High energy femtosecond 780nm laser based on all polarization-maintaining fiber system

Abstract

This invention provides a high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system. The device comprises two parts: the first part is a chirped pulse amplification system, including a seed source, a time-domain stretching stage, a first preventive stage, a frequency reduction stage, a second preventive stage, a main amplification stage, and a compression stage. These stages are connected sequentially. The second part is a frequency doubling system. The fiber laser uses a laser diode with a pigtail output as the pump source and doped fiber as the gain medium. The generated light propagates within the fiber, exhibiting strong environmental adaptability, and the light output from within the fiber has excellent beam quality, which is beneficial for improving the conversion efficiency of nonlinear crystals. This solves the problems of poor output beam quality and low conversion efficiency in traditional solid-state lasers.

Description

Technical Field

[0001] This invention belongs to the field of lasers. Background Technology

[0002] CPA: Chirped Pulse Amplifier.

[0003] CFBG: Chirped Bragg Fiber Grating

[0004] MgO: PPLN crystal: Periodically polarized lithium niobate crystal doped with MgO

[0005] In 1981, Professor Caves first proposed the concept of "squeezed states" and pointed out that squeezed state optical fields could improve the sensitivity of laser interferometry gravitational wave detection. Over the past four decades, squeezed state optical fields have not only been successfully used in quantum precision measurement fields such as gravitational wave detection, displacement measurement, and phase measurement—all of which break the standard quantum limit—but also, dual-mode squeezed states and multi-component entangled states prepared based on single-mode squeezed states play important roles in quantum information processing such as quantum computing and quantum communication. Parametric down-conversion processes pumped by femtosecond or picosecond pulses are one of the important methods for obtaining squeezed states of optical fields.

[0006] As the most important component of the compressed optical field, the development of novel femtosecond light sources will play a crucial role in the integrated innovation and core technology breakthroughs of the entire system. Currently, the pump source for the compressed optical field uses Ti:sapphire femtosecond lasers. Compared with all-fiber femtosecond lasers, Ti:sapphire laser systems still have many shortcomings: their large size and weight make it difficult to achieve system miniaturization and integration; and the free-space laser output affects the system integration and application flexibility.

[0007] With the rapid development of fiber laser technology, passive mode-locking, chirped pulse amplification (CPA), and frequency doubling techniques have enabled the achievement of ultrashort pulse laser output comparable to Ti:sapphire lasers, with more compact systems, higher integration, and better laser output stability. Considering current applications and development trends in optical field squeezed states, high-energy femtosecond erbium-doped fiber lasers and their frequency doubling systems will gradually replace Ti:sapphire lasers in the generation of optical field squeezed states.

[0008] Currently, there are no publicly available devices or solutions that utilize a high-energy 780nm femtosecond laser with an all-fiber structure as a compressed-state pump source. Generally, traditional compressed-state pump sources mostly employ all-solid-state lasers. These laser systems are relatively large, susceptible to external environmental interference, and have high overall costs. Furthermore, such lasers require complex and bulky water-cooling systems and numerous space-consuming components, which is detrimental to system packaging and integration.

[0009] Furthermore, most existing all-fiber 780nm femtosecond lasers use amplifiers made of non-polarization-maintaining fibers, resulting in polarization amplification that is highly sensitive to vibration, motion, and temperature changes. Therefore, the long-term stability of such 780nm femtosecond lasers cannot be guaranteed. Constructing a 1560nm femtosecond system using all-polarization-maintaining (all-PM) fibers is an effective method to improve polarization stability and stabilize 780nm femtosecond laser output. To date, only a few published papers have reported on femtosecond 780nm lasers based on all-polarization-maintaining fiber systems, but the single-pulse energies are only in the tens of nJ range, which is insufficient for current application requirements.

[0010] Using all-solid-state lasers as pump sources for compressed optical fields has the following disadvantages:

[0011] 1) Large size and complex structure make it difficult to miniaturize and integrate the light source.

[0012] 2) It requires a large number of space components, is easily affected by the external environment, and remains at the laboratory stage, failing to meet the application requirements of special environments.

