A high-energy ultra-short pulse laser

Abstract

The application belongs to the technical field of laser, and relates to a high-energy ultrashort pulse laser. The laser comprises a mode-locked fiber laser oscillator, a nonlinear amplifier, a stretcher, a pulse selection module, a pre-amplification stage, a main amplification stage and a compressor. In the laser, the cavity dispersion of the mode-locked fiber laser oscillator is negative dispersion which is designed optimally, and the output pulse is injected into the nonlinear amplifier after pre-chirp management, so that a flat wide spectrum can be obtained; the stretcher, the pulse selection module, the pre-amplification stage, the main amplification stage and the compressor are combined to realize further efficient amplification of the injected pulse. The application can adopt a full polarization maintaining structure which has high stability and reliability, and realizes common use of nonlinear amplification and chirped pulse amplification technology, so that the gain narrowing problem in the traditional chirped pulse amplification process can be overcome, the single pulse energy amplification limit of the nonlinear amplification technology can be broken through, and finally the output of high-energy ultrashort laser pulse is realized.

Description

Technical Field

[0001] This invention belongs to the field of laser technology and relates to a high-energy ultrashort pulse laser, more specifically, a high-energy ultrashort pulse laser based on the combined use of nonlinear amplification and chirped pulse amplification. Background Technology

[0002] Ultrafast lasers, with their extremely short pulse duration, high peak power, and wide spectral range, have excellent application value and broad prospects in many fields such as strong-field laser physics, industrial processing, and military defense. Femtosecond fiber lasers, as an important branch of ultrafast lasers, are currently the mainstream lasers in the industrial field. Due to the extremely high surface area-to-volume ratio of optical fibers, they have excellent heat dissipation capabilities, and no additional heat dissipation module is needed when the output power is less than 100W, which provides strong support for their integrated structure. In addition, femtosecond lasers with a fully polarization-maintaining fiber structure also have good resistance to environmental interference, ensuring their long-term operational stability. Furthermore, these lasers have high energy conversion efficiency and high beam quality, making them more advantageous in practical applications.

[0003] However, due to limitations imposed by the inherent properties of optical fiber materials and structures, as well as the damage threshold of devices, the single-pulse energy and average power of fiber lasers are difficult to further increase, gradually failing to meet the practical needs of current applications. Against this backdrop, laser amplification technology has begun to receive more attention and development. It is well known that the main obstacle faced by ultrashort laser pulses in fiber amplifiers is the nonlinear effect caused by the high peak power of the pulse in the fiber. The accumulated, uncompensated nonlinear phase shift leads to a series of problems, including pulse quality degradation. Therefore, high-energy ultrashort laser pulse generation technology based on a fully polarization-maintaining fiber structure with high stability has become a research hotspot in both basic scientific research and industrial applications.

[0004] To address these issues, two main approaches exist: avoiding the influence of nonlinear effects and actively utilizing them. The approach of avoiding strong nonlinear effects primarily employs chirped pulse amplification (CPA). This involves first stretching the pulse in the time domain to reduce peak power, thus preventing strong nonlinear effects during amplification. After sufficient amplification, a grating-based dispersion compensation device is used to compress the pulse, ultimately making the output pulse width close to the injected seed pulse. However, in practical applications, high-order dispersion mismatch between the stretcher and compressor often makes it difficult to compress the amplified pulse back to its original width. Furthermore, the peak power of the stretched pulse cannot support strong self-phase modulation to counteract the spectral narrowing caused by the limited gain bandwidth. Generally, this approach struggles to compress the pulse below 200 fs and inevitably results in a decrease in pulse quality. To overcome the gain narrowing effect of this technique, spectral filtering is typically used. However, spectral filtering requires additional optical components, is complex to adjust, and causes laser pulse loss.

[0005] On the other hand, nonlinear amplification technology is named for its active use of nonlinear effects to improve the performance of amplification systems, with self-similar amplification being one of the most effective schemes. The most significant characteristic of self-similar amplification is that the output pulse has excellent linear chirp characteristics, which can be compressed to near the transform limit using grating pairs. Furthermore, the spectrum can be nonlinearly broadened to several times the original spectrum without splitting, thus even compressing the pulse narrower than the seed pulse, making it possible to compress the pulse to below 100 fs. Simultaneously, this scheme effectively suppresses pulse splitting, making it ideal for obtaining high-energy outputs. These features are difficult to achieve with traditional chirped pulse amplification techniques. Even if some amplification systems have similar output performance, their complexity far exceeds that of self-similar amplification systems, thus hindering their widespread application.

[0006] While the unique advantages of self-similar amplification technology have attracted considerable attention, it is undeniable that it still has significant limitations. For example, it is difficult to obtain high-energy laser pulses above the microjoule level using self-similar amplification. Therefore, improving the laser structure to obtain higher-energy laser pulse output has become a new research direction in this field. Summary of the Invention

[0007] To overcome the shortcomings of chirped pulse amplification techniques and meet the practical needs of scientific research and industrial applications, our research group, based on long-term in-depth research, has successfully combined nonlinear amplification technology with chirped pulse amplification technology through ingenious improvements to the laser structure. This has resulted in a polarization-maintaining high-energy ultrashort pulse laser based on the combined use of nonlinear amplification and chirped pulse amplification. This laser can overcome the gain narrowing effect and break through the micro-joule level single-pulse energy amplification limit of self-similar amplification. This effectively solves the problem that ultrashort laser pulses cannot obtain a narrower pulse width due to the gain narrowing effect during high-energy pulse amplification, providing strong technical support for obtaining higher-energy laser pulse output using chirped pulse amplification technology.

[0008] To achieve the above objectives, this invention provides a high-energy ultrashort pulse laser for outputting high-energy broadband ultrashort laser pulses capable of overcoming gain narrowing effects. The laser of this invention includes a broadband seed laser source, a stretcher, a pulse selection module, a pre-amplification stage, a main amplification stage, and a compressor; wherein:

[0009] The broadband seed laser source consists of a mode-locked fiber laser oscillator and a nonlinear amplifier, and is used to output a broadband femtosecond laser that can overcome the gain narrowing effect during the chirped pulse amplification process;

[0010] The stretcher is connected to the output of the nonlinear amplifier and is used to fully stretch the broadband pulse output from the nonlinear amplifier in the time domain.

[0011] The pulse selection module is connected to the output of the stretcher and is used to tunably reduce the repetition frequency of the laser pulse injected into the subsequent amplification stage in order to maximize the single pulse energy under limited pump conditions.

[0012] The pre-amplification stage and the main amplification stage are connected in sequence to the output of the pulse selection module to amplify the injected laser pulses with chirped pulses.

[0013] The compressor is connected to the output of the main amplification stage and is used to perform dispersion compensation on the amplified laser pulse to compress it in the time domain, so as to obtain an ultrashort (femtosecond) laser pulse with high energy and high peak power.

