PUMP-PROBE THERMOREFLECTANCE

Pump-probe thermoreflectance is an optical technique used to measure heat transfer in bulk materials and micro- and nanoscale samples. The measurement typically uses two light sources, referred to as the pump and the probe. The pump generates a time-dependent heat flux at the sample surface, while the probe monitors the temperature response through a proportional change in surface reflectivity. Combined with a heat transfer model, the measured temperature response is used to infer transport properties such as the cross-plane thermal conductivity, in-plane thermal conductivity, heat capacity, and the thermal boundary conductance between materials. The measurement has diffraction-limited lateral spatial resolution and is effective on bulk materials and films as thin as a few nanometers. This chapter begins with a nonexhaustive overview of pump-probe thermoreflectance tailored to the measurement of heat transfer in small scale. This is followed by a description of the experimental setup and data analysis used in typical implementations of time- and frequency-domain thermoreflectance, and then a discussion on the measurement of in-plane and cross-plane heat transfer in bulk materials and thin films.