Extinction near-field optical microscopy

This work presents a novel approach for apertureless, near-field scanning optical microscopy based on extinction of the incident beam for samples illuminated in evanescent fields and scanned with non-contact atomic force methods. The scheme exploits shot-noise limited detection of changes in reflected light intensity due to near-field interactions between the sample and a sharp atomic force microscope (AFM) tip as a function of probe-sample geometry, providing both high sensitivity (<0.1 ppm Hz^0.5) and absolute cross-section data for comparison with near-field model predictions. Extinction cross-section data for a Si probe in an evanescent field is measured as a function of excitation laser wavelength, which compare qualitatively well with Mie and Rayleigh theory for an effective ellipsoid model of the AFM tip. Extinction methods are then used to image single Au-nanoparticles (radius ≈ 7 nm), with the signal magnitudes interpreted via simple electrostatic near-field models for the probe-sample interaction.