Long-delay data feedback ultrafast imaging time zero point positioning method and system

Abstract

The invention provides a long-delay data feedback ultrafast imaging time zero point positioning method and system, and relates to the technical field of ultrafast imaging, and the method comprises the steps: determining the position of a one-dimensional delay displacement table corresponding to a fuzzy time zero point through employing a sample instantaneous signal image; determining electron densities corresponding to different time delays according to the transmissivity-electron density conversion model and the sample instantaneous signal image; and improving a femtosecond laser processing theoretical model by using femtosecond laser processing attenuation data, aligning selected data points with a simulation curve of the electron density simulation evolution model, and reversely deducing a time point corresponding to an actual time zero point on a simulation time axis to obtain the actual time zero point. The method has no requirements on detection instruments and equipment, is not limited by the resolution precision of a detector, and can reversely calculate the accurate actual time zero point by comparing the collected data with the curve of the electron density simulation evolution model.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast imaging technology, and in particular to a method and system for long-delay data feedback ultrafast imaging time zero positioning. Background Art

[0002] Ultrafast dynamics is the foundation of all scientific research on ultrafast processes, including ultrafast manufacturing, ultrafast physics, and ultrafast chemistry. Ultrafast dynamics observation is the basic means to open the "black box" of transient processes such as chemical and physical changes in materials. It is also one of the current cutting-edge scientific research directions in aerospace, biomedicine, physical chemistry, special manufacturing, microelectronics and other fields.

[0003] Unconstrained by the bandwidth limitations of electronic systems, femtosecond laser-based ultrafast continuous imaging technology possesses the unique ability to record difficult-to-reproduce and irreversible transient dynamic processes. This technology enables high-sequence depth and high-temporal and spatial resolution imaging of ultrafast physical and chemical phenomena, making it an indispensable technology for exploring fundamental science and advancing precision measurement science. In particular, in femtosecond laser micro- and nanofabrication, the development of ultrafast continuous imaging technology is crucial for achieving full-timescale detection of complex, random, and difficult-to-reproduce ultrafast physical and chemical phenomena in manufacturing, as well as for resolving the challenges of high-precision, three-dimensional, and extreme manufacturing. Time zero, as the initial state of the transient process being studied in femtosecond laser micro- and nanofabrication, directly determines the temporal accuracy of all transient signal data.

[0004] Most current methods for determining the time zero point are based on the appearance of detection signals. This method is completely limited by the resolution accuracy of the detector. If the spatial resolution accuracy of the detector is low or the time zero point signal is weak, the time zero point positioning accuracy of ultrafast imaging will be seriously affected. Summary of the Invention

[0005] The problem to be solved by the present invention is that the current method for confirming the time zero point depends on the resolution accuracy of the detector, and the positioning accuracy of the time zero point is unstable and easily affected.

[0006] To solve the above problems, the present invention provides a method for time zero positioning of ultrafast imaging with long-delay data feedback, comprising:

[0007] The position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point is determined by using the instantaneous signal image of the sample obtained by the femtosecond laser ultrafast imaging device;

[0008] Determine the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the experimentally obtained instantaneous signal image of the sample, where the time delay is the optical path difference formed by the delay between the detection light and the pump light in the femtosecond laser ultrafast imaging device;

[0009] The attenuation data of samples processed by femtosecond laser were used to improve the theoretical model of femtosecond laser processing and obtain the electron density simulation evolution model;

[0010] Select multiple continuous data points from the electron density corresponding to different time delays, align the selected data points with the simulation curve of the electron density simulation evolution model, reversely infer the time point corresponding to the actual time zero on the simulation time axis, and obtain the time difference between the actual time zero and the theoretical time zero;

[0011] The position of the one-dimensional time-delay displacement stage corresponding to the fuzzy time zero point is used as a reference basis, and the position of the one-dimensional time-delay displacement stage corresponding to the actual time zero point is obtained according to the time difference.

[0012] Optionally, the determining the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point using the sample instantaneous signal image acquired by the femtosecond laser ultrafast imaging device comprises:

[0013] Experiments were conducted using a femtosecond laser ultrafast imaging device. The one-dimensional time-delay stage was adjusted to change the optical path of the detection light, and the ultrafast imaging results were observed. The moment when the plasma filaments visible to the naked eye appeared was determined as the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point.

[0014] Optionally, determining the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the instantaneous signal image of the sample obtained from the experiment includes:

[0015] The center of the sample's processing spot is selected as the optical axis. Starting from the position of the one-dimensional delay stage corresponding to the fuzzy time zero point, the position of the one-dimensional delay stage is adjusted to generate different time delays, wherein the different time delays constitute a preset time delay sequence;

[0016] Under different time delays, the corresponding sample instantaneous signal images are obtained;

[0017] Obtaining transmittances corresponding to different time delays according to the instantaneous signal image of the sample;

[0018] According to the transmittance and transmittance-electron density conversion model, the electron density corresponding to different time delays is obtained.

