A laser and plasma synergistic polishing device and method

Abstract

The application relates to the technical field of laser polishing, and discloses a laser and plasma cooperative polishing device and a polishing method, which comprise: a first light path used for transmitting first laser; a second light path used for transmitting second laser; a beam combining and focusing assembly arranged at the light output side of the first light path and the light output side of the second light path, which combines the first laser and the second laser and focuses the first laser to form a first focus point and focuses the second laser to form a second focus point; the first focus point is located at a first height of the surface of a sample to be polished, and the second focus point is located at a second height of the surface of the sample to be polished; the second laser focused first is used for preheating and activating the surface of the sample to be polished, and the first laser focused second is used for generating plasma to polish the preheated sample. The problems that the surface roughness is large and the surface roughness of optical level or atomic level cannot be achieved when the sample surface is directly processed by laser in the prior art are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser polishing, in particular to a laser and plasma cooperative polishing device and a polishing method. BACKGROUND

[0002] Laser processing technology has become an indispensable important means in modern industrial manufacturing due to its non-contact, high precision, high efficiency and high flexibility. Especially in high-end fields such as aerospace, microelectronics, biomedical, optical manufacturing, laser shows incomparable advantages in cutting, drilling, welding, etching, surface modification, additive manufacturing and other aspects compared with traditional mechanical processing. With the development of laser technology, especially ultrafast laser, laser processing has entered a new stage of ultra-fine and low damage. Ultrafast laser can realize "cold ablation" due to its extremely short pulse action time, which can significantly reduce the heat affected zone and avoid microcracks, thereby showing excellent performance in micro-nano processing and surface treatment of materials sensitive to thermal damage, such as hard and brittle materials.

[0003] However, although ultrafast laser processing can significantly reduce thermal damage, the material surface after processing still inevitably has certain residual roughness, laser-induced microstructure inhomogeneity or subsurface defects, which is difficult to directly meet the stringent requirements for ultra-smooth surface, high optical quality surface or specific functionalized surface. For example, in optical element manufacturing, the surface roughness needs to reach nanometer or even sub-nanometer level, and the surface after ultrafast laser etching often still needs subsequent mechanical grinding or chemical polishing to meet the requirements, which increases the process complexity and cost, and may introduce new pollution or damage. Although the existing ultrafast laser processing can effectively reduce thermal damage, its material removal mechanism (such as ablation plume injection, phase explosion, etc.) itself often leads to micro-undulation on the processed surface, forming a certain surface roughness. This makes it still need additional mechanical grinding or polishing post-processing steps if the optical or atomic flatness is required.

[0004] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0005] In view of the above problems of the prior art, the purpose of the present application is to provide a laser and plasma cooperative polishing device and a polishing method, which solves the problem that the surface roughness is large and cannot reach the optical or atomic level of surface roughness when directly processing the sample surface by laser.

[0006] The technical scheme of the present application is as follows:

[0007] On the one hand, the present application provides a laser and plasma cooperative polishing device, which comprises:

[0008] The first light path is used for transmitting the first laser;

[0009] The second light path is used for transmitting the second laser, wherein the first laser is delayed from the second laser;

[0010] The beam-combining and focusing assembly is arranged at the light-out side of the first light path and the light-out side of the second light path, so as to combine the first laser and the second laser and focus the first laser to form a first focus point and focus the second laser to form a second focus point respectively;

[0011] The first focus point is located at a first height of the surface of the sample to be polished, and the second focus point is located at a second height of the surface of the sample to be polished, wherein the second height is less than the first height;

[0012] The second laser focused first is used for preheating and activating the surface of the sample to be polished, and the first laser focused later is used for generating plasma to polish the preheated sample.

[0013] Optionally, the first light path comprises a first optical delay line arranged in the path of the first laser and used for adjusting the optical path of the first laser so as to delay the first laser from the second laser.

[0014] Optionally, the first light path further comprises a first beam-expanding assembly arranged at the light-out side of the first optical delay line, and the first laser is expanded by the first beam-expanding assembly to enter the beam-combining and focusing assembly so as to form the first focus point at the first height.

