Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
  • G02B27/0927—Systems for changing the beam intensity distribution, e.g. Gaussian to top-hat
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0004—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed
  • G02B19/0009—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having refractive surfaces only
  • G02B19/0014—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having refractive surfaces only at least one surface having optical power
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
  • G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
  • G02B19/0052—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a laser diode
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
  • G02B19/0095—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with ultraviolet radiation
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
  • G02B27/0938—Using specific optical elements
  • G02B27/095—Refractive optical elements
  • G02B27/0955—Lenses
  • G02B27/0961—Lens arrays

Definitions

• the present invention relates to a beam shaping device according to the preamble of claim 1.
• In the propagation direction of the laser radiation means mean propagation direction of the laser radiation, especially if this is not a plane wave or at least partially divergent.
• light beam, sub-beam or beam is meant, unless expressly stated otherwise, no idealized beam of geometric optics, but a real light beam, such as a laser beam with a Gaussian profile or a modified Gaussian profile, not infinitesimal small, but has an extended beam cross section.
• Typical laser light sources of such devices are for example Nd-YAG laser or excimer laser.
• Nd-YAG lasers not operated as single-mode lasers have a beam quality factor M 2 of about 8 to 25.
• the diffraction factor M 2 is a measure of the quality of the laser beam.
• a laser beam with a pure Gaussian profile has a diffraction factor M 2 of FIG.
• the diffraction factor M 2 corresponds approximately to the number of modes of the laser radiation.
• the diffraction factor M 2 has an influence on the focusability of the laser radiation.
• the thickness d or the beam waist in the focus area is proportional to the wavelength ⁇ of the laser beam to be focused and inversely proportional to the numerical aperture NA of the focusing lens.
• the following formula therefore applies for the thickness of the laser beam in the focus area: d oc
• the minimum thickness in the focal region or the beam waist in the focal region is additionally proportional to the diffraction factor according to the following formula:
• the diffraction factor M 2 can be different in size with respect to two directions perpendicular to the propagation direction of the laser radiation.
• the diffraction factor M x 2 is greater or smaller than the diffraction factor M y 2 .
• laser radiation is regularly homogenized before focusing in a working plane. This is done, for example, with lens arrays having a plurality of lenses, so that the laser radiation is split by these lenses in a plurality of sub-beams, which are superimposed in the working plane.
• the number of partial beams can not be arbitrarily increased, because with too large a number of partial beams with a corresponding superimposition of the partial beams in the working plane high frequency oscillations due to the interference between the Radiation caused. This would lead to a deterioration of the beam quality at the working level.
• the criterion for the occurrence of these high-frequency oscillations is the spatial coherence of the laser radiation in a direction perpendicular to the propagation direction.
• This spatial coherence is, the more light rays can be split into a larger number of partial beams, without causing high-frequency oscillations when superposed.
• the aforementioned diffraction factor M 2 or M x 2 or My 2 can be an indication of the spatial coherence, so that under large diffraction measure under certain circumstances, a division into a large number of partial beams is possible.
• intensity distributions in the direction perpendicular to the longitudinal extent of the line-like focus region are desired, which correspond to a so-called top-hat profile.
• an intensity distribution with a sharp intensity maximum may be more advantageous.
• the present invention has the object to further develop a device of the type mentioned in that influence on the intensity distribution in the direction can be taken perpendicular to the longitudinal extent of the linear focus area.
• the device comprises lens means, preferably in the propagation direction of the laser radiation movable lens means for influencing the linear intensity distribution in the working plane, being changed by changing the position of the lens means in the propagation direction of the laser radiation, the intensity profile perpendicular to the extension of the linear intensity distribution can.
• the intensity profile can change from a top hat shape to a shape that has a comparatively sharp maximum.
• a suitable intensity profile can be selected depending on the application.
• the device further comprises a telescope which is arranged in the propagation direction of the laser radiation behind the movable lens means, wherein the telescope is formed from at least two further lens means, at least in a direction perpendicular to the direction of the longitudinal extent of the linear intensity distribution Have refractive power.
• the telescope can in particular reduce the beam waist in the direction perpendicular to the longitudinal extent of the linear intensity distribution.
