Calibration method and calibration system for laser-induced damage threshold measurement system

Abstract

A calibration method and a calibration system for a laser-induced damage threshold measurement system. The calibration method comprises: acquiring a plurality of standard piece materials, each standard piece material having a corresponding quantitative characteristic point, different standard piece materials having different quantitative characteristic points, and when using a laser to irradiate the standard piece materials, the properties of the standard piece materials changing at the quantitative characteristic points, and the change being reversible (S10); using a plurality of lasers of different light intensities of a laser-induced damage threshold measurement system to respectively irradiate the plurality of standard piece materials, so as to establish a relationship of spatio-temporal characteristics between the light intensities and the quantitative characteristic points (S20); and, on the basis of the relationship, calibrating the laser-induced damage threshold measurement system (S30). The calibration method and the calibration system can effectively calibrate laser-induced damage threshold measurement systems, thereby comparing different laser-induced damage threshold measurement systems.

Description

Calibration method and calibration system for laser damage threshold measurement system Technical Field

[0001] This application relates to the technical field of laser damage threshold measurement, and in particular to a calibration method and calibration system for a laser damage threshold measurement system. Background Technology

[0002] Since Maiman invented the first laser in 1960, from the initial free-oscillating laser, through Q-switching technology, mode-locking technology, and then CPA and OPCPA technologies, the time scale of laser pulses has narrowed from the microsecond level to the femtosecond level, and the peak power of lasers has increased from the watt level to the petawatt level, an increase of at least 15 orders of magnitude. Five milestone high-power large-scale laser facilities have been built in the field of lasers. In this process, the problem of laser damage to optical materials has always plagued the development of laser technology, while also being the driving force for the development of new laser technologies and high-intensity laser materials.

[0003] Laser damage threshold is one of the core indicators for evaluating high-power laser materials. Laser damage threshold detection technology is a key technology for assessing the safe application of optical materials in high-power laser systems, and it is crucial for the design and long-term stable operation of high-energy / high-power laser systems. Due to the complexity of the causes and formation process of laser damage, and the probabilistic nature of the damage, the comparability of measurement results between different measurement laboratories is poor, and offline damage threshold measurement results are inconsistent with the experience of application on laser devices.

[0004] To address the issue of poor comparability in laser damage threshold measurements, researchers aimed to standardize the measurement process through testing standards to enhance comparability. Researchers discovered that measurement results from different laboratories for the same batch of samples showed a two-order-of-magnitude difference. To address this serious problem, the laser field conducted research on corresponding standardization techniques, resulting in the first draft standard for laser damage threshold measurement, ISO / DIS 11254, in 1995, which improved the comparability of results between different laboratories. my country has also gradually established some relevant standards for laser damage threshold testing technology and standardization. For example, GB / T 16601-1996, published in 1996, adopted ISO / DIS 11254, and GB / T 16601-2017, published in 2017, is also largely based on ISO 21254. In addition, industry standards for engineering evaluation have been established in the field of high-power lasers.

[0005] Despite the establishment of a series of standards, the comparability and confidence level of the measurement results still cannot meet the requirements for scientific research and calibration of optical materials (components) products.

[0006] The challenges faced by laser damage threshold measurement technology stem primarily from three levels of issues: ① Uncertainties arising from measurement system parameters, such as the spatiotemporal distribution characteristics of the measurement spot on the target surface and its damage detection capabilities; ② Due to its destructive nature, repeated measurements on the same sample are impossible, even for samples prepared in the same batch; ③ Uncertainties arising from the measurement method itself, as various measurement methods or the sampling and statistical methods specified in measurement standards can also lead to uncertainties. The first two levels of problems are intertwined, making it impossible to analyze the influence of the testing system and the object under test in practical work. This is why researchers in this field currently avoid the core challenges by conducting "simultaneous testing."

[0007] Therefore, there is an urgent need for an effective method to calibrate and compare different measurement systems.

[0008] Summary of the Invention

[0009] This application addresses the technical problem of poor comparability among different laser damage threshold measurement systems by providing a calibration method and system for laser damage threshold measurement systems. It employs standard materials with reversible change properties, enabling effective calibration of laser damage threshold measurement systems and subsequent comparison of different laser damage threshold measurement systems.

[0010] To address the aforementioned technical problems, this application provides, in one aspect, a calibration method for a laser damage threshold measurement system, comprising: acquiring multiple standard component materials, each standard component material having corresponding quantitative characteristic points, the quantitative characteristic points being different for different standard component materials, wherein, when the standard component material is irradiated with a laser, the properties of the standard component material change at the quantitative characteristic points, and the change is reversible; irradiating the multiple standard component materials with multiple lasers of different intensities using the laser damage threshold measurement system, establishing a relationship between the light intensity and the spatiotemporal characteristics of the quantitative characteristic points; and calibrating the laser damage threshold measurement system according to the relationship.

