EP4356489A1

EP4356489A1 - Co2 beam source having a catalyst

Info

Publication number: EP4356489A1
Application number: EP21740429.2A
Authority: EP
Inventors: Jonathan Mueller; Fabian GIUNTA; Morris DAHLINGER; Markus Karl
Original assignee: Trumpf Lasersystems for Semiconductor Manufacturing GmbH
Current assignee: Trumpf Lasersystems For Semiconductormanufacturing Se
Priority date: 2021-06-17
Filing date: 2021-06-17
Publication date: 2024-04-24
Also published as: CN117480693A; KR20240019838A; WO2022262980A1; US20240120700A1

Abstract

The invention relates to a CO2 beam source (1) comprising: at least one discharge tube (3) in which a laser gas is used as a laser medium; a fan (7) for supplying the laser gas into the at least one discharge tube (3) via at least one supply element (8, 9, 9') and for removing the laser gas (4) from the at least one discharge tube (3) via at least one removal element (10, 11) in a closed laser gas circuit; and at least one catalyst (18) for catalysing an oxidation of dissociation products which are created when the laser gas is excited, the at least one catalyst (18) comprising noble metal nanoparticles which are applied to a substrate. The at least one catalyst (18) is arranged inside the closed laser gas circuit so as to be spaced apart from the at least one discharge tube (3) in the flow direction of the laser gas, in order to reduce the deposition of degradation products formed in the at least one discharge tube (3) when the laser gas (4) is excited compared with an arrangement inside the at least one discharge tube (3). A temperature (T₁, T₂) of the at least one catalyst (18) is at least 60°C, preferably at least 100°C, and particularly preferably at least 150°C, when the CO₂ beam source (1) is operated.

Description

C0 ₂ beam source with a catalyst background of the invention

The invention relates to a CO ₂ beam source, comprising: at least one discharge tube, in which a laser gas serves as the laser medium, a blower for feeding the laser gas into the at least one discharge tube via at least one feed element and for discharging the laser gas from the at least one discharge tube via at least a discharge element in a closed laser gas circuit, and at least one catalyst for catalyzing an oxidation of dissociation products that arise when the laser gas is excited, the at least one catalyst comprising noble metal nanoparticles that are applied to a substrate.

For the purposes of this application, a C0 ₂ beam source is understood to mean a C0 ₂ laser or a C0 ₂ laser amplifier. In the latter case, the C0 ₂ laser amplifier typically serves to amplify a seed laser beam emitted by a seed laser. The laser gas of a C0 ₂ beam source is typically a mixture of He, N ₂ and C0 _2. The actual laser medium is the C0 ₂ , the He and N ₂ molecules are of supporting importance. Stimulating a C0 ₂ radiation source is electrical. In the discharge tube, typically a quartz glass tube, the laser gas is excited via a gas discharge at high DC voltage or high-frequency AC voltage. As a result of the excitation, a population inversion occurs. In the case of a C0 ₂ beam source in the form of a C0 ₂ laser, the laser medium is located in the beam path of a mirror arrangement functioning as a laser resonator.

Since the laser gas heats up considerably during operation of the C0 ₂ beam source, but the laser process comes to a standstill at temperatures above 300°C, the laser gas has to be cooled. The removal of the laser gas from the discharge tubes and feeding the laser gas back into the discharge tubes in a closed laser gas circuit allows such cooling via suitable additional devices, for example via heat exchangers.

C0 ₂ beam sources in the form of C0 ₂ laser amplifiers are used in particular for the generation of EUV radiation. The term EUV radiation refers to electromagnetic radiation with a wavelength between 10 nm and 120 nm. Compared to the currently widespread use of wavelengths around 200 nm, the use of EUV radiation for microlithographic production in the semiconductor industry allows the reliable manufacture of components with significant smaller structure sizes and thus leads to a corresponding increase in performance. In the so-called LPP process (“Laser Produced Plasma”), tin droplets are bombarded with laser pulses, which have been amplified in a CO ₂ laser amplifier, to generate the EUV radiation. The bombardment of the tin droplets creates a plasma that emits EUV radiation.

A particular challenge for the construction of C0 ₂ beam sources results from the formation of dissociation products by the gas discharge when exciting the laser gas. These dissociation products, including in particular carbon monoxide (CO), lead to a drop in the power and efficiency of the laser or the laser amplifier. As a countermeasure, the use of catalysts to oxidize the dissociation products, in particular to oxidize CO to CO ₂ , is described in the literature.

