Thin film plasma internal pressure measuring method and device based on spectral analysis

Abstract

The invention discloses a thin film plasma internal pressure measuring method and device based on spectral analysis. The method comprises the following steps: placing a to-be-measured optical thin film on a sample table, exciting plasma flash on the surface of the thin film by utilizing energy-adjustable pulse laser, collecting an emission spectrum under the conditions of preset integral time and delay time, selecting two spectral lines of the same element in the spectrum, and calculating the electron temperature through a relative intensity relationship. And calculating the electron density according to the full width at half maximum of the final line and an electron broadening model, and solving the internal pressure of the thin film plasma by adopting a state equation under the hypothesis of local heat balance and quasi-neutral. The device is composed of a laser light source, an attenuation system, a focusing system, a beam splitter, an energy meter, a sample table, a spectrograph and a computer control system. On the basis of the measured internal pressure, the internal pressure of films of different processes can be compared under the same experimental condition, and the method is used for evaluating the laser damage resistance of the film.

Description

Technical Field

[0001] This invention belongs to the field of optical testing technology, specifically relating to a method and apparatus for measuring the internal pressure of thin-film plasma based on spectral analysis. Background Technology

[0002] The performance limits of high-power laser systems largely depend on the laser-induced damage threshold of internal optical components. Taking multilayer or single-layer optical thin films as an example, under high-energy pulsed laser irradiation, the films not only undergo thermal processes such as melting and vaporization, but are also prone to mechanical damage such as delamination, cracking, and sputtering. This type of damage is often irreversible, and once it occurs, it can lead to a significant deterioration in the transmittance and reflectivity of optical components, or even cause the system to lose its functionality. Therefore, it is necessary to quantitatively characterize and evaluate the failure mechanism and damage resistance of thin films under laser irradiation.

[0003] Existing thin-film laser damage characterization methods mainly employ laser damage threshold testing, microscopic morphology observation, scattered light measurement, and photoacoustic detection. These methods often focus on statistically analyzing damage probability, observing the morphological characteristics of damage pits, or indirectly reflecting damage intensity by detecting shock waves and acoustic pressure signals, which can assess the damage resistance level of thin films to a certain extent. However, in the initial stage of laser-film interaction, the thin-film material rapidly generates laser-induced plasma. This plasma reaches a high-temperature, high-pressure state in a very short time, and when it expands outward, it forms a shock wave and applies transient high-pressure loads to the thin-film structure. This internal pressure evolution process is closely related to the mechanical failure of the thin film. Traditional criteria based on "whether damage occurs" or "damage morphology" are difficult to directly quantify the key physical parameter of internal plasma pressure, thus making it difficult to conduct a detailed comparison of the damage resistance of thin films from a mechanical loading perspective.

[0004] On the other hand, plasma emission spectra contain rich state information, and obtaining parameters such as electron temperature and electron density through spectral diagnostics is already a routine method in the field of plasma physics. In scenarios such as laser welding and material ablation, existing research has involved deploying optical acquisition systems near welding pinholes or ablation zones to collect plasma emission spectra. Spectral diagnostics are then used to obtain information such as electron temperature, electron density, and particle energy distribution, which is then used to analyze process characteristics such as weld formation quality, molten pool stability, and ablation efficiency. These methods generally use spectral diagnostic results as an auxiliary basis for process monitoring or control.

[0005] While existing work has demonstrated the feasibility of characterizing plasma states using emission spectroscopy in processing scenarios, several limitations remain. Firstly, current research primarily focuses on metal materials such as those used in deep-penetration welding of small holes. The geometry and constraint boundaries of the tested objects differ significantly from the plasma formation conditions in the open space on the surface of optical thin films, making it difficult to directly transfer the optical path arrangement, sampling area, and parameter selection to thin-film laser damage testing. Secondly, existing methods largely focus on weld quality, welding stability, or ablation efficiency, failing to establish a parameter selection and calculation process for thin-film plasma within the optical thin-film system. Furthermore, they do not systematically quantify the internal pressure of the thin-film plasma as a mechanically relevant quantity for evaluating the film's resistance to laser damage. Therefore, there is an urgent need to propose a testing method and device for quantitatively obtaining the internal pressure of the thin-film plasma based on emission spectroscopy, tailored to optical thin-film applications. This would introduce a physical quantity that directly reflects transient mechanical loads into thin-film laser damage research, enabling more refined comparison and analysis of the damage resistance performance of different thin-film fabrication processes and structures. Summary of the Invention

