EP2972562A1 - Device for homogenizing laser radiation - Google Patents

Abstract

The invention relates to a device for homogenizing laser radiation (100), said device comprising: a first lens array (1) with a first optically functional boundary surface (10), through which the laser radiation (100) can penetrate the first lens array (1) and with a second optically functional boundary surface (11), through which the laser radiation (100) can exit the lens array (1), at least one of the two optically functional boundary surfaces (10, 11) comprising a plurality of lens means (3) designed to sub-divide the laser radiation (100) into a plurality of sub-beams (101, 102, 103); and a second lens array (2) positioned in the beam path behind the first lens array (1), said array having a first optically functional boundary surface (20), through which the sub-beams (101, 102, 103) can penetrate the second lens array (1) and a second optically functional boundary surface (21), through which the sub-beams (101, 102, 103) can exit the second lens array (2), at least one of the two optically functional boundary surfaces (20, 21) having a plurality of lens means (4) which can refract the sub-beams (101, 102, 103) and the lens means (3) of the first lens array (1) being designed such that they can sub-divide the laser radiation (100) into a plurality of sub-beams (101, 102, 103) and form the latter in such a way that the sub-beams (101, 102, 103) illuminate the lens means (4) of the second lens array (2) in a substantially homogeneous manner.

Description

 Device for homogenizing laser radiation

The present invention relates to a device for

Homogenization of laser radiation, comprising

- A first lens array with a first optically functional

Interface through which the laser radiation can enter the first lens array, and with a second optically functional

Interface through which the laser radiation from the first

Lens array can emerge, wherein at least one of the two optically functional interfaces comprises a plurality of lens means which are adapted to divide the laser radiation into a plurality of sub-beams, and a second lens array, which is arranged in the beam path behind the first lens array, with a first optically functional interface, through which the partial beams can enter the second lens array, and with a second optically functional interface, through which the partial beams can emerge from the second lens array, wherein at least one of the two optically functional interfaces a plurality of

Includes lens means that can break the partial beams.

Definitions: In the propagation direction of the laser radiation means the mean propagation direction of the laser radiation, especially if this is not a plane wave or at least partially divergent. By laser beam, light beam, sub-beam or beam is, unless expressly stated otherwise, not an idealized beam of geometric optics meant, but a real light beam, such as a laser beam with a Gaussian profile or a modified Gaussian profile or a top Hat profile, which has no infinitesimal small, but an extended beam cross-section. Devices for the homogenization of laser radiation of the type mentioned are known from the prior art in different embodiments. They serve the purpose in one

Working level in at least one direction to provide the most homogeneous (uniform) distribution of the intensity of the laser radiation, as it is required for numerous applications, such as for applications in materials processing.

Imaging devices for homogenizing laser radiation are embodied in two stages and comprise a first lens array, which forms a first homogenization stage, with a plurality of lens means, in particular cylindrical lens means, on a first optically functional interface and / or a second optically functional interface. Furthermore, such include

Devices a second lens array, which is a second

Homogenization stage forms and in the propagation direction of the

Laser radiation is disposed behind the first lens array and on a first optically functional interface and / or a second optically functional interface, a plurality of lens means, in particular cylindrical lens means having. Furthermore

For example, such devices for homogenizing light often include a Fourier lens in the beam propagation direction behind the second lens array, usually as a spherical lens

is formed and disposed in the beam propagation direction behind the second lens array. The lens means of the first lens array are capable of dividing a collimated laser beam incident on the first lens array into a plurality of sub-beams. The second lens array in combination with the Fourier lens is capable of superimposing the partial beams in the working plane in such a way that a homogeneous (uniform) intensity distribution can be obtained there in at least one direction. The function of

Fourier lens may also be suitable in the second lens array be integrated, so that in a working plane a homogeneous

Intensity distribution can be obtained. The cross-sectional profiles of the cylindrical lens means of the first lens array are formed transversely to their respective cylinder axes spherical and thus can mathematically very easily by a single radius

(Radius of curvature) are described. Furthermore, the

Cross-sectional profiles of the cylindrical lens means of the second lens array transverse to their respective cylinder axes also spherical

educated.

