Parameter Screening Method for Femtosecond Laser Machined Nanobubble Structures

Abstract

The present invention relates to the field of femtosecond microfabrication in optical technology, and discloses a method for screening parameters of a femtosecond laser processed nanobubble structure to ensure the reliability of the processed nanobubble structure. The method includes: in a first polarization direction, screening out a parameter combination of the nanobubble through deploying a corresponding optical path system, where the parameter combination includes: spot size, line spacing size, repetition frequency, single pulse energy, peak power density, pulse density, and pulse width; then when the first polarization direction is successively changed to other polarization directions, while keeping the line spacing size, spot size, repetition frequency, peak power density, and pulse width in the parameter combination with the largest target wavelength and delay amount determined in the first polarization direction unchanged, screening out a parameter combination of single-layer nanobubbles corresponding to other polarization directions of the same optical path system by adjusting the pulse density and / or single pulse energy.

Description

Technical Field

[0001] The present invention relates to the field of femtosecond micromachining in optical technology, and particularly relates to a method for screening parameters of femtosecond laser processing of nano-bubble structures. Background Art

[0002] In 1996, scientists found that irradiating transparent materials with femtosecond lasers would change the refractive index of the materials. They further utilized this property to fabricate waveguides in fused silica using femtosecond lasers. At this stage, the modification of fused silica by femtoseconds remained in the isotropic stage. In 1999, it was also found that femtosecond lasers acting on fused silica could cause anisotropic refractive index changes in fused silica to achieve birefringence. This discovery made more applications such as phase modulation and data storage possible. Since 2003, after it was further discovered that this birefringence modification originated from the nano-layered structures formed in fused silica and was called nano-grating (Nano grating), many research groups have carried out research on the application and principle of this technology. For example, using nano-grating structures to fabricate geometric phase elements, and achieving high-density data storage with multi-layer nano-gratings.

[0003] The exploration of the formation principle of nano-gratings has also enabled people to further understand the formation mechanism of nano-gratings. Taylor's research revealed that the formation process of nano-gratings is mainly as follows:

[0004] First of all, the laser will be absorbed by the defects (Nonbridging oxygen hole centers) in fused silica to form spherical small bubbles. The spherical small bubbles will grow along the plane perpendicular to the polarization direction of the laser in the laser polarization electric field to form oblate small bubbles. As the growth in the vertical polarization plane progresses, the small bubbles gradually connect and form a sheet-like structure, that is, nano-grating. This process has also been confirmed under an electron scanning microscope.

[0005] Thereby, the intermediate state products in the formation process of nano-gratings have also attracted the interest of scientific researchers. When the initially formed spherical small bubble modification region is elongated to form an oblate structure, the anisotropic structure already endows fused silica with birefringence properties. Moreover, it has a high transmittance characteristic that nano-gratings do not have, and can still maintain a relatively high transmittance especially in the ultraviolet wavelength range. This gives it great application potential in the ultraviolet wavelength range.

[0006] The nanoporous structure is an intermediate state before the formation of a nanograting structure by femtosecond laser acting on fused silica, which means that the processing parameter window for modifying fused silica is much smaller than that of nanogratings. Too low laser power density means that quartz with a bandgap width of 9 eV (electron volt) is completely transparent. Sufficiently high power density (focusing, high pulse energy) is required to trigger the multi-electron absorption process so that the defects in the fused silica can absorb the laser to achieve modification. On the one hand, too high power density may directly damage the fused silica, and on the other hand, it may also cause the modified structure to quickly transition to the nanograting structure. In addition, the repetition frequency of the femtosecond laser also determines the cooling time between adjacent laser pulses in the fused silica and the corresponding thermal accumulation effect. The numerous processing parameters are interrelated, making the nanoporous processing quite challenging. Summary of the Invention

[0007] The object of the present invention is to disclose a method for screening parameters for femtosecond laser processing of nanoporous structures to ensure the reliability of the processed nanoporous structures.

