Laser method for the determination of the optical and thermal characteristics of diamond at high temperatures

The temporal and temperature dependences of the reflectivity, transmissivity, and absorptivity and of the heat capacity of thermally thin diamond plates were obtained in the course of heating up to 2500 °C at a rate of 10³ — 10⁴ K s^–1 by laser radiation with λ = 1.064 μm. The temperature range in which significant irreversible changes take place in the optical properties of diamond films was determined. These changes are associated with the formation of graphite microstructures in a thin surface layer about 100 nm thick. The formation of clusters of aromatic carbon atom groups with the sp² bonds is described. It is shown that the extinction coefficient of the modified layer is three orders of magnitude higher than that of the unmodified layer.