CO₂ beam source with catalyst

Abstract

The present invention relates to a CO2 beam source (1), the beam source comprising: at least one discharge tube (3) in which a laser gas is used as a laser medium; a blower (7) for supplying the laser gas to the at least one discharge tube (3) through at least one supply element (8, 9, 9') in a closed laser gas circuit and discharging the laser gas (4) from the at least one discharge tube (3) through at least one discharge element (10, 11); and at least one catalyst (18) comprising precious metal nanoparticles coated on a substrate and for promoting the oxidation of dissociation products generated when the laser gas is excited. The at least one catalyst (18) is disposed at a distance from the at least one discharge tube (3) in the direction of laser gas flow within the closed laser gas circuit to reduce the deposition of dissociation products generated in the at least one discharge tube (3) when the laser gas (4) is excited, compared to being disposed within the at least one discharge tube (3). When the CO2 beam source (1) is operated, the temperature (T1, T2) of at least one catalyst (18) is 60°C or higher, preferably 100°C or higher, particularly preferably 150°C or higher.

Description

Technology Field

[0001] The present invention relates to a CO2 beam source comprising at least one discharge tube in which a laser gas is used as a laser medium, a blower for supplying the laser gas into the at least one discharge tube through at least one supply element in a closed laser gas circuit and discharging the laser gas from the at least one discharge tube through at least one exhaust element, and at least one catalyst for promoting the oxidation of a dissociation product generated when the laser gas is excited, wherein the at least one catalyst comprises noble metal nanoparticles coated on a substrate. Background Technology

[0002] In the context of this application, a CO2 beam source is understood to mean a CO2 laser or a CO2 laser amplifier. In the latter case, the CO2 laser amplifier generally serves to amplify the seed laser beam emitted from the seed laser. The laser gas of a CO2 beam source is generally a mixture of He, N2, and CO2. Here, CO2 is used as the actual laser medium, while He and N2 molecules play a supporting role. The CO2 beam source is electrically excited. In a discharge tube, typically a quartz glass tube, the laser gas is excited via a gas discharge at a high DC voltage or a high-frequency AC voltage. As a result of this excitation, population inversion occurs. In the case of a CO2 beam source in the form of a CO2 laser, the laser medium is present in the beam path of a mirror array that functions as a laser resonator.

[0003] When the CO2 beam source is in operation, the laser gas is heated up strongly, and since the laser process stops at temperatures above 300°C, the laser gas must be cooled. In a closed laser gas circuit, this cooling is made possible by exhausting the laser gas from the discharge tube and supplying the laser gas back to the discharge tube, for example, through a suitable additional device such as a heat exchanger.

[0004] CO2 beam sources in the form of CO2 laser amplifiers are used specifically to generate EUV radiation. The term EUV radiation refers to electromagnetic radiation with wavelengths ranging from 10 nm to 120 nm. Compared to the currently widely used wavelengths around 200 nm, the use of EUV radiation in microlithography production in the semiconductor industry enables the stable production of components with substantially smaller structural sizes, thereby leading to improved performance. In the so-called LPP process ("laser-generated plasma"), a tin droplet is struck by a laser pulse amplified by a CO2 laser amplifier to generate EUV radiation. The impact on the tin droplet creates a plasma that emits EUV radiation.

[0005] A particular challenge regarding the configuration of CO2 beam sources arises from the generation of dissociation products resulting from gas discharge when the laser gas is excited. These dissociation products, particularly carbon monoxide (CO), reduce the performance and efficiency of the laser or laser amplifier. As a countermeasure, the use of catalysts to oxidize dissociation products, specifically to oxidize CO to CO2, has been described in the literature.

[0006] A CO2 laser having a closed laser gas circuit, a CO2 laser gas mixture, and an amplification volume is known from US Patent No. 4,756,000. A gas discharge in the amplification volume generates CO, oxygen, and excited oxygen species. A gold coating acts as a catalyst for the reaction of CO and excited oxygen to form CO2. To ensure contact with a substantial amount of excited oxygen, the gold coating is placed on the wall of the amplification volume or placed sufficiently close to the downstream end of the amplification volume. A disadvantage of this placement is that the gas discharge causes a deposition effect of decomposition products resulting from the excitation of the laser gas in the amplification volume and immediately downstream of the amplification volume, thereby leading to the decomposition of the catalyst and consequently the degradation of the CO2 laser.

