Unambiguous interferometric surface profilometry using ferroelectric liquid crystal modulators

We present a surface profiler that produces unambiguous, fringe-free, surface profiles. Each point in the output image has a modulus of the complex degree of coherence (|μ<sub>xy</sub>|) which varies monotonically as the optical path difference is increased from zero. To calculate |μ<sub>xy</sub>|, the profiler incorporates a novel Stokes polarimeter employing a polarization image splitter and ferroelectric liquid crystal wave plates. Rapid wave plate addressing, coupled with the image splitter, allows data to be collected in three video frames. We observe that manufacturing inaccuracies in wave plate retardance and alignment introduce an error to the calculated |μ<sub>xy</sub>| which can reintroduce ambiguity into the height measurement. We present a numerical correction which allows recovery |μ<sub>xy</sub>| from the measured data, thereby returning us to an unambiguous surface profile. Results for various surfaces, showing the effects of systematic error and applied correction terms, are given