Post-target film thickness measurement imaging system for laser ion acceleration and film thickness measurement method

Abstract

The invention discloses a behind-target film thickness measurement imaging system for laser ion acceleration, and the following light paths are formed behind a target: an incident light path in which an illumination light source emits incident light, the incident light enters a microscope objective after passing through a first beam splitting cube, and the incident light is focused and irradiated to the target through the microscope objective; and according to the reflection light path, reflected light is formed after the incident light irradiates the target, the reflected light enters the first beam splitting cube through the microscope objective and is split into two beams through the first beam splitting cube, one beam enters the spectrograph, the other beam enters the second beam splitting cube and is split into two beams through the second beam splitting cube, one beam enters the first camera, and the other beam enters the second camera. According to the behind-target film thickness measurement imaging system for laser ion acceleration disclosed by the invention, the problems of target imaging illumination and target film thickness detection are solved at the same time through one system, the complexity of the system is reduced, and the space is saved.

Description

Technical Field

[0001] The present invention relates to a post-target film thickness measurement and imaging system and a film thickness measurement method for laser ion acceleration, belonging to the field of thickness measurement. Background Art

[0002] Beam-target coupling (coupling a laser beam to a thin film target) is a key issue in laser ion acceleration, that is, before using a laser beam to hit the target, the target position is adjusted so that the laser focal length is located at a specified position on the target.

[0003] The existing method mainly focuses on the post-target system. Specifically, taking the post-target camera as a reference, the laser focal spot and the thin film target are adjusted to be at the same position in space to achieve beam-target coupling. However, this method generally requires independent components or optical paths when illuminating the target material in the target cavity, and different optical paths are required for illuminating transparent targets and metal targets. This results in complex optical path settings and the need to switch different units to achieve beam-target coupling, wasting a large amount of cost and time.

[0004] In addition, the target film thickness is also an important parameter in laser ion acceleration. The existing post-target system cannot measure the thickness of the target film in real time while imaging the target, and additional means are required to measure the target film thickness.

[0005] The existing film thickness measurement methods and devices cannot measure the thin film in a vacuum chamber. The traditional measurement methods are all off-line detections, and the equipment used for detection occupies a large space and is difficult to be placed in a vacuum chamber. For the above reasons, it is necessary to further study the beam-target coupling of the post-target film for laser ion acceleration and the measurement of the post-target film thickness to solve the above problems. Summary of the Invention

[0006] In order to overcome the above problems, the inventors have conducted in-depth research and designed a post-target film thickness measurement and imaging system for laser ion acceleration. A microscopic objective lens 2, a first beam splitting cube 31, a second beam splitting cube 32, a first camera 41, a second camera 42, an illumination light source 5, and a spectrometer 6 are arranged behind the target 1, and the following optical path is formed:

[0007] An incident optical path: The incident light is emitted from the illumination light source 5, enters the microscopic objective lens 2 after passing through the first beam splitting cube 31, and is focused by the microscopic objective lens 2 to irradiate the target 1.

[0008] A reflection optical path: After the incident light irradiates the target 1, a reflected light is formed. The reflected light enters the first beam splitting cube 31 through the microscopic objective lens 2, and is split into two beams by the first beam splitting cube 31. One beam enters the spectrometer 6, and the other beam enters the second beam splitting cube 32. The second beam splitting cube 32 splits it into two beams again. One beam enters the first camera 41, and the other beam enters the second camera 42.

[0009] In a preferred embodiment, the spectrometer 6 and the illumination light source 5 are arranged outside the vacuum chamber, and the target 1, the first beam splitting cube 31, the second beam splitting cube 32, the first camera 41 and the second camera 42 are arranged in the vacuum chamber.

[0010] In a preferred embodiment, the incident light emitted by the illumination light source 5 enters the optical path through a feedthrough optical fiber, and the spectrometer 6 obtains the reflected light in the optical path through a feedthrough optical fiber;

[0011] The feedthrough optical fiber connecting the illumination light source 5 and the feedthrough optical fiber connecting the spectrometer 6 are combined so that the incident light and the reflected light are coaxial, and further enables the spectrometer 6 to measure the incident light and the reflected light.

[0012] The feedthrough optical fiber connecting the illumination light source 5 and the feedthrough optical fiber connecting the spectrometer 6 are combined through a fiber feedthrough flange.

