Low repetition frequency optical fiber pulse laser amplification system and method

Abstract

The invention belongs to the technical field of optical fiber lasers, and particularly relates to a low-repetition-frequency optical fiber pulse laser amplification system and method.The low-repetition-frequency optical fiber pulse laser amplification system comprises a nanosecond pulse seed source and a first-stage amplification unit; the first-stage amplification unit comprises a first-stage pump light source, a first-stage wavelength division multiplexer and a first-stage gain optical fiber; the nanosecond pulse seed source is used for outputting nanosecond pulse seeds, and the primary pump light source is used for outputting pump light; the frequency of the pump light is lower than that of the nanosecond pulse seed, and the pump light is used for performing pulse pickup amplification on a signal corresponding to the frequency of the pump light in the nanosecond pulse seed to obtain a low-repetition-frequency pulse laser signal with the frequency smaller than 1kHz. According to the invention, a high-repetition-frequency seed and low-repetition-frequency pumping pulse scheme is adopted to carry out low-repetition-frequency amplification on a seed signal, so that spontaneous amplification radiation and random pulses generated in a system under a low-repetition-frequency condition are effectively inhibited, the stability of the system is further ensured, and the output energy of the system is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber lasers, and in particular relates to a low repetition rate optical fiber pulse laser amplification system and method. Background Art

[0002] Fiber lasers are widely used in industrial processing, military defense, and other fields due to their excellent beam quality, high conversion efficiency, and compactness. In recent years, as the manufacturing industry has increasingly stringent requirements for environmental protection and precision in production processes, the demand for pulsed fiber laser systems that combine high pulse energy and high peak power with a low repetition rate while maintaining the inherent advantages of fiber laser systems has greatly increased. However, the current high-power amplification of low-repetition-rate signals (10-100Hz) is still limited by factors such as spontaneous emission (ASE) and stimulated Raman scattering (SRS). To address this problem, various research institutions have proposed a number of solutions.

[0003] Chinese patent publication number CN119726327A discloses a low-repetition-rate pulsed fiber laser that is beneficial for suppressing ASE light. The patent comprises a low-repetition-rate, narrow-pulse-width seed source, which provides seed pulses with a repetition rate of 1kHz to 500kHz and a pulse width of 1ns to 50ns, and outputs them to a combiner module. A continuous injection source provides continuous laser light, which is output to the combiner module. The peak power of the seed pulse is at least 10 times the peak power of the continuous laser light, and the average power of the seed pulse is 0.5 to 1.5 times the average power of the continuous laser light. The combiner module simultaneously transmits the seed pulse and the continuous laser light to an amplifier module, which amplifies the power of the seed pulse to form a low-repetition-rate, narrow-pulse-width, high-peak pulse laser light and transmits it to a filter. This patent combines the continuous laser light with the pulse seed. During the power amplification process of the seed pulse, the continuous laser light has a certain inhibitory effect on ASE. A filter is then used to remove the continuous laser light component from the output laser light. However, this amplification system only amplifies lasers at frequencies between 1kHz and 500kHz, and does not address laser amplification solutions at lower repetition rates (10 to 100Hz). Furthermore, combining continuous light with pulsed seeds requires the introduction of additional filters and combiners, further increasing the cost of the laser system. Therefore, it is necessary to provide an improved low-repetition-rate fiber pulse laser amplification system to address the above issues. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-repetition-rate fiber pulse laser amplification system and method. By adjusting the pump pulse frequency to perform pulse picking and amplification in the seed signal, the higher-frequency pulse seed signal light can effectively suppress the ASE effect in the system under the low-frequency pump pulse amplification.