[0011] This application also provides a calibration system for a laser damage threshold measurement system, comprising a first laser source, a beam splitter, an attenuator, a detection delay unit, a pump delay unit, and a detector; wherein, the first laser source is used to generate the laser of the laser damage threshold measurement system; the beam splitter is used to split the laser into a detection beam and a pump beam, the detection beam reaching a standard material along a detection branch, and the pump beam reaching the standard material through a pump branch; the attenuator is used to attenuate the detection beam and / or the pump beam; the detection delay unit is disposed on the detection branch and is used to adjust the optical path of the detection beam; the pump delay unit is disposed on the pump branch and is used to adjust the optical path of the pump beam; the detector is used to detect the amount of reflected light and / or transmitted light on the surface of the standard material; the calibration system is used to perform the calibration method described above.

[0012] The calibration method for the laser damage threshold measurement system in this application obtains a standard material with reversible change properties and establishes a relationship between the light intensity and the spatiotemporal characteristics of the characteristic points for each laser damage threshold measurement system. Based on this relationship, the laser damage threshold measurement system is calibrated. On the one hand, it can calibrate a specific laser damage threshold measurement system and analyze the spot effect and pulse width calibration rate of the system. On the other hand, by using the same reusable standard material for different laser damage threshold measurement systems, the spatiotemporal characteristics of the pulsed laser of different laser damage threshold measurement systems can be compared, the spatiotemporal characteristics of different laser damage threshold measurement systems can be analyzed, and the value transfer between different laser damage threshold measurement systems can be realized.

[0013] Overview of the attached figures

[0014] The accompanying drawings are included to provide a further understanding of this application. They are incorporated into and constitute a part of this application. The drawings illustrate embodiments of this application and, together with this specification, serve to explain the principles of this application.

[0015] In the attached image:

[0016] Figure 1 is an exemplary flowchart of a calibration method for a damage threshold measurement system according to an embodiment of this application;

[0017] Figures 2 to 4 show schematic diagrams of the phase change region area on the surface of the thermally induced phase change material under three different conditions;

[0018] Figure 5 is a schematic diagram of the calibration system of a damage threshold measurement system according to an embodiment of this application.

[0019] Preferred embodiments of this application

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this application. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0021] As indicated in this application, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0022] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0023] Furthermore, although the terminology used in this application is selected from commonly known and used terms, some terms mentioned in this application's specification may have been chosen by the applicant according to his or her judgment, and their detailed meanings are explained in the relevant sections of the description herein. Moreover, this application is to be understood not only by the actual terms used, but also by the meaning implied by each term.

[0024] Flowcharts are used in this application to illustrate the operations performed by the system according to embodiments of this application. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, various steps can be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more steps may be removed from these processes.

[0025] Generally, comparison and calibration between different laser damage threshold measurement systems are performed using standard samples (materials). Since laser damage threshold measurement is a destructive measurement, it is impossible to reproduce the same sample across different measurement systems. This is the key reason for the poor comparability of different laser damage threshold measurement systems mentioned earlier. Based on this key reason, the inventors of this application have taken a different approach, proposing a technical concept that laser damage is unreproducible, but the effect of inducing laser damage can be reproduced. In other words, if the effect of inducing laser damage can be repeatedly recorded / eliminated using a certain material, then this material can become a standard transfer material, and the laser damage effect can be reproduced, thereby achieving the transfer of values ​​in laser damage threshold measurement. Furthermore, a new method for value transfer between different laser damage threshold measurement systems is proposed, namely, the calibration method for a laser damage threshold measurement system of this application.

[0026] Figure 1 is an exemplary flowchart of a calibration method for a damage threshold measurement system according to an embodiment of this application. Referring to Figure 1, the calibration method of this embodiment includes the following steps:

[0027] Step S10: Obtain multiple standard part materials. Each standard part material has corresponding quantitative characteristic points. Different standard part materials have different quantitative characteristic points. When the standard part material is irradiated with a laser, the properties of the standard part material change at the quantitative characteristic points, and the change is reversible.

[0028] Step S20: Using a laser damage threshold measurement system, multiple standard parts are irradiated with lasers of different intensities to establish the relationship between light intensity and the spatiotemporal characteristics of the measurement feature points;

[0029] Step S30: Calibrate the laser damage threshold measurement system according to the relationship.

