Femtosecond laser manufacturing parameter real-time monitoring system based on super-lens confocal focusing

Abstract

The invention provides a femtosecond laser manufacturing parameter real-time monitoring system based on super-lens confocal focusing, the system comprises a femtosecond laser processing light path system and a spectral pupil differential confocal axial monitoring light path system, the femtosecond laser processing light path system adopts a first wavelength light wave to process the surface of a sample; the spectral pupil differential confocal axial monitoring light path system monitors the axial position of the surface of the sample by adopting a second wavelength light wave; the femtosecond laser processing light path system and the spectral pupil differential confocal axial monitoring light path system are focused on the surface of a sample by adopting a super lens, the surface of the super lens is composed of nano-pillar arrays with different sizes and same azimuth angles, so that a first wavelength light wave and a second wavelength light wave are focused on the same plane, the first wavelength light wave has a long focal depth, and the second wavelength light wave has a long focal depth. The second wavelength light wave has a short focal depth. According to the invention, femtosecond laser processing can be monitored in real time, the anti-interference capability in the processing process can be improved, and the monitoring precision of the axial position is improved.

Description

Technical Field

[0001] The present invention relates to the field of optical technologies, and in particular, to a real-time monitoring system for femtosecond laser manufacturing parameters based on superlens confocal focusing. Background Art

[0002] Femtosecond laser manufacturing has extremely important application prospects in fields such as scientific frontiers and engineering technologies due to its advantages of wide material adaptability, high processing accuracy, ability to write three-dimensional structures of arbitrary shapes, and suitability for processing on curved substrates.

[0003] Precise monitoring of the morphological performance parameters of the processed sample during femtosecond laser manufacturing is the key to realizing femtosecond laser cross-scale micro-nano manufacturing. Femtosecond laser manufacturing based on point processing and long processing time generally has the following problems: non-linear removal makes the axial removal inaccurate; long-time drift makes the processing system unstable; non-stable point processing makes the processing scale small. Integrating laser manufacturing and monitoring is the main research focus to overcome the above problems. In the monitoring of the laser manufacturing process, accurate judgment of the position of the focused spot, real-time monitoring and detection such as automatic focusing and sample drift are crucial for three-dimensional micro-nano processing, and to a certain extent, determine the axial processing feature size.

[0004] However, in the prior art, the femtosecond laser manufacturing and monitoring system based on a classical focusing objective lens still has the following problems: (1) When a micro-objective lens with a large numerical aperture is used in the manufacturing and monitoring system, the foci of the processing beam and the monitoring beam will shift. Manual focusing is required during monitoring, and real-time monitoring of the processing process cannot be carried out. (2) During femtosecond laser manufacturing, if the focal depth of the processing beam is small, slight jitter of the translation stage will affect the processing quality of the processed sample, resulting in deformation or breakage of the sample. Therefore, how to ensure a long focal depth for the processing beam and a short focal depth for the monitoring beam at the same time is also the key to improving the anti-interference ability of the processing process and obtaining high-precision manufacturing and monitoring simultaneously. Summary of the Invention

[0005] In view of the above problems, the present invention provides a real-time monitoring system for femtosecond laser manufacturing parameters based on superlens confocal focusing to overcome the above problems.

[0006] The present invention provides a real-time monitoring system for femtosecond laser manufacturing parameters based on superlens confocal focusing. The system includes a femtosecond laser processing optical path system and a split-pupil differential confocal axial monitoring optical path system. The femtosecond laser processing optical path system processes the surface of a sample using light waves of a first wavelength; the split-pupil differential confocal axial monitoring optical path system monitors the axial position of the surface of the sample using light waves of a second wavelength. Among them, the femtosecond laser processing optical path system and the split-pupil differential confocal axial monitoring optical path system jointly use a superlens to focus on the surface of the sample. The surface of the superlens is composed of a nano-column array with different sizes and the same azimuth angle, so that the light waves of the first wavelength and the second wavelength are focused on the same plane, and the light waves of the first wavelength have a long depth of focus, and the light waves of the second wavelength have a short depth of focus.

[0007] Further, the femtosecond laser processing optical path system includes a femtosecond laser, a spatio-temporal shaping module, a two-dimensional scanner, and the superlens sequentially arranged along the optical path of the light waves of the first wavelength. The femtosecond laser injects the light waves of the first wavelength into the spatio-temporal shaping module. The spatio-temporal shaping module performs shaping on the light waves of the first wavelength in terms of time and space, and injects the shaped light waves of the first wavelength into the two-dimensional scanner. The two-dimensional scanner controls the light waves of the first wavelength to scan the surface of the sample according to the pattern to be processed, so that the light waves of the first wavelength emitted by the two-dimensional scanner are focused on the surface of the sample through the superlens, so as to perform femtosecond laser processing on the surface of the sample.

