WO2014067938A1

WO2014067938A1 - Multi-pass laser system with coupled multi-pass cells

Info

Publication number: WO2014067938A1
Application number: PCT/EP2013/072597
Authority: WO
Inventors: Joerg Neuhaus
Original assignee: Dausinger & Giesen Gmbh
Priority date: 2012-10-29
Filing date: 2013-10-29
Publication date: 2014-05-08
Also published as: DE102012021168A1; EP2912732A1; DE102012021168B4; WO2014067938A4

Abstract

The invention relates to a multi-pass laser system (1) with a beam coupling optical unit (2) and a beam uncoupling optical unit (3) for guiding an incident (4) and an emergent (5) radiation field and with a multi-pass cell (6), which multi-pass laser system comprises at least one or two focusing optical units (7) and two feedback optical units (8, 9) for guiding a multi-pass radiation field (11) consisting of a plurality of radiation branches (12) that extend in parallel in an intermediate zone (13) delimited by the focusing optical unit (7) and that are guided, via the focusing optical unit (7), onto one of the feedback optical units (8, 9) where they superimpose and penetrate a solid-state disk (14) arranged in front of one of the feedback optical units (8, 9) while superimposing one another in an active zone, said branches being coupled such that, proceeding from the incident (4) to the emergent (5) radiation field, all radiation branches (12) are passed through one by one. The multi-pass laser system is characterized for example in that the multi-pass laser system (1) comprises at least two multi-pass cells (6) and in that one of the feedback optical units (8, 9) is designed as a "common coupling optical unit" (10) to couple the two multi-pass radiation fields (11) of the two multi-pass cells (6) to one another.

Description

Multipass laser system with coupled multipass cells

The invention relates to a multipass laser system with a beam injection optics and a beam extraction optics for guiding an incident and falling radiation field and with a multipass cell, comprising at least one or two focusing optics, and two feedback optics for guiding a multipass radiation field from a plurality of radiation branches, which in a limited by the focusing optics Between the intermediate area parallel to each other and are guided over the focusing optics on a feedback optics on which they overlap and thereby enforce a arranged in front of one of the feedback optics solid disk overlapping in an active area, and are coupled such that starting from the incident to the outgoing radiation field all radiation branches be run through one after the other.

Such multipass laser systems are known, for example, from the published patent application EP 1286434 A1. There, the radiation branches of the multipass radiation field, which run parallel in the intermediate region between two focusing optics, are guided in one plane. The two feedback optics are arranged so that they each couple different pairs of radiation branches to each other, and so couple the multipass radiation field with itself, so that all radiation branches are passed through successively. The coupling of radiation branches takes place, for example, by a tilting of a feedback optical system about an axis perpendicular to the plane spanned by the radiation branches, or by an offset between the optical axes of the focusing and / or coupling optical systems, the offset being parallel to the plane spanned by the radiation branches he follows.

Multipass laser systems with multipass cells have the advantage that, in order to realize numerous transitions via an optical element, they require only a small number of optics, such as focusing optics, and are particularly easy to adjust, the distances between different radiation branches of the multipass radiation field, as opposed to those of individual optics guided radiation branches can be minimized and the number of radiation branches can be varied very easily.

The area of circular elements (e.g., lenses or mirrors) commonly used as focusing optics in conventional multipass laser systems scales quadratically with the number of radiating branches because the radiating branches are juxtaposed and as the number of radiating branches increases, a larger diameter of the focusing element is required. A doubling of the radiation branches thus results in a quadrupling of the area on the focussing element.

The optical surface of the conventional multipass laser systems mostly circular focusing optics is used there only to a fraction. In the case of a particularly large number of radiation branches guided side by side, the problem in particular arises that the radiation branches guided on the outside have a large distance to the center of the focusing optics. For optimum guidance of the beam branches to a common point on the coupling optics, it is necessary to use cost-intensive parabolic optics. When parabolic optics are used, slight deviations from the optimum telecentric arrangement desired in such a structure can occur even with radiation fields lying far to the outside.

The object of the invention is to provide a multipass laser system which makes better use of the area of the focusing elements used to guide the multipass radiation field and also prevents aberrations due to distances too great from the center of the focusing optics.

The object is achieved by a laser amplification system according to the preamble of claim 1, which is characterized in that the multipass laser system comprises at least two multipass cells and one of the feedback optics is designed as a "common coupling optics" to couple the two multipass radiation fields of the two multipass cells together , This has the advantage that with a doubling of the radiation branches guided via the focusing optics, the area required there does not quadruple, as is the case with conventional multipass laser systems, but only has to be doubled.

Also, in this case, the maximum distance of the radiation branches from the center of the respective focusing optics remains unchanged.

