Abstract:
A device for homogenizing light has at least two cylindrical lens arrays which are placed one behind the other in a direction of diffusion of the light to be homogenized and which each have convex and concave cylindrical lenses disposed next to one another in an alternating manner, the cylinder axes of these cylindrical lenses are aligned parallel to one another. In the direction, in which the cylindrical lenses are disposed next to one another, the concave cylindrical lenses of the first cylindrical lens array have a shaping, in particular, an extension or curvature different from that of the concave cylindrical lenses of the second cylindrical lens arrays.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This is a continuing application, under  35  U.S.C. § 120, of copending international application No. PCT/EP2005/000103, filed Jan. 7, 2005, which designated the United States; the prior application is herewith incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a device for homogenizing light containing a first cylindrical lens array through which the light to be homogenized can pass. The first cylindrical lens array has convex and concave cylindrical lenses with mutually parallel cylinder axes that are disposed next to one another in an alternating fashion. Furthermore, a second cylindrical lens array is provided through which the light that has passed through the first cylindrical lens array can pass. The second cylindrical lens array has convex and concave cylindrical lenses with mutually parallel cylinder axes that are disposed next to one another in an alternating fashion, and the cylinder axes of the cylindrical lenses of the second cylindrical lens array are aligned parallel to the cylinder axes of the cylindrical lenses of the first cylindrical lens array. The present invention further relates to a device using cylindrical mirror arrays instead of lens arrays.  
         [0004]     The above-named device is also intended to include cylindrical lens arrays with concave cylindrical lenses that are much smaller than the convex cylindrical lenses adjacent to them. For example, the concave cylindrical lenses can be merely depressions or approximately flat regions in the interspace between two convex cylindrical lenses. Devices of the aforementioned type are known. Such devices are used, for example, to homogenize comparatively inhomogeneous light such as issues, for example, from an excimer laser or from a laser diode bar.  FIG. 1  shows schematically the operating principle of such homogenization devices. In the case of the device depicted therein, the first cylindrical lens array  1  is disposed on a first substrate  2  and the second cylindrical lens array  3  is disposed on a second substrate  4 , the substrates  2 ,  4  being spaced apart from one another. Inhomogeneous light  5  striking the device is homogenized by the device by virtue of the fact that the individual cylindrical lenses of the cylindrical lens arrays  1 ,  3  distributes the light homogeneously over an angular range of the light field  6  emerging from the device. A field lens disposed downstream of the second substrate  4  can be used to transform the homogeneous angular distribution in the emerging light field  6  into a correspondingly homogeneous spatial distribution in an operating plane.  
         [0005]     As a rule, in the case of devices of the type mentioned at the beginning, the focal length of the convex cylindrical lenses of the second cylindrical lens array  3  will correspond approximately to the distance between the first and the second cylindrical lens arrays. In this way, the convex cylindrical lenses of the second cylindrical lens array will image a plane perpendicular to the propagation direction of the incident inhomogeneous light  5  in the region of the first cylindrical lens array into an operating plane.  
         [0006]      FIG. 2  shows in detail how incident inhomogeneous light  5  runs through convex and concave cylindrical lenses  7 ,  8  of the first cylindrical lens array  1  and convex and concave cylindrical lenses  9 ,  10  of the second cylindrical lens array  2 . In particular in  FIG. 2  are a component beam  11 , running in the left-hand image area, and a component beam  12 , running in the right-hand image area. These component beams  11 ,  12  of the light  5  to be homogenized pass through two concave cylindrical lenses  8  of the first cylindrical lens array. It is to be seen that the component beams  11 ,  12  are deflected to a large part through the concave cylindrical lenses  8  onto a convex cylindrical lens  9  of the second cylindrical lens array  2 . The convex cylindrical lens  9  reflects the imaged component beams  11 ,  12  at an angle such that upon superposition with the aid of a field lens they pass into the outer lateral regions of an illuminated region in an operating plane.  
