Optimization method for thickness coefficient of laser frequency converter device film layer

Abstract

The application provides an optimization method for thickness coefficients of a laser and frequency device film layer, the laser and frequency device comprising a frequency mixing crystal, the first side and the second side of the frequency mixing crystal being provided with an anti-reflection film structure, the anti-reflection film structure comprising four film layers, and the thickness coefficients of the film layers being obtained by the following steps: obtaining incident fundamental frequency light and initial set thickness coefficients of the film layers; taking the initial set thickness coefficients as initial values, and optimizing the thickness coefficients of the film layers so that the transmittance of the laser and frequency device to the incident fundamental frequency light and the emitted laser is within a respective transmittance preset range, and the absorption at the wavelength of the emitted frequency mixing laser is within a second preset range. The scheme significantly reduces the absorption of the frequency mixing laser emission side and the absorption of the entire frequency mixing device on the basis of considering the transmittance standard, thereby suppressing the photo-thermal coupling effect, improving the laser damage resistance of the frequency mixing crystal device, and effectively protecting the overall structure of the frequency mixing crystal device.

Description

Technical Field

[0001] This application relates to the field of laser device technology, and specifically to a method for optimizing the film thickness coefficient of laser and frequency devices. Background Technology

[0002] Laser frequency conversion technology has been widely used to expand the range of laser wavelengths, resulting in an increasingly diverse range of laser output wavelengths. Laser frequency conversion converts the frequencies of two input fundamental frequency laser beams using a nonlinear crystal to obtain a sum-frequency laser output. The nonlinear conversion crystal is the core device for achieving frequency conversion of two fundamental frequency beams. To reduce light energy loss due to Fresnel reflection and improve conversion efficiency, an anti-reflection coating must be deposited on its surface.

[0003] In the existing technology, antireflection coatings for two fundamental frequency light and sum frequency output light at the laser wavelengths are usually deposited on both ends of the nonlinear crystal to achieve high transmittance. However, when designing the film structure in the antireflection coating based on the pursuit of high transmittance, there is often a phenomenon where the energy of the high-flux laser damages the sum frequency device. Therefore, the damage resistance of such laser sum frequency devices is poor. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, this application aims to provide a method for optimizing the film thickness coefficient of a laser sum-frequency device. The laser sum-frequency device includes a sum-frequency crystal, which has a first side and a second side opposite to each other. An anti-reflection film structure is provided on both the first side and the second side. The anti-reflection film structure includes four film layers, and the four film layers are alternately arranged first film material and second film material along the direction away from the sum-frequency crystal. The refractive index of the first film material is higher than that of the second film material.

[0005] The thickness coefficient of each of the thin film layers is obtained through the following steps:

[0006] Obtain the incident fundamental frequency light and the initial set thickness coefficients of each thin film layer;

[0007] Using the initial set thickness coefficient as the initial value, the thickness coefficient of each thin film layer is optimized so that the transmittance of the laser sum-frequency device to the incident fundamental frequency light and the emitted laser is within their respective preset transmittance ranges, and the absorption rate at the wavelength of the emitted sum-frequency laser is within a second preset range. The emitted sum-frequency laser is obtained by irradiating the laser sum-frequency device with the incident fundamental frequency light.

[0008] According to the technical solution provided in the embodiments of this application, the total thickness of each film layer in the two antireflection film structures is less than the output wavelength of the emitted sum-frequency laser.

[0009] According to the technical solution provided in the embodiments of this application, the method for obtaining incident fundamental frequency light specifically includes the following steps:

[0010] A first fundamental frequency light and a second fundamental frequency light are acquired, and the first fundamental frequency light and the second fundamental frequency light are integrated into one path through a coupling mirror, thereby becoming the incident fundamental frequency light.

[0011] According to the technical solution provided in the embodiments of this application, the method for obtaining the first fundamental frequency light specifically includes the following steps:

[0012] The seed light from the first LD pump source is injected into the first nonlinear crystal to excite the first fundamental frequency light.

