Turning sound into light

SONOLUMINESCENCE – CREATION OF LIGHT FROM SOUND

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The pistol and mantis shrimps are both crustaceans that snap their claws and perform magic. The jet of water squeezed out from between their claws travels at such speed that it cavitates, that is, the liquid water under negative pressure is literally pulled apart into bubbles of water vapor. When the bubbles collapse in on themselves, they give off a loud snap, that is, a sudden, sharp cracking sound or movement. This in turn, amazingly, produces a small flash of light. The shrimp uses this sonic shock wave to stun or kill prey.

Mantis shrimp

 Physicists are more interested in the flash because we still don’t exactly know why it happens. Collapsing bubbles can also be created in a laboratory, simply by using sound. Sounds, as we know, are basically just molecules repeatedly pushing against each other and then pulling apart. If the sound waves are intense enough, the low pressure will again be low enough to pull the liquid apart into vapour and cause cavitation bubbles. The bubbles then collapse, and under certain circumstances, they produce light even brighter than the shrimp. This phenomenon of turning sound into light is known as sonoluminescence. This effect, discovered ten years ago, has been, and continues to be, the subject of considerable experiment and theoretical research.

apparition of bubble→slow expansion→quick and sudden contraction→emission of light

The light flashes are extremely short-lasting, only about a 100 picoseconds. Surprisingly, the light flashes are very high energy, that is, the collapsing bubbles may be up to ten times hotter than the surface of the sun.

Single bubble sonoluminescence

We don’t know for sure, though, how the inside of the bubble gets that hot, or what exactly is giving off the light. The bubble collapses so quickly that the gases inside are heated by compression. But the increased pressure might also cause water vapour in the bubble to rapidly condense back to liquid, releasing large amounts of latent heat. And the flash itself might come from glowing red hot Argon or Xenon gas in the air bubble, or from heat tearing water vapour apart into hydroxide and hydrogen ions, which the recombine and give off light. This might also happen from the whole interior of the bubble getting hot enough to become a glowing plasma, or it might be a combination of all the above reasons. Either way the cool thing about sonoluminescence is that it’s still not fully understood despite being fairly simple to create. I mean you can buy a basic sonoluminescence kit from the internet or just pet a mantis shrimp.
You can watch this video to get a better idea.