High-absorption grating-insulator-metal structures.

A thin grating-insulator-metal (GIM) structure consisting of a top metal grating layer on a dielectric layer and a bottom metal layer is proposed, which shows a broadband high absorption at a small thickness. This phenomenon is attributed to the appropriate effective surface permittivity of the top grating layer and the cavity resonance of the middle insulator layer. By optimizing the structural and material parameters, the materials of the GIM structure from top to bottom are Mn, Al2O3, and Mn with thicknesses of 10, 70, and 70 nm, respectively. The structure with these optimum parameters is fabricated and characterized, and an improved performance with absorption exceeding 90% in the visible region is obtained using Mn as the metal layers. The experimental results are in good agreement with the numerical values, depicting an ultrabroad absorption bandwidth. The conclusions presented here could have potential applications in optical devices used for optical displacement detection and visible light absorption.

Parametric Excitation of Optomechanical Resonators by Periodical Modulation.

Optical excitation of mechanical resonators has long been a research interest, since it has great applications in the physical and engineering field. Previous optomechanical methods rely on the wavelength-dependent, optical anti-damping effects, with the working range limited to the blue-detuning range. In this study, we experimentally demonstrated the excitation of optomechanical resonators by periodical modulation. The wavelength working range was extended from the blue-detuning to red-detuning range. This demonstration will provide a new way to excite mechanical resonators and benefit practical applications, such as optical mass sensors and gyroscopes with an extended working range.

Nanometer-precision linear sorting with synchronized optofluidic dual barriers.

The past two decades have witnessed the revolutionary development of optical trapping of nanoparticles, most of which deal with trapping stiffness larger than 10-8 N/m. In this conventional regime, however, it remains a formidable challenge to sort out sub-50-nm nanoparticles with single-nanometer precision, isolating us from a rich flatland with advanced applications of micromanipulation. With an insightfully established roadmap of damping, the synchronization between optical force and flow drag force can be coordinated to attempt the loosely overdamped realm (stiffness, 10-10 to 10-8 N/m), which has been challenging. This paper intuitively demonstrates the remarkable functionality to sort out single gold nanoparticles with radii ranging from 30 to 50 nm, as well as 100- and 150-nm polystyrene nanoparticles, with single nanometer precision. The quasi-Bessel optical profile and the loosely overdamped potential wells in the microchannel enable those aforementioned nanoparticles to be separated, positioned, and microscopically oscillated. This work reveals an unprecedentedly meaningful damping scenario that enriches our fundamental understanding of particle kinetics in intriguing optical systems, and offers new opportunities for tumor targeting, intracellular imaging, and sorting small particles such as viruses and DNA.