In contrast to the "common coupling optics" which couples the multipass radiation fields of two multipass cells, the feedback optics in the multipass laser system according to the invention are not used in a single multipass cell, as is the case with conventional multipass laser systems A multipass cell with feedback optics and "common coupling optics" is referred to as "outer multipass cell", while a multipass cell with two "common coupling optics" is referred to as "inner multipass cell." "can also be designed so that it includes only a single focusing optics. In this case, one of the feedback optics is then arranged directly in the intermediate region in which the radiation branches are guided parallel to one another and is designed such that the radiation branches of the multipass radiation field are coupled in pairs to one another. Such a feedback optics can be formed for example by a triple prism.

Comparable to the different coupling of the pairs of radiation probes by the two feedback optics in a single conventional multipass cell, the coupling of pairs of radiation probes in the two "outer multipass cells" differs via the feedback optics arranged there.As described above, this different coupling of the radiation pairs is effected, for example. in that the first feedback optic is tilted about an axis perpendicular to the plane spanned by the pairs of radiation pairs, or in that the optical axes of the focusing optics and / or feedback optics of the first multipass cell are offset relative to each other, wherein the offset is parallel to the plane spanned by the pairs of radiation probes. Because of the coupling thus achieved by the two feedback optics and the "common" coupling optics, all the radiation branches of all the multipass cells are consecutively traversed, starting from the incident beam field to the outgoing radiation field.

The coupling of the multipass cells with the aid of the "common coupling optics" can be effected by coupling each radiation branch guided by a focusing optics to a "common coupling optics" from the multipass radiation field of one multipass cell with one radiation branch each of the multipass radiation field of the other multipass cell. By way of example, a reflector may be understood as a "common coupling optics", in which case the two coupled multipass cells are expediently arranged symmetrically about the optical axis of the reflector, the "optical axis of the reflector" being that which passes through the point to which the Radiation branches are guided superimposing with the aid of the focusing optics, which is perpendicular to the reflection surface of the reflector. The coupling of two radiation branches takes place by reflection of the associated radiation fields on the reflector.

According to the invention, the term "focusing optics" does not necessarily mean a single mechanically independent optical element, but also, for example, a specific area or area on a focusing optical element, such as a parabolic mirror, a spherical mirror or a lens According to the invention, focusing optics comprised by a multipass laser system can also be formed by a single, correspondingly larger, focusing element, wherein a plurality of separate regions on the focusing element make up the plurality of focusing optics. Therefore, in one embodiment, the focusing optics necessary for guiding the multipass radiation fields to the "common coupling optics" are expediently formed by different regions on a single optical element, so that the optically unused surface necessary for forming the focusing optics can be further minimized The multipath radiation field of the multipass radiation field running parallel in the respective intermediate region is likewise parallel to the radiation branches of the multipass radiation field of the other multipass cells. and focusing optics basically corresponds to a "4f construction". The distance between coupling optics and the associated focusing optics for guiding the beam ungsäste on the coupling optics is equal to the focal length of the focusing optics. The focus of the radiation field within such a "4f structure" can be either essentially on the coupling optics or else in the intermediate region between the focusing optics. equal to the sum of the focal length of the individual focusing optics. In the case of the present multipass laser system, a deviation from an ordinary "4f structure" within the individual multipass cells is conceivable If the solid-state disk or the adaptive optics already have a refractive power (spherical aberration) or other aberrations cause deviations, the distance between the focusing optics are corrected in accordance with this refractive power, so that the incident radiation field is mapped parameters with identical beam even after several passes through the multi-pass beam guiding optics.

On the one hand, the multipass laser system can be designed in such a way that a laser radiation field is guided from the incident to the precipitating radiation branch, this being amplified as it passes through the multipass laser system. Then the multipass laser system is designed, for example, as a linear amplifier or else as an oscillator, wherein in the latter case the incident and failing radiation field outside the multipass laser system are additionally coupled to one another. On the other hand, it is also conceivable for a pump radiation field to be guided via the incident beam to the precipitating radiation branch through the multipass laser system, in which case the pump radiation field as multipass radiation field is at least partially absorbed in the solid state disk. It is also possible to combine two multipass laser systems according to the invention such that the pump radiation field is guided via the one multipass laser system according to the invention and the laser radiation field over the other multipass laser system according to the invention onto the solid-state disk.

It is favorable if the solid-state disk is arranged in front of a "common coupling optics." The number of passes of the radiation branches through the solid-state disk and the possible amplification or absorption of a laser radiation field or pump radiation field when passing from the incident to the failing radiation field can thus be maximized.

In another embodiment of the multipass laser system, a plurality of solid-state disks are arranged in front of different "common coupling optics".

In a further advantageous variant of the multipass laser system, the radiation branches in the multipass radiation field of the multipass cells are guided in two planes. In such a multipass cell, the planes are each spaced from the optical axis of the focusing optics of the multipass cells.

The feedback optics, via which in each case the multipass radiation field of a single multipass cell is coupled to itself, are designed so that in each case two radiation branches lying in different planes are coupled to one another.

