DE102022204081B4 - Device for direct laser interference structuring on surfaces of components - Google Patents

Abstract

Device for direct laser interference structuring on surfaces of components, in which a laser beam (1) emitted by a laser radiation source is directed onto an optical element (2, 13) which divides the laser beam (1) into at least two partial beams (1.1, 1.2) and the partial beams (1.1, 1.2) strike a first reflective optical element (3) in such a way that they strike reflective surfaces of a rotating polygon (5) through an opening (4.1) which is formed in a second reflective optical element (4) and from there the Partial beams (1.1, 1.2) are directed through the opening (4.1) to a third reflecting optical element (6) aligned at an angle greater than 0° and less than 90° in relation to their optical axes, the partial beams (1.1, 1.2) being directed from third reflective optical element (6) is directed at at least one concavely curved surface of the second reflective optical element (4) perpendicular to the axis of rotation (A) of the rotating polygon (5) and the partial beams (1.1, 1.2) are directed at at least one reflective surface (7A, 7B), which strike the fourth reflective optical element (7) aligned at an angle greater than 0° and less than 90° with respect to their optical axes and from there are directed towards the surface of the respective component (10), that they interfere with each other in the area of the surface of the component (10).

Description

The project that led to this application was funded by the European Union's Horizon 2020 research and innovation program under grant agreement No. 825132.

The invention relates to a device for direct laser interference structuring on surfaces of components. In this case, structural elements can be formed over a large area on or in a surface of a component by material removal or a locally defined modification of the component material can be achieved, which can correspond to structuring, for example by a locally defined increase in volume, a change in the optical refractive index or the reflectivity for incident electromagnetic radiation can be achieved.

The direct laser interference structuring (DLIP) process has proven successful for some applications in the past. It is particularly suitable for quick and large-area structuring of surfaces. A wide variety of optical arrangements are known for this purpose. For some applications, productivity is still not sufficient and there may also be deficits in the feasible structural periods Λ with regard to their miniaturization. As a rule, large-volume optical arrangements are also required in order to provide correspondingly large focal lengths and optical paths, which in turn can limit the possible applications.

From Raenke, F. et al. are in “High througput laser surface micro-structuring of polysterene by combining direct laser interference patterning with polygon scanner technology”; Materials Letters: X; Vol. 14, 2022, p. 100144 . - ISSN 2590-1508 Possibilities for surface structuring are described.

US 2020 / 0 101 560 A1 relates to a laser processing device.

It is therefore the object of the invention to provide options for large-area structuring on surfaces of components that require a relatively small volume for the required optical structure and enable very small, filigree structuring that can also be formed in a short time.

According to the invention, this object is achieved with a device which has the features of claim 1. Advantageous refinements and further developments of the invention can be realized with features specified in the dependent claims.

In the device according to the invention, a laser beam emitted by a laser radiation source is directed onto an optical element that divides the laser beam into at least two partial beams. The partial beams then impinge on a first reflective optical element in such a way that they impinge on reflective surfaces of a rotating polygon through an opening formed in a second reflective optical element. As is known, optical polygons have several reflective, flat and generally planar surfaces on their outer surface, which successively receive electromagnetic radiation, i.e. in this specific case the partial rays, as the polygon rotates and are reflected from there onto another reflective surface depending on the angle of impact Since the angle of incidence changes when the polygon is rotated, the angle at which the reflection from there also changes, so that the angle of incidence also changes accordingly on optical, in particular reflective, elements arranged subsequently in the beam path of the partial beams and also on the surface of the respective component can be changed. This means that large-area structuring can be achieved in a short time.

From the reflecting surfaces of the polygon, the partial beams are directed at a third reflective optical element aligned at an angle greater than 0° and less than 90° with respect to their optical axes through the opening formed in the second reflective optical element, whereby the Partial beams from the third reflective optical element are directed onto a concavely curved and reflective surface of the second reflective optical element perpendicular to the rotation axis A of the rotating polygon.

The partial beams subsequently hit a reflective surface in the beam path, which is aligned at an angle greater than 0° and less than 90° with respect to the fourth reflective optical element in relation to its optical axes. From there they are directed towards the surface of the respective component so that they interfere with one another in the area of the surface of the component. The plane in which the interference occurs can correspond to the respective surface of the component. However, this level can also be arranged at a small distance above or below the respective surface by appropriate focusing.

For this purpose, additional optical elements should also be arranged in the beam path of the partial beams, with which beam shaping and focusing can be achieved. These optical elements are preferably between the beam-splitting optical ones Element and the first reflecting surface of a correspondingly designed and arranged optical element, on which the partial beams strike first.

