GB2163896A

GB2163896A - Transverse flow CO2 laser

Info

Publication number: GB2163896A
Application number: GB08518622A
Authority: GB
Inventors: Hans Klingel
Original assignee: Trumpf SE and Co KG
Current assignee: Trumpf SE and Co KG
Priority date: 1984-08-03
Filing date: 1985-07-23
Publication date: 1986-03-05
Also published as: FR2568729B1; GB8518622D0; IT8560424V0; JPH0624270B2; IT209153Z2; DE3428653C2; JPS6143489A; GB2163896B; DE3428653A1; FR2568729A1

Abstract

A transverse flow CO2 laser with at least several hundred watts output, with a transverse flow duct 17 in which is disposed the discharge path for the laser beam, with mirror means for the laser beam in the end zone of the transverse flow duct and with two high frequency electrodes 13, 18 extending longitudinally of the transverse flow duct, has at least two parallel circular thin-walled tubes 11, 16 of dielectric material the outer surfaces of which form the duct faces and which contain the electrodes 13, 18. <IMAGE>

Description

SPECIFICATION Transverse flow COp laser The invention relates to a device according to the preamble to the Main Claim.

Such lasers are included in the molecular lasers.

They operate almost always continuously. Despite the fact that CO2 gave them their name, other substances such as for example N2 are represented in substantially higher percentages. The gas mixture can for example consist of 10% CO2, 20% N2 and 70%.

At around 15%, the efficiency of the CO2 laser is high in relation to other lasers. Its wave length is around 10.6 micrometers and lies thus in an atmospheric "window". As a result, it can also be guided over considerable distances in tha atmosphere with minimal damping. If it is desired to use the laser beam to cut through relatively thick metal plate, then with the current state of the art, cutting must be carried out in an oxygen atmosphere because those lasers which currently have to be sold in industrial production only give off energy continuously in a kilowatt range.

The molecule mixture used with CO2 lasers is used up at the laser and will be exhausted all the more quickly the greater the power which the laser has to produce.

In the case of longitudinal flow lasers- even if they are designed for high-speed longitudinal flow, the molecules remain in the discharge path for a relatively long time.

Transverse flow CO2 lasers have then the advantage that the molecules remain in the discharge path for only a very short time so that it is possible to achieve higher laser outputs.

However, transverse flow CO2 lasers are so expen size that it is difficult to sell machines which are equipped with them. If the price were tolerable, then this principle of laser beam generation could be installed in the substantially wider field which it merits.

CO2 lasers are too expensive because they employ complicated components which have been produced especially for the laser and which are not commercially available. Furthermore, curently used CO2 lasers make it impossible to adapt the principle to various levels of output. For example, with repeated use of the same inexpensive principle, it is not possible to increase the output as one does for example in the case of explosion engines, where the energy-generating unit is virtually always the same, the output being increased by multiplying the unit.

The object of the invention therefore is to indicate a structural principle in which it is possible to have recourse to simple component parts which on the one hand define the transverse flow duct while being on the other easily interchangeable and, thirdly, provide space for the high frequency electrodes and which finally can be used several times in the laser with the same structural philosophy.

According to the invention, this problem is resolved by the characterising features of the Main Claim.

Such tubes as are mentioned in the characterising part of the Main Claim are standard items in laboratory engineering in the chemicals industry, as raw material for applied arts, for low voltage lamps, for high voltage lamps, in the electronics industry in the form of ceramic components as carriers for resistor linings, capacitor linings or the like. By reason of their curved form, the tubes restrict the molecular mixture at a specific point as a jet does. At the same time, though, the tubes protect the high frequency electrodes which are of course made from metal and which are not so resistant to the temperatures which occur, to the discharge processes and to other stresses as dielectric material regularly is. One is free to give the high frequency electrodes the desired shape since they are only involved in creating the discharge and do not influence the flow.

Tubes are available inexpensively in highprecision production with any wall thickness and in a vast range of cross sectional forms, drawn or sintered.

