Mirror processing methods and laser processing systems

Abstract

The present invention relates to a method for processing a mirror (1) and a laser processing system (2). It is determined that the actual shape of the mirror surface (5) of the mirror (1) deviates from the expected target shape at least in one location. At this point, laser radiation (3) is then focused onto a material region (8) located on the back side of the mirror surface (5) of the mirror (1), thereby producing a local volume change (14). This local volume change (14) then causes a corresponding change in the shape (15) of the mirror surface (5) to at least partially correct the deviation from the expected shape.

Description

[Technical Field]

[0001] This invention relates to a laser processing system and method for mirror surface processing. [Previous Technology]

[0002] Mirrors are used in various technical fields and applications, such as changing the direction of light or laser radiation. The achievable performance and accuracy depend heavily on the shape or surface of the mirror. For example, errors or damage to the mirror surface and / or deviations from the expected or specified mirror shape can cause unexpected beam widening or impaired focusing or focal position shift of the mirror-reflected laser beam. Depending on the application, this can impair efficiency or processing speed, and even lead to damage or malfunction of the corresponding system. However, using conventional manufacturing processes does not always achieve the high-precision production of optical components and may increase process-related scrap in the production of optical components (e.g., mirrors), resulting in correspondingly high costs. Improvements are needed here. [Summary of the Invention]

[0003] One of the objectives of this invention is to improve the usability of mirrors.

[0004] This objective will be described through the independent claims. Other possible embodiments of the invention will be described in the appendices, description, and drawings. The features, advantages, and possible embodiments set forth in the description of the independent claims will be at least similar to the features, advantages, and possible embodiments of the other respective independent claims and possible combinations thereof, and may be combined with one or more appendices where necessary.

[0005] The method according to the invention is used for the production or processing of mirrors, particularly mirrors for reflecting or redirecting laser radiation. In the method according to an embodiment of the invention, a designated or predetermined target or expected shape of the mirror surface can first be detected. This may mean, for example, that the target or expected shape is recorded in a user interface or read from data memory.

[0006] In the method according to the invention, the mirror is in a prefabricated initial state. Therefore, the mirror can be assembled or has its basic elements or components, but has not yet been finalized or optimized. In this initial state, the mirror has a carrier substrate or base and a mirror surface assembled or configured on the front side of the carrier substrate or base. The mirror surface can be a processed, e.g., polished surface or side of the carrier substrate or base. Similarly, the mirror surface can be a coating of the carrier substrate or a separate component configured or attached to the carrier substrate. This mirror surface can be reflective, i.e., reflective at least for a predetermined wavelength. For example, for mirrors used in EUV light generation or EUV lithography, the mirror surface can be specular or reflective for wavelengths such as 7 nm to 15 nm, approximately 1 μm to 2 μm, and / or approximately 9 μm to 11 μm. However, the method according to the invention can also be used for other types of mirrors. To produce a mirror in its prefabricated initial state, conventional or classical manufacturing methods or surface treatment methods can be used, for example. However, this generally cannot guarantee that the surface quality or surface shape of the mirror is completely free of errors and tolerance deviations. Therefore, in its initial prefabricated state, the mirror may have a surface that deviates from a specified or predetermined target or desired shape. This specified target or desired shape may depend on the corresponding application and determine the final optical properties of the mirror.

[0007] In another method step according to the invention, at least one location is specifically and automatically determined where the actual shape of the mirror deviates from its designated target shape. The actual shape is or describes the true shape, true surface condition, or true surface quality that the mirror possesses in its prefabricated initial state. For example, this location can be determined or given through the mirror's coordinate system or two-dimensional coordinate information in the plane of the mirror.

