Nonlinear optical responses in two-dimensional transition metal dichalcogenide multilayer: WS2, WSe2, MoS2 and Mo0.5W0.5S2

Synthetic two-dimensional transition metal dichalcogenides such as tungsten disulphide (WS2), tungsten diselenide (WSe2), molybdenum disulphide (MoS2) as well as mixed molybdenum tungsten disulphide (Mo0.5W0.5S2) single crystals were grown by the chemical vapor transport method using halogens (bromine or chlorine) as transport agents. Multi-layer samples were cleaved from the single crystals, and their nonlinear optical (NLO) properties were obtained from both open aperture and closed aperture Z-scan measurements using a picosecond mode-locked Nd:YAG laser operating at a wavelength of 1064 nm, with pulse duration of 25 ps and 20 Hz repetition rate. Both WS2 and MoS2 exhibited nonlinear saturable absorption (SA), whereas WSe2 and Mo0.5W0.5S2 showed nonlinear two-photon absorption (2PA). A large 2PA coefficient beta as high as + 1.91x10(-8) cm/W was obtained for the Mo0.5W0.5S2, and an index of refraction coefficient gamma = -2.47x10(-9) cm(2)/W was obtained for the WSe2 sample. (C) 2016 Optical Society of America