WO2008110613A1

WO2008110613A1 - Device and method for guiding a light beam

Info

Publication number: WO2008110613A1
Application number: PCT/EP2008/053042
Authority: WO
Inventors: David Ashkenasi; Norbert Müller
Original assignee: Laser- Und Medizin-Technologie Gmbh Berlin
Priority date: 2007-03-13
Filing date: 2008-03-13
Publication date: 2008-09-18
Also published as: DE202008017745U1; DE112008000681A5

Abstract

The invention relates to a device for guiding a light beam with a light guiding element that is driven in a rotating or oscillating manner, the element having at least one optical group, which comprises at least two plane-parallel surfaces in an operational state, which are aligned at an inclination transversely to the light beam about an adjustable tilting angle. The invention further relates to a method for guiding a light beam, wherein a light beam is guided through an optical group having plane-parallel faces in at least one operational state. The optical group is moved continuously such that the direction of a surface normal of one of the planar faces of the optical group is changed periodically with respect to the optical axis.

Description

Apparatus and method for guiding a light beam

The invention presented here describes a method and a device for realizing a fast linear or circular or elliptical-shaped guidance of a light beam, in particular a laser beam by deflecting the beam from the original propagation direction or optical axis. Such a deflection is desired to perform a targeted micromachining of any materials by using focused laser radiation by a laser beam is focused on a workpiece and a combination of movements, of which at least one movement has a high speed, is performed. Such a variant in the laser micromachining for the introduction of linear sections, for the structuring of surfaces or for separating is referred to in this invention as a laser beam planer.

DE 40 26 130 A1 for this purpose is a device for deflecting a light beam with a combined mirror system, which allows to guide the light beam without distortion to the destination. This is mainly the labeling by laser beam. Mirror systems, which are arranged behind the focusing optics, do not permit a short focal-range focusing system, since in mirror systems - or even individual mirrors - the deflection of the beam is usually used for reflection, and this can only be realized with a certain optical path length. Moreover, if the mirror deflector is not compensated, distortion errors (pincushion and barrel distortion) such as those described in "Laser Beam Scanning" by Marshall, Dekker, Basel, 1985, at page 226 et seq.

Another disadvantage is the difficulty with mirror systems to realize small distances, as due to the property of the mirror (angle of incidence equal angle of reflection) extremely small angles of attack are required. These small ways can not be achieved by currently available drives (galvo systems) at high frequencies. Another drive option is piezoelectric drives, which cope well with these short distances; However, these have the disadvantage that the piezoceramic incorporated in continuous operation on one and the same place in the treads and this very quickly leads to failures. Another disadvantage of mirror systems is that the direction of movement must be reduced to zero before it can be accelerated in the opposite direction.

One previously known way of short-circuiting is the use of an F-theta objective behind the mirror system. The lenses currently available on the market have a minimum working distance of just under 30mm, but shorter focal lengths are often used in micromachining.

Furthermore, from DE 100 54 853 A1 discloses a method for introducing microbores in mainly metallic materials is known in which by means of rotating wedge plates, a beam is placed in tumbling motion about the optical axis. High rotational speeds are excluded in this method by the uneven mass distribution. In addition, the laser described represents a system which is equipped with pulse widths in the nanosecond range and moderate repetition rates and in combination with the slow movement of the tumbling jet is unsuitable for processing brittle materials. In addition, the deflected beam does not run parallel to the optical axis, which means that protection against machining residues can not be achieved without influencing the beam path and the beam quality. This is an essential point in laser micro machining, which influences the quality of the processing result.

From DE 101 05 346 A1 discloses a device for helical cutting holes in workpieces is known in which by means of wedge plates, a beam is deflected from the optical axis, which he rotates when turning the wedge plate combination about the optical axis. In addition, λ / 4 or λ% plates are also rotated in order to carry the polarization direction with respect to the processing. This system also serves to produce small holes in predominantly metallic materials with high efficiency. However, here too, the parameters necessary for the production of micrographs such as rotational speed, plane-parallel offset and wavelength independence are not given.

US Pat. No. 4,461,947 describes a method in which, by means of a lens arranged eccentrically on the optical axis, the rotation of which causes the beam to be set in a rotating movement with respect to the optical axis. Again, according to the described embodiments, the problem of unequal mass distribution that does not allow high speeds.

Finally, DE 10 2005 047 328 B3 discloses a method in which a dove prism is used as an image rotator in a hollow shaft motor. It is advantageously described that the setting of a parallel beam offset is independent of the rotation of the dove prism and thus the adjustment mechanism for the beam offset can be mechanically relatively easily performed. However, a disadvantage is also in this device, the non-rotationally symmetric mass distribution of the Dove prism, whereby an imbalance arises at high speeds. In addition, due to its geometry, the prism requires a relatively large hollow space. Ie the rotary drive, which limits the speed of the available motors.

