Near-field focusing properties of zone plates in visible regime - New insights

Rakesh G. Mote, Siu Fung Yu, B. K. Ng, Wei Zhou, Shu Ping Lau

Research output: Journal article publicationJournal articleAcademic researchpeer-review

55 Citations (Scopus)

Abstract

Near-field focusing properties of zone plates are investigated in the visible regime by a 3-dimensional finite-difference time-domain method. It is shown that Frensel zone plates (FZPs) with metallic coatings can achieve subwavelength focusing in the visible wavelength. The characteristics of subwavelength focusing are found to be independent of the type of metal coatings used. All the FZPs exhibit similar shift in focal length and depth of focus when compared with classical calculations. These results indicate that plasmonic waves do not contribute to subwavelength focusing. Instead the subwavelength focusing characteristic is attributed to the interference of diffracted evanescent waves from a large numerical aperture. It is found that the near-field focusing of FZPs suppresses higher order foci such that the corresponding diffraction efficiency is improved. The use of phase zone plate structured on glass without opaque coating is proposed to improve the diffraction efficiency of subwavelength focusing.
Original languageEnglish
Pages (from-to)9554-9564
Number of pages11
JournalOptics Express
Volume16
Issue number13
DOIs
Publication statusPublished - 23 Jun 2008
Externally publishedYes

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

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