DE19518177A1 - Diode laser pumped solid state laser - Google Patents

Abstract

A diode laser-pumped solid state laser with at least one rod or disc-shaped solid body (9) as the active medium and with diode lasers (10) from which the emitted radiation (11) is beamed into the solid body, wherein there are reflecting components (8) to guide and/or shape the beam, in which the solid body (9) is surrounded radially to its axis (2) by a glass or crystal surround (1) transparent to the emitted radiation, where the outer surface of the surround (1) is divided into at least two regions, one of which forms an irradiation region (7) for the emitted radiation and the other acts as a reflective surface (8) which reflects on the solid body (9) the radiation (11) passing through the surround (1).

Description

The invention relates to a diode laser-pumped solid-state laser at least one rod or disc conveyor serving as the active medium solid solids and with diode lasers, whose emitted radiation in the Solid body is irradiated, for beam guidance and / or shaping reflective elements are used.

Due to the rapid development of high-performance laser technology In recent years, lamps have become increasingly used for pumping festivals body lasers are used, replaced by diode lasers. Due The geometry of the active medium includes diode laser beams characterized by the elliptical beam cross section. The big axis this elliptical cross section runs perpendicular to the pn-overlap course of the diode structure (also known as fast direction), while the small axis parallel to the plane of the pn junction (also known as flow rich designated) runs. About this asymmetrical beam cross section in addition, the emerging radiation in the direction of the major axis, d. H. perpendicular to the plane of the pn junction or to the active layer shows a high divergence, with a beam opening angle of up to 90 °, while in the direction of the minor axis this divergence is only around 10 °.

Because of the special elliptical beam cross-section and the large Divergence perpendicular to the active plane (also known as the junction plane  net) and the relatively low divergence in the direction of the minor axis, depends on efficient pumping of solid-state lasers using such diodes laser crucial from the appropriate guiding and shaping of the diodes laser radiation. Furthermore, the achievable laser properties, like the beam quality and the output power, through the effective Ab leadership that is not greatly influenced by the laser process when the heat is carried.

There are various concepts for coupling diode laser radiation into Solid state media. An embodiment according to the preamble of the An saying 1 is in "Efficient continuous-wafe TEM₀₀ operation of a trans versely diode-pumped Nd: YAG laser "by D.R. Walker, C.J. Flood and HM. van Driel, July 15, 1994, Vol. 19, No. 14 / OPTICS LETTERS, Be te 1055 ff. Here, the diode laser radiation over el Liptic mirror irradiated into the solid medium. The single ones Laser diodes with their assigned elliptical mirrors are the same moderately spaced around the solid.

Another structure is in "Solid-state laser engineering" by Walter Köchner, Springer-Verlag, under the chapter "Laser-diode-pumped systems" described and outlined on page 134. In this arrangement, Dio denarrays around a solid-state laser rod in the radial and axial directions Distributed to the radiation of the individual laser diodes in the direction Coupling solids.

With the above arrangements, the gain distribution optimized depending on the application due to the different focus , but this requires focusing components, as in for example the elliptical or cylindrical mirrors, making the construction costs are increased.

Another way to insert the diode laser radiation into the solid couple, can be done using beam guidance elements.  

Starting from the prior art mentioned above, the The present invention has for its object an arrangement of a diode specify laser-pumped solid-state laser, in which on the one hand with a high efficiency the radiation emitted by diode lasers into the festival body medium can be coupled in, on the other hand, the loss heat can be dissipated in a simple manner and which is a great Va Rationalization in the construction offers, but still a compact structure.

The above task is in a diode laser pumped solid state water solved in that the solid from one for the dispensed Radiation transparent glass or crystal envelopes in radial direction device is encased to its axis, the outer surface of the enveloping body is divided into at least two areas, one of which is an on forms the beam area for the emitted radiation and the other area serves as a reflecting surface that passes through the envelope Radiation reflects on the solid.

