An ultra-low absorption CO2 laser double-sided antireflection film and its preparation method

Abstract

The present invention discloses a CO2 band ultra-low absorption double-sided anti-reflection film and a preparation method thereof, and a CO2 laser band ultra-low absorption double-sided anti-reflection film, wherein the structure of the film is: Air / qHpL / Sub / pLqH / Air; wherein Sub represents a substrate; H represents a high-refractive-index film material ZnSe film layer; L represents a low-refractive-index film layer, and L is a mixed film layer of two low-refractive-index film materials L1 film layer and L2 film layer. The refractive indices of the two low-refractive-index film materials L1 film layer and L2 film layer are both 1-1.6. The low-refractive-index film material L1 film layer and the low-refractive-index film material L2 film layer are made of different materials. The optical thickness ratio of the low-refractive-index film material L1 film layer: the low-refractive-index film material L2 film layer is controlled within a range of 1:3-1:6. The present invention coats a film system on both sides of the zinc selenide substrate and combines two low-refractive index film materials for mixed plating to achieve 10600nm anti-reflection, reduce absorption, and improve transmittance. The average transmittance is greater than 99.7%, the single-side reflection is less than 0.1%, and the absorption is reduced from the original 0.3% to less than 0.1%. The laser damage threshold is tested from the original 6000W / CM 2 Increased to 10000W / CM 2 .

Description

Technical Field

[0001] The invention relates to an ultra-low absorption CO2 laser double-sided anti-reflection film and a preparation method thereof, belonging to the field of anti-reflection films. Background Art

[0002] With the advancement of optoelectronics, particularly high-tech products like laser technology and fiber-optic communications, optical thin-film coatings are finding increasingly widespread application in fields such as basic optics, laser technology, and spectroscopy. For example, in high-power lasers, thin-film components with low absorption and high damage thresholds are crucial for achieving high-quality laser beams. Consequently, thin-film technology is rapidly developing.

[0003] In optical components, CO2 anti-reflection coatings offer the advantage of a simple preparation process. However, their challenges lie in their high absorption and low transmittance, making it difficult to increase transmittance above 99.7%. Furthermore, the laser damage threshold (LDT) of these coatings is also difficult to improve. This paper develops a double-sided anti-reflection coating with ultra-low absorption in the CO2 laser band, which reduces the absorption of the anti-reflection coating layer. By mixing the two coating materials in a controlled ratio, the researchers achieve improved transmittance and laser damage threshold. Summary of the Invention

[0004] The present invention provides a double-sided antireflection film with ultra-low absorption in the CO2 laser band and a preparation method thereof. Through film system design and process improvement, the film system is plated on both sides of the substrate to achieve 10600nm antireflection, with an average transmittance greater than 99.7%, a single-sided reflection less than 0.1%, and absorption reduced from the original 0.3% to less than 0.1%; the anti-laser damage threshold is reduced from the original 6000W / CM 2 Increased to 10000W / CM 2 .

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0006] A CO2 laser band ultra-low absorption double-sided anti-reflection coating has a structure of: Air / qHpL / Sub / pLqH / Air; wherein Sub represents a substrate; H represents a high-refractive-index ZnSe film layer, and the refractive index of the high-refractive-index ZnSe film layer is 2-3; L represents a low-refractive-index film layer, and L is a mixed film layer of two low-refractive-index film materials, L1 film layer and L2 film layer, and the refractive indices of the two low-refractive-index film materials, L1 film layer and L2 film layer, are both 1-1.6, and the low-refractive-index film material L1 film layer and the low-refractive-index film material L2 film layer are made of different materials, and the optical thickness ratio of the low-refractive-index film material L1 film layer: the low-refractive-index film material L2 film layer is controlled in a range of 1:3-1:6; and p and q represent the optical thickness coefficients of each film layer, respectively.

[0007] The values of p and q are related to the reference wavelength λ, and are 0≤ p ≤100, 0≤ q ≤200. Air represents the air side.

