Reconfigurable optical matter of polystyrene microparticles fabricated by optical trapping at solution surface.

Light-matter interactions are fundamental in materials fabrication and property control, with significant applications in broad fields. A notable phenomenon arises when optical forces are exerted among nanoparticles and microparticles, in which optical binding leads to the development of optical matters with a well-patterned structure. This work explores a dynamic optical matter of polystyrene microparticles (PS MPs) prepared at the air/solution interface under optical trapping, specifically focusing on the interactions between 1-µm and 20-µm PS MPs. We report the formation of an unprecedented three-dimensional (3D) bulky assembly where smaller particles form a necklace and belt assembly around the larger particle, created by multiple light scattering. The resulting assembly, which can exceed 50 µm in diameter, elongates light-matter interaction lengths and exhibits reconfigurability tuning optical conditions, forming a unique dynamic optical matter with a random and disordered structure. As a result, we demonstrate amplified spontaneous emissions in the 3D bulky assembly thanks to the feature of randomness and multiple light scattering. These findings present a new approach to the study of reconfigurable and tunable optical matter, opening avenues for novel applications in disordered photonics and material science.