[0013] 3) All-solid-state lasers have significant thermal effects when operating at high power, and problems such as thermal lensing can occur in the crystal. The beam quality of the output laser will be severely degraded, which is not conducive to the nonlinear frequency conversion process and results in low conversion efficiency. Summary of the Invention

[0014] This invention solves the following problems:

[0015] 1) Solving the problem of large size and complex structure of traditional all-solid-state lasers. Fiber has good flexibility and can be coiled in a small disk, which greatly reduces the space volume and is conducive to miniaturization and integration; at the same time, due to the large surface area to volume ratio of fiber, it has excellent heat dissipation performance, so there is no need for a large and complicated heat dissipation device, which is conducive to achieving low cost and small size;

[0016] 2) Solid-state lasers largely utilize space-based devices, and the light they generate is transmitted through the air, making them highly susceptible to interference from the external environment. Fiber lasers, on the other hand, use laser diodes with pigtail outputs as pump sources and doped optical fibers as gain media. The generated light propagates within the fiber, exhibiting strong environmental adaptability, and the light output from within the fiber possesses excellent beam quality, which is beneficial for improving the conversion efficiency of nonlinear crystals. This solves the problems of poor output beam quality and low conversion efficiency in traditional solid-state lasers.

[0017] 3) Using an all-fiber laser can achieve a compact, highly stable, and highly efficient light source.

[0018] The high-energy femtosecond 780nm laser device based on a fully polarization-maintaining fiber system described in this invention is as follows: Figure 1 As shown, the device comprises two parts. The first part is a chirped pulse amplification system, including: a seed source, a time-domain stretching stage, a first preventive stage, a down-amplifier stage, a second preventive stage, a main amplification stage, and a compression stage. These stages are connected sequentially. The second part is a frequency multiplication system.

[0019] In the diagram, 0101 represents the first laser diode, which can be a single-mode semiconductor laser diode with a center wavelength of 976nm. Its pigtail can be fused to the optical fiber using a fiber optic fusion splicer without spatial coupling. The function of the first laser diode is to provide energy, and the output light pumps the first polarization-maintaining fiber.

[0020] In the figure, 0201 is the first polarization-maintaining wavelength division multiplexer. The signal end pigtail is selected as a polarization-maintaining fiber, the pump end is connected to the pigtail of the first laser diode, and the output end is connected to the doped fiber. Its function is to couple the light output from the first laser diode into the doped fiber.

[0021] In the figure, 0301 is the first polarization-maintaining fiber, which is an erbium-doped fiber with positive dispersion. Its function is twofold: firstly, the erbium-doped fiber can provide gain, and secondly, the fiber with positive dispersion can compensate for the negative dispersion in the cavity, thus forming dispersion-managed mode-locking.

[0022] In the diagram, 0401 is a polarization-maintaining fiber beam splitter. A 1×2 polarization-maintaining fiber beam splitter can be used, with one end serving as the output and the other end returning to the cavity. All fiber pigtails are polarization-maintaining fibers. Their function is to output energy outside the cavity, serving as a seed source.

[0023] In the diagram, 0501 is the first polarization-maintaining fiber circulator. Input light enters through port 1 and exits through port 2. Light returning from port 2 can be output from port 3. All fiber pigtails are polarization-maintaining fibers. Their function is to provide unidirectional optical path conduction, and they can also be used with some reflective devices to form a laser cavity.

[0024] In the diagram, 0601 is a semiconductor saturable absorber. The semiconductor saturable absorber can be packaged in a flat-head fiber optic patch cord and placed in a flange, connected to it using a polarization-maintaining flat-head fiber optic patch cord.

[0025] In the diagram, 0701 is the first polarization-maintaining isolator, and all fiber pigtails are polarization-maintaining fibers. Adding a polarization-maintaining isolator ensures unidirectional optical path conduction, preventing reflected light from damaging components in the preceding optical path.

[0026] In the figure, 0302 is the second polarization-maintaining fiber. The polarization-maintaining dispersion compensation fiber is selected. Its function is to broaden the time-domain pulse width to the picosecond level. On the other hand, due to the small mode field of the dispersion compensation fiber, nonlinear effects are generated, which broadens the seed source spectrum.

