Optical Constants of Evaporated Barium in the Vacuum Ultraviolet*

The optical properties of evaporated barium films have been investigated in the wavelength range from 1500 to 3000 Å. Reflectance measurements were made at angles of incidence of 17.5° and 72.5° and the complex index of refraction obtained from graphical solutions of the Fresnel reflection equations. The films were prepared in an ultrahigh-vacuum reflectometer having a base pressure of about 5 × 10−10 torr. Radiation from a hydrogen glow-discharge source was dispersed by a normal-incidence vacuum monochromator which was optically connected to the ultrahigh-vacuum system by means of a sapphire window. The energy-loss function Im(1/∊), as computed from the optical constants, is compared with published characteristic electron-loss (CEL) data. The complex index of refraction was fitted to a Drude model for which the plasma energy was fixed at 7.4 eV and the damping at 1.6 × 10−16 sec.