  Photoacoustic (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.
