DE19510713A1 - Solid state laser device - Google Patents

Abstract

A solid-body laser device with a substantially rod or plate-shaped laser body (1) with a longitudinal axis (A), a resonator (4, 5) fitted axially parallel to the longitudinal axis of the laser body and a pump light source to excite the laser body, in which means (2, 3) for setting a predetermined temperature profile along the longitudinal axis are allocated to the laser body in such a way that, when the device is operating, there are periodically alternating regions of higher and lower laser body temperature.

Description

The invention relates to a solid-state laser device the type specified in the preamble of claim 1.

Solid-state lasers, which act as crystals as a laser-active medium or contain glasses, because of their relatively simple  Chen construction and the high achievable pulse power the most important laser types in practice.

They come with lamps of different gas filling and construction, LEDs or with lasers - such as semiconductor lasers - ge pumps, the pumping light source being selected so that the Most of the radiation emitted in the spectral range the absorption bands of the laser medium. For this Reason can be the use of near infrared (NIR) emit appropriate, by appropriate doping exactly on the Main absorption bands tunable, semiconductor lasers for Pumping YAG (yttrium aluminum garnet solid state lasers be very efficient from an energy perspective. Hereby will a pump light exploitation (expressed by the so-called "slope efficiency" - cf. the explanations continue un ten) from 70 to well over 90%. This pump light sources are therefore found in the so-called DPSS (Diode Pumped Solid-state) laser arrays are becoming increasingly common.

The increasing use and expected in the future market opportunities of the miniaturized DPSS-YAG Lasers also result from the possibility of using it simple construction high performance in impulse mode at ho forth repetition frequency as well as in continuous operation and to achieve an almost ideal Gaussian beam profile.

Here, however, occurs with the so-called "thermal lensing", the uncontrolled formation of lenticular Refractive index gradient ranges and, if necessary (due to high volume-specific pumping capacity) also of double breaking areas in the laser body a serious problem that  to an uncontrolled refraction of the laser beam and thus a severe deterioration in the beam quality leads.

The effects of thermal lensing are particular in connection with frequency multiplication (specifically doubling) of the laser radiation generated by non-li neare unacceptable effects because of the frequency doubling efficiency and thus the achievable output power with decreasing beam quality at the desired end frequency quenz drops sharply.

It was tried using laser crystals trapezoidal longitudinal section (so-called slab Geometry) where the beam is not straight along a crystal longitudinal axis, but after entering the Crystal zigzag in one at the Brewster angle Ver ver level between two opposite peripheral surfaces runs to the disturbing influence of the "thermal lensing" retire. A further development of this principle is in EP 0 301 526 B1 describes, according to which the beam in the Crystal screw-like under sequential refle xion spreads on all peripheral surfaces. The editing However, the crystals are very expensive The compensation effect has proven to be unsatisfactory and the laser threshold increases noticeably.

In the unpublished German patent application Az. P 44 02 688.4 has the inventor of the present application proposed for a transversely pumped DPSS laser the pump light in the direction of the longitudinal axis of a rod-shaped  to modulate the intensity of the laser crystal where through alternately arranged areas with high and with low energy density to be generated in the crystal. This procedure is with front-end pumped arrangements not feasible and requires reliable reali over a longer period of operation (during which Pa Parameter changes or failures of pump light sources must be expected) a complex control and con troll electronics.

The invention is therefore based on the object of a fixed Body laser device of the type mentioned at the beginning create with which a simplified and flexible on ver Different Device Configurations Customizable Sub pressure of uncontrolled "thermal lensing" reached becomes.

This task is accomplished by a solid state laser device solved with the features of claim 1.

The invention includes the idea through targeted local control of efficient heat dissipation from the Laser medium and / or local cooling and / or additional heating in the laser body (rod or plate) in the longitudinal direction, d. H. in the direction of the beam, alternating areas with higher and produce at a lower temperature. This will alternating refractive index gradients in the material with un different sign. After their passage fen has the beam shape of a in the longitudinal direction of the Crystal spreading beam compared to the beam shape of a beam like that without thermal effects in the material  there were no significant differences because the "Lensing" beam deflections or deformations at the individual refractive index gradients over the total essentially cancel the length of the laser body.

This idea has many different forms of expression in special solid-state laser configurations, also via the transversely pumped miniaturized DPSS laser out.

As a means of setting a predetermined temperature On the one hand, profiles can be on at least one circumference Surface of the laser body intended for high effective heat dissipation from the laser body to the environment (specifically the air) provided in the direction of the Longitudinal axis of the laser rod alternating periodically Ab cuts with higher and lower heat transfer resistance boasted.

This arrangement can be simple and inexpensive adjustable manner essentially by at least one me alternate periodically with the metallic heat sink the projections and recesses are formed in which the projections face the laser body and in good condition thermal contact on the peripheral surface, wäh rend the recesses each with a distance range form poor thermal contact with the laser body. On Place the distance areas between the areas with high thermal conductivity also heat-insulating area che be provided.  

Instead of a specially designed heat dissipation arrangement or in addition to this may still be one at the order active heat arranged on the front surface of the laser body and / or cooling device can be provided, which so out is that it leads in the direction of the longitudinal axis of the laser body periodically alternating areas with higher and lower peripheral temperature and therefore also temperature gradient generated inside the material.

