[16a-Z09-1~7] 3.1 Basic optics and frontier of optics

▲ [16a-Z09-5] Single anomalously large spherical assembly of polymer microparticles
formed by optical trapping at solution surface

〇(M2)Hsuan-Yin Wang¹, Tetsuhiro Kudo², Shuichi Toyouchi¹, Hiroshi Masuhara¹ (1.National Chiao Tung University, Taiwan, 2.Toyota Technological Institute, Japan.)

Keywords:optical trapping, optically evolved assembly

We irradiated 1064 nm continuous-wave (CW) laser on a 20 μm PS MP, which was trapped at the solution surface of D₂O. The laser light was propagating with whispering gallery modes (WGMs) at the 20 μm surface. The evanescent wave due to WGMs at 20 μm MP’s surface trapped many 1 μm PS MPs and the 1 μm PS MPs formed the necklace structure (Fig. 1B). With an increase of irradiation time, 1 μm PS MPs further formed outer packing structure. At 25-30 min after turning on the laser, the assembly grew more than 40 μm of size, and formed an enormous 3-D ball shaped assembly at the solution surface (Fig. 1C). By capturing back scattering light image of the assembly, we clearly observed light scattering surrounding the “big-ball” assembly (Fig. 1D). The surrounding 1 μm PS MP located at the outer packing structure started to disperse after trapping laser was switched off. Thus, we consider this spherical assembly formation is induced by optical force generated by the trapping laser irradiation. The evanescent wave of WGMs captures 1 μm PS MPs at the surface of a 20 μm PS MP, and the trapped 1 μm PS MPs scatter the laser and further gather the small PS MPs. As the laser intensity is high enough, scattering and gathering processes can be repeated growing the scattering ball. In this study, we have successfully extend our optically evolved assembly formation from 2-D to 3-D and will discuss dynamics and mechanism of this new optical trapping phenomenon.