[0030] The following description, in conjunction with the accompanying drawings, elaborates on steps S10 to S30.

[0031] Based on the above-mentioned concept of reproducing the effect of induced laser damage, the inventors of this application have studied the effect of induced laser damage and the corresponding standard part materials. The effect of induced laser damage will be explained first below.

[0032] The effect of laser-induced damage essentially concerns the fundamental mechanism of laser-induced damage, involving the basic physical processes of how laser energy is absorbed and coupled into the irradiated material. It is closely related to laser parameters, with the core parameter being the interaction time, i.e., the pulse width. The pulse width determines how the optical material absorbs laser energy during the interaction process, primarily through thermal absorption. When the pulse width is not too short, the material mainly obtains laser energy through thermal absorption, and subsequent thermal or thermodynamic effects cause melting and mechanical damage to the material.

[0033] It should be noted that this application does not limit the laser pulse width used in the method; any laser pulse width that conforms to the principle that laser irradiation has a thermal effect is applicable to this scheme. In some embodiments, the laser pulse width is defined as being greater than 1 ns, within which there is a significant thermal effect. The laser wavelength used by the inventors in the experiment was 1 μm, but this is not intended to limit the specific wavelength of the laser.

[0034] More specifically, in the calibration method of this application, the laser used to generate the thermal absorption effect during the calibration process is a single-pulse laser, which is beneficial for observing the thermal absorption effect of the standard material. In other embodiments, other forms of lasers can also be used, such as continuous lasers with a finite duration, and the pulse width can be modulated as needed.

[0035] Corresponding to the thermal absorption effect, in one embodiment, the standard material in step S10 is a thermally induced phase change material. This thermally induced phase change material changes temperature under laser irradiation, causing its properties to change. The quantitative characteristic point is the phase change light intensity of the laser corresponding to the property change.

[0036] It should be noted that thermotropic phase change materials refer to any material that undergoes a phase change after being heated by laser irradiation. The properties of the standard material referred to here are those related to the phase change. This application does not limit the specific type of thermotropic phase change material. The thermotropic phase change material can be a synthetic material. Those skilled in the art can manufacture or synthesize thermotropic phase change materials that meet the requirements as needed. Preferably, the thermotropic phase change material has characteristics such as a narrow phase change temperature range, controllable phase change direction, and easy characterization of phase change features. The transition metal oxides VO2, V2O5, and chalcogenide GST alloys described below all possess these characteristics.

[0037] It should be noted that the light intensity described in this application refers to energy density or power density, with the dimensions being J / cm². 2 or W / cm 2 In the embodiments described in this application, energy density is mainly used to characterize light intensity.

[0038] In one embodiment, the thermally induced phase change material comprises transition metal oxides VO2 and / or V2O5, which are crystalline phases. When the laser irradiation temperature is higher than the phase transition temperature, the crystalline phase changes, and when the laser irradiation temperature is lower than the phase transition temperature, the crystalline phase is restored. This embodiment includes three cases: the thermally induced phase change material includes VO2; the thermally induced phase change material includes V2O5; and the thermally induced phase change material includes both VO2 and V2O5.

[0039] Under laser irradiation, transition metal oxides (VO2) undergo a phase change when their surface temperature reaches Tc. The phase transition temperature Tc is approximately between 60°C and 70°C. Specifically, VO2 undergoes a metal-to-insulator transition near its phase transition temperature. When the temperature is above Tc, it exhibits a metallic state with low resistivity and high conductivity; when the temperature drops below Tc, VO2 reverts to an insulating state with high resistivity and low conductivity. In other words, the phase change of transition metal oxides (VO2) is reversible.

[0040] Based on the aforementioned characteristics of transition metal oxide VO2, it can be used repeatedly as a standard material, thereby ensuring the consistency of the test material and making the test results comparable across different laser damage threshold measurement systems.

[0041] For VO2, the quantitative characteristic point is the light intensity of the laser corresponding to the phase change of VO2, which is denoted as the "phase transition light intensity," i.e., the quantitative characteristic point is the "phase transition light intensity." In step S20, for example, for a laser damage threshold measurement system A (hereinafter referred to as "measurement system A"), its initial energy density f0 is set. VO2 is irradiated with laser at f0, and the reflected light and / or transmitted light generated on VO2 by the laser irradiation are detected in real time, thereby obtaining the transmittance and / or reflectance. When VO2 is in a metallic state and an insulating state, the transmittance and reflectance are different. For example, the reflectance in the metallic state is greater than that in the insulating state, and the transmittance in the metallic state is less than that in the insulating state. Therefore, by continuously changing the energy density f of measurement system A and simultaneously monitoring the transmittance and / or reflectance in real time, the relationship between different energy densities and phase transitions can be obtained, thus determining whether VO2 has undergone a phase transition, and when and at what energy density the phase transition occurred. Then, in step S30, measurement system A can be calibrated based on this relationship. Calibration of measurement system A may include recording or storing the relationship and mapping the relationship to measurement system A.

