Method and device for shape correction of an optical component using laser radiation

Abstract

The present invention relates to a method and a device for shape correction of an optical component using pulsed laser radiation. For this purpose, the component is measured, and excess material is determined by comparison with a target geometry. This excess material is then at least partially removed by processing with at least one pulsed laser beam with pulse durations of > 1 µs in order to approximate the actual geometry to the target geometry. During processing, the component is rotated about an axis of rotation at a certain speed, whereby the distance of the laser beam to the axis of rotation is changed at least temporarily. The rotational speed, the diameter of the laser beam on the component, and the temporal interval between the laser pulses are selected such that the material areas of the component removed by successive laser pulses do not overlap, as illustrated by way of example in Figure 3.

Description

Technical application area

[0001] The present invention relates to a method for shape correction of an optical component using pulsed laser radiation, in which the component is measured to obtain its actual geometry, and excess material is determined by comparison with a predetermined target geometry of the component and at least partially removed by processing with at least one pulsed laser beam in order to approximate the actual geometry to the target geometry. The invention also relates to a device configured for carrying out the method.

[0002] The production of many components often requires shape correction at the end of the manufacturing process. The production of optical components made of quartz glass, in particular, demands the highest degree of precision and reliability. Although machines for processing optical materials have been continuously developed in terms of dimension and precision over the last two centuries, the fundamental principle of subtractive material removal remains constant. Through conventional processes such as grinding and polishing, the glass material is gradually transformed into the desired shape, surface roughness is minimized, and subsurface damage (SSD) is successively eliminated.While planar and spherical optical components can be produced to a high quality standard thanks to the kinematic control of machining tools, and are inexpensive and widely available, aspherical and freeform optics require a more complex machining process involving line or point contact. The production times and costs for aspherical lenses significantly exceed those of spherical lenses, while precision is simultaneously reduced.

[0003] Particularly in the field of precision and ultra-precision manufacturing, as well as for numerous aspheres with medium requirements for dimensional accuracy, an additional manufacturing step for shape correction is required after shaping (mostly by grinding) and the polishing process, as shown schematically in Fig. Figure 1 illustrates a process chain for manufacturing optical components. In this process, final deviations between the actual and target geometry in the micro- to nanometer range are removed. This precision shape correction manufacturing step is time-consuming and costly. State of the art

[0004] Currently, methods such as magnetorheological finishing (MRF) and ion beam figuring (IBF) are used for precision and ultra-precision shape correction of optics. Key target parameters are the ablation rate (and thus process time) and the vertical (Δz) and lateral resolution of the material removal. The lateral resolution (spatial resolution) can be characterized by the smallest spatial wavelength λ to be corrected. O .

[0005] In MRF (Magnetic Reaming), a magnetic fluid containing abrasive particles is continuously applied to a magnetic carrier wheel and then guided into the working gap between the workpiece and the tool. The size of the carrier wheel limits the spatial resolution of MRF shape correction to approximately 2000 µm < λ. o < 3000 µm. Furthermore, concave surfaces with small radii of curvature cannot be processed due to the inherent limitations of the process. Particles of the polishing agent (cerium oxide, aluminum, carbonyl iron, and / or diamond nanoparticles) can be introduced into the optical surface and negatively affect the damage threshold of the optics in high-power laser applications.

[0006] In IBF, material is locally removed from the surface by ion bombardment. Similar to other sub-aperture methods (e.g., MRF), the workpiece shape correction is achieved via residence times, which are calculated based on the actual and target shapes. Disadvantages of IBF include the expensive equipment technology requiring a vacuum atmosphere and the low material removal rates (V). ab = 0.1 - 10 mm 3 / h) and thus long processing times. Spatial wavelengths of λ are usually used. o Corrected for wavelengths > 3000 µm using IBF. Correction of smaller spatial wavelengths down to λ. o A wavelength greater than 1000 µm is possible in principle. However, the removal rate decreases considerably with decreasing spatial wavelength, making IBF uneconomical in this case.

