Method and laser machining system for laser-based surface shape correction of a mirror

Abstract

The invention relates to a method and a laser machining system (2) for machining a mirror (1). In said method, at least one point is determined at which the actual shape of a mirror surface (5) of the mirror (1) deviates from a specified target shape. Laser radiation (3) is then radiated at this point in a focused manner into a material region (8) of the mirror (1) lying behind the mirror surface (5) and a local volume change (14) is produced there as a result. This local volume change (14) causes a corresponding change (15) in the shape of the mirror surface (5), in order to at least partially correct the deviation from the target shape.

Description

[0001] METHOD AND LASER PROCESSING SYSTEM FOR LASER-BASED SURFACE SHAPE CORRECTION OF A MIRROR

[0002] The present invention relates to a method and a laser processing system for processing a mirror.

[0003] Mirrors are used in various technical fields and applications, for example, to redirect light or laser radiation. The achievable performance and precision depend largely on the shape or surface of the respective mirror. For example, defects or damage to the mirror surface and / or deviations from a desired or specified surface shape of the mirror can lead to undesired beam expansion or impaired focusing or a shift in the focus position of a laser beam reflected by the mirror. Depending on the application, this can lead to losses in efficiency or processing speed or even to damage or failure of the respective system.However, the correspondingly high-precision production of optical components is not always practically feasible using conventional manufacturing processes, or can lead to increased process-related rejects in the production of corresponding optical components, such as mirrors, and thus to correspondingly high costs. Therefore, there is a need for improvements in this area.

[0004] The object of the present invention is to improve the usability of mirrors.

[0005] The object is achieved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the subclaims, the description and the drawing. Features, advantages and possible embodiments that are set out in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages and possible embodiments of the respective subject matter of the other independent claims as well as of any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims. The method according to the invention serves to manufacture or process a mirror, in particular a mirror intended for reflecting or deflecting laser radiation. In the method according to the invention, a predetermined or predefined target or desired shape of a mirror surface of the mirror can first be detected.This may mean, for example, that such a target or desired shape is captured via a user interface or read from a data storage device.

[0006] In the method according to the invention, the mirror is provided in a prefabricated initial state. Here, the mirror may already be assembled or have its essential elements or components, but may not yet have been finally finely machined or optimized, for example. In this initial state, the mirror has a carrier substrate or a base body and a mirror surface arranged or formed on a front side of the carrier substrate or base body. The mirror surface can be a machined, for example polished, surface or side of the carrier substrate or base body. Likewise, the mirror surface can be, for example, a coating of the carrier substrate or a separate component arranged or attached to the carrier substrate. The mirror surface can be specular, i.e., reflective for at least one predetermined wavelength.For example, for use of the mirror in EUV light generation or EUV lithography, the mirror surface can be specular or reflective for wavelengths in the range of, for example, 7 nm to 15 nm, approximately 1 pm to 2 pm and / or approximately 9 pm to 11 pm. However, the method according to the invention can also be applied to other types of mirrors. To produce the mirror in the prefabricated initial state, conventional or classic manufacturing methods or surface processing methods can be used, for example. However, this typically cannot guarantee a surface quality or surface shape of the mirror surface that is completely free of defects and tolerance deviations. In the prefabricated initial state, the mirror can therefore have a mirror surface that deviates from a predetermined or predefined target or desired shape.This specified target or desired shape can depend on the specific application and determine the final optical properties of the mirror.

[0007] In a further method step of the method according to the invention, at least one location is determined, in particular automatically, at which the actual shape of the mirror surface deviates from its specified target shape. The actual shape is or describes the real shape or the real surface condition or the real surface quality that the mirror surface has in its prefabricated initial state. The location can be determined or specified, for example, by a two-dimensional coordinate in a coordinate system of the mirror surface or in a plane of the mirror surface.