[0019] Optionally, the transmittance-electron density conversion model is:

[0020]

[0021] in, is the intrinsic dielectric function, is the refractive index of the material, i represents the imaginary part, c is the speed of light in a vacuum, T is the transmittance, ω is the detection laser frequency, d is the effective diameter of the plasma filament, is the free electron collision time, is the electron mass, is the dielectric constant of vacuum, is the charge of the electron.

[0022] Optionally, the electron density simulation evolution model is:

[0023]

[0024] in, is the multiphoton coefficient, is the ionization constant, for The signal intensity at the moment, for The electron density at time for The electron density at time is the decay rate, is the dielectric function of the material, is the intrinsic dielectric function, is the electron density, is the electron charge, To detect the laser frequency, i represents the imaginary part, is the electron mass, is the dielectric constant of vacuum, is the material refractive index, is the extinction coefficient, is the instantaneous surface reflectivity, is the laser flux, is the laser pulse width, is the tth moment, Indicates the Iterations.

[0025] On the other hand, the present invention also provides a long-delay data feedback ultrafast imaging time zero positioning system, comprising:

[0026] A fuzzy time zero point determination module is used to determine the position of the one-dimensional time delay displacement stage corresponding to the fuzzy time zero point using the sample instantaneous signal image obtained by the femtosecond laser ultrafast imaging device;

[0027] An electron density analysis module is used to determine the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the experimentally obtained instantaneous signal image of the sample, wherein the time delay is the optical path difference formed by the delay between the detection light and the pump light in the femtosecond laser ultrafast imaging device;

[0028] The evolution model improvement module is used to improve the femtosecond laser processing theoretical model using the attenuation data after femtosecond laser processing of samples to obtain an electron density simulation evolution model;

[0029] The actual time zero point analysis module is used to select multiple continuous data points from the electron density corresponding to different time delays, align the selected data points with the simulation curve of the electron density simulation evolution model, and reversely infer the time point corresponding to the actual time zero point on the simulation time axis to obtain the time difference between the actual time zero point and the theoretical time zero point;

[0030] The position analysis module is used to obtain the position of the one-dimensional time-delay displacement stage corresponding to the actual time zero point based on the time difference, taking the position of the one-dimensional time-delay displacement stage corresponding to the fuzzy time zero point as a reference.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point is determined by using the instantaneous signal image of the sample obtained by the femtosecond laser ultrafast imaging device; the electron density corresponding to different time delays is determined based on the transmittance-electron density conversion model and the instantaneous signal image of the sample obtained experimentally; the femtosecond laser processing theoretical model is improved using the attenuation data after femtosecond laser processing of the sample to obtain an electron density simulation evolution model; multiple continuous data points are selected from the electron density corresponding to different time delays, and the selected data points are aligned with the simulation curve of the electron density simulation evolution model to reversely infer the time point corresponding to the actual time zero point on the simulation time axis to obtain the time difference between the actual time zero point and the theoretical time zero point; based on the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point, the position of the one-dimensional time-delay stage corresponding to the actual time zero point is obtained according to the time difference. The above method has no requirements for detection instruments and equipment, and is not limited by the resolution accuracy of the detector. Even in cases where the spatial resolution accuracy of the detector is low or the time zero point signal is weak, the above method can be used to collect sufficient attenuation data, improve the electron density simulation evolution model, and then use the collected data to compare with the curve of the electron density simulation evolution model to reversely calculate the accurate actual time zero point. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic flow chart of a method for time zero positioning of ultrafast imaging using long-delay data feedback according to an embodiment of the present invention is shown;

[0034] Figure 2 A schematic structural diagram of a femtosecond laser ultrafast imaging device according to an embodiment of the present invention is shown;

[0035] Figure 3 shows the background image and signal image of the ultrafast imaging experiment in an embodiment of the present invention;

[0036] Figure 4 A schematic diagram of a fuzzy time zero point in an embodiment of the present invention is shown;

[0037] Figure 5 A schematic diagram showing the evolution of ultrafast imaging transmittance and electron density over time in an embodiment of the present invention is shown;

[0038] Figure 6 An improved flow chart of a femtosecond laser processing theoretical model according to an embodiment of the present invention is shown;

[0039] Figure 7 A schematic diagram showing a comparison between a curve of an electron density simulation evolution model and experimental data in an embodiment of the present invention is shown;

[0040] Figure 8 A schematic structural diagram of a long-delay data feedback ultrafast imaging time zero positioning system according to an embodiment of the present invention is shown.