[0006] This invention provides a method and apparatus for measuring the internal pressure of thin-film plasma based on spectral analysis, which solves the problem in the prior art that it is difficult to quantitatively obtain the internal pressure of thin-film plasma in optical thin-film laser damage tests.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for measuring the internal pressure of thin-film plasma based on spectral analysis, comprising:

[0009] The thin film sample to be tested is placed on the sample stage, and the adjustable energy pulsed laser output by the laser source and attenuation system is applied to the surface of the thin film sample through the focusing system, thereby generating thin film plasma flash on the surface of the thin film sample.

[0010] Under preset integration time and preset delay time conditions, the emission spectrum of the thin-film plasma flash is collected using a spectrometer;

[0011] Two emission lines of the same element are selected from the emission spectrum, one of which is the last line of the element. The electron temperature T of the thin film plasma is calculated based on the relative intensity of the two emission lines and the degeneracy, transition probability and wavenumber of the corresponding energy level.

[0012] Calculate the electron density N of the thin-film plasma based on the full width at half maximum (FWHM) of the last line in the emission spectrum and the electron temperature. e ;

[0013] Assuming that the thin-film plasma is in local thermal equilibrium and that the electron temperature is equal to the ion temperature and satisfies the quasi-neutrality condition, the thin-film plasma is treated as an ideal gas, and the internal pressure P of the thin-film plasma is calculated using the equation of state based on the electron temperature and electron density.

[0014] Furthermore, the step of calculating the electron temperature T of the thin-film plasma includes:

[0015] Two emission lines of the same element are selected from the emission spectrum, one of which is the last emission line of the element and the other is not the last emission line.

[0016] Substituting the intensities I1 and I2 of the two emission lines, the energy levels E1 and E2, the degeneracy g1 and g2, the transition probabilities A1 and A2, and the wave numbers ν1 and ν2 into the following equation (1):

[0017] (1)

[0018] Solve for the electron temperature T of the thin-film plasma, where is the Boltzmann constant.

[0019] Furthermore, the electron density of the thin-film plasma is calculated. The steps include:

[0020] Obtain the full width at half maximum (FWHM) Δλ / 2 of the last line of the thin-film plasma, and apply the electron broadening-dominated relation (2):

[0021] (2)

[0022] The electron density of the thin-film plasma was calculated. , where w is the electron broadening factor related to electron temperature.

[0023] Furthermore, the step of calculating the internal pressure P of the thin-film plasma using the equation of state based on the electron temperature and electron density includes:

[0024] Assume that the thin-film plasma consists of electrons and monovalent positive ions, and satisfies the quasi-neutrality condition. ,in For electron density, Let be the ion density; assuming the electron temperature and ion temperature are approximately equal. ;

[0025] Under the above assumptions, the thin-film plasma is considered as an ideal gas, and the total particle number density N is the sum of the electron density and the ion density, i.e. ;

[0026] According to the ideal gas law (3):

[0027] (3)

[0028] get: (4)

[0029] in, Where is Boltzmann's constant, and T is the electron temperature. This represents the electron density.

[0030] Furthermore, the thin film sample to be tested is an optical thin film, and the incident direction of the pulsed laser is perpendicular to the incident surface of the optical thin film.

[0031] Furthermore, the thin film sample to be tested is a thin film deposited on a substrate, and the thin film is a single-layer silicon oxide thin film with a 1 / 4 wavelength optical thickness.

