DE102016114702A1 - Laser amplification system and method for correcting an asymmetrical, transverse radiation pressure profile in a laser-active medium of a solid - Google Patents

Abstract

In order to improve a laser amplification system comprising a solid state having a laser active medium, a first pump radiation source for generating a first pump radiation field, the solid at least once, in particular multiple, interspersed to excite the laser-active medium to improve so that the beam quality is improved in a solid state laser is proposed that it comprises at least one second pump radiation source for generating at least one second pump radiation field, which at least simply, in particular repeatedly passes through the solid to excite the laser-active medium, wherein the first pump radiation field and the second pump radiation field are aligned so that in one of the Solid defined transversal plane, the sum of all first transverse components of the incident on the solid first pump radiation field and the sum of all second transverse components of the incident on the solid z Compensate or substantially compensate for wide pump radiation field.

Description

The present invention relates to a laser amplification system comprising a solid having a laser-active medium, a first pump radiation source for generating a first pump radiation field, which at least simply passes through the solid, in particular multiple, for exciting the laser-active medium.

Furthermore, the invention relates to a method for correcting an asymmetrical transverse radiation pressure profile on a laser active medium having solid state of a laser amplification system, which radiation pressure profile is generated by a first, the solid-penetrating pump radiation field.

A laser amplification system of the type described above for forming a solid-state laser is, for example, from WO 01/57970 A1 or the US 2001/0040909 A1 known. It is designed in such a way that the pump radiation field generated by a pump radiation source, for example a diode laser stack, can pass through the solid body several times in order to excite the laser-active material as optimally as possible. This will, as in the WO 01/57970 A1 or the US 2001/0040909 A1 described, the pump radiation field focused on the solid imaged and deflected after passing twice through the solid by means of a deflection again on the solid. The pump radiation field passes through the solid twice after each impact because it reflects on a highly reflective coated back of the solid and thus leaves the solid at the same angle, taking into account the law of reflection, as it has struck the solid.

A problem with this approach is the radiation pressure exerted by the pump radiation field by the multiple superposition of the individual pumping passages and radiation pressure forces from the absorption and emission processes on the laser-active medium in the solid state. In order to achieve a sufficient gain of the laser amplifier system, in particular work with pump power densities in the range of several kilowatts per square centimeter. Accordingly, the solid on which the pump radiation field is focused multiple imaging, applied to a very high area performance in the range of megawatts per square centimeter. Since the pump radiation field does not impinge on the solid perpendicular to a transverse plane defined by the solid, but obliquely, ie at an angle, a force parallel to the transverse plane also acts in the laser-active medium of the solid due to absorption and emission processes in addition to the radiation pressure exerted perpendicularly by the pump radiation field the solid, so a transversal force. The radiation pressure forces from the absorption and emission processes originate from the bound charges in the laser-active material and, in addition to the longitudinal component, generate a transverse force via the magnetic Lorentz force. This leads to an asymmetric deformation of the solid with depths in the nanometer range (see, for example M. Mansuripur: "Radiation pressure and the linear momentum of the electromagnetic field", Optics Express Vol. 22, 2004, p. 5375 ). It should be noted that the radiation pressure exerted on the solid body is not only dependent on the pump radiation field and its power, but also on the concentration of the laser-active material in the solid state. The higher the concentration of the laser-active material in the solid, the higher the transverse force effect. Since with each passage of the pump radiation field whose power is slightly lower due to the absorption of the solid, the respective acting transverse force decreases with each passage. The consequence of this is an asymmetrical deformation of the solid, which leads to an astigmatism or a higher deformation. This deformation has an effect on the quality of the laser modes, which form in the resonator of a solid-state laser, in which the solid body is arranged. As a result, it is therefore possible with the known laser amplification system in the solid-state laser preferably to excite laser modes whose beam profiles are not rotationally symmetrical.

It is therefore an object of the present invention to improve the beam quality in a solid-state laser, in particular in a disk laser.

This object is achieved in a laser amplification system of the type described above according to the invention that it comprises at least a second pump radiation source for generating at least a second pump radiation field, which at least simply, in particular multiple, passes through the solid to excite the laser-active medium, wherein the first pump radiation field and the second pump radiation field are aligned so that compensate in a defined by the solid transversal plane, the sum of all first transverse components of the incident on the solid first pump radiation field and the sum of all second transverse components of the incident on the solid second pump radiation field or substantially compensate.

The inventively proposed development of the known laser amplification system makes it possible in particular, a asymmetric deformation of the solid, for example in the form of a solid state disk, by the radiation pressure exerted by the first pump radiation field and the transversal forces acting thereon, also as transverse components of the radiation pressure forces exerted by the first pump radiation field, in the transverse plane, by applying at least one second to the solid body Pump radiation field which acts on the solid transverse force is compensated. If, for example, two pump radiation fields are generated, they are in particular aligned with the solid body in such a way that the respective resulting transverse components compensate each other. This can be achieved, in particular, by the fact that the transverse components of the radiation pressure forces acting on the solids by the pump radiation fields are directed in mutually opposite directions. Thus, the transverse forces acting on the solid body by the pump radiation fields cancel each other, so that there is no rotationally asymmetric deformation of the solid. Thus, an undesirable deformation of the laser modes forming in the resonator of the solid-state laser can be prevented, which deformation thus has a negative effect on a beam quality of the laser radiation generated by the solid-state laser. It can be formed in this way laser modes with a completely rotationally symmetrical in cross section beam profile. If more than two pump radiation fields are used, they are in particular aligned such that the pressure forces acting on the solid due to the pump radiation fields add up to zero in the transverse plane. In the case of two pump radiation fields, these are preferably offset in the transversal plane by 180 ° with respect to one another on the solid, with three pump radiation fields offset by an angle of 120 °. With more than two pump radiation fields, the angle in the transverse plane between the pump radiation fields is then predetermined according to the number of pump radiation fields.

