Unveiling and engineering of third order optical nonlinearities in NiCo$_2$O$_4$ nanoflowers

• Main Authors: Sharma, Ankit, Khan, Pritam, Mandal, Dipendranath, Pathak, Mansi, Rout, C. S, Adarsh, K. V
• Format: Journal Article
• Language: English
• Published: 15-08-2021
• Subjects: Physics - Optics
• DOI: 10.48550/arxiv.2108.06843

In this paper, we demonstrate NiCo$_2$O$_4$ (NCO) as an efficient new
nonlinear optical material with straightforward potential applications in
optical limiting devices. We obtain nonlinear absorption coefficient ($\beta$)
and nonlinear refractive index ($n_2$) in parallel by performing Z-scan
technique, in both open and closed aperture configurations, respectively. To
understand the mechanism responsible for third order optical nonlinearity in
NCO, we excited the sample with contrasting laser pulse durations, 7 ns and 120
fs, at two different off-resonant wavelengths. For ns excitation, nonlinearity
is mediated by excited state absorption (ESA) and free-carrier absorption, that
gives rise to large \b{eta}ESA and positive $n_2$. On the other hand, when
excited with fs laser, two-photon absorption (TPA) takes place and bound
carriers induce strong negative $n_2$. The values obtained for $\beta$ and
$n_2$ in NCO are found to be higher among the family of well-known conventional
transition metal oxides, therefore are promising for optics and other photonics
applications.