Zhaoguang Pang

Random Laser Based on Waveguided Plasmonic Gain Channels

A waveguide-plasmonic scheme is constructed by coating the matrix of randomly distributed gold nanoisland structures with a layer of dye-doped polymer, which provides strong feedback or gain channels for the emission from the dye molecules and enables successful running of a random laser. Excellent overlap of the plasmonic resonance of the gold nanoislands with the photoluminescence spectrum of the dye molecules and the strong confinement mechanism provided by the active waveguide layer are the key essentials for the narrow-band and low-threshold operation of this random laser. This kind of feedback configuration potentially enables directional output from such random lasers. The flexible solution-processable fabrication of the plasmonic gold nanostructures not only enables easy realization of such a random laser but also provides mechanisms for the tuning and multicolor operation of the laser emission.

Sensors Based on Plasmonic-Photonic Coupling in Metallic Photonic Crystals

An optical sensor based on the coupling between the plasmonic and photonic resonance modes in metallic photonic crystals is investigated. Large-area metallic photonic crystals consisting of periodically arranged gold nanostructures with dimensions down to sub-100 nm are fabricated using solution-processible gold nanoparticles in combination with interference lithography or interference ablation, which introduces a variety of fabrication techniques for the construction of this kind of sensor device. Sensitivity of the plasmonic response of the gold nanostructures to the changes in the environmental refractive index is enhanced through the coupling between the narrow-band photonic resonance mode and the relatively broad-band plasmon resonance, which is recognized as a Fano-like effect and is utilized to explore sensors. Theoretical modeling shows the characterization and the optimization of the sensitivity of this kind of sensor device. Theoretical and experimental results are demonstrated for the approaches to improve the sensitivity of the sensor device.

Achieving Continuous Sub-100-nm Plasmonic Nanowires as Long as Centimeters

Gold nanowires with a width smaller than 100nm and a length in the order of centimeters have been fabricated using colloidal gold nanoparticles. The dewetting of the colloidal solution of gold nanoparticles on the photoresist master grating with a small duty cycle is utilized to limit the amount of gold nanoparticles that are confined into the grating grooves after spin-coating, which favors the achievement of narrow gold nanowires. During the subsequent annealing process, the sublimation of the ligands covering the gold nanoparticles, the melting of the gold nanoparticles, and the removal of the photoresist master grating take place sequentially as the annealing temperature is increased from room temperature to about 450oC. Thus, high-quality gold nanowires are produced with excellent continuity in a large scale and excellent plasmonic response. These kinds of structures are important for sensitive biosensors with flexible dynamics in both the dimensions and the spectroscopic response.

Resonant orders of the coupled mode in waveguide metallic photonic crystals

Abstract. Metallic photonic crystals (MPCs) with different periods have been fabricated by solution-processed method. Scanning electron microscopy images show that the structures with their period larger than 400 nm can easily maintain their morphologies during the high temperature lift-off process. The optical properties of the waveguided MPCs with different periods have been investigated. With an increase in the period, high-order coupling between particle plasmon resonance and the waveguide resonance modes can be observed in the spectra. We found that the ±2 orders coupling of the structure with its period of 880 nm has similar tuning properties to the ±1st orders coupling of the 430 nm period structures, which infers us that we can use the structures with larger period that can be controllably fabricated to replace the ones with smaller period. The results we obtained in this work provide reference for further applications of the MPCs.

Fabrication of two-dimensional metallic photonic crystals using laser interference ablation

We demonstrate the fabrication of two-dimensional (2D) metallic photonic crystals (MPCs) based on colloidal gold nanoparticles, where laser interference ablation combining subsequent high temperature annealing is employed for the construction of 2D gold nano-dot arrays in square lattices. The microscopic and spectroscopic properties of the 2-D MPCs are systematically characterized by the scanning electron microscope and the angle-resolved optical extinction spectroscopic measurements, the strong coupling between the waveguide resonance mode and the particle plasmon resonance of the MPCs imply the success of the fabrication method, which show potential applications in optoelectronic devices and sensors.