Optical amplifier

Abstract

The optical amplifier comprises an amplification chamber, a first pump, a first heat exchanger, a second pump, and a novel catalyst module. The amplification chamber is configured to receive a laser beam and output an amplified laser beam. The first pump is configured to pump a gain medium into the gain medium system. The second pump is configured to pump a cooling fluid into the first heat exchanger. The first heat exchanger is positioned to transfer heat from the gain medium to the cooling fluid after the gain medium has passed through the amplification chamber. The novel catalyst module comprises a body and a catalyst disposed within the body. The body constitutes part of the gain medium system and is located downstream of the amplification chamber and upstream of the first heat exchanger. During use, the gain medium is adjacent to or in contact with the catalyst.

Description

Technical Field

[0001] (Cross - reference to related applications)

[0001] This application claims the priority of European application 23168804.5 filed on April 19, 2023, the entire content of which is incorporated herein by reference.

[0002]

[0002] The present invention relates to an optical amplifier configured to amplify a laser beam. This optical amplifier may form part of an amplification system of a laser system. The laser system may comprise a carbon dioxide (CO2) laser which may form part of a laser - produced plasma (LPP) radiation source. And the LPP radiation source may form part of a lithography system, i.e., may supply radiation to a lithography apparatus. The present invention also relates to a catalyst module for an optical amplifier.

Background Art

[0003]

[0003] A lithography apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus may project a pattern in a patterning device (e.g., a mask) onto a layer of radiation - sensitive material (resist) provided on a substrate.

[0004]

[0004] To project a pattern onto a substrate, a lithography apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features that can be formed on the substrate. Using a lithography apparatus that uses extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 - 20 nm, for example 6.7 nm or 13.5 nm, it may be possible to form smaller features on the substrate than using a lithography apparatus that uses radiation having a wavelength of, for example, 193 nm.

[0005]

[0005] One known type of EUV radiation source is a laser-generated plasma (LPP) source, in which a tin droplet is irradiated with a laser pulse to form a tin plasma that emits EUV radiation. To generate the tin plasma, the laser pulse is usually high power. To obtain the desired power, the laser pulse is usually amplified in an amplification system that has multiple optical amplifiers (e.g., single-pass amplifiers arranged in series).

[0006]

[0006] It may be desirable to provide alternative or improved optical amplifiers and components thereof that can at least partially solve one or more problems in known configurations, whether or not they are specified herein. [Overview of the project]

[0007]

[0007] According to a first aspect of the present disclosure, an optical amplifier is provided configured to amplify a laser beam, comprising: an amplification chamber configured to receive a laser beam at an inlet and output an amplified laser beam from an outlet; a first pump configured to feed a gain medium into a gain medium system comprising the amplification chamber; a first heat exchanger, which constitutes part of the gain medium system and is configured to transfer heat from the gain medium in the gain medium system to a cooling fluid in a cooling system after the gain medium has passed through the amplification chamber; a second pump configured to feed a cooling fluid to the first heat exchanger to exchange heat with the gain medium; and a catalyst module, wherein the catalyst module is a body, which constitutes part of the gain medium system and is disposed downstream of the amplification chamber so that the gain medium fed into the amplification chamber subsequently flows through the body and upstream of the first heat exchanger so that the gain medium fed into the body subsequently flows through the first heat exchanger; and a catalyst disposed within the body so that the gain medium is adjacent to or in contact with the gain medium when the gain medium is fed into the gain medium system by the first pump.

[0008]

[0008] The optical amplifier may constitute part of the carbon dioxide (CO2) laser. The gain medium may include a gas mixture. For example, the gain medium may include a mixture of any combination of carbon dioxide, helium and / or nitrogen. The cooling fluid may include a liquid and / or gas. The cooling fluid may include water. The first heat exchanger may be called a gas cooler.

[0009]

[0009] The amplification chamber of an optical amplifier is typically not a resonant cavity (in contrast to the main oscillation chamber of a laser). An optical amplifier may be a single-pass system in which, for example, the laser beam passes through the amplification chamber only once.

[0010]

[0010] The advantages of the optical amplifier according to the first embodiment will now be considered.

[0011]

[0011] In the plasma generation process within the optical amplifier, the gain medium may be depleted, which may reduce the optical amplification that can be achieved by the optical amplifier. For example, in a CO2 laser, CO2 is composed of carbon monoxide (CO) and oxygen (oxygen molecules O2 and oxygen ions O2). - It can be broken down into (both) CO2, CO2, and / or O2. Furthermore, it can be broken down into CO2, O2, and / or O2. - The accumulation of CO2 negatively impacts laser performance for two reasons: (a) it reduces the energy transfer rate of CO2 excitation from vibrationally excited nitrogen and carbon monoxide, and (b) it negatively affects the electron energy distribution.

[0012]

[0012] However, the dissociation process of the gain medium is typically a reversible reaction. Therefore, the dissociation of the gain medium (which depletes it) is accompanied by a recombination process that replenishes it. For example, recombination of CO and oxygen may occur. Thus, in an optical amplifier with a closed-loop gain medium system, the dissociation and recombination of the gain medium proceed until equilibrium is reached. There are many factors that affect the equilibrium level of dissociation, such as gas pressure, mixture composition, and radio frequency (RF) power density of the optical amplifier.

[0013]

[0013] The undesirable effects of decomposition can be addressed at least partially by incorporating a CO oxidation catalyst into the photoamplifier that facilitates the conversion of the dissociation products back to CO2. For example, in one known configuration, a gold-plated layer is provided on the gas-flow side of a heat exchanger (see first heat exchanger) provided for cooling the gain medium gas.

[0014]

[0014] In contrast, the main body of the catalyst module of the photoamplifier according to the first embodiment is located downstream of the amplification chamber and upstream of the first heat exchanger (not inside the first heat exchanger). This has many advantages over known configurations (in which the catalyst is located inside the heat exchanger).

[0015]

[0015] Firstly, the lifespan of the catalyst is finite because its chemical reactivity decreases over time. Therefore, it is desirable to replace the catalyst during the lifespan of the photoamplifier, but availability is lost during catalyst replacement. The main body of the catalyst module is located upstream of the first heat exchanger, so it can be removed (to facilitate catalyst replacement) without having to disturb the cooling system of the photoamplifier (i.e., draining, opening, leak testing and refilling). In other words, by positioning the catalyst material away from the first heat exchanger (and thus not in contact with the pipes of the first heat exchanger through which a cooling fluid such as water flows), the catalyst material can be replaced without disturbing the cooling system. Advantageously, this significantly reduces the time required for catalyst replacement and, consequently, significantly reduces the loss of availability of the photoamplifier.

[0016]

[0016] Secondly, the main body of the catalyst module is located downstream of the amplification chamber and upstream of the first heat exchanger, so that it is in the hottest part of the gain medium system (after it has been heated during optical amplification and before it has been cooled in the heat exchanger). This is advantageous because these types of catalysts generally perform better at high temperatures. Furthermore, since the catalyst is in contact only with the gain medium (and not with, for example, the pipes carrying the cooling fluid), it is thought that the catalyst life may be extended and the frequency of catalyst replacement will be reduced.

[0017]

[0017] The gain medium system of the optical amplifier comprises a first pump, an amplification chamber, a catalyst module, and a first heat exchanger. The gain medium system of the optical amplifier may be a closed-loop system.