[0032] Secondly, the present invention provides a method for evaluating the laser damage resistance of thin films, comprising:

[0033] Using the above-mentioned method for measuring the internal pressure of thin film plasma based on spectral analysis, under the same incident laser energy density and other experimental parameters, the internal pressure P of the thin film plasma generated by each of the same material thin films prepared by at least two different processes was measured.

[0034] By comparing the internal plasma pressure P of thin films produced by different processes, the thin film with the lower internal pressure under the same conditions is identified as the thin film with higher resistance to laser damage.

[0035] Thirdly, the present invention provides a thin-film plasma internal pressure measurement device based on spectral analysis, comprising:

[0036] A laser source and attenuation system are used to generate and modulate the pulsed laser energy incident on a thin film sample.

[0037] A focusing system is used to focus the pulsed laser output by the attenuation system onto the surface of the thin film sample, thereby generating a thin film plasma flash on the surface of the thin film sample.

[0038] A beam splitter and an energy meter are used. The beam splitter is located in the laser optical path before the focusing system to guide a portion of the pulsed laser to the energy meter, which measures the incident laser energy acting on the thin film sample in real time.

[0039] The sample stage is used to mount the thin film sample and can move in a plane to change the laser irradiation position;

[0040] A spectrometer is used to collect the emission spectrum of the thin-film plasma flash under preset integration time and preset delay time conditions;

[0041] A computer control system is used to control the working status of the laser source and attenuation system, the energy meter, the sample stage and the spectrometer, and to process the emission spectrum to calculate the electron temperature, electron density and internal pressure of the thin film plasma.

[0042] Furthermore, the spectrometer is a fiber optic spectrometer with a wavelength range of 200 nm to 1100 nm and a spectral resolution of no more than 0.02 nm.

[0043] Furthermore, the laser source is A solid-state laser with an output wavelength of 1064 nm and a pulse width of approximately 10 ns, wherein the attenuation system has an adjustable attenuation rate from 0% to 100%.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The proposed method for measuring the internal pressure of thin-film plasma based on spectral analysis, targeting the plasma characteristics formed by optical thin films under high-power laser irradiation, constructs a system from emission spectrum to electron temperature T and electron density N. e From the initial calculation to the complete calculation chain of internal pressure P; by introducing the intensity ratio of two spectral lines containing the last line of the same element, combined with the Stark broadening relation dominated by electron broadening and the ideal gas equation of state, this invention can simultaneously obtain T and N based on a single spectral measurement. e Key parameters such as P are used to quantitatively describe the excited state of the thin film using internal pressure, a physical quantity directly related to transient mechanical loads. This is beneficial for analyzing the laser damage mechanism of thin films from the perspective of mechanical loading.

[0046] The method for evaluating the laser damage resistance of thin films proposed in this invention uses the internal pressure P of the thin film plasma as a quantitative indicator reflecting the risk of mechanical failure of the thin film. Under the same incident laser energy density and experimental conditions, thin films of the same material prepared by different processes are compared. By comparing the internal pressure of different films under the same laser conditions, it is possible to distinguish the films with stronger mechanical load resistance under the same energy, which is beneficial for targeted optimization of thin film preparation processes and structural parameters, and also provides an intuitive and comparable evaluation basis for the selection of thin film types in engineering applications.

[0047] The thin-film plasma internal pressure measurement device proposed in this invention integrates a laser source and attenuation system, focusing system, beam splitter and energy meter, movable sample stage, spectrometer, and computer control system. It can stably generate thin-film plasma and complete emission spectrum acquisition and data processing under simulated actual working incident conditions of optical thin films. Through unified control of laser energy, spot position, and spectral acquisition parameters, this device improves the repeatability and comparability of measurement results, providing a convenient and reliable experimental platform for systematically studying the energy dependence of internal pressure in thin-film plasma and supporting the evaluation of thin film laser damage resistance.

[0048] Of course, implementing the various technical solutions of this invention does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained from these drawings without creative effort.

