Dielectric metasurfaces built up with nanostructures of high refractive index represent a powerful platform for highly efficient flat optical devices due to their easy-tuning electromagnetic scattering properties and relatively high transmission efficiencies. Here we show visible-frequency silicon metasurfaces formed by three kinds of nanoblocks multiplexed in a subwavelength unit to constitute a metamolecule, which are capable of wavefront manipulation for red, green, and blue light simultaneously. Full phase control is achieved for each wavelength by independently changing the in-plane orientations of the corresponding nanoblocks to induce the required geometric phases. Achromatic and highly dispersive meta-holograms are fabricated to demonstrate the wavefront manipulation with high resolution. This technique could be viable for various practical holographic applications and flat achromatic devices.

No abstract

An analysis of the photoacoustic (PA) signal from murine tissue in vivo revealed several benefits of contrast-enhanced PA imaging at a wavelength of 1064 nm. Of all the wavelengths tested in a range from 710 to 1064 nm, the background PA signal from tissue in vivo was lowest and more homogeneous at 1064 nm. For blood-laden tissue, the background PA signal was up to 70% less at 1064 nm. Furthermore, when plasmonic nanoparticles, such as silver nanoplates, were introduced in vivo as contrast agents, the contrast in PA images at 1064 nm increased 38% compared to 750 nm. Therefore, contrast-enhanced PA imaging at 1064 nm is advantageous because of the low and homogeneous signal from native tissue, enabling high contrast in PA imaging when exogenous, molecularly targeted agents are employed.