GB2177538A - Electrically activated gas laser - Google Patents

Abstract

An electrically activated gas laser has a closed housing in which the gas chamber contains a catalyst for adjusting and maintaining a chemical gas equilibrium. The catalytic reaction is enhanced by exposing the catalyst surfaces and/or molecules which are not readily deposited to radiation from the laser or from an external source. The flow of gas over the catalyst is regulated, and admixtures which assist the catalytic reaction but do not bring it about are introduced into catalyst surfaces in addition to the catalytically active areas or centres provided for gas regeneration. These measures are especially useful at high laser energy densities and dissociation rates, and when supersaturation of the catalyst surface with unwanted molecules is to be prevented.

Description

SPECIFICATION Process and apparatus for operating an electrically activated gas laser or laser amplifier This invention relates to a method of operating an electrically activated gas laser or laser amplifier and to a gas laser or laser amplifier operable according to this method.

German Offenlegungsschrift No. 31 48 570 discloses a laser having a closed housing, a voltage supply, and a catalyst system for producing and maintaining a chemical gas equilibrium. This prior specification in particular suggests surface and gas specific measures for extremes oftemperature and in dependence upon high gas pressures in orderto ensure a stable laserfunction and hence long service life. If such a laser is to be operated at high energy and power density (i.e.with a high ratio of pumping energy and powerto gas volume) and high gas dissociation, with the added difficulty of higher pulse rates these known measures are no longer sufficient.

Theywould,ifanything,resultin largerapparatus and produce the opposite result; i.e. low energy and power densities and low pulse rates. The disclosure of the above-mentioned prior specification is incorporated in this specification by reference.

It is an object of the present invention to improve the reaction of a catalyst provided in a gas laser of high energy density and to prevent the supersaturation of the catalyst surface with unwanted molecules.

According to a first aspect ofthe invention, there is provided a method of operating an electricallyactiva- ted gas laser or laser amplifier having a closed housing with a voltage supply and with a catalyst system for producing and maintaining a chemical gas equi librium, wherein:- (a) the catalyst surfaces and/or poorly adhering molecules are subjected to radiation, and/or (b) the flow of gays round the catalystsurfaces is regulated or adjusted, and/or (c) apart from the catalytically active areas serving for gas regeneration, admixtures which only supportthe catalytic reaction but do not themselves bring it about are introduced into the catalyst surfaces.In this way it is possible to produce a compact construction which is suitable both for extreme temperatures and temperature fluctuations as regards heat loss and environmental temperature, and is able to achieve high power and energy densities, gas dissociations and pulse repetition rates so that stable electric discharge characteristics are retained with a required average power, degree of efficiency, pulse form, wavelengths and, in the case of pulse lasers, pulse peak power and reproducibility.

A preferred method in accordance of the invention makes use of 02 - specific admixtures, paticularly admixtures which are metals, noble metals or metal oxides, e.g. V205 or 0504. These admixtures may be additionally activated and stabilised by the addition of specific molecules such as hydrocarbons, caesium orthorium. The flow of gas around the catalystsurfaces may be forced to take place of its own accord, and may be adjusted by means of flow channel, porous surfaces, membranes, filters, adsorbent surfaces, or a controllable by-pass.

When there is a high turnover of material, i.e. when the backformation of dissociation products per unit time is high, and possibly, in addition,thetem perature is low and unwanted gas admixtures are present, then the use of the catalysts is limited bythe following characteristics: The products preferentially deposited on a catalyst are the dissociation products and the secondary products, e.g. in CO2 lasers CO, H2, NO or NO2 molecules.

These are in most cases deposited much more rapidly than, for example, the 02 molecules. If the ratio of catalyst surface to dissociation products formed (especially, for example, the CO molecules) is too small, and especially if, in addition,thetemperature is low and gas admixtures (impurities) are present, then a saturation effect occurs or, expressed figuratively, a blockade takes place on the active catalyst surface. The result of this is that the time required forthe reactions proper of CO + Oo CO2, NO2s N+ 02, etc. increases and the catalyst is substantially less effective.

If it is not possible either to increase the active catalyst surface sufficiently (this measure would, however, maketheapparatus lesscompact)ortoraise the temperature, then the concentration of some of the less readily deposited dissociation products, e.g.

of 02,03 or N20, rises steeply and the electric discharge degenerates, e.g. into a spark discharge with an even higher dissociation. At the same time, oxide formation takes place on the internal surfaces ofthe laser due to the increase of 02 concentration. These plasma chemical processes may even be accompanied by changes in the catalyst surfaces, and may result in irreversible destruction ofthe laser gas, ofthe catalyst, ofthe electrodes and of the laser mirror.

