DE102016015785B4 - Beam adaptation device, frequency conversion unit, optical system and method for frequency conversion - Google Patents

Abstract

Beam adaptation device (21) for continuously variable adaptation of an electromagnetic radiation propagating along a beam axis (25) of the beam adaptation device (21) with regard to beam parameters such as lateral expansion and divergence, in particular for influencing astigmatism and non-rotationally symmetrical beam cross-sections, with an optical input element (39) with one First astigmatism lens unit (27) for receiving the electromagnetic radiation, which provides at least one first lens (L1) that can be tilted with respect to the beam axis (25) for astigmatism adjustment, the first lens (L1) being tiltable in any direction by an adjustable angle can be aligned, and a divergence adjustment lens unit (31) with a second lens (L2) for adjusting the divergence, the distance (d12) between the second lens (L2) and the first lens (L1) along the first astigmatism lens unit (27) the jet salmon (25) is adjustable, and an optical output element with a second astigmatism lens unit (29) with at least one with respect to the beam axis (25) for astigmatism adjustment tiltable third lens (L3), wherein the third lens (L3) in any direction an adjustable angle can be aligned tiltably and the distance (d23) between the second lens (L2) of the divergence adjustment lens unit (31) and the third lens (L3) along the beam axis (25) is adjustable.

Description

The present invention relates to a beam adapter, in particular for continuously variable adjustment of a laser beam with regard to beam parameters such as lateral expansion and divergence, especially for influencing astigmatism and non-rotationally symmetrical beam cross-sections. The invention also relates to a frequency conversion unit and a method for frequency conversion.

In complex optical systems, laser beams can have different input parameters that have to be adapted to narrow output specifications. Specific input parameters of a laser beam to be coupled into an optical system result, for example, from the characteristics of the individual beam sources or the beam sources in combination with beam guides or other optics placed in the beam. These differ, for example, from laser type to laser type, from series to series, from system (installation) to system. However, since complex optical systems (such as beam sources or beam guides) can seldom be set up or operated identically without tolerances, they can also arise between individual units of a series that are planned as similarly, e.g. from not completely identical or imperfect beam sources or beam guide individuals . Specific output parameters can result from special optical requirements and the optical process to be carried out in the optical system that receives the laser beam. Analogous to the input parameters, the required output parameters can be different and vary individually. However, due to the application or subsequent optics, these are often very tightly tolerated in order to enable precisely repeatable, precise laser applications / processes.

This refers to the lateral beam dimension and the divergence of a beam. This essentially refers to the 2nd moments of the field or intensity distributions, as they are in the standards ISO 13694 , ISO 11145 and ISO 11146 are defined. However, other suitable definitions can also be used.

In particular, the lateral extent of a laser beam and its divergence in several axes often have to be adapted differently between the beam source, beam guidance and application system. For many systems that receive such a beam, a particularly rotationally symmetrical beam is required, which the beam sources or the optical systems preceding the receiving system cannot provide with the required accuracy. In some recording systems, however, a precisely defined, non-rotationally symmetrical, for example elliptical and / or astigmatic, shape of the laser beam is also the aim of the adaptation. General shows US 2009/0257118 A1 a telescope arrangement for beam shaping, which has no variability in terms of beam adaptation due to the mirrors selected in advance, for example.

When generating, for example, ultraviolet (UV) laser radiation through non-linear frequency conversion, undesired aberrations in the amplitude and phase of the UV laser radiation can occur in a frequency conversion unit. Such aberrations are compensated, for example, by downstream optical systems designed for correction, see, for example US 2012/0120481 A1 and US 2004/0228372 A1 . However, optical components of such optical correction systems can experience a gradual influence (eg local destruction) on the surface, in particular a surface coating, that is detrimental to the function of the overall system due to the UV laser radiation.

Also disclosed DE 10 2010 003591 A1 an arrangement for frequency conversion in which, to compensate for a difference in the directions of propagation in a nonlinear crystal, a beam offset of two input beams is effected by a relatively small lens passage offset and / or tilted relative to the beam axis. Since only a small beam offset is required, excessive ellipticity of the incident laser beams is avoided. US 8422119 B1 further discloses a combination of a non-linear crystal for frequency conversion and a cylindrical lens which is arranged in front of the non-linear crystal for generating a special beam shape in the non-linear crystal.

Also reveal DE 601 20 905 T2 an optical system with electronic point size control and focus control, US 5745296 A a lens assembly for a multi-beam recorder and US 2012/0032065 A1 a dynamic wavefront control of a laser system with frequency conversion.

It is an object of one aspect of this disclosure to provide a variable astigmatic beam adapter. Another aspect of this disclosure is based on the object of providing the output beam of a frequency conversion unit, in particular a UV output beam, with a rotationally symmetrical expansion and / or divergence.

At least one of these objects is achieved by a beam adaptation device according to claim 1, a frequency conversion unit according to claim 10, and an optical system according to claim 13 and by a method for frequency conversion according to claim 15. Further developments are given in the subclaims.

In one aspect, a beam adaptation device for variable astigmatism setting and / or setting the lateral extent of an electromagnetic radiation propagating along a beam axis of the beam adaptation device comprises a first astigmatism lens unit for receiving the electromagnetic radiation, which has at least one tiltable with respect to the beam axis for astigmatism setting provides a first lens, a divergence adjustment lens unit with a second lens for adjusting the divergence, wherein the distance between the second lens and the first lens of the first astigmatism lens unit is adjustable along the beam axis, and a second astigmatism lens unit with at least one with respect to the beam axis for Astigmatism adjustment tiltable third lens. In this case, in particular for setting the size of the electromagnetic radiation on the third lens, the distance between the second lens and the third lens of the second astigmatism lens unit can be adjusted along the beam axis.

In a further aspect, a frequency conversion unit has a beam precompensation device with a beam adaptation device as described above for shaping the electromagnetic radiation provided by a beam source into an output beam with predetermined beam parameters and a device for frequency conversion with a frequency conversion crystal for generating a frequency-converted beam with the output beam. The device for frequency conversion is designed to generate the frequency-converted beam with a beam deformation that is asymmetrical with respect to the output beam in terms of beam shape and / or divergence.

In a further aspect, an optical system has a plurality of optical components influencing beam shape and / or divergence in the optical system and a beam adaptation device as described above for compensating for beam shape and / or divergence in the optical system. In this case, the compensation is carried out in particular after setting and / or replacing one of the optical components and / or for setting certain parameters of a beam generated with the optical system.

In a further aspect, a method for frequency conversion has the following steps: providing electromagnetic radiation propagating along a direction of propagation, adapting the electromagnetic radiation with a beam adaptation device as described above with regard to beam size and divergence for forming an output beam for frequency conversion in a frequency conversion crystal and generating of a frequency converted beam in the frequency conversion crystal. The adjustment in terms of beam size and divergence of the output beam takes place in such a way that the desired beam parameters of the frequency-converted beam are present.