On the one hand, an active, in particular elec trisch operated, cooling device with in the direction of Longitudinal axis of the laser body arranged at intervals cooling elements or areas can be provided. This can be about be a row arrangement of Peltier elements.

On the other hand, the alternating T gradients can also through an, in particular electrically operated, additional Heating device with in the direction of the longitudinal axis of the laser heating elements arranged at intervals or - areas are generated - in combination with, of course an effective heat dissipation device.

Also a combination of a heating and cooling device device with alternately arranged contact areas for Laser body is possible.

Finally, can be as simple, effective and an electrically operated arrangement available at low cost combined, working according to the Peltier effect Heating / cooling device with in the direction of the longitudinal axis of the Laser rod alternately arranged cooling and heating area Chen be provided.  

The special arrangements mentioned can each - individually or in combination - on two opposite each other lying side surfaces of the laser body.

The laser body is in particular a miniature laser crane stall made of Nd- or Yb-doped YAG with cuboid Ge stalt or at least one of the heat sink or Cooling and / or heating element facing flat surface. At a cuboid crystal can have the dimensions for example, be about 20 × 20 × 5 mm.

In a - practically preferred - transversely pumped The arrangement is at least one to the side of the laser body (Transversely) arranged pump light source provided substantially perpendicular to the direction of the longitudinal axis in shines in this. Preferably, however, several, in particular special NIR arranged on both sides of the laser body Semiconductor lasers are provided as pump light sources. Between the light emitting surfaces of the laser diodes and the solid laser bodies are preferred optical fibers for guidance the pump light provided. This makes it very compact Design of the pump unit as a laser diode optical fiber Block possible.

To realize a compact and at the same time geome highly stable laser device and for technology simplification are preferably at least La body and the resonator with the arrangement to heat derivation and / or the heating and / or cooling device as coherent compact unit built. Under use The commercially available cooling arrays are the laser body  per and the resonator advantageous on one - in particular double cascaded - Peltier element arrangement with Al₂O₃- Base plate, as a carrier using the SMD (surface mon days) technology mounted, specially applied to the carrier soldered or glued on thermally conductive.

The side surfaces of the laser body on which no pump light is coupled in, are used efficiently of the pump light metallized, to suppress parasitic rer fashions not polished. That about the other Side surface (s) of coupled pump light can be used multiple times can be diffusely reflected, but parasitic modes can not be reflected and amplified. The arrangement can therefore by the elimination of a fashion aperture (which also in disadvantageously a part of the generated beam hide and destroy it) simplified be designed.

The arrangement according to the invention is particularly advantageous for solid-state laser devices with frequency amplification fold, special -duplication, can be used for which too additionally in the laser cavity (i.e. between the resonator mirror) a frequency multiplier element, in particular a frequency doubler crystal (KDP = potassium diposphate, KTP = Potassium titanyl phosphate, lithium niobate or similar) with nonlin earen optical properties, is provided.

Since it is particularly in the case of such an arrangement on the stabilizer dimension and the relative position of the components ten arrives, here is the one already mentioned above Execution as a compact unit advantageous, the  Frequency doubler crystal in the coherent compact te unit is integrated. The laser body end face of the frequency doubler crystal especially at the same time as a fully reflective resonator mirror surface and the abge the frequency doubler crystal turned end face of the laser body as a coupling mirror be trained. This arrangement is - although high Requirements for the quality of the surface treatment the crystal faces represents - technologically relative easy to implement, and the scope of complex adjustments work is minimized.

The laser device built as a compact assembly expediently has a temperature sensor for sensing solution of the temperature, one connected to its output Control unit and a heater connected to its output and / or cooling device for keeping the tempera constant door of the module to avoid temperature fluctuations Geometric changes that worsen the La would minimize this parameter.

The arrangement according to the invention can be expedient be realized in connection with a pump arrangement, with which the laser crystal is illuminated as homogeneously as possible becomes. This can be done in the laser crystal on the sides areas over which the pump light is coupled, additional Lich diffuser elements incorporated in the manner of Ulbricht sphere.

On the other hand, it can also be advantageous with a Pump arrangement can be realized with the in the direction of  Laser body longitudinal axis periodically alternating areas height higher and lower luminance are generated. Important is in any case that the temperature field in the laser crisis tall long-term stable can be set.

An optimized operation of such a laser device becomes possible if a processing device is provided hen, the output side with a control input Heating and / or cooling device and / or the Steuereinrich device for the pump light source (s) is connected and via the a predetermined temperature profile and / or a pre agreed luminance distribution in the direction of the longitudinal axis of the laser body is adjusted or maintained.

In an advantageous embodiment, the laser resonator Means are provided for shaping the beam cross section with which it usually comes from the YAG laser not a priori circular beam cross section in the we can form a substantial circular cross-section. This can in the simplest case be a so-called fashion aperture (at who also optimizes the beam cross-section bought a loss of output power that can be extracted ) or it can be a suitably shaped refractor element ment can be used.

An even better frequency or mode characteristic can be provided by the additional provision of a so-called "Seeders", i.e. H. a laser diode with an optical arrangement for the longitudinal coupling of the radiation into the (Solid state) laser body through the rear mirror of the Resonators can be achieved. So that  Radiation of the solid-state laser without such Arrangement of several modes within a bandwidth of et wa has 4.4 GHz, essentially in one mode or Frequency locking ("injection locking").

