Optimal Nanoparticle Forces, Torques, and Illumination Fields

Yuxiang Liu, Lingling Fan, Yoonkyung E. Lee, Nicholas X. Fang, Steven G. Johnson, Owen D. Miller

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


A universal property of resonant subwavelength scatterers is that their optical cross-sections are proportional to a square wavelength, λ2, regardless of whether they are plasmonic nanoparticles, two-level quantum systems, or RF antennas. The maximum cross-section is an intrinsic property of the incident field: plane waves, with infinite power, can be decomposed into multipolar orders with finite powers proportional to λ2. In this article, we identify λ2/c and λ3/c as analogous force and torque constants, derived within a more general quadratic scattering-channel framework for upper bounds to optical force and torque for any illumination field. This framework also solves the reverse problem: computing globally optimal “holographic” incident beams, for a fixed collection of scatterers. We analyze structures and incident fields that approach the bounds, which for wavelength-scale bodies show a rich interplay between scattering channels, and we show that spherically symmetric structures are forbidden from reaching the plane-wave force/torque bounds. This framework should enable optimal mechanical control of nanoparticles with light.
Original languageEnglish (US)
Pages (from-to)395-402
Number of pages8
Issue number2
StatePublished - Dec 21 2018
Externally publishedYes

ASJC Scopus subject areas

  • Biotechnology
  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering


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