The object of the invention is to provide an improved apparatus for guiding a laser beam, which in particular allows to move the focus of a light beam at high web speed.

According to the invention this object is achieved by a device for guiding a light beam having a rotating or oscillating driven light guide element having at least one optical group, which in turn has at least in an operating state two plane-parallel surfaces which are aligned transversely to the light beam at an adjustable tilt angle. The term optical group is used here in a conventional manner so that the optical group may contain a single isolated optical element, or several directly adjacent optical elements, which, however, need not be cemented together in the present case. Rather, the term optical group should also refer to a combination of two optical elements which are displaceable relative to one another along mutually opposite, congruent surfaces, wherein a negligible air gap can also exist between the two surfaces lying opposite one another.

According to a first and second preferred embodiment, the optical group is formed by a single optical element with two plane-parallel surfaces, which is also referred to below as a plane-parallel plate.

In this case, the plane-parallel plate according to the first preferred embodiment variant is connected to a drive which is designed so that it puts the plane-parallel plate in operation in an oscillating pivoting movement about an at least approximately perpendicular to the optical axis pivot axis. In this embodiment, the light guide element is thus driven to oscillate about an at least approximately perpendicular to the optical axis extending pivot axis. Preferably, in this case, the pivot axis intersects the optical axis at right angles.

According to a second and third preferred embodiment, the light guide element is driven in rotation about a rotation axis extending parallel to the optical axis of the light beam. Preferably, in this case, the optical group is connected to an adjusting device, which makes it possible to adjust the tilt angle of the optical group. Particularly preferably, the adjusting device is designed so that it allows the setting of the tilt angle both at rest as well as rotating optical group.

A third preferred embodiment is characterized in that the optical group is formed by two optical elements and has two planar surfaces as end faces. Here, the optical elements of the optical group have mutually facing, complementary spherically curved surfaces, of which one curved surface forms a concave surface of the first optical element and the second curved surface forms a convex surface of the second optical element and the concave surface and the convex surface have the same radius of curvature. The two optical elements of the optical group are to be displaced relative to one another along the mutually facing spherical surfaces in such a way that the planar surfaces, as surfaces facing away from the respective spherical surface of a respective optical element, are either plane-parallel or at an angle to one another.

A further aspect of the invention consists in a method for guiding a light beam, in which a light beam is guided through an optical group having plane-parallel faces at least in an operating state, wherein the optical group is continuously moved such that the direction of a surface normal is one of the planar Periodically changes the end faces of the optical group with respect to the optical axis.

In this case, the optical group is preferably moved continuously in such a way that the angle between a surface normal of one of the planar end faces of the optical group and the optical axis changes in an oscillating manner. Preferably, a laser beam pulsed at a repetition rate is used as the light beam and the optical group is oscillated back and forth at an oscillation frequency which is tuned to the repetition rate. In this way, in particular, a desired pulse-to-pulse overlap can be set, as described in more detail below.

Alternatively, the optical group can be tilted relative to the optical axis and rotated, so that the surface normal of one of the planar end faces of the optical group rotates about the optical axis and thus changes its direction with respect to the optical axis. Here, too, it is advantageous if the light beam is a laser beam pulsed at a repetition rate and the optical group rotates at a rotational speed which is tuned to the repetition rate in order, for example, to achieve a desired pulse-to-pulse overlap.

The solution according to the invention and its variants have the advantage that a linear or circular deflection of the light beam for small to very small amplitudes can be realized with high web speeds without lingering in the end positions and with short focal length processing optics. Another advantage is that the straight or circular deflected beam is aligned in all positions parallel to the optical axis, and thus orthogonal to the workpiece. Particularly in the processing of brittle materials, such as glass or ceramic, this type of beam guidance results in a high quality of processing, which is reflected in the good edge quality (minimization of scalloping and cracking). Another advantage of the solution according to the invention is that the beam path is not further changed or disturbed except for the desired beam offset, with the result that the optimum focusing (with converging lens and high-quality laser radiation) is maintained. In particular, the solution according to the invention is not limited by restrictions with regard to the pulse duration or wavelength. Suitable arrangements in beam path or materials are known for all pulse durations from continuous wave (cw) to femtosecond pulses, which can be used as a plane-parallel offset plate (3) in the manner described. The beam deflection of different wavelengths can also be used with the described principle by suitable selection of materials from UV applications to infrared laser radiation.

