Wide-spectrum fiber laser nonlinear amplification device and working method

Abstract

The invention discloses a wide-spectrum fiber laser nonlinear amplification device and a working method. The device comprises a front-end light source, a first isolator, a nonlinear fiber laser amplification stage, a second isolator, a wide-spectrum fiber laser amplification stage and a compressor which are connected in sequence. The isolators ensure unidirectional transmission between the amplifiers. A picosecond or femtosecond light source at the front end passes through a nonlinear optical fiber laser amplifier, the spectrum is widened to the bandwidth of dozens of or even hundreds of nanometers under the action of strong nonlinearity, the process enables the pulse to have linear chirp in the time domain and break through the active gain bandwidth limit in the frequency domain, and the chirp removal pulse width is only dozens of femtoseconds. The wide-spectrum fiber laser amplification stage utilizes a large-mode-field-area fiber, the wide spectrum and linear chirp of laser can be maintained while pulse energy amplification is achieved, and the pulse width can still be compressed to tens of femtoseconds after the pulse passes through a compressor composed of a grating pair or a prism pair.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber laser technology, in particular to ultrafast optical fiber laser technology, and specifically to a broadband optical fiber laser nonlinear amplification device and a working method. Background Art

[0002] Ultrafast lasers have broad application prospects in both basic science and industrial fields, such as strong field physics, ultrahigh-speed phenomenon detection, high-precision measurement and processing, and biological microscopic imaging. Compared with solid-state lasers, fiber lasers have the advantages of good beam quality, high conversion efficiency, convenient thermal management, compact structure, and flexible operation. In order to obtain ultrafast lasers with high energy and narrow pulse width, chirped pulse amplification (CPA) technology has become a commonly used technical solution in femtosecond fiber systems. At present, fiber CPA systems need to use a stretcher to stretch the pulses before amplification to 10ps to 5ns; in order to ensure that the amplified pulses can be compressed to near-conversion limit pulses, the nonlinear phase shift accumulated during the amplification process should be controlled at a low level as much as possible; due to the gain narrowing effect accompanying the amplification process, the spectral width of the pulse will become narrower, so the pulse width generated by the CPA-based ultrafast fiber laser amplification system is usually above 200fs. However, many applications require laser pulse widths below hundreds of femtoseconds, including high-order harmonic generation of extreme ultraviolet pulses, multiphoton microscopy, and wide-spectrum mid-infrared optical frequency combs based on pulse self-difference frequencies.

[0003] Therefore, the researchers proposed a nonlinear amplification technology solution. When using gain fiber for amplification, the pulse width is deliberately kept at the picosecond or femtosecond level to accumulate a large amount of nonlinear phase shift, resulting in the spectrum of the amplified pulse being several times the input spectrum, and having a nearly linear chirp in the time domain. Therefore, after compression by traditional grating pairs, an ultrafast laser with a pulse width of less than 100fs can be generated. At present, nonlinear fiber laser amplification mainly includes self-similar amplification, pre-chirp managed amplification (PCMA), gain-managed nonlinear amplification and other methods. Among them, PCMA technology combined with large mode field fiber technology is currently the main means to obtain high-energy sub-hundred femtosecond ultrashort pulses, but the precise pre-chirp adjustment method and complex spatial optical path make the fiber laser system lose its flexible and compact advantages. For example, in Chinese patent application 202011559678.5, its pre-chirp management module, dual-pass fiber amplifier module, and pulse compression module are all composed of spatial optical paths. However, the nonlinear amplification system with an all-fiber structure often has a low output power, and the pulse energy is far less than the μJ level, such as the Chinese patent application 201710302907.7. The technical solution of gain-managed nonlinear amplification has been proposed since 2019. Relying on the effect of nonlinear attractors, it can also achieve several times spectral broadening and compression after sub-hundred femtosecond ultrashort pulse output (Optica6, 1328-1333 (2019)). However, in the above nonlinear amplification schemes, the technical solutions are all to amplify a narrowband seed light into a broadband spectrum, and it is often necessary to process the seed laser before amplification, such as using a pre-chirp component to compress the pulse to the femtosecond level, or using optical devices such as fiber gratings to filter and shape the spectrum of the seed laser, which leads to serious loss of signal light, making the seed laser energy extremely low, and the corresponding pulse energy after nonlinear amplification is difficult to exceed 1μJ. Summary of the invention

