Manufacturing method of aspheric fused quartz optical element

Abstract

The invention discloses a method for manufacturing an aspheric fused quartz optical element, which comprises the following steps of: S1, carrying out ultra-precision grinding on the aspheric fused quartz optical element to ensure that the surface shape error and the surface roughness of the ground surface meet the requirements; s2, performing magneto-rheological polishing and shaping on the aspheric fused quartz optical element; s3, the surface shape precision of the aspheric fused quartz optical element is detected, if the detection result meets the requirement, the step S4 is executed, and if the detection result does not meet the requirement, the step S2 is executed again; s4, the aspheric fused quartz optical element is subjected to fairing polishing; and S5, detecting the front shape of the transmitted wavefront of the aspheric fused quartz optical element, filtering the intermediate frequency band, then performing power spectral density analysis, if the intermediate-high frequency error meets the requirement, completing the processing, and if the intermediate-high frequency error does not meet the requirement, returning to the step S4. The method has the advantages of high precision, high efficiency, low damage, low cost and the like.

Description

Technical Field

[0001] The invention relates to the technical field of ultra-precision machining, and in particular to a method for manufacturing an aspherical fused quartz optical element. Background Art

[0002] At present, fused silica glass is a commonly used optical material in high-power laser systems. Due to its high intrinsic damage threshold and wide spectral transmittance, it is widely used in core components such as focusing transmission, diffraction gratings, windows and shielding. As the power of laser systems continues to increase, the requirements for manufacturing surface accuracy, surface quality and damage threshold of fused silica optical components are also constantly increasing. It is required that the surface error and roughness in the entire frequency band can be controlled within the nanometer scale, so there are very high requirements for the processing technology of fused silica optical components.

[0003] The traditional manufacturing of fused silica optical components is usually carried out according to the process of first cutting the blank, then grinding and shaping, and finally grinding and polishing. The processing cycle is long, and surface and sub-surface defects such as cracks, scratches and contamination will inevitably be introduced during the processing, which will have a serious impact on the performance and life of high-performance fused silica optical components. At the same time, with the complexity of optical design structures, the demand for complex aspheric fused silica components is also growing. In the process of precision / ultra-precision processing of optical components that need to be mass-produced, relying solely on a single technology or traditional process methods can no longer meet production needs.

[0004] Therefore, achieving high-precision, low-damage, high-efficiency and low-cost modern optical component processing technology has become a key technical challenge. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for manufacturing an aspheric fused quartz optical element with high precision, low damage, high efficiency and low cost.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for manufacturing an aspherical fused silica optical element comprises the following steps:

[0008] Step S1: ultra-precision grinding of the aspheric fused silica optical element to ensure that the surface error and surface roughness of the ground surface meet the requirements;

[0009] Step S2: performing magnetorheological polishing and shaping on the aspheric fused silica optical element;

[0010] Step S3: Detecting the surface accuracy of the aspheric fused silica optical element. If the detection result meets the requirements, proceed to step S4; if the detection result does not meet the requirements, return to step S2;

[0011] Step S4: smoothing and polishing the aspheric fused silica optical element;

[0012] Step S5: Detect the transmission wavefront shape of the aspheric fused silica optical element, filter the intermediate frequency band and then perform power spectrum density analysis. If the intermediate and high frequency errors meet the requirements, the processing is completed. If not, return to step S4.

[0013] As a further improvement of the above technical solution: before step S2, the ground surface of the aspheric fused quartz optical element is pre-treated and polished by controlling the asphalt disk to remove obvious visible grinding lines and damage, until the surface accuracy PV<1λ and there is no obvious damage and lines on the surface, the pre-treatment and polishing step is completed, otherwise the pre-treatment and polishing are performed again, wherein λ is the laser wavelength.

[0014] As a further improvement of the above technical solution: Step S2 specifically includes:

[0015] S2.1 Generate magnetorheological modification removal function: select the polishing wheel size that matches the curvature radius of the workpiece vertex, adjust the polishing wheel speed, magnetic field and magnetorheological polishing fluid parameters, form removal function spots by staying on the surface of the aspheric fused quartz optical element, detect the surface shape of the aspheric fused quartz optical element, and obtain a suitable magnetorheological removal function after subtracting it from the original surface shape;

[0016] S2.2 Magnetorheological polishing and shaping: The surface error obtained by detection is imported into the magnetorheological processing technology software, and the residence time required for magnetorheological polishing and shaping and the predicted surface shape after processing are calculated. The residence time is used to generate the CNC code required by the magnetorheological polishing machine tool, and magnetorheological polishing and shaping processing is performed on the aspheric fused quartz optical element.

