| Sumario: | Real time reflectivity measurements at the HeNe laser wavelength (λ=632.8 nm) have been performed in crystalline Sb under pulsed UV laser irradiation (λ=193 nm). For energy densities above 100 mJ cm -2, a transient low-reflectivity phase is observed, which is related to surface melting. The change of reflectivity of the solid material upon heating is small, and a maximum variation of -0.02 relative to the room-temperature value (RSb,rt) is determined for the solid material at the melting point. The value of the reflectivity of the liquid material is determined to be 0.94RSb,rt(632.8 nm)=0.67, which is lower than that of the solid and it is associated with a decrease of the absorption coefficient upon phase change. The analysis of reflectivity transients at energy densities just above the melting threshold suggests that melting nucleation proceeds inhomogeneously.
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