Polarization-Driven Ultrafast Optical Switching in TiS₃ Nanoribbons via Anisotropic Hot Carrier Dynamics

Layered quasi-1D nanomaterials exhibit strong linear dichroism and effective light-matter interactions, promising for novel information devices driven by light-polarization. In particular, their optical anisotropy and ultrafast photoresponse allow for polarization-controlled nanophotonic switches and modulators. However, the technology still requires substantial further studies due to an insufficient understanding of modulation mechanisms and limited investigations of a few materials. Here, transient absorption (TA) microscopy is employed to investigate the ultrafast polarization-based optical switching in TiS₃ nanoribbons, a rising quasi-1D material of the transition metal trichalcogenide family. Highly anisotropic sub-picosecond near-infrared modulation is observed, which is most pronounced when the polarization of the probe pulse is aligned with the nanoribbon axis but disappears as the polarization is rotated to the perpendicular orientation. The authors attribute this significant dependence on the probe polarization to the hot carrier-induced broadening of an anisotropic interband resonance, as supported by analyses of transient TA line shapes and first principles calculated optical transitions. Furthermore, a strong pump polarization-dependent modulation is obtained by tuning the pumping energy, enabling highly anisotropic all-optical switching controlled solely by polarization. These results offer comprehensive information on both probe- and pump-polarization-based modulations and a deeper physical understanding of polarization-dependent photoresponse through ultrafast hot carrier dynamics.