SEDL / STP / STP954-EB / STP23137S

Scanning Electron Microscopy Studies of Laser Damage Initiating Defects in ZnSe/ThF⁴ and SiH/SiO² Multilayer Coatings

Johnson, LF
Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

Ashley, EJ
Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

Donovan, TM
Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

Franck, JB
Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

Woolever, RW
Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

Dalbey, RZ
Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

Pages: 15    Published: Jan 1986

Download this paper for $25 PDF (684K)          View License Agreement
Abstract

Scanning electron microscopy (SEM) was used to identify four distinct laser damage morphologies in ZnSe/ThF⁴ multilayer mirrors. There were three types of defect-initiated damage morphologies. Oblong-shaped damage sites oriented perpendicular to the electric field vector of the laser were associated with particulates on or near the surface of the ZnSe/ThF⁴ multilayers. Circular-shaped damage sites were initiated by particulates embedded beneath the top ZnSe layer. Selective laser damage at pinholes was identified as the third defect-initiated damage morphology. In addition to defect-initiated damage, stress-related damage was indicated by cracks near or within laser damage craters and erosion sites. Selective laser damage at nodular growth defects in SiH/SiO² multilayers was also observed using SEM. Samples with different numbers of nodules were prepared in-house using RF-diode, reactive sputtering. The low-defect mirror had the highest laser damage onset, and the mirror with the highest number of nodules had the lowest laser damage onset.