用注入锁模法改善DFB激光器的频率响应

验证了通过注入锁模方法，分布反馈（DFB）半导体激光器的频率响应可以得到明显的改善．实验中通过一个环形器，将主激光器的输出光注入到从激光器．测量了从激光器在有注入光和没有注入光时的光谱和频率响应．发现在不同的注入光强度和波长下，激光器的调制带宽和弛豫振荡峰频率会发生变化．通过适当选择注入光的强度和波长，频率响应可以得到改善．激光器频率响应的改善可以用两个模式的拍频来解释，一个模式是从激光器的主模，另一个是主激光器的模式，该模式与从激光器的边带重合．该理论与实验结果符合得很好。

Nonlinear excitations in electron-positron-ion plasmas in accretion disks of active galactic nuclei

The propagation of acoustic nonlinear excitations in an electron-positron-ion (e-p-i) plasma composed of warm electrons and positrons, as well as hot ions, has been investigated by adopting a two-dimensional cylindrical geometry. The electrons and positrons are modeled by hydrodynamic fluid equations, while the ions are assumed to follow a temperature-parametrized Boltzmann distribution (the fixed ion model is recovered in the appropriate limit). This situation applies in the accretion disk near a black hole in active galactic nuclei, where the ion temperature may be as high as 3 to 300 times that of the electrons. Using a reductive perturbation technique, a cylindrical Kadomtsev-Petviashvili equation is derived and its exact soliton solutions are presented. Furthermore, real situations in which the strength of the nonlinearity may be weak are considered, so that higher-order nonlinearity plays an important role. Accordingly, an extended cylindrical Kadomtsev-Petviashvili equation is derived, which admits both soliton and double-layer solutions. The characteristics of the nonlinear excitations obtained are investigated in detail

Gu??a de museos y colecciones

T??t. tomado de la cub.

Estudo hidroquímico e dos isótopos de urânio nas águas subterrâneas em cidades do Estado do Amazonas (AM)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)