Arbitrary Three-Dimensional Alignment of Liquid Crystal Molecules via Laser Direct Writing

The precise construction of hierarchical ordered structures using nanomaterials as fundamental building blocks leads to enhanced optical, electromagnetic, and mechanical properties in functional devices. As one of the most promising functional nanomaterials, the three-dimensional (3D) assembly of liquid crystal (LC) molecules is crucial for the development of next-generation optical field modulation and stimulus response devices due to its distinct anisotropy and tunability. Spatial alignment of LC materials can be achieved through either contact or non-contact alignment methods. The contact alignment method can achieve orientation alignment of LC molecules through surface induced effects, shear forces, etc., but it is usually constrained by a low spatial resolution, material contamination and the lack of design freedom for processing. The non-contact alignment method can offer superior resolution and eliminate the contamination issue by aligning the LC molecules using electromagnetic fields. Nevertheless, it generally requires complex field-assisted (e.g. electric field, magnetic field) equipment and lacks the capacity for achieving arbitrary 3D alignment. Despite significant progress in LC alignment in recent years, a persistent challenge remains: the absence of a high-precision, non-contact, and straightforward method for achieving arbitrary 3D alignment of LC molecules.<br/>To address the above issue, we propose a novel approach that enables us to align the 3D director of LC via two photon polymerization-direct laser writing (TPP-DLW). TPP-DLW is a non-contact method that utilizes femtosecond laser pulses to precisely align LC without any field-assisted devices. TPP-DLW’s true 3D manufacturing capability facilitates the realization of arbitrary 3D spatial alignment. Its subwavelength resolution allows for the precise 3D assembly of LC with an accuracy of up to 140 nm. This method combines the advantages of both contact and non-contact alignment methods, achieving straightforward, high-precision, and high degree of design freedom 3D alignment of LC molecules. Finally, we have demonstrated the potential of this method by fabricating Fresnel zone plate devices for object imaging with polarization selection and spectral separation functions. We expect that this TPP-DLW alignment strategy will significantly contribute to the advancement of LC based optical processing, communication, and holographic displays and micro-robots, enabling extensive freedom and multifunctional capabilities.