According to the invention, a specially shaped glass or crystal envelope per, preferably in the form of a cylinder or cylinder section, in its outer configuration in the circumferential direction into individual areas or surface sections is divided, this section alternately te an irradiation area for the emitted diode radiation, which over these surfaces are coupled into the body, and reflection surfaces bil the. This means that radiation is emitted over the irradiation areas is coupled, either directly into the solid-state rod, which in the Envelope is preferably embedded tightly, radiated is, or on the respective reflective surfaces, for example, by a coating of the outside of the envelope in the area of this Re are formed, is reflected. At the same time they serve se reflective surfaces, heat loss within the envelope is created by heat conduction to the outside environment. It is him obvious that this gives a simple component with which to  one defines the diode laser radiation for pumping the solid the solid rod can be guided, on the other hand a heat guidance to the outside environment is achieved. The individual surface areas can vary in their extent and in the circumferential direction of the Envelope be dimensioned. In other words, this means that the Area over which the radiation from the diode laser is inserted into the envelope is radiated, can only be selected so large that it is just sufficient for the to absorb all of the radiation emitted by the diode lasers while the remaining areas can then be used as re flexion surfaces designed to dissipate the heat loss to the outside. The dimensioning and profiling described above is possible speeds with regard to the envelope are in particular simple means dere advantageous in that the geometry of the envelope to the un Different beam cross-section of the diode laser, as he did at the beginning is refined, can be adjusted.

The enveloping body is preferably constructed as a cylindrical part with in axially bounding end faces, which are then totally reflective for the diode laser radiation propagating in the envelope forms are. The diode laser radiation is over the surface segments in the form of the irradiation areas of the enveloping body and led to the solid; Radiation due to the beam diver genz or the reflections within the envelope to the end faces of the envelope is directed there by total reflection right inflected so that no losses caused by emerging from the envelope Radiation occur.

Preferably, the envelope is symme with respect to its cross section built up to a plane that contains the axis of the enveloping body. This ensures that the solid from the bottom different directions is pumped by the radiation of the diode laser. When building the envelope, care should be taken that the reflective surfaces the irradiation areas over which the diode beam  tion is radiated into the envelope, opposite, so that radiated radiation either hits the solid directly or on the one behind or opposite the irradiation surface reflecting surface of the enveloping body, then, at this reflection surface reflected to be directed at the solid. Out of this follows that it is advantageous that each irradiation area at least one Reflection area is assigned.

In a preferred development, the reflection surfaces are made in this way forms that they focus the radiation on the solid. Here the reflecting surfaces are dimensioned and curved so that they are in front preferably focus the radiation that is in the envelope over the is irradiated in each irradiation area, this reflection face lies.

However, in order to get the radiation from the diode laser directly without reflection The diode lasers, on the one hand, can radiate any lust into the solid be dimensioned so that their beam cross section the cross section of the Solid body illuminated approximately, so that almost all the radiation the diode laser strikes the solid-state rod directly. Such Defined illumination can also be achieved in that the Areas of the irradiation areas by a defined curvature diode laser in one direction or the other (also in Ab dependence of the position of the elliptical beam cross section of the diode laser) focus or expand.

It is known that individual diode lasers, to achieve higher Leis lines and power densities, for so-called diode laser arrays or Dio The laser field arrangements can be summarized, for example linear array arrangements in which the beam exit window of the one individual diode lasers lie on one line, or also to more di dimensional field arrangements, d. H. to such field arrangements where several line-shaped laser diode arrays can in turn be combined.  

With such diode laser arrays, large areas can be uniform be illuminated, which in turn with respect to the envelope is used to the extent that the irradiation areas are chosen to be relatively large can then be the same with such diode laser array arrangements can be moderately illuminated or their radiation evenly the respective irradiation area is radiated into the enveloping body becomes. In one embodiment, the size of the irradiation areas chosen about the same size as that of the reflection surfaces.