A particularly advantageous variant of the multipass laser system at least three multipass cells. In this case there is at least one "inner multipass cell" and exactly two "outer multipass cells". The "outer multipass cells" in each case comprise one of the two feedback optics for coupling the multipass radiation fields to themselves. The "inner multipass cells", on the other hand, comprise two "common coupling optics" for coupling the multipass radiation field of the "inner multipass cell" to the multipass radiation field of two adjacent ones Multipass cells, as well as two focusing optics for guiding the multipass radiation field to one of the two "common coupling optics." The coupling between "inner" and "outer" multipass cells takes place in such a way that, starting from the incident radiation field, all the radiation branches of all the multipass cells are passed through one after the other. In this case, it is also advantageous if the number of "inner multipass cells" is odd, since in this case the number of beam branches routed to the respective "common coupling optics" is the same.

In the case of numerous coupled multipass cells, it is advantageous to arrange the focusing optics for guiding the multipass radiation field on a "common coupling optics" in a circle with substantially the same angular distance around the optical axis of the "common coupling optics".

If a reflector is used as coupling optics, two focusing optics are then expediently arranged on opposite sides at the same distance from the optical axis of the reflector.

By means of a substantially uniform arrangement of the focusing optics distributed over a circle, it is possible, when using e.g. spherical astigmatism can be largely compensated.

It is also conceivable that in the case of numerous mutually coupled multipass cells, the individual focusing optics for guiding the radiation branches to one another "Common coupling optics" are arranged in several circles with different radii.

If particularly large diameters of the radiation fields on the coupling optics are desired, then it is favorable if the coupling optics is designed to form a highly convergent or divergent radiation field such that the focus of the multipass radiation fields lies within the intermediate region between the focusing optics and the radiation field the individual radiation branches is largely collimated during the transition via the focusing optics.

In a particularly advantageous embodiment of the multipass laser system, the input and output optics is then arranged in the intermediate region of a multipass cell such that the incident and outgoing radiation fields are coupled there to the multipass radiation field.

This has the advantage that, for optimum utilization of the surface on the focusing optics, the distance between the individual mutually parallel radiation branches can be chosen such that the radiation fields are superimposed on the focusing optics and are just barely separated in the region of the input and output optics.

Conceivable as input and output optics, for example, a mirror, is coupled through the reflection by the incoming and / or outgoing radiation field with one of the radiation branches of the multipass radiation field.

On the other hand, a folding optics with recesses for the incoming and outgoing radiation field as input and output optics is also conceivable. The folding optics for separating the incoming and outgoing radiation field from the multipass radiation field is arranged in the intermediate region of a multipass cell. Conveniently, the folding optics is then positioned at a position at which the diameter of the radiation fields guided along the radiation branches is smaller than the distance of the individual radiation branches from each other. The incoming and outgoing radiation field bypasses the folding optics guided, so that in such a case no input and output optics in the intermediate region of the multipass cell must be arranged.

Such an arrangement has the advantage that, when coupling in a laser imaginary field intended for amplification into the multipass laser system, the radiation branch coupled to the failing radiation field, which has the strongest power due to the reinforcement through the solid-state disk, is not guided via a coupling-out optical system in the intermediate region. On the other hand, an operation of the multipass laser system for guiding a pump radiation field for the solid-state disk is conceivable. In such a case, the incident radiation field has the greatest power. Again, this is coupled in such an arrangement in the Multipasslasersystem, without necessarily having to use a coupling optics with very high damage threshold. Only after a complete run through all the multipass cells and thus considerable power attenuation, the multipass radiation field is performed on the folding optics.

Any aberrations caused by the solid-state disk can lead to a shift of the focus within the intermediate region of the focusing optics and thus possibly to the destruction of the respective optics in the multipass cells. In particular, a folding optical system arranged in the intermediate region is then threatened with the destruction due to an excessive power density.

It is therefore particularly favorable if the input and output optics or the folding optics are arranged in an "outer multipass cell" whose focusing optics have a greater focal length than the other focusing optics of the multipass laser system.

In such a case, the focus in the intermediate region of the focusing optics of the "outer multipass cell" is greater than the focus in the remaining multipass cells, the maximum power density with a shift of the focus is in this case therefore limited. The input and output optics and the folding optics are better protected against possible destruction.

In another embodiment of the multipass laser system, the focusing mirror of an "outer multipass cell" has a lower focal length than those focusing mirrors which guide the multipass radiation field to the "common coupling optics". Furthermore, it has recesses through which the incoming and outgoing radiation fields are coupled to the multipass radiation field.

If a focusing lens with a smaller focal length is used for the "outer multipass cell", the distances between the focusing optics corresponding to the smaller focal length are reduced, and in such a case the diameters of the radiation fields on this focusing optics are reduced so that the radiation fields of the individual radiation branches are different from each other This has the advantage that, by means of corresponding recesses in this focusing optics, the radiation branches can be coupled in and out without additional input and output optics arranged in the intermediate region and thus too large power densities on the input and / or outcoupling optics can be prevented.

A particularly advantageous variant of the multipass laser system comprises at least three multipass cells, which are coupled to one another via exactly two "common coupling optics".

