WO2000021167A1

WO2000021167A1 - Co2-laser comprising carbon monoxide

Info

Publication number: WO2000021167A1
Application number: PCT/NL1999/000613
Authority: WO
Inventors: Iouri Borisovitch Oudalov; Serquei Alexandrovich Starostine; Peter Jacobus Maria Peters; Wilhelmus Jacobus Witteman
Original assignee: Stichting Voor De Technische Wetenschappen
Priority date: 1998-10-05
Filing date: 1999-10-04
Publication date: 2000-04-13
Also published as: EP1119889A1; DE69909113D1; ATE243889T1; DE69909113T2; EP1119889B1; NL1010246C2

Abstract

The present invention relates to a CO2 laser with a gold-comprising catalyst applied substantially over the entire length of the excitation cavity. The CO2 laser contains a gas comprising carbon dioxide and carbon monoxide. According to the invention, the molar ratio of carbon monoxide to carbon dioxide is at least 0.3. This is shown to shorten the starting-up time of the laser.

Description

CO₂-LASER COMPRISING CARBON MONOXIDE

The present invention relates to a C0₂ laser comprising at least two electrodes which, electrically isolated from each other, define a longitudinal excitation cavity, - which C0₂ laser further comprises an RF source for the supply of an alternating voltage over the electrodes, - wherein a gold-comprising catalyst is applied substantially over the entire length of the excitation cavity; and - a carbon dioxide- and carbon monoxide-comprising gas is present in the excitation cavity.

Such a C0₂ laser is known from the US patent publication 4,756,000, and more in particular, it describes an RF-operated laser provided with a gold catalyst. During operation of a C0₂ laser, a part of the carbon dioxide decomposes into carbon monoxide and oxygen. Certain ensuing decomposition products have an adverse effect on the power the laser is able to supply (column l, line 32) . In order to eliminate this adverse effect, the C0₂ laser described is provided with a gold catalyst which promotes the formation of C0₂ from CO and 0₂. In the light of the described insight that CO forms a monolayer on the gold, in this publication a gas mixture comprising a slight excess of CO (column 10 line 13) is preferred for a C0₂ laser. This excess is in particular the excess obtained by providing a catalytic gold surface with CO (activation before use of the laser) . It is said that the addition of CO does not work as rapidly as when using other gas mixtures (column 10, line 10) . It is the object of the present invention to provide an improved RF C0₂ laser having a shorter starting-up time.

To this end the C0₂ laser according to the invention is characterized in that the molar ratio of carbon monoxide to carbon dioxide is at least 0.3 and the surface 00/21167

2 of the gold-comprising portion of the gold-comprising catalyst is at least 10% of the surface facing the excitation cavity of one of the electrodes.

Contrary to the prevailing and in US 4,756,000 expressed opinion, applicant has surprisingly found, that (decomposition products of) CO is useful for a quick start . This means that a C0₂ laser can be used over a larger part of a working day and can thus be operated more economically. At the same time, the relatively high CO concentration ensures that the gold-comprising catalyst does not need to be heated. In addition to C0₂ and CO, a gas mixture for a C0₂ laser may also comprise other gasses known in the art to be used for this purpose, such as He and N₂. In the present application the term "substantially entire length" is understood to be a section that may or may not be interrupted, and an interruption (over the whole width) in the longitudinal direction is at most twice the distance between the electrodes .

According to a preferred embodiment the molar ratio of carbon monoxide to carbon dioxide is at least 0.5, more preferably at least 0.6.

Such molar ratios make it possible to realize shorter starting-up times.

According to an interesting embodiment, an element provided with the gold-comprising catalyst is positioned in the excitation cavity between the electrodes and substantially parallel thereto.

This shortens the average diffusion distance of oxygen and carbon monoxide to the catalyst . The element provided with the gold-comprising catalyst may be an element provided with passing-through openings.

The openings make it possible for the RF source to generate a plasma between the electrodes . The element may, for example, be a perforated plate, a comb-like plate, or a gauze.