A disadvantage of the devices known from the prior art for the homogenization of laser radiation is that the

Energy density (or intensity) of the partial beams on the individual lens means of the second lens array can be so high that the damage threshold of an optionally applied there

Antireflection coating is exceeded, so it too

Damage to this antireflection coating may occur.

The present invention is based on the object, a

Specify device for the homogenization of laser radiation of the type mentioned above, the energy density of the incident on the lens means of the second lens array in a simple manner

Can reduce partial beams.

This object is achieved by a device for homogenizing laser radiation of the type mentioned with the features of the characterizing part of claim 1. The subclaims relate to advantageous developments of the invention.

An inventive device for the homogenization of

Laser radiation is characterized in that the lens means of the first lens array are formed so that they the laser radiation split into a plurality of partial beams and can form them so that the partial beams, the lens means of the second

Lens arrays can illuminate substantially homogeneous. This approach exploits the fact that the first lens array of the two-stage (and thus imaging) device for homogenizing

Laser radiation essentially serves not to over-radiate the lens means of the second lens array and thus to expose an increased intensity. The lens means of the second lens array, on which the partial beams are refracted, are predominantly for the homogeneity of the laser radiation in the working plane

crucial. With the inventive device for

Homogenization of laser radiation can be achieved in an advantageous manner, that the energy density (or intensity) of the

Partial beams on the individual lens means of the second lens array can be reduced such that the damage threshold of the optionally applied there antireflection coating always

is exceeded, so that damage this

Antireflection coating can be effectively avoided.

Furthermore, aging effects that can occur when exposing the antireflection coating to electromagnetic radiation in the ultraviolet spectral range can be reduced in a particularly advantageous manner. After passing through the second lens array, a homogeneous angular distribution of the partial beams is obtained, which leads in the far-field optical in a working plane far enough away from the second lens array to a substantially homogeneous intensity distribution.

In a preferred embodiment, it is proposed that at least some of the lens means of the first lens array are formed aspherical or acylindrical. By this measure, the provided according to claim 1 lighting conditions for the second lens array realized in a surprisingly simple manner become. It is particularly preferred that all lens means of the first lens array are formed aspherical or acylindrical. As a result, the production of the first lens array can be effected in a particularly simple manner, since all lens means of the first lens array have (preferably identical) aspherical or acylindrical cross-sectional profiles. In contrast, the lens means of the second lens array preferably have a spherical

Cross-sectional profile on.

In a preferred embodiment, it is proposed that the lens means of the first lens array has a focal length fi and the

Lens means of the second lens array have a focal length f ₂ , wherein the focal lengths, are chosen so that = f ₂ .

In a particularly preferred embodiment, there is also the possibility that the lens means of the first lens array a

Focal length fi and the lens means of the second lens array have a focal length f ₂ , wherein the focal lengths f-ι, f ₂ are selected so that fi> f ₂ .

In a further particularly preferred embodiment, there is the possibility that the lens means of the first lens array a

Focal length fi and the lens means of the second lens array having a focal length f ₂ , wherein the focal lengths f-ι, f ₂ are selected so that fi <f ₂ .

It has been shown that different focal lengths f- ₁ , f _{2 of} the first and second lens arrays can advantageously improve the homogeneous illumination of the lens means of the second lens array.

In a particularly advantageous embodiment, the first lens array and the second lens array at a distance d are arranged to each other, wherein the distance d is chosen so that d = f ₂ . This is true only if the

Lens vertex of the lens means of the first lens array exactly to the lens peaks of their associated lens means of the second lens array show. Otherwise, the distance d would have to be corrected by T / n (T: lens thickness, n: refractive index). This length dimension must each be subtracted from d = f ₂ if one of the lens means of the first lens array with its vertex points away from the lens means associated with it of the second lens array.

