WO2021083487A1

WO2021083487A1 - Laser system and method for driving a laser system

Info

Publication number: WO2021083487A1
Application number: PCT/EP2019/079424
Authority: WO
Inventors: Wolfgang Braun; Jochen Mannhart
Original assignee: MAX-PLANCK-Gesellschaft zur Förderung der Wissenschaften e.V.
Priority date: 2019-10-28
Filing date: 2019-10-28
Publication date: 2021-05-06

Abstract

The present invention relates to a laser system for providing an application laser beam with adjustable application intensity, the laser system comprising a laser source providing an initial laser beam with an initial intensity and an initial direction, a tunable main beam splitter and a control beam dump. Further, the present invention relates to a method for driving a laser system for providing an application laser beam with a desired application intensity.

Description

LASER SYSTEM AND METHOD FOR DRIVING A LASER SYSTEM

The present invention relates to a laser system for providing an application laser beam with adjustable application intensity, the laser system comprising a laser source providing an initial laser beam with an initial intensity and an initial direc tion, a tunable main beam splitter and a control beam dump. Further, the present invention relates to a method for driving a laser system for providing an application laser beam with a desired application intensity.

Laser systems with beam splitters are well known and widely used in modern technology. High-power lasers, for instance for cutting or welding applications, are designed to operate at or close to their maximum intensity. Hence, modulation of the beam intensity is restricted to change the power in the higher intensity range or to on-off modulate the beam, the latter providing low intensities only time-averaged and hence possibly causing cyclical temperature variations, which may be destruc tive for sensitive applications.

In the new field of thermal laser epitaxy (TLE), laser beams are used to continu ously thermally evaporate and/or sublimate material in a controlled reaction at mosphere for a controlled deposition of these materials on a substrate. Especially, a simultaneous evaporation and/or sublimation of different materials allow a depo sition of multi-component chemical compounds. As different materials may com prise different, in particular even extremely different, vapor pressures, a wide range of different intensities of the laser beams used for evaporation and/or subli mation are needed. In particular, laser intensities both high enough to evaporate and/or sublimate materials with low vapor pressures and corresponding high melt- ing points like for instant tungsten, and laser intensities close to zero for materials with high vapor pressure, respectively, are needed for TLE applications.

In view of the above, it is an object of the present invention, to provide an im proved laser system and an improved method for driving a laser system, which does not have the aforementioned drawbacks of the state of the art. In particular, it is an object of the present invention to provide a laser system and a method for driving a laser system which allows providing at least one application laser beam provided by the laser system with an intensity adjustable over a wide range, in par ticular covering essentially zero intensity to maximum intensity, in an especially easy and cost-efficient way.

This object is satisfied by the patent claims. In particular, this object is satisfied by a laser system according to claim 1 and by a method for driving a laser system according to claim 16. The dependent claims describe preferred embodiments of the invention. Details and advantages described with respect to a laser system according to the first object of the invention also refer to a method according to the second aspect of the invention and vice versa, if of technical sense.

According to a first aspect of the invention, the object is satisfied by a laser system for providing an application laser beam with adjustable application intensity, the laser system comprising a laser source providing an initial laser beam with an ini tial intensity and an initial direction, a tunable main beam splitter and a control beam dump, wherein the initial laser beam impinges on the main beam splitter and is split by the main beam splitter into a transmitted laser beam continuing in the initial direction and a diverted laser beam in a diverted direction different to the initial direction, further wherein the transmitted intensity of the transmitted laser beam can be adjusted by tuning the main beam splitter beam between 0% or at least essentially 0% and 100% or at least essentially 100% of the initial intensity of the initial laser beam, thereby adjusting a ratio of the respective intensities of the transmitted laser beam and the diverted laser beam between at least essentially zero or zero by setting the transmitted intensity of the transmitted laser beam to 0% or at least essentially 0% of the initial intensity of the initial laser beam, and at least essentially infinite or infinite by setting the transmitted intensity of the trans mitted laser beam to 100% or at least essentially 100% of the initial intensity of the initial laser beam, and wherein either the transmitted laser beam is fed into the control beam dump as a control laser beam and the diverted laser beam is used as an application laser beam, or the transmitted laser beam is used as an applica tion laser beam and the diverted laser beam is fed into the control beam dump as a control laser beam.

The principal elements of a laser system according to the present invention are a laser source and a tunable main beam splitter. The laser source provides an initial laser beam with an initial intensity and an initial direction. Preferably, this initial intensity is at least as high as the highest application intensity of an application beam to be provided by the laser system according to the present invention. In particular, in embodiments of a laser system according to the present invention, which provide two or more application beams, preferably the initial intensity is at least as high as the sum of the application intensities of all application beams, more preferably as the product of the highest application intensity times the num ber of application laser beams provided by the laser system according to the pre sent invention. Providing the highest desired application energy can therefore be provided for any combination of application intensities of the application laser beams provided by the laser system according to the present invention.

In the laser system according to the present invention, the initial laser beam im pinges on the main beam splitter and is split into a transmitted laser beam continu ing in the initial direction and a diverted laser beam in a diverted direction different to the initial direction. For instance, the diverted direction can be perpendicular to the initial direction. Especially, this main beam splitter is an adjustable beam split- ter. In other words, the splitting of the initial laser beam into the diverted laser beam and the transmitted laser beam itself can be altered by operating the main beam splitter.

In particular, the main beam splitter is constructed such that the transmitted inten sity of the transmitted laser beam can be adjusted by tuning the main beam splitter between 0% or at least essentially 0% and 100% or at least essentially 100% of the initial intensity of the initial laser beam. In other words, the main beam splitter can be operated between two extreme conditions, whereby in one extreme condi tion, the initial laser beam is completely or at least completely diverted by the main beam splitter, resulting in an intensity of the transmitted laser beam of 0% or at least essentially 0% of the initial intensity, and in the other extreme condition, the initial laser beam is completely or at least completely transmitted through the main beam splitter, resulting in an intensity of the transmitted laser beam of 100% or at least essentially 100% of the initial intensity. Further, the adjustable main beam splitter can be tuned also in conditions between these extreme conditions, for ex ample stepwise, preferably continuous. As a result, the transmitted intensity can be adjusted, preferably continuously adjusted, over a wide range of intensities. Consequently, also the diverted intensity can be adjusted over a wide range of intensities, preferably also from 0% to 100% of the initial intensity. Preferably, the transmitted intensity of the transmitted laser beam and the diverted intensity of the diverted laser beam add up to 100% of the initial intensity of the initial laser beam. All of the above is described relating to an ideal main beam splitter, in which no intensity loss occurs, and is also valid accordingly for a real main beam splitter with small internal intensity loss.

