Nonlinear Optical Limiting with Hybrid Nanostructures of NiCo2O4 and Multiwall Carbon Nanotubes

Abstract: Nonlinear optical (NLO) response in terms of reverse saturable absorption (RSA) has been exploited extensively for optical limiting. Here, we experimentally demonstrate that flower-like hybrid nanostructures of NiCo2O4 and Multiwall Carbon Nanotubes (NCO@MWCNT) exhibit a strong non-linearity in their absorption, specifically an excited state absorption (ESA) induced RSA, when exposed to nanosecond laser pulses. We obtain strong nonlinear absorption coefficient (\b{eta}) and nonlinear refractive index (n2) in hybrid NCO@MWCNT, the values that are 2-times and 2-orders of magnitude higher, respectively compared to NCO or MWCNT alone. This offers straightforward application in optical limiting with optical limiting (FOL) and optical onset (FON) threshold ca. 2-10 times lower than benchmark NLO materials, e.g., graphene, family of 2-D transition metal dichalcogenides (TMDC) materials and recently established NCO. Notably, for femtosecond pumping, NLO response of NCO@MWCNT is dominated by saturable absorption (SA) with a week contribution from two photon absorption (TPA), arising respectively from MWCNT and NCO. A remarkable sign reversal along with a larger amplitude is obtained for n2 thanks to the charge transfer from MWCNT to NCO.