| Picosecond fiber lasers with high average power and good beam quality are in demand for a large amount of applications including medical treatments, material processing and efficient harmonic generation in nonlinear media to name but a few. In material processing green laser sources perform better than their counterpart IR sources. Therefore, green light laser source has a wider demand in the field of laser processing. For mode-locked laser source, modulator is the key part and researchers use SESAM to achieve mode-locking operation in most cases. But the SESAM shows the shortcomings such as high price, difficult fabrication and low damaging-threshold, which inspire scientists to look for saturable absorber with more excellent performance to replace. Against that backdrop, the two-dimensional new material gradually comes into people's field of horizons. In this paper, we do some experiments on Q-switched mode-locked operation generated from the photonic crystal fiber laser using topological insulator and molybdenum disulfide as the saturable absorbers, respectively. Besides, detailed research about double clad fiber amplifier and green laser achieved by frequency doubling are conducted in the meantime. The main points are presented as follows:The first section demonstrates the research on Q-switched mode-locked operation using two-dimension Bi2Te3 and MoS2 disulfide as saturable absorbers respectively. Firstly, the mechanism of mode-locked fiber lasers and the theory of propagation equations are introduced. Secondly, we introduce the fabrication process of the bismuth telluride and molybdenum disulfide in detail. The corresponding performance of the absorber is characterized by the SEM, Raman spectrum. Next, by inserting the two saturable absorbers into the large mode area photonic crystal fiber laser cavity respectively, the Q-switched mode-locked operations are achieved. With the application of bismuth telluride(Bi2Te3) saturable absorber, the fiber laser is capable of generating 185 mW average output power with Q-switched envelope pulse width as short as 500 ns centered at 1035 nm. On the other hand, the MoS2-based Q-switched mode-locked laser enables the highest output power of ~555 mW with the pulse duration of 280 ns corresponding to central wavelength of 1033 nm. Our study suggests that Nanomaterials: Bi2Te3 and MoS2 could be promising saturable absorbers in the fiber laser. Finally, we carried on the contrast experiment by using SESAM as saturable absorber. By adjusting the SESAM carefully, we achieve CW mode-locking operation.The second section demonstrates the experiments study on the Yb-doped fiber amplifier based on MOPA structure. The fiber amplifiers use two kinds of different double clad fibers in experiments respectively and seed by Yb-doped photonic crystal fiber laser. 12.53 W average power is achieved when the available incident pump power reaches 43.3W with the pulse width is 4.1 ps, corresponding to the fiber length of 3.0 m. Then we also obtain 18.10 W laser output at the same pump power with the pulse width of 1.6 ps, corresponding to the fiber length of 1.6 m. No obvious nonlinear effect was founded during the experiments.The third section demonstrates the theoretical and experimental investigation of frequency doubling which based on the fiber amplifier system above-mentioned. In the first place, proceeding from Maxwell equations, the second harmonic coupled wave equations about ultra-short pulse laser source are derived. Secondly, we lay emphasis on the theory of phase-match technique and nonlinear optical crystal BBO. Next, an experiment using BBO(?=23.2°, ?=0) is carried out, the green laser centered at 520 nm with 1.143 W is obtained at the fundamental power of 16.7 W. Finally, we analyze the reason for the low frequency doubling efficiency and point out that a good beam quality is necessary during the frequency doubling experiment. Further work will be focused on the pump source with high beam quality, narrow-linewidth and the appropriate nonlinear crystal to achieve high frequency doubling efficiency. |
PDF Full Text Request