From US 4,756,000 a C0 ₂ laser with a closed laser gas circuit, a C0 ₂ laser gas mixture and a gain volume is known. By a Gas discharge in the amplification volume produces CO, oxygen and excited oxygen species. A gold coating serves to catalyze the reaction of the CO with the excited oxygen to form CO _{2 .} The gold coating is placed on a wall of the amplification volume or sufficiently close to the downstream end of the amplification volume to ensure contact with a substantial amount of the excited oxygen. A disadvantage of such an arrangement is that the gas discharge leads to deposition effects of degradation products produced during the excitation of the laser gas in the amplification volume and immediately downstream of the amplification volume, which results in degradation of the catalyst and, as a result, a drop in performance of the CO ₂ laser.

DE 3523926 C2 describes an electrically excited CO ₂ laser with a closed laser gas cycle and a catalyst for producing and maintaining the chemical composition of the laser gas, with an additional radiation source serving to significantly increase the accumulation of molecules formed in the laser gas by dissociation on the catalyst to increase and / or wherein the gas flow around the catalyst surface is regulated so that the attachment of the laser gas formed by dissociation molecules on the catalyst is significantly increased.

In JPS6214486A a C0 ₂ laser is described with a catalyst unit which keeps the composition of the laser gas constant and thus the output power of the laser stable. For this purpose, the catalyst unit is designed as a self-regulating heating unit at the same time, whereby the temperature of the catalyst unit is automatically kept in a range in which the oxidation rate of CO is constant.

US 2015/0222083 A1 describes an EUV system including an optical amplifier system with a catalyst. In one embodiment, the catalyst comprises a substrate having openings and nanoparticles of a noble metal, eg gold, coated on the inner surfaces of the openings. It is stated that the temperature of the gas mixture in the catalyst can rise to up to 60° C. when the catalyst is arranged in an amplifier of the optical amplifier system or in a CO ₂ laser. The oxidation of CO using catalysts based on small gold particles is also discussed in detail in the article "Gold-Catalysed Oxidation of Carbon Monoxide" by GC Bond and DT Thompson, Gold Bull. 33, 41 (2000).

object of the invention

In contrast, it is the object of the invention to provide a CO ₂ beam source which has a high and long-term stable performance and efficiency.

subject of the invention

According to a first aspect, this object is achieved by a CO ₂ beam source of the type mentioned at the outset, in which the at least one catalyst is arranged within the closed laser gas circuit at a distance from the at least one discharge tube in the direction of flow of the laser gas, in order to prevent deposits from forming when the laser gas is excited to reduce degradation products formed in the at least one discharge tube compared to an arrangement within the at least one discharge tube, and in which a temperature of the at least one catalyst during operation of the CO ₂ jet source is at least 60° C., preferably at least 100° C., particularly preferably at least 150°C.

The gas discharge, which serves to excite the laser gas, degrades the walls of the at least one discharge tube. The degradation products formed in this way are deposited in the at least one discharge tube and in the laser gas circuit downstream adjacent to the at least one discharge tube. Because the discharge tubes are typically quartz glass tubes, the degradation products typically include quartz particles, particularly in the form of dust. If the degradation products are deposited on the at least one catalyst, its effectiveness decreases and the concentrations of the dissociation products in the closed laser gas circuit increase. As a result, the output power and efficiency of the C0 ₂ beam source decrease. It is therefore advantageous to arrange the catalyst within the closed laser gas circuit at a distance from the at least one discharge tube in the flow direction of the laser gas. A corresponding arrangement leads to a permanent high performance of the C0 ₂ beam source and thus allows long maintenance intervals.

When choosing the catalyst, it should be noted that excited, free-radical and/or atomic oxygen is present in a significant concentration only in the discharge tubes or downstream immediately adjacent to the discharge tubes. The possibility of an arrangement that is sufficiently spaced with regard to the deposition of the degradation products therefore only arises from the use of catalysts which not only enable the oxidation of dissociation products, in particular CO, with transient oxygen species, for example atomic, free-radical and/or excited oxygen, catalyze, but also the oxidation with molecular oxygen. Catalysts based on precious metal nanoparticles are suitable here, in principle even at room temperature.