[0014] Furthermore, according to some embodiments of the present invention, the mode-locked fiber laser oscillator in the high-energy ultrashort pulse laser of the present invention includes a saturable absorber, a lens group, a polarization-maintaining single-mode fiber, a gain fiber, a wavelength division multiplexer, a semiconductor laser, and a dispersion control module.

[0015] The intracavity dispersion distribution of the mode-locked fiber laser oscillator is designed to be adjustable to output seed laser pulses that match the optimal nonlinear amplification effect;

[0016] The nonlinear amplifier is connected to the output of the mode-locked fiber laser oscillator to achieve efficient nonlinear amplification. Between the nonlinear amplifier and the mode-locked fiber laser oscillator is a single-mode fiber that provides pre-chirped management for the output of the mode-locked fiber laser oscillator.

[0017] Furthermore, according to some embodiments of the present invention, the net intracavity dispersion of the mode-locked fiber laser oscillator in the above-mentioned high-energy ultrashort pulse laser is a negative dispersion that can be adjusted and controlled according to application requirements. Its dispersion control method is one or more combinations of the following: a combination of fibers with multiple dispersion types, a chirped fiber grating, and a dispersion-tunable spatial structure based on a diffraction grating.

[0018] The self-starting mode-locking method of the mode-locked fiber laser oscillator is one or a combination of saturable absorber mode-locking, nonlinear loop mirror mode-locking, and nonlinear polarization rotation mode-locking.

[0019] Preferably, the mode-locked fiber laser oscillator can utilize a saturable absorber mirror to achieve stable, rapid, self-starting mode-locking. The saturable absorber mirror simultaneously functions as a mode-locking device and a resonant cavity end mirror, thereby improving the integration of the mode-locked fiber laser oscillator. Furthermore, this type of mode-locked fiber laser oscillator also includes a lens group positioned between the fiber end and the saturable absorber mirror to focus the laser pulses output from the fiber cavity structure onto the saturable absorber mirror.

[0020] Furthermore, the saturable absorber reflector and lens group are one or a combination of two of the following: an optimized fixed integrated structure and a relatively position programmable and electrically controlled movable structure. The former can reduce the interference of external jitter on the oscillator output, while the latter can realize mode-locked feedback and tune the repetition frequency of the oscillator output, further optimizing the nonlinear amplification effect.

[0021] Preferably, the mode-locked fiber laser oscillator can also simultaneously employ a nonlinear loop mirror and a saturable absorber mirror to achieve hybrid modulation mode-locking. The saturable absorber mirror is used for the laser's self-starting mode-locking and, together with the ring-shaped laser transmission structure, forms a resonant cavity to achieve stable oscillation of the laser pulse.

[0022] Furthermore, the aforementioned ring laser transmission structure is one or more combinations of ring laser transmission structures that utilize the interference of two opposing laser pulses at the output end to achieve mode-locked modulation, such as a nonlinear optical ring mirror, a nonlinear optical ring mirror with a programmable phase-shifting element and a nonlinear amplifying ring mirror, or a nonlinear amplifying ring mirror with a highly nonlinear fiber.

[0023] More preferably, the saturable absorber in the saturable absorber mirror is one or more of the following: semiconductor saturable absorber, graphene, carbon nanotubes, and other functional optical elements that can introduce phase jitter.

[0024] As an alternative, the pump laser of the gain medium can be programmed to have a sufficiently large instantaneous surge current at startup, disturbances can be introduced by mechanical methods such as piezoelectric ceramics, and nonlinear phase shifts within the ring mirror can be calculated, utilizing only the nonlinearity within the ring mirror (high nonlinearity fiber can be added). In this case, the saturable absorber mirror can be replaced by an ordinary mirror, further reducing the complexity of the system.

[0025] Furthermore, according to some embodiments of the present invention, the gain fiber used in the nonlinear amplifier of the high-energy ultrashort pulse laser of the present invention is an active single-mode fiber with positive dispersion distribution. It can utilize the self-similar evolution theory of pulses to ensure that the amplitude shape of the laser pulse does not change during efficient amplification and can have linear chirp. Furthermore, it can obtain ultrashort pulses that can resist light wave splitting and have a smooth broadened spectrum. It can overcome the gain narrowing effect in the subsequent chirped pulse amplification process, so that the output pulse can be compressed narrower and ultrashort pulses with higher peak power can be obtained.

[0026] Furthermore, according to some embodiments of the present invention, the stretcher in the high-energy ultrashort pulse laser of the present invention is one or more of the following combinations: single-mode fiber stretcher, circulator combined with chirped fiber grating stretcher, diffraction grating pair stretcher, and chirped bulk Bragg grating stretcher, wherein the single-mode fiber stretcher can further promote the all-fiber integration of the system.

[0027] Furthermore, according to some embodiments of the present invention, the pulse selection module in the high-energy ultrashort pulse laser of the present invention is composed of an optical fiber coupler, a photodetector, a pulse selection synchronization control circuit, an acousto-optic modulator, and an optical fiber isolator, wherein the pulse selection synchronization control circuit includes a programmable FPGA board for changing the timing sequence.

[0028] Preferably, the pulse selector module consists of an acousto-optic modulator with fiber-optic coupled input and output terminals and a circuit for generating synchronous drive signals, and the circuit includes a programmable FPGA board for changing the timing.

[0029] Furthermore, according to some embodiments of the present invention, the gain fiber used in the pre-amplification stage of the high-energy ultrashort pulse laser of the present invention is an active fiber.

[0030] More preferably, the gain fiber used in the pre-amplification stage is an active double-clad large-mode-field fiber.

[0031] Furthermore, according to some embodiments of the present invention, the gain fiber used in the main amplification stage of the high-energy ultrashort pulse laser of the present invention is one or more of the following combinations: disk-shaped active photonic crystal fiber, rod-shaped active photonic crystal fiber, and solid-state laser amplification module.

[0032] Furthermore, according to some embodiments of the present invention, the compressor in the high-energy ultrashort pulse laser of the present invention is one or more of the following combinations: a diffraction grating pair compressor, a chirped volume Bragg grating compressor, and a special optical fiber for nonlinear pulse compression.

[0033] Furthermore, according to some embodiments of the present invention, the gain fiber used in the high-energy ultrashort pulse laser of the present invention contains one or more rare earth elements as doping elements, depending on the required wavelength, preferably one or more of ytterbium, thulium, and erbium.

[0034] Furthermore, according to some embodiments of the present invention, the optical fiber and optical fiber devices included in the high-energy ultrashort pulse laser of the present invention are selected as fully polarization-maintaining optical fibers and optical fiber devices, which can further improve the stability and reliability of the system.

[0035] On the other hand, the present invention also provides a broadband seed laser source, which outputs a flat broadband spectrum. This flat broadband spectrum is divided in the frequency domain using a spectral beam splitting method into multiple sub-spectrums with different center wavelengths. Each sub-spectrum with a different center wavelength is amplified separately, and finally, a high-energy ultrashort laser pulse is output using a spectral beam combining method. The broadband seed laser source consists of a mode-locked fiber laser oscillator and a nonlinear amplifier, wherein:

[0036] The mode-locked fiber laser oscillator includes a saturable absorber, a lens group, a polarization-maintaining single-mode fiber, a gain fiber, a wavelength division multiplexer, a semiconductor laser, and a dispersion control module.

