Multifunctional protective light window with visible light transparency and laser asymmetric transmission

Abstract

The application discloses a multifunctional protective light window of visible light transparent laser asymmetric transmission, which is composed of an asymmetric laser protection structure arranged on the surface of a transparent light window. The asymmetric laser protection structure is composed of five kinds of media, SiO2, low refractive index TiO2, high refractive index TiO2, LiNbO3 and Nb2O5. The five kinds of media are respectively denoted as A, B, C, D and E. The asymmetric laser protection structure is arranged as A(BA) N DA(CA) M EA(BA) N N and M are respectively the repeating period numbers of the media pairs (BA) and (CA), and M=N+1. The thicknesses of the media layers A, B, C, D and E suitable for 1064nm laser asymmetric protection are respectively 180.9nm, 131.4nm, 112.7nm, 238.6nm and 240.7nm. The application can be effectively used in a 1064nm wavelength laser asymmetric protection system, realizes high transmittance of weak light and asymmetric protection of strong light incident from different directions, and simultaneously realizes high transparency of visible light in the 400-780nm wavelength band.

Description

Technical Field

[0001] This invention relates to the field of multilayer film systems and asymmetric nonlinear laser protection, specifically to a visible light transparent multilayer film laser protection structure window with asymmetric nonlinear transmittance. It can be applied to nonlinear laser protection applications that require high transmittance for weak 1064nm laser light and asymmetric high attenuation rate for strong light, while also requiring high transmittance in the 400-780nm visible light band. Background Technology

[0002] Since the advent of lasers in the 1960s, high-energy laser technology has been widely used in industry, scientific research, and medicine. In different environments, higher requirements have been placed on laser protection. This is mainly because high-intensity lasers can cause permanent damage to human eyes and optoelectronic devices. Therefore, it is necessary to limit high-power lasers, but for lower-power lasers, such as those used for signal detection, high transmittance is required. Taking the commonly used 1064nm laser as an example, it can harm personnel and equipment under strong light, but can also be used for optoelectronic detection and information transmission under weak light. Meanwhile, in some applications, such as lidar, it is also necessary to ensure that one's own high-power laser can be transmitted, achieving asymmetric high-energy laser transmission. Furthermore, in some aerospace and other fields, not only laser protection is required, but also high transmittance in the 400-780nm visible light band. Therefore, it is necessary to develop a laser protection structure that can flexibly adjust the laser transmittance and achieve visible light transparency under different light intensities and incident directions.

[0003] Laser protection materials can prevent laser damage to humans, equipment, and other objects, and are of great significance in both civilian and military fields. Currently, commonly used laser protection technologies mainly utilize optical effects such as nonlinear absorption, scattering, and refraction. Among these, anti-saturation absorption is a common nonlinear absorption mechanism used to limit laser intensity. However, its stability limits its application. Laser limiting based on nonlinear scattering principles has a low output amplitude but a high limiting threshold, making it difficult to simultaneously achieve high transmittance under weak light and high attenuation under strong light. Laser limiting based on nonlinear refraction principles has a low limiting threshold, but its structural complexity in practical applications is high. Furthermore, these effects do not possess asymmetric characteristics; therefore, further research and innovation are needed to find solutions that can achieve asymmetric laser protection and visible light transparency to meet the needs of various application scenarios.

[0004] Patent 202110136570.3 discloses a laser protective coating and its preparation method. It provides the application of Y6 in optical limiting. The Y6 thin film, attached to a transparent substrate, forms an optical limiting device, specifically including the following steps: dissolving Y6 in chloroform to obtain a mixed solution, stirring the mixed solution, dropping the mixed solution onto a cleaned quartz sheet in a high-purity nitrogen environment, spin-coating to form a film, and then drying. Y6 is a suitable optical limiting material for protecting against strong lasers. However, this patent lacks optical transmittance, and low-power lasers cannot pass through due to its asymmetric transmission characteristics.

