Gas laser with at least one excitation tube wherethrough gas is actually flowing

An axial flow gas transport laser comprising an excitation tube through which gas flows along an axis of the tube, an inlet arrangement to feed gas towards the excitation tube and an outlet arrangement to discharge gas from the excitation tube. At least one of the inlet and outlet arrangements comprises a circumferential opening arrangement evenly distributed along the periphery of the excitation tube, substantially in a cross-section plane of the tube. A gas flow channel arrangement to the opening arrangement is directed at least substantially in the direction of the excitation tube axis and into the excitation tube at the opening arrangement for preventing wide-areal turbulances of the gas flowing in the excitation tube.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention is directed to a gas laser with at least one 
excitation tube wherethrough gas is axially flowing said laser comprising 
an electrode arrangement for electrical excitation of the gas within said 
tube and with at least one gas inlet and one outlet arrangement with 
respect to said excitation tube. 
It is known that one serious problem of axial gas laser is the occurrence 
of wide-areal gas turbulances within the excitation tube which occurrence 
should be prevented. The above expression "wide-areal" which will be used 
further in this description shall be defined as follows: 
Turbulances within a tube or a pipe are said "wide-areal" if the turbulance 
pattern seen in cross-sectional view has one turbulance center over the 
entire cross-sectional area of the tube. If turbulances occur with more 
than one center disposed within the tube's or pipe's cross-sectional areas 
they are said to be "small areal". 
The characteristics of turbulance along the excitation tube are highly 
influenced by the characteristics of a gas inlet zone and/or of a gas 
outlet zone for the gas with respect to the excitation tube and are mostly 
severely disturbed by these latter zones because in these zones a radial 
incoming gas flow must be directed in more axial direction at the inlet 
zone and a gas stream from more axial direction must be directed in more 
radial direction at the outlet zone which features may directly or by 
reaction cause said unwanted wide-areal turbulances throughout the 
excitation tube. 
It is an object of the present invention to prevent at a gas laser of the 
kind mentioned above occurrence of such wide areal turbulances and 
especially to prevent said inlet and outlet zones to generate such 
turbulances. To fulfill this target inlet and/or outlet arrangements of 
the gas laser comprise inlet and/or outlet means for said gas which are 
distributed around the circumference of the excitation stage tube said 
means steadily leading said gas from more radial into a more axial 
direction with respect to said tube for inlet and/or from a more axial 
direction into a more radial direction for outlet. 
By these inventive features a uniform distribution of gas streaming into 
the tube or streaming out of the tube is reached and the steady changement 
of gas flow direction prevents occurrence of the harmful wide-areal 
turbulances within the excitation tube. These inventive features and 
others which may further improve will become obvious from the following 
figures and the accompanying description. Specific examples of the 
invention are thus described by way of the following Figures.

FIG. 1 in principle shows the arrangement of a known high power gas laser. 
The laser shown is a two-stage laser with a first stage left-hand of the 
dotted line and a second stage right-hand thereof. As the laser 
arrangement is symmetrically built with respect to that dotted line only 
the stage left-hand of that line will be described. The arrangement 
comprises an excitation stage tube 1 at one end of which a cathode 3 and 
on the other end of which an anode 5 being provided. At one end of the 
excitation stage tube 1 an inlet pipe 9 discharges into an inlet zone 7 
and at the other end a discharge pipe 11 departs from an outlet zone 13 of 
the excitation stage tube 1. With the help of a blower 15 provided with an 
input and output side heat exchanger 17 and 19 a gas mixture as of 
carbonic acid, nitrogen and hydrogen is driven through the excitation 
stage tube 1 in the direction shown by the arrow. The central axis A of 
the both side opened excitation stage tube is the optical axis of the 
laser beam. As is further shown the electrodes 3 and 5 are fed by means of 
a high tension source 21, a control arrangement for instance in the form 
of a high voltage tube 23 whereby the tube 23 and a current regulation 25 
controlling the tube give the possibility to adjust the electrode current. 
The present invention is directed among others on measures at the inlet 
zone 7 and/or the outlet zone 13, additionally to features for the cathode 
and/or anode, all of these measures aerodynamically and/or electrically 
preventing the occurrence of wide areal turbulances within the excitation 
stage tube 1 and favouring a good mixture of the gas therein. 
By the help of the FIG. 2 to 16 measures which prevent wide areal 
turbulances within the excitation stage tube are described. 
Thereby the most important features, considered as primarly inventive, are 
shown and described in FIG. 5a to 6 and 8 to 12. 
In FIGS. 2 to 4 there are shown respective parts of a gasfeed pipe or inlet 
pipe 9 which may be used together with the inventive inlet arrangement of 
FIG. 5 to 6. In vicinity of the inlet zone 7, as shown in FIG. 2a, there 
is provided within the inlet pipe 9 one or more than one grids 28, 
preferably as shown, deposited in cross-sectional planes. By this 
provision there are generated small areal turbulances within pipe 9 as 
schematically shown in FIG. 2b. Wide areal turbulances, as also shown in 
FIG. 2b, are substantially prevented from occuring and propagating into 
the excitation tube 1. In FIG. 3a the grid 28 is replaced by multitude of 
walls 30 within the inlet pipe 9 which latter subdivides the flow 
cross-section. 
