Abstract
This paper demonstrates a new approach for generating ultrasound, utilizing evanescent light. Evanescent light generated during total internal reflection at the prism surface, is utilized for generating ultrasound in aluminum specimen. A pulsed ND:YAG laser operated at 1064 nm optical wavelength, with duration time of 3〜5 nsec, and energy density of 0.03〜0.85 J/cm^2 is used. It has been found that ultrasound can be generated in the aluminum specimen only by evanescent light. The amplitudes of ultrasound generated by evanescent light were unexpectedly nine times larger than the ones generated by direct laser irradiation. The obtained directivity pattern shows considerable intensity at 0°, which reveals that the ultrasound in this experiment is generated by ablation effect. According to the theoretical speculation, when the plasma generated by laser irradiation is confined geometrically, its impulse pressure is significantly enhanced. These results indicate that the possibility of a novel ultrasound pulse-echo transducer with near-field optics for measuring objects smaller than the wavelength of light.