[0037] The intracavity dispersion distribution of the mode-locked fiber laser oscillator is designed to be adjustable to output seed laser pulses that match the nonlinear amplification effect;

[0038] The nonlinear amplifier is connected to the output of the mode-locked fiber laser oscillator to achieve nonlinear amplification. Between the nonlinear amplifier and the mode-locked fiber laser oscillator is a single-mode fiber that provides pre-chirped management for the output of the mode-locked fiber laser oscillator.

[0039] Furthermore, according to some embodiments of the present invention, the net intracavity dispersion of the mode-locked fiber laser oscillator in the broadband seed laser source of the present invention is a negative dispersion that can be adjusted and controlled according to application requirements. Its dispersion control method is one or more combinations of the following: a combination of fibers with multiple dispersion types, a chirped fiber grating, and a dispersion-tunable spatial structure based on a diffraction grating.

[0040] The self-starting mode-locking method of the mode-locked fiber laser oscillator is one or a combination of saturable absorber mode-locking, nonlinear loop mirror mode-locking, and nonlinear polarization rotation mode-locking.

[0041] The gain fiber used in the nonlinear amplifier is an active single-mode fiber with positive dispersion distribution.

[0042] In addition, the aforementioned broadband seed laser source can serve not only as a high-quality seed source for fiber lasers, but also as a seed source for other solid-state lasers.

[0043] Specifically, compared with the prior art, the high-energy ultrashort pulse laser of the present invention can achieve the following beneficial effects:

[0044] (1) The mode-locked fiber laser oscillator used in the laser of the present invention is a fully polarization-maintaining femtosecond laser with adjustable intracavity dispersion distribution designed by the inventors. The mode-locked fiber laser oscillator can be coupled with chirped fiber grating for output, which can not only promote the all-fiber system, but also assist the intracavity dispersion design by using the chirped fiber grating.

[0045] (2) In this invention, a single-mode fiber with finely adjustable length is used for pre-chirp management between the mode-locked fiber laser oscillator and the nonlinear amplifier. This can introduce a certain initial chirp into the output pulse of the mode-locked fiber laser oscillator, thereby enabling the pulse to output a high-quality baseless pulse while exceeding the gain bandwidth limit during the nonlinear amplification process.

[0046] (3) The length of the active single-mode fiber in the nonlinear amplifier used in the laser of the present invention is optimized by numerical simulation and experiment. It can match the injected pulse situation and obtain a pulse output with good linear chirp characteristics after nonlinear amplification. The accumulated nonlinear chirp is minimal, so a pulse close to the transformation limit can be obtained by compression.

[0047] (4) The mode-locked fiber laser oscillator used in the laser of this invention has a net intracavity dispersion that can be adjusted and controlled according to application requirements, resulting in a negative dispersion that can output a seed laser pulse with optimal nonlinear amplification effect. As is well known, a positive dispersion cavity corresponds to a dissipative soliton pulse with a large number of positive chirps, while an unoptimized conventional negative dispersion cavity corresponds to a pulse with a distinct structure at the top of the output spectrum, neither of which is conducive to direct entry into the amplification stage for nonlinear amplification. In contrast, the laser pulse output by the negative dispersion cavity optimized in this invention has a greatly broadened spectrum after nonlinear amplification, exhibits a very smooth, flat, and clean spectral structure, and has no obvious Kelly sidebands, making it very suitable as a seed source for subsequent laser chirped pulse amplification systems.

[0048] (5) The laser of the present invention actively utilizes the nonlinear effect accumulated during the ultrashort pulse amplification process to build a broadband seed laser source, which can overcome the adverse effects caused by the narrowing effect of gain during the traditional chirped pulse amplification process, and finally achieves output laser pulses of less than 100fs or even shorter.

[0049] (6) The broadband seed laser source designed for the laser of the present invention can also use the method of spectral beam splitting to divide its output high-quality flat broadband spectrum in the frequency domain. After amplifying several spectral components with different center wavelengths, the final output of high-energy ultrashort laser pulses can be achieved by spectral beam combining.

[0050] (7) The broadband seed laser source designed in this invention can be used not only as a high-quality seed source for fiber lasers, but also as a seed source for other solid-state lasers.

[0051] (8) The high-energy ultrashort pulse laser provided by this invention has strong scientific research value and socio-economic significance. The corresponding scientific research results can be found in the optical journal "APPLIED OPTICS". Attached Figure Description

[0052] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments are briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the present invention, and not all embodiments. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This is a schematic diagram of the overall structure of the high-energy ultrashort pulse laser of the present invention.

[0054] Figure 2 is a schematic diagram of the mode-locked fiber laser oscillator structure in the high-energy ultrashort pulse laser of the present invention, wherein: Figure 2(a) is a mode-locked fiber laser oscillator based on a chirped fiber grating, and Figure 2(b) is a mode-locked fiber laser oscillator with a dispersion-tunable spatial structure based on a diffraction grating.

[0055] Figure 3 shows schematic diagrams of various modes-locked fiber laser oscillators based on hybrid mode-locked modulation provided by the present invention, wherein: Figure 3(a) is a schematic diagram of a laser based on hybrid mode-locked modulation, Figure 3(b) is a schematic diagram of a laser with adaptively adjustable output power, Figure 3(c) is a schematic diagram of a laser with added adjustment degree of freedom in a nonlinear amplifying ring, and Figure 3(d) is a schematic diagram of a laser with added adjustment degree of freedom in a linear arm.

[0056] Figure 4 This is a schematic diagram of the nonlinear amplifier structure in the high-energy ultrashort pulse laser of the present invention.

[0057] Figure 5 This is a spectrum of the amplifier output pulse corresponding to different net dispersion in the mode-locked fiber laser oscillator in the high-energy ultrashort pulse laser of this invention.

[0058] Figure 6 is a schematic diagram of the stretcher structure in the high-energy ultrashort pulse laser of the present invention, wherein: Figure 6(a) is a single-mode fiber stretcher, Figure 6(b) is a circulator combined with a chirped fiber grating stretcher, Figure 6(c) is a diffraction grating pair stretcher, and Figure 6(d) is a chirped bulk Bragg grating stretcher.

[0059] Figure 7 This is a schematic diagram of the pulse selection module structure in the high-energy ultrashort pulse laser of the present invention.

[0060] Figure 8 This is a schematic diagram of the pre-amplification stage structure in the high-energy ultrashort pulse laser of the present invention.

[0061] Figure 9 is a schematic diagram of the main amplification stage structure in the high-energy ultrashort pulse laser of the present invention, wherein: Figure 9(a) is the main amplification stage based on disk-shaped active photonic crystal fiber, and Figure 9(b) is the main amplification stage based on rod-shaped active photonic crystal fiber.

