Ultrafast Broadband Saturable Absorption in Sb2Se3 Nanowires

Abstract

Manipulating optical nonlinearity is a very fascinating prospective for both fundamental and technological purpose; offers a potential platform to explore the saturable absorption (SA) to the nanoscale limit. In this manuscript, we have focused on the tunable wavelength and pulse width dependent ultrafast broadband SA of Sb2Se3 nanowires in the resonant and the above bandgap excitations of 120 fs and 7 ns pulses. In this context, we numerically simulated the SA of Sb2Se3 nanowire with a two-level model. The solutions of the coupled rate equations for a Gaussian shaped pulse exactly reproduced the experimental results in both temporal and spatial domains. Our model provides a precise spacio-temporal analysis of carrier populations of each photo-excited state in the system. Moreover, excited state decay time (1.5 ns) and the ratio of excited state absorption cross section (σes) to the ground state absorption cross section (σgs) is less than unity for 1-D Sb2Se3 nanowires. Hence, Sb2Se3 nanowires can be employed as passive mode-lockers and essential photodetectors for ultrashort pulsed laser and can be tuned by wavelength and pulse width. These observations advise a remarkable nonlinear optical response which is expected to be comparable or even better than the graphene and 2D TMDC’s (MX2) like MoSe2, MoS2, WSe2, WS2 etc.