Recent advances in liquid metal photonics: technologies and applications [Invited]

Abstract

Near-room-temperature liquid metals offer unique and crucial advantages over solid metals for a broad range of applications that require soft, stretchable, and/or reconfigurable structures and devices. In particular, gallium-based liquid metals are the most suitable for a wide range of applications, not only owing to their low melting points but also thanks to their low toxicity and negligible vapor pressure. In addition, gallium-based liquid metals exhibit attractive optical properties, which make them highly suitable for a variety of photonics applications. This review summarizes the material properties of gallium-based liquid metals, highlights several effective techniques for fabricating liquid-metal-based structures and devices, and then focuses on the various photonics applications of these liquid metals in different spectral regions, following with a discussion on the challenges and opportunities for future research in this relatively nascent field.

Low-Loss Plasmonics with Nanostructured Potassium and Sodium–Potassium Liquid Alloys

“…The liquid nature of the NaK alloy over a wide range of composition and temperature windows and its liquid–solid phase transitions can be further conceived for low-loss metasurface designs to enable the efficient and novel modulation of optical performance. For example, by referring to the successful research on Ga, , our nanoembossing technique can be combined with micro/nanofluidic channels , to enable robust micro- and nanostructuring of the NaK alloys. In addition, Na/K/NaK liquid metals can be incorporated into flexible substrates to follow the changes of the substrates subjected to mechanical or thermal stimuli to exhibit tunable optical responses, potentially contributing to the broad discipline of flexible electronics.…”

“…Regarding plasmonic metals, approaches are mostly limited to mechanical actuation and modulating the dielectric environment because metals generally have high melting temperatures. ,,, One special case is gallium (Ga), a liquid metal with a melting temperature close to room temperature (29.8 °C). The properties of Ga can be controlled by introducing the solid–liquid phase transition, , and notably, its plasmonic properties in the liquid phase are much more desirable than those of its solid counterpart. − However, Ga has high optical loss over the visible to near-infrared (NIR) (Figure S1). Liquid metals with desirable optical properties are still lacking.…”

“…41−43 However, Ga has high optical loss over the visible to nearinfrared (NIR) (Figure S1). 42 Liquid metals with desirable optical properties are still lacking.…”

“…The properties of Ga can be controlled by introducing the solid–liquid phase transition, , and notably, its plasmonic properties in the liquid phase are much more desirable than those of its solid counterpart. − However, Ga has high optical loss over the visible to near-infrared (NIR) (Figure S1). Liquid metals with desirable optical properties are still lacking.…”

Laser-damage performance of gallium-alloy liquid metal mirrors

“…The unique properties of Ga have been explored in various fields including photonic applications. Ga-based liquid reflectors have been developed for telescopes, 8 , 9 demonstrated for laser mode locking, 10 stretchable optics, 11 optical switching, 12 and in an array of liquid metal photonics devices 13 , 14 . To the best of our knowledge, however, their use for optics suitable for high-power laser systems has not been previously reported.…”