A beam guiding device for laser radiation with ghost reflection suppression and a laser system having the beam guiding device.

Abstract

The present invention relates to a beam guiding device (15) and a laser system (13) equipped with the beam guiding device. The beam guiding device (15) includes a sensing mechanism (7) for detecting reflected laser radiation (5), a radiation-blocking element (12) arranged in the optical path, an optical element (17), and a transmission lens group (20) having at least one lens (20) for guiding laser radiation (1) in the direction of travel (2) and reflected laser radiation (5) in the opposite direction. The lens group (20) is designed such that a first back reflection (9) generated thereon is focused into a plane (22) conjugate to the plane (21) of the optical element (17) and the plane of the blocking element 12, and a second back reflection (11) generated thereon also has a large divergence, such that the second back reflection does not reach the sensing mechanism (7).

Description

Technical Field

[0001] The present invention relates to a beam guiding device for laser radiation and a laser system equipped with the beam guiding device. Prior Technology

[0002] In laser systems, unintended reflections may occur on different components of the guiding or deflecting beam. Depending on the application, these reflections may, for example, interfere with analysis or detection, or cause damage at higher laser powers. To avoid or reduce these problems, improvements are needed to conventional methods, which are often not effective in all situations. Summary of the Invention

[0003] One of the objectives of this invention is to reduce the interference caused by unwanted reflections in laser systems.

[0004] This objective can be achieved through the subject matter of the independent item. Other possible designs of the invention are given in the appendices, specification, and drawings. The features, advantages, and possible designs set forth in the description of one of the subject matter of the independent item should be regarded at least similarly as the features, advantages, and possible designs of the corresponding subject matter of the other independent items, as well as the features, advantages, and possible designs of any possible combination of subject matter of the independent items, combined with one or more appendices as needed.

[0005] According to embodiments of the present invention, a beam guiding device or beam guiding assembly is used to guide laser radiation, i.e., a continuous or pulsed laser beam. The beam guiding device includes a transmission lens group for guiding the laser radiation along the direction of travel, i.e., for guiding the laser beam in the direction of travel toward a predetermined effective focusing area. The lens group may be a single lens or may include multiple lenses or portions of lenses. Here, the effective focusing area refers to the focal region or focus on which the laser radiation is focused by the beam guiding device, and in this focal region or focus, the desired effect should be achieved by the laser radiation or in the intended operation. This can be, for example, by processing materials or heating or at least partially evaporating material droplets, such as tin droplets, through laser radiation to generate EUV light. In applications of EUV light generation, the corresponding material droplet will be located within the effective focusing area, the position of which should be determined by laser radiation or the material droplet should be at least partially converted into plasma by laser radiation. Furthermore, other focal regions may exist within the beam guiding device where the laser radiation is focused, but in which no material action is expected. Therefore, specifically, the beam guiding device can be pre-programmed or designed for EUV light generation, EUV lithography, or EUV driving lasers, i.e., corresponding laser systems for EUV light generation or EUV lithography. Specifically, the beam guiding device can be a focusing device for an EUV driving laser or include such a focusing device. Other applications or uses of the beam guiding device according to the present invention can also be achieved.

[0006] The beam guiding device also includes a detector or sensing mechanism for detecting laser radiation reflected backward from the effective focusing region through the lens assembly, i.e., the corresponding reverse laser beam. Therefore, the direction of travel is along one or more optical paths or beam paths from the laser radiation source through the lens assembly to the effective focusing region. Conversely, the reverse direction is from the effective focusing region through the lens assembly in the opposite direction and further to the sensing mechanism. Therefore, the corresponding optical path or beam path of the laser radiation reflected backward (i.e., the reverse laser beam) may partially or segmentally coincide with, and may partially or segmentally differ from, the optical path or beam path of the laser radiation propagating in the direction of travel (i.e., the laser beam in the direction of travel).

[0007] The sensing mechanism may include, for example, a camera, a CCD chip, a photodiode, or another light or radiation sensor. The sensing mechanism may be equipped with or coupled to evaluation electronics. This allows for the analysis (i.e., evaluation) of the measurement or sensor signals generated by the sensing mechanism in response to the detection or recording of reflected laser radiation, for example, to determine predetermined parameter values, such as the position of a material droplet. For this purpose, the intensity distribution and / or wavefront and / or phase shift of the reflected laser radiation may be evaluated, for example. Therefore, reflected laser radiation can be used, for example, as a basis for determining the position of a corresponding material droplet in EUV light generation and / or for determining or measuring wavefront deformation and / or aberrations.

