DE102019117880B4 - Laser system - Google Patents

Abstract

Laser system (100), in particular a solid-state disk laser system, comprising at least one solid-state disk (10) through which a radiation field within a laser resonator or a laser amplifier system can pass, wherein the solid-state disk (10) comprises a laser-active material and is arranged flat on a carrier structure (22) by means of one or more contacting elements (16, 18, 20), wherein the carrier structure (22) has compensation means (32) for compensating for a distortion of the radiation field, wherein the axial thickness of the carrier structure (22) varies over the radial extent (52) of the carrier structure (22) and wherein the carrier structure (22) is axially slotted in a lateral extent in order to influence both the radial heat transport and the deformation of the solid-state disk (10) by modifying the rigidity.

Description

State of the art

The invention relates to a laser system, in particular a solid-state disk laser system, comprising at least one solid-state disk, in particular a semiconductor disk, through which a radiation field within a laser resonator or a laser amplifier system can pass, wherein the solid-state disk comprises a laser-active material and is arranged flatly on a carrier structure by means of one or more contacting elements.

Such laser systems are conventional laser systems with a resonator or laser amplifier systems, whereby the optical behavior of the laser-active medium must be taken into account when designing the laser systems or laser amplifier systems and the resulting radiation field depends on the optical behavior of the laser-active medium.

When laser systems are implemented according to the disk laser concept, thermally induced phase disturbances of the radiation field are very small due to the typical properties of this concept.

Nevertheless, due to the combination of deformation of the solid-state disk/heat sink composite due to the temperature gradient as well as the thermal expansion of the laser crystal and the temperature-induced change in the refractive index of the laser crystal, a non-negligible thermal lensing effect can occur.

The EP 2 243 202 B1 discloses a solid-state laser with a resonator and a solid-state disk through which the radiation field passes, in which the radiation field is reflected onto at least one first adaptive optical mirror unit, with which a distortion of the radiation field is compensated by a thermal lens effect of the at least one solid-state disk. This makes it possible to essentially compensate for the distortion of the radiation field due to the thermal lens effect and thus to avoid the negative effects on the radiation field and on the beam quality. With the first adaptive optical mirror unit, the distortions of the radiation field are essentially compensated by the thermal lens effect of a maximum of two solid-state disks.

This means that the number of the first adaptive optical mirror units can be kept as low as possible. The first adaptive optical mirror unit is a thermally adaptive optical mirror unit whose reflection behavior can be thermally adjusted. One possibility is to realize the thermal adjustability due to thermal expansion in the mirror unit using heating coils that can be heated electrically, for example. Another possibility is to adjust the thermally adaptive optical mirror unit in such a way that the local thermal differential heating is achieved by an incident radiation field, for example infrared radiation.

Various solid-state laser systems are made of DE 4344227 A1 , EN 102014100204 A1 , DE 102012214970 A1 , RU2687088C1 , WO 2005091446 A1 , US20110206077 A1 , JP 2008004752 A known.

From the DE 10219004 A1 A laser beam source with a laser element is known which contains a thin crystal disk as a laser-active medium. To mechanically stabilize the laser element and to improve the thermal contact with a cooling element on the flat side of the crystal disk facing away from it, a cooling disk is arranged between the crystal disk and the cooling element.

Disclosure of the invention

The object of the invention is to provide a laser system in which effects of a thermal lens effect of the radiation field are reduced.

The objects are achieved by the features of the independent claims. Favorable embodiments and advantages of the invention emerge from the further claims, the description and the drawing.

The invention relates to a laser system, in particular a solid-state disk laser system, comprising at least one solid-state disk through which a radiation field within a laser resonator or a laser amplifier system can pass, wherein the solid-state disk comprises a laser-active material and is arranged flatly on a carrier structure by means of one or more contacting elements.

According to the invention, the support structure has compensation means for compensating a distortion of the radiation field. The axial thickness of the support structure varies over the radial extent of the support structure, and the support structure is axially slotted in the lateral extent in order to influence both the radial heat transport and the deformation of the solid-state disk by modifying the stiffness.

The solid-state disk can also be a semiconductor disk. An embodiment of the laser system according to the invention can also be an optically pumped semiconductor laser amplifier.

Optionally, at least the solid-state disk and/or the one or more contacting elements can have compensation means for compensating a distortion of the radiation field.

By varying the axial thickness of the support structure over a radial extension of the support structure, a suitable adjustment of the cooling of the solid-state disk by the support structure can be achieved. Mechanical deformation of the solid-state disk due to an inhomogeneous temperature distribution in the solid-state disk can also be reduced.

