Hydrogen defects and optical damage in LiNbO₃

The literature pertaining to hydrogen defects dissolved in lithium niobate has been reviewed. Particular attention has been given to the infra-red absorption spectra. The polarization variations of the spectra give indications about the structure of hydrogen defects in lithium niobate. In undoped crystals hydrogen defects sit in the close-packed oxygen plane, adjacent to vacant octahedral sites that result from nonstoichiometry. In magnesium doped crystals the observed threshold effect influences the hydrogen site; at low Mg concentrations there are sufficient vacant octahedral sites, but at high concentrations the hydrogen must sit adjacent to cations and are therefore pushed out of the close-packed oxygen plane. This changes the IR spectra. The hydrogen solution model is discussed with respect to optical damage effects in lithium niobate.