Method and system for regulating a dual-pulse laser-driven soft x-ray source

Abstract

This application discloses a method and system for controlling a dual-pulse laser-driven soft X-ray source. The method includes: determining the control vector for the current dual-pulse irradiation, the control vector including the ratio of the time delay and energy between the pre-pulse and the main pulse, the ratio of the equivalent diameters of the two light spots, the centroid offset, and the main pulse energy; controlling the pre-pulse to irradiate the target region to form a pre-plasma, and controlling the coupling of the main pulse with the pre-plasma according to the control vector to generate soft X-rays within the target band; acquiring the state vector, state reliability, and output vector generated from the pre-plasma diagnostic signal; calculating the control vector for the next irradiation based on the state vector, output vector, and response model and sending it to the actuator; and prohibiting the main pulse output when the state reliability is lower than a preset threshold or the safety constraints are not met. This application can compensate for output changes caused by target state drift and plasma evolution, improving in-band conversion efficiency, spectral stability, and operational safety.

Description

Technical Field

[0001] This application relates to the field of online diagnostic technology, and in particular to a method and system for controlling a dual-pulse laser-driven soft X-ray source. Background Technology

[0002] Laser-generated plasma soft X-ray sources ionize solid, liquid, gas, or cluster targets using high-power-density pulsed lasers, generating short-wave radiation. Compared to synchrotron radiation facilities, they offer advantages such as compact structure, synchronization with experimental processes, and selectability of target energy bands through target material and laser parameters. They can be used for soft X-ray lithography, microscopic imaging, absorption spectroscopy, semiconductor metrology, materials analysis, and plasma diagnostics. Dual-pulse drive typically utilizes a lower-energy pre-pulse to preheat, ablate, or expand the target material, followed by heating the pre-plasma with the main pulse to improve main pulse absorption and increase short-wave radiation output. Existing schemes disclose laser-plasma sources and drive systems that apply a pre-pulse before the main pulse, or enhance short-wave radiation by selecting the pre-main pulse energy ratio and time delay. However, these schemes typically rely on fixed parameters or optimal parameters obtained through pre-scanning.

[0003] Related technologies disclose methods to modify the energy of subsequent laser pulses based on the generated extreme ultraviolet energy using a proportional-integral control algorithm to reduce output oscillations caused by droplet-plasma interaction. They also disclose methods to adjust the pre-pulse energy based on the exposure dose. However, these methods primarily use radiation output energy as feedback and cannot directly distinguish between different causes such as pre-plasma density gradient mismatch, spot spatial misalignment, main pulse energy drift, target element damage, and debris accumulation. Existing experimental studies have also shown that the optimal time delay and energy ratio between the pre-pulse and main pulse vary with the target material, pulse width, focal spot, and plasma expansion state. A fixed time delay may not still correspond to the optimal state after drifts in target morphology, droplet size, focal position, or environmental pressure.

[0004] Therefore, there is a need for a dual-pulse laser-driven soft X-ray source control method and system that does not rely solely on single soft X-ray energy feedback, but instead establishes a pre-plasma observable state vector and uses pre-master pulse delay, energy ratio, spot ratio, relative spatial position, and master pulse energy as joint control variables, and performs closed-loop regulation under constraints of spectral purity, output fluctuation, and debris risk. Summary of the Invention

[0005] The purpose of this application is to provide a method and system for controlling a dual-pulse laser-driven soft X-ray source, which can effectively improve the in-band conversion efficiency, spectral stability and continuous operation safety of the dual-pulse laser-driven soft X-ray source.

