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We demonstrate that bulk Rb-doped KTiOPO₄ (RKTP) shows improved susceptibility to gray-tracking compared to flux-grown KTiOPO₄ . We show high-fidelity periodic poling of 1 mm thick RKTP with a period of 3.18 µm for second harmonic generation at 398 nm with a normalized conversion efficiency of 1.79%/Wcm. The crystal is used to frequency-double 138 fs-long pulses with an efficiency of 20% and a peak intensity of 560 MW/cm² without visible gray-tracking signs. We demonstrate that two-photon absorption is the predominant mechanism limiting the SHG efficiency in this spectral range at high peak powers and high repetition rates.

We study the thermal stability of domain walls in periodically poled Rb-doped KTP crystals. Domain-wall motion is observed after annealing the crystals above 550°C. This motion is highly anisotropic along the a- and b- crystallographic axes. Along the b-axis domain wall motion is in the order of tens of micrometers. In the a-direction, it results in either three orders of magnitude smaller domain wall displacement or in domain merging, depending on the initial domain configuration. We show that the thermal stability of the domain gratings depends on their periodicity, resulting in complete backswitching for sub-micrometer domains annealed at 730°C. [ABSTRACT FROM AUTHOR]

The article discusses a study of the high temperature (HT) behavior of ferroelectric domains in a periodically poled rubidium-doped potassium titanyl phosphate crystal by Bragg-Fresnel X-ray diffraction imaging. The authors invoked the generation of a built-in electric field in order to model and explain the development and partial disappearance of the inverted domain structure as the temperature increases. They found that at HT, the shape of the contrast image produced by the domains changed from straight parallel lines to a triangular inverted shape.