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Title:
GAS MIXTURE CONTROL IN OPTICAL AMPLIFIER SYSTEM
Document Type and Number:
WIPO Patent Application WO/2021/204482
Kind Code:
A1
Abstract:
A gas mixture control system for an optical amplifier system includes: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; and a trap structure between the input and the output. The trap structure is configured to interact with the gas mixture received from the optical amplifier system through the input. The trap structure includes a trap surface across which the gas mixture is passed. The trap surface defines an outer layer having a porosity defined by a roughness parameter R that is at least 100.

Inventors:
ZHANG KEVIN (US)
ROKITSKI ROSTISLAV (US)
BROWN DANIEL (US)
PURVIS MICHAEL (US)
HOFSTRA RAMON (NL)
VOORMA HARM-JAN (NL)
Application Number:
PCT/EP2021/055959
Publication Date:
October 14, 2021
Filing Date:
March 10, 2021
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
ASML NETHERLANDS BV (NL)
International Classes:
H01S3/036; G03F7/20; H05G2/00
Foreign References:
US20150222083A12015-08-06
US20100107870A12010-05-06
US4629611A1986-12-16
US4651324A1987-03-17
Attorney, Agent or Firm:
ASML NETHERLANDS B.V. (NL)
Download PDF:
Claims:
CLAIMS

1. A gas mixture control system for an optical amplifier system, the gas mixture control system comprising: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; and a trap structure between the input and the output, the trap structure configured to interact with the gas mixture received from the optical amplifier system through the input; wherein the trap structure includes a trap surface across which the gas mixture is passed, the trap surface defining an outer layer having a porosity defined by a roughness parameter R that is at least 100.

2. The gas mixture control system of claim 1, further comprising a heat exchanger between the input and the output, the heat exchanger configured to adjust a temperature of the modified gas mixture relative to the gas mixture.

3. The gas mixture control system of claim 2, wherein the heat exchanger is a coil type heat exchanger.

4. The gas mixture control system of claim 2, wherein the heat exchanger is a plate coil type heat exchanger.

5. The gas mixture control system of claim 2, wherein the trap structure is formed on the heat exchanger.

6. The gas mixture control system of claim 5, wherein the trap structure is formed at a region of the heat exchanger closest the input, and the trap structure extends over at least 20%, at least 30%, at least 50%, at least 60%, about 50%, or all of the extent of the heat exchanger.

7. The gas mixture control system of claim 2, wherein the heat exchanger includes a heat exchange surface across which the gas mixture flows, the heat exchange surface being thermally conductive.

8. The gas mixture control system of claim 7, wherein the heat exchange surface is coated with a catalyst that has a porosity defined by a roughness parameter R that is at least 100. 9. The gas mixture control system of claim 8, wherein the catalyst is configured to oxidize dissociated molecules within the gas mixture to thereby form the modified gas mixture.

10. The gas mixture control system of claim 8, wherein the catalyst comprises a precious metal.

11. The gas mixture control system of claim 10, wherein the precious metal is selected from the group consisting of platinum, palladium, and gold.

12. The gas mixture control system of claim 7, wherein the trap surface outer layer is a highly porous portion of the heat exchange surface of the heat exchanger.

13. The gas mixture control system of claim 12, wherein the highly porous portion of the heat exchange surface of the heat exchanger includes highly porous copper in which a size of the pores is at least as large as a size of contaminant particles within the gas mixture.

14. The gas mixture control system of claim 12, wherein the highly porous portion of the outer layer is positioned near the input.

15. The gas mixture control system of claim 12, wherein the highly porous portion of the outer layer covers at least 20%, at least 30%, at least 50%, at least 50%, about 50%, or all of the heat exchange surface.

16. A gas mixture control system for an optical amplifier system, the gas mixture control system comprising: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture from the optical amplifier system; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; and a trap structure between the input and the output, the trap structure configured to interact with the gas mixture received from the optical amplifier system through the input; wherein the trap structure includes a trap surface across which the gas mixture is passed, the trap surface defining an outer porous layer on a geometric base layer, and the outer porous layer has an interacting surface area that is at least ten times an interacting surface area of the geometric base layer.

17. The gas mixture control system of claim 16, wherein the geometric base layer includes heat exchange fins.

18. The gas mixture control system of claim 16, wherein the trap surface outer porous layer covers at least 20%, at least 30%, at least 50%, at least 60%, about 50%, or all of the geometric base layer.

19. The gas mixture control system of claim 16, wherein the trap surface outer porous layer covers a first portion of the geometric base layer and a second portion of the geometric base layer lacks the trap surface outer porous layer, wherein the second portion is between the first portion and the output.

20. The gas mixture control system of claim 19, wherein the second portion of the geometric base layer is a thermally conductive surface configured to remove heat from the gas mixture to form the modified gas mixture having a lower temperature than the gas mixture.

21. The gas mixture control system of claim 19, wherein the second portion includes a catalyst configured to oxidize dissociated molecules within the gas mixture to thereby form the modified gas mixture.

22. The gas mixture control system of claim 16, wherein the trap surface outer porous layer covers all of the geometric base layer.

23. The gas mixture control system of claim 16, wherein the outer porous layer has an interacting surface area defined by a porosity with pore size large enough to trap solid particles within the gas mixture and to reduce by half a number of solid particles within the gas mixture that coat the geometric base layer.

24. A gas mixture control system for an optical amplifier system, the gas mixture control system comprising: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture from the optical amplifier system; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; a trap structure between the input and the output, the trap structure configured to interact with the gas mixture received from the optical amplifier system through the input and to capture particles within the gas mixture; and a gas mixture apparatus between the trap structure and the output, the gas mixture apparatus configured to adjust one or more properties of the gas mixture to form the modified gas mixture.

25. The gas mixture control system of claim 24, wherein the trap structure comprises a trap surface defining an outer porous layer, the outer porous layer configured to capture the particles within the gas mixture.

26. The gas mixture control system of claim 25, wherein the outer porous layer of the trap structure is formed on at least a portion of an interacting surface of the gas mixture apparatus.

27. The gas mixture control system of claim 24, wherein the gas mixture apparatus comprises an interacting surface, the interacting surface configured to adjust one or more properties of the gas mixture to form the modified gas mixture.

28. The gas mixture control system of claim 27, wherein the interacting surface is a heat exchange surface.

29. The gas mixture control system of claim 27, wherein the interacting surface is a catalytic converter.

30. The gas mixture control system of claim 29, wherein the gas mixture includes carbon monoxide (CO), and the modified gas mixture is formed by oxidation due to interaction with the catalytic converter and includes carbon dioxide (CO2).

31. The gas mixture control system of claim 24, wherein the particles captured by the trap structure are solid particles produced during operation of the optical amplifier system.

32. The gas mixture control system of claim 31, wherein the solid particles include silicon dioxide (S1O2).

33. A method for producing light, the method comprising: supplying pump energy to a gain medium of at least one optical amplifier in an optical amplifier system to produce an amplified light beam, the gain medium in the form of a gas mixture within a tube; and replenishing the gas mixture during operation of the optical amplifier with a modified gas mixture, replenishing comprising: flowing at least some of the gas mixture out of the tube; removing solid particles from the gas mixture; after removing the solid particles from the gas mixture, interacting the gas mixture with a heat exchanger configured to cool the gas mixture to thereby form the modified gas mixture; and directing the modified gas mixture back into the tube.

34. The method of claim 33, wherein removing solid particles from the gas mixture comprises trapping the solid particles within pores of an outer porous layer formed on the heat exchanger.

35. The method of claim 33, wherein replenishing further comprises oxidizing dissociated molecules of the gas mixture to thereby form the modified gas mixture.

36. The method of claim 35, wherein oxidizing the dissociated molecules of the gas mixture comprises interacting the gas mixture with a catalyst applied to the heat exchanger.

37. A light source comprising: an optical amplifier system comprising one or more optical amplifiers, each optical amplifier including a gain medium in the form of a gas mixture that produces an amplified light beam when energy is supplied from an energy supply to pump the gain medium; and a heat exchanger fluidly connected to receive the gas mixture of the optical amplifier system through a fluid input port and to return a modified gas mixture to the optical amplifier system by way of a fluid output port, the heat exchanger comprising a trap structure configured to remove solid particles from the gas mixture, the solid particles produced during operation of the optical amplifier system, and the heat exchanger configured to, after solid particles have been removed, cool the gas mixture to thereby form the modified gas mixture.

38. The light source of claim 37, wherein the trap structure comprises a trap surface defining an outer porous layer, the outer porous layer configured to remove the solid particles within the gas mixture.

