Optical arrangement and laser system

[0044]figure 1 It is a schematic diagram of a laser system 10 for generating radiation having an intensity distribution L, which radiation has a linear beam section in the processing plane 12.

[0045]The laser system 10 includes at least one laser light source 14 for emitting laser radiation 16. The laser light source 14 is preferably designed as a multimode laser. The laser radiation 16 is optionally fed an input laser beam 20 via a pre-shaped optical unit 18. The pre-shaping optical unit 18 may, for example, have a collimating effect and/or shape the laser radiation 16 into an input laser beam 20 having an elliptical beam section.

[0046]The input laser beam 20 is guided through the shaping optical unit 22 and is emitted as a beam packet 24 therefrom. The beam packet 24 is converted into an output beam 28 by means of a homogenizing optical unit 26, as will be explained in more detail below. The output beam 28 can optionally be transformed into an intensity distribution L by means of a collimating and/or focusing optical unit 30.

[0047]In order to handle large surface areas, it may be desirable to obtain very elongated linear strength profiles. In this regard, it is conceivable to provide and arrange a plurality of laser systems (10, 10') of the mentioned type in such a way that the intensity distributions L, L'are complementary to each other to form an elongated line.

[0048]The shaping optical unit 22 and the homogenizing optical unit 26 are part of an optical device 32 in which the actual conversion of the laser radiation 16 emitted by the laser light source 14 into a linear form takes place. The optical device 32 may also include a pre-shaped optical unit 18 and/or a collimating/focusing optical unit 30.

[0049]figure 2 It is a perspective view showing the optical device 32. It is conceivable that the laser radiation 16 is first shaped into the input laser beam 20 by means of the deflection mirror 34 and/or the lens device 36. In the example shown, the optical elements of the pre-shaped optical unit 18 are designed such that the input laser beam has an elliptical beam cross section 38. Furthermore, the input laser beam 20 may be fed by laser radiation 16' from at least one additional laser light source. The laser radiation 16, 16' from different laser light sources can for example pass through a common deflection mirror 34 (figure 2 The dashed-dotted beam path in the) cluster together.

[0050]To illustrate the geometric relationship,figure 2 The Cartesian coordinate system (x, y, z) is shown in. In the example shown, the input laser beam 20 propagates in the z direction. The elliptical beam section 38 has a long axis along the y-axis, and accordingly has a small diameter along the x-axis.

[0051]As will be explained in more detail below, the shaping optical unit 22 shapes the input laser beam 20 into a beam packet 24, which is converted into an output beam 40 by means of the homogenization optical unit 26. The output beam 40 is on the working plane of the optical device 32. The direction (x) along the line in 42 extends in a linear manner.

[0052]image 3 It is a schematic diagram of the shaping optical unit 22 in one possible embodiment. In the example shown, the shaping optical unit is designed as a single-piece plate-shaped shaping body 44 made of a material transparent to laser radiation.

[0053]The shaping body 44 has a board front side 46 and a board rear side 48 extending parallel to the board front side 46. The area on the front side 46 of the board serves as a light incoupling surface and provides an input aperture 50 of the shaping optical unit 22 through which the input laser beam 20 can be coupled into the shaping body 44. The area on the back side 48 of the plate acts as a light out-coupling surface and provides an output aperture 52 through which the beam packet 24 exits.

[0054]Such asFigure 4 As schematically shown in, the shaping optical unit 22 functions in particular in such a way that the adjacent beam sections 54a, 54b, 54c of the input laser beam 20 are rearranged into beam packets when passing through the shaping optical unit 22 24 beam segments 56a, 56b, 56c. In the example shown, this is that the beam segments 54a, 54b, 54c coupled in through the input aperture 50 are guided by internal reflection into the shaping body 44 between the front side 46 and the back side 48 of the board, and reach the output aperture.口52 occurred. Since the beam segments 54a to 54c are coupled in at different positions through the input aperture, the beam segments 56a to 56c emitted from the output aperture 52 cover different optical path lengths. The shaping body 44 is specifically designed to make the optical paths of the different beam segments 56a to 56c different from each other, so that the beam packet 24 has greatly reduced spatial coherence, especially incoherent. This is in particular because the difference in the optical path length of the beam segments 56a to 56c is greater compared to the coherence length of the laser radiation 16.

[0055]Such asfigure 2 As indicated, the shaping optical unit 22 is arranged so that the output aperture 52 rotates about the z axis relative to the direction x of the line. In the example shown, this is characterized by the rotation angle α, which defines the acute angle enclosed between the orifice longitudinal direction 58 of the output orifice 52 and the line direction x. The orifice longitudinal direction 58 is the direction along which the elongated (rectangular in the example shown) output orifice 52 extends (seeimage 3 ).

[0056]The shaping optical unit 22 is preferably by means of an adjustable holding device 60 (infigure 2 Shown schematically in) is retained in the optical device 32. The holding device 60 is designed such that the rotation angle α is continuously adjustable.