In particular, following the aforementioned features of the main beam splitter, the ratio of the intensities of the transmitted laser beam and the diverted laser beam, respectively, can be adjusted between zero or essentially zero and infinite or es sentially infinite. A ratio of zero can be provided by setting the transmitted intensity of the transmitted laser beam to 0% of the initial intensity of the initial laser beam.

In other words, in the first case, the initial laser beam is completely diverted in the main beam splitter and the diverted intensity of the diverted laser beam reaches its maximum, in particular identical or at least close to the initial intensity of the initial laser beam. In the latter case it is vice versa, the initial laser beam is completely transmitted through the main beam splitter and the transmitted intensity of the transmitted laser beam reaches its maximum, in particular identical or at least close to the initial intensity of the initial laser beam, in other words 100% of the initial intensity. Simultaneously, the diverted intensity is as low as 0% or at least essentially 0% of the initial intensity; hence the ratio of the transmitted intensity to the diverted intensity is infinite or at least essentially infinite.

According to the present invention, either the transmitted laser beam is fed into the control beam dump as a control laser beam and the diverted laser beam is used as an application laser beam, or the transmitted laser beam is used as an applica tion laser beam and the diverted laser beam is fed into the control beam dump as a control laser beam.

In other words, as alternative embodiments of the laser system according to the present invention, both the transmitted laser beam and the diverted laser beam, respectively, can be used as application laser beam. As mentioned before, the diverted laser beam and the transmitted laser beam comprise different directions, preferably directions perpendicular to each other. The alternative usage of both the diverted laser beam and the transmitted laser beam as application laser beam, for instance provides the possibility to adapt the laser system according to the pre sent invention to spatial constraints on the beam path of the laser system itself and of the superordinate system, in which the laser system according to the present invention is integrated. In addition, also the initial and/or application intensity can be considered by choosing the embodiment of the laser system according to the present invention. In cases, in which a high application intensity is needed, prefer- ably the transmitted laser beam is used as application laser beam, as a heat load on the main beam splitter can be reduced by minimizing the amount of laser inten sity to be diverted by the main beam splitter. In the opposite case, in which low application intensities are needed, often accompanied by already a low initial in tensity, an especially accurate provision of the low application intensity can be provided by using the transmitted laser beam as application laser beam.

In summary a laser system according to the present invention is able to provide at least one application laser beam with an intensity adjustable over a wide range, in particular covering essentially zero intensity to maximum intensity. Especially, the main beam splitter of the laser system according to the present invention is capa ble of providing a transmitted laser with a transmitted intensity ranging from 0% or at least essentially 0% to 100% or at least essentially 100% of the initial intensity of the initial laser beam. Hence, this provision of a wide range of application inten sities of the application laser beam can be provided in an especially easy and cost-efficient way. In particular, in a laser system according to the present inven tion, both the diverted laser beam and the transmitted laser beam, respectively, of the main beam splitter can alternatively be used as application laser beam. Hence, spatial and load constraints can be considered in the setup of the laser system according to the present invention.

Further, a laser system according to the present invention can be characterized in that the control beam dump comprises an intensity sensor for measuring the in tensity of the control laser beam. As mentioned above, the initial laser beam is split by the main beam splitter in an application laser beam for further use and a control laser beam fed into a control beam dump. Essentially, the intensity of the control laser beam and the application intensity of the application laser beam add up at least almost to the initial intensity of the initial laser beam. In other words, the intensity sensor of the control beam dump measures the part of the initial intensity not diverted as application laser beam. Hence, the application intensity of the ap- plication laser beam can be derived at least indirectly by subtracting the intensity measured in the control beam dump from the initial intensity of the initial laser beam. Hence, an application laser beam with in particular continuously measured application intensity can be provided. Additionally, also a controlled adjustment of the application intensity by accordingly tuning the main beam splitter can be pro vided.

In addition, a laser system according to the present invention can comprise that the main beam splitter comprises a mirror element with a reflecting area for reflect ing the initial laser beam and an actuator mechanically connected to the reflecting area, whereby the reflecting area can be moved by the actuator between at least a first position and a second position, wherein the reflecting area in its first position is positioned such that the initial laser beam completely misses the reflecting area and wherein the reflecting area in its second position is positioned such that the initial laser beam completely impinges on the reflecting area. A beam splitter com prising a movable mirror element with a reflecting area driven by an actuator is an especially easy way to provide a beam splitter which is capable of adjusting a transmitted intensity of the transmitted laser beam between 0% and 100% of the initial intensity of the initial laser beam. The mirror element can be moved by the actuator between a first and a second position, essentially moving the reflecting area of the mirror element in and out of the initial laser beam. Preferably, the re flecting area is a planar reflecting area. As a tilt of the reflecting area with respect to the initial direction determines the difference between the initial direction and the diverted direction, this difference can also be adjusted easily. In its first posi tion, the reflecting area is positioned such that the initial laser beam completely misses the reflecting area. In other words, no laser light out of the initial laser beam is reflected on the reflecting area and hence the initial laser beam complete ly traverses the main beam splitter as transmitted laser beam, which accordingly comprises a transmitted intensity of at least essentially 100% of the initial intensity. Hence, with the reflecting area in its first position, the ratio of transmitted intensity to diverted intensity is infinite or at least essentially infinite. In contrast to that, in its second position, the reflecting area is positioned such that the initial laser beam completely impinges on the reflecting area. In other words, the initial laser beam is completely reflected on the reflecting area and hence the initial laser beam is fully diverted in the main beam splitter as diverted laser beam, which accordingly com prises a diverted intensity of at least essentially 100% of the initial intensity.

Hence, with the reflecting area in its second position, the ratio of transmitted inten sity to diverted intensity is zero or at least essentially zero.

