A laser system for extreme ultraviolet laser

Abstract

This invention relates to a laser system for extreme ultraviolet (EUV) lasers, comprising: a seed source for generating pulsed laser light with a center wavelength of 1980 nm ± 30 nm; a first-stage amplifier for amplifying the pulsed laser light; a beam splitter for splitting the amplified pulsed laser light into multiple laser beams; an electrically controlled optical delay line for dynamically adjusting the pulse delay of each of the multiple laser beams to synchronize the pulse time domain of all the multiple laser beams; a second-stage amplifier for amplifying each of the time-delay-controlled multiple laser beams to obtain multiple amplified laser beams; a third-stage amplifier for further amplifying each of the multiple amplified laser beams; and a beam combiner for coherently combining the secondary amplified multiple laser beams into a single, time-domain-synchronized, high-energy synthesized laser beam, which is used to generate EUV lasers. The high-energy synthesized laser obtained by this invention has an average power in the tens of kilowatts range and can be used as a pump laser for efficient EUV laser generation.

Description

Technical Field

[0001] This invention relates to the field of lasers, and more particularly to a laser system for extreme ultraviolet lasers. Background Technology

[0002] Photolithography is a crucial process in chip manufacturing, and extreme ultraviolet (EUV) lithography is one of the most advanced chip manufacturing technologies currently available.

[0003] The core of extreme ultraviolet (EUV) lithography technology lies in etching nanoscale microcircuits onto silicon wafers using 13.5nm wavelength EUV light. Currently, the world's only mass-producible EUV lithography machine uses laser plasma (LPP) light source technology, which generates plasma by bombarding molten tin droplets with a high-power carbon dioxide laser, thereby radiating EUV light. However, the aforementioned EUV lithography machine uses a carbon dioxide laser as the driving light source, resulting in extremely low energy conversion efficiency, with a conversion efficiency of only about 5% from electrical energy to EUV light energy; poor beam quality and stability, making it difficult to achieve high-precision beam control; and high system complexity and maintenance costs.

[0004] It is evident that the extreme ultraviolet laser source in existing extreme ultraviolet lithography machines is still insufficient to meet the requirements. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems, or at least partially solve the above-mentioned technical problems, the present invention provides a laser system for extreme ultraviolet laser.

[0006] In a first aspect, the present invention provides a laser system for extreme ultraviolet lasers, the laser system comprising: Seed source, used to generate pulsed laser with a center wavelength of 1980nm±30nm; The first-stage amplifier is used to amplify the pulsed laser; A beam splitter is used to split an amplified pulsed laser into multiple laser beams. An electrically controlled optical delay line is used to dynamically adjust the pulse delay of each of the multiple laser paths to synchronize the pulse time domain of all the multiple laser paths. The second-stage amplifier is used to amplify each of the multiple laser paths after time delay modulation to obtain amplified laser paths. The third-stage amplifier is used to amplify each of the multi-channel amplified lasers a second time; A beam combiner is used to coherently combine the secondary amplified multi-path laser beams into a high-energy synthesized laser beam that is pulse-synchronized in the time domain. The synthesized laser beam is used to generate extreme ultraviolet laser.

[0007] Optionally, the second-stage amplifier includes multiple thulium-doped fiber amplifiers, which are used to amplify each of the multiple laser paths after the time delay is adjusted, with each thulium-doped fiber amplifier corresponding to one of the multiple laser paths. The third-stage amplifier is the main amplifier, which is an ultra-large mode field rod-shaped thulium-doped fiber amplifier that uses ultra-large mode field rod-shaped thulium-doped fiber as the gain medium of the amplifier. The ultra-large mode field rod-shaped thulium-doped fiber amplifier is used to amplify multiple multi-channel lasers after amplification by multiple thulium-doped fiber amplifiers. Each ultra-large mode field rod-shaped thulium-doped fiber amplifier corresponds to one amplified laser.

[0008] Optionally, the laser system further includes: The main power detector is used to detect the power of the multi-channel laser amplified by the ultra-large mode field rod-shaped thulium-doped fiber amplifier; A feedback regulator is used to adjust the operating parameters of the ultra-large mode field rod-shaped thulium-doped fiber amplifier based on the detection results of the main power detector.