Advantageous developments of the invention are in the Un claims marked or become below together with the description of the preferred embodiment of the Invention illustrated with reference to the figures. Show it:

FIG. 1a is a schematic representation (in longitudinal section) an array of laser body and heat-dissipating device according ei ner embodiment of the invention,

FIG. 1b shows a schematic representation (in longitudinal section) an array of laser body and cooling arrangement according to a further embodiment of the invention,

Fig. 1c shows a schematic representation (in longitudinal section) an array of laser body, additional heating and heat dissipating body according to another embodiment of the invention,

Fig. 1d shows a schematic representation (in longitudinal section) an array of laser body and combined heating and cooling of the dung OF INVENTION arrangement according to another embodiment,

Fig. 2 is a schematic diagram for explaining the "thermal lensing" effect in the prior art,

Fig. 3a is a simplified longitudinal sectional view of a construction of the arrangement according to Fig. 1a,

FIG. 3b shows a simplified plan view of the design according to Fig. 2a,

Fig. 3c is a simplified cross-sectional view of the design according to Fig. 2a,

Fig. 4 is a simplified overall perspective view of a solid laser device according to one embodiment of the invention,

FIG. 4a is a detail view of a modification of the apparatus shown in Fig. 4,

Fig. 5 is a simplified overall perspective view of a solid laser device according to another execution form of the invention (with frequency doubling),

FIG. 5a is a detail view of a modification of the apparatus shown in Fig. 5,

Fig. 6 is a schematic diagram of a modification shown in FIG. 4 or FIG. 5 embodiments shown,

Fig. 7 is a simplified block diagram of a measuring and control circuit for a solid-state laser device according to an embodiment of the invention and

Fig. 8 is a graphical representation to illustrate an advantageous effect of the device according to the invention.

Fig. 1a shows in a schematic diagram (in longitudinal section) a rectangular in longitudinal section Nd-doped YAG laser crystal 1 with one each on the top side 1 a and the bottom 1 b arranged - shown in the figure only in part - metal body 2 and 3 made of solid aluminum for heat dissipation from the laser terminal to the surrounding atmosphere.

The heat dissipation bodies 2 , 3 constructed in the same way each have a profiled surface in the laser crystal surfaces 1 a or 1 b facing the surface with slots 2 a or 3 a which are rectangular in cross section, between which areas 2 b or in contact with the laser crystal 3 b of the heat sink 2 and 3 are arranged. In the contact areas 2 a ', 3 a' of the slots 2 a, 3 a there is no physical contact and thus a compared to the contact areas 2 b ', 3 b' of the projecting sections 2 b, 3 b with the laser crystal 1 greatly reduced heat conduction between the laser crystal and the heat dissipation bodies 2 , 3 .

Between the rear (left in the figure), provided with a fully reflective coating - the first resonator mirror - 4 end face 1 c and the front (right in the figure), with a partially reflective coating - forming the second resonator mirror - Be 5 provided end face 1 d of the laser crystal forms a laser beam (bundle) with a wavelength of 1064 nm in a known manner above a threshold power when pump light is irradiated - for example by InAlAs semiconductor laser diodes (not shown in this figure ) arranged laterally of the laser crystal 1 .

In the figure, there is a little above the longitudinal axis A of the crystal lying, d. H. a so-called offset having, partial beam R₀ shown.

The irradiated pump light heats the laser crystal 1 above the ambient temperature, so that heat is dissipated to the environment via the upper and lower side surfaces 1 a, 1 b and the heat dissipation bodies 2 , 3 adjacent to them.

As a result of the very different heat conduction between the laser crystal and the heat dissipation bodies in the areas 2 a ', 3 a' on the one hand and 2 b ', 3 b' on the other hand, there is a corresponding to the geometric shape of the surface of the heat dissipation bodies in the direction of the longitudinal axis A of the laser crystal 1 modulated dissipation of the heat energy. As a result of this, a temperature field of the shape shown in dashed lines in the figure forms in the laser crystal 1 , which is characterized by a periodicity of approximately elliptical isotherms I 1, I 2, I 3 in cross section in the direction of the longitudinal axis A.

Due to the temperature dependence of the refractive index of the Laser medium and - at least with higher pump powers - The occurrence of birefringence effects is formed at the same time correspond to the shape of the temperature field chende, surfaces R₁, R₂, R₃ having the same refractive index, spatial distribution of the refractive indices (to a certain extent a "refractive index field") in the laser crystal.

As shown schematically on the course of the beam R₀ in the figure, the spatial distribution of the refractive indices shown periodically causes alternating deflections of the beam in alternating directions with respect to the longitudinal axis A, so that with a corresponding shape of the refractive index field within the laser crystal 1 on the end faces 1 c, 1 d each result in a beam orientation parallel to the longitudinal axis A. This leads - if you consider the off-axis beams in their entirety - to form a beam with a high degree of parallelism and phase coherence and an advantageously almost ideal Gaussian energy distribution in the beam cross section.

The specified arrangement thus suppresses the disadvantageous effect of “thermal lensing” in conventional solid-state laser arrangements, as is sketched in FIG. 2.

Fig. 2 shows a laser crystal 1 'with conventional, along the side surfaces 1 a', 1 b 'substantially uniform heat dissipation and the course of the central beam R _m ' and an off-axis beam R₀ 'on isotherms I₁', I₂ ', I₃' , which also correspond to areas R₁ ', R₂', R₃ 'same cher refractive index. The schematically illustrated beam course illustrates the deviation of the course of the off-axis beam from the direction of the longitudinal axis A 'of the laser crystal as a result of the uncontrolled ge formed thermal lens, which also involves phase shifts and thus a deterioration in the coherence of the laser radiation.

