A passively Q-switched Ho:YVO\({}_{4}\) Laser at 2.05 \(\upmu\)m with Graphene Saturable Absorber  
Wenmiao Lin  
National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China; [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (Z.C. ); [EMAIL_ADDRESS] (B.Y. ); [EMAIL_ADDRESS] (T.D. ); [EMAIL_ADDRESS] (X.L.) Xiaoming Duan  
1 National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China; [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (Z.C. ); [EMAIL_ADDRESS] (B.Y. ); [EMAIL_ADDRESS] (T.D. ); [EMAIL_ADDRESS] (X.L.) Zheng Cui  
National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China; [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (Z.C. ); [EMAIL_ADDRESS] (B.Y. ); [EMAIL_ADDRESS] (T.D. ); [EMAIL_ADDRESS] (X.L.) Zheng Cui  
National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China; [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (Z.C. ); [EMAIL_ADDRESS] (B.Y. ); [EMAIL_ADDRESS] (T.D. ); [EMAIL_ADDRESS] (X.L.) Zheng Cui  
National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China; [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (Z.C. ); [EMAIL_ADDRESS] (B.Y. ); [EMAIL_ADDRESS] (T.D. ); [EMAIL_ADDRESS] (X.L.) Zheng Cui  
National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China; [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (Z.C. ); [EMAIL_ADDRESS] (B.Y. Graphene, which is a two-dimensional sheet of sp\({}^{2}\)-bonded carbon atoms arranged in a honeycomb lattice [11], has caused a flood of activities in the past few years, especially have particular capability in nonlinear saturable absorption. Graphene is a zero-bandgap material and the absorption in graphene is only determined by optical conductivity constant and independent of optical frequency. Thus graphene is an alternative for ultra-broadband saturable absorbers. Further investigations show that graphene has an ultrafast recovery time and moderate modulation depth, which suggests that it is a suitable saturable absorber for passive mode locking and Q-switching [12]. Considering its low saturation intensity, low-cost and easy fabrication, Graphene is an ideal SA [13]. At present, studies on passive Q-switching with graphene as saturable absorber are mainly focused on Nd-lasers and Er-lasers. In 2011, [PERSON] reported a graphene passively Q-switched Nd:GdVO\({}_{4}\) laser with 105-ns pulses and 2.3-W average output power [14]. In 2013, [PERSON] demonstrated a passive Q-switched Er:YAG laser with an average output power of 528 mW and the pulse energy of 7.08 \(\upmu\)J [15]. Up to now, graphene has also been employed as a saturable absorber in Q-switched laser sources operating in 2 \(\upmu\)m. In 2011, [PERSON] _et al._ demonstrated a passive Q-switched Tm:YAG laser with a graphene SA, and the shortest pulse duration was 2.08 \(\upmu\)s [16]. In 2013, [PERSON] _et al._ proved the graphene as SA in a Tm:LSO laser, acquired the maximum pulse energy of 14.0 \(\upmu\)J and the shortest pulse duration of 7.8 \(\upmu\)s [17]. In 2014, [PERSON] _et al._ used graphene to obtain a PQS Ho:LuAG laser with the maximum output power of 0.37 W with a pulse width of 784.7 ns [18]. In 2014, by using a graphene SA, a PQS Ho:YAG laser was demonstrated with the pulse width of 632 ns and pulse energy of 13.3 \(\upmu\)J [19]. However, there have been no reports on Ho:YVO\({}_{4}\) laser with graphene as saturable absorber as far as we know. Ho:YVO\({}_{4}\) has been shown to be an excellent laser host for 2 \(\upmu\)m laser radiation [20]. It is sufficiently hard (Mohs hardness 5), nonhygroscopic, and resistive to chemicals, with large emission cross section and long fluorescence decay lifetime of Ho \({}^{5}\)I\({}_{7}\) manifold (\(\sim\)4 ms). In addition, the relative large absorption cross section at 1.94 \(\upmu\)m [21], makes the Ho:YVO\({}_{4}\) able to be efficiently resonant pumped by 1.94 \(\upmu\)m Tm:YLF or Tm:YAP lasers [22].