| High-power ultrafast fiber laser amplification technology is now an important frontier in worldwide high-energy laser physics research,with applications in laser plasma accelerators,laser-driven inertial confinement nuclear fusion,laser weapons,and other fields.Based on the advancement of laser amplification technology and the parametric demand for drive light sources in the aforementioned high-energy laser physics applications,the development of coherent amplification networks based on ultrashort pulse fiber lasers has considered as an important direction for the investigation of highenergy laser drive sources in the aforementioned fields.Chirped Pulse Amplification(CPA)is one of the critical technologies for realizing the coherent beam combination system based on high average power and high energy fiber chirped pulse amplification,which is still in the early stages of development.There are many technical solutions to achieve coherent beam combination,one of which is polarization coherent beam combination technology,which not only effectively increases the average output power of the system,but also has a high combination efficiency,effectively reducing system loss,making it the ideal solution to achieve high average power,high energy fiber laser coherent beam combination system,and has great development potential.The fiber oscillator,high power chirped pulse fiber laser amplifier,and polarization coherent beam combination phase control system are the primary components of the ultrashort pulse fiber laser coherent beam combination system.The fiber laser oscillator is an important precondition for the coherent beam combination system's implementation,while the high-power chirped-pulse fiber laser amplifier is a crucial foundation for the system's reality.The coherent beam combination system of high-power fiber laser ultrashort pulses is the topic of this dissertation.A fiber laser oscillator as the seed source is used to propose a polarization coherent beam combination error locking approach based on outlier detection differential signal locking.By integrating the high-power chirped pulse fiber amplification approach with this technique,a high-power fiber laser ultrashort pulse coherent beam combination system was built.The output of high-power femtosecond pulse coherent synthesis is produced,which serves as a reference for future high-power laser driver development.The details are summarized as follows:1.A fiber laser oscillator is a necessary component for the development of a pulse coherent system,which is based on nonlinear amplified loop mirror mode-locking technology and nonlinear polarization rotation mode-locking technology to realize an integrated fiber laser oscillator.An ultrashort pulse output with a spectral width of 20 nm is accomplished by suitably improving the cavity structural design and intracavity dispersion.Given that the overall repetition frequency of the synthesis system is 1 MHz,a single frequency reduction of the seed source output pulse is required,and offered that the minimum gate width of the acousto-optic modulator is 20 ns,40 MH is chosen as the repetition frequency of the fiber oscillator for the subsequent high-power chirp pulse amplification system and pulse generation system.This provides dependable technical assistance for the following high-power chirped pulse amplification and pulse coherent synthesis systems.2.From the theoretical and experimental perspectives,the full-polarization chirped pulse amplification system based on photonic crystal fiber is systematically studied.The completely biased fiber optic chirp pulse amplification system is thoroughly investigated,beginning with the selection of the signal light wavelength and progressing through the selection and parameter design of the pulse stretcher,the design of the fiber amplifier,and the design of the final pulse compressor.A pulse amplification system based on chirped fiber gratings(CFBG)is designed,and a transmissive diffraction grating matching the CFBG dispersion is used as the pulse compressor to produce an ultrashort pulse with a repetition frequency of 1 MHz,an average output power of 100 W,and a pulse width of 320 fs.The front-end seed is modulated in the time domain using this system platform and acousto-optic modulation technology to generate a pulse string pattern signal.A pulse string mode signal output with a pulse string mode repetition frequency of 100 k Hz,an average output power of 20 W,and a pulse width of 340 fs is obtained with this fiber-optic amplification system.When combined with nonlinear frequency conversion technology,the system output wavelength is converted to UV wavelength using a nonlinear frequency doubling crystal to produce a UV pulse string with the maximum UV average output power of0.45 W and center wavelength of 261 nm.3.A theoretical model of the combination efficiency of the linearly polarized femtosecond pulse coherent synthesis system is established,and the factors influencing the coherent beam combination efficiency of the system are analyzed using the twopulse coherent synthesis system,and the relationship equations corresponding to the different influencing factors and the coherent beam combination efficiency are given from the perspectives of spatial beam coupling and time-domain pulse coincidenc Simultaneously,the impact of numerous aspects that may arise in real applications is examined,and the related expressions are provided.The theoretical analysis shows that for a femtosecond pulse with a central wavelength of 1030 nm and a spectral width of10 nm,a difference of about 20 ?m in optical range can cause a 5% loss in the synthesis efficiency of the system;considering only the effect of group velocity dispersion on the synthesis efficiency of the system,for a femtosecond pulse with a central wavelength of 1030 nm and a spectral width of 10 nm,a difference of 0.5 m in fiber length can cause a 4% loss in the synthesis efficiency.Based on this theoretical analysis,the system synthesis optical path requirements and phase-locked system control requirements are derived.Combined with the analysis of the existing coherent synthesis phase-locking techniques,the final experimental phase-locking method and control strategy are determined.4.The two 100-watt ultra-short pulse fiber coherent beam combination system was built,and the performance of the system was tested and verified under the condition of the average output power of 10 W at the time of the scheme design.The results show that the system can achieve the compensation of optical range difference drift within ±20?m,and the combination efficiency of the system is more than 90%,which meets the design requirements,and also shows that the system is at the world advanced level in terms of combination efficiency.The system performance was tested under the highest average output power operation,and a high-power femtosecond pulse coherent beam combination system with an average output power of 165 W after coherent beam combination,a compressed pulse light width of 800 fs,and a combination efficiency of90% was achieved.The first national pulse coherent beam combination system based on photonic crystal fiber line polarization was established,serving as a point of reference for national pulse coherent beam combination development in China. |
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