Study On Short Pulse Laser And High-repetition-rate Fiber Laser

Ultra-short laser pulses have always been the focus of attention and have important applications in ultrafast optics, optical communication, sensors, industrial machining and laser medicine science. In the meantime, ultra-short laser pulses operated at high repetition rates are quite useful in a large variety of scientific and technological applications, for example, biomedical imaging at megahertz repetition rates, high-speed telecommunication and optical sampling at gigahertz rates, and developing high-repetition-rate seed lasers for fusion laser systems. Besides, fiber laser has many advantages such as small size, light weight, maintenance-free, low cost, high stability, and low pumping threshold, so it has attracted great attention in our real life and scientific research. In this dissertation, experimental investigations were given on this topic about short pulse fiber laser and high-repetition-rate fiber laser.The detailed works in this dissertation include:1. Several short pulse fiber lasers which mode-locked by nonlinear polarization rotation were accomplished.1) A all-fiber mode-locked erbium-doped fiber laser was established with nonlinear polarization rotation effect in fiber and intra-cavity dispersion compensation. As a result, ultra-short pulses with pulse duration of263fs were produced in the mode-locked erbium-doped fiber laser.2) By using nonlinear polarization rotation effect, a half-space mode-locked erbium-doped fiber laser was realized. With master-slave cavity configuration, the mode-locked erbium-doped fiber laser was synchronized to ultra-short pulses at1030nm, ultra-short pulses with pulse duration of582fs at1531nm were produced.3) A square nanosecond mode-locked laser was achieved with long cavity by peak power clapping effect and nonlinear polarization rotation effect. The pulse duration changed as the pump power and polarization, and the pulse with widest pulse duration of12ns was obtained.4) A mode-locked ytterbium-doped fiber laser has been realized by using graphene as saturable absorber. Pulses with repetition rate of27MHz at1580nm were achieved.2. A mode-locked fiber laser system consisting of two coupled cavities was presented, and the laser system was mode-locked by coupled-cavity mode-locking and nonlinear polarization rotation effect. Pulses with high frequency of434.1MHz and1.09GHz, were generated in the coupled cavity. Besides, the fundamental repetition rates and high-order harmonic repetition rates at different pump powers of the left cavity were presented. Also the relationship between repetition rate of the coupled system and the left cavity length was studied. This presents an efficient way to get mode-locked laser pulses at high repetition rates.