Patent Application
20210119407
This application claims the priority, under 35 U.S.C. § 119, of German patent application DE 10 2019 216 259.2, filed Oct. 22, 2019; the prior application is herewith incorporated by reference in its entirety.
The invention relates to a device to protect laser optics from aging. The invention also relates to a laser system that has laser optics inside or outside a laser resonator that requires protection against aging, and to a method of operating such a laser system.
The term “laser system” is generally used to describe an optical system for generating and optionally guiding, shaping, converting and/or amplifying a laser beam. Such a laser system typically comprises a laser resonator that generates the laser beam and, if applicable, other optical components—which vary depending on the type of laser system.
The term “laser optics” generally refers to a certain optical component intended for use in a laser system—inside or outside the laser resonator—in particular a resonator mirror, an optical amplifier (power amplifier), a semiconductor absorber mirror (SESAM) or a non-linear crystal, such as is used for example for frequency conversion of the laser beam.
In laser systems with medium and high peak intensities, which are used for example for marking and also for cutting, milling or welding work, the laser optics of the respective laser system are regularly exposed to high loads in the beam region and are therefore frequently subject to rapid, localized aging (wear) at the affected locations. In order to delay the need for the replacement of the affected laser components and the associated operating costs as much as possible, locally-worn laser optics, for example resonator mirrors, are sometimes shifted or rotated perpendicularly to the laser beam, so that the point of impact of the laser beam on the laser optics is changed. One challenge in this is the required precision of the adjustment mechanism that must be used for this purpose, because the clearance of the adjustment mechanism required in order to make the adjustment may lead to a misalignment of the laser system and thus to mode instability or other malfunctions of the laser system. As a result, suitable adjustment mechanisms are very cumbersome and expensive.
It is accordingly an object of the invention to provide a method and a device, which overcome the above-mentioned and other disadvantages of the heretofore-known devices and methods of this general type and which enables laser optics to be protected against aging (i.e., wear) caused by the load of the laser beam, in a simple but effective way. The term “protection against aging” herein comprises any measure that delays the aging of the laser optics that would impair or prevent the continued use of the laser optics as a whole, and thus enables a particularly long-term use of the laser optics in a laser system. The term “protection against aging” thus also includes, in particular, those measures that accept local aging (wear) of the laser optics but enable continued use of the laser optics in spite of this local aging.
With the above and other objects in view there is provided, in accordance with the invention, a device for protecting laser optics from aging, the device comprising:
a beam displacement element disposed upstream of the laser optics in a beam travel direction for a parallel displacement or tilting of a laser beam impinging along an optical axis;
an adjusting apparatus coupled to said first beam displacement element and configured for adjusting a position of said beam displacement element or a part thereof in order to change a point of impact of the laser beam on the laser optics.
The laser optics, by way of example, is a resonator mirror, an optical amplifier, a semiconductor absorber mirror, and/or a non-linear crystal.
The laser optics requiring protection is arranged inside a laser resonator (hereinafter “internal laser optics”), for example a resonator mirror or a semiconductor absorber mirror (SESAM), or an optics arranged outside the laser resonator (hereinafter “external laser optics”), for example an optical amplifier or a non-linear crystal.
With the above and other objects in view there is also provided, in accordance with the invention, a method of operating a laser system having laser optics arranged in a beam path of a laser beam, the method comprises variably displacing the laser beam in parallel (by a parallel-shift) or by tilting with a beam displacement element disposed upstream of the laser optics to thereby change a point of impact of the laser beam on the laser optics in order to protect the laser optics from aging.
In other words, the objects of the invention are achieved, according to the invention, by a beam displacement element designed for parallel displacement or tilting of a laser beam inclined along an optical axis is used to change the point of impact of a laser beam on laser optics downstream of the beam displacement element, in order to protect the laser optics from aging. Thus, instead of adjusting the laser optics that require protection, the upstream beam displacement element is adjusted. This has the advantage that the laser optics that require protection do not need to be moved (and are not moved), thus avoiding the risk of misalignment of the laser system associated with adjustability or adjustment of the laser optics. An adjustment apparatus associated with the laser optics is no longer necessary and therefore preferably also not present, so as to save the manufacturing effort associated with such an adjusting apparatus.