[0015] The second light path comprises a beam-characteristics adjusting assembly, and the second laser is expanded by the beam-characteristics adjusting assembly to enter the beam-combining and focusing assembly so as to form the second focus point at the second height.

[0016] Optionally, the beam-characteristics adjusting assembly comprises a characteristics-adjusting convex lens and a characteristics-adjusting concave lens arranged on the same optical axis, and the height position of the second focus point is adjusted by adjusting the distance between the characteristics-adjusting convex lens and the characteristics-adjusting concave lens.

[0017] Optionally, the beam-combining and focusing assembly comprises a beam-combining optical element used for combining the first laser and the second laser into the same light path.

[0018] The focusing optical element is arranged at the light-out side of the beam-combining optical element and used for focusing the combined first laser and second laser to different height positions of the surface of the sample to be polished respectively.

[0019] The laser and plasma collaborative polishing device further comprises a laser used for generating laser pulses.

[0020] The beam splitting optical component is arranged at the light emitting side of the laser, the first light path is arranged at the first light emitting end of the beam splitting optical component, and the second light path is arranged at the second light emitting end of the beam splitting optical component.

[0021] The laser pulse is split into two beams of split laser by the beam splitting optical component, one of which enters the second light path to form the second laser;

[0022] The frequency doubling crystal is arranged in the first light path, and the other beam of split laser enters the first light path to be converted by the frequency doubling crystal to form the first laser.

[0023] Optionally, the first height H1 is:

[0024]

[0025] E p represents the single-pulse laser energy of the first laser, ρ0 represents the density of the ambient gas, and k is a comprehensive coefficient;

[0026] The second height H2 is:

[0027]

[0028] wherein, is the beam waist radius of the laser beam, is the wavelength of the second laser.

[0029] Optionally, the delay time Δt of the first laser relative to the second laser is:

[0030]

[0031] H1 is the first height, v s is the propagation speed of the plasma shock wave in the ambient gas, τ th is the thermal relaxation time required for the polished sample surface to be activated by the second laser.

[0032] In another aspect, the application also provides a laser and plasma cooperative polishing method, which is applied to the laser and plasma cooperative polishing device as described above, and the polishing method comprises the steps of:

[0033] emitting a laser pulse by the laser, splitting the laser pulse into two beams of split laser,

[0034] one of which is converted into the first laser through the first light path, and the other of which is converted into the second laser through the second light path, wherein the first laser is delayed relative to the second laser by being subjected to a delay process in the first light path;

[0035] The first laser and the second laser are combined by a beam combining and focusing assembly, and the first laser is focused to form a first focal point and the second laser is focused to form a second focal point respectively;

[0036] The second laser which is focused first is used for preheating and activating the surface of the sample to be polished;

[0037] The first laser which is focused later is used for generating plasma to polish the preheated sample.

[0038] Optionally, the first laser is a green light pulse, and the second laser is an infrared light pulse.

[0039] The laser and plasma cooperative polishing device and the polishing method provided by the application have at least the following beneficial effects: by adjusting the focal point position relationship and action time sequence of the first laser and the second laser, the energy deposition and interaction process can be accurately controlled, the second laser must reach the surface of the sample to be polished first, the surface of the sample to be polished is activated by the second laser first, thereby reducing the removal threshold of the polishing amount of the sample surface, facilitating subsequent rapid processing, and improving the processing efficiency and quality. Then, the first laser generates plasma, and the plasma shock wave acts on the activated sample surface, so that high-quality surface quality (low surface roughness) can be achieved by the plasma shock, and the difficulty of removing the excess amount of the sample surface by the plasma shock wave is reduced, thereby realizing efficient removal of the polishing excess amount. Under the combined action of the plasma shock wave and the activated surface, the material is efficiently and accurately removed at a lower threshold, and super-precision polishing is realized. Through the cooperation of the two, the material removal efficiency is improved while ensuring the nanoscale surface roughness and no subsurface damage. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 FIG. 1 is a schematic diagram of an optical path principle of a laser and plasma cooperative polishing device according to an embodiment of the application;

[0041] Figure 2 FIG. 2 is a flowchart of a laser and plasma cooperative polishing method according to an embodiment of the application.

