Pursuing the analogy between sonoluminescence and
the cavity magnetron, I googled the following very
intelligible description of the early development.
==============================================
By 1939, other researchers had discovered
that under certain conditions, the magnetron
could produce very high-frequency radio waves.
Boot and Randall decided to construct a
magnetron that could handle a lot of power
and generate microwaves efficiently. Most
electron tubes at that time used glass
envelopes to enclose the evacuated space
inside of the device. Instead of glass, Boot
and Randall made their magnetron tube
enclosure out of a solid block of copper,
which conducts heat very well.
In order to tune the tubes output wavelength
efficiently, they drilled special holes called
cavities into the block. Just as the length
of an organ pipe tunes the pipe to a certain
pitch, the size of a magnetrons cavities can
efficiently tune microwaves to a certain
wavelength. Then Boot and Randall put the entire
tube into a strong magnetic field that swept
electrons past the cavities in a rotary motion.
In February of 1940, the English researchers
tested their first working cavity magnetron.
They were amazed to find that it produced over
400 watts of power at the extremely short
wavelength of 9.8 cm (about 4 inches). This
was nearly a hundred times more power than
anyone else had ever produced at that
wavelength.
==============================================
Now the interesting thing about the above is that Boot
and Randall "...were amazed to find that [the magnetron]
produced over 400 watts of power..."
How does this amazement relate to sonoluminescence?
Well, "For unknown reasons, the addition of a small amount
of noble gas (such as helium, argon, or xenon) to the gas
in the bubble increases the intensity of the emitted light
dramatically."
Since the reasons are unknown one might justifiably infer
that the researchers who discovered this effect
"...were amazed to find that" the intensity of the emitted
light increased dramatically.
This suggests that the noble gas atoms are behaving as
cavity resonators for visible light in the same way as
Boot and Randall's cavities behave for microwaves.
If this explanation is correct then the reason for
the dramatic increase in the intensity of emitted light
is unknown no longer. <g>
Cheers,
Frank Grimer
