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

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 demonstrate remarkably contrasting ZCO. Ultrafast transient absorption measurements reveal ISC from singlet triplet state takes place 5 ps. For femtosecond laser pulses, when pulse duration is shorter than lifetime, saturable (SA) for all intensities. On contrary, longer nanosecond excitation, we observe transition SA reverse (RSA) at higher intensities via excited-state absorption. envisage benefiting and RSA, ZCO emerges potential candidate mode locking limiting devices.