[0005] To achieve the above-mentioned object, the present invention provides a low repetition rate fiber pulse laser amplification system, comprising a nanosecond pulse seed source and a first-stage amplification unit; the first-stage amplification unit comprises a first-stage pump light source, a first-stage wavelength division multiplexer, and a first-stage gain fiber; the nanosecond pulse seed source is used to output nanosecond pulse seeds, and the first-stage pump light source is used to output pump light;

[0006] The output ends of the nanosecond pulse seed source and the first-level pump light source are both connected to the input end of the first-level wavelength division multiplexer, and the output end of the first-level wavelength division multiplexer is connected to the first-level gain fiber, so as to coaxially couple the nanosecond pulse seed and pump light into the first-level gain fiber to achieve amplification;

[0007] The frequency of the pump light is lower than the frequency of the nanosecond pulse seed, and is used to perform pulse picking and amplification on the signal corresponding to the pump light frequency in the nanosecond pulse seed to obtain a low repetition rate pulse laser signal with a frequency less than 1 kHz.

[0008] Furthermore, the frequency of the nanosecond pulse seed source is 1 kHz-1.3 kHz, and the frequency of the pump light is 10-100 Hz.

[0009] Furthermore, it also includes a secondary amplification unit and a tertiary amplification unit which are sequentially arranged after the output end of the primary gain optical fiber along the signal transmission direction;

[0010] The secondary amplification unit includes a secondary pump light source, a secondary beam combiner and a secondary gain fiber arranged in sequence along the signal transmission direction; the tertiary amplification unit includes a tertiary pump light source, a tertiary beam combiner and a tertiary gain fiber arranged in sequence along the signal transmission direction;

[0011] The output ends of the primary gain fiber and the secondary pump light source are both connected to the input end of the secondary combiner, and the output ends of the secondary gain fiber and the tertiary pump light source are connected to the input end of the tertiary combiner.

[0012] Furthermore, a seed isolation filter is provided between the nanosecond pulse seed source and the first-stage wavelength division multiplexer;

[0013] The first-stage amplification unit further includes a first-stage isolation filter disposed between the first-stage gain optical fiber and the second-stage combiner;

[0014] The secondary amplification unit further includes a secondary isolation filter arranged between the secondary gain optical fiber and the tertiary combiner.

[0015] Furthermore, the output type of the three-stage gain optical fiber is connected to an optical fiber output collimator for outputting the low repetition rate pulse laser signal with a final amplification frequency less than 1 kHz.

[0016] Furthermore, the first-level gain fiber is a single-clad silica ytterbium-doped fiber, the second-level gain fiber and the third-level gain fiber are double-clad silica ytterbium-doped fibers, and the core diameters of the first-level gain fiber, the second-level gain fiber and the third-level gain fiber increase in sequence.

[0017] Furthermore, the core diameter of the primary gain fiber is 5-7 μm, and the pump absorption efficiency at 976 nm is 250 dB / m;

[0018] The core diameter of the secondary gain fiber is 10-20 μm, and the pump absorption efficiency at 976 nm is 4.3 dB / m;

[0019] The core diameter of the three-stage gain optical fiber is 20-1000 μm, and the pump absorption efficiency at 976 nm is 3.6 dB / m.

[0020] Furthermore, the primary pump light source, the secondary pump light source, and the tertiary pump light source are semiconductor pump lasers with a wavelength in the range of 915nm-1018nm;

[0021] The pumping lights generated by the primary pumping light source, the secondary pumping light source, and the tertiary pumping light source have the same frequency.

[0022] The present invention also provides a method for amplifying a low repetition rate pulse laser signal, comprising: outputting a nanosecond pulse seed from a nanosecond pulse seed source, then adjusting the frequency of the pump light in the amplification system to be lower than the frequency of the nanosecond pulse seed, performing pulse picking and amplification on a signal in the nanosecond pulse seed corresponding to the pump light frequency, and obtaining a low repetition rate pulse laser signal with a frequency less than 1 kHz.

[0023] Furthermore, the nanosecond pulse seed is sequentially amplified through three amplification systems, and the pump light sources of the three amplification systems generate the same frequency of pump light;

[0024] Specifically, the first-level pump light source injects the pump light into the first-level gain fiber through the first-level wavelength division multiplexer, amplifies the signal light, filters out the stray light components in the signal light through the first-level isolation filter, and then injects the signal light into the second-level gain fiber through the second-level combiner. The second-level pump light source injects the pump light into the second-level gain fiber through the second-level combiner, amplifies the signal light again, and then passes through the second-level isolation filter to select the wavelength and filter out the stray light.

