Ever since the first demonstration of the laser, people have wondered if the same thing could be done with sound. Over the last few years, there have been demonstrations that are close but, in my opinion, not quite there. That all changed with a recent publication that is, I think, the first truly convincing demonstration of a phonon laser (a phonon is the sound equivalent of a photon: the smallest increment of energy at a given tone).
Experimentally, what a Japanese team has done is really cool. But unless you happen to be a physicist, to fully appreciate it requires quite a diversion. So, I suggest that you take a moment to read the next section. If you are a physicist, feel free to skip ahead to "The Phonon Laser" section.
What makes a laser a laser?
It is actually harder to define a laser than you might think. For instance, a common description is a light source that has just a single color. Yet there are many lasers that emit a band of colors far broader than many lamps do. So, no, lasers do not necessarily emit a single color.