[0041] Description of Reference Numerals

[0042] 1. First aperture; 2. Second aperture; 3. Beam splitter; 4. First reflector; 5. Second reflector; 6. Attenuator; 7. Third aperture; 8. BBO frequency-doubling crystal; 9. Fourth aperture; 10. Fifth aperture; 11. Mechanical switch; 12. Third reflector; 13. 5x objective lens; 14. Sixth aperture; 15. Fourth reflector; 16. Fifth reflector; 17. One-dimensional time-delay stage; 18. Sixth reflector; 19. Seventh aperture; 20. Eighth aperture; 21. Three-dimensional sample translation stage; 22. 20x objective lens; 23. Color filter; 24. CCD camera. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application are clearly and completely described. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0044] Throughout this specification, references to the terms "embodiment," "one embodiment," and "an implementation" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or implementation are included in at least one embodiment or implementation of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or implementation. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or implementations.

[0045] like Figure 1 As shown, an embodiment of the present application provides a long-delay data feedback ultrafast imaging time zero point positioning method, comprising:

[0046] S1: Use the instantaneous signal image of the sample obtained by the femtosecond laser ultrafast imaging device to determine the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point.

[0047] S2: Determine the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the experimentally obtained instantaneous signal image of the sample, where the time delay is the optical path difference formed by the detection light lagging behind the pump light in the femtosecond laser ultrafast imaging device.

[0048] S3: Use the attenuation data after femtosecond laser processing of samples to improve the femtosecond laser processing theoretical model and obtain the electron density simulation evolution model.

[0049] S4: Select multiple continuous data points from the electron density corresponding to different time delays, use the selected data points to align with the simulation curve of the electron density simulation evolution model, reversely infer the time point corresponding to the actual time zero point on the simulation time axis, and obtain the time difference between the actual time zero point and the theoretical time zero point.

[0050] S5: Taking the position of the one-dimensional time-delay displacement stage corresponding to the fuzzy time zero point as a reference basis, the position of the one-dimensional time-delay displacement stage corresponding to the actual time zero point is obtained according to the time difference.

[0051] In this embodiment, the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point is first determined using a sample instantaneous signal image obtained by a femtosecond laser ultrafast imaging device. Due to the limited resolution accuracy of the human eye, the position corresponding to the fuzzy time zero point is inaccurate, but the fuzzy time zero point is near the real time zero point. The electron density corresponding to different time delays is determined based on the transmittance-electron density conversion model and the sample instantaneous signal image obtained experimentally. The femtosecond laser processing theoretical model is improved using the attenuation data after femtosecond laser processing of the sample to obtain an electron density simulation evolution model. The attenuation data includes the electron density and signal light intensity corresponding to different time moments. A plurality of continuous data points are selected from the electron density corresponding to different time delays, and the selected data points are aligned with the simulation curve of the electron density simulation evolution model to reversely infer the time point corresponding to the actual time zero point on the simulation time axis to obtain the time difference between the actual time zero point and the theoretical time zero point. The position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point is used as a reference basis, and the position of the one-dimensional time-delay stage corresponding to the actual time zero point is obtained based on the time difference. The above method has no requirements for detection instruments and equipment, and is not limited by the resolution accuracy of the detector. Even in cases where the spatial resolution accuracy of the detector is low or the time zero point signal is weak, the above method can be used to collect sufficient attenuation data, improve the electron density simulation evolution model, and then use the collected data to compare with the curve of the electron density simulation evolution model to reversely calculate the accurate actual time zero point, and then adjust the one-dimensional delay displacement stage to the position corresponding to the actual time zero point, so that the subsequent obtained sample instantaneous signal diagram can be accurately compared with the time point.

[0052] Furthermore, the proposed time zero positioning method is highly accurate. Because the electron density evolution model achieves sub-femtosecond temporal precision, the method is limited only by the accuracy of the one-dimensional time-delay stage. If a nanometer-scale high-precision time-delay stage is used, time zero positioning accuracy can reach femtoseconds. This method also requires minimal sample material requirements, enabling the use of common materials such as fused quartz, sapphire, and silicon as standard samples. This method is convenient and simple.

[0053] Each step is described in detail below.

[0054] S1: Use the instantaneous signal image of the sample obtained by the femtosecond laser ultrafast imaging device to determine the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point.

