Method and apparatus for scattering-type scanning near-field optical microscopy (s-snom)

A scanning near-field optical microscopy (s-SNOM) apparatus, being configured for scattering-type scanning near-field optical microscopy, comprising

• a scanning near-field optical microscope including an s-SNOM tip being configured for a placement at a near-field distance from a sample to be investigated, while being subjected to a mechanical oscillation, which provides a primary modulation,
• an illumination device being arranged for illuminating the oscillating s-SNOM tip with a sequence of illumination light pulses, wherein each of the illumination light pulses hits the s-SNOM tip at a specific s-SNOM tip modulation phase φi of the mechanical oscillation,
• a scattering light detector device being arranged for collecting scattering light pulse amplitudes Si, each of which being created by scattering one of the illumination light pulses at the s-SNOM tip,
• a mechanical oscillation detector device being arranged for collecting the s-SNOM tip modulation phase φi associated with each of the collected scattering light pulse amplitudes Si, and
• a demodulation device being arranged for calculating an s-SNOM near-field signal by demodulating a scattering light function S(φi) of the scattering light pulse amplitudes Si in dependency on the s-SNOM tip modulation phases φi, wherein
• the mechanical oscillation detector device is coupled with a phase shifter device,
• the phase shifter device is configured for splitting an output signal of the mechanical oscillation detector device into a first output signal portion and a second output signal portion being phase-shifted relative to the first output signal portion, and
• the demodulation device is configured for calculating the s-SNOM tip modulation phases φi of the primary modulation from the first and second output signal portions.