[0008] In a further method step of the method according to the invention, laser radiation, in particular a laser pulse or a sequence of laser pulses, is irradiated at this point into a material region of the mirror located behind the mirror surface. In this case, the laser radiation is or will be focused, in particular, only on this material region. A focal point or focal region of this laser radiation can therefore have the same two-dimensional coordinates as the specific location at which the actual shape of the mirror surface deviates from its desired shape, but can have different coordinates perpendicular to it. In other words, the laser radiation is not focused on or in the mirror surface itself, but at a certain distance from it.The fact that this focusing takes place behind the mirror surface means that the laser radiation is focused on the side facing the carrier substrate, i.e. a corresponding back side of the mirror surface, whereby the front side of the mirror surface is the side on or at which, when the mirror is used as intended, a reflection or deflection of radiation incident on it from outside the mirror ultimately takes place.

[0009] The laser radiation focused in this way in the material of the mirror creates or causes a local change in volume there. In other words, the focused laser radiation can cause a local volume defect or a local change in the material area of ​​the mirror lying behind the mirror surface. This can be caused, for example, by local thermal expansion and / or an influence on or destruction of chemical bonds within the material or the like. This local change in volume, in turn, causes a corresponding change in the shape of the mirror surface towards the desired shape, i.e. to at least partially compensate for or at least partially correct the deviation of the actual shape of the mirror surface from its desired shape. This is the case because the mirror surface itself is seamlessly bonded to the carrier substrate oris connected to the respective material region in which the volume change is brought about and has only limited stiffness or strength. Such an indirectly produced change in the shape of the mirror surface can, for example, be in the size range of a few nanometers up to a few micrometers or more in one or more dimensions. In the method proposed here, the mirror surface itself is therefore not directly processed. Rather, the material behind it is influenced by means of the laser radiation, thereby indirectly changing or adapting the shape, i.e. the surface contour of the mirror surface. This influence on the corresponding material or material region occurs only or primarily in the focal point or focal area of ​​the irradiated laser radiation.Depending on the materials used and the wavelength of the laser radiation, the material region can be an inner region surrounded by material and therefore does not have to be directly accessible from the outside. However, the laser radiation can pass through the carrier substrate and / or the mirror surface, for example, without leading to volume changes there, because the laser radiation is not focused there and therefore has, for example, too low an energy or power density. The material region located in the focal point or focus region of the laser radiation can, on the other hand, be permanently changed by the laser radiation focused there. This means that even after the laser radiation is switched off and, if applicable, after the material region or mirror surface has cooled down, the volume changes.of the mirror as a whole, the local volume change caused by the focused laser radiation and thus also the corresponding change in shape of the mirror surface is at least partially retained.

[0010] The mirror surface can be detected or measured using sensors, for example using a microscope or interferometric methods, in order to determine or record the actual shape. In this case, for example, the surface quality and / or the surface microstructure and / or surface defects and / or depressions or dents and / or grooves or furrows and / or the like can be detected or recorded. Likewise, the actual shape can be assumed to be at least essentially smooth, for example if the target shape provides for a predetermined microstructure of the mirror surface that is only created by the irradiated laser irradiation or the local volume change caused thereby, and the previous manufacturing process for producing the mirror in the prefabricated initial state does not include any steps to create such a microstructure.

[0011] The method according to the invention can enable the production of mirrors with a specific desired shape and relatively strict precision or tolerance requirements more easily and cost-effectively than would be the case, for example, when using conventional mechanical surface processing or surface manufacturing processes, such as mechanical polishing processes, in a design that allows a corresponding surface quality or surface finish of the mirror surface. The method according to the invention can be used, for example, to correct mirrors that were manufactured using conventional mechanical processes and would otherwise be classified as rejects due to surface defects or shape deviations. Such mirrors can then still be used for their original purpose after processing with the method according to the invention.Likewise, for example, an identical manufacturing process can be used to produce mirrors that are identical in accordance with the specifications, and then the method according to the invention can be applied to enable individual adaptations or optimizations of the individual mirrors with comparatively little effort.