         [0007]     This situation is illustrated schematically in  FIG. 3 . In  FIG. 3 , the intensity in an operating plane is plotted against a spatial coordinate or else against an angular coordinate. The light distribution depicted in  FIG. 3  has a middle, substantially homogeneous region  13  and two rises  14  at the end that are substantially caused by the aforementioned component beams  11 ,  12  or by further corresponding component beams that pass through the concave cylindrical lenses  8  of the first cylindrical lens array  1 . An explanation for this contribution is to be seen in that the concave cylindrical lenses  8  of the first cylindrical lens array  1  exhibit a very small radius, and thus a focal length that is likewise very small. Consequently, the virtual focal points of the concave cylindrical lenses  8  lie approximately in the plane of the first cylindrical lens array  1  and are imaged in the operating plane by the convex cylindrical lenses  9  of the second cylindrical lens array  2 .  
         [0008]     The rises  14  to be seen in  FIG. 3  and that are typical of the prior art are disruptive for a whole range of applications.  
       SUMMARY OF THE INVENTION  
       [0009]     It is accordingly an object of the invention to provide a device for homogenizing light which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which generates a more homogeneous light distribution in an operating plane.  
         [0010]     With the foregoing and other objects in view there is provided, in accordance with the invention, a device for homogenizing light. The device contains a first cylindrical lens array through which the light to be homogenized passes. The first cylindrical lens array has convex and concave cylindrical lenses with mutually parallel cylinder axes disposed next to one another in an alternating fashion. A second cylindrical lens array is provided through which the light that has passed through the first cylindrical lens array can pass. The second cylindrical lens array has convex and concave cylindrical lenses with mutually parallel cylinder axes disposed next to one another in an alternating fashion. The mutually parallel cylinder axes of the cylindrical lenses of the second cylindrical lens array are aligned parallel to the mutually parallel cylinder axes of the cylindrical lenses of the first cylindrical lens array. In the given direction in which the cylindrical lenses are disposed next to one another, the concave cylindrical lenses of the first cylindrical lens array have a configuration other than that of the concave cylindrical lenses of the second cylindrical lens array in the given direction in which the cylindrical lenses are disposed next to one another.  
         [0011]     It is provided that, in the direction in which the cylindrical lenses are disposed next to one another, the concave cylindrical lenses of the first cylindrical lens array exhibit a configuration other than the concave cylindrical lenses of the second cylindrical lens array in the direction in which the cylindrical lenses are disposed next to one another. For example, rises to be seen from  FIG. 3  can be avoided by specifically varying the extent and/or the curvature of the concave cylindrical lenses of the first and/or the second cylindrical lens array.  
         [0012]     For example, it can be provided in this case that, in the direction in which the cylindrical lenses are disposed next to one another, the concave cylindrical lenses of the second cylindrical lens array are larger, preferably much larger than the concave cylindrical lenses of the first cylindrical lens array. For example, the concave cylindrical lenses of the second cylindrical lens array can be at least twice as large in this direction as the concave cylindrical lenses of the first cylindrical lens array. By enlarging the concave cylindrical lenses of the second cylindrical lens array it is possible at least partially to prevent the component beams that have passed through the concave cylindrical lenses of the first cylindrical lens array from striking convex cylindrical lenses of the second cylindrical lens array. However, this results in that these component beams that have passed through the concave cylindrical lenses of the first cylindrical lens array are no longer capable of being deflected or imaged by the convex cylindrical lenses of the second cylindrical lens array into the lateral regions of the light field in the operating plane. The rises are thereby eliminated. The homogeneous region  13  to be seen from  FIG. 3  is thereby enlarged. In particular, because of the fact that the component beams that have passed through the concave cylindrical lenses of the first cylindrical lens array pass through the concave cylindrical lenses of the second cylindrical lens array, the outcome is that these component beams are distributed substantially over the entire width of the homogenized light field in the operating plane. The efficiency of the device (the light quantity in the homogeneous region or the light quantity overall) is raised in this way.  
         [0013]     There is, moreover, the possibility that, in the direction in which the cylindrical lenses are disposed next to one another, the convex cylindrical lenses of the first cylindrical lens array are larger, in particular larger by a multiple than the concave cylindrical lenses of the first cylindrical lens array. In particular, the concave cylindrical lenses can constitute merely depressions or virtually flat regions between the convex cylindrical lenses of the first cylindrical lens array.  
         [0014]     As in the prior art, it is also possible in the case of the present invention that the focal length of the convex cylindrical lenses of the second cylindrical lens array is approximately as large as the distance between the first cylindrical lens array and the second cylindrical lens array. The plane of the first cylindrical lens array is imaged into the operating plane in this way by the convex cylindrical lenses of the second cylindrical lens array.  
