Abstract:
An impedance matching circuit for a gas-laser excitation system includes a high-frequency connection line configured to be connected at a first connection point to a power source and at a second connection point to a gas-laser electrode. The impedance matching circuit is characterized in that an impedance of at least one section of the high-frequency connection line changes by a change to a configuration of the high-frequency connection line, in particular to at least one parameter of the high-frequency connection line in the at least one section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of and claims priority under 35 U.S.C. §120 to PCT Application No. PCT/EP2015/067390 filed on Jul. 29, 2015, which claims priority to German Application No. 10 2014 215 226.7, filed on Aug. 1, 2014. The entire contents of these priority applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to impedance matching in a gas laser excitation arrangement. 
       BACKGROUND 
       [0003]    High-power lasers having a light power of no less than 500 W can be used in laser processing, for example for marking metals or non-metals, for cutting, welding and processing materials, e.g., metals. 
         [0004]    In order to excite a gas laser, gas discharge is generally generated. The gas discharge is generally generated by supplying electrical power, in particular often by means of high-frequency (HF) electrical power. The electrical power is generally supplied by means of electrodes. The high-frequency power is often coupled in at one or more supply points on the electrode. The electrodes are commonly arranged in pairs, one of the electrodes commonly being at a static potential, in particular at earth potential. An electrical power source, e.g., a HF power source, is connected to the other electrode. A source and a load are connected to a high-frequency connecting line. The power source has an output impedance. The load has a load impedance. To improve the energy transfer from the source to the load, the load impedance has to be matched to the source impedance. This is commonly achieved by means of an additional impedance matching circuit connected between the load and the power source. 
       SUMMARY 
       [0005]    One aspect of the present invention features an impedance matching arrangement (or circuit) for a gas laser excitation arrangement (assembly or system). The impedance matching arrangement comprises a high-frequency connecting line which can be connected to a power source at a first connection point and to a gas laser electrode at a second connection point, the impedance of the high-frequency connecting line changing at least in one portion as a result of the design, in particular a parameter, of the high-frequency connecting line changing in this portion. According to the invention, the impedance is therefore matched by a part of the high-frequency connecting line itself. As a result, additional components can be eliminated. Simplified impedance matching can be achieved in the gas laser excitation arrangement. 
         [0006]    At a given geometric length, e.g., the prescribed length of a laser or laser electrode, the impedance can be matched over a comparatively wide range. It has been shown that even the frequency range in which impedance can be matched can be extended in this manner. Therefore, the high-frequency power can be used with a plurality of frequency components. 
         [0007]    The impedance can continuously change in the portion. In particular, the parameter of the high-frequency connecting line, for example the width of the high-frequency connecting line, can therefore continuously change in the portion. As a result, the electrical length or the transformation effect can be optimized with respect to the geometric length. 
         [0008]    The design of the portion can change by the shape, in particular the geometry or the cross section, of the high-frequency connecting line continuously changing in the at least one portion. 
         [0009]    The high-frequency connecting line can be designed to electromagnetically interact with the gas laser excitation arrangement in the portion. In this way, part of the gas laser excitation arrangement can also be used for impedance matching. 
         [0010]    The high-frequency connecting line can be designed as a coaxial cable comprising an inner conductor and an outer conductor, the cross section, in particular the magnitude or the area of the cross section, of the inner conductor and/or the outer conductor changing steadily in the portion. 
         [0011]    The inner conductor and/or the outer conductor can comprise portions of different constant cross sections, the cross section steadily changing at the transition from one cross section to the next cross section. The impendence matching can be adjusted by the cross section changing. The cross section can be changed in particular by the diameter or the width of the high-frequency connecting line changing in the portion. 
         [0012]    In this case, the diameter or the width of the high-frequency connecting line can change steadily in the portion. In particular, the high-frequency connecting line can be stepless in the portion. This results in a particularly broadband impedance matching. 
         [0013]    The high-frequency connecting line can be designed as a conductor path arrangement comprising a conductor path and a reference surface, the width of the conductor path changing, in particular steadily, in the portion. In this case, the conductor path can comprise a plurality of portions of different widths, the width steadily changing from one width to the next width. Impedance transformation can occur each time the width changes. 
