Time-Resolved Femtosecond Degenerate Four-Wave Mixing in LiNbO3：Fe,Mg Crystal

Forward degenerate four-wave mixing （DFWM） processes are investigated with a femtosecond pulsed laser in lithium niobate crystal doubly-doped with magnesium and iron （LiNbO3：Fe, Mg）. The pulse energy dependence reveals a pure third-order nonlinear response, and the third-order nonlinear susceptibility x^（3） in the material is evaluated to be 4.96 × 10^-13 esu. The time-resolved DFWM process shows a response time of x^（3） shorter than 100fs, which is due to the nonresonant electronic nonlinearities. Our results indicate that LiNbO3 crystals have potentials for ultrafast real-time optical processing systems, which require a large and fast x^（3） optical nonlinearity.     

微晶结构对氟氧化物玻璃陶瓷发光特性的影响

制备了成分相同的Er3+/Yb3+共掺氟氧化物玻璃和氟氧化物玻璃陶瓷样品，x射线衍射谱和荧光光谱表明热处理后玻璃陶瓷中形成了纳米结构的微晶，根据Judd Ofelt理论计算和差热曲线分析，证实稀土离子掺入PbF2微晶中.分别计算了热处理前后微晶态部分在玻璃体中所占的比例. 关键词： 微晶结构 玻璃陶瓷 荧光光谱     

Red Up-Conversion Luminescence Process in Oxyfluoride Glass Ceramics Doped with Er^3＋／Yb^3＋

The phonon-assisted quantum cutting (PQC) model is presumed to clarify the red up-conversion luminescence process in Er^3 /yb^3 co-doped glass ceramics by the excitation and emission spectra. The red up-conversion luminescence of Er^3 ions mainly comes from three-photon absorption by the PQC process when the rare earth ions are doped in the g/ass ceramics and excited by 98Ohm pumped-laser. Er^3 ions absorb three-photons and relax to the ^4G11/2 state and then emit red up-conversion luminescence by the PQC process. The factor coefficient for the relation of pump-laser power and up-conversion intensity (P-I) is found by the analysis of excitation spectra of the red luminescence, which plays a major role to understand the true red up-conversion luminescence process. The new P-I relation is explained by the model of PQC.     

Nanocrystal formation and structure in oxyfluoride glass ceramics

The up-conversion luminescent property of the oxyfluoride glass ceramics 30SiO_{2}\cdot15Al_{2}O_{3}\cdot (50--x)PbF_{2}\cdot xCdF_{2} doped with 4ErF_{3}\cdot1YbF_{3} has been investigated. Up-conversion luminescent intensity of Er^{3+} ions increased obviously after heat-treatment due to co-doping with CdF_{2}. The structure model of nanocrystals Pb_{x}Cd_{1-x}F_{2} was determined and the effect of CdF_{2} in oxyfluoride glass ceramics was explained by the analysis of x-ray diffraction data. Different nucleation temperatures of samples with different compositions were obtained by differential thermal analysis curves and the results showed the growth process of different nanocrystals in glass ceramics.     

Characterization of Photon Statistical Properties with Normalized Mandel Parameter

Normalized Mandel Parameter （Q） is introduced as a new measurement oi photon statistics. Dependences of Mandel parameter Q and corresponding normalized Mandel parameter （Q） on photon-counting time interval are experimentally investigated for pseudo-thermal light. We demonstrate that （Q） is more appropriate than Q, to measure the statistical deviation from Poisson distribution, because （Q） presents clearly both the intrinsic statistical properties and measuring effects. The advantages of （Q） in charactering nonclassical emissions are also discussed.     

Investigation on the phase shifts of extinction and phase gratings in polymethyl methacrylate

The phase shifts of the extinction and refractive index gratings to the illumination pattern are revealed in doped polymethyl methacrylate （PMMA）. The dynamic process of these shifts is studied via two-wave coupling at 351 nm. It is shown that these shifts are from the strain and the shrinkage inside the sample and accompanied with the photo-repolymerization process during the building process of the holographic grating. Such shifts will cause obvious energy exchange between the two recording beams and enough attention should be paid to the nonlocal property of the holographic gratings of the material in the application.     

Effect of nanocrystals on up-conversion luminescence of Er~(3+),Yb~(3+) co-doped glass-ceramics

A new class of transparent glass-ceramics attracted much attention in the past decades[1,2], in which the fluoride nanocrystals doped with rare earth ions were dispersed in an oxide network. The optical proper- ties of rare earth ions in oxyfluoride glass depend on the fluoride nanocrystals, and the mechanical proper- ties depend predominantly on the oxide host. Hence, the oxyfluoride glass-ceramics are promising materials for op- tical amplifiers and laser up-conversion applications[3,4]. Wan…