Artefacts in polarization modulation scanning near-field optical microscopes

The objective of this study is to model a polarization modulation scanning near-field optical microscope set-up (PM-SNOM) and demonstrate how the influence of real instruments as photodetector and lock-in produces a coupling between signals that generates intrinsic artefacts on experimental data. A simple polar coordinates mathematical framework has been used to derive an analytical expression of the relevant signals. A simulation of typical experimental cases is presented and contrast artefacts more than 100% are demonstrated. This study is effective for an accurate analysis of PM-SNOM tests and it is of general use for the discussion of artefacts in polarization modulation systems.