Another significant advantage is that the application can be controlled by the targeted control of the oscillation or rotation speed and thus the definition of a pulse-to-pulse overlap of the laser radiation on the workpiece to be machined, without entering the parameter field of the laser, eg the repetition rate, which in turn not only provides gentle processing, but also maximizes processing efficiency.

Due to the advantage of the mechanical adjustment of the beam offset (S), the amplitude can be adapted for a wide range of applications.

In addition, it is advantageous in the application that the beam can also strike the optics slightly eccentrically, without this having any effect on the beam offset. Likewise, the focal length can be determined by selecting a suitable focusing optics or their spatial position relative to the plane-parallel plate. It is even possible to use the same focusing optics which were also used before the use of the solution according to the invention.

In continuation of the inventive concept, several devices can be arranged one above the other, to two independent vibrations and to produce microbores with a rectangular profile by ablation. With the same arrangement also Lissajousfiguren can be created with all its variants. The suppression of the reversal points in the movement of the plane-parallel plate achieves a homogeneous distribution of the laser radiation over the surface.

One advantage of the embodiment variant with a rotationally driven, tilted plane-parallel plate (also referred to below as an offset plate) is the possibility of adjusting the beam offset during processing or else in a stationary position. This allows, coupled by a motorized X-Y drive to the device (such as on a CNC trajectory), a complex, program-based applications of the laser beam milling machine. Thus, also free-form removal tracks with adjustable width can be generated with the device according to the invention.

Even with non-rotating offset plate, the beam can be moved in one axis, which allows very narrow micro-trenches or a slot-shaped breakthrough or the separation of thin components.

According to a third embodiment variant, the angle adjustment takes place with two lenses with the same surface curvature, more precisely a combination of a concave lens and a convex lens. Depending on the desired angle, lens pairs with different radius pairs can be selected here. In addition, the order of the lens combination concave-convex or convex-concave can be reversed to achieve an angle reversal. This makes it possible, depending on the choice of the lens radii and order of the concave and convex lenses relative to the direction of laser beam to set a predetermined angle.

It is essential here that the tilt angle is limited only because of the beam distortion, but this can be compensated by the choice of materials. It is not necessary to specify micro or macro processing. dig, since this depends only on the selected lens diameters and the focal length of the focusing lens.

An essential component of this third embodiment are thus two with their curved surfaces superimposed plano-concave and plano-convex lenses. Preferably, the adjustment of the angle is the

Lenses to each other, which causes the angular position of the laser beam, realized so that I give a rotationally symmetric mass distribution. The

Angle adjustment of the focused processing beam is carried out analogously, as provided according to the second preferred embodiment for the plane-parallel plate. The adjustment of the beam offset is also analogous to the second preferred embodiment.

By simultaneously changing the diameter and angle of attack of the processing light beam even demanding machining shapes can be realized. For a reduction, for example, the diameter of the machining focus must be reduced with increasing z-feed (movement of the focus to the material surface). Such an embodiment for the introduction of holes also in greater depth of material, for the precise structuring of surfaces or for cutting in any contours is referred to in this invention as Laserstrahlfräse with selectable angle.

Another advantage of the third embodiment is that the Winkelein- position acts completely independent of the adjustment of the parallel beam offset and can thus serve to produce cavities with "punctiform" opening.

Likewise, the preparation of cylindrical holes with the smallest diameter, which in the conventional laser machining with a certain aspect ratio afflicted, ie, conical, are possible. Without angle of attack it is observed that with larger cutting or drilling depth the desired excavation depth is not achieved. Ablation is often caused by a notch or taper in the cutting width or in the drill hole. Hole diameter interrupted with increasing depth. A tracking of the focused laser radiation to a greater depth often leads to no solution, since then a large portion of the laser energy is absorbed or reflected at the already generated entrance opening and thus can not reach the surface to be processed in depth. The beam losses at the bore entrance thus prevent further removal in larger processing depth. A set angle of attack of the laser radiation above 0 °, which counteracts a notch of the processing in greater depth and thus minimizes the effect of rejuvenation during processing in greater depth or even completely excludes, thus ensuring the production of significantly higher aspect ratios. This method also prevents different diameters from being formed in the inlet and outlet bores of the workpiece as a result of absorption of the laser radiation at the workpiece edge. This is expediently carried out in that the jet flank, which is at the outer edge of the bore, is aligned coaxially with the axis of the bore. Thus, the minimum achievable diameter of the cylindrical bore is determined by the beam diameter at the level of the bore entrance.

Another advantage of the third embodiment is that when changing the angle of attack of the focused processing beam by tilting the concave lens and the convex lens relative to the optical axis, the optical beam path is not further changed or disturbed to the desired angular displacement, with the result that the optimum focusing for the processing is only minimally disturbed. Thus, an adjustment of the angle during processing without great influence on the other settings (laser parameters, machining distance, gas flow, etc.) optimized cutting and removal performance is possible.