[0025] The three-stage pump light source injects the pump light into the three-stage amplification unit through the three-stage beam combiner, which performs the final power amplification on the signal light.

[0026] Finally, the signal light output from the three-stage gain optical fiber enters the optical fiber output collimator to collimate the laser output.

[0027] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0028] 1. The low-repetition-rate fiber pulse laser amplification system provided by the present invention adopts a high-repetition-rate seed and low-repetition-rate pump pulse scheme to perform low-repetition-rate amplification on the seed signal. The higher-frequency pulse seed signal light can be amplified by the low-frequency pump pulse, which can effectively suppress the spontaneous amplification radiation and random pulses generated in the system under low-repetition-rate conditions, further ensuring the system stability and greatly improving the system output energy.

[0029] 2. A high-repetition-rate seed signal greater than 1kHz, output by a nanosecond pulse seed source, is sequentially amplified through three stages of amplification. During the amplification process, each pump source uses pulsed pumping, with the same frequency and aligned falling edges, to ensure effective pulse pickup and amplification of the high-repetition-rate pulse seed signal. In this case, only the portion of the seed signal with a frequency above 1kHz that corresponds to the pulsed pump frequency can effectively absorb the pump energy for amplification. The remaining seed signal not picked up by the pulsed pump absorbs the remaining pump light in the system, and therefore no longer converts to ASE. Consequently, ASE in the system is effectively suppressed.

[0030] 3. Compared with existing solutions currently used to suppress ASE in ultra-low repetition rate (10-100Hz) fiber pulse laser amplification: for example, inserting an AOM into the system for laser time-domain filtering or synchronously amplifying low repetition rate pulses and continuous optical signals and then filtering, these solutions all require the introduction of additional filtering devices into the laser system. Such filtering devices are often expensive and need to be customized. There is also insertion loss to a certain extent, which increases the complexity of the system structure and reduces the laser energy. The high repetition rate seed low repetition rate pump amplification solution proposed in the present invention is specifically aimed at 10-100Hz pulse laser amplification. It does not require the introduction of additional filtering devices into the system, ensures the simplicity of the system structure, and further reduces the cost of the laser system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic structural diagram of a low repetition rate fiber pulse laser amplification system provided by an embodiment of the present invention.

[0032] Figure 2 Schematic diagram of amplifying a high-repetition-rate seed signal with a low-repetition-rate pump pulse.

[0033] Figure 3 This is a time domain output diagram of the pulse after passing through the first-stage amplification unit of the present invention.

[0034] Figure 4 This is a time domain output diagram of the pulse after passing through the three-stage amplification unit of the present invention.

[0035] Figure 5 The present invention finally outputs an energy detection map after passing through three-stage amplification units.

[0036] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0037] 10-nanosecond pulse seed source; 11-seed isolation filter; 20-first-stage amplification unit; 21-first-stage pump light source; 22-first-stage wavelength division multiplexer; 23-first-stage gain fiber; 24-first-stage isolation filter; 30-second-stage amplification unit; 31-second-stage pump light source; 32-second-stage combiner; 33-second-stage gain fiber; 34-second-stage isolation filter; 40-third-stage amplification unit; 41-third-stage pump light source; 42-third-stage combiner; 43-third-stage gain fiber; 50-fiber output collimator. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0039] The present invention provides a low repetition rate fiber pulse laser amplification system, comprising a nanosecond pulse seed source and a first-stage amplification unit; the first-stage amplification unit comprises a first-stage pump light source, a first-stage wavelength division multiplexer, and a first-stage gain fiber; the nanosecond pulse seed source is used to output nanosecond pulse seeds, and the first-stage pump light source is used to output pump light;

[0040] The output ends of the nanosecond pulse seed source and the first-level pump light source are both connected to the input end of the first-level wavelength division multiplexer, and the output end of the first-level wavelength division multiplexer is connected to the first-level gain fiber, so as to coaxially couple the nanosecond pulse seed and pump light into the first-level gain fiber to achieve amplification;

[0041] The frequency of the pump light is lower than the frequency of the nanosecond pulse seed, and is used to perform pulse picking and amplification on the signal corresponding to the pump light frequency in the nanosecond pulse seed to obtain a low repetition rate pulse laser signal with a frequency less than 1 kHz.

