Nondestructive evaluation of polymers with optically generated thermal waves

Abstract Periodic illumination of an absorbing sample results in a surface temperature modulation which propagates into the sample as a highly attenuated and slow “thermal wave”. Thermal wave propagation depends on thermal properties and on their anisotropy. Boundaries affect both the phase and magnitude of the temperature modulation. Since thermal wave detection can be performed in a remote way, one can monitor the orientation of fibers and molecules without touching the sample. Scanned local inspection allows mapping of layer delamination caused by mechanical stress or electrical heating.