A comparison between conventional photothermal frequency scan and the lock-in rate window method in measuring thermal diffusivity of solids

A comparison between the conventional photothermal frequency scan method and the recently developed photothermal lock-in rate window technique for thermal diffusivity measurements of materials, is presented. In this comparison, a completely noncontact experimental configuration has been utilized based on infrared photothermal radiometry. This work shows that for thick materials with long thermal transport times across the sample where low-frequency measurements are required, the frequency scan method may be more appropriate due to its simplicity. The rate window method, however, gives superior signal-to-noise ratio (SNR) for materials with very short thermal transport times such as metal foils, which otherwise require high frequency, low SNR measurements. A further advantage of the pulse duration-scanned rate-window mode is that it does not require knowledge of the instrumental transfer function as an input.