[0017] As a further improvement of the above technical solution: in step S3, the surface shape detection of the aspheric fused quartz optical element is performed using a wavefront interferometer, and when the surface shape accuracy PV<0.2λ, the requirement is met.

[0018] As a further improvement of the above technical solution: step S4 specifically includes S4.1:

[0019] Obtain the smoothing processing NC code: import the surface error detected in step S3 into the smoothing and polishing processing software, calculate the surface accuracy after smoothing and the ability to maintain surface accuracy, select the smoothing and polishing parameters, and form the smoothing processing code used by the machine tool.

[0020] As a further improvement of the above technical solution: step S4 further includes S4.2:

[0021] Nano-sized cerium oxide powder is used as polishing abrasive to smooth aspheric fused quartz optical elements.

[0022] As a further improvement of the above technical solution: the smoothing processing time in step S4.2 is 15-25 minutes.

[0023] As a further improvement of the above technical solution: in step S5, a wavefront interferometer is used to detect the shape of the transmitted wavefront of the fused silica optical element, and the mid-high frequency band is filtered and then the power spectrum density analysis is performed. When the mid-high frequency error RMS is less than 5nm, the requirement is met, wherein the filtering frequency band is 0.33-33mm.

[0024] As a further improvement of the above technical solution: Step S1 specifically includes S1.1:

[0025] The surface of the aspherical fused quartz optical element was ground using a metal-based hemispherical diamond grinding wheel with a particle size of D30. The process parameters used were: workpiece speed of 30-60rpm, grinding wheel speed of 2500-4500rmp, grinding wheel feed speed of 0.02-0.05mm / min, and material removal of ≥120μm.

[0026] As a further improvement of the above technical solution: step S1 also includes S1.2:

[0027] The surface of the aspherical fused quartz optical element was ground using a resin-based hemispherical diamond grinding wheel with a particle size of D20. The process parameters used were: workpiece speed of 30-60rpm, grinding wheel speed of 2500-4500rmp, grinding wheel feed speed of 0.02-0.05mm / min, and material removal of ≥40μm.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] 1. The method for manufacturing an aspheric fused quartz optical element disclosed in the present invention adopts ultra-precision grinding as the entry process of the full-process processing of the fused quartz optical element, which effectively reduces the sub-surface damage of the fused quartz element caused by the ordinary grinding method, eliminates the grinding process to remove the damaged layer, and also reduces the amount of material removed in the subsequent magnetorheological shaping process, thereby improving the shape accuracy of the optical element after grinding (the surface shape error PV is within 2μm), shortening the overall process time, and improving the processing efficiency.

[0030] 2. The method for manufacturing aspheric fused quartz optical elements disclosed in the present invention directly removes the trace damage layer (about 4-5 μm) remaining after ultra-precision grinding through the efficient polishing and shaping ability of magnetorheological polishing, and controls the surface error PV within 1 / 5λ through shaping, so that the surface error converges quickly.

[0031] 3. The method for manufacturing an aspheric fused silica optical element disclosed in the present invention processes the aspheric fused silica optical element through smoothing processing, which can control the medium and high frequency errors within 5nm while keeping the low frequency surface accuracy unchanged as much as possible.

[0032] 4. The manufacturing method of the aspheric fused quartz optical element disclosed in the present invention realizes the convergence of the full-band error from low-frequency surface shape accuracy to nanometer-scale medium and high-frequency errors within the effective aperture of the aspheric fused quartz optical element to within nanometer precision through a short process method of ultra-precision grinding-magnetorheological polishing and shaping-smoothing processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a schematic flow chart of the method for manufacturing the aspheric fused silica optical element of the present invention.

[0034] Figure 2 This is the result of the workpiece shape error detection after ultra-precision grinding.

[0035] Figure 3 This is the surface roughness test result of the workpiece after ultra-precision grinding.

[0036] Figure 4 This is the initial surface error detection result of the workpiece after magnetorheological uniform polishing.

[0037] Figure 5 This is the final surface error detection result of the workpiece after magnetorheological shaping.