[0009] Optionally, the laser system further includes: A first isolator is disposed between the seed source and the first stage amplifier; A second isolator is disposed between the first stage amplifier and the second stage amplifier; The third isolator is located between the second-stage amplifier and the third-stage amplifier; The first isolator, the second isolator, and the third isolator are used to provide backlight protection isolation for the laser system.

[0010] Optionally, the seed source includes: The pump source is a semiconductor laser with a center wavelength of 793nm, which uses continuous laser output pump light; High-reflectivity gratings and low-reflectivity gratings are used to construct resonant cavities; A double-clad thulium-doped fiber is disposed in the resonant cavity to amplify the pump light after it passes through the double-clad thulium-doped fiber, so that it becomes a continuous signal light with a center wavelength of 1980nm±30nm. An active modulator, disposed within the resonant cavity, is used to convert continuous signal light input to the active modulator into pulsed laser light.

[0011] Optionally, when the pump source is an external positive pump source, the seed source is configured in sequence according to the optical path direction as the pump source, the high-reflectivity grating, the double-clad thulium-doped fiber, the active modulator, and the low-reflectivity grating.

[0012] Optionally, when the pump source is an external cavity reverse pump, the seed source is configured in sequence according to the optical path direction as the high-reflectivity grating, the active modulator, the double-clad thulium-doped fiber, the low-reflectivity grating, and the pump source.

[0013] Optionally, when the pump source is intracavity forward pumping, the seed source is configured in sequence according to the optical path direction as the high-reflectivity grating, the pump source, the double-clad thulium-doped fiber, the active modulator, and the low-reflectivity grating.

[0014] Optionally, when the pump source is intracavity reverse pumping, the seed source is configured in sequence according to the optical path direction as the high-reflectivity grating, the active modulator, the double-clad thulium-doped fiber, the pump source, and the low-reflectivity grating.

[0015] Optionally, the first stage amplifier is a thulium-doped fiber amplifier, and the pump source of the first stage amplifier is a multimode semiconductor laser with a center wavelength of 793nm. The second-stage amplifier is a thulium-doped fiber amplifier, and the pump source of the second-stage amplifier is a multimode semiconductor laser with a center wavelength of 793nm. The pump source of the third-stage amplifier is a thulium-doped fiber laser with a wavelength of 1910nm ± 10nm. The pump source of the third-stage amplifier operates in a continuous operating state and uses in-band pumping.

[0016] This invention provides a laser system for extreme ultraviolet (EUV) lasers. The laser system includes: a seed source for generating pulsed laser with a center wavelength of 1980nm ± 30nm; a first-stage amplifier for amplifying the pulsed laser; a beam splitter for splitting the amplified pulsed laser into multiple laser beams; an electrically controlled optical delay line for dynamically adjusting the pulse delay of each laser beam to synchronize the pulse time domain of all laser beams; a second-stage amplifier for amplifying each delayed laser beam to obtain a multi-channel amplified laser; a third-stage amplifier for further amplifying each laser beam; and a beam combiner for coherently combining the secondary amplified laser beams into a single, time-domain-synchronized, high-energy synthesized laser beam. The synthesized laser is used to generate EUV lasers. In this embodiment of the invention, a multi-stage amplifier is used to amplify the laser. Furthermore, the pulsed laser is split into multiple laser paths by a beam splitter, and each path is amplified multiple times and separately. These multiple amplifications are then coherently combined to obtain a synthesized laser. The resulting high-energy synthesized laser has an average power in the tens of thousands of watts, making it suitable as a pump laser for efficiently generating extreme ultraviolet lasers. In addition, each path is followed by an electrically controlled optical delay line to dynamically adjust the pulse delay of each path, ensuring pulse time-domain synchronization of the final coherently combined laser pulse. The coherent beam combining technology not only improves the output power but also achieves near-single-mode beam quality. Compared to the bulky size and complex structure of traditional carbon dioxide lasers, this invention employs an all-fiber structure, resulting in a compact system, simple structure, and low maintenance costs. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The diagram shown is a schematic diagram of a laser system for extreme ultraviolet lasers according to an embodiment of the present invention. Figure 2 The diagram shown is a schematic diagram of a laser system for extreme ultraviolet lasers according to an embodiment of the present invention. Figure 3 The diagram shown is a schematic diagram of a laser system for extreme ultraviolet lasers according to an embodiment of the present invention. Figure 4 The diagram shown is a schematic representation of the seed source according to an embodiment of the present invention; Figure 5 The diagram shown is a schematic representation of the seed source according to an embodiment of the present invention; Figure 6 The diagram shown is a schematic representation of the seed source according to an embodiment of the present invention; Figure 7 The diagram shown is a schematic diagram of the seed source according to an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Figure 1 The diagram shown is a schematic diagram of a laser system for extreme ultraviolet lasers according to an embodiment of the present invention. Figure 1 As shown, the laser system for extreme ultraviolet lasers includes: Seed source 110 is used to generate pulsed laser with a center wavelength of 1980nm±30nm; The first-stage amplifier 120 is used to amplify the pulsed laser; Beam splitter 130 is used to split the amplified pulsed laser into multiple laser beams; The electrically controlled optical delay line 140 is used to dynamically adjust the pulse delay of each of the multiple laser paths so as to synchronize the pulse time domain of all the multiple laser paths. The second-stage amplifier 150 is used to amplify each of the multiple laser paths after time delay modulation to obtain amplified laser paths. The third-stage amplifier 170 amplifies each of the multiple amplified lasers a second time. The beam combiner 160 is used to coherently combine the secondary amplified multi-path laser beams into a high-energy synthesized laser beam that is pulse-synchronized in the time domain. The synthesized laser beam is used to generate extreme ultraviolet laser.

