Xu Jingjun

Large-area high-performance SERS substrates with deep controllable sub-10-nm gap structure fabricated by depositing Au film on the cicada wing.

Noble metal nanogap structure supports strong surface-enhanced Raman scattering (SERS) which can be used to detect single molecules. However, the lack of reproducible fabrication techniques with nanometer-level control over the gap size has limited practical applications. In this letter, by depositing the Au film onto the cicada wing, we engineer the ordered array of nanopillar structures on the wing to form large-area high-performance SERS substrates. Through the control of the thickness of the Au film deposited onto the cicada wing, the gap sizes between neighboring nanopillars are fine defined. SERS substrates with sub-10-nm gap sizes are obtained, which have the highest average Raman enhancement factor (EF) larger than 2 × 108, about 40 times as large as that of commercial Klarite® substrates. The cicada wings used as templates are natural and environment-friendly. The depositing method is low cost and high throughput so that our large-area high-performance SERS substrates have great advantage for chemical/biological sensing applications.

Preparation and Size Characterization of Silver Nanoparticles Produced by Femtosecond Laser Ablation in Water

Femtosecond laser ablation of silver plate placed in water is used to produce nanoparticle suspension. The method is easy to operate and the suspension is relatively stable. The optical properties and the size distribution of the suspension are studied with UV–vis absorption spectroscopy and dynamic light scattering, respectively. The shape of the nanoparticles is investigated by an atomic force microscope, which is near spherical. There are two kinds of nanoparticles, small particles with diameter about 35 nm, and large particles with diameter about 120nm.

Fano Resonance Based on Multimode Interference in Symmetric Plasmonic Structures and its Applications in Plasmonic Nanosensors

A novel symmetric plasmonic structure consisting of a metal-insulator-metal waveguide and a rectangular cavity is proposed to investigate Fano resonance performance by adjusting the size of the structure. The Fano resonance originates from the interference between a local quadrupolar and a broad spectral line in the rectangular cavity. The tuning of the Fano profile is realized by changing the size of the rectangular cavity. The nanostructure is expected to work as an excellent plasmonic sensor with a high sensitivity of about 530 nm/RIU and a figure of merit of about 650.

Group velocity reduction of light pulses in photorefractive two-wave mixing

We show theoretically that the group velocity of light pulses can be reduced significantly by use of the steep dispersion properties of the phase coupling effect in the photorefractive two-wave mixing process. The group velocity of light pulses of the order of 0.1 m/s can be achieved in typical photorefractive BSO crystals with an appropriate externally applied electric field and moving gratings of appropriate speeds. It is also shown that the slowly propagating light pulses can be set to be amplified after passing through the photorefractive material.

Photorefractive Spatial Dark-Soliton Stripes in LiNbO3:Fe Crystal and Their Application

We observed the photorefractive spatial dark-soliton stripes in LiNbO3:Fe crystal, and demonstrate the planar waveguide property of refractive index profile induced by these spatial dark-soliton stripes. We suggest a new mothed to form the planar waveguide utilizing the grating fixing technique.

Light-climbing effect in LiNbO(3):Fe crystal.

The light-climbing effect in a LiNbO(3):Fe crystal sheet was experimentally studied, and the mechanism for light climbing proposed was proved to be correct. The relevant optical properties were investigated.

Laser-Driven Silver Nanowire Formation: Effect of Femtosecond Laser Pulse Polarization

We report our laser-driven method used to make large quantities of straight thin silver nanowires, and experimentally demonstrate that femtosecond laser pulse polarization has a prominent effect on formation of non-spherical shapes of nanoscale particles. Further, our experiment directly reveals that the underlying mechanism is plasmon-plasmon interaction, which can be controlled by polarization and plays a decisive role in this non-synthetic method for metal nanowire formation.

Enhancement of modulation depth of an all-optical switch using an azo dye-ethyl red film

The polymethyl methacrylate (PMMA.) film doped with an azo dye ethyl-red (ER,) film is employed to demonstrate the properties of an all-optical switch by its photoinduced dichroism and birefringence. We show how to enhance remarkably the modulation depth of all-optical switches almost to 100% by using two linear polarization beams: one beam is inclined at 45 degrees with respect to the probing beam and serves as a pumping beam, and the other beam is perpendicular to the probing beam and used as an erasing beam. Furthermore, a maximum-to-minimum output intensity ratio of 2000:1 is achieved in experiment, which is very useful and important for optical storages and image displays.

Nanocrystal formation and structure in oxyfluoride glass ceramics

The up-conversion luminescent property of the oxyfluoride glass ceramics 30SiO2.15Al2O3. (50–x)PbF2.xCdF2 doped with 4ErF3.1YbF3 has been investigated. Up-conversion luminescent intensity of Er3+ ions increased obviously after heat-treatment due to co-doping with CdF2. The structure model of nanocrystals PbxCd1−xF2 was determined and the effect of CdF2 in oxyfluoride glass ceramics was explained by the analysis of x-ray diffraction data. Different nucleation temperatures of samples with different compositions were obtained by differential thermal analysis curves and the results showed the growth process of different nanocrystals in glass ceramics.

Red Up-Conversion Luminescence Process in Oxyfluoride Glass Ceramics Doped with Er3+/Yb3+

The phonon-assisted quantum cutting (PQC) model is presumed to clarify the red up-conversion luminescence process in Er3+/Yb3+ co-doped glass ceramics by the excitation and emission spectra. The red up-conversion luminescence of Er3+ ions mainly comes from three-photon absorption by the PQC process when the rare earth ions are doped in the glass ceramics and excited by 980 nm pumped-laser. Er3+ ions absorb three-photons and relax to the 4G11/2 state and then emit red up-conversion luminescence by the PQC process. The factor coefficient for the relation of pump-laser power and up-conversion intensity (P-I) is found by the analysis of excitation spectra of the red luminescence, which plays a major role to understand the true red up-conversion luminescence process. The new P-I relation is explained by the model of PQC.