[0042] In some embodiments, the calibration system of this application can be used to detect the reflected light and / or transmitted light in real time. This calibration system is a time-resolved and spatially resolved pump-probe system. The calibration system of this application will be described later.

[0043] More specifically, experiments have shown that the phase transition temperature of VO2 is approximately 68℃, meaning that when laser irradiation raises the temperature of VO2 to 68℃, its crystal phase changes. When laser irradiation is stopped, or when the energy density of the laser irradiation is changed to lower the temperature below 68℃, the crystal phase of VO2 reverts to its insulating state. V2O5 is similar to VO2 in that they share the same phase transition properties, but differ in the corresponding temperatures. The phase transition temperature of V2O5 is approximately 257℃. Each material corresponds to a specific temperature.

[0044] In order to obtain multiple quantitative characteristic points corresponding to different temperatures, theoretically, the more standard materials corresponding to different phase transition temperatures used, the better, for example, 10 to 15.

[0045] In one embodiment, the thermally induced phase change material includes a chalcogenide GST alloy with a crystalline structure. When the chalcogenide GST alloy is irradiated with a laser using a laser damage threshold measurement system, the crystalline structure changes from a crystalline state to an amorphous state. When the chalcogenide GST alloy is irradiated with a second laser, the crystalline structure changes from an amorphous state to a crystalline state. The pulse width of the second laser pulse is smaller than the pulse width of the laser in the laser damage threshold measurement system.

[0046] Experiments have shown that the phase transition temperature of the chalcogenide GST alloy (GST-255) is approximately 600℃. Therefore, chalcogenide GST alloy can also be used as a standard component material. It should be noted that the phase transition principle of chalcogenide GST alloy differs from that of V₂O₅ and VO₂. V₂O₅ and VO₂ automatically revert to their crystalline phases upon temperature reduction, requiring no external intervention. The phase transition of chalcogenide GST alloy is a crystalline phase transition. The initial state of GST alloy is amorphous. When GST alloy is irradiated with a typical or ordinary nanosecond-level laser using a laser damage threshold measurement system, it transforms from an amorphous state to a crystalline state. Specifically, under laser irradiation, atoms remain between the glass transition temperature and melting temperature for an extended period, transitioning to a lower-energy crystalline structure, ultimately forming a crystalline structure with ordered atomic arrangement. The transformation of GST alloy from crystalline to amorphous requires short-pulse laser irradiation, such as picosecond-level (10⁻¹⁰) lasers. -12A short pulse of laser light (S) rapidly heats the material above its melting point, causing it to melt into a liquid state (disordered state). The temperature is then rapidly cooled, and the disordered atoms do not have time to rearrange, resulting in an amorphous state. Therefore, to restore the crystal phase of the chalcogenide GST alloy, a second-pulse laser with a pulse width on the order of picoseconds is required to irradiate the material. Therefore, for the use of chalcogenide GST alloys, the calibration method of this application further includes: after the properties of the chalcogenide GST alloy change and the quantitative characteristic point of the phase transition is obtained, irradiating the chalcogenide GST alloy with a second-pulse laser to restore the property changes of the chalcogenide GST alloy. Preferably, the pulse width of the second-pulse laser is on the order of picoseconds.

[0047] Laser pulses possess spatiotemporal characteristics, and therefore, the thermal effects produced by laser irradiation on material surfaces also exhibit corresponding spatiotemporal characteristics. Laser irradiation produces a laser spot on the material surface, which follows a Gaussian distribution in both time and space. For example, spatially, the energy is highest at the center of the spot and lowest at the edges, decreasing from the center outwards. Areas with high energy also have higher temperatures. Temporally, the laser energy increases sharply from t=0, and drops to zero after a pulse width of t=τ. Due to the spatiotemporal characteristics of laser irradiation, the temperature changes on the surface of phase transition materials also vary with time and space. To perform spatiotemporal analysis of this phase transition distribution, the spatial phase transition distribution can be analyzed at different points in time.

