Ultrafast nonlinear absorption in MoTe₂ and MoTe₂/MoS₂ nanocomposite films and its application to all-optical logic gates

We present a detailed theoretical analysis of ultrafast saturable absorption (SA) and reverse SA (RSA) in MoTe2 nano-films with femtosecond (fs) laser pulses at 800 nm. A transition from RSA to SA occurs on increasing the thickness from 30 nm to 80 nm at a constant pump intensity of 141 GW cm(-2). On the other hand, a transition from SA to RSA occurs upon increasing the pump intensity in an 80 nm thick MoTe2 nano-film. Theoretical results are in good agreement with reported experimental results. The effect of pump pulse intensity, pulse width, nonlinear absorption coefficient and sample thickness has been studied to optimize the SA <-> RSA transition. The results for low-power and high contrast all-optical switching in MoTe2 nano-films have been used to design all-optical fs NOT, OR, AND, as well as the universal all-optical NOR and NAND logic gates. The SA behavior of MoTe2/MoS2 nanocomposite films has been used to design all-optical AND and OR logic gates. The nanocomposite films of MoTe2/MoS2 possess a larger nonlinear optical response in comparison to MoTe2 and MoS2 nano-films and, therefore, all-optical logic gates designed using nanocomposite films result in a good switching contrast compared to pure MoTe2 nano-films. Ultrafast operation at relatively low pump intensities demonstrates the applicability of MoTe2 and MoTe2/MoS2 nano-films for ultrafast all-optical information processing.