[0008] To achieve the above object, the method disclosed by the present invention includes:

[0009] Step S0: Deploy an optical path system, which includes: a femtosecond laser light source capable of adjusting the pulse width, a power attenuation module capable of adjusting the single-pulse energy, a polarization control module, an objective lens, and a three-axis displacement stage for fixing the sample; the power attenuation module is deployed between the laser light source and the polarization control module, the polarization control module is used to adjust the polarization direction of the linearly polarized light output from the attenuated beam to the objective lens, and the three-axis displacement stage is used to sequentially switch the three-dimensional coordinates of the spot focused by the objective lens inside the sample;

[0010] Step S1: Set the first polarization direction of the linearly polarized light emitted by the objective lens;

[0011] Step S2: Adjust the optical path to determine the polarization direction to be calibrated of the linearly polarized light emitted by the objective lens and make the extinction ratio of the linearly polarized light emitted by the objective lens meet the requirements; then measure the diameter D of the spot below the objective lens, and determine the line pitch generated by the displacement of the three-axis displacement stage in the horizontal direction according to the spot diameter. The line pitch includes the row pitch and the column pitch, and the value range of the line pitch is D / 5 to D / 4;

[0012] Step S3: Measure the average power of the spot, and determine the single-pulse energy and peak power density of the laser according to the average power of the spot and the repetition frequency of the femtosecond laser;

[0013] Step S4: Adjust the power attenuation module and the laser light source to make the peak power density of the spot focused by the objective lens be 3 - 18 TW / cm 2Interval;

[0014] Step S5: Adjust the pulse density in the range of 50 p / um - 300 p / um; where the pulse density = femtosecond laser repetition frequency / displacement stage scanning speed;

[0015] Step S6: Change the specific values of the parameters corresponding to Step S2 to Step S5 within the corresponding ranges, and screen out each parameter combination of single-layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P-polarization and S-polarization directions < 5%. Among them, the diffraction efficiency = transmittance of the modified area / transmittance of the unmodified area; the polarization transmission difference between the P-polarization and S-polarization directions = transmittance of the P-polarized light emission - transmittance of the S-polarized light emission; each of the said parameter combinations includes: spot size, line spacing size, repetition frequency, single-pulse energy, peak power density, pulse density, and pulse width.

[0016] Optionally, the method of the present invention further includes:

[0017] Step S7: Determine the parameter combination with the largest delay amount corresponding to the first polarization direction from at least two parameter combinations screened in Step S6; then determine the layer spacing and number of layers of the nanobubbles corresponding to the half-wave delay amount for constructing the first-wavelength light beam currently emitted by the laser light source according to the parameter combination with the largest delay amount.

[0018] Furthermore, the method of the present invention further includes:

[0019] Step S8: Change the first polarization direction in Step S1 one by one to other polarization directions, and then, during the process of performing the series of steps of Step S2 to Step S6, keep the line spacing size, spot size, repetition frequency, peak power density, and pulse width in the parameter combination with the largest delay amount and the target wavelength determined in Step S7 unchanged, adjust the pulse density and / or single-pulse energy, and screen out at least one parameter combination of single-layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P-polarization and S-polarization directions < 5%.

[0020] Preferably, when there are at least two parameter combinations of single-layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P-polarization and S-polarization directions < 5% for any other polarization direction, perform a weighted operation on the detected diffraction efficiency and the polarization transmission difference between the P-polarization and S-polarization directions and then sort, and determine the optimal parameter combination according to the sorting result.

[0021] Furthermore, the method of the present invention further includes:

[0022] Step S9: Change the laser light source with the output beam of the first wavelength to the laser light source with the output beam of the second wavelength. During the process of executing the series of steps corresponding to steps S2 to S6, keep the line pitch size, spot size, repetition frequency, peak power density, and pulse width in the parameter combination with the largest determined delay amount in step S7 unchanged, and adjust the pulse density and / or single-pulse energy to screen out each parameter combination of the single-layer nanobubble with a diffraction efficiency > 95% and a polarization transmission difference between the P polarization and S polarization directions < 5%.

[0023] Step S10: Determine the parameter combination with the largest delay amount corresponding to the first polarization direction from at least two parameter combinations screened in step S9; then determine the layer pitch and number of layers for constructing the nanobubble with the half-wave delay amount corresponding to the second wavelength according to the parameter combination with the largest delay amount.

[0024] Step S11: Calibrate the parameter combinations of at least one single-layer nanobubble with a diffraction efficiency > 95% and a polarization transmission difference between the P polarization and S polarization directions < 5% corresponding to the second wavelength in other polarization directions by the same method of adjusting the pulse density as in step S8.

[0025] Preferably, the value range of the spot size D is 6 - 8 um.