[0004] The purpose of the present invention is to provide a broadband fiber laser nonlinear amplification device and working method to address the deficiencies of the prior art, especially the problem that it is difficult to balance the energy enhancement of sub-hundred-femtosecond pulses and system compactness in fiber amplifiers. This device combines the advantages of nonlinear amplification technology and large mode field area fiber, and directly amplifies the ultra-short pulses with linear chirp in the nonlinear fiber laser amplifier stage through the broadband fiber laser amplifier stage. Since the gain spectrum of the signal light in the nonlinear fiber laser amplifier stage has broken through the active gain bandwidth limit, and the upper edge of the spectrum is relatively flat, it will no longer be limited by the gain bandwidth in the broadband fiber laser amplifier stage, and the signal light can maintain the linear chirp in the time domain, the spectrum in the frequency domain can continue to be broadened, and the energy is further amplified in the large mode field area fiber. It is worth mentioning that the entire system does not require additional dispersion adjustment components and pulse shaping devices, and can directly output sub-hundred-femtosecond pulses of several microjoules after the compressor. This method greatly reduces the system loss while taking into account the advantages of the compact structure of the fiber laser.

[0005] The objective of the present invention is achieved through the following technical solutions: a broadband fiber laser nonlinear amplifier device, comprising a front-end light source, a first isolator, a nonlinear fiber laser amplifier stage, a second isolator, a broadband fiber laser amplifier stage and a compressor connected in sequence; the front-end light source is a picosecond or femtosecond ultrafast fiber laser light source; the first isolator and the second isolator are used to ensure unidirectional transmission between amplifiers; the nonlinear fiber laser amplifier stage is composed of a semiconductor pump source, a beam combiner or a wavelength division multiplexer and a gain fiber, and is used to achieve drastic spectrum broadening by utilizing the strong nonlinear effect caused by ultrashort pulses in the optical fiber; the broadband fiber laser amplifier stage is used to utilize the gain fiber and the high-power pump source to amplify the energy of the ultrafast laser with a wide spectrum input by the previous stage; under the action of the high nonlinear phase shift, the spectrum is broadened while maintaining the linear chirp in the time domain; the compressor is used to provide negative dispersion, and de-chirp the pulse with linear chirp to a pulse width close to the transformation limit.

[0006] Furthermore, the first isolator and the second isolator are implemented by optical fiber isolators or circulators.

[0007] Furthermore, the first isolator, the nonlinear fiber laser amplifier stage, the second isolator, and the broadband fiber laser amplifier stage are all connected by fiber fusion splicing.

[0008] Furthermore, the semiconductor pump source, beam combiner or wavelength division multiplexer and gain fiber are all spliced ​​by fiber fusion; the nonlinear fiber laser amplifier stage utilizes the strong nonlinear effect caused by ultrashort pulses in the optical fiber to achieve drastic spectrum broadening under the action of fiber gain, dispersion and self-phase modulation, and generate a wide-spectrum ultrafast laser with a bandwidth of tens or even hundreds of nanometers. At this time, the pulse has linear chirp in the time domain and is compressible; the amplification mechanism of self-similar amplification, pre-chirp management amplification and gain management nonlinear amplification can be adopted.

[0009] Furthermore, the output end of the gain optical fiber in the broadband optical fiber laser amplifier stage is collimated by two convex lenses or a collimator and output in a spatial optical path after passing through a dichroic mirror.

[0010] Furthermore, the broadband fiber laser amplifier stage is composed of a gain fiber and a pump source. Without entering the spatial optical path for propagation, the compressor uses fiber gratings, negative dispersion fibers, and hollow fibers as fiber dispersion compensation elements. The output end of the broadband fiber laser amplifier stage is fused to achieve an all-fiber structure.

