学科建设

学术报告:(1)Optical Pulling Force (2)Calculating and Engineering the Optical Gradient and Scattering Force

报告题目:

(1)Optical Pulling Force

(2)Calculating and Engineering the Optical Gradient and Scattering Force

报告人:吴紫辉教授,香港浸会大学物理系

报告时间:67号下午16:00-17:00

报告地点:物理科技楼101

Abstract for Optical Pulling Force

Every Photon carries a positive momentum of along its propagating direction. Thus one may expect light to "push" on objects standing on its path due the scattering force. Indeed, without an intensity gradient, it is counter intuitive for a light beam to pull particle backward. In this talk, we show the possibility for a forward propagating light beam to exert a backward scattering force that pulls a particle backward. We further show that it is the maximization of forward scattering via the interference of the radiation multipoles that is responsible for the backward forces. The necessary condition to achieve a pulling optical force requires both the particle and beam properties. This optical pulling adds an additional freedom to optical micromanipulation.

Abstract for Gradient and Scattering Force

 It is customary and useful to separate the optical force into two physically and mathematically distinct parts. The first is the conservative curl-less gradient force, which is responsible for optical trapping. The non-conservative divergence-less scattering and absorption force is responsible for optical rotation, particle transportation etc.

 Optical gradient force and scattering force for experimentally accessible particle sizes are never calculated. This problem remained unsolved for several decades. We report an analytical and a numerical approach to calculate them. We also provide a recipe to eliminate the scattering force.

 Owing to the scattering force, a collection of particles illuminated by light do not come to equilibrium, instead it reaches a steady state. In many situations, a conservative force is preferable and it will be beneficial to eliminate the scattering force. We will present a recipe that allows us to eliminate the scattering force for spherical particles.

报告人简介:

Dr. Jack Ng (吳紫輝博士) obtained his Ph.D. degree in physics from The Hong Kong University of Science and Technology (HKUST) when he was 24 years old in 2005. He has been a Research Assistant Professor in HKUST for two years before he joined Hong Kong Baptist University as a faculty member in 2012.

His research is currently focused on the theory of using electromagnetic waves to manipulate materials and also on the theory of advanced electromagnetic materials. The former area is important whenever small particles are involved, with applications in Biology being a fruitful example. The latter area is important for communication, optics, electromagnetics, etc.

He has published his research in prestige journals which include Nature Photonics, Physical Review Letters, Science Advances, etc.



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