Its fundamental is that the ray emitted from a focus ( front ) of elliptical will flock together on the other focus ( back ) by the reflection on the elliptical surface . we set a scatter aperture on the back focus 椭圆柱面的前焦线上是射线源，晶体固定在一个椭圆基底上，其表面构成一椭圆柱面， x射线经晶体衍射后会聚于后焦线上。