[0007] DE 3523926 C2 discloses an electrically excited CO2 laser having a closed laser gas circuit and a catalyst for generating and maintaining the chemical composition of the laser gas, wherein an additional beam source serves to substantially increase the attachment of molecules formed by dissociation in the laser gas to the catalyst and / or the gas flow around the catalyst surface is controlled to substantially increase the attachment of molecules formed by dissociation in the laser gas to the catalyst.

[0008] JPS6214486A discloses a CO2 laser equipped with a catalyst unit that maintains a stable laser output by maintaining a constant composition of the laser gas. For this purpose, the catalyst unit is designed to simultaneously function as a self-regulating heating unit, thereby automatically maintaining the temperature of the catalyst unit within a constant range of CO oxidation rates.

[0009] US 2015 / 0222083 A1 discloses an EUV system comprising an optical amplifier system equipped with a catalyst. In one embodiment, the catalyst comprises a substrate having an opening and nanoparticles made of a precious metal, such as gold, applied as a coating to the inner surface of the opening. It is specified that when the catalyst is placed in an amplifier or a CO2 laser of the optical amplifier system, the temperature of the gas mixture within the catalyst can rise up to 60°C.

[0010] The oxidation of CO using a catalyst based on small gold particles has also been examined in detail in the paper [GC Bond and DT Thompson's "Gold-Catalysed Oxidation of Carbon Monoxide", Gold Bull. 33, 41(2000)]. The problem to be solved

[0011] In this regard, the objective of the present invention is to provide a CO2 beam source with high performance and efficiency that is stable over the long term. means of solving the problem

[0012] This problem is achieved by a CO2 beam source of the type mentioned in the introduction, according to the first aspect, in order to reduce the deposition of decomposition products generated in at least one discharge tube when the laser gas is excited compared to placement in at least one discharge tube, at least one catalyst is placed at a distance from at least one discharge tube in the direction of laser gas flow within a closed laser gas circuit, and the temperature of at least one catalyst is 60°C or higher, preferably 100°C or higher, particularly preferably 150°C or higher during operation of the CO2 beam source.

[0013] The walls of at least one discharge tube are decomposed by a gas discharge that serves to excite the laser gas. The decomposition products formed here are deposited in at least one discharge tube and in the downstream laser gas circuit adjacent to at least one discharge tube. Since the discharge tube is typically a quartz glass tube, the decomposition products generally contain quartz particles, particularly in the form of dust. If decomposition products are deposited on one or more catalysts, their efficiency decreases and the concentration of dissociation products in the closed laser gas circuit increases. Consequently, the output performance and efficiency of the CO2 beam source are reduced. Therefore, it is advantageous to place the catalyst at a distance from at least one discharge tube in the direction of laser gas flow within the closed laser gas circuit. Proper placement ensures that the performance of the CO2 beam source remains consistently high, thereby extending the maintenance interval.

[0014] When selecting a catalyst, it should be noted that excited oxygen, radical oxygen, and / or atomic oxygen are present in significant concentrations only in the discharge tube or downstream immediately adjacent to the discharge tube. The possibility of sufficient separation regarding the deposition of decomposition products arises only when using a catalyst that promotes the oxidation of molecular oxygen as well as the dissociation products of transient oxygen species, such as atomic oxygen, radical oxygen, and / or excited oxygen, particularly CO. In this regard, catalysts based on precious metal nanoparticles are essentially suitable even at room temperature.

[0015] The effect of a catalyst generally increases with increasing temperature. However, in a closed circuit of a CO2 beam source, high temperatures are primarily generated in the discharge tube and the adjacent downstream area. Depending on the distance to the discharge tube, the temperature in the direction of the laser gas flow generally decreases continuously due to cooling. Therefore, when selecting a catalyst arrangement, a balance must be struck between reducing deposition effects and maintaining the highest possible temperature. The aforementioned temperature range is achieved in a CO2 beam source with sufficiently high output even at a sufficient distance from the discharge tube, enabling effective catalytic action to oxidize CO to CO2 using molecular oxygen via precious metal nanoparticle catalysts.

[0016] Essentially, it is possible to separate a portion of the laser gas flow from the actual laser gas circuit and pass it through a separate catalytic device using a conventional catalyst based on a uniform platinum or palladium layer. While such conventional catalysts enable the reaction of CO to CO2 using molecular oxygen, this requires temperatures exceeding approximately 250°C. For CO2 beam sources, such high temperatures are generally undesirable as they have adverse effects on the actual laser process. Therefore, these catalytic units must be heated and equipped with heaters, coolers, and, if necessary, their own blowers (gas pumps) in addition to the catalyst. Consequently, the cost of constructing such catalytic units is very high, particularly when a significant portion of the laser gas flow passes through this catalytic circuit. Furthermore, additional heating runs counter to the circuit's actual purpose, namely the cooling of the laser gas. Temperatures exceeding 250°C are achieved at the CO2 beam source located immediately downstream of the discharge tube without additional heating. However, since this is the region where deposition effects are most pronounced, placing a conventional catalyst in this area is meaningless.

[0017] In one embodiment, the flow path of the laser gas between the downstream end of at least one discharge tube and at least one catalyst is at least 5 cm, preferably at least 10 cm, and particularly preferably at least 15 cm. The deposition effect was found to decrease substantially exponentially along the flow path from the downstream end of at least one discharge tube. The half-length is several centimeters. Thus, the mentioned spacing value effectively reduces the deposition of decomposition products on at least one catalyst.

[0018] In a further embodiment, at least one catalyst is placed inside at least one of the feed elements. Through this placement, a sufficient clearance from the discharge tube is generally ensured because the flow path from the downstream end of the discharge tube to the feed element is sufficiently large. However, the catalyst may also be placed inside at least one of the discharge elements.

[0019] In a further embodiment, the blower is positioned centrally, and the CO2 beam source has a supply arm as a first supply element and a discharge arm as a second discharge element radially alternately in a first plane, and in a second plane, the discharge tubes are alternately connected to each other through the second supply element and the first discharge element, wherein at least one portion of at least one supply arm and / or at least one discharge arm is designed as a heat exchanger to cool the laser gas. For example, the CO2 beam source is designed with substantially discrete rotational symmetry, preferably with 4-fold rotational symmetry. Starting from the (radial) blower, the laser gas is supplied to the discharge tube through the supply arm and the second supply element, and is discharged from the discharge tube back to the blower through the first discharge element and the discharge arm. This design shortens the gas path between the discharge tube and the heat exchanger and features robustness and compactness against, for example, shock or vibration. Thus, very high laser output is achieved simultaneously. For higher laser output, the second plane may also have subplanes of two or more discharge tubes connected to each other through a second supply element and a first discharge element. To design at least one partial region of at least one supply arm and / or discharge arm as a heat exchanger, for example, at least one spiral cooling tube may pass through that partial region. A cooling liquid is guided through the cooling tube to cool the laser gas.

[0020] In a further improved embodiment of this embodiment, at least one inner surface of at least one supply arm in contact with the laser gas serves as a substrate for at least one catalyst. Alternatively, the outer surface of, for example, a spiral cooling tube in contact with the laser gas may also serve as a substrate for at least one catalyst. Alternatively, the inner surface of at least one discharge arm in contact with the laser gas and / or the outer surface of a cooling tube in contact with the laser gas and passing through a corresponding portion of the discharge arm may also serve as a substrate for at least one catalyst.

[0021] In a further embodiment, at least one catalyst is placed in at least one supply arm and / or at least one discharge arm upstream of at least one partial region designed as a heat exchanger. One advantage of this arrangement is that the upstream temperature of the partial region designed as a heat exchanger is relatively high. This is generally about 150°C to about 250°C upstream of the partial region of the discharge arm designed as a heat exchanger, and about 60°C to about 100°C upstream of the partial region of the supply arm designed as a heat exchanger. At the same time, this arrangement features sufficient distance and excellent accessibility between the laser gas flow path and the discharge tube. Starting from a conventional CO2 beam source, placing the catalyst therein requires only minimal structural adjustments.