The effectiveness of a catalyst generally increases with increasing temperature. High temperatures occur in the closed circuit of the C0 ₂ radiation source, however, primarily in the discharge tubes and adjacent to them downstream. As a function of the distance to the discharge tubes, the temperatures in the flow direction of the laser gas typically fall continuously due to the cooling. When choosing the arrangement of the catalytic converter, a balance must therefore be struck between a reduction in the deposit effects and the highest possible temperature. The temperature ranges mentioned enable the effective catalysis of the oxidation of CO to C0 ₂ with molecular oxygen by means of noble metal nanoparticle catalysts and are achieved in C0 ₂ jet sources with sufficiently high power at a sufficient distance from the discharge tubes.

In principle, it is also possible to decouple part of the laser gas flow from the actual laser gas circuit and to route it through a separate catalyst unit with a conventional catalyst based on a homogeneous platinum or palladium layer. Such conventional catalysts also allow the reaction of CO to CO ₂ with molecular oxygen, but require temperatures above about 250 ° C. Such high temperatures are counterproductive in the case of C0 ₂ beam sources for the actual laser process and are therefore generally undesirable. Such a catalyst unit would therefore have to be heated, i.e. a heater in addition to the catalytic converter,

Cooling and optionally have their own blower (gas pump). The structural outlay for such a catalytic converter unit is therefore very high, particularly if a significant proportion of the laser gas flow is to pass through this catalytic converter circuit. Furthermore, the additional heating counteracts the actual purpose of the circuit, namely the cooling of the laser gas. In certain circumstances, temperatures of more than 250° C. are reached in CO ₂ radiation sources immediately downstream of the discharge tubes, even without additional heating. However, since the deposit effects are most pronounced here, arranging a conventional catalytic converter in this area does not make sense.

In one embodiment, a flow path of the laser gas between a downstream end of the at least one discharge tube and the at least one catalyst is at least 5 cm, preferably at least 10 cm, particularly preferably at least 15 cm. The deposition effects have been found to fall off substantially exponentially as a function of flow path from the downstream end of the at least one arc tube. The half-length is a few centimeters. The distance values mentioned thus lead to an effective reduction in the deposition of degradation products on the at least one catalytic converter.

In a further embodiment the at least one catalyst is arranged within at least one of the feed elements. Such an arrangement generally ensures sufficient spacing from the discharge tubes, since the flow path from the downstream end of the discharge tubes to the feed element is sufficiently large. In principle, however, the catalytic converter can also be arranged within at least one of the discharge elements.

In a further embodiment, the blower is arranged centrally and the CO ₂ beam source has in a first plane radial and alternating feed arms as first feed elements and discharge arms as second discharge elements, and in a second plane the discharge tubes are alternately connected to one another via second feed elements and first discharge elements , wherein for cooling the laser gas at least a partial area of at least one feed arm and/or at least one Abführarms is designed as a heat exchanger. The CO ₂ beam source is, for example, essentially discretely rotationally symmetrical, preferably four-fold rotationally symmetrical. Starting from the (radial) fan, the laser gas is fed to the discharge tubes by means of the feed arms and the second feed elements and removed from the discharge tubes again to the fan by means of the first discharge elements and the discharge arms. Such a design results in short gas paths between the discharge tubes and the heat exchangers and is characterized by its compactness and its robustness, for example with regard to shocks or vibrations. At the same time, very high laser powers can be achieved. For even higher laser powers, the second level can also have two or more sub-levels of discharge tubes, which are connected to one another via the second feed elements and the first discharge elements. In order to form at least a partial area of at least one feed and/or discharge arm as a heat exchanger, at least one cooling pipe, for example a helical one, can be passed through the corresponding partial area. A cooling liquid is fed through the cooling tube to cool the laser gas.

In a development of this embodiment, at least one inner side of at least one feed arm, which is in contact with the laser gas, serves as a substrate for the at least one catalyst. Alternatively, an outside of the helical cooling tube, for example, which is in contact with the laser gas, can also serve as a substrate for the at least one catalyst. Alternatively, an inside of at least one removal arm in contact with the laser gas and/or an outside of a cooling tube in contact with the laser gas, which runs through the corresponding partial area of the removal arm, can also serve as the substrate of the at least one catalyst.

