Transient Thermoreflectance Technique

Determination of thermophysical properties is essential for thermal management of micro-and optoelectronics systems as device sizes are reducing day-by-day. Modulated thermoreflectance technique is one of the techniques for thermophysical property measurement of micro-/nanosystems. This technique examines the propagation of thermal waves generated by laser pulse. 

After completion of each laser pulse, the sample begins to cool down to the initial ambient temperature. A probing CW laser light is reflected from the sample surface at the heating spot center during this process, which is collected by a detector to provide instantaneous refleetivity. 

Let us consider a thin film of size d mounted on a substrate. The temperature above ambient is denoted as 0, C is the thermal capacitance, and k is the thermal conductivity. We assume the heat transfer within the metal film and the substrate heated by short-pulsed laser in time scale of about 100 ps is governed by the time-dependent heat conduction diffusion equation. 

subscript/ is for film and subscript s is for the substrate. The initial condition for the film and the substrate, respectively, are 

F is the fluence, R is the reflectance, and 5 is the energy deposition depth. The boundary condition at the interface (x = d) can be written as 

---

Stevens RJ, Smith AN, and Norris PM 2005 Measurement of thermal boundary conductance of a series of metal-dielectric interfaces by the transient thermoreflectance technique. J. Heat Transfer, 127, pp. 315-322. 

---