High-power 1.5 and 3.4 μm intracavity KTA OPO driven by a diode-pumped Q-switched Nd:YAG laser

With a non-critically phase-matched KTA crystal, a high-power intracavity optical parametric oscillator (IOPO) driven by a diode-side-pumped acousto-optically Q-switched Nd:YAG laser has been realized. The maximum average output power of 13.6 W at the signal wavelength of 1534 nm and 3 W at the idler wavelength of 3472.7 nm were obtained with the repetition rate of 18 kHz, giving the optical-optical conversion efficiency of about 5.7% from diode-power at 808 nm to OPO signal output, which was the highest conversion efficiency for intracavity KTA OPO with diode-side-pumping configurations to our best knowledge. At the highest output power of 13.6 W, the signal pulse duration of 5.46 ns was obtained, corresponding to the single pulse energy of 756 μJ and peak power of 138 kW, respectively.     

Facile liquid phase deposition of thick reflective GeO2 film for hollow waveguide delivery of CO2 laser radiation

A new idea of using LPD (liquid phase deposition) to prepare a GeO₂ thick reflective film for hollow waveguide delivery of CO₂ laser radiation was investigated in this work. The LPD process was achieved by designedly adding acid to GeO₂–aqueous ammonia. The addition of acid could induce the transformation of germanate ions into GeO₂ solutes, leading to the deposition of a GeO₂ ceramic film when the concentration of GeO₂ solute is higher than its saturation solubility. It was found that the highest film growth rate occurred at a pH value of 3, while a film with low surface roughness and good adhesion to the substrate was produced at a pH value of 2 and the film could be converted to a smooth, compact hexagonal GeO₂ film by heat treatment at 1120 °C for 30 min. Two abnormal dispersion bands within 7.6–9 μm and 9.6–11.2 μm were mainly caused by the silica glass substrate and the GeO₂ film, respectively. The film was thick enough to achieve the total reflectance of the CO₂ laser radiation. The use of this GeO₂ film in a hollow waveguide structure for CO₂ laser radiation delivery is discussed based on the transmission loss and the feasibility of the deposition of the GeO₂ film inside silica capillary tubes. The results show that the hollow waveguides with low transmission loss are most likely fabricated at a low cost using the LPD-derived GeO₂ reflective film. PACS 78.20.-e; 78.66.-w; 42.70.-a; 78.20.Ci; 78.40.-q     

Fe-B-Y-Nb bulk metallic glasses in relation to clusters

Bulk metallic glass formations in the Fe-B-Y-Nb quaternary alloy system were investigated by using the cluster line rule in combination with the minor alloying principle. The Fe-B-Y ternary system was selected as the basic system and the intersections of cluster lines were taken as the basic ternary compositions. The basic compositions were further alloyed with minor amounts of Nb. After 3–5 at.% Nb was added, the basic composition Fe_68.6B_25.7Y_5.7, which was developed from the most densely packed cluster Fe₈B₃, formed 3 mm bulk metallic glasses. These quaternary bulk metallic glasses (Fe_68.6B_25.7Y_5.7)_100−x Nb _x (x = 3–5 at.%) are expressed approximately with a unified simple composition formula: (Fe₈B₃)₁(Y, Nb)₁. The (Fe_68.6B_25.7Y_5.7)₉₇Nb₃ bulk metallic glass has the largest glass forming ability with the following characteristic parameters T _g = 907 K, T _x = 1006 K, T _g/T _l = 0.644, γ = 0.434, and longness t = 22 mm. The combination of the cluster line rule and the minor-alloying principle is a promising new route towards the quantitative composition design of multi-component metallic glasses. Supported by the National Natural Science Foundation of China (Grant Nos. 50671018, 50631010 and 50401020) and the National Basic Research Program of China (Grant No. 2007CB613902)     

Study on nitridation processes of β-Ga2O3 single crystal

Nitridated /3-Ga2Os (100) substrate was investigated as the substrate for CaN epitaxial growth.The effects of nitridation temperature and surface roughness of -Ga2O3 wafers on the formation of CaN were studied.     

电子束蒸发沉积Ir膜真空紫外反射特性

Ir是一种重要的真空紫外反射材料,在太阳物理、宇宙物理、生命科学、大气物理、同步辐射等方面有着十分重要的应用.对电子束蒸发沉积Ir膜在真空紫外波段的反射特性进行了系统的理论和实验研究.根据吸收材料基底上单层金属膜数学计算模型,对不同基片上各种厚度的Ir膜真空紫外反射率进行了优化计算.根据计算和前期实验结果,采用电子束蒸发方法,在石英、K9玻璃基片上沉积了不同厚度的Ir膜,在入射波长120 nm处获得了近30%正入射反射率,对应的Ir膜厚度为12 nm.过厚或过薄均不利于Ir膜反射率的提高.经退火处理后,Ir膜中张应力有所释放但并未消除,同时晶粒平均尺寸显著增大,反射率下降.     

一种用于电子纸的电泳液的显示性能研究

用有机颜料汉沙黄(P.Y.3)、苏丹黑和合适的稳定剂为原料配制了一种性能稳定的电泳显示液.分析了此电泳显示液中颜料微粒的带电机理及其影响因素,研究了在改变电压方向时反射光谱与吸收光谱的变化及其原因,光谱分析结果表明体系中存在的各种吸附使显示效果受到局限,反射谱与吸收谱的变化在表征器件的显示特性时呈现出一致性,器件的反射光强和反射率在不同波长上有区域选择性,同时对比度也有区域选择性,这决定了在监测器件的响应时应选择的波长范围以及可利用的光源.兼顾灵敏性和测试信号强度的需求,选用峰值波长为470 nm的蓝光二极管为光源,电泳槽的厚度为0.2 mm,用荧光光谱仪监测相同周期不同幅值脉冲电压作用下颜料微粒在493 nm波长处的反射光强的变化,并由示波器记录并输出反射光强随驱动电压的变化,还结合相关理论讨论了驱动电压对器件的反射光强和对比度的影响.     