[0008] Further, the split-pupil differential confocal axial monitoring optical path system includes a continuous laser, a first light source collimating module, a first beam splitter, a first dichroic mirror, a second beam splitter, and the superlens sequentially arranged along the incident optical path of the light waves of the second wavelength, and a split-pupil differential confocal detection module arranged on the reflection optical path of the light waves of the second wavelength; among them,

[0009] The continuous laser injects the light waves of the second wavelength into the first light source collimating module to form a parallel beam. The light waves of the second wavelength emitted by the first light source collimating module are refracted by the first beam splitter and then incident on the first dichroic mirror. The first dichroic mirror reflects the light waves of the second wavelength to the second beam splitter. The second beam splitter reflects the light waves of the second wavelength in a direction perpendicular to the surface of the sample. The light waves of the second wavelength reflected by the second beam splitter are focused on the surface of the sample after passing through the superlens. The light waves of the second wavelength reflected by the surface of the sample are reflected by the second beam splitter to the first dichroic mirror. The first dichroic mirror reflects the reflected light waves of the second wavelength to the first beam splitter. The first beam splitter refracts the reflected light waves of the second wavelength to the split-pupil differential confocal detection module. The split-pupil differential confocal detection module obtains a split-pupil differential confocal response curve, and the axial position of the surface of the sample is obtained according to the split-pupil differential confocal response curve.

[0010] Further, the system further includes a Raman spectroscopy detection module, which includes the metalens, a second beam splitter, a first dichroic mirror, a first focusing module, and a spectrometer disposed on the optical path of the Rayleigh light reflected from the surface of the sample.

[0011] The Rayleigh light reflected from the surface of the sample sequentially passes through the metalens, the second beam splitter, and the first dichroic mirror. The first dichroic mirror refracts the Rayleigh light reflected from the surface of the sample into the first focusing module, and the first focusing module converges the Rayleigh light reflected from the surface of the sample onto the spectrometer. The spectrometer analyzes and obtains the Raman spectral information of the surface of the sample to form the Raman spectroscopy detection module for monitoring the performance parameters of the surface of the sample.

[0012] Further, the system further includes a microscopic imaging optical path system, which includes a white light source, a third beam splitter, a fourth beam splitter sequentially arranged along the incident optical path of the third wavelength light wave, and a second focusing module and a CCD module disposed on the reflection optical path of the third wavelength light wave. The white light source emits the third wavelength light wave, and the third wavelength light wave is incident on the third beam splitter. The third beam splitter refracts the third wavelength light wave into the fourth beam splitter, and the fourth beam splitter reflects the third wavelength light wave in a direction perpendicular to the surface of the sample and focuses it on the surface of the sample through the second beam splitter and the metalens. The third wavelength light wave reflected from the surface of the sample is refracted into the fourth beam splitter through the metalens and the second beam splitter. The fourth beam splitter reflects the reflected third wavelength light wave into the third beam splitter, and the third beam splitter reflects the reflected third wavelength light wave into the second focusing module. The second focusing module converges the reflected third wavelength light wave onto the CCD module, and the CCD module determines the tilt and position of the sample.

[0013] Further, the metalens includes: a substrate and a nano-pillar array on the substrate, and the azimuth angle of each nano-pillar in the nano-pillar array is 0°, so that each nano-pillar is polarization-independent.

[0014] The nano-pillars at different positions in the nano-pillar array of the metalens independently regulate the first wavelength light wave and the second wavelength light wave, so that the first wavelength light wave satisfies the first phase distribution and the second wavelength light wave satisfies the second phase distribution; wherein,

[0015] The first phase distribution is expressed as:

[0016]

[0017] where λ 1 is the first wavelength light wave, f 1 is the focal length corresponding to λ 1 Δf 1 is the focal length difference corresponding to λ 1The corresponding depth of focus, R is the radius of the metalens, and r is the distance of each nanocylinder in the metalens plane from the center of the metalens;

[0018] The second phase distribution is expressed as:

[0019]

[0020] In the formula, λ 2 is the light wave of the second wavelength, f 2 is the focal length corresponding to λ 2 , and (x, y) is the position of each nanocylinder on the metalens in the metalens plane;

[0021] Among them, f 1 = f 2 so that the confocal planes of the light waves of the first wavelength and the second wavelength pass through the metalens, and Δf 1 is a preset value so that the light wave of the first wavelength has a preset depth of focus after passing through the metalens.

[0022] Further, each nanocylinder at each position in the nanocylinder array of the metalens is selected from a preset meta-atom response library according to the target phases corresponding to the light waves of the first wavelength and the second wavelength at the current position and a preset error calculation model, so that the errors of the phase modulation of the selected nanocylinders for the light waves of the first wavelength and the second wavelength satisfy a preset difference constraint condition; among them,

[0023] The meta-atom response library is a database of the correspondence between different geometric dimensions of the nanocylinders and the transmission coefficients corresponding to the light waves of the first wavelength and the second wavelength respectively;

[0024] The error calculation model is expressed by the following calculation formula:

[0025]

[0026] In the formula, ε is the error of the phase modulation of the nanocylinder for the light waves of the first wavelength and the second wavelength, t lr_λ1 is the transmission coefficient of the circular polarization conversion ability of the nanocylinder with different dimensions under the light wave of the first wavelength, is the target phase of the light wave of the first wavelength at the current position, t lr_λ2 is the transmission coefficient of the circular polarization conversion ability of the nanocylinder with different dimensions under the light wave of the second wavelength, is the target phase of the light wave of the second wavelength at the current position, and abs represents taking the absolute value.