[0011] Furthermore, the gain fiber in the broadband fiber laser amplifier stage adopts a rod-shaped photonic crystal fiber amplifier stage, and both ends of the fiber adopt spatially coupled bidirectional pumping or forward pumping or backward pumping to achieve energy enhancement of ultrashort pulses.

[0012] Furthermore, the compressor is composed of a grating pair or a prism pair.

[0013] A working method of the above-mentioned wide-spectrum fiber laser nonlinear amplifier device includes: a front-end light source passes through a first isolator to prevent the backward return light of the amplifier from damaging a seed source; the spectrum width is drastically widened to several times or dozens of times the input spectrum through the nonlinear effect caused in the nonlinear fiber laser amplifier stage, and at the same time, the evolution of the nonlinear attractor makes the ultrashort pulse have an approximately linear chirp in the time domain, and the pulse is compressed to a near-transformation limit pulse width through a linear compression method; then it passes through a second isolator and directly enters the wide-spectrum fiber laser amplifier stage, and the wide-spectrum laser is further amplified in a large mode field area optical fiber, while relieving the accumulation of harmful nonlinear phase shifts; finally, the pulse is compressed in the pulse time domain through a pulse compression device to obtain a high-energy ultrashort pulse with a pulse width of less than 100 femtoseconds.

[0014] The beneficial effects of the present invention are:

[0015] 1. The system has very low requirements for the front-end light source. It only requires the output end to have a narrow spectrum and a pulse width in the order of picoseconds or femtoseconds. There are no requirements for pulse energy, repetition frequency, or chirp. A mode-locked fiber oscillator or ultrafast fiber amplifier working in the positive dispersion region can be used. There are many general-purpose laser products on the market that can meet the requirements at a low cost.

[0016] 2. The system has strong universality and scalability. There is a great deal of freedom in the selection of the scheme of the nonlinear fiber laser amplifier stage. The reported self-similar amplification, pre-chirp management amplification, and gain management nonlinear amplification techniques can all realize the functions of the nonlinear fiber laser amplifier stage. There is also a great deal of freedom in the selection of the gain fiber of the broadband fiber laser amplifier stage, and it only needs to have a mode field area not less than that of the fiber of the previous amplifier stage. In addition, it is possible to choose whether the technical solution adopts an all-fiber structure according to actual use requirements.

[0017] 3. The broadband fiber laser nonlinear amplifier device and working method directly utilize the energy amplification of the pulse of the nonlinear amplifier stage. Compared with the existing technical solutions, the amplification process does not have pre-chirp / pre-compression components and pulse shapers, which greatly simplifies the amplification system, reduces the loss in the amplification process, and improves the amplification efficiency. The compressor compresses the pulse in the time domain, and can obtain ultra-short pulse output with a pulse width of less than 100 femtoseconds and high energy and high peak power. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0019] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0020] Figure 2 is a diagram of an experimental device in Example 1 of the present invention;

[0021] Figure 3 is the output spectrum diagram of each stage in Example 1 of the present invention, wherein, Figure 3 (a) is a spectrum diagram of the picosecond light source in Example 1; Figure 3 (b) is the output spectrum of the nonlinear fiber laser amplifier stage (dashed line) and the broadband fiber laser amplifier stage (solid line);

[0022] Figure 4 It is the final output pulse width measured by the autocorrelator in Example 1 of the present invention; wherein, the dotted line is a Gaussian fitting curve, and the result shows that the compressed pulse width is 76fs.

[0023] In the figure, a front-end light source 101, a first isolator 105, a nonlinear fiber laser amplifier stage 102, a second isolator 106, a broadband fiber laser amplifier stage 103, a compressor 104, a fiber isolator 201, a semiconductor laser 202, a beam combiner 203, a benefit fiber 204, a fiber isolator 205, a cladding light filter 206, a photonic crystal fiber 207, a first convex lens 208, a dichroic mirror 209, a second convex lens 210, a high-power semiconductor laser 211, a first reflector 212, a grating pair 213, and a second reflector 214 are shown. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] like Figure 1 As shown, the present invention provides a broadband fiber laser nonlinear amplifier device and a working method, the device includes a front-end light source 101, a first isolator 105, a nonlinear fiber laser amplifier stage 102, a second isolator 106, a broadband fiber laser amplifier stage 103 and a compressor 104 connected in sequence.

