| This dissertation can be summarized mainly in two parts. Firstly, it demonstrates the propagation characteristics of laser in photonic crystal fibers (PCFs) as well as the theoretical and experimental research of the controllable dispersion, nonlinearity, and photonic bandgap properties in PCFs; Secondly, it reports the construction of all PCF femtosecond laser amplifier based on Yb3+-doped single-polarization large mode area (LMA) PCFs. The impact of system parameters on output is analyzed, and the high power ultrafast pulses with high repetition rate are obtained. The detailed contents can be classified as follows:1. The dispersion characteristics of the air-hole-assistant solid-core PCF is designed with finite element method. Two zero dispersion points are obtained through controlling the size of the air holes in fiber core. The properties of the group velocity dispersion (GVD) and third-order dispersion (TOD) are optimized to fulfill the need of dispersion match when applying the fiber to the fiber stretcher. The dispersion measurement system is constructed based on the method of white light interferometry, and the dispersion property of the air-hole-assistant solid-core PCF is measured.2. The stable soliton self-frequency shift is obtained in the experiment with the help of the two zero dispersion points in air-hole-assistant solid-core PCF. Compared to the PCFs with only one zero dispersion point, the sensitivity of the self-frequency shift depending on input pulse energy is greatly canceled.3. The output pulses from PCF laser are compressed by the anomalous dispersion property and low nonlinear characteristic of the air core photonic band gap fiber. The achievement realizes the preparing step for the band gap fiber to be further used in PCF femtosecond chirp pulse amplifiers. A unique band-pass filter is invented based on the bend loss properties of the all solid photonic band gap fibers and Bragg-type fibers.4. The gain characteristic and self-phase modulation (SPM) effect in Yb3+-doped fiber in the amplifier are studied numerically. The change of output pulse energy of the amplifier is also analyzed. The influence of SPM on output in the process of amplification is studied by using Split-step Fourier method. The amplification and compensation processes of the pulses are further studied through theoretical analysis and numerical simulation. Furthermore, the compensation between TOD and nonlinear chirp is analysed. 5. An all PCF laser amplifier is constructed based on Yb3+-doped single-polarization double cladding LMA PCFs. To obtain the shortter pulses than the seed pulses, the method of nonlinear amplification is used. The dependence of output on certain parameters, e.g. mode-locking conditions of the oscillator, spectrum modulation of the oscillator, pump power of the amplifier, and the length of the active fiber, etc. is studied. Furthermore, the record of 39 fs shortest pulses is realized in fiber laser single stage amplifier. High energy pulses with 109 fs time duration, 23 W average power, and 50 MHz repetition rate (corresponding to 460 nJ pulse energy) are also obtained. Applying the system as laser source, the research of high power nonlinear optics, high power fourth harmonic generation, and high speed micromachining are further developed.
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