Optical angular momentum conversion in a nanoslit: reply.

We respond to a Comment on our Letter [Opt. Lett.37, 4946 (2012)], in which we reported on the spin-to-orbital optical angular momentum conversion of a circular nanoslit in a thin metal layer. We claimed, in an unfortunately worded sentence, that the conversion efficiency was independent of the slit's dichroism, which the Comment pointed out was incorrect. We acknowledge this and reiterate our original intention that as long as the dichroism is not too large, then it has little effect on the conversion efficiency in our system.

Optical angular momentum conversion in a nanoslit.

We demonstrate partial conversion of circularly polarized light into orbital angular momentum-carrying vortex light with opposite-handed circular polarization. This conversion is accomplished in a novel manner using the birefringent properties of a circular subwavelength slit in a thin metal film. Our technique can be applied over a very wide range of frequencies and even allows the creation of anisotropic vortices when using a slit without circular symmetry.

A subwavelength slit as a quarter-wave retarder.

We have experimentally studied the polarization-dependent transmission properties of a nanoslit in a gold film as a function of its width. The slit exhibits strong birefringence and dichroism. We find, surprisingly, that the transmission of the polarization parallel to the slit only disappears when the slit is much narrower than half a wavelength, while the transmission of the perpendicular component is reduced by the excitation of surface plasmons. We exploit the slit's dichroism and birefringence to realize a quarter-wave retarder.

Plasmonic tomography of optical vortices.

We present a method for analyzing the wavefront of optical vortices that does not involve interferometry but rather uses surface plasmon polaritons (SPPs). We employ a subwavelength slit in a gold film to cut slices from an optical vortex beam and measure the diffraction of the generated SPPs by scattering them off a second slit. By moving the slits across the vortex beam, we create a tomogram, from which we can determine the vortex charge of the incident beam at a glance. We present results for vortex beams of integer- and half-integer-vortex charge.