GB2235570A

GB2235570A - Gas flow cooled laser

Info

Publication number: GB2235570A
Application number: GB9013535A
Authority: GB
Inventors: Michael Auer; Ralf Swysen
Original assignee: Tzn Forschung & Entwicklung; TZN Forschungs- und Entwicklungszentrum Unterluss GmbH
Current assignee: Tzn Forschung & Entwicklung; TZN Forschungs- und Entwicklungszentrum Unterluss GmbH
Priority date: 1989-08-29
Filing date: 1990-06-18
Publication date: 1991-03-06
Also published as: DE3928540A1; GB9013535D0; DE3928540C2; FR2651385A1

Abstract

A gas flow laser has laser resonator tubes 2, 3, a collector 4 directly connected to a precooler 9 and this directly connected to a radial compressor 10, both outlets 11, 12 of radial compressor 10 being connected via gas deflecting parts 13, 14 to coolers 15, 16 which are directly connected to lens mounts 5 (6) (Fig 2), the axes of the coolers 9, 15, 16 being mutually parallel and perpendicular to the laser resonator. The gas guiding parts (except tubes 2, 3) are preferably rectangular cross-section; transitions to the tubes 2, 3 are detailed (Fig 3), flanges (25) in the lens mount system and the ends of tubes 2, 3 being shaped to reduce gas flow resistance (Fig. 4). Additional excitation paths may be included (Fig. 5). <IMAGE>

Description

1 T ITLE Laser The invention relates to a laser.

A laser is known for example from EP 0111045 but when this device is tested in practice it has been found that the output of the laser in relation to the overall volume is comparatively low.

The gas flow laser described in DE 36 43 755 Al, in which, in the main, the axis of the laser tube is perpendicular to that of the radial blower and thus direction taken by the flow of gas in the cooler and the gas inlets, also proved incapable of generating the output theoretically predicted based on the overall volume of the laser.

The article by Dr. B. Stein entitled "Lasertechnik und Lasertechnologie", in Militartechnik 3/89. pp. 149 et seq., also makes known a laser in which coolers are provided both on the inlet and on the outlet of a Roots blower. Owing to the size of this blower the entire laser system is comparatively large with the connection between the coolers and the actual laser being provided by means of long flexible tubes.

Finally, EP 0109025 describes a gas flow laser with - 2 40798/wsy a radial compressor and precoolers together with aftercoolers where the gas flow is taken by suction from the outer ends of the laser tubes and the cooled gas fed into the centre thereof. Apart from the costly arrangement of the coolers this laser suffers from the drawback that the current of gas flows to the mirrors in the laser resonator and these are rapidly contaminated by any particles of foreign matter contained in the gas. The power therefore inevitably decreases during the operation of the laser.

An object of this invention is to provide a laser generally of the kind mentioned wherein with an economical construction with optimum utilisation of space, high efficiency is provided.

According to this invention there is provided a laser device with a laser resonator and gas circulation, gas cooling and gas excitation systems, a compressor provided for the circulation of the gas, the compressor having an inlet and two outlets, a diffuser and gas deflection parts, the laser resonator having at least one laser tube formed from two longitudinal tubes with gas being supplied to the laser tube at an end and removed by suction from a central part by the compressori the diffuser of the compressor being directly connected with the outlets which are followed by coolers, wherein 3 40798/wsy the longitudinal tubes lead, in the central part of laser tube, into a collector with the outlet of the collector directly connected to a precooler which is directly connected with the iplet of the compressor, each outlet of the compressor being connected through gas deflecting parts with the inlets of the cooler of which the outlet is directly connected with a lens mount securing the longitudinal tubes, the axes of all the coolers being parallel and perpendicular to the laser resonator.

Compared with known lasers the output is almost doubled due, in particular, to the fact that both precoolers are used with the connection between these components and the radial compressor on the one hand and the laser tubes on the other being made as short as possible. This is achieved mainly by positioning all the coolers parallel to one another.

A further particular advantage resides in the fact that, with the exception of the tubes of the laser resonator, the further parts carrying a flow of gas have a rectangular cross section. In comparison with tubular components having a circular cross section those with a rectangular cross section offer the advantage that the speed at which the gas flows therethrough decreases to a greater extent. Both the loss of power through the flow 40798/wsy and also the lengths of the cooler for a given required volume are thus reduced.