Preferably, the lens means of the first lens array and / or the second lens array may be formed as a microlens means.

In a particularly preferred embodiment, it is proposed that the device comprises a Fourier lens means, the like

is formed and in the beam path so behind the second

Lens array is arranged so that it can be superimposed on the broken of the lens means of the second lens array partial beams in a working plane. As a result, a homogeneous intensity distribution can be obtained behind the second lens array in a working plane in the optical near field in the beam propagation direction.

In an alternative embodiment, there is the possibility that the second lens array is designed such that it has the partial beams refracted by its lens means in a working plane

can overlay. In this variant, the Fourier lens function is advantageously integrated in the second lens array.

In a particularly advantageous embodiment, it is proposed that

- The lens means of the first lens array are formed as cylindrical lens means whose cylinder axes are parallel to each other in extend a first direction and which are adapted to divide the laser radiation into a plurality of partial beams, and / or

 - The lens means of the second lens array are formed as cylindrical lens means whose cylinder axes extend parallel to each other in the first direction and the partial beams can break.

As a result, a particularly high beam quality can be obtained in the working plane.

In a particularly advantageous embodiment it can be provided that at least some of the cylindrical lens means of the first

Lens arrays, preferably all cylindrical lens means of the first

Lens arrays, viewed transversely to their respective cylinder axes have an aspherical cross-sectional profile.

It is in a preferred embodiment, the possibility that the cross-sectional profiles of at least some of

Cylinder lens means of the first lens array (preferably all cylindrical lens means of the first lens array) symmetrical to an orthogonal to the cylinder axis of the respective

Cylindrical lens means extending symmetry plane. It can also be provided according to a further embodiment, that the cross-sectional profiles of at least some of the cylindrical lens means of the first lens array are formed asymmetrically.

With the aid of the device presented here for the homogenization of laser radiation, in which the cross-sectional profiles of the lens means of the first lens array are aspherical or acylindrical, a reduction of the maximum intensity acting on the second lens array to approximately 50% of the original maximum intensity can be achieved. As a result, in particular damage to the antireflection coating can be effectively prevented. Furthermore, can Aging effects that occur when applying the

Antireflection coating can occur with electromagnetic radiation in the ultraviolet spectral range, effectively minimized.

The use of the device described above for the homogenization of laser radiation may be due to the homogeneity and / or the edge steepness of the

Intensity distribution in the work plane. Depending on

Application, this can be tolerable. Optionally, a correction by a suitable adaptation of the second

Lens arrays are made.

Other features and advantages of the present invention will become more apparent from the following description

Embodiments with reference to the accompanying

Illustrations. Show in it

Fig. 1 is a schematically simplified side view of a

 Apparatus for homogenizing light, which is designed according to a preferred embodiment of the present invention,

Fig. 2 is a schematic representation of an aspherical

 Cross-sectional profile of a cylindrical lens means of a first lens array of the device according to FIG. 1.

With reference to FIG. 1, a device for homogenizing laser radiation 100, which is embodied according to a preferred exemplary embodiment of the present invention, will be explained in more detail below. To simplify the rest

Explanations have been drawn in Fig. 1, a Cartesian coordinate system, which defines the y-direction and the orthogonal z-direction, which in this case is the propagation direction of the laser radiation 100. The x-direction of the Cartesian

Coordinate system extends logically into the drawing level.

The device for homogenizing laser radiation 100 is embodied in two stages and has a first lens array 1 with a first optically functional interface 10, which is embodied here flat, and with a second optically functional interface 11, which has a plurality of cylinder lens means arranged side by side in the y direction 3, whose cylinder axes extend parallel to each other in the x-direction (and thus in the drawing plane). The first lens array 1 is thus formed plano-convex. The first optically functional interface 10 of the first lens array 1 may have an antireflection coating to during the

Use to avoid reflection losses and to improve the transmission of the laser radiation 100 through the first lens array 1.

