Case Study of a Fly's Eye Homogenizer for the Calibration Illumination of Integral Field Units

ABSTRACT

Integral‐field unit spectrographs require a homogeneous calibration illumination of the field of view for proper flat and wavelength calibration (e.g., BlueMUSE which is currently under development for the VLT). This article presents the adaptation of a fly's eye homogenizer, frequently used in laser applications, to this task in astronomical instrumentation. It's capabilities will be compared to the frequently used integrating sphere. Motivation to this work is to develop a more efficient system in order to use fainter calibration sources and to maintain the possibility of mixing different sources. We find that such a system provides a homogeneous illumination of the near field of 2% rms measured for wavelengths 470, 530, and 630 nm and for seven individual sources that can be mixed. The system presented provides a measured focal ratio of and can be adapted to match to a specific telescope.