         [0015]     In accordance with a further preferred embodiment of the present invention, it is possible that the focal length of the concave cylindrical lenses of the first cylindrical lens array is substantially larger than the focal length of the convex cylindrical lenses of the second cylindrical lens array. As a result of this it can be achieved that the virtual focal points of the concave cylindrical lenses of the first cylindrical lens array are comparatively far removed from the focal plane of the second cylindrical lens array such that these focal points are not sharply imaged into the operating plane by the convex cylindrical lenses of the second cylindrical lens array. It is possible to achieve, in this way, that no rises are caused in the lateral regions of the light distribution in the operating plane even given comparatively small concave cylindrical lenses of the second cylindrical lens array, and therefore even given component beams that have passed through the convex cylindrical lenses of the second cylindrical lens array and previously passed through the concave cylindrical lenses of the first cylindrical lens array.  
         [0016]     It is, in particular, possible that, in the direction in which the cylindrical lenses are disposed next to one another, the concave cylindrical lenses of the first cylindrical lens array exhibit approximately the same extent as the convex cylindrical lenses of the first cylindrical lens array in the direction in which the cylindrical lenses are disposed next to one another. In the case of such an arrangement, the focal points of the concave cylindrical lenses can be clearly removed from the plane of the first cylindrical lens array.  
         [0017]     It is possible that the device contains a substrate on which the first cylindrical lens array and the second cylindrical lens array are disposed on mutually opposite sides. The substrate can then exhibit an appropriate thickness such that the first cylindrical lens array is removed from the second cylindrical lens array at the distance of the focal length of the convex cylindrical lenses thereof.  
         [0018]     It is, alternatively, possible that the device contains a first substrate and a second substrate differing from the first, in particular spaced apart from the first substrate, the first cylindrical lens array being disposed on the first substrate and the second cylindrical lens array being disposed on the second substrate. In the case of such a device, the distance between the substrates can then be adapted such that the distance between the first and second cylindrical lens array corresponds to the focal length of the convex cylindrical lenses of the second cylindrical lens array.  
         [0019]     In the case of such a device, it is, furthermore, possible that the device contains a third cylindrical lens array, which is disposed on the side of the first substrate that is opposite the first cylindrical lens array, and has convex and concave cylindrical lenses with mutually parallel cylinder axes that are disposed next to one another in an alternating fashion. The cylinder axes of the cylindrical lenses of the first cylindrical lens array are disposed perpendicular to the cylinder axes of the cylindrical lenses of the third cylindrical lens array.  
         [0020]     It can be provided, as an alternative or in addition thereto, that the device further contains a fourth cylindrical lens array, which is disposed on the side of the second substrate that is opposite the second cylindrical lens array, and has convex and concave cylindrical lenses with mutually parallel cylinder axes that are disposed next to one another in an alternating fashion. The cylinder axes of the cylindrical lenses of the second cylindrical lens array are disposed perpendicular to the cylinder axes of the cylindrical lenses of the fourth cylindrical lens array. The third and, if appropriate, fourth cylindrical lens arrays can be used to effect a homogenization of the light to be homogenized in a direction that is perpendicular to the direction in which the first and second cylindrical lens arrays contribute to a homogenization. To this end, the third and fourth cylindrical lens arrays can be configured in accordance with the first and second cylindrical lens arrays, in particular with regard to the widths of the concave cylindrical lenses of the third and fourth cylindrical lens arrays. Furthermore, the distance between the third and the fourth cylindrical lens arrays can also correspond substantially to the focal length of the convex cylindrical lenses of the third cylindrical lens array.  
         [0021]     It can be provided that in the direction in which cylindrical mirrors are disposed next to one another, the concave cylindrical mirrors of the first cylindrical mirror array exhibit a configuration other than, in particular an extent other than and/or a curvature other than the concave cylindrical mirrors of the second cylindrical mirror array in the direction in which the cylindrical mirrors are disposed next to one another. Finally, the same advantages are attained by this transfer of the properties of the cylindrical lens arrays to the cylindrical mirror arrays.  