[0008] The beam guiding device also includes a radiation barrier or blocking element that is impermeable to laser radiation. It is arranged in the optical path or beam path of the reflected laser radiation (i.e., the reverse laser beam) between the sensing mechanism and the lens group. The blocking element is sized in such a way that only the radially centered component of the reflected laser radiation is away from the sensing mechanism, while another portion or circumferential portion of the reflected laser radiation can pass through the blocking element to reach the sensing mechanism. Here, the radial direction can be perpendicular to the propagation direction of the reflected laser radiation along the reverse optical path, i.e., extending in the cross-section of the corresponding reverse laser beam leading to the sensing mechanism. Therefore, the diameter of the blocking element in this cross-section can be smaller than the diameter of the reverse laser beam (i.e., the light or radiation distribution of the reflected laser radiation) at that location. The blocking element can, for example, absorb the laser radiation incident upon it, or (e.g., in the case of a design employing corresponding wavelength selectivity or phase selectivity) absorb only unwanted interference reflections or back reflections from the lens group, or reflect, deflect, or scatter them from the reverse optical path.

[0009] The beam guiding device also includes optics arranged in the optical path or beam path of reflected laser radiation between the blocking element and the lens group. The optics are configured or designed to image the plane of the blocking element onto a plane optically conjugate to that plane, located between the optics and the lens group. This optically conjugate plane between the optics and the lens group is located in the reverse optical path, but specifically, it may also be located in the traveling optical path. The optics may include one or more optical elements or components, such as at least or exactly two lenses. These lenses do not necessarily have to be identical. Therefore, the distance between the first lens of the optics facing the effective focusing area and the conjugate plane may differ from the distance between the blocking element or the plane of the blocking element and the second lens of the optics facing the sensing mechanism. The plane of the blocking element here refers to the position of the blocking element in the longitudinal direction or along the propagation direction of the reverse optical path.

[0010] During the operation of the beam guiding device, i.e., when guiding laser radiation through the beam guiding device in the direction of travel, interfering reflections or back reflections, also known as ghost reflections, may occur on the lens group, specifically on different lens sides of one or more lenses in the lens group, for example on the front and inner back sides of the lens group. These interfering back reflections can then propagate in the reverse direction. According to the invention, the corresponding one or more lenses of the lens group are shaped in such a way that, of the two interfering back reflections, the first or focused back reflection is focused into a plane conjugate to the plane of the blocking element located between the optics and the lens group, and the other back reflection (i.e., the second or divergent back reflection), or at least a major portion of its intensity, has a large divergence, specifically based on the shape of the corresponding side of the corresponding lens, such that it cannot reach the sensing mechanism. The second back reflection originates from the corresponding lens. Therefore, for example, when the divergence between the corresponding side of the lens group or lens and the conjugate plane is relatively large, depending on the shape of the lens, the second back reflection can be focused outside or inside the lens, or it can be reflected in a scattering manner on the corresponding side of the lens. In this case, the second back reflection, or its main part, can be eliminated or at least significantly reduced, for example, by absorption at an opaque or non-radiative aperture or stop within the surrounding housing and / or the beam guide device. The focusing of the first back reflection in the conjugate plane indicates that the first back reflection propagates through the optics from there and is also refocused at the location of the blocking element. Thus, even if the location of the blocking element cannot be freely chosen, i.e., cannot be arbitrarily chosen, at least almost complete suppression of the first back reflection can be achieved.

[0011] In principle, placing a blocking element in the optical path is an effective way to block interfering back reflections. However, for this to work, the blocking element must ideally be placed at the location where the back reflection to be blocked is focused, or the blocking element must have the smallest possible diameter, specifically smaller than the diameter of the reverse laser beam to be detected. However, in actual beam guiding devices or laser systems, it is not always possible to freely or optimally position such a blocking element, for example, due to structural conditions or space constraints caused by other components or requirements. Here, this problem is solved by correspondingly adjusting the shape of the lens group or lens responsible for the interfering back reflection, in conjunction with the optics, that is, by utilizing different positions relative to the conjugate plane of the optics. For example, compared with conventional beam guiding devices with the same or similar design, a corresponding adjustment to the side of the lens or lens group responsible for the interfering back reflection may cause the same undesirable change in the output-side focal position of the beam guiding device. However, this effect is compensated here by similarly adjusting the shape of the other lens side (i.e., the other side of the same lens in the lens group and / or one side of another lens). In this way, compared with conventional lenses or conventional beam guiding devices, the focal position in the effective focusing area can remain unchanged, while still achieving improved suppression of the two interfering back reflections on the sensing mechanism. Depending on the situation, the component of the second back reflection that may propagate precisely at the center (i.e., on the optical axis of the lens group or the reverse optical path) can also be blocked by blocking elements, even if it is far from the sensing mechanism.

