High-power High Repetition Rate Femtosecond Fiber Laser At 1.0?m

In recent years,with the continuous development of relevant basic theories and technologies,high-power(high pulse energy)femtosecond lasers have been widely used in basic research and core industrial production in various fields,such as micro-and nano-machining,ultrafast optical diagnose,biophotonics and so on.At present,the main research directions can be divided into femtosecond lasers with low repetition rate and large pulse energy and femtosecond lasers with high repetition rate and high average power.The former one has been well studied,while the latter research is still in the initial stage.Moreover,compared with the solid-state femtosecond lasers,the research of high repetition rate and high average power femtosecond fiber lasers is very few.Especially,the Yb-doped double-cladding fiber(YDCF)as the gain medium has the advantages of all-fiber configuration,high beam quality,good compactness,low cost and long-term stability.Furthermore,the emergence of chirped pulse amplification(CPA,2018 Nobel Prize in Physics)enables producing high-power(high pulse energy)femtosecond pulses.Therefore,the development of high-power and high repetition rate femtosecond fiber lasers based on YDCF is of great technical value.This thesis focuses on high-power high repetition rate femtosecond fiber laser at 1.0 ?m.To this end,theoretical and experimental studies have been carried out:based on the physics of passive mode-locking at high repetition rates,we investigate the power scalability of high repetition rate femtosecond pulses by leveraging chirped pulse amplification and nonlinear chirped pulse amplification.The main contents of this thesis are as follows(1)On the basis of vector model of the GHz repetition rate passive mode-locking in short fiber laser cavities,the vectorial output characteristics are theoretically studied and experimental investigated.According to the theoretical findings,we design an experimental scheme to prevent the formation of polarization rotation locked vector soliton.Finally,1.2 GHz repetition rate passively mode-locked pulses are achieved at 1.0 ?m(2)Based on the optical power transmission equation and the rate equation,the gain fiber length of the main amplifier stage is obtained.A high-power and high repetition rate all-fiber pulse amplification system is constructed that seeded by a 1.0 ?m high repetition rate passively mode-locked fiber laser.Experimentally,we obtain a high power and high repetition rate picosecond pulse laser with an average power up to 165 W and a repetition rate of 1.2 GHz.The slope efficiency of the main amplifier is 77.8%.The standard deviation of the output power is less than 0.67%in 30 minutes.The beam quality M2 of the laser system is measured to be better than 1.4,specifically Mx2=1.39 and My2=1.11.(3)On the basis of high-power and high repetition rate all-fiber pulse amplification system,a pulse compression device is added to construct the CPA system.By optimizing the system,we finally achieve 108 W,1.2 GHz femtosecond pulses with single pulse energy 0.9?J and a pulse width of 473 fs.