In some embodiments, the first astigmatism lens unit, the divergence adjustment lens unit and / or the second astigmatism lens unit are designed such that the tiltability of the first lens and / or the third lens and the displaceability of the divergence adjustment lens unit by tilting and moving the corresponding lenses Adjust the size of the electromagnetic radiation at the second astigmatism lens unit and the divergence of the electromagnetic radiation in two independent directions down the beam of the second astigmatism lens unit. For example, the directions (main axes) of the beam expansion (on a reference plane) can be set independently of the directions (main axes) of the divergence. In general, the two main axes of beam expansion are always perpendicular to one another, just like the two main axes of divergence.

In some embodiments, the first astigmatism lens unit, the divergence adjustment lens unit and / or the second astigmatism lens unit are designed such that the tiltability and displaceability of the first lens and / or the third lens and the displaceability of the divergence adjustment lens unit allow the size and the Divergence of the electromagnetic radiation downstream of the beam adapter in independent directions not rotationally symmetrical to the optical axis, ie the main axes of the beam expansion (at a reference plane) and the main axes of the divergence can be selected independently of each other in their orientation and size.

In some embodiments, the beam adaptation device furthermore has an adjustment rail formed along the beam axis for positioning the first astigmatism lens unit, the second astigmatism lens unit and / or the divergence adjustment lens unit along the beam axis. Additionally or alternatively, the beam adaptation device can furthermore have at least one rotary holder for holding the first lens or the third lens, wherein the at least one rotary holder has at least one setting device for setting at least one tilt angle of the corresponding lens by at least one Has tilt axis. In particular, a tilt axis can run orthogonally to the beam axis.

In some embodiments, the beam adaptation device furthermore has a beam analysis unit which has a first detection unit for recording a beam profile of the electromagnetic radiation in an image plane, and an analysis lens which the beam profile in the area of the second astigmatism lens unit, in particular the third lens as the object plane, onto the Depicts image plane. Furthermore, the beam analysis unit can have at least one far-field detection unit for recording a beam profile of the electromagnetic radiation in a far-field plane after the second astigmatism lens unit. The beam analysis unit is designed in particular to analyze an analysis portion of the electromagnetic radiation.

In some embodiments, the beam adaptation device furthermore has a control unit for controlling the tilting of the first lens and / or the third lens and / or for controlling at least one of the distances between the divergence adjustment lens unit and the astigmatism lens units. The control can in particular take place as a function of the beam profiles detected with the beam analysis unit and, in particular, predetermined target beam profiles and / or measurement parameters relating to the beam.

One advantage of the concepts described here is the simplicity of the optical structure with which the task of setting the beam parameters can be achieved. Thus, the beam adaptation device can advantageously be constructed with a few spherical lenses that are easy to manufacture. Another advantage lies in the comparatively large tolerance of the beam adaptation device against misalignment and in the very flexible use of the beam adaptation device. Since the astigmatism of the tilted lenses increases slowly and continuously with the tilt angle, there can also be a high tolerance in the angles to be set.

The concepts described here can thus make an important contribution to being able to specify the divergence and the beam diameter more precisely, especially for free-beam guided ultrashort pulse (USP) lasers. The relative insensitivity when using spherical lenses to misalignment compared to using cylindrical lenses can also simplify the start-up of the beam adaptation device by the user, e.g. even after a long transport.

The concepts described here relate in particular to the beam shaping of pump and / or seed laser radiation for frequency conversion, in particular for UV radiation generation, and generally the flexible setting of beam parameters.

• 1A bis 1C eine beispielhafte schematische Darstellung eines variablen Strahlaufweiters zur Divergenzeinstellung,
• 2 eine schematische perspektivische Ansicht eines Strahldurchtritts durch eine verkippte rotationssymmetrische Linse,
• 3 eine beispielhafte Ausführungsform einer variablen astigmatischen Strahladaptionsvorrichtung,
• 4 eine beispielhafte Ausführungsform einer Strahlanalyseeinheit zur Analyse eines Ausgangsstrahls einer variablen astigmatischen Strahladaptionsvorrichtung,
• 5 eine Skizze zur Verdeutlichung nicht-vorkompensierter Frequenzkonversionseffekte,
• 6 eine beispielhafte Ausführungsform einer Frequenzkonversionseinheit mit einer variablen astigmatischen Strahladaptionsvorrichtung zur Vorkompensation der Strahlform,
• 7 schematische beispielhafte horizontale und vertikale Schnittansichten einer Frequenzkonversionseinheit zur Verdeutlichung der Vorkompensation und
• 8 eine beispielhafte Skizze eines optischen Systems mit einer Strahladaptionsvorrichtung.

Concepts are disclosed herein that allow aspects from the prior art to be improved at least in part. In particular, further features and their usefulness emerge from the following description of embodiments with reference to the figures. From the figures show:

• 1A to 1C an exemplary schematic representation of a variable beam expander for divergence adjustment,
• 2 a schematic perspective view of a beam passage through a tilted rotationally symmetrical lens,
• 3 an exemplary embodiment of a variable astigmatic beam adaptation device,
• 4th an exemplary embodiment of a beam analysis unit for analyzing an output beam of a variable astigmatic beam adaptation device,
• 5 a sketch to illustrate non-precompensated frequency conversion effects,
• 6th an exemplary embodiment of a frequency conversion unit with a variable astigmatic beam adaptation device for precompensation of the beam shape,
• 7th schematic exemplary horizontal and vertical sectional views of a frequency conversion unit to illustrate the precompensation and
• 8th an exemplary sketch of an optical system with a beam adaptation device.

Aspects described here are based in part on the knowledge that a system for variable beam expansion and beam parameter adjustment made up of several lenses that can be moved along the beam axis (e.g. converging lens, diverging lens, converging lens) can be supplemented by degrees of freedom of tilt and possibly transversal degrees of translational freedom with regard to one or more lenses. As a result, both the size and the divergence of the beam at the exit of the system in different axes (running transversely to the direction of propagation) can be freely influenced.

As mentioned at the beginning, different applications of laser systems, for example in material processing, require special and sometimes tightly tolerated beam parameters. These can, for example on a special optical element or on a workpiece to be machined. The beam parameters include, for example, a focus diameter, a roundness or ellipticity of the beam in the focus or in the vicinity of the focus and the axial position of the focus (in the direction of propagation of the laser radiation). Optical elements that may require appropriate beam parameters for special applications include, for example, DOEs and frequency conversion crystals. The transport of the laser light to the application can also place special demands on the required input beam parameters (e.g. for transport fibers or cutting optics of laser-based machine tools).