[0022] In a further embodiment, the CO2 beam source comprises at least one device for replacing at least one catalyst. Even though the arrangement of the catalyst according to the present invention significantly reduces the deposition of decomposition products on the catalyst, known aging effects still occur. Therefore, it is advantageous if the catalyst can be replaced as easily as possible. For this purpose, the catalyst is preferably designed as a separate component so that it can be easily inserted into and removed from the corresponding housing in a closed circuit. Thus, maintenance is particularly easy, and the CO2 laser does not operate for only a short time during maintenance.

[0023] In a further improved embodiment of this embodiment, at least one supply arm and / or at least one discharge arm has at least one closeable opening as a device for replacing at least one catalyst. In this case, at least one catalyst is placed in at least one supply arm and / or at least one discharge arm. The catalyst can be inserted and discharged again through the closeable opening of the corresponding supply arm or discharge arm. Here, the closeable opening is a flap or plate that can be hermetically closed, for example, using an O-ring, through a suitable screw connection and its seal. The closeable opening is larger than the cross-sectional area of ​​each catalyst so that the catalyst can be discharged in a linear motion and is easily accessible from the outside. Particularly advantageous is the combination of designing the catalyst as a separate component, placing it within the supply arm and / or discharge arm upstream of a partial area designed as a heat exchanger, and the interchangeability of the catalyst through the closeable opening within the supply arm and / or discharge arm. For example, compared to using the outer surface of a heat exchanger's spiral cooling tube as a substrate for the catalyst, it is the functional separation between the catalyst and the heat exchanger that enables easy replacement.

[0024] In additional embodiments, the precious metal nanoparticles are platinum nanoparticles, palladium nanoparticles, gold nanoparticles, nanoparticles made of alloys of these materials, or mixtures of these nanoparticles. Compared to conventional catalysts, precious metal nanoparticle-based catalysts are generally much more efficient in measuring catalyst conversion rates based on surface area. The aforementioned precious metal nanoparticles, in particular gold nanoparticles and / or platinum nanoparticles, have been shown to be particularly suitable for the application of this application.

[0025] In a further embodiment, the substrate of at least one catalyst is a metal substrate or a ceramic substrate. The metal may be, for example, steel or stainless steel, and the ceramic may be, for example, cordierite.

[0026] In a further embodiment, a substrate of one or more catalysts has a coating on which precious metal nanoparticles are applied, the coating preferably consists of at least partially a metal oxide, particularly preferably at least partially cerium oxide, aluminum oxide, titanium oxide, copper oxide, or a mixture thereof. In this case, the precious metal nanoparticles are applied directly to the coating and thus indirectly applied to the substrate through the coating. Here, the substrate serves as a mechanical support for the chemically active portion of the catalyst containing the coating and the precious metal nanoparticles. The coating may be applied to the substrate using a suitable deposition process or may be formed independently, for example, through the oxidation of the metal substrate.

[0027] In an improved example of this embodiment, the coating on the catalyst substrate is finely structured to increase the surface area. It is advantageous to maximize the surface area of ​​the catalyst to achieve the maximum possible conversion rate. Corresponding fine structuring can be achieved, for example, by depositing the coating as particles from a suspension.

[0028] In a further embodiment, the catalyst substrate is structured to increase the surface area. An increase in surface area can also be achieved by structuring the catalyst substrate in addition to or alternative to microstructuring the coating. For this purpose, the substrate may be, for example, an extruded profile. Here, the cross-section may have a regular pattern, for example, such as a square pattern. Alternatively, the substrate may be rolled corrugated cardboard.

[0029] In a further improved example of the present embodiment, the catalyst substrate is structured in a honeycomb shape to increase the surface area.

