Patent Publication Number: US-6665327-B1

Title: Gas laser device

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a gas laser assembly with at least one laser discharge tube with laser gas flowing through it in the flow direction, and in which at least one laser beam runs in the direction of the axis of the discharge tube, and at least one feed line for laser gas opens into the laser discharge tube through which the laser discharge tube is connected to a pressure source for laser gas, for example a laser gas pump, and the laser gas is introduced into the laser discharge tube. 
     In the case of a known generic gas laser arrangement, the a laser gas circulates by means of a laser gas pump. A heat exchanger is provided, both coming, between the laser gas pump and the laser discharge tube, i.e., in the feed line for the laser gas, and going, between the laser discharge tube and the laser gas pump. As a result, the laser gas that is heated inside the laser discharge tube when the laser arrangement is operating is cooled. The cooled laser gas is introduced into the laser discharge tube through a tubular section of the feed line, whose axis lies in a plane with the discharge tube axis and runs perpendicular to it. 
     Since the feed line extends at an angle to the laser discharge tube, at least with the tubular section described above, the laser gas entering the laser discharge tube experiences a deflection in its flow, namely with a deflection in the flow direction inside the discharge tube. Because of this, at least in the area of the laser discharge tube adjacent the opening to the feed line, when seen in cross section, the flow ratios for the laser gas introduced into the laser tube are uneven. This results in an uneven beam intensity profile, i.e., a non-uniform distribution of the power of the laser beam, over the cross section of the laser discharge tube. 
     This invention has set the goal of making an improvement in the distribution of the power of the laser beam over the cross section of the discharge tube. 
     SUMMARY OF THE INVENTION 
     The invention solves this problem in a gas laser arrangement of the type described at the beginning, by providing in the feed line to the laser discharge tube at least one spiral guide running about an open central cross section to the discharge tube. At least some of the laser gas is fed to the laser discharge tube through the spiral guide. By running at least some of the laser gas introduced into the laser discharge tube along a spiral guide path, especially in the area where the feed line opens into the laser discharge tube and in the section of the laser discharge tube adjacent that area, more uniform flow ratios for the laser gas are produced. In turn, this produces a distribution of the laser gas power over the discharge tube cross section that is relatively even. In addition, the spiral guide is characterized by the fact that a relatively long route for the laser gas is available with a small structural volume. 
     The invention offers a number of ways for making the spiral guide for the laser gas. Thus, the guide can be made by a corresponding machined spiral groove or channel for the guide track or by inserting a separate spiral-shaped guide element in the feed line. For example, it is conceivable to use a corresponding screw-shaped or spiral-shaped guide tube. as a spiral-type guide for the laser gas, the invention preferably has a corresponding open central portion aligned with the discharge tube for the laser beam. Because of its geometry, this type of guide channel is comparable to a guide thread or a section of a guide thread. 
     To achieve the desired guide effect with optimum results, the depth of this type of guide thread or channel is chosen so that it is relatively large. The invention provides that the depth of the guide channel be at least one fourth the inner diameter of the accompanying laser discharge tube. 
     Another version of the invention provides that the spiral-type guide for the laser gas have at least one corresponding guide spiral channel on the inner wall of the feed line for laser gas. The design and alignment of the guide spiral can influence the flow ratios produced. 
     One preferred embodiment of the gas laser arrangement in the invention is characterized by the fact that the spiral-type guide channel for the laser gas is provided in a guide tube forming the inside wall of at least one part of the feed line for the laser gas and disposed prior to the laser discharge tube in the direction in which the laser gas flows. The functional separation described between the laser discharge tube and the guide pipe makes sure that the laser gas flow, as soon as it reaches the area of the laser assembly in which the discharge takes place, is already optimized. It is also possible to combine guide tubes with different designs with the same laser discharge tube or to vary the flow ratios by corresponding alignment of the guide pipe in relation to the laser discharge tube to which it is connected. 
     To make the laser gas flow take the flow direction desired in the guide pipe along the shortest possible flow path, the invention provides that the guide tube have an inlet for the laser gas which is tangential to its cross section and the spiral guide channel in the direction in which the laser gas flows. The features mentioned prevent unwanted deflection and swirling when the laser gas enters the guide tube and thus create a condition which requires that the laser gas flow be guided over only a short distance for its alignment. 
