OPTICON FP7 (2013-2016) WP6 - Novel Dispersive and Holographic Optical Elements for Astronomy
WP leader: Filippo Zerbi(INAF)
Traditional (DCG-based) VPHGs are currently the baseline element for numerous astronomical instruments under design or construction, but the number of vendors of astronomical VPHGs in the world has recently fallen dramatically. Europe has lost its only VPHG producer, leaving us dependent on the single US producer remaining active in this market. This situation represents a risk for instrument development in terms of reduced variety and quality of the available devices as well as increased cost. It is vital to the European astronomical community that we establish new and reliable European suppliers.
We will address this problem by investigating new materials to replace Dichromated Gelatin (DCG) using specifically tailored photopolymers which are candidates to replace DCG in a wide range of astronomical applications, but their chemical synthesis and film deposition technique requires further study. For example suitable film preparations tailored to the specific chemical product, must be invented and applied The selected and optimized process then needs to be injected into the commercial market in order to set-up possible suppliers for the astronomical community. This requires a pre-prototyping and process standardization activity to allow industrial partners to take over the production using well understood recipes with adequate control over product quality and cost.
We will also investigate Photochromic-Based Holographic Optical Elements (HOE) for astronomy: a programme which has produced some outstanding and innovative results. It has opened up the study of the application of photosensitive and photochromic materials to astronomical Instrumentation and continued through the definition and production of performance-representative prototypes. The application of these materials to astronomical instrumentation is diverse and covers the area of gratings, masks, Fresnel Lenses, etc
A new factor which emerged during our earlier FP7 activity was the existence of polymer fibres close to astronomical science-grade qualification. Fibres were obtained with extraordinary low internal absorption over very long lengths and wide wavelength range. A number of samples of this type of fibre have been studied as part of our existing activity looking at those aspects related to astronomical application such as FRD, Scrambling, etc. The results are controversial but promising and certainly prompt further study of these devices. Telescopes and instruments have increased tremendously in size in the last decade and this trend will continue with the E-ELT. Longer fibre lines are thus required and this conflicts with the poor internal transmission of commonly used fibres. Polymer fibres with very high and broad-band internal transmission are good candidates to replace glass in these applications
We will also study how the use of Digital Micro-mirror Devices (DMD) in hologram recording can be ported into fields of interest for the astronomical instrumentation such as the measuring and characterization of complex-form optics via computer generated holograms.
