High-pulse-energy All-fiber Lasres Based On Gain-swithing Technique

Since the invention of the first Ruby laser in the beginning of 1960 s, as a comprehensively-used tool, lasers have affected and changed our daily life. In recent years, fiber lasers have been rapidly developed and replaced a certain amount of Nd:YAG laser and CO₂ laser in industrial laser market. The long and thin structure of optical fiber is good for heat management. However, it also leads to very high power densities and severe nonlinearity, which restricts the acquirement of high peak power and high pulse energy. Because of these unresolved issues, researcher have been trying to achieve high energy pulses from fiber by employing enormous approaches. These problems have drawn many attentions in recent years.The objective of this work is to achieve the fiber lasers that can output very high pulse energy by developing the undeveloped gain-switching pulse generation technique in fiber lasers. The primary contents and results of our research work include: 1) Theoretical investigation of the temporal and energy characteristics of gain-switched diode-pumped Er/Yb-codoped fiber lasers, which can provide important references for further relevant experiments; 2) Numerical calculation of the temporal characteristics of inband-pumped gain-switched Tm-doped fiber lasers. We determined the parameter space of the pump conditions that could generate the pulses having a Gaussian-like temporal shape and free from the trailing spikes and characterized the variation of the laser pulse widths at different laser configurations; 3) Numerical investigation of the lasing and thermal characteristics of kilowatt thulium-doped fiber lasers（TDFLs） under different pump transitions. We proposed tandem-pumped TDFLs for reducing the heat at high powers and discussed the related issues of design; 4) Experimental study of a hybrid-pumped gain-switched TDFL with a linear-polarized output. We acquired a pulse energy of 230 μJ, which is an order of magnitude higher than previous results; 5) Experimental investigation of an all-fiber thulium-doped amplifier seeded by an in-bandpumped gain-switched TDFL. We achieved a pulse energy of 7 mJ, which is the highest one among all-fiber 2-micron nanosecond fiber lasers; 6) Theoretical and experimental study of gain-switched mode-locking phenomenon. We reveal it is initialized from the mode beating among multiple random longitudinal modes of the gain-switched fiber lasers and enhanced and stabilized by the saturation absorption effect of the unpumped section of the gain fiber; 7) Designs of several fiber lasers for different usages and application of invention patents to protect these ideas.