[0055] Specifically, the femtosecond laser ultrafast imaging device can be a transmission type or a reflection type ultrafast imaging device. Figure 2As shown, the laser emits a femtosecond laser, which passes through the first aperture 1 and the second aperture 2 to reach the beam splitter 3 and is divided into two beams of laser: one beam of laser is used as pump light, which passes through the fourth aperture 9, the fifth aperture 10, the mechanical switch 11, the third reflector 12 and the 5x objective lens 13 to reach the sample. The sample is fixed on the three-dimensional sample translation stage 21, and the pump light processes the sample. The mechanical switch 11 is turned on and off to control whether the pump light passes through the mechanical switch 11 to reach the sample; the other beam of laser passes through the first reflector 4, the second reflector 5, the attenuation plate 6, the third aperture 7 and the BBO frequency doubling crystal 8 to form a detection light. The detection light passes through the sixth aperture 14, the fourth reflector 15 and the second reflector 16. The mirror 15, the sixth reflector 16, the sixth reflector 18, the seventh aperture 19 and the eighth aperture 20 reach the processing surface of the sample to detect the sample. The detection light is irradiated on the sample, and the CCD camera 24 under the sample collects the processing area of the sample cup after the detection light is irradiated. The instantaneous signal image of the sample collected by the CCD camera 24 is magnified by the 20x objective lens 22 and processed by the color filter 23. Among them, the sixth aperture 14, the fourth reflector 15 and the sixth reflector 16 are installed on the one-dimensional delay displacement stage 17. Adjusting the position of the one-dimensional delay displacement stage 17 can increase or decrease the optical path length of the detection light, thereby changing the time it takes for the detection light to reach the sample surface. While the pump light processes the sample, the probe light acquires the sample's state. To accurately capture the sample's processing state at different processing moments, detection and acquisition must begin at the very first moment of sample processing (i.e., time zero). This means that the processing timeline corresponds to the moment the sample's transient signal image is acquired, facilitating subsequent analysis of the processing state. When the pump light reaches the sample, followed by the probe light, there is a time delay relative to the pump light. Time zero is determined by observing the appearance of plasma filaments in the sample's transient signal image. However, plasma filaments are thin and difficult to discern with the naked eye, so sometimes the observed plasma filaments may represent processing conditions that occurred several seconds after processing.

[0056] Experiments were conducted using a femtosecond laser ultrafast imaging device. The optical path length of the probe light was altered by adjusting a one-dimensional time-delay stage 17. Ultrafast imaging results were observed, and the moment of visible plasma filaments was determined as the fuzzy time zero. The position of the one-dimensional time-delay stage 17 corresponding to the fuzzy time zero was then located. During the experiment, appropriate sample materials were selected and the laser flux was adjusted appropriately. The interaction between the sample material and the femtosecond laser was observed and data collected. The laser flux should be greater than the laser ablation threshold for the material. The observation time for the interaction between the sample and the femtosecond laser was determined based on the material's properties and should encompass the entire process of the material's transmittance or reflectance response after laser irradiation. The experimental procedure is as follows.

[0057] (1) Prepare a 10mm*10mm*1mm fused quartz and fix it on the three-dimensional sample translation stage 21. Adjust the z-axis of the sample stage to accurately adjust the sample surface to the focusing position of the probe light and the pump light. The sample is placed in the following direction: Figure 2 As shown in . The wavelength of the femtosecond laser is 1030 nm, the pulse width is 50 fs, and the mode is external triggering.

[0058] (2) Adjust the attenuation plate 6 to control the luminous flux to 3 J / cm 2 First, close the mechanical switch 11, and only allow the 515nm wavelength detection light after 8-fold frequency multiplication by the BBO crystal to irradiate the sample, and record the background image, such as Figure 3 (a); Turn on the mechanical switch 11 and record the instantaneous signal image of the sample after being processed by the 1030 nm pump light, as shown in Figure 3 As shown in (b), a thin filament can be observed in the image, which is the plasma filament formed by the propagation of femtosecond laser inside the material.

[0059] (3) Adjust the one-dimensional time-delay stage 17 to change the optical path of the detection light. During the adjustment process, observe the ultrafast imaging results and use the appearance of the plasma filament visible to the naked eye to preliminarily fuzzily locate the time zero point, such as Figure 4 As shown, the absolute position here is set to 0 in the translation stage software. Using this as a reference, the plasma filament state in the instantaneous signal image of the sample after 100 fs can be seen.

[0060] S2: Determine the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the experimentally obtained instantaneous signal image of the sample, where the time delay is the optical path difference formed by the detection light lagging behind the pump light in the femtosecond laser ultrafast imaging device.

[0061] S21: Select the processing spot center of the sample as the optical axis, and starting from the position of the one-dimensional delay stage corresponding to the fuzzy time zero point, adjust the position of the one-dimensional delay stage to generate different time delays, wherein the different time delays constitute a preset time delay sequence.

[0062] Specifically, the Drude model is used to invert the experimentally generated transient optical signals (such as reflectivity and transmittance) from the central region of the material response into the time-varying transient electron density. The center of the processing spot is selected as the optical axis. Starting from the fuzzy zero point, the position of the one-dimensional time-delay stage 17 is adjusted sequentially according to a preset time delay sequence, so that the probe light lags behind the pump light, creating an optical path difference and thus generating different time delays. Each 15μm step of the stage increases the optical path delay by 30μm, corresponding to a time delay of 100 fs.