[0027] Further, the geometric dimensions of the nanocylinder include the period, height, major axis length, and minor axis length. The period and height are fixed, and by changing the major axis length and minor axis length of the nanocylinder, the transmission coefficients corresponding to different geometric dimensions of the nanocylinder are obtained by simulation using the rigorous coupled-wave method.

[0028] A femtosecond laser manufacturing parameter real-time monitoring system based on hyperlens confocal focusing provided by the present invention uses a hyperlens to focus light waves of a first wavelength for femtosecond processing and light waves of a second wavelength for axial monitoring on the same plane, and enables the light waves of the first wavelength to have a long depth of focus and the light waves of the second wavelength to have a short depth of focus, so as to realize real-time axial position monitoring during the femtosecond laser processing. By increasing the depth of focus of the light waves of the first wavelength, the anti-interference ability during the processing is improved, and by reducing the depth of focus of the light waves of the second wavelength, the accuracy of axial position monitoring is improved.

[0029] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the description. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specifically gives the specific embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. In the drawings:

[0031] Figure 1 is the optical path schematic diagram of the femtosecond laser manufacturing real-time monitoring system according to the embodiment of the present invention;

[0032] Figure 2 is the detailed optical path diagram of the hyperlens in the system according to the embodiment of the present invention;

[0033] Figure 3 is the FDTD simulation intensity distribution of the xz cross-section of the hyperlens designed under the incident polarization condition according to the embodiment of the present invention, wherein,

[0034] (a) is the FDTD simulation intensity distribution when λ 1 = 780 nm;

[0035] (b) is the FDTD simulation intensity distribution when λ 2 = 633 nm;

[0036] Figure 4 is the FDTD simulation result of the long-short depth of focus confocal focusing of the processing beam and the monitoring beam according to the embodiment of the present invention, wherein,

[0037] (a) is the FDTD simulation intensity distribution of the long depth of focus when λ 1 = 780 nm;

[0038] (b) is the FDTD simulation intensity distribution of the short depth of focus when λ 2 = 633 nm;

[0039] Figure 5 is the optical path diagram of the femtosecond laser processing optical path system according to an embodiment of the present invention;

[0040] Figure 6 is the optical path diagram of the monitoring system according to an embodiment of the present invention;

[0041] Figure 7 is the pupil differential confocal response curve according to an embodiment of the present invention. Detailed implementation manners

[0042] Hereinafter, exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art.

[0043] Those skilled in the art of the present technology can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of those of ordinary skill in the art to which the present invention belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted in an idealized or overly formal sense unless specifically defined.

[0044] Refer to Figure 1 , the real-time monitoring system provided by the embodiment of the present invention includes a femtosecond laser processing optical path system 1 and a split-pupil differential confocal axial monitoring optical path system 2. Among them, the femtosecond laser processing optical path system 1 processes the surface of a sample with light waves of a first wavelength; the split-pupil differential confocal axial monitoring optical path system 2 monitors the axial position of the surface of the sample with light waves of a second wavelength. Among them, the femtosecond laser processing optical path system 1 and the split-pupil differential confocal axial monitoring optical path system 2 commonly use a metalens 5 to focus on the surface of the sample. The surface of the metalens 5 is composed of an array of nanocolumns 22 with different sizes and the same azimuth angle, so that light waves of the first wavelength and light waves of the second wavelength are focused on the same plane, and the light waves of the first wavelength have a long depth of focus, and the light waves of the second wavelength have a short depth of focus.

[0045] Among them, ensuring that light waves of the first wavelength and light waves of the second wavelength are focused on the same plane can realize real-time monitoring during the processing. Making the light waves of the first wavelength have a long depth of focus can avoid processing errors caused by slight disturbances of the platform, and the light waves of the second wavelength having a short depth of focus can improve the sensitivity of axial detection.

[0046] In a specific embodiment of the present invention, the light wave of the first wavelength is a processing beam, specifically 780 nm, and the light wave of the second wavelength is a monitoring beam, specifically 633 nm. The metalens 5 provided in the embodiment of the present invention focuses the light waves of the first wavelength and the second wavelength on the same plane, enabling real-time axial position monitoring during the femtosecond laser processing. By increasing the depth of focus of the light wave of the first wavelength, the anti-interference ability during the processing is improved, and by reducing the depth of focus of the light wave of the second wavelength, the accuracy of axial position monitoring is improved.

[0047] Referring to Figures 2 - 4 , to meet the requirements of femtosecond laser manufacturing and monitoring, in the embodiment of the present invention, a dual-wavelength and polarization-independent metalens 5 is designed for two working wavelengths of a processing beam (λ 1 : 780 nm) and a monitoring beam (λ 2 : 633 nm), aiming to focus the processing beam and the monitoring beam on the same focal plane. The designed metalens 5 of the present invention is composed of Figure 2 shown amorphous silicon nanocolumn arrays with different sizes and the same azimuth angle. Independent wavefront modulation of the processing beam and the monitoring beam is performed through the designed metalens 5.