To obviate these harmful effects, the catalyst surfaces or only individual molecules, e.g.the 02 molecules, e.g. the 02 molecule, may be activated by radiation so that the process of deposition at the centres of high effectiveness takes place more specifically and much more rapidly. This may be achieved either by direct radiation without shading, or with optical connecting means. The source of radiation may basically be the radiation field ofthe discharge, or of part of the laser radiation, or ofthe secondary action of the laser radiation. In pulse discharges, e.g. of a TE laser, the source of radiation may be the discharge carried out forpreionization of the gas prior to the main discharge. Additionally installed sources of radiation or indirect means for producing radiation, such as flash-lamps, arc discharges, surface discharges, radioactive radiators, glow discharges, photodissociation on surfaces (e.g. metals) orelectroluminescence could conceivably also be used, and the laser specific or additional sources of radiation may, if required, also be provided with auxiliary means for altering and/or selecting the wavelengths.

Such auxiliary means may comprise glasses, fluores- cent means, filters, frequency transforming means such as non-linear crystals, or raman cells, etc. The wavelengths may be optimised particularly in the case ofthe above-mentioned indirect means, by choice of materials (according to the emission spectra ofthe materials).

It has been found that in the absorption spectrum ofthe 2 molecule, wavelengths in the regions around 1200 (120 nm),of 1300-1700 (130tc 170 nm),and 1850 (185 nm) are particularlysuitablefor activation. In the case of a Pt catalyst on ceramics, for example, the region of around 6300 A (630 nm) is also particularly suitable.

These measures can be rendered particularly effective by connecting the catalyst and/or portions of the gas, e.g. in gas conducting channels, with the radiation means, which include the apparatus provided forwavelength alteration or selection and addit ionallyemployed optical means, i.e. by integrating all these components. The form of construction is advantageously a sandwich construction.

If catalyst surface can be enlarged geometrically, i.e. if it can be constructed sufficiently large, then the flow of, for example, CO or O2 overthe catalyst surface, and supersaturation ofthis catalyst surface, can be prevented in a balanced manner either bythis increase in size alone or in combination with the above described activation by radiation. The speed of deposition is influenced, preferably in a controlled manner and to an extent depending on the rate of formation of dissociation products and on thetem- perature, by flow channels and/or additional partly permeable walls (membranes), porous surfaces and/ or filter and/or adsorbent surfaces and/or a by pass(which maybedesignedsoastobecon- trollable).By these means, the deposition of CO molecules, for example, can be slowed down to such an extent relative to that of the 2 molecules thatthe two molecules are deposited in substantiallystoichiometric proportions, i.e. chemically balanced proportions, on the catalyst surface. The sub-division of the gas stream by a by-pass is advisable in lasers which have a passive or active, i.e. spontaneous or forced circulation of gas' and in which suitable adjustment or dimensioning of the flow prevents supersaturation ofthe catalyst.

Taken on its own or in combination with the method of radiation and/orthe"geometrical method" of the type described above, activation of the regions or centres of high catalyst activity can be achieved by supporting measures in accordance with the present invention. To this end, the catalyst is so constructed that, in addition to the catalytically active regions of its surface, which comprise, for example, noble metals on ceramics, and which may, for example, amountto only a few percent ofthetotal surface area, admixtures are introduced which act specifically on the less readily deposited atoms or molecules, e.g. 02 molecules.These admixtures con sist predominantly of (noble) metals or metal oxides such asV2O5 or 0504. These admixtures may also be producedorimprovedintheirfunction bytheaddi- tionofmoleculessuch as,forexample,CsorThto the laser gas. This requires special processes for conditioning, that is to say, processes in which the surfaces are adjusted to particular conditions by chemical pretreatment and stabilised and activated by thermal cycles in combination with the application of a vacuum and certain gas pressures and mixtures.

Hydrocarbons, for example, may be used forthis purpose. The desired catalytic reactions, e.g. CO+ Oo CO2, are promoted by the atomic vicinity ofthe molecules which areto be converted. Due to the activation and deposition (adsorption and possibly chemisorption) of the less readily deposited atoms or molecules, e.g. 02 molecules, an advantageous energy state is created for the subsequent reaction with the CO molecule,i.e. a sort of predissociation (= energy state close to the limit of dissociation) or sterip state (= geometrical position before and during the reaction) from which the catalytic conversion may then proceed directly and considerably more rapidly. Such additionally introduced regions orcentres could, or course, conceivably be produced and activated indirectly by molecules specially deposited forthis purpose. Thus, for example, deposited hydrocarbon molecules could influence the adsorption and reaction ofthe 02 molecule as required.

Claims (28)

1. A method of operating an electrically activated gas laser or laser amplifier having a closed housing with a voltage supply and with a catalyst system for producing and maintaining a chemical gas equilibrium, wherein; a) the catalyst surfaces and/or poorly adhering molecules are subjected to radiation, and/or b) the flow of gas round the catalyst surfaces is regulated or adjusted, and/or c) apart from the catalytically active areas serving for gas regeneration, admixtures which only support the catalytic reaction but do not themselves bring it about are introduced into the catalyst surfaces.

2. A method according to claim 1,whereinO2- specific admixtures are used.

3. A method according to claim 2, wherein the admixtures used are metals, noble metals or metal oxides, e.g. V205 or 0504.

