Abstract
We measure the far-field intensity of vortex beams going through nanoholes. The process is analyzed in terms of helicity and total angular momentum. It is seen that the total angular momentum is preserved in the process, and helicity is not. We compute the ratio between the two transmitted helicity components, γm,p. We observe that this ratio is highly dependent on the helicity (p) and the angular momentum (m) of the incident vortex beam in consideration. Due to the mirror symmetry of the nanoholes, we are able to relate the transmission properties of vortex beams with a certain helicity and angular momentum, with the ones with opposite helicity and angular momentum. Interestingly, vortex beams enhance the γm,p ratio as compared to those obtained by Gaussian beams.
Highlights
Proper control of the pitchfork hologram allows for the creation of a phase singularity of order l in the center of the beam, i.e. the phase of the beam twists around its center from 0 to 2πl radians in one revolution
The preparation of the input beam is finished by setting its polarization to either left circular polarization (LCP) or right circular polarization (RCP)
One single nanohole is probed at a time, and the beam is centered with respect to the nanohole with a nanopositing stage
Summary
The experiment has been carried out for six different incident fields: three different vortex beams with topological charge l = m − p = − 1, 0, 1 are created by the SLM and each of them is right and left circularly polarized (p = − 1, 1). Looking at the intensity patterns displayed, it can be seen that the direct component of the light transmitted through the nanohole has the same features as the incident beam. That is, both are roughly cylindrically symmetric, they have the same helicity, and the same AM.
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