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Yang Q.-X.,Yanshan University | Li Z.-Q.,Yanshan University | Zhu Y.-P.,Yanshan University | Yan J.-B.,Coal Chemical Industry Co.
Guangdian Gongcheng/Opto-Electronic Engineering | Year: 2010

To ensure turning-off the laser in the system of continuous wave cavity ring-down technology, a new method for modulating laser current, named as laser detuning is proposed. With this method, the resonant state between the laser and ring-down cavity is ended. Hence, the incident laser to the ring-down cavity can be turned off rapidly. This detuning method does not require external optical switches (such as the acousto-optic modulator) to turn off the laser source so the system is simpler than previous ones and the cost is lower than traditional systems. The continuous wave cavity ring-down system based on the laser detuning is designed. The operating principle and performance of various devices are analyzed. The characteristics of the detuning process are analyzed and the difference between the laser detuning and laser turn-off are compared. As a result, the turning-off time in the technology of modulating laser current is shorter than the traditional optical switches, and the exponential curve is more distinct. Source

Chang H.,University of Chinese Academy of Sciences | Li H.,CAS Beijing National Laboratory for Molecular | Zheng T.,University of Chinese Academy of Sciences | Zhang L.,University of Chinese Academy of Sciences | And 4 more authors.
Journal of Polymer Research | Year: 2013

As the external donor in Ziegler-Natta catalysts have an important influence on the stereo-defects distribution of polypropylene, the effects of the mixed external donors (the mixture of Donor-C (cyclohexylmethyldimethoxysilane) and Donor-N (n-propyltriethoxysilane)) on the isotactic sequence length and its distribution of polypropylene prepared by Ziegler-Natta catalyst through propylene bulk polymerization were studied through the Successive self-nucleating and annealing (SSA) and 13C-NMR techniques. The SSA results showed that the relative contents of the highest isotactic component and the lamellar thickness in the polypropylene chain gradually increased with the increase of the relative component of Donor-C in the C/N mixed external donors, indicating the isotactic sequence length of polypropylene got longer, and the lamellar thickness distribution of polypropylene became broader, revealing the isotactic sequence length distribution of polypropylene got broader. In addition, the 13C-NMR results showed that the average meso isotactic sequence length (MSL) of polypropylene gradually increased with the increase of the content of Donor-C in the C/N mixed external donors, which was in good coincident with the results calculated from SSA, showing a good correspondence between the SSA and 13C-NMR techniques. © 2013 Springer Science+Business Media Dordrecht. Source

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