Students harmonize with star in a jar

17 Jun 2002

Using $1.29 acrylic boxes from a dime store and simple electronics, undergraduate students and their UAH lab instructor are doing cutting edge research into sonoluminesence, a little understood phenomenon sometimes referred to as "a star in a jar."

In a back corner of a teaching lab, the student-built apparatus uses acoustic waves to suspend a microscopic bubble in water. Stretched and compressed by the force of sound waves, the bubble expands to a diameter of only 100 microns, then collapses to one one-millionth of that volume.

It does that 30,000 times a second, focusing acoustic energy by a factor of one trillion, generating temperatures hotter than the surface of the Sun and releasing with each cycle a faint flash of light that lasts 30 trillionths of a second. When the team looked at secondary acoustic waves in the water-filled vessel without the bubble, it found weak harmonic feedback, perhaps explaining why the bubble cannot be made brighter. Harmonic waves set up by that periodic shock may destructively interfere with the fundamental drive, limiting the light that is released, team leader UAH physics instructor Fred Seeley conjectured. The team is trying to control destructive harmonics to see if a brighter bubble can be made.