• the laser light source can emit multi-mode laser radiation, in which both the diffraction index M x 2 with respect to a first direction perpendicular to the propagation direction of the laser radiation is greater than 1, and the diffraction coefficient M y 2 with respect to a second direction perpendicular to the propagation direction is greater than 1.
• the apparatus further comprises beam transforming means arranged in the apparatus so as to be capable of transforming the laser radiation or partial beams of the laser radiation so as to increase the diffraction coefficient with respect to the first direction and to reduce the diffraction coefficient with respect to the second direction ,
• the beam transformation means may transform the laser radiation or partial beams of the laser radiation such that the diffraction coefficient and / or the spatial coherence properties with respect to the first direction of the laser radiation or each of the partial beams with the diffraction index and / or the spatial coherence properties with respect to the second direction are reversed or become.
• the diffraction factor for one of the two directions can be significantly smaller than before the beam transformation, whereas the diffraction factor for the other of the two directions after the beam transformation can be significantly larger than before the beam transformation.
• This is also due to the division of the laser radiation into a plurality of partial beams. This division can take place either in the beam transformation means or in separate beam splitting means arranged in front of the beam transformation means. It can be seen that, with respect to one of the two directions perpendicular to the direction of propagation, the diffraction factor can be reduced, in particular by the number of partial beams.
• the diffraction coefficient is significantly reduced in one direction and not much larger than 1 where the diffraction coefficient with respect to the other direction is increased from the state before the beam transformation.
• a very thin line is to be generated by the device according to the invention in a working plane, it is important that in the direction perpendicular to the longitudinal extent of the line a very good focus on a very small beam waist can be made.
• a very small diffraction coefficient with respect to this direction a very thin line-shaped profile can thus be achieved.
• a very defined intensity distribution can be generated with a top hat profile.
• the apparatus further comprises beam splitting means for splitting the laser radiation into a plurality of sub-beams, which are preferably arranged in the propagation direction of the laser radiation in front of the beam transformation means that they can Fourierransform Schl the laser radiation.
• the beam transformation means are arranged behind the beam splitting means, in particular in the output side Fourier plane of the beam splitting means. It can be achieved by means of the Fourier transformation that, with respect to the direction perpendicular to the longitudinal extent of the linear intensity distribution, an intensity profile is realized which deviates from a Gaussian shape. For example, a top hat profile or a profile with a comparatively sharp maximum can be achieved. In particular, it can be achieved by means of the Fourier transformation that a near field image of the partial beams emerging from the beam transformation means is produced in the working plane.
• Beam transformation means are known as such from the prior art, for example from EP 1 006 382 A1, EP 1 617 275 A1 and from EP 1 528 425 A1.
• the very inhomogeneous laser radiation of a semiconductor laser with very small diffraction factor M y 2 of the fast axis direction and very large diffraction factor M x 2 of the slow axis direction is transformed there such that the laser radiation after the beam transformation and corresponding collimation a comparable beam quality in both directions.
• the beam transformation means known per se are used for the opposite effect.
• FIG. 1 shows a schematic structure of a device according to the invention
• Fig. 2a is a plan view of the beam splitting means of a device according to the invention.
• FIG. 2b shows a side view of the beam splitting means according to FIG. 2a;
• Fig. 2c shows a cross section through the laser radiation after the
• 3a shows a plan view of the beam transformation means of the device according to the invention
• FIG. 3b shows a side view of the beam transformation means according to FIG. 3a;
• Fig. 3c is a perspective view of
• Fig. 3d shows a cross section through the laser radiation after
• FIG. 4a is a plan view of the beam combining means of the device according to the invention
• FIG. 4b shows a side view of the beam combining means according to FIG. 4a
• FIG. 4b shows a side view of the beam combining means according to FIG. 4a
• Fig. 4c shows a cross section through the laser radiation after
• Fig. 5a is a plan view of Homogenmaschines- and
• Fig. 5b is a side view of the homogenizing and focusing means according to Fig. 5a;
• Homogenizing means and a second embodiment of beam combining means of the device according to the invention are identical to Homogenizing means and a second embodiment of beam combining means of the device according to the invention.
