Localized polarization-guided alignment control in carbon nanotube films via femtosecond-pulse optical post-processing.

The physical properties of single-walled carbon nanotubes (CNTs) are highly sensitive to their alignment; therefore, making precise alignment control a central requirement for high-performance device architectures. However, conventional alignment techniques offer limited spatial programmability and remain inadequate for integrating heterogeneous CNT structures within a single film. Here, we report an optical post-processing technique to locally control the alignment of CNTs. We demonstrate that femtosecond-pulsed laser processing enables polarisation-guided alignment control of CNTs after film formation (post-processing). This process produces sub-micrometre scale locally aligned CNTs with thickness exceeding 200 nm and a nematic order parameter of 0.93 (strong directional order), demonstrating a high degree of orientational order and addressing a key bottleneck in spatially heterogeneous CNT integration. Additionally, these laser-aligned CNTs exhibit a direction-dependent optical and electrical response, functioning as a terahertz polariser with a polarisation ratio of 24.7; therefore, this technique enables the applications of CNT devices integrating heterogeneous structures like division-of-focal-plane polarisation cameras and on-chip polarisation routing.