[0013] According to the technical solution provided in the embodiments of this application, the method for obtaining the first fundamental frequency light specifically includes the following steps:

[0014] The seed light from the second LD pump source is injected into the second nonlinear crystal to excite the second fundamental frequency light.

[0015] According to the technical solution provided in the embodiments of this application, the method for optimizing the thickness coefficient of each thin film layer using the initially set thickness coefficient as the initial value specifically includes the following steps:

[0016] The transmittance preset ranges of the incident fundamental frequency light and the emitted laser are obtained, and the first preset thickness coefficient of each thin film layer is obtained with the transmittance preset range as the optimization target.

[0017] Based on the first set thickness coefficient of each of the thin film layers, the absorption rate of the first side surface along the crystal emission direction at the emission frequency laser wavelength is calculated;

[0018] The second preset range of the absorptivity at the emitted and frequency laser wavelengths is obtained, and the second preset range is used as the optimization target to obtain the second preset thickness coefficient of each film layer of the antireflective film structure on the first side.

[0019] Based on the second predetermined thickness coefficient of each of the thin film layers of the antireflection film structure on the first side, the absorption rate of the second side at the emitted laser wavelength along the crystal incident or emitted direction is calculated.

[0020] Using the second preset range as the optimization target, the second preset thickness coefficient of each film layer of the antireflective film structure on the second side is obtained.

[0021] According to the technical solution provided in the embodiments of this application, the crystal emission direction is with a sum-frequency crystal as the incident medium and air as the emission medium; the crystal incident direction is with a sum-frequency crystal as the emission medium and air as the incident medium.

[0022] According to the technical solution provided in the embodiments of this application, the first fundamental frequency light and the second fundamental frequency light are integrated into one path by a coupling mirror, and then reflected by a second reflecting mirror to become the incident fundamental frequency light.

[0023] In summary, this application proposes a method for optimizing the film thickness coefficient of a laser sum-frequency device. The laser sum-frequency device includes a sum-frequency crystal with opposing first and second sides. Antireflective film structures are provided on both the first and second sides. Each antireflective film structure includes four thin film layers, which are sequentially composed of alternating first and second thin film materials along the direction away from the sum-frequency crystal. The refractive index of the first thin film material is higher than that of the second thin film material. The thickness coefficient of each thin film layer is obtained through the following steps: acquiring the incident fundamental frequency light and the initial set thickness coefficient of each thin film layer; using the initial set thickness coefficient as the initial value, optimizing the thickness coefficient of each thin film layer so that the transmittance of the laser sum-frequency device to the incident fundamental frequency light and the emitted laser is within their respective preset transmittance ranges, and the absorptivity at the wavelength of the emitted sum-frequency laser is within a second preset range. The emitted sum-frequency laser is obtained by irradiating the laser sum-frequency device with the incident fundamental frequency light.

[0024] Compared with the prior art, the beneficial effects of this application are as follows: This method, while taking into account the transmittance standard, also takes into account the absorption rate of the entire device for the emitted sum-frequency laser, thereby reducing the absorption rate of the entire device for the sum-frequency laser, especially reducing the absorption rate of the antireflection film on the first side, i.e. the sum-frequency laser emission side, thereby improving the laser damage resistance of the sum-frequency crystal device, effectively protecting the overall structure of the sum-frequency crystal device, and also improving the sum-frequency efficiency of the nonlinear crystal. Attached Figure Description

[0025] Figure 1 A schematic diagram of the structure of a laser and frequency device provided in an embodiment of this application;

[0026] Figure 2 This application provides a diagram illustrating the use cases of laser and frequency devices in its embodiments.

[0027] Figure 3 The refractive index curve of the high refractive index film material provided in the embodiments of this application;

[0028] Figure 4 The refractive index curve of the low refractive index film material provided in the embodiments of this application is shown.