[0048] Furthermore, each nanocolumn 22 of the metasurface provided in the embodiment of the present invention satisfies the following conditions: when circularly polarized light is incident on a nanocolumn 22 with an azimuth angle of θ, the Jones vector of the outgoing light can be expressed as:

[0049]

[0050] where the transmission coefficient t ij in which the first subscript is the outgoing polarization state and the second subscript is the incident polarization state, and E x and E y are the polarization states of the outgoing light in the x and y directions respectively.

[0051] The first term in the formula is the non-polarization conversion term, and the energy of this part of the outgoing light can be reduced by optimizing the geometric dimensions of each unit nanocolumn 22 (making the nanocolumn 22 approximately regarded as a local half-wave plate). And exp ±i2θ is the phase modulation term caused by the polarization conversion process, which can be explained by the geometric phase principle. When left / right circularly polarized light is incident on a nanocolumn 22 with an azimuth angle θ = 0° / 90°, the phase modulation generated by the counter-rotating polarization channels is the same. And any polarization state can always be decomposed into the form of superposition of left- and right-handed circular polarization components with different amplitude ratios. Therefore, by fixing the azimuth angle of each unit nanocolumn 22 at 0°, adjusting the geometric dimensions of the anisotropic nanocolumns 22 according to the required phase distribution can achieve the required wavefront modulation function under polarization-independent conditions.

[0052] Further, to satisfy the condition that the first-wavelength light wave and the second-wavelength light wave are focused on the same plane, and the depth of focus of the first-wavelength light wave is greater than that of the second wavelength, the nanocolumns 22 at different positions in the nanocolumn 22 array of the metalens 5 independently regulate the first-wavelength light wave and the second-wavelength light wave, so that the first-wavelength light wave satisfies a first phase distribution and the second-wavelength light wave satisfies a second phase distribution; wherein,

[0053] The first phase distribution is expressed as:

[0054]

[0055] In the formula, λ 1 is the first-wavelength light wave, f 1 is the focal length corresponding to λ 1 Δf 1 is the depth of focus corresponding to λ 1 R is the radius of the metalens, and r is the distance of each nanocolumn in the metalens plane from the center of the metalens;

[0056] The second phase distribution is expressed as:

[0057]

[0058] In the formula, λ 2 is the second-wavelength light wave, f 2 is the focal length corresponding to λ 2 (x, y) is the position of each nanocolumn in the metalens plane on the metalens;

[0059] wherein, f 1 = f 2 so that the first-wavelength light wave and the second-wavelength light wave are confocal after passing through the metalens, and Δf 1 is a preset value so that the first-wavelength light wave has a preset depth of focus after passing through the metalens.

[0060] Further, the nanocolumns 22 at different positions in the nanocolumn 22 array of the metalens 5 are selected from a preset superatom response library according to the target phases corresponding to the first-wavelength light wave and the second-wavelength light wave at the current position and a preset error calculation model, so that the error of the phase regulation of the selected nanocolumns for the first-wavelength light wave and the second-wavelength light wave satisfies a preset difference constraint condition; wherein, the superatom response library is a database of the corresponding relationship between different geometric sizes of the nanocolumns 22 and the transmission coefficients corresponding to the first-wavelength light wave and the second-wavelength light wave respectively constructed based on the rigorous coupled-wave method.

[0061] The error calculation model is expressed by the following calculation formula:

[0062]

[0063] In the formula, ε is the error of the phase modulation of the nanocolumn 22 for the first-wavelength light wave and the second-wavelength light wave, and t lr_λ1 is the transmission coefficient of the circular polarization conversion ability of the nanocolumns 22 with different sizes under the first-wavelength light wave, is the target phase of the first-wavelength light wave at the current position, and t lr_λ2 is the transmission coefficient of the circular polarization conversion ability of the nanocolumns with different sizes under the second-wavelength light wave, is the target phase of the second-wavelength light wave at the current position, and abs represents taking the absolute value.

[0064] The transmission coefficient of the circular polarization conversion ability can be expressed by the transmission coefficients in the linearly polarized basis vectors as:

[0065]

[0066] In the formula, i = 1 or 2, and t xx is the transmission coefficient of the linearly polarized light with the outgoing polarization state and the incident polarization state both in the x direction, and t yy is the transmission coefficient of the linearly polarized light with the outgoing polarization state and the incident polarization state both in the y direction, and t xy is the transmission coefficient of the linearly polarized light with the outgoing polarization state in the x direction and the incident polarization state in the y direction, and t yx is the transmission coefficient of the linearly polarized light with the outgoing polarization state in the y direction and the incident polarization state in the x direction.

[0067] In the specific embodiment of the present invention, since the azimuth angles of the respective nanocolumns 22 are all 0°, thus t xy and t yx both have zero values.

[0068] Furthermore, the superatom response library is obtained by simulation using the rigorous coupled-wave method. In the embodiment of the present invention, the geometric dimensions of the nanocolumn 22 include a period P, a height H, a major axis length L, and a minor axis length W. The period P and the height H are fixed. By changing the major axis length L and the minor axis length W of the nanocolumn, and adopting the rigorous coupled-wave method, the amplitudes and phases of the transmission coefficients corresponding to different geometric dimensions of the nanocolumn are obtained by simulation.