However, another embodiment of the multipass laser system with "outer" and "inner multipass cells" is also conceivable, in which the "inner multipass cells" are coupled to one another via exactly one single "common coupling optics". In this case, the "inner multipass cells" comprise at least one deflecting element which is arranged in the intermediate region of the "inner multipass cell" to guide the radiation branches guided in parallel there via the second focusing optics again to the one "common coupling optics". At high pumping powers, thermal effects in the solid-state disk produce aberrations that manifest themselves in a change in the phase front of the radiation field. For multiple transitions across the solid state disk, these aberrations continuously add up and cause a significant degradation in beam quality. Aberrations are understood to mean spherical aberrations as well as aberrations of a higher order - also in the following.

One solution is to use a phase-front-correcting element to compensate for the phase-front-changes, e.g. an adaptive mirror. Such a mirror used in a laser resonator has been used e.g. in WO 2009 095 311. However, there has been reported only a simple transition across the solid state disk and the adaptive mirror. In a particularly advantageous embodiment of the multipass laser system, therefore, at least one of the coupling optics is additionally designed as a phase-front-correcting element for compensating phase-shift changes caused by the solid-state disk. The phase-front-correcting element is expediently designed so that it can be variably controlled to compensate for the aberrations introduced by the solid-state disk into the radiation field. If a plurality of solid-state disks, but only one phase-front-correcting element is arranged in the multi-pass beam guiding optics, the phase-front-correcting element is expediently designed to compensate the aberrations of all solid-state disks. This can be realized, for example, via a feedback signal that monitors the radiation field of an arbitrary radiation load and controls the phase-front-correcting element in accordance with this feedback signal.

Also conceivable are a plurality of phase-front-correcting elements arranged in the multi-pass laser system, these then only compensating proportionally for the aberrations caused by the solid-state disk or solid-state disks. A problem caused by the aberrations is, on the one hand, a possible large change in the diameter occurring along the radiation field and, on the other hand, a shift of existing foci. In the case of unfavorable positioning of, for example, input and output optics, this can lead to power losses and / or destruction of the optics due to excessive power densities.

In a multipass laser system with phase-front-correcting element, the refractive power of the feedback optics in an "outer multipass cell" is expediently constant and independent of any aberrations of the solid-state disk, in which case the coupling and decoupling of the incoming and outgoing radiation field in the intermediate region of this "outer multipass cell". he follows.

The coupling and decoupling can be done as described above, for example, by an arranged in the intermediate region input and output optics, by recesses in a folding optics arranged there or by recesses in the corresponding focusing optics with a smaller focal length.

Thereby, any aberrations caused by the solid-state disk can be corrected by the phase-front-correcting element, so that the development of the diameter of the radiation fields in the "outer multipass cell" with refractive power constant feedback optics is invariant to solid-disk aberrations.

In another variant of the multipass laser system with phase-front-correcting element, the input and output optics are arranged in a multipass cell in which the refractive power of the coupling optics is not constant, for example if a solid-state disk is arranged in front of the respective coupling optics or if the coupling optics is designed as an adaptive mirror , In this case, the multipass cells are expediently designed as multipass cells with radiation branches guided in two planes. The input and output optics are then arranged in one of the two planes. Since the radiation branches running in one plane in each case are traversed in the same direction, starting from the incident radiation field, the ratio of passes through the solid-state disks arranged in the multipass laser system is the same for transitions via coupling optics formed as phase-front-correcting elements. With appropriate control of the phase-front-correcting element for correcting the phase-front changes caused by the solid-state disk, the development of the diameters of the radiation fields along these radiation branches is the same and, with appropriate control of the adaptive mirror, also invariant with respect to these aberrations. A coupling and decoupling of the incoming or outgoing radiation field with radiation branches in this plane can thus be done without the risk that the diameter of the radiation fields due to aberrations of the solid state disk become too small or too large.

In one variant of the multipass laser system, the solid-state disk can be arranged in front of a "common coupling optics", while the feedback optics of an "outer multipass cell" is designed as a phase-front-correcting element. In this case, it is expedient that the phase-front-correcting element is designed to introduce larger aberration corrections compared to the number of propagated transitions across the solid-state disk.

On the other hand, it is also conceivable that in such a case the positions of the phase-front-correcting element and the solid-state disk are reversed. It is advantageous if the phase-front-correcting element is designed for correspondingly smaller aberration corrections.

A further variant provides that a plurality of coupling optics are designed as phase-front-correcting elements. It is particularly advantageous if a phase-front-correcting element for the correction of spherical aberrations and another phase-front-correcting element for the correction of higher-order aberrations are designed. In a multipass laser system with exactly two "common coupling optics", one of the two is expediently designed as a phase-front-correcting element, while a solid-state disk is arranged in front of the other.

It is particularly advantageous if the feedback optics in the "outer multipass cells" have a constant refractive power, preferably no refractive power.

