Time domain thermoreflectance
Time domain thermoreflectance is a pump-probe optical technique for measuring electron-phonon coupling, picosecond acoustics and thermal diffusion in thin films and nanomaterials. A pump laser rapidly heats a sample surface and a delayed probe laser measures the time dynamics of the surface temperature as it cools. Fitting this time decay allows quantification of thermal conductivity, interface thermal conductance, diffusivity or heat capacity of the underlying materials.
We have developed a two colour system based on a 130fs Ti:Saphire laser. The pump wavelength is the frequency doubled 415nm, with the probe wavelength at 830nm. This allows us to use an aluminium transducer, which is sensitive and self-passivating. A delay line allows us to measure delay times out to 6 ns. Samples results of AlN on InP are shown below.
Fitting the ratio of X/Y allows extraction of thermal conductivity of the AlN thin film and interace thermal resistance between AlN and InP. The system is also used to monitor non-linear optics and ultrafast dynamics, such as exciton relation and valleytronic effects in 2D nanomateirals. Additionally with a static magnetic field it can be used for TR-MOKE studies of spin relaxation in magnetic thin films.