Influence of water vapor on the susceptibility to electric-field damage of KTiOPO4

We demonstrate that the susceptibilities of hydrothermal and flux grown KTiOPO4 (KTP) crystals to electric-field induced darkening increase with increasing water vapor content of the atmosphere surrounding the crystals. Infrared spectroscopy shows that hydrogen ions from the atmosphere migrate into the crystals in the presence of the applied electric field and charge compensate the formation of Ti3+ defects which are responsible for damage. These observations suggest that KTP-based electro-optic devices should be operated in a dry environment to reduce their susceptibility to damage.