In principle, it is also possible to dispense with focusing systems, also referred to below as focusing devices, so that the pump radiation fields only pass through the solids once or twice. Twice only if a back of the solid is provided with a highly reflective coating, so that the pump radiation fields are reflected after passing through the solid once at the back and then pass through the solid again. However, the efficiency of such a laser system is not particularly high, since with only one or two passes of the pump radiation fields through the solid body, only a very small part of the power of the pump radiation fields can be absorbed by the solid. Therefore, it is advantageous if the laser amplification system is designed such that the pump radiation fields repeatedly pass through the solid, in particular at least three times.

It is advantageous if the laser amplification system comprises a first focusing device which generates a plurality of different branches of the first pump radiation field incident in the solid state and converts at least one branch emerging from the solid body into one of the branches which impinge on the solid and are different from the branching branch, and if the laser amplification system at least one second focusing device, which generates a plurality of different branches of the second pump radiation field incident in the solid state and thereby converts at least one branch emerging from the solid into one of the branches which impinge on the solid and are different from the branching branch. The operation of such focusing devices is described in detail in the WO 01/57970 A1 or the US 2001/0040909 A1 to which reference is made in full. The focusing devices make it possible for the pump radiation fields to pass through the solid body several times in order to achieve the highest possible excitation of the laser-active medium in the solid and thus a large amplification factor of the solid-state laser.

For the formation of a solid state laser, it is advantageous if the solid is formed in the form of a solid state disk. This can be coupled in particular with a heat sink in order to avoid heat accumulation in the solid.

The construction of the laser amplification system becomes particularly simple if it comprises a first pump radiation source and a second pump radiation source. Thus, if only two pump radiation sources are used, these can, as already mentioned, be arranged such that the pump radiation fields generated by them are aligned with mutually oppositely directed transverse components of the pressure forces acting on the solid. In the transverse plane, therefore, the pump radiation fields are directed by 180 ° offset to the solid. If the pump radiation fields do not strike the solid at the same angle with respect to the transverse plane, slightly different transverse forces can result with identical pump power of the pump radiation sources. These can be regulated, for example, by adjusting the power of a pump radiation field, so as to generate a greater or lesser transverse force, which then compensates or optimally compensates for the transversal component of the pressure force acting on the solid from the other pump radiation field.

According to a further preferred embodiment of the invention, it can be provided that the first focusing device comprises at least one first deflection unit for deflecting the first pump radiation field after passing through the solid on the solid body, that the at least one second focusing device comprises at least one second deflection unit for deflecting the at least one second pump radiation field after passing through the solid on the solid back and that the at least one first deflection and the at least one second deflection directing the first pump radiation field and the at least one second pump radiation field in the direction of the solid that in a defined by the solid transverse plane the sum all of the first transverse components of the incident on the solid deflected first pump radiation field and the sum of all second transverse components of the impact on the solid compensate or substantially compensate for the deflected at least one second pump radiation field. As with the first impingement of the pump radiation fields on the solid body is ensured by the formation of the focusing means that even after one or more times redirecting the pump radiation fields compensate their parallel to the transverse plane acting on the solid pressure forces. This is realized for any number of deflections of the pump radiation fields by appropriate arrangement and design of the focusing devices for the at least two pump radiation fields.

It is advantageous if the first focusing device comprises at least two first deflecting units and if the at least one second focusing device comprises at least two second deflecting units. In this way, it is possible, in particular, that the pump radiation fields generated by the pump radiation sources irradiate the solid body at least eight times, in particular sixteen times, so that the solid body can extract eight, in particular sixteen times, energy from the pump radiation fields by absorption in the laser-active medium. As a result, an amplification factor of the laser amplification system can be increased as desired.

The laser amplification system can be formed in a particularly simple manner if the at least one first deflection device comprises two reflection surfaces extending at an angle to one another and if the at least one second deflection unit comprises two reflection surfaces extending at an angle to one another. In particular, an angle between the reflecting surfaces of the deflecting units can be 90 °. Thus, it is possible in a simple manner, a pump radiation field, which has once irradiated the solid, was reflected at the back of the solid and then the solid has irradiated a second time to redirect back to the solid and optionally focus on this.

It is advantageous if the first focusing device has collimating and focusing elements which collimate the first pump radiation field directed away from the solid and focus the collimated first pump radiation field in the direction of the solid, and if the at least one second focusing device has collimating and focusing elements to collimate the at least one second pump radiation field directed away from the solid body and to focus the at least one second pump radiation field in the direction of the solid body between the collimated one. With such focusing devices, an expansion of the pump radiation field can be prevented by intermediate collimating. The focusing elements then in turn allow a re-admission or repeated loading of the solid by the pump radiation fields in a particularly small surface area in order to achieve optimal excitation of the same in the laser-active medium.

The structure of the laser amplification system becomes particularly simple if the first focusing device and the at least one second focusing device comprise a common focusing element. In particular, it may be a common parabolic mirror.

Furthermore, it is favorable if the first focusing device and the at least one second focusing device each comprise at least one collimating lens. Such a configuration makes it possible to counteract a widening of the pump radiation fields.