[0018]

[0018] The cooling system for the optical amplifier comprises a second pump and a first heat exchanger. The cooling system for the optical amplifier may be a closed-loop system and may further include a heat sink configured to dissipate heat from the cooling fluid within the cooling system. For example, the cooling system may be a two-phase system and the heat sink may include a condenser.

[0019]

[0019] It should be understood that the placement of the catalyst module body downstream of the amplification chamber means that most, or substantially all, of the gain medium supplied to the amplification chamber subsequently flows through the body. Furthermore, it should be understood that the placement of the catalyst module body upstream of the first heat exchanger means that most, or substantially all, of the gain medium supplied to the body subsequently flows through the first heat exchanger.

[0020]

[0020] The catalyst module may be removable from the photoamplifier independently of the first heat exchanger.

[0021]

[0021] Advantageously, this allows the catalyst module to be removed without interfering with the cooling system of the optical amplifier (i.e., draining, opening, leak testing, and refilling).

[0022]

[0022] According to a second aspect of the present disclosure, there is an optical amplifier configured to amplify a laser beam, comprising: an amplification chamber configured to receive a laser beam at an inlet and output an amplified laser beam from an outlet; a first pump configured to feed a gain medium into a gain medium system comprising the amplification chamber; at least one first heat exchanger constituting part of the gain medium system and configured to transfer heat from the gain medium in the gain medium system to a cooling fluid in a cooling system; at least one second pump configured to feed a cooling fluid to at least one first heat exchanger to exchange heat with the gain medium; and a catalyst module, wherein the catalyst module comprises a body constituting part of the gain medium system and a catalyst disposed within the body such that the gain medium is adjacent to or in contact with the gain medium when the gain medium is fed into the gain medium system by the first pump, and is removable from the optical amplifier independently of the at least one first heat exchanger.

[0023]

[0023] The photoamplifier according to a second aspect of the present disclosure is advantageous because the catalyst module is removable from the photoamplifier independently of at least one first heat exchanger. Preferably, the catalyst module is removable from the photoamplifier independently of all such first heat exchangers. Advantageously, this allows the catalyst module to be removed without interfering with the cooling system of the photoamplifier (i.e., draining, opening, leak testing and refilling).

[0024]

[0024] According to a third aspect of the present disclosure, there is an optical amplifier configured to amplify a laser beam, comprising: an amplification chamber configured to receive a laser beam at an inlet and output an amplified laser beam from an outlet; a first pump configured to feed a gain medium into a gain medium system comprising the amplification chamber; at least one first heat exchanger, which constitutes part of the gain medium system and is configured to transfer heat from the gain medium in the gain medium system to a cooling fluid in a cooling system; at least one second pump configured to feed a cooling fluid to at least one first heat exchanger to exchange heat with the gain medium; and a catalyst module, wherein the catalyst module comprises a body, which constitutes part of the gain medium system; and a catalyst disposed within the body, which is adjacent to or in contact with the gain medium when the gain medium is fed into the gain medium system by the first pump, and the optical amplifier constitutes part of the gain medium system but does not constitute part of the cooling system.

[0025]

[0025] The optical amplifier according to a third aspect of the present disclosure is advantageous because the catalyst module does not constitute part of the cooling system. Advantageously, this allows the catalyst module to be removed without interfering with the cooling system of the optical amplifier (i.e., venting, opening, leak testing, and refilling).

[0026]

[0026] According to a fourth aspect of the present disclosure, an optical amplifier configured to amplify a laser beam, comprising: an amplification chamber configured to receive the laser beam at an inlet and output an amplified laser beam from an outlet; a first pump configured to feed a gain medium into a gain medium system including the amplification chamber; at least one first heat exchanger configured to form part of the gain medium system and transfer heat of the gain medium in the gain medium system to a cooling fluid in a cooling system; at least one second pump configured to feed a cooling fluid into the at least one first heat exchanger to exchange heat with the gain medium; and a catalyst module. The catalyst module includes a main body forming part of the gain medium system, and a catalyst disposed in the main body such that the gain medium is adjacent to or in contact with the catalyst when the gain medium is fed into the gain medium system by the first pump. An optical amplifier is provided that is separate from the at least one first heat exchanger.

[0027]

[0027] The optical amplifier according to the fourth aspect of the present disclosure is advantageous in that the catalyst module is separate from the at least one first heat exchanger. Preferably, the catalyst module is separate from all such first heat exchangers. Advantageously, this allows the catalyst module to be removed without disturbing (i.e., draining, opening, leak testing, and refilling) the cooling system of the optical amplifier.

[0028]

[0028] In the optical amplifier according to any one of the first, second, or fourth aspects of the present disclosure, the catalyst module may form part of the gain medium system and may not form part of the cooling system.

[0029]

[0029] Advantageously, this allows the catalyst module to be removed without disturbing (i.e., draining, opening, leak testing, and refilling) the cooling system of the optical amplifier.

[0030]

[0030] In any one of the first, second, or third embodiments of the present disclosure, the catalyst module may be separate from the first heat exchanger.

[0031]

[0031] Advantageously, this allows the catalyst module to be removed without interfering with the cooling system of the photoamplifier (i.e., venting, opening, leak testing and refilling).

[0032]

[0032] In any of the first, second, third, or fourth aspects of this disclosure, the catalyst module may be located outside the optical amplifier.

[0033]

[0033] By providing a catalyst module located outside the optical amplifier, the catalyst module becomes accessible from outside the optical amplifier. Advantageously, this allows access to the catalyst module so that the catalyst can be replaced without having to disassemble the optical amplifier, significantly reducing the time required for catalyst replacement (and the time the optical amplifier is unavailable). Furthermore, providing a catalyst module located outside the optical amplifier simplifies the interface between the catalyst and the rest of the optical amplifier, potentially reducing the risk of contamination of the optical amplifier when the catalyst is being replaced.

[0034]

[0034] In any of the first, second, third, or fourth aspects of the present disclosure, the body of the catalyst module may define an inlet, an outlet, and a conduit or passage extending between the inlet and the outlet.

[0035]

[0035] In this specification, the direction extending generally from the inlet to the outlet (i.e., along the conduit or passage) may be referred to as the longitudinal direction. Similarly, the direction generally perpendicular to the longitudinal direction (i.e., the cross-sectional area of ​​the conduit or passage) may be referred to as the transverse direction. As will be further discussed below, in some embodiments the conduit or passage is not linear, and therefore, generally, the longitudinal and transverse directions vary along the conduit or passage.

[0036]

[0036] The catalyst may be located at least partially within the conduit or passage.

[0037]

[0037] The catalyst may be porous and may extend substantially over the entire lateral extent of the conduit or passage.

[0038]

[0038] For example, the catalyst may include a honeycomb structure or the like.

[0039]

[0039] In some embodiments, the body of the catalyst module, which constitutes part of the gain medium flow circuit, is shaped to reduce the pressure drop in the gas medium flow circuit (compared to known configurations) while maintaining the pressure drop on the catalyst, in order to satisfy the requirements of optical output and energy efficiency. As a result, the amount of power required to circulate the gain medium is reduced (compared to known configurations with the same mass flow rate). Furthermore, in some embodiments, the body of the catalyst module is shaped to guide the flow of the gain medium to the first heat exchanger more effectively (compared to known configurations), thereby further improving the thermal performance of the gain medium and reducing the pressure drop in the gain medium flow circuit. These advantages may be achieved by the following features relating to the shape of the body of the catalyst module, as will be considered below.

