EP1891718A1

EP1891718A1 - Laser system comprising several longitudinally pumped laser-active solid bodies

Info

Publication number: EP1891718A1
Application number: EP06754248A
Authority: EP
Inventors: Malte Kumkar
Original assignee: Trumpf Laser GmbH
Current assignee: Trumpf Laser GmbH
Priority date: 2005-06-10
Filing date: 2006-06-09
Publication date: 2008-02-27
Also published as: WO2006131385A1; US7542501B2; DE102005028131A1; US20080175296A1

Abstract

The aim of the invention is to obtain the optimum possible power yield for a laser system comprising a guide assembly (10) for a laser radiation field, the latter (16) extending through said assembly. The assembly comprises at least one laser-active solid body (20), which is penetrated by the resonator radiation field (16), a pump radiation guide assembly (60), which splits the pump radiation (64) into a first and a second partial radiation field (82, 84) and which feeds the first partial radiation field (82) into the solid body (20) via one end face (24) and the second partial radiation field (84) via the other end face (26) in a longitudinal direction. To achieve this aim, the laser radiation field (16) penetrates at least two laser-active solid bodies (20) consisting of an identical material and positioned in succession along the radiation axis (18) of said field, the pump radiation guide assembly (60) is configured in such a way that it feeds the first partial radiation field (82) and the second partial radiation field (84) into each of the solid bodies (20) and the pump radiation guide assembly (60) is configured in such a way that the pump power that is fed into each of the two or more solid bodies (20) by the two partial radiation fields (82, 84) can be adjusted in such a way that the effects of the thermal lenses (130), which are generated by the pump power in each of the two or more solid bodies (20), on the laser radiation field (16) are essentially identical.

Description

LASER SYSTEM WITH SEVERAL LONGITUDINAL PUMPED LASER ACTIVE SOLID BODIES

The invention relates to a laser system comprising a laser radiation field guide, in which extends a laser radiation field, at least one laser active field penetrated by the laser radiation field, extending in the direction of a longitudinal axis between two opposite end faces solid, a pump radiation source for generating pump radiation to the optical Pumping the laser-active solid, a pump radiation guide, which divides the pump radiation for pumping the solid in a first and a second partial radiation field, and which couples the first partial radiation field via the one end surface and the second partial radiation field via the other end surface in the longitudinal direction in the solid.

Such laser systems are known for example from DE 196 03 704 Al.

Such longitudinal pumping arrangements make it possible to keep the pumping power per end face, which can be coupled in by the end face, below the damage threshold, but the available power in such laser systems is limited.

The invention is therefore based on the object to obtain a stable as possible working laser system with the highest possible performance. This object is achieved in a laser system of the type described above according to the invention> that the laser radiation field passes through at least two successively arranged in the direction of its beam axis laser active solid material of identical material that the pump radiation guide is designed such that this in each of the solid first partial radiation field is coupled via the one end surface and the second partial radiation field via the other end surface and that the pump radiation guide is designed such that a pumping power coupled into each of the at least two solids can be adjusted such that the effects of the pump power in each the thermal lenses produced on the laser radiation field are substantially identical to the at least two solid bodies.

The advantage of the solution according to the invention is to be seen in that it offers a simple possibility of increasing the performance through the use of two or more solids, wherein at the same time despite using a plurality of solids stable operation of the laser system, in particular in a fundamental mode, is possible.

This stable operation of the laser system is achieved by the effect of the thermal lenses generated by the pump powers in each of the at least two solids on the laser radiation field being substantially identical, the beam quality of the laser radiation field, and thus also the beam quality of the decoupled output beam does not adversely affect. Furthermore, the advantage of the solution according to the invention is also to be seen in the fact that changes in the pump radiation source, in terms of wavelength or power, which is always to be expected especially when the pump radiation source is a laser diode or laser diodes, substantially not negatively affect the beam quality of the laser Radiation field, since they occur in each of the at least two forming thermal lenses in the same way and thus do not lead to a disturbance of the symmetries in the laser radiation field.

A particularly favorable solution provides that the partial radiation fields are coupled into the latter substantially parallel to the longitudinal axis of the respective solid, so that only the best possible coupling of the pumping power takes place due to the partial radiation fields.

It is particularly advantageous if the partial radiation fields are coupled into the latter in a manner substantially symmetrical to the beam axis within the respective solid body.

Such a solution makes it possible to achieve an undisturbed in the rotational symmetry to the beam axis excitation of the solid and thus a corresponding undisturbed amplification of the laser radiation field already on the optical pumping of the respective solid.

In order to achieve the same possible excitation conditions in all solids, it is preferably provided that the first partial radiation fields in each of the respective solids have a substantially identical radiation field form. Furthermore, it is provided that the second partial radiation fields in each of the respective solids have a substantially identical radiation field form.

Thus, it is not absolutely necessary that the radiation field shapes of the first and the second partial radiation field are identical. It is in principle sufficient if the first radiation field shapes and the second radiation field shapes are identical to each other.

With regard to the formation of the lens effect of the thermal lens that is as similar as possible, it is particularly favorable if the sum of the pump powers coupled into the respective solid body by the two partial radiation fields is approximately the same in each of the solids.

This feature means that it is primarily the sum of the pump powers that is present in each solid that determines the thermal lensing effect in a first approximation. How this sum of pumping power is composed can vary in principle in each of the solids.

It is advantageous, in particular, if in each of the solid bodies the first partial radiation fields are substantially identical in terms of their pumping power, in particular with respect to their spatial distribution of the pumping power.