[0007] Other well-known methods for increasing surface quality are computer-controlled polishing (CCP), reactive ion-beam etching (RIBE), plasma chemical vaporization machining (PCVM), and elastic emission machining (EEM).

[0008] All correction methods require measuring the current shape before machining to determine the excess material to be removed. This is done in separate measuring machines, as the measuring technology is generally not vacuum-compatible (IBF), and all other correction methods require a cleaned surface. Therefore, even for these methods, measuring directly in the machining tool necessitates at least some manual intervention by the user after the mechanical machining process.

[0009] Laser-based shape correction (LBF; Laser Beam Figuring) is currently under research. In this process, laser radiation with a typical wavelength of λ = 10.6 µm is focused onto a quartz glass surface, and material is selectively ablated in increments of one to several hundred nanometers. The laser radiation can be applied in either pulsed or modulated form. Modulation in the form of rectangular pulses can be generated using an acousto-optic modulator (AOM). The AOM acts as a fast optical switch, allowing the laser source to operate continuously at a stable point. Experiments and publications have already demonstrated that rectangularly modulated pulses enable the targeted ablation of material from the surface of the component in increments of just a few nanometers.

[0010] The LBF is still in the research and development phase and exhibits significant shortcomings. These shortcomings include, in particular, a low processing speed and a process accuracy that is difficult to control, caused by thermal effects during machining with overlapping pulses in the nanometer range. The higher the pulse frequency (and thus the processing speed), the more pronounced this problem becomes.

[0011] According to the current state of science and technology, the pulses in LBF are arranged in an overlapping manner to achieve surface processing.

[0012] US Patent 2008 / 0030876A1 describes a method for shape correction of an optical component using pulsed laser radiation according to the preamble of claim 1, in which the component is rotated about an axis of rotation passing through the component during processing with the laser beam, wherein the distance of the laser beam to the axis of rotation is changed at least temporarily. The laser pulses have pulse durations of < 1 ns and are preferably in the pico- or femtosecond range.

[0013] From DE 102 28 743 A1 a method for smoothing and polishing surfaces with laser radiation is known, in which the surface is first remelted in a first treatment step with continuous laser radiation or pulsed laser radiation with a pulse duration ≥ 100 µs and then, in a second treatment step with second laser parameters, any remaining microroughness on the surface is leveled.

[0014] JP 2011-212 726 A describes the laser processing of an organic recording material layer on the surface of a rotating disk, in which the laser beam is modulated according to the recording data. In a first processing step, the circular recording tracks are created at twice the spacing, and the remaining spaces are then filled with the missing recording tracks in a second processing step.

[0015] DE 10 2011 017 080 A1 describes a method for processing a workpiece with a pulsed laser beam generated by modulating a continuous laser beam with an acousto-optic modulator.

[0016] WO 2012 / 119 761 A1 describes a process for manufacturing optical components by processing with energetic radiation, in particular laser radiation. The manufacturing of an optical component, starting from a blank, involves coarse ablation, polishing, and fine ablation. Fine ablation is achieved with a laser beam by varying the speed of the laser beam across the material. The laser beam is guided across the surface of the component by means of a scanner or an axis system.

[0017] German patent DE 10 2018 005 218 A1 discloses a method and a device for modifying a material within a solid body, in which the focus of a laser beam is guided within the solid body by a scanning motion to inscribe at least one path into the solid body with the laser beam. In one embodiment, the solid body is guided by a polar motion on an ultra-precision machine. The method is used for shape generation but is not suitable for shape correction.

[0018] German patent DE 10 2017 002 986 B4 describes a method for manufacturing a transmittive optic and intraocular lens, in which a plastic blank is suitably ablated with an ablation laser and further processed with a polishing laser. Shape correction is not addressed in this document.

[0019] The object of the present invention is to provide a method and a device for shape correction of an optical component, enabling increased process speed and improved and reproducible process accuracy in shape correction. Optical components are understood to be elements used for the transmission or reflection of optical radiation in optical applications, such as optical lenses or mirrors. Description of the invention

[0020] The problem is solved by the method and the apparatus according to claims 1 and 15. Advantageous embodiments of the method and the apparatus are the subject of the dependent claims or can be found in the following description and the exemplary embodiments.