Fig. 1b shows (again in longitudinal section) a Prinzipdar position of a further arrangement of a laser crystal 1 and a cooling arrangement, which is formed here from a row of Peltier elements 6.1 to 6.4 or 6.5 to 6.8 arranged at predetermined intervals above and below the laser crystal .

The Peltier elements cool the laser crystal at the contact surfaces with its upper or lower side surface 1 a or 1 b, so basically they functionally take the place of the protrusions of the heat-dissipating bodies 2 , 3 facing the laser crystal in FIG. 1 a. In the figure it is assumed simplifying that the resulting temperature field and thus the spatial distribution of the refractive index corresponds to the conditions in Fig. 1a. In the Vorrich device according to Fig. 1b, of course, with separate control of the cooling elements 6.1 to 6.8, if necessary, by a suitable choice of the voltages of the individual cooling elements, a more differentiated and, above all, time-dependent variable control of the shape of the T-field and thus the beam path of the off-axis laser beam R₀.

This is a readjustment in an electrical-thermal way tion of the beam path and the phase relationships the laser device possible without changes to the structure. This enables a technologically advantageous Fixation of the elements immediately when producing the pre direction.

This advantage also has the arrangement shown in Fig. 1c - again in principle in longitudinal section - arrangement of laser body 1 , heat dissipation bodies 2 'and 3 ' and an additional heater from five in the heat dissipation body 2 'and five in the heat dissipation body 3 ' arranged electrical Heizelemen th 7.1 to 7.10 According to a further embodiment, as far as the heating elements can be individually controlled here.

The surface of the heat sink 2 'and 3 ' is not profiled in this embodiment on the side facing the laser crystal th, but can be completely flat, the heating elements can be used from the side facing away from the laser crystal.

Otherwise, it is assumed in Fig. 1c that the expansion and spacing of the heating elements correspond to those of the slots in Fig. 1a and the thermal effect of the heating elements, ie the influence on the temperature field in the laser crystal, that of the slots of the heat dissipation body 2 , 3rd is equivalent. Of course, these simplifying assumptions were only made with a view to clarity of presentation. The designer of the laser device will undertake the specific design with regard to the geometry and the thermal parameters according to the desired performance parameters. The dimensions and distances of the areas with higher and those with less cooling effect do not all have to be the same.

Fig. 1d shows a further schematic diagram of an arrangement of a laser body 1 and a combined heating and cooling arrangement of four cooling elements 6.1 to 6.4 or 5.6 to 8.6 and five heating elements 7.1 to 7.5 or 7.6 top in a to 7.10 or a lower heat dissipator 2 '' or 3 ''. Here, too, it is assumed in the drawing that the thermal conditions in the laser crystal resulting from the use of the cooling and heating elements correspond to those in the arrangement according to FIG. 1a.

However, it is clear that in particular this arrangement with active cooling and heating elements can enable a far more pronounced differentiation of the T field, ie the realization of substantially larger T gradients than the arrangement according to FIG. 1a. Here, too, individual control of the active elements enables a suitable shaping of the T field and thus of the refractive index field and thus also readjustment in an electrical-thermal way.

In the devices according to FIGS . 1b to 1d, however, the active elements can also be controlled in groups or all together - operated in series, for example. This simplifies the control and reduces the manufacturing costs, but reduces the possible variations in the formation of the refractive index field in the laser terminal.

Fig. 3a shows a simplified longitudinal sectional view of a technologically advantageous realizable design of the basic arrangement according to Fig. 1a, Fig. 3b shows a simplified top view and Fig. 3c shows a simplified cross-sectional view (perpendicular to the longitudinal axis of the laser crystal) of this design.

An aluminum oxide substrate 10 with surface metallization (in-plating) 10 a serves as a carrier, onto which an lower (passive) heat sink 11 and an upper (passive) heat sink 12 , each made of solid copper, are soldered. The heat sink 11 , 12 include between them the flat cuboid Nd: YAG or Yb: YAG laser crystal 1 ''. The laser crystal facing surfaces of the cooling body 11 , 12 are in the manner explained above with in the longitudinal axis direction of the crystal (x-direction) on the following and perpendicular to it (in the y-direction) he extending slots 11 a and 12 a and projections 11 b or 12 b profiled. They each have an In coating 11 c or 12 c on this surface, which serves to reduce the heat transfer resistance. The slots 12 a of the upper heat sink 12 here have a smaller depth than that of the lower heat sink 11 .

In the arrangement of Fig. 3a to 3c, the resonator are not mirror on the end faces of the laser crystal 1 mounted '', but it is believed the presence externally arranged (not shown in these figures) mirror. Accordingly, an axially offset beam R₀ '' penetrating both end faces of the laser crystal is shown, which enters and exits through special openings 12 d and 12 e of the upper heat sink 12 .

The upper and lower peripheral surface 1 a '' and 1 b '' of the laser crystal 1 '' are not polished, but with a reflective metallization 1 a / M '' or 1 b / M '' provided.