[0062] Figure 10 is a schematic diagram of the compressor structure in the high-energy ultrashort pulse laser of the present invention, wherein: Figure 10(a) is a transmission Treacy grating pair compressor, Figure 10(b) is a reflection Treacy grating pair compressor, Figure 10(c) is a chirped volume Bragg grating compressor, and Figure 10(d) is a hollow fiber compressor.

[0063] Reference numerals: 1: Mode-locked fiber laser oscillator; 2: Nonlinear amplifier; 3: Stretcher; 4: Pulse selector module; 5: Pre-amplification stage; 6: Main amplification stage; 7: Compressor; 8: First saturable absorber mirror; 9: First focusing lens; 10: First collimating lens; 11: First lens group; 12: First polarization-maintaining single-mode fiber; 13: First polarization-maintaining gain fiber; 14: First wavelength division multiplexer; 15: First semiconductor laser; 16: Chirped fiber grating; 17: First fiber isolator; 18: First fiber coupler; 19: Coupler lens; 20: Diffraction grating; 21: Coupler collimating lens. 22: First reflecting mirror; 23: Linear cavity output end; 24: Second fiber coupler; 25: Nonlinear amplifying ring mirror; 26: Linear arm; 27: Second polarization-maintaining single-mode fiber; 28: Ring mirror output end; 29: Highly nonlinear fiber; 30: Fourth semiconductor laser; 31: Fourth polarization-maintaining gain fiber; 32: Fifth wavelength division multiplexer; 33: Fifth polarization-maintaining gain fiber; 34: Fifth semiconductor laser; 35: Second fiber isolator; 36: First single-mode fiber; 37: Optical circulator; 38: Chirped fiber grating; 39: Front grating; 40: Third lens group; 41: Rear grating; 42: Second reflecting mirror 43: λ / 2 waveplate; 44: Polarizing beam splitter; 45: λ / 4 waveplate; 46: Chirped volume Bragg grating; 47: Fiber coupler; 48: Photodetector; 49: Pulse selection synchronization control circuit programmable FPGA board; 50: Acousto-optic modulator; 51: Third fiber isolator; 52: Sixth semiconductor laser; 53: Sixth wavelength division multiplexer; 54: Active double-clad large-mode-field fiber; 55: Fourth fiber isolator; 56: Disk-shaped active double-clad large-mode-field photonic crystal fiber; 57: Pump coupling lens; 58: Dichroic mirror; 59: High-power semiconductor laser; 60: Third reflecting mirror. 61: Spatial optical isolator; 62: First input coupling lens; 63: Rod-shaped active double-clad large-mode-field photonic crystal fiber; 64: First output coupling lens; 65: Second λ / 2 waveplate; 66: Fourth mirror; 67 and 68: Transmission grating; 69: Transmission Treacy grating pair; 70: High-reflection mirror; 71 and 72: Reflection grating; 73: Reflection Treacy grating pair; 74: Second chirped volume Bragg grating; 75: Second input coupling lens; 76: Hollow fiber; 77: Rare gas pump; 78: Rare gas cell; 79: Second output coupling lens; 80: Chirped mirror group;

[0064] 8': Second saturable absorber mirror; 9': Second focusing lens; 10': Second collimating lens; 11': Second lens group; 13': Second polarization-maintaining gain fiber; 14': Second wavelength division multiplexer; 15': Second semiconductor laser; 29': Fourth wavelength division multiplexer.

[0065] 13”: Third polarization-maintaining gain fiber; 14”: Third wavelength division multiplexer; 15”: Third semiconductor laser. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. This invention can also be implemented or applied through other different specific implementation methods, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this invention.

[0067] Furthermore, it should be understood that the scope of protection of this invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of this invention is for describing specific embodiments, not for limiting the scope of protection of this invention. In addition, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. In this invention, terms such as "first," "second," etc. (if present) are only used to distinguish similar objects, and not to describe a specific order or sequence.

[0068] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, apparatuses, and materials used in the embodiments, this invention can be implemented using any prior art methods, apparatuses, and materials similar to or equivalent to those described in the embodiments of this invention, based on the knowledge of those skilled in the art and the description of this invention.

[0069] In this invention, unless otherwise specified, all components, devices and materials involved can be obtained commercially or manufactured using conventional methods in the art.

[0070] Example: A high-energy ultrashort pulse laser

[0071] Figure 1This is a schematic diagram of a high-energy ultrashort pulse laser provided in an embodiment of the present invention. After the femtosecond laser generated by the mode-locked fiber laser oscillator 1 is output from the cavity, it is pre-chirped through a single-mode fiber of finely adjustable length, and then injected into the nonlinear amplifier 2 for efficient nonlinear amplification. At the same time, the mode-locked fiber laser oscillator 1 and the nonlinear amplifier 2 constitute a broadband seed laser source that can overcome the gain narrowing effect in the subsequent chirped pulse amplification system. The output seed laser pulse is injected into the stretcher 3, which fully stretches it in the time domain using the dispersion effect. Subsequently, the repetition frequency of the laser pulse is reduced by the pulse selection module 4, and then it is injected into the pre-amplification stage 5 and the main amplification stage 6 for further amplification. Finally, the pulse is injected into the compressor 7 for compression, thereby realizing the final high-energy ultrashort laser pulse output.

[0072] Figure 2 is a schematic diagram of the mode-locked fiber laser oscillator structure in the high-energy ultrashort pulse laser of the present invention. Figure 2(a) shows a schematic diagram of the structure of the mode-locked fiber laser oscillator based on a chirped fiber grating. The mode-locked fiber laser oscillator 1 is composed of a first saturable absorber mirror 8, a first lens group 11, a first polarization-maintaining single-mode fiber 12, a first polarization-maintaining gain fiber 13, a first wavelength division multiplexer 14, a first semiconductor laser 15, a chirped fiber grating 16, and a first fiber isolator 17. The first semiconductor laser 15 pumps the first polarization-maintaining gain fiber 13 through the first wavelength division multiplexer 14, causing population inversion and thus providing gain for the pulses oscillating within the cavity. After the laser beam diverges out from the first polarization-maintaining single-mode fiber 12, it is re-collimated and focused onto the first saturable absorber mirror 8 via the first lens group 11. The first saturable absorber mirror 8 provides rapid amplitude modulation, enabling the mode-locked fiber laser oscillator 1 to achieve self-starting mode-locking. The saturable absorber mirror 8 and the chirped fiber grating 16 constitute a pair of reflecting cavity mirrors for the mode-locked fiber laser oscillator 1. The chirped fiber grating 16 also functions as an intracavity dispersion compensation device, end mirror, and output end of the mode-locked fiber laser oscillator, making it a key component for the fully polarization-maintaining fiber configuration of the mode-locked fiber laser oscillator 1. The first fiber isolator 17 prevents back-propagating light from damaging the mode-locked fiber laser oscillator 1. By optimizing the intracavity dispersion, the output laser pulses can be made suitable for nonlinear amplification. The cavity exhibits negative dispersion, enabling the output of dispersion-managed soliton pulses. The spectral structure is very smooth and clean, without obvious Kelly sidebands.