[0006] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides a method for controlling a dual-pulse laser-driven soft X-ray source, wherein a controller performs the following steps: determining the control vector for the current dual-pulse irradiation, the control vector including the ratio of the time delay and energy between the pre-pulse and the main pulse, the ratio of the equivalent diameter of the pre-pulse spot to the equivalent diameter of the main pulse spot, the centroid offset, and the main pulse energy; controlling the pre-pulse to irradiate the target area to form a pre-plasma, and controlling the main pulse to couple with the pre-plasma according to the control vector to generate soft X-rays within the target band; acquiring the state vector, state confidence level, and output vector of the current irradiation generated by the pre-plasma diagnostic signal; the state vector at least includes the electron density gradient scale, equivalent energy, and centroid offset. The output vector includes at least three of the following: size, centroid location, and equivalent electron density. It also includes at least two of the following: soft X-ray energy within the target band, spectral purity, inter-pulse fluctuation index, and debris risk index. Based on the state vector, the output vector, and a pre-established or online-updated dual-pulse-plasma-soft X-ray response model, the control vector for the next dual-pulse irradiation is calculated within a preset feasible region and sent to the actuator. This ensures that the soft X-ray energy within the target band meets preset requirements, and that the spectral purity, inter-pulse fluctuation index, and debris risk index meet corresponding constraints. If the state reliability is lower than a preset threshold or the safety constraints are not met, the main pulse output is prohibited, degradation parameters are executed, recalibration is performed, or the system is shut down.

[0007] Secondly, this application provides a dual-pulse laser-driven soft X-ray source control system, the system comprising: Laser; A pulse distribution and synchronization module is used to distribute the laser pulses output by the laser into pre-pulses and main pulses; The pre-pulse control branch and the main pulse control branch are used to adjust the energy, spot size, and time delay of the pre-pulse and the main pulse, respectively. A beam combining and focusing module is used to guide the pre-pulse and the main pulse to the target action area inside the vacuum target chamber; a target assembly is disposed inside the vacuum target chamber; The diagnostic module is used to acquire pre-plasma diagnostic signals and soft X-ray output signals; A controller includes a memory and a processor, the memory storing a program, and the processor executing the program to implement the dual-pulse laser-driven soft X-ray source control method according to any one of claims 1 to 9; a pulse and beam actuator for adjusting the parameters of the pre-pulse and the main pulse according to a control vector.

[0008] In some embodiments, the state vector further includes a pre-pulse reflectivity; the electron density gradient scale is determined based on the reciprocal of the gradient of the logarithm of the electron density near the critical density surface along the main pulse propagation direction; and the equivalent electron density is obtained by inversion from at least one of interference phase shift, refraction deflection, absorption imaging, or calibrated emission images.

[0009] In some embodiments, a layered correction is performed based on the normalized overlap between the main pulse intensity distribution and the estimated electron density distribution: when the normalized overlap is below a preset lower limit, the ratio of centroid offset or equivalent diameter is corrected first; when the normalized overlap meets the requirements but the electron density gradient scale or the equivalent electron density deviates from the target range, the ratio of time delay or energy is corrected; when each state quantity is in the target range but the in-band energy is low, the main pulse energy or focus position is slightly corrected.

[0010] In some embodiments, the pre-plasma diagnostic signal includes at least three of the following: time-gated image, interference phase shift, shadow or refraction image, pre-pulse incident and reflected energy, target position, and vacuum pressure; each diagnostic signal is time-stamped with the same trigger reference, and after dark field subtraction, gain correction, spatial calibration, and outlier removal, the state vector and the state confidence level are generated.

[0011] In some embodiments, an effective range and heartbeat signal are set for each diagnostic channel; when some diagnostic signals are missing while the remaining diagnostic signals are valid, a reduced-dimensional state vector is generated based on the remaining valid diagnostic signals, and the main pulse energy is kept from increasing; when the time-gated image and the interferometric phase shift are missing at the same time, the main pulse is turned off, and only low-energy pre-pulse is allowed for diagnostic recovery.

[0012] In some embodiments, the spectral purity is the ratio of the energy within the target band to the total energy of the probe band; the inter-pulse fluctuation index is the coefficient of variation of the energy within the corresponding band for multiple consecutive irradiations, including the current irradiation; and the debris risk index consists of at least two of the following: particle flux, ion flux, change in transmittance of the collecting optical element, change in reflectance, and vacuum pressure transition. In some embodiments, at least one of constrained response surface optimization, model predictive control, recursive least squares combined with gradient update, and Bayesian optimization is used to obtain the control vector for the next double-pulse irradiation. The cost function on which it is based includes at least an in-band energy deviation term, a spectral purity deviation term, an inter-pulse fluctuation term, a debris risk term, and a control quantity change penalty term. Constraints are set on the absolute range of the control vector and the single-step change between two adjacent irradiations.

