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141.
This paper concerns a study of the detectability of dry contact kissing bonds in adhesive joints using three ultrasonic inspection techniques. Conventional normal incidence longitudinal and shear wave inspection were conducted on dry contact kissing bonds using a standard damped ultrasonic transducer and an electro-magnetic acoustic transducer (EMAT) respectively. The detectability of the dry contact kissing bonds was assessed by calculating the reflection coefficient of the imperfect interface at varying loads for a number of surface roughnesses. A high power ultrasonic method was also employed to determine the non-linear behavior of the adhesive interface. The non-linearity of the interface was determined by the ratio of the amplitudes of the first harmonic and fundamental frequencies of the transmitted waveform. It was found that the high power technique showed the greatest sensitivity to these kissing bonds at low contact pressures, however at high loads conventional longitudinal wave testing was more sensitive. It was also noted that a combination of two or more techniques could provide enhanced information about the kissing bond compared to a single technique alone. 相似文献
142.
A semi-analytical model for multiple mode axially symmetric wave propagation in finite solid cylindrical waveguides is presented. The model is designed as a tool for predicting and interpreting experimental signals. The model is based on a common experimental configuration and considers the excitation, propagation and reception of the ultrasonic signal in the waveguide. The Pochhammer-Chree solution for an infinite cylinder is the basis for the model. Extensions are made to enable comparison to experimental results. Comparisons with experiment are performed in the time, frequency and joint-time frequency domain for both narrow band and broad band excitation of the piezo-electric transducer. 相似文献
143.
Wupeng?GongEmail author Mali?Gong Qiang?Liu Fuyuan?Lu 《Optical and Quantum Electronics》2005,37(12):1109-1120
The effects of gain guiding and thermal guiding on the cavity mode formation for quasi-three-level microchip lasers are investigated.
A parameter describing the dominant guiding mechanisms at the lasing threshold is defined. Paraxial wave propagation equation
for the field envelope in the gain medium with thermal-induced refractive index profile and gain profile is derived. A comparison
between the calculated results and those of experiments reveals that this model is quite reasonable and applicable not only
to the Yb:YAG microchip laser, but also to other quasi-three-level microchip lasers. 相似文献
144.
The dynamic and laser characteristics of the self-Q-switched Cr,Yb:YAG laser were studied by solving the coupled rate equations; the effects of the pump rate, reflectivity of the output couplers and the concentrations of the saturable absorbers on the laser performance were investigated in detail and the numerical simulation of the Cr,Yb:YAG lasers was in good agreement with the experimental data. Better laser performance of the Cr,Yb:YAG self-Q-switched laser can be obtained by using high pump rate, higher concentration of the saturable absorber and suitable reflectivity of the output coupler according to our numerical calculations. A typical self-Q-switched laser pulse of 269.5 J pulse energy with 319 ps pulse width (FWHM) at a repetition rate of 3.1 kHz can be obtained with a monolithic laser cavity, which results in 843.5 kW peak power. 相似文献
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146.
氟氧化物玻璃中稀土ErYb与HoYb能量上转换特性研究 总被引:6,自引:0,他引:6
在特定恒温环境下烧结Er与Yb,Ho与Yb共掺杂氟氧化物两样品。用930nm激光激发,测得两样品的发光射荧光光谱,发现两样品发射荧光光谱中都分别有红光带和绿光带。由Er2O3,Ho2O3,Yb2O3的吸收谱及能级跃迁原理说明了两样品能量上转移机制及特性。 相似文献
147.
Lihe Zheng Guangjun Zhao Chengfeng Yan Xiaodong Xu Liangbi Su Yongjun Dong Jun Xu 《Journal of Raman spectroscopy : JRS》2007,38(11):1421-1428
Raman spectroscopy was used to study the molecular structure of a series of selected rare earth (RE) silicate crystals including Y2SiO5 (YSO), Lu2SiO5 (LSO), (Lu0.5Y0.5)2SiO5 (LYSO) and their ytterbium‐doped samples. Raman spectra show resolved bands below 500 cm−1 region assigned to the modes of SiO4 and oxygen vibrations. Multiple bands indicate the nonequivalence of the RE O bonds and the lifting of the degeneracy of the RE ion vibration. Low intensity bands below 500 cm−1 are an indication of impurities. The (SiO4)4− tetrahedra are characterized by bands near 200 cm−1 which show a separation of the components of ν4 and ν2, in the 500–700 cm−1 region which are attributed to the distorting bending vibration and in the 880–1000 cm−1 region which are attributed to the symmetric and antisymmetric stretching vibrational modes. The majority of the bands in the 300–610 cm−1 region of Re2SiO5 were found to arise from vibrations involving both Si and RE ions, indicating that there is considerable mixing of Si displacements with Si O bending modes and RE O stretching modes. The Raman spectra of RE silicate crystals were analyzed in terms of the molecular structure of the crystals, which enabled separation of the bands attributed to distinct vibrational units. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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高温固相法制备了Yb3+/Tm3+共掺的Sb2O4发光粉体,研究了其上转换发光性质。在980nm半导体激光器的激发下,样品发射较强的近红外(800nm)和较弱的蓝色(480nm)及红色(680nm)上转换发光。粉末样品中稀土Yb3+及Tm3+浓度对上转换发光性质具有显著的影响,随着Yb3+或Tm3+浓度的增加,上转换发光增强;Tm3+掺杂浓度达0.8%时其上转换发光强度达到最大,之后上转换发光随Tm3+浓度的增加而减弱,这是由于浓度猝灭引起的。探讨了粉末样品的上转换发光机理,在980nm激发下Tm3+的蓝光和近红外上转换发光均属于二光子的上转换发光过程。 相似文献