关于“三线八角”

两条直线AB、CD被第三条直线EF所截,形成了8个小于平角的角,我们通常将这样的几何模型简称为三线八角,如图1所示.其中没有公共顶点的角可分为三类,即同位角(如∠1和∠5)、内错角(如∠3和∠5)和同旁内角(如∠4和∠5).它们是进一步学习平行线的一个重要基     

Electromagnetically induced grating in a thermal N-type four-level atomic system

The electromagnetically induced grating effect in thermal and cold atoms has been studied theoretically. Studies have shown that, by adjusting the parameters, the first-order diffraction efficiency of the probe beam in the cold atomic system and the thermal atomic system is 34% and 31%, respectively, which is very close to the ideal diffraction efficiency of the sinusoidal grating. However, it is more difficult to prepare the cold atomic system than to prepare the thermal atomic system in the practical application, so the study of the electromagnetically induced grating effect in the thermal atomic system may be helpful for practical applications.