[0013] In some embodiments, the response model is established through a calibration phase: within an energy range below the operating upper limit, the time delay, energy ratio, equivalent diameter ratio, and centroid offset are sequentially changed according to a preset experimental design, and the corresponding state vector and output vector are recorded to identify the local response of each control component to the pre-plasma state, in-band energy, and debris risk; during the operation phase, the response model is updated online with small parameter perturbations when safety constraints are met.

[0014] In some embodiments, when the time delay between the pre-pulse and the main pulse is greater than the total delay of diagnosis, calculation and execution, at least one of the energy level, shutter release state and pointing bias of the main pulse is corrected within the same pulse pair according to the local response lookup table generated by the response model; when the pre-plasma diagnostic signal is saturated, missing or has insufficient state confidence, it is prohibited to increase the energy of the main pulse within the same pulse pair; otherwise, the state vector and output vector of the current irradiation are used to obtain the control vector for the next double-pulse irradiation.

[0015] According to the specific embodiments provided in this application, the following technical effects are disclosed: By incorporating the electron density gradient scale, equivalent size, centroid position, and equivalent electron density of the pre-plasma into the feedback, the pre-deployment state of the target material can be identified before the main pulse or between adjacent irradiations, rather than passively adjusting only after the output decreases, thus improving the timeliness of control. Jointly adjusting the time delay, energy ratio, equivalent spot diameter ratio, centroid offset, and main pulse energy can compensate for plasma expansion, target size changes, optical axis drift, and laser energy drift, respectively, improving output stability. Using in-band energy, spectral purity, inter-pulse fluctuations, and debris risk as multi-objective constraints can avoid extraspectral radiation and debris contamination caused by simply increasing the total radiation energy. The control vector for the next irradiation is obtained within a preset feasible region based on the state vector and output vector. When the state confidence is insufficient or the safety constraints are not met, the main pulse output is prohibited, degradation is performed, or recalibration is performed, reducing control abrupt changes caused by anomaly diagnosis and ensuring the safety of continuous operation. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A flowchart illustrating the dual-pulse laser-driven soft X-ray source control method provided in this application embodiment.

[0018] Figure 2A schematic diagram of the overall structure and closed-loop link of the control system for implementing the method of the embodiments of this application.

[0019] Figure 3 This is a schematic diagram showing the timing of the pre-pulse and main pulse, as well as the spatial relationship between the pre-plasma and the main pulse spot.

[0020] Figure 4 A schematic diagram of the process for generating pre-plasma state vectors and state confidence for multi-source diagnostic signals.

[0021] Figure 5 This is a schematic diagram of the closed-loop parameter update process based on the response model, cost function, and security constraints.

[0022] Figure 6 This is a schematic diagram illustrating the control feasible region, multi-objective constraints, and iterative trajectory, using the ratio of time delay to energy as an example. Detailed Implementation

[0023] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0024] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown, this embodiment provides a method for controlling a dual-pulse laser-driven soft X-ray source, including the following steps: S110. Determine the control vector for the current double-pulse irradiation. The control vector includes the ratio of the time delay and energy between the pre-pulse and the main pulse, the ratio of the equivalent diameter of the pre-pulse spot to the main pulse spot, the centroid offset, and the main pulse energy.

[0028] S120: Control the pre-pulse to irradiate the target area to form a pre-plasma, and control the main pulse to couple with the pre-plasma according to the control vector to generate soft X-rays in the target energy band.

[0029] S130. Obtain the state vector, state confidence level, and output vector of the current irradiation generated from the pre-plasma diagnostic signal. The state vector shall include at least three of the following: electron density gradient scale, equivalent size, centroid position, and equivalent electron density. The output vector shall include at least two of the following: soft X-ray energy within the target band, spectral purity, inter-pulse fluctuation index, and debris risk index.

[0030] S140. Based on the state vector, output vector, and pre-established or online-updated dual-pulse-plasma-soft X-ray response model, the control vector for the next dual-pulse irradiation is obtained within the preset feasible region and sent to the actuator, so that the soft X-ray energy in the target band meets the preset requirements and the spectral purity, inter-pulse fluctuation index, and debris risk index meet the corresponding constraints.

[0031] S150. When the state reliability is lower than the preset threshold or the safety constraints are not met, the main pulse output is prohibited, the degradation parameters are executed, the system is recalibrated, or the system is shut down.

