Mechanism of Nanosecond Heat Pulse Generation in Metallic Thin Films

Abstract

In order to understand more clearly the detailed mechanism by which phonons are generated in thin metallic heater films, we have carried out heat pulse experiments with heater excitation pulses only 1 ns long [1]. Previous workers have used pulse lengths typically of the order of 10–100 ns. In this long pulse regime, a steady-state power balance situation is reached where the power absorbed by the electrons in the heater is equal to that radiated into the substrate as phonons. By contrast, the results reported in the present paper correspond to the transient ‘warm-up’ period existing prior to establishment of the steady state. As will be seen, they differ significantly from observations made in the long pulse limit.