[0012] Therefore, this invention proposes adjusting or presetting the radius of curvature of one or more lens sides of one or more lenses in a lens or lens group in a certain way, such that, for example, compared with conventional lenses or lens groups, and specifically conventional biconvex lenses or plano-convex guides used in conventional beam guiding devices, the image-side focal position in the effective focusing area remains unchanged or constant. However, one of the two ghost reflections is focused in a plane conjugate to the plane of the blocking element, i.e., focused in the virtual blocking element plane, and is thus ultimately suppressed by the blocking element arranged there in the actual blocking element plane, while the other ghost reflection is extended or diverged to such an extent that it escapes at least partially or at least mostly from the intended optical path of the reverse laser beam before reaching the sensing mechanism. Thus, with regard to the latter ghost reflection, the maximum possible divergence can be achieved through the lens group design proposed herein. Even if other suppression measures (e.g., interference reflections based on polarization filtering) are not practically feasible, this design or form of the lens group can, for example, achieve suppression of the interference back reflections generated thereon. Specifically, this can be achieved by coordinating the shaping of the two sides or the radii of curvature of the lens or the lens group with each other, without requiring significant further changes to the beam guiding device.

[0013] The lens assembly can also be designed in such a way that two or more or all interfering back reflections generated on the lens assembly are intercepted or blocked in the conjugate plane by the blocking element. Specifically, such back reflections can be focused in the conjugate plane at least substantially through the appropriate shape of the lens assembly. The lens assembly can also be designed in such a way that two or more or all interfering back reflections generated on the lens assembly have a large divergence or are significantly scattered, so that they escape at least substantially or mostly in the sub-optical path in front of the sensing mechanism, i.e., do not reach the sensing mechanism.

[0014] The blocking element can be a separate component. In this case, the blocking element can extend longitudinally in the reverse direction, for example, in the form of a plate, disc, or rod, and can be cylindrical or have a polygonal cross-section or a cross-section corresponding to the cross-section of the reverse laser beam or the first back reflection in the region of the blocking element. Through the longitudinal extension (i.e., rod-shaped) of the blocking element in the reverse direction, the first back reflection or a portion thereof may, as appropriate, be incident on the outer surface of the blocking element and, for example, be absorbed there or scattered or reflected along the reverse optical path. This allows for particularly reliable or particularly complete blocking of the first back reflection, even if vibrations or thermally related displacements occur in the lens group and / or optics during the operation of the beam guiding device or the corresponding laser system. The first back reflection may not be blocked, or may not be blocked only on the end face of the blocking element facing the optics, or may be deflected from the optical path. The beam guiding device may also have adjustment or movement mechanisms for adjusting or moving the blocking element in the reverse direction and / or opposite to and / or perpendicular to the reverse direction. In this way, the position or orientation of the blocking element can be adjusted, for example, manually, by a motor, or automatically, to achieve at least maximum suppression of the first interference reflection and / or optimization or maximization of the intensity ratio between the reverse laser beam to be detected in the sensing mechanism and the portion of the first interference reflection that may reach there. The blocking element may also be a region of another optical element or component of the beam guiding device, which is accordingly coated or made of a corresponding material, specifically differing from the circumferential region of the corresponding element or component, in order to achieve the described function or effect of the blocking element. The region of another optical element or component surrounding this region (i.e., the blocking element) may, for example, be designed to be transparent to the reflected laser radiation, i.e., employing a transmissive design or serving as a deflector in the reverse optical path.

[0015] In one possible design of the invention, a coupling element is arranged between the blocking element and the lens group, specifically between the blocking element and the optics. Through this coupling element, laser radiation can be coupled into the beam guiding device in the direction of travel, i.e., towards the lens group or towards the effective focusing area. Reflected laser radiation can pass through the coupling element and reach the sensing mechanism in the reverse direction. The coupling element can be, for example, an optical beam splitter, i.e., a partially transparent mirror. Such an element can be arranged at an angle of 0° to 90°, specifically 45°, relative to the optical axis of the optics or relative to the local central longitudinal axis of the reverse optical path. When the coupling element is arranged between the sensing mechanism and the optics, the latter can be used to focus, shape, or redirect the laser beam in the direction of travel and the reverse laser beam. This achieves a particularly simple and compact structure for the beam guiding device. In this way, the beam paths of the laser beam in the direction of travel and the reverse laser beam from the coupling element to the effective focusing area can overlap, thereby achieving particularly compact and efficient beam guiding.