• 9a is a plan view of a second embodiment of the
• Beam splitting means of a device according to the invention with arranged behind this beam transformation means;
• FIG. 9b shows a side view of the beam splitting means and the beam transformation means according to FIG. 9a;
• Fig. 1 1 shows schematically a second intensity profile
• FIG. 12 shows a schematic side view of a region between the beam transformation means and the working plane of a further embodiment of a device according to the invention.
• FIG. 13a shows a view corresponding to FIG. 12, in which three different positions of the lens means for influencing the intensity distribution are shown;
• Fig. 13b schematically shows an intensity profile in front of the lens means
• Fig. 13c schematically shows an intensity profile in the working plane corresponding to the first position of the lens means
• Fig. 13d schematically shows an intensity profile in the working plane corresponding to the second position of the lens means
• Fig. 13e schematically shows an intensity profile in the working plane corresponding to the third position of the lens means
• Fig. 14a is a view corresponding to Fig. 12, in which three different positions of the lens means for influencing the intensity distribution are shown;
• Fig. 14b schematically shows an intensity profile in front of the lens means
• Fig. 14c schematically shows an intensity profile in the working plane corresponding to the first position of the lens means
• Fig. 14d schematically shows an intensity profile in the working plane corresponding to the second position of the lens means
• Fig. 14e schematically shows an intensity profile in the working plane corresponding to the third position of the lens means.
• the device comprises a laser light source 1, beam splitting means 2, beam transformation means 3, beam combining means 4, homogenizing means 5 and a lens arrangement 6 which can produce a linear intensity distribution of the laser radiation in the working plane 7.
• the laser light source 1 is designed as an Nd-YAG laser or as an excimer laser.
• the Nd-YAG laser for example, at the fundamental frequency or frequency doubled or tripled and so on.
• the emerging from the laser light source 1 laser radiation 8 for example, has a circular cross-section.
• the beam splitting means 2 are shown in detail in FIGS. 2a and 2b.
• the beam splitting means 2 is preceded by a telescope 9 of crossed two-sided cylindrical lenses 10 and 11.
• the telescope 9 widens the laser radiation 8 with respect to the x-direction and narrows the laser radiation 8 with respect to the y-direction (see FIGS. 2a and 2b).
• the beam splitting means 2 are formed as a cylindrical lens array, with the cylinder axes of the cylindrical lens array extending in the y direction.
• Fig. 2c shows that these partial beams 14 have a square cross-section.
• the beam transformation means 3 also comprise a cylindrical lens array with an array of convex cylindrical surfaces 15 on the entrance surface and an array of convex cylindrical surfaces 16 on the exit surface of the beam transformation means 3.
• the individual partial beams 14 are transformed in such a way that they appear mirrored at a plane which is parallel to the propagation direction z.
• FIG. 3d is indicated how the partial beams 14 in transformed partial beams 17th being transformed.
• the left-hand partial beam 14, which is shown in FIG. 2c, or partial-beam 17, which is on the left in FIG. 3d is provided on each of its sides with a letter a, b, c, d. It turns out that an interchange of these letters a, b, c, d takes place according to a pattern that corresponds to a reflection at a diagonal surface of these partial beams 14, 17.
• This transformation a rotation about the z-direction by 90 ° followed by a commutation of the sides a, c.
• the diffraction index of the sub-beams 17 is different from that of the sub-beams 14. More specifically, in each of the sub-beams 17, the diffraction coefficient M x 2 is 4 for the x-direction and the diffraction factor M y 2 is 1 for the y direction. Overall, a diffraction factor M x 2 equals 16 results for the x-direction for all four partial beams 17 together.
• the individual partial beams 17 strike the beam combining means 4.
• the beam combining means 4 are formed on the exit surface of the beam combining means 4 according to the beam splitting means 2 by an array of concave cylindrical surfaces 18 on the entrance surface and an array of convex cylindrical surfaces 19.
• a further telescope 20 is introduced into the beam path, which expands the beam in the y direction via correspondingly arranged cylindrical lenses 21, 22.
• the laser radiation 23 is a single laser beam with a square cross section.
• the Diffraction factor M x 2 equal to 16 for the x-direction
• the diffraction factor M y 2 equal to 1 for the y-direction.
• This laser radiation 23 passes through the homogenizing means 5 (see FIGS. 5a and 5b), which are formed as two successively arranged arrays of cylindrical lenses 24, 25.
