Thickness-dependent saturable absorption characteristics of TiS2 nanosheet-based thin films for potential ultrafast photonics applications

In this study, we investigated the nonlinear optical response of TiS 2 nanosheet-based thin films prepared by the ultrasonic spray deposition method, with particular emphasis on their saturable absorption (SA) behavior, which plays a key role in ultrafast photonic applications. Z-scan measurements under interband excitation revealed that the interplay between SA and excited-state absorption (ESA) strongly depends on the film thickness. To more accurately describe the observed behavior, a comprehensive model incorporating one photon absorption (OPA), two photon absorption (TPA), and ESA mechanisms was employed alongside the traditional SA model. The findings show that TiS 2 films can be tailored to operate efficiently across a broad range of optical intensity regimes, from low to high, through precise control of film thickness. This versatility makes them promising candidates for Q-switching and mode-locking in ultrafast photonic devices.