I read the first sound laser (or SASER) was made in 2010 here. But if we're talking about the state of the phonons emitted then we could say that any sound created by a planar vibration has a unique wave vector $\overrightarrow{k}$ and its phonons are spatially coherent.
Aren't sounds made by sinusoidal plane vibrations sound-lasers or SASERs?
ceillac
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