Preferably, a laser system according to the present invention can be improved by that the reflecting area is moved by the actuator perpendicular or at least essen tially perpendicular to the initial direction. In particular, the movement of the reflect ing area, and additionally of the whole mirror element, can be linear or comprise a rotation around a fixed axis perpendicular to the reflecting plane of the reflecting area. Moving the reflecting area perpendicularly to the initial direction is an espe cially easy way to move the reflecting area in and out of the region occupied by the initial laser beam. Especially, by implementing a movement of the reflecting area perpendicular to the initial direction, the aforementioned tilt of the reflecting area with respect to the initial direction is independent of the actual position of the re flecting area, hence resulting in a constant difference of the initial direction to the diverted direction likewise independent of the of the actual position of the reflecting area.

In a further improved embodiment of a laser system according to the present in vention, the actuator is manually and/or electromechanically and/or pneumatically and/or hydraulically driven. In particular, the actuator can be constructed according to the demands and/or constraints present in the actual laser system. An especial ly flexible laser system with respect to the main beam splitter can therefore be provided. In addition, a laser system according to the present invention can be characterized in that the laser system comprises an optical fiber element with a fiber coupler op tics for guiding the application laser beam and wherein the application laser beam is fed into the fiber coupler optics. In other words, the application laser beam is directed to its destination via the optical fiber element. The main part of the laser system, including at least the laser source and the main beam splitter, can there fore be positioned far away from the actual destination of a usage of the applica tion laser beam, in particular in a different room of even a different building. Spatial constraints in the application of a laser system according to the present invention can therefore be met more easily or even be completely avoided.

According to another embodiment, a laser system according to the present inven tion can be characterized in that the laser system comprises an initial beam split ter, in particular an initial beam splitter at least similarly constructed with respect to the main beam splitter, and an initial beam dump with an intensity sensor, wherein the initial beam splitter is arranged in the path of the initial laser beam to divert a defined fraction of the initial laser beam to the initial beam dump for an at least indirect measurement of the initial intensity of the initial laser beam by the intensity sensor of the initial beam dump. The initial beam splitter can also comprise a mir ror element with a reflecting area moved by an actuator.

Also different embodiments are possible, for instance an optical element with a partially reflecting surface. Especially, the initial beam splitter diverts a defined fraction of the impinging laser beam, namely the initial laser beam, into an initial beam dump equipped with an intensity sensor. In most of the cases, the defined fraction is chosen small, in particular smaller 10¹ , however preferably above the laser threshold to allow stable operation of the laser. By choosing a small defined fraction, a diminution of the initial intensity due to the initial beam splitter can be minimized. By choosing a fraction above the laser threshold, stable and reproduci ble operation of the laser without undesired intensity variations can be achieved. The intensity measurement of the intensity sensor installed in the initial beam dump allows, together with the known defined diverting fraction of the initial beam splitter, to calculate the actual present initial intensity of the initial laser beam. Fluctuations of this initial intensity can therefore be detected and be considered. In the following, the application intensity of the application laser beam can be provid ed with improved stability.

Further, a laser system according to the present invention can be improved by that the initial beam splitter is tunable for adjusting the defined fraction of the initial la ser beam diverted by the initial beam splitter. In other words, the defined fraction of the initial beam splitter can be altered, especially adapted for instance to the initial intensity of the initial laser beam. For instance, with an initial laser beam with high initial intensity, the defined fraction can be lowered. Accordingly, the defined fraction can be set to higher values, when an initial laser beam with low intensity is used. In particular, ideal working conditions for the intensity sensor of the initial beam dump can be provided independent of the initial intensity of the initial laser beam actual present in the laser system according to the present invention.

In addition, a laser system according to the present invention can be further im proved by that the initial beam splitter comprises a locking element to lock an ad justed defined fraction of the initial laser beam diverted by the initial beam splitter. After locking an adjusted defined fraction, an alteration, in particular an accidental alteration, of this defined fraction is not further possible. Calculation errors of the initial intensity caused by an unknowingly altered defined fraction of the initial beam splitter can therefore be avoided. Also, fluctuations of the defined fraction due to unwanted fluctuations or instabilities in the control elements can be avoided in this way.

Further, a laser system according to the present invention can be characterized in that the laser system comprises an application beam splitter, in particular an appli- cation beam splitter at least similarly constructed with respect to the main beam splitter, and an application beam dump with an intensity sensor, wherein the appli cation beam splitter is arranged in the path of the application laser beam to divert a defined fraction of the application laser beam to the application beam dump for an at least indirect measurement of the application intensity of the application laser beam by the intensity sensor of the application beam dump. Similar to the main beam splitter and the initial beam splitter, the application beam splitter can also comprise a mirror element with a reflecting area moved by an actuator. Again, also different embodiments are possible, for instance an optical element with a partially reflecting surface.

Especially, the application beam splitter diverts a defined fraction of the impinging laser beam, namely the application laser beam provided by the main beam splitter, into an application beam dump equipped with an intensity sensor. Analogous to the initial beam splitter, this measurement of the intensity sensor installed in the application beam dump allows, together with the known defined diverting fraction of the application beam splitter, to calculate the actual present application intensity of the application laser beam. Hence, the application intensity of the application laser beam can be adjusted a second time, in particular downstream of the main beam splitter.

For instance, in this embodiment of a laser system according to the present inven tion, the main beam splitter can provide a coarse adjustment of the application intensity of the application laser beam and the subsequently arranged application beam splitter can provide a fine adjustment of the application intensity of the appli cation laser beam. This allows adapting the main splitter and the application split ter for their respective purpose, in particular with respect to the expected intensity range to be covered and/or with respect to the needed adjustment accuracy. Additionally, also based on the measurements of the intensity sensor of the appli cation beam dump, fluctuations of this application intensity can be detected and subsequently be considered. Hence, the application intensity of the application laser beam can be provided with improved stability. All in all, with an application beam splitter, the adjustment of the application intensity of the application laser beam can be improved further.

Further, a laser system according to the present invention can be improved by that the application beam splitter is tunable for adjusting the defined fraction of the ap plication laser beam diverted by the application beam splitter. In other words and analogous to the initial beam splitter, the defined fraction of the application beam splitter can be altered, especially adapted for instance to the desired application intensity of the application laser beam. For instance, even with an unaltered main beam splitter, the application intensity of the final application laser beam can be adjusted using the application beam splitter by accordingly adjusting its defined fraction. Also the aforementioned fine adjustment of the application intensity of the application laser beam can be simplified by providing a tunable application beam splitter.