[0042] In the figure, 1 is a first optical path; 10 is a first laser; 11 is a frequency doubling crystal; 12 is a first mirror; 13 is a first optical delay line; 14 is a second mirror; 15 is a first beam expander assembly; 16 is a third mirror; 17 is a first focal point; 2 is a second optical path; 20 is a second laser; 21 is a fourth mirror; 22 is a beam characteristic adjusting assembly; 22a is a characteristic adjusting convex lens; 22b is a characteristic adjusting concave lens; 23 is a second focal point; 3 is a beam combining and focusing assembly; 31 is a beam combining optical element; 32 is a focusing optical element; 4 is a laser; 41 is a half-wave plate; 42 is a beam splitting optical element; and 5 is a sample stage. DETAILED DESCRIPTION

[0043] The application provides a laser and plasma synergistic polishing device and a polishing method. To make the purpose, technical solutions and effects of the application clearer and more explicit, the application is further described in detail below with reference to the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0044] Due to the difficulty of directly meeting the stringent requirements for super-smooth surfaces, high-optical-quality surfaces or specific functionalized surfaces by ultrafast laser processing. In addition to laser direct processing, laser-induced plasma technology is also widely studied and applied to material surface treatment. When high-intensity laser pulses are focused on the material surface or above it, the material or the surrounding gas will be ionized instantaneously, generating high-temperature and high-pressure plasma. The plasma is rich in active particles such as high-energy electrons, ions, atoms and free radicals. These particles interact with the material surface, which can achieve material removal, surface densification, hardening, defect repair, and even chemical modification, thereby achieving the purpose of surface polishing, roughness reduction or specific functionalization. As a non-contact method, laser-induced plasma polishing avoids scratches and pollutants caused by mechanical polishing, and has potential advantages for surface treatment of complex shapes or fragile materials. Although ultrafast laser and laser-induced plasma technology have made significant progress in precision machining and surface modification, they also have their own limitations, making it difficult for a single technology to meet all the needs of high-performance material surface treatment. In the process of laser-induced plasma polishing technology, the workpiece itself is not directly in the range of high-energy laser focus. When the workpiece surface position deviates far from the laser focus, the thermal-mechanical coupling effect of the plasma on the material surface will be significantly weakened, resulting in a decrease in the polishing efficiency of the method. Both have their own advantages and disadvantages in the processing process, so the scheme of the embodiment is proposed to combine the advantages of both, under the joint action of plasma shock wave and activated surface, the material is efficiently and accurately removed at a lower threshold, achieving super-precision polishing. The specific embodiments are as follows:

[0045] As Figure 1As shown, the embodiment proposes a laser and plasma synergistic polishing device, mainly comprising: a first light path 1, a second light path 2 and a beam combining and focusing assembly 3. The first light path 1 is used for transmitting the first laser 10, which can be a green light pulse. The second light path 2 is used for transmitting the second laser 20, which can be an infrared light pulse. The beam combining and focusing assembly 3 is arranged at the light output side of the first light path 1 and the light output side of the second light path 2, so as to combine the first laser 10 and the second laser 20 and respectively focus the first laser 10 to form a first focal point 17 and the second laser 20 to form a second focal point 23. The sample to be polished is placed on the sample table 5, so that the sample to be polished is located at the light output side of the beam combining and focusing assembly 3, so that the first focal point 17 is located at a first height above the surface of the sample to be polished, and the second focal point 23 is located at a second height above the surface of the sample to be polished, and the second height is less than the first height, that is, the second focal point 23 of the focused infrared light pulse is closer to or located on the surface of the sample to be polished, which is beneficial to the energy of the second focal point 23 to instantaneously preheat and activate the surface of the sample to be polished. The first focal point 17 of the focused green light pulse is slightly far from the surface of the sample to be polished, which can facilitate the extremely high peak power of the first focal point 17 to break through the air and generate a plasma plume. Moreover, the first laser 10 is delayed relative to the second laser 20, so that the second laser 20 acts on the sample to be polished first, and then the first laser 10 acts on the sample to be polished. Specifically, the focused second laser 20 is used to preheat and activate the surface of the sample to be polished first, and then the focused first laser 10 is used to generate plasma to polish the preheated sample.