[0008] The applicant has found through research that the low refractive index film material L1 film layer (YF3 film layer or YbF3 film layer) : The optical thickness ratio of the L2 film layer (BaF2 film layer) is controlled between 1:3 and 1:6, which has a decisive effect on the absorption value of the high-power laser film. By optimizing the film system and controlling the distribution of the temperature field and the thermal stress field to a certain extent, the absorption value of the film can be greatly reduced, and the anti-laser damage threshold can be significantly improved; on the other hand, taking into account the coating efficiency and the absorption, scattering, and looseness caused by the film layer, this application uses the least number of film layers and the matching of the film material thickness with minimum absorption. The thickness of the first group of YF3 or YBF3 film layers is 160±5nm, and the thickness of the BaF2 film layer is 945±5nm. The thickness of the second group of YF3 or YBF3 film layers is 270±5nm, and the thickness of the BaF2 film layer is 810±5nm. A CO2 band ultra-low absorption anti-reflection film with excellent optical and mechanical properties is obtained, which solves the problem of high absorption of the existing CO2 band anti-reflection film, improves the use effect of the lens, and extends the service life of the lens.

[0009] Preferably, the film layers on the front and back sides of the substrate are symmetrically arranged.

[0010] For the CO2 band, the film material's absorption within this band is the primary consideration. Taking into account absorption, refractive index, adhesion, moisture resistance, and temperature resistance, the preferred material for the high-refractive-index film layer is zinc selenide (ZnSe), while the low-refractive-index film layer uses a fluoride material. Furthermore, the low-refractive-index film material L1 is preferably YF3 or YbF3, and the low-refractive-index film material L2 is BaF2.

[0011] The ratio of the two low refractive index film materials is different. The two low refractive index film materials are mixed in proportion to achieve stress and absorption reduction.

[0012] The substrate is made of CO2 laser window glass with a refractive index of 2 to 3. Preferably, the substrate is made of zinc selenide with a thickness of 3±0.2 mm.

[0013] As a specific preferred solution of the present application, the ultra-low absorption CO2 laser double-sided anti-reflection film has a structure of: Air / 0.2H (pmL1pnL2) / Sub / (pnL2pmL1)0.2H / Air, wherein H represents the ZnSe film layer, L1 represents the YF3 film layer, and L2 represents the BaF2 film layer, wherein pm: pn=1:i, 3≤i≤6.

[0014] The method for preparing the above-mentioned CO2 laser band ultra-low absorption double-sided antireflection film comprises the following steps:

[0015] (1) Substrate heating: Before coating, the substrate is baked and heated in a vacuum state to increase the substrate temperature. The baking temperature is 150℃~250℃ and the time is 1~1.5h;

[0016] (2) Ion beam cleaning: The substrate is cleaned with an ion beam. The ion cleaning time is 1 to 15 minutes, the ion beam voltage is 200 to 400 V, and the ion beam current is 1 to 8 A.

[0017] (3) Film coating on the front side of the substrate: According to the film structure in the film design, each film layer is coated on the front side of the substrate in sequence;

[0018] (4) Coating of the back film of the substrate: After the coating of the front film is completed, take out the component and repeat steps (1) to (2) to coat each film layer on the back side in sequence.

[0019] The above method uses specific process conditions such as electron beam evaporation and appropriate baking temperature, and adopts a double-sided coating method. It can achieve good transmittance of 3mm thick zinc selenide lenses in the 10600nm band, with an average transmittance of more than 99.7%; it improves the optical efficiency of CO2 laser lenses and ensures the laser damage threshold of optical lenses, making this optical component have a longer service life in CO2 laser applications.

[0020] In order to improve the adhesion of the film layer, in step (1), before baking, wipe the substrate with a dust-free cloth dipped in a mixture of environmentally friendly wiping liquid and acetone with a volume ratio of (6-8):1.