[0022] In this embodiment of the invention, the first-stage amplifier 120 may include multiple stages of amplifiers, such as two-stage amplifiers or more stages of amplifiers.

[0023] In this embodiment of the invention, a multi-stage amplifier is used to amplify the laser. Furthermore, the pulsed laser is split into multiple laser paths by a beam splitter, and each path is amplified multiple times and separately. These multiple amplifications are then coherently combined to obtain a synthesized laser. The resulting high-energy synthesized laser has an average power in the tens of thousands of watts, making it suitable as a pump laser for efficiently generating extreme ultraviolet lasers. In addition, each path is followed by an electrically controlled optical delay line to dynamically adjust the pulse delay of each path, ensuring pulse time-domain synchronization of the final coherently combined laser pulse. The coherent beam combining technology not only improves the output power but also achieves near-single-mode beam quality. Compared to the bulky size and complex structure of traditional carbon dioxide lasers, this invention employs an all-fiber structure, resulting in a compact system, simple structure, and low maintenance costs.

[0024] In this invention, the seed source 110 can be a pump source for a thulium-doped fiber laser, with the center wavelength taken as the wavelength range of 1980nm±30nm at the maximum gain of the thulium laser. According to industry convention, the 2-micron band can also be equated with 1980nm±30nm.

[0025] In this embodiment of the invention, the seed source 110 can achieve pulse output parameters of 10 ns pulse width, 50 kHz repetition frequency, and 200 mW average power. The seed source 110 is followed by a first-stage amplifier 120 and a second-stage amplifier 150 to amplify the average power to 10 W. After passing through a third-stage amplifier 170, the average power of each path can be amplified to 500 W. In this embodiment of the invention, the beam splitter 130 can split the pulsed laser into multiple laser paths, for example, 20 paths, and can also be divided into more paths according to the power requirements after beam combining. After beam combining, it becomes a high-energy synthesized laser with pulse synchronization in the time domain. The synthesized laser is used to generate extreme ultraviolet laser, which can achieve extreme ultraviolet output of 10 kilowatts or higher.

[0026] In this embodiment of the invention, the second-stage amplifier 150 includes a plurality of thulium-doped fiber amplifiers, which are used to amplify each of the multiple laser paths after the time delay is adjusted, and each of the thulium-doped fiber amplifiers corresponds to one of the multiple laser paths. The third-stage amplifier 170 is the main amplifier, which is an ultra-large mode field rod-shaped thulium-doped fiber amplifier that uses ultra-large mode field rod-shaped thulium-doped fiber as the gain medium of the amplifier. The ultra-large mode field rod-shaped thulium-doped fiber amplifier is used to amplify multiple multi-channel lasers after amplification by multiple thulium-doped fiber amplifiers. Each ultra-large mode field rod-shaped thulium-doped fiber amplifier corresponds to one amplified laser.

