Femtosecond Nanostructuring of Glass with Optically Trapped Microspheres and Chemical Etching

Nanopatterning of silicon via the near-field enhancement effect upon double-pulse femtosecond laser exposure

Utilizing the near-field enhancement effect of a polystyrene microsphere, direct ablation of nanohole arrays by a temporal-shaping femtosecond (fs) laser pulse is presented. The nanohole arrays, which are circular, regular, and free of cracks, were processed without extra post-processing, and their average diameter decreased gradually, as the double-pulse delay increased until 2500 fs. The simulated results by a plasma model and finite difference time domain solution demonstrate that the size decrease of the structure is attributed to the increase of the ablation threshold of silicon. Through fs laser near-field fabrication, the FWHM of nanoholes can be reduced to approximately 50 nm (λ/16) and even to 23 nm when using the second harmonic laser at a wavelength of 400 nm.

Nanopatterning with Photonic Nanojets: Review and Perspectives in Biomedical Research

Nanostructured surfaces and devices offer astounding possibilities for biomedical research, including cellular and molecular biology, diagnostics, and therapeutics. However, the wide implementation of these systems is currently limited by the lack of cost-effective and easy-to-use nanopatterning tools. A promising solution is to use optical methods based on photonic nanojets, namely, needle-like beams featuring a nanometric width. In this review, we survey the physics, engineering strategies, and recent implementations of photonic nanojets for high-throughput generation of arbitrary nanopatterns, along with applications in optics, electronics, mechanics, and biosensing. An outlook of the potential impact of nanopatterning technologies based on photonic nanojets in several relevant biomedical areas is also provided.

Superlensing plano-convex-microsphere (PCM) lens for direct laser nano-marking and beyond

A high-performance all-dielectric lens, formed by integrating a conventional plano-convex lens with a high-index microsphere lens (PCM), was developed for far-field super-resolution applications. The PCM lens features a theoretical resolution of $\sim\lambda /{2.5}$∼λ/2.5 in air with a WD $\sim 2\;{\unicode{x00B5} \rm m}$∼2µm away from the lens. When combined with a femtosecond laser, the actual patterning resolution can reach $\sim\lambda /{3.5}$∼λ/3.5. The unusual focusing properties were theoretically and experimentally verified, and direct laser nano-writing of arbitrary patterns and nanostructures on various substrates was demonstrated. This Letter can be naturally extended to other super-resolution applications, including imaging, sensing, and trapping, with the potential of developing next-generation low-cost direct laser nano-marking machine and super-resolution imaging nanoscope.

Microparticle manipulation using femtosecond photonic nanojet-assisted laser cavitation

We report the effect of laser cavitation in water initiated by femtosecond pulses confined into subwavelength volume of photonic nanojet of spherical microparticles. The effect of nanoscale optical breakdown was employed for controllable and nondestructive micromanipulation of silica microspheres. We combine this technique with optical trapping for cyclic particle movements and estimate a peak velocity and an acceleration acquired by microspheres propelled by nanojet cavitation. Our study provides a strategy for nondestructive optical micromanipulation, cavitation-assisted drug delivery, and laser energy transduction in microdevices.