With regard to an arrangement of the irradiation areas relative to each because of the reflection surfaces there is an odd number of irradiation areas chosen, then, from the point of view that the number of Re inflection areas corresponds to the number of irradiation areas and this each have the same size, which means that symmetry a plane is present that contains the axis of the enveloping body, the Preferred structure already mentioned above can be achieved at which is in each case an irradiation area of a reflection surface. So that the outer body of the envelope is not too complicated is, on the other hand, he uniform radiation of the solid is sufficient, the number of irradiation areas should be an odd number not exceed between three and eleven.

The enveloping body according to the invention also offers the possibility, in addition to the Arrangement of a solid along the axis of the envelope, several Embed solid, for example three, which are then preferably sym arranged around the axis of the enveloping body to achieve the mentioned symmetry.

In order to dissipate the heat loss via the reflective surfaces can support on the outer surfaces of the reflective surfaces lines are arranged. It can be seen that despite such coolness directions a compact structure is achievable.  

Additional cooling measures can also be carried out by that the solid is cooled directly in the envelope by at for example, channels or channels surrounding the solid body in the enveloping body are provided to pass a cooling fluid therethrough.

The respective diode lasers are preferably with the large axis of their elliptical beam cross section substantially perpendicular to the axis arranged of the enveloping body, so that, precisely with regard to an enveloping body per, which is formed in the form of a short cylinder section, for example wise in the form of a disc-shaped part, the beam with a high Beam divergence directed towards these end faces of the enveloping body becomes. This can result in a high packing density of the diode lasers Pumps are used to be achieved.

Further details and features of the present invention will become apparent from the following description of exemplary embodiments using the Drawings. Show in the drawings

Fig. 1 shows schematically an embodiment of a cylindrical shell body according to the invention having a single solid-state rod that is embedded therein,

Fig. 2 is a disk-shaped casing body having a cross-sectional shape of the enveloping body corresponding to the Fig. 1,

Fig. 3 shows diagrammatically the beam path within an enveloping body, as shown in Figs. 1 and 2, in relation to a diode laser array,

Fig. 4 shows the arrangement of Fig. 3, wherein the beam path of the three diode arrays employed is shown schematically,

Fig. 5 diagrammatically shows a diode laser with the exiting from the exit surface typical spray cone,

FIG. 6A to 6D schematically illustrate various one and two dimensional diode laser arrays that can be used in conjunction with the Hüllkör by,

Fig. 7 is a comparable with the representation of Fig. 4, but in contrast to the arrangement of Fig. 4, the A beam areas are dimensioned smaller compared to the reflection areas in the circumferential direction of the envelope and the slow direction of the beam cross section of the diode laser parallel to Axis of the enveloping body or of the solid rod runs,

Fig. 8 is an arrangement of FIGS. 3 and 4 corresponding arrangement, although three solid bars are embedded in the casing body, and

FIG. 9 shows an arrangement corresponding to FIG. 1, with a cooling channel being provided around the solid body compared to FIG. 1.

In Fig. 1, a zy-cylindrical envelope 1 is schematically shown in a perspective view, which is limited in the direction of the axis 2 by end faces 3 which extend approximately perpendicular to the axis 2 . A continuous bore 4 runs along the axis 2 and is intended to receive a solid body rod of a diameter corresponding to the cross section of the bore 4 .

The cylindrical surface 5 is divided into six segments surface 6, wherein three flat surface segments 6 each form Einstrahlbereiche 7, while the other three curved surface segments form reflection surfaces 6. 8

While the casing body 1 of FIG. 1, the shape comprises an elongated Zy Linders, an enfolding body 1 is shown in FIG. 2, the same cross-sectional shape as the casing body 1 of FIG. 1 comprises, also with six surface segments, three of which segments Einstrahlbereiche 7 and three segments form reflection surfaces 8 , but are disk-shaped, ie have only a small extension in the direction of the axis 2 .

The enveloping bodies 1 , as shown in FIGS. 1 and 2, are each shown in a top view of their end face 3 in FIGS. 3 and 4. In Fig. 3, the three irradiation areas 7 of the envelope body 1 each have a diode laser array or a diode laser array arrangement 10 (also referred to in the figures as a "DL array"). The slow direction runs perpendicular to the axis 2 of the enveloping body 1 .

