Y G Tang

Enhancement of Raman scattering by field superposition of rough submicrometer silver particles

Wavelength-dependent surface-enhanced Raman spectra of methylene blue adsorbed on rough submicrometer silver particles were measured. Results revealed a high enhancement factor (105 ∼ 107), especially in the long-wavelength region. Investigation on the far- and near-field optical properties of the particles showed a remarkably enhanced dipole plasmon resonance due to the presence of a rough particle surface. Through analyzing the plasmon resonance modes and the superposition of radiation fields, we found that the rough surface-induced field superposition results in the redistribution of optical fields around the particle, which becomes a key factor responsible for the high enhancement effect of metal particles.

Real-time monitoring of ruling grating resolution by digital wavefront

In order to solve the problem that the grating quality cannot be monitored directly in real time, we provided a method based on Rayleigh criterion with our designing optical measurement structure to measure yaw and displacement errors of a grating ruling machine feeding system. Gratings are ruled with or without errors correction by the real-time monitoring system . It shows that the resolution obtained without errors correction is reduced from 99.97% to 87.47% of theoretical value, while the resolution obtained with errors correction is stable, remaining at 99.99%–97.21%. The experimental result is that the grating quality can be guaranteed by monitoring grating resolution in real time.

Use of metal-enhanced fluorescence spectroscopy for detection of polycyclic aromatic hydrocarbons in diesel oil emulsions in artificial seawater.

In this study, we employed the metal-enhanced fluorescence (MEF) method for the detection of polycyclic aromatic hydrocarbons (PAHs) in diesel oil emulsions in artificial seawater. Silver nanoparticles with an average diameter of 80 nm were immobilized onto silanized quartz as MEF substrates. Excited by illumination at 355 nm, a 4.6-fold increase in the fluorescence signals of PAHs was recorded when MEF substrates were used. The finite-difference time-domain (FDTD) method was used to provide mechanistic insights into the fluorescence enhancement. Monitoring water pollution has environmental significance and MEF spectroscopy is finding direct applications in this field.

Ruling of echelles and gratings with a diamond tool by the torque equilibrium method

Ruling of echelles and gratings by the torque equilibrium method is proposed to eliminate corrugated grating lines, rough blazed grating surfaces, and complex fabrication work such as step-by-step diamond tool deflection. A mathematical model of the torque equilibrium between the diamond tool and the metallic film during the ruling process is deduced to realize optimized diamond tool geometrical parameter design. Then, two echelles with identical areas of 80  mm×100  mm are separately ruled using the traditional deflecting tool ruling method and the proposed method, and the scatter light results for the two echelles are 9.6×10−4 and 3.1×10−4, respectively.