Resonantly Pumped Passively Q-switched Er:YAG Ceramic Laser With Graphene Saturable Absorber

Q-switched solid-state lasers operating in the eye-safe wavelength regime around1.6μm have a number of important applications, such as remote sensing, free-spacecommunications and laser radars. They also provide a good starting point formid-infrared (3-5μm) generation via nonlinear frequency conversion. In this thesis, weinvestigated output characteristics of1.6μm passively Q-switched polycrystallineEr:YAG ceramic laser using graphene as saturable absorber, both theoretically andexperimentally.At the beginning, a series of experiments were studied about Er/Yb co-dopedpumping source. Firstly, we studied a free-running Er/Yb co-doped fiber laser. Itgenerated75.5W output power at1.55μm for212.5W of incident pump power. Then,by changing the incident angle of a volume Bragg grating (VBG) which used as thewavelength selection element, the operating wavelength was tunable from1532to1570nm, with≥10.66W output power over the whole tuning range. Over13.1W CW outputpower was generated for51W of launched pump power. Finally, the operationwavelength of the Er/Yb fiber laser was locked at1532nm, to match the absorptionpeak of the Er:YAG ceramic. Under launched pump power of127.5W, the Er/Yb fiberlaser yielded a maximum output power of30.4W, corresponding to a slope efficiency of24.7%.For theoretical analysis, we first analyzed the theory of solid-state laser resonatordesign using ABCD law, and simulated the TEM00radius and the stable region of laserresonator by Matlab software. After that, an analytical expression for threshold pumppower of1.6μm Er:YAG laser, derived from the rate equations for an end-pumpedquasi-three-level laser, was analyzed and simulated. Finally, we analysed the operationwavelength of Er:YAG laser for different cavity loss.This thesis is focused on laser performance of passively Q-switched Er:YAGceramic laser. In this part, we first introduced the fabrication procedure and spectralcharacteristic of Er:YAG transparent laser ceramic. Then, we studied the laserperformance of Er:YAG laser in continuous-wave mode. In the last, we demonstrated apassively Q-switched polycrystalline Er:YAG ceramic laser at a central wavelength of1645nm with the help of a simple four-mirror folded configuration, pumped by the Er/Yb-doped fiber laser at1532nm. By using a graphene saturable absorber (GSA) asthe passive Q-switch, a528mW average output power was obtained with7.08μJ pulseenergy and74.6kHz pulse repetition rate under a4.14W incident pump power.