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Cr4+-Doped Y3Al5O12 as a Saturable Absorber for a Q-Switched and Mode-Locked 639-nm Pr3+-Doped LiYF4 Laser

We experimentally prove that a Cr4+-doped Y3Al5O12 (YAG) crystal exhibits saturable absorption in visible wavelengths at 639, 607, and 521 nm. From z-scan measurements, the saturation energies measured using laser pulse widths of 25 and 66 ns at 639 nm are estimated to ∼11.5 and 21.2 mJ/cm2, respectively. Therefore, the absorption response time will be shorter than these pulse widths. Using the Cr4+:YAG saturable absorber, we demonstrate for the first time, to the best of our knowledge, the passive Q-switched and the Q-switched mode-lock Pr3+-doped LiYF4 (YLF) lasers at 639 nm pumped by an InGaN diode laser.