Concentrated solar power (CSP) facilities heavily utilize parabolic troughs to collect and concentrate sunlight onto receivers that deliver solar thermal energy to heat engines for generating electricity. However, parabolic troughs are bulky and heavy and result in a large capital investment for CSP plants, thereby making it difficult for CSP technology to be competitive with photovoltaics. We present the design of a planar focusing collector (PFC) with focal length beyond the micron scale. The PFC design is based on the use of a nanostructured silver surface for linearly polarized singlewavelength light. The designed PFC consists of metallic nanogrooves on a dielectric substrate. The geometric properties, namely the width and depth, of a single-unit nanogroove allows for full control of the optical phase at desired spatial coordinates along the nanogroove short-axis for a single wavelength. Moreover, we show numerically that such phase control can be used to construct a phase front that mimics that of a cylindrical lens. In addition, we determine the concentration ratio by comparing the width of our PFC design to the cross-sectional width of its focal spot. We also determine the conversion efficiency at long focal lengths by evaluating the ratio of the collected optical power to the incoming optical power. Finally, we examine the focusing behavior across multiple wavelengths and angles of incidence. Our work shows how nano-optics and plasmonics could contribute to this important area of CSP technology.
Plasmonic nanoantennas make effective optical tweezers, owing to their characteristic field enhancement and confinement properties which produce large near-field intensity gradients. The trapping dynamics of plasmonic nanotweezers are strongly affected by their resonant optical absorption, which can produce significant heating and induce rapid convective flows in the surrounding fluid medium. We here consider a new class of plasmonic nanotweezers based on an array of elevated bowtie nanoantennas (BNA), whereby BNAs are suspended on optically transparent, 500-nm tall silica pillars. We discuss how the plasmonic properties of these pillar-BNAs (pBNAs) can be manipulated in large areas of 80 × 80-micron using low-input power densities. This modification in local plasmonic properties is expected to result in a much more complex optical trapping landscape. We also find that the temperature increase in the pBNAs is more than 10× higher than in comparable substrate-bound structures (for the same input intensity), in which the substrate acts as a heat sink that mitigates temperature increase, and we investigate the role of this enhanced thermo plasmonic heating on plasmonic trapping dynamics.