[0048] Taking measurement system A as an example, let's first consider the case where a pulse-heatable phase change material reaches its maximum temperature. Assume the observation duration is t = τ, meaning the entire pulse irradiation phase is observed, with all laser energy used for heating. Assume τ = 10 ns, and the pulse energy is 20 mJ. At this point, from the perspective of spatial temperature distribution, the region capable of inducing a phase change is the largest, and the temperature at the center is also the highest. Referring to Figure 2, the surface S1 of the VO2 material is shown as a square, and the circle represents the laser spot irradiated onto surface S1. The temperature at the center of the spot is the highest, Tmax, which we assume to be 102℃. To obtain the area of ​​the phase change region, an isotherm at 68℃ is needed. As shown in Figure 2, assuming the temperature at the circumference of a circle with radius r1 is T1 = 68℃, then the area of ​​the phase change region under this irradiation is πr1. 2 .

[0049] With a fixed observation duration t = τ, the energy or power of the incident laser is varied, for example, by attenuating the laser according to a preset method, such as reducing the energy to 15 mJ. The resulting laser spot is shown in Figure 3. Due to the reduced energy, the highest temperature at the center of the laser spot is Tmax = 80℃. Assuming the temperature at the circumference of a circle with radius r2 is T1 = 68℃, this indicates that the area of ​​the phase transition region under this irradiation is πr2. 2Clearly, the area of ​​the phase transition region in Figure 3 is significantly smaller than that in Figure 2. The change in energy can be achieved through energy decay, which will be explained later in conjunction with Figure 5.

[0050] Alternatively, the energy or power of the incident laser can be fixed, and the observation duration t can be changed to be less than τ, for example, reduced to 5 ns, meaning the observation is performed before the pulse completes. Referring to Figure 4, due to the shortened irradiation duration, the corresponding temperature also decreases, with the highest temperature at the center of the light spot, Tmax, being 90℃. Assuming the temperature at the circumference of a circle with radius r3 is T1 = 68℃, this indicates that the area of ​​the phase transition region under this irradiation is πr3. 2 The duration of observation can be changed by adjusting the delay between the pump and the detector, which will be explained later in conjunction with Figure 5.

[0051] Referring to Figures 2 to 4, the phase transition parameters shown in Table 1 below can be obtained for measurement system A:

[0052] Table 1

[0053] The data in rows 1-3 correspond to the examples shown in Figures 2-4, respectively. It can be seen that in all three examples, the spot area is the same, but the area of ​​the phase transition region is different.

[0054] Following the above approach, we can obtain the size of different phase transition regions corresponding to different energy densities and different observation times. For example, we can obtain a three-dimensional graph where the three coordinate axes are energy density, observation time, and phase transition region area, thereby correlating the spatiotemporal characteristics of the laser pulse with the spatiotemporal characteristics of the phase transition distribution.

[0055] During calibration, due to the short duration of laser pulses, achieving simultaneous temporal and spatial resolution within a single pulse is challenging. Therefore, this application proposes a time-resolved and spatially resolved pump detection technique. Figure 5 is a schematic diagram of a calibration system according to an embodiment of this application, which is a time-resolved and spatially resolved pump detection system. This calibration system can help establish the spatiotemporal correspondence between light intensity and phase transition characteristics. Referring to Figure 5, it includes a first laser source 310 and a beam splitter 320. Specifically, the first laser source 310 is an Nd:YAG laser source with a wavelength in the near-infrared band. The thermo-induced phase change material used in this application exhibits significant changes in optical transparency in the infrared band; therefore, using an Nd:YAG laser source is beneficial for effectively detecting the phase transition of the thermo-induced phase change material. As shown in Figure 5, the first laser source 310 emits laser light, which is then split into two paths by the beam splitter 320: 10% is the probe light and 90% is the pump light. That is, the ratio of the probe light to the pump light is 1:9. This ratio is merely an example; in other embodiments, the ratio of probe light to pump light can be adjusted as needed. The probe light reaches the surface of the thermo-phase change material S via probe branch 330, and the pump light reaches the surface of the thermo-phase change material S via pump branch 340. A probe delay unit 331 is provided in probe branch 330 to adjust the optical path of the probe light. A pump delay unit 341 is provided in pump branch 340 to adjust the optical path of the pump light. During calibration, by adjusting the probe delay unit 331 and pump delay unit 341, the optical path difference between the probe light and pump light can be adjusted accordingly, that is, the timing of the probe light and pump light reaching the surface of the thermo-phase change material S can be adjusted, thereby adjusting the delay between the pump and the detector. The calibration system also includes detectors, as shown in FIG. 5, which include a reflected light detector 351 and a transmitted light detector 352, used to detect the amount of reflected and transmitted light on the surface of the thermo-phase change material S, respectively, thereby obtaining reflectivity and transmittance. As mentioned earlier, the presence or absence of a phase transition in the thermally induced phase change material S can be determined based on reflectivity and / or transmittance. For time-resolved phase transition analysis, by changing the retardation amount (equivalent to changing the observation time mentioned earlier), and through multiple iterations, the time-resolved characteristics of the phase transition distribution can be obtained.