A particularly compact embodiment of the laser amplification system can be achieved, for example, in that the at least one first deflection unit and the at least one second deflection unit surround the solid in a ring shape. Alternatively, a rectangular arrangement of a plurality of deflection units can also be provided.

It is advantageous if the at least one first deflection unit and at least one second deflection unit define a double or multiple ring structure surrounding the solid. Thus, a particularly compact laser amplification system can be formed with a pumping module comprising the focusing devices.

Preferably, the laser amplification system comprises one, two, three, four, five or more second focusing means. The number of focusing devices preferably corresponds to the number of pumping radiation sources. If, for example, three second pump radiation sources are used, it is preferable for these three focusing devices to be provided, as well as a separate focusing device for the first pump radiation source.

Preferably, a back of the solid is coated highly reflective. If such a solid body is exposed to a pump radiation field, then this is reflected at the rear side of the solid, so that pump radiation generated by a pump radiation source can double-pass through the solid state in this way.

Particularly good excitation powers can be achieved in particular in that the first pump radiation source and the at least one second pump radiation source are in the form of a laser. In particular, they may be in the form of a diode laser or a fiber laser. In particular, a diode laser stack can be provided as pump radiation source.

Conveniently, the solid is a laser active crystal, in particular a yttrium aluminum garnet crystal. For example, it may be doped with ytterbium or holmium as the laser active material. By choosing the solid and the laser-active material contained in this, the wavelength of the solid-state laser can be specified in the desired manner.

To form a solid-state laser, it is favorable if the solid is arranged in a resonator which defines a resonator radiation field passing through the solid. In particular, the resonator may comprise two highly reflective elements, between which the resonator radiation field is formed.

The resonator can be formed in a particularly simple manner if the highly reflective rear side of the solid forms an end mirror of the resonator.

Furthermore, it is favorable if the resonator comprises a coupling-out mirror and if the resonator radiation field extends between the end mirror and the coupling-out mirror. In particular, the coupling-out mirror can be made partly transmissive or actively switchable in order to decouple laser radiation from the resonator with a wavelength predetermined by the laser-active material.

The object stated in the introduction is further achieved in a method of the type described above in that at least a second pumping radiation field is directed to the solid and that the first pumping radiation field and the at least one second pumping radiation field are aligned relative to each other, that in one of the solid defined transverse plane, the sum of all first transverse components of the incident on the solid body first pump radiation field and the sum of all second transverse components of the incident on the solid at least one second pump radiation field compensate or substantially compensate. The transversal components are to be understood as meaning, in particular, the portions of the radiation pressure forces in the transversal plane which act on the solid due to the pump radiation fields. As already described at the outset, the proposed method makes it possible to prevent or prevent rotationally asymmetric deformation of the solid by compensating for transversal radiation pressure forces caused by the radiation pressure generated by the pump radiation fields. In particular, this makes it possible to generate optimally rotationally symmetrical beam profiles of laser modes in a solid-state laser.

It is advantageous if the first pump radiation field and the at least one second pump radiation field are aligned relative to one another in such a way that the first transverse components of the first pump radiation field impinging on the solid body and second transverse components of the at least one second pump radiation field impinging on the solid body compensate in pairs or in the transverse plane essentially compensate. This is particularly well possible if an even number of pump radiation fields is used to excite the solid.

In order to achieve the highest possible amplification, it is advantageous if the first pump radiation field and the at least one second pump radiation field are deflected at least once in the direction towards the solid in order to at least double the number of passes through the solid. The more frequently a deflection is made possible, the more often the pump radiation fields can pass through the solid, so that it can remove the pumping radiation fields by absorption during each passage through the solid body.

Preferably, the first pump radiation field and the at least one second pump radiation field are focused at least in each case in the direction of the solid. So can one possible high energy density for excitation of the solid can be realized in this.

It is advantageous if the first and the at least one second pump radiation field are deflected several times in order to multiply the number of passes through the solid. In this way, a gain of the laser amplification system can be increased as desired.

For excitation and generation of laser radiation, it is favorable if a solid-state disk is used as the solid. Thus, in particular, a solid-state disk laser can be formed.

The following description of preferred embodiments of the invention is used in conjunction with the drawings for further explanation. Show it:

1 a schematic representation of the structure of a disk laser (prior art);

2 a schematic representation of acting on the disc of the disk laser transverse compressive forces at 8 times 2 round trips through the solid disk;

3 a schematic three-dimensional arrangement of a solid-state disk laser with two deflection units;

4 a schematic representation of an interferometer for representing a deformation of the impacted with the pump laser radiation solid state disk;

5 an interferogram of a spot spot distribution on a non-precisely adjusted solid disk;

6 FIG. 4: a representation of a laser mode from an I-resonator with a Ho: YAG slice; FIG.

7a : an interferogram taken with arrangement according to 4 at a pump power of 0 watts;

7b : an interferogram analog 7a at a pump power of 15 watts;

7c : an interferogram analog 7a at a pump power of 40 watts;

8a : a laser mode profile with an exactly adjusted pump module and a pump power of 15 watts;

8b : the laser mode profile analog 8a at a pump power of 30 watts;

8c : a laser mode profile analog 8a with a pump power of 40 watts;

9 : schematic representation of the simulation of the bending of a glass pane as a result of a vertical application to a pump laser radiation;

10 : schematic representation of an undeformed solid-state disk before being exposed to a pump laser radiation;

11 : a schematic representation of the deformation of a thin solid by the radiation pressure of a laser radiation field;

12 a schematic representation of the radiation pressure forces acting on a thin solid-state disk in the pumped laser-active medium thereof;