Furthermore, it is favorable if, in each of the solid bodies, the second partial radiation fields are substantially identical in terms of their pumping power, in particular with respect to their spatial distribution of the pumping power. A solution which is expedient with regard to the spatial distribution of the pumping power provides that the first and the second partial radiation field in each of the solids extend essentially mirror-symmetrically to an approximately central mirror plane of the solid in order to obtain the highest possible symmetry in the optical pumping of the solid.

A particularly favorable solution provides that the ratio of the pumped power injected from the first partial radiation field to the pumped-in power from the second partial radiation field is substantially the same in each of the solid bodies, since then even with a power loss of one partial radiation fields, for example due to power loss of the pumping radiation source supplying the same , the ratio of the thermal lenses in the solids remains with each other. It is particularly advantageous if each of the two partial radiation fields entering each of the solids couples into this approximately the same pump power in order to achieve the most uniform possible ratios in the optical pumping of the solids.

With regard to the polarization of the partial radiation fields, no further details were given in connection with the previous exemplary embodiments. Thus, one solution provides that the first and the second partial radiation field have a defined relative polarization in each of the solids.

It is particularly favorable if both partial radiation fields have the same polarization in each of the solids. In particular, the polarization of the partial radiation fields can thus be adapted to a preferred direction of the polarization in the solid state. With regard to the available pump radiation, no further details were given. The conditions according to the invention can be achieved in a particularly simple manner if the first partial radiation field originates from a pump radiation source for each solid arranged in the laser radiation field guidance.

Furthermore, it is advantageous if the second partial radiation field also originates from a pump radiation source for each solid arranged in the laser radiation field guidance.

In principle, it would be conceivable to provide two different pump radiation sources for the first and the second partial radiation field.

Another advantageous solution provides that the two partial radiation fields entering the respective solid body originate from the same pump radiation source. This does not necessarily mean that the partial radiation fields entering each of the solid bodies must originate from the same pump radiation source, but that this condition must be satisfied only for each one of the solids.

For example, it would be conceivable in such a solution that the two partial radiation fields originate from the same pump radiation source for at least two of the solids and, for example, another pump radiation source is provided for a further two of the solids.

Another solution provides that the laser system has two pump units, each of which pumps at least two solids with partial radiation fields from the same pump radiation source. However, it is particularly favorable if all partial radiation fields coupled into the at least two solids originate from a single pump radiation source.

With regard to the generation of the individual partial radiation fields, no further details were given in connection with the exemplary embodiments described so far. In principle, the distribution of the pump radiation into different partial radiation fields can take place, for example, via partially transparent mirrors.

It is particularly advantageous, however, if the division of the pump radiation into partial radiation fields via polarizers with polarization-dependent transmission and reflection, as by a simple division of a pump radiation field in partial radiation fields can be achieved and on the other hand in a simple manner the degree of division on the individual partial radiation fields adjustable is.

A further advantageous solution provides that the adjustable division of the pump power into the partial radiation fields via the relative adjustment between a polarizer with polarization-dependent transmission and reflection and an adjustable polarisationsbeeinflussenden element.

With regard to the nature of the optimal coupling of the partial radiation fields into the respective solids, no further details have so far been given. Thus, an advantageous solution provides that the partial radiation fields are coupled via folding mirrors of the resonator in the respective solid state. Furthermore, in connection with the previous explanation of the individual embodiments, no further details about the formation of the solid as such have been made. Thus, an advantageous solution provides that the at least two solids are formed identically.

Since in some solids the formation of the thermal lens is not the only effect occurring by the optical pumping, but rather an astigmatism caused by the thermal lens may occur, it is preferably provided that the at least two solids are arranged relative to the laser radiation field such that that a compensation of a condition caused by the respective thermal lens astigmatism takes place. An astigmatism can be due to a preferred direction in the solid state, a specific cooling geometry or a specific pumping professional! be conditional.

The compensation of the astigmatism merely means that the effects of the astigmatism, insofar as they lead to a deviation of the laser radiation field from a rotationally symmetrical to the beam axis cross-sectional shape, are compensated, so that the resonator has a substantially rotationally symmetrical to the beam axis cross-sectional shape.

Such a compensation of the astigmatism can in principle also take place in the coupling of several solids.

With regard to a simple solution according to the invention for

Compensation of the astigmatism of thermal lenses, it has proved to be advantageous if two of the solid state a compensation pair form and when the two solids are arranged relative to the laser radiation field such that a compensation of the conditional by the respective thermal lens astigmatism takes place.

It is particularly favorable if the solids of a compensation pair with the main axes of the astigmatism are rotated by 90 ° relative to one another. The major axes of astigmatism may be due to the pumping profile, the cooling geometry or the crystal geometry in the solid state.

Furthermore, it is provided for optimal optical excitation of such solid body, that the polarization direction of the laser radiation field is adapted to a major axis of polarization of the respective solid, so that the effects caused by the astigmatism in the same manner in the section of the laser radiation passing through the respective solid - enter field.

Expediently, the polarization direction of the laser radiation field is aligned parallel to the main axis of the polarization of the respective solid.

A solution particularly suitable with regard to the compensation of astigmatism provides that the solid bodies of a compensation pair are rotated with their main axes of polarization rotated by 90 ° relative to one another, so that in a simple manner the effects of the astigmatism of the thermal lens with respect to their deviation from one to Beam axis of the laser radiation field rotationally symmetric cross-sectional shape can be compensated. Appropriately, in such a solution, each solid is pumped through a first and a second partial radiation field whose polarization direction is aligned parallel to the main axis of the polarization of the respective solid.

