Abstract
We detected high‐frequency sound radiated by individual gas bubbles in response to modulated green light from an argon‐ion laser. The bubbles were in clear water and were attached to a needle. Their radii were typically less than 100 μm. The sound radiated in response to single light pulses, of duration ≃10 μs and power ≃2 W, exhibits the ringing of the bubble's monopole resonance. The resonance frequency fR was found by Fourier transforming this signature; typical values were 30 kHz. Bubbles were subsequently illuminated by bursts of pulses with a frequency f≃fR. The resulting sound was characterized by an initial buildup of its amplitude. The mechanism for driving the monopole oscillations appears to be the modulated optical radiation pressure on the bubble's surface rather than thermal expansion. Related experiments on the optical levitation of bubbles in water and the emission of sound from dyed drops in water will be discussed. [Work supported by ONR.]
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