ABSTRACT
This work investigates and compares three laser-based ac heating methods for measuring thermal diffusivity of free-standing thin-film structures. These methods employ a modulated laser beam as the heating source and a miniature thermocouple as the temperature sensor. Three laser beam configurations including uniform illumination, a line, and a point are utilized as the heating sources. Different models and systems are developed for these beam configurations. Samples studied include a GaAs/AlGaAs two-layer thin-film structure, a periodic GaAs/AlAs thin-film structure, and a silicon film. Both the phase and the amplitude signals of the ac temperature rise of samples are used to derive their thermal diffusivities. It is found that the uniform illumination method is more susceptible to error than the other two configurations due to two-dimensional effects. Both the line and the point source configurations yield satisfactory results.