[0029] 1. Sum-frequency crystal; 11. First side surface; 12. Second side surface; 2. First reflector; 3. Second reflector; 4. Coupler; 5. Second nonlinear crystal; 6. Second LD pump source; 7. First nonlinear crystal; 81. First antireflection film; 82. Second antireflection film; 9. First LD pump source. Detailed Implementation

[0030] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] Example 1

[0033] As mentioned in the background section, this application addresses the problems in the prior art. It proposes a method for optimizing the film thickness coefficient of a laser sum-frequency device. The laser sum-frequency device includes a sum-frequency crystal 1, which has opposing first side 11 and second side 12. Both the first side 11 and the second side 11 are provided with an anti-reflection film structure. The anti-reflection film structure includes four film layers, and the four film layers are alternately composed of a first film material and a second film material along a direction away from the sum-frequency crystal 1. The refractive index of the first film material is higher than that of the second film material.

[0034] The thickness coefficient of each of the thin film layers is obtained through the following steps:

[0035] Obtain the incident fundamental frequency light and the initial set thickness coefficients of each thin film layer;

[0036] Using the initial set thickness coefficient as the initial value, the thickness coefficient of each thin film layer is optimized so that the transmittance of the laser sum-frequency device to the incident fundamental frequency light and the emitted laser is within their respective preset transmittance ranges, and the absorption rate at the wavelength of the emitted sum-frequency laser is within a second preset range. The emitted sum-frequency laser is obtained by irradiating the laser sum-frequency device with the incident fundamental frequency light.

[0037] Specifically, the antireflective film structure on the first side is a first antireflective film 81, and the antireflective film structure on the second side is a second antireflective film 82.

[0038] Specifically, the sum-frequency crystal 1 is an LBO sum-frequency crystal 1, located in the middle. Antireflective film structures are designed on both sides of the sum-frequency crystal 1, forming a "thin film-substrate-thin film" system. The first side is the emission surface of the sum-frequency laser. The antireflective film structures on both sides are traditionally designed with four thin film layers. However, unlike traditional technologies, the thickness coefficients of the thin film layers on both sides are different. The optimized antireflective film structure of the first side can be expressed as: Sub / x 12 Hx 22 Lx32 Hx 42 L / Air; The optimized antireflective film structure on the second side can be represented as: Sub / x 52 Hx 62 Lx 72 Hx 82 L / Air; where Sub represents sum-frequency crystal 1, H represents high refractive index film material, L represents low refractive index film material, Air represents air, and x 12 ~x 42 x represents the thickness coefficient of each layer of the optimized antireflective film structure on the first side. 52 ~x 82 This represents the thickness coefficient of each layer in the optimized antireflective film structure on the second side. This method starts with an initial set thickness coefficient for each layer, and continuously optimizes the thickness coefficients of each layer. This optimization aims to achieve high transmittance of both the incident fundamental frequency light and the emitted laser, as well as the absorption rate at the emitted laser wavelength. With the coordination of these thickness coefficients, the entire laser-frequency device not only achieves high transmittance of both the incident fundamental frequency light and the emitted laser, but also reduces the absorption of the laser by the entire device. This effectively improves the laser damage resistance of the frequency crystal 1 device, protects the overall structure of the frequency crystal 1 device, and also improves the frequency efficiency of the nonlinear crystal.

[0039] In a preferred embodiment, the total thickness of each film layer in the two antireflection film structures is less than the output wavelength of the emitted sum-frequency laser.

[0040] Specifically, the total thickness of each film layer in both antireflection film structures is less than the output wavelength λ of the emitted and frequency-controlled lasers. sf This can effectively reduce the stress on the thin film.

[0041] In a preferred embodiment, the method for acquiring incident fundamental frequency light specifically includes the following steps:

[0042] The first fundamental frequency light and the second fundamental frequency light are acquired, and the first fundamental frequency light and the second fundamental frequency light are integrated into one path through the coupling mirror 4, thereby becoming the incident fundamental frequency light.

[0043] In a preferred embodiment, the method for obtaining the first fundamental frequency light specifically includes the following steps:

[0044] The seed light of the first LD pump source 9 is injected into the first nonlinear crystal 7 to excite the first fundamental frequency light.

