Time-gated scanning near-field optical microscopy

A time-gated scanning near-field optical microscope (SNOM) has been developed. The optical signal was recorded at the precise moment during the fiber tip oscillation period when it made contact with the sample surface. The use of such an approach substantially improves the signal-to-noise ratio for common SNOM applications such as frustrated total internal reflection, surface plasmon imaging, and fluorescence resonance energy transfer-based SNOM. The observed dependence of the frustrated total internal reflection optical signal on the gate delay time confirms that repetitive bumping is the mechanism responsible for the shear force tip-sample interaction.