Modeling of inhomogeneous heating behavior in ultrafast laser interaction with dielectric–dielectric nanocomposite with band gap contrast

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Inspired by the optical data storage and photothermal therapy applications of metal–dielectric nanocomposite materials relying on the difference in laser absorption mechanism between metal and dielectric, the ultrashort single pulse laser irradiation of zirconia–alumina nanocomposite, a dielectric–dielectric nanocomposite with band gap contrast, was investigated. A femtosecond (fs) laser of 250 fs pulse duration and 10 W maximum average power was used for the experiment. A seemingly unusual phase melting phenomenon - whereby the higher melting point zirconia phase (2715 °C) was melted, while the lower melting point alumina phase (2072 °C) remained intact - was observed, thereby suggesting a huge temperature heterogeneity in the composite under ultrashort single pulse laser irradiation. Theoretical modeling indicates that the material band gap plays a significant role in laser energy absorption under an intense laser field. A sharp increase in the total absorbed laser energy and concomitant temperature increase around the laser ablation threshold was revealed. Under appropriate laser fluence, the smaller band gap zirconia phase (5.8 eV) can absorb much more laser energy than the alumina phase (8.8 eV), resulting in a remarkable temperature difference between these two phases. This research demonstrates the capability of generating huge phase specific temperature differences in composite nanostructures composed of phases with band gap contrast by using ultrashort pulsed laser irradiation.