[0042] The repetition frequency of the nanosecond signal output by the nanosecond pulse seed source is generally between 1kHz and 1.3kHz. By adjusting the pump pulse frequency (10-100Hz), pulse picking and amplification are performed in the seed signal. The higher-frequency pulse seed signal light can effectively suppress the ASE effect in the system under the low-frequency pump pulse amplification. In addition, pulse picking based on the pump pulse and amplifying only the pulse signal of a specific frequency can effectively improve the seed pulse signal of about 1kHz to a low-repetition-rate signal below 100Hz. The low-repetition-rate fiber pulse laser system designed by the present invention adopts a high-repetition-rate pulse seed low-repetition-rate pump amplification scheme to pick up and amplify part of the low-repetition-rate signal in the seed. The remaining seed signal that is not effectively amplified absorbs the remaining pump light to a certain extent, suppressing the process of converting the remaining pump light into ASE, and effectively suppressing the generation of ASE during the laser amplification process.

[0043] In particular, the low repetition rate fiber pulse laser amplification system further comprises a secondary amplification unit and a tertiary amplification unit which are sequentially arranged after the output end of the primary gain fiber along the signal transmission direction;

[0044] The secondary amplification unit includes a secondary pump light source, a secondary beam combiner and a secondary gain fiber arranged in sequence along the signal transmission direction; the tertiary amplification unit includes a tertiary pump light source, a tertiary beam combiner and a tertiary gain fiber arranged in sequence along the signal transmission direction;

[0045] The output ends of the primary gain fiber and the secondary pump light source are both connected to the input end of the secondary combiner, and the output ends of the secondary gain fiber and the tertiary pump light source are connected to the input end of the tertiary combiner.

[0046] The wavelength division multiplexer (WDM) is used to combine and separate multiple wavelengths of light. Its core function is to efficiently couple pump light and signal light while minimizing energy loss. The gain fiber converts pump light energy into signal light energy through stimulated emission of radiation, achieving efficient laser amplification.

[0047] A seed isolation filter is further provided between the nanosecond pulse seed source and the first-stage wavelength division multiplexer;

[0048] The first-stage amplification unit further includes a first-stage isolation filter disposed between the first-stage gain optical fiber and the second-stage combiner;

[0049] The secondary amplification unit further includes a secondary isolation filter arranged between the secondary gain optical fiber and the tertiary combiner.

[0050] Specifically, the low repetition rate fiber pulse laser amplification system includes:

[0051] A nanosecond pulse seed source and a seed isolation filter arranged after the nanosecond pulse seed source;

[0052] The first-stage amplification unit provided at the output end of the nanosecond pulse seed source includes a first-stage pump light source, a first-stage wavelength division multiplexer, a first-stage gain fiber, and a first-stage isolation filter; a first-stage wavelength division multiplexer is further connected between the first-stage gain fiber and the output end of the seed source, and the input end of the wavelength division multiplexer is further connected to a first-stage pump light source;

[0053] The secondary amplification unit is provided after the primary amplification unit, and includes a secondary beam combiner, a secondary gain fiber, a secondary isolation filter and a secondary pump light source;

[0054] The third-stage amplification unit is arranged after the second-stage amplification unit, and includes a three-stage beam combiner, a three-stage gain fiber and a three-stage pump light source;

[0055] The optical fiber output collimator is located after the third-level gain fiber and is used for system output.

[0056] The nanosecond pulse seed source is used to output a high-repetition-rate pulsed seed laser exceeding 1kHz. The pump light source uses electronic control to achieve low-repetition-rate pulse pumping, which amplifies the high-repetition-rate seed laser pulse by pulse-pickup amplification. Multiple pumping passes through a wavelength division multiplexer and a beam combiner within the laser, increasing the output energy of the signal light and ultimately achieving high-energy, low-repetition-rate nanosecond pulsed laser output. Isolation filters at each stage block reflected light to prevent damage to the previous amplification unit, maintaining system stability.