[0032] The above method is executed by the controller and is applicable to, for example, Figure 2 The control system shown. (As shown) Figure 2 As shown, the control system includes a laser 100, a pulse distribution and synchronization module 110, a pre-pulse control branch 120, a main pulse control branch 130, a beam combining and focusing module 140, a vacuum target chamber 150, a target assembly 160, a soft X-ray collection module 170, a soft X-ray output terminal 180, a diagnostic module 190, a controller 200, and a pulse and beam actuator 210. The pre-pulse and main pulse can be generated by splitting the same laser pulse and adjusting them separately, or they can be generated by two lasers synchronized with a shared reference clock.

[0033] For the k-th double-pulse irradiation, the controller 200 uses the control vector uk to describe the time delay, energy ratio, spot ratio, spatial offset, and main pulse energy: (1) In equation (1), Δtk is the time delay between the pre-pulse and the main pulse; δrx,k and δry,k are the offsets of the centroids of the two light spots in mutually orthogonal directions. The energy ratio ρk and the equivalent diameter ratio βk of the light spots satisfy the following: (2) In equation (2), EP,k and EM,k are the pre-pulse energy and main pulse energy reaching the target action area, respectively; DP,k and DM,k are the equivalent spot diameters of the pre-pulse and main pulse on the predetermined reference plane, respectively. The equivalent spot diameter can be determined by the diameter of the enclosing circle containing a preset proportion of pulse energy, the second-order moment diameter, or an equivalent calibration definition, and the same definition is used in the same operating batch. In one embodiment, the time delay is 10 picoseconds to 500 nanoseconds, the energy ratio is 0.001 to 0.5, the equivalent diameter ratio is 0.2 to 2.0, and the absolute value of the centroid offset is not greater than 0.5 times the equivalent diameter of the pre-plasma.

[0034] like Figure 3 As shown, the pre-pulse first irradiates the target area within the vacuum target chamber 150, forming an outwardly expanding pre-plasma. The main pulse is incident after a time delay, and its spot is offset relative to the centroid of the pre-plasma. The density gradient and spatial scale at the arrival of the main pulse can be changed by adjusting the time delay; the pre-expansion degree of the target material can be changed by adjusting the energy ratio; and the spatial overlap between the main pulse and the absorbable plasma region can be changed by adjusting the equivalent diameter ratio and offset of the spot. After the main pulse couples with the pre-plasma, the target material forms a radiating plasma and generates soft X-rays within the target energy band, which are transmitted by the soft X-ray collection module 170 to the output terminal 180 and the diagnostic branch.

[0035] The target band can be set according to wavelength or photon energy, ranging from 0.1 nm to 10 nm, or from 0.5 keV to 2 keV photon energy; for water window microscopy applications, a sub-band ranging from approximately 2.3 nm to 4.4 nm can be selected. The target material selected according to the target band includes at least one of carbon, aluminum, silicon, titanium, copper, zirconium, molybdenum, tin, tantalum, tungsten, gold, bismuth and their alloys, compounds, or particulate dispersions; the target can be a solid target, a microstructured target, a rotating target, a ribbon target, a droplet target, a liquid jet target, a gas cluster target, or a liquid target containing target element particles.

[0036] like Figure 4 As shown, the diagnostic module 190 includes a gated plasma imaging unit 220, an interferometric or refraction measurement unit 230, a pre-pulse reflection measurement unit 240, and a target and environment measurement unit 250. At at least one diagnostic moment after the pre-pulse, each diagnostic unit acquires the pre-plasma diagnostic signal. After processing by the time alignment, calibration, and state estimation module 260, a state vector 270 and a state confidence level 280 are obtained. The outlier and missing measurement judgment module 290 marks data that are saturated, obstructed, have lost triggering, or exceed the calibration range. The state vector is represented as: (3) In equation (3), Ln,k is the electron density gradient scale near the critical density surface, Dp,k is the equivalent diameter of the pre-plasma, δrk is the offset of the pre-plasma centroid relative to the main pulse optical axis, Neq,k is the equivalent electron density obtained from the line integral electron density or the calibrated emission intensity, and Rp,k is the pre-pulse reflectivity. The electron density gradient scale can be expressed as: (4) In equation (4), ne is the electron density and z is the coordinate along the propagation direction of the main pulse. Each diagnostic signal is time-stamped with the same trigger reference, and after dark field subtraction, gain correction, spatial calibration and outlier removal, a state vector and state confidence are generated.