[0021] The control of the conditions during film preparation is also very critical. The preparation conditions of each film layer not only affect the properties such as the density of the single film layer, but also affect the bonding strength with the adjacent film layers and the optical properties of the entire film layer. Preferably, in step (3) and step (4):

[0022] YF3 (or YbF3) film coating: Place the YF3 (or YbF3) film material in a crucible or molybdenum boat and use electron beam evaporation or resistance heating to coat it. The background vacuum is higher than 9.5×10 -4 Pa, deposition rate 0.5 nm / s;

[0023] BaF2 film coating: BaF2 film material is placed in a crucible or molybdenum boat and coated by electron beam evaporation or resistance heating. The background vacuum is higher than 9.5×10 -4 Pa, deposition rate is 1-5 nm / s, preferably 1-3 nm / s;

[0024] ZnSe film coating: Place the ZnSe film material in a crucible or molybdenum boat and use electron beam evaporation or resistance heating to coat it. The background vacuum is higher than 9.5×10-4 Pa, deposition rate is 1-5 nm / s, preferably 1-2 nm / s;

[0025] It should be noted that the YF3 or YbF3 film layer and the BaF2 film layer are evaporated simultaneously, and the deposition ratio is ensured by adjusting the deposition rate. Further preferably, the deposition rate of YF3 or YbF3 is 0.5 nm / s, and the deposition rate of BaF2 is 1.5 nm / s, or the deposition rate of YF3 or YbF3 is 0.5 nm / s, and the deposition rate of BaF2 is 3 nm / s.

[0026] Through the above-mentioned film system design and process improvement, the film system is plated on both sides of the 3mm thick zinc selenide substrate to achieve 10600nm anti-reflection, reduce absorption, and improve transmittance. The average transmittance is ≥99.7%, and the single-side reflection is ≤0.1%. The laser damage threshold has been tested and increased from the original 6000W / CM 2 Increased to 10000W / CM 2 .

[0027] Background vacuum refers to the vacuum degree achieved by the vacuum pumping system in a certain space during vacuum coating, which just meets the vacuum degree required for the deposition of the plated object (different products have different requirements for background vacuum degree).

[0028] The technologies not mentioned in this invention are all referred to the prior art.

[0029] The ultra-low absorption CO2 laser double-sided anti-reflection film of the present invention is coated on both sides of the zinc selenide substrate. By combining two low refractive index film materials for mixed coating, it achieves 10600nm anti-reflection, reduces absorption, and improves transmittance. The average transmittance is greater than 99.7%, the single-sided reflection is less than 0.1%, and the absorption is reduced from the original 0.3% to less than 0.1%. The anti-laser damage threshold has been tested from the original 6000W / CM 2 Increased to 10000W / CM 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the structure of the 10600nm ultra-low absorption antireflection film in Example 1 of the present invention;

[0031] Figure 2 This is the design curve of the 10600nm ultra-low absorption antireflection film in Example 1 of the present invention;

[0032] Figure 3 This is the reflective coating curve of the ultra-low absorption anti-reflection film in the 10600 nm band in Example 1 of the present invention;

[0033] Figure 4: This is the transmission coating curve of the ultra-low absorption antireflection film in the 10600 nm band in Example 1 of the present invention;

[0034] Figure 5 Measured absorption curve of the ultra-low absorption antireflection film in the 10600 nm band in Example 1 of the present invention;

[0035] Figure 6 The surface shape of the lens before coating in Example 1 of the present invention;

[0036] Figure 7 This is the surface shape of the lens after coating in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0038] The thin film is prepared on a Nanguang 1100 vacuum chamber coater, using a combination of optical and crystal control systems for film thickness. This coater is equipped with dual evaporation sources: electron beam and thermal resistance evaporation. A condensation pump ensures an oil- and water-free environment within the equipment. Example

[0039] like Figure 1 As shown in the figure, a double-sided anti-reflection coating with ultra-low absorption in the CO2 laser band has the following structure: Air / 0.2H (pmL1pnL2) / Sub / (pnL2pmL1)0.2H / Air, where Sub represents the substrate, the material is zinc selenide, and the substrate thickness is 3mm; H represents the ZnSe film layer, L1 represents the YF3 film layer, and L2 represents the BaF2 film layer, where pm:pn=1:3, and the physical thicknesses are YF3270nm, BaF2810nm, and ZnSe 225nm, respectively. Example

[0040] The YF3 film layer in Example 1 was replaced with YbF3, and the rest was referred to Example 1. Example

[0041] The difference from Example 1 is that the physical thicknesses are 160 nm for YF3, 945 nm for BaF2, and 214 nm for ZnSe.