[0008] In another step of the method according to the invention, laser radiation, particularly laser pulses or a series of laser pulses, is then irradiated onto a material region located on the back of the mirror. The laser radiation is specifically focused only on this material region. Therefore, the focal point or focused area of ​​this laser radiation may have the same two-dimensional coordinates as a specific portion of the mirror's actual shape deviating from its target shape, but may have different coordinates perpendicular to it. In other words, the laser radiation is not focused on the mirror itself or within the mirror, but at a certain distance from the mirror. The fact that this focusing occurs on the back of the mirror means that the laser radiation is focused on the side facing the carrier substrate, i.e., approximately the corresponding back of the mirror, the side facing the mirror that, when the mirror is used as intended, ultimately experiences reflection or deflection of radiation incident upon it from outside the mirror.

[0009] Laser radiation focused in this manner onto the mirror material produces or causes a localized volume change. In other words, the focused laser radiation can cause localized volume defects or localized volume changes in a region of the material located on the back of the mirror. This change is caused, for example, by localized thermal expansion and / or by affecting or breaking chemical bonds within the material. This localized volume change, in turn, causes a corresponding change in the orientation of the mirror shape relative to the intended shape, meaning that it at least partially compensates for or corrects for the deviation between the actual and intended shapes of the mirror. This occurs because the mirror itself is seamlessly connected to the carrier substrate or the corresponding material region causing the volume change and has only limited stiffness or strength. The indirectly generated change in mirror shape can, for example, range in size from a few nanometers to a few micrometers or larger in one or more dimensions.

[0010] The method proposed herein does not directly modify the mirror itself. Instead, the material on its back is affected by laser radiation, indirectly altering or adjusting its shape, i.e., the surface profile of the mirror. The effect on the corresponding material or material region occurs only or primarily at the focal point or focused area of ​​the irradiated laser radiation. Depending on the material used and the wavelength of the laser radiation used, the material region can be an internal region surrounded by material, and therefore need not be directly obtained from the outside. However, the laser radiation can, for example, pass through the carrier substrate and / or through the mirror without causing a volume change at that point, because the laser radiation is not focused there and therefore has, for example, too low an energy or power density. However, the material region located at the focal point or focused area of ​​the laser radiation can be permanently altered by the laser radiation focused there. This means that even after the laser radiation is turned off and possibly after the material region or mirror has cooled, the local volume changes caused by the focused laser radiation, as well as the corresponding changes in the mirror shape, are at least partially preserved.

[0011] The mirror surface can be detected or measured using sensors, such as microscopes or interferometric methods, to determine or record the actual shape. For example, surface quality and / or surface microstructure and / or surface defects and / or dents or pits and / or grooves or channels and / or similar features can be recorded or detected. Similarly, it can be assumed that the actual shape is at least substantially smooth, for example, if the target shape provides the expected microstructure of the mirror surface, which is produced solely by laser irradiation or the resulting local volume changes, and the manufacturing process previously used to manufacture mirrors in a pre-fabricated initial state does not include any steps that produce such a microstructure.

[0012] Compared to, for example, using conventional mechanical surface finishing or surface manufacturing processes (e.g., mechanical polishing) in designs that allow for corresponding surface quality or surface finish of the mirror, the method according to the invention enables the easier and more economical production of mirrors with specific target shapes and relatively strict precision or tolerance requirements. The method according to the invention can be used, for example, for mirrors produced by conventional mechanical processes for correction and classified as scrap due to surface defects or shape deviations. After being treated with the method according to the invention, such mirrors can still be used according to their original purpose. Similarly, mirrors of the same specifications can be produced using the same manufacturing process, and individual mirrors can be individually adjusted or optimized with relatively little effort using the method according to the invention.

