Numerical Modeling\nof the Ultrafast Plasmonic Response\nof Titanium Nitride Nanostructures

Titanium\nnitride (TiN) is a promising plasmonic material\nthat has\ncome into the spotlight as a valid alternative to noble metals. As\nfor other plasmonic materials, great attention has been given to the\ndevelopment of TiN nanostructures so as to efficiently tune the plasmon\nresonance, also combining them in lattices and with other metals or\nsemiconductors. In addition, TiN boasts carrier cooling dynamics more\nthan one order of magnitude faster than that of gold, which gives\nit a clear advantage in many applications. However, the knowledge\nof the ultrafast optical response of TiN nanostructures is narrowed\ndown to experimental evidence, without a complete modeling. In this\nwork, we numerically model the nonequilibrium hot-carrier-mediated\nmechanisms and ultrafast nonlinear changes in the optical response\nof TiN nanostructures photoinduced by femtosecond laser pulses. Specifically,\nwe focus on nanodisks and nanospheres and compare our simulations\nwith experimental pump–probe measurements. Our approach enables\nus to disentangle the interband and intraband contributions to the\npermittivity modulation, pointing out the critical role of the interplay\nbetween the TiN interband transitions and the nanostructure optical\nresonances in the early stages of the photoinduced ultrafast dynamics.