Description:
GAS MIXTURE CONTROL IN OPTICAL AMPLIFIER SYSTEM

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63/008,701, filed April 11, 2020 and titled GAS MIXTURE CONTROL IN OPTICAL AMPLILIER SYSTEM, and which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] The disclosed subject matter relates to a system and method for processing a gas mixture in an optical amplifier system that produces an amplified light beam.

BACKGROUND

[0003] In semiconductor lithography (or photolithography), a lithography exposure apparatus (which is also referred to as a scanner) is a machine that applies a desired pattern onto a target region of the substrate. A patterning device, which is alternatively referred to as a mask or a reticle, can be used to generate the desired pattern to be formed. Transfer of the pattern is typically accomplished by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004] The substrate is irradiated by a light beam, which has a wavelength in the ultraviolet range, somewhere between visible light and x-rays, and thus has a wavelength between about 10 nanometers (nm) to about 400 nm. Thus, the light beam can have a wavelength in the deep ultraviolet (DUV) range, for example, with a wavelength that can fall from about 100 nm to about 400 nm or a wavelength in the extreme ultraviolet (EUV) range, with a wavelength between about 10 nm and about 100 nm. These wavelength ranges are not exact, and there can be overlap between whether light is considered as being DUV or EUV. For example, DUV excimer lasers are commonly used to produce the light beam. Examples of DUV excimer lasers include the krypton fluoride (KrF) laser at a 248 nm wavelength and the argon fluoride (ArF) laser at a 193 nm wavelength.

[0005] In both EUV and DUV systems, an amplified light beam needs to be produced from an optical amplifier system, in which a gain medium is supplied with energy to produce an amplified light beam.

SUMMARY

[0006] In some general aspects, a gas mixture control system for an optical amplifier system includes: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; and a trap structure between the input and the output. The trap structure is configured to interact with the gas mixture received from the optical amplifier system through the input. The trap structure includes a trap surface across which the gas mixture is passed. The trap surface defines an outer layer having a porosity defined by a roughness parameter R that is at least 10 or at least 100.

[0007] Implementations can include one or more of the following features. For example, the gas mixture control system can further include a heat exchanger between the input and the output. The heat exchanger can be configured to adjust a temperature of the modified gas mixture relative to the gas mixture. The heat exchanger can be a coil type heat exchanger. The heat exchanger can be a plate coil type heat exchanger. The trap structure can be formed on the heat exchanger. The trap structure can be formed at a region of the heat exchanger closest the input, and the trap structure can extend over at least 20%, at least 30%, at least 50%, at least 60%, about 50%, or all of the extent of the heat exchanger. The heat exchanger can include a heat exchange surface across which the gas mixture flows, the heat exchange surface being thermally conductive. The heat exchange surface can be coated with a catalyst that has a porosity defined by a roughness parameter R that is at least 10 or at least 100. The catalyst can be configured to oxidize dissociated molecules within the gas mixture to thereby form the modified gas mixture. The catalyst can include a precious metal. The precious metal can be selected from the group consisting of platinum, palladium, and gold. The trap surface outer layer can be a highly porous portion of the heat exchange surface of the heat exchanger. The highly porous portion of the heat exchange surface of the heat exchanger can include highly porous copper in which a size of the pores is at least as large as a size of contaminant particles within the gas mixture. The highly porous portion of the outer layer can be positioned near the input. The highly porous portion of the outer layer can cover at least 20%, at least 30%, at least 50%, at least 50%, about 50%, or all of the heat exchange surface.

[0008] In other general aspects, a gas mixture control system for an optical amplifier system includes: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture from the optical amplifier system; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; and a trap structure between the input and the output. The trap structure is configured to interact with the gas mixture received from the optical amplifier system through the input. The trap structure includes a trap surface across which the gas mixture is passed. The trap surface defines an outer porous layer on a geometric base layer. The outer porous layer has an interacting surface area that is at least ten times an interacting surface area of the geometric base layer.

[0009] Implementations can include one or more of the following features. For example, the geometric base layer can include heat exchange fins.

[0010] The trap surface outer porous layer can cover at least 20%, at least 30%, at least 50%, at least 60%, about 50%, or all of the geometric base layer. [0011] The trap surface outer porous layer can cover a first portion of the geometric base layer and a second portion of the geometric base layer can lack the trap surface outer porous layer. The second portion can be between the first portion and the output. The second portion of the geometric base layer can be a thermally conductive surface configured to remove heat from the gas mixture to form the modified gas mixture having a lower temperature than the gas mixture. The second portion can include a catalyst configured to oxidize dissociated molecules within the gas mixture to thereby form the modified gas mixture.

[0012] The trap surface outer porous layer can cover all of the geometric base layer.

[0013] The outer porous layer can have an interacting surface area defined by a porosity with pore size large enough to trap solid particles within the gas mixture and to reduce by half a number of solid particles within the gas mixture that coat the geometric base layer.

[0014] In other general aspects, a gas mixture control system for an optical amplifier system includes: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture from the optical amplifier system; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; a trap structure between the input and the output; and a gas mixture apparatus between the trap structure and the output. The trap structure is configured to interact with the gas mixture received from the optical amplifier system through the input and to capture particles within the gas mixture. The gas mixture apparatus is configured to adjust one or more properties of the gas mixture to form the modified gas mixture.

[0015] Implementations can include one or more of the following features. For example, the trap structure can include a trap surface defining an outer porous layer. The outer porous layer can be configured to capture the particles within the gas mixture. The outer porous layer of the trap structure can be formed on at least a portion of an interacting surface of the gas mixture apparatus.

[0016] The gas mixture apparatus can include an interacting surface. The interacting surface can be configured to adjust one or more properties of the gas mixture to form the modified gas mixture. The interacting surface can be a heat exchange surface. The interacting surface can be a catalytic converter. The gas mixture can include carbon monoxide (CO), and the modified gas mixture can be formed by oxidation due to interaction with the catalytic converter and can include carbon dioxide (CO2).

[0017] The particles captured by the trap structure can be solid particles produced during operation of the optical amplifier system. The solid particles can include silicon dioxide (S1O 2 ).

[0018] In other general aspects, a method for producing light includes: supplying pump energy to a gain medium of at least one optical amplifier in an optical amplifier system to produce an amplified light beam; and replenishing the gas mixture during operation of the optical amplifier with a modified gas mixture. The gain medium is in the form of a gas mixture within a tube. Replenishing the gas mixture with the modified gas mixture includes: flowing at least some of the gas mixture out of the tube; removing solid particles from the gas mixture; after removing the solid particles from the gas mixture, interacting the gas mixture with a heat exchanger configured to cool the gas mixture to thereby form the modified gas mixture; and directing the modified gas mixture back into the tube. [0019] Implementations can include one or more of the following features. For example, removing solid particles from the gas mixture can include trapping the solid particles within pores of an outer porous layer formed on the heat exchanger.

[0020] Replenishing can further include oxidizing dissociated molecules of the gas mixture to thereby form the modified gas mixture. Oxidizing the dissociated molecules of the gas mixture can include interacting the gas mixture with a catalyst applied to the heat exchanger.

[0021] In other general aspects, a light source includes: an optical amplifier system including one or more optical amplifiers that each include a gain medium in the form of a gas mixture; and a heat exchanger fluidly connected to receive the gas mixture of the optical amplifier system through a fluid input port and to return a modified gas mixture to the optical amplifier system by way of a fluid output port. The gain medium in the form of the gas mixture produces an amplified light beam when energy is supplied from an energy supply to pump the gain medium. The heat exchanger includes a trap structure configured to remove solid particles from the gas mixture. The solid particles are produced during operation of the optical amplifier system. After solid particles have been removed, the heat exchanger is configured to cool the gas mixture to thereby form the modified gas mixture. [0022] Implementations can include one or more of the following features. For example, the trap structure can include a trap surface defining an outer porous layer. The outer porous layer can be configured to remove the solid particles within the gas mixture.

DESCRIPTION OF DRAWINGS

[0023] Fig. 1 is a block diagram of a gas mixture control system that includes a trap structure and a gas mixture apparatus.

[0024] Figs. 2A-2D are a block diagrams of respective implementations of the gas mixture control system of Fig. 1.

[0025] Fig. 3 is a schematic diagram of an implementation of the gas mixture control system of Fig.

1, in which the gas mixture apparatus is a coil type heat exchanger and the trap structure is formed at a region of the coil type heat exchanger.

[0026] Fig. 4 A is a schematic diagram of an implementation of a base material of the heat exchanger of Fig. 3, in which the base material includes a smooth interacting surface.

[0027] Fig. 4B is a schematic diagram of another implementation of the base material of the heat exchanger of Fig. 3, in which the base material has an interacting surface that includes fins. [0028] Fig. 4C is a schematic diagram of another implementation of the base material of the heat exchanger of Fig. 3, in which the base material has an interacting surface that includes a highly porous film.