However, a laser beam source or a propagated laser radiation seldom corresponds exactly to the required requirements. In addition, beam sources, even if they are of the same design, often have slightly different beam parameters. For example, the optical elements used may deviate from the ideal or thermal or other physical effects may deform the beam differently. Correspondingly, a readjustment may be necessary depending on the beam source used, for example when a beam source is replaced. The discrepancies between the electromagnetic radiation provided by the beam source and the parameters required for the application consist, for example, in a deviation in the beam diameter (at a reference point) and the beam divergence. These deviations can be rotationally symmetrical. However, different sizes can also be required or adapted in different axes, i.e. a special non-circular or generally astigmatic beam can be present or required.

It is noted that the requirements of processes for laser processing on the laser beam with regard to the beam parameters are often so tight that extreme requirements are placed on the components of the laser system or the beam guidance. For example, astigmatism is easily and frequently caused by plan deflectors which, due to their manufacture or mounting, have a small (but not always identical) curvature. For precise laser material processing, an astigmatic beam is usually not tolerable.

The beam adaptation device disclosed herein allows the beam of a beam source to be adapted to the requirements of the application or the transport to the application. Scattering of the beam parameters can be compensated for by changing the size and divergence of the incident beam differently in different axes. With the beam adaptation device disclosed herein, the change in all degrees of freedom is continuously variable and even small deviations can be adjusted continuously.

Expanded by a beam analysis unit, the beam adaptation device disclosed herein can also enable characterization of the output beam or targeted adaptation of the output beam to required beam parameters.

In general, the beam adaptation device disclosed herein combines the principle of a variable beam expander (telescope) made up of several lenses with that of the tilted lens. The general (rotationally symmetrical) influencing of the beam size and divergence can be selected by choosing the lenses and their spacing. By tilting individual or several elements around several axes or a freely selected axis, the symmetry can also be broken in a targeted manner and the size of the beam in a reference plane and the divergence in freely selectable axes can be influenced differently. A generally adjustable astigmatism can thus be generated or an existing astigmatism can be compensated accordingly.

The effects of divergence adaptation (in connection with FIGS. 1A to 1C) and the generation of astigmatism by tilting lenses (in connection with 2 ) explained. Then, in conjunction with the 3 and 4th an exemplary implementation and an exemplary beam analysis unit are described. In connection with the 5 and 6th Finally, the application of a beam adaptation device in the context of a frequency conversion and its integration into a system that generates UV laser radiation is described.

1A shows a classic variable beam expander 1 of three lenses (or lens units): a first converging lens L1 , a divergent lens L2 and a second converging lens L3 . The beam expander 1 represents an exemplary basic structure of the beam adaptation device disclosed herein. The function can be clearly described as follows. The first two lenses L1 , L2 form, depending on their focal lengths f1, f2 and their distance d12, an element of variable focal length with which the divergence in a beam section 3 behind the two lenses L1 , L2 and in front of the second converging lens L3 can be changed. As in 1A is indicated, the beam propagates to the third lens arranged at a distance d23 from the second lens L3 and changes its size according to the set divergence.

The 1B and 1C show that a smaller distance d12 'increases the divergence and a larger distance d12''reduces the divergence (at least as long as the distance d12 is smaller than the distance between the converging lens L1 and that through the converging lens L1 generated focus). This also changes the size of the beam at the converging lens L3 (e.g. the beam diameter based on the FWHM of the intensity profile), whereby by moving the converging lens L3 (i.e. a change in the distance d23) the current size of the beam at the converging lens L3 can also be changed.

It can be seen that a desired (target) beam size is at the second converging lens L3 can be achieved in a wide range in any number of different ways, for example with a small divergence and a large distance d23 (propagation length) or a large divergence and a small distance d23.

The second converging lens L3 now changes the divergence of the beam again. Their influence on the divergence depends on the focal length of the second converging lens L3 and the size of the beam 3 at the second converging lens L3 from. The larger the beam at the second converging lens L3 and the smaller the focal length f3, the greater the change in divergence caused. The size of the beam is determined by a single lens (here by the second converging lens L3 ) unaffected.

Since, as stated above, the (nominal) beam size can be achieved with different divergences, it is possible, with a sensible choice of the focal length f3, to diverge the beam precisely in this way onto the second converging lens L3 to let that impinge through the second converging lens L3 the desired output divergence is achieved as an output beam parameter. For a correspondingly continuous setting of the output beam parameters, see in 1A for example, the adjustability of the distance d12 between the first converging lens L1 and the divergent lens L2 by the displaceability of the divergent lens L2 indicating arrow 5A and the adjustability of the distance d23 of the second converging lens L3 to divergent lens L2 by the displaceability of the converging lens L3 indicating arrow 5B indicated.

Used in the beam expander 1 only centered rotationally symmetrical lenses and assuming a beam path running along the common axis of symmetry of the rotationally symmetrical lenses, a rotationally symmetrical beam shaping takes place.

The beam adaptation device disclosed herein for variable astigmatism adjustment of electromagnetic radiation propagating along a direction of propagation is based on a combination of such a beam expander with the aspect of generating astigmatism when the beam passes through a tilted lens. The result is a variable beam expander which can change the size of the beam and the divergence in different transverse directions independently of one another. The directions of the change in size and those of the change in divergence do not have to coincide with one another, i.e. a general astigmatism can be generated, compensated or influenced as desired.

2 illustrates the influence of a tilting of a rotationally symmetrical lens L with respect to a beam axis predetermined by the direction of propagation of the beam 7th . The axis of symmetry 9 the lens L, which is also referred to as the optical axis of a rotationally symmetrical lens, runs at an angle φ to the beam axis 7th . In 2 the tilting takes place around a tilting axis 11 that are perpendicular to and through the beam axis 7th runs.

For an incident ray 13A the focal length of the lens L now depends on the orientation of the plane under consideration, since the curvature of the lens is no longer rotationally symmetrical to the beam axis 7th is. In the meridional plane 17A , in which the beam axis 7th as well as the axis of symmetry 9 the lens and on which the tilt axis 11 stands vertically, the focal length is shortened (focal length fm in 2 ) compared to the focal length in the sagittal plane 17th B (focal length fs in 2 ), which is also the beam axis 7th but contains to the meridional plane 17A is vertical and which is also the tilting axis 15th contains. Astigmatism occurs in the outgoing beam 13B .

In contrast to cylinder optics (which are fixed in the beam) or other non-rotationally symmetrical, fixed optics, the astigmatic effect of tiltable, rotationally symmetrical optics can be adjusted continuously, for example starting from a zero point (no tilting, identical focal lengths in all of the beam axis 7th containing planes, ie no astigmatic effect).