However, there are not only solids in which astigmatism is added in addition to the effect of the thermal lens, but also solid bodies in which birefringence caused by the same occurs in addition to the thermal lens.

For this reason, it is expediently provided in a further advantageous embodiment that the at least two solids are aligned relative to the laser radiation field such that a compensation of a birefringence caused by the respective thermal lens takes place.

Also in such a case it is expediently provided that in each case two of the solids form a compensation pair and that the two solids are arranged relative to the laser radiation field such that a compensation of the respective thermal lens and the birefringence takes place.

Also in this case, the birefringence is compensated only to the extent that the birefringence leads to deviations of a structure of the laser radiation field that is rotationally symmetrical with respect to the beam axis and the polarization state uniform over the beam cross section, so that the birefringence caused by the respective thermal lens is compensated to understand that their impact on one to the beam axis rotationally symmetrical structure of the laser radiation field and a uniform over the beam cross-section polarization state can be compensated.

Preferably, it is provided that the polarization directions of the laser radiation field in one of the solid bodies are rotated by 90 ° relative to the polarization directions of the amplifier radiation field in the other of the solids.

In the solution according to the invention, there is the possibility that the laser radiation field guidance is integrated in a resonator, so that the laser radiation field represents a resonator radiation field.

However, it is also conceivable to form a subarea of the laser radiation field guidance, for example comprising one or two of the plurality of solids, as a resonator with a resonator radiation field forming and the remaining part of the laser radiation field guidance for amplifying the laser radiation from the resonator with an amplifier radiation field.

Further features and advantages of the invention are the subject of the following description and the drawings of some embodiments.

In the drawing show:

Figure 1 is a schematic representation of a first embodiment of a laser system according to the invention with the formation of thermal lenses in the solids. Fig. 2 is a schematic representation of the effects of in the

Solid-state-forming thermal lenses in the first embodiment;

3 is a schematic representation similar to FIG. 2 of a variant of the first embodiment, comprising a resonator radiation field and an amplifier radiation field;

4 is a schematic representation of a second embodiment of a laser system according to the invention with more than two solids;

5 is a schematic representation of a third embodiment of a laser system according to the invention with more than two solids;

6 is a schematic representation of a fourth embodiment of a laser system according to the invention with more than two solids;

7 is a schematic representation of the first embodiment with additional representation of a compensation of a caused by the thermal lensing astigmatism and

Fig. 8 is a schematic representation similar to Figure 5 of the first embodiment in the case of a compensation of a caused by the thermal lens birefringence. A first exemplary embodiment of a laser amplifier system according to the invention, illustrated in FIG. 1, comprises a resonator designated as a whole by 10 and representing a laser radiation field guide, which has a first end mirror 12 and a second end mirror 14. Between these end mirrors 12 and 14 extends the laser radiation field denoted as a whole by 16 and representing a resonator radiation field along a beam axis 18, the resonator radiation field 16 comprising a plurality of laser active material and arranged successively in the direction of the beam axis 18, in particular of identical material and identical formed solid body 20, for example, the solid state 2Oi and 2O ₂ passes through, which extend with their longitudinal axes 22i and 22 ₂ approximately parallel to the course of the beam axis 18 in the solids 2Oi and 2O ₂ .

The resonator 16 occurs on end surfaces 24i and 26i and 24 ₂ and 26 ₂ in the solid 2O _x 2O or _2, and from these out.

Preferably, the Resonatorstrahlungsfeld 16 is formed so that it has in the region of the end mirror 12 and 14 each have a waist 28 and 30, while it between the end mirrors 12 and 14, for example, in his the solids 2Oi or 2O ₂ passing through sections 32i or 32 ₂ each have a portion 34i and 34 ₂ with maximum radiation field cross-section.

Further, the resonator 10 comprises for each of the still solid 2Oi and 2O ₂ a folding mirror set 36i and 3S ₁ and 36 ₂ and 38 _2, which folds the resonator 16 by reflection. The resonator 16 is preferably folded so that the exhibit in the solid bodies and 2Oi 2O ₂ extending portions 3I ₁ and 32 ₂ in the solid state or 2Oi 2O ₂ is substantially the same spatial geometric profile.

For optical pumping, a pump radiation source designated as a whole by 50 is provided, the pump radiation of which is supplied either directly or through a light guide 52 to a pump radiation guide designated as a whole by 60.

The pump radiation guide 60 has an optic 62, which transforms the divergent pump radiation 64 emerging from the light guide 52 into a collimated pump radiation field 66, which undergoes a complete depolarization through a depolarizer 68. This collimated and depolarized pump radiation field is transformed into a first pump radiation field branch 72 with a first polarization and a second pump radiation field branch 74 with a second polarization array substantially perpendicular to one of the polarization directions and substantially reflective for another one of the polarization directions Polarization is divided, wherein in each case a first partial radiation field 82i or 82 ₂ for the first solid 2Oi and the second solid 2O _{2 is} generated from the first pump radiation field branch 72, while from the second pump radiation field branch 74 each have a second partial radiation field 84 _X and 84th ₂ for the first solid 2O _x and the second solid 2O _{2 is} generated.