[0027] refer to Figure 2As shown, the second-stage amplifier 150 includes multiple amplifiers, such as second-stage amplifier 1, second-stage amplifier 2, and second-stage amplifier 3, etc. The number of second-stage amplifiers is the same as the number of multiple laser paths, and each amplifier amplifies one of the multiple laser paths. Similarly, the third amplifier 170 also includes multiple amplifiers, such as third-stage amplifier 1, third-stage amplifier 2, and third-stage amplifier 3, etc.

[0028] The ultra-large mode field rod-shaped thulium-doped fiber is used as the main amplification stage. The core diameter is 180±20μm and the numerical aperture is less than 0.01. The inner cladding diameter is about 380±20μm and the inner cladding numerical aperture is 0.25±0.03. The outer diameter of the rod-shaped fiber is 1mm.

[0029] The core diameter of the ultra-large mode field rod-shaped thulium-doped fiber amplifier can be 180±20μm, which can effectively suppress nonlinear effects and improve power carrying capacity.

[0030] Experiments and calculations show that for a laser with a repetition frequency of 50kHz, an average power of 500W, a pulse width of 10ns, and a single pulse energy of 10mJ, the corresponding peak power is 10MW, and the power density within the fiber core is approximately 3.9GW / cm², which is lower than the damage threshold of silica optical fiber. This improves the power carrying capacity and ensures the safe and stable operation of the system.

[0031] Figure 2 The diagram shown is a schematic diagram of a laser system for extreme ultraviolet lasers according to an embodiment of the present invention. In this embodiment, the laser system further includes: The main power detector 210 is used to detect the power of the multi-channel laser amplified by the ultra-large mode field rod-shaped thulium-doped fiber amplifier; Feedback regulator 220 is used to adjust the operating parameters of the ultra-large mode field rod-shaped thulium-doped fiber amplifier based on the detection results of the main power detector 210.

[0032] Figure 3 The diagram shown is a schematic diagram of a laser system for extreme ultraviolet lasers according to an embodiment of the present invention. The laser system further includes: The first isolator 310 is disposed between the seed source 110 and the first stage amplifier 120; The second isolator 320 is disposed between the first stage amplifier 120 and the second stage amplifier 150; The third isolator 330 is disposed between the second stage amplifier 150 and the third stage amplifier 170; The first isolator 310, the second isolator 320 and the third isolator 330 are used to protect the laser system from backlighting.

[0033] In this embodiment of the invention, the first stage amplifier 120 is a thulium-doped fiber amplifier, and the pump source of the first stage amplifier 120 is a multimode semiconductor laser with a center wavelength of 793nm. The second-stage amplifier 150 is a thulium-doped fiber amplifier, and the pump source of the second-stage amplifier 150 is a multimode semiconductor laser with a center wavelength of 793nm. The pump source of the third-stage amplifier 170 is a thulium-doped fiber laser with a wavelength of 1910nm ± 10nm. The pump source of the third-stage amplifier 170 operates in a continuous operating state and uses in-band pumping.

[0034] In this embodiment of the invention, multiple amplifiers can be added according to the amplification effect and requirements, and isolators can be added or removed as needed, thereby reducing the complexity of the system or providing more comprehensive backlight protection isolation for the system.

[0035] In this embodiment of the invention, the seed source 110 includes: The pump source is a semiconductor laser with a center wavelength of 793nm, which uses continuous laser output; The high-reflectivity grating 420 and the low-reflectivity grating 450 are used to form the resonant cavity; A double-clad thulium-doped fiber 430 is disposed in the resonant cavity to amplify the pump light after it passes through the double-clad thulium-doped fiber 430, so that it becomes a continuous signal light with a center wavelength of 1980nm±30nm. An active modulator 440 is disposed within the resonant cavity and is used to convert continuous signal light input to the active modulator 440 into pulsed laser light. The laser output unit 460 is used to output the pulsed laser.