In addition, a laser system according to the present invention can be further im proved by that the application beam splitter comprises a locking element to lock an adjusted defined fraction of the application laser beam diverted by the application beam splitter. After locking an adjusted defined fraction, an alteration, in particular an accidental alteration, of this defined fraction is not further possible. Calculation errors of the application intensity caused by an unknowingly altered defined frac tion of the application beam splitter can therefore be avoided.

In another embodiment, the laser system according to the present invention can be characterized in that the laser system comprises an examination beam splitter with a fixed splitting ratio and an examination beam dump with an intensity sensor, wherein the examination beam splitter is arranged in the path of the application laser beam to divert a fixed fraction of the application laser beam to the examina tion beam dump for an at least indirect measurement of the application intensity of the application laser beam by the intensity sensor of the examination beam dump. Similar to the initial beam splitter and the application beam splitter, the examina tion beam splitter diverts a fixed and hence defined fraction of the impinging laser beam, namely the application laser beam, into the examination beam dump equipped with an intensity sensor. Hence, the intensity measurement of the inten sity sensor installed in the examination beam dump allows, together with the known fixed splitting ratio of the examination beam splitter, to calculate the actual present application intensity of the initial laser beam.

In contrast to the initial beam splitter and the application beam splitter, the exami nation beam splitter comprises a fixed splitting ratio, in other words, the defined fraction of the impinging laser beam diverted by the examination beam splitter is constant and cannot be altered. In most of the cases, the fixed splitting ratio is chosen small, in particular smaller 10², preferably smaller 10⁴, especially smaller 10⁶. By choosing a small fixed splitting ratio, a diminution of the application inten sity due to the examination beam splitter can be minimized.

The examination beam splitter may be used to provide a control signal to control, adjust and/or stabilize the initial laser power, the initial beam splitter, the applica tion beam splitter or any combination of those, in particular to achieve a stable or exactly defined variation of the actual present application intensity of the applica tion laser beam.

In a further preferred embodiment of a laser system according to the present in vention, the laser system comprises at least one tunable further beam splitter ar ranged in the control laser beam, whereby a fraction of the control laser beam is diverted by the further beam splitter as a further application laser beam, and whereby the further beam splitter is at least similarly constructed with respect to the main beam splitter. Hereby the at least one tunable further beam splitter acts as second main beam splitter, again providing an application laser beam with an adjustable application intensity and a control laser beam with a correspondingly adjustable control intensity.

Especially, also in the application laser beam provided by the at least one further beam splitter, an application beam splitter and/or an examination beam splitter can be positioned. In other words, in this preferred embodiment, the laser system ac cording to the present invention can provide at least two application laser beams, each of them with individually adjustable application intensity. By providing two or more further beam splitters, the number of application laser beams providable by the laser system according to the present invention can be increased further.

Preferably, the laser system according to the present invention can be character ized in that the laser system comprises a control unit, wherein the control unit drives at least one of the tunable beam splitters based on at least one laser beam intensity measured by one of the intensity sensors. By basing the adjustments of the at least one tunable beam splitter on actual measurements of the respective intensity sensors, the control unit can preferably provide a closed loop control of the adjustable application intensity of the application laser beam, resulting in an in particular constant application intensity. In embodiments with at least one further beam splitter, all application laser beams provided by the laser system according to the present invention can be controlled by the control system.

According to a second aspect of the invention, the object is satisfied by a method for driving a laser system according to the first aspect of the invention for providing an application laser beam with a desired application intensity, comprising the following steps: a) Running the laser source at a first initial intensity of the initial laser beam, b) Adjusting the main beam splitter such that the application intensity of the application beam is at least essentially zero or zero, and c) Adjusting the main beam splitter to provide an application laser beam with the desired application intensity.

The method according to the second aspect of the invention is carried out with a suitable laser system according to the first aspect of the invention. Therefore, all advantages described above with respect to the laser system according to the first aspect of the invention can also be achieved by a method for driving this laser sys tem according to the second aspect of the invention.

In a first step a) of the method according to the present invention, the laser source of the laser system according to the present invention is run to provide an initial laser beam at a first initial intensity. In other words, after step a) of the method ac cording to the present invention, the initial laser beam is present in the laser sys tem, comprising a first initial intensity and impinging in an initial direction on the main beam splitter of the laser system according to the first aspect of the present invention.

Further, in the following step b), the main beam splitter is adjusted, in particular to provide an application laser beam with an application intensity of at least essential ly zero or zero. Hence, at the beginning of operation, the application laser is es sentially turned off. Damaging of delicate equipment positioned in the path of the application laser beam can thereby be avoided. As the laser system is constructed according to the first aspect of the present invention, both the diverted laser beam and the transmitted laser beam, respectively, of the main beam splitter can alter natively form the application laser beam.

In particular, steps a) and b) of the method according to the present invention can be carried out simultaneously or even in reversed order, whereby in the latter the adjusting of the main beam splitter is set such that the evanescent intensity of the application laser beam is prepared and will be established after switching on the laser source during step a). In the last step c) of the method according to the present invention, the main beam splitter is adjusted to provide an application laser beam with the desired applica tion intensity. In other words, after step c) of the method according to the present invention, the laser system driven according to a method according to the present invention provides at least one application laser beam with an application intensity adjusted to a desired value. If the laser system according to the first aspect of the invention comprises at least one further beam splitter for providing at least two application laser beams, during step c) also this at least one further beam splitter can likewise be adjusted to adjust the desired application intensity of the corre sponding application laser beam provided by the at least one further beam splitter. Analogous, in embodiments of a laser system according to the first aspect of the invention comprising at least one application beam splitter in the application laser beam, this at least one application beam splitter can also be adjusted during the executing of step c) of the method according to the second aspect of the present invention.