As the tilt angle increases, further higher-order imaging errors, such as coma, can occur in addition to astigmatism, but these effects (especially in the case of optics with small numerical apertures) can be at least partially neglected.

3 shows an exemplary embodiment of a beam adaptation device 21 which is based on the classic variable jet expander 1. On an adjustment rail 23 with a pair of rails extending along a beam axis 25th the beam adapter 21 (given by the preferred direction of propagation of a coupled laser beam) are a first converging lens unit 27 , a second positive lens unit 29 and a divergent lens unit disposed therebetween 31 arranged. At least two of the three units have one in the adjustment rail 23 engaging carriage 33 on. The converging lens units 27 , 29 are examples of astigmatism lens units that allow a locally like in 2 to make the astigmatism setting explained and thus to influence an astigmatism and a non-rotationally symmetrical lateral extension of a beam in the subsequent optical system. Further is the divergent lens unit 31 an example of a divergence adjustment lens unit which allows a divergence setting to be made and thus influences the divergence locally symmetrically and thus essentially only influences the mean lateral extent and the mean divergence in the subsequent optical system.

The first converging lens unit 27 is at one end of the adjustment rail 23 arranged and has at least one first converging lens LI, which with respect to. One to the beam axis 25th orthogonally extending plane is kept tiltable. That is, an optical axis (not explicitly shown) of the converging lens L1 can with respect to the beam axis 25th the beam adapter 21 be tilted. For this one recognizes in 3 a first swivel mount 35 around a first tilt axis 35A , which is perpendicular to a plane spanned by the pair of rails (here the xz plane), can be rotated on the slide 33 is provided. The tilt axis runs here 35A the swivel mount 35 especially through the beam axis 25th the beam adapter 21 (as long as there is no translation transverse to the beam axis 25th is made).

One can also be seen on the first rotating bracket 35 attached second swivel mount 37 to accommodate the converging lens L1 and for positioning them in the beam axis 25th . The second swivel mount 37 represents a second tilt axis 37A ready to be perpendicular to the first tilt axis 35A and in particular through the beam axis 25th the beam adapter 21 runs (as long as there is no translation transverse to the beam axis 25th is made). For clarity, the position of the second tilt axis is 37A due to the tilting around the first tilting axis 35A indicated by an angle φ1 in the coordinate system.

In addition, the first positive lens unit 27 one or more translation units (not shown) for moving the converging lens L1 transverse to the beam axis 25th have, which thus compensate for possible deflections of the beam propagation direction away from the beam axis 25th serve. In the exemplary embodiment of 3 is the sled 33 the first positive lens unit 27 eg stationary with the adjustment rail 23 screwed.

As a result, the first swivel mount allow it 35 and the second rotating bracket 37 who have favourited the converging lens L1 tilted in any direction by an adjustable angle φ to the beam axis 25th align.

At the other end of the adjustment rail 23 is the second positive lens unit 29 arranged, the second converging lens L3 analogous to the design of the first converging lens unit 27 is held tiltable about two axes. It can also be seen that the position of the second converging lens unit 29 via the associated carriage along the pair of rails, ie the beam axis 25th , can be moved and fixed locally.

The diffusing lens unit 31 also comprises a slide which can be displaced along the pair of rails 33 holding a bracket 38 carries, for example, the short focal length divergent lens L2 symmetrical to the beam axis 25th positioned.

The collecting lens L1 the first positive lens unit 27 and the divergent lens L2 the divergent lens unit 31 act as an optical input element 39 the beam adapter 21 and the converging lens L3 the second positive lens unit 29 represents the optical output element of the beam adaptation device 21 represent.

Even if the embodiment described above is designed with regard to widening the beam, those skilled in the art will recognize that embodiments of the concepts disclosed herein can also bring about a reduction in a beam dimension or a divergence, and can also include optical systems that leave one or more characteristics of the beam unchanged .

The person skilled in the art will recognize that other designs of variable beam expanders with more than three lenses can also provide a required beam adaptation. All lenses or some of the lenses (for example, if full freedom of adjustment is not required, only a single lens) can be kept tiltable.

In contrast to a system for fixed expansion based, for example, on two lenses, a system with three or more lenses in the configuration disclosed herein (or in a similar configuration) can also provide a tolerance range required with regard to the output beam properties in order to cover a range of input beam properties to be recorded provide full freedom in continuously variable adjustment.

The following is the effect of the beam adaptation device 21 with the aid of a round, anastigmatically collimated input beam, on which, for example, an out-of-roundness and an astigmatism are impressed. However, the functional principle can also be implemented for non-circular, astigmatic (convergent or divergent) input beams in which the roundness and astigmatism are changed, for example the divergence is reduced to a minimum corresponding to the steel, and the beam is converted into a round anastigmatic beam, for example becomes.

The shape of in the beam adapter 21 lenses used can be spherical or possibly partially or continuously aspherical. The lenses can be flat on one side or curved on both sides. In addition, surface curvatures in the same direction or in opposite directions are possible, the special shape of a lens being able to influence the effect of the desired astigmatism and the undesired higher order aberrations when tilted.

If the converging lens is tilted L1 is the lens combination L1 , L2 generally adjusted to an astigmatic diverging effect. The mean divergence can be determined by the distance between the lenses L1 and L2 can be freely adjusted to each other. The astigmatic difference can be determined by the effective one from the two tilt angles with respect to the tilt axes 35A , 37A resulting, tilt angle φ can be set. The orientation of the now minimal divergence in the meridional plane and the maximal divergence in the sagittal plane can be selected by the azimuth angle of the tilt axis assigned to the effective tilt angle (in the xy plane). If only one tilt is carried out, for example around the tilt axis 35A or the tilt axis 37A , this tilt axis corresponds to the effective tilt axis and the meridional and sagittal planes are defined by this tilt axis. The tilting can also be generated, for example, with corresponding rotary mounts with which the tilting axis can be rotated in the xy plane about the beam axis.

In summary, if there is a tilt, the beam expands after the lens combination L1 , L2 , ie the input optical element 39 , according to the set, non-rotationally symmetrical divergence and is given an elliptical profile.

The collecting lens L3 is now also tilted by an angle about an effective tilt axis lying in the xy plane. The lateral extent of the beam at the location of the converging lens L3 is from the converging lens L3 unaffected. The astigmatic effect of the converging lens L3 describes itself like that of the converging lens L1 , but with their own meridional and sagittal planes. The combination of that through the input optical element 39 generated astigmatism of the beam with that through the converging lens L3 generated astigmatism makes it possible to generate a general astigmatism of the output beam, which can be freely parameterized in a wide range.