[0029] Fig. 5 is a schematic diagram of an implementation of the gas mixture control system of Fig.

1, in which the gas mixture apparatus is a plate coil type heat exchanger and the trap structure is formed at a region of the plate coil type heat exchanger.

[0030] Fig. 6 is a block diagram of an implementation of a drive laser system that includes an optical amplifier system and the gas mixture control system of Fig. 1.

[0031] Fig. 7 is a block diagram of an implementation of an extreme ultraviolet (EUV) light system that includes the drive laser system of Fig. 6, a target material delivery system, and a beam delivery system.

[0032] Fig. 8 is a block diagram of an implementation of the optical amplifier system of the drive laser system of Fig. 6.

[0033] Fig. 9 is a block diagram of an implementation of a photolithography system that includes the EUV light system of Fig. 7.

[0034] Fig. 10 is a flow chart of a procedure for producing light in an optical amplifier system by supplying pump energy to a gain medium in the form of a gas mixture and replenishing the gas mixture during operation of the optical amplifier system.

DESCRIPTION

[0035] Referring to Fig. 1, a gas mixture control system 100 includes a trap structure 104 arranged relative to a gas mixture apparatus 106, the gas mixture apparatus 106 being configured to interact with a gas mixture 110 that is received from an optical amplifier system (such as the optical amplifier system 626 shown in Fig. 6 or the optical amplifier system 826 as shown in Fig. 8). The gas mixture 110 includes a gaseous gain medium that is the active medium within the optical amplifier system and thus contributes to the production of an amplified light beam from the optical amplifier system. The gas mixture 110 also includes contaminant particles 111 that can be produced during operation of the optical amplifier system. These contaminant particles 111, if left within the gas mixture 110, can reduce the effectiveness of the interaction between the gas mixture apparatus 106 and the gas mixture 110. The contaminant particles can also reduce the effectiveness of the gaseous gain medium in the gas mixture 110. And, because of this, the lifetime of the gas mixture apparatus 106 is reduced. The trap structure 104 is configured to capture these contaminant particles 111 that are within the gas mixture 110. The trap structure 104 is designed and positioned within the gas mixture control system 100 to prevent or significantly reduce the number of contaminant particles 111 of the gas mixture 110 that interact with the gas mixture apparatus 106. In this way, the gas mixture apparatus 106 is exposed to fewer contaminant particles 111, and the interaction between the gas mixture 110 and the gas mixture apparatus 106 is maintained, and the lifetime of the gas mixture apparatus 106 is increased. The interaction between the gas mixture apparatus 106 and the gas mixture 110 results in an adjustment of one or more properties of the gas mixture 110 to form a modified gas mixture 112 that is fed back into the optical amplifier system.

[0036] The gas mixture control system 100 includes a housing 107 configured to retain the gas mixture 110 flowing through the control system 100 in an interior cavity 101, an input 102 configured to receive the gas mixture 110 from the optical amplifier system, and an output 103 configured to provide or return the modified gas mixture 112 to the optical amplifier system. Each of the input 102 and the output 103 is configured to be fluidly connected to the optical amplifier system. The trap structure 104 is positioned in the interior cavity 101 of housing 107 between the input 102 and the output 103, and the gas mixture apparatus 106 is positioned in the interior cavity 101 of the housing 107 between the trap structure 104 and the output 103. The gas mixture 110 flows generally along or through the control system 100 from the input 102 to the output 103 along the X direction. In this way, the trap structure 104 is arranged so that the gas mixture 110 interacts with the trap structure 104 before interacting with the gas mixture apparatus 106. Thus, the contaminant particles 111 can be removed from the gas mixture 110 before it interacts with the gas mixture apparatus 106.

[0037] The trap structure 104 is any three-dimensional shape or design that has an extent along any or all of the X, Y, and Z directions. The trap structure 104 can be formed as a coating on a surface of another device or the trap structure 104 can be a solid structure. The trap structure 104 includes a trap surface 108 that defines an outer porous layer 105 configured to capture the contaminant particles 111 that are within the gas mixture 110.

[0038] In some implementations, the gas mixture apparatus 106 is a heat exchanger configured to adjust a temperature of the modified gas mixture 112 relative to the gas mixture 110. A heat exchanger transfers thermal energy within the gas mixture 110 into a cooling medium (or coolant). This heat can be transferred from the higher temperature region (the gas mixture 110) to the lower temperature region (coolant) by conduction, convection, radiation, or by any combination of these heat transfer methods. The thermal energy transfer is passive, which means it does not rely on any additional energy to promote the energy transfer.

[0039] In these implementations, the gas mixture 110 is enabled to flow across an interacting surface 109 of the gas mixture apparatus 106, the interacting surface 109 acting as a heat exchange surface. The interacting surface 109 is a heat exchange surface that is thermally conductive. During operation of the optical amplifier system, energy is transferred to the gain medium within the gas mixture 110, and the gas mixture 110 temperature rises. Such a rise in temperature can cause unwanted inefficiencies in the operation of the optical amplifier system. Accordingly, the temperature of the gas mixture 110 is regulated by way of the heat exchanger of the gas mixture apparatus 106 to thereby ensure that the temperature of the optical amplifier system remains within a reasonable range. As a heat exchanger, the gas mixture apparatus 106 can have a shape of a coil, such as shown in Fig. 3, in which coolant flows through an interior of the coil and the interacting surface 109 corresponds to an outer surface of the coil. In other implementations in which the gas mixture apparatus 106 is a heat exchanger, such as shown in Fig. 4, the gas mixture apparatus 106 can have a shape of a plate in which fluid pathways for a coolant are provided within an interior of the plate and the interacting surface 109 corresponds to an outer surface of the plate.

[0040] In some implementations, though not required, the interacting surface 109 of the gas mixture apparatus 106 is coated with a catalyst (such as the highly porous film 424C of Fig. 4C). The catalyst can include a precious metal. In these implementations, the gas mixture apparatus 106 also acts as a catalytic converter.

[0041] The contaminant particles 111 within the gas mixture 110 can be formed during operation of the optical amplifier system. For example, it is possible for solid particles to be etched from surfaces of components within the optical amplifier system that come in contact with the gas mixture 110 as it flows through the components of the optical amplifier system. For example, silicon dioxide (S1O2) or other crystalline structures, substances, or molecules can be etched from the surfaces of components (such as a discharge tube that is made of quartz) in the optical amplifier system. Such solid particles can be transferred with the flow of the gas mixture 110 across these component surfaces. The solid contaminant particles 111 are transferred with the gas mixture 111 into the interior 101 of the gas mixture control system 100 by way of the input 102. Without mitigating the impact of these contaminant particles 111, a layer of the contaminant particles 111 would accumulate on the interacting surface 109 of the gas mixture apparatus 106. And, this layer of the contaminant particles 111 on the interacting surface 109 acts to prevent or reduce the effectiveness of the interaction between gas mixture apparatus 106 and the gas mixture 110. When this happens, the gas mixture apparatus 106 does not adequately adjust one or more properties of the gas mixture 110 to form the modified gas mixture 112 that is provided back to the optical amplifier system. This inadequacy results in a decrease of efficiency of the optical amplifier system, and can ultimately lead to the optical amplifier system ceasing to properly function.

[0042] As a further example, in implementations that include a catalyst coating on the interacting surface 109 of the gas mixture apparatus 106, the gas mixture apparatus 106 also acts as a catalytic converter that is configured to oxidize dissociated molecules within the gas mixture 110. In particular, in some implementations in which the optical amplifier system is a carbon dioxide (CO2) laser amplifier, the gas mixture 110 within the optical amplifier system includes CO2 as the gain medium mixed with other molecules or elements such as helium, nitrogen, hydrogen, or water. During operation of the optical amplifier system, energy is transferred to the CO2 molecules by way of an electric discharge, and these CO2 molecules can dissociate into carbon monoxide (CO) and oxygen (O2). Unless the dissociated molecules are converted back into the original molecules of the gain medium, then the output power of the CO2 laser amplifier is reduced. The catalyst coating of the interacting surface 109 converts the dissociated molecules back into the original molecules by the process of catalytic conversion. If a catalyst coating is formed on the interacting surface 109, it can include a highly porous layer of a precious metal such as, for example, gold (Au), platinum (Pt), or palladium (Pd). A layer of solid contaminant particles 111 forming on the catalyst coating of the interacting surface 109 can thus prevent the dissociated molecules within the gas mixture 110 from interacting with the catalyst coating. Thus, the dissociated molecules within the gas mixture 110 are not adequately oxidized to form the original molecules of the gain medium. In this situation, the optical amplifier system is provided with a modified gas mixture 112 that includes the dissociated molecules and less of the molecules required for optical amplification, and the efficiency of the optical amplifier system is degraded during operation.

