DE102007028504B4 - Device for processing a workpiece by means of a laser beam - Google Patents

Abstract

Device for processing a workpiece by means of a laser beam with:
an optics housing (1), through which a laser beam path is guided from an optical fiber receptacle (2) to a laser beam outlet, an optical fiber receptacle (2) attached to the optical housing for coupling an optical fiber transmitting laser radiation, a collimation mirror (3) arranged in the optical housing in the optical housing arranged focusing mirror (4), wherein the collimating mirror directs the laser beam (5) coupled via an optical fiber in the optical housing to the focusing mirror, the optical fiber receptacle (2) is arranged and / or formed such that the center of the end face (7) the optical fiber coupled or docked thereto is at or near the focal point of the collimating mirror (3), and the focusing mirror focuses the laser beam (5) on or near the focal point of the focusing mirror;
characterized in that
the collimating mirror (3) and the focusing mirror (4) each have a mirror surface in the form of an off-axis paraboloid, that the center of the end face (7) of the optical fiber is not more than ...

Description

The The invention relates to a device for processing a workpiece by means of a laser beam according to the preamble of claim 1.

State of the art

The achievable average laser power and the beam quality of the available laser beam sources increases with their increasing level of development. This results in new requirements to the processing optics.

On the one hand, the damage threshold of the optical components is a problem which is often further reduced by application-related contamination of the surfaces. On the other hand, laser-induced thermal influences cause the laser focus to change in shape and position. In particular, the dependence of the refractive index of all transparent materials on the temperature and the thermal expansion coefficient of importance. These influences are described by way of example in: RJ Tangelder, LHJF Beckmann, J. Meijer: "Influence of Temperature Gradients on the Performance of ZnSe-Lenses", EOS / SPIE Conference on Lens and Optical Systems Design, Berlin, 14-18 September 1992, SPIE Proceedings vol., 1780. The demands on high performance laser processing optics have been met in the context of increasing CO ₂ laser performance by replacing transmissive elements such as ZnSe lenses with cooled and coated copper mirrors are robust, relatively insensitive to contamination and easy to clean.As the beam line in the case of CO ₂ lasers in the free jet and the necessary deflections are optionally made by means of plane mirrors, a nearly parallel laser steel is available at the optics input.Focused with one or more spherical mirrors, depending on the requirements of the focus or by means of other aspheric surfaces.

Compared to CO ₂ lasers shorter wavelength of solid state lasers such. B. Nd: YAG laser and the diode laser allows the beam transmission by means of optical fiber. Here, the laser beam is focused by the fiber end is imaged. For this purpose, the divergent laser beam emerging from the fiber is usually first collimated and then refocused in order to obtain the best possible combinability of the optical components. In the parallel beam section is then also easily a deflection, beam splitting or beam extraction for observation or analysis purposes possible. For laser beam shaping in fiber-coupled lasers, ie the imaging of the radiating fiber end surfaces, the use of transmissive elements has hitherto been customary. Individual applications also used metallic mirrors.

Around the significantly improved laser beam quality and the associated To obtain good focusability, must influence the laser radiation through the optical elements as possible be kept low. In Björn Wedel, Roman Low: "Focusing High-Brightness Lasers ", Laser Technik Journal, 5/2006, p. 47-51, different ways to the laser-induced thermal To reduce influence. In essence, this will be the reduction the material absorption and the number of optical elements as preferred options demonstrated. At the same time, an intensified cooling of the lenses ensures your frames to the exhaustion the larger power losses.

The use of cooled mirrors in processing optics is possible and is used in particular in CO ₂ laser processing optics. In DE 20 2006 015 539 U1 For example, water-cooled deflecting mirrors for CO ₂ and solid-state lasers are proposed.

There because of the fiber divergently exiting after the radiation the total focal length the processing optics in fiber-coupled lasers must be smaller, as with typical CO2 optics, only from a parallel beam have to focus the effect of optical errors is correspondingly greater.