[0050] Figure 1 This is a schematic diagram of the principle of the thin-film plasma internal pressure measurement device based on spectral analysis according to an embodiment of the present invention;

[0051] Figure 2 This is a comparison of spectral lines under different laser energies in an embodiment of the present invention (the sample is a silicon oxide thin film, and the incident laser energies are 70 mJ, 80 mJ, 90 mJ, 100 mJ, 110 mJ, and 115 mJ, respectively, with a spectral range of 200 nm to 1100 nm).

[0052] Figure 3 This is a comparison of spectral lines under different laser energies in the embodiments of the present invention (the sample is a silicon oxide thin film, and the incident laser energy ranges are 70 mJ, 80 mJ, 90 mJ, 100 mJ, 110 mJ, and 115 mJ, with a spectral range of 200 nm-300 nm).

[0053] Figure 4 This is a graph showing the change of plasma electron temperature with laser energy in an embodiment of the present invention;

[0054] Figure 5 This is a graph showing the variation of plasma electron density with laser energy in an embodiment of the present invention;

[0055] Figure 6 This is a graph showing the change in plasma internal pressure with laser energy according to an embodiment of the present invention. Detailed Implementation

[0056] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings. Similar elements in different embodiments are referred to by associated similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of this application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to this application are not shown or described in the specification. This is to avoid obscuring the core parts of this application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0057] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for the clear description of a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0058] From a physical perspective, when a laser pulse irradiates an optical thin film, the film material absorbs energy and undergoes localized ablation within a very short time, forming a high-temperature, high-pressure plasma plume in the ablated region. This plasma initially exhibits both a strong continuous spectrum and distinct atomic and ionic spectral lines. The relative intensity of these spectral lines is related to the number distribution of particles in the upper energy levels, while the broadening of the spectral lines contains information such as electron density. Therefore, by acquiring the emission spectrum of the thin-film plasma through appropriate time-gated acquisition and combining it with plasma spectral diagnostic methods, electron temperature and electron density can be obtained sequentially, and finally, the internal pressure of the plasma can be calculated using the equation of state.

[0059] In determining the electron temperature, this embodiment employs the relative intensity comparison method. Assuming that the thin-film plasma satisfies local thermal equilibrium at the time of observation, i.e., the electron velocity distribution approximately follows a Maxwell distribution, the bound electron distribution at each energy level satisfies a Boltzmann distribution, and the charged ion density satisfies the Sachs equation, then the excitation temperature can be considered as the electron temperature. For two emission spectral lines of the same element, their intensity, energy level energy, degeneracy, transition probability, and wavenumber satisfy the relationship shown in equation (1). By measuring the intensity of the two spectral lines and obtaining the relevant atomic parameters from a table, the electron temperature T can be calculated inversely.

[0060] (1)

[0061] In determining the electron density, this embodiment utilizes the functional relationship between the full width at half maximum (FWHM) of a spectral line dominated by Stark broadening and the electron density. For a suitable final line, when electron broadening is the dominant broadening mechanism, its FWHM Δλ / 2 is related to the electron density. The relationship shown in equation (2) is satisfied. The full width at half maximum (FWHM) of the final line is obtained through experimental fitting, and combined with the broadening factor w corresponding to the electron temperature, the electron density under different laser energy conditions can be calculated. .

[0062] (2)

[0063] In calculating the internal pressure, a thin-film plasma, under conditions of local thermal equilibrium and non-strong magnetization, can be considered as a mixed ideal gas composed of electrons and positive ions. The internal pressure is essentially the collisional effect of the random thermal motion of charged particles on the plasma boundary. Assuming the electron temperature and ion temperature are equal, both T, and the electron density is... The total positive ion density is Then, the pressure expression shown in equation (3) can be obtained from the ideal gas law.

[0064] (3)

[0065] Considering the plasma quasi-neutrality condition N e = ZN i Furthermore, by taking the monovalent ion Z≈1, we can obtain the simplified form shown in equation (4): P = 2k B TN e .

