Sonoluminescence is the production of light from sound. This effect,
discovered just over ten years ago, has been, and continues to be, the subject of considerable experimental and theoretical
research.
Sonoluminescence (SL)
refers to the phenomena in which a micron size gas bubble is both spatially trapped and oscillated by an acoustic field in
such a way that on each compression of the bubble a small burst of light is emitted. This light emission is in the form of
extremely short bursts (< 100ps), but is periodic, occuring in phase with each and every cycle of the driving pressure
field. Each bubble collapse produces about 500,000 photons.
The bubble collapse is so violent that some predicted theoretical accelerations are larger than those associated
with a Black Hole! The actual emission mechanism has not yet been explained, although theories are as plentiful as they are
diverse.
Students begin their exploration
by first understanding some basic acoustical principles, such as resonance behavior, quality factors, variation of sound speed
with temperature, and the eigenmode structure of a 3-dimensional resonance "cavity." Once these principles are understood
there are a large number of experiments that can be performed focusing on the liquid sample preparation and the light emitted
from the bubble.
The basic apparatus, shown to the
right, consists of a rectangular cell that houses the water with a high frequency piezo microphone, an ultrasonic horn that
is used to deliver acoustical energy to the system, and a control box that contains an integrated amplifier and resonance
detection circuitry. The control box also contains active components that can filter and rectify the signals from either the
cell's transducer or from the separate high frequency hydrophone probe.
Among
the other features in the control box are two separate adjustable power supplies, one for an optional temperature controlled
cell and another for an optional photomultiplier, as well as a peak detector for the photomultiplier unit.
