Optical investigation of the solid-liquid transition in gallium

Reflectance of thin gallium films in the spectral range 0.3-0.9 mu m is measured for several temperatures around the melting point. When melting occurs, the reflectance increases considerably in the whole spectral range (about 20% at 0.6 mu m). A free-electron model is assumed; this is found to be in good agreement with experiments on liquid-phase systems. A qualitative interpretation is proposed and is found to explain the considerable change occurring during melting.