The DE 10 2004 007 178 B4 discloses a laser processing head whose laser beam inlet is formed by a light exit surface of an optical fiber. The laser processing head includes a collimating mirror and a focusing mirror. The collimation mirror collimates the laser beam coupled in via the optical fiber and deflects it onto the focusing mirror, which finally focuses the laser beam into the working focus. In order to enable a two-dimensional scanning or scanning movement of the working focus, both the collimating mirror and the focusing mirror are each rotatable about an axis of rotation which is coaxial with a respective optical axis of the incident working beam path, the focusing mirror being rotated about its collimating mirror Rotary axis performs a pivoting movement about this axis of rotation, that is, the axis of rotation of the collimating mirror. In an implementation of this arrangement, because of the small number of mirror elements and the large deflection angles for optical reasons, the imaging quality will be very low and the achievable foci will be highly asymmetrical.

Another arrangement principle for a machining head discloses the DE 102 30 960 A1 , An ellipsoid and a paraboloid mirror become like that arranged so that their rotational symmetry axes are parallel, in particular collinear. However, the arrangement works only with a parallel beam at its entrance. Furthermore, these mirrors are only operated in pairs. A variation of the focal length by exchanging one of the mirrors for a mirror of another form is not possible or only with limitations in the imaging quality.

Next the systemic focus shift, due to material specific Absorption and temperature-dependent Refractive index of the transmissive optical elements of processing optics, In particular, the long-term drift of the focal position often causes quality restrictions in laser processing processes. These result in practice slowly accumulated contamination of optical surfaces Example on the side of the fiber coupling, by the fiber insertion in the industrial environment or on the process side through the machining process Even under the best precautions lead in the long run Schmauch and Particles to a pollution, which leads to an additional temperature increase one or more optical elements results, due to the material properties the transmitting elements, so for example, the protective glasses in one Focus drift results. The protective glasses used must be changed regularly, resulting in high operating costs leads. Mirror optics can on the other hand, as applied in practice, operated without protective glass become.

A cooling Although the lenses on their edge leads the at larger laser powers increased Loss, increases but at the same time the temperature and thus the radial refractive index gradient, which further aggravates the focus drift as pollution increases.

metal mirror with integrated cooling also have a temperature response due to thermal expansion. This is in comparison to the effect on the laser radiation to lenses much smaller. On the other hand, mirror systems offer less Degrees of freedom for correcting optical errors. For material processing Therefore, spherical-mirror-type optical imaging systems are for one very good picture quality elaborate, often unfavorable folded, big and contain in part considerable residual errors for the typical fiber-side numerical ones Apertures of about 0.1-0.2. These disadvantages are to be avoided by the invention.

In the DE 43 22 609 A1 a focusing device for high-power laser systems is shown, which consists of a plane deflection mirror and an off-axis parabolic mirror. By means of such a device, a parallel laser beam can be imaged onto a focal point. The DE 43 22 609 A1 points out that for a high image quality, however, it is necessary that the parabolic mirror must be precisely aligned, since otherwise such focusing optics showed a pronounced astigmatism. The DE 43 22 609 A1 proposes a method and a device for adjusting the beam guidance and shaping as well as for measuring and assessing the imaging properties of laser optics. The device essentially comprises at least one laser or a diode, a beam splitter and one or more spatially sensitive detector units, the radiation of the laser (s) divided by the beam splitter into a beam having at least two parallel beams or into a beam of a quasi-beam is converted, and wherein at least one of these rays falls on the detector units.

task

Of the The present invention is based on the object, a reliable, inexpensive Create device that is independent of laser power and temperature an emerging from an optical fiber laser radiation with good picture quality for material processing purposes focused.

These The object is achieved by having the features of claim 1 Device solved. advantageous Embodiments of the device according to the invention are in the dependent claims specified.