In a further embodiment, the at least one catalytic converter is arranged in at least one of the feed arms and/or in at least one of the discharge arms upstream of the at least one partial area which is designed as a heat exchanger. One advantage of such an arrangement is that the temperatures upstream of the partial areas designed as heat exchangers are comparatively high. These are typically between approx. 150° C. and approx. 250° C. upstream of the partial areas of the removal arms designed as heat exchangers and between approx. 60°C and approx. 100°C upstream of the sections of the feed arms designed as heat exchangers. At the same time, this arrangement is characterized by a sufficient distance between the flow path of the laser gas and the discharge tubes and good accessibility. Based on currently manufactured C0 ₂ jet sources, only minimal structural adjustments are necessary to arrange the catalyst there.

In a further embodiment, the CO ₂ jet source has at least one device for replacing the at least one catalyst. Even if the arrangement of the catalytic converter according to the invention leads to a significant reduction in the deposit of degradation products on the catalytic converter, certain aging effects nevertheless occur. It is therefore advantageous if the catalyst can be replaced as easily as possible. For this purpose, the catalytic converter is preferably designed as a separate component and is therefore easy to insert into a corresponding housing in the closed circuit and to remove again. The maintenance is particularly easy and the C0 ₂ laser is only briefly out of service during maintenance.

In a further development of this embodiment, at least one feed arm and/or at least one discharge arm has at least one closable opening as a device for exchanging the at least one catalyst. In this case, the at least one catalyst is arranged in at least one of the feed arms and/or in at least one of the discharge arms. The catalyst can be inserted and removed again via closable openings in the corresponding feed and discharge arms. The closable openings are, for example, flaps or plates, which can be closed airtight via suitable screw connections and by means of appropriate seals, for example using O-rings. The closable openings should be larger than the cross section of the respective catalyst so that it can be removed in a linear movement and is easily accessible from the outside. A combination of designing the catalysts as separate components with an arrangement in the feed and/or discharge arms upstream of the partial areas designed as heat exchangers and interchangeability of the catalysts via closable openings in the feed and/or discharge arms is particularly advantageous. Compared to using the outside of the z coil-shaped cooling tubes of the heat exchangers as substrates of the catalysts, it is precisely the separation of functions between the catalysts and the heat exchangers that enables easy replacement.

In a further embodiment, the precious metal nanoparticles are platinum nanoparticles, palladium nanoparticles, gold nanoparticles, nanoparticles made from an alloy of these materials or a mixture of these nanoparticles. Compared to conventional catalysts, catalysts based on noble metal nanoparticles are generally much more efficient, measured by the conversion of the catalyst based on its surface area. It has been shown that the precious metal nanoparticles mentioned, in particular gold nanoparticles and/or platinum nanoparticles, are particularly suitable for the present application.

In another embodiment, the substrate of the at least one catalyst is a metal substrate or a ceramic substrate. The metal can be steel or stainless steel, for example, and the ceramic can be cordierite, for example.

In a further embodiment, there is a coating on the substrate of the at least one catalyst, to which the noble metal nanoparticles are applied, the coating preferably being made at least partially of a metal oxide, particularly preferably at least partially of cerium oxide,

Aluminum oxide, titanium oxide, copper oxide or a mixture of these materials. In this case, the noble metal nanoparticles are applied directly to the coating and thus indirectly to the substrate via the coating. The substrate serves as a mechanical support for the chemically active part of the catalyst, which includes the coating and the noble metal nanoparticles. The coating can be applied to the substrate using a suitable deposition process or can form itself, for example via oxidation of a metal substrate.

In a development of this embodiment, the coating on the substrate of the catalyst is microscopically structured to increase the surface area. In order to achieve the highest possible conversion, it is advantageous for the catalyst to have as large a surface area as possible. A corresponding microscopic structuring can be achieved, for example, by depositing the coating as particles from a suspension.

In another embodiment, the substrate of the catalyst is textured to increase surface area. In addition or as an alternative to microscopic structuring of the coating, an increase in surface area can also be achieved by structuring the substrate of the catalyst. For this purpose, the substrate can be an extruded profile, for example. The cross section can have a regular pattern, for example a square pattern. Alternatively, the substrate can also be a rolled-up corrugated metal sheet.

In a development of this embodiment, the substrate of the catalyst is structured in a honeycomb manner to increase the surface area.