[0013] In one possible embodiment of the invention, laser radiation irradiates the carrier substrate along the direction of the back side of the mirror. For this purpose, the wavelength of the irradiated laser radiation can be matched with the carrier substrate, or the wavelength of the laser radiation and the carrier substrate can be matched to each other, such that the radiated laser is at least partially penetrable or transparent to the carrier substrate, and sufficient absorption can be achieved at the focal point of the laser radiation to cause a volume change. For example, glass or quartz glass can be used as the carrier substrate. Due to the design proposed herein, even if the mirror surface is opaque to laser radiation, such as being highly reflective or absorptive, the laser radiation can still transmit to cause the described volume change. Furthermore, it is particularly effective here to avoid the front side or surface of the mirror facing away from the carrier substrate being affected by laser radiation in an undesirable manner. Specifically, when the laser radiation reaches at least the back side of the mirror, at least a portion of the laser radiation energy has been coupled into the material region on the back side of the mirror, i.e., the laser radiation is correspondingly weakened. Similarly, a layer, for example, that cannot penetrate laser radiation can be arranged between the carrier substrate and the mirror. The material region where the laser radiation is focused can be located on the side of the layer that is impermeable to laser radiation and facing the carrier substrate. Because this layer can be thin compared to the carrier substrate, it can still cause changes to the mirror surface or the described surface or front shape if needed.

[0014] In another possible embodiment of the invention, laser radiation is emitted from the outside of the mirror along the direction of the front of the mirror and passes through the mirror surface along the direction of the carrier substrate. Therefore, a transparent mirror surface, i.e., one that is substantially transparent to the laser radiation wavelength, can be used. Depending on the material used for the mirror and / or, for example, the thickness of the carrier substrate, the laser radiation can be focused onto a material region on the back of the mirror, for example, even if the carrier substrate is too thick or too absorptive to the laser radiation. In this case, by irradiating the mirror through the front of the mirror, i.e., through the mirror surface, the material region that experiences a localized volume change due to the laser radiation can be relatively close to or near the mirror surface, and sufficiently strong, relatively fast, and sufficiently localized energy coupling can also be made possible.

[0015] In another possible embodiment of the invention, the mirror in its prefabricated initial state has an intermediate layer disposed between a carrier substrate and a mirror surface. This intermediate layer connects the mirror surface to the carrier substrate. Laser radiation is focused into this intermediate layer to produce localized volume changes in its material. In other words, the region of material in which laser radiation is focused to produce localized volume changes is or primarily comprises the material of the intermediate layer. The intermediate layer can be, for example, an adhesive, i.e., a bonding layer. Similarly, the material of the intermediate layer can be selected or specified to produce localized volume changes through energy coupling, particularly through laser radiation, changes that are stable and are at least partially retained even after the energy coupling has ended or after cooling. This means that the described method can also be used if the carrier substrate itself is not suitable for such localized volume changes.

[0016] In a possible further application of the invention, the material of the intermediate layer is selected or specified, and the irradiation of the intermediate layer by laser radiation, i.e., the energy input into the intermediate layer material caused by laser radiation, is coordinated or adjusted, thus producing a local volume change in the intermediate layer, and therefore the corresponding change in the final mirror shape is reversible. In addition, the duration and / or intensity and / or power and / or time irradiation mode of the laser radiation can be adjusted or set accordingly. This can be accomplished by ensuring that the intermediate layer material does not overheat, i.e., does not burn or char. To reverse or eliminate the resulting local volume change, the intermediate layer material or the entire mirror can be heated to, for example, a predetermined temperature. Mechanical tension can be used, for example, to maintain the local volume change or to soften the intermediate layer material, so that it returns to its original shape or original volume, for example, by refilling the cavity generated by the laser radiation. Due to the reversibility of the local volume change, the target shape of the mirror can be produced particularly effectively and accurately, for example, by performing multiple tests if necessary. Similarly, the same mirror can be flexibly shaped and used according to the needs of different applications or requirements. For example, after generating the first desired target shape, the mirror can be used for a first application, and then the same mirror can be used to generate another second target shape for subsequent applications. Ultimately, this can be particularly cost-effective and / or resource-saving compared to using separate, different mirrors.