The inventive device for machining a workpiece by means of a laser beam thus comprises an optical housing through which a laser beam path is guided by a Lichtleitfaseraufnahme to a Laserstrahlauslass, attached to the optical housing Lichtleitfaseraufnahme for coupling a laser radiation transmitting optical fiber, arranged in the optical housing collimating mirror and a arranged in the optical housing focusing mirror, wherein the collimating mirror directs the coupled via an optical fiber in the optical housing laser beam to the focusing mirror. According to the invention, the collimating mirror and the focusing mirror each have a mirror surface in the form of an off-axis paraboloid. The optical fiber receptacle is arranged and / or formed in such a way that the center of the end face of the optical fiber coupled or coupled thereto lies on or in the vicinity of the focal point of the collimation mirror, wherein the midpoint of the end face of the optical fiber is not more than 15, preferably not more than 5%. of the central radius of curvature of the collimating mirror is spaced from the focal point of the collimating mirror. Accordingly, the focusing mirror focuses the laser beam at or near the focal point of the focusing mirror, the laser beam focus being spaced no more than 15%, preferably not more than 5% of the central radius of curvature of the focusing mirror from the focal point of the focusing mirror. In other words, the focal point of the collimating mirror or focusing mirror lies at a distance of half the central radius of curvature from the vertex of a parabola defining the off-axis paraboloid on the axis of symmetry of the paraboloid.

The Invention thus provides a reliable, inexpensive realizable Device for material processing by means of fiber-coupled laser high performance available, the independent from the laser power and temperature emerging from an optical fiber Laser radiation with good imaging quality for material processing purposes focused.

The inventive device allows In addition, by varying the focal lengths of individual elements an adaptation to the requirements of the respective machining process within a modular system.

A advantageous embodiment of the device according to the invention is characterized characterized in that the focusing mirror with respect to the incident laser beam path is arranged so that in a mirror symmetry plane of the collimating mirror lying single rays of incident on the collimating mirror Laser beam path in a mirror symmetry plane of the focusing mirror lie and that of the rotational symmetry axis of the mirror surface of the Collimation mirror from counted order the impact points of the individual beams on the collimation mirror, starting with the rotational symmetry axis of the mirror surface of the Collimation mirror nearest Impact point with which of the rotational symmetry axis of the mirror surface of the Focusing mirror of counted Order of the impact points of the individual beams at the focusing mirror, beginning with the rotational symmetry axis of the mirror surface of the Focusing mirror nearest Impact point, matches.

By this embodiment the device according to the invention can optical errors of the imaging mirror system complete or near Completely be compensated.

The Mirror of the device according to the invention are preferably water cooled. An air cooling is also possible. The deflection angles at the mirrors are in the preferred embodiment 90 degrees, you can but also differ. Basically, the deflection angle in the range of 0 degrees to 180 degrees, with mirrors with central drilling or grazing Idea, lie. With the deflection angle varies with the same central curvature the focal length of the off-axis paraboloid. The embodiment of the device however, with deflection angles of 90 degrees, the use allows prismatic optics housing or housing parts, which is advantageous in terms of a modular design of the device is.

Of the Center of the endface the optical fiber is preferably located exactly at the focal point of the Collimation mirror and the focus center on the focus of the focusing mirror. The divergent laser beam emerging from the optical fiber strikes on the collimation mirror, is deflected and parallelized. The focusing mirror arranged at a distance deflects the latter parallelized laser beam and collects this in focus. Of the Focusing mirror can be any angle of rotation around the Axis of the laser beam between the mirrors opposite to the Have collimation mirror. For Fixed optics is the preferred orientation of the mirrors to each other such that the beam axis of the laser beam at the fiber exit and the Beam axis of the emanating from the focusing mirror laser beam in parallel are and have the same beam direction. Theoretically is for an axial bunch in this arrangement of paraboloidal surfaces an always ideal picture guaranteed. When imaging an extended fiber end cause it Astigmatism, coma and field tilt a magnification of the smallest focus diameter and a distortion of the intensity distribution in the vicinity of the Focus. The angle of rotation of the focusing mirror about the axis of the Laser beam between the mirrors has a special influence on the picture quality that consists of at least two off-axis paraboloid levels existing laser processing optics. By exchanging at least one the paraboloid, preferably the focusing mirror, against a Mirror of other focal length, is the adaptation of the optics to the machining task easily possible. The Effects of aberrations vary with the imaging ratio of Processing optics. For many Machining tasks is the image quality regardless of twist angle and Denomination sufficient. Are entrance and exit axis of the laser beam parallel and the beam direction opposite, a minimum occurs the error. Compensate the single errors of the parabolic surfaces each other. For the case of equal focal lengths of collimation and focusing mirror the compensation is almost complete. It's a diffraction-limited illustration about that entire field, too, for Fiber diameter up to approx. 1 mm and numerical apertures (NA) of 0.25 possible.