Further, a method according to the present invention can be characterized in that the first initial intensity of the initial laser beam is the maximum intensity providable by the laser source. Hence, as in step b) of the method according to the present invention the intensity of the application laser beam is set at least essentially zero, all or at least almost all intensity of the initial laser beam is provided after the main beam dump as control laser beam. Especially in an embodiment, in which the transmitted laser beam of the main beam dump is used as control laser beam, this can be provided easily. As the laser source already runs at its maximum intensity, in final step c) of the method according to the present invention, it is possible es- pecially easy and fast to adjust the application intensity of the at least one applica tion laser beam to the desired intensity value.

In an alternative embodiment, the method according to the present invention com prises that the first initial intensity of the initial laser beam is the minimal intensity which is providable by the laser source. As at the beginning of the method accord ing to the present invention, especially after step b), the initial laser beam is used completely or at least almost completely as control laser beam and therefore is completely or at least almost completely dumped in the control beam dump, run ning the laser source at its minimal intensity allows to minimize the energy con sumption at the beginning of the operation of the laser system according to the present invention. In addition, also an energy deposit in the main beam splitter can be minimized, especially if the diverted laser beam is used as control laser beam after the main beam splitter.

Further, a method according to the present invention can be improved by that dur ing step c) additionally to the adjustment of the main beam splitter also the initial intensity of the initial laser beam is accordingly increased. In step c) of the method according to the present invention, the main beam splitter is adjusted to provide an application laser beam with the desired application intensity. As at the beginning of an execution of step c) the laser source runs at its minimal intensity, the maximal application intensity is also limited to this minimal intensity. By accordingly increas ing the initial intensity of the initial laser beam while adjusting the main beam split ter, an especially fast way to reach the desired application intensity of the applica tion laser beam can be provided, especially in comparison to a successive adjust ing of the tunable main beam splitter and the intensity of the laser source, respec tively.

In a preferred embodiment of the method according to the present invention, a closed loop control is used for continuously providing the application laser beam at the desired application intensity. In a closed loop control, a permanent evaluation of the intensity of the application beam actually provided by the laser system and the desired application intensity is carried out, and based on that the components, especially the laser source and/or the beam splitters, of the laser system are read justed, if a discrepancy of the measured intensity and the desired intensity ex ceeds a certain threshold. Providing the application laser beam with the actual de sired application intensity can therefore be provided more easily and in particular in a continuous way.

Further, a method according to the present invention can be improved by that the closed loop control uses as input parameter at least one laser beam intensity measured by one of the intensity sensors of the laser system and drives at least one of the tunable beam splitters of the laser system. The laser system preferably comprises at least one tunable beam splitter, for instance used as main beam splitter, as initial beam splitter, as application beam splitter and/or as further beam splitter.

In addition, the laser system also comprises intensity sensors as part of a beam dump, for instance as part of the initial beam dump, as part of the application beam dump, as part of the control beam dump and/or as part of the examination beam dump. Hence, by using the intensity measurements of at least one of the intensity sensors of the laser system as basis for the closed loop control and by driving at least one of the tunable beam splitters based on this data, already exist ing elements of the laser system can be used for the closed loop control. In partic ular, all measured intensities can be used as input parameters and all tunable beam splitters can be driven based on this data by the closed loop control. Provid ing a closed loop control can thereby be provided more easily, additional compo nents for carrying out the closed loop control are not needed or at least a need for additional components is reduced. The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings. There is shown:

Fig. 1 A first embodiment of a laser system according to the present inven tion,

Fig. 2 A second embodiment of a laser system according to the present invention, Fig. 3 A third embodiment of a laser system according to the present inven tion,

Fig. 4 A fourth embodiment of a laser system according to the present in vention,

Fig. 5 A fifth embodiment of a laser system according to the present inven tion,

Fig. 6 A sixth embodiment of a laser system according to the present inven tion, and

Fig. 7 A possible embodiment of an application laser beam of a laser sys tem according to the present invention. In the following, several different possibilities for embodiments of a laser system 100 according to the present invention are described with respect to the drawings. These depicted embodiments are examples and do not limit the embodiments possible with respect to the laser system 100 according to the present invention. Figs. 1 and 2 show two basic embodiments of a laser system 100. Especially, the laser system 100 comprises as major components a laser source 10, a tunable main beam splitter 20, a control beam dump 34, a fiber element 12 equipped with a coupler optics 14 to lead the application laser beam 76 to its final destination and a control unit 16 to provide a closed loop control of the operation of the laser sys tem 100. The control beam dump 34 is equipped with an intensity sensor 60 to provide an intensity measurement of the intensity of the respective control laser beam 78. Especially, the control unit 16 uses the measurement of the intensity sensor 60 to adjust the tunable main beam splitter 20 and hence providing a closed loop control of the laser system 100.

The laser source 10 provides an initial laser beam 70 comprising an initial intensity 80 and an initial direction 90. The initial laser beam 70 impinges on the main beam splitter 20 and is subsequently divided in the main beam splitter 20 into a transmit ted laser beam 72 continuing in the initial direction 90 and a diverted laser beam 74 diverted by the main beam splitter 20 in a diverted direction 92 different, prefer ably perpendicular, to the initial direction 90.

Especially, the main beam splitter 20 comprises an actuator 40 connected to a reflecting area 44 of a mirror element 42. The actuator 40 is manually and/or elec- tromechanically and/or pneumatically and/or hydraulically driven. Hence, the actu ator 40 can move the reflecting area 44 to adjust the fraction, with which the initial laser beam 70 and its intensity 80 is diverted in the main beam splitter 20 into the diverted laser beam 74. In particular, the reflecting area 44 can be moved by the actuator 40 between a first position 46 a second position 48, in particular moved perpendicularly or at least essentially perpendicularly to the initial direction 90. Preferably, the movement of the reflecting area 44, and additionally of the whole mirror element 42, can be linear or comprise a rotation around a fixed axis per pendicular to the reflecting plane of the reflecting area 44. Hereby, the reflecting area 44 in its first position 46 is positioned such that the ini tial laser beam 70 completely misses the reflecting area 44 and hence the initial laser beam 70 is not diverted at all in the main beam splitter 20 and continues as transmitted laser beam 72.