[0069] In the specific embodiment of the present invention, the wavelengths of the incident light are respectively set as λ in= 633 nm and 780 nm. With the height H and period P of the nanocolumn 22 fixed, where the period P is set to 450 nm and the height H is set to 600 nm, a two-dimensional parametric scan (L: 60 nm to 350 nm, W: 60 nm to 350 nm) of the major axis length L and minor axis length W of the nanocolumn 22 is performed using the Rigorous Coupled-Wave Analysis (RCWA) method. The transmission coefficient t corresponding to different-sized nanocolumns 22 is obtained by simulation. lr The amplitude and phase of

[0070] In a specific embodiment of the present invention, a dual-wavelength, polarization-independent superlens 5 (NA > 0.7) with an aperture of 36 μm and a focal length of 18 μm is designed according to the above superlens 5 design method. The processing beam (780 nm) and the monitoring beam (633 nm) can be focused on the same focal plane. The designed superlens 5 is simulated by the Finite Difference Time Domain (FDTD) method. The working wavelengths are set to 633 nm and 780 nm respectively, and the incident polarization states are set to linearly polarized light in the x direction, linearly polarized light in the y direction, linearly polarized light at 45°, linearly polarized light at 135°, left-handed and right-handed circularly polarized light, and the intensity distributions of the xz cross-section under different incident conditions as shown in Figure 3 are obtained. In the simulation, when the wavelengths of the incident light are 633 nm and 780 nm, the average focal lengths corresponding to the six polarization states are 18.083 μm and 18.106 μm respectively. From the FDTD simulation results, it can be seen that the proposed method can focus the processing beam and the monitoring beam of two different wavelengths on the same focal plane.

[0071] Furthermore, the long focal depth lens has crucial application value in the fields of tomography, lithography, information processing, etc. To achieve the long focal depth focusing function, a continuously varying phase distribution modulated radially or angularly needs to be encoded in the optical element. To achieve a long focal depth for the processing beam and a short focal depth for the monitoring beam, the design method of axilenses is adopted in this project.

[0072] The superlens 5 in the embodiment of the present invention independently regulates the first wavelength light wave and the second wavelength light wave, where the required focal depth of the first wave light wave is Δf 1 , and the calculated and are encoded in the same superlens 5 at the same time, so that the long-short focal depth co-focusing function of the dual-wavelength, polarization-independent superlens 5 can be achieved for the processing beam and the monitoring beam. Based on the above long-short focal depth confocal focusing design method of the dual-wavelength, polarization-independent superlens 5, a superlens 5 with an aperture of 36 μm (due to the computer memory size, the simulation aperture of the superlens 5 is set to 36 μm) is designed. Among them, the 633 nm monitoring beam has a short focal depth f 2= 18 μm, the processing beam has a long depth of focus f 1 = 18 μm, Δf 1 = 6 μm. As Figure 4 The FDTD simulation results shown can effectively prove that the proposed method can independently control the processing beam and the monitoring beam to achieve long-short depth of focus confocal plane focusing.

[0073] When designing metasurfaces to achieve functional applications such as lens focusing and holographic imaging, considering factors such as computer memory and simulation time, metasurfaces of relatively small sizes (<100×100 μm 2 ) are usually designed, and simulation software is used to verify the feasibility of the design method. When actual processing is to be carried out, large-scale computer simulation is then used to design metasurfaces of larger sizes required. In this project, the aperture of the metalens 5 is expected to be 2.5 mm, NA > 0.7. The above simulation results can fully verify the feasibility of the long-short depth of focus confocal focusing design method for the dual-wavelength and polarization-independent metalens 5.

[0074] The metalens 5 provided in the embodiment of the present invention can not only focus the light waves of the first wavelength and the second wavelength on the same plane, but also can regulate the depth of focus of the light waves of the first wavelength and the depth of focus of the light waves of the second wavelength, and make the metalens 5 polarization-independent. It enables the metalens to not only focus the light waves of the first wavelength and the second wavelength on the same plane, but also can control the depth of focus of the light waves of the first wavelength to be greater than the depth of focus of the light waves of the second wavelength, so as to meet the requirements of the femtosecond laser manufacturing real-time monitoring system, which not only improves the anti-interference ability during the processing process, but also can improve the accuracy of axial position monitoring.

[0075] Specifically, Figure 1 is the optical path schematic diagram of the femtosecond laser manufacturing parameter real-time monitoring system according to the embodiment of the present invention, Figure 5 is the femtosecond laser processing optical path system 1 according to the embodiment of the present invention, consisting of Figure 1 and Figure 2 It can be seen that the femtosecond laser processing optical path system 1 and the split pupil differential confocal axial monitoring optical path system 2. The femtosecond laser processing optical path system 1 processes the sample surface with light waves of the first wavelength; the split pupil differential confocal axial monitoring optical path system 2 monitors the axial position of the sample surface with light waves of the second wavelength; wherein, the femtosecond laser processing optical path system 1 and the split pupil differential confocal axial monitoring optical path system 2 jointly use the metalens 5 to focus on the sample surface, and the light waves of the first wavelength have a long depth of focus, and the light waves of the second wavelength have a short depth of focus.