The arrangement of the mirror, in which the errors cancel, but is unsuitable for most applications, since fiber end and focus are on the same side of the processing optics and the accessibility to the workpiece is limited. By adding at least one further plane mirror, the compensation effect can also be realized for arrangements with good accessibility. These one or more plane mirrors must be arranged with their deflection directions so that lying in the mirror symmetry plane of the collimating mirror rays of the axial beam at the focusing mirror are also in the mirror symmetry plane of the focusing mirror and counted from the rotational symmetry axis of the collimating mirror from order of impingement of the rays of the axial bundle on the collimating mirror coincides with the counted from the rotational symmetry axis of the focusing mirror from the order of the impact points on the focusing mirror. The compensation also takes place for deflection angles not equal to 90 degrees, when the deflection angles of the paraboloid are the same size.

For the business in an industrial environment are preferably a cooling of the mirror and optionally other components, as well as protective measures such as Crossjet and / or Optics flushing, z. B. provided by clean air. Coatings of the mirrors enable a slight cleaning. Depending on the process conditions can therefore on protective glasses dispensed with and further thermal influences are avoided.

embodiments

following the invention will be described with reference to a several embodiments illustrative drawing explained in more detail. It show schematically:

1 the construction of a laser processing optics with two paraboloidal mirrors in uncompensated arrangement, each with 90 degrees of deflection at the paraboloidal mirrors;

2 the principle of operation of the invention in a simple embodiment, each with 90 degrees of deflection at the paraboloidal mirrors;

3 the operating principle of the invention in a further embodiment with an additional plane mirror, to correct the orientation of the paraboloid mirror to each other; and

4 the operating principle of the invention in a further embodiment with two additional plane mirror and some supplementary modules.

In 1 is the structure of a laser processing optics with two paraboloidal mirrors for imaging an end surface 7 an optical fiber in a focal plane 6 shown. An optical housing 1 contains fixed mirrors 3 and 4 and an optical fiber receptacle 2 for coupling a laser beam transmitting optical fiber. The mirror 3 acts as a collimation mirror, while the mirror 4 serves as a focusing mirror. The collimation mirror 3 parallelises the out of the fiber end face 7 emerging laser beam. In the example shown, the deflection angle 9 both 90 degrees. The collimation mirror 3 as shown in 1 spaced focusing mirrors 4 collects the laser beam in laser focus. collimation 3 and focusing mirror 4 are trained as off-axis paraboloids. The respective rotational symmetry axis of the rotated parabola 12 the mirror surfaces is drawn to illustrate the mirror shape. The levels in which the parabolas 12 both for the collimation mirror 3 as well as for the focusing mirror 4 are drawn, describe the levels in which there is a mirror symmetry of the off-axis paraboloid. Ideally, the center of the end face 7 the optical fiber on the axis of rotational symmetry 10 and the focal point of the collimation mirror 3 and the center of the focal plane 6 on the rotational symmetry axis 11 and the focal point of the focusing mirror 4 , The mapping of the axial point of the fiber end face into the image plane is accomplished by the use of off-axis paraboloids in the array 1 geometrically ideal. The image of the axial point is diffraction-limited. A recalculation shows, however, that as a aberration for the field points at the edge of the fiber end face, even at fiber diameters of 100 μm and fiber-side numerical aperture (NA) of only 0.1, there is no longer diffraction-limited imaging. At 200 μm and numerical aperture of 0.15, astigmatism, coma and field tilt are not negligible. That is, the image of the fiber edge is out of focus and the focal plane / image plane 6 is at an angle to the beam axis. In this arrangement, the mirror also occurs, depending on NA, a slightly asymmetric beam cone from the processing optics, which can interfere with an orientation-independent material processing.