Similarly, a change in the angle of attack of the focused processing beam by tilting the concave lens and the convex lens relative to the optical axis both during processing or in a stationary position is possible. With a non-rotating concave lens and convex lens, this allows the beam to be laterally displaced, for example, in the different To move axes, for example, by a motorized XY drive, which is coupled to the device or the workpiece (such as a CNC traversing unit). Here, by means of a complex, program-supported application of the laser beam milling machine with controllable angle of attack, also free-form removal tracks with adjustable width and angle of attack can be produced with the device according to the invention (approximately any slots inclined to the surface). Also, very small micro trenches or a slit-shaped breakthrough or the separation of thin components under an adjustable edge angle can be made possible during laser ablation, for example as preparation for (laser) welding of overlapping components or inclined edges in impact welding or for laser-assisted separation in corners and angles and for the removal (hole, slot, countersink, chamfer) in angular components or for the taper of a leg of angled components. Laser welding on inclined surfaces is also possible.

The described invention also permits independent movement of plane-parallel plate and the optical group comprising the lens combination concave lens and convex lens. This allows angular movement along a circular path with a small diameter, which can be controlled depending on the speed of the moving components. For example, e.g. in conjunction with a linear axis, a complex shaped track with changing geometries (removal width, angle of the wall surfaces, course, etc.) in the micrometer range possible by changing angles of attack.

In continuation of the inventive concept, by prior division of the laser beam, several devices according to the invention can be supplied and arranged on the circumference of a workpiece to be machined so as to execute several processing steps at the same time.

The invention will now be explained in more detail with reference to several embodiments with reference to the figures. From these shows: Figure 1 shows the physical action principle of the invention with its necessary components and their directions of movement.

2 is a partial sectional view of a possible realization variant with eccentric drive for tilting the plane-parallel

Plate;

3 is a perspective view of a machined workpiece with a removal track and an indication of the oscillating laser beam;

4 is a sectional view of a possible implementation variant with adjusting ring for tilting the plane-parallel plate.

5 shows a perspective view of a machined workpiece with a removal track and an indication of the tumbling laser beam;

Fig. 6 shows the physical action principle of the invention in combination with a plane-parallel plate as an application example. The necessary components and their directions of movement are shown;

Fig. 7 shows the physical working principle of the invention with the inclusion of the function of the plane-parallel plate in the lens combination.

The necessary components and their directions of movement are shown;

8 is a perspective view of a machined workpiece with a removal track and a counterbore and an indication of the tumbling focused laser beam; and 9 to 12 calculated by a simulation beam trajectories for different implementation examples of the laser beam cutter with selectable angle of attack.

The schematically outlined in Fig. 1 apparatus for micromachining of materials has an arrangement based on the physical principle of refraction of light on a plane-parallel plate 6.

The plane-parallel plate 6, which need not have a circular shape, can, as explained below to FIGS. 2 and 3, be set in a rapid pivoting movement. In addition, the distance from the focusing optics 4 can be changed.

Also, plane-parallel plate 6, as explained below to Figs. 4 and 5, are set in rotation and tilted.

When passing through the light beam 2 through a plane-parallel plate 6, a parallel displacement S occurs. The size of S is determined by the angle of incidence a of the incident beam 2 on the plane-parallel plate 6, the thickness d of the plane-parallel plate 6 and the refractive index n of the plane-parallel plate 6. It follows that S = f {O, d, n)

S o = dj * * si ^• nα 1 11 - ^{COS 0C}

Λi n ² - sin ² CC

[1]

If the plane-parallel plate 6 standing under the angle of incidence α and arranged behind the focussing lens 4 is set into a pivoting or tilting motion (see also the descriptions of FIGS. 2 and 3), the angle of incidence α continuously changes, which leads to a parallel movement. offset S and thus leads to the linear movement orthogonal to the optical axis. Depending on the distance or focal length of the lens, the focus be adapted to the respective working level and the corresponding processing.

If the plane-parallel plate 6 standing under the angle of incidence α, that is, tilted with respect to the light beam and arranged behind the focusing lens 4, is rotated (see also the descriptions of FIGS. 4 and 5), the beam moves due to the parallel offset S centric around the optical axis. Depending on the distance or focal length of the lens so the focus diameter can be adapted to the respective working plane and the corresponding processing. By tilting the plane-parallel plate 6, the angle of incidence a is changed, which results in the parallel offset S of the radiation. Thus, the diameter of the beam moving centrically around the optical axis is changed.