Further features and advantages of the invention result from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can each be implemented individually or together in any combination in a variant of the invention.

drawing

Exemplary embodiments are shown in the schematic drawing and are explained in the following description. Show it

1 shows a plan view of a C0 ₂ beam source in the form of a C0 ₂ laser with a folded laser resonator in a sectional view,

Fig. 2 is a perspective view of the C0 ₂ shown in Fig. 1 -

Beam source in the form of a C0 ₂ laser with catalysts arranged in feed arms and discharge arms of the C0 ₂ beam source,

3a,b,c schematic representations of catalysts whose substrates are structured differently to increase the surface area. In Fig. 1 and Fig. 2, a C0 ₂ -ray source 1 is shown in the form of a C0 ₂ laser, which has a square folded laser resonator 2 and is constructed essentially four-fold rotationally symmetrical. A laser gas 4, which consists of CO ₂ , He and N ₂ and serves as the laser medium, is excited via electrodes 5 in discharge tubes 3 . The electrodes 5 are arranged adjacent to the discharge tubes 3 and are connected to an HF generator (not shown here). For example, a tube generator with an excitation frequency of 13.56 MHz or 27.12 MHz can be used as the HF generator. The excitation of the laser gas 4 leads to a population inversion and a laser beam 6 forms in the laser resonator 2.

To cool the laser gas 4, it is removed from the discharge tubes 3 by means of a fan 7 (radial fan) arranged centrally in the folded laser resonator 2 and fed back to the discharge tubes 3 in a closed laser gas circuit K after cooling has taken place. For this purpose, the CO ₂ beam source 1 has, for example, four feed arms 8 as first feed elements and four second feed elements 9, 9', as well as four first discharge elements 10 and four discharge arms

11 as the second discharge elements.

The four feed arms 8 and the four discharge arms 11 are radial in a first plane

12 of the C0 ₂ beam source 1 is arranged, while the discharge tubes 3 are arranged in a second plane 13 and are connected to one another alternately via the second feed elements 9,9' and the first discharge elements 10. The second feed elements 9, 9' form the corners of the square laser resonator 2, while the first discharge elements 10 are arranged centrally along the edges of the square laser resonator 2.

The flow direction of the laser gas 4 inside the discharge tubes 3 and in the feed elements 8,9,9' and the discharge elements 10,11 is illustrated in FIG. 1 by arrows. Starting from the blower 7, the laser gas 4 flows through the four feed arms 8 and the four second feed elements 9, 9' arranged in the corners of the square laser resonator 2 into the discharge tubes 3. The laser gas 4 then flows through the discharge tubes 3 and over the first discharge elements 10 and the discharge arms 11 back to the blower 7. The laser beam 6 runs along the axes of the discharge tubes 3.

Deflection mirrors 14 in the second feed elements 9 serve to deflect the laser beam 6 by 90° in each case. A first resonator mirror 15 and a partially transmissive second resonator mirror 16 are arranged in one of the second feed elements 9'. The first resonator mirror 15 is highly reflective and reflects the laser beam 6 through 180°, so that the laser beam 6 again passes through the discharge tubes 3 in the opposite direction. The partially transmissive second resonator mirror 16 serves as a decoupling mirror, via which part 6' of the laser beam 6 is decoupled from the laser resonator 2, while the other part remains in the laser resonator 2 and passes through the discharge tubes 3 again.

In contrast to what is shown here, the CO ₂ beam source 1 can also have two sub-levels of discharge tubes 3 to increase the output, which are connected to one another via the second feed elements 9, 9′ and the first discharge elements 10 . The laser beam 6 is then diverted between the sub-levels, for example via periscopes.

Deviating from the illustration in FIG. 1 and FIG. 2, the CO ₂ beam source 1 can also be a CO ₂ laser amplifier. In this case, the resonator mirrors 15, 16 are replaced by windows. A laser beam 6 to be amplified, for example in the form of a seed laser beam, then passes through the CO ₂ beam source only once.

In Fig. 2, a feed arm 8 and a discharge arm 11 are shown in a partial section. Inside the feed arms 8 and the discharge arms 11, a partial area 17 is designed as a heat exchanger. In order to fulfill the function as a heat exchanger, in the case of the CO 2 jet source shown by way of example in FIG. Upstream of each of these partial areas 17 is a catalyst 18 for catalyzing the oxidation of dissociation products 19 (cf. Fig.

1) which arise when the laser gas 4 is excited, in particular CO, is arranged in a feed arm 8 and a discharge arm 11 . An advantage of this arrangement is the comparatively high catalyst temperatures with a sufficient distance from the discharge tubes 3 at the same time. The temperature Ti in the region of the catalyst 18 in the discharge arm 11 is typically in a value range between 150° C. and 250° C., while the temperature T ₂ in the area of the catalyst 18 in the feed arm 8 is typically in a value range between 60°C and 100°C.

