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We report on the dynamic melt-threshold method for the in situ determination of the effective thermal conductivity of thin layers in phase-change optical recording stacks. The method is based on the systematic variation of some of the thermal parameters of the thin films in the recording stack such that the temperature of the phase-change layer, calculated with a multilayer numerical model, equaled the measured melt temperature of the phase-change material. The laser power that causes the onset of melting, the melt-threshold power, was determined from the detectable reflection difference between the crystalline and molten state of the phase-change film and served as input for the model calculations. Melt-threshold experiments were performed for different recording velocities, stack structures, layer thicknesses and optical spot sizes. The melt-threshold method provided a consistent set of thermal parameters that accurately predicts the temperature distribution in a recording stack during erasing and recording of data. Hence, the method is very suitable to calibrate a multilayer thermal model that is used for the optimization of, for example, write strategies or thermal stack designs. The accuracy of the determined effective thermal conductivity of the dielectric layers is estimated to be within 10%–20%, that of the phase-change layer is determined with less accuracy. The melt-threshold method is easily extended to recording stacks with metal heat sink layers. © 2003 American Institute of Physics.