[0040]

[0040] In any of the first, second, third, or fourth aspects of this disclosure, the conduits or passages defined by the body of the catalyst module may be nonlinear.

[0041]

[0041] When the conduit or passage defined by the body of the catalyst module is non-linear, it should be understood that the inlet direction and outlet direction of the body of the catalyst module are different. For example, the body of the catalyst module may be in the shape of an elbow (i.e., a roughly L-shaped pipe) or a U-shaped pipe.

[0042]

[0042] The conduits or passages defined by the main body may follow at least one curved or bent portion, and the longitudinal spread of the catalyst may be greater in the portion of the conduit or passage closer to the outer part of the curved or bent portion, and smaller in the portion of the conduit or passage closer to the inner part of the curved or bent portion.

[0043]

[0043] Advantageously, this configuration allows for a more uniform pressure distribution downstream of the curved or bent section. When there are no obstructions in the conduit or passage, the pressure of the gain medium (fluid) downstream of the curved or bent section is higher closer to the surface defining the outer portion of the curved or bent section. Such a pressure gradient can be reduced by providing an obstruction (catalyst) with a larger longitudinal spread in the portion of the conduit or passage closer to the outer portion of the curved or bent section. This may result in more efficient cooling of the working medium in the first heat exchanger.

[0044]

[0044] In any of the first, second, third, or fourth aspects of the present disclosure, the lateral extension of the conduit or passage defined by the body of the catalyst module may increase in the flow direction of the gain medium.

[0045]

[0045] In other words, the cross-sectional area of ​​the conduit or passage defined by the body of the catalyst module may increase in the direction of the gain medium flow. This may promote laminar flow and reduce the amount of work that the first pump needs to do to achieve a predetermined mass flow rate of the gain medium.

[0046]

[0046] In any of the first, second, third, or fourth aspects of this disclosure, the catalyst may include gold or platinum.

[0047]

[0047] In any of the first, second, third, or fourth aspects of the present disclosure, the optical amplifier may comprise a plurality of amplification chambers, each configured to receive a laser beam at an inlet and output an amplified laser beam from an outlet, and the first pump may be configured to feed a gain medium into the gain medium system comprising the plurality of amplification chambers.

[0048]

[0048] In any of the first, second, third, or fourth aspects of the present disclosure, the optical amplifier may comprise a plurality of first heat exchangers, each constituting part of a gain medium system and configured to transfer heat from the gain medium in the gain medium system to a cooling fluid in a cooling system (for example, after the gain medium has passed through its or each amplification chamber).

[0049]

[0049] Each of the multiple first heat exchangers may receive a gain medium from one or more amplification chambers. For example, each of the multiple first heat exchangers may receive a gain medium from two amplification chambers.

[0050]

[0050] In any of the first, second, third, or fourth aspects of the present disclosure, the optical amplifier may comprise a plurality of catalyst modules, each of which comprises a body (optionally located downstream of at least one amplification chamber and upstream of a first heat exchanger) that constitutes part of a gain medium system, and a catalyst disposed within the body such that the gain medium is adjacent to or in contact with the gain medium when the gain medium is fed into the gain medium system by a first pump.

[0051]

[0051] According to a fifth aspect of the present disclosure, a catalyst module for an optical amplifier is provided according to any one of the first, second, third, or fourth aspects of the present disclosure.

[0052]

[0052] According to a sixth aspect of the present disclosure, an amplification system for use in a laser system is provided, comprising a plurality of optical amplifiers, wherein at least one of the plurality of optical amplifiers or each optical amplifier comprises an optical amplifier according to any one of the first, second, third, or fourth aspects of the present disclosure.

[0053]

[0053] According to a seventh aspect of the present disclosure, a laser system is provided comprising a laser configured to generate a laser beam and an amplification system according to a sixth aspect of the present disclosure configured to amplify the laser beam.

[0054]

[0054] According to an eighth aspect of the present disclosure, a radiation system is provided comprising an EUV radiation source and a laser system according to a seventh aspect of the present disclosure.

[0055]

[0055] According to a ninth aspect of the present disclosure, a radiation system is provided comprising an EUV radiation source and a laser system having an optical amplifier according to any one of the first, second, third, or fourth aspects of the present disclosure.

[0056]

[0056] According to a tenth aspect of the present disclosure, a lithography system is provided comprising a radiation system according to an eighth or ninth aspect of the present disclosure and a lithography apparatus. [Brief explanation of the drawing]

[0057]

[0057] Embodiments of the present invention will now be described with reference to the attached schematic diagrams, which are merely examples.

[0058] [Figure 1] This shows a lithography system equipped with a lithography device and a radiation source. [Figure 2] Figure 1 shows an exemplary amplification system for use in a laser system of the radiation system. [Figure 3] This is a schematic diagram of a first exemplary optical amplifier according to an embodiment of the present disclosure. [Figure 4]This is a schematic diagram of a second exemplary optical amplifier according to an embodiment of the present disclosure, which is a modified example of the optical amplifier shown in Figure 3. [Figure 5] This is a schematic diagram of a third exemplary optical amplifier according to an embodiment of the present disclosure, which is a modified example of the optical amplifier shown in Figure 3. [Figure 6] This is a perspective view of an exemplary optical amplifier according to an embodiment of the present disclosure. [Figures 7A-7B] Figure 6 shows a perspective view and a partial cross-sectional view of a catalyst module that constitutes a part of the optical amplifier shown in the figure. [Figure 8] Figure 6 shows the optical path defined by the optical amplifier. [Figure 9A] Figure 6 shows the gas channel within the optical amplifier, along which the gain medium flows as part of the gain medium system. [Figure 9B] Figure 6 shows an exploded view of the gas flow path within the optical amplifier, divided into a first part of the gain medium system and a second part of the gain medium system. [Modes for carrying out the invention]

[0059]

[0058] Figure 1 shows a lithography system comprising a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply this EUV radiation beam B to the lithography apparatus LA. The lithography apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0060]

[0059] The illumination system IL is configured to adjust the EUV radiation beam B before it is incident on the patterning device MA. For this reason, the illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. Both the faceted field mirror device 10 and the faceted pupil mirror device 11 give the EUV radiation beam B a desired cross-sectional shape and a desired intensity distribution. In addition to or instead of the faceted field mirror device 10 and the faceted pupil mirror device 11, the illumination system IL may include other mirrors or devices.

[0061]

[0060] After being adjusted in this manner, the EUV radiation beam B interacts with the patterning device MA. This interaction results in the generation of a patterned EUV radiation beam B'. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. For this purpose, the projection system PS may include a number of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image of a feature smaller than the corresponding feature in the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is shown in Figure 1 as having only two mirrors 13, 14, the projection system PS may include various numbers of mirrors (e.g., 6 or 8 mirrors).

[0062]

[0061] The substrate W may include a pre-formed pattern. In such cases, the lithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pre-formed pattern on the substrate W.

[0063]

[0062] A small amount of gas (e.g., hydrogen) at a relative vacuum, i.e., a pressure significantly below atmospheric pressure, may be supplied into the radiation source SO, the illumination system IL, and / or the projection system PS.