For example, for this purpose, the first pump radiation field branch 72 is deflected by a reflector 88 and a division unit 90 comprising a polarization-influencing element 92 and one for one of the polarization directions substantially transparent and for another of the Polarization directions substantially reflective polarizer 94, the partial radiation field 82i divided.

Thus, after passing through the graduation unit 90, the first pump radiation field branch 72 'continues with reduced pump power and then forms the partial radiation field 82 ₂ after being reflected by a reflector 96.

Similarly, the second pump radiation field branch 74 also passes through a division unit 100 comprising a polarization-influencing element 102 and a polarizer 104 substantially transparent to one of the polarization directions and substantially reflective to another of the polarization directions, which branches off the partial radiation field 84χ from the second pump radiation field branch 74, such that the second pump radiation field branch 74 'has a reduced pump power after passing through the graduation unit 100 and forms the partial radiation field 84 ₂ after being reflected by a reflector 106.

In order to achieve a defined radiation field shape of the partial radiation fields 82i and 84i entering the first solid 2Oi or the partial radiation fields 82 ₂ and 84 ₂ entering the second solid 2O ₂ , one for each of the partial radiation fields 82i and 84i or 82 ₂ and 84 _2, respectively imaging optics 112i and 114i and 112 ₂ and 114 ₂ provided, which 116i and 118i of the partial radiation fields generated a defined radiation field form 82i and 84 _X in the first solid 2Oi and also a defined radiation field form 116 ₂ and 118 ₂ in the second solid 2O ₂ , Preferably, the spatial radiation field shapes 116i or II6 _{2 of} the respective first partial radiation fields 82i and 82 ₂ and the spatial radiation field shapes II8 ₁ and 118 _{2 of} the second partial radiation fields 84i and 84 ₂ are identical.

It is even more advantageous if all radiation field shapes Ho ₁ and II8 ₁ and 116 ₂ and 118 ₂ are substantially identical, and preferably the radiation field shapes II6 ₁ and II81 of the partial radiation fields 82i and 84i cooperating in the first solid body 20i for pumping the laser-active material are identical to one another and mirror-symmetrical to a plane of symmetry 120.

The same applies to the radiation field shapes 116 ₂ and HS _{2 of} the partial radiation fields 82 ₂ and 84 ₂ for the optical pumping of the second solid state 2O ₂ .

Be able to couple the partial radiation fields 82 _X and 84i and 82 ₂ and 84 ₂ at the respective solid-state 2Oi or 2O ₂ substantially parallel to the path of the beam axis 18 of the resonator 16 in the respective solid state 2Oi or 2O _2, the coupling of the part of radiation is carried out - Fields 82i and 84i and 82 ₂ and 84 ₂ on the respective solid body 2O _x or 2O ₂ associated folding mirror 36i and 38i or 36 ₂ and 38 ₂ , and in that the folding mirrors 36, 38 for the partial radiation fields 82 and 84 are permeable.

In that the degree of division of the optical power between the partial radiation field 82 i and the remaining pump radiation field branch IT by the first division unit 90 or the degree of division of the pump power between the partial radiation field 84 i and the remaining second Pump radiation field branch 74 'is adjustable, it is possible to adjust the coupled by the two partial radiation fields 82 _X and 84i in the first solid state 2Oi pumping power and by the partial radiation fields 82 ₂ and 84 ₂ in the second solid state 2O ₂ coupled pump power.

As shown schematically in Fig. 2, resulting in the respective solid state 2Oi and 2O ₂ launched pump power due to the heating of the material in the respective solid state 2Oi or 2O ₂ to form a thermal lens 130i or 13O _2, referring to the resonator 16 affects.

With the solution according to the invention, it is now possible to adjust the pumping power injected in total into the first solid 2Oi and into the second solid 2O ₂ with regard to their absolute value and their spatial distribution such that the resulting thermal lenses 13Oi and 13O _{2 are} identical and Thus, always act in the same way on the Resonatorstrahlungsfeld 16, so that the Resonatorstrahlungsfeld 16, as shown in Fig. 2, a symmetric Resonatorstrahlungsfeld 16 is.

By adjusting the pump power of the single pump radiation source 50, the thermal lenses 13Oi and 13O ₂ can be varied while maintaining the distribution so as to easily adjust the desired course of the resonator radiation field 16 while maintaining the symmetry of the resonator radiation field 16.

The pump radiation guide 60 according to the invention fed with pump radiation from a single pump radiation source 50 has the advantage that even if the pump radiation source 50, for example, in terms of Wavelength of the pump radiation, or the power of the pump radiation changes which, however, remain the same in the solid bodies 2Oi and 2O ₂ thermal lenses 13Oi generated and 13O ₂ Although also change, so that the symmetry of the resonator 16 can be maintained and thus a total of the resonator 10 with a suitable design still optimally tuned to the set mode, for example, the fundamental mode works, so that the beam quality of an exiting for example by the end mirror 14 Nutzstrahls 132 remains unchanged, although the output from the pump radiation source 50 pump radiation, for example, in terms Wavelength and / or its performance has changed.

However, it would also be conceivable to feed the first pump radiation field branch 72 from a first pump radiation source and the second pump radiation branch 74 from a second pump radiation source. In this case, the ratio of the pumping power coupled in by the first partial radiation field 82 to the pumping power coupled in by the second partial radiation field 84 should then be the same in each of the solid bodies 20.