[0073] Specifically, the first lens group 11 in the mode-locked fiber laser oscillator 1 is used to focus the output laser pulse onto the first saturable absorber mirror 8 after the spot size is changed. The first lens group 11 includes a first collimating lens 10 and a first focusing lens 9. The first lens group 11 and the first saturable absorber mirror 8 can be integrated into a single structure to reduce system spatial jitter. Furthermore, the laser output from the first lens group 11 is transmitted to the first saturable absorber mirror 8 after beam expansion, which can help avoid damage to the saturable absorber. At the same time, the loose focusing method ensures that the laser pulse intensity at the focal spot is much lower than the damage threshold of the saturable absorber, thereby ensuring the long-term stable operation of the laser.

[0074] Figure 2(b) is a schematic diagram of a mode-locked fiber laser oscillator based on a dispersion-tunable spatial structure using a diffraction grating. This structure comprises a first saturable absorber mirror 8, a first lens group 11, a first polarization-maintaining single-mode fiber 12, a first polarization-maintaining gain fiber 13, a first wavelength division multiplexer 14, a first semiconductor laser 15, a first fiber coupler 18, a coupling lens 19, a diffraction grating 20, a coupling collimating lens 21, and a first mirror 22. The first semiconductor laser 15 pumps the first polarization-maintaining gain fiber 13 through the first wavelength division multiplexer 14, providing gain for the intracavity oscillating pulses. After diverging out from the first polarization-maintaining single-mode fiber 12, the laser is re-collimated and focused onto the first saturable absorber mirror 8 via the first lens group 11. The first saturable absorber mirror 8 acts as a cavity mirror and provides rapid amplitude modulation, enabling the mode-locked fiber laser oscillator 1 to achieve self-starting mode-locking. The first mirror 22, as the other end mirror of the resonant cavity, forms an equivalent grating pair with the coupling collimating lens 21 and the diffraction grating 20. By changing the relative distance between the diffraction grating 20 and the coupling collimating lens 21, the net dispersion within the cavity can be changed. Finally, the laser pulse is output through the linear cavity output end 23 of the first fiber coupler 18. This cavity dispersion-tunable structure has high design flexibility, which is beneficial for theoretically studying the influence of different types of injected seed laser pulses on the nonlinear amplification effect. It can output the injected pulse with the best matching effect according to different nonlinear amplification conditions.

[0075] Figure 3 shows schematic diagrams of various modes-locked fiber laser oscillators based on hybrid mode-locked modulation provided by the present invention. Figure 3(a) is a schematic diagram of a laser based on hybrid mode-locked modulation, which consists of a second saturable absorber mirror 8', a second lens group 11', a second fiber coupler 24, a nonlinear amplifying ring mirror 25, and a linear arm 26.

[0076] The nonlinear amplifying ring mirror 25 acts as a mode-locking element, providing amplitude modulation to generate an ultrashort pulse sequence. This is a novel mode-locking method utilizing the fiber Kerr effect, offering fast response, simple and stable structure, and high signal-to-noise ratio. The laser pulse is split into two equal-intensity pulses at the second fiber coupler 24 according to its splitting ratio, propagating clockwise and counterclockwise in opposite directions within the nonlinear amplifying ring mirror 25. The equal splitting ratio provides the nonlinear amplifying ring mirror 25 with the maximum modulation depth. The second polarization-maintaining gain fiber 13' is asymmetrically positioned within the nonlinear amplifying ring mirror 25. The pump light emitted from the second semiconductor laser 15' is injected into the first polarization-maintaining gain fiber 13 through the second wavelength division multiplexer 14', generating population inversion to provide a certain amplitude gain for the transmitted laser pulse. The second polarization-maintaining gain fiber 13', the second semiconductor laser 15', and the second wavelength division multiplexer 14' can be replaced by an editable phase-shifting element, achieving the same function. In addition, a section of fiber with a high nonlinear coefficient can be connected to the end of the second polarization-maintaining gain fiber 13' that is far away from the second fiber coupler 24, which can increase the phase shift difference between laser pulses propagating in opposite directions within the loop.

[0077] Simultaneously, part of the laser pulse modulated by the nonlinear amplifying ring mirror 25 is output through the second fiber coupler 24 to the linear arm 26 for further transmission, while another part is output from the ring mirror output end 28 at the second fiber coupler 24. The structure of the linear arm 26 greatly enhances the system's adjustment and detection freedom, facilitating real-time monitoring of the dynamic behavior of the laser pulse evolution within the cavity, and exploring the influence of physical parameters within the resonant cavity on key characteristics such as laser pulse output and mode-locking modulation. This has significant guiding significance for laser design and optimization. One end of the linear arm 26 is connected to the output end of the nonlinear amplifying ring mirror 25, and the other end transmits the laser pulse to the second saturable absorber mirror 8' after the laser pulse spot size is transformed through the second lens group 11'. This causes the laser pulse to oscillate back and forth within the resonant cavity. The second saturable absorber mirror 8' introduces amplitude modulation to complete the laser's self-starting mode-locking, and also acts as a reflective end mirror to allow the laser pulse output from the second lens group 11' to oscillate and propagate within the resonant cavity. The second lens group 11' includes a second collimating lens 10' and a second focusing lens 9'. The second lens group 11' and the second saturable absorber mirror 8' can be integrated into a single structure to reduce system spatial jitter. In the fully negative dispersion operating region, the laser pulse evolves into a stable near-soliton pulse in the nonlinear amplifying ring mirror 25, and then, after being filtered by the nonlinear amplifying ring mirror 25, a stable, spectrally smooth, and bandgap-free near-parabolic laser pulse is obtained at the output end 28 of the laser.

[0078] The hybrid modulation mode-locked fiber laser oscillator fully combines the advantages and characteristics of the nonlinear amplifying ring mirror 25 and the second saturable absorber mirror 8', which can enhance the stability of the laser while improving the self-starting mode-locking performance of the system.

[0079] Figures 3(b), (c), and (d) are schematic diagrams of the laser structure after increasing the degree of freedom of adjustment. Figure 3(b) is a schematic diagram of the laser structure with adaptive output power adjustment. In the nonlinear amplifying ring mirror 25, the end of the second polarization-maintaining gain fiber 13' away from the second fiber coupler 24 is connected to a high nonlinear fiber 29 with an extremely high nonlinear coefficient. The output end of the high nonlinear fiber 29 is connected to the second fiber coupler 24 through the second polarization-maintaining single-mode fiber 27, forming a closed ring structure. This allows the laser pulses propagating counterclockwise in the nonlinear amplifying ring mirror 25 to be amplified by the second polarization-maintaining gain fiber 13' and then input into the high nonlinear fiber 29, accumulating a larger nonlinear phase shift. This mechanism greatly increases the phase difference of the laser pulses propagating in opposite directions in the nonlinear amplifying ring mirror 25. By using the dissipation mechanism of solitons, the output power of the laser is passively adjusted, ensuring that the laser operates in single-pulse mode and a laser pulse sequence with continuously tunable output power can be obtained.

