菲涅耳透镜是一种折射式聚光器,它由平凸透镜演变而来。从图1(a)可知,当太阳光垂直平凸透镜入射时,第一个界面(平面)不改变光的传播方向,第二个界面(曲面)才会改变光的方向,使入射光会聚。科学家菲涅耳把平凸透镜的曲面分成许多个小单元,于是每个小单元的曲面可近似地看作为平面(如图1(b)],这样图中画有阴影线的部分便成了直角小棱镜。把许许多多直角小棱镜平板化(在一块平板上加工制成),便构成了菲涅耳透镜(也称平板透镜),见图1(c)。图2中△ABC代表菲涅耳透镜上任意一个直角小棱镜,∠a称棱镜的顶角,BC为棱镜底边,EN为斜 A Fresnel lens is a refractive condenser that evolved from a plano-convex lens. As can be seen from Fig.1 (a), when the solar vertical plano-convex lens is incident, the first interface (plane) does not change the propagation direction of light, and the second interface (curved surface) changes the direction of light and converges the incident light. The scientist Fresnel divides the surface of the plano-convex lens into many small units, so the surface of each small unit can be regarded as a plane approximately (as shown in Fig. 1 (b)], so the hatched part of the figure becomes a right angle Small prism. A large number of right-angle small prism plate (in a flat plate processing made), it constitutes a Fresnel lens (also known as flat-panel lens), shown in Figure 1 (c) Niels lens any one right-angle small prism, ∠ a said vertex angle of the prism, BC is the bottom edge of the prism, EN is oblique