[0016] In another possible design of the invention, the optical device is designed as a relay optical device having at least two lenses. Specifically, even if the position of the blocking element cannot be freely chosen or there are structural spaces of different sizes in front of and behind the optical device, it is possible to achieve imaging of the first back reflection focused between the optical device and the lens group onto the blocking element with particular precision, reliability, and space-saving, or by means of the limited requirements on the shape of the lens or lens group from which the back reflection to be suppressed originates.

[0017] In another possible design of the invention, the lens group is shaped such that the second back reflection or its beam path generated therein is incident on the side of the optics facing the lens group, in front of the sensing mechanism, and / or on the inner side of the housing surrounding the reverse optical path of the beam guiding device. This aperture stop may have an opening through which the laser beam and the reverse laser beam in the direction of travel can pass, wherein the maximum diameter or cross-section of the opening is limited by the aperture stop or the diameter of its central opening. One or more such aperture stops may be arranged along the beam paths of the laser beam and / or the reverse laser beam in the direction of travel. This aperture stop is not used for beam guiding outside its transmissible central region; therefore, the laser radiation incident upon it can be absorbed or blocked particularly effectively and reliably, and in appropriate designs, without damage. The same applies to the inner side of the housing. By shaping or designing the lens or lens group in a certain way so that the second back reflection is conveniently incident on the inner side of the housing in front of the optics, on the one hand, a particularly large portion of the second back reflection can be diverted from the reverse optical path in front of the sensing mechanism; on the other hand, the reflection on the inner side of the housing can be incident on the opposite side of the housing in front of the sensing mechanism and thus weakened again. Overall, this can further reduce the intensity of the component of the back reflection that may interfere with the sensing mechanism.

[0018] In one possible improvement of the invention, an absorbing material for absorbing reflected laser radiation is arranged at least in the region inside the housing where the second back reflection is incident. In other words, the inside of the housing may be at least partially or completely covered with the absorbing material, or the housing may be lined with the absorbing material. The appropriate absorbing material can be selected according to the wavelength of the laser radiation used in the corresponding application example to provide maximum absorptivity and minimum reflectivity. The housing, or its corresponding side or wall, can be easily designed in a sufficiently robust manner, or, for example, equipped with a cooling device on the outside to prevent damage caused by incident reflection. To achieve the highest possible absorptivity, the absorbing material may, for example, have a three-dimensional surface structure or microstructure, such as being composed of multiple cones or pyramids or corresponding remnants. Through the proposed arrangement of the absorbing material, the intensity component of the back reflection that may reach the sensing mechanism can be further minimized. In this case, this can be achieved in a particularly simple, efficient, and space-saving manner.

[0019] In another possible design of the invention, the lens group is a focusing lens along the direction of travel or includes such a lens. Through such a focusing lens or focusing lens, laser radiation guided along the direction of travel can be focused into an effective focusing area, thereby achieving the desired effect particularly effectively. Therefore, in principle, such a focusing lens is generally necessary in laser systems. The invention effectively addresses the almost unavoidable back reflection interference.

[0020] In another possible design of the invention, the lens group is the lens closest to the effective focusing area in the direction of travel or along the direction of travel, or includes the lens, i.e., a beamguide device, specifically a laser system equipped with the beamguide device, or the last or output-side lens. Therefore, viewed along the direction of travel, the lens or the entire lens group can be arranged behind the last mirror of the beamguide device. In this case, interfering back reflections generated on the lens or lens group are generally not easily suppressed, for example, by polarization-based filtering methods. Therefore, the invention can be particularly advantageously applied in this case.

[0021] In another possible design of the invention, the front side of the lens is concave relative to the center point of the lens group from which the back reflection originates, and the back side of the lens is convex. The front and back sides are curved in the same direction, making the lens generally concave-convex. In this case, the front side has a larger radius of curvature than the back side. In other words, the back side of the lens facing the effective focusing area is curved to a greater extent than the front side facing the optics. Through the concave shape or curvature of the front side, the first back reflection generated thereon can be focused onto a plane or position optically conjugate to the plane or position of the blocking element between the optics and the lens. Through the convex curvature of the back side, which is larger in magnitude, the second back reflection generated thereon or on its inner side can be focused between the conjugate plane and the back side, i.e., close to the lens or even focused within the lens, to obtain a particularly large divergence or a particularly large extension. This ultimately reduces the intensity of the second back reflection that may reach the sensing mechanism. Through this shape of the lens, the same focal length as, for example, a conventional biconvex lens, i.e., the same focal position in the effective focusing area, can be achieved. This allows the invention to be integrated into existing beam guiding devices or beam guiding device designs in a particularly simple way.