[0026] The present invention has the following beneficial effects:

[0027] 1. During the detection of the prepared sample, when the polarization transmission difference between the P light and S light increases, the nanobubble structure will transform into a nanograting structure; by making the polarization transmission difference between the P polarization and S polarization directions < 5% in the present invention, reliable parameters for processing nanobubbles can be simply and efficiently screened out.

[0028] 2. The diffraction efficiency is closely related to the overall performance of the nanobubble structure. By screening out the prepared samples with a diffraction efficiency > 95% in the prepared samples, parameter combinations for processing nanobubbles with stable performance can be reliably obtained.

[0029] 3. The parameter ranges such as the pulse density, peak power density, and line pitch are determined. According to the configuration attributes of the laser light source, power attenuation module, and three-axis displacement stage, the specific values of parameters such as the pulse density, pulse width, peak power density, and line pitch can be flexibly determined and changed, so that the parameter screening method of the present invention can be screened within an effective range, improving the screening efficiency.

[0030] Next, the present invention will be further described in detail with reference to the accompanying drawings. Description of the Drawings

[0031] The accompanying drawings, which form a part of this application, are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0032] Figure 1 is a structural block diagram of an optical path system disclosed in an embodiment of the present invention. Detailed implementation manners

[0033] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways defined and covered by the claims.

[0034] Embodiment 1

[0035] This embodiment discloses a method for screening parameters of a femtosecond laser processed nanobubble structure, including:

[0036] Step S0: Deploy an optical path system.

[0037] The optical path system in this step includes: a femtosecond laser light source capable of adjusting the pulse width, a power attenuation module capable of adjusting the single pulse energy, a polarization control module, an objective lens, and a three-axis displacement stage for fixing the sample; the power attenuation module is deployed between the laser light source and the polarization control module, and the polarization control module is used to adjust the polarization direction of the linearly polarized light output from the attenuated beam to the objective lens, and the three-axis displacement stage is used to sequentially switch the three-dimensional coordinates of the spot focused by the objective lens inside the sample.

[0038] Femtosecond (abbreviated as fs) is a unit of measurement for the length of time. 1 femtosecond is one quadrillionth of a second. The femtosecond laser light source used in this embodiment usually has the following characteristics: First, the duration of the femtosecond laser is extremely short, only a few femtoseconds, which is thousands of times shorter than the shortest pulse obtained by using electronic methods and is the shortest pulse that humans can obtain under experimental conditions; second, the femtosecond laser has a very high instantaneous power, which can reach petawatts, hundreds of times more than the total power generation of the world; third, the femtosecond laser can be focused into a spatial region smaller than the diameter of a hair, making the intensity of the electromagnetic field several times higher than the force of the atomic nucleus on its surrounding electrons, and many of these extreme physical conditions do not exist on Earth and cannot be obtained by other methods.

[0039] An optional optical path system structure is as Figure 1As shown in the figure, the femtosecond laser passes through the polarizer P1, and its polarization state is converted into linearly polarized light. Then it passes through the power attenuation module, which consists of a half-wave plate (HWP), a polarization beam splitting cube (PBS), and a light block (Block) that absorbs the S light. By rotating the angle of the HWP, the polarization azimuth angle of the laser can be changed to achieve attenuation. Finally, after passing through the PBS, the power of the femtosecond laser can be changed. The light emitted from the PBS is P light (i.e., the azimuth angle is 0°, and this azimuth angle takes the polarization direction of the beam emitted from P1 as 0°). After passing through the mirror, the original polarization ellipticity can be maintained to the greatest extent. Then it passes through the polarization control module for optical rotation, which consists of electro-optic devices such as electro-optic crystals (EOM) / liquid crystal devices and a quarter-wave plate (QWP). And the 0° fast axis of the QWP and the 0° fast axis of the EOM form a 45° angle, which can make the optical rotation angle range from 0 to 180°. Then it is focused into the sample (Sample) through the objective lens (OBJ). The sample is a hard and brittle material, such as N-BK7, sapphire, fused silica glass, etc. The sample is placed on the XYZ displacement stage (XYZ Stage), and the movement is controlled through the XYZ displacement stage.

[0040] In Figure 1 , the power attenuation module is used to finely adjust the single-pulse energy and peak power density. Among them, the real-time performance of switching the polarization direction in a rotational manner is relatively slow. In actual operation, the polarization control module is mainly used to adjust the polarization direction of the beam emitted by the objective lens and can compensate for the influence on the polarization direction generated by the aforementioned power attenuation module. Thereby, it effectively avoids the situation of attending to one thing and losing another between the parameters affected by attenuation and the adjustment of the polarization direction, and provides a basis for still using some calibration results to switch the polarization direction in the subsequent step S8 to improve the overall calibration efficiency.

