| Due to their ultrahigh peak power as well as the ultrashort width, ultrashort-pulse lasers have been widely used in the fields such as bio-medicine, basic research, energy and laser manufacturing. In recent two decades, to obtain the ultrashort pulses from the laser systems, people always adopt SESAM, the semiconductor saturable absorber mirror, as the modulator. However, with the development of the research, SESAM has shown its shortcomings like difficult fabrication, high price and low damaging-threshold. To find the substitutions for SESAM, scientists are developing the relative research actively. In recent years, scientists have kept trying to take several materials like topological insulators and molybdenum disulfide, both of which belong to the two-dimension layered materials and have attracted wide attention in the field of condensed-matter physics, into the research on new saturable absorbers. And they hope that these materials can be the new-comers beside SESAM as the saturable absorber.In this thesis, both research and experiments about Q-switched mode-locking operation generated from the Nd:YVO4 laser using topological insulators and molybdenum disulfide as the saturable absorbers are made. The main content can be outlined as follows:In the first part, we summarize the relative reports from both China and other countries on the saturable absorbers of topological insulator and molybdenum disulfide, and sum up the experience of them.At the same time,we introduce the basic theory of mode-locking lasers using saturable absorbers, and in detail, it includes the basic theory of mode-locking, the characteristics of the lasers under the mode-locking operation and the condition of mode-locking which is drawn from the mode-locking laser equation. In this part we also introduce the parameters of the saturable absorbers and the Z-scan technique of measuring the absorbers’ absorption and parameters. All of these are the basis in the following experiments and corresponding analysis.In the second part, we introduce the common ways of fabricating the nano-platelets of the two-dimension layered materials. We also finish the fabrication of the saturable absorbers which are used in our experiments. The corresponding characterizations of the saturable absorbers are finished at the same time. With the hydrothermal intercalation/exfoliation method, we fabricate the reflection-typetopological insulator:Bi2Te3 saturable absorber as well as the transmission-type one.The absorber’s SEM image, Raman spectrum and nonlinear saturable curve are also obtained. Using the polyol method, we fabricate the transmission-type topological insulator: Bi2Se3 saturable absorber and obtain its characterizations. By the hydrothermal intercalation/exfoliation method, we also fabricate the reflection-type molybdenum disulfide saturable absorber.Its characterizations are also obtained.In the third part, we build up the Nd:YVO4 laser owning the folded cavity, and we obtain both the Q-switched and Q-switched mode-locking operation from it by adopting the saturable absorbers we have fabricated. With the application of reflection-type Bi2Te3 saturble absorber, the Q-switched mode-locking operation owning the maximum average output power of 247 mW is obtained. In the experiment, we also obtain the Q-switched operation whose maximum average output power, shortest pulse width and highest repetition rate are 183 mW, 2 μs and151.5 kHz, respectively. By inserting the transmission-type Bi2Se3 saturable absorber into our laser, we obtain the Q-switched mode-locking operation owning the maximum average output power of 30.2 mW and the unstable modulation phenomenon whose maximum average output power is 148.3 mW. In the experiment using the reflection-type molybdenum disulfide saturable absorber, we obtain the Q-switched operation whose maximum average output power is 87.2 mW. The repetition rate of the Q-switched pulse is 135.1 kHz, and the pulse width is 2.5 μs. In this experiment, we also obtain the Q-switched mode-locking operation owing the average output power of 95.3 m W. All these results obtained from our experiments have demonstrated the potential of the new-type two-dimension materials like topological insulators and molybdenum disulfide as the new saturable absorbers. |
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