Making light of sound in solitary bubbles.Trapped in an intense sound wave, a tiny gas bubble in water can emit a string of flashes bright enough to be visible in an undarkened room. Producing a startling star·tle
v. star·tled, star·tling, star·tles
1. To cause to make a quick involuntary movement or start.
2. To alarm, frighten, or surprise suddenly. See Synonyms at frighten. sound-and-light show sound-and-light show
A theatrical entertainment presented at night in a historic, usually outdoor setting, using recorded sound, lighting, and other effects to relate the history of the place. Also called son et lumière. on an intriguingly small scale, this simple system serves as a remarkable microlaboratory for physics and chemistry.
Now, researchers have demonstrated that slight changes in the composition of the gas inside such a bubble can strongly influence the intensity and wavelengths of the light that escapes. For example, adding a small amount of argon argon (är`gŏn) [Gr.,=inert], gaseous chemical element; symbol Ar; at. no. 18; at. wt. 39.948; m.p. −189.2°C;; b.p. −185.7°C;; density 1.784 grams per liter at STP; valence 0. , xenon xenon (zē`nŏn) [Gr.,=strange], gaseous chemical element; symbol Xe; at. no. 54; at. wt. 131.29; m.p. −111.9°C;; b.p. −107.1°C;; density 5.86 grams per liter at STP; valence usually 0. , or helium to a nitrogen bubble substantially increases the intensity of ultraviolet light Ultraviolet light
A portion of the light spectrum not visible to the eye. Two bands of the UV spectrum, UVA and UVB, are used to treat psoriasis and other skin diseases. emission.
Physicists Robert Hiller, Keith Weninger, Seth J. Putterman, and Bradley P. Barber of the University of California, Los Angeles UCLA comprises the College of Letters and Science (the primary undergraduate college), seven professional schools, and five professional Health Science schools. Since 2001, UCLA has enrolled over 33,000 total students, and that number is steadily rising. , describe their findings in the Oct. 14 SCIENCE.
When an intense sound beam travels through water, it creates microscopic cavities that immediately fill with gas originally dissolved in the liquid. Such bubbles alternately expand and contract in step with regular changes in the sound wave's pressure.
During the contraction phase, a bubble can collapse so violently and rapidly that it concentrates the sound energy sufficiently to heat the enclosed gas to temperatures exceeding 10,000 kelvins. The heated gas luminesces, giving off an extremely bright flash of visible and ultraviolet light lasting less than 50 picoseconds.
Although researchers have known about this effect -- called sonoluminescence son·o·lu·mi·nes·cence
The production of light as a result of the passing of sound waves through a liquid medium. The sound waves cause the formation of bubbles that emit bright flashes of light when they collapse. -- since the 1930s, they still do not have a complete understanding of how it works (SN: 10/23/93, p.271). The experiments of Hiller and his coworkers represent one attempt to elucidate the process.
The researchers found that raising the noble gas content of a nitrogen bubble in water to 1 percent dramatically stabilizes the bubble's motion. It also increases the intensity of light emission by a factor of at least 10.
At the same time, the spectrum of light generated by a bubble depends strongly on the gas inside the cavity. A bubble containing argon produces ultraviolet light that peaks at a wavelength of 300 nanometers. However, a helium-laced bubble shows no such peak.
"Some exciting atomic physics may be occurring within the collapsing cavitation cavitation
Formation of vapour bubbles within a liquid at low-pressure regions that occur in places where the liquid has been accelerated to high velocities, as in the operation of centrifugal pumps, water turbines, and marine propellers. bubble that gives rise to [singlebubble sonoluminescence]," Lawrence A. Crum and Ronald A. Roy of the University of Washington in Seattle comment in the same issue of SCIENCE. "However, many of the results [Hiller and his colleagues] present are also anomalous and defy immediate explanation."
Clearly, further investigations are necessary to pin down how sonoluminescence occurs. At the same time, the new results suggest the possibility of using gas impurities for improved control of the characteristics of light emissions from collapsing bubbles.