[0037] After the main pulse interacts with the pre-plasma, the diagnostic branch acquires the target band energy EB,k, spectral purity Pk, coefficient of variation CVk of the band energy within the continuous window, and debris risk Fk. The output vector is expressed as: (5) The components in equation (5) are determined as follows: the in-band energy is obtained from a calibrated photodetector or spectrometer; the spectral purity is the ratio of the target band energy to the total energy of the diagnostic detection band; the coefficient of variation is calculated based on a sliding window containing the current irradiation; the debris risk consists of at least two of the following: the transmittance of the particle or ion sensor, the reflectivity of the collecting mirror or filter, the vacuum pressure transition, and the ejected particle signal in the target image. Different components are first normalized according to the calibration upper limit, and then synthesized using the maximum value, weighted sum, or risk level. The wavelength and photon energy satisfy the following relationship: (6) In equation (6), photon energy is expressed in kiloelectron volts and wavelength is expressed in nanometers.

[0038] like Figure 5 As shown, after each irradiation, the state vector and output vector are first acquired; the candidate control quantity prediction module 310 generates several candidate control vectors using the response model; the multi-objective cost calculation module 320 calculates the predicted cost of each candidate control vector; the constraint and rate of change check module 330 excludes candidate quantities that exceed the feasible region, have excessive single-step changes, or have exceeded the expected debris risk limit; the control quantity selection module 340 selects a control vector from the remaining candidate quantities and triggers the next pulse pair via the pulse pair trigger module 350; the in-band output and debris measurement module 360 ​​measures the output vector; after irradiation, the response model update module 370 updates the response model; if there are no candidate quantities that meet the constraints, the degradation, reset, or shutdown module 380 performs the corresponding processing. The control feasible region is as follows: Figure 6As shown, the operating point is determined by the laser output capability, optical component damage threshold, target ablation limit, main pulse and pre-plasma spatial overlap requirement, vacuum system capability, and debris risk limit. The controller searches for an operating point within the feasible region that balances in-band energy, spectral purity, output fluctuation, and debris risk, based on the following cost function: (7) In equation (7), EB,ref is the reference value of the target band energy; w1 to w4 are non-negative weights, which can be set according to application requirements: for lithography or measurement applications, the weights of in-band stability and spectral purity can be increased; for exploratory spectral experiments, the weights of in-band energy can be increased; and for continuous operation, the weights of debris risk and control change penalty can be increased; Q is the control quantity change penalty matrix. The control vector for the next double-pulse irradiation is obtained by solving the following equation: (8) In equation (8), f(xk,u) is the output prediction given the current state xk and the candidate control vector u; Δui,max is the maximum single-step change of the i-th control component. By simultaneously limiting the absolute range and single-step change of the control quantity, abrupt changes in the parameters of the pre-pulse or main pulse due to a single abnormality diagnosis can be avoided.

[0039] To reduce coupling misadjustment between control variables, the controller can employ a hierarchical correction strategy: the degree of coupling is characterized by the normalized overlap between the main pulse intensity distribution and the estimated electron density distribution. (9) In equation (9), V is the integration region. When the normalized overlap is lower than the set lower limit, the centroid offset or the equivalent diameter ratio of the spot is corrected first. When the normalized overlap meets the requirements but the electron density gradient scale or the equivalent electron density deviates from the target range, the time delay or energy ratio is corrected first. When each state quantity meets the target range but the in-band output is still too low, the main pulse energy or focusing position is slightly corrected.

[0040] The dual-pulse-plasma-soft X-ray response model is established through a startup calibration phase. This phase first checks the vacuum level, target position, beam coaxiality, diagnostic null point, and collection optical protection status. Then, within an energy range below the operating upper limit, the time delay, energy ratio, equivalent beam diameter ratio, and centroid offset are varied using orthogonal design, Latin hypercube design, local mesh scanning, or other experimental design methods. The corresponding state and output vectors are recorded to identify the local responses of each control component to the pre-plasma state, in-band energy, and debris risk. The response model can be a piecewise linear model, a polynomial response surface, a Gaussian process model, a neural network model, or a surrogate model combined with radiation fluid simulation. During the operation phase, the response model is updated online with small parameter perturbations only when safety constraints are met. The target pre-plasma state is calibrated together with the target energy band, main pulse wavelength, pulse width, polarization, incident angle, and target material.