As shown in FIG. 3b these walls 30 are preferably arranged to form a honey 
comb pattern 32. The arrangement of such walls too results in the above 
effect with respect to occurrence of small and prevention of wide areal 
turbulances. 
FIG. 4 shows a further kind of measure for the same target. Here the inlet 
pipe 9 is provided with steady cross-sectional narrowing 34, said 
narrowing being realized by a steady convergence, then a steady divergence 
of the wall in gas flow direction. This measure too provides the above 
mentioned turbulance characteristics. The measures described by FIGS. 2 to 
4 may be, if necessary, provided each separately or may be combined with 
each other in combination with the inlet arrangement shown and described 
later with the help of FIGS. 5 and 6. 
Primarily the generation of wide areal turbulances with respect to the 
cross-sectional area of the excitation tube is prevented by measures which 
will now be described with the help of FIGS. 5 and 6. In FIG. 5a the 
technique to solve this problem is generally shown. Along the 
circumference of the excitation stage tube 1 gas inlet openings 42 are 
provided either continuously or and as shown in the FIG. 5a and 5b 
discontinuosly distributed which latter are fed via a set of inlet pipes 
9a and which direct the stream of gas steadily from a more radial into a 
more axial direction, with respect to tube 1, this uniformly along the 
tube's periphery. 
As shown in FIG. 5b the direction of the flow channels in the pipes 9a at 
the inlet openings 42 is so that the gas inlet does at least substantially 
occur in direction of the axis A into the excitation stage tube 1, 
steadily and without encountering any corners where turbulances would be 
generated. 
To further make sure that departing from a common pressure gas feed pipe 
for inlet openings 42 or inlet pipes 9a all inlet openings 42 provided are 
fed equally, all these inlet pipes 9a are led to one common equalizing 
chamber 44, as schematically shown in FIG. 5a, which latter, on its turn, 
is fed by one gas inlet tube 46. By this technique a uniform substantially 
axial directed gas inlet flow along the circumference of the excitation 
stage tube 1 is realized. The features of FIGS. 2 to 4 can be, if 
necessary, incorporated in the inlet pipes 9a. 
FIG. 6 shows a preferred embodiment of the inlet arrangement. The 
excitation stage tube 1 is provided at its inlet side with an enlargement 
48 of its wall. Together with continuation part 50 of the excitation stage 
tube 1 which has the same inner diameter as the tube itself at its inlet 
zone there is realized an equalizing chamber 44a as an annular chamber 
around the axis A into which there is led at least one inlet feed pipe 9. 
The outlet from the annular equalizing chamber 44a is between the end of 
the part 50 directed towards the excitation stage tube and the beginning 
of the enlargement 48 whereby there is realized by these two parts 
steadily narrowing annular ring nozzle 52. Thus there is realized optimal 
uniformity of the gas discharge into the tube 1 predominantly in axial 
direction. As shown in that figure there may be provided alternatively or 
additively on the inner side of the part 50 and on its outer side i.e. 
directed towards the annular equalizing chamber 44a along the tube 
circumference, annular electrodes 54 and 54a. The further possibility to 
use the wall of the tube part 50 directly as an electrode is not shown 
within the Figures. The electrode in principle of annular form may be made 
as will be described below from independent electrode sectors deposited 
along the circumference which are electrically isolated from each other. 
Preferably these distinct, spacial electrode sectors or uninterrupted 
electrode rings carry sharp corners directed towards the excitation stage 
tube 1 as shown at 56 to generate locally very high field strength. 
The FIGS. 7a to 7c show measures which may be introduced if necessary to 
further improve turbulance behaviour and which are provided at the 
excitation stage tube itself. 
It is known that the tendency that single and thus wide areal turbulances 
occur over the flow cross-section of a tube is the higher the more the 
tube cross-section is exactly circular. As it is a target of all measures 
proposed to prevent that occurrence the flow cross-section of the 
excitation stage tube 1 departs according to FIGS. 7a to 7c from the 
circular form and shows for instance a triangular, four-angular, 
poly-angular or elliptical shape. The occurrence of symmetrical but small 
areal turbulances are shown in the FIG. 7. These turbulances favour a good 
mixture of the gas which flows axially through the excitation stage tube 
1. 
