Jiafang Li

Manipulation of plasmonic wavefront and light–matter interaction in metallic nanostructures: A brief review

The control and application of surface plasmons (SPs), is introduced with particular emphasis on the manipulation of the plasmonic wavefront and light?matter interaction in metallic nanostructures. We introduce a direct design methodology called the surface wave holography method and show that it can be readily employed for wave-front shaping of near-infrared light through a subwavelength hole, it can also be used for designing holographic plasmonic lenses for SPs with complex wavefronts in the visible band. We also discuss several issues of light?matter interaction in plasmonic nanostructures. We show theoretically that amplification of SPs can be achieved in metal nanoparticles incorporated with gain media, leading to a giant reduction of surface plasmon resonance linewidth and enhancement of local electric field intensity. We present an all-analytical semiclassical theory to evaluate spaser performance in a plasmonic nanocavity incorporated with gain media described by the four-level atomic model. We experimentally demonstrate amplified spontaneous emission of SP polaritons and their amplification at the interface between a silver film and a polymer film doped with dye molecules. We discuss various aspects of microscopic and macroscopic manipulation of fluorescent radiation from gold nanorod hybrid structures in a system of either a single nanoparticle or an aligned group of nanoparticles. The findings reported and reviewed here could help others explore various approaches and schemes to manipulate plasmonic wavefront and light?matter interaction in metallic nanostructures for potential applications, such as optical displays, information integration, and energy harvesting technologies.

Fabrication of three-dimensional woodpile photonic crystals in a PbSe quantum dot composite material

Incorporating active media into three-dimensional (3D) photonic crystals (PCs) is a useful step towards exploring the functionalities of PCs. Here we report, for the first time, on the fabrication of 3D woodpile PCs with a commercial PbSe quantum dot (QD) composite material by using the two-photon polymerization technique. The fabricated crystals possess photonic band gaps in the near-infrared wavelength region, which have a suppression rate of ~50% in the stacking direction, measured with an angle-resolved Fourier-transform infrared spectrometer. The woodpile structures fabricated under different conditions are also characterized by using a scanning near-field optical microscope, providing a useful feedback towards optimizing the fabrication of 3D woodpile PCs in QD composites.

Optical trapping of gold nanoparticles by cylindrical vector beam

Optical trapping of gold nanoparticles is experimentally demonstrated using radially and azimuthally polarized beams. The transverse optical trapping stiffness of gold nanoparticles is measured. The radially polarized beam exhibits a higher trapping efficiency than the azimuthally polarized beam and the Gaussian beam. The transverse stiffness of particles with different diameters is measured experimentally and calculated via the discrete-dipole approximation method, and good agreement between theory and experiment is found.

Efficient surface plasmon amplification from gain-assisted gold nanorods

We report on the efficient surface plasmon amplification by stimulated emission of radiation (spaser) from a gold nanorod coated with proper gain media. Numerical simulations show that the threshold of the nanorod-based spaser is nearly 1 order of magnitude lower than that of the core-shell nanosphere, which is verified by analysis with electrostatic theory. Furthermore, it is found that the nanorod-based nanosystem possesses unique optical properties such as wavelength tunability and polarization sensitivity.

Use of radially polarized beams in three-dimensional photonic crystal fabrication with the two-photon polymerization method

Radially polarized ultrafast laser beams are used in the fabrication of three-dimensional photonic crystals with the two-photon polymerization technique in organic-inorganic hybrid materials. It has been found that when a radially polarized beam is employed, the lateral size of the fabricated polymer rods is decreased by 27.5% from 138 to 100 nm under a threshold fabrication condition, leading to a 17.35% reduction in the filling ratio of the photonic crystal. A comparison of the stop gaps between radially polarized and linearly polarized beam illumination shows a higher suppression ratio in transmission and a wider wavelength range in the former case owing to the favorable tuning of the filling ratio of the three-dimensional photonic crystals.

Anisotropic and enhanced absorptive nonlinearities in a macroscopic film induced by aligned gold nanorods

Anisotropic and enhanced nonlinear absorption (NLA) has been observed from aligned gold nanorods (GNRs) embedded in a poly(vinyl alcohol) film, which was realized by a stretched-film method. Open-aperture Z-scan experiments revealed that the stretch process enhanced the NLA coefficient by approximately nine times and increased the anisotropic factor of NLA to ∼20. The enhancement in the NLA coefficient reached as high as ∼91 times after increasing the concentration of GNRs by four times and this is attributed to the plasmonic interaction between densely packed GNRs.

Tunable electroluminescence in planar graphene/SiO(2) memristors.

Electroluminescence and resistive switching are first realized simultaneously in graphene/SiO2 memristor devices. The electroluminescence peaks can be tuned between 550 nm and 770 nm reliably via setting the device to different resistance states by applying different voltages. The combination of resistive switching and electroluminescence may bring new functionalities for these memristor devices which are fully compatible with silicon-based electronics.

Engineering stop gaps of inorganic-organic polymeric 3D woodpile photonic crystals with post-thermal treatment

A method is reported for improving the spatial resolution and engineering the stop gaps of the inorganic-organic 3D woodpile photonic crystals (PhCs). The approach is based on the two-photon polymerization (2PP) of an inorganic-organic hybrid material and a post-thermal treatment (PTT) process. The effects of PTT on polymerized 1D, 2D and 3D structures have been characterized. Ultimately, the feature size of the suspended rods has been reduced to approximately 33 nm and the spatial resolution of inorganic-organic 3D woodpile PhCs has been improved from approximately 150 nm to approximately 86 nm. The approach is also demonstrated as a powerful tool to engineer the stop gaps of 3D PhCs. In particular, a combination of PTT and the threshold fabrication technique leads to the stop gap of a 3D woodpile PhC that can be tuned over a large wavelength range of approximately 318 nm from the near-infrared to visible region.

Near-field visualization of focal depth modulation by step corrugated plasmonic slits

Nanometric plasmonic slits with stepped corrugations have been designed and fabricated to achieve plasmonic focusing and focal depth modulation. A scanning near-field optical microscope is employed to directly visualize the transmitted light from the slits. The near-field and far-field two-dimensional images taken at different planes parallel to the slit surface unambiguously demonstrated the focusing effect of the nanoslits. Furthermore, by forming stepped corrugations with either a concave or a convex profile on both sides of the slits, the phase of the transmitted beam can be effectively manipulated, thus allowing an accurate tuning of the focal depth.

Two-Photon Polymerization for Three-Dimensional Photonic Devices in Polymers and Nanocomposites

Fabrication of micro- or nano-scale photonic devices in polymer materials to control and manipulate light propagation represents a hot topic nowadays. Compared with conventional semiconductor materials, polymers are easy to prepare and have the flexibility of incorporating active materials to realise various functionalities. As one of the most powerful tools in micro-optical fabrication, the two-photon polymerization technique has been widely employed recently to produce multifarious photonic devices, particularly the photonic crystals, which are promising candidates for integrated optical devices. In this article the recent advances in the fabrication of three-dimensional photonic devices such as diffractive optical elements, photonic crystals, and superprisms in polymer materials using the two-photon polymerization technique are reviewed. In particular, the fabrication of photonic crystals in nanocomposite polymers, which are formed by incorporating nanocrystal quantum dots into polymer materials, is demonstrated, providing an interesting physical platform for the investigation into new types of active micro-devices.