In the arrangement of the mirror 3 and 4 to 1 is the order of the impact points ( 8a ... 8e ) of the rays of the axial bundle on the collimation mirror 3 , from the rotational symmetry axis 10 of the collimation mirror 3 is counted out, inconsistent with the order of impingement points on the focusing mirror 4 , from the rotational symmetry axis 11 of the focusing mirror 4 counted out. The optical errors of the mirrors 3 and 4 are not compensated. Often, however, this imaging quality is sufficient. With relatively low demands on the imaging quality, a thermally stable, robust processing optics made of modular components can optionally be built with this arrangement.

2 shows a first, relatively simple embodiment of a device according to the invention, the parabolic mirror are arranged such that optical errors of the mirror are compensated. The device consists of the components optics housing 1 , Optical fiber receptacle 2 and in the optics housing 1 attached mirrors 3 and 4 , In this case, a first mirror with the shape of an off-axis paraboloid serves as a collimation mirror 3 for collimating the laser radiation and a second mirror having the shape of an off-axis paraboloid as a focusing mirror 4 for focusing the laser beam. The midpoint of the endface 7 the optical fiber lies on the rotational symmetry axis 10 and the focal point of the collimation mirror 3 , so that a deflection angle 9 at the collimation mirror 3 of 90 degrees. The out of the optical fiber at the Faserendfläche 7 Exiting laser radiation is thereby in one of the rotational symmetry axis of the collimating mirror 10 deflected parallel direction and collimated. This collimated laser beam again hits the focusing mirror at a distance 4 such that the deflection angle 9 on the focusing mirror 4 is also 90 degrees and the laser beam is focused such that the center of the focal plane on the rotational symmetry axis and the focal point of the focusing mirror 4 lies. Ideally, the center of the fiber end face 7 on the rotational symmetry axis 10 and at the focal point of the collimation mirror 3 and the center of the focal plane 6 on the rotational symmetry axis 11 and at the focal point of the focusing mirror 4 , The beam direction of the laser beam at the fiber end surface 7 and at the focus are opposite. By varying the angle of the rotational symmetry axis 10 of the collimation mirror 3 to the optical axis of the fiber end face 7 or the angle of the rotational symmetry axis 11 of the focusing mirror 4 to the optical axis of the focal plane 6 are also different deflection angle 9 adjustable.

In the arrangement according to 2 is the focusing mirror 4 with respect to the incident beam so arranged that in the mirror symmetry plane of the collimating mirror 3 extending rays of the axial bundle 8th also in the mirror symmetry plane of the focusing mirror 4 lie and that of the axis of rotational symmetry 10 of the collimation mirror 3 from counted order of impact points 8a to 8e the rays on the concave mirror surface of the collimating mirror 3 with that of the rotational symmetry axis 11 of the focusing mirror 4 from counted order of impact points 8a to 8e the rays on the concave mirror surface of the focusing mirror 4 matches. Furthermore, in this advantageous embodiment, the focal lengths of the two mirrors 3 and 4 and their deflection angle 9 equal. The same sequence of impact points, the same focal length and the same deflection angles are conditions for the complete or almost complete compensation of the optical errors of the parabolic surfaces. If a reduction in image quality is tolerated, one or more of these conditions may be compromised. The correct order also compensates for unequal focal lengths and unequal deflection angles, so that the correct sequence of impact points and thus the correct orientation of the paraboloidal mirrors should be maintained.