[0013] In a preferred embodiment, the spectrometer 6 measures the incident light and the reflected light to obtain the film thickness of the target 1.

[0014] In a preferred embodiment, the imaging magnification of the first camera 41 is less than that of the second camera 42;

[0015] The first camera 41 has a large field of view. By moving the position of the target 1, a light spot is obtained in the first camera 41 to roughly determine the position of the target 1;

[0016] The second camera 42 has a higher imaging magnification. Adjust the front and back positions of the target 1 in the optical path so that the light spot in the second camera 42 is circular and has the smallest diameter. At this time, the target 1 is located at the focal position of the optical path, and the angle between the incident light and the target film is 90 degrees, completing the beam-target coupling.

[0017] The present invention also discloses a method for measuring the film thickness behind the target for laser ion acceleration, and the film thickness of the target film is measured through the following steps:

[0018] S1. Irradiate the target, detect the incident light and the reflected light, and obtain the target film reflectivity,

[0019] S2. Determine the target film thickness according to the relationship between the reflectivity, the incident light wavelength and the target film thickness.

[0020] In a preferred embodiment, before S1, there is also S0. Perform beam-target coupling:

[0021] By moving the position of the target, a light spot is obtained in the first camera to roughly determine the position of the target; then adjust the front and back positions of the target in the optical path so that the light spot in the second camera is circular and has the smallest diameter, so that the target is located at the focal position of the optical path.

[0022] In a preferred embodiment, in S2, the relationship among the reflectivity, the wavelength of the incident light, and the thickness of the target film is as follows:

[0023]

[0024] where λ represents the wavelength of the incident light, θ represents the incident angle, and h represents the thickness of the target film;

[0025] R(h,λ,θ) represents the reflectivity of the target film to the incident light, and R 0 (λ,θ) represents the reflectivity of the target film interface determined by the Fresnel reflection law, and δ(h,λ,θ) represents the optical path difference of the target film. The optical path difference of the target film is expressed as:

[0026]

[0027] n(λ) represents the refractive index function of the target film material.

[0028] In a preferred embodiment, monochromatic light of at least two wavelengths is used as the incident light, and for each monochromatic light, a target film thickness is obtained independently through S1 to S2.

[0029] In a preferred embodiment, the method further includes:

[0030] S3. Obtain the film thickness resolution corresponding to different monochromatic lights, and select the target film thickness obtained corresponding to the monochromatic light with a smaller film thickness resolution as the final measurement result.

[0031] where the film thickness resolution is used to indicate the accuracy of film thickness measurement.

[0032] The beneficial effects of the present invention include:

[0033] (1) By one system, the problems of target imaging illumination and target film thickness detection are solved simultaneously, the complexity of the system is reduced, and space is saved;

[0034] (2) The target film thickness can be obtained in real time and online in the vacuum chamber, and the accuracy of film thickness measurement is high. Description of the Drawings

[0035] Figure 1 Shows the structural schematic diagram of a target back film thickness measurement and imaging system for laser ion acceleration according to a preferred embodiment of the present invention;

[0036] Figures 2 - 4 Shows the change of the reflectivity of the thin film with the wavelength at different thicknesses;

[0037] Figure 5 Shows the relationship between the thickness resolution and the film thickness and wavelength when s light is normally incident on the thin film.

[0038] Reference Signs:

[0039] 1 - Target;

[0040] 2 - Microscope Objective;

[0041] 5 - Illumination Light Source;

[0042] 6 - Spectrometer;

[0043] 31 - First Beam Splitting Cube;

[0044] 32 - Second Beam Splitting Cube;

[0045] 41 - First Camera;

[0046] 42 - Second Camera. Detailed Description of the Invention

[0047] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present invention will become more clear and definite.

[0048] The special term "exemplary" herein means "serving as an example, embodiment or illustration". Any embodiment described herein as "exemplary" need not be construed as superior or better than other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings need not be drawn to scale unless otherwise specified.

