and , i.e. (5) The surface temperatures are measured due to the change in the reflectivity with the temperature , i.e. , while this change is measured by the changes in the reflected intensity of a probe laser beam. The probe laser beam measures a weighted average of the temperature , i.e. (6a) This last integral (6a) can be simplified to an integral over : (6b) The surface temperature of a layered structure In the similar way, frequency domain solution for the surface temperature of a layered structure can be acquired. Instead of Eq. (2), Eq. (7) will be used for a layered structure. (7) (Λn: thermal conductivity of nth layer, Dn: thermal diffusivity of nth layer, Ln: thickness of nth layer) Using Eqs. (6) and (7), we can calculate the changes of temperature of a layered structure. Modeling of data acquired in time-domain thermoreflectance The acquired data from time-domain thermoreflectance experiments are required to be compared with the model. (8) (9) (10) (Q: quality factor of the resonant circuit) This calculated Vf/V0 would be compared with the measured one. Application Through this process of time-domain thermoreflectance, the thermal properties of many materials can be obtained. Common test setups include having multiple metal blocks connected together in a diffusion multiple, where once subjected to high temperatures various compounds can be created as a result of the diffusion of two adjacent metal blocks. An example would be a Ni-Cr-Pd-Pt-Rh-Ru diffusion multiple which would have diffusion zones of Ni-Cr, Ni-Pd, Ni-Pt and so on. In this way, many different materials can be tested at the same time. Lowest thermal conductivity for a thin film of solid, fully dense material (i.e. not porous) was also recently reported with measurements using this method. Once this test sample is obtained, time-domain thermoreflectance measurements can take place, with laser pulses of very short duration for both the pump and the probe lasers (<1 ps). The thermoreflected signal is then measured by a photodiode which is connected to a RF lock-in amplifier. The signals that come out of the amplifier consist of an in phase and out of phase component, and the ratio of these allow thermal conductivity data to be measured for a specific delay time. The data received from this process can then be compared to a thermal model, and the thermal conductivity and thermal conductance can then be derived. It is found that these