[0021] The proposed method employs laser-based shape correction (LBF) with pulsed laser radiation to correct or modify the shape of an optical component. This technique relies on heating the material and removing material at the vaporization temperature. The component is first measured to determine its actual geometry. Excess material is then determined by comparing this measurement with a predetermined target geometry. Subsequently, at least some of this excess material is removed by processing with at least one pulsed laser beam to approximate the actual geometry to the target geometry. A pulsed laser beam, in this context, refers not only to the beam from a pulsed laser source but also to a laser beam with pulsed amplitude modulation, where the minimum amplitude during modulation is less than 20% of the maximum amplitude, preferably zero.Modulation can be achieved, for example, by an acousto-optic modulator (AOM) in the beam path of the laser beam.

[0022] The proposed method is characterized by the fact that the processing is carried out with laser beam pulse durations of > 1 µs and the component is rotated at a (constant or varying) speed around an axis of rotation passing through the component during processing with the laser beam, for example by mounting it on a motor-driven rotary spindle, whereby the distance between the laser beam and the axis of rotation is changed at least temporarily. Preferably, the laser beam is moved radially relative to the axis of rotation, for example by a suitable linear movement of the laser optics. In the case of a rotationally symmetric component, the axis of symmetry of the component is preferably selected as the axis of rotation.The rotational speed, the beam diameter of the laser beam on the component, and the time interval between the pulses of the laser beam are chosen so that the material areas of the component removed by successive pulses of the laser beam do not overlap.

[0023] The rotation of the component, preferably performed using an ultra-precision lathe (UP lathe) with a repeatability of < 200 nm, preferably < 50 nm, and the selected pulse intervals enable increased process speed as well as improved and reproducible process accuracy. It was recognized that in previous applications of the LBF (Low Beam Fusion), the problems of thermal interaction between the pulses led to process accuracy that was difficult to control due to thermal effects, as the heat from preceding pulses increased the removal depth of subsequent pulses.The pulse spacing chosen in the proposed method, in which each subsequent pulse strikes the component at a distance from the preceding pulse such that it is not, or only minimally, within the temperature field of the preceding pulse, reduces the thermal interaction between successive pulses, thus enabling higher precision in the ablation process. The rotation of the component allows for machining using polar coordinates. The preferred use of a submerged arc lathe enables fast and precise guidance of the laser beam, preferably a focused laser beam, across rotationally symmetric components or surfaces, and—when using a fast-tool system—also across freeform surfaces. The implementation of a high spindle speed, e.g., 3.At 000 revolutions per minute, it is possible to spatially separate the heat-affected zones of the individual laser pulses sufficiently, even at significantly increased pulse frequencies. This results in both greater processing speed and more precise shape correction. Furthermore, in a submerged arc lathe, the actual shape can be measured without user intervention. Thus, iterative measurement and processing are possible, and the machine can independently process a component until the desired shape accuracy is achieved.

[0024] For precision laser machining, ultrashort pulse lasers with pulse durations in the picosecond and femtosecond range (USP laser radiation) are used according to the state of the art. However, when machining already polished glass surfaces, USP laser radiation always significantly increases the roughness, introduces subsurface damage, and thus destroys the polish. In contrast, the method proposed here corrects the shape of polished glass surfaces by thermal ablation with pulse durations in the microsecond range, i.e., by a factor of approximately 10. 6 The thermal effect is greater than with ultrashort pulse (USP) lasers, whereby the glass is also heated and softened significantly below the volume to be ablated. Therefore, the roughness does not increase significantly during thermal ablation.

[0025] However, in this thermal ablation process with pulse durations > 1 µs, centrifugal forces can lead to undesirable material flow and thus to deformation of the component's surface when the process is carried out on a lathe. Therefore, in the proposed method, the glass type of the component and the parameter space, in particular the rotational speed and pulse duration, are preferably selected such that the process can be advantageously carried out on a submerged arc lathe without undesirable surface deformation (> 10 nm) due to material flow. The process can thus be carried out in such a way that the deformation caused by centrifugal forces is less than 10 nm.

[0026] The proposed method is particularly advantageous for rotationally symmetric optical components where the axis of rotation is the component's axis of symmetry. The proposed method is especially beneficial for correcting the shape of fused silica optical components, since very small amounts of material can be removed using pulsed laser beam fusion (LBF) with fused silica, and even at very high rotational speeds, centrifugal forces do not deform the softened material, or only to a minimal extent.

[0027] To achieve the highest possible precision in shape correction, the actual geometry of the component is preferably measured with an accuracy of < 500 nm, and particularly preferably < 100 nm. Known optical measurement methods, especially interferometric methods, can be used for this purpose. If a submerged arc lathe is used, an existing measuring device on the lathe can also be utilized.

[0028] The component to be processed preferably already has a polished surface, as is typically the case, for example, at the end of a manufacturing chain for the production of the optical component when using the proposed method. In a particularly preferred embodiment of the method, the optical component is subjected to a further mechanical polishing after processing with the pulsed laser beam in order to reduce roughness for spatial wavelengths λ. oto reduce deviations of < 100 µm resulting from the processing of the optical component with laser radiation. Furthermore, it is advantageous to temper the component after shape correction in order to eliminate any shape deviations caused by compaction during processing.

[0029] In the proposed method, the spatial offset between successive pulses is preferably selected such that it corresponds to at least half the beam diameter of the laser beam on the component, and preferably to at least the full beam diameter of the laser beam on the component. The beam diameter of the laser beam on the component is generally the focus diameter, since the laser beam is focused onto the component or its surface for material removal. The beam diameter of the laser beam, or the focus diameter, is defined as 1 / e 2-Diameter to understand, i.e. the diameter at which the intensity in the beam profile is reduced to 1 / e 2 the maximum has dropped. The diameter of the material area of ​​the component ablated by a pulse should preferably be smaller than half the beam diameter of the laser beam on the component.

[0030] In an advantageous embodiment, the parameters for the laser beam pulses are selected such that material is both removed and the underlying material is heated to a temperature above its softening temperature and smoothed under the influence of surface tension, so that the roughness of the component, measured in Sa, over an area of ​​100 x 100 µm 2 increases by a maximum of 5 nm.

[0031] In the proposed method, shape correction is preferably performed using a CO2 laser or a UV laser. The laser radiation preferably has a wavelength in the range of 9–11 µm or < 180 nm. The pulse frequency of the laser radiation is preferably selected in the range of 1–100 kHz, particularly preferably in the range of 10–100 kHz, and the pulse duration preferably in the range of 1–50 µs. The parameters for shape correction are preferably selected such that the ablation depth per pulse is < 100 nm, preferably < 50 nm. Preferably, each pulse of the laser beam is assigned an individual pulse energy to enable optimal local adjustment of the ablation depth to the excess material determined by the target / actual comparison.This is particularly advantageous when generating the pulsed laser beam by modulating continuous laser radiation with an acousto-optic modulator (AOM), since the pulse duration and pulse amplitude can be changed from pulse to pulse, and the pulse frequency can also be varied across multiple pulses, by appropriately controlling the AOM. This then also enables the laser source to operate in a thermal equilibrium state, which is very advantageous with regard to ablation accuracy.

[0032] In a further advantageous embodiment, the outer areas of the component, located further out with respect to the axis of rotation, are machined at a constant feed rate by adjusting the rotational speed to the machining radius, while towards the center or axis of rotation, a constant (preferably high) rotational speed is maintained and the pulse frequency is adjusted to the machining radius. This allows for the selection of a high rotational speed even for machining the outer areas.

[0033] The advantageous configurations described in this application can of course also be combined with each other.

[0034] The proposed device is designed as an ultra-precision lathe, on which a laser beam source with corresponding laser optics, in one embodiment also a modulation device for modulating the laser beam, and positioning devices for varying the focus position in the beam direction and for displacing the laser beam radially to the axis of rotation of the lathe are arranged. Furthermore, the device also includes a measuring device for precisely measuring the actual shape of the component and a control device designed to control the lathe, the positioning devices, the modulation device, and the laser beam source for carrying out the proposed method.

[0035] The proposed method and associated apparatus can be advantageously used for shape correction of polished glass surfaces, particularly optics such as lenses or mirrors, and can either be performed in addition to or as a replacement for other surface post-processing. The main application area is the shape correction of precision optics, e.g., for applications in lithography, metrology, laser technology, or fusion technology.

[0036] The proposed method enables the controlled ablation of glass material in layers of preferably 1–100 nm for the precision shape correction of optics. The method employs deterministic ablation, as the laser beam tool does not experience mechanical wear. High rotational and peripheral speeds allow the heat-affected zones of the individual pulses to be separated. This increases both the precision and the achievable processing speed. The method can potentially increase the processing speed by a factor of more than 10 compared to known correction methods using laser beam fusion (LBF), which operate at approximately 1 kHz. When using a lathe, speeds of 10 to 100 kHz are possible. When using a submerged arc lathe, the lathe's measurement technology, if available, can advantageously be used to measure the geometry of the component, enabling measurement, processing, and re-measurement without operator intervention.Furthermore, problems that arise when measuring outside the machining center are avoided, particularly the necessary alignment of the coordinate systems between the measuring machine and the machining center. This method allows spheres and aspheres to be machined with virtually identical cycle times. Shape correction is performed not only in the range of MSFE (Mid-Spatial Frequency Errors), but also in other areas, making shorter spatial wavelengths than those achieved with IBF and MRF economically and technically feasible. Brief description of the drawings

[0037] The proposed method is explained in more detail below using exemplary embodiments in conjunction with the drawings. These show: Fig. 1 a process chain for the manufacture of optical components; Fig. 2 a schematic representation of the shape correction of a component using laser radiation according to the proposed method; Fig. 3 a schematic representation of the top view of a surface of an optical component to be corrected, in which the position of the individual pulses during a first revolution is indicated; Fig. 4 a schematic representation of the top view of a surface of the optical element to be corrected, in which the position of the individual pulses during the first revolution and during the second revolution is indicated; and Fig. 5 A schematic representation for defining the distance between two pulses within one revolution on a processing radius without thermal interaction. Ways to implement the invention

[0038] The proposed method enables shape correction of, for example, an optical component as it was obtained from a blank after shaping and polishing. Fig. Figure 1 shows a typical process chain for the production of optical components, as already described in the introduction. For the production of precision optics, the precision shape correction made possible by the present method can be used after shaping and polishing. The present method, in which successive pulses are distributed across the surface to be machined with a sufficiently large time interval between them so that the heat-affected zones of two successive pulses do not overlap, significantly increases the precision of the material removal. By using a rotating component with a submerged arc lathe, higher pulse frequencies and thus greater machining speeds can be achieved, as with previously known techniques.The proposed method and the associated device thus also enable more efficient and cost-effective shape correction of precision aspheres and freeform optics, fulfilling a key requirement in the photonics industry.

[0039] In contrast to the previously performed processing using scanners, in which the laser radiation is guided by deflecting mirrors and focused onto the surface of component 1, the proposed method, as exemplified in Fig. As shown in Figure 2, the component 1, which is to be corrected in shape, is rotated on an ultra-precision lathe (UP lathe) 2. The infeed movement 8 of the laser optics 3 is varied over a full rotation (360°). The processing can be carried out on several circular paths or on a spiral path on the surface of the component 1. The beam guidance is thus achieved via a polar movement with a synchronized guided infeed axis 8 (focus position, focus depth) on an UP lathe. Due to the rotational movement, this kinematics enables high precision on large areas without stitching and a high processing speed. In contrast to a linear scan with a scanner, no artifacts occur due to approach and retraction movements.

[0040] This kinematic system allows for the shape correction of both rotationally symmetric and non-rotationally symmetric components by appropriately varying the feed motion over a full rotation. Pulsed laser radiation or a pulsed laser beam 4 is used for processing, which can be generated, for example, by suitable modulation of continuous laser radiation. The wavelength of the laser radiation must be absorbed near the surface of the material being processed, as is the case, for example, when using infrared laser radiation (CO2 laser radiation) for processing quartz glass. The laser radiation is directed onto the material surface, preferably perpendicularly. However, oblique irradiation is also possible. The beam diameter can be in the range of 1 µm to 1 mm, preferably in the range of 100 µm to 500 µm.

[0041] The process is designed to correct an existing actual shape 5 of component 1 to a target shape 6 in the nanometer range for high-end optics. The process is particularly suitable for lenses with spherical, aspherical, or free-form contours.

[0042] Fig. Figure 3 shows an example of a top view of a surface to be corrected during a complete revolution (rotation through 360°).

[0043] The surface or component 1 to be corrected is moved at a circumferential speed v. Umfang 11, defined by the processing radius 14 (r1) around the center point M, is rotated. Pulses of laser radiation with the corresponding process parameters are coupled onto the surface at the processing radius r1. The following pulse and the preceding pulse have a distance d. U (12) This distance d UThe interval between a subsequent pulse and a preceding pulse is a crucial parameter in the execution of the process, as this interval significantly limits the controllability and precision of the heat-induced process. The interval d U In the present example, is defined by the focus diameter of the laser radiation and is limited to at least ½ * focus diameter (defined according to 1 / e 2 ), preferably set to at least 1 * focus diameter.

[0044] The in Fig. The surface shown schematically / exemplarily is the machined surface after the second cycle of the surface or component and excludes the machining after the first cycle. Fig. 3. It should be noted that the shape correction is performed with spatially and temporally separated pulses. There is no direct superposition of the pulses within a single revolution on the surfaces to be corrected. The superposition of the pulses, or the material areas removed by the pulses, only occurs in a subsequent revolution of the component.

[0045] The in Fig. Figure 4 shows the surface of the component with the areas 22 of the component removed by the individual pulses P2 from the second cycle U2, and has a distance d. U The single pulse P2 is activated, through which the areas 22 removed during the second revolution U2 overlap the areas 21 removed by the single pulses P1 from the first revolution U1, thus completing the surface correction along the machining radius r1. The correction process then continues at the machining radius r2 (15).

[0046] In this schematically represented example, the surface correction on a radius is completed in two passes. The number of passes can be variably increased to improve the controllability and precision of the heat-induced process. The procedure allows for multiple repetitions, with each individual pulse being set, omitted, or its parameters varied based on the excess material to be removed.

[0047] For the definition of the distance d U between two pulses within one revolution on any processing radius r is in Fig. Figure 5 shows a schematic representation of the temperature field distribution. Based on simulations with validated process parameter combinations, the pulse spacing d is determined. U with ½ * focus diameter (defined according to 1 / e 2 ), preferably at least 1 * focus diameter, defined.

[0048] In Fig.Figure 5 schematically depicts the temperature distribution in the form of temperature fields after the laser radiation is coupled into the surface of the component over time t. The distance d U The difference between a subsequent and a preceding pulse is defined as ½ * focus diameter (defined according to 1 / e 2), preferably at least 1 * focus diameter, is defined. The ablated areas 21 of the individual pulses are spatially and temporally offset and are smaller than the beam diameter. Immediately after the coupling of a pulse at time t = 0 s, the surface of the component heats up and reaches a temperature in area 21 over time t that leads to the ablation of the glass material. Due to the material ablation from the glass surface on the order of a few nanometers, the coupled heat is distributed in the glass and forms a temperature field at a time t1 (31) following t = 0 s. Depending on the selected process parameters, in particular the repetition rate of the modulated laser radiation f rep , a subsequent pulse at interval d occurs at time t2 UThe temperature field 31 is coupled into the glass surface from the preceding pulse. During the ongoing time, the temperature field 31 expands until time t2 (32). Simultaneously, a new temperature field of the subsequent pulse forms after time t2 (33). The temperature field of the second pulse grows after time t2 (33) to the temperature field of the second pulse after time t3 (34).

[0049] In a highly advantageous embodiment, the active laser medium is continuously excited and remains in a state of thermal equilibrium. Only through rapid control (e.g., using an acousto-optic modulator; AOM) are pulses with defined amplitude and duration extracted and transferred to the workpiece. The fluctuation in laser power, calculated as the standard deviation, should be < 0.5%, preferably even < 0.2%.

[0050] Typical laser powers used range from 1 W to 100 W, with the preferred range being greater than 80 W for high repetition rates of 100 kHz.

[0051] Other process parameters and their typical values ​​are: • The pulse interval d U depends on the repetition rate and the rotational speed 11. The pulses only need to be applied to the surface at points where material is to be removed. • The number of passes depends mainly on the surface quality to be corrected. A minimum of two passes is preferred. • The pulse duration is set between 1 µs < t p < 100 µs set. • Repetition rate is set between 0.1 kHz < f rep < 200 kHz set.

[0052] Instead of using constant process parameters for the respective component surface, individual process parameters can also be adjusted during the process. For example, the pulse duration can be changed during the process, and the ablation depth can be increased or decreased selectively. In addition to changing the pulse duration, the ablation depth can also be adjusted by changing the average laser power per pulse. Another example is adjusting the number of passes. Here, the surface is measured after a certain number of passes, and the target shape is corrected again based on the actual shape. This can be done in several iterations.

[0053] In addition to the problems already described, this method makes it possible to solve another problem. In contrast to long-wavelength surface structures, surface structures with short spatial wavelengths (λ) are used. oSurface roughness (< 100 µm) can be reduced to well below 1 nm by a (pitch) polishing process performed before or after the shape correction. Current economically viable shape correction methods for optics are limited to spatial wavelengths up to λ. o > 3000 µm. In total, a gap of approximately 100 µm < λ remains between polishing and shape correction in the spatial wavelength range. oSurface defects in the spatial wavelength range of < 3000 µm are called mid-spatial frequency errors (MSFE) and pose a significant challenge to the optics industry. They can severely and negatively impact the optical performance of precision optics, yet optics manufacturers currently lack a production method for the targeted elimination of MSFE. Laser-based shape correction, as proposed here, can close this gap. This enables the energy-efficient manufacturing of large and complex lens geometries, such as aspheres and freeform optics, making them cost-effectively accessible to the mass market. Reference symbol list 1 optical component 2 turns on a UP lathe 3 Laser optics 4 modulated or pulsed laser radiation 5 Current state 6 Target form 7 excess material 8 delivery directions 11 Circumferential speed Vumfang 12 Distance d U between the following pulse and the preceding pulse 13 Radius of the optical element R optik from the center point M 14 Machining radius r1 from center point M 15. Machining radius r2 from the center point M with r1 ≠ r2 21 Area recorded of a single pulse P1 during the first revolution U1 22 Area recorded of a single pulse P2 during the second revolution U2 31 Temperature field of pulse 1 after a time t1; T Feld1 (P1, t1) 32 Temperature field of pulse 1 after a time t2; T Feld2 (P1, t2) 33 Temperature field of pulse 2 after a time t2; T Feld1 (P2, t2) 34 Temperature field of pulse 2 after a time t3; T Feld2 (P2, t3)

Claims

[1] Method for shape correction of an optical component (1) using pulsed laser radiation, in which the component (1) is measured to obtain an actual geometry (5) of the component (1), and excess material (7) is determined by comparison with a predetermined target geometry (6) and is at least partially removed by processing with at least one pulsed laser beam (4) in order to at least approximate the actual geometry (5) to the target geometry (6), characterized by , that the processing is carried out with pulse durations of the laser beam (4) of > 1 µs and the component (1) is rotated about an axis of rotation passing through the component (1) during processing with the laser beam (4), whereby a distance of the laser beam (4) to the axis of rotation is changed at least temporarily, and A rotational speed, a beam diameter of the laser beam (4) on the component (1) and a time pulse interval of the laser beam (4) are selected such that the material areas of the component (1) removed by successive pulses of the laser beam (4) do not overlap. [2] Method according to claim 1, characterized by that the machining is carried out using an ultra-precision lathe that has a repeatability of < 200 nm, preferably < 50 nm. [3] Method Claim 1 or 2, characterized by , that the laser beam (4) is focused on the component (1) and that a focus of the laser beam (4) on the component (1) is appropriately tracked during processing by an adjusting device. [4] Method according to any one of claims 1 to 3, characterized by , that the laser beam (4) is guided during processing in such a way that the processing takes place on circular or spiral paths on the component (1). [5] Method according to claim 4, characterized by , that each circular or spiral path is swept over several times by the laser beam (4) for processing. [6] Method according to any one of claims 1 to 5, characterized by , that the rotational speed, the beam diameter of the laser beam (4) on the component (1) and the temporal pulse interval of the laser beam (4) are chosen such that successive pulses of the laser beam striking the component (1) have a center-to-center distance on the component (1) that is greater than half 1 / e 2 - The beam diameter of the laser beam (4) on the component (1) is preferably larger than the whole 1 / e 2 - Beam diameter. [7] Method according to any one of claims 1 to 6, characterized by , that parameters of the laser beam (4) are chosen such that the material area of ​​the component (1) removed by a pulse of the laser beam (4) has a smaller diameter than half 1 / e 2- Beam diameter of the laser beam (4) on the component (1). [8] Method according to any one of claims 1 to 7, characterized by , that the machining of more outward areas of the component (1) is carried out by adjusting the rotational speed to the machining radius with constant path speed and the machining of more inward areas is carried out by adjusting the time pulse interval to the machining radius with constant rotational speed. [9] Method according to any one of claims 1 to 8, characterized by , that the pulsed laser beam (4) is generated by modulating a continuous laser beam with an acousto-optic modulator, wherein the time pulse interval and / or pulse duration and / or pulse amplitude are varied for processing by controlling the acousto-optic modulator. [10] Method according to any one of claims 1 to 9, characterized by, that the parameters of the laser beam (4) are chosen such that both material of the component (1) is removed and underlying material is heated to a temperature above its softening temperature and smooths out under the influence of surface tension, thus resulting in a roughness of the component (1), measured in Sa, over an area of ​​100 x 100 µm 2 increases by a maximum of 5 nm. [11] Method according to any one of claims 1 to 10, characterized by , that a pulse frequency of the laser beam (4) is selected in the range of 1 - 100 kHz, preferably in the range of 10 - 100 kHz. [12] Method according to any one of claims 1 to 11, characterized by , that the pulse duration of the pulses of the laser beam (4) is chosen in the range between 1 and 50 µs. [13] Method according to any one of claims 1 to 12, characterized by , that after processing with the laser beam (4) the component (1) is tempered. [14] Method according to any one of claims 1 to 13, characterized by , that the component (1) is subjected to mechanical polishing after processing with the laser beam (4) in order to reduce roughness for spatial wavelengths λ o to reduce to < 100 µm even further. [15] Device for carrying out the method according to any one of claims 1 to 14, comprising a - Ultra-precision lathe with a repeatability of < 200 nm, - a laser arrangement for generating a pulsed laser beam (4), - a measuring device for measuring an actual geometry (5) of a component (1) clamped in the ultra-precision lathe and - a control device, wherein the laser arrangement is arranged such that the component (1) clamped in the ultra-precision lathe can be machined with the pulsed laser beam (4), and has adjusting devices for varying a focus position of the laser beam (4) in the beam direction and for displacing the laser beam (4) in a radial direction to the axis of rotation of the ultra-precision lathe, and wherein the control device is configured to control the ultra-precision lathe, the adjusting devices and the laser arrangement for carrying out the method according to one of claims 1 to 14. [16] Device according to claim 15, characterized by , that the laser arrangement comprises a laser beam source for generating continuous laser radiation and an acousto-optic modulator for generating the pulsed laser beam (4) from the continuous laser radiation.

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