[0030] Further features and advantages of the present invention will become apparent from the following description of exemplary embodiments of the present invention based on the drawings illustrating the essential details of the present invention and from the claims. Individual features may be implemented individually or in any combination of a number in variations of the present invention. Brief explanation of the drawing

[0031] An exemplary embodiment is illustrated in the schematic diagram and will be described in the specification below. FIG. 1 is a cross-sectional view of a CO2 beam source in the form of a CO2 laser having a folded laser resonator, and FIG. 2 is a perspective view of the CO2 beam source shown in FIG. 1 in the form of a CO2 laser with catalysts disposed on the supply arm and the exhaust arm of the CO2 beam source, and Figures 3a, 3b, and 3c are schematic diagrams of catalysts in which the substrate is structured differently to increase the surface area. Specific details for implementing the invention

[0032] FIGS. 1 and 2 illustrate a CO2 beam source (1) in the form of a CO2 laser, which has a square folded laser resonator (2) and is formed substantially four times in rotational symmetry. In the discharge tube (3), a laser gas (4) composed of CO2, He, and N2 and used as a laser medium is excited through an electrode (5). The electrode (5) is positioned adjacent to the discharge tube (3) and connected to an HF generator not shown herein. For example, a tube generator with an excitation frequency of 13.56 MHz or 27.12 MHz can be used as the HF generator. Population inversion occurs by the excitation of the laser gas (4), and a laser beam (6) is formed in the laser resonator (2).

[0033] To cool the laser gas (4), the laser gas is discharged from the discharge tube (3) through a blower (7) (radial blower) positioned in the center of the folded laser resonator (2) and then supplied back to the discharge tube (3) after cooling in the closed laser gas circuit (K). For this purpose, the CO2 beam source (1) has, for example, four supply arms (8) and four second supply elements (9, 9') as first supply elements and four first discharge elements (10) and four discharge arms (11) as second discharge elements.

[0034] Four supply arms (8) and four discharge arms (11) are radially arranged in the first plane (12) of the CO2 beam source (1), while the discharge tube (3) is arranged in the second plane (13) and is alternately connected to each other through the second supply element and the first discharge element (10). The second supply element (9, 9') forms the corners of the square laser resonator (2) here, while the first discharge element (10) is arranged in the center along the corners of the square laser resonator (2).

[0035] The flow direction of the laser gas (4) inside the discharge tube (3) and within the supply elements (8, 9, 9') and discharge elements (10, 11) is shown by arrows in FIG. 1. The laser gas (4) starts from the blower (7) and flows into the discharge tube (3) through four supply arms (8) and four second supply elements (9, 9') positioned at the corners of the square laser resonator (2). The laser gas (4) then flows back through the discharge tube (3) and returns to the blower (7) by the first discharge element (10) and discharge arm (11).

[0036] The laser beam (6) travels along the axis of the discharge tube (3). The deflection mirror (14) of the second supply element (9) serves to deflect the laser beam (6) by 90° in each case. A first resonator mirror (15) and a partially transparent second resonator mirror (16) are placed in one of the second supply elements (9'). The first resonator mirror (15) has high reflectivity and reflects the laser beam (6) by 180°, causing the laser beam (6) to pass through the discharge tube (3) again in the opposite direction. The partially transparent second resonator mirror (16) acts as a decoupling mirror, thereby separating a portion (6') of the laser beam (6) from the laser resonator (2), while the other portion remains in the laser resonator (2) and passes through the discharge tube (3) again.

[0037] Unlike what is illustrated herein, the CO2 beam source (1) may have two subplane discharge tubes (3) to enhance performance, and these discharge tubes are connected to each other through a second supply element (9, 9') and a first discharge element (10). The laser beam (6) is then redirected between the subplanes, for example, through a periscope.

[0038] Unlike the illustration in FIGS. 1 and 2, the CO2 beam source (1) may be a CO2 laser amplifier. In this case, the resonator mirrors (15, 16) are replaced with windows. The amplified laser beam (6) passes through the CO2 beam source only once, for example, in the form of a seed laser beam.

[0039] In FIG. 2, the supply arm (8) and the discharge arm (11) are each shown in partial cross-section. Inside the supply arm (8) and the discharge arm (11), a partial region (17) is designed as a heat exchanger. To function as a heat exchanger, a spiral cooling tube through which a cooling liquid flows is guided from the CO2 beam source exemplarily illustrated in FIG. 2 through this partial region (17). Upstream of this partial region (17), a catalyst (18) is placed in the supply arm (8) and the discharge arm (11) to promote the oxidation of the laser gas (4), particularly the dissociation product (19) (see FIG. 1) that occurs when CO is excited. The advantage of this arrangement is that the catalyst temperature is relatively high and at the same time, sufficient distance can be secured from the discharge tube (3). The temperature T1 of the catalyst (18) region in the discharge arm (11) is generally in the value range of 150°C to 250°C, while the temperature T2 of the catalyst (18) region in the supply arm (8) is generally in the value range of 60°C to 100°C.

