关于薄膜干涉中额外光程差的讨论

Discussion on additional optical path difference in thin film interference

就薄膜干涉中两反射光间的额外光程差问题展开论述。首先给出半波损失的概念,强调入射光在掠入射或正入射两种情况下,反射光才可产生半波损失。其次讨论薄膜干涉中各种情况下反射光间的额外光程差。第1种情况是折射率为n2的薄膜处于折射率为n1的介质中,可分为n1>n2和n1<n22种情况。第2种情况是薄膜上下表面以外介质折射率不同,又可分为n1>n2>n3,n1<n2<n3,n1>n2<n3及n1<n2>n34种情况。分别讨论了反射光间是否存在额外光程差,并且对入射角的范围作了说明,同时更正了部分文献的错误。与某些教科书给出的结论不同,当媒质的折射率逐次变化时,也会存在一个额外光程差,但不是λ/2;而当薄膜上下表面物理性质相反时,也有额外光程差不为λ/2的特例。

In this paper, the additional optical path difference between two reflected light in film interference is discussed. First, a clear interpretation of the concept of ＂half wave loss＂ is given. The condition of half wave loss, that the incident light must be nearly grazing or normal, is emphasized. Then the additional optical path difference between two reflected light, for all cases in thin film interference is discussed. The first case is when the film with refractive index nz is posted in the medium with refractive index nl. There are two situations in this case. One is when nl ~nz, the other is when nl ~ nz. The second case is when the refractive indexes of the three media change in order. There are four situations in this case, i.e. nl ~nz ~n3, nt ~n2 ~n3, n~ ~n2 ~n3 and nl ~nz ~n3 respectively. In each situation the existence of additional optical path difference is discussed and the reasonable values of the incident angle are given. Furthermore the errors in some literatures are pointed out. Different from the conclusions given by some textbooks, there will also be an additional optical path difference between two reflected light when the refractive indexes change in order,. while there exists the exception of no half wave loss when two interfaces have opposite properties.