A dual-band graded film and a method for manufacturing the same

Abstract

This invention relates to a dual-band graded coating and its preparation method, belonging to the field of optical coating technology. The invention aims to solve the problem of suppressing 700nm stray light from the conical aperture of the secondary mirror in an internally masked coronagraph in existing technologies. The dual-band graded coating of this invention uses Al / MgF2+(LaF3 / MgF2). 5 The LaF3 composite film structure employs a two-stage coating process, with different sized shielding caps used for different regions during each coating. The dimensional error in different regions is controlled within ±10 μm. This invention's dual-band graded-color film solves the problem of 700 nm stray light suppression in the secondary mirror's conical aperture of an internally shielded coronagraph, while maintaining the reflectivity of the 121.6 nm channel, achieving corona imaging in both 121.6 nm and 700 nm bands. The dual-band graded-color film of this invention achieves a graded-color film structure for the 700 nm channel, increasing its reflectivity from 3.7% to 86%. The Al / MgF2 graded-color film structure effectively suppresses stray light levels at 700 nm in the secondary mirror's conical aperture, achieving a stray light suppression level of 10 at 2.5 solar radii for the entire optical system. ‑8 Meanwhile, it did not affect the reflectivity of the 121.6nm channel.

Description

Technical Field

[0001] This invention relates to the field of optical coating technology, and in particular to a dual-band gradient film and its preparation method. Background Technology

[0002] The corona is the outermost layer of the Sun and the primary source of solar activity, such as solar flares and coronal mass ejections. The corona has a significant impact on Earth. Detection and research of the corona help unravel the mysteries of its origin and deepen our understanding of the Sun. Compared to the photosphere and chromosphere, the corona is extremely faint. Therefore, stray light suppression is the most crucial task in the development of coronagraphs. In an internally masked coronagraph, the secondary mirror is placed at the focal point of the primary mirror, ensuring that direct sunlight passes through the central aperture and enters the subsequent light trap. The secondary mirror has a conical aperture with a sharp edge in the center. If this edge has high reflectivity, its image on the detector will blur the image of the corona.

[0003] To address this issue, the LASCO camera at SOHO in the United States employs an Al / SiO2 gradient film coating strategy on the cutting edge, achieving better imaging results. However, LASCO can only image at the 700nm wavelength. Summary of the Invention

[0004] This invention aims to solve the problem of suppressing stray light at 700nm in the conical aperture of the secondary mirror of the internally shielded coronagraph in the prior art, while not affecting the reflectivity of the 121.6nm channel, and to achieve the technical problem of corona imaging in both 121.6nm and 700nm bands. It further provides a dual-band gradient film and its preparation method.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] A dual-band gradient film is disposed on a secondary mirror, wherein the secondary mirror is sequentially provided with region I, region II and region III;

[0007] The dual-band graded coating includes:

[0008] Al / MgF2 films and (LaF3 / MgF2) films are sequentially arranged in a direction away from region I. 5 LaF3 multilayer film;

[0009] An Al / MgF2 graded film and a (LaF3 / MgF2) film are sequentially arranged in a direction away from region II. 5 LaF3 multilayer film.

[0010] In the above technical solution, the Al / MgF2 film on region I includes: an aluminum film with a thickness of 70 nm, and a MgF2 thin film of 17.5 nm above the aluminum film.

[0011] In the above technical solution, the (LaF3 / MgF2) in region I and region II... 5 The thickness of a single LaF3 layer in the LaF3 multilayer film is 14.6 nm, and the thickness of a single MgF2 layer is 19.7 nm.

[0012] A method for preparing a dual-band graded coating includes the following steps:

[0013] (1) Substrate cleaning:

[0014] The substrate secondary mirror was ultrasonically cleaned with high-purity water and then centrifuged to dry.

[0015] (2) Al / MgF2 coating:

[0016] The secondary mirror region III and part of region II were covered with a shielding cap. The shadow effect was used to generate an Al / MgF2 gradient film in region II and an Al / MgF2 film in region I. Al film and MgF2 film were deposited by resistive evaporation and thermal evaporation, respectively.

[0017] (3) LaF3 / MgF2 coating:

[0018] Cover region III with a shielding cap, place LaF3 and MgF2 in the molybdenum boat respectively, and use thermal evaporation to alternately deposit LaF3 and MgF2 films on region I and region II of the secondary mirror obtained in step (2), for a total of 10 layers. Finally, deposit another layer of LaF3 film on the MgF2 film to obtain (LaF3 / MgF2). 5 LaF3 multilayer film.

[0019] In the above technical solution, the centrifugation speed in step (1) is 3000 rpm.