In Fig. 3b and 3c, the laser crystal 1 '' facing ends of optical fibers of two side pump light supply arrangements 13 and 14 are shown, and the beam path of the individual pump light beams is outlined (with dashed lines). In Fig. 3c can be seen here at good that the pump light between the top and bottom metallization 1 a / M '' or 1 b / M '' of the laser crystal is reflected many times and is therefore used extremely efficiently. As mentioned above, the non-polished, optically imperfect surface prevents at the same time that higher-order modes and in particular parasitic modes are amplified and can impair the beam quality.

In the example shown, the dimensions of the YAG crystal 1 '' approx. (L / W / H) 5/4 / 0.5 mm, that of the lower heat sink 11 approx. 7/5 / 1.5 mm, that of the upper Heatsink 12 (in the bent state) approx. 13/6 / 1.5 mm and the slot widths in the heat sinks approx. 0.5 mm.

Fig. 4 shows a simplified overall perspective view of a solid-state laser device in which the cooling arrangement in the design according to FIGS . 3a to 3c is realized. The reference numerals used in these figures for the parts shown there are also used in FIG. 4 and these elements are not described again here.

In Fig. 4 is - at three pumping light sources - more precisely Darge provides that at the end facing away from the laser crystal of the light guide 13 a, 13 b, 13 c and 14 a, 14 b, 14 c, a laser diode array 15 a, 15 b, 15 c or 16 a, 16 b, 16 c each with 1 to 4 W pump power is coupled.

This figure also shows a rear, fully reflective resonator mirror 17 and a front, semi-reflective render resonator mirror 18 . Both mirrors are angled twice, during assembly for adjustment bendable pads ("pads" or "legs") 17 a, 17 b or 18 a, 18 b with the local metallization 10 a 'of the carrier 10 ' soldered. Next, between the mirrors 17 , 18 and the laser crystal 1 '' each have an element 19 or 20 for beam shaping (z-axis expansion) of the laser beam generated and for reducing transverse modes of higher order, with which a circular beam cross-section is produced. These optical elements are just in case on metallization areas of the carrier 10 'tet.

The carrier 10 'is formed by a double cascaded Kühlan arrangement from three Al₂O₃ carrier plates 10.1 ', 10.2 'and 10.3 ' and an intermediate array 10.4 'and 10.5 ' of Peltier elements. Such an arrangement is geometrically highly stable with changing ambient temperatures or changing energy input, since the cascading of the Peltier arrangements automatically compensates for temperature gradients. On the surface of the upper plate 10.1 ', a temperature sensor 21 is arranged, via which the tem perature of the laser device is sensed and with the help of which this can be additionally regulated by suitable control of the Peltier elements.

FIG. 4a is a detailed representation of a with respect to the utilization of the pump radiation particularly advantageous from formation of the laser crystal in the arrangement of Fig. 4.

Here, the laser crystal 1 '''in addition to the base and top surface coating 1 b / M''' or 1 a / M '''for further homogenization of the pump light distribution inside the Kri stall on the long side surfaces 1 c'''And 1 d''' facing the optical fiber groups 14 and 13 and parallel to the direction of the laser beam R, each approximately opposite the ends of the optical fibers hemispherical depressions 1 c / S '''and 1 d / S''' on. These recesses worked into the laser medium act with regard to the pumping light beams emerging from the ends of the adjacent optical fibers according to the principle of the integrating sphere as scattering surfaces. In order to reduce reflection losses of the pump radiation on the side surfaces and thus to improve the coupling, it is additionally provided to fill the depressions with a gel 13 a or 14 a to adjust the refractive index ("index matching gel") into which the ends of the optical fibers Immerse 14 or 13 .

Fig. 5 shows in a (again simplified) perspective overall view of another solid-state laser device according to an embodiment of the invention, with which the frequency of the laser beam generated is additionally doubled. The formation and arrangement of the laser crystal is the same as in the device described above, so that the same reference numbers are used in this regard.

An essential difference is the structure of the Pumpan arrangement, which is formed here with two compact assemblies 22 , 23 from an integrated laser diode arrangement with beam focusing. (Such an arrangement is described in more detail in the earlier application of the inventor mentioned at the outset and is included here by reference in the subject matter of the present application.) The radiation from the line-like laser diodes is focused into a focal point by the elements for beam focusing; the laser crystal 1 '', however, is placed outside the focal length of the pump arrangements 22 , 23 , so that the pump light radiation is approximately linear over the length of the crystal.

Another significant difference from the laser device according to FIG. 4 is the presence of a KTP (potassium titanyl phosphate) frequency doubler crystal 24 , which is arranged with respect to the laser crystal beyond (in the figure on the right) the rear element 20 for beam shaping. The frequency doubler 24 is on bendable pads 24 a, 24 b, through which an initial Ju stierung the location relative to the other optical components is possible, soldered onto the upper carrier plate 10.1 '. Its end face 24 c facing away from the laser crystal has a convex shape with geometry that is very precisely adapted to the specific laser arrangement and has a mirror coating 25 , so that it also acts as a rear resonator mirror.

In a similar way, the front resonator mirror is here formed by a partially reflecting mirror coating 26 of the front end face of the laser crystal 1 ''.

With a temperature control of the KTP crystal 24 , a tuning of the effective resonator length of the arrangement can be achieved in a simple manner without mechanical intervention, without additional controllable refraction elements (such as a temperable quartz plate or a piezomechanical tuning element) being required. Alternatively, however, such an element can also be used - which is not shown in the figure. Depending on the specific design, a corresponding control unit must be provided for thermal or piezo-mechanical tuning of the laser arrangement.

