Measurement of the optical constants of Al above the melting point at λ=10.6 μm

The index of refraction, the extinction coefficient, and the absorptance of pure aluminum of technical quality were experimentally determined as a function of temperature for the CO2-laser wavelength. For the measurements, an ellipsometric setup was used. The absorptance jumps from 5% to 38% discontinuously at the melting point, where this result is weakly dependent on the laser power.