Abstract: A focused, cw CO$-2$/ laser is used to irradiatepolished Cu mirrors at power densities near 40kW/cm$+2$/. Uncoated mirrors and mirrors having areflection-enhancing Au coating with a protectiveY$-2$/O$-3$/ layer are tested. During irradiationin-situ measurements of the temperature distribution inthe surface are made and the morphology is monitored byinterferometry. Chemical changes are determined byex-situ x-ray photoemission and scanning Augermeasurements. Damage to uncoated mirrors is connectedwith irreversible deformation, an increase in thermalgradients under irradiation (attributable to increasedabsorption), and oxidation of the surface layer, withformation of Cu$-2$/O and CuO. While the whole surfacebecomes oxidized, the effect is strongest in the laserfocus, where an enhanced carbon content is also found.Similar thermal and morphological changes occur incoated mirrors under analogous irradiation conditions,but the relatively inert Y$- 2$/O$-3$/ protective layeris not chemically changed. Structural changes arepresent in the surface and may contribute to thechanged absorption. !5
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