In addition, it is also possible that the second optical

functional interface 11 of the first lens array 1 a

Having antireflection coating.

In the beam propagation direction (z-direction) behind the first lens array 1, a second lens array 2 is arranged, which forms a first optically functional interface 20, which is also planar and forms a light entrance surface, and a second optically functional interface 21, which forms a light exit surface and a plurality of juxtaposed in the y-direction

Cylindrical lens means 4 comprises. The cylinder axes of the cylindrical lens means 4 in turn extend parallel to one another in the x-direction and thus into the plane of the drawing. The second

Lens array 21 is thus also plano-convex. The first optically functional interface 20 of the second lens array 2 may preferably have an antireflection coating to

To reduce reflection losses and thereby improve the transmission of the laser radiation 100 through the second lens array 2. It is also possible for the second optically functional interface 21 of the first lens array 2 to have an antireflection coating.

The cylindrical lens means 3, 4 of the first lens array 1 and of the second lens array 2 are presently embodied as microcylinder lens means on a substrate. The two lens arrays 1, 2 are therefore in other words monolithic. The apparatus for homogenizing laser radiation 100 further comprises a spherically formed Fourier lens means 5, which in the

Beam path is disposed behind the second lens array 2.

The laser radiation 100, which is emitted by a laser light source not explicitly shown here, and with the aid of at least one

Kollimatormittels is collimated, first meets the first

Lens array 1. The collimated laser radiation 100, which may for example have an intensity profile in the form of a Gaussian profile, enters the first optically functional interface 10 in the first

Lens array 1 and is after the transmission at the

Light exit surface 11 of the cylindrical lens means 2 in one of the number of cylindrical lens means 2 corresponding number of

Partial beams 101, 102, 103 split. To present the

Representation not to complicate and make clearer, are in Fig. 1 in beam propagation direction behind the first

Lens array 1 deliberately only three partial beams 101, 102, 103 located.

In the further beam path, the partial beams 101, 102, 103 enter the second lens array 2 through the first optically functional interface 20, pass through this and are optically focused on the second lens array 2

functional interface 21 of the trained there

Cylinder lens means 4 again broken. The Fourier lens means 5 arranged in the beam path behind the second lens array 2 is capable of dividing the partial beams 101, 102, 103 in the

Working plane 6, which is the focal plane of the Fourier lens means 5, to superimpose such that there at least in one direction, a homogeneous (uniform) intensity distribution can be obtained.

The cylindrical lens means 3 of the first lens array 1 are so

designed such that they the laser radiation in such a plurality of Partial beams 101, 102, 103 divide and form them so that the partial beams 101, 102, 103, the cylindrical lens means 4 of the second lens array 2 can illuminate substantially homogeneous. This ensures that the energy density (or

Intensity) of the partial beams 101, 102, 103 to the individual

Cylinder lens means 4 of the second lens array 2 can be reduced such that the damage threshold of there optional

applied anti-reflection coating can always be fallen below, so that damage to the anti-reflection coating can be effectively avoided. Around

 Illumination conditions for the second lens array 2 to realize in a particularly simple manner, have the

Cylindrical lens means 3 of the first lens array 1 transversely to their respective cylinder axes considered an aspherical

Cross-sectional profile on. A cross-sectional profile of a cylindrical lens means 3 formed in this way is shown by way of example in FIG. The aspherical shape of the cross-sectional profile can be clearly seen. In contrast, the cylindrical lens means 4 of the second lens array 2 viewed transversely to their respective cylinder axes on a spherical cross-sectional profile.