[0012] In one possible embodiment of the present invention, the laser radiation is radiated through the carrier substrate in the direction of the rear side of the mirror surface facing the latter. For this purpose, the wavelength of the radiated laser radiation used can be matched to the carrier substrate or the wavelength of the laser radiation and the carrier substrate can be matched to one another such that the carrier substrate is at least partially permeable or transparent to the laser radiation and yet sufficient absorption to bring about the volume change is possible or occurs at the focal point of the laser radiation. Glass or quartz glass, for example, can be used as the carrier substrate. Due to the embodiment proposed here, the described volume change can also be brought about by means of the laser radiation if the mirror surface is opaque to the laser radiation, for example highly reflective or absorbent.In addition, this makes it particularly reliable to prevent a front side or surface of the mirror surface facing away from the carrier substrate from being influenced in an undesirable way by the laser radiation. In particular, when the laser radiation reaches at least the back side of the mirror surface, at least part of the energy of the laser radiation is already coupled into the material region behind the mirror surface, i.e. the laser radiation is correspondingly attenuated. Likewise, a layer that is opaque to the laser radiation can be arranged between the carrier substrate and the mirror surface, for example. The material region into which the laser radiation is focused can then lie on a side of this layer that is opaque to the laser radiation and faces the carrier substrate. Since such a layer can be thin, for example, compared to the carrier substrate, it can still possibly bring about the described change in shape of the mirror surface orfrom their surface or front.

[0013] In a further possible embodiment of the present invention, the laser radiation is radiated from outside the mirror toward the front of the mirror surface and through it toward the carrier substrate. For this purpose, a wavelength of laser radiation can be used for which the mirror surface is permeable, i.e., at least substantially transparent. Depending on the materials used for the mirror and / or, for example, the thickness of the carrier substrate, the laser radiation can thus be focused, for example, into the material region behind the mirror surface even if the carrier substrate is too thick or too strongly absorbent for the laser radiation.In this case, by irradiating the laser radiation through the front side of the mirror, i.e. through the mirror surface, as proposed here, the material region in which the local volume change is generated by means of the laser radiation can be relatively dense or close to the mirror surface and yet a sufficiently strong, relatively fast and sufficiently local energy coupling can be enabled.

[0014] In a further possible embodiment of the present invention, the mirror in its prefabricated initial state has an intermediate layer arranged between the carrier substrate and the mirror surface. This intermediate layer can thus connect the mirror surface to the carrier substrate. The laser radiation is focused into this intermediate layer to generate the local volume change in its material. In other words, the material region into which the laser radiation is focused to generate the local volume change is or primarily comprises material of the intermediate layer. The intermediate layer can, for example, be an adhesive, i.e., an adhesive layer.Likewise, a material of the intermediate layer can be specially selected or predetermined in such a way that local volume changes can be generated therein by coupling in energy, in particular by means of laser radiation, which changes in volume are stable, i.e. are retained at least partially even after the energy coupling has ended or after cooling. The method described can therefore, for example, also be used if the carrier substrate itself is not suitable for such a local volume change. In a possible development of the present invention, the material of the intermediate layer is or will be selected or predetermined in such a way and the irradiation of the laser radiation into it, i.e. an energy input into the material of the intermediate layer brought about by the laser radiation, is or will be coordinated orset so that the local volume change generated in the intermediate layer, and thus ultimately also the corresponding shape change of the mirror surface, is reversible. For this purpose, for example, the duration and / or intensity and / or power and / or a temporal irradiation pattern of the laser radiation can be adapted or set accordingly. This can be done, for example, in such a way that the material of the intermediate layer does not get too hot, i.e. does not burn or char, or the like. To reverse or cancel out the generated local volume change, the material of the intermediate layer or the mirror as a whole can be heated to a predetermined temperature, for example. This can be used, for example, to heat out mechanical stresses that maintain the local volume change, or to soften the material of the intermediate layer so that it returns to its original shape orreturns to its original volume, for example by refilling a cavity created by the laser radiation or the like. Such reversibility of the local volume change means that the target shape of the mirror surface can be created particularly reliably and precisely, for example in several attempts if necessary. Likewise, the same mirror can then be flexibly shaped and used as needed for different applications or requirements. For example, after creating a first predetermined target shape, the mirror can be used for a first application and then a different second target shape of the same mirror can be created in order to then use it for a different application. This can ultimately be particularly cost-effective and / or resource-saving, for example in comparison to using separate, different mirrors.

