HP 5501A Operating And Service Manual page 45

2.16 PLANE MIRROR INTERFEROMETER LASER BEAM PATH (Figure 2-76). The beam
entering the interferometer i s split into f, and f , , whh f, returning to the receiver after retro-
reflection by the reference cube corner. As in the linear interferometer, f, i s transmitted out
to the plane retroreflector and is reflected back on itself (Figure 2-76). The quarter-waveplate
causes the polarization of the return frequency to be rotated through 90 degrees so that f,kAf
is reflected out a second time where it is Doppler shifted again. The polarization of f,k2Af i s
rotated again through 90 degrees so it is now transmitted back of the receiver. Resolution
doubling is inherent because of the double Doppler shift.
Any tilting of the plane reflector relative to the beam axis results only in an offset of the
return, not in a tilt, since tilting of the first reflected beam i s exactly compensated by the
second reflection. See Figure 2-23 for plane mirror specifications.
QUARTER-WAVE PLANE
REFLECTOR
10706A
PLANE MIRROR INTERFEROMETER
Figure 2-76. Plane Mirror lnterferometer Laser Beam Path
2.16.1 10722A PLANE MIRROR CONVERTER
(Figure 2-76a). The Plane Mirror Converter with
an additional 10703A Retroreflector can be used
to convert an HP 10702 Linear lnterferometer to
a 10706A Plane Mirror Interferometer. This con-
figuration allows the 5501A Laser Measurement
system to make measurements of axial displace-
ment of a plane mirror. The stringent angular
alignment requirements imposed by roof prisms
of single-beam arrangements
i s
eliminated.
Due to the two reflections inherent in the Plane
Mirror Interferometer, there is optical resolu-
tion doubling.
I
Figure 2-76a. 70722A Plane Mirror Converter
The 5501A Laser Transducer System can perform either single or dual axis plane mirror measure-
ments. The dual axis option is particularly useful for X-Y stage applications. Typical measuring
setups for single axis and dual axis measurements are shown in Figures 2-76b and 2-34.