PHASE-TRANSITION STUDY OF HLINBO3 WAVE-GUIDES BY RAMAN-SPECTROSCOPY

New results on Raman spectra of protonated LiNbO3 are reported in order to clarify the sturctural and compositional changes in waveguide layers during proton exchange and post-exchange annealing processes. Samples with different degree of Li-H substitution exchanged in either neat or buffered benzoic and pyrophosphoric acid melts are investigated providing Raman and optical measurements simultaneously. The question of phase state of protonated layers at slow and rapid cooling after the annealing procedure is discussed. Qualitative and quantitative agreement between the structural data reported earlier for proton-exchanged powders and the Raman data obtained for protonated single crystals is established. A new band at 69 cm-1 is observed which is strongly intensity dependent upon the hydrogen presence in waveguide layers. By using this band the degree of proton exchange is determined for different treatment conditions of the samples.