[0005] Patent 202310535255.7 discloses the application of boron nitride aerogel in laser protection, laser protection materials, and laser protection methods. The laser protection material has a three-dimensional porous network structure assembled from boron nitride nanostructures. The provided laser protection material can effectively reflect laser light and manage the localized high-temperature field and thermal stress during laser irradiation. Furthermore, the preparation process of this laser protection material is simple, has a short preparation cycle, and uses mild reaction conditions. However, it is opaque in the visible light band and lacks asymmetric transmission characteristics.

[0006] Patent 202110435894.7 discloses an optical thin-film structure for achieving asymmetric light transmission. This thin-film structure utilizes surfaces of varying heights within the periodic array to achieve destructive interference. It reduces reflection during forward incidence and reduces transmission during reverse incidence, achieving the effect of asymmetric light transmission, i.e., unidirectional light transmission. However, it lacks high-power laser protection characteristics.

[0007] Patent 202111566213.7 provides an optical diode based on asymmetric reflection from a single-layer external chiral metasurface. The invention includes a light source, a linear polarizer, a broadband quarter-wave plate, a photodiode device, a polarization analysis and measurement system, and a spectrometer. The metasurface layer of the photodiode device is an external chiral structure array resonator, overcoming the limitations of asymmetric transmission rates within 25% and complex fabrication processes inherent in single-layer ultrathin chiral metamaterials, achieving the advantage of sub-micron-level photodiode effects. However, it lacks high-power laser protection and visible light transparency.

[0008] Currently, patents related to nonlinear laser protection only achieve protection against high-power lasers and asymmetric transmission, but none of these patents can simultaneously possess the functions of high transmittance in the visible light band, low-power laser transmittance, and asymmetric transmission of high-power lasers.

[0009] In summary, existing technologies cannot simultaneously achieve high transmittance in the visible light band, low-power laser transmission, and high-power laser asymmetric transmission. To address these shortcomings, this invention designs a novel multilayer film structure protective optical window. It utilizes SiO2, high-refractive-index TiO2, low-refractive-index TiO2, Nb2O5 linear media, and LiNbO3 nonlinear media as periodic medium layers and defect layers, respectively. By designing the arrangement, thickness, and number of repetition periods of the SiO2, high-refractive-index TiO2, low-refractive-index TiO2, Nb2O5, and LiNbO3 medium layers, it achieves high attenuation of strong light and high transmittance of weak light from different incident directions, while simultaneously achieving high transmittance in the visible light band. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a structure that can achieve weak light high transmission and asymmetric laser protection against 1064nm laser and high energy laser incident from different directions, while simultaneously achieving transparency in the visible light band, in order to overcome the shortcomings of the prior art.

[0011] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0012] A multifunctional protective optical window for asymmetric transmission of visible light transparent lasers is constructed by placing an asymmetric laser protection structure on the surface of the transparent optical window. The asymmetric laser protection structure is characterized by a multilayer film composed of five media: SiO2, low-refractive-index TiO2, high-refractive-index TiO2, LiNbO3, and Nb2O5. Let A, B, C, D, and E be the media of SiO2, low-refractive-index TiO2, high-refractive-index TiO2, LiNbO3, and Nb2O5, respectively. Then, the arrangement of the asymmetric laser protection structure is A (BA). N DA(CA) M EA(BA) N N and M are the number of repetition cycles of the medium pairs (BA) and (CA), respectively, and M = N + 1. The laser protection wavelength is 1064 nm, and the optical thicknesses of the medium layers A, B, C, D and E are 266 nm, 266 nm, 266 nm, 532 nm and 532 nm, respectively.

