Optical rotating device for injecting a laser beam and method for positioning a laser beam

Abstract

An optical rotating device for injecting a laser beam may include deflection devices between which the injected laser beam may rotate in the optical rotating device, and an extraction device that may extract the laser beam after carrying out a predetermined number of rotations in the rotating device. The deflection devices may be arranged such that the position of the laser beam during extraction is dependent on the number of rotations carried out in the optical rotating device.

Claims

1. An optical circulation device for coupling in a laser beam, comprising: deflection devices between which the coupled-in laser beam carries out circulations in the optical circulation device, and an out-coupling device configured for coupling out the laser beam after having carried out a predetermined number of circulations in the circulation device, wherein the deflection devices are designed and arranged in such a way that the position of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device; wherein the deflection devices are designed and arranged in such a way that at least three different positions of the laser beam when coupling out depend on three different numbers of circulations carried out in the optical circulation device.

2. The optical circulation device according to claim 1, wherein the deflection devices are designed and arranged in such a way that a lateral offset of the position of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device.

3. The optical circulation device according to claim 2, wherein the deflection devices are designed and arranged in such a way that in two dimensions a lateral offset of the position of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device.

4. The optical circulation device according to claim 1, wherein the deflection devices are designed and arranged in such a way that a beam angle of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device.

5. The optical circulation device according claim 1, wherein the deflection devices are designed and arranged in such a way that a circular path offset of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device.

6. The optical circulation device according to claim 1, wherein the out-coupling device comprises a Pockels cell.

7. The optical circulation device according to claim 6, wherein the Pockels cell is arranged in such a way that each circulation of the laser beam in the circulation device passes through the Pockels cell.

8. The optical circulation device according to claim 1, wherein the deflection devices are designed and arranged in such a way that the circulation of the laser beam in the circulation device is carried out in a spiral shaped path.

9. A method of positioning a laser beam, comprising: coupling a laser beam into an optical circulation device, carrying out a predetermined number of circulations of the laser beam in the optical circulation device, and coupling the laser beam out of the circulation device, wherein the position of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device; wherein carrying out a predetermined number of circulations and coupling the laser beam out of the circulation device includes operating deflection devices, between which the coupled-in laser beam carries out circulations in the optical circulation device, such that at least three different positions of the laser beam when coupling out depend on three different numbers of circulations carried out in the optical circulation device.

10. The method of claim 9, wherein the deflection devices are arranged such that a lateral offset of the position of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device.

11. The method of claim 10, wherein the deflection devices are arranged such that in two dimensions a lateral offset of the position of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device.

12. The method of claim 9, wherein the deflection devices are arranged such that a beam angle of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device.

13. The method of claim 9, wherein the deflection devices are arranged such that a circular path offset of the laser beam when coupling out depends on the number of circulations carried out in the optical circulation device.

14. The method of claim 9, wherein coupling the laser beam out of the circulation device includes operating an out-coupling device comprising a Pockels cell.

15. The method of claim 14, wherein the Pockels cell is arranged such that each circulation of the laser beam in the circulation device passes through the Pockels cell.

16. The method of claim 9, wherein the deflection devices are arranged that circulation of the laser beam in the circulation device is carried out in a spiral shaped path.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic diagram of an optical deflection device which is similar to a ring resonator,

(3) FIG. 2 is a schematic diagram of a rotating out-coupling switch element as an out-coupling mechanism for a circulation device, and

(4) FIG. 3 is a further schematic diagram of a rotating out-coupling switch element as an out-coupling mechanism for a circulation device.

DETAILED DESCRIPTION

(5) FIG. 1 shows in a schematic diagram an optical circulation device 10 as an optical arrangement that is realized external to a laser resonator as an independent component. The optical circulation device 10 is arranged with a substantially quadrangle arrangement that can be traversed by a laser beam. The quadrangle arrangement can be arranged for example horizontally, and comprises four deflection devices 11, 12, 13, and 14 at the four circulation corners thereof, which may be realized as deflecting mirrors or as deflecting prisms.

(6) A laser beam that is coupled into the optical circulation device 10 circulates in the quadrangular arrangement until it is again coupled out of the circulation device. The laser beam is deflected by the deflection devices 11, 12, 13, and 14 so that it stays within the circulation device 10.

(7) The optical circulation device 10 comprises an in-coupling mechanism 15 for coupling in the laser beam S. The optical circulation device 10 comprises an out-coupling mechanism 16 for coupling out the laser beam. The in-coupling mechanism 15 and the out-coupling mechanism 16 may be realized as a single component, or as multiple components, for example as a Pockels cell with thin-layer polarizer(s), as an acousto-optical modulator (AOM), and/or as moving optics.

(8) Furthermore, one or more further optical components 17, such as lenses, etc., may be arranged in the beam path of the circulation device 10. In particular, a polarization switch 16 is arranged in the beam path of the circulation device 10, which can change the polarization of radiation circulating in the circulation device so that the radiation is coupled out at the out-coupling mechanism 16.