With appropriate control of the phase front-correcting element, the radiation fields in the "outer multipass cells" are then invariant with respect to any aberrations through the solid-state disk.

It is then particularly expedient if the input and output optics are arranged in the intermediate region of an "outer multipass cell".

An advantageous embodiment of the multipass laser system according to the invention will be explained with reference to the embodiments illustrated in the drawings.

Show it:

Figure 1 is a schematic plan view of a conventional

Multipass laser system according to the preamble of claim 1 with exactly one multipass cell in which all the radiation branches are arranged in one plane and the radiation field is thrown back upon itself as it passes through the multipass laser system,

Figure 2 is a schematic three-dimensional representation of

inventive multipass laser system with two

Multipass cells, three each guided in a plane

Radiation branches where the radiation field is reflected in itself when passing through the multipass laser system,

Figure 3 is a schematic two-dimensional side view of

according to the embodiment of Figure 2,

Figure 4 is a schematic two-dimensional side view of a

Multipass laser system according to the invention, similar to that of Figure 3, but with arranged in two planes radiation branches,

Figure 5 is a schematic drawing of the invention

Multipass laser system in side view with three multipass cells and two "common coupling optics",

Figure 6 is a schematic drawing of the invention

Multipass laser system in side view with five multipass cells and two "common coupling optics",

Figure 7 is a schematic three-dimensional drawing of a

6 according to the invention, but with a circular arrangement of the individual multipass cells, wherein only one radiation branch is shown within the respective multipass radiation field for the purpose of simplification, 8 shows a schematic view of a multipass cell with folding mirror for coupling and decoupling an incoming and outgoing radiation field, FIG.

Figure 9 is a schematic representation of the impact points of various

Radiation branches on circular focusing optics according to two different embodiments and for comparison according to a conventional

Multi-pass laser system

FIG. 10 shows a three-dimensional representation of an embodiment with three multipass cells but only a single "common" one

Coupling optics ", wherein the Multipassstrahlungsfeld a multipass cell is deflected by a deflection mirror, wherein for simplicity only one radiation branch within a

Multipass radiation field is shown and

Figure 11 is a three-dimensional view of the embodiment

Figure 10 is reproduced, in which case the four focusing optics for guiding the multipass radiation fields on the "common

Coupling optics "are provided by respective areas on a single focusing element.

FIG. 1 shows a schematic representation of an embodiment of the multipass laser system (1) according to the preamble of claim 1. This is a conventional multipass laser system (1) with only one multipass cell (6). The radiation field to be guided by the multipass laser system (1) is coupled in as an incident radiation field (4) via a focusing lens (15) for shaping the radiation field into a multipass radiation field (11) via input and output optics (2, 3). The various radiation branches (12) guided parallel to one another in a gap (13) are guided via two focusing optics (7a, 7b) to respectively one first and second feedback optics (8, 9). The radiation branches (12) are superimposed on the feedback optics (8, 9) and pass through a solid-state disk (14) arranged in front of the first feedback optical system (8). By the two focusing optics (7a, 7b) are arranged slightly offset from each other, there is a respective different coupling of Strahlungsastpaaren (12) via the feedback optics (8,9). The multipass radiation field (11) is therefore completely traversed by the incident radiation field (4) up to the outgoing radiation field (5). Since the radiation branches (12) in the multipass radiation field (11) are arranged in one plane, the radiation field (11) is reflected in passing through the multipass laser system (1) in itself. The incident radiation field is guided out of the multipass laser system (1) in the same way as the incident radiation field via the same input and output optics (2, 3).

In this conventional multipass laser system (1), the points of incidence of the different radiation branches (12) on the focusing optics (7a, 7b) - shown here as lenses - are arranged in a line on the respective focusing optics (7a, 7b). The points of impact are shown schematically in the dashed circle, which is intended to show the outline of the lenses. The area on the lenses used (7a, 7b) is exploited only to a fraction. Furthermore, in such an arrangement both radiation branches (12) are present, which run very close to the optical axis of the focusing optics (7a, 7b), as well as those which already have a very large distance from the optical axis. The optical axes of the two focusing optics (7a, 7b) are shown in the illustration as a dashed line.

FIG. 2 shows an embodiment of a multipass laser system (1) according to the invention with two multipass cells (6a, 6b). The incident radiation field is coupled into the multipass radiation field (11b) of the first multipass cell (6b) via an input and output optical system (2, 3).

The first multipass cell (6b) comprises two focusing optics (7a, 7c) and two coupling optics (9, 10). The first coupling optics (9) is a feedback optics which reflects the multipass radiation field (11b) of the first multipass cell (6b) back into itself or couples to itself. Here, the feedback optics (9) is designed as a plane mirror, which couples the individual radiation branches (12a) by reflection with each other. Correspondingly symmetrical, the second multipass cell (6a) is formed. Although this includes no input and output optics, but also there arranged second coupling optics (8) is a feedback optics, which couples the multipass radiation field (11a) of the second multipass cell (6a) with itself. One of these two feedback optics (8, 9) is slightly tilted, so that in each case different pairs of radiation probes (12a, 12b) are coupled to one another in both multipass cells (6a, 6b).

