To increase the understanding of the damage sensitivity of nodular defects and provide exact evidence for theoretical study, the structures and the damage behavior of nodular defects in electron-beam deposited mirrors of HfO2/SiO2 are systemically investigated with a double-beam microscope (focused ion beam, scanning electron microscope). Nodular defects are classified into two kinds. In one kind the boundaries between nodules and the surrounding layers have become continuous for the last deposited materials, and in the other there are discontinuous boundaries between nodules and the surrounding layers. Nodular defects of the first kind typically have low domes, and the second have high domes. Laser damage experiments show that nodular defects of the first kind usually have a high laser resistance, and the laser-induced damage thresholds are limited in the second class of nodules. The dominant parameter of nodular defects related to damage is the height of the nodular defect.
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