
42-11Frequency Measurement
oscillators are oen found in telecommunication networks and as time base oscillators in test and mea-
surement
eq
uipment
. e
y
op
erate
at 6,
834,682,610
.90
4
Hz
,
th
e
re
sonance
fr
equency
of th
e
ru
bidium
ato
m
(
87
Rb), and use the rubidium frequency to control the frequency of a quartz oscillator. A micro-
wave
sig
nal
de
rived
fr
om
th
e
cr
ystal
os
cillator
is ap
plied
to th
e
87
Rb vapor within a cell, forcing the
ato
ms
in
to
a pa
rticular
en
ergy
st
ate
. An opt
ical
be
am
is th
en
pu
mped
in
to
th
e
ce
ll
an
d
is ab
sorbed
by
th
e
ato
ms
as it fo
rces
th
em
in
to
a se
parate
en
ergy
st
ate
. A ph
otocell
de
tector
me
asures
ho
w
mu
ch
of
th
e
be
am
is ab
sorbe ...