（Some TheoreticalAdvances in Optical Manipulation: What Is Not Anticipated from Lorentz Force）
主讲人：Jack Ng 吴紫辉副教授
吴紫辉博士(Dr. JackNg)于国际知名期刊发表论文40余篇(2019年止)，其中包括以第一作者或通讯作者发表在Nature Photonics, ScienceAdvances, 以及Physical Review Letters上的论文。他的研究领域集中于经典光学，包括：光学微操控、超材料，光子学等。光拉力是他的代表性的研究成果之一，以封面文章的形式发表于Nature Photonics上，迄今已被引几百次并被各类科学和大众传媒如Nature(News and Views), APS Physics, Discovery channel, BBC news, Nature Photonics (news and views), and Nature China, etc. 广泛报道。
Jack Ng graduatedfrom the Hong Kong University of Science and Technology (HKUST) with B.Sc. andPh.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 ofHKUST in 2010. He joined the Hong Kong Baptist University as an AssistantProfessor on 2012. In September 2019, he joined the Southern University ofScience and Technology (SUSTech), where he works until now.
He has published ~40 journal papers in internationally recognizedjournals, including Nature Photonics, Science Advances, Physical ReviewLetters, etc. His research is focused on classicaloptics, which includes optical micromanipulation, metamaterials, photonics,etc. His representative research work includes optical pulling, where theoriginal paper was cited hundreds of times and were widely reported byscientific and non-scientific media including Nature (News and Views), APSPhysics, Discovery channel, BBC news, Nature Photonics (news and views), andNature China, etc.
Thistalk has 2 parts: (1) opticalpulling at macroscopic distances and exceptional point in optical binding.These interesting phenomena are initially not expected from the Lorentz force.
(1) OpticalPulling at Macroscopic Distances
Light-inducedLorentz force can push or “trap” (confining) nanometer to micrometer sizedparticles. Such “optical tweezers” technique was awarded the 2018 Nobel Prizein Physics. In 2011, we theoretically proposed a completely unexpected third function,now called optical pulling or optical tractor beam. It offers the ability topull particle against light propagation. It has attracted significant interest,not just from the scientific community, but also the general public. Yet, itslimited microscopic range restricts its applicability: a long-ranged beamcannot pull.
Recently,by using a cocktail of independent yet compatible mechanisms, we proposed anovel way to achieve optical pulling for a macroscopic range. Further developmentof the technique suggests that pulling range may in principle reach tens oreven hundreds of meters.
(2) Optical Binding and ItsExceptional Point: More is different
Inhis seminal paper “More is different”, Anderson pointed out that “Thebehavior 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 afew particles.” Analogously, such statement also correctly describesoptical binding with many particles.
Proposedby Burns et al., the field of opticalbinding deals with how Lorentz force stably binds multiple microparticles intoa single entity. However, we discovered that, contrary to such insightfulproposal, the Lorentz force gradually loses its stability with increasing particle.All these are consequences of having an open system that possesses exceptionalpoints, the singularities in the vibrational frequency spectrum of thenon-Hermitian force constant matrix.
Stabilitycan be retained by introducing viscous damping medium, such as water. Suchbinding, primarily due to Lorentz force but has to be assisted by damping, maybe termed “opto-hydrodynamic binding.”