Improving stitching interferometry measurements by a continuous airflow.

Abstract

The stitching interferometry system of ALBA, based on a Fizeau interferometer, is robust to displacement errors and reference manufacturing errors. Nevertheless, it is very sensitive to environmental noise, particularly when measuring long mirrors. One way to reduce the impact of environmental noise is by averaging repeated measurements of the same surface area. However, averaging involves longer measurements, resulting in a compromise between time and measurement uncertainty. In this work, we explore the effect of a fan-generated continuous airflow to reduce the impact of environmental noise. In order to investigate this aspect, we evaluate the contribution of the airflow to Fizeau's surface reconstruction repeatability, conduct a frequency analysis of the interferometric acquisitions, and perform computational fluid dynamics simulations. Finally, we replicated ALBA's standard stitching measurement procedure, using a 550 mm section of an x-ray mirror, to assess the advantages of employing a fan with rotating blades for improving measurement repeatability.