[0041] For systems where the pre-master pulse delay is greater than the total delay of diagnosis, calculation, and execution, the pre-plasma rapid diagnostic results can be used for fine-tuning of the master pulse shutter, energy, or direction within the same pulse pair: Immediately after the pre-pulse, the pre-plasma profile, centroid, and reflectivity are extracted. The field-programmable gate array (FPGA) selects the master pulse energy level, shutter release state, and rapid mirror offset based on a pre-lookup local response model. The rapid channel only performs limited level corrections within the calibration range. If the rapid diagnostic signal is saturated, missing, or lacks sufficient confidence, increasing the master pulse energy within the same pulse pair is prohibited; only maintaining, reducing, or shutting down the master pulse is allowed. For picosecond-level systems or systems that cannot complete adjustment within the same pulse pair, the state vector and output vector of the current irradiation are used to obtain the control vector for the next irradiation. Both modes use the same state vector, constraints, and anomaly handling logic.

[0042] State reliability is jointly determined by the saturation level of the diagnostic signal, signal-to-noise ratio, timestamp integrity, spatial calibration validity, consistency of different diagnostic quantities, and whether the state is within the model training or calibration range. If the state reliability is below the first threshold, increasing energy control based on the state is prohibited; if the state reliability is between the first and second thresholds, only maintaining parameters or performing degraded parameters with reduced energy is allowed; only if the state reliability is not lower than the second threshold is full constraint optimization allowed. The main pulse trigger is also constrained by vacuum pressure, target position, shutter state, pre-pulse energy, spatial overlap, state of collection optical protection components, and debris risk. In case of an anomaly, the main pulse shutter is first closed, the original and processed data of several irradiations before the fault are saved, and then the trigger, target position, and diagnostic zero point are checked with a low-energy verification pulse, and the target position verification and diagnostic zero point verification are performed sequentially; after the verification is passed, a degraded control vector with limited energy and time delay changes is used to resume operation; if the verification fails, the system remains shut down.

[0043] The system sets effective ranges and heartbeat signals for each diagnostic channel. When the interference signal is temporarily missing but the gated image, pre-pulse reflectivity, and target data are valid, the controller uses a reduced-dimensional state vector and keeps the main pulse energy from increasing. When both the gated image and the interference signal are missing, the main pulse is shut down, and only low-energy pre-pulses are allowed for diagnostic recovery. When adjacent irradiations use different target units, the target unit number, initial position, historical irradiation count, historical state vector, and historical output vector are associated and stored. For a new target unit, an initial control vector is given based on the response model of adjacent units in the same batch. For units that have already been used, the upper limit of the pre-pulse or main pulse energy is reduced based on material loss and geometric changes, and the system switches to another target unit when the target unit's health falls below a threshold.

[0044] In one specific embodiment, the laser's center wavelength is 0.8 micrometers, 1.03 micrometers, or 1.064 micrometers. The pre-pulse and main pulse are formed by the same laser beam splitting. The target material is selected from molybdenum, zirconium, or their surface coatings. During stable operation, the controller ensures that the electron density gradient scale, pre-plasma equivalent diameter, and normalized overlap are within the target range. When the energy within the target band is insufficient, the controller corrects the parameters in the order of spatial density, then density, and finally main energy. After each irradiation, the controller moves to a new target point to reduce the impact of ablation pits on the next irradiation. In another implementation, the target assembly uses droplets, liquid jets, or particulate dispersions containing carbon, zirconium, molybdenum, or other target elements. A high-speed imager measures the droplet diameter, position, and velocity before it reaches the action zone. When the droplet diameter increases or the velocity changes, causing the pre-plasma equivalent size to be too large, the controller reduces the pre-pulse energy ratio or shortens the time delay. When the pre-plasma centroid deviates from the main pulse optical axis, spatial bias is corrected preferentially by rapidly rotating the mirror or by adjusting the target trigger timing. When spatial overlap meets the requirements but the in-band energy decreases and the out-of-spectrum energy increases, the main pulse energy is reduced or the time delay is changed to bring the equivalent electron density back to the target range. In another embodiment, the target energy band is 0.5 kEV to 2 kEV, and the target material is selected from titanium, copper, molybdenum, tin, tantalum, tungsten, gold, bismuth or a combination thereof. The collection branch is equipped with a grazing incidence mirror, a thin film filter and an energy spectrometer. The energy spectrometer integrates the target energy band and the adjacent background energy band to calculate the spectral purity. The target is controlled by setting the in-band energy to be no lower than a preset proportion of the reference value, the spectral purity to be no lower than the purity lower limit, the sliding window coefficient of variation to be no higher than the fluctuation upper limit and the debris risk to be no higher than the risk upper limit.

