光波的半波损失现象及其应用探析

Analysis of half-wavelength loss concept and application in light interference

半波损失是大学物理中的重点和难点问题。从菲涅尔公式出发,分析了半波损失的概念及其产生条件,并结合其在典型干涉现象中的应用,指出只有在垂直入射和掠入射两种情况下,从光疏媒质入射到光密媒质界面时,反射光具有半波损失;折射光在任何情况下均无半波损失;对一般斜入射,由于光振动矢量平行分量方向的特殊性,半波损失的概念没有任何意义。同时指出,折射光的振幅可以大于入射光的振幅,应从能量的角度正确理解这一结果。

The half-wavelength loss is a key concept difficult to be understood. From the Fresnel formulae in electromagnet wave theory, the concept and prerequisite of half-wavelength loss are analyzed. Combined with its application in typical interference experiments of light, it is pointed out that when light traveling in a medium of lower refractive index n1 is incident normal or parallel onto one of higher refractive index n2, the electric vector of the reflected light undergoes a 180° phase shift, which corresponding to a path difference of half a wavelength. This phase shift does not occur when n1 〉 n2, or for the refracted light in any cases. The concept of half-wavelength loss is not suitable for the inclined incident light. In addition, it is also pointed out that the amplitude of refracted light may be larger than that of the incident light, which is not contradict to the energy conservation.