[0057] Particularly, the first-level gain fiber is a single-clad ytterbium-doped fiber with a core diameter of 6 μm and a cladding diameter of 125 μm, and an absorption efficiency of 250 dB / m@976 nm.

[0058] The secondary gain optical fiber is a double-clad ytterbium-doped optical fiber with a core diameter of 10-20 μm and an inner cladding diameter of 125-130 μm, and an absorption efficiency of 4.3 dB / m@976 nm.

[0059] The three-stage gain optical fiber is a double-clad ytterbium-doped optical fiber with a core diameter of 20-1000 μm and an inner cladding diameter of 400-600 μm, and an absorption efficiency of 3.6 dB / m@976 nm.

[0060] The first-order gain optical fiber further includes a coating layer covering the outer periphery of the single-clad ytterbium-doped optical fiber.

[0061] The secondary gain fiber and the tertiary gain fiber further include a low refractive index outer cladding coated on the periphery of the inner cladding, that is, the refractive index of the outer cladding of the secondary gain fiber and the tertiary gain fiber is lower than that of the inner cladding and the core.

[0062] Furthermore, the secondary gain optical fiber and the tertiary gain optical fiber further include a coating layer coated on the periphery of the outer cladding.

[0063] The present invention also provides a method for amplifying a low repetition rate pulse laser signal, comprising: outputting a nanosecond pulse seed from a nanosecond pulse seed source, then adjusting the frequency of the pump light in the amplification system to be lower than the frequency of the nanosecond pulse seed, performing pulse picking and amplification on a signal in the nanosecond pulse seed corresponding to the pump light frequency, and obtaining a low repetition rate pulse laser signal with a frequency less than 1 kHz.

[0064] Furthermore, the nanosecond pulse seed is sequentially amplified through three amplification systems, and the pump light sources of the three amplification systems generate the same frequency of pump light;

[0065] Specifically, the first-level pump light source injects the pump light into the first-level gain fiber through the first-level wavelength division multiplexer, amplifies the signal light, filters out the stray light components in the signal light through the first-level isolation filter, and then injects the signal light into the second-level gain fiber through the second-level combiner. The second-level pump light source injects the pump light into the second-level gain fiber through the second-level combiner, amplifies the signal light again, and then passes through the second-level isolation filter to select the wavelength and filter out the stray light.

[0066] The three-stage pump light source injects the pump light into the three-stage amplification unit through the three-stage beam combiner, which performs the final power amplification on the signal light.

[0067] Finally, the signal light output from the three-stage gain optical fiber enters the optical fiber output collimator to collimate the laser output.

[0068] The following are specific embodiments

[0069] Example 1

[0070] See also Figure 1 The present invention provides a low repetition rate nanosecond fiber laser, comprising a nanosecond pulse seed source 10, a first-stage amplification unit 20, a second-stage amplification unit 30, a third-stage amplification unit 40, and a fiber output collimator 50. The first-stage amplification unit 20 and the second-stage amplification unit 30 are used to amplify the nanosecond seed laser generated by the nanosecond pulse seed source 10. The third-stage amplification unit 40 is the main amplification stage, used for the final amplification of the signal laser. The fiber output collimator 50 is used for laser energy transmission and output.

[0071] Specifically, the low repetition rate nanosecond fiber laser includes: a nanosecond pulse seed source 10, a seed filter isolator 11 provided at the output end of the nanosecond pulse seed source 10, a first-stage amplification unit 20 provided at the output end of the seed filter isolator 11, a second-stage amplification unit 30 provided at the output end of the first-stage amplification unit 20, a third-stage amplification unit 40 provided at the output end of the second-stage amplification unit 30, and a fiber output collimator 50 provided at the output end of the third-stage amplification unit 40.