[0063] S22: Acquire corresponding sample instantaneous signal images under different time delays.

[0064] S23: Obtaining transmittances corresponding to different time delays according to the instantaneous signal image of the sample.

[0065] Specifically, since the signal generation and decay process in fused silica after femtosecond laser processing typically completes within 1000 fs, images within a 1000 fs delay are recorded and data extracted. The transmittance T is obtained by dividing the grayscale value of the extracted signal image by the grayscale value of the background image, which satisfies the following relationship:

[0066] (1)

[0067] Where T is the transmittance, is the background light intensity, is the signal light intensity, d is the effective diameter of the plasma filament, c is the speed of light in vacuum, is the extinction coefficient, satisfying , is the refractive index of the material, i represents the imaginary part, is the dielectric function of the material.

[0068] S24: According to the transmittance and transmittance-electron density conversion model, the electron density corresponding to different time delays is obtained.

[0069] Specifically, according to the Drude model, the dielectric function of the material is It can be expressed as:

[0070] (2)

[0071] in, is the intrinsic dielectric function (taken as 2.14 for a wavelength of 515 nm), To detect the laser frequency, is the free electron collision time (0.2 fs for fused silica), i represents the imaginary part, is the electron charge, is the dielectric constant of vacuum, The mass of the electron.

[0072] Combining formula (1) and formula (2), we can get the electron density The relationship between transmittance T and the transmittance-electron density conversion model is:

[0073] (3)

[0074] According to formula (3), the transmittance change T measured in the pump-probe experiment can be converted into the time evolution law of the free electron density ,like Figure 5 As shown. Among them, is the intrinsic dielectric function, is the refractive index of the material, i represents the imaginary part, c is the speed of light in a vacuum, T is the transmittance, ω is the detection laser frequency, d is the effective diameter of the plasma filament, is the free electron collision time, is the electron mass, is the dielectric constant of vacuum, is the charge of the electron.

[0075] S3: Use the attenuation data after femtosecond laser processing of samples to improve the femtosecond laser processing theoretical model and obtain the electron density simulation evolution model.

[0076] Specifically, the attenuation data after femtosecond laser exposure were fitted to femtosecond laser processing theory, improving the femtosecond laser precision manufacturing theory to ensure that the simulated electron density evolution closely matches the electron density changes obtained from experimental data. Femtosecond laser manufacturing theory simulates the femtosecond-picosecond timescale and includes a two-temperature model and a plasma model. The attenuation data were fitted to the processing theory by improving the attenuation term. This involves performing a nonlinear numerical fit on the relationship between the decay rate of the experimental attenuation data and other parameters (such as time and electron density), thereby ensuring that the theoretical simulation corresponds to the experimental data.

[0077] Extracting the free electron density decay data to improve the femtosecond laser processing theory, such as Figure 6 The specific steps are as follows: The attenuation part is based on Perform slope fitting and bring it into the electron density evolution equation:

[0078] (4)

[0079] Where, is the multiphoton coefficient, is the ionization constant, which is related to the material properties. For fused silica materials, , The experimental data are based on The fitted Substituting into the evolution equation, we get the improved electron density simulation evolution model (referred to as the improved model):

[0080] (5)

[0081] in, Indicates the Iterations. Figure 6 As shown in Figure 2, the expression for the evolution of light intensity over time is:

[0082] (6)

[0083] in is the laser flux, is the laser pulse width, and all experimental parameters are adopted. is the instantaneous surface reflectivity, and its value is related to the dielectric function related:

[0084] (7)

[0085] In the above formula, for The signal intensity at the moment, for The electron density at time for The electron density at time is the decay rate, is the dielectric function of the material, is the intrinsic dielectric function, is the electron density, is the electron charge, To detect the laser frequency, i represents the imaginary part, is the electron mass, is the dielectric constant of vacuum, is the material refractive index, is the extinction coefficient, is the tth moment.

[0086] like Figure 6 As shown, input the initial light intensity , initial reflectivity , substitute into the improved formula (5) to get the next step electron density , substitute into formula (2) to update the dielectric function and obtain , according to formula (7), we can further get the instantaneous surface reflectivity at the next moment: , substitute into formula (6) to update the signal intensity at the next moment , and continue the calculation cycle. By looping the entire process, the electron density evolution after the improved model calculation can be obtained. In this process, the electron density is calculated based on the experimental data obtained. , and the law of free electron collision time changing with electron density (i.e. decay rate) is obtained by fitting. The decay rate Substituting into formula (5), we can obtain multiple theoretical data points of electron density, thus describing the following: Figure 7 The curve of the improved model is shown in the figure. The calculation found that the electron density evolution after the improved model calculation is basically consistent with the electron density change obtained from the experimental data, as shown in the figure. Figure 7 As shown, the data calculated by the improved model can be used as the standard data of the fused silica sample.

