Introduction

The effective manipulation of light and matter has been at the center of visual art and optics research for centuries. With tremendous advances in our ability to create and characterize materials at the nanoscale, scientists have uncovered that ancient art had indeed utilized some of the advanced material properties that are only being understood today. For instance, silver nanoparticles found in ancient stained glass are responsible for their vibrant colors, owing to the excitation of the collective charge oscillation, central to plasmonics, an active field of research today. Recently, plasmonic nanostructures have been used to produce colorful imagery that promise unprecedented detail (i.e. print resolutions at the optical diffraction limit ∼100,000 dpi), resistance to fading, and viewing angle independence. Similarly, nanostructures judiciously positioned onto a substrate or thin films form metasurfaces that control the phase of light, reinvigorating the field of holography and surface coloration. The rapid growth of these fields in the past decade and their overlap with visual art has led to this feature issue, aimed at capturing some of this excitement.

Summary of papers in the feature issue

The articles in this feature issue can broadly be clustered into the following topics: (1) laser/heat processing of metallic surfaces, (2) nanolithography and plasmonic colors, (3) tagging and identification of art pieces, (4) liquid crystals and waveguides for holography and displays, and (5) large area flexible photonic materials.

Photonics has a lot to offer in providing alternative routes to color creation that is not based on light absorption in dyes or pigments. Laser/heat processing of metallic surfaces involves the use of high-power pico- or femtosecond lasers or heat to create modifications to the surface of metals. These modifications can either be chemical in nature, e.g. surface oxidation; structural, e.g. formation of nanoparticles; or both. These methods are attractive as it allows a range of colors to be printed to form complex images simply by varying laser parameters. Guay et al performed a systematic study of the effect of laser repetition rate on the colors achieved on silver. The article by Andreeva et al. provides a comprehensive overview of various techniques of laser coloration of metals including the use of lasers to induce oxide formation, gratings, and nanoparticles with stunning art prints on centimeter-scale flat pieces of metals. Letsou et al. demonstrated that thin oxide films can also form on metal surfaces simply by heating metals such as Ni and Ti at elevated temperatures, producing a wide range of colors with perfect absorption at specific wavelengths. Nyga et al. investigated the colors arising from semicontinuous silver films and demonstrated a broader range of vibrant colors achieved as this film is irradiated with lasers. The authors cleverly prevented chemical degradation of silver during the laser irradiation by first coating the films with a protective layer of silicon oxide. Finally, Garcell et al. extends the functionality of laser-treated metal films beyond coloration. The authors demonstrated that Cu films exposed to laser can concomitantly be colorized and superhydrophobic.

Nanolithography and plasmonic color generation are heavily featured in the collection of papers here. Plasmonic colors have attracted tremendous interest recently because of several unique attributes e.g. non-iridescent colors, color permanence, high-resolution, etc. Plasmonic color generation occurs when light interacts with metallic nanostructures that support resonances due to collective charge oscillations in the visible spectrum. For a given material, these resonances are size and shape dependent. Ng et al. and Deshpande et al. report new results on electron beam lithography patterning of precisely sized nanodisks in a metal-insulator-metal configuration. These nanodisks sit above a continuous metal substrate and support the so-called gap plasmons. Ng et al. demonstrated that the resonances in Al structures with native aluminum oxide forming the gap can be effectively tuned from UV to IR, demonstrating the use of plasmonic structures that encode different sets of information for both visible and IR spectra. Deshpande et al. show that larger sized disks, which are easier to fabricate, can support third-order gap plasmons in the visible spectrum to produce colors. Song et al. show that e-beam patterned “i” shaped plasmonic antennas exhibit a broad color range with polarization effects that show three different images depending on the polarization state. While electron-beam lithography patterning can be potentially fast with industrial shaped-beam systems, it is often convenient to be able to form plasmonic resonators under ambient conditions with a simple laser beam. However, due to the inability to define the exact size and placement of particles that form, laser-beam methods result in a wider distribution of particle geometries. The works of Nyga et al., Garcell et al., Andreeva et al., Guay et al. produced plasmonic nanoparticles with a very narrow size distribution to generate colors by variations in laser writing speed, power, repetition rate, and exposure time.

Two papers discuss the application of plasmonic effects in tagging and identification of precious art. One approach by Ng et al demonstrates a new type of microtags with QR and bar codes hidden in both visible and IR spectra. These tags are small enough that they could be embedded unnoticed into art pieces. Farling et al. reports on a quality assurance protocol before colloidal silver nanoparticles are applied to art pieces for identification of specific pigments in art using surface-enhanced Raman spectroscopy (SERS).

In addition to laser prints on metals, several articles present art displays in the form of holograms, true color rainbows, and innovations in backlighting panels for displays. These technologies rely on the use of liquid crystals, underscoring the continued relevance of this versatile photonic material. Quesada et al. investigated various designs of lenticular lens plates made entirely of glass to guide bands of light for selective dimming of the backpanel in LCD displays. Doelman et al. presents a process and scheme to achieve multi-color holograms with photo-aligned liquid crystals to impart geometric phase to circularly polarized laser illumination. Finally, using liquid crystals in polarization gratings allowed authors Snik et al. to produce a true-color (not RGB) rainbow art installation in the Netherlands.

Two articles reported on the use of photonic materials in flexible sheets. Sergeyeva et al. introduces the modern fashion concept of glowing felt textiles out of plastic optical fibers. Besides high fashion, the authors also suggest several other applications of these optical fibers textiles such as wearable sensors and data transmission. Last but not least, Lozano et al. describe flexible films that provide a versatile solution for passive thermal management. These lightweight and conformal films consisting of polyethylene with inorganic nano-micro inclusions can be tailored to generate colors in the visible while providing radiative cooling to objects covered by these films.

Together these papers highlight innovations in photonics and the ongoing adoption of new technologies into visual arts and design. Both the arts and sciences involve collaborative processes driven by research and experimentation. Controlling light in art and design inspires and encourages the development of photonics materials.