The spacing of the catalysts 18 from the discharge tubes 3 serves to reduce the deposition of degradation products 20 (cf. FIG. 1) formed in the discharge tubes 3 when the laser gas 4 is excited on the respective catalyst 18 . A flow path L of the laser gas 4 running essentially vertically here between the downstream end 3' of the discharge tubes 3 and the catalyst 18 in the removal arm 11 is more than 15 cm in the example shown in FIG. In principle, however, a flow path L of the laser gas 4 of more than 5 cm or of more than 10 cm can be sufficient for reducing the deposits of the degradation products on the respective catalytic converter 18 .

As can also be seen in FIG. 2, the feed arms 8 and discharge arms 11 each have a closable opening 21 as a device for replacing the catalysts 18. The openings 21 can be closed, for example, with the aid of plates or flaps which are designed to be detachable or pivotable. The catalytic converters 18 are designed as separate components in the form of cassettes, which considerably simplifies their replacement. In Fig. 3a, b, c cross sections of cuboid catalysts 18 in the form of replaceable cassettes are shown schematically. The catalysts each include noble metal nanoparticles 22 and a substrate 23. On the substrate 23 is a coating 24 to which the noble metal nanoparticles 22 are applied. The coating 24 consists at least partially of aluminum oxide, but it can also at least partially consist of another metal oxide, for example cerium oxide, titanium oxide, copper oxide or a mixture of these materials. Alternatively, the substrate 23 can also be uncoated. In this case, the noble metal nanoparticles 22 are applied directly to the substrate 23 .

In Fig. 3a,b,c only isolated noble metal nanoparticles 22 are shown to simplify the representation. The noble metal nanoparticles 22 are gold nanoparticles in the example shown. However, the noble metal nanoparticles 22 can also be platinum nanoparticles, palladium nanoparticles, nanoparticles made from an alloy of these materials or a mixture of these nanoparticles or these nanoparticles with gold nanoparticles. The substrates 23 are structured to increase the surface area in order to increase the conversion of the catalysts 18 increase. Alternatively or additionally, the coating 24 can also be microscopically structured to increase the surface area.

The substrate 23 of the catalytic converter 18 shown in FIG. 3a is an extruded cordierite substrate, but it can also be another ceramic substrate. The cross section of the catalytic converter 18 has a square pattern.

In FIGS. 3b, c, the substrates 23 are metal substrates, more precisely steel substrates. In FIG. 3b, the structure for increasing the surface area is a honeycomb structure. In FIG. 3c, the substrate 23 is a rolled-up corrugated metal sheet or a corrugated foil.

Alternatively or in addition to the catalysts 18 shown in Fig. 3a-c in the form of exchangeable catalyst cassettes, at least one inner side of at least one feed arm 8 and/or discharge arm 11 that is in contact with the laser gas 4 can be used as a substrate 23 for one or more catalysts 18 serve. A ceramic coating, for example, can also be applied to the inside of the respective feed or removal arm 8, 11, which forms the substrate 23 for the precious metal nanoparticles 22.

Before installing the catalysts 18 in the C0 ₂ jet source 1, they must be carefully cleaned. In the present case, this is particularly important since the laser gas circuit K is closed. Dry mechanical processes are primarily suitable here, for example blowing off with nitrogen, wet processes (using H ₂ O +X) or ultrasonic cleaning. If necessary, further baking and activation steps must be carried out. When designing the catalytic converters 18, there must also be a trade-off between the pressure loss caused by the catalytic converters 18, the cooling effect of the heat exchangers and the effectiveness of the catalytic converters 18. For this purpose, the structure of the substrates 23 of the catalysts 18 and the essential geometry parameters, including the cross sections, the rib spacing, the length, etc., must be optimized. Also, when selecting the catalysts 18, care should be taken to ensure that no parasitic effects occur, such as "poisoning" of the active centers, which are then no longer active, or temperature-dependent absorption (CO ₂ , H ₂ 0) that lead to undesirable changes of the laser gas composition. The catalyst 18 should not be oversized in order to avoid the introduction of catalyst material, which only leads to parasitic effects and does not contribute to catalysis. In particular, the catalytic converter 18 should have no or as few surfaces as possible that are not subjected to flow and therefore do not contribute to the catalysis but only have a parasitic effect. The layer thickness of the coating 24 and the materials of the noble metal nanoparticles 22 and the coating 24 are then to be optimized.