[0064]

[0063] The radiation source SO shown in Figure 1 is of a type that may be called, for example, a laser-generated plasma (LPP) source. The laser system 1, which may include, for example, a CO2 laser, is configured to store energy in a fuel such as tin (Sn) supplied from, for example, a fuel ejector 3, via a laser beam 2. In the following description, tin will be mentioned, but any suitable fuel may be used. The fuel may be, for example, in liquid form, or may be, for example, a metal or alloy. The fuel ejector 3 may include a nozzle configured to guide tin, for example, in the form of droplets, along a trajectory toward a plasma-forming region 4. The laser beam 2 is incident on the tin in the plasma-forming region 4. The storage of laser energy in the tin generates a tin plasma 7 in the plasma-forming region 4. During the de-excitation and recombination of electrons by plasma ions, radiation including EUV radiation is emitted from the plasma 7.

[0065]

[0064] EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 includes, for example, a perionormal incident radiation collector 5 (sometimes more commonly called a normal incident radiation collector). The collector 5 may have a multilayer mirror structure configured to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an elliptical configuration with two foci. The first of the foci may be in the plasma formation region 4, and the second of the foci may be in the intermediate focus 6, which will be discussed below.

[0066]

[0065] The laser system 1 may be spatially separated from the radiation source SO. In such cases, the laser beam 2 may be delivered from the laser system 1 to the radiation source SO by a beam delivery system (not shown) which includes, for example, a suitable guide mirror and / or beam expander and / or other optical systems. The laser system 1, the radiation source SO, and the beam delivery system may together be considered a radiation system.

[0067]

[0066] The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at an intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present in the plasma formation region 4. The image at the intermediate focus 6 functions as a virtual radiation source for the illumination system IL. The radiation source SO is positioned such that the intermediate focus 6 is located at or near the aperture 8 of the closed structure 9 of the radiation source SO.

[0068]

[0067] Figure 1 shows the radiation source SO as a laser-generated plasma (LPP) source, but EUV radiation may be generated using any suitable radiation source such as a discharge-generated plasma (DPP) source or a free electron laser (FEL).

[0069]

[0068] Figure 2 shows an exemplary amplification system 16 for use in the laser system 1 of the radiation source SO shown in Figure 1. The amplification system 16 is sometimes called an optical amplification system. The laser system 1 may include a laser 18, such as a CO2 laser. The laser 18 may be configured to generate a laser beam 20. The laser 18 may be called a seed laser 18, and the laser beam 20 may be called a seed laser beam 20. The laser beam 20 may contain multiple pulses. The laser system 1 may include one or more optical elements, such as one or more mirrors, beam expanders, lenses and / or other elements (not shown), for guiding the laser beam to the amplification system 16.

[0070]

[0069] The amplification system 16 comprises a plurality of optical amplifiers 24a to 24d, four of which are shown in Figure 2. However, it should be understood that in other embodiments, the system may have more or fewer optical amplifiers than four. Generally, the amplification system 16 comprises at least one optical amplifier. Each of the optical amplifiers 24a to 24d is configured to amplify the laser beam 20 to produce an output laser beam 21. The output laser beam 21 may form a laser beam 2 that is incident on the tin in the plasma formation region 4, as shown in Figure 1.

[0071]

[0070] The amplification system 16 includes an optical system 26. The optical system 26 is sometimes called a relay optical system. The optical system 26 is configured to optically couple or connect at least one of the optical amplifiers 24a to 24d to at least one other of the optical amplifiers 24a to 24d. In this embodiment, the optical system 26 is configured to optically couple or connect the amplifiers 24a to 24d in series with each other. For example, the optical system 26 may be configured to optically couple or connect the optical amplifiers 24a to 24d with each other so that the laser beam 20 is directed from the first amplifier 24a to the second amplifier 24b, from the second amplifier 24b to the third amplifier 24c, and from the third amplifier 24c to the fourth amplifier 24d. The optical system 26 may include multiple optical elements such as multiple mirrors, lenses, telescopes and / or the like. The optical amplifiers 24a to 24d may be arranged to sequentially amplify the laser beam 20.

[0072]

[0071] The amplification system 16 may include an input section 25a into which, for example, a laser beam 20 is incident. The amplification system 16 may also include an output section 25b into which, for example, an amplified laser beam 21 is emitted. At the input section 25a of the amplification system 16, the laser beam may have an output of approximately 100W to 200W, for example, approximately 140W. At the output section 25b of the amplification system 16, the amplified laser beam 21 may have an output of approximately 25kW to 50kW.

[0073]

[0072] Some embodiments of the present invention relate to optical amplifiers, as described below. An exemplary optical amplifier 100 according to an embodiment of the present disclosure is schematically shown in Figure 3. The optical amplifier 100 may constitute part of the laser system 1 shown in Figure 1 and / or the amplification system 16 shown in Figure 2. For example, any or all of the optical amplifiers 24a to 24d shown in Figure 2 may include the optical amplifier 100 shown in Figure 3.

[0074]

[0073] The optical amplifier 100 is configured to amplify the laser beam. That is, the optical amplifier 100 is configured to receive an input laser beam 102 and output an amplified laser beam 104. The optical amplifier comprises an amplification chamber 106, a first pump 108, a first heat exchanger 110, a second pump 112, and a catalyst module 114. The amplification chamber 106 is sometimes referred to as the laser chamber.

[0075]

[0074] The amplification chamber 106 is configured to receive the laser beam 102 at the inlet and output the amplified laser beam 104 from the outlet. Those skilled in the art will understand that the amplification chamber 106 further comprises at least two electrodes and a power supply capable of applying a voltage between at least two electrodes, but for ease of understanding, these features are omitted in the schematic diagram of this optical amplifier 100.

[0076]

[0075] The first pump 108 is configured to feed the gain medium into the gain medium system 116, which includes the amplification chamber 106. The gain medium system 116 of the optical amplifier 100 comprises the first pump 108, the amplification chamber 106, the catalyst module 114, and the first heat exchanger 110. The gain medium system 116 of the optical amplifier 100 is a closed-loop system. The optical amplifier 100 may constitute part of a carbon dioxide (CO2) laser. The gain medium may include a gas mixture. For example, the gain medium may include a mixture of any combination of carbon dioxide, helium, and / or nitrogen.

[0077]

[0076] The first heat exchanger 110 (which constitutes part of the gain medium system 116) is configured to transfer the heat of the gain medium in the gain medium system 116 to the cooling fluid in the cooling system 118 after the gain medium has passed through the amplification chamber 106. The first heat exchanger 110 is sometimes called a gas cooler.

[0078]

[0077] Optionally, as shown in Figure 3, the gain medium system 116 of the optical amplifier 100 may further include a second heat exchanger 120 configured to transfer heat from the gain medium in the gain medium system 116 to a cooling fluid in the cooling system 118 after the gain medium has passed through the first pump 108 and before it enters the amplification chamber 106. The second heat exchanger 120 may constitute part of the same cooling system 118 as the first heat exchanger 110. Alternatively, the second heat exchanger 120 may constitute part of a separate cooling system from the cooling system of the first heat exchanger 110.

