Optical Infrared Coordination Network for Astronomy

Horizon 2020

JRA7 - Innovative Photosensitive Materials for Diffractive and Reflective Optical Elements


Dispersing Elements for Astronomy Workshop, Milan, October 2017This work package aims at developing innovative photosensitive materials for optical elements to be potentially used in the next generation of telescopes and astronomical instrumentation. Indeed, both telescopes and the instrumentation are featuring a strong increase in their complexity, which is not only due to the larger sizes, but also to the demanding performances and accuracy required by the new exciting scientific cases to be faced. The use of innovative materials and processes is a key strategy to reduce the complexity while keeping or improving the performances. Objective of this work is to keep part of the complexity in “smart” materials to develop both diffractive and reflective optical elements. Dispersing elements are key elements in modern spectrographs and Volume Phase Holographic Gratings (VPHGs) are ideal candidates since their compact format and large set of configurable options allow for reducing technical issues in complex instrumentation related to large optomechanical units. At present, VPHGs suffer from well-known limitations, e.g. the limited size, a high manufacturing complexity, only US manufacturers.

In this framework, we will develop innovative holographic materials and processes to meet the European astronomical community demand for gratings in the VIS-NIR spectral range. Starting from the preliminary results obtained with Bayfol® materials, the full process to obtain large size, high quality VPHGs for astronomy will be developed tackling also the optimization of optical properties, such as the wavefront quality. This will pave the way to industrial production of VPHGs in Europe and this option will be evaluated during the project. A strong synergy with WP14 (Time Domain Astronomy) will be established to design and produce VPGHs for low cost spectrographs. In parallel, new holographic materials will be developed to improve the performances of high dispersion VPHGs, thus enabling a new technology as an alternative to common processes based on Dichromated Gelatin (DCG) holographic materials.

Considering the reflective optics, deformable mirrors are widely used in adaptive optics mounted on telescopes and instrumentation, but they can be also used as active optical elements to improve the performances and facilitate the alignment of an optical system. In this activity, we will develop an innovative deformable mirror controlled by light (Photo Controlled Deformable Mirror, PCDM). In such mirrors, a light pattern projected on a slab of a photoconductive material generates virtual actuators able to deform the mirror surface. This platform offers control of the DM with a reduced system complexity with respect to the other technologies (electrostatic and piezoelectric) used in the astronomical field. It is crucial to understand if this new approach matches the requirements of deformable mirrors for astronomy mainly in terms of dynamic range, speed, stability. The modelling of the PCDM will be important to find key properties of the photoconductive material that affects the performances. The DMD (Digital Micromirror Device) technology will be the control-command tool for shaping the light pattern to be sent on the mirror, with high speed and fully reconfigurable dynamically, inducing the deformation of the mirror surface.

ESO Messenger Report

Workshop "Dispersing Elements for Astronomy: New Trends and Possibilities" [ESO/PDF]


Andrea Bianco -