[0036] In this embodiment of the invention, the pump source of the ultra-large mode field rod-shaped thulium-doped fiber amplifier adopts a co-band pumping method. The pump source is a thulium-doped fiber laser with a wavelength of 1910 nm ± 10 nm, and the pump source operates in a continuous state. The low heat load characteristic of co-band pumping can significantly improve the long-term stability and reliability of the system.

[0037] In this embodiment of the invention, the reflectivity of the high-reflectivity grating 420 is greater than 99%, and the transmittance of the low-reflectivity grating 450 is 10% to 30%.

[0038] In this embodiment of the invention, the pulse width of the pulsed light output by the active modulator 440 is 10ns to 200ns, and the repetition frequency is 40kHz to 60kHz.

[0039] In this embodiment of the invention, using a co-current pump is beneficial for improving pump conversion efficiency and reducing thermal efficiency.

[0040] The thulium-doped fiber laser with a wavelength of 1910nm±10nm employs a co-band pumping scheme, resulting in a quantum defect of less than 4%. This significantly reduces the thermal load on the ultra-large mode field rod-shaped thulium-doped fiber in the main amplification stage, while maintaining an optical-to-optical conversion efficiency of over 80%. Furthermore, the low thermal load characteristic simplifies system thermal management.

[0041] In this embodiment of the invention, the seed source and the pumps of each stage of the amplifier are all powered by 793nm LDs.

[0042] The pump source of this invention has advantages such as good beam quality, high electro-optical conversion efficiency, good thermal management performance, compact structure, easy modular construction, and convenient maintenance.

[0043] In this embodiment of the invention, there are various types of pump sources, therefore, there can also be various optical path structures in this embodiment of the invention.

[0044] Figure 4 The diagram shows a seed source according to an embodiment of the present invention. When the pump source is an external positive pump source 4101, the seed source 110 is configured in sequence according to the optical path direction as the pump source, the high-reflectivity grating 420, the double-clad thulium-doped fiber 430, the active modulator 440, the low-reflectivity grating 450 and the laser output unit 460.

[0045] Figure 5 The diagram shows a seed source according to an embodiment of the present invention. When the pump source is an external cavity reverse pump 4102, the seed source 110 is configured in sequence according to the optical path direction as the high-reflectivity grating 420, the active modulator 440, the double-clad thulium-doped fiber 430, the low-reflectivity grating 450, the pump source, and the laser output unit 460.

[0046] Figure 6 The diagram shows a seed source according to an embodiment of the present invention. When the pump source is an intracavity positive pump 4103, the seed source 110 is configured in sequence according to the optical path direction as the high-reflectivity grating 420, the pump source, the double-clad thulium-doped fiber 430, the active modulator 440, the low-reflectivity grating 450 and the laser output unit 460.

[0047] Figure 7 The diagram shows a seed source according to an embodiment of the present invention. When the pump source is an intracavity reverse pump 4104, the seed source 110 is configured in sequence according to the optical path direction as the high-reflectivity grating 420, the active modulator 440, the double-clad thulium-doped fiber 430, the pump source, the low-reflectivity grating 450, and the laser output unit 460.

[0048] This invention features high conversion efficiency and low thermal load. The ultra-large mode field rod-shaped thulium-doped fiber amplifier ensures the safe and stable operation of the system. Furthermore, by generating lasers from a single seed source, combined with amplification, beam splitting, and optical delay lines, precise pulse time-domain synchronization is achieved. A coherent beam combining scheme is employed, resulting in a single, time-domain pulse-synchronized high-energy synthesized laser. This synthesized laser is used to generate extreme ultraviolet (EUV) lasers, enabling EUV output at 10 kilowatts or higher. This coherent beam combining technology not only improves output power but also achieves near-single-mode beam quality, providing high-quality pump lasers for EUV sources. Simultaneously, this scheme utilizes an all-fiber structure, resulting in a compact, simple system with low maintenance costs. The low thermal load characteristic of co-pumping significantly improves the long-term stability and reliability of the system.

