Effects of annealing on luminescence efficiency of large-size YAG:Ce crystal grown by temperature gradient techniques

<正>YAG:Ce crystal with a diameter of 110 mm is successfully grown by the temperature gradient technique (TGT).The effects of annealing on the luminescence efficiency of YAG:Ce crystal are investigated,and the optimal annealing temperature and atmosphere are obtained.The mechanism of variation behavior of the luminescence efficiency of YAG:Ce under different annealing conditions is discussed and some details on the luminescence associated with color centers are analyzed.     

Atomic force microscopy investigation of growth process of organic TCNQ aggregates on SiO2 and mica substrates

<正>Deposition patterns of tetracyanoquinodimethane(TCNQ) molecules on different surfaces are investigated by atomic force microscopy.A homemade physical vapour deposition system allows the better control of molecule deposition. Taking advantage of this system,we investigate TCNQ thin film growth on both SiO_2 and mica surfaces.It is found that dense island patterns form at a high deposition rate,and a unique seahorse-like pattern forms at a low deposition rate.Growth patterns on different substrates suggest that the fractal pattern formation is dominated by molecule-molecule interaction.Finally,a phenomenal "two-branch" model is proposed to simulate the growth process of the seahorse pattern.     

Study of lower emittance dedicated synchrotron radiation mode for the BEPCⅡ

In this paper,a dedicated synchrotron radiation （SR） mode for the BEPCⅡ with an emittance of 85 nm has been designed,including the linear lattice,chromaticity correction and dynamic aperture optimization.The emittance of the new mode is about 60% of the previous mode used for routine operation of the BEPCⅡ .The effect of wigglers on the linear lattice was compensated and the total dynamic aperture including the wigglers’ nonlinear effect was estimated.The preliminary commissioning at the end of 2008 and the formal operation with the new mode confirmed its merits.     

Density functional theory study of surface catalysis and adsorption on several elements in Group I-B and VIII

This review deals with the high-throughput field in surface catalysis and adsorption. Special focus is placed on advanced methods for knowledge discovery such as density functional theory (DFT) simulations. An inventory of successful cases on several elements in Group I-B and VIII is reported, including the relevant data and knowledge management, which are very important in chemical industry, fuel cell, and environment protection, for both scientific and economical reasons.      

Three-dimensional photonic bandgap crystals of titania hollow spheres at visible wavelengths

A non-close-packed three-dimensional photonic crystal of titania hollow spheres has been fabricated. The fabricated process is based on the silica template technique, thermal sintering, and the sol–gel process. The band-structure calculations and optical measurements both indicate that a quasi-full three-dimensional photonic bandgap located at the visible wavelength has been presented between the eighth and ninth bands. This indicates that the non-close-packed structure of titania hollow spheres was easier to open the complete photonic bandgaps than other face-centered cubic structures made by self-assembling methods at the visible region.     

Up-conversion emissions of Er<Superscript>3+</Superscript>-Yb<Superscript>3+</Superscript> codoped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles by the arc discharge synthesis method

The Er³⁺-Yb³⁺ codoped Al₂O₃ nanoparticles with an average particle size of about 50 nm have been synthesized by an arc discharge synthesis method. The green and red up-conversion emissions centered at about 526, 547 and 677 nm, corresponding respectively to the ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, were detected by a 978-nm semiconductor laser diode excitation. The Annealing has evident effect on the up-conversion emissions of the samples: The red up-conversion emission is noticeable before annealing; however, the green up-conversion emission becomes predominant after annealing. The mixture of (Er,Yb)₃Al₅O₁₂ and α-(Al,Er,Yb)₂O₃ phases is more favorable for green up-conversion emissions due to an enhancement of the ESA (I) of ⁴I_11/2+a photon→⁴F_7/2 and ET (III) of ²F_5/2(Yb³⁺)+⁴I_11/2(Er³⁺)→²F_7/2(Yb³⁺)+⁴F_7/2(Er³⁺) processes. The two-photon absorption up-conversion process is involved in the green and red up-conversion emissions. The results have proved that arc discharge synthesis is a new promising preparation technology for optical materials. Supported by National Natural Science Foundation of China (Grant No. 10804015), the Scientific Research Foundation for Doctor of Liaoning Province (Grant No. 20071095), and the Educational Committee Foundation of Liaoning Province (Grant No. 2008123)     

从平面角和立体角讨论静电场中的某些电场等价性

本文利用平面角的概念讨论了均匀带电的直线微元和圆弧微元在圆心处的场强等价性,并将结论推广到一些均匀带电的线几何体;然后利用立体角的概念进一步讨论带电的平面微元和球面微元在球心处的场强等价关系,结果表明,只有非均匀的电荷面密度才能使两者等价．     

The generation of Entangled Qudits and their Application in Probabilistic Superdense Coding

A scheme of the generation of entangled qutrits is presented, and then is generalized to entangled ququads and entangled qudits. With the entangled qutrits, an experimental scheme of probability superdense coding with only linear optical elements is proposed. It is shown that this scheme will be suitable for the entangled ququads, even for the entangled qudits if some nonlinearity is used. This scheme is feasible in the laboratory with the current experimental technology.     

Laser diode end-pumped Yb:YAG/LBO green laser

With a type-I critical phase-matching LBO crystal, an intracavity frequency doubled solid-stated Yb:YAG green laser is reported. Using a plano-concave resonator, with pump power of 1.37 W, 24.5 mW TEM₀₀ continuous wave laser at 525 nm was obtained. The optical conversion efficiency is 1.8%. By adjusting the placed angle of LBO, several lasers wavelength from 525.0 to 537.8 nm could be extracted. The maximum output power at 537.8 nm is 3.1 mW.     

Performance of dispersed Rayleigh interferometer on the active cophasing and alignment testbed

We report the laboratory experiment on a segmented mirror testbed that shows the use of a dispersed Rayleigh interferometer to phase segmented mirrors.Segment alignment of tip-tilt is fulfilled by overlapping diffraction pattern centroids of the three individual segments on the focal plane.A spherical interferometer is introduced to evaluate the performance of piston, tip-tilt sensing, and control closed-loop, and finally a total residual root-mean-square (RMS) surface error of about 45 nm is achieved, in which a typical error of about 20 nm is contributed by piston.These results demonstrate that the dispersed Rayleigh interferometer can successfully sense the piston of segmented mirrors and be used in phasing segmented telescopes under extensive studies.