Furthermore, a known method, namely providing a heat sink with a non-constant thickness, can be used, the use of which is not previously known for the compensation of aspherical parts of the thermal lens, in order to compensate for a further aspherical part clearly outside the active region.

The contacting method by which the solid-state disk is arranged on the carrier structure can include, for example, gluing, soldering and/or optical bonding. The contacting elements can therefore be designed as adhesive films, solder films or bonding layers, for example. The thermal and mechanical properties of the contacting elements can be suitably adjusted via the structure of the contacting elements. The solid-state disk has a highly reflective coating on the back for laser systems. The contact between the solid-state disk and the carrier structure can be designed to be advantageous for thermal conductivity and mechanical/thermal strength.

Preferably, the solid-state disk, which is formed for example from an ytterbium-doped laser-active crystal material or laser crystal, such as yttrium aluminum garnet, can be rotationally symmetrical in order to offer a round beam cross-section a favorable utilization of the solid-state material. Advantageously, at least the solid-state disk and/or at least the carrier structure and/or at least the one or more contacting elements can be designed to compensate for a distortion of the radiation field, in particular geometric dimensions can be set favorably.

Preferably, the support structure can be connected to a cooling element or can itself be designed as a cooling element whose thermal conductivity is significantly higher than that of the solid-state disk, so that heat generated in the solid-state disk by the radiation field can be dissipated.

Compensation means for compensating for a distortion of the radiation field, such as can occur due to a thermal lens effect in the solid-state disk due to the heat generated by the radiation field, can advantageously be provided in the laser system itself, since this provides a high degree of flexibility in order to carry out an appropriate phase compensation to reduce the thermal lens effect.

In particular, to increase efficiency and reduce any additional heat input, it is particularly advantageous to use a source of radiation power in the solid-state disk as a compensation agent. Such a source is in the form of incoherent fluorescence radiation, which is generated at a comparable power level to the heat generated in the solid-state disk and is normally partially emitted. The rest of the fluorescence radiation is absorbed or reflected on the back of the solid-state disk or in the support structure. This fluorescence radiation can be used as a significant heat source by means of suitable absorbing structures in order to achieve a more homogeneous temperature distribution in the solid-state disk and thus a reduction in particular of so-called aspherical components of the thermal lens effect. The total fluorescence power in the case of a pulse amplifier operated at 1 kHz, for example, is significantly higher than in the case of a continuously operated laser resonator, and thus also the required heating power.

The advantages of the solution according to the invention with compensation means in the solid-state disk and/or in the carrier structure are that it is independent of the optical design of the resonator or laser system, since the compensation of the distortion of the radiation field takes place directly on the solid-state disk. Since the beam quality is only slightly or not at all influenced, the optical structure of the resonator or laser system can be simplified.

In this way, it is also possible to avoid or at least reduce unwanted radiation power peaks that could exceed the damage thresholds of optical elements and/or the solid-state disk.

This also increases the overall efficiency of the laser system, as the essential heating power does not have to be added additionally for compensation. The favorable distribution of the excitation energy also allows a higher efficiency to be achieved with a simpler optical structure.

The complexity of the laser system can be reduced because, if an additional heating laser is used at all, this can be a relatively small, compact system. This allows the advantage of a solid-state disk laser amplification system, the particularly efficient dissipation of heat to ensure a low temperature of the laser material, to be exploited favorably. The introduction of heating power at the front of the solid-state disk can be efficient because this heats the entire thickness and the thermal resistance from the back of the solid-state disk to the cooling is significantly smaller than the thermal resistance through the solid-state disk.

Another advantage is the reduced emission of fluorescence radiation. Since the fluorescence radiation is partially converted into heat, the fluorescence emitted by the solid-state disk into the environment decreases. This fluorescence could otherwise be absorbed by various components of the pump structure around the solid-state disk and lead to local heating, deformation and possibly damage.

It is also advantageous that parasitic effects can be suppressed with the solution according to the invention. Otherwise, the fluorescence could possibly interact with the excited ions in the solid-state disk and possibly be amplified, which could reduce the effective gain that can be achieved for the laser. This effect is known as "amplified spontaneous emission" (ASE). This effect can be amplified by ASE reflected back from the edge of the solid-state disk. Since this back reflection usually takes place with multiple reflections on the front and back of the solid-state disk, the effect can be advantageously suppressed by the partial absorption of the fluorescence radiation on the front due to the compensation means.

According to an advantageous embodiment of the laser system, at least one absorbing region for fluorescence radiation can be provided as a compensation means on the side of the solid-state disk facing away from the carrier structure. In particular, an area designed as an anti-reflective coating can be provided as an absorbing region for fluorescence radiation.

