Comment on: Computation of the optical trapping force using an FDTD based technique

In this comment, problems associated with an oversimplified FDTD based model used for trapping force calculation in recent papers "Computation of the optical trapping force using an FDTD based technique" [Opt. Express 13, 3707 (2005)], and "Rigorous time domain simulation of momentum transfer between light and microscopic particles in optical trapping" [Opt. Express 12, 2220 (2004)] are discussed. A more rigorous model using in Poynting vector is also presented.

A new strategy of enhancing two-photon absorption in benzothiazole-containing fluorene molecules: Introduction of auxiliary donor-acceptor effects

A series of benzothiazole-containing fluorene molecules have been designed and their one- and two-photon absorption properties have been investigated theoretically by using the ZINDO method. The effects of electron-excessive/deficient heterocyclic bridges as auxiliary donors (auxD)/acceptors (auxA) on TPA cross-sections were studied. The results show that the molecules with D-pi-auxA-A, D-aux D-pi-A, or D-auxD-pi-auxA-A structure types have large TPA cross-section, which can be a valuable strategy in the design of two-photon absorption materials. Also, a linear relationship between the first hyperpolarizability and the TPA cross-section is observed. (c) 2006 Elsevier B.V. All rights reserved.

Theoretical investigation on the one- and two-photon absorption properties for a series of symmetrical charge transfer fluorene-phenylene and fluorene-thiophene derivatives

One- and two-photon absorption properties of a series of fluorene derivatives with symmetrical charge transfer D-IT-D and A-IT-A structural motifs have been theoretically investigated with ZINDO/S method. The optimized structures and the characterization of frontier molecular orbitals were obtained by using AMI calculations. Two-photon absorption properties of molecules have been studied using three-state model. The calculation results have shown that fluorene-thiophene derivatives exhibit larger two-photon absorption cross-section as compared with other studied molecules. To illustrate the results, the crucial effects of thiophene ring on fluorenethiophene derivatives and the net charge changes on the pi-conjugated bridges are analyzed theoretically. (c) 2006 Elsevier B.V. All rights reserved.

Optical parameters and absorption of copper (II)-azo complexes thin films as optical recording media

Smooth thin films of three kinds of azo dyes of 2-(5'-tert-butyl-3'-azoxylisoxazole)-1, 3-diketones and their copper (II)-azo complexes were prepared by the spin-coating method. Absorption spectra of the thin films on a glass substrate in the 300-600 nm wavelength region were measured. Optical constants (complex refractive index N=n+ik) and thickness of the thin films prepared on single-crystal silicon substrate in the 300-600 nm wavelength region were investigated on rotating analyzer-polarizer type of scanning ellipsometer, and dielectric constants epsilon(epsilon=epsilon(1)+i epsilon(2)), absorption coefficients alpha as well as reflectance R of thin films were then calculated. In addition, one of the copper (II)-azo complex thin film prepared on glass substrate with an Ag reflective layer was also studied by atomic force microscopy (AFM) and static optical recording. AFM study shows that the copper (II)-azo complex thin film is very smooth and has a root mean square surface roughness of 1.89 nm. Static optical recording shows that the recording marks on the copper (II)-azo complex thin film are very clear and circular, and the size of the minimal recording marks can reach 200 nm. (c) 2004 Elsevier B.V. All rights reserved.

Synthesis, spectroscopic properties and thermal stability of metal(II) tetraazaporphyrin complexes with two strong wavelength absorption

Three kinds of metal(II) tetraazaporphyrin complexes with blue-violet and red light wavelength absorption were synthesized by refluxing tetraazaporphyrin ligand and different metal(II) ions, respectively. Their structures were confirmed by elemental analysis, LDI-TOF-MS, FT-IR and UV-Vis. The solubility of metal(II) tetraazaporphyrin complexes in organic solvents and absorption properties of their chloroform solution and films on K9 glass in the region 250-800 nm were measured. The influence on the difference of absorption maximum from metal(II) tetraazaporphyrin complexes to tetraazaporphyrin ligand by different metal(II) ions was studied. In addition, the thermal stability of the complexes was also evaluated. (c) 2006 Elsevier Ltd. All rights reserved.

Observation of ultrafast carrier dynamics in amorphous Ge2Sb2Te5 films induced by femtosecond laser pulses

The femtosecond pump-probe technique was used to study the carrier dynamics of amorphous Ge2Sb2Te5 films. With carrier density at around 10(20)-10(21) cm(-3), carriers were excited within 1 ps and recovered to the initial state for less than 3 ns. On the picosecond time scale, the carrier relaxation consists of two components: a fast process within 5 ps and a slow process after 5 ps. The relaxation time of the fast component is a function of carrier density, which increases from 1.9 to 4.3 ps for the carrier density changing from 9.7x10(20) cm(-3) to 3.1x10(21) cm(-3). A possible interpretation of the relaxation processes is elucidated. In the first 5 ps the relaxation process is dominated by an intraband carrier relaxation and the carrier trapping. It is followed by a recombination process of trapped carriers at later delay time. (c) 2007 American Institute of Physics.

