This paper reports on the manufacturing of a novel type of retroreflecting sheeting material. The geometry presented has high reflection efficiency even at large incident angles, and it can be manufactured at low cost through polymer replication techniques. The paper consists of two parts. A theoretical section outlining the design parameters and their impact on the optical performance, and secondly, an experimental part comprising both manufacturing and optical evaluation for a candidate retroreflecting sheet material in traffic control devices. Experimental data show that the retroreflecting properties are promising. The retroreflector consists of a front layer of densely packed spherical microlenses, a back surface of densely packed spherical micromirrors, and a transparent spacer layer with a thickness equal or not equal to the focal length of the lens. The master structures for the lens and mirror sides of the retroreflector were produced by thermal reflow of photoresist pads on silicon wafers. The silicon master structures were transferred into metallic counterparts by electroforming. The casting of the retroreflector was then done in a cavity being limited by the respective mould inserts for the lens and mirror sides.
The international DVD standard, ECMA-267, for compact discs with improved storage capacity is based on a semi- transmitting mirror. This coating provides a top memory layer that permits reading an opaque second mirror layer underneath. According to the standard, the top layer should have a reflectance in the interval 18-30 percent and simultaneously sufficient transmittance to permit a reflectance in the same interval from the bottom mirror layer, all at the reading wavelength 650 nm. The standard also includes the optical effects of the 550 micrometers polycarbonate disc and the 55 micrometers spacer layer used for protection.
The measurement of total scatter losses is a major prerequisite for the development, optimization and commercialization of high quality optical components. Especially in laser technology, optical scattering gained of importance in the source of the development of laser system with ever increasing output power and improved beam parameters. Besides its influence on the efficiency of laser systems and the beam steering arrangement, total scattering is an important safety aspect for application of these laser systems in materials processing, medicine and fundamental research. As a consequence of this global trend, working groups of TC 172/SC 9 initialized the development of an International Standard for the measurement of total scattering in optical components.
A light scattering model, based on scalar perturbation diffraction theory, has been used to derive surface roughness information from measurements on transparent thin film samples. The method utilizes the spectral behavior of the diffusely scattered reflectance (transmittance) as compared to the total reflectance (transmittance). By studying interference effects within the film, i.e. correlated and uncorrelated interface roughness contributions, it is possible to separate the origin of the scattering and extract statistical data of the boundaries. In this study, sputtered tin oxide films deposited onto glass substrate has been investigated. Optical characterization was made with a spectroscopic total integrating sphere (TIS) instrument in the wavelength range 0.4 less than lambda less than 1.0 micrometer. Surface roughness data from the light scattering model was compared with atomic force microscope (AFM) measurements through the use of power spectral density (PSD) functions. The AFM measurements made it possible to determine surface roughness scaling properties of sputtered tin oxide thin films with respect to film thickness and scan length.
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