The third "common coupling optics" (10) couples the two multipass radiation fields (11a, 11b) of the two multipass cells (6a, 6b) to each other, in front of which "common coupling optics" (10) a solid-state disk (14) is arranged. All radiation branches (12a, 12b) from both multipass cells (6a, 6b) thus penetrate the solid-state disk (14).

In the illustration, the individual focusing optics (7a) of both multipass cells (6a, 6b) for guiding the respective multipass radiation fields (11a, 11b) onto the "common coupling optics" (10) are formed as separate regions on a curved mirror (7a). This has the advantage that the optical surface can be used particularly effectively on this curved mirror (7a) All radiation branches (12a, 12b) of the two multipass radiation fields (11a, 11b) run parallel to one another in this case.

A rear view of the respective mirror is reproduced immediately adjacent to the focusing optics (7a, 7b, 7c) shown in FIG. 1, where the points of impingement of the individual radiation branches (12a, 12b) of the multipass radiation fields (11a, 11b) are shown schematically there.

The feedback optics (8) in this embodiment is designed as an adaptive mirror (18) for correcting any phase front changes caused by aberrations on the solid state disk (14). The adaptive mirror (18) is designed in such a way that it compensates for the respective phase front changes with appropriate control, the two at Transitions via the "common coupling optics" (10), or four passes through the solid state disk (14) occur.

In the embodiment shown in FIG. 2, too, the radiation field is reflected back in itself and is thus coupled out via the radiation path of the incident radiation field (4) as a precipitating radiation field (5).

In the embodiment in FIG. 1, each radiation branch is traversed twice in respectively different directions. If, in this conventional multipass laser system (1), the coupling optics (9) are designed as adaptive mirrors, this adaptive mirror should be designed in such a way that, with appropriate control of the adaptive mirror, the aberrations of the disc are compensated for two passes through the solid-state disk (14) become. In the change of direction in which the multipass radiation field (11) is reflected back into itself via the coupling optics (9), the ratio of the transitions via the adaptive optics (18) to the passes through the solid-state disk (14) changes. All radiation branches that are traversed in the same direction as the radiation field (12) coupled to the incident radiation field (4) have a radiation field that is invariant to changes in the aberrations of the solid state disk (14). Since, however, the radiation branch coupled to the input and output radiation field is traversed in two directions due to the change of direction on the feedback optics (9), the radiation field (11) is not invariant there with respect to aberrations of the disc. In the case of strong aberrations of the solid-state disk (14), decoupling is only possible with very large distances between the radiation branches (12), since the diameters of the radiation fields in the multipass radiation field (11) can assume very large values.

The situation is different with the multipass laser system (1) according to the invention, as shown in FIG. Since the feedback optics (9) in the multipass cell (6b), in which the input and output optics (2,3) are arranged has a constant refractive power and the adaptive mirror (18) in the other multipass cell (6a), the diameters of the radiation fields in the multipass cell (6b) with input and output optics (2, 3) with appropriate driving of the adaptive mirror (18) are invariant with respect to aberrations of the solid-state disk (14).

While a three-dimensional representation can be seen in FIG. 2, the same embodiment is shown in FIG. 3 from the side. The individual mutually parallel radiating branches (12a, 12b) within a single multipass cell (6a, 6b) are no longer separately recognizable in this form of representation. Only the schematically represented rear view of the respective focusing optics (7a, 7b, 7c) with the likewise reproduced impingement points of the radiation branches (12) reveals the individual radiation branches (12a, 12b) of this embodiment which are arranged one behind the other and visible in FIG.

The same form of representation is used in the following Figures 4, 5 and 6.

FIG. 4 shows a slight modification of the embodiment from FIGS. 3 and 4. In fact, these are again two multipass cells (6a, 6b), but the individual radiation branches (12a, 12b) in the respective multipass radiation fields (11a, 11b) extend in two planes.

In such an embodiment, the radiation field is no longer reflected in itself when passing through the multipass laser system (1) from the incident radiation field (2). Instead, the failing radiation field (5) is coupled out of the multipass radiation field (11b) of the first multipass cell (6b) via a separate coupling-out optical system (3).

In addition to the schematically illustrated impingement points on the focusing optics (7a, 7b, 7c), a numbering is additionally indicated which indicates the sequence in which the individual radiation branches (12) when passing through the multipass laser system (1) from the incident radiation field (4) from reproduces , Another embodiment is shown in FIG. There are three multipass cells (6a, 6b, 6c) coupled together. Instead of the previous embodiments, there are two "common coupling optics" (10a, 10b), and the number of transitions over the two "common coupling optics" (10a, 10b) is the same. The "common coupling optics" (10b) of the first and second multipass cells (6b, 6c) designed as adaptive mirrors (18) can therefore be controlled to compensate for aberrations of the solid-state disk (14) which already occurs during two passes through the solid-state disk (14). or a transition over the coupling optics (10a) arise.