13 a schematic representation of the effective pump laser radiation pressure p with back reflection of the pump laser radiation at the highly reflective back of the solid state disk, where p = 2 I / c with intensity I and speed of light c;

14 : a schematic of absorbed photon power for a 10% absorption of the pump laser radiation within the disk per pass;

15 : a schematic representation of a transverse compensation of the radiation pressure forces acting on the solid-state disk when using two pump radiation fields focused on the solid body offset by 180 °;

16 a schematic representation of the compensating transverse radiation pressure forces with two pump radiation sources and arranged in a double ring structure deflection units;

17 a schematic representation of the double ring structure of the deflecting corresponding to 16 ;

18 a schematic representation of acting in the transverse plane radiation pressure forces in a double ring structure, each with 2 x 12 radiation passes through the solid state disk;

19 a schematic alternative representation in the transverse plane of acting radiation pressure forces with a double ring structure defining deflection units for two pump radiation sources with a total of 2 times 12 radiation passes through the solid state disk;

20 a schematic representation of a double ring structure of the deflection and transverse radiation pressure forces at 2 times 14 radiation passes through the solid state disk;

21 : a schematic representation of effective radiation pressure forces in a double ring structure of the deflection units with a total of four pump radiation sources and 2 x 12 radiation passes through the solid state disk;

22 a schematic representation of the structure of the disk laser with a plan view of the reflective surface of the parabolic mirror;

23 a schematic representation of the acting compressive forces in a double ring structure of the deflection units of 22 schematically illustrated disk laser with three deflection units per ring of the double ring structure.

In 1 schematically is the structure of a disk laser known from the prior art 10 shown. It includes a thin solid disk 12 on a cold plate 14 arranged and their back 16 highly reflective coated.

A resonator 18 of the disk laser 10 is defined on the one hand by the back 16 who have an end-mirror 20 forms on the other hand by a Auskoppelspiegel 22 , The resonator 18 defines a resonator radiation field 24 ,

Through the Auskoppelspiegel 22 can laser radiation 26 depending on the choice of the material of the solid-state disk and the laser-active material contained in it are coupled out continuously or pulsed.

A pump radiation source 28 generates a pump radiation field 30 that has a focusing system 32 on the solid disk 12 is imaged and this possibly passes through several times after multiple redirection.

In 2 is shown schematically, which radiation pressure forces on the solid state disk 12 in a transverse plane defined by this 34 Act. In this schematic representation, it is assumed that the solid disk shown in dashed lines 12 sitting in the center of the illustrated ring structure.

The pump radiation field 30 hits the parabolic mirror at position "1" 38 of the focusing system 32 , From there, the pump radiation field 30 deflected and hits focused on the solid disk 12 , It works a transversal force 36a in the transverse plane 34 , After passing through the solid-state disk twice because of the highly reflective coated rear side 16 hits the pump radiation field 30 at the position "2" again on the parabolic mirror. To the pump radiation field 30 back to the solid disk 12 Being able to focus, it is about a first deflection unit 40 with two relative to a plane of symmetry 42 at an angle 44 of 90 ° aligned reflecting surfaces 46 and 48 back to the parabolic mirror 38 deflected to the position "3". From there passes through the radiation field 30 turn the solid disk twice, with a transverse force 36b on the solid disk 12 is exercised. The pump radiation field 30 meets at position "4" again on the parabolic mirror 38 ,

To the pump radiation field 30 back to the solid disk 12 to focus, that of the parabolic mirror 38 reflected beam from a second deflection unit 50 , the two also at an angle 52 of 90 ° against each other inclined reflection surfaces 54 and 56 includes. The second deflection unit 50 defines a symmetry plane 58 between the two reflection surfaces 54 and 56 , which are relative to the plane of symmetry 42 at an angle 60 is inclined.

With the second deflection unit 50 the pump radiation field is redirected to the parabolic mirror back to position "5". From there, the pump radiation field passes through the solid-state disk 12 again twice and exerts on this the transversal force 36c out.

The pump radiation field then hits the parabolic mirror again 38 , at position "6". The first deflection unit 40 leads the pump radiation field 30 back to the parabolic mirror 38 back, at position "7". From there, the pump radiation field 30 back to the solid disk 12 focuses and passes through them twice, taking the transversal force 36d in the transverse plane 34 on the solid disk 12 is exercised.

The pump radiation field then hits a back reflector 62 and goes through the focusing system 32 in the reverse direction until it's the focusing system 32 after reflection at the position "1" of the parabolic mirror 38 leaves.

The at each forward and return of the pump radiation field 30 through the solid-state disk 12 occurring transversal forces 36e . 36f . 36g and 36h are in 2 drawn, the transverse forces 36a and 36h . 36b and 36g . 36c and 36f such as 36d and 36e each pair in opposite directions.

However, the transversal forces start with the transversal force 36a successively in their size. This is because the pump radiation field 30 every time you run through the solid disk 12 deprived of radiation energy by absorption and thus the on the solid disk 12 acting radiation pressure is reduced.

Add up the drawn transversal forces 36a to 36h vectorially, a resulting transverse force vector results 2 is shown schematically. This results in a resulting, in the transverse plane 34 acting total force due to the pumping radiation field 30 generated transverse magnetic Lorentz force, originating from the bound charge carriers in the laser-active material, on the solid state disk 12 yields, with the undesirable consequence, that the solid-state disk 12 asymmetrically deformed and thus a beam profile of the laser modes of the solid-state laser also asymmetrically deformed.

In 3 is the structure of the disk laser 10 again shown schematically three-dimensional. The reference numbers used correspond to the reference numerals in FIG 1 according to the explanation too 2 added.