[0046] Therefore, in the embodiment, by adjusting the focal position relationship and action time sequence of the first laser 10 and the second laser 20, the energy deposition and interaction process can be accurately controlled, so that the second laser 20 must reach the surface of the sample to be polished before the first laser 10. In this way, the surface of the sample to be polished is activated by the second laser 20 first, so as to reduce the removal threshold of the polishing amount of the sample surface, which is beneficial to subsequent rapid processing and improves the processing efficiency and quality. Then, the first laser 10 generates plasma, and the plasma shock wave acts on the activated sample surface, so that high-quality surface quality (low surface roughness) can be achieved by plasma shock, and the difficulty of removing the excess amount of the sample surface by the plasma shock wave is reduced, thereby realizing efficient removal of the polishing excess amount. Under the joint action of the plasma shock wave and the activated surface, the material is efficiently and accurately removed at a lower threshold, realizing super-precision polishing. Through the synergy of the two, the material removal efficiency is improved while ensuring the nanoscale surface roughness and no subsurface damage.

[0047] The first laser 10 and the second laser 20 can be obtained by adjusting the laser emitted by one laser source, or emitted by different laser sources respectively. In order to make the consistency between the two lasers more stable, the same laser source is taken as an example for structural description in the embodiment, and the specific implementation is as follows:

[0048] The polishing device of the embodiment further includes a laser 4, a half-wave plate 41, and a beam splitting optical element 42. The half-wave plate 41 is arranged on the light emitting side of the laser 4, and the beam splitting optical element 42 is arranged on the light emitting side of the half-wave plate 41. The beam splitting optical element 42 can be a polarization beam splitter, which has a first light emitting end and a second light emitting end. The first light path 1 is arranged at the first light emitting end of the beam splitting optical element 42, and the second light path 2 is arranged at the second light emitting end of the beam splitting optical element 42.

[0049] The laser 4 is used to generate laser pulses, for example, femtosecond infrared pulse lasers with a center wavelength of 1030 nm to 1064 nm, a pulse width of 30 femtoseconds to 10 picoseconds, and a repetition frequency of 1 kHz to 1 MHz. After the laser pulses pass through the half-wave plate 41 and the polarization beam splitter, they are divided into two beams of split laser: one enters the first light path 1 as reflected light, and the frequency doubling crystal 11 is arranged in the first light path 1. The split laser enters the first light path 1 and passes through the frequency doubling crystal 11 to form the first laser 10 (green light), and is transmitted in the first light path. The other enters the second light path 2 as transmitted light to form infrared light, and is transmitted in the second light path. The light intensity of the two beams of split laser can be adjusted by rotating the angle of the half-wave plate 41. Generally, the light intensity of the first beam is greater than that of the second beam. For example, the half-wave plate 41 and the polarization beam splitter are used to divide the incident femtosecond infrared pulse laser (laser pulse) into two beams of linearly polarized light (two beams of split laser) according to a certain energy ratio (1:1 to 1:1000).

[0050] The split laser in the first light path 1 is converted by the frequency doubling crystal 11, which can be a BBO crystal. The frequency of the split laser (infrared pulse laser) in the first light path 1 is multiplied to convert it into a green light pulse with a center wavelength of 515 nm-532 nm.

[0051] The first light path 1 further comprises a first optical delay line 13, which is arranged in the path of the first laser 10 and is used to adjust the optical path of the first laser 10 so as to delay the first laser 10 relative to the second laser 20. In a specific structure, the first optical delay line 13 is located on the light-emitting side of the frequency-doubling crystal 11. The first laser 10 (green light pulse) emitted from the light-emitting side of the frequency-doubling crystal 11 is reflected by the first mirror 12 into the first optical delay line 13, and the emission time of the green light pulse is adjusted by the first optical delay line 13, so that the first laser 10 (green light pulse) is delayed relative to the second laser 20 (infrared light pulse) and enters the beam-combining and focusing assembly 3. The first optical delay line 13 is composed of a high-precision motorized translation stage and a corner cube prism or mirror group mounted on the stage. By controlling the displacement of the stage by a computer, the optical path of the first light path 1 is continuously adjusted, and the adjustment accuracy is better than 1 micrometer (corresponding to a time adjustment amount of about 3.3 femtoseconds), so as to realize the adjustment of the delay time.