[0020] In the above technical solution, crystal oscillators are used to control the film thickness and deposition rate in steps (2) and (3).

[0021] In the above technical solution, the specific steps in step (2) for depositing Al films and MgF2 films using resistive evaporation and thermal evaporation are as follows:

[0022] First, place the aluminum wire in a tungsten wire basket, with a base vacuum of 3*10. -4 Pa, at a rate of 1.0 nm / s, an Al film was deposited at room temperature using evaporation inhibition, and the thickness of the Al film was 70 nm.

[0023] Then, a 4.5 nm MgF2 thin film was deposited to cover the Al film;

[0024] Finally, the temperature was raised to 100°C and held for two hours to deposit the remaining 13 nm MgF2 film.

[0025] In the above technical solution, the conditions for alternating LaF3 and MgF2 film deposition in step (3) are as follows:

[0026] The background vacuum is 3*10 -4 Pa, substrate temperature 220℃, rate 0.2nm / s.

[0027] The present invention has the following beneficial effects:

[0028] The dual-band gradient film of this invention solves the problem of suppressing stray light at 700nm in the conical aperture of the secondary mirror of the internally masked coronagraph, while not affecting the reflectivity of the 121.6nm channel, thus realizing corona imaging in both 121.6nm and 700nm bands.

[0029] The dual-band graded coating of this invention uses Al / MgF2+(LaF3 / MgF2). 5 The LaF3 composite film structure is achieved through two coating processes, with different sized masking caps used for different areas during each coating. The dimensional error of different areas is controlled within ±10μm.

[0030] The dual-band gradient film of this invention achieves a gradient film structure with a 700nm channel, increasing its reflectivity from 3.7% to 86%. The Al / MgF2 gradient film structure effectively suppresses stray light at 700nm through the secondary mirror's conical aperture, achieving a stray light suppression level of 10 at 2.5 solar radii for the entire optical system. -8 Meanwhile, it did not affect the reflectivity of the 121.6nm channel. Attached Figure Description

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0032] Figure 1 This is a schematic diagram of the secondary mirror structure.

[0033] Figure 2 This is a schematic diagram of the multilayer film structure of region I and region II of the secondary mirror.

[0034] Figure 3 The images show a white light microscope image of the conical aperture region of the secondary mirror and a schematic diagram of the reflectance distribution in the gradient film region, where (a) is a microscope image and (b) is a schematic diagram of the reflectance distribution. Detailed Implementation

[0035] The inventive concept of this invention is as follows: The LASCO laser at SOHO in the United States employs an Al / SiO2 graded-film coating strategy on the cutting edge, which solves the problem of high stray light at the conical aperture of the secondary mirror, achieving better imaging results. However, LASCO can only image at the 700nm wavelength. This invention uses a LaF3 / MgF2 / Al / MgF2 thin film coated on the cutting edge, where Al / MgF2 is a graded-film coating, solving the problem of excessive stray light at 700nm and achieving good suppression of 700nm stray light, while having no impact on the reflectivity at 121.6nm. This invention uses a clever composite thin film structure, through two coatings, supplemented by sophisticated mechanical adjustments and shielding, to achieve dual-band corona imaging at 121.6nm and 700nm.

[0036] The present invention will now be described in detail with reference to the accompanying drawings.

[0037] This invention provides a dual-band graded coating, which is disposed on a secondary mirror. The secondary mirror is sequentially configured with region I, region II, and region III. (See also...) Figure 1 The dual-band graded coating comprises: an Al / MgF2 film and a (LaF3 / MgF2) film sequentially disposed in a direction away from region I. 5 LaF3 multilayer film; Al / MgF2 graded film and (LaF3 / MgF2) film sequentially arranged in the direction away from region II. 5 LaF3 multilayer film (see LaF3 multilayer film) Figure 2 (LaF3 / MgF2) 5 LaF3 multilayer film refers to alternating LaF3 and MgF2 films, totaling 10 layers, with a LaF3 film on the topmost MgF2 film, i.e. (LaF3 / MgF2). 5 The LaF3 multilayer film has a total of 11 layers.

[0038] Preferably, the Al / MgF2 film in region I comprises: an aluminum film with a thickness of 70 nm, and a MgF2 thin film of 17.5 nm above the aluminum film; the (LaF3 / MgF2) film in regions I and II... 5 The thickness of a single LaF3 layer in the LaF3 multilayer film is 14.6 nm, and the thickness of a single MgF2 layer is 19.7 nm.

[0039] The present invention provides a method for preparing a dual-band graded coating, comprising the following steps:

[0040] (1) Substrate cleaning:

[0041] The substrate secondary mirror was ultrasonically cleaned with high-purity water, and then centrifuged to dry at 3000 rpm.