[0027] In the diagram, 0702 is the second polarization-maintaining isolator, and all fiber pigtails are polarization-maintaining fibers. Adding a polarization-maintaining isolator ensures unidirectional optical path conduction, preventing reflected light from damaging components in the preceding optical path.

[0028] In the diagram, 0502 is the second polarization-maintaining fiber circulator. Input light enters through port 1 and exits through port 2. Light returning from port 2 can be output from port 3. All fiber pigtails are polarization-maintaining fibers.

[0029] In the diagram, 0801 is a chirped Bragg fiber grating, which can be either a total reflection or partial reflection grating. Bragg fiber gratings can provide positive dispersion, further widening the pulse width to the nanosecond level.

[0030] In the diagram, 0303 is the third polarization-maintaining fiber, which is made of erbium-doped fiber. Its function is to provide gain for signal light amplification and increase the signal light power to the level of hundreds of milliwatts.

[0031] In the diagram, 0202 is the second polarization-maintaining wavelength division multiplexer. The signal end uses a polarization-maintaining fiber as its pigtail, the pump end is connected to the pigtail of the second laser diode, and the output end is connected to the doped fiber. Its function is to couple the light output from the second laser diode into the doped fiber.

[0032] In the diagram, 0102 represents the second laser diode, which can be a single-mode semiconductor laser diode with a center wavelength of 976nm. Its pigtail can be fused to the optical fiber using a fiber optic fusion splicer, without the need for spatial coupling. The function of the second laser diode is to provide energy, and the output light pumps the third polarization-maintaining fiber.

[0033] In the diagram, 0703 is the third polarization-maintaining isolator, and all fiber pigtails are polarization-maintaining fibers. Adding a polarization-maintaining isolator ensures unidirectional optical path conduction, preventing reflected light from damaging components in the preceding optical path.

[0034] In the diagram, 0901 is an acousto-optic modulator, which reduces the pulse repetition frequency to 1MHz.

[0035] In the diagram, 0304 is the fourth polarization-maintaining fiber, which is made of erbium-doped fiber. Its function is to provide gain for signal light amplification and increase the signal light power to the level of hundreds of milliwatts.

[0036] In the diagram, 0203 is the third polarization-maintaining wavelength division multiplexer. The signal end uses a polarization-maintaining fiber as its pigtail, the pump end is connected to the pigtail of the third laser diode, and the output end is connected to the doped fiber. Its function is to couple the light output from the third laser diode into the doped fiber.

[0037] In the diagram, 0103 represents the third laser diode, which can be a single-mode semiconductor laser diode with a center wavelength of 976nm. Its pigtail can be fused to the optical fiber using a fiber optic fusion splicer, without the need for spatial coupling. The function of the third laser diode is to provide energy, and the output light pumps the fourth polarization-maintaining fiber.

[0038] In the diagram, 0704 is the fourth polarization-maintaining isolator, and all fiber pigtails are polarization-maintaining fibers. Adding a polarization-maintaining isolator ensures unidirectional optical path conduction, preventing reflected light from damaging components in the preceding optical path.

[0039] In the figure, 1001 is a pump combiner, which can be a (6+1)×1 pump signal combiner. Its input end is connected to the pigtail of the laser diode, and its output end is connected to the doped fiber. Its function is to couple the light output from the multimode laser diode into the doped fiber.

[0040] In the diagram, 1101 is a multimode laser diode. A semiconductor laser diode with a center wavelength of 976nm can be selected. Its pigtail can be fused to the optical fiber using a fiber optic fusion splicer without spatial coupling. The function of the laser diode is to provide energy, and the output light pumps the doped optical fiber.

[0041] In the diagram, 0305 is the fifth polarization-maintaining fiber, which is a polarization-maintaining large-mode-field erbium-ytterbium co-doped fiber. Its function is to provide gain for signal light amplification, increase the signal light power, and amplify the single-pulse energy to the μJ level.

[0042] In the diagram, 1201 is the first focusing lens, which expands the output signal light and collimates the laser output from the optical fiber.

[0043] In the diagram, 1301 is the first dichroic mirror, which separates the 976nm pump light from the 1560nm signal light.