According to an interesting embodiment, the gold- comprising catalyst is provided on an electrode. 00/21167

3

This actually creates two excitation cavities which may be in communication via, for example, passing-through openings that may be present in the electrode. In this embodiment, the outer two electrodes are electrically con- nected and together they are connected to the RF source, and possess a common potential with respect to the electrode comprising the catalyst.

In such a case the electrode may also be an electrode which is not provided with passing-through openings. According to a favourable embodiment the electrode provided with catalyst is an earthed electrode.

Such an electrode requires less cooling, which is especially advantageous when cooling an electrode provided with catalyst positioned substantially parallel between two other electrodes in the excitation cavity, since heat dissipation can only occur in the plane of the electrode. The present invention will now be elucidated with reference to the appended drawings, in which

Fig. 1 represents a schematic longitudinal cross section of a C0₂ laser according to the invention;

Fig. 2 represents a transversal cross section of the C0₂ laser according to line II-II shown in Fig. 1; and

Fig. 3 represents a graph in which the normalized power is plotted against the time for the C0₂ laser accor- ding to the invention and a reference C0₂ laser.

The C0₂ laser schematically represented in Fig. 1 comprises a first electrode 2 and a second electrode 3. Both electrodes are made of copper and connected to an RF source 4 (Rohde & Schwartz, VU-315, Germany) as shown in Fig. 2. Both electrodes were provided with a 2 micrometres layer of gold by means of vaporization. The electrodes were kept at a distance from each other by means of dielectric spacers 5, 6, made of ceramic material. In the embodiment described here, the spacers ensure that the electrodes 2, 3 are spaced at a 2 mm distance. The part of each electrode defining the excitation cavity is 37 cm long and the 15 mm wide. The electrodes 2, 3 are connected by means of shunt coils 7, in a manner known in the art. The C0₂ laser further comprises two mirrors 8 and 8' . 00/21167

The electrodes 2, 3 and the dielectric spacers 5, 6 define an excitation cavity 9, containing a C0₂-comprising gas .

The C0₂ laser described above, which is generally known in the art, was operated with various compositions of gas, as shown in Table I.

TABLE I

¹ Amounts of gas expressed as percentages by volume of the total gas composition.

The total gas pressure in each of the cases was 16 kPa. The effect of the gas composition on the starting- up time is shown in Fig. 3. The graph shows clearly that, surprisingly, an considerable excess of CO has a favourable effect on the starting-up time. Instead of obtaining a stable output after more than an hour, this can be realized after only a few minutes. Normalization for each gas composition resulted by dividing the power output by the ultimately realized constant power output.

Claims

1. A C0₂ laser comprising at least two electrodes which, electrically isolated from each other, define a longitudinal excitation cavity,

- which C0₂ laser further comprises an RF source for the supply of an alternating voltage over the electrodes,

- wherein a gold-comprising catalyst is applied substantially over the entire length of the excitation cavity; and a carbon dioxide- and carbon monoxide-comprising gas is present in the excitation cavity, characterized in that the molar ratio of carbon monoxide to carbon dioxide is at least 0.3 and the surface of the gold-comprising portion of the gold-comprising catalyst is at least 10% of the surface facing the excitation cavity of one of the electrodes .

2. A C0₂ laser according to claim 1, characterized in that the molar ratio of carbon monoxide to carbon diox- ide is at least 0.5.

3. A C0₂ laser according to claim 1, characterized in that the molar ratio of carbon monoxide to carbon dioxide is at least 0.6.

4. A C0₂ laser according to one of the preceding claims, characterized in that an element provided with the gold-comprising catalyst is positioned in the excitation cavity between the electrodes and substantially parallel thereto.

5. A C0₂ laser according to claim 4, characterized in that the element provided with the gold-comprising catalyst is an element provided with passing-through openings.

6. A C0₂ laser according to one of the preceding claims, characterized in that the gold-comprising catalyst is provided on an electrode.

7. A C0₂ laser according to claim 6, characterized in that the electrode provided with catalyst is an earthed electrode.