[0022] In another possible design of the invention, in addition to the lens group, the beam guiding device also has at least one additional transmissive optical element for guiding laser radiation along the direction of travel. This transmissive optical element may be, for example, another focusing lens or a window. Therefore, specifically, this at least one additional transmissive optical element may also be different from or separate from the aforementioned optical devices. The beam guiding device is here configured or designed to suppress interfering back reflections generated on the at least one additional transmissive optical element based on polarization. For this purpose, the beam guiding device may, for example, have at least one deflector in the reverse optical path comprising a polarization retardation layer and a polarizing mirror or polarizing filter. This achieves effective suppression of back reflections generated on the at least one additional transmissive optical element, which, for example, does not need to have a special shape or, for example, does not need to use another blocking element.

[0023] In another possible design of the invention, the position or plane of the blocking element is optically conjugate to the position or plane of the sensing mechanism. In other words, the sensing mechanism or its sensor or detector surface is arranged relative to the blocking element such that the light distribution present at the position or plane of the blocking element is imaged onto the sensing mechanism in a reverse optical path. For this purpose, the distance between the sensing mechanism and the blocking element along the reverse optical path can be adjusted accordingly, and / or a corresponding optical element, such as another lens, can be arranged between the sensing mechanism and the blocking element. In this case, the planes of the sensing mechanism and the blocking element (i.e., the end face or center point of the blocking element facing away from the sensing mechanism) can be optically conjugate to each other relative to the optical element or the other lens. Through the design proposed herein, the interfering effect of back reflection on the sensor data of the sensing mechanism or the analysis results based on such sensor data can be kept to a particularly low level.

[0024] The present invention also relates to a laser system having at least one laser radiation source and a beam guiding device according to the invention arranged downstream of the laser radiation source along the direction of travel (i.e., along the intended propagation direction of the laser radiation thus generated). Specifically, the laser system according to the invention may be a laser system combined with or corresponding to the beam guiding device according to the invention. A laser system according to an embodiment of the invention may, for example, be configured or set to generate EUV light, i.e., light with a center wavelength of 13.5 nm, for example, for EUV lithography. A laser system according to an embodiment of the invention may, for example, be designed as an EUV-driven laser. A method for generating such EUV light (i.e., extreme ultraviolet radiation) comprises irradiating a suitable material droplet, such as a molten tin droplet, with a strong laser pulse. This at least partially evaporates or converts the material droplet into plasma, which then emits EUV light. To achieve effective and reliable EUV light generation, it is advantageous to first determine the position of the respective material droplet before evaporating it. To address this, a weaker pre-laser pulse or measurement laser pulse can be emitted from the laser radiation source along the direction of travel via a beam guiding device. This beam guiding device does not evaporate the material droplet but, for example, only irradiates it and / or pre-processes it for the subsequent, stronger main laser pulse, i.e., by heating it. In this case, a portion of the pre-laser pulse or measurement laser pulse can be reflected back by the material droplet as reflected laser radiation, which is then detected by a sensing mechanism and subsequently analyzed to determine, for example, the position of the corresponding material droplet. In this application example, suppressing interfering back reflections may be particularly advantageous because if such back reflections enter the sensing mechanism and are superimposed on the laser radiation reflected by the material droplet there, the corresponding analysis results may be distorted. Interfering back reflections of the main laser pulse can also be suppressed or intercepted in the laser system according to the invention using the beam guiding device according to the invention. In this case, for example, the load or damage to the sensing mechanism can be reduced or avoided. Simple Explanation of the Diagram

[0025] Other features of the invention can be derived from the following description of the drawings and in conjunction with the drawings. The features and combinations thereof described above in the specification, as well as the features and combinations thereof shown below in the description of the drawings and / or individually in the drawings, may be used not only in the given combinations, but also in other combinations or individually, without departing from the scope of the invention. in: Figure 1 is a schematic diagram of laser beam guidance with interference back reflection according to prior art; Figure 2 shows the detected reflection intensity distribution generated by laser beam guidance according to prior art; Figure 3 is a schematic diagram of improved laser beam guidance with suppressed back reflection; and Figure 4 shows the detected reflection intensity distribution generated by improved laser beam guidance. Implementation

[0026] In these diagrams, elements that are identical or have the same function use the same element symbol.