[0015] In a further possible embodiment of the present invention, the material region in which the laser radiation is focused, and in which the local volume change is thus generated, is locally heated above its glass transition temperature by means of the laser radiation. The material region can therefore be in a rigid, glass-like state before the laser radiation is applied. Upon heating above the glass transition temperature, the material region can transition to a soft, rubber-like state. In this state induced by the laser radiation, the material region or the material therein can change its shape or volume. Cooling can then take place to below the glass transition temperature, although at least part of the local volume change is retained.This ensures that the mirror maintains its desired shape stably and reliably over time during regular use, where the temperature remains below the glass transition temperature. The laser radiation can be irradiated into an amorphous material or a correspondingly amorphous material region of the mirror. This could be, for example, an amorphous carrier substrate, such as glass, or an adhesive, such as the intermediate layer mentioned elsewhere.

[0016] In a further possible embodiment of the present invention, the processing of the mirror is carried out iteratively in several steps. During processing of the mirror, the mirror surface is observed by means of a sensor, in particular by means of an interferometer, and in this way the current actual shape is determined or any change in the shape of the mirror surface is monitored. The laser radiation is irradiated several times in succession, with only a part of the total volume change being generated in each case. At least in between, i.e. after each irradiation or after each laser pulse, a check is carried out based on corresponding sensor data from the sensor system to determine whether the desired shape of the mirror surface has already been achieved. In this case, laser radiation, for example one laser pulse in each case, can therefore be irradiated several times, each time with a power and duration, i.e. an energy input whichwhich is probably not suitable for generating the total volume change to be achieved at the respective location or necessary to compensate for or correct the initially determined deviation during or with one irradiation or a single irradiation phase, i.e., for example, with a single laser pulse. For example, depending on the respective remaining deviation and / or depending on the change in the actual shape of the mirror surface achieved with the respective last irradiation, the respective next irradiation can be adapted, for example with regard to duration and / or intensity and / or power and / or energy input and / or focus position and / or focus size or beam diameter and / or the like.

[0017] These steps are then repeated iteratively until the desired shape and / or a predetermined maximum volume change is achieved. The embodiment of the present invention proposed here allows the respective desired shape to be generated particularly precisely and reliably, particularly when the laser beam only allows a volume change in one direction, i.e., only an increase or decrease in volume. This eliminates the need to know or calculate an exact model for the generated volume change. Furthermore, this allows for responses to individual properties or behaviors of the respective mirror.For example, nominally or according to specifications, identical mirrors may differ in their microscopic behavior upon exposure to laser radiation, for example, due to different material defects or local inclusions of foreign or interfering materials, or different strengths or patterns of mechanical stresses present within the material of the respective mirror in the respective prefabricated initial state, and / or similar factors. Even in such cases, the process proposed here can gradually achieve or adjust the respective target shape. This ultimately further reduces the amount of mirror scrap.

[0018] In a further possible embodiment of the present invention, a distance of the focal point or focal area of ​​the laser radiation in the material of the mirror from the mirror surface or its back, i.e. the focus position relative to the mirror surface, is adjusted or set, in particular automatically, depending on the deviation to be compensated or corrected, i.e. the volume or shape change to be generated. In this case, a smaller distance is used for a larger deviation or a larger change in shape of the mirror surface to be generated. The embodiment of the present invention proposed here is based on the finding that a local volume change generated inside a material does not lead to a corresponding or constant shape change of a surface of the material over any arbitrary distance.Thus, varying the distance of the local volume change in the inner material region of the mirror from the mirror surface, i.e. the surface of the mirror, offers a further degree of freedom with regard to the resulting change in shape of the mirror surface. This allows different target shapes or different changes in shape of the mirror surface to be created particularly precisely and reliably. For example, particularly small changes in shape of the mirror surface can be created even if there is a lower limit on the minimum local volume change that can be generated or a minimum energy input to cause a local volume change and / or a minimum focus size or a minimum material area that can be influenced by the laser radiation and thus a minimum size of a producible local volume change.

