Optical arrangement for direct laser interference structuring

Abstract

An optical arrangement for direct laser interference structuring. A laser beam is directed to a reflecting mirror with inclined surface and strikes a first beam splitter, it is divided into two partial beams and one partial beam is deflected to a focusing element. The second partial laser beam is directed to a first pentamirror and after multiple reflection and/or refraction, the focusing element, or it is directed to a second beam splitter and is divided into a first partial beam and a third partial beam. The partial beams are directed to the focusing element by the first pentamirror and are directed by the focusing element to the surface to be structured interfering with each other. The reflecting mirror is moved in a translational manner, maintaining a 45° angle parallel to the optical axes of the emitted laser beam influencing the interference period Λ.

Claims

1. An optical arrangement for direct laser interference patterning, comprising: a laser beam having an optical axis is emitted from a laser beam source and is directed to a reflecting mirror which reflects the laser beam, and the reflecting mirror comprises a reflective surface that is inclined at an angle of 45° in relation to the optical axis of the laser beam; the laser beam reflected by the reflecting mirror is directed to a first beam splitter, which divides the reflected laser beam into first and second partial beams, and the first partial beam which has been obtained by the first beam splitter is reflected by the first beam splitter and an optical axis of the first partial beam is deflected in a direction of a focusing optical element; the second partial beam transmitted through the first beam splitter is directed to a first pentamirror or a pentaprism and thus is directed to the focusing optical element in a manner parallel to the optical axis of the first partial beam after multiple reflections or refractions in the first pentamirror or pentaprism, or a second beam splitter, which splits the second partial beam into a third partial beam and a fourth partial beam, both the third partial beam and the fourth partial beam having an optical axis, the third partial beam is directed on the focusing optical element parallel to the optical axis of the first partial beam after multiple reflections or refractions in the first pentamirror or pentaprism, and the fourth partial beam of the second partial beam and is directed on a second pentamirror or pentaprism and thus is directed to the focusing optical element parallel to the optical axes of the first partial beam and of the third partial beam of the second partial beam after multiple reflections or refractions in the second pentamirror or pentaprism; in order to form a patterning on or in the region of a surface, the partial beams are directed to the surface by the focusing optical element in a manner interfering with one another; and the reflecting mirror is translationally displaceable parallel to the optical axis of the laser beam emitted from the laser beam source and in a manner maintaining the angle of 45°, for influencing an interference period Λ.

2. The optical arrangement as claimed in claim 1, wherein the reflecting mirror is displaceable over a maximum distance corresponding to a length of a cathetus of an isosceles triangle, wherein a length of an area of the first beam splitter whereon the laser beam deflected by the reflecting mirror is incident, is a hypotenuse of the isosceles triangle.

3. The optical arrangement as claimed in claim 1, wherein in that a plane-parallel waveplate is arranged in a beam path of at least one partial beam upstream of the focusing optical element.

4. The optical arrangement as claimed in claim 1, wherein second reflecting mirrors are arranged in a beam path of the first partial beam in such a way that the first and the second partial beams and if necessary the third partial beam each travel a distance of equal length until being incident on the focusing optical element.

5. The optical arrangement as claimed in claim 1, wherein the partial beams are directed through a Dove prism arranged between the first beam splitter, the first pentamirror or the pentaprism, the second pentamirror or pentaprism and the focusing optical element.

6. The optical arrangement as claimed in claim 5, wherein the Dove prism is rotatable about an axis oriented parallel to the optical axes of the partial beams, said axes being oriented parallel to each other.