Further details and advantages of the construction of this invention will be described by reference toembodiments shown as examples in the drawings.

In the drawings:- Figure 1 shows a side view of a laser according to this invention, Figure 2 shows a plan view of the laser shown in Figure 1, Figure 3 shows a front view of the laser shown in Figure 1, Figure 4 shows a section of the laser shown in Figure 1, and Figure 5 shows a plan view of a further embodiment of the laser according to this invention.

Figures 1 to 4 show a laser 1 including a laser resonator which in the example described here consists of two laser tubes o.f which the beam paths are coupled by means of the deflecting mirror 7. Each laser tube is made up of two longitudinal tubes 2 and 3 and 2' and 3' respectively. The longitudinal tubes 2,3 and 2',3', are secured by one end to a collector 4 and by the other end to lens mounts 5 and 6.

On the side of the laser tube consisting of the 1 li 40798/wsy longitudinal tubes 2 and 3 situated opposite the deflecting mirror 7 the laser device according to this invention is equipped with a decoupling mirror 8 through which the laser light passes from the device. On the corresponding side of the laser tube consisting of the longitudinal tubes 2' and 3' a total-reflection mirror 23 is provided.

The collector 4 is directly connected by outlet 40 to a precoolerqwhich said precooler is directly connected with the inlet 100 of a radial compressor 10. The radial compressor is equipped with a diffuser 101 fitted with outlets 11 and 12. These outlets 11 and 12 are in their turn fitted with gas deflecting parts 13 and 14 followed by coolers 15 and 16. Finally, the coolers 15 and 16 are connected to the lens mounts 5 and 6, resulting in two separate gas circuits in the operation of theradial compressor 10.

The excitation of the laser gas is preferably effected by means of highfrequency energy. For this purpose the longitudinal tubes 2,3, and 2',3', are fitted with pairs of electrodes 17,18, and 17',18', respectively for capacitative HF excitation by which the HF energy is coupled into the laser tubes. The pairs of electrodes 18, 18', and 17,17', are connected via lines 19 and 20 with corresponding HF sources 21 and 22 respectively.

- 6 40798/wsy The method of operation of the laser'is now discussed in more detail. The gas heated in the laser tubes by HF excitation is first of all guided to flow through the collector 4 and the cooler 9 to the radial compressor 10. The radial compressor 10 causes the precooled and compressed gas to pass through the outlets 11 and 12 and the gas deflecting parts 13 and 14 into the coolers 15 and 16, where it again enters the laser tubes 2 and 3, 2' and 3-.

Among the important preconditions for a high laser output is a high rate of flow, both as regards mass and volume, of the laser gas mixture. In a practical example the radial compressor 10 used was designed for a pressure ratio (pressure side to suction side) of 1.4 (with a volumetric rate of flow of 2000-2500 m3/h and a mixture ratio of 70/25/5 %(vol) of He/N2/C02. With the gas guided in the manner illustrated in Figure 1 an effort was first of all made to keep the overall flow resistance as low as possible. As is known, an increase in the resistance causes the rate of flow in volume and mass to decrease.

According to this invention steps were taken to ensure that in addition to the use of a precooler 9 the geometrical arrangement of the aftercoolers 15 and 16 was such that their axes were parallel to one another -V 7 40798/wsy and perpendicular to the laser resonator.

It has been found to be of particular advantage if all parts for guiding the flow of gas other than the longitudinal tubes 2,3, and 2.,3', are as far as possible of rectangular cross section. An example of a ratio which has proved satisfactory is 10:1. The adoption of a rectangular cross section, however, necessitates transitions to the longitudinal tubes 2,3, and 2',3'. These transitions are preferably provided in the lens mounts 5 and 6 by giving the collector 4 a suitable shape.

