HP 5501A Operating And Service Manual page 85

REFLECTOR
A L I G N M E N T A I D
B E A M BENDER
Y A X l S SINGLE-BEAM INTERFEROMETER
I /
TEST POINT
LASER
-
I ,
-
50%
A
B E A M X A X I S
SPLITTER X A X I S L I N E A R
RECEIVER INTERFEROME
REFLECTOR
I N D I C A T O R
I D
X A X l S
RETROREFLECTOR
TER
Figure 2-54. A utoreflection A Iignment
For autoreflection alignment of the measurement system in Figure 2-54, perform the follow-
ing procedure:
NOTE
Steps 1 through 1 1 constitute the X-axis autoreflection alignment procedure.
1.
With all optical components in place, install the alignment targets on the interfero-
meter and the receiver (Figure 2-53c, position 1). Place a piece of opaque material
in front of the retroreflector.
2. With the laser beam passing through the 50% beam splitter, adjust the laser head and
interferometer until the laser beam enters one hole of the alignment target and exits
the other to impinge on the receiver alignment target centered on the hole over the
photodetector.
3. Place a reflector* between the interferometer and retroreflector so that the measure-
ment beam from the interferometer strikes its reflective surface. The reflector's sides
must be perpendicular to its front face within stringent tolerances (<I5 arcseconds):
Align the reflector with a precision indicator until its front surface is perpendicular
to the direction of travel in both angular axes.
4. Turn the front turret of the laser head to select the small aperture.
*A typical reflector i s the TRUE SQUARE manufactured by the Starret Co. This reflector, a s
well a s other similar commercially available reflectors, have proved ideal for this appli-
cation. Gage blocks (lo-blocks) should not be used since their sides may or may not be
perpendicular to their faces, depending on the technique of their manufacture.