         [0014]    The high-frequency connecting line can be designed as a conductor path arrangement comprising a conductor path and a reference surface, the distance from the conductor path to the reference surface changing, in particular steadily, in the portion. As a result of the distance changing, the interaction between the high-frequency connecting line and the reference surface also changes. This can also lead to impedance matching. 
         [0015]    Alternatively or additionally, the high-frequency connecting line can be designed as a conductor path arrangement comprising a conductor path and a reference surface, the dielectric constant of the dielectric between the conductor path and the reference surface changing, in particular steadily, in the portion. Changing the distance to the reference surface and/or changing the dielectric constant, in particular by using different dielectrics, allows impedance to be matched in a particularly simple technical manner. 
         [0016]    The high-frequency connecting line can have a predefined impedance at the first connection point that can be adjusted by means of the capacitive and/or inductive coupling between the high-frequency connecting line and a shield. This ensures that the impedance at the second connection point is precisely matched to the load. 
         [0017]    Another aspect of the present invention features a gas laser excitation arrangement comprising an impedance matching arrangement, the high-frequency connecting line extending at least in one portion at a defined distance to, in particular in parallel with, a gas laser electrode. This results in a particularly space-saving arrangement of the high-frequency connecting line. 
         [0018]    This gas electrode can be, at least in part, part of the impedance matching arrangement. When this is the case, the impedance matching arrangement has a particularly compact design. 
         [0019]    Alternatively or additionally, the gas electrode can be, at least in part, part of the high-frequency connecting line. 
         [0020]    A gas laser electrode can be connected to earth. 
         [0021]    The defined distance between the portion and the gas laser electrode can be determined in different ways. In particular, the defined distance may be no higher than 10 cm, in particular no higher than 5 cm, in particular no higher than 1 cm. Alternatively, the defined distance may be no more than ⅕, in particular no more than 1/10, of the wavelength of the high-frequency for which the impedance matching arrangement is designed. 
         [0022]    In another alternative, the defined distance may be no more than half, in particular no more than ⅕, in particular no more than 1/10, of the length of the high-frequency connecting line in the portion. 
         [0023]    Furthermore, the defined distance may be such that a high-frequency electric field is created between the high-frequency connecting line and the gas laser electrode when high-frequency power is conducted from the first connection point to the second connection point. In this case, a high-frequency electric field is not created or only a small high-frequency electric field is created outside of the portion. 
         [0024]    The high-frequency connecting line can have a predefined impedance at the first connection point, which can be adjusted in the portion by the distance and the area between the high-frequency connecting line and the gas laser electrode. It is thus also possible to adjust the impedance matching. 
         [0025]    The high-frequency connecting line can be surrounded by the gas discharge in the portion. Alternatively, the high-frequency connecting line can surround the gas discharge in the portion. 
         [0026]    According to an embodiment which is particularly advantageous in terms of size, the high-frequency connecting line can be arranged at least in part in the inner electrode of a coaxial laser. 
         [0027]    The gas laser electrode can be designed as a planar electrode. The high-frequency connecting line can comprise an outer conductor that forms part of the gas laser electrode. 
         [0028]    The reference surface of the impedance matching arrangement can be, at least in part, part of the gas laser excitation arrangement, it being possible for said reference surface to be in particular connected to an electrode. 
         [0029]    Further features and advantages of the invention can be found in the following description of an embodiment of the invention, by way of the drawings, which show details essential to the invention, and from the claims. The individual features may each be implemented in isolation or together in any desired combination in a variant of the invention. 
         [0030]    A preferred embodiment of the invention is shown schematically in the drawings and is described in greater detail in the following with reference to the drawings. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0031]      FIG. 1  is a partial sectional view of a diffusion-cooled gas laser excitation arrangement. 
           [0032]      FIG. 2  is an enlarged view of the gas laser excitation arrangement of  FIG. 1  in the region of a supply point. 
           [0033]      FIG. 3  is a schematic view illustrating an example of a gas laser excitation arrangement in the form of a slab laser. 
           [0034]      FIG. 4  is a schematic view illustrating another example of a gas laser excitation arrangement in the form of a slab laser. 
