A breakthrough instrument for wide-range wavelength and angle resolved light scattering measurements of high performances optical coatings

Abstract

Due to the diversity and complexity of optical functions they address, optical coatings are widely used in space optics but the level of both their specifications and performances is now so high that the characterization of their optical properties requires the development of extreme metrology. In this context we present in this paper the last state-of-the-art instrument for thin-films characterization. This apparatus is unique by the performances and the levels of detectivity achieved. It operates spectrally and angularly resolved characterization of Angle Resolved Scattering (ARS) over a wide and continuous spectral range from 400 nm to 1.7 μm. The spectral resolution is lower than 1 nm, while the angular resolution is lower than 1° with a precision better than 1%. The lowest levels of scattering measured are close to 10 -8 sr -1 , near to the limit of air particles scattering. The large angular range available offers the opportunity to evaluate scattering functions both in the forward and backward half-spaces. In specific configurations, this same setup records specular properties, achieving again unreached levels of detection and precision over the same spectral range and with the same resolution. All measurements have shown great agreement with theoretical designs and numerical predictions, for both scattering and transmittance records. This instrument is an upgraded version of an apparatus developed in the Scattering group for more than five years formerly operating in the visible wavelength spectrum and now extended to near-infrared with the same level of performances.

Development of an experimental facility for the measurement of photo-induced thermal emission in interferential filters

“…Optical coatings are currently used in several industrial and scientific areas such as spatial [1], [2], defense [3], [4] or energy conversion [5], [6], [7]. Their interaction with light has been investigated in detail, and today we have a great knowledge of processes such as absorption [8], [9], scattering [10], [11], laser induced damage threshold [12], [13] and others. Another phenomena that has not been deeply studied yet is time domain photo-induced thermal radiation (PhTR), though this can be extremely useful in industrial applications such as Daytime Radiative Cooling [5], [6], [7], thermal camouflage [3], [4], [14] or dynamic control of emissivity [15], [16].…”