(9) Here, the out-coupling mechanism 16 may be realized as a polarization beam splitter, which allows laser light of a predetermined polarization (for example p-polarization) passing through and thus leaves it within the circulation device 10, and which couples out laser light of a different polarization (for example s-polarization) of the circulation device 10. When the polarization switch 16 is actuated, then the laser light will be coupled out of the circulation device 10 when subsequently reaching the out-coupling mechanism 16. It is not necessary to realize the polarization switch 16 as a separate component, and the polarization switch 16 can be realized as a component of the extraction mechanism 16. The polarization switch 16 acts together with the out-coupling mechanism 16 in such a way that laser light that is in the circulation device is coupled out of the circulation device 10 after having carried out a predetermined number of circulations.

(10) The polarization switch 16 can be realized for example as a Pockels cell through which the laser beam coupled into the circulation device passes. A Pockels cell switches electronically and thus very fast.

(11) With the optical circulation device 10 shown in FIG. 1, the position of an external laser beam S can be affected as follows: At the in-coupling mechanism 15, a laser beam S is coupled into the circulation device 10. The coupled-in laser beam circulates in the circulation device 10 as coupled-in laser beam S.sub.1 in the first circulation (clockwise in the shown embodiment). In the first circulation, the laser beam S.sub.1 passes inter alia the polarization switch 16. Depending on how the polarization switch 16 is controlled, the laser beam 16 in the first circulation either maintains its polarization, or the polarization is changed. Depending on the polarization of the laser beam S.sub.1 in the first circulation, the laser beam is either coupled out at the out-coupling mechanism 16, or is directed as laser beam S.sub.2 into a second circulation around the circulation device 10.

(12) Here, the position of propagation, that is, the beam position, of the laser beam S.sub.2 in the second circulation is laterally offset with regard to the position of propagation of the laser beam S.sub.1 in the first circulation at the latest when arriving at the first deflection device 11. This offset is caused by a misadjustment of the deflection devices 11, 12, 13, and 14 when compared with an exact quadrangle circulation adjustment. After each further circulation through the circulation device 10, the laser beam S.sub.x+1 in the x+1-th circulation is laterally offset with respect to the laser beam S.sub.x in the previous x-th circulation. With this, the laser beam is laterally offset in the circulation device 10 depending on the number of circulations carried out.

(13) During each single circulation, the coupled-in laser beam passes through the polarization switch 16, which is realized for example as a Pockels cell. The polarization of the coupled-in laser beam can therefore be switched in each single circulation. With this, it is possible to set an exactly predetermined number of circulations carried out in the circulation device 10, depending on the operating setting of the out-coupling mechanism 16 respectively the polarization switch 16.

(14) The circulation device 10 here is independent of the type of laser system used for generating the laser beam S to be coupled in, and thus can be used with each (pulsed) laser. Therefore, any arbitrary laser source and laser process can be coupled into the circulation device 10. The circulation device 10 achieves an ultrafast beam splitting that can be used for example in industrial processes.

(15) The laser beam can pass through the circulation device 10 so that its q parameter is reproduced at a specific position within the circulation device 10 after one or more circulations.

(16) In one embodiment variant, the in-coupling mechanism may be omitted, as the beam position is geometrically separated from the other beam paths.

(17) It is not necessary that the laser beams, as shown in FIG. 1, circulate in the optical circulation device absolutely in parallel and/or laterally offset to each other. For example, it is also possible that the laser beams differ from each other in their angle of radiation, which may be advantageous at narrow apertures, for example at the out-coupling mechanism, an optional amplification and/or weakening in the circulation device, as well as at linear and non-linear optical components.

(18) If the out-coupling mechanism 16 comprises a Pockels cell, then the crystal thereof is preferably realized so large that, with a parallel offset of the laser beams, all laser beams up to a predetermined number of circulations are guided through the Pockels cell. This can be achieved particularly simple and cost effective with a lateral parallel offset of the laser beams, because the optical surfaces of the Pockels cell can be realized as elongated rectangles, with low requirements to the high voltage to be applied across the thin crystal of the Pockels cell.

(19) The circulation device can be constructed in such a way that the laser beams in all circulations pass through the Pockels cell at the same lateral position with a small individual angular offset with respect to each other. In this way, it is possible to cost effectively realize a circuit having a relatively small Pockels cell or small AOM as an out-coupling mechanism.

(20) Pockels cells and AOMs achieve very high repetition rates, so that fast circuits for circulation devices for high repetitive laser systems in the megahertz range can be realized.

(21) A conventional (slow) beam positioning concept can be arranged subsequent to the circulation device 10, for example for a macro positioning of the laser beam.

(22) It is not necessary here that the beam positions differ by a lateral parallel offset. Also other types of geometric differentiation can be achieved by the positioning and arrangement of the deflection devices 11, 12, 13, and 14, such as for example beam angle, different beam positions parallely offset on a circle path, as well as combinations of theses beam positions.

(23) Inside and outside of the circulation device, the beam positions can be positioned other than in a line. For example, a circulation device may be provided for a helical drilling method, wherein laser beams, depending on the number of circulations carried out, are coupled out offset in rotation from each other on a circular path. Within the circulation device, by means of suitable optical systems, the beam positions can be brought in arbitrary forms on a workpiece, for example in case of helical drilling in a micro material processing in a circular form and/or in a form of a circle segment. Using a suitable circulation device, the beam angle of the coupled-out laser beam when rotating (for example for a helical drilling) can be changed rapidly.

