| To make laser device more and more efficient, people never stop searching for new laser gain material ever since the day when laser was invented. According to different laser materials, there are four series of lasers, gaseous state laser, dye laser, semi-conductor laser and solid state laser. Due to the compactness, high efficiency, stable output and various pump modes, all-solid-state lasers have wide applications in national defense, scientific research and medical treatment. Single crystals are the most popular laser gain material,the variety of the single crystal allows various laser design proposals. Due to the good thermal and optical characteristics, Nd:YAG crystal has been considered to be an exellent laser gain medium in high power solid-state lasers, but it has its own defects, such as low doping level and high cost. Nd:YVO4 crystal has large absorption and emission cross-sections, it is favorable in middle-power and pulsed laser operation, but the serious thermal effect and low damage threshold show its limit in high-power laser applications.In recent years, people became more and more interested in ceramic lasers. As a newly developed laser material,transparent ceramics have a series of good characteristics, such as high thermal conductivity, low electrical conductivity, high hardness et al. Compared with glass, ceramic has better toughness and higher damage threshold. Compared with single crystal,ceramic has shorter growing period and higher doping level.With the development of the sintering technology, many excellent ceramic gain materials have been obtained, such as Nd:YAG ceramic, Yb:YAG ceramic, Yb:Y2O3 ceramic, Nd:Lu2O3 ceramic et al.Compared with Nd:YAG crystal, Nd:YAG ceramic has comparable optical and even better physicochemical characteristics. Meanwhile, ease of fabrication and high doping level make ceramic more useful in many fields.In this paper, we focused our research on the continuous wave (CW), pulsed and dual-wavelength Nd:YAG ceramic lasers, the main contents of this thesis are as following,1)LD-pumped CW 1064 nm,1338 nm and 946 nm Nd:YAG ceramic lasers were demonstrated. In the 1064 nm regime, we obtained 11.3 W CW output power at an incident pump power of 21.6 W, corresponding to an optical conversion efficiency of 52.3%, the slope efficiency was 54.4%. Under high pump power, no saturation was observed, which indicated higher power scaling can be expected. In the 1338 nm regime, we obtained 1.05 W CW output power at an incident pump power of 20.5 W, corresponding to an optical conversion efficiency of 5.1%. In the 946 nm regime, three different samples were used. With the 5 mm long Nd:YAG ceramic, we obtained 1.46 W CW output power at an incident pump power of 10.5 W, corresponding to an optical conversion efficiency of 13.9%, the slope efficiency was 17.9%.2) LD pumped Nd:YAG ceramic/KTP and Nd:YAG ceramic/BiBO green lasers were demonstrated. Through the experiment we found that the KTP crystal was superior to the BiBO crystal in frequency doubling. When the type-Ⅱcut KTP crystal was used as a frequency doubler, the maximum 532 nm green output was 1.86 W, and the optical conversion efficiency was 7%. The distribution of the green laser facula was found to be Gaussian type and the M2 factor was measured to be 1.7. To the best of our knowledge, this is the first report of a LD-end pumped high power Nd:YAG ceramic green laser.3) LD pumped Nd:YAG ceramic/Cr:YAG and Nd:YAG ceramic/GaAs passively Q-switched lasers were demonstrated. When the Cr:YAG crystal was used as saturable absorber, the largest pulse energy, shortest pulse width and highest peak power were measured to be 188μJ,3.16 ns and 59.5 kW, respectively. When the GaAs crystal was used as saturable absorber, the largest pulse energy, shortest pulse width and highest peak power were measured to be 41.6μJ,17 ns and 2.44 kW, respectively. Compared with the passively Q-switched results of Nd:LuVO4 and Yb:NaY(WO4)2 crystals, Nd:YAG ceramic has better performance.4) Three different kinds of dual-wavelength Nd:YAG ceramic lasers were studied. CW 1052 nm laser was obtained with Nd:YAG ceramic for the first time. The maximum output power was 6.19 W, corresponding to an optical conversion efficiency of 35.8% and slope efficiency of 39%. Using Cr:YAG as saturable absorber and frequency selector, we realized 1052 nm and 1064 nm dual-wavelength laser output, the largest pulse energy, shortest pulse width and highest peak power were measured to be 103.2μJ,4.8 ns and 21.5 kW, respectively. We realized 1319 nm and 1338 nm CW and pulsed dual-wavelength laser output. For both CW and pulsed output, we measured the ratio of 1319 nm and 1338 nm lasers. The maximum CW output power was 5.92 W and the pulsed part was 226 mW, the shortest pulse width and highest repetition rate were 15 ns and 133 kHz. Due to the high gain coefficient of laser materials, we realized 1064 nm Nd:YAG ceramic, Nd:YAG crystal and Nd:YVO4 crystal CW output laser without extra output coupler. The maximum output power was 1.74 W with Nd:YAG ceramic, corresponding to an optical conversion efficiency of 13.0%, the slope efficiency was 19.3%. Based on this idea, we realized 1064 nm,1319 nm and 1338 nm multi-wavelength laser output, the maximum output power was 3.2 W.With all the studies above, Nd:YAG ceramic has been proved to be an excellent laser gain material, which can find applications in variety of lasers.
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