[0045] In a preferred embodiment, the method for obtaining the first fundamental frequency light specifically includes the following steps:

[0046] The seed light of the second LD pump source 6 is injected into the second nonlinear crystal 5 to excite the second fundamental frequency light.

[0047] Specifically, the wavelength λ is obtained. ff1 The first fundamental frequency light and wavelength λ ff2 The second fundamental frequency light, and the first fundamental frequency light and the second fundamental frequency light are integrated into one path as the incident fundamental frequency light;

[0048] The first antireflective film 81 pairs with wavelength λ ff1 Wavelength λ ff2 and wavelength λ sf The laser light emitted exhibits high transmittance. The second antireflective film 82 has high transmittance for wavelengths λ. ff1 Wavelength λ ff2 The laser has high transmittance.

[0049] Specifically, the second antireflective film 82 is for wavelength λ ff1 Wavelength λ ff2 The laser has high transmittance to reduce optical loss within the resonant cavity. The first antireflective film 81 is effective for wavelength λ. ff1 Wavelength λ ff2 and wavelength λ sf All lasers have high transmittance, and the same purpose is to reduce the optical loss in the resonant cavity while ensuring the efficient output of the sum frequency light.

[0050] In a preferred embodiment, the method for optimizing the thickness coefficient of each thin film layer using the initially set thickness coefficient as the initial value specifically includes the following steps:

[0051] S1. Obtain the preset transmittance range of the incident fundamental frequency light and the emitted laser light respectively, and use the preset transmittance range as the optimization target to obtain the first preset thickness coefficient of each of the thin film layers.

[0052] S2. Based on the first set thickness coefficient of each of the thin film layers, calculate the absorption rate of the first side surface along the crystal emission direction at the emitted laser wavelength.

[0053] S3. Obtain the second preset range of the absorptivity at the emitted and frequency laser wavelengths, and use the second preset range as the optimization target to obtain the second preset thickness coefficient of each film layer of the antireflective film structure on the first side.

[0054] S4. Based on the second set thickness coefficient of each of the thin film layers of the antireflection film structure on the first side, calculate the absorption rate of the second side along the crystal incident or exit direction at the exit frequency laser wavelength.

[0055] S5. Using the second preset range as the optimization target, obtain the second preset thickness coefficient of each film layer of the antireflective film structure on the second side.

[0056] In a preferred embodiment, the crystal emission direction is such that the sum-frequency crystal 1 is the incident medium and air is the emission medium; the crystal incident direction is such that the sum-frequency crystal 1 is the emission medium and air is the incident medium.

[0057] In a preferred embodiment, the first fundamental frequency light and the second fundamental frequency light are integrated into one path by the coupling mirror 4, and then reflected by the second reflecting mirror 3 to become the incident fundamental frequency light.

[0058] The entire optimization process can be understood as follows:

[0059] First, high-refractive-index and low-refractive-index film materials are selected; and the first base film of the first side 11 is designed based on the first basic film system structure, which is: Sub / x 10 Hx 20 Lx 30 Hx 40 L / Air, where Sub represents sum-frequency crystal 1, H represents high refractive index film material, L represents low refractive index film material, Air represents air, and x 10 ~x 40 This indicates the thickness of each film layer in the first basic film system structure, which is set based on experience; specifically, the selected high refractive index film layer material is Ta2O5 thin film, and the selected low refractive index film layer material is SiO2 thin film.