[0057]Figure 5 The principle of operation of the homogenizing optical unit 26 is schematically shown. In principle, the homogenizing optical unit is arranged such that it captures the beam packet 24 and converts the beam packet into an output beam 40, which extends in a linear manner along the direction (x) of the line. The different beam segments 56a, 56b, 56c of the beam package 24 are mixed and superimposed, so that the desired linear intensity distribution is set in the working plane 42. Especially in combination with the shaping optical unit 22, which preferably eliminates the coherence of the input laser beam to a large extent, the mixing and superposition of the beam sections of the beam package 24 causes the output beam 28 to be largely uniform along the line direction x , And has a substantially constant intensity curve.

[0058]For example, the homogenization optical unit 26 may have at least one cylindrical lens array 62 that acts on the beam segments 56 a, 56 b, 56 c,... So that they overlap in the working plane 42. The homogenizing optical unit may also include a Fourier lens 64, which is designed to focus with respect to the x-axis. The Fourier lens 64 is specifically arranged such that the working plane 42 extends in the focal plane of the Fourier lens 64.

[0059]The homogenizing optical unit 26 preferably also includes a transverse optical unit 66 (seeFigure 6a ), the transverse optical unit 66 is designed to focus and/or image the beam packet 24 relative to the short axis y. For example, the lateral optical unit 66 includes a first condensing lens 68 and a second condensing lens 70, which are successively arranged on the beam path. In the focal plane 72 of the first converging lens 68, the intensity distribution substantially corresponds to the Fourier transform of the beam packet 24. For another embodiment, an optical low-pass filter 74 may be provided, for example in the form of a slit diaphragm in the focal plane 72. The optical low-pass filter 74 filters high spatial frequencies relative to the short axis y. The second condensing lens 70 is preferably arranged such that the focal plane 72 coincides with the object-side focal plane of the second condensing lens 70.

[0060]In principle, different embodiments of the transverse optical unit 66 are conceivable. In particular, it is not absolutely necessary to provide suchFigure 6a Symmetrical structure shown. Arrangements with more than two converging lenses or only one converging lens are also conceivable. The corresponding example is inFigure 6b to Figure 6d Shown schematically in.Figure 6b A transverse optical unit with a single effective converging lens 69 is shown, which produces an intermediate focus 71 for the beam package 24. The spatial frequency can be filtered in the intermediate focus 71, for example by means of a low-pass filter 74.Figure 6cShowingFigure 6a In an embodiment of the basic structure in which the condensing lenses 68 and 70 have different focal lengths. This results in an image ratio not equal to 1:1. inFigure 6d A structure with three converging lenses is schematically shown in. The first converging lens 68 also produces an intermediate focal point 71, in which the low-pass filter 74 can be used for filtering. With the arrangement of two lenses 70a and 70b, the filtered result is imaged in the working plane 42.

[0061]The influence of the rotation angle α between the longitudinal direction 58 of the aperture and the direction x of the line on the intensity curve of the output beam 28 along the minor axis y is given byFigure 7 show.Figure 7 Is a schematic view of the output orifice 52, which extends along the orifice longitudinal direction 58 in an elongated manner. In the example shown, the beam segments 56 a to 56 f of the beam packet 24 are emitted through the output aperture 52.

[0062]When passing through the homogenization optical unit 26 (seeFigure 5 ), the beam segments 56a to 56f are mixed and superimposed with respect to the long axis x (the direction of the line). Because adjacent beam segments 56a to 56f are offset from each other along the short axis y due to the rotation angle α, the mixing and superimposition result in the output beam 28 having a trapezoidal curve along the short axis y. The gradient of the side 76 of the intensity curve of the output beam 28 along the short axis y can be influenced by adjusting the rotation angle α.

[0063]for example,Figure 8 The intensity of the output beam 40 in the working plane 42 is shown as a function of the position coordinate along the short axis y. The intensity I and the position coordinate y are given in dimensionless units. The output beam 40 is shown with a non-zero rotation angle α between the longitudinal direction 58 of the aperture and the direction x of the line. Due to the homogenization by the homogenization optical unit 26, the intensity distribution 40 has a largely constant curve in the central area 78, and the side edges 76 fall in the peripheral area. The side edge 76 is produced by the fact that the beam segments 56a, 56b, 56c, ... of the beam packet 24 contribute less to the output beam 40 due to the rotation angle α in the peripheral area. The gradient of the side 76 can be determined by means of the width of the interval of the position coordinates along the short axis y, at which the intensity I increases from 10% of the value in the central area 78 to 90% (seeFigure 8 ). This allows to define a gradient triangle, from which the gradient can be determined as the quotient of the intensity increase (80%) and the required interval of position coordinates.

[0064]inPicture 9 Schematically shows the dependence of the side gradient (m) on the rotation angle α. In the case of a small angle (small angle approximation), the gradient of the side 76 decreases substantially in proportion to the rotation angle α.