Since the side of the solid-state disk facing away from the carrier structure usually has an anti-reflective coating, this can advantageously be used, if suitably designed, to absorb the fluorescence radiation in order to use the fluorescence radiation as a source for additional heating of the solid-state disk in a targeted manner in a certain spatial region of the solid-state disk.

It is advantageous to apply a non-reflective layer, such as chromium, to the surface of the solid-state disk, for example by vapor deposition, and then apply the actual anti-reflective layer with an interferometric effect to this layer. Chromium, for example, absorbs infrared radiation well and has a low angle dependence in absorption. The coating can also have modified properties in the radial direction, i.e. parallel to the surface of the solid-state disk.

Alternatively, it is also conceivable to apply one or more layers of graphene as an absorbing layer.

According to an advantageous embodiment of the laser system, an absorption level of the region absorbing the fluorescence radiation can be designed to vary radially, in particular to have an absorption level that changes essentially in stages in the radial direction. Depending on the type and structure of the distortion of the radiation field due to thermal lens effects, the coating can be designed to suitably vary radially as absorbing the fluorescence radiation in order to achieve a suitable temperature distribution in the solid-state disk as a compensation means.

According to an advantageous embodiment of the laser system, the absorbing region can have an inner radius that corresponds to at least 1.5 times a fundamental mode radius of the radiation, preferably at least 1.7 times the fundamental mode radius, very particularly preferably at least twice the fundamental mode radius. With these values, the influence on the laser fundamental mode can be kept low, since the laser fundamental mode is dampened by smaller radii due to absorption and scattering.

According to an advantageous embodiment of the laser system, a segment arranged on and/or in the solid-state disk for scattering and/or absorbing the fluorescence radiation can be provided as a compensation means. With the help of such a segment, the scattering and/or absorption of the fluorescence radiation can be specifically spaced. be used in a structured manner to achieve a suitable temperature distribution in the solid-state disk.

According to an advantageous embodiment of the laser system, the segment can be arranged on or in a side of the solid-state disk facing the carrier structure or facing away from it. In particular, the segment can be arranged close to the surface. In this way, scattering and/or absorption of the fluorescence radiation can be spatially structured in a targeted manner, in particular also used close to the surface, in order to achieve a suitable temperature distribution on the surface of the solid-state disk.

According to an advantageous embodiment of the laser system, the segment can be formed by mechanical material processing of the side and/or by means of ion implantation. This can achieve increased scattering and/or absorption for fluorescence radiation.

For example, lithography processes commonly used in semiconductor technology or similar microstructuring processes can be used as mechanical processing methods, whereby for laser wavelengths in the micrometer range, the structuring can also expediently be in the micrometer range.

According to an advantageous embodiment of the laser system, an area of the solid-state disk can be designed to scatter and/or absorb the fluorescent radiation by means of ion implantation. An optically inactive area that is arranged radially outside the optically active area of the solid-state disk can advantageously be selected as the area of the solid-state disk. Ion implantation can advantageously include the implantation of ions that preferentially interact with the fluorescent radiation, such as ytterbium, titanium, samarium or other elements that absorb the fluorescent radiation. The broadest possible absorption of the fluorescent radiation by the implanted ions is advantageous in this case.

According to an advantageous embodiment of the laser system, the carrier structure can have a locally specifically adjusted thermal conductivity as a compensation means. This allows the cooling of the solid-state disk to be influenced in a targeted manner in order to achieve a desired temperature distribution in the solid-state disk, which is suitable for compensating the thermal lens effect. In this way, a possible mechanical, for example aspherical, deformation of the solid-state disk can also be advantageously reduced.

By varying the axial thickness of the support structure over a radial extension of the support structure, a suitable adjustment of the cooling of the solid-state disk by the support structure can be achieved. Mechanical deformation of the solid-state disk due to an inhomogeneous temperature distribution in the solid-state disk can also be reduced.

Furthermore, a known method, namely providing a heat sink with a non-constant thickness, can be used, the use of which is not previously known for the compensation of aspherical parts of the thermal lens, in order to compensate for a further aspherical part clearly outside the active region.

Since the carrier structure has at least one specifically formed material inhomogeneity, in particular a slot structure, obliquely or perpendicular to the radial extension, according to an advantageous embodiment of the laser system, the carrier structure can be formed radially around the material inhomogeneity.

A known method, namely interrupting the cooling of the solid-state disk, is modified to radially non-homogeneous cooling in order to increase the efficiency of compensating the distortion of the radiation field. Furthermore, the efficiency of heat dissipation from the solid-state disk can still be kept at the usual level.