Complementary, the reflecting area 44 in its second position 48 is positioned such that the initial laser beam 70 completely impinges on the reflecting area 44 and hence the initial laser beam 70 is completely diverted in the main beam splitter 20 and continues as diverted laser beam 74. This provides the main beam splitter 20 as a tunable main beam splitter 20, whereby the transmitted intensity 82 of the transmitted laser beam 72 can be adjusted by tuning the main beam splitter 20 between 0% or at least essentially 0% and 100% or at least essentially 100% of the initial intensity 80 of the initial laser beam 70. Hence, by accordingly adjusting the main beam splitter 20, a ratio of the respective intensities 82, 84 of the trans mitted laser beam 72 and the diverted laser beam 74 can be set between at least essentially zero or zero by setting the transmitted intensity 82 of the transmitted laser beam 72 to 0% or at least essentially 0% of the initial intensity 80 of the initial laser beam 70, and at least essentially infinite or infinite by setting the transmitted intensity 82 of the transmitted laser beam 72 to 100% or at least essentially 100% of the initial intensity 80 of the initial laser beam 70.

A movement direction of the reflecting areas 44 shown in Fig. 1 and 2 is perpen dicular to the plane of projection. Nevertheless, the reflecting area 44 depicted in Fig. 1 is assumed to be in its first position 46, and the respective reflecting area 44 depicted in Fig. 2 is assumed to be in its second position 48. Hence, in Fig. 1 the transmitted laser beam 72 has its maximum transmitted intensity 82 and comple mentary in Fig. 2 the diverted laser beam 74 has its maximum diverted intensity 84. This is due to the fact that in Fig. 1 and 2 two different basic embodiments of a laser system 100 according to the present invention are shown, both at the begin ning of their respective operation. In Fig. 1 , the diverted laser beam 74 is used as application laser beam 76 and the transmitted laser beam 72 is used as control laser beam 78, respectively. As the laser system 100 is shown at the beginning of its operation, the laser source 10 is already running and provides the initial laser beam 70 in a first initial intensity 80. With the reflecting area 44 in its first position 46, the initial laser beam 70 com pletely misses the reflecting area 44 and therefore the transmitted laser beam 72 essentially corresponds to the initial laser beam 70 and impinges as control laser beam 78 onto the control beam dump 34. As there is no or at least essentially no interaction of the initial laser beam 70 with the main beam splitter 20, as first initial intensity 80 of the initial laser beam 70 the maximal intensity which is providable by the laser source 10 can be used. In the next step, the reflecting area 44 can be moved by the actuator into the initial laser beam 70 and hence increase the frac tion of the initial laser beam 70 diverted in the main beam splitter 20. By this, the main beam splitter 20 can be adjusted to provide an application laser beam 76 with the desired application intensity 86.

In contrast to that, in the embodiment of the laser system depicted in Fig. 2, the transmitted laser beam 72 is used as application laser beam 76 and the diverted laser beam 74 is used as control laser beam 78, respectively. Again, the laser sys tem 100 is shown at the beginning of its operation, the laser source 10 is already running to provide the initial laser beam 70 in a first initial intensity 80. With the reflecting area 44 in its second position 48, the initial laser beam 70 completely impinges on the reflecting area 44 and therefore the diverted laser beam 74 es sentially corresponds to the initial laser beam 70 and impinges as control laser beam 78 onto the control beam dump 34.

To avoid an unnecessary high stress of the components of the main beam splitter 20, as first initial intensity 80 of the initial laser beam 70 the minimal intensity which is providable by the laser source 10 can be used. Opposite to Fig. 1, in the next step, the reflecting area 44 can be moved by the actuator out of the initial la ser beam 70 and hence increase the fraction of the initial laser beam 70 transmit ted in the main beam splitter 20. By this, the main beam splitter 20 can be adjust ed to provide a transmitted laser beam 72 as an application laser beam 76 with the desired application intensity 86. In addition and additionally to the adjustment of the main beam splitter 20, also the initial intensity 80 of the initial laser beam 70 can be accordingly increased.

In summary, Fig. 1 and 2, respectively, depict two embodiments of a laser system 100 according to the present invention at the beginning of its operation. Hence the laser source 10 is already running and provides the initial laser beam 70 in a first initial intensity 80. To provide an application laser beam 74 with zero or at least zero application intensity 86, in the embodiment of a laser system 100 according to the present invention shown in Fig. 1, the reflecting area 44 is positioned in its first position 46, and hence the impinging initial laser beam 70 completely misses the reflecting area 44 of the initial beam splitter 20. In contrast to that, in the re spective embodiment shown in Fig. 2, the reflecting area 44 is positioned in its second position 48 and hence the initial laser beam 70 is fully diverted in the initial beam splitter 20. Starting from this respective position 46, 48, the application in tensity 86 of the respective application laser beam 76 can be adjusted over a wide range, starting from zero to a maximum value up to the initial intensity 80 of the initial laser beam 70.

Fig. 3 shows an improved embodiment of the laser system 100 already shown and described in detail with respect to Fig. 1, herewith referred to. In addition, in the respective embodiment depicted in Fig. 3 in the path of the initial laser beam 70 an initial beam splitter 22 is positioned. The initial beam splitter 22 can be at least similarly constructed with respect to the main beam splitter 20. In particular, the initial beam splitter 22 also is tunable and comprises an actuator 40. A small frac tion, for instance 10⁶ or smaller, of the initial laser beam 70 is diverted in the initial beam splitter 22 and is fed as diverted laser beam 74 into an initial beam dump 30 equipped with an intensity sensor 60. The initial beam splitter 22 further comprises a locking element 50 to lock the adjusted fraction. In other words, the intensity measurement of the intensity sensor 60 in the initial beam dump 30 allows to at least indirectly measure the initial intensity 80 of the initial laser beam 70. Provid ing the application laser beam 76 with the desired application intensity 86 can therefore be provided more easily. Analogous, the aforementioned initial beam splitter 22 can also be positioned in the initial laser beam 70 of the embodiment of the laser system 100 according to the present invention depicted in Fig. 2.

In Fig. 4, another possible improvement of the embodiment of the laser system 100 shown in Fig. 1 is depicted. Again, on the respective description with respect to the elements of the laser system 100 already shown and described in detail with respect to Fig. 1 is herewith referred. In addition, in the embodiment of Fig. 4, a further beam splitter 28 is positioned in the transmitted laser beam 72 after the main beam splitter 20. The further beam splitter 28 also comprises an actuator 40 and is constructed similarly to the main beam splitter 20, thereby also providing a transmitted laser beam 72 and a diverted laser beam 74, whereby the diverted laser beam 74 of the further beam splitter 28 is also used as application laser beam 76. The transmitted laser beam 72 of the further beam splitter 28 is used as control laser beam 78 of the whole laser system 100.

