Laser heterodyne interferometry plays a key role in the proof mass's monitor
and control by measuring its multiple degrees of freedom motions in the Space
Gravitational Wave Detection. Laboratory development of
polarization-multiplexing heterodyne interferometer (PMHI) using quadrant
photodetectors (QPD) is presented in this paper, intended for measuring the
translation and tilt of a proof mass. The system is of symmetric design, which
can expand to five degrees of freedom measurements based on
polarization-multiplexing and differential wavefront sensing (DWS). The
ground-simulated experimental results demonstrate that a measurement noise of 3
pm/Hz${}^{1/2}$ and 2 nrad/Hz${}^{1/2}$ at 1 Hz have been achieved respectively.
The tilt-to-length error is dominated by geometric misalignment for the current
system, the coupling of which is at micrometer level within a tilt range of
1000 {\mu}rad.