[0052] The optical path of the first laser (green light pulse) is precisely adjusted by the first optical delay line. The required time delay (τ) is set by the control software. For example, the relationship between the delay time τ and the optical path difference ΔL is: τ = ΔL / c (where c is the speed of light). The computer drives the motorized translation stage to move a distance of ΔL corresponding to the set τ, so as to ensure that the plasma shock wave generated by the green light pulse and the activation process of the sample surface by the infrared light pulse occur in a preset accurate timing.

[0053] Further, the first light path 1 further comprises a first beam expander 15, which is arranged on the light-emitting side of the first optical delay line 13. The first laser 10 passes through the first beam expander 15 to enter the beam-combining and focusing assembly 3 to form a first focal point 17 at a first height. In a specific process, the first laser 10 (green light pulse) emitted from the first optical delay line 13 changes direction by the second mirror 14 and enters the first beam expander 15. The first laser 10 (green light pulse) emitted from the first beam expander 15 enters the beam-combining and focusing assembly 3 by reflection of the third mirror 16, so that the focal points of the first laser 10 (green light pulse) and the second laser 20 (infrared light pulse) are coaxial but different in height after passing through the beam-combining and focusing assembly 3. The position of the first beam expander 15 is fixed, so the focal point position of the first laser 10 (green light pulse) after passing through the beam-combining and focusing assembly 3 is fixed and located above the sample surface. The height of the sample surface can be preset by adjusting the relative position of the beam-combining and focusing assembly 3 and the sample to be polished.

[0054] The second light path 2 specifically comprises a beam characteristic adjusting assembly 22 arranged at the second light exit end of the beam splitting optical component 42. The second laser 20 (infrared light pulse) emitted from the second light exit end enters the beam characteristic adjusting assembly 22 through reflection of the fourth mirror 21, and the second laser 20 passes through the beam characteristic adjusting assembly 22 for beam expansion and enters the beam combining and focusing assembly 3 to form the second focal point 23 at the second height. The core of the beam characteristic adjusting assembly 22 is a lens group with adjustable divergence angle. The interval of the lens group can be continuously adjusted by a precise manual or electric displacement table. By changing the interval, the divergence angle of the second laser 20 (infrared light pulse) in the second light path 2 can be continuously changed. Thus, the second height of the second focal point 23 can be adjusted and changed.

[0055] Further, the beam characteristic adjusting assembly 22 comprises a characteristic adjusting convex lens 22a and a characteristic adjusting concave lens 22b arranged on the same optical axis. The height position of the second focal point 23 is adjusted by adjusting the distance between the characteristic adjusting convex lens 22a and the characteristic adjusting concave lens 22b. For example, the characteristic adjusting concave lens 22b is movably arranged. By adjusting the interval between the characteristic adjusting concave lens 22b and the characteristic adjusting convex lens 22a, the wavefront curvature of the second laser 20 is changed. After passing through the beam combining and focusing assembly 3, the position of the obtained second focal point 23 moves on the optical axis. Through accurate adjustment, the second focal point 23 is located on the sample surface or at the second height away from the sample surface.

[0056] In addition, a second optical delay line can also be selected in the second light path 2. By arranging the second optical delay line, a wider range of optical path adjustment can be achieved. The second optical delay line can be similar to the first optical delay line 13, and respectively acts on the second light path 2 and the first light path 1. The second optical delay line cooperates with the first optical delay line 13 to expand the range of optical path adjustment, so that the delay time range of the two is larger.