[0043] Accordingly, as discussed herein, the gas mixture control system 100 is designed to include the trap structure 104 to interact with the gas mixture 110 that is received from the optical amplifier system through the input 102 and to capture the contaminant particles 111 within the gas mixture 110. To this end, the outer porous layer 105 on the trap surface 108 of the trap structure 104 includes pores that capture or trap the contaminant particles 111 as the gas mixture 110 flows across the trap surface 108. The outer porous layer 105 can be made of any material that can be made into a porous structure and that does not chemically alter or interfere with the gain medium molecules remaining within the gas mixture 110. For example, in some implementations, the porous layer 105 includes a metal or a metal alloy such as, for example, aluminum, copper, or copper alloys. In other implementations, the porous layer 105 includes a metal nitride or a metal carbide. In other implementations, the porous layer 105 includes a precious metal or alloy of precious metal such as, for example, gold, platinum, or palladium.

[0044] A porosity of the outer porous layer 105 is high enough to effectively trap the contaminant particles. The porosity of the layer 105 substantially increases a surface area of the layer 105 beyond what would normally be used for a structure within the interior cavity 101. The porosity is defined by a roughness parameter R, which is a ratio of an area of an interacting surface 105i of the outer porous layer 105 to an area of an interacting surface 114i of a geometric base layer 114. The geometric base layer 114 includes the geometric exterior surface of the trap structure 104. The area of the interacting surface 105i of the outer porous layer 105 is greater than the area of the interacting surface 114i of the geometric base layer 114. In one implementation, in order to trap the contaminant particles 111 from the gas mixture 110 in the outer porous layer 105, the roughness parameter R of the outer porous layer 105 is at least 100. In another implementation, the roughness parameter R of the outer porous layer 105 is at least 10 or in a range of between 10 and 1000. In other words, the interacting surface area of the outer porous layer 105 can be, for example, at least one order of magnitude greater than, at least two orders of magnitude greater than, or at least three orders of magnitude greater than the interacting surface area as the geometric base layer 114. [0045] The interacting surface 105i of the outer porous layer 105 has a porosity defining a pore size (or extent) that is large enough to trap the contaminant particles 111 of the gas mixture 110. In some implementations, the size of pores 105p on the interacting surface 105i can be in the range of sub nanometers to about 100 micrometers. For example, the outer porous layer 105 can reduce the number of contaminant particles 111 that remain in the gas mixture 110 by half. In this way, the pores 105p on the interacting surface 105i of the outer porous layer 105 capture the contaminant particles 111 within the gas mixture 110 by trapping the contaminant particles 111 within the pores as the gas mixture 110 flows across the interacting surface of the outer porous layer 105.

[0046] It is possible for the trap structure 104 and the trap surface 108 (that defines the outer porous layer 105) to perform more than just the function of capturing or containing the contaminant particles 111 that are within the gas mixture 110. For example, the trap surface 108 and the outer porous layer 105 can perform the additional function of oxidation of the dissociated molecules within the gas mixture 110. In such implementations, the size of the pores 105p can vary within a range of sizes across the interacting surface 105i. For example, the sizes of the pores 105p can vary across the interacting surface 105i from a pore size suitable for trapping the contaminant particles 111 to a pore size suitable for oxidizing the dissociated molecules within the gas mixture 110.

[0047] Other arrangements of the trap structure 104 and the gas mixture apparatus 106 are possible. [0048] Referring to Fig. 2A, an implementation 204A of the trap structure 104 is positioned adjacent to an implementation 206A of the gas mixture apparatus 106. The trap structure 204A includes a trap surface 208A that defines an outer porous layer 205A configured to capture the particles 111 that are within the gas mixture 110. The trap structure 204 A is positioned between the input 102 and the gas mixture apparatus 206A such that the contaminant particles 111 are captured within pores of the outer porous layer 205A before the gas mixture 110 interacts with the gas mixture apparatus 206A. The gas mixture apparatus 206 A includes an interacting surface 209 A to interact with the gas mixture 110 and form the modified gas mixture 112 before the modified gas mixture 112 is fed back into the optical source system. The gas mixture apparatus 206A is positioned between the trap structure 204A and the output 103 adjacent to the trap structure 204 A. In this implementation, the interacting surface 209 A of the gas mixture apparatus 206A may or may not include additional functional aspects for interacting with the gas mixture 110.

[0049] Referring to Fig. 2B, in other implementations, the trap structure 104 is formed as a trap structure 204B that is on or integral with an implementation 206B of the gas mixture apparatus 106. The trap structure 204B includes a trap surface 208B that defines an outer porous layer 205B configured to capture the particles 111 that are within the gas mixture 110. The trap structure 204B is formed on the gas mixture apparatus 206B at a region 215B of the gas mixture apparatus 206B that is closest to the input 102. In this way, the trap structure 204B captures the contaminant particles 111 within the gas mixture 110 before the gas mixture 110 interacts with the gas mixture apparatus 206B. The region 215B can be defined along a portion or extent of the gas mixture apparatus 206B so that a part of the gas mixture apparatus 206B (closest to the outlet 103) lacks the trap structure 204B. In the example of Fig. 2B, the trap structure 204B covers or extends along about 50% of the gas mixture apparatus 206B along the X direction. More generally, the trap structure 204B can extend over or cover at least 20%, at least 30%, at least 50%, at least 60%, or all of the extent in the X direction of the gas mixture apparatus 206B.

[0050] The gas mixture apparatus 206B includes an interacting surface 209B to interact with the gas mixture 110 and form the modified gas mixture 112 before the modified gas mixture 112 is fed back into the optical source system. In this implementation, the interacting surface 209B of the gas mixture apparatus 206B includes one or more additional functional aspects (such as a heat exchange function) for interacting with the gas mixture 110.

[0051] Referring to Fig. 2C, the trap structure 104 can be a trap structure 204C that is formed on or integral with a gas mixture apparatus 206C. In this implementation, the trap structure 204C and its outer porous layer 205C extend along the entirety of the gas mixture apparatus 206C. In this way, the outer porous layer 205C of the trap structure 204C performs two functions. The first function is to trap the contaminant particles 111 in the region that is closest to the input 102. The second function is to serve as an interacting surface 209C of the gas mixture apparatus 206C, such interacting surface 209C interacting with the gas mixture 110 to form the modified gas mixture 112 before the modified gas mixture 112 is fed back into the optical source system. As an example, the interacting surface 209C can constitute a heat exchanger configured to adjust the temperature of the modified gas mixture 112 relative to the gas mixture 110.

[0052] Referring to Fig. 2D, in other implementations, the trap structure 104 is a trap structure 204D including an outer porous layer 205D that is formed on or integral with a first portion of a gas mixture apparatus 206D. In these implementations, the interacting surface 209D of the gas mixture apparatus 206D that is not covered by the outer porous layer 205D of the trap structure 204D is formed as a second outer porous layer 213D. The outer porous layer 205D of the trap structure 204D is formed at a region 215D of the gas mixture apparatus 206D that is closest to the input 102. In the example of Fig. 2D, outer porous layer 205D of the trap structure 204D covers about 50% of the extent of the gas mixture apparatus 206D.

[0053] The second outer porous layer 213D interacts with the gas mixture 110 to form the modified gas mixture 112 before the modified gas mixture 112 is fed back into the optical source system.

Because the outer porous layer 205D of the trap structure 204D is positioned to remove (or substantially reduce) the contaminant particles 111 from the gas mixture 110 prior to the gas mixture 110 interacting with the second outer porous layer 213D, the function of the second outer porous layer 213D is not disrupted by the contaminant particles 111.

[0054] An example of this implementation is shown in Fig. 3, which is discussed next. [0055] In Fig. 3, an implementation 300 of the gas mixture control apparatus 100 is designed as a heat exchanger in which the gas mixture apparatus 106 is a coil type heat exchanger 306. In this implementation, the trap structure 104 is formed as an uncoated and highly porous structure 304 at a first region 315a of the heat exchanger 306 that is closest to the input 102. The interacting surface 109 of the heat exchanger 306 is a heat exchange surface 309 formed at a second region 315b.

[0056] The heat exchanger 306 is formed of a base material 322 that is thermally conductive yet not chemically reactive to the gas mixture 110. Moreover, the heat exchange surface 309 can be formed from or on the base material 322. The base material 322 is configured as a hollow tube that is in the shape of a coil whose rotational axis generally extends along the X direction. The base material 322 can be made of, for example, a metal such as copper, aluminum, iron, a precious metal, or alloys of such metals including steel and stainless steel. The base material 322 provides a geometric base layer (a geometry or shape such as a coil) that enables and promotes heat exchange between a coolant 320 (which flows through the coil tube) and the gas mixture 110. Figs. 4A-4C show specific implementations 422A-422C, respectively, of the base material 322.