According to an advantageous embodiment of the laser system, the one or more contacting elements can be designed as compensation means, which can include adhesive films, solder films or bonding layers, for example, between the solid-state disk and the carrier structure with different thermal conductivity. In this way, a spatially targeted variation of the heat transfer between the solid-state disk and the carrier structure is possible for the heat dissipation from the solid-state disk.

According to an advantageous embodiment of the laser system, the contacting elements can have different heat conduction coefficients. The contacting elements can, for example, be different adhesive materials by means of which the solid-state disk is thermally and mechanically bonded to the carrier structure. Epoxy adhesives can, for example, be used as adhesives. UV-curable adhesives can advantageously be used, which have low shrinkage when curing and high thermal resistance and mechanical rigidity. The thickness of the adhesive structure can can be suitably varied in order to achieve spatially different properties of the adhesive materials.

According to an advantageous embodiment of the laser system, the contacting elements can have different thicknesses. The thickness of the contacting elements can be suitably varied in order to achieve spatially different properties of the adhesive materials. In this way, a spatially different thermal conductivity can be achieved between the solid-state disk and the carrier structure.

According to an advantageous embodiment of the laser system, the one or more contacting elements can be thermally connected to the solid-state disk and the carrier structure in different ways. For example, different adhesives can be used to connect the contacting elements to the solid-state disk and/or the carrier structure, which have different thermal conductivity coefficients and thus enable targeted spatial heat dissipation from the solid-state disk. Epoxy adhesives, for example, can be used as adhesives, which have little shrinkage when curing. It is also possible to provide a connection via soldering or optical bonding.

For efficient heat dissipation and thus efficient laser operation, it is advantageous if the thermal resistance of the contact in the area of a radially inner contact element is low. The efficiency of compensating the aspherical components of the thermal lens effect by additional heating power from the absorption of fluorescence can be improved if the thermal resistance in the area of a radially middle contact element is very high, whereby the optimal values for the inner and outer radius of the contact element and the optimal value for the thermal resistance for the respective operating conditions can be advantageously determined on the basis of FEM calculations. The total fluorescence power in the case of a pulse amplifier operated at 1 kHz is significantly higher than in a continuously operated laser resonator, and thus also the heating power.

Whether a high or, better, a medium thermal resistance is achieved in a radially outer contacting element also depends on the operating conditions. In the case of very high average laser powers and especially when used as a pulse amplifier, a significantly increased fluorescence output can be expected due to ASE effects. In this case, a relatively low thermal resistance in a radially outer contacting element can be advantageous in order to avoid overheating at the radially outer edge of the solid-state disk.

Known methods, such as heating by irradiating electromagnetic radiation and electrical heating, can be used to achieve fine tuning. Interaction with the laser radiation can be expediently reduced by electrical heating elements, which are advantageously arranged on the side of the solid-state disk facing away from the carrier structure.

According to an advantageous embodiment of the laser system, compensation for clamping effects of the solid-state disk can be provided, in particular compensation for deformation of the solid-state disk. The thicknesses of the individual elements such as the solid-state disk and/or support structure can advantageously be selected to avoid deformation of the solid-state disk due to mechanical clamping. It is also possible to use adaptable clamping elements to reduce the mechanical deformation of the solid-state disk.

Heat sinks can advantageously be used, which include, for example, CVD diamond layers, metallic sinks such as copper/copper-tungsten, silicon carbide or similar materials. Heat sinks can advantageously be constructed from several materials.

According to an advantageous embodiment of the laser system, a radius of the solid-state disk of at least twice the radius of an area of the solid-state disk that is active for the radiation field, in particular of at least three times the radius of a fundamental mode, can be provided. In this way, effects of mechanical deformation and/or of an inhomogeneous temperature distribution in the solid-state disk can be suitably reduced.

The rigidity of the support structure varies radially. This can be achieved by an advantageous design of the laser system, for example, by varying the thickness of the support structure. The simplest implementation is a support structure that is spherically machined on the back. In this way, the effects of mechanical deformation and/or inhomogeneous temperature distribution in the solid-state disk can be suitably reduced.

The thickness of the carrier structure is designed to vary radially, so that according to an advantageous embodiment of the laser system, a cross section of the carrier structure is designed as a circular disk section In this way, effects of mechanical deformation and/or inhomogeneous temperature distribution in the solid-state disk can be suitably reduced.

drawing

Further advantages emerge from the following description of the drawings. The figures show embodiments of the invention. The figures, the description and the claims contain numerous features in combination. The person skilled in the art will also expediently consider the features individually and combine them into further useful combinations.