[0080] Figure 3(c) is a schematic diagram of a laser structure with added adjustment degrees of freedom in the nonlinear amplifying ring mirror 25. The output of the second wavelength division multiplexer 14' is connected to the input of the third wavelength division multiplexer 14". The third semiconductor laser 15” provides pumping to the third polarization-maintaining gain fiber 13” through the third wavelength division multiplexer 14”. The third polarization-maintaining gain fiber 13” is then connected to the second fiber coupler 24 to form a complete nonlinear amplifying ring mirror 25, amplifying the transmitted laser pulse sequence. The laser pulse input from the linear arm 26 into the nonlinear amplifying ring mirror 25 is split into two laser pulses via the second fiber coupler 24, which then pass sequentially through the second polarization-maintaining gain fiber 13' and the third polarization-maintaining gain fiber 13” in the nonlinear amplifying ring mirror 25, resulting in laser pulses transmitted in opposite directions. By providing amplitude gain and independently adjusting the pump power and adjustment path of the second semiconductor laser 15' and the third semiconductor laser 15" respectively, the nonlinear phase shift difference of the laser pulses propagating in opposite directions can be controlled, which can greatly improve the parameter adjustment range of the laser output pulse and increase the adjustability of the laser. At the same time, by utilizing the instantaneous response characteristics of the pump power of the second semiconductor laser 15' and the third semiconductor laser 15" in the nonlinear amplifying ring mirror 25, sufficient disturbance can be introduced, and the second saturable absorber reflector 8' in the laser can be replaced with a regular reflector to achieve self-starting mode-locking, thereby further improving the laser's operational stability and reducing costs.

[0081] Figure 3(d) is a schematic diagram of a laser structure with added adjustment degrees of freedom in the linear arm. The fourth semiconductor laser 30, pumped by the fourth wavelength division multiplexer 29', provides amplitude gain to the laser pulse input from the second fiber coupler 24 into the linear arm 26, further increasing the laser pulse energy. The laser pulse output from the fourth polarization-maintaining fiber 31 is expanded by the second lens group 11' and focused onto the second saturable absorber mirror 8', then reflected and coupled back into the linear arm 26, oscillating reciprocally within the laser resonant cavity. By independently controlling the pump power and adjustment method of the second semiconductor laser 15' and the fourth semiconductor laser 30, the parameter adjustment range of the laser output pulse can be greatly improved, the laser pulse energy increased, and the laser's adjustability enhanced.

[0082] Figure 4 This is a schematic diagram of the nonlinear amplifier 2 in the high-energy ultrashort pulse laser of the present invention. The output pulse of the mode-locked fiber laser oscillator 1 is injected into the nonlinear amplifier 2 for nonlinear amplification. The nonlinear amplifier 2 consists of a fifth wavelength division multiplexer 32, a fifth polarization-maintaining gain fiber 33, a fifth semiconductor laser 34, and a second fiber isolator 35. The fifth semiconductor laser 34 is injected into the fifth polarization-maintaining gain fiber 33 through the fifth wavelength division multiplexer 32, causing population inversion and thus providing amplitude gain for the pulse output from the mode-locked fiber laser oscillator 1. The second fiber isolator 35 can prevent back-propagating light from damaging the preceding stage. Simultaneously, by optimizing the fiber length between the mode-locked fiber laser oscillator 1 and the nonlinear amplifier 2, a certain pre-chirp management is implemented for the pulse injected into the nonlinear amplifier 2, which can improve the nonlinear amplification efficiency while ensuring the pulse width. When the fifth polarization-maintaining gain fiber 33 is a normal dispersion fiber, due to the interaction between normal dispersion and nonlinearity and gain, the laser pulse output by the mode-locked fiber laser oscillator 1 undergoes self-similar evolution in the nonlinear amplifier 2. That is, the shape of the laser pulse remains unchanged during the amplification process, while the pulse width and amplitude increase exponentially. This amplification mechanism improves the tolerance of the laser pulse to nonlinear phase shift, breaks through the power limitation of traditional soliton laser pulses, and the chirp of the output laser pulse is strictly linear. The shape of the output spectrum is flat and sufficiently wide, which can overcome the adverse effects caused by the gain narrowing effect during the chirped pulse amplification process, laying the foundation for obtaining ultra-short and ultra-intense laser pulses by compressing the pulse width.

[0083] Figure 5The figures show the spectra of amplifier output pulses corresponding to different net dispersion levels within the mode-locked fiber laser oscillator in the high-energy ultrashort pulse laser of this invention. The data shows that the spectrum of the seed laser pulse corresponding to the positive dispersion cavity does not broaden after injection into the nonlinear amplifier because the oscillator output pulse is a dissipative soliton pulse with a large amount of positive chirp. In contrast, the seed laser pulse corresponding to the unoptimized conventional negative dispersion cavity clearly shows a distinct structure at the top of the pulse spectrum after amplification, neither of which is conducive to direct nonlinear amplification. In comparison, the laser pulse output from the optimized negative dispersion cavity of this invention exhibits a significantly broadened spectrum after nonlinear amplification, with a very smooth, flat, and clean spectral structure and no obvious Kelly sidebands, making it highly suitable as a seed source for subsequent laser chirped pulse amplification systems.

[0084] Figure 6 is a schematic diagram of the stretcher structure in the high-energy ultrashort pulse laser of the present invention. Figure 6(a) shows the single-mode fiber stretcher, which is composed of a first single-mode fiber 36. It can utilize the accumulation of dispersion in the fiber along the length direction to stretch the nonlinearly amplified pulse to the order of hundreds of picoseconds in the time domain. This allows for full utilization of the advantages of chirped pulse amplification technology in the subsequent amplification process. At the same time, using single-mode fiber as a stretcher can further promote the all-fiber integration of the system.

[0085] Figure 6(b) shows a circulator combined with a chirped fiber grating stretcher. The laser pulse is injected into the chirped fiber grating 38 through the optical circulator 37. The grating period gradually changes along the direction of light propagation. Light of different frequency components is reflected at different grating periods, thus corresponding to different propagation paths. This introduces a time delay to stretch the laser pulse. Finally, the stretched pulse is output through the optical circulator 37.

[0086] Figure 6(c) shows the diffraction grating pair stretcher. The incident laser pulse is first diffracted by the front grating 39, achieving dispersion of different frequency components in different angular directions. The arrangement structure of the grating pair composed of the front grating 39 and the rear grating 41 causes different optical path lengths for different frequency components in the laser pulse. The third lens group 40 cooperates with the grating pair to form a 4f system. The second mirror 42 causes the laser pulse to pass through the stretcher 3 twice. Finally, the time interval between the separation of different frequency components in the stretcher 3 is increased, thereby achieving the stretching of the laser pulse in the time domain.