7. The optical arrangement as claimed in claim 1, wherein the first beam splitter is embodied in such a way that energy proportions in a ratio 50:50 are obtained for the first partial beam and the second partial beam, when the first and second partial beams are directed to a respective surface in a manner interfering with one another or the first beam splitter is embodied in such a way that energy proportions in a ratio 33:66 are obtained for the first partial beam and the second partial beam and the second beam splitter is embodied in such a way that energy proportions in the ratio 50:50 are obtained for the third partial beam of the second partial beam and the fourth partial beam, when the first, third, and fourth partial beams are directed to the respective surface in a manner interfering with one another.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in greater detail by way of example below. In so doing, the features can be combined with one another independently of the respective individual example or its illustration in a figure and the features are not bound to the respective individual example or the individual illustration.

(2) In the figures:

(3) FIG. 1 consisting of FIGS. 1A and 1B show, in schematic form, an example of an optical arrangement according to the invention with two interfering partial beams and influencing of the interference period by means of moving a reflecting element;

(4) FIG. 2 shows a schematic illustration of a second example of an arrangement according to the invention with three interfering partial beams;

(5) FIG. 3 shows two partial beams guided through a Dove prism;

(6) FIG. 4 shows a diagram that illustrates the influence on the interference period in μm by moving the reflecting element in mm and

(7) FIG. 5 consisting of FIGS. 5A, 5B, 5C, and 5D shows examples of pattern elements which are manufacturable with an arrangement according to the invention with changing polarization directions.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1A shows a schematic illustration of an example of an arrangement according to the invention, in which two partial beams 3 and 4 which are directed to a surface of a workpiece 9 to be patterned in a manner interfering with one another.

(9) A laser beam 2 is directed from a laser radiation source 1 to a reflecting element M, the reflecting area of which is oriented at an angle of 45° in relation to the optical axis of the laser beam 2 emitted from the laser radiation source 1. The reflected laser beam 2 is incident on a first beam splitter BS1, the area of said beam splitter that the laser beam 2 is incident on being inclined by 45° to said optical axis. A portion of the laser radiation is reflected at this area and in this way a first partial beam 3, having an optical axis parallel to the optical axis of the laser beam 2 originally emitted from the laser radiation source 1, is reflected in the direction of a focusing element L.

(10) A portion of the laser radiation of the laser beam 2 is transmitted through the first beam splitter BS1 so that a second partial beam 4 is incident on reflecting areas of a roof pentamirror RPM1. The second partial beam 4 is thus reflected in such a way that it is directed parallel to the optical axis of the first partial beam 3 in the direction of the focusing element L.

(11) The partial beams 3 and 4 are focused or deflected by the focusing element L in the direction of the surface of the workpiece 9 in a manner interfering with one another, on which surface a patterning should be formed.

(12) In the example shown in FIG. 1A, a plane-parallel waveplate (λ/2 plate) 5 is arranged in the beam path of the second partial beam 4, between the first roof pentamirror RPM1 and the focusing element L.

(13) Reflecting elements 6 are arranged in the beam path of the first partial beam 3, between the first beam splitter BS1 and the focusing element L. The reflecting elements 6 are arranged in such a way and are oriented with their reflecting areas, whereon the first partial beam 3 is incident, in such a way that the difference of the distances which the first partial beam 3 and the second partial beam 4 travel proceeding from the first beam splitter BS1 until being incident on the focusing element L is compensated and both partial beams 3 and 4 thus travel at least nearly or completely the same path distance.

(14) In the example shown in FIG. 1A, an optical telescope 8 and at least one element 10 forming the laser beam 2 are additionally arranged in the beam path of the laser beam 2 downstream of the laser beam source 1.

(15) The double-ended arrow is intended to indicate that the reflecting element M is movable translationally and parallel to the optical axis of the laser beam 2, emitted from the laser beam source 1 and not yet changed in its direction, in order to change the interference period Λ of the two partial beams 3 and 4.

(16) FIG. 1B shows the effect of a translational displacement of the reflecting element M. In the top illustration of FIG. 1B, the reflecting element M is displaced proceeding from a central position by a value of 7 mm in the direction of the laser beam source 1. In this way the optical axis of the laser beam 2 deflected by the reflecting element M is likewise displaced in the direction of the laser beam source 1. The result of this is that the distance between the optical axes of the two partial beams 3 and 4 increases and, in this way, so does the interference period Λ.