[0044] In the diagram, 1401 is the first half-wave plate, which can adjust the polarization state of the signal light.

[0045] In the diagram, 1501 is the first plane mirror. The function of the 1501 plane mirror is to redirect the reflected light by 90°.

[0046] In the diagram, 1601 is a transmission grating pair. By adding a plane mirror to form a double-pass structure, the pulse undergoes four diffractions as it passes through the grating pair, compensating for the introduced positive dispersion.

[0047] In the diagram, 1502 is the second plane mirror. The function of the 1502 plane mirror is to reflect the light transmitted from the transmissive grating back.

[0048] In the diagram, 1402 is the second half-wave plate, which can adjust the polarization state of the signal light.

[0049] In the diagram, 1202 is the second focusing lens, which can focus the output laser and reduce the laser spot entering the nonlinear crystal.

[0050] In the diagram, 1701 is a temperature-controlled furnace, which is used to regulate the temperature of the nonlinear crystal. Adjusting its operating temperature can achieve stable and efficient frequency doubling results.

[0051] In the figure, 1801 is a nonlinear crystal, specifically an MgO:PPLN crystal. By utilizing the frequency upconversion function of this crystal, low-frequency pump light can be converted into high-frequency signal light.

[0052] In the diagram, 1203 is the third focusing lens, which serves to expand the beam and collimate the output frequency-doubled light.

[0053] In the diagram, 1302 is the second dichroic mirror, which separates the signal light, the frequency-doubled light, and part of the combined light.

[0054] Based on the above description, the composition and function of each part of the dashed box in the figure will be summarized below.

[0055] First, an overview of each stage of the chirped pulse amplification system is given.

[0056] The seed source includes a first laser diode (0101), a first polarization-maintaining wavelength division multiplexer (0201), a first polarization-maintaining fiber (0301), a polarization-maintaining fiber beam splitter (0401), a first polarization-maintaining fiber circulator (0501), a semiconductor saturable absorber mirror (0601), and a first polarization-maintaining isolator (0701), which are used to generate microwatt-level 1560nm laser pulses as seeds.

[0057] The time-domain stretching stage includes a second polarization-maintaining fiber (0302), a second polarization-maintaining isolator (0702), a second polarization-maintaining fiber circulator (0502), and a chirped Bragg fiber grating (0801). Its function is to stretch the pulse output from the seed source in the time domain to the nanosecond level.

[0058] The first prevention stage includes a third polarization-maintaining fiber (0303), a second polarization-maintaining wavelength division multiplexer (0202), a second laser diode (0102), and a third polarization-maintaining isolator (0703). Its function is to boost the signal light output from the broadening stage to the level of hundreds of milliwatts.

[0059] The down-frequency stage includes an acousto-optic modulator (0901), which reduces the pulse repetition frequency to 1MHz.

[0060] The second prevention stage includes a fourth polarization-maintaining fiber (0304), a third polarization-maintaining wavelength division multiplexer (0203), a third laser diode (0103), and a fourth polarization-maintaining isolator (0704), the function of which is to boost the signal light output from the down-conversion stage to the level of hundreds of milliwatts.

[0061] The main amplification stage includes a multimode laser diode (1101), a pump combiner (1001), a fifth polarization-maintaining fiber (0305), a first focusing lens (1201), and a first dichroic mirror (1301). Its function is to increase the single-pulse energy of the signal light output from the second pre-amplification stage to the order of μJ.

[0062] The compression stage includes a first half-wave plate (1401), a first plane mirror (1501), a transmission grating pair (1601), and a second plane mirror (1502), and its function is to compress the pulse to the fs level through dispersion compensation.

[0063] Finally, an overview of the frequency multiplication system is provided.

[0064] The frequency doubling system includes a second half-wave plate (1402), a second focusing lens (1202), a temperature-controlled furnace (1701), a nonlinear crystal (1801), a third focusing lens (1203), and a second dichroic mirror (1302). Its function is to double the high-energy femtosecond 1560nm signal light output from the chirped pulse amplification system to the 780nm band.

[0065] The high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system designed in this invention does not require a complex and bulky water-cooling system, and has a significant advantage over the current mainstream solid-state lasers in terms of overall cost and operating cost.

