International round-robin experiment for angle-resolved light scattering measurement.

An international round-robin experiment has been conducted to test procedures and methods for the measurement of angle-resolved light scattering. ASTM E2387-05 has been used as the main guide, while the experience gained should also contribute to the new ISO standard of angle-resolved scattering currently under development (ISO/WD 19986:2016). Seven laboratories from Europe and the United States measured the angle-resolved scattering from Al/SiO-coated substrates, transparent substrates, volume diffusors, quasi-volume diffusors, white calibration standards, and grating samples at laser wavelengths in the UV, VIS, and NIR spectra.

Roughness and optical losses of rugate coatings.

Light-scattering measurements on rugate coatings made out of mixtures of Si(x)Ta(y)O(z) and Si(x)Hf(y)O(z) were performed. Through successive optimization steps for the substrate roughness and deposition parameters, the overall scattering loss could be reduced by 96% to 3.5 ppm.

Characterization of optical coatings using a multisource table-top scatterometer.

Light scattering measurement and analysis is a powerful tool for the characterization of optical and nonoptical surfaces. To enable a more comprehensive postmeasurement characterization, three visible laser sources were recently implemented in a highly sensitive table-top scatterometer with 3D spherical detection capability. Based on wavelength scaling, the instrument is utilized to characterize thin-film coatings and their substrates with respect to surface roughness, roughness growth, and contamination.

Scattering reduction through oblique multilayer deposition.

Scattering from multilayer coatings depends on the roughness of each interface as well as their cross-correlation properties. By depositing thin film coatings under oblique incidence, the cross-correlation properties can be specifically adapted and consequently also the scattering characteristics. This will be illustrated for Mo/Si multilayers, for which a scattering reduction of more than 30% can be achieved.

Evaluation of subsurface damage by light scattering techniques.

Subsurface damage (SSD) in optical components is almost unavoidably caused by mechanical forces involved during grinding and polishing and can be a limiting factor, in particular for applications that require high laser powers or an extreme material strength. In this paper, we report on the characterization of SSD in ground and polished optical surfaces, using different light scattering measurement techniques in the visible and extreme ultraviolet spectral ranges. The materials investigated include fused silica, borosilicate glass, and calcium fluoride.