Ramberg E G
RCA Laboratories, Princeton, New Jersey 08540, USA.
Appl Opt. 1967 Dec 1;6(12):2163-70. doi: 10.1364/AO.6.002163.
Expressions are derived for the dependence of the photoemission from thin films deposited on transparent substrates on the direction of illumination, as determined by optical factors alone. For normal incidence, the photoemission of very thin-film transparent photocathodes may be expected to be about 1.4 times as great for illumination from the glass side as for illumination from the vacuum side. Furthermore, if the index of refraction of the film is large compared with that of the substrate, the ratio, for natural light, is also almost independent of the angle of incidence for a wide angular range. For thicker films, both the optical constants of the film and the mean depth of origin of the photoelectrons play an important role. However, for strongly absorbing as well as nearly transparent photoemissive films, substantially higher photocurrent should be obtainable from a photoemissive film of optimum thickness illuminated through the substrate than for a thick film with similar optical constants illuminated from the vacuum side. An assumed simple proportionality between optical stimulus, here given by the square of the field intensity within the photosensitive film, and photoexcitation implies that the photoeffect studied is a volume effect and not dependent on the direction of the electric vector within the film.
仅由光学因素决定的情况下，推导出了沉积在透明衬底上的薄膜的光发射与照明方向之间的依赖关系表达式。对于垂直入射，对于非常薄的薄膜透明光电阴极，预计从玻璃侧照明时的光发射大约是从真空侧照明时的1.4倍。此外，如果薄膜的折射率与衬底的折射率相比很大，对于自然光，在很宽的角度范围内，该比值也几乎与入射角无关。对于较厚的薄膜，薄膜的光学常数和光电子的平均起源深度都起着重要作用。然而，对于强吸收以及几乎透明的光发射薄膜，通过衬底照明的最佳厚度的光发射薄膜应比从真空侧照明的具有相似光学常数的厚薄膜获得更高的光电流。光刺激（此处由感光薄膜内的场强平方给出）与光激发之间假定的简单比例关系意味着所研究的光效应是一种体效应，并且不依赖于薄膜内电矢量的方向。
