Reflectivity of Thin Silver Films and their Use in Interferometry

Publisher Website
Google Scholar
Abstract
A direct photoelectric method allowed the reflectivity R and the transmissivity T of partially reflecting films to be measured to an accuracy of 0.3% of the incident light intensity. For a large number of silver films, deposited on glass by evaporation in vacuo, the values of R and T were measured for visible light of five different wavelengths, in the range of high reflectivities (R>0.7). The change of R as a function of time was also studied. With only moderate control of the conditions of surface cleaning and evaporation, the values of R were nearly always found to he close to a `standard' curve giving R as a function of T, the wavelength, and the age of the film. Possible causes of scatter from this standard curve were investigated T was found not to obey an exponential law as a function of the thickness. On the basis of these results, resolving power and brightness of etalon fringes were plotted as functions of T. The conclusion is reached that, in most practical cases, the resolving power of etalons for visible light is limited by imperfections of the surfaces rather than by the reflectivity of the silver films, if their thickness is properly chosen.