[0027] Figure 1 is a partial schematic diagram illustrating a laser application according to prior art. Here, a conventional biconvex lens 3 focuses the traveling laser radiation 1 along the traveling direction 2 to an effective focusing region 4. In an application example of EUV light generation, specifically for EUV lithography, a tin droplet may be located there, for example. The traveling laser radiation 1 can be reflected at least partially as reflected laser radiation 5, which may have a higher or larger numerical aperture than the traveling laser radiation 1. The reflected laser radiation 5 then propagates in the reverse direction 6 to a sensing mechanism 7 schematically shown here, where the reverse laser beam is detected for analysis. However, the traveling laser radiation 1 can also be partially reflected on the front side 8 of the biconvex lens 3, resulting in an interfering or undesirable first back reflection 9. The traveling laser radiation 1 can also be partially reflected on the inner back side 10 of the biconvex lens 3, resulting in an interfering or undesirable second back reflection 11. Then, the first back reflection 9 and the second back reflection 11 also propagate to the sensing mechanism 7 in the reverse direction 6, and thus can interfere with or distort the intensity distribution of the reflected laser radiation 5 measured at that location.

[0028] As can be seen here, the focusing area is, for example, located between the coupling point of the laser radiation 1 in the direction of travel and the sensing mechanism 7, where the first back reflection 9 and the second back reflection 11 are focused and thus can be blocked. However, in practice, for example due to structural or optical limitations or boundary conditions, the corresponding blocking element 12 available for this purpose is not always precisely arranged in the focusing area. Such a blocking element 12 is exemplarily arranged here between the focusing area and the sensing mechanism 7. Thus, the blocking element 12 can block one component of the reflected laser radiation 5 that is actually to be detected through the sensing mechanism 7, but it can also block at least one component of the first back reflection 9 and the second back reflection 11.

[0029] However, even with this arrangement, larger components of the first back reflection 9 and the second back reflection 11 can still reach the sensing mechanism 7. Figure 2 shows a schematic diagram of the intensity distribution generated in the sensing mechanism 7 according to prior art. No intensity is measured in the central region blocked or concealed by the blocking element 12. However, there are areas with different intensities around it, caused by the reflected laser radiation 5, the first back reflection 9, and the second back reflection 11.

[0030] However, the interfering effects of the first back reflection 9 and the second back reflection 11 can be avoided or at least weakened. Figure 3 shows a partial schematic diagram of a laser system 13 with a corresponding configuration. Here, the laser system 13 includes a laser radiation source 14, schematically shown, which generates and emits traveling laser radiation 1. In this case, the traveling laser radiation 1 is guided within the laser system 13 in a modified beam guiding device 15. The beam guiding device 15 includes a coupling element 16 for coupling or deflecting the traveling laser radiation 1 into or along the main optical path of the beam guiding device 15. Optical devices are arranged downstream of the coupling element 16 along the traveling direction 2, and these optical devices are exemplarily designed here as relay optics 17 having two parallel focusing lenses. Furthermore, the beam guiding device 15 also includes at least one aperture stop 18 surrounding the main optical path. The aperture stop 18 is exemplarily arranged on or around one of the lenses of the relay optics 17.

[0031] Downstream of the relay optics 17, along the direction of travel 2, one or more additional optical elements or assemblies may be arranged, which are schematically referred to herein as additional optics 19. This additional optics 19 may, for example, include one or more focusing lenses and / or windows and / or, specifically, deflectors coated with a polarization retardation layer. At least one polarizing filter or polarizing filter structure for suppressing back reflections generated on, specifically, the transmission optical elements of the additional optics 19 may also be arranged as part of the additional optics 19, or, for example, at other locations along the optical path or optical axis of the beamguide 15. However, this suppression method is practically unusable for the last or output-side lens or lens group of the laser system 13 or the beamguide 15. The additional optics 19 is optional and may therefore be omitted or left blank, i.e., not containing any optical elements.

