Question:
How does an atomic clock measures the beats of a cesium atom?
Replies:
It is sort of like going into the bathroom and humming different pitches until you find the
pitch that resonates. (In most bathrooms, there are three sets of pitches that will resonate:
those with wavelengths equal to the distance between the walls, or between the floor and
ceiling, and sub-multiples.) Everybody else with a bathroom of precisely the same dimensions
will find the same pitches you found, and the group of you will then share a frequency
standard.
In a Cesium clock, you tune a microwave oscillator around until it has just the right
frequency to excite particular electrons of a
Cesium atom from one well-defined energy level to another well-defined level. (The reason
you use Cesium is that it has some very well-defined levels. Later, you will understand
that this means the levels are relatively long lived -- i.e., not damped.) When you have
tuned the oscillator to maximize the excitation of Cesium electrons, you know that the
microwave frequency is the same as the microwave frequency of any other Cesium clock --
so you have a standard that someone else can duplicate. Now all you have to do is declare
that umpty-ump cycles of such an oscillator is one second. You choose umpty-ump so that it
agrees with all other (mostly less precise) definitions of a second.
Here is more detail: http://tycho.usno.navy.mil/cesium.html
Tim Mooney
Rather than try to answer this question directly, I would rather direct you to the NIST
(National Institute of Science and Technology) web site that does a very thorough and
professional job of explaining your inquiry and the whole history of time standards:
NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.