In 4 is an interferometer arrangement 66 shown schematically to the deformation of the solid disk 12 due to the pumping radiation field 30 display.

From a measuring laser 68 emitted laser radiation 70 is via a beam splitter on the solid state disk 12 directed, on the same time the pump radiation field 30 incident. The of the solid disk 12 back-reflected laser radiation 70 meets the beam splitter again 72 and superimposed as laser radiation 70b with the laser radiation 70a coming directly from the beam splitter 72 impinges on an optical detector in the form of a camera chip.

In 7a is one with the interferometer arrangement 66 recorded interferogram represented with a pump power of 0 watts, ie without exposure to the solid state disk 12 with the pump radiation field 30 , The solid disk 12 here has a thickness of 300 microns.

In 7b is an interferogram of the solid-state disk 12 with a power of the pumping radiation field 30 represented by 15 watts. It creates a crater 76 by the longitudinal pump laser radiation pressure perpendicular to the transverse plane 34 is directed. This crater 76 Forms reversibly, so it disappears again after switching off the pump radiation source 28 ,

In 7c is an interferogram at a power of 40 watts of the pump radiation field and a pump beam field of 2 mm focus on the solid state disk 12 shown. A width 78 of the interferogram in 7c corresponds to 10 mm. The power density of the pump radiation field 30 is 2 kW / cm ² in the focus and the radius of curvature of the loaded disc can be estimated in the meter range.

In 8a is the profile of the laser mode of the disk laser 10 at exactly einjustiertem pump module, as in the interferograms of 7a to 7c is shown. The power of the pump radiation field 30 is at the laser mode profile in 8a 10 watts, in which 8b illustrated laser mode profile 30 watts and in the 8c illustrated laser mode profile 40 watts. All three laser mode profiles in the 8a to 8c show a deviation from the rotational symmetry obtained by the uncompensated transverse forces acting in the solid state disk 12 act, comes from. To the above explanation too 2 be referred here.

Further effects which result in a deviation of the laser mode profile from the rotational symmetry are, in particular, an asymmetrical pump leak distribution in the case of a solid disk which is not precisely adjusted 12 as exemplified in the interferogram of 5 is shown. In particular, by such adjustment errors or manufacturing inaccuracies in the deflection 40 and 50 Further deviations of the laser mode profile from the rotational symmetry may result.

6 shows by way of example a laser mode of an I-resonator with a solid disk in the form of a holmium-doped yttrium-aluminum-garnet (YAG) crystal having a thickness of 300 microns, which is pumped with a thulium fiber laser and a transfer fiber with 40 watts pumping power , A maximum laser power of the laser radiation emitted from the disk laser here is 8 watts. It can be clearly seen a deviation of the laser mode profile from the rotational symmetry.

In 9 is exemplified how a glass pane 80 with a total power of 1 MW, resulting from a pump power of 10 kW and a 20-times passage through the glass, bends in a longitudinal direction on a surface of 100 mm ² . A radiation pressure p is calculated here to be approximately 10 ^-3 N / mm ² . A thickness of the glass pane of 100 μm and a modulus of elasticity reduced by a few hundred degrees Celsius, taking into account the temperature prevailing inside the solid, were assumed. Taking into account the inside of the glass 80 prevailing temperature of a few hundred degrees Celsius results in a reduced modulus of elasticity, which leads to a facilitated bending.

9 shows the deflection of the 10 mm spaced apart support points 82 supported glass pane 80 as a function of a distance from a central axis of the glass pane 80 , At the center of the focus of the pump radiation field 30 on the glass 80 results in a deflection of about 0.1 microns due to the prevailing radiation pressure.

The effects of oblique, that is, at an angle 83 to a perpendicular to the transverse plane surface normals 84 is exemplary in 10 shown. The solid disk 12 a YAG crystal typically has a thickness 86 in a range of 100 to 300 microns. Local heating of the laser-active material of the solid 12 produces a temperature of a few hundred degrees Celsius by absorption inside the pumped volume and exhibits a relatively constant, rotationally symmetric temperature distribution. Therefore, the heating of the solid is not responsible for an asymmetric deformation of the solid state disk 12 , A top 88 the solid-state disk 12 radiates heat that can be measured with a thermal imager and is about 150 ° C, whereas the cooled back 16 has a temperature of about 50 ° C via the contacting material.

The impact of the on the solid disk 12 incident pumping radiation field 30 are exemplary in 11 shown. It formed a substantially hollow spherical depression 90 Also called crater, on top 88 the solid-state disk 12 and also into the contacting material, by the longitudinal radiation pressure parallel to the surface normal 84 ,

The solid disk 12 is with a layer 94 made of solder or epoxy glue on the cooling plate 14 contacted.

In 12 are the radiation pressure forces of the pump radiation field 30 on the solid disk 12 acting radiation pressure is shown schematically. The acting radiation pressure force 98 can be vectorially decomposed into the transversal force 36 , also referred to as transversal component, parallel to the transverse plane 34 and in a longitudinal force 96 parallel to the surface normal 84 , The radiation pressure forces result from the bound charges in the laser-active material by means of the magnetic Lorentz force: n + iĸ = √ε with refractive index n, absorption coefficient ĸ and complex dielectric constant ε. The transversal force 36 F _{t is} calculated with the aid of F _t -sinθ√ (ε-sin ² θ) E ² with angle θ and laser field strength E. The result for the radiation pressure from the absorption is p = I / c, where I corresponds to the intensity, which is absorbed by the material.