[0019] In a further possible embodiment of the present invention, a size of the material region of the mirror influenced by the focused laser radiation is adjusted or set, in particular automatically, depending on the deviation to be compensated or corrected, i.e. the shape change to be brought about. In the case of a larger deviation or a larger shape change to be brought about, a larger material region is influenced. The size of the influenced material region can mean its extent in one, two, or three directions or dimensions, for example its surface area in a plane extending parallel to the mirror surface or its volume. A minimum size can be predetermined by a minimum focus size or a maximum focusability of the laser radiation.Larger material areas, however, can be influenced by partial defocusing and / or by a movement of the focal point of the laser radiation in the material of the mirror, i.e., relative to the mirror surface. Such a movement can be realized, for example, by means of scanner optics, such as a galvo scanner or the like, of a laser processing system used for the method according to the invention. The embodiment of the present invention proposed here is based on the finding that a maximum volume change that can be generated in a specific point or area can be limited, but that larger changes in the shape of the mirror surface can be brought about by expanding the material area influenced by the laser radiation. This makes it possible to bring about particularly extensive changes in the shape of the mirror surface.Thus, the method according to the invention can be used in a particularly diverse or flexible manner and, if necessary, the rejection of mirrors can be further reduced.

[0020] In a further possible embodiment of the present invention, an aberration, i.e. an imaging error of the mirror or the mirror surface, is determined, in particular automatically, in the prefabricated initial state. An opposite pattern or a negative pattern of local volume changes is then generated in the mirror. This opposite or inverted pattern of local volume changes can, if necessary, be adapted or scaled with a factor that specifies or takes into account the size or extent of a change in shape of the mirror surface depending on the size or extent of the corresponding or responsible local volume change in the mirror. Through the pattern of local volume changes generated here, the aberration or imaging error of the mirror can ultimately be at least substantially compensated or corrected by the resulting corresponding changes in shape of the mirror surface.

[0021] In a further possible embodiment of the present invention, laser radiation is simultaneously irradiated at several spatially spaced locations on the mirror in order to simultaneously generate several volume changes to compensate for or correct several local deviations between the actual shape of the mirror surface and its desired shape. For this purpose, for example, several laser beams can be used simultaneously. This enables particularly rapid processing of the mirror. Thus, the method according to the invention can also be used efficiently and cost-effectively in the industrial series or mass production of mirrors.

[0022] In a further possible embodiment of the present invention, at least one volume change - planar or linear or line-shaped - extending parallel to the mirror surface and / or a plurality of individual, each point-like or extended volume changes are generated in a predetermined pattern. The generation of an extended volume change can mean that the extended volume change or the material region influenced by the laser radiation to generate an extended volume change is larger, in particular several times or many times larger, than the size of the focal point or focus diameter or focus volume of the laser radiation. The pattern creates an optically functional structure, for example a nanostructure or microstructure, in the mirror surface as a corresponding change in shape, for influencing at least one property of radiation incident thereon, in particular laser radiation.Such an optically functional structure can, for example, influence a phase or phase distribution and / or a beam shape of a laser beam reflected or deflected by the mirror surface. This means that a functional design of the mirror that goes beyond mere reflection or deflection can be realized individually and according to requirements. This can be achieved in particular by taking into account deviations of the actual shape from the specified target shape that already exist in the prefabricated initial state. Conventional methods for producing mirror surfaces, such as mechanical polishing processes, cannot easily be used to produce such functional structures with high precision. The present invention therefore offers a possibility for particularly flexible and, if necessary, cost-effective production of corresponding mirrors.

[0023] In a further possible embodiment of the present invention, the entire mirror is heated after the laser radiation has been applied, i.e. after the local volume change and the corresponding shape change have been generated. This completely or partially relieves any stresses thermally generated in the mirror material by the laser radiation and / or completely or partially reverses the generated volume change. The former can improve the robustness and reliability of the mirror. The latter can be applied, for example, after the mirror has been used as intended, in order to be able to process the mirror again as described for a different application or other requirements that require a different shape of the mirror surface, or to correct any processing errors, for example, a change in the shape of the mirror surface that is too great beyond the desired shape and was caused during a first processing attempt.This allows the mirror to be prepared for further processing. The mirror can, for example, be heated or baked in an oven. As described elsewhere, the local volume change can be reversible by heating, for example, above a certain predetermined temperature.