[0026] The front-end light source 101 is a picosecond or femtosecond ultrafast fiber laser light source, which can be a mode-locked fiber oscillator or an ultrafast fiber amplifier operating in the positive dispersion region, and its output pulse sequence should be picosecond or femtosecond pulses; the output end of the front-end light source 101 is connected to the input end of the first isolator 105.

[0027] The first isolator 105 and the second isolator 106 can be implemented by optical fiber isolators or circulators.

[0028] The output end of the first isolator 105 is connected to the input end of the nonlinear fiber laser amplifier stage 102 through fiber fusion splicing.

[0029] The nonlinear fiber laser amplifier stage 102 is composed of a semiconductor pump source, a beam combiner or a wavelength division multiplexer, and a section of gain fiber, and the above devices are all fiber-spliced; the nonlinear fiber laser amplifier stage utilizes the strong nonlinear effect caused by ultrashort pulses in the optical fiber, and under the action of nonlinear effects such as fiber gain, dispersion, and self-phase modulation, achieves the effect of drastic spectrum broadening, and produces a wide-spectrum ultrafast laser with a bandwidth of tens or even hundreds of nanometers. At this time, the pulse has linear chirp in the time domain and is compressible. The amplification mechanism of self-similar amplification, pre-chirp management amplification, and gain management nonlinear amplification can be adopted.

[0030] The output end of the nonlinear fiber laser amplifier stage 102 is connected to the input end of the second isolator 106; the output end of the second isolator 106 is connected to the input end of the wide spectrum fiber laser amplifier stage 103. The above devices are all fiber fusion spliced.

[0031] The broadband fiber laser amplifier stage 103 uses a gain fiber with a large mode field area and a high-power pump source to further amplify the energy of the ultrafast laser with a broadband spectrum input from the previous stage; because the laser of the previous stage is directly injected without generating additional losses, the pulse energy of the previous stage is tens or hundreds of nanojoules, and under the action of the high nonlinear phase shift, the spectrum can be further broadened and the linear chirp in the time domain can be maintained. At this time, the pulse has a higher energy, and the output end of the gain fiber is cut at an angle of 8 degrees, collimated by two convex lenses or a collimator, and directly output in the spatial optical path after passing through a dichroic mirror.

[0032] The compressor 104 is used to provide appropriate negative dispersion and de-chirp the linear chirp pulse to a pulse width close to the transform limit. A grating pair or a prism pair may be used.

[0033] In particular, the broadband fiber laser amplifier stage 103 is only composed of a gain fiber with a large mode field area and a pump source. Without entering the spatial optical path for propagation, the compressor 104 can use fiber gratings, negative dispersion fibers, and hollow fibers as fiber dispersion compensation elements. By fusing the output end of the broadband fiber laser amplifier stage 103, the entire experimental device can be fully fiberized.

[0034] The working principle of the present invention is as follows: the front-end light source in the present invention is a picosecond or femtosecond light source with a narrow spectral bandwidth, and the first isolator is used to prevent the backward return light of the amplifier from damaging the seed source. Because picosecond or femtosecond pulses have relatively high peak power, they are very likely to cause strong nonlinear effects in the nonlinear fiber laser amplifier stage, causing the spectral width to be drastically widened to several times or dozens of times the input spectrum. At the same time, the evolution of the nonlinear attractor makes the ultrashort pulse have an approximately linear chirp in the time domain, and the pulse can be compressed to a near-transformation limit pulse width by a simple linear compression method. When directly entering the wide-spectrum fiber laser amplifier stage through the second isolator, since no additional shaping device is introduced, the tiny chirp introduced by the short-length passive optical fiber can almost be ignored in the signal light. Therefore, the wide-spectrum laser is further amplified in the large mode field area optical fiber, and the larger mode field area alleviates the accumulation of harmful nonlinear phase shifts, and the pulse maintains good compressibility while effectively amplifying the energy. Finally, the pulse is compressed in the time domain by a pulse compression device commonly used on the market, and a high-energy ultrashort pulse with a pulse width of less than 100 femtoseconds can be obtained.

