Strong near-infrared nonlinear optical response in nanocrystalline TiN for pulse generation

Abstract

The fast nonlinear optical (NLO) response generated by the transient thermalization / cooling of photon excited conduction electrons in plasmonic materials can be exploited as efficient switching mechanism for all-optical devices, while most metallic nanostructures suffer from the poor resistance to intensified laser irradiation. Here, we demonstrate that the robust metallic nanocrystalline TiN (nc-TiN) thin film obtained by sputtering exhibit strong nonlinear optical response in the near infrared region with a large negative NLO absorption coefficient. According to femtosecond transient absorption spectra, the strong NLO response is revealed to associate with a rapid carrier thermalization / cooling process in a sub-picosecond time scale. Leveraging the temporal absorption modulation, we demonstrate the generation of ultrashort pulses in the 1.5 μm region mode-locked by using the nc-TiN based switch operating in both transmission and reflection mode. Combined with the high laser damage threshold, our results suggest that the nc-TiN thin films obtained by commercially viable sputtering process could find potential applications for the fabrication of NLO photonic devices.