• the arrays of cylindrical lenses 24, 25 are arranged approximately at a distance of the focal length of the cylindrical lenses in the z-direction relative to one another. Due to the beam transformation and the associated increase in the diffraction factor M x 2 from 4 to 16, up to 16 cylindrical lenses 24, 25 can be arranged next to one another in the x direction without unwanted interference effects occurring in the working plane 7.
• the laser radiation passes through the lens assembly 6 with two lens means 26, 27, which are formed as two spaced-apart cylindrical lenses, wherein the cylinder axis of the first formed as a cylindrical lens lens means 26 extends in the y-direction and the cylinder axis of second designed as a cylindrical lens lens means 27 extends in the x direction.
• the lens arrangement 6 not only focuses the laser radiation in such a way that a line-shaped intensity distribution 28 is produced in the working plane 7 (see FIG. 7), but also individual parts of the laser radiation due to the cylindrical lenses 24, 25 in FIG propagate different and / or same directions, superimposed in the working plane 7.
• This is the known principle for homogenization with cylindrical lens arrays and subsequent lenses, which serve as field lenses and superimpose the laser radiation in a working plane.
• the lens assembly 6 thus serves as a focusing agent and contributes to the homogenization.
• the linear intensity distribution 28 in the working plane 7 can be seen by way of example from FIG. 7.
• This line-shaped intensity distribution 28 is shown schematically and may have a length I between 10 mm and 1000 mm, for example of about 100 mm and a thickness d between 1 .mu.m and 100 .mu.m, for example of about 10 microns. It thus turns out that with the device according to the invention, even when using a multi-mode laser light source, a focus area with a very small thickness and possibly also a greater depth of field can be produced. It is quite possible to make the thickness of the intensity distribution 28 smaller than 10 ⁇ m. This depends, for example, on the numerical aperture of the lens used.
• the laser radiation may have a Gaussian distribution or a top-hat distribution or any other distribution.
• Fig. 8 shows a further embodiment of the
• Beam combining means comprise lens means 29 serving as Fourier lens or Fourier lens.
• lens means 29 serving as Fourier lens or Fourier lens.
• a Fourier transformation of the intensity distribution in the output plane 30 of the beam transformation means 3 into the input plane 31 of the homogenization means 5 takes place.
• the individual sub-beams 17, of which two are shown in FIG. 8, are superimposed on one another in the input plane 31 of the homogenizing means 5. Due to the fact that each of the individual partial beams 17 is incident from a different direction into the input plane 31, the number of cylindrical lenses 24, 25 of the homogenizing means 5 can be reduced, in particular by a factor corresponding to the number of partial beams 17 and thus the number the cylindrical surfaces 16 of the beam transformation means 3 corresponds.
• the lens means 29 may be formed as a single lens or as a plurality of lenses. If the lens means 29 are formed by a plurality of lenses, they are arranged in the apparatus such that the output plane 30 of the beam transformation means 3 is arranged in the input system focal plane of the lens means 29 and the input plane 31 of the homogenization means 5 in the output system Focal plane of the lens means 29 is arranged.
• the lens or the lenses of the lens means 29 may be formed as a cylindrical lens whose cylinder axis extends in the Y direction.
• FIG. 8 shows dashed lines of lens means 32 for collimating the laser radiation with respect to the Y direction.
• Lens means 32 are optional and may be disposed between the beam transformation means 3 and the lens means 29.
• the lens means 32 may be formed as a single lens or as a plurality of lenses.
• the lens or the lenses of the lens means 32 may be formed as a cylindrical lens whose cylinder axis extends in the X direction.
• FIGS. 9a and 9b show a second embodiment of beam splitting means 2 '.
• These beam splitting means 2 ' comprise two cylindrical lens arrays 33, 34.
• the first cylindrical lens array 33 has on its exit side a plurality of convex cylindrical lenses 35 arranged side by side in the X direction, the cylinder axes of which extend in the Y direction.
• the second cylindrical lens array 34 has on its entrance side a plurality of adjacent in the X direction convex cylindrical lenses 36, the cylinder axes also extend in the Y direction.
• the distance between the cylindrical lens arrays 33, 34 corresponds to the focal length f 35 of the cylindrical lenses 35 of the first cylindrical lens array 33.
