Comparative study of the steady and transient photoluminescence induced by plastic and brittle surface defects and their correlation to the laser damage performance of KDP crystal optics

The micro-defects on optics surfaces are generally regarded as the laser damage precursors under high-fluence laser irradiations (>8 J/cm(2), 355 nm, 3 ns). The photoluminescence (PL) emission process possesses strong commonality with the mechanisms of laser-induced damage (i.e., nonlinear ionization and decay of electrons under laser irradiation), that it could be applied to effectively characterize the effect of surface defects on the laser damage resistance of optical components. Nevertheless, the quantitative relationship between the defect morphology and its PL characteristics has not been established, restricting its practical application. Herein, the artificial indentations were prepared on KDP optics surfaces, and their PL spectra were detected and analyzed through a self-develop PL detection system. The concentration of atomic intrinsic defects accompanying visible surface defects and the transient PL lifetime were obtained. It is interestingly found that the concentrations of intrinsic defects in brittle defects are higher than those in plastic defects, which results in stronger PL signal intensity. The concentration changes of the oxygen vacancy defect (OVD) are the most significant with the degree of brittleness of the visible defects increasing. Additionally, the PL process of brittle defects decays faster than that of plastic defects. The laser-induced damage threshold (LIDT) of KDP optics in the lateral crack zones of the indentations is positively correlated with the PL lifetime and negatively correlated with the concentration of the OVD intrinsic defect. The concentrations of the OVD intrinsic defect and the PL lifetime are proposed to quantitatively characterize the brittleness and plasticity of the defects, which are strongly related to the LIDT. The PL spectra characteristics could provide a new pathway for predicting the laser damage resistance of the optics and revealing the mechanisms of laser induced damage.