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Photo-induced gratings in thin color center layers on lithium fluoride

Bonfigli, F. ; Vincenti, M. ; Almaviva, S. ; Montereali, R. ; Nogueira, R.N. ; Kalinowsky, H.

Applied Optics Vol. 48, Nº 31, pp. G38 - G43, November, 2009.

ISSN (print): 2155-3165
ISSN (online): 1559-128X

Journal Impact Factor: 1,763 (in 2008)

Digital Object Identifier: 10.1364/AO.48.000G38

We study the recording of permanent Bragg gratings on surface-colored lithium fluoride (LiF) crystals by
using the interference pattern of a continuous-wave UV argon-ion laser operating at 244 nm. Gratings
with spatial periodicity ranging from 400 to 1000nm are written by using a phase-mask interferometer
and are stable for several months after the writing process. Absorption and photoluminescence spectra
show the bleaching of primary F and F -aggregate laser-active color centers as a result of the process.
Confocal microscopy is used to determine the pitch and the profile of the fluorescent gratings. The UV
laser-induced optical bleaching in highly colored LiF ultrathin layers is responsible for the periodic
spatial modulation of absorption and photoemission properties that characterize the gratings. In the
colored surface layer, a reduction of as much as 50% of the initial color-center-induced refractive-index
increase has been estimated in the bleached areas.