[0042] In the above embodiments 1-3, the preparation method of the antireflection film includes the following steps:

[0043] (1) Substrate heating: Wipe the substrate with a dust-free cloth dipped in a mixture of environmentally friendly wiping liquid (Foshan Jiajin ECH-CS) and acetone in a volume ratio of 7:1, and bake and heat the substrate in a vacuum state to increase the substrate temperature. The baking temperature is 200℃~210℃ and the baking time is 1.5 hours;

[0044] (2) Ion beam cleaning: The substrate is cleaned with an ion beam. The ion cleaning time is 2 min, the ion beam voltage is 100 V, and the ion beam current is 4 A.

[0045] (3) Film coating on the front side of the substrate: According to the film structure in the film design, each film layer is coated on the front side of the substrate in sequence;

[0046] (4) Plating the film system on the reverse side of the substrate: After the film system on the front side is plated, remove the component and repeat steps (1) to (3) to plate each film layer on the reverse side in sequence;

[0047] In step (3) and step (4), ZnSe film coating: ZnSe film material is placed in a crucible and plated by electron beam evaporation, and the background vacuum is higher than 9.5×10 -4 Pa, deposition rate 0.5nm / s; BaF2 film coating: BaF2 film material is placed in a crucible and plated by electron beam evaporation. The background vacuum is higher than 9.5×10 -4 Pa, deposition rate of 3nm / s; YF3 or YbF3 film coating: YF3 or YbF3 film material is placed in a crucible and plated by electron beam evaporation. The background vacuum is higher than 9.5×10 -4 Pa, the deposition rate is 0.5-1nm / s. The YF3 film or YbF3 film and the BaF2 film are evaporated simultaneously (start and end at the same time).

[0048] The indicators were detected using a Bruker spectrophotometer. Figure 3-Figure 5 It can be seen that the single-side reflection of the antireflection film in Example 1 is less than 0.1%, the double-side transmittance is greater than 99.7%, and the absorption is reduced from the original 0.3% to less than 0.1%. After testing, the single-side reflection of the antireflection film in Examples 2 and 3 is less than 0.1%, the double-side transmittance is greater than 99.7%, and the absorption is reduced to less than 0.1%.

[0049] The laser damage threshold of the ultra-low absorption anti-reflection film in the 10600nm band in Example 1 was tested and increased from the original 6000W / CM 2 Increased to 10000W / CM 2 .

[0050] Figure 6-7 The surface shapes of the lens before and after coating in Example 1. It can be seen that the PV value before coating is 0.552, and the PV value after coating is 0.578. The surface shape does not change much, and it can be seen that the stress is very small.

[0051] In order to ensure the reliability of optical components, environmental tests were carried out on samples according to usage requirements:

[0052] Adhesion test: Use 1-inch wide 3M special tape to stick to the coating surface, then quickly pull it up in the vertical direction of the film surface, and repeatedly pull it 20 times. There is no film peeling phenomenon in Examples 1-3.

[0053] Wet heat test: After immersion in water at 50°C for 48 hours, the films of Examples 1-3 showed no changes.

[0054] High temperature resistance verification: After the temperature was raised to 300°C and baked for 12 hours and then returned to room temperature, there was no change in the film layers of Examples 1-3.

[0055] Comparative Example 1

[0056] The differences from Example 1 are: the physical thicknesses of YF3 are 270nm and BaF2 is 675nm, respectively, and the YF3 deposition rate is adaptively adjusted. The single-side reflectivity is 0.7%, the double-side transmittance is 98%, and the absorptivity is 0.5%. After baking at 300°C for 12 hours and then cooling to room temperature, the film shatters.

[0057] Comparative Example 2

[0058] The differences from Example 1 are: the physical thicknesses of YF3 are 120nm and BaF2 is 840nm, respectively, and the YF3 deposition rate is adaptively adjusted. The single-side reflectivity is 0.5%, the double-side transmittance is 98.5%, and the absorptivity is 0.35%. After baking at 300°C for 12 hours and cooling to room temperature, the film exhibits peeling.