Another possibility for influencing the plan offset S is achieved via the thickness d and the refractive index n of the plane-parallel plate 6. Hereby a preselection of the plan offset S can be determined. Due to the arrangement and the drive of the moving parts, it is possible to realize a wide variety of movement speeds and Strahlaus- deflections, wherein the moving beam follows approximately a sine function. The moving beam is always orthogonal to the working plane during the offset movement, which positively influences the quality of the processing.

2, a first embodiment of the invention is shown, which allows to offset a plane-parallel plate 6 in an oscillating movement, in which the plane-parallel plate 6 is tilted continuously oscillating. Here, the focusing optics 4 is in a socket that can be adapted to different variants with the aid of a corresponding tube (not shown). The plane-parallel plate 6 is guided in a second version, which in turn is mounted in a bearing block 12 so that it can be tilted perpendicular to the plane of the drawing. About the connecting rod 10 and its eccentric attachment to the crank disk 8, the plane-parallel plate 6 in an oscillating motion, about the rotation axis 14, offset. The crank disk 8 is here designed so that it provides for a balancing mass distribution, and so a swing - especially at high speeds - prevented.

By connecting an additional eccentric disc (not shown) with the crank disc 8, the angular adjustment and thus the tilt of the plane-parallel plate can be made individually. It follows that the beam offset S and thus the track to be processed is adjustable.

In order to protect optics and mechanics from the effects of machining, the device is integrated into a housing which is provided with a protective glass at the jet exit side (not shown). Advantage of the solution according to the invention is that the beam is parallel to the optical axis in each position of the plane-parallel plate 6 and can pass through the protective glass without interference.

In order to support workpiece machining, the housing also offers the possibility of providing a gas connection in order to create a corresponding (protective gas) atmosphere at the processing station.

FIG. 3 shows a workpiece 18 in which a free-formed trench 20, also referred to below as a removal track, has been removed, as can be produced with the device according to FIG. 2. In this case, the oscillating beam 16 describes a linear movement orthogonal to the working plane and thus carries material from the workpiece, similar to a planer. The efficiency of the removal is determined very strongly by the pulse-to-pulse overlap and thus by the oscillation speed of the plane-parallel plate 6.

Especially in applications where by linear movements of a few microns in connection with highly repetitive lasers or fast pulse repetition frequencies (eg 100 000 pulses per second) one possible gentle processing is required, high web speeds are required for extremely short distances.

The required oscillation and thus the speeds in rpm l / _rO at a given optimum pulse-to-pulse overlap O can be determined according to the following relationship:

wherein f _{r is} the number of laser pulses per second (repetition rate) determined, c / | _ the effective laser beam diameter on the work piece and S is the parallel displacement according to Equation [1]. Beam deflection and thus the amplitude is equal to 2 ^* S.

Application example 1 for the first embodiment variant:

During gentle and precise micro-removal with short-pulse laser radiation of a specific pulse duration and wavelength, an optimum pulse-to-pulse overlap of O = 75% is determined or determined to produce a microsection on a helical wire, ie after the action of the laser pulse on the surface to be processed the subsequent laser pulse on impact should cover 75% of the area irradiated by the previous laser pulse. The collimated laser beam has an effective diameter d _\ _ = 20 μm on the workpiece so that there is a mean distance of 50 μm between the laser pulses. A rectilinear machining with a deflection S = 0.1 mm is specified. If the laser processing is carried out with a repetition rate of f _r = 10 000 laser pulses per second, the result is a required number of revolutions U _r o = 4 500 U / min according to equation [2]. This corresponds to 9,000 changes of direction per minute at a line speed of 3.6 m / min on average.

Application example 2 for the first embodiment variant: For gentle and precise micro-removal with short-pulsed laser radiation of a specific pulse duration and wavelength, an optimal pulse-to-pulse overlap of O = 30% is determined or fixed to produce a precision cut on a ceramic material to be machined in order to heat up and thus to minimize the thermal shock. The bundled laser beam has an effective diameter d _\ _ = 10 μm on the material. A linear machining with a displacement of S = 0.25 mm is specified. If the laser processing takes place with a repetition rate of f _r = 5 000 laser pulses per second, the result is a required number of revolutions I o = 4 200 U / min according to equation [2].

As these calculations show, commercially available CNC machines (machining) are orders of magnitude removed with respect to the oscillation speeds resulting from the device and the consequent frequent change of direction.

FIG. 4 shows a sectional view of a second embodiment variant of the invention, in which a fixed tilt angle can be set and the plane-parallel plate 6 can be set in rotation at the set tilt angle. Here, the focusing optics is in a version that can be adapted to different variants with the aid of a corresponding tube. The plane-parallel plate 6 is guided in a second version, which in turn is mounted in a sleeve 22. The running sleeve 22 in turn is rotated by an externally acting force, in this embodiment, a toothed belt in rotation. Speed limiting acts only the storage of the sleeve 22, which is executed in the embodiment in the form of ball bearings. Of course, all other types of bearings are conceivable that allow a much higher speed, for example with magnetic, sliding or air bearing.