Edge-pumped passively Q-switched thin Nd:YAG slab lasers

We report a high-power thin Nd：YAG slab laser with slab dimension of 1 × 10 ×60 （mm） partially edgepumped by diode laser arrays. Passive Q-switching is achieved with a Cr^4＋ ：YAG microchip adopted as the saturable absorber mirror. The pulse duration is around 10 ns while the pulse repetition rate is higher than 10 kHz. The average output power of 70 W is obtained with a slope efficiency of 36%. The diffraction limited beam quality in the thickness direction is obtained by controlling the pump beam diameter inside the slab. The laser head is very compact with size of only 60 × 74×150 （mm）.     

Central neurocytoma: typical magnetic resonance spectroscopy findings and atypical ventricular dissemination

PURPOSE: Central neurocytomas (CNCs) are rare neuronal tumors that have a favorable prognosis and lower rate of recurrence compared with other intraventricular neoplasms. Although it may be difficult to distinguish CNC on conventional neuroimaging, typical MR spectroscopy (MRS) features have been reported. We describe the MRI and MRS features of CNC. MATERIALS AND METHODS: Eight patients with CNC were reviewed. Three patients underwent presurgical in vivo single-voxel MRS at short echo time (TE, 35 ms) and multi-voxel MR spectroscopic imaging at long TE (144 ms). The surgically resected tumor specimen of one of these patients was also studied ex vivo using high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance. RESULTS: All eight tumors were located in the lateral ventricles. In six patients, CNC extended into the third ventricle, and in two patients the tumor showed further contiguous intraventricular dissemination into the fourth ventricle. In all three patients who underwent MRS, a characteristic metabolite peak was detected at 3.55 parts per million (ppm) at both long and short TE. HRMAS confirmed the presence of elevated glycine (Gly) at 3.55 ppm, without increase in the concentration of myo-inositol found at the same chemical shift. Elevated choline (at 3.2 ppm) was also seen in all three patients. CONCLUSION: On MRS, CNCs have a typical appearance with a metabolite peak at 3.55 ppm due to increased Gly, and this feature may be helpful in presurgical diagnosis. Although they are rare benign intraventricular tumors, in atypical cases, CNCs can show extensive intraventricular dissemination into the fourth ventricle.     

Development and initial evaluation of 7-T q-ball imaging of the human brain

Diffusion tensor imaging (DTI) noninvasively depicts white matter connectivity in regions where the Gaussian model of diffusion is valid but yields inaccurate results in those where diffusion has a more complex distribution, such as fiber crossings. q-ball imaging (QBI) overcomes this limitation of DTI by more fully characterizing the angular dependence of intravoxel diffusion with larger numbers of diffusion-encoding directional measurements at higher diffusion-weighting factors (b values). However, the former technique results in longer acquisition times and the latter technique results in a lower signal-to-noise ratio (SNR). In this project, we developed specialized 7-T acquisition methods utilizing novel radiofrequency pulses, eight-channel parallel imaging EPI and high-order shimming with a phase-sensitive multichannel B0 field map reconstruction. These methods were applied in initial healthy adult volunteer studies, which demonstrated the feasibility of performing 7-T QBI. Preliminary comparisons of 3 T with 7 T within supratentorial crossing white matter tracts documented a 79.5% SNR increase for b=3000 s/mm2 (P=.0001) and a 38.6% SNR increase for b=6000 s/mm2 (P=.015). With spherical harmonic reconstruction of the q-ball orientation distribution function at b=3000 s/mm2, 7-T QBI allowed for accurate visualization of crossing fiber tracts with fewer diffusion-encoding acquisitions as compared with 3-T QBI. The improvement of 7-T QBI at b factors as high as 6000 s/mm2 resulted in better angular resolution as compared with 3-T QBI for depicting fibers crossing at shallow angles. Although the increased susceptibility effects at 7 T caused problematic distortions near brain-air interfaces at the skull base and posterior fossa, these initial 7-T QBI studies demonstrated excellent quality in much of the supratentorial brain, with significant improvements as compared with 3-T acquisitions in the same individuals.     

Treatment of nano-sized rutile phase TiO2 powder under ultrasonic irradiation in hydrogen peroxide solution and investigation of its sonocatalytic activity

The treated mixed-crystal TiO(2) powder with high sonocatalytic activity was obtained through utilizing ultrasonic irradiation in hydrogen peroxide solution. At the same time, some influencing factors (including heat-treated temperature and heat-treated time) on the sonocatalytic activity of treated mixed-crystal TiO(2) powder were also considered through the degradation of methylene blue in aqueous solution. In this work, it was found that the sonocatalytic degradation ratio of methylene blue in the presence of treated mixed-crystal TiO(2) powder was much higher than ones in the presence of nano-sized rutile phase TiO(2) powder and with onefold ultrasonic irradiation. At last, the methylene blue in aqueous solution was completely degraded and became some simple inorganic anions such as NO(3)(-), SO(4)(2-) and Cl(-). All experiments indicated that the sonocatalytic method adopting treated mixed-crystal TiO(2) powder as sonocatalyst was an advisable choice for the treatments of non- or low-transparent wastewaters in future.