The cooling plate 14 may be formed in particular of copper or diamond and a thickness 102 from about 1 to 2 mm. A thickness 104 the layer 94 Depending on the contacting method in the micrometer range. The solid disk 12 has a thickness of about 0.1 to 0.3 mm.

By the like in 12 drawn transversal force 36 results in a deviating from the rotational symmetry deformation of the recess 90 , which then leads to a deformation of the ideally rotationally symmetrical laser mode profile of the resonator radiation field 24 leads.

Due to the reflection of unabsorbed photons of the pump radiation field 30 on the highly reflective coated back 16 the solid-state disk 12 results in a double momentum transfer. This is schematically in 13 shown. Taking into account that the radiation pressure p corresponds to the energy density u of the electromagnetic wave, there is thus an actual prevailing radiation pressure in the range of approximately 10 ^-3 N / mm ² . The radiation pressure p is calculated as follows: p = 2 I / c, with intensity I and speed of light c.

14 shows by way of example the drop in the power of the pump radiation field 30 for a 10% absorption of the pump radiation field within the solid state disk 12 per run of the same. After one pass, therefore, the pump power falls in the pump radiation field 30 at 90% off and after ten passes it is only about 35% of the original power provided by the pump radiation source. The effect of this absorption of pump radiation in the solid state disk 12 became in connection with 2 already explained. It acts an asymmetrical radiation pressure in the transverse plane 34 on the solid disk 12 which results in astigmatism.

The solution of the now detailed problem of asymmetrical deformation of the solid-state disk 12 through the pump radiation field 30 applied radiation pressure will be exemplified in connection with 15 explained.

A second pump radiation source 28 ' is arranged so that the pump radiation field generated by this 30 ' 180 degrees opposite to the solid disk 12 incident. This adds up the radiation pressure forces 98 and 98 ' the on the solid disk 12 acting pump radiation fields 30 and 30 ' as drawn so that the oppositely directed transverse forces 36 and 36 ' pick up and get the Longitudinaldruckkräfte 96 and 96 ' add vectorially. This will indeed be perpendicular to the transverse plane 34 directed radiation pressure increases, but only by the pump radiation field 30 on the solid disk 12 acting transversal force 36 by the opposite transverse force 36 ' compensated. In this way, a deformation of the solid disk can be 12 effectively prevent. The one with a single pump radiation source 30 Forming astigmatism can be so effectively corrected.

In 16 is analog 2 schematically illustrated an embodiment according to the invention. It comprises a double ring structure 106 that have an inner ring 108 comprising the first and second deflection units 40 and 50 and an outer ring comprising deflecting units 40 ' and 50 ' includes. These are in the schematic, not projection-faithful representation of a part of the focusing system 32 in 17 designated accordingly.

This results in 16 schematically the inner ring 108 in accordance with the in 2 illustrated and described above arrangement. The outer ring including coupling of the radiation field 30 ' is arranged so that the transverse forces 36 that the radiation field 30 on the solid disk 12 exercises, by directly oppositely directed transverse forces 36 ' that the radiation field 30 ' on the solid disk, vectorially compensated to zero.

Each of the radiation fields 30 and 30 ' goes through the respective ring 108 respectively 110 , so a total of 2 times 8, so in total 16 Runs of the radiation fields 30 . 30 ' through the solid-state disk 12 result.

In 18 is schematically another alternative for a double ring structure 106 shown. It covers for the inner ring 108 and the outer ring 110 again two deflection units 40 and 50 respectively 40 ' and 50 ' ,

The passage through the pump radiation fields 30 and 30 ' through the focusing systems 32 and 32 ' takes place analogously as in connection with 2 explained in detail. 18 also shows the acting transverse forces, but only for the passage of the radiation fields 30 and 30 ' to the back reflectors. The at the return of the radiation fields 30 and 30 ' through the focusing systems 32 and 32 ' acting transversal forces are for clarity in 18 not shown. The illustrated double-ring structure allows for each radiation field 2 times 12, ie in total 24 Passages through the solid disk 12 ,

19 shows a further alternative arrangement for the passage of the radiation fields 30 and 30 ' through a double ring structure 106 , wherein each of the radiation fields 2 times 12, so a total of 24 times through the solid state disk. Again, only transverse forces for the trace to the back reflectors are represented by the beam positions 12 for the two rings 108 and 110 are represented schematically. The through the pump radiation sources 28 and 28 ' generated pump radiation fields 30 and 30 ' be on the parabolic mirror 38 at the positions 1 coupled.

In an analogous way shows 20 an embodiment of a double ring structure 106 with 2 times 14, so in total 28 Passed through the solid disk 12 for each of the two radiation fields 30 and 30 ' , Again, only the transverse forces in the trace of the radiation fields 30 and 30 ' to the back reflectors 62 and 62 ' shown.

21 shows by way of example a further option, by the pump radiation fields 30 and 30 ' compensate occurring transverse forces. It is shown here schematically a structure with a total of four focusing systems, which are analogous as described above of a total of four pump radiation fields. These are generated by four pump radiation sources, for example with a pump power of 10 kW each. Each double ring allows for each radiation field 2 times 12 radiation passes through the solid 12 So in total 24 Passageways.

Basically, as far as this is geometrically taking into account the real diameters of the pump radiation fields on the parabolic mirror 38 As well as real dimensions of the deflection form an arbitrary number of rings. Also, more than two deflection units can be provided per ring structure.