[0017] In another possible embodiment of the invention, laser radiation is focused on a material region therein, i.e., a material region in which local volume changes occur, and locally heated by laser radiation to above its glass transition temperature. Thus, before laser radiation irradiation, the material region can be in a rigid, glassy state. When heated above the glass transition temperature, the material region transforms into a soft state. In this state caused by laser radiation irradiation, the material region, or the material therein, can change its shape or volume. It can then be cooled below the glass transition temperature, although at least some of the local volume changes are retained. This ensures that the mirror maintains its desired shape in a stable and reliable manner during normal use, with the temperature remaining below the glass transition temperature. Laser radiation can therefore irradiate amorphous materials or corresponding amorphous material regions of the mirror. Examples include amorphous carrier substrates, such as those made of glass, or adhesives, such as intermediate layers mentioned elsewhere.

[0018] In another possible embodiment of the invention, the mirror processing is performed iteratively in several steps. During the mirror processing, the mirror surface is observed through a sensor system, particularly through an interferometer, and the current actual shape is determined or changes in the mirror surface shape are monitored. Laser radiation is applied several times consecutively, each time producing only a portion of the total volume change, and at least during this period, i.e., after each application or after each laser pulse, the target shape of the mirror surface is checked based on corresponding sensor data from the sensor system. In particular, laser radiation (e.g., one laser pulse at a time) can be applied multiple times, each time with a certain power and duration (i.e., energy input), which may not be suitable for producing the overall volume change achieved at the corresponding location, nor for compensating or correcting initially determined deviations during or through a single application or single application phase (i.e., one laser pulse). For example, the next application can be adjusted, for example, regarding the duration and / or intensity and / or power and / or energy input and / or focal position and / or focal size or beam diameter, based on the remaining deviation and / or the change in the actual shape of the mirror surface achieved by the previous application.

[0019] These steps are repeated iteratively until the target shape and / or the expected maximum volume change is achieved. Due to the implementation method of the invention presented herein, the corresponding expected shape can be produced with particular precision and efficiency, especially even if the volume change is only possible in one direction due to laser radiation, i.e., only an increase in volume or only a decrease in volume. This means that it is not necessary to know or calculate a precise model of the resulting volume change. Furthermore, it is possible to respond to the individual characteristics or behavior of the respective mirrors. For example, nominally or specifically identical mirrors may exhibit different microscopic behaviors upon laser radiation irradiation, or, for example, due to different material defects or foreign objects or local inclusions in the interfering material, or different intensities or patterns of mechanical stress and / or the like present in the corresponding pre-fabricated initial state within the material of the respective mirrors. Even in such cases, the corresponding target form can be gradually achieved or adjusted using the method presented herein. This means that the number of mirrors wasted can ultimately be further reduced.

[0020] In another possible embodiment of the invention, the distance between the focal point or focusing area of ​​the laser radiation in the mirror material and the mirror surface or back surface is automatically adjusted or regulated according to the deviation to be compensated or corrected, i.e., the volume or shape change to be generated, i.e., the focal position relative to the mirror surface. A smaller distance is used when the deviation is large or the mirror shape change is large. The embodiment of the invention presented herein is based on the understanding that local volume changes generated within the material do not cause a corresponding or constant change in the shape of the material surface at any distance. Therefore, changing the distance between the local volume change in the internal material region of the mirror and the mirror surface, and the mirror surface, further provides degrees of freedom regarding the resulting shape change of the mirror surface. This means that different desired shapes or different shape changes of the mirror surface can be generated particularly precisely and effectively. For example, even the smallest achievable local volume change or the smallest energy input causing the local volume change and / or the smallest focal size or smallest material area affected by laser radiation, thus limiting the minimum size of the achievable local volume change downwards, can cause particularly small changes in the mirror shape.

