The interference filter of the Fabry-Perot interferometer type first proposed by L.N. Hadley and D.M. Dennison is further exploited by computing numerically the spectral transmission with the aid of NOVA-840 computers. In this calculation the attentions are paid specially on the phase change in the thin solid films which affects the spectral location of the narrow pass band. Also, the location and the half-width of the pass band are checked as the functions of the optical thickness of the spacer. With those numerical analysis the interference filter is prepared by vacuum deposition technique, semitransparent metal layer and the spacer materials being silver and $MgF_2$.
The results of the numerical calculations are all confirmed upon plotting the spectral locations of the pass bands of 42 filters prepared in this present experiments. At λ = 0.5461μ, typical half-width of the first order Hadley-Demnison filter is found to have approximately 60 Å and the peak transmission is 40%.
In the present work the measurements of the geometrical thickness of both Ag film and $MgF_2$ film are made by Tolansky's multiple beam Fizeau interferometry. It is found Tolansky's fringe is most useful in the thickness measurement of suboptical wavelength dimension.