[0041] Step S1: Set the first polarization direction of the linearly polarized light emitted by the objective lens.

[0042] This step can be specifically adjusted through the Figure 1 polarization control module in. If necessary, it can also be measured by a polarization measuring instrument placed under the objective lens.

[0043] Step S2: Adjust the optical path to determine the polarization direction to be calibrated of the linearly polarized light emitted by the objective lens and make the extinction ratio of the linearly polarized light emitted by the objective lens meet the requirements. Then measure the diameter D of the light spot below the objective lens, and determine the line distance generated by the displacement of the three-axis displacement stage in the horizontal direction according to this light spot diameter. The line distance includes the row distance and the column distance, and the value range of the line distance is from D / 5 to D / 4.

[0044] Optionally, this step can be measured by a beam quality analyzer placed under the objective lens. In this embodiment, D = 4 / π * λ * F / Din, where λ is the laser wavelength, F is the focal length of the objective lens, and Din is the spot size incident on the objective lens. Preferably, the range of the spot diameter in this embodiment is 6-8um.

[0045] During the calibration process, the nanobubbles can adopt a uniform distribution state. The row pitch is the distance between adjacent two rows of nanobubble structures, which is related to the period and rate of the Y-axis direction of the three-axis displacement stage; the column pitch is the distance between adjacent two nanobubble structures in the same row, that is, the distance between adjacent two columns of nanobubble structures, which is related to the period and rate of the X-axis direction of the three-axis displacement stage. It should be noted that: too small line pitch is also likely to cause the nanobubble structure to become a nanograting structure; this step provides an effective range for the calibration of the nanobubble structure by selecting a reasonable line pitch range.

[0046] Step S3, measure the average power of the spot, and determine the single-pulse energy and peak power density of the laser according to the average power of the spot and the repetition frequency of the femtosecond laser.

[0047] In this step, the average power of the spot can be measured by a power meter placed under the objective lens. Among them, the average power of the laser is denoted as P avg , then the single-pulse energy S = P avg / R, where R is the repetition frequency of the femtosecond laser; the peak power density P density = P peak / (π*(D / 2)2) = S / PW / (π*(D / 2)2) = P avg / R / PW / (π*(D / 2)2), where P peak is the peak power; PW is the femtosecond laser pulse width (abbreviated as pulse width), and its laser pulse width range is usually 200-600fs.

[0048] Step S4, adjust the power attenuation module and the laser light source so that the peak power density of the focused spot of the objective lens is in the range of 3-18TW / cm 2 interval.

[0049] In this step, after the interval range of the peak power density is determined, based on the relationship between the parameters in step S3, a reasonable value range of the single-pulse energy can be obtained.

[0050] Step S5, adjust the pulse density, in the range of 50p / um - 300p / um; where the pulse density = the repetition frequency of the femtosecond laser / the scanning speed of the displacement stage.

[0051] In this step, based on the fact that in the actual mass production process, the laser repetition frequency is usually kept constant. Preferably, during the calibration process, the pulse density is also preferably adjusted only by the scanning speed of the displacement stage.

[0052] Corresponding to the subdivision of the line pitch in step S1 into the row pitch and the column pitch, the pulse density in this step is also divided into the pulse density in the X-axis direction and the pulse density in the Y-axis direction.

[0053] Step S6: Change the specific values of the parameters corresponding to steps S2 to S5 within the corresponding ranges, and screen out each parameter combination of the single-layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P-polarization and S-polarization directions < 5% in the prepared sample, where the diffraction efficiency = the transmittance of the modified area / the transmittance of the unmodified area; the polarization transmission difference between the P-polarization and S-polarization directions = the transmittance of the P-polarized light emitted - the transmittance of the S-polarized light emitted; each of the parameter combinations includes: spot size, line pitch size, repetition frequency, single-pulse energy, peak power density, pulse density, and pulse width.

[0054] Therefore, this embodiment has the following beneficial effects:

[0055] 1. During the detection of the prepared sample, when the polarization transmission difference between the P-light and S-light increases, the nanobubble structure will transform into a nanograting structure; by making the polarization transmission difference between the P-polarization and S-polarization directions < 5% in the present invention, reliable parameters for processing nanobubbles can be simply and efficiently screened out.