[0076] Further, the femtosecond laser processing optical path system 1 provided by the embodiments of the present invention includes a femtosecond laser 11, a spatio-temporal shaping module, a two-dimensional scanner 13, and the metalens 5 sequentially arranged along the optical path of the light wave of the first wavelength. The femtosecond laser 11 is used to incident the light wave of the first wavelength onto the spatio-temporal shaping module (spatio-temporal shaper 12). The spatio-temporal shaping module shapes the light wave of the first wavelength in terms of time and space, and then incident the shaped light wave of the first wavelength onto the two-dimensional scanner 13. The two-dimensional scanner 13 controls the light wave of the first wavelength according to the pattern to be processed, and scans the surface of the sample, so that the light wave of the first wavelength emitted by the two-dimensional scanner 14 is focused on the surface of the sample through the metalens 5, so as to perform femtosecond laser processing on the surface of the sample. In addition, the femtosecond laser processing optical path system 1 may further include an optical path adjustment module 14 composed of a diverging lens and a collimating lens, so as to expand the beam range of the light wave of the first wavelength.

[0077] It should be noted here that other optical lenses are also provided in the optical path of the femtosecond laser processing optical path system 1. The function of the other optical lenses is to converge light from different directions onto the same path and all convert it to be perpendicular to the surface of the sample. Since the other optical lenses do not change the transmission path of the light wave of the first wavelength, they will not be elaborated here.

[0078] Further, as Figure 6 shown, the split pupil differential confocal axial monitoring optical path system 2 includes a continuous laser 21, a first light source collimating module 22, a first beam splitter 23, a first dichroic mirror 42, a second beam splitter 41, and the metalens 5 sequentially arranged along the incident optical path of the light wave of the second wavelength, and a split pupil differential confocal detection module arranged on the reflection optical path of the light wave of the second wavelength.

[0079] The split pupil differential confocal axial monitoring optical path system 2 uses the continuous laser 21 to incident the light wave of the second wavelength onto the first light source collimating module 22 to form a parallel beam. Among them, the first light source collimating module may also be a collimating lens, which radially expands the continuous laser and converts it into a parallel beam.

[0080] The second-wavelength light wave emitted by the first light source collimation module 22 is incident on the first dichroic mirror 42 after being refracted by the first beam splitter 22. The first dichroic mirror 42 reflects the second-wavelength light wave to the second beam splitter 41. The second beam splitter 41 reflects the second-wavelength light wave in a direction perpendicular to the sample surface. The second-wavelength light wave reflected by the second beam splitter 41 is focused on the sample surface after passing through the superlens 5. The second-wavelength light wave reflected by the sample surface is reflected by the second beam splitter 41 to the first dichroic mirror 42. The first dichroic mirror 42 reflects the reflected second-wavelength light wave to the first beam splitter 22. The first beam splitter 22 refracts the reflected second-wavelength light wave to the pupil differential confocal detection module. The pupil differential confocal response curve is obtained by the pupil differential confocal detection module, and the axial position of the sample surface is obtained according to the pupil differential confocal response curve.

[0081] Further, the pupil differential confocal detection module includes a relay lens 24, a D-shaped aperture 25, and a pinhole quadrant detector 26 arranged in sequence along the optical path direction. The D-shaped aperture 25 can block half of the light beam. The pinhole quadrant detector 26 is two point detectors symmetric about the optical axis, obtaining a bipolar, highly sensitive, and highly linear axial response curve linearly related to the height change of the device under test, realizing the height measurement of the processing element. Cooperating with the galvanometer high-speed beam transverse scanning method, the transverse dimension of the processing element is measured.

[0082] As Figure 7 shown, the pupil differential confocal light intensity response curve can be obtained according to the pinhole quadrant detector 26. When the device under test is at the pre-focus position u 0 , the measured pre-focus light intensity signal I A reaches the peak value. When the device under test is at the post-focus position u 2 , the measured post-focus light intensity signal I B reaches the peak value. The two signals are differentially subtracted to obtain the pupil differential confocal signal I diff . When the device under test is at the focus position u 1 , the pupil differential confocal signal I diff reaches zero. The pupil differential confocal signal has good linearity near the zero point, with a large slope of the fitting line and bipolarity. For thin samples with height changes within the linear region, the height profile of the device under test can be obtained without axial scanning. For large-scale devices, axial scanning can be performed at a larger axial interval, reducing the number of scanning layers.

[0083] Further, the real-time monitoring system provided by the embodiment of the present invention further includes a Raman spectroscopy detection module 4. The Raman spectroscopy detection module 4 includes the metalens 5, a second beam splitter 41, a first dichroic mirror 42, a first focusing module 44, and a spectrometer 45 that are arranged on the optical path of the Rayleigh light reflected from the surface of the sample. The Rayleigh light reflected from the surface of the sample is reflected by the second beam splitter 41 to the first dichroic mirror 42. The first dichroic mirror 42 refracts the Rayleigh light reflected from the surface of the sample into the first focusing module 44. The first focusing module 44 focuses the Rayleigh light reflected from the surface of the sample on the spectrometer 45. The spectrometer 45 analyzes and obtains the Raman spectroscopy information of the surface of the sample to monitor the performance parameters of the surface of the sample.