         [0022]     In particular, the focal points of the concave cylindrical mirrors of the first cylindrical mirror array can therefore be disposed comparatively far from the plane of the first cylindrical mirror array. Furthermore, the concave cylindrical mirrors of the second cylindrical mirror array can also be larger, in particular much larger than the concave cylindrical mirrors of the first cylindrical mirror array. Furthermore, it is possible that the distance of the first cylindrical mirror array from the second cylindrical mirror array corresponds approximately to the focal length of the convex cylindrical mirrors of the second cylindrical mirror array. Furthermore, there can also be present third and/or fourth cylindrical mirror arrays which have cylindrical mirrors with cylinder axes that are aligned perpendicular to the cylinder axes of the cylindrical mirrors of the first and of the second cylindrical mirror arrays.  
         [0023]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0024]     Although the invention is illustrated and described herein as embodied in a device for homogenizing light, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
         [0025]     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0026]      FIG. 1  is a schematic diagram for illustrating the operating principle of a device for homogenizing light;  
         [0027]      FIG. 2 a  diagrammatic, side view of a device for homogenizing light in accordance with the prior art;  
         [0028]      FIG. 3  is a graph illustrating a light distribution in an operating plane that is generated by the prior device for homogenizing light in accordance with  FIG. 2 ;  
         [0029]      FIG. 4 a  diagrammatic, side view of a section of a first embodiment of a device according to the invention; and  
         [0030]      FIG. 5  is a diagrammatic view of a section of a second embodiment of the device according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     Cartesian coordinate systems are depicted in  FIG. 4  and in  FIG. 5  for the sake of elucidation. Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 4  thereof, there is shown a first embodiment of a device according to the invention that contains a first substrate  15  and a second substrate  16 . The first substrate  15  has a first cylindrical lens array  17  on its entrance surface, whereas an exit surface is of a flat configuration. As an alternative thereto, it is also possible likewise to provide the exit surface with a cylindrical lens array that is, for example, aligned in a fashion crossing the first cylindrical lens array  17 . The first cylindrical lens array  17  has convex cylindrical lenses  18  and concave cylindrical lenses  19  that are disposed next to one another in an alternating fashion. In the exemplary embodiment depicted in  FIG. 4 , only two concave cylindrical lenses  19  and one convex cylindrical lens  18  are indicated. However, a multiplicity of convex and concave cylindrical lenses  18 ,  19  can, or are to, be disposed next to one another in the X direction. In the X direction, that is to say in the direction in which the cylindrical lenses  18 ,  19  are disposed next to one another, the concave cylindrical lenses  19  are conspicuously less extended than the convex cylindrical lenses  18 .  
         [0032]     The second substrate  16  has on its entrance surface, that is to say on its side facing the first substrate  15 , a second cylindrical lens array  20  with convex cylindrical lenses  21  and concave cylindrical lenses  22 . The convex and concave cylindrical lenses  21 ,  22  are disposed next to one another in an alternating fashion in the X direction, it likewise being possible here to provide a multiplicity of convex and concave cylindrical lenses  21 ,  22  on the entrance surface of the substrate  16 . Furthermore, it is to be seen from  FIG. 4  that both the cylinder axes of the cylindrical lenses  18 ,  19  of the first cylindrical lens array  17 , and the cylinder axes of the convex and concave cylindrical lenses  21 ,  22  of the second cylindrical lens array  20  are aligned in the Y direction, that is to say in a direction perpendicular to the direction X in which the cylindrical lenses  18 ,  19 ,  21 ,  22  are disposed next to one another. The exit surface of the second substrate  16  is likewise of a flat configuration. Alternatively, it would also be possible likewise to provide the exit surface of the second substrate  16  with a further cylindrical lens array in the case of which the cylinder axes of the cylindrical lenses could be aligned perpendicular to the cylinder axes of the cylindrical lenses  21 ,  22  of the second cylindrical lens array  20 .  
         [0033]     It is to be seen from  FIG. 4  that in the X direction, that is to say in the direction in which the cylindrical lenses  18 ,  19 ,  21 ,  22  are disposed next to one another, the concave cylindrical lenses  22  of the second cylindrical lens array  20  are much larger than the concave cylindrical lenses  19  of the first cylindrical lens array  17 . In particular, in this exemplary embodiment the concave cylindrical lenses  22  of the second cylindrical lens array  20  are approximately twice as wide as the concave cylindrical lenses  19  of the first cylindrical lens array  17 .  