With a collar 24, a tilt angle of the plane-parallel plate 6 can be set both in the stationary state and during the fast rotation, ie the plane-parallel plate 6 can both in the stationary state as well as being tilted during the fast rotation so as to adjust an offset of the beam. In order to support the workpiece machining, the adjusting ring 24 also offers the possibility of providing a gas connection in order to create a corresponding (protective gas) atmosphere at the processing point. The protective glass 26 protects the internal components from contamination and damage by the residues of processing, without affecting the deflected beam.

FIG. 5 shows a workpiece 18 'in which a free-formed trench 20' is removed, as can be produced with the device according to FIG. 4. Here, the tumbling beam 28 describes a circular movement about the optical axis and thus carries - like a milling head - material from the workpiece. The efficiency of the removal is determined very strongly by the pulse-to-pulse overlap and thus by the rotational speed of the plane-parallel plate 6. Particularly in the case of laser radiation with a high repetition rate or pulse repetition frequency (eg 100,000 pulses per second) extremely gentle speeds (up to 100,000 rpm) are required for the gentlest possible machining.

The required speeds in rpm U _rJ for a given optimum pulse-to-pulse overlap O can be determined according to the following relationship:

wherein f _{r is} the number of laser pulses per second (repetition rate) determined, d _L is the effective laser beam diameter on the work piece and S is the parallel displacement according to Equation [1]. The circumference of the beam deflection is equal to 2 ^* π ^* p.

Application example 1 for the second embodiment variant: During gentle and precise micro-removal with short-pulsed laser radiation of a specific pulse duration and wavelength, an optimal pulse-to-pulse overlap of O = 50% is determined or determined to produce a microbore on a material to be machined, ie after the action of the laser pulse on the surface to be machined is to cover the subsequent laser pulses upon impact only about 50% of the area that has irradiated the previous laser pulse. The bundled laser beam has an effective diameter on the material c / | _ = 100 μm, ie a mean distance of 50 μm should lie between the laser pulses. A circular machining with a radius S = 0.5 mm is determined. If the laser processing is carried out with a repetition rate of f _r = 10,000 laser pulses per second, the result is a required number of revolutions l / _rT = 10,000 rev / min according to equation [3].

Application example 2 for the second embodiment variant:

For gentle and precise micro-removal with short-pulsed laser radiation of a specific pulse duration and wavelength, an optimum pulse-to-pulse overlap of O = 70% is determined or determined to produce a precision cut on a material to be machined. The bundled laser beam has an effective diameter c / | _ = 20 μm on the material. A circular machining with a radius S = 0.1 mm is determined. If the laser processing is carried out with a repetition rate of f _r = 10,000 laser pulses per second, the result is a required number of revolutions l / _rT = 6,000 rpm according to equation [3].

Application example 3 for the second embodiment variant:

In the case of gentle and precise micro-removal with ultra-short pulsed laser radiation of a specific pulse duration and wavelength, an optimum pulse-to-pulse overlap of O = 99% is determined or determined for producing a microstructure on a material to be machined. The bundled laser beam has on the material an effective diameter dι = 5 microns. A circular machining with a radius S = 1 mm is set. If the laser processing takes place with a repetition rate of f _r = 100 million laser pulses per second, the result is a required number of revolutions U _rJ = 50 000 rpm according to equation [3].

As these calculations show, commercially available CNC machines (machining) are orders of magnitude removed in terms of peripheral speeds resulting from the device.

The schematically illustrated in Fig. 6 third embodiment of a device for micromachining of materials has an arrangement based on the physical principle of refraction of light on optical surfaces of the components focusing lens 4, plane-parallel plate 6, concave lens 30 and convex lens 32. The concave lens 30 and the convex lens 32 form an optical group. The plane-parallel plate 6 and the concave 30 and convex lens 32 can be rotated together. In this case, the plane-parallel plate can be tilted by the angle α and bow the concave 30 and the convex lens 32 in equal parts by the angle ß and γ in the opposite direction. The distance of the focusing optics 4 can be changed to adjust the focal length.

The arrows in Fig. 6 indicate the articulation of the components, i. the forces that cause an adjustment, or rotation.