Alternatively, it is also possible, as shown in Fig. 3, with the two solids 2Oi and 2O ₂ build a resonator-amplifier arrangement, wherein the solid 2Oi of the Resonatorstrahlungsfeld 16a and the solid 2O ₂ are penetrated by the amplifier radiation field 16b However, the symmetry of the thermal lenses 130i and 13O ₂ remains and the laser radiation field 16 is mirror-symmetrical to the end mirror 14. The solution according to the invention is not limited to two solids 2Oi to 2O ₂ , but can, as shown in Fig. 4, be extended to a variety of solids 2Oi to 2O ₄ or even more solids 20.

For this purpose, the pump radiation guide 60 'is to be modified such that from the pump radiation field branches 72 and 74 by multiple provision of graduation units 90, 100, for example of graduation units 90i, 9O ₂ and 9O ₃ and 100i, 10O ₂ and 10O _3, the pump radiation field branch 72 in a total of four Partial radiation fields 82i, 82 ₂ , 82 ₃ and 82 _{4 is} divided, which preferably all have substantially the same pump power.

In the same way, the second pump radiation field branch 74 is divided by the division units 100i, 10O ₂ and 10O ₃ into a total of four partial radiation fields 84i to 84 ₄ , so that all of them likewise have substantially the same pumping power overall.

Thus can also be in the total of four solids 2Oi to 2O ₄ thermal lenses 130 generate, which are substantially identical, then the symmetric conditions shown in Fig. 2 that of the resonator radiation field 16 on four solid 2Oi to 2O ₄ extend to let.

If the pump power dependence of the total of four solids 2Oi to 2O _{4 is} not ideally identical, then the adjustable division of the pump radiation field branches 72, 74 into the partial radiation fields 82, 84 essentially allows an adaptation with the four solids 2O _x to 2O ₄ identical thermal lenses are achievable. In a third embodiment of a laser system according to the invention, shown in Fig. 5, a total of four solids, namely 20i _a , 20 _{2a /} 20i _b and 20 _{2b are provided} in a resonator 10 ", wherein the solid state 20 _la and 20 _2a by a pump radiation guide 60a are pumped according to the first embodiment, while the solid 20i _b and 20 _2b are pumped by also a pump radiation guide 60b according to the first embodiment and each of the pump radiation guides 60a and 60b has its own pumping radiation source 50a and 50b.

With the pumping radiation guides 60 _a and 60 _b , it is at least possible that the thermal lenses 130 are identical in the solid bodies 20 _ia and 20 _2a , or in the solids 20i _b and 20 _2b also the thermal lenses are substantially identical, however a disturbance of the symmetry occur in that the thermal lenses of the solid 20i _a and 20 _2a relative to the thermal lenses 20i _b and 20 _{2b are} different.

In a fourth exemplary embodiment, illustrated in FIG. 6, the design and arrangement of the pumping radiation guides 60a and 60b correspond to those of the third exemplary embodiment according to FIG. 5.

However, the laser radiation field guidance 10 '"is designed as a resonator only in the region passing through the solid bodies 20i _a and 20 _2a , so that an area formed as an amplifier follows the end mirror 14"' and comprises the solids 20i _b and 20 _2b .

Thus, the laser radiation field 16 "'is divided into a whole forming a Resonatorstrahlungsfeld 16"' a region and an amplifier radiation field 16 "'b forming area. Thus, the solid 20i _a and 20 _{2a form} a pair and the solid 20i _b and 20. _2b a pair, wherein for each pair, the symmetry of FIG. 2 is maintained by adjusting the pump power and this adjustment by adjusting the pump power within the Couples is simplified.

With regard to the other elements, the second embodiment, the third and the fourth embodiment are constructed and constructed in the same way as the first embodiment, so that with respect to the explanation of these elements and their function is fully incorporated by reference to the comments on the first embodiment.

In the context of the embodiments described so far, only the effects of the thermal lenses generated by the pumping power have been described. However, as shown in FIG. 7 in a laser system corresponding to the first embodiment, astigmatism of the thermal lenses may occur in addition to the thermal lenses 130, that is, as shown in FIG. 7, those in the solid state 2Oi and in the solid state 2O _{2 formed} by the optical pumping thermal lens 13O'i and 130 ' _{2 is} not rotationally symmetrical to the beam axis 18 is formed.

This may be due to an asymmetrical cooling geometry of the solid state 2O _x , 2O ₂ or unbalanced partial radiation fields 82, 84. However, there are also anisotropic solid-state materials which have astigmatic thermal lensing even with symmetrical cooling and symmetrical partial radiation fields 82, 84. Such materials are for example Nd: YLF or Nd: YVO ₄ . As shown in FIG. 7, each of the solid bodies 20χ and 20 _{2 has} a major axis Ai or A ₂ of astigmatism, which correspond to the major axes of the polarization P ₁ , P _{2 in} the case of astigmatism due to the crystal axes. This main axis A _1, A ₂ of the astigmatism resulting in the Ai or _A2 occurring focusing effect of the thermal lens 13O'i bzw.l30 _'2 is greater in the direction of this main axis perpendicular to said respective main axis Ai and A _2, , Starting from a round cross-section 140 of the resonator radiation field 16 in the region of the end mirror 12, as shown in FIG. 7, this results in the resonator radiation field 16 being more strongly focused in the direction of the main axis Ai when passing through the solid 20i, as shown in dashed lines in FIG in that the resonator radiation field 16 forms a first beam waist 142 in the main axis A _x and forms a second beam waist 144 in the direction perpendicular to the main axis A ₁ at a greater distance from the first solid body 2O _x .

