Nanosecond Laser Switching of Phase‐Change Random Metasurfaces with Tunable ON‐State

Abstract

that differ strongly from those of the constituent materials. Due to this remarkable flexibility, thin-film nanocomposites belong per se to the class of metasurfaces, whose fields of applications are constantly growing in key technological areas, including communications, energy, catalysis, and medicine. In the field of nanophotonics, the use of metasurfaces formed by planar arrangements of metallic and dielectric nanostructures has enabled the control of light at subwavelength scales, allowing light manipulation and processing in ways that are impossible to achieve with natural materials. [1][2][3][4] In particular, plasmonic metasurfaces based on nanostructured noble metals, either embedded in a dielectric film or deposited on top of a substrate, have shown extraordinary capabilities to strongly absorb, scatter, or confine incident light. More recently, nanostructures formed by high-index dielectric materials (mainly semiconductors such as Si and Ge) have gained momentum due to the particularities of their resulting electric and magnetic Mie resonances and have opened the field of the so-called Mie-resonant metaphotonics (also termed as Mie-tronics). [3,5,6] A relevant outcome of the improved understanding of these resonant phenomena has been acknowledged that there are alternative materials to the noble metals or conventional semiconductors that show plasmonic and Mie resonances, and, furthermore, that are better suited to address some specific nanophotonics applications. Among them are materials that offer plasmonic response in the ultraviolet, can withstand resonances at high temperature, or can be activated upon external excitation. [7][8][9][10] Bismuth (Bi) is one of such alternative materials and stands out due to its particular electronic structure, and optical and thermoelectronic properties. [11][12][13][14] Only very recently it has been shown that its electronic band structure displays giant interband electronic transitions in the mid-infrared, which, in turn, endows the dielectric function ε with a unique property that enables Bi-based nanostructures to show a dual behavior, enabling both plasmonic-like resonances in the ultraviolet and visible regions of the spectrum, and high-refractive-index Mie resonances in the near-and mid-infrared regions of the spectrum. [15,16] So far, metasurfaces based on Bi nanostructures have found applications in integrated photonic devices as perfect Random metasurfaces based on disordered phase-change nanostructures with broadband ultraviolet-visible plasmonic properties are fantastic platforms for the development of active photonic components due to their versatility. Here optical ON-OFF switching upon nanosecond laser irradiation of Bi-based random metasurfaces is demonstrated profiting from the solid-liquid phase transition of the Bi nanostructures. The fast switching time is revealed by using single-pulse real-time reflectivity measurements with sub-nanosecond temporal resolution. A sudden reflectivity decrease is observed upon laser excitation, triggered by hea...

Propagation dynamics of the solid–liquid interface in Ge upon ns and fs laser irradiation

“…In order to characterize the transient optical response of germanium upon ns and fs laser excitation, two different optical probe setups were used: with sub-ns temporal resolution and a temporal window up to several microseconds [20]. The complete temporal evolution of the reflectivity is recorded for a single pulse irradiation at a selected fluence.…”

“…A point-probing real-time reflectivity setup (Figure 1(b)), with sub-ns temporal resolution and a temporal window up to 200 ns [19]. The complete temporal evolution of the reflectivity is recorded for a single pulse irradiation at a selected fluence.…”

“…The real-time reflectivity setup, displayed in Figure 1(b), is described in detail in ref. [19]. Briefly, the probe beam is provided by a continuous wave laser at 532 nm which is temporally modulated by means of an acousto-optical modulator to produce single rectangular pulses of 10 µs duration, temporally synchronized with the pump pulse.…”

Lithography-Free Bismuth Metamaterials for Advanced Light Manipulation

“…Hence, in the investigation of bismuth metamaterial, developing lithography-free fabrication methods are highly desired. So far, the bismuth thin film, the bismuth nanoparticles embedded in a dielectric matrix, and the bismuth nanorod array are applied as the optical metamaterials for absorbers [45,[47][48][49][50][51][52], filters [49,53,54], and analog tuners for intensity and phase [55][56][57], as well as for thermaloptical switching [54,58,59]. Additionally, they can be prepared via lithography-free routes including regular physical vapor deposition (PVD) via magnetron sputter or thermal evaporation [32],pulse laser deposition (PLD) [60], and glazing-angle deposition (GLAD) [57].…”

Space and Time Modulations of Light with Metasurfaces: Recent Progress and Future Prospects

“…Bismuth nanostructures are nanoparticles based on the bismuth monoelement used because of its solid–liquid optical contrast with low melting points of about 270 °C. Recently, Alvarez-Algeria et al demonstrated the relevant properties of a random distribution of Bismuth-nanostructures in a dielectric matrix (PCRMs, phase change random metasurfaces). A nanosecond pulsed laser was used to melt the Bismuth-nanostructures with different filling factors, allowing a high optical contrast between the solid and liquid states (on/off state) and fast switching up to 10 ns and semivolatile behavior, which means staying at the melting phase without a permanent power supply for a given time duration.…”