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Creation of a needle of longitudinally polarized light in vacuum using binary optics


Recently many ideas have been proposed for the use of a longitudinal field for particle acceleration, fluorescent imaging, second-harmonic generation and Raman spectroscopy. A few methods to enhance the longitudinal field component have been suggested, but all have insufficient optical efficiency and non-uniform axial field strength. Here we report a new method that permits the combination of very unusual properties of light in the focal region, permitting the creation of a ‘pure’ longitudinal light beam with subdiffraction beam size (0.43λ). This beam is non-diffracting; that is, it propagates without divergence over a long distance (of about 4λ) in free space. This is achieved by focusing a radially polarized Bessel–Gaussian beam with a combination of a binary-phase optical element and a high-numerical-aperture lens. This binary optics works as a special polarization filter enhancing the longitudinal component.

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Figure 1: Electric energy density in the focal region of a NA = 0.95 lens illuminated with a radially polarized Bessel–Gaussian beam.
Figure 2: Schematic of the set-up.
Figure 3: Electric field amplitude transmission function on the aperture and the corresponding electric energy density profile on the focal plane of the NA = 0.95 lens illuminated with a radially polarized Bessel–Gaussian beam after additional phase modulation.
Figure 4: Contour plots for the electric and magnetic density distributions in the yz-plane after additional phase modulation.
Figure 5: Normalized Poynting vector field (colour density plots) and the energy flow (white field lines).
Figure 6: Polarization characteristic of the field in the focal region of the NA = 0.95 lens with a binary optical element.


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The author would like to thank T.D. Visser, S.F. Pereira, J.J.M. Braat and H.P. Urbach for their helpful discussion on radial polarized beam and F. Gan for his helpful discussions on binary optics. The authors would like to acknowledge the LTL project founded by Data Storage Institute.

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The basic idea to achieve subdiffraction and a non-diffracting longitudinal polarized beam was initiated by H.F., C.S. and L.S. were involved in the initial discussion of the idea. All calculations were carried out by H.F. and B.L. C.T.C. helped the planning of the work. The calculation data were analysed and discussed by all of the authors. The paper was drafted by H.F., and all authors contributed to the manuscript.

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Correspondence to Haifeng Wang.

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Wang, H., Shi, L., Lukyanchuk, B. et al. Creation of a needle of longitudinally polarized light in vacuum using binary optics. Nature Photon 2, 501–505 (2008).

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