[0079]

[0078] The second pump is configured to feed the cooling fluid to the first heat exchanger 110 (which constitutes part of the cooling system 118) to exchange heat with the gain medium. The cooling system 118 of the optical amplifier 100 comprises the second pump 112 and the first heat exchanger 110. Optionally, as shown in Figure 3, the cooling system 118 of the optical amplifier 100 may be a closed-loop system and may further include a heat sink 122 configured to dissipate heat from the cooling fluid in the cooling system 118. For example, the cooling system may be a two-phase system and the heat sink 122 may include a condenser. Optionally, as shown in Figure 3, the cooling system 118 of the optical amplifier 100 may further include a reservoir or tank 124 for containing the cooling fluid. The cooling fluid may include liquid and / or gas. The cooling fluid may include water.

[0080]

[0079] (Referring to Figures 6, 7A and 7B) As will be described in more detail below, the catalyst module 114 comprises a body and a catalyst 126 disposed within the body. The catalyst module 114 constitutes part of the gain medium system 116 and is disposed downstream of the amplification chamber 106 and upstream of the first heat exchanger 110. The catalyst 126 is disposed within the body such that the gain medium is adjacent to or in contact with the catalyst 126 when the gain medium is supplied into the gain medium system 116 by the first pump 108.

[0081]

[0080] The catalyst 126 may contain any suitable material. In some embodiments, the catalyst 126 may contain gold and / or platinum.

[0082]

[0081] The optical amplifier 100, schematically shown in Figure 3, is advantageous as will be explained below.

[0083]

[0082] In the plasma generation process within the optical amplifier 100, the gain medium may be depleted, which may reduce the optical amplification that can be achieved by the optical amplifier 100. For example, in a CO2 laser, CO2 is composed of carbon monoxide (CO) and oxygen (oxygen molecules O2 and oxygen ions O2). - It can be broken down into (both) CO2, CO2, and / or O2. Furthermore, it can be broken down into CO2, O2, and / or O2. - The accumulation of CO2 negatively impacts laser performance for two reasons: (a) it reduces the energy transfer rate of CO2 excitation from vibrationally excited nitrogen and carbon monoxide, and (b) it negatively affects the electron energy distribution.

[0084]

[0083] However, the dissociation process of the gain medium is typically a reversible reaction. Therefore, the dissociation of the gain medium (which depletes it) is accompanied by a recombination process that replenishes it. For example, recombination of CO and oxygen may occur. Thus, in the optical amplifier 100 having a closed-loop gain medium system 116, the dissociation and recombination of the gain medium proceed until equilibrium is reached. There are many factors that affect the equilibrium level of dissociation, such as gas pressure, composition of the mixture, and radio frequency (RF) power density of the optical amplifier.

[0085]

[0084] The undesirable effects of decomposition can be addressed at least partially by incorporating a CO catalyst into the photoamplifier that facilitates the conversion of the dissociation products back to CO2. For example, in one known configuration, a gold-plated layer is provided on the gas flow side of a heat exchanger (see first heat exchanger 110) provided for cooling the gain medium gas.

[0086]

[0085] In contrast, the main body of the catalyst module 114 of the optical amplifier 100 shown in Figure 3 is located downstream of the amplification chamber 106 and upstream of the first heat exchanger 110 (not inside the first heat exchanger). This has many advantages over known configurations (in which the catalyst is located inside the heat exchanger).

[0087]

[0086] Firstly, the lifespan of the catalyst 126 is finite because its chemical reactivity decreases over time. Therefore, it is desirable to replace the catalyst 126 during the lifespan of the optical amplifier as the laser output decreases, but availability is lost during catalyst replacement. The body of the catalyst module 114 is located upstream of the first heat exchanger 110, so it can be removed (to facilitate catalyst replacement) without having to disturb the cooling system 118 of the optical amplifier 100 (i.e., draining, opening, leak testing and refilling). In other words, by positioning the catalyst material 126 away from the first heat exchanger 110 (and thus not in contact with the pipes of the first heat exchanger 110 through which a cooling fluid such as water flows), the catalyst material 126 can be replaced without disturbing the cooling system 118. Generally, when the catalyst material 126 is removed or replaced, the gain medium system 116 is disturbed, and after such disturbance, a leak test of the gain medium system 116 may be performed, and the gain medium system 116 may be refilled. However, in some embodiments, an isolation valve may be provided to isolate the catalyst module 114 from the rest of the gain medium system 116. Advantageously, this may allow the catalyst module 114 to be removed without completely opening the gain medium system 116, which may mean that leak testing of the gain medium system 116 is not required. Advantageously, this significantly reduces the time required to replace the catalyst 126, and consequently, significantly reduces the loss of availability of the optical amplifier 100.

[0088]

[0087] Secondly, the body of the catalyst module 114 is located downstream of the amplification chamber 106 and upstream of the first heat exchanger 110, so that it is in the hottest part of the gain medium system 116 (after being heated during optical amplification in the amplification chamber 106 and before being cooled in the first heat exchanger 110). This is advantageous because these types of catalysts generally perform better at high temperatures. Furthermore, since the catalyst is in contact only with the gain medium (and not with, for example, the pipes carrying the cooling fluid), the lifespan of the catalyst 126 may be extended and the frequency of needing to replace the catalyst 126 may be reduced.

[0089]

[0088] In some embodiments of the optical amplifier 100, the catalyst module 114 is positioned so that it can be removed without disturbing the cooling system 118 of the optical amplifier 100 (i.e., draining, opening, leak testing, and refilling). For example, the catalyst module 114 may constitute part of the gain medium system 116 rather than part of the cooling system 118. Additionally or alternatively, the catalyst module 114 may be removable from the optical amplifier 100 independently of the first heat exchanger 110. Additionally or alternatively, the catalyst module 114 may be separate from the first heat exchanger 110.

[0090]

[0089] (Referring to Figures 6 to 9) In some embodiments of the optical amplifier 100, the catalyst module 114 may be located outside the optical amplifier 100. By providing the catalyst module 114 located outside the optical amplifier 110, the catalyst module 114 becomes accessible from outside the optical amplifier 100. Advantageously, this allows access to the catalyst module 114 so that the catalyst 126 can be replaced without having to disassemble the optical amplifier 100 (which may be a complex configuration involving many components, as is evident from Figures 6 to 9 and the accompanying description). Advantageously, this can significantly reduce the time required to replace the catalyst 126 (and the time the optical amplifier 100 is unavailable). Furthermore, providing the catalyst module 114 located outside the optical amplifier 100 can simplify the interface between the catalyst 126 and the rest of the optical amplifier 100, potentially reducing the risk of contamination of the optical amplifier 100 when the catalyst 126 is being replaced.

[0091]

[0090] (Referring to Figures 6 to 9) In some embodiments, the optical amplifier 100 may comprise a plurality of amplification chambers, each of which is configured to receive a laser beam at an inlet and output an amplified laser beam at an outlet, and a first pump is configured to feed a gain medium into a gain medium system comprising the plurality of amplification chambers. Figure 4 shows an exemplary optical amplifier 100a according to an embodiment of the present disclosure, which is largely the same form as the optical amplifier 100 schematically shown in Figure 3, but has two amplification chambers 106. For clarity and ease of understanding, the cooling system 118 is not shown in detail in Figure 4, but it will be understood that it may have any of the features shown in Figure 3 and described above. In this example, the radiated beam output from the outlet of the first amplification chamber 106 is received at the inlet of the second amplification chamber 106. In this example, the two amplification chambers 106 share a common first pump 108, a common catalyst module 114, and a common first heat exchanger 110.