[0013] A multifunctional protective optical window for asymmetric transmission of visible-light transparent laser is characterized by the following: at a laser wavelength of 1064 nm, the refractive index of the medium SiO2 is 1.47 with an extinction coefficient of 0; the refractive index of the low-refractive-index medium TiO2 is 2.03 with an extinction coefficient of 0; the refractive index of the high-refractive-index medium TiO2 is 2.36 with an extinction coefficient of 0; the medium layer Nb2O5 is a linear defect layer with a refractive index of 2.23 and an extinction coefficient of 0; and the medium layer LiNbO3 is a nonlinear defect layer with a linear refractive index of 2.21 and a nonlinear refractive index coefficient of 1.44 × 10⁻⁶. -11 cm2 / W, with an extinction coefficient of 0, and actual thicknesses of the dielectric layers SiO2, low-refractive-index TiO2, high-refractive-index TiO2, LiNbO3 and Nb2O5 are 180.9 nm, 131.4 nm, 112.7 nm, 238.6 nm and 240.7 nm, respectively.

[0014] In the embodiment, when the number of repetition cycles N = 6, the energy density of the 1064nm laser is less than 8.56mJ / cm². 2 At that time, this asymmetric laser protection structure is effective against A(BA). N The transmittance of the 1064nm laser incident on the D side is 78.78%, and the laser protection threshold is 25.16mJ / cm². 2 When the laser energy density is greater than 68.97 mJ / cm 2 At that time, the transmittance of its 1064nm laser was 2.69%. The laser emitted from EA(BA) N For side incidence, the transmittance ranges between 78.78% and 73.14% with increasing laser energy density. In the visible light 400-780nm band, A(BA) N The average transmittance at incidence on side D is 78.28%; EA(BA) N The average transmittance at side incidence is 78.28%.

[0015] In the embodiment, when the number of repetition cycles N = 7, the energy density of the 1064nm laser is less than 6.29mJ / cm². 2 At that time, this asymmetric laser protection structure is effective against A(BA). N The transmittance of the 1064nm laser incident on the D side is 87.4%, and the laser protection threshold is 27.14mJ / cm². 2 When the laser energy density is greater than 66.42 mJ / cm 2 At that time, the transmittance of its 1064nm laser was 3.69%. The laser emitted from EA(BA) N For side incidence, the transmittance ranges between 87.4% and 82.59% with increasing laser energy density. In the visible light band of 400-780 nm, A(BA) N The average transmittance incident on side D was 76.83%; EA(BA) N The average transmittance at side incidence is 76.83%.

[0016] In the embodiment, when the number of repetition cycles N = 8, the energy density of the 1064nm laser is less than 4.37mJ / cm². 2 At that time, this asymmetric laser protection structure is effective against A(BA). N The transmittance of the 1064nm laser incident on the D side is 89.6%, and the laser protection threshold is 31.44mJ / cm². 2When the laser energy density is greater than 63.42 mJ / cm 2 At that time, the transmittance of its 1064nm laser was 4.12%. The laser emitted from EA(BA) N For side incidence, the transmittance ranges between 89.6% and 84.79% with increasing laser energy density. In the visible light 400-780nm band, A(BA) N The average transmittance incident on side D was 76.24%; EA(BA) N The average transmittance at side incidence is 76.24%.

[0017] Compared with the prior art, the advantages of this invention are:

[0018] (1) The designed multilayer film periodic structure optical window can generate bandgap and passband structures, generate different electric field distributions in different incident directions, selectively block and allow light of specific wavelengths to propagate in specific directions, and achieve effective asymmetric laser protection and visible light band transparency.

[0019] (2) By utilizing the local optical field characteristics of the multilayer film periodic structure, the electric field intensity at the defect layer LiNbO3 is enhanced, the nonlinear effect is improved, and thus the laser protection threshold is reduced.

[0020] (3) The multilayer film periodic structured light window can be designed as needed to adapt to different wavelengths of laser, which makes it possible to protect against various lasers of different wavelengths, including visible light, infrared light and ultraviolet light.

[0021] (4) The multilayer film periodic structured optical windows are lightweight and thin, making them suitable for applications such as portable laser protection equipment and eye protection goggles. Compared with traditional laser protection materials, the structure of this invention is simpler in design, more stable in physical properties than liquid substances, and the structure of this invention is transparent to visible light.