[0087] S4: Select multiple continuous data points from the electron density corresponding to different time delays, use the selected data points to align with the simulation curve of the electron density simulation evolution model, reversely infer the time point corresponding to the actual time zero point on the simulation time axis, and obtain the time difference between the actual time zero point and the theoretical time zero point.

[0088] Specifically, five consecutive data points of the decay signal with a long delay after the femtosecond laser is applied are selected. These data points are then compared with the simulation results to determine the time corresponding to these five data points, and the time zero position is then inferred. The decay signal with a long delay after the femtosecond laser is selected to be just after the peak signal to ensure a high signal-to-noise ratio.

[0089] For example, in a repetitive experiment, ultrafast imaging signals were recorded within a 1000 fs delay. Five consecutive data points were selected from the decay signal at long delays after femtosecond laser exposure. The experimental data points corresponded to fuzzy times of 666 fs, 700 fs, 733 fs, 766 fs, and 800 fs. By comparing the experimental data points with the simulated standard data, the precise times corresponding to these five data points in the simulated data were found to be 700 fs, 733 fs, 766 fs, 800 fs, and 833 fs, respectively. The results show that the actual time zero position is 33 fs ahead of the fuzzy zero position set in step 1 (i.e., the time difference), corresponding to a displacement step size of 5 μm.

[0090] S5: Taking the position of the one-dimensional time-delay displacement stage corresponding to the fuzzy time zero point as a reference basis, the position of the one-dimensional time-delay displacement stage corresponding to the actual time zero point is obtained according to the time difference.

[0091] Specifically, move the one-dimensional time-delay stage 17 to the position corresponding to the fuzzy time zero point set in S1. Then, move the stage back again by 5 μm relative to this position to find the actual time zero point. Resetting this absolute position to 0 allows the time delay to be varied based on this time zero point for subsequent material experiments, achieving precise positioning of the time zero point for ultrafast imaging.

[0092] The long-delay data feedback method for ultrafast imaging time zero positioning, employed in this study, is simple and easy to implement. Because the transient signal caused by the interaction between the laser and the sample is stronger than the initial signal, this method cleverly exploits the characteristic of femtosecond laser-sample interaction, where the signal is more pronounced under long delays, and integrates an improved electron density simulation evolution model to accurately locate time zero. This method effectively circumvents the zero-point positioning challenge caused by weak signal noise interference near time zero, significantly improving the accuracy of ultrafast imaging time zero positioning. This method provides a more precise and reliable foundation for ultrafast dynamics observations and physicochemical mechanism studies, and has significant application value and broad development prospects in related fields.

[0093] In summary, the technical solution provided by this invention achieves precise reverse calculation of the time zero point by leveraging long-delay signal feedback and precise comparison with theoretical data. This innovative solution addresses the issues inherent in traditional ultrafast imaging time zero positioning, significantly enhancing the performance of ultrafast imaging systems. This is of great significance for advancing ultrafast dynamics research to higher precision and deeper levels, and is expected to provide strong technical support for cutting-edge research in multiple disciplines, such as physical chemistry, and contribute to further breakthroughs in related fields.

[0094] In summary, compared with the existing technology, the present invention has the following beneficial effects:

[0095] 1. The method of ultrafast imaging time zero point positioning using long-delay signal feedback adopted by the present invention has no requirements for the detector and is not limited by the resolution accuracy of the detector. Even in the case of low spatial resolution accuracy of the detector or weak time zero point signal, reverse deduction can be performed based on the high-intensity signal under long delay.

[0096] 2. The time zero point positioning method described in the present invention has high accuracy. Since the theoretical simulation time accuracy can reach the sub-femtosecond level, this method is only limited by the accuracy of the one-dimensional time delay displacement stage. If a nanometer-level high-precision time delay displacement stage is used, the time zero point positioning accuracy can reach the femtosecond level.

[0097] 3. The method of the present invention has low material requirements and can use common materials such as fused quartz, sapphire, silicon, etc. as standard samples, which is convenient and simple.

[0098] like Figure 8 As shown, an embodiment of the present application provides a long-delay data feedback ultrafast imaging time zero positioning system, comprising:

[0099] The fuzzy time zero point determination module 100 is used to determine the position of the one-dimensional time delay displacement stage corresponding to the fuzzy time zero point using the sample instantaneous signal image obtained by the femtosecond laser ultrafast imaging device.

[0100] The electron density analysis module 200 is used to determine the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the instantaneous signal image of the sample obtained experimentally, wherein the time delay is the optical path difference formed by the detection light lagging behind the pump light in the femtosecond laser ultrafast imaging device.