There is the possibility that the cross-sectional profiles of at least some of the cylindrical lens means 3 of the first lens array 1

are symmetrical to a plane of symmetry 7 extending orthogonal to the cylinder axis of the respective cylindrical lens means 3. This situation is shown in FIG. Preferably, the cross-sectional profiles of all cylindrical lens means 3 of the first

Lens arrays 1 symmetrical to a plane of symmetry 7. It may alternatively be provided that the cross-sectional profiles

at least some of the cylindrical lens means 3 of the first lens array 1 are formed asymmetrically. In the embodiment shown in Fig. 1, the

Cylindrical lens means 3 of the first lens array 1 has a focal length fi and the cylindrical lens means 4 of the second lens array 2 a

Focal length f ₂ , wherein the focal lengths f-ι, f ₂ are selected so that fi> f is ₂ . In an alternative embodiment, the

Focal lengths f-ι, f _{2 of} the cylindrical lens means 3 of the first lens array 1 and the cylindrical lens means 4 of the second lens array 2 also be chosen so that = f ₂ . In another alternative

Embodiment, it is also possible that the focal lengths f-ι, f ₂ are chosen so that <f ₂ . It has been shown that

different focal lengths f-ι, f ₂ advantageously the

Illumination of the cylindrical lens means 4 of the second array 2

can improve. The first lens array 1 and the second

Lens array 2 may preferably be arranged at a distance d from one another, which is selected such that d = f ₂ . Specifically, this is true only if the lens vertices of the cylindrical lens means 3 of the first lens array 1 point exactly to the lens vertices of their associated cylindrical lens means 4 of the second lens array 2. Otherwise, the distance d would have to be replaced by T / n (T:

Lens thickness, n: refractive index) are corrected. This

Length measure must be subtracted from d = f ₂ , if one of the cylindrical lens means 3 of the first lens array 1 with his

Vertex points away from its associated cylindrical lens means 4 of the second lens array 2.

With the help of the device presented here for the homogenization of laser radiation 100, in which the cross-sectional profiles of

Cylindrical lens means 3 of the first lens array 1 aspherical

a reduction of the maximum intensity acting on the second lens array 2 to approximately 50% of the original maximum intensity can be achieved. In the embodiment described here, only the second optically functional interfaces 11, 21 of the first and second lens arrays 1, 2 have a plurality of cylindrical lens means 3, 4. In principle, it may also be provided that the first optically functional interface 10 of the first lens array 1 comprises a number of cylinder lens means arranged side by side, the cylinder axes of which extend parallel to one another and perpendicular to the cylinder axes of the cylinder lens means 3 on the second optically functional interface 11. Preferably, the cylindrical lens means on the first optically functional interface 10 of the first lens array 1 also have an aspherical

Cross-sectional profile on. Furthermore, there is also the possibility that the first optically functional interface 20 of the second lens array 2 has a number of cylinder lens means arranged side by side, the cylinder axes of which are parallel to one another and

extend perpendicular to the cylinder axes of the cylindrical lens means 4 on the second optically functional interface 21.

Preferably, the cylindrical lens means on the first optically functional interface 20 of the second lens array 2 likewise have a spherical cross-sectional profile.

According to an alternative, not explicitly shown here

Embodiment, there is the possibility that the second

Lens array 2 is formed so that it can be superimposed on the part of his lens means 4 partial beams 101, 102, 103 in a working plane 6. The Fourier lens means 5 in FIG

 Beam propagation direction behind the second lens array 2 can be omitted in this variant, since the above-described function of the

Fourier lens 5 is integrated into the second lens array 2.

Basically, there is also the possibility of the apparatus for homogenizing laser radiation 100 entirely without

Fourier lens means 5 perform and the Fourier lens function also not to be integrated into the second lens array 2. After this

Passage of the laser radiation 100 through the second lens array 2, a homogeneous angular distribution of the partial beams 101, 102, 103 is achieved, which in the far field in a sufficiently far away from the second lens array 2 working level also to a in

Substantially homogeneous intensity distribution leads.

