Fu Han Ho

Nonlinear Optical Absorption in the AgOx-Type Super-Resolution Near-Field Structure

Nonlinear optical absorption in the AgOx-type super-resolution near-field structure [glass/ZnS–SiO2 (170 nm)/AgOx (15 nm)/ZnS–SiO2 (40 nm)] was investigated using a confocal Z-scan technique with a continuous He–Ne laser. The transmittance Z-scan shows that the sample undergoes a phase transition with increasing incident laser power. The phase transition of the sample with higher incident laser power is due to permanent local structure damage caused by the laser heating process.

Functional Structures of AgOx Thin Film for Near-Field Recording

The optical processes of the AgOx thin film under various laser pumping pulses are studied using an optical pump-probe system. Detailed changes of the reflectance measurements clearly show the different transition process of the dissociation of the AgOx thin film. The structures of dots and rings of written spots are observed in these processes. Two possible models of the distribution of the dissociated silver are proposed.

Nonlinear optical properties of the Au-SiO2 nanocomposite superresolution near-field thin film

A Au-SiO2 superresolution nanocomposite active nonlinear optical thin film is fabricated reproducibly by cosputtering method with the size of Au nano particles around 2 to 10 nm. Results of the Z-scan indicate that these nanocomposite Au-SiO2 films have nonlinear optical properties and enhanced transmittance at the focusing position. For a 15-nm-thick Au-SiO2 nanocomposite thin film, the transmittance can be 135% for a sample with an average grain size of around 5 nm.

Study of the focused laser spots generated by various polarized laser beam conditions

In this work, three‐dimensional near‐field imaging of the focused laser spot was studied theoretically and experimentally. In the theoretical simulation, we use the electromagnetic equivalent of the vectorial Kirchhoff diffraction integral to calculate the intensity distribution of the focal region, and a high depolarization is found in high numerical aperture systems (NA = 0.85). The experimental set‐up is based on a near‐field scanning optical microscope (NSOM) system. A high‐NA objective lens is used to focus incident light of various polarizations, and a tapered near‐field optical fibre probe of the NSOM system is used to determine the intensity of the focal field. The results show an asymmetric distribution of the focused intensity with the linear polarized laser beam.

Observation of liquid/liquid interface by atomic force microscopy

This research successfully measure the topography of liquid-liquid interface by using atomic force microscopy (AFM). In this paper, tapping mode AFM in liquid was used to directly probe the glycerol surface and sketch the topography of glycerol droplet in the silicone oil with respect to study the properties of liquid/liquid interfaces. In addition, to study the surface properties of liquid/liquid interface, the dependence of interfacial roughness on different viscosities was investigated as well. The roughness of liquid-liquid interface is low enough in the experimental results. Furthermore, as for the high resolution and convenience of AFM, the molecular structure of liquid might be investigated in the future.

Optical transition process in AgOx super-resolution near-field structure

A sandwiched 15 nm AgOx thin film of the super‐resolution, near‐field optical disk was studied using a confocal Z‐scan system. Nonlinear optical properties of quartz glass/ZnS–SiO2 (170 nm)/AgOx (15 nm)/ZnS–SiO2 (40 nm) were measured using a Q‐switch Nd : YAG pulse laser of wavelength 532 nm, pulse width 0.7 ns, and 15.79 kHz repetition rate. Transmittance and reflectance of the sandwiched AgOx thin film show important optical responses at the focused position of Z‐scan. The dissociation processes of AgOx, recombination of the silver and oxygen, and the resonance of the localized surface plasmon of the nano‐composites of the AgOx thin film are correlated to transmittance and reflectance at the focused position of the Z‐scan for different input laser powers. An irreversible upper threshold intensity of 4.40 × 106 mW cm−2 at the focused position was found. A reversible working window of the focusing intensity between 1.86 × 106 and 4.40 × 106 mW cm−2 was measured with sandwiched AgOx thin film alone. The near‐field interactions of the AgOx thin film and the recording layers of super‐resolution near‐field optical disk are also discussed.

Measurements of nonlinearity of AgOx super-resolution near-field structure

Third-order nonlinear optical properties of cover glass coated with different metal films are studied by using a focused pulse laser (λ=532 nm, pulse width 0.7ns, repetition rate 15.79kHz) with a Z-scan system. The results of open-aperture mode Z-scan shows high transmittance in the AgOx sample. The enhanced third-order nonlinear coefficients were examined by close-aperture mode Z-scan. The plasmon excitation and thermal relaxation were discussed for experimental results.

Far-field nonlinear optical absorption in AgOx superresolution near-field structure

Nonlinear optical properties of cover glass/ZnS-SiO2(130nm)/AgOx(15nm)/ZnS- SiO2(40nm) is studied by using a focused continuous-wave (CW) He-Ne laser ((lambda) equals632.8 nm) and a pulse laser ((lambda) equals532 nm, pulse width 0.7 ns, repetition rate 15.79 kHz) with a confocal Z-scan system. The transmission confocal Z-scan shows that the sample undergoes a phase transition at different incident intensities when the light source is changed. High reflectance happens at the focusing on AgOx film. The phase transition of the sample at higher incident laser power is due to silver oxide dissociating by the laser heating process.

Building the long, periodic ssDNA nanotemplate from tumor marker recognition for nanodevice

The programmable self-assembly of molecular nanostructures plays a crucial role in the development of nanodevices for molecule recognition. A self-assembly, periodic ssDNA nanotemplate based on aptameric recognition of tumor marker, PDGF was in situ constructed on the silicon-based substrate. The long, periodic ssDNA nanotemplate was further elongated up to 454 nm through rolling circle amplification at room temperature. The process of self-growing DNA nanotemplate based on aptameric recognition was directly visualized through nanoprobing technology.

Near-field images of surface plasmon eigenmodes in gold nanogratings

In this study, we have fabricated gold nanograting structures by using a focused-ion-beam system. The nano-optical properties were examined by using both the scattering- and transmission-mode near-field scanning optical microscope (NSOM). The surface plasmon (SP) eigenmode in this periodic nanostructure is directly observed by the scattering-mode NSOM. Two SP waves, localized fields and propagating waves, generating in the near field were found by the transmission-mode NSOM, and the dependence of wavelengths was studied. The relations of scattering- and transmission-mode results were discussed as well.