Imaging subwavelength holes using an apertureless near-field scanning optical microscope

We present investigations of the light scattered by subwavelength holes in a chromium film using an apertureless near-field scanning optical microscope, which operates either in the visible (λ=655 nm) or in the infrared (λ=10.6 μm). The near-field optical images exhibit patterns around the holes that seem to coincide with the component of the stray electrical field parallel to the tip axis. A tip–sample dipole coupling model provides a satisfactory description of the experimental data recorded in the infrared with light polarized normally to the sample surface.