Claims

claims: 1. Apparatus for homogenizing laser radiation (100), comprising  a first lens array (1) having a first optically functional interface (10) through which the laser radiation (100) can enter the first lens array (1), and a second optically functional interface (11) through which the  Laser radiation (100) from the first lens array (1)  can emerge, wherein at least one of the two optically functional interfaces (10, 11) a plurality of  Lens means (3) which are suitable, the  Laser radiation (100) into a plurality of partial beams (101, 102, 103) split, and  - A second lens array (2), which is arranged in the beam path behind the first lens array (1), with a first optically functional interface (20) through which enter the partial beams (101, 102, 103) in the second lens array (2) can, and with a second optically functional interface (21) through which the partial beams (101, 102, 103) from the second  Lens array (2) can emerge, wherein at least one of the two optically functional interfaces (20, 21) a  Comprising a plurality of lens means (4) capable of breaking the partial beams (101, 102, 103), characterized in that the lens means (3) of the first lens array (1) are adapted to receive the Laser radiation (100) in such a manner in a plurality of partial beams (101, 102, 103) and can form them so that the partial beams (101, 102, 103), the lens means (4) of the second lens array (2) can illuminate substantially homogeneous , 2. Device according to claim 1, characterized in that at least some of the lens means (3) of the first lens array (1) are formed aspherical or acylindrical. 3. Device according to claim 1 or 2, characterized in that all lens means (3) of the first lens array (1)  aspherical or acylindrical are formed. 4. Device according to one of claims 1 to 3, characterized  characterized in that the lens means (3) of the first Lens arrays (1) have a focal length fi and the lens means (4) of the second lens array (2) have a focal length f ₂ , wherein the focal lengths, are selected so that f ^ = f ₂ . 5. Device according to one of claims 1 to 3, characterized  characterized in that the lens means (3) of the first Lens arrays (1) have a focal length fi and the lens means (4) of the second lens array (2) have a focal length f ₂ , wherein the focal lengths, are selected so that> f ₂ . 6. Device according to one of claims 1 to 3, characterized  characterized in that the lens means (3) of the first Lens arrays (1) have a focal length fi and the lens means (4) of the second lens array (2) have a focal length f ₂ , wherein the focal lengths, are selected so that <f ₂ . 7. Device according to one of claims 4 to 6, characterized in that the first lens array (1) and the second lens array (2) are arranged at a distance d from one another, the distance d being selected such that d = f ₂ . 8. Device according to one of claims 1 to 7, characterized in that the lens means (3, 4) of the first Lens arrays (1) and / or the second lens array (2) are designed as a microlens means. 9. Device according to one of claims 1 to 8, characterized  in that the apparatus comprises a Fourier lens means (5) which is designed and arranged in the beam path behind the second lens array (2) such that it subtracts the partial beams (101, 101), which are refracted by the lens means (4) of the second lens array (2). 102, 103) in a working plane (6)  can overlay. 10. Device according to one of claims 1 to 8, characterized  characterized in that the second lens array (2) is designed so that it has the partial beams (101, 102, 103) which are broken by its lens means (4) in a working plane (6).  can overlay. 11. Device according to one of claims 1 to 10, characterized  marked that  - The lens means (3) of the first lens array (1) as  Cylindrical lens means (3) are formed, the cylinder axes extending parallel to each other in a first direction and which are adapted to the laser radiation (100) in a  Split plurality of sub-beams (101, 102, 103), and / or - The lens means (4) of the second lens array (2) as  Cylindrical lens means (4) are formed, the cylinder axes extending parallel to each other in the first direction and the partial beams (101, 102, 103) can break. 12. The device according to claim 11, characterized in that at least some of the cylindrical lens means (3) of the first Lens arrays (1), preferably all cylindrical lens means (3) of the first lens array (1), viewed transversely to their respective cylinder axes have an aspherical cross-sectional profile. Apparatus according to claim 11 or 12, characterized characterized in that the cross-sectional profiles of at least some of the cylindrical lens means (3) of the first lens array (1) extend symmetrically to an orthogonal to the cylinder axis of the respective cylindrical lens means (3) Symmetry plane (7) are. Device according to one of claims 11 to 13, characterized in that the cross-sectional profiles of at least some of the cylindrical lens means (3) of the first lens array (1) are formed asymmetrically.