[0101] The evolution model improvement module 300 is used to improve the femtosecond laser processing theoretical model using the attenuation data after the femtosecond laser processing the sample, and obtain the electron density simulation evolution model.

[0102] The actual time zero point analysis module 400 is used to select multiple continuous data points from the electron density corresponding to different time delays, align the selected data points with the simulation curve of the electron density simulation evolution model, and reversely infer the time point corresponding to the actual time zero point on the simulation time axis to obtain the time difference between the actual time zero point and the theoretical time zero point.

[0103] The position analysis module 500 is used to obtain the position of the one-dimensional delay displacement stage corresponding to the actual time zero point according to the time difference, using the position of the one-dimensional delay displacement stage corresponding to the fuzzy time zero point as a reference basis.

[0104] In this embodiment, the beneficial effects of the long-delay data feedback ultrafast imaging time zero point positioning system are similar to the beneficial effects of the long-delay data feedback ultrafast imaging time zero point positioning method described above, and are not repeated here.

[0105] An electronic device provided in an embodiment of the present application includes a memory and a processor; the memory is used to store a computer program; the processor is used to implement the long-delay data feedback ultrafast imaging time zero point positioning method as described above when executing the computer program.

[0106] An embodiment of the present application provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the long-delay data feedback ultrafast imaging time zero point positioning method as described above is implemented.

[0107] In this embodiment, the beneficial effects of the electronic device and the computer-readable storage medium are similar to the beneficial effects of the above-mentioned long-delay data feedback ultrafast imaging time zero point positioning method, and will not be repeated here.

[0108] Electronic device is intended to refer to various forms of digital electronic computing devices, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. Electronic device can also refer to various forms of mobile devices, such as personal digital assistants, cellular phones, smart phones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the present application described and / or claimed herein.

[0109] Electronic devices include a computing unit that can perform various appropriate actions and processes based on computer programs stored in read-only memory (ROM) or loaded from a storage unit into random access memory (RAM). RAM can also store various programs and data required for device operation. The computing unit, ROM, and RAM are connected to each other via a bus. An input / output (I / O) interface is also connected to the bus.

[0110] Those skilled in the art will appreciate that all or part of the processes in the above-described method embodiments can be implemented by instructing the relevant hardware through a computer program. The program can be stored in a computer-readable storage medium, and when executed, the program can include the processes in the above-described method embodiments. The storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM). In this application, the units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network elements. Some or all of these units can be selected based on actual needs to achieve the objectives of the embodiments of this application. Furthermore, the functional units in each embodiment of this application can be integrated into a single processing unit, each unit can exist physically separately, or two or more units can be integrated into a single unit. These integrated units can be implemented in either hardware or software functional units.

[0111] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A long-delay data feedback ultrafast imaging time zero positioning method, characterized in that: include: The position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point is determined by using the instantaneous signal image of the sample obtained by the femtosecond laser ultrafast imaging device; Determine the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the experimentally obtained instantaneous signal image of the sample, where the time delay is the optical path difference formed by the delay between the detection light and the pump light in the femtosecond laser ultrafast imaging device; The attenuation data of samples processed by femtosecond laser were used to improve the theoretical model of femtosecond laser processing and obtain the electron density simulation evolution model; Select multiple continuous data points from the electron density corresponding to different time delays, align the selected data points with the simulation curve of the electron density simulation evolution model, reversely infer the time point corresponding to the actual time zero on the simulation time axis, and obtain the time difference between the actual time zero and the theoretical time zero; The position of the one-dimensional time-delay displacement stage corresponding to the fuzzy time zero point is used as a reference basis, and the position of the one-dimensional time-delay displacement stage corresponding to the actual time zero point is obtained according to the time difference.

2. The long-delay data feedback ultrafast imaging time zero positioning method according to claim 1, characterized in that: The method of obtaining a sample instantaneous signal image by a femtosecond laser ultrafast imaging device and determining the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point comprises: Experiments were conducted using a femtosecond laser ultrafast imaging device. The one-dimensional time-delay stage was adjusted to change the optical path of the detection light, and the ultrafast imaging results were observed. The moment when the plasma filaments visible to the naked eye appeared was determined as the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point.

3. The long-delay data feedback ultrafast imaging time zero positioning method according to claim 1, characterized in that: Determining the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the instantaneous signal image of the sample obtained experimentally includes: The center of the sample's processing spot is selected as the optical axis. Starting from the position of the one-dimensional delay stage corresponding to the fuzzy time zero point, the position of the one-dimensional delay stage is adjusted to generate different time delays, wherein the different time delays constitute a preset time delay sequence; Under different time delays, the corresponding sample instantaneous signal images are obtained; Obtaining transmittances corresponding to different time delays according to the instantaneous signal image of the sample; According to the transmittance and transmittance-electron density conversion model, the electron density corresponding to different time delays is obtained.