In other words, by comprising a further beam splitter 28, the laser system 100 ac cording to the present invention can provide also an additional application laser beam 76 with an individually adjustable application intensity 86. Especially, be tween the main beam splitter 20 and the depicted further beam splitter 28, one or even several additional further beam splitters 28 can be positioned, indicated by the dotted part of the transmitted laser beam 72 between the main beam splitter 20 and the further beam splitter 28, respectively. Flence, a plurality of application laser beams 76, each with individually adjustable application intensity, can be pro vided in an accordingly constructed laser system 100 according to the present in- vention. Analogous, the aforementioned further beam splitter(s) 22 can also be positioned in the control laser beam 78 of the embodiment of the laser system 100 according to the present invention depicted in Fig. 2.

Also the embodiment of the laser system 100 depicted in Fig. 5 is based on the embodiment already shown and described with respect to Fig. 1 , herewith referred to. Additionally, in the respective embodiment of Fig. 5, an additional application beam splitter 24 is arranged in the diverted laser beam 74 originating from the main beam splitter 20, later on used as application laser beam 76. In the depicted embodiment of the laser system 100 according to the present invention, the appli cation beam splitter 24 is tunable and constructed at least similarly to the main beam splitter 20, namely the application beam splitter 24 also comprises an actua tor 40 and internally a mirror element with a reflecting area driven by the actuator 40.

Further, an application beam dump 32, equipped with an intensity sensor 60, is positioned such that a diverted laser beam 74 of the application beam splitter 32 is received by the application beam dump 32. The application beam splitter 24 di verts a defined fraction of the application laser beam 76 to an application beam dump 32 for an at least indirect measurement of the application intensity 86 of the application laser beam 76 by the intensity sensor 60 of the application beam dump 32. Flence, additionally to the adjustment of the application intensity 86 provided by the main beam splitter 20, the application intensity 86 of the application laser beam 76 can be adjusted a second time, in particular downstream of the main beam splitter 20.

For instance, the main beam splitter 20 can provide a coarse adjustment of the application intensity 86 of the application laser beam 76 and the subsequently ar ranged application beam splitter 24 can provide a fine adjustment of the applica tion intensity 86 of the application laser beam 76. This allows adapting the main splitter 20 and the application splitter 24 for their respective purpose, in particular with respect to the expected intensity range to be covered and/or with respect to the needed adjustment accuracy. In addition and similar to the aforementioned initial beam splitter 22 (see Fig. 3), the application beam splitter 24 comprises a locking element 50 to lock an adjusted defined fraction of the application laser beam 76 diverted by the application beam splitter 24. After locking an adjusted defined fraction, an alteration, in particular an accidental alteration, of this defined fraction is not further possible. Hence calculation errors of the application intensity 86 caused by an unknowingly altered defined fraction of the application beam split ter 24 can be avoided.

Fig. 6 shows an embodiment of the laser system 100 according to the present in vention, in which the features already depicted in Fig. 4 and 5 are combined. In particular, in the present embodiment, the laser system 100 comprises both a plu rality of further beam splitters 28, likewise resulting in a plurality of application la ser beams 76 with individually adjustable application intensities 86, and in each of the application beams 76 an application beam splitter 24 for a fine adjustment of the application intensities 86, respectively. For detailed description of the respec tive features please refer to the respective description above with respect to Figs.

4 and 5.

In Fig. 7 an examination beam splitter 26 is depicted, arranged in the application laser beam 76 of the laser system 100 according to the present invention. In this embodiment, the application laser beam 76 is provided as diverted laser beam 74 of an application beam splitter 24 as for instance already shown and described above with respect to Fig. 5. The examination beam splitter 26 diverts a fixed frac tion of the application laser beam 76 to an examination beam dump 36 equipped with an intensity sensor 60 for an at least indirect measurement of the application intensity 86 of the application laser beam 76. In contrast to the application beam splitter 24, the examination beam splitter 26 comprises a fixed splitting ratio, in other words, the defined fraction of the impinging application laser beam 76 divert ed by the examination beam splitter 26 is constant and cannot be altered. In most of the cases, the fixed splitting ratio is chosen small, in particular smaller 10², preferably smaller 10⁴, especially smaller 10⁶. By choosing a small fixed splitting ratio, a diminution of the application intensity 86 due to the examination beam splitter 24 can be minimized.

List of reference numerals

10 laser source

12 fiber element

14 coupler optics

16 control unit

20 main beam splitter

22 initial beam splitter

24 application beam splitter 26 examination beam splitter 28 further beam splitter

30 initial beam dump

32 application beam dump

34 control beam dump

36 examination beam dump

40 actuator

42 mirror element

44 reflecting area

46 first position

48 second position

50 locking element

60 intensity sensor

70 initial laser beam

72 transmitted laser beam 74 diverted laser beam 76 application laser beam 78 control laser beam 80 initial intensity

82 transmitted intensity

84 diverted intensity 86 application intensity 90 initial direction

92 diverted direction

100 laser system

Claims

1. Laser system (100) for providing an application laser beam (76) with adjust able application intensity (86), the laser system (100) comprising a laser source (10) providing an initial laser beam (70) with an initial intensity (80) and an initial direction (90), a tunable main beam splitter (20) and a control beam dump (34), wherein the initial laser beam (70) impinges on the main beam splitter (20) and is split by the main beam splitter (20) into a transmitted laser beam (72) continuing in the initial direction (90) and a diverted laser beam (74) in a di verted direction (92) different to the initial direction (90), further wherein the transmitted intensity (82) of the transmitted laser beam (72) can be adjusted by tuning the main beam splitter (20) between 0% or at least essentially 0% and 100% or at least essentially 100% of the initial intensity (80) of the initial laser beam (70), thereby adjusting a ratio of the respective intensities (82, 84) of the trans mitted laser beam (72) and the diverted laser beam (74) between at least essentially zero or zero by setting the transmitted intensity (82) of the transmitted laser beam (72) to 0% or at least essentially 0% of the initial in tensity (80) of the initial laser beam (70), and at least essentially infinite or infinite by setting the transmitted intensity (82) of the transmitted laser beam (72) to 100% or at least essentially 100% of the initial intensity (80) of the initial laser beam (70), and wherein either the transmitted laser beam (72) is fed into the control beam dump (34) as a control laser beam (78) and the diverted laser beam (74) is used as an application laser beam (76), or the transmitted laser beam (72) is used as an application laser beam (76) and the diverted laser beam (74) is fed into the control beam dump (34) as a control laser beam (78).

