In Chapter 2 two common configurations of near-field imaging, the NSOM and PSTM, were presented. In the NSOM configuration, the incident light is forced on a subwavelength aperture. The near-field light located near the aperture is used for illuminating the sample surface. Depending on the opacity of the sample, the transmitted or reflected photon by the surface is detected by a photodetector. Since the near-field intensity strongly depends on the aperture-sample distance, the aperture is normally kept at a constant distance in proximity to the surface. In the PSTM configuration, a sharp dielectric or metallic tip is typically used to scan in proximity to the sample located on the surface of a prism under the total internal reflection illumination. The tip acts as a scatterer to disturb and convert the near-field light into detectable far-field light.