For example, the converging lens L3 be tilted so that the through the lenses L1 and L2 caused direction-dependent different divergence is compensated again and a beam with non-rotationally symmetrical lateral extent and the same divergence in all directions or, for example, with direction-dependent minimally possible divergence is generated.

Since a real (thick) lens always causes a beam offset by tilting, the tiltability of a lens can, as mentioned above, be achieved by displacing the lens perpendicular to the beam axis 25th of the system can be added.

It goes without saying that the use of degrees of freedom in the system can be dispensed with if the aim is only to partially influence the beam. In particular, the tilting of only one lens is significantly easier to adjust than that of several lenses.

In an exemplary embodiment, the first converging lens L1 and the second converging lens L3 each has a planoconvex lens and the divergent lens is a biconcave lens. The divergent lens L2 has, as in the example of 3 , for example no degrees of freedom for tilting. The transverse layers along the beam axis 25th (z-positions) of the divergent lens L2 and the second converging lens L3 can be finely adjusted, for example, using a dovetail guide.

In addition to the explicitly explained embodiment with a converging lens each at the entrance and at the exit and a diffusing lens arranged in between, the first two lenses can be diffusing lenses and only the last lens can be designed as a converging lens. Furthermore, one diffusing lens each at the entrance and one at the exit and a converging lens arranged in between can be used in the beam adaptation device. Furthermore, one converging lens each at the entrance and one at the exit and a diverging lens arranged in between can be used in the beam adaptation device.

The degrees of freedom can generally, if necessary, for example via racks and gear wrenches, via threads or via Have lever tools fine-tuned. Furthermore, after the adjustment, degrees of freedom can be individually fixed in their position with, for example, fixing screws. Xy translations to be set using fine-thread pins can, for example, alternatively be held precisely in position using counter springs.

In some embodiments, for example, one tilt axis can be provided per (collective) lens, the orientation of the tilt axis around the beam axis 25th (z-axis) is rotatable. In contrast to the converging lens units 27 , 29 in 3 has for this purpose a converging lens unit instead of the first rotary holder, for example a rotary device, which aligns the tilt axis of the second rotary holder in the xy plane around the beam axis 25th makes freely selectable. The required orientations can thus be set, the tilt angle of the second rotary mount being the effective tilt angle and the tilt axis being the same as the effective tilt axis. Furthermore, in some embodiments, lenses can be positioned in tube systems, it being possible for a z-position to be adjustable, for example, via a thread or worm gear adjuster. It is important for the various embodiments that the direction of the axis of symmetry of the lenses to be tilted, ie the direction of the optical axis 9 the lens in 2 , can adjust freely. In general, a wide variety of analysis methods can be used to analyze the beam according to the variable astigmatic beam adapter, which provide information on divergence and beam size. Known methods for determining the beam diameter and determining the beam divergence include, in particular, the methods mentioned in ISO 11146. The use of wavefront sensors such as a Hartmann or Shack-Hartmann sensor is also possible. Different methods can also be combined with one another. In general, methods are preferable that enable a rapid characterization of the beam properties at the reference plane and thus display the effect of the adjustment of the variable astigmatic beam adapter directly in real time.

Since any additional optics in a subsequent optical system can influence both the size and the divergence of the beam, an intuitive and simple adjustment of the system in a few steps is not always possible.

The beam analysis can, however, have a simplifying effect on the adjustment process if the reference plane of the analysis is located directly on the last lens. Namely, if the beam is related to the position on the last lens (e.g. the converging lens L3 the beam adapter 21 the 3 ), this last lens has no or only a very slight influence on the beam size at this same reference plane, but only or primarily an influence on the divergence of the beam. The preceding degrees of freedom of adjustment of the beam adapter, for example that of the lens combination 39 , can be used approximately to adjust the output size of the beam at the reference plane without paying attention to the output divergence. The output divergence can then be adjusted with the degrees of freedom of the last lens, approximately without influencing the size. Insofar as these statements only apply approximately, a rapidly converging iterative method for adjusting the degrees of freedom can be used, which, unlike in the case of freely selected reference planes, converges reliably and quickly. This also works if the reference plane is not located directly on the last lens, but at a small distance (compared to the quotient of the beam diameter and divergence) down the beam.

If the beam is not directly accessible for characterization at a preferred reference plane, a suitable imaging method can be used to image the plane at a desired location. It is generally possible to sufficiently characterize the ray elsewhere and to calculate the properties at the preferred reference plane.

4th shows an exemplary embodiment of a beam analysis unit 41 to characterize an output beam 21A the beam adapter 21 which can be used in particular to adjust the beam adaptation device.

A part 43 of the output beam 21A (For example, light leakage through a deflecting mirror that functions as an attenuator 45 ) is used for beam analysis and guided through an analysis lens AL. After the analysis lens AL, the part 43 of the beam, for example with beam splitters 44 further divided into partial beams.

A first partial beam 43A is used to create an image of a beam profile P1 at the exit of the beam adaptation device 21 (for example based on an object plane O, which is at the location of the second converging lens L3 is selected) on an image plane E of the camera K1 through the analysis lens AL. The image of the beam profile P1 on the camera K1 is only on the size of the output beam 21A at the exit of the beam adaptation device 21 (e.g. on the second converging lens L3 ) dependent and not on the divergence. The effect of the second converging lens L3 the divergence is not detected in this way. This allows the first two lenses L1 , L2 the beam adapter 21 can be used to determine the beam size, for example using a Representation of the beam profile P1 on a beam profile monitor 47 to adjust.

Another partial beam 43B is used to take a far field image of the output beam on a camera K2 to generate, ie the camera K2 is located, for example, exactly in the focal plane of the analysis lens AL (but not necessarily in the focus of the beam). That from the camera K2 recorded image of the beam profile P2 is only from the divergence of the output beam 21A depends, not on the size of the output beam 21A at any real finite position. Hence the picture of the camera K2 used to reduce the divergence of the output beam 21A via the position and / or the angle of the second converging lens L3 to adjust.

In some parameter areas, the method described above may not be unique, for example if the output beam 21A is not collimated in front of the analysis lens AL, because generally the output beam 21A after the beam adaptation device 21 be convergent or divergent. In some embodiments the analysis unit 41 can be another partial beam 43C with another camera K3 be measured with regard to a suitable position along the direction of propagation in order to enable an unambiguous characterization of the beam. Further observation points in the beam can be useful in order to reduce the susceptibility of the method to measurement errors in practice. This means that additional detection units can optionally be installed in front of the camera K2 , between the camera K1 and the camera K2 or be provided behind the camera Kl for recording additional field levels.