Figure 3 shows how the transitions in the lens mount can be advantageously designed. The decoupling window associated with the laser tube consisting of the longitudinal tubes 2 and 3 is referenced 8, while a total-reflection mirror 23 is secured to the end of the longitudinal tube 2'. The lens mount 6 contains an insert 24 shown in broken lines. As the gas leaving the cooler 15 must enter the longitudinal tubes 2 and 2', the insert 24 is of a double-hump shape, the longitudinal tubes 2 and 2' being situated adjacent the highest point of the hump. The insert 24 is preferably removable and replaceable-and is shaped in such a way that the gas emerging at a low speed from the cooler 15 is guided into the laser tubes with only moderate losses.

- 8 40798/wsy The lens mount system includes flanges 25, which are so shaped that the gas, after being guided in the lens mount 6, flows at an angle of 450 instead of 90o when entering the laser tubes. This reduces the coefficient of resistance and thus the power loss in the flow. The longitudinal tubes 2,3, and 2',3', likewise are with advantage so constructed that the sides situated in the lens mounts 5 and 6 are cut at an angle of 450. The combination with the flanges described effectively reduces the resistance coefficient.

As may be seen from Figure 4, the transition from circular to rectangular cross section in the collector 4 This flange acts as a impact losses of the is provided diffuser and impinging gas by a flange 26 reduces the kinetic flow in the collector 4 1 9 40798/wsy The performance data of the laser described is summarised in the following table:

Overall volume of laser device: Decoupled laser output: Volumetric f low.. Rotation speed of compressor wheel Discharge volume: Number of discharge paths: Type of coupling: Excitation frequency: Maximum power of HF transmitter: Resonator 0. 6 r(A3 2 KW >1800 m3/h. 40,000 rpm. 0.6 x 10-3m3 4. Capacitative 27 MHz 15 kW. U- folded, stable To increase the laser output the device may be provided, for example with four further excitation paths as shown in Figure 5. The collector in this case is marked 4' and the deflecting mirrors 7', 7" and 7---. The item marked 8' is the decoupling window and that marked 23' the total reflecting mirror. The method of operation of this laser corresponds to that of the device described before. Needless to say, the size and shape of the collector 4' and the remaining parts relating to the gas circulation system now have to be adapted to the device consisting of four laser tubes.

1 -

Claims

40798/wsy 1. A laser device with a laser resonator and gas circulation, gas cooling and &as excitation systems, a compressor being provided for the circulation of the gas, the compressor having an inlet and two outlets, a diffuser and gas deflection parts, the laser resonator having at least one laser tube formed from two longitudinal tubes with gas being supplied to the laser tube at an end and removed by suction from a central part by the compressor',the diffuser of the compressor being directly connected with the outlets which are followed by coolers, wherein the longitudinal tubes lead, in the central part of the laser tube, into a collector with the outlet of the collector directly connected to a precooler which is directly connected with the inlet of the compressor, each outlet of the compressor being connected through gas deflecting parts with the inlets of the cooler of which the outlet is directly connected with a lens mount securing the longitudinal tubes, the axes of all the coolers being parallel and perpendicular to the laser resonator.

-1 40798/wsy
2. A laser in accordance with Claim 1, wherein apart from the longitudinal tubes, the components through which gas flows have a rectangular internal cross section.
3. A laser in accordance with Claim 1 or 2, wherein at least four longitudinal tubes form two parallel laser tubes wherein the paths of the rays are coupled together by means of deflecting mirrors.
4. A laser in accordance with any one of Claims 1 to 3, wherein the transitions between the longitudinal tubes and the collector form diffusers.
5. A laser in accordance with any one of Claims 2 to 4, wherein the lens mounts comprise a housing with a removable and replaceable insert, a transition zone from a rectangular to a circular cross section being provided by the said insert.
6. A laser in accordance with any one of Claims 1 to 5, wherein the longitudinal tubes are secured to the lens mounts by flanges, the said flanges being so constructed that the gas, after being guided in the lens mount, enters the longitudinal tubes at an angle of substantially 45o.

- 12 40798/wsy
7. A laser in accordance with Claim 6, wherein the longitudinal tubes are bevelled at an angle of 450 on the sides facing the lens mounts.
8. A laser constructed and arranged to function as described herein and exemplified with reference to the drawings.

Published 1991 atIbe Patent Office. State House. 66/71 High Halborn. London WClR4TP. Further copies May be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwrnfelinfach. Cross Keys, Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.