Peculiarities of temperature-dependent Sellmeier equations for periodically poled KTiOPO_4 crystal in the near-infrared and visibleranges

摘要

Crystals of periodically poled KTiOPO_4 (PPKTP) are considered to be promising candidates for the femtosecond OPOs when compared with conventional periodically poled LiNbO_3 (PPLN) crystals that suffer from the large photorefractive effect, thermal damage and high coercive field. In order to design the poling period of PPKTP crystal and to predict the desired wavelength tuning range with required spectral characteristics an accurate calculation using the wavelength- and temperature-dependent Sellmeier equations should be carried out. Although the Sellmeier equations for PPKTP have been published and revised several times, there are still some discrepancies between the measured and the theoretical results. It was reported that a temperature shift of approximately 25 °C has to be introduced in that equation in order to match the experimental results in the near-infrared range. In our work this effect is studied in detail in both the near-infrared and visible ranges in order to provide an accurate reference for the design of PPKTP crystals for various nonlinear frequency conversion applications.