We study the ultraslow optical solitons in a resonant three-level atomic system via electromagnetically induced transparency under a density-matrix （DM） approach. The results of linear and nonlinear optical properties are compared with those obtained by using an amplitude variable （AV） approach. It is found that the results for both approaches are the same in the linear regime if the corresponding relations between the population-coherence decay rates in the DM approach and the energy-level decay rates in the AV approach are appropriately imposed. However, in the nonlinear regime there is a small difference for the self-phase modulation coefficient of the nonlinear SchrSdinger equation that governs the time evolution of probe pulse envelope. All analytical predicts are checked by numerical simulations.
利用高压合成装置在6 GPa压力、700℃温度条件下合成了二维C60聚合相,并用X射线衍射(XRD)和高分辨核磁共振(NMR)等方法对样品进行了表征。XRD分析结果表明,C60分子在高温高压下发生了聚合反应,晶体结构由面心立方结构变为菱形结构,通过[2+2]加环反应在邻近分子间形成sp3杂化共价键1。3C核磁共振魔角谱(13C MAS NMR)在δ145和δ72处出现了两个共振峰,其中在δ145附近的峰展宽并有两个边带。δ145附近的峰的展宽与分裂主要是由于C60分子上出现了不等价的sp2杂化碳和高温高压条件下产生的结构无序,边带的形成说明了其结构的各向异性;位置为δ72附近的峰证明了聚合物内C60分子之间出现了sp3杂化键。
