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Researchers Find a Way to Tap into Long-Lived Sound Waves in Glass

A newly published study from Yale scientists reveals how to enhance the lifetime of sound waves traveling through glass — the material at the heart of fiber optic technologies.

Everyday experience tells us that glass (silica) is highly transparent. In fact, silica is one of the most transparent materials on earth. Light can propagate for tens of kilometers in silica before it experiences any appreciable weakening. This transparency, combined with glass’ formability and low cost, is why glass is used in so many of the fiber-optic technologies that shape the information age.

Yet silica also has a mysterious side. At room temperature, silica is an excellent acoustic material. You can demonstrate this by tapping a wine glass with a fork and listening to it ring for several seconds. However, in sharp contrast with most materials, this resonance is quickly muted when the glass is cooled to cryogenic temperatures.

These peculiar acoustic properties are at the heart of long-standing mysteries in glass physics. In the 1960s scientists discovered many perplexing properties of glass: It conducted heat much less efficiently than expected, and it heated up much more slowly than anticipated. These puzzling discoveries were ultimately explained by localized absorbers within glass that interact with sound waves in the same manner that atoms interact with light. To this day however, the true nature of these “acoustic atoms” is not fully understood.

In addition, absorption by these “acoustic atoms” has another consequence that intrigues scientists. At low temperatures the amplitude of a sound wave affects how long it will ring. Roughly speaking, this means you can make your wine glass ring longer by turning on your stereo, which causes the glass to vibrate at altogether different frequencies. Moreover, the duration of the ringing increases as the stereo volume is turned up.

Yale scientists have used this concept to control the lifetime of sound within glass. By shining laser light into fiber optic waveguides made of glass, they were able to probe and generate acoustic waves in the fiber core. By generating an intense acoustic wave at one frequency (i.e. “turning on the stereo”) and probing at another (“tapping a wine glass”), the researchers were able to extend the lifetime of a sound wave.

The researchers said that because glass is the backbone of a range of cutting-edge technologies, the findings open the possibility of new forms of high-precision sensing and information processing.

“Our work takes an important step toward engineered sound dynamics in glass,” said Peter Rakich, assistant professor of applied physics and physics at Yale and principal investigator of the study.

First author Ryan Behunin, an associate research scientist in Rakich’s lab, said, “Our results demonstrate a new paradigm for achieving higher performance in optomechanical systems.”

The discovery is described in the January edition of the journal Nature Materials.

Co-authors of the study were Yale graduate student Prashanta Kharel and associate research scientist William Renninger.

Publication: R. O. Behunin, et al., “Engineering dissipation with phononic spectral hole burning,” Nature Materials (2016) doi:10.1038/nmat4819

Source: Jim Shelton, Yale University

Material Science Madness: Crazy Metal Melts in Your Hand...!!
There is an incredible metal that shatters like glass, melts in a human hand, attacks other metals but is non-toxic to humans, and acts like an alien life form when exposed to sulfuric acid and dichromate solution. It sounds too amazing to be true, but gallium is an absolutely real chemical element that’s found in some of the gadgets we use every day.

But perhaps more interestingly, there are a ton of insane experiments scientists like to do with gallium. Thanks to its odd properties and behavior, gallium can do some pretty strange things in the lab. The above video shows what happens when gallium “attacks” aluminum.

The “gallium beating heart” experiment is a popular one that shows how gallium can act like a living thing when submerged in sulfuric acid and a dichromate solution. By altering the surface tension of the gallium, the scientists are able to make the metal look like an organic beating heart.

The melting gallium spoon is a fun demonstration that makes good use of gallium’s 85 degree (F) melting point. A gallium spoon stirs hot water and immediately melts into a puddle on the bottom of the mug. The video above warns against using it for pranks, but we have to admit it would be really, really hard to resist.