Shencheng Fu

Photoinduced anisotropy and polarization holographic gratings formed in Ag/TiO2 nanocomposite films.

Formation of anisotropy and polarization holographic gratings (s-s, p-p, and s-p) in Ag/TiO2 nanocomposite films were investigated using Nd:YAG lasers (532 nm) as pumping and writing source, respectively. The observations can be well explained by the anisotropic photodissolution of Ag nanoparticles, the photomobility and reduction of Ag+ ions, and the light scattering induced by Ag nanoparticles. Taking these effects into account, a phenomenological model based on simultaneous formation of the absorption grating and the two coupling phase gratings is proposed and found to be in good agreement with the measurements. The main differences in the three polarization grating formation processes are also discussed.

Blu-ray-sensitive localized surface plasmon resonance for high-density optical memory

Tunable spectrum-response is desired for efficient photo-energy transformation. Blu-ray (~405u2009nm) and polarization sensitive Ag/TiO2 nanocomposite films are thus fascinating in application of fast-response and high-density optical memory device. The Ag/TiO2 film has the ability of replicating hologram based on optical coherence by laser-stimulated dissolution of Ag nanoparticles (NPs). The rate and efficiency of the dissolution are supposed to be enhanced by introducing uniform and small-sized Ag NPs in TiO2 nanoporous films. However, no effective methods have been proposed to resolve this issue by now. Here, we develop a simple method of thermal-reduction to obtain high-density, space-dispersed and extremely small-sized Ag NPs in TiO2 nanoporous films pretreated with tannic acid. The film shows both high and narrow absorbance band centered at ~405u2009nm. Diffraction efficiency of the blu-ray holographic storage in the Ag/TiO2 film is improved by one order of magnitude compared to the traditional UV-reduced sample. Based on such properties, polarization-multiplexing holograms are able to be written at 405u2009nm and readout with little crosstalk. This work provides effective solutions for sensitizing localized surface plasmon resonance at near-UV region, extending the growth range of Ag NPs in the volume of TiO2, and resultantly, realizing high-density optical memory.

Multiplexed holographic gratings recorded by 405nm laser in polymer film containing spirooxazines

Multiple holographic gratings were recorded by 405nm laser in the same location of spirooxazine doped polymer films using peristrophic multiplexing techniques. Diffraction efficiency of each grating was controlled almost uniform by adjusting recording time. It was found that the growth rate of the holographic grating recorded later was lower than that of the earlier one, resulting from the decreased population of spirooxazine molecules. A kinetics description for the overlapped isomerization gratings agrees well with experimental results. Due to the thermal stability of the isomerization grating, multiple interference fringes in the photochromic film were reserved and observed by Confocal Laser Scanning Microscope.

Fluorescent Holographic Fringes with a Surface Relief Structure Based on Merocyanine Aggregation Driven by Blue-violet Laser

Stability and integration are the goals for developing photonic devices. Spirooxazines have the property of photoinduced merocyanine-aggregation in polymer matrix, which can be applied to fluorescence emission and stable information storage. Although visible light coherent radiation with UV-assist has been used to achieve polarization-modulated holographic memory in spirooxazine doped PMMA films, the complexity of optical systems is increased and the aggregation ability of merocyanine is decreased. Here, we report that fluorescent holographic gratings with a surface relief structure can be inscribed in the film via sole irradiation of 403.4u2009nm. Time-dependent photo-anisotropy and holographic dynamics were both investigated with different power densities of the near-UV laser. The non-exponential photokinetics was explained by the sequential formation of mono- and aggregate-merocyanine molecules. The appearance of merocyanine aggregates is found to be beneficial to the long-term holographic memory with fluorescent emission. This work provides a research strategy for the integrity of storage, display and micro-fabrication of organic functional-devices.

Visible laser-assisted reduction of plasmonic Ag nanoparticles with narrow-band optical absorption for colored holographic reconstruction

Noble metal plasmonic resonance has been utilized in optical data storage widely for its excellent photo-transformation efficiency. TiO2 nanoporous films deposited with Ag nanoparticles present outstanding polarization-response and color-modulation ability. However, the low exposure-sensitivity at single wavelength inhibits their application in optical information processing, which is urgent to be improved by innovative methods. Here, we report that Ag nanoparticles were deposited efficiently via continuous laser irradiation in the TiO2 nanoporous film treated by tannic acid, presenting high-efficient monochromic absorption property. As a result, two sets of holograms were recorded sequentially at the same point of the film with orthogonal circular polarization configurations. The colored reconstruction of the mixed holograms was achieved by utilizing laser polarization state as chrominance segmentation channel. Our method provides a distinctive route for enhancing the photo-energy conversion efficiency of plasmonic nanoparticles, and paves a way to develop advanced display device.

Selective photo-oxidation induced bi-periodic plasmonic structures for high-density data storage

Stable and controllable optical memory is necessary for the development of current information technology. In this context, Ag/TiO2 films have received much attention for their photosensitivity in wavelength and polarization, which can be applied to high-density optical storage. Here, we carried out dual-wavelength holographic recording using 403.4xa0nm and 532xa0nm lasers, and obtained mixed microfringes based on selective photodissolution of Ag nanoparticles of various sizes in TiO2 nanoporous films. Two recording methods of simultaneous and sequential multiplexing were investigated. It was found that using simultaneous irradiation it is easier to obtain equivalent efficiency in both spectral hole burning and multiplexed grating diffraction, compared with the sequential one. The results can be explained by the Time-accumulation effect during Ag+ ion diffusion and migration in holographic recordings. Based on such properties, multiplexed-holographic fringes with uniform contrast were reserved by simultaneous recording in Ag/TiO2 films. This work provides a new strategy for fabrication of photonic devices with complex microstructures.

Nonvolatile plasmonic holographic memory based on photo-driven ion migration

Stability of data storage is essential for optical information processing. TiO2 nanoporous films loaded with small-sized Ag nanoparticles thus attracted much attention due to their fast and polarization-sensitive photochemical response, which is able to realize optical phase modulation and high-density optical memory. However, little attention was given to the modulation of the silver ion migration, which plays a key role in anti-erasure of the recorded hologram. In this paper, the strong coupling of two phase gratings was achieved by long-term recording in the Ag-TiO2 film irradiated with a pair of coherent left- and right-hand circular polarization lights from a Blu-ray (∼405u2009u2009nm) laser. The migration of Ag+ ions was enhanced by the electronic field gradient force. A stable polarization holographic grating was obtained by this method and observed by a polarizing microscope. This work provided a strategy for a nonvolatile device based on photo-driven ion migration.

Multi-wavelength holographic storage in PMMA film containing spirooxazines

Holographic gratings were recorded in spirooxazine doped PMMA films by blue-violet laser (405nm), Nd:YAG laser (532nm) and He-Ne laser (632.8nm), respectively. It was found that the photo-dynamics of the holographic grating was dependent on recording wavelength for the photochromic characteristics of spirooxazines. A theoretical description of orientation and isomerization gratings agrees well with the experimental results. It was also found that a pure isomerization grating is formed by two interferential 405nm beams while a mixed grating consisting of isomerization and orientation components is formed by the visible interferential beams (532nm or 632.8nm). Due to the long life of the isomerization gratings, the holographic interference fringes with different periods were clearly observed by Confocal Laser Scanning Microscope.