[0057] The highly porous structure 304 is formed on the heat exchanger 306 at the region 315a by a manufacturing process that is applied to the base material of the heat exchanger 306. For example, the heat exchanger 306 base material can be a metal, such as copper or a copper alloy. The manufacturing process that forms the highly porous structure 304 can include one of etching or electro-chemically treating the base material of the heat exchanger 306 at the region 315a to convert the outermost layer of the base material into a highly porous state. In the example of Fig. 3, the structure 304 is formed to cover about 50% of the base material of heat exchanger 306. The highly porous structure 304 captures the contaminant particles 111 by trapping the contaminant particles 111 within the pores as the gas mixture 110 flows across the interacting surface of the structure 304.

[0058] In one example, the manufacturing process that forms the highly porous structure 304 can include a combined process of loose powder sintering and chemical de-alloying. In this example, the combination of manufacturing processes can form a highly porous structure 304 that is defined by both of a high surface area and a high fluid permeability. Loose powder sintering is performed by pouring or vibrating a metal powder into a mold, then heating the metal powder to a sintering temperature at a compacted pressure. Chemical de-alloying is performed by forming a film of a metal alloy, then etching the film with an etchant to remove one or more alloys from the precursor metal alloy. By combining loose powder sintering and chemical de-alloying, the metal alloy is formed into a highly porous structure with a high permeability by loose powder sintering and a high surface area (including both internal and external surfaces) by chemical de-alloying.

[0059] For example, loose powder sintering can be performed by mixing pure copper (Cu) and pure zinc (Zn) powders in equal parts, and a percentage by volume (for example, 50%, 60%, 70%, or 80%) of potassium carbonate (K 2 CO 3 ) powder. The mixture can be compacted at a pressure of 200 Megapascals (MPa) and sintered at a temperature of 850 °C for 4 hours to form a highly porous and highly permeable Cu-Zn alloy. Chemical de-alloying can then be performed by immersing the Cu-Zn alloy in hydrogen chloride (HC1) to etch the zinc, forming a highly porous copper structure with high permeability and high surface area. When the heat exchanger 306 base material is copper, the highly porous structure 304 can be formed on the heat exchanger 306 in this way.

[0060] As mentioned, the heat exchange surface 309 of the heat exchanger 306 is formed at the second region 315b. The heat exchange surface 309 is in the shape of a coil of a base material 322. In some implementations, such as shown in Fig. 4A, a surface 409A of the coil shape is a smooth surface of a base material 422A. A smooth surface 409A formed into the coil shape promotes heat exchange between the coolant 320 and the gas mixture 110 that flows over the surface 409 A.

[0061] Referring to Fig. 4B, to improve the heat exchange between the coolant 320 and the gas mixture 110, a surface area of the interacting surface 409B is increased beyond that of the smooth surface 409 A by adding ridges or fins 424B to the base material 422B. Heat exchange can be greatly determined by the shape and design of these fins 424B. Thus, it is possible to optimize the shape and size of the fins 424B to help to maximize the transfer of heat from the gas mixture 110 to the coolant 320.

[0062] Referring to Fig. 4C, in some implementations, and in order to improve the heat exchange between the coolant 320 and the gas mixture 110, a surface area of the interacting surface 409C is increased beyond that of the smooth surface 409A by adding a highly porous layer or film 424C on top of the base material 422C. The highly porous film 424C can be formed of precious metal (such as gold, platinum, or palladium) or an alloy of a precious metal.

[0063] The highly porous film 424C is coated on the interacting surface 409C using any suitable manufacturing process. The manufacturing process that forms the highly porous film 424C can include one of electrochemical de-alloying, chemical de-alloying, electrochemical deposition, and sputter deposition.

[0064] For example, a highly porous film of gold can be formed as the highly porous film 424C by first coating a thin film of a gold-silver (Au-Ag) alloy on the interacting surface 409C, then de alloying the Au-Ag alloy film with a nitric acid under anionic conditions to prepare the highly porous film 424C of gold.

[0065] In another example, the highly porous film of gold can be formed as the highly porous film 424C by a multi-cyclic process of electrodeposition and electrochemical de-alloying. First, in this example, a thin film of a gold-zinc (Au-Zn) alloy is formed on the interacting surface 409C by electrodeposition. Second, the Au-Zn alloy film is electrochemically de-alloyed. Next, another thin film of Au-Zn alloy is formed on the interacting surface 409C by electrodeposition. The steps of electrodeposition and electrochemical de-alloying are repeated in cycles until the highly porous film 424C of gold is formed. Depending on the manufacturing method used, a range of pore sizes of the highly porous film 424C can be achieved. In addition, a working temperature of the highly porous film 424C is dependent on the selected manufacturing process that prepares the highly porous film 424C.

[0066] In some implementations, the highly porous film 424C can also function as a catalyst such that the gas mixture 110 is oxidized as it interacts with the highly porous film 424C to form the modified gas mixture 112. In these implementations, the highly porous film 424C is made up of a catalyst, which can be any substance that causes or accelerates the chemical reaction (in this case, oxidation), without being affected. Thus, the catalyst of the film 424C participates in the reaction but is neither a reactant nor a product of the reaction it catalyzes. For example, in these implementations, the highly porous film 424C is a metal substance such as platinum, rhodium, palladium, or gold, or mixtures of any of these elements. Additionally, for example, the highly porous film 424C functioning as a catalyst can be defined by a roughness parameter R that is at least 100.

[0067] Referring again to Fig. 3, the heat exchanger 306 includes the uncoated and highly porous structure 304 at the region 315a that is closest to the input 102. In some implementations, the heat exchanger 306 can also include the highly porous film 424C as a coating on the heat exchange surface 309 at the region 315b that is closest to the output 103. For example, the highly porous film 424C can be formed to cover about 50% of the extent of heat exchanger 306.

[0068] In operation, the gas mixture 110 flows across the uncoated and highly porous structure 304 and the contaminant particles 111 within the gas mixture 110 are trapped within the pores of the structure 304. Thus, as the gas mixture 110 travels across the heat exchanger 306 generally along the X direction, it will contain fewer and fewer of the contaminant particles 111, and by the time the gas mixture 110 reaches the highly porous film 424C coated on the heat exchange surface 309, contaminant particles 111 within the gas mixture 110 are less likely to clog the pores of the film 424C and the film 424C can operate more efficiently as a heat exchanger. In implementations that include the highly porous film 424C acting as a catalyst, the gas mixture 110 is more efficiently oxidized by the highly porous film 424C when the gas mixture 110 flows across the highly porous film 424C at the region 315b. The modified gas mixture 112 output from the heat exchange surface 309 is fed back into the optical source system.

[0069] Referring to Fig. 5, an implementation 500 of the gas mixture control apparatus 100 is designed as a heat exchanger in which the gas mixture apparatus 106 is a plate coil type heat exchanger 506. The trap structure 104 is formed as an uncoated and highly porous structure 504 at a first region 515a of the plate coil type heat exchanger 506 that is closest to the input 102. The interacting surface 109 of the heat exchanger 506 is a heat exchange surface 509 formed at a second region 515b.

[0070] Similar to the heat exchange surface 309 of Fig. 3, the heat exchange surface 509 is formed of a base material 522 and can be formed from or on the base material 522. In the example of Fig. 5, the base material 522 is configured as a plate that is embedded with hollow tubes that extend linearly in the X direction and are offset along the Y direction. Each hollow tube connects with an adjacent hollow tube at one end by a connecting portion of hollow tube that extends in the Y direction. The base material 522 promotes heat exchange between a coolant 520 (which flows through the hollow tubes embedded in the plate) and the gas mixture 110. The base material 522 can be one of the implementations 422A-422C as shown and described with reference to Figs. 4A-4C, respectively. [0071] Also similar to the highly porous structure 304 of Fig. 3, the highly porous structure 504 is formed on the heat exchanger 506 at the region 515a by one of the manufacturing processes (described with reference to Fig. 3), including etching or electro-chemically treating the base material 522 of the heat exchanger 506 at the region 515a. In the example of Fig. 5, the highly porous structure 504 is formed to cover about 50% of the base material 522 of the heat exchanger 506.