[0056] It should be noted that the calibration system of this application is based on the laser damage threshold measurement system to be calibrated, wherein the first laser source 310 is the laser source of the laser damage threshold measurement system itself. The detection delay unit 331, pump delay unit 341 and detector in the calibration system can also be those present in the laser damage threshold measurement system. The calibration system of this application is based on these hardware facilities, combined with standard parts materials, and controls the hardware settings to execute the calibration method of this application.

[0057] In some embodiments, the calibration method of this application further includes step S20: changing the delay between the pump and the detector in the laser damage threshold measurement system to obtain the transmittance and / or reflectance under different delay values. The transmittance and / or reflectance are used to characterize the phase transition light intensity, and the relationship between the delay value and the phase transition light intensity is used to characterize the temporal resolution of the phase transition distribution of the thermally induced phase transition material.

[0058] For spatial resolution of phase transitions, the target surface characteristics of the laser are determined by the laser and the focusing system, and their complete description is two-dimensional data. For the phase transition of GST alloys, offline spatial resolution measurements can be performed. However, for self-recovering phase transition materials such as VO2 and V2O5, it is challenging to rapidly obtain their phase transition distribution during laser irradiation. Therefore, this application proposes a method of layer-by-layer clipping and attenuation of the pulse intensity, transforming the spatial distribution into the area of ​​the phase transition region under different attenuation rates.

[0059] Referring to Figure 5, an attenuator 332 is also provided in the detection branch 330 to attenuate the detection light, and an attenuator 342 is also provided in the pump branch 340 to attenuate the pump light. By adjusting the attenuators 332 and 342, the laser energy actually irradiated onto the surface of the thermally induced phase change material S can be adjusted. Step S20 of this application further includes:

[0060] The pulse intensity of the laser is clipped and attenuated layer by layer to obtain the phase transition region area under different attenuation rates. The relationship between the phase transition region area and the phase transition light intensity is used to characterize the spatial resolution of the phase transition distribution of thermally induced phase change materials.

[0061] Attenuators 332 and 342 can be used in combination to attenuate the probe light and pump light respectively. This application does not limit the specific attenuation amount, the clipping step size, or whether the two lights are attenuated synchronously or asynchronously. Those skilled in the art can flexibly control the attenuators based on the ideas in this application to obtain the relationship between the phase transition region area and the phase transition light intensity. It is understood that to improve spatial resolution, the smaller the clipping step and the more clipping operations, the higher the spatial resolution.

[0062] The relationship between the size of the phase transition region and the probe spot affects the transmittance and reflectance intensity. By using the above-mentioned layer-by-layer clipping attenuation method, the two-dimensional phase transition problem can be transformed into a one-dimensional problem of intensity dynamic range.

[0063] This method is also applicable to GST alloys. For any thermo-induced phase change material, the spatially resolved characteristics of its phase change distribution can be obtained using the layer-by-layer clipping attenuation method.

[0064] After measuring a measurement system A and obtaining the spatiotemporal characteristic relationship between its energy density and phase transition light intensity, steps S20 and S30 can be executed for another laser damage threshold measurement system B (hereinafter referred to as "measurement system B") to calibrate the measurement system B.

[0065] Since the standard parts used are made of the same materials, the calibration results of measurement system A and measurement system B are comparable. By comparing their corresponding relationships, measurement system A and measurement system B can be analyzed and evaluated.

[0066] Referring to Figure 5, the calibration system also includes a second laser source 360. Specifically, for GST, this second laser source 360 ​​is a picosecond-level laser. During the calibration process, the first laser source 310 first irradiates the GST alloy, causing a phase transition, i.e., from an amorphous state to a crystalline state. After completing one phase transition detection, the second laser source 360 ​​irradiates the GST alloy, thereby restoring its crystal structure, i.e., changing it back from a crystalline state to an amorphous state.

[0067] In one embodiment, the thermally induced phase change material includes transition metal oxides VO2 and V2O5 and chalcogenide GST alloys, thus obtaining at least three quantitative characteristic points corresponding to different temperatures. These three quantitative characteristic points can be used as values ​​to calibrate different laser damage threshold measurement systems.