The circularly-cylindrical form provides a very clear inflow behaviour and outflow behaviour. At assembly, too, any position of the tubes is correct because they are of course circularly cylindrical.

The features according to Claim 2 provide tubes which are adequately flexurally resistant, which insulate the high frequency electrodes, which are insensitive to heat and of which the behaviour in heat is predictable.

By reason of the features according to Claim 3, a material is obtained which of itself has a very smooth surface and which therefore offers a very low resistance to flow even if it receives no further polishing orthe like. Rods can be checked from outside for instance to determine the location of the electrodes and during assembly it is easier to look into the cavity.

The features of Claim 4 provide tubes which do not melt, in contrast for example to Pyrex (RTM) or Duran (RTM) glass.

By reason of the features according to Claim 5, there is no need to handle the tubes in order to fit the high frequency electrodes, which would for instance be possible by a vaporizing technique, galvanic treatment or the like. If the tube is damaged, for example cracked, then the high frequency electrode may still be intact and suitable for further use.

By reason of the features of Claim 7, the pattern of the electro-magnetic field can be adapted to the flow restriction of the molecular mixture and thus particu larlyfavourable discharge paths may be obtained.

As a result of the features of Claim 8, the electrodes are always at the same distance from the duct surfaces.

When the molecular mixture is blown into the transverse flow duct, then the discharge path is blown in an undesired manner downstream of the duct centre.

However, by reason of the features of Claim 9, it is possible to locate the discharge path more upstream, where it is wanted.

The features accordirg to Claim 10 make it possible so to dispose the tubes as is most suitable from the point of view of flow, while the high frequency electrodes largely determine the location of the discharge path.

By virtue of the features according to Claim 11, the location of the discharge path can be determined.

With a high-speed molecular mixture for example the high frequency electrodes can be moved against the direction of flow so that the discharge path stays where it is.

By reason of the features according to Claim 12, it is possible also to move the high frequency electrode by rotating the tube. This may be of advantage for instance if the tube is long. Of course, the tubes should be constructed to be very flexurally resistant.

High frequency electrodes on the other hand are sometimes of strip copper plate and have little inherent resistance of their own. By reason of the features according to Claim 12, the tube can also support such high frequency electrodes. The whole assembly can then be produced and sold by the metre.

By virtue of the features according to Claim 13, it is possible easily to have two discharge paths with good flow properties so that a double-fold laser is created.

The features according to Claim 14 make it possible to contribute to various power ratings of such lasers. If the transverse flow duct is widerthen more laser-usable molecular mixture is supplied and the output can be greater while the high frequency electrodes are supplied with a higher level of power.

If they have no apertures in their walls, the tubes can serve at the same time as cooling tubes.

Preferred embodiments of the invention are described by way of example hereinafter and are illustrated in the accompanying drawings, in which: Figure 1 is a diagramatic cross-section through a first embodiment Figure 2 is, compared with Figure 1, an enlarged view of the end showing the pattern of field lines with electrodes constructed as segments of the circle, Figure 3 is a view similar to Figure 2 but with electrodes in a leading position, Figure 4 is a diagramatic view in the direction of the flow duct showing an electrode displacement and current supply.

Figure 5 is an end view of an embodiment with two discharge paths and three tubes, showing the overall arrangement, Figure 6 shows the beam pattern for a device according to Figure 5.

The tube 11 is circularly cylindrical, has an outside diameter of about 100 mm and a wall thickness of approximately 3 mm. It consists of quartz. The tube 11 is 30 toY0 centimetres long. At fits ends, for mounting purposes, it transverses not shown walls ofthe device which extend at a right angle to the longitudinal axis of the tube 11. At the top, the tube 11 is adjacent a supporting wail or baffle 12. Inside and at the bottom of the tube 11 there is a copper strip 13 which serves as a high frequency electrode and which is connected to a high frequency generatop in a manner not shown. The copper strip 13 has the form of a flat channel. Disposed in the tube 11 are electrically non-conductive spacers 14 of stellate form which keep the copper strip 13 in position.The copper strip 13 extends substantially over 60 degrees of the circumference.

