@article{THESIS,
      recid = {12314},
      author = {Nagasamudram, Saispoorthi},
      title = {Optical Magnetic Dipole Mie Resonances and Electrodynamic  Interactions in High-Index Dielectric Nanoparticle Based  Optical Matter Systems},
      publisher = {University of Chicago},
      school = {Ph.D.},
      address = {2024-06},
      number = {THESIS},
      pages = {223},
      abstract = {Light-matter interactions have been a subject of  fascination for many years. One of the ways to examine the  interactions of matter on the micro or nano scale with  light is to use optical tweezers or optical trapping. When  two or more micron- or nano-sized particles are illuminated  by an optical trap, their mutual scattering of light  results in active, non-equilibrium and self-organizing  ordered structures known as optical matter. This phenomenon  is known as optical binding.

Optical binding between pairs  of metallic nanoparticles such as silver (Ag NPs) and gold  (Au NPs), which manifest a strong plasmonic electric dipole  (ED) resonance, have been explored extensively in the past.  However, experimental studies of optical binding  interactions between a pair of high-index dielectric  nanoparticles have not been previously reported. As will be  shown in this thesis, due to their high index of  refraction, silicon nanoparticles (Si NPs) exhibit a  significant optical magnetic dipole (MD) resonance at  vis/IR frequencies. We show in this thesis the new  experimental phenomenon of magnetic optical binding in  pairs of Si NPs. 

The pairwise interactions between  nanoparticles in optical matter systems lead to interesting  dynamics including non-reciprocal (i.e., unequal and  opposite) effects and the emergence of new forces  associated with them. These effects have been studied in  the context of Ag NP heterodimers where the broken symmetry  due to their dissimilar sizes leads to non-reciprocity in  the system. However, experimental studies of non-reciprocal  forces in high-index dielectric nanoparticle heterodimers  have not been previously reported. In this thesis, we  provide experimental evidence of optical magnetic binding  induced non-reciprocal forces in pairs of Si NP  heterodimers. We also show that the behavior of the  non-reciprocal forces in Si NP heterodimers is different  from that observed in Ag NP heterodimers. 

We extend our  study of optical matter from just pairwise interactions  between two nanoparticles to arrays of more than two  nanoparticles. The many-body interactions that arise from  such systems are of great interest. We present a new way to  break symmetry and generate non-reciprocal forces in a  system of optically bound Ag NP nanoparticles through  many-body electrodynamic coupling. We show that the  non-reciprocal forces are many-body in nature and only  arise for three or more particles maintained in a bent  configuration where the OM system is not spatially  symmetric. The requisite symmetry breaking is realized in  experiment by trapping many Ag nanoparticles using an  optical ring trap to sustain the bent configuration.

We  also explore the collective scattering of many-body optical  matter systems. This is done by using the theory of  collective modes formulated earlier in the context of Ag  NPs. We extend the investigation of collective modes to  many-body optical matter systems consisting of Si NPs. We  show that there are significant differences between the  many-body behavior in Ag NP and Si NP optical matter  systems. The advantage of the collective mode approach is  that it helps us reduce the complicated many-body nature of  the scattering of light by multiple nanoparticles to a few  dominant collective scattering modes.},
      url = {http://knowledge.uchicago.edu/record/12314},
      doi = {https://doi.org/10.6082/uchicago.12314},
}