Análise de cobertura de metal-metal por XRF

A proposta do referente estudo foi medir a espessura do depósito de um metal em outro metal base, ou seja, utilizar o processo eletroquímico de Galvanoplastia ou eletrodeposição deste metal, por meio da técnica de fluorescência de raios X (XRF). O uso desta técnica justificou-se pelo interesse em reduzir os custos excessivos durante o processo eletroquímico, bem como, minimizar as possíveis margens de erros para obter resultados satisfatórios nas medidas. Neste trabalho, incluíram-se as medidas da espessura do Níquel (Ni) e análises da intensidade de radiação incidentes e a radiação atenuante, em função da espessura dos elementos Cromo (Cr) e Zinco (Zn), considerando como metal base o elemento Ferro (Fe). Em decorrência disso, em todos os casos foram simulados os processos de deposição do metal onde foram incluídos os resultados de absorção de raios X, além de desprezar a influência de outros fatores como a temperatura, o pH, o tratamento de superfície, entre outros, os quais são necessários para considerar em cada caso.

Three-photon absorption-induced fluorescence and optical limiting effects in a fluorene derivative

This paper reports on the steady-state fluorescence, three- photon absorption-induced fluorescence emission and subsequently induced optical limiting behaviour of a fluorene derivative with D-pi-D structural motifs. The lifetime of the steady-state fluorescence is 0.903 ns. Large optical limiting behaviour induced by 3PA has also been demonstrated, and the nonlinear absorption coefficient gamma derived from 3PA fitting curves is 5.92 x 10(-20) cm(3)/W-2 and the corresponding molecular 3PA cross-section sigma(3)' is 1.14 x 10(-76) cm(6) s(2).

A large-area photolithography technique based on surface plasmons leakage modes

An atomic force microscope (AFM) assisted surface plasmons leakage radiation photolithography technique has been numerically demonstrated by using two-dimensional finite-difference time-domain (2D-FDTD) method. With the aid of a metallic AFM tip, particular characteristic of the Kretstchmann configuration to excite surface plasmons (SPs) is utilized to achieve large-area patterns with high spatial resolution and contrast, the photoresist could be exposed with low power laser due to the remarkable local field enhancement at the metal/dielectric interface and the resonant localized SPs modes near the tip. Good tolerance on the film thickness and incident angle has been obtained, which provides a good practicability for experiments. This photolithography technique proposed here can realize large-area, high-resolution, high-contrast, nondestructive, arbitrary-structure fabrication of nanoscale devices. (c) 2007 Elsevier B.V. All rights reserved.

A Z-scan model for optical nonlinear nanometric films

The Z-scan technique is useful for measuring the nonlinear refractive index of thin films. In conventional Z-scan theories, two effects are often ignored, namely the losses due to the internal multi-interference and the nonlinear absorption inside the sample. Therefore, the theories are restricted to relatively thick films. For films thinner than about 100 nm, the two effects become significant, and thus cannot be ignored. In the present work, we present a Z-scan theory that takes both effects into account. The proposed model calculation is suitable for optical nonlinear films of nanometric thickness. With numerical simulations, we demonstrate dramatic deviations from the conventional Z-scan calculations.

Cr~(2+):ZnSe的激光输出和调谐性能

Cr~(2+):ZnSe具有很宽的吸收带和发射带,是中红外波段优秀的可调谐激光材料。从吸收光谱、发射光谱以及角度调谐输出对Cr~(2+):ZnSe晶体的激光输出性能进行了研究。采用真空高温扩散法制备Cr~(2+):ZnSe晶体.获得了高浓度的Cr~(2+)离子掺杂的厚1.7 mm,直径10 mm的薄片ZnSe晶体。使用中心波长2.05μm,最大输出功率8 W的Tm离子掺杂的光纤激光器抽运,使用平凹腔结构搭建谐振腔,获得了最大平均功率1.034 W,中心波长2.367μm,线宽10 nm的连续激光输出。利用角度调谐的方法,对Cr:ZnSe晶体的调谐性能进行了研究,在100 nm范围内获得了调谐输出。

Cr^4＋：YAG被动调QNd：YAG陶瓷激光器的研究

介绍了近几年迅速发展的一种新型激光介质——透明Nd：YAG多晶陶瓷的发展状况，对比分析了多晶陶瓷与单晶的光谱特性、激光特性和连续实验研究情况。并对钛宝石激光器调谐至808nm，端面抽运Nd：YAG陶瓷被动调Q全固态激光器的脉冲运转进行了较为详细的理论分析和实验研究。采用初始透射率为90％的Cr^4＋：YAG可饱和吸收晶体，被动调Q的阈值功率为119mW，当端面抽运功率为465mW时，获得波长为1064nm，脉宽为16ns，重复频率为18．18kHz，单脉冲能量为3．4μJ，平均输出功率为61mW的稳定调Q