989 resultados para RESONANCE SPECTRA


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0.5 at.% Yb:YAlO3(YAP), 5 at.% Yb:YAP and 15 at.% Yb:YAP were grown using the Czochralski method. Their absorption and fluorescence spectra were measured at room temperature and their emission line shape was calculated using the method of reciprocity. It was observed that the fluorescence spectra changed appreciably with the increasing of Yb concentration. For 0.5 at.% Yb:YAP, the line shape of fluorescence is very similar with the calculated emission line shape; with the increasing of Yb doping concentration, the line shape of fluorescence is very different from the calculated emission line shape. These phenomena are caused by the strong self-absorption at 979 and 999 nm for Yb:YAP. (c) 2005 Elsevier B.V. All rights reserved.

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kinds of Yb3+- and Na+-codoped CaF2 laser crystal with different Na:Yb ratios of 0, 1.5, and 10 are grown by the temperature gradient technique. Room-temperature absorption, photoluminescence spectra, and fluorescence lifetimes belonging to the transitions between ground state F-2(7/2) and excited state F-2(5/2) of Yb3+ ions in the three crystals are measured to study the effect of Na+. Experimental results show that codoping Na+ ions in different Na:Yb ratios can modulate the spectroscopy and photoluminescence properties of Yb3+ ions in a CaF2 lattice in a large scope. (c) 2005 Optical Society of America

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Undoped Y2SiO5 single crystal was grown by the Czochralski method. The samples were optically polished after orienting and cutting. The rhombus and quadrangular dislocation etching pits, the low-angle grain boundaries and the inclusions in the samples were observed using optical microscope and scanning electron microscope. The absorption spectra were measured before and after H-2 annealing or air annealing. The absorption edge of Y2SiO5 crystal was determined to be about 202 nm. The absorption coefficient of Y2SiO5 crystal decreased after H-2 annealing and obviously increased after air annealing. (C) 2005 Elsevier B.V. All rights reserved.

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A V:YAG single crystal was grown by the temperature gradient technique (TGT) with graphite-heating elements. The as-grown crystal has different colorations of light green and yellow brown in different parts. Distribution of vanadium in three samples with different colorations was determined by inductively coupled plasma-mass spectrometry. From the absorption spectrum of the yellow-brown part with peaks at 370, 820 and 1320nm, we can deduce that the reducing atmosphere of carbon diffused from the heating elements can increase the concentration of tetrahedral V3+ ions and induce F color centers. All three samples exhibited light-green color after annealing in vacuum or H-2 atmospheres. In the vacuum annealing process, the V3+ ions in tetrahedral positions were enhanced through two methods: one method is the exchanging of octahedral V3+ and tetrahedral Al3+ ions in neighboring sites under thermal excitation, the other is that F color centers were thoroughly eliminated and the escaped free electrons could be captured by V ions with higher valance states to further improve the concentration of tetrahedral V3+ ions. Besides the two mechanisms, the H-2 annealing process greatly improved the V-tetra(3+) ions through the reduction effect of H-2. (c) 2006 Elsevier B.V. All rights reserved.

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应用中频感应提拉法生长出不同掺杂浓度的Yb:FAP激光晶体,运用电感耦合等离子体原子发射光谱仪(ICP-AES)测定了Yb^3+离子存Yb:FAP晶体中的分凝系数约为0.03。随着晶体的生长,晶体中Yb^3+离子的轴向浓度逐渐增大。研究Yb:FAP晶体在77K和300K温度下的吸收光谱发现,振动谱的变化主要是由电子-声子近共振耦合作用引起的。系统地研究了不同Yb^3+离子掺杂浓度Yb:FAP晶体的吸收光谱和荧光光谱。通过吸收光谱的测量计算了晶体的吸收截面。Yb:FAP晶体在904nm和982nm处存在Yb

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LiAlO2 single crystals doped with Ti at concentration 0.2 at.% are grown by the Czochralskl technique with dimensions Phi 42 x 55 mm. Ti ions in the crystal are quadrivalence proven by comparing the absorption and fluorescence spectra of pure LiAlO2 and Ti: LiAlO2. After air and Li-rich atmosphere annealing, the absorption peaks in the range of 600-800nm disappear. We conclude that 682 and 756nm absorption peaks are attributed to the V-Li and V-O absorptions, respectively. The peaks at 716nm and 798nm may stem from the V-Li(+) and F+ absorptions. The colour-centre model can be applied to explain the experimental phenomena. Ti4+-doping produces more lithium vacancies in the LiAlO2 crystal. The intensities of [LiO4] and the associated bonds remain unchanged, which improves the anti-hydrolyzation and thermal stability of LiAlO2 crystals.