[0056] 2. The diffraction efficiency is closely related to the overall performance of the nanobubble structure. By screening out the prepared samples with a diffraction efficiency > 95% in the prepared sample, a parameter combination for processing nanobubbles with stable performance can be reliably obtained.

[0057] 3. The parameter ranges such as the pulse density, peak power density, and line pitch are determined. According to the configuration attributes of the laser light source, power attenuation module, and three-axis displacement stage, the specific values of the pulse density, pulse width, peak power density, line pitch, etc. can be flexibly determined and changed, so that the parameter screening method of the present invention can be screened within an effective range, improving the screening efficiency.

[0058] Embodiment 2

[0059] On the basis of Embodiment 1, this embodiment further includes the following steps:

[0060] Step S7: Determine the parameter combination with the largest delay amount corresponding to the first polarization direction from at least two parameter combinations screened in step S6; then determine the layer pitch and the number of layers of the nanobubbles that construct the half-wave delay amount corresponding to the first wavelength light beam currently emitted by the laser light source according to the parameter combination with the largest delay amount.

[0061] In this step, number of layers = half - wave / delay amount per single layer; therefore, the larger the delay amount of a single - layer nanobubble, the smaller the number of layers required for processing to construct a half - wave, thus improving the processing efficiency.

[0062] Example 3

[0063] Based on the above Example 2, in this example, considering that in the geometric phase element actually prepared, the polarization directions corresponding to the nanobubble structures between layers may be different, and the polarization directions corresponding to the nanobubble structures within the same layer may also be different. For this reason, the method of this example further includes:

[0064] Step S8: Change the first polarization direction in Step S1 to other polarization directions one by one. Then, during the process of performing the series of steps from Step S2 to Step S6, keep the line distance size, spot size, repetition frequency, peak power density, and pulse width in the parameter combination with the largest target wavelength and delay amount determined in Step S7 unchanged, and adjust the pulse density and / or single - pulse energy to screen out at least one parameter combination of single - layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P - polarization and S - polarization directions < 5%.

[0065] Preferably, when there are at least two parameter combinations of single - layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P - polarization and S - polarization directions < 5% for any other polarization direction, perform a weighted operation on the detected diffraction efficiency and the polarization transmission difference between the P - polarization and S - polarization directions and then sort them, and determine the optimal parameter combination according to the sorting result.

[0066] Example 4

[0067] Based on the above three examples, this example further improves the resource utilization rate of the optical path system and some calibration results. For this reason, the method of this example further includes:

[0068] Step S9: Change the laser light source with the output beam of the first wavelength to a laser light source with the output beam of the second wavelength. Then, during the process of performing the series of steps corresponding to Step S2 to Step S6, keep the line distance size, spot size, repetition frequency, peak power density, and pulse width in the parameter combination with the largest delay amount determined in Step S7 unchanged, and adjust the pulse density and / or single - pulse energy to screen out each parameter combination of single - layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P - polarization and S - polarization directions < 5%.

[0069] Step S10: Determine the parameter combination with the largest delay amount corresponding to the first polarization direction from at least two parameter combinations screened in Step S9; then determine the layer distance and number of layers for constructing the nanobubble with the half - wave delay amount corresponding to the second wavelength according to the parameter combination with the largest delay amount.

[0070] Step S11: Calibrate the parameter combinations of at least one monolayer nanobubble with a diffraction efficiency > 95% and a polarization transmission difference between the P-polarization and S-polarization directions < 5% corresponding to the second wavelength in other polarization directions by the same method of adjusting the pulse density as in Step S8.

[0071] Accordingly, in the present invention, when the laser light source changes or the laser wavelength emitted by the adjustable laser light source changes, it is necessary to re-calibrate the remaining parameters with reference to the similar methods and partial calibration results in the above three embodiments.