[0066] (4)

[0067] Therefore, in obtaining T and N e Based on this, the internal pressure P of the thin-film plasma can be calculated, and its variation with incident laser energy can be analyzed.

[0068] Example 1:

[0069] This embodiment provides a method and apparatus for measuring the internal pressure of thin-film plasma based on spectral analysis. The schematic diagram of the apparatus is shown below. Figure 1 As shown. The entire system consists of a laser source and attenuation system, focusing system, beam splitter, energy meter, sample stage, spectrometer, and computer control system.

[0070] High power was used in the experiment. A solid-state laser is used as the laser source, with an output wavelength of 1064 nm. The single-pulse energy is adjustable from 5 mJ to 140 mJ, and the pulse width is approximately 10 ns. After being focused by the focusing system, the spot radius on the thin film sample surface is approximately 0.3 mm. An attenuation system is positioned between the laser output and the focusing system, with an attenuation rate continuously adjustable from 0% to 100%, used for fine control of the pulse energy incident on the thin film sample. The focusing system has a focal length of approximately 50 mm and is used to focus the attenuated laser beam onto the sample surface.

[0071] A beam splitter is placed in front of the focusing system to reflect a small portion of the laser energy to the energy meter, which monitors the incident energy of each laser pulse in real time; the majority of the laser energy is transmitted and focused onto the sample surface. When the laser energy acting on the thin film surface exceeds its damage threshold, a noticeable thin-film plasma flash is formed above the film surface. The spectrometer collects the plasma emission spectrum via optical fiber and transmits the spectral data to a computer. The sample stage can move two-dimensionally in a plane to adjust the laser irradiation position on the thin film sample, avoiding cumulative damage caused by repeated excitation at the same point. The computer control system is used to synchronously control the operating status of the laser, attenuation system, energy meter, sample stage, and spectrometer, and to perform subsequent processing and parameter calculations on the acquired spectra.

[0072] Considering the strong continuous background spectrum in the early stages of thin-film plasma flash formation, its short duration, and rapid decay rate, an integration time of 5 ms was selected in this embodiment to ensure that the spectrometer can receive sufficient effective spectral information. Meanwhile, relevant literature indicates that the ignition time of thin-film plasma flash is on the order of tens of nanoseconds. To avoid acquiring the background signal before ignition and to ensure that only the emission spectrum after ignition is acquired, a delay time of 50 ns was chosen in the experiment. The matching setting of the integration time and the delay time balances both signal-to-noise ratio and time resolution.

[0073] The spectrometer used was an AVANTES AvaSpec-2048 fiber optic spectrometer with a spectral response range of 200 nm to 1100 nm and a spectral resolution of approximately 0.02 nm, covering the characteristic spectral lines of silicon in the ultraviolet region as well as continuous background radiation. The energy meter used was a Newport No. 2936-R. To ensure the repeatability of the measurement results, this embodiment kept the laser input voltage constant during the experiment, adjusting the output energy through an attenuation system.

[0074] In this embodiment, the thin film sample selected for testing is a single-layer silicon oxide film deposited on a transparent substrate, with an optical thickness of one-quarter of the working wavelength, approximately λ / 4. Six typical incident laser energy conditions were designed for the experiment, corresponding to 70 mJ, 80 mJ, 90 mJ, 100 mJ, 110 mJ, and 115 mJ. Laser emission was repeated multiple times under each energy condition to obtain a stable average spectrum. The output emission spectrum is shown below. Figure 2 and Figure 3 As shown, where Figure 2 The overall spectral variation trend in the 200nm to 1100nm band is given. Figure 3 The magnified view shows the spectral structure in the 200 nm to 300 nm range. Multiple characteristic spectral lines of silicon can be observed in the 200 nm to 300 nm band, and their peak intensity increases significantly with increasing incident laser energy, indicating that the number of excited-state particles in the thin-film plasma increases accordingly with increasing laser energy.