Claims

1. An ultra-low absorption CO2 laser double-sided antireflection film, characterized by: Its structure is: Air / qHpL / Sub / pLqH / Air; wherein Sub represents the substrate; H represents the high-refractive-index film material ZnSe film layer, and the refractive index of the high-refractive-index film material ZnSe film layer is 2~3; L represents the low-refractive-index film layer, and L is a mixed film layer prepared by simultaneously evaporating two low-refractive-index film materials L1 film layer and L2 film layer, and the refractive indices of the two low-refractive-index film materials L1 film layer and L2 film layer are both 1~1.6, and the low-refractive-index film material L1 film layer and the low-refractive-index film material L2 film layer are made of different materials, and the optical thickness ratio of the low-refractive-index film material L1 film layer: the low-refractive-index film material L2 film layer is controlled in a range of 1:3~1:6; p and q represent the optical thickness coefficients of each film layer, respectively, 0≤ p ≤100, 0≤ q ≤200; The low refractive index film material L1 film layer is a YF3 film layer or a YbF3 film layer, and the low refractive index film material L2 film layer is a BaF2 film layer.

2. The ultra-low absorption CO2 laser double-sided antireflection film according to claim 1, characterized in that: The substrate material used is zinc selenide with a thickness of 3±0.2 mm.

3. The ultra-low absorption CO2 laser double-sided antireflection film according to claim 1 or 2, characterized in that: Its structure is: Air / 0.2H (amL1anL2 ) / Sub / (anL2 amL1)0.2H / Air, where H represents the ZnSe film layer, L1 represents the YF3 film layer, and L2 represents the BaF2 film layer, and am:an=1:i, 3≤i≤6.

4. The method for preparing the ultra-low absorption CO2 laser double-sided antireflection film according to any one of claims 1 to 3, characterized in that: The steps include: (1) Substrate heating: Before coating, the substrate is baked and heated in a vacuum state to increase the substrate temperature. The baking temperature is 150℃~250℃ and the time is 1~1.5h; (2) Ion beam cleaning: The substrate is cleaned with an ion beam. The ion cleaning time is 1 to 15 minutes, the ion beam voltage is 200 to 400 V, and the ion beam current is 1 to 8 A. (3) Film coating on the front side of the substrate: According to the film structure in the film design, each film layer is coated on the front side of the substrate in sequence; (4) Coating of the back film of the substrate: After the coating of the front film is completed, take out the component and repeat steps (1) to (2) to coat each film layer on the back side in sequence.

5. The preparation method according to claim 4, wherein: In step (1), before baking, wipe the substrate with a dust-free cloth dipped in a mixture of environmentally friendly wiping liquid and acetone in a volume ratio of (6-8):

1.

6. The preparation method according to claim 4 or 5, characterized in that: In step (3) and step (4), ZnSe film coating: ZnSe film material is placed in a crucible or molybdenum boat and plated by electron beam evaporation or resistance heating. The background vacuum is higher than 9.5×10 -4 Pa, the deposition rate is 1~2nm / s.

7. The preparation method according to claim 4 or 5, characterized in that: In step (3) and step (4), YF3 film coating: the YF3 film material is placed in a crucible or a molybdenum boat and plated by electron beam evaporation or resistance heating. The background vacuum is higher than 9.5×10 -4 Pa, the deposition rate is 0.5~1nm / s; YbF3 film coating: the YbF3 film material is placed in a crucible or a molybdenum boat and plated by electron beam evaporation or resistance heating. The background vacuum is higher than 9.5×10 -4 Pa, and the deposition rate is 0.5~1nm / s.

8. The preparation method according to claim 4 or 5, characterized in that: In step (3) and step (4), BaF2 film coating: BaF2 film material is placed in a crucible or molybdenum boat and plated by electron beam evaporation or resistance heating. The background vacuum is higher than 9.5×10 -4 Pa, the deposition rate is 1~3nm / s.

Images