Due to the astigmatism of the thermal lens 13O'i, the resonator radiation field 16 with respect to the beam axis 18 after passing through the solid 2Oi has a non-rotationally symmetrical cross-sectional shape, as for example at the cross-sectional shape 146 of the resonator radiation field 16 after passing through the solid 2Oi and at the cross-sectional shape of the beam waistings 142 and 144 and at their distance from each other in the direction of the beam axis 18 shows.

Furthermore, in order to obtain an optimum image for compensation of the astigmatism of the section 32i of the resonator radiation field 16 in the first solid 2Oi in the section 32 _{2 of} the resonator 16 in the solid state 2O ₂ , between the compensating pair forming solids 2Oi and 2O ₂ an imaging optics 134 is provided, which comprises two imaging optics 136 and 138, which has a plane Mi which perpendicular to the beam axis 18 in the first solid 2Oi, in a plane M _{2 of} the solid 2O ₂ images, which also runs in this perpendicular to the beam axis 18, and vice versa.

In order to compensate for this no longer rotationally symmetric deformation of the resonator radiation field 16, the solids 2Oi and 2O ₂ with their major axes of the astigmatism Ai, A ₂ are arranged such that they are rotated by 90 ° relative to each other, as shown in Fig. 7.

This arrangement of the solid state 2Oi and 2O ₂ causes the resonator radiation field 16 after passing through the first solid 2O _x when passing through the second solid 2O ₂ again "sees" an astigmatism, which is however tilted by 90 °, since the main axis A ₂ of Astigmatism in the second solid 2O _{2 is} rotated.

Now, if the effect of the thermal lens 13O'i equal to the effect of the thermal lens 130 ' ₂ , but with an astigmatism, which is rotated by 90 ° between the thermal lenses 13O'i and 130' ₂ , so compensate for the effects of astigmatism the thermal lenses 13O'i and 130 ' ₂ such that the resonator radiation field 16 again has a substantially round cross-sectional shape 148 at the end mirror 14.

In the previous explanation of the compensation of the caused by the thermal lensing astigmatism has not been discussed in more detail on the polarization of the resonator 16 itself. If the astigmatism of the thermal lens 130 is independent of the incident polarization and if the polarization is not influenced by the thermal lens 130, the polarizer 150 can select the one linear polarization independent of the major axes Ai, A _{2 of} the astigmatism.

Frequently, the astigmatism of the thermal lens 130 is associated with a preferred direction of polarization Pi, P ₂ in the solid state. For example, it is assumed in FIG. 7 that the polarizer 150 preferably has a polarization direction PR of the resonator radiation field at the outcoupling mirror 14, which coincides both with the preferred direction of the polarization P _{2 of} the solid ₂ O ₂ and with a major axis of the astigmatism A ₂ associated with this polarization direction.

As shown in FIG. 7, the polarizer 150 causes the output beam 132 coupled out of the resonator radiation field 16 to be polarized in such a way that there is a constant phase relationship between perpendicular polarization components over the cross section thereof.

In the simplest case, this is achieved by a linear polarization of the resonator radiation field 16.

To compensate for the astigmatism when using solids 20 with a preferred direction of polarization Pi, P ₂ , which coincides with a major axis of the astigmatism Ai, A _{2 of} the thermal lens 130, the polarization direction PR of the resonator radiation field 16 is to be aligned so that it with the main axis P of polarization in the respective solid 2O _x or 2O ₂ coincide (Fig. 7). For this reason, the polarization PRi of the Resonatorstrahlungsfeides 16 in the first solid 2Oi is aligned so that it is parallel to the main axis Pi and Ai and in the second solid 2O ₂ , the polarization PR _{2 of} the Resonatorstrahlungsfeldes 16 to align so that these parallel to the main axis P ₂ and A ₂ runs.

For rotation or reflection of the polarization PR of the resonator radiation field 16 in a direction perpendicular thereto, a polarization-influencing element 152 is to be provided between the solids 2Oi and 2O ₂ which converts the polarization PRi of the resonator radiation field 16 in the polarization direction PR ₂ in the region of the first solid 2Oi before the resonator radiation field 16 passes through the second solid 2O ₂ and vice versa.

With regard to the optical excitation of the solids 2Oi and 2O ₂ , no further details have been given so far. Thus, the optical excitation of the first solid 2O _x expediently takes place with a polarization OPi, which leads to the preferred direction of the polarization P ₁ . P ₂ is aligned the same. A suitable orientation provides that the polarization OPi runs parallel to the main axis Pi, wherein both partial radiation fields 82i and 84i are polarized parallel to that of the direction OPi.

In contrast, an excitation is of the solid 2O ₂ with a polarization OP _2, which is the same orientation to the preferred direction of polarization, in particular runs parallel to the main axis P _2, wherein also in this case, the partial radiation fields 82 ₂ and 84 ₂ parallel to the polarization OP ₂ , are polarized. In another type of solids 20, there is no preferred direction of polarization along the direction of the resonator radiation field 16. In such solid bodies, the thermal lens 130 "i and 130" ₂ additionally comprises a birefringence, for example a rotationally symmetric stress birefringence, in which a radial polarization component RP and an azimuthal polarization component AP have different magnitudes.