[0057] The beam combining and focusing assembly 3 in this embodiment specifically includes a beam combining optics 31 and a focusing optics 32. The beam combining optics 31 can be a dichroic beam combiner, which is used to combine the first laser 10 and the second laser 20 into the same optical path. Its film system is designed to have high reflectivity for 515-532nm green light and high transmittance for 1030-1064nm infrared light. Therefore, the first laser 10 (green light pulse) can be reflected into the focusing optics 32 for focusing to obtain the first focal point 17, and the second laser 20 (infrared light pulse) can be reflected into the focusing optics 32 for focusing to obtain the second focal point 23. The first focal point 17 and the second focal point 23 are coaxial. The focusing optics 32 is located on the light-emitting side of the beam combining optics 31 and is used to focus the combined first laser 10 and second laser 20 at different height positions on the surface of the sample to be polished. The focusing optics 32 can be a dichroic achromatic objective or a single convex lens, located after the beam combining optics 31, which focuses the combined green light pulse and infrared light pulse onto a region a certain distance above the sample to be polished and onto the sample surface, respectively.

[0058] like Figure 1 As shown, the first laser (green pulse) is expanded by the first beam expander, reflected by the third mirror, and reflected by the beam combiner. It is then focused by the focusing optics onto the surface of the sample to be polished on the sample stage 5 at a first height H1 above it. Its extremely high peak power can break down air, generating a plasma plume. The first height H1 (green light focusing height) is a key parameter for achieving efficient polishing, and its value is determined by the following model:

[0059]

[0060] In the above formula, E p The single-pulse laser energy represents the first laser, ρ0 represents the density of the ambient gas, and k is a comprehensive coefficient related to specific process conditions and target material. The determination of this comprehensive coefficient k requires calibration through experiments targeting the target material and a specific process environment. The specific method is as follows: With all other laser and process parameters fixed, the first focal height H1 is systematically changed, and polishing experiments are conducted, measuring the material removal rate and surface roughness under different H1 values. Within the process window where the material removal rate is high and the surface quality is optimal, the corresponding H1 value is selected, combined with the currently used single-pulse energy E. p The k value is derived by inversely using the model, taking into account the propagation characteristics of plasma shock waves, energy attenuation laws, and the optimal effect range for interaction with materials. By precisely focusing green light at the height determined by the above model, the generated plasma can achieve optimal interaction with the sample surface activated by infrared laser, thereby realizing efficient and high-precision polishing of materials.

[0061] Taking the polishing of a single-crystal silicon wafer as an example, assuming the center wavelength of the laser is λ0 = 1030 nm, the wavelength of the green light generated by the frequency doubling crystal is λ G =515 nm, pulse width τ p =500 fs, the single-pulse energy E of the first laser (green light) after beam splitting. p =75 μJ, assuming focusing with an objective lens of NA = 0.4, the theoretical diffraction-limited waist radius ω of green light is... 0G ≈ 0.61 * λ G / NA = 0.61 * 515 nm / 0.4 ≈ 0.785 μm. Peak energy density F at the green light focal point. G = E p / (π*ω 0G 2)≈38.8J / cm². For femtosecond lasers, the air breakdown threshold is approximately 10. 13 ~ 10 14 The power density at the green light focal point is on the order of W / cm². G = F G / τ p = 38.8 J / cm² / (500 × 10 -15 s) ≈ 7.76 × 10 13 W / cm², within the air breakdown threshold range, can effectively ionize air to generate plasma. For 500 fs green light, the single-pulse ablation threshold of silicon is taken as 0.3 J / cm². To avoid direct ablation of the silicon surface by the focused green light spot, the green light focus needs to be located at a distance H1 above the silicon surface. When the green light focus is at a height H1, the light spot will expand at the sample surface due to diffraction. The beam radius ω at the surface... H1 ≈ω 0G *sqrt(1+(H1 / Z RG Rayleigh length of green light: Z² RG = π*ω 0G ² / λ G = π*(0.785 μm)² / 0.515 μm ≈ 3.76 μm. The required energy density F of the laser irradiation on the sample surface is... s Below the ablation threshold of silicon, to ensure that the laser itself does not directly ablate the material: F s =E p / (π*ω s ²)<0.3 J / cm², thus obtaining ω s >89 μm. Due to ω s Much greater than ω 0G The value of H1 will also be much greater than Z. RGTherefore, the far-field approximation formula for beam propagation can be used to obtain H1>(π*ω). 0G *ω s ) / λ G ≈427 μm. For ease of calculation, we take H1=500 μm and air density ρ0=1.225 kg / m³. Based on the model above, we can calculate k≈0.013. The value of k can be determined in the above way.

