On the Thermal Characterization of Insulating Solids Using Laser-Spot Thermography in a Front Detection Configuration

The application of the laser-spot active lock-in infrared thermography technique for the simultaneous measurement of the thermal diffusivity and conductivity of thermal insulators is an advantageous method that takes advantage of the heat losses by conduction from the sample to the surrounding air to recover the thermal conductivity in addition to the thermal diffusivity, which is the parameter usually determined using this technique. Here we introduce results obtained using a front detection configuration. We foresee it as a complementary modality for that presented using a rear detection configuration. In the current method, the measurement time is reduced at least one order of magnitude using modulation frequencies of tenths of Hz instead of the smaller frequencies commonly used in the rear configuration. The method allows us the work with thicker samples and lower excitation powers. One noticeable distinction in the current report, as seen from numerical calculations and experimental measurements, is that we unveil the presence of maxima and minima in the amplitude profiles at distances from the heating point that are closely related to the thermal wave wavelength. This interesting behavior reminds us of the well-known highly damped character of thermal waves and the standing wave conditions like those that have been used commonly to explain other photothermal phenomena. Finally, we will comment on the usefulness of the method to characterize anisotropic samples.