Optical properties of evaporated magnesium oxide films in the 0.22-8micro wavelength region.

This paper presents data on the optical properties of evaporated MgO films in the wavelength region from 0.22 micro to 8 micro. The films were deposited in high vacuum with an electron gun at a rate of about 20 A/sec, and their refractive indices were determined using three different techniques. The absorptance of the films was found to be negligible over the wavelength region measured. Films deposited on substrates of 50 degrees C had refractive indices of 1.70 at lambda = 0.55 micro and 1.62 at lambda = 4 micro, while those condensed at 300 degrees C showed at the same wavelengths n-values of 1.74 and 1.66, respectively. All MgO films were found to be crystalline showing the cubic structure and lattice constant of the bulk material. Their crystal size increased with increasing substrate temperature. MgO proved to be a suitable film compound for producing three-layer antireflection coatings on glass. It can also be used in combination with SiO(2) or MgF(2) for preparing protected Al front surface mirrors with 95% reflectance at lambda = 0.25 micro. During extended exposure to normal air a hazy, bluish scattering coating forms on the surface of MgO films that limits their usefulness as an optical coating material.