The protective device according to the invention comprises a first beam displacement element that is or may be located upstream of the laser optics, which effects a parallel displacement or tilting of a laser beam that is incident along an optical axis. The protective device further comprises a first adjusting apparatus coupled to the first beam displacement element, by means of which the location (i.e. the position and/or orientation) of the first beam displacement element or a part thereof is adjustable, so that the point of impact of the laser beam on the laser optics may be changed.
The laser system according to the invention comprises a laser resonator for generating a laser beam and the above-described protective device.
A substantial advantage of the invention is that the beam displacement element and the associated positioning apparatus may be manufactured with comparatively little difficulty. This is due in particular to the fact that the exact position of the beam displacement element is not critical for the functioning of the laser system. The adjusting apparatus associated with the beam displacement element is therefore not required to have a high level of mechanical precision.
Preferably, the beam displacement element may be rotated about any axis of rotation oriented in any manner relative to the optical axis (for example coaxial, parallel, intersecting or skewed), using the adjusting apparatus. Additionally or alternatively, the beam displacement element may be tilted around a tilt axis arranged perpendicular to the axis of rotation, using the adjusting apparatus.
In a particularly simple and expedient embodiment, the beam displacement element is formed by a plane-parallel transparent plate or a transparent wedge plate that is arranged obliquely to the optical axis. Alternatively, the beam displacement element within the scope of the invention may also be formed by a reflective element, in particular by a pair of mirrors that are plane-parallel or tilted relative to one another.
In order to minimize an undesired influence of the beam displacement element on the polarization of the laser beam, an entry surface of the beam displacement element on which the incident laser beam impinges is preferably furnished with an anti-reflective coating.
In an advantageous embodiment of the invention, in addition to the first beam displacement element described above, a second beam displacement element is furnished that is or may be placed downstream of the laser optics requiring protection. This second beam displacement element is used for parallel displacement or tilting of the laser beam that the laser optics reflect or transmit, so as to compensate for the parallel displacement or tilting of the laser beam caused by the first beam displacement element. The second beam displacement element deflects the laser beam, which was deflected away from the optical axis by the first beam displacement element, in particular back to the optical axis.
The second beam displacement element is preferably adjustable so that position (i.e. the position and/or orientation) of the second beam displacement element tracks an adjustment of the first beam displacement element. The position of the second beam displacement element is thus adjustable (and is adjusted) such that the second beam displacement element always compensates for the parallel displacement or tilting of the laser beam caused by the first beam displacement element, irrespective of the position of the first beam displacement element. In an expedient configuration, for this purpose, the second beam displacement element is likewise coupled with the first adjusting apparatus. For example, the first beam displacement element and the second beam displacement element are mounted on a common shaft of the first adjusting apparatus so that they are rotationally fixed relative to one another but may be rotated together relative to the surrounding space. In an alternative embodiment of the invention, the second beam displacement element is coupled to a second adjusting apparatus (separate from the first adjusting apparatus). The second adjusting apparatus moves the second displacement element to follow any adjustment of the first beam displacement element.
The second beam displacement element is also preferably formed by a plane-parallel transparent plate or a transparent wedge plate, arranged obliquely to the optical axis. Alternatively, within the scope of the invention, the second beam displacement element may also be formed by a reflective element, in particular a pair of plane-parallel or mutually-tilted mirrors. The first beam displacement element and second beam displacement element are preferably similar in design.
During operation of the laser system, the location of the point of impact on the laser optics requiring protection is preferably changed by adjusting the respective beam displacement element or elements when the function of the laser system is impaired by local aging (wear) of the laser optics.
