A liquid crystal based polarimetric system, a process for the calibration of this polarimetric system, and a polarimetric measurement process intended for measuring the representative parameters of a sample in which the polarimetric system contains an excitation section emitting a light beam that passes through a polarization state generator (PSG) and onto a sample. After reflection or transmission by the sample, the beam goes through an analysis section with a polarization state detector (PSD). The PSG and PSD each have a first and a second liquid crystal elements LC.sub.j (j=1,2) having, for each LC.sub.j element of the PSG (respectively for each LC.sub.j element of the PSD), an extraordinary axis making an angle .theta..sub.j (resp. .theta.'.sub.j) with respect to the polarization direction (i), and a retardation .delta..sub.j (resp (.delta.'.sub.j) between its ordinary and extraordinary axes, the liquid crystals LC.sub.j elements being positioned in reverse order in the PSD with respect to the LC.sub.j elements of the PSG.