title: Photo-induced gratings in thin color center layers on lithium fluoride.
abstract: 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 1000 nm 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.
authors.affiliation: Department of Physical Technologies and New Materials, ENEA, Frascati Research Center,via Enrico Fermi 45, 00044 Frascati (RM), Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Bonfigli
authors.forename: Maria Aurora
authors.initials: MA
authors.lastname: Vincenti
authors.forename: Salvatore
authors.initials: S
authors.lastname: Almaviva
authors.forename: Rosa Maria
authors.initials: RM
authors.lastname: Montereali
authors.forename: Enrico
authors.initials: E
authors.lastname: Nichelatti
authors.forename: Rogério N
authors.initials: RN
authors.lastname: Nogueira
authors.forename: Hypolito José
authors.initials: HJ
authors.lastname: Kalinowski