15 May 2017 Photopolymers for holographic optical elements in astronomy
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Holographic Optical Elements (HOEs) cover nowadays a relevant position as dispersing elements in astronomical spectrographs because each astronomical observation could take advantage of specific devices with features tailored for achieving the best performances. The design and manufacturing of highly efficient and reliable dispersive elements require photosensitive materials as recording substrate where it is possible to precisely control the parameters that define the efficiency response (namely both the refractive index modulation and the film thickness). The most promising materials in this field are the photopolymers because, beside the ability to provide the tuning feature, they bring also advantages such as self-developing, high refractive index modulation and ease of use thanks to their simple thin structure, which is insensitive from the external environment. In particular, Bayfol HX photopolymers were characterized with the purpose to use them as new material for astronomical Volume Phase Holographic Gratings. We designed and manufactured VPHGs for astronomical instrumentation and we demonstrated how photopolymers are reliable holographic materials for making astronomical devices with performances comparable to those provided by VPHGs based on Dichromated Gelatins (DCGs), but with a much simpler production process. Moreover, the versatility of these materials allowed us to propose and realize novel architectures of the spectroscopic dispersive elements. A compact and unique single prism device was realized for a FOSC spectrograph and new multi-layered devices are proposed, stacking VPHGs one on top of the other to obtain many spectra in the instrument’s detector, with advantages as increase of resolution and signal to noise ratio with respect to the classical single dispersive element.
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A. Zanutta, A. Zanutta, E. Orselli, E. Orselli, T. Fäcke, T. Fäcke, A. Bianco, A. Bianco, } "Photopolymers for holographic optical elements in astronomy", Proc. SPIE 10233, Holography: Advances and Modern Trends V, 1023316 (15 May 2017); doi: 10.1117/12.2264975; https://doi.org/10.1117/12.2264975

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