[0072] The nanosecond pulse seed source 10 is used to output a high repetition rate pulse signal of more than 1kHz; after passing through the seed isolation filter 11, it is injected into the first-stage amplification unit 20;

[0073] The first-stage amplification unit 20 includes a first-stage wavelength division multiplexer 22 provided at the output end of the seed isolation filter 11, a first-stage gain fiber 23 provided at the output end of the first-stage wavelength division multiplexer 22, a first-stage pump light source 21 provided at the input end of the first-stage wavelength division multiplexer 22, and a first-stage isolation filter 24 provided at the output end of the first-stage gain fiber 23;

[0074] The secondary amplification unit 30 includes a secondary combiner 32 provided at the output end of the primary isolation filter 24, a secondary gain fiber 33 provided at the output end of the secondary combiner 32, a secondary pump light source 31 provided at the input end of the secondary combiner 32, and a secondary isolation filter 34 provided at the output end of the secondary gain fiber 33;

[0075] The three-stage amplification unit 40 includes a three-stage combiner 42 provided at the output end of the secondary isolation filter 34 , a three-stage gain fiber 43 provided at the output end of the three-stage combiner 42 , and a three-stage pump light source 41 provided at the input end of the three-stage combiner 42 .

[0076] The first-stage amplifier unit 20 uses a first-stage gain fiber 23 to amplify the signal laser. The first-stage gain fiber 23 is a single-clad silica ytterbium-doped fiber with a core diameter of 6 μm and a cladding diameter of 125 μm. The second-stage amplifier unit 30 uses a second-stage gain fiber 33 to amplify the light. The second-stage gain fiber 33 is a double-clad silica ytterbium-doped fiber with a core diameter of 20 μm and an inner cladding diameter of 125 μm. The third-stage amplifier unit 40 uses a third-stage gain fiber 43 to amplify the light. The third-stage gain fiber 43 is a double-clad silica ytterbium-doped fiber with a core diameter of 50 μm and an inner cladding diameter of 400 μm.

[0077] Specifically, quartz ytterbium-doped fiber serves as a gain medium. When light is incident on the fiber, the energy carried by the incident light excites the electrons in the medium to a higher energy level due to the absorption of the medium. Through the relaxation phenomenon, the electrons transition from the high energy level to the ground state, releasing energy and emitting photons. In this embodiment of the present invention, the nanosecond pulse seed source 10 is used to output a 1064nm band signal light with a repetition rate of 1.3kHz and a pulse width of 10ns. The input end of the seed isolation filter 11 is connected to the output end of the nanosecond seed module to prevent the backward return light in the first-stage amplification unit from damaging the seed source.

[0078] Specifically, the output wavelength of the seed signal light is within the range of 1050 to 1070 nm. The seed isolation filter 11 includes a bandpass filter with a central wavelength of 1064 nm and an output bandwidth of 8 nm. After passing through the isolation filter, the output wavelength of the seed signal light is 1060 nm to 1068 nm.

[0079] Specifically, the primary pump light source 21 , the secondary pump light source 31 , and the tertiary pump light source 41 are all pulse pumps, and the repetition frequencies of their output pulses are the same and aligned with the falling edges of the corresponding seed signals to be amplified.

[0080] Specifically, the length of the first-stage gain fiber 23 is 1.5 m, the length of the second-stage gain fiber 33 is 3.5 m, and the length of the third-stage gain fiber 43 is 4 m.

[0081] Specifically, the seed isolation filter 11 also includes an isolator. This is a passive optical isolator device that allows light to pass in one direction, and its operating principle is based on the non-reciprocity of Faraday rotation. The seed isolation filter 11 is a passive device that allows light to pass in one direction but blocks light in the opposite direction. This restricts the direction of light transmission, allowing it to travel in only one direction. Light reflected by the optical fiber is effectively isolated by the primary isolation filter 24, improving light transmission efficiency.

[0082] Specifically, in this embodiment of the present invention, the operating principles of the primary isolation filter 24 and the secondary isolation filter 34 are similar to those of the seed isolation filter 11. The input end of the primary isolation filter 24 is connected to the primary gain fiber 23, and the passive optical fiber corresponding to the primary isolation filter 24 matches the primary gain fiber 23. The input end of the secondary isolation filter 34 is connected to the secondary gain fiber 33, and the passive optical fiber corresponding to the secondary isolation filter 34 matches the secondary gain fiber 33.