Alternatively, the location of the point of impact is proactively changed at shorter intervals, so that the respective laser optics requiring protection undergo wear uniformly over a longer period of time and over a larger area (relative to the diameter of the laser beam). In particular, the point of impact changes at such brief intervals that there is no discernible wear of the respective laser optics between two changes, or even continuously during operation of the laser system. The proactive, in particular continuous change of the point of impact is preferably used in applications where thermal effects (in particular local overheating) play a significant role in the aging of the laser optics requiring protection, because the proactive movement of the laser beam relative to the laser optics enables effective heat dissipation.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for protecting the laser optics of a laser system against aging, 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.
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.
Parts, elements, and structures that correspond to one another are assigned the same reference signs throughout the drawing figures.
Referring now to the figures of the drawing in detail and first, particularly, to
Deviating from the conventional design, the resonator 2 in
To rotate the plate 22 and thus change the point of impact 18, the protective device 16 comprises an adjusting apparatus 30. In the embodiment shown in
In another variant, not explicitly shown, of the device 16 for protecting the flat end mirror 10, the plane-parallel plate 22 may only be tilted about the tilt axis 36, but is not rotatable about the axis of rotation 24. The plate 22, in this case, is thus mounted to be rotationally fixed with respect to a rotation about either the optical axis 6 or a parallel rotation axis in the resonator 2. In this embodiment, the adjusting apparatus 30 only has the actuator 38, but not the stepping motor 32 and shaft 34.
In the embodiment shown in
In the embodiment shown in
In all the exemplary embodiments described above, the laser beam 6, which is offset in parallel or tilted by the protective device 16, is reflected into itself by the end mirror 10. After reflection in the end mirror 10, the beam thus returns in the same way through the plane-parallel plate 22 or the wedge plate 44. Both end faces of the parallel plate 22 and the two end faces 46 and 48 of the wedge plate 44 thus form entry surfaces for the laser beam 6. In order to prevent the polarization of the laser beam 6 from being influenced by partial reflection at these entry surfaces, the end faces of the parallel plate 22 and the two end faces 46 and 48 of the wedge plate 44 are preferably furnished with a (polarization-independent) anti-reflective coating.
Finally,
The laser system 4 shown in
Likewise analogously to the exemplary embodiment shown in
In addition to the plate 60, the protective device 58 comprises as a second beam displacement element an additional transparent plane-parallel plate 78, in particular made of glass, which is placed downstream of the laser optics 56 and deflects back to the optical axis 8 the laser beam 6 reflected or transmitted by the laser optics 56. This second plate 78 is arranged mirror-symmetrically to the first plate 60 and always tracks a rotation of the first plate 60. For this purpose, the plates 60 and 78 are preferably coupled to one another with the shaft 76 so that they are rotationally fixed, as
Additionally or alternatively to the rotatability described above, in additional variants of the protective device 58 the two plates 60 and 78 may be tilted—analogously to
In order to prevent the polarization of the laser beam 6 from being influenced by partial reflection at the plates 60 and 78, the end faces of these plates 60 and 78 facing toward the resonator 2 (which in turn form entry surfaces for the laser beam 6) are preferably furnished with an anti-reflective coating.
In the operation of the above-described embodiments of the laser system 4, the location of the point of impact 18 or 68 on the end mirror 10 or the external laser optics 56 is preferably changed by adjusting the respective beam displacement elements, i.e. the plane-parallel plates 22, 60 or the wedge plate 44, whenever the function of the laser system 4 is impaired by local aging (wear) of the associated laser optics, i.e. the end mirror 10 or external laser optics 56. Alternatively, for this purpose the respective device 16 or 58 changes the location of the point of impact 18 or 68 of the laser beam 6 on the respective laser optics requiring protection proactively, in particular continuously.
The invention has been made particularly clear in the exemplary embodiments described above, but is not limited thereto. Rather, additional embodiments of the invention may be derived from the claims and the above description.
Following is a list of reference numerals used in the above description and in the drawing figures:
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 216 259 | Oct 2019 | DE | national |