[0024] In a further possible embodiment of the invention, laser radiation is irradiated in a focused manner into the material region behind the mirror surface, with an intensity distribution such that the desired target shape is largely achieved. Such an intensity distribution can be achieved, for example, by means of a focused projection irradiated into the material region behind the mirror surface. In this context, "focused irradiation" means that a projection plane of the projection runs parallel to a mirror plane along which the mirror surface extends at least partially or against which the mirror surface rests tangentially.In this possible embodiment, a projection optics in the form of a projection lens or a projection mirror is arranged between a beam output for the laser radiation and the mirror surface, by means of which projection the projection is irradiated in a focused manner into the material region behind the mirror surface. This possible embodiment is particularly advantageous because it allows a larger area of ​​the material region behind the mirror surface to be processed. The present invention also relates to a laser processing system. The laser processing system according to the invention has at least one laser radiation source, a focusing unit arranged downstream of this laser radiation source for focusing laser radiation generated by means of the laser radiation source into a predetermined processing field in which a mirror to be processed can be arranged, and a sensor system for detecting a shape of a mirror surface of such a mirror orfor monitoring a change in the shape of the mirror surface for changes in shape and a control device. The laser processing system is designed to carry out the method according to the invention, in particular automatically or semi-automatically. For this purpose, the control device can have, for example, a processing device, such as a microprocessor or microchip or microcontroller or the like, and a computer-readable data memory coupled thereto. A corresponding operating or computer program can then be stored therein, which codes or implements the method steps, measures or sequences or corresponding control instructions described in connection with the method according to the invention. This operating or computer program can then be executable by means of the processing device in order to carry out the corresponding method or to bring about its execution.For this purpose, the control device can, for example, control the laser radiation source and / or the focusing unit accordingly. Likewise, the laser processing system can have further components, for example, components that can be controlled by the control device, such as the scanner optics mentioned elsewhere and / or an adjustment or displacement device for adjusting a position or orientation of a processing head of the laser processing system relative to the processing field and / or for moving a mirror to be processed relative to the laser radiation source or a processing head of the laser processing system. The laser processing system according to the invention can, in particular, be the laser processing system mentioned in connection with the method according to the invention or correspond thereto.In particular, the laser radiation source of the laser processing system according to the invention can be configured or designed to generate laser pulses, in particular ultrashort pulses of laser radiation. This allows the coupling of energy into the respective mirror to be controlled particularly precisely and reliably.

[0025] Further features of the invention can be derived from the following description of the figures and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures alone, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0026] The drawing shows:

[0027] Fig. 1 is a schematic representation of a mirror in a first variant and of a laser processing system for processing the mirror by means of laser radiation;

[0028] Fig. 2 is a schematic representation of the mirror with a change in shape of a mirror surface of the mirror in the first variant produced as a result of the processing;

[0029] Fig. 3 is a schematic representation of a mirror in a second variant and of a laser processing system for processing the mirror by means of laser radiation;

[0030] Fig. 4 is a schematic representation of the mirror with a change in shape of a mirror surface of the mirror in the second variant produced as a result of the processing.

[0031] Identical or functionally equivalent elements are provided with the same reference numerals in the figures.

[0032] Fig. 1 shows a schematic diagram illustrating a method for processing a mirror 1 in a first variant. Here, the mirror 1 is shown in a sectional side view. A laser processing system 2, also shown schematically here, is provided for processing the mirror 1. This system allows laser radiation 3 to be focused onto a carrier substrate 4 of the mirror 1. A mirror surface 5 of the mirror 1 is formed on one side of this carrier substrate 4, which in this case is at least substantially perpendicular to the plane of the drawing.

[0033] The laser processing system 2 comprises a laser radiation source 6 for generating the laser radiation 3. Furthermore, the laser processing system 2 has a focusing unit 7 on the output side for focusing the laser radiation 3. In this case, the laser radiation 3 is focused by the focusing unit 7 into a material region 8 located behind the mirror surface 5 in the carrier substrate 4.

[0034] The mirror 1 can have, for example, a quartz glass body as the carrier substrate 4, which is provided with a highly reflective, for example dielectric, coating that forms the mirror surface 5. A local defect, such as a microcrack, can be generated in the material of the carrier substrate 4 by the laser radiation 3, for example an ultrashort laser pulse, by means of two-photon absorption. Such microcracks lead to a locally reduced density and thus to a local volume expansion in the material region 8. This region can be located directly beneath the mirror surface 5 or at least close enough to it that the shape of the mirror surface 5 can also be changed.

