Novel results on thermal diffusivity measurements on anisotropic materials using photothermal methods

We have applied two photothermal techniques (infrared radiometry and mirage) and conventional procedures to measure the thermal diffusivity of a highly anisotropic sample of pyrolytic graphite. Unexpected and strongly differing results are obtained with each technique. A theoretical analysis indicates that whereas the mirage technique gives a measure of the elements of the thermal diffusivity tensor, infrared radiometry yields the elements of another thermal magnitude represented by the inverse of this tensor.