In particular, FIG. 5 shows an embodiment with two adaptive mirrors (18a, 18b). The first adaptive mirror (18a) is designed to compensate for simple spherical aberrations of the solid-state disk (14), while the second adaptive mirror (18b) can be controlled to compensate for higher-order phase front changes.

In a further embodiment, which can be seen in FIG. 6, the multipass laser system (1) is expanded by two further multipass cells (6a, 6b, 6c, 6d, 6e). While an embodiment is shown in FIG. 6, in which all focusing optics (7a-7j) arranged on the same side of the "common coupling optics" (10a, 10b) are arranged in a line, the focusing optics in FIG Guiding the multipass radiation fields (12a-12e) to the respective "common coupling optics" (10a, 10b) in a circle around the optical axis of the respective "common coupling optics" (10a, 10b) .For simplicity, only one radiation branch is shown in FIG (12) shown within a multipass radiation field (11).

FIG. 8 shows the multipass cell (6a) of an embodiment of a multipass laser system (1) according to the invention, in which the incoming and outgoing radiation field is coupled to the multipass radiation field (11). All others with this multipass cell (6a) via the "common coupling optics" (10a) coupled multipass cells (6b, ...) are not shown in the figure for the sake of simplicity.

In the embodiment, as shown in Figure 8, the coupling and decoupling of the incoming and outgoing radiation field takes place in that all other beam ungsäste (12) of the multipass radiation field (11) by a folding mirror (17) are deflected. This takes place at a point at which the radiation fields of the individual radiation branches (12) have a diameter which is smaller than the distance of the respective radiation branches (12). The incident and falling radiation field can therefore be guided past the folding mirror (17).

While the incident radiation field has a very low power during operation as a laser amplifier system, the power of the individual radiation branches (12) increases from one pass to the next through the multipass laser system (1). In particular, the difference in the power of the individual radiation branches (12) of the first multipass cell (6a) in the case of several mutually coupled Multipasszellen (6) in the Multipasslasersystem (1) and thus increasing number of passes through a solid state disk (14) to amplify the radiation field larger ,

The embodiment shown in FIG. 8 makes it possible to decouple a radiation field (5) with a power which is higher at the location of the folding mirror (17) than would allow the damage threshold of the folding mirror (17) to pass through the folding mirror (17). The power density can be selected to be higher than the damage threshold of the folding mirror (17), the more multipass cells (6) are arranged in the multipass laser system (1) each with a solid disk (14) arranged in these multipass cells (6) Multipass cells (6b ...) the difference in the power density of the individual radiation branches (12) in the first multipass cell (6a) increases and the respective previously passing radiation branch (12) in the first multipass cell (6a) a correspondingly lower power density during the transition over the Folding mirror (17) generated. The number of multipass cells (6), which can be arranged around two "common coupling optics" (10a, 10b) similar to the embodiment shown in Figure 7, is ultimately arbitrary, while in Figure 7 only four multipass cells with their four focusing optics (7) are used. for each coupling optics (10a, 10b) are arranged on a circle around the optical axis of the "common coupling optics" (10a, 10b), the number of corresponding focusing optics (7) can be expanded to six or 18, as shown schematically in FIG. FIG. 9 also shows for comparison purposes the impact points on a focusing mirror of radiation branches (12) corresponding to a conventional multipass laser system (1). It is thereby clear that the number of radiation branches (12) can be approximately doubled with respect to each other while the area on the focusing optics (7) remains constant and the radiation branches (12) remain at a constant distance.

A further embodiment of the multipass laser system (1) is shown in FIG. 10, wherein only one radiation branch within a multipass radiation field is shown here, similar to the representation in FIG. 7 for the sake of simplicity. In this embodiment, three multipass cells (6a, 6b, 6c) are coupled together by precisely one single "common coupling optics" (10a), for which the focusing optics (7c, 7e, 7b, 7d) are circular about the optical axis of the common coupling optics "(10a) arranged. While the first and third multipass cells (6a, 6c) are each designed as an "outer multipass cell" (6a, 6c), such that in each case a feedback optical system (8, 9) displays the multipass radiation field (12a, 12c) of the individual multipass cell (6a, 6c). 6c) with itself, the second multipass cell (6b) is an "inner multipass cell" (6b). This "inner multipass cell" (6b) is deflected via a deflecting mirror (16) in the intermediate region between the focusing optics (7d, 7c), so that the multipass radiation field (12b) of this "inner multipass cell" (6b) is superimposed on the "common coupling optics". (10a) is guided. Such an arrangement is conceivable, for example, as a pump arrangement in which the solid-state disk (14) is pumped through the multipass radiation field (12) of the multipass laser system. The embodiment of FIG. 10 is shown somewhat differently in FIG. 11. There, the four focusing optics (7b, 7c, 7d, 7e) for guiding the multipass radiation fields to the "common coupling optics" are provided on a single focusing optic by respective regions (7b, 7c, 7d, 7e) If all radiating branches also overlap in a common point on the "common coupling optics" (10a), the deflecting element (16) must be formed by two mirrors, so that all of the intermediate region (13) is directed onto the "common focusing optics" (7b, 7c , 7d, 7e) extending radiation branches of the multipass radiation fields (11a, 11b) parallel to each other.