In some embodiments the analysis unit 41 all or part of the beam positions or images to be analyzed can be projected onto a single camera chip and / or onto the beam profile monitor 47 can be presented together and / or evaluated with a corresponding computer-based analysis. Furthermore, instead of the beam splitting after the analysis lens AL, the (attenuated) output beam can already be used 21A divided in order to analyze these parts with several adapted lenses or with other measuring means.

Furthermore, for example, a Shack-Hartmann sensor can be installed at the beam exit, for example behind the last lens L3 used to measure both profile and divergence of the output beam 21A to be determined at this point. Here, too, a reference plane can be mapped onto the sensor, whereby the use of relay optics (eg an f-2f-f system), which by itself does not insert any wavefront curvature, can be useful.

With reference to the application in frequency conversion, the nAspekte described here are also based in part on the knowledge that if a laser beam in the e.g. infrared frequency range of the primary beam source before the frequency conversion (or between frequency conversion stages in the e.g. infrared and visible frequency range) an opposing phase and / or amplitude deformation is impressed, after the superposition of which with the aberration caused in the frequency converter an improved beam profile of the frequency-converted beam can be generated.

As mentioned at the beginning, the generation of UV laser radiation by non-linear frequency conversion based on e.g. an infrared laser beam can lead to undesirable aberrations in the amplitude and phase of the UV laser radiation generated. Such aberrations can be caused, for example, by the so-called walk-off effect, by facets of the nonlinear crystal or the nonlinear crystals tilted against the beam, generally by crystal defects or surface shape defects, such as are undesirable and not always complete, for example due to the anisotropy of the crystals or production processes can be reproducibly generated, or are caused by other, possibly still unknown effects or by various (principal or faulty) effects in auxiliary or follow-up optics for frequency conversion, such as in optics for separating the harmonics.

With the aim of keeping such aberrations as low as possible and thereby having to provide as few or no optics as possible (which are susceptible to UV radiation) for subsequent correction of the aberrations, it is proposed here to give the laser beam a suitable, in particular adjustable, spatial one before the frequency conversion To impress phase and amplitude adaptations, which are superimposed with the aberrations in the conversion crystal and / or any unavoidable subsequent optics in such a way that (almost) the desired beam properties are obtained again at the output of the overall system. With this precompensation, the number of optics exposed to UV-induced destruction can be kept small.

The beam adaptation device described here can be used to provide one or more output beams for the frequency conversion that compensate for the aberration-causing property of the conversion crystal, for example when generating the third harmonic (THG) in the UV, or when generating UV radiation through the 2nd . or 4th harmonic (SHG, 4thHG), generally when generating higher harmonics. The precompensation with the beam adaptation device relates in particular to a non-rotationally symmetrical beam shape on the Entry into the conversion crystal, as described below in connection with the 5 to 7th is explained.

In addition to the explicitly mentioned generation of UV radiation, the beam adaptation device can also be used before an SHG or another frequency conversion with target wavelengths below 550 nm, for example, because in this wavelength range it can also be advantageous to use as few high-power optics as possible. For example, many optical materials and coatings can no longer be used in a high-power laser beam in this wavelength range because they begin to absorb and build up thermal lenses. Furthermore, e.g. gaseous ambient air contamination from light in the range of 550 nm and less can deposit on optics. It is therefore advantageous to reduce the number of optics from the range of short-wave light behind a frequency conversion. This can be made possible, for example, by the beam adaptation in the beam adaptation device before the frequency conversion.

Advantages from a pre-compensation of aberrations impressed downstream with the help of the beam adaptation device can also result for lasers with a longer wavelength, e.g. infrared (IR) lasers, if a subsequent compensation or avoidance of the aberration, e.g. due to poor accessibility, e.g. through piping or encapsulation at these points, is not possible or not possible. In a conversion crystal, for example, the already mentioned walk-off effect can be present, which means that one of the wavelengths required for the non-linear process does not propagate in exactly the same direction as the other. This can result in an out-of-round frequency-converted beam. 5 illustrates this for the construction of a frequency conversion unit with a conventional beam expander (see, for example, the beam expander 1aus 1 ), which has an input laser beam with a symmetrical beam profile 1A converted into a correspondingly larger symmetrical beam profile 1A '. The frequency conversion results in an arrangement of one or more non-linear crystals 55 Eg UV radiation is generated in an area that is in the direction of 61 is extended, for example, by the walk-off and accordingly has a non-rotationally symmetrical, non-circular beam profile 1A ″. Examples of frequency conversion crystals include beta barium borate (beta-BaB ₂ O ₄ , BBO), lithium triborate (LiB ₃ O ₅ , LBO), cesium lithium borates (CsLiB ₆ O ₁₀ , CLBO), potassium dihydrogen phosphate (KH ₂ PO ₄ , KDP) .

When using a beam adapter 21 For the variable astigmatism setting, this ovality can be compensated for by a corresponding counter-rotating ovality in or near the crystal of the beam on which the frequency conversion is based (for example the output beam of the beam adaptation device).

6th shows a frequency conversion unit 51 with a beam precompensation device 53 and an arrangement 54 of one or more conversion crystals 55 . 6th additionally shows three beam profiles as they develop on the beam axis.

The frequency conversion is based on a beam source 52 out. This is, for example, a Yb: YAG, Yb: Glass, Nd: YAG, Nd: YVO, Nd: Glass or Nd: YLF laser or another solid-state or fiber laser with, for example, the laser-active ions ytterbium or neodymium in one Host material. The beam source 52 can furthermore be a solid-state or fiber laser with other laser-active materials or other host materials or a diode laser or a gas laser. In general, the beam source 52 be a laser beam source that emits electromagnetic radiation 52A , ie laser radiation in the wavelength range from eg 500 nm to eg 1600 nm, in particular from 800 nm to 1100 nm, further in particular the wavelengths from 1030 nm, 1047 nm, 1051 nm, 1064 nm, 1070 nm, and / or 1080 nm, emitted and as input radiation for the beam precompensation device 53 , especially for their beam adaptation device 21 for variable astigmatism adjustment. 6th again shows an exemplary symmetrical beam profile 1A this primary radiation.

The beam adaptation device 21 is set so that an output beam 53A the beam precompensation device 53 having predetermined beam parameters in or close to one of the frequency conversion crystals 55 lead to a beam shape enlarged on one side. A correspondingly out-of-round (eg elliptical) beam profile 53 ' is in 6th for example at the exit of the beam adaptation device 21 indicated.

7th illustrates an exemplary setting of the beam adaptation device 21 in two orthogonal planes, the xz (horizontal) plane and the yz (vertical) plane as well as an exemplary orientation of a conversion crystal 55 which leads to a walk-off in the xz plane in the "-x" direction for the wavelength underlying the walk-off.