[0072] In operation, the gas mixture 110 flows across the uncoated and highly porous structure 504 and the contaminant particles 111 within the gas mixture 110 are trapped within the pores of the highly porous structure 504. The plate coil type heat exchanger 506 provides an expansive surface area of the highly porous structure 504, allowing the highly porous structure 504 to capture more of the contaminant particles 111 (compared to the coil type heat exchanger 306 of Fig. 3). Thus, as the gas mixture 110 travels across the plate coil type heat exchanger 506 generally along the X direction, it will contain fewer and fewer of the contaminant particles 111. Additionally, the expansive surface area of the plate coil type heat exchanger 506 allows the heat exchanger 506 to remove heat from the gas mixture 110 more efficiently and at an increased rate.

[0073] In implementations that include the highly porous film 424C coated on the heat exchange surface 509, contaminant particles 111 within the gas mixture 110 are less likely to clog the pores of the film 424C by the time the gas mixture 110 reaches the highly porous film 424C. Moreover, the plate coil type heat exchanger 506 provides a more expansive surface area of the film 424C (compared to the coil type heat exchanger 306). Thus, the film 424C can operate more efficiently as a heat exchanger. In implementations that include the highly porous film 424C acting as a catalyst, the gas mixture 110 is more efficiently oxidized by the highly porous film 424C when the gas mixture 110 flows across the highly porous film 424C at the region 315b. Because the plate coil type heat exchanger 506 provides the expansive surface area of the film 424C, the film 424C can include a large number of catalytic sites, increasing the rate of oxidation of the gas mixture 110 when the gas mixture 110 flows across the highly porous film 424C.

[0074] Referring to Fig. 6, the gas mixture control system 100 can be designed to remove contaminant particles 111 from a gas mixture 610 produced during operation of an optical amplifier system 626 in a drive laser system 635. The drive laser system 635 includes the optical amplifier system 626 along with other optical components such as pre-amplifiers. The drive laser system 635 also include the gas mixture control system 100. The optical amplifier system 626 includes at least one optical amplifier 629 having the gas mixture 610, which includes a gain medium of molecules capable of optically amplifying the desired wavelength at a high gain, an excitation source such as an electrical source, and internal optics. The gas mixture 610 within the optical amplifier 629 is contained within an enclosed volume 627 such as a tube. The gain medium within the gas mixture 610 of the optical amplifier system 626 contributes to the production of an amplified light beam 631 from the optical amplifier system 626.

[0075] The tube can be hermetically sealed. Moreover, the tube can house an energy source configured to supply energy to the gain medium of the gas mixture 610 within the tube. For example, the energy source can include a pair of electrodes that form a potential difference and, in operation, excite the gain medium.

[0076] The drive laser system 635 can also include a controller 634 that performs various tasks such as monitoring components within the optical amplifier 629 and the gas mixture control system 100, performing analyses or calculations based on the monitored information, and providing instructions to components within the drive laser system 635 based on the results of the analysis or calculations. [0077] The gas mixture 610 also includes the contaminant particles 111 that can be produced during operation of the optical amplifier system 626. The contaminant particles 111 can be formed during operation of the optical amplifier system 626. For example, solid particles can be etched from surfaces of the components within the optical amplifier system 626 that come in contact with the gas mixture 610 as it flows through the components. For example, silicon dioxide (S1O2) or other crystalline structures, substances, or molecules can be etched from the surfaces of the enclosed volume 627 in the optical amplifier system 626. The solid contaminant particles 111 can reduce the efficiency of the optical amplifier system 626, disrupting the production of the amplified light beam 631 from the optical amplifier system 626.

[0078] The gas mixture 610 from the optical amplifier 629 flows out of the enclosed volume 627 of the optical amplifier 629 through an enclosed pipe or tube 632 toward the gas mixture control system 100 and flows into the interior 101 of the housing 107 through the input 102 as gas mixture 110. After interacting with the trap structure 104 and the gas mixture apparatus 106, a modified gas mixture 612 flows out of the of the housing 107 through the output 103, and flows through an enclosed pipe or tube 633 and into the enclosed volume 627 of the optical amplifier 629 to be reused during operation and production of the amplified light beam 631. The pipes 632, 633 can be made of a material such as, for example, stainless steel, aluminum, or a metal alloy, that does not react to the gas mixture 610 or the modified gas mixture 612 that flow through the pipes 632, 633, respectively.

[0079] The trap structure 104 captures the contaminant particles 111 that are within the gas mixture 610 when the gas mixture interacts with the trap structure 104 of the gas mixture control system 100. The trap structure 104 is designed and positioned within the gas mixture control system 100 to prevent or significantly reduce the number of the contaminant particles 111 that interact with the gas mixture apparatus 106 and reduce the efficiency of the optical amplifier system 626. As described above, the outer porous layer 105 on the trap surface 108 of the trap structure 104 includes pores that capture or trap the contaminant particles 111 as the gas mixture 610 flows across the trap surface 108. In this way, the gas mixture control system 100 removes contaminant particles 111 from the gas mixture 610 produced during operation of the optical amplifier system 626, increasing the efficiency and lifetime of the optical amplifier system 626.

[0080] The gas mixture apparatus 106 of the gas mixture control system 100 adjusts one or more properties of the gas mixture 610 to form the modified gas mixture 612 that is fed back into the optical amplifier system 626. For example, the gas mixture apparatus 106 can be a heat exchanger (such as the heat exchanger 306 of Fig. 3 or the heat exchanger 506 of Fig. 5) used to adjust the temperature of the gas mixture 110 to form the modified gas mixture 612. Thus, for example, the controller 634 could monitor the temperature of the gas mixture 110 within the pipe 632, determine the temperature of the gas mixture 610, and send a signal to the gas mixture apparatus 106 to adjust the temperature of the gas mixture 610 to a particular value to form the modified gas mixture 612 that is fed back to the optical amplifier system 626 through the pipe 633.

[0081] During operation of the optical amplifier system 626, energy is transferred to the gain medium within the gas mixture 610, and the gas mixture 610 temperature rises. The rise in temperature of the gas mixture 610 can cause additional inefficiencies in the operation of the optical amplifier system 626. Accordingly, in the example that includes the gas mixture apparatus 106 as a heat exchanger, the temperature of the gas mixture 610 is regulated by the gas mixture apparatus 106 to thereby ensure that the temperature of the optical amplifier system 626 remains within a reasonable range.

[0082] The gas mixture control system 100 can also be used to remove contaminant particles 111 from the gas mixture 610 produced during operation of the optical amplifier system 626 as part of an extreme ultraviolet (EUV) light system. Referring to Fig. 7, an EUV light system 740 includes the drive laser system 635 of Fig. 6 (a light source) that produces the amplified light beam 631, a target material delivery system 748 configured to produce a target material 743, and a beam delivery system 745 that is configured to receive the amplified light beam 631 emitted from the drive laser system 635 and to direct the amplified light beam 631 toward a target location 750, which receives the target material 743. The beam delivery system 745 includes a beam transport system 746 and a final focus assembly 747 that focuses the amplified light beam 631 at a focal location 742. The interaction between the amplified light beam 631 and the target material 743 produces plasma 744 that emits EUV light or radiation 75 L A light collector 755 collects and directs collected EUV light 752 toward an optical apparatus 754 such as a lithography tool.

[0083] The extreme ultraviolet light system 740 or the drive laser system 635 includes the gas mixture control system 100 that receives the gas mixture 110 that includes the contaminant particles 111 from the optical amplifier 629, removes the contaminant particles 111 within the gas mixture 610, and re-introduces the modified gas mixture 612 back into the optical amplifier 629. The gas mixture control system 100 can also adjust one or more properties of the gas mixture 610 to form the modified gas mixture 612 that is fed back into the optical amplifier 629. In this way, the gas mixture 610 is effectively maintained for use by the optical amplifier 629.

[0084] The optical amplifier 629 may or may not have laser mirrors or other feedback devices that form a laser cavity. Thus, the drive laser system 635 produces the amplified light beam 631 due to the population inversion in the gain media of the optical amplifiers 629 even if there is no laser cavity. Moreover, the drive laser system 635 can produce an amplified light beam 631 that is a coherent laser beam if there is a laser cavity to provide enough feedback to the drive laser system 635. The term “amplified light beam” encompasses one or more of: light from the drive laser system 635 that is merely amplified but not necessarily a coherent laser oscillation and light from the drive laser system 635 that is amplified and is also a coherent laser oscillation.

[0085] The optical amplifiers 629 in the drive laser system 635 can include as a gas mixture 610 a filling gas that includes CO2 and can amplify light at a wavelength of between about 9100 and about 11000 nm, and in particular, at about 10600 nm. Suitable amplifiers and lasers for use in the drive laser system 635 can include a pulsed laser device, for example, a pulsed, gas-discharge CO2 laser device producing radiation at about 9300 nm or about 10600 nm, for example, with DC or RF excitation, operating at relatively high power, for example, lOkW or higher and high pulse repetition rate, for example, 50kHz or more. The optical amplifiers 629 in the drive laser system 635 can also include a cooling system such as a liquid-cooling system that can be used when operating the drive laser system 635 at higher powers. The liquid-cooling system can employ water, which can be kept at a lower temperature than the optical amplifiers.