[0035] To detect the actual shape of the mirror surface 5, the laser processing system 2 also has a sensor system 9. Furthermore, the laser processing system 2 comprises a control device 10, which is connected to the laser radiation source 6 and the sensor system 9 via an interface 11. Schematically indicated, the control device 10 comprises a processor 12 and a data memory 13, for example, for processing sensor data from the sensor system 9 and for controlling the laser radiation source 6 depending thereon.

[0036] To illustrate a processing result, Fig. 2 shows a schematic representation of the mirror 1 after processing by means of the laser processing system 2 or the laser radiation 3. The laser radiation 3 focused in the material region 8 has created a volume defect 14 there, here, for example, a local increase in volume of the carrier substrate 4. This volume defect 14 has caused a corresponding change in shape 15 of the mirror surface 5 at the location of the volume defect 14. The laser radiation 3 therefore directly influences or modifies only the carrier substrate 4, without damaging the mirror surface 5 or, for example, influencing its reflectivity. Thus, by creating at least one volume defect 14 behind the mirror surface 5, the corresponding change in shape 15 of the mirror surface 5 can be controlled and locally generated or written accordingly.This allows, for example, production-related deviations from a specified target or nominal shape to be compensated or corrected, or to specifically create specific mirror surface shapes or optically functional structures of the mirror surface 5. For example, more complex mirrors 1 or mirror surface shapes can be created from relatively simple and standardized base mirrors. For example, the laser radiation 3 can be used to create an aspherization of an initially provided spherical mirror 1, or to produce a phase correction mirror for aberrated optical systems, or similar applications.

[0037] In the example shown in Fig. 1, the laser radiation 3 is irradiated through the carrier substrate 4. Thus, the affected material region 8 can, for example, be located relatively close to the mirror surface 5 even if the latter is opaque to the laser radiation 3.

[0038] Likewise, in other cases, the laser radiation 3 can be radiated from a different direction. Fig. 3 shows a schematic representation to illustrate a corresponding method. Here, too, the mirror 1 is shown in a sectional side view. However, by means of the laser processing system 2, the laser radiation 3 is radiated in the direction of the mirror surface 5 and through it. Furthermore, the mirror 1 has a multi-layer or multi-part construction. An intermediate layer 16 is located between the carrier substrate 4 and the mirror surface 5. This intermediate layer 16 can, for example, be an adhesive layer that connects the carrier substrate 4 to the mirror layer 5 or to a second substrate on or upon which the play layer 5 is formed. Such a second substrate can, for example, be thinner and / or made of a different material than the carrier substrate 4.In particular, the mirror layer 5 or also this second substrate can be at least substantially transparent to the laser radiation 3.

[0039] The laser radiation 3 is focused here into the intermediate layer 16. The material of this intermediate layer 16 - similar to the carrier substrate 4 in the variant shown in Fig. 1 - can be locally heated above its glass transition temperature, whereby a corresponding local volume change can be caused. This can be at least partially retained even after subsequent cooling of the intermediate layer 16 to below its glass transition temperature. For illustration, Fig. 4 shows a schematic representation of the mirror 1 after processing. Here, the permanent or stable local volume change in the intermediate layer 16 is identified as a corresponding local volume defect 14. This has also led to a corresponding local deformation of the second substrate and to a corresponding surface deformation or shape change 15 of the mirror surface 5.

[0040] Likewise, the various directions of incidence of the laser radiation 3 can be interchangeable. Thus, for example, in the multi-layer or multi-part design of the mirror 1 shown in Fig. 3, the laser radiation 3 could be radiated through the carrier substrate 4 toward a rear side of the mirror layer 5 facing said substrate or focused into the intermediate layer 16. In the manner described here, not only individual, point-like shape changes 15 can be created, but also extensive shape changes 15 or, for example, several adjacent or overlapping shape changes 15 or a pattern of shape changes 15 can be created. Overall, the examples described demonstrate how a surface correction of mirrors can be carried out.