[0022] In summary, this invention can be effectively used in a 1064nm wavelength asymmetric laser protection system to achieve high transmittance for weak light and high attenuation rate for strong light with different incident directions, while simultaneously achieving transparency in the visible light band. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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 drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 It is a multifunctional protective light window for asymmetric transmission of visible light transparent laser.

[0025] Figure 2 For A(BA) when the repetition period N=6. N D-side incident electric field distribution diagram.

[0026] Figure 3 For EA(BA) when the repetition period N=6. N Side-incident electric field distribution diagram.

[0027] Figure 4 For A(BA) when the repetition period N=7. N D-side incident electric field distribution diagram.

[0028] Figure 5 For EA(BA) when the repetition period N=7. N Side-incident electric field distribution diagram.

[0029] Figure 6 For A(BA) when the repetition period N=8. N D-side incident electric field distribution diagram.

[0030] Figure 7 For EA(BA) when the repetition period N=8. N Side-incident electric field distribution diagram.

[0031] Figure 8 Let A(BA) be the result of repetition periods N=6, N=7, and N=8. N Broadband transmittance diagram of incident light on side D.

[0032] Figure 9 Let A(BA) be the result of repetition periods N=6, N=7, and N=8. N Transmittance diagram of the D-side incident light near 1064 nm.

[0033] Figure 10 For the cases where the repetition period N=6, N=7, and N=8, EA(BA) is calculated. N Transmittance diagram for wide-band side-incidence radiation.

[0034] Figure 11 For the cases where the repetition period N=6, N=7, and N=8, EA(BA) is calculated. N Transmittance diagram near 1064nm incident from the side.

[0035] Figure 12 This is a graph showing the transmittance of a 1064nm wavelength laser as a function of the incident direction and incident light energy density. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. These described embodiments are merely a part of the embodiments of the present invention, and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0037] This invention addresses asymmetric protection systems for 1064nm wavelength lasers, designing a multilayer protective structure with transparent and asymmetric nonlinear transmittance in the visible light band. Medium A is selected as SiO2 (silicon dioxide) with a refractive index of 1.47 and an extinction coefficient of 0. Medium B is selected as low-refractive-index TiO2 (titanium dioxide) with a refractive index of 2.03 and an extinction coefficient of 0. Medium C is selected as high-refractive-index TiO2 (titanium dioxide) with a refractive index of 2.36 and an extinction coefficient of 0. Medium D is selected as Nb2O5 (silicon dioxide) with a refractive index of 2.23 and an extinction coefficient of 0. The defect layer E is selected as LiNbO3 (lithium niobate) with a linear refractive index of 2.21 and a nonlinear refractive index coefficient of 1.44 × 10⁻⁶. -11 cm 2 / W, with an extinction coefficient of 0. The thicknesses of dielectric layers A, B, C, D, and E are 180.9 nm, 131.4 nm, 112.7 nm, 238.6 nm, and 240.7 nm, respectively.

[0038] When the incident light wavelength is 1064 nm, under low incident light energy density, A(BA) N D-side incidence and EA(BA) N When incident from the side, this wavelength is precisely located at the defect state position, resulting in high transmittance. As the incident light energy density increases, A(BA)... N When incident from the D side, the light field is localized in the LiNbO3 layer. Due to its large third-order nonlinear coefficient, the defect states shift, resulting in a decrease in transmittance at 1064 nm; EA(BA). N When incident from the side, the light field is localized in the Nb2O5 layer. Due to its small third-order nonlinear coefficient, the defect states do not move much, and the transmittance at 1064nm changes little; thus achieving the asymmetric light protection effect under high incident light energy density.