[0068] It should be noted that thermally induced phase change materials with higher phase change temperatures can be achieved by adjusting the material formulation, thereby obtaining more quantitative characteristic points.

[0069] Using the calibration system described above, the temporal and spatial resolutions of the phase transition distribution of the thermally induced phase transition material corresponding to the spatiotemporal characteristics of the pulsed laser in the laser damage threshold measurement system can be obtained. Step S20, which establishes the relationship between energy density and the spatiotemporal characteristics of the magnitude feature points, includes:

[0070] The functional relationship PC(I, r, t) between phase transition light intensity and energy density is employed, where PC represents the light intensity of the laser when its properties change (specifically, power density in this embodiment), I represents the phase transition light intensity, r represents the laser spot size, and t represents time. When the spot is circular, r can specifically be the spot radius, thus characterizing spatial properties. This functional relationship includes at least three-dimensional information and can be represented as a matrix or by a dynamic physical image, used to depict the dynamic relationship between the laser field, temperature difference, and phase transition thin film material phase structure distribution. Based on this functional relationship, the spot size effects and pulse width scaling law of the laser damage threshold testing system can also be analyzed.

[0071] For different measurement systems, their corresponding functional relationships PC(I, r, t) can be obtained, making the transfer of values ​​between different measurement systems possible. Furthermore, the effectiveness, reliability, applicable conditions, and scope of the value transfer method can be determined by comprehensively considering the pulse width scaling rate in laser damage threshold testing and the spot effect in space, through iteration and experimental verification.

[0072] The calibration method of this application makes it possible to perform segmented (or multi-point) calibration of the laser pulse energy density within the measurement range of the laser damage threshold testing system by using thermally induced phase change materials applicable to different laser timescales and with different phase transition point temperatures.

[0073] It should be understood that the embodiments described above are merely illustrative. The embodiments described herein may be implemented in hardware, software, firmware, middleware, microcode, or any combination thereof. For hardware implementation, the processor may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and / or other electronic units designed to perform the functions described herein, or combinations thereof.

[0074] Some aspects of this application can be executed entirely by hardware, entirely by software (including firmware, resident software, microcode, etc.), or by a combination of hardware and software. The aforementioned hardware or software may be referred to as a "data block," "module," "engine," "unit," "component," or "system." The processor may be one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DAPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or combinations thereof. Furthermore, aspects of this application may manifest as computer products residing in one or more computer-readable media, including computer-readable program code. For example, computer-readable media may include, but are not limited to, magnetic storage devices (e.g., hard disks, floppy disks, magnetic tapes, etc.), optical discs (e.g., compressed CDs, digital multifunction DVDs, etc.), smart cards, and flash memory devices (e.g., cards, sticks, key drives, etc.).

[0075] A computer-readable medium may contain a propagated data signal containing computer program code, for example, on baseband or as part of a carrier wave. This propagated signal may take various forms, including electromagnetic, optical, and so on, or suitable combinations thereof. A computer-readable medium can be any computer-readable medium other than a computer-readable storage medium, which can be connected to an instruction execution system, apparatus, or device to enable communication, propagation, or transmission of a program for use. The program code located on the computer-readable medium can be propagated through any suitable medium, including radio, cable, fiber optic cable, radio frequency signals, or similar media, or any combination of the above media.

[0076] The basic concepts have been described above. Obviously, for those skilled in the art, the above disclosure is merely illustrative and does not constitute a limitation of this application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are suggested in this application, and therefore remain within the spirit and scope of the exemplary embodiments of this application.

[0077] Furthermore, this application uses specific terms to describe embodiments of the application. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic related to at least one embodiment of the application. Therefore, it should be emphasized and noted that "an embodiment," "one embodiment," or "an alternative embodiment" mentioned twice or more in different locations in this specification do not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0078] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used in the description of embodiments are modified in some examples with the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification are approximate values, which may be changed according to the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of range in some embodiments of this application are approximate values, in specific embodiments, such values ​​are set as precisely as feasible.

Claims

1. A calibration method for a laser damage threshold measurement system, characterized in that, The application relates to a method for calibrating a laser damage threshold measurement system. The method comprises the following steps: acquiring a plurality of standard materials, each of which has a corresponding value characteristic point, wherein the value characteristic points of different standard materials are different, and when the standard materials are irradiated by laser, the properties of the standard materials change at the value characteristic points, and the change is reversible; using a laser damage threshold measurement system to irradiate the plurality of standard materials with a plurality of different laser intensities respectively, and establishing a relationship between the laser intensity and the space-time characteristics of the value characteristic points; 2. The calibration method of claim 1, wherein, calibrating the laser damage threshold measurement system according to the relationship.