[0041] LIST OF REFERENCE SYMBOLS

[0042] 1 mirror

[0043] 2 laser processing systems

[0044] 3 Laser radiation

[0045] 4 Carrier substrate

[0046] 5 Mirror surface

[0047] 6 Laser radiation source

[0048] 7 Focusing unit

[0049] 8 Material area

[0050] 9 Sensor technology

[0051] 10 Control device

[0052] 11 Interface

[0053] 12 processors

[0054] 13 Data storage

[0055] 14 Volume defect

[0056] 15 Change in shape

[0057] 16 Intermediate layer

Claims

PATENT CLAIMS 1. A method for processing a mirror (1), wherein - the mirror (1) is provided in a prefabricated initial state, in which the mirror (1) has a carrier substrate (4) and, on a front side thereof, a mirror surface (5) which deviates from a predetermined desired shape, - at least one point is determined at which the actual shape of the mirror surface (5) deviates from its desired shape, - at this point, laser radiation (3) is irradiated in a focused manner into a material region (8) of the mirror (1) located behind the mirror surface (5), thereby generating a local volume change (14) there, which causes a corresponding change in shape (15) of the mirror surface (5) to at least partially correct the deviation.

2. Method according to claim 1, characterized in that the laser radiation (3) is radiated through the carrier substrate (4) in the direction of a rear side of the mirror surface (5) facing the latter.

3. Method according to one of the preceding claims, characterized in that the laser radiation (3) is radiated from outside the mirror in the direction of the front side of the mirror surface (5) and through it.

4. Method according to one of the preceding claims, characterized in that the mirror (1) in the prefabricated initial state has an intermediate layer (16) which is arranged between the carrier substrate (4) and the mirror surface (5), and the laser radiation (3) is focused into this intermediate layer (16) in order to produce the local volume change (14) in its material.

5. Method according to claim 4, characterized in that the material of the intermediate layer (16) is predetermined and the irradiation of the laser radiation (3) is adjusted therein such that the generated local volume change (14) of the material of the intermediate layer (16) is reversible.

6. Method according to one of the preceding claims, characterized in that the material region (8) is heated by means of the laser radiation (3) above its glass transition temperature.

7. Method according to one of the preceding claims, characterized in that the processing of the mirror (1) is carried out iteratively in several steps by - the mirror surface (2) is observed during the processing of the mirror (1) by means of a sensor system (9), in particular by means of an interferometer, and thus the current actual shape of the mirror surface (5) is monitored, - the laser radiation (3) is irradiated several times in succession, whereby only a part of the total volume change (14) is generated in each case and in between it is checked based on corresponding sensor data of the sensor system (9) whether the desired shape of the mirror surface (5) has been achieved, and - this is repeated until the desired shape and / or a predetermined maximum volume change (14) is reached.

8. Method according to one of the preceding claims, characterized in that a distance of a focal point of the laser radiation (3) from the mirror surface (5) is adjusted, in particular automatically, depending on the deviation, wherein a smaller distance is used in the case of a larger deviation.

9. Method according to one of the preceding claims, characterized in that a size of the material region (8) of the mirror (1) influenced by the focused laser radiation (3) is adjusted, in particular automatically, as a function of the deviation, wherein in the case of a larger deviation a larger material region (8) is influenced.

10. Method according to one of the preceding claims, characterized in that an aberration of the mirror (1) in the prefabricated initial state is determined and an opposite pattern of local volume changes (14) is generated.

11. Method according to one of the preceding claims, characterized in that laser radiation (3) is irradiated simultaneously at several spatially spaced locations in order to simultaneously produce several volume changes (14) for correcting several deviations.

12. Method according to one of the preceding claims, characterized in that at least one volume change (14) extending parallel to the mirror surface (5) and / or a plurality of volume changes (14) are generated in a predetermined pattern and thereby an optically functional structure (15) is generated in the mirror surface (5) for influencing at least one property of radiation incident thereon, in particular a phase and / or a beam shape.

13. Method according to one of the preceding claims, characterized in that after generating the local volume change (14) the entire mirror (1) is heated and thereby thermally induced stresses in the mirror (1) are reduced by the laser radiation (3) and / or the generated volume change (14) is reversed.

14. Laser processing system (2), comprising a laser radiation source (6), a focusing unit (7) arranged downstream of the laser radiation source (6) for focusing laser radiation (3) generated by the laser radiation source (6) into a processing field in which a mirror (1) to be processed can be arranged, a sensor system (9) for detecting a shape of a mirror surface (5) and a control device (10), wherein the Laser processing system (2) is arranged to carry out a method according to one of the preceding claims.

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