• 1 eine optische Wegdifferenz eines Strahlungsfelds nach der Reflektion an einer Festkörperscheibe, aufgetragen über dem Radius der Festkörperscheibe;
• 2 eine schematische Schnittdarstellung durch ein Lasersystem nach einem Ausführungsbeispiel der Erfindung mit eingezeichneter Intentensitätsverteilung eines Grundmodes des Strahlungsfelds;
• 3 eine schematische Schnittdarstellung durch ein Lasersystem nach einem weiteren Ausführungsbeispiel der Erfindung;
• 4 eine schematische Schnittdarstellung durch ein Lasersystem nach einem anderen Ausführungsbeispiel der Erfindung; und
• 5 eine schematische Schnittdarstellung durch ein Lasersystem nach einem anderen Ausführungsbeispiel der Erfindung.

Examples include:

• 1 an optical path difference of a radiation field after reflection from a solid disk, plotted over the radius of the solid disk;
• 2 a schematic sectional view through a laser system according to an embodiment of the invention with the intensity distribution of a fundamental mode of the radiation field drawn in;
• 3 a schematic sectional view through a laser system according to a further embodiment of the invention;
• 4 a schematic sectional view through a laser system according to another embodiment of the invention; and
• 5 a schematic sectional view through a laser system according to another embodiment of the invention.

Embodiments of the invention

In the figures, components of the same type or with the same effect are numbered with the same reference symbols. The figures show only examples and are not to be understood as limiting.

Directional terminology used below with terms such as "left", "right", "top", "bottom", "before", "behind", "after" and the like is intended only to facilitate understanding of the figures and is in no way intended to limit the scope. The components and elements shown, their design and use may vary in accordance with the considerations of a person skilled in the art and may be adapted to the respective applications.

1 shows an optical path difference (OPD) of a radiation field after reflection on a solid disk, plotted against the radius of the solid disk. The difference in the optical path length through the solid disk minus an average spherical wavefront distortion (resulting aspherical wavefront distortion) in µm is plotted as a function of the radius R of the solid disk in mm.

When laser systems are implemented according to the disk laser concept, the thermally induced phase disturbances are very small due to the typical properties of this concept.

Nevertheless, due to the combination of deformation of the composite of solid-state disk and heat sink, which is usually designed as a support structure, due to the temperature gradient as well as the thermal expansion of the laser crystal and the temperature-related change in the refractive index of the laser crystal, a non-negligible thermal lens effect occurs, which causes a distortion of the radiation field.

This thermal lens can be divided into a spherical part and an aspherical part. The spherical part influences the stability range of the laser resonator. This can be compensated by a suitable design of the resonator and spherical compensation optics. The aspherical part influences the resulting laser mode. When operating close to the fundamental mode, significant parts may be diffracted into higher modes, the so-called diffraction loss, so that the efficiency drops or the laser cannot be operated at all. This also applies to operation as a laser.

If the excitation energy is introduced into the laser crystal homogeneously in a rotationally symmetrical centered area of the laser crystal, the typical aspherical part of the 1 shown course. This usually does not improve with, for example, inhomogeneous introduction of the excitation energy. In particular, the edge 56 shown at the edge of the area where the excitation energy is introduced leads to significant losses for the fundamental mode, which in the case of a laser resonator leads to reduced efficiency, up to non-functioning, or in the case of a laser, depending on the specific optical design, to reduced efficiency and/or possibly dramatic deterioration of the beam quality.

2 shows a schematic representation of a radial section through a laser system 100 according to an embodiment of the invention. For clarification, an intensity distribution 40 of a fundamental mode of the radiation field is shown.

The example in 2 The laser system 100 shown comprises a solid-state disk 10 through which a radiation field can pass as part of a resonator of a laser system. The solid-state disk 10 comprises a laser-active material and is arranged flat on a carrier structure 22 by means of one or more contacting elements 16, 18, 20.

The 2 shows a typical structure of a solid-state disk laser system in radial section. The solid-state disk 10 is mounted on a carrier structure 22, which also serves as a heat sink and can be water-cooled, for example, from the side facing away from the solid-state disk 10. In conventional solid-state disk lasers, the carrier structure 22 is of constant thickness. The region 12 represents the laser-active part of the solid-state disk 10, in which the excitation power is absorbed and the laser amplification process takes place. A significant part of the heat output is generated in the active region 12.

The contacting elements 16, 18, 20 represent the connection to the carrier structure. 2 In the embodiment shown, all areas of the contacting elements 16, 18, 20 have the same properties.