3. The calibration method of claim 1, wherein, The laser comprises single-pulse laser or continuous laser with limited time, and the laser intensity is energy density or power density.

4. The calibration method of claim 3, wherein, The standard materials comprise a thermal phase change material, the temperature of the thermal phase change material changes under laser irradiation, the properties of the thermal phase change material change, and the value characteristic point is the phase change intensity of the laser corresponding to the change of the properties.

5. The calibration method of claim 3, wherein, The thermal phase change material comprises transition metal oxide VO2 and / or V2O5, the properties are crystal phase, the crystal phase changes when the temperature of the thermal phase change material is greater than the phase change temperature after laser irradiation, and the crystal phase restores when the temperature of the thermal phase change material is less than the phase change temperature after laser irradiation.

6. The calibration method of claim 3, wherein, The thermal phase change material comprises a chalcogenide GST alloy, the properties are crystal structure, the crystal structure changes from amorphous state to crystal state when the chalcogenide GST alloy is irradiated by the laser of the laser damage threshold measurement system, and the crystal structure changes from crystal state to amorphous state when the chalcogenide GST alloy is irradiated by a second pulse laser, wherein the pulse width of the second pulse laser is less than the pulse width of the laser of the laser damage threshold measurement system. The step of establishing the relationship between the laser intensity and the space-time characteristics of the value characteristic points comprises the following steps: obtaining a function relationship PC(I, r, t) between the phase change intensity and the laser intensity, wherein PC represents the laser intensity of the laser when the properties change, I represents the phase change intensity, r represents the laser spot size, and t represents time; and the step of calibrating the laser damage threshold measurement system according to the relationship comprises the following steps:

7. The calibration method of claim 6, wherein, analyzing the spot effect and pulse width calibration rate of the laser damage threshold measurement system according to the function relationship. The application further relates to a method for calibrating a laser damage threshold measurement system.

8. The calibration method of claim 6, wherein, The method comprises the following steps: when the thermal phase change material is a chalcogenide GST alloy, after the properties of the chalcogenide GST alloy change, the chalcogenide GST alloy is irradiated by a second pulse laser, so that the change of the properties of the chalcogenide GST alloy is restored, wherein the pulse width of the second pulse laser is less than the pulse width of the laser of the laser damage threshold measurement system. The step of establishing the relationship between the laser intensity and the space-time characteristics of the value characteristic points further comprises the following steps: The delay amount between the pump light and the probe light in the laser damage threshold measurement system is changed, the transmittance and / or reflectance under different delay amounts are obtained, the transmittance and / or reflectance are used to characterize the phase transition light intensity, and the relationship between the delay amount and the phase transition light intensity is used to characterize the time resolution of the phase transition distribution of the thermal-induced phase change material.

9. The calibration method of claim 8, wherein, The step of establishing the relationship between the light intensity and the space-time characteristics of the characteristic points further comprises: The pulse intensity of the laser is attenuated layer by layer, the phase transition area under different attenuation rates is obtained, and the relationship between the phase transition area and the phase transition light intensity is used to characterize the spatial resolution of the phase transition distribution of the thermal-induced phase change material.

10. The calibration method of claim 9, wherein, The step of calibrating the laser damage threshold measurement system according to the relationship further comprises: The time resolution and the spatial resolution of the phase transition distribution of the thermal-induced phase change material corresponding to the space-time characteristics of the pulse laser of different laser damage threshold measurement systems are compared.

11. A calibration system for a laser damage threshold measurement system, characterized in that The laser damage threshold measurement system comprises a first laser source, a beam splitter, an attenuator, a probe delay unit, a pump delay unit and a detector. The first laser source is used to generate the laser of the laser damage threshold measurement system. The beam splitter is used to divide the laser into probe light and pump light, the probe light reaches the standard material along a probe branch, and the pump light reaches the standard material through a pump branch. The attenuator is used for the probe light and / or the pump light to attenuate. The probe delay unit is arranged on the probe branch and is used to adjust the optical path of the probe light. The pump delay unit is arranged on the pump branch and is used to adjust the optical path of the pump light. The detector is used to detect the amount of reflected light and / or transmitted light on the surface of the standard material. The calibration system is used to perform the calibration method according to any one of claims 1-10.

12. The calibration system of claim 11, wherein, The second laser source is further included, which is used to irradiate the chalcogenide GST alloy, so that the property change of the chalcogenide GST alloy is recovered.

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