New approach for the critical size of nodular defects: the mechanical connection

Abstract

The purpose of this paper is to determine the effect induced by the nodular defects in optical thin films under laser irradiation. A strong correlation between the size distribution of defects in optical thin films. The deposition parameters and the laser damage threshold is found. With this approach of the defects in thin films, it confirms that the size of a nodular defect is a critical parameter, while the density of the defects is not. The observations of damaged ares, performed by Scanning Electron MIcroscope (SEM), show that of the smallest ejected nodular defects associated with damaged zones, correspond to a critical mean size around 4 micrometers . A mechanical approach is also used to understand the role of the nodular defects under a mechanical solicitation. During the mechanical experiments it appears that depending on the nodular defects sizes, the initiation of cracking was more or less delayed. From the mechanical experiments, a critical size of about 4 micrometers is deduced. Besides, the analysis of these two different experiments points out that the laser damage induced by nodular defects is strongly related to mechanical fracture parameters.