[0021] In another possible embodiment of the invention, the size of the material region of the mirror affected by focused laser radiation is adjusted or calibrated, particularly automatically, according to the deviation to be compensated or corrected, i.e., the shape change to be achieved. A larger deviation or shape change will affect a larger material area. The size of the affected material region may refer to a range in one, two, or three directions or dimensions, for example, a surface range parallel to the mirror surface or a plane of volume extension. The minimum size can be determined by the minimum focal size or maximum focusability of the laser radiation. However, a larger material region may be affected by partial defocusing and / or movement of the laser radiation focus within the mirror material (relative to the mirror surface). This movement can be achieved, for example, by scanning optics, such as a current scanner, in a laser processing system according to the method of the invention. The embodiments of the invention presented herein are based on the understanding that the maximum volume change that can be produced at a certain point or region is limited, but a greater change in mirror shape can be achieved by expanding the material region correspondingly affected by laser radiation. This means that a particularly wide range of mirror shape changes can be achieved. Therefore, the method according to the invention can be used in a particularly diverse or flexible manner, and can further reduce the waste of mirrors if necessary.

[0022] In another possible embodiment of the invention, the aberrations, i.e., imaging errors, of the mirror or mirror surface are automatically determined, particularly in a pre-formed initial state. Subsequently, an inverse or inverted pattern of local volume changes is generated in the mirror image. This inverse or inverted pattern of local volume changes can be adjusted or scaled by taking into account factors of the magnitude or degree of changes in the shape of the mirror surface, depending on the magnitude or degree of the corresponding or corresponding local volume changes in the mirror. By means of the pattern of local volume changes generated herein, the aberrations or imaging errors of the mirror can ultimately be at least substantially compensated or corrected through the corresponding shape changes of the resulting mirror surface.

[0023] In another possible embodiment of the invention, laser radiation is simultaneously applied to several spatially spaced locations on the mirror to simultaneously generate several volumetric changes, compensating for or correcting several local deviations between the actual and target shapes of the mirror surface. Furthermore, multiple laser beams can be used simultaneously, enabling particularly rapid mirror processing. Therefore, the method according to the invention can also be used effectively and at low cost for serial or large-scale production in the mirror industry.

[0024] In another possible embodiment of the invention, at least one planar or linear or linear extension of volume change parallel to the mirror surface and / or a large number of individual point or extension volume changes produce the desired pattern. Producing extensive volume changes can mean that the extensive volume change, or the area of ​​the material affected by laser radiation to produce the extensive volume change, is larger than the size, diameter, or volume of the laser radiation focal point, particularly by several times or many times. This pattern produces an optical functional structure in the mirror surface, such as a nanostructure or microstructure, as a corresponding shape change to influence at least one characteristic of the radiation irradiated thereon, particularly laser radiation. Such an optical functional structure can influence, for example, the phase or phase distribution and / or beam shape of a laser beam reflected or deflected on the mirror surface. This means that the functional design of a mirror beyond mere reflection or redirection can be implemented individually as needed. This can be achieved, in particular, by taking into account the deviation between the actual shape already present in the prefabricated initial state and the desired target shape. Conventional methods used for producing mirrors, such as mechanical polishing processes, are not readily available for high-precision production of such functional structures. Therefore, the present invention provides the possibility of producing the corresponding mirrors with particular flexibility and low cost.

[0025] In another possible embodiment of the invention, the entire mirror is heated after it has been irradiated with laser radiation, i.e., after local volume changes and corresponding shape changes have occurred. As a result, the stress generated by the heat of the laser radiation in the mirror material is completely or partially reduced and / or the resulting volume changes are completely or partially reversed. The former can improve the robustness and reliability of the mirror. The latter can, for example, be applied to the mirror as intended to enable reprocessing of the mirror for different purposes or other requirements, for which different mirror shapes are needed, or to correct possible processing errors, such as excessive changes in mirror shape beyond the target shape caused in the first processing attempt. This means that the mirror can be ready for another processing attempt. For example, the mirror can be heated or baked in an oven. As described elsewhere, local volume changes can be reversed by heating, for example, above a predetermined temperature.