[0039] For the multilayer film laser protection structure of the present invention, the electric field distribution of the structure was obtained by simulation using the finite-difference time-domain method. By changing the incident light energy density and incident direction, the relationship between the transmittance of the multilayer film structure and the incident light energy density was obtained. Figures 2 to 7 As shown, the defect mode field distributions of the structure of the present invention under different incident directions for N=6, N=7, and N=8 can be observed. When N=6, A(BA) NThe incident electric field intensity on the D side was enhanced by 25.6 times in the LiNbO3 defect layer, EA(BA). N The side-incident electric field intensity was increased by 11.8 times in the Nb₂O₅ defect layer; at N=7, A(BA) N The incident electric field intensity on the D side was enhanced by 40.3 times in the LiNbO3 defect layer, EA(BA). N The side-incident electric field intensity was increased by 17.9 times in the Nb₂O₅ defect layer; at N=8, A(BA) N The incident electric field intensity on the D side was enhanced by 66.1 times in the LiNbO3 defect layer, EA(BA). N The intensity of the side-incident electric field was increased by 26.3 times in the Nb2O5 defect layer; the enhanced electric field is conducive to generating nonlinear effects.

[0040] Figures 8 to 11 This is a transmittance-wavelength relationship diagram for the structure of this invention. In the visible light 400-780nm band, when the number of repetition periods N=6, A(BA) N The average transmittance at incidence on side D is 78.28%; EA(BA) N The average transmittance at side incidence is 78.28%; when the number of repetition cycles N = 7, A(BA) N The average transmittance incident on side D was 76.83%; EA(BA) N The average transmittance at side incidence is 76.83%; when the number of repetition cycles N = 8, A(BA) N The average transmittance incident on side D was 76.24%; EA(BA) N The average transmittance at side incidence is 76.24%, achieving high transmittance in the visible light band. At a wavelength of 1064 nm, with a repetition period N = 6, A(BA) N D-side incidence and EA(BA) N The side-incident transmittance is 78.78%; when the number of repetition cycles N = 7, A(BA) N D-side incidence and EA(BA) N The side-incident transmittance is 87.4%; when the number of repetition cycles N = 8, A(BA) N D-side incidence and EA(BA) N The side-incident transmittance is 89.6%.

[0041] like Figure 12 As shown, by changing the incident direction and incident light energy density, the transmittance-incident light energy density relationship diagram is obtained. It can be seen that when the number of repetition cycles N = 6, A(BA) N When incident from side D, the laser energy density is less than 8.56 mJ / cm². 2 The laser transmittance is 78.78%, and the laser protection threshold is 25.16 mJ / cm².2 When the laser energy density is greater than 68.97 mJ / cm 2 At that time, the laser transmittance was 2.69%; laser EA(BA) N For side incidence, the transmittance ranges between 78.78% and 73.14% as the laser energy density increases. The number of repetition cycles N = 7, A(BA). N When incident from side D, the laser energy density is less than 6.29 mJ / cm². 2 The laser transmittance is 87.4%, and the laser protection threshold is 27.14 mJ / cm². 2 When the laser energy density is greater than 66.42 mJ / cm 2 At that time, the laser transmittance was 3.69%; laser EA(BA) N For side incidence, the transmittance ranges between 87.4% and 82.59% as the laser energy density increases. The number of repetition cycles N = 8, A(BA). N When incident from side D, the laser energy density is less than 4.37 mJ / cm². 2 The laser transmittance is 89.6%, and the laser protection threshold is 31.44 mJ / cm². 2 When the laser energy density is greater than 63.42 mJ / cm 2 At that time, the laser transmittance was 4.12%; laser EA(BA) N When incident from the side, the transmittance ranges between 89.6% and 84.79% as the laser energy density increases.

Claims

1. A multifunctional protective optical window for asymmetric transmission of visible light transparent laser, comprising an asymmetric laser protection structure placed on the surface of the transparent optical window, characterized in that: The asymmetric laser protection structure is composed of five kinds of medium arrangement of SiO2, low refractive index TiO2, high refractive index TiO2, Nb2O5 and LiNbO3, and is arranged as A(BA) N DA(CA) M EA(BA) N , N and M are the repetition period numbers of medium pairs (BA) and (CA) respectively, M=N+1, the laser protection wavelength is 1064nm, and the optical thicknesses of medium layers A, B, C, D and E are 266nm, 266nm, 266nm, 532nm and 532nm respectively.

