30 January 2002 New facility for large-scale DCG transmission holographic gratings: status and evaluation
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Abstract
The recent interest of the astronomer community for volume phase holographic gratings is directly related to the enhancement of spectrograph throughput since the grating can rise higher diffraction efficiency. Indeed, dichromated gelatin technology has demonstrated capability for 70-90% efficiency. From the heritage of several diffractive and holographic projects and applications, the Centre Spatial de Liege has recently decided to invest in the large-scale DCG grating technology. This paper will present the new facility presently under construction. The goal is to be ready to respond to the market demand in 2002 with a capacity for producing 30 cm dia. holographic gratings. The challenge is not the size itself but the quality control in each process step. Thanks to the heritage of space instrumentation, CSL is trained to fulfill requirements on product and quality control. Large clean rooms are equipped with DCG coating machine, optical bench, development lab, and conditioning processes. The grating period may range from 325 to 3000 lp/mm. Low frequencies are especially hard to holographically record because it induces a cumbersome set-up. The working wavelength of DCG gratings is limited by the gelatin transmissivity (from 350 nm to 2 micrometers ). But the actual limitation factor in the IR is the refractive index modulation, equivalent to etching depth on ruled gratings: working wavelength of 1.5 micrometers means a need for 3 times the modulation of a visible grating. Large efforts are needed to insure that IR volume-phase gratings can reach efficiency higher than alternative grating technologies. In that field, this paper presents experimental results on small grating samples. A realistic performance goal is discussed to advise the astronomer community of our near-future products.
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Serge LM Habraken, Serge LM Habraken, Philippe C. Lemaire, Philippe C. Lemaire, Pierre-Alexandre Blanche, Pierre-Alexandre Blanche, Claude A. J. Jamar, Claude A. J. Jamar, } "New facility for large-scale DCG transmission holographic gratings: status and evaluation", Proc. SPIE 4485, Optical Spectroscopic Techniques, Remote Sensing, and Instrumentation for Atmospheric and Space Research IV, (30 January 2002); doi: 10.1117/12.454282; https://doi.org/10.1117/12.454282
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