Method and Apparatus for Scattering-Type Scanning Near-Field Optical Microscopy (s-snom)

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This patent introduces an improved method and apparatus for scattering-type scanning near-field optical microscopy (s-SNOM). By synchronizing pulsed laser illumination with the mechanical oscillation phase of an atomic force microscope (AFM) tip, and using dual-phase signal processing, the system can break conventional constraints imposed by lock-in detection between laser repetition rates and tip oscillation frequencies. The innovation enables independent optimization of both parameters, reduces data processing complexity and requirements, and enhances measurement precision and flexibility for nanoscale optical imaging and material characterization.

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• High-resolution nanoscale imaging and mapping of material surfaces
• Chemical composition analysis at the nanometer scale in materials science
• Investigating biological samples with enhanced spatial resolution
• Conducting time-resolved optical spectroscopy on advanced materials
• Characterizing nanostructures, thin films, and semiconductor devices
• Studying optical properties in areas where conventional s-SNOM techniques are cost- or complexity-prohibitive
• Integration into advanced AFM and SNOM systems for research or industrial quality control

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• Decouples laser pulse rate from tip oscillation frequency, providing greater flexibility in experiment setup and hardware choices
• Reduces complexity and computational requirements compared to phase-domain sampling and traditional lock-in detection
• Allows use of cost-effective, lower repetition-rate pulsed lasers together with higher-frequency AFM tip oscillations, lowering overall system cost
• Improves precision and reliability of near-field signal extraction, enhancing measurement accuracy
• Facilitates real-time or live display of measurements due to efficient and fast processing algorithms
• Easily extendable to support multiple modulations or signal channels for advanced experimental configurations
• Enhances sensitivity and enables more robust and versatile nanoscale optical characterization

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Patent Abstract

A method of scattering-type scanning near-field optical microscopy (s-SNOM) comprises placing an s-SNOM tip 11 at a near-field distance from a sample 1 and subjecting the s-SNOM tip 11 to a mechanical oscillation, which provides a primary modulation, illuminating the oscillating s-SNOM tip 11 with a sequence of illumination light pulses, wherein each of the illumination light pulses hits the s-SNOM tip 11 at a specific s-SNOM tip modulation phase φi of the mechanical oscillation, collecting scattering light pulse amplitudes Si, each being created by scattering one of the illumination light pulses at the s-SNOM tip 11, using a scattering light detector device 30, collecting the s-SNOM tip modulation phase φi associated to each of the collected scattering light pulse amplitudes Si, using a mechanical oscillation detector device 40, and 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 each of the s-SNOM tip modulation phases φi is obtained by splitting an output signal of the mechanical oscillation detector device 40 into a first output signal portion X and a second output signal portion Y being phaseshifted relative to the first output signal portion X and calculating the s-SNOM tip modulation phase φi of the primary modulation from the first and second output signal portions X, Y. Furthermore, a scanning near-field optical microscopy apparatus 100 is described.