Both amorphous and crystalline silicon are ubiquitous materials for electronics, photonics, and microelectromechanical systems. On-demand control of Si crystallinity is crucial for device manufacturing and to overcome the limitations of current phase-change materials (PCM) in active photonics. Fast reversible phase transformation in silicon, however, has never been accomplished due to the notorious challenge of amorphization. It is demonstrated that nanostructured Si can function as a PCM, since it can be reversibly crystallized and amorphized under nanosecond laser irradiation with different pulse energies. Reflection probing on a single nanodisk's phase transformations confirms the distinct mechanisms for crystallization and amorphization. The experimental results show that the relaxation time of undercooled silicon at 950 K is 10 ns. The phase change provides a 20% nonvolatile reflectivity modulation within 100 ns and can be repeated over 400 times. It is shown that such transformations are free of deformation upon solidification. Based on the switchable photonic properties in the visible spectrum, proof-of-concept experiments of dielectric color displays and dynamic wavefront control are shown. Therefore, nanostructured silicon is proposed as a chemically stable, deformation free, and complementary metal-oxide-semiconductor compatible (CMOS) PCM for active photonics at visible wavelengths.

Recent developments in reconfigurable photonic devices highly rely on the effective refractive index change enabled by phase change materials (PCMs) as either dielectric surroundings or constituting materials. This universal characteristic, tunable refractive index, is shared among various kinds of PCMs and has been successfully utilized to achieve multilevel modulations for both free-space and integrated photonics. In this Perspective, we briefly recapitulate the fundamental mechanisms of phase transitions for three dominant PCMs. The progress in integrating different PCMs with on-chip silicon photonics and periodic antenna arrays are reviewed and analyzed in parallel. We also discuss the existing problems of PCM photonics, for example, the compatibility with commercial production line, the stability issue, and accessibility of the stimuli. In the end, we provide the outlook for the improving material engineering of PCM and multi-functional PCM-based photonics devices.

In this study, we observe and study the early evolution of cavitation bubbles generated during pulsed laser ablation of titanium targets in different liquid environments utilizing a high-resolution stroboscopic shadowgraphy system. A hydrodynamic model is proposed to calculate the early pressure changes within the bubble and in the surrounding fluid. Our results show that the cavitation bubble is a low-pressure region that is bounded by a high-pressure fluid lamina after the incipient stage, and its evolution is primarily affected by the liquid density. Moreover, the initial bubble pressure increases substantially in high viscosity liquids. This work illuminates how the liquid properties affect the early bubble dynamics and is a step towards a deeper understanding of laser-materials interactions in liquid environments.

Chemical doping has been extensively studied for control of charge carrier polarity and concentration in two-dimensional (2D) van der Waals materials. However, conventional routes by substitutional doping or absorbed molecules suffer from degradation of the electrical mobility due to structural disorder, while the maximum doping density is set by the solubility limit of dopants. Here, we show that laser assisted chlorination can achieve high doping concentration (> 3×10 13 cm − 2 ) in graphene monolayer with minimal mobility drop, while holding reversibility and spatial selectivity. Such superior doping scheme is enabled by two lasers with selected photon energies and geometric con gurations, resulting to high Cl coverage ratio (C 2 Cl) and subsequent local Cl-removal without damaging graphene. Based on this method, we demonstrate rewritable graphene photodetector, manifesting high quality reversible doping patterns in graphene. We believe that the presented results offer a new route for chemical doping of 2D materials that may enable exotic optoelectronic applications.

Pulsed laser processing plays a crucial role in additive manufacturing and nanomaterial processing. However, probing the transient temperature field during the pulsed laser interaction with the processed materials is challenging as it requires both high spatial and temporal resolution. Previous transient thermometry studies have measured neither sub-100 µm spatial resolution nor sub-10 ns temporal resolution. The temperature field induced by Gaussian laser beam profiles has also not been accounted for. Here, we demonstrate a 9 ns rise time, 50 µm sized Pt thin-film sensor for probing the temperature field generated by a nanosecond pulsed laser on a semiconductor thin film. The measurement error sources and associated improvements in the thin film fabrication, sensor patterning, and electrical circuitry are discussed. We carried out the first experimental and theoretical analysis of spatial resolution and accuracy for measuring a Gaussian pulse on the serpentine structure. Transparent silica and sapphire substrates, as well as 7–45 nm insulation layer thicknesses, are compared for sensing accuracy and temporal resolution. Finally, the measured absolute temperature magnitude is validated through the laser-induced melting of the 40 nm thick amorphous silicon film. Preliminary study shows its potential application for probing heat conduction among ultrathin films.