[0092]

[0091] As will be further described below (referring to Figures 6 to 9), in some embodiments the optical amplifier 100 may include a plurality of first heat exchangers 110, each constituting part of a gain medium system 116, and configured to transfer heat from the gain medium in the gain medium system 116 to a cooling fluid in a cooling system 118 after the gain medium has passed through the amplification chamber 106.

[0093]

[0092] Generally, the optical amplifier 100 may include a plurality of catalyst modules 114 in the configuration described above with reference to Figure 3. Generally, one catalyst module 114 may be provided upstream of each first heat exchanger 110.

[0094]

[0093] Figure 5 shows an exemplary optical amplifier 100b according to an embodiment of the present disclosure, which is largely the same form as the optical amplifier 100 schematically shown in Figure 3, but has two first heat exchangers 106, two catalyst modules, and two amplification chambers 106. For clarity and ease of understanding, the cooling system 118 is not shown in detail in Figure 5, but it will be understood that it may have any of the features shown in Figure 3 and described above. Each of the first heat exchangers 106 may constitute an individual cooling system 118 or part of a single common cooling system 118. In this example, the radiated beam output from the outlet of the first amplification chamber 106 is received at the inlet of the second amplification chamber 106. In this example, the two amplification chambers 106 share a common second heat exchanger 120.

[0095]

[0094] Each of the multiple first heat exchangers 110 may receive a gain medium from one or more amplification chambers 106. For example, each of the multiple first heat exchangers 110 may receive a gain medium from two amplification chambers 106 (see Figure 4).

[0096]

[0095] A specific example of the optical amplifier 200, which is an embodiment of the optical amplifier of the type schematically shown in Figures 3 to 5 and described above, will now be described with reference to Figures 6 to 9B.

[0097]

[0096] Figure 6 shows the optical amplifier 200. Figures 7A and 7B show a perspective view and a partial cross-sectional view, respectively, of a catalyst module that constitutes a part of the optical amplifier 200 shown in Figure 6. Figure 8 shows the optical path defined by the optical amplifier 200 shown in Figure 6. Figures 9A and 9B show the gas flow path within the optical amplifier 200 shown in Figure 6, through which the gain medium flows as part of the gain medium system.

[0098]

[0097] The optical amplifier 200 comprises a central support 202, an optical interface module 204, three corner modules 206, four side modules 208, and sixteen tubes 210. The central support 202 includes a generally square frame.

[0099]

[0098] The optical interface module 204, the three corner modules 206, and the four side modules 208 are connected to and supported by the central support 202. Specifically, the optical interface module 204 and the three corner modules 206 are located at different corners of the roughly square frame of the central support 202. The four side modules 208 are located at different sides of the roughly square frame of the central support 202, between two corner modules 206, or between a corner module 206 and the optical interface module 204.

[0100]

[0099] Two of the tubes 210 extend between each side module 208 and each of the two corner modules (either corner modules 206 or optical interface modules 204) adjacent to the side module 208. Each of the tubes 210 extends in a direction generally parallel to the side of the roughly square frame of the central support 202. Each of the tubes 210 may be formed from quartz.

[0101] [000100] Each of the tubes 210 may be an amplification chamber, and may be generally similar to the amplification chamber 106 shown in Figures 3 to 5. Each of the tubes 210 is configured to receive the laser beam 102 at the inlet (one end of the tube 210) and output the amplified laser beam 104 from the outlet (second end of the tube 210).

[0102] [000101] The optical amplifier 200 further comprises at least two electrodes and a power supply capable of applying voltage between at least two electrodes and within the tube 210, but please note that these mechanisms are omitted in the optical amplifier 200 shown in Figure 6 for the sake of clarity. In practice, a pair of electrodes may be provided outside each tube 210. One or more radio frequency (RF) signals may be used to excite molecules in the gas mixture. One or more radio frequency signals may consist of one or more radio frequency pulses. Alternatively, one or more radio frequency signals may consist of continuous wave radio frequency signals. One or more radio frequency signals may be applied to the gas mixture to generate a population inversion of the molecules in the gas mixture. This may amplify the laser beam passing through the gas mixture.

[0103] [000102] The tubes 210 constitute part of a closed-loop gain medium system configured to provide gas flow through each tube 210 during use. The gas flow through these tubes 210 will be further described below with reference to Figures 9A and 9B.

[0104] [000103] The optical interface module 204 defines an optical inlet 212 and an optical outlet 214. Each of the optical inlet 212 and the optical outlet 214 has an opening in the body of the optical interface module 204. When in use, an input laser beam 216 (see Figure 8) may be guided into the optical inlet 212. This input laser beam 216 may then propagate into the first tube of the tube 210. Specifically, the input laser beam 216 propagates along the optical path 218 defined by the optical amplifier 200, passes through each tube 210 in sequence, and exits from the optical outlet 214 as an amplified laser beam 220.

[0105] [000104] Although not shown in Figure 6, the optical inlet 212 and optical outlet 214 each have a window through which the laser beams 216 and 220 can pass as they propagate while maintaining the working medium (gas mixture) inside the tube 210.

[0106] [000105] The optical amplifier 200 further comprises a plurality of optical elements 222a to 222h that define the optical path 218. The optical elements 222a to 222h are reflectors or mirrors. The optical elements 222a to 222h are configured to guide the input laser beam 216 through the gas mixture in the tube 210 along the optical path 218. The optical elements 222a to 222h are supported by an optical interface module 204 and three corner modules 206. Specifically, each of the optical interface module 204 and the three corner modules 206 supports two optical elements 222a to 222h. The optical path 218 comprises a first portion 218a and a second portion 218b. The first portion 218a of the optical path 218 is defined by three optical elements 222a to 222c from each of the three corner modules 206. The first portion 218a of the optical path 218 is approximately square, and the laser beam propagates in one direction around the approximately square frame of the central support 202. Similarly, the second portion 218b of the optical path 218 is approximately square, defined by three optical elements 222f-222h from each of the three corner modules 206. The second portion 218b of the optical path 218 is approximately square, and the laser beam propagates in the opposite direction around the approximately square frame of the central support 202 to the first portion 218a of the optical path 218. Two optical elements 222d-222e, supported by the optical interface module 204, are configured to guide the laser beam from the first portion 218a of the optical path 218 to the second portion 218b of the optical path 218.

[0107] [000106] As described above, the tubes 210 constitute part of a closed-loop gain medium system configured to supply a gas flow that passes through each tube 210 during use. This closed-loop gain medium system will now be described with reference to Figures 6 and 9.

[0108] [000107] The optical amplifier 200 further comprises at least one first pump (not visible in Figure 6), eight first heat exchangers 224, eight catalyst modules 226, and eight second heat exchangers 228.

[0109] [000108] The first pump may be similar in nature to the first pump 108 in Figure 1 and is configured to feed the gain medium into a gain medium system 230 comprising a second heat exchanger 228, 16 tubes 210, 8 catalyst modules 226, and 8 first heat exchangers 224. The gain medium system 230 may be similar in nature to the gain medium system 116 of the optical amplifier 100 shown in Figure 3. The gain medium system 230 is a closed-loop system. The optical amplifier 200 may constitute part of a carbon dioxide (CO2) laser. The gain medium may contain a gas mixture. For example, the gain medium may contain a mixture of any combination of carbon dioxide, helium, and / or nitrogen.