[0087] Figure 6(d) shows a chirped Bragg grating stretcher. First, the polarization direction of the incident laser pulse is rotated to S-polarization using a λ / 2 waveplate 43. The pulse is then reflected at the polarization beam splitter 44 and injected into the chirped Bragg grating 46. Light of different frequency components is reflected at different positions, thus corresponding to different propagation paths, thereby introducing a time delay to stretch the laser pulse. At the same time, the optical axis of the λ / 4 waveplate 45 is at 45° to the vertical direction. The laser pulse is reflected twice by the chirped Bragg grating 46 and passes through the λ / 4 waveplate 45, which is equivalent to passing through a λ / 2 waveplate. The polarization direction changes from S-polarization to P-polarization, so it can be transmitted at the polarization beam splitter 44, realizing the output of the stretched pulse.

[0088] Figure 7 This is a schematic diagram of the pulse selection module 4 in the high-energy ultrashort pulse laser of the present invention. The pulse selection module 4 consists of an optical fiber coupler 47, a photodetector 48, a programmable FPGA board 49 for pulse selection synchronization control circuit, an acousto-optic modulator 50, and a third optical fiber isolator 51. Since the seed pulse has already had its energy amplified before broadening, it is sufficient to ensure that the pulse still has enough single-pulse energy to enter the next amplification stage after passing through the pulse selection module 4, thus eliminating the need for an additional amplification stage to pre-compensate for energy loss. Furthermore, to ensure single-pulse energy while avoiding Raman scattering effects caused by excessively low repetition frequencies, the repetition frequency of the laser system needs to be tuned through the pulse selection module 4. The pulse selection module 4 can control the repetition frequency of the output pulse of the mode-locked fiber laser oscillator, reducing it to hundreds of kHz to 1 MHz, thereby ensuring that the single-pulse energy is maximized under limited pump conditions. After the pulse is injected into the pulse selection module 4, it is output from the Tap end of the fiber optic coupler 47. The photodetector 48 converts this into an electrical signal, thus obtaining the pulse's time characteristics. The signal is then processed by the pulse selection synchronization control circuit on the programmable FPGA board 49 to transmit the required target repetition frequency information to the acousto-optic modulator 50, ultimately enabling control of the output pulse's repetition frequency. The third fiber optic isolator 51 prevents back-transmitted light from damaging the preceding stage.

[0089] Figure 8This is a schematic diagram of the pre-amplification stage 5 in the high-energy ultrashort pulse laser of the present invention. The pre-amplification stage 5 consists of a sixth semiconductor laser 52, a sixth wavelength division multiplexer 53, an active double-clad large-mode-field fiber 54, and a fourth fiber isolator 55. The sixth semiconductor laser 52 pumps the active double-clad large-mode-field fiber 54 through the sixth wavelength division multiplexer 53, causing population inversion and thus providing sufficient gain for the down-repetition-rate pulse. This gain fiber uses a double-clad fiber with a larger core diameter, which not only allows for higher rare-earth ion doping to provide higher gain but also suppresses the performance degradation caused by excessive accumulation of nonlinear effects due to higher peak power. The pre-amplification stage 5 ensures that the single-pulse energy is maximized before being injected into the main amplification stage 6, thereby reducing the gain requirement of the main amplification process. This approach also ensures that spontaneous emission noise is reduced without causing significant stimulated Raman scattering noise, greatly improving the quality of the output pulse. The fourth fiber isolator 55 prevents back-propagating light from damaging the preceding stage.

[0090] Figure (9) is a schematic diagram of the main amplification stage structure in the high-energy ultrashort pulse laser of the present invention. Figure 9(a) is a schematic diagram of the main amplification stage structure based on a disk-shaped active photonic crystal fiber. This structure consists of a disk-shaped active double-clad large-mode-field photonic crystal fiber 56, a pump coupling lens 57, a dichroic mirror 58, a high-power semiconductor laser 59, a third reflecting mirror 60, and a spatial optical isolator 61. The high-power semiconductor laser 59 is pumped back into the disk-shaped active double-clad large-mode-field photonic crystal fiber 56 through the pump coupling lens 57, causing population inversion, thereby further improving the gain of the output light pulse of the pre-amplification stage 5. The output light pulse of the disk-shaped active double-clad large-mode-field photonic crystal fiber 56 is input to the compressor 7 through the dichroic mirror 58 and the third reflecting mirror 60 shared with the pump. The spatial optical isolator 61 can prevent the back-transmitted light from damaging the previous stage.

[0091] Figure 9(b) is a schematic diagram of the main amplification stage structure based on a rod-shaped active photonic crystal fiber. This structure consists of a first input coupling lens 62, a rod-shaped active double-clad large-mode-field photonic crystal fiber 63, a first output coupling lens 64, a high-power semiconductor laser 59, and a spatial optical isolator 61. The high-power semiconductor laser 59 is directly pumped to the rod-shaped active double-clad large-mode-field photonic crystal fiber 63 via its output pigtail, causing population inversion and further increasing the gain of the laser pulse injected into the pre-amplification stage 5 through the first input coupling lens 62. The output light pulse from the rod-shaped active double-clad large-mode-field photonic crystal fiber 63 is collimated by the first output coupling lens 64 and injected into the compressor 7 through the spatial optical isolator 61. The spatial optical isolator 61 prevents back-propagating light from damaging the preceding stage.

[0092] Figure (10) is a schematic diagram of the compressor structure in the high-energy ultrashort pulse laser of the present invention. Figure 10(a) is a transmission Treacy grating pair compressor, which is composed of a second λ / 2 waveplate 65, a fourth mirror 66, a transmission Treacy grating pair 69 and a high-reflection mirror 70. The output light pulse of the main amplification stage 6 is polarized and matched to the polarization requirements of the transmission Treacy grating pair 69 by the second λ / 2 waveplate 65. The amount of introduced dispersion is controlled by adjusting the distance between the two parallel transmission gratings 67 and 68 in the transmission Treacy grating pair 69. At the same time, the high-reflection mirror 70 allows the light pulse to pass through the transmission Treacy grating pair 69 twice, which improves the dispersion compensation efficiency. Through further fine dispersion control, the pulse width can be compressed to the transformation limit of hundreds of femtoseconds, and its spectral width can be maintained at tens of nanometers. Its pulse energy can reach several microjoules. This has broken through the limitation of the output spectral width of traditional chirped pulse amplification technology, and can also cross the microjoule output threshold of self-similar amplification technology, ultimately obtaining high-energy ultrashort laser pulses.

[0093] Figure 10(b) shows a reflective Treacy grating pair compressor, which consists of a second λ / 2 waveplate 65, a fourth mirror 66, a reflective Treacy grating pair 73, and a high-reflection mirror 70. The output light pulse of the main amplification stage 6 is polarized and matched to the polarization requirements of the reflective Treacy grating pair 73 by the second λ / 2 waveplate 65. The amount of introduced dispersion can be controlled by adjusting the distance between the two parallel reflective gratings 71 and 72 in the reflective Treacy grating pair 73, thereby achieving controllable and efficient compression of the laser pulse.

