Broadband photocarrier dynamics and nonlinear absorption of PLD-grown WTe2 semimetal films

WTe2 is a unique material in the family of transition metal dichalcogenides and it has been proposed as a candidate for type-II Weyl semimetals. However, thus far, studies on the optical properties of this emerging material have been significantly hindered by the lack of large-area, high-quality WTe2 materials. Here, we grow a centimeter-scale, highly crystalline WTe2 ultrathin film (similar to 35 nm) by a pulsed laser deposition technique. Broadband pump-probe spectroscopy (1.2-2.5 mu m) reveals a peculiar ultra-fast optical response where an initial photo-bleaching signal (lasting similar to 3 ps) is followed by a long-lived photoinduced absorption signature. Nonlinear absorption characterization using femtosecond pulses confirms the saturable absorption response of the WTe2 ultrathin films, and we further demonstrated a mode-locked Thulium fiber laser using a WTe2 absorber. Our work provides important insights into linear and nonlinear optical responses of WTe2 thin films. Published by AIP Publishing.