Abstract
The applicability of terahertz waves to the detection of rust under coatings is discussed, focusing on the
electromagnetic waves generated from chaotic multimode semiconductor laser oscillations. The
corrosion states of steel used for the cross-arms of electric transmission lines are provided as maps with
a special resolution down to the sub-mm level to reveal transfusion of rust fluid. These analyses are
made possible by the chemical structure of rust, which shows an absorption band tail in the terahertz
frequency region. Terahertz waves generated by the optical excitation of photoconductive antennas
using a chaotic laser show that the absorption band tail extends to around 180 GHz. Chaotic laser
systems using small and inexpensive semiconductor lasers are potentially promising tools for detecting
underfilm corrosion.