[0040] The spacing of the catalyst (18) from the discharge tube (3) serves to reduce the deposition of decomposition products (20) (see FIG. 1) formed in the discharge tube (3) when the laser gas (4) is excited on each catalyst (18). Here, the substantially vertical flow path (L) of the laser gas (4) between the downstream end (3') of the discharge tube (3) and the catalyst (18) of the discharge arm (11) exceeds 15 cm in the embodiment shown in FIG. 2. However, basically, a flow path (L) of the laser gas (4) exceeding 5 cm or 10 cm may be sufficient to reduce the deposition of decomposition products on each catalyst (18).

[0041] As can also be seen in FIG. 2, the supply arm (8) and the discharge arm (11) each have a closing opening (21) as a device for replacing the catalyst (18). The opening (21) can be closed, for example, with the help of a plate or flap designed to be detachable or rotatable. The catalyst (18) is designed as a separate component in the form of a cassette so that replacement is very easy. In FIG. 3a, FIG. 3b, and FIG. 3c, a cross-section of the rectangular catalyst (18) is schematically illustrated in the form of a replaceable cassette. The catalyst comprises a precious metal nanoparticle (22) and a substrate (23). On the substrate (23), there is a coating (24) to which the precious metal nanoparticle (22) is applied. The coating (24) is composed at least partially of aluminum oxide, but may also be composed at least partially of other metal oxides, for example, cerium oxide, titanium oxide, copper oxide, or a mixture of these materials. Alternatively, the substrate (23) may not be coated. In this case, the precious metal nanoparticles (22) are applied directly to the substrate (23).

[0042] In FIGS. 3a, 3b, and 3c, only the separated precious metal nanoparticles (22) are shown for simplicity of explanation. In the illustrated embodiment, the precious metal nanoparticles (22) are gold nanoparticles. The precious metal nanoparticles (22) may also be platinum nanoparticles, palladium nanoparticles, nanoparticles made of an alloy of these materials, or a mixture of these nanoparticles or a mixture of these nanoparticles and gold nanoparticles. The substrate (23) is structured to increase the surface area to increase the conversion rate of the catalyst (18). Alternatively or additionally, the coating (24) may also be finely structured to increase the surface area.

[0043] The substrate (23) of the catalyst (18) shown in FIG. 3a is an extruded cordierite substrate, but it may also be another ceramic substrate. The cross-section of the catalyst (18) has a square pattern here.

[0044] In FIG. 3b and FIG. 3c, the substrate (23) is a metal substrate, more precisely a steel substrate. In FIG. 3b, the structure for increasing the surface area is a honeycomb structure. In FIG. 3c, the substrate (23) is a rolled corrugated cardboard or corrugated cardboard film. Alternatively or additionally to the catalyst in the form of an interchangeable catalyst-cassette shown in FIG. 3a through 3c, at least one inner surface of at least one supply arm (8) and / or discharge arm (11) in contact with the laser gas (4) may serve as a substrate (23) for one or more catalysts (18). Additionally, a ceramic coating, for example, may be applied to the inner surface of each supply or discharge arm (8, 11) forming the substrate (23) for the precious metal nanoparticles (22).

[0045] Before installing the catalyst (18) in the CO2 beam source (1), it must be carefully cleaned. This is particularly important in the current case because the laser gas circuit (K) is closed. Suitable for this is primarily a mechanical drying process, such as a nitrogen blowing process, a wet process (using H2O + x), or ultrasonic cleaning. If necessary, additional baking and activation steps are performed. When designing the catalyst (18), a balance must be struck between the pressure loss caused by the catalyst (18), the cooling effect of the heat exchanger, and the efficiency of the catalyst (18). To this end, the structure of the substrate (23) of the catalyst (18), as well as substantial geometric parameters including cross-section, rib spacing, length, etc., must be optimized. Additionally, when selecting the catalyst (18), care must be taken to avoid parasitic effects, such as "poisoning" of active centers that are no longer activated, or temperature-dependent absorption (CO2, H2O) that may cause undesirable changes in the laser gas composition. To avoid the introduction of catalytic materials that cause only parasitic effects and do not contribute to catalytic action, the catalyst (18) must not be excessive in size. In particular, the catalyst (18) must not have a surface that is not exposed to flow and does not contribute to catalytic action and only causes parasitic effects, or it must have as little as possible of such a surface. Therefore, the layer thickness of the coating (24) and the materials of the precious metal nanoparticles (22) and the coating (24) must also be optimized.