The regions 24, 26 represent the coating on the side 36 facing away from the carrier structure 22, the front side of the solid-state disk 10. In conventional solid-state disk lasers according to the state of the art, the coating 24, 26 has the same properties. The coating regions 24, 26 usually represent anti-reflection layers and can include, for example, coatings with Ta ₂ O ₅ , SiO ₂ , Al ₂ O ₃ .

To illustrate the geometric relationships, the typical radial intensity distribution 40 of a fundamental mode of the radiation field is shown above the radial section of the laser system 100, where w0 is the so-called mode radius of the fundamental mode. The intensity distribution 40 is shown above the lateral extension of the solid-state disk 10, which is rotationally symmetrical with an axis of symmetry 66. The radii for the values 1.7 x w0 and 3 x w0 are also shown. The solid-state disk 10 has a maximum radius 68, the support structure a maximum radius 52 as lateral extension.

In the 2 In the embodiment shown, the solid-state disk 10 is assigned compensation means 32 for compensating for a distortion of the radiation field. An absorbing region 26 for fluorescence radiation is provided as compensation means 32 on the side 36 of the solid-state disk 10 facing away from the carrier structure 22. In the embodiment shown, the solid-state disk 10 has an anti-reflective coating on the front side 36, which is divided into two regions 24, 26, with the radially outer region 26 being provided as an absorbing region 26 for fluorescence radiation.

In the modification of the disk laser structure according to the invention, the realization of the coating regions 24, 26 on the front side 36 is such that in region 24 it is designed as in the usual design, while in region 26 the coating is realized to be absorbing over a wide angle range for the fluorescence wavelengths.

The absorption can be constant in the radial direction or can vary radially, e.g. increasing absorption towards the outside. In particular, the absorption can have an absorption level that changes substantially in stages in the radial direction. Since absorption at the fluorescence wavelengths simultaneously means absorption at the laser wavelength, the absorbing region 26 can have an inner radius 48 of at least 1.5 x w0, preferably 2 x w0, where w0 represents the fundamental mode radius. In the 2 For comparison, the radius 48 of approximately 1.7 x w0 is shown.

A simple implementation for such a coating of the front side 36 can be achieved, for example, by vapor-depositing the solid-state disk 10 with a thin layer of chromium before applying the coating, with the region 24 being covered by a cover or a protective lacquer. After removing the cover or the protective lacquer, a conventional coating can then be applied. The radius of the region 24 relative to the radius of the absorbing region 26 can be conveniently determined by thermal-mechanical modeling or experimentally.

In 3 is a schematic sectional view through a laser system 100 according to a further embodiment of the invention. In the 3 In the embodiment shown, a segment 28 arranged in the solid-state disk 10 for scattering and/or absorbing the fluorescent radiation is provided as compensation means 32. The segment 28 is arranged close to the surface on the side 36 of the solid-state disk 10 facing away from the carrier structure 22.

3 shows the same section of the solid disk 10 as in 2 shown, only with a modification of the front side 36 of the solid-state disk 10. In the usual designs, the Solid-state disk 10 has a constant, unprocessed thickness and surface. By processing the surface of the front side 36, as can be done, for example, with laser material processing, a scattering and absorption point can be introduced into the surface of the front side 36.

Another possibility for introducing additional heat into the solid-state disk 10 can be achieved by increasing scattering and absorption at surface structures. By surface processing at the location of the segment 28, for example by mechanical material processing and/or laser material processing, the absorption of the fluorescence and the laser radiation can be increased locally.

An increase in absorption can alternatively be achieved by targeted ion implantation in a region 14 of the solid-state disk 10. The optically non-active region 14, which is arranged radially outside the optically active region 12 of the solid-state disk 10, can be advantageously selected as the region of the solid-state disk. Here, the ion density can be specifically optimized depending on the radial and depth. The ions can be absorbent for the pump wavelength and/or for the fluorescence wavelength. In this case, too, the area of the free aperture can advantageously be selected to be large enough so as not to dampen the absorption of the desired fundamental mode too much.

Likewise, the location of the segment 28 relative to the non-active region 14 of the solid-state disk 10 can be optimized to ensure low wavefront distortion of the radiation field within the solid-state disk 10. The arrangement and design of the segment 28 can be advantageously optimized through modeling and/or experiments.

4 shows a schematic sectional view through a laser system 100 according to another embodiment of the invention, in which the carrier structure 22 has a locally specifically adapted thermal conductivity as a compensation means 32. The carrier structure 22 has at least one specifically formed material inhomogeneity 30, in particular a slot structure, obliquely or perpendicular to the radial extension 52. In particular, the material inhomogeneity 30 can be formed radially all the way around.