[0062] like Figure 1 As shown, the second laser (infrared pulse) in the second optical path first passes through a beam characteristic adjustment component with an adjustable divergence angle. By adjusting the spacing between the lenses in this lens group, the divergence angle of the infrared laser can be changed. After the divergence angle is changed, the infrared laser is focused to the second focal point by the beam combining optics and focusing optics, and the position of the second focal point moves along the optical axis. Through precise adjustment, the second focal point is made to fall exactly on the surface of the sample or at a distance from the sample surface, i.e., the second height H2 (infrared light focusing height) at the Rayleigh length (Z). R Within the range, that is:

[0063]

[0064] In the above, The beam waist radius is... The wavelength of the second laser is specified. The second focal point is positioned within the second height H2 to avoid excessive defocusing, which would result in insufficient energy density at the laser spot and fail to preheat and activate the sample surface. The purpose of this infrared laser is to utilize its energy for instantaneous preheating and activation of the sample surface.

[0065] In the first and second optical paths described above, the optical delay line formed by the computer-controlled translation stage allows for femtosecond-level adjustment of the arrival time of the green light pulse in the first optical path relative to the infrared light pulse in the second optical path. This enables the plasma shock wave to act on the surface of the sample to be polished after activation by infrared light, thereby achieving the best synergistic removal effect. The infrared light pulse used for activation must arrive at the surface of the sample to be polished before the green light pulse (plasma excitation light). The optimal delay time Δt can be as follows:

[0066] ;

[0067] In the above formula, the delay time Δt between the first laser (green pulse) and the second laser (infrared pulse) is a positive value, therefore the green light arrives Δt time after the infrared light. H1 is the height (first height) of the green light focus (first focus) relative to the surface of the sample to be polished, and v s Let τ be the propagation speed of the plasma shock wave in the ambient gas. thThe thermal relaxation time or electron-lattice coupling time required for the surface of the sample to be activated by infrared light.

[0068] In the polishing process of the sample, the first focus and the second focus are both scanned on the surface of the sample to be polished according to a preset path by controlling the scanning galvanometer or moving the sample table, so that the entire selected area is uniformly polished.

[0069] In some embodiments, as shown in Figure 2 Also proposed is a laser and plasma collaborative polishing method, which is applied to the laser and plasma collaborative polishing device as described above, and the polishing method comprises the steps of:

[0070] Step S100, emitting a laser pulse by a laser, and splitting the laser pulse into two beams.

[0071] Step S200, converting one of the two beams into a first laser through a first optical path, and converting the other beam into a second laser through a second optical path, wherein the first laser is delayed relative to the second laser by performing a delay process on the first laser in the first optical path.

[0072] Step S300, focusing the first laser and the second laser by a focusing assembly to form a first focus and a second focus, respectively.

[0073] Step S400, using the second laser focused first to preheat and activate the surface of the sample to be polished.

[0074] Step S500, using the first laser focused second to generate plasma to polish the preheated sample.

[0075] In the polishing process of the sample, the first focus and the second focus are both scanned on the surface of the sample to be polished according to a preset path by controlling the scanning galvanometer or moving the sample table, so that the entire selected area is uniformly polished. Finally, under the combined action of the plasma shock wave and the activated surface, the material is efficiently and accurately removed at a lower threshold, achieving super-precision polishing.

[0076] In summary, the laser and plasma collaborative polishing device and the polishing method proposed in the present application mainly activate the surface of the sample by focusing infrared light on the surface of the sample, and polish the sample activated on the surface by exciting plasma by focusing green light on a certain height above the sample. Through the collaborative action of femtosecond laser and plasma, efficient, high-precision and low-damage polishing of the material is achieved.