[0026] In another possible embodiment of the invention, laser radiation is focused onto a material region on the back of a mirror, the material region having an intensity distribution that largely achieves the desired target shape. This intensity distribution can be achieved, for example, by projection onto the material region on the back of the mirror in a focused manner. Here, focused illumination means that the projection plane of the projection extends parallel to the mirror plane, and the mirror extends along the mirror plane in at least some areas or rests tangentially on the mirror plane. In this possible embodiment, a projection optics element in the form of a projection lens or projection mirror is arranged between the beam output for laser radiation and the mirror, by which the material region on the back of the mirror is focused and projected. This possible configuration is particularly advantageous because it allows for the processing of a larger area of ​​material on the back of the mirror.

[0027] The present invention also relates to a laser processing system. The laser processing system according to the invention comprises at least one laser radiation source, a focusing unit disposed downstream therefrom for focusing laser radiation generated by the laser radiation source onto a predetermined processing area in which a mirror to be processed may be disposed, a sensor system for detecting the shape of the mirror surface or for monitoring changes in the shape of the mirror surface to understand the shape changes, and a control device. The laser processing system is configured to perform the method according to the invention, particularly automatically or semi-automatically. For this purpose, the control device may, for example, have a processor, such as a microprocessor, microchip, or microcontroller, and computer-readable data memory coupled thereto. A corresponding operation or computer program, which encodes or implements in conjunction with the method steps, measurements, or processes or corresponding control instructions described in accordance with the method according to the invention, can then be stored therein. This operation or computer program can then be executed through the processing equipment to perform the corresponding method or realize its execution mode. For this purpose, the control device may, for example, control the laser radiation source and / or the focusing unit accordingly. Similarly, the laser processing system may have other components, such as scanner optics as mentioned elsewhere, controllable via a control device, and / or adjustment or displacement devices for adjusting the position or orientation of the processing end of the laser processing system relative to the processing area and / or for moving the mirror to be processed relative to the laser radiation source or the processing end of the laser processing system. The laser processing system according to the invention is particularly a laser processing system in conjunction with the method according to the invention, or a laser processing system corresponding thereto. In particular, the laser radiation source of the laser processing system according to the invention can be set or designed to generate laser pulses, especially ultrashort pulses of laser radiation. This means that energy coupling to the corresponding mirror can be controlled with particular precision and reliability.

[0028] Further features of the invention can be seen from the following description and drawings. The features and combinations thereof described above in the specification, as well as the features and combinations thereof shown below in the description and / or alone in the drawings, can be used not only in the form specified in each case, but also in other combinations or alone, without departing from the scope of the invention.

Implementation Method

[0033] Components that are identical or have the same function in the figure have the same reference numerals.

[0034] Figure 1 is a schematic diagram illustrating the method for processing mirror 1 in the first variant. Mirror 1 is shown here in a cross-sectional side view. Laser processing system 2 is provided for processing mirror 1, which is shown schematically. Thus, laser radiation 3 can be focused onto the carrier substrate 4 of mirror 1. On one side of the carrier substrate 4, a mirror surface 5 of mirror 1 is formed, which is at least substantially perpendicular to the drawing.

[0035] The laser processing system 2 includes a laser radiation source 6 for generating laser radiation 3. In the present case, the laser radiation 3 is focused by the focusing unit 7 onto a material region 8 located behind the mirror surface 5 in the carrier substrate 4.

[0036] The mirror 1 may have, for example, a quartz glass body as the carrier substrate 4, which has a highly reflective coating, such as a dielectric coating, forming the mirror surface 5. Local defects, such as microcracks, can be generated in the material of the carrier substrate 4 by means of laser radiation 3, such as an ultrashort laser pulse, through two-photon absorption. Such microcracks cause a local density reduction, and thus cause local volume expansion in the material region 8. This can be located directly below the mirror surface 5, or at least very close to the mirror surface, so that the shape of the mirror surface 5 can also be changed.