Under the tube 11 is an identical second tube 16.

Between the two tubes 16 there is thus a transverse flow duct 17 through which the molecular mixture is forced at a pressure of 50 - 200 hectopascals. The width of the transverse flow duct 17 is 10 - 50 mm at its narrowest point. Its configuration is defined by the circular peripheral form of the tubes 11 and 16.

Provided at the top in the tube 16 is a copper strip 18 which is constructed in the same way as the copper strip 13 and it serves as the other high frequency electrode. Spacers not shown likewise keep it in place and it is connected to the other pole of the high frequency generator. Shown in Figure 2 are the dielectric field lines 19 which, as is well known, always end at a right angle 21 to the surface of the copper strips 13, 18. As can be seen from Figure 2, this provides an extremely favourable field line pattern which is adapted to the initially diminishing and then later increasing cross-section ofthetrans- verse flow duct 17.

It is assumed in Figure 3 that the molecular mixture is forced into the transverse flow duct 17 in accordance with the arrow 22. Were there no flow influence from the molecular mixture, the discharge volume would be disposed where the cross 23 is shown in the drawing, i.e. in the central plane 24.

Also with regard to mirror geometry, the discharge space is best located in this central plane 24, because where the location of the mirror is concerned, it is easiest on structural grounds to work according to the central plane 24.

However, if the molecular mixture is blown according to the arrow 22, then the discharge volume moves downstream to the circle 26 which is shown in broken lines.

Comparison of Figure 2 with Figure 3 shows that in Figure 3 the copper strips 13, 18 are displaced contrary to the direction of the arrow 22, so that the centre of gravity of the field lines is roughly at the point 27. By virtue of this leading position, it is possible in spite of the flow according to the arrow 22 to have the discharge volume located at the cross 23. Howfarthe copper strips 13,18 have to extend asymetrically rightwards will naturally depend upon the flow veolcity of the molecular mixture in the transverse flow duct 17.

If in the case of self-supporting copper strips an adjustment of the copper strips 13, 18 is desired, then Figure 4 proposes a solution for the tube 11.

Coaxially of the geometrical longitudinal axis 28 there is here at the end of the tube 11 a metal gearwheel 29 which is rotatably mounted. The left hand end ofthe copper strip 13 is mechanically rigidly and electrically couductively mounted on its right side 31. An electrical wiper contact 33 presses against the other side 32 of the gearwheel 29 and is connected to one pole of the high frequency generator. In a mirror opposite location on the right of the copper strip 13 is an identical gearwheel 29 on which is attached that end of the copper strip 13. A shaft 34 extends above the baffle 12 which is not shown here, parallei with the longitudinal axis 28 and can be rotated to left or right by a servomotor not shown here. Rotationally rigid on the shaft 34 is an electrically insulating gearwheel 36 which engages with the gearwheel 29.A gearwheel identical to the gearwheel 36 is provided over on the right and meshes with the gearwheel 29. The transmission ratio is small so that the copper strip 13 can be accurately adjusted in its position.

Provided for the tube 16 is an identical adjusting means which must however not be electrically applied to the same potential. It is possible with such a device to bring the copper strips 13, 18 for instance out of the position shown in Figure 2 and into that shown in Figure 3.

If the tubes 11, 16 are so long that the copper strips 13, 18 are flexible and spacers are required, then the tube 11 is rotationally rigidly connected to the gearwheel 29 so that the tube 11 rotates together with the copper strip 13. It is necessary then to ensure that those gaskets 37 which seal the periphery of the tube 11 in respect of the side wall 38 permit a rotation without losing any sealing tightness.

Naturally this also applies to the other end and in respect of the tube 11 and to both ends where the tube 16 is concerned.

