Optical trapping and shooting of chiral nanostructured microbullets

Nanostructured optical materials, such as metasurfaces and liquid crystals, can realize a customizable photonic bandgap and chirality, making them ideal for advanced photonic applications. At the nanoscale, these materials can alter the linear and angular momentum of photons, leading to remarkable optomechanical phenomena. However, the impact of combining chirality and a photonic bandgap on optical trapping and radiation pressure is not well understood. In this work, we present how circularly polarized light with wavelength within the photonic bandgap of the particle, can achieve optical trapping and propulsion of chiral liquid crystal polymer microparticles. These particles, polymerized from chiral liquid crystal precursors, exhibit a layered nanostructure with right-handed helicity and a photonic bandgap aligned with the wavelength of the trapping laser. When illuminated with left-circularly polarized light, opposite in handedness to the particle’s helicity, the light is transmitted, resulting in a stable optical trap at the equilibrium position, as illustrated in (a). In contrast, when switching the polarization to right-circularly polarized light, which matches the particle’s handedness, trapping is prevented, as the light is reflected by the photonic bandgap and produces a strong recoil force that pushes the particle out of the focal spot, as in (b). We validate this mechanism experimentally, as shown in a sequence of video frames: the particle remains stably trapped and can be transported with left-handed circular polarization (c). Upon switching to right-handed polarization, the particle is suddenly ejected from the focal plane, evidenced by expanding diffraction rings (d). The resulting propulsion drives the microparticles at speeds up to 234 μm/s. The optical blaster concept opens new avenues for ultrafast microvehicles, microrobots, microsurgery, and precise manipulation of nanoscale objects.