3 shows a further advantageous embodiment of the device according to the invention. Across from 2 leads to the addition of a plane mirror 13 for improved accessibility of the machining head to the workpiece. The inventive order and location of the impact points on the respective mirrors with respect to the rotational axis of symmetry and beam axis is also given in this embodiment. Again, the focus mirror 4 with respect to the incident beam so arranged that in the mirror symmetry plane of the collimating mirror 3 extending rays of the axial bundle 8th also in the mirror symmetry plane of the focusing mirror 4 lie and that of the axis of rotational symmetry 10 of the collimation mirror 3 from counted order of impact points 8a to 8e the rays at the collimation mirror 3 with that of the rotational symmetry axis 11 of the focusing mirror 4 from counted order of impact points 8a to 8e the rays at the focusing mirror 4 matches. Would the plane mirror 13 the laser beam 5 in the other direction, rotated by 180 degrees with respect to the incident beam direction at 90 degrees, the conditions for compensation of optical errors would not exist. The image quality would be comparable to the arrangement after 1 ,

If the folding of the laser beam is effected by further plane mirrors, the condition for the order and position of the impact points on the relevant mirror must always be observed to compensate for the optical errors. Then also a convolution of the beam path from the representation plane of 3 out possible.

4 shows a further advantageous embodiment of the device according to the invention. Across from 3 leads to the addition of a partially transparent plane mirror 14 to an arrangement with a stretched design, at the same time is through the partially transparent plane mirror 14 a metrological detection of the processing space by means of a sensor device 15 possible. This sensor device 15 may consist of one and / or more sensors, the physical properties of the process or the process environment via the sensor beam path 16 to capture. For example, this sensor device can also be a simple Be observation camera. The sensor device 15 can also be in continuation of the incident laser beam 5 be arranged to detect properties of the laser radiation. This variant is not shown. In 4 Furthermore protective measures or protective devices are shown schematically. A rinsing device 18 generated by clean air or another gas overpressure inside the optical housing 1 and thus reduces the risk of penetration of smoke and other impurities. A crossjet device 17 protects by a transverse to the laser beam arranged gas jet, the interior of the optical housing from spatters. Alternatively, as a protective measure, an axial gas jet can also take place through a preferably coaxial nozzle.

With The processing optics of the type according to the invention, it is possible laser radiation with very high power after a fiber transmission without or with reduced influences on the beam properties both for welding and soldering processes but also z. B. for coating and insert cutting. The special form of compensation of the optical Error of the beam-forming individual elements is particularly advantageous for the Welding and To cut.

If different imaging ratios are required for the machining processes of a 1: 1 imaging ratio, other imaging ratios with little influence on the beam quality and the thermal stability can be achieved by adding weak, thin lenses to the mirror arrangements according to the invention. By using the additional lenses in front of the collimation mirror 3 and / or after the focusing mirror 4 become fiber end face and / or focus for the off-axis paraboloid mirror surfaces to virtual, on the respective rotational symmetry axes and the associated focal points of the mirror 3 . 4 lying points. To compensate for the optical errors of the mirror surfaces, the conditions mentioned can be met. The thermal stability of the processing optics with respect to the focus shift is largely achieved by the fact that the transmitting elements have only large focal lengths with respect to the mirrors and the thickness is only slight.

1

optics housing

2

Lichtleitfaseraufnahme

3

collimation

4

focusing

5

laser beam

6

focal plane (Image plane)

7

End face of the optical fiber

8th

radiate of the axial beam

8a

of impact Ray A

8b

of impact Beam B

8c

of impact Beam C

8d

of impact Ray D

8e

of impact Ray F

9

deflection

10

Rotational symmetry axis of the collimation mirror

11

Rotational symmetry axis of the focusing mirror

12

parabola

13

plane mirror

14

partially transparent plane mirror

15

sensor device

16

Sensor beam path

17

Crossjet facility

18

flushing

Claims (14)