[0060] Then, the incident fundamental frequency light is incident through the first base film into the laser and frequency device, based on x 10 ~x 40 A genetic algorithm is used for numerical optimization to obtain the wavelength λ. ff1 Wavelength λ ff2 and wavelength λ sf The first initial membrane structure that meets the transmittance standard is: Sub / x 11 Hx 21 Lx 31 Hx 41 L / Air, where x 11 ~x 41 This represents the thickness coefficient of each film layer in the first initial film system structure;

[0061] Next, the thickness of each membrane layer in the first initial membrane structure is used as the thickness of each membrane layer in the second initial membrane structure. A first initial membrane is designed on the first side 11, and a second initial membrane is designed on the second side 12, based on the first initial membrane structure. The second initial membrane structure is: Sub / x 51 Hx 61 Lx 71 Hx 81 L / Air, where x51 ~x 81 x represents the thickness coefficient of each film layer in the second initial film system structure. 51 ~x 81 With x 11 ~x 41 Corresponding equal;

[0062] Next, using the absorptivity of the first side at the emitted and frequency laser wavelengths as the control target, and with the crystal as the incident medium and air as the emitted medium, the thickness of each layer in the first initial film system structure was optimized to obtain the optimized thickness of each layer in the first initial film system structure, denoted as x. 12 ~x 42 .

[0063] Explanation of the principle for optimizing the absorptivity of the first side: Based on the analysis of optical path transmission in actual operation and the calculation of the electric field distribution in the "thin film-substrate-thin film" system, it can be seen that even if the film structure of the thin films on both sides of the substrate (sum frequency crystal 1) is exactly the same, there are significant differences in the electric field intensity distribution. The electric field intensity of the first side 11 is higher than that of the second side 12, and the sum frequency output wavelength is closer to the short wave direction. According to the extinction coefficient dispersion law, the absorptivity is greater at this wavelength. Therefore, it is necessary to focus on optimizing the absorptivity of the first side 11 of the sum frequency crystal 1, that is, the absorptivity of the antireflection film on the sum frequency laser emission side.

[0064] Next, based on the thickness x of each film layer in the second initial film system structure 51 ~x 81 And the thickness x of each film layer in the optimized first initial film system structure. 12 ~x 42 The second initial film pair is used to apply a frequency laser wavelength λ. sf The transmittance at the point is limited to a first preset range. The absorption rate of the entire sum-frequency device ("thin film-substrate-thin film") at the emitted sum-frequency laser wavelength is used as the control target for further optimization to obtain the final optimized thickness coefficient of each thin film layer.

[0065] Specifically, A1e(λ) is the second absorptivity, A1i(λ) is the third absorptivity, and T1(λ) is the transmittance of the first side 11, which is equal in both the emission and incident directions; A2(λ) is the first absorptivity, and T2(λ) is the transmittance of the second side 12, which is equal in both the emission and incident directions; the film materials are all oxide thin film materials with a wavelength range of 400nm to 1500nm. The first absorptivity is the absorptivity of the first initial film to the laser light emitted from the crystal; the second absorptivity is the absorptivity of the second initial film to the laser light emitted from the crystal; and the third absorptivity is the absorptivity of the second initial film to the laser light emitted from the crystal.

[0066] For x10 ~x 40 A genetic algorithm is used for numerical optimization to find the optimal wavelength λ. ff1 , λ ff2 and λ sf To achieve higher transmittance, x 11 ~x 41 Then, calculate the absorption rates A1e(λ), A1i(λ), and A2(λ);

[0067] The x obtained above 11 ~x 41 Meanwhile, the thickness of each film layer in the second initial film system structure of the second side 12, i.e., x 51 ~x 81 respectively with x 11 ~x 41 Corresponding equal;

[0068] Furthermore, regarding x 12 ~x 42 and x 51 ~x 81 The first side 11 pairs of wavelengths λ sf Transmittance T1(λ) sf Limiting the absorption rate to within the range of 50% to 90%, the overall absorption rate and the first absorption rate of the entire "thin film-substrate-thin film" system are further optimized and controlled to obtain the final optimized thickness coefficients of each film layer, thereby obtaining the film system structure.