In 7th is the beam path of the unaffected wavelength in the conversion crystal 55 with a pair of solid lines 57A and the beam path of the affected wavelength with a dashed pair of lines 57B drawn. The latter runs in the horizontal plane at a walk-off angle to the beam axis 25th . Lies in the yz direction no walk-off effect in front of and the beam paths (dashed-solid line pairs 57A , 57B) accordingly run parallel in the yz plane.

Without a corresponding beam adaptation device, this can, as in 5 made clear, lead to a broadening of the UV radiation generated in the horizontal plane. This is in 7th by dotted arrows of different lengths indicating the beam diameter 59A , 59B (see also the frequency-converted radiation in 5 ).

As in 7th Also shown, the beam adapter fits 21 however, the beam parameters of the output beam 53A in such a way that with essentially the same divergence, for example, the output beam 53A is greater in the y direction than in the x direction. The adjustment of the beam size can at least partially compensate for the different beam diameters in the two directions of the UV radiation generated 54A cause. This is in 7th by solid arrows of the same length, indicating the beam diameter in the planes 60 and in 6th through a round beam profile 54 ' after the frequency conversion unit 51 made clear.

In other words, the method proposed herein for frequency conversion sets the output beam 53A with a variable astigmatic beam adapter in the horizontal direction (ie in the walk-off direction) is smaller than in the vertical direction, so that the walk-off effect is pre-compensated. An essentially round, frequency-converted beam is then obtained after the conversion 54A .

As an example in 7th shown is the first converging lens L1 around the vertical axis and the second converging lens L3 be tilted about the horizontal axis. The distances between the lenses L1 , L2 and L3 have also been adjusted to produce an output beam 53A is formed with the desired divergence in the corresponding planes.

With a given crystal orientation and length, walk-off is always the same, so that one could choose appropriate fixed optics that do not shape the beam in an adjustable manner to compensate for it. The use of a variable astigmatic beam adapter has the advantage that, if the actual source and strength of the astigmatism and the out-of-roundness due to the superposition of other different causes of aberrations (see above) or sources (including a possibly unpredictable astigmatic out-of-round source 52 A) cannot precisely predict whether a fine adjustment of the precompensation can be carried out in the respective frequency conversion mechanism.

For example, imperfections in the conversion crystals or the subsequent optics can affect the required precompensation. For example, the optical surface of the crystals can have a slight cylinder as a result of the polishing or there is an anisotropy of the crystal (s) that has an effect. Because of the large number of parameters (known and unknown), the use of a beam adaptation device for variable beam shaping is particularly useful here, since the beam parameters can easily be adapted from laser system to laser system to the special conditions.

In particular, this would not be possible with a cylindrical lens or a single tilted lens. Even two tilted lenses can still offer insufficient flexibility, since the difference between the two axes can then be variably adjusted, but the mean magnification of the beam cannot. In addition, the mean magnification changes compared to the setup with lenses straight into the beam.

In addition to the exemplary in 6th In addition or as an alternative, a further beam precompensation device can be provided in front of one or more special conversion crystals or in front of each individual conversion crystal.

The example given of the use of a beam adaptation device for frequency conversion shows that beam adaptation devices can generally be used in optical systems when, for a wide variety of reasons (e.g. replacement of components with non-identical properties, poor access options, e.g. due to closed / piped systems, operating parameters - dependent influencing of beam parameters etc.) a high degree of flexibility with regard to a continuously variable adjustment of the laser beam is required.

The beam adaptation device disclosed herein makes it possible, with simple means, to provide the respectively desired output parameter of a laser beam for a large number of input parameters. Accordingly, optical influences of the most varied of components in optical systems can be compensated flexibly with the beam adaptation devices disclosed herein.

This means that the concept of pre-compensation can generally also be transferred to non-UV systems if, for example, subsequent correction is not possible or is only possible with difficulty for other reasons (e.g. accessibility).

8th Figure 11 generally shows a beam adapter device 71 that are in an optical system 73 eg to compensate for differences in interchangeable optical components 75 (Laser sources, lenses, mirrors, laser media, pump sources) or to set certain application-specific output beam parameters. For example, a control unit allows 77 the setting of distance parameters and / or angle parameters with respect to the lenses of the beam adaptation device 71 .

With a view to the general applicability of the beam adaptation device, the wavelength range also extends to shorter and longer wavelengths with respect to the exemplary wavelengths specified above. For example, ZnSe lenses for CO2 lasers can also enable the beam adaptation device to be designed in the corresponding wavelength range of the CO2 laser.

For example, the beam adaptation device can be used in processing optics for beam tools which are intended to reproducibly produce a round spot of a defined size in a defined position after the processing optics. Such processing optics require an anastigmatic and round input beam of defined size and divergence, which can be provided with the beam adaptation device. Furthermore, diffractive optical elements (DOE), for example, can benefit from input beams with reproducible, adjustable, precisely defined and tightly tolerated beam parameters.

It is explicitly emphasized that all features disclosed in the description and / or the claims are viewed as separate and independent of one another for the purpose of the original disclosure as well as for the purpose of restricting the claimed invention, regardless of the combinations of features in the embodiments and / or the claims should. It is explicitly stated that all range specifications or specifications of groups of units disclose every possible intermediate value or subgroup of units for the purpose of the original disclosure as well as for the purpose of restricting the claimed invention, in particular also as a limit of a range specification.

Claims (18)