• a comparable intensity profile can be independent of the design of the beam splitting means 2, 2 'as a cylindrical lens formed lens means 37 are arranged, which are arranged behind the beam transformation means 3 or alternatively behind the homogenization means 5.
• the cylinder axis of the lens means 37 extends in the X direction (see Figs. 9a and 9b).
• the lens means 37 are movable in the propagation direction Z of the laser radiation.
• the Z position of the lens means 37 it is possible to influence the intensity profile obtained in the working plane 7 in the Y direction or in the direction perpendicular to the longitudinal extent of the linear intensity distribution 28.
• by changing the Z position of the lens means 37 from an intensity profile having a top hat shape 38 to an intensity profile having a shape 39 (see Fig. 11) can be changed, which has a comparatively sharp maximum.
• Such an intensity profile has proven to be particularly advantageous in some applications.
• FIGS. 12 to 14 e the same parts are provided with the same reference numerals as in FIGS. 1 to 11.
• the distances between the illustrated optical elements in the propagation direction z of the light are not reproduced true to scale.
• the lens means 37, 40 can therefore influence the working plane 7 in the Y-direction or in the direction perpendicular to the longitudinal extension of the linear Intensity distribution 28 obtained intensity profile.
• the lens means 37 may be the movable lens means 37 shown by way of example in FIGS. 9a and 9b.
• the homogenizing means 5 and the lens means 26 designed as a cylindrical lens are only shown in dashed lines in FIG. 12, because their cylinder axes extend in the y-direction, so that these lenses have no influence on that in the working plane 7 in the Y direction or in the direction take perpendicular to the longitudinal extent of the line-shaped intensity distribution 28 obtained intensity profile. Furthermore, the cylindrical lens designed as lens means 27 and the working plane 7 are located.
• the lens means 37 have a focal length f 37 of 30 mm
• the lens means 40 has a focal length f 4 o of 1000 mm
• the lens means 27 has a focal length f 27 of 30 mm.
• the distance between the lens means 40 and the lens means 27 corresponds to the sum f 4 o + f 2 7 of the focal lengths f 40 , f 2 7 of the lens means 40 and the lens means 27, ie, for example 1030 mm.
• the lens means 40 and the lens means 27 thus form a telescope which can transmit an intensity distribution present in front of the lens means 40 into the working plane 7.
• an intensity distribution in the Y direction as shown in FIG. 13b results in the input-side focal plane of the lens means 37.
• F (x) is the Fourier transform of a top hat intensity distribution.
• This top-hat distribution is transmitted through the telescope, which is formed by the lens means 40 and the lens means 27, in the working plane 1 ⁇ .
• the laser radiation thus has a top-hat distribution in the Y direction or in the direction perpendicular to the longitudinal extent of the linear intensity distribution 28, as shown in FIG. 13c.
• FIGS. 14a to 14e show a case comparable to FIGS. 13a to 13e, in which only the intensity distribution in the Y direction in the input-side focal plane of the lens means 37 of the distribution according to FIG.
• a top hat Distribution corresponds.
• Such a distribution is present in the input-side focal plane of the lens means 37, for example, when the beam splitting means 2 are constructed as shown in FIGS. 2a and 2b. Then, with lens means 37i in the first position, an intensity distribution results in the output-side focal plane 41 1 , which corresponds to a (sin (x)) / x distribution. A corresponding distribution then also results in the working plane 7-1 (see FIG. 14c).
• Displacement of the lens means 37 into the second or third positions designated 37 2 and 37 3 results in distributions in the working plane 7 2 , 7 3 according to FIGS. 14 d and 14 e. It thus turns out that even with a top-hat distribution in the input-side focal plane of the lens means 37, comparable intensity distributions (see FIGS. 14c to 14e) to the case according to FIGS. 13a to 13e in the working plane 7i, 7 2 , 7 3 can be achieved.
• the lens means 37 may consist of a single cylindrical lens or a plurality of lenses. Furthermore, the lens means 40 may consist of a single cylindrical lens or of a plurality of lenses. Furthermore, the lens means 27 may consist of a single cylindrical lens or of a plurality of lenses.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Laser Beam Processing (AREA)
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