[0069] The specific application environment of the laser and frequency devices involved in this scheme is as follows: the seed light of the first LD pump source 9 is injected into the first nonlinear crystal 7, and the excitation wavelength is λ. ff1 The first fundamental frequency light and the seed light from the second LD pump source 6 are injected into the second nonlinear crystal 5, with an excitation wavelength of λ. ff2 The second fundamental frequency light, the two fundamental frequency lights are integrated into one channel by the M1 coupling mirror 4, and after being reflected by the second reflecting mirror 3, they are incident on the sum-frequency crystal 1 to generate sum-frequency laser with a wavelength of λ. sf It can be expressed by formula (1):

[0070] λ sf =λ ff1 λ ff2 / (λ ff1 +λ ff2 ) Formula (1)

[0071] Furthermore, the crystal and frequency process optical path, such as Figure 2 As shown, the first reflecting mirror 2 for λ ff1 , λ ff2 and λ sf High reflectivity at the same wavelength; second reflecting mirror 3 for λ ff1 , λff2 High reflectivity at the same wavelength, for λ sf High wavelength transmission means that the generated sum-frequency laser is output by the second reflecting mirror 3.

[0072] Furthermore, a schematic diagram of the antireflection film structure on both sides of the LBO crystal is shown below. Figure 1 As shown, the design of the antireflective films on both sides requires not only high transmittance but also low absorptivity to reduce the destructive effects of photothermal coupling. For example... Figure 2 As shown, the incident fundamental frequency light is incident on the LBO crystal through the anti-reflection film structure of the first side 11. The generated sum-frequency laser is either reflected by the anti-reflection film structure of the second side 12 or at the first reflector 2, and then output through the anti-reflection film structure of the first side 11 and the second reflector 3.

[0073] Example 2

[0074] Based on Example 1, this example provides a specific implementation method, the specific process of which is as follows:

[0075] 1) The wavelength λ of the first fundamental frequency light ff1 The wavelength λ of the second fundamental frequency light is 1064nm. ff2 The output wavelength λ of the sum-frequency laser is 1319nm. sf It is 589nm;

[0076] 2) The refractive indices of the selected high and low refractive index film materials are respectively as follows: Figure 3 and Figure 4 As shown, the extinction coefficient of the Ta2O5 thin film at the sum-frequency output wavelength is 1×10⁻⁶. -4 The extinction coefficient of the SiO2 thin film at the sum-frequency output wavelength is 1×10⁻⁶. -5 ;

[0077] 3) For the membrane structure Sub / x 10 Hx 20 Lx 30 Hx 40 L / Air and Sub / x 50 Hx 60 Lx 70 Hx 80 L / Air was optimized using a genetic algorithm with 900nm as the reference wavelength. The initial optimization results were Sub / 0.5704H 0.3230L 1.4825H1.3544L / Air and Sub / 0.5704H 0.3230L 1.4825H 1.3544L / Air, i.e., x 11 ~x 41 and x 51 ~x 81The values ​​were equal, at 0.5704, 0.3230, 1.4825, and 1.3544 respectively, with an overall absorption rate of 1327 ppm and a first absorption rate of 669 ppm.

[0078] 4) Focusing on optimizing the absorbance of the first initial film structure, specifically Sub / 0.5704H 0.3230L 1.4825H 1.3544L / Air, the incident medium was changed to LBO crystal material, and the exit medium was changed to air. The calculated result was Sub / 0.5401H0.3368L 1.4772H 1.3498L / Air, i.e., x 12 ~x 42 The values ​​were 0.5401, 0.3368, 1.4772, and 1.3498, respectively, and the first absorption rate decreased to 648 ppm after optimization;

[0079] 5) The absorbance control of the second initial film structure Sub / 0.5704H 0.3230L 1.4825H 1.3544L / Air was optimized again, limiting the transmittance range at 589nm to between 70% and 80%. The genetic algorithm was used for optimization, and the calculated result was Sub / 0.4888H 0.4650L 1.0331H 1.4385L / Air;

[0080] 6) The final membrane system design result is x 53 =0.4888, x 63 =0.4650, x 73 =1.0331, x 83 =1.4385, x 13 =0.5401, x 23 =0.3368, x 33 =1.4772, x 43 =1.3498;

[0081] The final experimental results are as follows: the overall transmittance of the system at the fundamental frequency light at 1064 nm and 1319 nm is 99.63% and 99.60%, respectively; the transmittance of the sum frequency light on the first side at 589 nm is 99.87%.