As shown in Fig. 8 at a corresponding to the first embodiment laser system, the thermal lens 13Oi of the solid body 20i having a major axis of the birefringence in the direction of the radial polarization RPi and another main axis of the birefringence in the direction of the azimuthal polarization AP _x on. The orientation of these major axes is uniform in a cylindrical coordinate system, based on a Cartesian coordinate system location-dependent. A solid state material exhibiting such behavior is, for example, Nd: YAG.

The refractive power of the thermal lens is thus different for the polarization component RPi and APi. Furthermore, the polarization state of a laser radiation field 16 generally changes when passing through the respective solid 20 with the birefringence described, since a phase shift occurs between the two polarization components oriented along the principal axes of the birefringence. This means in this example that for each laser radiation field 16 whose polarization is not aligned purely azimuthally or purely radially across the beam cross-section, a change of the polarization state occurs when passing through the solid 20, this change over the cross-section is not uniform. For example, due to the stress birefringence, the radial polarization component RPi is focused more strongly than the azimuthal polarization component APi.

Associated with this is an increased phase velocity of the radial polarization component compared to the azimuthal polarization component which results in a change in the phase relationship between the polarization components as they pass through the solid.

The different focussing of the radial and azimuthal polarization component results in their beam waists being arranged in the direction of the beam axis 18 at different points TR and TA.

In this exemplary embodiment, too, an output beam 132 having a rotationally symmetrical cross-sectional shape with a fixed phase relationship between mutually perpendicular polarization components is sought, in which case linear polarization is ensured by the polarizer 150.

If a linear polarization PRi and PR ₂ and a rotationally symmetrical cross-sectional shape 160 and 168 of the resonator radiation field 16 in the region of the endgame gels 12 and 14 of the resonator 10 are assumed, then the birefringence of the thermal lens 130 "i in the solid state 2Oi leads to an elliptical polarization of the resonator radiation field 16 outside the major axis coincident with the direction of polarization PR _x , as represented by the cross-sectional shape 162. This elliptical polarization of the resonator radiation field 16 outside the main axis RP ₁ and AP ₁ coinciding with the polarization direction PR ₁ is therefore to be compensated for in addition to the different focusing which results for the different polarization components RP ₁ and AP ₁ .

For this reason, in the area of the imaging optics 134 present for the same reasons as in the correction of the astigmatism, the polarization-rotating element 152 is provided, which rotates each polarization component RP and AP of the resonator radiation field 16 by 90 °, so that a radial polarization component RP _{1 of} the resonator radiation field 16, which is focused more strongly in the solid state 2O ₁ and has a higher phase velocity than the azimuthal polarization AP ₁ , in the solid state 2O ₂ as the polarization component AP ₂ experiences the weaker focus and lower phase velocity, while an azimuthal polarization component AP ₁ of

Resonator radiation field 16 in the solid state 2O _{1 is} focused less and has a higher phase velocity than the radial polarization RP ₁ , in the solid state 2O ₂ as the polarization component RP ₂ undergoes the stronger focus and higher phase velocity.

Now the resonator radiation field 16 is composed of the components AP and RP and thereby each portion of the resonator radiation field 16 in a solid 20 is subjected to the effect for the polarization component AP and in the other solid 20 the effect for the polarization component RP. In summary, the effect of birefringence in all parts over the entire beam cross section can be canceled, and thus achieve a substantial compensation of birefringence. The embodiment according to the invention allows the birefringence to be compensated for by virtue of the fact that the birefringence caused by the thermal lens 130 is set largely identically by suitable division of the pumping power onto the solids 2Oi and 2O ₂ in the two solids.

Such solid bodies, in which the birefringence associated with the thermal lens 130 "dominate the birefringence, are optically largely isotropic, neglecting thermally or mechanically induced effects, so that the polarization direction is irrelevant in optical pumping of the solids 2Oi and 2O ₂ In this embodiment, therefore, optical pumping of the solid state 2Oi and 2O ₂ with each polarization direction is possible, but also the optical pumping in this embodiment should be such that the thermal lenses 130 "i and 130" _{2 are the} same size as in FIG Described in connection with the first embodiment.

Claims

1. A laser system comprising a laser radiation field guide (10), in which a laser radiation field (16) extends, at least one of the Resonatorstrahlungsfeld (16) interspersed laser-active, in the direction of a longitudinal axis (22) between two opposite end surfaces (24, 26) extending solid state body (20), a pump radiation source (50) for generating pump radiation for optically pumping the laser-active solid (20), a pump radiation guide (60) which the pump radiation for pumping the solid (20) into a first and a second partial radiation field (82 , 84) and which couples the first partial radiation field (82) into the solid body (20) via the one end surface (24) and the second partial radiation field (84) via the other end surface (26), characterized in that the laser beam Radiation field (16) at least two in the direction of its beam axis (18) successively arranged laser-active solid (20) from i that the pump radiation guide (60) is formed in such a way that it couples the first partial radiation field (82) into the first partial radiation field (82) via the one end surface (24) and the second partial radiation field (84) via the other end surface (26) the pump radiation guide (60) is designed such that a pumping power coupled into each of the at least two solids (20) by the two partial radiation fields (82, 84) is adjustable such that the effects of by the pumping power in each of the at least two solids (20) generated thermal lenses (130) to the laser radiation field (16) are substantially identical.

2. Laser system according to claim 1, characterized in that the partial radiation fields (82, 84) are coupled substantially parallel to the longitudinal axis (22) of the respective solid body (20) in this.

3. Laser system according to claim 1 or 2, characterized in that the partial radiation fields (82, 84) are coupled substantially symmetrically to the beam axis (18) within the respective solid body (20) in this.