[0072] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for screening parameters of a femtosecond laser processed nano-bubble structure, characterized in that, Including: Step S0: Deploy an optical path system, which includes a femtosecond laser light source capable of adjusting the pulse width, a power attenuation module capable of adjusting the single-pulse energy, a polarization control module, an objective lens, and a three-axis displacement stage for fixing the sample. The power attenuation module is deployed between the laser light source and the polarization control module. The polarization control module is used to adjust the polarization direction of the linearly polarized light output from the attenuated beam to the objective lens. The three-axis displacement stage is used to sequentially switch the three-dimensional coordinates of the spot focused by the objective lens inside the sample. Step S1: Set the first polarization direction of the linearly polarized light emitted by the objective lens. Step S2: Adjust the optical path to determine the polarization direction to be calibrated of the linearly polarized light emitted by the objective lens and make the extinction ratio of the linearly polarized light emitted by the objective lens meet the requirements. Then measure the diameter D of the spot below the objective lens, and determine the line distance generated by the displacement of the three-axis displacement stage in the horizontal direction according to the spot diameter. The line distance includes the row distance and the column distance, and the value range of the line distance is D / 5 to D / 4. Step S3: Measure the average power of the spot, and determine the single-pulse energy and peak power density of the laser according to the average power of the spot and the femtosecond laser repetition frequency. Step S4, adjust the power attenuation module and the laser light source so that the peak power density of the focused spot of the objective lens is in the range of 3-18 TW / cm 2 interval; Step S5: Adjust the pulse density, with a range from 50 p / um - 300 p / um; where the pulse density = femtosecond laser repetition frequency / displacement stage scanning speed. Step S6: Change the specific values of the parameters corresponding to Step S2 to Step S5 within the corresponding ranges, and screen out various parameter combinations for preparing a single-layer nanobubble with a diffraction efficiency > 95% and a polarization transmission difference between the P polarization and S polarization directions < 5%. Among them, the diffraction efficiency = transmittance of the modified area / transmittance of the unmodified area; the polarization transmission difference between the P polarization and S polarization directions = transmittance of the P-polarized light output - transmittance of the S-polarized light output. Each of the parameter combinations includes: spot size, line distance size, repetition frequency, single-pulse energy, peak power density, pulse density, and pulse width.

2. The method according to claim 1, characterized in that, Also including: Step S7: Determine the parameter combination with the largest delay corresponding to the first polarization direction from at least two parameter combinations screened in Step S6; then determine the layer distance and number of layers of the nanobubble corresponding to the half-wave delay amount for constructing the first-wavelength beam currently emitted by the laser light source according to the parameter combination with the largest delay.

3. The method according to claim 2, wherein Also including: Step S8: Change the first polarization direction in Step S1 to other polarization directions one by one. Then, during the process of performing the series of steps from Step S2 to Step S6, keep the line distance size, spot size, repetition frequency, peak power density, and pulse width in the parameter combination with the largest delay determined in Step S7 unchanged, adjust the pulse density and / or single-pulse energy, and screen out at least one parameter combination for a single-layer nanobubble with a diffraction efficiency > 95% and a polarization transmission difference between the P polarization and S polarization directions < 5%.

4. The method according to claim 3, characterized in that Also including: When there are at least two parameter combinations of single-layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P-polarization and S-polarization directions < 5% in any other polarization direction, after weighted calculation and sorting based on the detected diffraction efficiency and the polarization transmission difference between the P-polarization and S-polarization directions, the optimal parameter combination is determined according to the sorting result.

5. The method according to any one of claims 1 to 4, characterized in that It further includes: Step S9: Change the laser source with the output beam of the first wavelength to a laser source with the output beam of the second wavelength. During the process of executing the series of steps corresponding to Step S2 to Step S6, keep the line pitch size, spot size, repetition frequency, peak power density, and pulse width in the parameter combination with the largest delay amount determined in Step S7 unchanged, and adjust the pulse density and / or single-pulse energy to screen out each parameter combination of single-layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P-polarization and S-polarization directions < 5%. Step S10: Determine the parameter combination with the largest delay amount corresponding to the first polarization direction from at least two parameter combinations screened in Step S9; then determine the layer pitch and number of layers for constructing the nanobubbles with the half-wave delay amount corresponding to the second wavelength according to the parameter combination with the largest delay amount. Step S11: Calibrate the parameter combinations of single-layer nanobubbles with a diffraction efficiency > 95% and a polarization transmission difference between the P-polarization and S-polarization directions < 5% corresponding to the second wavelength in other polarization directions by the same method of adjusting the pulse density as in Step S8.

6. The method according to any one of claims 1 to 4, characterized in that, The specific calculation formula for the value of the spot size D is: D = 4 / π * λ * F / Din, where λ is the laser wavelength, F is the objective lens focal length, and Din is the spot size incident on the objective lens.

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