Highly Efficient Passively $Q$ -switched Yb:YAl$_{3}$ (BO$_{3}$)$_{4}$–Cr $^{4 +}$:YAG Laser End-Pumped by a High-Power Diode

We report, for the first time to our knowledge, the passively $Q$-switched laser performance of the Yb:YAl$_{3}$(BO$_{3}$) $_{4}$ crystal operating at ${\sim} {\hbox {1}}\ \mu$m with a Cr $^{4+}$:YAG crystal used as the saturable absorber. Employing a compact plano-concave resonator end pumped by a high-power diode, we obtained by using a 2 mm thick $a$ -cut crystal a $\sigma$-polarized average output power of 4.15 W at 1041.3 nm with optical-to-optical and slope efficiencies as high as 48.3% and 59%, respectively. The $Q$-switched output power generated with the $c$-cut crystal (2 mm thick) was lower due to the crystal inhomogeneity: 3.15 W with a slope efficiency of 48%. The highest pulse energy, shortest pulse duration and highest peak power achieved with the $a$- and $c$-cut crystals were found to be nearly identical, being 139 $\mu$ J, 18 ns, and 7.33 kW, respectively.