FIG. 5a is a detailed illustration of a formation of the laser crystal which is particularly advantageous with regard to the use of the pump radiation in the arrangement according to FIG. 5, only the details which differ from FIGS . 3a to 3c or FIG. 5 being explained below.

Here, the laser crystal 1 '''' for further homogenization of the pump light distribution inside the crystal on the long side faces 1 c '''' and 1 d '''', the den Laser denio blocks 22 and 23 (see Fig face. 5) depending weils an approximately semi-cylindrical groove 1 c / N '''' or 1 d / N '''' on. These recesses incorporated in the laser medium act - analogously to the hemispherical indentations according to FIG. 4 - with respect to the (outside the side surfaces of the laser crystal 1 '''' focused) pumping light beam according to the principle of the integrating sphere as scattering surfaces.

Features of the arrangements shown as examples in FIGS. 4 and 5 can also be combined with one another; For example, a device with a frequency doubler can also have one or two separate resonator mirrors, or in the case of a device without frequency doubling, at least one of the resonator mirrors can be formed on an end face of the laser crystal. Both the laser crystal and the frequency doubler can also be made from another material known for the respective purpose: Nd- or Yb-doped glass can be used as the laser material and KDP (potassium diphosphate) or lithium niobate can be used for the frequency doubler.

A simple Peltier element arrangement can also be used as the carrier or, if necessary, simply a good heat-conducting support plate - to increase the cooling effect also with ribbing or u. U. with liquid cooling - serve. The fixation of the components on the carrier can, for example, by be made of a thermally conductive adhesive.

Fig. 6 is a schematic diagram for explaining a further modification of the embodiments of a solid-state laser device explained above, with which a narrowing of the spectral bandwidth and a unification of the phase position of the generated laser beam bundle can be achieved.

The solid-state laser designated YAG in this figure Bodies with a laser wavelength of 1064 nm are in Usually assigned two resonator mirrors ML1 and ML2 net. The front, semi-transparent mirror ML2 is on the the convex forehead facing away from the solid-state laser body YAG area of an intracavitary area - referred to here as KTP Frequency doubler crystal formed, the rear mirror  ML1 separately. With r1 and r2 the mirror radii are the Re designated sonator mirror, with r3 the radius of the front KTP face. Typically r1 is in the range of 10 cm, r2 and r3 are a few mm. To the mirror or end faces is in each case with "AR..." the existing its an anti-reflective coating and with "HR ..." one highly reflective coating for a certain world length marked.

Extra Cavity (in the figure on the left of the front mirror ML2) a collimator lens COL2 is shown. Other opti cal elements and the pump arrangement are here to the club fold omitted. The conditions regarding the Beam frequencies can be determined by specifying the wavelengths (1064 nm = primary wavelength, 532 nm = wavelength according to Fre doubling of the frequency) at various points in the arrangement clarifies. The adjustment after the adjustment takes place on the way described above, that is, by T- Control of the frequency doubler, what in the figure with an arrow with the reference symbol TC is illustrated.

On the side of the solid-state laser arrangement is an InGaAs LAD laser diode arranged, also at a wave length of 1064 nm with an output power of approx. 50 mW emitted. After passing through a col limator lens COL1 and two deflecting mirrors M1 and M2 with a transmission coefficient of approx. 1% longitudinal coupled into the solid-state laser arrangement. There be this narrow-band radiation has a frequency and Injection locking of the solid state perlaser YAG emitted radiation on the radiation of the Semiconductor laser LAD, the so-called "seeder".  

The principle explained in FIG. 6 using a linear resonator arrangement is basically also analogous to a ring resonator arrangement (known per se and therefore not shown separately here), the coupling of the laser diode radiation into the solid body laser at an angle to its longitudinal axis takes place, which is matched to the geometry of the ring resonator.

With this arrangement, the frequency can be even better vote, with the simultaneous vote of effek tive resonator length and phase length of the seeder in particular a single piezomotor longi (not shown) tudinally displaceable plane-parallel quartz plate in the Beam path can be inserted by the Seeder and the laser radiation at a small angle is penetrated diagonally.

Fig. 7 is a simplified block diagram of an electrical thermal measuring and control circuit 100 for a solid state laser device according to an embodiment of the invention for controlling the beam parameters. This - in the sense of an example for a variety of possible control circuits to be understood - circuit is particularly suitable for temporary use with the laser arrangement, such as for initial adjustment or readjustment after prolonged operation.

The starting point is a cooling arrangement for the Laserkri stall according to Fig. 1b individually addressable pel with four animal elements 6.1 to 6.4 above the laser crystal 1 and four also individually controllable elements Peltier 5.6 to 8.6 below the crystal.

The measuring and control circuit 100 comprises a planar optical sensor arrangement in the form of a CCD matrix 101 , which is arranged opposite the front light exit surface of the laser 1 such that an image of the laser beam is generated on it during operation of the laser. The number of image recording elements in the matrix is selected in accordance with the quality requirements for the laser beam.