[0084] Further, the real-time monitoring system provided by the embodiment of the present invention further includes a microscopic imaging optical path system 3. The microscopic imaging optical path system 3 includes a white light source 31, a third beam splitter 32, and a fourth beam splitter 33 that are sequentially arranged along the incident optical path of the third-wavelength light wave, and a second focusing module 34 and a CCD module 35 that are arranged on the reflection optical path of the third-wavelength light wave. The white light source 31 emits a third-wavelength light wave. The third-wavelength light wave is incident on the third beam splitter 32. The third beam splitter 32 refracts the third-wavelength light wave into the fourth beam splitter 33. The fourth beam splitter 33 reflects the third-wavelength light wave in a direction perpendicular to the surface of the sample and focuses it on the surface of the sample through the second beam splitter 41 and the metalens 5. The third-wavelength light wave reflected from the surface of the sample is refracted by the metalens 5 and the second beam splitter 41 into the fourth beam splitter 33. The fourth beam splitter 33 reflects the reflected third-wavelength light wave into the third beam splitter 31. The third beam splitter 31 reflects the reflected third-wavelength light wave into the second focusing module 34. The second focusing module 34 focuses the reflected third-wavelength light wave on the CCD module 35. The CCD module 35 determines the tilt and position of the sample.

[0085] The Raman spectroscopy detection module 4 provided by the embodiment of the present invention simultaneously monitors the morphology and performance parameters of the sample. The post-aperture laser differential confocal system 2 and the microscopic imaging system 3 are used to monitor the morphological parameters of the sample. Taking advantage of the wide application range and rich measurement information of Raman spectroscopy, the Rayleigh light and the reflected light reflected from the sample are collected by the metalens 5 and then coupled into the spectrometer. By analyzing the detected spectral data, the performance parameters such as the composition, stress, and temperature of the sample are monitored in real time. This lays a foundation for integrating the monitoring system with the processing system in the later stage of the project to achieve real-time monitoring of the morphology and performance of the processing area.

[0086] A femtosecond laser manufacturing parameter real-time monitoring system based on hyperlens confocal focusing provided by the present invention uses a hyperlens 5 to focus the light wave of the first wavelength for femtosecond processing and the light wave of the second wavelength for axial monitoring on the same plane, and enables the light wave of the first wavelength to have a long depth of focus and the light wave of the second wavelength to have a short depth of focus, so as to realize real-time axial position monitoring during the femtosecond laser processing process, and by increasing the depth of focus of the light wave of the first wavelength, improve the anti-interference ability during the processing process, reduce the depth of focus of the light wave of the second wavelength, and improve the accuracy of axial position monitoring.

[0087] In addition, those skilled in the art can understand that although some embodiments herein include certain features included in other embodiments rather than other features, the combination of features of different embodiments means that it is within the scope of the present invention and forms different embodiments. For example, any one of the claimed embodiments can be used in any combination.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A femtosecond laser manufacturing parameter real-time monitoring system based on superlens confocal focusing, characterized in that: The system comprises: a femtosecond laser processing optical path system and a pupil differential confocal axial monitoring optical path system, wherein the femtosecond laser processing optical path system processes the sample surface using a first wavelength light wave; and the pupil differential confocal axial monitoring optical path system monitors the axial position of the sample surface using a second wavelength light wave; wherein the femtosecond laser processing optical path system and the pupil differential confocal axial monitoring optical path system jointly use a super lens to focus on the sample surface, and the surface of the super lens is composed of an array of nanocolumns with different sizes and the same azimuth angle, so that the first wavelength light wave and the second wavelength light wave are focused on the same plane, and the first wavelength light wave has a long focal depth, and the second wavelength light wave has a short focal depth.

2. The system according to claim 1, characterized in that The femtosecond laser processing optical path system includes a femtosecond laser, a space-time shaping module, a two-dimensional scanner and the super lens which are sequentially arranged along the optical path of the first wavelength light wave. The femtosecond laser inputs the first wavelength light wave into the space-time shaping module, the space-time shaping module performs temporal and spatial shaping on the first wavelength light wave, and inputs the shaped first wavelength light wave into the two-dimensional scanner. The two-dimensional scanner controls the first wavelength light wave to scan the sample surface according to the pattern to be processed, so that the first wavelength light wave emitted by the two-dimensional scanner is focused on the sample surface through the super lens, so as to perform femtosecond laser processing on the sample surface.

