Research On The Generation Of High Power And High Energy Femtosecond Pulses From Mode-locked Fiber Laser Systems

As the development of science and technology, many applications requiregeneration of much higher energy ultrashort pulses from the mode-locked fiber lasersystems. A very efficient solution is the implement of the Yb-doped large mode areaphotonic crystal fibers. In this thesis, the equivalent saturable absorbing of thenonlinear polarization rotation in the above fiber is adopted to realize the passivemode-locking, avoiding the damage of SESAM due to the overloaded heat depositionin high power operation. Several mode-locked fiber laser systems are constructed, andthey can directly generate ultrashort laser pulses of the Watt-level average power,corresponding to single pulse energy of hundreds of nanojoules. Besides, theintracavity dynamics are investigated to gain a deep sight. On the other hand, thespatio-and temporal-shapings are also conducted to enhance the pulse quality of thefiber amplifier systems. The main contents of this thesis are as follows,1. A brief introduction is first devoted to the history of the mode-locked fiber lasers.The physical effects and the corresponding numerical techniques involved in themode-locked fiber lasers are also illuminated.2. Two high coupling efficiency fiber laser resonators with multi-pass cells (MPC)are designed based on the ABCD matrix methods of the Gaussian beams. Thecorresponding experiments show excellent agreement with the anticipations.3. Based on the resonators designed in part2, two high power and high energymode-locked fiber lasers are constructed in the normal-and in the net abnormaldispersion regime, respectively. The all normal dispersion dissipative solitonmode-locked fiber laser can generate stable mode-locked pulses of314nJ energy(4.9W average power), and the extracavity dechirped75fs pulses enable a peakpower as high as3MW. Further64nJ energy and25fs duration pulses (1Waverage power) can be generated from the extracavity pulse spectra-broadeningand compression of the above pulses, corresponding to>2MW peak power. Theamplifier-similariton mode-locked fiber laser operating in the large net abnormaldispersion regime can generate pulses of energy as high as137nJ (2.1W averagepower) and the dechirped pulse duration can reach as short as44fs, correspondingto2MW peak power. 4. A fiber-based beam shaper is designed and manufactured to enable directgeneration of Bessel-pulses from the high power and high energy fiber amplifiersystems. The system can directly output Bessel pulses of18.7W average power,corresponding to329nJ energy. A filter-based shaping of the seeding pulses isemployed in the system to generate the rather clean dechirped pulses, and theresulting38fs and248nJ dechirped pulses allows the peak intensity to reach10GW/cm~2level.5. For the mismatch of high order dispersion in the fiber amplifier systems, a vectordispersion compensation system is designed and realized based on the amulti-pass cell with Gires-Tournois (GT) mirrors and a pair of gratings. Thecompensation system can effectively suppress the pedestals of dechirped pulsesfrom the high power and high energy fiber amplifier systems, which results in the44fs and531nJ pedestal-suppressing pulses, corresponding to more than10.8MW peak power.