The output of the CCD matrix 101 is connected to the input of a preprocessing unit 102 for interference suppression and signal level adjustment. Its output is connected to an input of a comparator unit 103 , the other input of which is connected to the data output of a sample image memory 104 , in which at least one predetermined laser beam cross section is stored, which should be used as the basis for the control or setting of the laser device. In the comparator unit 103 , the real beam cross section recorded by the CCD matrix 101 is compared with the pattern beam cross section and a signal sequence which characterizes the comparison result is provided at the output. Processing width and speed of the units 102 and 103 and the storage capacity of the memory 104 are selected in accordance with the number of image recording elements of the CCD matrix 101 .

The signals specifying the result of the beam comparison are fed to the data input of a processing unit 105 , which is formed, for example, by a microprocessor and is connected to the output of the comparator unit 103 and which furthermore has a data memory (RAM) 106 and a program memory (for example an EPROM) in the usual manner. 107 is connected. The processing unit can optionally - which is shown by dashed lines - be connected to the output of a temperature sensor (according to the figure of the sensor 21 from Fig. 4 or 5), so that the temperature of the Laseranord voltage in the control of Cooling arrangement arrives.

In the processing unit 105 , a set of control data for the voltage supply of the individual Peltier elements is calculated by calling up a program and pre-stored data for correcting the T field in the laser crystal 1 by changing the operating voltage of the Peltier elements 6.1 to 6.8 , and finally a voltage supply unit 108 is supplied for the cooling elements and a corresponding setting of the operating voltages and thus the cooling capacities of the Peltier elements. This leads to a shape of the T-field in the laser crystal, with which the desired laser beam parameters are achieved. The setting of the voltage supply unit can be locked after completion of the setting process.

The processing program for the measured beam data can be an iterative pro in the arrangement described be grams, with the ver changed beam parameters are recorded and a next one Iteration step can be used as a basis. Especially A fuzzy logic algorithm is well suited for this.

To display the recorded data and processing results for an operator and to influence the processing process, the components mentioned are each connected to a display and input unit 109 , such as the screen and keyboard of a conventional PC.

A basically completely analog circuit can be used to control or set an active heating arrangement according to FIG. 1c or a combined cooling and heating arrangement according to FIG. 1d. Furthermore, in a similar way - as an alternative or in addition to the control of the temperature field - the separate control of several pump light sources can be used to control the luminance distribution of the pump light in the solid-state laser.

In FIG. 8 is a graphical representation for Verdeutli monitoring an advantageous effect of the apparatus according to the invention optionally.

The laser output power P _out as a function of the pump power P _in is shown in a logarithmic representation using typical curve profiles. The dashed line shows a curve for a Yb-YAG laser device according to the prior art, while the solid curve ve is the characteristic curve of a device constructed according to an embodiment of the invention. It can be seen that in the latter, both the increase in the linear region (“slope”) and the achievable maximum output power (based on the threshold power) are significantly higher.

The invention is not restricted in its implementation to the preferred embodiment given above game. Rather, a number of variants are conceivable which of the solution shown also in principle use different types of designs.

Claims (25)

