1981 年 37 巻 10 号 p. 504-509
Experiments of the degenerate parametric amplification were done in a plane progressive wave tube. Due to the parametric interaction of a powerful pump wave and a weak signal wave, SPL of the weak signal wave was about 2dB higher than that of the pump-free wave in postshock region. By the use of an amplitude-modulated signal instead of the added signal at the source, a 2dB improvement in gain was obtained in the parametric sound pressure amplitude. It was also observed that the initial phase of the weak signal wave governs its propagating behavior remarkably and that the difference of amplitudes between the pump and the weak signal waves plays an important role in the parametric amplification.