At least one optical element can be arranged in the beam path of the partial beams, with which focusing in one axial direction and focusing in an axial direction aligned perpendicular thereto can be achieved.

The partial beams can be directed onto the reflective surface of the first reflective optical element by means of a fifth reflective optical element, which is preferably rotatable about at least one axis B or aligned at an angle of 45° in relation to the optical axis of the incident partial beams they hit the first reflective optical element. In this way, the partial beams can be redirected and extended until they hit the surface of the component.

The reflecting surfaces of the first reflective optical element and the third reflective optical element should be aligned such that the partial beams are guided through the opening in the area of the second reflective optical element in which the opening is formed. The opening surrounded by a reflecting surface of the second optical element should have a rectangular or square outer contour so that the partial beams, depending on the angle of impact on the reflecting surfaces of the first optical element and the reflecting surfaces of the rotating polygon, are guided unhindered through the opening.

Beam traps should be arranged in the beam path of the partial beams, onto which partial beams of higher refraction order impinge. The beam traps should be provided with cooling and prevent higher-order partial beams from also striking other reflective surfaces or the surface of the component.

The first reflective optical element and the third reflective optical element should preferably be aligned at an angle between 40° and 50° in relation to the optical axis of the partial beams.

The partial beams can additionally be directed onto the reflective surface of the first reflective optical element using at least a fifth reflective optical element. The partial beams from the reflecting surface of the fifth reflecting optical element can impinge on the reflecting surface of the first reflecting optical element, so that from there they impinge on a reflecting surface of the rotating polygon and are reflected there back towards the third reflecting optical element , in order in turn to be directed from the third reflective optical element onto the reflecting surface of the second reflective optical element which is concavely curved in relation to the rotation axis A of the polygon, before the partial beams, after reflection on the second reflective optical element, are directed towards the fourth reflective optical element the surface of the component to be structured can be redirected. The partial beams are aligned in relation to one another in such a way that they interfere with one another in the area of the surface of the component to be structured in order to be able to form the respective structuring.

A fifth reflecting optical element can advantageously be pivoted about at least one axis of rotation B in order to be able to further influence the laser beam in its angular arrangement. If there is a possibility of rotation about two axes of rotation aligned perpendicular to one another, it is also possible to use two fifth reflective optical elements, in which a second fifth reflective optical element can be pivoted about an axis that is oriented at 90 ° in relation to axis B , a two-dimensional deflection of the laser beam can be achieved.

A fourth reflective optical element can have two reflective surfaces with which reflection of the partial beams in different axial directions can be achieved.

For large-area structuring, a preferably translational relative movement of the component and device can be carried out. Particularly preferably, only the component is moved.

Advantageously, the first reflective optical element and the second reflective optical element can form F-theta optics.

The partial beams can advantageously be directed towards the surface of the component at an angle α between the two partial beams, which is less than 20°, preferably less than 15° and particularly preferably less than 10°. The partial beams should cover a path of at least 500 mm, preferably at least 600 mm, on their path between the beam-splitting optical element and the surface of the component to be structured. This can be done by multiple reflections in below different and also in opposite directions, so that the entire volume required for the optical structure can be kept small and all optical elements can be accommodated in a small space in one housing.

Advantageously, the partial beams that impinge on the third reflecting optical element from reflecting surfaces of the rotating polygon can impinge on a convexly curved surface whose reflecting surface is rotationally symmetrical. The optical axes of the convexly and concavely curved reflective optical elements are aligned coaxially with one another.

With the invention, structure periods Λ of less than 20 μm, preferably less than 15 μm and particularly preferably less than 10 μm can be achieved.

Reflecting surfaces of optical elements can be coated with an interference layer system tailored to the wavelength of the laser radiation of the partial beams.

The invention will be explained in more detail below by way of example.

• 1 in schematischer Form ein Beispiel einer erfindungsgemäßen Vorrichtung und
• 2 ein weiteres Beispiel in einer anderen perspektivischen Darstellung.

Show:

• 1 in schematic form an example of a device according to the invention and
• 2 another example in a different perspective view.

At the in 1 and 2 In the example shown, the laser beam 1 emitted by a laser radiation source, not shown, strikes the beam-splitting diffractive optical element 13 through a plurality of beam-shaping optical elements 11 and 12, and with this two partial beams 1.1 and 1.2 are obtained, which are directed at one of the partial beams 1.1 and 1.2 by 90 ° deflecting reflective element 8 and from there are reflected in such a way that a partial beam 1.1 or 1.2 hits a surface of a prism 2 or emerges from it, so that they are reflected at certain angles from different directions through several optical elements 14 to 16 onto a reflective surface the at least one fifth reflective optical element. The example shown here is a fifth reflective optical element 9, which can be pivoted about two axes aligned perpendicular to one another in order to enable a two-dimensional deflection of the partial beams. However, two fifth reflective optical elements can also be arranged one after the other in the beam path of the partial beams, in a form not shown, onto which the partial beams 1.1 and 1.2 can be reflected and further directed from there.

