HP 5501A Operating And Service Manual page 87

15.
Place a reflector between the interferometer and the retroreflector so that the mea-
surement beam from the interferometer strikes its reflective surface. Align the ref4ector
with a precision indicator until its front surface is perpendicular to the direction of
travel in both angular axes (<I5 arcseconds).
Place alignment aid over output aperture of single beam interferometer a s shown in
Fig. 2-54. Edges of alignment aid must be parallel to sides of single beam interferometer
housing. Adjust the single beam interferometer angularly until the return beam reflected
from the reflector returns and is centered on the small aperture of the laser head. Slight
lateral adjustments of the interferometer may be required to ensure that the reference
beam from the interferometer is centered on the receiver alignment target. Do not
adjust the laser head.
For high accuracy alignment and installations where there is
less than 0.5 metre (20 inches) between the laser head and re-
flector, perform steps 17 through 19.
17. Remove the receiver alignment target and interferometer alignment target and rotate
the turret of the laser head to select the large aperture.
18. With a fast responding voltmeter (preferably a meter type) attached to the receiver
test point, angularly fine adjust the laser beam (laser head or interferometer, depend-
ing on axis) until a signal is received on the receiver. (The voltmeter will suddenly
jump to some value greater than 0.25 volts.) This is a critical adjustment and may
initially require great care to achieve the desired result.
Peak the voltmeter reading (which will be fluctuating) by fine adjusting the laser
beam in both angular axes. This will align the laser beam to within f15 arcseconds to
the reflector surface. If the reflector surface is aligned to the direction of travel within
k15 arcseconds, the laser beam will be aligned to the direction of travel within k30
arcseconds or approximately 0.04 parts per million. That
is,
0.04 micrometre per metre
of travel (0.04 microinches per inch) of cosine error.
20. Lock down the single beam interferometer securely making sure the alignment is not
disturbed. Remove the reflector. Remove the alighment aid.
Remove the receiver alignment target and interferometer alignment target and rotate
the turret on the laser head to the large aperture. Verify that the LED indicator on the
receiver is illuminated and the voltage at the receiver test point
is
between 0.6 and
1.5 Vdc.
2.46 Plane Mirror Interferometer Alignment Procedure
This procedure covers specifically the alignment of the 10706A Plane Mirror lnterferometer
a s applied to an X-Y positioning device using flat mirrors a s retroreflectors. In this procedure
it
is assumed that the mirror surfaces are flat to within the tolerances required for operation
of the plane mirror interferometer (refer to Measurement Components) and they have been
aligned perpendicular to each other and perpendicular to their respective directions of travel.
Figure 2-55 illustrates the most common 2-axis plane mirror interferometer installation.
The alignment of the plane mirror interferometer is very similar to the autoreflection align-
ment technique previously described. In most cases, the accuracy demands of the X-Y
positioning devices used, along with the relatively short travels encountered, dictate that the
high accuracy alignment technique described in the autoreflection alignment procedure be
used.