Device for processing a workpiece by means of a laser beam, comprising: an optical housing ( 1 ) through which a laser beam path from an optical fiber receptacle ( 2 ) is guided to a laser beam outlet, an optical fiber receptacle attached to the optical housing ( 2 ) for coupling a laser beam transmitting optical fiber, a arranged in the optical housing collimating mirror ( 3 ) and a focusing mirror arranged in the optical housing ( 4 ), wherein the Kollimationsspiegel the coupled via an optical fiber in the optical housing laser beam ( 5 ) to the focusing mirror, the optical fiber receptacle ( 2 ) is arranged and / or formed such that the center of the end face ( 7 ) of the optical fiber coupled or coupled thereto on or in the vicinity of the focal point of the collimation mirror ( 3 ), and the focusing mirror the laser beam ( 5 Focused on or near the focal point of the focusing mirror, characterized in that the collimating mirror ( 3 ) and the focusing mirror ( 4 ) each have a mirror surface in the form of an off-axis paraboloid, that the center of the end face ( 7 ) of the optical fiber is not more than 15%, preferably not more than 5% of the central radius of curvature of the collimating mirror ( 3 ) is spaced from the focal point of the collimating mirror and that the laser beam focus is spaced no more than 15%, preferably not more than 5% of the central radius of curvature of the focusing mirror from the focus of the focusing mirror. Device according to claim 1, characterized in that the optical fiber receptacle ( 2 ) is arranged and / or formed such that the center of the end face ( 7 ) of the optical fiber coupled or connectable thereto at the focal point of the collimation mirror ( 3 ) lies. Apparatus according to claim 1 or 2, characterized in that the focusing mirror the laser beam ( 5 ) focused on the focus of the focusing mirror. Device according to one of claims 1 to 3, characterized in that the focusing mirror ( 4 ) with respect to the incident laser beam path is arranged so that in a mirror symmetry plane of the collimating mirror ( 3 ) lying single rays of the collimating mirror ( 3 ) incident laser beam path in a mirror symmetry plane of the focusing mirror ( 4 ) and that of the rotational symmetry axis of the mirror surface of the collimating mirror ( 3 ) from counted order of impact points ( 8a ... 8e ) of the individual beams at the collimation mirror, beginning with the axis of rotation of the mirror surface of the collimation mirror ( 3 ) nearest point of impact ( 8a ), with the rotational symmetry axis ( 11 ) of the mirror surface of the focusing mirror ( 4 ) from counted sequence of impact points ( 8a ... 8e ) of the individual beams at the focusing mirror ( 4 ), starting with the axis of rotation symmetry ( 11 ) of the mirror surface of the focusing mirror ( 4 ) nearest point of impact ( 8a ) matches. Device according to one of claims 1 to 4, characterized in that the collimation mirror ( 3 ) and the focusing mirror ( 4 ) are formed and arranged so that they each have the incident laser beam with the same deflection angle ( 9 ) distract. Device according to one of claims 1 to 5, characterized in that the collimation mirror ( 3 ) and the focusing mirror ( 4 ) have the same focal length. Device according to one of claims 1 to 6, characterized in that in the laser beam path between the collimating mirror ( 3 ) and the focusing mirror ( 4 ) at least one laser beam path deflecting plane mirror ( 13 ) is arranged. Device according to one of claims 1 to 7, characterized in that in the laser beam path at least one of the laser beam path deflecting, partially transmissive plane mirror ( 14 ), wherein this plane mirror at least one sensor device ( 15 ), the physical variables of the machining process or the process environment via a sensor beam path ( 16 ) detected. Apparatus according to claim 8, characterized in that the sensor device ( 15 ) consists of an observation camera. Device according to one of claims 1 to 9, characterized in that at least one of the mirrors ( 3 . 4 . 13 . 14 ) is provided with a cooling device. Device according to one of claims 1 to 10, characterized in that at least one of the mirrors ( 3 . 4 . 13 . 14 ) is water cooled and / or air cooled. Device according to one of claims 1 to 11, characterized in that the optical housing ( 1 ) with at least one device ( 17 . 18 ) for protecting the optical housing ( 1 ) is provided against ingress of dirt. Device according to claim 12, characterized in that the device ( 17 ) to protect the optical housing against the ingress of dirt outside the optical housing ( 1 ) generated transversely to the laser beam extending gas stream. Device according to claim 12 or 13, characterized in that the device ( 18 ) to protect the optical housing against the ingress of dirt, the optical housing ( 1 ) produced with overpressure purging gas stream.