[0082] The overall absorption rate was reduced from 1327 ppm using the traditional design method to 840 ppm, and the first absorption rate on the first side was reduced from 669 ppm to 462 ppm, achieving the expected results.

[0083] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. The above descriptions are only preferred embodiments of this application. It should be noted that due to the limitations of written expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of this invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of this application.

Claims

1. A method for optimizing the film thickness coefficient of laser and frequency devices, characterized in that, The laser sum-frequency device includes a sum-frequency crystal (1), which has a first side (11) and a second side (12) opposite to each other; both the first side (11) and the second side (12) are provided with anti-reflection film structures, which include four film layers, and the four film layers are alternately arranged first film material and second film material along the direction away from the sum-frequency crystal (1), and the refractive index of the first film material is higher than that of the second film material; The thickness coefficient of each of the thin film layers is obtained through the following steps: Obtain the incident fundamental frequency light and the initial set thickness coefficients of each thin film layer; Using the initial set thickness coefficient as the initial value, the thickness coefficient of each thin film layer is optimized so that the transmittance of the laser sum-frequency device to the incident fundamental frequency light and the emitted laser is within their respective preset transmittance ranges, and the absorption rate at the wavelength of the emitted sum-frequency laser is within a second preset range. The emitted sum-frequency laser is obtained by irradiating the laser sum-frequency device with the incident fundamental frequency light. The total thickness of each film layer in both antireflective film structures is less than the output wavelength of the emitted and frequency-controlled laser. The method for optimizing the thickness coefficient of each thin film layer using the initially set thickness coefficient as the initial value specifically includes the following steps: The transmittance preset ranges of the incident fundamental frequency light and the emitted laser are obtained, and the first preset thickness coefficient of each thin film layer is obtained with the transmittance preset range as the optimization target. Based on the first set thickness coefficient of each of the thin film layers, the absorption rate of the first side surface along the crystal emission direction at the emission frequency laser wavelength is calculated; The second preset range of the absorptivity at the emitted and frequency laser wavelengths is obtained, and the second preset range is used as the optimization target to obtain the second preset thickness coefficient of each film layer of the antireflective film structure on the first side. Based on the second predetermined thickness coefficient of each of the thin film layers of the antireflection film structure on the first side, the absorption rate of the second side at the emitted laser wavelength along the crystal incident or emitted direction is calculated. Using the second preset range as the optimization target, the second preset thickness coefficient of each film layer of the antireflective film structure on the second side is obtained; The crystal emission direction is with the sum-frequency crystal (1) as the incident medium and air as the emission medium; the crystal incident direction is with the sum-frequency crystal (1) as the emission medium and air as the incident medium.

2. The method for optimizing the film thickness coefficient of laser and frequency devices according to claim 1, characterized in that: The method for acquiring incident fundamental frequency light specifically includes the following steps: The first fundamental frequency light and the second fundamental frequency light are acquired, and the first fundamental frequency light and the second fundamental frequency light are integrated into one path through the coupling mirror (4) to become the incident fundamental frequency light.

3. The method for optimizing the film thickness coefficient of laser and frequency devices according to claim 2, characterized in that: The method for obtaining the first fundamental frequency light specifically includes the following steps: The seed light of the first LD pump source (9) is injected into the first nonlinear crystal (7) to excite the first fundamental frequency light.

4. The method for optimizing the film thickness coefficient of laser and frequency devices according to claim 2, characterized in that: The method for obtaining the first fundamental frequency light specifically includes the following steps: The seed light from the second LD pump source (6) is injected into the second nonlinear crystal (5) to excite the second fundamental frequency light.

5. The method for optimizing the film thickness coefficient of laser and frequency devices according to claim 2, characterized in that: The first fundamental frequency light and the second fundamental frequency light are integrated into one path by the coupling mirror (4), and then reflected back by the second reflecting mirror (3) to become the incident fundamental frequency light.

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