[0035] In Example 1, the structure of a broadband fiber laser nonlinear amplifier device of the present invention is described. Figure 2 It is a high-energy ultrashort pulse fiber amplifier. It includes: picosecond light source, nonlinear fiber amplifier stage, broadband fiber laser amplifier stage, and pulse compressor. The repetition frequency of the picosecond light source is 10MHz, and the spectrum is as follows Figure 3As shown in (a), the central wavelength is 1040nm, the bandwidth is 2.3nm, the pulse width is 2ps, the average power is 13mW, and the pulse energy is 1.3nJ. Through the fiber isolator 201 with a core / cladding ratio of 10 / 125μm, the output end of the isolator is connected to the input end of the nonlinear fiber laser amplifier. The semiconductor laser 202 with a central wavelength of 976nm is injected through the fiber pump arm of the combiner 203, and a gain management nonlinear amplification process occurs in the 4.5m long gain fiber 204 (core / cladding ratio of 10 / 125μm, absorption coefficient 5dB / m@976nm), and the spectrum is greatly broadened in the long-wave direction (such as Figure 3 (as shown by the dotted line in (b)), the average power is amplified to 500mW, the pulse energy is 50nJ, and the de-chirped pulse width is measured by a compressor to be 66fs. The amplified signal light enters the broadband fiber laser amplifier stage through the fiber isolator 205 with a core / cladding ratio of 10 / 125μm. The pumping mode is backward pumping. The high-power semiconductor laser 211 is coupled into the photonic crystal fiber 207 after being collimated by the first convex lens 208 and the second convex lens 210. A cladding light filter 206 is fused at the front end of the photonic crystal fiber. The signal light is further amplified to 30W in the 3m long photonic crystal fiber 207 (core / cladding ratio of 40 / 200μm, absorption coefficient of 10dB / m@976nm), and the output spectrum is shown in FIG. Figure 3 As shown by the solid line in (b), the signal light is separated by a 976nm / 1064nm dichroic mirror 209 and enters the compressor. The laser first passes over the first reflector 212 without passing through the first reflector 212, passes through the 1000 line / nm grating pair 213, and is reflected back by the second reflector 214. The height of the reflected laser is slightly lowered by adjusting the second reflector 214, and hits the mirror surface of the first reflector 212. After passing through the grating pair 213 twice, the signal light is applied with appropriate negative dispersion, the pulse is compressed in the time domain, and the de-chirped pulse is extracted. The pulse width of the final output is measured by an autocorrelator to be 76fs, as shown in FIG. Figure 4 The final output power is 27W, corresponding to a diffraction efficiency of 90% and a pulse energy of 2.7μJ.

[0036] In Example 2, the nonlinear fiber laser amplifier stage 102 includes: a low-power pump source, a wavelength division multiplexer, and a single-clad single-mode ytterbium-doped fiber. The broadband fiber laser amplifier stage 103 includes: a high-power pump source, a beam combiner, and a large-mode-area ytterbium-doped fiber. The compressor 104 is a chirped fiber grating with a large-mode-area ytterbium-doped fiber with a consistent core / cladding ratio, providing negative dispersion matching the amplifier stage. Under this condition, the present invention can realize an all-fiber structure.

[0037] In Example 3, the second isolator 106 is a spatial optical isolator, and the gain fiber in the broadband fiber laser amplifier stage 103 can adopt a rod-shaped photonic crystal fiber amplifier stage. The two ends of the fiber adopt spatially coupled bidirectional pumping or forward pumping or backward pumping, which can achieve ultrashort pulses with higher power and higher energy than Example 1.

