Constant Velocity Flying Spot for the estimation of in-plane thermal diffusivity on anisotropic materials

The Flying-Spot infrared thermography was introduced more than twenty years ago to detect narrow cracks. Recent progress made in optical control, lasers and infrared cameras allows extending the Flying-Spot technique for a quantitative thermal analysis. In this work, we propose a Constant Velocity Flying Spot to measure the in-plane thermal diffusivity of isotropic and anisotropic materials. We demonstrate that the logarithmic temperature profiles perpendicular to the laser motion are parabolic functions from which the thermal diffusivity along this direction is obtained. We have investigated two equivalent experimental configurations: (a) Moving laser with motionless sample and (b) moving sample with motionless laser spot. Both are of practical interest: the first one leads to identify thermal heterogeneities in macroscopic samples and the second one leads to measure the thermal properties of materials in in-line production processes. Measurements performed on calibrated samples (from insulators to good thermal conductors) with both configurations confirm the reliability of the method to measure the in-plane thermal diffusivity with an error less than 4%.