[0045] This embodiment provides a dual-pulse laser-driven soft X-ray source control system, such as... Figure 2As shown, the system includes a laser 100, a pulse distribution and synchronization module 110, a pre-pulse control branch 120, a main pulse control branch 130, a beam combining and focusing module 140, a vacuum target chamber 150, a target assembly 160, a soft X-ray collection module 170, a soft X-ray output terminal 180, a diagnostic module 190, a controller 200, and a pulse and beam actuator 210. The controller 200 includes a memory and a processor. The memory stores a program, and when the processor executes the program, it implements the dual-pulse laser-driven soft X-ray source control method of Embodiment 1.

[0046] Specifically, the pulse distribution and synchronization module 110 is used to distribute the laser pulses output by the laser 100 into pre-pulses and main pulses and keep them synchronized; the pre-pulse control branch 120 and the main pulse control branch 130 are used to adjust the energy, spot size, and time delay of the pre-pulse and main pulse, respectively; the beam combining and focusing module 140 is used to guide the pre-pulse and main pulse to the target action area within the vacuum target chamber 150; the diagnostic module 190 is used to acquire the pre-plasma diagnostic signal and the soft X-ray output signal; the controller 200 is used to obtain the control vector for the next double-pulse irradiation based on the state vector, output vector, and response model; and the pulse and beam actuator 210 is used to adjust the parameters of the pre-pulse and main pulse according to the control vector. The steps implemented by the processor when executing the program are the same as in Embodiment 1, and will not be repeated here.

[0047] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling a dual-pulse laser-driven soft X-ray source, characterized in that, The method includes: Determine the control vector for the current double-pulse irradiation. The control vector includes the ratio of the time delay and energy between the pre-pulse and the main pulse, the ratio of the equivalent diameter of the pre-pulse spot to the main pulse spot, the centroid offset, and the main pulse energy. The pre-pulse is controlled to irradiate the target area to form a pre-plasma. The main pulse is then controlled to couple with the pre-plasma according to the control vector to generate soft X-rays within the target's energy band. The state vector, state confidence, and output vector of the current irradiation are obtained from the pre-plasma diagnostic signal. The state vector includes three of the following: electron density gradient scale, equivalent size, centroid position, and equivalent electron density. The output vector includes soft X-ray energy in the target band and two of the following: spectral purity, interpulse fluctuation index, and debris risk index. Based on the state vector, the output vector, and the dual-pulse-plasma-soft X-ray response model, the control vector for the next dual-pulse irradiation is obtained within the preset feasible region and sent to the actuator, so that the soft X-ray energy in the target band meets the preset requirements and the spectral purity, inter-pulse fluctuation index, and debris risk index meet the corresponding constraints. When the state reliability is lower than the preset threshold or the safety constraints are not met, the main pulse output is prohibited, degradation parameters are executed, recalibration is performed, or the machine is shut down.

2. The method for controlling a dual-pulse laser-driven soft X-ray source according to claim 1, characterized in that, The state vector also includes the pre-pulse reflectivity; the electron density gradient scale is determined based on the reciprocal of the gradient of the logarithm of the electron density near the critical density surface along the main pulse propagation direction; the equivalent electron density is obtained by inversion from at least one of interference phase shift, refraction deflection, absorption imaging, or calibrated emission images.