[0086] In some implementations, such as shown in Fig. 8, an exemplary optical amplifier system 826 includes a first amplifier that acts as a pre-amplifier 862, and a plurality 861 of optical amplifiers 829. The pre-amplifier 862 can be a diffusion-cooled CO2 laser such as the TruCoax CO2 laser produced by TRUMPF Inc. of Farmington, CT. The optical amplifiers 829 within the plurality 861 can be fast axial flow high-power CO2 lasers with wear-free gas circulation and capacitive radio-frequency excitation such as the TruFlow CO2 laser produced by TRUMPF Inc. of Farmington, CT.

[0087] Referring again to Fig. 7, the final focus assembly 747 focuses the amplified light beam 631 so that the diameter of the beam 631 is at a minimum in the focal region 742. In other words, the final focus assembly 747 causes the radiation in the amplified light beam 631 to converge as it propagates toward the focal region 742 in a direction 749 of propagation. In the absence of a target material 743, the radiation in the amplified light beam 631 diverges as the beam 631 propagates away from the focal region 742 in the direction 749. [0088] The final focus assembly 747 is that part of the beam delivery system 745 that modifies the wavefront of the amplified light beam 631 to change its beam divergence and cause it to focus at the focal location 742. The final focus assembly 747 can include one or more transmissive optical elements each having a curved surface, or one or more reflective optical elements, each having a curved surface.

[0089] The light collector 755 captures at least some of the EUV light 751 emitted from the plasma 744 and directs the captured light 752 to an optical apparatus 754 that uses the captured extreme ultraviolet light 752 in a specific application. The light collector 755 has a first focus at or near the target location 750 or the focal location 742, and a second focus at an intermediate location 753 (also called an intermediate focus) where the EUV light 752 can be output from the extreme ultraviolet light system 740 and can be input to the optical apparatus 754.

[0090] The amplified light beam 631 is a pulsed light beam and it includes at least a first set of pulses that are focused at the focal location 742 to enable interaction between the amplified light beam 631 and the target material 743 to cause the target material 743 to be converted into the plasma 744 that emits extreme ultraviolet light 751. The focal location 742 needs to be close enough to the target material 743 to enable the amplified light beam 631 to interact with the target material 743 in a manner that causes the target material 743 to be converted into the plasma that emits extreme ultraviolet light 751. Thus, it is possible for the focal location 742 to overlap the target location 750, but not actually overlap with the target material 743. In other implementations, the focal location 742 overlaps the target material 743.

[0091] The amplified light beam 631 can optionally include a second set of pulses that condition the target material 743 in some way, but do not interact to cause the target material 743 to be converted into a plasma that emits extreme ultraviolet light 751. This second set of pulses can be interspersed spatially and temporally with the first set of pulses along the same beam path. For example, the second set of pulses can be configured to interact with the target material 743 before it reaches the target location 750 so as to modify a geometric distribution of the target material 743 before it reaches the target location 750. The second set of pulses can be referred to as “pre-pulses” or a pre-pulse beam.

[0092] Moreover, while only one amplified light beam 631 is shown in Fig. 7 as being directed to the target location 750, in other implementations, the drive laser system 635 can produce two or more amplified light beams 631 along spatially distinct beam paths or overlapping beam paths that are temporally displaced from each other. For example, a pre-pulse beam can be directed toward a first target location and a main beam can be directed toward a second target location (the target location 750) at the output of the final focus assembly 747.

[0093] Referring to Fig. 9, in some implementations, the extreme ultraviolet light system 740 is used in a photolithography system 960 to supply extreme ultraviolet (EUV) light 752 to an optical apparatus such as a lithography exposure apparatus 965. The photolithography system 960 includes one or more master controllers 968 connected to one or more control or actuation systems 963 that are connected to components within the extreme ultraviolet light system 740.

[0094] The EUV light 752 is directed to the lithography exposure apparatus 965, which uses this light 752 to create a pattern on a wafer 966. The EUV light 752 may be directed through an illuminator 967, which can include optical elements such as reflective optical elements that modify aspects such as the wavefront curvature of the EUV light 752. For example, the illuminator 967 can include one or more reflectors coated with a special coating (such as a multilayer coating) that is able to reflect as much EUV light 752 as possible. Because such reflectors tend to absorb some of the EUV light 752, it may be advantageous to use as few as possible.

[0095] The EUV light 752 exiting the illuminator 967 is directed to a reflective mask 970. The EUV light 752 exiting the reflective mask 970 is directed through a set 968 of projection optics, which include one or more reflectors coated with a special coating for reflecting the EUV light 752 and also are configured to focus the EUV light 752 to the wafer 966. The projection optics set 968 adjusts the range of angles for the EUV light 752 impinging on the wafer 966, and enables the image transfer to occur from the reflective mask 970 to the photoresist on the wafer 966. For example, the projection optics set 968 can include a series of four to six curved mirrors, reducing the size of the image and focusing the image onto the wafer 966. Each of these mirrors bends the EUV light 752 slightly to form the image that will be transferred onto the wafer 966.

[0096] Moreover, the lithography exposure apparatus 967 can include, among other features, a lithography controller 972, air conditioning devices, and power supplies for the various electrical components. In some implementations, the wafer 966 is carried on a wafer stage 973 and an immersion medium 974 can be supplied to cover the wafer 966 for immersion lithography. In other implementations, the wafer 966 is not covered by an immersion medium 974.

[0097] The wafer 966 can be processed using any number of process steps, which can be one or more of a combination of process steps such as etching, deposition, and lithography processes with a different mask to create a pattern of openings (such as grooves, channels, or holes) in the material of the wafer or in materials deposited on the wafer.

[0098] Referring to Fig. 10, a procedure 1080 is performed for producing light. The procedure 1080 can be performed with respect to the drive laser system 635 that includes the optical amplifier system 626 and the gas mixture control system 100 (Figs. 1 6). The procedure 1080 can also be performed with respect to any one of the implementations of the gas mixture control system 100, including, for example, the gas mixture control systems 200A, 200B, 200C, and 200D (of respective Figs. 2A-2D), and the gas mixture control systems 500 and 600 that are each designed as a heat exchanger (respectively, Figs. 5 and 6); and the implementation of the optical amplifier system 826 (Fig. 8). In the following, the procedure 1080 is discussed with respect to the drive laser system 635, the optical amplifier system 626, and the gas mixture control system 100.

[0099] The procedure 1080 includes supplying pump energy to a gain medium of an optical amplifier to produce the amplified light beam (1081). For example, pump energy can be supplied to the gas mixture 610 within the enclosed volume 627 of the optical amplifier 629 in the optical amplifier system 626 to produce the amplified light beam 631. The pump energy can be supplied to the gain medium within the gas mixture 610 by way of the electrodes. The amplified light beam 631 is produced by the population inversion in the gain medium of the gas mixture 610 within the optical amplifier 629.

[0100] During operation of the optical amplifier, the gas mixture is replenished with the modified gas mixture (1082). For example, during operation of the optical amplifier system 626, the pump energy that is supplied to the gain medium within the gas mixture 610 causes the gas mixture 610 temperature to rise, and this rise in temperature of the gas mixture 610 can cause inefficiencies in the operation of the optical amplifier system 626. Thus, the gas mixture 610 is replaced with the modified gas mixture 612, which is at a lower temperature than the gas mixture 610.

[0101] In order to replenish the gas mixture 610 with the modified gas mixture 612, at least some of the gas mixture is flowed out of the enclosed volume (1083). For example, the gas mixture 610 from the optical amplifier 629 flows out of the enclosed volume 627 of the optical amplifier 629 through the enclosed pipe or tube 632 toward the gas mixture control system 100. The gas mixture flows into the interior 101 of the housing 107 of the gas mixture control system 100 through the input 102.

[0102] The solid contaminant particles are removed from the gas mixture (1085). As an example, the trap structure 104 captures the solid contaminant particles 111 that are within the gas mixture 610 when the gas mixture 610 interacts with the trap structure 104 of the gas mixture control system 100.

As described above, in some implementations, the outer porous layer 105 on the trap surface 108 of the trap structure 104 includes pores that capture or trap the solid contaminant particles 111 as the gas mixture 610 flows across the trap surface 108.

[0103] After the solid contaminant particles are removed from the gas mixture (1085), the gas mixture is interacted with a heat exchanger configured to cool the gas mixture to thereby form the modified gas mixture (1087). For example, the gas mixture 610 interacts with the gas mixture apparatus 106 of the gas mixture control system 100.