The radiation, which is given by the respective diode laser field arrangements 10, is radiated into the envelope body 1 via the irradiation regions 7 . The radiation 11 either strikes the solid rod 9 directly, as is indicated in FIG. 3 by the central beam emanating from the lower diode laser array 10 , or passes the solid rod 9 , strikes the opposite reflection surface 8 and is from there, due to the curvature of the reflection surface 8 , focused on the solid-state rod 9 . A corresponding radiation emanates from the two other diode laser field arrangements 10 , as shown in FIG. 4, so that the solid-state rod 9 is irradiated uniformly from all sides of the arrangement.

The Einstrahlbereiche 7 are dimensioned such that they correspond in size to the extension of the diode laser array 10, respectively, is so that the whole irradiation region 7 array by the radiation of the diode laser illuminated 10th Furthermore, as is clear from FIGS. 3 and 4, the arrangement is arranged symmetrically to a fictitious plane which contains the axis 2 of the enveloping body 1 . The reflection surfaces 8 , which are preferably formed by reflecting layers applied to the envelope from the outside, are totally reflective for the diode laser radiation. As can be seen from FIGS. 3 and 4, the reflecting surfaces 8 form a relatively large surface area, with respect to the entire enveloping body 1 , which is suitable for dissipating heat generated in the enveloping body 1 to the outside environment. Through these reflective surfaces, a measure is therefore taken at the same time in order to cool the enveloping body, which is very important for the achievable laser property of the solid-state laser, such as beam quality and output power.

The individual areas, ie the irradiation areas 7 and the reflection surfaces 8 , can be dimensioned in a defined manner in their radial and axial extent. While in the figures the irradiation areas 7 are shown as flat parts of the surface, they can also have a curvature in order to either focus or expand the radiation emitted by the diode lasers of the field arrangement 10 , the beam cross-section required for such measures a diode laser is typical, which is shown in FIG. 5 and will be explained below, is taken into account.

In order to keep losses on the two end faces 3 of the enveloping body 1 low, these are preferably totally reflective in order to reflect back radiation 11 , which emanates from the diode laser field arrangements 10 and strikes these end faces 3 , into the enveloping body 1 . If necessary, these end faces 3 can be curved in order to achieve a focusing effect; planar end faces 3 are preferred, however, in order to achieve a simple geometry of the enveloping body 1 , the radiation components which impinge on these end faces 3 within the enveloping body 1 being kept low by a de-defined arrangement of the diode lasers of the field arrangement 10 .

If necessary, additional cooling measures can be taken in the area of the reflecting surfaces 8 on the outside of the enveloping body 1 in order to remove the heat loss generated in the enveloping body 1 more quickly to the outside. Since the heat loss is transported through the volume of the enveloping body 1 , the enveloping body is preferably made of a highly heat-conducting and highly transmissive material, such as for example sapphire.

As already mentioned above, the elliptical beam cross section of a diode laser must be taken into account when orienting the diode laser field arrangement 10 relative to the irradiation regions 7 or the axis 2 of the enveloping body 1 .

In Fig. 5 a typical structure of a single diode laser 12 is shown schematically, but without heat sink and other supply lines. The structure has a heavily doped p⁺ phase 13 , a p phase 14 and an n phase 15 . The reference numeral 20 denotes the exit surface of an emitting zone of the active medium, which has a certain extent in the direction of the plane of the transition of the p-phase 14 and the n-phase 15 , while being relatively narrow perpendicular to these planes. Due to the geometry of the active Me diums emerges from the exit surface 20 of the indicated typical Strah lenkegel of which has an elliptical cross-section, the major axis 16 is perpendicular to the plane of the pn junction, while the small axis 17 of the elliptical cross-section parallel to the level of the pn junction. Typically, the large extent of the jet cone perpendicular to the plane of the pn junction, which is also referred to as the "fast direction", is afflicted with a divergence angle 18 of approximately 90 °, while the jet cone is in the direction of the minor axis 17 or perpendicular to the fast direction, which is also referred to as the "slow direction", has a divergence angle 19 of approximately 10 °.