Beam adaptation device (21) for continuously variable adaptation of an electromagnetic radiation propagating along a beam axis (25) of the beam adaptation device (21) with regard to beam parameters such as lateral expansion and divergence, in particular for influencing astigmatism and non-rotationally symmetrical beam cross-sections, with an optical input element (39) a first astigmatism lens unit (27) for receiving the electromagnetic radiation, which provides at least one first lens (L1) that can be tilted with respect to the beam axis (25) for astigmatism adjustment, the first lens (L1) in any direction at an adjustable angle can be tilted aligned, and a divergence adjustment lens unit (31) with a second lens (L2) for adjusting the divergence, wherein the distance (d12) between the second lens (L2) and the first lens (L1) of the first astigmatism lens unit (27) along the beam axis (25 ) is adjustable, and an optical output element with a second astigmatism lens unit (29) with at least one third lens (L3) which can be tilted with respect to the beam axis (25) for astigmatism adjustment, the third lens (L3) being tiltable in any direction by an adjustable angle and the distance (d23) is adjustable between the second lens (L2) of the divergence adjustment lens unit (31) and the third lens (L3) along the beam axis (25). Beam adaptation device (21) according to Claim 1 , wherein the first lens (L1) and / or the third lens (L3) is a, in particular a rotationally symmetrical, converging lens and / or the second lens (L2) is a, in particular rotationally symmetrical, divergent lens. Beam adaptation device (21) according to Claim 1 , wherein the first lens (L1) and / or the third lens (L3) is a, in particular rotationally symmetrical, divergent lens and / or the second lens (L2) is a, in particular rotationally symmetrical, converging lens. Beam adaptation device (21) according to Claim 1 , wherein the first lens (L1) and / or the second lens (L2) is a, in particular rotationally symmetrical, divergent lens and / or the third lens (L3) is a, in particular rotationally symmetrical, converging lens. Beam adaptation device (21) according to one of the preceding claims, wherein the first lens (L1), the second lens (L2) and / or the third lens (L3) are rotationally symmetrical lenses and / or wherein the first lens (L1) and / or the third lens (L3) can be displaced at least in a direction orthogonal to the beam axis (25). Beam adaptation device (21) according to one of the preceding claims, wherein the first astigmatism lens unit (27), the divergence adjustment lens unit (31) and / or the second astigmatism lens unit (29) are designed in such a way that due to the tiltability of the first lens (L1) and / or the third lens (L3) and the displaceability of the second lens (L2) and / or the third lens (L3) by tilting and moving the corresponding lenses, the size of the electromagnetic Allow radiation to be set at a reference plane after the beam adaptation device (21) and the divergence of the electromagnetic radiation in two independent directions. Beam adaptation device (21) according to one of the preceding claims, further comprising an adjustment rail (23) formed along the beam axis (25) for positioning the first astigmatism lens unit (27), the second astigmatism lens unit (29) and / or the divergence adjustment lens unit (31) along the beam axis (25) and / or with at least one rotating bracket (35, 37) for holding the first lens (L1) or the third lens (L3), the at least one rotating bracket (35, 37) having at least one adjusting device for adjusting at least one tilt angle (φ, φ1) of the lens (L1, L3) has at least one tilt axis (35A, 37A), and in particular a tilt axis (35A, 37A) runs orthogonally to the beam axis (25). Beam adaptation device (21) according to one of the preceding claims, further comprising a beam analysis unit (41) a first detection unit (K1) for recording a beam profile (P1) of the electromagnetic radiation in an image plane (E), an analysis lens (AL) which images the beam profile (P1) in the region of the second astigmatism lens unit (29), in particular the third lens (L3) as the object plane (O), onto the image plane (E), and at least one far field detection unit (K2) for recording a beam profile (P2) of the electromagnetic radiation in the far field after the second astigmatism lens unit (29), wherein in particular the beam analysis unit (41) is designed to analyze an analysis portion (43) of the electromagnetic radiation. Beam adaptation device (21) according to one of the preceding claims, further with a control unit (77) for controlling the tilting of the first lens (L1) and / or the third lens (L3) and / or for controlling at least one of the distances (d12, d23) between the lenses (L1, L2, L3), in particular depending on the beam profiles (P1, P2, P3, ...) detected with the beam analysis unit (41) and in particular predetermined target beam profiles and / or measurement parameters related to the beam. Frequency conversion unit (51) with a beam precompensation device (53) with a beam adaptation device (21) according to one of the Claims 1 to 9 for shaping the electromagnetic radiation (52A) provided by a beam source (52) into an output beam (53A) with predetermined beam parameters and a device for frequency conversion with at least one frequency conversion crystal (55) for generating a frequency-converted beam (54A) with the output beam (53A) , the device for frequency conversion being designed in such a way that the frequency-converted beam (54A) is not generated deformed rotationally symmetrically with respect to beam shape and / or divergence of the output beam (53A). Frequency conversion unit (51) according to Claim 10 , wherein the device for frequency conversion is designed to generate the frequency-converted beam (54A) by a frequency conversion mechanism that effects a non-rotationally symmetrical beam shape, and / or the predetermined beam parameters with regard to a non-rotationally symmetrical deformation of the beam and in particular to form an asymmetrical beam shape (53 ') ) of the output beam (53A) are predetermined in the frequency conversion crystal (55) and / or the device for frequency conversion at least partially compensates for the asymmetry in the frequency-converted beam (54) in terms of beam shape and / or divergence and / or the device for frequency conversion includes a frequency conversion mechanism that is used for correspondingly predetermined beam parameters of the output beam (53A) generate a frequency-converted beam (54) which is rotationally symmetrical with regard to beam shape and / or divergence. Frequency conversion unit (51) according to Claim 10 or 11 , wherein the frequency conversion crystal (55) is characterized by a walk-off direction (61) present during the frequency conversion with respect to the direction of propagation of the output beam (53A), the frequency conversion mechanism to a beam shape of the frequency-converted beam enlarged in the walk-off direction (61) (54A) and the beam precompensation device (53) provides such predetermined beam parameters of the output beam (53A) that the beam shape of the output beam (53A) in or near the frequency conversion crystal perpendicular to the walk-off direction and to the direction of propagation is greater than in the walk- off direction. Optical system (73) with a plurality of beam shape and / or divergence in the optical system (73) influencing optical components (75) and a beam adaptation device (71) according to one of the Claims 1 to 9 to compensate for beam shape and / or divergence in the optical system (73), in particular after setting and / or replacing one of the optical components (75) and / or for setting certain parameters of a beam generated with the optical system (73). Optical system (73) according to Claim 12 , furthermore with a control unit (77) for setting a distance parameter and / or an angle parameter with respect to lenses (L1, L2, L3) of the beam adaptation device (71). Method for frequency conversion with the steps of providing electromagnetic radiation (52A) propagating along a direction of propagation, adapting the electromagnetic radiation (52A) with a beam adaptation device (21) according to one of the Claims 1 to 9 in terms of beam size and divergence for forming an output beam (53A) for frequency conversion in at least one frequency conversion crystal (55) and generating a frequency-converted beam (54A) in the frequency conversion crystal (55), with the adjustment in terms of beam size and divergence of the output beam (53A) to desired beam parameters of the frequency converted beam (54A). Procedure according to Claim 15 wherein the adaptation results in a rotational symmetry of the frequency-converted beam (54A). Procedure according to Claim 15 or 16 , the electromagnetic radiation (52A) being laser radiation in the wavelength range from 500 nm to 1600 nm, in particular in the wavelength range from 800 nm to 1100 nm, and the frequency-converted beam (54A) being in the wavelength range from 250 nm to 600 nm, and in particular harmonic radiation second, third or higher order of the electromagnetic radiation (52A). Method according to one of the Claims 15 to 17th , wherein the frequency conversion is characterized by a walk-off direction (61) present during the frequency conversion with respect to the direction of propagation of the output beam (53A) and the adaptation of the output beam causes the beam shape of the output beam (53A) in or close to the frequency conversion crystal perpendicular to Walk-off direction and the direction of propagation is greater than in the walk-off direction.

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