In the case of the embodiment shown in Figure 5, three tubes 39,41,42 are provided all of which are located in the central plane 24. In this way, two transverse flow ducts 43, 44 are formed which produce two discharge paths. Provided in the tube 41 are two copper strips 46, 47 which are at equal potential and which are disposed at 12.00 o'clock and at 6.00 o'clock. They are connected to one pole of the high frequency generator, not shown. Like the tube 11, the tube 39 has, at around 6.00 o' clock, a copper strip 48 while the tube 42 like the tube 16 has a copper strip 49 at 12.00 o' clock.

The entire device is disposed in a cylinder 51 which is tight in relation to electro-magnetic rays.

Provided at the bottom is an assembly 52 which according to the arrow 22 circulates the molecular mixture and at the same time cools it. The outer defining wall which restricts the molecular mixture is constituted by an inner cylinder 53 disposed eccentrically in relation to the cylinder 51. It has at 12.00 o' clock a cut-out into which the bottom zone of the tube 39 is fitted. The inner boundary to the current of molecular mixture is a smaller inner cylinder 54 which is displaced still farther downwardly in an eccentric fashion, a recess being provided at 12.00 o' clock into which is fitted the top part of the tube 42. Furthermore, there is a guide member 56 having substantially circular outer faces and formed like one fifth of the moon, within which is located the tube 41 as shown in Figure 5, the tube 41 having its upper and lower portions protruding from this guide member 61. The guide member 56 is provided in the upper half space between the inner cylinder 53 and the inner cylinder 54.

In the case of the last embodiment shown in Figure 6, four tubes 57, 58, 59, 61 are provided so that three transverse flow ducts are formed which lead to two laser beam paths 62, 63. Here, therefore, a double-folded laser is provided. It goes without saying that the tubes 57,58,59 are likewise provided with the necessary electrodes. The resultant beam pattern can be seen in Figure 6. Here a 1800 mirror 67 is required which can easily be accommodated in the mirror head by virtue of the location of the laser beam paths. Shown on the left is an end mirror 69 and a neutralizing mirror 71.

Claims

1. Transverse flow CO2 laser having at least several hundred watts output, with a transverse flow duct in which is disposed the discharge path for the laser beam, with duct surfaces defining the transverse flow duct, with mirror means for the laser beam, in the end zone of the transverse flow duct and with two high frequency electrodes extending longitudinally of the transverse flow duct, characterised by the following features a) There are provided at least two circularly cylindrical tubes of dielectric material which are situated opposite and parallel with each other and the outer surfaces of which constitute the duct faces and which are of thin-walled construction b) The high frequency electrodes are located in the tubes.

2. Device according to Claim 1, characterised in that the material is ceramic.

3. Device according to Claim 1, characterised in that the material is inorganic glass.

4. Device according to Claim 3, characterised in that the glass is quartz glass.

5. Device according to Claim 1, characterised in that the high frequency electrodes are components separate from the tubes.

6. Device according to Claim 1, characterised in that the high frequency electrodes are in one piece with the tubes.

7. Device according to Claim 1, characterised in that the high frequency electrodes extend convexly and are provided close to the duct faces.

8. Device according to Claim 7, characterised in that the high frequency electrodes extend in a circularly cylindrical manner.

9. Device according to Claim 1, characterised in that viewed in the direction of flow of gas the high frequency electrodes have a greater area before than after the centre of the duct.

10. Device according to Claim 1, characterised in that the high frequency electrodes are stationary in relation to the transverse flow duct.

11. Device according to Claim 1, characterised in that the high frequency electrodes are displaceable in relation to the transverse flow duct.

12. Device according to one or more of the Claims, characterised in that the high frequency electrodes are rotationally rigidly connected to the tube and in that the rod is rotatable about its axis of rotation.

13. Device according to Claim 1, characterised in that at least three tubes are provided which define two transverse flow ducts between them and in that the middle tube(s) in each case have two high frequency electrodes directed towards the other tubes and in that mirror means are provided to fold the laser beam.

14. Device according to Claim 1, characterised in that the height of the transverse flow duct is variable.

15. Transverse flow C02 laser as claimed in Claim 1, substantially as herein described with reference to and as illustrated by any one of the examples shown in the accompanying drawings.