(17) In the middle illustration of FIG. 1B, the reflecting element M is likewise translationally displaced proceeding from a central position by a value of 7 mm in the direction of the laser beam source 1 in the direction pointing away from the laser radiation source 1. In this way the optical axis of the portion of the laser beam 2 deflected by the reflecting element M is likewise displaced away from the laser beam source 1. The result of this is that the distance between the optical axes of the two partial beams 3 and 4 decreases and, in this way, so does the interference period Λ.

(18) At the very bottom of FIG. 1B, a partial illustration of the beam paths of the two partial beams 3 and 4 after passing through the focusing element L is shown. The interference volume, which can be obtained by means of the interfering partial beams 3 and 4, is shown in a region above the surface of the workpiece 9, which is intended to be patterned.

(19) In FIGS. 1A and 1B, OA designates the mean optical axis of the obtained partial beams 3 and 4.

(20) The first beam splitter BS1 splits the laser beam 2 in such a way that the partial beams 3 and 4 have at least approximately the same energy.

(21) In FIG. 2, a further example of an arrangement according to the invention is shown. Here, a laser beam 2 is directed to an area of a reflecting element M and therefrom is reflected to the first beam splitter BS1, as in the example according to FIGS. 1A and 1B. A first partial beam 3 is reflected from first beam splitter BS1 in the direction of a surface of a workpiece 9. The partial beam 4 transmitted through the first beam splitter BS1 is directed to a second beam splitter BS2. In doing so, a first partial beam 4.1 obtained by the second beam splitter is incident on reflecting areas of a roof pentamirror RPM2. A second partial beam 4.2 obtained by the second beam splitter BS2 is incident on reflecting areas of a roof pentamirror RPM2. The partial beams 4.1 and 4.2 are reflected by the RPM 1 and RPM 2 in the direction of the surface of the workpiece 9 to be patterned.

(22) Apart from the splitting into three partial beams 3, 4.1 and 4.2, the example according to FIG. 2 does not differ from the example according to FIGS. 1A and 1B. In this example, too, partial beams 4.1 and 4.2 can be given a defined polarization by a plane-parallel waveplate (λ/2 plate) 5. Reflecting elements 6 can be arranged in the beam path of the first partial beam 3, between the first beam splitter BS1 and the focusing element L, which reflecting elements can be used for compensating the path lengths of the partial beams 3, 4.1 and 4.2. The three partial beams 3, 4.1 and 4.2 can be directed to the respective surface by the focusing optical element L.

(23) In the left illustration of FIG. 2, this example is shown in a plan view.

(24) FIG. 3 schematically shows two partial beams 3 and 4 guided through a Dove prism DP. In doing so, the partial beams 3 and 4 are refracted and reflected multiple times and, in this way, their direction is changed. A change in the orientation of the partial beams 3 and 4, interfering with one another, can be achieved by means of rotating the Dove prism DP about the optical axis OA, which, in addition to the interference with a corresponding interference period Λ, can in turn lead to a possible change in the orientation of pattern elements to be formed on the surface 9.

(25) In FIG. 5, four different calculated interference profile intensities that are producible with the invention are shown, which in turn correspond to accordingly formable pattern elements. The changes can be realized solely through a change in the polarization of partial beams. The polarization vectors used in doing so are indicated with arrows. The polarization can be adapted accordingly by the plane-parallel waveplates 5.

(26) The polarization can be carried out by λ/2 plates for each partial beam individually. FIG. 5A shows a situation, in which each partial beam has an identically oriented polarization. By means of rotating the waveplate, further polarization states can be realized, and so the polarization of each partial beam is oriented at 60° (FIG. 5B), 45° (FIG. 5C) or arbitrarily (FIG. 5D).