[0077] When it is understood that the application of the present application is not limited to the above examples, and that all modifications and changes which can be made according to the above description by those of ordinary skill in the art are intended to be within the scope of the appended claims.

Claims

1. A laser and plasma synergistic polishing apparatus, characterized by, Comprise: A first light path for transmitting a first laser; A second light path for transmitting a second laser, wherein the first laser is delayed from the second laser; A beam combining and focusing assembly disposed at the light exit side of the first light path and the light exit side of the second light path to combine the first laser and the second laser and focus the first laser to form a first focal point and the second laser to form a second focal point respectively; Wherein the first focal point is located at a first height of the surface of the sample to be polished, and the second focal point is located at a second height of the surface of the sample to be polished, and the second height is less than the first height; The second laser is used to preheat and activate the surface of the sample to be polished by being focused first, and the first laser is used to generate plasma to polish the preheated sample by being focused later; The first height H1 is: wherein E p represents the single pulse laser energy of the first laser, p0 represents the density of the ambient gas, and k is a comprehensive coefficient; The second height H2 is: wherein is the beam waist radius of the light beam, is the wavelength of the second laser light; The delay time Δt of the first laser from the second laser is: H1 is a first height, v s is the propagation speed of the plasma shock wave in the ambient gas, τ th is the thermal relaxation time required for the polished sample surface to be activated by the second laser.

2. The laser and plasma synergistic polishing apparatus of claim 1, wherein, The first light path comprises a first optical delay line disposed on the path of the first laser and used to adjust the optical path of the first laser to delay the first laser from the second laser.

3. The laser and plasma synergistic polishing apparatus of claim 2, wherein, The first light path further comprises a first beam expander disposed at the light exit side of the first optical delay line, and the first laser is expanded by the first beam expander to enter the beam combining and focusing assembly to form the first focal point at the first height; The second light path comprises a beam characteristic adjusting assembly, and the second laser is expanded by the beam characteristic adjusting assembly to enter the beam combining and focusing assembly to form the second focal point at the second height.

4. The laser and plasma synergistic polishing apparatus of claim 3, wherein, The beam characteristic adjusting assembly comprises a characteristic adjusting convex lens and a characteristic adjusting concave lens disposed on the same optical axis, and the height position of the second focal point is adjusted by adjusting the distance between the characteristic adjusting convex lens and the characteristic adjusting concave lens.

5. The laser and plasma synergistic polishing apparatus of claim 3, wherein, The beam combining and focusing assembly comprises a beam combining optical element for combining the first laser and the second laser into the same light path; A focusing optical element located at the light exit side of the beam combining optical element for focusing the combined first laser and second laser at different height positions of the surface of the sample to be polished respectively.

6. The laser and plasma synergistic polishing apparatus of claim 1, wherein, The laser and plasma collaborative polishing device further comprises a laser for generating a laser pulse; A beam splitting optical element disposed at the light exit side of the laser, the first light path is disposed at a first light exit end of the beam splitting optical element, and the second light path is disposed at a second light exit end of the beam splitting optical element; The laser pulse is split into two beams of split laser by the beam splitting optical element, one of which enters the second light path to form the second laser; A frequency doubling crystal is disposed in the first light path, and the other beam of split laser enters the first light path to be converted by the frequency doubling crystal to form the first laser.

7. A method of laser and plasma synergistic polishing, characterized in that, Applied to the laser and plasma collaborative polishing device as claimed in any one of claims 1-6, the polishing method comprises the steps of: The laser pulses are emitted by a laser, and the laser pulses are split into two beams; One of the two beams is converted into the first laser through a first optical path, and the other beam is converted into the second laser through a second optical path, wherein the first laser is delayed in the first optical path, and the first laser is delayed relative to the second laser; The first laser and the second laser are combined by a beam combining and focusing assembly, and the first laser is focused to form a first focal point, and the second laser is focused to form a second focal point; The second laser focused first is used for preheating and activating the surface of the sample to be polished; The first laser focused later is used for generating plasma to polish the preheated sample.

8. The laser and plasma synergistic polishing method of claim 7, wherein, The first laser is a green light pulse, and the second laser is an infrared light pulse.

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