| Ultrashort pulsed lasers, with the merit of high peak power, high pulse energy and low thermal effect, have wide applications in many areas. In recent years, many emerging nano-materials have proven to be ideal saturable absorbers and been applied for short pulses generation with high performance. This thesis mainly investigated the optical properties especially saturable absorption of new nano-materials and their device applications for mode-locked fiber lasers. Three types of new nano-materials have been studied as below:1. Graphene-Bi2Te3 heterojunction materials are fabricated as saturable absorbers. Our work suggests that the exciton relaxation time of graphene-Bi2Te3 heterostructure is tunable depending on the coverage of Bi2Te3, and their modulation depth is also tunable. Its modulation depth is much higher than monolayer graphene due to larger absorption from Bi2Te3 nanocrystals. Furthermore, through controlling the optical properties of heterojunction saturable absorbers, we can achieve different output states in fiber lasers.2. Black phosphorus-polymer composites are firstly fabricated as saturable absorbers. Two fabrication approaches were demonstrated to produce BP-polymer composite films. The ease of handling of such BP-polymer composite thin films affords new opportunities for wide photonic applications.3. Plasmonic Cu3-xP nanocrystals(NCs) are firstly fabricated as saturable absorbers. We compared the difference in the optical properties of the samples before and after in-situ thermal treatment at high temperature. It is found that the optical nonlinearities also become stronger due to the increase of intensity of plasmon absorption after thermal treatment. Following we demonstrated the use of plasmonic Cu3-xP NCs as simple and effective saturable absorbers in a 1.5 μm Q-switched laser. Through comparing the performance of different laser devices, it is found that the saturable absorbers after thermal treatment can generate more stable pulses with higher pulse energy. |
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