In FIG. 11, furthermore, the outcoupling mirror (3) is designed such that it reflects the radiation field back into itself. If the laser amplifier system (1) is used as a pumping concept in this embodiment, then 48 transitions can be realized via the solid-state disk (14).

LIST OF REFERENCE NUMBERS

1. Multipass laser system

2. Radiation coupling optics

3. Beam extraction optics

4. incident radiation field

5. failing radiation field

6th multipass cell

7. Focusing optics

8. first feedback optics

9. second feedback optics

10. "common coupling optics"

11. Multipass radiation field

12. Radiation branches

13. intermediate area

14. Solid disk

15. Focusing lens for shaping the incident radiation field

16. deflecting mirror

17. folding mirror

18. Adaptive optics

Claims

claims

1. Multipass laser system (1) with a beam injection optics (2) and a beam extraction optics (3) for guiding an incident (4) and outgoing (5) radiation field and with a multipass cell (6) comprising at least one or two focusing optics (7), and two feedback optics (8, 9) for guiding a multipass radiation field (11) out of a plurality of radiation branches (12) which run parallel to one another in an intermediate region (13) delimited by the focusing optics (7) and via the focusing optics (7) to one of the Be fed feedback optics (8,9) on which they overlap, thereby prevail over a front of one of the feedback optics (8,9) arranged solid disk (14) in an active area overlapping, and are coupled such that starting from the incident (4 ) to the outgoing (5) radiation field all radiation branches (12) are passed through successively, characterized in that the multipass laser system (1) wenigs at least two multipass cells (6) and one of the feedback optics (8,9) as "common coupling optics" (10) is designed to couple the two Multipass radiation fields (11) of the two Multipasszellen (6) with each other.

2. Multipass laser system (1) according to claim 1, characterized in that the beam injection optics (2) designed to form a highly convergent or divergent radiation field and in the intermediate region (13) of a multipass cell (6) is arranged.

3. Multipass laser system (1) according to at least one of the preceding claims, characterized in that the Multipasslasersystem (1) comprises at least three mutually coupled Multipasszellen (6), in which exactly two multipass cells (6) as "outer multipass cells" each having a feedback optics ( 8, 9) and a "common coupling optics" (10) and the remaining multipass cells (6) are designed as "inner multipass cells" each with two "common coupling optics" (10). Multipass laser system (1) according to claim 3, characterized in that the focusing optics (7) for guiding the Multipassstrahlungsfeldes (11) on a "common coupling optics" (10) circularly at substantially the same angular distance about the optical axis of the "common coupling optics" (10 ) are arranged.

Multipass laser system (1) according to one of Claims 3 or 4, characterized in that the focusing optics (7) of an "outer multipass cell" (6) have a greater focal length than the focal length of the remaining focusing optics (7) of the multipass laser system and the input and output / or coupling-out optics (2, 3) are arranged in this "outer multipass cell" (6).

Multipass laser system (1) according to at least one of claims 3 to 5, characterized in that the focusing optics of an "outer Mulitipasszelle" (6) for guiding the Multipassstrahlungsfeldes (11) on a feedback optics (8,9) has a lower focal length than the focusing optics (7) for guiding the Multipassstrahlungsfeldes (11) on the "common coupling optics" (10), wherein the incoming and outgoing radiation field (4,5) with the Multipass radiation field (11) via recesses in the focusing optics (7) with the lower focal length is coupled.

Multipass laser system (1) according to at least one of claims 3 to 6, characterized in that an "inner multipass cell" (6) via exactly one single "common coupling optics" (10) is coupled to the other multipass cells (6) and thereby a deflection optics ( 16) which is arranged in the intermediate region (13) of the "inner multipass cell" (6) in order to guide the radiation branches (12) guided there in parallel over the two focusing optics (7) to the one "common coupling optics" (10). Multipass laser system (1) according to at least one of the preceding claims, characterized in that one of the coupling optics (8, 9, 10) is designed as a phase-front-correcting element for compensation of phase-front changes caused by the solid-state disk (14).

9. Multipass laser system (1) according to claim 8, characterized in that the input and output optics (2,3) in an "outer multipass cell" (6) is arranged and arranged in this "outer multipass cell" (6) feedback optics (8 , 9) has a constant refractive power, preferably no refractive power.

10. Multipass laser system (1) according to any one of claims 8 or 9, characterized in that the Multipasslasersystem (1) has exactly two "common coupling optics" (10) and one of the two "common coupling optics" (10) is designed as a phase front-correcting element while in front of the other "common coupling optics" (10) a solid state disk (14) is arranged.