4 shows the same section of the solid disk 10 as the 2 and 3 , only with a modification 30 of the support structure 22 on the underside 70 of the support structure 22. The support structure 22 is axially slotted in lateral extension in order to influence both the radial heat transport and the deformation of the solid-state disk 10 by modifying the stiffness.

By modifying the support structure 22 through the slot 30, the radial heat transport can be reduced in order to achieve an effective difference in cooling between the center and edge area of the solid-state disk 10. The slot 30 in the support structure 22 reduces the material heat transport in the heat sink, so that an increased temperature within the solid-state disk 10 is established in the outer area due to poorer coolant flow and lower radial cooling within the heat sink. The location for local modification of the support structure 22 in order to achieve additional heat input in the outer area can be advantageously optimized by thermal-mechanical modeling and/or experiments.

As a further possibility to make the heat conduction from the solid-state disk 10 into the carrier structure 22 and within the carrier structure 22 laterally variable, the axial thickness 58 of the carrier structure 22 can be varied via the radial extension 52 of the carrier structure 22. As in the embodiments in the 2 to 5 As shown, the thickness 58 of the support structure 22 can decrease from a maximum thickness 60 at the center of the support structure 22 to a minimum thickness 62 at the edge of the support structure 22.

In a further embodiment, in a modification of the thermal connection between solid-state disk 10 and carrier structure 22, for example, the one or more contacting elements 16, 18, 20 as compensation means 32 between solid-state disk 10 and carrier structure 22 can be designed to have different thermal conductivity. The contacting elements 16, 18, 20 can have different thermal conductivity coefficients, for example. The one or more contacting elements 16, 18, 20 can also be thermally connected to the solid-state disk 10 and the carrier structure 22 in different ways, for example by using different adhesives for connection.

For efficient heat dissipation and thus efficient laser operation, it is advantageous if the thermal resistance of the contact in the area of the radially inner contact element 16 is low. The efficiency of compensating the aspherical components of the thermal lens effect by additional heating power from the absorption of fluorescence can be improved if the thermal resistance in the area of the radially middle contact element 18 is very high, with the optimal values for the inner and outer radius of the contact element 18 and The optimal value for the thermal resistance for the respective operating conditions can be advantageously determined on the basis of FEM calculations.

Whether a high or, better, a medium thermal resistance is realized in the radially outer contacting element 20 also depends on the operating conditions. In the case of very high average laser powers and then especially when operating as a pulse amplifier, a significantly increased fluorescence power due to ASE effects can be expected. Here, a relatively low thermal resistance in the contacting element 20 can be advantageous in order to avoid overheating at the edge of the solid-state disk 10.

The thermal connection can be modified by introducing material with different thermal conductivity, using different adhesives with different thermal properties, by omitting the thermal connection or by modifying the adhesive thickness in the different contacting elements 16, 18, 20.

By introducing electrical heating power into the solid-state disk 10, a slight influence on the laser amplification process can be achieved by introducing the electrical power at the rear side 38 of the solid-state disk 10, e.g. into the contacting elements 16, 18, 20. This is not very efficient, but can be used to "fine-tune" the additional heating. This can sensibly be done in the contacting elements 18 and 20. In addition to a radially symmetrical heating system, an azimuthally varying heating system is also suitable here in order to compensate for small asymmetries.

In 5 is a schematic sectional view through a laser system 100 according to another embodiment of the invention, in which means for compensating clamping effects of the solid-state disk 10 are provided as compensation means 32. In particular, the compensation means 32 can be provided for compensating a deformation of the solid-state disk 10.

Temperature gradients in the composite of solid-state disk 10 and support structure 22 as well as the different thermal expansion coefficients of solid-state disk 10 and support structure 22 can lead to a bending of this composite under thermal load. Due to the clamping conditions at the radially outer edge of solid-state disk 10 and/or support structure 22, in 5 purely schematically indicated by the clamping 72, further non-spherical phase disturbances can arise.

A compensation means 32 for reducing these disturbances can be a sufficiently large inner diameter of the clamping device 72, ie a sufficiently large free “mechanical aperture”. In the 2 It is indicated that the radius of the solid disk 10 is greater than 3 x w0, and accordingly also at least the inner radius 74 of the clamping. Since in 5 the clamping element 72 acts on the support structure 22, the inner radius 74 of the clamping element 72 is even larger than 3 x w0.