[0049] The present invention provides a post - target film thickness measurement and imaging system for laser ion acceleration. As Figure 1 shown, a microscope objective 2, a first beam splitting cube 31, a second beam splitting cube 32, a first camera 41, a second camera 42, an illumination light source 5 and a spectrometer 6 are arranged behind the target 1, thereby forming the following optical paths:

[0050] Incident optical path: Incident light rays are emitted from the illumination light source 5, enter the microscope objective 2 after passing through the first beam splitting cube 31, and are focused by the microscope objective 2 to irradiate the target 1.

[0051] Reflected optical path: After the incident light irradiates the target 1, reflected light is formed. The reflected light enters the first beam splitting cube 31 through the microscope objective 2, and is split into two beams by the first beam splitting cube 31. One beam enters the spectrometer 6, and the other beam enters the second beam splitting cube 32. The second beam splitting cube 32 splits it into two beams again. One beam enters the first camera 41, and the other beam enters the second camera 42.

[0052] A beam splitting cube is a half - reflector that can strictly divide the beam splitting ratio of reflected light and transmitted light into 1:1. In the present invention, the beam splitting cube uses a non - polarized beam splitting cube.

[0053] In a preferred embodiment, the target 1, the first beam-splitting cube 31, the second beam-splitting cube 32, the first camera 41 and the second camera 42 are arranged in a vacuum chamber, and the spectrometer 6 and the illumination light source 5 are arranged outside the vacuum chamber, thus saving the volume of the vacuum chamber.

[0054] In a preferred embodiment, the incident light rays emitted by the illumination light source 5 enter the optical path through a feedthrough optical fiber, and the spectrometer 6 obtains the reflected light rays in the optical path through a feedthrough optical fiber;

[0055] Furthermore, the feedthrough optical fiber connecting the illumination light source 5 and the feedthrough optical fiber connecting the spectrometer 6 are combined, so that the incident light rays and the reflected light rays are coaxial, and further the spectrometer 6 can measure the incident light rays and the reflected light rays.

[0056] In the present invention, by making the incident light rays and the reflected light rays coaxial, the spectrometer 6 measures the incident light rays and the reflected light rays to obtain the film thickness of the target 1; the position of the target 1 is adjusted through the imaging of the first camera 41 and the second camera 42 to achieve beam-target coupling. In the system, the microscope objective can both image and focus, that is, a set of systems is used to simultaneously achieve film thickness measurement and target illumination imaging.

[0057] In a preferred embodiment, the feedthrough optical fiber connecting the illumination light source 5 and the feedthrough optical fiber connecting the spectrometer 6 are combined through an optical fiber splitter and an optical fiber feedthrough flange.

[0058] According to the present invention, the imaging magnification of the first camera 41 is less than that of the second camera 42;

[0059] The first camera 41 has a large field of view. By moving the position of the target 1, a light spot is obtained in the first camera 41 to roughly determine the position of the target 1;

[0060] The second camera 42 has a higher imaging magnification. The front and back positions of the target 1 in the optical path are adjusted so that the light spot in the second camera 42 is circular and has the smallest diameter. At this time, the target 1 is located at the focusing position of the optical path, and the angle between the incident light and the target film is 90 degrees, completing the beam-target coupling.

[0061] According to the present invention, the target is a transparent thin film target, and the thickness of the target film is less than 150 nm.

[0062] Traditional film thickness measurement methods are generally reflection spectroscopy methods, Figures 2 - 4The reflectance curves of films with different thicknesses are shown. According to reflectance spectrometry, the reflectance spectra corresponding to different thicknesses are unique. Therefore, the film thickness can be inversely solved by measuring the reflectance spectrum of the thin film. However, the inventor found that this method has great limitations. When using a conventional light source for measurement, when the film thickness is very small, the oscillation of the reflectance spectrum becomes very slow, and the oscillation frequency is close to the quasi-Gaussian envelope of the usual white light source, resulting in a large error. Therefore, when the thickness of the film to be measured is less than 150 nm, the measurement accuracy is significantly deteriorated, and even the situation where no numerical value can be measured occurs. Although the measurement accuracy can be further improved by using an ultraviolet broadband light source, the cost is very high. Even when using an ultraviolet broadband light source, it is only possible to measure the thickness of films above 60 nm, and still cannot achieve the measurement of film thickness below 50 nm. According to a method for measuring the thickness of the film behind the target for laser ion acceleration provided by the present invention, it is implemented by using the above system, and the thickness of the thick film is measured by reflectance spectrometry;

[0063] The thickness of the target film is measured by the following steps:

[0064] S1. Irradiate the target, detect the incident light and the reflected light, and obtain the reflectance of the target film;

[0065] S2. Determine the thickness of the target film according to the relationship between the reflectance, the wavelength of the incident light, and the thickness of the target film.

