Saturable absorption mode-locking based on intersubband transitions in quantum wells at 2 µm

Here we first report the first demonstration of passive mode locking in a Ti-sapphire laser end-pumped Tm3+,Ho3+:YAG laser utilizing ISBTs in InGaAs/AlAsSb quantum wells grown on an InP substrate. The experimental setup is schematically shown in Fig. 1. The pump source is a tunable Ti-sapphire laser with a maximum output power of 2.2 W at 785 nm, corresponding to the peak absorption of the Tm3+, Ho3+:YAG crystal. A 4.9 mm-long 5at.%- Tm3+,0.4at.%-Ho3+:YAG crystal is employed and water-cooled to 15AcircdegC. The n-doped InGaAs/AlAsSb QWs are inserted in the cavity under Brewster angle in order to achieve an electric field component along the growth direction of the QWs. The whole cavity length is 53.3 cm. The output coupler has a transmission of 0.5% at 2 Icircfrac14m. A maximum output power of 40 mW is obtained at a center wavelength of 2.09 Icircfrac14m.