[0042] (2) Al / MgF2 coating:

[0043] The secondary mirror region III and part of region II were covered with a shielding cap. The shadow effect was used to generate an Al / MgF2 gradient film in region II and an Al / MgF2 film in region I. Al film and MgF2 film were deposited by resistive evaporation and thermal evaporation, respectively.

[0044] The specific steps for depositing Al films and MgF2 films using resistive evaporation and thermal evaporation, respectively, are as follows:

[0045] First, place the high-purity aluminum wire in a tungsten wire basket, with a base vacuum of 3*10. -4 Pa, at a rate of 1.0 nm / s, an Al film was deposited at room temperature using evaporation inhibition, and the thickness of the Al film was 70 nm.

[0046] Then, a 4.5 nm MgF2 thin film was rapidly deposited to cover the Al film and prevent Al film oxidation;

[0047] Finally, the temperature was raised to 100°C and held for two hours to deposit the remaining 13 nm MgF2 film.

[0048] (3) LaF3 / MgF2 coating:

[0049] Cover region III with a shielding cap, place LaF3 and MgF2 in the molybdenum boat respectively, and use thermal evaporation to alternately deposit LaF3 and MgF2 films on region I and region II of the secondary mirror obtained in step (2), for a total of 10 layers. Finally, deposit another layer of LaF3 film on the MgF2 film to obtain (LaF3 / MgF2). 5 LaF3 multilayer film;

[0050] The conditions for alternating LaF3 and MgF2 film deposition are: a base vacuum of 3*10 -4 Pa, substrate temperature 220℃, rate 0.2nm / s.

[0051] Preferably, in steps (2) and (3), a crystal oscillator is used to control the film thickness and deposition rate.

[0052] Example

[0053] The preparation process of the dual-band graded coating of the present invention includes the following steps:

[0054] (1) Substrate cleaning:

[0055] The substrate secondary mirror was ultrasonically cleaned with high-purity water and then centrifuged at 3000 rpm.

[0056] (2) Al / MgF2 coating:

[0057] Regions III and part of region II were covered with a masking cap. An Al / MgF2 gradient film was created in region II using the shading effect, and an Al / MgF2 film was created in region I. Al and MgF2 films were deposited using both anti-evaporation and thermal evaporation methods, respectively. The size and height of the masking cap were determined through multiple trials. The diameter of the masking cap covering parts of regions II and III was 8.95 mm, and the distance from the mirror surface was 3.16 mm.

[0058] Al and MgF2 thin films were deposited using a resistive thermal evaporation process employing a three-step method. First, high-purity aluminum wire was placed in a tungsten wire basket, with a base vacuum of 3*10⁻⁶. -4 At a deposition rate of 1.0 nm / s, an Al film with a thickness of 70 nm was deposited at room temperature using a barrier vapor deposition method. Then, a 4.5 nm MgF2 film was rapidly deposited to cover the Al film and prevent its oxidation. Finally, the temperature was raised to 100 °C and held for two hours to deposit the remaining 13 nm MgF2 film. A crystal oscillator was used to control the film thickness and deposition rate during the deposition process.

[0059] (3) LaF3 / MgF2 coating:

[0060] Region III was covered with a shielding cap. The size and height of the shielding cap were determined through multiple trials. The diameter of the shielding cap for region III was 7.70 mm, and the distance from the mirror surface was 0.2 mm. LaF3 and MgF2 were placed in a molybdenum boat, and LaF3 and MgF2 films were alternately deposited on regions I and II of the secondary mirror obtained in step (2) using a thermal evaporation method, for a total of 10 layers. Finally, a LaF3 film was deposited on the topmost MgF2 film to obtain (LaF3 / MgF2). 5 LaF3 multilayer film, with a base vacuum of 3*10 -4 The substrate temperature was 220℃, the deposition rate was 0.2 nm / s, and the thicknesses of the LaF3 and MgF2 films were 14.6 nm and 19.7 nm, respectively, for a total of 11 layers. A crystal oscillator was used to control the film thickness and deposition rate during the deposition process. Table 1 shows the dimensions, coatings, thin film requirements, and experimental reflectivity of different regions of the secondary mirror.

[0061] Table 1 shows the dimensions, coatings, thin film requirements, and test reflectivity of different regions of the secondary mirror.