The two fifth reflective optical elements 9A and 9B can each be pivoted about an axis of rotation, one axis of rotation being aligned with the axis of rotation B and the other axis of rotation at an angle of 90° thereto.

From there, the partial beams are directed towards a reflective surface of the first reflective optical element 3. With the fifth reflecting element(s) 9, 9A and 9B you can change the point of impact and thus also the angle of impact with which the partial beams 1.1 and 1.2 hit the reflecting surface of the first reflecting optical element 3, which subsequently also affects the rest Beam guidance of the two partial beams 1.1 and 1.2 affects.

The partial beams 1.1 and 1.2 reflected from the surface of the first reflective optical element 3 are then reflected in the direction of the polygon 5 so that they impinge on one of the rotating reflective surfaces of the polygon 5. Only two of these reflective surfaces of the polygon 5 are shown in the illustration. The polygon 5 rotates about its axis of rotation A.

On their way in their beam path, the partial beams 1.1 and 1.2 pass through the opening 4.1, which is formed with a concave surface in the second reflective optical element 4, and strike the reflective surfaces of the polygon 5 and from there become a reflective convex surface of the third reflective optical element 6 to impinge on the reflective surface of the second reflective optical element 4 and from there to impinge on reflective surfaces of the fourth reflective optical element 7A and 7B. With the reflecting surfaces 7A and 7B, a partial beam 1.1 is directed at an angle of 86° and the other partial beam 1.2 at an angle of 94° towards the surface of the component 10, so that a value α of 8° results.

Claims (9)

Device for direct laser interference structuring on surfaces of components, in which a laser beam (1) emitted by a laser radiation source is directed onto an optical element (2, 13) which divides the laser beam (1) into at least two partial beams (1.1, 1.2) and the partial beams ( 1.1, 1.2) impinge on a first reflective optical element (3) in such a way that they impinge on reflective surfaces of a rotating polygon (5) through an opening (4.1) which is formed in a second reflective optical element (4) and from there the partial beams (1.1, 1.2) at an angle greater than 0° and less than 90° in relation to them optical axes aligned third reflective optical element (6) are directed through the opening (4.1), the partial beams (1.1, 1.2) from the third reflective optical element (6) being at least perpendicular to the axis of rotation (A) of the rotating polygon (5) concavely curved surface of the second reflective optical element (4) are directed and the partial beams (1.1, 1.2) are directed onto at least one reflective surface (7A, 7B) which is at an angle greater than 0° and less than 90° in relation to it fourth reflective optical element (7) aligned with optical axes and from there are directed towards the surface of the respective component (10) so that they interfere with one another in the area of the surface of the component (10). Device according to Claim 1 , characterized in that the optical element (2, 13) dividing the laser beam (1) into partial beams is a diffractive optical element. Device according to one of the preceding claims, characterized in that the partial beams (1.1, 1.2) are formed with a plurality of optical elements (11, 12, 14, 15, 16) arranged in their beam path and focused in the direction of the component surface. Device according to one of the preceding claims, characterized in that the partial beams (1.1, 1.2) are directed with a fifth reflecting optical element (9) onto the reflecting surface of the first reflecting optical element (3). Device according to one of the preceding claims, characterized in that the partial beams (1.1, 1.2) by means of at least a fifth reflecting optical element (9, 9A, 9B), which is/are preferably rotatable about at least one axis (B) or at an angle of 45 ° in relation to the optical axis of the incident partial beams (1.1, 1.2), are directed towards the reflective surface of the first reflective optical element (3). Device according to one of the preceding claims, characterized in that beam traps are arranged in the beam path of the partial beams (1.1, 1.2), which impinge on the partial beams of a higher order of refraction. Device according to one of the preceding claims, characterized in that the first reflective optical element (3) and fourth reflective optical element (7) are at an angle between 40° and 50° in relation to the optical axis of the partial beams (1.1, 1.2) with their reflective ones Surfaces are aligned. Device according to one of the preceding claims, characterized in that the partial beams (1.1, 1.2) are at an angle between the two partial beams (1.1, 1.2), which is less than 15°, preferably less than 10°, in the direction of the surface of the component ( 10) are directed. Device according to one of the preceding claims, characterized in that the partial beams (1.1, 1.2), which impinge on the third reflecting optical element (6) from reflecting surfaces of the rotating polygon (5), on an axis of rotation (A) of the rotating polygon hits a convexly curved surface.

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