Fighting the devil within: improving image quality by thwarting local turbulence

Image quality is sensitive to temperature fluctuations on the optical path, even if these are not fully developed turbulence. Thus, it's crucial to control the thermal environment, be it on a test bench in the laboratory, in instruments (e.g., entrance windows, near electronics), within domes and telescope structures. It is especially crucial where the beam is small (i.e., going through a focus) and the power spectrum of the refractive index can be anything from high frequencies to just tiptilt. We have used our optical turbulence sensor AIRFLOW to explore how a DT of a few degrees in the optical path can undo a lot of what an AO system can improve, and we are using our devices to study quantitative ways to minimize the image degradation induced by temperature fluctuations. These may include counterintuitive measures such as fans mixing the air at different temperatures, because mechanical turbulence with no DT doesn't produce optical turbulence.