This work shows how the efficiency of subwavelength dielectric gratings can be substantially enhanced with the application of a thin gold layer between the grating and the substrate. This is an interesting result because flat optical elements are easier to integrate with other devices such as diode lasers and sensors, but are often difficult to design and fabricate because they require features with large aspect ratios. Thinning the dielectric layer of gratings could help in reducing their aspect ratio, but this also often reduces the grating's efficiency. To get rid of this tradeoff between thickness and efficiency, the authors show how an ultra-thin grating's interaction with surface plasmons within an underneath uniform gold layer can increase the diffraction efficiency significantly (about 4 times).
As for application, the authors show how their technique can be used to obtain optical vortex beams with various configurations (single vortices with a well-defined number of twists or more complex arrangements). Since these beams are important for applications such as telecommunications or all-optical manipulation of micro-/nano-structures, this work can help in the cost reduction and miniaturization of systems aimed at such applications.