Optical Properties of MgO and MgF2 in the Extreme Ultraviolet Region

Measurements of the optical properties of MgO and MgF2 have been extended from 29 to 80 eV. Reflectance and emission spectra were obtained for single crystals and transmittance spectra for thin films. The extinction coefficients for single crystals of MgO and MgF2 are relatively large (>0.07 up to 80 eV), and sum-rule calculations show the values to be reasonable. Structures in the extinction coefficients are identified as due to interband transitions from the core electron states to the conduction bands and to excitons associated with the Mg 2p to conduction-band transitions in the two materials. The optical constants are used to identify the nature of characteristic energy losses reported in the literature. The extinction coefficients of thin films of MgO and MgF2 are less than for the single crystals.