DFB laser frequency stabilization unit at 1572 nm

Abstract

The knowledge of the bi-directional scattering distribution function (BSDF) of an optical component is an import requirement for the design and assessment of high-performance optical instruments. However, precise BSDF measurement with high resolution close to the specular beam can be very challenging and require sophisticated instrumentation.In this paper, we present a newly developed scatterometer, the "Enhanced Resolution Light Scattering Analyzer for Curved Gratings (single detector axis)" -ELSA/CG-S which is designed specifically to measure the BSDF of curved optical components with a very high resolution not only close to the specular direction, but throughout the whole angular measurement range with an instrument signature that can compete with the top of the class of current commercially available instruments. The distinguishing feature of the instrument is the use of a high-resolution silicon sCMOS imaging detector which enables fast acquisition times and provides access to a two-dimensional section of the BSDF around the main detection plane of the instrument with an out-of-plane FoV of about ±0.6°.In the following, we will describe the general design of the instrument and explain the measures that have been taken to enable a very low stray light signature with the chosen detection scheme. After this, we will assess the instruments capabilities and present measurements of the instrument signature and BRDF measurements of plane and curved diffraction gratings with high groove densities. These measurements will also demonstrate the additional value that is provided by using an imaging detector. All measurements will be compared to results obtained with ESTEC's commercial CASI scatterometer from The Scatter Works, that represent the current state of the art.