Over the coming months, the world’s largest Fabry-Pérot interferometer (FPI) will be assembled and tested at the Kiepenheuer Institute for Solar Physics. Among its main components are two high-purity quartz glass disks, each coated on one side with a highly reflective layer. The coated surface has a diameter of 28 cm and its mean evenness does not exceed the incredible value of 0.000 000 001 m. By way of comparison, if lake Titisee in the Black Forest had this evenness, this would imply that the height of its waves remains below 5 micrometers (1/10 of a hair). On a smaller scale, the roughness of the coated surface is even 10 times better, reaching the size of individual atoms.

The data archive of the GREGOR infrared spectrograph (GRIS, Collados et al. 2012, AN 333, 872) is online now. GRIS data prior to 2017 is open access and now available through the GRIS data archive. It contains more than 500 data sets recorded in the years between 2014 and 2016. Most of them are single raster scans recorded in spectropolarimetric mode in the 1.08µm and 1.56µm wavelength bands. Some of them are measurements in spectroscopic mode, time sequences capturing the evolution of solar features, and observation in other wavelength bands such as 2.2µm.