4. A method according to claim 2 or claim 3, wherein the admixtures are additionally activated and stabilised by the addition of specific molecules, e.g. hydrocarbons, caesium orthorium.

5. A method according to any preceding claim, wherein radiation ofthe absorption spectrum ofthe 02 molecules is used, e.g. in the regions of around 1200 of 1300 -1700 , and of around 1850 .

6. A method according to any preceding claim, wherein a platinum catalyst on ceramics is activated with radiation in the region of around 6300 .

7. A method according to any preceding claim, wherein the catalyst surfaces or the atoms or molec uses which are to be reacted are subjected to radiation, either directly or via optical means, by a radiation field ofthe electric discharge, a radiation field of preionization, the radiation of the laser, the secondary radiation resulting from laser radiation, or additionally provided sources of radiation.

8. A method according to any preceding claims, wherein the flow of gas, which is either forced or takes place of its own accord, is controlled by means of flow channels, porous su rfaces, membranes, filters, adsorbent surfaces, or a controllable by-pass.

9. An electrically activated gas laser or laser amplifier having a closed housing with a voltage supply and with a catalyst system for producing and maintaining a chemical gas equilibrium, wherein the catalyst system has a catalyst surface located so that, in operation ofthe laser or laser amplifier, it is subject to radiation.

10. A laser or laseramplifieraccording to claim 9, whereintheclosed housing has a resonator chamber.

11. A laser or laser amplifier according to claim 9 orclaim 10, wherein the catalyst surface is arranged to besubjectto discharge radiation.

12. A laseror laser amplifier according to claim 9 or claim 10, wherein the catalyst surface is arranged to be subject to preionisation radiation.

13. Alaserorlaseramplifieraccordingtoclaim9 or claim 10, wherein the catalyst surface is arranged to be subjectto laser radiation or secondary radiation arising from the laser radiation.

14. A laser or laser amplifier according to claim 9 or claim 10, wherein the catalyst surface is arranged to be subject to radiation from a source outside the laser or laser amplifier.

15. Alaserorlaseramplifieraccording to any of claims9to 14, including optical coupling meansfor directing the said radiation at the catalyst surface.

16. Apparatusforcarrying out a method according to any of claims 1 to 8, the housing ofwhich apparatus is provided with a resonator chamber having a voltage supply and a catalyst, wherein the catalyst surfaces and the atoms or molecules which are to be reacted are either directly arranged, without any shading, in a radiation field of discharge, of pre ionisation, of radiation of the laser, of the secondary action ofthe laser radiation, or additionally provided sources of radiation, ortheyareconnectedtothe said radiation fields or sources of radiation via optical means.

17. Apparatus according to claim 16,whereinthe catalyst and/or gas supply channels are connected to the sources of radiation and additionally used optical means, e.g. in a sandwich formation.

18. Apparatus according to claim 16,wherein the catalyticily active centres or regions and the admixtures which assist catalysis do not, each on their own, cover the entire catalyst surface.

19. Apparatus according to claim 16,whereinthe admixtures assisting the catalytic reaction are 02- specific.

20. Apparatus according to claim 19,whereinthe admixtures consist of metals, noble metals or metal oxides, e.g. V2o5 or 0s04 which, if required, are additionally activated by additions such as hydrocarbons, caesium orthorium.

21. Apparatus according to claim 16, wherein a flashlamp, a spark discharge, a surface discharge, a photodissociation on surfaces, as electroluminescence, a radioactive radiator or a glow discharge is provided as an additional source of radiation.

22. Apparatus according to any of claims 16 to 21, wherein the sources of radiation are equipped with auxiliary means for altering and/orselectingthe wavelengths, e.g. glasses, filters, meansfortransforming the frequency or means for fluorescence.

23. A method operating an electrically activated gas laser or laser amplifier having a closed housing with a voltage supply and with a catalyst system for producing and maintaining a chemical gas equi librium, wherein the catalyst surfaces ofthe catalyst system are subjected to radiation

24. A method operating an electrically activated gas laser or laser amplifier having a closed housing with a voltage supply and with a catalyst system for producing and maintaining a chemical gas equilibrium, wherein molecules loosely adhering to the catalyst surface are subjected to radiation.

25. A method operating an electrically activated gas laser or laser amplifier having a closed housing with a voltage supply and with a catalyst system for producing and maintaining a chemical gas equilibrium, wherein the flow of gas over catalyst surfaces of the catalyst system is controlled.

26. A method operating an electrically activated gas laser or laser amplifier having a closed housing with a voltage supply and with a catalyst system for producing and maintaining a chemical gas equilibrium,wherein admixtures are introduced into the catalyst surfaces ofthe catalyst system except for those parts of the surfaces which are catalytically ac- tive areas serving for gas regeneration, the admixtures being selected as only supporting the catalytic reaction but not themselves bringing it about.

27. A method of operating a laser or laser amplifier, the method being substantially as herein described.

28. A laser or laser amplifier constructed and arranged substantially as herein described.