     In this sense, another variation of the invention makes use of the feature that the inlet for the laser gas in the guide tube is designed as a tubular inlet line and the axis of the inlet line runs in the direction of the section of the spiral guide connected to the inlet line. This avoids unwanted unevenness of flow when the laser gas enters the guide tube which would, if necessary, make it difficult to produce optimized flow ratios in the laser discharge tube downstream from the guide pipe. 
     According to the invention, the spiral-type guide can be designed to be single-threaded. In one preferred embodiment, however, a multi-threaded spiral-type guide is provided. 
     The flow ratios produced can be influenced by the geometry of the spiral-type guide. Structurally very simple embodiments are produced when the spiral-type guide is designed with a constant diameter of the free cross section at the discharge tube of the laser beam and/or with a constant spiral pitch. When the diameter of the free cross section of the spiral-type guide is constant, the guide path takes a spiral course. But, as stated already above, the guide track can, if necessary, also have a spiral shape, and then the diameter of the free cross section of the spiral-type guide can change in the direction of the spiral axis. According to the invention, the spiral pitch can also be chosen so that it changes in the direction of the axis of the spiral. 
     Finally, it is an advantage for the flow ratios in the laser-discharge tube if—as also provided in the invention—the spiral axis of the spiral-type guide runs in the flow direction and preferably coincides with the discharge-tube axis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be explained in greater detail below by reference to the schematic drawings of exemplary embodiments. 
     FIG. 1 is a schematic illustration of a so-called “folded” gas laser assembly embodying the present invention; 
     FIG. 2 is a fragmentary sectional view of the corner area II in FIG. 1 with two guide pipes; 
     FIG. 3 is a cross sectional view along the line III—III in FIG. 2; 
     FIG. 4 is an enlarged longitudinal cross sectional view of one of the guide pipes in FIG. 2; 
     FIG. 5 is an end view of the guide pipe in FIG. 4 in the direction of arrow V in FIG. 4; and 
     FIG. 6 is a schematic illustration of another gas laser assembly embodying the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The gas laser assembly  1  of FIG. 1 includes a square folded laser discharge unit  2  with four laser discharge tubes  3 ,  4 ,  5 ,  6  connected to one another by the corner housings  7 ,  8 ,  9 ,  10 . Electrodes  11  on their outer walls are assigned in pairs and are connected to a high-frequency generator  12 . A laser beam  13  running in the direction of the axes of the laser discharge tubes  3 ,  4 ,  5 ,  6  is shown in dashes in FIG.  1 . Deflection mirrors  14 ,  15 ,  17  in the corner housings  7 ,  8 ,  10  are used to deflect the laser beam  13  by 90°. The laser beam  13  is uncoupled at an uncoupling mirror  18 . A return mirror  19  is adjacent to the uncoupling mirror  18  in the known way. 
     In the center of the folded laser discharge assembly  2  is a radial fan  20  which provides the pressure source for the laser gas. It is driven by a fan motor  21  and connected to the corner housings  7 ,  8 ,  9 ,  10  by feed lines  22 ,  23 ,  24 ,  25  for the laser gas. Suction lines  26 ,  27 ,  28 ,  29  extend between the suction housings  30 ,  31 ,  32 ,  33  and the radial fan  20 . Heat exchangers  34  are provided both in the feed lines  22 ,  23 ,  24 ,  25  and in the suction lines  26 ,  27 ,  28 ,  29 . The direction in which the laser gas flows inside the laser discharge tubes  3 ,  4 ,  5 ,  6  is shown by the arrow  35 . Other arrows symbolize the flow direction of the laser gas in the feed lines  22 ,  23 ,  24 ,  25  and in the suction lines  26 ,  27 ,  28 ,  29 . 
     Starting from the radial fan  20 , laser gas is transported by the feed lines  22 ,  23 ,  24 ,  25  through the respective heat exchanger  34  to the corner housings  7 ,  8 ,  9 ,  10 . There, as can be seen in FIG. 2, the laser gas stream is split into two partial streams, each of which is fed to a guide tube  36  which is an integral part of the respective feed line  22 ,  23 ,  24 ,  25 . In FIG. 3, the respective partial stream of laser gas enters the guide pipe  36  through a tubular tangential inlet line  37 . Each guide pipe  36  is adjacent the laser discharge tube  3 ,  4 ,  5 ,  6  in the direction  35  in which the laser gas flows therethrough. FIG. 2 shows the laser-discharge tubes  5 ,  6  and the associated guide pipes  36  in the corner housing  10 . Guide tubes  36  opposite one and the same laser discharge tube  3 ,  4 ,  5 ,  6  are shown as mirror images in a plane running perpendicular to the plane of the drawing of FIG.  1  and perpendicular to the respective axis of the discharge tube. 
