Jf. Power et Mc. Prystay, NONDESTRUCTIVE OPTICAL DEPTH PROFILING IN THIN-FILMS THROUGH ROBUST INVERSION OF THE LASER PHOTOPYROELECTRIC EFFECT IMPULSE-RESPONSE, Applied spectroscopy, 49(6), 1995, pp. 725-746
The laser photopyroelectric effect measures an optical absorption dept
h profile in a thin film through the spatial dependence of a heat flux
source established below the film surface by light absorption from a
short optical pulse. In this work, inverse depth profile reconstructio
n was achieved by means of an inverse method based on the expectation-
minimum principle (as reported in a companion paper), applied in conju
nction with a constrained least-squares minimization, to invert the ph
otopyroelectric theory. This method and zero-order Tikhonov regulariza
tion were applied to the inversion of experimental photopyroelectric d
ata obtained from samples with a variety of discrete and continuous de
pth dependences of optical absorption. While both methods were found t
o deliver stable and accurate performance under experimental condition
s, the method based on the constrained expectation-minimum principle w
as found to exhibit improved resolution and robustness over zero-order
Tikhonov regularization.