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The Ho3+/Pr3+ co-doped NaYF4 single crystals with various Pr3+ concentrations and constant Ho3+ molar percentage of ~1% were grown by an improved Bridgman method. Compared with the Ho3+ single-doped NaYF4 crystal, an obviously enhanced emission band at 2.85 μm is observed under 640 nm excitation. The Judd-Ofelt strength parameters (Ω 2, Ω 4 and Ω 6) are calculated, the radiative transition probabilities (A), the fluorescence branching ratios (β) and the radiative lifetime (τ rad) are obtained in the meantime. The energy transfer from Pr3+ to Ho3+ and the optimum fluorescence emission of Ho3+ ions around 2.85 μm are investigated. Moreover, the maximum emission cross section of above samples at 2.85 μm is calculated to be 0.72×10-20 cm2 for the NaYF4 single crystal with Ho3+ molar percentage of 1% and Pr3+ molar percentage of 0.5% according to the measured absorption spectrum. All results suggest that the Ho3+/Pr3+ co-doped NaYF4 single crystal may have potential applications in mid-infrared lasers.  相似文献   
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基于三次方程的LSB隐藏信息的盲检测   总被引:1,自引:0,他引:1  
该文提出基于最小平方策略以及导出的三次方程的检测最低有效位(LSB)隐藏信息容量的新算法。与Dumitrescu等人(2003)提出的方法比较,新算法具有下列优点:检测的前提条件更宽松、虚警概率更低(由13%降至4%左右),估计的精度提高约9%,而且检测速度更快。该文还给出了具体的检测步骤和相关的理论推导。  相似文献   
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视频图像序列运动参数估计与动态拼接   总被引:2,自引:0,他引:2  
本文采用多重分层叠代算法来估计全局运动参数,并提出应用于动态拼接的运动分割新方法,实现既有摄像机运动又有物体运动的视频图像序列自动拼接。我们的方法基本步骤如下:首先进行全局运动参数的初始估计,并且在分层叠代过程中进行区域分类,得到初始运动模板。接着空间分割原始图像,先根据图像的空间属性由底向上分层合并图像空间区域,再利用视频图像时间属性进一步向上合并,得到图像空间分割结果。然后结合初始运动模板和图像空间分割结果,采用区域分类新方法重新对图像空间分割结果的每个区域进行分类。然后根据分类结果逐步精确求解全局运动参数。最后进行图像合成,得到全景拼接图像。我们的方法利用了多重分层叠代的优点,并且充分考虑到视频图像空间和时间上的属性,实现了运动物体和覆盖背景的精确分割,避免了遮挡问题对全局运动参数估计精度的影响。而且在图像合成时我们解决了拼接图可能产生模糊或某些区域不连续等问题。实验结果表明我们的方法实现了动态视频图像序列高质量的全景拼接。  相似文献   
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Tm3+ doped Na5Lu9F32 single crystal with high optical quality was grown by an improved Bridgman method. The Judd-Ofelt intensity parameters Ωt (t=2, 4, 6) were calculated according to the measured absorption spectra and physical-chemical properties of the obtained Na5Lu9F32 single crystal. The stimulated emission cross-section of the 3F4→3H6 transition (~1.8 μm) is 0.35×10-20 cm2 for Tm3+ doped Na5Lu9F32 single crystal. The emission spectra under the excitation of 790 nm laser diode (LD) and fluorescence lifetime at 1.8 μm were measured to reveal the fluorescence properties of Tm3+ doped Na5Lu9F32 single crystal. The research results show that the Tm3+ doped Na5Lu9F32 single crystal has larger stimulated emission cross-section compared with other crystals. All these spectral properties suggest that this kind of Tm3+doped Na5Lu9F32 crystal with high physical-chemical stability and high-efficiency emission at 1.8 μm may be used as potential laser materials for optical devices.  相似文献   
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