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Lateral optical forces induced by linearly polarized laser beams have been predicted to deflect dipolar particles with opposite chiralities toward opposite transversal directions. These “chirality-dependent” forces can offer new possibilities for passive all-optical enantioselective sorting of chiral particles, which is essential to the nanoscience and drug industries. However, previous chiral sorting experiments focused on large particles with diameters in the geometrical-optics regime. Here, we demonstrate, for the first time, the robust sorting of Mie (size ~ wavelength) chiral particles with different handedness at an air–water interface using optical lateral forces induced by a single linearly polarized laser beam. The nontrivial physical interactions underlying these chirality-dependent forces distinctly differ from those predicted for dipolar or geometrical-optics particles. The lateral forces emerge from a complex interplay between the light polarization, lateral momentum enhancement, and out-of-plane light refraction at the particle-water interface. The sign of the lateral force could be reversed by changing the particle size, incident angle, and polarization of the obliquely incident light.Optical sorting: Forcing mirror-image microparticles to go their own wayA setup that uses lasers to automatically sort compounds with nearly imperceptible chemical differences could improve the efficiency of drug manufacturing. Many pharmaceuticals are difficult to purify because they are chiral, meaning they exist as one of two mirror-image structures that rotate in opposite directions under linearly polarized light. Cheng-Wei Qiu from the National University of Singapore and colleagues now report that lateral forces generated by a mix of reflected and refracted light rays can separate chiral microspheres floating on the surface of water. The team developed a line-shaped optical trap to hold a mix of chiral particles in place, and then directed a polarized laser beam into the trap. Microscopic imaging revealed that particles with identical chirality moved laterally when exposed to the beam, with velocities dependent on incident angle and microparticle size.

Photopolymerizable liquid crystals, also known as reactive mesogens, are leading candidates for additive manufacturing of smart microdevices via two‐photon lithography (TPL). While substantial advancements are made toward innovative applications, precise control of molecular alignment during fabrication, essential for tailoring complex optical and mechanical responses, remains a significant challenge. Current solutions require elaborate multi‐step procedures or customized setups to achieve 2D or 3D alignment patterns. Herein, the deterministic effect of TPL on the orientation of mesogenic moieties is reported, under optimized printing conditions. Specifically, a single‐step simple method is developed for aligning the nematic director in situ, with sub‐diffraction‐limited resolution, during 3D printing. Based on the conventional TPL workflow, the “director‐tuning mode” (DiTuM) relies on the anisotropic photopolymerization reaction occurring along the print path at low laser scan speeds (≈0.1mm s−1). A TPL‐induced “easy axis” arises for the mesogenic moieties, programmable in direction and strength, and competes with the initial alignment to create potentially convolute 3D director fields. The method holds considerable promise for 3D/4D printing, enabling advanced functionalities, and offers a robust platform for anti‐counterfeiting applications, leveraging the unique optical signatures generated by complex microstructures. Manipulating material properties at the microscale is crucial for 3D printing of smart microdevices. Two‐photon lithography directly patterns molecular alignment in liquid crystal resists. The polymerization reaction wavefront along the writing path induces an easy‐axis for the mesogenic moieties. This competes with the rubbing‐induced alignment to create a programmable director and optical axis fields, enabling tailored functionalities.

Hierarchical surface structuring is a critical aspect of advanced materials design, impacting fields ranging from optics to biomimetics. Among several laser-based methods for complex structuring of photo-responsive surfaces, the broadband vectorial interferometry proposed here offers unique performances. Such a method leverages a polychromatic laser source, an unconventional choice for holographic encoding, to achieve deterministic multiscale surface structuring through interference light patterning. Azopolymer films are used as photosensitive substrates. By exploring the interaction between optomechanical stress modulations at different spatial periodicities induced within the polymer bulk, we demonstrate the emergence of hierarchical Fourier surfaces composed of multiple deterministic levels. These structures range from sub-micrometer to tens of micrometers scale, exhibiting a high degree of control over their morphology. The experimental findings reveal that the optical encoding scheme significantly influences the resulting topographies. The polarization light patterns lead to more regular and symmetric hierarchical structures compared to those obtained with intensity patterns, underscoring the role of vectorial light properties in controlling surface morphologies. The proposed method is fully scalable, compatible with more complex recording schemes (including multi-beam interference), and it is applicable to a wide range of advanced technological fields. These include optics and photonics (diffractive elements, polarimetric devices), biomimetic surfaces, topographical design, information encoding, and anti-counterfeiting, offering a rapid, reliable, and versatile strategy for high-precision surface structuring at a submicrometric scale.

Laser interferometry is a consolidated technique for materials structuring, enabling single step and large area patterning. Here we report the investigation of the morphological modification encoded on a thin film of a photosensitive material by the light interference pattern obtained from a laser operating in multiline mode. Four lines with equal intensity are retained, with the same p linear polarization. An azopolymer is exploited as medium for the holographic recording. Optical microscopy and profilometer measurements analyze the modification induced in the bulk and on the surface of the irradiated area. We show that the intensity profile of the interference patterns of two laser beams is the one obtained assuming each line of the laser as an independent oscillator of given intensity and wavelength, and how these light structures are faithfully replicated in the material bulk and on the topography of the free surface. Patterns at different length scales are achievable in a single step, that can be traced back to both interference fringes and wave envelopes. The proposed multi-wavelength holographic patterning provides a simple tool to generate complex light structures, able to perform multiscale modifications of photoresponsive materials