Observation of the Pressure Dependence of Nonlinear Interactions in a Focused Coherent Acoustic Beam in Superfluid Helium
Observation of the Pressure Dependence of Nonlinear Interactions in a Focused Coherent Acoustic Beam in Superfluid Helium
复制标题
超流氦中聚焦相干声束非线性相互作用的压力依赖性观察
DOI：
10.7567/jjaps.26s3.9
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
J. Foster
中科院分区：
文献类型：
--
作者：
D. R. Wright;B. Hadimioglu;L. J. L. C. Jr.;C. Quate;J. Foster
我们研究了8GHz聚焦声束在50mK附近超流氦中的饱和和受激衰减。由于色散是压力的函数，因此存在不同的非线性过程占主导地位的各种区域。在低压（向上色散）下，噪声的参数自增强导致信号快速衰减。在中等压力下（线性色散），谐波形成导致饱和（“冲击波”）。在更高的压力下（向下色散），主焦点的功率远远超过冲击波起始阈值，然后迅速耗尽，这似乎是自发衰变的四声子参数增强。我们相信这是声学中四声子参量混频的第一个实验证据。
We have studied the saturation and stimulated decay of an 8 GHz focused acoustic beam in superfluid helium near 50 mK. Because the dispersion is a function of pressure, there are various regimes where different nonlinear processes dominate. At low pressures (upward dispersion) parametric self-enhancement of the noise causes rapid signal depletion. At intermediate pressures (linear dispersion) harmonic formation leads to saturation (a “shock wave”). At still higher pressures (downward dispersion) the power in the main focus far exceeds the shock onset threshold before depleting rapidly in what appears to be a four-phonon parametric enhancement of the spontaneous decay. We believe this to be the first experimental evidence of four-phonon parametric mixing in acoustics.