Regensburg 2022 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 19: Poster Monday: Scanning Probe Techniques 1

O 19.2: Poster

Montag, 5. September 2022, 18:00–20:00, P4

Live demodulation of pseudo-heterodyne SNOM at kHz repetition rates — •Philipp Schwendke¹, Samuel Palato¹, Nicolai Große², and Julia Stähler¹ — ¹PC dept., FHI of the MPG and HU Berlin — ²ELAB, FHI of the MPG

Scanning near-field optical microscopy (SNOM) allows the spectroscopic investigation of functional surfaces with spatial resolution beyond the diffraction limit. For the observation of electron dynamics on a femtosecond and nanometre scale, common setups rely on high repetition rate laser systems in order to avoid the Nyquist limit, imposed by signal modulation through the tapping AFM tip. Phase-domain sampling schemes allow sample rates below the Nyquist frequency, permitting the use of kHz-class optical amplifiers for tunable wavelengths down to the UV and femtosecond time resolution. We introduce quadrature demodulation for a robust and fast signal demodulation, while also simplifying the experimental setup.

Here, we illustrate and evaluate different methods for signal modulation and data analysis, with the aim of increasing the signal to noise ratio while maintaining high spatial resolution. The near-field contribution is identified through retraction curves, while noise and overall performance is evaluated on real-space images of a Si test sample, showing a significant signal contrast at high harmonic orders of tapping modulation. The presented methods are straightforward to combine with established optical methods, paving the way towards time-resolved SNOM and nano-spectroscopy.