3. The system according to claim 2, characterized in that The pupil differential confocal axial monitoring optical path system includes a continuous laser, a first light source collimation module, a first beam splitter, a first dichroic mirror, a second beam splitter and the super lens, which are sequentially arranged along the incident optical path of the second wavelength light wave, and a pupil differential confocal detection module arranged in the reflected optical path of the second wavelength light wave; wherein, The laser incidents the second wavelength light wave onto the first light source collimation module to form a parallel light beam. The second wavelength light wave emitted by the first light source collimation module is refracted by the first beam splitter and then incident on the first dichroic mirror. The first dichroic mirror reflects the second wavelength light wave to the second beam splitter. The second beam splitter reflects the second wavelength light wave in a direction perpendicular to the sample surface. The second wavelength light wave reflected by the second beam splitter passes through the super lens and is focused on the sample surface. The second wavelength light wave reflected by the sample surface is reflected by the second beam splitter to the first dichroic mirror. The first dichroic mirror reflects the reflected second wavelength light wave to the first beam splitter. The first beam splitter refracts the reflected second wavelength light wave to the pupil differential confocal detection module. The pupil differential confocal detection module obtains a pupil differential confocal response curve, and the axial position of the sample surface is obtained according to the pupil differential confocal response curve.

4. The system according to claim 3, characterized in that The system further comprises a Raman spectrum detection module, which comprises the super lens, a second beam splitter, a first dichroic mirror, a first focusing module and a spectrometer arranged on the optical path of the Rayleigh light reflected from the sample surface. The Rayleigh light reflected from the sample surface passes through the superlens, the second beam splitter and the first dichroic mirror in sequence. The first dichroic mirror refracts the Rayleigh light reflected from the sample surface into the first focusing module. The first focusing module converges the Rayleigh light reflected from the sample surface onto the spectrometer. The spectrometer analyzes and obtains Raman spectrum information of the sample surface, so as to form a Raman spectrum detection module to monitor the performance parameters of the sample surface.

5. The system according to claim 3, characterized in that The system also includes a microscopic imaging optical path system, which includes a white light source, a third beam splitter, a fourth beam splitter, and a second focusing module and a CCD module arranged in sequence along the incident optical path of a preset third wavelength light wave, wherein the white light source emits a third wavelength light wave, the third wavelength light wave is incident on the third beam splitter, the third beam splitter refracts the third wavelength light wave into the fourth beam splitter, the fourth beam splitter reflects the third wavelength light wave in a direction perpendicular to the sample surface, and focuses on the sample surface through the second beam splitter and the super lens, the third wavelength light wave reflected from the sample surface is refracted into the fourth beam splitter through the super lens and the second beam splitter, the fourth beam splitter reflects the reflected third wavelength light wave into the third beam splitter, the third beam splitter reflects the reflected third wavelength light wave into the second focusing module, the second focusing module converges the reflected third wavelength light wave on the CCD module, and the CCD module determines the tilt and position of the sample.

6. The system according to claim 1, characterized in that The superlens comprises: a substrate and a nanocolumn array on the substrate, wherein the azimuth angle of each nanocolumn in the nanocolumn array is 0°, so that the polarization of each nanocolumn is independent; The nanopillars at different positions in the nanopillar array of the superlens independently regulate the first wavelength light wave and the second wavelength light wave, so that the first wavelength light wave satisfies the first phase distribution and the second wavelength light wave satisfies the second phase distribution; wherein, The first phase distribution is expressed as: Wherein, λ1 is the first wavelength light wave, f1 is the focal length corresponding to λ1, Δf1 is the focal depth corresponding to λ1, R is the radius of the superlens, and r is the distance between each nanocolumn in the superlens plane and the center of the superlens; The second phase distribution is expressed as: Where λ2 is the second wavelength light wave, f2 is the focal length corresponding to λ2, and (x, y) is the position of each nanocolumn on the superlens in the superlens plane; Among them, f1=f2 so that the first wavelength light wave and the second wavelength light wave have a common focal plane after passing through the super lens, and Δf1 is a preset value so that the first wavelength light wave has a focal depth of a preset length after passing through the super lens.

7. The system according to claim 6, characterized in that The nanocolumns at various positions in the nanocolumn array of the superlens are selected from a preset superatom response library according to the target phases corresponding to the first wavelength light wave and the second wavelength light wave at the current position and a preset error calculation model, so that the error of the selected nanocolumns in phase regulation of the first wavelength light wave and the second wavelength light wave satisfies the preset difference constraint condition; wherein, The super-atom response library is a database of corresponding relationships between the transmission coefficients of different geometrical sizes of nanorods and the first wavelength light wave and the second wavelength light wave respectively; The error calculation model is expressed as the following calculation formula: Where ε is the error of the nanorod in controlling the phase of the first wavelength light wave and the second wavelength light wave, t lr_λ1 is the transmission coefficient of circular polarization conversion capability of nanorods of different sizes under the first wavelength light wave, is the target phase of the first wavelength light wave at the current position, t lr_λ2 is the transmission coefficient of circular polarization conversion capability of nanorods of different sizes under the second wavelength light wave, is the target phase of the second wavelength light wave at the current position, and abs represents the absolute value.

8. The system according to claim 7, characterized in that The geometric dimensions of the nanocolumns include period, height, major axis length and minor axis length. The period and height are fixed. The transmission coefficients corresponding to different geometric dimensions of the nanocolumns are obtained by changing the major axis length and minor axis length of the nanocolumns using a rigorous coupled wave method based simulation.

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