[0075] In the electronic temperature calculation process, this embodiment follows the aforementioned principle, from... Figure 3 Two emission lines of silicon, the same element, are selected from the spectrum shown. One line is the last emission line of the element, and the other is not. By comparing with the standard atomic spectral database, the two emission lines selected in this embodiment are Si(I)₂ 12.41 nm (measured value 212.96 nm) and Si(I)₂ 88.16 nm (measured value 288.95 nm) from the NIST library, where 288.16 nm (measured value 288.95 nm) is the last emission line. The intensities I1 and I2 of the two emission lines are measured, and the degeneracy g1 and g2, energy E1 and E2, transition probabilities A1 and A2, and wavenumbers ν1 and ν2 of the corresponding energy levels are obtained by referring to the table. Substituting the above parameters into equation (1), the electron temperature T of the thin film plasma under different incident laser energies can be obtained. The calculation results are as follows. Figure 4 As shown.

[0076] In the electron density calculation, this embodiment uses the Si(I) 288.16nm (measured value 288.95nm) spectral line as the last line and measures its full width at half maximum (FWHM) Δλ / 2 under different incident laser energies. Considering that electron broadening plays a dominant role in the broadening of this spectral line in laser-induced thin-film plasma, equation (2) can be used to describe the relationship between the full WHM and the electron density. Substituting the measured Δλ / 2 and the electron temperature T obtained according to equation (1) into equation (2), and using the broadening coefficient w given in the literature or database, the corresponding electron density can be obtained. The result is as follows Figure 5 As shown.

[0077] After obtaining the electron temperature T and electron density Next, in this embodiment, the internal pressure P of the thin-film plasma is calculated according to equations (3) and (4). Specifically, the electron density is... and the assumed monovalent positive ion density Substituting into the ideal gas law, under quasi-neutral conditions... and In this case, equation (3) is simplified to , Take the Boltzmann constant as 1.38 × 10⁻⁶ -23 J / K, T is measured in K. Unit conversion The calculated changes in internal pressure with incident laser energy are as follows: Figure 6 As shown.

[0078] For ease of explanation, this embodiment provides calculation results for six typical incident laser energies: the thin film is a single layer. A thin silicon oxide film of thickness is given by laser parameters: wavelength 1064 nm, pulse width 10 ns, focused spot radius 0.3 mm. If the incident laser energy is... At that time, the thin-film plasma electron temperature value is The plasma electron density value is The internal pressure value of the plasma is .

[0079] The above-mentioned film is a single layer A thin silicon oxide film of thickness is given by laser parameters: wavelength 1064 nm, pulse width 10 ns, focused spot radius 0.3 mm. If the incident laser energy is... At that time, the thin-film plasma electron temperature value is The plasma electron density value is The internal pressure value of the plasma is .

[0080] The thin film is a single layer A thin silicon oxide film of thickness is given by laser parameters: wavelength 1064 nm, pulse width 10 ns, focused spot radius 0.3 mm. If the incident laser energy is... At that time, the thin-film plasma electron temperature value is The plasma electron density value is The internal pressure value of the plasma is .

[0081] The thin film is a single layer A thin silicon oxide film of thickness is given by laser parameters: wavelength 1064 nm, pulse width 10 ns, focused spot radius 0.3 mm. If the incident laser energy is... At that time, the thin-film plasma electron temperature value is The plasma electron density value is The internal pressure value of the plasma is .

[0082] The thin film is a single layer A thin silicon oxide film of thickness is given by laser parameters: wavelength 1064 nm, pulse width 10 ns, focused spot radius 0.3 mm. If the incident laser energy is... At that time, the thin-film plasma electron temperature value is The plasma electron density value is The internal pressure value of the plasma is .

[0083] The thin film is a single layer A thin silicon oxide film of thickness is given by laser parameters: wavelength 1064 nm, pulse width 10 ns, focused spot radius 0.3 mm. If the incident laser energy is... At that time, the thin-film plasma electron temperature value is The plasma electron density value is The internal pressure value of the plasma is The typical values ​​for electron temperature, electron density, and internal pressure at typical incident laser energies can be found by referring to [reference needed]. Figures 4 to 6 The number of data points in the data is roughly consistent with the results reported in relevant literature.

