Femtosecond filamentation and supercontinuum generation in silver-nanoparticle-doped water

The authors report the investigation of filament and supercontinuum generation by focusing a femtosecond laser beam into water doped with silver nanoparticles. The silver nanoparticles enhance the nonlinear optical response of water, leading to broadening of supercontinuum spectra in self-focused femtosecond filaments. During the propagation of the supercontinuum light in the filament, the silver nanoparticles preferentially scatter the short-wavelength light near the plasmon resonant wavelength peak, followed by the scattering of the long-wavelength light. Thus, a side view of the filament shows a full-color spectrum in the visible range, which is herein called "rainbow filament." (c) 2007 American Institute of Physics.

超分辨远场生物荧光成像——突破光学衍射极限

长期以来,远场光学荧光显微镜凭借其非接触、无损伤、可探测样品内部等优点,一直是生命科学中最常用的观测工具。但由于衍射极限的存在,使传统的宽场光学显微镜横向和纵向的分辨率分别仅约为230 nm和1000 nm。为了揭示细胞内分子尺度的动态和结构特征,提高光学显微镜分辨率成为生命科学发展的迫切要求,在远场荧光显微镜的基础上,科学家们已经发展出许多实用的提高分辨率甚至超越分辨率极限的成像技术。例如,采用横向结构光照明提高横向分辨率到约100 nm,利用纵向驻波干涉效应将纵向分辨率提高5~10倍。然而,直到在光学荧光显微镜中引入非线性效应后,衍射极限才被真正突破,如受激荧光损耗显微镜利用非线性效应实现了30~50 nm的三维分辨率。另外应用荧光分子之间能量转移共振原理以及单荧光分子定位技术也可以突破衍射极限,甚至可以将分子定位精度提高到几个纳米的量级。

Photorefractive performance of a novel multifunctional inorganic-organic hybridized nanocomposite sensitized by CdS nanoparticles

A novel multifunctional inorganic-organic photorefractive (PR) poly(N-vinyl)-3-[p-nitrophenylazolcarbazolyl-CdS nanocomposites with different molar ratios of US to poly(N-vinyl)-3-[p-nitrophenylazo]carbazolyl (PVNPAK) were synthesized via a postazo-coupling reaction and chemically hybridized approach, respectively. The nanocomposites are highly soluble and could be obtained as film-forming materials with appreciably high molecular weights and low glass transition temperature (T,) due to the flexible spacers. The PVNPAK matrix possesses a highest-occupied molecular orbital value of about -5.36 eV determined from cyclic voltammetry. Second harmonic generation (SHG) could be observed in PVNPAK film without any poling procedure and 4.7 pm/V of effective second-order nonlinear optical susceptibility is obtained. The US particles as photosensitizers had a nanoscale size in PVNPAK adopting transmission electron microscopy. The improvement of interface quality between US and polymer matrix is responsible for efficient photoinduced charge generation efficiency in the nanocomposites. An asymmetric optical energy exchange between two beams on the polymer composites PVNPAK-CdS/ECZ has been found even without an external field in two-beam coupling (TBC) experiment, and the TBC gain and diffraction efficiency of 14.26 cm(-1) and 3.4% for PVNPAK-5-CdS/ECZ, 16.43 cm(-1) and 4.4% for PVNPAK-15-CdS/ECZ were measured at a 647.1 nm wavelength, respectively.

Read-only memory disk with AgOx super-resolution mask layer

A novel read-only memory (ROM) disk with an AgOx mask layer was proposed and studied in this letter. The AgOx films sputtered on the premastered substrates, with pits depth of 50 nm and pits length of 380 nm, were studied by an atomic force microscopy. The transmittances of these AgOx films were also measured by a spectrophotometer. Disk measurement was carried out by a dynamic setup with a laser wavelength of 632.8 nm and a lens numerical aperture (NA) of 0.40. The readout resolution limit of this setup was λ/(4NA) (400 nm). Results showed that the super-resolution readout happened only when the oxygen flow ratios were at suitable values for these disks. The best super-resolution performance was achieved at the oxygen flow ratio of 0.5 with the smoothest film surface. The super-resolution readout mechanism of these ROM disks was analyzed as well.

Two- and three-photon absorption in a novel fluorene-based compound

A novel symmetrical charge transfer fluorene-based compound 2,7-bis (4-methoxystyryl)-9, 9-bis (2-ethylhexyl)-9H-fluorene (abbreviated as BMOSF) was synthesized and its nonlinear absorption was investigated using two different laser systems: a 140-fs, 800-nm Ti:sapphire laser operating at 1-kHz repetition rate and a 38-ps, 1064-nm Nd:YAG pulsed laser operating at 10-Hz repetition rate, respectively. Unique nonlinear absorption properties in this new compound were observed that rise from multiphoton absorption. The nonlinear absorption coefficients were measured to be 6.02

纳米光存储薄膜结构的光学性质

近场超分辨纳米薄膜结构可以突破衍射极限实现纳米尺寸信息存储,是下一代海量存储技术的重要方案之一,也是纳米光子学研究中的热点。纳米膜层结构基于激光作用下的非线性局域光学效应实现超分辨。分析了超分辨近场薄膜结构突破衍射极限的光学原理,对超分辨纳米薄膜结构的表面等离子体激发特性、非线性光学特性、近场光学特性和超透镜效应等重要光学性质的最新研究进展做了系统介绍。

Spectral investigation of Yb-doped calcium pyroniobate crystal

Ytterbium-doped calcium pyroniobate single crystal has been grown for the first time. Spectral properties of Yb: Ca2Nb2O7 were investigated by emission and absorption spectra. Its cooperative luminescence and fluorescence lifetime were also studied. Yb ions in Ca2Nb2O7 showed very broad absorption and emission bandwidth and relatively large absorption and emission cross-sections. Along with other optical properties, this Yb-doped crystal would be a potential self-frequency doubling femtosecond laser gain material. (C) 2007 Published by Elsevier B.V.

