Passive Q-switched mode locking of a diode-pumped Tm:SSO laser near 2 μm

With a fiber-coupled 790 nm laser diode array as the pump source and a 4 at.% Tm:Sc2SiO5 (Tm:SSO) crystal, laser action near 2 mu m wavelength was successfully obtained with a compact four-mirror fold cavity. Using broadband carbon nanotube as the saturable absorber, a passively Q-switched mode-locked (QML) Tm: SSO laser is realized for the first time. 100% modulation depth of mode locking has been achieved. The duration of the mode-locked pulse is estimated to be about sub-100 ps with 92.6 MHz repetition rate within a Q-switched pulse envelope. The spectrum of the QML laser is centered at 1967.4 nm with a broad spectral region of similar to 23 nm. A maximum average output power of 195 mW and Q-switched pulse energy of 4.7 mu J is obtained. The dependence of the operational parameters on pump power was also investigated experimentally.