In the embodiments described so far, as shown in FIGS. 1 to 4, the diode laser array arrangement 10 is preferably arranged such that the slow direction of the individual diode lasers 12 of the array arrangement is perpendicular to the axis 2 of the solid-state rod 9 or Envelope 1 runs. In this way, an extremely high pump power density can be achieved and an extremely compact pulse laser can thus be constructed.

Examples of the structure of diode laser field arrangements 10 which can be used in the embodiments of the enveloping body 1 are shown in FIGS. 6A to 6D. Since individual laser beam sources in the form of diode lasers can only be scaled to higher powers to a limited extent, a greater number of individual diode lasers are combined to form different arrays or field arrangements in order to achieve higher laser powers and power densities, as is shown in the figures.

Here, one can differentiate between linear field arrangements, as shown in FIGS . 6A and 6C, double-linear field arrangements, as shown, for example, in FIG. 6B, and two-dimensional arrays according to the schematic representation of FIG. 6D.

As FIGS. 6A to 6D show, diode laser field arrangements 10 in the irradiation areas can be used in accordance with their dimensions and power densities in order to irradiate the radiation from the individual laser diodes into the enveloping body 1 .

In FIG. 7 shows an embodiment of a diode laser pumped solid-state laser is shown with a casing body 1, in which the A bright areas 7, in their radial extension to the axis 2 of the shell body 1, are dimensioned substantially smaller lying as each individual between the Einstrahlbereichen 7 Reflection surfaces 8 , the reflection surfaces 8 being approximately five times larger than the irradiation regions 7 when viewed in the radial direction. Again, three irradiation areas 7 are provided, each with an intermediate reflection surface 8 . The arrangement in FIG. 7 is suitable for such structures of a diode laser-pumped solid-state laser in which the slow direction of the individual diode lasers of the diode laser field arrangement 10 runs parallel to the cylinder axis 2 of the solid-state rod 9 . The diode laser radiation is in turn irradiated through the three irradiation areas 7 in the envelope body 1 , which are flat and are formed by a highly transmit coating on the glass body. A portion of the Dio is denstrahlung directly irradiated to the solid-state rod 9, as the radiation path, shows the other part impinges on the saw tung in beam Rich behind the field-state rod 9 disposed reflection surface 8, from where they are made, due to the concave curvature of the reflection surface 8 , is focused into the solid-state rod 9 . The effectiveness of the laser can be increased by the multiple reflection within the glass body.

The embodiment of FIG. 7 has the advantage over the embodiment of FIG. 3 that with a certain size of the enveloping body 1 more diode arrays 10 can be arranged around the circumference of the enveloping body 1 . In addition, the pump power density distribution in the solid can be set more easily. This concept is advantageous for continuously operated (cw) lasers.

Furthermore, the embodiment of FIG. 7 has the advantage that the large dimensioning of the reflection surfaces 8 , in comparison to the embodiment of FIGS. 3 and 4, a higher heat dissipation of heat from United pleasure can be achieved within the envelope body 1 .

Fig. 8 shows schematically a further embodiment, wherein the shape of the enveloping body 1 and the arrangement of the diode laser array 10 corresponds to the embodiment of FIGS. 3 and 4, in which, however, three solid rods 9 are embedded in the enveloping body 1 compared to the previous embodiment . The individual solid rods are sym metrically of the casing body 1 evenly distributed about the axis 2, wherein each weils two solid rods 9 are aligned with their axes 22 so that the axes of the respective two solid rods 9 lie in a plane gene that is parallel to the plane of the Irradiation areas 7 runs. This embodiment has the advantage that the thermal load on the solid-state medium is reduced, and in addition the area which is opposed to the radiation of the diode laser array arrangements 10 is increased.