An example of an arrangement with three deflection units, symbolically represented by the three arrows 112 are shown in connection with the disk laser 10 in 22 shown. Here is an example of a collimation lens 116 plotted to collimate the from the pump radiation source 28 generated pump radiation field 30 ,

An associated double ring structure with two focusing systems 32 and 32 ' is in 23 shown schematically with three symmetry planes 114 and three planes of symmetry 114 ' the three deflection units as well as the on the festköperscheibe 12 acting transverse forces when passing through the focusing systems 32 and 32 ' to the back reflectors 62 and 62 ' out.

As already mentioned, the laser amplification systems described can basically be scaled arbitrarily as far as this is not dictated by purely spatial restrictions on the arrangement of the deflection units, both in terms of the number of deflection units and the number of focusing systems. In particular, arrangements with an odd number of rings are also conceivable, in which case the pump radiation fields of odd number are offset relative to one another on the solid-state disk 12 must be focused, that in each case the transverse components of the radiation pressure forces from the pump radiation fields on the solid state disk 12 be exercised, compensated or substantially compensated.

The laser amplification systems described are particularly suitable for use in medical technology and in material processing, because they can be used to generate laser beams with high power and high beam quality.

LIST OF REFERENCE NUMBERS

10

disk laser

12

Solid state disk

14

cooling plate

16

back

18

resonator

20

end mirror

22

output mirror

24

resonator radiation

26

laser radiation

28

Pump radiation source

30, 30 '

Pump radiation field

32, 32 '

focusing device

34

transverse plane

36, 36 '

transversal

38

parade

40, 40 '

first deflection unit

42, 42 '

plane of symmetry

44, 44 '

angle

46, 46 '

reflecting surface

48, 48 '

reflecting surface

50, 50 '

second deflection unit

52, 52 '

angle

54, 54 '

reflecting surface

56, 56 '

reflecting surface

58, 58 '

plane of symmetry

60, 60 '

angle

62, 62 '

back reflector

66

interferometer

68

measuring laser

70

laser radiation

72

beamsplitter

74

deflector

76

crater

78

width

80

pane

82

bases

83

angle

84

surface normal

86

thickness

88

top

90

deepening

94

layer

96, 96 '

longitudinal force

98, 98 '

Radiation jerk force

100

pump focus

102

thickness

104

thickness

106

Double ring structure

108

inner ring

110

outer ring

112

arrow

114

mirror plane

116

collimating lens

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 01/57970 A1 [0003, 0003, 0009]
• US 2001/0040909 A1 [0003, 0003, 0009]

Cited non-patent literature

• M. Mansuripur: "Radiation pressure and the linear momentum of the electromagnetic field", Optics Express Vol. 22, 2004, p. 5375 [0004]

Claims (20)

