Photothermal radiometry has been used to obtain thermal wave images in
the vicinity of indentations in WC-6% Ni coated with chemical vapor d
eposited (CVD) diamond. Features in the magnitude and phase of the the
rmal signal profile are consistent with a one-dimensional thermal wave
theory that assumes (i) an air gap extending well beyond the visibly
observable indented region, and (ii) a thermal resistance interface be
tween the diamond film and the substrate over the entire coated surfac
e. The theory allows us to estimate the air gap thickness, which decre
ases as the distance from the indented region increases. Air gap varia
tions of tens of nanometers appear to be easily detectable.