As already explained with reference to FIG. 1, a parallel displacement S occurs when the light beam 2 passes through an inclined plane-parallel plate 6. The size of S is determined by the angle of incidence a of the incident beam 2 on the plane-parallel plate 6, the thickness d of the plane-parallel plate 6 and the refractive index n of the plane-parallel plate 6. It follows for the beam offset in air (refractive index for air n _L = 1): S = f {O, d, n):

Upon further passage, the beam 2 impinges on a lens combination consisting of a concave lens 30 with refractive index ni and a convex lens 32 with refractive index n ₂ with a common axis of rotation. This combination of lenses resembles a variable prism in optical efficiency. It is known that an optical beam guided through the prism, for example a laser beam, is deflected by an angle δ. If the prism is surrounded by the refractive index (n ₁₂ = H ₁ = n ₂ ) of air (refractive index of air n _L = 1), one obtains for the exit angle δ at the prism formed by the lens combination: δ = f (χ β, γ, n ₁₂ )

δ = aresine cos χ * sin β - sin χ y W ₁₂ ² - sin ² β [4]

If the plane-parallel plate 6 arranged at the angle of incidence Ct relative to the laser beam and arranged behind the focusing lens 4 and the lens combination of concave 30 and convex lens 32 are set in rotation, the beam moves on the basis of the parallel offset S at an angle δ on a conical surface Path around the optical axis. Depending on the choice of the focal length of the focusing lens 4 or distance of the focusing lens 4 to the workpiece 18, the focus diameter can be adapted to the respective working plane and the corresponding processing.

With inclination of the lens combination of concave 30 and convex lens 32 in the opposite direction and an angular reversal of the angle of attack δ can be achieved. Angle reversal can also be achieved with an unchanged angle of inclination by a simple exchange of the order within the lens combination of concave 30 and convex lens 32.

In addition to angular adjustment of a, ß and γ for adjusting the parallel offset S and the angle of attack δ can also by the choice of the thickness of the plane-parallel plate d, as well as influencing the refractive index n, H ₁ , n ₂ of said optical components focusing lens 4, concave 30 and convex lens 32 influence on the parameters S and δ are taken. With the last-mentioned influencing variables, a preselection of the parameters S and δ can be determined, wherein tilt and inclination of the fine adjustment are used.

The simple relationships are shown in equations [1] and [4]. Because of the complexity of the calculation, simulation programs or testing are required for the parameters to be selected.

Due to the arrangement of the moving parts, whereby the optical axis coincides with the mechanical axis, as well as their design, an uneven distribution of the masses eccentric axis avoided, so that a very high rotational speed and thus a very high processing speed can be achieved.

Application example for the third embodiment

If a laser beam with a diameter of 5mm and a lens of f = 50mm is focused onto a focus area of 50μm, a beam cone of approx. 6 ° is created. If you now want to introduce a cylindrical bore in a workpiece, the beam cone must be changed at an angle so that on the outside of the beam rotated in diameter perpendicular to the bore axis. For this purpose, as shown in FIG. 6, the concave lens 30 and the convex lens 32 are inclined with their common pivot point symmetrically opposite to each other out of the axis. The inclination is here about 3 °.

As this example shows, compensation for the production of cylindrically small holes with a laser beam is required by tilting the beam axis and thus the optical axis. Of course it is also possible to produce undercuts or undercuts. Fig. 7 shows a structure analogous to FIG. 6, in which the plane-parallel plate 6 is summarized in the components Konkav- 30 and convex lens 32, therefore referred to as a plane-parallel plate with concave lens 40 and plane-parallel plate with convex lens 42. This means that the Lens combination against each other and also can be tilted together around their main plane. Such solutions can also be used with a fixed angle α (or exchangeable exchangeable sets).

FIG. 8 shows a workpiece 18 "in which a freely shaped removal track 20" has been introduced, as can be produced with the devices according to FIGS. 6 or 7. Here, the tumbling beam 34 describes a concentric movement about the optical axis and thus carries - similar to a milling head with a conical milling tool material from the workpiece. The efficiency of the removal is very strongly determined by the pulse-to-pulse overlap and thus by the rotational speed of the optical components plane-parallel plate 6, the concave lens 30 and the convex lens 32.

Implementation Examples:

FIGS. 9 to 12 show results of numerical calculations for the beam path of the focused laser beam for different conversion examples of the device of FIG. 6 with regard to the selection and arrangement of the optical components for the described invention. In the four examples, a selection was made of the optical components focusing lens 4, plane-parallel plate 6, concave lens 30 and convex lens 32 in a numerical simulation for beam propagation with different parameters such as the distance between the surfaces, refractive index, radii of curvature and tilt angle , calculated. The following table shows the application-relevant results for a focused laser beam with a focusing lens 4 of the focal length of 30 mm and a beam diameter of the incident laser beam 2 in front of the focusing lens 4 of 2mm. For the simulation a laser beam with an optimal mode profile TEM _O o was chosen. The parameters for Fig. 9 produce a cone. In Fig. 10 results in a truncated cone with a straight side surface, ie a cylindrical bore. For FIGS. 11 and 12, angles are selected to produce an undercut, which are thus also used in the literature for inclined beams.

