Spectral Reflectivity of Ceramics of Cubic Zirconium Oxide on the Wavelength of $0.63$ $\mu$m under Intense Surface Heating above the Melting Point and Subsequent Cooling

The experimental data on the normally hemispherical reflectivity of zirconium oxide ceramics are obtained for the wavelength of $0.63$ $\mu$m in the course of the first cycle of heating by concentrated laser radiation up to temperatures above the melting point and free cooling in ambient air. The obtained data are compared with analogous results of the second and subsequent cycles of heating and cooling. Analysis is made of the effect of the temperature field in the heated layer on the reflectivity and on the "effective" temperature measured by a pyrometer.