Polarization contrast in reflection near-field optical microscopy with uncoated fibre tips

Using cross-hatched, patterned semiconductor surfaces and round 20-nm-thick gold pads on semiconductor wafers, we investigate the imaging characteristics of a reflection nearfield optical microscope with an uncoated fibre tip for different polarization configurations and light wavelengths. It is shown that cross-polarized detection allows one to effectively suppress far-field components in the detected signal and to realize imaging of optical contrast on the subwavelength scale. The sensitivity window of our microscope, i.e. the scale on which near-field optical images represent mainly optical contrast, is found to be approximate to 100 nm for light wavelengths in the visible region. We demonstrate imaging of near-field components of a dipole field and purely dielectric contrast (related to well-width fluctuations in a semiconductor quantum well) with a spatial resolution of approximate to 100 nm. The results obtained show that such a nearfield technique can be used for polarization-sensitive imaging with reasonably high spatial resolution and suggest a number of applications for this technique.