Claims

Claim 1 A CO2 beam source (1) comprising at least one discharge tube (3) in which a laser gas (4) is used as a laser medium, a blower (7) for supplying the laser gas to the at least one discharge tube (3) through at least one supply element (8, 9, 9') in a closed laser gas circuit (K) and discharging the laser gas (4) from the at least one discharge tube (3) through at least one discharge element (10, 11), and at least one catalyst (18) for promoting the oxidation of a dissociation product (19) generated when the laser gas (4) is excited, wherein the at least one catalyst (18) is placed inside the at least one discharge tube (3) in the direction of flow of the laser gas (4) within the closed laser gas circuit (K) to reduce the deposition of a decomposition product (20) generated in the at least one discharge tube (3) when the laser gas (4) is excited, compared to being placed inside the at least one discharge tube (3). A discharge tube (3) is positioned at a distance from the discharge tube (3), and when the CO2 beam source (1) is operated, the temperature (T1, T2) of the at least one catalyst (18) is 60°C or higher, or 100°C or higher, or 150°C or higher; the blower (7) is positioned in the center, and the CO2 beam source (1) has a supply arm (8) as a first supply element and a discharge arm (11) as a second discharge element radially alternately in a first plane (12), and in a second plane (13), the discharge tube (3) is alternately connected to each other through the second supply elements (9, 9') and the first discharge element (10), and to cool the laser gas (4), at least one portion (17) of at least one supply arm (8), at least one discharge arm (11), or both of these is formed as a heat exchanger, and at least one inner surface of the at least one supply arm (8) in contact with the laser gas (4) is the at least one A CO2 beam source characterized by being used as a substrate for a catalyst (18). Claim 2 A CO2 beam source according to claim 1, characterized in that the flow path (L) of the laser gas (4) between the downstream end (3') of the at least one discharge tube (3) and the at least one catalyst (18) is 5 cm or more, or 10 cm or 15 cm or more. Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 A CO2 beam source according to claim 1, wherein the at least one catalyst (18) is positioned upstream of the at least one partial region (17) formed as a heat exchanger in at least one supply arm (8), at least one discharge arm (11), or both of these. Claim 7 A CO2 beam source according to claim 1, wherein the CO2 beam source (1) has at least one device (21) for exchanging the at least one catalyst (18). Claim 8 A CO2 beam source according to claim 7, wherein at least one supply arm (8), at least one discharge arm (11), or both of these have at least one closeable opening (21) as a device (21) for exchanging the at least one catalyst (18). Claim 9 A CO2 beam source characterized in that, in claim 1 or 2, the precious metal nanoparticles (22) are platinum nanoparticles, palladium nanoparticles, gold nanoparticles, nanoparticles made of an alloy of these materials, or a mixture of these nanoparticles. Claim 10 A CO2 beam source according to claim 1 or 2, wherein the substrate (23) of the at least one catalyst (18) is a metal substrate or a ceramic substrate. Claim 11 A CO2 beam source according to claim 1 or 2, wherein the coating (24) on which the precious metal nanoparticles (22) are applied is on the substrate (23) of the at least one catalyst (18), and the coating is composed at least partially of a metal oxide, or at least partially of cerium oxide, aluminum oxide, titanium oxide, copper oxide, or a mixture of these materials. Claim 12 A CO2 beam source according to claim 11, characterized in that the coating (24) on the substrate of the catalyst (18) is finely structured to increase the surface area. Claim 13 A CO2 beam source according to claim 1 or 2, wherein the substrate (23) of the catalyst is structured to increase the surface area. Claim 14 A CO2 beam source according to claim 12, wherein the substrate (23) of the catalyst (18) is structured in a honeycomb shape to increase the surface area.

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