Heterodyne method with an infrared camera for the thermal diffusivity estimation with periodic local heating in a large range of frequencies (25 Hz to upper than 1 kHz)

In this article, an aliasing method is introduced in order to measure short time thermal phenomena with infrared thermography devices based on focal plane array systems with snapshot mode possibilities. The principle is to create an electronic stroboscope between the IR camera recording frequency (typically 25 Hz) and the periodic thermal laser excitation at high frequency (between 25 Hz to 10 kHz). It is then possible to record thermal signal variations related to high frequencies at the standard frame rate of classical IR cameras. The main advance of the proposed methods consists in processing the phase lags from the signals recorded on the same exact time scale (snapshot mode) of the camera instead of considering the lag between the laser excitation and the camera response. With the help of this method, an experimental application of periodic point source theory on estimation of the in-plane thermal diffusivity has been tested.