1. Solid-state laser device with a substantially rod-shaped or plate-shaped laser body ( 1 ; 1 '') with a longitudinal axis (A), an axis parallel to the longitudinal axis of the laser body arranged resonator ( 4 , 5 ; 17 , 18 ; 25 , 26 ) and one Pump light source ( 15 a to 15 c, 16 a to 16 c; 22 , 23 ) for excitation of the laser body, characterized in that the laser body has means ( 2 , 3 ; 6.1 to 6.8 ; 7.1 to 7.10 ; 2 ′ ′, 3 ′ ′ ; 11 , 12 ) for setting a predetermined temperature profile in the direction of the longitudinal axis in such a way that areas of higher laser body temperature and areas of lower laser body temperature are periodically alternating in operation of the device. 2. Solid-state laser device according to claim 1, characterized in that the means for setting a predetermined temperature profile on a peripheral surface ( 1 a, 1 b; 1 a '', 1 b ''; 1 a / M '', 1 b / M '') of the laser body ( 1 ; 1 '') provided arrangement ( 2 , 3 ; 11 , 12 ) for heat dissipation from the laser body to the environment, which periodically alternating sections in the direction of the longitudinal axis (A) of the laser body pers ( 2 a, 2 b, 3 a, 3 b; 11 a, 11 b, 12 a, 12 b) with higher and those with lower heat transfer resistance. 3. Solid-state laser device according to claim 2, characterized in that the arrangement for heat dissipation at least one metallic heat-conducting body ( 2 , 3 ; 11 , 12 ) with periodically alternating projections ( 2 b, 3 b; 11 b, 12 b) and recesses ( 2 a, 3 a; 11 a, 12 a) comprises, wherein the projections of the laser body ( 1 ; 1 '') face and rest in good thermal contact on the circumferential surface, while the savings each with a distance range form poor thermal contact with the laser body. 4. Solid state laser device according to one of the preceding claims, characterized in that the means for setting a predetermined temperature profile arranged on the peripheral surface ( 1 a, 1 b) of the laser body ( 1 ) - active heating and / or cooling device ( 6.1 to 6.8 ; 7.1 to 7.10 ) which, in the direction of the longitudinal axis (A) of the laser body, periodically alternate areas with higher and lower peripheral temperature. 5. Solid-state laser device according to claim 4, characterized in that an active, in particular electrically operated, cooling device with cooling elements or regions ( 6.1 to 6.8 ) arranged at intervals in the direction of the longitudinal axis of the laser body ( 1 ) is provided. 6. Solid-state laser device according to claim 4, characterized in that a, in particular special electrically operated, heating device with heating elements or regions ( 7.1 to 7.10 ) arranged at intervals in the direction of the longitudinal axis of the laser body ( 1 ) is provided. 7. Solid state laser device according to claim 4, because characterized in that an elec trisch operated, especially after the Peltier effect working, heating / cooling device with in the direction of Longitudinal axis of the laser body alternately arranged cooling and heating areas is provided. 8. Solid-state laser device according to one of claims 2 to 7, characterized in that on two opposite side surfaces ( 1 a, 1 b) of the laser body ( 1 ; 1 '') each have an arrangement for heat dissipation device ( 2 , 3 ; 2 '' , 3 '', 11 , 12 ) and / or a heating and / or cooling device ( 6.1 to 6.8 ; 7.1 to 7.10 ) is arranged. 9. Solid state laser device according to one of the preceding claims, characterized in that the laser body is a, in particular quaderför shaped, miniature laser crystal ( 1 ; 1 '') made of Nd- or Yb-doped YAG. 10. Solid-state laser device according to one of the preceding claims, characterized in that at least one transversely to the laser body ( 1 '') arranged pump light source ( 15 a to 15 c, 16 a to 16 c; 22 , 23 ) is provided. 11. Solid-state laser device according to claim 10, characterized in that a plurality of transversely to the laser body, in particular on both sides of the laser body, arranged semiconductor laser ( 15 a to 15 c, 16 a to 15 c; 22 , 23 ) are provided as pump light sources. 12. Solid-state laser device according to claim 11, characterized in that between the light exit surfaces of the semiconductor laser ( 15 a to 15 c, 16 a to 16 c) and the laser body ( 1 '') optical fibers ( 13 a to 13 c, 14 a to 14 c) are provided for guiding the pump light. 13. Solid state laser device according to one of claims 10 to 12, characterized in that on the side facing the pump light sources ( 1 c ''', 1 d'''; 1 c '''', 1 d '''') of the laser body ( 1 ''', 1 '''') With tel ( 1 c / S''', 1 d / S '''; 1 c / N'''', 1 d / N'''') to Homogenization of the pump light distribution are provided. 14. Solid state laser device according to claim 13, there characterized in that the means  for homogenizing the pump light distribution in the laser body-integrated recesses with essentially are spherical or cylindrical boundary surface. 15. Solid state laser device according to one of claims 2 to 14, characterized in that at least the laser body ( 1 '') with the resonator ( 17 , 18 ; 25 , 26 ) and the arrangement for heat dissipation ( 11 , 12 ) and / or the active Heating and / or cooling device as a coherent compact assembly on a Trägerele element ( 10 ; 10 ') is constructed. 16. Solid-state laser device according to claim 15, characterized in that the laser body ( 1 '') with the resonator ( 17 , 18 ; 25 , 26 ) on a double cascaded Peltier element arrangement ( 10 '), in particular with Al₂O₃ base plate ( 10.1 '), Mounted as a carrier element, in particular soldered on or thermally conductive glued on. 17. Solid state laser device according to one of claims 9 to 16, characterized in that the side surfaces ( 1 a / M '', 1 b / M '') of the laser body ( 1 ''), to which no pump light is coupled, not polished and are preferably metallized. 18. Solid-state laser device according to one of the preceding claims, characterized in that a frequency multiplier element ( 24 ), in particular a special frequency doubler crystal, is provided. 19. Solid-state laser device according to claim 18 and claim 15 or 16, characterized in that the frequency multiplier element ( 24 ) is integrated in the coherent compact assembly. 20. Solid-state laser device according to claim 18 or 19, characterized in that the end face facing away from the laser body ( 24 c) of the frequency doppler crystal as a fully reflecting resonator mirror surface ( 25 ) and the end face facing the frequency doubler crystal of the laser body ( 1 '') as an output mirror ( 26 ) is formed. 21. Solid state laser device according to one of the preceding the claims, characterized net that a control device for the pump light source (s) for the optional setting of one in the direction of the Longitudinal axis of the laser body homogeneous or a perio alternating areas of higher and lower light density luminance profile is provided. 22. Solid-state laser device according to claim 21, characterized in that a processing device ( 105 ) is provided, the output side with a control input of the heating and / or cooling device ( 8.1 to 6.8 ) and / or the control device for the pump light source (n ) is connected and via which a certain temperature profile and / or a predetermined luminance distribution in the direction of the longitudinal axis of the laser body ( 1 ; 1 '') is set or maintained. 23. Solid-state laser device according to claim 22, characterized in that one with egg nem input of the processing device ( 105 ) connected light sensor unit ( 101 ) for detecting the beam profile of the laser beam generated in the laser body ( 1 ) as a control variable for the temperature profile and / or the light density distribution is provided. 24. Solid-state laser device according to one of claims 13 to 23, characterized in that the compact assembly has a temperature sensor ( 21 ) for detecting the temperature, a control unit connected to its output ( 21 ) and a heating and / or cooling device connected to its output ( 6.1 to 6.8 ) to maintain the temperature profile of the assembly. 25. Solid state laser device according to one of the preceding the claims, characterized net that a longitudinal from the back of the full reflective resonator mirror (ML1) radiating Semiconductor laser (LAD) for frequency and phase locking  the solid-state laser radiation is provided.