[0066] Preferably, before S1, there is also S0. Perform beam-target coupling.

[0067] In S0, by moving the position of the target 1, a light spot is obtained in the first camera 41, and the position of the target 1 is roughly determined; then, the front and rear positions of the target 1 in the optical path are adjusted so that the light spot in the second camera 42 is circular and has the smallest diameter, so that the target 1 is located at the focusing position of the optical path.

[0068] According to the present invention, in S1, the specific calculation formula of the reflectance is a conventional technical means in the art and will not be elaborated here.

[0069] According to the present invention, in S2, the relationship between the reflectance, the wavelength of the incident light, and the thickness of the target film is:

[0070]

[0071] wherein, R(h, λ, θ) represents that the reflectance R is a parameter associated with the thickness h of the target film, the wavelength λ of the incident light, and the incident angle θ, and R 0 (λ, θ) represents the reflectance R at the interface of the target film 0 is a parameter associated with the wavelength λ of the incident light and the incident angle θ, and δ(h, λ, θ) represents that the optical path difference δ of the target film is a parameter associated with the thickness h of the target film, the wavelength λ of the incident light, and the incident angle θ. In the present invention, the incident angle θ is 90 degrees.

[0072] Furthermore, the optical path difference of the target film is expressed as:

[0073]

[0074] n(λ) represents the refractive index function of the target film material. Although it is a parameter associated with the wavelength λ of the incident light, the error introduced by it is very small. Therefore, generally speaking, n(λ) is set as a constant. In the present invention, preferably, the refractive index of the target film material at the wavelength λ = 600 is taken as the value of n(λ).

[0075] Furthermore, according to the present invention, when the incident light is S light, the reflectivity R 0 (λ,θ) of the target film interface determined by the Fresnel reflection law is denoted as R s (λ,θ), and is expressed as:

[0076]

[0077] When the incident light is P light, the reflectivity R 0 (λ,θ) of the target film interface determined by the Fresnel reflection law is denoted as R p (λ,θ), and is expressed as:

[0078]

[0079] S light and P light are common light classification methods in light reflection and refraction. Among them, S light refers to the light whose polarization direction is perpendicular to the plane formed by the incident light and its normal line, and P light refers to the light whose polarization direction is in the plane formed by the incident light and its normal line.

[0080] According to a preferred embodiment of the present invention, monochromatic light of at least two wavelengths is used as the incident light, and for each monochromatic light, a target film thickness is obtained independently through S1 to S2 respectively.

[0081] Furthermore, according to the present invention, there is also step S3: obtaining the film thickness resolution corresponding to different monochromatic lights, and selecting the target film thickness obtained corresponding to the monochromatic light with a smaller film thickness resolution as the final measurement result.

[0082] Among them, the film thickness resolution is used to indicate the accuracy of film thickness measurement.

[0083] The inventor found that when the target film thickness is in the interval of [0, λ / 4], the reflectivity of the target film for monochromatic light with a wavelength of λ increases monotonically with the target film thickness, as Figure 5As shown, when the target film thickness is within the range of [0, λ / 4], the target film thickness can be directly solved through S3 based on the reflectivity obtained in S2. However, there are differences in the target film thicknesses solved under different wavelength light sources. One of the problems to be solved by the present invention is how to determine which wavelength light source can solve the target film thickness with higher accuracy.

[0084] In the present invention, this problem is solved by setting the film thickness resolution, and the film thickness resolution is used to indicate the accuracy of film thickness measurement. When the film thickness resolution is smaller, it means the measurement result is more accurate. When the film thickness resolution is greater than or equal to 1, it indicates that the accuracy of the test result is insufficient.

[0085] In S3, the film thickness resolution Δ is expressed as:

[0086]

[0087] λ represents the wavelength of the incident light, θ represents the incident angle, h represents the target film thickness; n represents the refractive index of the target film material. Among them, the target film thickness is the film thickness measured corresponding to this monochromatic light. Preferably, the refractive index of the target film material when the wavelength λ = 600 nm is taken as the value of the refractive index n of the target film material in the present invention. In another preferred embodiment, when the wavelength of the monochromatic light is 405 nm, n = 1.505; when the wavelength of the monochromatic light is 780 nm, n = 1.485.