2. Laser system (100) according to claim 1 , wherein the control beam dump (34) comprises an intensity sensor (60) for measuring the intensity of the control laser beam (78).

3. Laser system (100) according to one of the preceding claims, wherein the main beam splitter (20) comprises a mirror element (42) with a reflecting area (44) for reflecting the initial laser beam (70) and an actuator (40) mechanically connected to the reflecting area (44), whereby the reflect ing area (44) can be moved by the actuator (40) between at least a first po sition (46) and a second position (48), wherein the reflecting area (44) in its first position (46) is positioned such that the initial laser beam (70) com pletely misses the reflecting area (44) and wherein the reflecting area (44) in its second position (48) is positioned such that the initial laser beam (70) completely impinges on the reflecting area (44).

4. Laser system (100) according to claim 3, wherein the reflecting area (44) is moved by the actuator (40) perpendicular or at least essentially perpendicular to the initial direction (90).

5. Laser system (100) according to claim 3 or 4, wherein the actuator (40) is manually and/or electromechanically and/or pneumatically and/or hydraulically driven.

6. Laser system (100) according to one of the preceding claims, wherein the laser system (100) comprises an optical fiber element (12) with a fiber coupler optics (14) for guiding the application laser beam (76) and wherein the application laser beam (76) is fed into the a fiber coupler optics (14).

7. Laser system (100) according to one of the preceding claims, wherein the laser system (100) comprises an initial beam splitter (22), in particular an initial beam splitter (22) at least similarly constructed with re spect to the main beam splitter (20), and an initial beam dump (30) with an intensity sensor (60), wherein the initial beam splitter (22) is arranged in the path of the initial laser beam (70) to divert a defined fraction of the initial la ser beam (70) to the initial beam dump (30) for an at least indirect meas urement of the initial intensity (80) of the initial laser beam (70) by the inten sity sensor (60) of the initial beam dump (30).

8. Laser system (100) according to claim 7, wherein the initial beam splitter (22) is tunable for adjusting the defined frac tion of the initial laser beam (70) diverted by the initial beam splitter (22).

9. Laser system (100) according to claim 8, wherein the initial beam splitter (22) comprises a locking element (50) to lock an adjusted defined fraction of the initial laser beam (70) diverted by the initial beam splitter (22).

10. Laser system (100) according to one of the preceding claims, wherein the laser system (100) comprises an application beam splitter (24), in particular an application beam splitter (24) at least similarly constructed with respect to the main beam splitter (20), and an application beam dump (32) with an intensity sensor (60), wherein the application beam splitter (24) is arranged in the path of the application laser beam (76) to divert a defined fraction of the application laser beam (76) to the application beam dump (32) for an at least indirect measurement of the application intensity (86) of the application laser beam (76) by the intensity sensor (60) of the applica tion beam dump (32).

11. Laser system (100) according to claim 10, wherein the application beam splitter (24) is tunable for adjusting the de fined fraction of the application laser beam (76) diverted by the application beam splitter (24).

12. Laser system (100) according to claim 11 , wherein the application beam splitter (24) comprises a locking element (50) to lock an adjusted fraction of the application laser beam (76) diverted by the application beam splitter (24).

13. Laser system (100) according to one of the preceding claims, wherein the laser system (100) comprises an examination beam splitter (26) with a fixed splitting ratio and an examination beam dump (36) with an in tensity sensor (60), wherein the examination beam splitter (26) is arranged in the path of the application laser beam (76) to divert a fixed fraction of the application laser beam (76) to the examination beam dump (36) for an at least indirect measurement of the application intensity (86) of the applica tion laser beam (76) by the intensity sensor (60) of the examination beam dump (36).

14. Laser system (100) according to one of the preceding claims, wherein the laser system (100) comprises at least one tunable further beam splitter (28) arranged in the control laser beam (78), whereby a fraction of the control laser beam (78) is diverted by the further beam splitter (28) as a further application laser beam (76), and whereby the further beam splitter (28) is at least similarly constructed with respect to the main beam splitter (20).

15. Laser system (100) according to one of the claims 2 to 14, wherein the laser system (100) comprises a control unit (16), wherein the control unit (16) drives at least one of the tunable beam splitters (20, 22, 24, 28) based on at least one laser beam intensity (80, 82, 84, 86) measured by one of the intensity sensors (60).

16. A method for driving a laser system (100) according to one of the preceding claims for providing an application laser beam (76) with a desired applica tion intensity (86), comprising the following steps: a) Running the laser source (10) at a first initial intensity (80) of the ini tial laser beam (70), b) Adjusting the main beam splitter (20) such that the application inten sity (86) of the application beam is at least essentially zero or zero, and c) Adjusting the main beam splitter (20) to provide an application laser beam (76) with the desired application intensity (86).

17. A method according to claim 16, wherein the first initial intensity (80) of the initial laser beam (70) is the max imum intensity providable by the laser source (10).

18. A method according to claim 16, wherein the first initial intensity (80) of the initial laser beam (70) is the min imal intensity which is providable by the laser source (10).

19. A method according to claim 18, wherein during step c) additionally to the adjustment of the main beam split ter (20) also the initial intensity (80) of the initial laser beam (70) is accord ingly increased.

20. A method according to one of the claims 16 to 19, wherein a closed loop control is used for continuously providing the applica tion laser beam (76) at the desired application intensity (86).

21. A method according to claim 20, wherein the closed loop control uses as input parameter at least one laser beam intensity (80, 82, 84, 86) measured by one of the intensity sensors (60) of the laser system (100) and drives at least one of the tunable beam splitters (20, 22, 24, 28) of the laser system (100).