Device for generating a linear intensity distribution in a working plane

Abstract

Device for generating a linear intensity distribution in a working plane (20), comprising at least one laser light source (11), optics (14) which shape the light (12) emitted by the at least one laser light source (11) in a first direction (X) and/or in a second direction (Y), a beam transformation device (13) increasing the beam quality factor (M.sub.x.sup.2) with respect to the first direction (X) and decreasing the beam quality factor (M.sub.y.sup.2) with respect to the second direction (Y), as well as an objective (17) acting in the second direction (Y) and a focusing device (18) acting in the second direction (Y), which is arranged behind the objective (17), wherein the objective (17) and the focusing device (18) image into the working plane (20) a plane (19) behind the beam transformation device (13) in which the light (12) in the second direction (Y) has an intensity distribution with a super-Gaussian profile or with a profile similar to a super-Gaussian profile.

Claims

1. A device comprising a laser light source configured to emit light during operation of the device, optics that shape the light with respect to beam cross-sections of the light and divergences of the light in a first direction, a second direction, or both the first direction and the second direction, the first direction and the second direction being perpendicular to each another and perpendicular to a propagation direction of the light, a beam transformation device on which the light shaped by the optics impinges, the beam transformation device configured to increase a beam quality factor with respect to the first direction and decreasing a beam quality factor with respect to the second direction, and an objective acting in the second direction and a focusing device acting in the second direction arranged behind the objective, wherein the objective and the focusing device are configured to image a plane behind the beam transformation device into a working plane, wherein the light in the second direction has an intensity distribution with a super-Gaussian profile.

2. The device according to claim 1, wherein the objective has a focal length between 2,000 mm and 30,000 mm, between 5,000 mm and 20,000 mm, or between 7,000 mm and 13,000 mm.

3. The device according to claim 1, wherein the objective comprises cylindrical lenses acting in the second direction.

4. The device according to claim 1, wherein the objective comprises three lenses acting in the second direction, at least one of which is movable relative to the other lenses.

5. The device according to claim 1, wherein the focusing device comprises one or more lenses acting in the second direction.

6. The device according to claim 1, wherein a rear focal plane of the objective coincides with a front focal plane of the focusing device.

7. The device according to claim 1, wherein plane imaged by the objective and the focusing device is arranged between a front focal plane of the objective and the objective.

8. The device according to claim 1, wherein the depth of field of the profile of the intensity distribution in the working plane is greater than 0.1 mm, or greater than 0.5 mm; wherein the depth of field is a region where a super-Gaussian factor of the intensity distribution in the second direction is greater than 3.

9. The device according to claim 1, wherein the intensity distribution has a greater intensity in the working plane than in planes arranged immediately in front of or behind it.

10. The device according to claim 1, wherein the laser light source is a multimode laser light source.

11. The device according to claim 1, wherein the optics are between the laser light source and the beam transformation device and are anamorphic optics.

12. The device according to claim 1, wherein the device comprises a homogenizing device acting in the first direction.

13. The device according to claim 12, wherein the homogenizing device is arranged behind the beam transformation device.

14. The device according to claim 12, wherein the homogenizing device comprises two cylindrical lens arrays and a Fourier lens acting in the first direction.

Description

(1) Further features and advantages of the invention are illustrated by the following description of preferred embodiments with reference to the enclosed drawings. Therein shows:

(2) FIG. 1 a schematic side view of a part of a first embodiment of a device according to the invention, the side view showing an objective and a focusing device;

(3) FIG. 2 a schematic side view of the first embodiment of a device according to the invention in which an optional homogenizing device is illustrated;

(4) FIG. 3a a schematic side view of a part of a second embodiment of a device according to the invention, the side view showing an objective and a focusing device, wherein the lenses of the objective are in a first position;

(5) FIG. 3b a schematic side view of the device as shown in FIG. 3a, the lenses of the objective being in a second position;

(6) FIG. 3c a schematic side view of the device as shown in FIG. 3a, the lenses of the objective being in a third position;

(7) FIG. 4 a diagram that schematically illustrates energy density profiles of super-Gaussian and Gaussian profiles at different values of the factor G;

(8) FIG. 5 schematically a linear intensity distribution with clarification of the line width in longitudinal direction and the line width in transverse direction;

(9) FIG. 6 schematically the intensity distribution in the near field behind three lenses of a beam transformation device;

(10) FIG. 7a-h Raytracing simulation results illustrating, for an example configuration of a device according to FIG. 1, the variation of the super-Gaussian profile along the optical axis;

(11) FIG. 8 a diagram showing the change in the super Gaussian factor G along the optical axis;

(12) FIG. 9a-d Raytracing simulation results which, for an example configuration of a device according to U.S. Pat. No. 8,270,084, illustrate the change of the super-Gaussian profile along the optical axis;

(13) FIG. 10 a perspective view of an exemplary beam transformation device;

(14) FIG. 11 schematic side view of a part of a device according to U.S. Pat. No. 8,270,084;

(15) FIG. 12a-d intensity distributions in line transverse direction for different positions of a cylindrical lens of the device according to FIG. 11.

