Abstract:
The invention relates to a pump arrangement for transversally pumping an active medium, especially a laser rod, wherein two pump light sources are arranged on a plane perpendicular to the longitudinal axis of the active medium, especially pertaining to the laser rod. The value of the smallest angle between the central axes of the pump light sources is less than 180°. A pump arrangement is also provided which illuminates the active medium in a particularly uniform manner.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a pump arrangement for the transversal pumping of an active medium. 
   2. Description of the Related Art 
   It is known that active medium of a laser with diode lasers can be pumped longitudinally or transversally (see, for example, Eichler, Eichler; Laser-Bauformen, Strahlführung, Anwendung [Types of Lasers, Beam Guidance, Application], Springer, 3rd Edition, Page 150). For the transversal pumping, a laser diode is located laterally with respect to the active material, so that the laser beam strikes the active medium from the side. As a result of this arrangement, however, it is not possible to illuminate the interior of the active medium uniformly. 
   SUMMARY OF THE INVENTION 
   An object of this invention is to create a pump arrangement for transversal pumping that illuminates the active medium uniformly. 
   The invention teaches that two pump light sources are located in a plane that is perpendicular to the longitudinal axis of the active medium, in particular a laser rod, whereby the size of the smallest angle between the center axes of the pump light sources is less than 180°. Therefore two pump light sources are used that are in all cases not exactly opposite each other, i.e. the pump light sources are oriented in a plane at an angle to each other. This transversal pump arrangement makes possible a uniform illumination of the active medium. 
   It is thereby advantageous if the angle between the center axes of the pump light sources in a plane is 120° or 90°. 
   An advantageous realization of the pump arrangement claimed by the invention has two groups of pump light sources in different planes, whereby the planes are oriented perpendicular to the longitudinal axis of the active medium, in particular of a laser rod. The pump light sources are therefore distributed parallel over the length of the active medium, which results in a particularly good illumination. 
   Each group of pump light sources advantageously has two pump light sources. 
   A particularly favorable illumination of the active medium can be achieved if the center axes of the pump light sources in a first plane are rotationally offset with respect to the center axes of the pump light sources of a second plane by an angle around the longitudinal axis of the active medium, in particular of the laser rod. The pump light sources are thus not only located along the active medium, but also strike the active medium from different directions. 
   It is particularly advantageous if the angle that describes the rotation of the center axes of the pump light sources with respect to the longitudinal axis of the laser rod is 180°. 
   In one advantageous configuration, at least one pump light source is realized in the form of a laser diode. It is also advantageous if a laser diode emits a linear laser beam. 
   In an additional advantageous configuration of the pump arrangement claimed by the invention, the pump light beam can be formed by at least one lens system, in particular a micro lens system for laser diode radiation. 
   It is particularly advantageous if the pump arrangement claimed by the invention has a water cooling system, in particular a flowtube system. 
   The flowtube advantageously has at least one reflective coating, in particular made of gold and/or silver. 
   It is also advantageous if the reflective coating is surrounded by at least one thermally conductive layer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of one embodiment of the pump arrangement according to the present invention; 
       FIG. 2  is a schematic view of the arrangement of the pump light sources; 
       FIG. 3  is a perspective view of a central piece of one embodiment of the pump arrangement claimed by the invention; 
       FIG. 4  is a perspective view of a laser diode as the pump light source; 
       FIG. 5  is a perspective schematic view of a flowtube as the cooling system; 
       FIG. 5   a  is a sectional view of the flowtube illustrated in  FIG. 5 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows one embodiment of a pump arrangement which can be used as a pump chamber for a laser resonator or as an optical amplifier for a laser beam. 
   The pump arrangement has four pump light sources  3   a ,  3   b ,  3   c ,  3   d  which are realized in the form of edge-emitting laser diodes. The pump light sources  3   a ,  3   b ,  3   c ,  3   d  are arranged around a laser rod  5  as the active medium, so that the laser rod  5  can be pumped transversally. The radiation in the laser rod  5 , i.e. between the resonator surfaces, is indicated by arrows in  FIG. 1 . The laser rod  5  has a longitudinal axis A. 
   The pump light sources  3   a ,  3   b ,  3   c ,  3   d  are thereby arranged in groups in two different planes  10 ,  20  (see in particular  FIG. 2 ), whereby the planes  10 ,  20  are perpendicular to the longitudinal axis A of the laser rod  5 . 
   The first group of pump light sources  3   a ,  3   b  lies in the first, front plane  10  in  FIG. 1  and the second group of pump light sources  3   c ,  3   d  lies in the second, rear plane  20  in  FIG. 1 . 
   The pump light sources  3   a ,  3   b ,  3   c ,  3   d  are oriented in the respective planes  10 ,  20  at a right angle B 1 , B 2  to each other. Basically, other angles B in a plane are also conceivable, as long as the pump light sources  3   a ,  3   b ,  3   c ,  3   d  in a plane  10 ,  20  are not diametrically opposite each other. If they were diametrically opposite each other, the angle would be exactly 180°. The invention teaches that the angle B is therefore less than 180°. 
   As is more clearly illustrated in  FIG. 2 , the pump light sources that are arranged in pairs are also rotated with respect to one another by a determined angle. 
   The pump light sources  3   a ,  3   b ,  3   c ,  3   d , on the end that points toward the laser rod  5 , a wedge-shaped realization (see also  FIG. 4 ), so that the pump laser diodes can be placed as close as possible to the laser rod  5 . In this case, the laser rod can have a diameter of up to 6 mm. The pump length of the laser rod  5  is twice the length of the pump light sources  3   a ,  3   b ,  3   c ,  3   d , which in this case are identical pump light sources. 
