2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/26133Photoacoustic (PA) wave has been examined in a superconductor of the first kind, Pb single crystal. The PA wave is induced by optical excitation of electronic state and propagates from normal into superconductive phases below T$_{\rm C}$. It is clearly shown by wavelet analysis that the measured PA wave includes two different components. The high-frequency component is MHz-ultrasonic and the relative low-frequency one is induced by thermal wave. The latter is observed in a similar manner irrespective of T$_{\rm C}$. On the other hand, the MHz-frequency component is obviously enhanced below T$_{\rm C}$. The behavior is reproduced by the change of attenuation of longitudinal ultrasonic wave and is consistent with BCS theory.5 pages, 5 figures (fig.3 is colored), RevTeX4; the text is modifiedMaterials Sciencetext