Laser amplification system comprising a solid containing a laser-active medium ( 12 ), a first pump radiation source ( 28 ) for generating a first pump radiation field ( 30 ), which is the solid ( 12 ) at least simply, in particular multiply, interspersed to excite the laser-active medium, characterized by at least one second pump radiation source ( 28 ' ) for generating at least one second pump radiation field ( 30 ' ), which is the solid ( 12 ) at least once, in particular multiple, interspersed to excite the laser-active medium, wherein the first pump radiation field ( 30 ) and the second pump radiation field ( 30 ' ) are aligned so that in one of the solid ( 12 ) defined transversal plane ( 34 ) the sum of all first transversal components ( 36 ) of the solid ( 12 ) incident first pump radiation field ( 30 ) and the sum of all second transverse components ( 36 ' ) of the solid ( 12 ) incident second pump radiation field ( 30 ' ) compensate or substantially compensate. Laser amplification system according to claim 1, characterized by a first focusing device ( 32 ), which are several different in the solid state ( 12 ) incident branches of the first pump radiation field ( 30 ) and at least one of the solids ( 12 ) precipitating branch into one of the solids ( 12 ) and which differs from the branching branch branches, and by at least one second focusing device ( 32 ' ), which are several different in the solid state ( 12 ) incident branches of the second pump radiation field ( 30 ' ) and at least one of the solids ( 12 ) precipitating branch into one of the solids ( 12 ) and transforming branches that are different from the branching branch. Laser amplification system according to one of the preceding claims, characterized in that the solid state ( 12 ) in the form of a solid-state disk ( 12 ) is trained. Laser amplification system according to one of the preceding claims, characterized by a first pump radiation source ( 28 ) and a second pump radiation source ( 28 ' ). Laser amplification system according to claim 4, characterized in that the first pump radiation source ( 28 ) and the second pump radiation source ( 28 ' ) and / or the first focusing system ( 32 ) and the second focusing system ( 32 ' ) are aligned so that the at least one first transverse component ( 36 ) of the first, on the solid ( 12 ) directed pump radiation field ( 30 ) and the at least one second transversal component ( 36 ' ) of the second, on the solid ( 12 ) directed pump radiation field ( 30 ' ) offset by 180 ° to each other on the solid ( 12 ) are aligned. Laser amplification system according to one of Claims 2 to 5, characterized in that the first focusing device ( 32 ) at least one first deflection unit ( 40 . 50 ) comprises for deflecting the first pump radiation field ( 30 ) after passing through the solid ( 12 ) on the solid ( 12 ) that the at least one second focusing device ( 32 ' ) at least one second deflection unit ( 40 ' . 50 ' ) comprises for deflecting the at least one second pump radiation field ( 30 ' ) after passing through the solid ( 12 ) on the solid ( 12 ) and that the at least one first deflection unit ( 40 . 50 ) and the at least one second deflection unit ( 40 ' . 50 ' ) the first pump radiation field ( 30 ) and the at least one second pump radiation field ( 30 ' ) so in the direction of the solid state ( 12 ), that in one of the solids ( 12 ) defined transversal plane ( 34 ) the sum of all first transversal components ( 36 ) of the solid ( 12 ) incident deflected first pump radiation field ( 30 ) and the sum of all second transverse components ( 36 ' ) of the solid ( 12 ) deflecting deflected at least one second pump radiation field ( 30 ' ) compensate or substantially compensate. Laser amplification system according to claim 6, characterized in that the first focusing device ( 32 ) at least two first deflection units ( 40 . 50 ) and that the at least one second focusing device ( 32 ' ) at least two second deflection units ( 40 ' . 50 ' ) and / or that the at least one first deflection device ( 40 . 50 ) two at an angle ( 44 ) mutually extending reflection surfaces ( 46 . 48 . 54 . 56 ) and that the at least one second deflection unit ( 40 ' . 50 ' ) two at an angle ( 52 ) mutually extending reflection surfaces ( 46 ' . 48 ' . 54 ' . 56 ' ). Laser amplification system according to one of claims 2 to 7, characterized in that the first focusing device ( 32 ) has collimating and focussing elements corresponding to that of the solid ( 12 ) directed first pump radiation field ( 30 ) and between the collimated first pump radiation field ( 30 ) towards the solid state ( 12 ), and that the at least one second focusing device ( 32 ' ) has collimating and focussing elements corresponding to that of the solid ( 12 ) directed at least one second pump radiation field ( 30 ' ) and between the collimated at least one second Pump radiation field ( 30 ' ) towards the solid state ( 12 ) focus. Laser amplification system according to claim 8, characterized in that the first focusing device ( 32 ) and the at least one second focusing device ( 32 ' ) a common focusing element, in particular a common parabolic mirror ( 38 ) and / or that the first focusing device ( 32 ) and the at least one second focusing device ( 32 ' ) at least one collimating lens ( 116 ). Laser amplification system according to one of claims 6 to 9, characterized in that the at least one first deflection unit ( 40 . 50 ) and the at least one second deflection unit ( 40 ' . 50 ' ) the solid state ( 12 ) surrounded annularly. Laser amplification system according to one of claims 6 to 10, characterized in that the at least one first deflection unit ( 40 . 50 ) and the at least one second deflection unit ( 40 ' . 50 ' ) one the solid ( 12 ) surrounding double or multiple ring structure ( 106 ) define. Laser amplification system according to one of Claims 2 to 11, characterized by one, two, three, four, five or more second focusing devices ( 32 ' ). Laser amplification system according to one of the preceding claims, characterized in that a rear side ( 16 ) of the solid ( 12 ) is highly reflective coated and / or that the first pump radiation source ( 28 ) and the at least one second pump radiation source ( 28 ' ) in the form of a diode laser or a fiber laser, and / or that the solid state ( 12 ) is a laser-active crystal, in particular a yttrium-aluminum-garnet crystal, and / or that the solid ( 12 ) Contains ytterbium or holmium, in particular doped with ytterbium or holmium. Laser amplification system according to one of the preceding claims, characterized in that the solid state ( 12 ) in a resonator ( 18 ), which is a solid ( 12 ) resonator radiation field ( 24 ) Are defined. Laser amplification system according to claim 14, characterized in that the highly reflective rear side ( 16 ) of the solid ( 12 ) an end mirror ( 20 ) of the resonator ( 18 ) and / or that the resonator ( 18 ) a Auskoppelspiegel ( 22 ) and that the resonator radiation field ( 24 ) between the end mirror ( 20 ) and the Auskoppelspiegel ( 22 ). Method for correcting an asymmetrical transverse radiation pressure profile on a solid containing a laser-active medium ( 12 ) of a laser amplification system, which radiation pressure profile through a first, the solid state ( 12 ) passing through the pump radiation field ( 30 ) is generated, characterized in that at least one second pump radiation field ( 30 ' ) on the solid ( 12 ) and that the first pump radiation field ( 30 ) and the at least one second pump radiation field ( 30 ' ) are aligned relative to each other so that in one of the solid ( 12 ) defined transversal plane ( 34 ) the sum of all first transversal components ( 36 ) of the solid ( 12 ) incident first pump radiation field ( 30 ) and the sum of all second transverse components ( 36 ' ) of the solid ( 12 ) impinging at least one second pump radiation field ( 30 ' ) compensate or substantially compensate. Method according to claim 16, characterized in that the first pump radiation field ( 30 ) and the at least one second pump radiation field ( 30 ' ) are aligned relative to one another in such a way that in the transversal plane ( 34 ) the first transversal components ( 36 ) of the solid ( 12 ) incident first pump radiation field ( 30 ) and second transversal components ( 36 ' ) of the solid ( 12 ) impinging at least one second pump radiation field ( 30 ' ) compensate in pairs or substantially compensate. Method according to claim 17, characterized in that the first pump radiation field ( 30 ) and the at least one second pump radiation field ( 30 ' ) at least once in the direction of the solid ( 12 ) to reduce the number of passes through the solid ( 12 ) at least to double and / or the first pump radiation field ( 30 ) and the at least one second pump radiation field ( 30 ' ) at least in each case in the direction of the solid ( 12 ) are focused. Method according to one of claims 16 to 18, characterized in that the first and the at least one second pump radiation field ( 30 . 30 ' ) are redirected several times to the number of passes through the solid ( 12 ) to multiply. Method according to one of claims 16 to 19, characterized in that as solid state ( 12 ) a solid state disk ( 12 ) is used.

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