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The development of efficient ultrafast laser sources based on Yb-doped crystals is very important for a variety of optical applications such as nonlinear spectroscopy, nonlinear microscopy, telecommunications etc. A powerful and high beam quality (near diffraction limited: M2~1) pump laser is desirable to mitigate the effect of reabsorption loss that Yb-doped crystals exhibit and realize highly efficient operation in both continuous-wave (CW) and pulsed domains. Unfortunately, there are no commercially available laser diodes that can provide both high beam quality and high output power (>1 W) simultaneously. This thesis presents the development of a powerful and high beam quality pump laser and then utilizes this pump laser to demonstrate the efficient operation of Yb:YAG laser in CW domain and Yb:KGW laser in both the CW and pulsed domains. In the first part of the thesis, a high-power compact CW Nd:YAG laser was built with greatly improved beam quality operating at 946 nm. A maximum output power of 9.98 W with beam quality factor M2 ~ 5 was obtained. I also demonstrated a highly efficient and tunable CW Yb:YAG laser pumped by the developed Nd:YAG laser. The maximum CW output power of 4.37 W was obtained at 1030 nm with optical-to-optical efficiency of 70% with respect to the absorbed pump power. Wavelength tuning of Yb:YAG laser was then explored due to metrological applications such as references for high-resolution spectroscopy or dimensional metrology. The laser produced a continuously tunable operation over 100 nm from 1000 nm to 1100 nm. This is the most tunable laser among bulk crystalline Yb:YAG solid-state lasers. Due to the increasing interest in dual-wavelength (DW) operation for the use as an optical source for terahertz (THz) radiation, this thesis also gave a demonstration of DW Yb:YAG laser operation. This is the first demonstration of DW operation of Yb:YAG laser pumped by a Nd:YAG laser at 946 nm. The latter part of the thesis concentrated on devel

High power diode-pumped solid state (DPSS) lasers are a rapidly growing technology that is attractive for various applications in scientific and industrial fields. DPSS lasers are highly efficient, reliable and durable with superior beam quality when compared to flash-lamp pumped solid state lasers. Double-tungstate crystal of neodymium-doped potassium gadolinium tungstate (Nd:KGW) is one of the most effective active media used in DPSS lasers for generation of continuous wave radiation and ultrashort (i.e. picosecond, 10-12 s) pulses. Unfortunately, the thermal conductivity of KGW host crystals is relatively low (~3 Wm-1K-1). This low thermal conductivity and large quantum defect while pumping with ~808 nm lead to significant thermo-optical distortions. One way to minimize thermo-optical distortions is to reduce the quantum defect. This can be done by pumping at longer wavelengths as compared to conventional 808 nm. In this work we demonstrate what we believe is the first continuous wave Nd:KGW laser with hot band diode pumping at ~910 nm. This pumping wavelength reduced the quantum defect by >46% as compared to the conventional ~808 nm pumping and resulted in significantly lower thermal lensing. The laser produced 2.9 W of average output power at 1067 nm in a diffraction limited beam for an absorbed pump power of 8.3 W. The slope efficiency and optical-to-optical efficiency were found to be 43% and 35%, respectively. Significant reduction of quantum defect offered by this pumping wavelength and availability of suitable high power laser diodes opens an attractive way to further power and efficiency scaling of the Nd:KGW lasers.