[0038] In summary, the present invention provides a wide-spectrum fiber laser nonlinear amplification device and a working method, which has a flexible, compact structure and universality, can output high-energy sub-hundred-femtosecond pulses with low cost and simple structure, and has important application prospects in the fields of strong field physics, high-precision measurement and processing, and biological microscopy imaging.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0040] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A broadband fiber laser nonlinear amplifier, characterized in that: It comprises a front-end light source, a first isolator, a nonlinear fiber laser amplifier stage, a second isolator, a wide-spectrum fiber laser amplifier stage and a compressor connected in sequence; the front-end light source is a picosecond or femtosecond ultrafast fiber laser light source; the first isolator and the second isolator are used to ensure unidirectional transmission between amplifiers; the nonlinear fiber laser amplifier stage is composed of a semiconductor pump source, a beam combiner or a wavelength division multiplexer and a gain fiber, and is used to achieve drastic spectrum broadening by utilizing the strong nonlinear effect caused by ultrashort pulses in the optical fiber; the wide-spectrum fiber laser amplifier stage is used to utilize the gain fiber and the high-power pump source to amplify the energy of the ultrafast laser with a wide spectrum input by the previous stage; under the action of the high nonlinear phase shift, the spectrum is broadened while maintaining the linear chirp in the time domain; The compressor is used to provide negative dispersion and de-chirp a pulse with linear chirp and compress it to a pulse width close to the transform limit.

2. The broadband fiber laser nonlinear amplifier device according to claim 1, characterized in that: The first isolator and the second isolator are implemented by a fiber optic isolator or a circulator.

3. The broadband fiber laser nonlinear amplifier according to claim 1, characterized in that: The first isolator, the nonlinear fiber laser amplifier stage, the second isolator, and the broadband fiber laser amplifier stage are all connected by fiber fusion splicing.

4. The broadband fiber laser nonlinear amplifier device according to claim 1, characterized in that: The semiconductor pump source, beam combiner or wavelength division multiplexer and gain fiber are all spliced ​​by fiber fusion; the nonlinear fiber laser amplifier stage utilizes the strong nonlinear effect caused by ultrashort pulses in the optical fiber to achieve drastic spectrum broadening under the effects of fiber gain, dispersion and self-phase modulation, and generates a wide-spectrum ultrafast laser with a bandwidth of tens or even hundreds of nanometers. At this time, the pulse has linear chirp in the time domain and is compressible; the amplification mechanism of self-similar amplification, pre-chirp management amplification and gain management nonlinear amplification can be adopted.

5. The broadband fiber laser nonlinear amplifier according to claim 1, characterized in that: The output end of the gain optical fiber in the broadband optical fiber laser amplifier stage is collimated by two convex lenses or a collimator, and is output in a spatial optical path after passing through a dichroic mirror.

6. The broadband fiber laser nonlinear amplifier according to claim 1, characterized in that: The broadband fiber laser amplifier stage is composed of a gain fiber and a pump source. Without entering the spatial optical path for propagation, the compressor uses fiber gratings, negative dispersion fibers, and hollow fibers as fiber dispersion compensation elements. The output end of the broadband fiber laser amplifier stage is fused to achieve an all-fiber structure.

7. The broadband fiber laser nonlinear amplifier according to claim 1, characterized in that: The gain fiber in the broadband fiber laser amplifier stage adopts a rod-shaped photonic crystal fiber amplifier stage, and the two ends of the fiber adopt a spatially coupled bidirectional pumping or forward pumping or backward pumping mode to achieve energy enhancement of ultrashort pulses.

8. The broadband fiber laser nonlinear amplifier device according to claim 1, characterized in that: The compressor is composed of a grating pair or a prism pair.

9. A method for operating the broadband fiber laser nonlinear amplifier according to claim 1, characterized in that: include: The front-end light source passes through the first isolator to prevent the backward return light of the amplifier from damaging the seed source; Through the nonlinear effect caused in the nonlinear fiber laser amplifier stage, the spectral width is drastically broadened to several times or dozens of times the input spectrum. At the same time, the evolution of the nonlinear attractor makes the ultrashort pulse have an approximately linear chirp in the time domain. The pulse is compressed to a near-transformation limit pulse width through linear compression; then it passes through the second isolator and directly enters the wide-spectrum fiber laser amplifier stage. The wide-spectrum laser is further amplified in the large mode area fiber, while the accumulation of harmful nonlinear phase shifts is alleviated; finally, the pulse is compressed in the time domain through a pulse compression device to obtain a high-energy ultrashort pulse with a pulse width of less than 100 femtoseconds.

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