[0094] Figure 10(c) shows a chirped Bragg grating compressor. The laser pulse is directly injected into the second chirped Bragg grating 74. Light of different frequency components is reflected at different positions, thus corresponding to different propagation paths. This allows for the introduction of time delay to compress the pulse, which is then output through the fourth reflector 66.

[0095] Figure 10(d) shows a hollow fiber compressor, consisting of a second input coupling lens 75, a hollow fiber 76, a rare gas pump 77, a rare gas pool 78, a second output coupling lens 79, a chirped mirror assembly 80, and a fourth mirror 66. The rare gas pump 77 fills the rare gas pool 78 with rare gas, filling the hollow fiber with rare gas, including but not limited to neon, krypton, and argon. The gas pressure in the hollow fiber 76 can be optimized and adjusted according to the parameters of the incident laser pulse. The laser pulse is injected into the hollow fiber 76 through the second input coupling lens 75 and undergoes strong nonlinear interaction with the rare gas during transmission. This generates new frequency components through self-phase modulation, fully broadening its spectrum and providing good linear chirp. After being output through the second output coupling lens 79, dispersion compensation is performed using the chirped mirror assembly 80. By selecting the appropriate chirped mirror model and reflection path based on the required chirp compensation amount, ultra-high efficiency compression can be achieved.

[0096] In the examples provided by this invention, the fiber optic components can be integrated with each other to increase the compactness of the overall system structure without affecting the realization of the system performance. Furthermore, all the optical fibers and fiber optic devices used have polarization-maintaining characteristics, which can ensure the stability and reliability of the system.

[0097] The preferred embodiments and examples of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments and examples. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the concept of the present invention.

Claims

1. A high-energy ultrashort pulse laser, used to output high-energy broadband ultrashort laser pulses capable of overcoming gain narrowing effects, characterized in that, The high-energy ultrashort pulse laser includes a broadband seed laser source, a stretcher, a pulse selection module, a pre-amplification stage, a main amplification stage, and a compressor; wherein: The broadband seed laser source consists of a mode-locked fiber laser oscillator and a nonlinear amplifier, and is used to output a broadband femtosecond laser that can overcome the gain narrowing effect during the chirped pulse amplification process. The net intracavity dispersion of the mode-locked fiber laser oscillator is negative dispersion, which can be adjusted and controlled according to application requirements. After nonlinear amplification, the laser pulse output from the negative dispersion cavity has a greatly broadened spectrum, and the spectral structure is smooth, flat, and clean, without obvious Kelly sidebands, making it suitable as a seed source for subsequent laser chirped pulse amplification systems. The dispersion control method is one or more combinations of various dispersion types of optical fibers, chirped fiber gratings, and dispersion-tunable spatial structures based on diffraction gratings. The self-starting mode-locking method of the mode-locked fiber laser oscillator is one or a combination of saturable absorber mode-locking, nonlinear loop mirror mode-locking, and nonlinear polarization rotation mode-locking. The stretcher is connected to the output of the nonlinear amplifier and is used to stretch the broadband pulse output from the nonlinear amplifier in the time domain. The pulse selection module is connected to the output of the stretcher and is used to tunably reduce the repetition frequency of the laser pulse injected into the subsequent amplification stage in order to maximize the single pulse energy under limited pumping conditions. The pulse selection module consists of an optical fiber coupler, a photodetector, a pulse selection synchronization control circuit, an acousto-optic modulator, and an optical fiber isolator. The pulse selection synchronization control circuit includes a programmable FPGA board for changing the timing. The pre-amplification stage and the main amplification stage are connected in sequence to the output of the pulse selection module to amplify the injected laser pulses with chirped pulses. The compressor is connected to the output of the main amplification stage and is used to perform dispersion compensation on the amplified laser pulse to compress it in the time domain, so as to obtain an ultrashort laser pulse with high energy and high peak power.

2. The high-energy ultrashort pulse laser according to claim 1, characterized in that, The mode-locked fiber laser oscillator includes a saturable absorber, a lens group, a polarization-maintaining single-mode fiber, a gain fiber, a wavelength division multiplexer, a semiconductor laser, and a dispersion control module. The intracavity dispersion distribution of the mode-locked fiber laser oscillator is designed to be adjustable, which is used to output seed laser pulses that match the nonlinear amplification effect. After nonlinear amplification, a pulse output with good linear chirp characteristics can be obtained, and the accumulated nonlinear chirp is minimal. Thus, a pulse close to the transform limit can be obtained through compression. The saturable absorber reflector and lens group are one or a combination of two of the following: a fixed integrated structure and a relatively position programmable and electrically controlled movable structure. The former can reduce the interference of external jitter on the oscillator output, while the latter can realize mode-locked feedback and tune the repetition frequency of the oscillator output, further optimizing the nonlinear amplification effect. The nonlinear amplifier is connected to the output of the mode-locked fiber laser oscillator to achieve nonlinear amplification. Between the nonlinear amplifier and the mode-locked fiber laser oscillator is a single-mode fiber that provides pre-chirp management for the output of the mode-locked fiber laser oscillator. This can introduce a certain initial chirp into the output pulse of the mode-locked fiber laser oscillator, thereby enabling the pulse to output a high-quality baseless pulse while exceeding the gain bandwidth limit during the nonlinear amplification process.

3. The high-energy ultrashort pulse laser according to claim 1, characterized in that, The gain fiber used in the nonlinear amplifier is an active single-mode fiber with positive dispersion distribution. It can utilize the self-similar evolution theory of pulses to ensure that the amplitude shape of the laser pulse does not change during efficient amplification and can have linear chirp. This results in an ultrashort pulse that can resist light wave splitting and has a smooth broadened spectrum, thus overcoming the gain narrowing effect in the subsequent chirped pulse amplification process.

4. The high-energy ultrashort pulse laser according to claim 1, characterized in that, The stretcher is one or more of the following combinations: single-mode fiber stretcher, circulator combined with chirped fiber grating stretcher, diffraction grating pair stretcher, and chirped volume Bragg grating stretcher; The gain fiber used in the main amplification stage is one or more of the following: disk-shaped active photonic crystal fiber, rod-shaped active photonic crystal fiber, and solid-state laser amplification module. The compressor is one or more of the following: a diffraction grating pair compressor, a chirped volume Bragg grating compressor, and a special optical fiber for nonlinear pulse compression.

5. The high-energy ultrashort pulse laser according to claim 1, characterized in that, The gain fiber used in the high-energy ultrashort pulse laser is doped with one or more rare earth elements, depending on the required wavelength.

6. The high-energy ultrashort pulse laser according to any one of claims 1-5, characterized in that, The high-energy ultrashort pulse laser contains optical fibers and optical fiber devices that are fully polarization-maintaining.

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