[0049] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0050] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A laser system for extreme ultraviolet lasers, characterized in that, The laser system includes: Seed source, used to generate pulsed laser with a center wavelength of 1980nm±30nm; The first-stage amplifier is used to amplify the pulsed laser; A beam splitter is used to split an amplified pulsed laser into multiple laser beams. An electrically controlled optical delay line is used to dynamically adjust the pulse delay of each of the multiple laser paths to synchronize the pulse time domain of all the multiple laser paths. The second-stage amplifier is used to amplify each of the multiple laser paths after time delay modulation to obtain amplified laser paths. The third-stage amplifier is used to amplify each of the multi-channel amplified lasers a second time; A beam combiner is used to coherently combine the secondary amplified multi-path laser beams into a high-energy synthesized laser beam that is pulse-synchronized in the time domain. The synthesized laser beam is used to generate extreme ultraviolet laser.

2. The laser system according to claim 1, characterized in that, The second-stage amplifier includes multiple thulium-doped fiber amplifiers, which are used to amplify each of the multiple laser streams after the time delay is adjusted, with each thulium-doped fiber amplifier corresponding to one of the multiple laser streams. The third-stage amplifier is the main amplifier, which is an ultra-large mode field rod-shaped thulium-doped fiber amplifier that uses ultra-large mode field rod-shaped thulium-doped fiber as the gain medium of the amplifier. The ultra-large mode field rod-shaped thulium-doped fiber amplifier is used to amplify multiple multi-channel lasers after amplification by multiple thulium-doped fiber amplifiers. Each ultra-large mode field rod-shaped thulium-doped fiber amplifier corresponds to one amplified laser.

3. The laser system according to claim 2, characterized in that, The laser system also includes: The main power detector is used to detect the power of the multi-channel laser amplified by the ultra-large mode field rod-shaped thulium-doped fiber amplifier; A feedback regulator is used to adjust the operating parameters of the ultra-large mode field rod-shaped thulium-doped fiber amplifier based on the detection results of the main power detector.

4. The laser system according to claim 1, characterized in that, The laser system also includes: A first isolator is disposed between the seed source and the first stage amplifier; A second isolator is disposed between the first stage amplifier and the second stage amplifier; The third isolator is located between the second-stage amplifier and the third-stage amplifier; The first isolator, the second isolator, and the third isolator are used to provide backlight protection isolation for the laser system.

5. The laser system according to claim 1, characterized in that, The seed source includes: The pump source is a semiconductor laser with a center wavelength of 793nm, which uses continuous laser output pump light; High-reflectivity gratings and low-reflectivity gratings are used to construct resonant cavities; A double-clad thulium-doped fiber is disposed in the resonant cavity to amplify the pump light after it passes through the double-clad thulium-doped fiber, so that it becomes a continuous signal light with a center wavelength of 1980nm±30nm. An active modulator, disposed within the resonant cavity, is used to convert continuous signal light input to the active modulator into pulsed laser light.

6. The laser system according to claim 5, characterized in that, When the pump source is an external positive pump source, the seed source is configured in sequence according to the optical path direction as the pump source, the high-reflectivity grating, the double-clad thulium-doped fiber, the active modulator, and the low-reflectivity grating.

7. The laser system according to claim 5, characterized in that, When the pump source is an external reverse pump, the seed source is configured in sequence according to the optical path direction as the high-reflectivity grating, the active modulator, the double-clad thulium-doped fiber, the low-reflectivity grating, and the pump source.

8. The laser system according to claim 5, characterized in that, When the pump source is intracavity forward pumping, the seed source is configured in sequence according to the optical path direction as the high-reflectivity grating, the pump source, the double-clad thulium-doped fiber, the active modulator, and the low-reflectivity grating.

9. The laser system according to claim 5, characterized in that, When the pump source is an intracavity reverse pump, the seed source is configured in sequence according to the optical path direction as the high-reflectivity grating, the active modulator, the double-clad thulium-doped fiber, the pump source, and the low-reflectivity grating.

10. The laser system according to claim 1, characterized in that, The first stage amplifier is a thulium-doped fiber amplifier, and the pump source of the first stage amplifier is a multimode semiconductor laser with a center wavelength of 793nm. The second-stage amplifier is a thulium-doped fiber amplifier, and the pump source of the second-stage amplifier is a multimode semiconductor laser with a center wavelength of 793nm. The pump source of the third-stage amplifier is a thulium-doped fiber laser with a wavelength of 1910nm ± 10nm. The pump source of the third-stage amplifier operates in a continuous operating state and uses in-band pumping.

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