   The pump light sources  3   a ,  3   b ,  3   c ,  3   d  and the laser rod  5  are located on a central piece  2  with spokes  7   a ,  7   b  (see  FIG. 3 ). Located around the laser rod  5  is a flowtube  4  which acts as a cooling system and is explained in greater detail in connection with  FIG. 5 . In the central piece  2  there are channels for the cooling water supply to the pump light sources  3   a ,  3   b ,  3   c ,  3   d  and to the laser rod  5 . 
   In the exemplary embodiment illustrated here, the pump light sources  3   a ,  3   b ,  3   c ,  3   d  are all constructed identically. Alternatively, different models of light sources can also be used. 
     FIG. 2  is a schematic illustration of the arrangement of the pump light sources  3   a ,  3   b ,  3   c ,  3   d  to show the geometric relationships. The illustration in  FIG. 2  is a view in perspective, whereby in this case the pump light sources  3   a ,  3   b ,  3   c ,  3   d  are represented only by lines. 
   The planes  10 ,  20  are perpendicular to the longitudinal axis of the laser rod  5 . The first plane  10  is thereby located in front of the second plane  20  in the direction of the view shown in the drawing. In the first plane, there are two pump light sources  3   a ,  3   b  that are at an angle B 1 =90° to each other. The invention teaches that this angle can be between (almost) 0° and less than 180°. 
   Two pump light sources  3   c ,  3   d  are located in the second plane at an angle of B 2=90 ° to each other. The invention teaches that this angle can also be between (almost) 0° and less than 180°. 
   The pump light sources  3   a ,  3   b  in the first plane  10  each have center axes Ca, Cb. The pump light sources  3   c ,  3   d  in the second plane have respective center axes Cc, Cd. 
   The center axes Ca, Cb of the pump light sources  3   a ,  3   b  in the first plane  10  are rotated with respect to the center axes Cc, Cd of the pump light sources  3   c ,  3   d  in the second plane  20  by an angle of 180° around the longitudinal axis A of the laser rod  5 . 
   With this arrangement, which is offset along the longitudinal axis A, it becomes possible to achieve a particularly uniform illumination of the laser rod  5 . 
   In  FIG. 3 , the central piece  2  is shown in detail, although without the pump light sources  3   a ,  3   b ,  3   c ,  3   d  and without the laser rod  5 . In the center, the openings are visible as the flow tube holders  8 . 
   The central piece  2  has two spokes  7   a ,  7   b  which are used for the installation of the pump light sources  3   a ,  3   b ,  3   c ,  3   d . The spokes are arranged at an angle of 90° from each other. In the spokes  7   a ,  7   b  are channels for the cooling water supply. To provide power to the laser diodes, contact is achieved by means of a laminated printed circuit board, which makes possible a simple installation of the diodes. 
   As shown in  FIG. 1 , two laser diodes are located on each of the spokes  7   a ,  7   b  in the form of pump light sources  3   a ,  3   b ,  3   c ,  3   d.    
     FIG. 4  shows an individual pump light source  3   a , which is realized for installation into the pump arrangement claimed by the invention. A diode laser array is located between two clamping jaws  31 . The clamping jaws  31  are beveled by 45° on the side that faces the laser rod  5 . 
   The angle of the bevel can alternatively be smaller than 45°. Connections (feed and drain) for the water supply are integrated into the clamping jaws  31 . The diode laser beam  34  can be shaped by micro lenses that are not shown in the drawing. The wider part of the jaw is used for fastening to the spokes  7   a ,  7   b  (see  FIGS. 1 and 3 ). 
     FIG. 5  is a schematic view in perspective of a flowtube  4  which is used as a cooling system for the laser rod  5  (not shown here). 
   The flowtube  4  is provided with various coatings (See  FIG. 5   a ), which are removed in the areas in which the diode radiation  36  enters the laser rod  5  for transversal pumping. The side opposite the pump beam can be provided with a reflective coating. The flowtube  4  has uncoated sealing surfaces  40  on the ends. 
   The flowtube  4  is shown in cross section in  FIG. 5   a . The laser rod  5  is located inside the flowtube. Said laser rod is surrounded by the actual flow tube  4 . The flowtube  4  is provided on its outward-facing surface with a reflective coating  41 . If this reflective coating  41  does not have sufficient thermal conductivity, it can be surrounded (as shown here) by a thermally conductive coating  42  (e.g. copper, nickel), so that the heat that results from residual absorption can be discharged via the cooling medium. 
   The realization of the invention is not limited to the preferred exemplary embodiments described above. On the contrary, there are a number of conceivable variants that make use of the pump arrangement claimed by the invention even in fundamentally different realizations. 
   NOMENCLATURE 
   
       
         1  Pump chamber 
         2  Central piece 
         3  Pump light source (laser diodes  3   a ,  3   b ,  3   c ,  3   d ) 
         4  Cooling system (flowtube) 
         5  Laser rod 
         6  End pieces 
         7   a ,  7   b  Spokes 
         8  Flow tube holder 
         10  First plane 
         20  Second plane 
         30  Diode laser array 
         31  Clamping jaws 
         32  Beveled edges 
         33  Water feed and drain 
         34  Diode beam 
         40  Sealing surfaces 
         41  Reflective coating 
         42  Thermally conductive coating 
       A Longitudinal axis of the laser rod 
       B Angle between two pump light sources in a plane 
       C Center axis of the pump light sources