Nonlinear optical absorption of TiTe₂ nanosheets and its application for pulse laser generation

Two-dimensional TiTe₂ materials have excellent optical and electrical properties due to their unique semi-metallic properties and are widely used in detectors, photocatalysis, and field effect tubes. However, their potential in field of nonlinear optics (NLO) and ultrafast photonics has not been explored. In this paper, TiTe₂ nanosheets are prepared by liquid-phase exfoliation, and their excellent nonlinear optical properties are being demonstrated. Z-scan measurements show that their nonlinear absorption coefficients are -6.83 ± 0.52 and -15.10 ± 0.82 cm GW^-1 at 1560 and 2000nm, respectively, exhibiting saturable absorption properties. Two saturable absorbers (SA) based on TiTe₂ nanosheets are prepared, one by encapsulating TiTe₂ nanosheets in a polyvinyl alcohol (PVA) film and the other by depositing them on D-shape fiber (DSF). Finally, a Q-switched operation is achieved using TiTe₂-PVA SA, with the maximum output power of 14.2 mW, corresponding to a pulse energy of up to 212.9 nJ. Stable mode-locked operation is achieved using TiTe₂-DSF SA with a signal-to-noise ratio and pulse duration of 70 dB and 788 fs, respectively. Notably, this is the first time that TiTe₂ nanosheets have been used as SA. The results suggest that TiTe₂ nanosheets are a high-performance nonlinear material that provides a new impetus for the development of NLO and ultrafast photonics.