[0062]

[0063] The dual-band gradient film of the present invention has a uniform (LaF3 / MgF2) coating deposited in region I of the secondary mirror. 5 The LaF3+Al / MgF2 composite multilayer film; the secondary mirror region II is a graded-color film region, and only Al / MgF2 is a graded-color film, meaning that the reflectivity gradient is only achieved in the 700nm wavelength band, increasing from 3.7% to 86%. This region has a uniform (LaF3 / MgF2) coating.5 LaF3 multilayer films only exhibit 78.3% reflectance at 121.6 nm, and this film system has no effect on reflectance at 700 nm. Al / MgF2 has 72% and 86% reflectance at 121.6 nm and 700 nm, respectively (see...). Figure 3 Region III is the uncoated area. As can be seen from Appendix 1, the dimensional accuracy requirements for different regions are high, reaching the micrometer level. The size of the gradient film region, the formation of the gradient film, and the isolation from other regions are achieved by adding masking caps of different sizes and precise mechanical adjustments.

[0064] The dual-band gradient film of this invention solves the problem of suppressing stray light at 700nm in the conical aperture of the secondary mirror of the internally masked coronagraph, while not affecting the reflectivity of the 121.6nm channel, thus realizing corona imaging in both 121.6nm and 700nm bands.

[0065] The dual-band graded coating of this invention uses Al / MgF2+(LaF3 / MgF2). 5 The LaF3 composite film structure is achieved through two coating processes, with different sized masking caps used for different areas during each coating. The dimensional error of different areas is controlled within ±10μm.

[0066] The dual-band gradient film of this invention achieves a gradient film structure with a 700nm channel, increasing its reflectivity from 3.7% to 86%. The Al / MgF2 gradient film structure effectively suppresses stray light at 700nm through the secondary mirror's conical aperture, achieving a stray light suppression level of 10 at 2.5 solar radii for the entire optical system. -8 Meanwhile, it did not affect the reflectivity of the 121.6nm channel.

[0067] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a dual-band graded-color film, characterized in that, Includes the following steps: (1) Substrate cleaning: The substrate secondary mirror was ultrasonically cleaned with high-purity water and then centrifuged to dry; the secondary mirror was divided into three regions: region I, region II, and region III. (2) Al / MgF2 coating: The secondary mirror region III and part of region II were covered with a shielding cap. The shadow effect was used to generate an Al / MgF2 gradient film in region II and an Al / MgF2 film in region I. Al film and MgF2 film were deposited by resistive evaporation and thermal evaporation, respectively. (3) LaF3 / MgF2 coating: Cover region III with a shielding cap, place LaF3 and MgF2 in the molybdenum boat respectively, and use thermal evaporation to alternately deposit LaF3 and MgF2 films on region I and region II of the secondary mirror obtained in step (2), for a total of 10 layers. Finally, deposit another layer of LaF3 film on the MgF2 film to obtain (LaF3 / MgF2). 5 LaF3 multilayer film; The specific steps for depositing Al films and MgF2 films using resistance evaporation and thermal evaporation in step (2) are as follows: First, place the aluminum wire in a tungsten wire basket, with a background vacuum of 3×10⁻⁶. -4 Pa, at a rate of 1.0 nm / s, an Al film was deposited at room temperature using evaporation inhibition, and the thickness of the Al film was 70 nm. Then, a 4.5 nm MgF2 thin film was deposited to cover the Al film; Finally, the temperature was raised to 100℃ and held for two hours to deposit the remaining 13nm MgF2 film. The conditions for alternating LaF3 and MgF2 film deposition in step (3) are as follows: The background vacuum is 3×10⁻⁶. -4 Pa, substrate temperature 220℃, rate 0.2nm / s.

2. The method for preparing a dual-band graded film according to claim 1, characterized in that, In step (1), the centrifugation speed is 3000 rpm.

3. The method for preparing a dual-band graded film according to claim 1, characterized in that, In steps (2) and (3), a crystal oscillator is used to control the film thickness and deposition rate.

4. A dual-band graded coating prepared by the preparation method of claim 1, which is disposed on a secondary mirror, wherein the secondary mirror is sequentially provided with region I, region II and region III; Its features are, The dual-band graded coating includes: Al / MgF2 films and (LaF3 / MgF2) films are sequentially arranged in a direction away from region I. 5 LaF3 multilayer film; An Al / MgF2 graded film and a (LaF3 / MgF2) film are sequentially arranged in a direction away from region II. 5 LaF3 multilayer film; The Al / MgF2 film in region I comprises: an aluminum film with a thickness of 70 nm, and a MgF2 thin film of 17.5 nm above the aluminum film; The (LaF3 / MgF2) described in Region I and Region II 5 The thickness of a single LaF3 layer in the LaF3 multilayer film is 14.6 nm, and the thickness of a single MgF2 layer is 19.7 nm.

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