         [0034]     Also depicted in  FIG. 4  are component beams  23 ,  24  of the light  25  to be homogenized that pass through the concave cylindrical lenses  19  of the first cylindrical lens array  17 . By contrast with the component beams  11 ,  12  in accordance with the prior art (see  FIG. 2 ), the component beams  23 ,  24  do not pass through the convex cylindrical lenses  21  of the second cylindrical lens array  20 , or do so only insubstantially, but pass through the expanded concave cylindrical lenses  22  of the second cylindrical lens array. Consequently, the component beams  23 ,  24  of the concave cylindrical lenses  22  of the second cylindrical lens array  20  are deflected in such a way that they are distributed in the operating plane over a wide region, in particular over the entire width of the homogenized light field. The lateral rises  14  in accordance with the prior art, which are to be seen from  FIG. 3 , are avoided in this way.  
         [0035]     The second embodiment, to be seen from  FIG. 5 , of the device according to the invention also contains a first substrate  26  and a second substrate  27 . On its entrance surface, the first substrate  26  has a first cylindrical lens array  28  with convex cylindrical lenses  29  and concave cylindrical lenses  30 . On its entrance surface, that is to say on its side facing the first substrate  26 , the second substrate  27  has a second cylindrical lens array  31  with convex cylindrical lenses  32  and concave cylindrical lenses  33 . In the case of both substrates  26 ,  27 , not only the depicted numbers of cylindrical lenses  29 ,  30 ,  32 ,  33 , but a multiplicity of cylindrical lenses  29 ,  30 ,  32 ,  33  can be disposed next to one another in an alternating fashion.  
         [0036]     In the case of the exemplary embodiment in accordance with  FIG. 5 , by contrast with the exemplary embodiment in accordance with  FIG. 4 , in the X direction, that is to say in the direction in which the cylindrical lenses  29 ,  30  are disposed next to one another in an alternating fashion, the concave cylindrical lenses  30  of the first cylindrical lens array  28  are approximately of the same width or the same extent as the convex cylindrical lenses  29  of the first cylindrical lens array  28 . By contrast therewith, the concave cylindrical lenses  33  of the second cylindrical lens array  31  are conspicuously smaller than the convex cylindrical lenses  32  of the second cylindrical lens array  31 .  
         [0037]     On the basis of the substantially equal width of the concave and convex cylindrical lenses  30 ,  29  of the first cylindrical lens array  28 , a focal length f 1k  of the concave cylindrical lenses  30  of the first cylindrical lens array  28  is comparatively large, that is to say, in particular, approximately twice as large as the height or the extent of the convex cylindrical lenses  29  in a propagation direction Z of the light to be homogenized. Furthermore, a focal length f 2v  of the convex cylindrical lenses  32  of the second cylindrical lens array  31  is depicted in  FIG. 5  by way of explanation. It may be gathered from  FIG. 5  that this focal length f 2v  of the convex cylindrical lenses  32  corresponds approximately to the distance between the first cylindrical lens array  28  and the second cylindrical lens array  31 . Because of the comparatively large focal length f 1k  of the concave cylindrical lenses  30  of the first cylindrical lens array  28 , the virtual focal point  34  indicated schematically in  FIG. 5  of the concave cylindrical lenses  30  is not imaged into the operating plane by the convex cylindrical lens  32  of the second cylindrical lens array  31 . This is illustrated in  FIG. 5  by component beams  35 ,  36 ,  37  depicted by way of example.  
         [0038]     In the case both of the embodiment in accordance with  FIG. 4  and of the embodiment in accordance with  FIG. 5 , the vertex lines of the convex cylindrical lenses  18 ,  29  of the first cylindrical lens arrays  17 ,  28  are aligned with the vertex lines of the convex cylindrical lenses  21 ,  32  of the second cylindrical lens array  20 ,  31  in the propagation direction of the light to be homogenized. Furthermore, the vertex lines of the concave cylindrical lenses  19 ,  30  of the first cylindrical lens array  17 ,  28  are also aligned with the vertex lines of the concave cylindrical lenses  22 ,  33  of the second cylindrical lens array  20 ,  31 .