[0037] To detect the actual shape of the mirror surface 5, the laser processing system 2 also includes a sensor system 9. Additionally, the laser processing system 2 includes a control device 10, which is connected to the laser radiation source 6 and the sensor system 9 via an interface 11. The control device 10, shown schematically, includes a processor 12 and a data memory 13, for example, processing sensor data from the sensor system 9 and controlling the laser radiation source 6 accordingly.

[0038] To illustrate the processing results, Figure 2 schematically presents a view of the mirror 1 after processing using the laser processing system 2 or laser radiation 3. The laser radiation 3, focused on the material region 8, has generated a volume defect 14 there, such as a local increase in the volume of the carrier substrate 4. This volume defect 14 causes a corresponding shape change 15 of the mirror surface 5 at the location of the volume defect 14. The laser radiation 3 only directly affects or modifies the carrier substrate 4 without damaging the mirror surface 5 or, for example, affecting its reflectivity. Therefore, by generating at least one volume defect 14 on the back side of the mirror surface 5, the corresponding shape change 15 of the mirror surface 5 can be controlled and correspondingly generated or written locally. This allows, for example, deviations related to the production of the intended target or target shape to be compensated or corrected, or to produce a specific mirror shape or optical functional structure of the mirror surface 5. For example, a more complex mirror 1 or mirror surface shape can be produced in a relatively simple and standardized manner as a basic mirror. For example, using laser radiation 3, an aspherization of the initially provided spherical mirror can be produced, or a phase correction mirror for an aberration optical system can be produced, etc.

[0039] In the example shown in Figure 1, laser radiation 3 irradiates through the carrier substrate 4. This means that the affected material region 8 can, for example, be relatively close to the mirror surface 5, even though it is not penetrable by laser radiation 3.

[0040] Similarly, in other cases, laser radiation 3 can be emitted from different directions. Figure 3 illustrates a schematic diagram of the corresponding method. Mirror 1 is shown here in a cross-sectional side view. However, with the aid of the laser processing system 2, laser radiation 3 is emitted here along the direction of the mirror surface 5 and through the mirror surface 5. In addition, mirror 1 is constructed as multiple layers or multiple parts. An intermediate layer 16 exists between the carrier substrate 4 and the mirror surface 5. This intermediate layer 16 may be, for example, an adhesive layer that connects the carrier substrate 4 to the mirror surface 5, or to a second substrate formed thereon or on the mirror surface 5. Such a second substrate may, for example, be thinner than the carrier substrate 4 and / or made of a different material than the carrier substrate 4. In particular, the mirror surface 5 or the second substrate may be at least substantially transparent to laser radiation 3.

[0041] Laser radiation 3 is focused onto 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, thereby causing a corresponding local volume change. This can be at least partially maintained even after the intermediate layer 16 is subsequently cooled below its glass transition temperature. For illustration, FIG. 4 is a schematic diagram of the processed mirror 1. Here, the permanent or stable local volume change in the intermediate layer 16 is characterized as a corresponding local volume defect 14. This also leads to a corresponding local deformation of the second substrate and a corresponding surface deformation or shape change 15 of the mirror surface 5.

[0042] Similarly, the different irradiation directions of laser radiation 3 can be interchanged. Therefore, for example, in the multi-layer or multi-part structure of mirror 1 shown in FIG3, laser radiation 3 can pass through the carrier substrate 4 and irradiate along the rear side of the mirror surface 5 facing the carrier substrate, or be focused into the intermediate layer 16.

[0043] The manner described herein can produce not only individual point-like shape changes 15, but also a wide range of shape changes 15 or, for example, several adjacent or overlapping shape changes 15 or patterns of shape changes 15.

[0044] In general, the described examples illustrate how to perform mirror correction. [Simplified Explanation of the Diagram]

[0029] Figure 1 is a schematic diagram of a mirror in one embodiment and a laser processing system for processing the mirror using laser radiation;

[0030] Figure 2 is a schematic diagram of a mirror whose mirror surface shape has changed due to processing in one embodiment.

