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

Abstract

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.

Ultrafast Visible/Near‐Infrared Dual‐Band Selective Optical Switching via Polarization Control in Layered Low‐Symmetry TlSe

“…These timescales agree with the carrier cooling timescales of other layered nanomaterials. [37,45,[71][72][73] Furthermore, the second rising dynamics slows down as the pump fluence increases (Figure S6, Supporting Information). This trend is attributed to the hot-phonon bottleneck effect, [74] further validating the carrier-cooling-originated responses.…”

“…[36,45,60] Because the dual-band selective modulation in this study relies on spectral profile variations, modulations were explored by focusing on the dependence of probe polarization, which determines the information state of the optical signals. [36,37,61] Next, we extracted E pr -dependent line-cut profiles from the TA maps in Figure 2a-f at t = 1 ps, as indicated by the circles in Figure 2g-l. Then, we fitted the −ΔT∕T 0 spectra with phenomenological Gaussians to resolve the different polarization dependencies of the modulation peaks.…”

“…This band-selective modulatability is a unique characteristic rarely observed in other layered low-symmetry materials. For example, recent investigations of black phosphorus, [38,60,64] Te, [43] TaIrTe 4 , [42] SnSe, [41] SnS, [44] ZrTe 5 , [36] and TiS 3 [37] have revealed ultrafast polarization-dependent optical modulations; however, these are limited to single-band switching. Although ReS 2 allows the polarization-selective modulation of band-edge excitons, [39] the small energy spacing between the excitons (≈30 meV) [65,66] presents challenges in band-selective modulation.…”

“…[33] Moreover, the low-symmetry layered materials can be utilized for polarization-selective optical switching on femtosecond to picosecond timescales, owing to their high polarization selectivity, ultrafast nonlinear response, and strong light-matter interactions. [24,[34][35][36][37][38][39][40][41][42][43][44][45] This enables modulation operating at frequencies beyond the GHz-to-THz range. However, most of these modulations are limited to a narrow band or lack energy-distinguishable polarization selectivity, [35][36][37][38][39][40][41][42][43][44][45] making them unsuitable for dual-channel selective operation.…”

“…[24,[34][35][36][37][38][39][40][41][42][43][44][45] This enables modulation operating at frequencies beyond the GHz-to-THz range. However, most of these modulations are limited to a narrow band or lack energy-distinguishable polarization selectivity, [35][36][37][38][39][40][41][42][43][44][45] making them unsuitable for dual-channel selective operation. These limitations highlight the need for further research on a wide range of materials.…”