Research On High-power All-fiber Femtosecond Laser Operated At 1.55 ?m And 2 ?m

Owing to the unique advantages of compact structure,good beam quality,high peak power and high pulse energy,high power ultrafast fiber lasers can be used in many fields,such as generation of THz and supercontinuum,micromachining,medical surgery,optical imaging,environment monitoring.Besides,High-power femtosecond fiber lasers with same repetition rate and different central wavelength could extend to mid-infrad region by nonlinear frequency convertion.The researches of high power ultrafast fiber lasers,not only have important academic significance,but also have practical significance.The main contents of our research on this subject are shown as following:1.The development of passively mode-locked Er-doped fiber lasers and high power ultrafast fiber lasers in 1.55 ?m band was introduced firstly.Then,the development of the wavelength tunable femtosecond Raman soliton fiber lasers in 2 ?m band based on soliton self-frequency shift(SSFS)was illustrated.Finally,high-energy wavelength tunable ultrafast fiber lasers around 2 ?m have also been illustrated.2.The physical mechanism of mode-locking and the generation of soliton pulse in fiber laser was studied firstly.Then the theory of stimulated Raman scatting and SSFS was studied.Finally,the energy level of Er-doped fiber and Tm-doped fiber,different kind of structure of fiber amplifier and some influence factors of chirped pulse amplification(CPA)system was introduced.3.We demonstrated an all-fiber Er-doped CPA system based on compression in hollow-core photonic band gap fiber(PBGF).The CPA system was seeded by a self-starting carbon nanotube(CNT)mode-locked Er-doped fiber laser.The dispersion compensating fiber(DCF)not only served as the pulse stretcher but also was used for broadening the spectrum in the CPA system.The system's performance was greatly improved by this technique.Finally,our system produced pulses with 346.5 fs duration and 83.1 n J pulse energy.The peak power of the system was estimated to be 234.7 k W.This is the shortest pulse duration ever reported in Watt-level all-fiber CPA system in 1.55 ?m band.4.The amplification characteristics of different kinds of Er-doped fiber and pump mode were studied firstly.The CPA syetem was builded based on the same CNT mode-locked Er-doped fiberl laser.Then the wavelength tunable Raman solitons were directly genenrated via SSFS.Finally,Raman solitons with wavelength tunability from1.81-2.05 ?m are gennerated by SSFS in 200 m polarization mantaining fiber(PM80G).5.Raman solitons with central wavelength of 1909.9 nm,1969.9 nm and 2029.6 nm were sent into 1.5 m double-cladding Tm-doped fiber(DC-TDF)after the pre-amplifier.The DC-TDF was adopted as both gain medium and Raman shifter.Raman solitons with wavelength tunability of 421 nm from1.95-2.37 ?m,a minimum pulse duration of 105.8 fs,a maixium of pulse energy of 12.9 n J and a maxium of peak power of 91.1 k W were gennerated by pumping the Raman soliton with central wavelength of 1909.9 nm.Solitons with >10 n J pulse ernergy could be achieved in the 2.17–2.37 ?m tuning range.The conversion efficiency of the Raman soliton varied between 70% and 100%.Synchoronous high power ultrafast pulses with same pules repetition in both 1.55 ?m band and 2 ?m band could directly generated by our system.