[0088] In a preferred embodiment, among the two wavelengths of monochromatic light, one is a monochromatic light with a wavelength greater than 600, and the other is a monochromatic light with a wavelength less than 600.

[0089] More preferably, 780 nm monochromatic light and 405 nm monochromatic light are selected as the incident light. After a large number of experiments, the accuracy of the final film thickness detection result is extremely high when these two monochromatic lights are used in combination.

[0090] Examples

[0091] Example 1

[0092] Adopt Figure 1 The device shown is used to measure the target film. The thickness of the target film is 50 nm. Among them, in the incident light path, the illumination light source 5 emits incident light, which enters the microscopic objective lens 2 after passing through the first beam splitting cube 31, and is focused by the microscopic objective lens 2 to irradiate the target 1; in the reflection light path, the incident light forms reflected light after irradiating the target 1. The reflected light enters the first beam splitting cube 31 through the microscopic objective lens 2, and is split into two beams by the first beam splitting cube 31. One beam enters the spectrometer 6, and the other beam enters the second beam splitting cube 32, and is split into two beams again by the second beam splitting cube 32. One beam enters the first camera 41, and the other beam enters the second camera 42.

[0093] The film thickness measurement steps are as follows:

[0094] S0. By moving the position of the target 1, obtain a light spot in the first camera 41 to roughly determine the position of the target 1; then adjust the front and back positions of the target 1 in the optical path so that the light spot in the second camera 42 is circular and has the smallest diameter, making the target 1 located at the focusing position of the optical path.

[0095] S1. Irradiate the target, detect the incident light and the reflected light, and obtain the reflectivity of the target film.

[0096] S2. Determine the thickness of the target film according to the relationship between the reflectivity, the wavelength of the incident light, and the thickness of the target film.

[0097] S3. Obtain the film thickness resolution corresponding to different monochromatic lights, and select the thickness of the target film obtained corresponding to the monochromatic light with a smaller film thickness resolution as the final measurement result.

[0098] In S2, the relationship between the reflectivity, the wavelength of the incident light, and the thickness of the target film is:

[0099]

[0100]

[0101] The incident light is S light, and the reflectivity R of the target film interface determined by the Fresnel reflection law 0 (λ,θ) is denoted as R s (λ,θ), and is expressed as:

[0102]

[0103] Among them, when the incident light is a 405 nm light source, the refractive index function n of the target film of this material takes a constant value of 1.505; when the incident light is a 780 nm light source, the refractive index function n of the target film of this material takes a constant value of 1.485.

[0104] Use 780 nm monochromatic light and 405 nm monochromatic light as the incident light. For each monochromatic light, obtain a target film thickness through S1 - S2. Among them, the target film thickness obtained by the 780 nm monochromatic light is 51.11 nm, and the target film thickness obtained by the 405 nm monochromatic light is 50.86 nm.

[0105] In S3, the film thickness resolution Δ is expressed as:

[0106]

[0107] Among them, the resolution corresponding to the 780 nm monochromatic light is 0.3435, and the resolution corresponding to the 405 nm monochromatic light is 0.2526. Then the finally measured film thickness is 50.86 nm, and the deviation from the actual film thickness is 1.72%.

[0108] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "front", "rear", etc. is based on the orientation or positional relationship in the working state of the present invention. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third", and "fourth" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0109] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection in general; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0110] The present invention has been described above in combination with preferred embodiments. However, these embodiments are only exemplary and only serve an illustrative role. On this basis, various substitutions and improvements can be made to the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A post-target film thickness measurement and imaging system for laser ion acceleration, characterized in that, a microscopic objective lens (2), a first beam splitting cube (31), a second beam splitting cube (32), a first camera (41), a second camera (42), an illumination light source (5) and a spectrometer (6) are arranged behind the target (1), thereby forming the following optical path: An incident optical path, in which incident light rays are emitted by the illumination light source (5), enter the microscopic objective lens (2) after passing through the first beam splitting cube (31), and are focused by the microscopic objective lens (2) to irradiate the target (1); A reflection optical path, in which the incident light forms reflected light after irradiating the target (1), the reflected light enters the first beam splitting cube (31) through the microscopic objective lens (2), is split into two beams by the first beam splitting cube (31), one beam enters the spectrometer (6), and the other beam enters the second beam splitting cube (32), and is split into two beams again by the second beam splitting cube (32), one beam enters the first camera (41), and the other beam enters the second camera (42).

