In the present work, some MoS 2 and WS 2 nanosheets were prepared and characterized. Depending on the preparation procedures, trigonal prismatic (2H) or octahedral (1T) coordination of the metal atoms was obtained, exhibiting metallic (1T) or semiconducting (2H) character. Both MoS 2 and WS 2 nanosheets were found exhibiting large nonlinear optical (NLO) responses, strongly dependent on their metallic (1T) or semiconducting (2H) character. Therefore, the semiconducting character of MoS 2 and WS 2 exhibits positive nonlinear absorption and strong self-focusing behavior, while their metallic character counterparts exhibit strong negative nonlinear absorption and important self-defocusing behavior. In addition, the semiconducting MoS 2 and WS 2 were found exhibiting important and very broadband optical limiting (OL) action extending from 450 to 1750 nm. Therefore, by selecting the crystalline phase of the nanosheets, that is, their semiconduction/metallic character, their NLO response can be greatly modulated. The results of the present work demonstrate unambiguously that the control of the crystalline phase of MoS 2 and WS 2 provides an efficient strategy for 2D nanostructures with custom-made NLO properties for specific optoelectronic and photonic applications such as OL, saturable absorption, and optical switching.

Graphene derivatives and defect-engineered graphenes have attracted the interest of researchers owing to the excellent and tunable properties they exhibit. In this work the optical limiting performance of two defect-engineered boron- and nitrogen-doped reduced graphene oxides is investigated. Both graphenes are found to exhibit exceptional and broadband optical limiting action ranging from 532 to 2200 nm. Their optical limiting efficiency was found to be superior to that of all the other graphene derivatives studied to date, exhibiting a gradually decreasing optical limiting onset, reaching the record low value of ∼0.002 J cm–2 at 2200 nm. The results demonstrate the potential of engineering the defects of such reduced graphene oxides, resulting in very broadband and efficient optical limiting graphene derivatives, showing a promising method to further tailor their optical and optoelectronic properties.

In the present work, the nonlinear optical properties of some single- and few-layered graphene dispersions under femtosecond laser excitation were studied using the Z-scan technique and are compared in order to evaluate the effect of the number of graphenic layers and the influence of the laser excitation conditions on the measurements. The experimental evidences obtained indicate that the nonlinear optical response of these graphenes’ dispersions under low repetition rate laser excitation conditions (i.e., 10 Hz) is several orders of magnitude lower than that reported using higher repetition rate laser excitation conditions (as e.g., kHz, MHz). To further investigate these experimental findings, Z-scan combined with a thermal lensing measurement technique was used to study the presence and the building of thermal/cumulative effects occurring under high repetition rate conditions. It was shown that thermal/cumulative effects were dominant, obscuring entirely the observation of the electronic origin nonlinear optical response. The contributions of both mechanisms were evaluated and unambiguously distinguished. To the best of our knowledge, this is the first work, investigating the nonlinear optical properties of single- and few-layered graphene, under low and high repetition rate laser excitation, providing a more accurate insight about the nonlinear optical response of graphene.