Title: Comment on Photothermal radiometry parametric identifiability theory for reliable and unique nondestructive coating thickness and thermophysical measurements, J. Appl. Phys. 121(9), 095101 (2017),
Abstract: A recent paper [X. Guo, A. Mandelis, J. Tolev and K. Tang, J. Appl. Phys.,
121, 095101 (2017)] intends to demonstrate that from the photothermal
radiometry signal obtained on a coated opaque sample in 1D transfer, one should
be able to identify separately the following three parameters of the coating:
thermal diffusivity, thermal conductivity and thickness. In this comment, it is
shown that the three parameters are correlated in the considered experimental
arrangement, the identifiability criterion is in error and the thickness
inferred therefrom is not trustable.