GB2182483A

GB2182483A - Gas laser apparatus

Info

Publication number: GB2182483A
Application number: GB08526988A
Authority: GB
Inventors: Jill Courtney; David Ian Wheatley
Original assignee: Ferranti PLC
Current assignee: Ferranti International PLC
Priority date: 1985-11-01
Filing date: 1985-11-01
Publication date: 1987-05-13
Also published as: GB8526988D0; JPS62165382A; IT1199284B; DE3637376A1; IT8648603A0; FR2589639A1

Abstract

A gas laser comprises a plurality of gas discharge tubes (3, 4, 5, 6) arranged to form a folded optical cavity. Each discharge tube has at least two gas flow ports associated with it so that a gaseous active medium may flow through the discharge tube. A supporting structure is provided to support the discharge tubes and has at least one hollow support member (1, 2) connected to a gas flow port of each discharge tube. A heat exchanger (15) is provided to remove heat from the gas leaving the discharge tubes, and a pump (14) circulates the gas around a number of parallel paths each including a gas discharge tube, the hollow support members (1, 2) and the heat exchanger (15). A pair of electrodes (7, 8) is associated with each discharge tube for the production of an electric discharge in the gas flowing through the tube. <IMAGE>

Description

SPECIFICATION Gas laser apparatus This invention relates to gas laser apparatus of the type known as fast axial flow lasers.

These are gas lasers in which heat resulting from the laser action is removed by circulation of the gas without the need to cool the laser discharge tube itself. Fast axial flow lasers are often multi-fold lasers, that is the optical cavity of the laser is folded into a number of sections each comprising one or more gas discharge tubes. It is therefore necessary to provide not only mechanical support for the gas discharge tubes but also arrangements for passing gas into and out of the gas discharge tubes. If the laser has a high power output then it is not possible simply to circulate the gas through each discharge tube in succession, and therefore a number of parallel gas circulation paths exist. This all helps to complicate the structure of the laser and hence increase its cost.

It is an object of the present invention to provide gas laser apparatus of the type referred to above having a relatively simple construction.

According to the present invention there is provided gas laser apparatus which includes a plurality of gas discharge tubes arranged to form a folded optical cavity, each discharge tube having at least two gas flow ports associated therewith through which a gaseous laser active medium may flow into and out of the tube, a supporting structure arranged to support the plurality of gas discharge tubes and having at least one hollow support member connected to one gas flow port of each gas discharge tube, a heat exchanger operable to remove heat from the gas flowing out of each gas discharge tube, pump means for causing the gas to circulate around a number of parallel paths each including at least part of a gas discharge tube, the said hollow support member and the said heat exchanger, and a pair of electrodes associated with each gas discharge tube for the production of an electric discharge through the gas flowing therethrough.

The invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram illustrating the main features of a first embodiment of the invention; Figure 2 is a similar diagram of a second embodiment; Figure 3 is a front elevation view showing the main features of a laser incorporating the invention; Figure 4 is a view along-the line IV-IV of Fig. 3; and Figure 5 shows the main gas flow features of the laser of Fig. 3.

Referring now to Fig. 1, this shows two vertical tubular support members 1 and 2 and, supported between them, four gas discharge tubes, 3, 4, 5 and 6. Each of the discharge tubes has an anode electrode 7 towards one end and a cathode electrode 8 towards the other end. Two end mirrors 9 and 10 are supported on the member 1 at one end of each of the gas discharge tubes 3 and 6. An intermediate mirror 11 is supported on the member 1 at one end of each of gas discharge tubes 4 and 5. Support member 2 carries two more intermediate mirrors 12 and 13, mirror 12 being at one end of discharge tubes 3 and 4 and mirror 13 being at one end of discharge tubes 5 and 6. One of the end mirrors, say mirror 10, is made partially transmitting whilst all the other mirrors are fully reflecting.The mirrors are positioned so that a folded optical cavity is produced between the two end mirrors 9 and 10 such that laser action may take place inside the cavity.

A gaseous active medium, such as a mixture of carbon dioxide, helium and nitrogen, is provided and is circulated through the gas discharge tubes 3, 4, 5 and 6 by a circulating pump 14 of a suitable type. Gas from the pump passes into the hollow support member 1 and thence into each of the four discharge tubes. After passing through the discharge tubes the gas enters the other hollow support member and passes through a heat exchanger 15 back to the pump. Some form of gas supply means is necessary, though this is not shown for simplicity. The gas supply may be provided from cylinders of the three gases and is passed into the system through suitable regulating valves. The gas passes from the support member 1 along four parallel paths before reaching the support member 2 and returning to a common circulation path.

Clearly the arrangement which has been described may be modified in a number of ways.

It is possible, for example, to pass gas into the discharge tubes through connections or ports in the centre of each tube, and allow the gas to flow outwards along each tube to the ends, where it flows into both of the support members 1 and 2. Fig. 2 shows such an arrangement, again in schematic form. In this case two separate heat exchangers 15 may be provided, each connected to one of the support members 1 and 2. A single pump 14 may be used as in the case of Fig. 1, or each parallel path may be provided with a separate pump 14. Manifold 16 feeds gas to the centre of each tube and may also act as a further support member.

It is usual to have the gas discharge in each tube extending from anode to cathode in the direction of gas flow. In the embodiment of Fig. 2, therefore, each of the discharge tubes 3, 4, 5, and 6 has two anodes 7 and two cathodes 8, so that two discharge regions are formed in each tube. This increases the maximum output power of the laser.

