distribution The beam profile of the high-energy broadband pulsed laser to be tested is used to initialize the multi-wavelength complex amplitude optical field; S32: Perform forward propagation calculations on the optical field for each wavelength component, sequentially passing through: Fourier transform, spatial constraints, inverse Fourier transform, propagation to the coding plane, multiplication by the modulation function T(x,y), and propagation to the detector plane to obtain the estimated complex amplitude at each wavelength; S33: Perform diffraction-spectral dual-mode constraint correction. This step includes: (1) Calculate the composite estimated intensity of the incoherent superposition of the estimated intensities of each wavelength; (2) Combine the synthesized estimated intensity with the intensity of the recorded single-frame diffraction image. Compare and calculate the global intensity correction factor; (3) Calculate the energy percentage of each wavelength component in the synthesized optical field in the current iteration; (4) Perform dynamic correction of spectral weights: compare and correct the energy percentage with the target spectral weights to generate a spectral weight correction factor; (5) Combine the global intensity correction factor and the spectral weight correction factor to jointly correct the amplitude of the light field at each wavelength; S34: Backpropagate the corrected light field to the initial plane, apply spatial support domain constraints, and update the light field estimate; S35: Repeat S32-S34 until the convergence condition is met; S4: Output the results. Output the near-field complex amplitude distribution obtained from the final iteration, and obtain the far-field focal spot distribution through Fourier transform.

5. The online measurement method for the high-energy broadband pulsed laser light field and far-field focal spot according to claim 4, characterized in that, In step S33, the global intensity correction factor is calculated using the following formula: In the formula, This is the global amplitude correction factor for the nth iteration; The intensity of a single frame of diffraction image; The synthesized broadband intensity of the nth iteration; The regularization constant is one, which is to prevent the synthesis intensity from being equal to the normalization constant. When the estimated value of some pixels is close to zero, the denominator being zero or too small can cause the formula calculation result to overflow or produce a large error.

6. The online measurement method for the high-energy broadband pulsed laser light field and far-field focal spot according to claim 4, characterized in that, The dynamic correction of spectral weights in step S33 specifically includes: The formula for calculating the energy percentage of each wavelength is as follows: ， In the formula, This is a provisional estimate of the total energy of the k-th wavelength in the nth iteration; This represents the amplitude distribution of the k-th wavelength after global correction in the n-th iteration. The formula for calculating the spectral weighting correction factor is as follows: In the formula, This is the spectral scaling correction factor for the k-th wavelength in the nth iteration; The target spectral intensity weight for the k-th wavelength; This is a provisional estimate of the total energy of the k-th wavelength in the nth iteration; Temporarily estimate the sum of the total energy for all wavelengths; The regularization constant is two, which is to prevent the current energy percentage of a certain wavelength from being affected. When the value is very close to zero, the denominator becomes too small, resulting in a small correction factor. To prevent computational instability or overflow, ensure numerical robustness. The amplitude is corrected using the spectral weighting correction factor, as shown in the following formula: ； In the formula, This represents the final corrected amplitude of the k-th wavelength in the nth iteration. This is the spectral scaling correction factor for the k-th wavelength in the nth iteration; This represents the amplitude distribution of the k-th wavelength after global spatial correction in the n-th iteration.

7. The online measurement method for the high-energy broadband pulsed laser light field and far-field focal spot according to claim 6, characterized in that, The joint correction in step S33 specifically includes: By keeping the estimated phase of each wavelength channel on the plane of the area array optical intensity detector unchanged, and replacing the optical field function with the corrected amplitude, a new planar optical field of the area array optical intensity detector is constructed. , This represents the final corrected complex amplitude field of the k-th wavelength on the light intensity detector plane during the nth iteration. Let i be the original phase distribution of the k-th wavelength on the light intensity detector plane in the n-th iteration, where i is the imaginary unit.

8. The online measurement method for the high-energy broadband pulsed laser light field and far-field focal spot according to claim 5, characterized in that, In step S34, the radius of the spatial support domain constraint adopts a dynamic adjustment strategy, using a larger constraint radius in the initial iteration and gradually decreasing to the actual beam size as the number of iterations increases.

9. The online measurement method for the high-energy broadband pulsed laser light field and far-field focal spot according to claim 5, characterized in that, The convergence condition is that the relative error between the synthesized estimated intensity and the measured diffraction intensity image is less than a preset threshold ε. th , where ε th ≤10 -3 .

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