[0032] This last or output-side lens group is represented here by a single lens, which is designed here as a focusing lens 20. It is the last lens of the laser system 13 or beamguide 15, i.e., the lens closest to the effective focusing area 4 along the travel direction 2. Here, on the lens group, specifically in the example shown here, the first back reflection 9 can also be specifically generated on the front surface 8 of the focusing lens 20, and the second back reflection 11 can be generated on the inner back surface 10 of the focusing lens 20. In the laser system 13 or beamguide 15 shown here, the position of the blocking element 12, i.e., the intensity distribution there or the corresponding blocking element plane 21 perpendicular to the local reflection 6, is imaged onto the optical conjugate plane 22 via the relay optics 17. This conjugate plane 22 is located here between the relay optics 17 and the focusing lens 20. With respect to the blocking element plane 21 and the conjugate plane 22, the beam focused in the conjugate plane 22 is also focused in the blocking element plane 21 after passing through the relay optics 17 in the reverse direction 6, and thus focused onto the blocking element 12 disposed there. Specifically, this means that interfering back reflections, ghost reflections, or ghost beams focused or focused in the conjugate plane 22 are at least almost completely suppressed on the actual blocking element 12, depending on the implementation of the blocking element 12, for example, absorbed or reflected or scattered from the main optical path of the beam guide 15. Therefore, the conjugate plane 22 can be referred to or understood as a virtual blocking element or filter plane.

[0033] This is used to suppress the first back reflection 9. For this purpose, the shape or radius of curvature of the front surface 8 of the focusing lens 20 is designed, or modified compared to the conventional biconvex lens 3 shown in FIG. 1, so that the first back reflection 9 is thus focused at least substantially in the conjugate plane 22, or has at most a diameter corresponding to the diameter of the blocking element 12. In this way, the first back reflection 9 is also focused onto the blocking element 12 by the relay optics 17, thereby effectively suppressing the first back reflection 9 in the intensity distribution detected or measured by the sensing mechanism 7.

[0034] As already shown, the position of the blocking element 12 cannot be freely chosen, but is fixed by structural conditions, and is therefore known. The relay optics 17 can also be fixed by requirements for guiding the laser radiation 1 in the direction of travel 2 and / or by mechanical or structural conditions, and is therefore known. This also creates the position of the conjugate plane 22. Accordingly, starting from the conventional beam guidance shown in FIG1, the shape of the front surface 8 of the biconvex lens 3 can be intuitively changed or bent in some way so that the focal point of the first back reflection 9 generated on the front surface 8 falls into the conjugate plane 22. To avoid or minimize necessary changes to other components or the resulting changes in the characteristics or performance of the laser system 13, the back surface 10 can also be adjusted accordingly to compensate for changes in focal length or focal point position. For this purpose, for example, the radii of curvature of the front surface 8 and the back surface 10 can be changed in the same direction starting from the conventional biconvex lens 3. Here, the concave-convex shape of the focusing lens 20 is thus created. For the traveling laser radiation 1 passing through the adjusted focusing lens 20 along the traveling direction 2, the changes made to the focusing lens 20 compared to the conventional biconvex lens 3 can be canceled out at least in the first order, i.e., without considering aberrations. Therefore, in both the conventional beam guidance shown in FIG1 and the improved beam guidance shown in FIG3, the traveling laser radiation 1 can be focused at the same position without further changes, so that the effective focusing area 4 does not shift relative to the mounting position of the laser system 13, the biconvex lens 3, or the focusing lens 20. Therefore, for example, there is no need to adjust the varying distance between the laser system 13 and the fixed preset effective focusing area 4, or to adjust the mounting position of the focusing lens 20.

[0035] Due to the greater curvature of the back surface 10 of the focusing lens 20 compared to the front surface 8, the second back reflection 11 generated therein achieves a correspondingly greater expansion or divergence. Therefore, the second back reflection 11 is not focused in the conjugate plane 22. However, the second back reflection 11, or at least a major portion of it, escapes from the main optical path of the beam guide device 15, preventing it from reaching the sensing mechanism 7. The second back reflection 11 can be intercepted, for example, on its path along the reverse direction 6 at the aperture stop 18 and / or on the inside of the beam guide housing 23, shown schematically here, i.e., absorbed or deflected away from the sensing mechanism 7. Therefore, through the beam guide device 15 presented herein, both the first back reflection 9 and the second back reflection 11 can be effectively suppressed or weakened, enabling a more precise or accurate and reliable analysis of the intensity distribution or radiation of the reflected laser radiation 5 detected by the sensing mechanism 7.

[0036] Figure 4 illustrates, exemplarily, a schematic diagram of the possible intensity distribution on the sensing mechanism 7. Here, the central region is also concealed or suppressed by the blocking element 12. Around it, there exists a region primarily corresponding to the reflected laser radiation 5 and an interfering radiation region 24, in which the intensity caused by the interfering back reflection is significantly weakened compared to the reflected laser radiation 5 and compared to the region interfering with the first back reflection 9 and the second back reflection 11 shown in Figure 2.

