The "Garage-Built Rubidium Standard" discussion brought to mind an
experimental
setup in a physics lab at U. C. Berkeley years ago. It was one of a
number of
elective experiments for the laboratory section of a Modern Physics
course.
The objective was probably to demonstrate Zeeman line splitting. I
suspect
much of the equipment was surplus from the nearby Radiation Laboratory.
The setup was shrouded by heavy black theater curtains that hung from the
ceiling to
darken the experimental area. There were two, about one-inch-diameter,
rubidium-
filled glass spheres, each surrounded by Helmholtz coils. The first also
had a toroidial
resistance heater coil controlled by a Variac. It served as the light
source when
energized by RF from the Helmholtz coil. The temperature had to be in the
correct
range in order for the bulb to luminance.
The second bulb was the reaction sphere. Its Helmholtz coil was fed with
a trapezoidal
waveform from a sweep generator along with direct current from a powers
supply. The
Helmholtz coil also received an RF signal of about 50 MHz from a General
Radio unit oscillator
(possibly through an amplifier). A rather expensive-looking, ¼-inch
thick, roughly 2-inch
by 2-inch filter or diffraction grating (that was normally carefully kept
is in a heavy-wool
envelope) was placed in a holder between the spheres. There were probably
some other
optical elements too, but it has been too long to remember.
On the far side of the reaction sphere was some sort of photodetector that
fed an old
Dumont oscilloscope with the beam being swept horizontally from the sweep
generator.
If you managed to get the pip on the scope (not many student-pairs
succeeded) the rest
was calculation. One of the required calculations was the force of
gravity acting on the
experiment. This experiment was notable as an instructive exercise in
getting old,
recalcitrant test instruments to all function at the same time, more so
than the
theoretical physics. If one could acquire the rubidium –filled spheres
and filter, a
working rubidium standard could probably be constructed in the garage.
Bruce, KG6OJI
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