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TWO
FREQUENCY
ZEEMAN
LASER
BEAM
S ~ L I ~ E B
FIXED
REFERENCE
CUBE-CORNER
EXTERNAL
CUBE-CORNER
f 2 - ( f l
+ A f l
)
REFERENCE
SIGNAL
0
Laser
generates
light
of
two
slightly
different
Photodetector
changes
f,
and
(fl&Af,)
to
elec-
frequencies
with
opposite
circular
polarizations.
trical
signal.
One
of
the
two
frequencies
f,,
is
optically
@Photodetector
changes
reference
beam,
f,
and
separated
and
sent
to
the
movable
external
f,,
to
electrical
signal.
cube-corner
reflector.
AC
amplifier
separates
measurement
frequency
The
second
frequency,
f , ,
is
optically
separated
@difference
signal
f2
-
(f,fAf,).
and
sent
to
a
fixed
reflector
and
then
rejoins
f,
at
the
beam
splitter
to
produce
an
interference
AC
amplifier
separates
reference
frequency
signal
at
about
2
MHz.
' d ifference
signal
(
FIT
the
movable
reflector
moves.
the
returning
Pulse
converter
extracts
Afl
and
outputs
one
beam
frequency
will
be
Doppler-shifted
slightly
per
quarter
wavelength
of
motion.
up
or
down
by
Af,
depending
on
direction
of
motion.
Figure
7-3.
Typical
Laser
Transducer
System
Block
Diagram
1.1
1
TYPlUL
APPLlCATlONS
AND
MEASUREMENTS
DOWN
Any
machine
with
an
accurate
positioning
requirement
is
a
candidate
for the
Laser
Trans-
ducer.
Those
with
multiple
axes
such
as
numerically-controlled
machine
tools
and
coordinate
measuring
machines
benefit
especially
from
its
multiaxis
capability.
NC
machine
tools,
transfer
machines,
and
other
equipment
having
long
axes
can
take
advantage
of
the
fact
that,
unlike
other
position
transducers,
a
laser
beam
is
the
same
price
regardless
of
its
length.
At
the
other
end
of
the
size
scale,
two-axis
machines
with
X-Y
motion,
used
for
integrated
circuits
manufacturing
and
photogrammetry,
profit
from
the
Laser
Transducer's
unique
plane-mirror
measurement
technique.
Many
machines
with
an
ultra-fine resolution
requirement,
such
a s
the
above
X-Y
stages
and
coordinate
measuring
machines,
microscopes,
grinders,
dilato-
meters,
and
manometers
can
fully
utilize
quarter-wavelength-of-light
or
better
resolution.
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