[0084] Combination Figures 4 to 6 It can be seen that, under the test conditions of this embodiment, as the incident laser energy gradually increases from 70 mJ to 115 mJ, the electron temperature of the thin-film plasma generally shows a slow decreasing trend, and the electron density is at... The pressure fluctuates slightly within a small range, while the overall trend of internal pressure decreases slightly with increasing energy but remains largely unchanged. This trend shows good consistency in magnitude and variation law with the conclusions in published literature regarding the changes in laser-induced plasma electron temperature, electron density, and internal pressure with laser energy, indirectly verifying the reliability of the internal pressure measurement method based on spectral analysis in this embodiment.

[0085] Example 2:

[0086] Based on the measurement platform and calculation method of Example 1, this example provides an application method for evaluating the laser damage resistance of thin films.

[0087] First, optical thin films of the same material are prepared under at least two different process conditions. For example, thin film A and thin film B are prepared on the same substrate using different sputtering powers, gas pressures, or annealing processes. Thin film A and thin film B are respectively mounted on a sample stage, and the thin film plasma emission spectra generated by the two films under the same incident laser energy density and the same integration time and delay time are measured under the same experimental setup and testing procedures as in Example 1.

[0088] Then, referring to Example 1, the electron temperature T and electron density N were calculated. e Using the method of internal pressure P, the spectral data of thin films A and B under various incident laser energy conditions were processed one by one to obtain the corresponding internal pressure curves P. A(E) and P B(E) By comparing the internal pressures of the two films at a specific representative incident energy (e.g., energy density close to the operating conditions of the thin film), if the internal pressure of film A is significantly lower than that of film B under the same laser energy density, it indicates that film A experiences a smaller transient mechanical load when subjected to a laser pulse of the same energy, and its resistance to laser damage is relatively higher; conversely, film B has a higher resistance to laser damage.

[0089] Through the above embodiment 2, the internal pressure of the thin film plasma can be used as a mechanically related quantitative index to characterize the comprehensive damage resistance of the thin film, providing an intuitive basis for comparison of thin film schemes with different deposition processes, material ratios or structural designs, and also providing experimental support for the selection and optimization of optical thin films in high-power laser systems.

[0090] Furthermore, while the operations are described in a specific order, this should not be construed as requiring these operations to be performed in the specific order shown or in a sequential order. In certain environments, multitasking and parallel processing may be advantageous. Similarly, while several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of this disclosure. Certain features described in the context of individual embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments.

Claims

1. A method for measuring internal pressure of a thin film plasma based on spectral analysis, characterized by, The method comprises the following steps: placing a to-be-tested thin film sample on a sample stage, and using an adjustable energy pulse laser output by a laser light source and an attenuation system to act on a surface of the thin film sample through a focusing system, so as to generate a thin film plasma flash on the surface of the thin film sample; under the condition of a preset integration time and a preset delay time, collecting an emission spectrum of the thin film plasma flash by using a spectrometer; selecting two emission spectral lines of the same element in the emission spectrum, one of which is a last line of the element, and calculating an electron temperature T of the thin film plasma according to relative intensities of the two emission spectral lines, degeneracy of corresponding energy levels, transition probability and wave number. calculating an electron density N of the thin film plasma from the full width at half maximum of the last line in the emission spectrum and the electron temperature e ; under the premise that the thin film plasma is in local thermal equilibrium, the electron temperature is equal to the ion temperature and satisfies a quasi-neutral condition, regarding the thin film plasma as an ideal gas, and calculating an internal pressure P of the thin film plasma by using a state equation according to the electron temperature and the electron density.

