Abstract
We report on the fabrication of metasurface phase plates consisting of gold nanoantenna arrays that generate Laguerre-Gaussian modes from a circularly polarized Gaussian input beam. The corresponding helical phase profiles with radial discontinuities are encoded in the metasurfaces by the orientation of the nanoantennas. A common-path interferometer is used to determine the orbital angular momentum of the generated beams. Additionally, we employ digital holography to record the detailed phase profiles of the Laguerre-Gaussian modes. This method allows a simple and direct quantitative comparison of the measured phase profiles of the generated Laguerre-Gaussian beams with the theoretically expected phase profiles. Experiments with different laser sources demonstrate the broadband operation of the metasurfaces.
Highlights
Optical vortex beams have been the subject of intense research activities in recent years[1,2] and have found numerous applications in optical micromanipulation,[3] quantum optics,[4] imaging,[3] and communications.[5]
As a consequence of this, optical vortex beams possess annular intensity cross sections with strictly zero on-axis intensity. They carry an orbital angular momentum (OAM) of l per photon, which is independent of the polarization state of the beam
Optical vortex beams can be generated by a number of different methods, e.g., astigmatic mode converters,[1] spiral phase plates,[6] spatial light modulators,[7,8] and diffraction gratings.[9]
Summary
Optical vortex beams have been the subject of intense research activities in recent years[1,2] and have found numerous applications in optical micromanipulation,[3] quantum optics,[4] imaging,[3] and communications.[5]. Invited Article: Direct phase mapping of broadband Laguerre-Gaussian metasurfaces By encoding an azimuthal phase factor exp(ıφl) into the metasurface, one can generate an optical vortex beam with topological charge l from a Gaussian input beam.
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