; initiation of second-order optical non-linearity in glasses
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initiation of second-order optical non-linearity in glasses


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     Sigaev V.N.1, Sarkisov P.D.1, Stefanovich S.Yu.2, Pernice P.3, Aronne A.3, Champagnon B.4,
                            Zakharkin D.A.5, Sakharov V.V.5, Baskov P.B.5
     Mendeleev University of Chemical Technology, Miusskaya sq.,9, Moscow 125190, Russia
   L.Ya.Karpov Institute of Physical Chemistry, ul. Vorontsovo pole,10, Moscow 104306, Russia
            University of Naples “Federico Secondo”, P.lle Tecchio, Naples 80125, Italy
                          University of Lyon-1, Villeurbanne 69622, France
    All-Russian Institute of Chemical Technology, Kashirskoe shosse, 33, Moscow 115509, Russia

         Modern data on non-linear optical properties of glasses induced by bulk or surface
nanostructuring with non-centrosymmetric crystals, amorphous nanostructuring, and poling, are
shortly reviewed in the present report.
         Glasses are considered to be optically isotropic media that, theoretically, can not exhibit
second-order optical non-linearity (SONL) and second harmonic generation (SHG) effect.
However, many attempts have been undertaken for the last decade to induce optical non-linearity in
glasses and some observations of SHG in glassy materials have been recently reported. They may
be subdivided to two main groups depending on the mechanism originating the SHG. The first
group is formed by poled glasses, where the non-linearity is induced by exposition of glasses to an
appropriate external excitation field, such as high power infrared laser beam (laser-poling), or high
voltage DC-electric field at temperatures about 100-300°C (thermal-poling), or ultraviolet laser
beam coupled with a high voltage DC-electric field (UV-poling). Nanostructured glasses (NG), i.e.
transparent or slightly opalescent glasses containing nano-scaled highly polarizable crystals (-
BaB2O4, LiNbO3, BaTiO3, KNbO3, KNbSi2O7, KTiOPO4, etc) form the second group.
     In the development of new non-linear optic media, the crystallisation behaviour of glasses in the
K2O-TiO2-P2O5 (KTP) system near the KTiOPO4 composition as well as glasses of compositions
xK2O.xNb2O5.(1-2x)SiO2 (KNS), with x from 0.167 to 0.3, and lanthanum borogermanate (LBG)
glasses near the stoichiometry of stillwellite LaBGeO5 has been studied by DTA, XRD, EM and
SHG to isolate composition ranges where bulk precipitation of ferroelectric KTiOPO4, KNbO3,
KNbSi2O7 or LaBGeO5 occurs. NGs exhibit SONL, the nature of that is connected with their
crystallisation behaviour. Amorphous nanostructuring of glasses for initial stage of phase separation
is proposed to may induce moderate SHG effect too. It was first established SHG may be induced in
glasses by hot extrusion at temperatures just above Tg value.
     This work was supported by NATO, grant SfP-977980, Russian Foundation for Basic Research
(RFBR), grant 02-03-32105, and the program of RFBR and Belarussian FBR, grant 02-03-81002.

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