Roles of absorbing defects and structural defects in multilayer under laser radiation were investigated. The HfO2/SiO2, dielectric mirrors for 355 nm were prepared by conventional electron beam deposition. Two kinds of HfO2 with different purity were chosen as the high index material, and impurity content of the materials was accessed by glow discharge mass spectrometer (GDMS) and X-ray photoelectron spectroscopy (XPS). Laser damage testing was performed in both the "1-on-1" and "s-on-1" regime, using 355 nm pulsed laser at a pulse length of 8 ns. It was found that the single-shot laser-induced damage threshold (LIDT) is much higher than that of the multi-shot, and the absorbing defects hindered the improvement of laser damage resistivity greatly in the single-shot process, but in multi-shot mode the main factor influencing LIDT is accumulation of irreversible changes of structural defects. Optical microscopy and surface profiler were employed in mapping laser-induced damage morphology features after irradiation. (C) 2003 Published by Elsevier B.V.