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For the first time, the effect of Na+ on crystal structure, valence state of Yb ions, spectroscopic properties of YbF3-doped CaF2 system was systematically studied. Na+ can greatly suppress the deoxidization of Yb3+ to Yb2+. Absorption and emission spectra showed codoping Na+ with different Na:Yb ratios can modulate the spectroscopy and photoluminescence properties of Yb3+ ions in CaF2 lattice in a large scope. The emission lifetime and quantum efficiency of Yb3+ in CaF2 were greatly enhanced by the codopant of Na+. The potential laser performances of the new Yb, Na-codoped CaF2 crystals were predicted. (c) 2005 Elsevier B.V. All rights reserved.

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Yb:Y3Al5O12 (Yb:YAG) single crystals with Yb doping concentration 0.5 at.%, 5 at.%, 15 at.%, 25 at.%, 50 at.%, 100 at.% and Yb:YAlO3 (Yb:YAP) single crystals with Yb doping concentration 0.5 at.%, 5 at.%, 15 at.%, 30 at.% were grown by the Czochralski process. The fluorescence spectra of these crystals and the effects of self-absorption on the shape of the fluorescence spectra were studied. Through comparing the fluorescence spectra of Yb:YAG and Yb:YAP, all results indicate that the effects of self-absorption on the fluorescence spectra of Yb:YAP are remarkably stronger than that of Yb:YAG at the same Yb concentration. (c) 2006 Elsevier B.V. All rights reserved.

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gamma-LiAlO2 single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X-ray rocking curve and chemical etching. The effects of air-annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO2 were also investigated in detail. The results show that the as-grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0 x 10(3) cm(-2). The VTE-treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air-annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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This paper reports that the TM3+:Lu2SiO5 (Tm:LSO) crystal is grown by Czochralski technique. The room-temperature absorption spectra of Tm:LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Omega(2)=9.3155 x 10(-20) cm(2), Omega(4)=8.4103 x 10(-20) cm(2), Omega(6)=1.5908 x 10(-20) cm(2), the fluorescence lifetime is calculated to be 2.03 ms for F-3(4) -> H-3(6) transition, and the integrated emission cross section is 5.81 x 10(-18) cm(2). Room-temperature laser action near 2 mu m under diode pumping is experimentally evaluated in Tm:LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuous-wave maximum output power of 0.67 W. The emission wavelengths of Tm:LSO laser are centred around 2.06 mu m with spectral bandwidth of similar to 13.6 nm.

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The electronic structures and absorption spectra for the perfect PbMoO4 crystal and the crystal containing lead vacancy V-Pb(2-) with lattice structure optimized are calculated using density functional theory code CASTEP. The calculated absorption spectra of the PbMoO4 crystal containing V-Pb(2-) exhibit three absorption bands peaking at 2.0 eV (620 nm), 3.0 eV (413 run) and 3.3 eV (375 nm), which are in good agreement with experimental values. The theory predicts that the 390 nm, 430 nm and 580 run absorption bands are related to the existence of V-Pb(2-) in the PbMoO4 crystal.

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National Nature Science Foundation of China (Grant No. 60607015)

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Electric fields inside guided-mode resonance filters (GMRFs) may be intensified by resonance effects. The electric field enhancement is investigated in two GMRFs: one is resonant at normal incidence, the other at oblique incidence. It is shown that the two GMRFs exhibit different behaviors in their electric enhancement. Differences between the electric field distributions of the two GMRFs arise because coupling between counter-propagating modes occurs in the first case. It is also shown that the order of the electric field of maximum amplitude can be controlled by modulation of the dielectric constant of the grating. (c) 2006 Optical Society of America.

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A normal-incidence nonpolarizing guided-mode resonance filter is designed. There are two waveguide layers and one grating layer in the filter. By adjusting the distance between the two waveguide layers, the same resonance wavelength for both TE and TM polarization can be achieved. An antireflection design method is also used to decrease the sideband reflection of the filter. The results show that the filter has high reflection, more than 99.9% at 500 nm, and the FW-HMs of TE- and TM-polarized light are 2.16 and 0.15 nm, respectively. (C) 2009 Optical Society of America