[0038] Figure 6 It is the detection result of medium and high frequency errors of the workpiece after smoothing. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0041] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0042] In the present invention, unless otherwise clearly specified and limited, the terms "assemble", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0043] Figures 1 to 6 An embodiment of the method for manufacturing an aspheric fused silica optical element of the present invention is shown. This embodiment takes the Heraeus 3002 aspheric fused silica optical element as an example. The effective aperture of the aspheric fused silica optical element is 56 mm, and the vertex curvature radius R=99.339276 mm. Finally, the manufacturing method of the present invention achieves the convergence of nanometer-level surface accuracy and medium and high frequency errors. The specific process is as follows:

[0044] 1. Raw material pretreatment and ultra-precision grinding steps:

[0045] 1) Cut the fused quartz glass blank rod into blank raw materials according to the required size and shape, and retain the processing allowance required for subsequent grinding and polishing;

[0046] 2) Grind and shape the fused quartz glass blank according to the Fancheng method to form the required aspheric shape of the fused quartz optical element, and ensure the form and position tolerances. Specifically, a metal-based cup-shaped diamond grinding wheel with a particle size of D56 is used, the grinding wheel speed is 2600 rpm, the workpiece speed is 50 rpm, the grinding wheel feed speed is 0.06 mm / min, the material removal amount is ≥ 0.5 mm, and a three-coordinate machine is used for detection. The form and position tolerances are controlled within the required range;

[0047] 3) Ultra-precision grinding of fused quartz optical elements to control surface shape accuracy and sub-surface defect layer depth, first use a metal-based hemispherical diamond grinding wheel with a particle size of D30, a grinding wheel speed of 3200 rpm, a workpiece speed of 40 rpm, a grinding wheel feed speed of 0.04mm / min, and a material removal amount of ≥120μm; then use a resin-based hemispherical diamond grinding wheel with a particle size of D20, a grinding wheel speed of 3200 rpm, a workpiece speed of 40 rpm, a grinding wheel feed speed of 0.04mm / min, and a material removal amount of ≥40μm. Use a three-coordinate machine and a white light interferometer to detect the ground surface. After evaluation, the shape error PV<1.5μm and the surface roughness Ra<150nm, then the sub-surface defect layer depth SSD<5μm can be controlled. Figure 2-Figure 3 shown.

[0048] 2. Pretreatment steps before polishing of optical components:

[0049] 4) Using the computer controlled optical surface shaping (CCOS) method, the ground surface of the fused quartz optical element is pre-treated and polished by controlling the asphalt disk to remove the obvious visible grinding lines and damage. The surface accuracy of the element is tested using a non-contact profilometer and an ultra-depth microscope. When the surface accuracy PV<1λ (λ is the laser wavelength, in this embodiment, λ=632.8nm), and there is no obvious damage and lines on the surface, the pre-treatment and polishing step is completed; otherwise, step 4) is repeated until the processing result meets the requirements, such as Figure 4 As shown in the figure, the pre-processing step before polishing is helpful to achieve the purpose of rapid convergence of surface shape error.

[0050] 3. Magnetorheological shaping steps for nanometer-level surface accuracy of optical components:

[0051] 5) In order to ensure the convergence efficiency and machining accuracy of low-frequency surface shape errors, the polishing wheel size matching the radius of curvature of the workpiece vertex is selected, the polishing wheel speed, magnetic field and magnetorheological polishing fluid parameters are adjusted, and removal function spots are formed by staying on the fused quartz surface. The surface shape of the fused quartz element is detected by wavefront interferometer, and the appropriate magnetorheological removal function is obtained by subtracting the original surface shape;

[0052] 6) Using magnetorheological processing software, the detected surface error is imported into the magnetorheological processing software, and the residence time required for magnetorheological polishing and shaping and the predicted surface shape after processing are accurately calculated. The residence time is used to generate the numerical control code required by the magnetorheological polishing machine tool, and magnetorheological efficient polishing and shaping processing is performed on the aspheric optical element;

[0053] 7) After processing, the wavefront interferometer is used again to detect the surface shape of the fused quartz optical element. When the surface shape accuracy PV<0.2λ (λ=632.8nm), the magnetorheological polishing process is completed. Otherwise, repeat steps 5-6 until the detection accuracy of the wavefront interferometer after processing meets the accuracy requirements. Figure 5 shown.

[0054] 4. Steps for smoothing the errors of optical components at nanometer level in medium and high frequency:

[0055] 8) Import the optical element surface error obtained by step 7 into the smoothing and polishing process software, calculate the surface accuracy and surface accuracy maintenance capability after smoothing, select appropriate smoothing and polishing parameters, and generate the smoothing processing NC code used by CCOS machine tools;

[0056] 9) Nano-scale cerium oxide powder was used as the polishing abrasive for fused quartz optical components, and the fused quartz components were smoothed for 20 minutes;

[0057] 10) Use a wavefront interferometer to detect the shape of the transmitted wavefront of the fused silica optical element, and perform power spectrum density analysis after filtering the intermediate frequency band (the filter band is 0.33mm-33mm). When the intermediate and high frequency error RMS <5nm, the intermediate and high frequency smoothing of the optical element is completed; otherwise, repeat steps 8 to 10 until the intermediate and high frequency errors meet the accuracy requirements. Figure 6 shown.

