Laser conditioning of optical coatings: some issues in the characterization by atomic force microscopy

Abstract

We have studied the changes of dielectric optical coatings after laser conditioning using atomic force microscopy (AFM). Laser conditioning is the process which consists of illuminating a film by a laser below damage threshold in order to increase this threshold value. This method is implemented for optics used in high fluence laser beam such as Nd-glass lasers (1064 nm, 3 ns pulse length). We have studied e-beam evaporation deposited highly reflective multilayer Zr02/5i02 mirrors, and also single layers of 5i02, Hf02 and Zr02.We have observed the modification of the surface after laser conditioning using the AFM. We find that this process results in localized minimization or elimination of defects (nodules, craters etc...). Furthermore, the origin of the increase in the size of the hillocks observed after laser conditioning and previously reported by other groups, has been experimentally identified as an instrumental artifact.One major mechanism supposed to be responsible for laser conditioning effects consists of "laser cleaning" for which absorbing contaminants (especially water) are desorbed before damage occurs5. O-8194-1407-7194/$6.OO SPIE Vol. 2114/355 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx