The growth and characterisation of tantalum and niobium doped KTP

It is known that compositional modification of KTP can be used to tailor its linear and nonlinear properties. Substitution of Ta or Nb onto Ti sites in KTP increases the birefringence to potentially allow SHG phase matching into the technologically important blue region. Crystals were grown using a top seeded solution technique that incorporates a crystal weighing facility. Ta or Nb doping of the growth solution affects the growth temperature and causes habit modification of the crystals. X-ray topographical examination of the doped crystals revealed a high degree of imperfection compared with undoped KTP. Measurements of Curie temperature showed T-c to be significantly lowered by doping. Device-quality crystals were prepared to enable physical and optical property determination and SHG device trials. The NCPM SHG wavelength was shifted as far as 917 nm, the shift being proportional to the dopant concentration in the crystal. Although Ta and Nb showed similar effects, Ta doping is more effective because the segregation coefficient of Ta is twice that of Nb. X-ray structure determination confirmed that this is due to the ability of Ta to substitute on both distinct Ti sites, while Nb can occupy only one site. Thus, Ta:KTP can usefully extend the phase matching range of KTP.