Alternatively, it may also be advantageous if the radius of the solid-state disk 10 and the mechanical clamping 72 is selected to be greater than twice the radius of the “active” area of the solid-state disk 10. As in 2 As shown, a radius 68 of the solid-state disk 10 of at least twice a radius 48 of a region 12 of the solid-state disk 10 that is active for the radiation field, in particular of at least three times a fundamental mode radius w0, can advantageously be provided.

Another effective method for minimizing these additional non-spherical phase disturbances is a radial variation of the mechanical stiffness of the composite of solid disk 10 and support structure 22. A technically simple solution for this is the 4 indicated radial reduction of the axial thickness 58 of the support structure 22. The thickness 58 of the support structure 22 can decrease from a maximum thickness 60 in the center of the support structure 22 to a minimum thickness 62 at the edge of the support structure 22.

It can also be advantageous if the rigidity of the support structure 22 is designed to vary radially. In particular, a thickness 58 of the support structure 22 can be designed to vary radially. A cross section of the support structure 22 can thus expediently be designed as a circular disk section.

A favorable variation can be determined iteratively using FEM methods due to the complex relationships between heat input, different expansion coefficients, elastic moduli, etc. For reasons of technical manufacturability, a spherical shape is recommended, which can only be an approximation, but already brings clear advantages.

Claims (17)

Laser system (100), in particular a solid-state disk laser system, comprising at least one solid-state disk (10) through which a radiation field within a laser resonator or a laser amplifier system can pass, wherein the solid-state perscheibe (10) comprises a laser-active material and is arranged flat on a carrier structure (22) by means of one or more contacting elements (16, 18, 20), wherein the carrier structure (22) has compensation means (32) for compensating a distortion of the radiation field, wherein the axial thickness of the carrier structure (22) varies over the radial extent (52) of the carrier structure (22) and wherein the carrier structure (22) is axially slotted in lateral extent in order to influence both the radial heat transport and the deformation of the solid-state disk (10) by modifying the rigidity. Laser system according to Claim 1 , wherein at least the solid-state disk (10) and/or the one or more contacting elements (16, 18, 20) have compensation means (32) for compensating a distortion of the radiation field. Laser system according to Claim 1 or 2 , wherein at least one absorbing region (26) for fluorescent radiation is provided as compensation means (32) on the side (36) of the solid-state disk (10) facing away from the carrier structure (22), in particular wherein a region (26) designed as an anti-reflective coating is provided as an absorbing region (26) for fluorescent radiation. Laser system according to Claim 3 , wherein an absorption coefficient of the region (26) absorbing the fluorescence radiation is designed to vary radially, in particular having an absorption coefficient that varies substantially in stages in the radial direction. Laser system according to Claim 3 or 4 , wherein the absorbing region (26) has an inner radius (48) which corresponds to at least 1.5 times a fundamental mode radius w0 of the radiation, preferably at least 1.7 times the fundamental mode radius w0, very particularly preferably at least 2 times the fundamental mode radius w0. Laser system according to one of the preceding claims, wherein a segment (28) arranged on and/or in the solid-state disk (10) for scattering and/or absorbing the fluorescence radiation is provided as compensation means (32). Laser system according to Claim 6 , wherein the segment (28) is arranged on or in a side (38) or a side (36) of the solid-state disk (10) facing the carrier structure (22), in particular is arranged close to the surface. Laser system according to Claim 6 or 7 , wherein the segment (28) is formed by mechanical material processing of the side (36, 38). Laser system according to one of the preceding claims, wherein a region (14) of the solid-state disk (10) is formed by means of ion implantation for scattering and/or absorbing the fluorescence radiation. Laser system according to one of the preceding claims, wherein the carrier structure (22) has a locally specifically adapted thermal conductivity as a compensation means (32). Laser system according to one of the preceding claims, wherein the one or more contacting elements (16, 18, 20) are designed to have different thermal conductivity as compensation means (32) between the solid-state disk (10) and the carrier structure (22). Laser system according to Claim 11 , wherein the contacting elements (16, 18, 20) have different thermal conduction coefficients. Laser system according to Claim 11 or 12 , wherein the contacting elements (16, 18, 20) have a different thickness. Laser system according to one of the Claims 11 until 13 , wherein the one or more contacting elements (16, 18, 20) are thermally differently connected to the solid-state disk (10) and the carrier structure (22). Laser system according to one of the preceding claims, wherein compensation of a deformation of the solid-state disk (10) is provided. Laser system according to Claim 15 , wherein a radius (68) of the solid-state disk (10) of at least twice a radius (48) of a region (12) of the solid-state disk (10) active for the radiation field, in particular of at least three times a fundamental mode radius w0 is provided. Laser system according to Claim 15 or 16 , wherein a cross section of the support structure (22) is formed as a circular disk section.

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