Angle-resolved scattering: an effective method for characterizing thin-film coatings

Abstract

Light scattered from interface imperfections carries valuable information about its origins. For single surfaces, light-scattering techniques have become a powerful tool for the characterization of surface roughness. For thin-film coatings, however, solving the inverse scattering problem seemed to be impossible because of the large number of parameters involved. A simplified model is presented that introduces two parameters: Parameter δ describes optical thickness deviations from the perfect design, and parameter β describes the roughness evolution inside the coating according to a power law. The new method is used to investigate structural and alteration effects of HR coatings for 193 nm, as well as laser-induced degradation effects in Rugate filters for 355 nm.

Light scattering characterization of optical components for space applications

“…Various instruments for angle resolved scatter measurements were developed at Fraunhofer IOF together with analysis techniques to link the measured light scattering distributions to the corresponding surface or thin film properties [4][5][6][7][8][9]. This includes systems for different spectral regions, such as extreme ultraviolet, ultraviolet, visible, near-infrared, and infrared, applying different measurement principles.…”

“…The main difference between both systems is that MLS-1600 has a tunable laser source, based on an optical parametric oscillator, which offers the selection of arbitrary wavelengths between 250 nm and 1.5 µm [6]. ALBATROSS, in contrast, uses a pool of single laser sources with discrete wavelengths between 325 nm and 10.6 µm [5]. Both systems offer highest flexibility and sensitivity while simultaneously meeting the requirements for highly resolved light scattering measurements.…”

Vane-free design for star trackers and telescopes

“…The instrument is located in a clean room (ISO 7) under laminar flow boxes (effective ISO 5) and capable to perform measurements ranging between 325 nm and 10600 nm illumination wavelength. The scatterometer achieves the sensitivities and dynamic ranges necessary to characterize high end optical components, materials, and black coatings [8].…”

Light scattering techniques for the characterization of optical components

“…Various instruments for angle resolved scatter measurements were developed at Fraunhofer IOF together with analysis techniques to link the measured light scattering distributions to the corresponding surface or thin film properties [8][9][10][11]. This includes systems for different spectral regions using various detector elements and measurement principles.…”