Passively $Q$-switched Ytterbium-Doped Double-Clad Fiber Laser With a Cr$^{4+}$:YAG Saturable Absorber

A high-power and high-repetition-rate passively Q -switched ytterbium-doped single-mode double-clad fiber laser was built using a Cr ⁴⁺ :YAG saturable absorber (SA). Two different SAs with initial transmissions of T _omicron = 30% and T _omicron = 50% were studied. At the maximum coupled pump power of 9.8 W, an output power of 4.7 W, pulse duration of 143 ns, pulse repetition rate of 253 KHz, pulse energy of 18.5 muJ, and slope efficiency of 49% were obtained with the T _omicron = 30% SA.