8 ITMP3 / 8éme conférence internationale de photoacoustique et photothermique
J. Phys. IV France 04 (1994) C7-55-C7-58
Non-linearity in photothermal radiometric imagingU. Netzelmann
Fraunhofer-Institute for Nondestructive Testing (IzfP), University, Bldg. 37, 66123 Saarbrücken, Germany
Non-linear effects occurring in photothermal microscopes based on principle of photothermal radiometry are studied as a function of the laser power and of the modulation frequency. For stainless steel, a second harmonic component of up to 11 % of the fundamental amplitude is found. Phase shifts of up to 20 degrees are observed as a function of the modulation frequency. The nonlinearity is mainly due to Stefan-Boltzmann's law. The experimental results are in good agreement with a theoretical model based on the static and oscillating temperature distribution.
© EDP Sciences 1994