2. The multifunctional protective optical window for asymmetric transmission of visible light transparent laser according to claim 1, characterized in that: At 1064nm laser, the refractive index of medium SiO2 is 1.47, the extinction coefficient is 0, the refractive index of low refractive index medium TiO2 is 2.03, the extinction coefficient is 0, the refractive index of high refractive index medium TiO2 is 2.36, the extinction coefficient is 0, the medium layer Nb2O5 is a linear defect layer, the refractive index is 2.23, the extinction coefficient is 0, the medium layer LiNbO3 is a nonlinear defect layer, the linear refractive index is 2.21, the nonlinear refractive index coefficient is 1.44×10 -11 cm 2 / W, the extinction coefficient is 0, and the actual thicknesses of the medium layers SiO2, low refractive index TiO2, high refractive index TiO2, Nb2O5 and LiNbO3 are 180.9nm, 131.4nm, 112.7nm, 238.6nm and 240.7nm respectively.

3. The multifunctional protective optical window for asymmetric transmission of visible light transparent laser according to claim 1, characterized in that: With a repetition cycle number N=6, the laser beam originates from A(BA). N When incident from the D side, the energy density of the 1064nm laser is less than 8.56mJ / cm². 2 At that time, the transmittance of this asymmetric laser protection structure to 1064nm laser was 78.78%, and the laser protection threshold was 25.16mJ / cm. 2 When the laser energy density is greater than 68.97 mJ / cm 2 At that time, the transmittance of its 1064nm laser was 2.69%; the laser from EA(BA) N When incident from the side, the transmittance ranges between 78.78% and 73.14% as the laser energy density increases.

4. The multi-functional protective window of claim 1, wherein the window is transparent to visible light and asymmetrically transmits laser light. At the repetition number N = 6, in the visible light 400-780 nm band, A(BA) N The average transmittance of D side incidence is 78.28%; EA(BA) N The average transmittance of side incidence is 78.28%.

5. The multi-functional protective window of claim 1, wherein the window is transparent to visible light and asymmetrically transmits laser light. When the number of repetition cycles N = 7, the laser is incident from A (BA) N When the energy density of 1064 nm laser is less than 6.29 mJ / cm 2 , the transmittance of the asymmetric laser protection structure to 1064 nm laser is 87.4%, and the laser protection threshold is 27.14 mJ / cm 2 When the energy density of 1064 nm laser is greater than 66.42 mJ / cm 2 , the transmittance of 1064 nm laser is 3.69%; when the laser is incident from EA (BA) N , the transmittance increases between 87.4% and 82.59% with the increase of laser energy density.

6. The multi-functional protective window of claim 1, wherein the window is transparent to visible light and asymmetrically transmits laser light. At the number of repeating cycles N = 7, in the visible light 400-780 nm band, A(BA) N The average transmittance of D side incidence is 76.83%; EA(BA) N The average transmittance of side incidence is 76.83%.

7. The multi-functional protective window of claim 1, wherein the window is transparent to visible light and asymmetrically transmits laser light. When the laser is incident from side A (BA) N When the laser energy density is less than 4.37 mJ / cm 2 When the laser energy density is greater than 63.42 mJ / cm 2 When the laser energy density is greater than 63.42 mJ / cm 2 When the laser energy density is greater than 63.42 mJ / cm N When the laser is incident from side EA (BA) When the laser energy density is greater than 63.42 mJ / cm 8. The multi-functional protective window of claim 1, wherein: the window is transparent to visible light and asymmetrically transmits laser light. At the repetition number N = 8, in the visible light 400-780 nm band, A(BA) N The average transmittance of D side incidence is 76.24%; EA(BA) N The average transmittance of side incidence is 76.24%.

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