3. The method for controlling a dual-pulse laser-driven soft X-ray source according to claim 2, characterized in that, Layered correction is performed based on the normalized overlap between the main pulse intensity distribution and the estimated electron density distribution: when the normalized overlap is lower than a preset lower limit, the ratio of centroid offset or equivalent diameter is corrected first; when the normalized overlap meets the requirements but the electron density gradient scale or the equivalent electron density deviates from the target range, the ratio of time delay or energy is corrected; when each state quantity is in the target range but the in-band energy is low, the main pulse energy or focus position is slightly corrected.

4. The method for controlling a dual-pulse laser-driven soft X-ray source according to claim 1, characterized in that, The pre-plasma diagnostic signal includes at least three of the following: time-gated image, interference phase shift, shadow or refraction image, pre-pulse incident and reflected energy, target position, and vacuum pressure. Each diagnostic signal is time-marked with the same trigger reference and is then processed by dark field subtraction, gain correction, spatial calibration, and outlier removal to generate the state vector and the state confidence level.

5. The method for controlling a dual-pulse laser-driven soft X-ray source according to claim 4, characterized in that, Set the effective range and heartbeat signal for each diagnostic channel; when some diagnostic signals are missing while the rest are valid, generate a reduced-dimensional state vector based on the remaining valid diagnostic signals and keep the main pulse energy from increasing; when both the time-gated image and the interferometric phase shift are missing, turn off the main pulse and only allow diagnostic recovery with a low-energy pre-pulse.

6. The method for controlling a dual-pulse laser-driven soft X-ray source according to claim 1, characterized in that, The spectral purity is the ratio of the energy in the target band to the total energy in the detector band; the inter-pulse fluctuation index is the coefficient of variation of the energy in the corresponding band for multiple consecutive irradiations, including the current irradiation; the debris risk index consists of at least two of the following: particle flux, ion flux, change in transmittance of the collecting optical element, change in reflectance, and vacuum pressure transition.

7. The method for controlling a dual-pulse laser-driven soft X-ray source according to claim 1, characterized in that, When obtaining the control vector for the next double-pulse irradiation, at least one of the following is used: constrained response surface optimization, model predictive control, recursive least squares combined with gradient update, and Bayesian optimization. The cost function used includes at least the in-band energy deviation term, the spectral purity deviation term, the inter-pulse fluctuation term, the debris risk term, and the control quantity change penalty term. Constraints are set on the absolute range of the control vector and the single-step change between two adjacent irradiations.

8. The method for controlling a dual-pulse laser-driven soft X-ray source according to claim 1, characterized in that, The response model is established through a calibration phase: within an energy range below the working upper limit, the time delay, energy ratio, equivalent diameter ratio, and centroid offset are changed sequentially according to a preset experimental design, and the corresponding state vector and output vector are recorded to identify the local response of each control component to the pre-plasma state, in-band energy, and debris risk. During the operation phase, the response model is updated online with small parameter perturbations when the safety constraints are satisfied.

9. The method for controlling a dual-pulse laser-driven soft X-ray source according to claim 8, characterized in that, When the time delay between the pre-pulse and the main pulse is greater than the total delay of diagnosis, calculation and execution, at least one of the energy level, shutter release state and pointing bias of the main pulse is corrected within the same pulse pair according to the local response lookup table generated by the response model; when the pre-plasma diagnostic signal is saturated, missing or has insufficient state confidence, it is prohibited to increase the energy of the main pulse within the same pulse pair; otherwise, the state vector and output vector of the current irradiation are used to obtain the control vector for the next double-pulse irradiation.

10. A dual-pulse laser-driven soft X-ray source control system, characterized in that, The system includes: Laser; A pulse distribution and synchronization module is used to distribute the laser pulses output by the laser into pre-pulses and main pulses; The pre-pulse control branch and the main pulse control branch are used to adjust the energy, spot size, and time delay of the pre-pulse and the main pulse, respectively. A beam combining and focusing module is used to guide the pre-pulse and the main pulse to the target action area inside the vacuum target chamber; a target assembly is disposed inside the vacuum target chamber; The diagnostic module is used to acquire pre-plasma diagnostic signals and soft X-ray output signals; A controller includes a memory and a processor, the memory storing a program, and the processor executing the program to implement the dual-pulse laser-driven soft X-ray source control method according to any one of claims 1 to 9; a pulse and beam actuator for adjusting the parameters of the pre-pulse and the main pulse according to a control vector.

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