(16) In the figures, identical and functionally identical parts are provided with the same reference signs. In addition, some of the figures have Cartesian coordinate systems drawn into them for clarification.

(17) The embodiments disclose a device for generating a laser beam with a linear intensity distribution in a working plane. FIG. 5 shows schematically and not to scale such a linear intensity distribution having a width FW.sub.x in a first direction X corresponding to the longitudinal direction of the line and a width FW.sub.y in a second direction Y perpendicular to the first direction X corresponding to the transverse direction of the line. In the working plane, the laser radiation has a super-Gaussian intensity distribution in the transverse direction or in the second direction Y, respectively.

(18) The embodiments shown include one or more laser light sources 11, such as a multimode solid-state laser emitting light 12 (see FIG. 2). In particular, the light source 11 may have a beam quality factor M.sup.2>>1.

(19) The embodiments shown also include a beam transformation device 13 for improving beam quality in the narrow axis or Y-direction and for mode enrichment in the long axis or X-direction.

(20) Anamorphic optics 14 are provided between the laser light source 11 and the beam transformation device 13. The anamorphic optics 14 form the required beam cross-sections and divergences for the first and second directions X, Y for the downstream beam transformation device 13.

(21) In the first direction X, for example, an elongated intensity distribution is produced, which is divided into N partial beams with an identical width in front of or directly in the beam transformation device 13 with respect to the first direction X. The intensity distribution is divided into N partial beams with an identical width. The beam transformation device 13 spatially rearranges these partial beams in such a way that M′.sub.y.sup.2 for the second direction Y becomes significantly smaller and M′.sub.x.sup.2 for the first direction X significantly larger than M.sup.2 of the original laser beam: M′.sub.y.sup.2=M.sup.2/N and M′.sub.x.sup.2=M.sup.2*N.

(22) The beam transformation device 13, for example, can be designed as described in U.S. Pat. No. 8,270,084 or illustrated in FIG. 10 as a refractive cylindrical lens array telescope in which the cylindrical axes of the cylindrical lenses are rotated by 45° about the Z-direction or include an angle of 45° with the first and second directions X, Y.

(23) It is also possible to provide other refractive or reflective beam transformation devices, such as in the U.S. Pat. No. 5,825,551, which perform the same function.

(24) The beam transformation device 13 generates a series of equally sized partial beams 15 with super-Gaussian-like profiles in the second direction Y (see FIG. 6) at the output side in the near field. The far field is arranged at a distance of several meters behind the beam transformation device 13, for example, and can have a Gaussian distribution.

(25) An optional homogenization device 16 acting in the first direction X is provided behind the beam transformation device 13, which homogenization device 16 can be designed, for example, as an imaging homogenizer and can have two cylindrical lens arrays and a Fourier lens acting in the first direction X. The homogenization device 16 can be designed, for example, as an imaging homogenizer and can have two cylindrical lens arrays as well as a Fourier lens acting in the first direction X. The task of the homogenizing device 16 is to ensure a highly homogeneous intensity distribution in the working plane along the first direction X and, by mixing the partial beams 15, also to compensate for any asymmetry of the partial beams 15 in the second direction Y (compare, for example, the left and the right partial beams 15 in FIG. 6), so that an identical super-Gaussian cross section is achieved along the entire line.

(26) The device shown also includes a long focal length objective 17 and a focusing device 18 for the second direction Y or the transverse direction of the line, respectively. The objective 17 and the focusing device 18 are arranged behind the beam transformation device 13 and behind the homogenization device 16, respectively.

(27) The objective 17 and the focusing device 18 together form a projection system for the second direction Y. The projection system images the super-Gaussian intensity distribution from the near field of the beam transformation device 13 (see plane 19 in FIG. 1) into a working plane 20, whereby the Gaussian-like far field distribution behind the beam transformation device 13 is located far away from the focus outside the desired depth of field.

