Characterization Method
Non contact measurement techniques that use ultra short laser pulses to excite a sample and monitor its thermal response provide data on the nanometer scale. Employing optical pump probe thermal testing allows researchers to measure the thermal conductivity of thin films and interface resistances without physical sensors. One laser acts as the heater while the second laser detects changes in the reflectivity of the surface as it cools.
This method is essential for studying materials used in advanced semiconductor nodes.
Physics Mechanism
The change in the temperature of the material alters its refractive index and surface height. In optical pump probe thermal testing these small variations are captured by a photodetector with extremely high sensitivity. The resulting signal is a direct function of the heat diffusion into the bulk of the material.
Mathematical models then fit the data to extract the physical properties of the layers.
Sampling Rate
Using femtosecond pulses allows the system to capture thermal events that happen much faster than electronic sensors can record. The delay between the two lasers in optical pump probe thermal testing is controlled with sub picosecond accuracy using a mechanical stage. This high resolution makes it possible to see heat transport across a single atomic interface.
Very few other techniques offer this level of detail for layered structures.
Equipment Sensitivity
Successful execution requires a stable environment free from vibration and temperature swings. Because optical pump probe thermal testing relies on minute changes in light intensity even small amounts of dust can ruin the measurement. The sample surface must be polished to a mirror finish to ensure a clean reflection.
High costs limit this technique to specialized research and development laboratories.
