In this paper a method to obtain very high diffraction efficiency fixe
d holograms in lithium niobate is presented. The procedure consists in
a first step of high temperature recording and fixing of a hologram w
ith very high refractive index modulation, followed by a second step o
f controlled thermal erasure until the point of maximum diffraction ef
ficiency is achieved. (C) 1998 Elsevier Science B.V.