A model for the calculation of the diffuse reflectance and transmittance of a single interference layer with rough interfaces on a transparent substrate is presented. The model is based on electric field calculations and scalar scattering theory, and it assumes that the interfaces of the layer are totally uncorrelated. Examples are given of calculated spectra in which the parameters of the model are varied systematically to show the influence from different interface roughness and refractive index combinations as well as absorption in the film. A wavelength-dependent effective root-mean-square roughness is introduced. This depends on the nature of the roughness, and the bandwidth limits are given by the experimental conditions. Finally, total integrated scattering spectra are calculated and the importance of taking multiple reflections in the substrate into account is shown.
A spectroscopic total-integrated-scatter instrument has been constructed. It uses a Coblentz sphere for the collection of the scattered light and a lamp with a monochromator as a light source. It can be used to measure diffuse reflectance as well as transmittance. The instrument has been used to measure diffuse reflectance of thermally and chemical-vapor-deposition oxidized silicon wafers. Comparisons are made with measurements by using a spectrophotometer with an integrating sphere. The data have been interpreted with a parameterized model for light scattering from a double layer, to obtain rms surface roughness values for the two interfaces of the oxide film.
A model for the calculation of diffuse reflectance and transmittance of a single interference layer on a transparent substrate is applied to pyrolytically deposited tin oxide films on glass. Total as well as diffuse reflectance and transmittance spectra were measured in an integrating sphere, and scattering levels between 0.002 and 0.1 were recorded. The optical constants and the thickness of the films were determined from the total reflectance and transmittance spectra. The wavelength-dependent effectiveroot-mean-square roughness of aluminum-coated tin oxide front surfaces was determined by the application of the scalar scattering theory. Surface roughness values between 5 and 25 nm were obtained. The obtained effective rms roughness values of the air-film interface were used together with the other film parameters to calculate the diffuse reflectance and transmittance spectra of the tinoxide-coated glass substrates. A comparison between calculated and experimental spectra showed good agreement for diffuse reflectance, diffuse transmittance, and total integrated scattering spectra.
A method for correcting integrating-sphere signals that considers differences in the angular distribution of scattered light is extended to sources of errors that are due to stray light from imperfect optical components. We show that it is possible to measure low levels of scattering, below 1%, by using a standard integrating sphere, provided that the various contributions to stray light are taken into account properly. For low-scattering samples these corrections are more important than those from the angular distribution of the scattering. A procedure for the experimental determination of stray-light components is suggested. Simple, easy to use, compact equations for the diffuse and specular reflectance and transmittance values of the sample as functions of the recorded signals are presented.
A digital holographic interferometry setup used to measure radial vibrations along a rotating shaft is presented. A continuous Nd:YAG laser and a high-speed digital camera are used for recording the holograms. The shaft was polished optically smooth to avoid speckle noise from the rotating surface. The light reflected from the shaft was directed onto a diffuser which in turn was imaged by the holographic system. Simultaneous measurements with a laser vibrometer were performed at one point and comparisons between the signals showed good agreement. It is shown that different vibration components of a rotating shaft can be simultaneously measured with this technique.