The FIGS. 8 to 12 show important measures and respective at the outlet zone 
13 of the excitation stage tube 1. To make sure that the gas outlet does 
not act backwards into the excitation stage tube as concerns the 
occurrence of wide areal turbulances there is inventively provided as 
shown in FIG. 8 at the outlet zone 13, in analogy to the measures proposed 
at the inlet zone according to FIG. 5b, an outlet arrangement which is 
shown in FIG. 8 with openings 58 discontinusly arranged along the 
circumference of the excitation stage tube 1 or continuously formed as 
shown in FIG. 9. They steadily lead the outlet gas from a more axial 
direction into a more radial direction with respect to the tube 1. 
According to FIG. 8 outlet openings 58 are distributed along the 
circumference of the tube 1 which all are provided with steady bent outlet 
pipes 11a which latter communicate (not shown) with a collecting chamber. 
According to FIG. 9 there is provided at the outlet zone a steadily 
continously widening annular outlet slot 60 around the circumference of 
tube 1 this ring slot being realized by enlarging the tube 1 and 
introducing at the side opposite to the tube 1 a tube sector 64 into said 
enlargement 62 so that there is formed a collecting annular chamber 66 
around axis A and the annular outlet slot 60. The collecting chamber 66 
communicates with the outlet pipe 11. Here too there is proposed to 
arrange in the region of the outlet slot 60 an electrode as a cathode 68 
e.g. a ring cathode with unsteady contours 70 and with a coresponding 
electrical tap 72. 
The kind of realization according to FIG. 10 shows again an annular chamber 
66 formed by enlarging the diameter of the tube whereby a multitude of 
ring lamellas 74 provide for several ring outlet slots 60a, 60b . . . one 
behind the other which provide for steady changement of gas flow 
direction. Here too the ring lamellas may be additionally used as 
electrodes as a cathode and are then provided with electric taps 72. 
FIG. 11 schematically shows the construction of the outlet zone 13 in 
analogy to the construction shown in FIG. 10 but for a two stage laser as 
shown in FIG. 1. 
FIG. 12 shows an arrangement which is in principle analoguous to that shown 
in FIG. 11 i.e. provided for a two-stage laser. Instead of continuous 
annular lamellas one or several bucket rings 76 are provided. To favour 
the gas to discharge into the outlet pipe 11 especially the realization 
forms of the FIGS. 10 to 12 and as shown in FIG. 12 can be provided with 
an additional high pressure gas pipe 78 ending within the collecting 
chamber 66 and preferably having a mouth which is arranged coaxially to 
the mouth of the pipe 11. Through this high pressure gas pipe 78 a gas 
beam G2 is blown through the chamber 66 and favours in the sense of 
vectorial addition of the gas beam impacts the exhaust of the gases G 
coming from the excitation stage tube 1. 
The FIGS. 13 and 14 show an electrode arrangement of a cathode and/or anode 
which has the target to realize desired turbulance characteristics 
eventually in combination with one or several of the measures described up 
to now, now on an electrical way. For this purpose the anode 80 and/or the 
cathode 82 are in principle formed as ring electrodes. The ring is as 
especially shown in FIG. 13 not continuously used as an electrode but 
presents axially directed single electrode dips 84, isolated from each 
other. 
These electrode dips 84 are mounted so as to be electrically isolated from 
each other and are each provided with an electric contact 86. As shown in 
the Figure the electrode dips 84 of the anode 80 are connected to 
connections 86a O those of the cathode 82 to connections 86k which are 
each accordingly led to inputs of a control unit 88. The control unit 88 
is fed with a clock signal from a generator 90 and from a high tension 
source 38. The unit 88 acts as a multiplexer unit with multiplexer 
switches S.sub.a and S.sub.k which switch simultaneously a preselectable 
one or more than one of the anode electrode dips 84 and one or more than 
one of the cathode electrode dips 82 on to the high tension source 38. If 
for instance on the anode and on the cathode side there is switched 
simultaneously one electrode dip each the field pattern along the 
excitation stage 1 will be governed by the circulating angular position of 
these dips simultaneously connected to the voltage source with respect to 
the axis A. As shown there can be realized an electrical eddy field 
pattern with the help of which the gas turbulance within the excitation 
stage tube may be influenced. 
The FIGS. 15 and 16 show further electrode arrangements for anode and/or 
cathode application to further fulfill the object mentioned above as 
concerns the occurrence of turbulances within the excitation stage tube if 
necessary. Between the excitation stage tube 1 and its continuation part 
1a for the laser beam along axis A the electrode is, as shown in. FIG. 15, 
mounted as a cylindrical electrode 92. The cylinder electrode is so 
dimensioned that it forms substantially no stop with respect to the inner 
wall of the tube 1 and 1a respectively. The electrode rests for instance 
with circular collars 94 against the tube 1 and 1a. If following the 
excitation stage tube 1 the cross-sectional dimension of a continuation 
tube 1a has to be changed with respect to the cross-sectional area of the 
excitation stage tube 1 then the electrode is made in a divergent shape as 
shown in FIG. 16 for the electrode 96, whereby the inner walls of the tube 
1 and 1a are again linked substantially without any stops and, radially, 
without any groove which is realized with a thin interior collar 94i.