[0066] The high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system designed in this invention has a simple structure and the fully fiber-based pump source design is easy to integrate. Therefore, it is easy to realize a compact, low-cost, miniaturized, integrated high-energy femtosecond 780nm fiber laser.

[0067] The high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system designed in this invention can achieve MHz pulse output with a maximum single pulse energy on the order of uJ, which can meet the needs of different applications. Attached Figure Description

[0068] Figure 1 Chirped pulse amplification system connection diagram

[0069] Figure 2 Connection diagram of frequency multiplication system device Detailed Implementation

[0070] The high-energy femtosecond 780nm laser device based on a fully polarization-maintaining fiber system described in this invention consists of a chirped pulse amplification system and a frequency doubling system. The chirped pulse amplification system includes a seed source, a time-domain stretching stage, a first pre-amplification stage, a frequency reduction stage, a second pre-amplification stage, a main amplification stage, and a compression stage. The seed source is used for high-quality femtosecond laser pulse output. After the output signal pulse enters the stretching stage, its time domain is stretched. Subsequently, after pre-amplification, frequency reduction, pre-amplification, and main amplification to increase the single-pulse energy, the compression stage compensates for dispersion, restoring the femtosecond level. Then, the high-energy femtosecond pulse enters the frequency doubling system to obtain a high-energy femtosecond 780nm laser output.

[0071] The overall technical principles and implementation process of the technical solution are as follows:

[0072] (1) The device uses a mode-locked laser as the seed source of the chirped pulse amplification system. The seed source adopts an all-fiber structure design and, based on the passive mode-locking principle, can output femtosecond pulse lasers with high beam quality. Passive mode-locking refers to inserting a saturable absorber into the resonant cavity of a free-oscillating laser and adjusting the loss in the cavity through its nonlinear absorption characteristics. When the mode-locking condition is met, a series of mode-locked pulses can be obtained. The physical saturable absorber device has a long recovery time, which makes it easy for the saturable absorber to saturate into long pulses in the initial stage of continuous wave operation and easy to self-start, thus improving the stability of the fiber laser. Therefore, the fiber laser designed in this invention uses a semiconductor saturable absorber mirror (0601) as the saturable absorber, which can realize a truly all-fiber structure, avoid the use of spatial components, reduce the loss of the resonant cavity, is easy to integrate, and has low cost.

[0073] (2) The fiber laser designed in this invention is based on the chirped pulse amplification principle and consists of a seed source, a time-domain stretching stage, a first prevention stage, a frequency reduction stage, a second prevention stage, a main amplification stage, and a compression stage. In the chirped pulse amplification system, the ultrashort pulses output by the fiber oscillator need to be further stretched to reduce the peak power of the pulses during amplification, thereby avoiding the generation of nonlinear effects. The light output from the seed source passes through the second polarization-maintaining fiber (0302) in the stretching stage. Due to the small mode field area of ​​the stretching fiber itself, its nonlinear parameters are high. Therefore, after passing through the stretching fiber, the pulse is not only stretched in the time domain, but also further stretched in the spectrum due to nonlinear effects. Subsequently, when it enters the chirped Bragg fiber grating (0801) in the stretching stage, it obtains a greater stretching. Since most of the energy of the pulse is lost after passing through the stretching stage, the first prevention stage is used to reverse amplify the signal light, thereby increasing the optical power of the signal light. The amplified signal light is then passed through an acousto-optic modulator (0901) to reduce the repetition frequency. In fiber-based power amplification, reducing the repetition frequency increases the peak power of the pulse. This effect of increasing single-pulse energy is optimal when the average power loss due to the reduced repetition rate is effectively compensated. After passing through the acousto-optic modulator (0901), the signal light power is significantly attenuated, so a second pre-amplification stage is needed to further amplify the down-frequency signal light. After obtaining sufficient signal light, the pulse enters the main amplification stage to further enhance the single-pulse energy. The main amplification uses the fifth polarization-maintaining fiber (0305) for amplification; the shorter gain fiber can avoid accumulating too much nonlinear effect during the main amplification process. The pulse output from the main amplification is collimated and focused by the first focusing mirror (1201) and filtered by the first dichroic mirror (1301) to remove residual pump light, and then enters the compression stage through the half-wave plate (1401). After passing through the compression grating (1601), the dispersion is fully compensated, and a pulse output of hundreds of femtoseconds can be obtained.