[0110] [000109] Figure 9A shows the gas flow path within the optical amplifier 200 shown in Figure 6, along which the gain medium flows as part of the gain medium system 230. The axes of the optical amplifier 200 are shown in Figure 6. The axial direction will be understood as the direction parallel to axis 232. The radial direction will be understood as the direction perpendicular to axis 232 and passing through axis 232.

[0111] [000110] In this embodiment, the gain medium system 230 comprises a first portion 230a and a second portion 230b. Two turbines (or a first pump) are provided, namely a first turbine 244a (Schematically shown as a gray ellipse) configured to feed the gain medium into the first portion 230a of the gain medium system 230, and a second turbine 244b (Schematically shown as a gray ellipse) configured to feed the gain medium into the second portion 230b of the gain medium system 230. Figure 9B shows an exploded view of the gain medium system 230, in which the first portion 230a and the second portion 230b of the gain medium system 230 are separated axially to facilitate understanding of the gas flow through the gain medium system 230.

[0112] [000111] Two turbines 244a and 244b are operable to pump the gain medium radially outward from the center of the optical amplifier 200 and through eight second heat exchangers 228. The first turbine 244a is operable to pump the gain medium radially outward from the center of the optical amplifier 200 and through four second heat exchangers 228, and the second turbine 244b is operable to pump the gain medium radially outward from the center of the optical amplifier 200 and through the other four second heat exchangers 228. The flow of the gain medium through the second heat exchangers 228 is schematically shown by dotted lines in Figures 9A and 9B. The second heat exchangers 228 are configured to transfer heat from the gain medium in the gain medium system 230 to a cooling fluid in a cooling system (not shown) after the gain medium has passed through the first pump 108 and before it enters the amplification chamber of 16 tubes 210.

[0113] [000112] The gain medium from each of the second heat exchangers 228 then flows axially into one of the three corner modules 206 or the optical interface module 204, where the flow is divided and flows through two of the 16 tubes 210 toward the two side modules 208. The flow of the gain medium through the tubes 210 is schematically shown by solid lines in Figures 9A and 9B.

[0114] [000113] The flows from each pair of generally coaxial tubes 210 flow into one of the side modules 208 from both directions, where these flows merge and flow into one of the eight catalyst modules 226. Within each catalyst module 226, the flow begins generally radially outward, curves around until it becomes generally radially inward, and flows into one of the first heat exchangers 224. The flow of the gain medium through the catalyst modules 226 and the first heat exchangers 224 is schematically shown by dashed lines in Figures 9A and 9B.

[0115] [000114] The catalyst module 226 constitutes part of the gain medium system 230 and is located downstream of the two amplification chambers (i.e., the two tubes 210) and upstream of one of the first heat exchangers 224. Each of the first heat exchangers 224 is configured to transfer the heat of the gain medium in the gain medium system 230 to a cooling fluid in a cooling system (not shown) after the gain medium has passed through the two amplification chambers (i.e., the two tubes 210). The first heat exchangers 224 are sometimes referred to as gas coolers. After passing through the first heat exchangers 224, the gain medium is returned to the two turbines 244a and 244b.

[0116] [000115] The gas mixture of the gain medium may be continuously supplied to the gain medium system 230, for example. The gas mixture may contain carbon dioxide, oxygen, carbon monoxide, nitrogen, hydrogen, xenon, and / or helium.

[0117] [000116] As shown in Figures 7A and 7B, the catalyst module 226 comprises a main body 234 and a catalyst 236 disposed within the main body 234. The catalyst 236 is disposed within the main body 234 such that the gain medium is adjacent to or in contact with the catalyst 236 when the gain medium is supplied into the gain medium system 230 by the first pump.

[0118] [000117] The body 234 of the catalyst module 226 defines an inlet 234a, an outlet 234b, and a conduit or passage 238 extending between the inlet 234a and the outlet 234b. The direction extending roughly from the inlet 234a to the outlet 234b (i.e., along the conduit or passage 238) is sometimes referred to herein as the longitudinal direction. The longitudinal direction is generally shown by an arrowed line in Figure 7B. Similarly, the direction roughly perpendicular to the longitudinal direction (i.e., the cross-sectional area of ​​the conduit or passage 238) is sometimes referred to as the transverse direction. Note that the conduit or passage 238 is not linear, and therefore, the longitudinal and transverse directions generally vary along the conduit or passage 238.

[0119] [000118] As is most clearly seen in Figure 7B, the catalyst 236 is partially positioned near the outlet 234b in the conduit or passage 238. In this embodiment, the catalyst 236 protrudes slightly from the outlet 234b out of the body 234.

[0120] [000119] The catalyst 236 is porous and extends substantially over the entire lateral extent of the conduit or passage 238. For example, the catalyst 236 may include a honeycomb structure or the like.

[0121] [000120] In some embodiments, the body 234 of the catalyst module 226, which constitutes part of the gain medium flow circuit 230, is shaped to reduce the pressure drop in the gas medium flow circuit 230 (compared to known configurations) while maintaining the pressure drop on the catalyst 236, in order to satisfy the requirements of optical output and energy efficiency. As a result, the amount of power required to circulate the gain medium is reduced (compared to known configurations with the same mass flow rate). Furthermore, in some embodiments, the body 234 of the catalyst module 226 is shaped to more effectively guide the flow of the gain medium to the first heat exchanger 224 downstream (compared to known configurations), thereby further improving the thermal performance of the gain medium and reducing the pressure drop in the gain medium flow circuit 230. These advantages may be achieved by the following features relating to the shape of the body 234 of the catalyst module 226, as will be considered below.

[0122] [000121] As seen in Figures 7A and 7B, the conduits or passages 238 defined by the body 234 of the catalyst module 226 are nonlinear. In the embodiments shown in Figures 7A and 7B, the body 234 of the catalyst module 226 has the shape of a U-shaped pipe. As already described above, the inlet and outlet directions of the body 234 of the catalyst module 226 are different. Throughout the catalyst module 226, the flow begins at the inlet 234a generally radially outward (including the axial component) and bends around until it becomes generally radially inward at the outlet 234b (at the outlet 234b the flow flows into one of the first heat exchangers 224).

[0123] [000122] The conduit or passage 238 defined by the main body 234 follows at least one curved or bent portion, and the longitudinal spread of the catalyst 236 is greater in the portion of the conduit or passage closer to the outer portion of the curved or bent portion, and smaller in the portion of the conduit or passage closer to the inner portion of the curved or bent portion. For example, as can be seen in Figure 7B, the longitudinal spread 240 of the catalyst 236 in the portion of the conduit or passage 238 closer to the outer portion of the curved or bent portion is greater than the longitudinal spread 242 of the catalyst 236 in the portion of the conduit or passage 238 closer to the inner portion of the curved or bent portion.

[0124] [000123] Advantageously, this configuration allows for a more uniform pressure distribution downstream of the curve or bend. If there are no obstructions in the conduit or passage 238, the pressure of the gain medium (fluid) downstream of the curve or bend increases closer to the surface defining the outer portion of the curve or bend. Such a pressure gradient can be reduced by providing an obstruction (catalyst 236) with a larger longitudinal extension in the portion of the conduit or passage closer to the outer portion of the curve or bend. This may result in more efficient cooling of the working medium in the first heat exchanger 224.

