Some optical and magneto-optical studies on thin absorbing films

Abstract

An up-to-date review of methods of determining optical constants n and k of optically absorbing material in bulk and film form is given. It is shown in this thesis that an analytical method which involves measuring R and at an angle of incidence 0 is capable of yielding n and k values accurate to 0.05 providing R and R aremeasured to -0.004 at values of 0 close to 74?. At angles other than 74° the method can become very insensitive to changes in n and k, particularly at normal incidence. For a thin absorbing film supported by a dielectric substrate, an optimized reflection ratio method for determining optical constants has been devised. Measurement of (R/R ) is made at two values of and the film thickness d is determined independently. Optimum valuesof 0 are given for 1< n <4, 0.2 An up-to-date review of methods of determining optical constants n and k of optically absorbing material in bulk and film form is given. It is shown in this thesis that an analytical method which involves measuring R and at an angle of incidence 0 is capable of yielding n and k values accurate to 0.05 providing R and R aremeasured to -0.004 at values of 0 close to 74?. At angles other than 74° the method can become very insensitive to changes in n and k, particularly at normal incidence. For a thin absorbing film supported by a dielectric substrate, an optimized reflection ratio method for determining optical constants has been devised. Measurement of (R/R ) is made at two values of and the film thickness d is determined independently. Accuracies in n and k can be obtained if (R /R) is measured to -0.01 and to-0.005. A simple reflectometer is described to measure R and R to 0.006 at non-normal incidence in the wavelength range 400-700nm. An optical cell and a Helmholtz coil system are described which facilitate low temperature optical constants and megneto-optical measurements. The optical constants of U.H.V. deposited Ni films are reported for film thicknesses 25 to 60nm, and are shown to have very little thickness dependence.Optically opaque, polycrystalline Gd films deposited in U.H.V. onto float-glass substrates are shown to be almost completely orientated with the c-axis perpendicular to the plane of the film. Dispersion curves of are reported for the paramagnetic and ferromagnetic phases of such films, and are similar to previous work. Some observedsecondary structure at appears to have previously gone unobserved. The results of preliminary, transverse feiromagnetic Kerr effect measurements on Gd films are also reported.Electron microscopy and optical constants studies of Tb and films evaporated at < 9 x 10 torr, are presented and shown to be in accordance with a previous study of the terbium oxide system. A [omega] dispersion curve is also given for a metallic Tb film.