[0037] Overall, the described examples demonstrate how improved ghost point suppression can be achieved.

[0038] 1: Laser radiation in the direction of travel 2: Direction of travel 3: Biconvex lens 4: Effectively focus on the region 5: Reflected laser radiation 6: Reverse 7: Sensing Mechanism 8: Front 9: First dorsal reflection 10: Back 11: Second dorsal reflex 12: Blocking element 13: Laser System 14: Laser radiation source 15: Beam Guiding Device 16: Coupling element 17: Relay Optical Devices 18: Aperture stop 19: Additional optical components 20: Focusing lens 21: Blocking element plane 22: Conjugate plane 23: Beam Guiding Housing 24: Interference radiation area

Claims

1. A beam guiding device (15) for guiding laser radiation, comprising: a lens group (20) including at least one lens (20) for guiding the laser radiation (1) in a direction of travel (2) to a predetermined effective focusing area (4); a sensing mechanism (7) for detecting reflected laser radiation (5) passing through the lens (20) in the reverse direction (6) from the effective focusing area (4); and a blocking element (12) impermeable to the reflected laser radiation (5), the blocking element being arranged in the beam path of the reflected laser radiation (5) between the sensing mechanism (7) and the lens group (20) and being sized in a certain way such that the blocking element only causes the radially centered component of the reflected laser radiation (5) to move away from the sensing mechanism (7), and another portion of the reflected laser radiation (5) can pass through the blocking element (12) to reach the sensing mechanism (7), the blocking element (12) being arranged in the blocking element (12). An optics (17) in the beam path of the reflected laser radiation (5) between the lens group (20) and the lens group (20) images the plane (21) of the blocking element (12) onto a conjugate plane (22) between the optics (17) and the lens group (20), wherein the lens group (20) is designed such that, in two back reflections (9, 11) generated on different lens sides of the lens group (20) when the laser radiation (1) is incident on the lens group (20) along the travel direction (2), the first back reflection (9) is focused onto the conjugate plane (22) between the optics (17) and the lens group (20), and at least one major portion of the second back reflection (11) has a large divergence, such that it cannot reach the sensing mechanism (7).

2. The beam guidance device as claimed in claim 1, wherein, A coupling element (16) is arranged between the blocking element (12) and the lens group (20). The laser radiation (1) can be coupled to the beam guiding device (15) along the travel direction (2) through the coupling element (16), and the reflected laser radiation (5) can pass through the coupling element (16) to reach the sensing mechanism (7).

3. The beam guidance device as requested in item 1 or 2, wherein, The optical device (17) is designed as a relay optical device (17) with at least two lenses.

4. The beam guidance device as requested in item 1 or 2, wherein, The lens group (20) is configured such that the second back reflection (11) is incident in front of the sensing mechanism (7) onto the aperture stop (18) surrounding the optical path of the reflected laser radiation (5) and / or onto the inner side of the housing (23) surrounding the optical path of the beam guiding device (15).

5. The beam guidance device as described in claim 4, wherein, At least in the area inside the housing (23) where the second back reflector (11) is incident, there is an absorbing material for absorbing the reflected laser radiation (5).

6. The beam guidance device as requested in item 1 or 2, wherein, The lens group (20) is or includes a lens that focuses along the direction of travel (2).

7. The beam guidance device as requested in item 1 or 2, wherein, The lens group (20) is or includes the lens of the beam guiding device (15) that is closest to the effective focusing area (4) along the travel direction (2).

8. The beam guidance device as requested in item 1 or 2, wherein, The front (8) of the lens of the lens group (20) is concave and the back (10) of the lens is convex, wherein the front (8) has a larger radius of curvature than the back (10).

9. The beam guidance device as requested in item 1 or 2, wherein, In addition to the lens group (20), the beam guiding device (15) also has at least one additional transmission optical element (19) for guiding the laser radiation (1) at least along the direction of travel (2), and the beam guiding device is configured to suppress back reflections generated thereon based on polarization.

10. The beam guidance device as claimed in claim 1 or 2, wherein, The plane (21) of the blocking element (12) is optically conjugate with the plane of the sensing mechanism (7).

11. A laser system having a laser radiation source (14) and a beam guiding device (15) as claimed in claim 1 or 2, the beam guiding device being arranged downstream of the laser radiation source along the direction (2) of travel of the laser radiation (1) generated therefrom.

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