In the figures, 3 aspects are shown. Top left, the 3-D focus, as it corresponds to a shot profile of CO ₂ lasers in Plexiglas; Right above the beam distortion. Here, a uniform, round dot pattern of the laser source was propagated through the optics and displayed the grid point distribution at the processing point; Below the beam path with the angle of attack and beam offset in the side view.

List of reference and formula symbols for FIGS. 1 to 12

2 incident beam

4 focusing lens 6 plane-parallel plate

8 crank disc

10 connecting rods

12 bearing block

14 rotary axis 16 oscillating beam

18 workpiece

18 'workpiece

18 "workpiece

20 trench / removal track 20 'trench / removal track

20 "ditch / removal track

22 barrel sleeve

24 collar

26 protective glass 28 tumbling / rotating jet

30 concave lens

32 convex lens

34 focused beam

36 Machining focus with the required intensity for removal or welding

38 Drilling with countersink 40 plane-parallel plate with concave lens 42 plane-parallel plate with convex lens

α angle of incidence β tilt angle of (30) γ tilt angle of (32) δ angle of attack of the focused laser beam on (18) χ angle of the prism faces d thickness of (6) f _r number of laser pulses per second (repetition rate) n refractive index of (6) rπ refractive index of (30) n ₂ refractive index of (32) n _L refractive index of air (n _L = 1)

O pulse-to-pulse overlap

S Parallel offset of the beam

U _r o Speed of oscillation optics given O

U _r j Speed of the tumble optics given O

Claims

claims

1. A device for guiding a light beam, characterized by a rotating or oscillating driven light guide element having at least one optical group having at least in an operating state two plane-parallel surfaces, which are aligned transversely to the light beam inclined by an adjustable tilt angle.

2. A device for guiding a light beam according to claim 1, characterized in that the optical group is formed by a single optical element with two plane-parallel surfaces.

3. A device for guiding a light beam according to claim 1 or 2, characterized in that the optical group of two optical see elements is formed and has two planar surfaces as end faces, wherein the optical elements of the optical group

have mutually facing, complementary spherical surfaces, of which one spherical surface forms a concave surface of the first optical element and the second spherical surface forms a convex surface of the second optical element and the concave surface and the convex surface have the same radius of curvature and

- Are so relative to each other along the facing spherical surfaces to move so that the flat surfaces as the respective spherical surface of a respective optical element facing away surfaces either plane parallel or at an angle to each other.

4. A device for guiding a light beam according to one of claims 1 to 3, characterized in that the light guide element is driven to oscillate about an at least approximately perpendicular to the optical axis extending pivot axis.

5. A device for guiding a light beam according to claim 4, characterized in that the pivot axis intersects the optical axis at right angles.

6. A device for guiding a light beam according to one of claims 1 to 3, characterized in that the light guide element extending about a parallel to the optical axis of the light beam

Rotary axis is driven to rotate.

A light beam guiding apparatus according to claim 6, characterized in that the apparatus comprises adjusting means for adjusting the tilt angle of the optical group connected to the optical group and configured to adjust the tilt angle of the optical group.

8. A device for guiding a light beam according to claim 7, characterized in that the adjusting device is designed so that it allows the setting of the tilt angle both at rest as well as rotating optical group.

9. Device according to one of claims 1 to 8, characterized in that it is connected to a pulsed laser as a source of the light beam.

10. A method for guiding a light beam, characterized in that a light beam is guided through an optical group with at least in an operating state to each other plane-parallel end faces, wherein the optical group is continuously moved so that the direction of a surface normal of one of the flat end faces of the optical group changes periodically with respect to the optical axis.

1 1. A method according to claim 10, characterized in that the optical group is continuously moved such that the angle between a surface normal of one of the planar end faces of the optical group and the optical axis changes oscillatingly.

12. The method of claim 1 1, characterized in that the light beam is a pulsed with a repetition rate laser beam and the optical group is oscillated back and forth with an oscillation frequency, which is tuned to the repetition rate.

13. The method according to claim 10, characterized in that the optical group is tilted relative to the optical axis and rotated, so that the surface normal of one of the planar end faces of the optical group rotates about the optical axis and thus changes its direction relative to the optical axis ,

14. The method according to claim 13, characterized in that the light beam is a pulsed with a repetition rate laser beam and the optical group rotates at a speed which is tuned to the repetition rate.