Phase-shifting Moiré topography using optical demodulation on liquid crystal matrices

To date, the use of liquid crystal grid projection for profilometric applications is gaining in popularity because of its flexibility. Liquid crystal projection devices allow easy adaption of the grid pitch (and thus sensitivity) in for instance Moiré topography, and in-plane translation of the grid position is also readily achieved. However, all methods either use Fourier transform profilometry or digital demodulation in the computer, with the advantage being the measurement speed. The major disadvantage is that the resolution is compromised. Only optical demodulation combined with phase-shifting methods does not yield any resolution. In this paper, we describe a technique which performs this optical demodulation as well as the grid projection with grids on liquid crystal light modulators. This entirely liquid crystal Moiré projection profilometer thus achieves higher resolution, flexibility and ease-of-use than the solely LCD grid projection setups. Theory and application examples are given in this paper, and a study is made of different parameters and algorithms influencing the resolution.