2. The post-target film thickness measurement and imaging system for laser ion acceleration according to claim 1, characterized in that, the spectrometer (6) and the illumination light source (5) are arranged outside the vacuum chamber, and the target (1), the first beam splitting cube (31), the second beam splitting cube (32), the first camera (41) and the second camera (42) are arranged in the vacuum chamber.

3. The post-target film thickness measurement and imaging system for laser ion acceleration according to claim 1, characterized in that, the incident light rays emitted by the illumination light source (5) enter the optical path through a feedthrough optical fiber, and the spectrometer (6) obtains the reflected light rays in the optical path through a feedthrough optical fiber; the feedthrough optical fiber connecting the illumination light source (5) and the feedthrough optical fiber connecting the spectrometer (6) are combined, so that the incident light rays and the reflected light rays are coaxial, and further the spectrometer (6) can measure the incident light rays and the reflected light rays; the feedthrough optical fiber connecting the illumination light source (5) and the feedthrough optical fiber connecting the spectrometer (6) are combined through a fiber feedthrough flange.

4. The post-target film thickness measurement and imaging system for laser ion acceleration according to claim 1, characterized in that, the thickness of the target film is obtained by measuring the incident light rays and the reflected light rays with the spectrometer (6).

5. The post-target film thickness measurement and imaging system for laser ion acceleration according to claim 1, characterized in that, the imaging magnification of the first camera (41) is less than that of the second camera (42); the first camera (41) has a large field of view, and the position of the target (1) is roughly determined by moving the position of the target (1) to obtain a light spot in the first camera (41); the second camera (42) has a higher imaging magnification, and the front and back positions of the target (1) in the optical path are adjusted so that the light spot in the second camera (42) is circular and the diameter is the smallest. At this time, the target (1) is located at the focusing position of the optical path, and the angle between the incident light and the target film is 90 degrees, and the beam-target coupling is completed.

6. A method for measuring the thickness of a post-target film for laser ion acceleration, characterized in that, the thickness of the target film is measured through the following steps: S1. Irradiate the target, detect the incident light and the reflected light, and obtain the reflectivity of the target film, S2. Determine the target film thickness according to the relationship between the reflectivity, the incident light wavelength, and the target film thickness.

7. The method for measuring the post-target film thickness for laser ion acceleration according to claim 6, characterized in that, before S1, there is also S0. Perform beam-target coupling: By moving the target position, obtain a light spot in the first camera and roughly determine the target position; then adjust the front and back positions of the target in the optical path so that the light spot in the second camera is circular and has the smallest diameter, so that the target is located at the optical path focusing position.

8. The method for measuring the post-target film thickness for laser ion acceleration according to claim 6, characterized in that, In S2, the relationship between the reflectivity, the incident light wavelength, and the target film thickness is: where λ represents the wavelength of the incident light, θ represents the incident angle, and h represents the target film thickness; R(h, λ, θ) represents the reflectivity of the target film to the incident light, and R 0 (λ, θ) represents the reflectivity of the target film interface determined by the Fresnel reflection law. δ(h, λ, θ) represents the optical path difference of the target film, and the optical path difference of the target film is expressed as: n(λ) represents the refractive index function of the target film material.

9. The method for measuring the post-target film thickness for laser ion acceleration according to claim 6, characterized in that, Use monochromatic light of at least two wavelengths as the incident light, and for each monochromatic light, independently obtain a target film thickness through S1 to S2 respectively.

10. The method for measuring the post-target film thickness for laser ion acceleration according to claim 6, characterized in that, This method further includes: S3. Obtain the film thickness resolution corresponding to different monochromatic lights, and select the target film thickness obtained corresponding to the monochromatic light with a smaller film thickness resolution as the final measurement result, wherein the film thickness resolution is used to indicate the accuracy of film thickness measurement.

Images