           [0035]      FIG. 5  is a schematic view illustrating a further example of a gas laser excitation arrangement in the form of a slab laser. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]      FIG. 1  is a partial sectional view of a diffusion-cooled gas laser excitation arrangement  1 . The gas laser excitation arrangement  1  comprises an outer electrode  2  in which cooling pipes  3  for a coolant, e.g., cooling liquid, are arranged. The outer electrode  2  is made of metal and is connected to earth. The discharge gap  4  is directly below the electrode  2 . The second electrode is denoted by reference numeral  5 . 
         [0037]    A dielectric  6  is located above the second electrode  5  and can be constructed from a plurality of different layers of material. In the embodiment shown, power is supplied centrally, based on the length of the electrode  5 , at a location (or a supply point)  10 . 
         [0038]    It can be seen in the enlarged view of  FIG. 2  that the discharge gap  4  is between the electrode  2  and the electrode  5 . In this case, the electrodes  2  and  5  are arranged coaxially with one another. A high-frequency connecting line  11   a ,  11   b  is connected to a power source  20 , which generates high-frequency power, at a first connection point  20 . 1  and to an electrode  5  at a second connection point  10 . 1 . The high-frequency connecting line extends in the portion  11   b  thereof inside the electrode  5  and substantially in parallel with the extension direction thereof. A shield  22  is provided in a first region  21  between the connecting line  11   b  and the electrode  5 . The shield  22  comprises, in the region of the supply point  10 , a recess  7  through which the high-frequency connecting line  11   b  is guided to the electrode  5 . The shield  22  is also provided in a second region  23 . However, there is no high-frequency connecting line in this region  23 . The shield  22  is connected to earth just like the electrode  2 . In the embodiment shown, the electrode  2 , the shield  22  and the portion  11 b of the high-frequency connecting line extend substantially in parallel with one another. The shield  22  extends in parallel with the electrode  5  in the second region  23  too. 
         [0039]    The diameter of the part of the high-frequency connecting line  11   b  that extends coaxially with the electrode  5  and the shield  22  becomes smaller at two locations approaching the supply point  10 . However, the transition from one diameter to another diameter is steady, as can be seen at the locations  24   a ,  24   b . The change in diameter corresponds to a change in the design of the high-frequency connecting line in the part  11   b  of the high-frequency connecting line. The impedance changes as a result of the diameter changing. 
         [0040]      FIG. 3  show a gas laser excitation arrangement  1 ′ in the form of a slab laser. A discharge gap  4 ′ is located between an electrode  2 ′, which is connected to earth, and an electrode  5 ′. The electrode  5 ′ is connected at connection point  10 . 1 ′ to the power source  20  at connection point  20 . 1 ′ via a high-frequency connecting line  11   a ,  11   b ′. In a first region  21 ′, a shield  22 ′, which is connected to earth, is provided between the portion  11   b ′ of the high-frequency connecting line and the electrode  5 ′. On the right-hand side of the supply point  10 ′, it is only the shield  22 ′ that is provided and not a high-frequency connecting line. Therefore, only the shield  22 ′ and part of the electrode  5 ′ are provided in the region  23 ′. The shield  22 ′ comprises a recess  7 ′ through which the electrode  5 ′ can be contacted. It can be seen that the width B of the high-frequency connecting line  11   b ′ becomes smaller approaching the supply point  10 ′ at the connection point  10 . 1 ′. The transition between the widths is steady, as can be seen at the location  24 ′. This results in impedance matching. The change in width corresponds to a change in the design of the high-frequency connecting line in the part  11   b  of the high-frequency connecting line. 
         [0041]      FIG. 4  shows another embodiment of the invention, the high-frequency connecting line having, in this case, a constant width B in the region  11   b ′, but having different heights h 1 , h 2  to the shield  22 ′, which can be referred to as reference surfaces. In region  24 ′, the height h 1  has changed into height h 2  in a steady manner. There is no step-like transition. Even by the distance from h 1  to h 2  changing, the design of the high-frequency connecting line  11   b ′ also changes and thus results in impedance matching. 
         [0042]    In another embodiment according to  FIG. 5 , the high-frequency connecting line  11   b ′ has in turn a constant width. However, the dielectric between the high-frequency connecting line  11   b ′ and the shield  22 ′, which also acts as a reference surface, is not constant. In particular, the dielectric continuously changes in a region  24 ′; but this cannot be shown graphically. This also results in impedance matching. The different options for impedance matching from  FIGS. 3 to 5  can also be combined with one another in any desired combination. 
         [0043]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.