Wavelength conversion based on degenerate-four-wave-mixing with continuous-wave pumping in silicon nanowire waveguide

We present a comprehensive numerical study on the all-optical wavelength conversion based on the degenerate four-wave-mixing with continuous-wave pumping in the silicon nanowire waveguide. It is well known that the conversion efficiency and the 3-dB bandwidth can be greatly affected by the phase-matching condition. Through proper design of the waveguide cross-section, its dispersion property can be adjusted to satisfy the phase-matching condition and therefore effective wavelength conversion can be achieved in a large wavelength range. Generally, the group velocity dispersion plays a dominant role in the wavelength conversion. However, the fourth-order dispersion takes an important effect on the wavelength conversion when the group velocity dispersion is near the zero-point. Furthermore, the conversion efficiency and the 3-dB bandwidth can also be affected by the interactive length and the initial pump power. Through the numerical simulation, the optimal values for the interactive length and the initial pump power, which are functions of the propagation loss, are obtained to realize the maximum conversion efficiency. (C) 2008 Elsevier B.V. All rights reserved.

Research progress of electronic properties of self-assembled semiconductor quantum dots

Self-assembled semiconductor quantum dot is a new type of artificially designed and grown function material which exhibits quantum size effect, quantum interference effect, surface effect, quantum tunneling-Coulumb-blockade effect and nonlinear optical effect. Due to its advantages of less crystal defects and relatively simpler fabrication technology, this material may be of important value in the research of future nanoelectronic device. In the order of vertical transport, lateral transport and charge storage, recent advances in the electronic properties of this material are brefly introduced, and the problems and perspectives are analyzed.

Dielectric relaxation of poled polymer DCNP/PMMA

We have prepared the polymer thin films of a 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DChTP)/poly (methyl methacrylate) (PMMA) guest-host system by spin coating. In order to investigate their temporal and temperature stability, we have measured their dielectric relaxation spectra including the frequency dependence of the real and imaginary parts of dielectric constants. The investigated frequency ranged from 50 Hz to 10 MHz. The measured temperature range above the glass transition temperature T-g (95 degrees C) of the DCNP/PMMA system was from 95 degrees C to 1250C. By using the Adam-Gibbs model, the temperature dependence of the characteristic time tau above T-g was fitted, and the values of the characteristic times tau below T-g were estimated. The lifetimes of the polymer were evaluated by the Kohlrausch-Williams Watts (KWW) empirical decay model. (C) 2000 Elsevier Science B.V. All rights reserved.

Investigation of the polyetherketone guest-host DR1/PEK-c polymer films by real-time monitoring of the second-harmonic generation

The real-time monitoring of the second-harmonic generation (SHG) was used to optimize the poling condition and to study the nonlinear optical (NLO) properties of the polyetherketone (PEK-c) guest-host polymer films. The high second-order NLO coefficient chi(33)((2)) = 11.02 pm/v measured at 1.064 mu m was achieved when the weight percent of DR1 guest in the polymer system is 20%. The NLO activity of the poled DR1/PEK-c polymer film can maintain more than 80% of its initial value when temperature is under 100 degrees C, and the normalized second-order NLO coefficient can maintain more than 85% after 2400 s at 80 degrees C. (C) 2000 Elsevier Science Ltd. All rights reserved.

Interactions of three dual-dressing effects of four-wave mixing in a five-level atomic system

We study the four-wave mixing (FWM) in an opening five-level system with two dressing fields. There are three kinds of doubly dressing mechanisms (parallel cascade, sequential cascade, and nested cascade) in the system for doubly dressed four-wave mixing. These mechanisms reflect different correlations between two dressing fields and different effects of two dressing fields to the FWM. Investigation of these mechanisms is helpful to understand the generated high-order nonlinear optical signal dressed by multi-fields.

Z-scan theory based on a diffraction model

Based on Fresnel-Mrchhoff diffraction theory, a diffraction model of nonlinear optical media interacting with a Gaussian beam has been set up that can interpret the Z-scan phenomenon in a new way. This theory not only is consistent with the conventional Z-scan theory for a small nonlinear phase shift but also can be used for larger nonlinear phase shifts. Numerical computations indicate that the shape of the Z-scan curve is greatly affected by the value of the nonlinear phase shift. The symmetric dispersionlike Z-scan curve is valid only for small nonlinear p base shifts (\Deltaphi(0)\ < pi), but, with increasingly larger nonlinear phase shifts, the valley of the transmittance is severely suppressed and the peak is greatly enhanced. The power output through the aperture will oscillate with increasing nonlinear phase shift caused by the input laser power. The aperture transmittance will attenuate and saturate with increasing Kerr constant. (C) 2003 Optical Society of America.

Corona poling of liquid crystalline polymers with nitroazobenzene side chains

The orientational behavior of liquid crystalline polymers with para-nitro azobenzene as side chains under electric field was studied by UV-visible spectroscopy. The results showed that lambda(max) of the poled polymer films was around 394nm, compared to that of the unpoled films, the absorption decreased due to poling. The orientational parameters increased linearly with the increase of the electric field. The temporal stability of the poled polymer film is good at room temperature. This kind of materials showed promise application as nonlinear optical component in photorefractive polymers.