Claims

patent claims

1. C0 ₂ beam source (1), comprising: at least one discharge tube (3), in which a laser gas (4) serves as the laser medium, a blower (7) for feeding the laser gas (4) into the at least one discharge tube (3) via at least one feed element (8,9,9') and for discharging the laser gas (4) from the at least one discharge tube (3) via at least one discharge element (10,11) in a closed laser gas circuit (K), and at least one catalyst ( 18) for catalyzing an oxidation of dissociation products (19) which arise when the laser gas (4) is excited, the at least one catalyst (18) comprising noble metal nanoparticles (22) which are applied to a substrate (23), characterized that the at least one catalyst (18) is arranged within the closed laser gas circuit (K) in the direction of flow of the laser gas (4) at a distance from the at least one discharge tube (3) in order to prevent deposits of when the laser gas (4) is excited in the mind to reduce at least one discharge tube (3) formed degradation products (20) compared to an arrangement within the at least one discharge tube (3), and that a temperature (Ti, T ₂ ) of the at least one catalyst (18) during operation of the C0 ₂ - Radiation source (1) is at least 60°C, preferably at least 100°C, particularly preferably at least 150°C.

2. C0 ₂ beam source according to claim 1, characterized in that a flow path (L) of the laser gas (4) between a downstream end (3') of the at least one discharge tube (3) and the at least one catalyst (18) has at least 5 cm, preferably 10 cm, particularly preferably at least 15 cm.

3. C0 ₂ jet source according to claim 1 or 2, characterized in that the at least one catalyst (18) is arranged within at least one of the feed elements (8,9,9').

4. C0 ₂ jet source according to any one of the preceding claims, characterized in that the fan (7) is arranged centrally and the C0 ₂ - jet source (1) in a first plane (12) radially and alternating feed arms (8) as the first feed elements and removal arms (11) as second removal elements, and in a second plane (13) the discharge tubes (3) are connected to one another alternately via second delivery elements (9, 9') and first removal elements (10), with cooling of the laser gas (4 ) at least one partial area (17) of at least one feed arm (8) and/or at least one discharge arm (11) is designed as a heat exchanger.

5. C0 ₂ beam source according to claim 4, characterized in that at least one of the laser gas (4) in contact with the inside of at least one feed arm (8) serves as a substrate of the at least one catalyst (18).

6. C0 ₂ jet source according to claim 4 or 5, characterized in that the at least one catalyst (18) is located in at least one of the feed arms (8) and/or in at least one of the discharge arms (11) upstream of the at least one partial area (17) , which is designed as a heat exchanger, is arranged.

7. C0 ₂ jet source according to one of the preceding claims, characterized in that the C0 ₂ jet source (1) has at least one device (21) for replacing the at least one catalyst (18).

8. C0 ₂ jet source according to Claim 7, characterized in that at least one feed arm (8) and/or at least one discharge arm (11) has at least one closable opening (21) as the device (21) for replacing the at least one catalyst (18). having.

9. C0 ₂ beam source according to one of the preceding claims, characterized in that the noble metal nanoparticles (22) are platinum nanoparticles, palladium nanoparticles, gold nanoparticles, nanoparticles from an alloy of these materials or a mixture of these nanoparticles.

10. C0 ₂ beam source according to one of the preceding claims, characterized in that the substrate (23) of the at least one catalyst (18) is a metal substrate or a ceramic substrate.

11. C0 ₂ beam source according to one of the preceding claims, characterized in that on the substrate (23) of the at least one catalyst (18) is a coating (24) on which the noble metal nanoparticles (22) are applied, wherein the coating preferably consists at least partially of a metal oxide, particularly preferably at least partially of cerium oxide, aluminum oxide, titanium oxide, copper oxide or a mixture of these materials.

12. C0 ₂ beam source according to one of the preceding claims, characterized in that the coating (24) on the substrate of the catalyst (18) is microscopically structured to increase the surface area.

13. C0 ₂ jet source according to one of the preceding claims, characterized in that the substrate (23) of the catalyst is structured to increase the surface area.

14. C0 ₂ jet source according to claim 12, characterized in that the substrate (23) of the catalyst (18) is structured in a honeycomb manner to increase the surface area.