[0104] The modified gas mixture is directed back into the enclosed volume of the optical amplifier system (1089) to thereby replenish the gas mixture with the modified gas mixture during operation of the optical amplifier system (1082). For example, after interacting with the trap structure 104 and the gas mixture apparatus 106, the modified gas mixture 612 flows out of the interior 101 of the housing 107 through the output 103, and flows through an enclosed pipe or tube 633 and into the enclosed volume 627. [0105] In this way, the optical amplifier 629 is exhausted of the gas mixture 610 that is operating at an inefficient temperature, and is replenished with the modified gas mixture 612 that has a decreased temperature. Moreover, this replenishment is performed more efficiently because the contaminant particles 111 are removed from the gas mixture 610 prior to the gas mixture 610 being cooled by the heat exchanger of the gas mixture apparatus 106. Overall, the efficient replenishment of the gas mixture 610 with the modified gas mixture 612 during operation of the optical amplifier system 626 increases the efficiency of the optical amplifier system 626 and provides for efficient production of the amplified light beam 631 by the optical amplifier system 626.

[0106] Other aspects of the invention are set out in the following numbered clauses.

1. A gas mixture control system for an optical amplifier system, the gas mixture control system comprising: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; and a trap structure between the input and the output, the trap structure configured to interact with the gas mixture received from the optical amplifier system through the input; wherein the trap structure includes a trap surface across which the gas mixture is passed, the trap surface defining an outer layer having a porosity defined by a roughness parameter R that is at least 100

2. The gas mixture control system of clause 1, further comprising a heat exchanger between the input and the output, the heat exchanger configured to adjust a temperature of the modified gas mixture relative to the gas mixture.

3. The gas mixture control system of clause 2, wherein the heat exchanger is a coil type heat exchanger.

4. The gas mixture control system of clause 2, wherein the heat exchanger is a plate coil type heat exchanger.

5. The gas mixture control system of clause 2, wherein the trap structure is formed on the heat exchanger.

6. The gas mixture control system of clause 5, wherein the trap structure is formed at a region of the heat exchanger closest the input, and the trap structure extends over at least 20%, at least 30%, at least 50%, at least 60%, about 50%, or all of the extent of the heat exchanger.

7. The gas mixture control system of clause 2, wherein the heat exchanger includes a heat exchange surface across which the gas mixture flows, the heat exchange surface being thermally conductive.

8. The gas mixture control system of clause 7, wherein the heat exchange surface is coated with a catalyst that has a porosity defined by a roughness parameter R that is at least 100. 9. The gas mixture control system of clause 8, wherein the catalyst is configured to oxidize dissociated molecules within the gas mixture to thereby form the modified gas mixture.

10. The gas mixture control system of clause 8, wherein the catalyst comprises a precious metal.

11. The gas mixture control system of clause 10, wherein the precious metal is selected from the group consisting of platinum, palladium, and gold.

12. The gas mixture control system of clause 7, wherein the trap surface outer layer is a highly porous portion of the heat exchange surface of the heat exchanger.

13. The gas mixture control system of clause 12, wherein the highly porous portion of the heat exchange surface of the heat exchanger includes highly porous copper in which a size of the pores is at least as large as a size of contaminant particles within the gas mixture.

14. The gas mixture control system of clause 12, wherein the highly porous portion of the outer layer is positioned near the input.

15. The gas mixture control system of clause 12, wherein the highly porous portion of the outer layer covers at least 20%, at least 30%, at least 50%, at least 50%, about 50%, or all of the heat exchange surface.

16. A gas mixture control system for an optical amplifier system, the gas mixture control system comprising: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture from the optical amplifier system; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; and a trap structure between the input and the output, the trap structure configured to interact with the gas mixture received from the optical amplifier system through the input; wherein the trap structure includes a trap surface across which the gas mixture is passed, the trap surface defining an outer porous layer on a geometric base layer, and the outer porous layer has an interacting surface area that is at least ten times an interacting surface area of the geometric base layer.

17. The gas mixture control system of clause 16, wherein the geometric base layer includes heat exchange fins.

18. The gas mixture control system of clause 16, wherein the trap surface outer porous layer covers at least 20%, at least 30%, at least 50%, at least 60%, about 50%, or all of the geometric base layer.

19. The gas mixture control system of clause 16, wherein the trap surface outer porous layer covers a first portion of the geometric base layer and a second portion of the geometric base layer lacks the trap surface outer porous layer, wherein the second portion is between the first portion and the output. 20. The gas mixture control system of clause 19, wherein the second portion of the geometric base layer is a thermally conductive surface configured to remove heat from the gas mixture to form the modified gas mixture having a lower temperature than the gas mixture.

21. The gas mixture control system of clause 19, wherein the second portion includes a catalyst configured to oxidize dissociated molecules within the gas mixture to thereby form the modified gas mixture.

22. The gas mixture control system of clause 16, wherein the trap surface outer porous layer covers all of the geometric base layer.

23. The gas mixture control system of clause 16, wherein the outer porous layer has an interacting surface area defined by a porosity with pore size large enough to trap solid particles within the gas mixture and to reduce by half a number of solid particles within the gas mixture that coat the geometric base layer.

24. A gas mixture control system for an optical amplifier system, the gas mixture control system comprising: an input configured to be fluidly connected to the optical amplifier system to receive a gas mixture from the optical amplifier system; an output configured to be fluidly connected to the optical amplifier system to provide a modified gas mixture to the optical amplifier system; a trap structure between the input and the output, the trap structure configured to interact with the gas mixture received from the optical amplifier system through the input and to capture particles within the gas mixture; and a gas mixture apparatus between the trap structure and the output, the gas mixture apparatus configured to adjust one or more properties of the gas mixture to form the modified gas mixture.

25. The gas mixture control system of clause 24, wherein the trap structure comprises a trap surface defining an outer porous layer, the outer porous layer configured to capture the particles within the gas mixture.

26. The gas mixture control system of clause 25, wherein the outer porous layer of the trap structure is formed on at least a portion of an interacting surface of the gas mixture apparatus.

27. The gas mixture control system of clause 24, wherein the gas mixture apparatus comprises an interacting surface, the interacting surface configured to adjust one or more properties of the gas mixture to form the modified gas mixture.

28. The gas mixture control system of clause 27, wherein the interacting surface is a heat exchange surface.

29. The gas mixture control system of clause 27, wherein the interacting surface is a catalytic converter. 30. The gas mixture control system of clause 29, wherein the gas mixture includes carbon monoxide (CO), and the modified gas mixture is formed by oxidation due to interaction with the catalytic converter and includes carbon dioxide (CO2).

31. The gas mixture control system of clause 24, wherein the particles captured by the trap structure are solid particles produced during operation of the optical amplifier system.

32. The gas mixture control system of clause 31, wherein the solid particles include silicon dioxide (S1O2).

33. A method for producing light, the method comprising: supplying pump energy to a gain medium of at least one optical amplifier in an optical amplifier system to produce an amplified light beam, the gain medium in the form of a gas mixture within a tube; and replenishing the gas mixture during operation of the optical amplifier with a modified gas mixture, replenishing comprising: flowing at least some of the gas mixture out of the tube; removing solid particles from the gas mixture; after removing the solid particles from the gas mixture, interacting the gas mixture with a heat exchanger configured to cool the gas mixture to thereby form the modified gas mixture; and directing the modified gas mixture back into the tube.

34. The method of clause 33, wherein removing solid particles from the gas mixture comprises trapping the solid particles within pores of an outer porous layer formed on the heat exchanger.

35. The method of clause 33, wherein replenishing further comprises oxidizing dissociated molecules of the gas mixture to thereby form the modified gas mixture.

36. The method of clause 35, wherein oxidizing the dissociated molecules of the gas mixture comprises interacting the gas mixture with a catalyst applied to the heat exchanger.

37. A light source comprising: an optical amplifier system comprising one or more optical amplifiers, each optical amplifier including a gain medium in the form of a gas mixture that produces an amplified light beam when energy is supplied from an energy supply to pump the gain medium; and a heat exchanger fluidly connected to receive the gas mixture of the optical amplifier system through a fluid input port and to return a modified gas mixture to the optical amplifier system by way of a fluid output port, the heat exchanger comprising a trap structure configured to remove solid particles from the gas mixture, the solid particles produced during operation of the optical amplifier system, and the heat exchanger configured to, after solid particles have been removed, cool the gas mixture to thereby form the modified gas mixture.

38. The light source of clause 37, wherein the trap structure comprises a trap surface defining an outer porous layer, the outer porous layer configured to remove the solid particles within the gas mixture. [0107] Other implementations are within the scope of the following claims.