[0031] Figure 3 is a schematic diagram of a mirror and a laser processing system for processing a mirror using laser radiation in another embodiment;

[0032] Figure 4 is a schematic diagram of a mirror whose mirror shape has been changed due to processing in another embodiment.

Claims

1. A method for processing a mirror, wherein: A mirror (1) is provided in a prefabricated initial state, wherein the mirror (1) has a carrier substrate (4) and a mirror surface (5) formed on its front side that deviates from a predetermined target shape. At least one location is identified where the actual shape of the mirror surface (5) deviates from its target shape. At this location, a laser radiation (3) is focused onto a material region (8) located on the back side of the mirror surface (5) of the mirror (1), where a local volume change is generated, thereby causing a corresponding change in the shape of the mirror surface (5) to at least partially correct the deviation.

2. The method according to claim 1, wherein the laser radiation (3) passes through the carrier substrate (4) and irradiates the rear side of the mirror surface (5) facing the carrier substrate (4).

3. The method according to claim 1 or 2, wherein the laser radiation (3) is directed from the outside of the mirror toward the front of the mirror surface (5) and passes through it.

4. The method according to claim 1 or 2, wherein the mirror (1) in the prefabricated initial state has an intermediate layer (16) disposed between the carrier substrate (4) and the mirror surface (5), and the laser radiation (3) is focused into the intermediate layer (16) to produce the local volume change in its material.

5. The method according to claim 4, wherein the material of the intermediate layer (16) is prefabricated and the irradiation of the laser radiation (3) is adjusted in such a way that the local volume change generated in the material of the intermediate layer (16) is reversible.

6. The method according to claim 1 or 2, wherein the material region (8) is heated above its glass transition temperature by the laser radiation (3).

7. The method according to claim 1 or 2, wherein the processing of the mirror (1) is carried out iteratively in several steps: during the processing of the mirror (1), the mirror surface (5) is observed through a sensor system (9), in particular through an interferometer, and thus the current actual shape of the mirror surface (5) is monitored; the laser radiation (3) is irradiated repeatedly, each time producing only a portion of the total volume change, and between each irradiation, it is checked whether the target shape of the mirror surface (5) has been achieved based on the corresponding sensor data from the sensor system (9), and this action is repeated until the expected shape and / or the expected maximum volume change is achieved.

8. The method according to claim 1 or 2, wherein the distance between the focal point of the laser radiation (3) and the mirror surface (5) is adjusted according to the deviation, particularly automatically, wherein a smaller distance is used when the deviation is large.

9. The method according to claim 1 or 2, wherein the size of the material area (8) of the mirror (1) affected by the focused laser radiation (3) is adjusted according to the deviation, in particular automatically, the material area (8) affected being larger when the deviation is greater.

10. The method according to claim 1 or 2, wherein the aberration of the mirror (1) is determined in a prefabricated initial state and an opposite local volume change pattern is generated.

11. The method according to claim 1 or 2, wherein the laser radiation (3) simultaneously irradiates several spatially spaced locations to simultaneously generate multiple volume changes to correct multiple deviations.

12. The method according to claim 1 or 2, wherein in a predetermined pattern, at least one volume change and / or multiple volume changes extending parallel to the mirror surface (5) are generated, thereby creating an optical functional structure in the mirror surface (5) for influencing at least one characteristic of the radiation irradiated thereon, particularly phase and / or beam shape.

13. The method according to claim 1 or 2, wherein after the local volume change is generated, the entire mirror (1) is heated, thereby reducing the thermally induced stress in the mirror (1) caused by the laser radiation (3) and / or reversing the resulting volume change.

14. A laser processing system comprising a laser radiation source (6), a focusing unit (7) disposed downstream thereof for focusing laser radiation (3) generated by the laser radiation source (6) onto a processing area in which a mirror (1) to be processed may be disposed, a sensor system (9) for detecting the shape of a mirror surface (5), and a control device (10), wherein the laser processing system (2) is configured to perform a method according to claim 1 or 2.

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