In FIG. 9, in addition to the embodiment of FIG. 1, an annular space 22 is left around the solid body rod 9 , through which a fluid circulates, which dissipates the heat loss within the enveloping body 1 .

As the above description shows, a compact, yet effective arrangement of a diode laser-pumped solid-state laser is created using the described enveloping body, into which one or more solid-state rods 9 are used as the active medium.

Claims (16)

1. Diode laser-pumped solid-state laser with at least one serving as an active medium, rod-shaped or disk-shaped solid and with diode lasers, the emitted radiation of which is radiated into the solid, reflecting elements being used for beam guidance and / or shaping, characterized in that the solid body ( 9 ) is encased in a radial direction to its axis by a transparent glass or crystal envelope ( 1 ) for the emitted radiation, the outer surface ( 5 ) of the envelope ( 1 ) being divided into at least two areas ( 6 ) is one of which forms an irradiation region ( 7 ) for the emitted radiation and which serves as a reflection surface ( 8 ) at the other region, which reflects through the envelope ( 1 ) through radiation ( 11 ) onto the solid ( 9 ). 2. Diode laser-pumped solid-state laser according to claim 1, characterized in that the end faces ( 3 ) of the enveloping body ( 1 ), which axially limit the enveloping body ( 1 ), are totally reflective for the diode laser radiation ( 11 ) which propagates in the enveloping body ( 1 ) are. 3. Diode laser-pumped solid-state laser according to claim 1 or 2, characterized in that the reflection surface ( 8 ) of the irradiation area ( 7 ) is arranged opposite. 4. Diode laser-pumped solid-state laser according to claim 3, characterized in that each irradiation area ( 7 ) is assigned at least one reflection surface ( 8 ). 5. diode laser-pumped solid-state laser according to one of claims 1 to 4, characterized in that the reflection surface ( 8 ), the radiation ( 11 ) focuses on the solid body ( 9 ). 6. Diode laser-pumped solid-state laser according to claim 5, characterized in that the focused radiation approximately illuminates the cross section of the solid body ( 9 ). 7. Diode laser-pumped solid-state laser according to one of claims 1 to 6, characterized in that the irradiation areas ( 7 ) and / or the reflection surfaces ( 8 ) have the same size. 8. Diode laser-pumped solid-state laser according to one of claims 1 to 7, characterized in that the number of irradiation areas ( 7 ) corresponds to the number of reflection surfaces ( 8 ). 9. Diode laser-pumped solid-state laser according to one of claims 1 to 8, characterized in that the number of irradiation areas ( 7 ) is odd and is at least three. 10. Diode laser-pumped solid-state laser according to one of claims 1 to 9, characterized in that the irradiation regions ( 7 ) and the re reflection surfaces ( 8 ) are arranged symmetrically to a plane which contains the central axis ( 2 ) of the enveloping body ( 1 ). 11. Diode laser-pumped solid-state laser according to one of claims 1 to 10, characterized in that in the enveloping body ( 1 ) a plurality of solid bodies ( 9 ) are embedded. 12. Diode laser-pumped solid-state laser according to one of claims 1 to 11, characterized in that the enveloping body ( 1 ) is provided with cooling devices. 13. Diode laser pumped solid state laser according to claim 12, characterized in that the heat loss generated in the solid body ( 9 ) is dissipated by heat conduction through the envelope body ( 1 ) to the outer surface ( 5 ), the cooling devices on the outer surfaces of the reflection surfaces ( 8 ) are arranged. 14. Diode laser-pumped solid-state laser according to claim 12 or 13, characterized in that the cooling devices surround the solid body ( 9 ) directly. 15. Diode laser-pumped solid-state laser according to claim 1, characterized in that the diode lasers, which are assigned to an irradiation area, are combined to form at least one array or field arrangement ( 10 ). 16. Diode laser-pumped solid-state laser according to one of claims 1 to 15, characterized in that the respective diode lasers are arranged with the major axis of their elliptical beam cross section substantially perpendicular to the axis ( 2 ) of the envelope body ( 1 ).