[0083] Specifically, the first-stage wavelength division multiplexer 22, the second-stage combiner 32, and the third-stage combiner 42 are optical devices that realize the distribution or combination of optical signal power among different optical fibers, and are constructed by utilizing the mutual exchange of guided wave energy in adjacent optical fiber core regions on different optical fiber surfaces.

[0084] Specifically, in this embodiment of the present invention, the input end of the first-stage wavelength division multiplexer 22 is connected to the output end of the seed isolation filter 11, and the output end of the first-stage wavelength division multiplexer 22 is connected to the first-stage gain fiber 23. The input end of the second-stage combiner 32 is connected to the output end of the first-stage isolation filter 24, and the output end of the second-stage combiner 32 is connected to the second-stage gain fiber 33. The input end of the tertiary combiner 42 is connected to the output end of the second-stage isolation filter 34, and the output end of the tertiary combiner 42 is connected to the tertiary gain fiber 43.

[0085] Specifically, the optical fiber output collimator 50 is connected to the three-stage gain optical fiber 43 for the final output of the laser system.

[0086] Specifically, the primary pump light source 21, the secondary pump light source 31, and the tertiary pump light source 41 are respectively connected to the pump arms of the primary wavelength division multiplexer 22, the secondary combiner 32, and the tertiary combiner 42 to provide pump energy for the amplification system.

[0087] like Figure 2 As shown, the seed pulse signal output by the pulse seed source is 1.3kHz, and the pump pulse signal output by the pump light source is 100Hz. Therefore, on average, one seed pulse is amplified normally in 13 seed pulse signals. The first-stage amplification unit 20 outputs a pulse signal as shown in FIG. Figure 3 As shown, among every 13 signals, there is one with relatively high intensity, while the remaining signals are relatively weak. After passing through the secondary amplification unit 30 and the tertiary amplification unit 40, the stronger signal is continuously amplified, while the weaker signal is gradually attenuated during the amplification process until it becomes too weak to be detected. Figure 5 The final laser energy output by the system is 11.04mJ.

[0088] In summary, unlike existing technical solutions, the present invention provides a low-repetition-rate nanosecond pulsed fiber laser that uses a pulse seed to output a high-repetition-rate pulse signal laser. Low-repetition-rate pump output is achieved through electrically controlled pump light sources. The high-repetition-rate pulse signal laser is pulse-pickup and amplified, while the remaining seed signal that is not effectively amplified is used to absorb the remaining pump light to suppress the generation of ASE. The low-repetition-rate fiber pulse laser amplification system provided by the present invention can achieve higher-energy laser output through clever suppression of ASE. The pulsed fiber laser of the present invention has a simple structure, low cost, and is easy to integrate into laser systems.

[0089] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A low repetition rate fiber pulse laser amplification system, characterized in that: It includes a nanosecond pulse seed source and a first-level amplification unit; the first-level amplification unit includes a first-level pump light source, a first-level wavelength division multiplexer and a first-level gain fiber; the nanosecond pulse seed source is used to output nanosecond pulse seeds, and the first-level pump light source is used to output pump light; The output ends of the nanosecond pulse seed source and the first-level pump light source are both connected to the input end of the first-level wavelength division multiplexer, and the output end of the first-level wavelength division multiplexer is connected to the first-level gain fiber, so as to coaxially couple the nanosecond pulse seed and pump light into the first-level gain fiber to achieve amplification; The frequency of the pump light is lower than the frequency of the nanosecond pulse seed, and is used to perform pulse picking and amplification on the signal corresponding to the pump light frequency in the nanosecond pulse seed to obtain a low repetition rate pulse laser signal with a frequency less than 1 kHz.

2. The low repetition rate fiber pulse laser amplification system according to claim 1, characterized in that: The frequency of the nanosecond pulse seed source is 1 kHz-1.3 kHz, and the frequency of the pump light is 10 Hz-100 Hz.

