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  1. OA@INAF
  2. PRODOTTI RICERCA INAF
  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
  4. 1.01 Articoli in rivista
Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/28526
Title: Experimental characterization of modal noise in multimode fibers for astronomical spectrometers
Authors: OLIVA, Ernesto 
RAINER, Monica 
TOZZI, Andrea 
SANNA, Nicoletta 
Iuzzolino, M.
BRUCALASSI, ANNA 
Issue Date: 2019
Journal: ASTRONOMY & ASTROPHYSICS 
Number: 632
First Page: A21
Abstract: Starting from our puzzling on-sky experience with the GIANO-TNG spectrometer we set up an infrared high resolution spectrometer in our laboratory and used this instrument to characterize the modal noise generated in fibers of different types (circular and octagonal) and sizes. Our experiment includes two conventional scrambling systems for fibers: a mechanical agitator and an optical double scrambler. We find that the strength of the modal noise primarily depends on how the fiber is illuminated. It dramatically increases when the fiber is under-illuminated, either in the near field or in the far field. The modal noise is similar in circular and octagonal fibers. The Fourier spectrum of the noise decreases exponentially with frequency; i.e., the modal noise is not white but favors broad spectral features. Using the optical double scrambler has no effect on modal noise. The mechanical agitator has effects that vary between different types of fibers and input illuminations. In some cases this agitator has virtually no effect. In other cases, it mitigates the modal noise, but flattens the noise spectrum in Fourier space; i.e., the mechanical agitator preferentially filters the broad spectral features. Our results show that modal noise is frustratingly insensitive to the use of octagonal fibers and optical double scramblers; i.e., the conventional systems used to improve the performances of spectrographs fed via unevenly illuminated fibers. Fiber agitation may help in some cases, but its effect has to be verified on a case-by-case basis. More generally, our results indicate that the design of the fiber link feeding a spectrograph should be coupled with laboratory measurements that reproduce, as closely as possible, the conditions expected at the telescope
URI: http://hdl.handle.net/20.500.12386/28526
URL: http://arxiv.org/abs/1910.09795v2
https://www.aanda.org/articles/aa/abs/2019/12/aa36610-19/aa36610-19.html
ISSN: 0004-6361
DOI: 10.1051/0004-6361/201936610
Bibcode ADS: 2019A&A...632A..21O
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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