4. Laser system according to one of the preceding claims, characterized in that the first partial radiation fields (82) in each of the respective solids (20) have a substantially identical radiation field form (116).

5. Laser system according to one of the preceding claims, characterized in that the second partial radiation fields (84) in each of the respective solids (20) have a substantially identical radiation field form (118).

6. Laser system according to one of the preceding claims, characterized in that the sum of the through the two partial radiation fields (82, 84) in the respective solid state (20) coupled pump power in each of the solid state (20) is approximately equal.

7. Laser system according to one of the preceding claims, characterized in that in each of the solid state (20), the first partial radiation fields (82) are formed substantially equal in terms of their pumping power.

8. Laser system according to one of the preceding claims, characterized in that in each of the solid state (20), the second partial radiation fields (84) are formed substantially equal in terms of their pumping power.

9. Laser system according to one of the preceding claims, characterized in that the first and the second partial radiation field (82, 84) in each of the solid body (20) to an approximately central mirror plane (120) of the solid body (20) extend substantially mirror-symmetrically.

10. Laser system according to one of the preceding claims, characterized in that the ratio of the first partial radiation field (82) coupled pumping power to the second partial radiation field (84) coupled pumping power in each of the solid state (20) is substantially equal.

11. Laser system according to one of the preceding claims, characterized in that the first and the second partial radiation field (82, 84) in each of the solids (20) have a defined relative polarization (OP).

12. Laser system according to claim 11, characterized in that in each of the solid bodies (20) both partial radiation fields (82, 84) have the same polarization (OP).

13. Laser system according to one of the preceding claims, characterized in that the first partial radiation field (82) for each in the laser radiation field guide (10) arranged solid body (20) originates from a pump radiation source (50).

14. Laser system according to one of the preceding claims, characterized in that the second partial radiation field (84) for each in the laser radiation field guide (10) arranged solid body (20) originates from a pump radiation source (50).

15. Laser system according to one of the preceding claims, characterized in that the two in the respective solid state (20) entering partial radiation fields (82, 84) originate from the same pump radiation source (50).

16. A laser system according to claim 15, characterized in that the two partial radiation fields (82, 84) originate from the same pump radiation source (50) for at least two of the solids (20).

17. A laser system according to claim 16, characterized in that it comprises two pumping units (50a, 50b) each of which pumps at least two solids with partial radiation fields (82, 84) from the same pumping radiation source (50a, b).

18. Laser system according to one of claims 13 to 17, characterized in that all in the at least two solid bodies (20) coupled partial radiation fields (82, 84) originate from a single pumping radiation source (50).

19. Laser system according to one of the preceding claims, characterized in that the division of the pump radiation into partial radiation fields (82, 84) via polarizers (70, 94, 104) takes place with polarization-dependent transmission and reflection.

20. Laser system according to one of the preceding claims, characterized in that the adjustable division of the pump power in the partial radiation fields (82, 84) via the relative adjustment between a polarizer (94, 104) with polarization-dependent transmission and reflection and an adjustable polarisationsbeeinflussenden element (92,102 ) he follows.

21. Laser system according to one of the preceding claims, characterized in that the partial radiation fields (82, 84) via folding mirrors (36, 38) of the resonator (10) are coupled into the respective solid state (20).

22. Laser system according to one of the preceding claims, characterized in that the at least two solid bodies (20) are formed identically.

23. Laser system according to one of the preceding claims, characterized in that the at least two solid bodies (20) relative to the laser radiation field (16), are arranged such that a compensation of the respective thermal lens (130 ') conditional astigmatism takes place.

24. A laser system according to claim 23, characterized in that in each case two of the solids (20) form a compensation pair and that the two solids (20) relative to the laser radiation field (16) are arranged such that a compensation by the respective thermal lens (130) conditional astigmatism occurs.

25. A laser system according to claim 24, characterized in that the solids (20) of a compensation pair with main axes (A) of the astigmatism are rotated by 90 ° to each other.

26. Laser system according to one of claims 23 or 25, characterized in that the polarization direction (PR) of the amplifier radiation field (16) is adapted to a main axis (P) of the polarization of the respective solid (20).

27. Laser system according to claim 26, characterized in that the polarization direction (PR) of the laser radiation field (16) is aligned parallel to the main axis (P) of the polarization of the respective solid (20).

28. A laser system according to any one of claims 24 to 27, characterized in that the solid state (20), a compensation pair with their main axes (P) of the polarization are arranged rotated by 90 ° to each other.

29. Laser system according to one of claims 23 to 28, characterized in that each solid body (20) by a first and a second partial radiation field (82, 84) is pumped, the polarization direction (OP) parallel to a major axis (P) of the polarization of the respective Solid body (20) is aligned.

30. Laser system according to one of claims 1 to 22, characterized in that the at least two solid bodies (20) relative to the laser radiation field (16) are aligned such that a compensation of a by the respective thermal lens (130 ") conditional birefringence occurs ,

31. A laser system according to claim 30, characterized in that in each case two of the solids (20) form a compensation pair and that the two solids (20) relative to the laser radiation field (16) are arranged such that a compensation of the respective thermal lens (130 ") and birefringence occurs.

32. A laser system according to claim 30 or 31, characterized in that the polarization directions (PRi) of the laser radiation field (16) in one of the solid state (20) relative to the polarization directions (PR ₂ ) of the laser radiation field (16) in the other the solid state (20) and 90 ° are rotated.