Figs. 3, 4 and 5 show the main features of a practical form of laser according to the invention. Fig. 3 shows the complete laser, which is a multi-fold laser having five discharge tubes 31, 32, 33; 34 and 35. Each of these is supported on two vertical hollow support members 36-and 37 which are joined by a hollow horizontal member 38 to form a hollow H-shaped structure. This forms the main support for the laser, and rests on a base plate 39.

Each of the laser discharge tubes includes two Tee-pieces 40 which provide exit gas flow ports 41 from the discharge tube into one or other of the support members 36 and 37. On each side of each Tee-piece 30 is a cathode electrode 42, there being four cathode electrodes in each of the discharge tubes 31 to 35.

Each of the laser discharge tubes is also provided with four gas inlet ports 43, which are partly hidden in Fig. 3, and a gas flow connection is attached to each of these ports.

Each gas flow connection contains an anode electrode, positioned off the axis of the discharge tube itself, and not visible in the drawing.

The end of each discharge tube is attached to an assembly 44 which carries the end mirrors 45 and intermediate mirrors 46 which form the folded optical cavity. The upper end mirror 45 forms the output window of the laser. The assemblies 44 are carried on the Hshaped support member by frame members 47, and may be braced by struts or crossmembers (not shown). Also shown in Fig. 4 are various elements of the gas circulation system, namely the circulating Roots blowers 48, gas supply trunks 49 and 50 and manifolds 51. These will be described in more detail later.

Fig. 4 shows an end view of the main features of the laser of Fig. 3. One vertical support member 36 is visible, resting on the base plate 39 and supporting the end assembly 44.

The Roots blower 48 is connected to the support member 36 by trunking 52 and to the delivery trunk 49.

Fig. 5 shows the gas circulation system in greater detail, omitting the discharge tubes and associated features. The gas flow ports 41 in the support members 36 and 37 are shown, as are the Roots blowers 48, deliver trunks 49 and 50 and the manifolds 51. Fig.

5 shows how each of the manifolds 51 is connected to each gas inlet port 43 of the discharge tubes by a gas flow connection 53.

These gas flow connections will probably be flexible hoses.

The complete gas circulation system is therefore as follows:- gas enters each laser discharge tube through four gas inlet ports 43 and flows along the tube to the adjacent Teepiece 40 and gas exit port 41. The gas from each tube flows into the two vertical support members 36 and 37 and from there through the trunk 52 to one or other of the two Roots blowers 48. From the blower gas passes into trunk 49 and through the two pipes 50 to the inlet manifolds 51 and back into the laser discharge tubes.

As has already been mentioned, it is necessary to remove excess heat from the gas as it is circulated. Each of the vertical support members 36 and 37 therefore contains a heat exchanger in the form of an arrangement of pipes carrying water or some other suitable fluid. The heat exchangers, shown in outline at 54 in Fig. 4, extend for most of the length of the support members 36 and 37.

If one blower should fail, or should be shut down for some reason, it is still possible to circulate the gas through the horizontal hollow member 38 which interconnects the two support members 36 and 37.

In operation, therefore, gas is circulated around the path described in detail above, passing through the five gas discharge tubes in parallel. Each discharge tube has four separate discharge regions, between each anode and an adjacent cathode, and the gas flow is always in the direction from anode to cathode.

The laser described above is built around a simple supporting structure which is also used as part of the gas circulation path and houses the heat exchangers in a convenient manner.

Many of the features described may be modified without departing from the invention. For example the construction and arrangement of each discharge tube may be considerably simplified. Similarly, the heat exchangers may be made as separate units outside the support members 36 and 37. Gas pumps other than Roots blowers may be used, though with the rates of gas flow usually required some form of positive-displacement pump is advisable.

The simpler constructions of Figs. 1 and 2 may be used for simpler and lower power lasers.

Claims

1. Gas laser apparatus which includes a plurality of gas discharge tubes arranged to form a folded optical cavity, each discharge tube having at least two gas flow ports associated therewith through which a gaseous laser active medium may flow into and out of the tube, a supporting structure arranged to support the plurality of gas discharge tubes and having at least one hollow support member connected to one gas flow port of each gas discharge tube, a heat exchanger operable to remove heat from the gas flowing out of each gas discharge tube, pump means for causing the gas to circulate around a number of parallel paths each including at least part of a gas discharge tube, the said hollow support member and the said heat exchanger, and a pair of electrodes associated with each gas discharge tube for the production of an electric discharge through the gas flowing therethrough.

2. Laser apparatus as claimed in Claim 1 in which each gas discharge tube comprises a number of gas discharge regions, each region having a gas inlet port, a gas exit port and a pair of electrodes, each gas exit port communicating with a hollow support member.

3. Laser apparatus as claimed in Claim 2 in which two adjacent gas discharge regions of a gas discharge tube share a common gas flow port.

4. Laser apparatus as claimed in any one of Claim 1 to 3 in which the heat exchanger is located inside said hollow support member.

5. Laser apparatus as claimed in any one of Claims 1 to 4 in which the pump means comprises a positive-displacement pump.

6. Laser apparatus as claimed in Claim 5 in which the positive-displacement pump is a Roots blower.

7. Laser apparatus as claimed in any one of the preceding claims in which the pair of electrodes comprise an anode and a cathode, the anode electrode being located in a gas flow port of each gas discharge tube.

8. Gas laser apparatus substantially as herein described with reference to the accompanying drawings.