Unfolding the Origin of the Ultrafast Optical Response of Titanium Nitride

Ultrafast plasmonics is driving growing interest for the search of novel plasmonic materials, overcoming the main limitations of noble metals. In this framework, titanium nitride (TiN) is brought in the spotlight for its refractory properties combined with an extremely fast electron-lattice cooling time (<100 fs) compared to gold (approximate to 1 ps). Despite the results reported in literature, a clear-cut explanation of the origin of the ultrafast and giant optical response of TiN-based materials upon excitation with femtosecond laser pulses is still missing. To address this issue, an original model is introduced, capable of unfolding the modulation of TiN optical properties on a broad bandwidth, starting from the variations of electronic and lattice temperatures following ultrafast photoexcitation. The numerical analysis is validated on ultrafast pump-probe spectroscopy experiments on a simple structure, a TiN film on glass. This approach enables a complete disentanglement of the interband and intraband contributions to the permittivity modulation. Moreover, it is also shown that, varying the synthesis conditions of the TiN film, not only the static, but also the dynamical optical response can be efficiently tuned. These findings pave the way for a breakthrough in the field: the design of TiN-based ultrafast nanodevices for all-optical modulation of light

Photosensitivity in glasses

A photosensitive glass containing a small amount of a photosensitive metal such as Au, Ag, or Cu, and a sensitizer of CeO2, is expressed a function of the redox reaction induced by the irradiation of ultraviolet light. In particular, a photosensitive glass is an indispensable material in the photolithography technique, which is valuable in the microprocessing of glass substrates. Here we aim to discuss the photosensitivity of glass from the perspectives of photochemical, photophysical, and photothermal mechanisms. In particular, from three different points of view (photothermal, photochemical, and photophysical interactions), various intriguing phenomena induced by ultrashort pulse lasers are addressed. Furthermore, a new type of photosensitivity exhibiting nonreciprocal characteristics is also discussed