(24) The beam position of the different coupled-out laser beams can overlap in part. The optical assembly of the circulation device can be realized such that the q parameter of the laser beam at the exit, where the laser beam is coupled out, is the same for all number of beam circulations. Preferably, the circulation device is realized such that the q parameter is the same for all coupled-out laser beams.

(25) The circulation device shown in FIG. 1 is of spiral shape and in form of a quadrangle. As an alternative, the circulation device can be realized in form of a triangle, or generally in polygon form, comprising a corresponding number of deflection devices. The circulation device can be realized with only two deflection devices, in which case the circulation device is realized substantially longitudinal and resembles a classic laser resonator having two deflection mirrors, between which the laser beam circulates. In such a longitudinal form, a beam positioning of the coupled-out laser beams depending on the number of circulations carried out in the circulation device can be achieved for example by arranging reflective surfaces of the two deflection devices not parallel to each other, but with a slight offset to each other.

(26) As an optical component 17, or in addition to other components, a gain medium may be arranged in the circulation device that can compensate for losses in the circulations of the laser beam.

(27) As an alternative to using a Pockels cell, coupling out can be performed mechanically. This is slower, but also cheaper as no expensive Pockels cell is needed. For this, for example a rotating mirror can be used as an out-coupling mechanism 16, as it is shown in FIGS. 2 and 3.

(28) FIGS. 2 and 3 respectively show schematically an embodiment of a rotating out-coupling mirror as an out-coupling mechanism 16. A conventional cylindrical mirror substrate may be provided as mirror substrate. A portion of the mirror surface has a highly reflective coating, while the remainder of the substrate is almost lossless transmissive for laser light. Beam positions for the first to tenth circulation of a leaser beam are arranged to extend from the outside to the center of rotation of the mirror. When the laser beam traverses a transmissive region of the substrate, shown as white in FIGS. 2 and 3, the laser beam remains in the circulation devices for at least one more circulation. When the laser beam traverses a reflective region, shown hatched in FIGS. 2 and 3, the laser beam is coupled out.

(29) With the mirror position as shown in FIG. 2, a laser beam would be reflected at the 6.sup.th circulation and thus would be coupled out. With the mirror position as shown in FIG. 3, a laser beam would be reflected at the 5.sup.th circulation and thus would be coupled out.

(30) The mirrors shown in FIGS. 2 and 3 are rotatable about their center of rotation so that depending on the mirror position a laser beam is extracted from the circulation device after a different number of circulations.

(31) In case that higher rates of coupling out are desired, a second or third Pockels cell can be used in order to increase switching speed.

(32) Moreover, further switches (such as for example one or more Pockels cells) can be arranged in the circulation device to reverse the direction of a lateral offset of the beam axis of the laser beam by 180. In this way, a lateral offset by a predetermined distance in a first direction per circulation can be reversed in a lateral offset by a same predetermined distance in opposite direction per each successive circulation. In the i-th circulation after this beam reversal, the laser beam would thus have the same beam position as in the i-th circulation prior to the beam reversal. In this way it is possible to allow for further (different) numbers of circulations for coupling out same beam positions.

(33) Moreover, switches (such as for example one or more Pockels cells) can be arranged in the circulation device for turning by 90 the direction in which a lateral offset of the beam axis takes place per circulation. In subsequent circulations after actuating the switch, thus, there results with each circulation a lateral offset of the beam axis in a direction rotated by 90. Hereby it is possible to adjust the beam position, such as for example the beam angle, in two dimensions.

(34) Moreover, it is possible to achieve a lateral offset of the laser beam in a second direction, whereby the number of obtainable beam positions when coupling out is quadrupled. For this, the circulation device can be supplemented by a second sub-circulation device whose beam axis path is offset by 90 with respect to the beam axis path of the first sub-circulation device. The circulation device thus comprises two sub-circulation devices. The beam axes in the two sub-circulation devices may be offset from one another at an angle other than 90, making it possible to realize finely adjustable out-coupling patterns of the beam positions, similar to moir patterns. The second sub-circulation device can be of a larger dimension so that the beam circulations in the two sub-circulation devices do not interact with each other. Alternatively, the sub-circulation devices can be arranged in series to successively adjust both dimensions of the beam position.

(35) A workpiece can be arranged after the circulation device, onto which the coupled-out laser beam is projected. With successively coupled-out laser beams having different beam positions, a sort of print image can be created on the workpiece. This can be used for example for producing print cylinders, or for other applications in which a pattern is to be produced on a surface.

LIST OF REFERENCE NUMERALS

(36) 10 circulation device 11 deflection device 12 deflection device 13 deflection device 14 deflection device 15 in-coupling mechanism 16 out-coupling mechanism 16 polarization switch 17 optical component S external laser beam S.sub.1 laser beam in first circulation S.sub.2 laser beam in second circulation S.sub.3 laser beam in third circulation S.sub.4 laser beam in fourth circulation S.sub.n laser beam in n-th circulation