[Lecture] Some theoretical advances in optical manipulation: what is not anticipated from lorentz force

2019-12-15

Title: Some theoretical advances in optical manipulation: what is not anticipated from lorentz force
Speaker: Associate Prof. Jack Ng,South University of Science and Technology of China
Venue: Room 213, Building No.18, Wushan Campus
Time: December 20, Friday, 11:00

Biography:
Jack Ng graduated from the Hong Kong University of Science and Technology (HKUST) with B.Sc. and Ph.D. degrees. He then proceeded with his postdoctoral work with his Ph.D. supervisor Prof. Che-Ting Chan, and he became a Research Assistant Professor of HKUST in 2010. He joined the Hong Kong Baptist University as an Assistant Professor on 2012. In September 2019, he joined the Southern University of Science and Technology (SUSTech), where he works until now.

He has published 40 journal papers in internationally recognized journals, including Nature Photonics, Science Advances, Physical Review Letters, etc. His research is focused on classical optics, which includes optical micromanipulation, metamaterials, photonics, etc. His representative research work includes optical pulling, where the original paper was cited hundreds of times and were widely reported by scientific and non-scientific media including Nature (News and Views), APS Physics, Discovery channel, BBC news, Nature Photonics (news and views), and Nature China, etc.

Abstract:
This talk has 2 parts:

(1)   Optical Pulling at Macroscopic Distances

Light-induced Lorentz force can push or “trap” (confining) nanometer to micrometer sized particles. Such “optical tweezers” technique was awarded the 2018 Nobel Prize in Physics. In 2011, we theoretically proposed a completely unexpected third function, now called optical pulling or optical tractor beam. It offers the ability to pull particle against light propagation. It has attracted significant interest, not just from the scientific community, but also the general public. Yet, its limited microscopic range restricts its applicability: a long-ranged beam cannot pull.

Recently, by using a cocktail of independent yet compatible mechanisms, we proposed a novel way to achieve optical pulling for a macroscopic range. Further development of the technique suggests that pulling range may in principle reach tens or even hundreds of meters.

(2)   Optical Binding and Its Exceptional Point: More is different

In his seminal paper “More is different”, Anderson pointed out that “The behavior of large and complex aggregates of elementary particles, it turns out, is not to be understood in terms of simple extrapolation of the properties of a few particles.” Analogously, such statement also correctly describes optical binding with many particles.

Proposed by Burns et al., the field of optical binding deals with how Lorentz force stably binds multiple microparticles into a single entity. However, we discovered that, contrary to such insightful proposal, the Lorentz force gradually loses its stability with increasing particle. All these are consequences of having an open system that possesses exceptional points, the singularities in the vibrational frequency spectrum of the non-Hermitian force constant matrix.

Stability can be retained by introducing viscous damping medium, such as water. Such binding, primarily due to Lorentz force but has to be assisted by damping, may be termed “opto-hydrodynamic binding.”




Announced by the School of Physics and Optoelectronic Technology



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