(28) The objective 17, for example, can have two cylindrical lenses 21, 22 which are arranged one behind the other at a distance d in the Z-direction. For example, the focusing device 18 may have one cylindrical lens 26 or several cylindrical lenses acting in the second direction Y (see FIG. 1 and FIG. 3). The rear focal plane F′.sub.17 of the objective corresponds to the front focal plane F.sub.18 of the focusing device 18. The plane 19, in which the super-Gaussian intensity distribution from the near field of the beam transformation device 13 is arranged, lies between the front focal plane F.sub.17 of the objective 17 and the first cylindrical lens 21 of the objective 17.

(29) FIG. 1 illustrates by the beam 23 that the projection system transmits a Gaussian-like distribution from the far field of the beam transformation device 13 into infinity. FIG. 1 further illustrates by the beam 24 that the projection system images the near field of the beam transformation device 13 with the super-Gaussian distribution from plane 19 into the area of the rear focal plane F′.sub.18 of the focusing device 18.

(30) The magnification V of such a projection system with spatially identical positions for the rear focal plane F′.sub.17 of the objective and the front focal plane F.sub.18 of the focusing device 18, remains constant for any position of plane 19 relative to the cylindrical lens 21:
V=−f′.sub.17/f′.sub.18=FW.sub.y/FW′.sub.y  (1)
where f′.sub.17 is the effective focal length of the objective 17, f′.sub.18 is the focal length of the focusing device 18, FW.sub.y is the width of the linear intensity distribution in the plane 19 and FW′.sub.y is the width of the linear intensity distribution in the working plane 20.

(31) From (1) it follows that at a given width FW.sub.y of the super-Gaussian distribution in plane 19, the focal length of the focusing device f′.sub.18 and the required line width FW′.sub.y in the working plane 20 for the required effective focal length f′.sub.17 of the objective 17 is yielded:
f′.sub.17=(FW.sub.y/FW′.sub.y)f′.sub.18  (2)

(32) If the plane 19 coincides with the front focal plane F.sub.17 of the objective 17, the cylindrical lenses 21, 22 collimate the light, whereby the focusing device 18 images the super Gaussian distribution into its rear focal plane F′.sub.18.

(33) If the plane 19 is located at a distance z.sub.SG from the front focal plane F.sub.17 of the objective 17, then the imaging takes place at a distance Δz.sub.SG=z.sub.SG (f′.sub.17/f′.sub.18).sup.2 from the rear focal plane of the focusing device F′.sub.18. A positive z.sub.SG, which is to be present when the plane 19 is located between the front focal plane F.sub.17 of the objective 17 and the first cylindrical lens 21, increases the working distance of the projection system.

(34) The far field of the beam transformation device 13 with a Gaussian-like intensity distribution is transferred by the cylindrical lenses 21, 22 into the rear focal plane F′.sub.17 of the objective 17. Since this focal plane F′.sub.17 coincides with the front focal plane F.sub.18 of the focusing device 18, the Gaussian-like distribution behind the focusing device 18 is imaged into infinity.

(35) In the vicinity of the rear focal plane F′.sub.18 of the focusing device 18 there is therefore only one intensity distribution, which is a super-Gaussian intensity distribution. The intensity assumes a maximum value at this point, whereby the super-Gaussian parameter G corresponds to its value at the input of plane 19.

(36) In the following an example shall be considered in which the formation of a super-Gaussian distribution with a width FW.sub.y in transverse direction FW.sub.y=26 μm is to take place in a projection system with the effective focal length f′.sub.17 of the objective 17 f′.sub.17=8,664 mm and the focal length f′.sub.18 of the focusing device 18 f′.sub.18=195 mm. Thus the focal length f′.sub.21 of the cylindrical lens 21 f′.sub.21 should be 500 mm and the distance d between the cylindrical lenses 21, 22 d=300 mm. This results in the focal length f′.sub.22 of the second cylindrical lens 22 to f′.sub.22=−212 mm, as well as the distance S between the first cylindrical lens 21 and the front focal plane F.sub.17 of the objective 17 to S=−20,910 mm and the distance S′ between the second cylindrical lens 22 and the rear focal plane F′.sub.17 of the objective to S′=3,466 mm.

(37) Since plane 19, in which the super-Gaussian intensity distribution from the near field of the beam transformation device 13 is arranged, cannot normally be further than about 1,000 mm from the cylindrical lens 21 in a real optical system with limited length, the super-Gaussian distribution at the exit is not arranged in the rear focal plane F′.sub.18 of the focusing device 18, but at a distance of (20910−1000)/(8664/195).sup.2=10 mm behind it.

(38) If a stable super Gaussian distribution is desired along the Z-axis in the vicinity of working plane 20, for example within ±DOF.sub.SG (where DOF.sub.SG corresponds to the depth of field of the super-Gaussian distribution), then the Gaussian distribution must be arranged on the input side at a distance from plane 19 that is significantly longer than DOF.sub.SG (f′.sub.17/f′.sub.18).sup.2. For DOF.sub.SG=0.5 mm, for example, this is 0.5*(8664/195).sup.2=987 mm. In practice, the Gauss distribution is several meters away from the beam transformation device 13, for example more than 3 meters, with optimal design. Thus, the formulated condition of depth of field is fulfilled.

(39) FIG. 7a to FIG. 7h show for the described example system with FW.sub.y=26 μm the change of the super Gaussian profile in line transverse direction or in Y-direction for different distances Δz′ from working plane 20. FIG. 7e shows the profile in working plane 20 with Δz′=0, whereas FIG. 7a shows the profile for Δz′=−0.5 mm and FIG. 7h shows the profile for Δz′=0.4 mm. It turns out that the profile hardly changes over a range of ±0.5 mm.

(40) FIG. 8 illustrates the change in the super-Gaussian factor G as a function of the distance Δz′ from the working plane 20. It shows that for the above-mentioned range of ±0.5 mm the super Gaussian factor G is essentially greater than 4.

(41) In the embodiment shown in FIG. 3a to FIG. 3c, the long focal length objective 17 is designed as a zoom objective for the Y-direction with variable effective focal length f′.sub.min<f′.sub.17<f′.sub.max. For example, the objective 17 has three cylindrical lenses 21, 22, 25, whose distance can be changed at least partially to vary the line width. The objective 17 can be constructed in such a way that when the magnification is changed by shifting the second and third cylindrical lenses 22, 25 along the optical axis or along the Z-direction, respectively, the rear objective focal plane F′.sub.17 remains in an almost unchanged position corresponding to the front focal plane of the focusing device 18.

(42) Accordingly, the system remains relatively insensitive to the input-side position of plane 19 in which the super-Gaussian intensity distribution from the near field of the beam transformation device 13 is arranged, the line focus remaining in the same Z-position when varying the line width.

(43) It is also possible to change the focal length of the objective 17 by shifting the first and second cylindrical lenses 21, 22 or by shifting the first and the third cylindrical lenses 21, 25.

(44) FIG. 3a to FIG. 3c show three configurations of the objective 17 designed as a zoom lens with different magnifications, which lead to different widths of the super-Gaussian line in the working plane 20.

(45) The second and third cylindrical lenses 22, 25 are movable in the pictured version. Three magnifications V=FW′.sub.y/FW.sub.y=f′.sub.18/f′.sub.17 are achieved by three different focal lengths f′.sub.17 of the lens 17.

(46) For example, the cylindrical lenses 21, 22, 25 of objective 17 may have focal lengths f′.sub.21=−450 mm, f′.sub.22=216 mm and f′.sub.25=−123 mm and the focusing device 18 may have a focal length f′.sub.18=195 mm.

(47) For the first configuration according to FIG. 3a this results in a longer focal length f′.sub.17=12,878 mm and a distance S′=4,239 mm.

(48) For the second configuration according to FIG. 3b there is a medium focal length f′.sub.17=10,009 mm and a distance S′=4,284 mm.

(49) For the third configuration according to FIG. 3c a shorter focal length f′.sub.17=7,912 mm and a distance S′=4,190 mm result.

(50) With an input-side width of the super-Gaussian distribution FW.sub.y=2.2 mm, the super-Gaussian line width FW.sub.y can be varied between 34 μm and 55 μm with the zoom objective.

(51) In the above example, in extreme zoom configurations, the rear focal plane F′.sub.17 of objective 17 shifts by up to ±47 mm relative to the front focal plane F.sub.18 of focusing device 18. This shift also affects the location of the Gaussian distribution behind focusing device 18. If for a medium zoom configuration, e.g. according to FIG. 3b, where the Gaussian-like far field image is located in infinity, the Gaussian distribution for the extreme zoom configurations may be located in the Z position of ±(f′.sub.18).sup.2/Δz=±809 mm relative to the super-Gaussian distribution in the working plane 20. Since this distance is large compared to the desired DOF.sub.SG, the depth of field of the super-Gaussian distribution is not affected.