Time Domain Thermo-Reflectance (TDTR) Technique

Frequency-doubled Nd:Yd laser pulses ( 532nm, ~ 10ns ) are focused onto the sample and work as a heating source. Surface temperature of the sample will rise up rapidly, which affects the reflectivity of the sample. A much weaker continuous pulse (He-Ne, 632nm) is focused at the center of pump beam and detect the reflectivity change in time domain. Reflectivity change in time domain is proportional to  the surface temperature, which is related to the thermal properties of the sample. A 1-D thermal conduction model is also used to simulate the surface temperature change. Thermal properties are extracted by fitting the experimental results with simulations.