Exploration of the correlation between weak absorption and thermal-stress for KDP and 70%-DKDP crystals

For KDP and 70%-DKDP crystals, knowledge of thermal-stress distribution induced by weak absorption effect is crucial for their applications, especially in high-power laser systems. Based on photo-thermal common-path interferometry (PCI) technique, the correlations of weak absorption effect with different crystal orientations were systematically evaluated at 1064 nm. An obviously anisotropic property is demonstrated, and a similar pattern of z > x > I > II is also represented for KDP and 70%-DKDP crystals. More importantly, crystal uniformity could be reflected by the weak absorption results, indicating that PCI method could be considered as a novel way to identify the crystal quality. Meanwhile, Thermal parameters including thermal expansion and thermal conductivity were obtained. Using the finite-element method (FEM), the temperature gradients and thermal-stresses along z and x-cut samples were distinctly explored, implying that the corresponding distributions are mainly attributed to crystal orientations. Importantly, another fundamental factor is confirmed that the variation of deuterium content could influence the behaviors of temperature gradients and thermal-stresses distributions. Thus, taking advantage of PCI and FEM as a new approach is more conducive to better understanding the mechanism of laser-matter interactions. (C) 2019 Elsevier B.V. All rights reserved.