2. The method of claim 1, wherein the method is performed by a spectrometer. The step of calculating the electron temperature T of the thin film plasma comprises the following steps: selecting two emission spectral lines of the same element in the emission spectrum, one of which is a last line of the element, and the other is a non-last line; putting intensities I1 and I2 of the two emission spectral lines, energy levels E1 and E2, degeneracy g1 and g2, transition probability A1 and A2 and wave number v1 and v2 into the following formula (1): （1） Solving for the electron temperature T of the thin film plasma, where is the Boltzmann constant.

3. The method of claim 1, wherein the method is performed by a spectrometer. The step of calculating the electron density of the thin film plasma includes: obtaining a full width at half maximum Δλ / 2 of the last line of the thin film plasma, and according to an electron broadening dominant relationship formula (2): （2） The electron density of the thin film plasma is calculated where is the electron broadening coefficient related to the electron temperature.

4. The method of claim 1, wherein the method is performed by a spectrometer. The step of calculating the internal pressure P of the thin film plasma by using the state equation according to the electron temperature and the electron density comprises the following steps: Assume that the thin film plasma consists of electrons and singly charged positive ions and satisfies the quasi-neutrality condition where is the electron density, is the ion density; assume that the electron temperature is approximately equal to the ion temperature, ; Under the above assumptions, the thin film plasma is considered as an ideal gas, and the total particle number density N is the sum of the electron density and the ion density, i.e. ; according to an ideal gas state equation (3): （3） obtaining: （4） wherein, is the Boltzmann constant, T is the electron temperature, is the electron density.

5. The method for measuring internal pressure of a thin film plasma based on spectral analysis according to claim 1, wherein, The to-be-tested thin film sample is an optical thin film, and an incident direction of the pulse laser is perpendicular to an incident surface of the optical thin film.

6. The method of claim 5, wherein the step of measuring the pressure inside the thin film plasma is performed by a spectroscopic analysis. The to-be-tested thin film sample is a thin film deposited on a substrate, and the thin film is a single-layer silicon oxide thin film with a 1 / 4 wavelength optical thickness.

7. A method for evaluating the laser damage resistance of a thin film, characterized by, The method comprises the following steps: under the condition of the same incident laser energy density and the same other experimental parameters, measuring internal pressures P of thin film plasmas generated by at least two thin films of the same material prepared by different processes respectively by using the method in any one of claims 1 to 6; comparing the internal pressures P of the thin film plasmas corresponding to the thin films prepared by different processes, and determining the thin film corresponding to the smaller internal pressure under the same condition as the thin film with higher laser damage resistance.

8. A device for measuring internal pressure of a thin film plasma based on spectral analysis, characterized by The method comprises the following steps: a laser light source and an attenuation system, used for generating and adjusting pulse laser energy incident on a thin film sample; a focusing system, used for focusing the pulse laser output by the attenuation system to a surface of the thin film sample, so as to generate a thin film plasma flash on the surface of the thin film sample; a beam splitter and an energy meter, the beam splitter is arranged in a laser light path before the focusing system, used for guiding part of the pulse laser to the energy meter, and the energy meter is used for measuring incident laser energy acting on the thin film sample in real time; a sample stage, used for installing the thin film sample and capable of moving in a plane to change a laser irradiation position; a spectrometer, used for collecting an emission spectrum of the thin film plasma flash under the condition of a preset integration time and a preset delay time. A computer control system is used to control the working states of the laser light source and the attenuation system, the energy meter, the sample stage and the spectrometer, and to process the emission spectrum data to calculate the electron temperature, electron density and internal pressure of the thin film plasma.

9. The thin film plasma internal pressure measurement apparatus based on spectroscopic analysis according to claim 8, wherein, The spectrometer is an optical fiber spectrometer with a wavelength range of 200-1100 nm and a spectral resolution of no more than 0.02 nm.

10. The thin film plasma internal pressure measuring apparatus based on spectroscopic analysis according to claim 8, wherein, The laser light source is A solid state laser with an output wavelength of 1064 nm and a pulse width of about 10 ns, the attenuation system having an adjustable attenuation rate of 0% to 100%.

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