4. The long-delay data feedback ultrafast imaging time zero positioning method according to claim 3, characterized in that: The transmittance-electron density conversion model is: in, is the intrinsic dielectric function, is the refractive index of the material, i represents the imaginary part, c is the speed of light in a vacuum, T is the transmittance, ω is the detection laser frequency, d is the effective diameter of the plasma filament, is the free electron collision time, is the electron mass, is the dielectric constant of vacuum, is the charge of the electron.

5. The long-delay data feedback ultrafast imaging time zero positioning method according to claim 1, characterized in that: The electron density simulation evolution model is: in, is the multiphoton coefficient, is the ionization constant, for The signal intensity at the moment, for The electron density at time for The electron density at time is the decay rate, is the dielectric function of the material, is the intrinsic dielectric function, is the electron density, is the electron charge, To detect the laser frequency, i represents the imaginary part, is the electron mass, is the dielectric constant of vacuum, is the material refractive index, is the extinction coefficient, is the instantaneous surface reflectivity, is the laser flux, is the laser pulse width, is the tth moment, Indicates the Iterations.

6. A long-delay data feedback ultrafast imaging time zero positioning system, characterized in that: include: A fuzzy time zero point determination module is used to determine the position of the one-dimensional time delay displacement stage corresponding to the fuzzy time zero point using the sample instantaneous signal image obtained by the femtosecond laser ultrafast imaging device; An electron density analysis module is used to determine the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the experimentally obtained instantaneous signal image of the sample, wherein the time delay is the optical path difference formed by the delay between the detection light and the pump light in the femtosecond laser ultrafast imaging device; The evolution model improvement module is used to improve the femtosecond laser processing theoretical model using the attenuation data after femtosecond laser processing of samples to obtain an electron density simulation evolution model; The actual time zero point analysis module is used to select multiple continuous data points from the electron density corresponding to different time delays, align the selected data points with the simulation curve of the electron density simulation evolution model, and reversely infer the time point corresponding to the actual time zero point on the simulation time axis to obtain the time difference between the actual time zero point and the theoretical time zero point; The position analysis module is used to obtain the position of the one-dimensional time-delay displacement stage corresponding to the actual time zero point based on the time difference, taking the position of the one-dimensional time-delay displacement stage corresponding to the fuzzy time zero point as a reference.

7. The long-delay data feedback ultrafast imaging time zero positioning system according to claim 6, characterized in that: The method of obtaining a sample instantaneous signal image by a femtosecond laser ultrafast imaging device and determining the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point comprises: Experiments were conducted using a femtosecond laser ultrafast imaging device. The one-dimensional time-delay stage was adjusted to change the optical path of the detection light, and the ultrafast imaging results were observed. The moment when the plasma filaments visible to the naked eye appeared was determined as the position of the one-dimensional time-delay stage corresponding to the fuzzy time zero point.

8. The long-delay data feedback ultrafast imaging time zero positioning system according to claim 6, characterized in that: Determining the electron density corresponding to different time delays based on the transmittance-electron density conversion model and the instantaneous signal image of the sample obtained experimentally includes: The center of the sample's processing spot is selected as the optical axis. Starting from the position of the one-dimensional delay stage corresponding to the fuzzy time zero point, the position of the one-dimensional delay stage is adjusted to generate different time delays, wherein the different time delays constitute a preset time delay sequence; Under different time delays, the corresponding sample instantaneous signal images are obtained; Obtaining transmittances corresponding to different time delays according to the instantaneous signal image of the sample; According to the transmittance and transmittance-electron density conversion model, the electron density corresponding to different time delays is obtained.

9. The long-delay data feedback ultrafast imaging time zero positioning system according to claim 8, characterized in that: The transmittance-electron density conversion model is: in, is the intrinsic dielectric function, is the refractive index of the material, i represents the imaginary part, c is the speed of light in a vacuum, T is the transmittance, ω is the detection laser frequency, d is the effective diameter of the plasma filament, is the free electron collision time, is the electron mass, is the dielectric constant of vacuum, is the charge of the electron.

10. The long-delay data feedback ultrafast imaging time zero positioning system according to claim 6, characterized in that: The electron density simulation evolution model is: in, is the multiphoton coefficient, is the ionization constant, for The signal intensity at the moment, for The electron density at time for The electron density at time is the decay rate, is the dielectric function of the material, is the intrinsic dielectric function, is the electron density, is the electron charge, To detect the laser frequency, i represents the imaginary part, is the electron mass, is the dielectric constant of vacuum, is the material refractive index, is the extinction coefficient, is the instantaneous surface reflectivity, is the laser flux, is the laser pulse width, is the tth moment, Indicates the Iterations.

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