ABSTRACT
Advanced SiO2-Al2O3 aerogel materials have outstanding potential in the field of thermal insulation. Nevertheless, the creation of a mechanically robust and low-cost SiO2-Al2O3 aerogel material remains a considerable challenge. In this study, SiO2-Al2O3 aerogel based on coal gangue, which is a type of zero-cost inorganic waste, was constructed in porous agarose aerogel beads, followed by simple chemical vapor deposition of trimethylchlorosilane to fabricate SiO2-Al2O3/agarose composite aerogel beads (SCABs). The resulting SCABs exhibited a unique nanoscale interpenetrating network structure, which is lightweight and has high specific surface area (538.3 m2/g), hydrophobicity (approximately 128°), and excellent thermal stability and thermal insulation performance. Moreover, the compressive strength of the SCABs was dramatically increased by approximately a factor of ten compared to that of native SiO2-Al2O3 aerogel beads. The prepared SCABs not only pave the way for the design of a novel aerogel material for use in thermal insulation without requiring expensive raw materials, but also provide an effective way to comprehensively use coal gangue.
ABSTRACT
Ultrathin flat optics allow control of light at the subwavelength scale that is unmatched by traditional refractive optics. To approach the atomically thin limit, the use of 2D materials is an attractive possibility due to their high refractive indices. However, achievement of diffraction-limited focusing and imaging is challenged by their thickness-limited spatial resolution and focusing efficiency. Here we report a universal method to transform 2D monolayers into ultrathin flat lenses. Femtosecond laser direct writing was applied to generate local scattering media inside a monolayer, which overcomes the longstanding challenge of obtaining sufficient phase or amplitude modulation in atomically thin 2D materials. We achieved highly efficient 3D focusing with subwavelength resolution and diffraction-limited imaging. The high focusing performance even allows diffraction-limited imaging at different focal positions with varying magnifications. Our work paves the way for downscaling of optical devices using 2D materials and reports an unprecedented approach for fabricating ultrathin imaging devices.
ABSTRACT
Heavily doped colloidal plasmonic nanocrystals have attracted great attention because of their lower and adjustable free carrier densities and tunable localized surface plasmonic resonance bands in the spectral range from near-infra to mid-infra wavelengths. With its plasmon-enhanced optical nonlinearity, this new family of plasmonic materials shows a huge potential for nonlinear optical applications, such as ultrafast switching, nonlinear sensing, and pulse laser generation. Cu3-xP nanocrystals were previously shown to have a strong saturable absorption at the plasmonic resonance, which enabled high-energy Q-switched fiber lasers with 6.1 µs pulse duration. This work demonstrates that both high-quality mode-locked and Q-switched pulses at 1560 nm can be generated by evanescently incorporating two-dimensional (2D) Cu3-xP nanocrystals onto a D-shaped optical fiber as an effective saturable absorber. The 3 dB bandwidth of the mode-locking optical spectrum is as broad as 7.3 nm, and the corresponding pulse duration can reach 423 fs. The repetition rate of the Q-switching pulses is higher than 80 kHz. Moreover, the largest pulse energy is more than 120 µJ. Note that laser characteristics are highly stable and repeatable based on the results of over 20 devices. This work may trigger further investigations on heavily doped plasmonic 2D nanocrystals as a next-generation, inexpensive, and solution-processed element for fascinating photonics and optoelectronics applications.