[0074] (3) The core component of the frequency doubling device is a nonlinear crystal (1801). The frequency doubling process converts a lower frequency signal light wave into a shorter wavelength frequency-doubled light through second-order nonlinear optical interaction. Typically, after being pumped by a signal light with a center wavelength of 1560nm, the nonlinear crystal can be converted into a frequency-doubled light output with a wavelength of 780nm through a nonlinear frequency conversion process. The specific working process is as follows: First, the collimated light that is expanded and output passes through a second half-wave plate (1402) to adjust the polarization state of the incident light to a linear polarization state along the thickness direction of the crystal. The incident light is then focused by a second focusing lens (1202), with the focal point located inside the nonlinear crystal (1801). A nonlinear crystal (1801) is placed in a recess within a temperature-controlled furnace (1701), which is fixedly mounted on a three-dimensional adjustment frame. The position of the nonlinear crystal is adjusted by regulating the three-dimensional adjustment frame, thereby ensuring it is in a suitable position to improve the conversion efficiency of the signal light. The temperature of the crystal is regulated by setting up the temperature-controlled furnace, resulting in high-efficiency frequency-doubled light output. The light is then expanded and collimated by a third focusing lens (1203). Finally, after the signal light is stripped away by a second dichroic mirror (1302), a high-energy femtosecond 780nm frequency-doubled laser is output.

Claims

1. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system, characterized in that: The system comprises two parts. The first part is a chirped pulse amplification system, including a seed source, a time-domain stretching stage, a first pre-amplifier stage, a frequency reduction stage, a second pre-amplifier stage, a main amplification stage, and a compression stage, all connected in sequence. The second part is a frequency doubling system. The seed source includes a first laser diode (0101), a first polarization-maintaining wavelength division multiplexer (0201), a first polarization-maintaining fiber (0301), a polarization-maintaining fiber beam splitter (0401), a first polarization-maintaining fiber circulator (0501), a semiconductor saturable absorber mirror (0601), and a first polarization-maintaining isolator (0701), which generates a microwatt-level 1560nm laser pulse as a seed. The time-domain stretching stage includes a second polarization-maintaining fiber (0302), a second polarization-maintaining isolator (0702), a second polarization-maintaining fiber circulator (0502), and a chirped Bragg fiber grating (0801), which stretches the pulse output from the seed source in the time domain to the nanosecond level. The first prevention stage includes a third polarization-maintaining fiber (0303), a second polarization-maintaining wavelength division multiplexer (0202), a second laser diode (0102), and a third polarization-maintaining isolator (0703), which enhances the signal light output from the broadening stage to the level of hundreds of milliwatts; the frequency reduction stage includes an acousto-optic modulator (0901), which reduces the pulse repetition frequency to 1MHz; the second prevention stage includes a fourth polarization-maintaining fiber (0304), a third polarization-maintaining wavelength division multiplexer (0203), a third laser diode (0103), and a fourth polarization-maintaining isolator (0704), which enhances the signal light output from the frequency reduction stage to the level of hundreds of milliwatts; the main amplification stage includes a multimode laser diode (1101), a pump combiner (1001), a fifth polarization-maintaining fiber (0305), a first focusing lens (1201), and a first dichroic mirror (1301), which enhances the single-pulse energy of the signal light output from the second pre-amplification stage to the level of μJ; The compression stage includes a first half-wave plate (1401), a first plane mirror (1501), a transmission grating pair (1601), and a second plane mirror (1502), which compresses the pulse to the fs level through dispersion compensation; the frequency doubling system includes a second half-wave plate (1402), a second focusing lens (1202), a temperature-controlled furnace (1701), a nonlinear crystal (1801), a third focusing lens (1203), and a second dichroic mirror (1302), which doubles the high-energy femtosecond 1560nm signal light output from the chirped pulse amplification system to the 780nm band; The output of the semiconductor saturable absorber mirror (0601) is connected to the first polarization-maintaining fiber circulator (0501). The light output from the seed source passes through the second polarization-maintaining fiber (0302) in the broadening stage, and then enters the chirped Bragg fiber grating (0801) in the broadening stage, where it obtains a larger broadening. The signal light is amplified by the first anti-large stage, and the amplified signal light passes through the acousto-optic modulator (0901) to reduce the repetition frequency. After passing through the acousto-optic modulator (0901), the signal light power is significantly attenuated. The signal light is further amplified by adding a second pre-amplification stage. The main amplification uses the fifth polarization-maintaining fiber (0305) for amplification. The pulse output from the main amplification is collimated and focused by the first focusing lens (1201) and the first dichroic mirror (13). 01) After filtering out the residual pump light, it enters the compression stage through a half-wave plate (1401); the pulse passes through a transmission grating pair (1601), the dispersion is fully compensated, the beam is expanded and collimated, and then passes through a second half-wave plate (1402) to adjust the polarization state of the incident light to a linear polarization state along the crystal thickness direction; the incident light is focused by a second focusing lens (1202), with the focal point located inside the nonlinear crystal (1801); the nonlinear crystal (1801) is placed in the groove of a temperature-controlled furnace (1701), which is fixedly placed on a three-dimensional adjustment frame, and then expanded and collimated by a third focusing lens (1203); finally, after the signal light is stripped by a second dichroic mirror (1302), a high-energy femtosecond 780nm frequency-doubled laser is output; The seed source is used in the output of high-quality femtosecond laser pulses. After the output signal light pulse enters the broadening level, the time domain is broadened. Then, after pre-amplification and frequency reduction, large-scale prevention, and main amplification to increase the energy of the single pulse, the energy is compensated for by the bed shrinking stage and reaches the femtosecond level again. The high-energy femtosecond pulse enters the frequency doubling system to obtain high-energy femtosecond 780nm laser output.

2. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system according to claim 1, characterized in that: The first laser diode can be a single-mode semiconductor laser diode with a center wavelength of 976nm. Its pigtail and optical fiber are fused together by an optical fiber fusion splicer, and the output light pumps the first polarization-maintaining optical fiber.

3. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system according to claim 1, characterized in that: The first polarization-maintaining wavelength division multiplexer uses a polarization-maintaining fiber as its signal end pigtail, connects its pump end to the pigtail of the first laser diode, and connects its output end to a doped fiber, thus coupling the light output from the first laser diode into the doped fiber.

4. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system according to claim 1, characterized in that: The first polarization-maintaining fiber is an erbium-doped fiber with positive dispersion.

5. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system according to claim 1, characterized in that: The polarization-maintaining fiber beam splitter uses a 1×2 polarization-maintaining fiber beam splitter, with one end serving as the output and the other end returning to the cavity. All optical fibers and pigtails are polarization-maintaining fibers; The energy is output outside the cavity as a seed source.

6. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system according to claim 1, characterized in that: The second laser diode is a single-mode semiconductor laser diode with a center wavelength of 976nm. Its pigtail and optical fiber are fused together by an optical fiber fusion splicer, and the output light pumps the third polarization-maintaining optical fiber.

7. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system according to claim 1, characterized in that: Acousto-optic modulator, reducing the pulse repetition frequency to 1MHz.

8. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system according to claim 1, characterized in that: The pump combiner is a (6+1)×1 pump signal combiner. Its input end is connected to the pigtail of the laser diode, and its output end is connected to the doped fiber. Its function is to couple the light output from the multimode laser diode into the doped fiber.

9. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system according to claim 1, characterized in that: The multimode laser diode, a semiconductor laser diode with a center wavelength of 976nm, is used. Its pigtail and optical fiber are fused together by an optical fiber fusion splicer, and the output light pumps the doped optical fiber. The fifth polarization-maintaining fiber is a polarization-maintaining large-mode-field erbium-ytterbium co-doped fiber, which provides gain for signal light amplification and amplifies the single-pulse energy to the μJ level.

10. A high-energy femtosecond 780nm laser based on a fully polarization-maintaining fiber system according to claim 1, characterized in that: The first dichroic mirror separates the 976nm pump light from the 1560nm signal light.

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