Frequency domain thermoreflectance
Frequency domain thermoreflectance is a complimentary technique to TDTR, where both the pump and probe lasers are CW diode lasers, and there are no moving parts. By sweeping the modulation frequency from DC-50MHz we can probe thermal transport as a function of depth in the sample. The FDTR is particularly useful in measuring interface thermal resistance across the boundary between two materials.
The system uses a 100mW 405nm pump diode and a 520nm 100mW probe laser optimised for an Au transducer. Balanced detection is used to reduce noise at low frequencies. The system is integrated with a closed loop liquid helium cryostat allowing us to measure thermal transport down to 4K.