[0125] [000124] As seen in Figures 7A and 7B, the lateral extension of the conduit or passage 238 defined by the body 234 of the catalyst module 226 increases in the direction of the gain medium flow. This promotes laminar flow and may reduce the amount of work that the first pump needs to do to achieve a predetermined mass flow rate of the gain medium.

[0126] [000125] Some embodiments of the present disclosure relate to a catalyst module for an optical amplifier, which may be in general form of the catalyst modules 114 and 226 described above.

[0127] [000126] Some embodiments of the present disclosure relate to an amplification system for use in a laser system, the system comprising a plurality of optical amplifiers, at least one of the plurality of optical amplifiers or each optical amplifier comprising optical amplifiers 100, 200 of the substantially above-described form.

[0128] [000127] Some embodiments of the present disclosure relate to a laser system comprising a laser configured to generate a laser beam and an amplification system configured to amplify the laser beam.

[0129] [000128] Some embodiments of the present disclosure relate to a radiation system comprising an EUV radiation source and a laser system.

[0130] [000129] Although this text specifically refers to the use of lithography equipment in the manufacture of ICs, it should be understood that the lithography equipment described herein has other applications. Other possible applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, and the like.

[0131] [000130] While the text specifically refers to embodiments of the present invention in relation to lithography apparatus, embodiments of the present invention may be used in other apparatuses. Embodiments of the present invention may constitute part of a mask inspection apparatus, a metrology apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses are generally referred to as lithography tools. Such lithography tools may operate under vacuum conditions or ambient (non-vacuum) conditions.

[0132] [000131] Where permitted by context, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored in a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random access memory (RAM), magnetic storage media, optical storage media, flash memory devices, propagating signals of electrical, optical, acoustic or other forms (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and instructions may be described herein as performing specific actions. However, such descriptions are merely for convenience, and it should be understood that such actions actually originate from a computing device, processor, controller, or other device that performs the firmware, software, routines, instructions, etc., and that in performing them, actuators or other devices may interact with the material world.

[0133] [000132] Although specific embodiments of the present invention have been described above, it will be understood that the present invention can be practiced in ways other than those described. The above description is illustrative and not limiting. Accordingly, it will be obvious to those skilled in the art that the above invention can be modified without departing from the scope of the claims below.

Claims

1. An optical amplifier configured to amplify a laser beam, An amplification chamber configured to receive the aforementioned laser beam at the inlet and output the amplified laser beam from the outlet, A first pump configured to supply the gain medium into the gain medium system equipped with the amplification chamber, A first heat exchanger, which constitutes part of the gain medium system and is configured to transfer the heat of the gain medium in the gain medium system to the cooling fluid in the cooling system after the gain medium has passed through the amplification chamber, A second pump configured to supply a cooling fluid to the first heat exchanger in order to exchange heat with the gain medium, Equipped with a catalyst module, The catalyst module, A main body, which constitutes part of the gain medium system, is disposed downstream of the amplification chamber so that the gain medium supplied to the amplification chamber subsequently flows through the main body, and upstream of the first heat exchanger so that the gain medium supplied to the main body subsequently flows through the first heat exchanger. When the gain medium is fed into the gain medium system by the first pump, the gain medium is adjacent to or in contact with a catalyst disposed within the main body, A light amplifier that has the use of a light amplifier.

2. The optical amplifier according to claim 1, wherein the catalyst module is removable from the optical amplifier independently of the first heat exchanger.

3. An optical amplifier configured to amplify a laser beam, An amplification chamber configured to receive the aforementioned laser beam at the inlet and output the amplified laser beam from the outlet, A first pump configured to supply the gain medium into the gain medium system equipped with the amplification chamber, A first heat exchanger, which constitutes part of the gain medium system and is configured to transfer heat from the gain medium in the gain medium system to the cooling fluid in the cooling system, At least one second pump configured to supply a cooling fluid to the at least one first heat exchanger in order to exchange heat with the gain medium, Equipped with a catalyst module, The catalyst module, The main body which constitutes part of the aforementioned gain medium system, When the gain medium is fed into the gain medium system by the first pump, the gain medium is adjacent to or in contact with a catalyst disposed within the main body, An optical amplifier having a first heat exchanger that is removable from the optical amplifier independently of the at least one first heat exchanger.

4. An optical amplifier according to any one of claims 1 to 3, wherein the catalyst module constitutes part of the gain medium system and does not constitute part of the cooling system.

5. The optical amplifier according to any one of claims 1 to 4, wherein the catalyst module is separate from the first heat exchanger.

6. An optical amplifier according to any one of claims 1 to 5, wherein the catalyst module is disposed outside the optical amplifier.

7. The photoamplifier according to any one of claims 1 to 6, wherein the main body of the catalyst module defines an inlet, an outlet, and a conduit or passage extending between the inlet and the outlet.

8. The optical amplifier according to claim 7, wherein the catalyst is at least partially disposed within the conduit or passage.

9. The photoamplifier according to claim or claim 8, wherein the catalyst is porous and extends substantially over the entire lateral extent of the conduit or passage.

10. The optical amplifier according to any one of claims 7 to 9, wherein the conduit or passage defined by the body of the catalyst module is nonlinear.

11. The conduit or passage defined by the main body follows at least one curved or bent portion, The optical amplifier of claim 10, wherein the longitudinal spread of the catalyst is greater in the portion of the conduit or passage closer to the outer portion of the curved or bent portion, and smaller in the portion of the conduit or passage closer to the inner portion of the curved or bent portion.

12. The optical amplifier according to any one of claims 7 to 11, wherein the lateral spread of the conduit or passage defined by the body of the catalyst module increases in the flow direction of the gain medium.

13. The photoamplifier according to any one of claims 1 to 12, wherein the catalyst comprises gold or platinum.

14. The system comprises a plurality of amplification chambers, each configured to receive the laser beam at an inlet and output an amplified laser beam from an outlet. An optical amplifier according to any one of claims 1 to 13, wherein the first pump is configured to feed the gain medium into the gain medium system comprising the plurality of amplification chambers.

15. An optical amplifier according to any one of claims 1 to 14, comprising a plurality of first heat exchangers, each constituting part of the gain medium system, and configured to transfer heat from the gain medium in the gain medium system to the cooling fluid in the cooling system after the gain medium has passed through the or each amplification chamber.

16. Equipped with multiple catalyst modules, Each of the aforementioned plurality of catalyst modules, A main body comprising a part of the aforementioned gain medium system, disposed downstream of at least one amplification chamber and upstream of the first heat exchanger, When the gain medium is fed into the gain medium system by the first pump, the gain medium is adjacent to or in contact with a catalyst disposed within the main body, An optical amplifier having any one of claims 1 to 15.

17. A catalyst module for a photoamplifier according to claims 1 to 16.

18. An amplification system for use in laser systems, Equipped with multiple optical amplifiers, An amplification system in which at least one or each of the plurality of optical amplifiers has an optical amplifier according to any one of claims 1 to 16.

19. A laser configured to generate a laser beam, The amplification system according to claim 18, configured to amplify the laser beam, A laser system equipped with [the following features].

20. EUV radiation source and The laser system according to claim 19, A radiation system equipped with the following features.

21. EUV radiation source and A laser system comprising an optical amplifier according to any one of claims 1 to 16, A radiation system equipped with the following features.

22. A radiation system according to claim 20 or 21, Lithography equipment, A lithography system equipped with [the following features].

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