Pulse-duration dependence of saturable and reverse saturable absorption in ZnCo2O4 microflowers

TL;DR

This study investigates how pulse duration affects saturable and reverse saturable absorption in ZnCo2O4 microflowers, revealing their potential for optical devices due to their nonlinear optical properties.

Contribution

It demonstrates the dependence of optical nonlinearity on pulse duration in ZnCo2O4, linking intersystem crossing lifetime to saturable and reverse saturable absorption behaviors.

Findings

Ultrafast ISC occurs in 5 ps in ZnCo2O4.

SA dominates with femtosecond pulses, RSA with nanosecond pulses.

ZnCo2O4 shows potential for mode locking and optical limiting.

Abstract

We employed open-aperture Z-scan technique to unveil the third-order optical nonlinearity in ZnCo2O4 (ZCO) microflowers. Our results indicate that intersystem crossing (ISC) lifetime can be used as simple tool to demonstrate remarkably contrasting optical nonlinearity in ZCO. Ultrafast transient absorption measurements reveal that ISC from singlet to triplet state takes place in 5 ps. For femtosecond laser pulses, when the pulse duration is shorter than ISC lifetime, saturable absorption (SA) takes place for all intensities. On the contrary, when the pulse duration is longer than ISC for nanosecond excitation, we observe transition from SA to reverse SA (RSA) at higher intensities via excited-state absorption. We envisage that benefiting from SA and RSA, ZCO emerges as potential candidate for mode locking and optical limiting devices.