3. The low repetition rate fiber pulse laser amplification system according to claim 1, characterized in that: It also includes a secondary amplification unit and a tertiary amplification unit which are sequentially arranged after the output end of the primary gain optical fiber along the signal transmission direction; The secondary amplification unit includes a secondary pump light source, a secondary beam combiner and a secondary gain fiber arranged in sequence along the signal transmission direction; the tertiary amplification unit includes a tertiary pump light source, a tertiary beam combiner and a tertiary gain fiber arranged in sequence along the signal transmission direction; The output ends of the primary gain fiber and the secondary pump light source are both connected to the input end of the secondary combiner, and the output ends of the secondary gain fiber and the tertiary pump light source are connected to the input end of the tertiary combiner.

4. The low repetition rate fiber pulse laser amplification system according to claim 3, characterized in that: A seed isolation filter is further provided between the nanosecond pulse seed source and the first-stage wavelength division multiplexer; The first-stage amplification unit further includes a first-stage isolation filter disposed between the first-stage gain optical fiber and the second-stage combiner; The secondary amplification unit further includes a secondary isolation filter arranged between the secondary gain optical fiber and the tertiary combiner.

5. The low repetition rate fiber pulse laser amplification system according to claim 3, characterized in that: The output type of the three-stage gain optical fiber is connected to an optical fiber output collimator, which is used to output the low repetition rate pulse laser signal with a final amplification frequency less than 1 kHz.

6. The low repetition rate fiber pulse laser amplification system according to claim 3, characterized in that: The primary gain fiber is a single-clad silica ytterbium-doped fiber, the secondary gain fiber and the tertiary gain fiber are double-clad silica ytterbium-doped fibers, and the core diameters of the primary gain fiber, the secondary gain fiber and the tertiary gain fiber increase in sequence.

7. The low repetition rate fiber pulse laser amplification system according to claim 6, characterized in that: The core diameter of the first-level gain fiber is 5-7 μm, and the pump absorption efficiency at 976 nm is 250 dB / m; The core diameter of the secondary gain fiber is 10-20 μm, and the pump absorption efficiency at 976 nm is 4.3 dB / m; The core diameter of the three-stage gain optical fiber is 20-1000 μm, and the pump absorption efficiency at 976 nm is 3.6 dB / m.

8. The low repetition rate fiber pulse laser amplification system according to claim 3, characterized in that: The primary pump light source, the secondary pump light source, and the tertiary pump light source are semiconductor pump lasers with wavelengths within the range of 915nm-1018nm; The pumping lights generated by the primary pumping light source, the secondary pumping light source, and the tertiary pumping light source have the same frequency.

9. A method for amplifying a low repetition rate pulse laser signal, characterized in that: The low repetition rate fiber pulse laser amplification system according to any one of claims 1 to 8 comprises: a nanosecond pulse seed source outputting a nanosecond pulse seed, then adjusting the frequency of the pump light in the amplification system to be lower than the frequency of the nanosecond pulse seed, performing pulse picking and amplification on a signal in the nanosecond pulse seed corresponding to the pump light frequency, and obtaining a low repetition rate pulse laser signal with a frequency less than 1 kHz.

10. The method for amplifying a low repetition rate pulse laser signal according to claim 9, characterized in that: Passing the nanosecond pulse seed through three amplification systems in sequence to amplify the signal, wherein the pump light sources of the three amplification systems generate pump lights of the same frequency; Specifically, the first-level pump light source injects the pump light into the first-level gain fiber through the first-level wavelength division multiplexer, amplifies the signal light, filters out the stray light components in the signal light through the first-level isolation filter, and then injects the signal light into the second-level gain fiber through the second-level combiner. The second-level pump light source injects the pump light into the second-level gain fiber through the second-level combiner, amplifies the signal light again, and then passes through the second-level isolation filter to select the wavelength and filter out the stray light. The three-stage pump light source injects the pump light into the three-stage amplification unit through the three-stage beam combiner, which performs the final power amplification on the signal light. Finally, the signal light output from the three-stage gain optical fiber enters the optical fiber output collimator to collimate the laser output.

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