[0058] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the technical content disclosed above without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for manufacturing an aspherical fused silica optical element, characterized in that: The following steps are involved: Step S1: ultra-precision grinding of the aspheric fused silica optical element to ensure that the surface error and surface roughness of the ground surface meet the requirements; Step S2: performing magnetorheological polishing and shaping on the aspheric fused silica optical element; Step S3: Detecting the surface accuracy of the aspheric fused silica optical element. If the detection result meets the requirements, proceed to step S4; if the detection result does not meet the requirements, return to step S2; Step S4: smoothing and polishing the aspheric fused silica optical element; Step S5: Detect the transmission wavefront shape of the aspheric fused silica optical element, filter the intermediate frequency band and then perform power spectrum density analysis. If the intermediate and high frequency errors meet the requirements, the processing is completed. If not, return to step S4.

2. The method for manufacturing an aspheric fused silica optical element according to claim 1, characterized in that: Before step S2, the ground surface of the aspherical fused quartz optical element is pre-treated and polished by controlling the asphalt disk to remove obvious visible grinding lines and damage until the surface accuracy PV<1λ and there is no obvious damage and lines on the surface. The pre-treatment and polishing step is completed, otherwise the pre-treatment and polishing are performed again, where λ is the laser wavelength.

3. The method for manufacturing an aspherical fused silica optical element according to claim 2, characterized in that: Step S2 specifically includes: S2.1 Generate magnetorheological modification removal function: select the polishing wheel size that matches the curvature radius of the workpiece vertex, adjust the polishing wheel speed, magnetic field and magnetorheological polishing fluid parameters, form removal function spots by staying on the surface of the aspheric fused quartz optical element, detect the surface shape of the aspheric fused quartz optical element, and obtain a suitable magnetorheological removal function after subtracting it from the original surface shape; S2.2 Magnetorheological polishing and shaping: The surface error obtained by detection is imported into the magnetorheological processing technology software, and the residence time required for magnetorheological polishing and shaping and the predicted surface shape after processing are calculated. The residence time is used to generate the CNC code required by the magnetorheological polishing machine tool, and magnetorheological polishing and shaping processing is performed on the aspheric fused quartz optical element.

4. The method for manufacturing an aspherical fused silica optical element according to claim 3, characterized in that: In step S3, the surface shape of the aspheric fused silica optical element is detected by using a wavefront interferometer. When the surface shape accuracy PV<0.2λ, the requirement is met.

5. The method for manufacturing an aspherical fused silica optical element according to claim 1, characterized in that: Step S4 specifically includes S4.1: Obtain the smoothing processing NC code: import the surface error detected in step S3 into the smoothing and polishing processing software, calculate the surface accuracy after smoothing and the ability to maintain surface accuracy, select the smoothing and polishing parameters, and form the smoothing processing code used by the machine tool.

6. The method for manufacturing an aspherical fused silica optical element according to claim 5, characterized in that: Step S4 also includes S4.2: Nano-sized cerium oxide powder is used as polishing abrasive to smooth aspheric fused quartz optical elements.

7. The method for manufacturing an aspherical fused silica optical element according to claim 6, characterized in that: The smoothing process time in step S4.2 is 15-25 minutes.

8. The method for manufacturing an aspherical fused silica optical element according to claim 1, characterized in that: In step S5, a wavefront interferometer is used to detect the shape of the transmitted wavefront of the fused silica optical element, and the mid-high frequency band is filtered and then the power spectrum density analysis is performed. When the mid-high frequency error RMS is less than 5nm, the requirement is met, wherein the filtering frequency band is 0.33-33mm.

9. The method for manufacturing an aspherical fused silica optical element according to any one of claims 1 to 8, characterized in that: Step S1 specifically includes S1.1: The surface of the aspherical fused quartz optical element was ground using a metal-based hemispherical diamond grinding wheel with a particle size of D30. The process parameters used were: workpiece speed of 30-60rpm, grinding wheel speed of 2500-4500rmp, grinding wheel feed speed of 0.02-0.05mm / min, and material removal of ≥120μm.

10. The method for manufacturing an aspherical fused silica optical element according to claim 9, characterized in that: Step S1 also includes S1.2: The surface of the aspherical fused quartz optical element was ground using a resin-based hemispherical diamond grinding wheel with a particle size of D20. The process parameters used were: workpiece speed of 30-60rpm, grinding wheel speed of 2500-4500rmp, grinding wheel feed speed of 0.02-0.05mm / min, and material removal of ≥40μm.

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