     In FIG. 3, a spiral-type guide  38  for the laser gas is provided on the inside of each guide pipe  36  which is provided by a spiral guide channel  39  on the inner wall of the guide pipe  36  which runs around a free or open central area  40  to the discharge tube of the laser beam  13 . The adjacent sections of the spiral guide channel  39  border a guide channel for laser gas which is open to the open center  40  and has the shape of a spiral thread. The axis  41  of the guide spiral channel  39  coincides with the axis of the laser discharge tube to which it connects and the axis of the laser beam  13 . The axis  42  of the tangential inlet line  37  is inclined to the vertical as seen in FIG.  4  and runs in the direction of the section of the guide spiral channel  39  connecting to the tangential inlet line  37 . The diameter of the guide spiral  39  and thus the spiral-type guide  38  indicates: the open central area  40  extending to the discharge tube of the laser beam  13  is constant in the direction of the axis  41  of the guide spiral channel  39 . The same is true of the pitch of the guide spiral channel  39 , which is shown in FIG. 4 by the angle of pitch α. 
     The stream of laser gas produced by the radial fan  20  is deflected when it enters the guide pipe by the tangential inlet line  37  in the direction of the section of the guide spiral channel  39  attached to it. This in turn leads at least the radially outer part of the stream of laser gas adjacent to the guide pipe  36  into a spiral path in the direction of the laser discharge tube. As a result, the peripheral portion of the stream of laser gas then enters the laser discharge tube with a corresponding spiral direction, and the gas is substantially uniformly distributed about the cross section of the laser discharge tube. Because of the ratios of the streams inside the laser discharge tubes  3 ,  4 ,  5 ,  6 , there is an even distribution of the power of the laser beam over its cross section. 
     Each partial stream of laser gas that enters through a guide tube  36  into the laser discharge tube to which it is connected meets as seen in FIG. 1, inside of the suction housing  30 ,  31 ,  32 ,  33  with the partial stream of laser gas introduced through the guide pipe  36  of the corner housing  7 ,  8 ,  9 ,  10  opposite the same laser discharge tube. The combined partial streams are then directed through the suction lines  26 ,  27 ,  28 ,  29 , and the heat exchanger  34  connected in them to the radial fan  20 . 
     FIG. 6 shows a gas laser assembly  101  which, instead of the folded laser discharge assembly loading unit  2  in FIG. 1, includes a straight-line discharge assembly  102  with a single laser discharge tube  103 . Inside the laser discharge tube  103  runs a laser beam  113  which is uncoupled by an uncoupling mirror  118 . Opposite the uncoupling mirror  118  is a return mirror  119 . The voltage needed is applied to electrodes  111  on the outer wall of the laser discharge tube  103  by means of a high frequency generator  112 . 
     A pressure source for laser gas in the form of a radial fan  120  feeds laser gas through feed lines  122 ,  123  to the inside of the laser discharge tube  103  and sucks heated laser gas out of it through a suction line  126 . The direction in which the laser gas flows inside the laser discharge tube  103  is symbolized by the arrow  135 . A heat exchanger  134  is connected in the feed lines  122 ,  123  and in the suction line. The streams of laser gas that enter the laser discharge tube  103  are aligned properly in the manner described in FIGS. 1 to  5  using corresponding guide tubes  136  with spiral-type guide channels for the laser gas. 
     The spiral-type guide for laser gas can also be formed by inserting a spiral element in the form of a screw, spring or a cold spiral and/or bounded by a perforated tube against the open cross section to the discharge tube for the laser beam. 
     The passage of a outer portion of the laser gas through the channel of the spiral guide ensures good distribution of the gas about the periphery as it enters the laser discharge tube. Although this portion of the gas has a spiral component of motion as it enters the laser discharge tube, it does not produce unwanted turbulence as the gas flows though the tube. 
     By improving the uniformity of the laser gas distribution and flow though the cross section of the laser discharge tube, the profile of the laser beam intensity is significantly improved.