Measurements of the thermal diffusivity of aluminum using frequency-scanned, transient, and rate window photothermal radiometry. Theory and experiment

The thermal diffusivity of various types of aluminunl has been measured, using a completely noncontact experimental configuration based on infrared photothermal radiometry. Photothcrmal response transients, conventional frequency scans, and pulse duration- or repetition rate-scanned rate windows have been investigated. It has been shown that the conventional fiʹequency scan is not suitable for measurements of ah,ninum with a short thermal transport time such as foils, due to an extremely degraded signal-to-noise ratio (SNR I. Also, it has been found that the conventional frequency scan method is less sensitive to the actual value of thermal diffusivity than the rate-window scan. The ratewindow method, furthermore, gives superior SNR especially tbr thin metals and yields excellent agreement between the theory and the data. An advantage of the paise duration-scanned rate window mode is that it does not reqt, ire knowledge of the instrumental transfer function as an input. The transient response gives the worst SNR but is best for the physical iInterpretation of the photothermal signals. In addition, it has been shown that the infrared photothermal radiometric transmission mode is less sensitive to surface roughness than the reflection mode and, therefore, is preferable for thermal diffusivity measurements of alt, minum and of good thermal conductors, in general.